Method for detecting microcrack

Abstract

A method for detecting a microcrack (34) generated on a surface (33) of a silicon substrate (32), the method comprising: detecting a height profile of the surface (33) of the silicon substrate (32) by using a quantitative phase microscope; extracting a raised region (35) of the surface (33) on the basis of the detected height profile; and identifying the extracted raised region (35) of the surface (33) as a region in which the microcrack (34) is present.

Description

Microcrack detection method

[0001] The present invention relates to a method for detecting microcracks that occur in a wafer or an insulating film formed on the surface of the wafer.

[0002] In a semiconductor manufacturing process, defects may occur in a wafer or an insulating film formed on the surface of the wafer, etc. As methods for detecting such defects during the manufacturing process, Patent Document 1 discloses a method for detecting defects using a laser beam and a method for detecting defects using light scattering under an applied static stress.

[0003] International Publication No. 2011 / 062279A1

[0004] Incidentally, minute cracks of several hundred nanometers or less, called microcracks, may occur in wafers or in insulating films formed on the wafer surface. In recent years, with the miniaturization of semiconductors, there has been an increasing need to detect such microcracks. However, although microcracks can be detected using a scanning electron microscope, they have been difficult to detect using optical devices.

[0005] Therefore, an object of the present disclosure is to detect microcracks using an optical device.

[0006] The microcrack detection method disclosed herein is a method for detecting microcracks that have occurred on the surface of an object to be inspected, and is characterized by using a quantitative phase microscope to detect a height profile of the surface of the object to be inspected, extracting a raised area on the surface based on the detected height profile, and identifying the extracted raised area on the surface as an area where a microcrack exists.

[0007] This disclosure utilizes the characteristic that when a microcrack occurs, the area around the microcrack rises slightly. A quantitative phase microscope can detect height with high accuracy of several nanometers. However, the horizontal resolution of a quantitative phase microscope is not very high, at around 1 μm (1,000 nm). For this reason, simply inspecting the surface of an object to be inspected with a quantitative phase microscope makes it difficult to detect microcracks with widths of several hundred nanometers or less (0.5 to 0.6 μm or less).

[0008] Meanwhile, research by the inventors has revealed that the area surrounding a microcrack is raised by approximately 20-30 nm to 100 nm within a range of 10 μm to 20 μm (10,000 nm to 20,000 nm). Such raised areas can be detected using a quantitative phase microscope. Therefore, the present disclosure employs a method for detecting the height profile of the surface of an object to be inspected using a quantitative phase microscope, extracting a raised area on the surface based on the detected height profile, and identifying the extracted raised area on the surface as the area where a microcrack exists. This makes it possible to detect microcracks of several hundred nanometers or less (0.5 to 0.6 μm or less) using an optical device such as a quantitative phase microscope, which has low horizontal resolution.

[0009] In the microcrack detection method of the present disclosure, the position and shape of the microcrack may be identified based on the discontinuity in the height profile contained in the extracted raised region.

[0010] The inventors' research has revealed that there may be a difference in height between one side of a microcrack and the other side of the microcrack of approximately 20-30 nm to 100 nm. Furthermore, as explained above, quantitative phase microscopy can detect height with high accuracy of several nanometers. Therefore, when observing microcracks with a quantitative phase microscope, the microcracks appear as discontinuities in the height profile. Therefore, the position and shape of the microcrack can be identified based on the discontinuities in the height profile. This makes it possible to detect microcracks of several hundred nanometers or less (0.5-0.6 μm or less) using an optical device such as a quantitative phase microscope, which has low horizontal resolution.

[0011] In the microcrack detection method of the present disclosure, the height profile may be displayed on a display with the color continuously changing according to the height, and discontinuous portions may be determined as areas where the color is discontinuous.

[0012] This makes it possible to easily detect the position and shape of microcracks based on the color image displayed on the display.

[0013] In the microcrack detection method of the present disclosure, a grid-like detection area array may be set on the surface of the object to be inspected, and if the difference in detection height between adjacent detection areas is equal to or greater than a threshold value, it may be determined that a microcrack exists at the boundary between the adjacent detection areas.

[0014] This allows automatic detection of microcracks.

[0015] In the microcrack detection method of the present disclosure, the object to be inspected may be a silicon wafer or an insulating film formed on the surface of a silicon wafer.

[0016] This makes it possible to detect microcracks that occur in the silicon wafer or in the insulating film formed on the surface of the silicon wafer.

[0017] The present disclosure can detect microcracks using optical devices.

[0018] 1 is a schematic system diagram showing the configuration of a quantitative phase microscope to which a microcrack detection method according to an embodiment is applied. FIG. 2 is a plan view of a silicon substrate on which microcracks have occurred. FIG. 3 is a cross-sectional view of a silicon substrate on which microcracks have occurred, taken along the line A-A in FIG. 2. FIG. 4 is a graph showing the change in actual height around a microcrack in the line A-A in FIG. 2 and the change in detected height detected by a quantitative phase microscope. FIG. 5 is a diagram showing an image in which the detected height detected by the quantitative phase microscope shown in FIG. 4 is displayed on a display with the color continuously changing according to the height. FIG. 6 is a diagram showing the detected height detected by the quantitative phase microscope shown in FIG. 6 and the color continuously changing according to the height. FIG. 7 is an explanatory diagram showing a lattice-shaped detection area array set on the surface of a silicon substrate, the detected height detected by the quantitative phase microscope in each detection area, and the detected crack.

[0019] Hereinafter, a method for detecting microcracks 34 (see FIG. 2) according to an embodiment will be described with reference to the drawings. First, a schematic configuration of a quantitative phase microscope 100 to which the method for detecting microcracks 34 according to an embodiment will be described with reference to FIG.

[0020] 1, the quantitative phase microscope 100 includes a stage 11, a mirror 12, a mirror driver 13, a light source 14, a first objective lens 15, a second objective lens 16, a beam splitter 17, a lens 18, a camera 19, a controller 10, and a display 20. In the following description, the surface of the stage 11 is referred to as the XY plane, and the up-down direction is referred to as the Z direction.

[0021] The stage 11 holds a silicon wafer 30, which is the object to be detected, on its upper surface. The stage 11 moves in the X and Y directions in response to commands from the control unit 10. The light source 14 emits light of a specific wavelength. The control unit 10 is a computer that includes a CPU 10A and a memory 10B that stores control data and control programs. The mirror driver 13 adjusts the position of the mirror 12 in response to commands from the control unit 10. The light source 14 also emits light of a specific wavelength in response to commands from the control unit 10. The camera 19 outputs an image detected by an internal imaging element to the control unit 10. The display 20 displays the image data input from the control unit 10.

[0022] Light emitted from the light source 14 is split by the beam splitter 17. One beam passes through the first objective lens 15 and illuminates the surface 30A of the silicon wafer 30 held on the stage 11. The light reflected from the surface 30A of the silicon wafer 30 passes through the first objective lens 15, the beam splitter 17, and the lens 18 and enters the camera 19, where it forms an image on the image sensor in the camera 19. Meanwhile, the other beam split by the beam splitter 17 passes through the second objective lens 16 and illuminates the surface of the mirror 12. The light reflected by the mirror 12 passes through the second objective lens 16, the beam splitter 17, and the lens 18 and enters the camera 19, where it forms an image on the image sensor in the camera 19.

[0023] Interference fringes are formed by the phase difference between the light reflected from the surface 30A of the silicon wafer 30 and the light reflected from the mirror 12, depending on the unevenness of the surface 30A of the silicon wafer 30. The image sensor of the camera 19 detects an image of the interference fringes and outputs it to the control unit 10.

[0024] The control unit 10 adjusts the position of the mirror 12 using the mirror driving unit 13, and acquires image data of multiple types of interference fringes from the camera 19. The control unit 10 detects a height profile of the surface 30A of the silicon wafer 30 based on the acquired image data of the multiple interference fringes. The control unit 10 displays the detected height profile of the surface 33 of the silicon wafer 30 on the display 20 by continuously changing the color according to the height.

[0025] Next, a method for detecting microcracks 34 using a quantitative phase microscope 100 will be described with reference to FIGS. 2 to 5. First, a silicon substrate 32 undergoing manufacture, in which microcracks 34 have occurred, will be described with reference to FIGS. 2 and 3. The silicon substrate 32 is the object to be inspected. As shown in FIG. 3, the silicon substrate 32 is a silicon wafer 30 having an insulating film 31 formed on its surface 30A. Microcracks 34 have occurred on the surface 33 of the insulating film 31. The microcracks 34 penetrate the insulating film 31 and reach the silicon wafer 30. As shown in FIG. 3, both sides of the microcracks 34 are raised above the surface 33 of the insulating film 31. The height of the raised portions is approximately 20-30 nm to 100 nm. Furthermore, as shown in FIG. 2, the raised portions are formed with a width of 10 μm to 20 μm (10,000 nm to 20,000 nm) along the direction in which the microcracks 34 extend. When the microcracks 34 occur in this way, a raised region 35 is formed that rises by about 20-30 nm to 100 nm within a periphery ranging from 10 μm to 20 μm (10,000 nm to 20,000 nm).

[0026] 4 schematically shows the change in actual height around the microcrack 34 in the raised region 35 at cross section A-A shown in FIG. 2. The width of the raised region 35 is approximately 18 μm. Symbols X1 to X18 in FIG. 4 indicate the resolution width in the X direction, which is the horizontal direction of the quantitative phase microscope 100. The resolution width is approximately 1 μm. Therefore, the total length from width X1 to width X18 in FIG. 4 is approximately 18 μm.

[0027] As shown by the solid line 41 in the upper diagram of Fig. 4, the actual height gradually increases from the general portion of the insulating film 31 toward the positive side in the X direction. Then, as shown by the solid line 42 in Fig. 4, the actual height drops in a V-shape at the position of the microcrack 34 present at width X10. Then, once the actual height exceeds the microcrack 34, it gradually decreases toward the positive side in the X direction. The actual height then becomes the height of the general portion of the insulating film 31.

[0028] When the height of the surface 33 of the insulating film 31 is detected by the quantitative phase microscope 100, the height is detected as a representative value of each height within the resolution range from width X1 to width X18. The representative value is, for example, a median or an average value. Therefore, each detected height within width X1 to width X18 is the value indicated by the black circle 43 in the lower graph of FIG. 4. The profile of the detected height is indicated by the solid line 44 in the lower graph of FIG. 4.

[0029] The horizontal resolution of the quantitative phase microscope 100 is about 1 μm. This resolution is greater than the width of the microcrack 34, which is several hundred nanometers or less (0.5 to 0.6 μm or less). For this reason, the quantitative phase microscope 100 cannot detect the V-shaped drop in height (indicated by the solid line 42) caused by the microcrack 34 that exists with width X10.

[0030] On the other hand, the quantitative phase microscope 100 can detect height with a high accuracy of several nanometers. Therefore, the difference in height between the black dots 43 can be detected with an accuracy of several nanometers. Therefore, if the detected heights detected by the quantitative phase microscope 100 are displayed on the display 20 in a continuously changing color according to the height, an image like that shown in FIG. 5 will result. In FIG. 5, the white region indicates the smooth general portion of the surface 33 of the insulating film 31. Region 45 indicates the range where the surface 33 of the insulating film 31 is slightly higher than the general portion, for example, by 10 nm. Similarly, region 46 indicates the range where the surface 33 is approximately 20 nm higher than the general portion, and region 47 indicates the range where the surface 33 is approximately 30 nm higher than the general portion. In FIG. 5, regions 45-47 are shaded in a stepwise manner for display purposes, but in reality, the color of regions 45-47 changes continuously according to the detected height.

[0031] Therefore, when the height profile of the surface 33 of the insulating film 31 is displayed as a color image on the display 20 with the color continuously changing according to the height, the raised region 35 is displayed distinctly from the smooth general portion of the surface 33, as shown in regions 45 to 47 in FIG.

[0032] As explained above, the raised region 35 is a region formed around the microcrack 34. Therefore, by extracting the regions 45 to 47 in Fig. 5 that correspond to the raised region 35, it is possible to identify the region where the microcrack 34 exists.

[0033] Next, detection of a microcrack 34 when the heights on both sides of the microcrack 34 are different will be described with reference to FIGS.

[0034] 6 , a case will be described in which the height of the left side of the microcrack 34 is higher than the height of the right side of the microcrack 34, for example, by about 30 nm. In this case, the actual height of the surface 33 of the insulating film 31 gradually increases from the general portion of the insulating film 31 toward the positive X-direction, as indicated by the solid line 51 in FIG. 6 . Then, as indicated by the solid line 53 in FIG. 6 , the actual height drops in a V-shape at the position of the microcrack 34, which exists at width X10. Because the left side of the microcrack 34 is higher than the right side, once the actual height exceeds the microcrack 34, as indicated by the solid line 52, the actual height gradually decreases from a position higher than the right side toward the positive X-direction.

[0035] The detected heights for each of widths X1 to X18 are the values ​​indicated by black dots 55 in the lower graph of Fig. 6. The profile of the detected heights is indicated by a solid line 56 in the lower graph of Fig. 6. The quantitative phase microscope 100 can detect heights with high accuracy on the order of several nanometers, and therefore can detect the height of width X10 as being higher than width X9, as shown in Fig. 6. Therefore, the height difference between widths X9 and X10 is detected.

[0036] If the height profile detected by the quantitative phase microscope 100, as shown in the lower graph of Fig. 6, is displayed as a color image on the display 20 with the color continuously changing according to height, the image shown in Fig. 7 will result. In Fig. 7, the white region indicates the smooth general portion of the surface 33 of the insulating film 31. Region 61 indicates the range where the surface 33 of the insulating film 31 is higher than the general portion by about 10 nm. Similarly, regions 62, 63, 64, and 65 indicate the ranges where the surface 33 is higher than the general portion by about 20 nm, 30 nm, 40 nm, and 50 nm, respectively.

[0037] 7, the regions 61 to 65 are displayed with shading that changes in stages for display purposes, but in reality, the colors of the regions 61 to 65 change continuously according to the detection height. Therefore, the color changes continuously at the boundary between the regions 61 and 62.

[0038] On the other hand, the color changes discontinuously between an area 63 on the right side of the microcrack 34 and an area 65 on the left side of the microcrack 34. In this way, the discontinuous color portion corresponds to the microcrack 34.

[0039] Therefore, like the boundary between the region 63 on the right side of the microcrack 34 and the region 65 on the left side of the microcrack 34 shown in Figure 7, the microcrack 34 extends in the Y direction, and its length can be detected as the length where the color of the boundary between the region 63 on the right side of the microcrack 34 and the region 65 on the left side of the microcrack 34 is discontinuous.

[0040] In this way, when the heights of both sides of the microcrack 34 are different, the position and shape of the microcrack 34 can be detected based on the color image displayed on the display 20.

[0041] Next, a method for automatically detecting the microcracks 34 will be described with reference to FIG.

[0042] As previously explained with reference to Figures 6 and 7, when the heights on both sides of the microcrack 34 are different, the quantitative phase microscope 100 detects the height difference between width X9 and width X10 shown in Figure 6. Therefore, as shown in Figure 8, a lattice-shaped detection area array 80 is set on the surface 33 of the insulating film 31. R(i, j) in Figure 8 indicates the detection area at coordinates (i, j). The detection area R(i, j) has a length Xs in the X direction and a length Ys in the Y direction. Xs and Ys are set to lengths similar to the resolution of the quantitative phase microscope 100, for example, about 1 µm.

[0043] The quantitative phase microscope 100 then detects the height of each detection region R(i, j). The height of each detection region R(i, j) is the detection height H(i, j) indicated by a black circle in FIG. 8. The control unit 10 of the quantitative phase microscope 100 calculates the difference between the detection height H(i, j) and the detection height H(i+1, j) between adjacent detection regions, for example, the detection region R(i, j) and the detection region R(i+1, j). When a difference of a threshold value, for example, several nanometers or more, is detected between the detection height H(i, j) of the detection region R(i, j) and the detection height H(i+1, j) of the adjacent detection region R(i+1, j), the control unit 10 determines that a microcrack 34 exists at the boundary between the adjacent detection regions R(i, j) and R(i+1, j). Similarly, if there is a difference greater than or equal to the threshold between the detection height H(i, j+1) and the detection height H(i+1, j+1) of adjacent detection areas R(i, j+1) and R(i+1, j+1), the control unit 10 determines that a microcrack 34 exists at the boundary between the adjacent detection areas R(i, j+1) and R(i+1, j+1).

[0044] On the other hand, if there is no height difference greater than or equal to the threshold between the detection height H(i, j) of the adjacent detection region R(i, j) and the detection height H(i, j+1) of the adjacent detection region R(i, j+1), or between the detection height H(i+1, j) of the adjacent detection region R(i+1, j) and the detection height H(i+1, j+1) of the detection region R(i+1, j+1), the control unit 10 determines that no microcracks 34 exist at the boundaries between the adjacent detection regions R(i, j) and R(i, j+1), and between the adjacent detection regions R(i+1, j) and R(i+1, j+1).

[0045] Then, the control unit 10 identifies the position and shape of the microcrack 34 extending in the Y direction along the boundary between adjacent detection regions R(i, j) and R(i+1, j) and the boundary between adjacent detection regions R(i, j+1) and R(i+1, j+1), as shown by the solid line 34A in Figure 8.

[0046] As described above, the control unit 10 can automatically identify the position and shape of the microcracks 34 .

[0047] 10 Control unit, 10A CPU, 10B Memory, 11 Stage, 12 Mirror, 13 Mirror driver, 14 Light source, 15 First objective lens, 16 Second objective lens, 17 Beam splitter, 18 Lens, 19 Camera, 20 Display, 30 Silicon wafer, 30A, 33 Surface, 31 Insulating film, 32 Silicon substrate, 34 Microcrack, 35 Protruding region, 45-47, 61-65 Region, 80 Detection region array, 100 Quantitative phase microscope, H Detection height, R Detection region.

Claims

1. A method for detecting microcracks that have occurred on the surface of an object to be inspected, comprising: detecting a height profile of the surface of the object to be inspected using a quantitative phase microscope; extracting a raised area on the surface based on the detected height profile; and identifying the extracted raised area on the surface as an area where a microcrack exists.

2. A method for detecting microcracks according to claim 1, characterized in that the position and shape of the microcracks are identified based on discontinuities in the height profile contained in the extracted raised region.

3. A method for detecting microcracks according to claim 2, characterized in that the height profile is displayed on a display with a color that changes continuously according to height, and the discontinuous portion is a portion where the color is discontinuous.

4. A method for detecting microcracks according to claim 1, characterized in that a grid-like array of detection areas is set on the surface of the object to be inspected, and when the difference in detection height between adjacent detection areas is equal to or greater than a threshold value, it is determined that a microcrack exists at the boundary between the adjacent detection areas.

5. A method for detecting microcracks according to any one of claims 1 to 4, characterized in that the object to be inspected is a silicon wafer or an insulating film formed on the surface of the silicon wafer.

Images