JP2006093285A - Method for dicing wafer from rear surface - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect a street on the surface of a wafer surely from the rear surface in the method for dicing the wafer from the rear surface. <P>SOLUTION: Prior to dicing a wafer having ground rear surface, rear surface of the wafer is roughened to have an arithmetic average roughness of 0.01 μm or less. When the arithmetic average roughness is set at such a level or below, wrong recognition of the street and a grinding scar is eliminated and the street can be detected surely. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of detecting a street formed on the surface of a wafer from the back side and dicing from the back side.

  A wafer that is partitioned by a street and has multiple devices formed on the front side is divided into individual devices by grinding the back side to a predetermined thickness and then dicing by cutting along the street. It is used in various electronic devices.

  When dicing, it is necessary to pick up an image of the street formed on the front surface and detect its position. Therefore, when shifting from grinding of the back surface to dicing, it is necessary to reverse the front and back of the wafer.

  However, when reversing the front and back of the wafer, since the wafer is thinly formed by grinding the back surface, the handling is difficult, and cracks and chips may occur. In view of this, a technique for dicing by detecting streets formed on the front surface of the wafer from the back side of the wafer using an infrared alignment unit has been proposed and put into practical use (for example, see Patent Document 1). According to such a technique, it is not necessary to reverse the front and back of the wafer when moving from grinding the rear surface to dicing.

JP-A-10-284449

  However, when the back surface of the wafer is ground, grinding marks are formed on the back surface. Therefore, when the focus of the objective lens constituting the infrared alignment unit is adjusted to the surface of the wafer on which the street S is formed, the thickness of the wafer is particularly reduced. When it is as thin as 100 μm or less and 50 μm or less, for example, as shown in FIG. 10, not only the street S on the front surface of the wafer but also the grinding marks 3 formed on the back surface may be imaged. And if the street S and the grinding trace 3 are imaged, the street S and the grinding trace 3 cannot be clearly distinguished and recognized, so the street position may be erroneously recognized.

  Therefore, the problem to be solved by the present invention is to make it possible to reliably detect the street on the front surface from the back surface in dicing from the back surface side of the wafer.

  The present invention provides a grinding process for grinding a back surface of a wafer partitioned by streets and having a plurality of devices formed on the surface, and a street formed on the wafer surface by infrared alignment from the back surface side of the wafer whose back surface is ground. The present invention relates to a dicing method from the back surface of a wafer provided with a dicing process for detecting and performing dicing along the street from the back surface side. Before the dicing process, the arithmetic average roughness of the back surface of the wafer is 0.01 μm or less. A back surface processing step of processing the back surface is performed so that Here, the arithmetic average roughness of the back surface of the wafer can be obtained by integrating the absolute value of the unevenness of the curve indicating the shape of the back surface. The back surface processing step is performed by polishing, CMP, etching, or the like.

  When the back surface of the wafer is ground so that the thickness of the wafer becomes 100 μm or less in the grinding process, it is particularly desirable to perform the back surface processing step. The dicing process is preferably performed by either dicing with a cutting blade or dicing with laser light.

  According to the present invention, the back surface is processed before the dicing step so that the arithmetic average roughness is 0.01 μm or less. Therefore, when alignment is performed from the back surface side in the dicing step, the streets and grinding marks are removed. Since misidentification is eliminated and the street can be reliably detected, dicing can be performed with high accuracy. In particular, when the thickness of the wafer is 100 μm or less in the grinding process, since the grinding marks are clearly imaged together with the street during the alignment as it is, the arithmetic average roughness of the back surface is 0.01 μm or less. It is effective to do.

  As shown in FIG. 1, a plurality of devices D are defined by streets S on a surface W1 of a wafer W to be ground. In grinding the back surface of the wafer W, for example, as shown in FIG. 2, the front surface W1 of the wafer W is adhered to the adhesive surface of the tape T adhered to the back surface of the frame F, and the wafer W passes through the tape T. Thus, the wafer W is stably supported by being integrated with the frame F. By sticking the front surface W1 of the wafer W on the adhesive surface of the tape T, the back surface W2 of the wafer W is exposed. Further, as shown in FIG. 3, the wafer W may be supported by sticking the surface W1 of the wafer W to a hard plate P made of glass, polyethylene terephthalate, or the like.

  If the explanation is continued based on the example of FIG. 2, the back surface W2 of the wafer W integrated with the frame F via the tape T is ground to a predetermined thickness by the grinding device 1 shown in FIG. The grinding apparatus 1 includes a chuck table 10 that holds a wafer to be ground, a grinding unit 11 that grinds the wafer held on the chuck table 10, and a grinding feed unit that causes the grinding unit 11 to approach or separate from the chuck table 10. 12.

  The chuck table 10 includes a suction unit 100 that sucks and holds the wafer W and a fixing unit 101 that fixes the frame F.

  The grinding means 11 includes a spindle 110 having a vertical axis, a drive source 111 that rotationally drives the spindle 110, a grinding wheel 113 that is fixed at a lower end of the spindle 110 via a wheel mount 112, and a grinding wheel 113. The grinding wheel 114 is fixed to the lower surface, and the grinding wheel 114 is rotated as the spindle 110 is rotated by being driven by the drive source 111.

  The grinding feed means 12 includes a pair of guide rails 121 arranged in a direction perpendicular to the wall 120, a ball screw 122 arranged in parallel to the guide rail 121, and a pulse motor 123 connected to one end of the ball screw 122, , Slidably engaged with the guide rail 121 and an inner nut screwed into the ball screw 122, and a support portion 124. The ball screw 122 is driven by the pulse motor 123 to rotate. The support part 124 is guided by the guide rail 121 and moves up and down, and the grinding means 11 supported by the support part 124 is also moved up and down.

  When the front surface W1 side of the wafer W is held in the chuck table 10 and the back surface W2 is exposed, the chuck table 10 moves in the horizontal direction, so that the wafer W is positioned directly below the grinding means 11. When the wafer W is positioned directly below the grinding means 11, the wafer W is rotated by the rotation of the chuck table 10, and the grinding means 11 is lowered while the grinding wheel 114 is rotated, and comes into contact with the back surface W <b> 2 of the wafer W for grinding. And is ground to a predetermined thickness (grinding step).

  Next, the surface roughness is reduced by removing as much as possible the grinding traces formed on the back surface of the wafer W formed to a predetermined thickness (not necessarily completely removed) and performing a flattening process. Improve and make the street clearly detectable by the alignment from the back side (back side processing step). For example, as shown in FIG. 5, the back surface is polished by the same operation as in the case of grinding using a grinding wheel 115 with small abrasive grains instead of the grinding wheel 114 in the grinding apparatus 1 of FIG. Is done by doing. Further, planarization can be performed by CMP (Chemical mechanical polishing), dry etching, wet etching, or the like. In FIG. 5, parts other than the polishing wheel 115 are denoted by the same reference numerals as those of the grinding apparatus 1 of FIG. 4.

  When the back surface processing step is performed and the arithmetic average roughness Ra defined by JISB0601, ISO 4287 or the like of the back surface W2 of the wafer W is set to 0.01 μm or less, the street S is clearly defined at the time of alignment from the back surface in the dicing process described later. It can be recognized and detected.

  Here, the arithmetic average roughness Ra when the back surface W2 is formed in the curved shape shown in FIG. 6, for example, will be described. In FIG. 6, the X axis indicates the length in the plane direction, and the Y axis indicates the height in the vertical direction of the back surface W2, that is, the unevenness of the back surface W2. Of the curve indicating the shape of the back surface W2, the portion protruding upward is defined as a peak, the portion recessed downward is defined as a valley, and the valley is folded back toward the peak with respect to the center line m (y = 0). The Y coordinate of the average line a obtained by averaging the heights is Ra. Assuming that the curve of the surface W1 is y = f (x), the arithmetic average roughness Ra can be obtained from the following equation by integrating the absolute value of f (x).

  In the above equation, L indicates a reference length, and the arithmetic average roughness Ra per unit reference length is obtained by using the above equation.

  The wafer W whose arithmetic mean roughness Ra of the back surface W2 has been improved as described above is then divided into individual devices using, for example, the dicing apparatus 2 shown in FIG. The dicing apparatus 2 shown in FIG. 7 includes a holding table 20 that holds a wafer, a cutting feed unit 21 that cuts and feeds the holding table 20 in the X-axis direction, and an infrared alignment unit 22 that detects a street to be cut on the wafer. A cutting means 23 for cutting the detected position, an index feeding means 24 for indexing and feeding the cutting means 23 in the Y-axis direction, and a cutting feed means 25 for cutting and feeding the cutting means 23 in the Z-axis direction are provided. .

  The holding table 20 includes a suction unit 200 that sucks and holds the wafer W, and a fixing unit 201 that fixes the frame F integrated with the wafer W.

  The cutting feed means 21 includes a ball screw 210 disposed in the X-axis direction, a pair of guide rails 211 disposed in parallel to the ball screw 210, a drive source 212 coupled to one end of the ball screw 210, and an internal nut ( (Not shown) are screwed into the ball screw 210 and the lower part is slidably engaged with the guide rail 211, and the connecting part 214 that connects the moving base 213 and the holding table 20 is formed. When the ball screw 210 is rotated by being driven by the driving source 212, the moving base 213 is guided by the guide rail 211 and moved in the X-axis direction, and the holding base 213 connected to the moving base 213 is accordingly moved. The table 20 is also configured to move in the X-axis direction.

  The cutting means 23 has a configuration in which a cutting blade 232 is attached to the tip of a spindle 231 that is rotatably supported by a housing 230, and is driven by a motor (not shown) to rotate the spindle 231. Accordingly, the cutting blade 232 rotates.

  The infrared alignment means 22 is fixed to the side portion of the housing 230 constituting the cutting means 23. The infrared alignment unit 22 includes an imaging unit 220 that captures an image of a wafer using infrared rays, and a detection unit 221 that detects a street to be cut on the wafer by processing based on an image acquired by the imaging unit 220.

  The index feeding means 24 includes a ball screw 240 disposed in the Y-axis direction, a pair of guide rails 241 disposed in parallel to the ball screw 240, a pulse motor 242 connected to a different end of the ball screw 240, and an internal nut. (Not shown) includes a moving base 243 slidably engaged with the guide rail 241 and screwed to the ball screw 240. When the ball screw 240 is driven by the pulse motor 242, the ball screw 240 is rotated. Accordingly, the moving base 243 is guided by the guide rail 241 and moves in the Y-axis direction.

  The notch feeding means 25 includes a wall portion 250 erected from the moving base 243, a ball screw (not shown) disposed in the Z-axis direction along the side surface of the wall portion 250, and a guide disposed in parallel with the ball screw. A rail 251, a pulse motor 252 connected to one end of the ball screw, and a support portion 253 that supports the cutting means 23 by slidingly engaging the guide rail 251 with an internal nut screwed into the ball screw. When the ball screw rotates by being driven by the pulse motor 252, the support portion 253 is guided by the guide rail 251 and moves in the Z-axis direction.

  When the wafer W integrated with the frame F is held by the holding table 20, it is driven by the cutting feed means 21 and the holding table 20 is moved in the X-axis direction, and is also driven by the indexing feed means 24 to be infrared alignment means. 22 moves in the Y-axis direction, and the imaging unit 220 is positioned immediately above the wafer W. Then, driven by the cutting and feeding means 25, the imaging unit 220 descends to image the wafer W, the wafer W is transmitted from the back surface W2 side by infrared rays and focused on the front surface W1, and the street S formed on the front surface W1. (See FIG. 1).

  When the surface of the wafer W is detected using infrared rays, for example, an image as shown in FIG. In this image, the grinding marks are removed by the back surface processing step, and the arithmetic average roughness Ra of the back surface W2 is 0.01 μm or less. Therefore, the detection unit 221 constituting the alignment means 22 clearly defines the street S1. It can be recognized and detected. Moreover, even if some grinding traces remain, it is confirmed that the street S1 and the grinding traces are not misidentified if the arithmetic average roughness is 0.01 μm or less.

  As shown in FIG. 9, an alignment reference line 220 a is formed on the lens of the imaging unit 220, and the infrared alignment unit 22 is moved so that the alignment reference line 220 a is positioned at the center of the street S. As shown in FIG. 7, the infrared alignment means 22 and the cutting means 23 are integrated, and as shown in FIG. 9, the cutting blade 232 constituting the cutting means 23 is in the X-axis direction of the alignment reference line 220a. Since it is on the extension line, when the alignment reference line 220a is positioned at the center of the street S1, the cutting blade 232 is aligned with the street S1.

  Accordingly, when the holding table 20 shown in FIG. 7 is moved in the + X direction in this state, and the cutting blade 23 is lowered and the cutting blade 232 that rotates at high speed is cut into the street S1, the center of the street S1 is cut. Is done. In addition, the holding table 20 is reciprocated in the X-axis direction while indexing and feeding the cutting means 23 in the Y-axis direction at every street interval, and the cutting blades 232 are successively cut into the street so that all streets in the same direction are cut. Is done.

  Further, when the wafer W is rotated 90 degrees by rotating the holding table 20 and then the infrared alignment and cutting similar to the above are performed, all the streets are cut vertically and horizontally, and the wafer W is diced individually. Device D.

  In the above example, dicing by cutting has been described. However, dicing by laser light may be performed in the dicing process. In this case, laser light is irradiated from the back side.

It is a perspective view which shows an example of a wafer. It is a perspective view which shows an example of the wafer integrated with the flame | frame via the tape. It is a perspective view which shows an example of the wafer united with the hard plate. It is a perspective view which shows an example of a grinding device. It is a schematic sectional drawing which shows an example of a grinding | polishing process. It is explanatory drawing which shows the calculation method of arithmetic average roughness. It is a perspective view which shows an example of a dicing apparatus. It is explanatory drawing which shows the detected street. It is explanatory drawing which shows the positional relationship of a cutting blade and an imaging means. It is explanatory drawing which shows a street and a grinding trace.

Explanation of symbols

W: Wafer W1: Front surface W2: Back surface D: Device S: Street T: Tape F: Frame P: Hard plate 1: Grinding device 10: Chuck table 100: Suction part 101: Fixing part 11: Grinding means 110: Spindle 111: Driving source 112: Wheel mount 113: Grinding wheel 114: Grinding wheel 115: Polishing wheel 12: Grinding feed means 120: Wall part 121: Guide rail 122: Ball screw 123: Pulse motor 124: Supporting part 2: Dicing device 20: Holding table 200: Suction unit 201: Fixed unit 21: Cutting feed unit 210: Ball screw 211: Guide rail 212: Drive source 213: Moving base 214: Connection unit 22: Infrared alignment unit 220: Imaging unit 221: Detection unit 23: Cutting unit 230: Housing 231 : Spindle 232: Cutting blade 24: Index feed means 240: Ball screw 241: Guide rail 242: Pulse motor 243: Moving base 25: Cutting feed means 250: Wall part 251: Guide rail 252: Pulse motor 253: Support part

Claims (3)

A grinding process for grinding a back surface of a wafer partitioned by streets and having a plurality of devices formed on the front surface, and detecting a street formed on the front surface of the wafer by infrared alignment from the back surface side of the ground wafer. And a dicing method from the back surface of the wafer comprising a dicing process for performing dicing along the street from the back surface side,
A dicing method from the back surface of the wafer, wherein a back surface processing step is performed before the dicing step so that the arithmetic average roughness of the back surface of the wafer is 0.01 μm or less. The dicing method from the back surface of the wafer according to claim 1, wherein in the grinding step, the back surface of the wafer is ground so that the thickness of the wafer becomes 100 μm or less. The dicing method from the back surface of the wafer according to claim 1, wherein the dicing step is performed by either dicing by a cutting blade or dicing by laser light.

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