JPH11111724A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method through which the oxygen concentration in the surface layer section of a semiconductor substrate can be reduced by effectively suppressing an oxide film effect such that oxygen atoms are scattered inwards from an oxide film. SOLUTION: When the temperature of a semiconductor substrate on which an oxide film has been formed is lowered from the temperature of a heat- treating process after the substrate has been heat-treated at a temperature >=1,000 deg.C in a heat-treating process, the temperature is lowered at a first temperature-lowering rate within the temperature range which is higher than about 1,000 deg.C and a second temperature-lowering rate, which is smaller than the first rate within the temperature range from about 900 deg.C to about 1,000 deg.C. Then the temperature is lowered at a third temperature-lowering rate which is larger than the second rate within the temperature range lower than about 900 deg.C.

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 device having a heat treatment step of heat treating a semiconductor substrate having an oxide film formed thereon.

[0002]

2. Description of the Related Art A semiconductor substrate originally contains various impurities and minute crystal defects caused by the impurities.
The crystal defects include, for example, oxygen precipitate nuclei as minute defects caused by oxygen as an impurity. When the concentration of impurity oxygen increases, oxygen of impurities may aggregate into oxygen precipitation nuclei and grow into oxygen precipitates due to a heat process at the time of manufacturing the semiconductor device. If this oxygen precipitate exists in the surface layer of the semiconductor substrate, the device characteristics deteriorate. In particular, with the increase in the degree of integration of semiconductor devices, the presence of oxygen precipitates in a semiconductor substrate has become a major problem.

For this reason, reducing the oxygen concentration in the surface layer of the semiconductor substrate has become an important issue, and techniques for reducing the oxygen concentration in the semiconductor substrate, such as oxygen outward diffusion, have become increasingly important.

[0004]

However, in the case of a semiconductor substrate on which an oxide film is formed, there is a problem that even if a heat treatment is performed for oxygen outward diffusion, the oxygen concentration cannot be reduced below a certain value. Was. The present inventors have found that the cause is an oxide film effect in which oxygen atoms constituting the oxide film diffuse inward into the semiconductor substrate during the heat treatment (Abe et al., Proceedings of the 43rd JSAP). , 28a-
X-6 (1996)). However, the mechanism of the oxide film effect has not been clarified, and no measures have been clarified to effectively prevent inward diffusion of oxygen atoms.

An object of the present invention is to provide a method of manufacturing a semiconductor device capable of effectively suppressing an oxide film effect in which oxygen atoms diffuse inward from an oxide film and reducing the oxygen concentration in a surface layer portion of a semiconductor substrate. Is to do.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor device having a heat treatment step of heat-treating a semiconductor substrate on which an oxide film is formed at a temperature of 1000 ° C. or more, and a temperature lowering step of lowering the temperature from the heat treatment step. In the manufacturing method, in the temperature decreasing step, the temperature is decreased at a first temperature decreasing rate in a range of about 1000 ° C. or more, and the temperature is decreased at a second temperature decreasing rate smaller than the first temperature decreasing rate in a range of about 1000 ° C. or less. The present invention is attained by a method of manufacturing a semiconductor device.

In the method of manufacturing a semiconductor device described above,
In the temperature lowering step, at a temperature of about 900 ° C. or less, the second
It is desirable to lower the temperature at a third temperature lowering rate that is higher than the temperature lowering rate. The object is a method of manufacturing a semiconductor device, comprising: a heat treatment step of heat-treating a semiconductor substrate on which an oxide film is formed at a temperature of about 1000 ° C. or more; and a temperature-falling step of decreasing the temperature from the temperature of the heat treatment step. , In a range of about 1000 ° C. or more, the temperature is lowered at a temperature lowering rate larger than the average
In a temperature range of not less than about 1000 ° C. and not more than about 1000 ° C., the temperature is lowered at a temperature lowering rate smaller than the average temperature lowering rate.

[0008] The above object is to provide a heat treatment step of heat-treating a semiconductor substrate having an oxide film formed thereon at a temperature of 1000 ° C or higher.
A method of manufacturing a semiconductor device having a temperature lowering step of lowering the temperature from the temperature of the heat treatment step.
In the range of 000 ° C. or more, the temperature is lowered at a rate of about 4 ° C./min or more, and in the range of about 900 ° C. or more and about 1000 ° C. or less, the temperature is lowered at a rate of about 2 ° C./min or less.
The following range is achieved by a method for manufacturing a semiconductor device, characterized in that the temperature is lowered at a rate of about 4 ° C./min or more.

In the above-described method of manufacturing a semiconductor device,
The temperature lowering step is performed at a temperature of about 1100 ° C. or more for about 10 ° C.
It is desirable to lower the temperature at a rate of not less than ° C./min. In the above-described method for manufacturing a semiconductor device, it is preferable that in the temperature lowering step, the temperature is lowered at a rate of about 5 ° C./min or more in a range from about 1050 ° C. to about 1100 ° C.

In the method of manufacturing a semiconductor device described above,
The temperature lowering step is performed at a temperature of about 5 ° C. /
It is desirable to lower the temperature at a rate of at least one minute.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a semiconductor device according to one embodiment of the present invention will be described with reference to the drawings. The present inventor has proposed a CZ (Czochralsk) having an oxide film formed thereon.
i) To investigate the mechanism of oxygen outward diffusion in the crystal,
FZ (Floating) with almost zero oxygen concentration
A sample in which an oxide film was formed on a Zone) crystal and a sample of a CZ crystal in which an oxide film was not formed were prepared. These samples were heat-treated in an inert gas. In addition, in order to preserve the state at the heat treatment temperature, a sample that was subjected to rapid cooling without performing a normal (comparative) temperature lowering treatment was also prepared. Then, the amount of oxygen inside the sample is measured by a low-temperature infrared absorption method (Low-temper).
attuned absorption
method, and the oxygen concentration distribution was measured using a secondary ion mass spectrometer (SIMS: Secondary Ion M).
was measured using an associometer.

FIG. 1 shows the measurement results of the oxygen content in the sample by the low-temperature infrared absorption method. From this measurement result, in the sample in which the oxide film was formed on the FZ crystal, the intrusion of oxygen into the crystal was not observed at around 1000 ° C., but as the heat treatment temperature was raised further, the amount of oxygen that entered the crystal as the heat treatment temperature increased It became clear that there would be more. FIG. 2 shows a measurement result of the oxygen concentration distribution inside the sample by SIMS. From this measurement result, it was found that in the sample in which the oxide film was formed on the FZ crystal, the higher the heat treatment temperature, the higher the oxygen concentration in the crystal surface layer. Furthermore, a large difference was observed in the oxygen concentration profile of the surface layer between the sample cooled in the sequence of the comparative example and the sample cooled rapidly. In the case of a CZ crystal having no oxide film formed thereon, it was found that the higher the heat treatment temperature, the lower the oxygen concentration in the crystal surface layer.

When the FZ crystal on which the oxide film is formed is heat-treated, oxygen atoms are diffused inward from the oxide film into the FZ crystal at the beginning of the heat treatment (flux fi), as shown in FIG.
On the other hand, it is considered that a phenomenon in which oxygen atoms diffused inward into the FZ crystal diffuse outward again (flux fo) occurs at the same time. When a CZ crystal on which an oxide film is not formed is heat-treated, oxygen atoms do not diffuse inward from the oxide film as shown in FIG. It is thought that only the phenomenon occurs.

Therefore, in the case of a CZ crystal on which an oxide film is formed, as shown in FIG. 3C, the phenomenon of FIG. 3A and the phenomenon of FIG. Thought,
It is considered that the inward diffusion of the flux fi and the outward diffusion of the flux fo + F occur simultaneously. 3A and 3B, the absolute values of the flux fo and the flux F are different depending on the internal oxygen concentration, but the same temperature is used. It is considered characteristic.

On the premise of the mechanism shown in FIG. 3, the above experimental results show that (1) in a temperature range of about 1050 ° C. or higher, the amount of oxygen penetrating into the crystal increases as the heat treatment temperature increases, and (2) 1000 ° C. This indicates that oxygen hardly penetrates into the crystal in the vicinity, and the following conclusions 1 to 3 were obtained from these experimental results. (Conclusion 1) In a temperature range of about 1050 ° C. or more, the flux fi is larger than the flux fo, and the tendency becomes more remarkable as the temperature increases.

(Conclusion 2) The temperature T at which the flux fi and the flux fo become equal between about 1000 ° C. and 1050 ° C.
There is one. In addition, about 800 ° C. to 850
The diffusion coefficient of oxygen at 100 ° C. is about 1/100 of that at 1000 ° C. (Conclusion 3) There is a temperature T2 where the diffusion of oxygen can be ignored between about 800 ° C and 850 ° C.

Further, at the temperature T1 or lower, the flux fo
Is larger than the flux fi, that is, the inversion of the flux occurs from the SIMS results in FIG. The oxygen concentration profile is clearly different between a sample that has been quenched after heat-treating the FZ crystal and a sample that has not been quenched and has been cooled down in sequence r of the comparative example. The oxygen concentration in the quenched sample monotonically increases toward the oxide film / silicon interface, whereas the non-quenched sample has a polar region around 7 μm in the surface layer and then decreases toward the interface. . This means that oxygen is emitted from the FZ crystal by outward diffusion during the temperature decrease.

The problem is at which temperature the phenomenon occurs during the cooling, which can be between temperature T1 and temperature T2. If the flux fi is higher than the flux fo even between the temperature T1 and the temperature T2, the temperature of the oxide film is constantly reduced from the oxide film to the temperature T2.
As oxygen continues to diffuse outwards into the Z crystal, the penetration of oxygen into the FZ crystal should continue to increase. Further, the temperature T2
Since oxygen hardly diffuses below, oxygen does not diffuse outward from the FZ crystal, and the oxygen concentration in the surface layer cannot be reduced. That is, unless it is considered that oxygen is diffused outward between the temperature T1 and the temperature T2, a contradiction occurs with the experimental result. From such considerations, the following conclusion 4
Reached.

(Conclusion 4) When the temperature is lower than T1, the flux f
o becomes larger than the flux fi. From this,
As shown in FIG. 4, the temperature T1 at which the inward diffusion flux fi and the outward diffusion flux fo are inverted is approximately 1
The temperature T2 between 000 ° C. and 1050 ° C. and at which the diffusion of oxygen atoms can be ignored is approximately 800 ° C. to 850 ° C.
I knew it was between.

Therefore, in the temperature decreasing step of this embodiment,
For example, as shown in FIG. 5, in the range of 1000 ° C. or higher, the temperature lowering rate is set higher than the conventional one (for example, about 4 ° C./min or more), and in the range of 900 ° C. or higher and 1000 ° C. or lower, the temperature lowering rate is lower than the conventional one. In the range of 900 ° C. or less, the temperature lowering rate is set higher than in the past (for example, about 4 ° C./min or more) in order to shorten the total cooling time.

Further, even in the range of 1000 ° C. or more,
It is desirable to increase the cooling rate as the temperature increases. For example, as shown in FIG. 5, the temperature lowering rate is further increased in the range of 1050 ° C. or more (for example, about 5 ° C./min or more), and the temperature decreasing rate is further increased in the range of 1100 ° C. or more (for example, about 10 ° C.). / Min).

Further, even in the range of 900 ° C. or less, it is desirable to increase the temperature decreasing rate as the temperature decreases. For example, as shown in FIG. 5, it is desirable to further increase the temperature lowering rate (for example, about 5 ° C./min or more) in the range of 850 ° C. or less. As described above, according to the present embodiment, in the range of about 1000 ° C. or higher, the temperature lowering rate is set higher than usual, and the temperature lowering time in which inward diffusion is large is shortened.
In the range of 00 ° C. or lower, the temperature lowering rate is set lower than usual to increase the temperature lowering time during which outward diffusion increases, so that the oxide film effect of oxygen atoms diffusing inward from the oxide film is effectively suppressed. In addition, the oxygen concentration in the surface portion of the semiconductor substrate can be reduced.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above-described embodiment, the temperature decreasing process of the outward diffusion heat treatment in an argon atmosphere has been described, but the temperature decreasing process of another heat treatment may be used. Further, in the above embodiment, the outward diffusion heat treatment of the silicon substrate has been described, but the heat treatment of another semiconductor substrate may be performed.

[0024]

EXAMPLE An FZ crystal silicon substrate on which an oxide film having a thickness of about 300 nm was formed was heated at 1150.degree.
Heat treatment was performed for a time, and then the temperature was lowered according to the temperature lowering sequence of the embodiment of FIG. That is, 1150 ° C or less 1
In the range of 100 ° C or higher, the temperature is reduced at a rate of 10 ° C / min.
In the range of 100 ° C or lower and 1050 ° C or higher, the cooling rate is 5 ° C / min.
In the range of 1000 ° C. or less and 900 ° C. or more, at a rate of 2 ° C./min and 900 ° C. or less, 850 ° C./min.
1 ° C. or more at a rate of 4 ° C./min, 850 ° C. or less and 750 ° C. or more at a rate of 5 ° C./min.
The temperature was lowered from 150 ° C. to 750 ° C. over 110 minutes.

The FZ whose temperature has been decreased by such a temperature decreasing sequence
The oxygen concentration of the crystal silicon substrate surface layer was measured by SIMS. FIG. 6 shows the measurement results. The oxygen concentration at the surface of the silicon substrate, that is, about 7 μm from the interface between the oxide film and the silicon substrate is 1.4 × 10 ¹⁷ [atoms / c].
m ³ ]. As a comparative example, an FZ crystal silicon substrate on which an oxide film having a thickness of about 300 nm was formed was heat-treated at 1150 ° C. for 18 hours in an argon atmosphere, and then cooled according to a temperature decreasing sequence of the comparative example of FIG. That is, the same 110 minutes are applied from 1150 ° C to 750 ° C,
The temperature was lowered at the average rate. The cooling rate is about 3.7
° C / min.

The FZ whose temperature has been decreased by such a temperature decreasing sequence
The oxygen concentration of the crystal silicon substrate surface layer was measured by SIMS. FIG. 6 shows the measurement results. The oxygen concentration at the surface of the silicon substrate, that is, about 7 μm from the interface between the oxide film and the silicon substrate is 1.7 × 10 ¹⁷ [atoms / c].
m ³ ]. As is clear from FIG. 6, the oxygen concentration was reduced by 20% or more in the example in comparison with the comparative example.

[0027]

As described above, according to the present invention, about 100
In the range of 0 ° C. or more, the temperature is decreased at the first temperature decreasing rate,
In the range below 000 ° C., the temperature was lowered at the second temperature lowering rate smaller than the first temperature lowering rate. The oxide film effect of inward diffusion of oxygen atoms from the film can be effectively suppressed, and the oxygen concentration in the surface portion of the semiconductor substrate can be reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing the amount of oxygen diffused into an FZ crystal by a low-temperature infrared absorption method.

FIG. 2 is a graph showing oxygen in-diffusion profiles in FZ crystal at the time of rapid cooling and the temperature drop of a comparative example.

FIG. 3 is an explanatory diagram of a mechanism of oxygen outward diffusion in a CZ crystal on which an oxide film is formed.

FIG. 4 is a graph showing a hypothesis of a relationship between an inward diffusion flux fi and an outward diffusion flux fo in an FZ crystal on which an oxide film is formed.

FIG. 5 is a graph showing a temperature drop sequence of an example and a comparative example.

FIG. 6 is a graph showing the oxygen concentration in the surface layer of the silicon substrate of the example and the comparative example.

Claims (7)

[Claims] 1. A semiconductor substrate on which an oxide film is formed is 100
A method of manufacturing a semiconductor device, comprising: a heat treatment step of performing a heat treatment at a temperature of 0 ° C. or higher; and a temperature lowering step of lowering the temperature from the temperature of the heat treatment step. Wherein the temperature is lowered at a second temperature lowering rate smaller than the first temperature lowering rate in a range of about 1000 ° C. or less. 2. The method of manufacturing a semiconductor device according to claim 1, wherein in the temperature lowering step, the temperature is lowered at a third temperature lowering rate higher than the second temperature lowering rate in a range of about 900 ° C. or less. Manufacturing method of a semiconductor device. 3. A semiconductor substrate on which an oxide film has been formed is approximately 10
In a method for manufacturing a semiconductor device, comprising: a heat treatment step of performing a heat treatment at a temperature of 00 ° C. or higher; and a temperature lowering step of lowering the temperature from the temperature of the heat treatment step; A method for manufacturing a semiconductor device, wherein the temperature is lowered at a temperature lowering rate higher than a temperature lowering rate, and the temperature is lowered at a temperature lowering rate smaller than the average temperature lowering rate in a range of about 900 ° C. or more and about 1000 ° C. or less. 4. The method according to claim 1, wherein the semiconductor substrate on which the oxide film is formed is 100
In a method for manufacturing a semiconductor device, comprising: a heat treatment step of performing a heat treatment at a temperature of 0 ° C. or higher; and a temperature lowering step of lowering the temperature from the temperature of the heat treatment step, wherein the temperature lowering step is performed at about 4 ° C./min. The temperature is lowered at the above rate, and in the range of about 900 ° C or more and about 1000 ° C or less, about 2 ° C /
A method for manufacturing a semiconductor device, comprising: lowering a temperature at a rate of not more than about 900 ° C .; 5. The method of manufacturing a semiconductor device according to claim 4, wherein in the temperature decreasing step, the temperature is decreased at a rate of about 10 ° C./min or more in a range of about 1100 ° C. or more. Production method. 6. The method for manufacturing a semiconductor device according to claim 4, wherein the temperature lowering step is performed at about 5 ° C. in a range of about 1050 ° C. or more and about 1100 ° C. or less.
A method of manufacturing a semiconductor device, wherein the temperature is decreased at a rate of at least / min. 7. The method for manufacturing a semiconductor device according to claim 4, wherein in the temperature decreasing step, the temperature is decreased at a rate of about 5 ° C./min or more in a range of about 850 ° C. or less. A method for manufacturing a semiconductor device, comprising: