JP7730664B2 - Wafer processing method - Google Patents

Description

The present invention relates to a method for processing a wafer on one side of which a post region with multiple fine posts and a peripheral excess region surrounding the post region are formed.

Wafer surfaces with multiple ICs, LSIs, and other devices formed on them, separated by planned division lines, have their back surfaces ground by a grinding machine to the desired thickness, and are then separated into individual device chips by a dicing machine for use in electrical devices such as mobile phones and personal computers.

The grinding device is equipped with at least a chuck table for holding the wafer, a grinding means having a rotatable grinding wheel with a ring-shaped arrangement of grinding stones for grinding the wafer held on the chuck table, a grinding feed means for feeding the grinding means, and a measuring means for measuring the thickness of the wafer, and is capable of processing the wafer to the desired thickness (see, for example, Patent Document 1).

JP 2009-246098 A

However, there are cases where it is necessary to grind the surface of a wafer that has a post region on one side where multiple fine posts are formed and a peripheral excess region surrounding the post region, and to accurately grind the posts to the desired height. However, a specific method for achieving such processing has not yet been established, making it difficult to implement.

The present invention was developed in consideration of the above facts, and its main technical objective is to provide a wafer processing method that can grind the surface of a wafer on one side of which a post region with multiple fine posts and a peripheral excess region surrounding the post region are formed, and accurately grind the height of the posts to the desired height.

In order to solve the above-mentioned main technical problem, according to the present invention, a method for processing a wafer having a post region in which a plurality of fine posts are formed and a peripheral excess region surrounding the post region formed on one side thereof includes a holding step of holding the other side of the wafer on a chuck table, a peripheral height detection step of detecting the height position of the surface of the peripheral excess region of the wafer held on the chuck table with a laser displacement meter, and after the peripheral height detection step, rotating the chuck table and moving a grinding wheel having grinding stones arranged in an annular shape. a grinding step in which grinding means having a rotatable wheel is brought close to a wafer held on a chuck table and the post region of the wafer is ground so that the grinding wheel passes through the center of rotation of the wafer; and a grinding termination step in which, during the grinding step, the height position of the post being ground in the post region is detected by a laser displacement meter and the grinding step is terminated when the difference between the height position of the post and the height position of the surface of the outer periphery excess region detected in the outer periphery height detection step reaches a predetermined value.

It is preferable to detect at least one of breakage and chipping of the post during the grinding completion process.

The wafer processing method of the present invention is a method for processing a wafer having a post region in which a plurality of fine posts are formed and a peripheral excess region surrounding the post region formed on one side, and includes a holding step of holding the other side of the wafer on a chuck table, a peripheral height detection step of detecting the height position of the surface of the peripheral excess region of the wafer held on the chuck table with a laser displacement meter, and after the peripheral height detection step, rotating the chuck table and bringing grinding means equipped with a rotatable grinding wheel on which grinding stones are arranged annularly close to the wafer held on the chuck table, and aligning the center of rotation of the wafer with the grinding stone. The method comprises a grinding step for grinding the post region of the wafer so that a stone passes through, and a grinding termination step for detecting the height position of the post being ground in the post region with a laser displacement meter while the grinding step is being carried out, and terminating the grinding step when the difference between the height position of the post and the height position of the surface of the outer periphery excess region detected by the outer periphery height detection step reaches a predetermined value. This solves the problem of difficulty in grinding the post height to the desired height when grinding a wafer on one side of which a post region with multiple fine posts and an outer periphery excess region surrounding the post region are formed.

1 is an overall perspective view of a grinding apparatus suitable for the wafer processing method of the present embodiment. 2A is a block diagram showing an outline of a laser displacement meter disposed in the grinding apparatus shown in FIG. 1; FIG. 2B is a conceptual diagram of laser light decomposed so that the focal positions differ for each wavelength in the vertical direction; FIG. (a) is a perspective view showing an embodiment of the holding step, and (b) is a cross-sectional view taken along the line AA in (a). FIG. 10 is a perspective view showing an embodiment of a peripheral height detection step. 10A and 10B are perspective views showing embodiments of a grinding step and a grinding finishing step. 10 is a graph based on data showing changes in post height caused by a grinding process. FIG. 10 is a perspective view of the wafer after the grinding step is completed. 10 is a graph based on data on post breakage and chipping detected in the grinding completion process.

Embodiments of a wafer processing method based on the present invention will be described in detail below with reference to the accompanying drawings.

Figure 1 shows an overall perspective view of a grinding apparatus 1 suitable for implementing this embodiment. The grinding apparatus 1 shown in Figure 1 includes a holding means 3 equipped with a chuck table 32 that holds a plate-shaped workpiece by suction, a grinding means 4 that grinds the workpiece held by suction on the chuck table 32, a laser displacement meter 5 that detects the height position of the workpiece surface, and a control means 100 that controls each operating part. The workpiece in this embodiment is a wafer 10 shown in Figure 3(a), and details will be described later.

The grinding apparatus 1 shown in FIG. 1 includes an apparatus housing 2. The apparatus housing 2 has a roughly rectangular parallelepiped main body 21 and an upright wall 22 attached to the rear end of the main body 21 and extending in the vertical direction. The holding means 3 is disposed in the main body 21, and bellows means 6a and 6b are disposed on both sides of the holding means 3 in the X-axis direction indicated by the arrow X. The main body 21 contains a moving means (not shown) for moving the chuck table 32 of the holding means 3 in the X-axis direction. Operated by the moving means, the bellows means 6a and 6b can be extended and retracted, and the unprocessed wafer 10 can be moved between a loading/unloading area at the front of the figure, where the wafer is placed on the chuck table 32, and a processing area at the back of the figure, where the wafer is processed directly below the grinding means 4. For ease of explanation, the control means 100 is shown outside the grinding apparatus 1 in FIG. 1, but in reality it is housed inside the apparatus housing 2.

The grinding means 4 is disposed on the front surface of the upright wall 22. The grinding means 4 comprises a movable base 41 and a spindle unit 42 attached to the movable base 41. The rear side of the movable base 41 engages with a pair of guide rails 221, 221 attached to the upright wall 22 of the device housing 2, and is attached so as to be slidable in the Z-axis direction (up and down) relative to the guide rails 221, 221.

The spindle unit 42 includes a spindle housing 421 supported by a support portion 413 formed integrally with the movable base 41, a rotating spindle 422 rotatably held by the spindle housing 421, and a servo motor 423 disposed as a rotational drive means for rotating the rotating spindle 422. The lower end of the rotating spindle 422 protrudes downward from the spindle housing 421, and a wheel mount 424 is disposed at the lower end. A grinding wheel 425 is attached to the underside of the wheel mount 424, and multiple grinding stones 426 are disposed in an annular shape on the underside of the grinding wheel 425 (see also Figure 5). In this embodiment, the grinding stone 426 is selected to have a roughness and material suitable for grinding posts 12 (see Figure 3) formed on the surface 10a of the wafer 10, which will be described later. For example, a vitrified grinding stone with a roughness of #4000 is selected.

The grinding device 1 shown in FIG. 1 is equipped with a grinding feed means 7 that moves the grinding means 4 in the vertical direction along the pair of guide rails 221, 221. The grinding feed means 7 is equipped with a male threaded rod 71 that is disposed on the front side of the upright wall 22 and extends in the vertical direction. The upper and lower ends of the male threaded rod 71 are rotatably supported by the upright wall 22. A pulse motor 72 is disposed at the upper end of the male threaded rod 71 as a drive source for rotating the male threaded rod 71, and the output shaft of the pulse motor 72 is connected to the male threaded rod 71. A threaded connection portion (not shown) is formed on the rear surface of the movable base 41, and a female threaded hole extending in the vertical direction is formed in the connection portion, into which the male threaded rod 71 is threaded. Such a grinding feed means 7 can lower the grinding means 4 together with the moving base 41 by rotating the pulse motor 72 forward, and can raise the grinding means 4 together with the moving base 41 by rotating the pulse motor 74 backward.

As shown in FIG. 1, the laser displacement meter 5 is disposed on the main body 21 of the device housing 2 at a position close in the Y-axis direction to the area in which the chuck table 32 moves in the X-axis direction, and is disposed on the side wall 23 formed along the X-axis direction. The laser displacement meter 5 is driven by a moving means (not shown) disposed inside the side wall 23, and is configured to be movable along a sliding groove 231 in the side wall 23 formed in the direction indicated by X1 in the figure.

The function of the laser displacement meter 5 will be explained in more detail with reference to Figure 1 and the block diagram showing an outline of the laser displacement meter 5 shown in Figure 2(a). The laser displacement meter 5 comprises a detection unit 51, a light source 52 disposed within the detection unit 51, a beam splitter 53 that transmits a portion of the laser light L0 emitted from the light source 52, a projection lens 54 (e.g., a chromatic aberration lens) that splits the laser light L0 that has passed through the beam splitter 53 into laser light beams of different wavelengths (L1-L2) and generates focal points in the vertical direction, a convex lens 55A that focuses the laser light that is reflected by the surface 10a of the workpiece (wafer 10 in the figure) and then reflected back by the beam splitter 53 and split, and a portion of the reflected light focused by the convex lens 55A that focuses the laser light reflected by the surface 10a of the workpiece (wafer 10 in the figure) and then split by the beam splitter 53. The system comprises a pinhole mask 56 with a pinhole 56a that passes only the laser light of the wavelength most focused on the surface of the workpiece (a portion of L1-L2 in the figure), a convex lens 55B that converts the laser light that passes through the pinhole 56a into a substantially parallel beam, a diffraction grating 57 that reflects the laser light emitted from the convex lens 55B in different directions for each wavelength, and a wavelength detector 58 that receives the laser light reflected by the diffraction grating 57 and includes a high-resolution light-receiving element that identifies the wavelength of the received laser light depending on the position at which it is received; the wavelength detector 58 is connected to control means 100.

The detection unit 51 has an air flow path 51a that communicates vertically. High-pressure (e.g., 0.5 MPa) air 50 is introduced into the air flow path 51a from an air supply source (not shown). The high-pressure air 50 introduced into the air flow path 51a is sprayed from the laser irradiation port 51b at the bottom end of the detection unit 51 toward the measurement unit directly below at a flow rate of, for example, 160 L/min. When the height position of the surface of the workpiece is detected using the laser displacement meter 5, the spray of high-pressure air 50 blows away dust, machining fluid, etc. adhering to the surface of the workpiece positioned directly below the detection unit 51, allowing the height position of the surface of the workpiece to be detected with high accuracy.

In this embodiment, the laser light L0 emitted from the light source 52 is, for example, white light, including not only visible light wavelengths but also a wide range of wavelengths from 350 nm to 1400 nm. The light source 52 is selected to emit light with a stable intensity across all wavelength bands. As shown in the conceptual diagram in Figure 2(b), the laser light emitted from the laser irradiation port 51b of the detection unit 51 is decomposed vertically so that the focal positions differ for each wavelength. In this embodiment, the laser light is decomposed into a range from laser light L1 with a wavelength of 350 nm to laser light L2 with a wavelength of 1400 nm, with focal positions formed over a vertical range of 7 mm (7000 μm). With this configuration, if the surface 10a of the wafer 10 is at position Z1 shown by the solid line in Fig. 2(b), it will coincide with the focal position of the laser light L1 (wavelength 350 nm), and light with a wavelength of 350 nm will be mainly reflected from the surface 10a of the wafer 10. If the surface 10a' of the wafer 10' is at position Z2 below shown by the dashed-dotted line in Fig. 2(b), it will coincide with the focal position of the laser light L2 (wavelength 1400 nm), and light with a wavelength of 1400 nm will be mainly reflected from the surface 10a' of the wafer 10'. Furthermore, if the surface 10a of the wafer 10 is located somewhere between positions Z1 and Z2, laser light of any wavelength between 350 nm and 1400 nm corresponding to that position will mainly be reflected. Furthermore, by providing a pinhole mask 56 with the pinholes 56a described above, only the primarily reflected wavelength is efficiently guided to the diffraction grating 57, and the laser light is irradiated at a position corresponding to the wavelength of the light receiving element in the wavelength detector 58, allowing the wavelength of the laser light primarily reflected by the workpiece to be accurately identified.

The wavelength signal of the wavelength identified and output by the wavelength detector 58 is transmitted to the control means 100, where it is compared with Table T, pre-stored in the control means 100, in the comparison unit 110 configured in the control means 100 based on the wavelength. As shown on the right side of Figure 2(a), Table T identifies the wavelength of the light detected by the wavelength detector 58 within the range of 350 nm to 1400 nm, making it possible to determine the height position relative to the focal position of the laser light with a wavelength of 350 nm as the reference (0 mm). In this embodiment, the wavelength detector 58 is composed of a high-resolution light-receiving element, and by comparing it with Table T, it is possible to accurately determine the height position of the workpiece surface in 0.5 μm increments. In addition to the comparison unit 110, the control means 100 also includes a grinding completion determination unit 120 for executing the grinding completion process. The function and operation of the grinding completion determination unit 120 will be described later.

The grinding apparatus 1 suitable for this embodiment has a configuration generally as described above, and the wafer processing method performed using the grinding apparatus 1 will be described below.

As shown in FIG. 3(a), the workpiece in this embodiment is a circular silicon substrate wafer 10, e.g., 150 mm in diameter. One surface of the wafer 10, i.e., the central portion of the surface 10a shown in the figure, is formed with a post region 14, in which multiple fine posts 12 made of nickel are formed, and an annular peripheral excess region 16 surrounding the post region 14. The diameter of the post region 14 is, e.g., 138 mm, and the width of the peripheral excess region 16 is 6 mm. As shown in FIG. 3(a), which shows an enlarged portion of the post region 14, the posts 12 are generally cylindrical, with a diameter of 0.5 mm, the spacing between adjacent posts 12 being 0.5 mm, and the height before grinding being 80 μm. As can be seen from Figure 3(b), which shows the A-A cross section of Figure 3(a), the height of the posts 12 before processing (80 μm) is based on the height of the peripheral excess region 16, and in this embodiment, the height of these posts 12 is ground to the desired height (25 μm). The other surface (back surface 10b) of the wafer 10 does not have the above-mentioned posts 12 and is a flat surface. The dashed line 11 that separates the post region 14 and the peripheral excess region 16 on the front surface 10a of the wafer 10 shown in Figure 3(a) is added for convenience of explanation and is not actually shown.

When carrying out the wafer processing method of this embodiment, as shown in FIG. 3(a), the back surface 10b of the wafer 10 is placed on the chuck table 32, and the suction means (not shown) is activated to suction-hold the wafer 10 to the chuck table 32 (holding process).

Next, the above-mentioned moving means is activated to move the chuck table 32 in the X-axis direction, and as shown in FIG. 4, the peripheral excess region 16 of the wafer 10 is positioned directly below the detection unit 51 of the laser displacement meter 5. As described above, the laser displacement meter 5 can also be moved in the X-axis direction within the main body 21 of the apparatus housing 2. Therefore, the chuck table 32 can be moved to the processing area directly below the grinding means 4, and the position of the laser displacement meter 5 can be fine-tuned to position the peripheral excess region 16 of the wafer 10 directly below the detection unit 51 of the laser displacement meter 5. Next, the laser displacement meter 5 is activated to spray high-pressure air 50 from the laser irradiation port 51b of the detection unit 51, and to irradiate laser light L0 from the light source 52, and the wavelength λ1 of the laser light reflected by the surface 10a of the peripheral excess region 16 of the wafer 10 held on the chuck table 32 is detected. In this embodiment, the position of the detection unit 51 of the laser displacement meter 5 is adjusted in advance so that the surface 10a of the wafer 10 is positioned between the focal position of the 350 nm wavelength laser light L1 and the focal position of the 1400 nm wavelength laser light L2, and the wavelength λ1 is detected at approximately the midpoint between 350 nm and 1400 nm. When detecting the height position of the surface 10a of the peripheral excess region 16, the chuck table 32 may be rotated in the direction indicated by arrow R1 in FIG. 4, and the average value of the wavelengths of the laser light reflected at multiple positions may be calculated as the wavelength λ1.

Here, the wavelength λ1 (e.g., 735.1 nm) detected by the wavelength detector 58 as described above is transmitted to the comparison unit 110 of the control means 100, and by comparing this wavelength λ1 with table T, it is determined that the height position of the surface of the outer periphery excess region 16 is Z3 (e.g., 3675.5 μm) (outer periphery height detection process). The value of Z3 is stored in the grinding completion determination unit 120 disposed in the control means 100. Note that, as described above, the height position Z3 obtained by comparing the detected wavelength λ1 with table T is the distance from a position based on the focal position of the laser light L1 having a wavelength of 350 nm, and this reference position is set to be sufficiently above the surface 10a of the wafer 10.

Next, the above-mentioned moving means is operated to move the chuck table 32 to the processing area directly below the grinding means 4, and the center of rotation of the chuck table 32 is positioned at a position where the grinding wheel 426 of the grinding means 4 passes, as shown in Figure 5. Next, the rotating spindle 422 of the grinding means 4 is rotated in the direction indicated by arrow R2 at a predetermined rotational speed (e.g., 2000 rpm), and the rotational drive means (not shown) is operated to rotate the chuck table 32 in the direction indicated by arrow R3 at a predetermined rotational speed (e.g., 100 rpm). Next, the grinding feed means 7 is operated to lower the grinding means 4 in the direction indicated by arrow R4, bringing it closer to the surface 10a of the wafer 10 held on the chuck table 32. While supplying a processing fluid (grinding water) (not shown), the grinding stone 426 arranged on the underside of the grinding wheel 425 is brought into contact with the post regions 14 on the surface 10a of the wafer 10, and the post regions 14 on the surface 10a of the wafer 10 are ground at a predetermined lowering speed (e.g., 0.5 μm/sec) (grinding process).

When the above-described grinding process is performed, the grinding completion process described below is also performed in parallel. More specifically, as shown in FIG. 5, the detection unit 51 of the laser displacement meter 5 is positioned above the post region 14 of the wafer 10 held on the chuck table 32. If the chuck table 32 has been moved near the processing area when the above-described outer periphery height detection process is performed, it is only necessary to fine-tune the position of the detection unit 51 of the laser displacement meter 5. Next, high-pressure air 50 is sprayed from the laser irradiation port 51b of the detection unit 51 toward the post region 14, and laser light L0 is irradiated from the light source 52. When the grinding process is being performed, processing fluid (grinding water) is supplied onto the front surface 10a of the wafer 10, and the processing fluid containing grinding debris overflows outward from the grinding wheel 425, covering the front surface 10a of the wafer 10. However, as described above, high-pressure air 50 is sprayed from the laser irradiation port 51b of the detection unit 51, so the machining fluid is removed from the predetermined position (on the circumference indicated by the dashed line 18) that serves as the measurement area of the post region 14 where the laser light is irradiated. Then, while the chuck table 32 makes one rotation, the wavelength λ2 of the laser light reflected at the predetermined position 18 of the post region 14 is detected by the wavelength detector 58.

As described with reference to FIG. 3, the post region 14 is formed with multiple minute posts 12. Therefore, the wavelength detected by the wavelength detector 58 repeatedly varies between the wavelength λ1 of the laser light reflected at the height of the surface 10a where the posts 12 are located (the same height as the peripheral excess region 16) and the wavelength λ2 (λ2 < λ1) of the laser light reflected at the top of the post 12. If the wavelength λ2 is, for example, 719.1 nm before the grinding process is performed or immediately after the grinding process is started, the height position Z4 of the post 12 before or at the beginning of grinding is detected to be, for example, 3595.5 μm by comparing the wavelength λ2 (719.1 nm) with the table T. The value of Z4 is constantly stored in the grinding completion determination unit 120, and the specific height of the post 12 is detected by repeatedly calculating the difference between Z3 and Z4. The height data of the post 12 detected based on the wavelength detected in this way is shown in a graph, for example, as shown on the left side of Figure 6.

While the grinding process is being performed, the grinding completion determination unit 120 repeatedly calculates the difference between Z3 and Z4, for example, at a frequency of 10 kHz (10,000 times per second), to determine whether the height of the post 12 has reached a predetermined value (25 μm in this embodiment). If the height of the post 12 has not reached the predetermined value (25 μm), the grinding process continues. As the grinding process progresses and the post 12 is ground, the wavelength λ2 of the laser light reflected from the top of the post 12 becomes 730.1 nm, and the height position Z4 detected by comparing the wavelength λ2 with table T becomes 3650.5 μm. As a result, the difference between the height positions Z3 (3675.5 μm) and Z4 (3650.5 μm) of the surface 10a of the peripheral excess region 16 is determined to be 25 μm, as can be seen from the graph shown on the right side of Figure 6. Based on this determination, the control means 100 issues an instruction to end the grinding process. As a result, the wafer 10 is brought to the desired state as shown in Figure 7, and the grinding process and grinding completion process are completed.

During the grinding completion process, the height of the post region 14 can be displayed as a graph, as shown in FIG. 8, based on the wavelength detected by the wavelength detector 58. This graph provides a detailed view of the surface 10a of the wafer 10 and the shape of the posts 12. By examining the shape of the graph (16C, 16D) shown in FIG. 8 during or after the grinding process is completed, it is possible to detect at least one of the broken posts 12, as shown in A, or the chipped posts 12, as shown in B. Such detection can be performed by the operator managing the grinding apparatus 1 visually inspecting the graph displayed on a monitor (not shown) connected to the control means 100. Automatic detection (check process) is also possible using an image processing program stored in the control means 100. The inclusion of such a check process not only contributes to wafer quality control when implementing the wafer processing method described above, but also allows for the rapid determination of appropriate processing conditions for the wafer processing method to prevent broken or chipped posts 12.

This embodiment solves the problem of difficulty in grinding the posts to the desired height when grinding a wafer that has a post region with multiple fine posts and a peripheral excess region surrounding the post region formed on one side.

1: Grinding device 2: Device housing 21: Main body 22: Upright wall 3: Holding means 32: Chuck table 4: Grinding means 41: Moving base 42: Spindle unit 421: Spindle housing 422: Rotating spindle 423: Servo motor 424: Wheel mount 425: Grinding wheel 426: Grinding stone 5: Laser displacement meter 51: Detection unit 51a: Air flow path 51b: Laser irradiation port 52: Light source 53: Beam splitter 54: Projection lenses 55A, 55B: Convex lens 56: Pinhole mask 56a: Pinhole 57: Diffraction grating 58: Wavelength detector 6a, 6b: Bellows means 7: Grinding feed means 100: Control means 110: Collation unit 120: Grinding completion determination unit

Claims (2)

A method for processing a wafer having a post region in which a plurality of fine posts are formed and a peripheral excess region surrounding the post region formed on one surface, comprising:
a holding step of holding the other surface of the wafer on a chuck table;
a peripheral height detecting step of detecting the height position of the surface of the peripheral excess region of the wafer held on the chuck table by a laser displacement meter;
a grinding step in which , after the outer periphery height detection step has been carried out, the chuck table is rotated, and a grinding means having a rotatable grinding wheel with grinding stones arranged annularly is brought close to the wafer held on the chuck table, and the post region of the wafer is ground so that the grinding stone passes through the center of rotation of the wafer;
a grinding termination step in which, during the grinding step, a height position of the post to be ground in the post region is detected by a laser displacement meter, and the grinding step is terminated when a difference between the height position of the post and the height position of the surface of the outer periphery excess region detected by the outer periphery height detection step reaches a predetermined value;
A wafer processing method comprising the steps of: The wafer processing method according to claim 1, wherein at least one of breakage and chipping of the post is detected during the grinding completion step.