JPS599623B2 - Method for cooling induction heated vapor deposition equipment and cooling device therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cooling method, and more particularly to a method for cooling an induction heated vapor deposition apparatus.

Inductively heated deposition systems typically include a deposition enclosure (within which is disposed a susceptor-supported wafer surrounded by essentially non-electrically insulated windings of an RF induction heating coil). (such as epitaxial quartz tubes or Bel Shears).

When current is passed through the coil winding, the coil induces heating of the susceptor to a temperature (at least 500 DEG C.) sufficient to cause the gases passing through the deposition enclosure to precipitate epimexially onto the wafer. Disadvantageously, as the susceptor heats the wafer, it also heats the encapsulation, thereby promoting precipitation of gases passing through the encapsulation onto the inner walls of the encapsulation. Such deposits on the inner walls of the deposition enclosure have a detrimental effect on the quality of the material growing within the deposition enclosure, promoting the formation of spikes, pits, and various other surface defects. Such precipitates may also contain dopant from a given operation, in which case the precipitate may act as an unwanted source of dopants in future continuous operations. To remove these precipitates once formed, the deposition enclosure must be removed from the stream for cleaning, thereby reducing the productivity of the deposition apparatus. To prevent the formation of such precipitates, it is common to cool the deposited enclosure by any of a variety of known techniques. For example, air,
Nitrogen or other gas may be directed in a cooling stream onto the exterior of the deposition enclosure to absorb and remove heat therefrom. A water jacket may be placed around the vapor deposition enclosure, through which water flowing absorbs and removes heat from the exterior surface of the vapor deposition enclosure. The deposition enclosure may be at least partially surrounded by a black box that absorbs radiant heat from its outer surface. An exhaust system, such as a shielded envelope tube, may be used to remove heat from the immediate vicinity of the external surface of the body being deposited. However, all of the known cooling techniques unduly increase the capital and operating costs of the system (
(e.g., by requiring expensive gas cooling, heat exchangers, exhaust ducts, etc.) without providing sufficient cooling. To fully understand the complexity of the problem, it is used. This cooling technique not only avoids any possibility of short circuits across the RF coil (a typical voltage difference of about 16 kilovolts exists at this point) but also between adjacent windings of the RF coil or within one winding. It must be understood that short circuits from the line to ground must also be avoided.

There is a fundamental match between the oscillator circuit of the RF induction source (or generator) and the coil induction frequency of the susceptor within the vapor deposition enclosure. Any frequency change from the normal frequency (typically around 4.5 MHz, but depending on the equipment used) due to a mismatch as a result of a minimal short circuit or grounding of the coil windings will be within 1 millivolt. However, this results in loss of oscillator tuning and therefore effective loss of power. Accordingly, one object of the present invention is to provide an economical and efficient method for cooling an induction heated deposition apparatus.

Another object of the invention is to provide the above method which is safe and easy to operate.

Yet another object of the invention is to provide an apparatus for use in such a cooling method.

It has been found that the above and related objects of the invention are obtained in a cooling method consisting of the use of deionized water sprayed directly onto the deposition apparatus.

In the past, the high operating potential of RF coils (up to 16 kilovolts or more) has been considered by those skilled in the art to make the use of direct water cooling techniques extremely hazardous to nearby personnel; It has been found that deionized water, which has a resistivity of one tag ohm, can be safely used in such cooling processes. Deionization of water increases its resistivity to the point that the spray can be safely used in the process. Furthermore, deionization of water avoids the precipitation of material on the outer surface of the vaporized inclusion as the water spray evaporates, thereby affecting the temperature profile maintained within the vaporized inclusion and thus reducing the desirability of materials that require removal. Minimize the formation of no localized precipitates. More particularly, the present invention provides an induction heating system comprising an electrically grounded vapor deposition enclosure and an RF induction heating coil having an essentially electrically non-insulated winding disposed around the vapor deposition enclosure. The present invention relates to a method for cooling a vapor deposition apparatus.

The method consists of spraying a deionized liquid having a resistivity of at least 14 tag ohms directly onto the device.

The deionized liquid is typically at room temperature, preferably deionized water. The deionized liquid is generally sprayed directly onto the deposited enclosure and coil windings, preferably onto the top of the device. The deionized liquid is preferably applied in a volumetric pattern such that the hotter sections of the deposition enclosure receive a greater volume of deionized liquid than the cooler sections. In a preferred embodiment of the invention, the device is placed over a container adapted to receive a fluid, the ends of the coil being threaded through the bottom of the container, and the ends of the coil being connected to the container and its liquid contents. electrically isolated from

The coil ends are preferably wrapped in polytetrafluoroethylene to electrically isolate the coil ends. Another aspect of the invention relates to an improvement in an apparatus suitable for use in cooling such an inductively heated vapor deposition apparatus, providing access to the vapor deposition enclosure for spraying such deionized liquid directly onto the enclosure. and means for recovering the sprayed liquid.

Preferably, the collection means comprises a container adapted to receive the liquid, and the vapor deposition device is arranged above the bottom of the container such that the ends of the coil pass through the bottom of the container, and the vapor deposition device is arranged above the bottom of the container, with the ends passing through the bottom of the container. electrically isolated from its liquid contents.

The blowing means, the collecting means and the coil end are preferably independently grounded. Now the drawings, especially the first and second figures.
Referring to the figures, an induction heated deposition apparatus, generally designated 10, is illustrated.

Apparatus 10 is mounted within an open-topped container 12 or pan adapted to receive a fluid and includes a vapor deposition enclosure 1.
4 (for example, a horizontal quartz epitaxy tube) and the vapor-deposited enclosure 14
an RF induction heating coil 16 coated on the inside with water and having a winding 18 disposed around the RF induction heating coil 16 . As is customary in such devices, an inlet conduit 20 is provided to deliver the gases necessary for crystal growth to the inlet end of the deposition chamber 14, while a deposition enclosure is provided to remove unused gas flowing in the direction of arrow 23. An outlet conduit 22 is connected to the outlet end of body 14 . Suitable spacers (not shown) made of electrically insulating material are used to maintain the spacing of the coil windings 18.
One end 24 of the RF induction coil 16 is fixed to an RF induction source such as a generator (not shown), and the other end 24 is grounded.
A stepped susceptor (not shown), which is tuned to the oscillator circuit of the generator, is arranged within the deposition enclosure 14. All of the above elements (with the exception of pan 12) are known in induction heated deposition apparatus and will not be further described here. Next, the novel features of the present invention will be described.
The known device 10 is located intermediate the top and bottom of the pan 12, with the bottom of the coil winding 18 preferably being about a finch (about 17.780!IL) above the bottom of the pan;
A gas inlet 20 and a gas outlet 22 extend through the pan side walls.

Pan 12 is preferably an electrically grounded frame (not shown)
1 inch below the bottom of the pan 12 for reasons explained below.
! L) It has an electrically insulated drain 26 to keep it above and discard the excess. Disposed above the deposition apparatus 10 is a spray system, generally designated 30, which spray system 30 extends over the top of the apparatus disposed thereon, and more particularly over the deposition enclosure 14 and the coil windings 18. It consists of a liquid conduit 32 having a plurality of nozzles 34 adapted to atomize the liquid.

Spray system 30 is connected to a source (not shown) of deionized liquid, preferably deionized water, having a resistivity of at least 14 tag ohms, which source is connected to conduit 32.
and thus through the atomizing nozzle 34 onto the device 10 . The deionized liquid is at least 14
The condition that it must have a resistivity of 14 to 18 Tag ohms, preferably 14 to 18 Tag ohms, means that the path of the deionized fluid distributed along the vaporized enclosure and the RF coil is uncontrollable. It is based on the assumption that at some point the distributed spray may constitute an electrical path exposed to the full power of the RF source (approximately 16K in this case). The deionized (i.e., non-mineralized) nature of the fluid sprayed onto the deposition apparatus may cause localized cooling on its outer walls, eventually requiring closure of the apparatus for precipitate removal. There is no mineral precipitate that will prevent it from forming. too. Of course, the spray system 30 is constructed of a material that does not adversely affect the deionized nature or high resistivity of the fluid passing therethrough in the direction of arrow 35. Since both ends 24 of the RF coil 16 pass through the bottom of the container 12 and there is a shallow reservoir of fluid 38 above the bottom of the pan (see FIG. 2), each end 24 of the RF coil has a total of 40
It is shielded from the pan 12 (and the fluid therein) by an isolation assembly shown at . Referring now specifically to FIG. 3, each isolation assembly 40 includes a pair of coaxial tubes with an inner tube 42 made of Teflon (DuPont's registered trademark for polytetrafluoroethylene) and an outer tube 42 at each end. and a threaded aluminum outer tube 44.

A Teflon rim 46 is positioned intermediate each end of the tubes 42, 44, while an aluminum rim 46 is placed on each end of the outer aluminum tube 44 to mechanically lock the rim 46 with the tubes 42, 44. A nut 48 is screwed on. Fitted onto the outer end of each aluminum nut 48 is a Teflon bushing 50 that connects the coil end 24 and inner tube 4.
2 and has an inner flange 52 extending downwardly to seal the coil end 24 from exposure to fluid in the reservoir. Top of isolation assembly 40 (i.e. top of bush 50)
extends approximately 3 inches (about 7.62 CfL) above the bottom of the pan and thus about υ 2 inches (about 5.08?) above the level of the fluid in the sump. The presence of fluid in the sump also helps to keep the pan 12, and therefore the Teflon portion of the isolation assembly 40 passing therethrough, cool (which could otherwise crack);
Positioning the top of isolation assembly 40 above the level of the fluid in the sump minimizes the possibility that fluid in the sump provides a direct electrical path between the two coil ends 24. The minimum thickness of the inner sleeve 42 of the isolation assembly 40 depends on the type of material used.

Polytetrafluoroethylene has a dielectric capacity of 1 kilovolt per millimeter of thickness, so it has a dielectric capacity of 0.060 inches (0.060 inches).
The inner sleeve thickness of 1524 (Mlt) is more than sufficient for power applications including up to 16 kilovolts. Polytetrafluoroethylene is well known for its ability to withstand high temperatures without melting, its insulating properties, its ease of machining, its nonporous nature, and its ability to withstand temperature differences without cracking. Plastics are preferred because of their malleability. Isolation assemblies 40 utilized on both ends 24 of the RF coil are only required because the ends pass directly through the fluid boule at the bottom of pan 12.

If the RF coil 24 is connected from the pan 12 through its side (
The isolation assembly 40 may be absent altogether if it is removed (not at the bottom) and above the level of the fluid accumulated therein. Deionized fluid may also be directed by nozzles 34 on both sides and at the bottom of the deposition enclosure 14, provided that the pan 12 has sufficient height to ensure collection of the dispensed spray. It is usually the top of the deposition encapsulant 10 that is the hottest and therefore requires the greatest amount of cooling. Varying the spacing of the nozzles 34 so that the hot section always receives a larger volume of deionized liquid than the cooler section (e.g., by clustering the nozzles at the hot end of the deposition apparatus as shown in Figure 1). ) or by varying the volumetric capacity of a particular nozzle 34. The required resistivity of the fluid, the fluid volume fraction utilized, the spray angle and the spray pattern to be employed will all vary with the particular application. and the amount of cooling desired (as determined by the available RF source power and the tendency of the gas to condense on the deposited inclusion walls), the area of the deposited inclusion, the RF power range employed, and the susceptor temperature selection. and depends on factors such as contour.

RF power range up to 16 kilovolts and susceptor temperature of at least 500°C, typically 1000-1200°C
and for a given application involving deposition from ChlorOsilane gas, suitable parameters are: Water specific resistance 14~
18 tag ohm nozzle spray angle 80-90 tag nozzle spray pattern Nozzle volume for complete cone system: 0.052 gallons per minute at 30 psig Nozzle spacing: 8 inches (20.32 (177!)
For tubes, the center-to-center spacing is 8 inches (20.
32 CTIL) Inner sleeve thickness of isolation assembly: 0.060 inch (A). 1524
(7n) The method described above is suitable for use in operations requiring minimal amounts of deionized fluid, but if larger volumes are required, the used deionized fluid is simply discarded. It is more economical to collect, cool and recycle it than to collect it, cool it and recycle it.

As a safety measure, drain 26, pan 12, vapor deposition enclosure 1
4. Furthermore, the fluid conduit 32 should also be independently grounded. Additionally, the walls of pan 12 should be of sufficient height to prevent sprayed liquid from splashing back from the deposition enclosure and pan 12. Although the object of the invention is a cooling method, it goes without saying that care must be taken to avoid overcooling the vapor-deposited enclosure, especially local overcooling thereof. For this purpose, the deionized fluid is preferably at or near room temperature and the nozzles 34 are spaced far enough apart to minimize spray overlap. on the other hand,
A row of nozzles 34 extending along the length of the deposition enclosure 14
Multiple parallel rows of nozzles 34 may be used if the nozzles 34 cannot provide sufficient cooling because of the width of the deposition enclosure 14. According to the invention, the walls of the deposition enclosure can be easily and economically cooled, resulting in less deposition on the inner walls of the deposition enclosure, thereby improving the quality of the epitaxial crystals deposited (spikes, pits, etc.). Maintenance is minimized by minimizing surface defects and V)), contamination of future operations with absorbed dopants is minimized, and gas cooling, water jackets, black boxes and exhaust systems are not required. Therefore, operating costs can be reduced. Accordingly, the present invention provides a cooling method that is economical, efficient, safe and easy to operate. Now that the preferred embodiments of the invention have been illustrated and described in detail, various modifications and improvements in the invention will become readily apparent to those skilled in the art.

Accordingly, the spirit and scope of the invention should be limited only by the claims appended hereto, and not by the above disclosure.

[Brief explanation of the drawing]

FIG. 1 is a fragmentary top view of an apparatus useful in the method of the present invention; FIG. 2 is a fragmentary side elevation partially sectioned along line 2--2 of FIG. 1; and FIG. 3 is a RF FIG. 3 is a fragmentary, enlarged side elevational view, partially in section, of the encapsulated end of the coil; Explanation of symbols of main parts, vapor deposition equipment...10, 1
2... Container, 14... Evaporation inclusion body, 16... RF
Induction heating coil, 18... Coil winding, 34... Nozzle.

Claims (1)

Claims: 1. An induction heated heating coil comprising an electrically grounded vapor deposition encapsulant and an RF induction heating coil having an essentially electrically non-insulated winding disposed around the vapor deposition encapsulant. A method for cooling a deposition apparatus comprising the step of spraying a deionized liquid having a resistivity of at least 14 megohms directly onto the apparatus. 2. The method of claim 1, wherein the deionized liquid is deionized water. 3. A method according to claim 1 or claim 2, characterized in that the deionized liquid is sprayed directly onto the evaporative inclusion and the coil winding. 4. A method according to claim 3, characterized in that the deionized liquid is sprayed directly onto the top of the device. 5. The method of claim 1, wherein the deionized liquid is at room temperature. 6. In claim 1, the deionized liquid is sprayed in a pattern such that hotter areas of the vapor deposition enclosure receive a greater volume of the deionized liquid than cooler areas. How to characterize it. 7. In claim 1, the device is disposed within a container adapted to receive a fluid, the ends of the coil passing through the bottom of the container, and the ends of the coil extending through the bottom of the container and its liquid contents. A method characterized by electrical isolation from objects. 8. The method of claim 1, wherein the coil ends are wrapped in polytetrafluoroethylene to electrically isolate the coil ends. 9. The method of claim 7 including the step of maintaining a liquid level in the container below the top of the wrapped coil end. 10. Cooling an induction heated deposition apparatus comprising an electrically grounded deposition enclosure and an RF induction heating coil having an essentially electrically non-insulated winding disposed around the deposition enclosure. in an apparatus for at least 14
means positioned in a position accessible to the inclusion body for spraying a deionized liquid having a resistivity of one megohm directly onto the inclusion body; and means for collecting the sprayed liquid. A device comprising: 11. The device according to claim 10, wherein the deionized liquid is deionized water. 12. The apparatus of claim 10, wherein said spraying means is arranged to spray said deionized liquid directly onto said enclosure and said coil winding. 13. The apparatus of claim 12, wherein said spraying means is arranged to spray said deionized liquid directly onto the top of said vapor deposition apparatus. 14. In claim 10, the spraying means applies the deionized liquid in a pattern such that hotter areas of the vapor deposition enclosure receive a larger volume of the deionized liquid than cooler areas. A device characterized in that it is arranged to spray. 15. In claim 10, the recovery means comprises a container configured to receive a liquid, and the vapor deposition device is arranged so that both ends of the coil pass through the bottom of the container. Apparatus, characterized in that it is located higher up and that said ends are electrically isolated from said container and its liquid contents. 16. The apparatus of claim 15, wherein the coil ends are wrapped in polytetrafluoroethylene to electrically isolate the coil ends. 17. The apparatus of claim 15, including means for maintaining a liquid level within the container below the top of the wrapped coil end. 18. The apparatus of claim 17, wherein said level maintenance means comprises means for maintaining said liquid level approximately 1 inch (2.54 cm) above the bottom of said container. 19. The apparatus according to claim 10, comprising means for independently grounding the spraying means and the collecting means. 20. The device according to claim 15, wherein the coil end is grounded.