Wafer processing method and laser irradiation apparatus

Abstract

To provide a method of processing a wafer, forming no deep grooves with sharp angles like fangs in cross section on both sides of a projected dicing line in a width direction, thereby causing no deterioration in quality.SOLUTION: A method includes a functional layer removing process and a device chip fabricating process. The functional layer removing process includes the steps of: removing a functional layer with the use of a laser applying apparatus that includes an oscillator for oscillating a laser beam, a condenser for condensing the laser beam and for positioning a spot smaller than the width of projected dicing lines on the projected dicing lines, a spot shaper disposed between the oscillator and the condenser to shape the spot into a slender spot, and a branch generator for branching a plurality of the spots in a processing direction and for positioning a spot longer side in a projected dicing line width direction and a spot shorter side in a processing direction; and expanding a processing area by moving long sides of a plurality of spots branched by the activation of the branch generator to pass each other in the projected dicing line width direction. The steps are repeatedly carried out to remove the functional layer stacked on the projected dicing lines.SELECTED DRAWING: Figure 5

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 film on the upper surface of a semiconductor substrate and partitioning a plurality of devices by a dicing line into individual device chips, and a laser irradiation device that removes the functional layer of 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 dicing line along the dicing line.

Background Art

[0002] A wafer having a surface formed by partitioning a plurality of devices such as ICs and LSIs by a dicing 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 dicing 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 in which the Low-k film laminated on the dicing line is removed by irradiation with a laser beam to expose the semiconductor substrate, and then the dicing line from which the Low-k film has been removed is cut 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

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 groove 230 in which the semiconductor substrate is exposed, a deep, sharp groove 232, 232 resembling a fang when viewed in cross-section is formed on both sides of the width direction of the division line 210, as shown in the figure. Due to the shape of these grooves 230, a problem arises in which 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 exposed semiconductor substrate along the division lines 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 to position a spot smaller than the width of the division line on the division line; and the oscillator A wafer processing method is provided, comprising: a removal step of irradiating a laser beam onto a line to be divided to remove a functional layer using a laser irradiation device comprising: a spot forming unit disposed between the laser irradiation device and a light concentrator for forming the spot into an elongated shape; a branching generation unit for branching the spot into at least two in the processing direction, positioning the longer side of the spot in the width direction of the line to be divided and positioning the shorter side in the processing direction; and an expansion step of operating the branching generation unit to move the longer sides of the at least two branched spots so as to pass each other in the width direction of the line to be divided, thereby expanding the processing area, wherein the removal step and the expansion step are repeated to remove a functional layer stacked on the line to be divided.

[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 device for removing a functional layer along a division line 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, the 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 forming unit disposed between the oscillator and the concentrator and shaping the spot into an elongated form; and a branching generation unit that branches the spot into at least two in the processing direction, positioning the longer side of the spot in the width direction of the division line and the shorter side in the processing direction. The system includes a control means that repeatedly performs a removal step of irradiating a laser beam onto the division line to remove the functional layer, and an expansion step of operating the branch generation unit to move the longer sides of the at least two branched spots so as to pass each other in the width direction of the division line, thereby expanding the processing area. A laser irradiation device is provided. [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 to position a spot smaller than the width of the division line on the division line; a spot forming unit disposed between the oscillator and the concentrator to form the spot into an elongated shape; and a unit that branches the spot into at least two in the processing direction. The laser irradiation device includes a branch generation unit that positions the long side of a spot in the width direction of the planned division line and the short side in the processing direction. The device includes a removal step of irradiating the planned division line with a laser beam to remove the functional layer, and an expansion step of operating the branch generation unit to move the long sides of the at least two branched spots so that they pass each other in the width direction of the planned division line, thereby expanding the processing area. Since the removal step and the expansion step are repeatedly performed to remove the functional layer stacked on the planned division line, the processing area on the planned division line can be gradually expanded during processing. Laser processing on both sides of the spot in the width direction of the planned division line is dispersed without concentration, and sharp, fang-like grooves are not formed on both sides of the planned division line. Therefore, even if a device chip manufacturing process is performed on these grooves, the problem of reduced flexural strength of the device chip and deterioration of device chip quality is resolved.

[0012] Furthermore, the laser irradiation apparatus of the present invention is a laser irradiation apparatus that removes the functional layer 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, along the division lines using a laser beam irradiation means, the laser beam irradiation means 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 lines on the division lines, a spot forming unit disposed between the oscillator and the concentrator and shaping the spot into an elongated form, and a branching generation unit that branches the spot into at least two in the processing direction and positions the long side of the spot in the width direction of the division lines and the short side in the processing direction. The system includes a control means that repeatedly performs a removal step of irradiating a laser beam onto the division line to remove the functional layer, and an expansion step of operating the branch generation unit to move the longer sides of the at least two branched spots so as to pass each other in the width direction of the division line, thereby expanding the processing area. Therefore, the processing area on the planned division line can be gradually expanded in the width direction, and laser processing can be performed in a dispersed manner without concentration on both sides of the spot in the width direction of the planned division line, thereby achieving processing without the formation of sharp, fang-like grooves on both sides of the planned division line. Consequently, even if the above-mentioned device chip generation process is performed on the grooves, 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 in an annular frame F via protective tape T, as shown in the figure. The laser irradiation device 1 is disposed on a base 2 and includes at least a 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 a holding means 3 for holding the wafer 10, an alignment means 6 for imaging the wafer 10 held by the holding means 3 and performing an alignment process, an X-axis moving means 4a for moving the holding means 3 in the X-axis direction, a Y-axis moving means 4b for moving the holding means 3 in the Y-axis direction, a frame body 5 consisting of 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 a control means 100 for controlling each operating portion.

[0018] The holding means 3 is a means for holding the wafer 10 with the XY plane specified by the X coordinate and the Y coordinate as the 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 the XY plane specified by the X coordinate and the Y coordinate as the 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. Around the suction chuck 36, four clamps 37 for gripping the frame F when holding the wafer 10 on the chuck table 35 are arranged at equal intervals.

[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 direction movable plate 31, and moves the X-axis direction movable plate 31 in the X-axis direction along a pair of guide rails 2A, 2A arranged along the X-axis direction on the base 2. The Y-axis moving means 4b converts the rotational motion of the motor 44a into linear motion via the ball screw 44b, transmits it to the Y-axis direction movable plate 32, and moves the Y-axis direction movable plate 32 in the Y-axis direction along a pair of guide rails 31a, 31a arranged along the Y-axis direction on the X-axis direction movable plate 31.

[0020] Inside the horizontal wall portion 5b of the frame body 5, an optical system constituting the above-described laser beam irradiating means 7 and an alignment means 6 are accommodated. On the lower surface side of the tip of the horizontal wall portion 5b, a condenser 71 which constitutes a part of the laser beam irradiating means 7 and irradiates the wafer 10 with a laser beam is disposed. The alignment means 6 is an imaging means for imaging the wafer 10 held by the holding means 3 and detecting the position and orientation of the wafer 10, the laser processing position where the laser beam should be irradiated, etc., and is disposed at a position adjacent in the X-axis direction indicated by the arrow X in the figure with respect to the above-described condenser 71.

[0021] FIG. 2 shows a block diagram showing an outline of the optical system of the above-described laser beam irradiating means 7. The laser beam irradiating means 7 includes an oscillator 72 that oscillates a laser beam LB, a repetition frequency adjuster 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 1 / 2 wavelength plate 74 that rotates the polarization direction of the linearly polarized laser beam that has passed through the attenuator 73, and a first beam splitter 75 that guides the laser beam LB1 (indicated by a one-dot chain line) whose polarization direction has been rotated by the first 1 / 2 wavelength plate 74 and adjusted to S polarization to the first path Q1 and guides the laser beam LB2 (indicated by a broken line) adjusted to P polarization to the 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 the condensing path Q3.

[0022] The first path Q1 is provided with a first shutter 76a that allows or blocks the laser beam LB1 guided from the first beam splitter 75, a spot forming section 76c with a slit 76d that forms an elongated spot shape for the laser beam LB1, 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 branching generation unit 79 and a light concentrator 71 including a focusing lens 71a. The branching generation unit 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 branches the incident laser beam into two laser beams so that the output of the incident laser beam is halved, 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 two mutually orthogonal linearly polarized states, and a detailed explanation is omitted. The branching generation unit 79 is connected to a control means 100 and is equipped with rotational drive means (not shown) that can precisely rotate the second half-wave plate 79a in the direction indicated by arrow R1 and the Wallaston prism 79b in the direction indicated by arrow R2 by any angle.

[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 branch generation unit 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 an 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 of the first shutter 76a' shown by the dashed line to close the first path Q1, and the second shutter 77a is moved to the position of the second shutter 77a shown 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 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 irradiate the functional layer 16 and the semiconductor substrate of the wafer 10 with a laser beam LB of an absorbing wavelength, 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 leaks 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 reflection mirror 77b and is guided to the branch generation unit 79 via the second beam splitter 78. As explained with reference to Figure 2, the laser beam LB2 guided to the branching generation unit 79 has its polarization direction rotated by the rotation of the second half-wave plate 79a, which constitutes the branching generation unit 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 the rotation of the branch generation unit 79, corresponding to the width (60 μm) required to remove the functional layer 16 on the 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 width 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 laser beam LB to oscillate from the oscillator 72. 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 the arrow X1 in the X-axis direction, 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), and forms 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 forming section 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 forming section 76c. The laser beam LB2 thus formed is then guided via the second beam splitter 78 to a branch generation section 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 laser beam LB, adjusted to the desired repetition frequency by the repetition frequency adjustment unit 70, is emitted from the oscillator 72. The laser beam LB1, guided to the branch generation unit 79 via the first path Q1, has its polarization direction rotated by the rotation of the second half-wave plate 79a constituting the branch generation unit 79, and reaches the Wallaston prism 79b constituting the branch generation unit 79. The laser beam LB1 that reaches the Wallaston prism 79b is branched into P-polarized LB1a and S-polarized LB1b so that the output is halved, as shown in Figure 5(a). The branched P-polarized LB1a and S-polarized LB1b are focused by the concentrator 71 and irradiated onto the division line 14 as spots P3 and P4 smaller than the width of the division line 14. Spots P3 and P4 are irradiated at positions separated in the processing direction on the division line 14 of the wafer 10. As shown in Figure 5(b), the spots P3 and P4 formed by the P-polarized LB1a and S-polarized LB1b irradiated onto the division line 14 have their long sides positioned in the width direction (Y-axis direction) of the division line and their short sides positioned in the processing direction (X-axis direction). In the initial state, as shown in Figure 5(b), both spots P3 and P4 are positioned in the center of the width direction of the division line 14 and are positioned parallel to each other. In this embodiment, the dimensions of spots P3 and P4 are set so that the short side is 6 μm and the long side is 45 μm. In particular, the length of the longer side is set to be smaller than the outer width (60 μm) of the two grooves 18a and 18b, and more preferably smaller than the inner width (50 μm). Also, the distance between spot P3 and spot P4 in the X-axis direction is set to 250 μm.

[0039] While irradiating the predetermined division line 14 with the P-polarized LB1a and S-polarized LB1b described above, the X-axis moving means 4a is operated to process the material in the direction indicated by 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 spots P3 and P4. In this embodiment, the laser processing conditions are set so that the functional layer 16 is not completely removed in a single removal step, and the removal step is repeated so that the groove 19 formed by spots P3 and P4 (see Figure 5(d)) reaches the desired depth to completely remove the functional layer 16 and expose the semiconductor substrate 15 (for example, 8 passes).

[0040] In this embodiment, the functional layer removal step is performed along with the extension step described below. As described above, both spot P3 and spot P4 in their initial state are positioned in the center of the width direction of the division line 14, at separate positions in the processing direction (X-axis direction), and their Y-axis coordinates coincide, that is, they are positioned so as not to pass each other in the width direction of the division line 14. From this state, each time a removal step is performed, the Wallaston prism 79b of the branch generation unit 79 is rotated slightly, and the second half-wave plate 79a is rotated in accordance with this, so that the long sides of spot P3 and spot P4, which have branched from the laser beam LB1 into two, pass each other in the width direction of the division line, that is, they are moved by a small distance in the directions shown by arrows R5 and R6 in Figure 5(c). In this embodiment, with each removal step, spot P3 is moved 1 μm in the direction indicated by arrow R5 and spot P4 is moved 1 μm in the direction indicated by arrow R6, expanding the area to be laser-processed by the removal step by 2 μm in the Y-axis direction. In this embodiment, this expansion step is inserted between 8 removal steps and repeated 7 times, performing a total of 8 removal steps for one planned division line 14. The laser beam irradiation means 7, X-axis moving means 4a, Y-axis moving means 4b, and the rotational drive means of the chuck table 35 (not shown) are operated to perform the removal and expansion steps on all planned division lines 14 formed on the wafer 10, forming grooves 19 on all planned division lines 14 where the semiconductor substrate 15 is exposed, as shown in Figure 5(d). Since the processing depth in one removal step in this embodiment is 1.5 μm, the final shape of the groove 19 formed will be 60 μm wide and 12 μm deep, as shown in Figure 5(d). In this embodiment, as described above, by performing the width-regulating groove formation process before the functional layer removal process, the width of the groove 19 formed in the planned division line 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, for example, using 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 groove 19 formed along the division line 14, and the wafer 10 is fed in the X-axis direction to cut to a depth that completely cuts the division line 14 of the wafer 10. By carrying out this cutting process along the groove 19 formed along 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 either transported to a pickup device to perform 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, by including an expansion step in which the long sides of at least two spots P3 and P4 irradiated during the repeatedly performed removal step are moved so as to pass each other in the width direction of the division line 14, the processing area on the division line 14 can be gradually expanded during processing. As a result, the laser processing on both sides of the spots in the width direction of the division line 14 is dispersed without concentration, and 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 on the grooves 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, laser processing can be performed while gradually expanding the processing area on the division line 14. This makes it easy to perform processing in which the laser processing is dispersed rather than concentrated on both sides of the spot in the width direction of the division line 14, and enables processing in which sharp, fang-like grooves are not formed on both sides of the division line 14. Therefore, even if the device chip generation process is performed on the groove 19 described above, the problem of reduced flexural strength of the device chip and deterioration of device chip quality is resolved.

[0046] The present invention is not limited to the embodiments described above. In the wafer processing method described above, a width-restricting groove formation step is performed to form two grooves 18a and 18b that restrict the width of the division line 14 before the functional layer removal step is performed, but this width-restricting groove formation step may be omitted. If the width-restricting 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 forming section 76c disposed between the oscillator 72 and the concentrator 71, and the branch generation section 79 of the above-described configurations should be included.

[0047] Furthermore, in the above-described embodiment, the laser beam LB1 is guided to the Wallaston prism 79b in the functional layer removal process to split it into two spots P3 and spot P4, but the present invention is not limited thereto. For example, by arranging a diffraction grating element (DOE) 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, for example, to form four spots (4-branch) or eight spots (8-branch), thereby more finely dispersing the concentration of laser processing on the division line 14. [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 section 76d: Slit 77a: Second shutter 77b: Reflective mirror 78: Second Beam Splitter 79: Branch generation section 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: Groove 100: Control means 200: Wafer 210: Planned split line 220: Functional Layer 230: Groove 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 polarized light LB1b:S polarization LB2a:P polarized light LB2b:S polarization

Claims

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, In the functional layer removal process, A removal step involves 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 a spot smaller than the width of the division line on the division line; a spot forming unit disposed between the oscillator and the focuser and shaping the spot into an elongated form; and a branching generation unit that branches the spot into at least two in the processing direction, positioning the longer side of the spot in the width direction of the division line and the shorter side in the processing direction, to irradiate the division line with a laser beam to remove the functional layer; The system includes an expansion step which involves operating the branch generation unit to move the longer sides of the two branched spots so that they pass each other in the width direction of the planned division line, thereby expanding the processing area. A wafer processing method comprising repeatedly performing the removal step and the expansion step to remove functional layers stacked on a line to be divided.

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.

3. The wafer processing method according to claim 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.

4. The wafer processing method according to claim 1, wherein the device chip production 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.

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 The system 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, a spot forming unit disposed between the oscillator and the focuser and shaping the spot into an elongated form, and a branching generation unit that branches the spot into at least two in the processing direction, positioning the longer side of the spot in the width direction of the division line and the shorter side in the processing direction. A laser irradiation device comprising control means for repeatedly performing a removal step of irradiating a line to be divided with a laser beam to remove a functional layer, and an expansion step of operating the branch generation unit to move the longer sides of the at least two branched spots so as to pass each other in the width direction of the line to be divided, thereby expanding the processing area.

Images