JP6742772B2 - Chamfering device and chamfering method - Google Patents

Description

INDUSTRIAL APPLICABILITY The present invention is suitable for performing, as a semiconductor substrate, a process of removing an unbonded part that is unavoidably left on the outer peripheral portion on the upper surface side of a bonded wafer or a wafer with a film formation layer, that is, a process of forming a terrace shape. A chamfering device and a chamfering method.

As an SOI wafer having advantages such as high speed of elements and low power consumption, as a bonded wafer, another silicon wafer is bonded to one silicon wafer on which an oxide film (insulating film) is formed, One of the bonded silicon wafers is ground and polished to form an SOI layer, and oxygen ions are implanted into the silicon wafer, followed by high-temperature annealing to form a buried oxide film inside the silicon wafer. Then, an ion implantation layer is formed by implanting hydrogen ions or the like on the surface layer portion of the silicon wafer (the wafer on the active layer side) that is to be the SOI layer side, in which the upper portion of the oxide film is the SOI layer. Known is one that is bonded to a silicon wafer.

In addition, as a method of forming a thin film of silicon oxide or aluminum as a material of a circuit on a wafer, a sputtering method in which ions are bombarded with a metal such as aluminum to peel off molecules and atoms, and deposited on the wafer, copper wiring is used. An electroplating method for forming a film, a CVD method in which a special gas is supplied to the surface of a wafer to cause a chemical reaction, and a layer of molecules generated there is formed into a film, and a silicon oxide film is formed on the surface by heating the wafer. Thermal oxidation to form, etc. are known.

When manufacturing a bonded wafer or a wafer with a film formation layer, in order to prevent the generation of particles due to peeling and separation, the process of removing the unbonded part inevitably remaining on the outer periphery of the bonded wafer, that is, the terrace part forming process is performed. is needed. In other words, a chamfering machine is used for a crystal unstable region near the edge of a monolithic wafer (physically bonded or crystal grown product) having two or more different material properties, or a part that causes device characteristics such as shape sag. Is being removed.

Therefore, in order to obtain a bonded wafer with improved quality of the terrace portion of the active layer side wafer at low cost without causing scratches in the chamfered part or collapse of the chamfered shape, after the bonding strengthening heat treatment, surface polishing or etching is performed on the active layer side. After thinning the wafer, it is known to perform mirror-chamfering processing and terrace processing on the supporting substrate wafer, which is described in Patent Document 1, for example.

Further, wafers used as materials for semiconductor devices, electronic parts, etc., and plate-shaped bodies of various shapes of brittle materials, such as sapphire, SiC (silicon carbide), GaN (gallium nitride), LT (lithium tantalate), LN. A compound semiconductor such as (lithium niobate) or a wafer in the form of a plate of an oxide is sliced by a slicing device, and then chamfered at the outer peripheral portion in order to prevent cracking or chipping of the periphery thereof.

In addition, even for plate-like bodies (workpieces) made of brittle materials, it is possible to perform high-precision chamfering without cracking or chipping, and high-precision finishing. It is known that chamfering is performed by applying sonic vibration, and is described in Patent Document 2, for example.

JP, 2010-135662, A JP, 2015-174180, A

In the above-mentioned conventional technique, the one described in Patent Document 1 is suitable for a supporting substrate wafer in which the active layer side wafer is thinned, but is an integral wafer having two or more different material properties (physically bonded or crystallized). It is difficult to apply it to a crystal unstable region near the edge of a grown product) or a portion that causes deterioration of device characteristics due to shape sag or the like.

Therefore, it is preferable to apply ultrasonic vibration to the wafer for processing, but it is not enough to simply perform the processing as described in Patent Document 2.

In particular, in the thickness direction of the wafer, so-called Z-cut (feed in the thrust direction), when the work is fed in while the grindstone is rotating, the upper layer portion is easily cracked when it is thinned. Further, in this cutting direction, since the contact area is large, the grindstone is likely to be clogged. Further, since a thrust load is applied to the wafer, a compressive stress is generated, and the wafer is in a state close to film processing and often cleaves. Further, the coolant does not flow over the entire ground surface, resulting in poor lubrication, and sludge discharge performance is reduced.

The object of the present invention is to solve the above-mentioned problems of the prior art, and in particular, in the formation of the terrace shape by the Z notch and the processing of forming the terrace shape on the upper surface layer side, cracks in the substrate surface layer portion, the oxide film layer, and the bonding buffer. It is to eliminate layer peeling and the like, and to perform low damage processing even on a cleavable work (workpiece). Further, it is intended to maintain the grinding performance due to the sharpness of the grindstone or the accuracy of the grindstone shape by the low damage processing.

In order to achieve the above object, the present invention relates to a chamfering device for grinding an end surface of a plate-shaped workpiece, a vibrating flange fitted and fixed to a spindle of a grinding unit, and a Z direction built in the vibrating flange. A piezoelectric element that vibrates ultrasonically, and a grindstone provided on the lower surface of the outer periphery and fitted to the vibrating flange, and cut in the Z direction while applying ultrasonic vibration to the grindstone by the piezoelectric element. Then, a terrace is formed on the end surface of the work material.

Further, in the above, it is preferable that the grindstone has a tapered portion formed on the outer peripheral portion, the taper portion having a larger upper side and a smaller lower side.

Further, in the above, it is preferable that the tapered portion is tapered at 90° or more and 150° or less from the horizontal plane.

Further, in the above, it is preferable that the grindstone is divided into a plurality of pieces in the circumferential direction of the grindstone wheel, and a discharge hole is provided between the divided pieces.

Further, in the above, it is desirable that the grindstone wheel is taper-fitted to the vibration flange.

Further, in the above, it is desirable that the piezoelectric element be supplied with power to be driven via a slip ring provided on the spindle.

Further, in the above structure, it is preferable that the piezoelectric element has an annular shape and is built in the vibration flange.

Further, the present invention is a chamfering method for forming a terrace shape on an end surface of a plate-shaped work material, wherein ultrasonic waves are applied in the Z direction to a grindstone having a tapered portion whose upper side is large and whose lower side is small on an outer peripheral portion. A terrace is formed on the end surface of the workpiece by cutting in the Z direction while applying vibration.

Further, the present invention is a chamfering method for forming a terrace shape on the active layer side of a wafer in which an upper layer of a support substrate is an active layer, and a tapered portion whose upper side is large and whose lower side is small is formed on an outer peripheral portion. The whetstone is cut in the Z direction while applying ultrasonic vibration in the Z direction to form the terrace shape.

Further, in the above method, it is desirable to remove the active layer and reuse the support substrate.

According to the present invention, the vibration flange is fixed to the spindle of the grinding unit, and while ultrasonic vibration is applied to the grindstone by the piezoelectric element in the Z direction (thickness direction), cutting is performed in the Z direction to form a terrace on the end surface of the workpiece. Since grinding is performed to form, the ultrasonic vibration direction and the cutting direction match, and in the process of forming the terrace shape from the upper surface side, cavitation is caused on the side that is parallel to the cutting direction and It is possible to realize low damage machining of vertical machining surface.

Therefore, it is possible to eliminate cracks in the surface layer that is the vertical surface and peeling of the oxide film layer and the bonding buffer layer, while promoting cleaning of the grinding surface and discharge of grinding debris to maintain the grinding performance or the accuracy of the grindstone shape. Can be maintained.

The front view which shows the principal part which concerns on one Embodiment of this invention. Enlarged view of the main part in FIG. The top view which shows the principal part which concerns on one Embodiment of this invention. Sectional view perpendicular to the surface of the grinding wheel according to one embodiment of the present invention and parallel sectional view Explanatory drawing which shows the procedure of Z notch which concerns on one Embodiment of this invention. A graph showing changes over time in the removal amount and spindle current when ultrasonic vibration is not applied in the Z-direction cut FIG. 4 is a graph showing changes in removal amount and spindle current with time when ultrasonic vibration is applied by Z-direction cutting according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 is a front view showing a main part of a chamfering device according to an embodiment of the present invention, FIG. 3 is a plan view, FIG. 2 is an enlarged view of a main part in FIG. 1, and FIG. It is sectional drawing perpendicular|vertical to a surface, and sectional drawing parallel.

The chamfering device 50 utilizes ultrasonic vibrations to obtain wafers and plate-like bodies (workpieces) of brittle materials of various shapes, for example, sapphire, SiC (silicon carbide), GaN (gallium nitride), LT (lithium tantalate). ) And other compound semiconductors, and an apparatus for chamfering the outer peripheral portion of an oxide work. However, it is possible to chamfer the outer peripheral portion of the plate-shaped body made of any material, not limited to the plate-shaped body made of brittle material. In the following, the work to be chamfered will be described as a wafer.

As shown in the figure, the chamfering device 50 includes a wafer feeding unit 50A and a grinding unit 50B. A pair of Y-axis guide rails 52, 52 are laid at predetermined intervals on a horizontally arranged base plate 51 of the wafer feed unit 50A. A Y-axis table 56 is slidably supported on the pair of Y-axis guide rails 52, 52 via Y-axis linear guides 54, 54,....

A nut member 58 is fixed to the lower surface of the Y-axis table 56, and a Y-axis ball screw 60 is screwed into the nut member 58. Both ends of the Y-axis ball screw 60 are rotatably supported by bearing members 62, 62 arranged on the base plate 51 between the pair of Y-axis guide rails 52, 52, and one end thereof has a Y-shape. The shaft motor 64 is connected.

By driving the Y-axis motor 64, the Y-axis ball screw 60 rotates, and the Y-axis table 56 slides horizontally (Y-axis direction) along the Y-axis guide rails 52, 52 via the nut member 58. ..

A pair of X-axis guide rails 66, 66 is laid on the Y-axis table 56 so as to be orthogonal to the pair of Y-axis guide rails 52, 52. An X-axis table 70 is slidably supported on the pair of X-axis guide rails 66, 66 via X-axis linear guides 68, 68,.

A nut member 72 is fixed to the lower surface of the X-axis table 70, and an X-axis ball screw 74 is screwed onto the nut member 72. Both ends of the X-axis ball screw 74 are rotatably supported by bearing members 76, 76 disposed on the X-axis table 70 between the pair of X-axis guide rails 66, 66. An output shaft of an X-axis motor (not shown) is connected to the end. Therefore, by driving the X-axis motor, the X-axis ball screw 74 rotates, and the X-axis table 70 slides horizontally (X-axis direction) along the X-axis guide rails 66, 66 via the nut member 72. To do.

A Z-axis base 80 is erected vertically on the X-axis table 70, and a pair of Z-axis guide rails 82, 82 are laid on the Z-axis base 80 at a predetermined interval. A Z-axis table 86 is slidably supported on the pair of Z-axis guide rails 82, 82 via Z-axis linear guides 84, 84.

A nut member 88 is fixed to the side surface of the Z-axis table 86, and a Z-axis ball screw 90 is screwed onto the nut member 88. Both ends of the Z-axis ball screw 90 are rotatably supported by bearing members 92, 92 arranged on the Z-axis base 80 between the pair of Z-axis guide rails 82, 82, and the lower end thereof. The output shaft of the Z-axis motor 94 is connected to.

The Z-axis ball screw 90 is rotated by driving the Z-axis motor 94, and the Z-axis table 86 is slid in the vertical direction (Z-axis direction) along the Z-axis guide rails 82 and 82 via the nut member 88. .. A θ-axis motor 96 is installed on the Z-axis table 86.

An output shaft of the θ-axis motor 96 is connected to a θ-axis shaft 98 having a θ-axis (rotational axis θ) parallel to the Z-axis as an axis, and an adsorption table (holding table) is attached to an upper end of the θ-axis shaft 98. ) 10 are connected horizontally. The wafer W to be chamfered on the terrace is placed on the suction table 10 and held by vacuum suction.

In the wafer feed unit 50A, the suction table 10 is horizontally moved in the Y-axis direction in the drawing by driving the Y-axis motor 64, and horizontally moved in the X-axis direction in the drawing by driving the X-axis motor. Then, the Z-axis motor 94 is driven to vertically move in the Z-axis direction in the figure, and the θ-axis motor 96 is driven to rotate about the θ-axis.

A frame 102 is installed on the base plate 51 of the grinding unit 50B. An outer peripheral motor 104 is installed on the gantry 102, and an output shaft of the outer peripheral motor 104 is connected to a spindle 106 having a rotation axis CH parallel to the Z axis as an axis. The grindstone wheel 108 for chamfering the outer peripheral portion of the wafer W is detachably mounted on the spindle 106 and is rotated by being driven by the outer peripheral motor 104. A nozzle 121 (FIG. 3) that discharges a coolant (grinding liquid) toward a processing point where the wafer W contacts the grindstone wheel 108 is provided.

In the chamfering device 50 configured as described above, the wafer W is chamfered as follows. As a preparatory step before carrying out the chamfering process, the wafer W to be chamfered is placed on the suction table 10 and held by suction. Then, the outer peripheral motor 104 and the θ-axis motor 96 are driven to rotate both the grindstone wheel 108 and the suction table 10 in the same direction at high speed. For example, the rotation speed of the grindstone wheel 108 is 3000 rpm, and the rotation speed of the suction table 10 is a speed at which the outer peripheral speed of the wafer W is 5 mm/sec.

Further, the Z-axis motor 94 is driven to adjust the height of the suction table 10 so that the height of the wafer W corresponds to the height of the grinding groove of the grindstone wheel 108. Further, the X-axis motor is driven to match the position of the θ axis (rotation axis θ), which is the rotation axis of the wafer W, with the rotation axis CH of the grindstone wheel 108 in the X-axis direction.

Next, as a step of performing the chamfering process, the Y-axis motor 64 is driven to send the wafer W toward the grindstone wheel 108. Then, the wafer W is decelerated immediately before the outer peripheral portion of the wafer W contacts the grindstone wheel 108, and then the wafer W is sent toward the grindstone wheel 108 at a low speed. As a result, the outer peripheral portion of the wafer W is brought into sliding contact with the grindstone wheel 108, and is ground and chamfered in minute amounts, as described below. Further, the coolant is discharged from the nozzle 121 toward the processing point, and at the same time as the processing point is cooled, the grinding dust and the abrasion powder (crushed and dropped abrasive grains) of the grindstone are discharged.

Then, when the outer peripheral portion of the wafer W reaches the deepest portion of the grinding groove and a predetermined time elapses, the chamfering process is finished, and the wafer W is moved in a direction away from the grindstone wheel 108 to a position where the wafer W is collected. Let

FIG. 2 is an enlarged view of a main part in FIG. 1. Reference numeral 22 denotes a vibration flange, which has a ring-shaped piezoelectric element 21 incorporated therein and is fitted and fixed to the spindle 106. The grindstone wheel 108 is taper-fitted to the vibration flange 22 so as not to cause vibration loss.

The size of the ring-type piezoelectric element 21 is set so that the outermost circumference thereof approaches the innermost circumference of the grindstone 24. Further, the ring-type piezoelectric element 21 is supplied with power to be driven through a slip ring 23 provided on the spindle 106 and capable of withstanding high rotation, and vibrates ultrasonically in the vertical direction, that is, the Z direction in the figure.

The ultrasonic wave is, for example, a sound wave having a frequency of 20 kHz or higher, and the ring-type piezoelectric element 21 vibrates in the Z direction by the ultrasonic wave having a frequency of 20 kHz. However, you may vibrate with the ultrasonic wave of a frequency of 20 kHz or more. Further, it may be a sound wave having a frequency lower than 20 kHz depending on processing conditions.

4 is a sectional view perpendicular to the surface of the grindstone wheel 108, and the lower diagram is a sectional view parallel to the surface of the grindstone wheel 108. FIG. 4 shows the grindstone wheel 108, and the grindstone 24 is provided on the lower surface of the outer periphery thereof. The grindstone 24 has a tapered portion 26 formed on the outer peripheral portion thereof and having a taper of 90° or more and 150° or less from a horizontal plane whose upper side is large and whose lower side is small. The grindstone 24 is segmented in the circumferential direction of the grindstone wheel 108, that is, divided into a plurality of pieces, and discharge holes 25 for discharging grinding dust and the like are provided between the divided pieces.

FIG. 5 is an explanatory view showing the procedure of Z incision (thrust direction feed), showing a case where the upper layer of the bonded wafer, that is, the active layer 30 or the adhesive layer 31 is removed and the support substrate 32 is not processed. It is suitable for the following cases. The intermediate layer between the active layer 30 and the support substrate 32 is bonded with a thermosetting or UV adhesive to form an adhesive layer 31, which has high mechanical bonding strength. The active layer 30 is made of a material (Si) having a relatively high material strength, and has a large finished thickness on the active layer side. The active layer 30 may be formed by film formation, but the film thickness is large and the material strength is strong.

Finally, the bonding is peeled off and only the active layer 30 is used, and the support substrate 32 is made to contribute to ensuring the overall material strength during the manufacturing process and only as a film forming base material, and is recycled for reuse. The support substrate 32, such as glass or alumina-based sintered body, has high cost, moldability, wear resistance, and the like, and does not contribute to device characteristics.

First, as shown in (b), when the thickness error due to film formation is large, the upper plane of the active layer 30 is smoothed. Next, as shown in (c), the chamfering device starts cutting in the Z direction while applying ultrasonic vibrations in the Z direction. That is, an infeed is performed in which the rotating grindstone 24 is lowered from the top with respect to the object to be ground (work) that rotates, and the grinding is performed until the specified thickness is reached.

The grindstone 24 is a metal bond having a mesh size of about #400 to #800, and is adjusted in consideration of the life and processing quality of the grindstone 24. The spindle rotation speed on the grindstone side is 1000 to 4000 rpm, the rotation speed on the workpiece side is 50 to 200 rpm, and the cutting speed is preferably 0.1 to 5 mm/sec, but it is appropriately selected depending on the material.

Next, in (d), the tapered portion of the grindstone 24 is set to 90° or more and 150° or less from the horizontal plane to promote the cavitation effect for improving the workability of the active layer 30 having high material strength. Then, the terrace of the active layer 30 is formed, and the adhesive layer 31 is removed. Next, the support substrate 32 and the adhesive layer 31 are peeled off as shown in (e), or chips are formed by dicing before or after peeling.

As described above, by propagating the ultrasonic vibration to the processing grindstone, it is possible to prevent clogging at the processing point due to the cavitation effect, which makes it difficult for the coolant to enter and the sludge to be hardly discharged. In particular, in cutting in the Z direction, by providing ultrasonic vibration in the Z direction and having a taper portion that is tapered in the Z direction, cavitation can be effectively applied in the taper portion. Therefore, the cleaning of the grinding surface and the discharge of grinding debris are promoted up to the horizontal processing surface in FIG. 5, which is a surface vertical to the cutting direction, and the protruding amount of the grinding abrasive grains is stably ensured to improve the processing quality. improves.

Further, since the abrasive grains are vibrated in the Z direction, which is the feed direction (removal direction), the original cutting ability and the vibration acceleration motion of the abrasive grains are added, and the grinding performance is improved. Further, by providing the tapered portion, the grinding resistance becomes a component force in the horizontal direction which is lateral to the Z-cutting direction, so that the pushing force at the time of processing is suppressed and the grinding object (workpiece) is cut. Bending load can be reduced.

This makes it possible to perform low-damage processing in the Z direction, and realize processing that does not crack even on a cleavable work. In particular, even in the process of forming the terrace shape from the Z direction on the upper surface side of the monolithic wafer (physically bonded or crystal grown product) having two or more different material properties, cracking or oxidation of the substrate surface layer part It is possible to eliminate peeling of the coating layer and the bonding buffer layer.

Also, by matching the cutting direction with the ultrasonic vibration direction, cavitation occurs on the side that is parallel to the ultrasonic vibration direction and the cutting direction, and damage due to cavitation occurs on the brittle surface side of the vertical surface. do not do. Then, if the direction perpendicular to the cutting direction is set as the vibration direction, the grinding performance can be prioritized, and the cavitation and cutting directions can be selectively used according to the application such as rough machining and precision machining. As a result, the lubrication failure and the processing load on the abrasive grains are dispersed, so that the shape maintenance performance of the grindstone is improved, the work quality is stabilized, and the grindstone life is improved.

Further, the increased mobility of the abrasive grains improves the processing efficiency, and realizes a higher processing speed than the normal processing speed. In addition, the prevention of clogging and the improvement of processing performance enable the use of a grindstone with a wide contact area, so that the shape accuracy and grindstone life can be improved.

FIG. 6 is a graph showing the time variation of the removal amount and the spindle current when ultrasonic vibration is not applied in the Z-direction cutting as in the prior art, in which the spindle current increases with the lapse of machining time and clogging occurs. You can see that it is progressing. In this example, the processing feed speed is about 0.1 μm/s and the removal amount is about 20 μm. It is difficult to increase the processing feed speed and the removal amount more than this because of the processing quality and the like.

FIG. 7 is a graph showing the changes over time in the removal amount and spindle current when ultrasonic vibration is applied by cutting in the Z direction. The processing conditions were such that the grindstone 24 was a metal bond having a mesh size of #600, ultrasonic vibration was 20 kHz, amplitude was 2 μm, spindle rotation speed was 1000 rpm, and work-side rotation speed was 100 rpm.

The spindle current was not observed to increase with the passage of processing time, was stable, and removal was progressing well. In addition, in this example, the processing feed rate is about 0.8 μm/s and the removal amount is about 45 μm, so that the processing time can be shortened, the processing quality is improved, and the cracks on the surface layer of the substrate are improved as compared with those in FIG. Also, peeling of the oxide film layer and the bonding buffer layer did not occur.

W wafer (workpiece)
10 Adsorption Table 21 Piezoelectric Element 22 Vibrating Flange 23 Slip Ring 24 Grinding Stone 25 Discharge Hole 26 Tapered Part 30 Active Layer 31 Adhesive Layer 32 Supporting Substrate 50 Chamfering Device 50A Wafer Feeding Unit 50B Grinding Unit 106 Spindle 108 Grinding Wheel

Claims (9)

In a chamfering device for grinding the end surface of a plate-shaped work material,
A vibration flange fitted and fixed to the spindle of the grinding unit,
A piezoelectric element built in the vibration flange and ultrasonically vibrating in the Z direction;
A grindstone is provided on the lower surface of the outer periphery, and a grindstone wheel fitted to the vibration flange,
Equipped with
The grinding wheel is taper fitted to the vibrating flange,
A chamfering device, characterized by cutting the grindstone in the Z direction while applying ultrasonic vibration by the piezoelectric element to form a terrace on the end surface of the workpiece. The chamfering device according to claim 1, wherein the grindstone has a tapered portion formed on an outer peripheral portion of which an upper side is larger and a lower side is smaller. The chamfering device according to claim 2, wherein the tapered portion has a taper of 90° or more and 150° or less from a horizontal plane. 4. The grindstone is divided into a plurality of pieces in the circumferential direction of the grindstone wheel and is arranged, and a discharge hole is provided between the divided pieces. Chamfering device. The piezoelectric element is chamfered according to any one of 4 from claim 1, characterized in that the power driven through a slip ring provided on the spindle is supplied. The piezoelectric element is an annular shape, chamfering apparatus according to any one of claims 1 to 5, characterized in that incorporated in the vibration flange. A chamfering method for forming a terrace shape on an end surface of a plate-shaped workpiece,
A vibration flange fitted and fixed to the spindle of the grinding unit,
A piezoelectric element built in the vibration flange and ultrasonically vibrating in the Z direction;
A grindstone is provided on the lower surface of the outer periphery, and a grindstone wheel fitted to the vibration flange,
Equipped with
The grinding wheel uses a chamfering device that is taper fitted to the vibration flange,
And forming a terrace on the end face of the workpiece by cutting in the Z direction while applying ultrasonic vibration to the Z-direction to the grindstone tapered portion is formed to the upper large bottom is smaller in the outer peripheral portion Chamfer method. A chamfering method for forming a terrace shape on the active layer side of the wafer in which the upper layer of the supporting substrate is an active layer,
A vibration flange fitted and fixed to the spindle of the grinding unit,
A piezoelectric element built in the vibration flange and ultrasonically vibrating in the Z direction;
A grindstone is provided on the lower surface of the outer periphery, and a grindstone wheel fitted to the vibration flange,
Equipped with
The grinding wheel uses a chamfering device that is taper fitted to the vibration flange,
Chamfering method characterized by forming the terrace shape cuts in the Z direction while applying ultrasonic vibration to the Z-direction to the grindstone tapered portion is formed to the upper large bottom is smaller in the outer peripheral portion. 9. The chamfering method according to claim 8 , wherein the active layer is removed and the supporting substrate is reused.