JPH05299413A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent a semiconductor substrate surface from being undulated by forming a coating thereon before taking it out of a heat treatment chamber. CONSTITUTION:In a heat treatment furnace 1 a silicon substrate 10 having a exposed surface is treated by heating to remove oxygen contained therein. A coating which will not be etched in an atmosphere outside the heat treatment furnace 1 is formed on the surface of the silicon substrate 10 before taking it therefrom. The heat treatment to the silicon substrate 10 is conducted at 90 deg.C or above. An oxide or nitride film is preferable for the coating formed on the surface of the silicon substrate 10. This obtains a semiconductor substrate excellent in quality without deteriorating the working efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device 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 silicon obtained by such a method contains oxygen of about 10 ¹⁸ cm ⁻³ , and this oxygen has a problem that various characteristics of the semiconductor device are adversely affected. For example, a thermal oxide film formed on the surface of a silicon substrate made of such silicon has a thickness of 10 ⁶ When a high electric field of about V / cm is applied, dielectric breakdown occurs with a certain probability. It is known that this cause is an oxygen precipitate existing near the surface of the silicon substrate.

Therefore, a method has been proposed in which a silicon substrate is subjected to high temperature heat treatment to remove oxygen precipitates. This method, after accommodating a single crystal silicon substrate in a heat treatment furnace,
The silicon substrate is subjected to a high temperature heat treatment at about 1000 ° C. to 1200 ° C. for several hours in a gas atmosphere such as argon 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 near the substrate surface can be removed.

However, when using this method, it was necessary to take care so that water did not enter the heat treatment furnace. This is because, when water is present in the heat treatment furnace during the high temperature heat treatment, silicon is etched by the reaction of Si + H ₂ O → SiO + H ₂ and the height of the substrate surface becomes 0.
This is because undulations of about 1 to 1 μm occur and the long-term reliability of the semiconductor element deteriorates due to the undulations. Therefore, the water contained in the base material of the heat treatment furnace and the water contained in the gas introduced into the heat treatment furnace are controlled so that the water does not exist in the heat treatment furnace during the high temperature heat treatment.

However, even if the moisture in the heat treatment furnace is removed during the high temperature heat treatment, the surface of the substrate is exposed to the outside air containing water vapor when the silicon substrate is taken out of the heat treatment furnace after the high temperature heat treatment. It was difficult to completely prevent the occurrence of. It has been found that this problem can be prevented by sufficiently lowering the temperature in the heat treatment furnace and then taking out the silicon substrate from the heat treatment furnace.However, in this case, the temperature lowering time becomes longer, so that the problem that the work efficiency decreases there were.

[0007]

As described above, in the conventional method for removing the oxygen precipitates of the silicon substrate, the temperature in the heat treatment furnace is sufficiently lowered in order to prevent the long-term reliability of the semiconductor device from being deteriorated. After that, since the silicon substrate was taken out, there was a problem that the cooling time was long and the working efficiency was lowered.

The present invention has been made in view of the above circumstances, and an object thereof is to prevent the occurrence of undulations on the substrate surface without causing a decrease in work efficiency by forming oxygen precipitates in the vicinity of the substrate surface. An object of the present invention is to provide a method of manufacturing a semiconductor device that can be manufactured.

[0009]

In order to achieve the above-mentioned object, a method of manufacturing a semiconductor device according to the present invention includes heat-treating a semiconductor substrate in which a substrate surface is exposed in a heat treatment container and including the semiconductor substrate in the semiconductor substrate. And removing the oxygen contained therein, and before removing the semiconductor substrate from the inside of the heat treatment container, a step of forming a film that is not etched in the outside air of the heat treatment container on the surface of the semiconductor substrate, To do. When the semiconductor substrate is a silicon substrate, the heat treatment is preferably performed at 900 ° C or higher.

The film formed on the surface of the semiconductor substrate is preferably an oxide film or a nitride film. In this case, it is desirable that the oxide film is formed in an oxygen atmosphere at about 600 to 850 ° C, and more preferably at about 700 to 850 ° C. On the other hand, the nitride film is formed at 1000 ° C.
It is desirable to carry out in the above nitrogen atmosphere. Further, the film thickness of the oxide film and the nitride film is preferably 0.3 nm or more.

[0011]

In the method of manufacturing a semiconductor device of the present invention, since the film is formed on the surface of the substrate before taking out the semiconductor substrate from the heat treatment container, the substrate surface is not etched by oxygen and moisture contained in the outside air. It can be prevented. Therefore, when the semiconductor substrate is taken out from the heat treatment container, there is no problem that the surface of the substrate is uneven. Moreover, since such a film can be formed at a temperature higher than the take-out temperature at which no undulation occurs on the substrate surface, the semiconductor substrate can be taken out from the heat treatment container at this temperature, and the work efficiency is lowered. Does not happen.

[0012]

Embodiments will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a heat treatment apparatus according to the first embodiment of the present invention.

The heat treatment furnace 1 comprises a single crystal silicon substrate 10
This is a container for high-temperature heat treatment of, and is heated by a heat heater (not shown). Heat treatment furnace 1
A gas inlet pipe 5 is provided in the upper part of the above, while a gas exhaust pipe 6 is provided in the lower part. The gas introduction pipe 5 is connected to a high-purity argon gas source (not shown) and a high-purity oxygen gas source (not shown), and the gas of each gas source is selectively opened and closed by opening and closing the valves 3 and 4. Can be introduced to. Next, a heat treatment method of the silicon substrate 10 using the heat treatment apparatus configured as described above will be described.

First, after closing the valve 4, the valve 3 is opened and a high-purity argon gas having an impurity content such as water content of 0.1 ppm or less and a flow rate of 20 l / min is heat-treated through the gas introduction pipe 5. It is introduced into the furnace 1. This high-purity argon gas is exhausted to the outside through the gas exhaust pipe 6, and thereby water and the like in the heat treatment furnace 1 is removed. The pressure in the heat treatment furnace 1 is normal pressure. After that, the temperature in the heat treatment furnace 1 is controlled as shown in FIG. That is, first, the temperature in the heat treatment furnace 1 is maintained at 700 ° C. under normal pressure, and then the support base 2 having the silicon substrate 10 mounted in the center portion of the heat treatment furnace 1 is held.
Set up.

Next, in order to replace the oxygen gas, water and the like mixed in the heat treatment furnace 1 with the above steps with high-purity argon gas, the furnace is left at 700 ° C. for about 30 minutes at normal pressure. After this atmospheric pressure, the temperature in the heat treatment furnace 1 is raised to 1200 ° C., and this state is maintained for about 60 minutes to remove oxygen precipitates near the surface of the silicon substrate 10. Here, in order to remove the oxygen precipitates, the temperature in the heat treatment furnace 1 was set to 1200 ° C. However, if the temperature is above 900 ° C., the oxygen precipitates can be removed.

Next, the temperature in the heat treatment furnace 1 is kept at 70 at atmospheric pressure.
After lowering the temperature to 0 ° C., the valve 3 is closed. Next, the valve 4 is opened, and high-purity oxygen gas having an impurity content such as water content of 0.1 ppm or less and a flow rate of 20 l / min is introduced into the heat treatment furnace 1. The pressure in the heat treatment furnace 1 at this time is also normal pressure. By holding this state for about 30 minutes, a silicon oxide film having a thickness of about 0.5 nm is formed on the surface of the silicon substrate 10 from which the oxygen precipitates have been removed. Finally, the support 2 and the silicon substrate 10 are taken out of the heat treatment furnace 1 at a temperature of 700 ° C. or lower.

Silicon substrate 1 obtained by the above method
When 0 was observed, the surface was very flat without any fine undulations. Moreover, oxygen precipitates were also completely removed. The reason why such a good quality single crystal silicon substrate 10 is obtained will be explained as follows.

FIG. 3 is a characteristic diagram showing the relationship between the take-out temperature of the silicon substrate which has been subjected to the high temperature heat treatment and the undulation density on the surface of the silicon substrate. In the figure, a curve a represents a characteristic curve when oxygen gas was introduced into the heat treatment furnace immediately before taking out the silicon substrate. The flow rate of oxygen gas is 10
The introduction time is 10 minutes in liters / minute. The curve b is a characteristic curve when oxygen gas is not introduced. It can be seen from this figure that when the extraction temperature is 850 ° C. or lower, the undulation density when oxygen gas is introduced is smaller than that when oxygen gas is not introduced. Further, it is understood that when the take-out temperature is 800 ° C. or lower, the undulation density when oxygen gas is introduced is 1/2 or less as compared with when oxygen gas is not introduced. The difference in the undulation density is considered to be as follows.

When the take-out temperature is higher than 850 ° C., 2Si + O ₂ → 2 due to oxygen or water vapor in the outside air
The surface of the silicon substrate is etched by the reaction of SiO or Si + H ₂ O → SiO + H ₂ . Therefore, when the extraction temperature is higher than 850 ° C., more oxygen comes into contact with the surface of the silicon substrate by the amount of introduced oxygen, resulting in a higher undulation density.

On the other hand, when the take-out temperature is 850 ° C. or lower, the oxidation rate of silicon becomes faster than the etching rate of silicon, so that the surface of the silicon substrate is oxidized and an oxide film is formed. Once the oxide film is formed,
No etching of silicon occurs because the etching rate is slower than the oxidation rate. The thickness of this oxide film is 0.3.
nm or more is preferable.

It can be seen from FIG. 3 that etching of the substrate surface can be prevented by lowering the take-out temperature to about 600 even when oxygen gas is not introduced. In this case, however, the high temperature heat treatment time is effectively lengthened. However, there arises a problem that work efficiency is reduced. For example, 600 by natural cooling
When the temperature is lowered to 0 ° C, the temperature is lowered at a rate of 1.6 to 2.0 ° C / minute, so that it takes about 50 to 63 minutes, which is about 20 to 33 minutes longer than that of this example. .. Further, in the present embodiment, the silicon substrate was held in the oxygen gas atmosphere for 30 minutes, but a similar effect can be expected even for a shorter time of about 10 to 15 minutes.

In order to prevent the occurrence of undulations on the substrate surface, a method of forming an oxide film on the substrate surface before the high temperature heat treatment can be considered. In this method, oxygen precipitation on the substrate surface, which is the purpose of the high temperature heat treatment, is considered. Removal of objects is hindered. FIG. 4 is a characteristic diagram showing the relationship between the depth from the surface of the substrate and the density of oxygen precipitates. Substrate temperature is 1200 ° C
Is.

From this figure, the high temperature heat treatment using O ₂ (the two-dot chain line connecting the circles in the figure) is the high temperature heat treatment using Ar (the line connecting the ● in the figure) and H ₂ It can be seen that the oxygen precipitation density in the vicinity of the substrate surface is higher than that of the high temperature heat treatment used (the line connecting the X marks in the figure). That is, the effect of removing oxygen precipitates is originally small in the vicinity of the substrate surface, and when an oxygen film is formed on the substrate surface, the effect of removing oxygen precipitates becomes even smaller.

Thus, according to this embodiment, an oxygen precipitate in the vicinity of the surface of the substrate can be removed, and a silicon substrate having no undulations on the surface of the substrate can be obtained without lowering the extraction temperature. A high-quality silicon substrate that can contribute to realization can be obtained without lowering work efficiency.

FIG. 5 is a schematic configuration diagram of a heat treatment apparatus according to the second embodiment of the present invention. The parts corresponding to those of the heat treatment apparatus of FIG. 1 are designated by the same reference numerals as those of FIG. 1, and detailed description thereof will be omitted.

The heat treatment apparatus of this embodiment differs from that of FIG. 1 in that a gas exhaust pipe 22 connected to a vacuum exhaust device 20 is added to the lower portion of the heat treatment furnace 1, and a valve 23 is provided in the gas exhaust pipe 6. Especially. That is, this heat treatment apparatus is configured to have a higher gas exhaust capacity than the previous heat treatment apparatus. Next, a heat treatment method of the heat treatment apparatus configured as described above will be described. Basically, it is the same as the case of the previous embodiment.

First, with the valve 21 closed and the valve 23 open, high-purity argon gas was introduced into the heat treatment furnace 1 in the same manner as in the previous embodiment, and then the silicon substrate 10 was subjected to high temperature heat treatment to obtain the substrate surface. Oxygen precipitates in the vicinity are removed.

Next, the temperature in the heat treatment furnace 1 is lowered to 800 ° C. or lower, after which the valve 23 is closed and the valve 21 is opened, and the argon gas in the heat treatment furnace 1 is exhausted by the vacuum exhaust device 20 to perform the heat treatment. The pressure in the furnace 1 is reduced to 100 Torr or less.

Finally, with the valve 23 closed, the valve 2
1 is closed, the valve 4 is opened, high-purity oxygen gas is introduced into the heat treatment furnace 1 at a flow rate of 1 liter / min, and an oxide film is formed on the substrate surface. The silicon substrate 10 is taken out. The introduction flow rate of the high-purity oxygen gas is not limited to the value described above, and may be any amount as long as an oxide film having a desired film thickness is formed.

In this embodiment, since the argon gas in the heat treatment furnace 1 and the high-purity oxygen gas are exchanged by using the vacuum exhaust device 20, the argon gas can be surely exhausted and the inside of the heat treatment furnace 1 can be surely discharged. The distribution of high-purity oxygen gas can be made uniform. Therefore, due to the non-uniform distribution of the high-purity oxygen gas in the heat treatment furnace 1, a region where the high-purity oxygen gas pressure is low is generated and the silicon substrate 10 is not etched.

Therefore, it is necessary to set the temperature in the heat treatment furnace 1 to be low at the time of introducing the high-purity oxygen gas so that the silicon substrate 10 is not etched even if a region where the pressure of the high-purity oxygen gas is low is generated. Is eliminated, the heat treatment time can be shortened.

Thus, in this embodiment as well, the same effects as in the previous embodiment can be obtained, and high-purity oxygen gas can be introduced into the heat treatment furnace 1 at a higher temperature than in the previous embodiment. Therefore, there is also an advantage that the work efficiency is further improved. Note that hydrogen gas may be used instead of argon gas. The point is that, when removing the oxygen precipitates, it is sufficient that a film that hinders the removal of the oxygen precipitates is not formed on the substrate surface. FIG. 6 is a schematic configuration diagram of a heat treatment apparatus according to the third embodiment of the present invention. The heat treatment apparatus of this embodiment is shown in FIG.
The difference from that is that a gas introduction pipe 30 for introducing the high-purity oxygen gas into the heat treatment furnace 1 is separately provided.

That is, the high-purity oxygen gas is introduced into the heat treatment furnace 1 through the gas introduction pipe 30 extending into the heat treatment furnace 1. Further, the gas introducing pipe 30 in the heat treatment furnace 1 is provided with a large number of holes. Therefore, when the heat treatment apparatus of this embodiment is used, the high-purity oxygen gas introduced into the heat treatment furnace 1 through the gas introduction pipe 30 by opening the valve 4 after the high temperature heat treatment is dispersed from the holes of the gas introduction pipe 30. Then, the entire heat treatment furnace 1 is instantly spread. Therefore, also in this case, the distribution of the high-purity oxygen gas in the heat treatment furnace 1 can be made more uniform, so that an effect superior to that of the previous embodiment can be obtained. Next, a heat treatment method according to the fourth embodiment of the present invention will be described.

In the above embodiment, the case where the oxide film is formed on the surface of the silicon substrate has been described, but the present inventors have confirmed that the same effect can be obtained by forming the nitride film on the surface of the silicon substrate. did.

FIG. 7 is a characteristic diagram showing the relationship between the nitrogen gas introduction temperature and the undulation density on the surface of the silicon substrate. The flow rate of nitrogen gas is 10 liters /
Min, introduction time is 30 minutes, and take-out temperature is 800 ° C. For comparison, the undulation density when nitrogen is not introduced is shown by a dotted line.

From this figure, it can be seen that a nitride film is formed on the surface of the substrate by using nitrogen gas at 1000 ° C. or higher.
Further, the lower limit of the film thickness of the nitride film, which shows the effect of suppressing the undulation, is 0.
It was confirmed to be 3 nm. Further, as in the case of the oxide film, as shown in FIG. 4, the nitride film also has a high oxygen precipitation density in the vicinity of the substrate surface. Get smaller.

Next, the heat treatment method using nitrogen gas when the heat treatment apparatus of FIG. 1 is used will be specifically described. Figure 8
FIG. 4 is a diagram showing the relationship between the temperature in the heat treatment furnace 1 and the heat treatment time in this example.

First, the valve 4 was closed and the valve 3 was opened, and high-purity argon gas having an impurity content of 0.1 ppm or less and a flow rate of 20 l / min was fed into the heat treatment furnace 1 at atmospheric pressure. After that, the temperature in the heat treatment furnace 1 is set to 700 ° C.
Set to. Next, the support base 2 on which the silicon substrate 10 is mounted is placed in the heat treatment furnace 1 at the center of the furnace, and this state is set to 3
Hold for 0 minutes.

Next, the temperature in the heat treatment furnace 1 is set to 1200 at normal pressure.
After raising the temperature to 0 ° C. and maintaining this state for about 60 minutes, the temperature in the heat treatment furnace 1 is lowered at a rate of 5 ° C./min. That is,
The high temperature treatment at 1000 ° C. or higher is for 40 minutes. At this time, the valve 3 is closed, the valve 4 is opened, and high-purity nitrogen gas having an impurity content of 0.1 ppm or less such as water is sent into the heat treatment furnace 1 at normal pressure at a flow rate of 20 liters / minute. As a result, the surface of the silicon substrate 10 has a thickness of about 0.5 nm.
A silicon nitride film is formed. Then, when the temperature inside the heat treatment furnace 1 is lowered to 700 ° C., the silicon substrate 10 and its supporting base 2 are taken out from the heat treatment furnace 1.

According to this embodiment, since the surface of the silicon substrate 10 is protected by the nitride film, the silicon substrate 1 is taken out from the heat treatment furnace 1 in order to take it out.
Even if 0 comes into contact with the outside atmosphere, no undulation occurs on the silicon surface. Further, since the nitride film is not formed during the high temperature heat treatment, oxygen precipitates can be completely removed. Further, the present embodiment using nitrogen gas is superior to the previous embodiment using oxygen gas in terms of preventing flame generation. Note that a gas such as hydrogen gas may be used instead of the argon gas as in the previous embodiment. Further, in the present embodiment, the case where the heat treatment apparatus of FIG. 1 is used has been described, but the same effect can be obtained by using the heat treatment apparatus of FIG. 5 and the heat treatment apparatus of FIG.

The present invention is not limited to the above embodiment. For example, in the above embodiment, the case of the silicon substrate has been described, but the present invention can be applied to other semiconductor substrates.

Similar effects can be expected by introducing a gas other than oxygen gas and nitrogen gas into the heat treatment furnace after the high temperature heat treatment. The point is to form a film on the substrate surface that is not etched in the open air.

Further, the heat treatment apparatus is not limited to the one described above, and for example, a combination of the heat treatment apparatus of FIG. 5 and the heat treatment apparatus of FIG. 6, that is, the vacuum exhaust device 2
It is also possible to use a heat treatment apparatus provided with 0 and the gas introduction pipe 30.

Furthermore, in the above embodiment, the silicon substrate was heat-treated in a gas atmosphere to remove oxygen precipitates.
The oxygen precipitates may be removed by another heat treatment method, for example, heat treatment by vacuum heating. In addition, various modifications can be made without departing from the scope of the present invention.

[0045]

As described above in detail, according to the present invention, it is possible to obtain a high-quality semiconductor substrate that can contribute to the realization of a semiconductor device having long-term reliability without lowering work efficiency.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a heat treatment apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between heat treatment time and heat treatment furnace temperature.

FIG. 3 is a characteristic diagram showing the relationship between the take-out temperature and the undulation density on the surface of the silicon substrate.

FIG. 4 is a characteristic diagram showing the relationship between the depth from the substrate surface and the density of oxygen precipitates.

FIG. 5 is a schematic configuration diagram of a heat treatment apparatus according to a second embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of a heat treatment apparatus according to a third embodiment of the present invention.

FIG. 7 is a characteristic diagram showing a relationship between a nitrogen gas introduction temperature and an undulation density on the surface of a silicon substrate.

FIG. 8 is a diagram showing the relationship between the temperature in the heat treatment furnace and the heat treatment time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Heat treatment furnace 2 ... Support stand 3,4,21,23 ... Valve 5,30 ... Gas introduction pipe 6 ... Gas exhaust pipe 10 ... Silicon substrate 20 ... Vacuum exhaust device

Front page continuation (72) Inventor Hideyuki Kobayashi 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside Toshiba Research Institute Co., Ltd. Incorporated company Toshiba Research Institute (72) Inventor Akito Yamamoto 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research Institute

Claims (2)

[Claims] 1. A step of heat-treating a semiconductor substrate in which a substrate surface is exposed in a heat treatment container to remove oxygen contained in the semiconductor substrate; and a step of removing the semiconductor substrate from the heat treatment container,
And a step of forming a coating on the surface of the semiconductor substrate that is not etched in the outside air of the heat treatment container. 2. A step of heat-treating a silicon substrate in which a surface of the substrate is exposed in a heat treatment container in a gas atmosphere in which a silicon compound is not formed, and before the silicon substrate is taken out from the heat treatment container, the silicon substrate is treated with oxygen. Exposing to an atmosphere or a nitrogen atmosphere to form an oxide film or a nitride film on the surface of the silicon substrate.