Title:

Gas introduction system for a reactor

Document Type and Number:

United States Patent 20020073924

Kind Code:

Abstract:

A process chamber has one or more gas inlets. One gas inlet is formed as a ring surrounding the periphery of a substrate retained in the process chamber. Added control over a deposition process is obtained by such a ring. In one embodiment, the ring is moveable. Various arrangements of gas inlets and valves are described.

Inventors:

Chiang, Tony P. (Santa Clara, CA, US)
Leeser, Karl F. (Sunnyvale, CA, US)
Brown, Jeffrey A. (San Francisco, CA, US)
Babcoke, Jason A. (Menlo Park, CA, US)

Plaque It!

What is claimed is:

1. A processing system comprising: a process chamber; and at least a first gas inlet into said process chamber.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. application Ser. No. 09/902,080, entitled “Variable Gas Conductance Control For A Process Chamber,” filed Jul. 9, 2001. The present application also claims priority from Provisional Application Serial No. 60/281,628, entitled “A Reactor For Atomic Layer Deposition,” filed Apr. 5, 2001, incorporated herein by reference.

[0002] This application is also related to the following co-pending applications, which are incorporated herein by reference:

[0003] U.S. application Ser. No. 09/812,352, entitled “System And Method For Modulated Ion-Induced Atomic Layer Deposition (MII-ALD),” filed Mar. 19, 2001.

[0004] U.S. application Ser. No. 09/812,486, entitled “Continuous Method For Depositing A Film By Modulated Ion-Induced Atomic Layer Deposition (MII-ALD),” filed Mar. 19, 2001.

[0005] U.S. application Ser. No. 09/812,285, entitled “Sequential Method For Depositing A Film By Modulated Ion-Induced Atomic Layer Deposition (MII-ALD),” filed Mar. 19, 2001.

[0006] U.S. application Ser. No. 09/854,092, entitled “Method And Apparatus for Improved Temperature Control In Atomic Layer Deposition,” filed May 10, 2001.

[0007] U.S. Provisional Application Serial No. 60/255,812, entitled “Method For Integrated In-Situ Cleaning And Subsequent Atomic Layer Deposition Within A Single Processing Charnber,” filed Dec. 15, 2000.

FIELD OF THE INVENTION

[0008] The present invention relates to advanced thin film deposition apparatus and methods used in semiconductor processing and related technologies.

BACKGROUND

[0009] As integrated circuit (IC) dimensions shrink, the ability to deposit conformal thin film layers with excellent step coverage at low deposition temperatures is becoming increasingly important. Thin film layers are used, for example, as MOSFET gate dielectrics, DRAM capacitor dielectrics, adhesion promoting layers, diffusion barrier layers, and seed layers for subsequent deposition steps. Low temperature processing is desired, for example, to prevent unwanted diffusion of shallow junctions, to better control certain reactions, and to prevent degradation of previously deposited materials and their interfaces.

[0010] The need for conformal thin film layers with excellent step coverage is especially important for high aspect ratio trenches and vias, such as those used in metallization layers of semiconductor chips. For example, copper interconnect technology requires a continuous thin film barrier layer and a continuous thin film copper seed layer to coat the surfaces of trenches and vias patterned in an insulating dielectric prior to filling the features with copper by electrochemical deposition (ECD or electroplating).

[0011] A highly conformal, continuous barrier layer is required to prevent copper diffusion into the adjacent semiconductor (i.e., silicon) material or dielectric. The barrier layer also often acts as an adhesion layer to promote adhesion between the dielectric and the copper seed layer. Low dielectric constant (i.e., low-k) dielectrics are typically used to reduce inter- and intra-line capacitance and cross-talk, but often suffer from poorer adhesion and lower thermal stability than traditional oxide dielectrics, making the choice of a suitable adhesion layer more critical. A non-conformal barrier layer, or one with poor step coverage or discontinuous step coverage, can lead to copper diffusion and current leakage between adjacent metal lines or to delamination at either the barrier-to-dielectric or barrier-to-seed layer interfaces, both of which adversely affect product lifetime and performance. The barrier layer should also be uniformly thin, to most accurately transfer the underlying trench and via sidewall profile to the subsequent seed layer, and have a low film resistivity (e.g., ρ<500 μΩ-cm) to lessen its impact on the overall conductance of the copper interconnect structures.

[0012] A highly conformal, uniformly thin, continuous seed layer with low defect density is required to prevent void formation in the copper wires. The seed layer carries the plating current and acts as a nucleation layer. Voids can form from discontinuities or other defects in the seed layer, or they can form from pinch-off due to gross overhang of the seed layer at the top of features, both trenches and vias. Voids adversely impact the resistance, electromigration, and reliability of the copper lines, which ultimately affects the product lifetime and performance.

[0013] Traditional thin film deposition techniques, for example, physical vapor deposition (PVD) and chemical vapor deposition (CVD), are increasingly unable to meet the requirements of advanced thin films. PVD, such as sputtering, has been used for depositing conductive thin films at low cost and at relatively low substrate temperature. Unfortunately, PVD is inherently a line of sight process, resulting in poor step coverage in high aspect ratio trenches and vias. Advances in PVD technology to address this issue have resulted in high cost, complexity, and reliability issues. CVD processes can be tailored to provide conformal films with improved step coverage. Unfortunately, CVD processes often require high processing temperatures, result in the incorporation of high impurity concentrations, and have poor precursor (or reactant) utilization efficiency, leading to a high cost of ownership.

[0014] Atomic layer deposition (ALD), or atomic layer chemical vapor deposition (AL-CVD), is an alternative to traditional CVD methods to deposit very thin films. ALD has several advantages over PVD and traditional CVD. ALD can be performed at comparatively lower temperatures (which is compatible with the industry's trend toward lower temperatures), has high precursor utilization efficiency, can produce conformal thin film layers (i.e., 100% step coverage is theoretically possible), can control film thickness on an atomic scale, and can be used to “nano-engineer” complex thin films.

[0015] A typical ALD process differs significantly from traditional CVD processes. In a typical CVD process, two or more reactant gases are mixed together in the deposition chamber where either they react in the gas phase and deposit on the substrate surface, or they react on the substrate surface directly. Deposition by CVD occurs for a specified length of time, based on the desired thickness of the deposited film. Since this specified time is a function of the flux of reactants into the chamber, the required time may vary from chamber to chamber.

[0016] In a typical ALD process deposition cycle, each reactant gas is introduced sequentially into the chamber, so that no gas phase intermixing occurs. A monolayer of a first reactant is physi- or chemisorbed onto the substrate surface. Excess first reactant is pumped out, possibly with the aid of an inert purge gas. A second reactant is introduced to the deposition chamber and reacts with the first reactant to form a monolayer of the desired thin film via a self-limiting surface reaction. The self-limiting reaction halts once the initially adsorbed first reactant fully reacts with the second reactant. Excess second reactant is pumped out, again possibly with the aid of an inert purge gas. A desired film thickness is obtained by repeating the deposition cycle as necessary. The film thickness can be controlled to atomic layer (i.e., angstrom scale) accuracy by simply counting the number of deposition cycles.

[0017] Physisorbed precursors are only weakly attached to the substrate. Chemisorption results in a stronger, more desirable bond. Chemisorption occurs when adsorbed precursor molecules chemically react with active surface sites. Generally, chemisorption involves cleaving a weakly bonded ligand (a portion of the precursor) from the precursor, leaving an unsatisfied bond available for reaction with an active surface site.

[0018] The substrate material can influence chemisorption. In current dual damascene copper interconnect structures, a barrier layer such as tantalum (Ta) or tantalum nitride (TaN) must often simultaneously cover silicon dioxide (SiO ₂ ), low-k dielectrics, nitride etch stops, and any underlying metals such as copper. Materials often exhibit different chemical behavior, especially oxides versus metals. In addition, surface cleanliness is important for proper chemisorption, since impurities can occupy surface bonding sites. Incomplete chemisorption can lead to porous films, incomplete step coverage, poor adhesion between the deposited films and the underlying substrate, and low film density.

[0019] The ALD process temperature must be selected carefully so that the first reactant is sufficiently adsorbed (e.g., chemisorbed) on the substrate surface, and the deposition reaction occurs with adequate growth rate and film purity. A temperature that is too high can result in desorption or decomposition (causing impurity incorporation) of the first reactant. A temperature that is too low may result in incomplete chemisorption of the first precursor, a slow or incomplete deposition reaction, no deposition reaction, or poor film quality (e.g., high resistivity, low density, poor adhesion, and/or high impurity content).

[0020] Traditional ALD processes have several disadvantages. First, since the process is entirely thermal, selection of an appropriate process temperature is often confined to a narrow temperature window. Second, the small temperature window limits the selection of available precursors. Third, metal precursors that fit the temperature window are often halides (e.g., compounds that include chlorine, flourine, or bromine), which are corrosive and can create reliability issues in metal interconnects. Fourth, either gaseous hydrogen (H ₂ ) or elemental zinc (Zn) is often used as the second reactant to act as a reducing agent to bring a metal compound in the first reactant to the desired oxidation state of the final film. Unfortunately, H ₂ is an inefficient reducing agent due to its chemical stability, and Zn has a low volatility and is generally incompatible with IC manufacturing. Thus, although conventional ALD reactors are suitable for elevated-temperature ALD, they limit the advancement of ALD processing technology.

[0021] Plasma-enhanced ALD, also called radical enhanced atomic layer deposition (REALD), was proposed to address the temperature limitations of traditional thermal ALD. For example, in U.S. Pat. No. 5,916,365, the second reactant passes through a radio frequency (RF) glow discharge, or plasma, to dissociate the second reactant and to form reactive radical species to drive deposition reactions at lower process temperatures. More information on plasma-enhanced ALD is included in “Plasma -enhanced atomic layer deposition of Ta and Ti for interconnect diffusion barriers,” by S. M. Rossnagel, et al., Journal of Vacuum Science and Technology B 18(4) July/August 2000 pp. 2016-2020.

[0022] Plasma enhanced ALD, however, still has several disadvantages. First, it remains a thermal process similar to traditional ALD since the substrate temperature provides the required activation energy, and therefore the primary control, for the deposition reaction. Second, although processing at lower temperatures is feasible, higher temperatures must still be used to generate reasonable growth rates for acceptable throughput. Such temperatures are still too high for some films of interest in IC manufacturing, particularly polymer-based low-k dielectrics that are stable up to temperatures of only 200° C. or less. Third, metal precursors, particularly for tantalum (Ta), often still contain chlorine as well as oxygen impurities, which results in low density or porous films with poor barrier behavior and chemical instability. Fourth, the plasma enhanced ALD process, like the conventional sequential ALD process described above, is fundamentally slow since it includes at least two reactant gases and at least two purge or evacuation steps, which can take up to several minutes with conventional valve and chamber technology.

[0023] Conventional ALD reactors, including plasma enhanced ALD reactors, include a vertically-translatable pedestal to achieve a small process volume, which is important for ALD. A small volume is more easily and quickly evacuated (e.g., of excess reactants) than a large volume, enabling fast switching of process gases. Also, less precursor is needed for complete chemisorption during deposition. For example, the reactors of U.S. Pat. No. 6,174,377 and European Patent No. 1,052,309 A2 feature a reduced process volume located above a larger substrate transfer volume. In practice, a typical transfer sequence includes transporting a substrate into the transfer volume and placing it on top of a moveable pedestal. The pedestal is then elevated vertically to form the bottom of the process volume and thereby move the substrate into the process volume. Thus, the moveable pedestal has at least a vertical translational and possibly a second rotational degree of freedom (for high temperature process uniformity).

[0024] Typical ALD reactors have significant disadvantages. First, conventional ALD reactors suffer from complex pedestal requirements, since the numerous facilities (e.g., heater power lines, temperature monitor lines, and coolant channels) must be connected to and housed within a pedestal that moves. Second, in the case of plasma enhanced ALD, the efficiency of radical delivery for deposition of conductive thin films is significantly decreased in downstream configurations in which the radical generating plasma is contained in a separate vessel remote from the main process chamber (see U.S. Pat. No. 5,916,365). Both gas phase and wall recombinations reduce the flux of useful radicals to the substrate. In the case of atomic hydrogen (H), recombination results in diatomic H ₂ , a far less effective reducing agent. Other disadvantages of known ALD reactors exist.

[0025] Accordingly, improved ALD reactors are desirable to make ALD better suited for commercial IC manufacturing. Desirable characteristics of such reactors might include higher throughput, improved deposited film characteristics, better temperature control for narrow process temperature windows, and wider processing windows (e.g., in particular with respect to process temperature and reactant species).

SUMMARY

[0026] A deposition system in accordance with one embodiment of the present invention includes a process chamber and one or more gas inlets. One gas inlet is formed as a ring surrounding the periphery of a substrate retained in the process chamber. Added control over a deposition process is obtained by such a ring. In one embodiment, the ring is moveable. Various arrangements of gas inlets and valves are described.

[0027] These and other aspects and features of the disclosed embodiments will be better understood in view of the following detailed description of the exemplary embodiments and the drawings thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is a schematic diagram of a novel ALD reactor.

[0029] FIG. 2 shows various embodiments of the shield and shadow ring overlap region of FIG. 1 .

[0030] FIG. 3 is a schematic diagram showing top introduction of gas into the process chamber of the ALD reactor of FIG. 1 .

[0031] FIG. 4 is (a) a schematic diagram and (b) a plan view schematic diagram showing side introduction of gas into the process chamber of the ALD reactor of FIG. 1 . FIG. 5 is (a) a schematic diagram and (b) a plan view schematic diagram showing both top and side introduction of gas into the process chamber of the ALD reactor of FIG. 1 .

[0032] FIG. 6 is a schematic diagram of a control system for the pedestal of FIG. 1 .

[0033] FIG. 7 is a schematic diagram of a circuit for electrical biasing of the electrostatic chuck of FIG. 1 .

[0034] FIG. 8 is a front-side perspective view of a novel ALD reactor.

[0035] FIG. 9 is a back-side perspective view of the ALD reactor of FIG. 8 .

[0036] FIG. 10 is a back-side perspective view, from below, of the ALD reactor of FIG. 8 .

[0037] FIG. 11 is a front-side cutaway perspective view of the ALD reactor of FIG. 8 .

[0038] FIG. 12 is a front-side cutaway perspective view of the ALD reactor of FIG. 8 .

[0039] FIG. 13 is a cross-sectional view of a chamber portion of the ALD reactor along line 13 - 13 of FIG. 8 .

[0040] FIG. 14 is a detailed cross-sectional view of the right side of the chamber portion of FIG. 13 showing a load shield position.

[0041] FIG. 15 is a detailed cross-sectional view of the right side of the chamber portion of FIG. 13 showing a low conductance process shield position.

[0042] FIG. 16 is a detailed cross-sectional view of the right side of the chamber portion of FIG. 13 showing a high conductance process shield position.

[0043] FIG. 17 is a detailed cross-sectional view of the right side of the chamber portion of FIG. 13 showing a purge shield position.

[0044] FIG. 18 is a schematic diagram of a valve system for gas delivery in the ALD reactor of FIG. 8 .

[0045] FIG. 19 is a schematic diagram of a valve system for gas delivery in the ALD reactor of FIG. 8 .

[0046] FIG. 20 is a schematic diagram of a valve system for gas delivery in the ALD reactor of FIG. 8 .

[0047] FIG. 21 is a schematic diagram of a valve system for gas delivery in the ALD reactor of FIG. 8 .

[0048] FIG. 22 is a schematic diagram of a valve system for gas delivery in the ALD reactor of FIG. 8 .

[0049] FIG. 23 is a perspective cross-section of two embodiments of a showerhead for gas distribution.

[0050] FIG. 24 is a perspective cross-section of an embodiment of a shield assembly for the ALD reactor of FIG. 8 .

[0051] FIG. 25 is a perspective cross-section of an embodiment of a shield assembly for the ALD reactor of FIG. 8 .

[0052] FIG. 26 is a perspective cross-section of an embodiment of a shield assembly for the ALD reactor of FIG. 8 .

[0053] FIG. 27 is a cutaway perspective view of an embodiment of an electrostatic chuck assembly for the ALD reactor of FIG. 8 .

[0054] FIG. 28 is a schematic diagram of a control system for the electrostatic chuck assembly of FIG. 27 of the ALD reactor of FIG. 8 .

[0055] FIG. 29 is a schematic diagram of a control system including an alternative energy source for the electrostatic chuck assembly of FIG. 27 of the ALD reactor of FIG. 8 .

[0056] FIG. 30 is a perspective view of an embodiment of a portion of an electrostatic chuck assembly for the ALD reactor of FIG. 8 .

[0057] FIG. 31 is a schematic diagram of a circuit for electrical biasing of the electrostatic chuck of the ALD reactor of FIG. 8 .

[0058] FIG. 32 is a schematic diagram of a circuit for electrical biasing of the electrostatic chuck of the ALD reactor of FIG. 8 .

[0059] FIG. 33 is a schematic diagram of a circuit for electrical biasing of the electrostatic chuck of the ALD reactor of FIG. 8 .

[0060] FIG. 34 is a schematic illustration of a conventional ALD process.

[0061] FIG. 35 is a schematic illustration of a novel ALD process.

[0062] FIG. 36 shows timing diagrams for (a) a typical prior art ALD process and (b) a novel ALD process.

[0063] FIG. 37 shows timing diagrams for an alternative embodiment of a novel ALD process.

[0064] FIG. 38 shows timing diagrams for an alternative embodiment of a novel ALD process.

[0065] FIG. 39 is a schematic illustration of a novel chemisorption technique for ALD processes.

[0066] FIG. 40 is a schematic diagram of a circuit for electrical biasing of the electrostatic chuck of the ALD reactor of FIG. 8 for improved chemisorption.

[0067] In the drawings, like or similar features are typically labeled with the same reference numbers.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0068] Basic ALD Reactor Design

[0069] FIG. 1 is a schematic diagram of a novel ALD reactor 2 . Reactor 2 includes a stationary pedestal 4 , which may include an electrostatic chuck (ESC) 6 on top of which a substrate 8 rests. Substrate 8 is usually a semiconductor wafer (e.g., silicon), but may be a metallized glass substrate or other substrate. A chamber lid 10 and ESC 6 define the top and bottom boundaries, respectively, of a process chamber 12 . The surrounding wall of chamber 12 is defined by a moveable shield 14 , which is attached to a plurality of shield support legs 16 . The volume of process chamber 12 is smaller than prior art batch reactors, but may be similar in size to prior art single wafer systems. The configuration of reactor 2 , however, provides an overall volume of reactor 2 that can be smaller than that of prior art reactors, while providing the small volume of process chamber 12 .

[0070] The small volume of process chamber 12 achieves the advantages of small process volumes discussed above, including quick evacuation, fast switching of process gases, and less precursor required for complete chemisorption. The volume of process chamber 12 cannot be made arbitrarily small, however, since substrate 8 must still be transferred into, and out of, process chamber 12 .

[0071] In FIG. 1 , the fixed position of pedestal 4 , including its supporting hardware, simplifies overall design of reactor 2 , allowing ease of use and maintenance as well as improved performance. In comparison to massive moveable pedestals in prior art reactors, shield 14 includes less associated hardware and is much lighter, which allows precision positioning of shield 14 to adjust the conductance of, and facilitate pumping of, chamber 12 with rapid response.

[0072] A chamber body 18 surrounds shield 14 , chamber lid 10 , and pedestal 4 (including ESC 6 ), defining an annular pumping channel 20 exterior to shield 14 . During processing, shield 14 separates process chamber 12 , at low pressure, from annular pumping channel 20 , which is maintained at a lower pressure than the chamber to maintain a clean background ambient in reactor 2 . The volume of chamber 12 is coupled to annular pumping channel 20 via a shield conductance upper path 22 and a shield conductance lower path 24 . Upper path 22 and lower path 24 are each defined by portions of shield 14 and corresponding features of stationary components of reactor 2 . In the embodiment shown in FIG. 1 , upper path 22 , typically a variable low leakage path during processing, is bounded by an inner wall of shield 14 and chamber lid 10 . Lower path 24 , a variable high leakage path through a shield and shadow ring overlap region 26 , is bounded by a portion of shield 14 and a shadow ring 28 . Shadow ring 28 is actually separate from ESC 6 and is shown in greater detail in subsequent figures.

[0073] The structures of shield 14 and shadow ring 28 may vary to provide different conductances of lower path 24 as shown in FIG. 2 , which shows various embodiments of the shield and shadow ring overlap region 26 of FIG. 1 . The conductance of a flow path is related to the length of the restriction as well as the physical dimensions of the path. For example, a shorter path with a large cross-sectional area has a higher conductance. For the embodiments shown in FIG. 2 , the structural configurations of shield 14 and shadow ring 28 result in a highest conductance path 30 , a second highest conductance path 32 , a third highest conductance path 34 , and a lowest conductance path 36 . Practitioners in the art will appreciate that many other embodiments of shield and shadow ring overlap region 26 are possible.

[0074] Various shield positions are employed throughout a novel ALD process. Raising shield 14 to its highest position (along with shadow ring 28 ) allows for introduction or removal of substrate 8 . Dropping shield 14 to its lowest position allows rapid evacuation of chamber 12 via upper path 22 by exposure to the vacuum of annular pumping region 20 . Shield 14 is positioned at intermediate positions during processing depending on gas delivery and conductance requirements.

[0075] The motion of shield 14 can be used to precisely control the spatial relationship between shield 14 and shadow ring 28 , thereby providing a tunable conductance for chamber 12 primarily via lower path 24 . This allows quick, precise control of the pressure in chamber 12 , even during processing, which is not possible in prior art methods that employ a moveable pedestal since vertical motion of substrate 8 is undesirable during processing. The tunable conductance also allows quick, precise control of the residence time of gases introduced to chamber 12 for multiple flow rates, and it allows minimal waste of process gases.

[0076] Basic Gas Introduction to an ALD Reactor

[0077] Reactor 2 of FIG. 1 supports gas introduction through multiple points, including top introduction, side introduction, or a combination of both top and side introductions.

[0078] FIG. 3 is a schematic diagram showing top introduction of gas into process chamber 12 of ALD reactor 2 of FIG. 1 . A top mount feed (not shown) has a single introduction point (or multiple introduction points) with an optional added device (not shown), such as a showerhead and/or a baffle, to ensure that a top introduction flow distribution 38 is uniform over the substrate. The added device includes at least one passage, and may include many. The added device may also include intermediate passages to regulate gas distribution and velocity.

[0079] FIG. 4 is (a) a schematic diagram and (b) a plan view schematic diagram showing side introduction of gas into process chamber 12 of ALD reactor 2 of FIG. 1 . Gas is introduced from a gas channel 40 in shield 14 into process chamber 12 through orifices in an inner wall of shield 14 . Gas is introduced in a symmetric geometry around substrate 8 designed to ensure that a side introduction flow distribution 42 is even. In addition, the plane of the gas introduction may be adjusted vertically relative to substrate 8 before or during gas introduction, which can be used to optimize flow distribution 42 .

[0080] FIG. 5 is (a) a schematic diagram and (b) a plan view schematic diagram showing both top and side introduction of gas into process chamber 12 of ALD reactor 2 of FIG. 1 . The gases for novel ALD processes, including precursor and purge gases, can be introduced through the same introduction path or separate paths as desired for optimal performance and layer quality.

[0081] Basic Electrostatic Chuck Assembly Design for an ALD Reactor

[0082] Reactor 2 of FIG. 1 can be used in a deposition process where the activation energy for the surface reaction is provided by ions created in a plasma above the substrate. Thus, atomic layer deposition can be ion-induced, rather than thermally induced. This allows deposition at much lower temperatures than conventional ALD systems. Given the sufficiently low process temperatures, pedestal 4 may include an electrostatic chuck (ESC) 6 for improved temperature control and improved radio frequency (RF) power coupling.

[0083] Additional detail of ion-induced atomic layer deposition may be found in the following related applications. U.S. application Ser. No. 09/812,352, entitled “System And Method For Modulated Ion-Induced Atomic Layer Deposition (MII-ALD),” filed Mar. 19, 2001, assigned to the present assignee and incorporated herein by reference. U.S. application Ser. No. 09/812,486, entitled “Continuous Method For Depositing A Film By Modulated Ion-Induced Atomic Layer Deposition (MII-ALD),” filed Mar. 19, 2001, assigned to the present assignee and incorporated herein by reference. U.S. application Ser. No. 09/812,285, entitled “Sequential Method For Depositing A Film By Modulated Ion-Induced Atomic Layer Deposition (MII-ALD),” filed Mar. 19, 2001, assigned to the present assignee and incorporated herein by reference.

[0084] FIG. 6 is a schematic diagram of a control system 44 for pedestal 4 of FIG. 1 . Substrate 8 rests on an annular sealing lip 46 defining a backside gas volume 48 between substrate 8 and a top surface 50 of ESC 6 of pedestal 4 . The backside gas flows from a backside gas source 52 along a backside gas line 54 , through a backside gas passageway 56 in ESC 6 , and into gas volume 48 . The backside gas improves the thermal communication between substrate 8 and ESC 6 by providing a medium for thermal energy transfer between substrate 8 and ESC 6 . A means of flow control, such as a pressure controller 58 , maintains the backside gas at a constant pressure, thus ensuring a uniform substrate temperature.

[0085] Substrate temperature is modulated by heating or cooling ESC 6 . A temperature sensor 60 is coupled via a sensor connection 62 to a temperature monitor 64 . A temperature controller 66 controls a heater power supply 68 applied via an electrical connection 70 to a resistive heater 72 embedded in ESC 6 . A coolant temperature and flow controller 74 , as is widely known, controls the coolant from a coolant supply 76 as it flows in a plurality of coolant channels 78 in pedestal 4 .

[0086] ESC 6 includes at least a first electrode 80 and a second electrode 82 embedded in a dielectric material. FIG. 7 is a schematic diagram of a circuit 84 for electrical biasing of electrostatic chuck 6 of pedestal 4 of FIG. 1 . First electrode 80 and second electrode 82 are biased with different DC potentials to provide the “chucking” action that holds substrate 8 ( FIG. 1 ) to ESC 6 prior to plasma ignition and during deposition. The biasing scheme of FIG. 7 allows establishment of the electrostatic attraction (i.e., “chucking”) at low biases that would be insufficient to generate enough electrostatic attraction with a conventional monopolar chuck. In FIG. 7 , one terminal of a DC power supply 86 is coupled via a first inductor 88 to first electrode 80 . The other terminal of DC power supply 86 is coupled via a second inductor 90 to second electrode 82 . Inductors 88 and 90 serve as RF filters.

[0087] RF power (e.g., at 13.56 MHz) is also supplied simultaneously to both first electrode 80 and second electrode 82 using an RF generator 92 coupled to a ground terminal 94 . A first capacitor 96 and a second capacitor 98 are respectively coupled between RF generator 92 and first electrode 80 and second electrode 82 . Capacitors 96 and 98 serve as DC filters to block the DC voltage from power supply 86 . Circuit 84 allows improved coupling of RF power to substrate 8 during processing due to the close proximity (e.g., 0.6 mm-2 mm spacing) of substrate 8 to first electrode 80 and second electrode 82 embedded in ESC 6 .

[0088] Since substrate 8 is in such close proximity to first and second electrodes 80 and 82 , the transmission efficiency of RF power through the intervening dielectric of ESC 6 is higher than in conventional reactors where RF power is applied to electrodes at a greater distance from the substrate. Thus, less power is needed to achieve sufficient RF power coupling to substrate 8 in novel ALD reactor 2 ( FIG. 1 ), and the same power to generate the bias on substrate 8 can also be used to create a plasma above substrate 8 at very low powers (e.g., <600W, and typically <150W).

[0089] ALD Reactor Detail

[0090] FIG. 8 , FIG. 9 , FIG. 10 , FIG. 11 , and FIG. 12 show external views and internal cutaway views of a novel ALD reactor 100 . FIG. 8 is a front-side perspective view of reactor 100 . FIG. 9 is a back-side perspective view of reactor 100 . FIG. 10 is a back-side perspective view, from below, of reactor 100 . FIG. 1 is a front-side cutaway perspective view of reactor 100 . FIG. 12 is another front-side cutaway perspective view of reactor 100 .

[0091] Referring to FIG. 8, a substrate 8 ( FIG. 12 ) is transferred into or out of a process chamber 12 ( FIG. 11 and FIG. 12 ) of reactor 100 through a substrate entry slot 102 in a slit valve 104 . Substrate 8 is loaded onto or unloaded from the pedestal (e.g., an electrostatic chuck assembly 106 as seen in FIG. 11 and FIG. 12 ) by a plurality of lift pins 108 . In the load or unload position, the tips of lift pins 108 extend through orifices in an electrostatic chuck (ESC) 6 to hold substrate 8 above the top surface of ESC 6 . In the process position, the tips of lift pins 108 retract below the top surface of ESC 6 allowing contact between substrate 8 and ESC 6 ( FIG. 11 and FIG. 12 ).

[0092] Referring to FIG. 11 and FIG. 12 , lift pins 108 extend downward from process chamber 12 in the interior of reactor 100 through an electrostatic chuck assembly 106 (including ESC 6 , a cooling plate 110 , and a baseplate 112 ) to the exterior under-side of reactor 100 . Each of lift pins 108 is attached to a lift pin spider 114 to coordinate their motion. Vertical translation of lift pin spider 114 is accomplished with an off-axis lift pin actuator 116 (e.g., a pneumatic cylinder), which controls motion of a tie rod 118 that is coupled to lift pin spider 114 by a spherical joint 120 as seen in FIG. 10 . Spherical joint 120 transmits lifting forces to lift pin spider 114 but no moments.

[0093] Referring to FIG. 11 , to facilitate substrate transfer, a moveable shield 14 , must be in a load position. Shield 14 is raised or lowered using a linear motor 122 , which moves a linear motor output rod 124 attached to a shield lift spider 126 by a collet clamp 128 (best seen in FIG. 10 ). Each one of a plurality of shield support legs 16 ( FIG. 11 ) extends through a shield support leg seal 130 and is coupled between shield lift spider 126 and shield 14 . The axis of linear motor 122 is aligned with the axis of process chamber 12 resulting in no net moments on shield lift spider 126 . Lift pin spider 114 rides a portion of linear motor output rod 124 , coaxial with output rod 124 and shield lift spider 126 . Lift pin spider 114 , however, is unaffected by movement of rod 124 , and this arrangement results in no net moments on lift pins 108 .

[0094] As mentioned above, linear motor 122 provides actuation of shield 14 . This is in contrast to conventional moveable pedestals wherein slower stepper motors are used for actuation. Conventional rotational stepper motors use lead screws (possibly in conjunction with a gear train), which are slow but capable of moving heavy masses, to effect movement of the heavy pedestal. Linear motor 122 does not use a gear train, but instead directly drives the load. Linear motor 122 includes a plurality of alternating magnets to effect motion of output rod 124 .

[0095] Linear motor 122 can be a commercially available linear motor and typically includes a sleeve having a coil and a moveable rod enclosing the series of alternating magnets. The movement of the rod through the sleeve is precisely controlled, using a Hall Effect magnetic sensor, by a signal applied to the coil. In one embodiment, pulses applied to the coil precisely control the position of the rod with respect to the sleeve, as is well known. Since shield 14 is a light weight compared to conventional heavy pedestals, linear motor 122 provides high performance positioning, with response times on the order of milliseconds. Linear motor 122 thus provides a quicker response and more accurate shield positioning than is achievable with conventional stepper or servo motors used to actuate the pedestal of conventional ALD reactors.

[0096] Referring to FIG. 11, a pump, such as a turbomolecular pump 132 , maintains a background ambient pressure as low as a few microtorr or less in an annular pumping channel 20 surrounding shield 14 . Pump 132 is attached to reactor 100 at an angle such that a circular pump throat 134 is fully exposed to a narrow pumping slot 136 aft of process chamber 12 , maximizing the conductance between them. In this manner, pump 132 with a diameter, d, has maximum exposure to pumping slot 136 of height, h (where h<d), with minimum restriction between pump 132 and chamber 12 (see also FIG. 13 discussed below). For specific processing applications, a pumping speed restrictor 138 can be inserted at pump throat 134 to restrict the conductance as needed. In some embodiments, a pressure controlling throttle valve (e.g., a butterfly valve) can be used instead of, or in conjunction with, restrictor 138 . Pressure in pumping slot 136 and annular pumping channel 20 is monitored by a pump pressure sensor 140 mounted on the top surface of reactor 100 .

[0097] Process chamber 12 is bounded on top by a chamber lid 10 . Pressure in process chamber 12 of reactor 100 may be on the order of a few microtorr up to several torr. The pressure of chamber 12 is monitored by a fast chamber pressure sensor 142 and a precision chamber pressure sensor 144 , both of which are mounted on an upper peripheral flange of chamber lid 10 ( FIG. 8 ). The temperature of chamber lid 10 is controlled by fluid flowing in a plurality of lid cooling/heating channels 146 ( FIG. 11 ). One possible path of gas introduction to process chamber 12 is through a showerhead three-way valve 148 mounted centrally on chamber lid 10 . Another possible method of gas introduction to process chamber 12 is through a shield gas channel 40 .

[0098] RF power is transferred to electrodes in ESC 6 via an RF conductor 150 shielded within an RF insulator tube 152 . A gas medium (commonly referred to as a backside gas) is provided via a backside gas valve 154 to ESC 6 to improve the thermal coupling between ESC 6 and substrate 8 . During processing, an optional shadow ring 28 rests on a portion of ESC 6 fully surrounding a peripheral edge of substrate 8 .

[0099] FIG. 13 is a cross-sectional view of a chamber portion 156 of ALD reactor 100 along line 13 - 13 of FIG. 8 . Substrate entry slot 102 is shown on the left hand side extending through a chamber body 18 . Pumping slot 136 , of height h, is shown on the right hand side extending through chamber body 18 to pump throat 134 , of diameter d. The temperature of chamber body 18 is controlled by fluid flowing in a chamber cooling/heating channel 158 .

[0100] Chamber lid 10 rests atop chamber body 18 . A vacuum seal, to maintain low pressure in the interior of reactor 100 , is maintained through the use of an upper O-ring 160 between chamber lid 10 and chamber body 18 . Laterally spaced from O-ring 160 between chamber lid 10 and chamber body 18 is an upper RF gasket 162 , forming an RF shield. The temperature of chamber lid 10 is controlled by fluid flowing in lid cooling/heating channels 146 . Alternatively, the temperature of chamber lid 10 may be controlled by an electric or resistive heater or other cooling/heating means.

[0101] The pressure in process chamber 12 is monitored, in part, by fast chamber pressure sensor 142 , which is mounted on an upper peripheral flange of chamber lid 10 . Pressure sensor 142 monitors the pressure in a pressure tap volume 164 , which is coupled to process chamber 12 by a pressure sensor orifice 166 . This arrangement allows exposure of pressure sensor 142 to the pressure of chamber 12 , while preventing plasma and other process chemistries from reaching, and possibly damaging, pressure sensor 142 .

[0102] Gases can be introduced into process chamber 12 through a showerhead gas feed inlet 168 , which leads to a plenum 170 above a showerhead 172 attached to a lower surface of chamber lid 10 . Showerhead 172 includes a showerhead lip 174 and a plurality of showerhead gas orifices 176 , which are used to distribute gas evenly into process chamber 12 .

[0103] Substrate 8 rests on an upper surface of an ESC assembly 106 , which includes in part, ESC 6 , cooling plate 110 , and baseplate 112 . The vertical spacing between the upper surface of ESC assembly 106 and showerhead 172 may be 0.3 inches to 1 inch, typically less than 0.6 inches. Backside gas passageway 56 is shown centrally located in and extending through ESC 6 . ESC 6 , which includes the largest portion of the upper surface on which substrate 8 rests, is held in contact with cooling plate 110 using a clamp ring 178 , which overlaps a surrounding flange at the base of ESC 6 . A plurality of clamp ring fasteners 180 , each extending through clamp ring 178 into cooling plate 110 , secure the connection between ESC 6 and cooling plate 110 . A process kit 182 fully surrounds clamp ring 178 and electrically hides clamp ring fasteners 180 from ESC 6 and substrate 8 . For a more detailed view of clamp ring 178 , fasteners 180 , and process kit 182 , see FIG. 16 , discussed below.

[0104] The temperature of cooling plate 110 is controlled using fluid flowing in a plurality of coolant channels 78 as shown in FIG. 13 . An upper surface of cooling plate 110 is patterned to create a plurality of thermal breaks 184 , or gaps, between ESC 6 and cooling plate 110 . Thermal breaks 184 increase the temperature difference between ESC 6 and cooling plate 110 . This allows the temperature of ESC 6 to rise substantially higher than the temperature of baseplate 112 , which stays relatively cool. For a more detailed view of thermal breaks 184 , see FIG. 27 , discussed below.

[0105] As shown in FIG. 13, a lower surface of cooling plate 110 is attached to an upper surface of baseplate 112 . The upper surface of baseplate 112 forms the lower walls of coolant channels 78 in cooling plate 110 . A vacuum seal, to maintain low pressure in the interior of reactor 100 , is maintained through the use of an O-ring 186 between baseplate 112 and chamber body 18 . Laterally spaced from O-ring 186 between baseplate 112 and chamber body 18 is an RF gasket 188 .

[0106] One of the plurality of lift pins 108 is shown in retracted process position, with the tip of lift pin 108 below the top surface of ESC 6 . Lift pin 108 extends through a lift pin seal 190 , which maintains the low pressure in the interior of reactor 100 . A lift pin bushing 192 reduces friction during vertical translation of lift pin 108 through aligned orifices in baseplate 112 , cooling plate 110 , and ESC 6 .

[0107] In FIG. 13 , shield 14 is shown in an intermediate process position. Process chamber 12 is thus bounded on the top by showerhead 172 , on the bottom largely by ESC 6 , and on the sides by shield 14 to confine a plasma 194 . Shield 14 includes shield gas channel 40 and is attached to each shield support leg 16 using a shield cap 196 . Each shield support leg 16 extends through shield support leg seal 130 , which maintains the low pressure in the interior of reactor 100 . A plurality of shield support leg bushings 198 reduce friction during vertical translation of shield support legs 16 through orifices in baseplate 112 .

[0108] A shadow ring hook 200 is attached to a lower portion of shield cap 196 . Shadow ring hook 200 is shown interdigitated with shadow ring 28 , which fully surrounds a peripheral edge of ESC assembly 106 and rests on a process kit bevel 202 of process kit 182 . Shadow ring 28 protects the underlying portions of ESC assembly 106 during deposition onto substrate 8 . Shadow ring 28 also defines the circumferential region near the edge of substrate 8 where deposition is masked. Shadow ring 28 also plays a role in defining the chamber conductance. For a more detailed view of process kit bevel 202 , see FIG. 16 , discussed below.

[0109] In FIG. 13 , two leakage paths modulate gas flow between process chamber 12 and annular pumping channel 20 , which is largely bounded by chamber body 18 , chamber lid 10 , and ESC assembly 106 . The leakage occurs due to differing pressures between process chamber 12 and annular pumping channel 20 . A shield conductance upper path 22 is bounded on one side by an inner upper surface of shield 14 , and on the other side by outer surfaces of chamber lid 10 and showerhead 172 . A shield conductance lower path 24 is bounded on one side by surfaces of a lower portion of shield 14 , shield cap 196 , and shadow ring hook 200 , and on the other side by surfaces of shadow ring 28 . Upper path 22 leads from process chamber 12 to an upper portion 204 of annular pumping channel 20 , while lower path 24 leads from process chamber 12 to a lower portion 206 of annular pumping channel 20 .

[0110] Shield 14 can be vertically translated by either raising it into upper portion 204 of annular pumping channel 20 or lowering it into lower portion 206 of annular pumping channel 20 . As shield 14 is translated, the conductances of upper path 22 and lower path 24 are changed. The variations in conductance can be controlled to vary the pressure in process chamber 12 in a controlled manner as needed for various steps in an atomic layer deposition process sequence.

[0111] Shield Operation

[0112] Unlike in conventional ALD reactors, reactor 2 includes a stationary pedestal 4 (see FIG. 1 ). For example, reactor 100 of FIG. 12 includes ESC assembly 106 . Transfer of substrate 8 into process chamber 12 of reactor 100 is facilitated through the use of moveable shield 14 , which also plays a significant role during processing.

[0113] Various shield positions are employed throughout the ALD process. FIG. 14 , FIG. 15 , FIG. 16 , and FIG. 17 show detailed cross-sectional views of the right side of chamber portion 156 of FIG. 13 , showing shield 14 in a substrate load shield position 208 ( FIG. 14 ), a low conductance process shield position 210 ( FIG. 15 ), a high conductance process shield position 212 ( FIG. 16 ), and a purge shield position 214 ( FIG. 17 ).

[0114] In load shield position 208 of FIG. 14 , shield support legs 16 are raised by linear motor 122 ( FIG. 8 ). When shield 14 is raised above a certain point, shadow ring hook 200 contacts shadow ring 28 and lifts it as well. Shield 14 and shadow ring 28 are then raised together. Shield 14 enters upper portion 204 of annular pumping channel 20 . Shield 14 and shadow ring 28 can be raised until shadow ring 28 contacts showerhead lip 174 , which prevents shadow ring 28 from contacting showerhead 172 .

[0115] Load shield position 208 thus allows loading (or unloading) of substrate 8 into (or out of) process chamber 12 via substrate entry slot 102 ( FIG. 13 ). For example, to load substrate 8 into process chamber 12 , a substrate blade or paddle (not shown) carries substrate 8 into process chamber 12 . Lift pins 108 are raised by lift pin actuator 116 ( FIG. 10 ) to contact substrate 8 and lift it off the top surface of the blade. The blade is then retracted out of chamber 12 through entry slot 102 . Lift pins 108 are retracted past the top surface of ESC 6 allowing substrate 8 to rest on ESC 6 as shown in FIG. 14 . A similar process is followed to unload substrate 8 from chamber 12 .

[0116] In an alternative embodiment, shadow ring 28 is not used, and shield 14 forms variable conduction paths with other surfaces that may be fixed or moveable. In some embodiments, it is possible that the load position may be achieved by lowering shield 14 sufficiently so that substrate 8 may pass over the top edge of shield 14 .

[0117] Once substrate 8 has been loaded into process chamber 12 , shield 14 is lowered by linear motor 122 ( FIG. 8 ) for processing. The low conductance process shield position 210 shown in FIG. 15 , shows the positions of shield 14 and shadow ring 28 at the moment that shadow ring 28 contacts process kit 182 . An angled shadow ring seat 216 of shadow ring 28 rests on process kit bevel 202 of process kit 182 . This is the only point of contact between shadow ring 28 and process kit 182 . Air gaps separate shadow ring 28 and process kit 182 away from each edge of process kit bevel 202 . The airgaps between shadow ring 28 and process kit 182 allow for differential thermal expansion of shadow ring 28 and process kit 182 during processing. The angle of process kit bevel 202 helps center shadow ring 28 , through interaction with the angle of shadow ring seat 216 , so that the edge of substrate 8 is shadowed uniformly by a shadow ring edge 218 of shadow ring 28 .

[0118] Lowering shield 14 into process position creates shield conductance upper path 22 and shield conductance lower path 24 , as described with respect to FIG. 13 above. While it is possible to reduce the conductance of lower path 24 to zero ( FIG. 15 ), during deposition upper path 22 generally forms a low conductance leakage path, while lower path 24 generally forms a higher conductance leakage path ( FIG. 16 ).

[0119] By changing the relative position of shield 14 to shadow ring 28 , the conductance out of chamber 12 can be modulated. This modulation, in turn, alters the pressure of chamber 12 . The high conductance process shield position 212 shown in FIG. 16 , shows the positions of shield 14 and shadow ring 28 at an intermediate step of an ALD process. Lower path 24 includes several distinct regions: a plurality (three in this embodiment) of fixed conductance regions 220 (fixed gaps between shadow ring hook 200 and shadow ring 28 ) interspersed with a plurality (two in this embodiment) of variable conductance regions 222 (variable gaps). The volumes of fixed conductance regions 220 and variable conductance regions 222 can be precisely controlled (by precise positioning of shield 14 by linear motor 122 ) to adjust the conductance of lower path 24 , and therefore the pressure of chamber 12 , as needed during the process.

[0120] In purge shield position 214 of FIG. 17 , shield support legs 16 are lowered by linear motor 122 ( FIG. 8 ). Shield 14 and shadow ring hook 200 are lowered into lower portion 206 of annular pumping channel 20 . Shadow ring 28 remains seated on process kit 182 . Both shield conductance upper path 22 and shield conductance lower path 24 become high conductance paths. Purge shield position 214 allows quick evacuation of the gases in process chamber 12 into annular pumping channel 20 due to the high conductances created and the lower pressure of annular pumping channel 20 compared to chamber 12 .

[0121] As mentioned above, linear motor 122 ( FIG. 8 ) provides actuation of shield 14 . This allows quick and accurate variation of the conductance of shield conductance upper and lower paths 22 and 24 . This translates into quick and accurate variation of the pressure in process chamber 12 for given gas flows into process chamber 12 .

[0122] In some embodiments, a throttle valve (i.e., a butterfly valve, a variable position gate valve, a pendulum valve, etc.) positioned at pump throat 134 ( FIG. 13 ) can also be used in conjunction with moveable shield 14 to effect quick pressure changes in process chamber 12 by modulating the maximum pumping speed of pump 132 ( FIG. 12 ). The throttle valve augments the pressure range achievable in process chamber 12 , providing a “coarse adjustment” of the pressure in process chamber 12 , while shield 14 provides a “fine adjustment” of the pressure.

[0123] Showerhead and Shield Design for Gas Introduction and Temperature Control

[0124] The novel hardware for ALD reactor 100 ( FIG. 11 ) supports the introduction of gases into process chamber 12 through multiple points. The primary introduction point is through the top of reactor 100 , in particular, through showerhead three-way valve 148 (mounted on chamber lid 10 ) and showerhead 172 (best seen in FIG. 13 ). Gases may also be introduced into chamber 12 through shield 14 , which may be additionally configured for temperature control.

[0125] FIG. 18 is a schematic diagram of a novel valve system 224 for gas delivery in ALD reactor 100 of FIG. 8 . This embodiment delivers a single precursor and a purge gas to process chamber 12 , either separately or in a mixed proportion. The purge gas is used to purge the chamber and as the gas source to strike a plasma. A carrier gas for the precursor flows from a first gas source 226 , and the purge gas flows from a second gas source 228 .

[0126] When either the carrier gas or the purge gas is not flowing to chamber 12 , it is diverted by a first three-way valve 230 and a purge three-way valve 232 , respectively, through a pump bypass gas line 234 to a vacuum pump 236 . Utilization of vacuum pump 236 allows the carrier and purge gases to flow in steady state conditions even when they are not flowing to chamber 12 . This avoids disturbances in the gas flows caused by the long settling times of gas sources that are switched on and off.

[0127] A showerhead three-way valve 148 controls access to a chamber gas line 238 , which leads to process chamber 12 . Three-way valve 148 , located centrally on chamber lid 10 as seen in FIG. 11 , provides at least two distinct advantages. First, gases introduced to chamber 12 can be switched rapidly with minimal loss or delay. Second, gases are isolated from each other outside of chamber 12 , resulting in no cross-contamination of reactants.

[0128] A first on/off valve 240 is coupled between first ends of a second on/off valve 242 and a third on/off valve 244 . The opposite ends of second and third on/off valves 242 and 244 are each coupled to a first precursor source 246 . First on/off valve 240 is also coupled between first three-way valve 230 and showerhead three-way valve 148 via a gas line 248 and a gas line 250 , respectively. Precursor source 246 can be isolated by closing on/off valves 242 and 244 . This may be done, for example, to change precursor source 246 . In this case, on/off valve 240 may be closed, or opened to allow carrier gas to flow through three-way valves 230 and 148 into chamber 12 . During deposition, first on/off valve 240 is normally closed, and second and third on/off valves 242 and 244 are normally open.

[0129] Three-way valves 230 , 232 , and 148 are switched synchronously to deliver either precursor or purge gas to chamber 12 . When delivering precursor, purge three-way valve 232 is switched to flow the purge gas to vacuum pump 236 , and showerhead three-way valve 148 is switched to the precursor side. Simultaneously, three-way valve 230 is switched to allow carrier gas to flow from first gas source 226 through gas line 248 and on/off valve 242 into precursor source 246 . The carrier gas picks up precursor in precursor source 246 , typically by bubbling through a liquid source. The carrier gas, now including precursor, flows through on/off valve 244 , through gas line 250 , through showerhead three-way valve 148 , through chamber gas line 238 , and into chamber 12 .

[0130] When delivering purge gas, first three-way valve 230 is switched to flow the carrier gas to vacuum pump 236 . Purge three-way valve 232 and showerhead three-way valve 148 are switched to allow purge gas to flow from second gas source 228 through a gas line 252 and chamber gas line 238 into chamber 12 .

[0131] Valve system 224 keeps gas line 248 charged with carrier gas, gas line 250 charged with carrier plus precursor, and gas line 252 charged with purge gas. This allows fast switching between gas sources by significantly reducing the gas delivery time to chamber 12 . Valve system 224 also minimizes waste of gases since gas lines do not need to be flushed between deposition steps. Furthermore, any gas bursts from transient pressure spikes upon gas switching, due to the charged gas lines, would only help the initial stages of chemisorption or surface reaction.

[0132] Practitioners will appreciate that alternative embodiments of valve systems for gas delivery to reactor 100 are possible. In the embodiment shown in FIG. 18 , two separate gas sources are shown providing the carrier gas and the purge gas, which may be different gases. It is possible, however, that in some embodiments the same gas used as the purge gas may be used as the carrier gas for the precursor. In this case, separate gas sources may be used as shown in FIG. 18 , or first gas source 226 may be used singly in a valve system 254 , which has many similar components to valve system 224 of FIG. 18 , as shown schematically in FIG. 19 . Valve system 254 can be simplified by replacing three-way valve 230 with a T-junction 256 as shown schematically in FIG. 20 for a valve system 258 , which has many similar components to valve system 224 of FIG. 18 . As in valve system 224 of FIG. 18 , showerhead three-way valves 148 in valve system 254 ( FIG. 19 ) and valve system 258 ( FIG. 20 ) control the flow of purge gas or carrier-plus-precursor gas to chamber 12 . As shown in valve system 254 ( FIG. 19 ) and valve system 258 ( FIG. 20 ), pump 236 may not be used in some embodiments.

[0133] In some embodiments, gas delivery of multiple precursors may be desirable. Two embodiments of multiple precursor delivery are shown in the schematic diagrams of a valve system 260 in FIG. 21 and a valve system 262 in FIG. 22 . Valve systems 260 ( FIG. 21 ) and 262 ( FIG. 22 ) each have many similar components to valve system 224 of FIG. 18 . Valve systems 260 ( FIG. 21 ) and 262 ( FIG. 22 ) are shown configured for two precursor sources, but may be further adapted for additional precursor sources. In each of valve systems 260 ( FIG. 21 ) and 262 ( FIG. 22 ), a second three-way valve 264 controls the flow of carrier gas to a second precursor source 266 . A fourth on/off valve 268 , a fifth on/off valve 270 , and a sixth on/off valve 272 are coupled similarly to, and operate similarly to, valves 240 , 242 , and 244 , respectively, to control the flow of carrier gas through second precursor source 266 . A gas line 274 , similar to gas line 248 , is coupled between three-way valve 264 and on/off valve 270 .

[0134] In FIG. 21 , valve system 260 further includes a third gas source 276 in addition to first and second gas sources 226 and 228 of valve system 224 of FIG. 18 . A third three-way valve 278 , coupled to on/off valve 272 via a gas line 280 , controls delivery of the second precursor to showerhead three-way valve 148 via a gas line 282 . A fourth three-way valve 284 controls delivery of the purge gas via gas line 252 and a gas line 286 to three-way valve 278 , which directs the purge gas to showerhead three-way valve 148 as needed via gas line 282 .

[0135] In FIG. 22 , valve system 262 is shown configured to use gas source 226 for both the purge and carrier gases. The carrier gas is delivered from gas source 226 to three-way valve 264 via a gas line 288 . The purge gas is delivered to the second terminal of a third three-way valve 278 (and similar valves of any additional precursor sources) via gas line 252 . The third terminal of three-way valve 278 is coupled to the second terminal of showerhead three-way valve 148 via gas line 282 . Three-way valve 278 thus controls delivery of the second precursor and the purge gas to showerhead three-way valve 148 .

[0136] Other modifications may be made for alternative embodiments of the valve systems of FIGS. 18, 19 , 20 , 21 , and 22 . The functions of showerhead three-way valve 148 may be accomplished instead with an equivalent network of on/off valves (similar to valves 240 , 242 , and 244 ) and fittings. Metering valves may be added to branches to regulate the flow for specific branches. Pressure sensors may be added to branches and coupled with the valve actuation to introduce known amounts of reactant. Valve timing may be manipulated to deliver “charged” volumes of gas to process chamber 12 . The traditional valves may be replaced with advanced designs such as micro-electromechanical (MEM) based valves or valve networks. The entire valve system can be heated to prevent condensation of reactants in the network.

[0137] FIG. 23 is a perspective cross-section of two embodiments of a showerhead 172 for gas distribution. Showerhead 172 is designed to have a larger diameter, and thus a larger area, than substrate 8 and ESC 6 ( FIG. 13 ). Showerhead 172 includes a plurality of mounting holes 290 used to facilitate attachment of showerhead 172 to chamber lid 10 with a plurality of fasteners (see FIG. 13 ). Showerhead 172 also includes a plurality of pressure sensor orifices 166 , one for each pressure sensor used to sense the pressure in process chamber 12 . For example, fast chamber pressure sensor 142 and precision chamber pressure sensor 144 ( FIG. 8 ) would each require a pressure sensor orifice 166 in showerhead 172 . Showerhead 172 also includes showerhead lip 174 peripherally around the edge of showerhead 172 used to prevent shadow ring 28 from hitting showerhead 172 .

[0138] Showerhead 172 also includes a cavity 292 centrally located in an upper surface of showerhead 172 as shown in FIG. 23 ( a ). Cavity 292 forms plenum 170 ( FIG. 13 ) upon attachment of showerhead 172 to chamber lid 10 . A plurality of showerhead gas orifices 176 are arranged within cavity 292 in a pattern designed for a particular gas flow distribution. The diameter of cavity 292 is designed to be larger than the diameter of substrate 8 ( FIG. 13 ). In the embodiment of FIG. 23 ( b ), showerhead 172 includes a cavity 294 that is similar to cavity 292 of FIG. 23 ( a ), but cavity 294 has a diameter designed to be smaller than the diameter of substrate 8 . Practitioners will appreciate that a number of different diffusing devices may be used to tailor the directionality of the gas flows as needed.

[0139] As mentioned above, gas may also be introduced into process chamber 12 through shield 14 . This allows cylindrical gas introduction around the volume of process chamber 12 as discussed above with reference to FIG. 4 . FIG. 24 is a perspective cross-section of an embodiment of a shield assembly 296 , including a shield gas channel 40 , for ALD reactor 100 of FIG. 8 . A plurality of shield support legs 16 attach to shield cap 196 , which is attached to the base of shield 14 . Most of shield support legs 16 are solid. Gas is introduced into shield 14 , through at least one hollow shield support leg 298 , which extends through shield cap 196 into shield gas channel 40 in shield 14 .

[0140] Shield gas channel 40 is annular and runs completely around the base of shield 14 . Shield gas channel 40 is a high conductance channel that allows introduced gas to distribute evenly around shield gas channel 40 of shield 14 before introduction into process chamber 12 ( FIG. 13 ). Gas is introduced to chamber 12 through a plurality of gas flow orifices 300 , which are evenly spaced along shield gas channel 40 and extend through an inner wall of shield 14 into process chamber 12 . The gas introduction path of shield assembly 296 is designed to ensure uniform gas flow around substrate 8 as discussed with reference to FIG. 4 .

[0141] Introduction of gas through shield 14 allows tremendous flexibility in designing ALD processes. In some embodiments, the same gas introduced through showerhead 172 can be simultaneously introduced through shield 14 to provide improved coverage in process chamber 12 and on substrate 8 ( FIG. 13 ). Alternatively, in some embodiments, one gas can be introduced through showerhead 172 while a different gas is introduced through shield 14 , allowing improved gas isolation and quicker cycling of the gases.

[0142] Movement of shield 14 , either before or during the gas flow, allows gas to be introduced at different planes within process chamber 12 , parallel to the plane of substrate 8 . The shield motion can be used to optimize the gas flow distribution of a particular ALD process.

[0143] As discussed previously, another role of shield 14 is to confine plasma 194 during processing ( FIG. 13 ), which can result in heating of shield 14 . To maintain the shield at an acceptable process temperature, a cooling/heating channel can be incorporated in the shield design. This also helps prevent deposition on shield 14 .

[0144] FIG. 25 is a perspective cross-section of an embodiment of a shield assembly 302 , including a shield cooling/heating channel 304 , for ALD reactor 100 of FIG. 8 . Shield assembly 302 includes some shield support legs 16 , which are solid, attached to shield cap 196 at the base of shield 14 . Similar to shield assembly 296 of FIG. 24 , which includes gas channel 40 , a cooling or heating fluid flows up into shield 14 through at least one hollow shield support leg 306 , which extends through shield cap 196 into cooling/heating channel 304 in shield 14 . Shield cooling/heating channel 304 is annular and runs about two-thirds of the way around the base of shield 14 . The cooling or heating fluid flows down, out of shield 14 , through at least one other hollow shield support leg (not shown), which is similar to hollow shield support leg 306 .

[0145] Cooling or heating of shield 14 using a fluid flowing in cooling/heating channel 304 also allows improved control of the temperature of gases introduced into process chamber 12 through shield 14 . FIG. 26 is a perspective cross-section of an embodiment of a shield assembly 308 , including both shield gas channel 40 and shield cooling/heating channel 304 , for ALD reactor 100 of FIG. 8 . In the embodiment shown in FIG. 26 , gas channel 40 is located above cooling/heating channel 304 . Hollow shield support leg 306 extends through shield cap 196 into cooling/heating channel 304 to allow fluid flow. Hollow shield support leg 298 extends through shield cap 196 and cooling/heating channel 304 into gas channel 40 to allow gas introduction from shield 14 into process chamber 12 via gas flow orifices 300 .

[0146] Practitioners will appreciate that shield assembly