METHOD FOR PROCESSING A WAFER

Abstract

Processing method for a wafer (10) having several components (12) formed in respective areas on a front face (10a) of the wafer (10), wherein the areas are delimited by several intersecting provided division lines (14), the method comprising: a plastic application step of coating the front side (10a) of the wafer (10) with a liquid plastic (L) to cover an area of ​​the wafer (10) in which the multiple components (12) are located; a plastic curing step of curing the liquid plastic (L) to a protective layer (L'); and a planarization step of a flat shaping of the protective layer (L'), wherein the planarization step comprises the steps of holding a back side (10b) of the wafer (10) on a clamping table, exposing the front side (10a) of the wafer (10) and cutting the protective layer (L') to form a flat protective layer (L') with a cutting unit (31) using a single-point cutting tool (34).

Description

BACKGROUND OF THE INVENTIONField of the invention

[0001] The present invention relates to a method for processing a wafer having a plurality of components formed in corresponding regions on a front side of the wafer, the regions being delimited by a plurality of intersecting, provided parting lines formed thereon. Description of the related art

[0002] Wafers with multiple components such as integrated circuits (ICs) or large-scale integration (LSI) circuits formed in corresponding regions on a front side of the wafer, the regions being delimited by a plurality of intersecting predetermined dividing lines formed thereon, are divided into individual component chips by a dividing device. The divided component chips are used in electronic devices such as mobile phones and personal computers.

[0003] A technology has been proposed in the art for applying a laser beam, whose wavelength is transmittable through a wafer, to the wafer while positioning the focused spot of the laser beam within the wafer at positions aligned with provided dividing lines on a front surface of the wafer, thereby forming modified layers in the wafer, thereafter grinding a back surface of the wafer to thin the wafer to a desired thickness, and then dividing the wafer into individual device chips at the modified layers along the provided dividing lines (see, for example, JP 2014-78569 A).

[0004] In the prior art, a technology has also been proposed for applying a laser beam whose wavelength can be absorbed by a wafer to the wafer, wherein the focused spot of the laser beam is positioned at predetermined dividing lines on the wafer, thereby forming grooves in the wafer by laser ablation, and then dividing the wafer into individual device chips at the grooves along the predetermined dividing lines (see, for example, JP 2004-188475 A).

[0005] JP 2017-5056 A relates to a wafer processing method in which a plurality of intended dividing lines are formed in a lattice shape on the surface of a wafer, and in which a wafer in which a component is formed in a plurality of regions divided by the plurality of dividing lines is divided into individual components along the intended dividing lines, and in which the individual components are coated with a plastic. PRESENTATION OF THE INVENTION

[0006] Some wafers have components formed thereon that have surface irregularities on their front surfaces, such as protruding electrodes called "bumps." If such a wafer is processed according to the technology disclosed in JP 2014-078569A, the wafer could break due to the bumps.

[0007] It is assumed that the technology disclosed in JP 2004-188475A is applied to a wafer with bumps as described above, and the front side of the wafer is coated with a protective layer of liquid plastic. Since the protective layer has thickness irregularities, when the wafer is processed by laser ablation with a laser beam having a wavelength absorbable by the wafer, while the focused spot of the laser beam is positioned on the front side of the wafer along the designated dividing lines, grooves of different depths can be formed in the wafer along the designated dividing lines. If the wafer is then to be divided into individual component chips along the grooves, the grooves of different depths make it difficult to properly divide the wafer into individual component chips without causing damage to the wafer.

[0008] It is therefore an object of the present invention to provide a method of processing a wafer having protrusions on a front side thereof for dividing the wafer into individual device chips without breaking or damaging the wafer.

[0009] According to one aspect of the present invention, a processing method is provided for a wafer having a plurality of components formed in respective regions on a front side of the wafer, the regions being delimited by a plurality of intersecting predefined dividing lines. The method includes a resin application step of coating the front side of the wafer with a liquid resin to cover a region of the wafer in which the plurality of components are present, a resin curing step of curing the liquid resin into a protective layer, and a planarization step of planarizing the protective layer.

[0010] The planarization step includes the steps of holding a back side of the wafer on a chuck table, exposing the front side of the wafer, and cutting the protective layer to make the protective layer planar with a cutting unit having a single-point cutting tool.

[0011] Preferably, the method further comprises a modified layer forming step of forming modified layers in the wafer along the respective predetermined dividing lines by applying a laser beam having a wavelength transmissible through the wafer to the wafer from the back side of the wafer along the predetermined dividing lines while positioning a focused spot of the laser beam within the wafer; and a dividing step of grinding the back side of the wafer with grindstones to finish the wafer to a predetermined thickness and dividing the wafer into individual device chips along the modified layers.Preferably, the method further comprises a grinding step of grinding a back surface of the wafer with grindstones to finish the wafer to a predetermined thickness, a modified layer forming step of forming modified layers in the wafer along the respective predetermined dividing lines by applying a laser beam having a wavelength transmissible through the wafer to the wafer from the back surface of the wafer along the predetermined dividing lines while positioning a focused spot of the laser beam within the wafer, and a dividing step of dividing the wafer into individual device chips by applying external forces to the wafer.

[0012] Preferably, the method further comprises a laser ablation step of performing laser ablation on the wafer along the intended dividing lines by positioning a focused spot of a laser beam having a wavelength absorbable by the wafer on the front side of the wafer along the intended dividing lines and applying the laser beam to the wafer.

[0013] Preferably, the method further comprises a groove-forming step of forming grooves in the wafer along the respective predetermined dividing lines on the front side of the wafer prior to the plastic deposition step. The plastic deposition step, the plastic curing step, and the planarization step are performed after the groove-forming step. A dividing step of grinding a back side of the wafer with grindstones to finish the wafer to a predetermined thickness and dividing the wafer into individual device chips by exposing the grooves is performed after the planarization step.

[0014] In the wafer processing method according to the present invention, since the protective layer on the front side of the wafer is formed uniformly in thickness, the wafer is prevented from being broken even when a laser beam having a wavelength transmittable through the wafer is applied to the wafer along the predetermined dividing lines to form modified layers in the wafer, then the back side of the wafer is ground with grindstones to finish the wafer to a predetermined thickness, and the dividing step is performed to divide the wafer into individual device chips along the modified layers.Furthermore, even when the laser ablation step is performed to perform laser ablation on the wafer along the designated dividing lines by positioning a focused spot of a laser beam having a wavelength that can be absorbed by the wafer on the front side of the wafer along the designated dividing lines, and then dividing the wafer into individual device chips, grooves formed in the wafer by laser ablation are uniform in depth because the protective layer on the front side of the wafer is uniform in thickness, so that the wafer can be properly divided into individual device chips without being damaged.

[0015] The above and other objects, features and advantages of the present invention, as well as the mode for carrying them into effect, will best become apparent and the invention itself will be best understood by studying the following description and appended claims with reference to the attached drawings which show a preferred embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a perspective view of a wafer as a workpiece and an apparatus for coating the workpiece with a liquid plastic; Fig. 1B is a perspective view illustrating the manner in which a plastic application step is carried out; Fig. 2 is a perspective view illustrating the manner in which a plastic curing step is carried out; Fig. 3 is a perspective view illustrating the manner in which a planarization step is carried out; Fig. 4A is a perspective view of a laser processing apparatus; Fig. 4B is a perspective view illustrating the manner in which a modified layer forming step is carried out; Fig. 4C is a cross-sectional view of a Fig. 4B; Fig. 5A is a perspective view illustrating the manner in which a dividing step of dividing the wafer into individual device chips is performed on modified layers; Fig. 5B is a perspective view illustrating the wafer that has been divided into individual device chips in the dividing step; Fig. 6 is a perspective view illustrating the manner in which a grinding step of grinding a back surface of the wafer with grindstones is carried out; Fig. 7A is a perspective view illustrating the manner in which a modified layer forming step is carried out on the substrate shown in Fig. 6 is carried out on the ground wafer; Fig. Figure 7B is an enlarged fragmentary cross-sectional view of the Fig. 7A; Fig. Figure 8 is a perspective view illustrating the manner in which the wafer having the Fig. 7A, is held by an annular frame; Fig. 9 is a perspective view illustrating the manner in which a dividing step of dividing the wafer into individual device chips is carried out; Fig. 10A is a perspective view illustrating the manner in which an ablation processing step is performed; Fig. 10B is a perspective view illustrating the wafer used in the Fig. 10A shown ablation processing step has been divided into individual device chips; Fig. 10C is a perspective view of the wafer after removal of a protective layer from the Fig. wafer shown in Figure 10B; Fig. 11A is a perspective view illustrating the manner in which a groove forming step is carried out; Fig. 11B is an enlarged fragmentary cross-sectional view of the Fig. 11A; Fig. 11C is a perspective view of the wafer in which grooves have been formed in the groove forming step; Fig. 12 is a perspective view illustrating the manner in which a dividing step of grinding the back surface of the wafer by grindstones is carried out to divide the wafer into individual device chips; Fig. 13A is a perspective view illustrating the manner in which the wafer, which has been divided into individual device chips, is supported by an annular frame; and Fig. 13B is a perspective view illustrating the manner in which a protective layer is removed from the wafer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] A method of processing a wafer as a workpiece according to a preferred embodiment of the present invention will be described in detail below with reference to the drawings.

[0017] Fig. 1A illustrates a wafer 10 to be processed by the wafer processing method according to the present embodiment, as well as a partially illustrated apparatus 20 for coating the wafer 10 with a liquid plastic. The wafer 10 is, for example, a silicon wafer. The wafer 10 has a plurality of components 12 formed in corresponding regions on a front side 10a of the wafer 10, wherein the regions are delimited by a plurality of intersecting, provided dividing lines 14. Each of the components 12 has a plurality of bumps 16 on its front side, as shown on an enlarged scale in an upper inset in Fig. 1A. The bumps 16 are protruding electrodes for electrical connection to external circuits and are formed, for example, from an alloy of lead and tin as main components.

[0018] In the wafer processing method according to the present embodiment, a resin application step is first performed to coat the front surface 10a of the wafer 10 with a liquid resin L, which will be described later, and to cover a region of the wafer 10 where the components 12 are present. Specifically, the wafer 10 is supplied to the apparatus 20 for coating the wafer 10 with the liquid resin L. The apparatus 20 includes at least a chuck table 21 and a support base 23. The chuck table 21 has an upper holding surface 22 made of an air-permeable, porous material. The chuck table 21 is connected to a suction means (not shown) which, when actuated, generates and transmits a negative pressure to the holding surface 22.An electric motor (not shown) is housed on the support base 23, which rotates a rotary shaft 24 about its central axis in order to rotate the clamping table 21 attached to the upper end of the rotary shaft 24.

[0019] The wafer 10 delivered to the apparatus 20 is placed on the chuck table 21 with a front side 10a of the wafer 10 facing upward and a back side 10b facing downward, and then the suction means connected to the chuck table 21 is actuated to hold the wafer 10 on the holding surface 22 under the negative pressure applied to the holding surface 22.

[0020] When the wafer 10 has been held under suction on the chuck table 21, as shown in Fig. 1B, a liquid resin supply nozzle 25 is positioned directly above the center of the wafer 10, and the electric motor housed on the support base 23 is energized to rotate the rotary shaft 24 and the chuck table 21 about their central axis in the direction indicated by an arrow R1. Then, the liquid resin supply nozzle 25 supplies a predetermined amount of liquid resin L from an ejection port 25a to the wafer 10 to coat the front surface 10a of the wafer 10. The liquid resin L is, for example, an epoxy resin curable by exposure to ultraviolet rays. The liquid resin supply nozzle 25 may supply the liquid resin L from the ejection port 25a in a single burst or in multiple consecutive bursts.The amount of liquid plastic L supplied from the discharge opening 25a to the wafer 10 is determined such that the liquid plastic L applied to the front side 10a is sufficient to cover an area of ​​the wafer 10 in which the components 12 are located. The plastic application step is now complete.

[0021] Then, a plastic curing step is carried out to cure the liquid plastic L applied to the wafer 10. To carry out the plastic curing step, the process shown in a left section of Fig. 2 is positioned directly above the wafer 10 held by the device 20. Then, the ultraviolet ray application means 26 applies ultraviolet rays UV to the liquid plastic L that has coated the wafer 10. When exposed to the applied UV radiation, the liquid plastic L is cured, forming a protective layer L' on the front side 10a of the wafer 10, as shown in a right-hand portion of Fig. 2. The plastic curing step is now complete. According to the present embodiment, the liquid plastic L on the front side 10a of the wafer 10 is selected to be a plastic that is curable when exposed to UV rays. However, the liquid plastic L could, for example, be a plastic that is curable over time. If the liquid plastic L is a plastic that is curable over time, the plastic application step is followed by a standby step as the plastic curing step, in which the wafer 10 is left on the chuck table 21 until the liquid plastic L applied to the wafer 10 is cured.

[0022] The protective layer L' is formed with a sufficient thickness to embed the bumps 16 on the components 12. Overall, the protective layer L' containing the bumps 16 tends to have surface irregularities 18. The protective layer L' has thickness irregularities due to surface irregularities on the front side 10a of the wafer 10 and shrinkage induced when the liquid plastic L is cured into the protective layer L'. When a laser beam is applied to the front side 10a of the wafer 10 to form dividing grooves in the wafer 10 along the intended dividing lines 14 by laser ablation, the grooves are likely to have different depths, which tend to cause a processing error.Furthermore, although attempts may be made to hold the protective layer L' in one position and grind the back surface 10b of the wafer 10 to thin the wafer 10, the wafer 10 may be broken or damaged due to the surface irregularities 18. According to the present embodiment, a planarization step is performed to make the protective layer L' flat.

[0023] Fig. Figure 3 shows in perspective a partially shown cutting device 30 suitable for performing the planarization step. As in Fig. 3, the cutting device 30 includes a cutting unit 31 mounted on a device body for vertical movement. The cutting unit 31 includes a movable base 32 that is vertically movable by a cutter feed mechanism (not shown), and a spindle unit 33 mounted on the movable base 32. The spindle unit 33 is supported on the movable base 32 by a support member 32a mounted on a front surface of the movable base 32.

[0024] The spindle unit 33 includes a spindle housing 33a mounted on the support member 32a, a rotatable spindle 33b rotatably mounted in the spindle housing 33a, and a servomotor 33c as a rotary actuator for rotating the rotatable spindle 33b about its vertical center axis. The rotatable spindle 33b has a lower end portion projecting downward beyond a lower end of the spindle housing 33a. A single-point cutting tool attachment 33d, which has the shape of a circular plate, is attached to a lower end of the rotatable spindle 33b.

[0025] The single-point cutting tool attachment 33d has a tool attachment hole 33e defined therein, which extends vertically through the single-point cutting tool attachment 33d in an outer peripheral portion thereof spaced radially outward from the center axis of the rotatable spindle 33b. A single-point cutting tool 34 is inserted into the tool attachment hole 33e and held in position by a fastening bolt 35 that is screwed into an unillustrated internally threaded hole defined laterally in the single-point cutting tool attachment 33d and has a tip end pressed against the single-point cutting tool 34. According to the present embodiment, the single-point cutting tool 34 is formed as a rod-shaped cutting tool made of tool steel such as a cemented carbide alloy. The single-point cutting tool 34 has a cutting edge formed of diamond or the like at its lower distal end.The single-point cutting tool attached to the single-point cutting tool attachment 34 is rotatable in unison with the single-point cutting tool attachment 33d when the rotatable spindle 33b is rotated by the servo motor 33c.

[0026] The cutting device 30 has a clamping table mechanism 36. The clamping table mechanism 36 has a rotatable clamping table 36a in the shape of a circular plate. The clamping table 36a has an upper support surface made of an air-permeable, porous material and is connected to a suction source (not shown). The clamping table mechanism 36 has a moving mechanism (not shown) housed in the device body of the cutting device 30. The moving mechanism moves the clamping table 36a together with a cover member 36b in the direction indicated by an arrow R3. Fig. 3, the chuck table 36a holds the wafer 10 supplied from the device 20 by suction to the holding surface thereof.

[0027] The Fig. The cutting device 30 shown in Figure 3 is constructed substantially as described above. The planarization step performed according to the present embodiment using the cutting device 30 will be described below.

[0028] The wafer 10 is held under suction on the chuck table 36a of the cutting device 30, while the protective layer L' on the front side 10a is facing upward. The servo motor 33c is then energized to rotate the single-point cutting tool attachment 33d about its central axis in the direction indicated by an arrow R2, and the unillustrated cutting mechanism is actuated to lower the single-point cutting tool attachment 33d to a predetermined height, where the cutting edge of the single-point cutting tool 34 attached to the single-point cutting tool attachment 33d can remove the surface irregularities 18 of the protective layer L' on the wafer 10.The unillustrated moving mechanism is actuated to move the chuck table mechanism 36 in the direction indicated by arrow R3, causing the chuck table 36a with the wafer 10 mounted thereon to pass through a region below the single-point dicing tool mount 33d. As the chuck table 36a with the wafer 10 held thereon passes through the processing area, the surface irregularities 18 are removed from the protective layer L' on the wafer 10 by the single-point dicing tool 34, as shown in a lower inset in FIG. Fig. 3. The planarization step is now complete.

[0029] According to the present invention, the planarization step may not necessarily be performed by the cutting device 30 and could be performed, for example, using a polishing device or the like.

[0030] The method for processing a wafer according to the present embodiment, which includes the plastic application step, the plastic curing step, and the planarization step described above, advantageously enables each of the various types of division for dividing the wafer 10 into individual component chips as described below. The first division of the various types of division is described below with reference to the Fig. 4A to 4C, 5A, 5B, 13A and 13B.

[0031] Fig. 4A shows in perspective the wafer 10 with the planar protective layer L' formed according to the above wafer processing method and a laser processing apparatus 40 suitable for performing the first division. As shown in Fig. 4A, the laser processing apparatus 40 includes, on a base table 40a, a laser application unit 41 for applying a laser beam to the wafer 10 as a workpiece, that is, a target to be processed, a holding unit 42 for holding the wafer 10, an image pickup unit 43 for picking up an image of the wafer 10 held by the holding unit 42, a feed mechanism assembly 44 for processing feeding and index feeding the laser application unit 41 and the holding unit 42 relative to each other and for moving the image pickup unit 43 and the holding unit 42 relative to each other, and a frame 45 having a vertical wall 45a erected from the base table 40a behind the feed mechanism assembly 44 and a horizontal wall 45b extending horizontally from an upper end portion of the vertical wall 45a.

[0032] The horizontal wall 45b of the frame 45 houses an unillustrated optical system of the laser deposition unit 41. The laser deposition unit 41 includes a beam condenser 41a disposed on the lower surface of a distal end portion of the horizontal wall 45b. The beam condenser 41a is movable in the Z-axis directions, that is, in vertical directions indicated by an arrow Z. According to the present embodiment, the laser deposition unit 41 is capable of selectively emitting a laser beam having a wavelength transmissible through the wafer 10 and a laser beam having a wavelength absorbable by the wafer 10. The image pickup unit 43 is positioned on the lower surface of the distal end portion of the horizontal wall 45b at a position adjacent to the beam condenser 41a in X-axis directions, that is, horizontal directions indicated by an arrow X.The image pickup unit 43 includes a conventional visible light image pickup unit such as a charge-coupled device (CCD) for picking up images based on a visible light beam, an infrared ray applying means for applying infrared rays to a workpiece, an optical system for picking up infrared rays emitted from the infrared ray applying means, and an image pickup unit such as an infrared CCD for outputting an electrical signal representing the infrared rays picked up by the optical system.

[0033] As in Fig. 4A, the holding unit 42 includes a rectangular X-axis movable plate 42a movably mounted on the base table 40a for movement in the X-axis directions, a rectangular Y-axis movable plate 42b movably mounted on the X-axis movable plate 42a for movement in the Y-axis directions, that is, horizontal directions perpendicular to the X-axis directions, a hollow cylindrical support post 42c fixedly attached to an upper surface of the Y-axis movable plate 42b, and a rectangular cover plate 42d fixedly attached to an upper end of the support post 42c. The cover plate 42d has an elongated hole defined therein for receiving an upwardly extending chuck table 42e. The clamping table 42e is rotatable about its vertical central axis by actuating means (not shown) housed in the support post 42c.The clamping table 42e has a substantially horizontally positioned suction clamping device 42f in the form of a circular plate made of an air-permeable, porous material. The suction clamping device 42f is fluidly connected to the suction means (not shown) via a fluid channel extending through the support post 42c.

[0034] The feed mechanism assembly 44 includes an X-axis feed mechanism 46 and a Y-axis feed mechanism 47. The X-axis feed mechanism 46 converts the rotary motion of an electric motor 46a into linear motion with a ball screw 46b and transmits the linear motion to the X-axis movable platen 42a, thereby performing machining feeding of the X-axis movable platen 42a in one of the X-axis directions or the other along a pair of guide rails 40b arranged on the base table 40a and extending in the X-axis directions.The Y-axis feed mechanism 47 converts a rotary motion of an electric motor 47a into a linear motion with a ball screw 47b and transmits the linear motion to the Y-axis movable plate 42b, thereby indexing the Y-axis movable plate 42b in one of the Y-axis directions or the other along a pair of guide rails 42g arranged on the X-axis movable plate 42a and extending in the Y-axis directions.

[0035] The Fig. The laser processing apparatus 40 shown in Figure 4A is constructed substantially as described above. A formation step for modified first-division layers performed using the laser processing apparatus 40 will be described in detail below.

[0036] First, as in Fig. 4A, the wafer 10 is placed on the suction chuck 42f of the chuck table 42e and held under suction while the protective layer L' formed on the front side 10a is directed downward and the back side 10b is directed upward.

[0037] The feed mechanism assembly 44 is actuated to move the wafer 10 held on the chuck table 42e to a position directly below the image pickup unit 43. When the wafer 10 reaches the position directly below the image pickup unit 43, the image pickup unit 43 captures an image of the wafer 10. Specifically, the image pickup unit 43 is electrically connected to a controller and a display unit, not shown. The image pickup unit 43 applies infrared rays to the back surface 10b of the wafer 10 on the chuck table 42e and captures an image of the wafer 10. The controller then detects, based on the captured image, one of the designated dividing lines 14 to which a laser beam is to be applied on the front surface 10a having the protective layer L' formed thereon.The control unit then stores the X and Y coordinates representing the position information of the intended dividing line 14 and performs alignment processing for rotating the chuck table 42e to align the intended dividing line 14 with the X-axis directions.

[0038] After the alignment processing, the X-axis feed mechanism 46 is actuated to move the chuck table 42e in one of the X-axis directions and position the detected intended dividing line 14 of the wafer 10 directly under the beam condenser 41a of the laser application unit 41, as shown in Fig. 4B. Then, at the same time as the X-axis feed mechanism 46 is actuated to feed the chuck table 42e in the X-axis direction for processing, the beam condenser 41a is moved in one of the Z-axis directions to position a focused spot P1 of a laser beam LB1, whose wavelength is transmittable through the wafer 10, within the wafer 10, and the laser application unit 41 emits and applies the laser beam LB1 to the back surface 10b of the wafer 10, thereby forming a modified layer 100 in the wafer 10 along the detected designated dividing line 14, as shown in Fig. 4C. After the modified layer 100 has been formed in the wafer 10 along the designated dividing line 14, the Y-axis feed mechanism 47 is actuated to index feed the chuck table 42e in one of the Y-axis directions by a distance corresponding to the distance between adjacent designated dividing lines 14 and position a next designated dividing line 14, on which no modified layer 100 has been formed, directly below the beam condenser 41a of the laser deposition unit 41.Then, at the same time that the X-axis feed mechanism 46 is operated to feed the chuck table 42e in one of the X-axis directions for processing, the beam condenser 41a is moved in one of the Z-axis directions, if necessary, to position the focused spot P1 of the laser beam LB1 within the wafer 10, and the laser application unit 41 emits the laser beam LB1 and applies it to the back surface 10b of the wafer 10, thereby forming a modified layer 100 in the wafer 10 along the next designated dividing line 14.

[0039] The above laser processing sequence is repeated to process the wafer 10 in one of the X-axis directions, index the wafer 10 in one of the Y-axis directions, and apply the laser beam LB1 to the wafer 10 while processing the wafer 10 in the X-axis direction, thereby forming modified layers 100 in the wafer 10 along all the designated dividing lines 14 extending in a first direction. Then, the wafer 10 is rotated 90 degrees to align all the designated dividing lines 14 extending in a second direction perpendicular to the first direction and which have not been subjected to processing with the X-axis directions. Thereafter, the above laser processing sequence is repeated to form modified layers 100 in the wafer 10 along all the designated dividing lines 14 extending in the second direction.In this way, the modified layers 100 are formed in the wafer 10 along all the designated dividing lines 14 formed on the front side 10a of the wafer 10. The modified layer formation step is now complete.

[0040] For example, the processing conditions for the modified layer training step are set as follows. Wavelength: 1342 nm Average output power: 1.0 W Repetition frequency: 90 kHz Feed speed: 700 mm / second

[0041] After the formation step for modified layers, the wafer 10 is subjected to a Fig. 5A shown grinding device 50 (partially shown) to perform a dividing step. As shown in Fig. 5A, the grinding device 50 includes a chuck table 51 rotatable about its central axis by unillustrated rotary actuating means, and a grinding unit 52. The grinding unit 52 includes a rotatable spindle 52a rotatable by unillustrated rotary actuating means, a wheel mount 52b attached to a lower end of the rotatable spindle 52a, and a grinding wheel 52c attached to a lower surface of the wheel mount 52b. A plurality of grinding stones 52d are attached in an annular array to a lower surface of the grinding wheel 52c.

[0042] As in Fig. As shown in Fig. 5A, the wafer 10 fed to the grinding device 50 is held on the chuck table 51 under suction with the protective layer L' formed on the front surface 10a facing downward and the back surface 10b facing upward. Then, the rotatable spindle 52a of the grinding unit 52 is rotated about its central axis at a speed of, for example, 6000 rpm in the direction indicated by an arrow R4, and the chuck table 51 is rotated about its central axis at a speed of, for example, 300 rpm in the direction indicated by an arrow R5. Then, an unillustrated grinding feed mechanism coupled to the grinding unit 52 is actuated to lower the grinding unit 52 in the direction indicated by an arrow R6, thereby bringing the grinding stones 52d into grinding contact with the back surface 10b of the wafer 10.After the grinding stones 52d are brought into grinding contact with the back surface 10b of the wafer 10, the grinding feed mechanism feeds, i.e., lowers, the grinding unit 52 at a grinding feed speed of, for example, 1 µm / second. The wafer 10 is ground by the grinding stones 52d while measuring its thickness with a contact thickness gauge (not shown), so that the wafer 10 can be ground to a predetermined final thickness. Then, external forces are applied to the ground wafer 10 to divide the wafer 10 into individual device chips 12' along the modified layers 100 formed in the wafer 10 along the designated dividing lines 14, as shown in FIG. Fig. 5B. At this point, the division step is complete. The first division is now complete.

[0043] After the wafer 10 has been divided into individual component chips 12' in the first division as described above, the wafer 10 is then sent to a pick-up step (not shown) if required. In the pick-up step, as shown in Fig. 13A, an annular frame F having an opening Fa capable of receiving the wafer 10 is prepared, and the wafer 10 is turned over to face the protective layer L' formed on the front side 10a upward and the back side 10b downward, and is positioned centrally in the opening Fa. The wafer 10 is held by the annular frame F by an adhesive tape T applied to both and disposed therebetween. Then, as shown in Fig. 13B, the protective layer L' is removed from the wafer 10, exposing the front side 10a of the wafer 10, which has been divided into the individual component chips 12', so that the individual component chips 12' can be easily picked up.

[0044] Before the first division, the plastic deposition step, the plastic curing step, and the planarization step had already been performed, and the thickness of the protective layer L' had been uniformed. Therefore, even if the back surface 10b of the wafer 10 is ground by the grindstones 52d and the wafer 10 is divided into individual device chips 12' in the division step following the modified layer formation step, the wafer 10 is prevented from breaking.

[0045] The various types of division referred to above include a second division that can be performed in combination with the wafer processing method, which includes the plastic deposition step, the plastic curing step, and the planarization step. The second division will be described below with reference to the Fig. 6 to 9 described.

[0046] Before the second division, the plastic application step, the plastic hardening step, and the planarization step have already been performed. No modified layer formation step has been performed on the wafer 10, and the wafer 10 with the protective layer L' formed on its front side 10a is fed to the grinding device 50 described above with reference to FIG. Fig. 5A and Fig. 5B to perform a grinding step. As described in Fig. 6, the wafer 10 delivered to the grinding apparatus 50 is held on the chuck table 51 under suction with the protective layer L' formed on the front surface 10a facing downward and the back surface 10b facing upward. Then, the rotatable spindle 52a of the grinding unit 52 is rotated about its central axis in the direction indicated by arrow R4 at a speed of, for example, 6000 rpm, and the chuck table 51 is rotated about its central axis in the direction indicated by arrow R5 at a speed of, for example, 300 rpm. Then, the grinding feed mechanism (not shown) coupled to the grinding unit 52 is actuated to lower the grinding unit 52 in the direction indicated by arrow R6, bringing the grinding stones 52d into grinding contact with the back surface 10b of the wafer unit 10.After the grinding stones 52d are brought into grinding contact with the back surface 10b of the wafer 10, the grinding feed mechanism feeds, ie, lowers, the grinding unit 52 at a grinding feed speed of, for example, 1 µm / second. The wafer 10 is ground by the grinding stones 52d while its thickness is measured with a contact thickness gauge (not shown), so that the wafer 10 can be ground to a predetermined final thickness. At this point, the grinding process is terminated.

[0047] After the wafer 10 has been ground to a predetermined final thickness in the grinding step, the wafer 10 is subjected to the process described above with reference to Fig. 4A to 4C to perform the modified layer formation step. The wafer 10 is placed on the suction chuck 42f of the chuck table 42e and held under suction while the protective layer L' formed on the front side 10a is directed downward and the back side 10b is directed upward. The above-described alignment process is performed on the wafer 10, and then the X-axis feed mechanism 46 is actuated to move the chuck table 42e in one of the X-axis directions and position one of the intended dividing lines 14 of the wafer 10 directly under the beam condenser 41a of the laser deposition unit 41, as shown in Fig. 7A. Then, at the same time as the X-axis feed mechanism 46 is actuated to feed the chuck table 42e in the X-axis direction for processing, the beam condenser 41a is moved in one of the Z-axis directions to position a focused spot P2 of a laser beam LB2, whose wavelength is transmissible through the wafer 10, within the wafer 10, and the laser application unit 41 emits and applies the laser beam LB2 to the back surface 10b of the wafer 10, thereby forming a modified layer 110 in the wafer 10 along the designated dividing line 14 extending in a first direction, as shown in Fig. 7B. After the modified layer 110 has been formed in the wafer 10 along the designated dividing line 14, the Y-axis feed mechanism 47 is actuated to index feed the chuck table 42e in one of the Y-axis directions by a distance equal to the distance between adjacent designated dividing lines 14 and position a next designated dividing line 14, on which no modified layer 110 has been formed, directly below the beam condenser 41a of the laser deposition unit 41.Then, at the same time that the X-axis feed mechanism 46 is operated to machine the chuck table 42e in one of the X-axis directions, the beam condenser 41a is moved in one of the Z-axis directions, if necessary, to position the focused spot P2 of the laser beam LB2 within the wafer 10, and the laser application unit 41 emits the laser beam LB2 and applies it to the back surface 10b of the wafer 10, thereby forming a modified layer 110 in the wafer 10 along the next designated dividing line 14.

[0048] The above laser processing sequence is repeated to process the wafer 10 in one of the X-axis directions and index the wafer 10 in one of the Y-axis directions and apply the laser beam LB2 to the wafer 10 while processing the wafer 10 in the X-axis direction, thereby forming modified layers 100 in the wafer 10 along all the designated dividing lines 14 extending in the first direction. Then, the wafer 10 is rotated 90 degrees to align all the designated dividing lines 14 extending in a second direction perpendicular to the first direction and which have not been subjected to processing with the X-axis directions. Thereafter, the above laser processing sequence is repeated to form modified layers 110 in the wafer 10 along all the designated dividing lines 14 extending in the second direction.In this way, the modified layers 100 are formed in the wafer 10 along all the designated dividing lines 14 formed on the front side 10a of the wafer 10. The modified layer formation step is now complete.

[0049] For example, the machining conditions for the modified layer formation step of the second division are set as follows. Wavelength: 1064 nm Average output power: 1.0 W Repetition frequency: 80 kHz Feed speed: 300 mm / second

[0050] After the modified layer formation step, the wafer 10 is removed from the laser processing device 40. Then, as shown in Fig. 8, a ring frame F having an opening Fa capable of accommodating the wafer 10 therein is prepared for performing a dividing step, and the wafer 10 is held by the ring-shaped frame F by an adhesive tape T attached to and interposed between both, while the protective layer L' formed on the front side 10a is directed upward and the back side 10b is directed downward. Then, as shown in Fig. 9, the protective layer L' is removed from the wafer 10. After the protective layer L' has been removed from the wafer 10, external forces G are applied radially outward to the wafer 10 to pull the adhesive tape T in radially outward directions, dividing the wafer 10 into individual device chips 12'. At this point, the dividing step is complete. The second division is now complete.

[0051] The second division offers the same advantages as the first division, since the plastic deposition step, the plastic curing step, and the planarization step have already been performed. Accordingly, the wafer 10 can be easily divided into individual component chips 12' in the second division.

[0052] The various division types mentioned above include a third division for dividing the wafer 10 into individual component chips. The third division can be carried out in combination with the method for processing a wafer, which includes the plastic deposition step, the plastic curing step, and the planarization step. The third division will be described below with reference to Fig. 10A to 10C.

[0053] After the plastic application step, the plastic curing step and the planarization step, in the third division, as in Fig. 10A, an annular frame F having an opening Fa capable of accommodating the wafer 10 is prepared, and the wafer 10 with the protective layer L' formed on its front side 10a is positioned centrally in the opening Fa with the protective layer L' facing upward. The wafer 10 is held by the annular frame F by an adhesive tape T applied to and interposed between both. Since the protective layer L' is formed on the front side 10a of the wafer 10, the wafer 10 is held by the adhesive tape T with the front side 10a facing upward. Fig. 10A is directed upwards.

[0054] The wafer 10 is then fed to the laser processing apparatus 40 described above with reference to Fig. 4A to 4C to perform a laser ablation step. The wafer 10 is placed on the suction chuck 42f of the chuck table 42e and held under suction while the protective layer L' formed on the front surface 10a is facing upward. Then, the above-described alignment processing is performed on the wafer 10 held on the chuck table 42e based on an image of the wafer 10 captured by the image capturing unit 43 of the laser processing apparatus 40. Specifically, the control unit detects one of the intended dividing lines 14 formed on the front surface 10a from the captured image. The unillustrated rotation actuator coupled to the chuck table 42e is operated to rotate the wafer 10 to bring the intended dividing line 14 into alignment with the X-axis directions.The control unit, not shown, stores the position information of the detected intended dividing line 14.

[0055] Then, the beam condenser 41a of the laser application unit 41 is positioned based on the position information of the detected intended dividing line 14 in alignment with the intended dividing line 14 extending in a first direction as shown in Fig. 10A. At the same time that the X-axis feed mechanism 46 is actuated to feed the chuck table 42e for processing in one of the X-axis directions, the beam condenser 41a is moved in one of the Z-axis directions to position a focused spot of a laser beam LB3, whose wavelength can be absorbed by the wafer 10, on the front side 10a along the designated dividing line 14. The laser application unit 41 emits the laser beam LB3 and applies it to the wafer 10, thereby forming a dividing groove 120 in the protective layer L' and the wafer 10 along the designated dividing line 14 extending in the first direction by laser ablation. The protective layer L' and the wafer 10 are refracted along the dividing groove 120.After the dividing groove 120 is formed in the protective layer L' and the wafer 10 along the designated dividing line 14, the Y-axis feed mechanism 47 is operated to index feed the chuck table 42e and thus the wafer 10 in one of the Y-axis directions by a distance corresponding to the interval between adjacent designated dividing lines 14 and to position a next designated dividing line 14 on which no dividing groove 120 extending in the first direction has been formed directly below the beam condenser 41a of the laser deposition unit 41.Then, at the same time that the X-axis feed mechanism 46 is actuated to machine the chuck table 42e in one of the X-axis directions, the beam condenser 41a is moved in one of the Z-axis directions, if necessary, to position the focused spot of the laser beam LB3 on the front surface 10a along the next designated dividing line 14, and the laser application unit 41 emits and applies the laser beam LB3 to the wafer 10, thereby forming a dividing groove 120 in the protective layer L' and the wafer 10 along the next designated dividing line 14. Similarly, dividing grooves 120 are formed in the protective layer L' and the wafer 10 along all the designated dividing lines 14 extending in the first direction.Then, the wafer 10 is rotated 90 degrees to align all the intended dividing lines 14 extending in a second direction perpendicular to the first direction and which have not been subjected to processing with the X-axis directions. Thereafter, the above laser processing sequence is repeated to form dividing grooves 120 in the protective layer L' and the wafer 10 along all the intended dividing lines 14 extending in the second direction. In this way, the dividing grooves 120 are formed in the protective layer L' and the wafer 10 along all the intended dividing lines 14 provided on the front side 10a of the wafer 10, as shown in FIG. Fig. 10B. The laser ablation step is now complete.

[0056] For example, the laser processing conditions in the laser ablation step of the third division are set as follows. Wavelength: 355 nm Average output power: 3.0 W Repetition frequency: 50 kHz Feed rate: 10 mm / second

[0057] As in Fig. 10B, the wafer 10 is divided into individual device chips 12' as the protective layer L' and the wafer 10 are broken along the dividing groove 120. The protective layer L' is removed as needed to expose the front side 10a of the wafer 10, as shown in Fig. 10C, wherein the device chips 12' are provided for inclusion. The protective layer L' could be removed by various processing methods. For example, a solvent for dissolving the protective layer L' could be applied to the surface thereof, or an adhesive tape with a suitable adhesive force could be attached to the surface of the protective layer L' and pulled on it to peel off the protective layer L'.

[0058] The above-mentioned various division types include a fourth division for dividing the wafer 10 into individual component chips. The fourth division can be carried out in combination with the method for processing a wafer, which includes the plastic deposition step, the plastic curing step, and the planarization step. The fourth division will be described below with reference to the Fig. 11A to 13B.

[0059] In the fourth division, a groove forming step is carried out before the plastic application step to form grooves in the wafer 10 along the intended division lines 14 formed on the front side 10a of the wafer 10. Specifically, the wafer 10 is fed to a cutting device 60, which is arranged in Fig. 11A. As shown in Fig. 11A, the cutting device 60 includes a chuck table (not shown) for holding the wafer 10 under suction thereto, and a cutting unit 62 for cutting the wafer 10 held under suction on the chuck table. The chuck table is rotatable about its vertical center axis. The cutting device 60 also includes an X-axis moving means (not shown) for processing the chuck table and thus the wafer 10 held thereon in an X-axis direction indicated by an arrow X. The cutting unit 62 includes a spindle housing 63, a spindle 64 rotatably supported in the spindle housing 63 for rotation about its horizontal central axis extending parallel to a Y-axis direction indicated by an arrow Y, an annular cutting blade 65 held at a distal end of the spindle 64, and a blade cover 66 covering the cutting blade 65.The cutting device 60 further includes Y-axis movement means (not shown) for indexing the cutting blade 65 in the Y-axis direction. The spindle 64 is rotatable by a spindle motor (not shown).

[0060] To perform the groove forming step according to the present embodiment, the wafer 10 is placed on the chuck table of the cutting device 60 with the front side 10a facing upward and held under suction. One of the designated dividing lines 14 of the wafer 10 extending in a first direction is aligned with the X-axis direction and is positioned in alignment with the cutting blade 65. The cutting blade 65, which rotates at a high speed in the direction indicated by an arrow R7, is positioned in alignment with the designated dividing line 14 aligned with the X-axis direction.Then, the cutting blade 65 is forced to cut into the wafer 10 from the front side 10a to a depth that stops short of the back side 10b but reaches at least a final thickness of the components 12, and at the same time, the chuck table is machined in the X-axis direction, whereby a groove 130 is formed in the wafer 10 along the intended dividing line 14, as shown in FIG. Fig. 11B. Thereafter, the cutting blade 65 of the cutting unit 62 is index-fed in the Y-axis direction in alignment with a next intended dividing line 14 in which no groove 130 has been formed, the next intended dividing line 14 extending in the first direction and located adjacent to the intended dividing line 14 in which the groove 130 has just been formed. Then, the cutting blade 65 cuts into the wafer 10, forming a groove 130 in the wafer 10 along the next intended dividing line 14. The above cutting processing is repeated to form grooves 130 in the wafer 10 along all the intended dividing lines 14 extending in the first direction.Then, the chuck table is rotated 90 degrees to align one of the intended dividing lines 14 of the wafer 10, which extend in a second direction perpendicular to the first direction, in the X-axis direction and position the intended dividing line 14 in alignment with the cutting blade 65. The above cutting process is repeated to form grooves 130 in the wafer 10 along all of the intended dividing lines 14 extending in the second direction. As shown in FIG. Fig. As shown in Figure 11C, the grooves 130 are now formed in all the designated parting lines 14 formed on the front side 10a of the wafer 10. The groove formation step is now complete.

[0061] After the groove forming step, the plastic application step, in which the front side 10a of the wafer 10 is coated with the liquid plastic L to cover an area of ​​the wafer 10 in which the components 12 are present, the plastic hardening step of hardening the liquid plastic L in the protective layer L', and the planarization step of forming the protective layer L' into a planar shape are carried out. After the planarization step, the wafer 10 with the evenly formed protective layer L' is formed into a Fig. 12, to perform a dividing step. The grinding device 50 shown in Fig. The grinding device 50 shown in Figure 12 is the same as that described above with reference to Fig. 6 and will not be described in detail below. The protective layer L' of the wafer 10 is placed on the clamping table 51 of the grinding device 50 and held under suction. As shown in Fig. 12, the back side 10b of the wafer 10 is ground with the grinding stones 52d until the grooves 130 are exposed and the wafer 10 is finished to achieve a final thickness of the components 12. As shown in an upper inset in Fig. As shown in Figure 13A, the wafer 10 is divided into individual component chips 12'. The division step is now complete.

[0062] At the time when the wafer 10 is simply divided into the component chips 12', the wafer 10 remains integral and retains its shape due to the protective layer L' attached to the front side 10a. As shown in Fig. As shown in Figure 13A, an annular frame F having an opening Fa capable of accommodating the wafer 10 is prepared, and the wafer 10 is turned over to face the protective layer L' formed on the front side 10a upward and the back side 10b downward, and is positioned centrally in the opening Fa. The wafer 10 is held by the annular frame F by an adhesive tape T applied to both and disposed therebetween. Then, as shown in Fig.13B, the protective layer L' is removed from the wafer 10, exposing the front side 10a of the wafer 10, which has been divided into the individual component chips 12', so that the individual component chips 12' can be easily picked up. When the fourth division is performed, the plastic application step, the plastic curing step, and the planarization step are also performed in combination therewith. Since the protective layer L' has a uniform thickness, when the division step is performed to turn over the back side 10b of the wafer 10 and divide the wafer 10 into individual component chips 12', the wafer 10 is prevented from being broken.

Claims

[1] A processing method for a wafer (10) having a plurality of components (12) formed in respective regions on a front side (10a) of the wafer (10), the regions being delimited by a plurality of intersecting dividing lines (14), the method comprising: a plastic application step of coating the front side (10a) of the wafer (10) with a liquid plastic (L) to cover a region of the wafer (10) in which the plurality of components (12) are present; a plastic curing step of curing the liquid plastic (L) to a protective layer (L'; and a planarization step of planarizing the protective layer (L'), wherein the planarization step comprises the steps of holding a back side (10b) of the wafer (10) on a chuck table, exposing the front side (10a) of the wafer (10), and cutting the protective layer (L') to make the protective layer (L') planar with a cutting unit (31) having a single-point cutting tool (34). [2] A processing method for a wafer (10) according to claim 1, further comprising: a modified layer forming step of forming modified layers (100) in the wafer (10) along the respective provided dividing lines (14) by applying a laser beam having a wavelength transmittable through the wafer (10) to the wafer (10) from a back side (10b) of the wafer (10) along the provided dividing lines (14) while positioning a focused spot of the laser beam within the wafer (10); and a dividing step of grinding the back side (10b) of the wafer (10) with grindstones (52d) to finish the wafer (10) to a predetermined thickness, and dividing the wafer (10) into individual component chips (12') along the modified layers (100). [3] A processing method for a wafer (10) according to claim 1, further comprising: a grinding step of grinding a back surface (10b) of the wafer (10) with grindstones (52d) to finish the wafer (10) to a predetermined thickness; a modified layer forming step of forming modified layers (100) in the wafer (10) along the respective provided dividing lines (14) by applying a laser beam having a wavelength transmittable through the wafer (10) to the wafer (10) from the back side (10b) of the wafer (10) along the provided dividing lines (14) while positioning a focused spot of the laser beam within the wafer (10); and a dividing step of dividing the wafer (10) into individual component chips (12') by exerting external forces on the wafer (10). [4] A processing method for a wafer (10) according to any one of the preceding claims, further comprising: a laser ablation step of performing laser ablation on the wafer (10) along the provided dividing lines (14) by positioning a focused spot of a laser beam having a wavelength that is absorbable by the wafer (10) on the front side (10a) of the wafer (10) along the provided dividing lines (14) and applying the laser beam to the wafer (10). [5] A processing method for a wafer (10) according to claim 1 or 4, when dependent on either of claims 1 or 2, further comprising: a groove forming step of forming grooves in the wafer (10) along the respective provided dividing lines (14) on the front side (10a) of the wafer (10) before the plastic application step, wherein the plastic application step, the plastic curing step and the planarization step are carried out after the groove forming step, and wherein a dividing step of grinding a back surface (10b) of the wafer (10) with grindstones (52d) to finish the wafer (10) to a predetermined thickness and dividing the wafer (10) into individual component chips (12') by exposing the grooves is carried out after the planarization step.

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