JP6120597B2 - Processing method - Google Patents

Description

  The present invention relates to a wafer processing method in which a rear surface of a wafer such as a semiconductor wafer is ground to form a circular concave portion and an annular convex portion surrounding the circular concave portion on the rear surface side.

  In the manufacturing process of a semiconductor device, a grid-like division line is set on the surface of a disk-shaped wafer made of a semiconductor material such as silicon or gallium arsenide, and a large number of rectangular device regions surrounded by the division line. In addition, a device having an electronic circuit such as an IC or LSI is formed. This wafer is divided into a large number of chip-like devices by cutting along a predetermined division line after undergoing a predetermined process such as grinding the back surface and thinning it to a set thickness. The device thus obtained is packaged with resin or ceramic and mounted on various electronic devices. In recent years, as electronic devices become smaller and lighter, wafers may be processed extremely thin, for example, with a thickness of 100 μm or less.

  By the way, if the wafer is thinned, the rigidity is lowered and handling becomes difficult. Therefore, grinding is performed on the back surface of the wafer to remove the outer peripheral portion, and a circular concave portion is formed on the rear surface side, and a thick annular convex portion is left as a reinforcing portion on the outer peripheral portion so that the entire wafer has a concave cross section. A technique for processing and solving the handling problem is known (Patent Document 1).

JP 2007-019461 A

  By the way, when the wafer is ground, grinding debris is generated from the wafer, and abrasive grains are separated from the grinding wheel of the grinding wheel due to wear. When grinding is performed so as to form a circular concave portion on the back surface of the wafer as described above, these grinding scraps and abrasive grains are hardly removed from the circular concave portion and stay. As a result, a phenomenon occurs in which the grinding wheel that grinds the back surface bites these grinding scraps and abrasive grains staying in the circular recess, and in that case, there is a possibility that scratches may occur on the back surface of the wafer. . In particular, when the degrown abrasive grains are relatively large, for example, # 320, scratches are formed deeply. Therefore, even if grinding is continued after the scratches are formed, the scratches cannot be sufficiently removed and the scratches are removed from the wafer. Will remain. Scratches remaining on the wafer may cause a reduction in the bending strength of the wafer, and may cause cracks from the scratch to cause damage to the wafer.

  The present invention has been made in view of the above circumstances, and its main technical problem is that foreign matters such as grinding dust and abrasive grains may stay in the circular recess when the circular recess is formed on the back surface of the wafer by grinding. It is in providing the processing method which can reduce.

The processing method of the present invention comprises a wafer holding step for holding the front surface side of a wafer with a holding table to expose the back surface of the wafer, and rotating the holding table holding the wafer, and a grinding wheel having an annular shape smaller in diameter than the wafer. An annular projection that forms a circular recess by grinding the rear surface of the wafer by rotating the disposed grinding wheel while making contact with the back surface of the wafer and moving the grinding wheel relatively close to the wafer. A grinding step for forming a grinding wheel, wherein grinding is performed while supplying a grinding fluid to at least the grinding wheel and the wafer from the inside of the grinding wheel, and the grinding wheel from the outside of the grinding wheel. processing method der the foreign matter removing fluid out the grinding while supplying to said circular inner recess in is formed by grinding The holding table is formed in a biconcave shape centered on the rotation axis, and is ground by the grinding wheel in a radial region from the apex to the outer periphery, and in the grinding step, the foreign matter removing fluid is , On the outer side of the grinding wheel and on the radial region side where the wafer is ground by the grinding wheel, in a direction opposite to the rotation of the holding table, and toward a processing point where the grinding wheel contacts the wafer A processing method characterized by being supplied .

  According to the present invention, during grinding to form a circular recess on the back surface of the wafer, by supplying a foreign substance removing fluid into the circular recess, foreign matter such as grinding dust generated by grinding or abrasive grains degreasing from the grinding wheel Are discharged from the circular recess along the flow of the foreign substance removing fluid. For this reason, it is possible to suppress the generation of scratches on the back surface of the wafer due to the grinding wheel biting foreign matter. Moreover, since the foreign substance in a circular recessed part is removed during grinding, processing time can be shortened compared with the case where a foreign substance is removed after grinding, for example.

In the present invention, in the grinding step, the foreign substance removing fluid is preferably supplied in a state of being substantially perpendicular to the inner peripheral wall of the circular recess of the wafer .

In the present invention, after the grinding step is performed, the holding table that holds the wafer is rotated, and the finish grinding wheel that includes abrasive grains having a smaller particle diameter than the grinding wheel and that has a smaller diameter than the wafer is rotated. The method further includes a finish grinding step of bringing the circular concave portion into contact with the circular concave portion formed on the back surface of the wafer and moving it relatively close to the wafer to finish grinding the circular concave portion.
Further, the present invention includes a form in which the foreign matter removing fluid is the same liquid as the grinding liquid.

  According to the processing method of the present invention, there is provided a processing method capable of reducing the possibility that foreign matters such as grinding dust and abrasive grains stay in the circular recess when forming the circular recess on the back surface of the wafer by grinding. There are effects such as.

BRIEF DESCRIPTION OF THE DRAWINGS (a) Perspective view of (a) perspective view of a wafer to be back-ground by a processing method according to an embodiment of the present invention and a protective member attached to the back of the wafer; It is. It is a perspective view which shows the grinding apparatus which implements the processing method of one Embodiment suitably, and shows the (a) wafer holding step and (b) grinding step of the processing method. It is sectional drawing which shows the wafer holding step of the processing method. It is sectional drawing which shows the detail of the shape of the holding surface of the holding table of a grinding device. It is a top view which shows the positional relationship of the horizontal direction of the holding table and the grinding wheel which hold | maintain a wafer. It is sectional drawing which shows the grinding step of the processing method of one Embodiment. It is sectional drawing which shows the state which is supplying the cooling fluid to the boundary part of the outer peripheral surface of a grinding wheel and the internal peripheral wall of the annular convex part of a wafer in a grinding step. This is an example for confirming the effect of removing foreign matter depending on the direction in which the foreign matter removing fluid is supplied into the circular recess, and showing that the direction opposite to the rotation direction of the wafer is the best. It is a figure which shows the Example of the direction where the supply direction of the foreign material removal fluid in a circular recessed part opposes the rotation direction of a wafer.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[1] Wafer Reference numeral 1 in FIG. 1 denotes a disk-shaped wafer whose back surface is ground in one embodiment. The wafer 1 is a semiconductor wafer having a thickness of, for example, about several hundred μm. A large number of rectangular devices 2 are arranged on the surface 1 a of the wafer 1. The device 2 is provided by forming an electronic circuit made of, for example, an IC or LSI on the surface of a large number of rectangular areas defined by the grid-shaped division lines 3.

  In carrying out the back surface grinding of the wafer 1, in order to protect the device 2, a disk-shaped protective member 5 is stuck on the entire surface 1 a. The protective member 5 is, for example, one in which an adhesive layer is formed on one side of a resin base material, and the surface 1a of the wafer 1 is adhered to the adhesive layer. The back surface 1b of the wafer 1 is thinned to a predetermined thickness by grinding a circular portion corresponding to a device forming region where a large number of devices 2 on the front surface 1a side are formed. Accordingly, by the back surface grinding, a circular concave portion is formed in the circular portion corresponding to the device forming region on the back surface 1b, and an annular convex portion surrounding the circular concave portion is formed on the outer peripheral portion. Hereinafter, the processing method of the back surface grinding of the wafer 1 which concerns on this embodiment is demonstrated.

[2] Processing Method First, as shown in FIGS. 2A and 3, the wafer 1 is held by the holding table 10 of the grinding apparatus. As shown in FIG. 3, the wafer 1 is placed and held on the upper surface of the holding table 10 via the protective member 5, and the back surface 1b, which is the surface to be ground, is exposed (wafer holding step).

  As shown in FIG. 2, the grinding apparatus includes a holding table 10 and a grinding means 20 disposed on the holding table 10.

  As shown in FIG. 3, the holding table 10 has a configuration in which a disc-shaped holding portion 12 formed of a porous body is fitted on the upper surface of a frame body 11 made of a metal such as stainless steel, and has a vertical direction. The rotary shaft 10a extending in the direction is supported so as to be rotatable, and is rotationally driven by a rotational driving means (not shown).

  The holding unit 12 made of a porous body has a diameter similar to that of the wafer 1, and the wafer 1 is placed and held concentrically on a horizontal holding surface 13 that is the upper surface of the holding unit 12. A gap 14 is formed between the lower surface of the holding part 12 and the frame body 11, and a suction path 15 communicating with the holding part 12 through the gap 14 is formed at the center of the frame body 11. A suction pipe 17 communicating with the suction source 16 is connected to the suction path 15, and an electromagnetic switching valve 18 is interposed in the middle of the suction pipe 17. By operating the suction source 16 and opening the electromagnetic switching valve 18, a negative pressure is generated on the holding surface 13, and the wafer 1 is sucked and held on the holding surface 13 via the protective member 5 by this negative pressure action. .

  Strictly speaking, the holding surface 13 of the holding table 10 is not flat, and as shown in FIG. 4 (FIG. 4 exaggeratedly shows the shape of the holding surface 13), the cross-sectional shape is a double axis centered on the rotation axis. It is formed in a concave shape. That is, a vertex 13a is formed at the center of the holding surface 13, and a very shallow groove-shaped recess 13c along the circumferential direction is formed in a radial region around the vertex 13a from the vertex 13a toward the outer peripheral edge 13b. Yes. In this case, the heights of the apex 13a and the outer peripheral edge 13b are approximately the same, and the cross-sectional shape of the recess 13c in the radius region is formed bilaterally symmetrical. As the dimensions of the holding surface 13, for example, the diameter is about 100 mm, and the depth of the recess 13c is about several μm.

  The wafer 1 sucked and held on the holding surface 13 of the holding table 10 via the protective member 5 is deformed following the shape of the holding surface 13. That is, the upper surface (back surface 1 b) of the wafer 1 is deformed into a biconcave state having the same shape as the holding surface 13.

  After the wafer is sucked and held on the holding table 10, the holding table 10 is then rotated to rotate the wafer 1, and the grinding means 20 is lowered with respect to the exposed back surface 1 b of the wafer 1 as shown in FIG. Then, by bringing the grinding wheel 25 of the grinding wheel 24 included in the grinding means 20 into contact with each other in a rotating state, a circular recess 1c is formed on the back surface 1b as shown in FIGS. 5 and 6, and an annular shape surrounding the circular recess 1c. Protrusions 1d are formed (grinding step). During this grinding step, grinding is performed while supplying a grinding fluid to at least the grinding wheel 24 and the wafer 1 from the inside of the grinding wheel 24. Further, as shown in FIG. Grinding is performed while supplying the foreign substance removing fluid F into the circular recess 1 c formed by grinding at 25.

  As shown in FIG. 2, the grinding means 20 has a cylindrical housing 21 supported so as to be movable up and down. In the housing 21, a spindle 22 whose rotation axis extends in the vertical direction and whose lower end protrudes downward from the housing 21 is rotatably supported. A disc-shaped grinding wheel 24 is connected to the spindle 22 at the lower end of the spindle 22. It is fixed concentrically. The housing 21 incorporates a spindle motor (not shown) that rotates the grinding wheel 24 together with the spindle 22 at a high speed.

  As shown in FIG. 4, the grinding wheel 24 is detachably fixed to a flange 23 formed at the lower end of the spindle 22. A plurality of grinding wheels 25 are annularly arranged and fixed to the outer periphery of the lower surface of the grinding wheel 24. As the grinding wheel 25, a material corresponding to the material of the wafer 1 to be ground is used. For example, a diamond grinding wheel formed by solidifying diamond abrasive grains with a binder such as metal bond or resin bond is used.

  As shown in FIG. 5, the diameter of the rotation trajectory 25 </ b> A of the plurality of grinding wheels 25 is set to be about the radius of the wafer 1. (The same position as the rotation center 10a of the holding table 10), that is, a position that passes through the rotation center of the wafer 1 and touches the outer periphery of the device formation region of the wafer 1 (the boundary between the formed circular recess 1c and the annular protrusion). Is positioned. Inside the grinding wheel 24, a grinding liquid supply nozzle (not shown) for supplying a grinding liquid to the back surface 1b of the wafer 1 and the grinding wheel 25 during grinding is disposed.

  Further, the holding surface 13 of the holding table 10 has a biconcave cross section as shown in FIG. 2, and the wafer 1 is sucked and held by the holding surface 13 in a deformed state following this holding surface shape. . For this reason, as shown in FIG. 5, the processing point 25a that is actually ground by the rotating grinding wheel 25 is a semicircular arc portion indicated by oblique lines. That is, the grinding wheel 25 at the processing point 25a of the semicircular arc part comes into contact with the radius region of the back surface 1b of the wafer 1 and the wafer 1 rotates to form a circular recess 1c. In the illustrated example, the processing point 25a is on the rear side (left side in FIG. 5) of the holding table 10 in the rotational direction, but on the opposite side, on the front side in the rotational direction of the holding table 10 (right side in FIG. 5). ) May be set.

  Further, as shown in FIG. 2, a foreign substance removing fluid supply is provided at a predetermined position around the holding table 10 to supply the foreign substance removing fluid F into a circular recess 1c formed on the back surface 1b of the wafer by grinding with a grinding wheel 25. A nozzle 30 is provided. The tip of the foreign substance removal fluid supply nozzle 30 is formed at a discharge port having a diameter of about 1 to 3 mm, for example, and extends toward a circular recess 1c formed on the back surface 1b of the wafer 1 by grinding. The foreign matter removing fluid supply nozzle 30 is communicated with a foreign matter removing fluid supply source 32 via a supply pipe 31. In the middle of the supply pipe 31, an electromagnetic switching valve 33 is interposed. By operating the foreign matter removal fluid supply source 32 to open the electromagnetic switching valve 33, the foreign matter removal fluid supply nozzle 30 enters the circular recess 1c. The foreign substance removing fluid F is supplied in the ejected state.

  As shown in FIGS. 2B and 6, in the grinding step, the rotating wheel is rotated by rotating the grinding wheel 24 in the same direction as the holding table 10 (arrow G direction) and lowering the grinding means 20. The grinding wheel 25 of the rotating grinding wheel 24 is brought into contact with the radius region of the back surface 1b of 1 to form a circular concave portion 1c and an annular convex portion 1d. During grinding, the grinding fluid is supplied from the grinding fluid nozzle in the grinding wheel 24 to the wafer 1 and the grinding wheel 25, and at the same time, the foreign matter removal fluid F is supplied from the foreign matter removal fluid supply nozzle 30 into the circular recess 1c. . The grinding fluid and the foreign matter removing fluid F are not particularly limited and are appropriately selected. For example, both are the same and pure water or the like is used. In the illustrated example, the rotation direction of the grinding wheel 24 and the holding table 10 is counterclockwise, but the rotation direction of both is not limited to this, and may be clockwise, or both rotation directions may be different from each other. .

  The circular concave portion 1c and the annular convex portion 1d are formed on the back surface 1b of the wafer 1 by the above method. The thickness of the region of the circular recess 1c is measured by a thickness measuring device (not shown). When the thickness reaches a predetermined thickness, the grinding means 20 is retracted upward to finish grinding. After the grinding, the wafer 1 is unloaded from the holding table 10 by handling the annular convex portion 1d around the circular concave portion 1c, and sent to the next step.

[3] Effect of Embodiment According to the processing method of the above embodiment, by supplying the foreign substance removing fluid F into the circular recess 1c during grinding to form the circular recess 1c on the back surface 1b of the wafer 1, Foreign matters such as grinding waste generated by grinding and abrasive grains removed from the grinding wheel 25 are discharged from the circular recess 1c along the flow of the foreign matter removing fluid. For this reason, it is possible to prevent the grinding wheel 25 from biting foreign matter and causing scratches on the back surface 1b of the wafer. Moreover, since the foreign substance in the circular recessed part 1c is removed during grinding, processing time can be shortened compared with the case where a foreign substance is removed after grinding, for example.

  In addition to the liquid such as the pure water, the foreign substance removing fluid F may be any appropriate one as long as it can remove foreign substances. For example, compressed air may be ejected to remove foreign substances. Further, when grinding the back surface 1b, as shown in FIG. 7, from the outside of the grinding wheel 24 to the outer peripheral surface of the grinding wheel 25 and the boundary portion with the inner peripheral wall of the annular convex portion 1d formed by the outer peripheral surface, A separate coolant may be supplied from the coolant supply nozzle 40. By supplying the coolant C in this way, it is possible to suppress wear on the outer peripheral side of the grinding wheel 25, in particular, the lower end corner portion of the grinding wheel 25 that is easily worn. The cooling liquid C in this case may be the same as the grinding liquid, and for example, pure water or the like is used.

  In the said embodiment, although the grinding process was demonstrated as 1 time, you may divide and grind a grinding process into 2 times of rough grinding and finish grinding. In that case, the grinding wheel 25 of the grinding wheel 24 has a roughness of about # 320, for example, during rough grinding, and the foreign material removing fluid F is supplied into the formed circular recess 1c to produce grinding dust generated by grinding. And foreign matters such as abrasive grains shed from the grinding wheel 25 are removed. Foreign substances are likely to be generated during rough grinding, and the supply of the foreign substance removing fluid F is effective. In the subsequent finish grinding, a grinding wheel of the same size equipped with a grinding wheel containing abrasive grains having a grain size smaller than that of the grinding wheel 24 for rough grinding is brought into contact with the circular recess 1c formed by rough grinding. The circular recess 1c is finish ground (finish grinding step). In the finish grinding, if foreign matter is expected to be generated, the foreign matter removing fluid F is supplied into the circular recess 1c, and if no foreign matter is expected to be generated, the foreign matter removing fluid F is supplied into the circular recess 1c. There is no need to supply.

"Supply direction of foreign substance removal fluid"
In the present invention, during the grinding step, grinding is performed while supplying the foreign substance removing fluid into the circular concave part formed on the back surface of the wafer, but the holding table is used as the supply direction of the foreign substance removing fluid supplied into the circular concave part. The direction opposite to the rotation is a preferred mode. Hereinafter, the Example performed about the supply direction of the foreign material removal fluid is described.

  8A to 8D are the same conditions as in FIG. 5, that is, the rotation direction of the grinding wheel 24 and the wafer 1 is the same, and the processing point 25 a of the grinding wheel 25 with respect to the wafer 1 is behind the rotation direction of the holding table 10. As an example, an experiment example in which the supply direction of the foreign substance removal fluid F is changed is shown. (A) to (d) are the following conditions, and except for (a), the foreign matter removing fluid F is supplied from the opposite side of the processing point 25a.

(A) No supply of foreign matter removing fluid: Comparative example other than the present invention.
(B) The foreign matter removing fluid F is supplied in the same direction as the rotation direction of the wafer 1.
(C) The foreign substance removal fluid F is supplied in a direction opposite to the rotation direction of the wafer 1.
(D) F is supplied to the foreign substance removing fluid at an angle relatively close to a right angle in the same direction as the rotation direction of the wafer 1 and toward the inner peripheral wall of the annular protrusion 1d.

  Twenty-five wafers were ground under each of the conditions (a) to (d), and the number of wafers on which scratches that were presumed to be caused by the inclusion of foreign matter after grinding were counted. As a result, (a) 10 sheets, (b) 5 sheets, (c) 4 sheets, and (d) 6 sheets. According to this, it was found that the supply of the foreign substance removal fluid into the circular recess 1c is effective, and the supply direction of the foreign substance removal fluid is preferably the direction facing the rotation direction of the wafer as shown in (c).

  9A to 9D assume that the supply direction of the foreign substance removal fluid F is a direction opposite to the rotation direction of the wafer 1 under the same conditions as in FIG. An experimental example is shown. (A) to (d) are the following conditions, and except for (a), the foreign matter removing fluid F is supplied from the opposite side of the processing point 25a.

(A) No supply of foreign matter removing fluid: Comparative example other than the present invention.
(B) The foreign matter removing fluid F is supplied on the side opposite to the processing point 25a.
(C) The foreign matter removing fluid F is supplied toward the machining point 25a on the machining point 25a side.
(D) The foreign matter removing fluid F is supplied toward the rotation center of the wafer 1 from the side opposite to the processing point 25a.
(E) The foreign matter removing fluid F is supplied at an angle relatively close to a right angle toward the inner peripheral wall of the annular convex portion 1d on the processing point 25a side.

  Twenty-five wafers were ground under each of the conditions (a) to (e), and the number of wafers on which scratches that were presumed to be caused by the inclusion of foreign matter after grinding were counted. As a result, (a) 10 sheets, (b) 1 sheet, (c) 0 sheet, (d) 1 sheet, and (e) 0 sheet. Therefore, it is effective to remove the foreign matter so that the supply direction of the foreign matter removing fluid is opposite to the rotation direction of the wafer. In particular, the foreign matter is directed toward the processing point 25a as shown in (c) and (e). It has been found that supplying the removal fluid is more effective because the foreign matter generated by grinding is immediately removed and it is prevented that the foreign matter moves around to the opposite side of the processing point 25a. Further, as shown in (e), when the foreign matter removing fluid is supplied toward the inner peripheral wall of the annular convex portion 1d at an angle close to a right angle, the circular convex portion 1d can be easily discharged and the foreign matter can be easily discharged. No abrasive grains remained inside, and it was confirmed that this direction was also effective for removing foreign matter.

  DESCRIPTION OF SYMBOLS 1 ... Wafer, 1a ... Wafer surface, 1b ... Wafer back surface, 1c ... Circular recessed part, 1d ... Circular convex part, 10 ... Holding table, 10a ... Rotating shaft, 13a ... Vertex, 25 ... Grinding wheel, 24 ... Grinding wheel , F ... Foreign matter removal fluid

Claims (4)

A wafer holding step of holding the front side of the wafer with a holding table and exposing the back side of the wafer;
While rotating the holding table holding the wafer, rotating the grinding wheel in which the grinding wheel having a smaller diameter than the wafer is disposed is brought into contact with the back surface of the wafer and moved relatively close to the wafer. Grinding a back surface of the substrate to form a circular concave portion and forming an annular convex portion surrounding the circular concave portion, and
In the grinding step, at least the circular recess formed by grinding with the grinding wheel from the outside of the grinding wheel while performing grinding while supplying a grinding liquid to the grinding wheel and the wafer from the inside of the grinding wheel. A processing method for carrying out grinding while supplying a foreign substance removing fluid inside ,
The holding table is formed in a biconcave shape centering on the rotation axis, and is ground by the grinding wheel in a radial region from the apex to the outer periphery,
In the grinding step, the foreign matter removing fluid is disposed on the outside of the grinding wheel and on the radial region side where the wafer is ground by the grinding wheel, in the direction facing the rotation of the holding table, and on the grinding wheel Is supplied toward a processing point that contacts the wafer . 2. The processing method according to claim 1, wherein in the grinding step, the foreign substance removing fluid is supplied in a state of being substantially perpendicular to the inner peripheral wall of the circular recess of the wafer . After the grinding step is performed, the holding table holding the wafer is rotated and formed on the back surface of the wafer while rotating a finishing grinding wheel containing abrasive grains having a smaller particle diameter than the grinding wheel and having a smaller diameter than the wafer. 3. The processing method according to claim 1, further comprising a finish grinding step in which the circular recess is finish ground by being brought into contact with the circular recess and moved relatively close to the wafer. 4. The foreign substance removal fluid processing method according to any one of claims 1 to 3, characterized in that the same liquid and grinding fluid.

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