Chip manufacturing method

Abstract

To provide a manufacturing method for a chip capable of suppressing the occurrence of problems when dividing a wafer to which a tape is pasted on the back surface side where a metal film is provided to manufacture a chip.SOLUTION: An outer circumferential area of a metal film and the back side of an outer circumferential area of a substrate are removed. Thereby, the outer circumferential area of the substrate is exposed and an expose surface where a portion close to a wafer surface is located outside than a portion far away from the wafer surface is formed on the back side of the outer circumferential area of the wafer. Thereby, when a tape is pasted to the back side of the wafer, it is possible to eliminate or narrow a gap between the tape and the outer circumferential area of the wafer. As a result, the occurrence of problems when the wafer is divided to manufacture a chip can be suppressed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a chip manufacturing method for manufacturing chips by dividing a wafer along planned dividing lines set in a grid pattern. [Background technology]

[0002] Vertical power device chips are generally manufactured by dividing a wafer along dividing lines set in a grid pattern. The wafer has, for example, a disk-shaped substrate made of a semiconductor material, and an impurity region doped with impurities formed on the surface side of the substrate.

[0003] Furthermore, metal films that function as electrodes are provided on both sides of the wafer. Specifically, an electrode pattern including a plurality of patterned metal films is provided on the front side of each of the plurality of regions of the wafer divided by the planned dividing lines, and a metal film that covers the entire back surface of the substrate is provided on the back side of the wafer.

[0004] When dividing such a wafer along the dividing lines, it is necessary to divide the substrate together with the metal film formed on the backside of the substrate. However, the method suitable for dividing a substrate made of a semiconductor material is not necessarily the same as the method suitable for dividing a metal film. Therefore, dividing both at the same time using the same method may result in a deterioration in processing quality.

[0005] In view of this, a method has been proposed in which, prior to dividing the substrate along the dividing lines, a region of the metal film along the dividing lines is removed (see, for example, Patent Document 1). Specifically, in this method, a rotating annular cutting blade is first brought into contact with the metal film provided on the back surface of the substrate along the outer periphery of the wafer. This removes part of the metal film and part of the substrate, exposing the back surface side of the outer periphery of the substrate.

[0006] Next, the position of the planned dividing line is identified and alignment (alignment of the wafer and the cutting blade) is performed by referring to an image of the front side of the wafer's peripheral region formed by imaging from the back side of the wafer (the back side of the substrate) using light of a wavelength that transmits through the substrate. Next, the rotating annular cutting blade is brought into contact with the area of ​​the metal film along the planned dividing line. This removes the area of ​​the metal film on the back side of the substrate that is along the planned dividing line.

[0007] Next, the back side of the wafer is attached to tape that covers the openings in the annular frame, thereby forming a work unit in which the wafer and the annular frame are integrated. Next, a mask with openings formed in areas along the planned division lines is placed on the front side of the substrate.

[0008] Next, with the atmosphere of the chamber in which the work unit is placed evacuated, plasma etching is performed on the substrate from the front side through the mask, which allows the wafer to be divided into chips without deteriorating the processing quality when dividing the wafer along the planned division lines. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2020-113614 Summary of the Invention [Problem to be solved by the invention]

[0010] In the above-described method, the peripheral region of the metal film and the back side of the peripheral region of the substrate are removed to expose the back side of the peripheral region of the substrate. As a result, a step is formed on the back side of the peripheral region of the wafer. Then, in the above-described method, tape is attached to the back side of the wafer to form a work unit, and then plasma etching is performed on the substrate included in this work unit.

[0011] However, when applying tape to the backside of the wafer, there is a risk that the tape will not adhere to the wafer due to the step formed on the backside of the peripheral region, which means that a work unit may be formed with a gap between the tape and the peripheral region of the wafer.

[0012] When dividing a wafer using plasma etching, the atmosphere in the chamber where the work unit is placed must be evacuated, and if there is a gap between the tape and the outer periphery of the wafer, the air in the gap may expand, causing the tape to peel off from the outer periphery of the wafer.

[0013] Furthermore, in wafers with such gaps, the tape does not adhere sufficiently to the outer periphery of the wafer, which can cause problems even when the wafer is divided by methods other than plasma etching.

[0014] For example, when a wafer is divided using an annular cutting blade, the wafer tends to move when it comes into contact with the rotating cutting blade during division, which can result in chipping at the edges of the chips produced by dividing the wafer.

[0015] Furthermore, when an altered layer is formed inside a wafer using a laser beam and then an external force is applied to the wafer to separate the wafer using the altered layer as the separation starting point, chips may fly off when the external force is applied to the wafer. Specifically, after the wafer is separated, chips including part of the outer peripheral region of the wafer may peel off from the tape and fly out.

[0016] Furthermore, when laser ablation is used to divide a wafer, the wafer is heated by a laser beam irradiated onto the wafer to cause laser ablation, and therefore, if there is a gap between the tape and the outer peripheral region of the wafer, the air in the gap may expand, causing the tape to peel off from the outer peripheral region of the wafer.

[0017] In view of the above, an object of the present invention is to provide a chip manufacturing method that can suppress the occurrence of problems when manufacturing chips by dividing a wafer having tape attached to the back side on which a metal film is formed. [Means for solving the problem]

[0018] According to the present invention, a method for manufacturing chips by dividing a wafer including a substrate and a metal film provided so as to cover the back surface of the substrate along planned dividing lines set in a grid pattern, the method comprising the steps of: a protective member adhering step of adhering a protective member to a front surface of the wafer that is the surface opposite to the metal film; an exposed surface forming step of removing a peripheral region of the metal film and the back surface side of the peripheral region of the substrate while the wafer is held via the protective member after the protective member adhering step has been performed, thereby exposing the peripheral region of the substrate and forming an exposed surface on the back surface side of the peripheral region of the wafer in which a portion of the wafer closer to the front surface is outer than a portion of the wafer further from the front surface; and an image of the peripheral region of the wafer formed by imaging the back surface of the wafer using light of a wavelength that transmits the substrate after the exposed surface forming step has been performed. a metal film removal step of removing the area of ​​the metal film along the planned dividing line while the wafer is held via the protective member after the alignment step has been performed; a work unit formation step of forming a work unit in which the wafer and the annular frame are integrated by removing the protective member from the front surface of the wafer and adhering the back surface of the wafer to tape that covers an opening in the annular frame after the metal film removal step has been performed; and a division step of dividing the wafer along the planned dividing line while the wafer is held via the tape after the work unit formation step has been performed.

[0019] In the dividing step, it is preferable to divide the wafer by placing a mask on the surface of the wafer, the mask having openings formed in areas along the intended dividing lines, and then performing plasma etching on the substrate through the mask.

[0020] Alternatively, in the dividing step, it is preferable to divide the wafer by bringing a rotating annular cutting blade for dividing the substrate into contact with the substrate from the front surface side along the planned dividing lines.

[0021] Alternatively, in the dividing step, it is preferable to form an altered layer inside the substrate by irradiating the substrate from the surface side along the intended dividing line with a laser beam of a wavelength that passes through the substrate so that the focal point of the laser beam is positioned inside the substrate, and then apply an external force to the substrate to divide the wafer using the altered layer as the dividing starting point.

[0022] Alternatively, in the dividing step, it is preferable to divide the wafer by irradiating the substrate from the front surface side along the dividing lines with a laser beam having a wavelength that is absorbed by the substrate.

[0023] Furthermore, in the metal film removing step, it is preferable to remove the region of the metal film along the planned dividing line by bringing a rotating annular cutting blade for removing the metal film into contact with the metal film.

[0024] Alternatively, in the metal film removing step, it is preferable to remove the region of the metal film along the intended dividing line by irradiating the metal film with a laser beam having a wavelength that is absorbed by the metal film.

[0025] In addition, in the exposed surface forming step, it is preferable to remove the outer peripheral region of the metal film and the back side of the outer peripheral region of the substrate by contacting a rotating annular exposed surface forming cutting blade with the metal film and the substrate. Furthermore, in the work unit forming step, it is preferable that the exposed surface and the metal film are attached to the tape. [Effects of the Invention]

[0026] In the present invention, prior to forming the work unit, the peripheral region of the metal film and the back side of the peripheral region of the substrate are removed to expose the peripheral region of the substrate, and an exposed surface is formed on the back side of the peripheral region of the wafer such that the portion closer to the front side of the wafer is more outward than the portion further away. This eliminates or narrows the gap between the tape and the peripheral region of the wafer when applying tape to the back side of the wafer. As a result, problems occurring when dividing the wafer into chips can be suppressed. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1(A) is a top view that schematically shows an example of a wafer, and FIG. 1(B) is a side view that schematically shows an example of a wafer. [Figure 2] FIG. 2 is a flow chart showing a schematic example of a method for manufacturing a chip. [Figure 3] FIG. 3(A) is a side view that schematically shows the state of the protective member adhering step, and FIG. 3(B) is a side view that schematically shows the wafer after the protective member adhering step. [Figure 4] Figure 4(A) is a side view that schematically shows how the back side of the peripheral region of the wafer is imaged, Figure 4(B) is a partially cross-sectional side view that schematically shows how the exposed surface formation step is performed, and Figure 4(C) is a side view that schematically shows the wafer after the exposed surface formation step. [Figure 5] FIG. 5(A) is a side view that schematically shows how the surface side of the outer peripheral region of the wafer is imaged, and FIG. 5(B) is a partially cross-sectional side view that schematically shows how the alignment step is performed. [Figure 6] FIG. 6(A) is a partial cross-sectional side view that schematically shows the state of the metal film removing step, and FIG. 6(B) is a side view that schematically shows the wafer after the metal film removing step. [Figure 7] FIG. 7(A) is a partially cross-sectional side view that schematically shows the work unit forming step, and FIG. 7(B) is a partially cross-sectional side view that schematically shows an example of a work unit. [Figure 8]FIG. 8 is a partial cross-sectional side view that schematically shows a work unit including a divided wafer. [Figure 9] 9(A) and 9(B) are side views schematically showing modified examples of the wafer after the exposed surface forming step. [Figure 10] 10(A), 10(B), and 10(C) are side views schematically showing modified examples of the exposed surface forming step. DETAILED DESCRIPTION OF THE INVENTION

[0028] Embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 1(A) is a top view schematically showing an example of a wafer, and Fig. 1(B) is a side view schematically showing the example of a wafer. The wafer 11 shown in Fig. 1(A) and Fig. 1(B) has a substrate 13. This substrate 13 is made of, for example, a semiconductor material (e.g., silicon (Si)) that reflects visible light and transmits infrared light.

[0029] The wafer 11 is composed of an area used for device fabrication (device area) and a peripheral surplus area surrounding the device area. The peripheral surplus area is an area that cannot be used for device fabrication because it is not possible to ensure the surface area or flatness required for device fabrication.

[0030] Furthermore, the device region of the wafer 11 is divided into a plurality of regions by planned division lines set in a grid pattern, and an electrode pattern 15 is provided on the front surface side of each region (surface 13a of the substrate 13). For convenience, this electrode pattern 15 is shown by a rectangular solid line in Figures 1(A) and 1(B), etc., but it may include, for example, a plurality of electrodes each patterned into a desired shape.

[0031] The peripheral excess area of ​​the wafer 11 is also divided into a plurality of areas by dividing lines set in a grid pattern, and a dummy pattern 17 is provided on the surface side of each area. For convenience, this dummy pattern 17 is shown by a rectangular parallelepiped dotted line in Figures 1(A) and 1(B), but it has the same structure as the electrode pattern 15, except for, for example, a portion where an electrode cannot be provided because the substrate 13 is not present.

[0032] In addition, a metal film 19 is provided on the back surface side of the wafer 11 so as to cover the entire back surface 13b of the substrate 13. Then, by dividing the wafer 11 along the planned dividing lines, vertically structured power device chips each including a part of the substrate 13, the electrode pattern 15, and a part of the metal film 19 are manufactured from the device region of the wafer 11.

[0033] There are no limitations on the material, shape, structure, size, etc. of the substrate 13. The substrate 13 may be made of a semiconductor material other than silicon (e.g., silicon carbide (SiC) or gallium nitride (GaN)). Similarly, there are no limitations on the type, number, shape, structure, size, arrangement, etc. of the chips manufactured from the wafer 11.

[0034] 2 is a flowchart schematically illustrating an example of a method for manufacturing chips from wafer 11. In this method, first, a protective member is attached to the front surface of wafer 11 including substrate 13 and metal film 19 provided so as to cover rear surface 13b of substrate 13 (protective member attachment step: S1).

[0035] Fig. 3(A) is a side view schematically showing the protective member attaching step (S1), and Fig. 3(B) is a side view schematically showing the wafer 11 after the protective member attaching step (S1). The protective member 21 shown in Fig. 3(A) and Fig. 3(B) has, for example, a flexible film-like tape substrate and an adhesive layer (glue layer) provided on one surface of the tape substrate.

[0036] Specifically, the tape substrate is made of polyolefin (PO), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polystyrene (PS), or the like. The adhesive layer is made of ultraviolet-curable silicone rubber, an acrylic material, an epoxy material, or the like. The adhesive layer side of the protective member 21 is pressed against the front surface side of the wafer 11 (the front surface 13a side of the substrate 13), thereby adhering the protective member 21 to the front surface of the wafer 11.

[0037] Next, the peripheral region of the metal film 19 and the back surface 13b side of the peripheral region of the substrate 13 are removed to expose the peripheral region of the substrate 13 and form an exposed surface on the back surface side of the peripheral region of the wafer 11 in which the portion closer to the surface of the wafer 11 is outer than the portion further away (exposed surface forming step: S2).

[0038] Fig. 4(A) is a side view schematically showing how the backside of the peripheral region of wafer 11 is imaged, Fig. 4(B) is a side view schematically showing the exposed surface forming step (S2), and Fig. 4(C) is a side view schematically showing wafer 11 after the exposed surface forming step. Note that the X-axis direction (left-right direction) and the Y-axis direction (front-back direction) shown in Fig. 4(A) and Fig. 4(B) are directions perpendicular to each other on a horizontal plane, and the Z-axis direction (up-down direction) is a direction (vertical direction) perpendicular to the X-axis direction and the Y-axis direction, respectively.

[0039] The exposed surface forming step (S2) is performed, for example, by a cutting device 2. The cutting device 2 has a cylindrical chuck table 4. The chuck table 4 is connected to a rotation mechanism (not shown). The chuck table 4 has a generally horizontal upper surface. When the rotation mechanism operates, the chuck table 4 rotates around a rotation axis that passes through the center of the upper surface and is perpendicular to the upper surface.

[0040] A cylindrical recess is formed in the upper part of the chuck table 4, and a porous plate is fixed in this recess. This porous plate is in communication with a suction source (not shown), such as a vacuum pump, via a communication passage or the like provided inside the chuck table 4. When this suction source is activated, negative pressure is generated in the space near the upper surface of the chuck table 4.

[0041] Therefore, the upper surface of the chuck table 4 can function as a holding surface for holding the wafer 11. For example, by operating the suction source with the wafer 11 placed on the upper surface of the chuck table 4 via the protective member 21, the wafer 11 is held by the chuck table 4.

[0042] Furthermore, the chuck table 4 is connected to an X-axis direction movement mechanism (not shown). The X-axis direction movement mechanism includes, for example, a ball screw. When this X-axis direction movement mechanism operates, the chuck table 4 moves along the X-axis direction.

[0043] An imaging unit 6 is provided above the chuck table 4. The imaging unit 6 has a visible light camera 8 and an infrared camera 10 provided adjacent to each other. The visible light camera 8 is a camera that uses visible light to capture an image of the upper surface of the chuck table 4, and the infrared camera 10 is a camera that uses infrared light to capture an image of the upper surface of the chuck table 4.

[0044] The visible light camera 8 includes, for example, a light source such as an LED (Light Emitting Diode) that emits visible light, an objective lens, and an imaging element such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal Oxide Semiconductor) image sensor. The infrared camera 10 also includes, for example, a light source that emits infrared light, an objective lens, and an imaging element.

[0045] Furthermore, the imaging unit 6 is connected to a Z-axis direction moving mechanism (not shown) and a Y-axis direction moving mechanism (not shown) that can operate independently of each other. Each of the Z-axis direction moving mechanism and the Y-axis direction moving mechanism includes, for example, a ball screw. When the Z-axis direction moving mechanism operates, the imaging unit 6 moves along the Z-axis direction, and when the Y-axis direction moving mechanism operates, the imaging unit 6 moves along the Y-axis direction.

[0046] A cutting unit 12 is also provided above the chuck table 4. This cutting unit 12 has a spindle 14 extending along the Y-axis direction. A rotation drive source (not shown) such as a motor is connected to the base of this spindle 14, and a replaceable annular cutting blade 16 for forming an exposed surface is attached to the tip of the spindle 14.

[0047] The exposed surface forming cutting blade 16 is a hub-type cutting blade that is configured by integrating an annular base made of, for example, metal, with an annular cutting edge that follows the outer periphery of the base. The cutting edge of the hub-type cutting blade is obtained by fixing abrasive grains made of, for example, diamond or cubic boron nitride (cBN) with a bonding material such as nickel.

[0048] Furthermore, a washer-type cutting blade consisting only of an annular cutting edge may be applied as the exposed surface forming cutting blade 16. A washer-type cutting blade (cutting edge) is obtained by fixing abrasive grains made of, for example, diamond or cBN with a bonding material such as resin.

[0049] Furthermore, the cutting edge of the exposed surface-forming cutting blade 16 has a shape such that the outer surface on the side closer to the center of the chuck table 4 (front side) corresponds to the side of a truncated cone in a plan view, and the outer surface on the side farther from the center (rear side) corresponds to the side of a cylinder. That is, the outer diameter of the front side of the cutting edge decreases toward the front end, and the outer diameter is constant at the rear side of the cutting edge. The inclination angle of the front lower end of the cutting edge relative to the holding surface of the chuck table 4 is, for example, 45°.

[0050] The cutting unit 12 is also connected to a Z-axis direction moving mechanism (not shown) and a Y-axis direction moving mechanism (not shown), which can operate independently of each other. Each of the Z-axis direction moving mechanism and the Y-axis direction moving mechanism includes, for example, a ball screw. When the Z-axis direction moving mechanism operates, the cutting unit 12 moves along the Z-axis direction, and when the Y-axis direction moving mechanism operates, the cutting unit 12 moves along the Y-axis direction.

[0051] The Z-axis direction moving mechanism and the Y-axis direction moving mechanism for moving the cutting unit 12 may move the imaging unit 6 together with the cutting unit 12. In other words, the Z-axis direction moving mechanism and the Y-axis direction moving mechanism may move a structure in which the cutting unit 12 and the imaging unit 6 are integrated.

[0052] When the exposed surface forming step (S2) is performed in the cutting device 2, first, the wafer 11 is placed on the holding surface of the chuck table 4 via the protective member 21 so that the center of the wafer 11 overlaps the center of the chuck table 4 in a plan view. Next, the suction source communicating with the porous plate of the chuck table 4 is operated. As a result, the wafer 11 is held by the chuck table 4.

[0053] Next, the peripheral region of the wafer 11 is imaged using the visible light camera 8 (see FIG. 4(A)). At this time, the visible light irradiated from the visible light camera 8 is reflected by the substrate 13 of the wafer 11 and the metal film 19 provided on the back surface 13b of the substrate 13, so that an image of the back surface side of the peripheral region of the wafer 11 is formed.

[0054] Next, referring to this image, the chuck table 4 and / or cutting unit 12 are moved so that the center of the wafer 11 is positioned in the Y-axis direction when viewed from the spindle 14 in a plan view, and the cutting blade 16 for forming the exposed surface is positioned directly above the outer peripheral region of the wafer 11.

[0055] Next, while rotating the exposed surface forming cutting blade 16 via the spindle 14, the cutting unit 12 is lowered so that the front lower end of the exposed surface forming cutting blade 16 is positioned at a predetermined height where it contacts the outer peripheral region of the wafer 11. Next, while keeping the exposed surface forming cutting blade 16 rotating, the chuck table 4 holding the wafer 11 is rotated at least once (see FIG. 4(B)).

[0056] This removes the peripheral region of the metal film 19 and the back surface 13b side of the peripheral region of the substrate 13, exposing the peripheral region of the substrate 13. Also, on the back surface side of the peripheral region of the wafer 11, a first exposed surface 11a is formed, which is inclined so that the portion closer to the surface of the wafer 11 is located further outward than the portion farther away, and a generally flat second exposed surface 11b is formed outside the first exposed surface (see FIG. 4(C)).

[0057] This first exposed surface 11a is a surface formed by cutting with the front side of the exposed surface forming cutting blade 16. The first exposed surface 11a has a shape corresponding to the side surface of a truncated cone whose upper bottom surface is located on the back surface of the wafer 11 and whose lower bottom surface is located inside the wafer 11.

[0058] The second exposed surface 11b is a surface formed by cutting with the rear side of the exposed surface forming cutting blade 16. The second exposed surface 11b has an annular shape that spreads outward in the radial direction of the wafer 11 from the lower bottom surface of the truncated cone.

[0059] Next, by referring to an image of the front side of the peripheral region of the wafer 11, the position of the planned dividing line is identified and alignment (alignment of the wafer 11 with the cutting blade) is performed (alignment step: S3), and then the area of ​​the metal film 19 along the planned dividing line is removed (metal film removal step: S4).

[0060] Fig. 5(A) is a side view showing a schematic image of the front surface of the peripheral region of wafer 11, and Fig. 5(B) is a partial cross-sectional side view showing a schematic image of the alignment step (S3). Fig. 6(A) is a partial cross-sectional side view showing a schematic image of the metal film removal step (S4), and Fig. 6(B) is a side view showing a schematic image of wafer 11 after the metal film removal step (S4).

[0061] The alignment step (S3) and the metal film removal step (S4) are performed, for example, by the above-described cutting device 2. However, the cutting blade attached to the tip of the spindle 14 is replaced from the exposed surface forming cutting blade 16 to the metal film removing cutting blade 18 prior to the alignment step (S3).

[0062] This metal film removing cutting blade 18 is a hub-type or washer-type cutting blade, similar to the exposed surface forming cutting blade 16. However, the cutting edge of the metal film removing cutting blade 18 has a cylindrical shape with a roughly constant outer diameter from the front end to the rear end, and its thickness (length along the Y-axis direction) is shorter than the thickness of the exposed surface forming cutting blade 16 and the width of the planned dividing line of the wafer 11.

[0063] When the alignment step (S3) is performed in the cutting device 2, first, an image of the peripheral region of the wafer 11 is captured using the infrared camera 10 (see FIG. 5(A)). At this time, infrared rays emitted from the infrared camera 10 pass through the second exposed surface 11b of the wafer 11 and penetrate the substrate 13, so that an image of the front side of the peripheral region of the wafer 11 is formed.

[0064] Next, by referring to this image, the positions of the planned dividing lines of the wafer 11 are identified. Specifically, the peripheral excess area of ​​the wafer 11 is divided into a plurality of areas by the planned dividing lines, and a dummy pattern 17 is provided on the front surface side of each area. In this case, this image includes a plurality of dummy patterns 17 that are provided discretely. Therefore, by referring to this image, the positions between adjacent dummy patterns 17 can be identified as the positions of the planned dividing lines.

[0065] Next, alignment (alignment of the wafer 11 with the cutting blade 18 for removing the metal film) is performed (see FIG. 5(B)). Specifically, first, the chuck table 4 holding the wafer 11 is rotated so that the linearly extending portion of the planned dividing line of the wafer 11 is parallel to the X-axis direction. Then, the chuck table 4 and / or the cutting unit 12 are moved so that this portion is positioned in the X-axis direction when viewed from the cutting blade 18 for removing the metal film in a plan view.

[0066] Next, the cutting unit 12 is lowered so that the lower end of the metal film removal cutting blade 18 is positioned lower than the back surface 13b of the substrate 13 and higher than the front surface 13a thereof. Next, while rotating the metal film removal cutting blade 18 via the spindle 14, the chuck table 4 is moved so that the wafer 11 is cut from one end to the other in the X-axis direction by the metal film removal cutting blade 18 (see FIG. 6(A)).

[0067] This removes the area along the division lines of the metal film 19 of the wafer 11 and the back side of the area along the division lines of the substrate 13. As a result, linear grooves are formed on the back side of the wafer 11. Next, the same operation is repeated to form lattice-shaped grooves 11c on the back side of the wafer 11 (see FIG. 6(B)).

[0068] Next, the back side of the wafer 11 is attached to tape that covers the opening of the annular frame, thereby forming a work unit in which the wafer 11 and the annular frame are integrated (work unit forming step: S5). Fig. 7(A) is a partially cross-sectional side view that schematically shows the work unit forming step (S5), and Fig. 7(B) is a partially cross-sectional side view that schematically shows an example of a work unit formed in the work unit forming step (S5).

[0069] The annular frame 23 shown in Figures 7(A) and 7(B) is made of, for example, a metal material. Similarly to the protective member 21, the tape 25 shown in Figures 7(A) and 7(B) has a flexible film-like tape substrate and an adhesive layer (glue layer) provided on one surface of the tape substrate. Furthermore, the adhesive layer side of the outer peripheral region of the tape 25 is adhered to the annular frame 23. This closes the opening of the annular frame 23.

[0070] Then, in the work unit formation step (S5), the protective member 21 attached to the front side of the wafer 11 is removed, and the back side of the wafer 11 is pressed against the adhesive layer side of the central region of the tape 25 (see FIG. 7(A)). As a result, the electrode patterns 15 and dummy patterns 17 provided on the front side of the wafer 11 are exposed, and a work unit 27 is formed in which the wafer 11 and the annular frame are integrated (see FIG. 7(B)).

[0071] Here, on the back side of the outer peripheral region of wafer 11, a first exposed surface 11a is formed, which has a shape corresponding to the side of a truncated cone, with its upper bottom surface located on the back side of wafer 11 and its lower bottom surface located inside wafer 11. Therefore, in the work unit formation step (S5), tape 25 can be attached to the back side of the outer peripheral region of wafer 11 (first exposed surface 11a and second exposed surface 11b) without locally excessively stretching tape 25.

[0072] Next, the wafer 11 is divided along the planned division lines (division step: S6). This division step (S6) is performed using plasma etching as described in, for example, the above-mentioned Patent Document 1 (JP 2020-113614 A). Figure 8 is a partial cross-sectional side view schematically showing a work unit 27 including a wafer 11 divided using plasma etching.

[0073] Specifically, in the dividing step (S6) performed using plasma etching, first, the atmosphere of the chamber in which the work unit 27 is placed is evacuated while the wafer 11 is held via tape 25. Next, a mask having openings formed in areas along the planned dividing lines is placed on the surface of the wafer 11.

[0074] Next, plasma etching is performed on the substrate 13 through a mask from the front side of the wafer 11. As a result, the wafer 11 is divided along the planned dividing lines, and vertically structured power device chips 29 are manufactured, each including a part of the substrate 13, the electrode pattern 15, and a part of the metal film 19 (see FIG. 8).

[0075] In the method shown in Figure 2, prior to forming the work unit 27, the peripheral region of the metal film 19 and the back surface 13b side of the peripheral region of the substrate 13 are removed to expose the peripheral region of the substrate 13, and an exposed surface (first exposed surface 11a) is formed on the back surface side of the peripheral region of the wafer 11, in which the portion closer to the surface of the wafer 11 is outer than the portion farther away (see the exposed surface forming step (S2) described above).

[0076] This makes it possible to eliminate or narrow the gap between the tape 25 and the outer peripheral region of the wafer 11 when adhering the tape to the backside of the wafer 11 (see the work unit formation step (S5) described above). As a result, when the atmosphere of the chamber in which the work units 27 are placed is evacuated to separate the wafer 11 using plasma etching, it is possible to reduce the likelihood that the tape 25 will peel off from the outer peripheral region of the wafer 11.

[0077] 9A, the exposed surface 11d may be formed on the entire back surface side of the peripheral region of the wafer 11 such that the portion closer to the front surface of the wafer 11 is located further outward than the portion farther from the front surface of the wafer 11.

[0078] Alternatively, in the exposed surface forming step (S2) of the present invention, as shown in Fig. 9(B), a stepped exposed surface 11e may be formed on the back side of the peripheral region of the wafer 11, such that the portion closer to the front surface of the wafer 11 is located more outward than the portion further away. That is, in the exposed surface forming step (S2) of the present invention, the second exposed surface 11b (see Fig. 4(C) etc.) may not be formed.

[0079] When the second exposed surface 11b is formed in the exposed surface forming step (S2), an image can be formed by capturing an image of the front surface side of the outer peripheral region of the wafer 11 using infrared rays that pass through the generally flat second exposed surface 11b. This is therefore preferable in that it makes it easy to obtain a clear image to be referred to when performing the alignment step.

[0080] On the other hand, if the second exposed surface 11b is not formed in the exposed surface forming step (S2), the width of the outer peripheral region of the wafer 11 that is removed in the exposed surface forming step (S2) can be narrowed, which is preferable in that it may be possible to widen the range of the device region of the wafer 11.

[0081] In the exposed surface forming step (S2) of the present invention, the exposed surface may be formed using a cutting blade other than the above-mentioned exposed surface forming cutting blade 16. Figures 10(A), 10(B), and 10(C) are side views schematically showing an example of such an exposed surface forming step (S2).

[0082] This exposed surface forming step (S2) is performed, for example, by the above-mentioned cutting device 2. However, the cutting blade 20 for forming an exposed surface attached to the tip of the spindle 14 has a cutting edge having a shape different from the cutting edge of the above-mentioned cutting blade 16 for forming an exposed surface. Specifically, the cutting edge of the cutting blade 20 for forming an exposed surface has a cylindrical shape with a roughly constant outer diameter from the front end to the rear end.

[0083] In this exposed surface forming step (S2), first, the chuck table 4 holding the wafer 11 and the cutting blade 20 for forming an exposed surface are rotated (see FIG. 10(A)). Next, while the chuck table 4 and the cutting blade 20 for forming an exposed surface are kept rotating, the cutting unit 12 is lowered so that the cutting blade 20 for forming an exposed surface comes into contact with the back surface of the outer peripheral region of the wafer 11 (see FIG. 10(B)).

[0084] Then, the chuck table 4 and the exposed surface forming cutting blade 20 are rotated, and the cutting unit 12 is moved along the Y-axis direction while being lowered so as to move the cutting unit 12 away from the chuck table 4 (see FIG. 10(C)). As a result, for example, an exposed surface 11d as shown in FIG. 9(A) can be formed on the back side of the outer peripheral region of the wafer 11.

[0085] In this exposed surface forming step (S2), a spiral staircase-like exposed surface can be formed on the back side of the outer peripheral region of the wafer 11 by slowing down the rotation speed of the chuck table 4 that holds the wafer 11. In this exposed surface forming step (S2), an exposed surface 11e as shown in Fig. 9(B) can also be formed by alternately lowering the cutting unit 12 and moving it along the Y-axis direction rather than simultaneously.

[0086] Furthermore, in the metal film removal step (S4) of the present invention, laser ablation may be used to remove the areas along the planned division lines of the metal film 19. The laser beam used in this metal film removal step (S4) may be, for example, a pulsed laser beam having a wavelength (e.g., 532 nm) that is absorbed by the metal film 19.

[0087] For example, in the metal film removal step (S4) of the present invention, the repetition frequency of the laser beam may be set to 10 kHz to 200 kHz and the spot diameter may be set to 1 μm to 2 μm, and the laser beam may be irradiated onto the metal film 19 along the planned dividing lines of the wafer 11, thereby removing the areas of the metal film 19 along the planned dividing lines.

[0088] Furthermore, in the dividing step (S6) of the present invention, a method other than plasma etching may be used to divide the wafer 11. For example, in the dividing step (S6) of the present invention, the wafer 11 may be divided by bringing a rotating annular cutting blade (substrate dividing cutting blade) into contact with the substrate 13 from the front surface 13a side of the substrate 13 along the planned dividing line.

[0089] In this case, the wafer 11 is cut and divided with no or a narrow gap between the tape 25 and the outer peripheral region of the wafer 11. This suppresses vibration of the wafer 11 that comes into contact with the rotating cutting blade during division of the wafer 11. As a result, it is possible to reduce the likelihood of chipping occurring at the edges of the chips produced by dividing the wafer 11.

[0090] Furthermore, in the dividing step (S6) of the present invention, a laser beam may be used to form an affected layer inside the wafer 11, and then an external force may be applied to the wafer 11 to divide the wafer 11 using the affected layer as the dividing starting point. The laser beam used in this dividing step (S6) may be, for example, a pulsed laser beam having a wavelength that is transparent to the substrate 13 (for example, a wavelength of 1064 nm).

[0091] For example, in the division step (S6) of the present invention, the repetition frequency of the laser beam may be set to 10 kHz to 50 kHz, and the focal point may be positioned inside the substrate 13, and the laser beam may be irradiated from the surface 13a side of the substrate 13 along the planned division line of the wafer 11, thereby forming an altered layer inside the wafer 11.

[0092] In this case, an external force is applied to the wafer 11 to divide the wafer 11 with no or a narrow gap between the tape 25 and the outer peripheral region of the wafer 11. This reduces the likelihood that a chip including a part of the outer peripheral region of the wafer 11 will peel off from the tape 25 and fly out during division of the wafer 11.

[0093] In the dividing step (S6) of the present invention, laser ablation may be used to divide the wafer 11. The laser beam used in this dividing step (S6) may be, for example, a pulsed laser beam having a wavelength that is absorbed by the substrate 13 (for example, a wavelength of 355 nm).

[0094] For example, in the dividing step (S6) of the present invention, the wafer 11 may be divided by irradiating the laser beam onto the substrate 13 from the surface 13a side of the substrate 13 along the planned dividing lines of the wafer 11, with the repetition frequency of the laser beam set to 10 kHz to 200 kHz and the spot diameter set to 1 μm to 10 μm.

[0095] In this case, laser ablation occurs in the wafer 11 and the wafer 11 is divided when there is no or a narrow gap between the tape 25 and the outer peripheral region of the wafer 11. Therefore, peeling of the tape 25 from the outer peripheral region of the wafer 11 due to heating of the wafer 11 accompanying laser ablation can be suppressed.

[0096] In addition, the structures and methods according to the above-described embodiments can be modified as appropriate without departing from the scope of the present invention. [Explanation of symbols]

[0097] 11: Wafer (11a: first exposed surface, 11b: second exposed surface, 11c: groove) (11d,11e:Exposed surface) 13: Substrate (13a: front surface, 13b: back surface) 15: Electrode pattern 17: Dummy pattern 19: Metal film 21: Protective material 23: Annular frame 25: Tape 27: Work Unit 29: Tip 2:Cutting device 4: Chuck table 6: Imaging unit 8: Visible light camera 10: Infrared camera 12: Cutting unit 14: Spindle 16: Cutting blade for forming exposed surfaces 18: Cutting blade for removing metal film 20: Cutting blade for forming exposed surfaces

Claims

1. A method for manufacturing chips by dividing a wafer including a substrate and a metal film provided so as to cover a rear surface of the substrate along planned dividing lines set in a grid pattern, a protective member attaching step of attaching a protective member to a surface of the wafer opposite to the metal film; an exposed surface forming step in which, after the protective member adhering step has been performed, the peripheral region of the metal film and the back side of the peripheral region of the substrate are removed while the wafer is held via the protective member to expose the peripheral region of the substrate and to form an exposed surface on the back side of the peripheral region of the wafer in which the portion closer to the front surface of the wafer is located outside the portion farther from the front surface; an alignment step of, after the exposed surface forming step, identifying positions of the planned dividing lines and performing alignment by referring to an image of the front side of the outer peripheral region of the wafer formed by imaging the back side of the wafer using light of a wavelength that transmits through the substrate; a metal film removing step of removing an area of ​​the metal film along the planned dividing lines while the wafer is held via the protective member after the alignment step is performed; a work unit forming step of forming a work unit in which the wafer and the annular frame are integrated by removing the protective member from the front surface of the wafer and attaching the back surface of the wafer to a tape that closes the opening of the annular frame after the metal film removing step is performed; a dividing step of dividing the wafer along the planned dividing lines while the wafer is held via the tape after the work unit forming step is performed; A method for manufacturing a chip, comprising:

2. The method for manufacturing chips as described in claim 1, characterized in that in the dividing step, a mask having openings formed in areas along the intended dividing lines is placed on the surface of the wafer, and then the wafer is divided by performing plasma etching on the substrate through the mask.

3. 2. The method for manufacturing chips according to claim 1, wherein in the dividing step, the wafer is divided by contacting a rotating annular substrate dividing cutting blade with the substrate from the front surface side along the intended dividing line.

4. A method for manufacturing chips as described in claim 1, characterized in that in the dividing step, a laser beam having a wavelength that passes through the substrate is irradiated from the surface side of the substrate along the intended dividing line with the focal point positioned inside the substrate, thereby forming an altered layer inside the substrate, and then an external force is applied to the substrate to divide the wafer using the altered layer as the dividing starting point.

5. 2. The method for manufacturing chips according to claim 1, wherein in the dividing step, the wafer is divided by irradiating the substrate from the front surface side along the intended dividing line with a laser beam having a wavelength that is absorbed by the substrate.

6. A method for manufacturing a chip as described in any one of claims 1 to 5, characterized in that in the metal film removal step, the area of ​​the metal film along the intended dividing line is removed by contacting a rotating annular metal film removal cutting blade with the metal film.

7. A method for manufacturing a chip as described in any one of claims 1 to 5, characterized in that in the metal film removal step, the area of ​​the metal film along the intended dividing line is removed by irradiating the metal film with a laser beam of a wavelength that is absorbed by the metal film.

8. A method for manufacturing a chip as described in any one of claims 1 to 7, characterized in that in the exposed surface forming step, the peripheral region of the metal film and the back side of the peripheral region of the substrate are removed by contacting a rotating annular exposed surface forming cutting blade with the metal film and the substrate.

9. A method for manufacturing a chip described in any one of claims 1 to 8, characterized in that in the work unit formation step, the exposed surface and the metal film are attached to the tape.

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