Processing method for work-piece

Abstract

To provide a processing method that performs edge trimming for removing a portion of a chamfered part on an outer periphery of a work-piece and then performs thinning thereof, in which quality in processing a work-piece can be prevented from deteriorating.SOLUTION: A processing method for a work-piece, which has a first surface and a second surface and has a chamfered part formed on an outer periphery thereof, includes at least a chamfered-part removing step of removing the chamfered part along an edge of the outer periphery of the work-piece by a predetermined depth from the first surface side to form a step part on the edge of the outer periphery, and a thinning step of thinning the work-piece into a predetermined thickness from the first surface side. In the thinning step, a measuring step of measuring a position of a bottom surface of the step part is executed. Further in the thinning step, processing of the work-piece is completed before the thickness of the work-piece becomes equal to a thickness of the position of the bottom surface of the step part.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to an edge trimming technique for removing a portion of a chamfer on the periphery of a workpiece. [Background technology]

[0002] Conventionally, silicon wafers with multiple IC, LSI, and other devices formed on their surface are ground to a specified thickness on the backside, and then cut into individual devices using a cutting machine for use in electrical equipment such as mobile phones and personal computers.

[0003] In recent years, the development of 3D stacked wafers has progressed in line with the trend toward lower profile and higher integration of device chips. This is a technology in which multiple wafers are stacked and bonded to a base wafer and connected to each other with through-silicon vias (TSVs) (also known as WOW: Wafer-on-Wafer).

[0004] Development is also progressing on wafers (also known as SOI: Silicon on Insulator) in which a bond wafer (a wafer for making devices) is bonded to a base wafer via an oxide film.

[0005] The wafer is thinned by, for example, bonding two wafers together, and then grinding the back surface of one of the wafers to a predetermined thickness using a known grinding device.

[0006] When the backside of one wafer is ground, the chamfered portion of the wafer becomes a knife edge, which breaks off and splashes onto the workpiece, damaging it. The knife edge can also cause edge chipping.

[0007] Therefore, as disclosed in Patent Document 1, for example, a technique has been put into practical use in which edge trimming is performed before bonding, in which part of the chamfered portion on the outer periphery of one of the wafers is removed by cutting to form a step portion, and the edge-trimmed wafer is then bonded to the other wafer.

[0008] However, there is a concern that foreign matter such as cutting debris (contamination) generated during edge trimming before bonding may remain. If this foreign matter becomes trapped between the two wafers, it will significantly reduce the quality of the bonded wafer.

[0009] On the other hand, for example, as disclosed in Patent Document 2, a technique is also known in which, after bonding wafers together, a step portion is formed in the chamfered portion on the outer periphery of one of the wafers, and then the back surface of one of the wafers is thinned. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-245167 [Patent Document 2] Japanese Patent Publication No. 2022-165203 Summary of the Invention [Problem to be solved by the invention]

[0011] When implementing a method similar to that of Patent Document 2, when grinding one of the wafers, it is necessary to stop the grinding process before the thickness of the wafer reaches the bottom of the step. This is because grinding up to the bottom of the step creates a sharper knife edge, which may cause chipping (faults) in that area. In the technology of Patent Document 2, a modified layer is formed in advance in the edge-trimmed peripheral excess region, and the peripheral excess region is then divided and removed from the stacked wafers.

[0012] Conventionally, the thickness of the wafer is measured while grinding, and grinding is stopped before the wafer thickness reaches the bottom of the step. However, there is a problem that accurate measurement is not possible due to factors such as the precision of the wafer thickness before processing (variation in thickness before processing) and measurement errors, and grinding ends up reaching the bottom of the step.

[0013] Furthermore, when the peripheral excess region resulting from edge trimming is divided as in Patent Document 2, the divided debris becomes processing debris and may adhere to the wafer as foreign matter.

[0014] In view of the above problems, the present invention relates to a processing method that performs edge trimming to remove a portion of the chamfered portion on the outer periphery of a workpiece, followed by thinning, and proposes a new technology for preventing a decrease in the processing quality of the workpiece. [Means for solving the problem]

[0015] The problem to be solved by the present invention is as described above, and the means for solving this problem will now be described.

[0016] According to one aspect of the present invention, there is provided a method for processing a workpiece having a first surface and a second surface and a chamfered portion formed on its outer periphery, the method including at least a chamfer removing step of removing the chamfer from the first surface side along the outer periphery of the workpiece to a predetermined depth to form a step on the outer periphery, and a thinning step of thinning the workpiece from the first surface side to a predetermined finishing thickness, wherein the thinning step includes a measuring step of measuring the position of the bottom surface of the step, and the thinning step ends the processing before the thickness of the workpiece reaches the position of the bottom surface of the step.

[0017] Furthermore, according to one aspect of the present invention, in the measurement step, a non-contact thickness measuring device is used to measure the difference in height between the surface on the first surface side of the workpiece and the bottom surface of the step portion.

[0018] Furthermore, according to one aspect of the present invention, the non-contact thickness measuring device is configured as a single unit that can simultaneously measure the height position of the surface on the first surface side of the workpiece and the height position of the bottom surface of the step portion.

[0019] According to one aspect of the present invention, the measuring step is performed continuously during the thinning step. [Effects of the Invention]

[0020] The present invention provides the following effects. That is, according to one aspect of the present invention, when thinning the workpiece from the first surface side, the difference between the position of the surface on the first surface side of the workpiece and the position of the bottom surface of the step portion is measured, and processing is terminated before the thickness of the workpiece reaches the position of the bottom surface of the step portion, so that the bottom surface of the step portion is not ground.As a result, even if a knife edge is formed at the bottom of the step portion, grinding or chipping at that location can be suppressed, and a decrease in the processing quality of the workpiece can be prevented. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 2 is a diagram showing an example of a first wafer and a second wafer. [Figure 2] 1A and 1B are diagrams showing examples of bonded wafers. [Figure 3] FIG. 10 is a diagram showing the location of a chamfered portion of a bonded wafer. [Figure 4] 10A to 10C are diagrams illustrating a chamfered portion removing step. [Figure 5] 10A to 10C are diagrams illustrating a chamfered portion removing step. [Figure 6] FIG. [Figure 7] FIG. [Figure 8] 1A is a diagram illustrating the state at the start of grinding, and FIG. 1B is a diagram illustrating the state at the end of grinding. [Figure 9]1A is a diagram illustrating an example of a non-contact thickness measuring device, and FIG. 1B is a diagram illustrating another example of a non-contact thickness measuring device. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a first wafer 11 and a second wafer 12, and FIG. 2 shows an example of a bonded wafer 10 formed by bonding two wafers 11 and 12 together.

[0023] As shown in FIGS. 1 and 2, the bonded wafer 10 is formed by bonding a surface 11a of a first wafer 11 and a surface 12a of a second wafer 12 together to form a single plate-like object.

[0024] Dividing lines are set in a grid pattern on the surface 11a of the first wafer 11 and the surface 12a of the second wafer 12, and devices are formed in each area defined by the dividing lines.

[0025] The present invention can also be applied to a case where, for example, another base wafer is bonded in addition to the wafers 11 and 12. The present invention can also be applied to a single wafer having a chamfered portion formed on the outer periphery, instead of a bonded wafer.

[0026] Furthermore, devices may not be formed on either or both of the first and second wafers shown in Figure 1. The thickness of each wafer is, for example, 775 µm.

[0027] FIG. 3 shows an example of the configuration of the outer periphery of the bonded wafer 10. As shown in FIG. The first wafer 11 has a silicon wafer 11c coated with a 1 μm protective layer and a 5 μm device layer 11d formed on the front surface 11a of the silicon wafer 11c. The back surface 11b of the silicon wafer 11c is exposed as the back surface of the first wafer 11.

[0028] The second wafer 12 includes a silicon wafer 12c coated with a 1 μm protective layer and a 10 μm logic layer 12d formed on the front surface 12a of the silicon wafer 12c. The back surface 12b of the silicon wafer 12c is exposed as the back surface of the second wafer 12.

[0029] Then, the device layer 11d of the first wafer 11 and the logic layer 12d of the second wafer 12 are bonded together via a bonding layer 13 having a thickness of 1 μm to 3 μm.

[0030] 3, the corners of the outer peripheral edge of the first wafer 11 are chamfered to form a chamfered portion 11m. Similarly, the corners of the outer peripheral edge of the second wafer 12 are chamfered to form a chamfered portion 12m.

[0031] Next, a method for processing the bonded wafer 10 configured as above will be described. The processing method according to the present invention can be widely applied to workpieces having a first surface and a second surface and a chamfered portion formed on the outer periphery. In the bonded wafer 10 shown in Fig. 3, the first surface is the back surface 11b of the first wafer 11, the second surface is the back surface 12b of the second wafer 12, and the chamfered portion is the chamfered portion 11m of the first wafer 11.

[0032] <Chamfer removal step> As shown in FIGS. 4 and 5, this is a step in which a chamfered portion 11m is removed to a predetermined depth from the back surface 11b side, which is the first surface, along the outer periphery of the bonded wafer 10, thereby forming a step portion 15 on the outer periphery.

[0033] This chamfered portion removal step can be performed using a cutting device 20 having a cutting blade 21 that rotates at high speed and a chuck table 22 that holds the bonded wafer 10 by suction and rotates it in a horizontal plane.

[0034] The cutting blade 21 is fixed to the tip of a spindle 24 that is rotated by a motor (not shown) inside a spindle housing 23. The spindle housing 23 is configured to be movable in the axial direction C of the spindle and in the height direction Z by a moving device (not shown). The movement of the spindle housing 23 is controlled by a control device (not shown), so that the lower end of the cutting blade 21 is positioned at a predetermined position.

[0035] The chuck table 22 is configured to rotate about a vertical rotation axis by a motor (not shown) and to be movable in a horizontal plane by a processing feed mechanism (not shown). By controlling the movement of the chuck table 22 by a control device (not shown), the outer periphery of the bonded wafer 10 held on the chuck table 22 is positioned at a predetermined position.

[0036] In the above configuration, as shown in FIG. 4, the bonded wafer 10 is held by the chuck table 22, and the chuck table 22 is moved to position the outer periphery of the bonded wafer 10 directly under the cutting blade 21. Next, as shown in FIG. 5, the cutting blade 21 is rotated at high speed and lowered to a predetermined cutting depth, thereby cutting into the chamfered portion 11m. Next, the chuck table 22 is rotated, and the chamfered portion 11m on the outer periphery is continuously removed in the circumferential direction. The chuck table 22 is rotated 360 degrees or more, and the entire outer periphery of the chamfered portion 11m is removed, forming the annular step portion 15. This process is called edge trimming.

[0037] The processing conditions for this edge trimming are, for example, as follows. <Edge trimming processing conditions> Cutting blade thickness: 3mm Spindle speed: 30,000 rpm Chuck table rotation speed: 5 to 20° / sec Trimming width: 0.5mm~

[0038] 5, the step portion 15 is formed by a height gap between the first surface (back surface 11b) of the bonded wafer 10 and a bottom surface 15d of the step portion 15. If the bottom surface 15d is thin, this portion becomes a knife edge.

[0039] The bottom surface 15d of the step portion 15 is formed, for example, at a height position Zd of 5 μm from the surface 11a of the silicon wafer 11c of the first wafer 11. In other words, the silicon wafer 11c is trimmed so that the thickness of the portion that forms the bottom surface 15d is 5 μm.

[0040] <Thinning step> As shown in FIGS. 6 and 7, this is a step of thinning the first surface (rear surface 11b) of the bonded wafer 10 to a predetermined finished thickness.

[0041] This thinning step can be performed using a grinding device 30 having a grinding wheel 31 that rotates at high speed and a chuck table 32 that holds the bonded wafer 10 by suction and rotates it in a horizontal plane.

[0042] The grinding wheel 31 has a plurality of grinding stones 36 attached at intervals around the circumference at its bottom, and is fixed to the bottom of a wheel mount 34 that is driven to rotate by a motor (not shown). The wheel mount 34 is adapted to be fed downward for grinding by a drive device (not shown).

[0043] The chuck table 32 is configured to rotate on a vertical rotation axis by a motor (not shown), and to be movable in a horizontal plane by a processing feed mechanism (not shown).

[0044] In the above configuration, as shown in Fig. 6, the grinding wheel 31 and the chuck table 32 are rotated while the grinding wheel 31 is lowered to bring the grinding stone 36 into contact with the first surface (back surface 11b) of the bonded wafer 10, thereby performing the grinding process. As shown in Figs. 8(A) and 8(B), as the grinding process progresses, the first wafer 11 is thinned, and the height of the back surface 11b of the first wafer 11 gradually approaches the bottom surface 15d of the step portion 15, and grinding ends when the finishing thickness Tw is reached.

[0045] The grinding conditions are, for example, as follows: <Grinding conditions> Spindle speed: 3000 rpm Chuck table rotation speed: 300 rpm Grinding feed rate Rough grinding: 6μm / s Finish grinding: 0.6 μm / s Finishing thickness: 5-10μm ·TTV(Total Thickness Variation): 1.5μm

[0046] <Measurement steps> In the thinning step, a measuring step is carried out to measure the height position of the bottom surface 15d of the step portion 15.

[0047] Specifically, as shown in Figure 9(A), a non-contact thickness measuring device 40 measures the difference Zm between the height position Z1 of the back surface 11b, which is the first surface side of the bonded wafer 10, and the height position Z2 of the bottom surface 15d of the step portion 15.

[0048] 9(A), the non-contact thickness measuring device 40 is configured as a single unit that can simultaneously measure, for example, the height position Z1 of the surface on the first surface side and the height position Z2 of the bottom surface of the step portion. This makes it possible to simplify the positioning mechanism for positioning the non-contact thickness measuring device 40 and reduce the number of parts.

[0049] The non-contact thickness measuring device 40 calculates the difference Zm between the height positions Z1 and Z2 and outputs it to the control device 5, which monitors the difference Zm. Note that the non-contact thickness measuring device 40 may measure only the height positions Z1 and Z2, and the calculation of the difference Zm may be performed by the control device 5.

[0050] Alternatively, as shown in FIG. 9(B), two non-contact thickness measuring devices 41 and 42 may be used to measure the height positions Z1 and Z2 individually, and the control device 5 may monitor the difference Zm.

[0051] The measurement step continues during the thinning step, and as the thinning progresses, the difference Zm decreases as shown in Figures 8(A) and 8(B), and when this difference Zm reaches a "predetermined value," the control device 5 shown in Figure 7 stops the grinding process. Specifically, the motor (not shown) that drives the wheel mount 34 and the drive device (not shown) that feeds the wheel mount 34 downward for grinding are stopped, thereby stopping the grinding process.

[0052] Here, the "predetermined value" that is the target value of the difference Zm is, for example, 5 μm, and by stopping the grinding process when this 5 μm is reached, it is possible to prevent the grinding wheel 36 (FIG. 8(A)) from reaching the bottom surface 15d of the step portion 15 and grinding the bottom surface 15d. Note that if the bottom surface 15d is thin, this portion will become a knife edge, but it is possible to reliably prevent chipping due to grinding the knife edge and the entanglement of the separated knife edge portion.

[0053] According to the above method, the condition of the step portion 15 is directly monitored, and processing can be stopped so as not to grind the bottom surface 15d. For example, in the conventional method of measuring the thickness of the wafer and stopping processing, there is a concern that the bottom surface 15d of the step portion 15 may be ground away due to the thickness accuracy of the wafer before processing (individual differences in thickness before processing) or measurement errors. However, according to the present invention, this problem can be reliably avoided.

[0054] As described above, in the present invention, when thinning the workpiece from the first surface side, the difference between the position of the surface on the first surface side of the workpiece and the position of the bottom surface of the step portion is measured, and processing is terminated before the thickness of the workpiece reaches the position of the bottom surface of the step portion.This means that the bottom surface of the step portion is not ground, and even if a knife edge is formed at the bottom of the step portion, grinding or chipping at that location can be suppressed, preventing a decrease in the processing quality of the workpiece. [Explanation of symbols]

[0055] 5. Control device 10 Bonded wafer 11 First wafer 11a surface 11b Back side 11c silicon wafer 11d Device Layer 11m chamfered section 12 Second wafer 12a surface 12b Back 12c silicon wafer 12d Logic Layer 12m chamfered section 13 Bonding layer 15 Step 15d bottom 20 Cutting equipment 21 Cutting blade 22 Chuck table 23 Spindle housing 24 spindles 30 Grinding equipment 0 31 Grinding Wheel 32 Chuck table 34 Wheel mount 36 Grinding Wheel 40 Measuring instruments Z1 height position Z2 height position Zm difference

Claims

1. A method for machining a workpiece having a first surface and a second surface and a chamfered portion formed on an outer periphery, comprising: a chamfer removing step of removing the chamfer from the first surface side along the outer circumferential edge of the workpiece to a predetermined depth to form a step portion on the outer circumferential edge; a thinning step of thinning the workpiece from the first surface side to a predetermined finishing thickness; At least In the thinning step, a measuring step is carried out to measure the position of the bottom surface of the step portion; In the thinning step, the processing is terminated before the thickness of the workpiece reaches the level of the bottom surface of the step portion. Processing method of workpiece.

2. In the measuring step, measuring a difference between the height position of the surface on the first surface side of the workpiece and the height position of the bottom surface of the step portion using a non-contact thickness measuring device; 2. The method for processing a workpiece according to claim 1.

3. Non-contact thickness measuring instruments are The height position of the surface on the first surface side of the workpiece and the height position of the bottom surface of the step portion are simultaneously measured by one unit.

3. The method for processing a workpiece according to claim 2.

4. The measuring step includes: Continued during the thinning step, 4. The method for processing a workpiece according to claim 1.

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