Wafer processing method

Abstract

To provide a wafer processing method with which it is possible to suppress the separation of function layers.SOLUTION: The wafer processing method processes a wafer along a scheduled divide line, the wafer in which a function layer that includes devices is laminated on a substrate. The method comprises: a degenerated region formation step 101 in which the function layer is irradiated, along the scheduled divide line, with a laser beam of a wavelength having absorptivity for the substrate and having absorptivity for the function layer that is lower than the absorptivity for the substrate, with its output restricted from applying ablation processing to the function layer, and two lengths of degenerated region extending along the scheduled divide line are formed, with a prescribed space therebetween, in the inside of the function layer; a function layer removal step 102 in which a laser beam is radiated between the degenerated regions after implementation of the degenerated region formation step 101, and a first processing groove for removing the function layer is formed; and a substrate processing step 103 in which the substrate is processed along the first processing groove after implementation of the function layer removal step 102.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a wafer processing method. [Background technology]

[0002] BACKGROUND ART A processing method has been conventionally used in which a wafer in which functional layers including devices are stacked on a substrate such as silicon is processed along planned dividing lines (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-173475 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, the processing method disclosed in Patent Document 1 has a problem in that the functional layer peels off when a laser beam is irradiated onto the functional layer to form a processing groove, so a solution has been taken to slow down the processing feed rate in order to prevent the functional layer from peeling off.

[0005] However, in this case, there is a problem that the thermal damage caused by the laser beam becomes large, and the die strength of the device chips after separation decreases.

[0006] An object of the present invention is to provide a wafer processing method that can suppress peeling of a functional layer. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the wafer processing method of the present invention is a wafer processing method for processing a wafer having functional layers including devices stacked on a substrate along a planned dividing line, and is characterized by comprising: a modified area forming step for irradiating a laser beam having a wavelength that is absorbable by the substrate and has a lower absorbability for the functional layer than the absorbability for the substrate along the planned dividing line under processing conditions that restrict continuous ablation processing of the functional layer, thereby forming two modified areas extending along the planned dividing line within the functional layer at a predetermined interval; a functional layer removal step for irradiating a laser beam between the modified areas after the modified area forming step to form a first processing groove that removes the functional layer; and a substrate processing step for processing the substrate along the first processing groove after the functional layer removal step.

[0008] In the wafer processing method, the functional layer may be an oxide film.

[0009] In the wafer processing method, the affected region forming step may involve irradiating a laser beam having a wavelength in the ultraviolet region.

[0010] In the wafer processing method, the output of the laser beam per spot irradiated in the affected region forming step may be smaller than the output of the laser beam per spot irradiated in the functional layer removing step. [Effects of the Invention]

[0011] The present invention has an effect of suppressing peeling of the functional layer. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view schematically showing a wafer to be processed by the wafer processing method according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view schematically showing a main part of the wafer shown in FIG. [Figure 3]FIG. 3 is a flowchart showing the flow of the wafer processing method according to the first embodiment. [Figure 4] FIG. 4 is a cross-sectional view schematically showing a main part of the wafer during the affected region forming step of the wafer processing method shown in FIG. [Figure 5] FIG. 5 is a plan view schematically showing a main part of the wafer after the affected region forming step of the wafer processing method shown in FIG. [Figure 6] FIG. 6 is a plan view schematically showing another example of a main part of a wafer after the affected region forming step in the wafer processing method shown in FIG. [Figure 7] FIG. 7 is a cross-sectional view schematically showing a main part of the wafer after the functional layer removing step of the wafer processing method shown in FIG. [Figure 8] FIG. 8 is a cross-sectional view schematically showing a main part of the wafer after the substrate processing step of the wafer processing method shown in FIG. [Figure 9] FIG. 9 is a plan view schematically showing a main part of a wafer in which processed grooves are formed on both edges of the dividing line by a conventional processing method. [Figure 10] FIG. 10 is a flowchart showing the flow of the wafer processing method according to the second embodiment. [Figure 11] FIG. 11 is a cross-sectional view schematically showing a main part of a wafer during the affected region forming step of the wafer processing method shown in FIG. [Figure 12] FIG. 12 is a cross-sectional view schematically showing a main part of the wafer after the outer processing groove forming step of the wafer processing method shown in FIG. [Figure 13] FIG. 13 is a cross-sectional view schematically showing a main part of the wafer after the functional layer removing step of the wafer processing method shown in FIG. [Figure 14] FIG. 14 is a cross-sectional view schematically showing a main part of the wafer after the substrate processing step of the wafer processing method shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] Modes (embodiments) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the contents described in the following embodiments. Furthermore, the components described below include those that can be easily imagined by a person skilled in the art and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the configuration can be made within the scope of the gist of the present invention.

[0014] [Embodiment 1] A wafer processing method according to a first embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a perspective view schematically showing a wafer to be processed by the wafer processing method according to the first embodiment. Fig. 2 is a cross-sectional view schematically showing a main part of the wafer shown in Fig. 1. Fig. 3 is a flowchart showing the flow of the wafer processing method according to the first embodiment.

[0015] (wafer) The wafer processing method according to the first embodiment is a method for processing a wafer 1 shown in Fig. 1. In the first embodiment, the wafer 1 is a wafer such as a disk-shaped semiconductor wafer having a substrate 2 made of silicon or the like. As shown in Fig. 1, the wafer 1 has devices 5 formed in regions partitioned in a grid pattern by a plurality of planned dividing lines 4 formed in a grid pattern on the surface 3 of the wafer 1.

[0016] The device 5 is, for example, an integrated circuit such as an IC (Integrated Circuit) or an LSI (Large Scale Integration), a CCD (Charge Coupled Device), or a memory (semiconductor storage device).

[0017] In embodiment 1, the wafer 1 has a functional layer 6 laminated on the surface of the substrate 2, as shown in Figures 1 and 2. In embodiment 1, the functional layer 6 is made of an oxide film (SiO2) and includes the above-mentioned device 5. The functional layer 6 is easily peeled off from the substrate 2 when the wafer 1 is cut from the front surface 3 side with a cutting blade. Thus, in embodiment 1, the wafer 1 has a functional layer 6 including the device 5 laminated on the substrate 2.

[0018] (Wafer Processing Method) The wafer processing method according to the first embodiment is a method of processing a wafer 1, in which a functional layer 6 including devices 5 is stacked on a substrate 2, along planned division lines 4 that partition the wafer 1 into a plurality of devices 5. Note that in the first embodiment, the wafer processing method is also a method of dividing (corresponding to processing) the wafer 1 along the planned division lines 4 into individual device chips 10 (shown in FIG. 1 ). Note that the device chips 10 include a portion of the substrate 2 and the devices 5.

[0019] As shown in Fig. 3, the wafer processing method includes an affected region forming step 101, an affected region forming step 101, and a substrate processing step 103. In the wafer processing method of the first embodiment, as shown in Fig. 1, a disk-shaped tape 11 having a diameter larger than that of the wafer 1 is attached to the back surface 9 behind the front surface 3, an annular frame 12 is attached to the outer edge of the tape 11, and the wafer 1 supported by the frame 12 is processed.

[0020] (Affected region formation step) Fig. 4 is a cross-sectional view schematically showing a main part of a wafer during the affected region forming step of the wafer processing method shown in Fig. 3. Fig. 5 is a plan view schematically showing a main part of a wafer after the affected region forming step of the wafer processing method shown in Fig. 3. Fig. 6 is a plan view schematically showing another example of a main part of a wafer after the affected region forming step of the wafer processing method shown in Fig. 3.

[0021] The affected area forming step 101 is a step in which a laser beam 21 (shown in FIG. 4) having a wavelength that is absorbable by the substrate 2 and has a lower absorbability by the functional layer 6 than by the substrate 2 is irradiated along the planned division line 4 under processing conditions that restrict continuous ablation processing of the functional layer 6, thereby forming two affected areas 13 (shown in FIG. 4) extending along the planned division line 4 at a predetermined interval inside the functional layer 6. Note that performing continuous ablation processing means forming a continuous processed groove in the functional layer 6. A continuous processed groove refers to, for example, a processed groove that is formed uninterruptedly along the planned division line 4 in the area where the device chip 10 is formed, and that has a concave shape from the surface 3.

[0022] 4 suction-holds the back surface 9 of the wafer 1 on the holding surface of the holding table via tape 11, and clamps the frame 12 with a clamping section. In the first embodiment, in the affected area forming step 101, the laser processing device 20 images the front surface 3 of the wafer 1 with an imaging unit (not shown), detects the planned dividing lines 4, and performs alignment to align the laser beam application unit 22 with the planned dividing lines 4.

[0023] In embodiment 1, in the affected area forming step 101, the laser processing device 20 moves the wafer 1 and the laser beam application unit relatively along the planned dividing lines 4, and causes the laser beam application unit 22 to sequentially irradiate both widthwise edges of each planned dividing line 4 with a laser beam 21 having a wavelength that is absorbed by both the substrate 2 and the functional layer 6 of the wafer 1, as shown in Fig. 4. Note that in embodiment 1, in the affected area forming step 101, the laser processing device 20 sets the focal point 23 of the laser beam 21 at the interface 7 between the substrate 2 and the functional layer 6, and irradiates the laser beam 21 onto the wafer 1 along each planned dividing line 4, but in the present invention, the focal point 23 may also be set on the surface 3 of the wafer 1, i.e., the surface of the functional layer 6.

[0024] In addition, in the first embodiment, the laser beam 21 irradiated onto the wafer 1 in the affected area forming step 101 has a wavelength that is absorbed by the substrate 2 and the functional layer 6, and therefore ablation processing is performed on both the substrate 2 and the functional layer 6. Furthermore, the laser beam 21 has a wavelength that is less absorbable by the functional layer 6 than by the substrate 2.

[0025] However, in the modified area forming step 101 in the embodiment 1, the laser beam 21 is irradiated onto the wafer 1 at a wavelength that is less absorbable in the functional layer 6 than in the substrate 2, and at an output that restricts ablation of the functional layer 6, i.e., an output that is weaker than the output for ablation of the functional layer 6. For this reason, in the modified area forming step 101 in the embodiment 1, the laser processing device 20 heats and modifies the functional layer 6 near the focal point 23 of the laser beam 21, thereby forming modified areas 13 extending along the planned division line 4 inside the functional layer 6 on both edges of the planned division line 4.

[0026] The altered region 13 refers to a region in which the density, refractive index, mechanical strength, or other physical properties are different from those of the surrounding area. The altered region 13 is, for example, a melt-treated region, a crack region, a dielectric breakdown region, a refractive index change region, or a mixture of these regions. In the first embodiment, the altered region 13 has lower thermal conductivity than the other unaltered regions of the functional layer 6.

[0027] In the first embodiment, in the affected area forming step 101, the laser processing device 20 emits a laser beam from an oscillator having a wavelength of 355 nm, a repetition frequency of 200 kHz, and an average output of 1.0 W to 1.5 W, and branches the laser beam emitted by the oscillator into ten beams in the longitudinal direction of the dividing lines 4 for irradiation. For this reason, the average output per spot of the laser beam 21 actually irradiated onto the wafer 1 is 0.1 W to 0.15 W. That is, in the first embodiment, the affected area forming step 101 irradiates the wafer 1 with a laser beam 21 having a wavelength in the ultraviolet range.

[0028] Furthermore, in embodiment 1, in the affected area forming step 101, the relative speed of the laser beam 21 to the wafer 1 along the planned division line 4 (hereinafter referred to as the processing feed speed) is set to 30 mm / sec, and the spot of the focal point 23 of the laser beam 21 is set to a circle with a diameter of 6 μm to 8 μm.

[0029] Under these processing conditions, in the affected area forming step 101 in embodiment 1, the laser processing device 20 forms affected areas 13 extending along the division line 4 at both edges of the division line 4 inside the functional layer 6, forming two affected areas 13 at a predetermined interval inside the functional layer 6 for each division line 4, as shown in FIG. 5 . Note that in the present invention, when forming the affected areas 13 in the affected area forming step 101, pores 14 extending from the affected area 13 toward the surface 3 and opening onto the surface 3 may be formed, as shown in FIG. 6 . While FIG. 6 shows circular spot-shaped pores 14, instead of pores 14, processed grooves extending from the affected area 13 toward the surface 3, opening onto the surface 3, and extending in the longitudinal direction of the division line 4 may also be formed. In the case of processed grooves, forming continuous processed grooves would cause film peeling of the functional layer 6, as in the prior art. Therefore, the processing conditions, for example, the output per spot, are adjusted so that multiple openings reaching the surface 3 are formed discontinuously with a predetermined gap between them.

[0030] (Functional layer removal step) Fig. 7 is a cross-sectional view schematically showing a main part of the wafer after the functional layer removal step of the wafer processing method shown in Fig. 3. The functional layer removal step 102 is a step of irradiating a laser beam 21 between the affected regions 13 after the affected region formation step 101 is performed, to form a first processing groove 15 that removes the functional layer 6.

[0031] In the first embodiment, in the functional layer removal step 102, the laser processing device 20 irradiates the wafer 1 with a laser beam 21 from the laser beam application unit 22 along the planned dividing lines 4 while moving the wafer 1 and the laser beam application unit 22 relatively along the planned dividing lines 4. Note that in the first embodiment, in the affected area formation step 101, the laser processing device 20 sets the focal point 23 of the laser beam 21 on the surface 3 of the functional layer 6, and irradiates the laser beam 21 at the center of each planned dividing line 4 in the width direction.

[0032] In the first embodiment, in the functional layer removal step 102, the laser beam 21 is irradiated onto the wafer 1 under processing conditions that allow ablation of the functional layer 6, for example, an output per spot that is stronger than the output in the affected area formation step 101. Therefore, in the first embodiment, in the functional layer removal step 102, the laser processing device 20 performs ablation processing on the functional layer 6 and the substrate 2 at the center in the width direction of each planned division line 4, removing a portion of these, and forming a first processing groove 15 that divides the functional layer 6 at each planned division line 4, as shown in FIG.

[0033] In the first embodiment, in the functional layer removal step 102, a laser beam having a wavelength of 355 nm, a repetition frequency of 40 kHz to 60 kHz, and an average output of 2.5 W to 5.0 W is emitted from an oscillator, and the laser beam 21 emitted from the oscillator is split into two beams in the width direction of the planned division lines 4 and irradiated. The average output per spot of the laser beam 21 is 1.25 to 2.5 W. In the first embodiment, the processing feed rate in the functional layer removal step 102 is set to 100 mm / sec to 400 mm / sec, and the spot at the focal point 23 of the laser beam 21 is set to a circle with a diameter of 30 μm to 60 μm. That is, in the first embodiment, the functional layer removal step 102 irradiates the wafer 1 with a laser beam 21 having a wavelength in the ultraviolet region. Thus, in the wafer processing method of embodiment 1, the output of the laser beam 21 per spot irradiated in the affected area formation step 101 is smaller than the output of the laser beam 21 per spot irradiated in the functional layer removal step 102.

[0034] In the first embodiment, in the functional layer removal step 102, the altered region 13 is cracked by the laser beam 21 before other regions of the functional layer 6, releasing the stress generated in the functional layer 6 and preventing cracks from occurring outside the functional layer 6 and separating the functional layer 6. This allows the laser processing device 20 to perform ablation processing on the functional layer 6 between the altered regions 13 of each planned division line 4, thereby forming first processing grooves 15 between each functional layer 6, with the substrate 2 exposed at the bottom, while preventing peeling of the functional layer 6. Furthermore, in conventional processing methods, when forming processing grooves in the functional layer 6, cracks occur when the functional layer 6 softened by the heat of the laser beam 21 is rapidly cooled. Therefore, the processing feed rate is slowed down to accumulate heat in the functional layer 6 during processing, thereby preventing rapid cooling of the functional layer 6. However, in the first embodiment, the output per spot in the functional layer removal step 102 is small, so the thermal effect is small and rapid cooling can be prevented. Therefore, the processing feed speed when forming the affected region 13 can be increased, improving productivity.

[0035] (Substrate processing step) Fig. 8 is a cross-sectional view schematically showing a main part of the wafer after the substrate processing step of the wafer processing method shown in Fig. 3. The substrate processing step 103 is a step of processing the substrate 2 along the first processing groove 15 after the functional layer removal step 102 is performed.

[0036] In the first embodiment, in the substrate processing step 103, the laser processing device 20 irradiates the wafer 1 with a laser beam 21 from the laser beam application unit 22 along the planned dividing lines 4 while moving the wafer 1 and the laser beam application unit 22 relatively along the planned dividing lines 4. Note that in the first embodiment, in the affected area forming step 101, the laser processing device 20 sets the focal point 23 of the laser beam 21 on the bottom surface of the first cutting groove 15, and irradiates the laser beam 21 onto the bottom surface of the first cutting groove 15 formed on each planned dividing line 4.

[0037] In the first embodiment, in the substrate processing step 103, the wafer 1 is irradiated with a laser beam 21 under processing conditions that allow ablation of the substrate 2, for example, at an output stronger than the output in the affected region forming step 101. Therefore, in the first embodiment, in the substrate processing step 103, the laser processing device 20 performs ablation on the bottom surfaces of the first grooves 15 formed along each of the division lines 4, thereby forming second grooves 16 narrower than the first grooves 15, as shown in FIG. 8 . In the substrate processing step 103, the laser processing device 20 opens the second grooves 16 on the back surface 9 of the wafer 1, i.e., penetrates the wafer 1 with the second grooves 16, thereby dividing the wafer 1 into individual device chips 10. Thus, in the first embodiment, in the substrate processing step 103, the wafer 1 is divided into a plurality of device chips 10.

[0038] 9, the conventional processing method irradiates both edges of each division line 4 in the width direction with a laser beam 21 having a wavelength absorbed by the functional layer, and ablates both edges of each division line 4 of the functional layer 6 to form a processed groove 200. In this process, the conventional processing method slows down the processing feed rate to prevent the functional layer 6 from cooling rapidly after thermal expansion due to irradiation with the laser beam 21, thereby maintaining the functional layer 6 in a soft state and preventing cracking and peeling of the functional layer 6. However, the conventional processing method tends to reduce the flexural strength of the device chip 10 after division due to damage caused by heat.

[0039] In contrast to such conventional processing methods, the wafer processing method according to embodiment 1 cracks the functional layer 6 at both edges of the planned division line 4 inside the functional layer 6 before other regions do, thereby releasing internal stress and forming an altered region 13 that acts as a breakwater in the altered region forming step 101. For this reason, in the wafer processing method according to embodiment 1, even if the processing feed rate in the functional layer removing step 102 is faster than that in the altered region forming step 101, the altered region 13 becomes the starting point for cracking of the functional layer 6, and the altered region 13 is cracked before other regions, thereby releasing stress corresponding to the functional layer 6, thereby preventing the functional layer 6 outside the altered region 13 from peeling off.

[0040] As a result, the wafer processing method according to the first embodiment has the effect of suppressing peeling of the functional layer 6.

[0041] Furthermore, the wafer processing method according to embodiment 1 allows the processing feed rate in the functional layer removal step 102 to be faster than that in the affected area formation step 101, thereby suppressing thermal damage caused by the laser beam 21 and improving the flexural strength of the device chip 10.

[0042] 9 is a plan view schematically showing a main part of a wafer in which processed grooves are formed on both edges of the dividing line by a conventional processing method. In FIG. 9, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

[0043] [Embodiment 2] A wafer processing method according to embodiment 2 will be described with reference to the drawings. FIG. 10 is a flowchart showing the flow of the wafer processing method according to embodiment 2. FIG. 11 is a cross-sectional view schematically showing a main part of a wafer during an affected region forming step of the wafer processing method shown in FIG. 10. FIG. 12 is a cross-sectional view schematically showing a main part of a wafer after an outer processing groove forming step of the wafer processing method shown in FIG. 10. FIG. 13 is a cross-sectional view schematically showing a main part of a wafer after a functional layer removing step of the wafer processing method shown in FIG. 10. FIG. 14 is a cross-sectional view schematically showing a main part of a wafer after a substrate processing step of the wafer processing method shown in FIG. 10. In FIGS. 10, 11, 12, 13, and 14, the same parts as those of embodiment 1 are designated by the same reference numerals, and their description will be omitted.

[0044] The wafer processing method according to the second embodiment is a method of dividing the wafer 1 into individual device chips 10 along the planned dividing lines 4, as in the first embodiment. As shown in Fig. 10, the wafer processing method according to the second embodiment includes an affected region forming step 101, an outer processed groove forming step 110, an inner processed groove forming step 111, and a substrate processing step 103.

[0045] In embodiment 2, in the affected area formation step 101, as in embodiment 1, affected areas 13 extending along the planned division line 4 are formed on both edges of the planned division line 4 inside the functional layer 6, as shown in Figure 11, and two affected areas 13 are formed inside the functional layer 6 at each planned division line 4 with a predetermined distance between them.

[0046] The outer processing groove forming step 110 is a step of removing the inner edge of the affected region 13 after the affected region forming step 101 is performed, and forming outer processing grooves 17, with the substrate 2 exposed at the bottom, on both widthwise edges of each planned dividing line 4. In the second embodiment, in the outer processing groove forming step 110, the laser processing apparatus 20 irradiates the wafer 1 with a laser beam 21 from the laser beam application unit 22 along the planned dividing line 4 while moving the wafer 1 and the laser beam application unit 22 relatively along the planned dividing line 4.

[0047] In the first embodiment, in the affected area forming step 101, the laser processing device 20 sets the focal point 23 of the laser beam 21 on the inner edge of the affected area 13 on the surface 3 of the functional layer 6, and irradiates the laser beam 21 onto each affected area 13 of each planned dividing line 4. The inner edge of the affected area 13 refers to the edge of the two affected areas 13 formed on each planned dividing line 4 that is closer to the center of the planned dividing line 4.

[0048] In the second embodiment, in the outer groove forming step 110, the laser beam 21 is irradiated onto the wafer 1 under processing conditions that enable ablation of the functional layer 6, for example, at a stronger output per spot than in the affected area forming step 101. Therefore, in the first embodiment, in the outer groove forming step 110, the laser processing device 20 performs ablation of the functional layer 6 on the inner edge of the affected area 13 of each planned dividing line 4, the inner edge of the affected area 13, and the upper surface of the substrate 2, removing a portion of these, as shown in Fig. 12, dividing the functional layer 6 along each planned dividing line 4, removing the inner edge of the affected area 13, and forming an outer groove 17 whose bottom surface exposes the substrate 2.

[0049] In the second embodiment, in the outer groove forming step 110, a laser beam having a wavelength of 355 nm, a repetition frequency of 120 kHz to 200 kHz, and an average output of 0.1 W to 3.0 W is emitted from an oscillator, and the laser beam 21 emitted from the oscillator is branched into two beams in the width direction of the division lines 4 and irradiated. Because the laser beam 21 is branched, the average output per spot is 0.05 W to 1.5 W. In the first embodiment, in the outer groove forming step 110, the processing feed rate is set to 100 mm / sec to 400 mm / sec, and the spot at the focal point 23 of the laser beam 21 is set to a circle with a diameter of 6 μm to 8 μm.

[0050] In embodiment 2, in the inner processing groove formation step 111, as in embodiment 1, the laser processing device 20 performs ablation processing on the functional layer 6 and substrate 2 at the center of the width of each planned division line 4, removing a portion of them, and dividing the functional layer 6 at each planned division line 4 to form an inner processing groove 15 that is connected to the outer processing groove 17, as shown in Figure 13.

[0051] In the second embodiment, in the inner groove forming step 111, a laser beam having a wavelength of 355 nm, a repetition frequency of 40 kHz to 60 kHz, and an average output of 2.5 W to 5.0 W is emitted from an oscillator, and the laser beam 21 emitted from the oscillator is branched into two beams in the width direction of the division line 4 and irradiated. Because the laser beam 21 is branched, the average output per spot of the laser beam 21 is 1.25 W to 2.5 W. In the first embodiment, in the functional layer removing step 102, the processing feed rate is set to 100 mm / sec to 400 mm / sec, and the spot at the focal point 23 of the laser beam 21 is set to a circle with a diameter of 30 μm to 60 μm. In the second embodiment, the outer groove forming step 110 and the inner groove forming step 111 are combined to form the functional layer removing step 102.

[0052] In the second embodiment, in the substrate processing step 103, as in the first embodiment, the laser processing device 20 performs ablation on the bottom surface of the first groove 15 to form a second groove 16 narrower than the first groove 15 on the bottom surface of the first groove 15, as shown in Fig. 14. In the second embodiment, in the substrate processing step 103, the laser processing device 20 opens the second groove 16 on the back surface 9 of the wafer 1, that is, penetrates the wafer 1 with the second groove 16, thereby dividing the wafer 1 into individual device chips 10.

[0053] As with embodiment 1, the wafer processing method of embodiment 2 has the effect of suppressing peeling of the functional layer 6 by forming, in the affected area formation step 101, affected areas 13 which have lower thermal conductivity than the functional layer 6 and are less likely to peel off from the substrate 2 at both edges of the planned division line 4 inside the functional layer 6.

[0054] The present invention is not limited to the above-described embodiment. In other words, various modifications can be made without departing from the gist of the present invention. For example, in the substrate processing step 103, the bottom surface of the first groove 15 may be cut with a cutting blade, the bottom surface of the first groove 15 may be plasma etched, or a laser beam may be irradiated with a focal point set on the interior of the substrate 2 to form a modified layer inside the substrate, and an external force may be applied to divide the substrate starting from the modified layer. Also, in the present invention, the wafer 1 does not need to be divided into individual device chips 10 in the substrate processing step 103. [Explanation of symbols]

[0055] 1 wafer 2 boards 3 surface 4 Planned division line 5 Devices 6 Functional Layers 9 Back side 10 Device Chips 13 Altered Area 15 1st machining groove 21 Laser beam 101 Affected area formation step 102 Functional layer removal step 103 PCB Processing Steps

Claims

1. A wafer processing method for processing a wafer having a functional layer including a device stacked on a substrate along a planned dividing line, comprising: a modified region forming step of irradiating a laser beam having a wavelength that is absorbed by the substrate and that is less absorbed by the functional layer than by the substrate along the intended dividing line under processing conditions that restrict continuous ablation processing of the functional layer, thereby forming two modified regions extending along the intended dividing line within the functional layer at a predetermined interval; a functional layer removing step of irradiating a laser beam between the affected regions after the affected region forming step to form a first groove for removing the functional layer; A wafer processing method comprising: a substrate processing step of processing the substrate along the first processing groove after the functional layer removal step is performed.

2. 2. The wafer processing method according to claim 1, wherein the functional layer is an oxide film.

3. 2. The wafer processing method according to claim 1, wherein the affected region forming step involves irradiating a laser beam having a wavelength in the ultraviolet region.

4. A wafer processing method as described in claim 1, characterized in that the output of the laser beam per spot irradiated in the affected area formation step is smaller than the output of the laser beam per spot irradiated in the functional layer removal step.

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