JPS61111994A - Cvd device - Google Patents

Abstract

PURPOSE:To prevent reverse diffusion of an impurity gas of an exhaust system, and not to make lessen exhaust conductance, by setting a constriction ring having a smaller constriction diameter than the diameter of an exhaust pipe in the vicinity of the outlet of a reaction tube. CONSTITUTION:The quartz reaction tube 2 is set in the electrical resistance type furnace 1. After the furnace is evacuated, the jig 4 is transferred to a given temperature distribution zone at the central part of the furnace 1 by the magnet boat loader 6 while circulating H2 through the gas piping 7. A low-temperature precipitate is much attached to the exhaust pipe 9, a contaminating gas such as HCl, etc. is permeated into the interior of the reaction tube 2 by reverse diffusion, and the substrate 5 is most liable to corrode when it is set in a high-temperature part. Consequently, the surface of the substrate 5 is made rough and loses mirror surface properties before an epitaxial reaction occurs. Crystallixability is also damaged by reverse diffusion of various impurity gases. In order to prevent these reverse diffusion phenomena, a constriction ring having a smaller constriction diameter than the diameter of the exhaust pipe 9 or the outlet branch pipe 12 of the reaction tube 2.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a reduced pressure hot wall C used for epitaxial growth and CVD of polycrystalline silicon, silicon oxide films, etc.
This relates to a VD device.

[Background of the invention]

Documents related to the conventional CVD method include 1, for example, Japanese Patent Application Laid-Open No.
There is No. 6-74922.

In conventional atmospheric pressure CVD, for example silicon epitaxy,
In order to avoid vapor phase thermal decomposition of the source gas, a reaction condition is adopted in which the concentration of the source gas is 1 mol % or less relative to the carrier gas. Let me give you a specific example.

For example, use H2 as a carrier gas at 100Q/111in.
When the source gas is fed at a rate of 1-Q/min or less, the flow rate of H2 is extremely large.

On the other hand, in the reduced pressure method, the effective concentration decreases due to pressure (g
/ Q unit, the volume of the denominator increases due to pressure), gas phase thermal decomposition is suppressed and a large value can be taken as a 1 molar (mol) concentration. To give a specific example, when, for example, H2 is sent in as a carrier gas to 2b, the source gas can be sent as 2Q/+ain.

Depending on the pressure conditions, it is also possible to use 100% source gas. Therefore, the flow rate of H2 as a carrier gas is 115 to 1150 in the normal pressure method for the same number of 6 wafers to be loaded in the reduced pressure hot wall method.

However, when the carrier flow rate is low (i.e., the flow rate is slow), back-diffusion occurs, and impurities in the exhaust system diffuse back into the reaction tube, resulting in contamination of the clean mirror surface and the performance of the epitaxial film deposited on it. It will cause deterioration. In particular, when using a chloride-based silicon source gas (lower chlorides tend to cause gas-phase thermal decomposition), HCl1 generated by decomposition is adsorbed by deposits attached to the exhaust pipe wall. As a result of back-diffusion, the surface of the substrate (wafer) in the high-temperature area is half-heartedly engraved before and after the epitaxial reaction, causing the crystal surface to deteriorate. In addition, back diffusion of oil vapor from the vacuum pump also occurs, causing crystal deterioration.

[Purpose of the invention]

The present invention has been made to solve the problems of the prior art described above, and it
In a VD device, the purpose is to prevent back diffusion of impurity gas in the exhaust system and to prevent the exhaust conductance from becoming small.

[Summary of the invention]

For example, in the low-pressure epitaxial reaction of silicon (Si), high-temperature decomposition products (such as silicon fine powder) of the source gas (e.g., 5iH2 (Jl); dichlorosilane) are generated and are discharged by a vacuum pump through an exhaust pipe. However,
On the way, it condenses and adheres to the cold exhaust pipe wall. At high temperatures, most of SL precipitates, but at low temperatures, it precipitates in the form of Si, H, and also occludes HCu. This low-temperature condensate has a high vapor pressure and easily adsorbs various gases, so it is a major source of contamination and back-diffuses into one reaction tube, contaminating the inside of the clean reaction tube.

In general, to prevent back diffusion in a flowing pipe, Re
It is said that the flow rate condition is -8c>IO (where Re: Reynolds number, SC: Schmidt number). However, the above conditions change depending on the concentration of contamination due to back diffusion, and it is a case-to-case situation. The inventors are S
In hot wall epitaxy of iH2CM, -H, system, we experimented with the flow rate and the contamination status of the substrate, and found conditions of Re) 20.

In order to prevent back diffusion, the pipe diameter may be set to satisfy the above-mentioned Re > 20, which corresponds to a pipe diameter of 420 nm when the N2 flow rate is 2Q/ll1in. In terms of flow velocity, if the flow velocity is 0.1 m/s or more when converted to 1 atm at room temperature, back diffusion will not occur. However, if the diameter of the exhaust pipe is made small in order to prevent back diffusion, the exhaust resistance will increase, the required exhaust capacity of the vacuum pump will increase, and the equipment cost will increase. Therefore, the present invention satisfies the contradictory conditions of back diffusion and exhaust resistance by providing an aperture ring that partially has a small diameter aperture.

This aperture ring has the purpose of preventing contaminant gas generated from low-temperature precipitates from back diffusing into the reaction tube in which the substrate is set, and is preferably located near the outlet of the reaction tube. However, since high-temperature gas flows here, the material should preferably be heat resistant, and holes should be made as appropriate depending on the structural material of the reactor.

[Embodiments of the invention]

The present invention will be explained in detail below using examples.

FIG. 1 shows one embodiment of the present invention, and is an explanatory diagram of the configuration of a reduced pressure hot wall CVD apparatus.

In the figure, 1 is an electric resistance heating furnace, in which a quartz reaction tube 2 is set. A substrate 5 is placed on the jig 4 vertically or at an inclined angle. The jig 4 carrying the board 5 is first set in the jig storage tube 3 at room temperature. The steps up to this point are performed while flowing N2 to block air.

After the pressure is reduced, the jig 4 is transported to a predetermined temperature distribution zone in the center of the heating furnace 1 using a magnetic boat loader 6 while flowing N2 through the gas pipe 7. At this time, the N2 gas is discharged via the discharge pipe 9 leading to the vacuum pump, but in order to prevent damage to the quartz reaction tube due to thermal expansion, a bellows expansion pipe 8 is inserted between the quartz reaction tube 2 and the discharge pipe 9. is placed. Many low-temperature precipitates adhere to the discharge tube 9, and contaminant gases such as HCa enter the reaction tube 2 due to back diffusion, but they are most likely to be engraved when the substrate 5 is set in a high temperature section. Therefore, the surface of the substrate 5 becomes rough and loses its specularity before the epitaxial reaction occurs. During the epitaxial reaction, the precipitation reaction takes precedence over the etching of HCIL, so it is relaxed, but there is also back-diffusion of various impurity gases, which impairs crystallinity. Furthermore, it becomes necessary to quickly move the substrate from a high temperature to a low temperature even after the epitaxial reaction. In order to prevent these back-diffusion phenomena, an aperture ring 10 having an aperture smaller in diameter than the outlet pipe 9 or the outlet branch pipe 12 of the reaction tube 2 is set.

By applying the device of the present invention, 50 4-inch SL substrates were charged in a 130 nmφ quartz reaction tube, and 5iH2Cn
, = 2 n /main, H, carrier = 2 Q
/min growth condition, 2011ITlφ between the 50m+φ reaction tube outlet branch pipe and the 100mmφ discharge tube.
By inserting the aperture ring, a high-quality epitaxial substrate was obtained without losing the mirror surface of the substrate.

FIG. 2 is a diagram illustrating the configuration of a quartz reaction tube in which the outlet branch pipe flange and the aperture ring are shared.

Normally, a quartz reaction tube is provided with a quartz inlet side connecting flange 11 and an outlet branch pipe 12 which are thinner than the main tube at both ends of the main tube (reaction tube 2), as shown in FIG. This is an embodiment in which the outlet connection flange and the aperture ring 10 are shared.

FIG. 3 is an explanatory diagram of a structure in which a part of the outlet branch pipe of a quartz reaction tube is processed to have a small diameter so as to have the same effect as an aperture ring.

Both ends of the reaction tube 2 are provided with connecting flanges 11 and 13, respectively, and in this embodiment, a narrow diameter aperture ring 14 is provided by machining the outlet branch pipe 12.

Figure 4 shows stainless steel piping connected to the quartz reaction tube.
FIG. 7 is an explanatory diagram of the configuration when the aperture ring is also made of steel.

A bellows telescoping pipe 8 is attached to the connecting flange 13 of the outlet branch pipe 12 of the quartz reaction tube 2 with an O-ring seal, and a diaphragm ring 18 made of stainless heat-resistant steel and a discharge pipe are attached to the flange 17 on the opposite side of the bellows telescoping pipe 8. 9 flange 1
9 are bolted together via an O-ring. In this case, water cooling jackets 15 and 20 are provided in the vicinity of the connection flange 13 and the flange 19 of the discharge pipe 9 for water cooling in order to prevent thermal damage to the O-ring due to high temperature gas.

〔Effect of the invention〕

As explained above, according to the present invention, the carrier gas H2
Under a low flow rate of , it is possible to design and manufacture a reduced pressure hot wall CVD apparatus without increasing the capacity of the vacuum pump or deteriorating crystallinity due to back diffusion.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of a reduced pressure hot wall CVD apparatus of the present invention, and FIGS. 2, 3, and 4 are all explanatory diagrams of the configuration of an aperture ring of the present invention. 1... Heating furnace 2... Reaction tube 3... Jig storage tube 8... Bellows expansion tube 9... Discharge pipe 10.14.18... Squeezing ring 12.
・・Outlet branch pipe

Claims (1)

[Claims] A CVD apparatus characterized in that an aperture ring having an aperture diameter smaller than the diameter of an exhaust pipe is provided near the outlet of a reaction tube.