WAFER PROCESSING PROCESS

Abstract

Wafer processing method for dividing a wafer (10) with a component area (10c) on its front face (10a), wherein the component area (10c) has several separate regions in which several components (12) are individually formed such that they are separated by several division lines (14), wherein a test element group (16) is formed at each division line (14), wherein the wafer (10) is divided along the division lines (14) to obtain several component chips, each having one of the several components (12), wherein the wafer processing method comprises: a film joining step of placing a thermoplastic polymer film (20) on the front (10a) of the wafer (10), wherein the thermoplastic polymer film (20) has a size capable of covering the device area (10c), and next of performing a thermocompression joining to join the polymer film (20) to the front (10a) of the wafer (10), thereby protecting the front (10a) of the wafer (10) with the polymer film (20); a test element group cutting step of applying a first laser beam through the polymer film (20) onto the wafer (10) along each division line (14) in a state in which a focal point of the first laser beam is arranged at each division line (14), thereby cutting the test element group (16) formed at each division line (14); a formation step of a modified layer by applying a second laser beam to a back side (10b) of the wafer (10) along each division line (14) in a state in which a focal point of the second laser beam is arranged within the wafer (10) in a region corresponding to each division line (14), wherein the second laser beam has a transmission wavelength for the wafer (10), thereby forming a modified layer (110) within the wafer (10) along each division line (14); and a wafer splitting step of applying an external force to the wafer (10) after performing the test element group cutting step and the modified layer formation step, thereby splitting the wafer (10) along the splitting lines (14) to obtain the device chips.

Description

TECHNICAL BACKGROUNDTechnical field

[0001] The present invention relates to a wafer processing method for processing a wafer in which a test element group (TEG) is formed on each dividing line. Description of related technology

[0002] A plurality of devices, such as integrated circuits (ICs) and large-scale integrated circuits (LSIs), are individually formed on a front surface of a wafer in a plurality of separate regions defined by a plurality of dividing lines. The wafer thus having the plurality of devices is divided along the dividing lines using, for example, a laser processing device. That is, a laser beam is applied to the wafer such that it is focused within the wafer in a region corresponding to each dividing line, thereby forming a modified layer within the wafer along each dividing line. Thereafter, an external force is applied to the wafer to thereby divide the wafer along the dividing lines, thus obtaining a plurality of individual device chips individually having the plurality of devices.The component chips are used in various electrical devices such as mobile phones and computers (see, for example, Japanese patent JP 3 408 805 B2).

[0003] Furthermore, there is a case where a TEG for use in evaluation and analysis of each component is formed in advance along each dividing line, the TEG being a group of metal-containing elements. When dividing a wafer with such a TEG formed along each dividing line, it is necessary to apply a laser beam to the wafer in a state where a focal point of the laser beam is located on an upper surface of each dividing line, thereby cutting the TEG along each dividing line.

[0004] Further prior art helpful for understanding the present invention can be found in the following documents: WO 2014 / 157 471 A1 relates to the use of an adhesive tape characterized in that an adhesive layer is laminated to a surface of a base layer.

[0005] US 2017 / 0 162 521 A1 relates to an image processing method comprising a stacked element removal step in which a laser beam having an absorption wavelength for a stacked element is formed through a protective layer along each division line formed on the front side of a wafer, thereby performing ablation to remove the stacked element present at each division line, a division step of applying an external force to the wafer to divide the wafer into individual device chips along each line on which a modified layer is formed in advance, and a plasma etching step of supplying an etching gas in a plasma state to the wafer from the front side thereof after performing the stacked element removal step or after performing the division step.thereby avoiding damage due to ablation in the stacked element removal step.

[0006] US 2014 / 0 295 646 A1 relates to a partition film with a protective layer forming layer, which has a substrate layer, an adhesive layer and a protective layer forming layer, and wherein the protective layer is formed in a region surrounding the protective layer forming layer in a plan view. PRESENTATION OF THE INVENTION

[0007] When cutting the TEG along each dividing line by applying a laser beam to the front side of the wafer in the state where the focal point of the laser beam is located at the TEG, thereby performing ablation, there occurs such a problem that dirt particles disperse from the position where the laser beam is applied, causing contamination of a focusing lens.

[0008] To address this problem, a protective tape is applied to the front surface of the wafer to suppress the dispersion of contaminants, and a laser beam is applied to the front surface of the wafer via the protective tape. However, when the protective tape is peeled off from the front surface of the wafer, a problem arises in that an adhesive contained in the protective tape may remain on the front surface of the wafer, causing a reduction in the quality of each component. In particular, in the case where a laser beam having a transmission wavelength for the wafer (as used in forming a modified layer within the wafer) is used to perform ablation and thereby cut the TEG, the above contamination problem is likely to occur.

[0009] It is therefore an object of the present invention to provide a wafer processing method that can prevent contamination of a focusing lens with the dirt particles when applying a laser beam to a wafer on which a TEG is formed at each dividing line, thereby cutting the TEG, and also prevent a reduction in the quality of each device.

[0010] According to one aspect of the present invention, a wafer processing method is provided for dividing a wafer having a device region on its front side, the device region having a plurality of separate regions in which a plurality of devices are individually formed such that they are separated by a plurality of dividing lines, with a TEG formed on each dividing line, the wafer being divided along the dividing lines to obtain a plurality of device chips individually comprising the plurality of devices. The wafer processing method comprises: a film bonding step of placing a thermoplastic polymer film on the front side of the wafer, the thermoplastic polymer film having a size capable of covering the device region, and then performing thermocompression bonding to bond the polymer film to the front side of the wafer.whereby the front side of the wafer is protected with the polymer film; a TEG cutting step of applying a first laser beam through the polymer film to the wafer along each dividing line in a state where a focal point of the first laser beam is located at each dividing line, thereby cutting the TEG formed at each dividing line; a modified layer forming step of applying a second laser beam to a back side of the wafer along each dividing line in a state where a focal point of the second laser beam is located within the wafer in a region corresponding to each dividing line, the second laser beam having a transmission wavelength for the wafer,whereby a modified layer is formed within the wafer along each division line; and a wafer dividing step of applying an external force to the wafer after performing the TEG cutting step and the modified layer forming step, thereby dividing the wafer along the division lines to obtain the device chips.

[0011] Preferably, the wafer processing method further comprises, before or after performing the TEG cutting step, a wafer carrying step of carrying the wafer via a dividing band on an annular frame having an inner opening capable of accommodating the wafer, the dividing band being attached to the back side of the wafer and to the annular frame in a state where the wafer is arranged in the inner opening of the annular frame, and the second laser beam being applied to the back side of the wafer via the dividing band in the modified layer forming step. Preferably, the wafer processing method further comprises a film peeling step of peeling the polymer film from the front side of the wafer before performing the wafer dividing step.Preferably, the first laser beam to be used in the TEG cutting step is the same as the second laser beam to be used in the modified layer forming step.

[0012] Preferably, the thermoplastic polymer film is a polyolefin film or a polyester film.

[0013] The polyolefin film is preferably made of polyethylene, polypropylene, or polystyrene. If the polyolefin film is made of polyethylene, the polyolefin film is preferably heated to a temperature in the range of 120°C to 140°C in the film-bonding step. If the polyolefin film is made of polypropylene, the polyolefin film is preferably heated to a temperature in the range of 160°C to 180°C in the film-bonding step. If the polyolefin film is made of polystyrene, the polyolefin film is preferably heated to a temperature in the range of 220°C to 240°C in the film-bonding step.

[0014] The polyester film is preferably made of polyethylene terephthalate or polyethylene naphthalate. If the polyester film is made of polyethylene terephthalate, the polyester film is preferably heated to a temperature in the range of 250°C to 270°C in the film-bonding step. If the polyester film is made of polyethylene naphthalate, the polyester film is preferably heated to a temperature in the range of 160°C to 180°C in the film-bonding step.

[0015] The wafer processing method of the present invention is a method for dividing a wafer having a device region on its front side. The device region includes a plurality of separated regions in which a plurality of devices are individually formed so as to be separated by a plurality of dividing lines. Further, a TEG is formed in advance on each dividing line. The wafer is divided along the dividing lines by this method, thereby obtaining a plurality of device chips each having a plurality of the plurality of devices. The wafer processing method includes a film bonding step, a TEG dicing step, a modified layer forming step, and a wafer dividing step.In the film bonding step, a thermoplastic polymer film sized to cover the device area of ​​the wafer is placed on the front side of the wafer. Next, thermocompression bonding is performed to bond the polymer film to the front side of the wafer, thereby protecting the front side of the wafer with the polymer film. In the TEG cutting step, a first laser beam is applied to the wafer via the polymer film along each dividing line in the state where the focal point of the first laser beam is positioned at each dividing line, thereby cutting the TEG formed at each dividing line.In the modified layer forming step, a second laser beam having a transmission wavelength suitable for the wafer is applied to the back surface of the wafer along each dividing line in the state where the focal point of the second laser beam is located within the wafer in a region corresponding to each dividing line, thereby forming a modified layer within the wafer along each dividing line. In the wafer dividing step, after performing the TEG cutting step and the modified layer forming step, an external force is applied to the wafer, thereby dividing the wafer along the dividing lines to obtain device chips.With this configuration, when the first laser beam is applied to the TEG to cut the TEG in the TEG cutting step, the polymer film attached to the front side of the wafer in the film bonding step suppresses the dispersion of dirt particles generated from the wafer, thus preventing contamination of a focusing lens with the dirt particles. Furthermore, the polymer film is bonded to the wafer in the film bonding step by thermocompression bonding. Accordingly, there is no possibility that, for example, an adhesive, wax, liquid plastic, or the like remains on each component when the polymer film is peeled off from the front side of the wafer, thus preventing deterioration in the quality of each component.

[0016] The above and other objects, features and advantages of the present invention and the mode for carrying them out will become more apparent and the invention itself will be best understood by studying the following description and the appended claims with reference to the attached drawings which show a preferred embodiment of the invention. SHORT DESCRIPTION OF THE FIGURES Fig. 1A is a perspective view illustrating a manner of placing a film on the front side of a wafer in a film attaching step according to a preferred embodiment of the present invention; Fig. 1B is a perspective view illustrating a state in which the film is arranged on the front side of the wafer; Fig. 2A, Fig. 2B and Fig. 2C are partially sectional side views for illustrating a manner of bonding the film to the front side of the wafer by thermocompression bonding in the film bonding step; Fig. 3 is a side view of a wafer unit obtained by the foil bonding step; Fig. 4 is a perspective view illustrating a wafer carrying step according to this preferred embodiment; Fig. 5A is a perspective view illustrating a TEG cutting step according to this preferred embodiment; Fig. 5B is a perspective view illustrating a state obtained by the TEG cutting step; Fig. 6 is a perspective view illustrating a forming step of a modified layer according to this preferred embodiment; Fig. 7 is a perspective view illustrating a film peeling step according to this preferred embodiment; Fig. 8 is a partially sectional side view illustrating a wafer dividing step according to this preferred embodiment; Fig. 9A is a perspective view illustrating a modification of the film bonding step; and Fig. 9B is an enlarged sectional view of an essential part of the Fig. 9A shown configuration. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0017] A preferred embodiment of the wafer processing method according to the present invention will now be described in detail with reference to the accompanying drawings.

[0018] Before performing the wafer processing method according to this preferred embodiment, a circular wafer 10 and a circular foil 20 are prepared as shown in Fig. 1A. The wafer 10 is formed of silicon carbide (SiC). The wafer 10 has a front side 10a and a back side 10b. A plurality of intersecting dividing lines 14 are formed on the front side 10a of the wafer 10 to thereby define a plurality of separate regions in which a plurality of devices 12 are individually formed. The plurality of dividing lines 14 consist of a plurality of parallel dividing lines extending in a first direction and a plurality of parallel dividing lines extending in a second direction perpendicular to the first direction. The plurality of devices 12 and the plurality of dividing lines 14 are formed in a central device region 10c on the front side 10a of the wafer 10. The device region 10c is surrounded by an outer peripheral region 10d in which no devices are formed. Furthermore, as shown in a circled region P in Fig. 1A, where this region P is an enlarged perspective view of a portion of the device region 10c of the wafer 10, a TEG 16 as a group of elements for use in evaluating and analyzing each device 12 is formed at a portion of each dividing line 14. The TEG 16 comprises a metal. The film 20 has a front surface 20a and a back surface 20b. The film 20 has substantially the same size (diameter) as that of the wafer 10. The film 20 is a thermoplastic polymer film such as a polyolefin film or a polyester film. In this preferred embodiment, a polyethylene (PE) film is selected as an example of the polyolefin film for the film 20.In the present invention, it is not always necessary to make the size of the film 20 the same as the size of the wafer 10, but it is sufficient if the film 20 has a size capable of covering at least the device region 10c. (Foil connection step)

[0019] After preparing the wafer 10 and the film 20, a circular support table 40 having a front side 40a is provided on the upper surface of a rectangular base 50 at a central portion thereof in the state that the front side 40a of the support table 40 is as shown in Fig. 1A. The film 20 is placed on the front side 40a of the support table 40 at a central portion thereof in the state in which the front side 20a of the film 20 is directed upward. The diameter of the support table 40 is larger than the diameter of the film 20 (see Fig. 1B). Further, the wafer 10 is placed on the front side 20a of the film 20 in the state in which the back side 10b of the wafer 10 is directed upwards, that is, the front side 10a of the wafer 10 is as shown in Fig. 1A is directed downward. At this time, the wafer 10 is aligned with the film 20 arranged on the support table 40. The front side (upper surface) 40a of the support table 40 is flat and is coated with a fluoroplastic. As shown in Fig. As shown in Figure 2, the support table 40 includes an electric heater 42 as a heating means and also includes a temperature sensor (not shown). The electric heater 42 and the temperature sensor are connected to a control unit and a power source (both not shown), allowing the temperature of the support table 40 to be adjusted to a desired temperature.

[0020] After arranging the film 20 on the support table 40 and arranging the wafer 10 on the film 20 in the state in which the back side 10b of the wafer 10 is as shown in Fig. 1B is directed upwards, a thermocompression bonding is carried out to bond the film 20 as shown in Fig. 2A, Fig. 2B and Fig. 2C to the wafer 10. This thermocompression bonding will now be described in more detail.

[0021] As in Fig. 2A, the thermocompression bonding is performed using a thermocompression bonding device 60. The thermocompression bonding device 60 includes an enclosing cover member 62 for forming an enclosed environment together with the base 50 in the state in which the support table 40 is arranged in the enclosed environment. Fig. 2A to 2C, only the enclosing cover member 62 is shown in a vertical section to simplify the illustration of the internal configuration. The enclosing cover member 62 is a box-shaped member configured to cover the entire upper surface of the base 50 in such a manner that the wafer 10 and the film 20 placed on the support table 40 provided on the base 50 can be enclosed by the enclosing cover member 62. The enclosing cover member 62 has a rectangular upper wall 62a and a rectangular cylindrical side wall 62b extending downward from the outer periphery of the rectangular upper wall 62. The enclosing cover member 62 is open at its lower end opposite the upper wall 62a. The upper wall 62a has a central opening 62c for inserting a support shaft 64a of a pressing member 64.The support shaft 64a of the pressing member 64 is inserted vertically movably through the central opening 62c of the upper wall 62a. Furthermore, a sealing structure 62d is disposed between the support shaft 64a and the upper wall 62a to seal the gap therebetween in the central opening 62c. The sealing structure 62d allows the vertical movement of the support shaft 64a and the hermetic sealing of an interior space S of the enclosing cover member 62 to form the enclosed environment. A pressure application plate 64b is connected to the lower end of the support shaft 64a. Thus, the pressing member 64 consists of the support shaft 64a and the pressure application plate 64b. The pressure application plate 64b is a circular member having a diameter substantially larger than that of the wafer 10. Preferably, the diameter of the pressure application plate 64b is set slightly larger than that of the support table 40.Further, an elastic sealing member 62e is provided on the lower end surface of the side wall 62b of the enclosing cover member 62 so as to extend over the periphery of the side wall 62b. The elastic sealing member 62e functions to seal the interior space S of the enclosing cover member 62 together with the base 50. Although not shown, a drive means for vertically moving the pressing member 64 is provided above the pressing member 64.

[0022] After the wafer 10 has been placed over the film 20 on the support table 40 arranged on the base 50 in the state in which the back side 10b of the wafer 10 is directed upward, the enclosing cover member 62 is positioned above the base 50 so as to cover the support table 40 as shown in Fig. 2A. Thereafter, the enclosing cover member 62 is lowered until the lower end surface of the side wall 62b abuts the upper surface of the base 50, as shown in Fig. 2B. Thus, the enclosing cover member 62 is placed on the upper surface of the base 50 so as to enclose the inner space S in which the wafer 10 and the film 20 are arranged on the support table 40. At this time, the pressure application plate 64b is positioned as shown in Fig. 2B, positioned above the upper surface of the wafer 10. When the enclosing cover member 62 is placed on the base 50, the elastic sealing member 62e provided on the lower end surface of the side wall 62b comes into close contact with the upper surface of the base 50, thereby forming a hermetic seal. The base 50 has a suction hole 52 near the support table 40. The suction hole 52 is connected to a suction means (not shown) for creating a vacuum. Accordingly, the internal space S defined by the enclosing cover member 62 together with the base 50 is connected to the suction means via the suction hole 52.

[0023] In this way, the enclosing cover element 62 is placed on the base 50 to thereby define the interior space S of the enclosing cover element 62 as shown in Fig. 2B into an enclosed environment. Thereafter, the suction means is actuated to suck the air in the internal space S through the suction hole 52, thereby evacuating the internal space S in which the wafer 10 is present to obtain a near-vacuum state. Simultaneously, the electric heater 42 included in the support table 40 is actuated to heat the film arranged on the support table 40 so as to be sandwiched between the wafer 10 and the support table 40. At this time, the temperature of the support table 40 is controlled by the temperature sensor and the control unit (both not shown) to heat the film to a temperature (120°C to 140°C) near the melting point of polyethylene constituting the film 20 in this preferred embodiment.When heating the film 20 as mentioned above, the pressure application plate 64b is lowered to apply uniform pressure to the entire upper surface (back side 10b) of the wafer 10 as shown in FIG. Fig. 2C. Since the internal space S in which the wafer 10 is present has been evacuated to a near vacuum state, the air remaining between the wafer 10 and the film 20 is sucked out. Further, the film 20 is heated to the above temperature so that it becomes soft, thereby increasing adhesion, so that the wafer 10 is bonded to the film 20 by thermocompression bonding, thereby forming a wafer unit W. That is, the wafer unit W consists of the wafer 10 and the film 20 bonded to each other. In this way, the film bonding step is completed. By performing the film bonding step, at least the device region 10c formed on the front side 10a of the wafer 10 is covered with the film 20. That is, the device region 10c is protected by the film 20.

[0024] After completing the film bonding step, the operation of the suction means is stopped, and the operation of the electric heater 42 is also stopped. Thereafter, the pressure application plate 64b is raised, and the enclosing cover member 62 is also raised. When the temperature of the film 20 is lowered to a temperature close to room temperature, the wafer unit W can be removed from the support table 40. In this preferred embodiment, the upper surface 40a of the support table 40 is coated with a fluoroplastic. Accordingly, even if the film 20 is heated to increase its adhesion, the film 20 can be easily peeled off from the support table 40 after performing the film bonding step.

[0025] The wafer unit W formed by performing the foil bonding step will now be described in more detail with reference to Fig. 3. As described above, the film 20 is heated in a sealed environment under vacuum and thereby softened in the film bonding step. Further, pressure is applied to the wafer 10 in the state in which the film 20 has been softened in the film bonding step, so that the wafer 10 is supported on the film 20 with sufficient supporting force without using, for example, an adhesive or wax. Furthermore, the air remaining near the TEG 16, while the TEG is formed at each parting line 14 formed on the front side 10a of the wafer 10 in this preferred embodiment, can also be completely exhausted in the film bonding step. Accordingly, each component 12 and each TEG 16, as shown in Fig. 3 is shown in the circled area Q, where the circled area Q is an enlarged sectional view of a part of the wafer unit W into which film 20 softened by heating is inserted so that the film 20 can be tightly bonded to the wafer 10. That is, the wafer 10 and the film 20 can be firmly bonded to each other to obtain the wafer unit W. (TEG cutting step)

[0026] After performing the foil bonding step, a TEG cutting step is performed to cut the TEG 16 formed at each parting line 14. The TEG cutting step will now be described in more detail.

[0027] Before performing the TEG cutting step, the wafer unit W peeled off from the support table 40 of the thermocompression bonding device 60 is attached to a dividing belt T in the state in which the back side 10b of the wafer 10 is as shown in Fig. 4. The dividing tape T is a circular adhesive tape, and the unit wafer W is attached to a central portion of the dividing tape T. Further, an outer portion of the dividing tape T is attached to an annular frame F having an inner opening Fa for receiving the unit wafer W. Thus, the unit wafer W is carried on the annular frame F via the dividing tape T in the state where the unit wafer W is arranged in the inner opening Fa of the annular frame F (wafer carrying step). That is, the unit wafer W is attached to the dividing tape T in the state where the film 20 bonded to the front surface 10a of the wafer W is directed upward or exposed upward.

[0028] After performing the wafer carrying step, the wafer unit W carried on the annular frame F via the dividing belt T is formed into a Fig. 5A shown known laser processing device 70. In Fig. 5A shows a part of the laser processing apparatus 70. The laser processing apparatus 70 includes a holding means (not shown) for holding the wafer unit W supported on the annular frame F via the dividing band T in the state where the dividing band T is directed downward, that is, the film 20 is directed upward. The laser processing apparatus 70 further includes an alignment means (not shown) including an imaging camera for imaging the wafer 10, and a laser beam application means 72 for applying a laser beam LB to the wafer 10. In the state where the wafer unit W supported on the annular frame F via the dividing band T is held by the holding means, alignment is performed by the alignment means.That is, the focus position of the laser beam LB to be applied by the laser beam application means 72 is aligned with a predetermined one of the dividing lines 14 extending in the first direction of the wafer.

[0029] After performing the above alignment, the focal point of the laser beam LB to be focused by a focusing lens 72a provided in the laser beam application means 72 is arranged at a predetermined starting position on the predetermined dividing line 14 (e.g., at one end of the predetermined dividing line 14) on the wafer 10. By performing the alignment, the dividing lines 14 extending in the first direction are parallel to the Fig. 5A by an arrow X. Thereafter, the laser beam LB is applied to the wafer 10 by the laser beam application means 72, and at the same time, the holding means holding the wafer unit W is moved in the X direction by a moving means (not shown). Accordingly, the laser beam LB is applied to the wafer 10 via the film 20 along the predetermined dividing line 14. That is, ablation is performed along the predetermined dividing lines 14 to form a laser-machined groove 100 as shown in Fig. 5A. At the same time, the TEG 16 formed on the predetermined parting line 14 is cut by the laser-machined groove 100. Thereafter, the holding means is moved in the Y direction by the moving means, and the laser beam LB is similarly applied along all other parting lines 14 extending in the first direction. Thereafter, the holding means is rotated by 90 degrees to similarly apply the laser beam LB along all other parting lines 14 extending in the second direction perpendicular to the first direction. Consequently, a plurality of laser-machined grooves 100 are formed as shown in Fig. 5B, the laser beam LB is similarly formed along all the intersecting dividing lines 14 formed on the front surface 10a of the wafer 10, thereby cutting all the TEGs 16 formed along all the intersecting dividing lines 14. In this way, in the TEG cutting step, the laser beam LB is applied to the front surface 10a of the wafer 10 via the film 20 along each dividing line 14, which film 20 has been bonded to the wafer 10 by thermocompression bonding. Accordingly, the film 20 can prevent the scattering of dirt particles generated from the wafer 10 during ablation, thereby suppressing contamination of the focusing lens 72a. Thus, the TEG cutting step is completed.

[0030] For example, laser processing in the TEG cutting step is carried out under the following conditions. Wavelength: 1064 nm Repetition frequency: 60 kHz Average power: 1 W Feed speed: 600 mm / s

[0031] After performing the TEG cutting step, a modified layer formation step is performed to form a modified layer within the wafer 10. The modified layer formation step will now be described in more detail. (Formation step of the modified layer)

[0032] The formation of the modified layer in this preferred embodiment can be carried out using the above-mentioned laser processing apparatus 70. After performing the TEG cutting step, the wafer unit W supported on the annular frame F via the dividing band T is first removed from the holding means. Then, as shown in Fig. 6, the wafer unit W supported on the annular frame F via the dividing band T is turned over so that the wafer unit W is directed downwards and the dividing band T is directed upwards. Thereafter, the thus turned wafer unit W is again held by the holding means. After holding the wafer unit W on the holding means, the alignment means is actuated to bring about the alignment between the laser application position of the laser beam LB and a predetermined one of the dividing lines 14 extending in the first direction on the wafer 10. As shown in Fig. As shown in Fig. 6, in the modified layer forming step, the laser beam LB is applied to the back surface 10b of the wafer 10 via the dividing band T in the state where the front surface 10a of the wafer 10 is facing upward. Accordingly, the alignment means includes an infrared light application means and an infrared imaging means for imaging the dividing lines 14 from the back surface 10b of the wafer 10 using infrared light.

[0033] After performing the alignment, the laser beam application means 72 is actuated to position the focal point of the laser beam LB within the wafer 10 in a region corresponding to the predetermined dividing line 14. Thereafter, the laser beam LB is applied to the back side 10b of the wafer 10 via the dividing band T. At the same time, the holding means holding the wafer unit W is rotated in the direction shown in Fig. 6 is moved in the X direction indicated by an arrow X. By performing the alignment, the predetermined dividing line 14 extending in the first direction is aligned parallel to the X direction. As shown in the laser processing conditions described above, the laser beam LB to be applied by the laser beam application means 72 has a transmission wavelength (= 1064 nm) for SiC forming the wafer 10, so that a modified layer 110 as a division starting point within the wafer 10 along the predetermined dividing line 14 is formed by applying the laser beam LB to the wafer 10. Thereafter, the holding means is in the Fig. 6, the holding means is moved in the Y direction indicated by an arrow Y to similarly form a plurality of modified layers 110 within the wafer 10 along all other dividing lines 14 extending in the first direction. Thereafter, the holding means is rotated 90 degrees to similarly form a plurality of modified layers 110 within the wafer 10 along all other dividing lines 14 extending in the second direction perpendicular to the first direction. As a result, the plurality of modified layers 110 are formed within the wafer 10 along all intersecting dividing lines 14 formed on the front side 10a of the wafer 10. Thus, the modified layer forming step is completed. (Wafer dividing step)

[0034] After performing the modified layer formation step, a wafer dividing step is performed to divide the wafer 10 into individual device chips (the devices 12) by applying an external force to the wafer 10. The wafer dividing step will now be described in more detail.

[0035] Before performing the wafer dividing step, a foil peeling step is performed to, as in Fig. 7, peeling the film 20 from the wafer 10 supported on the annular frame F via the dividing band T. When peeling the film 20, it is preferable to heat the film 20 to soften it so that the film 20 can be peeled off more easily. Furthermore, there is a case where, according to the material of the film 20, the adhesion of the film 20 is reduced by cooling the film 20. In this case, the film 20 may be cooled to reduce its adhesion in the film peeling step. Accordingly, whether to heat or cool the film 20 can be selected according to the properties of the material of the film 20. In this preferred embodiment, the wafer 10 is supported on the film 20 by thermocompression bonding. That is, for example, no liquid plastic, adhesive, or wax is present between the film 20 and the wafer 10.Accordingly, when peeling off the film 20 from the front surface 10a of the wafer 10, there is no possibility of such liquid plastic, adhesive, or wax remaining on each component 12, thereby preventing deterioration of the quality of each component 12.

[0036] After peeling off the film 20 from the wafer 10, the wafer carried on the annular frame F via the dividing belt T is transferred to a dividing device 80 for performing the wafer dividing step as shown in Fig. 8 shown.

[0037] The wafer dividing step using the dividing device 80 will now be described in more detail.

[0038] The wafer dividing step is carried out by the dividing device 80, a part of which is shown in a vertical section in Fig. 8. The dividing device 80 includes a frame holding member 81 having an annular shape, a plurality of clamps 82 provided on the outer periphery of the frame holding member 81 for clamping the annular frame F placed on the upper surface of the frame holding member 81, and a cylindrical expanding drum 83 surrounded by the frame holding member 81 for expanding the dividing band T attached to the annular frame F held by the clamps 82. The expanding drum 83 is open at its upper end. The frame holding member 81 is vertically movably supported by a plurality of support members 84 arranged around the expanding drum 83. Each support member 84 consists of an air cylinder 84a and a piston rod 84b extending upward from the air cylinder 84a. The upper end of each piston rod 84b is fixed to the lower surface of the frame holding member 81.Accordingly, when each air cylinder 84a is operated to move each piston rod 84b vertically, the frame holding member 81 is moved vertically by each piston rod 84b.

[0039] The expansion drum 83 has an outer diameter that is smaller than the inner diameter of the annular frame F and has an inner diameter that is larger than the diameter of the wafer 10 supported on the annular frame F via the dividing band T. Accordingly, the upper end of the expansion drum 83 is positioned below an annular exposed portion of the dividing band T defined between the wafer 10 and the annular frame F. The frame holding member 81 is arranged to be vertically moved by the supporting means 84 so as to have an initial position at which the upper surface of the frame holding member 81 is substantially at the same level as that of the upper end of the expansion drum 83, as shown in Fig. 8 by a dashed line, and assumes an operating position in which the frame holding member 81 is lowered from the initial position so as to thereby reach a state in which the upper end of the expanding drum 83 has a relatively higher level than the upper surface of the frame holding member 81, as shown by a solid line in Fig. 8 shown.

[0040] When the frame holding member 81 is lowered from the initial position to thereby relatively change the position of the upper end of the expanding drum 83 from the position shown by the dashed line to the position shown by the solid line, the dividing band T supported on the annular frame F is expanded by the upper end of the expanding drum 83. That is, the dividing band T is an expandable band configured to be expanded by applying a tensile force thereto. As a result, an external force (tensile force) is applied to the wafer 10 mounted on the dividing band T in its radially outward direction.Accordingly, the wafer 10 is divided along each division line 14 where the laser-machined groove 100 has been formed in the TEG dicing step and the modified layer 110 has been formed in the modified layer forming step, thereby obtaining a plurality of device chips including each of the plurality of devices 12. Thus, the wafer dividing step is completed.

[0041] By performing the wafer dividing step, the wafer 10 is divided into the plurality of component chips having each of the plurality of components in the state where all adjacent component chips are spaced apart from each other on the dividing tape T. In this state, a picker 85 is actuated to hold each component chip under suction and then separate each component chip from the dividing tape T. Thereafter, each component chip is transferred to an apparatus for performing the next step or stored in a storage case. Thus, the wafer processing method in this preferred embodiment is completed.

[0042] While in the above preferred embodiment, the dividing device 80 is used to apply an external force to the wafer 10 in its radially outward direction and thereby divide the wafer 10 into the individual component chips, a means for applying an external force to the wafer 10 to divide the wafer 10 into the individual component chips is not limited to the above. For example, a wedge-shaped member may be used to press the wafer 10 along each dividing line 14, thereby applying an external force to the wafer 10 to divide the wafer 10 along each dividing line 14. As another example, a roller-shaped pressure applying means may be used to press the wafer 10 from above, thereby applying an external force to the wafer 10 to divide the wafer 10 along each dividing line.

[0043] The TEG cutting step in this preferred embodiment uses the same laser beam as the laser beam to be used in the modified layer forming step. In the TEG cutting step, the focal point of the laser beam is positioned on the upper surface of each dividing line 14 to perform ablation, thereby cutting the TEG formed on each dividing line 14. This means that it is not necessary to prepare a separate laser beam application means for performing the TEG cutting step in addition to the laser beam application means 72 for performing the modified layer forming step, thus achieving good economy. However, the present invention is not limited to this configuration.This means that an additional laser beam application means capable of applying a laser beam with a different wavelength that enables the cutting of the TEG can be prepared to perform the TEG cutting step.

[0044] While in this preferred embodiment, the wafer carrying step of carrying the wafer 10 over the dividing belt T on the annular frame F is performed before performing the TEG cutting step, the wafer carrying step may be performed after performing the TEG cutting step.

[0045] While the film 20 in this preferred embodiment is a polyethylene film, the present invention is not limited to this configuration. That is, the film 20 capable of protecting the front surface 10a of the wafer 10 by thermocompression bonding without the need for, for example, a liquid resin, an adhesive, or a wax can be suitably selected from a polyolefin film and a polyester film. Examples of the polyolefin film include a polyethylene (PE) film, a polypropylene (PP) film, and a polystyrene (PS) film. Further, examples of the polyester film include a polyethylene terephthalate (PET) film and a polyethylene naphthalate (PEN) film.

[0046] In this preferred embodiment, the film 20 is heated in the film-bonding step by thermocompression bonding to a temperature (120°C to 140°C) near the melting point of polyethylene. However, in the case where the film 20 is any thermoplastic polymer film other than a polyethylene film, the film 20 is preferably heated to a temperature near the melting point of the material of the selected film. For example, in the case where the film 20 is a polypropylene film, the film 20 is preferably heated in the film-bonding step to a temperature in the range of 160°C to 180°C near the melting point of polypropylene. In the case where the film 20 is a polystyrene film, the film 20 is preferably heated in the film-bonding step to a temperature in the range of 220°C to 240°C near the melting point of polystyrene.Furthermore, in the case where the film 20 is a polyethylene terephthalate film, the film 20 is preferably heated in the film-bonding step to a temperature in the range of 250°C to 270°C near the melting point of polyethylene terephthalate. In the case where the film 20 is a polyethylene naphthalate film, the film 20 is preferably heated in the film-bonding step to a temperature in the range of 160°C to 180°C near the melting point of polyethylene naphthalate.

[0047] While the enclosing cover element 62 is used in this preferred embodiment to form an enclosed environment, the present invention is not limited to this configuration. For example, a modification as shown in Fig. 9A and Fig. 9B. In this modification, a holding means 90 having a vacuum chuck 91 is used, wherein the vacuum chuck 91 has a diameter larger than that of the film 20. The wafer 10 is held via the film 20 on the vacuum chuck 91 of the holding means 90. Moreover, the entire upper surface of the vacuum chuck 91, which holds the wafer 10 and the film 20, is covered with a film member 200. That is, both the wafer 10, the film 20, and the exposed upper surface of the vacuum chuck 91 are completely covered with the film member 200. In this state, a suction means (not shown) is operated to create a vacuum Vm as shown in Fig. 9A onto the vacuum chuck 91, thereby evacuating the interior of an environment formed by the film member 200 together with the upper surface of the vacuum chuck 91. Fig. 9B is an enlarged sectional view of an essential part of the embodiment shown in Fig. 9A. As shown in Fig. 9B, a roller 210 having a heating means (not shown) is used to apply pressure to the entire back surface 10b of the wafer 10 via the film member 200 while heating the film 20 to a desired temperature, thereby performing thermocompression bonding of the film 20 to the wafer 10 in the film bonding step.

Claims

[1] A wafer processing method for dividing a wafer (10) having a device region (10c) on its front side (10a), the device region (10c) having a plurality of separated regions in which a plurality of devices (12) are individually formed so as to be separated by a plurality of dividing lines (14), a test element group (16) being formed on each dividing line (14), the wafer (10) being divided along the dividing lines (14) to obtain a plurality of device chips having a respective one of the plurality of devices (12), the wafer processing method comprising: a film bonding step of placing a thermoplastic polymer film (20) on the front side (10a) of the wafer (10), the thermoplastic polymer film (20) having a size capable of covering the device region (10c), and next performing thermocompression bonding to bond the polymer film (20) to the front side (10a) of the wafer (10), thereby protecting the front side (10a) of the wafer (10) with the polymer film (20); a test element group cutting step of applying a first laser beam through the polymer film (20) to the wafer (10) along each dividing line (14) in a state where a focal point of the first laser beam is located at each dividing line (14), thereby cutting the test element group (16) formed at each dividing line (14); a modified layer forming step of applying a second laser beam to a back surface (10b) of the wafer (10) along each dividing line (14) in a state where a focal point of the second laser beam is positioned within the wafer (10) in an area corresponding to each dividing line (14), the second laser beam having a transmission wavelength for the wafer (10), thereby forming a modified layer (110) within the wafer (10) along each dividing line (14); and a wafer dividing step of applying an external force to the wafer (10) after performing the test element group cutting step and the modified layer forming step, thereby dividing the wafer (10) along the dividing lines (14) to obtain the device chips. [2] A wafer processing method according to claim 1, further comprising: a wafer carrying step of carrying the wafer (10) via a dividing band on an annular frame having an inner opening capable of accommodating the wafer (10), before or after performing the test element group cutting step, wherein the dividing band is attached to the back side (10b) of the wafer (10) and to the annular frame in a state in which the wafer (10) is arranged in the inner opening of the annular frame, a second laser beam which is applied to the back side (10b) of the wafer (10) through the division band in the formation step of the modified layer. [3] The wafer processing method according to claim 1 or 2, further comprising: a film peeling step of peeling the polymer film (20) from the front side (10a) of the wafer (10) before performing the wafer dividing step. [4] A wafer processing method according to any one of the preceding claims, wherein the first laser beam to be used in the test element group cutting step is the same as the laser beam to be used in the modified layer forming step. [5] A wafer processing method according to any one of the preceding claims, wherein the thermoplastic polymer film (20) is formed from a material selected from the group consisting of polyolefin and polyester. [6] A wafer processing method according to any one of the preceding claims, wherein the thermoplastic polymer film (20) comprises a polyolefin film formed from a material selected from the group consisting of polyethylene, polypropylene and polystyrene. [7] The wafer processing method according to claim 6, wherein the polyolefin film is formed of polyethylene, and wherein the polyolefin film is heated to a temperature in the range of 120°C to 140°C in the film bonding step. [8] The wafer processing method according to claim 6, wherein the polyolefin film is formed of polypropylene, and wherein the polyolefin film is heated to a temperature in the range of 160°C to 180°C in the film bonding step. [9] The wafer processing method according to claim 6, wherein the polyolefin film is formed of polystyrene, and wherein the polyolefin film is heated to a temperature in the range of 220°C to 240°C in the film bonding step. [10] The wafer processing method according to any one of the preceding claims, wherein the thermoplastic polymer film (20) comprises a polyester film formed from a material selected from the group consisting of polyethylene terephthalate and polyethylene naphthalate. [11] The wafer processing method according to claim 10, wherein the polyester film (20) is formed of polyethylene terephthalate, and wherein the polyester film (20) is heated to a temperature in the range of 250°C to 270°C in the film bonding step. [12] The wafer processing method according to claim 10, wherein the polyester film (20) is formed of polyethylene naphthalate, and wherein the polyester film (20) is heated to a temperature in the range of 160°C to 180°C in the film bonding step.

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