JPH04167433A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To sharply reduce the danger of a high-temperature heat treatment in a hydrogen atmosphere and to completely remove an oxygen precipitate by a method wherein, after a first high-temperature heat treatment has been executed in an inert gas atmosphere, a second high-temperature heat treatment is executed in an atmosphere which contains hydrogen gas. CONSTITUTION:By a first heat treatment process executed in an argon gas atmosphere, an interlattice oxygen concentration in a silicon wafer is reduced to 1/5 or lower at a depth of 5mum from the surface of the wafer as compared with that before the heat treatment. In succession, a second process is executed. First, a valve 3 at a hydrogen gas pipe is opened; high-purity hydrogen gas whose impurity content of moisture or the like has been reduced to 0.1ppm or lower is made to flow into at 1l/min. At this time, since residual oxygen inside a heat treatment furnace has already been replaced sufficiently with argon gas, a danger such as an explosion or the like which is caused when the hydrogen gas is introduced hardly exists. A residual oxygen precipitate, at about 0.1/cm<2>, which exists near the surface of the wafer by a reduction effect of oxygen disappears completely.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for manufacturing a semiconductor device having excellent long-term reliability. The present invention relates to a heat treatment method for semiconductor wafers.

(Prior art) A silicon semiconductor single crystal grown by the C2 (Czochralski) method contains about 1018/an3 of oxygen, and its behavior has a large effect on semiconductor characteristics such as LSI characteristics. ing.

When a high electric field of several M V/an is applied to a thermal oxide film formed on a semiconductor substrate such as silicon, dielectric breakdown occurs accidentally in the thermal oxide film with a certain probability. It is known that the cause is oxygen precipitates present near the surface of the semiconductor substrate. Conventionally, a high temperature hydrogen annealing method has been used as a method for removing this oxygen precipitate. That is, the semiconductor substrate to be processed is heated to 1000°C to 1200°C.
This is a method of annealing in a hydrogen atmosphere at a temperature of about °C. Through this treatment, interstitial oxygen in the substrate is diffused outward,
It detaches from the substrate surface to the outside, reduces precipitated oxygen,
Oxygen precipitates can be removed from near the substrate surface.

However, handling hydrogen gas at such high temperatures for several hours is extremely dangerous, and practical use was not possible unless safety issues such as explosion-proof measures were resolved. As a method to avoid safety issues, there is also known a technique of using an inert gas such as argon or nitrogen instead of hydrogen gas. Although this method can diffuse interstitial oxygen in the substrate outward, it is not effective in reducing precipitated oxygen, so a small amount of oxygen precipitates remain near the substrate surface, resulting in accidental The dielectric breakdown that occurs cannot be completely eliminated.

FIG. 4 shows the effects of the two methods described above. The depth distribution of the oxygen precipitate density (/an3) in the semiconductor substrate is shown when the substrate is annealed at 1200° C. for 1 hour in hydrogen and argon atmospheres, respectively. The vertical axis represents the oxygen precipitate density, and the horizontal axis represents the depth (μm) from the semiconductor substrate surface (union). Looking at this figure, it can be seen that if the first method, which is annealing treatment in a hydrogen atmosphere, is performed, there are almost no oxygen precipitates in the region up to 40 μm from the wafer surface.

On the other hand, the second method, such as argon,
According to the annealing treatment in an inert gas atmosphere, approximately 1/al]3 oxygen precipitates remain in the above region. Therefore, in the second method, it was impossible to sufficiently remove oxygen precipitates and form an active region with excellent device characteristics near the surface of the unino.

(Problems to be Solved by the Invention) As described above, in the conventional technology, methods using hydrogen gas have safety problems, and methods using inert gas do not sufficiently remove oxygen precipitates. The problem was that I couldn't do it. The present invention was made in view of the above circumstances, and provides a method for manufacturing a semiconductor device that can significantly reduce the risk of high-temperature heat treatment in a hydrogen atmosphere and completely remove oxygen precipitates. is intended to provide.

[Structure of the invention]

(Means for Solving the Problems) The present invention relates to a method for manufacturing a semiconductor device,
The method is characterized by comprising a step of heat treating the semiconductor chip \ in an inert gas atmosphere, and a step of heat treating the semiconductor chip 1 in an atmosphere containing hydrogen gas after this step.

(Function) By the high temperature heat treatment in the first inert gas atmosphere,
The interstitial oxygen in the semiconductor wafer diffuses out, the size of the oxygen precipitates decreases, and most of the oxygen precipitates disappear. Next, the second high-temperature heat treatment step is performed in an atmosphere containing hydrogen gas, so the residual oxygen precipitates that were not removed in the first treatment can be completely eliminated by the reducing effect of hydrogen. This can prevent accidental dielectric breakdown of the thermal oxide film.

The second high-temperature heat treatment step can be performed continuously by introducing hydrogen gas into the heat treatment furnace after the first high-temperature heat treatment. At that time, the inert gas used in the first heat treatment step was
It will be used continuously and hydrogen gas will be added to it. The effect appears when the amount added is from several percent to several ten percent.

During the first high-temperature heat treatment, residual oxygen in the furnace is sufficiently replaced with inert gas, so there is almost no danger when introducing hydrogen gas, and special Since there is no need to provide time for atmosphere replacement, processing time can be shortened. Of course, it is not necessary to use the same inert gas for the first and second gases, but doing so would complicate the processing operation. The inert gas is not particularly limited and may be argon or nitrogen, but if the heat treatment temperature is set to 1100°C or higher, a reaction between the semiconductor wafer and the nitrogen gas will start.
If nitrogen is used, this temperature must be avoided. The heat treatment temperature is required to be about 1000°C to 1200°C in all steps. When the temperature is low, the processing time becomes long, and when the temperature is high, the processing time becomes short. Appropriate processing time is approximately 10 minutes to 24 hours.

Furthermore, the diffusion length of interstitial oxygen in the semiconductor wafer during the first high-temperature heat treatment is approximately 10 μm even if a trench structure is taken into consideration, as long as there is no oxygen in the active region of the wafer. If the above exists, the object of the present invention can be achieved. The heat treatment conditions for the diffusion length to be 10 μm are 1200° C. for 40 minutes, 1100° C. for 3 hours, and 1000° C. for 16 hours. When this diffusion length is increased by 10 times, the heat treatment time becomes 100 times, and when this diffusion length is reduced to 1/10, it becomes 1'/100. In the first treatment, the interstitial oxygen concentration in the wafer is reduced and the effect of the present invention appears due to the following reasons:
A diffusion length of about 175 is required (see Figure 5). Therefore, the diffusion length for carrying out the present invention is approximately 5 μm in a semiconductor device having a normal structure, and approximately 50 μm in a semiconductor device having a wrench structure.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of a heat treatment apparatus for performing high-temperature heat treatment of the present invention, and FIG. 3 is an explanatory diagram of the supply amounts of inert gas and hydrogen gas used in the heat treatment of the present invention. . First, the content of impurities such as moisture is reduced to 0. ] High purity argon gas kept below ppm is passed through the pipe to the intake port 4.
from there into the heat treatment furnace 1 of this apparatus at a rate of 191/min. The gas that has passed through the furnace is exhausted to the outside through the exhaust port 5. The heat treatment furnace is kept at a temperature of 800° C., and a support base 2 on which a silicon wafer 10 is mounted is arranged in the center thereof. Next, after leaving the furnace for about 10 minutes so that the oxygen gas, moisture, etc. that were mixed into the furnace when inserting the wafer were sufficiently replaced with argon gas, the temperature inside the furnace was raised to 1200°C. was held for about 60 minutes. The interstitial oxygen concentration distribution in the depth direction in the silicon wafer 10 at this time is
Shown in Figure 2. The vertical axis is the interstitial oxygen concentration (/a[13),
The horizontal axis represents the depth (μm) from the wafer surface. As shown in this figure, by the first heat treatment step carried out in an argon gas atmosphere, the interstitial oxygen concentration in the silicon wafer was reduced to 115 or less at a depth of 5 μm from the wafer surface to the level before heat treatment. ing.

Further, with this outward diffusion of interstitial oxygen, the density of oxygen precipitates near the wafer surface is also reduced to about 0.1 particles/a [13]. This is as shown in FIG. 4 above.

The above is the first step, and the second step follows.

First, open the valve 3 of the hydrogen gas pipe and reduce the content of impurities such as moisture to 0. ] High-purity hydrogen gas kept at ppm or less flows in at a rate of 11 per minute. At this time, the residual oxygen in the heat treatment furnace 1 has already been sufficiently replaced by argon gas, so there is almost no risk of explosion due to the introduction of hydrogen gas. This state was maintained for 10 minutes. The atmosphere inside the furnace at that time was 95% argon and 5% hydrogen by volume.
It is a mixed state. The heat treatment temperature was maintained at 1200°C. Due to the reduction effect of hydrogen, residual oxygen precipitates of about 0.1/a [13] existed near the wafer surface.
completely disappeared. After the second step is completed, the hydrogen gas valve 3 is closed, the temperature inside the furnace is lowered to 800°C, and the silicon wafer 10 and its support 2 are
is taken out from the heat treatment furnace 1.

The silicon wafer subjected to the above treatment is subjected to thermal oxidation treatment to form a silicon oxide film. A capacitor having a gate area of 10×2 is formed on the silicon wafer by using the oxide film on the wafer as a gate insulating film. Next, we investigated the breakdown voltage of this gate insulating film and found that it was several M V
Even when an electric field of /an was applied, no accidental dielectric breakdown was observed.

In the embodiments, only silicon wafers have been described, but it goes without saying that the present invention can be applied to other semiconductor wafers.

〔Effect of the invention〕

As explained above, by heat-treating a semiconductor wafer using the method of the present invention, oxygen precipitates near the wafer surface can be completely removed without any danger, and semiconductor devices with high long-term reliability can be formed. It becomes possible to provide semiconductor wafers for

[Brief explanation of drawings]

FIG. 1 is a sectional view of a heat treatment apparatus for carrying out the heat treatment of the present invention, FIG. 2 is a diagram of the interstitial oxygen concentration distribution in the wafer obtained by the first heat treatment step of the present invention, and FIG. , an explanatory diagram of the supply amount of inert gas and hydrogen gas used in the heat treatment of the present invention, FIG. 4 is a diagram of the density distribution of oxygen precipitates in a conventional wafer, and FIG. 5 is a diagram of the oxygen concentration and oxygen in the wafer. FIG. 2 is a characteristic diagram showing the relationship between . DESCRIPTION OF SYMBOLS 1...Heat treatment furnace, 2...Support stand, 3...Hydrogen gas pipe knob, 4...Intake port, 5...Exhaust port, 10...Wafer. (8733) Agent Patent attorney Yoshiaki Inomata (and 1 other person) (Fat)] ■) Passenger 澹罎GTK Book 1 and meritorious service (cri'l) Figure 5

Claims (1)

[Claims] 1. A method for manufacturing a semiconductor device, comprising the steps of: heat treating a semiconductor wafer in an inert gas atmosphere; and, after this step, heat treating the semiconductor wafer in an atmosphere containing hydrogen gas.