JPS6312376B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and particularly to a gettering method.

According to the manufacturing method of the present invention, it is possible to suppress leakage current of a semiconductor element particularly requiring an N-type silicon substrate to an extremely low level, prevent deterioration of semiconductor element characteristics, and obtain a high-yield, high-quality semiconductor device. .

In conventional methods, oxygen inherent in the silicon substrate precipitates due to the thermal history of the device process and appears as internal defects and surface defects. Although internal defects are effective due to gettering effects, surface defects cause a decrease in the characteristics and yield of semiconductor devices.

In order to remove surface defects, there is a so-called intrinsic gettering (IG) technique, which is a method in which heat treatment is performed to form a surface defect-free layer and to form internal defects during or before device processing. but,
IG processing has various restrictions. Examples include optimizing the oxygen concentration in a silicon substrate, and optimizing heat treatment and device processes for forming defect-free layers and internal defects.

If the selection of oxygen concentration or heat treatment is even slightly incorrect, internal defects may reach the surface or may not be formed, resulting in deterioration of the characteristics of the semiconductor device and lowering manufacturing yield and quality. There was a problem with the decline.

There is also a method of using epitaxial wafers to remove surface defects, but since known epitaxial growth is generally performed at high temperatures of 1000°C or higher, oxygen precipitated nuclei (internal defect nuclei) in the silicon substrate are dissolved. Therefore, there was a limit to increasing the internal defect density.

FIG. 1 is a cross-sectional view of a silicon wafer using a conventional manufacturing method. First, an N-type substrate 1 in which the oxygen concentration in the silicon crystal is 18×10 ¹⁷ cm ^-3 and the antimony concentration is 1×10 ¹⁵ cm ^-3 is prepared (first
Diagram a). Thereafter, internal defects 2 and surface defects 3 caused by oxygen are formed in the silicon substrate 1 through various heat treatments for forming a semiconductor element (FIG. 1b).

FIG. 2 is a cross-sectional view of a silicon wafer subjected to IG treatment to remove surface defects. For example, the concentration of oxygen in a silicon crystal is 19× ¹⁰ cm
^-3 , and an N-type substrate 4 having an antimony concentration of 1×10 ¹⁵ cm ^-3 is prepared (FIG. 2a). First, heat treatment is performed at a temperature of 1200°C for 3 hours to diffuse oxygen on the surface of the silicon substrate 4 outward, lowering the concentration of oxygen near the surface.Furthermore, heat treatment is performed at a temperature of 750°C for 10 hours to grow internal defect nuclei 5. (Figure 2b). Thereafter, internal defects 6 are formed in the silicon substrate 4 by various heat treatments for forming a semiconductor element (FIG. 2c). In this example, the defects 7 reach the surface of the silicon substrate 4 because the oxygen concentration in the silicon crystal is high.

Generally, as the heat treatment for forming semiconductor elements becomes high temperature and long, or when the concentration of oxygen in the silicon substrate is extremely high, internal defects may extend to the surface. Also,
If the oxygen concentration is too low, internal defects may not form. In any case, appropriate oxygen concentration
You need to select IG processing, and if you choose incorrectly,
This causes product leakage current.

FIG. 3 is a cross-sectional view of a silicon substrate and an epitaxial layer when an epitaxial wafer is used, which is a technique for removing surface defects similar to the IG technique.

First, for example, an N-type silicon substrate 8 having an oxygen concentration of 16×10 ¹⁷ cm ^-3 and an antimony concentration of 1×10 ¹⁵ cm ^-3 is prepared (FIG. 3a). Next, an N-type silicon crystal 9 having a thickness of 10 .mu.m and a resistivity of 5 .OMEGA.cm is epitaxially grown at 1170.degree. C. using a known method, for example, using silicon tetrachloride (FIG. 3b). At that time, the oxygen precipitated nuclei (internal defect nuclei) in the silicon substrate dissolve and their density becomes extremely low. Next, by performing a heat treatment for forming a semiconductor element, the epitaxial layer 9 becomes a defect-free layer since it does not contain oxygen, and no internal defects are formed in the silicon substrate 8 (FIG. 3c). Alternatively, it is only formed in a very small amount, has no gettering effect, is susceptible to contamination, and causes product leakage current.

As described above, in the conventional method, it was necessary to select the oxygen concentration and the heat treatment for forming internal defects according to the thermal history for forming the semiconductor element. If even a slight deviation from the optimum value occurs, defects may occur even on the surface of the silicon substrate, or the gettering effect may be lost, leading to deterioration of the semiconductor element, leading to a decrease in yield and quality.

The present invention eliminates the above-mentioned drawbacks, and in particular, when the concentration of oxygen contained in the silicon crystal is [Oi], the concentration of boron is [B], and the concentration of N-type impurity is [D], [D]>[B]≧ [Oi]≧14×10 ¹⁷ cm ^-3 Silicon epitaxial crystal is grown on an N-type substrate, and by simply going through the device process, an extremely high density of internal defects is formed on the substrate, and the epitaxial layer and the surface of the epitaxial layer are The leakage current of the semiconductor element can be suppressed to an extremely low level without the formation of defects, and deterioration of the semiconductor element can be prevented and a high-yield, high-quality semiconductor device can be obtained.

In the present invention, when the concentration of oxygen in the silicon crystal is [Oi] and the concentration of boron is [B], [B]≧
It has been found that when [Oi]≧14×10 ^17, extremely high density internal defects are likely to be formed in the silicon crystal. However, it cannot be applied as is to semiconductor devices that require N-type silicon crystal, but if the concentration of N-type impurity is [D], [D]>[B]≧[Oi]≧14×
It becomes applicable by setting 10 to ¹⁷ .

In the manufacturing method of the present invention, the concentration of oxygen contained in the silicon crystal is [Oi], the concentration of boron is [B],
When the concentration of N-type impurity is [D], [D]>
[B] ≧ [Oi] ≧ 14 × 10 ¹⁷ cm ^-3 Includes a step of growing a silicon epitaxial crystal on an N-type substrate, and a step of forming an element constituting a semiconductor device on the silicon epitaxial crystal. It is characterized by this.

The present invention will be described in detail below based on Examples.

FIG. 4 is a cross-sectional view of a silicon substrate and a silicon epitaxial layer when the method of the present invention is carried out. First, for example, the concentration of oxygen is 15 × ¹⁰ cm
^-3 , an N-type silicon substrate 10 having a boron concentration of 3×10 ¹⁸ cm ^-3 and an antimony concentration of 6×10 ¹⁸ cm ^-3 is prepared (FIG. 4a). Then, in a known manner, for example using silicon tetrachloride and at a temperature of 1170°C, the thickness is
N-type silicon crystal 11 with a resistivity of 10 μm and a resistivity of 5 Ω-cm
(Figure 4b). Next, a process for forming a semiconductor element is performed (FIG. 4c). At such times, various heat treatments are applied, so that internal defects 12 are formed in the N-type substrate 10. At this time [B]≧
[Oi]≧14×10 ¹⁷ cm ^-3 , so even though it is an epitaxial wafer, internal defects 1 are extremely dense.
2 is formed. Furthermore, since the epitaxial layer 11 does not contain oxygen, no internal defects occur and the semiconductor element forming region (epitaxial layer 11) can be a completely defect-free layer.

The above embodiment is explained based on the following conditions: oxygen concentration [Oi] in the silicon substrate = 15 x 10 ¹⁷ cm ^-3 , boron concentration [B] = 3 x 18 cm, and antimony concentration [D] = 6 x
10 ¹⁸ , but it is sufficient if [D]>[B]≧[Oi]≧14× ¹⁰¹⁷ . Further, the epitaxial growth method, the thickness and specific resistance of the grown layer are not limited.

As explained in detail above, according to the present invention, a surface defect-free layer can be reliably formed, internal defects can be formed at an extremely high density, the process tolerance is widened, and the leakage current of the formed semiconductor element can be extremely reduced. The cost can be kept low, and a high yield and high quality semiconductor device can be obtained.

[Brief explanation of the drawing]

Figure 1 a-b, Figure 2 a-c and Figure 3 a-c
4A to 4C are schematic cross-sectional views of main steps in a conventional manufacturing method, and FIGS. 4A to 4C are schematic cross-sectional views of main steps in a manufacturing method according to an embodiment of the present invention. 1, 4, 8, 10... silicon substrate, 2, 6,
12...Internal defect, 3,7...Surface defect, 5...
Internal defect nucleus, 9, 11...Epitaxial crystal.

Claims (1)

[Claims] 1. When the concentration of oxygen contained in a silicon crystal is expressed as [Oi], the concentration of boron as [B], and the concentration of N-type impurity as [D], [D]>[B] ≧〔Oi〕≧
A semiconductor device comprising the steps of growing a silicon epitaxial crystal on an N-type substrate of 14×10 ¹⁷ cm ^-3 and forming an element constituting the semiconductor device on the silicon epitaxial crystal. Production method.