DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] The present invention shall be generally described with reference to FIGS. 1 - 2 . Thereafter, other embodiments, illustrations, and applications of the present invention shall be described with reference to FIGS. 3 - 4 .

[0023] FIG. 1 illustrates a substrate assembly 17 and a metal/metal oxide composite structure 12 formed according to the present invention on a surface 18 of the substrate assembly 17 , e.g., an oxygen-containing surface portion. FIG. 1 is illustrative of the use of a composite metal/metal oxide structure 12 for any application such as those requiring the benefits provided thereby as further described below. For example, the application may be a capacitor electrode application. As such an electrode, the composite metal/metal oxide structure 12 may be used to prevent oxygen diffusion through the electrode of the capacitor, provide an enhanced surface area, etc. Further, for example, the composite metal/metal oxide structure 12 may be used in the formation of storage cell capacitors for use in semiconductor devices, e.g., memory devices. As further described herein, the structure 12 may be used within a stack of layers forming an electrode of a capacitor, or may be used as the capacitor electrode by itself. One skilled in the art will recognize that various semiconductor processes and structures for various devices, e.g., CMOS devices, memory devices, etc., would benefit from the characteristics of the composite metal/metal oxide structure 12 of the present invention, and in no manner is the present invention limited to the illustrative embodiments described herein.

[0024] As used in this application, “substrate assembly” refers to either a semiconductor substrate, such as the base semiconductor layer, e.g., the lowest layer of a silicon material in a wafer, or a silicon layer deposited on another material, such as silicon on sapphire, or a semiconductor substrate having one or more layers or structures formed thereon or regions formed therein. When reference is made to a substrate assembly in the following description, various process steps may have been previously used to form or define regions, junctions, or various structures or features and openings, such as vias, contact openings, high aspect ratio openings, etc.

[0025] According to the present invention, the substrate assembly 17 includes at least a portion thereof that is an oxygen-containing surface portion upon which at least a portion of the composite metal/metal oxide structure 12 is formed. Such an oxygen-containing surface portion is shown as the dashed line surface portion 19 . The oxygen-containing surface portion 19 may be, for example, formed of any oxygen-containing material such as any oxide material. For example, the oxide material may include borophosphosilicate glass (BPSG), phosphosilicate glass (PSG), tetraethylorthosilicate glass (TEOS), ozone-enhanced TEOS, or any other oxygen-containing material.

[0026] The composite metal/metal oxide structure 12 includes a first metal layer 13 including grain boundaries 14 thereof illustratively shown within first metal layer 13 . Further, the composite structure 12 includes metal oxide regions 16 formed on at least portions of the first metal layer 13 at grain boundaries 14 thereof. The metal oxide regions 16 are formed, as described further below with reference to FIG. 2 , through selective oxidation of a second metal layer 15 (as shown by dashed line 15 in FIG. 1 ) formed on the first metal layer 13 . The selective oxidation of the second metal layer 15 is performed by diffusion of oxygen from the oxygen-containing surface portion 19 of substrate assembly 17 through the grain boundaries 14 of the first metal layer 13 .

[0027] Preferably, the metal oxide regions 16 are formed on at least portions of the first metal layer 13 at one or more grain boundaries 14 thereof by providing an oxygen diffusion barrier layer 20 (also shown in dashed line form in FIG. 1 ) on at least a portion of the second metal layer 15 which is to be selectively oxidized. Upon thermal treatment of the substrate assembly 17 having the first metal layer 13 , the second metal layer 15 , and the oxygen diffusion barrier layer 20 formed thereon, selective oxidation of the one or more regions of the second metal layer 15 occurs at one or more grain boundaries 14 of the first metal layer 13 resulting in the metal oxide regions 16 and unoxidized portions of the second metal layer 15 generally between the metal oxide regions 16 formed at the grain boundaries 14 . The composite metal/metal oxide structure 12 is thereafter formed by removing the oxidation diffusion barrier layer 20 and the unoxidized portions of the second metal layer 15 resulting in the non-dashed composite structure 12 shown in FIG. 1 .

[0028] Preferably, the first metal layer 13 is formed of at least one metal selected from a group of platinum, palladium, rhodium, and iridium. More preferably, as shall be described further below with reference to FIG. 2 , the first metal layer is formed of at least platinum.

[0029] Preferably, the second metal layer 15 is formed of at least one metal selected from a group of ruthenium, osmium, rhodium, iridium, and cerium. More preferably, the second metal layer 15 is formed of at least ruthenium. As such, with a second metal layer 15 formed of such materials, the metal oxide regions 16 will include, for example, ruthenium oxide, osmium oxide, etc. depending upon the material used.

[0030] Preferably, the oxygen diffusion barrier layer 20 is a layer that is less permeable to oxygen than the oxygen-containing surface portion 19 . As such, oxygen diffusing through the grain boundaries 14 of the first metal layer 13 during thermal treatment will oxidize localized regions about the grain boundaries 14 at the surface 21 of the first metal layer 13 to form the metal oxide regions 16 . For example, the oxidation diffusion barrier layer 20 may be formed of at least one of silicon nitride, silicon oxynitride, and aluminum oxide. Preferably, a silicon nitride layer 20 is used to passivate the underlying structure.

[0031] The first and second metal layers 13 , 15 are preferably formed by chemical vapor deposition processes (CVD) as known to those skilled in the art. However, such layers may be formed by atomic layer deposition (ALD), evaporation, sputtering, or any other method suitable to form such layers. Preferably, however, CVD is used to obtain uniformity so as to provide enhanced step coverage. The present invention, however, is not limited to any particular method of forming such layers.

[0032] Preferably, the first metal layer 13 is formed to a thickness of about 20 Å to about 1000 Å. More preferably, the first metal layer 13 has a thickness in the range of about 50 Å to about 200 Å. In addition, the second metal layer 15 is formed to a thickness of about 20 Å to about 1000 Å. More preferably, the second metal layer 15 has a thickness of about 50 Å to about 200 Å. Yet still further, the oxidation diffusion barrier layer 20 is preferably formed to a thickness of about 100 Å to about 500 Å.

[0033] The method of forming a composite metal/metal oxide structure 12 according to the present invention will be better understood from the more detailed description provided with reference to FIG. 2 . However, for clarity and simplicity, and with reference to preferred materials, the method of forming the metal/metal oxide structure shall be described with reference to FIG. 2 wherein a composite platinum/ruthenium oxide electrode structure 38 as shown in FIG. 2D (e.g., where the first metal layer is platinum and the second metal layer is ruthenium) is formed according to the present invention. However, one skilled in the art will recognize that such processing is applicable to the other materials described herein as well. Further, the method as described with reference to FIGS. 2 A- 2 E shall be described with respect to the composite platinum/ruthenium oxide structure 38 being used as a bottom electrode of a capacitor structure 50 , as shown in FIG. 2E . However, although the present invention is particularly advantageous for use of the composite structure as a bottom electrode, the present invention is not limited to this application only and may well be used for any other applications wherein a conductive structure is required.

[0034] In accordance with the present invention, FIG. 2A shows a substrate assembly 22 including an oxygen-containing surface portion 27 . As described previously herein, the oxygen-containing surface portion 27 may be formed of any oxygen-containing material such as BPSG. As shown in FIG. 2A, a platinum layer 24 is formed on surface 23 of the substrate assembly 22 . Preferably, the platinum layer 24 is formed by CVD. As CVD of platinum is known in the art, further details with respect to the formation thereof shall not be provided in any further detail. For example, an oxidizing ambient in the CVD of platinum may be used (e.g., an O ₂ or N ₂ O ambient environment). With control of the oxidizing environment, excess oxygen can be added during deposition of the platinum to enhance oxidation of the ruthenium during the subsequent thermal treatment.

[0035] After formation of the platinum layer 24 on surface 23 of the substrate assembly 22 , a ruthenium layer 28 is formed on the platinum layer 24 . The ruthenium layer 24 is also preferably deposited by CVD. Again, as CVD of ruthenium is known in the art, further details with respect thereto shall not be further provided.

[0036] The deposited metal layers 24 , 28 each have respective grain boundaries 26 , 29 therein. As illustratively shown in FIG. 2 B, platinum layer 24 has grain boundaries 26 extending therethrough from the surface 23 of substrate assembly 22 on which it is formed to the upper surface 31 of the platinum layer 24 . Likewise, ruthenium layer 28 includes grain boundaries 29 extending from surface 31 of the platinum layer 24 on which it is formed through the upper surface 33 thereof.

[0037] Further, as shown in FIG. 2B, a silicon nitride layer 30 is formed on the ruthenium layer 28 . Formation of the silicon nitride as the oxidation diffusion barrier layer may be attained by any suitable method as known to those skilled in the art.

[0038] One skilled in the art will recognize that the thickness of layers will vary depending on various factors, including but not limited to the application where the structure is to be used. Generally, however, preferably, the layers are formed to thicknesses in the ranges as described with reference to FIG. 1 . The ruthenium layer 28 preferably has a thickness such that it is entirely oxidized in the local region about the grain boundaries 26 through the surface 33 thereof during the thermal treatment of the structure.

[0039] With the platinum layer 24 , the ruthenium layer 28 , and the silicon nitride layer 30 formed on the oxygen-containing surface portion 27 of substrate assembly 22 , a thermal treatment is performed. The resultant structure following the thermal treatment is shown in FIG. 2C . Preferably, the stack of layers is annealed at elevated temperatures under vacuum or reducing conditions to allow oxygen diffusion from the oxygen-containing surface portion 27 through grain boundaries 26 of the platinum layer 24 . As a result of such oxygen diffusion through the grain boundaries 26 of the platinum layer 24 , selective oxidation of localized regions of the ruthenium layer 28 occurs at the grain boundaries 26 of the platinum layer 24 on surface 31 thereof. As shown in FIG. 2 C, such oxidation results in a ruthenium/ruthenium oxide layer 40 including ruthenium oxide regions 42 formed on surface 31 of the platinum layer 24 at the grain boundaries 26 and unoxidized portions 44 of the ruthenium layer located between such ruthenium oxide regions 42 at portions of surface 31 that are relatively distant from the grain boundaries 26 , e.g., outside of the local regions about the grain boundaries 26 .

[0040] Preferably, the anneal of the stack of layers on substrate assembly 22 is performed at temperatures greater than about 300° C. More preferably, such temperatures are greater than about 500° C. Also preferably, the anneal is performed in a non-oxidizing atmosphere, e.g, a nitrogen atmosphere.

[0041] The anneal preferably is a furnace anneal performed at such elevated temperatures. However, an anneal may be performed using rapid thermal processing (RTP) techniques and further may be performed by a combination of steps at varied temperatures. However, preferably, at least one anneal temperature is in the ranges described above.

[0042] With the local ruthenium oxide regions 42 formed at the grain boundaries 26 of platinum layer 24 , the composite platinum/ruthenium oxide structure 38 as shown in FIG. 2D may be formed upon the removal of the silicon nitride layer 30 and the unoxidized portions 44 of the ruthenium/ruthenium oxide layer 40 . The removal of the silicon nitride layer 30 may be accomplished by any suitable process. For example, silicon nitride may be removed by various fluorine-containing etch gases such as CF ₄ /O ₂ , CF ₄ /H ₂ , C ₂ F ₆ , etc., in a dry etch or plasma etch process.

[0043] The ruthenium/ruthenium oxide layer 40 including both unoxidized ruthenium portions 44 and ruthenium oxide regions 42 is processed to selectively remove the unoxidized ruthenium portions 44 relative to the ruthenium oxide regions 42 , and desirably relative to the underlying platinum layer 24 . Such removal of the unoxidized ruthenium portions 44 may be accomplished using any suitable selective wet etch process or dry etch process. As one specific example of a wet etch process used to selectively remove the unoxidized ruthenium portions 44 , a wet etchant comprising ceric ammonium nitrate and acetic acid may be used.

[0044] One skilled in the art will recognize that any processes that remove the unoxidized ruthenium portions 44 preferentially over the ruthenium oxide regions 42 may be used according to the present invention. The remaining ruthenium oxide regions 42 constitute, together with the underlying platinum layer 24 , an enhanced surface area layer compatible with high dielectric constant materials.

[0045] As shown in FIG. 2 E, capacitor structure 50 is completed by the formation of dielectric material 52 on the platinum/ruthenium oxide composite electrode 38 and formation of a second electrode or top electrode 54 formed on at least a portion of the dielectric layer 52 . The dielectric material 52 is preferably a high dielectric constant material interposed between the composite electrode 38 and second electrode 54 . As used herein, a high dielectric constant material preferably has a dielectric constant of at least 9, and more preferably a dielectric constant of at least 20. For example, the high dielectric constant material may be any suitable material having a desirable dielectric constant, such as Ta ₂ O ₅ , Ba _x Sr _(1−x) TiO ₃ [BST], BaTiO ₃ ,SrTiO ₃ ,PbTiO ₃ , Pb(Zr, Ti)O ₃ [PZT], (Pb,La)(Zr,Ti)O ₃ [PLZT], (Pb,La)TiO ₃ [PLT], KNO ₃ , LiNbO ₃ , ZrO ₂ , HfO ₂ , Zr-silicate, Hf-silicate, and Al ₂ O ₃ .

[0046] With use of the high dielectric constant material 52 , diffusion barrier properties of electrodes is particularly important. For example, to function well as a bottom electrode of a capacitor structure, the electrode layer or stack of layers must act as an effective barrier to the diffusion of silicon and oxygen, particularly due to the processes used to form the high dielectric constant materials. Such diffusion barrier properties are required when the substrate assembly 22 includes a silicon-containing surface upon which the capacitor is formed, e.g., polysilicon, silicon substrate material, n-doped silicon, p-doped silicon, etc., since oxidation of the diffused silicon may result in degraded capacitance, e.g., capacitance for a memory device. In addition, the electrode stack must act as an oxygen barrier, for example, to prevent an underlying silicon-containing surface from oxidizing. The formation of the composite structure 38 according to the present invention provides such barrier properties.

[0047] The second electrode or top electrode 54 may be formed of any suitable conductive material. For example, the electrode may include a stack of layers or a single layer. The electrode 54 may be formed of any suitable material such as those typically used in the formation of electrodes such as tungsten nitride, titanium nitride, tantalum nitride, ruthenium, rhodium, iridium, ruthenium oxide, iridium oxide, platinum, palladium, any combination thereof, or any other conductive material typically used as an electrode or electrode layer of a storage cell capacitor.

[0048] As shown in FIG. 2 E, grain boundaries 53 of the dielectric material 52 match the grain boundaries 26 of the platinum layer 24 . In other words, such grain boundaries of the high dielectric layer 52 and of the composite structure 38 are aligned. However, as shown in FIG. 3 , such grain boundaries may be mismatched between the dielectric material and platinum layer.

[0049] In FIG. 3, a capacitor structure 60 shows such a mismatch. The capacitor structure 60 includes the composite platinum-ruthenium oxide composite structure 38 as the bottom electrode with dielectric material 62 and second electrode 64 formed thereover. As shown, grain boundaries 63 of the dielectric material 62 are not aligned with the grain boundaries 26 of the platinum layer 24 .

[0050] After the high dielectric constant material is deposited, the two scenarios described with reference to FIGS. 2E and 3 may be attained. In other words, either the grain boundaries of the dielectric material match with the grain boundaries 26 of the platinum as illustratively shown in FIG. 2 E, or such grain boundaries are mismatched as shown in FIG. 3 . However, in both cases, whether matched or mismatched, the bottom composite platinum/ruthenium oxide electrode provides various advantages.

[0051] For example, the present invention utilizes the diffusion of oxygen through the grain boundaries 26 of the platinum layer 24 to obtain a composite bottom electrode 38 that includes platinum layer 24 and local ruthenium oxide regions 42 formed on grain boundaries thereof. This composite platinum/ruthenium oxide electrode 38 is an advantageous barrier to oxygen diffusion during high temperature processes in oxidizing atmospheres. For example, during high temperature oxidizing processes, such as those used to form the high dielectric constant material (e.g., a BST deposition process), oxygen diffusion through the grain boundaries 26 of the platinum layer 24 is prevented by having the ruthenium oxide regions 42 on the grain boundaries 26 of the platinum material 24 . Such barrier properties are generally important in forming such high dielectric constant materials. Further, the composite platinum/ruthenium oxide electrode also acts as a sink for oxygen vacancies in high permittivity oxide materials. This provides for improved dielectric performance, e.g., improved resistance degradation lifetime or fatigue for ferroelectric oxide dielectrics.

[0052] Further, high temperature processing in conjunction with use of platinum may create various problems. For example, a balling out problem, e.g., the formation of islands in the platinum, can sometimes occur. With the use of the ruthenium and silicon nitride layers on top of the platinum material layer 24 , such island formation problems can be prevented during high temperature processing. Also, stress in the platinum layer 24 , which causes the island formation, can be reduced by having the ruthenium oxide regions 42 formed at the grain boundaries. Such stress relief can be thought of as the ruthenium oxide regions 42 generally gluing the platinum material 24 at the grain boundaries. This enables the platinum material 24 to be a stable bottom electrode for use with high dielectric constant materials.

[0053] Yet further, the dielectric properties of the high dielectric constant material 52 can be tailored using the platinum/ruthenium oxide bottom electrode 38 . For example, the size of the ruthenium oxide regions 42 can be controlled by the oxidation process used to form such oxide regions 42 , e.g., time of oxidation, temperature, ambient, pressure, etc. Further, the unoxidized ruthenium removal process may also be used to control the size of such metal oxide regions or islands, e.g., time of etching, temperature, type of etchant used (such as an etchant that is less selective to ruthenium oxide), etc.

[0054] Generally, the size of the ruthenium oxide regions 42 will determine, permittivity, leakage, resistance degradation, fatigue and other properties of the structure. For example, with smaller ruthenium oxide regions 42 , less leakage occurs with more platinum at the interface with the high dielectric constant material 52 . However, with the use of larger ruthenium oxide regions 42 , longer resistance degradation over the lifetime of the structure occurs. Such resistance degradation involves oxygen vacancy migration. For example, ruthenium oxide regions will act as a sink for oxygen vacancies. Further, for example, permittivity can be affected by the texture of the dielectric films which can be affected by the density of the platinum/ruthenium oxide areas. Therefore, generally the process can be optimized to achieve a size of ruthenium oxide regions 42 desired in the capacitor structure 50 . As such, the present invention provides flexibility for tailoring the dielectric properties of the high dielectric material 52 in the capacitor structure 50 .

[0055] FIG. 4 illustrates the use of a metal/metal oxide composite electrode in a storage cell container capacitor application, e.g., a DRAM storage cell capacitor. In this illustrative application of the present invention, device structure 100 is fabricated according to conventional processing techniques through the formation of an opening 184 prior to depositing a bottom composite electrode structure 187 therein. A bottom electrode 187 , including a metal/metal oxide composite structure as previously described herein, is formed in opening 184 according to the present invention.

[0056] The substrate assembly 181 may include various elements, such as field oxide regions, active regions, i.e., those regions of a silicon substrate not covered by field oxide, word lines, field effective transistors (FETs), source/drain regions created in the silicon substrate, etc. An insulative layer, e.g., BPSG, of oxide material 183 is formed over the substrate assembly 181 . The opening 184 in the insulative layer 183 may be a small high aspect ratio opening. As described herein, small high aspect ratio openings have feature sizes or critical dimensions below about 1 micron (e.g., such as a diameter width of an opening being less than about 1 micron) and aspect ratios greater than about 1. For example, an opening of 1 micron and a depth of 3 microns has an aspect ratio of 3. The present invention is particularly beneficial for forming the bottom electrode 187 in small high aspect ratio features due to the use of CVD or ALD processes for forming conformal platinum and ruthenium layers over step structures.

[0057] As shown in FIG. 4 , electrode 187 , including the composite metal/metal oxide structure as previously described herein, is formed on the one or more side wall surfaces 186 and may also be formed on the bottom surface 185 ; the surfaces 186 and 185 defining opening 184 . For example, the electrode may be formed by planarizing a composite metal/metal oxide material that is formed over the entire structure. As such, the planarization would remove desired regions such that the composite metal/metal oxide material only remains in opening 184 for forming the bottom electrode 187 . The electrode 187 includes metal layer 189 and metal oxide regions 188 formed at grain boundaries thereof according to the present invention. Substantially the same processing techniques as described elsewhere herein may be used to form the composite metal/metal oxide structure. For example, the oxidation diffusion barrier layer used to form the metal oxide regions may be formed such that it fills the opening during performance of the process as described previously herein.

[0058] Such metal oxide regions 188 may form at the platinum grain boundaries of the platinum adjacent the bottom surface 185 of the substrate assembly 181 even though the substrate assembly 181 may not include oxygen at this location. For example, during deposition of the platinum, an excess amount of oxygen may be incorporated into the platinum as previously mentioned herein. As such, for example, preferential oxidation of ruthenium over the oxidation of the substrate assembly 181 , e.g., a silicon containing bottom surface region, may occur to form the ruthenium oxide regions 188 in such regions adjacent the bottom surface 185 during the thermal treatment. Further, this region at the bottom surface 185 is typically very small, e.g., such as in small aspect ratio openings, compared to the other regions, e.g., sidewalls 186 , at which the ruthenium oxide will readily form.

[0059] Thereafter, dielectric layer 191 , e.g., a high dielectric constant material, is formed relative to the electrode 187 . Further thereafter, the second electrode 192 is formed relative to the dielectric material 191 . For example, such an electrode may be of any conductive material or materials typically used for electrodes. One example of a container capacitor typically including electrodes formed on surfaces requiring conformal formation of a bottom electrode is described in U.S. Pat. No. 5,270,241 to Dennison, et al., entitled “Optimized container stacked capacitor DRAM cell utilizing sacrificial oxide deposition and chemical mechanical polishing,” issued Dec. 14, 1993.

[0060] All patents, patent documents, and references cited herein are incorporated in their entirety as if each were incorporated separately. This invention has been described with reference to illustrative embodiments and is not meant to be construed in a limiting sense. As described previously, one skilled in the art will recognize that various other illustrative applications may use the techniques as described herein to take advantage of the beneficial characteristics of structures formed thereby. Various modifications of the illustrative embodiments, as well as additional embodiments to the invention, will be apparent to persons skilled in the art upon reference to this description.