JP2818250B2 - Method and apparatus for evaluating semiconductor substrate - Google Patents

Description

Description: Object of the Invention (Industrial Application Field) The present invention relates to a method and apparatus for evaluating a semiconductor substrate for detecting a defect inside the substrate using a light scattering tomography image by a laser beam. .

(Prior Art) Conventionally, as a method for evaluating a defect in a semiconductor substrate, there is an evaluation method using light scattering tomography using laser light.

For example, a semiconductor substrate is cleaved, and a laser beam is irradiated in a direction perpendicular to the substrate when it enters the substrate by about 10 μm in a direction perpendicular to the cleavage plane. At this time, the laser light scattered by a defect or the like (light scatterer) in the substrate comes out of the substrate through the cleavage plane. Hereinafter, the laser light that has come out is referred to as scattered light. The scattered light is received by, for example, an image pickup tube and converted into an electric signal. Next, the electric signal is converted into an image and displayed on, for example, a CRT. Hereinafter, this image is referred to as a light scattering tomography image.

In this light scattering tomography image, a crystal defect or the like in the semiconductor substrate is reflected and projected. Thus, the light scattering tomography image is one means used for detecting a crystal defect or the like in a semiconductor substrate.

Further, a YAG laser is used for generating the laser light. This is because the light is well transmitted through silicon, which is a main component of a normal semiconductor substrate. Its wavelength is about 1.06
μm.

Incidentally, the value of the wavelength of 1.06 μm is very similar to the dimension (〜1.2 μm) of one element formed on the semiconductor substrate. The elements on the substrate are usually
They are formed so as to be regularly arranged to form a periodic element array. Here, when the wavelength of light incident on the substrate is close to the period of the element array formed on the substrate, interference fringes are generated in the light scattering tomography image, and defects inside the substrate are determined. There is a problem that it becomes impossible. That is, in the conventional evaluation method using light scattering tomography using laser light, evaluation cannot be performed after an element is formed on a semiconductor substrate.

If the semiconductor substrate on which the element is formed or is being formed can be evaluated, it is possible to examine what process and what kind of internal defect has occurred, and this can be a measure for improving the process in which this defect has occurred.

(Problems to be solved by the invention) The present invention has been made in view of the above points,
It is an object of the present invention to provide a method and apparatus for evaluating a semiconductor substrate that can detect defects inside the substrate even on a semiconductor substrate on which elements are regularly formed.

[Structure of the Invention] (Means for Solving the Problems) A method for evaluating a semiconductor substrate according to the present invention is directed to a semiconductor substrate for obtaining a light scattering tomography image of the semiconductor substrate by a laser beam, thereby detecting defects inside the substrate. In the evaluation method, a plurality of incident angles of the laser beam with respect to the substrate are arbitrarily changed, a plurality of the incident angles are set, the laser beam is irradiated at each of the plurality of set incident angles, and each light scattering tomography image obtained thereby Is performed to obtain one light scattering tomography image.

Further, the incident angle is at least one of the laser beams.
It is characterized in that scanning is performed as long as an optical path difference of wavelength is generated.

In addition, the evaluation apparatus includes: means for placing the semiconductor substrate and moving the semiconductor substrate in a horizontal direction; means for irradiating the substrate surface with a laser beam at a predetermined angle; and applying the laser beam to the substrate surface. Means for changing an incident angle; means for receiving scattered light generated from the inside of the substrate by the laser beam and converting the scattered light into an electric signal; and storing the electric signal obtained every time the incident angle is changed. Means for extracting each of the stored electric signals and synthesizing them, and means for converting the synthesized electric signals into one image.

(Operation) In the method for evaluating a semiconductor substrate as described above, a light scattering tomography image is obtained every time the incident angle of the laser beam to the semiconductor substrate is different. Here, if the angle of incidence of the laser light is changed so as to cause an optical path difference of one wavelength of the laser light, light scattering tomography images having phases opposite to each other are obtained, and these are superimposed on each other. When the images are combined, interference fringes can be canceled each other. Therefore, even with a substrate on which elements are regularly arranged, a light scattering tomography image free of interference fringes can be obtained.

In addition, according to the above-described device, since means for changing the incident angle of the laser light is provided, the incident angle of the laser light can be set arbitrarily.

(Embodiment) An evaluation method and an evaluation apparatus for a semiconductor substrate according to an embodiment of the present invention will be described below with reference to the drawings.

First, a method for evaluating a semiconductor substrate according to an embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a sectional view for explaining the principle of the evaluation method of the present invention.

First, as shown in FIG. 1, the elements 2 are regularly arranged on the surface of the substrate 1 with a period d. With respect to such a substrate 1, a laser beam 3 (3 ₁ , 3
₂ ) When the light scattering tomography image is obtained by irradiating
An image having interference fringes 4 to 7 as shown in the figure is obtained. As described above, the interference fringes 4 to 7 appear in both the vertical and horizontal directions. That is, both the black portions (reference numerals 4 and 6) and the white portions (reference numerals 5 and 7) of the image are portions affected by the interference fringes. Although the defect 8 inside the substrate is slightly visible, it is not a clear image, so that it is difficult to evaluate the substrate. Conventionally, the evaluation of the substrate could not be performed due to the interference fringes 4 to 7.

Therefore, in the present invention, the light scattering tomography image is obtained every time the incident angle θ of the laser beam 3 is changed by changing the incident angle θ of the laser beam 3. At this time, interference fringes occur in the obtained light scattering tomography images. However, when the respective images are combined into one, the interference fringes disappear, and a clear image as shown in FIG. 4 can be obtained. . Thus, no interference fringes appear at all, and the defects 8 inside the substrate can be clearly seen. In order to obtain the image shown in FIG. 4, for example, the incident angle θ of the light is changed until an optical path difference of at least one wavelength of the laser light 3 is generated, and several images are obtained in this range and are superposed. good.

Here, regarding the optical path difference of one wavelength of the laser beam 3, the first
This will be described in more detail with reference to FIG. 2 and FIG. As shown in FIG. 1, first, a laser beam 3, especially a laser beam 3 ₁ ,
Let's divide it into two components, 3 ₂ . This is because the laser light 3
Since the laser beam 3 has a finite width, the laser beam 3 can be divided into several components within the finite width. These laser light component 3 _1, mutual distance between the 3 ₂ are the same as the period d of the element array. First, in the case of incident angle theta = 0 ° of the laser beam from the laser light component 3 _first light source, the distance to the substrate surface (hereinafter referred optical path length), and the laser light component 3 ₂ and the optical path length is not changed at all . However,
By varying only the angle of incidence theta, a laser beam component 3 _1, between the laser light component 3 _2, the difference d · sin [theta becomes the optical path length, i.e., causing the optical path difference. If this optical path length is changed by one wavelength of the laser beam,
As shown in FIG. 2, the amplitude A from the point a to the point b due to the wave 3 'of the laser beam and the amplitude A' from the point b to the point c have mutually opposite phases.

In the present invention, images at incident angles θ that are in opposite phases to each other are superimposed on each other so that interference fringes are canceled out from each other. As a result, a clear image as shown in FIG. 4 can be obtained.

As described above, according to the evaluation method according to the present invention, it is possible to evaluate even a substrate having a regular element arrangement with a period d shown in FIG. That is, it is possible to detect an internal defect in the substrate 1 after or during the formation of the element on the substrate 1.

Next, specific numerical values are applied to the cross-sectional view of FIG. 1, and the evaluation apparatus according to the present invention will be described with reference to FIGS.

FIG. 5 is a perspective view schematically showing an evaluation device of the first embodiment according to the present invention, and FIG. 6 is a block diagram showing a processing procedure of data obtained by the evaluation device shown in FIG. FIG. 7 is a perspective view schematically showing an evaluation apparatus according to a second embodiment of the present invention.

The laser beam 3 shown in FIG. 1 easily passes through silicon.
YAG laser light is used. The wavelength λ of the YAG laser is about 1.06 μm
It is. The period d of the elements arranged on the substrate 1 is 1.2 μm.
m.

In this case, the incident angle θ that produces an optical path difference of 1.06 μm, which is the same as the wavelength λ of the YAG laser, can be obtained by the following equation.

d.sin θ = nλ (n is an integer) Here, when the values of n are 0 and 1, θ = 0 ゜ to 62.05 ゜. That is, when the incident angle θ becomes about 62.05 °, the optical path difference (d · sin θ in the figure) becomes approximately 1.06 μm.

Here, using the evaluation device shown in FIG. 5, the incident angle θ =
From 0 °, for example, every time the incident angle θ is increased by 2 °, a light scattering tomographic image is obtained, and this is increased to an incident angle θ = 64 °, for a total of 33 °.
Obtain two light scattering tomography images.

Next, the configuration and operation of the evaluation device shown in FIG. 5 will be described, and a method of processing data obtained by this evaluation device will be described with reference to FIG.

As shown in FIG. 5, a wafer 11 (corresponding to 1 in FIG. 1) divided by a predetermined cross section is placed on the sample stage 10. The sample stage 10 moves in the directions of arrows A and A 'in the figure. The cross section 12 of the wafer 11 is a mirror surface such as a cleavage surface or a mirror-polished surface. Also, the wafer 11 has
As in FIG. 1, regularly arranged elements are formed. The surface on which this element is formed is, for example, a sample stage.
It is facing 10 side. This means that the element formation surface is the stage
You don't have to face 10 side. Such a wafer 11
13 device light (YAG laser 13 light (3 in FIG. 1)
(Equivalent to). The irradiation position of the YAG laser light 13 is set to a position, for example, about 10 μm inside the substrate from the surface of the cross section 12. This is in consideration of the fact that a defect inside the wafer 11 can be detected and scattered light due to the defect can be emitted to the outside via the cross section 12. The width of the YAG laser light 13 is about 4 μm. This Y
The AG laser 13 is generated by a YAG laser generator 14 and condensed by a condenser lens 16 via an optical fiber 15 and irradiated. The condenser lens 16 is attached to a support 17. The support 17 is mounted on a rail 18 formed in an arc shape, for example, in a state of being fitted. The support 17 has a built-in pulse motor 19. The pulse motor 19 causes the support base 17 to move along the rails 18 in directions indicated by arrows B and B 'in FIG. As described above, the angle of incidence of the YAG laser beam 13 on the wafer 11 can be changed by moving the support 17 along the rail 18. Above pulse motor
19 is controlled by a pulse motor control device 20, and a control signal is transmitted to the pulse motor 19 via a cable 21.
The YAG laser light 13 applied to the element formation surface of the wafer 11 emits light scattered by internal defects to the outside of the substrate,
Discharge via section 12 above. This emitted scattered light 22
Is received by the objective lens 23. The scattered light 22 received by the objective lens 23 becomes light L1 and enters the image pickup tube 24 shown in the block diagram of FIG. 6, where the light L1 is converted into an electric signal. This electrical signal is sent to and stored in the frame memory 25. Here, scattered light can be obtained over the entire cross section 12 of the wafer 11 by appropriately moving the sample stage 10 in the direction of arrow A or A 'in FIG. The image of the scattered light obtained over the entire cross section 12 is stored in the frame memory 25 as one image. In this embodiment, since 33 images are obtained as described above, for example, the frame memory 25 having 33 or more storage frames is used. When the one image is stored in the frame memory 25, a signal notifying the completion of the storage is sent to the computer 26. The computer that detected this signal 26
Sends a signal S2 to the pulse motor control device 20 shown in FIG. The pulse motor control device 20 that has detected this signal S2
Sends a control signal to the pulse motor 19, and moves the support 17 by a predetermined amount, in this embodiment, by an amount that changes the incident angle of the YAG laser 13 by 2 °.

In the present embodiment, such an operation is repeated 33 times so that the frame memory 25 has an incident angle θ of 0 ° to
Up to 64 °, 33 images obtained every 2 ° are stored. 33
Is stored, a signal indicating completion of storage of a predetermined number is output to the computer 26. When the computer 26 detects this, each of the 33 images stored in the frame memory 25 is called, and a predetermined image combining operation is started. This image synthesizing method may be a known image synthesizing method.
When the image combination is completed, the combined light scattering tomography image is displayed on the CRT 27. An example of this combined light scattering tomography image is already shown in FIG.

Further, by the function of the computer 26, the combined light scattering tomography image can be stored in the optical disk (or magnetic disk) 28. Further, if the test data is input to the computer 26, the test data can be printed out by the printer 29,
The synthesized light scattering tomography image can be copied on paper by the hard copy machine 30.

Further, the functions of the computer 26 may be further developed and images before combining may be individually called and displayed on the CRT 27 (however, the images include interference fringes).

The individual images can be stored on the optical disk 28, the test data can be individually printed out by the printer 29, or the individual images can be copied by the hard copy 30. Optional.

Next, an evaluation device according to a second embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 7, a wafer 41 (corresponding to 1 in FIG. 1) divided by a predetermined cross section is mounted on the sample stage 40. The cross section 42 of the wafer 41 is a cleavage plane,
Or it is a mirror surface like a mirror polished surface.
On the wafer 41, elements arranged regularly are formed. The surface on which this element is formed is the sample stage
Facing the 40 side. This means that the element formation surface is the stage
You don't have to face the 40 side. Such a wafer 41
The YAG laser beam 43 (3 in FIG.
(Equivalent to). The irradiation position of the YAG laser beam 43 is set to a position, for example, about 10 μm inside the substrate from the surface of the cross section. The width of the YAG laser beam 43 is set to about 4 μm. The YAG laser light 43 is generated by a YAG laser generator built in a support base 44, collected by a condenser lens 45, and irradiated. Thus, the above
The YAG laser generator may be built in the support base 44,
As in the evaluation device shown in FIG. 5, the YAG laser generator is placed outside, and the condensing lens 45 is connected with an optical fiber or the like.
You may lead to. The support base 44 to which the condenser lens 45 is attached moves in the directions of arrows C and C 'in FIG. The sample stage 40 is mounted on a rail 46 formed in a circular shape, for example, in a state of being fitted. Further, a pulse motor 47 is connected to the center of the sample stage 40, that is, the center of the rail 46. The pulse motor 47 moves the sample stage 40 along the rail 46 in the directions indicated by arrows D and D 'in FIG. As described above, by rotating the sample stage 40 integrally with the rail 46, the incident angle of the YAG laser beam 43 with respect to the wafer 41 can be changed. The pulse motor 47 includes a pulse motor control device 48
The control signal is transmitted to the pulse motor 47 via the cable 49. The YAG laser beam 43 applied to the element formation surface of the wafer 41 emits light scattered by internal defects to the outside of the substrate through the cross section.
The emitted scattered light 50 is received by the objective lens 51. The scattered light 50 received by the objective lens 51 becomes light L1,
The light enters the image pickup tube 24 shown in the block diagram of FIG.
Are converted to electrical signals. The subsequent data processing method is as described in the first evaluation device.

However, when obtaining a light scattering tomography image of the entire cross section 42, according to the evaluation apparatus shown in FIG. 7, the support base 44 to which the condenser lens 45 is attached is moved along the wafer 41 along the arrow C or C. ′ Direction.

In addition, the pulse motor control device 48 detects the signal S2 output from the computer 26 shown in FIG. 6, sends a control signal to the pulse motor 47, and moves the sample stage 40 by a predetermined amount, in this embodiment, the YAG laser light. Move the incident angle of 43 only by 2 °.

As described above, in the evaluation apparatus according to the present invention, by moving the sample stage or the portion irradiated with the laser light so that the incident angle of the laser light to the substrate changes,
Means for changing the incident angle of the laser beam on the substrate is provided. Therefore, the incident angle of the laser beam can be set arbitrarily, and the method for evaluating a substrate according to the present invention can be realized.

Therefore, it is possible to evaluate the semiconductor substrate on which the element is formed or in the middle of the formation, and the tomographic image obtained thereby can be used to determine, for example, what kind of internal defect occurred during which process. This can be a measure for improving the process in which this defect has occurred.

[Effects of the Invention] As described above, according to the present invention, a semiconductor substrate evaluation method and an evaluation apparatus capable of detecting a defect inside a substrate even with a semiconductor substrate on which elements are regularly formed are provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the principle of the present invention, FIG. 2 is a view showing the wave of a laser beam, FIG. 3 is a light scattering tomography image at an incident angle of 0 °, and FIG. FIG. 5 is a perspective view schematically showing a first evaluation device according to the present invention, FIG. 6 is a block diagram of a data processing method according to the present invention, and FIG. It is a perspective view which shows roughly 2 evaluation apparatuses. 1 ... substrate, 2 ... element, 3 ... laser light, 4-7 ...
Interference fringe, 8 Internal defect, 10 Sample stage, 11
Wafer, 12 ... Wafer cross section, 13 ... YAG laser, 14
…… YAG laser generator, 15 …… Optical fiber, 16 ……
Condenser lens, 17 support base, 18 rail, 19 pulse motor, 20 pulse motor controller, 21 cable, 22 scattered light, 23 objective lens, 24 imaging tube,
25 …… Frame memory, 26 …… Computer, 27 …… CR
T, 28 ... disk, 29 ... printer, 30 ... hard copy, 40 ... sample stage, 41 ... wafer, 42 ... cross section of wafer, 43 ... YAG laser, 44 ... support base, 45 ...
... Condenser lens, 46 ... Rail, 47 ... Pulse motor, 48
…… Pull motor controller, 49… Cable, 50 …… Scattered light, 51 …… Objective lens.

Claims (3)

(57) [Claims] 1. A method for evaluating a semiconductor substrate, wherein a light scattering tomography image of a semiconductor substrate is obtained by a laser beam and a defect in the substrate is detected by the laser scattering tomographic image. A plurality of light scattering tomography images are obtained by irradiating the laser light at each of the plurality of set angles of incidence, and combining the obtained light scattering tomography images. A method for evaluating a semiconductor substrate, the method comprising: 2. The method for evaluating a semiconductor substrate according to claim 1, wherein said incident angle is scanned so as to produce an optical path difference of at least one wavelength of said laser light. 3. A means for placing a semiconductor substrate and moving the same in a horizontal direction; a means for irradiating a laser beam at a predetermined angle with respect to the substrate surface; and an incident angle of the laser beam with respect to the substrate surface. Means for receiving the scattered light generated from the inside of the substrate by the laser light, and converting the scattered light into an electric signal; and means for storing the electric signal obtained every time the incident angle is changed. An evaluation apparatus for a semiconductor substrate, comprising: means for extracting each of the stored electric signals and synthesizing each of the electric signals; and means for converting the synthesized electric signal into one image.