Wafer with locally thinned structure

Abstract

A wafer with a locally thinned structure, wherein the wafer comprises a plurality of grains. Each of the plurality of grains includes at least one element and at least one back groove. The at least one element is formed on a top surface of the wafer. The at least one back groove is formed by laser processing, wherein the at least one back groove has an opening on a bottom surface of the wafer. In each of the plurality of grains, a region occupied by the opening of the at least one back groove and a region occupied by the bottom surface of the at least one back groove are respectively associated with the at least one element.

Description

[Technical Field]

[0001] The present invention relates to a wafer having a locally thinned structure, and more particularly to a wafer having a locally thinned structure formed by laser processing. [Previous Technology]

[0002] Conventional techniques typically employ grinding methods to thin the entire back side of a wafer. When the wafer thickness is reduced too much, especially when it is less than 100 μm, the wafer is prone to bending and warping. Particularly in fields such as Vertical Cavity Surface Emitting Lasers (VCSELs), many epitaxial layers are formed on the front side of the wafer, leading to significant stress accumulation. Once the wafer is thinned too much, the degree of warping becomes very severe. This makes the wafer difficult to handle and subsequent processing extremely challenging. Furthermore, using conventional grinding methods to thin the entire back side of a wafer typically results in a high breakage rate. For example, when thinning silicon carbide (SiC) wafers used in power devices, such as silicon carbide-metal oxide semiconductor field-effect transistors (SiC MOSFETs @1200V-6500V) with voltage ratings of 1200V to 6500V, the silicon carbide wafers need to be thinned to a thickness of less than 150μm; however, the breakage rate is generally around 3% to 5%. As another example, when thinning silicon carbide wafers used in radio frequency (RF) devices, sometimes the required thickness of the thinned silicon carbide wafer is less than 100μm; however, the breakage rate will be higher than 5%. On the other hand, conventional polishing methods are very expensive.

[0003] Another prior art technique attempts to address the warpage problem caused by wafer thinning. This prior art technique uses a smaller grinding wheel with a diameter smaller than one of the wafer's diameters to grind the back side of the wafer, thereby thinning the central portion of the back side. Only the annular frame at the wafer edge remains un-thinned. While the annular frame at the wafer edge can reduce the degree of wafer warpage, when the central portion of the back side is thinned too much, the support stress in the central portion of the wafer may still be insufficient, or wafer warpage may still occur. [Summary of the Invention]

[0004] The technical problem to be solved by the present invention is how to provide a wafer with a locally thinned structure so that wafer warping does not occur.

[0005] To solve the aforementioned problems and achieve the desired effect, the present invention provides a wafer with a locally thinned structure, comprising a wafer including a plurality of grains, wherein each of the plurality of grains includes at least one element and at least one backside recess. The at least one element is formed on one upper surface of the wafer. The at least one backside recess is formed by laser processing, wherein the at least one backside recess has an opening on one lower surface of the wafer. In each of the plurality of grains, a region occupied by the opening of the at least one backside recess is associated with the at least one element.

[0006] In practice, in each of the plurality of grains, the area occupied by the opening of at least one back groove is determined based on at least one feature of interest, wherein the at least one feature of interest is associated with at least one element.

[0007] In practice, in each of the plurality of grains, at least one feature of interest is located within the area occupied by the opening of at least one back groove, or is identical to the area occupied by the opening of at least one back groove.

[0008] In practice, in each of the plurality of grains, a region occupied by the bottom surface of at least one back groove is associated with at least one element.

[0009] In practice, in each of the plurality of grains, the area occupied by the bottom surface of at least one back groove is determined based on at least one feature of interest, wherein the at least one feature of interest is associated with at least one element.

[0010] In practice, in each of the plurality of grains, at least one feature of interest is located within the area occupied by the bottom surface of at least one back groove, or is identical to the area occupied by the bottom surface of at least one back groove.

[0011] In practice, in each of the plurality of grains, the area occupied by the bottom surface of at least one back groove is within the area occupied by the opening of at least one back groove, or is identical to the area occupied by the opening of at least one back groove.

[0012] In practice, in each of the plurality of grains, the area occupied by the bottom surface of at least one back groove is within the area occupied by the opening of at least one back groove, wherein one of the sidewalls of at least one back groove is stepped, tapered, or a combination of stepped and tapered.

[0013] In practice, in each of the plurality of grains, the area occupied by the bottom surface of at least one back groove is identical to the area occupied by the opening of at least one back groove, wherein one of the sidewalls of at least one back groove is upright.

[0014] In practice, in each of the plurality of grains, the wafer has a desired thickness in the area occupied by the bottom surface of at least one back groove.

[0015] When implemented, the required thickness is greater than 10μm.

[0016] In practice, in each of the plurality of grains, the wafer has a first desired thickness in a region occupied by the bottom surface of one of the at least one back groove; and the wafer has a second desired thickness in a region occupied by the bottom surface of the other of the at least one back groove, wherein the first desired thickness is less than, equal to or greater than the second desired thickness.

[0017] In practice, in each of the plurality of grains, the bottom surface of at least one back groove includes a first bottom surface of at least one back groove and a second bottom surface of at least one back groove, the wafer having a first desired thickness in a first region occupied by the first bottom surface of at least one back groove; and the wafer having a second desired thickness in a second region occupied by the second bottom surface of at least one back groove, wherein the first desired thickness is less than, equal to or greater than the second desired thickness.

[0018] In practice, the first required thickness is greater than 100 nm.

[0019] In practice, in each of the plurality of grains, the ratio of the area occupied by the bottom surface of at least one back groove to the area occupied by the opening of at least one back groove is greater than or equal to 0.5 and less than or equal to 1.

[0020] In practice, each of the plurality of grains includes a plurality of sub-grains, and each of the plurality of sub-grains includes at least one of at least one element formed on the surface of the wafer.

[0021] In practice, the ratio of the area occupied by the opening of at least one back groove of any of the plurality of grains to the area occupied by any one of the plurality of grains is less than or equal to 0.98.

[0022] In practice, in each of the plurality of grains, at least one of the back grooves is adjacent to another of the at least one back groove; wherein a gap between an area occupied by an opening of the at least one back groove and an area occupied by an opening of the other of the at least one back groove is greater than or equal to 10 μm.

[0023] In practice, the wafer is made of at least one material selected from the group consisting of: glass, silicon carbide, gallium nitride, gallium nitride on silicon carbide substrate, gallium nitride on silicon substrate, silicon, germanium silicon, gallium arsenide, gallium oxide, gallium antimonide, aluminum nitride, sapphire, gallium phosphide, indium phosphide, indium arsenide, zinc selenide, and diamond.

[0024] To further understand the present invention, the following preferred embodiments are described in detail with reference to drawings and reference numbers, illustrating the specific composition of the present invention and the effects it achieves.

Implementation Method

[0026] Please refer to Figure 1, which is a cross-sectional schematic diagram of a specific embodiment of a partial wafer thinning system of the present invention. The partial wafer thinning system 1 of the present invention includes a driving device 2, an image capturing device 3, a laser device 4, a carrier device 5, and a control integration device 8.

[0027] In this embodiment, the carrier device 5 includes a clamping element 50, wherein the carrier device 5 has a hollow central portion 51. The clamping element 50 surrounds the hollow central portion 51 of the carrier device 5. The clamping element 50 of the carrier device 5 is used to clamp one peripheral edge of a wafer 6, so that the wafer 6 can be carried by the carrier device 5. The carrier device 5 is disposed on the driving device 2. In this embodiment, the wafer 6 is carried by the carrier device 5 with one upper surface 60 of the wafer 6 facing downward (that is, one lower surface 63 of the wafer 6 faces upward), wherein the wafer 6 includes a plurality of dies 61. Please refer to FIG2, which is a schematic diagram of one upper surface of a wafer in FIG1. ​​Please also refer to FIG3, which is a partial enlarged view of region X in FIG2, which shows a schematic diagram of one upper surface of a die. In this embodiment, each of the plurality of dies 61 includes only one element 7 (generally, each of the plurality of dies 61 may include at least one element 7, and / or some other elements, and / or an integrated circuit). In this embodiment, element 7 is a power element (e.g., a power metal-oxide-semiconductor field-effect transistor MOSFET). Element 7 includes a first source electrode 70, a second source electrode 71, a third source electrode 72, a gate electrode 73, and a gate finger 74, wherein the first source electrode 70, the second source electrode 71, the third source electrode 72, the gate electrode 73, and the gate finger 74 are formed on the upper surface 60 of the wafer 6, wherein the gate finger 74 has a very fine shape compared to one of the shapes of each of the three source electrodes 70, 71, 72. Element 7 may further include a drain electrode; however, in this embodiment, the drain electrode of element 7 has not been formed. Therefore, the drain electrode of element 7 is not shown in the figure.

[0028] In this embodiment, Figures 1-3 show an X-axis direction, a Y-axis direction, and a Z-axis direction, wherein the Y-axis direction is perpendicular to both the X-axis and Z-axis directions, and the X-axis direction is perpendicular to the Z-axis direction. In this embodiment, the driving device 2 includes a three-axis moving platform (including an X-axis moving platform, a Y-axis moving platform, and a Z-axis moving platform), wherein the driving device 2 can move the wafer 6 carried by the carrier device 5 along any one of the X-axis, Y-axis, and Z-axis directions. Therefore, the driving device 2 can generate a relative displacement between the image capturing device 3 and the wafer 6 carried by the carrier device 5 along any one of the X-axis, Y-axis, and Z-axis directions; and the driving device 2 can also generate a relative displacement between the laser device 4 and the wafer 6 carried by the carrier device 5 along any one of the X-axis, Y-axis, and Z-axis directions. In this embodiment, the drive device 2 has a hollow central portion 20, wherein the hollow central portion 20 of the drive device 2 corresponds to the hollow central portion 51 of the support device 5 and is located below the hollow central portion 51 of the support device 5.

[0029] In this embodiment, the image capturing device 3 includes an image capturing element 30 and a light source 32, wherein the image capturing element 30 has a lens 31. The light source 32 is a coaxial light source. The image capturing element 30 of the image capturing device 3 is used to capture images. The light source 32 is mounted on a protruding connecting portion 33 of the lens 31 for emitting light. One end of the lens 31 faces the upper surface 60 of the wafer 6. The image capturing device 3 is disposed below the hollow central portion 20 of the driving device 2 (or a part of the image capturing device 3 (e.g., a part of the lens 31) is disposed within the hollow central portion 20 of the driving device 2), so that the light emitted by the light source 32 can pass through the lens 31, and then through the hollow central portion 20 of the driving device 2 and the hollow central portion 51 of the carrier device 5, to illuminate at least a portion of the upper surface 60 of the wafer 6 (e.g., at least one die 61), and so that the image capturing element 30 of the image capturing device 3 can capture the image of at least one die 61 (from the upper surface 60 of the wafer 6). In some other embodiments, the light emitted by the light source 32 can illuminate the entire upper surface 60 of the wafer 6, so that the image capturing element 30 of the image capturing device 3 can capture the image of each of a plurality of dies 61 (from the upper surface 60 of the wafer 6).

[0030] In this embodiment, the control integration device 8 is connected to the driving device 2, the carrier device 5, the image capturing element 30 of the image capturing device 3, the light source 32 of the image capturing device 3, and the laser device 4. The control integration device 8 is connected to the carrier device 5 via the driving device 2. The control integration device 8 can control the carrier device 5 to clamp or release the peripheral edge of the wafer 6 via the clamping element 50 of the carrier device 5. The control integration device 8 can control the driving device 2 to drive movement, such as a relative displacement between the image capturing device 3 and the wafer 6 carried by the carrier device 5, and / or a relative displacement between the laser device 4 and the wafer 6 carried by the carrier device 5. The control integration device 8 can control the light source 32 of the image capturing device 3 to emit light, illuminating at least one die 61 or each of a plurality of dies 61. The control integration device 8 can control the image capturing element 30 of the image capturing device 3 to capture an image of at least one die 61 or an image of each of a plurality of dies 61. The control integration device 8 further includes an image recognition element 80, wherein the image recognition element 80 of the control integration device 8 can receive the image captured by the image capturing element 30 of the image capturing device 3, and then perform image recognition on the image captured by the image capturing element 30 of the image capturing device 3. Furthermore, the control integration device 8 can also control the laser device 4 to perform localized laser thinning processing on the lower surface 63 of the wafer 6.

[0031] The present invention further provides a method for partial wafer thinning, comprising the following steps: Step A: providing a wafer 6 supported by a carrier device 5, wherein the wafer 6 includes a plurality of dies 61, each of the plurality of dies 61 including at least one element 7 formed on an upper surface 60 of the wafer 6; Step B: determining at least one feature of interest for each of the plurality of dies 61 (described in further detail below), wherein the at least one feature of interest for each of the plurality of dies 61 is respectively related to the element 7 formed on the upper surface 60 of the wafer 6. At least one element 7 is associated with each of the plurality of grains 61; Step C: Based on at least one feature of interest of each of the plurality of grains 61, determine at least one thinning start region (described in further detail below) and at least one region of interest (described in further detail below) of each of the plurality of grains 61, wherein the at least one feature of interest of each of the plurality of grains 61 is located within or identical to the at least one thinning start region of each of the plurality of grains 61. At least one region of interest for each of the plurality of dies 61 is respectively (determined) within at least one thinning start region for each of the plurality of dies 61 (but not entirely identical to at least one thinning start region for each of the plurality of dies 61), or is respectively identical to at least one thinning start region for each of the plurality of dies 61; Step D: At least one image of each of the plurality of dies 61 is captured by an image capturing device 3 (in this embodiment, at least one image of each of the plurality of dies 61 is captured from the upper surface 60 of the wafer 6). Step E: An image recognition element 80 performs image recognition on at least one image to identify at least one feature of interest in each of the plurality of dies 61; and Step F: A laser device 4 performs local laser thinning on a lower surface 63 of the wafer 6 in at least one thinning start region in each of the plurality of dies 61 to locally thin the wafer 6 in at least one thinning start region in each of the plurality of dies 61, so that the wafer 6 has a desired thickness in at least one of the at least one region of interest in each of the plurality of dies 61.

[0032] In this invention, the required thickness of wafer 6 is not a measured thickness of wafer 6. When a user performs local thinning on the lower surface 63 of wafer 6 within a thinning start area of ​​a die 61, the user desires that after the wafer 6 is locally thinned, it has a specific thickness within the thinning start area of ​​the die 61, where this specific thickness is the required thickness. The user relies on experience to achieve the required thickness of wafer 6 within the thinning start area of ​​the die 61 after local thinning. For example, the user can select a suitable laser device 4 and, at a specific laser energy density, perform local thinning on the lower surface 63 of wafer 6 within the thinning start area of ​​the die 61 for a specific time (or a specific amount of laser pulses) for a specific duration. After the wafer 6 is locally thinned, the user can measure the thickness of wafer 6 within the thinning start area of ​​the die 61. Users can change parameters, such as different laser devices 4, different wafers (made of different materials), different laser energy densities, or different durations (or different amounts of laser pulses), to compare the differences in results with different parameters. Users can rely on this experience to achieve the desired thickness of wafer 6 in the thinning start region of the die 61 after local thinning of wafer 6. After local thinning of the lower surface 63 of wafer 6 in at least one thinning start region of each of the plurality of dies 61, the user can measure the thickness of wafer 6 in at least one thinning start region of each of the plurality of dies 61. The measured thickness of wafer 6 in at least one thinning start region of each of the plurality of dies 61 is the result measured by the user. The difference between the measured thickness of wafer 6 in at least one thinning start region of each of the plurality of dies 61 and the desired thickness can be controlled to be very small (e.g., less than 2 μm).

[0033] Please refer to Figure 4, which is a schematic diagram of a specific embodiment of a region of interest and a thinning start region on the upper surface of the grain in Figure 3. Please also refer to Figure 5, which is a schematic diagram of a region of interest and a thinning start region on the lower surface of one of the grains in Figure 4. In this embodiment, the wafer 6 is made of silicon carbide (SiC). The wafer 6 has not yet been diced into separate individual grains (wafers). The dashed dicing lines 65 in Figures 2-5 are the boundaries of each of the plurality of grains 61. After the wafer 6 has been partially thinned by the local laser thinning process of the present invention, and after all back-side processes (optionally) have been completed on a back side of the wafer 6 (e.g., a back-side metal process for forming the drain electrode of the element 7), the wafer 6 can be diced into separate individual grains (wafers) along these dashed dicing lines 65. Dividing the wafer 6 into separate individual grains (wafers) can be achieved by blade cutting, laser stealth cutting, plasma cutting, scribing and break, or other methods. When wafer 6 is diced into separate individual dies (wafers), a portion of the area adjacent to the dashed dicing line 65 is lost. In this embodiment, in each of the plurality of dies 61, each of the three source electrodes 70, 71, and 72 of element 7 occupies a front area on the upper surface 60 of wafer 6 (as shown in FIG. 3); while the three back areas on the lower surface 63 of wafer 6 (as shown in FIG. 5) correspond to the three front areas of the three source electrodes 70, 71, and 72 on the upper surface 60 of wafer 6, respectively. In each of the plurality of dies 61, the three back areas on the lower surface 63 of wafer 6 are the areas mapped onto the lower surface 63 of wafer 6 along a direction from the upper surface 60 of wafer 6 to the lower surface 63 of wafer 6 and perpendicular to the upper surface 60 of wafer 6 (the opposite direction of the Z-axis direction), respectively. Each of the three back face regions on the lower surface 63 of wafer 6 has an identical shape and an identical area to each of the three corresponding front face regions of the three source electrodes 70, 71, 72 of element 7 on the upper surface 60 of wafer 6. Wafer 6 has a uniform thickness T; therefore, if the drain electrode of element 7 (not yet formed; not shown in the figure) is formed directly on the lower surface 63 of wafer 6 (where wafer 6 has a uniform thickness T), then the on-resistance of element 7 is related to a shortest distance between the drain electrode of element 7 (not shown in the figure) and each of the three source electrodes 70, 71, 72 of element 7. That is, the on-resistance of element 7 is related to the uniform thickness T of wafer 6 within the three front face regions of the three source electrodes 70, 71, 72 of element 7.

[0034] Since the on-resistance of element 7 is related to the thickness of wafer 6 within the three front regions of the three source electrodes 70, 71, 72 of element 7 (that is, related to the shortest distance between the drain electrode (not shown) of element 7 and each of the three source electrodes 70, 71, 72 of element 7), if the local laser thinning process of the present invention is performed on the lower surface 63 of wafer 6 within the three back regions of a die 61 (corresponding to the three front regions of the three source electrodes 70, 71, 72 of element 7), the thickness of wafer 6 within the three front regions of the three source electrodes 70, 71, 72 of element 7 in die 61 will be locally thinned, and three back grooves of die 61 (not shown) will be formed on the back of wafer 6. That is, the shortest distance between each of the three source electrodes 70, 71, 72 of the element 7 of the die 61 on the upper surface 60 of wafer 6 and the bottom surface of each of the three back grooves (not shown) of the die 61 is reduced. Then, after forming one drain electrode (not shown) of the element 7 of the die 61 on the bottom surface of the three back grooves (not shown) of the die 61, the shortest distance between the drain electrode (not shown) of the element 7 of the die 61 and each of the three source electrodes 70, 71, 72 of the element 7 of the die 61 is shortened, thereby reducing the on-resistance of the element 7 of the die 61.

[0035] Therefore, in this embodiment, in each of the plurality of dies 61, the three source electrodes 70, 71, 72 of the element 7 of the die 61 formed on the upper surface 60 of the wafer 6 can be determined as a feature of interest for the die 61. In each of the plurality of dies 61, if the thickness of the wafer 6 within the three front regions (regions occupied by the features of interest) of the three source electrodes 70, 71, 72 of the element 7 of the die 61 can be locally thinned by the laser device 4 in the three corresponding back regions of the die 61 by performing the laser thinning process of the present invention on the lower surface 63 of the wafer 6, thereby effectively reducing the on-resistance of the element 7 of the die 61; at the same time, the heat dissipation effect of the element 7 of the die 61 can be effectively enhanced. In some embodiments, the criteria for determining the features of interest of the die 61 may depend on the actual design of the element 7 of the die 61 and the requirements for the performance and characteristics of the element 7 of the die 61.

[0036] However, in this embodiment, the front area of ​​the first source electrode 70 is very close to the front area of ​​the second source electrode 71, and the front area of ​​the second source electrode 71 is also very close to the front area of ​​the third source electrode 72 (as shown in FIG3, a portion of the very fine gate finger 74 is located between the front area of ​​the second source electrode 71 and the front area of ​​the third source electrode 72); therefore, if the local laser thinning process of the present invention is performed on the lower surface 63 of the wafer 6 in the three corresponding back areas of the die 61 by the laser device 4, two very thin sidewalls (not shown in the figure) will be formed on the back side of the wafer 6. One of the two very thin sidewalls (not shown) on the back side of wafer 6 corresponds to a front region between the front region of the first source electrode 70 and the front region of the second source electrode 71; the other of the two very thin sidewalls (not shown) on the back side of wafer 6 corresponds to a front region between the front region of the second source electrode 71 and the front region of the third source electrode 72. These two very thin sidewalls (not shown) are redundant. Because these two very thin sidewalls (not shown) are too thin, they may be easily damaged (e.g., cracked) during wafer 6 processing; the broken fragments may then contaminate wafer 6, other products, or equipment in the cleanroom. Removing these two very thin sidewalls (not shown) will not adversely affect the performance or characteristics of component 7. Furthermore, removing these two very thin sidewalls simplifies the process when performing the localized laser thinning process of this invention.

[0037] Please refer to Figure 6, which is a cross-sectional view along section line A-A' of Figure 5 before the wafer is partially thinned by the local laser thinning process of the present invention. Please also refer to Figure 7, which is a cross-sectional view along section line B-B' of Figure 5 before the wafer is partially thinned by the local laser thinning process of the present invention. To avoid the formation of these two very thin sidewalls (not shown in the figure) after the local laser thinning process of the present invention, the local laser thinning process of the present invention not only needs to process the lower surface 63 of the wafer 6 in the three back areas of each of the plurality of grains 61 (corresponding to the three front areas of the three source electrodes 70, 71, 72 of the element 7), but also needs to process the lower surface 63 of the wafer 6 in one back area of ​​each of the plurality of grains 61 (corresponding to the front area between the front area of ​​the first source electrode 70 and the front area of ​​the second source electrode 71 of the element 7 of each of the plurality of grains 61) and in another back area of ​​each of the plurality of grains 61 (corresponding to the front area between the front area of ​​the second source electrode 71 and the front area of ​​the third source electrode 72 of the element 7 of each of the plurality of grains 61). Therefore, in this invention, one of the thinning start regions of each of the plurality of grains 61 can be defined as one specific region of each of the plurality of grains 61, wherein when performing the local laser thinning process of this invention, the laser device 4 performs local laser thinning on the lower surface 63 of the wafer 6 within the specific region (thinning start region) of each of the plurality of grains 61. In this embodiment, one of the thinning start regions 64 of each of the plurality of grains 61 is defined and shown in Figures 4-7. In each of the plurality of grains 61, the thinning start region 64 includes: (a) three back surface regions corresponding to the three front surface regions of the three source electrodes 70, 71, and 72 of the element 7; (b) one back surface region corresponding to the front surface region between the front surface region of the first source electrode 70 and the front surface region of the second source electrode 71 of the element 7; and (c) another back surface region corresponding to the front surface region between the front surface region of the second source electrode 71 and the front surface region of the third source electrode 72 of the element 7. After performing the local laser thinning process of the present invention on the lower surface 63 of the wafer 6 within the thinning start region 64 of each of the plurality of grains 61, the aforementioned two very thin sidewalls (not shown in the figure) will not appear.

[0038] In fact, in this embodiment, if the three front regions of the three source electrodes 70, 71, 72 of the element 7 of each of the plurality of grains 61, the front region between the front region of the first source electrode 70 and the front region of the second source electrode 71 of the element 7 in each of the plurality of grains 61, and the front region between the front region of the second source electrode 71 and the front region of the third source electrode 72 of the element 7 in each of the plurality of grains 61 are respectively merged into one non-separated front region of each of the plurality of grains 61, then the non-separated front region of each of the plurality of grains 61 is actually one minimum non-separated front region of each of the plurality of grains 61, which covers the feature of interest of each of the plurality of grains 61 (covering one minimum non-separated front region of the three front regions of the three source electrodes 70, 71, 72 of the element 7 of each of the plurality of grains 61). That is, in this embodiment, the thinning start region 64 of each of the plurality of grains 61 can be determined as the non-separated front region corresponding to each of the plurality of grains 61.

[0039] After performing the local laser thinning process of the present invention on the lower surface 63 of the wafer 6 within the thinning start region 64 of each of the plurality of grains 61, at least one back groove (not shown in the figure) of each of the plurality of grains 61 is formed on the back side of the wafer 6. Since the local laser thinning process of the present invention is performed by the laser device 4, the shape of one sidewall of one of the at least one back groove (not shown in the figure) of each of the plurality of grains 61 can be upright (perpendicular to the lower surface 63 of the wafer 6), stepped, tapered (not perpendicular to the lower surface 63 of the wafer 6), or a combination of stepped and tapered shapes. When the local laser thinning process is completed (or stopped), the bottom surface of one of the at least one back groove (not shown in the figure) of each of the plurality of grains 61 is formed, and the area occupied by the bottom surface of one of the at least one back groove (not shown in the figure) of each of the plurality of grains 61 is defined. The area occupied by the bottom surface of at least one back groove (not shown) of each of the plurality of grains 61 must be within (but not identical to) the thinning start area 64 of each of the plurality of grains 61, or identical to the thinning start area 64 of each of the plurality of grains 61. In this invention, a region of interest (not shown) of each of the plurality of grains 61 defines the area occupied by the bottom surface of at least one back groove (not shown) of each of the plurality of grains 61; that is, the region of interest (not shown) of each of the plurality of grains 61 defines the area when the local laser thinning process is completed (or stopped). In this embodiment, a region of interest 62 of each of the plurality of grains 61 is defined and shown in Figures 4-7.

[0040] Please refer to Figures 8 and 9 simultaneously, which are cross-sectional views along the A-A' and B-B' sections of Figure 5, respectively, after the wafer has undergone local thinning in the starting region of the die to be thinned by the local laser thinning process of the present invention. Please also refer to Figure 10, which is a three-dimensional view of the lower surface of the wafer in Figure 5 after the wafer has undergone local thinning in the starting region of the die to be thinned by the local laser thinning process of the present invention. In this embodiment, after the local laser thinning process of the present invention is performed on the lower surface 63 of the wafer 6 within the starting region 64 of each of the plurality of dies 61, a back groove 75 of each of the plurality of dies 61 is formed on the back side of the wafer 6. The back groove 75 of each of the plurality of dies 61 has a bottom surface 76, a sidewall 77, and an opening 78 on the lower surface 63 of the wafer 6. In this embodiment, the region of interest 62 of each of the plurality of grains 61 (a region occupied by the bottom surface 76 of the back groove 75 of each of the plurality of grains 61) is respectively (determined to be) identical to the thinning start region 64 of each of the plurality of grains 61; therefore, the shape of one of the sidewalls 77 of the back groove 75 of each of the plurality of grains 61 is upright. After the local laser thinning process of the present invention is performed on the lower surface 63 of the wafer 6 within the thinning start region 64 of each of the plurality of grains 61, the local laser thinning process is completed (or stopped) within the region of interest 62 of each of the plurality of grains 61, such that the wafer 6 has a desired thickness D within the region of interest 62 of each of the plurality of grains 61. Subsequently, a back metal (not shown) can be formed on the lower surface 63 of wafer 6, the bottom surface 76 of the back groove 75 of each of the plurality of grains 61, and the sidewall 77 of the back groove 75, such that one drain electrode (not shown) of the element 7 of each of the plurality of grains 61 is formed at least on the bottom surface 76 of the back groove 75. The shortest distance between the drain electrode (not shown) of the element 7 of each of the plurality of grains 61 and each of the three source electrodes 70, 71, and 72 of the element 7 is shortened; therefore, the on-resistance of the element 7 of each of the plurality of grains 61 can be effectively reduced; at the same time, the heat dissipation effect of the element 7 of each of the plurality of grains 61 can be effectively enhanced.

[0041] In Figure 10, wafer 6 has the desired thickness D within the region of interest 62; and wafer 6 has a uniform thickness T in the region outside the thinning start region 64 of each of the plurality of grains 61 (as shown in Figures 8 and 9). Therefore, wafer 6 has a thickness T not only at one of the peripheral edges (near the dashed cut line 65) of each of the plurality of grains 61, but also in one frontal region of one of the gate electrodes 73 of element 7, in one frontal region between the frontal region of the gate electrode 73 of element 7 and the frontal region of the first source electrode 70, and in one frontal region between the frontal region of the gate electrode 73 of element 7 and the frontal region of the third source electrode 72. Therefore, the mechanical strength of the entire wafer 6 is improved.

[0042] Before the local laser thinning process of the present invention is performed on the lower surface 63 of the wafer 6 by the laser device 4 in the thinning start area of ​​each of the plurality of dies 61, the region of interest and the thinning start area of ​​each of the plurality of dies 61 must be determined. In this embodiment, the region of interest 62 and the thinning start area 64 of each of the plurality of dies 61 may be determined based on the features of interest of each of the plurality of dies 61 (e.g., the features of interest of each of the plurality of dies 61 are respectively related to the performance and characteristics of the element 7 of each of the plurality of dies 61), the shape of one of the sidewalls 77 of the back groove 75 of each of the plurality of dies 61 (e.g., determining that the shape of the sidewalls 77 of the back groove 75 is upright, stepped, tapered, or a combination of stepped and tapered), and other criteria (e.g., as mentioned above, in order to remove two very thin sidewalls).

[0043] In the embodiments of Figures 1-10, the method for partial wafer thinning of the present invention includes the following steps: Step A: A wafer 6 is provided, which is supported by a carrier device 5, wherein an upper surface 60 of the wafer 6 faces downward (i.e., a lower surface 63 of the wafer 6 faces upward), the wafer 6 includes a plurality of dies 61, and an element 7 (including three source electrodes 70, 71, 72, a gate electrode 73, and a gate finger 74) of each of the plurality of dies 61 is respectively formed on the upper surface 60 of the wafer 6, wherein the wafer 6 has a uniform thickness T; Step B: The three source electrodes 70, 71, 72, 73, 74 ...3, 74, 73, 74, 73, 73, 74, 73, 73, 74, 73, 73, 74, 73, 73, 74, 73, 73, 74, 73, 73, 74, 73, 73, 74, 73, 73, 74, 73, 73, 74, 73, 73, 74, 73, 73, 73, 74 72 is determined as one feature of interest for each of the plurality of grains 61; Step C: Based on the feature of interest for each of the plurality of grains 61, one thinning start region 64 and one region of interest 62 are determined for each of the plurality of grains 61, wherein the thinning start region 64 for each of the plurality of grains 61 is determined to correspond to one non-separated front region for each of the plurality of grains 61, wherein the non-separated front region for each of the plurality of grains 61 is (1) the three front regions of the three source electrodes 70, 71, 72 of the element 7 of each of the plurality of grains 61, (2) the front region between the first source electrode 70 of the element 7 and the front region of each of the plurality of grains 61) The front regions between the front regions of the second source electrode 71 and (3) the front regions between the front regions of the second source electrode 71 and the third source electrode 72 of the element 7 in each of the plurality of grains 61, which are merged into a combined region, are each a minimum non-separated front region of the plurality of grains 61. Each minimum non-separated front region covers the feature of interest of each of the plurality of grains 61 (covering the minimum non-separated front region of the three front regions of the three source electrodes 70, 71, and 72 of the element 7 of the plurality of grains 61). The feature of interest 62 of each of the plurality of grains 61 is respectively (determined to be) identical to the plurality of grains 61. Step D: The image capturing element 30 of an image capturing device 3 captures at least one image of each of the plurality of dies 61 (in this embodiment, at least one image of each of the plurality of dies 61 is captured from the upper surface 60 of the wafer 6); Step E: The image recognition element 80 of a control integration device 8 performs image recognition on at least one image of each of the plurality of dies 61 captured by the image capturing element 30 of the image capturing device 3 to identify the features of interest of each of the plurality of dies 61.And step F: A laser device 4 performs local laser thinning on the lower surface 63 of the wafer 6 within the thinning start region 64 of each of the plurality of dies 61, so as to locally thin the wafer 6 within the thinning start region 64 of each of the plurality of dies 61, so that the wafer 6 has a desired thickness D within the region of interest 62 of each of the plurality of dies 61.

[0044] Please refer to Figure 11, which is a cross-sectional schematic diagram of the dies cut from the wafer of Figure 8. After the wafer 6 is locally thinned by the local laser thinning process of the present invention, one of the drain electrodes (not shown) of the element 7 of each of the plurality of dies 61 can be formed at least on the bottom surface 76 of the back groove 75 of each of the plurality of dies 61. The wafer 6 can then be cut into separate individual dies (wafers) along these dashed cutting lines 65. Figure 11 shows one of the separate individual dies (wafers) 61. The sidewall 77 of the back groove 75 of the separate individual die (wafer) 61 has a sidewall thickness T1. Therefore, not only is the mechanical strength of the entire wafer 6 improved, but the mechanical strength of each separate individual die (wafer) 61 is also improved after the plurality of dies 61 are cut into separate individual dies (wafers) 61. In this embodiment, the element 7 is a power element. Before performing the die attach process, it is best to fill the back groove 75 of the separated die (wafer) 61 with thermally conductive dielectric material to effectively enhance the heat dissipation of the component 7.

[0045] In some embodiments, if the front area of ​​the first source electrode 70 of the element 7 is not very close to the front area of ​​the second source electrode 71 of the element 7, and the front area of ​​the second source electrode 71 of the element 7 is not very close to the front area of ​​the third source electrode 72 of the element 7, then the thinning start area 64 of each of the plurality of grains 61 can be determined as the three back areas of the element 7 of each of the plurality of grains 61 (corresponding to the three front areas of the three source electrodes 70, 71, 72 of the element 7 of each of the plurality of grains 61).

[0046] Please refer to Figure 12, which is a schematic diagram of another specific embodiment of a region of interest and a thinning start region on the lower surface of the grain in Figure 3. Please also refer to Figure 13, which is a schematic cross-sectional view along the C-C' section line of Figure 12 before the wafer is locally thinned by the local laser thinning process of the present invention. The main structure of the specific embodiments in Figures 12 and 13 is generally the same as the structure of the specific embodiments in Figures 1 to 7, except that the region of interest 62 of each of the plurality of grains 61 is respectively (determined to be) within the thinning start region 64 of each of the plurality of grains 61 (but not entirely the same as the thinning start region 64 of each of the plurality of grains 61). In this embodiment, the features of interest and the region of interest 62 of each of the plurality of grains 61 are the same as those of each of the plurality of grains 61 in the embodiments of Figures 1-7; however, the thinning start region 64 of each of the plurality of grains 61 in this embodiment is wider than the thinning start region 64 of each of the plurality of grains 61 in the embodiments of Figures 1-7. Please also refer to Figure 14, which is a cross-sectional view along the C-C' section line of Figure 12 after the wafer has been partially thinned in the thinning start region of the grains by the local laser thinning process of the present invention. After the local laser thinning process of the present invention is performed on the lower surface 63 of the wafer 6 in the thinning start region 64 of each of the plurality of grains 61, a back groove 75 of each of the plurality of grains 61 is formed on the back side of the wafer 6. Each of the plurality of grains 61 has a backside groove 75 having a bottom surface 76, a sidewall 77, and an opening 78 on the lower surface 63 of the wafer 6. In this embodiment, the region of interest 62 of each of the plurality of grains 61 is respectively (determined) within the thinning start region 64 of each of the plurality of grains 61 (but not entirely the same as the thinning start region 64 of each of the plurality of grains 61); and one of the shapes of the sidewalls 77 of the backside groove 75 of each of the plurality of grains 61 is (determined) tapered (the tapered sidewalls 77 of the backside groove 75 can be achieved through a combination of many steps). The area occupied by the opening 78 of the backside groove 75 of each of the plurality of grains 61 on the lower surface 63 of the wafer 6 is entirely the same as the thinning start region 64 of each of the plurality of grains 61. The region of interest 62 of each of the plurality of grains 61 is identical to the region occupied by the bottom surface 76 of the back groove 75 of each of the plurality of grains 61.The area occupied by the opening 78 of the back groove 75 of each of the plurality of grains 61 is wider than the area occupied by the bottom surface 76 of the back groove 75 of each of the plurality of grains 61; therefore, when a back metal (not shown) is formed on the lower surface 63 of the wafer 6, the bottom surface 76 of the back groove 75 of each of the plurality of grains 61, and the sidewall 77 of the back groove 75, this results in a back metal of a more uniform thickness (not shown). In this embodiment, the wafer 6 has a desired thickness D within the region of interest 62 of each of the plurality of grains 61.

[0047] Please refer to Figure 15, which is a cross-sectional schematic diagram of another specific embodiment of a region of interest and a thinning start region of a die before the wafer is locally thinned by the local laser thinning process of the present invention. In this embodiment, a wafer 6 includes a plurality of dies 61, wherein each of the plurality of dies 61 includes only one element 7 (the element 7 is not a power element as shown in Figure 3), wherein the features of interest of each of the plurality of dies 61 are respectively determined as the element 7 of each of the plurality of dies 61 on the upper surface 60 of the wafer 6, wherein the thinning start region 64 of each of the plurality of dies 61 is respectively determined such that the features of interest of each of the plurality of dies 61 are respectively within the thinning start region 64 of each of the plurality of dies 61 (but not entirely the same as each of the plurality of dies 61). The thinning start region 64 of one of the plurality of grains 61; the thinning start region 64 of each of the plurality of grains 61 respectively covers one active region of the element 7 of each of the plurality of grains 61 on the upper surface 60 of the wafer 6, wherein the region of interest 62 of each of the plurality of grains 61 is respectively (determined to be) within the thinning start region 64 of each of the plurality of grains 61 (but not entirely the same as the thinning start region 64 of each of the plurality of grains 61), and the region of interest 62 of each of the plurality of grains 61 is respectively (determined to be) identical to the feature of interest of each of the plurality of grains 61. Please also refer to FIG16, which is a cross-sectional schematic diagram of the grains in FIG15 after the wafer has been partially thinned in the thinning start region of the grains by the local laser thinning process of the present invention. After performing the local laser thinning process of the present invention on the lower surface 63 of the wafer 6 within the thinning start region 64 of each of the plurality of grains 61, a back groove 75 of each of the plurality of grains 61 is formed on the back side of the wafer 6. The back groove 75 of each of the plurality of grains 61 has a bottom surface 76, a sidewall 77, and an opening 78 on the lower surface 63 of the wafer 6. In this embodiment, the region of interest 62 of each of the plurality of grains 61 is respectively (determined to be) within the thinning start region 64 of each of the plurality of grains 61 (but not entirely the same as the thinning start region 64 of each of the plurality of grains 61), and the shape of one of the sidewalls 77 of the back groove 75 of each of the plurality of grains 61 is (determined to be) stepped. The area occupied by the opening 78 of the back groove 75 of each of the plurality of grains 61 on the lower surface 63 of the wafer 6 is identical to the thinning start area 64 of each of the plurality of grains 61. The area of ​​interest 62 of each of the plurality of grains 61 is identical to the area occupied by the bottom surface 76 of the back groove 75 of each of the plurality of grains 61. The area occupied by the opening 78 of the back groove 75 of each of the plurality of grains 61 is wider than the area occupied by the bottom surface 76 of the back groove 75 of each of the plurality of grains 61.The sidewalls 77 (stepped sidewalls) of the back recesses 75 of each of the plurality of dies 61 can have different shape designs (e.g., two-step, three-step, or more-step, with each step having a different height or a uniform height). The design of one of the shapes of the sidewalls 77 (stepped sidewalls) of the back recesses 75 of each of the plurality of dies 61 can be designed based on the performance or characteristics of the element 7, or other criteria. In this embodiment, the wafer 6 has a desired thickness D within the region of interest 62 of each of the plurality of dies 61.

[0048] Please refer to Figure 17, which is a cross-sectional schematic diagram of another specific embodiment of two regions of interest and two thinning start regions of a die before the wafer is locally thinned by the local laser thinning process of the present invention. In this embodiment, a wafer 6 includes a plurality of dies 61, each of the plurality of dies 61 including an element 7 and an element 7', wherein the element 7 and the element 7' are not power elements as shown in Figure 3, wherein two features of interest of each of the plurality of dies 61 are determined respectively, wherein one of the first features of interest of each of the plurality of dies 61 is determined to be the element 7 of each of the plurality of dies 61; and one of the second features of interest of each of the plurality of dies 61 is determined to be the element 7 of each of the plurality of dies 61. The element 7' of one of the plurality of grains 61; wherein one thinning start region 64 of each of the plurality of grains 61 is determined such that the first feature of interest of each of the plurality of grains 61 is respectively within the thinning start region 64 of each of the plurality of grains 61 (but not entirely the same as the thinning start region 64 of each of the plurality of grains 61; the thinning start region 64 of each of the plurality of grains 61 respectively covers one active region of the element 7 of each of the plurality of grains 61 on the surface 60 above the wafer 6); and the plurality of One of the thinning start regions 64' of each of the plurality of grains 61 is determined to be identical to a second feature of interest of each of the plurality of grains 61 (the thinning start regions 64' of each of the plurality of grains 61 respectively cover an active region of one of the elements 7' of each of the plurality of grains 61 on the surface 60 above the wafer 6); wherein one of the features of interest 62 of each of the plurality of grains 61 is respectively (determined to be) within the thinning start region 64 of each of the plurality of grains 61 (but not identical to the second feature of interest of each of the plurality of grains 61). Each of the plurality of grains 61 has a thinning start region 64; and each of the plurality of grains 61 has a region of interest 62' that is (determined to be) identical to the thinning start region 64' of each of the plurality of grains 61; wherein the region of interest 62' of each of the plurality of grains 61 is (determined to be) identical to a first feature of interest of each of the plurality of grains 61; and the region of interest 62' of each of the plurality of grains 61 is (determined to be) identical to a second feature of interest of each of the plurality of grains 61. In this embodiment, in each of the plurality of grains 61, there is a gap between the thinning start region 64 and the thinning start region 64'; wherein one of the gaps between the first feature of interest (element 7) and the second feature of interest (element 7') is larger than the gap between the thinning start region 64 and the thinning start region 64'.In this embodiment, in each of the plurality of grains 61, the gap between the thinning start region 64 and the thinning start region 64' is greater than or equal to a gap threshold; therefore, (1) two separate thinning start regions (thinning start region 64 and thinning start region 64' in this embodiment) can be determined, wherein these two separate thinning start regions (thinning start region 64 and thinning start region 64' in this embodiment) respectively cover the first feature of interest (element 7) and the second feature of interest (element 7'), or (2) a non-separate thinning start region can be determined (not shown in this embodiment), wherein this non-separate thinning start region covers the first feature of interest (element 7) and the second feature of interest (element 7'); for example, the non-separate thinning start region can be determined as a merged region formed by merging the thinning start region 64 and the thinning start region 64'. Please also refer to Figure 18, which is a cross-sectional view of the grains in Figure 17 after local thinning of the starting region of the grains to be thinned by the local laser thinning process of the present invention. After the local laser thinning process of the present invention is performed on the lower surface 63 of the wafer 6 in the starting region 64 and the starting region 64' of the thinning process of the present invention in each of the plurality of grains 61, a back groove 75 and a back groove 75' of the element 7 of each of the plurality of grains 61 are formed on the back side of the wafer 6. The back groove 75 of the element 7 of each of the plurality of grains 61 has a bottom surface 76, a side wall 77, and an opening 78 on the lower surface 63 of the wafer 6. The back groove 75' of the element 7' of each of the plurality of grains 61 has a bottom surface 76', a side wall 77', and an opening 78' on the lower surface 63 of the wafer 6. In this embodiment, the region of interest 62 of each of the plurality of dies 61 is respectively (determined) within the thinning start region 64 of each of the plurality of dies 61 (but not entirely identical to the thinning start region 64 of each of the plurality of dies 61), and the shape of one of the sidewalls 77 of the back recess 75 of the element 7 of each of the plurality of dies 61 is (determined) tapered (the tapered sidewalls 77 of the back recess 75 can be achieved through a combination of many steps). The area occupied by the opening 78 of the back recess 75 of the element 7 of each of the plurality of dies 61 on the lower surface 63 of the wafer 6 is identical to the thinning start region 64 of each of the plurality of dies 61. The region of interest 62 of each of the plurality of dies 61 is identical to the area occupied by the bottom surface 76 of the back recess 75 of the element 7 of each of the plurality of dies 61.The area occupied by the opening 78 of the back groove 75 of each of the plurality of grains 61 is wider than the area occupied by the bottom surface 76 of the back groove 75 of each of the plurality of grains 61; therefore, when a back metal (not shown) is formed on the lower surface 63 of the wafer 6, the bottom surface 76 of the back groove 75 of each of the plurality of grains 61, and the sidewall 77 of the back groove 75, this results in a back metal of more uniform thickness (not shown). The region of interest 62' of each of the plurality of grains 61 is (determined) identical to the thinning start region 64' of each of the plurality of grains 61; therefore, one of the shapes of the sidewall 77' of the back groove 75' of each of the plurality of grains 61 is upright. The area occupied by the opening 78' of the back recess 75' of each of the plurality of grains 61 on the lower surface 63 of the wafer 6 is identical to the thinning start area 64' of each of the plurality of grains 61. The area of ​​interest 62' of each of the plurality of grains 61 is identical to the area occupied by the bottom surface 76' of the back recess 75' of each of the plurality of grains 61. The opening 78' of the back recess 75' of each of the plurality of grains 61 and the bottom surface 76' of the back recess 75' of each of the plurality of grains 61 have identical shapes and identical areas. In this embodiment, wafer 6 has a desired thickness D in the region of interest 62 of each of the plurality of dies 61; and wafer 6 has a desired thickness D' in the region of interest 62' of each of the plurality of dies 61, wherein the desired thickness D is not equal to the desired thickness D' (in this embodiment, the desired thickness D' is greater than the desired thickness D).

[0049] In some embodiments, each of the plurality of grains 61 has a plurality of features of interest. For example, in each of the plurality of grains 61, if the gap between any two separate features of interest of grain 61 is less than the gap threshold, then a non-separated thinning start region 64 of grain 61 will be determined, wherein the non-separated thinning start region 64 of grain 61 covers the two separate features of interest of grain 61; and if the gap between the two separate features of interest of grain 61 is greater than or equal to the gap threshold, then (1) a non-separated thinning start region 64 of grain 61 can be determined, wherein the non-separated thinning start region 64 of grain 61 covers the two separate features of interest of grain 61, or (2) two separate thinning start regions of grain 61 can be determined separately, wherein the two separate thinning start regions of grain 61 respectively cover the two separate features of interest of grain 61, and the gap between the two separate thinning start regions of grain 61 must also be greater than or equal to the gap threshold. Therefore, the gap threshold is one of the minimum gaps between two separate thinning initiation regions of grain 61. In some embodiments, the gap threshold is greater than or equal to 120 μm and less than or equal to 150 μm. In other embodiments, the gap threshold is greater than or equal to 100 μm and less than or equal to 120 μm. In other embodiments, the gap threshold is greater than or equal to 80 μm and less than or equal to 100 μm. In other embodiments, the gap threshold is greater than or equal to 50 μm and less than or equal to 80 μm. In other embodiments, the gap threshold is greater than or equal to 20 μm and less than or equal to 50 μm. In other embodiments, the gap threshold is greater than or equal to 15 μm and less than or equal to 20 μm. In other embodiments, the gap threshold is greater than or equal to 10 μm and less than or equal to 15 μm.

[0050] Please refer to Figure 19, which is a schematic diagram of another specific embodiment of a region of interest and a thinning start region on the lower surface of the grain in Figure 3. Please also refer to Figure 20, which is a schematic cross-sectional view along the D-D' section line of Figure 19 before the wafer is locally thinned by the local laser thinning process of the present invention. The main structure of the specific embodiments in Figures 19 and 20 is generally the same as that of the specific embodiments in Figures 1 to 7. However, the features of interest for each of the plurality of grains 61 include (determined to include) the three source electrodes 70, 71, 72, gate electrode 73, and gate finger 74 of the element 7 of each of the plurality of grains 61 respectively formed on the upper surface 60 of the wafer 6 (that is, in each of the plurality of grains 61, the features of interest include (determined to include) the element 7 formed on the upper surface 60 of the wafer 6); the thinning start region 64 of each of the plurality of grains 61 is determined respectively, such that The features of interest for each of the plurality of grains 61 are respectively within the thinning start region 64 of each of the plurality of grains 61 (but not identical to the thinning start region 64 of each of the plurality of grains 61; the thinning start region 64 of each of the plurality of grains 61 respectively covers the three source electrodes 70, 71, 72, gate electrode 73 and gate finger 74 of the element 7 of each of the plurality of grains 61 on the upper surface 60 of the wafer 6); and the regions of interest 62 of each of the plurality of grains 61 are respectively (determined to be) identical to the thinning start region 64 of each of the plurality of grains 61. That is, in this embodiment, the active region of element 7 of each of the plurality of dies 61 is respectively within the thinning start region 64 of each of the plurality of dies 61 (but not entirely the same as the thinning start region 64 of each of the plurality of dies 61) and respectively within the region of interest 62 of each of the plurality of dies 61 (but not entirely the same as the region of interest 62 of each of the plurality of dies 61). Please also refer to FIG21, which is a cross-sectional view along the D-D' section line of FIG19 after the wafer has been partially thinned in the thinning start region of the die by the partial laser thinning process of the present invention. Please also refer to FIG22, which is a perspective view of the lower surface of the wafer in FIG19 after the wafer has been partially thinned in the thinning start region of the die by the partial laser thinning process of the present invention. After performing the local laser thinning process of the present invention on the lower surface 63 of the wafer 6 within the thinning start region 64 of each of the plurality of grains 61, a back groove 75 of each of the plurality of grains 61 is formed on the back side of the wafer 6. The back groove 75 of each of the plurality of grains 61 has a bottom surface 76, a sidewall 77, and an opening 78 on the lower surface 63 of the wafer 6.In this embodiment, the region of interest 62 of each of the plurality of grains 61 is (determined to be) identical to the thinning start region 64 of each of the plurality of grains 61; therefore, the shape of one sidewall 77 of the back groove 75 of each of the plurality of grains 61 is upright. The area occupied by the opening 78 of the back groove 75 of each of the plurality of grains 61 on the lower surface 63 of the wafer 6 is identical to the thinning start region 64 of each of the plurality of grains 61. The region of interest 62 of each of the plurality of grains 61 is identical to the area occupied by the bottom surface 76 of the back groove 75 of each of the plurality of grains 61. The opening 78 of the back groove 75 of each of the plurality of grains 61 and the bottom surface 76 of the back groove 75 of each of the plurality of grains 61 have identical shapes and identical areas. In this embodiment, wafer 6 has a desired thickness D in the region of interest 62 of each of the plurality of grains 61.

[0051] In the embodiment of FIG21, after the wafer 6 is locally thinned by the local laser thinning process of the present invention, one of the drain electrodes (not shown) of the element 7 of each of the plurality of grains 61 can be formed at least on the bottom surface 76 of the back groove 75 of each of the plurality of grains 61. The wafer 6 can then be cut along these dashed cutting lines 65 into separate individual grains (wafers), wherein the main structure of each of the separate individual grains (wafers) 61 in the embodiment of FIG21 is substantially the same as that in the specific embodiment of FIG11, except that the sidewall thickness of one of the sidewalls 77 is slightly thinner than the sidewall thickness T1 of the sidewall 77 in the embodiment of FIG11. After the plurality of grains 61 are cut into separate individual grains (wafers) 61, the mechanical strength of each of the separate individual grains (wafers) 61 can also be improved.

[0052] Please refer to Figure 23, which is a cross-sectional schematic diagram of the dies cut from the wafer of Figure 21. In the embodiment of Figure 21, after the wafer 6 is locally thinned by the local laser thinning process of the present invention, one drain electrode (not shown) of the element 7 of each of the plurality of dies 61 can be formed at least on the bottom surface 76 of the back groove 75 of each of the plurality of dies 61. The wafer 6 can then be cut into separate individual dies (wafers) along the sidewalls 77 of the back grooves 75 of each of the plurality of dies 61 (rather than along these dashed cutting lines 65). Figure 23 shows one of the separate individual dies (wafers) 61. The structure of the separate individual die (wafer) 61 in the embodiment of Figure 23 does not have the back groove 75 (does not have the sidewalls 77 of the back groove 75). Thermal dielectric material can be directly coated on the bottom surface 76 to more effectively enhance the heat dissipation of the element 7.

[0053] In some embodiments, the partial wafer thinning system 1 of the present invention further includes a distance measuring device (not shown in the figure), wherein the distance measuring device is disposed on the lower surface 63 of the wafer 6 (e.g., the distance measuring device is disposed next to the laser device 4). Before the laser device 4 performs the partial laser thinning process of the present invention on the lower surface 63 of the wafer 6 within the thinning start region 64 of each of a plurality of dies 61, the distance measuring device is moved to a measuring position on the lower surface 63 of the wafer 6 (e.g., the distance measuring device is moved to a point on the lower surface 63 of the wafer 6, wherein the point is within the thinning start region 64 of one die 61). Then, the distance measuring device measures an initial distance between the distance measuring device and the point on the lower surface 63 of the wafer 6. Then, the distance measuring device is removed. After performing the local laser thinning process of the present invention on the lower surface 63 of wafer 6 within the thinning start region 64 of each of a plurality of dies 61, a distance measuring device is moved to the measuring position or another measuring position (above another point within the thinning start region 64 of another die 61), and then the distance measuring device measures a final distance between the distance measuring device and the bottom surface 76 of the back groove 75 of one die 61 (or the bottom surface 76 of the back groove 75 of another die 61). Since wafer 6 originally has a uniform thickness T, the measured thickness of wafer 6 can be calculated as follows: The difference X between the measured thickness of wafer 6 within the thinning start region 64 of die 61 and the desired thickness can be controlled to be very small (e.g., less than 2 μm). In some embodiments, the difference X is less than 6 μm. In some embodiments, the difference X is less than 4 μm. In some embodiments, the difference X is less than 2 μm.

[0054] In some embodiments, the partial wafer thinning system 1 of the present invention further includes a distance measuring device (not shown in the figure), wherein the distance measuring device is disposed on the lower surface 63 of the wafer 6 (e.g., the distance measuring device is disposed next to the laser device 4). Before the laser device 4 performs the partial laser thinning process of the present invention on the lower surface 63 of the wafer 6 within the thinning start region 64 of each of a plurality of dies 61, the distance measuring device is moved to a measuring position on the lower surface 63 of the wafer 6 (e.g., the distance measuring device is moved to a point on the lower surface 63 of the wafer 6, wherein the point is within the thinning start region 64 of one die 61). Then, the distance measuring device measures an initial distance between the distance measuring device and the point on the lower surface 63 of the wafer 6. Then, the distance measuring device is removed. After performing the local laser thinning process of the present invention on the lower surface 63 of the wafer 6 within the thinning start region 64 of each of the plurality of dies 61, the distance measuring device is moved to a plurality of final measuring positions. Each final measuring position is located on the thinning start region 64 of one of the dies 61 (the plurality of final measuring positions correspond to the thinning start region 64 of each of the plurality of dies 61); that is, after performing the local laser thinning process of the present invention, each final measuring position is located on the bottom surface 76 of a back groove 75 of one of the dies 61. Then the distance measuring device measures a plurality of final distances between the distance measuring device and the bottom surface 76 of the back groove 75 of each of the plurality of dies 61. Assuming there are N grains 61 (grain 61, grain 61, ..., grain 61) and N final distances (final distance, final distance, ..., final distance) are measured, then the N measured thicknesses (measured thickness, measured thickness, ..., measured thickness) can be calculated. Since wafer 6 originally has a uniform thickness T, for the th () grain 61, the th () measured thickness of wafer 6 can be calculated as follows: , where. For the th grain 61, the th () difference X between the th measured thickness and the desired thickness of wafer 6 within the th starting region 64 of the th grain 61 can be controlled to be very small (e.g., less than 2 μm). The variation of one of the N measured thicknesses (measured thickness, measured thickness, ..., measured thickness) of wafer 6 can also be controlled to be very small (e.g., less than 2 μm). In some embodiments, the variation of the N measured thicknesses is less than 6 μm. In some embodiments, the variation of the N measured thicknesses is less than 4 μm. In some embodiments, the variation coefficient of the N measured thicknesses is less than 2 μm.

[0055] Please also refer to Figure 24, which is a cross-sectional view of the wafer along the E-E' section line of Figure 22 after the wafer has been partially thinned in the starting area of ​​the die by the local laser thinning process of the present invention. In Figure 24, the plurality of dies 61 includes at least a first die 611, a second die 612, a third die 613, a fourth die 614, and a fifth die 615. The first die 611 has a first back groove 751; the second die 612 has a second back groove 752; the third die 613 has a third back groove 753; the fourth die 614 has a fourth back groove 754; and the fifth die 615 has a fifth back groove 755. The first grain 611 has a desired thickness D1; ​​the second grain 612 has a desired thickness D2; the third grain 613 has a desired thickness D3; the fourth grain 614 has a desired thickness D4; and the fifth grain 615 has a desired thickness D5. In this embodiment, the desired thickness D1 = desired thickness D2 = desired thickness D3 = desired thickness D4 = desired thickness D5 = desired thickness D.

[0056] In some embodiments, the required thicknesses D1, D2, D3, D4, and D5 may be completely different. In other embodiments, some of the required thicknesses D1, D2, D3, D4, and D5 may be the same, while others may be different (e.g., required thickness D1 = D2, required thickness D3 = D4, or required thicknesses D1, D3, and D5 may be completely different).

[0057] In the embodiment of FIG. 24, in any two adjacent grains 61 (for example, the first grain 611 and the second grain 612 are adjacent), the first grain 611 has a unique thinning start region 64 (not shown in the figure), which defines a region occupied by an opening of one of the first back grooves 751 of the first grain 611; the second grain 612 has a unique thinning start region 64 (not shown in the figure), which defines a region occupied by an opening of one of the second back grooves 752 of the second grain 612. The opening of the first back groove 751 of the first grain 611 is adjacent to the opening of the second back groove 752 of the second grain 612; that is, the thinning start region 64 (not shown in the figure) of the first grain 611 is adjacent to the thinning start region 64 (not shown in the figure) of the second grain 612. Therefore, one of the gaps between the opening of the first back groove 751 of the first grain 611 and the opening of the second back groove 752 of the second grain 612 is one of the gaps between the thinning start region 64 (not shown in the figure) of the first grain 611 and the thinning start region 64 (not shown in the figure) of the second grain 612. In any two adjacent grains 61, there is a gap between one opening of the back groove of one of the two adjacent grains 61 and one opening of the back groove of the other of the two adjacent grains 61; in some embodiments, the gap is greater than 100 μm; in other embodiments, the gap is greater than 120 μm; in other embodiments, the gap is greater than 150 μm; in other embodiments, the gap is greater than 170 μm; in other embodiments, the gap is greater than 200 μm; in other embodiments, the gap is greater than 250 μm.

[0058] Please refer to Figure 25, which is a cross-sectional schematic diagram of another specific embodiment of a region of interest and a region to be thinned starting area of ​​a die before the wafer is locally thinned by the local laser thinning process of the present invention. In this embodiment, a wafer 6 includes a plurality of dies 61, wherein each of the plurality of dies 61 includes only one element 7, and the element 7 of each of the plurality of dies 61 is a vertical cavity surface-emitting laser (VCSEL). Laser), wherein the feature of interest of each of the plurality of dies 61 is respectively determined as an element 7 of each of the plurality of dies 61 on the upper surface 60 of the wafer 6, wherein the thinning start region 64 of each of the plurality of dies 61 is respectively determined such that the feature of interest of each of the plurality of dies 61 is respectively within the thinning start region 64 of each of the plurality of dies 61 (but not identical to the thinning start region 64 of each of the plurality of dies 61; the thinning start region 64 of each of the plurality of dies 61 respectively covers one active region of the element 7 (VCSEL) of each of the plurality of dies 61 on the upper surface 60 of the wafer 6), wherein the region of interest 62 of each of the plurality of dies 61 is respectively (determined to be) identical to the thinning start region 64 of each of the plurality of dies 61. In this embodiment, in each of the plurality of dies 61, element 7 includes an upper electrode 801, a lower electrode 81, an upper distributed Bragg reflector (DBR) 82, a quantum well region 83, and a lower distributed Bragg reflector 84. The lower distributed Bragg reflector 84 is formed on the upper surface 60 of the wafer 6, the quantum well region 83 is formed on the lower distributed Bragg reflector 84, the upper distributed Bragg reflector 82 is formed on the quantum well region 83, the upper electrode 801 is formed on the upper distributed Bragg reflector 82, and the lower electrode 81 is formed on the upper surface 60 of the wafer 6. The upper distributed Bragg reflector 82 includes a plurality of upper layers; the quantum well region 83 includes a plurality of middle layers; and the lower distributed Bragg reflector 84 includes a plurality of... The lower layer includes an upper distributed Bragg reflector 82, a quantum well region 83, and a lower distributed Bragg reflector 84, which are not located outside the thinning start region 64 (outside the region of interest 62). The feature of interest (the element 7 (VCSEL)) of each of the plurality of grains 61 is located within the thinning start region 64 of each of the plurality of grains 61 (but not identical to the thinning start region 64 of each of the plurality of grains 61) and within the region of interest 62 of each of the plurality of grains 61 (but not identical to the region of interest 62 of each of the plurality of grains 61).After so many layers (including multiple upper layers of the upper distributed Bragg reflector 82, multiple middle layers of the quantum well region 83, and multiple lower layers of the lower distributed Bragg reflector 84) are formed on the surface 60 of wafer 6, wafer 6 is subjected to enormous stress.

[0059] If a conventional wafer thinning process (e.g., mechanical polishing or chemical mechanical planarization) is performed on the lower surface 63 of wafer 6, wafer 6 will become thinner after the wafer 6 thinning process (overall thinning). Because wafer 6 is thinner, it becomes difficult for wafer 6 to balance the enormous stress caused by the many layers formed on the upper surface 60 of wafer 6. Therefore, the warping of wafer 6 becomes severe, and may even lead to edge cracking of wafer 6. Furthermore, when the diameter of wafer 6 is less than 3 inches, the stress-induced warping of wafer 6 may be less noticeable, while when the diameter of wafer 6 is greater than or equal to 4 inches, 6 inches, 8 inches, or larger, the stress-induced warping of wafer 6 becomes very significant.

[0060] In the embodiment of FIG25, the feature of interest of each of the plurality of dies 61 respectively includes (is determined to include) the element 7 of each of the plurality of dies 61; the thinning start region 64 of each of the plurality of dies 61 is determined such that the feature of interest of each of the plurality of dies 61 is respectively within the thinning start region 64 of each of the plurality of dies 61 (but not identical to the thinning start region 64 of each of the plurality of dies 61; the thinning start region 64 of each of the plurality of dies 61 respectively covers one active region of the element 7 of each of the plurality of dies 61 on the upper surface 60 of the wafer 6), and the region of interest 62 of each of the plurality of dies 61 is respectively (determined to be) identical to the thinning start region 64 of each of the plurality of dies 61. Please also refer to Figure 26, which is a cross-sectional view of the grains in Figure 25 after local thinning of the starting region of the grains to be thinned by the local laser thinning process of the present invention. After the local laser thinning process of the present invention is performed on the lower surface 63 of the wafer 6 within the starting region 64 of the grains to be thinned of each of the plurality of grains 61, a back groove 75 of each of the plurality of grains 61 is formed on the back side of the wafer 6. The back groove 75 of each of the plurality of grains 61 has a bottom surface 76, a side wall 77, and an opening 78 on the lower surface 63 of the wafer 6. In this embodiment, the region of interest 62 of each of the plurality of grains 61 is (determined) identical to the starting region 64 of the grains to be thinned of each of the plurality of grains 61; therefore, the side wall 77 of the back groove 75 of each of the plurality of grains 61 is upright. The area occupied by the opening 78 of the back groove 75 of each of the plurality of grains 61 on the lower surface 63 of the wafer 6 is identical to the thinning start region 64 of each of the plurality of grains 61. The region of interest 62 of each of the plurality of grains 61 is identical to the area occupied by the bottom surface 76 of the back groove 75 of each of the plurality of grains 61. The opening 78 of the back groove 75 of each of the plurality of grains 61 and the bottom surface 76 of the back groove 75 of each of the plurality of grains 61 have identical shapes and identical areas. In this embodiment, the wafer 6 has a desired thickness D within the region of interest 62 of each of the plurality of grains 61; and the wafer 6 has a uniform thickness T outside the region of interest 62 of each of the plurality of grains 61 (outside the thinning start region 64). Therefore, the mechanical strength of the wafer 6 is improved. The structure of wafer 6 is sufficient to balance the enormous stress caused by the many layers formed on surface 60 of wafer 6. Therefore, wafer 6 will not experience warping.

[0061] In the embodiment of FIG. 26, after the wafer 6 is locally thinned by the local laser thinning process of the present invention, if the wafer 6 is cut into separate individual dies (wafers) along these dashed cutting lines 65, each of the separate individual dies (wafers) 61 may have a sidewall 77 of a back groove 75. The thickness of the sidewall 77 of the back groove 75 of each of the separate individual dies (wafers) 61 is slightly less than a thickness T2. The structure of the wafer 6 in a single separate individual die (wafer) 61 is sufficient to balance the huge stress caused by the many layers formed on the upper surface 60 of the wafer 6. Therefore, not only is the mechanical strength of the entire wafer 6 improved, but the mechanical strength of each separate individual die (wafer) 61 is also improved after the plurality of dies 61 are cut into separate individual dies (wafers) 61.

[0062] Please refer to Figure 27, which is a cross-sectional schematic diagram of another specific embodiment of a region of interest and a region to be thinned in a die before the wafer is locally thinned by the local laser thinning process of the present invention. In this embodiment, a wafer 6 includes a plurality of dies 61, wherein each of the plurality of dies 61 includes only one element 7 (the element 7 is not a power element as shown in Figure 3), wherein the features of interest of each of the plurality of dies 61 are respectively determined as the element 7 of each of the plurality of dies 61 on the upper surface 60 of the wafer 6, wherein the region to be thinned in the region 64 of each of the plurality of dies 61 is respectively determined such that the features of interest of each of the plurality of dies 61 are respectively in the region to be thinned in the region 64 of each of the plurality of dies 61. Within a thinning start region 64 (but not entirely identical to the thinning start region 64 of each of the plurality of grains 61; the thinning start region 64 of each of the plurality of grains 61 respectively covers an active region of one of the elements 7 of each of the plurality of grains 61 on the upper surface 60 of the wafer 6), wherein the region of interest 62 of each of the plurality of grains 61 is respectively (determined) within the thinning start region 64 of each of the plurality of grains 61 (but not entirely identical to the thinning start region 64 of each of the plurality of grains 61). In this embodiment, in each of the plurality of grains 61, the region of interest 62 includes a first sub-region of interest 621, a second sub-region of interest 622, a third sub-region of interest 623, a fourth sub-region of interest 624, and a fifth sub-region of interest 625. Please also refer to Figure 28, which is a cross-sectional view of the grains in Figure 27 after local thinning of the starting region of the grains to be thinned by the local laser thinning process of the present invention. After the local laser thinning process of the present invention is performed on the lower surface 63 of the wafer 6 within the starting region 64 of each of the plurality of grains 61, a back groove 75 of each of the plurality of grains 61 is formed on the back side of the wafer 6. The back groove 75 of each of the plurality of grains 61 has a bottom surface 76 (including a first bottom surface 761, a second bottom surface 762, a third bottom surface 763, a fourth bottom surface 764, and a fifth bottom surface 765), a main sidewall 77, a first sidewall 770, a second sidewall 771, and an opening 78 on the lower surface 63 of the wafer 6. In this embodiment, the region of interest 62 of each of the plurality of grains 61 is (determined) within the thinning start region 64 of each of the plurality of grains 61 (but not entirely the same as the thinning start region 64 of each of the plurality of grains 61); and the shape of one of the main sidewalls 77 of the back groove 75 of each of the plurality of grains 61 is (determined) tapered (the tapered main sidewalls 77 of the back groove 75 can be achieved through a combination of many steps).The shape of one of the first sidewalls 770 and one of the second sidewalls 771 of the back groove 75 of each of the plurality of grains 61 is determined to be upright. The area occupied by the opening 78 of the back groove 75 of each of the plurality of grains 61 on the lower surface 63 of the wafer 6 is identical to the thinning start area 64 of each of the plurality of grains 61. The area of ​​interest 62 of each of the plurality of grains 61 is identical to the area occupied by the bottom surface 76 (including the first bottom surface 761, the second bottom surface 762, the third bottom surface 763, the fourth bottom surface 764, and the fifth bottom surface 765) of the back groove 75 of each of the plurality of grains 61. The area occupied by the opening 78 of the back groove 75 of each of the plurality of grains 61 is wider than the area occupied by the bottom surface 76 of the back groove 75 of each of the plurality of grains 61. In this embodiment, wafer 6 has a desired thickness D1 in a first sub-region of interest 621 and a fifth sub-region of interest 625 of each of the plurality of grains 61; wafer 6 has a desired thickness D2 in a second sub-region of interest 622 and a fourth sub-region of interest 624 of each of the plurality of grains 61; and wafer 6 has a desired thickness D3 in a third sub-region of interest 623 of each of the plurality of grains 61; wherein the desired thickness D3 is greater than the desired thickness D1; ​​and the desired thickness D1 is greater than the desired thickness D2.

[0063] The partial wafer thinning method of the present invention does not require photolithographic processes. For example, a photoresist is formed on the lower surface 63 of wafer 6, and then a photomask is used for exposure and development to expose the thinning start area 64 of each of the plurality of grains 61. Then, dry etching or wet etching is performed to form a back groove 75 of each of the plurality of grains 61. If the user wants to form the back groove 75 of the embodiment of FIG28 by photolithographic processes, this requires many complex procedures. In contrast, it is very simple to form the back groove 75 of the embodiment of FIG28 using the partial wafer thinning method of the present invention. The partial wafer thinning method of the present invention can not only easily form back grooves 75 with complex shapes, but also easily control the depth of the back groove 75. In addition, when using photolithographic processes to form back grooves 75, if wafer 6 is made of silicon carbide (a very hard material), the etching rate will be very slow. This means that more time is needed to etch the silicon carbide wafer 6 to form the back recess 75. In contrast, forming the back recess 75 using the partial wafer thinning method of the present invention is very fast. For example, when using a lithography process to form the back recess 75, if it is made of gallium arsenide (GaAs), a material that is not as hard as silicon carbide, the etching rate is faster than etching silicon carbide. However, in comparison, forming the back recess 75 using the partial wafer thinning method of the present invention is still faster than etching gallium arsenide using a lithography process (faster than etching gallium arsenide using a lithography process). Furthermore, during the etching of gallium arsenide, the depth variation of the back recess 75 is affected by temperature gradients and the concentration gradients of the etching solution / gas. Therefore, the depth variation of the back recess 75 will be quite large.

[0064] Please refer to Figure 29, which is a cross-sectional schematic diagram of another specific embodiment of a partial wafer thinning system of the present invention. The main structure of the specific embodiment in Figure 29 is generally the same as that of the specific embodiment in Figure 1. However, the wafer 6 is transparent, and the image capturing element 30 of the image capturing device 3 is disposed on the lower surface 63 of the wafer 6 (for example, the image capturing element 30 is disposed next to the laser device 4). The light source 32 of the image capturing device 3 is disposed below the hollow central portion 20 of the driving device 2. The light source 32 is a non-coaxial light source. The light emitted by the light source 32 can pass through the hollow central portion 20 of the driving device 2 and the hollow central portion 51 of the carrier device 5 to illuminate at least a portion of the wafer 6 (for example, at least one die 61), and enable the image capturing element 30 of the image capturing device 3 to capture the image of at least one die 61 (the outline of the element 7 of at least one die 61) from the lower surface 63 of the wafer 6 (because the wafer 6 is transparent). In some other embodiments, the light emitted by the light source 32 can illuminate the entire wafer 6, so that the image capturing element 30 of the image capturing device 3 can capture an image of each of the plurality of dies 61 (the outline of the element 7 of each of the plurality of dies 61) from the lower surface 63 of the wafer 6 (because the wafer 6 is transparent).

[0065] In some embodiments, (not shown in the figure) the wafer 6 is transparent, the image capturing element 30 of the image capturing device 3 is disposed below the hollow central portion 20 of the driving device 2, and the light source 32 of the image capturing device 3 is a non-coaxial light source. The light source 32 is disposed on the lower surface 63 of the wafer 6 (for example, the light source 32 is a ring light source disposed between the lower surface 63 of the wafer 6 and the laser device 4; or the light source 32 is disposed next to the laser device 4).

[0066] In some other embodiments, (not shown in the figure) the wafer 6 is transparent, and the image capturing element 30 and the light source 32 of the image capturing device 3 are disposed on the lower surface 63 of the wafer 6 (for example, the image capturing element 30 and the light source 32 are disposed next to the laser device 4).

[0067] In some embodiments, the hollow central portion 51 of the support device 5 may also be non-hollow, wherein the hollow central portion 51 of the support device 5 may be made of a transparent material, such as glass.

[0068] Please refer to Figure 30, which is a cross-sectional schematic diagram of one of the two grains after the wafer has been partially thinned by the local laser thinning process of the present invention. The main structure of the embodiment in Figure 30 is substantially the same as that of the embodiment in Figure 18, except that the wafer 6 includes a plurality of grains 61 and a plurality of grains 61', each of the plurality of grains 61 including an element 7, and the plurality of grains 61' Each of the plurality of grains 61 includes an element 7', wherein one feature of interest of each of the plurality of grains 61 is respectively determined as element 7 of each of the plurality of grains 61; and one feature of interest ' of each of the plurality of grains 61' is respectively determined as element 7' of each of the plurality of grains 61'; wherein one thinning start region 64 of each of the plurality of grains 61 is respectively determined such that the feature of interest of each of the plurality of grains 61 is respectively within the thinning start region 64 of each of the plurality of grains 61 (but not entirely identical to the thinning start region 64 of each of the plurality of grains 61). 64); and one of the thinning start regions 64' of each of the plurality of grains 61' is determined to be identical to the feature of interest of each of the plurality of grains 61'; wherein one of the feature of interest 62 of each of the plurality of grains 61 is (determined to be) within the thinning start region 64 of each of the plurality of grains 61 (but not identical to the thinning start region 64 of each of the plurality of grains 61); and one of the feature of interest 62' of each of the plurality of grains 61' is (determined to be) identical to the thinning start region 64' of each of the plurality of grains 61'.In this embodiment, after performing the local laser thinning process of the present invention on the lower surface 63 of the wafer 6 in the thinning start region 64 of each of the plurality of grains 61 and in the thinning start region 64' of each of the plurality of grains 61', a back groove 75 of each of the plurality of grains 61 and a back groove 75' of each of the plurality of grains 61' are formed on the back side of the wafer 6; wherein the back groove 75 of each of the plurality of grains 61 has a bottom surface 76, a sidewall 77 and an opening 78 on the lower surface 63 of the wafer 6; wherein the back groove 75' of each of the plurality of grains 61' Each of the plurality of grains 61 has a bottom surface 76', a sidewall 77', and an opening 78' on the lower surface 63 of the wafer 6; wherein the shape of one of the sidewalls 77 of the back groove 75 of each of the plurality of grains 61 is (determined to be) tapered (the tapered sidewalls 77 of the back groove 75 can be achieved through a combination of many steps); wherein the area occupied by the opening 78 of the back groove 75 of each of the plurality of grains 61 on the lower surface 63 of the wafer 6 is identical to the thinning start area 64 of each of the plurality of grains 61; wherein the area of ​​interest 62 of each of the plurality of grains 61 is identical to the area occupied by the bottom surface 76 of the back groove 75 of each of the plurality of grains 61; wherein one of the sidewalls 77' of the back groove 75' of each of the plurality of grains 61' is upright; wherein the plurality of grains 61' The area occupied by the opening 78' of the back groove 75' of each of the plurality of grains 6 on the lower surface 63 of the wafer 6 is identical to the thinning start area 64' of each of the plurality of grains 61'; the area of ​​interest 62' of each of the plurality of grains 61' is identical to the area occupied by the bottom surface 76' of the back groove 75' of each of the plurality of grains 61'; the opening 78' of the back groove 75' of each of the plurality of grains 61' and the bottom surface 76' of the back groove 75' of each of the plurality of grains 61' have identical shapes and identical areas; the wafer 6 has a desired thickness D in the area of ​​interest 62 of each of the plurality of grains 61; and the wafer 6 has a desired thickness D' in the area of ​​interest 62' of each of the plurality of grains 61', wherein the desired thickness D is not equal to the desired thickness D' (in this embodiment, the desired thickness D' is greater than the desired thickness D).

[0069] Please refer to Figure 31, which is a partially enlarged schematic diagram of another specific embodiment of the lower surface of a wafer before it is partially thinned by the local laser thinning process of the present invention. In this embodiment, a wafer 6 includes a plurality of grains 61, including a first grain 611, a second grain 612, a third grain 613, a fourth grain 614, a fifth grain 615, a sixth grain 616, a seventh grain 617, an eighth grain 618, a ninth grain 619, and some other grains 61. The dashed cutting line 65 in Figure 31 is the boundary of each of the plurality of grains 61. A region of interest 62 and a thinning start region 64 for each of the first grain 611, the second grain 612, the third grain 613, the fourth grain 614, the fifth grain 615, the sixth grain 616, the seventh grain 617, the eighth grain 618, the ninth grain 619, and some other grains 61 are determined and shown in FIG. 31. After performing step C (at least after the thinning start region 64 for each of the plurality of grains 61 is determined), the method of partial wafer thinning of the present invention further includes the step of dividing the plurality of grains 61 into grain groups 68, wherein each of the grain groups 68 includes at least two grains 61; and wherein, in each of the grain groups 68, any one grain 61 is adjacent to at least one other grain 61. One of the grain groups 68 is shown in the middle of FIG. 31. A grain group 68 located in the middle of Figure 31 includes nine grains 61 (including a first grain 611, a second grain 612, a third grain 613, a fourth grain 614, a fifth grain 615, a sixth grain 616, a seventh grain 617, an eighth grain 618, and a ninth grain 619); wherein, in this grain group 68, any two adjacent grains 61 have a boundary region 66 between the thinning start region 64 of the two adjacent grains 61;For example, the first grain 611 and the second grain 612 are two adjacent grains 61, and there is a boundary region 66 between the thinning start region 64 of the first grain 611 and the thinning start region 64 of the second grain 612. Please also refer to FIG32, which is a schematic diagram of the lower surface of the wafer in FIG31 after the wafer has been partially thinned by the local laser thinning process of the present invention. In this embodiment, in step F of the local wafer thinning method of the present invention, the laser device 4 performs local laser thinning processing on the lower surface 63 of the wafer 6 not only within the thinning start region 64 of each of the plurality of grains 61, but also within a boundary region 66 between any two adjacent grains 61 in each of the grain groups 68, such that the wafer 6 performs local laser thinning processing within the thinning start region 64 of each of the plurality of grains 61 and within the boundary region 66 between any two adjacent grains 61 in each of the grain groups 68. The wafer 6 is locally thinned within the following regions: (In this embodiment, in the grain group 68 shown in FIG31, the wafer 6 is thinned within the following regions: the starting region 64 of the nine grains 61 from the first grain 611 to the ninth grain 619; the boundary region 66 between the starting regions 64 of the first grain 611 and the second grain 612; the boundary region 66 between the starting regions 64 of the second grain 612 and the third grain 613; the boundary region 66 between the starting regions 64 of the first grain 611 and the fourth grain 614; and the boundary region 66 between the second grain 612 and the fifth grain 615.) Within the boundary region 66 between the respective thinning initiation regions 64, within the boundary region 66 between the third grain 613 and the sixth grain 616, within the boundary region 66 between the fourth grain 614 and the fifth grain 615, within the boundary region 66 between the fifth grain 615 and the sixth grain 616, within the boundary region 66 between the fourth grain 614 and the seventh grain 617, and within the boundary region 66 between the fifth grain 615 and the eighth grain 618. The grains are partially thinned in the boundary region 66 between the thinning start regions 64, the boundary region 66 between the thinning start regions 64 of the sixth grain 616 and the ninth grain 619, the boundary region 66 between the thinning start regions 64 of the seventh grain 617 and the eighth grain 618, and the boundary region 66 between the thinning start regions 64 of the eighth grain 618 and the ninth grain 619, respectively, to form a non-separated back groove 67 for each of the grain groups 68, wherein the non-separated back groove 67 of each of the grain groups 68 has an opening.In any of the grain groups 68, the area occupied by the opening of the non-separated back groove 67 of the grain group 68 can be defined by a merged area formed by merging the thinning start area 64 of each grain 61 in the grain group 68 and the boundary area 66 between the thinning start areas 64 of any two adjacent grains 61 in the grain group 68 (in this embodiment, in the grain group 68 shown in FIG31, the opening of the non-separated back groove 67 is as shown in FIG32). The required thickness of wafer 6 within the boundary region 66 between the thinning start regions 64 of any two adjacent dies 61 in the grain group 68 may be the same as, or different from, the required thickness of wafer 6 within the region of interest 62 of any two adjacent dies 61 in the grain group 68 (in this embodiment, the required thickness of wafer 6 within the boundary region 66 between the thinning start regions 64 of any two adjacent dies 61 in the grain group 68 may be the same as the required thickness of wafer 6 within the region of interest 62 of any two adjacent dies 61 in the grain group 68).

[0070] In some embodiments, a wafer 6 includes a plurality of grains 61, wherein the plurality of grains 61 includes N grains 61 (e.g., N = 80, i.e., the wafer 6 includes 80 grains 61); after performing step C (at least after the starting region 64 to be thinned of each of the plurality of grains 61 is determined), the method of partial wafer thinning of the present invention further includes the following step: dividing M of the N grains 61 into at least two grain groups 68, wherein N and M are positive integers, wherein any two grain groups 68 respectively include P grains 61 and Q grains 61 of the M grains 61, wherein, or, P and Q are positive integers; that is, any two grain groups 68 may respectively contain the same number of grains 61 or different numbers of grains 61; wherein, in each of the grain groups 68, any one grain 61 is adjacent to at least one other grain 61. For example, at that time, the M grains 61 are M of the N grains 61; and at that time, the M grains 61 are the N grains 61. The M grains 61 among the N grains 61 can be divided into two grain groups 68, three grain groups 68, or more grain groups 68. For example, when N=97 and M=97, the M (97) grains 61 can be divided into 9 grain groups 68 (each of the 9 grain groups 68 includes 9 grains 61) and another 4 grain groups 68 (each of the 4 grain groups 68 includes 4 grains 61). In another example, when N=97 and M=81, the M (81) grains 61 can be divided into 6 grain groups 68 (each of the 6 grain groups 68 includes 9 grains 61) and another 3 grain groups 68 (each of the 3 grain groups 68 includes 9 grains 61), while the remaining 16 grains 61 of the N (97) grains 61 are not divided into any grain group 68. For another example, when N=97 and M=81, the M (81) grains 61 can be divided into 5 grain groups 68 (each of the 5 grain groups 68 includes 9 grains 61), another 3 grain groups 68 (each of the 3 grain groups 68 includes 8 grains 61) and another 2 grain groups 68 (each of the 2 grain groups 68 includes 6 grains 61), while the remaining 16 grains 61 of the N (97) grains 61 are not divided into any grain group 68.

[0071] Please refer to Figure 33, which is a partially enlarged schematic diagram of another specific embodiment of the lower surface of a wafer after it has been partially thinned by the local laser thinning process of the present invention. In this embodiment, a wafer 6 includes a plurality of grains 61, wherein each of the plurality of grains 61 includes nine sub-grains (including a first grain 691, a second grain 692, a third grain 693, a fourth grain 694, a fifth grain 695, a sixth grain 696, a seventh grain 697, an eighth grain 698, and a ninth grain 699); wherein, in each of the plurality of grains 61, the dashed cutting line 65' represents the nine sub-grains (including the first grain 691, the second grain 692, the third grain 693, the fourth grain 694, the fifth grain 695, the sixth grain 696, the seventh grain 697, the eighth grain 698, and the ninth grain 699). The boundary between sub-grains 698 and the ninth sub-grain 699; wherein each of the nine sub-grains includes at least one element (not shown) formed on the upper surface 60 of the wafer 6; wherein, in each of the plurality of grains 61, a feature of interest is determined to be a non-separated region occupied by a combination of at least one element of each of the nine sub-grains; wherein, in each of the plurality of grains 61, a thinning start region 64 is determined such that the feature of interest is within the thinning start region 64 (but not identical to the thinning start region 64); wherein, in each of the plurality of grains 61, a region of interest 62 is (determined to be) identical to the thinning start region 64. After performing the local laser thinning process of the present invention on the lower surface 63 of the wafer 6 within the thinning start region 64 of each of the plurality of grains 61, a back groove 75 of each of the plurality of grains 61 is formed on the back side of the wafer 6. In each of the plurality of grains 61, the back groove 75 has a bottom surface, a sidewall, and an opening on the lower surface 63 of the wafer 6; one of the sidewalls of the back groove 75 is upright; the area occupied by the opening of the back groove 75 on the lower surface 63 of the wafer 6 is identical to the thinning start area 64; the area of ​​interest 62 is identical to the area occupied by the bottom surface of the back groove 75; wherein the dashed cut lines 65' (the boundaries between the nine sub-grains) are within the area occupied by the bottom surface of the back groove 75. The wafer 6 has a desired thickness (not shown) within the area of ​​interest 62 of each of the plurality of grains 61. In this embodiment, the wafer 6 will be cut into a plurality of separate, independent sub-grains along these dashed cut lines 65'. In some embodiments, wafer 6 will be cut along these dashed cutting lines 65 into a plurality of separate independent grains 61, and each of the plurality of grains 61 will be cut along these dashed cutting lines 65' into 9 separate independent sub-grains.

[0072] In the embodiments of Figures 8-10, 21, and 26, the shape of one of the sidewalls 77 of the back groove 75 of each of the plurality of grains 61 is upright (perpendicular to the lower surface 63 of the wafer 6); while in the embodiment of Figure 14, the shape of one of the sidewalls 77 of the back groove 75 of each of the plurality of grains 61 is tapered (not perpendicular to the lower surface 63 of the wafer 6), but steep (i.e., the slope of one of the sidewalls 77 is large; for example, the slope of one of the sidewalls 77 is equal to 4, 5, 6, 7, 8, 9, or 10). In some other embodiments, the shape of one of the sidewalls 77 of the back groove 75 of each of the plurality of grains 61 is tapered, but not steep (for example, the slope of one of the sidewalls 77 is equal to 3, 2, or 1). In the embodiment of Figure 16, the shape of one of the sidewalls 77 of the back groove 75 of each of the plurality of grains 61 is stepped. In some other embodiments, the shape of one of the sidewalls 77 of the back groove 75 of each of the plurality of grains 61 may be a combination of a stepped shape and a tapered shape.

[0073] Wafer 6 has a desired thickness D within a region of interest 62 of each of a plurality of grains 61. In some embodiments, the desired thickness D is greater than or equal to 200 μm and less than or equal to 300 μm. In other embodiments, the desired thickness D is greater than or equal to 100 μm and less than or equal to 200 μm. In other embodiments, the desired thickness D is greater than or equal to 50 μm and less than or equal to 100 μm. In some embodiments, the desired thickness D is greater than or equal to 20 μm and less than or equal to 50 μm. In other embodiments, the desired thickness D is greater than or equal to 10 μm and less than or equal to 20 μm.

[0074] In the embodiment of FIG. 28, wafer 6 has a desired thickness D2 within a second sub-region of interest 622 and a fourth sub-region of interest 624 of each of a plurality of grains 61. In some embodiments, the desired thickness D2 is greater than or equal to 200 μm and less than or equal to 300 μm. In some other embodiments, the desired thickness D2 is greater than or equal to 100 μm and less than or equal to 200 μm. In some other embodiments, the desired thickness D2 is greater than or equal to 50 μm and less than or equal to 100 μm. In some other embodiments, the desired thickness D2 is greater than or equal to 20 μm and less than or equal to 50 μm. In some other embodiments, the desired thickness D2 is greater than or equal to 10 μm and less than or equal to 20 μm. In some other embodiments, the desired thickness D2 is greater than or equal to 5 μm and less than or equal to 10 μm. In some other embodiments, the desired thickness D2 is greater than or equal to 2 μm and less than or equal to 5 μm. In some other embodiments, the desired thickness D2 is greater than or equal to 1 μm and less than or equal to 2 μm. In some embodiments, the desired thickness D2 is greater than or equal to 500 nm and less than or equal to 1 μm. In some embodiments, the desired thickness D2 is greater than or equal to 200 nm and less than or equal to 500 nm. In some embodiments, the desired thickness D2 is greater than or equal to 100 nm and less than or equal to 200 nm.

[0075] In some embodiments, the region of interest 62 or the second sub-region of interest 622 has a circular shape, wherein the diameter of one of the circles of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 10000 μm and less than or equal to 15000 μm. In other embodiments, the diameter of the circle of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 5000 μm and less than or equal to 10000 μm. In other embodiments, the diameter of the circle of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 2000 μm and less than or equal to 5000 μm. In other embodiments, the diameter of the circle of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 1000 μm and less than or equal to 2000 μm. In other embodiments, the diameter of the circle of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 500 μm and less than or equal to 1000 μm. In some other embodiments, the diameter of the circle of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 200 μm and less than or equal to 500 μm. In some other embodiments, the diameter of the circle of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 120 μm and less than or equal to 200 μm. In some other embodiments, the diameter of the circle of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 80 μm and less than or equal to 120 μm. In some other embodiments, the diameter of the circle of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 30 μm and less than or equal to 80 μm. In some other embodiments, the diameter of the circle of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 10 μm and less than or equal to 30 μm. In some other embodiments, the diameter of the circle of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 5 μm and less than or equal to 10 μm.

[0076] In some embodiments, the region of interest 62 or the second sub-region of interest 622 has an elliptical shape, wherein one minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is smaller than one major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622. In some embodiments, the minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 10000 μm and less than or equal to 15000 μm, and the major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is less than or equal to 30000 μm. In other embodiments, the minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 5000 μm and less than or equal to 10000 μm, and the major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is less than or equal to 20000 μm. In some other embodiments, the minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 2000 μm and less than or equal to 5000 μm, and the major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is less than or equal to 15000 μm. In some other embodiments, the minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 1000 μm and less than or equal to 2000 μm, and the major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is less than or equal to 6000 μm. In some other embodiments, the minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 500 μm and less than or equal to 1000 μm, and the major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is less than or equal to 3000 μm. In some other embodiments, the minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 200 μm and less than or equal to 500 μm, and the major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is less than or equal to 1500 μm. In some other embodiments, the minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 120 μm and less than or equal to 200 μm, and the major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is less than or equal to 600 μm. In some other embodiments, the minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 80 μm and less than or equal to 120 μm, and the major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is less than or equal to 360 μm. In some other embodiments, the minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 30 μm and less than or equal to 80 μm, and the major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is less than or equal to 240 μm.In some other embodiments, the minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 10 μm and less than or equal to 30 μm, and the major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is less than or equal to 90 μm. In some other embodiments, the minor axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is greater than or equal to 5 μm and less than or equal to 10 μm, and the major axis of the ellipse of the region of interest 62 or the second sub-region of interest 622 is less than or equal to 30 μm.

[0077] In some embodiments, the starting region 64 to be thinned has a circular shape, wherein the diameter of the circle of the starting region 64 to be thinned is greater than or equal to 10000 μm and less than or equal to 15000 μm. In other embodiments, the diameter of the circle of the starting region 64 to be thinned is greater than or equal to 5000 μm and less than or equal to 10000 μm. In other embodiments, the diameter of the circle of the starting region 64 to be thinned is greater than or equal to 2000 μm and less than or equal to 5000 μm. In other embodiments, the diameter of the circle of the starting region 64 to be thinned is greater than or equal to 1000 μm and less than or equal to 2000 μm. In other embodiments, the diameter of the circle of the starting region 64 to be thinned is greater than or equal to 500 μm and less than or equal to 1000 μm. In other embodiments, the diameter of the circle of the starting region 64 to be thinned is greater than or equal to 200 μm and less than or equal to 500 μm. In some other embodiments, the diameter of the circle of the starting region 64 to be thinned is greater than or equal to 120 μm and less than or equal to 200 μm. In some other embodiments, the diameter of the circle of the starting region 64 to be thinned is greater than or equal to 80 μm and less than or equal to 120 μm. In some other embodiments, the diameter of the circle of the starting region 64 to be thinned is greater than or equal to 30 μm and less than or equal to 80 μm. In some other embodiments, the diameter of the circle of the starting region 64 to be thinned is greater than or equal to 10 μm and less than or equal to 30 μm. In some other embodiments, the diameter of the circle of the starting region 64 to be thinned is greater than or equal to 5 μm and less than or equal to 10 μm.

[0078] In some embodiments, the thinning start region 64 has an elliptical shape, wherein one minor axis of the ellipse is smaller than one major axis. In some embodiments, the minor axis of the ellipse is greater than or equal to 10000 μm and less than or equal to 15000 μm, and the major axis is less than or equal to 30000 μm. In other embodiments, the minor axis of the ellipse is greater than or equal to 5000 μm and less than or equal to 10000 μm, and the major axis is less than or equal to 20000 μm. In other embodiments, the minor axis of the ellipse is greater than or equal to 2000 μm and less than or equal to 5000 μm, and the major axis is less than or equal to 15000 μm. In some other embodiments, the minor axis of the ellipse of the starting region 64 to be thinned is greater than or equal to 1000 μm and less than or equal to 2000 μm, and the major axis of the ellipse is less than or equal to 6000 μm. In some other embodiments, the minor axis of the ellipse of the starting region 64 to be thinned is greater than or equal to 500 μm and less than or equal to 1000 μm, and the major axis of the ellipse is less than or equal to 3000 μm. In some other embodiments, the minor axis of the ellipse of the starting region 64 to be thinned is greater than or equal to 200 μm and less than or equal to 500 μm, and the major axis of the ellipse is less than or equal to 1500 μm. In some other embodiments, the minor axis of the ellipse of the starting region 64 to be thinned is greater than or equal to 120 μm and less than or equal to 200 μm, and the major axis of the ellipse is less than or equal to 600 μm. In some other embodiments, the minor axis of the ellipse of the starting region 64 to be thinned is greater than or equal to 80 μm and less than or equal to 120 μm, and the major axis of the ellipse is less than or equal to 360 μm. In some other embodiments, the minor axis of the ellipse of the starting region 64 to be thinned is greater than or equal to 30 μm and less than or equal to 80 μm, and the major axis of the ellipse is less than or equal to 240 μm. In some other embodiments, the minor axis of the ellipse of the starting region 64 to be thinned is greater than or equal to 10 μm and less than or equal to 30 μm, and the major axis of the ellipse is less than or equal to 90 μm. In some other embodiments, the minor axis of the ellipse of the starting region 64 to be thinned is greater than or equal to 5 μm and less than or equal to 10 μm, and the major axis of the ellipse is less than or equal to 30 μm.

[0079] In some embodiments, the region of interest 62 has a rectangular shape, wherein a first set of sides of the rectangle of the region of interest 62 is less than or equal to a second set of sides of the rectangle of the region of interest 62. In some embodiments, the first set of sides of the rectangle of the region of interest 62 is greater than or equal to 10000 μm and less than or equal to 15000 μm, and the second set of sides of the rectangle of the region of interest 62 is less than or equal to 30000 μm. In other embodiments, the first set of sides of the rectangle of the region of interest 62 is greater than or equal to 5000 μm and less than or equal to 10000 μm, and the second set of sides of the rectangle of the region of interest 62 is less than or equal to 20000 μm. In other embodiments, the first set of sides of the rectangle of the region of interest 62 is greater than or equal to 2000 μm and less than or equal to 5000 μm, and the second set of sides of the rectangle of the region of interest 62 is less than or equal to 15000 μm. In some other embodiments, the first side group of the rectangle of the region of interest 62 is greater than or equal to 1000 μm and less than or equal to 2000 μm, and the second side group of the rectangle of the region of interest 62 is less than or equal to 6000 μm. In some other embodiments, the first side group of the rectangle of the region of interest 62 is greater than or equal to 500 μm and less than or equal to 1000 μm, and the second side group of the rectangle of the region of interest 62 is less than or equal to 3000 μm. In some other embodiments, the first side group of the rectangle of the region of interest 62 is greater than or equal to 200 μm and less than or equal to 500 μm, and the second side group of the rectangle of the region of interest 62 is less than or equal to 1500 μm. In some other embodiments, the first side group of the rectangle of the region of interest 62 is greater than or equal to 120 μm and less than or equal to 200 μm, and the second side group of the rectangle of the region of interest 62 is less than or equal to 600 μm. In some other embodiments, the first side group of the rectangle of the region of interest 62 is greater than or equal to 80 μm and less than or equal to 120 μm, and the second side group of the rectangle of the region of interest 62 is less than or equal to 360 μm. In some other embodiments, the first side group of the rectangle of the region of interest 62 is greater than or equal to 30 μm and less than or equal to 80 μm, and the second side group of the rectangle of the region of interest 62 is less than or equal to 240 μm. In some other embodiments, the first side group of the rectangle of the region of interest 62 is greater than or equal to 10 μm and less than or equal to 30 μm, and the second side group of the rectangle of the region of interest 62 is less than or equal to 90 μm. In some other embodiments, the first side group of the rectangle of the region of interest 62 is greater than or equal to 5 μm and less than or equal to 10 μm, and the second side group of the rectangle of the region of interest 62 is less than or equal to 30 μm.

[0080] In some embodiments, the thinning start region 64 has a rectangular shape, wherein a first side group of the rectangle of the thinning start region 64 is less than or equal to a second side group of the rectangle of the thinning start region 64. In some embodiments, the first side group of the rectangle of the thinning start region 64 is greater than or equal to 10000 μm and less than or equal to 15000 μm, and the second side group of the rectangle of the thinning start region 64 is less than or equal to 30000 μm. In other embodiments, the first side group of the rectangle of the thinning start region 64 is greater than or equal to 5000 μm and less than or equal to 10000 μm, and the second side group of the rectangle of the thinning start region 64 is less than or equal to 20000 μm. In other embodiments, the first side group of the rectangle of the thinning start region 64 is greater than or equal to 2000 μm and less than or equal to 5000 μm, and the second side group of the rectangle of the thinning start region 64 is less than or equal to 15000 μm. In some other embodiments, the first side group of the rectangle of the starting region 64 to be thinned is greater than or equal to 1000 μm and less than or equal to 2000 μm, and the second side group of the rectangle of the starting region 64 to be thinned is less than or equal to 6000 μm. In some other embodiments, the first side group of the rectangle of the starting region 64 to be thinned is greater than or equal to 500 μm and less than or equal to 1000 μm, and the second side group of the rectangle of the starting region 64 to be thinned is less than or equal to 3000 μm. In some other embodiments, the first side group of the rectangle of the starting region 64 to be thinned is greater than or equal to 200 μm and less than or equal to 500 μm, and the second side group of the rectangle of the starting region 64 to be thinned is less than or equal to 1500 μm. In some other embodiments, the first side group of the rectangle of the starting region 64 to be thinned is greater than or equal to 120 μm and less than or equal to 200 μm, and the second side group of the rectangle of the starting region 64 to be thinned is less than or equal to 600 μm. In some other embodiments, the first side series of the rectangle of the starting region 64 to be thinned is greater than or equal to 80 μm and less than or equal to 120 μm, and the second side series of the rectangle of the starting region 64 to be thinned is less than or equal to 360 μm. In some other embodiments, the first side series of the rectangle of the starting region 64 to be thinned is greater than or equal to 30 μm and less than or equal to 80 μm, and the second side series of the rectangle of the starting region 64 to be thinned is less than or equal to 240 μm. In some other embodiments, the first side series of the rectangle of the starting region 64 to be thinned is greater than or equal to 10 μm and less than or equal to 30 μm, and the second side series of the rectangle of the starting region 64 to be thinned is less than or equal to 90 μm. In some other embodiments, the first side series of the rectangle of the starting region 64 to be thinned is greater than or equal to 5 μm and less than or equal to 10 μm, and the second side series of the rectangle of the starting region 64 to be thinned is less than or equal to 30 μm.

[0081] In some embodiments, the region of interest 62 has a polygonal shape. In some embodiments, the region of interest 62 has an L-shaped shape. In some embodiments, the region of interest 62 has a triangular shape. In some embodiments, the region of interest 62 has an oblong shape. In some embodiments, the starting region 64 to be thinned has a polygonal shape. In some embodiments, the starting region 64 to be thinned has an L-shaped shape. In some embodiments, the starting region 64 to be thinned has a triangular shape. In some embodiments, the starting region 64 to be thinned has an oblong shape.

[0082] In this invention, the required thickness D in the region of interest 62 of each of the plurality of grains 61 is independent of the shape of the region of interest 62 of each of the plurality of grains 61 and is independent of the area of ​​the region of interest 62 of each of the plurality of grains 61.

[0083] In some embodiments, the ratio of the region of interest 62 to the starting region of thinning 64 (i.e., the ratio of the area occupied by the bottom surface 76 of the back recess 75 to the area occupied by the opening 78 of the back recess 75) is greater than or equal to 0.98 and less than or equal to 1. In some embodiments, the ratio of the region of interest 62 to the starting region of thinning 64 is greater than or equal to 0.95 and less than or equal to 0.98. In some embodiments, the ratio of the region of interest 62 to the starting region of thinning 64 is greater than or equal to 0.9 and less than or equal to 0.95. In some embodiments, the ratio of the region of interest 62 to the starting region of thinning 64 is greater than or equal to 0.8 and less than or equal to 0.9. In some embodiments, the ratio of the region of interest 62 to the starting region of thinning 64 is greater than or equal to 0.7 and less than or equal to 0.8. In some embodiments, the ratio of the region of interest 62 to the starting region of thinning 64 is greater than or equal to 0.6 and less than or equal to 0.7. In some embodiments, the ratio of the region of interest 62 to the starting region to be thinned 64 is greater than or equal to 0.5 and less than or equal to 0.6.

[0084] In some embodiments, the ratio of the thinning start region 64 of the die 61 to the region occupied by the die 61 (i.e., the ratio of the region occupied by the opening 78 of the back groove 75 to the region occupied by the die 61) is greater than or equal to 0.95 and less than or equal to 0.98. In some embodiments, the ratio of the thinning start region 64 of the die 61 to the region occupied by the die 61 is greater than or equal to 0.9 and less than or equal to 0.95. In some embodiments, the ratio of the thinning start region 64 of the die 61 to the region occupied by the die 61 is greater than or equal to 0.85 and less than or equal to 0.9. In some embodiments, the ratio of the thinning start region 64 of the die 61 to the region occupied by the die 61 is greater than or equal to 0.8 and less than or equal to 0.85. In some embodiments, the ratio of the thinning start region 64 of the die 61 to the region occupied by the die 61 is greater than or equal to 0.7 and less than or equal to 0.8. In some embodiments, the ratio of the thinning start region 64 of the die 61 to the region occupied by the die 61 is greater than or equal to 0.6 and less than or equal to 0.7. In some embodiments, the ratio of the thinning start region 64 of the die 61 to the region occupied by the die 61 is greater than or equal to 0.5 and less than or equal to 0.6. In some embodiments, the ratio of the thinning start region 64 of the die 61 to the region occupied by the die 61 is greater than or equal to 0.4 and less than or equal to 0.5. In some embodiments, the ratio of the thinning start region 64 of the die 61 to the region occupied by the die 61 is greater than or equal to 0.3 and less than or equal to 0.4. In some embodiments, the ratio of the thinning start region 64 of the die 61 to the region occupied by the die 61 is greater than or equal to 0.2 and less than or equal to 0.3. In some embodiments, the ratio of the thinning start region 64 of the die 61 to the region occupied by the die 61 is greater than or equal to 0.1 and less than or equal to 0.2.

[0085] In some embodiments, the light source 32 may be other types of light sources (e.g., a non-coaxial light source), such as a ring light source, at least one line light source, a surface light source, a diffused dome light source, or other types of light sources.

[0086] In some embodiments, the wafer 6 is made of at least one material selected from the group consisting of: glass, silicon carbide (SiC), gallium nitride (GaN), gallium nitride on silicon carbide substrate (GaN on SiC), gallium nitride on silicon substrate (GaN on Si), silicon (Si), silicon germanium (SiGe), gallium arsenide (GaAs), gallium oxide (Ga2O3), gallium antimonide (GaSb), aluminum nitride (AlN), sapphire, gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), zinc selenide (ZnSe), and diamond.

[0087] In some embodiments, the drive device 2 further includes a rotating platform (not shown in the figure), wherein the rotating platform of the drive device 2 is disposed on the three-axis moving platform of the drive device 2, and the bearing device 5 is disposed on the rotating platform of the drive device 2, wherein the wafer 6 carried by the bearing device 5 can rotate along the Z-axis passing through one of the centers of the rotating platform (or along the Z-axis passing through one of the centers of the wafer 6) by means of the rotating platform.

[0088] In some embodiments, the support device 5 is disposed on one of the X-axis moving platform and the Y-axis moving platform of the drive device 2 (not shown in the figure), and the image capturing device 3 is disposed on the Z-axis moving platform (not shown in the figure).

[0089] In some embodiments, the driving device 2 further includes a rotating platform (not shown in the figure), wherein the rotating platform of the driving device 2 is disposed on a combination of the X-axis moving platform and the Y-axis moving platform of the driving device 2 (not shown in the figure), and the carrying device 5 is disposed on the rotating platform of the driving device 2, and the image capturing device 3 is disposed on the Z-axis moving platform (not shown in the figure), wherein the wafer 6 carried by the carrying device 5 can rotate along the Z-axis passing through the center of one of the rotating platforms (or along the Z-axis passing through the center of one of the wafer 6) by means of the rotating platform.

[0090] In some embodiments, the support device 5 is disposed on one of the X-axis moving platform and the Y-axis moving platform of the drive device 2 (not shown in the figure), and the laser device 4 is disposed on the Z-axis moving platform (not shown in the figure).

[0091] In some embodiments, the drive device 2 further includes a rotating platform (not shown in the figure), wherein the rotating platform of the drive device 2 is disposed on a combination of the X-axis moving platform and the Y-axis moving platform of the drive device 2 (not shown in the figure), and the carrier device 5 is disposed on the rotating platform of the drive device 2, and the laser device 4 is disposed on the Z-axis moving platform (not shown in the figure), wherein the wafer 6 carried by the carrier device 5 can rotate along the Z-axis passing through the center of one of the rotating platforms (or along the Z-axis passing through the center of one of the wafer 6) by means of the rotating platform.

[0092] In the method for partial wafer thinning of the present invention, step C is performed after step B and before step F. For example, (1) step C is performed after step B, step D is performed after step C, step E is performed after step D, and step F is performed after step E; or (2) step D is performed after step B, step C is performed after step D, step E is performed after step C, and step F is performed after step E; or (3) step D is performed after step B, step E is performed after step D, step C is performed after step E, and step F is performed after step C.

[0093] The above description is a specific embodiment of the present invention and the technical means used. Many changes and modifications can be derived from the disclosure or teachings herein, which can still be regarded as equivalent changes to the concept of the present invention. The effects produced do not exceed the essential spirit covered by the specification and drawings, and should all be regarded as within the technical scope of the present invention. This is hereby stated.

[0094] In summary, based on the content disclosed above, the present invention can indeed achieve the intended purpose of the invention and provide a wafer with a locally thinned structure, which has great industrial applicability. Therefore, an invention patent application is filed in accordance with the law. [Simplified Explanation of the Diagram]

[0025] [Figure 1] is a cross-sectional schematic diagram of a specific embodiment of a partial wafer thinning system according to the present invention. [Figure 2] is a schematic diagram of the upper surface of a wafer in Figure 1. [Figure 3] is a partially enlarged view of region X in Figure 2, showing a schematic diagram of the upper surface of a grain. [Figure 4] is a schematic diagram of a specific embodiment of a region of interest and a thinning start region on the upper surface of the grain in Figure 3. [Figure 5] is a schematic diagram of a region of interest and a thinning start region on the lower surface of a grain in Figure 4. [Figure 6] is a cross-sectional schematic diagram along section line A-A' of Figure 5 before the wafer is partially thinned by the partial laser thinning process of the present invention. [Figure 7] is a cross-sectional schematic diagram along section line B-B' of Figure 5 before the wafer is partially thinned by the partial laser thinning process of the present invention. [Figure 8] is a cross-sectional view along section line A-A' of Figure 5 after the wafer has undergone local thinning in the starting region of the die to be thinned by the local laser thinning process of the present invention. [Figure 9] is a cross-sectional view along section line B-B' of Figure 5 after the wafer has undergone local thinning in the starting region of the die to be thinned by the local laser thinning process of the present invention. [Figure 10] is a perspective view of the lower surface of the wafer in Figure 5 after the wafer has undergone local thinning in the starting region of the die to be thinned by the local laser thinning process of the present invention. [Figure 11] is a cross-sectional view of the die cut from the wafer in Figure 8. [Figure 12] is a schematic diagram of another specific embodiment of a region of interest and a starting region of thinning on the lower surface of the die in Figure 3. [Figure 13] is a cross-sectional view along section line C-C' of Figure 12 before the wafer undergoes local thinning by the local laser thinning process of the present invention. [Figure 14] is a cross-sectional view along the C-C' section line of Figure 12 after the wafer has undergone local thinning in the starting region of the die by the local laser thinning process of the present invention. [Figure 15] is a cross-sectional view of another specific embodiment of a region of interest and a starting region of thinning for a die before the wafer has undergone local thinning by the local laser thinning process of the present invention. [Figure 16] is a cross-sectional view of the die in Figure 15 after the wafer has undergone local thinning in the starting region of thinning for a die by the local laser thinning process of the present invention. [Figure 17] is a cross-sectional view of another specific embodiment of two regions of interest and two starting regions of thinning for a die before the wafer has undergone local thinning by the local laser thinning process of the present invention. [Figure 18] is a cross-sectional view of the die in Figure 17 after the wafer has undergone local thinning in the starting region of thinning for a die by the local laser thinning process of the present invention. [Figure 19] is a schematic diagram of another specific embodiment of a region of interest and a region to be thinned starting on the lower surface of the grain in Figure 3. [Figure 20] is a schematic cross-sectional view along the D-D' section line of Figure 19 before the wafer is locally thinned by the local laser thinning process of the present invention.[Figure 21] is a cross-sectional view along section line D-D' of Figure 19 after the wafer has undergone local thinning in the starting region of the die by the local laser thinning process of the present invention. [Figure 22] is a perspective view of the lower surface of the wafer in Figure 19 after the wafer has undergone local thinning in the starting region of the die by the local laser thinning process of the present invention. [Figure 23] is a cross-sectional view of the die cut from the wafer in Figure 21. [Figure 24] is a cross-sectional view along section line E-E' of Figure 22 after the wafer has undergone local thinning in the starting region of the die by the local laser thinning process of the present invention. [Figure 25] is a cross-sectional view of another specific embodiment of a region of interest and a starting region of thinning of a die before the wafer undergoes local thinning by the local laser thinning process of the present invention. [Figure 26] is a cross-sectional view of the grain in Figure 25 after local thinning of the starting region of the grain by the local laser thinning process of the present invention. [Figure 27] is a cross-sectional view of another specific embodiment of a region of interest and a starting region of thinning of a grain before local thinning of the wafer by the local laser thinning process of the present invention. [Figure 28] is a cross-sectional view of the grain in Figure 27 after local thinning of the starting region of the grain by the local laser thinning process of the present invention. [Figure 29] is a cross-sectional view of another specific embodiment of a local wafer thinning system of the present invention. [Figure 30] is a cross-sectional view of one specific embodiment of two grains after local thinning of the wafer by the local laser thinning process of the present invention. [Figure 31] is a partially enlarged view of another specific embodiment of a lower surface of a wafer before local thinning of the wafer by the local laser thinning process of the present invention. [Figure 32] is a schematic diagram of the lower surface of the wafer in Figure 31 after the wafer has been partially thinned by the local laser thinning process of the present invention. [Figure 33] is a partially enlarged schematic diagram of another specific embodiment of the lower surface of a wafer after the wafer has been partially thinned by the local laser thinning process of the present invention.

Claims

1. A wafer having a locally thinned structure, wherein the wafer comprises a plurality of grains, wherein each of the plurality of grains comprises: At least one element is formed on one of the upper surfaces of the wafer; and at least one back groove is formed by laser processing, wherein the at least one back groove has an opening on one of the lower surfaces of the wafer, and the opening of the at least one back groove occupies a region; wherein, in each of the plurality of dies, the wafer has a first desired thickness in a region occupied by a first bottom surface of one of the at least one back groove, and the region occupied by the first bottom surface is projected onto the upper surface of the wafer to form a bottom surface projection region, and one active region of the at least one element is completely located within the bottom surface projection region.

2. A wafer with a locally thinned structure as described in claim 1, wherein, In each of the plurality of grains, the area occupied by the opening of the at least one back groove is determined based on at least one feature of interest, wherein the at least one feature of interest is associated with the at least one element.

3. A wafer with a locally thinned structure as described in claim 2, wherein, In each of the plurality of grains, the area occupied by the opening of the at least one back groove is projected onto the upper surface of the wafer to form an opening projection area, and the at least one feature of interest is within or identical to the opening projection area.

4. A wafer with a locally thinned structure as described in claim 1, wherein, In each of the plurality of grains, the region occupied by the first bottom surface is determined based on at least one feature of interest.

5. A wafer with a locally thinned structure as described in claim 4, wherein, In each of the plurality of grains, the at least one feature of interest is associated with the active region of the at least one element.

6. A wafer with a locally thinned structure as described in any one of claims 2 to 5, wherein, In each of the plurality of grains, the at least one feature of interest is located within or identical to the projection region of the bottom surface.

7. A wafer with a locally thinned structure as described in any one of claims 1 to 5, wherein, In each of the plurality of grains, the area occupied by the first bottom surface of the at least one back groove is within the area occupied by the opening of the at least one back groove, or is entirely the same as the area occupied by the opening of the at least one back groove.

8. A wafer with a locally thinned structure as described in any one of claims 1 to 5, wherein, In each of the plurality of grains, the first required thickness is greater than 10 μm.

9. A wafer with a locally thinned structure as described in any one of claims 1 to 5, wherein, In each of the plurality of grains, the wafer has the first required thickness in the region occupied by the first bottom surface of one of the at least one back groove; and the wafer has a second required thickness in the region occupied by the second bottom surface of the other of the at least one back groove, wherein the first required thickness is less than, equal to or greater than the second required thickness, wherein the first required thickness is greater than 100 nm.

10. A wafer with a locally thinned structure as described in any one of claims 1 to 5, wherein, In each of the plurality of grains, the first bottom surface includes a first bottom surface and a second bottom surface, the wafer having the first required thickness in a first region occupied by the first bottom surface; and the wafer having a second required thickness in a second region occupied by the second bottom surface, wherein the first required thickness is less than, equal to or greater than the second required thickness.

11. A wafer with a locally thinned structure as described in claim 10, wherein the first required thickness is greater than 100 nm.

12. A wafer having a partially thinned structure as described in any one of claims 1 to 5, wherein each of the plurality of grains includes a plurality of sub-grains, each of the plurality of sub-grains including at least one of the at least one element formed on the upper surface of the wafer.

13. A wafer with a locally thinned structure as described in any one of claims 1 to 5, wherein, In each of the plurality of grains, one of the at least one back groove is adjacent to another of the at least one back groove; wherein a gap between an area occupied by an opening of one of the at least one back groove and an area occupied by an opening of one of the at least one back groove is greater than or equal to 10 μm.

14. A wafer having a partially thinned structure as described in any one of claims 1 to 5, wherein the wafer is made of at least one material selected from the group consisting of: glass, silicon carbide, gallium nitride, gallium nitride on silicon carbide substrate, gallium nitride on silicon substrate, silicon, germanium silicon, gallium arsenide, gallium oxide, gallium antimonide, aluminum nitride, sapphire, gallium phosphide, indium phosphide, indium arsenide, zinc selenide, and diamond.

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