JPH05121387A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To remove oxygen deposit near a surface of an Si substrate without generating rises and falls on a surface of the substrate by heat treating the substrate before forming an element in an N2 gas atmosphere containing a water content of 500ppb or less at 900 deg.C or above. CONSTITUTION:A heat treating vessel 3 is held at 750'C, Ar dry gas is fed to an inner tube 1 through a gas introducing tube 4, and N2 gas containing a water content of 50ppb or less is fed to the tube 2 through a gas introducing tube 6. Then, an Si substrate 8 is contained in the tube 1, and sealed. Moisture of the atmosphere invaded into the tube 1 is diffused in a base material for constituting the tube 1. Thereafter, the tube 1 is heated to 850 deg. to vaporize the moisture in the material of the tube 1 and to discharge it out of the tube 1. The moisture is discharged out of a discharge tube 5 by the dried Ar gas. The vessel 3 is heated to 1200 deg. by a heater. Since the N2 gas containing the water content of 50ppb or less flows in a part heated to 900 deg.C or higher of the tube 1, invasion of the moisture in the outside is shut OFF.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor substrate having a step of forming a good quality semiconductor substrate.

[0002]

2. Description of the Related Art Conventionally, single crystal silicon has been formed by using a growth method such as a CZ (Czochralski) method.

However, the single crystal silicon obtained by this kind of method contains about 10 ¹⁸ [cm ⁻³ ] of oxygen, and this oxygen greatly affects various characteristics of the semiconductor device. was there.

For example, a thermal oxide film formed on a substrate made of such single crystal silicon has a thermal conductivity of 10 ⁶ [V / cm]
When a high electric field of about a certain degree is applied, with a certain probability, accidentally,
Causes dielectric breakdown. It is known that this is due to oxygen precipitates existing near the surface of the substrate.

Therefore, a method has been proposed in which a silicon substrate is subjected to a high temperature heat treatment to remove oxygen precipitates. FIG. 3 is a sectional view of the heat treatment apparatus used at this time. This heat treatment apparatus is roughly divided into a heat treatment container 11, a non-oxidizing gas introduction pipe 12 provided at one end of the heat treatment container,
Non-oxidizing gas exhaust pipe 1 provided at the other end of the heat treatment container
3 and a heater (not shown) for controlling the temperature of the gas in the heat treatment container.

In order to remove oxygen precipitates by using the heat treatment apparatus constructed as described above, first, the heat treatment container 11 is used.
The silicon substrate 14 is housed therein, and then the silicon substrate 14 is subjected to a high temperature heat treatment at about 1000 ° C. to 1200 ° C. for several hours in a gas atmosphere in which a film of a semiconductor compound such as an oxide film or a nitride film is not formed on the silicon surface. By this high-temperature heat treatment, interstitial oxygen in the substrate diffuses outward and is released from the substrate surface to the outside or is reduced, so that oxygen precipitates are removed from the vicinity of the substrate surface.

However, when a high temperature heat treatment is performed for several hours with the semiconductor surface exposed, for example, if a thermal oxide film is formed on this silicon substrate, a minute defect region is generated in the thermal oxide film. However, there is a problem that the withstand voltage is lowered. As a result, there is a problem that the long-term reliability of the element formed on the silicon substrate is reduced.

[0008]

As described above, in order to prevent the reliability of the semiconductor device from being deteriorated by the oxygen precipitates near the surface of the silicon substrate, the oxygen precipitates are removed from the silicon substrate by the high temperature heat treatment. However, the high temperature heat treatment causes a problem that the long-term reliability of the element formed on the silicon substrate deteriorates.

The present invention has been made in consideration of the above circumstances, and an object thereof is to prevent oxygen precipitates near the surface of a silicon substrate from impairing long-term reliability of an element on the substrate. It is an object of the present invention to provide a method for manufacturing a semiconductor substrate having a process that can be removed.

[0010]

In order to achieve the above object, the first method of manufacturing a semiconductor device according to the present invention uses a silicon substrate having a water content of 50 ppb or less and a temperature of 900 ° C.
It is characterized in that it has a step of heat treatment in the above gas atmosphere.

According to a second method for manufacturing a semiconductor device of the present invention, a silicon substrate is placed in a heat treatment container, and a gas having a water content of 50 ppb or less is flown into the heat treatment container while the heat treatment container is heated to 800 times. Holding for 30 minutes or more in the temperature range of 90 ° C. or higher and 900 ° C. or lower, after which the silicon substrate has a water content of 50 ppb or less and a temperature of 90
And a heat treatment step under a condition that the substrate surface is exposed in a gas atmosphere at 0 ° C. or higher.

Furthermore, in a third method of manufacturing a semiconductor device of the present invention, a silicon substrate is placed in a heat treatment container, and the silicon substrate has a water content of 50 ppb or less and a temperature of 9 ppm.
The method is characterized by comprising a step of performing a heat treatment under a condition that a substrate surface is exposed in a gas atmosphere of 00 ° C. or higher, and flowing a gas having a water content of 50 ppb or less along the outer wall of the heat treatment container during the heat treatment.

[0013]

The inventors of the present application have found that the causes of the long-term reliability deterioration of the element due to the above-mentioned heat treatment are as follows.

That is, with the surface of the semiconductor substrate exposed,
When high-temperature heat treatment is performed for several hours, undulations having a height of about 0.1 μm to 1 μm occur on the surface of the silicon substrate. For this reason, for example, when a thermal oxide film is formed on this silicon substrate, a minute defect region is generated in the thermal oxide film and the withstand voltage is reduced, resulting in a significant decrease in device reliability.

Furthermore, the present inventors have found that the surface of the silicon substrate is undulated during the high temperature heat treatment because the water vapor in the heat treatment container and the silicon substrate react with each other such as Si + H ₂ O → SiO + H _2. It was confirmed that the surface was etched.

The present inventors have also examined the relationship between the heat treatment temperature, the water content in the atmosphere, and the density of minute defects in the thermal oxide film formed on the silicon substrate after the heat treatment. The result is shown in FIG. From this figure, it can be seen that the density of minute defects increases as the water content increases. This is because the more the water content, the more the above etching reaction occurs. When the heat treatment temperature is 900 ° C or higher,
It can be seen that the etching reaction becomes remarkable. However, in any case of 900 ° C., 1000 ° C. and 1100 ° C., it is found that the fine defect density becomes almost zero when the water content becomes 50 ppb or less. That is, in order to suppress the generation of undulations on the surface of the silicon substrate, the water content should be 50 p
It can be seen that it may be set to pb or less. If the heat treatment temperature is lower than 900 ° C., the above etching reaction may be prevented, but at such a low temperature, the removal of oxygen precipitates cannot be effectively performed, which is not practical.
The presence of water vapor in the heat treatment container is as follows. The first reason is that the gas such as Ar gas or H ₂ introduced into the heat treatment container via the gas introduction pipe contains water. The second reason is that when the silicon substrate is housed in the heat treatment container, moisture in the outside air enters the heat treatment container. The third reason is that the moisture in the outside air that has soaked into the heat treatment container becomes steam during the heat treatment and enters the heat treatment container.

[0017]

Embodiments will be described below with reference to the drawings. First, a heat treatment method for a silicon substrate according to an embodiment of the present invention will be described in consideration of the above circumstances. FIG. 2 is a sectional view of the heat treatment apparatus used in this embodiment.

This heat treatment apparatus is roughly divided into the inner tube 1
And a heat treatment container 3 composed of an outer pipe 2 provided on the outer periphery of the inner pipe 1, and a gas introduction pipe 4 provided at one end of the inner pipe 1.
A gas discharge pipe 5 provided at the other end of the inner pipe 1 and an outer pipe 2
On the gas introduction pipe 6 provided at one end of the outer pipe 2, a gas discharge pipe 7 provided at the other end of the outer pipe 2, and a heater (not shown). The inner pipe 1, the outer pipe 2, the gas introduction pipes 4, 6 and the gas discharge pipes 5, 7 are all made of quartz. In addition, the gas introduced into the inner pipe 1 and the outer pipe 2 through the gas introduction pipes 4 and 6 is discharged outside the pipes through the gas discharge pipes 5 and 7, respectively. The temperature of the gas in the inner tube 1 and the inner tube 2 is adjusted by the heater. Next, a heat treatment method for a silicon substrate using the heat treatment apparatus configured as described above will be described.

First, the heat treatment container 3 is kept warm at 750 ° C.,
In this state, an argon (Ar) gas having a water content of 20 ppb is introduced as a dry gas into the inner pipe 1 through the gas introduction pipe 4, and the moisture content as a dry gas is supplied to the outer pipe 2 through the gas introduction pipe 6. Injects 20 ppb of nitrogen (N ₂ ) gas. As a result, it is possible to prevent the inconvenience caused by the moisture of the first reason.

Next, the silicon substrate 8 is housed in the inner tube 1 and sealed. Here, the moisture in the outside air that has entered the inner tube 1 diffuses into the base material forming the inner tube 1. Then, the inner tube 1 is heated to 850 ° C. by a heater and kept in this state for 30 minutes to evaporate the moisture diffused in the base material of the inner tube 1,
Discharge to outside. At this time, since the argon (Ar) gas having a small water content is flowing into the inner pipe 1, the water vapor evaporated from the base material of the inner pipe 1 is effectively discharged from the gas discharge pipe 5.
Can be discharged outside. As a result, it is possible to prevent the inconvenience caused by the moisture for the second reason.

Next, the heat treatment container 3 is heated to 1200 by a heater.
The temperature is raised to 0 ° C. and this state is maintained for 1 hour. At this time, regarding the portion of the inner tube 1 heated to 900 ° C. or higher,
Moisture content between the outer surface of the part and the outside is 20 pp
Since the N ₂ gas of b is flowing, it is possible to prevent the moisture from the outside from soaking into the inner tube 1. As a result, it is possible to prevent the inconvenience caused by the moisture for the third reason. Finally, the temperature of the heat treatment container 3 is adjusted to 750 ° C. by adjusting the heater, and this state is maintained for a predetermined time. When the silicon substrate 8 obtained by the above method was observed, it was found that the surface was very flat without any fine undulations.

As described above, the good quality of the silicon substrate 8 can be obtained in the moisture contained in the Ar gas or the N ₂ gas introduced into the heat treatment container 3 and in the base material constituting the heat treatment container 3. This is because by controlling the water content contained in the heat treatment atmosphere, water vapor, which causes undulations on the surface of the silicon substrate 8 during the high temperature heat treatment, can be removed from the heat treatment atmosphere. Further, when a thermal oxide film was formed on the silicon substrate 8 and the density of minute defects was examined, the value was 0.1 /
cm ² The following was confirmed.

Thus, according to the present embodiment, the silicon substrate 8 is not undulated on the surface of the silicon substrate 8.
It is possible to remove the oxygen precipitates in the vicinity of the surface of, and thus improve the long-term reliability of the element formed on the silicon substrate 8.

In this embodiment, 20 ppb of Ar gas was passed through the inner tube 1, but the same effect can be obtained if it is 50 ppb or less. Further, although Ar gas was passed through the inner tube 1 as a dry gas, other inert gas having a low water content (50 ppb or less) may be used. Similarly, N ₂ gas was flown through the outer tube 2, but other gas such as H ₂ gas having a small water content may be used. The point is that the water content is low,
Any material that does not form a semiconductor compound on the surface of the silicon substrate may be used.

Further, in this embodiment, the inner tube 1 was heated to 850 ° C. by the heater and kept in this state for 30 minutes.
Similar effects can be obtained under the conditions of 800 ° C. or higher and 30 minutes or longer.

Further, in the present embodiment, the heat treatment container 3 is heated to 1200 ° C. by the heater. However, if the inner tube 1 is heated to 900 ° C. or higher, it may be 1200 ° C. or lower or higher. .. Further, although the case of the silicon substrate has been described in the present embodiment, the defects can be similarly reduced in the case of other semiconductor substrates.

[0027]

As described in detail above, according to the present invention, oxygen precipitates in the vicinity of the surface of a silicon substrate can be removed without causing undulations on the surface of the silicon substrate.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a heat treatment temperature, a water content and a fine defect density.

FIG. 2 is a sectional view of a heat treatment apparatus according to an embodiment of the present invention.

FIG. 3 is a sectional view of a conventional heat treatment apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Inner pipe, 2 ... Outer pipe, 3 ... Heat treatment container, 4 ... Gas introduction pipe, 5 ... Gas discharge pipe, 6 ... Gas introduction pipe, 7 ... Gas discharge pipe, 8 ... Silicon substrate, 11 ... Heat treatment container, 12 ... Gas introduction pipe, 13 ... Gas discharge pipe, 14 ... Silicon substrate.

Front page continuation (72) Inventor Kunihiro Terasaka, 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Research Institute

Claims (3)

[Claims] 1. A method of manufacturing a semiconductor device, comprising a step of heat-treating a silicon substrate in a gas atmosphere having a moisture content of 50 ppb or less and a temperature of 900 ° C. or more under the condition that the surface of the substrate is exposed. 2. A silicon substrate is placed in a heat treatment container, and the heat treatment container is kept in a temperature range of 800 ° C. or more and 900 ° C. or less for 30 minutes or more while flowing a gas having a water content of 50 ppb or less in the heat treatment container. And the process of doing
And a step of heat-treating the silicon substrate in a gas atmosphere having a moisture content of 50 ppb or less and a temperature of 900 ° C. or more under the condition that the surface of the substrate is exposed. 3. A step of placing a silicon substrate in a heat treatment container and heat treating the silicon substrate in a gas atmosphere having a water content of 50 ppb or less and a temperature of 900 ° C. or more under the condition that the substrate surface is exposed. A method of manufacturing a semiconductor device, wherein a gas having a water content of 50 ppb or less is flowed along the outer wall of the heat treatment container during the heat treatment.