JPH08247956A - Internal defect inspection method for crystal - Google Patents

Abstract

(57) [Summary] [Purpose] The focus of the light beam with the surface of the crystal to be inspected as the reference plane is accurately and easily adjusted, and subsequent inspections are performed with this focus position as the reference. By doing so, highly reliable inspection results can be stably obtained. [Structure] A reflective layer 8 configured as a flat crystal and capable of reflecting a light beam for inspection is formed on a part of the surface of a semiconductor substrate W to be inspected. Prior to the irradiation of the light beam for inspection, as shown by the solid line, the reflection layer 8 is irradiated with the light beam, and the focus of the light beam is focused on the surface of the reflection layer 8 based on the observation result of the reflected light from the reflection layer 8. To match. The subsequent inspection is performed by moving the semiconductor substrate W within the surface and scanning the surface with a light beam focused on the surface of the reflective layer 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting minute internal defects possessed by a flat crystal such as a semiconductor substrate by using a light beam irradiated on the surface thereof.

[0002]

2. Description of the Related Art Semiconductor substrates used in the manufacture of various semiconductor devices are made by slicing a crystal such as Si, GaAs, InP into a thin flat plate, and precisely forming one surface (hereinafter referred to as the surface) on which the circuit is formed. It is obtained by polishing. Such a semiconductor substrate generally contains various impurities that are mixed in at the growth stage as a crystal body as internal defects, and the presence of these internal defects causes the semiconductor manufactured by the circuit formation on the surface to be produced. This is a factor that deteriorates the manufacturing yield of devices and reduces the reliability of product devices.

Under these circumstances, conventionally, there has been proposed an inspection method for inspecting a plate-shaped crystal body such as a semiconductor substrate or the like to know in advance whether or not an internal defect exists in these crystal bodies. One of such inspection methods is, for example, the method disclosed in Japanese Patent Laid-Open No. 24541/1992. This inspection method uses the fact that when a crystal to be inspected is irradiated with a light beam, the transmitted light to the inside is scattered by defects existing at the transmission position, and the scattered light is observed outside the crystal. This is a method of detecting the presence or absence of an internal defect based on the result.

Since most of the semiconductor substrates are opaque crystal bodies that do not transmit visible light, in the above-mentioned inspection, light that can be transmitted to the inside is used in the infrared region longer than the band gap of the crystal to be inspected. A light beam having a wavelength is used. Further, the irradiation of the light beam is performed on a surface finished with high precision in order to eliminate the influence of scattered light on the irradiation surface, and the observation of scattered light by internal defects is also performed on the surface. It is done from a different direction.

The inspection device used for carrying out the above inspection method is "K. Moriya, H. Wada, K. Hirai; J. Crystal Growth".
128 (1993) 304-309 '', a laser source emitting an infrared laser and an imaging means for observing scattered light so that the mounting stage of the semiconductor substrate to be inspected faces from different directions. Is arranged.

Due to the operation of the mounting stage, the semiconductor substrate on the mounting stage is divided into two directions (X direction and Y direction) orthogonal to each other in the surface and a direction (Z direction) orthogonal to these directions. It can be moved, and can also be moved in an oblique direction (YZ direction or the like). Further, the image pickup means has an optical system that changes the focal position according to the operation of the mounting stage and enlarges the vicinity of the irradiation position of the light beam, and is configured to take an enlarged image through this optical system. The image processing unit includes an image processing unit that performs a predetermined process (for example, binarization process, degeneration process, etc.) on the image pickup result, a display unit that displays the processed image, and the like.

The inspection of internal defects by this apparatus is carried out by placing a semiconductor substrate (crystal) to be inspected on a mounting stage, and then irradiating the surface of this semiconductor substrate with a light beam emitted from the laser source, At this time, an optical image of scattered light emitted to the surface side in the vicinity of the irradiation position is imaged by the image pickup means, and the image pickup result is displayed on the display unit after predetermined image processing by the image processing unit. It is performed by a procedure of visually observing the displayed contents, and by this observation, the presence or absence of the internal defect can be known including the size and position of each internal defect.

[0008]

In the conventional method for inspecting internal defects as described above, the main object to be inspected is a semiconductor substrate. The main purpose is to detect the presence of internal defects in the manufacture of semiconductor devices. It is to eliminate the influence. The problem in the manufacture of semiconductor devices is only the region where the depth from the surface on which the circuit is formed is about several μm, and the depth from the surface is roughly estimated.
It is important to accurately determine the presence or absence of internal defects in this region including the region of 10 μm or less, including the distribution in the depth direction from the surface.

In the above-described inspection apparatus, the focal position of the light beam emitted from the laser source is fixed on the surface of the semiconductor substrate to be inspected mounted on the mounting stage, and the semiconductor is moved by the operation of the mounting stage. Substrate in X direction and Y
By the procedure of moving in the −Z direction, the presence or absence of the internal defect can be known including the distribution state in the depth direction.

At this time, in order to know the distribution state of the internal defects in the depth direction, it is necessary to accurately focus the light beam on the surface of the semiconductor substrate. This focusing is performed for moving the mounting stage. There is a limit to making it depend on the precision of the mechanical system. So, in the past, prior to the start of the inspection, after performing focusing depending on the accuracy of the mechanical system,
The surface of the semiconductor substrate is irradiated with a light beam, the scattered light from the surface is observed, and the focus position is finely adjusted based on this observation result, so that accurate focusing is performed.

However, since the surface of the semiconductor substrate is highly accurately polished for the purpose of forming a circuit, which is the original purpose, the scattered light from the surface required for the zero point correction is small, For example, when there is an internal defect near the surface, the scattered light due to this defect is mistaken for the scattered light from the surface, which makes it difficult to identify the surface, and there is a high possibility that incorrect focusing is performed. There is a problem in that the reliability of the inspection performed while maintaining the above-mentioned deteriorates, and the correct distribution of internal defects cannot be obtained.

The present invention has been made in view of such circumstances, and the focusing of the light beam onto the surface of the crystal body to be inspected is performed with high precision and easily, and the reliability of the subsequent inspection is improved. It is an object of the present invention to provide a method for inspecting an internal defect of a crystal body, which can stably obtain highly reliable inspection results.

[0013]

A method for inspecting an internal defect of a crystal body according to the present invention comprises irradiating a surface of a flat crystal body with a light beam having a wavelength capable of transmitting the crystal body, By observing the scattered light of the light beam due to the defect inside the body, in the internal defect inspection method of the crystal body to detect the presence or absence of the defect based on the observation result at each focal position, in the part on the surface The reflection layer of the light beam is formed, the irradiation of the reflection layer is performed prior to the irradiation of the light beam for the detection, and the focus position of the light beam is based on the observation result of the reflected light from the reflection layer. It is characterized by adjusting.

[0014]

In the present invention, a reflecting layer made of a material capable of reflecting the light beam is formed on a part of the surface of the crystal to be inspected, which is irradiated with the light beam, and is placed on the mounting stage. Prior to the irradiation of the light beam for the inspection performed by mounting the crystal on, the light beam is first irradiated onto the formation portion of the reflection layer and reflected on the reflection layer, and the observation result of the reflected light Adjust the focus position of the light beam based on, to properly focus on the surface of the reflective layer, the subsequent inspection adjusts the focus position in consideration of the thickness of the reflective layer,
Correctly focus the light beam on the surface. In addition,
If the thickness of the reflective layer is thin enough (several hundreds to thousands of angstroms), it is not necessary to adjust the focus position and the inspection can be performed with the focus position adjusted on the surface of the reflection layer. .

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a schematic view showing an example of an inspection apparatus used for carrying out the method for inspecting an internal defect of a crystal according to the present invention (hereinafter referred to as the method of the present invention).

The basic structure of the inspection apparatus shown in the figure is based on the above-mentioned "K. Moriya, H. Wada, K. Hirai; J. Crystal Growth 1
28 (1993) 304-309 ”, and as shown in the figure, the supporting leg 10 is formed with high precision in a vertical direction on the vibration damping base 1 that blocks the vibration transmission from the outside. And a flat mounting stage 2 inclined at a predetermined angle with respect to the upper end of the support leg 10 and mounted horizontally on the mounting surface of the mounting stage 2 facing upward. A laser source 3 for emitting an infrared laser is arranged at a position facing directly from the one side, and an image pickup means 4 is arranged at a position facing the same from vertically above.

The mounting stage 2 at the tip of the supporting leg 10 can be moved in the horizontal direction and in a direction orthogonal to this in the mounting surface described above, and can be moved in the vertical direction using the supporting leg 10 as a guide. It is configured to be operable. The semiconductor substrate (crystal) W to be inspected is mounted on the mounting surface of the mounting stage 2 with one surface to be inspected facing upward, and the semiconductor substrate W thus mounted is: By the operation of the mounting stage 2 described above, in addition to the two directions (X and Y directions) orthogonal to each other in the one plane, it is possible to separately move in the directions (Z direction) orthogonal to each of them. By the combined operation of the Y direction and the Z direction, the semiconductor substrate W can be moved in a direction parallel to the surface (YZ direction).

The operation of the mounting stage 2 for moving the semiconductor substrate W is performed in accordance with a drive signal given from the stage controller 6 to a driving means (not shown) attached to the mounting stage 2. , And is issued according to a control signal from the measurement control unit 5 using a microprocessor.

The laser source 3 which faces the mounting surface of the mounting stage 2 configured as described above from the horizontal side and the image pickup means 4 which faces the mounting surface from above vertically are mounted on the damping base 1 by a supporting means (not shown). It is fixed. As shown in the figure, the laser source 3 uses a reflecting mirror to change the optical path of the infrared laser oscillated by the laser oscillator 30.
It is converted by 31 and is condensed by the objective lens 32, and is irradiated as a light beam focused on the surface of the semiconductor substrate W mounted on the mounting stage 2. Focusing of the light beam is performed by operating the mounting stage 2 according to a drive signal from the stage control unit 6.

On the other hand, the image pickup means 4 is a TV as an image pickup device.
On the incident side of the camera 40, an enlarging cylinder 41 having a lens (not shown) is provided facing the mounting stage 2, and the surface of the semiconductor substrate W mounted on the mounting stage 2 is magnified through the enlarging cylinder 41. The TV camera 40 takes an image, and an image processing unit 42 that performs a predetermined process on the image obtained by the image pickup and a display unit (CRT) that displays the processed image.
Display) 43 and.

The magnifying barrel 41 has a focus adjusting mechanism 44 for adjusting the focus position by moving the built-in lens in the optical axis direction.
Is attached, which is driven by a drive signal given from the focus control section 7, so that the image pickup by the TV camera 40 is performed in accordance with the focus position of the light beam emitted from the laser source 3. is there. As the focus position adjusting mechanism 44, a known mechanism used in various optical devices can be used.

The inspection of the internal defect by the inspection apparatus configured as described above is performed by placing the semiconductor substrate W to be inspected on the mounting stage 2 and then irradiating the surface of the semiconductor substrate W with the light emitted from the laser source 3. This is performed by the procedure of irradiating the beam, and at this time, the vicinity of the irradiation position is enlarged by the enlargement cylinder 41 and imaged by the TV camera 40. The irradiation position of the light beam is scanned along the surface of the semiconductor substrate W by the operation of the mounting stage 2 according to the drive signal from the stage controller 6, and the TV is displayed.
The image pickup by the camera 40 is performed by the focus adjusting mechanism 44 in accordance with the focus position of the light beam.

The image pickup result of the TV camera 40 is the image processing unit 42.
Given to the display unit 43, after being subjected to image processing such as extraction of an infrared image having a wavelength corresponding to the light beam, binarization processing based on a predetermined threshold value, and degeneracy processing. And is given to the measurement control unit 5 and stored in the storage means attached thereto.

As shown by the broken line in FIG. 2, when the light beam is transmitted through the semiconductor substrate W to be inspected, the image displayed on the display unit 43 is scattered by the internal defect A existing in this transmission path. The presence or absence of the internal defect A of the semiconductor substrate W is detected by observing the display image of the display unit 43, including the distribution in the depth direction at each position on the surface.

In the method of the present invention performed by using the inspection apparatus as described above, as the semiconductor substrate W to be inspected, as shown in FIG. 2, the reflection layer 8 is formed on a part of one surface irradiated with the light beam. The formed semiconductor substrate W is used. The reflective layer 8 can reflect an infrared beam having a wavelength that passes through the semiconductor substrate W and is a material that can be easily deposited on the semiconductor substrate W (for example, platinum, gold, aluminum, or the like).
It is formed of a metal material such as silver) having a sufficient thickness to reflect light.

In FIG. 2, the reflective layer 8 is formed in the vicinity of the peripheral edge of the semiconductor substrate W which is not used for forming the semiconductor device, but the position of the reflective layer 8 is not limited to this, and the surface is not limited to this. It can be formed at an appropriate position above. Further, the planar size and shape of the reflective layer 8 are not limited, but it is desirable to make the size as small as possible within the range that does not hinder the alignment of the light beam described later. Specifically, the plane size of one semiconductor device manufactured using the semiconductor substrate W as a material is sufficient.

The method of the present invention is started on the condition that the semiconductor substrate W having the reflection layer 8 as described above is mounted on the mounting stage 2 and, for example, a predetermined inspection start operation is performed. Then, in the method of the present invention, in order to make the focal point of the light beam emitted from the laser source 3 exactly in the vicinity of the surface of the semiconductor substrate W as a preparation performed before the above-described operation for the regular inspection, the inspection is performed. The focal position of the light beam at that time is corrected based on observation of the reflected light from the reflective layer 8.

FIG. 3 is a flow chart showing this correction procedure. After the inspection start operation is performed, first, the irradiation position of the light beam is irradiated so that the light beam emitted from the laser source 3 is irradiated on the portion of the semiconductor substrate W on the mounting stage 2 where the reflective layer 8 is formed. It is changed, and the imaging region by the imaging means 4 is changed following this (step 1).
This operation is performed by moving the mounting stage 2 and moving the semiconductor substrate W in the X and Y directions by the operation of the stage controller 6 according to the control signal from the measurement controller 5.

After completing such alignment, the focal position of the light beam emitted from the laser source 3 is sequentially changed within a predetermined range (step 2), and the image pickup means 4 is used at each position. Imaging is performed (step 3), and it is determined based on the imaging result whether the focal position of the light beam matches the surface of the reflective layer 8 (step 4).

The change of the focal position of the light beam in step 2 is performed by moving the mounting stage 2 on which the semiconductor substrate W is mounted by the operation of the stage controller 6 according to the control signal from the measurement controller 5, as described above. It is done with all the effort. At this time, the focus adjusting mechanism 44 attached to the image pickup means 4 is also operated so that the image pickup is performed according to the focal position of the light beam in the subsequent step 3.

By the above-described operation, the light beam emitted from the laser source 3 is irradiated to the portion where the reflective layer 8 is formed on the surface of the semiconductor substrate W, as shown by the solid line in FIG. The reflection layer 8 is formed by using a material capable of reflecting the light beam, and the light beam irradiated as described above is reflected by the reflection layer 8 and the imaging unit 4 exposed to the irradiation site has no reflection. The spot of the light beam on the surface of the reflective layer 8 is imaged.

The determination in step 4 is made, for example, by comparing the size of the spot image that appears in the image pickup result of the image pickup means 4 obtained each time the focus position is changed, and this determination is made for each change. Image processing result of the imaging result at the position
It can be sequentially displayed on the display unit 43 via 42, and can be performed by an inspection operator who visually observes the display unit 43. Further, the imaging result is given to the measurement control unit 5 via the image processing unit 42, It can also be performed according to a predetermined determination logic stored in the measurement control unit 5. At this time, since the high-level reflected light from the reflective layer 8 serves as the determination reference, the above-described determination can be performed with high accuracy without being influenced by the scattered light from the inside of the semiconductor substrate W.

As a result of the above determination, when it is determined that the focal point of the light beam coincides with the surface of the reflective layer 8, the scanning position of the light beam is changed while maintaining the focal point position at this time, and the entire region of the semiconductor substrate W is changed. Is performed (step 5). At the time of this inspection operation, since the light beam which is correctly focused on the surface of the reflective layer 8 (in the vicinity of the surface of the semiconductor substrate W) is used, the presence or absence of the internal defect by the procedure as described above is determined by the accurate depth direction. It will be detected including the distribution.

Incidentally, prior to the transition to the above-mentioned inspection operation, the focal position of the light beam is finely adjusted in consideration of the thickness of the reflective layer 8 so that the focal position is adjusted to the surface of the semiconductor substrate W. Good. However, as described above, the thickness of the reflective layer 8 is sufficient as long as it reflects light, and in reality, it is only about several hundred to several thousand angstroms, and the surface of the reflective layer 8 at this level. There is almost no possibility that an accuracy problem will occur due to the inspection with the focus on.

FIG. 4 is a comparison of the results obtained by carrying out the conventional inspection method and the method of the present invention using a semiconductor substrate made of As-Grown silicon crystal as a sample, and comparing them with each other. The horizontal axis represents the depth from the surface of the specimen, and the vertical axis represents the detection density of internal defects at each depth position. When comparing the result by the conventional inspection method shown in white in the figure with the result by the method of the present invention which is also shown by hatching, particularly, the inspection region near the surface of the specimen (the depth from the surface is It can be seen that the density obtained by the method of the present invention in the range of 0 to 11.25 μm) is sufficiently higher than that by the conventional method, and the difference from the density in other areas having a large depth from the surface is small. .

The As-Grown silicon crystal used as the test specimen generally contains internal defects as oxygen precipitates with a substantially constant distribution in the depth direction. It is clear that the results according to the inventive method are close to the actual distribution. On the other hand, according to the conventional inspection method, it is apparent that the defect distribution state different from the actual state is obtained in the inspection region near the surface. This is because the focusing of the light beam on the surface of the specimen before the start of the inspection is performed based on the slight reflected light from the precisely polished surface, and as a result, the surface of the specimen and the focal position of the light beam are This is because the inspection is executed based on the incorrect correspondence relationship of

When a semiconductor substrate is to be inspected, as described above, in order to eliminate the influence of the presence of internal defects on the manufacturing of semiconductor devices, in particular, the distribution of internal defects near the surface on which the circuit is formed is accurate. It is important to know that the effective implementation of the method of the present invention is
It is clear from the result of FIG.

In this embodiment, the case where the semiconductor substrate W is the inspection object is described, but the method of the present invention is
It is needless to say that the same effect can be obtained by being applicable to the inspection of all flat crystal bodies.

[0039]

As described in detail above, in the method of the present invention, a reflective layer is formed on a part of the inspection surface of a flat crystal, and the crystal is placed on a mounting stage. Prior to the irradiation of the light beam for the inspection to be performed, the formation of the reflective layer is irradiated with the light beam, and the focus of the light beam is adjusted based on the observation result of the reflected light from the reflective layer.
This adjustment can be performed with high accuracy and easily, and reliable inspection results can be stably obtained with the adjusted focus as a reference. For example, by applying it to the inspection of a semiconductor substrate, this is used as a material. It can contribute to the improvement of manufacturing yield of semiconductor devices and the reliability of product devices.
The present invention has excellent effects.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an inspection apparatus used for carrying out the method of the present invention.

FIG. 2 is a perspective view showing an example of a semiconductor substrate to be inspected used for carrying out the method of the present invention.

FIG. 3 is a flowchart showing a procedure for carrying out the method of the present invention.

FIG. 4 is a graph showing an inspection result by the method of the present invention in comparison with that by a conventional inspection method.

[Explanation of symbols]

 1 Vibration suppression base 2 Mounting stage 3 Laser source 4 Imaging means 5 Measurement control unit 6 Stage control unit 7 Focus control unit 30 Laser oscillator 32 Objective lens 40 TV camera 41 Enlarging tube 42 Image processing unit 43 Display unit 44 Focus adjustment mechanism A Internal defect W Semiconductor substrate

Claims (1)

[Claims] 1. A surface of a flat crystal body is irradiated with a light beam having a wavelength capable of passing through the crystal body, and scattered light of the light beam due to defects inside the crystal body is observed,
In the internal defect inspection method of the crystal for detecting the presence or absence of the defect based on the observation result at each focal position, a reflective layer of the light beam is formed on a part of the surface, and light for the detection is formed. An internal defect inspection method for a crystal body, comprising: irradiating the reflective layer before irradiating the beam, and adjusting a focal position of the light beam based on an observation result of reflected light from the reflective layer.