Wafer inspection methods

Abstract

To provide an inspection method of a wafer capable of preventing a formation of an inadequacy division origin in the wafer.SOLUTION: An inspection method of a wafer, for inspecting the wafer in which a device is formed in a plurality of regions that is segmented by a street, includes: a laser beam irradiation step of forming a cracking that is expanded toward a first surface of a second surface of the wafer from a modified layer as well as forming the modified layer into an inner part of the wafer by irradiating a laser beam of a wavelength having a transmissivity to the wafer along a direction parallel to the street; and a determination step of determining whether or not the street is set along a predetermined crystal orientation on the basis of an extension direction of the cracking exposed to the first surface and the second surface.SELECTED DRAWING: Figure 2

Description

Technical Field

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[0001] The present invention relates to a method for inspecting a wafer in which devices are formed in a plurality of regions partitioned by streets.

Background Art

[0002] In the manufacturing process of device chips, a wafer in which devices are formed in a plurality of regions partitioned by a plurality of intersecting streets (lines to be divided) is used. By dividing this wafer along the streets, device chips having devices can be obtained. The device chips are incorporated into various electronic devices such as mobile phones and personal computers.

[0003] For wafer dicing, a dicing apparatus that cuts a wafer with an annular cutting blade is used. In recent years, the development of a process for dicing a wafer by laser processing has also been advanced. For example, while condensing a laser beam having a wavelength that is transmissive to the wafer inside the wafer and scanning along the street, a modified layer is formed along the street inside the wafer, and cracks are extended from the modified layer toward the front or back surface of the wafer. The region where the modified layer or cracks of the wafer are formed becomes more brittle than other regions. Therefore, when an external force is applied to the wafer, the modified layer and the cracks function as dicing starting points, and the wafer is diced along the street (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Devices formed on crystalline wafers such as single-crystal silicon wafers are arranged along a predetermined crystal orientation, taking into consideration the electrical properties of the devices and the mechanical properties of the wafer. After a street is set based on the device arrangement, a laser beam is irradiated along the street to form splitting points (modified layers and cracks).

[0006] Here, it has been confirmed that the form of the splitting starting point formed along the street differs depending on the crystal orientation of the wafer. Therefore, when forming splitting starting points on a wafer, the laser beam irradiation conditions are set based on the crystal structure of the wafer in the length direction of the street. This ensures that appropriate splitting starting points are formed according to the crystal orientation of the wafer, making it easier for the wafer to split along the street.

[0007] However, if the street is set in a direction other than usual, the modified layer will be formed in a state where the crystal orientation of the wafer and the irradiation conditions of the laser beam are not aligned. In this case, processing defects such as cracks extending from the modified layer meandering relative to the street are more likely to occur, and it becomes difficult to properly form the splitting starting point. As a result, the wafer may not be split as intended, which may lead to a decrease in the quality of the device chip.

[0008] This invention has been made in view of the above problems and aims to provide a wafer inspection method that can prevent the formation of inappropriate splitting points on the wafer. [Means for solving the problem]

[0009] According to one aspect of the present invention, a wafer inspection method for inspecting a wafer in which devices are formed in a plurality of regions demarcated by streets, comprising: a laser beam irradiation step of irradiating the wafer with a laser beam of a wavelength that is transparent to the wafer along a direction parallel to the streets, thereby forming a modified layer inside the wafer and forming cracks extending from the modified layer toward a first or second surface of the wafer; and a determination step of determining whether the streets are set toward a predetermined crystal orientation based on the direction of extension of the cracks exposed toward the first or second surface. In this determination step, the straightness of the crack exposed on the first or second surface is compared with a reference value to determine whether the street is set along the predetermined crystal orientation. A method for inspecting wafers is provided. Furthermore, according to another aspect of the present invention, a wafer inspection method is provided for inspecting a wafer on which devices are formed in a plurality of regions demarcated by streets, comprising: a laser beam irradiation step of irradiating the wafer with a laser beam of a wavelength that is transparent to the wafer along a direction parallel to the streets to form a modified layer inside the wafer and form cracks extending from the modified layer toward a first or second surface of the wafer; and a determination step of determining whether the streets are set along a predetermined crystal orientation based on the direction of extension of the cracks exposed on the first or second surface, wherein the determination step determines whether the streets are set along the predetermined crystal orientation based on the similarity between an image of the cracks exposed on the first or second surface and a reference image. Furthermore, according to another aspect of the present invention, a wafer inspection method is provided for inspecting a wafer on which devices are formed in a plurality of regions demarcated by streets, comprising: a laser beam irradiation step of irradiating the wafer with a laser beam of a wavelength that is transparent to the wafer along a direction parallel to the streets to form a modified layer inside the wafer and form cracks extending from the modified layer toward a first or second surface of the wafer; and a determination step of determining whether the streets are set along a predetermined crystal orientation based on the direction of extension of the cracks exposed on the first or second surface, wherein the determination step determines whether the streets are set along the predetermined crystal orientation by a trained model that outputs a determination result of the direction of the streets when an image of the cracks exposed on the first or second surface is input.

[0010] Preferably, in the laser beam irradiation step, the laser beam is irradiated under irradiation conditions for forming the modified layer along the predetermined crystal orientation, and if it is determined in the determination step that the street is set along the predetermined crystal orientation, the laser beam is irradiated onto the wafer along the street under the irradiation conditions, and if it is determined in the determination step that the street is not set along the predetermined crystal orientation, the irradiation of the laser beam onto the wafer is interrupted. Preferably, the wafer includes a device region on which the device is formed and an outer peripheral excess region surrounding the device region where the device is not formed, and in the laser beam irradiation step, the laser beam is irradiated onto the outer peripheral excess region. Preferably, the wafer inspection method further includes a notification step that notifies the operator if it is determined in the determination step that the street is not set along a predetermined crystal orientation. [Effects of the Invention]

[0011] In a wafer inspection method according to one aspect of the present invention, a modified layer and cracks are formed on the wafer by irradiating it with a laser beam, and then it is determined whether or not the street is set along a predetermined crystal orientation based on the direction of crack propagation exposed on the first or second surface of the wafer. This prevents the formation of inappropriate splitting points on the wafer due to irradiation under irradiation conditions that do not match the crystal orientation of the laser beam. [Brief explanation of the drawing]

[0012] [Figure 1] This is a perspective view of the wafer. [Figure 2] This is a flowchart showing the wafer inspection method. [Figure 3]This is a perspective view showing a laser processing machine. [Figure 4] This is a cross-sectional view showing a portion of the excess area on the outer edge of the wafer. [Figure 5] Figure 5(A) is a schematic diagram showing the (100) plane of single-crystal silicon, Figure 5(B) is an image showing cracks formed on a wafer where the street is set parallel to the cleavage direction, and Figure 5(C) is an image showing cracks formed on a wafer where the street is set tilted 45° with respect to the cleavage direction A. [Figure 6] This is a block diagram of the controller. [Modes for carrying out the invention]

[0013] Hereinafter, an embodiment according to one aspect of the present invention will be described with reference to the attached drawings. First, an example of the configuration of a wafer to be inspected by the wafer inspection method according to this embodiment will be described. Figure 1 is a perspective view showing wafer 11.

[0014] Wafer 11 is a disc-shaped crystalline wafer (substrate) comprising a surface (first surface) 11a and a back surface (second surface) 11b that are generally parallel to each other. Examples of crystalline wafers include single-crystal silicon wafers, single-crystal wafers made of III-V compound semiconductors such as gallium arsenide (GaAs), and sapphire wafers. For example, as wafer 11, a single-crystal silicon wafer in which the main surfaces (surface 11a and back surface 11b) are composed of (100) planes is used. However, there are no restrictions on the material, shape, structure, size, etc. of wafer 11.

[0015] Wafer 11 is partitioned into a plurality of rectangular regions by a plurality of streets (planned division lines) 13 arranged in a grid pattern so as to intersect each other. Further, on the surface 11a side of the regions partitioned by the streets 13, devices 15 such as IC (Integrated Circuit), LSI (Large Scale Integration), LED (Light Emitting Diode), and MEMS (Micro Electro Mechanical Systems) devices are formed respectively. However, there are no restrictions on the type, quantity, shape, structure, size, arrangement, etc. of the devices 15.

[0016] The devices 15 are arranged along a predetermined crystal orientation in consideration of the electrical characteristics of the devices 15 and the mechanical characteristics of the wafer 11, etc. Therefore, the streets 13 are also set along a predetermined direction with respect to the crystal orientation of the wafer 11.

[0017] The wafer 11 includes a substantially circular device region 17A in which a plurality of devices 15 are formed, and an annular outer peripheral surplus region 17B surrounding the device region 17A. The outer peripheral surplus region 17B is an annular region with a predetermined width (for example, about 2 mm) including the outer peripheral edge of the surface 11a, and corresponds to a region where no device 15 is formed. In FIG. 1, a virtual boundary between the device region 17A and the outer peripheral surplus region 17B is shown by a two-dot chain line.

[0018] By dividing the wafer 11 into a grid along the streets 13, a plurality of device chips each having a device 15 are manufactured. For example, by irradiating the wafer 11 with a laser beam, a modified layer is formed inside the wafer 11 along the streets 13, and cracks are extended from the modified layer toward the surface 11a or the back surface 11b of the wafer 11. In this case, the irradiation conditions of the laser beam are set such that the region of the wafer 11 irradiated with the laser beam is modified (altered) by multi-photon absorption.

[0019] The modified layer or the region where cracks are formed on the wafer 11 becomes more brittle than other regions. Therefore, when an external force is applied to the wafer 11, the wafer 11 is divided along the street 13 starting from the modified layer and the cracks. That is, the modified layer and the cracks function as a division starting point (a trigger for division).

[0020] It has been confirmed that the mode of the division starting point formed along the street 13 varies depending on the crystal orientation of the wafer 11. Therefore, when forming a division starting point on the wafer 11, the irradiation conditions of the laser beam are set based on the crystal structure of the wafer 11 in the length direction of the street 13. However, if the street 13 is set in a direction different from the normal one, the modified layer is formed in a state where the crystal orientation of the wafer 11 and the irradiation conditions of the laser beam do not match. In this case, processing defects such as the cracks extending from the modified layer meandering with respect to the street 13 are likely to occur, and it becomes difficult to appropriately form the division starting point.

[0021] Therefore, in the present embodiment, before forming the modified layer along the street 13, the modified layer and the cracks are formed experimentally on a part of the wafer 11. Then, based on the extending direction of the cracks exposed on the front surface 11a or the back surface 11b of the wafer 11, it is determined whether the street 13 is set along a predetermined crystal orientation. Thereby, it is possible to prevent the wafer 11 from being irradiated with the laser beam under inappropriate irradiation conditions that do not match the crystal orientation.

[0022] Hereinafter, a specific example of the inspection method for the wafer according to the present embodiment will be described. FIG. 2 is a flowchart showing the inspection method for the wafer. In the present embodiment, a laser beam irradiation step S1 of irradiating the wafer 11 with a laser beam to form a modified layer and cracks, a determination step S2 of determining whether the street 13 is set along a desired crystal orientation based on the extending direction of the cracks, and a notification step S3 of notifying the operator of the determination result are sequentially performed.

[0023] A laser processing device is used to perform laser processing on the workpiece for inspection of wafer 11. Figure 3 is a perspective view of the laser processing device 2. In Figure 3, the X-axis direction (processing feed direction, first horizontal direction) and the Y-axis direction (indexing feed direction, second horizontal direction) are perpendicular to each other. The Z-axis direction (height direction, vertical direction, up and down direction) is perpendicular to the X-axis and Y-axis directions.

[0024] The laser processing apparatus 2 includes a chuck table (holding table) 4 for holding the wafer 11. The upper surface of the chuck table 4 is a flat surface that is generally parallel to the horizontal direction (XY plane direction) and constitutes the holding surface for holding the wafer 11. The holding surface is connected to a suction source (not shown), such as an ejector, via a flow channel (not shown), a valve (not shown), etc., formed inside the chuck table 4.

[0025] The chuck table 4 is connected to a moving unit (not shown) and a rotational drive source (not shown). The moving unit is, for example, a ball screw type moving mechanism, which moves the chuck table 4 along the X-axis and Y-axis. The rotational drive source is composed of a motor or the like, which rotates the chuck table 4 around a rotation axis that is approximately perpendicular to the holding surface.

[0026] The laser processing apparatus 2 also includes a laser irradiation unit 6. The laser irradiation unit 6 includes a laser oscillator (not shown) such as a YAG laser, YVO4 laser, or YLF laser, and a laser processing head 8 positioned above the chuck table 4. The laser processing head 8 has a built-in optical system that guides the pulsed laser beam emitted from the laser oscillator to the wafer 11, and the optical system includes optical elements such as a focusing lens that focuses the laser beam. The wafer 11 is processed by the laser beam 10 irradiated from the laser processing head 8 toward the chuck table 4.

[0027] Furthermore, an imaging unit (camera) 12 is provided above the chuck table 4. For example, the imaging unit 12 is mounted on the laser irradiation unit 6 so as to be adjacent to the laser processing head 8. The imaging unit 12 is equipped with an imaging element such as a CCD (Charged-Coupled Devices) sensor or a CMOS (Complementary Metal-Oxide-Semiconductor) sensor, and generates an image (imaging image) of the wafer 11 by imaging the wafer 11.

[0028] Furthermore, the laser processing apparatus 2 includes a controller (control unit, control unit, control device) 14 that controls the laser processing apparatus 2. The controller 14 is connected to the components that make up the laser processing apparatus 2 (chuck table 4, laser irradiation unit 6, imaging unit 12, etc.) and controls the operation of the laser processing apparatus 2 by outputting control signals to each component.

[0029] For example, the controller 14 is composed of a computer and includes a calculation unit that performs calculations necessary for the operation of the laser processing device 2, and a storage unit that stores various information (data, programs, etc.) used for the operation of the laser processing device 2. The calculation unit includes a processor such as a CPU (Central Processing Unit). The storage unit includes memory such as ROM (Read Only Memory) and RAM (Random Access Memory).

[0030] When processing the wafer 11 with the laser processing apparatus 2, the wafer 11 is supported by a frame 19 for ease of handling (transportation, holding, etc.). The frame 19 is an annular member made of metal such as SUS (stainless steel), and a circular opening 19a is provided in the center of the frame 19, penetrating the frame 19 in the thickness direction. The diameter of the opening 19a is larger than the diameter of the wafer 11.

[0031] A sheet 21 supporting the wafer 11 is fixed to the back surface 11b of the wafer 11. For example, the sheet 21 is a circular tape with a larger diameter than the wafer 11, and includes a film-like substrate and an adhesive layer (glue layer) provided on the substrate. The substrate is made of a resin such as polyolefin, polyvinyl chloride, or polyethylene terephthalate. The adhesive layer is made of an epoxy, acrylic, or rubber-based adhesive. The adhesive layer may also be made of an ultraviolet-curing resin that hardens when exposed to ultraviolet light.

[0032] With the wafer 11 positioned inside the opening 19a of the frame 19, the central part of the sheet 21 is attached to the back surface 11b of the wafer 11, and the outer edge of the sheet 21 is attached to the frame 19. As a result, the wafer 11 is supported by the frame 19 via the sheet 21.

[0033] In the laser beam irradiation step S1, the wafer 11 is first held by the chuck table 4. For example, the wafer 11 is placed on the chuck table 4 such that the front surface 11a faces upward and the back surface 11b (sheet 21 side) faces the holding surface of the chuck table. The frame 19 is fixed by a plurality of clamps (not shown) provided around the chuck table 4. Then, by applying the suction force (negative pressure) of the suction source to the holding surface of the chuck table 4, the wafer 11 is held by the chuck table 4 via the sheet 21.

[0034] Next, the chuck table 4 is rotated to align the length of the predetermined street 13 with the X-axis direction. The position of the chuck table 4 is also adjusted so that the focal point of the laser beam 10 coincides with the position of the outer peripheral excess region 17B of the wafer 11 in the Y-axis direction. Furthermore, the position of the laser processing head 8 and the arrangement of the optical system are adjusted so that the focal point of the laser beam 10 is positioned at the same height as the inside of the wafer 11 (between the front surface 11a and the back surface 11b).

[0035] Then, while irradiating the laser beam 10 from the laser processing head 8, the chuck table 4 is moved along the X-axis direction. As a result, the chuck table 4 and the laser beam 10 move relative to each other along the X-axis direction at a predetermined speed (processing feed rate). Consequently, the laser beam 10 is irradiated from the surface 11a side of the wafer 11 along a direction parallel to the street 13, with the focal point located inside the wafer 11, onto the outer peripheral excess region 17B.

[0036] The irradiation conditions for the laser beam 10 are set so that the area of ​​the wafer 11 irradiated by the laser beam 10 is modified (altered) by multiphoton absorption. Specifically, the wavelength of the laser beam 10 is set so that at least a portion of the laser beam 10 penetrates the wafer 11. In other words, the laser beam 10 is a laser beam with a wavelength that is penetrating to the wafer 11. The irradiation conditions for the other laser beams 10 are also set so that the wafer 11 is appropriately modified. For example, if the wafer 11 is a single-crystal silicon wafer, the irradiation conditions for the laser beam 10 can be set as follows. Wavelength: 1064nm Average output: 1W Repeat frequency: 100kHz Machining feed rate: 800 mm / s

[0037] Figure 4 is a cross-sectional view showing a portion of the excess region 17B on the outer periphery of the wafer 11. When the laser beam 10 is irradiated onto the wafer 11 under the above irradiation conditions, the region inside the wafer 11 where the laser beam 10 is focused and its vicinity are modified (altered) by multiphoton absorption. As a result, a modified layer (altered layer) 23 is formed inside the wafer 11.

[0038] When the modified layer 23 is formed, cracks 25 occur in the modified layer 23, and the cracks 25 extend from the modified layer 23 along the thickness direction of the wafer 11. The cracks 25 then reach the surface 11a and / or back surface 11b of the wafer 11 and are exposed on the surface 11a and / or back surface 11b. Figure 4 shows an example where the cracks 25 reach the surface 11a of the wafer 11 (the surface to which the laser beam 10 is incident).

[0039] As the laser beam 10 is scanned, the modified layer 23 is formed along a direction parallel to the street 13 (X-axis direction), and the cracks 25 extending from the modified layer 23 are sequentially connected to each other. As a result, as shown in Figure 3, the cracks 25 exposed on the surface 11a and / or back surface 11b of the wafer 11 extend along a direction parallel to the street 13 (X-axis direction).

[0040] Next, the determination step S2 is performed. In the determination step S2, first, the area of ​​the wafer 11 irradiated by the laser beam 10 is imaged by the imaging unit 12 (see Figure 4). This obtains an image (imaged image) of the cracks 25 exposed on the surface 11a of the wafer 11.

[0041] The manner in which the cracks 25 extend varies depending on the crystal orientation of the wafer 11. Therefore, the images acquired by the imaging unit 12 may display cracks 25 of various shapes depending on the direction of the street 13. Below, the relationship between crystal orientation and cracks 25 will be explained using the case where the wafer 11 is a single-crystal silicon wafer as an example.

[0042] Figure 5(A) is a schematic diagram showing the (100) plane of single-crystal silicon. For example, wafer 11 is a single-crystal silicon wafer in which the main surfaces (front surface 11a and back surface 11b) are composed of (100) planes, and the {111} plane and {110} plane are cleavage planes. Wafer 11 is then cleaved along the cleavage direction A, which is parallel to the cleavage plane. In the manufacture of device chips, single-crystal silicon wafers called "0-degree wafers" are often used, in which the street 13 is set along the direction D1 parallel to the cleavage direction A, or single-crystal silicon wafers called "45-degree wafers" are often used, in which the street 13 is set along the direction D2 tilted 45° with respect to the cleavage direction A.

[0043] When a modified layer 23 (see Figure 4) is formed on a wafer 11 with street 13 set parallel to the cleavage direction A, cracks 25 (see Figure 3) exposed on the surface 11a of the wafer 11 tend to extend straight parallel to street 13. Therefore, linear cracks 25 are displayed in the image acquired by the imaging unit 12. Figure 5(B) is an image diagram showing an image (imaging image) 20A of cracks 25 formed on a wafer 11 (0-degree product) with street 13 set parallel to the cleavage direction A.

[0044] On the other hand, when a modified layer 23 (see Figure 4) is formed on a wafer 11 in which street 13 is set to be tilted with respect to the cleavage direction A, the cracks 25 (see Figure 3) exposed on the surface 11a of the wafer 11 tend to extend in a random, meandering manner. Therefore, non-linear cracks 25 are displayed in the image acquired by the imaging unit 12. Figure 5(C) is an image diagram showing an image (acquired image) 20B of cracks 25 formed on a wafer 11 (45-degree product) in which street 13 is set to be tilted at 45° with respect to the cleavage direction A.

[0045] As shown in Figures 5(B) and 5(C), the cracks 25 exposed on the surface 11a and / or back surface 11b of the wafer 11 propagate with different behavior depending on the relationship between the crystal orientation of the wafer 11 and the direction of the street 13. Therefore, by observing the cracks 25 propagating along the surface 11a and / or back surface 11b of the wafer 11, it is possible to determine whether or not the street 13 is set along a predetermined crystal orientation.

[0046] For example, in the laser beam irradiation step S1 described above, the wafer 11 is processed under processing conditions for forming a modified layer 23 on the wafer 11, where the street 13 is set parallel to the cleavage direction A. Therefore, if the wafer 11 is a 0-degree product, the laser beam 10 is irradiated onto the wafer 11 under irradiation conditions suitable for forming the modified layer 23. On the other hand, if the wafer 11 is a 45-degree product, the laser beam 10 is irradiated onto the wafer 11 under irradiation conditions unsuitable for forming the modified layer 23.

[0047] Then, in the determination step S2, the processed wafer 11 is imaged by the imaging unit 12 (see Figure 3). At this time, if the wafer 11 is a 0-degree product, an image 20A (see Figure 5(B)) representing a linear crack 25 extending parallel to the street 13 is acquired. On the other hand, if the wafer 11 is a 45-degree product, an image 20B (see Figure 5(C)) representing a meandering crack 25 is acquired. Based on the acquired image of the crack 25, it is determined manually or automatically whether the street 13 is set along a predetermined crystal orientation (whether the wafer 11 is a 0-degree product or a 45-degree product).

[0048] The determination of whether Street 13 is set along a predetermined crystal orientation is performed automatically, for example, by the controller 14. Figure 6 is a block diagram of the controller 14.

[0049] Figure 6 shows blocks representing the functional configuration of the controller 14, as well as blocks representing the laser irradiation unit 6 and the imaging unit 12. The laser processing apparatus 2 also includes a display unit (display section, display device) 30 capable of displaying various types of information, and a notification unit (notification section, notification device) 32 capable of notifying the operator of information. The display unit 30 and the notification unit 32 are connected to the controller 14.

[0050] The display unit 30 can be composed of various types of displays, for example, a touch panel display. In this case, the operator can input information to the laser processing device 2 by touching the display unit 30. That is, the display unit 30 also functions as an input unit (input device) for inputting various types of information to the laser processing device 2. However, the input unit may be an input device such as a mouse, keyboard, or control panel that is provided separately and independently from the display unit 30.

[0051] The notification unit 32 is, for example, an indicator light (warning light) that lights up or flashes to notify the operator when an abnormality occurs in the laser processing device 2. However, there are no restrictions on the type of notification unit 32. For example, the notification unit 32 may be a speaker that notifies the operator of information by sound or voice.

[0052] The controller 14 includes a determination unit 14a for determining the direction of the street 13, and a determination information storage unit 14b for storing information (data, programs, etc.) used for determination by the determination unit 14a. When the wafer 11 (see Figure 4) on which the modified layer 23 and cracks 25 are formed is imaged by the imaging unit 12, an image of the cracks 25 exposed on the front surface 11a or back surface 11b of the wafer 11 (imaged image, see image 20A in Figure 5(B) and image 20B in Figure 5(C)) is acquired and input to the determination unit 14a. The determination unit 14a then determines whether the street 13 is set along a predetermined crystal orientation based on the imaged image and the information stored in the determination information storage unit 14b.

[0053] For example, the determination unit 14a determines the direction of the street 13 by image processing such as pattern matching. Specifically, the determination information storage unit 14b has in advance stored as a reference image an image of a crack 25 formed when the street 13 is set parallel to the cleavage direction A of the wafer 11 (see Figure 5(A)) (see image 20A in Figure 5(B)). When the captured image is input to the determination unit 14a from the imaging unit 12, the determination unit 14a compares the captured image with the reference image and calculates the similarity. The determination unit 14a then compares the calculated similarity with a reference value (threshold) stored in the determination information storage unit 14b to determine whether the wafer 11 is a 0-degree product or not. This automatically determines whether the street 13 is set along a predetermined crystal orientation.

[0054] However, there are no restrictions on the method for determining the direction of street 13. For example, the determination unit 14a may determine the direction of street 13 based on the shape tolerance of the crack 25. Specifically, the determination unit 14a performs image processing on the captured image input from the imaging unit 12 and calculates the straightness of the crack 25. Then, the determination unit 14a compares the calculated straightness with a reference value (threshold) stored in the determination information storage unit 14b to determine whether the wafer 11 is a 0-degree product or not.

[0055] Furthermore, the determination unit 14a can also determine the direction of street 13 using a trained model constructed by machine learning. For example, a neural network trained to output a determination result for the direction of street 13 when an image of crack 25 is input is stored in the determination information storage unit 14b. In this case, the determination unit 14a determines the angle of street 13 by inputting the image of crack 25 into the neural network read from the determination information storage unit 14b.

[0056] The controller 14 also includes a drive control unit 14c that generates control signals to drive each component of the laser processing device 2. When the determination unit 14a determines the direction of the street 13, the determination unit 14a inputs the determination result to the drive control unit 14c. The drive control unit 14c then notifies the operator of the determination result by activating the display unit 30 and the notification unit 32 (notification step S3). The drive control unit 14c also outputs control signals to each component of the laser processing device 2 based on the determination result, thereby controlling the operation of the laser processing device 2.

[0057] For example, if the irradiation conditions of the laser beam 10 (see Figures 3 and 4) are set to be suitable for processing a 0-degree wafer, and the determination unit 14a determines that the wafer 11 is a 0-degree wafer, the drive control unit 14c outputs a control signal to the display unit 30, and the display unit 30 displays information (message, image, etc.) indicating that the wafer 11 is a 0-degree wafer (notification step S3). In addition, the drive control unit 14c outputs a control signal to the laser irradiation unit 6, etc., and the wafer 11 is processed under the processing conditions for a 0-degree wafer.

[0058] Specifically, the laser beam 10 is irradiated along the street 13 of the wafer 11 under irradiation conditions suitable for processing a 0-degree wafer. As a result, a modified layer 23 (see Figure 4) is formed on the wafer 11 in a grid pattern along the street 13. In addition, cracks 25 (see Figure 4) extending from the modified layer 23 reach the surface 11a and / or back surface 11b of the wafer 11 and propagate straight along the street 13.

[0059] The modified layer 23 may be formed in multiple layers in the thickness direction of the wafer 11. For example, if the wafer 11 is a single-crystal silicon wafer with a thickness of 200 μm or more, forming two or more modified layers 23 makes it easier to properly separate the wafer 11. When forming multiple modified layers 23, the laser beam 10 is irradiated multiple times along each street 13 while changing the position of the focal point of the laser beam 10 in the thickness direction of the wafer 11.

[0060] Subsequently, an external force is applied to the wafer 11, causing it to split along the street 13, starting from the modified layer 23 and the crack 25. There are no restrictions on the method of applying the external force to the wafer 11. For example, an expandable sheet that can be expanded by applying an external force is used as the sheet 21 (see Figure 3). In this case, an external force is applied to the wafer 11 by pulling the sheet 21 radially outward to expand it, causing the wafer 11 to break along the street 13. The expansion of the sheet 21 may be performed manually by an operator or automatically using a dedicated expansion device.

[0061] However, depending on the irradiation conditions of the laser beam 10, the thickness of the wafer 11, etc., the cracks 25 may reach the front surface 11a and back surface 11b of the wafer 11 when the modified layer 23 is formed. In this case, the wafer 11 will be split along the street 13 when the modified layer 23 is formed.

[0062] On the other hand, if the determination unit 14a determines that the wafer 11 is not a 0-degree product, the drive control unit 14c outputs a control signal to each component of the laser processing apparatus 2, and the processing of the wafer 11 is temporarily interrupted. This prevents the wafer 11 from being processed under inappropriate processing conditions.

[0063] Furthermore, the operator is notified that street 13 is not set along the predetermined crystal orientation (notification step S3). For example, the drive control unit 14c notifies the operator of the error by outputting a control signal to the display unit 30 to display information (message, image, etc.) indicating that the wafer 11 is not a 0-degree wafer. The drive control unit 14c also outputs a control signal to the notification unit 32 (warning light, speaker, etc.) to send a warning to the notification unit 32. As a result, the operator is notified that street 13 is not set along the predetermined crystal orientation, and the operator can quickly take measures such as retrieving the wafer 11 or changing the irradiation conditions of the laser beam 10.

[0064] As described above, in the wafer inspection method according to this embodiment, after irradiating the wafer 11 with a laser beam 10 to form a modified layer 23 and cracks 25, it is determined whether the street 13 is set along a predetermined crystal orientation based on the direction of extension of the cracks 25 exposed on the surface 11a or back surface 11b of the wafer 11. This prevents the formation of inappropriate splitting points on the wafer 11 due to irradiation conditions that do not match the crystal orientation of the laser beam 10.

[0065] In the above embodiment, an example was described in which the laser beam 10 is irradiated from the surface 11a side of the wafer 11 (see Figures 3 and 4). However, the laser beam 10 can also be irradiated from the back surface 11b side of the wafer 11. In this case, the device 15 formed on the surface 11a side of the wafer 11 will be less affected by the irradiation of the laser beam 10. However, whether the laser beam 10 is irradiated from the surface 11a side or the back surface 11b side of the wafer 11 can be appropriately selected depending on the processing to be performed on the wafer 11.

[0066] Furthermore, the wafer 11 may be subjected to a thinning process by grinding the back surface 11b side of the wafer 11 with a grinding wheel. In this case, before grinding the wafer 11, a laser beam 10 may be irradiated from the back surface 11b side of the wafer 11 to the area overlapping with the device region 17A (see Figure 1) to form a modified layer 23 and cracks 25 (see Figure 4). Specifically, the modified layer 23 is formed at a position overlapping with the street 13 or device 15 within the device region 17A.

[0067] The irradiation conditions for the laser beam 10 are set so that cracks 25 extending from the modified layer 23 do not reach the surface 11a of the wafer 11. The direction of the street 13 is then determined based on the shape of the cracks 25 exposed on the back surface 11b of the wafer 11. Subsequently, the back surface 11b of the wafer 11 is ground down, thinning the wafer 11 to a predetermined thickness, and removing the modified layer 23 and cracks 25. Therefore, the modified layer 23 and cracks 25 formed for the inspection of the wafer 11 do not remain in the final manufactured device chip.

[0068] Furthermore, although the above embodiment describes a case where the controller 14 of the laser processing apparatus 2 determines the direction of the street 13 (see Figure 6), the determination of the direction of the street 13 may also be performed by an operator. For example, the operator can directly visually inspect the wafer 11 on which the modified layer 23 and crack 25 are formed, or visually inspect the image of the crack 25 displayed on the display unit 30 to confirm the shape of the crack 25. Based on the shape of the crack 25, the operator can then determine whether the street 13 is set along a predetermined crystal orientation (for example, whether the wafer 11 is a 0-degree or 45-degree product).

[0069] Furthermore, the structures, methods, etc., according to the above embodiments can be modified as appropriate without departing from the scope of the objectives of the present invention. [Explanation of Symbols]

[0070] 11 wafers 11a Surface (first side) 11b Back side (2nd side) 13th Street (planned division line) 15 devices 17A Device Area 17B Peripheral surplus region 19 frames 19a aperture 21 sheets 23. Modified layer (altered layer) 25. Cracks 2. Laser processing equipment 4. Chuck table (holding table) 6. Laser irradiation unit 8 Laser processing heads 10 Laser beams 12 Imaging Unit (Camera) 14. Controller (control unit, control unit, control device) 14a Judgment Unit 14b Judgment information storage unit 14c Drive Control Unit 20A, 20B Images (Acquired Images) 30 Display unit (display unit, display device) 32. Notification Unit (Notification Section, Notification Device)

Claims

1. A wafer inspection method for inspecting a wafer in which devices are formed in multiple areas demarcated by streets, A laser beam irradiation step involves irradiating the wafer with a laser beam of a wavelength that is penetrating to the wafer along a direction parallel to the street, thereby forming a modified layer inside the wafer and forming cracks that extend from the modified layer toward the first or second surface of the wafer. The method includes a determination step of determining whether the street is set along a predetermined crystal orientation based on the direction of extension of the crack exposed on the first or second surface, A wafer inspection method characterized in that, in the determination step, it is determined whether or not the street is set along the predetermined crystal orientation by comparing the straightness of the crack exposed on the first surface or the second surface with a reference value.

2. A wafer inspection method for inspecting a wafer in which devices are formed in a plurality of regions demarcated by streets, A laser beam irradiation step involves irradiating the wafer with a laser beam of a wavelength that is penetrating to the wafer along a direction parallel to the street, thereby forming a modified layer inside the wafer and forming cracks that extend from the modified layer toward the first or second surface of the wafer. The method includes a determination step of determining whether the street is set along a predetermined crystal orientation based on the direction of extension of the crack exposed on the first or second surface, A wafer inspection method characterized in that, in the determination step, it is determined whether the street is set along the predetermined crystal orientation based on the similarity between the image of the crack exposed on the first or second surface and a reference image.

3. A wafer inspection method for inspecting a wafer in which devices are formed in a plurality of regions demarcated by streets, A laser beam irradiation step involves irradiating the wafer with a laser beam of a wavelength that is penetrating to the wafer along a direction parallel to the street, thereby forming a modified layer inside the wafer and forming cracks that extend from the modified layer toward the first or second surface of the wafer. The method includes a determination step of determining whether the street is set along a predetermined crystal orientation based on the direction of extension of the crack exposed on the first or second surface, A wafer inspection method characterized in that, in the determination step, when an image of the crack exposed on the first surface or the second surface is input, a trained model that outputs a determination result for the direction of the street is used to determine whether or not the street is set along the predetermined crystal orientation.

4. In the laser beam irradiation step, the laser beam is irradiated under irradiation conditions for forming the modified layer along the predetermined crystal orientation, If the determination step determines that the street is set along the predetermined crystal orientation, the laser beam is irradiated onto the wafer along the street under the irradiation conditions. A wafer inspection method according to any one of claims 1 to 3, characterized in that if it is determined in the determination step that the street is not set along the predetermined crystal orientation, the irradiation of the laser beam to the wafer is interrupted.

5. The wafer includes a device region on which the device is formed and an outer peripheral surplus region surrounding the device region where the device is not formed. The wafer inspection method according to any one of claims 1 to 3, characterized in that the laser beam irradiation step involves irradiating the outer peripheral excess region with the laser beam.

6. A wafer inspection method according to any one of claims 1 to 3, further comprising a notification step of notifying the operator if it is determined in the determination step that the street is not set along a predetermined crystal orientation.

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