Wafer processing method and laser irradiation apparatus
The wafer processing method and laser irradiation apparatus address the issue of grooves forming on division lines by shaping the laser beam and using controlled polarization to maintain chip quality and strength, ensuring effective device chip production.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- DISCO CORP
- Filing Date
- 2022-05-17
- Publication Date
- 2026-06-15
Smart Images
Figure 0007873989000001 
Figure 0007873989000002 
Figure 0007873989000003
Abstract
Description
【Technical Field】 【0001】 The present invention relates to a method for processing a wafer that divides a wafer having a surface formed by laminating a functional layer on the upper surface of a semiconductor substrate and partitioning a plurality of devices by a planned division line into individual device chips, and a laser irradiation device that removes the functional layer of the wafer having a surface formed by laminating a functional layer on the upper surface of a semiconductor substrate and partitioning a plurality of devices by a planned division line along the planned division line. 【Background Art】 【0002】 A wafer having a surface formed by partitioning a plurality of devices such as ICs and LSIs by a planned division line is divided into individual device chips by a dicing device equipped with a rotatable cutting blade, and is used in electric devices such as mobile phones and personal computers. 【0003】 In particular, in a wafer in which a low dielectric constant insulating film called a Low-k film is laminated as a functional layer on the upper surface of a semiconductor substrate and a plurality of devices are formed, when the planned division line of the wafer is cut with a cutting blade, the Low-k film peels off like mica from the cutting portion of the cutting blade, causing a problem of damaging the device. 【0004】 Therefore, the applicant of the present application has proposed a technique of removing the Low-k film laminated on the planned division line by irradiating with a laser beam to expose the semiconductor substrate, and then cutting the planned division line from which the Low-k film has been removed with a cutting blade so that the Low-k film does not peel off (see, for example, Patent Document 1). 【Prior Art Documents】 【Patent Documents】 【0005】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2005-064231 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0006】 By the way, as can be seen from Figure 7, which shows the prior art, when a laser beam LB0 having a spot diameter P0 corresponding to the width of the division line 210 formed on the wafer 200 is repeatedly irradiated for an arbitrary number of passes along the processing direction (direction perpendicular to the drawing) along the longitudinal direction of the division line 210, and the functional layer 220 made of a Low-k film stacked on the division line 210 is removed to form a recess 230 in which the semiconductor substrate is exposed, as shown in the figure, sharp, deep grooves 232, 232 are formed on both sides of the width direction of the division line 210, as seen in the figure, and due to the shape of these recesses 230, the flexural strength of the individually divided device chips decreases, resulting in a deterioration of quality. 【0007】 The present invention has been made in view of the above facts, and its main technical problem is to provide a wafer processing method and laser irradiation apparatus that, even when a functional layer laminated on a division line is removed and the semiconductor substrate is exposed by irradiating the division line with a laser beam along the processing direction of the division line, does not result in the formation of sharp, deep grooves resembling fangs when viewed in cross-section on both sides in the width direction of the division line, thus preventing deterioration of wafer quality. [Means for solving the problem] 【0008】 To solve the above-mentioned main technical problems, the present invention provides a wafer processing method for dividing a wafer having a surface formed by stacking functional layers on the upper surface of a semiconductor substrate and dividing a plurality of devices by division lines into individual device chips, comprising: a functional layer removal step of removing the functional layers stacked on the division lines to expose the semiconductor substrate; and a device chip generation step of cutting the division lines on the exposed semiconductor substrate to generate individual device chips, wherein the functional layer removal step comprises: an oscillator that emits a laser beam; a concentrator that focuses the laser beam emitted by the oscillator and positions the spot on the division line; and a spot shaping device disposed between the oscillator and the concentrator that shapes the spot into an elongated shape and positions the polarization direction of the linearly polarized laser beam in the direction of the longer side of the spot. The laser beam, which has been shaped into a spot by the spot shaping machine, is guided, and the laser beam The P-polarized light is positioned on the inclined surface of the recess formed by positioning the longer side of the spot in the width direction of the planned division line, while the shorter side of the spot is positioned in the processing direction. It includes and is configured with a spot controller that adjusts accordingly. A wafer processing method is provided, which includes a removal step of irradiating a line to be divided with a laser beam using a laser irradiation device to remove a functional layer, and performing the removal step multiple times to remove the functional layer stacked on the line to be divided and expose the semiconductor substrate. 【0009】 It is preferable to perform a width-regulating groove formation step before carrying out the functional layer removal step, in which two grooves are formed by irradiating with a laser beam to regulate the width of the division line. Furthermore, a protective film coating step may be included before the functional layer removal step and the width-regulating groove formation step, in which a protective film is coated onto the surface of the wafer. In addition, the device chip manufacturing step may include cutting the division line with a cutting blade, cutting the division line with a laser beam, or cutting the division line with plasma etching. 【0010】 Furthermore, in order to solve the above-mentioned main technical problems, the present invention provides a laser irradiation apparatus for removing the functional layer of a wafer having a surface formed by stacking functional layers on the upper surface of a semiconductor substrate and dividing a plurality of devices by division lines, along the division lines using a laser beam irradiation means, wherein the laser beam irradiation means comprises an oscillator that emits a laser beam, a focuser that focuses the laser beam emitted by the oscillator and positions a spot smaller than the width of the division line on the division line, and a device disposed between the oscillator and the focuser that shapes the spot into an elongated shape. Along with this, the polarization direction of the linearly polarized laser beam is positioned in the direction of the longer side of the spot. Spot molding machine and The laser beam formed by the spot molding machine is guided, and the laser beam A laser irradiation device is provided that includes a spot controller which positions P-polarized light on the inclined surface of a recess formed by positioning the long side of the spot in the width direction of the planned division line, and positions the short side of the spot in the processing direction. [Effects of the Invention] 【0011】 The wafer processing method of the present invention is a wafer processing method for dividing a wafer having a surface formed by stacking functional layers on the upper surface of a semiconductor substrate and dividing a plurality of devices by division lines into individual device chips, comprising: a functional layer removal step of removing the functional layers stacked on the division lines to expose the semiconductor substrate; and a device chip generation step of cutting the division lines on the exposed semiconductor substrate to generate individual device chips, wherein the functional layer removal step comprises: an oscillator that emits a laser beam; a concentrator that focuses the laser beam emitted by the oscillator and positions the spot on the division line; and a spot shaping device disposed between the oscillator and the concentrator that shapes the spot into an elongated shape and positions the polarization direction of the linearly polarized laser beam in the direction of the longer side of the spot. The laser beam, which has been shaped into a spot by the spot shaping machine, is guided, and the laser beam The P-polarized light is positioned on the inclined surface of the recess formed by positioning the longer side of the spot in the width direction of the planned division line, while the shorter side of the spot is positioned in the processing direction. It includes and is configured with a spot controller that adjusts accordingly.The process includes a removal step in which a laser beam is irradiated onto the planned division line using a laser irradiation device to remove the functional layer. This removal step is performed multiple times to remove the functional layer stacked on the planned division line and expose the semiconductor substrate. As the removal step is performed repeatedly, P-polarized light is irradiated onto and transmitted to the inclined surface of the recess formed in the width direction of the planned division line, preventing the formation of sharp, fang-like grooves on both sides of the planned division line. Therefore, even if a device chip manufacturing process is performed on the recess, the problem of reduced flexural strength of the device chip and deterioration of device chip quality is eliminated. 【0012】 Furthermore, the present invention relates to a laser irradiation apparatus that removes a functional layer along a division line from a wafer having a surface formed by stacking functional layers on the upper surface of a semiconductor substrate and dividing a plurality of devices by division lines, using a laser beam irradiation means, wherein the laser beam irradiation means comprises an oscillator that emits a laser beam, a focuser that focuses the laser beam emitted by the oscillator and positions a spot smaller than the width of the division line on the division line, and a device disposed between the oscillator and the focuser that shapes the spot into an elongated shape. Along with this, the polarization direction of the linearly polarized laser beam is positioned in the direction of the longer side of the spot. Spot molding machine and The laser beam formed by the spot molding machine is guided, and the laser beam Since the system includes a spot controller that positions P-polarized light on the inclined surface of a recess formed by positioning the long side of the spot in the width direction of the planned division line, and positions the short side of the spot in the processing direction, a removal step can be performed to remove the functional layer by irradiating the planned division line with a laser beam using a laser irradiation device that positions P-polarized light on the inclined surface of a recess formed by positioning the long side of the spot in the width direction of the planned division line, and positions the short side of the spot in the processing direction, thereby achieving processing that does not form sharp, fang-like recesses on both sides of the planned division line. Therefore, even if the above-mentioned device chip generation process is performed on the recess, the problem of reduced flexural strength of the device chip and deterioration of device chip quality is resolved. [Brief explanation of the drawing] 【0013】 [Figure 1] This is an overall perspective view of the laser irradiation device. [Figure 2] This block diagram shows a schematic representation of the optical system of the laser beam irradiation means installed in the laser irradiation device shown in Figure 1. [Figure 3] This is a perspective view showing a wafer to be processed in this embodiment and an embodiment of laser processing being performed on the wafer. [Figure 4] (a) A side view of an embodiment of the width-regulating groove formation process, (b) A plan view of the embodiment shown in (a), and (c) An enlarged cross-sectional view of section AA in (b). [Figure 5] (a) A side view of an embodiment of the functional layer removal process, (b) A plan view showing the initial state of the embodiment shown in (a), (c) A plan view showing the state after the functional layer removal process is completed, and (d) A cross-sectional view showing an enlarged view of the BB cross section in (c). [Figure 6] This is a partially enlarged cross-sectional view showing an embodiment of the device chip manufacturing process. [Figure 7] This is a partially enlarged cross-sectional view showing an embodiment of the process of removing the functional layer in the prior art. [Modes for carrying out the invention] 【0014】 Hereinafter, embodiments relating to a wafer processing method and a laser irradiation apparatus suitable for realizing the functional layer removal step of the wafer processing method will be described in detail with reference to the attached drawings. 【0015】 The wafer processing method of the present invention includes at least a functional layer removal step of removing the functional layer stacked on the division lines of a wafer having a surface formed by stacking a functional layer on the upper surface of a semiconductor substrate and dividing a plurality of devices by division lines, thereby exposing the semiconductor substrate, and a device chip generation step of cutting the division lines on the exposed semiconductor substrate to generate individual device chips. Figure 1 shows a laser irradiation apparatus 1 suitable for performing the functional layer removal step of the wafer processing method of the present invention, as well as the width regulation groove formation step described later. 【0016】 The laser irradiation device 1 is a device that performs laser processing on a wafer 10 held via a protective tape T on an annular frame F as shown in the figure. The laser irradiation device 1 is disposed on a base 2 and includes at least laser beam irradiation means 7 for irradiating the wafer 10 with a laser beam. 【0017】 In addition to the laser beam irradiation means 7 described above, the laser irradiation device 1 includes holding means 3 for holding the wafer 10, alignment means 6 for imaging the wafer 10 held by the holding means 3 and performing an alignment process, X-axis moving means 4a for moving the holding means 3 in the X-axis direction, Y-axis moving means 4b for moving the holding means 3 in the Y-axis direction, a frame body 5 including a vertical wall portion 5a erected on the side of the X-axis moving means 4a and the Y-axis moving means 4b on the base 2 and a horizontal wall portion 5b extending horizontally from the upper end portion of the vertical wall portion 5a, and control means 100 for controlling each operating portion. 【0018】 The holding means 3 is means for holding the wafer 10 with an XY plane specified by X coordinates and Y coordinates as a holding surface. As shown in FIG. 1, it includes a rectangular X-axis direction movable plate 31 mounted on the base 2 so as to be movable in the X-axis direction, a rectangular Y-axis direction movable plate 32 mounted on the X-axis direction movable plate 31 so as to be movable in the Y-axis direction, a cylindrical support column 33 fixed to the upper surface of the Y-axis direction movable plate 32, and a rectangular cover plate 34 fixed to the upper end of the support column 33. A chuck table 35 extending upward through a long hole formed on the cover plate 34 is disposed on the cover plate 34. The chuck table 35 is configured to be rotatable by a rotation driving means (not shown) housed in the support column 33. On the upper surface of the chuck table 35, a circular suction chuck 36 formed of a porous material having air permeability and having an XY plane specified by X coordinates and Y coordinates as a holding surface is disposed. The suction chuck 36 is connected to a suction means (not shown) by a flow path passing through the support column 33, and four clamps 37 for gripping the frame F when holding the wafer 10 on the chuck table 35 are arranged at equal intervals around the suction chuck 36. 【0019】 The X-axis moving means 4a converts the rotational motion of the motor 42a into linear motion via the ball screw 42b and transmits it to the X-axis movable plate 31, moving the X-axis movable plate 31 in the X-axis direction along a pair of guide rails 2A, 2A arranged on the base 2 along the X-axis direction. The Y-axis moving means 4b converts the rotational motion of the motor 44a into linear motion via the ball screw 44b and transmits it to the Y-axis movable plate 32, moving the Y-axis movable plate 32 in the Y-axis direction along a pair of guide rails 31a, 31a arranged on the X-axis movable plate 31 along the Y-axis direction. 【0020】 The horizontal wall portion 5b of the frame 5 houses the optical system and alignment means 6 that constitute the laser beam irradiation means 7. A light concentrator 71, which constitutes part of the laser beam irradiation means 7 and irradiates the wafer 10 with a laser beam, is disposed on the lower surface of the tip of the horizontal wall portion 5b. The alignment means 6 is an imaging means that images the wafer 10 held by the holding means 3 to detect the position and orientation of the wafer 10, the laser processing position to be irradiated with the laser beam, etc., and is disposed adjacent to the light concentrator 71 in the X-axis direction indicated by arrow X in the figure. 【0021】 Figure 2 shows a block diagram illustrating the schematic of the optical system of the laser beam irradiation means 7 described above. The laser beam irradiation means 7 includes an oscillator 72 that oscillates a laser beam LB, a repetition frequency adjustment unit 70 that adjusts the repetition frequency of the oscillator 72 to a desired frequency, an attenuator 73 that adjusts the output of the laser beam LB oscillated by the oscillator 72, a first half-wave plate 74 that rotates the polarization direction of the linearly polarized laser beam that has passed through the attenuator 73, a first beam splitter 75 that guides the laser beam LB1 (shown by a dashed line), whose polarization direction has been rotated by the first half-wave plate 74 and adjusted to S polarization, to a first path Q1 and guides the laser beam LB2 (shown by a dashed line), which has been adjusted to P polarization, to a second path Q2, and a second beam splitter 78 that selectively guides the laser beam LB1 guided to the first path Q1 and the laser beam LB2 guided to the second path Q2 to a focusing path Q3. 【0022】 The first path Q1 is equipped with a first shutter 76a that allows or blocks the laser beam LB1 guided from the first beam splitter 75, a spot shaper 76c with a slit 76d formed therein that shapes the spot shape of the laser beam LB1 into an elongated shape, and a reflective mirror 76b that changes the optical path of the laser beam LB1. 【0023】 The second path Q2 is provided with a second shutter 77a that allows or blocks the laser beam LB2 guided from the first beam splitter 75, and a reflective mirror 77b that changes the optical path of the laser beam LB2. 【0024】 The focusing path Q3 is equipped with a spot controller 79 and a concentrator 71 including a focusing lens 71a. The spot controller 79 includes a second half-wave plate 79a that rotates the polarization direction of the incident linearly polarized laser beam, and a Wallaston prism 79b that splits the incident laser beam into two laser beams so that the output of the incident laser beam is halved depending on the rotation state, forming two spots spaced apart in any direction. The Wallaston prism 79b is a polarizing prism that is generally known to separate incident light into linearly polarized light that is orthogonal to each other, and a detailed explanation is omitted. The spot controller 79 is connected to a control means 100 and is equipped with a rotation drive means (not shown) that allows the second half-wave plate 79a to be precisely rotated by any angle in the direction indicated by arrow R1, and the Wallaston prism 79b to be precisely rotated by any angle in the direction indicated by arrow R2. 【0025】 The control means 100 is composed of a computer and includes a central processing unit (CPU) that performs calculations according to a control program, a read-only memory (ROM) for storing the control program and the like, a read-write random access memory (RAM) for temporarily storing detected values, calculation results, etc., an input interface, and an output interface (details are not shown). The control means 100 is connected to an alignment means 6, a repeat frequency adjustment unit 70, a spot controller 79, and also to a first shutter 76a, a second shutter 77a, an X-axis moving means 4a, a Y-axis moving means 4b, etc. (some connections are omitted in Figure 2). Information detected by image data captured by the alignment means 6 is stored in appropriate memory and displayed on a display means (not shown). 【0026】 The laser irradiation apparatus 1 of this embodiment has a configuration that is generally as described above, and the functional layer removal step and the device chip generation step of the wafer processing method of this embodiment, which are carried out using the laser irradiation apparatus 1, will be described below. In the wafer processing method described below, a width regulating groove formation step is also performed before the functional layer removal step, in which two grooves are formed by irradiating with a laser beam to regulate the width of the division line. 【0027】 The wafer 10 processed in the wafer processing method of this embodiment is, for example, the wafer 10 shown in Figure 3. The wafer 10 is a wafer having a surface 10a formed by laminating a functional layer 16 on the upper surface of a semiconductor substrate (for example, a substrate made of silicon (Si)) and dividing a plurality of devices 12 by division lines 14. For example, the wafer has a diameter of 200 mm, a thickness of 700 μm, a functional layer 16 thickness of 10 μm, and a division line 14 width of 70 μm. The functional layer 16 is formed by laminating a functional film such as a low-dielectric constant insulating film (Low-k film) made of an inorganic film such as SiOF or BSG (SiOB) or an organic film such as a polymer film such as polyimide or parylene on the surface of the semiconductor substrate in order to improve the processing ability of the devices 12 formed on the wafer 10. The composition of the film is appropriately adjusted according to the type of device 12. Furthermore, as shown in the figure, the wafer 10 of this embodiment is supported by an annular frame F having an opening via adhesive tape T. 【0028】 Although not an essential component of the wafer processing method of the present invention, when carrying out the wafer processing method described below, it is preferable to perform a protective film coating step to coat the surface 10a of the wafer 10 with an appropriate protective film in order to prevent debris, cutting chips, etc., scattered during the functional layer removal step and the device chip generation step from adhering to the surface 10a of the wafer 10. This protective film can be realized, for example, by dropping a liquid resin onto the surface 10a of the wafer 10 and diffusing and coating it by rotating the wafer 10 at high speed, or by coating it with a protective sheet made of resin formed in a shape corresponding to the shape of the wafer 10. 【0029】 Once the wafer 10 described above is prepared, the wafer 10 is placed on the chuck table 35 of the laser irradiation device 1 and held in place by suction using a suction means (not shown) and gripping with a clamp 37. Next, the X-axis moving means 4a and Y-axis moving means 4b are activated to position the wafer 10 directly below the alignment means 6 shown in Figure 1. Then, the alignment means 6 photographs the wafer 10, and the chuck table 35 is rotated by a rotational drive means (not shown) to align the direction of the predetermined division line 14 in the X-axis direction, and align the division line 14 perpendicular to the division line 14 in the Y-axis direction. Furthermore, position information defined by the XY coordinates of the division line 14 to be processed is stored in the control means 100. 【0030】 In this embodiment, before performing the functional layer removal process, a width-regulating groove formation process is carried out as follows, in which a laser beam is irradiated onto the wafer 10 to form two grooves that regulate the width of the division line 14. 【0031】 When performing the width regulation groove formation process, the first shutter 76a, as described in Figure 2, is moved to the position 76a' indicated by the dashed line to close the first path Q1, and the second shutter 77a is moved to the position indicated by the solid line to open the second path Q2. Then, the X-axis moving means 4a and the Y-axis moving means 4b are activated to position the laser processing start position on the predetermined division line 14 directly below the light concentrator 71 of the laser beam irradiation means 7. 【0032】 In the state described above, when the oscillator 72 of the laser beam irradiation means 7 is activated to oscillate a laser beam LB with a wavelength that is absorbed by the functional layer 16 and the semiconductor substrate of the wafer 10, the polarization direction of the laser beam LB that has passed through the attenuator 73 is rotated by the first half-wave plate 74 and adjusted to P polarization, and the resulting laser beam LB2 is guided to the second path Q2 side via the first beam splitter 75. Since the first path Q1 is closed by the first shutter 76a', any leaked light that has leaked to the first path Q1 side via the first beam splitter 75 is blocked by the first shutter 76a'. The laser beam LB2 guided to the second path Q2 side has its optical path changed by the reflective mirror 77b and is guided to the spot controller 79 via the second beam splitter 78. As explained with reference to Figure 2, the laser beam LB2 guided to the spot controller 79 has its polarization direction rotated by the rotation of the second half-wave plate 79a, which constitutes the spot controller 79, indicated by R1, and reaches the Wallaston prism 79b. Following the rotation of the second half-wave plate 79a, the Wallaston prism 79b rotates as indicated by arrow R2, splitting into P-polarized LB2a and S-polarized LB2b so that the output is halved each, as shown in Figures 4(a) and (b). This forms spots P1 and P2 with a diameter of 5 μm, which are then irradiated from the concentrator 71 onto the functional layer 16 on the division line 14, as shown in Figure 3. 【0033】 The widthwise spacing between the two spots P1 and P2 described above is set by rotating the spot controller 79, corresponding to the width (60 μm) of the functional layer 16 to be removed along the planned division line 14. For example, as shown in Figure 4(b), the widthwise spacing between spots P1 and P2 can be adjusted to a desired interval by moving them from the positions of spots P1' and P2' in the directions of arrows R3 and R4. 【0034】 In the state described above, the repetition frequency adjustment unit 70 adjusts the repetition frequency of the laser beam LB emitted from the oscillator 72, causing the oscillator 72 to emit the laser beam LB. Simultaneously, the X-axis moving means 4a is activated to move the wafer 10 together with the chuck table 35 in the direction indicated by arrow X1, repeatedly irradiating the division line 14 with P-polarized LB2a and S-polarized LB2b (for example, 3 passes). This removes the functional layer 16 as shown in Figure 4(b) and Figure 4(c), forming two grooves 18a and 18b leading to the semiconductor substrate 15. In this embodiment, as shown in Figure 4(b), the division line 14 is processed so that its inner width is 50 μm and its outer width is 60 μm, relative to its width of 70 μm. 【0035】 The laser processing described above is performed on all the division lines 14 formed on the surface 10a of the wafer 10 by appropriately operating the laser beam irradiation means 7, the X-axis moving means 4a, the Y-axis moving means 4b, and the rotational drive means of the chuck table 35 (not shown), thereby forming the two grooves 18a and 18b described above on all the division lines 14. The width regulating groove formation process is then carried out. 【0036】 The other laser processing conditions used in the width-regulating groove formation process described above are as follows, for example. Wavelength: 355nm Repetition frequency: 1000kHz Average output: 0.8W Pulse width: 10 ps Machining feed rate: 300 mm / second 【0037】 After the width regulation groove formation process described above is carried out, the functional layer removal process described below is performed. This functional layer removal process involves removing the functional layer 16 stacked on the division line 14 to expose the semiconductor substrate 15. First, the second shutter 77a, as described in Figure 2, is moved to the position indicated by the dashed line 77a' to close the second path Q2. Next, the first shutter 76a is moved to the position indicated by the solid line to open the first path Q1. In this state, the laser beam LB emitted from the oscillator 72 is polarized by the first half-wave plate 74, and the laser beam LB1, whose polarization direction is adjusted to S polarization, is guided from the first beam splitter 75 to the first path Q1. The laser beam LB1, guided to the first path Q1, is led via the reflective mirror 76b to a spot shaping device 76c that functions as a mask, and is shaped into an elongated spot shape with a short side and a long side by a slit 76d formed in the spot shaping device 76c. The laser beam LB1 thus shaped is then guided via the second beam splitter 78 to a spot controller 79 and a concentrator 71 located in the focusing path Q3. 【0038】 As described above, once the laser beam irradiation means 7 is set, the X-axis moving means 4a and Y-axis moving means 4b are operated to position the laser processing start position on the predetermined division line 14 directly below the concentrator 71 of the laser beam irradiation means 7. Then, the oscillator 72 oscillates the laser beam LB, which has been adjusted to the desired repetition frequency by the repetition frequency adjustment unit 70. The laser beam LB1, guided to the spot controller 79 via the first path Q1, has its polarization direction rotated by the rotation of the second half-wave plate 79a constituting the spot controller 79, and reaches the Wallaston prism 79b constituting the spot controller 79. The laser beam LB1 that reaches the Wallaston prism 79b is rotated by the second half-wave plate 79a so that it is P-polarized with respect to the Wallaston prism 79b. Then, by appropriately rotating the second half-wave plate 79a and the Wallaston prism 79b, which constitute the spot controller 79, a spot P3 of a single laser beam LB1 is positioned on the division line 14 from the Wallaston prism 79b, as shown in Figure 5(a). Furthermore, as shown in Figures 5(b) to (d), the long side of the spot P3 is positioned so as to be P-polarized relative to the inclined surface 19a of the recess 19 formed by positioning the spot P3 in the width direction of the division line 14, and the short side is positioned so as to be in the processing direction of the division line 14. In this embodiment, the dimensions of the spot P3 are set so that the short side is 6 μm and the long side is 55 μm, and the end of the long side of the spot P3 is positioned on the pre-formed grooves 18a and 18b. 【0039】 While irradiating the predetermined division line 14 with the laser beam LB1 described above, the X-axis moving means 4a is operated to process the wafer in the direction indicated by the arrow X1 in Figure 5(b), thereby performing a removal step in which the functional layer 16 on the division line 14 is removed by the spot P3. The recess 19 (see Figure 5(d)) formed in the division line 14 of the wafer 10 by the spot P3 completely removes the functional layer 16 and exposes the semiconductor substrate 15, and this removal step is repeated a predetermined number of times (for example, number of passes = 7) so that the resulting depth is the desired depth. 【0040】 Furthermore, the laser beam irradiation means 7, the X-axis moving means 4a, the Y-axis moving means 4b, and the rotational drive means of the chuck table 35 (not shown) are activated to perform the predetermined number of removal steps described above on all the division lines 14 formed on the wafer 10, thereby forming recesses 19 on all the division lines 14 where the semiconductor substrate 15 is exposed, as shown in Figure 5(d). In this embodiment, as described above, by performing the width-regulating groove formation step before the functional layer removal step, the width of the recesses 19 formed on the division lines 14 can be reliably formed to be 60 μm. 【0041】 The laser processing conditions in the functional layer removal process of this embodiment are, for example, as follows: Wavelength: 355nm Repetition frequency: 200kHz Average output: 3.0W Pulse width: 10 ps Machining feed rate: 200 mm / second 【0042】 As described above, once the functional layer removal process is performed, a device chip generation process is carried out to cut the division line 14 where the semiconductor substrate 15 is exposed and generate individual device chips. The device chip generation process can be carried out using, for example, a well-known dicing apparatus (not shown in the figure). For example, as shown in Figure 6, a cutting process is performed in which a high-speed rotating cutting blade 9 (only the tip is shown) is positioned in a recess 19 formed along the division line 14, and the wafer 10 is fed in the cutting direction to a depth that completely cuts the division line 14 of the wafer 10, and the wafer 10 is fed in the X-axis direction for processing. By carrying out this cutting process along the recess 19 formed in all the division lines 14, the devices 12 of the wafer 10 are divided into individual device chips, and the device chip generation process of this implementation is completed. Thus, the wafer processing method including the functional layer removal process and the device chip generation process of the present invention is completed. Furthermore, the device chip manufacturing process of the present invention is not limited to dividing along the division line 14 using the cutting blade 9 of the dicing apparatus described above, but may also be carried out by, for example, cutting the division line with a laser beam or cutting the division line with plasma etching. 【0043】 The wafer 10 on which the wafer processing method described above has been performed is transported to a pickup device that performs the next process, such as a pickup process, or it is placed in a cassette that contains multiple wafers 10 and transported to another processing device. 【0044】 According to the wafer processing method of this embodiment, during the removal step of the repeatedly performed functional layer removal process, P-polarized light is irradiated onto and transmitted to the inclined surface 19a of the recess 19 formed in the width direction of the division line 14, so that sharp, fang-like grooves are not formed on both sides of the division line 14. Therefore, even if a device chip generation process is performed to divide the wafer 10 along the recess 19, the problem of reduced flexural strength of the device chip and deterioration of device chip quality is eliminated. 【0045】 Furthermore, by employing the laser irradiation device 1 of the above-described embodiment as a laser irradiation device for performing the functional layer removal process, it is possible to perform a process in which P-polarized light is irradiated onto the inclined surface 19a of the recess 19 formed in the width direction of the division line 14 and transmitted through it, so that sharp, fang-like grooves are not formed on both sides of the division line 14. Therefore, even if a device chip manufacturing process is performed to divide the wafer 10 along the recess 19, the problem of reduced flexural strength of the device chip and deterioration of device chip quality is eliminated. 【0046】 The present invention is not limited to the embodiments described above. In the wafer processing method described above, a width-regulating groove formation step is performed to form two grooves 18a and 18b that regulate the width of the division line 14 before the functional layer removal step is performed, but this width-regulating groove formation step may be omitted. If the width-regulating groove formation step is omitted, the second path Q2 described above may also be omitted, and at least the oscillator 72, the concentrator 71, the spot shaping device 76c disposed between the oscillator 72 and the concentrator 71, and the spot controller 79 of the above-described configurations should be included. 【0047】 Furthermore, in the above-described embodiment, the laser beam LB2 is guided to the Wallaston prism 79b in the width regulation groove formation process to split it into two spots P1 and spot P2, but the present invention is not limited thereto. For example, by arranging diffraction grating elements (DOEs) on the path between the second half-wave plate 79a and the Wallaston prism 79b to form multiple interference fringes, it is possible to increase the number of branches of the laser beam LB2, for example, to four branches forming four spots, or eight branches forming eight spots. [Explanation of symbols] 【0048】 1: Laser irradiation device 2: Base 3: Holding means 31:X-axis movable plate 32: Y-axis movable plate 33: Strut 34: Cover board 35: Chuck Table 36: Suction Chuck 37: Clamp 4a:X-axis movement means 4b: Y-axis movement means 5:Frame body 5a: Vertical wall 5b:Horizontal wall part 6: Alignment means 7: Laser beam irradiation means 70: Repeat frequency adjustment section 71: Light concentrator 72: Oscillator 73: Attenuator 74: First half-wave plate 75: First Beam Splitter 76a: First shutter 76b: Reflective mirror 76c: Spot molding machine 76d: Slit 77a: Second shutter 77b: Reflective mirror 78: Second Beam Splitter 79: Spot controller 79a: Second half-wave plate 79b: Wallaston prism 9: Cutting blade 10: Wafer 10a: surface 12: Devices 14: Planned division line 15: Semiconductor substrates 16: Functional Layer 18a, 18b: Groove 19: Recess 100: Control means 200: Wafer 210: Planned split line 220: Functional Layer 230: Recess 232: Deep groove P1, P2: Spot P3, P4: Spot Q1: First route Q2: Second route Q3: Light-gathering path LB0, LB, LB1, LB2: Laser beam LB1a:P polarization LB1b:S polarization LB2a:P polarized light LB2b:S polarization
Claims
[Claim 1] A wafer processing method for dividing a wafer having a surface formed by stacking functional layers on the upper surface of a semiconductor substrate and partitioning multiple devices by planned division lines into individual device chips, A functional layer removal process involves removing the functional layers stacked on the line to be divided to expose the semiconductor substrate, The process includes a device chip manufacturing process which involves cutting the planned division lines on the semiconductor substrate to generate individual device chips, The functional layer removal process includes a removal step of irradiating the line to be divided with a laser beam to remove the functional layer using a laser irradiation device comprising: an oscillator that emits a laser beam; a focuser that focuses the laser beam emitted by the oscillator and positions the spot on the line to be divided; a spot shaping device disposed between the oscillator and the focuser that shapes the spot into an elongated shape and positions the polarization direction of the linearly polarized laser beam in the direction of the long side of the spot; and a spot controller that guides the laser beam whose spot shape has been formed by the spot shaping device and adjusts the laser beam to position the P-polarized light on the inclined surface of a recess formed by positioning the long side of the spot in the width direction of the line to be divided, and to position the short side of the spot in the processing direction. A wafer processing method comprising performing the removal step multiple times to remove the functional layers stacked on the line to be divided, thereby exposing the semiconductor substrate. [Claim 2] The wafer processing method according to claim 1, wherein, before performing the functional layer removal step, a width-regulating groove forming step is performed in which two grooves are formed by irradiating with a laser beam to regulate the width of the line to be divided. [Claim 3] The wafer processing method according to claim 1 or 2, further comprising a protective film coating step of coating the surface of the wafer with a protective film before the functional layer removal step and the width regulating groove formation step. [Claim 4] The wafer processing method according to claim 1, wherein the device chip manufacturing step includes cutting the lines to be divided with a cutting blade, cutting the lines to be divided with a laser beam, or cutting the lines to be divided with plasma etching. [Claim 5] A laser irradiation apparatus for removing a functional layer along a division line from a wafer having a surface formed by stacking functional layers on the upper surface of a semiconductor substrate and dividing multiple devices by division lines, using a laser beam irradiation means, The laser beam irradiation means is A laser irradiation device comprising: an oscillator that emits a laser beam; a concentrator that focuses the laser beam emitted by the oscillator and positions a spot smaller than the width of the division line on the division line; a spot shaping device disposed between the oscillator and the concentrator that shapes the spot into an elongated shape and positions the polarization direction of the linearly polarized laser beam in the direction of the longer side of the spot; and a spot controller that guides the laser beam shaped by the spot shaping device and positions P-polarized light on the inclined surface of a recess formed by positioning the longer side of the spot in the width direction of the division line, and positions the shorter side of the spot in the processing direction.