JP7648900B2 - Crack detection apparatus and method - Google Patents

Description

The present invention relates to a crack detection device and method, and more particularly to a crack detection device and method for detecting cracks formed inside a workpiece.

Conventionally, laser dicing devices are known that focus a laser beam on the inside of a workpiece, such as a silicon wafer, and irradiate the laser beam along the planned cutting line to form a laser processing area that will be the starting point for cutting inside the wafer along the planned cutting line. The wafer with the laser processing area formed is then cut along the planned cutting line by a cutting process such as expanding or breaking, and separated into individual chips.

When a laser-processed area is formed on a wafer using a laser dicing device, a crack propagates from the laser-processed area in the thickness direction of the wafer. If the crack reaches the surface (device surface) of the wafer, it can be properly cut into chips (semiconductor devices) during the cutting process.

Therefore, after forming the laser processing area using a laser dicing device and before the cutting process, by detecting whether the laser processing area that serves as the starting point for dividing the wafer has been properly formed, i.e., by detecting the crack depth of the crack formed inside the wafer, it is possible to accurately predict whether the wafer will be divided into chips in the cutting process.

Patent documents 1 and 2 disclose a crack detection device and method for non-destructively detecting the crack depth of cracks formed inside a wafer.

JP 2017-133997 A JP 2020-076651 A

However, because semiconductor device patterns are formed on wafers, the amount of light reflected from the wafer is affected by the reflectance of the pattern, even when a measurement operation is performed in an area where no cracks have been formed. With conventional crack detection devices, the reflectance of the pattern is superimposed on the detection results of the reflected light, resulting in a problem of reduced detection accuracy for the crack position.

One possible solution to the above problem would be to use the reflectance of the pattern measured in advance before laser processing the wafer, and compare it with the measurement results taken at the same position after laser processing to detect the crack position. However, even if the reflectance of the pattern measured in advance is used, there is a problem in that the influence of the reflectance of the pattern cannot be sufficiently eliminated for the following reasons.

First, an overview of crack detection will be given. In the above-mentioned crack detection device, as shown in (a) and (b) of FIG. 14, detection light L1 is incident on the wafer W (oblique illumination) and reflected light L2 from the wafer W is detected. The crack depth of a crack formed inside the wafer W is detected by detecting the signal intensity of this reflected light L2.

Figure 15 is a plan view showing an example of a measurement position on a wafer W, and Figure 16 is a graph showing the relationship between the focal point position (amount of movement in the height direction) of reflected light L2 from the wafer W and the detection result of signal intensity. In Figure 15, the measurement position is shown by superimposing the lens pupil 504A of the focusing lens 504 on the wafer W. The measurement positions in Figures 15 (a) and (b) correspond to the detection results in Figures 16 (a) and (b), respectively.

In the example shown in FIG. 15, a semiconductor device on a wafer W is divided by streets (planned cutting lines) ST, and a crack is formed along the center of the street ST. When crack detection is performed using the above-mentioned crack detection device, the detection light L1 that obliquely illuminates the wafer W and the reflected light L2 from the wafer W have optical paths along a plane (a plane along the direction indicated by arrows AR1 and AR2 in FIG. 15) that is perpendicular to the direction of the street ST (hereinafter referred to as the street direction D1), as shown in FIG. 15. In the following description, the plane defined by the optical paths of the detection light L1 and the reflected light L2 is referred to as the "optical path plane."

In this case, as shown in (a) and (b) of FIG. 15, if the measurement position of the crack is shifted, the detection result of the signal intensity of the reflected light L2 will differ, as shown in (a) and (b) of FIG. 16. In particular, when the pattern is fine, the change in signal intensity due to the shift in the measurement position becomes significant. Therefore, even if the reflectance of the pattern measured in advance is used, the influence of the reflectance of the pattern cannot be sufficiently eliminated.

The present invention was made in consideration of these circumstances, and aims to provide a crack detection device and method that can accurately detect the crack depth of cracks formed inside a wafer.

In order to achieve the above object, the crack detection device according to the first aspect of the present invention is a crack detection device that detects the crack depth of a crack formed along a planned cutting line of a street between semiconductor devices on a wafer, and includes a crack detection means that obliquely illuminates the wafer with detection light from a position eccentric to the main optical axis in an oblique direction and detects the crack depth of the crack based on the reflected light from the wafer, and an optical path surface tilting means that tilts the optical path surface determined by the optical paths of the detection light and the reflected light with respect to the width direction of the street.

In the crack detection device according to the second aspect of the present invention, in the first aspect, the optical path surface tilting means tilts the optical path surface with respect to the width direction of the street so that when the detection light is scanned in the depth direction of the wafer, the reflection of the detection light on the wafer occurs within the range of the street.

The crack detection device according to the third aspect of the present invention is the first or second aspect, and includes a limiting member having an opening at a position eccentric to the main optical axis, which blocks a portion of the light emitted from the light source unit with the opening and emits it as detection light, and the optical path surface tilting means includes a limiting member rotating means for tilting the optical path surface with respect to the width direction of the street by rotating the limiting member around the main optical axis.

The crack detection device according to the fourth aspect of the present invention is any one of the first to third aspects, and includes a stage on which a wafer is placed, and the optical path surface tilting means includes a stage rotation means for tilting the optical path surface with respect to the width direction of the street by rotating the stage around the main optical axis.

The crack detection method according to the fifth aspect of the present invention is a method for detecting the crack depth of a crack formed along a planned cutting line of a street between semiconductor devices on a wafer, and includes the steps of: tilting an optical path plane determined by detection light that is obliquely illuminated obliquely from a position eccentric to the main optical axis and the optical path of the reflected light from the wafer, with respect to the width direction of the street; and, with the optical path plane tilted with respect to the width direction of the street, obliquely illuminating the wafer with the detection light, and detecting the crack depth based on the reflected light from the wafer.

According to the present invention, it is possible to accurately detect the crack depth of a crack formed inside a wafer.

FIG. 1 is a block diagram showing a crack detection device according to a first embodiment of the present invention. FIG. 2 is a diagram showing a state in which the workpiece is obliquely illuminated with detection light. FIG. 3 is a diagram showing a state in which the workpiece is subjected to oblique illumination with detection light. FIG. 4 is a diagram showing a state in which the workpiece is subjected to oblique illumination with detection light. FIG. 5 is a diagram showing the state of reflected light received by a photodetector. FIG. 6 is a diagram showing the state of reflected light received by a photodetector. FIG. 7 is a diagram showing the state of reflected light received by a photodetector. FIG. 8 is a diagram for explaining the path along which light reflected from the workpiece reaches the condenser lens pupil. FIG. 9 is a plan view showing the optical path surface. FIG. 10 is an enlarged plan view showing the lens pupil of the condenser lens. FIG. 11 is a front view showing the optical paths of detection light and reflected light for crack detection. FIG. 12 is a graph showing the relationship between the focal point position of the reflected light from the wafer and the detection result of the signal intensity. FIG. 13 is a block diagram showing a crack detection device according to a second embodiment of the present invention. FIG. 14 is a diagram (perspective view and plan view) showing the optical paths of detection light and reflected light for crack detection. FIG. 15 is a plan view showing an example of measurement positions on a wafer. FIG. 16 is a graph showing the relationship between the focal point position of the reflected light from the wafer and the detection result of the signal intensity.

Below, an embodiment of the crack detection device and method according to the present invention will be described with reference to the attached drawings.

[First embodiment]
FIG. 1 is a block diagram showing a crack detection device according to a first embodiment of the present invention.

The crack detection device 10 according to this embodiment detects the crack depth of a crack K formed inside the wafer W by irradiating the wafer W with detection light L1 and detecting reflected light L2 from the wafer W. The crack detection device 10 is used in combination with a laser dicing device (not shown) that forms a laser processed area inside the wafer W. In the following explanation, the components related to the crack detection device 10 will be explained, and the configuration of the laser dicing device will not be explained.

In the following explanation, a three-dimensional Cartesian coordinate system is used in which the stage 510 on which the wafer W is placed is a plane parallel to the XY plane, and the Z direction is the depth direction of the wafer W.

As shown in FIG. 1, the crack detection device 10 according to this embodiment includes a light source unit 100, an illumination optical system 200, an interface detection optical system 300, a crack detection optical system 400, a control unit 500, a focus adjustment mechanism 502, a condenser lens 504, an operation unit 506, a display unit 508, and a stage 510. The wafer W to be measured is placed on the stage 510 so that its front surface Wa is in contact with the stage 510, and the interface of the wafer W and the cracks K formed inside the wafer W are detected by detecting the reflected light L2 from the wafer W when the detection light L1 from the light source unit 100 is incident on the back surface side Wb.

The light source unit 100 emits detection light L1 that is used to detect the interface of the wafer W and to detect cracks K formed inside the wafer W. Here, when the wafer W is a silicon wafer, it is preferable to use infrared light with a wavelength of 1,000 nm or more as the detection light L1.

The light source unit 100 includes a light source 102, a collimating lens 104, and a limiting member 106. The light source 102, the collimating lens 104, and the limiting member 106 are arranged along a main optical axis AX that is coaxial with the lens optical axis of the focusing lens 504.

The light source 102 emits detection light L1 along the main optical axis AX. For example, an LED (Light Emitting Diode) light source can be used as the light source 102. The light source 102 is connected to the control unit 500, and the emission of the light source 102 is controlled by the control unit 500.

The collimating lens 104 adjusts the detection light L1 emitted from the light source 102 so that it becomes parallel light.

An opening 106A is formed in the limiting member 106. The limiting member 106 is a light-shielding member that blocks a portion of the detection light L1 from the collimator lens 104. The limiting member 106 can be moved in and out of the optical path of the detection light L1 by a drive mechanism (e.g., a motor M1). The control unit 500 controls the motor M1 for moving the limiting member to control the movement of the limiting member 106. The control unit 500 also controls the motor M2 for rotating the limiting member to rotate the limiting member 106 around the main optical axis AX. When the crack detection optical system 400 detects a crack K, the limiting member 106 blocks a portion of the detection light L1 to decenter the detection light L1 with respect to the main optical axis AX. The limiting member 106 will be described later.

The illumination optical system 200 guides the detection light L1 emitted from the light source unit 100 to the condenser lens 504. The illumination optical system 200 includes relay lenses 202 and 206 and a mirror 204. The detection light L1 emitted from the light source unit 100 passes through the relay lens 202 and is reflected by a mirror (e.g., a total reflection mirror) 204, causing the optical path to be bent. The detection light L1 reflected by the mirror 204 passes through the relay lens 206 and is emitted toward the condenser lens 504.

The condenser lens 504 condenses (focuses) the detection light L1 emitted from the illumination optical system 200 onto the wafer W. The condenser lens 504 is disposed at a position facing the wafer W and is coaxial with the main optical axis AX.

The focus adjustment mechanism 502 adjusts the focusing position of the detection light L1 on the wafer W. The focus adjustment mechanism 502 includes a drive unit that moves at least one of the focusing lens 504 and the stage 510 on which the wafer W is placed. The focus adjustment mechanism 502 is capable of moving the focusing position of the detection light L1 in the XYZ directions by adjusting the relative position between the focusing lens 504 and the stage 510 in the XYZ directions.

When the focusing lens 504 is configured to be movable in the Z direction together with the processing head (not shown) of the laser dicing device, the focus adjustment mechanism 502 may include a drive mechanism for the processing head. In this case, it becomes possible to combine the position adjustment (coarse adjustment) of the focusing point by the drive mechanism for the processing head and the position adjustment (fine adjustment) of the focusing point by the piezoelectric actuator.

The reflected light L2 collected by the collecting lens 504 and reflected by the wafer W is guided to the interface detection optical system 300 and the crack detection optical system 400, and is used to detect the interface and cracks of the wafer W, respectively.

The control unit 500 includes a CPU (Central Processing Unit) that controls the operation of each part of the crack detection device 10, a ROM (Read Only Memory) that stores a control program, and an SDRAM (Synchronous Dynamic Random Access Memory) that can be used as a working area for the CPU. The control unit 500 accepts operation inputs from an operator via an operation unit 506 (e.g., a keyboard, and a pointing device such as a mouse or a touch panel), and transmits control signals corresponding to the operation inputs to each part of the crack detection device 10 to control the operation of each part.

The display unit 508 is a device that displays an operation GUI (Graphical User Interface) and images (e.g., crack detection results, etc.). For example, a liquid crystal display can be used as the display unit 508.

(Interface detection optical system)
Next, a description will be given of interface detection of the wafer W. In the following description, a case will be described in which the interface of the front surface Wa (the surface in contact with the stage 510) of the wafer W is detected and the crack depth is detected based on the interface position of the front surface Wa of the wafer W. Note that, in detecting the crack depth, the back surface Wb of the wafer W may be used as the reference, or it is also possible to take an average value of the crack depths detected based on both the front and back surfaces of the wafer W as the reference.

The interface detection optical system 300 is an optical system for detecting the interface (front surface Wa or back surface Wb) of the wafer W, and includes a half mirror 302, a relay lens 304, a half mirror 306, and a photodetector 308.

When detecting the interface of the wafer W, the control unit 500 irradiates the detection light L1 onto the wafer W while retracting the limiting member 106 from the optical path of the detection light L1. Here, the control unit 500 and the interface detection optical system 300 each function as part of the interface detection means.

The half mirror 302 transmits the detection light L1 from the illumination optical system 200 to the condenser lens 504 side and reflects the reflected light L2 (first reflected light) from the wafer W. The reflected light L2 from the wafer W is reflected by the half mirror 302, the optical path is bent, and the reflected light L2 is guided to the relay lens 304. The reflected light L2 that has transmitted through the relay lens 304 is reflected by the half mirror 306 and guided to the photodetector 308.

The photodetector 308 is a device that receives reflected light L2 from the wafer W and detects the interface of the wafer W, and includes a detector body 308A and a pinhole panel 308B.

The detector body 308A can be a photodetector (PD, e.g., a photodiode) that converts received light into an electrical signal and outputs it to the control unit 500.

A pinhole is formed in the pinhole panel 308B to allow a portion of the incident light to pass through. The pinhole panel 308B is positioned on the light receiving surface side of the detector body 308A so that the pinhole is on the optical axis of the reflected light L2.

The interface detection optical system 300 is an optical system in which the position of the pinhole in the pinhole panel 308B is optically conjugate with the position of the focusing point of the focusing lens 504.

The control unit 500 moves the condenser lens 504 and the stage 510 relatively in the Z direction while moving the limiting member 106 out of the optical path of the detection light L1 and irradiating the detection light L1 onto the wafer W. The control unit 500 detects the reflected light L2 when the detection light L1 is focused on the interface (front surface Wa or back surface Wb) of the wafer W, and calculates the position of the interface of the wafer W in the Z direction from the position of the focal point at that time.

(Optical system for crack detection)
Next, detection of the crack K formed inside the wafer W will be described.

The crack detection optical system 400 includes a relay lens 402, a half mirror 404, and photodetectors 406 and 408.

When detecting a crack K formed inside the wafer W, the control unit 500 inserts the limiting member 106 into the optical path of the detection light L1. Here, the control unit 500, the limiting member 106, and the crack detection optical system 400 each function as part of the crack detection means. The limiting member 106 has an opening 106A at a position offset from the main optical axis AX, and the light of the detection light L1 that passes through the opening 106A is irradiated onto the wafer W. As a result, the detection light L1 that is eccentric with respect to the main optical axis AX is irradiated onto the wafer W.

The reflected light L2 (second reflected light) from the wafer W is reflected by the half mirror 302, and then passes through the relay lens 304 and the half mirror 306 in sequence, before entering the relay lens 402. The reflected light L2 that passes through the relay lens 402 is received by the photodetectors 406 and 408 via the half mirror 404. Here, the transmittance and reflectance of the light that enters the half mirror 404 are each approximately 50%.

The photodetectors 406 and 408 are devices for receiving reflected light L2 from the wafer W and detecting cracks K inside the wafer W. The photodetector 406 includes a detector body 406A and a pinhole panel 406B, and the photodetector 408 includes a detector body 408A and a pinhole panel 408B.

The detector bodies 406A and 408A can be photodetectors (e.g., photodiodes) that convert received light into an electrical signal and output it to the control unit 500.

Pinhole panels 406B and 408B have pinholes formed to allow a portion of the incident light to pass through. Pinhole panels 406B and 408B are disposed on the light receiving surface side of detector bodies 406A and 408A, respectively. Pinhole panels 406B and 408B are disposed so that the pinholes are positioned offset from the optical axis of reflected light L2.

2 to 4 are explanatory diagrams showing the state when the detection light L1 is obliquely illuminated on the wafer W. FIG. 2 shows a case where a crack K exists at the focal point of the condenser lens 504, FIG. 3 shows a case where the crack K does not exist at the focal point of the condenser lens 504, and FIG. 4 shows a case where the focal point of the condenser lens 504 coincides with the crack depth (crack bottom end position) of the crack K. FIGS. 5 to 7 show the state of the reflected light L2 received by the photodetectors 406 and 408, and correspond to the cases shown in FIGS. 2 to 4. FIG. 8 is a diagram for explaining the path of the reflected light L2 from the wafer W to reach the condenser lens pupil 504a. Note that here, the detection light L1 passes through the first region G1 on one side (the right side of FIG. 8) of the condenser lens pupil 504a, and the case where the wafer W is obliquely illuminated is described.

As shown in FIG. 2, when a crack K is present at the focal point of the focusing lens 504, the detection light L1 is totally reflected by the crack K, and the reflected light L2 travels along a path on the same side of the optical path of the detection light L1 with respect to the main optical axis AX, and becomes a component that reaches the same area of the focusing lens pupil 504a as the detection light L1. That is, as shown in FIG. 8, when the path of the detection light L1 from the light source 102 is irradiated onto the wafer W via the focusing lens 504, is R1, the reflected light L2 totally reflected by the crack K inside the wafer W travels along a path R2 on the same side (right side in FIG. 8) of the path R1 of the detection light L1 with respect to the main optical axis AX and passes through the first area G1 of the focusing lens pupil 504a.

As shown in FIG. 3, if no crack K is present at the focal point of the focusing lens 504, the detection light L1 is reflected by the surface Wa of the wafer W, and the reflected light L2 is a component that reaches the area of the focusing lens pupil 504a on the opposite side to the detection light L1. That is, as shown in FIG. 8, the reflected light L2 reflected by the surface Wa of the wafer W passes through the second area G2 of the focusing lens pupil 504a by following a path R3 on the opposite side (left side in FIG. 8) of the main optical axis AX from the path R1 of the detection light L1.

As shown in Figure 4, when the focal point of the focusing lens 504 coincides with the lower end position of the crack K, the detection light L1 is split into a reflected light component L2a that is totally reflected by the crack K and reaches an area on the same side of the focusing lens pupil 504a as the detection light L1, and a non-reflected light component L2b that is not totally reflected by the crack K but is reflected by the surface Wa of the wafer W and reaches an area on the opposite side of the focusing lens pupil 504a as the detection light L1. That is, as shown in FIG. 8, of the reflected light L2, the reflected light component L2a that is totally reflected by the crack K inside the wafer W passes through a first region G1 of the condenser lens pupil 504a along a path R2 on the same side of the main optical axis AX as the path R1 of the detection light L1 (the right side in FIG. 8), while the non-reflected light component L2b that is not totally reflected by the crack K and is reflected by the surface Wa of the wafer W passes through a second region G2 of the condenser lens pupil 504a along a path R3 on the opposite side of the main optical axis AX as the path R1 of the detection light L1 (the left side in FIG. 8).

The pinhole panels 406B and 408B are positioned so that the pinholes are optically conjugate with the first region G1 and the second region G2 of the focusing lens pupil 504a. This allows the detector body 406A and the detector body 408A to selectively receive light that has passed through the first region G1 and the second region G2 of the focusing lens pupil 504a, respectively.

In the example shown in FIG. 2 (where crack K exists at the focal point of focusing lens 504), as shown in FIG. 5, of detector body 406A and detector body 408A, reflected light L2 is received by light receiving surface 406C of detector body 406A, and the level of the detection signal output from light receiving surface 406C becomes higher than the level of the detection signal output from light receiving surface 408C of detector body 408A.

On the other hand, in the example shown in FIG. 3 (where crack K does not exist at the focal point of focusing lens 504), as shown in FIG. 6, of detector body 406A and detector body 408A, reflected light is received by light receiving surface 408C of detector body 408A, and the level of the detection signal output from light receiving surface 408C becomes higher than the level of the detection signal output from light receiving surface 406C.

In the example shown in FIG. 4 (where the focusing point of the focusing lens 504 coincides with the lower end position of the crack K), as shown in FIG. 8, the components L2a and L2b of the reflected light L2 are received by the light receiving surfaces 406C and 408C, respectively, and the levels of the detection signals output from the light receiving surfaces 406C and 408C are approximately equal.

In this way, the amount of light received by the light receiving surfaces 406C and 408C changes depending on whether or not a crack K is present at the focal point of the focusing lens 504. In this embodiment, this property is utilized to detect the crack depth (the crack bottom end position or the crack top end position) of a crack K formed inside the wafer W.

Specifically, when the detection signal outputs from the light receiving surfaces 406C and 408C are D1 and D2, respectively, the evaluation value S indicating the relationship between the focusing point of the focusing lens 504 and the crack depth of the crack K can be expressed by the following equation.

S=(D1-D2)/(D1+D2)...(1)
In equation (1), when the condition S = 0 is satisfied, that is, when the amount of light received by the light receiving surfaces 406C and 408C is the same, this indicates that the focusing point of the focusing lens 504 and the bottom end position of the crack (or the top end position of the crack) coincide with each other.

The control unit 500 controls the focus adjustment mechanism 502 (focus point changing means) to sequentially change the focus point of the focusing lens 504 from the interface position Z(0) of the surface Wa in the thickness direction (Z direction) of the wafer W while sequentially acquiring detection signals output from the light receiving surfaces 406C and 408C, and calculates the evaluation value S shown in equation (1) based on this detection signal. By evaluating this evaluation value S, the crack depth (bottom end position or top end position of the crack) of the crack K can be detected.

In this embodiment, photodetectors are used as the detector bodies 308A, 406A, and 408A, but the present invention is not limited to this. For example, an infrared camera or the like may be used instead of the photodetector.

When detecting cracks K, the half mirror 306 may be removed from the optical path of the reflected light L2. In this case, the half mirror 306 of the interface detection optical system 300 may be replaced with a total reflection mirror, a dichroic mirror, or the like.

In addition, in this embodiment, the transmittance and reflectance of the light incident on the half mirror 404 are each approximately 50%, but the present invention is not limited to this. If the transmittance and reflectance of the half mirror 404 are different, when calculating the evaluation value S, the outputs D1 and D2 of the detection signals from the photodetectors 406 and 408 may be multiplied by weighting coefficients according to the transmittance and reflectance of the half mirror 404.

In this embodiment, when performing crack detection, the method of oblique illumination (hereinafter also referred to as the illumination method) is switched to detect the crack depth multiple times, and the average value of the multiple detection results is calculated as the crack depth. Here, switching the illumination method refers to switching the mode of eccentricity of the detection light L1 (for example, the distance and position between the opening through which the detection light L1 is emitted and the main optical axis).

Specifically, the restricting member 106 is rotated to move the position of the opening 106A to position 106B in FIG. 1, thereby changing the eccentricity of the detection light L1 and detecting the crack depth twice. The average value of the two detection results is then calculated as the crack depth.

In this embodiment, the restricting member 106 having one opening 106A formed therein is rotated, but the present invention is not limited to this. For example, the restricting member 106 may be provided with multiple openings that can be opened and closed.

In addition, in each of the above embodiments, the limiting member 106 is used to block part of the detection light L1 to perform oblique illumination, but the present invention is not limited to this. For example, oblique illumination may be performed by disposing the light source 102 of the light source unit 100 offset from the main optical axis AX. In this case, it is preferable that the optical axis of the light source 102 is parallel to the main optical axis AX.

In addition, in each of the above embodiments, the crack detection optical system 400 is provided with two photodetectors, but the present invention is not limited to this. For example, instead of the half mirror 404 and the photodetectors 406 and 408, a two-part photodetector whose light receiving surface is divided into two may be provided, and the evaluation value S may be calculated from the output of each light receiving surface. Also, a photodetector whose light receiving surface is divided into a number of parts according to the type of illumination method may be used.

The configuration for guiding the detection light L1 and the reflected light L2 is merely an example and is not limited to the above-described embodiments. For example, it is also possible to arrange the light source 102, the condenser lens 504, and the stage 510 on which the wafer W is placed in a straight line without providing the mirror 204.

[Light path surface]
Next, the optical path surface AR according to this embodiment will be described. In the crack detection device 10 according to this embodiment, the angle _θm of the optical path surface AR with respect to the street width direction D2 (direction perpendicular to the street direction D1) can be changed in the range of 0°<| _θm |<90° by adjusting the rotation angle of the limiting member 106 (see FIG. 1). Here, the limiting member 106, the control unit 500, and the motor M2 are examples of an optical path surface tilting means, and the motor M2 is an example of a limiting member rotating means. In this embodiment, the above crack detection process is performed after the process of tilting the optical path surface AR with respect to the street width direction D2.

Figure 9 is a plan view showing the light path surface AR, and Figure 10 is a plan view showing an enlarged lens pupil 504A of the focusing lens 504. Note that the symbol DP in the figure indicates the device pattern, and the symbol ST indicates the street (planned cutting line) formed between the semiconductor devices on the wafer W.

As shown in FIG. 9, by adjusting the rotation angle of the limiting member 106, it is possible to tilt the angle |θ _m | of the optical path surface AR with respect to the street width direction D2 (the direction perpendicular to the street direction D1) in the range of 0° to 90°. By tilting the optical path surface AR with respect to the street width direction D2 in this manner, it is possible to suppress deviation of the reflection position in the street width direction D2 that occurs when the position of the focal point of the detection light L1 is scanned in the Z direction.

In addition, when |θ _m | ≈ 90°, the optical paths of the detection light L1 and the reflected light L2 overlap with the street direction D1, making measurement difficult, so it is preferable to set |θ _m | to a value sufficiently smaller than 90° (for example, 80° or less).

Hereinafter, a method for determining the angle _θm of the optical path surface AR with respect to the street width direction D2 will be described with reference to FIGS.

Assuming that the angle of incidence of the detection light L1 with respect to the wafer W is θ, when the relative position in the Z direction between the focusing lens 504 and the wafer W changes by ΔZ as shown in (a) and (b) of Figure 11, the amount of movement in the Y direction of the position of the focusing point, ΔY, is expressed by the following formula (A).

ΔY=ΔZ×tanθ…(A)
In FIG. 11, when the detection light L1 scans only a scan range _ZR in the Z direction, the detection light movement distance _Lm of the detection light L1 (movement distance in a direction perpendicular to the main optical axis AX) is expressed by the following formula (B).

L _m =Z _R ×tanθ…(B)
When the street width _Lst is larger than the detection light travel distance _Lm ( _Lst > _Lm ), that is, when the detection light travel distance _Lm when the detection light L1 is scanned only in the scan range _ZR falls within the street ST without tilting the optical path plane AR (when the focal point position of the detection light L1 is scanned in the depth direction of the wafer W, the detection light L1 is reflected on the wafer W within the range of the street ST), _θm = 0°.

On the other hand, when the detection light travel distance _Lm is equal to or greater than the street width _Lst ( _Lst ≦ _Lm ), that is, when the detection light travel distance _Lm does not fall within the street ST, the inclination angle θm of the optical path surface AR is determined so that the detection light travel distance _Lm falls within the street ST (so that the reflection of the detection light L1 on the wafer W occurs within the range of the street ST when the focal point position of the detection light _L1 is scanned in the depth direction of the wafer W). Specifically, when _Lm2 = _Lm × cos _θm , _θm is determined so that _Lst > _Lm2 . At this time, _θm is expressed by the following formulas (C1) and (C2).

cosθ _m <(L _st /L _m )...(C1)
θ _m < arccos(L _st /L _m )...(C2)
By determining the angle _θm as described above, it is possible to suppress the effect of the reflectance of the pattern on the signal intensity, as shown in Fig. 12. This allows the measurement position to be a position where the change in the reflectance of the pattern is small, and the effect of fine patterns can be suppressed.

According to this embodiment, by tilting the optical path plane AR, which is determined by the detection light L1 and the reflected light L2 irradiated to the wafer W during crack detection, with respect to the street width direction D2, it is possible to sufficiently eliminate the influence of the reflectance of the pattern, and it becomes possible to detect the crack depth with high accuracy.

Second Embodiment
Next, a second embodiment of the present invention will be described with reference to Fig. 13. In the following description, the same components as those in the first embodiment will be denoted by the same reference numerals and description thereof will be omitted.

In this embodiment, the optical path surface tilting means for tilting the optical path surface AR with respect to the street width direction D2 is different from that in the first embodiment.

13, the crack detection device 10A according to this embodiment includes a rotation mechanism 512 for rotating the stage 510 around the main optical axis (Z axis). By rotating the stage 510 using this rotation mechanism 512, the angle θ _m of the optical path surface AR with respect to the street width direction D2 can be changed within the range of 0°<|θ _m |<90°. Here, the control unit 500 and the rotation mechanism 512 are an example of an optical path surface tilting means, and the rotation mechanism 512 is an example of a stage rotating means.

In this embodiment, as in the first embodiment, the influence of the reflectance of the pattern can be sufficiently eliminated by tilting the optical path surface AR with respect to the street width direction D2, making it possible to detect the crack depth with high accuracy.

It is also possible to combine the optical path surface tilting means of the first and second embodiments.

10, 10A...crack detection device, 100...light source unit, 102...light source, 104...collimating lens, 106...limiting member, 200...illumination optical system, 202...relay lens, 204...mirror, 206...relay lens, 300...interface detection optical system, 302...half mirror, 304...relay lens, 306...half mirror, 308...photodetector, 400...crack detection optical system, 402...relay lens, 404...half mirror, 406, 408...photodetector, 500...control unit, 502...focus adjustment mechanism, 504...condensing lens, 506...operation unit, 508...display unit, 510...stage, 512...rotation mechanism, M1, M2...motor

Claims (5)

A crack detection device for detecting a crack depth of a crack formed along a planned cutting line of a street between semiconductor devices on a wafer, comprising:
a crack detection means for obliquely illuminating the wafer with detection light from a position eccentric to a main optical axis in an oblique direction and detecting a crack depth of the crack based on the light reflected from the wafer;
an optical path surface tilting means for tilting an optical path surface determined by the optical paths of the detection light and the reflected light with respect to a width direction of the street;
A crack detection device comprising: The crack detection device according to claim 1, wherein the optical path surface tilting means tilts the optical path surface with respect to the width direction of the street so that the detection light is reflected on the wafer within the range of the street when the detection light is scanned in the depth direction of the wafer. a limiting member having an opening at a position eccentric to the main optical axis, the limiting member blocking a part of the light emitted from the light source unit at the opening and emitting the part of the light as the detection light;
3. The crack detection device according to claim 1, wherein the optical path surface tilting means includes a limiting member rotating means for tilting the optical path surface with respect to a width direction of the street by rotating the limiting member about the main optical axis. a stage on which the wafer is placed,
4. The crack detection device according to claim 1, wherein the optical path surface tilting means includes a stage rotation means for tilting the optical path surface with respect to the width direction of the street by rotating the stage around the main optical axis. 1. A method for detecting a crack depth of a crack formed along a planned cutting line of a street between semiconductor devices on a wafer, comprising:
a step of tilting an optical path plane determined by detection light that is obliquely illuminated in an oblique direction from a position eccentric to a main optical axis onto the wafer and an optical path of reflected light from the wafer with respect to a width direction of the street;
a step of obliquely illuminating the wafer with the detection light while tilting the optical path surface with respect to a width direction of the street, and detecting a crack depth of the crack based on the light reflected from the wafer;
A crack detection method comprising:

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