JPH10293102A - Detecting method of defect in semiconductor or the like - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect accurately the internal defect of a semiconductor or the like. SOLUTION: In this method, a laser beam 101 is made incident on an object 105 to be inspected constituted of a semiconductor wafer, a scattering image formed by the scattered light generated thereby from the object 105 is obtained through a microscope and detection of an internal defect of the object 105 is executed on the basis of the image. In this case, a normal line 106 of the surface of the object 105, an observational optical axis 108 of the microscope and an incident light axis 110 of the laser beam 101 are so disposed as to be within the same plane and the incident light axis 110 of the laser beam 101 is made to enter the object 105 obliquely from above on one side and to proceed through the object 105 downward on the other side, becoming the optical axis 102 of retracted light 104, while the microscope is disposed so that the object 105 be observed from above on the other side. Thereby the whole of the scattering image of the defect brought about by the refracted light 104 is observed by the microscope.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for illuminating an internal defect of an object to be inspected such as a semiconductor wafer by using a laser beam or the like and observing the scattered light thereof for detection.

[0002]

2. Description of the Related Art FIG. 4 of the conventionally known Japanese Patent Application Laid-Open No. Hei 4-24541 shows that the depth of a laser beam incident on a test object made of gallium arsenide by appropriately selecting the wavelength of the laser beam to be incident. When the internal defect of the test object made of gallium arsenide is measured due to such characteristics, for example, when a laser beam having a wavelength of about 900 nm is used, the surface of the test object can be measured. It is described that the laser beam incident from the front side can be sufficiently attenuated near the back surface (line 13 in the upper right column of the sixth sheet to line 11 of the lower column in the sixth sheet). Also, JP-A-3-238348 and JP-A-4-268.
No. 45 discloses a method for measuring internal defects of a transparent body using a plurality of wavelengths having different transmission characteristics. In this method, optical information at a plurality of wavelengths is compared to detect internal defects by distinguishing from surface defects. Is described.

[0003]

The above-mentioned known Japanese Patent Application Laid-Open No. Hei 4-
As disclosed in Japanese Patent No. 24541, as shown in FIG. 4, the depth of penetration into a test object is controlled by applying the absorption characteristics of an incident laser beam. JP-A-3-238348 and JP-A-Hei 4
The same applies to Japanese Patent Application Publication No. 26845, but in each case, it is not possible to detect a surface defect or a defect inside a certain depth, even if the depth of the object can be controlled. That is,
Even if the depth into the test object is controlled, this means that information up to the controlled depth can be obtained, and not that information obtained only at that depth can be obtained. In order to accurately obtain information on internal defects in the depth direction of a semiconductor wafer or the like, the normal to the surface of the test object, the observation optical axis of the microscope, and the incident optical axis of the laser beam must be in the same plane. And the incident optical axis of the laser beam is obliquely incident on the object to be measured from one side above, and travels inside the object downward as the optical axis of refracted light toward the other side downward. When the microscope is arranged so as to observe the object to be inspected from above the other side, the whole can be observed.

[0004]

According to the present invention, a laser beam 101 is incident on a test object 105 formed of a semiconductor wafer, and a scattered image generated by the scattered light from the test object 105 is transmitted through a microscope 109. In the method for detecting an internal defect of the object to be measured 105 based on this, a normal 106 of the surface of the object to be measured 105, an observation optical axis 108 of the microscope 109, and an incident optical axis of the laser beam 101 Numerals 110 are arranged so as to be in the same plane, and the incident optical axis 1 of the laser beam 101 is
Reference numeral 10 denotes a refracted light 104 which is obliquely incident on the object to be measured 105 from one side upper side and moves the inside of the object to be measured 105 downward toward the other side.
The optical axis 102 of the microscope 109
Are arranged so as to observe the test object 105 from above the other side, and the bending light 10
4 is a method for detecting a defect in a semiconductor or the like in which a scattered image of the defect is observed as a whole.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus which can carry out the method for detecting a defect in a semiconductor or the like according to the present invention will be described with reference to FIGS. 1 and 2. In FIG. 1, reference numeral 103 denotes a semiconductor or the like in advance as shown in FIG. , The reflectance R and the scattering intensity S with respect to the wavelength λ of the incident light are obtained in a graph, and a diagram of the change in the scattering intensity S from the surface defect and the change in the scattering intensity S from the internal defect is created. A laser device for outputting a laser beam 101 having a wavelength λ1 for generating a relatively large amount of optical information on the surface of a semiconductor or the like and a wavelength λ2 for generating a relatively large amount of optical information inside a test object. Lens 107 for irradiating the test object 105 with light, and a microscope 109 for receiving scattered light from the test object 105 caused by the laser beam 101 and enlarging the scattered image. And an image sensor 111 for photoelectrically converting the enlarged scattered image to obtain an image signal of the scattered image.
Projection means 113 for projecting a pattern used for focusing the microscope 109 on the test object 105 onto the test object 105, and an angle θ between the normal line of the test object 105 and the optical axis of the microscope 109. And a stage 115 which is held at 5 to 35 degrees and is moved by a driving means (not shown).

[0006] The microscope 109 is connected to the objective lens 1.
17 and an imaging lens 119. The projection means 113 is illuminated by the spatial modulation element pattern 121, the light source 123, the convex lens 125 for irradiating the light emitted from the light source 123 to the spatial modulation element pattern 121, the diffusion plate 127 and the convex lens 129, and A light projection lens 131 and a half mirror 133 for forming an image of the spatial modulation element pattern 121 at the focal position of the microscope 109 are provided. The spatial modulation element pattern 121 is disposed on the focal plane of the half mirror 133.

[0007]

Next, the operation will be described. FIG. 2 is a principle diagram illustrating the principle of observation of the test object 105 by the apparatus of FIG. In the figure, reference numeral 201 denotes a TV camera including the image sensor 111 and the imaging lens 119. The TV camera 201 and the objective lens 117 constitute an observation system. Normal line (line parallel to the surface) 106 of the surface of the test object 105 such as a semiconductor wafer
The observation optical axis 108 of the TV camera 201 of the observation system and the incident optical axis 110 of the laser beam 101 are arranged so as to be in the same vertical plane when viewed from above.
05 and the incident optical axis 1 of the laser beam 101 from above one side
And the laser beam 101 is refracted in the test object 105.
The optical axis 102 of the one bending light 104 is set so that the angle α formed with the vertical line is approximately 16%. This refracted light 10
4 is observed with the TV camera 201 inclined to the other side by the angle θ, the field of view 203 is as shown in the drawing of FIG.
The observation can be performed by being divided into measurement areas 1a, 2a, 3a, and 4a corresponding to the depths of the layers 1b, 2b, 3b, and 4b of the test object 105.

More specifically, the light source 123 is turned on by the apparatus shown in FIG. 1, and the spatial light modulating element pattern 121 is passed through the convex lens 125, the diffusion plate 127 and the convex lens 129.
And the image of the pattern 121 for focusing is projected onto the test object 105 via the objective lens 117. Next, the stage 115 is controlled and moved so that the contrast of the projected image of the spatial modulation element pattern 121 is maximized between the measurement areas 2a and 3a. Next, the stage 115 is moved longitudinally by a predetermined distance so that the focal position corresponds to the depth position of the boundary between the layers 2b and 3b. Next, the focal point 205 of the laser beam 101 from the laser device 103 is set at the measurement area 1a, which is a desired detection target layer.
Laser beam 1 corresponding to 2a, 3a and 4a
Adjust the position of 01. As a result, the measurement areas 1a to 4a in the visual field 203 correspond to the layers 1b to 4b.
To the extent that b-4b is covered, an image such as a defect in the visual field 203 can be obtained together with information on the layer in which it exists. The depth of field in this case is, for example, about 40 μm when the magnification of the observation system is 20 ×, and 15 μm when the magnification of the observation system is 50 ×.
It is about μm. Further, the projection of the spatial modulation element pattern 121 is stopped when it becomes unnecessary so as not to hinder observation. This is not the case when a pattern having no pattern that hinders observation is used as the spatial modulation element pattern 121.

Further, in order to perform detection in a range beyond the visual field 203, the laser beam 101 is reciprocated in a direction perpendicular to the maximum tilt direction of the test object 105, and the test object 105 is moved in the maximum tilt direction. By moving the object 105 in parallel to the direction, as shown in FIG.
For example, the scattered image of a defect in a three-dimensional region of about 200 × 200 × 16 μm shows any one of the measurement areas 1a to 4a.
At the same time as the information on the depth position that was detected.

FIG. 4 is an explanatory diagram for explaining the resolution in this detection. As shown in the drawing, the resolution in the surface direction of the test object 105 defined by the interval between each scanning line in the scanning by the laser beam 101 is about 0.4.
Assuming that the refraction angle α of the laser beam 101 in the test object 105 is about 16%, the resolution in the depth direction is about 1.
4 μm. The resolution in the depth direction can be improved to about 1 μm by improving the resolution in the surface direction.

FIG. 5 is a schematic diagram showing a defect detection method according to another embodiment of the present invention. Here, as a laser device,
A dye laser, a Tit sapphire laser, or the like, which is a wavelength tunable laser, is used. The laser beam 101 emitted from the laser is expanded via a collimator 301 and is irradiated on a test object 105. In this case, it is not necessary to divide the measurement area in the field of view of the TV camera 201. The direction of the normal to the surface of the test object 105 is made to coincide with the direction of the optical axis of the TV camera 201.
Otherwise, the configuration is the same as in FIG.

FIG. 6 is used as a test object 105. SOI (Silicon on Insulat) with multilayer structure of Si crystal
or) is a cross-sectional view of a structured wafer. This wafer is Si substrate 4
01, a 0.2 μm thick oxide film (Si
O ₂ ) layer 403 and a 1 μm thick layer
It has a Si layer 405.

In this configuration, to detect a defect,
The observation system is focused on the surface of the wafer in the same manner as described above. However, here, the Si layer 405 within the depth of focus is used.
Further, since it is intended to detect a defect localized in the SiO ₂ layer 403, there is no need to further adjust the focal position. Then, the irradiation area of the laser beam 101 is set to the TV camera 201.
Irradiation is performed so as to coincide with the visual field of, and observation is performed.

FIG. 7 is an explanatory view showing the state when the laser beam 101 is irradiated on the wafer. FIG. 3A shows a case where the reflectance on the wafer surface is large, and FIG. 3B shows a case where the reflectance is small. In addition, the graphs on the left side of each of FIGS. 7A and 7B are graphs showing the change of the light intensity 1 of the refracted light by the laser beam 101 having the incident intensity of 1 ° with respect to the wafer depth D. Note that a curve 509 is an attenuation curve due to absorption.

As shown in FIG.
Is separated into reflected light 501 and refracted light 503, and the interference between the reflected light on the surface of the wafer (Si crystal having a refractive index of 3.5) and the surface of the SiO ₂ layer 403 (refractive index of 1.5) The reflectivity R on the wafer surface fluctuates with a larger width as shown in FIG. 8 in accordance with the wavelength λ of the laser light than in the case of a wafer containing only Si crystals. When the reflectance is large (λ2, λ4
,..., Λ12), as shown in FIG. 3A, when the intensity of the scattered light 507 from the defect 505 at the boundary between the Si layer 405 and the SiO ₂ layer 403 is small and the reflectance is small (λ2,
.lambda.3,..., .lambda.11) become larger as shown in FIG.

Therefore, wavelengths λ 1, λ 3 having low reflectance
,..., Λ11 using the laser beam 101,
A scattered image from a defect inside the layer 403 is effectively detected, and a scattered image from dust or a scratch on the wafer surface is mainly detected by using a laser beam having a wavelength λ2, λ4,...
Then, by comparing these scattered images, surface defects and internal defects are clearly distinguished. Further, as shown in FIG. 8, the vertical vibration of the reflection intensity due to the interference has a wavelength of 4
Observed above 00 nm. Therefore, since light having a wavelength of 400 to 2,000 nm sufficiently enters the inside of the layer, internal defects are observed using laser light in this wavelength range. On the other hand, light having a wavelength of less than 400 nm does not enter the inside of the layer. Surface defects may be observed using laser light of ６650 nm or ordinary light, and internal defects and surface defects may be distinguished.

In addition, instead of changing the wavelength of the laser beam, as shown in FIG.
At the wavelength λ / 2 (=
400-1300 nm) and a second harmonic generation element 805 having a wavelength λ, which is incident on a wafer, and scattered light from surface defects and internal defects is scattered light of the fundamental wave and the second harmonic, respectively. Alternatively, an image may be formed using another observation system.

FIG. 10 shows an example of the scattered image thus obtained. However, as for the wafer to be inspected 105, the thickness of the Si layer 405 is 1 μm and the thickness of the SiO ₂ layer 403 is 0.4 to 0.5 μm, and as shown in FIG. The surface 11 is left as it is, but the other half is a surface 14 exposing the pits 13 of the internal defect by etching.
Is used. FIG. 10A shows a wavelength of 940 nm.
500 μm in which the internal scatter image due to the laser light
FIG. 4B shows the state of the visual field in four directions, and FIG.
2 shows the state of the field of view of the same portion where the surface scattered image by the laser light appears remarkably. Portion 11a corresponds to surface 11, and portion 14a corresponds to surface 14. In FIG. 10B, dust images on the surface 11 appear at the portion 11a, and countless minute pit images on the surface 11 appear at the portion 14a. Portions 11a and 14a of FIG.
, No minute pit image appears, and numerous dusts, scratches and internal defects on the surface appear innumerably. FIG.
Is a graph showing changes in reflectance R and scattering intensity S with respect to the wavelength λ of incident light on the wafer. In the figure, a curve 151 shows a change in reflectance by calculation, a curve 153 shows a change in reflectance by actual measurement, a curve 155 shows a change in scattering intensity from a surface defect, and a curve 157 shows a change in scattering intensity from an internal defect. From this graph, it can be seen that laser light having a wavelength of 940 nm is suitable for detecting internal defects, and laser light having a wavelength of 1000 nm is suitable for detecting surface defects.

FIGS. 13A and 13B show another test object 10.
5 the same place, the wavelength 1000n reaching inside
The state of a visual field of 500 μm square when observed with a laser beam of m and a laser beam of a wavelength of 451 nm is shown. By comparing the two, a scattered image from an internal defect can be recognized.

[0020]

As shown in FIG. 4 of the above-mentioned Japanese Patent Application Laid-Open No. Hei 4-24541, the depth of penetration into the object to be inspected by applying the absorption characteristics of the incident laser beam. This point is described in
Japanese Patent Application Laid-Open No. 238348/1992 and Japanese Patent Application Laid-Open No. Hei 4-26845 are also similar. Can not. That is, even if the depth into the object to be inspected is controlled, this means that information up to the controlled depth can be obtained, and not that the information is further advanced to obtain only the depth. However, according to the present invention, a laser beam 101 is made incident on a test object 105 made of a semiconductor wafer, and a scattered image generated by the scattered light from the test object 105 is reflected by a microscope 1.
09 and detecting the internal defect of the object to be detected 105 based on the detected object.
The normal 106 of the surface, the observation optical axis 108 of the microscope 109, and the incident optical axis 110 of the laser beam 101
Are arranged so as to be on the same plane, and the incident optical axis 110 of the laser beam 101
The microscope 109 is obliquely incident on the object 5 and travels in the test object 105 toward the lower side on the other side as the optical axis 102 of the refracted light 104.
5 so that the microscope 109 can be observed.
This is a method for detecting a defect in a semiconductor or the like in which a scattered image of the defect due to the bending light 104 is observed as a whole. (A) The normal 106 of the surface of the test object 105 and the microscope 109 Since the observation optical axis 108 and the incident optical axis 110 of the laser beam 101 are arranged so as to be in the same plane, the microscope 109 can favorably observe a defect inside the test object 105. (B) Since the incident optical axis 110 of the laser beam 101 is obliquely incident on the test object 105 from above one side of the test object 105, the incident optical axis 110 is
Refracted light 104 travels downward in the area 05 on the other side. (C) The microscope 109 is the refracted light 104 of the test object 105
Is arranged so as to be observed from the upper side on the other side, so that there is an effect that the scattering image of the defect caused by the bending light 104 can be observed by the microscope 109 as a whole.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of a defect detection device.

FIG. 2 is a principle diagram for explaining the observation principle of the first embodiment.

FIG. 3 is an explanatory diagram in which a test object is scanned in a raster scan.

FIG. 4 is an explanatory diagram of resolution.

FIG. 5 is a schematic diagram of a defect detection method according to another embodiment.

FIG. 6 is a sectional view of a wafer having a multilayer structure.

FIG. 7 is an explanatory diagram when a laser beam is applied to a wafer having a multilayer structure.

FIG. 8 is a graph showing the reflectance on the surface and inside of the wafer.

FIG. 9 is an explanatory diagram of a laser beam including a fundamental wave and a second harmonic.

FIG. 10 is a schematic view of the wafer obtained from FIG. 9;

FIG. 11 is a perspective view of FIG. 10;

FIG. 12 is a graph showing details of the graph in FIG. 8;

FIG. 13 is a state diagram of a scattered image of an internal defect.

[Explanation of symbols]

101: irradiation laser beam, 102: optical axis, 103: laser device, 104: refracted light, 105: test object, 106: normal, 107: condenser lens, 108: optical axis, 109: microscope, 110: light Axis 111, imaging device 113, projection means 115, stage 117, objective lens 119
Imaging lens, 121 ... spatial modulation element pattern, 123 ...
Light source, 125: convex lens, 127: diffusion plate, 129: convex lens, 131: light projecting lens, 133: half mirror.

Claims (1)

[Claims] A laser beam is made incident on a test object made of a semiconductor wafer, and a scattered image generated by the laser light from the test object is generated by a microscope.
09 for detecting defects on the surface and inside of the object to be measured 105 based on the normal line 106 of the surface of the object to be measured 105, the observation optical axis 108 of the microscope 109 and the laser The incident optical axis 110 of the beam 101 is disposed so as to be in the same plane, and the incident optical axis 110 of the laser beam 101 is obliquely incident on the test object 105 from above one side and enters the test object 105. The microscope 109 is arranged so as to be viewed downward from the other side and becomes the optical axis 102 of the refracted light 104, and the microscope 109 is arranged so as to observe the test object 105 from the upper side on the other side. A method for detecting a defect in a semiconductor or the like in which a scattering image of the defect by the light 104 is observed as a whole.