Processing methods

Abstract

To provide a processing method capable of suppressing failure after a division of a wafer.SOLUTION: A processing method is a processing method of a wafer, having a front surface and a rear surface of a back surface of the front surface, and to which a division schedule line is set, comprising: a holding step 1001 of holding the front surface side of the wafer with a holding unit to exposure the front surface; and a modification layer formation step 1002 of repeating an irradiation of a laser beam along the division scheduled line from the front surface side while positioning a focal point of the laser beam of a wavelength having a penetrability of the wafer to an inner part of the wafer by changing a height position, and forming a plurality of modification layers to a thickness direction of the wafer along the same division scheduled line. In the modification layer formation step 1002, a modification layer is formed sequentially toward a direction from the rear surface to the front surface, and the modification layer is sequentially formed toward a direction directed to the rear surface from the front surface before an achievement of a first predetermined distance that a clack is generated when it is tried to form the modification layer in a second region at the front surface side, and the modification layer cannot be formed.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for processing a wafer having a first surface and a second surface on the back of the first surface, on which a planned division line is set.

Background Art

[0002] In the manufacturing process of semiconductor devices, a plurality of semiconductor devices are formed on a wafer, and the plurality of semiconductor devices are manufactured by dividing the wafer along a planned division line.

[0003] In recent years, a method has been widely adopted in which a laser beam having a wavelength that is transmissive to the wafer is irradiated onto the wafer to form a modified layer, which is a region modified inside the wafer, and then an external force is applied to the wafer to divide it starting from the modified layer.

[0004] Depending on the thickness and material of the wafer, a plurality of layers of modified layers are formed in the thickness direction of the wafer along the planned division line (see, for example, Patent Document 1). Usually, the position of the condensing point of the laser beam is formed in order from the surface of the wafer that is irradiated with the laser beam, i.e., the surface far from the incident surface of the laser beam, across to the incident surface (see, for example, Patent Document 2). This is because even if an attempt is made to condense the laser beam at a position farther from the incident surface in a state where the modified layer has already been formed on the incident surface side, the condensing of the laser beam is hindered by the already formed modified layer.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] On the other hand, when forming a modified layer sequentially from a position farther from the incident surface toward the incident surface, if the thickness of the unmodified layer region is insufficient, the modified layer formed in the unmodified region may meander or not be sufficiently modified, resulting in disorder in the formed modified layer.

[0007] If the modified layer is disordered, problems can arise such as the chip size of the formed semiconductor device not falling within the acceptable range, or a large amount of fragmentation waste being generated during splitting. Furthermore, if the fragmentation waste adheres to the device, it degrades its properties and interferes with subsequent processes such as bonding and packaging.

[0008] The object of the present invention is to provide a processing method that can suppress defects after wafer division. [Means for solving the problem]

[0009] To solve the above-mentioned problems and achieve the objective, the present invention provides a processing method for a wafer having a first surface and a second surface on the back of the first surface, wherein a division line is set, comprising: a holding step of holding the first surface side of the wafer with a holding unit to expose the second surface; and a modified layer formation step of positioning a focal point of a laser beam with a wavelength that is transparent to the wafer inside the wafer and irradiating the laser beam from the second surface side along the division line, repeating this while changing the height position of the focal point, thereby forming a plurality of modified layers in the thickness direction of the wafer along the same division line, wherein the modified layer formation step is characterized in that modified layers are formed sequentially in the direction from the first surface toward the second surface, and modified layers are formed sequentially in the direction from the second surface toward the first surface before the region on the second surface side where a modified layer has not yet been formed reaches a thickness where cracks would occur if a modified layer were to be formed, making it impossible to form a modified layer.

[0010] The present invention relates to a processing method for a wafer having a first surface and a second surface on the back of the first surface, wherein a division line is set, comprising: a holding step of holding the first surface side of the wafer with a holding unit to expose the second surface; and a modified layer formation step of positioning a focal point of a laser beam with a wavelength that is transparent to the wafer inside the wafer and irradiating the laser beam from the second surface side along the division line, repeating this while changing the height position of the focal point, thereby forming a plurality of modified layers in the thickness direction of the wafer along the same division line, wherein in the modified layer formation step, modified layers are formed sequentially in the direction from the first surface toward the second surface, and modified layers are formed sequentially in the direction from the second surface toward the first surface before the region on the second surface side that has not yet formed a modified layer reaches a thickness where cracks would occur if a modified layer were to be formed, making it impossible to form a modified layer,In the modified layer formation step, the laser beam is positioned at a first focusing point on the first surface and a second focusing point on the second surface side of the first focusing point, and is irradiated along the planned division line. When forming the modified layer sequentially in the direction from the first surface toward the second surface, the first focusing point is positioned ahead of the second focusing point in the processing direction. When forming the modified layer sequentially in the direction from the second surface toward the first surface, the second focusing point is positioned ahead of the first focusing point in the processing direction. Characterized by .

[0011] In the processing method described above, the modified layer formation step includes the formation of a first modified layer formed with the laser beam positioned at the first focal point, a crack extending from the first modified layer in the thickness direction of the wafer, a second modified layer formed with the laser beam positioned at the second focal point, and a crack extending from the second modified layer in the thickness direction of the wafer, and the first focal point and the second focal point may be positioned at a location where the first modified layer and the second modified layer are connected by the crack.

[0012] The present invention relates to a processing method for a wafer having a first surface and a second surface on the back of the first surface, wherein a division line is set, comprising: a holding step of holding the first surface side of the wafer with a holding unit to expose the second surface; and a modified layer formation step of positioning a focal point of a laser beam with a wavelength that is transparent to the wafer inside the wafer and irradiating the laser beam from the second surface side along the division line, repeating this while changing the height position of the focal point, thereby forming a plurality of modified layers in the thickness direction of the wafer along the same division line, wherein in the modified layer formation step, modified layers are formed sequentially in the direction from the first surface toward the second surface, and modified layers are formed sequentially in the direction from the second surface toward the first surface before the region on the second surface side that has not yet formed a modified layer reaches a thickness where cracks would occur if a modified layer were to be formed, making it impossible to form a modified layer, In the modified layer formation step, the laser beam is moved relative to the wafer in the processing direction, and the focal point of the laser beam is positioned at different locations in the thickness direction of the wafer and irradiated. The laser beam is also moved relative to the wafer in the processing direction, and the focal point on the first surface is positioned further forward in the processing direction than the focal point on the second surface, and the laser beam is irradiated onto the wafer to form half of the modified layer on the first surface of the wafer, of which multiple modified layers are to be formed on the wafer. After forming half of the modified layer on the first surface of the wafer, the laser beam is moved relative to the wafer in the processing direction, and the focal point on the second surface is positioned further forward in the processing direction than the focal point on the first surface, and the laser beam is irradiated onto the wafer to form the remaining half of the modified layer on the second surface of the wafer, of which multiple modified layers are to be formed on the wafer. Characterized by . [Effects of the Invention]

[0013] The present invention has an effect of suppressing defects after wafer dicing.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is a perspective view of a wafer to be processed in the processing method according to Embodiment 1. [Figure 2] FIG. 2 is a perspective view showing a configuration example of a laser processing apparatus for implementing the processing method according to Embodiment 1. [Figure 3] FIG. 3 is a diagram schematically showing the configuration of a laser beam irradiation unit of the laser processing apparatus shown in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view schematically showing a main part of an example of a wafer in which a modified layer is formed by the processing method according to Embodiment 1. [Figure 5] FIG. 5 is a flowchart showing the flow of the processing method according to Embodiment 1. [Figure 6] FIG. 6 is a cross-sectional view schematically showing a main part of a wafer after forming the modified layer on the back side most in the modified layer forming step of the processing method shown in FIG. 5. [Figure 7] FIG. 7 is a cross-sectional view schematically showing a main part of a wafer after forming the modified layers up to the third layer on the back side in the modified layer forming step of the processing method shown in FIG. 5. [Figure 8] FIG. 8 is a cross-sectional view schematically showing a main part of a wafer after forming the modified layer on the front side most in the modified layer forming step of the processing method shown in FIG. 5. [Figure 9] FIG. 9 is a cross-sectional view schematically showing a main part of an example of a wafer in which a modified layer is formed by the processing method according to Embodiment 2. [Figure 10] FIG. 10 is a cross-sectional view schematically showing a main part in a state of forming two modified layers on the back side in the modified layer forming step of the processing method according to Embodiment 2. [Figure 11] FIG. 11 is a cross-sectional view schematically showing a main part in a state of forming two modified layers in the center in the modified layer forming step of the processing method according to Embodiment 2. [Figure 12]FIG. 12 is a cross-sectional view schematically showing a main part of a state in which two modified layers on the front surface side in the modified layer formation step of the processing method according to Embodiment 2 are formed. [Figure 13] FIG. 13 is a cross-sectional view schematically showing a main part of a state in which three modified layers on the back surface side in the modified layer formation step of the processing method according to Embodiment 3 are formed. [Figure 14] FIG. 14 is a cross-sectional view schematically showing a main part of a state in which three modified layers on the front surface side in the modified layer formation step of the processing method according to Embodiment 3 are formed.

MODE FOR CARRYING OUT THE INVENTION

[0015] The mode (embodiment) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. Further, the constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Also, various omissions, substitutions, or changes in the configuration can be made without departing from the gist of the present invention.

[0016] 〔Embodiment 1〕 The processing method according to Embodiment 1 of the present invention will be described based on the drawings. FIG. 1 is a perspective view of a wafer to be processed in the processing method according to Embodiment 1. FIG. 2 is a perspective view showing a configuration example of a laser processing apparatus for carrying out the processing method according to Embodiment 1. FIG. 3 is a diagram schematically showing the configuration of a laser beam irradiation unit of the laser processing apparatus shown in FIG. 2. FIG. 4 is a cross-sectional view schematically showing a main part of an example of a wafer in which a modified layer is formed by the processing method according to Embodiment 1. FIG. 5 is a flowchart showing the flow of the processing method according to Embodiment 1.

[0017] (Wafer) The processing method according to Embodiment 1 is a processing method for the wafer 1 shown in Figure 1. The wafer 1 to be processed by the processing method according to Embodiment 1 is a disc-shaped semiconductor wafer or optical device wafer, etc., with a substrate 2 made of silicon, sapphire, gallium arsenide, or SiC (silicon carbide), etc. In Embodiment 1, the wafer 1 has a second surface, which is a front surface 3, and a first surface, which is a back surface 4, on the back side of the front surface 3, and the front surface 3 and the back surface 4 are formed in a parallel disc shape. Multiple division lines 5 are set on the front surface 3, and devices 6 are formed in each region partitioned in a grid shape by the division lines 5.

[0018] In Embodiment 1, device 6 is a MEMS (Micro Electro Mechanical System), but in the present invention, it is not limited to MEMS and may be, for example, an integrated circuit such as an IC (Integrated Circuit) or LSI (Large Scale Integration), an image sensor such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), or various types of memory (semiconductor memory devices).

[0019] The wafer 1 is divided into individual devices 6 by a laser processing apparatus 100 shown in Figures 2 and 3, which irradiates it with a laser beam 121 along the division line 5. In Embodiment 1, when the laser beam 121 is irradiated onto the wafer 1 by the laser processing apparatus 100, a disc-shaped protective tape 10 (shown in Figure 3) with a larger diameter than the wafer 1 is attached to the back surface 4, and an annular frame (not shown) with an inner diameter larger than the outer diameter of the wafer 1 is attached to the outer edge of the protective tape 10, and the wafer is supported within an opening inside the annular frame.

[0020] In Embodiment 1, the wafer 1 to be processed is, as described above, a disc-shaped semiconductor wafer or an optical device wafer, but the present invention is not limited to these and may be various plate-shaped workpieces. Furthermore, in the present invention, the wafer 1 to be processed may not have a device 6 formed on its surface 3.

[0021] (Laser processing equipment) The laser processing apparatus 100 shown in Figure 2 is a processing apparatus that laser processes (equivalent to processing) a wafer 1. The laser processing apparatus 100 shown in Figure 2 is a processing apparatus that irradiates the surface 3 of the wafer 1 with a pulsed laser beam 121 (shown in Figure 3) of a wavelength that is transparent to the substrate 2 and protective tape 10 that make up the wafer 1, along the planned division line 5.

[0022] As shown in Figure 2, the laser processing apparatus 100 includes a holding unit 110 for holding the wafer 1, a laser beam irradiation unit 120, a moving unit 130, an imaging unit 140, and a control unit 190 which is a control means.

[0023] The holding unit 110 holds the wafer 1 on a holding surface 111 parallel to the horizontal direction. The holding surface 111 is disc-shaped and made of porous ceramic or the like, and is connected to a suction source via a suction path or the like. The back surface 4 of the wafer 1 is placed on the holding surface 111 via a protective tape 10. The holding unit 110 holds the wafer 1 placed on the holding surface 111 by suction from the holding surface 111, which is then sucked by the suction source. Multiple clamping parts 112 are arranged around the holding unit 110 to hold an annular frame that supports the wafer 1 within the opening.

[0024] Furthermore, the holding unit 110 is rotated by the rotational movement unit 134 of the moving unit 130 around an axis that is perpendicular to the holding surface 111 and parallel to the Z-axis direction which is also parallel to the vertical direction. Together with the rotational movement unit 134, the holding unit 110 is moved in the X-axis direction (corresponding to the processing direction) parallel to the horizontal direction by the X-axis movement unit 131 of the moving unit 130, and moved in the Y-axis direction which is parallel to the horizontal direction and perpendicular to the X-axis direction by the Y-axis movement unit 132. The holding unit 110 is moved by the moving unit 130 between the processing area below the laser beam irradiation unit 120 and the loading / unloading area where the wafer 1 is loaded and unloaded, away from below the laser beam irradiation unit 120.

[0025] The laser beam irradiation unit 120 is a laser irradiation means equipped with a focusing lens 122 that focuses and irradiates a pulsed laser beam 121 (shown in Figure 3) onto a wafer 1 held by a holding unit 110. In Embodiment 1, a part of the laser beam irradiation unit 120 is supported so as to be movable in the Z-axis direction by a Z-axis moving unit 133 of a moving unit 130 provided on a vertical wall 102 erected from the main body 101 of the apparatus, as shown in Figure 2.

[0026] As shown in Figure 3, the laser beam irradiation unit 120 includes an oscillator 123 that emits a pulsed laser beam 121 with a wavelength that is transparent to the substrate 2 and protective tape 10 of the wafer 1, a focusing lens 122 that focuses the laser beam 121 emitted from the oscillator 123 onto the wafer 1 held on the holding surface 111 of the holding unit 110, and a reflecting mirror 124 that reflects the laser beam 121 emitted from the oscillator 123 toward the focusing lens 122.

[0027] The focusing lens 122 is positioned opposite the holding surface 111 of the holding unit 110 in the Z-axis direction. The focusing lens 122 is a focusing optical element that focuses and irradiates a pulsed laser beam 121 onto the wafer 1 held by the holding unit 110. The focusing lens 122 passes the laser beam 121 emitted from the oscillator 123 and focuses the laser beam 121 at the focusing point 126.

[0028] Furthermore, in Embodiment 1, the laser beam irradiation unit 120 includes a branching unit 125 capable of branching the laser beam 121 emitted from the oscillator 123. In Embodiment 1, the branching unit 125 is a so-called LCOS-SLM (Liquid Crystal On Silicon-Spatial Light Modulator) that adjusts the optical characteristics of the laser beam 121 emitted from the oscillator 123.

[0029] In Embodiment 1, the branching unit 125 has a display surface that displays a pattern for adjusting the optical characteristics of the laser beam 121, and adjusts the optical characteristics of the laser beam 121 by reflecting the laser beam 121 emitted by the oscillator 123 onto the display surface that displays the pattern. In Embodiment 1, the branching unit 125 can branch the laser beam 121 by displaying a pattern for branching the laser beam 121 on the display surface. In Embodiment 1, the branching unit 125 is positioned between the reflective mirror 124 and the focusing lens 122.

[0030] The moving unit 130 moves the holding unit 110 and the focusing point 126 of the laser beam 121 irradiated by the laser beam irradiation unit 120 relatively in the X-axis direction, Y-axis direction, Z-axis direction, and around an axis parallel to the Z-axis direction. The X-axis direction and Y-axis direction are mutually orthogonal and parallel to the holding surface 111 (i.e., the horizontal direction). The moving unit 130 includes an X-axis moving unit 131, which is a processing feed unit that moves the holding unit 110 in the X-axis direction; a Y-axis moving unit 132, which is an indexing feed unit that moves the holding unit 110 in the Y-axis direction; a Z-axis moving unit 133, which moves the focusing lens 122 included in the laser beam irradiation unit 120 in the Z-axis direction; and a rotational moving unit 134, which rotates the holding unit 110 around an axis parallel to the Z-axis direction.

[0031] The Y-axis movement unit 132 is a unit that relatively indexes and feeds the holding unit 110 and the focusing point 126 of the laser beam 121 of the laser beam irradiation unit 120. In Embodiment 1, the Y-axis movement unit 132 is installed on the main body 101 of the laser processing apparatus 100. The Y-axis movement unit 132 supports the movable plate 103 that supports the X-axis movement unit 131 so as to be movable in the Y-axis direction.

[0032] The X-axis movement unit 131 is a feeding means that feeds the holding unit 110 and the focusing point 126 of the laser beam 121 of the laser beam irradiation unit 120 relative to each other for processing. The X-axis movement unit 131 is installed on the moving plate 103. The X-axis movement unit 131 supports a second moving plate 104 that supports a rotational movement unit 134 that rotates the holding unit 110 around an axis parallel to the Z-axis direction, and the second moving plate 104 is movable in the X-axis direction. The second moving plate 104 supports the rotational movement unit 134 and the holding unit 110. The Z-axis movement unit 133 is installed on the vertical wall 102 and supports the laser beam irradiation unit 120 so as to be movable in the Z-axis direction. The rotational movement unit 134 supports the holding unit 110.

[0033] The X-axis moving unit 131, the Y-axis moving unit 132, and the Z-axis moving unit 133 are equipped with a well-known ball screw rotatably mounted around its axis, a well-known pulse motor for rotating the ball screw around its axis, and a well-known guide rail that supports the moving plates 103 and 104 so as to be movable in the X-axis or Y-axis direction, and also supports the laser beam irradiation unit 120 so as to be movable in the Z-axis direction. The rotational moving unit 134 is equipped with a motor for rotating the holding unit 110 around its axis, etc.

[0034] Furthermore, the laser processing apparatus 100 includes an X-axis position detection unit (not shown) for detecting the position of the holding unit 110 in the X-axis direction, a Y-axis position detection unit (not shown) for detecting the position of the holding unit 110 in the Y-axis direction, and a Z-axis position detection unit for detecting the position of the focusing lens 122 included in the laser beam irradiation unit 120 in the Z-axis direction. Each position detection unit outputs the detection result to the control unit 190.

[0035] The imaging unit 140 images the wafer 1 held by the holding unit 110. The imaging unit 140 is equipped with an image sensor such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary MOS) image sensor whose objective lens is facing in the Z-axis direction.

[0036] The imaging unit 140 acquires the image captured by the image sensor and outputs the acquired image to the control unit 190. The imaging unit 140 also images the wafer 1 held on the holding surface 111 of the holding unit 110 and acquires an image for performing alignment, which involves positioning the wafer 1 with the laser beam irradiation unit 120.

[0037] The control unit 190 controls the aforementioned components of the laser processing apparatus 100 to cause the laser processing apparatus 100 to perform laser processing operations on the wafer 1. The control unit 190 is a computer having an arithmetic processing unit with a microprocessor such as a CPU (central processing unit), a storage device with memory such as ROM (read-only memory) or RAM (random access memory), and an input / output interface device. The arithmetic processing unit of the control unit 190 performs calculations according to the computer program stored in the storage device and outputs control signals for controlling the laser processing apparatus 100 to the aforementioned components of the laser processing apparatus 100 via the input / output interface device, thereby realizing the functions of the control unit 190.

[0038] Furthermore, the laser processing apparatus 100 includes a display unit, which is a display means consisting of a liquid crystal display device that displays the status of processing operations and images, and an input unit, which is an input means used by the operator to input processing conditions and the like. The display unit and the input unit are connected to the control unit 190. The input unit consists of at least one of a touch panel provided on the display unit and an external input device such as a keyboard.

[0039] (Processing method) The processing method according to Embodiment 1 involves a laser processing apparatus 100 irradiating a wafer 1 with a laser beam 121 from the surface 3 side along the planned division line 5 to form a modified layer 7 (shown in Figure 4) inside the substrate 2 of the wafer 1 along the planned division line 5. In Embodiment 1, as shown in Figure 4, the processing method forms multiple layers (five layers in Embodiment 1) of the modified layer 7 at mutually different positions in the thickness direction of each planned division line 5 of the wafer 1.

[0040] The modified layer 7 refers to a region whose density, refractive index, mechanical strength, and other physical properties differ from those of the surrounding area. Examples include melted regions, cracked regions, dielectric breakdown regions, refractive index change regions, and regions where these regions are mixed. Furthermore, the modified layer 7 has lower mechanical strength and other properties than other parts of the substrate 2 of the wafer 1. When the modified layer 7 is formed inside the substrate 2 of the wafer 1, cracks 8 are formed that extend from the modified layer 7 in the thickness direction of the wafer 1 (hereinafter simply referred to as the thickness direction).

[0041] In Embodiment 1, the region 12 within a first predetermined distance 11 from the surface 3 side, which is the second surface of the wafer 1, is a region where, if the modified layer 7 is formed on the back surface 4 side, which is the first surface, even if a focal point 126 is set within this region 12 and a laser beam 121 is irradiated from the surface 3 side, cracks will occur due to the impact of the laser beam 121 irradiation before the modified layer 7 can be formed, and the modified layer 7 cannot be formed. In other words, the first predetermined distance 11 is a thickness where, if the modified layer 7 is formed on the back surface 4 side, which is the region 12, cracks 8 will occur and the modified layer 7 cannot be formed.

[0042] The processing method according to Embodiment 1 comprises a holding step 1001 and a modified layer forming step 1002, as shown in Figure 5.

[0043] (Holding step) The holding step 1001 is a step in which the back surface 4 side of the wafer 1 is held by the holding unit 110 to expose the front surface 3. In the holding step 1001, the control unit 190 of the laser processing apparatus 100 with the configuration described above receives and registers the processing conditions input by the operator, and the wafer 1 is placed on the holding surface 111 of the holding unit 110, which is positioned in the loading / unloading area, with the back surface 4 side via the protective tape 10. The processing conditions include the output of the laser beam 121, the repetition frequency, the movement speed of the holding unit 110 in the X-axis direction when irradiating the wafer 1 with the laser beam 121 (hereinafter referred to as the processing feed speed), the position of the focal point 126 in the thickness direction of the wafer 1 when forming each layer of modified layer 7 to be formed in each planned division line 5, and the order in which the multiple layers of modified layer 7 to be formed in each planned division line 5 are formed.

[0044] In Embodiment 1, during the holding step 1001, when the control unit 190 receives a processing operation start instruction from the operator, the laser processing apparatus 100 starts the processing operation, i.e., the processing method according to Embodiment 1, and the control unit 190 suction-holds the wafer 1 to the holding surface 111 of the holding unit 110, and clamps the annular frame with the clamp portion 112.

[0045] (Modified layer formation step) Figure 6 is a schematic cross-sectional view of the main part of the wafer after the most backside modified layer has been formed in the modified layer formation step of the processing method shown in Figure 5. Figure 7 is a schematic cross-sectional view of the main part of the wafer after the first three modified layers on the backside have been formed in the modified layer formation step of the processing method shown in Figure 5. Figure 8 is a schematic cross-sectional view of the main part of the wafer after the most frontside modified layer has been formed in the modified layer formation step of the processing method shown in Figure 5.

[0046] The modified layer formation step 1002 is a step in which, after performing the holding step 1001, a focal point 126 of a laser beam 121 with a wavelength that is transparent to the wafer 1 is positioned inside the wafer 1, and the laser beam 121 is irradiated from the surface 3 side along the planned division line 5, and this is repeated while changing the height position of the focal point 126, thereby forming multiple modified layers 7 in the thickness direction of the wafer 1 along the same planned division line 5.

[0047] In the modified layer formation step 1002, the laser processing apparatus 100 uses a control unit 190 to control a moving unit 130 to move the holding unit 110 to the processing area, and an imaging unit 140 captures an image of the wafer 1 held by the holding unit 110 to acquire an image and perform alignment. In the modified layer formation step 1002, as shown in Figure 6, the focusing point 126 of the laser beam irradiation unit 120 is positioned inside the substrate 2, and the laser processing apparatus 100 irradiates the wafer 1 with a pulsed laser beam 121 from the surface 3 side of the wafer 1 along the planned division line 5 while moving the holding unit 110 and the laser beam irradiation unit 120 relatively along the planned division line 5. In Embodiment 1, the laser processing apparatus 100 uses a control unit 190 to control a branching unit 125, and irradiates the laser beam 121 without branching the laser beam 121 to the branching unit 125.

[0048] In Embodiment 1, in the modified layer formation step 1002, the laser processing apparatus 100 first forms the modified layer 7 closest to the back surface 4 among the multiple modified layers 7 based on processing conditions, and then sequentially forms the modified layers 7 in the direction from the back surface 4 toward the front surface 3. Specifically, in Embodiment 1, in the modified layer formation step 1002, the laser processing apparatus 100 sets a focusing point 126 at the height position when the modified layer 7 closest to the back surface 4 is formed, based on the processing conditions of the control unit 190, and while moving the holding unit 110 in the X-axis direction (parallel to the planned division line 5) on the X-axis moving unit 131 of the moving unit 130, the laser beam 121 is irradiated along the planned division line 5 to the center of each planned division line 5 in the width direction of the wafer 1 held by the holding unit 110. Thus, in Embodiment 1, in the modified layer formation step 1002, the laser processing apparatus 100 forms the modified layer 7 closest to the back surface 4 among the multiple modified layers 7, as shown in Figure 6.

[0049] In Embodiment 1, in the modified layer formation step 1002, the laser processing apparatus 100 sets a focusing point 126 at the height position where the second modified layer 7 is formed from the back surface 4 based on the processing conditions of the control unit 190, and while moving the holding unit 110 in the X-axis direction on the X-axis moving unit 131 of the moving unit 130, the laser processing apparatus 100 irradiates the center of each planned division line 5 in the width direction of each planned division line 5 of the wafer 1 held by the holding unit 110 along the planned division line 5. Thus, in Embodiment 1, in the modified layer formation step 1002, the laser processing apparatus 100 forms multiple modified layers 7 (three layers in Embodiment 1) from the back surface 4 side, as shown in Figure 6.

[0050] In Embodiment 1, in the modified layer formation step 1002, before forming the modified layer 7 in the second region 14 (corresponding to the region without a modified layer) located on the back surface 4 side of the aforementioned region 12 and within a second predetermined distance 13 from the surface 3, the laser processing apparatus 100 sets a focusing point 126 at the height position for forming the modified layer 7 closest to the surface 3 based on the processing conditions, and while moving the holding unit 110 in the X-axis direction on the X-axis moving unit 131 of the moving unit 130, the laser beam 121 is irradiated along the division line 5 to the center of each division line 5 in the width direction of the wafer 1 held by the holding unit 110. Thus, in Embodiment 1, in the modified layer formation step 1002, before forming the modified layer 7 in the second region 14 located on the back surface 4 side of the aforementioned region 12 and within a second predetermined distance 13 from the surface 3, the laser processing apparatus 100 forms the modified layer 7 closest to the surface 3 in the aforementioned region 12, as shown in Figure 8. Furthermore, the second predetermined distance 13 mentioned above is longer than the first predetermined distance 11.

[0051] In Embodiment 1, during the modified layer formation step 1002, the laser processing apparatus 100 sets a focusing point 126 at the height position where the second modified layer 7 is formed from the surface 3, based on the processing conditions set by the control unit 190. The laser processing apparatus 100 moves the holding unit 110 in the X-axis direction using the X-axis moving unit 131 of the moving unit 130, and irradiates the center of each planned division line 5 in the width direction of the wafer 1 held by the holding unit 110 with the laser beam 121 along the planned division line 5. Thus, in Embodiment 1, during the modified layer formation step 1002, the laser processing apparatus 100 forms the modified layers 7 sequentially in the direction from the surface 3 side to the back surface 4 side within the second region 14 on the surface 3 side, before reaching the first predetermined distance 11 from the surface 3 where cracks occur and the modified layer 7 cannot be formed if the second region 14 on the surface 3 side attempts to form the modified layer 7, thereby forming all the layers of modified layer 7 specified by the processing conditions on each planned division line 5, as shown in Figure 4.

[0052] In the modified layer formation step 1002, the laser processing apparatus 100 forms all the modified layers 7 specified by the processing conditions inside the wafer 1 along all the planned division lines 5. Then, it stops irradiating the laser beam 121 from the laser beam irradiation unit 120, moves the holding unit 110 to the loading / unloading area, stops the suction holding of the holding unit 110, and releases the clamping of the annular frame of the clamping part 112, thereby ending the processing operation, i.e., the processing method according to Embodiment 1. After that, the wafer 1 is divided into individual devices 6 starting from the modified layer 7, with the protective tape 10 expanded.

[0053] In the processing method according to Embodiment 1 described above, in the modified layer formation step 1002, the modified layer 7 is formed sequentially in the direction from the back surface 4 to the front surface 3, and the modified layer 7 is formed sequentially in the direction from the front surface 3 to the back surface 4 before reaching the first predetermined distance 11 in which cracks occur and the modified layer 7 cannot be formed in the second region 14, which is the region on the front surface 3 where the modified layer has not yet been formed. For this reason, the processing method according to Embodiment 1 can suppress the meandering of the modified layer 7 closest to the front surface 3, can sufficiently form the modified layer 7 closest to the front surface 3, and can suppress the occurrence of disorder in the modified layer 7 closest to the front surface 3.

[0054] Therefore, the processing method according to Embodiment 1 can suppress the size of the individually divided devices 6 from falling outside the acceptable range, suppress the generation of fragmentation waste during division, suppress the adhesion of fragmentation waste to the divided devices 6 and the resulting degradation of their properties, and suppress any interference with subsequent bonding and packaging. As a result, the processing method according to Embodiment 1 has the effect of suppressing defects in the wafer 1 after division.

[0055] [Embodiment 2] The processing method according to Embodiment 2 of the present invention will be described with reference to the drawings. Figure 9 is a schematic cross-sectional view showing the main part of an example of a wafer on which a modified layer has been formed by the processing method according to Embodiment 2. Figure 10 is a schematic cross-sectional view showing the main part of the state in which two modified layers are formed on the back side of the modified layer formation step of the processing method according to Embodiment 2. Figure 11 is a schematic cross-sectional view showing the main part of the state in which two central modified layers are formed in the modified layer formation step of the processing method according to Embodiment 2. Figure 12 is a schematic cross-sectional view showing the main part of the state in which two modified layers are formed on the front side of the modified layer formation step of the processing method according to Embodiment 2. Note that Figures 9, 10, 11, and 12 use the same reference numerals as Embodiment 1 for the same parts and their descriptions are omitted.

[0056] The processing method according to Embodiment 2 involves forming multiple modified layers 7 (six layers in Embodiment 2) at mutually different positions in the thickness direction of each planned division line 5 of the wafer 1, as shown in Figure 9. Furthermore, in the processing method according to Embodiment 2, in the modified layer formation step 1002, as shown in Figure 10, the control unit 190 of the laser processing apparatus 100 controls the branching unit 125 to branch the laser beam 121 emitted by the oscillator 123 into two beams. While moving the laser beam 121 in the X-axis direction relative to the wafer 1, the focal point 126 of the laser beam 121 is positioned at the focal point 126 on the back surface 4 side (hereinafter referred to as the first focal point 126-1, as shown in Figure 10, etc.) and at the focal point 126 on the front surface 3 side of the first focal point 126-1 (hereinafter referred to as the second focal point 126-2, as shown in Figure 10, etc.), and the beam is irradiated along the planned division line 5 in this state, thereby forming two modified layers 7 by moving the holding unit 110 in the X-axis direction in a single motion.

[0057] Furthermore, in Embodiment 2, the processing method involves forming a modified layer 7 (hereinafter referred to as the first modified layer 7-1) with the laser beam 121 positioned at the first focal point 126-1, and a crack 8 extending from the first modified layer 7-1 in the thickness direction of the wafer 1. Also, forming a modified layer 7 (hereinafter referred to as the second modified layer 7-2) with the laser beam 121 positioned at the second focal point 126-2, and a crack 8 extending from the second modified layer 7-2 in the thickness direction of the wafer 1. The first focal point 126-1 and the second focal point 126-2 are positioned at the location where the first modified layer 7-1 and the second modified layer 7-2 are connected by the crack 8.

[0058] In Embodiment 2, in the modified layer formation step 1002, the laser processing apparatus 100 first forms the modified layers 7-1 and 7-2 closest to the back surface 4 among the multiple modified layers 7 based on processing conditions, and then forms the modified layers 7-1 and 7-2 sequentially in the direction from the back surface 4 toward the front surface 3. Specifically, in Embodiment 2, in the modified layer formation step 1002, the laser processing apparatus 100 sets the first focusing point 126-1 and the second focusing point 126-2 at the height position when the control unit 190 forms the two modified layers 7-1 and 7-2 closest to the back surface 4 among the multiple modified layers 7 based on processing conditions, and while moving the holding unit 110 in the X-axis direction on the X-axis moving unit 131 of the moving unit 130, it irradiates the center of each planned division line 5 in the width direction of the wafer 1 held by the holding unit 110 with two laser beams 121 along the planned division line 5.

[0059] At this time, the laser processing apparatus 100 moves two laser beams 121 relative to the holding unit 110 in the X1 direction (corresponding to the processing direction and one of the directions parallel to the planned division line 5) to irradiate the wafer 1, as shown in Figure 10, for example, and the first focal point 126-1 of the laser beam 121 that forms the first modified layer 7-1 closer to the back surface 4 is positioned in front of the second focal point 126-2 in the X1 direction. Thus, in Embodiment 2, in the modified layer formation step 1002, the laser processing apparatus 100 forms the two modified layers 7-1 and 7-2 closest to the back surface 4 among the multiple modified layers 7.

[0060] In Embodiment 2, during the modified layer formation step 1002, the laser processing apparatus 100 sets a first focusing point 126-1 and a second focusing point 126-2 at the height position when forming the two modified layers 7-1 and 7-2 that are in the center of the thickness direction of the multiple modified layers 7 (closer to the surface 3 than the two modified layers 7-1 and 7-2 that have already been formed and are closest to the back surface 4), based on the processing conditions set by the control unit 190. The laser processing apparatus 100 moves the holding unit 110 in the X-axis direction using the X-axis moving unit 131 of the moving unit 130, and irradiates the center of each planned division line 5 in the width direction of the wafer 1 held by the holding unit 110 with a laser beam 121 along the planned division line 5.

[0061] At this time, the laser processing apparatus 100 moves two laser beams 121 relative to the holding unit 110 in the X2 direction (opposite to the X1 direction and corresponding to the processing progress direction, and the other direction parallel to the planned division line 5) as shown in Figure 11, and irradiates the wafer 1, while the first focusing point 126-1 is positioned in front of the second focusing point 126-2 in the X2 direction. Thus, in the modified layer formation step 1002, the laser processing apparatus 100 forms the two central modified layers 7-1 and 7-2 of the multiple modified layers 7.

[0062] Thus, in Embodiment 2, in the modified layer formation step 1002, the laser processing apparatus 100 positions the first focusing point 126-1 in front of the second focusing point 126-2 in the X1 and X2 directions, and forms the first modified layer 7-1 on the back surface 4 side before the second modified layer 7-2 on the front surface 3 side, thereby forming the modified layers 7-1 and 7-2 sequentially in the direction from the back surface 4 side to the front surface 3 side.

[0063] In Embodiment 2, in the modified layer formation step 1002, before the laser processing apparatus 100 forms the modified layer 7 in a second region 14 within a second predetermined distance 13 from the surface 3, the control unit 190 sets a first focusing point 126-1 and a second focusing point 126-2 at height positions when forming the two modified layers 7-1 and 7-2 that are closest to the surface 3 (closer to the surface 3 than the modified layer 7 that has already been formed) among the plurality of modified layers 7, based on the processing conditions. The laser processing apparatus 100 then moves the holding unit 110 in the X-axis direction on the X-axis moving unit 131 of the moving unit 130, and irradiates the center of each planned division line 5 in the width direction of the wafer 1 held by the holding unit 110 with a laser beam 121 along the planned division line 5.

[0064] At this time, the laser processing apparatus 100 moves two laser beams 121 in the X1 direction, which is parallel to the X-axis direction relative to the holding unit 110, as shown in Figure 12, and irradiates the wafer 1, while positioning the second focusing point 126-2 in the X1 direction in front of the first focusing point 126-1. Thus, in the modified layer formation step 1002 in Embodiment 2, the laser processing apparatus 100 forms all the modified layers 7 of the layers specified by the processing conditions on each planned division line 5, as shown in Figure 9.

[0065] Thus, in Embodiment 2, in the modified layer formation step 1002, when the laser processing apparatus 100 forms the modified layer 7 in a second region 14 within a second predetermined distance 13 from the surface 3, the second focusing point 126-2 is positioned in front of the first focusing point 126-1 in the X1 direction, and the second modified layer 7-2 on the surface 3 side is formed before the first modified layer 7-1 on the back surface 4 side, and the modified layers 7 are formed sequentially in the direction from the surface 3 side to the back surface 4 side.

[0066] In Embodiment 2, in the modified layer formation step 1002, the laser processing apparatus 100 forms all the modified layers 7 specified by the processing conditions inside the wafer 1 along all the planned division lines 5, and then terminates the processing method in the same manner as in Embodiment 1. After that, the wafer 1 is divided into individual devices 6 starting from the modified layers 7.

[0067] In the processing method according to Embodiment 2, in the modified layer formation step 1002, the modified layer 7 is formed sequentially in the direction from the back surface 4 side toward the front surface 3 side, and the modified layer 7 is formed sequentially in the direction from the front surface 3 side toward the back surface 4 side before reaching the first predetermined distance 11 in which cracks occur when attempting to form the modified layer 7 in the second region 14, which is the region on the front surface 3 side where the modified layer has not yet been formed, and the modified layer 7 cannot be formed. As a result, the processing method according to Embodiment 2 has the effect of suppressing defects after the wafer 1 is divided, similar to Embodiment 1.

[0068] Furthermore, in the processing method according to Embodiment 2, the laser beam 121 emitted by the oscillator 123 is split into two, and the focal points 126 of the laser beam 121 are positioned at a first focal point 126-1 on the back surface 4 side and a second focal point 126-2 on the front surface 3 side, respectively, and irradiated along the planned division line 5. Since two modified layers 7-1 and 7-2 are formed by a single movement of the holding unit 110 in the X-axis direction, productivity can be improved.

[0069] Furthermore, in the processing method according to Embodiment 2, when the modified layer 7 is formed sequentially in the direction from the back surface 4 to the front surface 3, the first focusing point 126-1 is positioned in front of the second focusing point 126-2 in the X1 and X2 directions, so that the formation of the first modified layer 7-1 is not affected by the second modified layer 7-2.

[0070] Furthermore, in the processing method according to Embodiment 2, before forming the modified layer 7 in the second region 14 within a second predetermined distance 13 from the surface 3, the second focusing point 126-2 is positioned in front of the first focusing point 126-1 in the X1 direction, and the modified layer 7 is formed sequentially in the direction from the surface 3 side toward the back surface 4 side. As a result, in the processing method according to Embodiment 2, when forming the second modified layer 7-2 closest to the surface 3, the first modified layer 7-1 is not formed on the back surface 4 side of this second modified layer 7-2, so that the second modified layer 7-2 closest to the surface 3 does not meander, a second modified layer 7-2 closest to the surface 3 can be sufficiently formed, and disturbances in the second modified layer 7-2 closest to the surface 3 can be suppressed.

[0071] Furthermore, in the processing method according to Embodiment 2, the first focusing point 126-1 and the second focusing point 126-2 are positioned at locations where the first modified layer 7-1 and the second modified layer 7-2 are connected by cracks 8 extending from these modified layers 7-1 and 7-2, thus preventing the generation of fragmented debris. In particular, since wafer 1, in which device 6 is a MEMS, cannot be cleaned, preventing the generation of fragmented debris is important, and problems such as the device 6 not being able to perform its function due to fragmented debris can be suppressed.

[0072] [Embodiment 3] The processing method according to Embodiment 3 of the present invention will be described with reference to the drawings. Figure 13 is a schematic cross-sectional view showing the main part of the state in which the three modified layers are formed on the back side of the modified layer formation step of the processing method according to Embodiment 3. Figure 14 is a schematic cross-sectional view showing the main part of the state in which the three modified layers are formed on the front side of the modified layer formation step of the processing method according to Embodiment 3. Note that the same reference numerals are used for the same parts as in Embodiment 1 in Figures 13 and 14, and their descriptions are omitted.

[0073] The processing method according to Embodiment 3 forms multiple layers (six layers in Embodiment 3, similar to Embodiment 2) of modified layers 7 at mutually different positions in the thickness direction of each planned division line 5 of the wafer 1. Furthermore, in the processing method according to Embodiment 3, in the modified layer formation step 1002, as shown in Figure 13, the control unit 190 of the laser processing apparatus 100 controls the branching unit 125 to branch the laser beam 121 emitted by the oscillator 123 into three (multiple) beams. While moving the laser beam 121 in the X-axis direction relative to the wafer 1, multiple (three in Embodiment 3) focal points 126 of the laser beam 121 are positioned at mutually different positions in the thickness direction of the wafer 1, and the beam is irradiated along the planned division line 5, thereby forming multiple layers (three layers in Embodiment 3) of modified layers 7 with a single movement of the holding unit 110 in the X-axis direction.

[0074] In Embodiment 3, in the modified layer formation step 1002, the laser processing apparatus 100 first forms multiple modified layers 7 sequentially in the direction from the back surface 4 toward the front surface 3, based on the processing conditions. Specifically, in Embodiment 2, in the modified layer formation step 1002, the laser processing apparatus 100 sets a focusing point 126 at the height position when forming the three modified layers 7 closer to the back surface 4, based on the processing conditions of the control unit 190, and while moving the holding unit 110 in the X-axis direction on the X-axis moving unit 131 of the moving unit 130, it irradiates the center of each planned division line 5 in the width direction of the wafer 1 held by the holding unit 110 with three laser beams 121 along the planned division line 5.

[0075] At this time, the laser processing apparatus 100 moves three laser beams 121 in the X1 direction, which is parallel to the X-axis direction relative to the holding unit 110, as shown in Figure 13, and irradiates the wafer 1 with the laser beams 121, while positioning the focal point 126 on the back surface 4 side in front of the focal point 126 on the front surface 3 side in the X1 direction. Thus, in the modified layer formation step 1002 in Embodiment 3, the laser processing apparatus 100 forms half of the modified layer 7 on the back surface 4 side of the multiple modified layers 7 to be formed on the wafer 1.

[0076] In Embodiment 3, in the modified layer formation step 1002, the laser processing apparatus 100 forms half of the modified layer 7 on the back surface 4 side of the wafer 1, one of the multiple modified layers 7 to be formed on the wafer 1. Before forming the modified layer 7 in the second region 14 within a second predetermined distance 13 from the surface 3, the control unit 190 sets a focusing point 126 at the height position when forming the three modified layers 7 closer to the surface 3, one of the multiple modified layers 7, based on the processing conditions. The holding unit 110 is moved in the X-axis direction by the X-axis moving unit 131 of the moving unit 130, and three laser beams 121 are irradiated along the division line 5 at the center of each division line 5 in the width direction of the wafer 1 held by the holding unit 110.

[0077] At this time, the laser processing apparatus 100 moves three laser beams 121 in the X2 direction, which is parallel to the X-axis direction relative to the holding unit 110, as shown in Figure 14, and irradiates the wafer 1 with the laser beams 121, while positioning the focal point 126 on the surface 3 side in front of the focal point 126 on the back surface 4 side in the X2 direction. Thus, in the modified layer formation step 1002 in Embodiment 3, the laser processing apparatus 100 forms the remaining half of the modified layer 7 on the surface 3 side of the multiple modified layers 7 to be formed on the wafer 1.

[0078] Thus, in Embodiment 3, when the laser processing apparatus 100 forms three (half) of the multiple modified layers 7 closer to the back surface 4, it positions the focal point 126 on the back surface 4 side forward in the X1 direction compared to the focal point 126 on the front surface 3 side, and irradiates the wafer 1 with the laser beam 121, thereby forming the modified layers 7 on the back surface 4 side before the modified layers 7 on the front surface 3 side, and forming the modified layers 7 sequentially in the direction from the back surface 4 side toward the front surface 3. Also in Embodiment 3, when the laser processing apparatus 100 forms three (the remaining half) of the multiple modified layers 7 closer to the front surface 3, it positions the focal point 126 on the front surface 3 side forward in the X2 direction compared to the focal point 126 on the back surface 4 side, and irradiates the wafer 1 with the laser beam 121, thereby forming the modified layers 7 on the front surface 3 side before the modified layers 7 on the back surface 4 side, and forming the modified layers 7 sequentially in the direction from the front surface 3 side toward the back surface 4. In the processing method according to Embodiment 3, similar to Embodiment 2, the focusing point 126 is positioned at a location where the modified layers 7, which are formed at intervals in each thickness direction, are connected by cracks 8.

[0079] In the processing method according to Embodiment 3, in the modified layer formation step 1002, the modified layer 7 is formed sequentially in the direction from the back surface 4 side toward the front surface 3 side, and the modified layer 7 is formed sequentially in the direction from the front surface 3 side toward the back surface 4 side before reaching the first predetermined distance 11 in which cracks occur when attempting to form the modified layer 7 in the second region 14, which is the region on the front surface 3 side where the modified layer has not yet been formed, and the modified layer 7 cannot be formed. As a result, the processing method according to Embodiment 3 has the effect of suppressing defects after the wafer 1 is divided, similar to Embodiment 1.

[0080] Furthermore, the processing method according to Embodiment 3 involves splitting the laser beam 121 emitted by the oscillator 123 into three beams, positioning the focal points 126 of the laser beams 121 at different locations in the thickness direction of the wafer 1, and irradiating along the planned division line 5. This allows for the formation of three modified layers 7 by a single movement of the holding unit 110 in the X-axis direction, thereby improving productivity.

[0081] Furthermore, in the processing method according to Embodiment 3, the laser beam 121 is moved in the X1 direction relative to the wafer 1 to form half of the modified layer 7 on the back surface 4 side, and the laser beam 121 is moved in the X2 direction relative to the wafer 1 to form the remaining half of the modified layer 7 on the front surface 3 side. As a result, a predetermined number of modified layers 7 can be formed on each planned division line 5 with a single reciprocating movement of the holding unit 110 in the X-axis direction. Consequently, the laser processing apparatus 100 can improve productivity.

[0082] It should be noted that the present invention is not limited to the embodiments described above. That is, it can be implemented with various modifications without departing from the core of the present invention. In embodiments 1 to 3, the front surface 3 of the wafer 1 is the second surface and the back surface 4 is the first surface. In the modified layer formation step 1002, the modified layer 7 is formed sequentially in the direction from the back surface 4 toward the front surface 3. The modified layer 7 is formed sequentially in the direction from the front surface 3 toward the back surface 4 before reaching a first predetermined distance 11 in which cracks occur and the modified layer 7 cannot be formed in the second region 14 on the front surface 3 side, which is the region where the modified layer has not yet been formed.

[0083] However, in the present invention, especially when the device 6 is not a MEMS, the front surface 3 of the wafer 1 is designated as the first surface and the back surface 4 as the second surface, and a protective tape 10 is attached to the front surface 3. In the modified layer formation step 1002, a laser beam 121 may be irradiated from the back surface 4 side. In this case, the modified layer 7 closest to the front surface 3 is formed, and then modified layers 7 are formed sequentially in the direction from the front surface 3 toward the back surface 4. Modified layers 7 are formed sequentially in the direction from the back surface 4 toward the front surface 3 before reaching a first predetermined distance 11 where cracks occur and modified layers 7 cannot be formed in the second region 14, which is the unformed modified layer region on the back surface 4 side. In this case, the first predetermined distance 11 is the thickness at which, if the modified layer 7 is formed on the front surface 3 side of the region 12 within the first predetermined distance 11 from the back surface 4 side, which is the second surface of the wafer 1, cracks 8 occur and modified layers 7 cannot be formed. The second region 14 is the region within the second predetermined distance 13 from the back surface 4 in the thickness direction.

[0084] Furthermore, in the present invention, a protective tape 10 may be attached to the second surface of the wafer 1, and in the modified layer formation step 1002, a laser beam 121 may be irradiated from the second surface side of the wafer 1 through the tape to form the modified layer 7. [Explanation of Symbols]

[0085] 1 wafer 3 Surface (2nd side, 1st side) 4. Reverse side (Front side 1, Front side 2) Planned division lines (5 divisions) 7. Modified layer 7-1 First Modified Layer 7-2 Second Modified Layer 8 cracks 11. First predetermined distance (thickness at which a modified layer cannot be formed) 14. Second region (region where the modified layer has not yet formed) 110 Holding Unit 121 Laser beam 126 Focusing points 126-1 1st focal point 126-2 2nd focal point 1001 Holding step 1002 Modified layer formation step X,X1,X2 Processing direction

Claims

1. A method for processing a wafer having a first surface and a second surface on the back of the first surface, wherein a division line is set, A holding step in which the first side of the wafer is held by a holding unit to expose the second side, The process includes a modified layer formation step in which a laser beam with a wavelength that is transparent to the wafer is focused at a focal point within the wafer, and the laser beam is irradiated from the second surface side along the planned division line, with the height of the focal point being changed repeatedly to form a plurality of modified layers in the thickness direction of the wafer along the same planned division line, The modification layer formation step involves sequentially forming the modification layer in the direction from the first surface toward the second surface, and forming the modification layer sequentially in the direction from the second surface toward the first surface before the region on the second surface side where the modification layer has not yet formed reaches a thickness where cracks would occur if the modification layer were to be formed, making it impossible to form the modification layer.

2. A method for processing a wafer having a first surface and a second surface on the back of the first surface, wherein a division line is set, A holding step in which the first side of the wafer is held by a holding unit to expose the second side, The process includes a modified layer formation step in which a laser beam with a wavelength that is transparent to the wafer is focused at a focal point within the wafer, and the laser beam is irradiated from the second surface side along the planned division line, with the height of the focal point being changed repeatedly to form a plurality of modified layers in the thickness direction of the wafer along the same planned division line, In the modified layer formation step, the modified layer is formed sequentially in the direction from the first surface toward the second surface, and before the region on the second surface where the modified layer has not yet formed reaches a thickness where cracks would occur and the modified layer cannot be formed, the modified layer is formed sequentially in the direction from the second surface toward the first surface. In the modified layer formation step, the laser beam is positioned at a first focusing point on the first surface side and a second focusing point on the second surface side of the first focusing point, and is irradiated along the planned division line. When forming modified layers sequentially in the direction from the first surface toward the second surface, the first focusing point is positioned ahead of the second focusing point in the processing direction. A processing method in which, when forming modified layers sequentially in the direction from the second surface toward the first surface, the second focusing point is positioned ahead of the first focusing point in the processing direction.

3. In the modified layer formation step, A first modified layer formed with the laser beam positioned at the first focal point, and a crack extending from the first modified layer in the thickness direction of the wafer. A second modified layer is formed with the laser beam positioned at the second focal point, and a crack is formed extending from the second modified layer in the thickness direction of the wafer. The processing method according to claim 2, wherein the first light-gathering point and the second light-gathering point are positioned at the location where the first modified layer and the second modified layer are connected by the crack.

4. A method for processing a wafer having a first surface and a second surface on the back of the first surface, wherein a division line is set, A holding step in which the first side of the wafer is held by a holding unit to expose the second side, The process includes a modified layer formation step in which a laser beam with a wavelength that is transparent to the wafer is focused at a focal point within the wafer, and the laser beam is irradiated from the second surface side along the planned division line, with the height of the focal point being changed repeatedly to form a plurality of modified layers in the thickness direction of the wafer along the same planned division line, In the modified layer formation step, the modified layer is formed sequentially in the direction from the first surface toward the second surface, and before the region on the second surface where the modified layer has not yet formed reaches a thickness where cracks would occur and the modified layer cannot be formed, the modified layer is formed sequentially in the direction from the second surface toward the first surface. In the modified layer formation step, The laser beam is moved relative to the wafer in the processing direction, and the focal point of the laser beam is positioned at different locations in the thickness direction of the wafer and irradiated. The laser beam is moved relative to the wafer in the processing direction, and the focal point on the first surface is positioned ahead of the focal point on the second surface in the processing direction, and the laser beam is irradiated onto the wafer to form the modified layer on the first surface half of the wafer, of which a plurality of modified layers are to be formed on the wafer. A processing method characterized by forming one half of the modified layer on the first side of the wafer, of which a plurality of modified layers are to be formed on the wafer, and then moving a laser beam relative to the wafer in the processing direction, positioning the focal point on the second side ahead of the focal point on the first side in the processing direction, and irradiating the wafer with the laser beam to form the remaining half of the modified layer on the second side of the wafer, of which a plurality of modified layers are to be formed on the wafer.

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