JPH01250738A - Measuring apparatus of crystallizability of semiconductor material - Google Patents

Abstract

PURPOSE:To effect the accurate quantitative measurement of the crystallizability of a semiconductor material, by a construction wherein the intensity of a scattered light generated by application of an infrared laser beam into the semiconductor material to be measured is measured and an information on the intensity is outputted accurately. CONSTITUTION:A chopper mirror 3 switches selectively the direction of advance of a laser beam 1R from an infrared laser oscillator 1 either to the inside or outside of a semiconductor material T to be measured. An infrared sensor 2 senses a scattered light generated from the advancing beam 1R or the laser beam led thereto. A corner mirror 9 and a chopper mirror 4 lead the beam 1R made to advance outside the material T by the mirror 3, to the sensor 2 as a reference light. By this constitution, the intensity of the beam 1R as the scattered light and the reference light is detected by the same sensor 2, and by calculating 25 the ratio or the difference between detected values of two lights, a measured value is obtained with a laser power, a drift of amplifier, etc. removed. Accordingly, qualitative evaluation of the quality of crystallizability of a compound semiconductor such as GaAs can be implemented accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an apparatus for quantitatively measuring the crystallinity of a semiconductor material.

<Prior art> -a. As a method for quantitatively evaluating the crystallinity of a semiconductor material, the number of etch pits generated by etching the sample surface is counted under a microscope field, and the sample is determined based on the etch pit density. There is a so-called etch focus method that evaluates the crystallinity of .

<Problems to be Solved by the Invention> By the way, according to the above-mentioned etch pit method, it is up to the observer to decide which image among the microscopic images is regarded as one etch pit, and the counting criterion is Due to the ambiguity, the obtained count values are not very accurate, and there is a risk that there will be large discrepancies in the count values depending on individual observers, especially when the number of etch focuses is extremely large. In order to solve this problem, a microscope image is taken with a camera or the like, the I-most image is binarized by image processing, and etch bits are automatically counted from the binary image.

Although a device has been developed that
It is extremely difficult to set the threshold value for binarizing a captured image to an appropriate value, and a technique for obtaining accurate etch bit counts has not yet been established.

From the above, it is difficult to say that the etch bit density obtained by the etch bit method is information that accurately represents the crystallinity of a semiconductor material.

An object of the present invention is to provide an apparatus that can accurately quantitatively measure the crystallinity of a semiconductor material.

<Means for Solving the Problems> A configuration for achieving the above object will be described with reference to FIG. 1 corresponding to an embodiment. A beam direction switching means (first chopper mirror) 3 that selectively switches the traveling direction of the beam rR to either inside or outside the semiconductor material T to be measured, and a laser beam IR that moves inside the semiconductor material T to be measured T. The infrared sensor 2 receives the scattered light generated by the traveling or the guided laser beam, and the infrared sensor 2 receives the laser beam IR traveling outside the semiconductor material to be measured T using the beam direction switching means 3.
a beam direction changing means (corner mirror 9, second chopper mirror 4) that guides the laser beam as a reference light to a beam direction, and a calculation means for calculating the ratio or difference between the detected value of the scattered light and the detected value of the laser beam IR as the reference light. (divider) 25.

It is generally known that when an infrared laser beam is irradiated into a semiconductor material, scattered light is generated due to defects, impurities, etc. interposed between the crystals of the material, and the intensity of the light is determined by the intensity of the laser beam within the material. Although it shows a value that correlates with the state of existence of defects, impurities, etc. in the progressing region, the intensity of the scattered light is very weak, and simply measuring the intensity cannot be used to measure the oscillation power of the laser oscillator, the drift of the amplifier in the light receiving system, etc. Due to this influence, it is not possible to obtain very accurate measurements.

Therefore, the laser beam IR as scattered light and reference light
By detecting the intensity of 2 with the same sensor 2 and calculating the ratio or difference between the two detected values, it is possible to obtain an accurate measurement value with laser power, amplifier drift, etc. removed.

<Example> Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line 1--2 of the mask 7.

The infrared laser oscillator 1 is, for example, Ga S + Cd
It is used to oscillate an infrared laser beam IR that passes through the crystal of the sample T made of a semiconductor material such as Te, and uses, for example, a HeNe laser, a YAG laser, a semiconductor laser, or the like.

A beam chopper 5 and a first chopper mirror 3 are arranged on the traveling optical path of the oscillated laser beam IR from the infrared laser oscillator 1.

The beam chopper 5 is rotationally driven based on the supplied drive signal, and can interrupt the progress of the laser beam IR at predetermined intervals.

The first chopper mirror 3 is configured to be rotationally driven based on a supplied drive signal and to either reflect the laser beam IR or open its traveling optical path. The laser beam IR reflected by the sample T enters the sample T from its end surface Ta.

An infrared objective lens 6 is disposed on the side of the surface Tb of the sample T so that its optical axis 6a is perpendicular to the center of movement of the laser beam IR within the sample T. Scattered light generated by irradiation with a laser beam IR can be focused.

A mask 7 is arranged along the image plane 6b of the objective lens 6. As shown in FIG. 2, this mask 7 has a slit-shaped through hole 7a in a portion corresponding to an area on the image plane 6b of the objective lens 6 corresponding to the area in which the laser beam IR travels in the sample T. The mask 7 blocks the progress of stray light such as light scattered at each end face of the sample T, other than scattered light from defects, impurities, etc. present in the sample T.

Two infrared cylindrical lenses 8a, 8b and an infrared sensor 2 are sequentially arranged on the optical axis 6a of the objective lens 6 at the rear stage of the mask 7, and the light passing through the through hole 7a of the mask 7 is transmitted to each cylindrical lens 8a. , 8b, the light is independently focused and incident on the infrared sensor 2 in a direction perpendicular to the plane of the paper and in a direction along the plane of the paper.

The infrared sensor 2 is capable of detecting light having a wavelength in the infrared region with sufficient sensitivity, and is made of, for example, Ge or Se.

A semiconductor sensor such as PbS or InAs is used.

On the other hand, the oscillation laser beam I from the infrared laser oscillator 1
On the traveling optical path of R, a corner mirror 9 is disposed downstream of the first chopper mirror 3.

The corner mirror 9 is made of the same type of crystal as the sample T, and the reflective surface 9a is coated with a metal film.

An attenuator 10 and an infrared focusing lens 1 are placed on the traveling optical path of the laser beam IR reflected by the corner mirror 9.
A first and a second chopper mirror 4 are arranged in sequence, and the laser beam IR that has passed through the focusing lens 11 is reflected by the second chopper mirror 4 and focused onto the light receiving surface of the infrared sensor 2 .

The attenuator 10 is for attenuating the amount of the laser beam IR reflected by the corner mirror 9 to an order close to the amount of scattered light from the sample T.

The second chopper mirror 4 is rotationally driven based on the supplied drive signal, and the laser beam IR that passes through the focusing lens 11 is
or two cylindrical lenses f3
It is configured to open the traveling optical path of the scattered light that has passed through a and f3b.

Now, the output signal of the infrared sensor 2 is amplified by the amplifier 21, and then the switches 22a, 22a, Z+
22b or 22b2 becomes "closed" according to the drive signal, so that the integrators 23a++23az and 23b.

Or lead to 23b2. Integrators 23a1 and 23
The output of a2 is supplied to a differential amplifier 24a, and the outputs of integrators 23b and 23b2 are supplied to a differential amplifier 24b, and each differential amplifier 24a, 24b calculates the difference between the two supplied integral values. .

Then, the ratio of the output value a of the differential amplifier 24a to the output value S of the differential amplifier 24b is calculated by the divider 25 at the next stage.

The above beam chopper 5, each chopper mirror 3°4, and each switch 22a+, 22ag, 22tz.

22b2 is supplied with a drive signal from the sequence controller 12, and each device is driven and controlled based on a time chart described later.

Note that it is desirable that the end surface Ta and the surface Tb of the sample T on the beam incidence side are sufficiently mirror-polished to prevent the incident laser beam IR and scattered light from defects etc. from scattering on each surface. It is desirable that the beam exit side end surface Td and back surface TC are also sufficiently polished in order to reduce stray light due to scattering on each surface. The end faces Tb and Td on the beam incidence side and the exit side may be hexagonal planes of the crystal.

Next, the operation will be explained with reference to a time chart shown in FIG. 3 and a diagram showing the output of the infrared sensor 2.

First, when the operation starts, the beam chopper 5 repeats opening and closing operations at predetermined intervals, and the first chopper mirror 3 synchronizes with the beam chopper 5 and moves to the "reflection position" or the "opening position" at each cycle. Similarly, the second chopper mirror 4 switches to the first chopper mirror 3.
Switch to the opposite position.

With the above operation, the output of the sensor 2 indicates the intensity of the scattered light and the laser beam IR when the beam chopper 5 is open t and t, and the output of the sensor 2 indicates the intensity of the scattered light and the laser beam IR when the beam chopper 5 is open t and t, respectively, and when the beam chopper 5 is closed t
2 and t4 indicate the intensity of background light.

Switch, 7-chi 22a1 and 22a2 are "ON" only for the time excluding the influence of the rise and fall of the output of sensor 2 while beam chopper 5 is in open position and closed position, respectively, and this operation The integral value of the intensity of the scattered light and the background light is obtained, and the difference between the two values is determined.

Similarly, the switches 22b and 22b2 are turned ON while the beam chopper 5 is open t and closed t4, respectively, and by this operation, the integrated value of the intensity of the laser beam IR and the background light is obtained. , the difference between the two values is found.

Then, the ratio of the difference in this integral value to the difference in the integral value found earlier, that is, the laser beam! The intensity ratio of scattered light to R is calculated.

The intensity ratio of the laser beam IR and the scattered light obtained as described above indicates a value of scattering power that correlates to the state of existence of defects, impurities, etc. in the traveling region of the laser beam IH in the sample T, Using this scattering power, that is, information quantitatively indicating the crystallinity of the sample T, the quality of the crystallinity of the sample T can be evaluated.

Here, by calculating the intensity ratio of the scattered light and the laser beam IR detected by the same light receiving system as the scattered light, attenuation of the laser oscillation power of the infrared laser oscillator 1,
More accurate information can be obtained by removing the influence of drift of the amplifier 21 that amplifies the output of the infrared sensor 2,
Moreover, since the corner mirror 9 that guides the laser beam IR to the infrared sensor 2 is made of the same type of crystal as the sample T,
The influence of reflection of the laser beam IR and scattered light on the beam incident end face Ta and surface Tb of the sample T can also be reduced.

In addition to the above configuration, a means is provided to translate the sample T in a predetermined step in a direction perpendicular to the plane of the paper, and the average value of the intensity ratio between the scattered light and the laser beam IR obtained at each step is calculated. This will allow you to obtain more accurate information.

In addition, in the above examples, scattered light and laser beam! Although the present invention is configured to calculate the intensity ratio between the scattered light and the laser beam IR, the present invention is not limited thereto. , whose attenuation rate changes based on the electrical signal, and set the output value of the intensity difference calculator to "zero".
The attenuator may be drive-controlled to achieve this, and an electrical signal required for the drive control may be detected.

In this case, the influence of non-linearity etc. of the infrared sensor 2 can be automatically removed, and more accurate information can be obtained than in the above embodiment.

<Effects of the Invention> As explained above, according to the present invention, the intensity of scattered light generated by irradiating an infrared laser beam into a semiconductor material to be measured is measured, and information regarding the intensity is accurately output. With this structure, it becomes possible to quantitatively evaluate the quality of crystallinity of compound semiconductors such as GaAs and CdTe more accurately than before, and it is possible to evaluate the quality of compound semiconductors produced by loft. This will greatly contribute to management and evaluation of device performance when devices are formed using compound semiconductor crystals.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a cross-sectional view of the mask 7 taken along the line ■-■, and FIG. 3 is a diagram together with a time chart and a diagram showing the output of the infrared sensor 2. . 1... Infrared laser oscillator 2... Infrared sensors 3 and 4... First and second chopper mirrors 9.
... Corner mirror 25 ... Divider TR ... Laser beam T ... Sample patent applicant Shimadzu Corporation Agent
Patent Attorney Nishi 1) Arata

Claims (1)

[Claims] A device that quantitatively measures the crystallinity of a semiconductor material to be measured from the intensity of scattered light generated by irradiating an infrared laser beam into the semiconductor material to be measured, and includes an infrared laser oscillator and a laser beam from the oscillator. beam direction switching means for selectively switching the traveling direction of the laser beam to either inside or outside the semiconductor material to be measured; and scattered light generated by the laser beam traveling within the semiconductor material to be measured, or a guided laser beam; an infrared sensor for receiving the beam, a beam direction changing means for guiding the laser beam traveling outside the semiconductor material to be measured to the infrared sensor as a reference light by the beam direction switching means, and a detected value of the scattered light and the reference light as the reference light. An apparatus for measuring crystallinity of a semiconductor material, characterized in that it comprises a calculation means for calculating a ratio or a difference between the detected value of a laser beam and the detected value of a laser beam.