JPH01107518A - Vapor growth method - Google Patents

Abstract

PURPOSE:To form a film with good reproducibility by providing a discharge amount control line in a discharge line in case of switching a reaction gas supply line to a purge gas supply line, thereby setting the gas discharge amount and gas conditions of a step of extracting gas in a reaction tube of previous step of vapor growth to the same as those of the step of vapor growth. CONSTITUTION:In purge gas lines 3, 3A, 3B, purge gases 2 controlled by flowrate controllers 1 flow to a reaction tube 5 which is reduced under pressure by a gas discharge system 4, and is discharged through a discharge line 6 to a discharge (I). In this case, in the first purge, the pressure is high due to a large quantity of purge gas flowing from two systems, is then reduced in quantity to one system, discharge amount is further suppressed by the operation of a discharge control line, and regulated substantially to the same conditions as those of a step of vapor growth. Then, the purge line is turned OFF, the gas in the tube is extracted, but since the pressure is reduced in the second purge, the time of gas extraction is shortened, and pressure change due to the introduction of reaction gas is reduced, thereby forming a film with good reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a vapor phase growth method, and more particularly to a gas supply method during the vapor phase growth process of semiconductors.

Conventional Technology Pressure changes during the process of vapor phase growth of semiconductors destabilize the atmosphere within the reaction tube and affect film uniformity.

For example, in the case of forming a Po1y-5i film, the reaction rate is fast and the influence of temperature variations in the reaction tube is small, but Si3
On the other hand, in the case of nitrogen film formation, the reaction rate is slow, and by suppressing the temperature variation within the reaction tube to ±0.3°C or less, it is possible to obtain a low value for intra-batch variation. This means that depending on the film to be formed, strict conditions are required for temperature variations within the reaction tube, and temperature changes during the film formation process must also be suppressed.

An example of the conventional method will be described below using FIG. 3, which is a gas system diagram.

In the purge process, the purge gas 2 controlled by the flow rate controller 1 passes through the purge gas supply lines 3 and 3', is introduced into the reaction tube 5 whose pressure is reduced by the exhaust system 4, and is then passed through the exhaust line/6. Displacement volume goes to exhaust l.

On the other hand, depending on the type of film to be formed, one of the reaction gas lines 7.89 is selected and activated, and while controlled by the flow rate controller 1 in the same manner as the purge gas, air is first flowed to the exhaust gas (2). At this time, the atmosphere inside the reaction tube is kept in a purged state.

After the reaction gas has been sufficiently flushed and the reaction tube has been sufficiently purged, the purge gas supply lines 3, 3' are stopped, the pressure is sufficiently reduced, and then the reaction gas is introduced into the reaction tube. The reaction gas flow rate at this time changes the pressure during film formation. When the pressure is changed by the flow rate of the reactant gas, the uniformity of the formed film is greatly affected. This will be explained below. The requirements for film formation are gas flow rate, pressure, and temperature. Figure 4 shows the correlation between gas flow rate and pressure while keeping the temperature constant. This is done by placing the gas inlet at the top of the reaction tube (Top) and the exhaust at the bottom (Bo
The temperature distribution inside the reaction tube was investigated under various conditions using a vertical reactor installed in a gas flow chamber (Gas FloWC).
control, b indicates pressure adjustment using exhaust conductance (Kxhausst Control).

When the pressure is changed by the flow rate of the reactant gas as described above, a change is observed in the temperature inside the reaction tube near the reactant gas inlet, as shown on the right side of FIG. 4. This is because even if the film is formed for the same time, the thickness of the deposited film is different between the top part where the temperature is decreasing and the part where the temperature is stable, and therefore the intra-batch variation becomes high.

Therefore, an exhaust control line 10 was provided in the exhaust line 6 to add gas, and the pressure was changed by adjusting the flow rate. In this case, no temperature change was observed near the reactant gas inlet. (FIG. 4b) For this reason, in the film formation process, that is, the vapor phase growth process, the exhaust amount is adjusted and set so as to obtain an appropriate gas flow rate and pressure. For example, the pressure is 6
When setting to oPa, use 800c of N2 gas for purging.
I have to run c/win. On the other hand, if the flow rate of the reaction gas in the vapor phase growth process is made approximately the same as that of the N2 gas for purging, the same pressure can be maintained, but in this case, the amount of introduced gas is large and the reaction gas inlet in the reaction tube is Since the temperature decreases in the vicinity, the amount of reaction gas is set to a condition where no temperature change occurs, for example, soo/win, and the exhaust control line 1 is
Gas is added to 0 to change the exhaust volume to maintain the same pressure as in the purge process. This is because the heater heating conditions must be changed in order to maintain the same amount of gas introduced and to prevent the temperature inside the reaction tube from changing. This is because it takes a lot of time and effort to establish these soaking conditions.

, Problems to be Solved by the Invention When film formation is performed using such an apparatus in which the inside of the reaction tube is under reduced pressure, it is necessary to purge the tube, air-flow the reaction gas, and switch off the gas system from the tube degassing state to the vapor phase growth state. When switching, a time difference occurs in the electrical switching operation, causing pressure fluctuations, which makes the atmosphere inside the reaction tube unstable. Changes in the atmosphere, ie, pressure, tube temperature, gas amount, and gas temperature, affect the reaction rate, film uniformity, and the like.

Means for Solving the Problems The present invention focuses on the fact that the above problems are caused by pressure changes before the reaction gas is introduced into the reaction tube, that is, before vapor phase growth. - Perform two-stage purging by changing the amount of gas and the amount of exhaust gas, and in the second purge, when switching the gas system between the pipe purge process and the vapor growth process,
In order to prevent pressure changes inside the tube, an inert gas introduction line for exhaust volume control is installed between the exhaust part of the reaction tube and the exhaust system, and the same amount of inert gas as the gas phase reaction process passenger is introduced into the tube. In addition to the purge process, reaction gas air flow process, and gas phase reaction process, the exhaust volume is set to be the same in all processes.

Function Conventionally, switching between the purge process and the vapor growth process required the following operations.

(1) Closing the purge gas (2) Venting the gas inside the pipe (3) Opening the reactant gas introduction into the pipe/evacuation control line (3) requires two operations: introducing the reactant gas into the pipe and opening the evacuation control line. Therefore, changes in the time difference and displacement difference due to electrical switching caused fluctuations in the pressure inside the pipe. Therefore, by using the above means, in (3), it is sufficient to perform only the operation of introducing the reaction gas into the tube, and the purge step, the step of degassing the inside of the tube, and the introduction of the reaction gas into the tube, that is, the vapor phase growth step, can all be performed under the same exhaust state. Because of this, pressure changes do not occur due to differences in displacement.

Example An embodiment of the present invention will be described below with reference to FIG.

3.3 people, 3B is a purge gas line, and the purge gas 2 controlled by each flow controller 1 flows into the reaction tube 5, which is reduced in pressure by the exhaust system 4, and is exhausted through the exhaust line 6 to the exhaust gas I. The configuration is such that

First, in the first purge, the exhaust control line is not activated and the purge gas flowing from the purge lines 3A and 3B is strongly pulled. At this time, the amount of purge gas set to n for each of purge lines 3 and 3B enhances the purging effect in the flow pipe.

Next, as a second purge, purge line 3BiOFFKL
The amount of purge gas is reduced and the exhaust control line is activated to create the same conditions as in the vapor phase growth process. The amount of gas flowing into the purge line 3B at this time is approximately the same as the amount of reaction gas in the vapor phase growth process. Next, reaction gas lines 7 and 8 selected depending on the type of film to be formed. Activate one of 9 and first flush air to the exhaust ■. Next, after degassing the purge gas line 3m-0FFl and the reaction tube S, the reaction gas is switched so that it flows into the reaction tube, and vapor phase growth is performed.

Next, after stopping the reaction gas supply and venting the reaction gas inside the tube,
To prevent gas from being entrained inside the pipe, purge gas is first flowed through purge line 3M, and then purge gas is flowed through purge line 3B to sufficiently purge the inside of the pipe. Then, the exhaust line 6 is turned off, and when the pressure reaches about 30 mHg, the purge line 3 is activated to flow a large amount of purge gas into the pipe to return the pressure to normal pressure. Figures 2 and 6 show the correlation between the passage of time and the pressure inside the tube in each process of purging, degassing, and vapor phase growth.
As shown in the figure.

Figure 2 shows the method of the present invention, in which 2
The pressure is high due to the large amount of purge gas flowing from the system, and then the purge is reduced to one system, and the exhaust amount is suppressed by operating the exhaust control line, adjusting to almost the same conditions as in the vapor phase growth process. After that, the purge line is
FF is performed to vent gas inside the tube, but since the pressure is low in the second purge, the time for venting is short and there is little change in pressure due to the introduction of the reaction gas.

Figure 6 shows the conventional method, in which the pressure is high due to the large amount of gas taking into consideration the purge effect, and the purge line is turned off.
It also takes more time to vent the gas inside the tube than in the method of the present invention. In addition, the two operations of introducing the reaction gas after degassing and activating the exhaust control line must be performed at the same time, but there is a time lag in the changeover, resulting in pressure fluctuations until the vapor phase growth conditions are reached. It turns out that it is unstable.

Therefore, according to the present invention, the following effects can be obtained.

Effects of the Invention According to the method of the present invention, pressure fluctuations during gas switching are extremely small, and the atmosphere inside the reaction tube is kept stable.

In addition, it is possible to suppress changes in the internal temperature of the tube due to pressure fluctuations, which improves the uniformity of the film within the batch, which was conventionally affected by temperature, gas reactions, and pressure, and enables film formation with good reproducibility. .

[Brief explanation of the drawing]

Fig. 1 is a gas system diagram according to the method of the present invention, Fig. 2 is a diagram showing the time course of each process and the pressure inside the pipe according to the method of the present invention,
Fig. 3 is a gas system diagram according to the conventional method, Fig. 4 shows the temperature distribution in the pipe depending on the gas amount and pressure, and Fig. 4a shows the data after pressure adjustment according to the amount of reactant gas introduced. Figure 5 is a diagram showing the time course of each process and the pressure inside the pipe according to the conventional method. 1...Flow rate controller, 2...Purge gas, 3...Purge gas supply line, 4...
・Exhaust system, 5...Reaction tube, 6...
・Exhaust line, 7. 8. 9... Reaction gas line, 10... Exhaust control line. Name of agent: Patent attorney Toshio Nakao and 1 other name
Ki, Ku I) Yoshin Kakeru I) Fig. 2 II Kikan 5 - - and Niwa Sopu F Ki (1) Shoulder F Min (ri Fig. 4 (OJ) Uenoi 12 (b) Way High tL

Claims (2)

[Claims] (1) In vapor phase growth with controlled pressure and gas flow rate, when switching between the reaction gas supply line and the purge gas supply line, an exhaust volume control line is provided in the exhaust line to ensure that the gas in the reaction tube, which is a pre-process of vapor phase growth, is switched between the reaction gas supply line and the purge gas supply line. A vapor phase growth method in which the exhaust volume and gas conditions of the extraction process are the same as those of the vapor phase growth process. (2) The vapor phase growth method according to claim 1, in which two-stage purging is performed by changing the amount of purge gas and the amount of exhaust gas.