JPH0116378B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for measuring crystal plane orientation using laser Raman spectroscopy.

Semiconductor bulk crystals such as gallium arsenide (GaAs) and gallium phosphide (GaP) are cut into wafer shapes and commercially available as substrates for various semiconductor devices. Currently, X-ray diffraction is mainly used to determine the plane orientation of these crystals;
Because it handles wires, the equipment becomes large-scale, including safety measures, and setting up the measurement system necessary to accurately measure surface orientation requires high precision, advanced technology, and time. There were major problems such as:

The present invention solves these problems caused by using X-ray diffraction by using laser Raman spectroscopy. Raman light is introduced into a spectrophotometer, and the ratio of the peak intensity of the Raman band corresponding to the TO phonon and the peak intensity of the Raman band corresponding to the LO phonon in the spectrum of the Raman light is determined. Rotate the crystal body by 180° in the plane where the laser beam is incident, perform the above (a), and calculate the ratio of the peak intensities, and calculate the value of the two ratios obtained in the above (a) and (b). It is characterized by finding the plane orientation of the crystal from.

Below, crystals with zinc blende structure (Zincblend type crystals)
The present invention will be explained in detail by taking this as an example. When a Zincblend crystal is measured using the backscattering method, due to the selection rule, the spectrum due to LO phonons from the (100) plane is
Spectra due to TO phonons appear from the (110) plane. And the plane orientation of the crystal surface is (100)
If it is out of plane, as shown in Figure 1, LO,
Both spectra due to TO phonones appear.

The surface orientation dependence of the LO and TO phonon intensities at this time can be calculated from the Raman tensor of first-order Raman scattering. Now, let us assume that the main axes of the crystal are X, Y, and Z, and that the actual crystal plane (X'-Y') is tilted by φ° from the (100) to (110) direction. When the laser beam is incident, there are three possible positional relationships between the main axes X, Y, and Z of the crystal and the direction Ki in which the laser beam travels within the crystal: a, b, and c shown in FIG. 2.
It is arranged so that it coincides with the Z′ axis in the direction in which the scattered light travels toward Ks in the figure. Further, q is the direction in which the phonon moves, and θ is the angle between Ki and the Z axis. In FIG. 2, a and b have the Y-axis and Y' axis coincident, and a and b have a relationship in which the crystal plane (X'-Y' plane) is rotated 180° about the Z' axis. In addition, the X axis and the X' axis of c coincide with each other, and φ is expressed as a rotational deviation on the Y-Z plane, as can be seen from FIG. 2d, which is a perspective view of c.

Here, if the arrangement in Figure 2 a is A ₊ and the arrangement in b is A _- , the LO and TO phonon intensities I ^LO and I ^TO are given by the following equations.

I ^LO _HV =A _H d _L ² cos ² (3θ/2±2φ) …(1) I ^TO _HV =A _H d _T ² sin ² (3θ/2±2φ) …(2) I ^LO _HH =0 … (3) I ^TO _HH = A _H d _T ² sin ² (θ±2φ) …(4) In the above equation, ± corresponds to A ₊ and A _- , and the subscript H indicates that the polarized light is parallel to the incident plane (P polarized light) , V indicate that the polarization is perpendicular to the plane of incidence (S polarization), respectively. HV indicates that the incident light is P-polarized light and the scattered light is S-polarized light, and HH indicates that both the incident light and the scattered light are P-polarized light. d _L and d _T are the scattering efficiency of LO and TO phonons,
A _H is a constant when P-polarized light is incident.

From the above equation, if the ratio of the LO phonon intensity and TO phonon intensity for A ₊ and A _- , respectively, is r ₊ and r _- , then
r ₊ and r _- are r±=I ^TO _HV /I ^LO _HV = (d _T /d _L ) ² tan ² (3θ/2±2φ)...(5). Next, finding the ratio of r ₊ and r _- , we get r _- /r ₊ = tan ² (3θ/2-2φ)/tan ² (3θ/2+2φ)...(6). In equation (6), θ is defined as sinθ=
(sinθi)/n, and therefore r ₊ and r _-
If is determined by measurement, φ can be determined from equation (6).

FIG. 3 shows an example of an apparatus for implementing the present invention based on the above-mentioned concept. In the figure, 1 is a semiconductor substrate serving as a sample, which is held on a rotatable holder 2, and a laser oscillator 3 is mounted on the surface of the substrate 1.
The laser beam 4 generated in is irradiated. Raman scattered light 5 generated during irradiation is introduced into a laser Raman spectrophotometer 7 via an analyzer 6 that selectively passes P-polarized light and S-polarized light.
8 is a switching mechanism for switching the analyzer 6; 9
1 is a drive mechanism such as a pulse motor for rotating the holder 2 about the shaft 10, and 11 is a drive power source for supplying current to the drive mechanism 9.
A central control device 12 performs arithmetic processing based on measurement data from the spectrophotometer 7, and sends control signals to the switching mechanism 8, drive power source 11, and spectrophotometer 7 according to measurement procedures.

Here, an example will be shown in which a semi-insulating GaAs substrate having a plane orientation tilted by φ° from the (100) to (110) direction was measured using the above-mentioned apparatus. X', Y', and Z' axes are set for the substrate 1 held on the holder 2, as shown in FIGS. 3 and 4. The substrate surface to be measured lies within the X'-Y' plane, and is set so that the cut section of the substrate and the Y' axis have an inclination of 45 degrees, as shown in FIG. Laser light 4 is P-polarized light,
The Raman light is incident along the X'-Z' plane at an angle inclined by θi° from the direction perpendicular to the substrate surface, and among the Raman light generated thereby, that in the Z'-axis direction is introduced into the spectrophotometer 7.

First, the control device 12 sets the switching mechanism 8 to extract the P-polarized Raman scattered light from the analyzer 6, and also sets the spectrophotometer to detect the peak of the spectrum shown in FIG. 1 by the LO phonon. Set 7. At this time, the spectral intensity obtained from the spectrophotometer 7 is I ^LO _HH ,
It can be seen from the above equation (3) that I ^LO _HH is 0. And from this, the angle between the cleavage plane and the Y′ axis is
It can be confirmed that the angle is 45°.

After confirmation, the control device 12 switches the analyzer 6 so that the S-polarized light among the Raman scattered light reaches the spectrophotometer. In this state, the control device 12
commands the spectrophotometer 7 to measure the peak intensity I ^LO _HV due to the LO phonon and the peak intensity I ^TO _HV due to the TO phonon. If the state at this time is A ₊ in Figure 2, then by finding the ratio of the two peak intensities measured here, r ₊ in equation (5) is calculated.
can be obtained.

Next, the control device 12 sends a command to the drive power source 11 to rotate the holder 2 by 180 degrees about the shaft 10. As a result, the substrate 1 also has a surface including the substrate surface.
It will rotate 180°. In this state, the control device 12 again controls the peak intensity I ^LO _HV due to the LO phonon.
and spectrophotometer 7 to measure the peak intensity I ^TO _HV due to TO phonon. It goes without saying that the state at this time corresponds to A _- in FIG. 2, and by finding the ratio of the two peak intensities measured here, r _- in equation (5) can be obtained.

After r ₊ and r _- are obtained in this way, the control device 12 calculates φ based on equation (6). In addition, prior to the calculation, the operator calculates the incident angle θi of the laser beam 4 on the substrate surface and the refractive index n of GaAs (n=4.25 when using the 5145 Å line of an argon laser as the laser beam).
If θ is input to the control device 12, θ can be immediately calculated from Snell's law as described above, so φ can be obtained from equation (6).

The surface orientation is 0° (±0.5°) from (100) to (110),
As a result of measuring two types of commercially available semi-insulating GaAs substrates tilted by 2° (±0.5°) using the procedure described above, each φ
Measured values of = 0.043° and 1.86° were obtained, confirming that they were within the error range. In addition, we also measured the board tilted by 5° (±0.5°).
A measured value of φ=6.5° was obtained. In this case, the reason for the large error may be that the peak intensity due to TO phonon obtained with the A _- configuration is below the detection limit of the spectrophotometer (2.5 pulse/sec), and it is possible that the detection limit of the device could be improved. , it can be easily inferred that even in the case of this sample, it would be possible to keep it within the error range.

As described in detail above, according to the present invention, since the surface orientation can be determined using laser Raman spectroscopy, accurate measurement can be easily performed without the risk of exposure unlike the conventional method using X-rays.

Note that the above is an example, and many modifications are possible. For example, it can be applied not only to Zincblend crystals but also to other crystal systems in exactly the same way.

[Brief explanation of drawings]

Figure 1 is a diagram showing spectra due to LO and TO phonons, and Figure 2 is a diagram showing the relationship between the main axes X, Y, and Z of the crystal and the direction Ki in which the laser beam travels when the laser beam is incident on the crystal plane. , FIG. 3 is a diagram showing an example of an apparatus for carrying out the method according to the present invention, and FIG. 4 is a diagram showing the inclination between the cleavage surface of the substrate and the Y' axis. 1: Semiconductor substrate, 2: Holder, 3: Laser oscillator, 4: Laser light, 5: Raman scattered light, 6: Analyzer, 7: Laser Raman spectrophotometer, 8: Switching mechanism, 9: Drive mechanism, 12: Central control Device.

Claims (1)

[Claims] 1 (a) Irradiating the surface of the crystal with a laser beam and introducing the Raman light generated thereby into a spectrophotometer,
determining the ratio of the peak intensity of the Raman band corresponding to the TO phonon and the peak intensity of the Raman band corresponding to the LO phonon in the spectrum of the Raman light; (b) the laser beam of the crystal is incident on the crystal; (c) Determine the plane orientation of the crystal from the two ratio values obtained in (a) and (b) above by rotating the plane by 180° within the plane in which it exists and performing (a) above. A crystal plane orientation measurement method consisting of: 2 Laser oscillator for generating laser light to irradiate the crystal surface and the peak intensity of the Raman band corresponding to TO phonon and the Raman band corresponding to LO phonon in the spectrum of Raman light generated from the crystal surface. a Raman spectrophotometer for detecting; a rotation mechanism for rotating the crystal body by 180 degrees within a plane on which the laser beam enters the crystal body; and a rotation mechanism for rotating the crystal body by 180 degrees by the rotation mechanism. Claim 1 comprising calculation means for determining the plane orientation of the crystal from the peak intensity of the Raman band corresponding to the TO phonon and the peak intensity of the Raman band corresponding to the LO phonon detected by the spectrophotometer before and after. Apparatus for carrying out the method described in Section 1.