Production of high-purity polycrystalline silicon rod for semiconductor applications

Abstract

Disclosed are a processes and reactors for rapidly producing large diameter, high-purity polycrystalline silicon rods for semiconductor applications by the deposition of silicon from a gas containing a silane compound. The equipment includes a reactor vessel which encloses a powder catcher having a cooled surface. Also within the vessel is a cylindrical water jacket which defines multiple reaction chambers. The silicon powder generated in this process adheres to the coolest surfaces, which are those of the powder catcher, and is thereby collected. Little of the powder adheres to the walls of the reaction chambers. In some embodiments, a fan can be provided to increase gas circulation.

Description

This is a continuation of application Ser. No. 296,964, filed Aug. 26, 1994, ≦<T1≦<T3, where T1 is the wall temperature of the reaction chambers 3, T2 is the wall temperature of the powder catchers 5 and 6, and T3 is the wall temperature of the upper section of the verger-type cover 1. By making the wall temperature T3 of the reactor ceiling section high, the adhesion of silicon powder to the ceiling section further decreases.

It is desirable that the wall temperature T1 of the reaction chambers 3 be 25°C or more. Further, the temperature of the lower cover section 1b opposed to the reaction chambers 3 is also set to be 25°C or more. A cooling water at a temperature of 30°C to 40°C can be easily obtained by utilizing equipment such as a cooling tower. It is desirable for the wall temperature T2 of the powder catchers 5 and 6 to be 25°C or less. Also in this regard, a cooling water at a temperature of 10°C to 15°C can be easily achieved by directly utilizing water drawn from a well. Cooling water at a temperature of approximately 5°C can be easily supplied by utilizing equipment such as a chiller.

It has been experimentally ascertained that circulating silicon powder is most likely to adhere to and accumulate on surfaces of the lowest temperature. The lower the temperature, the greater the amount of adhesion. A cooling water temperature around 5°C is desirable for the powder catchers 5 and 6 for powder removal efficiency. It is desirable that the wall temperature of the reactor ceiling section, i.e., the temperature T3 of the upper cover section 1a, be 70°C or more. When using water, the phenomenon of boiling may take place at a mean water temperature of around 85°C, depending upon the conditions, so that it is more desirable to use a heating medium other than water when a temperature of 85°C or more is involved. When the difference between the temperatures T1 and T3 becomes approximately 30°C or more, the effect of preventing the silicon powder adhesion to the reactor ceiling section becomes remarkably high.

By installing the heat shield plate 15 above the reaction chambers 3 and keeping the walls in the region above the reaction chambers 3, to which silicon powder should not adhere, at high temperature, little silicon powder adheres in this region. The heat shield plate 15 may consist of a polished metal plate having high reflectance, for example, a stainless steel plate, which excels in heat resistance and corrosion resistance. A ceramic plate excelling in heat resistance, such as a quartz glass plate, may also be used for the heat shield plate 15. The plate 15 may be annular or a series of separate plates.

While, in the embodiment described above, the reaction chambers 3 are formed as cylindrical spaces having vertical openings through the outer peripheral surface of the water jacket 4, from which the grown polycrystalline silicon rods are extracted, this should not be construed restrictively. It is also possible to form the reaction chambers as completely cylindrical spaces having no such openings, the grown polycrystalline silicon rods being extracted by pulling them upwards out of the reaction chambers. Further, it is also possible to provide reaction chambers on both the outer and the inner peripheral surfaces of the water jacket 4. Or, the water jacket that is equipped with reaction chambers may be provided in a central region of the reactor, with the powder catchers arranged around it.

When the fan 20 is used, its rotating drive shaft extends through the base plate 2 and connects to a driving motor (not shown). To prevent the escape of silane gas, which is inclined to ignite spontaneously upon coming into contact with air, a shaft seal or insulation is provided. Such sealing can be easily realized utilizing known devices such as magnetic seals. The speed of rotation is selected to provide a gas flow rate which minimizes the deposition of powder at locations from which it can slough off onto the growing rods. The optimum speed will depend on the size and shape of the reactor and composition of the circulating gas. Thus, for any given reactor, the best speed is determined by experimentation.

In the embodiment of FIG. 4, a verger-type cover or bell 101 and a round base plate 102 provide a reactor vessel. A cylindrical partition member 103, that is a heat exchanger or water jacket and that is shaped to define multiple reaction chambers 103, is provided inside a cylindrical space defined by the cover 101 and base plate 102. A powder catcher 105 is positioned at an elevation above the tops of the reaction chambers 103. The illustrated powder catcher is a cylindrical array of heat exchange tubes 130 that are concentrically arranged. The array is in the shape of a disk having a central vertical passageway 132. Multiple thin fins (not shown) may be attached to the tubes 130 to increase the area of the cooled surface that is provided by the powder catcher. The illustrated powder catcher 105 is positioned so that it is not directly over the reaction chambers 103. This arrangement reduces the small likelihood of agglomerated powder falling from the powder catcher into one of the reaction chambers. The arrangement is also advantageous in that an unobstructed region 133 is provided over the reaction chambers so that heated gas is free to rise up and away from the growing rods 119 at a rapid rate.

The water jacket 104 and powder catcher 105 are positioned and spaced such that gas which exits from the tops of the reaction chambers 103 flows through the array of tubes 130 and into the passageway 132. The passageway 132, along with a central passageway 134 defined by the water jacket 104, serves as gas downflow passageway. The reaction chambers 103 consist of cylindrical spaces arranged at equal intervals in the vicinity of the outer periphery of the water jacket 104. Openings leading from the outer periphery of the water jacket 104 to the reaction chambers 103 are provided for purpose of enabling the extraction of polycrystalline silicon rods which have been completely grown.

The cover 101 and the tubes 130 of the powder catcher 105 are at least partially hollow and serve as water cooled heat exchangers. The cover 101 is formed by connecting upper and lower cover sections 101a and 101b with each other. The lower surface of the upper cover section 101a serves as the reactor vessel ceiling. Provided in the upper cover section 101a are a cooling water inlet 101c and a cooling water outlet 101d. Provided in the lower cover section 101b are a cooling water inlet 101e and a cooling water outlet 101f. As it moves from the inlet 101c to the outlet 101d, cooling water flows through the space between the inner and outer walls of the cover. Connected to the bottom of the water jacket 104 are cooling water supply pipes 107a and 107c which extend from below through the base plate 102. Extending through the upper cover section 101a are water supply pipes 107b which provide cooling water to manifolds 136 for distribution into the tubes 130. Heated water from the tubes 130 is removed via a discharge pipe 107d which also extends through the upper cover section 101a. The water flowing through the water cooling jacket 104 and tubes 130 may be replaced by another fluid cooling or a heating medium.

Electrodes 109 extend from below through the base plate 102, through the intermediation of insulating members 108, and are arranged at positions corresponding to the centers of the reaction chambers 103. Chucks 110 are attached to the tips of the electrodes 109.

Resistant plates (not shown) can be arranged at appropriate intervals inside the reactor as explained with regard to the embodiment of FIGS. 1-3. The plates extend transversely to gas downflow passageways to regulate gas flow. Provided in the space above the water jacket 4 is are heat shield/deflector plates 115. The plates 115 are positioned so that gas which rises from the reaction chambers 103 is channeled into the powder catcher 105.

An exhaust pipe 116 extends through the base plate 102 and can be used to remove spent reactant gas. Reactant gas pipes 111a allow reactant gas to be evenly ejected into each reaction chamber through openings 113a on the surface of the water cooling jacket 104. To provide an even gas distribution, the openings are provided at multiple positions and at multiple elevations. Gas added at the higher elevations makes up for the depletion of silicon from the reactant gas that moves upwardly in the reaction chambers 103.

Polycrystalline silicon rods are produced by the apparatus of FIG. 4 by positioning silicon starter filaments 117 are in the reaction chambers 103 where they are held by the chucks 110. Pairs of silicon starter filaments 117 are connected to each other at their upper ends through silicon bridges 118. Cooling water is circulated through the cover 101, the water jacket 104 and the powder catcher 105. The silicon starter filaments 117 are heated by directly supplying electricity thereto through the electrodes 109. Then, a silicon-bearing reactant gas is fed into the reactor through the reactant gas pipes 111a and the gas nozzles 113a. Then, while ascending inside the reaction chambers 103, which are heated by the silicon starter filaments 117, the gas reacts to deposit polycrystalline silicon 119 on the silicon starter filaments 117. Reactant gas which has moved upwards beyond the reaction chambers 103, in a laminar convection flow, next passes through the heat exchange tube array and along the wall surfaces of the powder catcher tubes 130, descends through the passageways 132 and 134, and then returns to the reaction chambers 103. A fan mechanism (not shown) can be located in or below the passageway 134.

The powder catcher 105 performs the two functions of collecting silicon powder and effecting heat exchange. Accordingly, the temperature in the reaction chambers 103 can be independently regulated to achieve the best growth conditions for polycrystalline silicon rods. Since floating silicon powder collects on cool surfaces, such as on the walls of the powder catcher tubes 130, accumulation thereof on the walls of the reaction chambers 103 and the reactor ceiling section can be avoided to a large degree.

Another embodiment, as shown in FIG. 5, is closely related to the embodiment of FIG. 4, with like elements being similarly numbered, but incremented by 100 in FIG. 5. In the apparatus of FIG. 5, reactant gas moves upwardly from the reaction chambers 203 into a tube array of the powder catcher 205 where the gas is cooled and powder deposits. The cooled gas is not returned to the bottom of the reactor via a central passageway, but instead moves down from the powder catcher and descends along the cooled wall 240 of the water jacket 204. A top plate 242 is provided at the top of the water jacket 204 to direct gas back outwardly to the region above the reaction chambers 203. An exhaust pipe 216 extends through the base plate 202 and top plate 242, for removing spent reactant gas when necessary.

Yet another embodiment is shown in FIG. 6. This embodiment is closely related to the embodiment of FIG. 5, with like elements being similarly numbered, but incremented by 100 in FIG. 6. In the apparatus of FIG. 5, reactant gas moves upwardly from the reaction chambers 303 into a powder catcher 305 having two concentric tube arrays. An inner array 350 is similar to the tube array of FIGS. 4 and 5. An outer tube array 352 concentrically surrounds the inner array 350. The outer tube array 352 provides an additional surface for the deposit of powder. Most conveniently the inner and outer arrays are in fluid communication with one another so that a single source of cooled water can feed both arrays. In the illustrated embodiment cooling embodiment, both a cooling water supply pipe 307b and a cooling water discharge pipe 307d enter the reactor through the same opening. And, both pipepipes are connected to both arrays by manifolds 356b and 356d respectively. e respectively, where the gas is cooled and powder deposits.

Having illustrated and described the principles of our invention, it should be apparent to those persons skilled in the art that such an invention may be modified in arrangement and detail without departing from such principles. For example the powder catcher used in the above described reactors could be constructed in a variety of configurations, including some combination of cooled tubes, cooled plates, and/or cooled wall surfaces, or the like. We claim as our invention all such modifications as come within the true spirit and scope of the following claims.

Claims

1. A process for the production of polycrystalline silicon rods from a silicon-bearing gas, the process comprising:

providing a reactor vessel having an interior surface including a floor, a wall and a ceiling, the vessel containing a cooled partition with a wall which defines multiple reaction chambers and containing a powder catcher which is displaced from the reaction chambers, has a cooled wall, and is in the form of a heat exchange tube array;

positioning a starter filament in each reaction chamber where a polycrystalline silicon rod is to be grown;

heating the starter filaments;

passing a silicon-bearing reactant gas through the reaction chambers such that polycrystalline silicon deposits on the starter filaments and forms silicon powder due to the thermal decomposition of a silicon compound in the reactant gas; and

passing the reactant gas, with entrained silicon powder, from the reaction chambers into contact with the cooled wall of the powder catcher.

2. The process as defined by claim 1, further comprising regulating the flow of the reactant gas by positioning a flow resistant plate along the path of reactant gas flowing inside the reactor vessel.

3. The process as defined by claim 1, further comprising inhibiting deposition of silicon powder on the ceiling of the reactor above the reaction chambers by positioning a metal or ceramic heat shield plate above the reaction chambers such that reactant gas exiting the reaction chambers is diverted from flowing directly to the ceiling of the vessel.

4. The process as defined by claim 1, further comprising:

providing the powder catcher in the shape of a cylinder; and

injecting the reactant gas alongside and in a circumferential direction with respect to the powder catcher.

5. The process as defined by claim 1, further comprising maintaining the relationship of T2≦<T1≦<T3 where T1 is the wall temperature of the reaction chambers, T2 is the wall temperature of the powder catcher, and T3 is the reactor ceiling temperature.

6. The process as defined by claim 5, further comprising maintaining the temperature to be T1>25°C, T2<25°C, and T3>70°C

7. A process for the production of polycrystalline silicon rods from a silicon-bearing gas, the process comprising:

providing a reactor vessel having an interior surface including a floor, a wall and a ceiling, the vessel containing a cooled partition with a wall which defines multiple reaction chambers and containing a powder catcher which is displaced from the reaction chambers, has a cooled wall, and is in the shape of a disk that defines a central vertical passageway and that is located at an elevation above the tops of the reaction chambers;

positioning a starter filament in each reaction chamber where a polycrystalline silicon rod is to be grown;

heating the starter filaments;

passing a silicon-bearing reactant gas through the reaction chambers such that polycrystalline silicon deposits on the starter filaments and forms silicon powder due to the thermal decomposition of a silicon compound in the reactant gas; and

passing the reactant gas, with entrained silicon powder, from the reaction chambers into contact with the cooled wall of the powder catcher.

8. A process for the production of polycrystalline silicon rods from a silicon-bearing gas, the process comprising:

providing a reactor vessel having an interior surface including a floor, a wall, and a ceiling, the vessel containing (a) a cooled partition with a wall which defines multiple reaction chambers, (b) a powder catcher which is displaced from the reaction chambers, has a cooled wall, and is in the form of a heat exchange tube array, and (c) a recirculation fan positioned between the powder catcher and the reaction chambers;

positioning a starter filament in each reaction chamber where a polycrystalline silicon rod is to be grown;

heating the starter filaments;

passing a silicon-bearing reactant gas through the reaction chambers such that polycrystalline silicon deposits on the starter filaments and forms silicon powder due to the thermal decomposition of a silane gas in the reactant gas, the silane gas being selected from the group consisting of monosilane, disilane, and mixtures thereof;

passing the reactant gas, with entrained silicon powder, from the reaction chambers into contact with the cooled wall of the powder catcher; and

operating the recirculation fan to move reactant gas from the vicinity of the powder catcher back into the reaction chambers.

9. The process as defined by claim 8, wherein a metal or ceramic heat shield plate is installed in the top section of the reactor.

10. The process as defined by claim 8, further comprising channeling all reactant gas in the vicinity of the powder catcher through the recirculation fan.

11. The process as defined by claim 8, further comprising inhibiting deposition of silicon powder on the ceiling of the reactor above the reaction chambers by positioning a metal or ceramic heat shield plate above the reaction chambers such that reactant gas exiting the reaction chambers is diverted from flowing directly to the ceiling of the vessel.

12. The process as defined by claim 8, further comprising:

providing the powder catcher in the shape of a cylinder; and

injecting monosilane gas alongside and in a circumferential direction with respect to the powder catcher.

13. The process as defined by claim 8, further comprising maintaining the relationship of T2≦<T1≦<T3 where Ti is the wall temperature of the reaction chambers, T2 is the wall temperature of the powder catcher, and T3 is the reactor ceiling temperature.

14. The process as defined by claim 13, further comprising maintaining the temperature to be T1>25°C, T2<25°C, and T3>70°C

15. A process for the production of polycrystalline silicon rods from a silicon-bearing gas, the process comprising:

providing a reactor vessel having an interior surface including a floor, a wall, and a ceiling, the vessel containing (a) a cooled partition with a wall which defines multiple reaction chambers, and (b) a powder catcher which comprises a cooled wall provided by a heat exchange tube array in the shape of disk that defines a vertical passageway and which is displaced from and located at an elevation above the reaction chambers;

positioning a starter filament in each reaction chamber where a polycrystalline silicon rod is to be grown;

heating the starter filaments;

passing a silicon-bearing reactant gas through the reaction chambers such that polycrystalline silicon deposits on the starter filaments and forms silicon powder due to the thermal decomposition of a silane gas in the reactant gas, the silane gas being selected from the group consisting of monosilane, disilane, and mixtures thereof;

passing the reactant gas, with entrained silicon powder, from the reaction chambers into the tube array where the silicon powder deposits the cooled wall;

passing the reactant gas from the tube array into the passageway; and

recirculating at least a portion of the reactant gas from the passageway into the reaction chambers. 16. The process as defined by claim 1, further comprising providing the powder catcher at a location that is not

over the reaction chambers.17. The process as defined by claim 7, further comprising providing the powder catcher at a location that is not over the reaction chambers.18. The process as defined by claim 8, further comprising providing the powder catcher at a location that is not over the reaction chambers.19. The process as defined by claim 10, further comprising providing the powder catcher at a location that is not over the reaction chambers.20. The process as defined by claim 12, further comprising providing the powder catcher at a location that is not over the reaction chambers.21. The process as defined by claim 15, further comprising providing the powder catcher at a location that is not over the reaction chambers.