JP5121390B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a processing method for grinding a convex portion of a wafer in which only a region on the back surface side corresponding to a device forming region is removed by forming a desired thickness to form a concave portion, and as a result, the outer peripheral surplus region becomes a convex portion. .

  A semiconductor chip having an electronic circuit such as an IC or LSI formed on its surface is now indispensable for downsizing various electric / electronic devices. A semiconductor chip is a disk-shaped semiconductor wafer (hereinafter, referred to as a wafer), which is divided into grid-like rectangular areas by dividing lines called streets, and an electronic circuit is formed in these rectangular areas. It is manufactured in the process of cutting and dividing.

  In such a manufacturing process, before the wafer is divided into semiconductor chips, the back surface opposite to the device surface on which the electronic circuit is formed is ground by a grinding apparatus and thinned to a predetermined thickness. Yes. The purpose of grinding the back surface is to further reduce the size and weight of the electronic device and to improve the heat dissipation and maintain the performance. Such a wafer thinned by backside grinding is less rigid than the wafer before thinning, and there is a problem that handling and transporting of the wafer after backside grinding becomes difficult. Therefore, in order to ensure rigidity, only the area on the back side corresponding to the device formation area where the device is formed is ground, and a convex part is formed as a reinforcement in the outer peripheral surplus area that is the outer periphery of the device formation area To be done.

  Thus, by forming the convex portion in the outer peripheral surplus region, the outer thickness is maintained and the rigidity of the wafer is ensured, and the wafer is easily handled and transported after the backside grinding. However, if the convex portion is formed in the outer peripheral surplus region, there arises a problem that the convex portion becomes an obstacle during the dicing process for dividing into semiconductor chips. Therefore, when a convex part is formed in an outer periphery surplus area, it is necessary to remove a convex part before performing a dicing process. As a method of removing the convex portion, for example, there is a method of Patent Document 1.

JP 2007-19379 A

  As in Patent Document 1, the back surface may be covered with a metal film such as gold, silver, or titanium after the back surface grinding of the wafer. In such a case, if the convex portion is ground without measuring the thickness of the wafer, it is excessively ground, and the metal film in the region corresponding to the device formation region may be peeled off. On the other hand, when the amount of grinding of the convex part becomes too small and the convex part remains without being removed, the convex part may become an obstacle during the dicing process as described above. For this reason, it is preferable to measure the thickness of the device formation region and the thickness of the outer peripheral surplus region by using a thickness measuring instrument to grind the convex portion. However, in a contact-type thickness measuring device in which a contact terminal is brought into contact with a measurement location, the contact terminal damages the metal film and cannot be used. Further, the non-contact type thickness measuring instrument is affected by grinding water supplied to the grinding surface of the wafer during grinding, and the thickness of the wafer cannot be measured accurately. Therefore, the thickness of the concave and convex portions of the wafer is measured by a non-contact type sensor before grinding, and only the convex portion is measured by a contact type sensor during grinding. When an error occurs due to temperature drift, which is a deviation in measured values caused by changes in the surface, or due to the influence of foreign matter adhering to the holding surface, and the thickness of the concave part that serves as a reference for grinding the convex part is temporarily measured with a contact-type sensor Need to be estimated.

  Therefore, the present invention provides a device forming region in a processing method in which only the region on the back surface side corresponding to the device forming region is removed by a desired thickness, and as a result, the convex portion of the wafer whose outer peripheral surplus region becomes a convex portion is removed. It is an object of the present invention to provide a wafer processing method capable of measuring the thickness of the outer peripheral region and the thickness of the outer peripheral surplus region and reliably grinding the outer peripheral surplus region to the optimum thickness.

The present invention removes a region on the back surface side corresponding to a device formation region by a predetermined thickness from a wafer having a device formation region having a plurality of devices formed on the surface and an outer peripheral surplus region surrounding the device formation region. A recess is formed, and as a result, a metal film is coated on the recess of the wafer whose outer peripheral surplus region has become a protrusion, and then the protrusion that is no longer needed is ground. A first thickness measuring step of measuring the thickness of the outer peripheral surplus area in which the convex part of the wafer is formed and the thickness of the device forming area in which the concave part is formed by a non-contact sensor; The thickness is measured in a second thickness measuring step and a first thickness measuring step in which the thickness of the outer peripheral area where the convex portion of the wafer is formed is measured by a contact type sensor while the back surface is adsorbed in the exposed direction. The The thickness of the peripheral surplus region is a, the thickness of the peripheral surplus region measured in the second thickness measurement step is a ′, and the thickness of the device formation region measured in the first thickness measurement step is b. In this case, the difference a′−a is obtained as a measurement error, and b is added to the difference a′−a to calculate the thickness b ′ of the device formation region that is expected to be measured by the contact sensor. And a convex portion grinding step of grinding the thickness of the outer peripheral surplus region of the wafer adsorbed on the adsorption table to a desired value on the basis of b. .

  The present invention measures the thickness of the concave and convex portions of a wafer in which the back surface of the device formation region is concave and the back surface of the peripheral surplus region is convex, and the peripheral surplus region is ground to a desired thickness. . In the first thickness measuring step, the thickness a of the outer peripheral surplus region and the thickness b of the device forming region are measured using a non-contact sensor. Next, in the second thickness measurement step, the thickness a ′ of the outer peripheral surplus area is measured in a state where the wafer is sucked onto the suction table. In the device formation region thickness calculation step, the thicknesses a and a ′ of the outer peripheral region obtained in the respective thickness steps and the thickness b of the device formation region will be measured by a contact sensor. The predicted thickness b ′ = (a′−a) + b of the device formation region is calculated. Through these steps, the thickness b 'of the device formation region of the wafer that is attracted to the suction table is obtained without bringing anything into contact with the concave portion of the wafer that is the back surface of the device formation region. With reference to the thickness b 'of the device formation region, the convex portion of the wafer is ground. In the grinding of the convex portion, since the grinding of the convex portion is controlled by using the thickness b ′ + α (remaining margin of the convex portion) of the device forming region as a desired grinding amount, the thickness b ′ of the device forming region becomes a reference. .

  For example, a metal film such as gold, silver, or titanium may be formed on the back surface of the wafer. It is not preferable to measure. In addition, since grinding water is supplied to the grinding surface of the wafer during grinding, the thickness of the convex part and the concave part can be accurately measured using a non-contact sensor on the suction table. Have difficulty. For this reason, it is difficult to measure the thickness of the device formation region serving as a reference for grinding using the sensor in the state of being sucked by the suction table. However, in the present invention, in order to obtain the thickness b ′ of the device forming region that is a reference for grinding without bringing anything into contact with the concave portion of the wafer, the outer peripheral surplus region has a desired thickness without damaging the back surface of the device forming region. Can be reliably ground.

  In addition, when the thickness of one wafer is measured by a plurality of thickness measuring instruments, an error may occur in the measurement value due to the influence of temperature drift, foreign matter attached to the holding surface, and the like. For example, if the measurement result of the non-contact type sensor is “100”, the contact type sensor becomes “101” and the value “200” becomes “201”. This is a case where the value of the error is constant without being proportional. Therefore, when measuring the thickness of a wafer using a plurality of thickness measuring devices at a plurality of locations, it is preferable to grasp a shift error occurring between the measured values and correct the measured values. In the present invention, the thicknesses of the concave and convex portions are measured at different locations using two non-contact type and contact type thickness measuring instruments, so there is a shift error between the measured values. May occur. However, by obtaining the thicknesses a and a ′ of the convex portions as described above, it is possible to grasp a shift error generated between the non-contact type thickness measuring device and the contact type thickness measuring device. Using the thicknesses a and a ′ of the convex portions, a′−a that is a difference between the measurement values is obtained, and added to the thickness b of the device formation region, so that the gap between the non-contact sensor and the contact sensor is increased. The thickness b ′ of the device forming region in consideration of the generated shift error is obtained. As a result, a desired grinding result can be obtained even if a shift error occurs in the measurement results using different sensors.

  In the present invention, when grinding a convex portion of a wafer having a concave portion on the back surface corresponding to the device formation region and a convex portion on the back surface of the outer peripheral surplus region, the wafer serving as a reference for grinding without contacting the concave portion of the wafer In order to obtain the thickness of the device forming region, it is possible to reliably grind the outer peripheral surplus region to a desired thickness without damaging the back surface of the device forming region. As a result, the occurrence of grinding errors can be suppressed, and the processing efficiency can be improved.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[1] Semiconductor wafer Reference numeral 1 in FIG. 1 denotes a disk-shaped semiconductor wafer. The wafer 1 is a silicon wafer or the like, and the thickness before processing is, for example, about 700 μm. On the surface 1 a of the wafer 1, a plurality of rectangular semiconductor chips (devices) 3 are partitioned by grid-like division planned lines 2. An electronic circuit (not shown) such as an IC or an LSI is formed on the surface of the semiconductor chip 3.

  The plurality of semiconductor chips 3 are formed in a substantially circular device formation region 4 concentric with the wafer 1. The device forming region 4 occupies most of the wafer 1, and the outer periphery of the wafer 1 around the device forming region 4 is an annular outer peripheral region 5 in which the semiconductor chip 3 is not formed. A V-shaped notch 6 indicating a semiconductor crystal orientation is formed at a predetermined location on the outer peripheral surface of the wafer 1. The notch 6 is formed in the outer peripheral surplus region 5.

  As shown in FIG. 2, in the wafer 1, a region on the back surface 1 b side corresponding to the device formation region 4 is ground to a predetermined thickness. By this grinding, on the back surface 1b of the wafer 1, a concave portion 4A is formed in a region corresponding to the device forming region 4, and an annular convex portion 5A is formed around the concave portion 4A. Further, after grinding on the back surface 1b side corresponding to the device formation region 4, the concave portion 4A is coated with a metal film such as gold, silver, titanium, etc., and then the convex portion 5A is ground. In performing such processing, the protective tape 7 is attached to the entire surface 1a on which the semiconductor chip 3 is formed. When the back surface grinding or the convex portion 5A is ground, the wafer 1 is placed with the front surface 1a aligned with the chuck table of the grinding apparatus in order to expose the back surface 1b. The protective tape 7 is affixed to the surface 1a in order to prevent and protect the surface 1a from coming into direct contact with the chuck table and damaging the electronic circuit or the like. For example, the protective tape 7 has a structure in which an adhesive of about 5 to 20 μm is applied to one side of a soft resin base sheet such as polyolefin having a thickness of about 70 to 200 μm, and the adhesive is used as the surface 1 a of the wafer 1. It is pasted according to.

  As described above, the back surface side grinding corresponding to the device forming region 4 and the convex portion 5A are ground with the back surface exposed and held on the chuck table, and the grindstone tool disposed opposite to the chuck table is rotated while the wafer 1 is rotated. This is done by a grinding apparatus configured to press against the back surface 1b.

[2] Grinding apparatus Referring to FIGS. 3 to 8, the region corresponding to the back surface 1b side of the device forming region 4 of the wafer 1 (grinding for forming the recess 4A) and the processing method of this embodiment are suitable. A grinding apparatus to be implemented will be described.
According to this grinding apparatus 10, the surface 1 a side of the wafer 1 is attracted to the suction surface of the vacuum chuck type chuck table 30 via the protective tape 7, and the wafer 1 is held. Rough grinding and finish grinding are sequentially performed on the wafer 1 by 40A and 40B.

  As shown in FIG. 3, the grinding apparatus 10 has a rectangular parallelepiped base 11, and the wafer 1 is placed in a supply cassette 12 </ b> A that is detachably set at a predetermined position on the base 11. A plurality are stacked and stored with the side up. One wafer 1 stored in the supply cassette 12A is pulled out by the transfer robot 13, placed on the positioning table 14 with the front and back turned upside down and the back side facing up. It is done. The positioning table 14 is a table having a vacuum mechanism capable of vacuum-sucking the wafer 1, but at the stage where the wafer 1 is placed, the plurality of positioning pins 14 </ b> A are simultaneously directed toward the center of the positioning table 14 without being vacuumed. By moving, the center of the positioning table 14 and the center of the wafer 1 are aligned with each other for positioning. Thereafter, the wafer 1 is fixed by vacuum suction, the positioning table 14 is rotated, and the position of the notch 6 of the wafer 1 is detected by the notch sensor 15. Next, the thickness b of the concave portion 4A and the thickness a of the convex portion 5A of the wafer 1 are measured using the first thickness measuring device 16 shown in FIG. 4 provided in the vicinity of the positioning table 14. In the description here, “thickness of the concave portion” means the thickness of the device forming region 4 formed by thinning the concave portion 4A, and “thickness of the convex portion” This refers to the thickness of the surplus region 5.

  As shown in FIG. 4, the first thickness measuring device 16 includes a linear guide 17 fixed to the base 11, a slider 18 slidably mounted on the linear guide 17, and a side end portion on the slider 18. The arm 19 is attached, and the measuring head 20 is attached to the tip of the arm 19. As the measuring head 20, a generally known laser displacement meter or the like is used. The measuring head 20 fixed to the tip of the arm 19 is moved by the linear guide 17 through the slider 18 so as to be able to advance and retreat in the center direction of the positioning table 14. The thicknesses of the convex portions 5A and the concave portions 4A may be measured by another measuring device in addition to being performed on the grinding device 10, and the results may be fed back to the grinding device 10. In general, a laser displacement meter is easily affected by water droplets or the like and is limited to use in a dry environment. Therefore, the laser displacement meter cannot be used in a situation where a liquid such as grinding water in the vicinity of the grinding units 40A and 40B is used.

  A turntable 35 that is rotationally driven in the R direction (shown in FIG. 3) is provided on the base 11, and a plurality of (in this case, three) disks are provided on the outer periphery of the turntable 35. -Shaped chuck tables 30 are arranged at equal intervals in the circumferential direction. These chuck tables 30 are rotatably supported with the Z direction (vertical direction) as a rotation axis, and are driven to rotate by a drive mechanism (not shown).

  The wafer 1 that has been positioned on the positioning table 14 is picked up from the positioning table 14 by the supply arm 21, and the surface 1 a side on which the protective tape 7 is adhered is placed on one chuck table 30 that is operated in vacuum. It is placed concentrically in the state of facing. As shown in FIG. 5 (b), the chuck table 30 has a circular suction portion 32 formed of a porous member at the center upper portion of a frame 31. The wafer 1 is placed on the upper surface 32 a of the suction portion 32. The protective tape 7 is adhered and held in a state where the protective tape 7 is in close contact and the back surface 1b is exposed. For this reason, the electronic circuit of the semiconductor chip 3 on the surface 1a side of the wafer 1 is protected by the protective tape 7 and is prevented from being damaged.

  The wafer 1 held on the chuck table 30 is fed to a primary grinding position below the rough grinding unit 40A by rotating the turntable 35 by a predetermined angle in the R direction (clockwise direction). At this position, the wafer 1 is roughly ground by the grinding unit 40A. Next, the turntable 35 is again rotated by a predetermined angle in the R direction to feed the wafer 1 to a secondary grinding position below the finish grinding unit 40B. At this position, the wafer 1 is finish ground by the grinding unit 40B. The

  Each of the grinding units 40A and 40B has the same configuration, and is distinguished by the fact that the grindstones to be mounted are different for rough grinding and finish grinding. As shown in FIGS. 5 and 6, the grinding units 40 </ b> A and 40 </ b> B include a cylindrical spindle housing 41 whose axial direction extends in the Z direction, and a spindle shaft that is coaxially and rotatably supported in the spindle housing 41. 42, a motor 43 that is fixed to the upper end of the spindle housing 41 and rotationally drives the spindle shaft 42, and a disk-shaped flange 44 that is coaxially fixed to the lower end of the spindle shaft 42.

  As shown in FIG. 5B, a grindstone wheel 45 for forming a recess is detachably attached to the flange 44. The grindstone wheel 45 has a plurality of grindstones 47 arranged in an annular shape and fixed to the lower surface of an annular frame 45a. The cutting edge that is the lower end surface of the grindstone 47 is set to be orthogonal to the axial direction of the spindle shaft 42. As the grindstone 47, for example, a material obtained by mixing, molding, and sintering diamond abrasive grains in a glassy bond material is used. The grinding outer diameter of the grindstone wheel 45 corresponds to the radius of the recess 4 </ b> A formed to be slightly smaller than the radius of the wafer 1. The frame 45a of the grindstone wheel 45 is formed in a conical shape whose diameter decreases as the lower portion goes downward, and the outer diameter of the lower end surface on which the grindstone 47 is arranged has a dimension corresponding to the radius of the recess 4A. .

  The grindstone 47 fixed to the grindstone wheel 45 is for rough grinding and finish grinding. The grindstone wheel 45 for which the grindstone 47 is for rough grinding is mounted on a grinding unit 40A for rough grinding. Further, the grindstone wheel 45 in which the grindstone 47 is used for finish grinding is mounted on a grinding unit 40B for finish grinding. As the grinding wheel 47 for rough grinding, for example, one containing relatively coarse abrasive grains of about # 320 to # 600 is used. Further, as the grindstone 47 attached to the grinding unit 40B for finish grinding, for example, a grindstone containing relatively fine abrasive grains of about # 2000 to # 8000 is used. Each of the grinding units 40A and 40B is provided with a grinding water supply mechanism (not shown) for supplying grinding water for cooling and lubrication of the grinding surface or discharging grinding debris.

  Each of the grinding units 40A and 40B is attached to the front surface of a pair of left and right columns 26 arranged in the X direction that are erected on the back end of the base 11. The mounting structure of each grinding unit 40A, 40B with respect to each column 26 is the same and is symmetrical in the X direction.

  The front surface 26a on the front side in the Y direction of each column 26 is a vertical surface with respect to the upper surface of the base 21, but tapers back obliquely at a predetermined angle from the center in the X direction toward the end. Formed on the surface. The horizontal direction of the taper surface 26a, that is, the taper direction, is the position of the chuck table 30 positioned at the corresponding front machining position (the left primary machining position in the left column 26 and the right secondary machining position in the right column 26). It is set to be parallel to a line connecting the rotation center and the rotation center of the turntable 35.

  As shown in FIGS. 3 and 7, the taper surface 26 a of each column 26 is provided with a pair of upper and lower guides 51 parallel to the taper direction, and the X-axis slider 52 slides on the guides 51. It is installed freely. The X-axis slider 52 is reciprocated along the guide 51 by a ball screw type feed mechanism (not shown) driven by a servo motor 53. The reciprocating direction of the X-axis slider 52 is parallel to the direction in which the guide 51 extends, that is, the taper direction of the tapered surface 26a.

  The front surface of the X-axis slider 52 is a surface along the X / Z direction, and the grinding units 40A and 40B are installed on the front surface so as to be movable up and down in the Z direction (vertical direction). These grinding units 40 </ b> A and 40 </ b> B are slidably mounted via a Z-axis slider 55 on a guide 54 that extends in the Z direction and is provided on the front surface of the X-axis slider 52. Each grinding unit 40A, 40B is moved up and down in the Z direction via a Z-axis slider 55 by a ball screw type feed mechanism 57 driven by a servo motor 56.

  As described above, the direction connecting the rotation center of each chuck table 30 positioned at the primary processing position and the secondary processing position and the rotation center of the turntable 35 (indicated by an arrow F in FIGS. 7 and 8). The direction (hereinafter referred to as the inter-axis direction) is set parallel to the taper direction of the front surface 26a of the column 26, that is, the direction in which the guide 51 extends. In each grinding unit 40A, 40B, the center of rotation of the grinding wheel 45 (axial center of the spindle shaft 42) corresponds to the corresponding machining position (primary machining position in the grinding unit 40A, and secondary machining position in the finishing grinding unit 40B). The position is set so as to exist directly above the inter-axis direction connecting the rotation center of the chuck table 30 and the rotation center of the turntable 35. Therefore, when the grinding units 40A and 40B move along the guide 51 together with the X-axis slider 52, the rotation center of the grinding wheel 45 is set to move along the inter-axis direction.

  By the way, when grinding the concave portion 4A and the convex portion 5A, the thickness of the wafer 1 is measured by the contact-type second thickness measuring device 60 provided in the vicinity of each processing position in both rough grinding and finish grinding. Are measured one by one, and the grinding amount is controlled based on the measured value. As shown in FIG. 5A, the second thickness measuring device 60 is configured by a combination of a reference height gauge 61 and a movable height gauge 62.

  The height gauges 61 and 62 are respectively provided with probes 61 a and 62 a, the probe 61 a of the reference side height gauge 61 comes into contact with the surface 31 a of the frame 31 of the chuck table 30, and the probe 62 a of the movable side height gauge 62 is convex on the wafer 1. It is set so as to contact the part 5A. In the second thickness measuring device 60, the thickness measurement value of the wafer 1 attracted to the chuck table 30 is output by comparing the height positions of the contact points of the probes 61a and 62a. The contact point of the probe 61a of the movable height gauge 61 when the concave portion 4A is formed and the thickness of the device forming region 4 is measured is preferably the outer peripheral side of the concave portion 4A as shown by the broken line in FIG.

  The wafer 1 that has been ground is collected as follows. First, the finishing grinding unit 40B is raised and retracted from the wafer 1, while the turntable 35 is rotated by a predetermined angle in the R direction so that the wafer 1 is mounted on the chuck table 30 from the supply arm 21. Return to position. The vacuum operation of the chuck table 30 is stopped at this attachment / detachment position, and then the wafer 1 is moved to the cleaning unit 23 by the recovery arm 22 and cleaned.

  In the cleaning unit 23, the wafer 1 is sucked and held on a rotary suction table having the same diameter as that of the wafer 1, and cleaning water such as pure water is dropped near the center of the wafer 1 while rotating at about 1000 rpm. The back side is cleaned. Thereafter, dry air is blown and dried while the rotational speed is increased to about 2000 to 3000 rpm. The wafer 1 cleaned by the cleaning unit 23 is transferred and accommodated in the collection cassette 12B by the transfer robot 13.

[3] Grinding method for forming recesses and processing method of this embodiment The above is the configuration of the grinding apparatus 10, and the method for forming the recesses and the grinding method of the protrusions that is the processing method of this embodiment will be described next. .
(A) Grinding method for forming recesses First, the distance between the axes of the grinding unit 40A (40B) is adjusted for forming the recesses 4A. The grinding unit 40A (40b) moves the X-axis slider 52, so that the grinding outer diameter of the grinding wheel 45 facing the back surface of the wafer 1 is set to the device formation region 4 of the wafer 1 as shown in FIGS. It is located in the recessed part formation position corresponding to the radius. This recess formation position is a position where the cutting edge of the grindstone 47 passes near the rotation center of the wafer 1 and the outer peripheral edge of the device formation region 4, and in this case, is closer to the outer periphery of the turntable 35 than the rotation center of the wafer 1. .

  Next, the wafer 1 to be ground is taken out from the supply cassette 12A by the transfer robot 13, placed on the positioning table 14, and determined at a fixed position. When the wafer 1 is positioned, it is picked up from the positioning table 14 by the supply arm 21 and mounted on the chuck table 30 waiting at the attachment / detachment position with the surface to be ground (the back surface on which the semiconductor chip 3 is not formed) facing upward. Placed.

  The wafer 1 placed on the chuck table 30 is transferred to the primary grinding position by the rotation of the turntable 35 in the R direction. The recess 4A of the wafer 1 positioned at the primary grinding position is roughly ground to a predetermined thickness by the grinding unit 40A. In the primary grinding position, it is preferable to grind to a thickness of about 20 to 40 μm after finish grinding. When the recess 4A is ground to a predetermined thickness, the grinding unit 40A is retracted from the wafer 1, the turntable 35 is rotated, and the wafer 1 is positioned at the secondary grinding position. Next, the wafer 1 is finish-ground by the grinding unit 40B in the same manner as the primary grinding. The wafer 1 that has been subjected to the secondary grinding is returned to the attachment / detachment position when the turntable 35 further rotates in the R direction.

  On the surface to be ground after rough grinding at the time of forming the recesses 4A, the grinding striations 9 exhibiting a pattern in which a large number of arcs are drawn radially remain. The grinding striation 9 is a trajectory of crushing by abrasive grains in the grindstone, and is a mechanical damage layer including microcracks and the like. The grinding striation 9 by rough grinding at the time of forming the recess 4A is removed by finish grinding at the time of forming the recess 4A, but a new grinding streak may remain even by finish grinding.

  The wafer 1 on the chuck table 30 returned to the attachment / detachment position is picked up by the recovery arm 22 as described above, transferred to the cleaning unit 23, washed with water and dried. The wafer 1 cleaned by the cleaning unit 23 is transferred and accommodated in the collection cassette 12B by the transfer robot 13. The above is the overall operation of the grinding apparatus 10 at the time of forming the recesses, and this operation is repeated to grind a large number of wafers 1 continuously.

(B) Grinding method for convex grinding First, the distance between the axes of the grinding unit 40A (40B) is adjusted for grinding the convex 5A. As shown in FIGS. 6 and 8, the grinding unit 40A (40b) moves the X-axis slider 52 so that the grindstone 47 of the grindstone wheel 45 facing the back surface of the wafer 1 contacts the convex portion 5A. Positioned at the grinding position.

  Next, the wafer 1 is taken out from the supply cassette 12 </ b> A by the transfer robot 13 and placed on the positioning table 14 and determined at a certain position in the same manner as in the method for forming the recess. When the wafer 1 is positioned, the thicknesses of the concave portions 4A and the convex portions 5A of the wafer 1 are measured by the first thickness measuring device 16 (first thickness measuring step). In the first thickness measurement step, first, the measurement head 20 of the first thickness measuring device 16 moves until it is disposed immediately above the convex portion 5A. When the measurement head 20 is disposed immediately above the convex portion 5A, the measurement head 20 irradiates the convex portion 5A with laser light, and the thickness a of the convex portion 5A of the wafer 1 is measured. After the thickness a of the convex portion 5A is measured, the measuring head 20 further moves inward, and the thickness b of the concave portion 4A is measured in the same manner as the measurement of the convex portion 5A. When the thickness a of the convex portion 5A and the thickness b of the concave portion 4A are measured, the measuring head 20 moves outward and the measuring head 20 retracts from the wafer 1. Next, the wafer 1 is picked up from the positioning table 14 by the supply arm 21 and placed on the chuck table 30 waiting at the attachment / detachment position with the surface to be ground (the back surface 1b on which the semiconductor chip 3 is not formed) facing upward. Is done.

  The wafer 1 is transferred to the primary grinding position by the rotation of the turntable 35 in the R direction. Once transferred, the thickness a 'of the convex portion 5A of the wafer 1 is measured (second thickness measuring step). In the second thickness measuring step, the reference-side probe 61a of the second thickness measuring device 60 is brought into contact with the frame 31a, and the movable-side probe 62a is brought into contact with the surface of the convex portion 5A to thereby form the convex portion 5A. Is measured. Thereafter, the thicknesses a and a ′ of the convex portions 5A and the thickness b of the concave portions 4A obtained by the thickness measuring devices 16 and 60 are supplied to the arithmetic unit, and the concave portions 4A of the wafer 1 held on the chuck table 30 are obtained. The thickness b ′ = (a′−a) + b is calculated. (Device formation region thickness calculation step) Based on the calculated thickness b 'of the concave portion 4A, grinding is performed until the convex portion 5A has a desired thickness (convex portion grinding step). In grinding the convex portion 5A, since the grinding of the convex portion 5A is controlled with the thickness b ′ + α (remaining margin of the convex portion 5A) of the concave portion 4A as a desired grinding amount, the thickness b ′ of the concave portion 4A is used as a reference. Become. At this time, the thickness of the convex portion 5A is measured one by one, and the grinding amount is controlled. In the primary grinding position, it is preferable to grind from the bottom surface of the recess 4A to +20 to 40 μm. When the convex portion 5A reaches a desired thickness, the grinding unit 40A is retracted. Next, the turntable 35 rotates in the R direction, and the wafer 1 moves to the secondary grinding position. Next, the convex portion 5A is finish-ground in the same manner as in the primary grinding position. The wafer 1 that has been subjected to the secondary grinding is returned to the attachment / detachment position when the turntable 35 further rotates in the R direction.

  The wafer 1 on the chuck table 30 returned to the attachment / detachment position is picked up by the recovery arm 22 in the same manner as the above-described method of forming the recess, transferred to the cleaning unit 23, washed with water and dried. The wafer 1 cleaned by the cleaning unit 23 is transferred and accommodated in the collection cassette 12B by the transfer robot 13. The above is the overall operation of the grinding apparatus 10 of the present embodiment, and this operation is repeated to grind a large number of wafers 1 continuously.

  In the present embodiment, the thickness of the concave portion 4A and the convex portion 5A of the wafer 1 in which the back surface of the device forming region 4 is concave and the back surface of the outer peripheral surplus region 5 is convex is measured, and the convex portion 5A has a desired thickness. To grind. In the first thickness measurement step, the thickness a of the convex portion 5A and the thickness b of the concave portion 4A are measured using the first thickness measuring device 16. Next, in the second thickness measuring step, the thickness a ′ of the convex portion 5 </ b> A is measured using the second thickness measuring device 60 while the wafer 1 is attracted to the chuck table 30. In the device formation region thickness calculation step, the thickness b ′ = (a ′) of the concave portion 4A is obtained using the thicknesses a and a ′ of the convex portion 5A and the thickness b of the concave portion 4A obtained in the respective thickness steps. -A) + b is calculated. Through these steps, the thickness b 'of the recess 4A of the wafer 1 in the state of being attracted to the chuck table 30 is obtained without making any contact with the recess 4A of the wafer 1.

  For example, a metal film such as gold, silver, or titanium may be formed on the back surface 1b of the wafer 1, so that a contact terminal of a contact-type measuring instrument is brought into contact with the thickness b of the recess 4A. It is not preferable to measure. Further, since grinding water or the like is supplied to the grinding surface of the wafer 1 at the time of grinding, the thickness b of the concave portion 4A and the thickness a of the convex portion 5A are accurately determined using a non-contact type measuring device during grinding. It is difficult to measure. For this reason, it is difficult to measure the thickness b 'of the concave portion 4A serving as a grinding reference by using the above measuring devices during grinding while being attracted to the chuck table 30. However, in the present invention, in order to obtain the thickness b ′ of the concave portion 4A serving as a reference for grinding without bringing the concave portion 4 into contact with the concave portion 4 of the wafer 1, the convex portion 5A can be formed as desired without damaging the back surface of the device forming region 4. It can be reliably ground to a thickness.

  Further, when the thicknesses of the concave portions 4A and the convex portions 5A of the wafer 1 are measured by the thickness measuring devices 16 and 60, the thickness is measured by the temperature drift of the measuring devices 16 and 60 or the foreign matter attached to the upper surface 32a of the suction portion 32. There may be an error in the value. Therefore, when measuring the thickness of the wafer 1 at a plurality of locations using the thickness measuring devices 16 and 60, it is preferable to grasp the shift error generated between the measured values and correct the measured values. . In the present embodiment, the thickness of the concave portion 4A and the convex portion 5A is determined on the positioning table 14 and the chuck table 30 by using the non-contact type first thickness measuring device 16 and the contact type second thickness measuring device 60. Since measurement is performed, there is a possibility that a shift error occurs between the respective measured values. However, the shift error generated between the first thickness measuring device 16 and the second thickness measuring device 60 can be grasped by obtaining the thicknesses a and a 'of the convex portion 5A as described above. The first thickness measuring device 16 and the second thickness are obtained by obtaining a′−a which is a difference between the measurement values using the thicknesses a and a ′ of the convex portion 5A and adding the thickness to the thickness b of the concave portion 4A. The thickness b ′ of the concave portion 4A in which a shift error generated between the measuring device 60 and the measuring device 60 is taken into consideration is obtained.

It is the (a) perspective view and (b) side view of the wafer processed with the processing method of one embodiment of the present invention. It is a perspective view which shows the back surface side of the wafer in which the recessed part was formed in the back surface. It is a perspective view which shows the grinding processing apparatus which can implement suitably the processing method of one Embodiment. It is a side view which shows a mode that the thickness of the wafer hold | maintained at the positioning table is measured with the 1st thickness measurement apparatus with which the grinding processing apparatus shown in FIG. 3 is provided. It is the (a) perspective view and (b) side view which show the state which is grinding the back surface side corresponding to the device area | region of a wafer with the grinding unit with which the grinding processing apparatus shown in FIG. 3 is equipped. It is the (a) perspective view and the (b) side view which show the state which is grinding the convex part of a wafer with the grinding unit with which the grinding processing apparatus shown in FIG. 3 is equipped. It is a top view which shows the position of the grinding unit when grinding the back surface side corresponding to the device formation area of a wafer. It is a top view which shows the position of a grinding unit when grinding a convex part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wafer 1b ... Back side of wafer 3 ... Semiconductor chip (device)
DESCRIPTION OF SYMBOLS 4 ... Device formation area 4A ... Concave part 5 ... Periphery surplus area | region 5A ... Convex part 16 ... 1st thickness measuring device (non-contact type sensor)
30 ... Chuck table (Suction table)
60 ... Second thickness measuring instrument (contact type sensor)

Claims (1)

A wafer having a device forming region having a plurality of devices formed on the surface and an outer peripheral surplus region surrounding the device forming region is removed by removing a predetermined thickness of a region on the back surface side corresponding to the device forming region. Forming, as a result, a metal film is coated on the concave portion of the wafer whose outer peripheral surplus region has become a convex portion, and then the convex portion that has become unnecessary is ground,
A first thickness measuring step of measuring, by a non-contact sensor, a thickness of an outer peripheral surplus region where the convex portion of the wafer is formed before grinding and a thickness of a device forming region where the concave portion is formed;
A second thickness measuring step of measuring the thickness of the outer peripheral surplus region where the convex portion of the wafer is formed with a contact sensor in a state where the wafer is sucked in a direction in which the back surface is exposed to the suction table of the grinding device; ,
The thickness of the outer peripheral surplus region measured in the first thickness measuring step is set as a, the thickness of the outer peripheral surplus region measured in the second thickness measuring step is set as a ′, and the first thickness measuring step In this case, the thickness of the device formation region measured in step b is defined as b. In this case, the difference a′−a is obtained as a measurement error, and b is added to the difference a′−a. A device formation region thickness calculating step of calculating a device formation region thickness b ′ predicted to be;
A wafer processing method comprising: a convex portion grinding step of grinding the thickness of the outer peripheral surplus region of the wafer adsorbed on the adsorption table to a desired value on the basis of b ′.

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