Method of processing pasted wafer

Abstract

To provide a novel technique for accurately measuring the thickness of a ground wafer in a pasted wafer which is formed by pasting a ground wafer to be ground onto a support substrate.SOLUTION: A method of processing a pasted wafer is for thinning a ground wafer to a finished thickness for a pasted wafer which is formed by pasting a ground wafer onto a support substrate, the method including: measuring an overall thickness of the pasted wafer with a first measuring instrument; measuring the thickness of the ground wafer with a second measuring instrument; and at a timing when the ground wafer has been thinned to a thickness that does not permit measurement by the second measuring instrument, performing remaining grinding required to reach the finished thickness from the thickness of the ground wafer at that timing while measuring the overall thickness with the first measuring instrument.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a processing method for thinning a wafer to be ground to a finish thickness, for a bonded wafer formed by bonding a wafer to a support substrate. [Background technology]

[0002] In the semiconductor device manufacturing process, streets are formed in a grid pattern on the wafer surface, and devices such as ICs and LSIs are formed in the areas partitioned by the streets. After the backside of these wafers is ground to thin them to a specified thickness, they are divided along the streets using a cutting device or the like to produce individual semiconductor device chips.

[0003] When a wafer is thinned to the above-described degree, its thickness may become 100 μm or less, requiring careful handling. Therefore, in order to reinforce the thinned wafer when it is subjected to various processes such as a plasma etching process, an electrode formation process, and a metal film coating process by sputtering, or to facilitate handling of the wafer when it is transported to each process, it is known to bond the wafer to a support substrate having higher rigidity than the wafer to be thinned before the thinning process, so that the entire surface of the wafer is supported by the support substrate.

[0004] For example, Patent Documents 1 and 2 disclose that when grinding the backside of a wafer to be thinned, a support substrate (carrier wafer) is attached to the front side of the wafer for the purpose of protecting the front side and for facilitating handling during and after grinding and thinning. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-149877 [Patent Document 2] Patent Publication No. 2021-190642 Summary of the Invention [Problem to be solved by the invention]

[0006] Depending on the backside grinding process used to thin the wafer, the finished wafer thickness may be set to an extremely thin value of 2 μm or less, making it difficult to control the finished thickness. For example, when backside grinding, it is possible to measure the total thickness of the wafer and support substrate in real time while grinding, but when thinning the wafer to a thickness of 1.0 μm, it is necessary to measure and monitor the total thickness more accurately.

[0007] On the other hand, even if the total thickness of the wafer and the supporting substrate is measured in real time, there is a concern that the actual wafer thickness may not be the finished thickness due to variations in the thickness of the supporting substrate.

[0008] In view of the above problems, the present invention proposes a novel technique for accurately measuring the thickness of a wafer to be ground in a bonded wafer formed by bonding a wafer to be ground and a support substrate. [Means for solving the problem]

[0009] The problem to be solved by the present invention is as described above, and the means for solving this problem will now be described.

[0010] According to one aspect of the present invention, there is provided a processing method for thinning a bonded wafer, which is formed by bonding a wafer to be ground and a support substrate, to a finish thickness, the processing method for a bonded wafer including measuring the total thickness of the bonded wafer with a first measuring device and measuring the thickness of the wafer to be ground with a second measuring device.

[0011] Furthermore, according to one aspect of the present invention, when the wafer to be ground has been thinned to a thickness that cannot be measured by the second measuring device, the remaining grinding required to reach the finishing thickness from the thickness of the wafer to be ground at that time is carried out while measuring the total thickness by the first measuring device.

[0012] According to one aspect of the present invention, the grinding method includes a finishing thickness setting step of setting a finishing thickness of the wafer to be ground, a measurable range setting step of setting a range of thicknesses of the wafer to be ground that can be measured by a second measuring device, a holding step of holding a support substrate of the bonded wafer on a holding table and exposing the back surface of the wafer to be ground, a total thickness measuring step of measuring the total thickness of the bonded wafer by the first measuring device, a grinding step of grinding the wafer to be ground, a step of referring to a second measurement value by the second measuring device as the thickness of the wafer to be ground in the grinding step, a first measurement value referring step of referring to the first measurement value by the first measuring device when the second measurement value falls below a lower limit value of the measurable range in the grinding step, and a grinding ending step of ending grinding when grinding has progressed by the difference between the lower limit value and the finishing thickness after the first measurement value referring step.

[0013] According to one aspect of the present invention, the first measuring device and the second measuring device are capable of measuring thickness in a non-contact manner.

[0014] According to one aspect of the present invention, the first measuring instrument is a white light confocal measuring instrument, and the second measuring instrument is an infrared spectroscopic interferometer. [Effects of the Invention]

[0015] The present invention provides the following effects. That is, according to one aspect of the present invention, two types of measuring instruments are used in combination, one measuring instrument is used to measure the total thickness of the bonded wafer, and the other measuring instrument is used to measure the thickness of the wafer to be ground, which is to be back-ground, thereby making it possible to accurately control the thickness of the wafer to be ground without being affected by variations in the thickness of the support substrate. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram showing an example of a bonded wafer. [Figure 2] FIG. 1 is a diagram showing an example of a grinding device. [Figure 3] FIG. 2 is a diagram for explaining a first measurement value, a second measurement value, etc. [Figure 4] 3 is a flow chart illustrating steps of a grinding method. [Figure 5] (A) is a diagram showing the state at the start of grinding, and (B) is a diagram showing the state after grinding has progressed. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an example of a bonded wafer W formed by bonding a wafer 10 to be ground, the back surface of which is to be ground, and a support substrate 20 together.

[0018] The wafer 10 to be ground shown in Figure 1 has a plurality of devices 11 formed on the front surface 10a of the silicon wafer, with planned division lines 13 set in a grid pattern between each device 11. The front surface 10a of the silicon wafer is attached to the front surface 20a of a support substrate 20, and the back surface 10b of the silicon wafer is exposed. The exposed back surface 10b of the silicon wafer is thinned by grinding. Note that the wafer 10 to be ground may not have the devices 11 formed thereon.

[0019] 1 is attached to the support substrate 20 via a temporary adhesive, or may be directly bonded to the support substrate 20. The wafer 10 to be ground is, for example, thinned by grinding and then peeled off from the support substrate 20, or is transported together with the support substrate 20 and subsequently subjected to another process.

[0020] The material of the wafer 10 to be ground may be silicon, but is not limited to, for example, LT (lithium tantalate), LN (lithium niobate), sapphire, GaN, GaAs, etc.

[0021] 1 may be made of, for example, silicon, LT (lithium tantalate), LN (lithium niobate), sapphire, GaN, GaAs, or may be made of resin or glass, similar to the grinding wafer 10. The shape of the support substrate 20 is, for example, a disk-shaped wafer having approximately the same diameter as the grinding wafer 10.

[0022] Alternatively, the bonded wafer W may be an SOI (Silicon-On-Insulator) wafer in which an oxide film layer is interposed between two wafers.

[0023] The bonded wafer W configured as above is subjected to a grinding process by a grinding device 3 shown in FIG.

[0024] The grinding device 3 includes a grinding unit 30, a holding table 35, a controller 5, a first measuring device 41, and a second measuring device 42.

[0025] The grinding unit 30 is composed of a spindle 31 that is rotated by a motor (not shown), a wheel mount 32 that is provided at the lower end of the spindle 31, and a grinding wheel 34 that has multiple grinding stones 33 arranged circumferentially.

[0026] The spindle 31 is configured to be raised and lowered in the Z-axis direction (height direction) by a motor (not shown), whereby the wheel mount 32 and grinding wheel 34 are fed downward for processing.

[0027] The holding table 35 is rotated at a predetermined rotation speed by a motor (not shown). The upper surface of the holding table 35 is configured as a holding surface 35a where negative pressure is generated by suction from a suction source (not shown), and the lower surface of the bonded wafer W (the lower surface 20b of the support substrate 20) is suction-held by the holding surface 35a.

[0028] In a state where the lower surface of the bonded wafer W is held by the holding surface 35a, the back surface 10b of the wafer to be ground 10 to be ground is exposed upward.

[0029] The controller 5 controls a motor that raises and lowers the spindle 31 to feed the grinding wheel 34 downward, a motor that rotates the spindle 31, and a motor that rotates the holding table 35. A first measuring instrument 41 and a second measuring instrument 42 are also connected to the controller 5, and measurement values ​​from each measuring instrument are input.

[0030] The first measuring device 41 is a measuring device for measuring the thickness of the bonded wafer W, and can be configured, for example, by a well-known white light confocal measuring device (NHG).

[0031] The first measuring device 41, which is composed of a white light confocal measuring device (NHG), can measure the total thickness T1 (T1=K1-K2) of the bonded wafer W from the distance K1 to the holding surface 35a of the holding table 35 and the distance K2 to the top surface of the bonded wafer W (the back surface 10b of the wafer 10 to be ground).

[0032] The measurement range of the first measurement device 41, which is made up of a white light confocal measurement device (NHG), is generally not particularly limited, but one that can measure in units of at least 0.1 μm is used.

[0033] The second measuring device 42 is a measuring device for measuring the thickness of the wafer 10 to be ground whose back surface is ground, and can be configured, for example, by a well-known infrared spectroscopic interferometer (NCG).

[0034] The second measuring instrument 42, which is composed of an infrared spectroscopic interferometer (NCG), can measure the thickness T2 (T2=K3-K4) of the wafer 10 to be ground from the distance K3 to the boundary Wk of the bonded wafer W and the distance K4 to the top surface of the bonded wafer W (the back surface 10b of the wafer 10 to be ground).

[0035] The second measuring device 42, which is an infrared spectroscopic interferometer (NCG), has a measurement range of 1.5 μm to 9 μm when the material of the ground wafer 10 and the support substrate 20 is silicon, for example. In other words, measurement is possible when the thickness T2 of the ground wafer 10 is in the range of 1.5 μm to 9 μm.

[0036] Therefore, as will be described in detail later, the thickness of the wafer 10 to be ground cannot be measured by the second measuring device 42 until grinding begins and the wafer 10 to be ground has thinned to a thickness that can be measured by the second measuring device 42 (for example, 9 μm or less), and the controller 5 does not refer to the value of the second measuring device 42.

[0037] As grinding progresses and the ground wafer 10 becomes thinner to a thickness that can be measured by the second measuring device 42 (for example, 9 μm or less), the controller 5 can refer to the value of the second measuring device 42 and recognize the thickness of the ground wafer 10 alone.

[0038] When the grinding of the wafer 10 to be ground progresses further and the thickness becomes thinner than a measurable thickness (for example, less than 1.5 μm), the thickness of the wafer 10 to be ground cannot be measured by the second measuring device 42, and the controller 5 does not refer to the value of the second measuring device 42.

[0039] Next, a description will be given of a method for grinding a bonded wafer W using the grinding apparatus 3 configured as above. Fig. 4 is a flowchart showing steps constituting the grinding method.

[0040] As shown in Figures 5(A) and (B), in the following example, a bonded wafer W is formed by bonding a wafer 10 to a support substrate 20, and the wafer 10 to be ground is thinned to a finishing thickness Tz.

[0041] <Finishing thickness setting step> As shown in FIG. 5(B), this is a step for setting the finishing thickness Tz of the wafer 10 to be ground.

[0042] Specifically, for example, an operator operates a touch panel or the like (not shown) to store the finished thickness Tz of the ground wafer 10 in the controller 5. The finished thickness Tz is set to, for example, 1.0 μm.

[0043] <Measurable range setting steps> This is a step for setting the range of thickness of the wafer to be ground 10 that can be measured by the second measuring instrument 42.

[0044] Specifically, for example, an operator operates a touch panel (not shown) or the like to store the measurement range of the second measuring device 42 (for example, 1.5 μm (lower limit) to 9 μm (upper limit)) in the controller 5. This measurement range is set in accordance with the specifications of the second measuring device 42 (infrared spectroscopic interferometer (NCG)), the material of the ground wafer 10 to be measured, and the like.

[0045] <Holding step> As shown in FIG. 2, this is a step in which the support substrate 20 of the bonded wafer W is held by the holding table 35, and the back surface 10b of the wafer 10 to be ground is exposed.

[0046] Specifically, the support substrate 20 of the bonded wafer W is placed on the holding surface 35a of the holding table 35, and suction is started to hold the bonded wafer W by the holding table 35. Then, the back surface 10b of the wafer 10 to be ground is exposed upward, thereby making the back surface 10b of the wafer 10 to be ground ready to be ground.

[0047] <Total thickness measurement step> As shown in FIGS. 3 and 5(A), this is a step of measuring the thickness (total thickness T1) of the bonded wafer W.

[0048] Specifically, this is a step in which the first measuring device 41, which is composed of a white light confocal measuring device (NHG), measures the total thickness T1 (T1=K1-K2) of the bonded wafer W from the distance K1 to the holding surface 35a of the holding table 35 and the distance K2 to the top surface of the bonded wafer W (the back surface 10b of the wafer 10 to be ground).

[0049] For example, the holding table 35 is moved horizontally, or the first measuring instrument 41 is moved horizontally, and the first measuring instrument 41 is placed directly above the holding surface 35a, and the distance K1 from the first measuring instrument 41 to the holding surface 35a of the holding table 35 is measured.

[0050] After measuring the distance K1, the first measuring device 41 is positioned above the wafer 10 to be ground to measure the distance K2, and the value obtained by subtracting the distance K2 from the distance K is measured as the total thickness T1.

[0051] From the start of the grinding step until the end of grinding, the first measuring device 41 is positioned above the wafer 10 to be ground, and the total thickness T1 is measured by monitoring the distance K2 from the wafer 10. As grinding progresses, the distance K2 increases, and accordingly the total thickness T1 decreases.

[0052] <Grinding step> This is a step in which the wafer to be ground 10 is ground by the grinding unit 30 (FIG. 2).

[0053] Specifically, the controller 5 rotates the holding table 35 at a predetermined rotation speed to rotate the bonded wafer W, and also rotates the grinding wheel 34 at a predetermined rotation speed while lowering it at a predetermined processing feed rate.

[0054] 5(A), in the grinding step, the first measuring device 41 measures the thickness T1 of the bonded wafer W, and the controller 5 monitors the measured value as a first measured value S1. The first measured value S1 (thickness T1) decreases as the grinding progresses.

[0055] 5(A), in the grinding step, the second measuring device 42 measures the thickness T2 of the wafer 10 to be ground, and the controller 5 monitors the measured value as a second measured value S2. Note that the thickness T2 is not measured until it falls within the set range set in the measurable range setting step.

[0056] <Second measurement value reference step> As shown in FIG. 5(B), in the grinding step, the controller 5 refers to the second measurement value S2 as the thickness of the wafer 10 to be ground when the thickness T2 of the wafer 10 to be ground is within the measurable range.

[0057] Specifically, as grinding progresses and the thickness T2 reaches the set range set in the measurable range setting step, the second measurement value S2 measured by the second measuring instrument 42 is output to the controller 5, and the controller 5 refers to the second measurement value S2 as the thickness T2 of the wafer 10 to be ground.

[0058] When the finished thickness Tz is within the measurable range, the controller 5 ends the grinding when the second measurement value S2 (thickness T2) reaches the finished thickness Tz.

[0059] In this case, the thickness T2 of the wafer 10 to be ground measured by the second measuring device 42 can be managed as the finishing thickness Tz, and the thickness of the wafer 10 to be ground can be accurately controlled without being affected by variations in the support substrate 20.

[0060] <First measurement value reference step> As shown in FIG. 5(B), in the grinding step, the controller 5 refers to the first measurement value when the second measurement value S2 falls below the lower limit value D of the measurable range.

[0061] Specifically, for example, if the lower limit value D of the measurable range of the second measuring device 42 is 1.5 μm and the finishing thickness Tz is 1.0 μm, when the ground wafer 10 becomes thinner than 1.5 μm, the second measuring device 42 cannot measure it, and therefore it will not be possible to recognize that the finishing thickness Tz=1.0 μm has been reached.

[0062] Therefore, when the second measurement value S2 of the second measuring device 42 reaches the lower limit value D (1.5 μm), the controller 5 refers to the first measurement value S1 of the first measuring device 41 and performs grinding of the difference Zs (0.5 μm), which is the remaining grinding amount required to get from the lower limit value D (1.5 μm) to the finishing thickness Tz (1.0 μm), based on the first measurement value S1.

[0063] <Grinding end step> In the grinding step, the controller 5 ends the grinding when the grinding has progressed by the difference Zs between the lower limit value D and the finish thickness Tz after the first measurement value referring step.

[0064] Specifically, as described above, the controller 5 switches the measurement value to be referenced in the first measurement value reference step to the first measurement value S1, and then ends the grinding when grinding has progressed by the difference Zs (0.5 μm).

[0065] In this way, by referring to the second measurement value S2, it is known that the thickness of the wafer 10 to be ground is 1.5 μm, and by further grinding the remaining thickness of 0.5 μm using the first measurement value S1, it is possible to end the grinding when the final finishing thickness Tz (1.0 μm) is reached.

[0066] In this case, by grinding the thickness T2 of the wafer 10 to be ground by an additional 0.5 μm from a state in which the thickness T2 is 1.5 μm, the finished thickness Tz (1.0 μm) can be controlled, and the thickness of the wafer 10 to be ground can be accurately controlled without being affected by variations in the support substrate 20.

[0067] The present invention can be carried out as described above. That is, the method is a processing method for thinning a bonded wafer formed by bonding a wafer to be ground and a support substrate to a finishing thickness, and includes measuring the total thickness of the bonded wafer with a first measuring device and measuring the thickness of the wafer to be ground with a second measuring device, and when the wafer to be ground has been thinned to a thickness that cannot be measured with the second measuring device, the remaining grinding required to reach the finishing thickness from the thickness of the wafer to be ground at that time is carried out while measuring the total thickness with the first measuring device.

[0068] In this way, by using two types of measuring instruments in combination, one measuring instrument to measure the total thickness of the bonded wafer W, and the other measuring instrument to measure the thickness of the ground wafer 10 itself to be back-ground, it is possible to accurately control the thickness of the ground wafer 10 without being affected by variations in the thickness of the support substrate 20.

[0069] Furthermore, if the second measuring device 42 is configured as an infrared spectroscopic interferometer (NCG) that measures the thickness of the wafer 10 to be ground, there is a lower limit (for example, 1.5 μm), so it is not possible to measure or control the thickness in the so-called "ultra-thin region" below the lower limit, but by combining it with the measurement of the total thickness by the first measuring device (white light confocal measuring device (NHG)), it becomes possible to measure and control the thickness in the "ultra-thin region." Furthermore, by making it possible for both the first measuring device and the second measuring device to measure the thickness non-contact, it is possible to proceed with the grinding process while monitoring changes in thickness. [Explanation of symbols]

[0070] 3 Grinding equipment 5 Controller 10 wafers 10a surface 10b back side 11 Devices 13 Planned division line 20 Support substrate 20a surface 20b Bottom side 30 Grinding Unit 31 Spindle 32 Wheel mount 33 Grinding Wheel 34 Grinding Wheel 35 Holding table 35a Holding surface 41 Measuring instruments 42 Measuring instruments D Lower limit K1 distance K2 distance K3 Distance K4 Distance S1 measurement value S2 measurement value T1 full thickness Tz Finishing Thickness W wafer Wk border Zs difference

Claims

1. A processing method for thinning a ground wafer to a finish thickness, the method comprising the steps of: measuring the total thickness of the bonded wafer with a first measuring device; and measuring the thickness of the ground wafer with a second measuring device; A method for processing a bonded wafer, comprising:

2. At a timing when the ground wafer is thinned to a thickness that cannot be measured by the second measuring device, The remaining grinding required from the thickness of the wafer to be ground at that timing to the finish thickness is performed while measuring the total thickness with the first measuring device.

2. The method for processing a bonded wafer according to claim 1,

3. a finishing thickness setting step of setting a finishing thickness of the wafer to be ground; a measurable range setting step of setting a range of thickness of the ground wafer that can be measured by the second measuring device; a holding step of holding a support substrate of the bonded wafer by a holding table and exposing the back surface of the wafer to be ground; a total thickness measuring step of measuring the total thickness of the bonded wafer by the first measuring device; a grinding step of grinding the wafer to be ground; In the grinding step, a step of referring to a second measurement value by the second measuring device as a thickness of the wafer to be ground; a first measurement value referring step of referring to the first measurement value measured by the first measuring device when the second measurement value falls below a lower limit value of a measurable range in the grinding step; a grinding termination step of terminating grinding when grinding has progressed by the difference between the lower limit value and the finish thickness after the first measurement value reference step, 3. The method for processing a bonded wafer according to claim 2, wherein the method comprises:

4. the first measuring device and the second measuring device are capable of measuring thickness in a non-contact manner; 4. The method for processing a bonded wafer according to claim 3.

5. the first measuring device is a white light confocal measuring device; the second measuring instrument is an infrared spectroscopic interferometer; 5. The method for processing a bonded wafer according to claim 4.

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