Title:
CONTINUOUS DEPOSITION REACTOR
United States Patent 3785853


Abstract:
A plurality of gas deposition chambers are arranged in a row and positioned over a heating slab. A work-piece carrying pallet is advanced through the row of deposition chambers by a moving ribbon and two cables which also provide rotary motion to the pallet as it is being advanced. Preheat and cooling stations are provided at opposite ends of the row of deposition chambers and are each provided with a collimated gas flow "curtain" by the use of honeycomb material positioned in the path of a gas stream.



Inventors:
Kirkman, Earl L. (Felton, CA)
Bowers, Gerald M. (Saratoga, CA)
Application Number:
05/256478
Publication Date:
01/15/1974
Filing Date:
05/24/1972
Assignee:
UNICORP INC,US
Primary Class:
Other Classes:
118/500, 118/719, 118/725, 118/730, 198/375, 198/793, 198/803.2
International Classes:
C23C16/54; (IPC1-7): C23C11/06
Field of Search:
118/47-49.1,322,500-503,52-57 117
View Patent Images:
US Patent References:
3709672METHOD AND APPARATUS FOR FLUORINE SURFACE TREATMENT OF GLASS ARTICLESJanuary 1973Urbano et al.
3672948N/AJune 1972Foehring et al.
3659551GLASS TREATING TUNNELMay 1972McKinstry
3645545ENTRANCE-EXIT ATMOSPHERIC ISOLATION DEVICEFebruary 1972Garnache et al.
3598082CONTINUOUS EPITAXIAL DEPOSITION SYSTEMAugust 1969Rice
3576247APPARATUS FOR ORIENTING CONTAINERSJune 1969Caulford et al.
3147135Method and apparatus for washing and waxing vehicles and the likeSeptember 1964Brown
2579737Apparatus for rotating and spray painting disksDecember 1951Giordano, Jr.
2376980Spray coating machineMay 1945Petersen et al.
2295928Method and apparatus for glazing ceramic wareSeptember 1942Bower



Primary Examiner:
Kaplan, Morris
Attorney, Agent or Firm:
Karl, Limbach Et Al A.
Claims:
We claim

1. A continuous deposition reactor, comprising:

2. A continuous deposition reactor according to claim 1 wherein the deposition chamber has an interior wall shape of a pyramid with its bottom opening being rectangular in shape and formed by the bottom edge termination of said pyramidal shaped walls, the bottom edges of the pyramidal shaped forming walls being spaced a constant distance from said surface.

3. A continuous deposition reactor according to claim 2 wherein there are a plurality of the pyramid-like deposition chamber associated with said means to heat and move said pallets and each of the pyramidal interior shaped deposition chambers is oriented relative to one another with one bottom edge side of its rectangularly shaped opening being parallel with one side of the rectangularly shaped opening of an adjoining deposition chamber.

4. A continuous deposition reactor according to claim 3 wherein adjoining deposition chambers share a common wall structure.

5. A continuous deposition reactor according to claim 4 wherein said common wall structure is cooled to prevent deposition on the interior wall surface of the deposition chambers.

6. A continuous deposition reactor according to claim 3 wherein an elongated venting chamber is provided along both sides of said row of deposition chambers for exhausting gas from within said chambers through a gap between the bottom edge of its outside walls and the surface.

7. A continuous deposition reactor according to claim 6 wherein the bottom outside edges of said deposition chamber walls include a flange attached thereto and extending downward below the bottom edge of the deposition chamber forming walls in a manner to form a gap for exhausting the chambers into the vacuum chambers that is below the top surface of a pallet to be passed along the heated surface, whereby deposited particles move into the vacuum chamber.

8. A continuous deposition reactor according to claim 6 wherein each of the deposition chambers is held to a frame that is adjustable in elevation relative to the surface, whereby the deposition gas pressure within the chambers may be controlled.

9. A continuous deposition reactor according to claim 1 which additionally comprises a preheat section adjacent one end of the deposition chamber for heating a pallet to a predetermined temperature before it enters the deposition chamber, said preheat section including:

10. A continuous deposition reactor according to claim 9 wherein said plurality of tubular gas collimating members are formed of a honeycomb cellular material.

11. A continuous deposition reactor according to claim 1 which additionally comprises a cooling section positioned adjacent one end of the deposition chamber for cooling a pallet after passing through the deposition chamber, said cooling section including:

12. A continuous deposition reactor according to claim 11 wherein said plurality of tubular gas collimating members are formed of a honeycomb cellular material.

13. A continuous deposition reactor according to claim 1 wherein said means for giving motion to said member and to each of said pair of pallet supporting elements includes a single motor means that drives each of these elements.

14. A continuous deposition reactor, comprising:

15. A continuous deposition reactor according to claim 14 wherein said elongated carrier travels along the bottom surface in a slot provided therein, said carrier being held below said surface in a position for its pins to protrude upward above said surface for engaging a pallet, and further wherein said heating means includes means beneath the bottom surface for heating said surface, whereby pallets passing thereover are heated from the bottom surface.

16. A continuous deposition reactor according to claim 14 wherein each of said pair of transmission members is guided along a predetermined path on the bottom surface by an associated groove in said bottom surface that restrains the cable against lateral movement and holds a portion of the cable above the bottom surface so that a pallet moving along the bottom surface is not in direct contact therewith but rather is carried by said pair of cables.

17. A continuous deposition reactor according to claim 14 which additionally comprises:

18. A continuous deposition reactor according to claim 14 wherein said elongated carrier and said pair of cables are all given motion by a common motor source through appropriate motion transmitting elements.

19. A continuous deposition reactor according to claim 14 wherein the relative speeds of each of the pair of transmission members relative to the speed of the elongated carrier is such that a pallet carried by said transmission members and a pin of said carrier is rotated about said pin without significant slippage between either of said pair of transmission members and said pallet.

20. A continuous deposition reactor according to claim 18 wherein each of said pair of transmission members is formed from a single continuous wire cable and further wherein each of said pair of cables is driven in opposite directions relative to the heated surface, the distance between said elongated carrier and each of said pair of cables being different and further being calculated so that a pallet carried by said cables will be given rotary motion about one of said pins that engages the pallet without substantial slippage between either of the cables and said pallet.

21. A method of moving a pallet across a heated surface through a gas deposition chamber, comprising the steps of:

22. A continuous deposition reactor, comprising:

Description:
BACKGROUND OF THE INVENTION

The present invention relates generally to the art of depositing thin layers of material on a heated surface in an appropriate gaseous atmosphere, and more specifically to improved techniques and mechanical elements for accomplishing such a deposition process.

The need for depositing thin layers of materials on substrates of various types is found in a number of technical areas. Generally the technique includes the heating of a substrate through a supporting pallet or susceptor in the presence of a gaseous atmosphere such that the hot substrate surface causes a chemical reaction among the various gases in the atmosphere to result in depositing a thin layer of material on the substrate. One specific technical area in which this general technique is used is for the deposition of layers on semi-conductor elements, such as depositing a thin layer of silicon dioxide onto a silicon wafer substrate. In performing this particular deposition, a silicon wafer is mechanically or chemically cleaned, placed on a pallet either alone or along with a plurality of other wafers and the wafer is then heated through heating of the pallet. The heated pallet and wafers are then moved into a deposition chamber wherein an appropriate gaseous mixture exists. An example of such a mixture is the combination of silane (SiH4), oxygen for the appropriate reaction and an inert carrier gas such as nitrogen. The gaseous mixture can further be provided with the material for doping the resulting silicon dioxide layer to provide a certain resistivity, or the silicon dioxide layer can remain undoped.

One prior machine for making such gas depositions in forming semi-conductor elements is a rotating silicon oxide reactor manufactured and sold by Hugle Industries of Sunnyvale, California under their tradename of ROTOX. Wafers are carried by a pallet and four pallets are held by a rotating platform. By rotating the platform, a given pallet may be moved from a loading/unloading station to preheat station, then into a single heated gas deposition chamber, to a cooling station and then back to the loading/unloading station. A nitrogen curtain isolates the deposition chamber from the atmosphere but yet permits the transfer of pallets therethrough. The pallet is slowly rotated while in the deposition chamber. Audible sounds are automatically provided to tell the operator when a pallet should be removed from the deposition chamber. The RoTOX machine is semi-continuous and contains many automatic features. It is, however, a primary object of the present invention to provide an improved machine which increases the potential production per unit time.

It is another object of the present invention to provide a semi-automatic machine for a deposition process for reducing the necessity of operator control.

It is yet another object of the present invention to provide a deposition machine that minimizes undesirable deposition on machine parts.

It is a more specific object of the present invention to provide an improved deposition machine with a pallet advancing and rotating mechanism adaptable for continuous operation.

It is yet another specific object of the present invention to provide a deposition machine with an improved gas curtain for isolating its deposition chamber from the atmosphere.

SUMMARY OF THE INVENTION

These and additional objects are accomplished by the techniques of the present invention wherein, briefly, a plurality of pallets that each support work pieces such as silicon wafers are successively pulled through at least one deposition chamber which forms a deposition zone. A source is provided for heating the pallets in the deposition zone. Radiant heat energy, induction, heated walls or a heated deposition chamber floor slab may be employed. A gas inlet within the chamber supplies the required gaseous atmosphere for reaction with the hot surface of a work piece being drawn through the deposition zone.

The use of a plurality of deposition chambers adjacent one another in a row has certain advantages over the use of a single chamber to form the deposition zone. The gaseous atmosphere may be the same in each of the row of deposition chambers or, alternatively, different gaseous atmospheres may be employed for sequentially depositing layers of different compositions onto a substrate, one on top of the other. When the same gaseous atmosphere is used, the plurality of chambers has the advantage of permitting more pallets per unit of time being passed through a gas deposition atmosphere. A plurality of small deposition chambers are preferred to one large chamber of an equal length since the small chambers permit better control of gas flow and density when striking the work pieces, thereby permitting the formation of thin layers with better uniformity and respectability.

At one end of the deposition zone, a preheat station is provided for raising the temperature of the pallet prior to its entering the deposition zone. The preheat station also includes a gas flow which is collimated by use of a honeycomb material before crossing an aperture through which a pallet travels when passing from the preheat zone into the deposition zone. Similarly, a cooling station is provided adjacent another end of the deposition zone and a similar collimated gas curtain is provided. The gas curtains help to prevent atmospheric gases from entering the deposition chamber or chambers and also to contain the deposition gases within the chamber or chambers.

Pallets are pulled in line from a loading station in advance of the preheat station, through the preheat station, through the chamber or chambers of a deposition zone, through the cooling station and lastly to an unloading station at an end of the machine. The pallets are preferably so pulled by a flexible ribbon having a plurality of pins periodically spaced along its length and extending upward therefrom. Each pin engages an aperture in a pallet bottom. The flexible tape is continuously driven and preferably is carried by a slot beneath the surface of a floor member in a manner to permit the pins on the flexible member to extend above these surfaces for engaging pallets.

It is desirable in many cases that the pallets be given rotary motion simultaneously with translational motion through the various stations of the machine, at least in its deposition zone. In this case, only one flexible ribbon is employed and each pallet is engaged by only one of its pins at the pallet's center from its bottom side. The pins do not hold the weight of their associated driven pallets but rather the pallet is supported against gravity, in at least the deposition zone, by a pair of cables that are guided along the heated surface in paths parallel to the flexible ribbon slot but on opposite sides thereof. These cables are given motion in opposite directions with speeds that rotate a pallet simultaneously with its being linearly advanced by the ribbon and one of its pins. Such rotation is desirable to compensate for any deposition gas density variations in a deposition chamber. The flexible ribbon and the pair of cables are all preferably given motion by a common motor source through appropriate mechanical elements so that their relative speeds remain fixed.

Additional objects, advantages and various aspects of the techniques of the present invention will become apparent from the following detailed description which should be taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a deposition machine incorporating the various aspects of the present invention;

FIG. 2 is a partially sectioned view of the machine of FIG. 1 taken across section 2--2 of FIG. 1;

FIG. 3 is a top view of the machine of FIG. 1;

FIGS. 4 and 5 show an enlarged view of the pallet support and pulling mechanism taken across section 4--4 of FIG. 2;

FIG. 6 is a cross-sectional view of the preheat station of the machine of FIGS. 1 and 3 taken across section 6--6 of FIG. 3;

FIG. 7 is a side sectional view of the preheat section of the machines of FIGS. 1 and 3 taken across section 7--7 of FIG. 6;

FIG. 8 is a sectional view of a deposition chamber taken across section 8--8 of FIG. 3;

FIG. 9 is a side sectional view of two deposition chambers taken across section 9--9 of FIG. 3;

FIG. 10 is a side sectional view of the cooling station taken across station 10--10 of FIG. 3, and also shows the cable driving mechanism; and

FIG. 11 is is a top view of the cooling station and cable driving mechanism taken across section 11--11 of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring primarily to FIGS. 1 and 3, the various sections of a machine embodying the various aspects of the present invention are described. A loading station 11 is provided with an idler roller assembly 13 for holding a flexible ribbon 15. The roller assembly 13 is rotatably attached to a frame member 17. The flexible ribbon 15 is driven at a uniform velocity across the top of the frame member 17 in a direction away from the loading station 11 and into a preheat station 19. The ribbon 15 contains a plurality of pins attached thereto and extending substantially perpendicular to the ribbon 15. One such pin 21 is shown in FIGS. 1 and 3 in the loading work station 11. A work piece supporting pallet is positioned in the loading station in a manner that the pin 21 extends upward into an aperture formed in the middle of the pallet, as described hereinafter in more detail.

After loading, a pallet is drawn by the motion of the ribbon 15 through an opening in a baffle 23 into the preheat work station 19. While travelling between the baffle 23 and a baffle 25, a pallet is heated to a very high temperature and thus the substrates to be coated by gas deposition are also heated. The temperature desired may be in the region of 350° to 450° C. depending on the particular materials and the desired coating characteristics. After preheating, the pallet is drawn by the continued motion of the ribbon 15 through an opening in the baffle 25 into the deposition zone 27. The deposition zone 27 includes a plurality of deposition chambers, the number of chambers shown herein to be five. These five chambers are formed in part by five pyramidal shaped shells 29, 31, 33, 35 and 37 which have gas inlets 39, 41, 43, 45 and 47, respectively, installed on their top surfaces. It is through these gas inlets that the deposition gases which react in the presence of the hot wafer surfaces are supplied to each of the deposition chambers. The shells 29, 31, 33, 35 and 37 are removably clamped, such as by a clamp 49, to a deposition head frame 51 that extends the length of the deposition zone 27 between the baffle 25 and a baffle 53. This removability permits access to the interior of each deposition chamber for cleaning and other purposes. The deposition head support 51 is made to be vertically adjustable relative to a support frame 55 of the machine by hand operated cranks 57 and 59 at opposite ends of the deposition zone. As is explained hereinafter, this vertical adjustment affects the gas pressure within each of the deposition chambers.

The interior surface of the deposition head frame 51 is itself shaped from two outside sides of a lower portion of each deposition chamber. The other two sides of each deposition chamber are formed by cross pieces within the frame, for example wedges 61, 63, 65, and 67 which each form one side wall of each of two adjacent deposition zones. These wedge like elements are further water cooled to maintain the temperature of the surfaces below that temperature which will cause deposition gases to coat a layer of material thereon.

A heating slab 69 extends through the preheat zone 19 and deposition zone 27 in order to bring the work piece carrying pallets up to a desired temperature in the preheat zone 19 and thereafter to maintain their temperature in the deposition zone 27. The work piece carrying pallets are pulled by the ribbon 15 along the heating slab very close to its top heating surface but not in direct contact therewith.

A ribbon 15 pulls each pallet completely through the deposition zone 27, through an opening in the baffle 53 and into a cooling work station 71. The cooling work station 71 includes a slab 73 that is cooled by passing heat transferring liquid in pipes about the slab 73. A pallet is then delivered through an opening in a baffle 75 to an unloading work station 77 by the continuous motion of the flexible ribbon 15. It is at this work discharge end that the driving motor for the ribbon 15 and associated gears and pulleys are located.

In order to isolate the deposition chambers from the atmosphere as much as possible, a gas curtain is provided as part of the preheat zone 19 and the cooling zone 71 adjacent the openings in the baffles 25 and 53 for entrance and exit, respectively, of a pallet. A supply pipe 79 provides an inert gas flow downward toward the heating slab 69 as part of the preheat section 19. Similarly, a pipe 81 provides a source of inert gas for a gas curtain in the cooling section 71. The gases introduced to form the gas curtains as well as those supplied to the gas deposition chambers are all vented through vent pipes extending the length of the machine on either side thereof which are connected by some convenient means to a vacuum source.

Besides the lower frame portion, the machine elements are supported by suspending the baffles 23, 25, 53 and 75 from higher frame members (not shown) with cables attached to their upper corners in a manner shown in FIGS. 1 and 2. The flexible ribbon 15 is continuous, looping back from the unloading stage 11 under the main operable portions of the deposition machine.

Referring primarily to FIGS. 2, 4, and 5, the structure of the heating slab 69, its associated elements, and the technique for moving a pallet through the various work stations of the machine may be described. The heating slab 69 is viewed in FIG. 2 from its end in the preheat section 19. A pair of dowel pins 83 and 85 are rigidly attached to the machine frame in the vacinity of the baffle 23 of FIG. 1 and are loosely received by cooperating apertures in an end of the heater slab 69 in a manner that the heater slab 69 can expand and contract over the dowel pins 83 and 85.

A slot 87 extending the length of the heater block 69 is provided in the top surface thereof. Guide rods 91 and 93 are permanently attached to the bottom of the slot 87 and provide a minimum contact support for the ribbon 15 as it is drawn along the length of the heater pad 69.

The heater block 69 is covered with two stainless steel plates 95 and 97 that each extend the length of the heater block 69. The plates 95 and 97 are attached to the top surface of the heater block 69 in a manner to form a space 99 therebetween through which pins attached to the flexible ribbon 15, such as pins 101 and 103, may protrude upward. The plates 95 and 97 by extending over a portion of the slot 87 of the heating block 69 limit the exposure of this slot to unwanted deposition therein. The plates 95 and 97 are removable from the heater block 69 for cleaning by etching or some other appropriate process without having to remove the entire heating block 69 from the machine. Cleaning will be required periodically since layers of material will be depositioned thereon in the gas deposition zone 27.

It will be noted primarily from FIG. 4 that a pallet 105 that is being carried through the various work stations of the machine includes a hole 107 at its center that extends a distance through its thickness from its bottom surface. The hole 107 receives a pin 103 and both are preferably round with a loose connection therebetween in order to permit rotation of the pallet 105 with respect to the pin 103.

The pin 103 and hole 107 in the pallet 105 are further designed so that the pin does not carry any of the weight of the pallet. This is accomplished by making the depth of the hole 107 longer than required to accept the full length of the pin 103. The weight of the pallets as they pass through the deposition zone of the machine is carried by a pair of cables 109 and 111 that run the length of the heater block 69. The cables 109 and 111 are guided by V-shaped grooves 113 and 115, respectively, in the surfaces of plates 95 and 97. Frictional engagement between the underside of the pallets and the top of the cables 109 and 111 permits running these cables at a speed relative to the speed of the ribbon 15 that will rotate the pallets about their associated ribbon pin as that pin drives a pallet along the length of the heater block 69. For counterclockwise rotation of the pallet 105 when looking down upon it, the cable 115 is driven in the same direction but faster than the ribbon 15 while the cable 113 is driven in a direction opposite to that of the ribbon 15. The grooves 113 and 115 in the heater block plates 95 and 97 hold the cables at a fixed distance from and parallel to the slot 99 along the length of the heater block 69. Each of the cables 109 and 111 contacts its associated heater plate at two points around its outer surface and at one point with the pallet.

In order to permit easy rotation of the pallet 105, the grooves 113 and 115 are designed with respect to the size of the cables 109 and 111 so that the cables support each pallet a small distance 117 above the top surface of the plates 95 and 97. The space 117 is made to be very small so that heat transfer from the covering plates 95 and 97 to the pallet is efficient. The result of rotation of the pallet 105 as it is pulled along by its pin 103 through the deposition zone 27 of the machine is that its wafers, such as wafers 119 and 121, are passed through a large cross-section of the deposition gas within each deposition chamber to compensate for any non-uniformities in gas distribution across the pallet 105 while in the deposition zone. This technique of compensation has been found to be easier than attempting to make the gas distribution highly uniform.

It has been found to be most convenient to drive both of the cables 109 and 111 as well as the ribbon 115 from a single electrical motor source. It has further been found easiest to use a single continuous length of cable to form the two cable sections 109 and 111 and thereby to advance the cable at the same speed relative to the heater block 69, but, of course, in different directions. It will be appreciated that if the cables 109 and 111 are travelling at the same speed and contact the pallet 105 at the same radial distance from its driving pin 103 when that pin is not moving, there will be rotation of the pallet 105 without any substantial slip between the cables 109 and 111 and the bottom surface of the pallet 105. However, when forward motion is given to the pin 103, the radial distances from the pin 103 to the points of contact by the cables 109 and 111 must be made unequal. In the embodiment shown in the drawings, the cable 111 that moves in the same direction as the driving pin 103 is spaced closer to the pin slot 99 than is the cable 109 which travels in the opposite direction on the opposite side of the pin slot 99. This assures rotation of the pallet 105 without substantial slip between it and the cables 109 and 111, simultaneously with the pallet being advanced along the length of the heater block 69. This is accomplished with a very simple mechanical drive means, the details of which are shown in FIG. 10.

The heater block 69 is heated by a plurality of heater cartridges such as those shown in FIG. 2, one of which is identified with the reference numeral 123. These heater cartridges extend in holes provided through the heater block 69 across its width. When a heater cartridge burns out, it is easily removed and replaced with another one. Thermocouples, not shown, are also desirably affixed to the surface of the heater block 69 at various locations along its length in order to monitor its temperature. The temperature of the wafers or other substrates carried by the pallets is controlled by the heater block temperature and thus also the chemical reactions between the substrate surfaces and the deposition gas are controlled thereby.

Specific structure of the individual chambers in the deposition zone 27 may best be observed with respect to FIGS. 8 and 9. The perspective view of FIG. 2 also shows some deposition chamber detail. Each of the deposition chambers within the deposition zone 27, such as the chamber formed partially by the shell 37, has a small cross-sectional area at its top portion through which a gas supply hose 47 passes for connection with a gas diffusion discharge jet 125. The jet 125 is movable for vertical positioning by means of a boss 127. The cross-sectional shape of the deposition chamber internal space shown in FIG. 8 is recilinear, or in this case a square, at any position along its height when observed by a projection upon a horizontal plane. A bottom square opening for exposing work pieces on a pallet 129 to the gaseous atmosphere within the deposition chamber is formed by the lower edges of the pyramidal sides which lie in an imaginary plane identified by the reference character 131. This plane is parallel to the heater surface and spaced a distance therefrom which permits passage of a pallet and its wafers or other work pieces from one deposition chamber to the other under the influence of the ribbon 15. The sides of each deposition chamber extend no lower than the plane 131 on the edges wherein adjoining deposition chambers are joined together.

However, along the outside walls of each deposition chamber are flanges 133 and 135 that extend the entire length of the deposition zone 27 on opposite sides thereof. These flanges 133 and 135 extend closer to the heating block 69 than the imaginary plane 131 in a manner to form slits 137 and 139 extending the length of the deposition zone 27 on opposite sides thereof. The slits 137 and 139 serve to exhaust the gaseous atmosphere from within each of the deposition chambers. These slits are made to be at an elevation below the surface of a pallet so that any particulate material that is deposited and then broken away into particles will be exhausted out of the deposition chambers through the slits 137 and 139 rather than finding their way to the work pieces carried by the top surface of the pallet. This particular structure improves the resulting work product.

As part of the exhaust system, exhaust chambers 141 and 143 are provided on opposite sides of the deposition zone and extend its full length. These chambers are formed, respectively, by metal shells 145 and 147. The shells 145 and 147 are pivotable about pivot rods 149 and 151, respectively, in order to provide for access to the sides of the machines when these chamber structures are pivoted downward and out of the way. The exhaust chambers 141 and 143 are connected to some convenient vacuum source (not shown).

The height of the slits 137 and 139 are adjustable by moving the deposition zone frame structure 51 up and down with respect to the rest of the machine. Such an adjustment controls the deposition gas pressure within each of the deposition chambers. The frame 51 is adjustable by the mechanisms 57 and 59 at opposite ends thereof. The adjusting mechanism 57 is shown in some detail in FIG. 7 wherein a bracket 153 is attached to the baffle 25. A crank 155 and a worm 157 are attached to a shaft that is journaled in the bracket 153. The worm 157 when rotated by the crank 155 drives a worm gear 159 up and down a threaded shaft 161. The worm gear 157 is threaded in its interior opening and the threaded shaft 161 is rigidly attached to the deposition zone frame 51.

The heater block 69 is supported by small cross-sectional support pins at periodic locations along its length. Referring again to FIG. 8, pins 163, 165 and 167 are shown to support the heater block 69 across its width on a support frame plate 169. These pins are made of a small area in order to reduce the heat removed thereby from the heater block 69. A heat reflecting shield 171 is positioned beneath the heater block 69 and has sides that wrap around and extend upwards adjacent the sides of the heater block 69 to reflect upwards. This heat reflecting shield also forms a chamber under the heating block 69 that is purged by an inert gas (such as nitrogen) that is introduced therein by a number of gas diffuser nozzles extending the length of the deposition zone, such as the nozzles 173 and 175. The gas introduced in this region is also exhausted through the exhaust chambers 141 and 143.

The preheat station 19 is shown in detail in FIGS. 6 and 7 wherein it will be noted that the heater slab 69 extends thereinto and contains a density of heater cartridges, including the cartridges 123, that is greater than the density of heater cartridges along the heater slab 69 within the deposition zone 27.

An opening 177 in the baffle 25 permits enough space for a pallet containing wafers or other work pieces to pass therethrough from the preheat zone 19 to the deposition zone 27. Since the atmosphere within the deposition chambers of the deposition zone 27 is carefully controlled, it is desirable that no undesired gases enter through the opening 177. It is further desired that the deposition gases within the deposition chambers not escape through the opening 177. Therefore, a gas curtain is provided within the preheat section 19 adjacent the opening 177 which permits the pallets and wafers to pass therethrough but at the same time helps isolate the deposition chamber gas atmosphere from the outside. The gas curtain within the preheat section 19 is chosen to be an inert gas such as nitrogen and preferably the same gas that is used as a carrier for the gaseous mixture within the deposition chambers.

The gas input through a hose 79 in the preheat section 19 is passed through an enclosure 179 to a diffusion gas head 181 wherein the gas is discharged in random directions. Beneath the gas head 181 is a block of honeycomb material 183 which is used for its characteristic of providing a large number of small tube-like openings oriented in a vertical direction for collimating the gas flow downward past the opening 177. Each of the tube-like openings is preferably in the order of less than one-eighth of an inch across. Other specific structures than the honeycomb material could be used, but the honeycomb material is preferred for its convenience of already providing a large number of small tube-like structures held together and further does so with a very thin wall structure therebetween.

A purging inert gas is also provided beneath the heater block 69 by nozzles 172 and 174. Both this purging gas and the gas curtain above the heater block 69 are exhausted into exhaust chambers 176 and 178 on sides of the preheat section. The chambers 176 and 178 are constructed of shells that are pivotable away from the machine in order to provide access to the sides of the preheat section.

The cooling station 71 has its cooling block 73 positioned so that the flexible ribbon 15 draws a pallet thereover for cooling. The pallets are drawn from the last of the deposition chambers within the deposition zone 27 to the cooling station 71 through an opening 185 in the baffle 53. The cooling station 73 is cooled by passing a liquid, such as water, through a tubular structure 187 that is in contact with the cooling block 73. The liquid in the tube 187 is cooled by external configuration equipment (not shown). The cooling block structure is similar to that of the heating block 69 with respect to the accommodation to the ribbon 15 and the cables 113 and 115, as described with respect to FIG. 3. However, there is a significant difference in that a slot 189 in the surface of the cooling block for carrying and guiding the cable 113 has a rectangular shape in cross-section and is deep enough so that the cable 113 is lodged beneath the surface of the cooling block 73. The cable 115 is recessed in a similar slot 191. The cables 113 and 115 thereby do not support a pallet in the cooling station 19 but rather the pallet is in direct contact with the top surface of the cooling block 73. There is no need in the cooling station 71 for rotating the pallets.

The cooling station 71 also provides a gas curtain for preventing exchange of atmospheric gases through the opening 185 into the deposition chambers. The gas supply hose 81 passes through a cover enclosure 193 and terminates in a diffusing gas nozzle 195. A block of honeycomb material 197 is positioned beneath the gas diffusing head 195. The bottom edge of the honeycomb material 197 is adjacent the upper edge of the slot 185. The gas discharged from the honeycomb material 185 is thus collimated since the individual passages of the honeycomb material 195 are small, such as less than one-eighth inch across, to reduce turbulence and maintain a uniform downward gas flow.

Referring again to FIGS. 10 and 11, a preferred mechanical drive system for the ribbon 15 and the cables 113 and 115 is described. A single electric motor 199 mounted on a frame member 201 applies motion through appropriate motion translating elements, as shown, to a ribbon driving pulley assembly 203 which is rotatably held by a machine frame member 205. Associated pulley assemblies 207 and 209 assure that the ribbon 15 is held firmly by the driving pulley 203 to prevent slippage therebetween. The pulley assembly 207 includes two rollers spaced apart on its rotating shaft in order to provide a space therebetween for the pins attached to the ribbon 15 to travel.

As mentioned hereinabove it is preferred for simplicity and assurance of the proper speed relationship that the cables 113 and 115 be in fact a single continuous cable that is driven at one point. A driving pulley 211 receives motion from the motor 199 by appropriate motion transmitting elements. The cable section 115 reaches the pulley 211 after first passing over an idler direction changing pulley 213. A second direction changing pulley 215 directs the cable across the width of the machine to another direction changing idler pulley 217. The path of the cable continues through another pulley (not shown) in order to give it a vertical direction to contact an idler pulley 19 to give the cable direction along the opposite side of the deposition machine. There are numerous specific mechanical drive arrangements possible, but the single motor drive arrangement with a single pallet rotating cable is preferred for simplicity and ease of controlling the relative velocities between the ribbon and cable sections.

The various aspects of the present invention have been described with respect to a preferred embodiment thereof, but it will be understood that the invention is entitled to protection within the full scope of the appended claims.