JPH01226149A - Vapor growth apparatus - Google Patents

Abstract

PURPOSE:To form a vapor growth film with a uniform thickness by a method wherein the spacings of wafer arrangement are tight on the upstream side of a reactive gas flow in a reaction tube and rough on the downstream side of the reactive gas flow. CONSTITUTION:A vapor growth apparatus is composed of a reaction tube 1 which can be depressurized and has the supply inlet of reactive gas at its one end and the exhaust outlet of the gas at its other end, a heating means 2 provided around the reaction tube 1 and a wafer carrying means 7 which contains wafers 8 and is inserted into the reaction tube 1. At that time, the spacings for arranging the wafers 8 in the means 7 are tight on the upstream side of a reactive gas flow in the reaction tube 1 and rough on the downstream side of the reactive gas flow. With this construction, the quantity of the reactive gas is small on the upstream side and large on the downstream side. Even if the reactive gas concentration is lowered on the downstream side by consumption, a vapor growth film with a uniform thickness can be formed while the temperature is maintained uniform.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is directed to semiconductors! ! ! The present invention relates to a vapor phase growth apparatus that is suitably used when growing a thin film on a wafer in a deposition process.

Conventional technology In semiconductor manufacturing processes, polycrystalline silicon films, silicon nitride films, silicon oxide films, etc. play important roles as conductive films and insulating films. A batch type vapor phase growth apparatus is used.

Referring to FIG. 5, an example of a conventional gas phase I& One end of the reaction tube 11 is open and can be sealed with a door device 13. Moreover, from this recent example, the structure is such that N2 gas and reaction gas are supplied into the reaction tube 11 via the N, lf gas on-off valve 14 and the reaction gas on-off valve 15. A vacuum cutoff valve 16 is provided at the other end of the reaction tube 11 .

A semiconductor wafer 18 is loaded on the carrier boat 17 and inserted into the reaction tube 11 from the opening at one end.

Next, the operation of the vapor phase growth apparatus constructed as above will be explained.

First, the wafer 18 is loaded onto the carrier boat 17, and the door device 1 is placed inside the reaction tube 11 which has been preheated by the heating means 12.
Open 3 and insert. At this time, N2 gas is supplied to the inside of the reaction tube 11 via the N2 gas on-off valve 14, and the pressure becomes atmospheric. After the insertion is completed, close the N2 gas on-off valve 14, close the reaction tube 11 with the door device 13, and open the vacuum cutoff valve 1.
6 is opened, and the inside of the reaction tube 11 is evacuated under reduced pressure using a vacuum source (not shown).

Wait until the wafer 18 reaches a predetermined temperature, during which time the vacuum shutoff valve 16 is closed, and the reaction tube 11 is closed.
Perform Kuchenk. After confirming that the predetermined temperature has been reached, the vacuum cut-off valve 16 and the reaction gas on-off valve 15 are opened, a reaction gas is supplied into the reaction tube 11, and vapor phase growth is performed on the wafer 18.

When a thin film of a predetermined thickness is formed by vapor phase growth, the reaction gas on-off valve 15 is closed and the inside of the reaction tube 11 is evacuated under reduced pressure. Next, close the vacuum cut-off valve 16 and use N2. N2 gas is supplied into the reaction tube 11 through the f gas on-off valve 14 to bring it to atmospheric pressure.

Thereafter, the N2 gas on-off valve 14 is closed, the door device 13 is opened, and the wafer 18 on the carrier boat 17 is taken out from the reaction tube 11, thereby completing the vapor phase growth process.

Incidentally, it is known that the growth rate of a film produced during vapor phase growth is greatly influenced by the reaction gas concentration and reaction temperature.

That is, the film growth rate W is given by the following equation.

W=A exp(E/RT)X where C: reaction gas concentration, T: reaction temperature, E: activation energy, R: gas constant, A: constant.

However, in the vapor phase growth apparatus configured as described above, the supplied reactive gas is consumed from the upstream side, and the concentration of the reactive gas decreases as it reaches the downstream side.
The thickness of the rJ film formed on the reaction tube 8 becomes non-uniform depending on its position within the reaction tube 11.

Therefore, even if the reaction gas concentration decreases downstream, the wafer 1
In order to form a thin film with a uniform thickness on the surface of the reaction tube 11, a temperature gradient is provided in the heating means 12 to control the temperature distribution within the reaction tube 11.
Lower one end of the reaction tube 11, that is, the upstream side of the reaction gas flow! It is sufficient to set the end side, that is, the downstream side, high, and such a measure has been taken in the past.

Problems to be Solved by the Invention However, in the case of polycrystalline silicon films, for example, the size of the crystal grains in the vapor-grown film that is produced varies depending on the reaction temperature, and if the crystal grain sizes differ,
In the subsequent etching process, the etching speed is different. Therefore, in order to perform the same etching, it is necessary to divide the etching into a plurality of times and perform the etching by determining the optimum etching conditions for each time, which leads to a problem that the efficiency is seriously reduced. Further, in the silicon nitride film, there is a problem in that the temperature difference between the upstream side and the downstream side causes non-uniform gas stress, and because of this non-uniformity, the subsequent etching process has to be divided into multiple steps.

Further, as a method of keeping the film thickness constant without making the temperature uniform, there is a method of significantly increasing the supply amount of the reactant gas to such an extent that even if the reactant gas is consumed, the concentration thereof is not significantly affected. However, there are problems in that a large amount of reaction gas must be disposed of unused and a large exhaust pump is required to exhaust the large amount of reaction gas.

In view of the above-mentioned conventional problems, the present invention makes it possible to make the temperature inside the reaction tube uniform without adversely affecting the subsequent process, and to form a thin film of uniform thickness with a relatively small amount of reactant gas supplied. The purpose of the present invention is to provide a vapor phase growth apparatus that can perform the following steps.

Means for Solving the Problems In order to achieve the above object, the present invention provides a reaction tube which can be depressurized and is formed with a reaction gas supply port at one end and a discharge port at the other end, and a reaction tube which is arranged around the reaction tube. In a vapor phase growth apparatus equipped with a heating means provided and a wafer holding means loaded with a wafer and inserted into a reaction tube, the arrangement pitch of the wafers in the wafer holding means is controlled by the flow of reaction gas in the reaction tube. The upstream side of the direction is dense and the downstream side is coarse.

Further, the posture of the wafer in the wafer holding means is set to be approximately perpendicular to the flow direction of the reaction gas on the upstream side of the flow direction of the reaction gas in the reaction tube, and to a posture substantially perpendicular to the flow direction of the reaction gas on the downstream side. It may also be placed in a tilted position.

According to the present invention, by making the arrangement pitch of the wafers denser on the upstream side and coarser on the downstream side in the flow direction of the reaction gas in the reaction tube, the amount of reaction gas flowing between the wafer and the phenol is reduced upstream. Even if the amount of reaction gas is high on the downstream side and high on the upstream side, and low on the downstream side, a gas-phase formed film with a uniform thickness can be formed.

To explain in detail, the reaction gas amount Q flowing into the narrow space between the wafers arranged vertically at short pitches in the gas flow direction and the vJl of the wafers is such that no gas flow occurs;
Since it flows only in the form of molecular diffusion, it is given by the following equation according to Fick's law.

Here, C: reaction gas concentration, D: diffusion constant, d: wafer diameter, 11: wafer pinch, r: coordinate system taken in the wafer radial direction (see FIG. 2).

Therefore, on the upstream side in the flow direction of the reaction gas, the wafer pitch h
By making small, the amount of reactive gas that moves between wafers due to molecular diffusion can be suppressed, and as a result, the thickness of the vapor-phase grown film can be kept small. On the other hand, if the Fehave h is increased on the downstream side, the amount of reactive gas that moves between the wafers can be increased and the film thickness can be increased. As a result, it is possible to form a vapor phase grown film with a uniform thickness without flowing a large amount of reaction gas while keeping the reaction temperature uniform, and post-processes can be simplified.

Furthermore, if the wafers are placed in an almost perpendicular position to the flow direction of the reaction gas on the upstream side and tilted on the downstream side, the reaction gas will flow between the wafers only by molecular diffusion on the upstream side, but on the downstream side Since the inflow also occurs due to gas flow, the amount of inflowing gas increases, and as a result, a vapor phase growth film with a uniform thickness can be formed while keeping the reaction temperature uniform as described above.

To explain in detail, when the wafer is tilted, the sum total Q of the amount of reactive gas that flows in due to the gas flow at the flow rate V flowing from the main gas part between the wafers and the amount of reactive gas that flows in due to molecular diffusion is approximately as follows. Expressed by the formula.

10v◆dII11cosθ Here, V: the flow velocity between the wafers, θ: the inclination angle of the wafer with respect to the attitude perpendicular to the gas flow direction, and the pond is the same as above.

Note that when the inclination angle θ is small, the flow velocity V is small.

On the other hand, if the θ gas becomes too strong, b cos θ becomes small, which is the same as reducing the wafer pitch, which is not good.

Therefore, by appropriately tilting the wafers on the downstream side, the amount of reaction gas carried by the gas flowing between the wafers can be increased, and the thickness of the vapor-phase grown film can be made uniform.

Example Embodiments of the present invention will be described below with reference to the drawings.

tjS1 and FIG. 2 show the first embodiment of the present invention,
f:tS1 In the figure, 1 is a reaction tube made of quartz, around which a heating means 2 such as a resistance heater is arranged. One end of the reaction tube 1 is open and can be sealed with a door device 3. Also, from near this one end, N
:! 〃N2 via the gas on-off valve and reaction gas on-off valve 5! f
It is configured to supply gas and reaction gas into the reaction tube 1. A vacuum cutoff valve 6 is provided at the other end of the reaction tube 1 . A semiconductor wafer 8 is loaded onto the carrier boat 7 and inserted into the reaction tube 1 through the opening at one end. The wafers 8 are arranged densely in the region A on the upstream side in the flow direction of the reaction gas, and loosely in the region B on the downstream side.
loaded on top.

Next, the operation of the vapor phase growth apparatus having the above configuration will be explained.

First, the wafers 8 are loaded onto the carrier boat 7 as described above, and the door device 3 is opened and inserted into the reaction tube 1 which has been preheated to about 615° C. by the heating means 2. At this time, N2ff gas is supplied to the inside of the reaction tube 1 via the N2 gas on-off valve 4, and the pressure becomes atmospheric. After completion of insertion, N2 gas on/off valve 4
is closed, the vacuum shutoff valve 6 is opened with the inside of the reaction tube 1 sealed by the door device 3, and the reaction tube 1 is closed by an exhaust pump (not shown).
Evacuate the inside.

Thereafter, until the wafer 8 reaches a predetermined temperature,
Wait for 15 minutes, during which time the vacuum cutoff valve 6 is closed, and the reaction tube 1 is cleaned. After confirming that the predetermined temperature has been reached, the vacuum cutoff fP6 and the reaction gas on-off valve 5 are opened, and the reaction gas (in the case of forming a polycrystalline silicon film, monosilane gas (Sill=)) is supplied into the reaction tube 1. death,
A vapor phase growth film is formed on the wafer 8 at a pressure of about 0.2 to 0.3 Torr.

At this time, the set temperature of the heating means 2 is uniform in the axial direction of the reaction tube 1, and the wafers 8 on the carrier boat 7 are at a substantially uniform temperature. However, since the arrangement pitch of the wafers 8 is dense on the upstream side and coarse on the downstream side in the flow direction of the reaction gas, the amount of reaction gas flowing between the wafers 8 and 8 due to molecular diffusion as described above is smaller on the upstream side. Therefore, even if the reactive gas is consumed on the upstream side and the reactive gas concentration becomes low on the downstream side, a vapor-phase grown film can be uniformly formed.

When a thin film of a predetermined thickness is formed by continuing the vapor phase growth for a predetermined time, the reaction gas on-off valve 5 is closed and the inside of the reaction tube 1 is evacuated under reduced pressure. Next, Shin’g! The shutoff valve 6 is closed, and N2 gas is supplied into the reaction tube 1 via the N2 gas on-off valve 4 to bring it to atmospheric pressure. Thereafter, the N2 gas on-off valve 4 is closed, the door device 3 is opened, and the wafers 8 on the carrier boat 7 are taken out from the reaction tube 1, thereby completing all the vapor phase growth processing.

Next, an experimental example based on this embodiment will be explained in comparison with a conventional example.

First, the reaction gas (Heffs is the base and SiH, 2
0%) is supplied at a rate of 500 cc per minute, and the pressure is 0.37 or
r, at a constant temperature of 625℃, when 150 wafers with a diameter of 6 inches are loaded at a pitch of 4.8cm and a polycrystalline silicon film is grown in a vapor phase for 15 minutes, the 26th to 125th wafers from the gas introduction side are loaded. Average film thickness 52o for 100 sheets up to the eyes
1. The error was ±36%.

On the other hand, when the gas inlet side was set at 600° C. and the exhaust side was set at 650° C. to create a substantially linear temperature gradient and vapor phase growth was performed with other conditions being the same, the average film thickness was 1150, with an error of ±2%. However, in this case, the sizes of the crystal grains are different, and the etching speed is different.

Therefore, when vapor phase growth is performed with the reactant gas flowing at 4300 cc/min and the pond conditions being the same, the average I15! Thickness 129
There were 0 people, with an error of ±5%. In this case, a large amount of reaction gas is required.

On the other hand, the wafer pitch is 1111 cranes for the 1st to 90th wafers, 7WI11 for the 91st to 150th wafers,
When the reaction gas is supplied at 2,700 cc/min and other conditions are kept the same, the average film thickness is 1,230 λ, and the error is ±5.
′! It became 6. That is, the variation in film thickness could be suppressed to the same level with 63% of the amount of gas compared to simply increasing the amount of reaction gas while keeping the temperature uniform.

Next, a second embodiment of the present invention will be described with reference to FIG.

The difference between this second embodiment and the first embodiment is that in the upstream region C, the arrangement pitch of the wafers 8 is relatively small, and the posture thereof is approximately perpendicular to the flow direction of the reaction gas. In the downstream region, the placement pinch was relatively large and the posture was tilted by θ°.

In this case as well, as already explained in detail, the reactive gas flows between the wafers 8.8 on the upstream side only by molecular diffusion, but the reaction gas flows between the wafers 8.8 on the downstream side due to the inclination. Since the reaction gas also flows in due to the gas flow, the amount of inflow increases, and as a result, a uniform vapor phase growth film of the film 17 can be formed while keeping the reaction temperature uniform as described above.

Effects of the Invention According to the vapor phase growth apparatus of the present invention, as described above, the wafers are arranged densely on the upstream side in the flow direction of the reaction gas in the reaction tube, and narrowly on the downstream side, so that the wafers are Even if the amount of reactant gas flowing in during the process is small on the upstream side and large on the downstream side, and the concentration of the reactant gas becomes low on the downstream side due to consumption of the reactant gas, it is possible to maintain a uniform film thickness while keeping the temperature uniform. By forming a phase-grown film, for example, in the case of a polycrystalline silicon film, the size of the crystal grains becomes uniform, and the subsequent etching process can be simplified.

Furthermore, even if the wafer is placed in an approximately perpendicular position to the flow direction of the reactant gas on the upstream side and tilted on the downstream side, the reactant gas will flow only by molecular diffusion between the T-evaporators on the upstream side, and the downstream On the side, it also flows in due to gas flow, so
The amount of inflowing gas increases, and the same effect as above can be obtained.

[Brief explanation of the drawing]

tjS1 is a schematic configuration diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of the same action, fjS3 is a schematic diagram of the second embodiment of the invention, The figure is a schematic diagram of a conventional example. 1...Reaction tube 2...Heating means 5...Reaction gas opening/closing property 6...Vacuum cutoff Valve 7...Carrier boat 8...Wafer. Acting M Shima Patent Attorney Toshio Nakao and 1 other expert Figure 2 1, / shi-1111= No. 31 shi===2=≦

Claims (2)

[Claims] (1) A reaction tube that can be depressurized and has a reaction gas supply port at one end and a discharge port at the other end, a heating means arranged around the reaction tube, and a wafer loaded and reacted. In a vapor phase growth apparatus equipped with a wafer holding means inserted into a tube, the arrangement pitch of the wafers in the wafer holding means is set to be dense on the upstream side in the flow direction of the reaction gas in the reaction tube and coarse on the downstream side. A vapor phase growth apparatus characterized by: (2) A reaction tube that can be depressurized and has a reaction gas supply port at one end and a discharge port at the other end, a heating means arranged around the reaction tube, and a wafer loaded and reacted. In a vapor phase growth apparatus equipped with a wafer holding means inserted into a tube, the posture of the wafer in the wafer holding means is approximately perpendicular to the flow direction of the reaction gas on the upstream side of the flow direction of the reaction gas in the reaction tube. A vapor phase growth apparatus characterized in that the downstream side is tilted with respect to the flow direction of the reactant gas.