JPH0555233A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To decrease crystal defects in the surface of an Si semiconductor substrate and sections in the vicinity of the surface by lowering the oxygen concentration of a section near the surface of the Si semiconductor substrate. CONSTITUTION:One main surface 2 changed into a mirror surface of an Si semiconductor substrate 1 is heated by a lamp by using a light source having a wavelength of 1-0.3mum under a vacuum, of 10<-6> Torr or less, and heated at 400-800 deg.C. Consequently, oxygen in the Si semiconductor substrate 1 is diffused outward at a low temperature because one main surface 2 is heated under the high vacuum. Since one main surface 2 is heated by the lamp within a range of the wavelength of 1-0.3mum, only a section near the surface can be heated, and a low oxygen-concentration region region 3 can be formed on the surface of the Si semiconductor substrate as shown in (b).

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, and more particularly to reducing the oxygen concentration near the surface of the semiconductor substrate for the purpose of reducing crystal defects caused by oxygen precipitation on the surface of the semiconductor substrate and in the vicinity thereof. The present invention relates to a method for manufacturing a semiconductor substrate.

[0002]

2. Description of the Related Art An Si single crystal which is usually pulled by the Czochralski method (CZ method) contains sufficient oxygen to form an oxygen precipitate when subjected to an appropriate heat treatment. When a semiconductor circuit element is formed on a Si semiconductor substrate manufactured from CZ-Si single crystal, oxygen precipitation occurs inside the semiconductor substrate due to heat treatment in manufacturing the circuit element.
This oxygen precipitate has a gettering effect of capturing contaminant impurities such as heavy metals that deteriorate the characteristics of semiconductor circuit elements. Therefore, it is preferable that a large number of oxygen precipitates exist inside the Si semiconductor substrate, which is a region where no semiconductor element is formed. On the other hand, oxygen precipitation on the surface of the Si semiconductor substrate and immediately below it, that is, on the semiconductor circuit element active region, induces dislocations, stacking faults, etc., and these defects, or oxygen precipitation itself, increase leakage current, decrease memory retention time, etc. This causes deterioration of semiconductor circuit element characteristics.

Therefore, as shown in FIG. 5A, in the conventional Si semiconductor substrate 31, the Si semiconductor substrate 31 having one principal surface finished as a mirror surface 32 is heated at a high temperature of 1100 ° C. or higher for several hours in a non-oxidizing atmosphere. Heat treatment is performed to reduce oxygen on the surface of the Si semiconductor substrate 31 by outward diffusion. As shown in FIG. 5B, the Si semiconductor substrate 31 has a low oxygen concentration region 33 in which the oxygen concentration decreases near the surface as it approaches the surface.
However, a high oxygen concentration region 34 having a uniform oxygen concentration and higher than the low oxygen concentration region is formed. When the oxygen concentration near the surface of the Si semiconductor substrate is reduced, oxygen precipitates on the surface of the Si semiconductor substrate and near the surface are also reduced. For example, as shown in FIG. 5C, heat treatment is performed in nitrogen at 700 ° C. for 16 hours, and then 10 times.
Even after the nitrogen heat treatment at 00 ° C. is performed for 8 hours, oxygen precipitates are not formed on the surface or the vicinity of the surface, that is, the semiconductor circuit element formation region. On the other hand, oxygen precipitates 35 are formed inside the Si semiconductor substrate.

By thus reducing the oxygen concentration near the surface of the Si semiconductor substrate, even if many oxygen precipitates 35 effective for gettering are generated inside the Si semiconductor substrate, the surface of the Si semiconductor substrate and the semiconductor circuit are The element active region can be kept defect-free or unhindered.

[0005]

In the conventional Si semiconductor substrate, a high temperature heat treatment of 1100 ° C. or higher is added for a number of times in order to obtain a low oxygen concentration region near the surface of the Si semiconductor substrate. This high-temperature heat treatment has a drawback that slippage (slip) due to thermal stress occurs, and the Si semiconductor substrate surface easily reacts with the atmospheric gas to cause crystal defects. In addition, high-temperature heat treatment is generally performed in an electric furnace, but in order to reduce thermal stress, the furnace entrance and exit must be performed at a low speed, and the total time spent for high-temperature heat treatment is extremely long and The sex is bad. Further, there are problems that heavy metals are contaminated from the electric heating furnace and that they are diffused throughout the Si semiconductor substrate during the heat treatment.

In addition, oxygen near the surface is diffused outward by the high temperature heat treatment, but at the same time, oxygen precipitation nuclei (generally called fine clusters of oxygen and carbon) inside the Si semiconductor substrate are decomposed. There is also a problem that the formation of oxygen precipitates in the subsequent process is reduced. Also, smaller oxygen precipitates are less likely to cause secondary defects and are desirable for preventing plastic deformation of the Si semiconductor substrate. However, when the number of oxygen precipitates decreases as in the above case, the size of each oxygen precipitate is reduced. Is large, secondary defects are generated, and plastic deformation of the Si semiconductor substrate is likely to occur.

[0007]

According to the method of manufacturing a semiconductor substrate of the present invention, at least one surface obtained by cutting out from a Si single crystal ingot pulled up by the CZ method, polishing, and etching, and finishing at least one surface is a mirror surface. A wavelength of 1 on a mirror surface of a Si semiconductor substrate in a high vacuum of 10 ^-6 Torr or less.
The lamp has a step of heating with a light source of ˜0.2 μm. At this time, the surface of the Si semiconductor substrate is 400 ° C to 800 ° C.
Heat to.

[0008]

By heating under high vacuum, oxygen in the Si semiconductor substrate diffuses outward even at a relatively low temperature. Further, when the lamp heating is performed in the wavelength range of 1 to 0.3 μm, only the surface vicinity of the Si semiconductor substrate is heated and oxygen can be diffused outward. As described above, by applying the semiconductor substrate manufacturing method of the present invention, the low oxygen concentration region can be formed near the surface of the Si semiconductor substrate by the low temperature heat treatment.

[0009]

The present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view in order of manufacturing steps of an embodiment of a method for manufacturing a semiconductor substrate of the present invention.

First, the specific resistance 10 raised by the CZ method
~ 20 Ω · cm, oxygen concentration 1.6 × 10 ¹⁸ pieces / cm
^From a P-type Si single crystal ingot of ³ (OLD ASTM method), a single-sided mirror-like Si semiconductor substrate 1 as shown in FIG. 1A is cut, etched, and polished. A wavelength of 0.46 μm is applied to the mirror surface 2 of the Si semiconductor substrate 1.
Lamp light with a mirror surface temperature of 600 ° C
It was applied under a vacuum of × 10 ^-9 Torr for 10 minutes to outwardly diffuse oxygen on both front and back surfaces of the Si semiconductor substrate. The mirror surface temperature was measured with an infrared thermometer. After this 1 × 10 ^-9 To
The Si semiconductor substrate is cooled for 30 minutes under the pressure of rr, and the low oxygen concentration region 3 where the oxygen concentration near the surface decreases as it approaches the surface as shown in FIG. A Si semiconductor substrate 1 having an oxygen concentration region 4 was obtained.
This completes the semiconductor substrate of one embodiment.

Next, the distribution of oxygen precipitates when this substrate is heated will be described with reference to FIG. This Si semiconductor substrate 1 is heat-treated in nitrogen gas at 700 ° C. for 16 hours, and then the next heat treatment is performed in nitrogen gas at 1,000 ° C. for 8 hours. Crystal defects composed of oxygen precipitates do not occur in the oxygenated region, and the amount of oxygen precipitates increases from this region toward the high oxygen concentration region 4. Approximately 5 × per square centimeter in the high oxygen concentration region 4.
10 ⁵ oxygen precipitates 5 were formed. In the example of the mirror surface 2, the depth of the low oxygen concentration region 3 where the concentration of oxygen precipitates changes was about 50 μm from the surface. The average diameter of the oxygen precipitates 5 was 50 nm.

In the conventional manufacturing method, the surface low oxygen concentration region 33 of the mirror surface 32 was formed by the method described with reference to FIG. Figure 5
In order to obtain the low oxygen concentration region 33 of 50 μm as shown in FIG.
It was necessary to perform a heat treatment in nitrogen gas at 0 ° C. for 2 hours to perform outward diffusion of oxygen. Next, 700 ℃ 16 hours, 1
After the suffocation heat treatment at 000 ° C. for 8 hours, about 1 × 10 ⁵ / cm ² of oxygen precipitates 35 were generated in the high oxygen concentration region 34 as shown in FIG. 5C. The average diameter of the oxygen precipitates 35 is 70
nm.

In one embodiment of the present invention, the time required to obtain a low oxygen concentration region having a depth of about 50 μm from the mirror surface 2 is
The total heating time and cooling time was 40 minutes. In the conventional example, in order to suppress the plastic deformation due to thermal stress, it took one hour to enter or leave the electric heating furnace, so the total time is four hours. By applying the present invention, the time required for outward diffusion of oxygen can be shortened to 1/6 of that of the conventional method. Also,
In the example of the present invention, when the heat treatment of the subsequent step was applied, about 5 times as many oxygen precipitates as in the conventional example could be obtained inside the Si semiconductor substrate. In that case, the size of oxygen precipitates was smaller in the example of the present invention than in the conventional example, and when the warpage of the Si semiconductor substrate was measured, the average of 15 μm in the example of the present invention and the average of 20 μm in the conventional example. By applying it, the warpage of the Si semiconductor substrate could be suppressed.

The Si semiconductor substrate shown in FIG. 1 (b) of the embodiment of the present invention and the Si semiconductor substrate shown in FIG. 5 (b) of the conventional example are subjected to X-ray tomography (X-ray-tomography).
When observed with XRT), 1 out of 20 in the conventional example
Although one or two slips were observed on the sheet,
In one embodiment of the present invention, no slip occurred. Further, each of the Si semiconductor substrates was subjected to hydrogen combustion oxidation at 1.100 ° C. for 2 hours, then selectively etched, and the mirror surface was observed with an optical microscope. In the conventional example, one to three stacking faults were found on the surface of the Si semiconductor substrate, but in one example of the present invention, the surface was defect-free. As described above, by applying the present invention, it is possible to reduce crystal defects generated due to damage during outward diffusion of oxygen.

Further, each S of the embodiment of the present invention and the conventional example
When the semiconductor substrate was etched with a mixed acid of hydrofluoric acid and nitric acid and the minority carrier lifetime was measured, it was 100 to 120 μsec in the example of the present invention and 80 to 90 μsec in the conventional example. In the example of the present invention, since no gas system is used, the heavy metal contamination is less than that of the electric heating furnace, and the heavy metal contamination during outward diffusion of oxygen remains on the surface and can be removed by etching. It is considered that in the conventional example, the extension has been diffused into the inside of the Si semiconductor substrate, so that it cannot be completely removed and the lifetime is deteriorated.

With respect to the examples of the present invention, the effect of the present invention was confirmed by changing the conditions of vacuum degree, heat treatment temperature, and light source wavelength. To heat only near the surface of the Si semiconductor substrate,
Considering absorption into the semiconductor substrate, a wavelength of 1 to 0.3 μm is considered appropriate. Further, in order to stably obtain good semiconductor circuit element characteristics, it is necessary to form a low oxygen concentration region having a depth of 30 μm or more. Vacuum degree is 10 ^-6 to 10 ^-3 Tor
For r, long-term heat treatment at 800 ° C. for 1 hour or more was required to obtain a low oxygen concentration region of 30 μm. In order to shorten the time, heat treatment at a temperature higher than 800 ° C must be performed. However, the surface temperature of the Si semiconductor substrate is 800 ° C.
When the height was higher, the Si semiconductor substrate was plastically deformed by thermal stress and slippage occurred. Also, the cooling time becomes longer. On the other hand, at a temperature lower than 400 ° C., the outward diffusion rate of oxygen was small and a low oxygen concentration region of 30 μm could not be obtained. Therefore, in the practice of the present invention, 10 ^-6 Tor
The surface temperature of the Si semiconductor substrate is 400 ° C under a vacuum of r or less.
It is appropriate to perform lamp heating such that the temperature reaches 800 ° C.

FIG. 3 shows a sectional view of another embodiment of the present invention.

On the mirror surface 22 of the n-type Si semiconductor substrate 21 having a specific resistance of 1 × 10 ⁻³ Ω · cm, which was obtained by cutting out from the CZ—Si single crystal ingot shown in FIG. Lamp heating at 800 ° C. under a pressure of 1 × 10 ⁻⁶ Torr is performed for 15 minutes with an infrared lamp having a wavelength of 1 μm.
During heating, the surface of the substrate 21 opposite to the mirror surface 22 is brought into contact with the surface of the substrate holding jig or the like to reduce the temperature rise and oxygen diffusion into the vacuum. As a result of this, FIG.
As in (b), the substrate has a slightly low-concentration region on its back surface, but its existence can be ignored. (Even in the above-described embodiment, the low-concentration region becomes shallower where the holding jig comes into contact with the substrate). The lamp heating temperature of 800 ° C. is a value measured on the mirror surface of the substrate with an infrared thermometer. Mirror surface 22 of substrate 21
A low oxygen concentration region 23 in which the oxygen concentration decreases as it approaches the mirror surface is formed on the side of, and the oxygen concentration is substantially uniform under the low oxygen concentration region 23. A high oxygen concentration region 24 having a higher oxygen concentration is formed. This completes another embodiment of the present invention.

Next, an example of use and effect of the substrate 21 will be described with reference to FIG. The substrate 21 of FIG.
As shown in (a), heat treatment was performed in nitrogen gas at 650 ° C. for 10 hours to form oxygen precipitation nuclei 25 inside the high oxygen concentration region 24. As shown in FIG. 4B, when an n ⁻ epitaxial layer 26 was grown on the Si semiconductor substrate 21 at 1050 ° C. for 50 μm, oxygen precipitates 27 were formed in the high oxygen concentration region 24.
There has occurred. After selective etching, it was observed with an optical microscope, but no crystal defect was observed on the n ⁻ epitaxial layer 26. About 3 × 10 ⁵ pieces /
cm ² of oxygen precipitate was generated.

When the nitrogen heat treatment is applied to the Si semiconductor substrate at 650 ° C. for 10 hours without forming the low oxygen concentration region, n ⁻
After growth of the epitaxial layer 26, about 3 × 10 ⁵ pieces / cm ²
Although oxygen precipitates 27 were generated, 10 to 15 stacking faults were generated on the n ⁻ epitaxial layer. It is considered that crystal defects on the surface of the Si semiconductor substrate affected the epitaxial growth. When epitaxial growth is performed on the Si semiconductor substrate without any treatment, 1 to 4 surface stacking faults occur,
The oxygen precipitation inside the substrate was about 2 × 10 ⁴ .

In order to obtain an epitaxial substrate having a good surface condition while increasing oxygen precipitates in the Si semiconductor substrate, it is necessary to form a low oxygen concentration region near the surface of the Si semiconductor substrate to reduce crystal defects on the surface. There is. Meanwhile, FIG.
When a low oxygen concentration region is formed by a conventional method as shown in Fig. 3, when epitaxial growth is performed by adding nitrogen treatment at 650 ° C for 10 hours, 1 to 3 stacking faults on the surface are oxygen precipitates in the substrate. Was about 9 × 10 ⁴ pieces / cm ² .
In the embodiment of the present invention, it is possible to obtain an epitaxial substrate in which a larger number of oxygen precipitates are formed inside the Si semiconductor substrate and the number of surface defects is smaller than in the conventional method.

[0023]

As described above, according to the present invention, the lamp is heated on the surface of the Si semiconductor substrate on which the semiconductor circuit elements are formed by using a light source having a wavelength of 1 μm to 0.2 μ under a high vacuum of 10 ⁻⁶ Torr or less. It is possible to cause outward diffusion of oxygen at a low temperature of 400 ° C. to 800 ° C. and reduce the oxygen concentration near the surface including the semiconductor circuit element active region.

By lowering the temperature of the outward diffusion process of oxygen, there is an effect that slippage (slip) due to thermal stress can be suppressed and the time required for entering and exiting the furnace can be shortened. Since heating is performed in a vacuum, the surface of the Si semiconductor substrate does not react with the atmospheric gas to cause crystal defects. Since the heavy metal contamination during the heat treatment does not diffuse inside the Si semiconductor substrate due to the low temperature heat treatment and remains on the surface, it can be removed in a subsequent step such as cleaning. Furthermore, since only the vicinity of the surface of the Si semiconductor substrate is heated to a high temperature, oxygen precipitation nuclei inside the Si semiconductor substrate do not decompose and disappear during the heat treatment. Therefore, a large amount of oxygen precipitates are formed inside the Si semiconductor substrate in the subsequent step, and at the same time, the growth of individual oxygen precipitates is suppressed and the plastic deformation of the Si semiconductor substrate due to the generation of secondary defects can be avoided.

[Brief description of drawings]

FIG. 1 is a sectional view in order of manufacturing steps, showing an embodiment of the present invention.

FIG. 2 is a sectional view showing a usage example of an embodiment of the present invention.

FIG. 3 is a cross-sectional view for each manufacturing process showing another embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a usage example of another embodiment of the present invention.

FIG. 5 is a cross-sectional view of manufacturing steps showing a conventional manufacturing method.

[Explanation of symbols]

 1,21,31 Si semiconductor substrate 2,22,32 Mirror surface 3,23,33 Low oxygen concentration region 4,24,34 High oxygen concentration region 5,27,35 Oxygen precipitate 25 Oxygen precipitation nucleus 26 Epitaxial layer

Claims (3)

[Claims] 1. A method of manufacturing a semiconductor substrate, comprising the step of heating the semiconductor substrate in a vacuum to form a low oxygen concentration region on the surface of the semiconductor substrate. 2. The manufacturing method according to claim 1, wherein the vacuum is 10 ⁻⁶ Torr or less. 3. The heating temperature is 400 ° C. or higher and 800 ° C.
The method of manufacturing a semiconductor substrate according to claim 1, wherein: