Processing device

Abstract

Processing device (2) comprising: a holding means (22) for holding a workpiece (11); a grinding means (38a, 38b) for grinding the workpiece held by the holding means; and a gettering capacity determining means (50) for determining whether a grinding distortion generated by grinding the workpiece (11) held by the holding means (22) by the grinding means (38a, 38b) has a gettering capacity or not, wherein the getter capacity determining means (50) comprises: a laser beam irradiation unit (80) for irradiating the workpiece (11) with a pulse laser beam (L) having a predetermined wavelength, a microwave transmitting / receiving unit (82) for transmitting microwaves (M1) towards the workpiece (11) and receiving microwaves (12) reflected from the workpiece (11), wherein the gettering capacity determining means (50) is configured to measure an attenuation time of the microwaves (M2) and to determine the gettering capacity by comparing this attenuation time with a predetermined reference time.

Description

Background of the inventionField of the invention

[0001] The present invention relates to a machining apparatus that grinds a workpiece having a plate shape. Description of the state of the art

[0002] For small-sized and lightweight electronic devices such as mobile phones, a component chip containing a component such as an integrated circuit (IC) is an essential component structure. The component chip is fabricated by dividing the surface of a wafer made of a material such as silicon with several systematic dividing lines called streets, forming a component in each area, and then dividing the wafer along the streets.

[0003] In recent years, there have been increasing opportunities to process a wafer on which components have been formed (device wafer) into a thin wafer for the purpose of reducing the size and weight of the device chip, etc. However, when the device wafer is polished to reduce its thickness to 100 μm or less, for example, the gettering effect for suppressing the movement of metal elements harmful to the devices is reduced, and device malfunction often occurs. To solve this problem, a processing method has been proposed in which a gettering layer that traps metal elements is formed in a device wafer (see, for example, JP 2009-94326 A).

[0004] In this processing method, the device wafer is ground under specified conditions to form the getter layer, which includes a specified grinding distortion, while maintaining the flexural strength of the device wafer.

[0005] JP 2011 - 101 913 A and US 5 196 786 A disclose further prior art. Summary of the invention

[0006] However, the getter layer formed by the above-described processing method does not always exhibit favorable gettering ability. For example, a method of actually contaminating the device wafer with metal elements can be used to determine the gettering ability of the getter layer. However, in this case, it becomes impossible to obtain a device chip as a non-defective product. That is, there is a problem in that it is impossible to incorporate this determination method into the device wafer processing step.

[0007] Therefore, it is an object of the present invention to provide a machining apparatus that can determine the gettering capability of a workpiece in one machining step.

[0008] The present invention is defined by the processing device according to the features of independent claim 1. Dependent claim 2 relates to a preferred development.

[0009] According to one aspect of the present invention, a machining apparatus is provided that includes a holding means for holding a workpiece and a grinding means for grinding the workpiece held by the holding means. The machining apparatus includes a gettering ability determination means for determining whether or not a grinding distortion generated by grinding the workpiece held by the holding means by the abrasive has sufficient gettering ability.

[0010] In the present invention, the machining apparatus may further include grinding distortion removing means for removing a part of the grinding distortion generated by grinding by the abrasive.

[0011] The machining apparatus according to the present invention includes the gettering ability determination means for determining whether the grinding distortion generated by grinding the workpiece has gettering ability or not, in addition to the holding means for holding the workpiece and the grinding means for grinding the workpiece. Therefore, the machining apparatus can determine the gettering ability of the workpiece in the machining step.

[0012] The above and other objects, features and advantages of the present invention and the manner of 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 accompanying drawings which show a preferred embodiment of the invention. Short description of the drawings Fig.1 is a perspective view schematically showing a machining apparatus according to an embodiment; Fig. 2A is a perspective view schematically showing an example of a workpiece to be machined by the machining apparatus according to the embodiment; Fig. 2B is a perspective view schematically showing how a protective member is adhered to the workpiece; Fig. 3 is a perspective view schematically showing a grinding distortion removing unit included in the machining apparatus; and Fig. 4 is a partially sectioned side view schematically showing a gettering capacity determining unit included in the processing apparatus. Detailed description of the preferred embodiment

[0013] An embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a perspective view schematically showing a machining apparatus according to the present embodiment. As shown in Fig. 1, the machining apparatus 2 includes a base 4 that supports the respective structures. An opening 4a is formed on the front end side of the upper surface of the base 4. A first conveying unit 6 that conveys a workpiece is provided in this opening 4a. Further, in a region at the front of the opening 4a, arrangement tables 10a and 10b are formed, on which cassettes 8a and 8b, each capable of accommodating a plurality of workpieces, are arranged.

[0014] Fig. 2A is a perspective view schematically showing an example of a workpiece to be machined by the machining apparatus according to the present embodiment. As shown in Fig. As shown in Fig. 2A, a workpiece 11 is, for example, a plate-shaped object (wafer) formed of a semiconductor material such as silicon and having a substantially circular shape, and a front surface 11a is divided into a device region 13 as a central region and a peripheral excess region 15 surrounding the device region 13. The device region 13 is further divided into a plurality of regions by streets (scheduled dividing lines) 17 arranged in a lattice array, and a device 19 such as an IC is formed in each region. An outer periphery 11c of the workpiece 11 is subjected to chamfering and is slightly rounded.

[0015] A protective member for protecting the components 19 is adhered to the side of the front surface 11a of this workpiece 11. Fig.2B is a perspective view schematically showing how the protective member is adhered to the workpiece 11. As in Fig. As shown in Fig. 2B, a protective member 21 is formed in a circular disk shape having substantially the same diameter as the workpiece 11, and an adhesive layer is provided on a front surface 21a side. As the protective member 21, for example, an adhesive tape, a resin substrate, the same plate-shaped object (wafer) as the workpiece 11, etc. can be used. The front surface 21a side of this protective member 21 is arranged to be opposite to the front surface 11a side of the workpiece 11, and the protective member 21 and the workpiece 11 are overlapped with each other. This makes it possible to adhere the protective member 21 to the front surface 11a side of the workpiece 11 with the adhesive layer interposed therebetween.

[0016] On an inclined rear side of the opening 4a, an alignment mechanism 12 is provided for positional alignment of the workpiece 11. This alignment mechanism 12 includes a temporary placement table 14 on which the workpiece 11 is temporarily placed, and performs, for example, positional alignment of the center of the workpiece 11 conveyed from the cassette 8a by the first conveying unit 6 and temporarily placed on the temporary placement table 14. A gate-shaped support structure 16 spanning the alignment mechanism 12 is arranged on a side surface of the base 4. This support structure 16 is provided with a second conveying unit 18 for conveying the workpiece 11.The second conveying unit 18 can move in the left-right direction (X-axis direction), the front-back direction (Y-axis direction), and the up-down direction (Z-axis direction), and conveys the workpiece 11 whose position has been aligned by the alignment mechanism 12, for example, toward the back.

[0017] An opening 4b is formed at the rear of the opening 4a and the alignment mechanism 12. In this opening 4b, a rotary table 20 is arranged, which rotates around a rotation axis extending along the vertical direction and has a circular disk shape. Four chuck tables (holding means) 22, which hold the workpiece 11 under suction, are arranged at substantially equal angular intervals on the upper surface of the rotary table 20. The workpiece 11 conveyed from the alignment mechanism 12 by the second conveying unit 18 is conveyed to the chuck table 22, which is located at a loading / unloading position A on the front side, with the side of a rear surface 11b exposed to the upper side.The rotary table 20 rotates in a rotation direction R shown in the diagram to arrange each of the chuck tables 22 at the respective positions in the order of the loading / unloading position A, a rough grinding position B, a fine grinding position C, and a grinding distortion removal position D. Each chuck table 22 is connected to a rotation drive source (not shown) such as a motor and rotates about a rotation axis extending along the vertical direction. The upper surface of each chuck table 22 serves as a holding surface for holding the workpiece 11 under suction. This holding surface is connected to a suction source (not shown) through a flow path (not shown) formed inside the chuck table 22.The front surface 11a side (protection member 21 side) of the workpiece 11 conveyed to the chuck table 22 is sucked by a negative pressure from the suction source acting on the holding surface.

[0018] A wall-shaped support structure 24 extending upward is provided upright on the rear side of the rotary table 20. Two elevating / lowering units 26 are provided on the front surface of the support structure 24. Each elevating / lowering unit 26 includes two elevating / lowering guide rails 28 extending along the vertical direction (Z-axis direction), and a elevating / lowering table 30 is slidably arranged on the elevating / lowering guide rails 28. A nut member (not shown) is fixed to the rear surface side (rear surface side) of the elevating / lowering table 30, and a elevating / lowering ball screw 32 parallel to the elevating / lowering guide rails 28 is screwed to this nut member. A raising / lowering pulse motor 34 is connected to one end portion of the raising / lowering ball screw 32.Rotating the raising / lowering ball screw 32 by the raising / lowering pulse motor 34 causes the raising / lowering table 30 to move up and down along the raising / lowering guide rails 28.

[0019] A fixing component 36 is provided on the front surface (surface) of the raising / lowering table 30. A grinding unit (abrasive) 38a for rough grinding the workpiece 11 is fixed to the fixing component 36 of the raising / lowering table 30 at a position above the rough grinding position B. On the other hand, a grinding unit (abrasive) 38b for fine grinding the workpiece 11 is fixed to the fixing component 36 of the raising / lowering table 30 at a position above the fine grinding position C. A spindle 42 constituting a rotary shaft is housed in spindle housings 40 of the grinding units 38a and 38b, respectively, and a disk attachment 44 having a circular disk shape is fixed to the lower end portion (tip portion) of each spindle 42.A grinding wheel 46a with grindstones for rough grinding is mounted on the lower surface of the wheel mount 44 of the grinding unit 38a, and a grinding wheel 46b with grindstones for fine grinding is mounted on the lower surface of the wheel mount 44 of the grinding unit 38b. A rotational drive source (not shown), such as a motor, is connected to the upper end side of each spindle 42, and the grinding wheels 46a and 46b rotate by rotational force transmitted from the rotational drive source. Rough grinding or fine grinding of the workpiece 11 can be performed by lowering the grinding wheel 46a or 46b and bringing it into contact with the rear surface 11b side of the workpiece 11 while rotating the chuck table 22 and the spindle 42, while supplying a grinding solution such as treated water.

[0020] A grinding distortion removing unit (grinding distortion removing means) 48 that partially removes grinding distortion of the workpiece 11 ground by the grinding units 38a and 38b is provided near the grinding distortion removing position D. Further, a gettering ability determining unit (gettering ability determining means) 50 that determines the gettering ability of the workpiece 11 is arranged above the loading / unloading position A. The workpiece 11 ground by the grinding units 38a and 38b undergoes partial grinding distortion removal in the grinding distortion removing unit 48 and then undergoes gettering ability determination in the gettering ability determining unit 50.A cleaning unit 52 that cleans the workpiece 11 is provided at the front of the alignment mechanism 12, and the workpiece 11 whose gettering ability has been determined is conveyed from the chuck table 22 to the cleaning unit 52 by the second conveying unit 18. The workpiece 11 cleaned by the cleaning unit 52 is conveyed to the first conveying unit 6 to be accommodated in the cassette 8b.

[0021] Fig. 3 is a perspective view schematically showing the grinding distortion removing unit 48 included in the machining apparatus 2. As shown in Fig.3, a block-shaped support structure 54 is provided upright on the upper surface of the base 4. A horizontal movement unit 56, which moves the grinding distortion removing unit 48 in the horizontal direction (the X-axis direction in this embodiment), is provided on the rear surface of the support structure 54. The horizontal movement unit 56 includes a pair of horizontal guide rails 58 fixed to the rear surface of the support structure 54 and parallel to the horizontal direction (X-axis direction). A horizontal movement table 60 is slidably arranged on the horizontal guide rails 58. A nut member (not shown) is fixed to the front surface side of the horizontal movement table 60, and a horizontal ball screw (not shown) parallel to the horizontal guide rails 58 is screwed to this nut member.A pulse motor 62 is connected to one end portion of the horizontal ball screw. Rotation of the horizontal ball screw by the pulse motor 62 causes the horizontal motion stage 60 to move along the horizontal guide rails 58 in the horizontal direction (X-axis direction).

[0022] A vertical movement unit 64, which moves the grinding distortion removal unit 48 in the vertical direction (Z-axis direction), is provided on the rear surface side of the horizontal movement table 60. The vertical movement unit 64 includes a pair of vertical guide rails 66 fixed to the rear surface of the horizontal movement table 60 and parallel to the vertical direction (Z-axis direction). A vertical movement table 68 is slidably arranged on the vertical guide rails 66. A nut member (not shown) is fixed to the front surface side (rear surface side) of the vertical movement table 68, and a vertical ball screw (not shown) parallel to the vertical guide rails 66 is screwed to this nut member. A pulse motor 70 is connected to one end portion of the vertical ball screw.Rotating the vertical ball screw by the pulse motor 70 causes the vertical motion table 68 to move along the vertical guide rails 66 in the vertical direction (Z-axis direction).

[0023] The grinding distortion removing unit 48 for partially removing the grinding distortion of the workpiece 11 is attached to the rear surface (surface) of the vertical movement table 68. A spindle 74 constituting a rotary shaft is housed in a spindle housing 72 of the grinding distortion removing unit 48, and a disk attachment 76 having a circular disk shape is attached to the lower end (tip) part of the spindle 74. A polishing disk 78 having substantially the same diameter as the disk attachment 76 is attached to the lower surface of the disk attachment 76. The polishing disk 78 includes a disk base 78a formed of a metal material such as stainless steel. A polishing pad 78b having a circular disk shape is attached to the lower surface of the disk base 78a.The grinding distortion of the workpiece 11 can be removed by lowering the polishing wheel 78 during the rotation of the chuck table 22 and the spindle 74, and bringing the polishing pad 78b into contact with the back surface 11b side of the workpiece 11 while supplying a polishing solution. In this grinding distortion removal unit 48, the workpiece 11 is polished so that a certain amount of grinding distortion remains. This can maintain the bending strength of the workpiece 11 while ensuring the gettering ability.

[0024] Fig. 4 is a partially sectioned side view schematically showing the gettering capacity determination unit 50 included in the processing apparatus 2. As in Fig.4, the gettering capacity determination unit 50 includes a laser beam irradiation unit 80 that irradiates the workpiece 11 located at the loading / unloading position A with a pulse laser beam L having a predetermined wavelength (e.g., 904 nm, 532 nm, 349 nm, etc.). Near the laser beam irradiation unit 80, a microwave transmitting / receiving unit 82 is arranged, which transmits (radiates) microwaves (electromagnetic waves) M1 toward the workpiece 11 and receives microwaves (electromagnetic waves) M2 reflected from the workpiece 11. By this microwave transmitting / receiving unit 82, a change in the intensity of the microwaves M2 reflected from the rear surface 11b side of the workpiece 11 can be detected.

[0025] As in Fig.As shown in Fig. 4, if the gettering ability of the workpiece 11 having a getter layer 23 with a predetermined grinding distortion is determined, first, the microwaves (electromagnetic waves) M1 are emitted (radiated) from the microwave transmitting / receiving unit 82 toward the rear surface 11b of the workpiece 11. In this state, when the area irradiated with the microwaves M1 is irradiated with the pulse laser beam L from the laser beam irradiation unit 80, excess carriers (electrons, holes) are generated on the rear surface 11b side of the workpiece 11, and the reflectance of the microwaves M1 increases. That is, the intensity of the microwaves M2 received by the microwave transmitting / receiving unit 82 becomes higher.Thereafter, during the period in which irradiation with the pulsed laser beam L is not performed, the reflectance of the microwaves M1 progressively decreases due to the recombination of the charge carriers. This means that the microwaves M2 are progressively attenuated.

[0026] As a result of extensive studies, the present inventor found a relationship that the lifetime of the carriers generated by irradiation with the pulse laser beam L (the time from carrier generation to recombination) is shorter as the gettering ability of the getter layer 23 is higher. Subsequently, the present inventor completed the present invention based on an idea that the gettering ability can be determined by measuring the attenuation time of the microwaves M2, which corresponds to the lifetime of the carriers. Specifically, the attenuation time of the microwaves M2 on the workpiece 11 as the detection target is measured, and the gettering ability is determined by comparing this attenuation time with a predetermined reference time. As the reference time, for example, the attenuation time of the microwaves M2 on a wafer in which the getter layer 23 is not formed (bare wafer) can be used.

[0027] For example, when the wavelength of the pulse laser beam L is set to 904 nm, it is determined that the workpiece 11 whose attenuation time is equal to or shorter than 94% of the reference time has gettering ability. Further, when the wavelength of the pulse laser beam L is set to 532 nm, it is determined that the workpiece 11 whose attenuation time is equal to or shorter than 75% of the reference time has gettering ability. Furthermore, when the wavelength of the pulse laser beam L is set to 349 nm, it is determined that the workpiece 11 whose attenuation time is equal to or shorter than 45% of the reference time has gettering ability. However, the wavelength of the pulse laser beam L that can be used for this determination method is not limited to the above-described 904 nm, 532 nm, and 349 nm.

[0028] Furthermore, it is also possible to determine the bending strength of the workpiece 11 by a similar method. When the wavelength of the pulse laser beam L is set to 904 nm, it is determined that the workpiece 11 whose attenuation time is equal to or longer than 85% of the reference time has favorable bending strength. Further, when the wavelength of the pulse laser beam L is set to 532 nm, it is determined that the workpiece 11 whose attenuation time is equal to or longer than 55% of the reference time has favorable bending strength. Furthermore, when the wavelength of the pulse laser beam L is set to 349 nm, it is determined that the workpiece 11 whose attenuation time is equal to or longer than 20% of the reference time has favorable bending strength.Also in the case of determining the bending strength of the workpiece 11, the pulse laser beam L can be used, which has a wavelength different from the 904 nm, 532 nm and 349 nm described above.

[0029] If it is determined by this gettering ability determination unit 50 that the gettering ability of the workpiece 11 is insufficient, it is preferable to perform the respective steps of rough grinding, fine grinding, and grinding distortion removal again to increase the gettering ability of the workpiece 11.

[0030] Next, an experiment conducted to confirm the validity of the determination performed in the getter capacity determination unit 50 described above is described. (Experiment)

[0031] In this experiment, the above-described attenuation time, metal contamination resistance, and bending strength were tested on the workpieces 11 in which the getter layer 23 was formed under mutually different conditions (Condition 1 to Condition 10). The wavelengths of the pulse laser beam L irradiated onto the workpieces 11 were three kinds of wavelengths, 904 nm, 532 nm, and 349 nm. The experimental result when the wavelength of the pulse laser beam L was set to 904 nm is shown in Table 1. The experimental result when the wavelength of the pulse laser beam L was set to 532 nm is shown in Table 2. The experimental result when the wavelength of the pulse laser beam L was set to 349 nm is shown in Table 3. In each table, "OK" represents the favorable condition, and "NG" represents the defective condition.Further, in each table, the experimental result of a wafer in which the getter layer 23 was not formed (bare wafer) is shown as a reference. (Table 1) Damping time (%) Metal contamination Flexural strength reference 100 NG OK State 1 87, 4 OK OK Condition 2 88,46 OK OK Condition 3 88,46 OK OK Condition 4 91,58 OK OK Condition 5 90,24 OK OK Condition 6 89,79 OK OK Condition 7 94, 04 NG OK Condition 8 90, 13 OK OK Condition 9 105, 12 NG OK Condition 10 84, 8 OK NG (Table 2) Damping time (%) Metal contamination Flexural strength reference 100 NG OK State 1 73,34 OK OK Condition 2 61,02 OK OK Condition 3 60, 52 OK OK Condition 4 62, 88 OK OK Condition 5 62, 76 OK OK Condition 6 60, 14 OK OK Condition 7 75,43 NG OK Condition 8 57, 65 OK OK Condition 9 125,03 NG OK Condition 10 54,72 OK NG (Table 3) Damping time (%) Metal contamination Flexural strength reference 100 NG OK State 1 21,59 OK OK Condition 2 30,75 OK OK Condition 3 35, 21 OK OK Condition 4 43, 42 OK OK Condition 5 42,95 OK OK Condition 6 42,01 OK OK Condition 7 45,12 NG OK Condition 8 36, 38 OK OK Condition 9 114,7 NG OK Condition 10 19,38 OK NG

[0032] Through the respective tables, it can be confirmed that the above-described determination is valid. For example, the workpiece 11 is machined to meet the following condition to ensure both the gettering ability and the bending strength. Specifically, when the wavelength is 904 nm, the attenuation time is equal to or longer than 85% of the reference time and equal to or shorter than 94% of the reference time. When the wavelength is 532 nm, the attenuation time is equal to or longer than 55% of the reference time and equal to or shorter than 75% of the reference time. When the wavelength is 349 nm, the attenuation time is equal to or longer than 20% of the reference time and equal to or shorter than 45% of the reference time.

[0033] As described above, the machining apparatus 2 according to the present embodiment includes the gettering ability determination unit (gettering ability determination means) 50 that determines whether the grinding distortion generated by grinding the workpiece 11 has gettering ability or not, in addition to the chuck tables (holding means) 22 that hold the workpiece 11 and the grinding units (grinding means) 38a and 38b that grind the workpiece 11. Therefore, the machining apparatus 2 can determine the gettering ability of the workpiece 11 in the machining step.

[0034] The present invention is not limited to the description of the above embodiment and can be implemented with various modifications. For example, in the above embodiment, the attenuation time of the microwaves M2 on a wafer in which the gettering layer 23 is not formed (bare wafer) is used as the reference time. However, the reference time can be arbitrarily changed. For example, the attenuation time of the microwaves M2 on the workpiece 11 whose gettering ability is optimized can be used as the reference time. Further, in the above embodiment, the microwave transmitting / receiving unit 82 is described, which integrally includes the transmitting part that transmits (radiates) the microwaves M1 toward the workpiece 11 and the receiving part that receives the microwaves (electromagnetic waves) M2 reflected from the workpiece 11.However, the transmitting part and the receiving part of the microwave transmitting / receiving unit may be separate parts. Furthermore, in the above embodiment, the grinding distortion removal unit (grinding distortion removal means) 48 is described, which polishes the workpiece 11 (usually CMP) to partially remove the grinding distortion. However, the grinding distortion removal unit (grinding distortion removal means) may be configured to remove the grinding distortion by another method, such as dry etching, wet etching, plasma etching, or dry polishing.

[0035] The present invention is not limited to the details of the preferred embodiment described above. The scope of the invention is defined by the appended claims.

Claims

[1] Processing device (2) comprising: a holding means (22) for holding a workpiece (11); a grinding means (38a, 38b) for grinding the workpiece held by the holding means; and a gettering capacity determining means (50) for determining whether a grinding distortion generated by grinding the workpiece (11) held by the holding means (22) by the grinding means (38a, 38b) has a gettering capacity or not, wherein the getter capacity determining means (50) comprises: a laser beam irradiation unit (80) for irradiating the workpiece (11) with a pulse laser beam (L) having a predetermined wavelength, a microwave transmitting / receiving unit (82) for transmitting microwaves (M1) towards the workpiece (11) and receiving microwaves (12) reflected from the workpiece (11), wherein the gettering capacity determining means (50) is configured to measure an attenuation time of the microwaves (M2) and to determine the gettering capacity by comparing this attenuation time with a predetermined reference time. [2] Processing device (2) according to claim 1, further comprising: a grinding distortion removing means (48) for removing a part of the grinding distortion generated by grinding by the abrasive.

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