Wafer processing method with intermediate element

Abstract

A method for processing a wafer (11) having, on a front side (11a) thereof, a central region (19) in which a plurality of components (15) each formed with a plurality of elevations (17) are arranged, and a peripheral edge region (21) surrounding the central region (19), the method comprising: an intermediate member preparation step for preparing an intermediate member (14) including a flexible member (16) corresponding to the central region (19) of the wafer (11) and an adhesive member (18) arranged at a peripheral edge of the flexible member (16); an adhering step for adhering the intermediate member (14) to a holding plate (12) by the adhesive member (18) and for adhering the wafer (11) to the intermediate member (14) adhered to the holding plate (12) by the adhesive member (18) in a state in which the central region (19) of the wafer (11) is in contact with the flexible member (16); a grinding step for grinding a back surface (11b) of the wafer (11) after the adhesion step has been performed; and a peeling step of cutting and removing the adhesive member (18) from the intermediate member (14) using a cutting unit (50) having a cutting blade (54) attached to a spindle (52) and peeling the wafer (11) from the holding plate (12) after the grinding step has been performed.

Description

BACKGROUND OF THE INVENTIONField of the InventionThe present invention relates to a method for processing a wafer, in which each device has a plurality of bumps (bumps), and an intermediate member used in the processing method.Description of the Prior ArtA semiconductor wafer having a plurality of devices such as ICs and LSIs formed on a front side thereof and divided by a plurality of division lines (streets) formed in a lattice pattern is processed to have a predetermined thickness by grinding the back side thereof by a grinding apparatus. Thereafter, the wafer is cut along the division lines by a cutting device (dicing saw) to be divided into individual devices. The thus-divided devices are widely used in various electronic devices such as mobile phones and personal computers.The grinding apparatus for grinding the back surface of the wafer includes a chuck table for holding the wafer and an abrasive in which a grinding wheel having a grinding stone or grinding stones for grinding the wafer held on the chuck table is rotatably mounted, whereby the wafer can be ground to a desired thickness with high accuracy. In order to grind the back surface of the wafer, the front surface of the wafer on which the plurality of devices are formed needs to be held on the chuck table by suction. Therefore, a protective tape is usually adhered to the front surface of the wafer so that the devices are not damaged (see, for example, JP H05-198 542 A).In recent years, there has been a development toward electronic devices having smaller size and thickness, and it has been required that the size and thickness of semiconductor devices to be incorporated into the electronic devices are reduced. However, when the back surface of a wafer is ground to reduce the thickness of the wafer to, for example, 100 μm or less or further to 50 μm or less, the rigidity of the wafer is significantly reduced, thereby making it very difficult to subsequently handle the wafer. Further, such a wafer may be distorted and the wafer itself may be broken due to the distortion. In order to solve such a problem, a wafer holding system (WSS) has been used. In the WSS, the front side of a wafer is preliminarily adhered to a rigid protective member by using an adhesive, and thereafter, the back side of the wafer is ground to thin the wafer with a predetermined thickness (see, for example, JP 2004-207 606 A).Further information helpful in understanding the present application can be found in the following documents:WO 2013 / 129 705 A1 relates to a method for producing a semiconductor device having a treated element.DE 10 2013 219 271 A1 relates to a protective element and a wafer processing method using a protective element.SUMMARY OF THE INVENTIONHowever, in the WSS, it is difficult to peel off a wafer from the protective tape or the protective member without breaking the wafer. In particular, in recent years, there have been developments toward larger wafer diameters and smaller final thickness values for wafers, so that it has become more difficult to peel a wafer off a protective member without breaking the wafer. In addition, there is another problem that a paste (an adhesive) or an adhesive remains on the front side of the device after the wafer is peeled from the protective member. Specifically, in the case of a wafer having a plurality of bumps (bumps) formed on each device, unevenness caused by the bumps makes it difficult to adhere the wafer to the protective member in a planar state, and in addition, the paste or the adhesive is left between the bumps.Accordingly, it is an object of the present invention to provide a processing method for a wafer, by which it is ensured that a paste (an adhesive) or an adhesive is prevented from remaining between protrusions when a protective member is peeled off, and that the protective member can be easily peeled off.According to an aspect of the present invention, there is provided a method of processing a wafer having, on a front surface thereof, a central portion in which a plurality of devices each formed with a plurality of bumps (bumps) are arranged, and a peripheral edge portion surrounding the central portion, the method including: an intermediate member preparation step of preparing an intermediate member including a bendable member corresponding to the central portion of the wafer and an adhesive member arranged on a peripheral edge of the bendable member; an adhesion step of adhering the intermediate member to a holding plate through the adhesive member and adhering the wafer to the intermediate member adhered to the holding plate through the adhesive member in a state where the central portion of the wafer is in contact with the bendable member; a grinding step for grinding a back surface of the wafer after the adhering step is performed; and a peeling step for peeling the wafer from the holding plate after the grinding step is performed.According to another aspect of the present invention, there is provided an intermediate member for use in a method of processing a wafer having, on a front surface thereof, a central portion in which a plurality of devices each formed with a plurality of bumps (bumps) are arranged, and a peripheral edge portion surrounding the central portion, the intermediate member including: a bendable member corresponding to the central portion of the wafer; and an adhesive member arranged at a peripheral edge of the bendable member and corresponding to the peripheral edge portion of the wafer.According to the method for processing a wafer of the present invention, the wafer is adhered to the holding plate through the intermediate member including the bendable member corresponding to the central portion of the wafer to be adhered and the adhering member disposed at the peripheral edge of the bendable member. Therefore, the wafer is adhered to the holding plate through the intermediate member without inserting a paste (an adhesive) or an adhesive in the central portion of the wafer. Accordingly, a situation in which a paste or an adhesive remains between protrusions when the wafer is peeled from the holding plate can be avoided.Since the wafer is adhered to the holding plate by the adhesive member disposed at the peripheral edge of the bendable member, the wafer can be easily peeled from the holding plate. In addition, since the wafer is adhered to the holding plate in the state where the bendable member is in contact with the central portion of the wafer, the unevenness caused by the protrusions is absorbed by the bendable member and the wafer is adhered to the holding plate in a state where the back surface of the wafer is flat.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 be best understood by studying the following description and appended claims with reference to the accompanying drawings showing some preferred embodiments of the invention.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a perspective view of a wafer suitable for performing the processing method according to the present invention; FIG. 2 is a sectional view of a wafer, an intermediate member, and a holding plate subjected to adhesion in an adhering step; FIG. 3A is a plan view of an intermediate member in which an adhesive member is disposed along the entire circumference of a bendable member; FIG. 3B is a plan view of an intermediate member in which adhesion members are disposed at plural locations on the outer periphery of a bendable member; FIG. 4 is a sectional view of the wafer, the intermediate member, and the holding plate after the adhering step is performed; FIG. 5A is a sectional view showing a state in which a protective tape is adhered to the holding plate; FIG. 5B is a partially cut side view showing a manner in which the protective tape is cut and planar by a tool cutting device; FIG. 6 is a perspective view showing a grinding step; FIG. 7 is a sectional view showing a transfer step; FIGS. 8A and 8B are sectional views showing a first embodiment of a peeling step; and FIG. 9 is a sectional view showing a second embodiment of the peeling step.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTSEmbodiments of the present invention will be described below in detail with reference to the drawings. Referring to FIG. 1, there is shown a perspective view of a semiconductor wafer (hereinafter also referred to as "wafer" for short) 11 suitable for processing by the processing method of the present invention. The semiconductor wafer 11 has a front side 11 aand a back side 11 b. The front surface 11 ais formed with a plurality of streets (division lines) 13 perpendicularly crossing each other, and a device 15 is formed in each of regions partitioned by the streets 13. The semiconductor wafer 11 is formed by, for example, a silicon wafer having a thickness of 700 μm.As shown in FIG. 1 in an enlarged view, a plurality of bumps (bumps) 17 having a protrusion-like shape are formed along each of four edges of each device 15. Since the bumps 17 are thus formed along the four edges of each device 15, the semiconductor wafer 11 includes a central portion (bump forming portion) 19 in which the bumps 17 are formed and a peripheral edge portion (peripheral portion in which no bumps are formed) 21 surrounding the central portion 19.Referring to FIG. 2, there is shown a sectional view of the wafer 11 and a holding plate 12 and an intermediate member 14 to be adhered to the front surface 11 aof the wafer 11. The holding plate 12 is made of, for example, a silicon wafer or a glass wafer. Note that a chamfered portion 11 ehaving an arc shape extending from the front side to the back side is formed at a peripheral portion of the wafer 11, and when the back side 11 bof the wafer 11 is ground in a later-described grinding step to reduce the thickness of the wafer 11 to a predetermined value, a sharp edge is formed at the peripheral portion of the wafer 11 by a part of the chamfered portion 11 e. To solve this problem, it is preferable that, at least before performing the grinding step, edge trimming is performed in which a part of the chamfered portion 11 eof the wafer 11 in a circular shape is removed by a cutting blade.The intermediate member 14 includes a resilient member 16 formed of a rubber, a foamed rubber or the like and an adhesive member 18 disposed around the resilient member 16. The adhesive member 18 is formed of, for example, an adhesive. If the wafer 11 is subjected to heat treatment after the adhesion step described later is performed, a heat-resistant adhesive member is used as the adhesive member 18. As shown in FIG. 3A, the intermediate member 14 includes the bendable member 16 that is circular and the adhering member 18 that is continuously disposed over the entire circumference of the bendable member 16. Alternatively, as shown in FIG. 3B, an intermediate member 14A includes a bendable member 13 that is circular and adhesion members 18 that are disposed at multiple locations around the circumference of the bendable member 16.In the processing method for a wafer of the present invention, after the intermediate member 14 is prepared, an adhering step is performed in which, as shown in FIG. 4, the intermediate member 14 is adhered to the holding plate 12 through the adhering member 18 and the wafer 11 is adhered to the intermediate member 14 adhered to the holding plate 12 through the adhering member 18 in a state in which the central portion (bump forming portion) 19 of the wafer 11 is in contact with the bendable member 16. After the adhering step is performed, the wafer 11 is adhered to the holding plate 12 only by the adhering member 18 disposed on the periphery of the intermediate member 14.Before performing a grinding step for grinding the back surface 11 bof the wafer 11, a tape 20 including a base material and a paste (an adhesive) is preferably adhered to the holding plate 12 as shown in FIG. 5A to ensure sufficient accuracy with respect to the back surface 11 bof the wafer 11. After the tape is adhered, the tape 20 is cut and formed flat by a tool cutter as shown in FIG. 5B. In FIG. 5B, reference numeral 22 denotes a tool cutting unit of the tool cutting apparatus. The tool cutting unit 22 includes a spindle 24 driven to rotate, a mount 26 fixed to the tip of the spindle 24, and a tool disk 28 detachably mounted on the spindle 24.In the step of forming the tape 20 flat, the wafer 11 is suction-held by a chuck table 32 of the tool cutting apparatus with the tape 20 exposed. Subsequently, the cutting tool 30 is placed in such a position as to cut into the band 20 to a predetermined depth, the tool disk 28 is held at a rotation of, for example, 2000 U / min, and while the chuck table 32 is moved at a predetermined feed speed in the direction of the arrow A, the band 20 is cut by the cutting tool 30 in a rotating manner.At the time of this rotary cutting, the chuck table 32 is fed in the direction of the arrow A without rotation. When the step of forming the tape 20 flat is performed, sufficient parallelism is obtained between the back surface 11 bof the wafer 11 and the (front) surface of the tape 20. However, if sufficient parallelism is secured between a holding surface (lower surface) of the holding plate 12 and the back surface 11 bof the wafer 11 when the wafer 11 is adhered to the holding plate 12 through the intermediate member 14, the tape 20 does not necessarily need to be adhered to the holding plate 12.After the adhering step shown in FIG. 4 is performed or after the tape planar forming step shown in FIG. 5B is performed, the grinding step for grinding the back surface 11 bof the wafer 11 is performed. In the grinding step, as shown in FIG. 6, the holding plate 12 is suction-held by a chuck table 48 of the grinding apparatus with the back surface 11 bof the wafer 11 exposed. In FIG. 6, a grinding unit 36 includes a spindle 38 driven to rotate, a disk mount 40 fixed to the tip of the spindle 38, and a grinding wheel 42 detachably mounted to the disk mount 40 by a plurality of screws 41. the grinding wheel 42 includes an annular disk base 44 and a plurality of grinding stones 46 fixedly mounted to a lower end peripheral portion of the disk base 44 in an annular pattern.In the grinding step, while the chuck table 48 is held at, for example, 300 U / min for rotation in the direction of the arrow a and the grinding wheel is held at, for example, 6000 U / min for rotation in the direction of the arrow b, a grinding unit feeding mechanism (not shown) is driven to bring the grinding stones 46 of the grinding wheel 42 into contact with the back surface 11 bof the wafer 11. Thereafter, the grinding wheel 42 is fed downward (for grinding) at a predetermined feed rate and a predetermined amount. While the thickness of the wafer 11 is measured by a contact thickness measurement device or a non-contact thickness measurement device, the wafer 11 is ground to a predetermined thickness (for example, 100 μm).Note that the grinding step is not limited to the embodiment illustrated in FIG. 6. For example, a configuration may be adopted in which, by using a grinding wheel whose size approximately corresponds to the radius of the wafer 11, the back surface 11 bcorresponding to the central portion 19 of the wafer is ground to form a circular recess, and the back surface corresponding to the peripheral edge portion 21 is left unchanged to form an annular protrusion surrounding the circular recess.After the grinding step is performed, in order to ensure operability in the subsequent steps, a transfer step of adhering the back surface 11 bof the wafer 11 to a dicing tape T whose peripheral portion is adhered to an annular frame F is preferably performed as shown in FIG. 7. After the transfer step is performed, a peeling step for peeling the wafer 11 from the holding plate 12 is performed. In a first embodiment of the peeling step, as shown in FIG. 8A, while the wafer 11 is being suction-held by the dicing tape T from a chuck table (not shown), the adhesive member 18 of the intermediate member 14 is cut and removed by a cutting unit 50. The cutting unit 50 includes a vertically disposed spindle 52 and a cutting blade 54 attached to a tip portion of the spindle 52.In the first embodiment of the peeling step, the cutting blade 54 rotated at a high speed in the direction of the arrow A is caused to cut into the adhesive member 18 of the intermediate member 14, and the chuck table (not shown) is rotated at a low speed in the direction of the arrow R 1, thereby cutting and removing the adhesive member 18. After removing the adhesive member 18, the holding plate 12 is peeled together with the bendable member 16 from the wafer 11 adhered to the dicing tape T as shown in FIG. 8B.Next, a second embodiment of the peeling step will be described with reference to FIG. 9. In the peeling step in this embodiment, an ordinary cutting unit 50A having a spindle 52 extending in a horizontal direction is used. A cutting blade 54 rotated in the direction of the arrow A at a high speed is caused to cut into a peripheral portion of the holding plate 12 to a point close to a lower end portion of the adhesive member 18, and a chuck table (not shown) is rotated in the direction of the arrow R 1 at a low speed, thereby cutting and removing the adhesive 18 together with the peripheral portion of the holding plate 12. Thereby, as in the embodiment shown in FIG. 8B, the holding plate 12 together with the bendable member 16 can be removed from the wafer 11 adhered to the dicing tape T.The present invention is not limited to the details of the preferred embodiments described above. The scope of the invention is defined by the appended claims.

Claims

A method of processing a wafer (11) having, on a front surface (11a) thereof, a central portion (19) in which a plurality of devices (15) each formed with a plurality of bumps (17) are arranged, and a peripheral edge portion (21) surrounding the central portion (19), the method comprising: an intermediate member preparing step of preparing an intermediate member (14) including a bendable member (16) corresponding to the central portion (19) of the wafer (11) and an adhesive member (18) arranged on a peripheral edge of the bendable member (16); a adhering step of adhering the intermediate member (14) to a holding plate (12) through the adhering member (18) and adhering the wafer (11) to the intermediate member (14) adhered to the holding plate (12) through the adhering member (18) in a state where the central portion (19) of the wafer (11) is in contact with the bendable member (16); a grinding step of grinding a back surface (11b) of the wafer (11) after the adhering step is performed; and a peeling step of cutting and removing the adhering member (18) from the intermediate member (14) using a cutting unit (50) having a cutting blade (54) attached to a spindle (52) and peeling the wafer (11) from the holding plate (12) after the grinding step is performed.The method for processing a wafer (11) according to claim 1, further comprising a transfer step of adhering the wafer (11) to a dicing tape (T) having a peripheral portion adhered to an annular frame (F) after the grinding step is performed and before the peeling step is performed.

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