JPS62115346A - Method and instrument for measuring impurity concentration in semiconductor crystal - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] By effectively utilizing the advantages of two measurement methods: light absorption and photoluminescence (hereinafter abbreviated as PL), impurity 'Th concentration distribution in semiconductor crystals can be measured non-destructively. The method and apparatus are presented.

[Industrial application field]

The present invention relates to a method for evaluating semiconductor crystals, particularly III.
- A method and apparatus for non-destructively measuring impurity concentration distribution in a group V compound semiconductor.

One method for evaluating semiconductor crystals is to measure impurity concentration distribution, but a non-destructive measurement method with excellent quantitative properties and high detection sensitivity is desired.

[Conventional technology]

Conventional methods for non-destructively measuring impurity concentration distribution in semiconductor crystals include optical absorption and PL.

■ Light absorption method In this method, when the absorption wavelength of an impurity is known, the semiconductor crystal to be measured is irradiated with light of that wavelength and the absorption is observed.The stronger the light absorption, the higher the impurity concentration. Therefore, it has excellent concentration quantitative properties.

However, since the semiconductor crystal to be measured is a thin wafer with a thickness of 500 μm or less, it cannot absorb much light, and therefore the detection sensitivity is low.

■ PL method In this method, the semiconductor crystal to be measured is irradiated with monochromatic light with a wavelength of 0.488 μm emitted from, for example, an argon (^r) laser and the PL emission with a wavelength corresponding to the impurity level is observed. is high, but the emission intensity does not necessarily correspond to the impurity concentration.

The reason for this is that the strength depends not only on the impurity concentration but also on various crystal imperfections such as dislocations, and therefore this method cannot be used for quantitative analysis.

Therefore, in this case, even if an attempt is made to measure the impurity distribution in the wafer, in most cases only information mixed with dislocation density, unexplained defect density, etc. will be obtained.

[Problem that the invention seeks to solve]

Conventional nondestructive methods for measuring impurity concentrations in semiconductor crystals have not been able to simultaneously improve quantitative performance and detection sensitivity.

[Means for solving problems]

To solve the above problem, the semiconductor crystal to be measured is irradiated with light having a wavelength corresponding to the energy difference between the acceptor level to be measured and the conduction band edge as excitation light, and the wavelength region to be detected is
111 A method for measuring impurity impurity level in which the emission intensity is measured by setting it in an intermediate band between a constant acceptor level and the conduction band edge, and a method for measuring the impurity level, and light having a wavelength corresponding to the energy difference between the acceptor level to be measured and the conduction band edge. An excitation light irradiation means for irradiating a semiconductor crystal to be measured with excitation light, and a detection means for measuring emission intensity by setting the detection wavelength range to an intermediate band between the acceptor level to be measured and the conduction band edge. Achieved by measuring equipment.

The in-plane distribution of seismic intensity of impurities can be determined by making the semiconductor crystal to be measured movable.

[Effect]

In the present invention, when a semiconductor crystal to be measured is irradiated with monochromatic light of a wavelength that causes light absorption by specific impurities (7 receptors to be measured) contained therein, I)L with a longer wavelength than this light is emitted. In addition, the wavelength band to be detected is set to the intermediate band between the acceptor level to be measured and the edge of the conduction band, which is deeper than the acceptor level to be measured (in the center of the forbidden band width) caused by crystal defects, for example. When the wavelength band corresponding to the defect level (approached) is set, the detected Pl and light remain unchanged in the plane regardless of the defect density, and excitation (knocks electrons from the measured 7 receptor level to the conduction band) Only +1!7 reports of light absorption (which sometimes occurs) are obtained, and the intensity of the Pl light corresponds to the acceptor concentration to be measured.

As described above, it is necessary to select the wavelength of 1) to be observed that corresponds to a transition that is less affected by defects such as dislocation, that is, a wavelength that corresponds to a deep defect level.

〔Example〕

FIG. 1 is a block diagram schematically showing an apparatus used for measuring impurity concentration in a semiconductor crystal according to the present invention.

In the figure, the light emitted from light a1 of a halogen lamp, etc.
It passes through a spectrometer 2 to produce quasi-chromatic light 3.

This monochromatic light 3 is focused by a lens 4 onto a semiconductor crystal (sample) to be measured 5! Shoot jq.

The sample 5 is held in a cooling tank 6 with an optical window.

l'L7 emitted from the sample 5 is beamed by a lens 8, subjected to spectrum analysis by a spectrometer, and then converted into an electrical signal by a detector 1o.

After the electrical signal is amplified by the amplifier 11, it is sent to the computer 1.
Sent to 2.

The cooling tank 6 is fixed to a moving stage 13 and moves parallel to the spectrometer 9. The operation of the moving stage 13 is controlled by a computer 12.

Next, a measurement example will be explained.

A description will be given by taking as an example a semi-insulating gallium arsenide (Sr-GaAS) substrate grown by the liquid capsule Czochralski method as a sample to be measured, and carbon (C) as an impurity (acceptor) to be measured. The sample is kept at a concentration of 4.2.

In this case, the wavelength of the monochromatic light 3, which is the excitation light, is selected to be 0.830 μm, which is the energy difference between the acceptor level of C and the edge of the transmission band.

PL appears as a wide spectrum involving deep quasi over a wavelength range of 1.5 to 2.2 μm, but here, we will take the approximate center of this wavelength range and -1.9 μm.
Set to .

In measurements using the normal PL method, as mentioned above, the excitation wavelength is larger than the forbidden band width, that is, 0.8 l.
Light with a wavelength shorter than zm is used. 1.9 in such a case
The PL intensity in μm hardly changes within the wafer plane.

However, as in the present invention, the excitation wavelength is 0.830 μm.
If , the l)L intensity of 1.9 μm changes depending on the position within the wafer plane as shown in FIG.

FIG. 2 is a diagram showing the distribution of the intensity of a circle of 1.9 μm within the wafer surface.

The change in PL intensity is the result of information on absorption intensity by C acceptors appearing as PL intensity, and corresponds to non-uniformity of C concentration.

In the embodiment, the spectrometers 2 and 9 are used as the measuring device, but if the sample to be measured or the impurity to be measured is constant, an interference filter may be used instead.

Furthermore, by using a stage that can move the sample not only horizontally but also vertically, a two-dimensional distribution can be measured.

Furthermore, by changing the wavelength of the excitation light, the non-uniformity of different types of acceptor concentrations can be measured.

〔Effect of the invention〕

As explained in detail above, according to the present invention, i+! similar to that obtained by optical absorption measurement! 7 reports with high sensitivity P
Since it can be obtained by L measurement, the impurity Y seismic intensity distribution within the surface of the wafer to be measured can be measured with high sensitivity and non-destructively.

[Brief explanation of drawings]

Is the first part an impurity in the hemihemiform crystal according to the present invention? A block diagram showing the outline of the device used for H degree measurement, Figure 2 is 1.9
FIG. 3 is a diagram showing the distribution of il+ and intensity in μm within the wafer surface. In the figure, ■ is a light source such as a halogen lamp, 2.9 is a spectrometer, 3 is excitation light (bright color light), 4.8 is a lens, 5 is a semiconductor crystal to be measured (sample), 6 is a cooling tank, and 7 is an IIL. . 10 is a detector, 11 is an amplifier, 12 is a computer ＼ 13 is a moving stage. Incident, 1985 Patent Application No. 255409 2, title of invention: Weidian method and apparatus for determining impurity concentration in semiconductor crystal 3;
Relationship with the case of a person who performs extraction '1Ii-,i乍1gun1tomoAddress 1015 Kamiodanaka, Nakahara-ku, Yozaki City, Kanagawa Prefecture? ! i' ground (522
) Name Fujitsu Co., Ltd. 4.
Agent address: 1015 Kamiodanaka, Nakahara-ku, Yozaki City, Kanagawa Prefecture Tomi
Shitsu Co., Ltd. January 28, 1985 (Shipping date) 6.

Claims (3)

[Claims] (1) Light with a wavelength corresponding to the energy difference between the acceptor level to be measured and the conduction band edge is irradiated onto the semiconductor crystal to be measured as excitation light, and the wavelength range to be detected is set between the acceptor level to be measured and the conduction band edge. 1. A method for measuring impurity concentration in a semiconductor crystal, the method comprising measuring the emission intensity in an intermediate band between the two. (2) excitation light irradiation means for irradiating the semiconductor crystal to be measured with light of a wavelength corresponding to the energy difference between the acceptor level to be measured and the conduction band edge; 1. An apparatus for measuring impurity concentration in a semiconductor crystal, comprising: a detection means for measuring emission intensity by being set in an intermediate band between the edges. (3) The device for measuring impurity concentration in a semiconductor crystal according to claim 2, wherein the semiconductor crystal to be measured is movable.