JPS6197193A - Reaction tube for reduced pressure hot wall cvd - Google Patents

Abstract

PURPOSE:To obtain an epitaxial film having uniform film thickness and good quality with high efficiency but without causing deposition of pulverized fine particles by arranging an internal tube in the low temp. section and an internal tube in the high temp. section so as to permit exchange by pulling the both tubes to the outside and performing crystal growth in such reaction tube. CONSTITUTION:An internal tube 15 in the low temp. section is arranged to a zone between an inlet side of gas and neighbourhood of set position of a substrate 6 in the inside of a quartz reaction tube 2 and a jig housing tube 3 of a reaction tube for a reduced pressure hot wall CVD process, so as to permit exchange of the internal tube in the low temp. section by pulling out said tube, and an internal tube 16 in the high temp. section is arranged to the neighborhood of a set position of the substrate 6 so as to permit pulling out. A jig 5 mounting many silicon substrates are set in the reaction tube 2 at the center of an electric furnace 1, to which reaction gas, carrier gas, doping gas are fed through a gas feeding line 7 to cause epitaxial reaction growing an epitaxial film uniformly. By pulling out and exchanging the internal tube 15, 16 deposited with reaction products after several times of the reaction, an epitaxial film having good quality with no deposition of powdery body is obtd. with + or -5% precision of film thickness and + or -10% precision of specific resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention mainly relates to a reaction tube of a reduced pressure real wall CVD apparatus for forming silicon epitaxial crystals. , reduced pressure hot wall C to form a silicon oxide film, etc.
It can also be applied to VD.

[Background of the invention]

Until now, high-frequency heating has often been used for silicon epitaxy. In this case, the silicon substrate is locally heated and an epitaxial reaction occurs at the substrate interface, but the reaction tube wall is a cold wall and hardly any reaction products adhere to the tube wall. However, since silicon substrates could only be placed two-dimensionally on the heating plate, mass loading was not possible and production efficiency was poor.

On the other hand, the true wall method in which the reaction tube is heated from the outside using an electric furnace has the advantage of being able to load a large amount of substrates three-dimensionally into one reaction tube, but reaction products are deposited on the walls of each reaction tube. These tube wall precipitates become powder when the jig carrying the substrate is transported back and forth to the high-temperature reaction zone inside the electric furnace or taken out, and fly up and adhere to the substrate surface, causing defects in the epitaxial crystal. do. As a countermeasure to this problem, attempts have been made to use a method of attaching a wheel to the substrate jig, and a soft landing method in which the reactor is moved within the hollow space of the reaction tube to the desired location without sliding on the tube wall. There is also a method of cleaning the tube wall by vapor-phase etching the tube wall precipitates with HCQ, but this method does not sufficiently clean the low-temperature tube wall. Insert the inner tube further,
There is also a method of taking it outside and washing it after the epitaxial reaction, but if the inner tube is long, it causes difficulties in fitting with the reaction tube and handling (Japanese Patent Application Laid-open No. 55-110033, JP-A No. 55-153323). , Japanese Patent Publication No. 59-50093).

[Purpose of the invention]

The present invention has been made in order to solve the above-mentioned problems, and in a reduced pressure hot wall CVD apparatus, an inner tube divided into a plurality of parts is provided inside the reaction tube, and the inner tube is disposed in the movement path of the substrate mounting jig, and Because of the low temperature, soft tube wall deposits are likely to form, and the areas where cleaning by HCa vapor phase etching is incomplete are divided into one short inner tube (called the low-temperature section inner tube), and the areas that are exposed to the outside are separated. The purpose is to prevent epitaxial crystals from becoming defective due to powdered fine particles and to increase production efficiency by facilitating removal and frequent washing.

In addition, the separately divided inner tube (referred to as the high temperature inner tube) has
Weld the doping nozzle tube inside.

In addition to supporting and reinforcing the thin nozzle tube, the structure allows it to be separated from the reaction tube, making it easier to manufacture the reaction tube, install the nozzle, and repair it.

[Summary of the invention]

The reduced pressure hot wall silicon epitaxial reaction operation involves placing the epitaxial substrate in a predetermined high temperature zone in the axial center of a quartz reaction tube inserted into an electric furnace, and flowing the reaction gas under reduced pressure. This is done by In this case, a temperature gradient is formed in the axial direction of the reaction tube from room temperature to a predetermined high temperature zone. The reaction gas performs an epitaxial reaction on the substrate, and at the same time, a reacted 1° acid is deposited on the inner wall of the reaction tube. This tube wall precipitate begins to form at a tube wall temperature of about 400° C. upstream of the substrate and adheres to the inside of the reaction tube up to the high temperature section. The presence of precipitates on the tube wall is a drawback of the hot wall method.Adhesion on the tube wall causes a drop in the concentration of the reactant gas, which causes changes in the growth rate, that is, non-uniformity in the epitaxial film thickness. When the jig is moved, the tube wall precipitates are powdered and become trapped in J), which makes the epitaxial crystal defective.

Precipitates on the tube wall in the high temperature reaction zone where the substrate is set are relatively hard and difficult to powder, and can be removed by vapor phase etching using MCl1. On the other hand, the tube wall precipitates that adhere to the low-temperature area upstream of the substrate have a complex Six Hy shape and are very soft, and are also known to have the property of easily adsorbing various impurity gases. At first glance, low-temperature precipitates can be compared to soot in a flue, and some of them are also dispersed by the circulating gas. Furthermore, it was found that the low-temperature precipitates were particularly easily powdered by the movement of the substrate mounting jig, and accounted for most of the powder in the reaction tube. Since this precipitate adheres to the low-temperature tube wall, it is difficult to remove it even by vapor phase etching using HCA.

Therefore, in the present invention, an inner tube (low-temperature section inner tube) is provided which is divided into sections where low-temperature precipitates are attached, and the short inner tube section is configured to be taken out to the outside and cleaned. Washing may be performed after each epitaxial reaction, but 4 to 5 times
It is sufficient to take out and wash once for every reaction.

On the other hand, there is another inner tube (
A nozzle pipe for supplying doping gas is attached to the high temperature section inner pipe).

The characteristic of the reduced pressure hot wall method is that it increases production efficiency by utilizing the space inside the reaction tube and densely loading a large number of substrates. It has the effect of suppressing When a large number of substrates are charged, the reaction gas is converted into an epitaxial film and is consumed, causing a concentration change in the gas flow direction, resulting in non-uniformity in film thickness and resistivity. Therefore, it is necessary to take some measures to correct the decrease in the concentration of the reactant gas.

To make the film thickness uniform, there are methods such as replenishing silicon source gas midway, inserting a tube nozzle, and using a double tube reaction tube with a porous nozzle inside.
In either case, the structure is such that the source gas passes through the high-temperature tube wall side, which causes problems such as consumption of the source gas and blockage of the flow path due to gas-phase thermal decomposition. A good alternative method is to utilize the fact that the reaction mechanism is interfacial reaction rate-determining, and to provide a temperature gradient in the gas flow direction.

On the other hand, uniformization of the epitaxial film resistivity must depend on replenishment of doping gas.

If the doping gas is used alone, it will not be deposited on the high-temperature tube wall, and it can be supplied by using a separate piping from that for supplying the source gas. There is also a method in which only the doping gas is ejected from the inner porous wall of a double-tube reaction tube, but there are many problems with the diameter and number of pores, their processing, and uniform gas ejection. found that it is best to inject the doping gas using a tube with several nozzle holes. However, since it is a long tube with a small diameter, it is easily distorted by heat, and the support method had some drawbacks. Therefore, in the present invention, the nozzle tube is reinforced by welding the doping gas replenishment nozzle tube to the inside of another inner tube (high temperature section inner tube) using the one-split inner tube method. Because it has a structure that can be separated from the reaction tube, it is easy to manufacture,
It is also easy to take it outside for repair. The number of nozzle pipes is about 4 to 12, and the structure is such that the board mounting jig can be moved by providing a space between the pipes. [Embodiments of the Invention] Hereinafter, the present invention will be described. will be explained in detail using examples.

Figure 1 shows the reduced pressure hot wall silicone according to the present invention.
FIG. 2 is an explanatory diagram of the structure of an epitaxial device.

In the figure, 1 is an electric resistance heating furnace (electric furnace), 2 is a quartz reaction tube, 3 is a jig storage tube, 4 is a closed autoloader for moving the jig, and 15 is a gas at the tip that contacts the reaction gas. A board mounting jig equipped with a rectifier, 6 a board, 7 a gas supply pipe, 8 a doping gas supply pipe, 9 an exhaust tail pipe of a reaction tube, 10, 11 a joint, 12 a connecting pipe, 13 a doping gas nozzle pipe 14 is a multi-tubular nozzle pipe, 15 is a low temperature section inner tube, 16 is a high temperature section inner tube, and 17 is a back diffusion prevention ring.

An example of the structure and dimensions of the main parts is as follows.

The main body of the reaction tube 2, which is inserted into the electric furnace 1 and heated from the outside of the tube, has an inner diameter of 140+nn+φ and a length of 2200 mm. The jig storage tube 3 connected to the reaction tube 2 has an inner diameter of 140 mm.
nuaφ and length 600n+i. A low temperature section inner tube 15 and a high temperature section inner tube 16 inserted into the reaction tube 2 and the jig storage tube 3
Both are quartz tubes with an outer diameter of 136+smφ, a wall thickness of 3+am, and a length of 1400 mm. The nozzle tube 14 installed inside the high temperature section inner tube 16 is a quartz tube with an outer diameter of 61φ.

The operation of silicon epitaxial growth using this apparatus will be explained.

A jig 5 mounting a large number of silicon substrates 6 (50 4-inch substrates in this example) back to back is connected to a gas supply pipe 7.
Without flowing N2 gas, set the jig in the jig storage tube 3 and seal it, then start the epitaxy operation. First, the reaction system is evacuated, and by further circulating N2 gas, HCl1 and 0□ remaining in the reaction tube and the exhaust system are sufficiently removed. After that, the autoloader 4 is activated and the foil plate mounting jig 5 is transported to the center of the electric furnace 1.
A temperature gradient of up to 80° C. is provided, which serves to make the epitaxial film thickness uniform.

The surface of the substrate set in the high-temperature section is annealed seven times under reduced pressure and H2 flow to remove the native oxide film.

The epitaxial reaction is carried out by supplying reaction gases SiH, CQ, Jarya gas H2, and doping gas PH through the gas supply piping system 7. In addition, doping gas PH3 (H, diluted) is introduced from the rear of the reaction tube 2 through the pipe 8, and is ejected from the multi-tube nozzle pipe 14 to make the resistivity of the epitaxial film on multiple substrates uniform. There is. The resistivity is mostly controlled by the doping gas ejected from the nozzle, and although normal doping is performed on the leeward side of the nozzle outlet, the crystals are doped almost uniformly on the upwind side due to back diffusion of the doping gas. Rather, the PH supplied from upstream of the substrate plays the role of slight correction of resistivity. The gas flow rate in this example is Ht ” 2 Q /win, SiH,C
a, = 2 Q /win, mainstream P H, = 0. IQ
/win (4 ppm at Hz dilution), nozzle P H
3=0.4 Q/wlin, the pressure inside the reaction tube is 0.3
Torr. At that time, the growth rate of the epitaxial film was 0.347 sin. Figure 2 is a detailed explanatory diagram of the inner tube and the doping gas nozzle tube. The inner tube close to the inner wall of the reaction tube 2 is divided into two parts, consisting of an inner tube 15 as a low temperature section and an inner tube 16 as a high temperature section. In this embodiment, the nozzle pipe 14, which has several ejection ports, consists of four pipes, and is welded to the high-temperature section inner pipe 16 to be reinforced against thermal distortion.

13 is a manifold for the nozzle pipe, and also serves as a rear rectifier for the gas flow. 18 is a manifold support rod. As shown in FIG. 1, the manifold 13 is connected to a pipe 8 from the outside by a connecting pipe 12 that passes through the exhaust tail pipe 9 of the reaction tube. Joint lO connects tail pipe 9 and communication pipe 1
2, and the joint 11 connects the communication pipe 12 and the piping 8. Further, a ring 17 made of a narrow flow path is placed in the tail pipe 9 of the reaction tube to prevent impurity gases from the exhaust system from diffusing back into the reaction tube. The inner tube 16 to which the nozzle tube 14 is welded can be separated from the reaction tube by a joint 1O111 and taken out from the gas inlet side of the reaction tube. A small hole 19 provided in the inner tube 16 is for drawing out the inner tube.

FIG. 3 is a sectional view taken along the plane taken along line A-A' in FIG. 2 and seen in the direction of the arrow, showing the positional relationship between the nozzle pipe 14, the board mounting jig 5, and the board 6. It is. When the jig moves, it moves on the four walls of the inner tube without touching the nozzle tube. Since the high temperature zone is located near the nozzle tube 14, tube wall deposits can be cleaned by HCQ vapor phase etching, and the high temperature section inner tube 16 is pulled out less frequently.

On the other hand, the other inner tube 15 is in a low temperature section, and soft tube wall deposits adhere to it, and MCI! Since it is difficult to remove even by gas phase etching, it is pulled out from the gas inlet end of the reaction tube after several epitaxial reactions, replaced, and washed.

〔Effect of the invention〕

By performing an epitaxial reaction operation using the reaction tube structure of the present invention as described above, a high quality epitaxial film with no powder adhesion can be formed on a large number of substrates with a film thickness accuracy of ±5% and a specific resistance. It is possible to manufacture with an accuracy of ±10%, which improves production efficiency.

[Brief explanation of drawings]

Figure 1 shows the reduced pressure hot wall silicone according to the present invention.
FIG. 2 is a detailed explanatory diagram of the inner tube and doping gas nozzle pipe, and FIG. 3 is a view taken along the plane taken along the line A-A' in FIG. 2. . 1... Electric furnace 2... Reaction tube 3... Jig storage tube 4... Autoloader 5... Board mounting jig 6... Board 7... Gas supply piping 8... Doping gas supply pipe 9...Exhaust tail pipe 13 of the reaction tube...Manifold 14 of the doping nozzle pipe...
・Multi-tube nozzle pipe 15...low temperature section inner pipe 16...
High temperature section inner tube

Claims (1)

[Claims] The low-temperature section inner tube is provided with an inner tube inserted into the interior and divided into at least two parts, and the low-temperature section inner tube provided from the gas inlet side to the vicinity upstream of the substrate setting position is arranged to be drawn out and replaceable, and furthermore, the inner tube of the low temperature section is arranged so as to be able to be pulled out and replaced. A reaction tube for reduced pressure hot wall CVD, characterized in that the reaction tube is equipped with at least one high-temperature section inner tube having a multi-tube nozzle inside for circulating doping gas around the position.