JPH08330373A - Evaluation of polycrystalline material - Google Patents

Abstract

PURPOSE: To evaluate the grain diameter and orientation of polycrystalline material in line at the manufacturing site with high accuracy even when the polycrystalline surface is covered with an oxide film, etc. CONSTITUTION: Laser beams projected from a light source 1 are s-polarized by a polarizer 2, unnecessary beams are removed by a filter 3 and the beam diameter is adjusted to a desired size by a lens 4. The laser beams are applied to a polycrystalline sample 5 by rotating the polarizer 2 or the sample 5. The obtained second harmonic is received by a photomultiplier 9 through a filter 6, lens 7 and a polarizer 8, are detected by a photo counting system 10 and the data is saved in a personal computer 11. When the beam diameter is sufficiently larger than the grain diameter, the strength change dependent on the rotating angle is not detected in the obtained second harmonic. The grain diameter is obtained from the beam diameter wherein the strength change dependent on the rotation angle has occurred. The crystal orientation is obtained from the pattern of the strength change dependent on the rotation angle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a polycrystalline material which nondestructively detects the crystal orientation and the crystal grain size of the polycrystalline material.

[0002]

2. Description of the Related Art As a conventional crystallinity evaluation method, there is an observation method using an electron microscope or X-ray diffraction. As the electron microscope, a transmission type, a reflection type, and a scanning type are used. In the method of using the transmission type, electrons accelerated by a high voltage are transmitted through the inside of the sample, and a material is obtained by using a diffracted electron beam. Observe the internal structure. When a scanning electron microscope is used, the crystal state of the sample surface is evaluated by scanning a finely focused electron beam on the sample and recording the secondary electrons obtained at that time. The X-ray diffraction method is a method of irradiating the sample surface with X-rays from various angles and analyzing the crystal structure from the direction and intensity of the diffraction lines.

In recent years, semiconductor materials have been evaluated by Raman scattering. Raman scattering refers to inelastic scattering of light accompanied by elementary excitation or extinction. For example, JP-A-4
In the evaluation method described in JP-A-43661, the surface of the polycrystalline material is scanned with a laser beam having a first beam diameter, and a first intensity change in which the intensity of the Raman scattering peak changes on the surface is obtained, Scanning with a laser beam having a second beam diameter smaller than the first beam diameter is performed to obtain a second intensity change in which the intensity of the Raman scattering peak changes on the surface, and the first intensity change and the second intensity change. Compare the changes,
When there is a difference more than the measurement accuracy by Raman spectroscopy,
The crystal grain size of the polycrystalline material is determined to be smaller than the first beam diameter and larger than the second beam diameter.

Further, in the method described in the above publication,
The Raman scattering peak is obtained by rotating the laser beam relative to the polycrystalline material, and scanning with the second beam diameter is performed twice at different polarization angles to determine the orientation of each crystal grain from the intensity of the Raman scattering peak. Is measured and the grain size and crystal grain orientation are simultaneously determined.

[0005]

Among the above-mentioned conventional methods for evaluating a polycrystalline material, the one using an electron microscope requires a special sample preparation. Therefore, the sample must be returned to the semiconductor manufacturing process after the inspection. I can't. Moreover, since the evaluation method using a transmission electron microscope and the evaluation method by X-ray diffraction include information on the volume through which an electron beam or X-ray is transmitted, the crystal plane orientation and the grain size can be obtained only as average information. , It is not possible to extract highly accurate information from the surface / interface. Further, the electron microscope method and the X-ray diffraction method require expensive and large-scale equipment, and thus it is difficult to adopt them as in-line evaluation methods at the manufacturing site.

The Raman scattering measurement is for observing the scattering from the crystal surface. Therefore, if an oxide film is formed on the surface in the measurement in the atmosphere, accurate information from the crystal surface of interest can be obtained. Disappear. Further, in the conventional Raman scattering method, when a material layer such as an insulator is deposited on a polycrystal, it is impossible to obtain information at the interface of the polycrystal existing in the lower layer.

The present invention has been made in view of the above problems of the conventional example, and an object thereof is to select information from the crystal surface / interface nondestructively without using a large-scale device. Therefore, the crystal grain size and crystal orientation of the polycrystalline material can be measured in-line even in the air or in a state of being covered with another film.

[0008]

In order to achieve the above object, according to the present invention, a laser beam having a different beam diameter is rotated or rotated on a sample surface of a polycrystalline material relative to the sample surface. Determining the crystal orientation and crystal grain size of the polycrystalline material by displacing it and making it incident, observing the second harmonic for each beam diameter, and measuring the rotation angle or movement amount dependency of the second harmonic intensity. A method for evaluating a polycrystalline material is provided.

[0009]

In the present invention, the second phenomenon that occurs at the polycrystalline interface
The crystal orientation and grain size are evaluated by using the harmonics. The polarization P of the medium can be expressed as P = Χ ⁽¹⁾ E + (dΧ ⁽¹⁾ / dq) ΔqE + Χ ⁽²⁾ EE + ... (1). Here, Χ ⁽¹⁾ and Χ ⁽²⁾ represent the first-order linear susceptibility tensor and the second-order nonlinear susceptibility tensor, respectively. Further, q represents a reference coordinate, and E represents a photoelectric field. In this equation, the first term is a term indicating linear reflection and refraction. The second term is a term indicating Raman polarization, and is a term in which polarization is modulated by the frequency of q when the polarizability of the medium is a function of the displacement of the medium represented by the reference coordinate q. Third
The term is a quadratic non-linear term that generates a second harmonic or the like, and is a polarization proportional to the square of the electric field.

While the conventional evaluation method using Raman scattering utilizes linear Raman polarization, the present invention is
The crystal orientation / crystal grain size on the surface / interface is evaluated by using the second harmonic resulting from the third term of the equation (1). The second harmonic is generated from the surface / interface where the crystal inversion symmetry is broken. The principle of the evaluation method of the present invention will be described based on the third term of the equation (1). The inversion means observing the physical quantity by inverting the coordinates, and can be expressed by replacing -x with x in the case of one-dimensional consideration.
Since the electric field is a field independent of matter, E _−x = −E _x , but if the polarization has inversion symmetry, P _−x = −P _x ,
If there is no inversion symmetry, then P _−x ≠ −P _x . Therefore, P- _x = Χ _xxx ⁽²⁾ E _-x E _-x = Χ _xxx ⁽²⁾ E _x E _x -P _x = -Χ _xxx ⁽²⁾ E _x E _x . If there is inversion symmetry (P _-x = -P _x ), Χ
_{If xxx} ⁽²⁾ = -Χ _xxx ⁽²⁾ = 0 and the inversion symmetry is broken (P _-x ≠ -P _x ), Χ _xxx ⁽²⁾ ≠ 0.

As described above, since the evaluation method according to the present invention utilizes the second harmonic generated at the interface where the crystal inversion symmetry is broken, another film such as an insulating layer is formed on the polycrystalline material layer. It is possible to measure through this coating even after being applied. Therefore, for example, even if the surface of a polycrystalline body is covered with a natural oxide film due to exposure to the atmosphere, highly accurate measurement is possible regardless of the presence of this coating.

In the present invention, for example, by changing the magnification of the laser condenser lens, beams having different diameters are made incident on the sample, and the sample or the polarization plane is rotated for each beam diameter, whereby the second harmonic is generated. The rotation angle dependence of the wave is measured. Then, by determining the beam diameter when the intensity change does not appear in the second harmonic with respect to the rotation angle and the beam diameter when it appears, the crystal grain size is determined to be between these two beam diameters. Then, the crystal orientation of the polycrystalline material is obtained from the rotation angle dependence of the second harmonic obtained by the beam diameter where the intensity change appears. That is, as described later, the crystal orientation is obtained from the obtained pattern of intensity change of the second harmonic.

When a beam having a diameter sufficiently larger than the grain size is incident on the polycrystalline body, the spatial distribution of the second-order nonlinear polarization is averaged, so that the second harmonic wave has a rotation angle dependence. Not shown. When the beam diameter is changed to be about the crystal grain size by changing the beam diameter, the second harmonic becomes rotation-dependent.

In an optical system for measuring a polycrystalline material, in the second harmonic measuring device, by changing the incident angle, the polarization direction of incident or reflected light, and the crystal axis of the sample, the irradiation position remains the second harmonic. The intensity of can be measured. By comparing the theoretical formula derived by the combination of these parameters with the measurement result, the plane orientation of each individual crystal grain can be determined.

For example, when an experiment is conducted with s-polarized light (polarization in which the electric field component of the incident light is perpendicular to the incident surface) 45 ° incidence / sample rotation / s-polarized light reception, surfaces oriented in (111) and (110) The patterns of the second harmonic light intensity I _SH obtained from the interface can be expressed by I _SH = C | sin3δ | ² I _SH = C ′ | sin3δ + 1.5sin4δ | ² , respectively. Here, C and C ′ are proportional constants including the Fresnel coefficient, and δ is the sample rotation angle. When the beam diameter is about the same as or the same as the size of the crystal grain, the pattern shown by the above equation appears and the crystal orientation can be known.

FIG. 1 is a diagram showing the rotation angle dependence of the second harmonic light intensity obtained when the crystal grain size is comparable to or larger than the beam diameter, and FIG. 2 is the crystal grain size. FIG. 6 is a diagram showing the rotation angle dependence of the second harmonic light intensity obtained when is sufficiently smaller than the beam diameter. In addition,
Although the intensity change pattern of the second harmonic light from the surface / interface oriented to (100) is not shown in order to make the figure easier to see, it is not possible to use another suitable optical system in the case of (100) orientation as well. A unique pattern that differs from the orientation of appears.

[0017]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 3 is a schematic configuration diagram of a measuring device used in one embodiment of the present invention. Laser light of laser light source 1 composed of Nd-YAG laser (λ = 1064 nm)
Is s-polarized through the polarizer 2, unnecessary wavelength components are cut by the filter 3, the beam diameter is adjusted by the lens 4, and then incident on the sample 5 at 45 °. Only the target wavelength (λ = 532 nm) of the second harmonic wave generated from the sample is selectively transmitted by the filter 6, and the lens 7
Is collected by. Next, the s-polarized component is received by the photomultiplier tube 9 through the polarizer 8. A weak signal is detected by the photon counting system 10 and the data is saved in the personal computer 11.

As a concrete sample, a thermal oxide film of 5000 Å is formed on a silicon substrate, and a polysilicon film is formed thereon.
Deposit 1 μm at 50 ° C. Then 850 in nitrogen atmosphere
After annealing at 30 ° C. for 30 minutes and forming a natural oxide film in the atmosphere, a film was used. For this sample, Nd-YA
The laser beam of the G laser is focused by a lens and the diameter on the sample is φ = 1.5 μm, 14.5 μm,
The measurement was performed at each beam diameter. Optical system is s-polarized 4
It was 5 ° incidence / sample rotation / s-polarized light reception. The observation results when the laser beam diameter was φ = 1.5 μm and 14.5 μm were as shown in FIGS. 1 and 2.

The present invention is preferably implemented by the measuring device shown in FIG. 3, but is not limited to the device having such a configuration. For example, a device in which the order of the polarizer, the filter, the lens, etc. is changed can be used. Further, in the above embodiment, the plane of polarization of the laser beam was rotated relative to the sample, but instead of this method, the sample was moved relative to the laser beam. May be scanned by a laser beam.

[0020]

As described above, in the method for evaluating a polycrystalline material according to the present invention, a laser beam having a different beam diameter is applied to the sample surface while being rotated or moved relative to the sample surface. Since the grain size and crystal orientation of the polycrystalline material are evaluated using the harmonics, the following effects can be enjoyed.

Since non-destructive measurement is possible without using an expensive and large-scale device, in-line measurement / evaluation is possible. Since the evaluation method uses the second harmonic generated at the interface where the crystal inversion symmetry is broken, even if an amorphous material is deposited on the polycrystalline material, it is not interfered by this and highly accurate evaluation is possible. It can be performed. For the same reason as above, even if the natural oxide film is crystallized on the surface of the polycrystal, it does not affect the measurement result, so that the polycrystal of the material which is easily oxidized can be evaluated in the atmosphere.

[Brief description of drawings]

FIG. 1 is a diagram showing the rotation angle dependence of the second harmonic light when the laser beam diameter is smaller than the crystal grain diameter in the example of the present invention.

FIG. 2 is a diagram showing the rotation angle dependence of the second harmonic light when the laser beam diameter is sufficiently larger than the crystal grain diameter in the example of the present invention.

FIG. 3 is a schematic configuration diagram of a measuring device used in an embodiment of the present invention.

[Explanation of symbols]

 1 Laser Light Source 2, 8 Polarizer 3, 6 Filter 4, 7 Lens 5 Sample 9 Photomultiplier Tube 10 Photon Counting System 11 Personal Computer

Claims (5)

[Claims] 1. A laser beam having a different beam diameter is incident on a sample surface of a polycrystalline material by rotating or moving the beam relative to the sample surface, and observing the second harmonic for each beam diameter. A method for evaluating a polycrystalline material, characterized in that the crystal orientation and the crystal grain size of the polycrystalline material are determined by measuring the rotation angle or movement amount dependency of the second harmonic intensity. 2. The method for evaluating a polycrystalline material according to claim 1, wherein the s-polarized wave is incident on the sample at an angle of 45 °. 3. Recognizing the beam diameters of the two laser beams before and after the intensity change of the second harmonic reflected wave appears, and determining that the crystal grain size of the polycrystalline material is between these two beam diameters. The method for evaluating a polycrystalline material according to claim 1, wherein: 4. The method for evaluating a polycrystalline material according to claim 1, wherein the crystal orientation of the polycrystalline material is determined from an intensity waveform depending on a rotation angle or a moving distance of the second harmonic reflected wave. 5. An amorphous material layer is formed on a polycrystalline material layer, and a laser beam is made incident through the amorphous material layer to determine the crystal orientation and the crystal grain size of the polycrystalline material. The method for evaluating a polycrystalline material according to claim 1.