JPH1070165A - Measuring method of semiconductor lifetime - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avert the effect on the surface recoupling velocity of the photo- excited minor carriers, by a method wherein the second conductivity type second semiconductor region internally extending from the surface of the first semiconductor region having a pair of main surfaces to be the first conductivity type substrate is formed by diffusion. SOLUTION: A measuring system for measuring the lifetime is composed of laser beams in wavelength of about 906nm and probing μ wave 22. As for the measuring substrate of the lifetime, a specimen wherein a p type semiconductor region 12 as for the second conductivity type is formed in thickness t2 of about 100μm on an n type Si substrate 11 as for the first conductivity type in thickness t1 of about 1000μm by diffusion is used. Through these procedures, precise lifetime can be measured since the n type Si substrate 11 using the specimen formed of the p type semiconductor region 12 is not affected by the surface recoupling rate of photo-excited minor carriers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring the lifetime of a semiconductor device.

[0002]

2. Description of the Related Art In most cases, the electrical characteristics of a semiconductor wafer are obtained by contact measurement which requires electrode attachment. In this case, destruction of a crystal is inevitable.
Naturally, there is a high demand for non-contact measurement for the purpose of improving the production yield and the like. The current lifetime measurement method is
ac-PV (photovoltage) method, MOS Ct method, J
There are methods such as the IS method. These measurement methods have excellent characteristics in resolution, measurement accuracy, and the like, but most of the measurement methods require electrode attachment, and thus may introduce new defects into the wafer. In order to prevent the introduction of such new defects, a technique disclosed in Japanese Patent Publication No. Sho 52-36817 is known. According to this conventional technique, it is said that the attenuation of the resistivity reduced by the minority carriers excited by light irradiation is detected by a μ wave, and the lifetime can be measured in a non-contact manner from an attenuation curve of a reflected μ wave.

Further, in order to accurately measure the effective lifetime, B. in Electrochem. Soc., 709 (1958)
The literature of uck, TM, Mckim, FS shows a method of forming an oxide film on the surface of a semiconductor wafer for measurement in order to reduce the surface recombination speed.

[0004]

However, in the former prior art, the effective lifetime τ _eff is determined by both the surface recombination of the excited carriers and the bulk recombination at a deeper part in the wafer. . Therefore, when the thickness of the substrate is 2 to 3 times or less the diffusion length of the minority carrier, the influence of surface recombination is strong, and it has been difficult to accurately measure the lifetime due to recombination in bulk. Also, in the latter conventional technique, when the thickness of the substrate is small, the effective lifetime depends on the thickness of the substrate, so that it has been difficult to accurately measure the lifetime.

An object of the present invention is to provide a method for accurately measuring the lifetime, which solves the problems of the conventional method for measuring the lifetime of a minority carrier.

More specifically, an object of the present invention is to provide a method for measuring a lifetime in which the influence of surface recombination of minority carriers excited by light is prevented.

[0007]

In order to achieve the above-mentioned object, the present invention relates to a method for measuring the attenuation of carriers excited by light using a μ-wave as a probe and a lifetime measuring device for determining a lifetime. A second semiconductor region of a second conductivity type extending from the surface of the first semiconductor region serving as a semiconductor substrate of the first conductivity type having a surface is formed by diffusion to eliminate the influence of the surface recombination speed, and the first semiconductor is removed. Measured the lifetime of an area.

Furthermore, the impurity concentration of the second semiconductor region is
The lifetime of the semiconductor was measured so as to be 1 × 10 ¹⁷ or less per 1 m ³ .

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a method for measuring a lifetime according to the present invention. In the figure, a measurement system for measuring a lifetime is composed of a laser beam 21 having a wavelength of 906 nm and a probe μ-wave 22. 11 is a cross-sectional structure of a measurement substrate which is a feature of the present invention.
An n-type semiconductor region having 0 Ω · cm and a thickness t1 of 200 to 2000 μm, 12 has a surface impurity concentration of 1 × 10 ¹⁷ per m ³
This is a p-type semiconductor region having the following depth t2 of 5 to 150 μm. The operation for accurately determining the bulk lifetime by using such a semiconductor wafer will be described with reference to the following drawings. FIG. 2 shows the temporal change in resistivity after the light pulse is turned off. In FIG. 2, n having a thickness of 1000 μm
The p-type semiconductor region 12 according to the present invention is
A sample formed with a thickness of 00 μm and a sample not formed with the p-type semiconductor region 12 are shown. p-type semiconductor region 12
In the case of an n-type Si substrate in which is not formed, most of the minority carriers excited by light recombine at the surface as the substrate thickness becomes thinner, so that the time required to recover the resistivity at the time of thermal equilibrium is short, and the effective Typical lifetime also shows a short value. On the other hand, the n-type S of the sample in which the p-type semiconductor region 12 according to the present invention is formed.
Since the i-substrate is not affected by surface recombination, an accurate lifetime can be measured.

FIG. 3 shows a temporal change of the concentration distribution of holes, which are minority carriers in the semiconductor, in order to explain the operation of the present invention in detail. FIG. 3A shows a temporal change of the minority carrier concentration after the light pulse is turned off in the case of the n-type Si substrate in which the p-type semiconductor region 12 is not formed. After the light pulse is turned off, the excited carriers diffuse into the substrate, but are affected by surface recombination. In particular, the carrier concentration on the semiconductor surface (at a position of 0 μm) and the back surface of the semiconductor (at a position of 1000 μm) is lower than that of the bulk. Significantly, the net excited carrier concentration disappears due to this surface recombination, thus accelerating the reduction in bulk. Therefore,
The effective lifetime is observed shorter than the true value. On the other hand, as shown in FIG.
In the case of an n-type Si substrate on which the type semiconductor region 12 is formed,
After the light pulse is turned off, the excited carriers diffuse into the substrate. However, since the n-type Si substrate 11 has a structure sandwiched by the p-type semiconductor regions 12, the semiconductor surface (position is 0 μm)
m) and the back surface of the semiconductor (at a position of 1000 μm) are not affected by surface recombination, and the ideal carrier concentration attenuation is shown. In other words, after the light pulse is turned off, the carriers diffuse into the substrate, but the carriers diffused into the n-type substrate are trapped by the potential difference corresponding to the built-in potential generated at the pn junction, so that the minority carriers are confined. The recombination component is reduced, and the effective lifetime can be accurately determined.

As described above, according to the present invention, the minority carrier concentration after the light pulse is turned off can prevent the influence of the surface recombination, and it can be understood that accurate measurement of the lifetime is possible.

FIG. 4 shows the dependency of the effective lifetime on the substrate thickness for explaining the effect of the present invention. Curve (a)
Indicates that the p-type semiconductor region 12 is not formed
In the case of the type Si substrate, when the substrate thickness exceeds 3000 μm, the effective lifetime does not depend on the substrate thickness, but when the substrate thickness is 3000 μm or less, the effective lifetime becomes thinner. It is declining. Lifetime of carrier independent of substrate thickness is about 100
Assuming that this value is a true lifetime value, the diffusion length of the carrier is about 500 μm. However, when the thickness of the substrate is several times less than this diffusion length, the rate of surface recombination is large. This is because the effective lifetime depends on the substrate thickness. Therefore, the substrate thickness 30
If the thickness is less than 00 μm, the effective lifetime depends on the thickness of the substrate.

In the present invention, as shown by the curve (b), p
In the n-type substrate on which the type semiconductor region 12 is formed, the substrate thickness 4
With a thickness of 00 μm or more, the effective lifetime was not affected by surface recombination and became independent of the thickness of the substrate, so that an accurate lifetime could be measured.

This effect was confirmed by making the p-type diffusion layer thicker than 5 μm. Note that the impurity concentration of the p-type diffusion layer limits the depth at which the microwave can enter the substrate.
Therefore, in order to measure a substrate having a thickness of about 1000 μm, the impurity concentration of the diffusion layer is desirably 1 × 10 ¹⁷ or less per 1 m ³ .

As described above, according to the present invention, the first
Although the conductivity type is described as n-type and the second conductivity type as p-type, the effect of the present invention is not limited to this, and the first conductivity type is p-type.
The second conductivity type may be an n-type.

[0017]

According to the present invention, the substrate of the first conductivity type includes:
By forming the second conductivity type diffusion layer and eliminating the surface recombination speed, the lifetime of the first conductivity type layer can be accurately measured.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a measuring system for measuring a lifetime according to the present invention and a sectional shape of a measuring element.

FIG. 2 is a characteristic diagram showing a temporal change in resistivity after an optical pulse is turned off according to the present invention.

FIG. 3 is a characteristic diagram showing a temporal change of a minority carrier concentration after an optical pulse is turned off according to the present invention.

FIG. 4 is a characteristic diagram showing the substrate thickness dependence of the effective lifetime τ _eff according to the present invention.

[Explanation of symbols]

11 n-type substrate, 12 p-type diffusion layer, 21 laser light,
22: Probe microwave.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masanori Takada 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Yutaka Sato 7-2, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 In the Power & Electric Equipment Development Division, Hitachi, Ltd.

Claims (2)

[Claims] 1. A first semiconductor, which is a first conductivity type semiconductor substrate having a pair of main surfaces, using a lifetime measuring device for determining a lifetime using a microwave as a probe for attenuation of carriers excited by light. Forming a second semiconductor region of a second conductivity type extending from the surface of the region to the inside by diffusion to eliminate the influence of the surface recombination speed and measuring the lifetime of the first semiconductor region; Lifetime measurement method. 2. The method according to claim 1, wherein the impurity concentration of the second semiconductor region is 1 × 10 ¹⁷ per m ³ or less.