JPH07226384A - Reactor for chemical vapor deposition of semiconductor grade silicon - Google Patents

Abstract

PURPOSE: To reduce silicon dusts in a reactor by a method wherein a heat transmission element through which heat is released to the outside is provided in a reaction chamber and the temperature of mixed gas existing in the reaction chamber is lowered while a plurality of heated silicon devices are not practically shielded from the heat emitted from the heated silicon devices. CONSTITUTION: A reaction chamber which is suitable for the chemically depositing silicon onto a plurality of heated silicon devices 7 from mixed gas consisting of chlorosilane expressed by a formula: Cln SiH4-n [wherein (n) denotes 1, 2, 3 or 4] and hydrogen is composed of a base part 1 and a vessel 8 placed on the base part 1. A heat transmission element 12 through which heat is released to the outside is provided in the reaction chamber. With this constitution, the temperature of the mixed gas existing in the reaction chamber is lowered while a plurality of the heated silicon devices 7 are not substantially shielded from the heat emitted from the heated silicon devices 7.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is an excellent reactor for producing semiconductor grade silicon by chemical vapor deposition of chlorosilane on a heated silicon device. The reactor is characterized by arranging a heat exchange element within the reactor to reduce the mixed average gas temperature without substantially shielding the heated silicon element from radiant heat emitted from other heated silicon elements. . Reducing the mixed mean gas temperature reduces harmful homogeneous nucleation of silicon in the reactor and increases the operating efficiency of the reactor.

[0002]

BACKGROUND OF THE INVENTION The manufacture of semiconductor grade silicon is typically performed by chemical vapor deposition (CVD) of high purity silane or halosilane on a heated silicon device. Such methods are well known in the art and are described in US Pat.
3,638; 3,147,141; 3,099,53
4; 4,150,168 and 4,173,944. The CVD method requires heating a heating element, typically a heated silicon element, above the decomposition temperature of the silane or halosilane fed to the reactor. When the silicon is non-uniformly deposited on the heating element, the heating element increases the surface area and increases the radiant heat from the element. Radiant heat transfer between the heating elements must be maintained at the required temperature by passing current through the elements. It is important for efficient operation of the CVD reactor as it reduces the amount of current.

However, the convective heat released from the device raises the mixed mean gas temperature of the reactor. When the mixed average gas temperature of the reactor reaches a critical temperature, uniform (or equal) nucleation of silicon occurs in the reactor. The silicon dust formed by the homonucleation process coats the reactor walls and acts as an insulating material, continuing to raise the mixed average gas temperature. As a result of this increase in reactor mixed average gas temperature, uniform nucleation and further silicon dust formation are increased.
This silicon dust typically contains high levels of contaminants that settle on the product semiconductor silicon, resulting in unacceptable contaminant levels and surface defects.

In order to prevent problems associated with silicon dust formed by uniform (or equivalent) nucleation, silane is typically powered down during the course of operation, or silane supplied to the reactor. Alternatively, it is necessary to reduce the mol% of halosilane. Both of these improvements reduce the heterogeneous production of silicon to a low efficiency reactor.

[0005]

The present invention introduces a CVD reactor that deposits chlorosilane gas on a heated silicon device. It is characterized in that a heat exchange element is installed in the reactor. The heat exchange element is sized and designed to not substantially shield the heated silicon element from radiant heat emitted from other heated silicon elements. The heat exchange element acts to remove convective heat from the gas mixture, thereby lowering the temperature of the gas mixture and reducing homonuclear formation of silicon dust in the reactor. The reduction of silicon dust in the reactor allows the reactor to operate for long periods at high silicon device temperatures and high mol% chlorosilane feed gas. This gives a high yield of semiconductor grade silicon from the reactor over the operating period.

US Pat. No. 4,150,168,
A CVD method is taught to deposit silane (SiH ₄ ) on a heated silicon device. In principle, it provides a uniformly shaped silicon device suitable for floating zone processing. It describes the use of thermal insulators to isolate each of the silicon elements in the reactor from radiant heat emitted by other silicon elements. It has been reported that the thermal shielding of each of the rods provides a more uniform rod temperature, resulting in more uniform rod growth. It also teaches that high temperature pyrolysis reactions of silanes, i.e. homonuclear formation, occur which are not observed in the pyrolysis of halosilanes such as chlorosilanes. It also reports that this homonucleation process can be reduced by using those thermal insulators.

Although this document teaches that the production of silicon by homonucleation does not occur in a CVD reactor for vapor deposition of chlorosilanes, we have found that this is not the case. We have reached the critical temperature for the mixed average gas temperature of the CVD reactor for the thermal decomposition of chlorosilanes on heated silicon devices. It was found that the silicon dust formed by homonucleation adversely affects the operation (performance) of the reactor. In contrast to the teachings of the prior art, it is not necessary to completely shield each silicon element from the radiant heat emitted by other heated silicon elements in order to reduce this homonucleation process.

[0008]

We have found that in order to lower the mixed average gas temperature without completely shielding the heated silicon element from the radiant heat emitted from the heated silicon element, C
It has been found that a heat exchange element can be placed in the VD reactor.

According to the present invention, the formula Cl _n SiH _4-n [n is 1, 2 or more is provided on the base (1) and a plurality of heated silicon elements (7) arranged on the base and arranged in the reaction chamber. Three
Or 4], which comprises a vessel (8) forming a reaction chamber suitable for chemical vapor deposition of silicon from a gaseous mixture of chlorosilane and hydrogen, and a heat transfer element for externally cooling the reaction chamber. (12) is arranged to reduce the temperature of the mixed gas present in the reaction chamber without substantially shielding the plurality of heated silicon elements (7) from the radiant heat emitted from the heated silicon elements (7). A substantially sealed semiconductor grade silicon chemical vapor deposition reactor is provided.

The advantages of the heat exchange element arrangement are: (1) the convective heat from the mixed gas can be removed to reduce the production of silicon dust by homonucleation, and (2) the radiation emitted by each silicon element from each element. It is possible to reduce the current to the individual silicon elements, since they are not substantially shielded from heat.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a schematic diagram of a typical reactor useful for chemical vapor deposition of chlorosilanes on heated silicon devices, the reactor having heat exchange elements disposed therein. Reactors for chemical vapor deposition of silane and chlorosilane on heating elements are well known in the art, and the heat exchange elements of the present invention are used in such reactors to deposit chlorosilane on heated silicon elements to produce semiconducting silicon. Expected to be possible. Such a reactor is described in U.S. Pat. No. 3,053,638; 3,1.
47,141; 3,099,534; 4,150,16
8 and 4,173,944.

The reactor of FIG. 1 comprises a substrate 1. The substrate 1 has a flow path arranged therein and has an inlet pipe 2 and an outlet pipe 3 to circulate a coolant through the substrate 1. A supply nozzle 4 for supplying hydrogen and chlorosilane gas separately or as a mixture is also arranged on the substrate 1. The number of supply nozzles is not limited to two provided on the substrate, and a plurality of supply nozzles can be provided at an appropriate place in the reactor. The substrate 1 includes an exhaust port 5 that removes the gas generated during the deposition process. Board 1
Includes a connector 6 that provides a means of supplying current to the silicon element 7 to heat it. Substrate 1 has a plurality of connectors and a plurality of silicon elements 7 in the reactor.
It turns out that can be heated.

A container 8 is placed on the substrate 1. Container 8
Are fixed in contact with the substrate 1 to form a substantially sealed reactor. The “substantially sealed reactor” means the substrate 1
It means that the contact with the vessel 8 in the above is sufficient to bring the reactor under non-atmospheric pressure. Generally, it is desirable to seal the substrate 1 to the vessel 8 to minimize gas leakage from the reactor. In the preferred design, the container 8 is a double wall with cooling channels between the walls of the container. Inlet port 9 and outlet port 10 provide a means for passing coolant through the cooling flow path of the container. The container wall has an observation window 11. The vessel is not limited to the three viewing windows as shown, and may include as many windows as are required without the windows or to monitor the interior of the reactor. The viewing window 11 can be made of a transparent material that can withstand the heat of the reactor and does not contaminate the semiconductor silicon produced therein. A heat exchange element 12 is attached to the center of the container 8. The heat exchange element 12 of FIG. 1 consists of two concentric tubes that form an inner chamber and an outer chamber.
The inlet port 13 pumps the coolant to the inner flow passage to circulate downward, and to the outer flow passage to discharge it from the outlet port 14. The location of the heat exchange element in the reactor is not critical, as long as it is in contact with the gas mixture in the reactor without substantially shielding the plurality of silicon elements 7 from radiant heat emitted from the silicon elements. Everything is possible. In another arrangement, the heat exchange element 12 can be attached to the substrate 1.

FIG. 2 is a cross-sectional view of a useful configuration of heat exchange element 12. The heat exchange element of FIG. 2 is composed of two concentric tubes that form an inner flow path and an outer flow path and can circulate a cooling fluid.
A plurality of silicon elements 7 are arranged around the heat exchange element 12. The heat exchange element 12 and the plurality of silicon elements 7 are surrounded by a container wall 8 containing a chamber for circulating a cooling fluid.

FIG. 3 is a cross-sectional view of a more desirable configuration of heat exchange element 12. In FIG. 3, the heat exchange element 12 consists of an inner tubular channel surrounded by four double-walled fins. The double wall provides a channel within the fin that allows the coolant to flow therethrough. The inner tubular channel is connected to the channel in the fin, thereby creating a continuous channel through which the coolant can flow. Those skilled in the art will appreciate that the heat exchanging element 12 shown in FIG. 3 is not limited to four fins and may include any suitable number of fins. A plurality of silicon elements 7 are arranged around the heat exchange element shown in FIG. The heat exchange element 12 and the plurality of silicon elements 7 in FIG. 3 are surrounded by a container wall 8 containing a chamber for circulating a cooling fluid.

In practice, the present invention provides the formula Cl _n SiH _4-n [n on a plurality of heated silicon elements placed indoors.
= 1, 2, 3 or 4]. A substantially sealed reactor comprising a vessel forming a suitable chamber for the chemical vapor deposition of silicon from a gaseous mixture of chlorosilane and hydrogen. The reactor of the present invention is designed to reduce the temperature of a mixed gas existing in a room without substantially shielding the plurality of heated silicon elements from radiant heat emitted from other silicon elements. It consists of heat transfer elements that are cooled from.

Substantially enclosed reactors for chemical vapor deposition of silicon on heated silicon devices have been described in the techniques discussed above. A schematic of such a useful reactor is shown in FIG. By "substantially sealed reactor" is meant that the reactor is sufficiently sealed to operate under non-atmospheric pressure conditions. It is generally desirable to seal the reactor to minimize gas leakage from the reactor.

The function of the present invention is to improve reactor efficiency by removing convective heat from the gas mixture without substantially shielding the plurality of heated silicon elements from the radiant heat emitted from the silicon elements. . Thus, externally cooled heat transfer elements can be designed to effectively increase the convective heat transfer area within the reactor. Such a design is shown in FIG. 1, where the heat transfer element consists of two concentric tubes forming an inner hole and an outer hole for circulating the heat transfer medium. An example of a preferred heat transfer element is shown in FIG. 3 and consists of an inner hole surrounded by four fins having holes for circulating heat transfer fluid. The preferred heat transfer element shown in FIG. 3 is not limited to four fins and can have multiple fins.

The heat transfer element is designed such that when placed in the reactor chamber, the plurality of heated silicon elements does not substantially shield the radiant heat emitted from the silicon elements.
By "substantially shielded" is meant that 50% or less, preferably 20% or less, of the radiant heat emitted from the heated silicon element is shielded from contact with other heated silicon elements in the reactor. Examples of such heat transfer elements and their positions are shown in FIGS. 1, 2 and 3.

The location of the heat transfer element in the reactor chamber can be such that it is in contact with the gas mixture and does not substantially shield the plurality of heated silicon elements from the radiant heat emitted by the silicon elements. The heat transfer element can be hung from the reaction vessel wall as shown in FIG. 1 or mounted on the substrate of the reactor. The heat transfer elements can also be arranged concentrically within the reactor. The reactor can include one or more heat transfer elements as long as the heat transfer elements do not substantially shield the heated silicon elements from the radiant heat emitted from the silicon elements.

The heat transfer element is externally cooled. External cooling is achieved by passing a suitable heat transfer medium through one or more channels or holes in the heat exchanger. Such heat transfer media include polydimethylsiloxane fluid, water and gaseous coolant, with polydimethylsiloxane fluid being preferred.

The heat transfer element is a conventional material suitable for making a chemical vapor deposition reactor used for the pyrolysis of chlorosilanes on heated silicon elements to produce silicon for semiconductor blades, such as high carbon steel. Can be made.

The substantially enclosed reactor comprises a plurality of heated silicon elements and must contain more than one heated silicon element, the upper limit of which is limited by the particular reactor design. .

The present reactor, which is substantially sealed, has the formula Cl _n SiH _4-n (n = 1,
It is used in the chemical vapor deposition of a gas mixture consisting of chlorosilane and hydrogen represented by 2, 3 or 4). The preferred chlorosilane is tetrachlorosilane. Generally, hydrogen gas is fed to the reactor in molar excess with respect to the chlorine liberated from the chlorosilane during the pyrolysis of the chlorosilane. Hydrogen gas is used as a carrier gas and a diluent gas for the chlorosilane fed to the reactor.

The heat transfer capacity of the heat transfer element is determined by standard thermodynamic considerations such as the surface area of the heat transfer element, the thermal conductivity of the constituent materials, the temperature and heat capacity of the heat transfer medium. In general, it is desirable to keep the internal temperature of the reactor gas below the temperature at which the particular chlorosilanes form large amounts of silicon by homonuclear formation that is detrimental to the manufacturing process. This temperature depends on the particular chlorosilane and the reactor used.

The present invention is particularly useful in the manufacture of semiconductor grade silicon for use in processes such as the Czochralski method of pulling a silicon single crystal from a silicon melt. "Semiconductor grade silicon" generally means 99.
It means a material that is 9% by weight or more of silicon.

The following example is provided to demonstrate the advantages of the invention.

Example 1 The working effect of a heat exchange element placed in an industrial reactor for chemical vapor deposition of trichlorosilane was investigated.

The reactor was of conventional design containing a plurality of silicon devices similar to that shown in FIG. The feed to the reactor was a mixture of hydrogen and trichlorosilane. The initial temperature of the silicon device was 1060 ° C, and this temperature was gradually lowered to 965 ° C over the experimental period.
Baseline experiments were performed without heat exchange elements. The baseline experimental objective was to operate the reactor before the mixed average gas temperature reached the point where homonucleation required a reduction in the amount of trichlorosilane fed to the reactor affecting the performance of the reactor. It was to determine the length of time possible and to measure the deposition rate of silicon.

For the reactor used, the mixed average gas temperature was 6 as measured by a thermocouple installed in the vent of the reactor.
It was determined experimentally that at 50 ° C., the level of homonucleation affects the performance of the reactor to the extent that the mol% of trichlorosilane fed to the reactor is reduced. For the baseline experiment, the mixed average gas temperature remains 42
A critical temperature of 650 ° C. was reached in about 33 hours for the time run, necessitating a reduction in the mol% of trichlorosilane fed to the reactor. The average silicon deposition rate for the baseline experiment was 1.2 mm / hr.

In a comparative experiment, a heat exchange element similar to that described in FIG. 3 was placed in the reactor. A heat exchange fluid (trade name: Syltherm,
The heat exchange element was cooled by circulating it through a Dow Corning product. The heat exchange fluid had a temperature of 190 ° C. measured at the inlet of the heat exchange element. Comparative experiments were performed similar to those described in the baseline experiment. The temperature distribution of the silicon device was controlled to be similar to the temperature distribution of the silicon device in the reference line experiment. The comparative experiment was run for 43 hours, at which time the mixed average gas temperature reached a critical temperature of 650 ° C. and the experiment was stopped. The average deposition rate of silicon in the comparative experiment was 1.3 mm / hr.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a typical reactor in which heat exchange elements useful for chemical vapor deposition of chlorosilanes are placed on a heated silicon device.

FIG. 2 is a cross-sectional view of an exemplary reaction with a heat exchange element useful in the practice of the present invention.

FIG. 3 is a cross-sectional view of an exemplary reactor with another heat exchange element useful in the practice of the present invention.

[Explanation of symbols]

 1 Substrate 2 Inlet Pipe 3 Outlet Pipe 4 Supply Noise 5 Exhaust Port 6 Connector 7 Silicon Element 8 Container 9 Inlet Port 10 Outlet Port 11 Window 12 Heat Exchange Element 13 Inlet Port 14 Outlet Port

Claims (2)

[Claims] 1. A base (1) and a plurality of heated silicon elements (7) disposed on the base and disposed in a reaction chamber, wherein Cl _n SiH _4-n [n is 1, 2, 3 Or 4], which comprises a vessel (8) forming a reaction chamber suitable for chemical vapor deposition of silicon from a gaseous mixture of chlorosilane and hydrogen, and a heat transfer element for externally cooling the reaction chamber. (12) is arranged to reduce the temperature of the mixed gas present in the reaction chamber without substantially shielding the plurality of heated silicon elements (7) from the radiant heat emitted from the heated silicon elements (7). Featuring a substantially sealed semiconductor grade silicon chemical vapor deposition reactor. 2. The formula Cl in a substantially sealed reactor comprising: (A) a base (1) and a vessel (8) defining a reaction chamber, wherein a plurality of heated silicon elements (7) are arranged in the reaction chamber.
_A gaseous mixture of chlorosilane and hydrogen represented by _n SiH _4-n [n is 1, 2, 3 or 4] is supplied, and (B) a heated silicon element (7) is passed through an electric current to bring the silicon element into chlorosilane Above the decomposition temperature of the element, thereby non-uniformly depositing elemental silicon on the heated silicon element (7), heating the mixed gas in the reaction chamber, and (C) cooling from the outside arranged in the reaction chamber. By passing a heat exchange fluid through the heat transfer element (12),
Reducing the production of silicon by homogeneous nucleation in the reaction chamber without substantially shielding the plurality of heated silicon elements (7) from the radiant heat emitted from the heated silicon elements (7). Semiconductor grade
Silicon manufacturing method.