JP2009050944A - Substrate thickness measuring method and substrate processing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a stable measurement value without being affected by processing water in measuring the thickness of a substrate by using interference waves of laser beams. <P>SOLUTION: A cylindrical cover 74 is continued to an opening of a laser head part 70, and with an inner space 75 of the cover 74 filled with water W supplied from a water supply pipe 76, laser beams L are irradiated from a laser beam irradiation end part 71 to a wafer 1. The laser beams L permeate a glass plate 73 of the laser head part 70 and the water W in the inner space 75 and are irradiated to the wafer 1. From the interference waves generated by reflected light of each of a precessed face (back face 1b) and a lower face (surface 1a) of the wafer 1, the thickness of the wafer 1 is detected. Entry of grinding water (processing water) to a laser beam irradiation region is blocked, to maintain the laser beam irradiation state at a constant level all the time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a processing apparatus that performs processing such as grinding and polishing on a substrate such as a semiconductor wafer, and a substrate thickness measurement method that is suitable for use in such processing.

  In the manufacturing process of a semiconductor device, in order to obtain a target thickness of the device, thinning is performed by back-grinding at the stage of a semiconductor wafer which is an aggregate of a large number of devices. In accordance with the recent remarkable thinning of devices, the wafer is processed to be thinner, and therefore, the thickness management requires higher accuracy. Wafer grinding and polishing can proceed while measuring the thickness, but as a means of measuring the thickness in such a form, contact is made by detecting the displacement of the thickness while bringing the measuring probe into contact with the work surface. The equation is known (see Patent Document 1).

  However, the contact-type thickness measuring means has a problem that the surface to be processed is damaged by the contacting probe, and the damage causes a reduction in the bending strength of the wafer. This problem becomes prominent because the influence of the depth of the flaw is large, particularly when the wafer is relatively thin. In that respect, a non-contact type capable of measuring the thickness without bringing a probe or the like into contact with the wafer is advantageous in that the bending strength is not lowered.

  Examples of the non-contact type thickness measuring means include those using ultrasonic waves and those using laser light. In the ultrasonic method, an ultrasonic wave with a predetermined frequency is emitted toward one side of the wafer, and the thickness is measured from the waveform of the interference wave between the reflected wave from the front surface of the wafer and the reflected wave from the back surface. (See Patent Document 2). However, such an ultrasonic type has a limitation in roughness and thickness, such as when the surface on which the ultrasonic wave is incident is rough or when the thickness is thick, the roughness and thickness are limited. There is a drawback that is not enough.

  The laser beam type is the same principle as the ultrasonic type, and irradiates a laser beam of a predetermined frequency toward one side of the wafer, and the reflected wave of the laser beam from the surface of the wafer and the reflected wave from the back side The thickness can be measured from the waveform of the interference wave (see Patent Document 3). This laser beam type is not particularly limited by the roughness or thickness of the object to be measured, and is intended to eliminate the disadvantages of the ultrasonic type.

Japanese Patent Laid-Open No. 2001-9716 JP-A-8-210833 JP 9-36093 A

  When the back surface of a wafer is ground or polished, processing water is usually supplied for the purpose of lubrication, cooling and cleaning of the processed portion. The processing water supplied to the processing part flows and is drained by flowing on the processing surface including grinding scraps and polishing scraps generated in the processing, and may be splashed by a rotating tool. When a laser beam for thickness measurement is irradiated to a wafer in such an environment, the film thickness of the processing water flowing on the wafer fluctuates or splashes pass through the laser beam. For this reason, fluctuations in the refractive index of the laser beam and situations in which the laser beam is difficult to transmit occur, and the interference wave is not stable, resulting in a problem that the measured thickness value is not stable.

  Therefore, the present invention provides a substrate thickness measurement method capable of obtaining a stable measurement value without being affected by the processing water when measuring the thickness of the substrate using the interference wave of the laser beam, and its It is an object of the present invention to provide an apparatus for processing a substrate capable of performing the method.

  In the substrate thickness measuring method of the present invention, one surface side of the substrate is held in accordance with the holding means of the processing apparatus, and when processing the other exposed surface of the substrate, the processing is performed before or after processing. A method of measuring a thickness of a substrate, wherein a laser beam irradiation end portion of a laser beam irradiation means for irradiating a laser beam toward another surface of the substrate in a direction substantially orthogonal to the other surface is provided on the substrate. In a state of being opposed to each other and filling a liquid in a space formed between the laser light irradiation end and the other surface of the substrate, the laser light is irradiated from the laser light irradiation end toward the substrate, Receiving the interference wave of the reflected light from one surface of the substrate and the reflected light from the other surface of the substrate, and deriving the thickness of the substrate based on the waveform of the interference wave Yes. The processing referred to in the present invention is mainly grinding or polishing.

  In the thickness measuring method of the present invention, the laser beam is irradiated in a direction substantially orthogonal to the surface to be processed (other surface) of the substrate, and from the surface to be processed and from one surface matched to the holding means. The thickness of the substrate is derived based on the interference wave of each reflected wave. In this method, in the present invention, the space of the laser light irradiation area between the irradiation end portion which is the laser light irradiation port and the substrate is filled with a liquid such as water, and the laser light is irradiated through the liquid. . By maintaining this state, even when processing is performed while supplying processing water to the substrate, the processing water does not enter because the space in the laser light irradiation area is filled with liquid. The splash is prevented from flying. That is, the state in which the laser beam is transmitted through the liquid is maintained, and the irradiation state of the laser beam is not disturbed by the processing water. For this reason, the inconvenience that the refractive index of the laser beam fluctuates and the laser beam does not smoothly pass through the irradiation region does not occur. Thereby, the laser beam is always applied to the substrate in a constant state, the interference wave is stabilized, and as a result, an accurate thickness measurement value can be obtained.

  Since the thickness measuring method of the present invention is a non-contact type using an interference wave of laser light, it is not particularly limited to the roughness or thickness of the substrate, and the processing surface on which the laser light is incident is relatively Even if it is rough or a substrate having a relatively large thickness, the thickness can be measured accurately. Moreover, since it is not a contact type, it cannot be overemphasized that the malfunction of reducing a bending strength does not generate | occur | produce, without scratching a board | substrate.

  Next, the substrate processing apparatus of the present invention can suitably carry out the thickness measuring method of the present invention, and holds one surface side of the substrate in accordance with the holding means of the processing apparatus. In the processing apparatus for processing the other surface exposed, a laser beam irradiation end for irradiating the laser beam in a direction substantially perpendicular to the other surface toward the other surface of the substrate held by the holding means is provided. A cylindrical cover member that surrounds and partitions a space extending from the laser light irradiation end to the other surface of the substrate, and into which the laser light irradiated from the laser light irradiation end is passed, A liquid supply means for supplying a liquid to the inside of the cover member and filling the interior with the liquid; a reflected light from one surface of the substrate of the laser light irradiated from the laser light irradiation means; and another surface A light receiving means for receiving the interference wave with the reflected light from the light, and received by the light receiving means. It is characterized by having a thickness measuring means comprising a converting means for converting the interference wave waveform to a thickness of the substrate. The processing performed by the processing apparatus of the present invention is mainly grinding or polishing.

  In the processing apparatus of the present invention, liquid such as water is supplied from the liquid supply means to the inside of the cover member to fill the inside of the cover member with the liquid, and while maintaining this state, from the laser light irradiation end of the laser head portion The thickness of the substrate is measured by irradiating the substrate with laser light. A laser light irradiation region between the laser light irradiation end and the substrate is surrounded by a cover member, and the inside of the cover member is filled with a liquid, and the laser light passes through the liquid and is irradiated onto the substrate. Here, when the processing is performed while supplying the processing water to the substrate, the processing water and the splash of the processing water do not enter the inside of the cover member, and the laser beam is kept in a state of transmitting the liquid. The irradiation state is not disturbed by the processing water. Therefore, the laser beam is always applied to the substrate in a constant state, the interference wave is stabilized, and as a result, an accurate thickness measurement value can be obtained.

  The processing apparatus of the present invention includes a form in which the laser head portion of the thickness measuring means is supported so as to be capable of reciprocating between two positions, ie, a thickness measuring position of the substrate and a retracted position outside the holding means. This configuration is preferable in that the laser head unit is moved to the retracted position, thereby enabling maintenance work that is difficult to perform due to interference of the laser head unit when the laser head unit is in the thickness measurement position.

  According to the present invention, when measuring the thickness of the substrate using the interference wave of the laser beam, the laser beam irradiation region from the laser beam irradiation end to the substrate is filled with the liquid, and the laser beam is applied to the liquid. As a result, it is possible to obtain a stable thickness measurement value without being affected by the processing water.

  Hereinafter, an embodiment in which the present invention is applied to backside grinding of a semiconductor wafer (substrate) will be described with reference to the drawings. Reference numeral 1 in FIG. 1 indicates a disk-shaped semiconductor wafer (hereinafter abbreviated as a wafer) that is thinned by back grinding. The wafer 1 is a silicon wafer or the like, and the thickness before processing is, for example, about 700 μm and uniform. A plurality of rectangular semiconductor chips 3 are defined on the surface (one surface) 1 a of the wafer 1 by grid-like division lines 2. An electronic circuit (not shown) such as an IC or an LSI is formed on the surface of the semiconductor chip 3. A V-shaped notch 4 indicating a semiconductor crystal orientation is formed at a predetermined location on the peripheral surface of the wafer 1.

  The wafer 1 is cut into a large number of semiconductor chips 3 by cutting along the planned dividing line 2, but before that, the back surface (other surface) 1b is ground to obtain the semiconductor chips 3 to be obtained. The entire thickness is reduced to a target thickness (for example, 10 to 100 μm). The back surface grinding of the wafer 1 is suitably performed by a grinding apparatus (processing apparatus) 10 according to an embodiment shown in FIG.

  As shown in FIG. 1, a protective tape 5 is attached in advance to the front surface 1a of the wafer 1 provided to the grinding apparatus 10 for back surface grinding. As the protective tape 5, for example, a tape in which an acrylic adhesive having a thickness of about 10 to 20 μm is applied to one side of a base material such as polyethylene having a thickness of about 100 to 200 μm is preferably used. The purpose of sticking the protective tape 5 is to prevent the electronic circuit formed on the surface of the semiconductor chip 3 from being damaged during back surface grinding.

  According to the grinding apparatus 10, the protective tape 5 adhered to the surface 1 a is adsorbed to the horizontal adsorption surface of a vacuum chuck type chuck table (holding means) 20 to hold the wafer 1, and two grinding units (coarse) Rough grinding and finish grinding are sequentially performed on the back surface 1b of the wafer 1 by 30A and 30B.

Hereinafter, the configuration and operation of the grinding apparatus 10 will be described.
The grinding apparatus 10 has a rectangular parallelepiped base 11, and the wafer 1 is a surface on which a protective tape 5 is attached in a supply cassette 12 that is detachably set at a predetermined location on the base 11. A plurality are stacked and stored with the 1a side up. One wafer 1 is pulled out from the supply cassette 12 by the transfer robot 13, and the wafer 1 is inverted and placed on the positioning table 14 with the back surface 1b facing upward, where a certain position is obtained. Decided.

  A turntable 25 that is rotationally driven in the R direction is provided on the base 11, and a plurality of (in this case, three) disk-shaped chuck tables 20 are provided on the outer periphery of the turntable 25. Are arranged at equal intervals in the circumferential direction. These chuck tables 20 are rotatably supported, and are rotated in one direction or both directions by a rotation driving mechanism (not shown).

  The wafer 1 positioned on the positioning table 14 is picked up from the positioning table 14 by the supply arm 15 and further concentrically with the back surface 1b to be ground on the one chuck table 20 being vacuum operated. Placed on. As shown in FIG. 3A, the chuck table 20 has a circular suction portion 22 formed of a porous member at the center upper portion of a frame body 21, and the wafer 1 is placed horizontally on the suction portion 22. The protective tape 5 is aligned with the suction surface 22a, which is the upper surface, and the back surface 1b is attracted and held in an exposed state. The adsorption surface 22 a is formed in the same plane as the surface 21 a of the frame body 21.

  The wafer 1 held on the chuck table 20 as described above is fed to the primary processing position below the rough grinding unit 30A when the turntable 25 rotates by a predetermined angle in the R direction, and is ground at this position. The back surface 1b is roughly ground by the unit 30A. Next, the turntable 25 is again rotated by a predetermined angle in the R direction to feed the wafer 1 to a secondary machining position below the finish grinding grinding unit 30B. At this position, the back surface 1b is finish ground by the grinding unit 30B. The

  Two columns 16A and 16B arranged in the X direction are erected at the end on the back side of the base 11, and on the front surfaces of these columns 16A and 16B, the grinding units 30A and 30B are respectively provided in the Z direction ( It is installed so that it can be raised and lowered in the vertical direction. That is, a guide 41 extending in the Z direction is provided on the front surface of each column 16A, 16B, and each grinding unit 30A, 30B is slidably mounted on the guide 41 via a slider 42. The grinding units 30 </ b> A and 30 </ b> B are moved up and down in the Z direction via a slider 42 by a ball screw type feed mechanism 44 driven by a servo motor 43.

  The grinding unit 30B for finish grinding has a cylindrical spindle housing 31 whose axial direction extends in the Z direction, and a spindle shaft 32 that is rotationally driven by a spindle motor 33 is supported in the spindle housing 31. ing. A grindstone wheel 35 is attached to the lower end of the spindle shaft 32 via a flange 34.

  The grindstone wheel 35 has a plurality of grindstones 37 arranged and fixed to the lower surface of an annular frame 36. The grinding surface formed by the lower surface of the grindstone 37 is set to a plane orthogonal to the axial direction of the spindle shaft 32. Therefore, the ground surface is parallel to the chucking surface 22 a of the chuck table 20. As the grindstone 37, for example, a diamond-bonded material mixed with a glassy bond material, molded, and sintered is used.

  The grinding unit 30B for finish grinding and the grinding unit 30A for rough grinding have the same configuration, that is, the grinding unit 30A includes the spindle housing 31, spindle shaft 32, spindle motor 33, flange 34, and A grindstone wheel 35 including a frame 36 and a grindstone 37 is provided. The grinding units 30A and 30B are distinguished by the fact that the grinding wheel 37 of the grinding wheel 35 is different from that for rough grinding and that for finish grinding.

  As the grindstone 37 attached to the grinding unit 30A for rough grinding, for example, one containing relatively coarse abrasive grains of about # 320 to # 400 is used. Further, as the grindstone 37 attached to the grinding unit 30B for finish grinding, for example, a grindstone containing relatively fine abrasive grains of about # 2000 to # 8000 is used. Each of the grinding units 30A and 30B 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 scraps.

  The grinding wheel 35 rotates integrally with the spindle shaft 32, and the grinding outer diameter of the rotating grinding wheel 37 is set to be approximately equal to the diameter of the wafer 1. Further, the position where the wafer 1 is processed, which is determined by rotating the turntable 25 by a predetermined angle, is a wafer that rotates as the cutting edge that is the lower surface of the grindstone 37 passes through the rotation center of the wafer 1 and the chuck table 20 rotates. 1 is set at a position where the entire back surface 1b can be ground.

  The back surface 1b of the wafer 1 is ground by the grinding units 30A and 30B at each processing position of the primary processing and the secondary processing. In the backside grinding of the wafer 1, the chuck table 20 rotates to rotate the wafer 1, and the grinding wheel 37 of the rotating grinding wheel 35 is rotated while the grinding mechanism 30A (30B) is lowered by the feeding mechanism 44. This is done by pressing against the exposed back surface 1b of the wafer 1. During back grinding, grinding water is supplied from each of the grinding units 30A and 30B toward the grinding portion. The wafer 1 is thinned to the target thickness through rough grinding and finish grinding. The thickness of the wafer 1 is measured in the following manner before and after grinding.

  In the grinding apparatus 10, as shown in FIG. 2, the thickness of the wafer 1 is measured by the contact-type first thickness measuring device 50 on the rough grinding side, and the non-contact type according to the present invention is provided on the finish grinding side. The thickness of the wafer 1 is measured by the second thickness measuring device 60.

  The first thickness measuring instrument 50 on the rough grinding side is disposed in the vicinity of the primary processing position on the base 11, and is configured by a combination of a reference side height gauge 51 and a movable side height gauge 52. Each of the height gauges 51 and 52 is provided with probes 51a and 52a, respectively, the probe 51a of the reference-side height gauge 51 contacts the surface 21a of the frame 21 of the chuck table 20, and the probe 52a of the movable height gauge 52 is a workpiece to be ground. It is set so as to contact the front surface (in this case, the back surface 1b of the wafer 1). In the first thickness measuring device 50, the thickness of the wafer 1 is detected by comparing the height positions of the contact points of the probes 51a and 52a.

  When rough grinding is performed by the grinding unit 30A on the wafer 1 moved to the primary processing position, the thickness of the wafer 1 is measured by the first thickness measuring device 50 before the actual grinding. However, it is confirmed whether or not there is a difference from the thickness among various preset processing conditions. If it is confirmed that the thickness measured by the first thickness measuring instrument 50 is substantially the same as the set thickness, the grinding unit 30A waiting above the wafer 1 is lowered at a high speed.

  Such a lowering of the grinding unit 30A at a high speed is performed by grinding at a speed of, for example, about 5 mm / second to the grinding start position immediately before the lower surface, which is the cutting edge of the grindstone 37, contacts the surface to be ground (back surface 1b) of the wafer 1. This operation lowers the unit 30A, and is performed to shorten the total time required for grinding. If the thickness of the wafer 1 measured by the first thickness measuring instrument 50 is not as set, the grindstone 37 does not come into contact with the wafer 1 and the grindstone 37 moves down to just before the wafer 1. As described above, adjustment work such as changing the descending amount at high speed according to the thickness measurement value is performed.

  When the grinding unit 30A is lowered at a high speed, the grinding unit 30A is ground and fed at a grinding feed rate (for example, about 4 μm / second) to start air cutting, and then the rotating grindstone 37 is ground on the wafer 1. The back surface 1b is ground by pressing against the back surface 1b. During the back surface grinding, the thickness of the wafer 1 is continuously measured by the first thickness measuring device 50, and the feed amount of the grinding unit 30A by the feed mechanism 44 is controlled based on the measured value. In the rough grinding, grinding is performed to, for example, 20 to 40 μm before the target thickness of the wafer 1 after finish grinding, and the rest is ground by finish grinding. When the measured value of the first thickness measuring instrument 50 reaches the target thickness in the rough grinding, the grinding unit 30A is raised to the standby position, and the rough grinding is finished.

  Next, the wafer 1 is sent to the secondary processing position and subjected to finish grinding. In the finish grinding, the thickness of the wafer 1 is measured by the second thickness measuring device 60 as described above. The second thickness measuring device 60 is a non-contact type that measures the thickness using the interference wave of the laser beam, and can suitably implement the thickness measuring method of the present invention.

  As shown in FIG. 3, the second thickness measuring device 60 includes a frame 61 having an inverted L shape, and a laser head unit 70 provided at the tip of the frame 61. The frame 61 has a hollow cylindrical shape, and a cylindrical stand portion 61a whose axis extends in a substantially vertical direction (Z direction in FIG. 1), and extends substantially horizontally from the upper end of the stand portion 61a in the direction of the secondary processing position. It is comprised from the arm part 61b. A cylindrical laser head portion 70 whose axis extends in a substantially vertical direction is formed integrally with the frame 61 at the tip of the arm portion 61b. As shown in FIG. 4, the laser head unit 70 is also hollow, and its inside communicates with the inside of the frame 61.

  As shown in FIG. 3B, the frame 61 is attached so as to be movable up and down along a guide 63 provided on the base 11 via a thin plate-like bracket 62. The bracket 62 is driven up and down along the guide 63 by a lift drive mechanism (not shown). A motor 64 is fixed between the stand portion 61 a and the attachment portion to the guide 63 on the bracket 62. The stand portion 61a of the frame 61 is supported at the tip of the bracket 62 via a bearing member 65 so as to be rotatable about the axis. A gear 61A is formed on the outer periphery of the stand portion 61a, and a belt 66 is wound around the drive shaft of the gear 61A and the motor 64.

  When the motor 64 is driven, the power is transmitted to the stand portion 61a via the belt 66 and the gear 61A, whereby the laser head portion 70 turns in a substantially horizontal direction. The laser head unit 70 reciprocally swivels between a measurement position just above the wafer 1 at the secondary processing position and a retreat position outside the chuck table 20 and further outside the turntable 25. It is made like that. Further, the laser head unit 70 moves up and down integrally with the bracket 62.

  As shown in FIG. 4, a laser beam irradiation end portion 71 that irradiates the laser beam L downward is supported by the support plate 72 while penetrating the support plate 72. ing. A glass plate 73 that closes the tip opening of the laser head unit 70 is liquid-tightly mounted below the support plate 72. The lower end surface of the laser light irradiation end portion 71 is kept in contact with the inner surface of the glass plate 73. A space 75 is formed further below the glass plate 73 constituting the tip of the laser head unit 70 by a cylindrical cover 74 that extends integrally with the laser head unit 70 and extends downward.

  A laser unit 80 having a laser light source is accommodated in the base 11, and the laser light L oscillated by the laser light source is guided to the optical fiber 81 and vertically downward from the laser light irradiation end portion 71. It comes to be irradiated towards. Further, in the laser unit 80, the laser beam L irradiated from the laser beam irradiation end portion 71 is reflected on the wafer 1 and receives the interference wave that goes back through the laser beam irradiation end portion 71 and the optical fiber 81. (Light receiving means) is also equipped. In addition, as a light source of the laser beam to irradiate, SLD (super luminescent diode) etc. whose wavelength is about 0.8-1.3 micrometers are used suitably.

  Further, a water supply pipe (liquid supply means) 76 for supplying water (liquid) W to the internal space 75 of the cover 74 is provided inside the laser head unit 70. The water supply pipe 76 passes through the support plate 72 and the glass plate 73 and is supported by the support plate 72 and the glass plate 73. A water supply hose 91 passed through the frame 61 is connected to the upper end of the water supply pipe 76. The water supply hose 91 is guided into the base 11 and connected to a water supply source 90 such as a water supply pump.

  According to the second thickness measuring device 60 having the above configuration, the thickness of the wafer 1 is measured as follows. First, the laser head unit 70 is disposed and held immediately above the wafer 1 at the measurement position, that is, the secondary processing position. For this purpose, the vertical position of the bracket 62 is adjusted so that the laser head unit 70 is higher than the wafer 1, and then the motor 64 is driven to turn the arm unit 61 b in the direction of the secondary processing position. The head unit 70 is disposed at the measurement position. The thickness measurement point of the wafer 1 in this case is the outer peripheral side close to the outer peripheral edge as shown in FIG. Next, the bracket 62 is lowered and the lower end surface of the laser head unit 70 is brought close to the upper surface of the wafer 1 as shown in FIG. From the viewpoint of reducing the amount of water supplied from the water supply pipe 76, the gap 77 is preferably as small as possible.

  Subsequently, water W is discharged from the water supply source 90 through the water supply hose 91 and from the water supply pipe 76, and the internal space 75 of the cover 74 is kept in a state where the water W is filled and no air is mixed therein and is sealed with the water W. To do. The water W supplied to the internal space 75 is discharged from a gap 77 that is vacant between the laser head unit 70 and the wafer 1. By discharging the amount of water exceeding the amount of drainage from the gap 77 from the water supply pipe 76, the internal space 75 can be filled with water. In addition, the timing which takes out the water W from the water supply pipe 76 is not limited to the above, What is necessary is just to select an appropriate timing.

  Next, laser light is oscillated by the laser light source in the laser unit 80, and the laser light L is irradiated from the laser light irradiation end portion 71. The laser light L passes through the glass plate 73 and further passes through the water W filling the internal space 75 and reaches the wafer 1. Here, for measuring the thickness of the wafer 1, the first reflected light reflected by the upper surface of the wafer 1 (the back surface 1b to be ground) and the surface 1a which is transmitted through the inside of the wafer 1 and forms the lower surface. The interference wave with the second reflected light reflected at is used. These reflected lights are reflected on the upper and lower surfaces of the wafer 1 and then interfere with each other to generate an interference wave. The interference wave passes through the laser beam irradiation end 71 and the optical fiber 81 and is received by the photodiode in the laser unit 80.

  The interference wave between the first reflected light and the second reflected light received by the photodiode is analyzed by a control unit (not shown) equipped with a detection circuit and the like, and is converted into an electrical signal or the like according to the waveform. The The numerical value corresponds to the thickness of the wafer 1, and the thickness of the wafer 1 is detected by this.

  The above is the principle of measuring the thickness of the wafer 1 by the second thickness measuring device 60. The thickness measurement of the wafer 1 by the second thickness measuring device 60 is performed after the wafer 1 is sent to the secondary processing position. First, it is performed prior to finish grinding. That is, the thickness of the rough ground wafer 1 is measured again. This is the same as that performed at the rough grinding position, and the thickness of the wafer 1 is different from the preset thickness after rough grinding. This is done to see if there is any. Then, when it is confirmed that the thickness measured by the second thickness measuring device 60 is substantially the same as the set thickness, the finishing grinding unit 30B waiting above the wafer 1 has the same high speed as described above. The feeding operation is executed, and the finishing grindstone 37 is lowered to just before the wafer 1.

  Subsequently, the grinding unit 30B is ground and fed, and the back surface 1b of the wafer is ground while the thickness of the wafer 1 is measured by the second thickness measuring device 60. When the measured value of the second thickness measuring device 60 reaches the target thickness in the finish grinding, the grinding unit 30B is raised to the standby position to finish the finish grinding.

  As described above, when rough grinding and finish grinding are performed on the back surface 1b of the wafer 1 to thin the wafer 1 to a target thickness, the wafer 1 is recovered as follows. First, the turntable 25 rotates by a predetermined angle in the R direction, and the wafer 1 is returned from the secondary processing position to the attachment / detachment position (position where the wafer 1 is placed on the chuck table 20 by the supply arm 15). The vacuum operation of the chuck table 20 is stopped at this attachment / detachment position, and then the wafer 1 is transferred to the spinner type cleaning device 18 by the recovery arm 17. The wafer 1 is dried by spraying nitrogen gas or air after the cleaning water is supplied to the non-ground surface in the cleaning device 18. The wafer 1 is transferred and accommodated from the cleaning device 18 into the collection cassette 19 by the transfer robot 13. On the chuck table 20 from which the wafer 1 has been removed, grinding dust and the like are removed by the cleaning water discharged from the nozzle 26.

  Thus, the back surface 1b of the wafer 1 is ground and thinned to the target thickness. The thinned wafer 1 is finally cut and divided along the planned dividing line 2 and separated into a plurality of semiconductor chips 3. The wafers 1 that have been roughly ground at the primary processing position are successively sent to the secondary processing position, and the wafers 1 are finish-ground while the thickness is measured by the second thickness measuring device 60. When the processing of the wafer 1 is completed or when periodic maintenance is performed on the chuck table 20 and the turntable 25, the motor 64 is operated to move the laser head unit 70 to the retracted position.

  Now, according to the second thickness measuring instrument 60 in the above embodiment, the laser light irradiation area between the laser light irradiation end 71 of the laser head 70 and the wafer 1 is the interior of the glass plate 73 and the cover 74. There is only water W that fills the space 75, and the mediation boundary (in this case, the boundary between the glass plate 73 and the water W and the boundary between the water W and the upper surface of the wafer 1) is always kept constant. . Further, the water W filling the internal space 75 is in a positive pressure state and is always drained from the gap 77. When the back surface 1b of the wafer 1 is being ground, the grinding water is supplied from the grinding units 30A and 30B to the grinding portion, and the grinding water flows on the surface to be ground, which is the upper surface of the wafer 1, including grinding debris. In some cases, the grindstone 37 is drained and sprayed by the high-speed rotating grindstone 37.

  Here, the water W supplied from the water supply pipe 76 to the internal space 75 of the cover 74 is always drained from the gap 77 to the ground surface of the wafer 1 in a positive pressure state. For this reason, the grinding water flowing on the surface to be ground is pushed by the drainage from the internal space 75 and never enters the cover 74. That is, the dirty grinding water enters the internal space 75 of the cover 74, and the laser light L does not pass through the grinding water. On the other hand, the splash of grinding water hits the cover 74 and does not enter the internal space 75, and the laser light L does not pass through the splash.

  Therefore, the irradiation state of the laser light L is not disturbed by the grinding water, and the laser light L always transmits only the water W filling the glass plate 73 and the internal space 75. For this reason, the inconvenience that the refractive index of the laser beam L fluctuates and the laser beam L does not smoothly pass through the irradiation region does not occur. Thereby, the laser beam L is always applied to the wafer 1 in a constant state, the interference wave is stabilized, and as a result, an accurate thickness measurement value can be obtained.

  Further, since the second thickness measuring device 60 is a non-contact type using an interference wave of the laser beam L, it is particularly limited by the roughness of the back surface 1b of the wafer 1 on which the laser beam L is incident and the thickness of the wafer 1. It is not something. For example, even when the roughness of the back surface 1b is relatively rough, for example, Ra: 0.17 to 0.24 and Ry: 1.2 to 1.7, the thickness can be sufficiently measured. Further, since it is a non-contact type, there is no problem that the bending strength is lowered without damaging the wafer 1. Note that the first thickness measuring instrument 50 used during rough grinding is a contact type in which the probes 51a and 52a are in contact with the back surface 1b of the wafer 1, and there is a risk of scratching reducing the bending strength. Is smaller than the damage due to rough grinding and disappears in the finish grinding of the next process.

  In the above embodiment, the second thickness measuring device 60 capable of performing the thickness measuring method according to the present invention is applied to the finish grinding side of the grinding apparatus 10 for grinding the back surface 1b of the wafer 1. The invention is not limited to grinding, but can be applied to other processing apparatuses such as a polishing apparatus that polishes while measuring the thickness of a workpiece.

It is the (a) perspective view of the semiconductor wafer ground back by the grinding device concerning one embodiment of the present invention, and (b) the side view. 1 is an overall perspective view of a grinding apparatus according to an embodiment. 3A is a side view and FIG. 3B is a perspective view showing a grinding unit, a chuck table, and a second thickness measuring instrument for finish grinding of the grinding apparatus shown in FIG. 2. It is sectional drawing which shows the principal part of the 2nd thickness measuring device which concerns on one Embodiment.

Explanation of symbols

1 ... Semiconductor wafer (substrate)
1a: Wafer surface (one surface)
1b ... Back side of wafer (other side)
3 ... Semiconductor chip 10 ... Grinding equipment (processing equipment)
20 ... Chuck table (holding means)
30A, 30B ... Grinding unit 70 ... Laser head part 71 ... Laser light irradiation end part 74 ... Cover 75 ... Internal space 76 ... Water supply pipe (liquid supply means)
80 ... Laser unit L ... Laser light W ... Water (liquid)

Claims (5)

A method of measuring the thickness of a substrate during or before or after processing when holding one surface side of a substrate in accordance with a holding means of a processing apparatus and processing the other exposed surface of the substrate. ,
A laser beam irradiation end portion of a laser beam irradiation unit that irradiates a laser beam in a direction substantially orthogonal to the other surface toward the other surface of the substrate is disposed so as to face the substrate.
In a state where a space formed between the laser light irradiation end and the other surface of the substrate is filled with a liquid, the laser light is irradiated from the laser light irradiation end toward the substrate,
Receiving the interference wave of the laser light reflected from one surface of the substrate and the light reflected from the other surface, and deriving the thickness of the substrate based on the waveform of the interference wave Substrate thickness measurement method.   2. The substrate thickness measuring method according to claim 1, wherein the processing on the substrate is grinding or polishing. In a processing apparatus that holds one surface side of the substrate in accordance with the holding means of the processing apparatus and processes the other surface that is exposed on the substrate,
A laser head unit including a laser beam irradiation end that irradiates a laser beam in a direction substantially orthogonal to the other surface of the substrate held by the holding unit;
Surrounding and partitioning a space extending from the laser light irradiation end to the other surface of the substrate, a cylindrical cover member through which the laser light irradiated from the laser light irradiation end is passed,
Liquid supply means for supplying liquid to the inside of the cover member and filling the inside with liquid;
A light receiving means for receiving an interference wave between the reflected light from one surface of the substrate and the reflected light from the other surface of the laser light emitted from the laser light irradiating means;
An apparatus for processing a substrate, comprising: a thickness measuring means including a converting means for converting a waveform of the interference wave received by the light receiving means into a thickness of the substrate.   The substrate processing apparatus according to claim 3, wherein the processing of the substrate is grinding or polishing.   4. The laser head portion of the thickness measuring means is supported so as to be capable of reciprocating between two positions of a substrate thickness measuring position and an outward retracted position of the holding means. Or the substrate processing apparatus according to 4.

Images