JPH11160230A - Method and apparatus for detecting crystal defect near surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve depth resolution by moving a high-magnification optical system lens close to a crystal surface without interrupting an advancement of a light entering to the crystal surface. SOLUTION: Lights 12 of a plurality of wavelengths and different penetration depths are brought into the same position of a crystal surface 11. Scattering lights 13 are detected via a lens 14 of an optical system. A crystal defect in the vicinity of the surface is detected on the basis of a difference of detected values. The incident lights 12 are sent from sideways of the lens 14 via a semitransparent mirror 10 set above the lens 14 of the optical system to enter the crystal surface 11 through the lens 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for irradiating light such as an infrared laser beam onto the surface of a crystal of a semiconductor or the like, based on the scattered light. The present invention relates to a method for detecting near-surface crystal defects for detecting an internal defect having a refractive index different from that of a parent phase as a light scattering center, and a detection apparatus used for the method.

[0002]

2. Description of the Related Art Conventionally, there is known a method for detecting a crystal defect near a semiconductor surface by utilizing the fact that a semiconductor crystal has a property of transmitting infrared rays (Japanese Patent Laid-Open No. 7-29442).
2). In this conventional method, as shown in FIG. 4, an infrared laser beam is emitted from a plurality of laser oscillators at a predetermined angle from a diagonal angle to the surface of a silicon wafer 1 mounted on a stage 2 and movable in horizontal X and Y directions. Light is incident from the light source 4 configured. The incident laser light penetrates into the silicon wafer 1 to a depth corresponding to the wavelength, and if a crystal defect exists in the crystal, light scattering occurs due to the laser light.
The scattered light is collected by an infrared microscope 5 located above the silicon wafer 1 and detected by an infrared vidicon 6. Crystal defects are detected as scattering centers (scatterers). The output of the infrared vidicon 6 is displayed on a monitor 7 controlled by the personal computer 3. The detection of the scattering center (scattering body) is performed again by irradiating the same incident position with a laser beam having a different wavelength from the light source 4. As a result, the internal defect at that depth can be calculated based on the difference between the detected values of these scattering centers (scatterers). Also, the movement of the stage 2 in the X and Y directions,
The ON / OFF operation of the oscillation of the light source 4 and the focusing operation of the infrared microscope 5 are all controlled by the personal computer 3.

In this conventional method, the depth resolution depends on the depth of focus of the objective lens 8 of the optical system housed in the infrared microscope 5 as shown in FIG. For example, when a 50 × objective lens is attached to the infrared microscope 5, focus is achieved in a range of about ± 10 μm. That is, in this case, the depth resolution is about 20 μm. In order to increase the depth resolution, a method of changing the objective lens to a high magnification can be considered. Generally, in an optical system,
It is known that when the magnification of the objective lens is increased, the working distance (the distance between the objective lens and the crystal surface) is reduced in proportion thereto. For example, if the magnification of the objective lens is 80
When the magnification is 100, 150, and 150, the working distances are 4.10 mm, 3.18 mm, and 1.00 mm, respectively.
This means that if the objective lens is not brought closer to the sample in proportion to the increase in the magnification of the objective lens, the focus will not be achieved.

[0004]

Therefore, in the above conventional example, when the infrared microscope 5 accommodating the objective lens 8 is to approach the surface of the sample silicon wafer 1 as shown in FIG. Laser light 9 obliquely incident on the surface of the wafer 1 collides with the side surface of the infrared microscope 5 containing the objective lens 8, causing a problem that the laser light 9 cannot be incident on the surface of the silicon wafer 1. An object of the present invention is to provide a method for detecting near-surface crystal defects that can improve the depth resolution by bringing a high-magnification optical system lens close to the crystal surface without obstructing the path of incident light incident on the crystal surface. To provide.

Another object of the present invention is to provide a near-surface crystal in which a high-magnification optical lens can be brought close to the crystal surface without disturbing the path of incident light incident on the crystal surface to improve the depth resolution. An object of the present invention is to provide a defect detection device.

[0006]

The invention according to claim 1 is
As shown in FIG. 1, light 12 having a plurality of wavelengths having different penetration depths is respectively incident on the same position on a crystal surface 11, and the scattered light 13 is detected via a lens 14 of an optical system. It is an improvement of a method for detecting a crystal defect near a surface for detecting a crystal defect based on a difference in the value of incident light 1.
2 is incident on the crystal surface 11 through the lens 14 of the optical system. According to the present invention, the path of the incident light 12 entering the crystal surface 11 is not obstructed by the lens 14 of the optical system. Therefore, a high-magnification optical system lens can be used and brought closer to the crystal surface 11 to improve the depth resolution. The invention according to claim 2 is the invention according to claim 1, wherein the incident light 12 passes through the lens 14 from the side of the lens 14 via the semi-transparent mirror 10 provided above the lens 14 of the optical system. In this method, the light is incident on the crystal surface 11. According to the present invention, the incident light 12 is reflected by the semi-transparent mirror 10 and then enters the crystal surface 11 from the side of the lens 14 through the lens 14.
Lens 14 can be brought closer to crystal surface 11 without obstructing the course of the lens. Semi-transparent mirror 10
Since the scattered light 13 is transmitted, the detection accuracy of the crystal defect does not decrease due to the presence of the semi-transparent mirror 10.

According to a third aspect of the present invention, as shown in FIGS. 1 and 2, a plurality of light sources 15 having a plurality of wavelengths having different penetration depths enter the same position on a crystal surface 11 respectively.
And light collecting means 17 including lenses 14 and 16 of an optical system for collecting scattered light 13 in which incident light 12 from light source 15 is scattered on crystal surface 11, and scattered light 13 from light collecting means 17 is detected. Detecting means 18, calculating means 19 for calculating a crystal defect based on the detection result of the detecting means 18, and the incident light 12 from the light source 15 passing through the lens 14 of the optical system to the crystal surface 1.
1 is a device for detecting near-surface crystal defects, comprising: According to the present invention, since there is provided an incident means for entering the incident light 12 from the light source 15 to the crystal surface 11 through the lens 14 of the optical system, the path of the incident light 12 is obstructed by the lens 14 of the optical system. Instead, it is possible to use a high-magnification optical system lens and bring it closer to the crystal surface 11 to improve the depth resolution. The invention according to claim 4 is the invention according to claim 3, wherein the incident means includes the semi-transparent mirror 10 provided above the lens 14 of the optical system. According to the present invention, the incident light 12 is
After the light is reflected by the lens 14, the light enters the crystal surface 11 through the lens 14 from the side of the lens 14.
Can be approached. Further, the semi-transparent mirror 10 has the scattered light 1
3, the detection accuracy of crystal defects does not decrease due to the presence of the semi-transparent mirror 10.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a detection apparatus used for carrying out the method for detecting near-surface crystal defects according to the present invention.
A description will be given based on FIG. As shown in FIGS. 1 and 2, a crystalline silicon wafer 1 in which a crystal defect is detected
1 has its surface mirror-polished and is mounted on a stage 20. The stage 20 is movable in an X direction and a Y direction orthogonal to each other in a horizontal plane by a drive mechanism (not shown) controlled by the personal computer 19. Silicon wafer 1
A light source 15 for irradiating the infrared laser light 12 on the surface thereof is disposed obliquely above 1. The light source 15 is composed of, for example, a plurality of laser oscillators, and the laser light emitted from each laser oscillator has a different wavelength. Alternatively, a laser oscillator capable of continuously changing the wavelength may be used.

Above the silicon wafer 11, an infrared microscope 17 is provided as a light collecting means for collecting scattered light 13 generated when the laser light 12 as incident light is incident on the surface of the silicon wafer 11. An infrared vidicon 18 is arranged above the infrared microscope 17, and the scattered light 13 collected by the infrared microscope 17 is detected by the infrared vidicon 18. As shown in FIG. 1, a pair of opposed and separated objective lenses 14 and 16 are housed in an infrared microscope 17, and a semi-transparent mirror 10 is provided between these lenses. The laser beam 12 traveling horizontally from the light source 15 is incident on the semi-transparent mirror 10 in the infrared microscope 17, where its direction is changed to approximately 90 degrees vertically and is incident on the lower objective lens 14, refracted and silicon The light enters a predetermined position on the surface of the wafer 11.

The laser beam 12 incident on the surface of the silicon wafer 11 penetrates to the inside of the silicon wafer 11 to a depth corresponding to the wavelength thereof. 13
Is generated. The scattered light 13 is collected by the objective lenses 14 and 16 in the infrared microscope 17, enters the infrared vidicon 18, and is detected. After a part of the scattered light 13 that has passed through the lower objective lens 14 in the infrared microscope 17 passes through the semi-transparent mirror 10,
The light is refracted by the upper objective lens 16, enters the infrared vidicon 18, and is detected.

As shown in FIG. 2, the output of the scattered light 13 detected by the infrared vidicon 18, ie, the detected scattered light 13
Is displayed on the monitor 21 controlled by the personal computer 19. The movement of the stage 20 in the X and Y directions, the on / off operation of the oscillation of the light source 15, the focusing operation of the infrared microscope 17, and the like are all controlled by the personal computer 19.

[0012]

Next, a method for detecting near-surface crystal defects according to an embodiment of the present invention will be described with reference to the above-described detection apparatus shown in FIGS. <Embodiment 1> In the above apparatus, a semiconductor laser having a wavelength of 810 nm (hereinafter, referred to as a light source 15) capable of detecting a crystal defect from the surface of the silicon wafer 11 to a depth of about 20 μm as the light source 15
A laser A (abbreviated as laser A) and a semiconductor laser (hereinafter abbreviated as laser B) with a wavelength of 670 nm capable of detecting crystal defects from the surface of the silicon wafer 11 to a depth of about 1.5 μm were used. The objective lens 14 of the infrared microscope 17
Has a magnification of 150 times, and the working distance (distance between the objective lens 14 and the silicon wafer 11) at which the focal point is adjusted to the surface is 1
mm. First, the focus of the objective lens 14 was adjusted to the surface, and an area of 2 mm in the X direction and 2 mm in the Y direction was scanned, and scattering defects were counted.

When the laser A was used, the number of scattering defects was 23, and when the laser B was used, the number of crystal defects was 21. Therefore, the crystal surface 11
As a result, almost the same number of crystal defects were detected even when the penetration length was different due to the different wavelength. Next, the same measurement was performed by shifting the focal point of the objective lens 14 to a depth of 3 μm from the surface. The number of laser A was 20 and the number of laser B was 0. Therefore, the depth of focus of this objective lens is ± 1.5 μm
It is considered within.

Comparative Example 1 As shown in FIGS. 3 and 4,
The incident light from the light source 4 is directed obliquely upward from the silicon wafer 1
The procedure was substantially the same as in Example 1 (objective lens x 150), except that the light was directly incident on the surface of No. 1. As a result, the incident light collides with the side surface of the infrared microscope 5 containing the objective lens 8, and it was impossible to detect a crystal defect near the surface of the silicon wafer 1.

[0015]

As described above, according to the present invention, light of a plurality of wavelengths having different penetration depths is incident on the same position on the crystal surface, and the scattered light is transmitted through the lens of the optical system. A method for detecting crystal defects near the surface that detects and detects crystal defects based on the difference between these detection values,
Since the incident light is made to enter the crystal surface through the lens of the detection optical system, a high-magnification optical system lens can be brought close to the crystal surface without disturbing the path of the incident light entering the crystal surface to improve the depth resolution. Can be improved.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a main part of an apparatus for detecting near-surface crystal defects according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing the whole of FIG. 2;

FIG. 3 is an explanatory view showing a main part of a conventional apparatus for detecting near-surface crystal defects.

FIG. 4 is an explanatory view showing the whole of FIG. 3;

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 semi-transparent mirror 11 crystal surface 12 incident light 13 scattered light 14, 16 lens of optical system 15 light source 17 condensing means 18 detecting means 19 calculating means

Claims (4)

[Claims] 1. A plurality of wavelengths of light (12) having different penetration depths are respectively incident on the same position on a crystal surface (11), and their scattered light (13) is passed through a lens (14) of an optical system. A method for detecting and detecting crystal defects near the surface that detects crystal defects based on the difference between these detection values, wherein the incident light (12) is applied to the crystal surface (11) through the lens (14) of the optical system. A method for detecting near-surface crystal defects, which is incident. 2. The incident light (12) passes through the lens (14) from the side of the lens (14) through a semi-transparent mirror (10) provided above the lens (14) of the optical system, and The detection method according to claim 1, wherein the light is incident on the surface (11). 3. A light source for irradiating light (12) of a plurality of wavelengths having different penetration depths into the same position on a crystal surface (11).
(15), a condensing means including an optical lens (14, 16) for condensing scattered light (13) in which incident light (12) from the light source (15) is scattered on the crystal surface (11) ( 17), and detection means for detecting scattered light (13) from the light collection means (17)
(18), calculating means (19) for calculating a crystal defect based on the detection result of the detecting means (18), and incident light (12) from the light source (15) to the lens (1
A near-surface crystal defect detection device, comprising: an incidence means for entering the crystal surface (11) through 4). 4. The detecting device according to claim 3, wherein the incident means includes a semi-transparent mirror provided above the lens of the optical system.