JP2701809B2 - Silicon single crystal substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a silicon single crystal substrate used as a substrate of a semiconductor device.

[0002]

2. Description of the Related Art As a silicon single crystal substrate of a semiconductor device, a so-called CZ substrate formed by a pulling method is used except for a special purpose. Since a crucible made of quartz (SiO ₂ ) is usually used in the pulling method, CZ
The substrate contains about 10 ¹⁷ to 10 ¹⁸ / cm ^{3 of} oxygen. This oxygen initially exists between the lattices in a solid solution state, but is precipitated by heat treatment. For this oxygen precipitation, what serves as a precipitation nucleus is required.

In a silicon single crystal containing oxygen, 450 ° C.
Thermal donor due to moderate heat treatment
Occurs and the resistivity decreases. It is believed that the generation of this thermal donor is closely related to the precipitation of oxygen. Thus, silicon single crystals usually contain isotopes, and unless special processing such as enrichment is applied,
The isotope ratio remains the natural silicon isotope ratio.

[0004]

In the above-described conventional silicon single crystal, there is a phenomenon that heat treatment generates oxygen precipitates or thermal donors in the crystal. There is a problem that the characteristics of the semiconductor device cannot be controlled completely, and there is a problem that variations in the characteristics of the elements increase. Therefore, an object of the present invention is to provide a silicon single crystal substrate in which oxygen precipitation is suppressed.

[0005]

Means for Solving the Problems] silicon single crystal substrate according to the present invention for achieving the above object, isotope Si ²⁹ of Si ²⁸ in the area formed of at least the device, S
The composition ratio of i ³⁰ are offset from the composition ratio of the natural Si ± 10% or more, and characterized in that the Si ^28, Si ^29, any composition ratio of Si ³⁰ also below 99% is there.

[0006]

Next, embodiments of the present invention will be described with reference to the drawings. In the silicon single crystal substrate of the present invention, in at least the device formation region, the abundance ratio of the isotopes Si ²⁹ and Si ³⁰ in the crystal deviates from the natural abundance ratio by ± 10% or more. The natural silicon isotope abundance is: Si ²⁸ : Si ²⁹ : Si ³⁰ = 92.23: 4.67:
Since it is 3.10, the content ratio of Si ²⁹ is 4.20% or less, or 5.14% or more. The content ratio of Si ³⁰ is 2.79% or less or 3.41% or more. Another condition to be satisfied by the silicon single crystal substrate according to the present invention is Si ²⁸ , Si ²⁹ , Si ³⁰
Is 99% or less.

In the silicon single crystal substrate according to the present invention, as shown in FIG. 1A, the entire substrate is a Si substrate 1 whose component ratio is adjusted to the above isotope ratio, or FIG.
As shown in (b), the Si substrate 3 whose component ratio is not adjusted
On top, a crystal layer of the Si epitaxial layer 2 whose component ratio is adjusted to the above isotope ratio is provided. The substrate or crystal in which these component ratios have been adjusted is separated into each isotope using a well-known isotope separation technique, and then adjusted to a desired isotope ratio, or a specific isotope is obtained from natural silicon. It can be formed by drawing or by adding specific isotopes to natural silicon.

In a study on the oxygen precipitation process in a silicon single crystal, the present inventors have found that oxygen is easily precipitated in a silicon single crystal having a specific isotope ratio. Therefore, a silicon single crystal in which oxygen precipitation is suppressed can be obtained by avoiding silicon having an isotope ratio that easily precipitates oxygen.

A silicon single crystal is mainly produced by gradually cooling from a liquid phase to a solid phase. At that time, Si ²⁹ or Si ³⁰ having a slightly higher freezing point aggregates first to form fine aggregates in the crystal. create. This mass of slightly different elements can serve as nuclei for oxygen precipitation. As described above, the natural silicon isotope abundance ratio is as follows: Si ²⁸ : Si ²⁹ : Si ³⁰ = 92.23:
The ratio is 4.67: 3.10, but at such an abundance ratio, lumps are particularly likely to occur. However, for example, Si ²⁹ and S
Isotope abundance ratio: Si ²⁸ : i ³⁰ less than half of natural:
With silicon of Si ²⁹ : Si ³⁰ = 96.5: 2.0: 1.5, agglomeration hardly occurs, and Si ²⁹ and Si ³⁰ tend to be evenly dispersed in the Si ²⁸ crystal. Further, even if a lump is formed, its size and density can be kept low. When the size of the mass is small, the possibility of becoming a nucleus of oxygen precipitation is reduced. Conversely, in silicon in which the abundance ratio of Si ²⁹ and Si ³⁰ is increased, for example, Si ²⁸ : Si ²⁹ = 50: 50, isotopes are not mixed to form a cluster.

In the present invention, by changing the isotope ratio of silicon from the natural ratio in this way, the size and density of the isotope clusters that can serve as precipitation nuclei are controlled, whereby the oxygen precipitates and thermal donors are reduced. The occurrence is suppressed. Thus, in order to significantly increase the purity of a particular isotope,
The cost increases geometrically depending on the purity. However, according to the experiment of the present inventors, no special effect was obtained from the viewpoint of oxygen precipitates even when the purity was increased to a high purity. Therefore, in the present invention, the purity of each isotope is set to 99%.
% Or less. When a semiconductor device is manufactured using such a silicon single crystal substrate of the present invention, it is possible to suppress the occurrence of defects, to improve the manufacturing yield of semiconductor devices, and to obtain a device having extremely uniform characteristics. it can.

[0011]

Next, an embodiment of the present invention will be described. [First Example] The ratio of Si ²⁹ to Si ³⁰ to Si ²⁸ was increased to twice that of natural. That is, Si ²⁸ : Si ²⁹ :
A silicon substrate having an isotope ratio of Si ³⁰ = 84.46: 9.34: 6.20 was obtained, and this was heat-treated in an electric furnace at 1000 ° C. for 16 hours in a nitrogen atmosphere. FIG. 2 shows the Si after heat treatment.
FIG. 3 is a plan view showing a state of oxygen precipitation on a substrate 1. As shown in the figure, the amount of oxygen precipitate 4 is extremely small.

Comparative Example 1 For comparison, a silicon substrate having a natural isotope abundance ratio was subjected to the same heat treatment.
FIG. 3 shows a Si substrate 3 whose component ratio is not adjusted after heat treatment.
It is a top view which shows the oxygen precipitation situation of. As shown in the figure, many oxygen precipitates 4 were observed in the conventional Si substrate.

[0013] A Second Embodiment] The ratio of Si ²⁹ and Si ³⁰ against Si ²⁸ is reduced to one third of the natural. That is,
Si ²⁸ : Si ²⁹ : Si ³⁰ = 97.41: 1.56: 1.
A silicon substrate having an isotope ratio of 03 was obtained, and 450
Heat treatment was performed at 30 ° C. for 30 minutes in a nitrogen atmosphere. The density of generated thermal donors after the heat treatment was lower than the measurement sensitivity of the measuring device.

Comparative Example 2 For comparison, when a silicon substrate having a natural isotope abundance ratio was subjected to the same heat treatment, the generation density of thermal donors was 7 × 10 ¹⁵ cm ^-3 .

[0015]

As described above, the silicon single crystal substrate according to the present invention has an isotope ratio that makes it difficult for silicon isotopes to form a mass when the crystal is pulled up, or reduces the size and density of the mass. Therefore, oxygen precipitation and thermal donors generated by the heat treatment can be suppressed low. Therefore, according to the present invention, it is possible to improve the manufacturing yield and suppress the variation in the characteristics of the semiconductor device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a silicon single crystal substrate for describing an embodiment of the present invention.

FIG. 2 is a plan view showing the state of oxygen precipitation according to an example of the present invention.

FIG. 3 is a plan view showing a state of oxygen precipitation in a conventional example.

[Explanation of symbols]

 1 Si substrate with adjusted component ratio 2 Si epitaxial layer with adjusted component ratio 3 Si substrate without adjusted component ratio 4 Oxygen precipitate

Claims (2)

(57) [Claims] 1. The composition ratio of isotopes Si ²⁹ and Si ³⁰ of Si ²⁸ at least in a region where a device is formed is a natural Si.
± 10% or more from the composition ratio at
A silicon single crystal substrate, wherein the composition ratio of any of i ²⁸ , Si ²⁹ , and Si ³⁰ is 99% or less. 2. The silicon single crystal substrate according to claim 1, wherein the epitaxial layer made of the material having the limited composition ratio is formed on a single crystal silicon substrate whose composition ratio is not adjusted.