JP2832272B2 - Crystal defect observation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for observing internal defects in a semiconductor crystal used for a semiconductor device.

[0002]

2. Description of the Related Art Conventionally, as a method for observing internal defects 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 a wafer from an irradiation surface side or a cleavage surface side perpendicular to the wafer surface. Adjustment of the defect detection sensitivity and the like is performed exclusively by changing the intensity of the irradiation laser light.

[0003]

However, according to such a conventional technique, there is a problem that when the intensity of the irradiation laser beam is increased to observe a finer defect, the semiconductor crystal is destroyed. Further, relying only on the intensity of the irradiation laser light is not preferable in terms of the device configuration and power consumption.

An object of the present invention is to provide an apparatus 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 the above object, the present invention irradiates a laser beam onto a flat surface of a semiconductor crystal, and receives scattered light generated from a defect in the semiconductor crystal by the laser beam. When obtaining the information on the defect, the wavelength of the laser light is set based on the change in the scattering intensity due to the defect with respect to the change in the wavelength of the laser light and the change in the absorption coefficient of the laser light in the semiconductor crystal. ing.

[0006]

In this configuration, the scattering intensity from the defect and the absorption coefficient change with respect to the wavelength of the irradiation laser light as shown in the graph of FIG. The scattering intensity I changes as shown in FIG. 1 because the refractive index of the defect relative to the refractive index ε of the silicon crystal around the defect is ε + レ ー ザ ε, the volume of the defect is V, and the wavelength of the irradiation laser light is λ.
Then, the scattering intensity I due to the defect becomes I∝λ ^-4 (△
ε * V) ² , which is inversely proportional to the fourth power of the wavelength and is affected by Δε and V. Therefore, the laser beam is irradiated toward the surface of the semiconductor wafer,
In the case of observing 90 ° scattering from the cleavage plane side, a high scattering intensity and a small absorption coefficient are more suitable for observing finer defects. Preferably, the wavelength is set in the range of 970 to 1035 nm. Also, when irradiating a 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 relatively small in order to suppress the effects of reflection and scattering from the back surface of the silicon wafer. It is preferable to irradiate a laser beam having a wavelength 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 diagram showing a crystal defect observation apparatus according to one embodiment of the present invention. As shown in FIG. 1, the apparatus includes a laser irradiation means 7 for irradiating a convergent laser beam 5 toward a surface 3 of a silicon wafer 1, and a scattered light 11 generated from a defect 9 in the silicon wafer 1 by the laser beam 5. And observation means 13 for obtaining information on the defect 9. The laser irradiating means 7 has a laser device (not shown) and a condensing lens 15 for condensing laser light emitted from the laser device and irradiating the laser light to the surface 3. The observation unit 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, a device that emits laser light having a wavelength in the range of 970 to 1035 nm is set, or is adjusted so as to emit laser light of such a wavelength.

In this configuration, when the focused laser beam 5 is irradiated toward the surface 3, scattered light is generated from the defect 9, which is observed through the microscope 17. , The radiated laser beam is moderately attenuated in the silicon wafer, and the scattering intensity is not so strong. Light is clearly observed. FIG. 3 is a schematic view showing a crystal defect observation apparatus according to another embodiment of the present invention. 2 denote the same components. In FIG. 3, reference numeral 23 denotes a cleavage plane of the silicon wafer 1. In this case, the laser device is 96
It is set so as to emit laser light having a wavelength in the range of 0 to 1010 nm.

In this configuration, when the focused laser beam 5 is irradiated toward the surface 3, scattered light in the 90 ° direction among the 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 so much attenuated in the silicon wafer 1 and the scattering intensity due to the defect 9 is large. Is observed, and even if the defect 9 is minute, the image data can be obtained.

In other observation modes, for example, when irradiating laser light from the front surface of the wafer and observing scattered light from the back surface, the wavelength of the irradiating laser light is optimized based on data as shown in FIG. By doing so, efficient observation can be performed.

Further, the above-mentioned observation means may be one using a photosensitive material other than one using a television camera or the like. 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 light is set based on the change in the absorption coefficient and the scattering intensity with respect to the wavelength of the laser light.
Information based on scattered light of defects 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 the drawings]

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

FIG. 2 is a schematic diagram showing a crystal defect observation device according to one 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.

[Description of Signs] 1: Silicon wafer, 3: Surface, 5: Convergent laser beam,
7: laser irradiation means, 9: defect, 11: scattered light, 13:
Observation means, 15: condenser lens, 17: microscope, 19: television camera, 21: back surface, 23: cleavage plane.

Claims (2)

(57) [Claims] 1. A crystal defect observing apparatus comprising: a laser irradiating means for irradiating a laser beam onto a semiconductor crystal; and a light receiving means for receiving internal scattered light generated from a defect inside the crystal by the laser light. The irradiating means generates laser light of a first wavelength when receiving internal scattered light by the laser light radiated toward the crystal surface through another surface substantially perpendicular to the surface, A crystal defect observation apparatus, wherein when internal scattered light is received via the same surface as the surface, a laser beam having a second wavelength different from the first wavelength is generated. 2. The semiconductor crystal is a silicon crystal,
2. The crystal defect observation device according to claim 1, wherein the first wavelength is in a range of 970 to 1035 nm, and the second wavelength is in a range of 960 to 1010 nm. 3.