JPH07151697A - Apparatus and method for observing crystal defect - Google Patents

Abstract

PURPOSE:To make possible the observation of a defect of a semiconductor crystal efficiently even in a relatively less intensity of a laser light by setting the wavelength of the laser light based on changes in the intensity of scattering due to the defect with respect to changes in the wavelength of the laser light and changes in absorption coefficient of the laser light in the semiconductor crystal. CONSTITUTION:A laser apparatus is so set to emit a laser light with a wavelength in a range of 960-1010nm. When a focused laser light 5 is made to irradiate a surface 3, scattered light in the direction of 90 deg. out of the scattered light 11 generated by a defect 9 is observed through a cleaved surface. In this case, as the wavelength of the irradiated laser beam 5 is set in a range of 960-1010nm, the incident laser luminous flux and the scattered light 11 within a silicon wafer 1 are not attenuated so much while the image of the defect 9 is observed efficiently because of a large intensity of scattering by the defect 9 thereby making possible the obtaining of an image data even when the defect 9 is very small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for observing internal defects in semiconductor crystals used in semiconductor devices.

[0002]

2. Description of the Related Art Conventionally, as a method of observing an internal defect of a semiconductor wafer or the like, a laser beam is irradiated from the wafer surface,
There is known a method of observing a defect image by receiving only scattered light generated from a defect in the wafer from the irradiation surface side or the cleavage surface side perpendicular to the wafer surface. The defect detection sensitivity and the like are adjusted by changing the intensity of the irradiation laser beam.

[0003]

However, according to such a conventional technique, there is a problem that the semiconductor crystal is destroyed when the intensity of the irradiation laser beam is increased to observe smaller defects. In addition, it is not preferable to rely only on the intensity of the irradiation laser beam in this way in terms of the device configuration and power consumption.

An object of the present invention is to provide an apparatus and method capable of efficiently observing a defect in a semiconductor crystal even with a relatively small laser beam intensity in view of the problems of the prior art.

[0005]

In order to achieve this object, the present invention irradiates a flat surface of a semiconductor crystal with a laser beam and receives the scattered light generated by a defect in the semiconductor crystal by the laser beam. Then, in obtaining the information of the defect, the wavelength of the laser light is set based on the change of the scattering intensity due to the defect with respect to the change of the wavelength of the laser light and the change of the absorption coefficient of the laser light in the semiconductor crystal. ing.

[0006]

In this structure, the scattering intensity and the absorption coefficient from the defect change with respect to the wavelength of the irradiation laser light as shown in the graph of FIG. 1 in the case of a silicon crystal as an example. The scattering intensity I changes as shown in FIG. 1 because the refractive index of the defect is ε + Δε with respect to the refractive index ε of the silicon crystal around the defect, the volume of the defect is V, and the wavelength of the irradiation laser beam is λ.
Then, the scattering intensity I due to the defect is I ∝λ ^-4 (△
This is because it is inversely proportional to the fourth power of the wavelength as in ε * V) ² and is influenced by Δε and V. Therefore, by irradiating the laser beam toward the surface of the semiconductor wafer,
In the case of observing 90 ° scattering from the cleavage plane side, the scattering intensity is high and the absorption coefficient is small is suitable for observing smaller defects. Therefore, in the case of a silicon wafer, the irradiation laser beam from FIG. It is preferable to set the wavelength within the range of 970 to 1035 nm. In addition, when irradiating the laser beam from the front surface of the silicon wafer and observing scattered light from the front surface, the absorption coefficient is relatively large and the scattering intensity is high to suppress the influence of reflection and scattering from the back surface of the silicon wafer. It is preferable to irradiate a laser beam having a wavelength in the range of 960 to 1010 nm, which is relatively small.

[0007]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic view showing a crystal defect observing apparatus according to an embodiment of the present invention. As shown in the figure, this device receives a laser irradiation means 7 for irradiating the surface 3 of the silicon wafer 1 with a converged laser beam 5, and a scattered light 11 generated by a defect 9 in the silicon wafer 1 by the laser beam 5. An observation means 13 for obtaining information on the defect 9 is provided. The laser irradiation means 7 has a laser device (not shown) and a condenser lens 15 that condenses and irradiates the laser light emitted by the laser device onto the surface 3. The observation means 13 includes a microscope 17 that receives the scattered light 11 and a television camera 19 that photoelectrically converts a defect image formed by the microscope 17 to obtain image data. As the laser device, one that emits laser light having a wavelength in the range of 970 to 1035 nm is set, or the laser device is adjusted and set so as to emit laser light having such a wavelength.

In this structure, when the focused laser beam 5 is irradiated toward the surface 3, scattered light is generated from the defect 9 and is observed through the microscope 17. The wavelength of the laser beam is as described above. Since the irradiated laser light is appropriately attenuated in the silicon wafer, and the scattering intensity is not so strong, it is not significantly affected by reflection and scattering on the back surface 21 and is scattered from the defect 9. The light is clearly visible. FIG. 3 is a schematic view showing a crystal defect observation apparatus according to another embodiment of the present invention. 2 that are the same as those in FIG. 2 indicate the same components. In FIG. 3, reference numeral 23 is a cleavage plane of the silicon wafer 1. In this case, the laser device is 96
It is set to emit laser light having a wavelength in the range of 0 to 1010 nm.

In this structure, when the focused laser light 5 is irradiated toward the surface 3, scattered light in the 90 ° direction among scattered light generated by the defect 9 is observed through the cleavage plane 23. Since the wavelength of the laser beam 5 is set as described above, the incident laser beam and the scattered light 11 are not significantly attenuated in the silicon wafer 1 and the scattering intensity by the defect 9 is large, so that the defect 9 can be efficiently obtained. Image is observed and even if the defect 9 is minute, its image data can be obtained.

Even in another observation mode, for example, when the laser light is irradiated from the front surface of the wafer and the scattered light is observed from the back surface, the wavelength of the irradiation laser light is optimized based on the data shown in FIG. By doing so, efficient observation can be performed.

Further, the above-mentioned observation means may be one using a television camera or the like, or one using a photosensitive material. Alternatively, a cross-sectional image may be obtained by scanning with irradiation laser light.

[0013]

As described above, according to the present invention, the wavelength of the irradiation laser beam is set based on the change of the absorption coefficient and the scattering intensity with respect to the wavelength of the laser beam.
Information based on the scattered light of the defect can be obtained very efficiently. Therefore, even smaller defects can be observed without the risk of destroying the semiconductor crystal by the irradiation laser beam.

[Brief description of drawings]

FIG. 1 is a graph showing changes in absorption coefficient and scattering intensity with respect to a wavelength of irradiated laser light in a silicon crystal.

FIG. 2 is a schematic diagram showing a crystal defect observing apparatus according to an embodiment of the present invention.

FIG. 3 is a schematic view showing a crystal defect observation apparatus according to another embodiment of the present invention.

[Explanation of symbols]

1: silicon wafer, 3: surface, 5: focused laser beam,
7: Laser irradiation means, 9: Defects, 11: Scattered light, 13:
Observation means, 15: condensing lens, 17: microscope, 19: TV camera, 21: back surface, 23: cleavage surface.

Claims (4)

[Claims] 1. A laser irradiating means for irradiating a flat surface of a semiconductor crystal with a laser beam and an observing means for receiving scattered light generated by a defect in the semiconductor crystal by the laser beam to obtain information on the defect. In the crystal defect observing apparatus having the, the wavelength of the laser light irradiated by the laser irradiation means, in the change of the scattering intensity due to the defect with respect to the change of the wavelength of the laser light A crystal defect observing apparatus characterized by being set based on the above. 2. The observing means receives scattered light scattered from the defect in a direction of about 90 ° with respect to the irradiation laser beam through another surface of the semiconductor crystal which is substantially perpendicular to the flat plane. The semiconductor crystal is a silicon crystal, and the set wavelength is 970 to 1035.
The crystal defect observing apparatus according to claim 1, wherein the crystal defect observing apparatus is in the range of nm. 3. The semiconductor crystal is a silicon crystal having another surface parallel to the flat surface, and the observation means receives scattered light from the defect via the flat surface. The set wavelength is 960 to 101
2. It is within the range of 0 nm.
The described crystal defect observation device. 4. A crystal defect observing method for obtaining information of the defect by irradiating a flat surface of a semiconductor crystal with a laser beam and receiving scattered light generated from a defect in the semiconductor crystal by the laser beam. The crystal defect observing method is characterized in that the wavelength of the laser light is set based on a change in scattering intensity due to the defect with respect to a change in wavelength of the laser light and a change in absorption coefficient of the laser light in the semiconductor crystal.