Wafer processing method

Abstract

To provide a wafer processing method for dividing a wafer into individual device chips without breaking or damaging the wafer even when a projection exists on the surface of the wafer.SOLUTION: A method for processing a wafer 10 formed on a surface 10a where a plurality of devices 12 are partitioned by a division schedule line 14 includes: a resin coating step of coating a liquid resin L onto the surface 10a of the wafer 10, and coating a part constituting the devices; a resin curing step of curing the coated liquid resin; and a flattening step of flattening the cured resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for processing a wafer having a plurality of devices formed on its surface, the surface being partitioned by dividing lines. [Background technology]

[0002] Wafers with multiple devices such as ICs and LSIs formed on their surface, partitioned by planned division lines, are then separated into individual device chips by a dicing machine and used in electrical equipment such as mobile phones and personal computers.

[0003] In addition, a technology has been proposed in which a laser beam having a wavelength that is transparent to the wafer is irradiated at a focal point inside the wafer corresponding to the planned dividing line, forming a modified layer along the planned dividing line, and then grinding the back surface to form the desired thickness, and dividing the wafer into individual device chips (see Patent Document 1).

[0004] In addition, a technology has been proposed in which the focal point of a laser beam with a wavelength that is absorbed by the wafer is positioned on the intended dividing line, and ablation processing is performed to form grooves and divide the wafer into individual device chips (see Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2014-078569 [Patent Document 2] Patent Publication No. 2004-188475 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the technology described in Patent Document 1 is applied to a wafer on which unevenness, such as protruding electrodes called bumps, is formed on the surface of a device, there is a problem that the wafer may be damaged due to the bumps.

[0007] Furthermore, when the technology described in Patent Document 2 is applied to a wafer having bumps formed thereon, and the surface is coated with a protective film made of a liquid resin, the film thickness becomes non-uniform. Therefore, even if an attempt is made to position the focal point of a laser beam having a wavelength that is absorbed by the wafer on the intended dividing line, perform ablation processing to form grooves, and divide the wafer into individual device chips, the depth of the grooves becomes non-uniform, making it difficult to properly divide the wafer into individual device chips without damaging the wafer.

[0008] The present invention has been made in view of the above-mentioned facts, and its main technical object is to provide a wafer processing method that can divide a wafer into individual device chips without breaking or damaging the wafer, even if protrusions are present on the surface of the wafer. [Means for solving the problem]

[0009] In order to solve the above-mentioned main technical problem, according to the present invention, there is provided a method for processing a wafer in which a plurality of devices, each having a plurality of protruding electrodes on its surface, are formed on a surface partitioned by planned dividing lines, the method comprising: a resin coating step of applying a liquid resin to the surface of the wafer a plurality of times to cover at least the protruding electrodes and also to cover portions constituting the devices; a resin hardening step of hardening the coated liquid resin to form a protective film; a planarizing step of planarizing the protective film; a modified layer forming step of holding the protective film and irradiating the wafer with a laser beam having a wavelength that is transparent to the wafer, with the focal point positioned inside from the back surface corresponding to the planned dividing lines, to form a modified layer along the planned dividing lines; and a dividing step of holding the protective film and grinding the back surface of the wafer with a grinding wheel to finish the wafer to a predetermined thickness and divide the wafer into individual device chips from the modified layer. the thickness of the protective film before the planarization step is performed is ensured to be such that the protruding electrodes are not exposed on the surface even when the protective film is planarized in the planarization step;A wafer processing method is provided in which the planarization is performed so that the protruding electrodes are not exposed on the surface when the protective film is planarized in the planarization step.

[0010] In the planarization step, the back surface of the wafer is preferably held on a chuck table, the front surface of the wafer is exposed, and the resin is cut and planarized by cutting means equipped with a cutting tool. [Effects of the Invention]

[0013] The wafer processing method of the present invention is a method for processing a wafer on which a plurality of devices, each having a plurality of protruding electrodes on its surface, are formed on a surface partitioned by planned division lines, and includes a resin coating step of applying a liquid resin to the surface of the wafer a plurality of times to cover at least the protruding electrodes and also to cover portions constituting the devices; a resin hardening step of hardening the coated liquid resin to form a protective film; a planarizing step of planarizing the protective film; a modified layer forming step of holding the protective film and irradiating the wafer with a laser beam having a wavelength that is transparent to the wafer, with the focal point positioned inside from the back surface corresponding to the planned division lines, to form a modified layer along the planned division lines; and a dividing step of holding the protective film and grinding the back surface of the wafer with a grinding wheel to finish the wafer to a predetermined thickness and divide the wafer into individual device chips from the modified layer. the thickness of the protective film before the planarization step is performed is ensured to be such that the protruding electrodes are not exposed on the surface even when the protective film is planarized in the planarization step; In the planarization step, when the protective film is planarized, the planarization is performed so that the protruding electrodes are not exposed on the surface, and therefore the thickness of the film formed on the surface of the wafer becomes uniform.Even when performing a modified layer formation step in which a laser beam having a wavelength that is transparent to the wafer is irradiated from a focal point positioned inside the back surface corresponding to the planned dividing lines to form a modified layer along the planned dividing lines, and a dividing step in which the back surface of the wafer is ground with a grinding wheel to finish the wafer to a predetermined thickness and divide the wafer into individual device chips from the modified layer, damage to the wafer is prevented, and the thickness of the film formed on the surface of the wafer is uniform, so that the wafer can be properly divided into individual device chips. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1( a ) is a perspective view of a wafer as a workpiece, a liquid resin coating device, and a perspective view showing an embodiment of a resin coating step. [Figure 2] FIG. 10 is a perspective view showing an embodiment of a resin curing step. [Figure 3] 1 is a perspective view illustrating an embodiment of a planarization step. [Figure 4] FIG. 1A is a perspective view of a laser processing device, FIG. 1B is a perspective view showing an embodiment of a modified layer forming step, and FIG. 1C is a cross-sectional view of the wafer shown in FIG. [Figure 5] FIG. 1A is a perspective view showing an embodiment of a dividing step for dividing a wafer into individual device chips from a modified layer, and FIG. 1B is a perspective view showing a wafer divided into individual device chips by the dividing step of FIG. [Figure 6] FIG. 10 is a perspective view showing an embodiment of a grinding step in which the back surface of the wafer is ground with a grinding wheel. [Figure 7] 7A is a perspective view showing an embodiment of a modified layer forming step performed on a wafer ground by the grinding step of FIG. 6, and FIG. 7B is a cross-sectional view of the wafer shown in FIG. [Figure 8] 8 is a perspective view showing a mode in which the wafer that has undergone the modified layer forming step shown in FIG. 7 is held by a frame. FIG. [Figure 9] FIG. 1 is a perspective view illustrating an embodiment of a dividing step for dividing a wafer into individual device chips. [Figure 10] (a) A perspective view showing an embodiment of the ablation processing step, (b) A perspective view showing a wafer divided into individual device chips by (a), and (c) A perspective view showing a state in which the protective film has been removed from the wafer shown in (b). [Figure 11] FIG. 1A is a perspective view showing an embodiment of a groove forming step, FIG. 1B is a cross-sectional view of the wafer shown in FIG. 1A, and FIG. 1C is a perspective view of the wafer on which grooves have been formed by the groove forming step. [Figure 12] FIG. 10 is a perspective view showing an embodiment of a dividing step in which the back surface of the wafer is ground with a grinding wheel to divide the wafer into individual device chips. [Figure 13]FIG. 1A is a perspective view showing how a wafer divided into individual device chips is supported by a frame, and FIG. 1B is a perspective view showing how a protective film is removed from the wafer. DETAILED DESCRIPTION OF THE INVENTION

[0015] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of a wafer processing method according to the present invention will be described in detail with reference to the accompanying drawings.

[0016] 1(a) shows a wafer 10 to be processed by the wafer processing method of this embodiment, and a liquid resin coating apparatus 20 (only a portion of which is shown). The wafer 10 is formed, for example, from a silicon (Si) substrate. The wafer 10 has a surface 10a partitioned by planned division lines 14, on which a plurality of devices 12 are formed. As shown in an enlarged partial view at the top of the figure, each device 12 has a plurality of bumps 16 formed thereon. The bumps 16 are protruding electrodes for electrically connecting the devices 12 to the outside, and are, for example, alloy electrodes primarily composed of lead and tin.

[0017] In the wafer processing method of this embodiment, first, a resin coating step is performed in which a liquid resin L, described below, is applied to the surface 10a of the wafer 10 to cover the portions that constitute the device 12. More specifically, the wafer 10 is transported to a liquid resin coating apparatus 20 shown in the figure. The liquid resin coating apparatus 20 includes at least a chuck table 21 and a support base 23. The holding surface 22 of the chuck table 21 is formed of a porous material with breathability. The chuck table 21 is connected to a suction means (not shown), and by operating the suction means, a suction negative pressure is generated on the holding surface 22. An electric motor (not shown) is disposed inside the support base 23, and is capable of rotating the chuck table 21 together with a rotation shaft 24.

[0018] The wafer 10 transported to the liquid resin coating device 20 is placed on the chuck table 21 of the liquid resin coating device 20 with the front surface 10a facing upward and the back surface 10b facing downward, and the suction means is activated to hold the wafer 10 by suction on the holding surface 22.

[0019] As shown in FIG. 1(b), after the wafer 10 is suction-held on the chuck table 21, the liquid resin supply nozzle 25 is positioned directly above the center of the wafer 10. The electric motor of the support base 23 is operated to rotate the chuck table 21 together with the rotary shaft 24 in the direction indicated by the arrow R1. A predetermined amount of liquid resin L is supplied from the nozzle 25a of the liquid resin supply nozzle 25 and applied to the front surface 10a of the wafer 10. For example, an epoxy resin that hardens when irradiated with ultraviolet light is used as the liquid resin L. The supply of the liquid resin L from the nozzle 25a is not limited to one time, but may be multiple times. The amount of liquid resin L supplied from the nozzle 25a is set to an amount sufficient to coat the front surface 10a of the wafer 10 with the liquid resin L and to cover the portions that constitute the device 12. This completes the resin coating process.

[0020] Next, a resin curing step is performed to harden the liquid resin L coated on the wafer 10. To perform the resin curing step, for example, as shown on the left side of FIG. 2, an ultraviolet irradiation means 26 is positioned directly above the wafer 10 held in the liquid resin coating apparatus 20. Next, ultraviolet rays (UV) are irradiated from the ultraviolet irradiation means 26 toward the liquid resin L coated on the wafer 10. This hardens the liquid resin L, and as shown on the right side of FIG. 2, a protective film L' made of the hardened liquid resin L is formed on the front surface 10a of the wafer 10, completing the resin curing step. While a resin that hardens upon irradiation with ultraviolet rays (UV) is selected as the liquid resin L coated on the front surface 10a of the wafer 10 in this embodiment, the present invention is not limited thereto. For example, the liquid resin L may be a resin that hardens over time. In this case, the resin curing step corresponds to a step of waiting until the liquid resin L applied to the wafer 10 hardens after the resin coating step is completed.

[0021] Although the protective film L' described above is formed to a thickness sufficient to absorb the bumps 16 formed on the device 12, the overall thickness of the protective film L' is affected by the unevenness of the front surface 10a of the wafer 10 and by shrinkage during curing, resulting in unevenness 18. In this state, even if a laser beam is irradiated onto the front surface 10a of the wafer 10 to form division grooves along the division lines 14 by ablation, the groove depth may not be uniform, resulting in processing defects. Furthermore, even if the back surface 10b of the wafer 10 is ground to thin the wafer 10 while holding the protective film L', the unevenness 18 may damage or break the wafer 10. Therefore, in this embodiment, a planarization process is performed to planarize the protective film L' made of the cured resin as described above.

[0022] 3 shows a cutting device 30 (only a part thereof is shown) suitable for carrying out the planarization step of this embodiment. The cutting device 30 includes a cutting unit 31 that is mounted so as to be movable in the vertical direction. The cutting unit 31 includes a movable base 32 that is moved in the vertical direction by a cutting feed means (not shown), and a spindle unit 33 mounted on the movable base 32. A support member 32a is mounted on the front surface of the movable base 32, and the spindle unit 33 is supported by the support member 32a.

[0023] The spindle unit 33 includes a spindle housing 33a mounted on the support member 32a, a rotary spindle 33b rotatably disposed in the spindle housing 33a, and a servo motor 33c as a drive source for driving the rotary spindle 33b to rotate. The lower end of the rotary spindle 33b protrudes downward beyond the lower end of the spindle housing 33a, and a disk-shaped tool mounting member 33d is provided on the lower end side.

[0024] The tool bit mounting member 33d has a tool bit mounting hole 33e that penetrates vertically through a portion of its outer periphery that is eccentric from the rotation axis. A tool bit 34 is inserted into the tool bit mounting hole 33e, and a tightening bolt 35 is threaded into an internally threaded hole formed on the side of the tool bit mounting member 33d to tighten and secure the tool bit. In the illustrated embodiment, the tool bit 34 is formed into a rod shape from tool steel such as a cemented carbide alloy, and a cutting edge formed of diamond or the like is provided at the lower tip of the tool bit 34. The tool bit 34 mounted on the tool bit mounting member 33d is rotated together with the tool bit mounting member 33d by the rotation of the rotating spindle 33b driven by the servo motor 33c.

[0025] The cutting device 30 is provided with a chuck table mechanism 36. The chuck table mechanism 36 is provided with a rotatably arranged, disk-shaped chuck table 36a. The holding surface of the chuck table 36a is formed of a breathable material and is connected to a suction source (not shown). The chuck table mechanism 36 is provided with a movement mechanism (not shown) housed inside the cutting device 30, which can move the chuck table 36a together with the cover member 36b in the direction indicated by arrow R3. The cutting device 30 shown in FIG. 3 holds the wafer 10 transferred from the liquid resin coating device 20 on the chuck table 36a by suction.

[0026] The cutting device 30 shown in FIG. 3 is generally configured as described above, and the planarization step of this embodiment, which is carried out using the above-described cutting device 30, will be described below.

[0027] The wafer 10 is placed on the chuck table 36a of the cutting device 30 shown in FIG. 3 and held by suction with the protective film L' side facing upward. The servo motor 33c is driven to rotate the tool holder 33d in the direction indicated by arrow R2, and a notched feed means (not shown) is operated to lower the wafer 10 to a predetermined height to remove the irregularities 18 on the protective film L' on the wafer 10. The moving means (not shown) is operated to move the chuck table mechanism 36 in the direction indicated by arrow R3 in FIG. 3, causing the chuck table 36a holding the wafer 10 to pass through the processing area below the tool holder 33d. As the chuck table 36a holding the wafer 10 passes through the processing area in this manner, the irregularities 18 are removed from the protective film L' on the wafer 10, completing the planarization process, as shown in the lower part of FIG. 3.

[0028] The planarization step of the present invention is not limited to planarization using the cutting device 30 described above, but may be planarization using, for example, a polishing device or the like.

[0029] By employing the wafer processing method including the resin coating step, resin curing step, and planarization step described above, various dividing processes for dividing the wafer 10 into individual device chips, which will be described below, can be carried out effectively. A first embodiment of the dividing process will be described with reference to Figures 4, 5, and 13.

[0030] 4(a) shows an overall perspective view of a laser processing apparatus 40 suitable for the first dividing process, together with a wafer 10 on which a flat protective film L' has been formed based on the above-mentioned wafer processing method. The laser processing apparatus 40 is arranged on a base 40a and includes a laser irradiation means 41 that irradiates a laser beam onto the wafer 10 to be processed, a holding means 42 that holds the wafer 10, an imaging means 43 that images the wafer 10 held by the holding means 42, a feeding means 44 that feeds the laser irradiation means 41 and the holding means 42 relatively for processing and also moves the imaging means 43 and the holding means 42 relatively, and a frame 45 that includes a vertical wall 45a erected on the back side of the feeding means 44 on the base 40a and a horizontal wall 45b extending horizontally from the upper end of the vertical wall 45a.

[0031] An optical system (not shown) constituting the laser irradiation means 41 is housed inside the horizontal wall portion 45b of the frame 45. A condenser 41a constituting part of the laser irradiation means 41 is disposed on the lower surface side of the tip of the horizontal wall portion 45b. The following description will be given assuming that the laser irradiation means 41 of this embodiment can switch between irradiating a laser beam having a wavelength that is transmissive to the wafer 10 and a laser beam having a wavelength that is absorbent by the wafer 10. The imaging means 43 is disposed adjacent to the condenser 41a in the X-axis direction indicated by the arrow X in the figure. The imaging means 43 includes a normal imaging element (CCD) that captures images using visible light, infrared irradiation means that irradiates the workpiece with infrared rays, an optical system that captures the infrared rays irradiated by the infrared irradiation means, and an imaging element (infrared CCD) that outputs an electrical signal corresponding to the infrared rays captured by the optical system.

[0032] As shown in FIG. 4(a), the holding means 42 includes a rectangular X-axis direction movable plate 42a mounted on a base 40a so as to be movable in the X-axis direction; a rectangular Y-axis direction movable plate 42b mounted on the X-axis direction movable plate 42a so as to be movable in the Y-axis direction perpendicular to the X-axis direction; a cylindrical support 42c fixed to the upper surface of the Y-axis direction movable plate 42b; and a rectangular cover plate 42d fixed to the upper end of the support 42c. A chuck table 42e is disposed on the cover plate 42d and extends upward through an elongated hole formed in the cover plate 42d. The chuck table 42e is rotatable by a rotation drive means (not shown) housed in the support 42c. A circular suction chuck 42f made of a breathable porous material and extending substantially horizontally is disposed on the chuck table 42e. The suction chuck 42f is connected to a suction means (not shown) via a flow path passing through the support 42c.

[0033] The feed means 44 includes an X-axis feed means 46 and a Y-axis feed means 47. The X-axis feed means 47 converts the rotational motion of the motor 47a into linear motion via a ball screw 47b and transmits the linear motion to the X-axis movable plate 42a, moving the X-axis movable plate 42a back and forth in the X-axis direction along a pair of guide rails 40b, 40b arranged on the base 40a along the X-axis direction. The Y-axis feed means 47 converts the rotational motion of the motor 47a into linear motion via a ball screw 47b and transmits the linear motion to the Y-axis movable plate 42b, moving the Y-axis movable plate 42b back and forth in the Y-axis direction along a pair of guide rails 42g, 42g arranged on the X-axis movable plate 42a along the Y-axis direction.

[0034] The laser processing apparatus 40 shown in FIG. 4(a) has a configuration roughly as described above, and the modified layer formation step of the first dividing process, which is performed using this laser processing apparatus 40, will be described in more detail.

[0035] First, as shown in FIG. 4(a), the wafer 10 is placed on the suction chuck 42f of the chuck table 42e with the protective film L' side facing downward and the back surface 10b side of the wafer 10 facing upward, and is held by suction.

[0036] The wafer 10 held by the chuck table 42e is moved to a position directly below the imaging means 43 by operating the above-mentioned feeding means 44, and is then imaged. The imaging means 43 is connected to a control means and a display means (not shown), and detects the dividing lines 14 formed on the side of the wafer 10 where the protective film L' is formed and to be irradiated with a laser beam by irradiating the back surface 10b of the wafer 10 with infrared light and taking an image. The X and Y coordinates, which are position information of the detected dividing lines 14, are stored in the control means, and the chuck table 42e is rotated to align the predetermined dividing lines 14 in the X-axis direction (alignment).

[0037] After the above alignment is performed, the feeding means 44 is operated to move the chuck table 42e in the X-axis direction, and the wafer 10 is positioned directly below the condenser 41a of the laser irradiation means 41, as shown in FIG. 4(b). Next, the feeding means 44 is operated and the condenser 41a is moved in the Z-axis direction (up and down) indicated by the arrow Z in the figure, so that the focal point P1 of the laser beam LB1, which has a wavelength that is transparent to the wafer 10 and is irradiated by the laser irradiation means 41, is positioned inside a position corresponding to the predetermined dividing lines 14 from the back surface 10b side of the wafer 10, as shown in FIG. 4(c), and the modified layer 100 is formed. After the modified layer 100 is formed along the predetermined dividing lines 14, the wafer 10 is indexed and fed in the Y-axis direction by the distance corresponding to the dividing lines 14, and the unprocessed dividing lines 14 adjacent in the Y-axis direction are positioned directly below the condenser 41a. Then, in the same manner as described above, the focal point P1 of the laser beam LB1 is positioned inside the position corresponding to the planned dividing line 14 of the wafer 10 and irradiated, and the wafer 10 is processed and fed in the X-axis direction to form a modified layer 100.

[0038] The above-described laser processing is repeated, processing and feeding the wafer 10 in the X-axis direction and the Y-axis direction, to form modified layers 100 along all of the dividing lines 14 along the X-axis direction. Next, the wafer 10 is rotated 90 degrees, and the unprocessed dividing lines 14 perpendicular to the dividing lines 14 along which the modified layers 100 have already been formed are aligned in the X-axis direction. Then, the laser beam LB1 is irradiated to each of the remaining dividing lines 14 in the same manner as described above, with the focal point P1 of the laser beam LB1 positioned, to form modified layers 100 inside the wafer 10 along all of the dividing lines 14 formed on the front surface 10a of the wafer 10 (modified layer forming step).

[0039] The processing conditions for the laser processing carried out in the modified layer forming step are set, for example, as follows. Wavelength: 1342nm Average power: 1.0W Repetition frequency: 90kHz Feed speed: 700mm / sec

[0040] After the modified layer forming step described above has been performed, the wafer 10 is transferred to a grinding apparatus 50 (only a portion of which is shown) shown in Fig. 5(a). The grinding apparatus 50 includes a chuck table 51 that can be rotated by a rotary drive means (not shown), and grinding means 52. The grinding means 52 includes a rotary spindle 52a that can be rotated by a rotary drive means (not shown), a wheel mount 52b attached to the lower end of the rotary spindle 52a, and a grinding wheel 52c attached to the lower surface of the wheel mount 52b, and a plurality of grinding stones 52d are arranged in an annular shape on the lower surface of the grinding wheel 52c.

[0041] 5(a), the wafer 10 transported to the grinding device 50 is suction-held on the chuck table 51 with the side on which the protective film L' is formed facing downward and the back surface 10b facing upward. Then, the rotating spindle 52a of the grinding means 52 is rotated in the direction indicated by arrow R4 at, for example, 6000 rpm, and the chuck table 51 is rotated in the direction indicated by arrow R5 at, for example, 300 rpm. Then, the grinding feed means (not shown) is operated to lower the grinding wheel 52d in the direction indicated by arrow R6, bringing it into contact with the back surface 10b of the wafer 10, and grinding is performed at a grinding feed rate of, for example, 1 μm / sec. At this time, grinding can be carried out while measuring the thickness of the wafer 10 with a contact-type measuring gauge (not shown), and by grinding until the predetermined finished thickness is reached, an external force is applied to the wafer 10, and the wafer 10 is divided into individual device chips 12' along the modified layers 100 formed along the planned division lines 14, as shown in Figure 5(b) (division step). This completes the first division process.

[0042] As described above, once the wafer 10 has been divided into individual device chips 12' by the first dividing process, it is sent to a pick-up process (not shown) as necessary. For example, as shown in FIG. 13(a), an annular frame F having an opening Fa large enough to accommodate the wafer 10 is prepared, and the wafer 10 is inverted and positioned in the center of the opening Fa with the protective film L' side facing upward and the back surface 10b side of the wafer 10 facing downward, and held in place by adhesive tape T. Then, as shown in FIG. 13(b), the protective film L' is removed to expose the front surface 10a side of the wafer 10 divided into the individual device chips 12', allowing for easy pick-up.

[0043] In the first dividing process described above, the resin coating process, resin hardening process, and planarization process are carried out in advance, and the thickness of the protective film L' is made uniform. Therefore, even if a dividing process is carried out after the modified layer forming process, in which the back surface 10b of the wafer 10 is ground with a grinding wheel and the wafer 10 is divided into individual device chips 12', damage to the wafer 10 is prevented.

[0044] Next, the second dividing process carried out in combination with the wafer processing method including the above-mentioned resin coating step, resin hardening step, and planarization step will be described below with reference to FIGS.

[0045] In the second dividing process, the wafer 10, which has undergone the resin coating process, resin curing process, and planarization process described above, and on which the protective film L' has been formed, is transferred to the grinding device 50 described with reference to FIG. 5 without undergoing the modified layer forming process. Then, as shown in FIG. 6, the wafer 10 transferred to the grinding device 50 is suction-held on the chuck table 51 with the side on which the protective film L' has been formed facing downward and the back surface 10b facing upward. The rotating spindle 52a of the grinding means 52 is rotated in the direction indicated by arrow R4 at, for example, 6000 rpm, and the chuck table 51 is rotated in the direction indicated by arrow R5 at, for example, 300 rpm. The grinding feed means is then operated to lower the grinding wheel 52d in the direction indicated by arrow R6 to contact the back surface 10b of the wafer 10, and the wafer is ground at a grinding feed rate of, for example, 1 μm / sec. At this time, grinding can be carried out while measuring the thickness of the wafer 10 with a contact-type measuring gauge (not shown), and the wafer 10 is ground until it reaches the predetermined finished thickness (grinding step).

[0046] After the above-described grinding process is performed to adjust the thickness of the wafer 10 to the finished thickness, the wafer 10 is transported to the laser processing apparatus 40 described with reference to FIG. 4. Then, the wafer 10 is placed on the chuck table 42e of the laser processing apparatus 40 with the back surface 10b side facing upward and held by suction. After the above-described alignment, the wafer 10 is moved in the X-axis direction to be positioned directly below the condenser 41a of the laser irradiation means 41, as shown in FIG. 7(a). Next, the above-described feeding means 44 is operated, and the laser irradiation means 41 positions a focal point P2 of a laser beam LB2 having a wavelength that is transparent to the wafer 10 at a position inside the predetermined dividing line 14 from the back surface 10b side of the wafer 10 and irradiates the laser beam LB2, forming a modified layer 110, as shown in FIG. 7(b). Once the modified layer 110 has been formed along the predetermined dividing lines 14, the wafer 10 is indexed and fed in the Y-axis direction by the distance corresponding to the dividing lines 14, and the adjacent unprocessed dividing lines 14 in the Y-axis direction are positioned directly below the condenser 41a. Then, in the same manner as described above, the focal point P2 of the laser beam LB2 is positioned inside the position corresponding to the dividing lines 14 on the wafer 10 and irradiated, and the wafer 10 is processed and fed in the X-axis direction to form the modified layer 110.

[0047] By repeating the above-described processing, the wafer 10 is processed and fed in the X-axis direction and the Y-axis direction, and modified layers 110 are formed along all of the dividing lines 14 along the X-axis direction. Next, the wafer 10 is rotated 90 degrees, and the unprocessed dividing lines 14 perpendicular to the dividing lines 14 along which the modified layers 110 have already been formed are aligned in the X-axis direction. Then, the laser beam LB2 is irradiated to each of the remaining dividing lines 14 in the same manner as described above, with the focal point P2 of the laser beam LB2 positioned, to form modified layers 110 inside the wafer 10 along all of the dividing lines 14 formed on the front surface 10a of the wafer 10 (modified layer forming step).

[0048] The processing conditions for the laser processing carried out in the modified layer forming step in the second dividing process are set, for example, as follows. Wavelength: 1064nm Average power: 1.0W Repetition frequency: 80kHz Feed speed: 300mm / sec

[0049] As described above, after the modified layer forming step has been performed, the wafer 10 is carried out from the laser processing apparatus 40, and as shown in FIG. 8, the wafer 10 is positioned in the center of a previously prepared annular frame F having an opening Fa capable of accommodating the wafer 10, with the protective film L' side facing upward and the back surface 10b side of the wafer 10 facing downward, and is held in place via adhesive tape T. Next, once the wafer 10 is held in the frame F, the protective film L' is removed as shown in FIG. 9. Once the protective film L' has been removed, an external force G is applied so as to pull the adhesive tape T outward around the wafer 10, and the wafer 10 is divided into individual device chips 12' (dividing step).

[0050] By carrying out the second dividing process described above, the resin coating process, resin hardening process, and planarization process are also carried out, so that the same effects as those of the first dividing process described above can be achieved, and the wafer 10 can be successfully divided into individual device chips 12'.

[0051] Furthermore, a third embodiment of the dividing process for dividing the wafer 10 into individual device chips, which is carried out in combination with the wafer processing method including the above-mentioned resin coating step, resin hardening step, and planarization step, will be described with reference to FIG. 10.

[0052] In the third dividing process, after the above-described resin coating step, resin curing step, and planarization step are performed, as shown in Fig. 10(a), the wafer 10 on which the protective film L' is formed is positioned in the center of an opening Fa of an annular frame F having an opening Fa capable of accommodating the wafer 10, and is held with the protective film L' side facing upward via adhesive tape T. Since the protective film L' is formed on the front surface 10a of the wafer 10 as described above, the wafer 10 shown in Fig. 10(a) is held with the front surface 10a side facing upward.

[0053] The wafer 10 described above is transported to the laser processing apparatus 40 described with reference to FIG. 4 and held by suction on the chuck table 42e. The wafer 10 transported to the laser processing apparatus 40 is held by suction on the chuck table 42e with the front surface 10a coated with the protective film L' facing upward. The wafer 10 held on the chuck table 42e is aligned using an imaging means 43 arranged in the laser processing apparatus 40 to detect the positions of the dividing lines 14 formed on the front surface 10a, and the wafer 10 is rotated by a rotation driving means that rotates the chuck table 42e, thereby aligning the predetermined dividing lines 14 in the X-axis direction. Information on the detected positions of the dividing lines 14 is stored in a control means (not shown).

[0054] 10(a), based on the position information detected by the above-described alignment, the condenser 41a of the laser irradiation means 41 is positioned on the dividing line 14 in a predetermined direction, and a laser beam LB3 having a wavelength absorbable by the wafer 10 is irradiated by positioning the focal point on the surface 10a of the wafer 10 corresponding to the dividing line 14, and the wafer 10 is processed and fed together with the chuck table 42e in the X-axis direction to perform ablation processing along the predetermined dividing line 14 of the wafer 10, thereby forming dividing grooves 120 that break the protective film L' and the wafer 10. After the dividing grooves 120 are formed along the predetermined dividing lines 14, the wafer 10 is indexed and fed in the Y-axis direction by the interval of the dividing lines 14, and an unprocessed dividing line 14 adjacent in the Y-axis direction is positioned directly below the condenser 41a. Then, in the same manner as described above, the focal point of the laser beam LB3 is positioned on the dividing lines 14 of the wafer 10 and irradiated, and the wafer 10 is processed and fed in the X-axis direction to form division grooves 120. Similarly, the wafer 10 is processed and fed in the X-axis direction and Y-axis directions to form division grooves 120 along all of the dividing lines 14 along the X-axis direction. Next, the wafer 10 is rotated 90 degrees to align the unprocessed dividing lines 14 perpendicular to the dividing lines 14 along which division grooves 120 have already been formed in the X-axis direction. Then, in the same manner as described above, the focal point of the laser beam LB3 is positioned corresponding to each of the remaining dividing lines 14 and irradiated, and division grooves 120 are formed along all of the dividing lines 14 formed on the front surface 10a of the wafer 10, as shown in FIG. 10(b). This completes the ablation processing step.

[0055] The processing conditions for the laser processing carried out in the ablation processing step in the third dividing process are set, for example, as follows. Wavelength: 355nm Average power: 3.0W Repetition frequency: 50kHz Processing feed rate: 10 mm / sec

[0056] 10(b), the dividing grooves 120 are used to break the protective film L' and the wafer 10 and divide the wafer 10 into individual device chips 12', so the protective film L' is removed as necessary to expose the front surface 10a of the wafer 10 as shown in FIG. 10(c), making it suitable for picking up the device chips 12'. The protective film L' can be removed by any suitable method, for example, by supplying a solvent that dissolves the protective film L' to the surface, or by attaching an adhesive tape with suitable adhesive strength to the surface on which the protective film L' is formed and then peeling it off.

[0057] Furthermore, a fourth embodiment of the dividing process for dividing the wafer 10 into individual device chips, which is carried out in combination with a wafer processing method including the above-mentioned resin coating process, resin hardening process, and planarization process, will be described with reference to Figures 11 to 13.

[0058] When the fourth dividing process is performed, a groove forming step is performed on the wafer 10 to form grooves along the dividing lines 14 formed on the front surface 10a of the wafer 10 before the resin coating step is performed on the wafer 10. More specifically, the wafer 10 is first transported to a cutting device 60 shown in Fig. 11. The cutting device 60 includes a chuck table (not shown) that holds the wafer 10 by suction, and cutting means 62 that cuts the wafer 10 held by suction on the chuck table. The chuck table is configured to be rotatable, and includes moving means (not shown) that feeds the wafer 10 together with the chuck table for processing in the direction indicated by arrow X in the figure. The cutting means 62 includes a spindle housing 63, a spindle 64 disposed in and held by the spindle housing 63 in the Y-axis direction indicated by the arrow Y in the figure, an annular cutting blade 65 held at the tip of the spindle 64, and a blade cover 66 that covers the cutting blade 65, and also includes a Y-axis moving means (not shown) that indexes and feeds the cutting blade 65 in the Y-axis direction. The spindle 64 is rotationally driven by a spindle motor (not shown).

[0059] To perform the groove forming process of this embodiment, first, the wafer 10 is placed on the chuck table of the cutting device 60 with the front surface 10a facing upward and held by suction. The predetermined division runs 14 of the wafer 10 are aligned in the X-axis direction and aligned with the cutting blade 65. Next, the cutting blade 65, rotated at high speed in the direction indicated by arrow R7, is positioned on the division lines 14 aligned in the X-axis direction and cuts from the front surface 10a to a depth that does not reach the back surface 10b but reaches at least the finished thickness of the device 12. The chuck table is then moved in the X-axis direction to form grooves 130 as shown in FIG. 11(b). Next, the cutting blade 65 of the cutting means 62 is indexed and moved to a division line 14 adjacent in the Y-axis direction to the division line 14 where the groove 130 has been formed but where no groove 130 has been formed. By repeating these steps, grooves 130 are formed along all of the division lines 14 along the X-axis direction. Next, the chuck table is rotated 90 degrees, and the direction perpendicular to the direction in which the grooves 130 were previously formed is aligned with the X-axis direction. The above-mentioned cutting process is then performed on all of the planned dividing lines 14 that have now been aligned with the X-axis direction. As shown in FIG. 11(c), grooves 130 are formed along all of the planned dividing lines 14 formed on the wafer 10, completing the groove forming process.

[0060] After the groove forming step, the following steps are performed: a resin coating step in which liquid resin L is applied to the front surface 10a of the wafer 10 to cover the portions constituting the devices 12; a resin curing step in which the coated liquid resin L is cured; and a planarization step in which the cured resin is planarized. After the planarization step, the wafer 10 with the protective film L' formed thereon is transferred to a grinding apparatus 50 shown in FIG. 12. The grinding apparatus 50 is the same as the grinding apparatus 50 described with reference to FIG. 6, and a detailed description thereof will be omitted. The side of the wafer 10 with the protective film L' formed thereon is placed on the chuck table 51 of the grinding apparatus 50 and held by suction. As shown in FIG. 12, the back surface 10b is ground with a grinding wheel 52d to expose the grooves 130 and finish the wafer 10 to the finished thickness of the devices 12. As a result, the wafer 10 is divided into individual device chips 12' as shown in the upper part of FIG. 13(a), completing the division step.

[0061] As described above, when the wafer 10 is divided into device chips 12′, the shape of the wafer 10 is maintained by the protective film L′, so as shown in the figure, an annular frame F having an opening Fa capable of accommodating the wafer 10 is prepared, and the wafer 10 is inverted so that the protective film L′ side faces upward and the back surface 10b side of the wafer 10 faces downward, and positioned in the center of the opening Fa and held in place by adhesive tape T. Then, as shown in FIG. 13(b), by removing the protective film L′, the front surface 10a side of the wafer 10 divided into individual device chips 12′ is exposed, allowing the chips to be easily picked up. In this way, even when the fourth dividing process is performed, the thickness of the protective film L' is made uniform by combining the above-mentioned resin coating process, resin hardening process, and planarization process, so that even when a dividing process is performed in which the back surface 10b of the wafer 10 is ground with a grinding wheel and the wafer 10 is divided into individual device chips 12', damage to the wafer 10 is prevented. [Explanation of symbols]

[0062] 10: Wafer 10a: surface 10b: Back side 12: Device 12': Device chip 14: Planned division line 16: Bump 18: Unevenness 20: Liquid resin coating device 21: Chuck table 22: Holding surface 23: Support base 24: Rotation axis 25: Liquid resin supply nozzle 25a: Nozzle 26: Ultraviolet irradiation means 30: Cutting equipment 31: Cutting unit 32: Mobile base 32a: Support member 33: Spindle unit 33a: Spindle housing 33b: Rotating spindle 33c: Servo motor 33d: Tool holder 33e: Tool mounting hole 34: Byte 35: Bolt 36: Chuck table mechanism 36a: Chuck table 36b: Cover member 40: Laser processing equipment 41: Laser irradiation means 42: Holding means 42a: X-axis movable plate 42b: Y-axis movable plate 42c: Post 42d: Cover plate 42e: Chuck table 42f: Suction chuck 42g: Guide rail 43: Imaging means 44:Transportation means 45:Frame body 45a: Vertical wall section 45b:Horizontal wall part 50: Grinding equipment 51: Chuck table 52: Grinding means 52a: Rotating spindle 52b: Wheel mount 52c: Grinding wheel 52d: Grinding wheel 60: Cutting equipment 62: Cutting means 63: Spindle housing 64: Spindle 65: Cutting blade 66: Blade cover 100, 110: Modified layer 120: Dividing groove 130: Groove

Claims

1. A method for processing a wafer having a plurality of devices, each having a plurality of protruding electrodes on its surface, formed on the surface of the wafer, the surface being partitioned by planned division lines, comprising: a resin coating step of applying a liquid resin to the surface of the wafer multiple times to cover at least the protruding electrodes and also to cover the portions constituting the device; a resin curing step of curing the coated liquid resin to form a protective film; a planarization step of planarizing the protective film; a modified layer forming step of irradiating the wafer with a laser beam having a wavelength that is transparent to the wafer while holding the protective film, from a focal point positioned inside the wafer from the rear surface corresponding to the intended dividing lines to form a modified layer along the intended dividing lines; a dividing step of grinding the back surface of the wafer with a grinding wheel while holding the protective film to finish the wafer to a predetermined thickness and dividing the wafer into individual device chips at the modified layer; The present invention is configured to include: the thickness of the protective film before the planarization step is performed is ensured to be such that the protruding electrodes are not exposed on the surface even when the protective film is planarized in the planarization step; The wafer processing method includes flattening the protective film in the flattening step so that the protruding electrodes are not exposed on the surface.

2. 2. The wafer processing method according to claim 1, wherein the planarization step comprises holding the back surface of the wafer on a chuck table, exposing the front surface of the wafer, and cutting the resin with cutting means equipped with a cutting tool to planarize the wafer.

Images