JPS5835932A - Gettering of impurities - Google Patents

Abstract

PURPOSE:To make defects to be generated in the whole region of the pattern adhering part, and to control quantitatively distribution inside of the surface of the defects having ability to absorb impurities by a method wherein a thin film having the edges is provided on the back of a semiconductor substrate, and the heat treatment is performed at the prescribed temperature. CONSTITUTION:An Si3N4 film or a polycrystalline Si thin film, etc., having internal stress is adhered on the back of the semiconductor substrate 2 of Si, GaAs, InSb, etc., according to the means of evaporation, etc. Then the film is made to be survived locally according to the photo etching method to form the thin film 1 having the edges. At this constitution, stress to be applied to the substrate 2 is decided as follows. Namely, when the substrate is the Si substrate, because yield stress to be generated when the heat treatment at 1,000 deg.C is performed to the substrate thereof is 7X10<5> dyne/cm<2>, the value obtained by dividing the product of internal stress of the thin film and thickness of the film by pattern breadth is specified to 2.8X10<5> dyne/cm<2> or more. Accordingly distribution inside of the surface of the defects to act as to absorb impurities is controlled quantitatively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gettering method for collecting harmful impurities such as heavy metal particles from a semiconductor substrate in a semiconductor device manufacturing process.

It is generally known that when heavy metal particles (eg, Fe, Or, etc.) are contained in a semiconductor substrate, which is a material for a semiconductor device, the electrical characteristics of a semiconductor element formed in the substrate are deteriorated. Conventionally, methods have been proposed in which such harmful impurities are mechanically strained on the back surface of the RIUENO by means such as gettering, and methods are applied such as applying a thin film with film stress to the entire surface (for example, , see Japanese Patent Application Laid-Open No. 55-17073). However, these methods have problems such as poor reproducibility because it is difficult to control the degree of distortion on the back surface, and warping may occur due to the addition of distortion.

The present invention is characterized in that it includes a step of forming a thin film having a roughness and a hardness on the back surface of a semiconductor substrate, and a step of subsequently heat-treating the substrate.The purpose of the present invention is to quantitatively control the distortion of the substrate. Another object of the present invention is to provide an impurity gettering method that causes less warping of the substrate.

First, the principle of the gettering method according to the present invention will be explained using the drawings.

FIG. 1 is a perspective view showing a cross section of a thin film having a wide strip pattern formed on the back surface of a semiconductor substrate. In the figure, 1 represents a thin film and 2 represents a semiconductor substrate. The edges of the wide thin film 1 correspond to X=O and x=L. in this case,
The substrate 2 receives forces from two edges of the thin film 1, X20 and x=L. Each component of stress within the substrate is expressed as follows using elastic body theory. Here, σ8. σ represents the normal stress in the X direction and the normal stress in the X direction, respectively, and τ8. represents shear stress. The first and second items on the right side are stress components due to the edges of each X ``'' 0 + x =L. The constant F is the product of the internal stress of the thin film 1 and the film thickness. From equations (1) to (3), near the back surface of the substrate (y20) where the absolute value of stress is large, σ8 is several orders of magnitude larger than other components, indicating that the distortion of the substrate is mainly controlled by repulsion. be guided.

FIG. 2 is a diagram showing the distribution of stress within the substrate generated by a thin film with a band-like pattern, and is the distribution of σ near the back surface of the substrate.

The figure shows a film stress of 3.5 x 109dyn/7 and a film thickness of 3.
000^, and the pattern width is 100 μm.

σ8 takes the minimum value at the center of the pattern. In general, if the stress value exceeds the material's yield stress, defects (crystal defects such as dislocations) will occur.
occurs. Therefore, under conditions where the stress value at the center of the batten is greater than the yield stress, defects can occur throughout the pattern adhered area.

Under these conditions, it is possible to increase the amount of defects that function as impurity absorption, which is the object of the present invention, and it is easy to quantitatively control the amount of defects.

In general, the yield stress of a material decreases when held at high temperatures, so heat treatment (e.g., 75
By raising the temperature once to 0 to 1300° C. and then lowering it, defects can be generated with less stress than when no stress treatment is performed.

The conditions for this are It makes me laugh.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 3 is a cross-sectional perspective view of a semiconductor substrate showing an embodiment of the present invention. The gettering method of the present invention is as follows.

It is based on the above principle, and by using a plurality of thin films 1 having a band-like pattern, it is possible to form defects that function as impurity absorption over the entire back surface of the substrate 2, and also to quantitatively control the in-plane distribution. With this method, the area of the thin film deposited part can be made smaller compared to the substrate area (defects are more likely to occur at the edges), so the warpage of the substrate is better than with the conventional gettering method, which deposits the thin film uniformly. It also has the advantage of being able to reduce

This will be explained in detail below.

Semiconductor substrate 2 (Si substrate in this example, but G
A thin film such as a silicon nitride film or polysilicon having internal stress is formed on the back surface of a substrate (which may be an aAs substrate, an InSb substrate, etc.) by OVD, vapor deposition, sputtering, or the like. Next, by leaving this thin film locally by ordinary photolithography, the thin film 1 having edges can be easily formed on the back surface of the semiconductor substrate 2. The stress applied to the substrate 2 is determined as follows. 100 for 8i board
When heat treatment is performed at 0°C, the yield stress at that temperature is 7 x 105 dyn/(J, so the formula (5
), the product F of the internal stress of the thin film and the film thickness divided by the batten width must be 2.8 x 105 dyn/(7 or more. For example, if the internal stress is 3.5 x 10'
dyn/c4.

If the batten width is 3.2 mm, the thickness of the thin film should be 1000 A or more.

Although the case of a thin film with a band-shaped pattern having edges has been described above, similar effects can be expected in the case of other shapes such as a lattice-like or circular pattern.

FIG. 4 is a perspective view showing a cross section of another embodiment of the present invention, in which a thin film with a circular pattern is formed on the back surface of a semiconductor substrate.

By making the diameter of the circular pattern sufficiently small, defects can be generated in the area where the pattern is adhered, so that the in-plane distribution of defects that act as impurity absorption can be quantitatively controlled.

As explained above, the method for forming distortion on the back side of a substrate for genotattering according to the present invention involves controlling the film stress, film thickness, batten size (sparseness/denseness of the batten), and heat treatment temperature of the thin film deposited on the backside. This method has the advantage of being able to quantitatively control the in-plane distribution of defects that function to absorb harmful impurities within the substrate. Additionally, since the area of the thin film deposited part can be made smaller compared to the substrate area, it has the advantage of reducing warpage compared to the conventional gettering method, which uniformly deposits a thin film that causes distortion on the back surface. .

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a cross section of a semiconductor substrate for explaining the present invention in detail, FIG. 2 is a diagram showing the distribution of stress within the substrate caused by the thin film of the band-shaped baton, and FIGS. 3 and 4 are Both are perspective views showing a cross section of a semiconductor substrate in an embodiment of the present invention. 1...Thin film 2...Semiconductor substrate patent applicant
Nippon Telegraph and Telephone Public Corporation Patent Attorney Junnosuke Nakamura 2013 Wa11 Figure 2/Gutanki e, 4.4

Claims (1)

[Claims] An impurity gettering method for a semiconductor substrate, comprising the steps of forming a thin film having an edge on the back surface of the semiconductor substrate, and then heat-treating the substrate.