Method for machining workpiece

Provided is a method for machining a workpiece including a substrate that has front and back surfaces and a ductile material layer that contains a ductile material and is disposed on the front or back surface. The method includes a tape bonding step of bonding a tape on a side of the substrate of the workpiece, a holding step of holding the workpiece by a holding table via the tape, and a cutting step of relatively moving the holding table and a cutting blade to cause the cutting blade to cut into the ductile material layer and the substrate. In the cutting step, the cutting blade is rotated such that a portion of the cutting blade, the portion being located on a forward side in a moving direction of the cutting blade relative to the holding table, cuts into the workpiece from the ductile material layer toward the substrate.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for machining a workpiece including a substrate and a ductile material layer.

Description of the Related Art

In electronic equipment including mobile phones and personal computers, device chips with devices such as electronic circuits included therein are arranged as essential configuration elements. Such device chips are obtained by defining a wafer, which is formed, for example, of a semiconductor material such as silicon (Si), on a side of a front surface thereof into a plurality of regions along scheduled division lines (hereinafter called “streets”), forming devices in the individual regions, and then dividing the wafer along the streets.

In recent years, there are increasing cases to dispose a film formed of a metal such as copper (Cu) (hereinafter called a “metal film”) on a back surface of a wafer for realization of various functions required for device chips. When dividing such a workpiece with a wafer and a metal film included therein, a tape, for example, is bonded to a side of the metal film of the workpiece to hold the workpiece on the side of the metal film (via the tape) such that the wafer is exposed. Subsequent cutting of the workpiece with a cutting blade, which is being rotated in such a direction as cutting into the workpiece from a side of the wafer to the side of the metal film, makes it possible to cut and divide the workpiece into a plurality of device chips.

With the above-mentioned method, however, the metal film formed of such a ductile metal is stretched toward the tape by the rotating cutting blade, so that rough metal edges called “burrs” tend to occur from the metal film. Such burrs act as a cause of occurrence of a failure such as short-circuiting between terminals, for example, when mounting such a device chip on a printed circuit board, and hence there is a need to fully suppress the occurrence of burrs when dividing a workpiece that includes a metal film.

To resolve such a problem, a method has been proposed to cut a metal film by irradiating a laser beam (see, for example, JP 2018-78162 A). According to this method, after a workpiece is cut from a side of a wafer under conditions that a cutting blade would not cut into the metal film, the laser beam is irradiated to cut the metal film. As no cutting blade is used in the cutting of the metal film, the metal film remains free of burrs that would otherwise occur through contact with a rotating cutting blade.

SUMMARY OF THE INVENTION

With a method that cuts a metal film with a laser beam as mentioned above, however, a cutting apparatus and a laser processing apparatus have to be used in combination, leading to a problem that its equipment and steps tend to become complex. Complex equipment and steps in turn lead to an increase in cost required for the processing of the workpiece.

The present invention therefore has, as an object thereof, the provision of a method for machining a workpiece having a substrate such as a wafer and a ductile material layer such as a metal film, which can machine the workpiece through simple steps and can suppress the occurrence of burrs from the ductile material layer.

In accordance with an aspect of the present invention, there is provided a method for machining a workpiece including a substrate that has a front surface and a back surface and a ductile material layer that contains a ductile material having ductility and is disposed on the front surface or the back surface of the substrate. The method includes a tape bonding step of bonding a tape on a side of the substrate of the workpiece, a holding step of holding the workpiece by a holding table via the tape such that the ductile material layer is exposed, and a cutting step of, after performing the holding step, relatively moving the holding table and a cutting blade to cause the cutting blade to cut into the ductile material layer and the substrate, so that the workpiece is cut. In the cutting step, the cutting blade is rotated such that a portion of the cutting blade, the portion being located on a forward side in a moving direction of the cutting blade relative to the holding table, cuts into the workpiece from the ductile material layer toward the substrate.

Preferably, the ductile material layer may be disposed on the back surface of the substrate, the workpiece may further include a plurality of devices disposed on a side of the front surface, and the ductile material layer may be formed from a metal film.

Preferably, the method may further includes, after performing the holding step but before performing the cutting step, a position detecting step in which a position where the cutting blade is to be caused to cut into the workpiece is detected based on an image acquired by imaging the front surface of the substrate through the holding table and the tape.

Preferably, the substrate may be formed from silicon carbide (SiC).

In the machining method according to the aspect of the present invention, the workpiece is held by the holding table via the tape such that the ductile material layer is exposed, and the cutting blade is then rotated such that a portion of the cutting blade, the portion being located on the forward side in the moving direction of the cutting blade relative to the holding table, cuts into the workpiece from the ductile material layer toward the substrate, so that the workpiece is cut.

Accordingly, even in a situation where the ductile material layer with the ductile material contained therein is brought into close contact with the cutting blade and is stretched, the cutting blade comes into contact with the substrate formed with a material harder than the ductile material, so that the ductile material held in close contact with the cutting blade is removed from the cutting blade and remains substantially unstretched. As a consequence, the occurrence of burrs from the ductile material layer can be suppressed.

Further, the machining method according to the aspect of the present invention does not need to use a cutting apparatus and a laser processing apparatus in combination unlike a case that the ductile material layer is cut by a laser beam, and therefore, the workpiece can be machined by simple steps. According to the machining method of the aspect of the present invention, the workpiece can be machined by the simple steps, and the occurrence of burrs from the ductile layer can be suppressed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the attached drawings, a description will be made about an embodiment of the present invention.FIG.1is a perspective view depicting a workpiece1to be machined by a machining method according to the embodiment. As depicted inFIG.1, the workpiece1in the embodiment includes a substrate (wafer)11formed in a disc shape by using a semiconductor material such as SiC.

The substrate11is defined into a plurality of small regions by a plurality of mutually intersecting streets13, and devices (power devices)15such as inverters or converters for use in control of electric power are formed in the individual small regions. The resulting pattern of the devices15is configured to be distinguishable, for example, from a side of a front surface11aof the substrate11.

On a side of a back surface11bof the substrate11, the back surface11bbeing on a side opposite to the front surface11a, a ductile material layer17containing a ductile material such as a metal is disposed. The ductile material layer17is a metal film formed to a thickness of approximately 0.1 to 30 μm, for example, with a metal such as gold (Au), silver (Ag), Cu, aluminum (Al), titanium (Ti) or nickel (Ni), and functions as a heat sink, a die attach adhesive (paste), or the like.

The ductile material layer17is also formed in regions that overlap the streets13as seen from a side of the front surface11aor from a side of the back surface11bof the substrate11. The ductile material layer17may be a single-layer metal film formed with an alloy containing such a metal as mentioned above. As an alternative, the ductile material layer17may have a stacked structure in which a plurality of metal films, each being formed with a single kind of metal or metal alloy, is overlaid one over the other or another.

The workpiece1in the embodiment includes the disc-shaped substrate11formed with SiC or the like, and no significant limitation is imposed on the material, shape, structure, size, or the like of the substrate11. Examples of the workpiece1may also include a substrate11formed with another semiconductor such as Si, gallium arsenide (GaAs), or gallium phosphide (GaP), or a material such as a ceramic or resin. As will be described subsequently herein, however, the substrate11needs to be formed with a material that is harder than the ductile material contained in the ductile material layer17. Similarly, no limitations are imposed on the kind, number, shape, structure, size, arrangement, and the like of the devices15either. No devices15may be formed on the substrate11.

In the machining method according to the embodiment, a tape21(seeFIG.2) which is greater than the workpiece1is first bonded to a side of the substrate11of the workpiece1(in other words, the side of the front surface11aof the substrate11, that is, a side opposite to the ductile material layer17) (tape bonding step).FIG.2is a perspective view depicting the workpiece1with the tape21bonded thereon.

The tape21typically includes a film-shaped base material21a(seeFIG.7, etc.) and a glue layer21bdisposed on one side of the base material21a, and allows visible light to transmit therethrough. The base material21aof the tape21is formed, for example, with a material such as a polyolefin, polyvinyl chloride, or polyethylene terephthalate, while the glue layer21bof the tape21is formed, for example, with an acrylic or rubber-based material. If the tape21is brought on a side of the glue layer21bthereof into close contact with the side of the front surface11aof the substrate11, the tape21is bonded to the workpiece1.

On an outer peripheral portion on the side of the glue layer21bof the tape21, an annular frame23formed with a metal such as stainless steel or Al is fixed, for example. Therefore, the workpiece1is supported on the annular frame23via the tape21. However, the workpiece1can also be machined without using the tape21and the frame23.

As a further alternative, it is also possible to use a tape21that does not have the glue layer21b. If this is the case, the tape21is bonded to the substrate11and the frame23by a method such as heat bonding that applies a pressure while heating. The use of the tape21, which does not have the glue layer21b, further facilitates below-described positional matching (hereinafter called “alignment”) between a cutting blade52and the streets13of the workpiece1. From this viewpoint of facilitating the alignment, it is desired to use a tape21including a planar base material21a(for example, a base material21athat has not been subjected to an embossing treatment).

After the tape21has been bonded to the workpiece1, the workpiece1is held on the side of the substrate11thereof via the tape21such that the ductile material layer17is exposed (holding step).FIG.3is a perspective view depicting a cutting apparatus2for use in the machining method according to the embodiment. InFIG.3, a configuration element of the cutting apparatus2is indicated by a function block, and some configuration elements of the cutting apparatus2are omitted or simplified. In the following description, X-axis direction (machining feed direction), Y-axis direction (indexing feed direction), and Z-axis direction (height direction) are perpendicular to one another.

As depicted inFIG.3, the cutting apparatus2includes a bed4. On an upper surface of the bed4, an X/Y moving mechanism (machining feed mechanism and indexing feed mechanism)8is arranged. The X/Y moving mechanism8includes a pair of X-axis guide rails10, which is fixed on the upper surface of the bed4and is substantially parallel to the X-axis direction. On the X-axis guide rails10, an X-axis moving table12is attached in a slidable fashion.

On a side of a lower surface of the X-axis moving table12, nut portions (not depicted) are arranged. An X-axis ball screw14, which is substantially parallel to the X-axis guide rails10, is in threaded engagement with the nut portions. On an end of the X-axis ball screw14, an X-axis pulse motor16is connected. Rotation of the X-axis ball screw14by the X-axis pulse motor16causes the X-axis moving table12to move in the X-axis direction along the X-axis guide rails10. Besides the X-axis guide rails10, an X-axis scale10ais arranged for use upon detection of a position of the X-axis moving table12in the X-axis direction.

On an upper surface of the X-axis moving table12, a pair of Y-axis guide rails20is arranged substantially in parallel to the Y-axis direction. To the Y-axis guide rails20, a Y-axis moving table22is attached in a slidable fashion.FIG.4is a perspective view depicting a section of the cutting apparatus2, the section including the Y-axis moving table22, andFIG.5is a cross-sectional view depicting another section of the cutting apparatus2, the section including the Y-axis moving table22. InFIG.5, hatching of cross-sections is omitted for the sake of convenience of a description.

As depicted inFIGS.4and5, the Y-axis moving table22includes a bottom wall portion22a, which has a rectangular shape as seen from the Z-axis direction. On an end of the bottom wall portion22ain the Y-axis direction, a side wall portion22bis connected at a lower end thereof. The side wall portion22bhas a rectangular shape as seen from the Y-axis redirection. To an upper end of the side wall portion22b, a top wall portion22cis connected at an end thereof in the Y-axis direction. The top wall portion22chas a rectangular shape similar to that of the bottom wall portion22aas seen from the Z-axis redirection. Between the bottom wall portion22aand the top wall portion22c, a space22dis hence formed which is extending to an outside at the other ends of the bottom and top wall portions22a,22cin the Y-axis direction and also at opposite ends of the bottom and top wall portions22a,22cin the X-axis direction.

On a side of a lower surface of the bottom wall portion22aof the Y-axis moving table22, nut portions22e(seeFIG.5) are arranged, and a Y-axis ball screw24, which is substantially parallel to the Y-axis guide rails20, is in threaded engagement with the nut portions22e. On an end of the Y-axis ball screw24, a Y-axis pulse motor26is connected.

Rotation of the Y-axis ball screw24by the Y-axis pulse motor26causes the Y-axis moving table22to move in the Y-axis direction along the Y-axis guide rails20. Besides the Y-axis guide rails20, a Y-axis scale20a(seeFIG.3) is disposed for use upon detection of a position of the Y-axis moving table22in the Y-axis direction.

On a side of an upper surface of the top wall portion22cof the Y-axis moving table22, a holding table (chuck table)28is arranged for use upon holding the workpiece1. The holding table28is supported on the top wall portion22cin a fashion such that the holding table28can rotate about an axis of rotation which is substantially parallel to the Z-axis direction.

The holding table28includes a cylindrical frame member30formed, for example, using a metal represented by stainless steel. On an upper portion of the frame member30, a disc-shaped holding member32is disposed to close an opening on a side of the upper portion of the frame member30. The holding member32has a substantially planar upper surface32aand a lower surface32b(seeFIG.7, etc.) on a side opposite to the upper surface32a, and is formed with a transparent material, such as soda glass, borosilicate glass, or quartz glass, that allows visible light to transmit therethrough.

As depicted inFIG.4, in the upper surface32aof the holding member32, a plurality of grooves32cis formed for use upon suction of the workpiece1. A suction source (not depicted) including a vacuum ejector or the like is connected to the grooves32c, so that a negative pressure generated at the suction source is allowed to act on the grooves32c.

The holding member32is configured such that visible light is allowed to transmit through the holding member32at at least a region thereof other than the grooves32cand the like and the workpiece1and the like disposed on a side of the upper surface32aof the holding member32can be imaged from a side of the lower surface32bof the holding member32. In the embodiment, the holding member32formed in its entirety with the transparent material is described. It is, however, required for the holding member32to allow visible light to transmit through at least the portion thereof. In other words, the holding member32is not required to be formed with the transparent material alone.

On the side wall portion22bof the Y-axis moving table22, a rotary drive source34such as an electric motor is arranged. On a pulley portion30adisposed on an outer periphery of the frame member30and a pulley34aconnected to a rotating shaft of the rotary drive source34, a belt36is wrapped to transmit power of the rotary drive source34. The holding table28is therefore rotated about the axis of rotation, which is substantially parallel to the Z-axis direction, by the power transmitted from the rotary drive source34via the belt36.

On an outer peripheral portion of the frame member30, a plurality of clamps30bis arranged, in addition to the pulley portion30a, for use when fixing the annular frame23. The clamps30bare fixed on the frame member30in a fashion such that they do not interfere with rotation of the holding table28. The holding table28is also moved together with the X-axis moving table12and Y-axis moving table22in the X-axis direction and Y-axis direction by the above-mentioned X/Y moving mechanism8.

As depicted inFIG.3, a column-shaped or wall-shaped support structure38is disposed on the upper surface of the bed4in a region where the support structure38does not overlap the X/Y moving mechanism8. On a side wall of the support structure38, a Z-axis moving mechanism40is arranged. The Z-axis moving mechanism40includes a pair of Z-axis guide rails42, which is fixed on the side wall of the support structure38and is substantially parallel to the Z-axis direction.

To the Z-axis guide rails42, a spindle housing46which includes a cutting unit (machining unit)44is attached in a slidable fashion. On a side wall of the spindle housing46, the side wall being on a side of the support structure38, nut portions (not depicted) are disposed, and a Z-axis ball screw48is in threaded engagement with the nut portions. The Z-axis ball screw48is substantially parallel to the Z-axis guide rails42.

To an end portion of the Z-axis ball screw48, a Z-axis pulse motor50is connected. Rotation of the Z-axis ball screw48by the Z-axis pulse motor50causes the spindle housing46to move in the Z-axis direction along the Z-axis guide rails42. Besides the Z-axis guide rails42, a Z-axis scale (not depicted) is disposed for use upon detection of a position of the spindle housing46in the Z-axis direction.

The cutting unit44includes a spindle (not depicted) as a rotating shaft parallel to the Y-axis direction. The spindle is supported in a state that it can be rotated by the above-mentioned spindle housing46. A distal end portion of the spindle is exposed from the spindle housing46. On the distal end portion of the spindle, the cutting blade52with abrasive grains such as diamond fixed thereon by a binder such as a metal is fitted. To a side of a proximal end of the spindle, on the other hand, a rotary drive source (not depicted) such as an electric motor is connected.

On the spindle housing46of the cutting unit44, an upper imaging unit54is fixed to image the workpiece1and the like, which are held by the holding table28, from above. The upper imaging unit54is therefore moved together with the cutting unit44in the Z-axis direction by the Z-axis moving mechanism40.

In a region on the upper surface of the bed4, the region being remote in the Y-axis direction from the X/Y moving mechanism8, a pillar-shaped or panel-shaped imaging unit support structure56is disposed.FIG.6is a perspective view depicting a further section of the cutting apparatus2, the further section including the imaging unit support structure56. On a side wall of the imaging unit support structure56, an imaging unit moving mechanism58is arranged.

The imaging unit moving mechanism58includes a pair of Z-axis guide rails60, which is fixed on the side wall of the imaging unit support structure56and is substantially parallel to the Z-axis direction. To the Z-axis guide rails60, a Z-axis moving plate62is attached in a slidable fashion. Nut portions (not depicted) are arranged on the side wall of the Z-axis moving plate62, the side wall being on a side of the imaging unit support structure56, and a Z-axis ball screw64is in threaded engagement with the nut portions. The Z-axis ball screw64is substantially parallel to the Z-axis guide rails60.

To an end portion of the Z-axis ball screw64, a Z-axis pulse motor66is connected. Rotation of the Z-axis ball screw64by the Z-axis pulse motor66causes the Z-axis moving plate62to move in the Z-axis direction along the Z-axis guide rails60. Besides the Z-axis guide rails60, a Z-axis scale (not depicted) is disposed for use upon detection of a position of the Z-axis moving plate62in the Z-axis direction.

On the Z-axis moving plate62, a lower imaging unit70is fixed via a support arm68elongated in the Y-axis direction. The lower imaging unit70includes an illumination apparatus72configured to irradiate visible light onto an upper object (the workpiece1in the embodiment) and a camera74having an imaging element to receive light reflected from the object and to form an image.

To configuration elements such as the X/Y moving mechanism8, rotary drive source34, Z-axis moving mechanism40, cutting unit44, upper imaging unit54, imaging unit moving mechanism58, and lower imaging unit70, a control unit76is connected. The control unit76is configured, for example, by a computer including a processing apparatus such as a central processing unit (CPU) and a storage apparatus such as a flash memory, and controls operations of the individual configuration elements such that the workpiece1is adequately machined. Functions of the control unit76are realized by operating the processing apparatus according to software stored in the storage apparatus.

When holding the workpiece1on the side of the substrate11, the tape21bonded to the side of the substrate11of the workpiece1is first brought into contact with the upper surface32aof the holding member32of the holding table28as depicted inFIG.5. A negative pressure generated at the suction source is then allowed to act on the grooves32c. In addition, the frame23is fixed by the clamps30b. As a consequence, the workpiece1is held on the holding table28with the side of the ductile material layer17being exposed upward.

After the workpiece1has been held on the side of the substrate11thereof by the holding table28, desired one of the streets13, in other words, a position where the cutting blade52is to be caused to cut into the workpiece1is detected based on an image acquired by imaging the workpiece1from below (position detecting step).FIG.7is a fragmentary cross-sectional view illustrating how the workpiece1is imaged from below.

Descried specifically, operations of the X/Y moving mechanism8and imaging unit moving mechanism58are controlled by the control unit76such that, as illustrated inFIG.7, the lower imaging unit70is arranged below the region of the holding member32where visible light is allowed to transmit. Specifically, the lower imaging unit70is inserted into the space22dbetween the bottom wall portion22aand the top wall portion22cof the Y-axis moving table22. A positional relation between the holding member32and the lower imaging unit70is adjusted as desired within a range suited for imaging the workpiece1.

As mentioned above, the portion of the holding member32and the tape21allow visible light to transmit therethrough. Therefore, the front surface11aof the substrate11can be imaged to form an image if visible light is irradiated from the illumination apparatus72of the lower imaging unit70toward the workpiece1above the illumination apparatus72and light reflected by the lower surface of the workpiece1(the front surface11aof the substrate11) is received at the imaging element of the camera74. As described above, the front surface11aof the substrate11is imaged through the holding member32(holding table28) and the tape21in the embodiment.

The image acquired by the camera74is sent, for example, to the control unit76. The control unit76applies pattern matching, which extracts characteristic patterns or the like of the devices15, to the image sent from the camera74, and detects the position of the desired street13where the cutting blade52is to be caused to cut into the workpiece1. The detected position of the desired street13is stored in the storage apparatus of the control unit76.

Subsequent to the detection of the position of the desired street13, the rotating cutting blade52is caused to cut into the workpiece1to cut the workpiece1(cutting step).FIG.8is a fragmentary cross-sectional view illustrating how the workpiece1is cut. Described specifically, operation of the rotary drive source34is controlled, for example, by the control unit76such that the desired street13to be machined is brought into substantially parallel to the X-axis direction. In addition, operation of the X/Y moving mechanism8is controlled by the control unit76such that the position of the cutting blade52is aligned above an extension of the desired street13to be machined.

Operation of the Z-axis moving mechanism40is then controlled by the control unit76to adjust the position of the cutting unit44in the Z-axis direction such that the height of the lower extremity of the cutting blade52becomes lower than the height of the lower surface of the workpiece1(the front surface11aof the substrate11). Subsequently, as illustrated inFIG.8, the holding table28is moved in the X-axis direction (a first direction X1) by the X/Y moving mechanism8while rotating the cutting blade52. In other words, the holding table28and the cutting blade52are relatively moved in the X-axis direction.

Here, representing a direction in which the cutting blade52moves relative to the holding table28as a second direction X2(a direction opposite to the first direction X1), a direction R1in which the cutting blade52is rotated is set such that a portion52aof the cutting blade52, the portion52abeing located on a forward side in the second direction X2, cuts into the workpiece1from the ductile material layer17toward the substrate11. In other words, the cutting blade52is rotated such that the portion52aof the cutting blade52moves downwardly from above.

Even in such a situation that the ductile material layer17with the ductile material contained therein is brought into close contact with the cutting blade52and would hence be stretched by the cutting blade52, the rotation of the cutting blade52in the direction R1as described above brings the cutting blade52into contact with the substrate11formed with the material harder than the ductile material, so that the ductile material held in close contact with the cutting blade52is removed from the cutting blade52and remains substantially unstretched. Therefore, the occurrence of burrs from the ductile material layer17can be suppressed.

By the procedures described above, the cutting blade52is caused to cut into the workpiece1(the ductile material layer17and the substrate11) along the desired street13to be machined. As a result, the workpiece1is cut along the desired street13. These procedures are repeated until the workpiece1is cut along all the streets13set on the workpiece1.

It has already been confirmed that, if the conditions to be described next are satisfied, the occurrence of burrs from the ductile material layer17can be suppressed at a particularly high level. Use of such a thin cutting blade52as satisfying these conditions also significantly contributes to the suppression of the occurrence of burrs in that the volume of the ductile material layer17to be removed by cutting is reduced.

Material of substrate: SiC

Thickness of substrate: 50 μm or greater but 360 μm or smaller

Thickness of ductile material layer: 0.1 μm or greater but 30 μm or smaller

Intervals of streets: 0.5 mm or greater but 5 mm or smaller

Kind of cutting blade: electroformed blade

Thickness of cutting blade: 15 μm or greater but 40 μm or smaller

Grain size (grit) of abrasive grains contained in cutting blade: #1200 or greater but #2000 or smaller

Rotational speed of cutting blade (peripheral speed of cutting blade): 15,000 rpm or higher but 30,000 rpm or lower (2,600 m/min or higher but 5,300 m/min or lower)

Feed rate of holding table: 20 mm/s or higher but 100 mm/s or lower if a ductile material layer is formed on the C surface of SiC; 1 mm/s or higher but 10 mm/s or lower if a ductile material layer is formed on the Si surface of SiC

As described above, in the machining method according to the embodiment, after the workpiece1has been held by the holding table28via the tape21such that the ductile material layer17is exposed, the cutting blade52is rotated such that the portion52aof the cutting blade52, the portion52abeing located on the forward side in the moving direction (the second direction X2) of the cutting blade52relative to the holding table28, cuts into the workpiece1from the ductile material layer17toward the substrate11. As a result, the workpiece1is cut.

Even in such a situation that the ductile material layer17with the ductile material contained therein is brought into close contact with the cutting blade52and would hence be stretched by the cutting blade52, the cutting blade52comes into contact with the substrate11formed with the material harder than the ductile material, so that the ductile material held in close contact with the cutting blade52is removed from the cutting blade52and remains substantially unstretched. As a consequence, the occurrence of burrs from the ductile material layer17can be suppressed.

Also, in the machining method according to the embodiment, it is unnecessary to use a cutting apparatus and a laser processing apparatus in combination unlike a case that the ductile material layer17is cut by a laser beam, and therefore, the workpiece1can be machined by the simple steps. According to the machining method of the embodiment, the workpiece1can be machined by the simple steps, and the occurrence of burrs from the ductile material layer17can be suppressed.

It is to be noted that the present invention can be practiced with various changes without limitation to or by the description of the above-mentioned embodiment. For example, it has been confirmed that, when a workpiece including a substrate formed with Si is machined, satisfaction of the following conditions makes it possible to suppress the occurrence of burrs from a ductile material layer at a high level. Use of such a thin cutting blade as satisfying these conditions also significantly contributes to the suppression of the occurrence of burrs in that the volume of the ductile material layer to be removed by cutting is reduced.

Material of substrate: Si

Thickness of substrate: 10 μm or greater but 300 μm or smaller

Thickness of ductile material layer: 0.1 μm or greater but 30 μm or smaller

Intervals of streets: 0.1 mm or greater but 5 mm or smaller

Kind of cutting blade: electroformed blade

Thickness of cutting blade: 5 μm or greater but 40 μm or smaller

Grain size (grit) of abrasive grains contained in cutting blade: #1500 or greater but #3500 or smaller

Rotational speed of cutting blade (peripheral speed of cutting blade): 15,000 rpm or higher but 60,000 rpm or lower (2,600 m/min or higher but 10,500 m/min or lower)

Feed rate of holding table: 30 mm/s or higher but 200 mm/s or lower

In the embodiment mentioned above, the description is made about the example in which the workpiece1is cut by the cutting blade52. However, the machining method according to the present invention can also be applied when half-cutting a workpiece by a cutting blade. If this is the case, it is only necessary to adjust the position of the cutting unit in the Z-axis direction such that the height of the lower extremity of the cutting blade becomes higher than the lower surface of the workpiece (the front surface of the substrate) and lower than the height of an interface between the substrate and the ductile material layer (the back surface of the substrate).

In the embodiment mentioned above, the description is also made about the example in which the workpiece1including the metal film as the ductile material layer17is machined. The ductile material layer included in the workpiece is, however, not required to be such a metal film insofar as it contains a ductile material having higher ductility than that of the material of the substrate. For example, the ductile material layer may be a resin film or the like formed using a resin. Further, the ductile material layer may be arranged on the side of the front surface of the substrate.

Besides, the structures, methods, and the like according to the above-mentioned embodiment and modifications can be practiced with changes as needed to such extent as not departing from the scope of the object of the present invention.