CHIP MANUFACTURING METHOD

A chip manufacturing method for manufacturing a plurality of chips by dividing a workpiece with a plurality of intersecting streets set thereon includes a cutting step of cutting a front surface of the workpiece by a cutting blade to thereby form cut grooves along the streets, and then a grinding step of grinding a back surface on the side opposite to the front surface of the workpiece to thereby thin the workpiece to a finish thickness of reaching the cut grooves and to divide the workpiece into the plurality of chips. The cut grooves are formed such that the position of the groove bottom in the thickness direction of the workpiece varies in the width direction of the cut groove, and, in the grinding step, grinding is started from that tip of the groove bottom of the cut groove which is remote from the front surface of the workpiece.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a manufacturing method for manufacturing a plurality of chips by dividing a workpiece with a plurality of intersecting streets set thereon.

Description of the Related Art

As a technique for thinning a semiconductor wafer and dividing the wafer into individual device chips, a process called dicing before grinding (DBG) has been proposed (see, for example, Japanese Patent Laid-open No. 2003-007653).

In the DBG process, a front surface side of the wafer formed with devices is cut along streets by a cutting blade to form cut grooves having a depth smaller than a thickness of the wafer along the streets. Thereafter, a front surface protective member is disposed on the front surface side of the wafer, and then a back surface side of the wafer is subjected to grinding, so that the grooves are exposed on the back surface side of the wafer and the wafer is divided into a plurality of device chips.

SUMMARY OF THE INVENTION

However, the method disclosed in Japanese Patent Laid-open No. 2003-007653 has a problem that, when the back surface side of the wafer is gradually ground, the groove bottoms of the cut grooves would become thinner and be cracked during grinding, and fragments would drop. If the fragments are deposited on other devices during a later step or handling of the wafer, device defects might be caused.

Accordingly, it is an object of the present invention to provide a chip manufacturing method by which it is possible to restrain fragments from dropping during grinding.

In accordance with an aspect of the present invention, there is provided a manufacturing method for manufacturing a plurality of chips by dividing a workpiece with a plurality of intersecting streets set thereon, the manufacturing method including a cutting step of cutting one surface of the workpiece by a cutting blade to thereby form cut grooves along the streets, and a grinding step of grinding another surface on a side opposite to the one surface of the workpiece to thereby thin the workpiece to a finish thickness of reaching the cut grooves and to divide the workpiece into the plurality of chips, after the cutting step is carried out. In the manufacturing method, the cut grooves are formed such that a position of a groove bottom in a thickness direction of the workpiece varies in a width direction of the cut groove, and, in the grinding step, grinding is started from a tip of the groove bottom.

Preferably, in the cutting step, depths of all the groove bottoms of the cut grooves from the one surface are greater than the finish thickness from the one surface. Preferably, in the cutting step, the cut grooves are formed by a cutting blade of which a blade thickness is gradually reduced toward a tip.

Preferably, in the cutting step, the cutting blade is caused to cut into each street a plurality of times with a cutting-in depth and a cutting-in position varied.

The present invention produces an effect that it is possible to restrain fragments from dropping during grinding.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detail below with reference to the drawings. The present invention is not to be limited by the contents of the embodiments described below. In addition, the constituent elements described below include those which can easily be conceived of by a person skilled in the art and those which are substantially the same. Further, the configurations described below can be combined with one another as required. Besides, various kinds of omission, replacement, or modification of the configuration can be made in such ranges as not to depart from the gist of the invention.

First Embodiment

A manufacturing method according to a first embodiment of the present invention will be described with reference to the drawings.FIG.1is a perspective view schematically depicting a workpiece as an object to the processed by the manufacturing method according to the first embodiment.FIG.2is a flowchart depicting the flow of the manufacturing method according to the first embodiment.

The manufacturing method according to the embodiment is a method of processing a workpiece1depicted inFIG.1. The workpiece1as the object to be processed by the manufacturing method according to the embodiment is a wafer such as a disk-shaped semiconductor wafer or optical device wafer having a substrate2formed of silicon (Si), gallium arsenide (GaAs), silicon carbide (SiC), sapphire, or the like.

The workpiece1has a plurality of intersecting streets4set on a front surface3(corresponding to one surface) thereof, and devices5are respectively formed in regions partitioned by the streets4on the front surface3. The devices5are, for example, integrated circuit devices such as integrated circuits (ICs) or large scale integration (LSI) circuits, image sensors such as charge coupled device (CCD) image sensors or complementary metal oxide semiconductor (CMOS) image sensors, optical devices such as light-emitting diodes (LEDs), micro electro mechanical systems (MEMS), or semiconductor memories (semiconductor storage devices).

The workpiece1is thinned to a finish thickness6, and is divided along the streets4into individual chips10. Note that the chips10each include a part of the substrate2and the device5.

In addition, in the first embodiment, unillustrated test element groups (TEGs) are formed on the front surface3in the streets4. The TEG is an element configured by use of conductive metal and is used for evaluation for finding out problems on design basis or manufacture basis that have occurred in the devices5.

Note that, in the present invention, the workpiece1may not have the devices5formed thereon, and are not limited to such wafers as semiconductor wafers and optical device wafers; for example, the workpiece1may be a rectangular package substrate having a plurality of devices which are sealed with resin, a ceramic substrate, a glass substrate, or the like.

The manufacturing method according to the first embodiment is a method of manufacturing a plurality of chips10by dividing the workpiece1formed with the plurality of intersecting streets4along the streets4. The manufacturing method according to the first embodiment includes a cutting step101and a grinding step102, as depicted inFIG.2.

FIG.3is a front view of a cutting unit used in the cutting step of the manufacturing method depicted inFIG.2.FIG.4is a front view of an edge point of a cutting blade of the cutting unit depicted inFIG.3.FIG.5is a perspective view schematically depicting the cutting step of the manufacturing method depicted in FIG.2.FIG.6is a sectional view depicting a major part of the workpiece that has undergone the cutting step of the manufacturing method depicted inFIG.2.FIG.7is a front view of a modification of the cutting unit depicted inFIG.3.FIG.8is a front view of an edge point of a cutting blade of the cutting unit depicted inFIG.7.

The cutting step101is a step of cutting the front surface3of the workpiece1by the cutting blade21depicted inFIGS.3and4, to thereby form cut grooves11(depicted inFIGS.5and6) along the streets4. In the first embodiment, the cutting blade21used in the cutting step101is mounted to a tip of a spindle23of a cutting unit22of a cutting apparatus20, is rotated around an axis of the spindle23, and cuts the workpiece1.

In the first embodiment, the cutting blade21is an extremely thin cutting grindstone having a substantially annular shape. In the first embodiment, the cutting blade21is what is generally called a hub blade that includes an annular base24and an annular cutting edge25disposed at a peripheral edge of the annular base24and used to cut the workpiece1. The cutting edge25is configured by abrasive grains of diamond, cubic boron nitride (CBN), or the like and a bonding material (binder) such as metal or resin, and is formed in a predetermined thickness. Note that, in the present invention, the cutting blade21may be what is generally called a washer blade that does not include the annular base24but only the annular cutting edge25.

In the first embodiment, an edge point26of the cutting edge25of the cutting blade21is formed in a V shape in which it is the greatest in outside diameter at the center in the thickness direction and is gradually reduced in outside diameter from the center in the thickness direction toward both surfaces. In the first embodiment, the cutting blade21is what is generally called a V blade. In the first embodiment, the edge point26of the cutting edge25of the cutting blade21has two tip surfaces271and272that intersect each other and are flat in section, as depicted inFIG.4. Note that an angle θ formed between the tip surfaces271and272of the edge point26of the cutting edge25of the cutting blade21is not less than 120° but not more than 160°. Thus, in the cutting step101, the cut grooves11are formed by the cutting blade21of which the blade thickness is gradually reduced toward the tip.

In the cutting step101of the first embodiment, the cutting apparatus20performs alignment in which a back surface7(corresponding to the other surface) of the workpiece1is held under suction on a holding surface of a chuck table, the chuck table is moved toward a processing region, the workpiece1is imaged by an unillustrated imaging unit, and alignment between the street4and the cutting edge25of the cutting blade21is performed. In the cutting step101of the first embodiment, while supplying cutting water to the cutting blade21rotated around an axis and moving the workpiece1and the cutting unit22relative to each other along the street4, the cutting apparatus20causes the cutting blade21to sequentially cut into the streets4in a cutting-in depth greater than the finish thickness6, to thereby form the workpiece1with the cut grooves11along the streets4, as depicted inFIG.5.

In the cutting step101of the first embodiment, the cutting apparatus20causes the cutting blade21to cut once into each street4from the front surface3side of the workpiece1in a cutting-in depth greater than the finish thickness6. Hence, in the cutting step101of the first embodiment, the cutting apparatus20forms the cut groove11having a V-shaped groove bottom12at each street4, as depicted inFIG.6. In this way, in the cutting step101of the first embodiment, the depths of all the groove bottoms12of the cut grooves11from the front surface3are formed to be greater than the finish thickness6from the front surface3, and the cut grooves11are each formed such that the position of the groove bottom12in the thickness direction of the workpiece1varies in the width direction of the cut groove11.

In addition, in the first embodiment of the present invention, a cutting blade21-1used in the cutting step101may be what is generally called a one-side V blade in which a tip surface273of the edge point26of the cutting edge25is formed of one surface which is inclined relative to the axis and the section of which is flat.

In addition, in the cutting step101of the first embodiment, the cut grooves11having a width13of not less than 50 μm but not more than 150 μm are formed. Besides, in the present invention, the width13of the cut grooves11is preferably such a width that the TEG formed on the street4can completely be removed by cutting.

Note that the cutting blade21or21-1to be used in the above-described cutting step101may be such a blade that the edge point26of the cutting edge25is in an R shape or tapered, but, in that case, management of the shape of the edge point26is difficult (shaping into a desired shape is difficult), and, hence, the cutting blade21or21-1to be used in the cutting step is preferably the V blade depicted inFIG.4or the one-side V blade depicted inFIG.8. Besides, the cutting blade21or21-1is desirably subjected to checking of the shape of the edge point26of the cutting edge25at a predetermined timing and is desirably subjected to dressing to be reshaped into the V shape or the one-side V shape.

When the shape of the edge point26of the cutting edge25of the cutting blade21or21-1is reshaped, the cutting edge25is caused to cut into a dress board to reshape the edge point26. Specifically, when the shape of the edge point26of the cutting edge25of the cutting blade21or21-1is reshaped, the cutting edge25is caused to cut into the dress board in the same motion as that in flat dressing (that is, the rotating cutting blade21is moved along the axis from a state in which the cutting blade21is positioned at a predetermined cutting-in depth and is positioned on the peripheral side of the dress board). Note that, by adjustment of the kind of the dress board to be used (the size of the abrasive grains contained and the binder) and the Y-axis moving speed, an inclination in the thickness direction is formed at the edge point26of the cutting edge25of the cutting blade21or21-1. In the case of forming the edge point26into the one-side V shape, the cutting blade21is moved in only one way in the axis direction to form the one-side V shape, and, in the case of forming the edge point26into the V shape, the cutting blade21is moved in only one way in the axis direction to form an inclination in a region of one half in the thickness direction and is thereafter moved in the other way in the axis direction to form an inclination in the region of the remaining one half in the thickness direction.

FIG.9is a perspective view schematically depicting a state in which the front surface protective member is stuck to the front surface of the workpiece in the grinding step of the manufacturing method depicted inFIG.2.FIG.10is a sectional view schematically depicting a major part of the workpiece with the front surface protective member stuck to the front surface thereof in the grinding step of the manufacturing method depicted inFIG.2.FIG.11is a perspective view schematically depicting an intermediate point of grinding of the back surface of the workpiece in the grinding step of the manufacturing method depicted inFIG.2.FIG.12is a sectional view schematically depicting a major part of the workpiece of which the back surface is ground in the grinding step of the manufacturing method depicted inFIG.2.FIG.13is a sectional view schematically depicting a major part of the workpiece that has undergone the grinding step of the manufacturing method depicted inFIG.2.

The grinding step102is a step of grinding the back surface7as the other surface on the side opposite to the front surface3of the workpiece1to thereby thin the workpiece1to the finish thickness6of reaching the cut grooves11and to divide the workpiece1into a plurality of chips10, after the cutting step101is carried out. In the grinding step102of the first embodiment, the front surface protective member14depicted inFIGS.9and10is stuck to the front surface3of the workpiece1.

Note that, in the first embodiment, the front surface protective member14is a pressure sensitive adhesive tape including a base material configured by flexible and non-sticky resin and a glue layer laminated on the base material and configured by flexible and sticky resin. In the present invention, the front surface protective member14may be a glueless tape which has no glue layer but only a base material configured by non-sticky thermoplastic resin and is to be thermocompression-bonded to the workpiece, or may be a hard plate formed in a disk shape from rigid resin.

In the grinding step102of the first embodiment, a grinding apparatus30holds under suction the front surface3side of the workpiece1by a holding surface32of a chuck table31, with the front surface protective member14therebetween. In the grinding step102of the first embodiment, while rotating a grinding wheel34for grinding around an axis by the spindle33, rotating the chuck table31around an axis, and supplying grinding water from an unillustrated grinding water nozzle, the grinding apparatus30puts a grinding grindstone35of the grinding wheel34into contact with the back surface7of the workpiece1and brings the grinding grindstone35closer to the chuck table31at a predetermined feed rate, to thereby grind the back surface7side of the workpiece1by the grinding grindstone35, as depicted inFIG.11.

In the grinding step102of the first embodiment, the grinding apparatus30grinds the workpiece1from that tip of the groove bottom12of the cut groove11which is on the side remote from the front surface3, as depicted inFIG.12. In the grinding step102of the first embodiment, as depicted inFIG.13, when the thickness of the workpiece1has become the finish thickness6, the grinding apparatus30spaces the grinding wheel34away from the back surface7of the workpiece1, to thereby finish the grinding step102. As a result, the cut grooves11are exposed on the back surface7side of the workpiece1, and the workpiece1is divided into the individual chips10. In this way, in the grinding step102of the first embodiment, the workpiece1is ground from the tip of the groove bottom12of the cut groove11.

The manufacturing method according to the first embodiment described above is configured such that, in the cutting step101, the cut grooves11are formed in such a manner that the depth of the groove bottom12of the cut groove11from the front surface3varies in the width direction. Hence, in the grinding step102of the manufacturing method according to the first embodiment, the workpiece1is gradually ground from that tip of the groove bottom12of the cut groove11which is remote from the front surface3, and, accordingly, fragments are less likely to drop into the cut grooves11.

Consequently, the manufacturing method according to the first embodiment produces such an effect that it is possible to restrain the fragments from dropping during grinding.

Second Embodiment

A manufacturing method according to a second embodiment of the present invention will be described with reference to the drawings.FIG.14is a front view of a cutting unit used in a cutting step of the manufacturing method according to the second embodiment.FIG.15is a front view of an edge point of a cutting blade of the cutting unit depicted inFIG.14.FIG.16is a sectional view schematically depicting a major part of a workpiece during a cutting step of the manufacturing method according to the second embodiment.FIG.17is a front view of a modification of the cutting unit depicted inFIG.14.FIG.18is a front view of the edge point of the cutting blade of the cutting unit depicted inFIG.17.FIG.19is a sectional view schematically depicting a major part of a workpiece with a front surface protective member stuck to a front surface thereof in a grinding step of the manufacturing method according to the second embodiment.FIG.20is a sectional view schematically depicting a major part of a workpiece at an intermediate point of grinding of a back surface thereof in the grinding step of the manufacturing method according to the second embodiment.FIG.21is a sectional view schematically depicting a major part of the workpiece that has undergone the grinding step of the manufacturing method according to the second embodiment. InFIGS.14,15,16,17,18,19,20, and21, the same parts as those in the first embodiment described above are denoted by the same reference characters, and descriptions of them are omitted.

In the second embodiment, a cutting blade21-2used in the cutting step101is configured such that a tip surface274of the edge point26of the cutting edge25is formed to be flat along the axis, as depicted inFIGS.14and15. In the cutting step101of the second embodiment, the cutting apparatus20causes the cutting blade21-2to cut into each street4of the workpiece1a plurality of times with the cutting-in depth varied at least once, to thereby form the cut grooves which are parallel to one another and are continuous with one another. In this way, in the cutting step101of the second embodiment, as depicted inFIG.16, the cutting apparatus20causes the cutting blade21-2to cut into each street4a plurality of times with the cutting-in depth and the cutting-in position varied, to thereby form one cut groove11with a step formed at the groove bottom12at each street4.

Note that, in the example depicted inFIG.16, the cutting blade21-2is caused to cut into each street4three times at different positions in the width direction, such that the cutting-in depths of the cutting blade21-2at both ends in the width direction of the street4indicated by a broken line and a long and two short dashes line are the same, whereas the cutting-in depth of the cutting blade21-2at the center in the width direction of the street4indicated by a solid line is deeper than the cutting-in depths at both ends in the width direction. Note that, in the second embodiment, also, the cutting-in depth of the cutting blade21-2is greater than the finish thickness6.

In this way, in the cutting step101of the manufacturing method according to the second embodiment, the depths from the front surface3of all the groove bottoms12of the cut grooves11are formed to be greater than the finish thickness6from the front surface3, and the cut grooves11each have a step formed at the groove bottom12in the thickness direction of the workpiece1, such that the position of the groove bottom12varies in the width direction of the cut groove11.

Note that, in the second embodiment of the present invention, a cutting blade21-3used in the cutting step101may be configured such that a tip surface275of the edge point26of the cutting edge25is arcuate in section, as depicted inFIGS.17and18. Note that, in the second embodiment of the present invention, a mode in which the cut groove11is formed by three times of cutting at each street4is not limitative, and it is sufficient that the cut groove11is formed by a plurality of times of cutting. Further, the form in which the center in the width direction of the cut groove11is the deepest is not limitative, and the cut groove11may be formed such that the cut groove11becomes deeper from one side toward the other side in the width direction of the groove.

In the grinding step102of the manufacturing method according to the second embodiment, as in the first embodiment, the front surface protective member14is stuck to the front surface3of the workpiece1, as depicted inFIG.19. In the grinding step102of the manufacturing method according to the second embodiment, as in the first embodiment, the back surface7of the workpiece1is ground, and the workpiece1is ground from that tip of the groove bottom12of the cut groove11which is on the side remote from the front surface3, as depicted inFIG.20. In the grinding step102of the manufacturing method according to the second embodiment, as in the first embodiment, when the thickness of the workpiece1has become the finish thickness6, the grinding apparatus30spaces the grinding wheel34away from the back surface7of the workpiece1, to thereby end the grinding step102, as depicted inFIG.21. As a result, the cut grooves11are exposed on the back surface7side of the workpiece1, and the workpiece1is divided into the individual chips10. In this way, in the grinding step102of the first embodiment, the workpiece1is ground from the tip of the groove bottom12of the cut groove11.

The manufacturing method according to the second embodiment is configured such that, in the cutting step101, the cut grooves11are formed in such a manner that the depth from the front surface3of the groove bottom12of the cut groove11varies in the width direction, and, in the grinding step102, the workpiece1is gradually ground from that tip of the groove bottom12of the cut groove11which is on the side remote from the front surface3; hence, as in the first embodiment, the manufacturing method according to the second embodiment produces an effect that it is possible to restrain the fragments from dropping during grinding.

Next, the inventor of the present invention checked the effect of the manufacturing method according to the first embodiment. In checking, the dropped state of fragments in the grinding step102when the cut grooves11were formed by cutting blades21having different angles θ and other relevant matters were checked. The results are set forth in Table 1 below.

Note that, in Comparative Example 1, the cut grooves11were formed by cutting each street4only once by the cutting blade21-2having an angle θ of 180 degrees, that is, the cutting blade21-2depicted inFIG.15. In Comparative Example 2, the cut grooves11were formed by cutting each street4only once by a cutting blade21having an angle θ of 170 degrees. In Comparative Example 3, the cut grooves11were formed by cutting each street4only once by a cutting blade21having an angle θ of 110 degrees.

In the First Inventive Item, the cut grooves11were formed by cutting each street4only once by a cutting blade21having an angle θ of 160 degrees. In the Second Invention Item, the cut grooves11were formed by cutting each street4only once by a cutting blade21having an angle θ of 150 degrees. In the Third Inventive Item, the cut grooves11were formed by cutting each street4only once by a cutting blade21having an angle θ of 140 degrees. In the Fourth Inventive Item, the cut grooves11were formed by cutting each street4only once by a cutting blade21having an angle θ of 130 degrees. In the Fifth Inventive Item, the cut grooves11were formed by cutting each street4only once by a cutting blade21having an angle θ of 120 degrees.

According to Table 1, in Comparative Examples 1 and 2, dropping of fragments occurred during the grinding step102. In Comparative Example 3, dropping of fragments did not occur, but, due to an increase in the cutting-in amount of the cutting blade21, the processing time for forming the cut grooves11was prolonged unfavorably.

In contrast to these Comparative Examples 1, 2, and 3, the First to Fifth Inventive Items were free of the problem of fragments dropping during the grinding step102, and were free of the problem of prolongation of the processing time for forming the cut grooves11.

According to Table 1, it has been made clear that, when the cut grooves11are formed by a cutting blade21having an angle θ of not less than 120 degrees but not more than 160 degrees, preferably an angle θ of not less than 120 degrees but not more than 130 degrees, there arises no problem of dropping of fragments during the grinding step102and also no problem of prolongation of the processing time for forming the cut grooves11.

Note that the present invention is not to be limited to the above-described embodiments. In other words, various modifications can be made in carrying out the present invention in such ranges as not to depart from the gist of the invention.