Methods for processing wafers

Abstract

Method for processing a wafer (W) by inserting the wafer (W) into a holding opening of a carrier (2) for holding the wafer (W) and inserting the carrier (2) holding the wafer (W) between an upper rotary table (3) and a lower rotary table (4) to process the two faces of the wafer (W) simultaneously, the method comprising the following steps: Determining the height position of the upper rotary table (3) using a laser displacement sensor (5) before processing the wafer (W), while the support (2) holding the wafer (W) is inserted between the upper rotary table (3) and the lower rotary table (4); and Determine that the wafer (W) is not being held normally, in order to repeat the wafer (W) holding process if a difference between the determined height position and a reference position exceeds a limit value, wherein the laser displacement sensor (5) is a digital CCD laser micrometer of the transmission type, and a sensor attachment (13) is arranged in a shaft (12) which is movable upwards and downwards in an up-and-down movement of the upper rotary table (3), and the sensor attachment (13) is positioned such that it blocks a laser of the transmission-type digital CCD laser micrometer when the carrier (2) holding the wafer (W) is inserted between the upper and lower rotary tables (3, 4).

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for processing a wafer, comprising holding a wafer in a holding opening of a carrier and processing both wafer surfaces, and more particularly to a method for detecting that the wafer is not normally held in the holding opening to prevent the wafer from breaking. STATE OF THE ART

[0002] In the past, a method for manufacturing a semiconductor wafer such as a mirror-polished silicon wafer generally included a slicing process for slicing a single crystal rod manufactured by a single crystal manufacturing apparatus to obtain a wafer in the shape of a thin disc, a chamfering process for chamfering an outer peripheral portion of the wafer obtained by the slicing process to prevent breakage and a chip in the wafer, a lapping process for lapping the chamfered wafer to flatten the wafer, an etching process for removing mechanical damage remaining on the front surface of the chamfered and lapped wafer, a polishing process for polishing the front surface of the etched wafer into a mirror-smooth surface, and a cleaning process for cleaning the polished wafer.

[0003] In addition to lapping, a technique known as double-head grinding, in which both sides are ground simultaneously using a single grindstone, is also used for leveling. Furthermore, there are double-sided polishing, in which both sides are polished simultaneously, and single-sided polishing, in which one side is polished.

[0004] Furthermore, one of the purposes of the lapping process, for example, is to provide the wafer obtained by slicing with a predetermined thickness and to achieve the required dimensional accuracy, such as flatness and parallelism. It is generally known that the wafer subjected to lapping has the highest dimensional accuracy, and it is believed that this dimensional accuracy determines the final shape of the wafer; therefore, dimensional accuracy is very important in the lapping process.

[0005] Furthermore, in the lapping technique, a lapping device is known with which lapping is carried out by imparting relative motion to the rotary tables and the wafers by combining three types of motion: the rotary motion of the concentric rotary tables, the orbital motion of a circular wafer support with respect to a main body of the device, and the rotary motion of the round wafer support (see, for example, Patent Document 1). This lapping device is, for example, as shown in Fig. 5(A) and (B) shown.

[0006] As in Fig. As shown in Figures 5(A) and (B), a lapping device 101 includes an upper rotary table 103 and a lower rotary table 104 disposed vertically facing each other. These upper and lower rotary tables 103 and 104 are rotated in opposite directions by a drive unit (not shown). The lower rotary table 104 has a sun gear 110 at the center of its upper surface, and an annular internal gear 109 is provided at its periphery.

[0007] Furthermore, a gear portion 111 is formed on the outer periphery of each wafer support carrier 102, which meshes with the sun gear 110 and the internal gear 109, forming a gear structure. A plurality of holding openings 107 are provided in the wafer support carriers 102. The wafers W to be lapped are inserted into the holding openings 107 and held.

[0008] The wafer holding carriers 102 are inserted between the upper and lower turntables 103 and 104 and perform planetary gear motion, that is, perform rotation and rotation between the upper and lower turntables 103 and 104 which rotate while facing each other. To perform lapping, a turbid solution containing polishing abrasive grains such as alumina (Al2O3) or silicon carbide (SiC) and a liquid such as water containing a surfactant, the turbid solution being called slurry, is poured via a caster through a through hole 112 provided in the upper turntable 103 into a space between the upper and lower turntables 103 and 104 to put the abrasive grains between the wafers W and the upper and lower turntables 103 and 104, and the molds of the upper and lower turntables 103 and 104 are transferred to the wafers W.Since the upper and lower turntables and supports wear out with use, it is necessary to replace the upper and lower turntables and supports with new ones after they have been used for a period of time.

[0009] To complete processing when the wafer thickness reaches the target thickness, processing is also performed while measuring the wafer thickness. For example, the crystal size determination method is known for performing processing while measuring the wafer thickness (see Patent Document 2).

[0010] The crystal sizing method utilizes a piezoelectric effect generated when a crystal held in a holding hole of a carrier is processed with wafers. This method indirectly measures the thickness of the wafers by measuring the thickness of the crystal, utilizing the fact that the frequency becomes high as the crystal becomes thinner. JP H02-106269A discloses a polishing machine for polishing a workpiece while pressing it between upper / lower surface plates when the workpiece is positioned between the upper / lower surface plates by lowering the upper surface plate, wherein a detector detects the abnormal position in the vertical direction of the upper surface plate member.US 2011 / 0 159 783 A1 discloses a method for polishing a substrate by a polishing apparatus comprising a polishing table having a polishing surface, an upper ring for holding a substrate and pressing the substrate against the polishing surface, and a vertically movable mechanism for moving the upper ring in a vertical direction. The upper ring is moved to a first height before pressing the substrate against the polishing surface, and then the upper ring is moved to a second height after pressing the substrate against the polishing surface. JP 2006-224 233 A discloses a manufacturing method for a glass substrate for mask blanks, including a glass polishing process in which a main surface of the glass substrate is polished. CITATION LISTPATENT LITERATURE Patent document 1: JP H10 - 180 624 A Patent document 2: JP H11 - 285 969 A Patent document 3: JP H02 - 106 269 A Patent document 4: US 2011 / 0 159 783 A1 Patent document 5: JP 2006 - 224 233 A SUMMARY OF THE INVENTION TECHNICAL PROBLEM

[0011] The wafer W and a crystal are inserted into the holding holes of the carrier by an operator or a robot arm. Sometimes, a wafer does not fit snugly into the holding hole of the carrier or protrudes beyond the holding hole due to the rotation of the turntables, resulting in the wafer being out of place (hereinafter referred to as holding failure). Accordingly, operators must inspect the wafer and crystal by touch after the wafer and crystal are inserted into the holding holes of the carrier. Such direct inspection by touch is time-consuming and inefficient. Furthermore, operators may overlook a holding failure and begin processing, resulting in breakage of the wafer and crystal.Such a problem could occur not only in the lapping described above, but also in double-sided polishing, where both surfaces of the wafer are polished simultaneously.

[0012] The present invention has been made in view of the problems described above, and its object is to provide a wafer processing method which can automatically and precisely determine whether the wafer is not held normally due to holding failure before starting processing to prevent the wafer from breaking, and to improve operation efficiency by eliminating the need for an operator to perform touch inspection when setting the wafer in a holding hole of a carrier for holding the wafer, and for inserting the carrier holding the wafer between an upper turntable and a lower turntable to process both surfaces of the wafer simultaneously. SOLUTION TO THE PROBLEM

[0013] To achieve the above-described object, the present invention provides a method for processing a wafer, in which the wafer is inserted into a holding hole of a carrier for holding the wafer, and for inserting the carrier holding the wafer between an upper turntable and a lower turntable to process both surfaces of the wafer simultaneously, comprising the steps of: detecting a height position of the upper turntable by a laser displacement sensor before processing the wafer while inserting the carrier holding the wafer between the upper turntable and the lower turntable; and detecting that the wafer is not normally held to perform the wafer holding again when a limit is exceeded between the detected height position and a reference position, as further defined in the claims.

[0014] Such a method can eliminate the need for operator touch inspection and automatically detect holding failure precisely, thus efficiently processing the wafer while preventing the wafer from breaking.

[0015] The reference position is preferably a height position of the upper turntable which is detected by the laser displacement sensor before the detecting step while the carrier not holding a wafer is inserted between the upper turntable and the lower turntable.

[0016] In this way, holding failure can be accurately detected without being affected by variations in the thickness of the turntables and the carrier caused by repeated wafer processing.

[0017] The method may include holding a crystal for measuring the wafer thickness in a holding opening provided in the carrier separately from the holding opening for holding the wafer to determine whether the crystal is not held normally, together with determining that the wafer is not held normally.

[0018] Such a method can also automatically detect a crystal holding failure by measuring the thickness of the wafer to be processed.

[0019] The laser displacement sensor is a transmission type digital CCD laser micrometer as further defined in the claims.

[0020] The CCD laser micrometer can detect the height position of the upper turntable more accurately, making it possible to detect the holding failure more precisely. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0021] The method of the present invention includes detecting the height position of an upper turntable using a laser displacement sensor while inserting a wafer-holding carrier between the upper turntable and a lower turntable, and determining that the wafer is not normally held to perform wafer holding again when the difference between the detected height position and a reference position exceeds a threshold value before inserting the wafer-holding carrier between the upper turntable and the lower turntable to simultaneously process both wafer surfaces. Therefore, the method can eliminate the need for operator touch inspection and automatically accurately detect holding failure, thereby efficiently processing the wafer while preventing the wafer from breakage. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a schematic view of an example of a lapping apparatus that can be used in a method of machining a workpiece of the present invention; Fig. Figure 1B is a schematic top view of the device in Fig. 1A; Fig. 2 is a schematic view illustrating how a holding failure is detected in a method of machining a workpiece of the present invention; Fig. 3A is a schematic view of an exemplary method of mounting a laser displacement sensor used in a method of machining a workpiece of the present invention; Fig. Figure 3B is an enlarged view of an area near the laser displacement measuring device in Fig. 3A; Fig. Figure 4 is a representation of the results of the example; Fig. 5A is a schematic view of a conventional lapping apparatus; and Fig. Figure 5B is a schematic top view of the device of the Fig. 5A. DESCRIPTION OF EMBODIMENTS

[0022] Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments but is defined in the claims.

[0023] In a process such as lapping or double-side polishing, in which a carrier holding a wafer is sandwiched between an upper and lower turntable and both wafer surfaces are processed simultaneously, the wafer may not be properly held in a holding hole of the carrier, resulting in a holding failure. Conventionally, operators must therefore perform a touch inspection after the wafer and, if necessary, a crystal have been inserted into the corresponding holding holes of the carrier.

[0024] The present inventor considered how to automatically detect the holding failure without operator inspection by touch, and found that the holding failure causes the height position of the upper turntable to deviate from a proper position when the carriers are inserted between the upper and lower turntables, and can be precisely detected by detecting the deviation of the height position of the upper turntable using a laser displacement sensor. The present inventor thus completed the present invention.

[0025] The present invention is directed to a method for processing a wafer, in which the wafer is inserted into a holding opening of a carrier, the carrier holding the wafer is inserted between an upper and a lower turntable, and both wafer surfaces are processed simultaneously, and can be used for, for example, double-sided lapping and double-sided polishing.

[0026] A method according to the invention for processing a wafer by double-sided lapping will now be described by way of example.

[0027] Fig. 1A and Fig. 1B are schematic views of an example of a lapping apparatus that can be used in a method of processing a wafer of the present invention. As in Fig. As shown in Figure 1A, a lapping device 1 includes an upper turntable 3 and a lower turntable 4 arranged to face each other vertically. The upper turntable 3 remains in the rest position, and the lower turntable 4 is rotated by a drive unit 6.

[0028] As in Fig. As shown in Fig. 1B, the lower turntable 4 has a sun gear 10 at the center of its upper surface, and an annular internal gear 9 is provided at its periphery. The sun gear 10 and the internal gear 9 mesh with a gear 11 formed on the outer peripheral surface of each carrier 2 holding the wafers W, and these gears as a whole constitute a gear structure.

[0029] A plurality of holding openings 7 are provided in the carrier 2. Wafers W to be lapped are arranged and held in the respective holding openings 7.

[0030] Each of the carriers 2 holding the wafers W is inserted between the upper and lower turntables 3 and 4 and rotated between the rotating lower turntable 4 and the upper turntable 3 remaining at rest about its axis and about the rotational axis of the lower turntable (ie, a planetary gear movement). Although the Fig. 1A is a three-way type lapping device in which the lower rotary table 4, the sun gear 10, and the internal gear 9 rotate, respectively, the invention may also employ a four-way type lapping device in which the upper rotary table 3, the lower rotary table 4, the sun gear 10, and the internal gear 9 rotate, respectively.

[0031] Before the wafers W are lapped with such a lapping device, the wafers W are inserted and held in the holding openings 7 of each of the carriers 2. A crystal for measuring the thickness of the wafers W can also be inserted and held in a holding opening provided in each of the carriers separately from the holding openings 7 for holding the wafers. As shown in Fig. As shown in Fig. 1B, the crystal 8 is held in the holding hole located in the center of each carrier, and the holding holes 7, in which, for example, the wafers W are held, are arranged around the central holding hole. The wafers and the crystals are inserted into the holding holes by an operator or a robot arm.

[0032] As in Fig. As shown in Figure 1A, each of the carriers holding the wafers is inserted between the upper and lower turntables 3 and 4. In this state, the height position of the upper turntable 3 is detected by a laser displacement sensor 5. The difference between the detected height position and a reference position (a suitable position) is calculated. Here, a plurality of height positions are preferably detected at multiple measurement points by a plurality of laser displacement sensors, and the number of laser displacement measuring devices is not particularly limited. As shown in Fig. As shown in Figure 1A, the laser displacement sensors can be arranged on the respective shafts, which are configured to move in conjunction with, for example, the up-and-down movement of the upper turntable. Alternatively, as many laser displacement sensors as supports can be used to measure the height positions of the upper turntable above the corresponding supports, thereby detecting a holding failure with greater certainty.

[0033] Therefore, the laser displacement sensors are used to detect the height positions at the multiple measurement points, and the differences between the respective height positions and a predetermined reference position are calculated. The predetermined reference position is preferably a height position at which a holding failure does not occur, i.e., in a normal state. In this way, the holding failure can be detected more reliably, regardless of the location where the holding failure occurred, even if the holding failure occurred at multiple locations.

[0034] Alternatively, the reference position can be set to each of the detected height positions to calculate the differences. Of course, the present invention also encompasses calculating a difference between a single height position of the upper turntable, measured at a single measurement point, and the reference position.

[0035] In addition, the use of the laser displacement sensor makes the height position of the upper turntable possible with high precision.

[0036] As in Fig. 2, when a failure occurs in holding a wafer or a crystal in the holding hole, the height position of the upper turntable deviates from a suitable position, ie, the reference position, in a range corresponding to the failure ('A' in Fig. 2). The failure can be determined by evaluating the difference between these positions. Specifically, a threshold value is provided with respect to the difference between the detected height position and the reference position, and it is determined that the wafer(s) are not being held normally, so the holding is repeated if the difference exceeds the threshold value. It is determined that the wafer(s) are being held normally if the difference does not exceed the threshold value at all measurement points.

[0037] Lapping begins after the wafer holding failure is eliminated. Specifically, a turbid solution (called a slurry) of polishing abrasive grains such as aluminum oxide (Al2O3) or silicon carbide (SiC) and a liquid such as water containing a surfactant is supplied from a spout through a through-hole provided in the upper turntable 3 into a space between the upper and lower turntables 3 and 4 to force the abrasive grains between the wafers W and the upper and lower turntables 3 and 4, and both surfaces of the wafers W are lapped.

[0038] Such a method can accurately detect wafer and crystal holding failures without operator touch inspection and can be easily automated by using a controller that automatically performs control to evaluate the difference between the detected height position and the reference position and to stop wafer processing when a holding failure is detected. The method can therefore process the wafer while preventing the wafer and crystal from breaking during use.

[0039] Here, the reference position is preferably a height position of the upper turntable which is detected before the above detection of the height position of the upper turntable by the laser displacement sensor while the carrier not holding a wafer is inserted between the upper turntable and the lower turntable.

[0040] Since wafer processing is repeated, the thickness of the turntables, carriers, polishing pads of a polishing jig, etc., changes over time. Furthermore, cleaning or maintenance of a jig can slightly change the position of the turntables. These changes can cause the reference position, which was set as the appropriate position, to deviate from the appropriate position. Resetting the reference position to an appropriate position before each wafer processing in the above manner advantageously makes it possible to reliably detect a holding failure with high precision.

[0041] Alternatively, the reference position used in the next processing may be set to a height position of the upper turntable when it is determined that the wafer is held normally in the current processing to shorten the setting time of the reference position, instead of readjusting the reference position by detecting the height position of the upper turntable each time before detecting the height position of the upper turntable in the above manner.

[0042] The laser displacement sensor 5 is a digital CCD laser micrometer of the transmission type as defined in the claims, for example in Fig. 3A and Fig. 3B. As shown in Fig. 3B, a sensor boss 13 is disposed in a shaft 12 movable up and down in an up and down motion of the upper turntable 3, and the sensor boss 13 is positioned to block a laser when the carriers holding the wafers are inserted between the upper and lower turntables.

[0043] This makes it possible to detect the height position of the upper turntable and, therefore, the holding failure with high precision. Furthermore, the wafer processing method of the present invention can be readily applied to both a lapping apparatus and a double-side polishing apparatus, regardless of the type and structure of the apparatus.

[0044] Furthermore, the difference between the height position of the upper turntable and the reference position can be evaluated not only before but also during wafer processing to detect an abnormality such as the protrusion of wafers and a crystal from the holding holes when used. EXAMPLES

[0045] Hereinafter, the present invention will be described in more detail by way of an example and a comparative example of the present invention, but the present invention is not limited to these examples but is defined in the claims. (Example)

[0046] According to the wafer processing method of the present invention, silicon wafers having a diameter of 300 mm were processed with the method described in Fig. 1A and Fig. 1B to evaluate the accuracy of holding failure detection. Two digital transmission-type CCD laser sensors (IG028 manufactured by KEYENCE Corporation) were used as laser displacement sensors. As shown in Fig. As shown in Figure 3, the two sensors were mounted on the respective shafts, positioned on opposite sides with respect to a central shaft. Repeated accuracy tests of the sensors showed that the sensors have an average accuracy of 0.01 µm with a maximum / minimum difference of 0.06 µm.

[0047] When the carriers were not holding a wafer and were inserted between the upper and lower turntables, the height position of the upper turntable was detected using the laser displacement sensors, and the reference position was set to the detected height position. A crystal for measuring the wafer thickness was then inserted into the holding hole located in the center of each of the Fig. 1B, and four silicon wafers were inserted into the holding openings around the holding opening arranged in the center of each of the carriers.

[0048] The height positions of the upper turntable were then detected by the laser displacement sensors in a state where the carriers holding the wafers were inserted between the upper and lower turntables, and the differences between the respective detected height positions and the reference position were calculated. It was determined that the wafers were not being held normally if at least one of the differences exceeded a threshold of 0.15 mm. Lapping of the wafers was started after ruling out the holding failure.

[0049] The results obtained by repeating the above lapping are shown in Fig. 4. As in Fig.As shown in Figure 4, the holding failure actually occurred twice, and both times the failure was detected. In all lapping operations except these two cases, it was determined that the wafers were held normally and no wafer breakage occurred. The accuracy of detecting the holding failure was 100%.

[0050] Accordingly, it was confirmed that the wafer processing method of the present invention can automatically and precisely detect whether the wafer is not normally held due to a holding failure before processing to prevent the wafer from breaking and eliminate the need for touch inspection by the operator to improve operation efficiency. (Comparison example)

[0051] Silicon wafers were lapped under the same conditions as in the example, except that an operator holding failure was observed.

[0052] During lapping, the holding failure was overlooked and the wafer broke.

[0053] It should be noted that the present invention is not limited to the above embodiment but is defined in the claims.

Claims

[1] A method for processing a wafer (W) by inserting the wafer (W) into a holding opening of a carrier (2) for holding the wafer (W) and inserting the carrier (2) holding the wafer (W) between an upper turntable (3) and a lower turntable (4) to process the two surfaces of the wafer (W) simultaneously, the method comprising the following steps: Determining a height position of the upper turntable (3) by means of a laser displacement sensor (5) before processing the wafer (W) while the carrier (2) holding the wafer (W) is inserted between the upper turntable (3) and the lower turntable (4); and Determining that the wafer (W) is not held normally to perform the holding of the wafer (W) again when a difference between the detected height position and a reference position exceeds a limit value, wherein the laser displacement sensor (5) is a digital CCD laser micrometer of the transmission type, and a sensor attachment (13) is arranged in a shaft (12) which is movable up and down in an up and down movement of the upper turntable (3), and the sensor attachment (13) is positioned so as to block a laser of the transmission-type digital CCD laser micrometer when the carrier (2) holding the wafer (W) is inserted between the upper and lower turntables (3, 4). [2] A method for processing a wafer (W) according to claim 1, wherein the reference position is a height position of the upper turntable (3) which is detected by the laser displacement sensor (5) before the detecting step while the carrier (2) not holding a wafer (W) is interposed between the upper turntable (3) and the lower turntable (4). [3] A method of processing a wafer (W) according to claim 1 or 2, wherein a crystal (8) for measuring the wafer thickness is held in a holding hole provided in the carrier (2) separately from the holding hole for holding the wafer (W) to determine whether the crystal (8) is not held normally, together with determining that the wafer (W) is not held normally.

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