JPH08261927A - Intra-crystal flaw detecting device - Google Patents

Abstract

PURPOSE: To provide an intra-crystal flaw detecting device capable of detecting a fine flaw in a measured object without enlarging a device structure. CONSTITUTION: This intra-crystal flaw detecting device is provided with a pulse laser device 1 emitting a pose laser beam 2 having the wavelength twice or above of the absorption end wavelength of a measured crystal 3, a light converting optical system 6 collecting the pulse laser beam on the measured crystal, a scanning system 10 for scanning the pulse laser beam in the measured crystal, a filter 7 transmitting only the second harmonic wave from the measured crystal, and a detecting system for detecting the transmitted light from the filter 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting defects inside a crystal used in the field of crystal growth and semiconductor wafer manufacturing, and more particularly to a crystal suitable for use in the field of silicon wafer manufacturing for large capacity memories. The present invention relates to an internal defect detection device.

[0002]

2. Description of the Related Art Conventionally, an infrared tomograph has been known as a method for detecting a defect inside a semiconductor crystal such as silicon. As described on page 102 of "Semiconductor Material Defect Evaluation Technology (published by Science Forum)", the crystal under measurement is irradiated with light having a wavelength longer than the absorption edge wavelength of the crystal, and the inside of the crystal is irradiated. The method is to monitor the light scattered by a defect with a television camera and measure the position and size of the defect. The feature of this method is that it is not necessary to use a laser device as a light source, and only the scattered light is detected as a signal to be detected. Therefore, it is possible to detect defects and foreign matters inside the crystal with a simple device.

However, in this method, even if there is no defect, Rayleigh scattered light is always generated as background noise, so that there is a limit to increase the detection sensitivity of the defect, and the defect size that can be detected uses Mie scattering. Therefore, it cannot be 1/10 or less of the wavelength.

On the other hand, by detecting the second harmonic (hereinafter abbreviated as SHG) from the surface of the crystal, not inside the crystal, and examining the angle / polarization dependence of the intensity change, foreign matter adhering to the surface and A method for determining the crystal orientation is known (J. Vac. Sci. Technol. B3 (5), p1467 Sep / Oct (198
Five)). This method uses pulsed laser light having a wavelength longer than the absorption edge wavelength of the crystal as a light source, and is most effective when an isotropic crystal that does not originally generate SHG is targeted. Generated by breaking the symmetry at
Is detected, it is possible to obtain only information for one to two atomic layers from the surface. That is, it can be seen that SHG can be generated from a region (several angstroms) much smaller than the wavelength.

However, this method requires the measurement in a high vacuum because the crystal surface is to be measured.
The device becomes large-scale.

[0006]

SUMMARY OF THE INVENTION The present invention has been devised in order to eliminate such disadvantages of the prior art, and its main purpose is to make the inside of the object to be measured without making the device structure large. It is an object of the present invention to provide a crystal internal defect detection device capable of detecting the microscopic defects.

[0007]

According to the present invention, there is provided a pulse laser device which emits a pulse laser beam having a wavelength which is at least twice the absorption edge wavelength of the crystal to be measured.
A focusing optical system for focusing the pulsed laser light on the crystal to be measured,
A scanning system for scanning the pulsed laser light in the crystal to be measured, a filter for transmitting only the second harmonic from the crystal to be measured, and a detection system for detecting the transmitted light from the filter were provided. This is achieved by providing a crystal internal defect detection device characterized by the above. In particular, it is suitable when the crystal to be measured is a silicon crystal.

[0008]

When a pulsed laser beam is irradiated to a crystal having no central symmetry (anisotropic), nonlinear electronic polarization vibrating at a frequency twice the laser frequency occurs, and SHG is generated as a polarization wave of the electronic polarization. To do. It is said that SHG does not occur in an isotropic substance such as silicon, but SHG occurs because the central symmetry is broken at the surface of silicon or the interface between silicon and another substance. This SHG is
Unlike SHG in the case of an anisotropic crystal, only 1 to 2 atomic layers contribute to SHG, so it is very weak and usually unobservable. However, since the intensity of SHG increases in proportion to the square of the electric field intensity of the pulsed laser light, it can be observed by using the pulsed laser light (about 10 GW) having a large peak value output. Since the defect inside the crystal is considered to form an interface with the crystal base material, SHG is generated from the region of 1 to 2 atomic layers around the defect. as a result,
Defects of several Angstroms can be detected.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram of a crystal internal defect detection apparatus according to an embodiment of the present invention. The internal defect detection apparatus of the present embodiment irradiates the measured crystal 3 with the pulsed laser light 2 output from the pulsed laser apparatus 1 and observes the SHG 4 generated inside the crystal with the CCD camera 5. An example in which a silicon ingot is used as the crystal to be measured will be described below.

The band gap of silicon is about 1e.
Since it is V, it becomes transparent to light having a wavelength of 1.24 μm or more. Therefore, the pulse laser device 1 has a Q-s
w. A YAG laser-excited parametric oscillator was used to generate pulsed laser light 2 having a wavelength of 2.5 μm.
The pulsed laser light 2 passes through the focusing optical system 6 and is focused inside the crystal to be measured 3. Here, the condensing optical system 6 is f =
It was composed of a 200 mm convex lens. In the initial arrangement, the positions of the center of the measured crystal 3 and the spot of the pulsed laser light 2 are aligned.

The CCD camera 5 is installed from above the crystal 3 to be measured, focusing on the focal position of the pulse laser beam 2. A bandpass filter 7 for a wavelength of 1.25 μm is arranged between the CCD camera 5 and the crystal 3 to be measured, the Rayleigh scattered light 8 of the pulse laser light 2 is removed, and only the SHG 4 is transmitted. It is displayed on the monitor 9.

The crystal 3 to be measured is installed on a scanning system 10 composed of an XYZ stage and a rotary stage so that the pulsed laser light 2 scans the crystal 3 to be measured thoroughly. By moving and rotating the scanning system 10,
Each time it is rotated by 0 °, the crystal 3 to be measured moves by 100 μm in the direction away from the condensing optical system 6. Then, after the measurement of one surface is completed, the surface is measured by moving it by 100 μm in the vertical direction. At this time, if the CCD camera 5 is also attached to the scanning system 10, in-plane defect distribution measurement becomes easy.

FIG. 2 is a schematic diagram showing how SHG4 is generated from a defect. Since the interface 12 is formed between the defect 11 and the crystal base material, the symmetry is broken and SH
G4 has occurred. Since SHG4 is generated between 1 and 2 atomic layers around the defect, the defect size can be detected even at the atomic level. For this reason, in the past, several tens of n
Although it was the limit to detect the defect of m,
By using the interface SHG4, it became possible to detect defects of several angstroms.

In the present invention, even if the number of measurement points in the vertical direction of the silicon ingot is reduced in order to shorten the measurement time, there is no problem because the defect distribution is regular.

[0016]

As described above, according to the apparatus of the present invention, the pulse laser light whose SHG is transparent to the object to be measured is used, and S due to the symmetry breaking around the defect inside the object to be measured.
By detecting HG, it is possible to provide a crystal internal defect detection device capable of detecting defects of several angstroms.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a crystal internal defect detection device that is an embodiment of the present invention.

FIG. 2 is a schematic diagram showing how SHG is generated from a defect.

[Explanation of symbols]

 1 pulse laser device 2 pulse laser light 3 crystal to be measured (silicon ingot) 4 SHG 5 CCD camera 6 condensing optical system 7 bandpass filter 8 Rayleigh scattered light 9 monitor 10 scanning system 11 defect 12 interface (area where SHG occurs)

Claims (2)

[Claims] 1. A pulse laser device that emits a pulse laser beam having a wavelength that is at least twice the absorption edge wavelength of the crystal to be measured, a condensing optical system that condenses the pulse laser light onto the crystal to be measured, and A scanning system for scanning the pulsed laser light in the measured crystal, and a second system from the measured crystal.
A crystal internal defect detection device comprising: a filter that transmits only harmonics; and a detection system that detects light transmitted from the filter. 2. The crystal internal defect detection device according to claim 1, wherein the measured crystal is a silicon crystal.