Patent Application
20240189962
The present invention relates to a dressing member for use in dressing grinding stones.
Device chips with devices included therein are manufactured by dividing a wafer, on which the devices are formed, into individual chips. Further, a package substrate is formed by mounting such device chips on a predetermined substrate, and covering and sealing the device chips with a resin layer (mold resin). By dividing and singulating such a package substrate, package devices are each manufactured including a plurality of the packaged devices. Device chips and package devices are incorporated in various kinds of electronic equipment such as mobile phones and personal computers.
Reflecting a move toward smaller electronic equipment in recent years, there is a growing demand for thinner device chips and package devices. Processing may hence be performed to grind and thin a wafer or a package substrate by a grinding apparatus before its division. The grinding apparatus includes a chuck table that holds a workpiece, and a grinding unit that applies grinding processing to the workpiece. The grinding unit includes a spindle, and an annular grinding wheel with a plurality of grinding stones included thereon is mounted on a distal end portion of the spindle. The workpiece is ground by being held on the chuck table, and grinding stones at grinding surfaces thereof being brought into contact with the workpiece while the chuck table and the grinding wheel are rotated (see JP 2000-288881A).
A grinding stone is formed by fixing abrasive grits of diamond or the like with a binder (bonding material). It is to be noted that, unless the abrasive grits of the grinding stone are appropriately exposed from the binder, the grinding stone has low grinding ability, leading to an increased force (grinding load) acting on a workpiece and the grinding stone during grinding processing. This is more likely to cause a processing failure such as chipping on the workpiece. If there are variations in height positions of grinding surfaces of a plurality of grinding stones, a workpiece is not ground uniformly and has lowered quality. Dressing may therefore be performed with tuning of conditions of grinding stones by purposely abrading the grinding stones on a side of their grinding surfaces before the grinding or in the course of the grinding of the workpiece (see JP 2009-142906A). The dressing of the grinding stones is performed by bringing the grinding stones into contact with a member for dressing (dressing member, dressing board) while rotating the grinding stones. This causes abrasive grits of the grinding stones to be appropriately exposed from a binder (setting), and also allows the grinding surfaces of the grinding stones to align (truing).
A dressing member for use in dressing grinding stones is formed by fixing abrasive grits with a binder (bonding material). As the abrasive grits for the dressing member, ceramic grits having sharp-cornered random shapes (angular shapes), such as white alundum (WA) or green carborundum (GC), are used in general. If dressing of grinding stones is performed using the above-described dressing member, however, sharp corners of the abrasive grits of the angular shape, the abrasive grits protruding from the binder of the dressing member, come into contact with the grinding stones, so that deep irregularities and scratches are more likely to be formed on the side of the grinding surfaces of the grinding stones. If a workpiece is ground by grinding stones of such conditions, an unstable grinding load is applied, so that a processing failure is more likely to occur.
After a dressing member has been ground by grinding stones, a step called “provisional grinding” is therefore performed. In this provisional grinding step, a test workpiece (dummy wafer) is additionally ground by the grinding stones to bring the side of grinding surfaces of the grinding stones into conditions suited for grinding workpieces. By performing the provisional grinding, irregularities and scratches formed on the side of the grinding surfaces of the grinding stones are removed or reduced. In the provisional grinding, however, there is a need to grind a number (for example, approximately 400 to 500 pieces) of test workpieces. This leads to increases in the time and cost required for the dressing of the grinding stones.
With such problems in view, the present invention has as an object thereof the provision of a dressing member that can simplify a dressing step for grinding stones.
In accordance with an aspect of the present invention, there is provided a dressing member for use in dressing grinding stones containing spherical abrasive grits, and a binder fixing the abrasive grits.
Preferably, the abrasive grits may be silica grits, and the abrasive grits may have a ratio of minor axis to major axis of 0.7 or greater. Also preferably, the abrasive grits may be contained at a content of 20 wt % or higher but 80 wt % or lower. Also preferably, the abrasive grits may have an average grit size of 0.1 μm or greater but 3.5 μm or smaller. Also preferably, the binder may be a vitrified bond or a resin bond.
The dressing member according to the aspect of the present invention contains spherical abrasive grits. This suppresses the formation of irregularities and scratches caused by contact of the dressing stones and the abrasive grits during dressing, and simplifies a dressing step for the grinding stones.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing a preferred embodiment of the invention.
With reference to the attached drawings, a description will hereinafter be made of an embodiment according to an aspect of the present invention. A description will first be made about a configuration example of a grinding apparatus that can perform dressing of grinding stones with a dressing member according to this embodiment.
The grinding apparatus 2 is a processing apparatus that grinds a workpiece 11. For example, the workpiece 11 is a disk-shaped wafer made from a semiconductor material such as single crystal silicon, and includes a front surface (first surface) 11a and a back surface (second surface) 11b, which are substantially parallel to each other. The workpiece 11 is defined into a plurality of rectangular regions by a plurality of streets (scribe lines) arrayed in a grid pattern such that they intersect together. Further, the regions defined by the streets are formed on a side of the front surface 11a with devices (not depicted) such as integrated circuits (ICs), large scale integration (LSI) circuits, light emitting diodes (LEDs), or micro electro mechanical systems (MEMS) devices, respectively.
By dividing the workpiece 11 along the streets, a plurality of devices chips is manufactured with the devices included respectively therein. If the workpiece 11 is thinned before its division by grinding the workpiece 11 on a side of the back surface 11b with the grinding apparatus 2, thinned device chips are obtained.
However, no limitations are imposed on the material, shape, construction, size, and the like of the workpiece 11. For example, the workpiece 11 may be a substrate (wafer) made from a semiconductor (GaAs, InP, GaN, SiC, or the like) other than silicon, glass (silica glass, borosilicate glass, or the like), a ceramic, resin, a metal, or the like. Further, no limitations are imposed on the kind, number, shape, construction, size, arrangement, and the like of the devices, and no devices may be formed on the workpiece 11.
The grinding apparatus 2 includes a chuck table (holding table) 4 that holds the workpiece 11. The chuck table 4 has an upper surface, which is a planar surface substantially parallel to a horizontal plane (X-Y plane), and configures a holding surface 4a that holds the workpiece 11. Described specifically, the chuck table 4 includes a cylindrical frame body (main body portion) 6 made from metal such as stainless steel (SUS), glass, ceramic, or resin. A cylindrical recessed portion 6b is disposed in a central potion on a side of an upper surface 6a of the frame body 6. A disk-shaped holding member 8 made from a porous material such as porous ceramics is fitted in the recessed portion 6b of the frame body 6. The holding member 8 includes a number of pores that establish communication from an upper surface to a lower surface of the holding member 8. The upper surface of the holding member 8 configures a circular suction surface 8a that draws the workpiece 11 under suction when holding the workpiece 11 on the chuck table 4. By the upper surface 6a of the frame body 6 and the suction surface 8a of the holding member 8, the holding surface 4a of the chuck table 4 is configured. The holding surface 4a is connected to a suction source (not depicted) such as an ejector via the pores included in the holding member 8, a flow passage (not depicted) disposed inside the frame body 6, a valve (not depicted), and the like.
To the chuck table 4, a moving unit (not depicted) is connected to move the chuck table 4 along the horizontal direction (X-Y plane direction). The moving unit is configured, for example, by a moving mechanism of the ball screw type or a turntable. To the chuck table 4, a rotary drive source (not depicted) such as a motor is also connected to rotate the chuck table 4 about an axis of rotation set substantially perpendicular to a radial direction of the holding surface 4a.
A grinding unit 10 is disposed above the chuck table 4 to apply grinding processing to the workpiece 11. The grinding unit 10 includes a cylindrical spindle 12 arranged along the Z-axis direction. To a proximal end portion (upper end portion) of the spindle 12, a rotary drive source (not depicted) such as a motor is connected to rotate the spindle 12. On a distal end portion (lower end portion) of the spindle 12, a disk-shaped wheel mount 14 made from metal or the like is fixed. On a side of a lower surface of the wheel mount 14, an annular grinding wheel 16 is detachably secured to grind the workpiece 11. The grinding wheel 16 is fixed on the wheel mount 14, for example, by fixtures such as bolts.
The grinding wheel 16 includes an annular wheel base 18, which is made from metal such as aluminum or stainless steel and is formed with substantially the same diameter as the wheel mount 14. The wheel base 18 is fixed on a side of an upper surface thereof to a side of a lower surface of the wheel mount 14. On a side of a lower surface of the wheel base 18, a plurality of grinding stones 20 is fixed. For example, the grinding stones 20 are each formed in a parallelepiped shape, and are arrayed at substantially equal intervals in an annular pattern along the direction of a periphery of the wheel base 18. Lower surfaces of the grinding stones 20 configure grinding surfaces 20a that grind the workpiece 11. The grinding stones 20 contain abrasive grits made of diamond, cubic boron nitride (cBN), or the like, and a binder (bonding material), such as a metal bond, resin bond, or vitrified bond, that keeps the abrasive grits fixed. However, no limitations are imposed on the material, shape, construction, size, and the like of the grinding stones 20. Further, the number of the grinding stones 20 can also be set as desired.
By power transmitted from the rotary drive source (not depicted), which is connected to the spindle 12, via the spindle 12 and wheel mount 14, the grinding wheel 16 is rotated about an axis of rotation that is substantially parallel to the Z-axis direction. When the grinding wheel 16 is rotated, the grinding stones 20 are each caused to rotate about the axis of rotation of the spindle 12 and grinding wheel 16 and along a rotation track (rotation path) substantially parallel to the horizontal plane (X-Y plane).
To the grinding unit 10, a moving unit (not depicted) is connected to move (lift and lower) the grinding unit 10 along the Z-axis direction. The moving unit is configured, for example, by a Z-axis moving mechanism of the ball screw type. Described specifically, the moving unit includes a ball screw (not depicted) arranged along the Z-axis direction, a pulse motor (not depicted) that rotates the ball screw, and a nut portion (not depicted) that is connected to the grinding unit 10 and maintained in threaded engagement with the ball screw. When the grinding unit 10 is lifted up or down by the Z-axis moving mechanism, the grinding wheel 16 is relatively moved with respect to the chuck table 4, so that the holding surface 4a and the grinding wheel 16 separate from or approach each other.
Inside or adjacent to the grinding unit 10, a grinding fluid supply channel (not depicted) is disposed to supply liquid (grinding fluid) such as pure water. When grinding the workpiece 11 by the grinding wheel 16, the grinding fluid is supplied to the workpiece 11 and grinding stones 20. As a consequence, the workpiece 11 and grinding stones 20 are cooled, and at the same time debris (grinding debris) occurred by grinding processing is washed away.
The grinding apparatus 2 further includes a controller (control unit, control section, control device) (not depicted) that controls the grinding apparatus 2. The controller is connected to elements (the chuck table 4, grinding unit 10, and the like) of the grinding apparatus 2, and generates control signals to control operations of the individual elements. For example, the controller is configured by a computer, and includes a processing section that performs processing needed to operate the grinding apparatus 2, and a storage section that stores various kinds of information (data, programs, and the like) to be used in the operation of the grinding apparatus 2. The processing section is configured including a processor such as a central processing unit (CPU). The storage section is configured including a memory such as a read only memory (ROM) or a random access memory (RAM).
When grinding the workpiece 11 by the grinding apparatus 2, the workpiece 11 is first held on the chuck table 4. For example, the workpiece 11 is arranged on the chuck table 4 such that the side of the front surface 11a faces the holding surface 4a and the side of the back surface 11b (the surface to be ground) is exposed upward. When a suction force (negative pressure) of the suction source is caused to act on the holding surface 4a with the workpiece 11 arranged on the chuck table 4, the workpiece 11 is held under suction on the chuck table 4. It is to be noted that a protective sheet may be fixed on the side of the front surface 11a of the workpiece 11 to protect the workpiece 11.
Next, the chuck table 4 is positioned below the grinding wheel 16. Further, with the chuck table 4 and spindle 12 kept rotating, the grinding unit 10 is lifted down at a predetermined speed, so that the grinding wheel 16 is caused to approach the workpiece 11. When the grinding surfaces 20a of the grinding stones 20 come into contact with the back surface 11b of the workpiece 11, the workpiece 11 is ground off on the side of the back surface 11b, and therefore the workpiece 11 is ground and thinned.
It is to be noted that before the grinding or in the course of the grinding of the workpiece 11 by the grinding stones 20, dressing is performed to tune conditions of the grinding stones 20 by having the grinding stones 20 purposely abraded on a side of the grinding surfaces 20a. The dressing of the grinding stones 20 is performed by bringing the grinding stones 20 into contact with a member for dressing (dressing member, dressing board) while rotating the grinding stones 20.
The abrasive grits have a ratio of minor axis a to major axis b (aspect ratio a/b) of, for example, 0.7 or greater, preferably 0.8 or greater, more preferably 0.9 or greater. Here, the minor axis a of each abrasive grit 23 corresponds to the length of a shortest straight line connecting two points on a surface of the abrasive grit 23 through a center (the center of gravity) of the abrasive grit 23. On the other hand, the major axis b of the abrasive grit 23 corresponds to the length of a longest straight line connecting two points on the surface of the abrasive grit 23 through the center (the center of gravity) of the abrasive grit 23. If the abrasive grits 23 are in a form of prolate spheroids (rotational ellipsoids obtained by rotating ellipses about their major axes), for example, the minor axis a corresponds to a short diameter of each abrasive grit 23, while the major axis b corresponds to a long diameter of the abrasive grit 23.
Further, the abrasive grits 23 have a circularity of, for example, 0.95 or higher, preferably 0.96 or higher, more preferably 0.97 or higher. In addition, the abrasive grits 23 have a convexity of, for example, 0.97 or higher, preferably 0.98 or higher, more preferably 0.99 or higher, and the abrasive grits 23 have a solidity of, for example, 0.94 or higher, preferably 0.95 or higher, more preferably 0.96 or higher.
The amount of the abrasive grits 23 contained in the binder 25 is adjusted according to the strength or the like required for the dressing member 21. For example, the content of the abrasive grits 23 is set at 20 wt % or higher but 80 wt % or lower, with 40 wt % or higher but 80 t % or lower being preferred. This content corresponds to the ratio of a mass of the abrasive grits 23 to a mass of the binder 25 with the abrasive grits 23 contained therein (the sum of the mass of the binder 25 and a mass of the abrasive grits 23).
Furthermore, the abrasive grits 23 have a grit size set as needed within a range in which appropriate dressing can be applied to the grinding stones 20. For example, the abrasive grits 23 have an average grit size of 0.1 μm or greater but 3.5 μm or smaller. It is to be noted that the above-described value of the average grit size of the abrasive grits 23 corresponds to a grit diameter (median diameter, d50, 50% diameter) at a cumulative value of 50% in a grit size distribution measured by a laser diffraction scattering method.
As the binder 25, a glassy vitrified bond containing SiO2 or the like as a main component, a resin bond containing resin as a main component, or the like can be used. Inside the binder 25, a number of pores (not depicted) are formed. However, no limitations are imposed on the material of the binder 25.
As depicted in
The dressing member 21 is positioned concentrically with the holding surface 4a such that the axis of rotation of the chuck table 4 passes through a center of the dressing member 21. Further, the support member 27 is positioned such that the suction surface 8a (see
Next, a positional relation between the chuck table 4 and the grinding wheel 16 is adjusted. Described specifically, the chuck table 4 is positioned such that the center of the dressing member 21 and the rotation track of the grinding stones 20 overlap in the Z-axis direction.
Next, with the chuck table 4 and grinding wheel 16 kept rotating, the chuck table 4 and the grinding wheel 16 are moved relative to each other along a direction (Z-axis direction) parallel to the axis of rotation of the grinding wheel 16. Described specifically, the grinding unit 10 is lifted down at a predetermined speed along the Z-axis direction, whereby the grinding wheel 16 is caused to approach the dressing member 21. When the grinding stones 20 come into contact with the dressing member 21, the grinding stones 20 then grind the entirety on the side of the first surface 21a of the dressing member 21 while rotating so as to pass through the axis of rotation of the chuck table 4. As a consequence, the grinding stones 20 are abraded on the side of the grinding surfaces 20a, so that dressing is applied to the grinding stones 20.
Here if the abrasive grits 23 (see
In this embodiment, on the other hand, the spherical abrasive grits 23 are contained in the dressing member 21. The spherical abrasive grits 23 therefore come into contact at smooth surfaces (curved surfaces) thereof with the side of the grinding surfaces 20a of the grinding stones 20 when the dressing member 21 is ground by the grinding stones 20. This provides soft contact between the grinding stones 20 and the abrasive grits 23, thereby avoiding the formation of deep irregularities and scratches on the side of the grinding surfaces 20a of the grinding stones 20. As a result, it is possible to omit or shorten the provisional grinding to be performed after the grinding of the dressing member 21.
It is to be noted that the abrasive grits 23 have hardness lower than that of the binder 25 in the grinding stones 20. As a consequence, irregularities and scratches are less likely to be formed on the binder 25 when the abrasive grits 23 and the binder 25 come into contact with each other. For example, the abrasive grits 23 have Mohs hardness equal to or lower than that of the binder 25. A high/low relation in hardness between the abrasive grits 23 and the binder 25 can be verified by measuring the hardness of the abrasive grits 23 and binder 25 in the same manner, and then comparing their measurement values.
As described above, the dressing member 21 according to this embodiment contains the spherical abrasive grits 23. This suppresses the formation of irregularities and scratches through contact between the grinding stones 20 and the abrasive grits 23 during dressing. As a result, the time and cost required for provisional grinding are significantly reduced, and the dressing step for the grinding stones 20 is simplified.
It is to be noted that the construction, method, and the like according to the above-described embodiment can be practiced with appropriate changes or modifications within the scope not departing from the object of the present invention.
The present invention is not limited to the details of the above-described preferred embodiment. The scope of the invention is defined by the appended claims and all changes and modifications as fall within the equivalence of the scope of the claims are therefore to be embraced by the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-195388 | Dec 2022 | JP | national |
