JP2011216763A - Method of processing wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a wafer of sapphire etc., from breaking or cracking by causing neither warping of the wafer nor peeling of an outer peripheral edge from an adhesive due thereto even when the wafer is thinned to an extremely thin thickness of ≤50 μm.SOLUTION: An outer peripheral inclined surface Wb whose outer periphery is inclined such that the wafer W increases in outer diameter from a reverse surface W2 to a top surface W1 is formed over the entire outer periphery of the wafer W by grinding, the entire outer peripheral inclined surface Wb of the wafer W and the top surface W1 of the wafer W are coated with an adhesive 20 to stick the side of the top surface W1 of the wafer W on a support member 2, and the reverse surface W2 is ground in this state. The wafer W never warps during the grinding of the reverse surface W2, and the outer peripheral edge of the wafer W does not peel from the adhesive 20, so that the wafer W is prevented from breaking or cracking.

Description

  The present invention relates to a wafer processing method for grinding and thinning a back surface of a wafer having a circuit forming surface on the front surface.

  When grinding hard wafers such as sapphire, SiC, GaN, etc., use a hot-melt adhesive such as wax, and fix the wafer by sticking the surface side, which is the circuit forming surface, to a support member such as glass. is doing. The support member is sucked and held on the chuck table of the grinding device to expose the back surface of the wafer, and the back surface is ground. In this way, by fixing the wafer to the support member using a hot-melt type adhesive, for example, even if the wafer is warped by being thinned to a thickness of 100 μm or less, the wafer is bonded. Grinding can be performed without peeling from the agent.

Japanese Patent No. 3055401

  However, when a hard wafer such as sapphire is further thinned, for example, so as to have a thickness of 50 μm or less, the following problem occurs even when it is fixed with a hot-melt adhesive. That is, the wafer such as sapphire is thinned to a thickness of 50 μm or less because the outer periphery is end-face polished and chamfered to prevent chipping on the outer periphery. The chamfered outer periphery has a knife edge shape, and the outer periphery has a knife edge shape, so that the peripheral edge 60a of the wafer 60 is warped as shown in FIG. Will peel off. Then, by continuing grinding in this state, the wafer 60 is cracked or cracked due to the peeling of the wafer 60 from the adhesive 61.

  The present invention has been made in view of the above-mentioned facts, and its main technical problem is that a wafer such as sapphire is chamfered by thinning the wafer to a very thin thickness of 50 μm or less. It is to provide a wafer processing method that prevents the outer periphery from being peeled off from the adhesive due to the warpage of the wafer caused by grinding, and prevents the wafer from cracking and cracking due to the peeling from the adhesive. .

  The present invention relates to a wafer processing method for grinding a back surface of a disk-shaped wafer having a circuit forming surface on its surface and thinning it to a predetermined thickness. The outer diameter of the wafer extends from the back surface to the front surface over the entire circumference of the wafer. An inclined surface forming step for forming an outer peripheral inclined surface whose outer periphery is inclined so as to increase in diameter toward the diameter, and an adhesive is applied to the entire outer peripheral inclined surface of the wafer and the surface of the wafer, and the surface side of the wafer is adhered to the support member. An attaching step, a grinding step of grinding the back surface until the wafer is formed to a predetermined thickness, and a peeling step of peeling the adhesive and the support member from the wafer after the grinding step is completed. Examples of the wafer include, but are not limited to, sapphire, SiC, and GaN.

  In the present invention, in the inclined surface forming step, an outer peripheral inclined surface whose outer periphery is inclined is formed so that the outer diameter of the wafer increases from the back surface to the front surface over the entire outer periphery of the wafer. Since the adhesive is applied to the entire inclined surface and the surface of the wafer and the front side of the wafer is adhered to the support member and the grinding process is performed in that state, the wafer is not warped during grinding, Since the outer peripheral edge does not peel from the adhesive, it is possible to prevent the wafer from being cracked or cracked.

It is a front view which shows an example of a wafer. It is explanatory drawing which shows the mode of an inclined surface formation process. It is a perspective view which shows the wafer in which the outer periphery inclined surface was formed. It is sectional drawing which expands and shows an outer periphery inclined surface. It is sectional drawing which shows schematically the state which adheres a wafer to a supporting member using an adhesive agent. It is sectional drawing which shows schematically the state which solidifies an adhesive agent. It is sectional drawing which shows a grinding process schematically. It is sectional drawing which shows the state which the grinding process was complete | finished schematically. It is sectional drawing which shows schematically the state which affixed the tape on the back surface of the wafer. It is sectional drawing which shows the state which peels a supporting member schematically. It is sectional drawing which shows schematically the wafer after peeling a supporting member, an adhesive agent, a tape, and a flame | frame. It is sectional drawing which shows schematically the state which immersed the wafer, the adhesive agent, the tape, and the flame | frame in warm water. It is sectional drawing which shows schematically the state which swollen the adhesive agent and peeled from the wafer. It is a front view which shows the wafer by which the outer periphery inclined surface was formed and was ground. It is a front view which shows another example of the wafer by which the outer periphery inclined surface was formed and was ground. It is a table | surface which shows the result of an Example. It is sectional drawing which shows the state which the curvature generate | occur | produced in the wafer and peeled from the adhesive agent.

  A wafer W shown in FIG. 1 is a hard disk-shaped wafer made of sapphire, silicon carbide (SiC), gallium nitride (GaN), or the like, and has an end face Wa having a half-section in order to prevent chipping or cracking. It is chamfered in a circle. A circuit is formed on the surface W1 of the wafer W.

  As shown in FIG. 2, the front and back surfaces of the wafer W are reversed and the end surface Wa of the wafer W is ground to form the outer peripheral inclined surface Wb shown in FIG. For example, as shown in FIG. 2, an outer peripheral grinding device 1 in which a grinding wheel 11 is mounted on the lower end of a rotatable rotating shaft 10 is used, and the axis of the rotating shaft 10 is relatively inclined with respect to the surface direction of the wafer W. In this state, the wafer W is rotated, and the grinding wheel 11 rotating in the direction of the arrow R is brought into contact with the end surface Wa. Then, with the grinding wheel 11 in contact with the end surface Wa, the rotating shaft 10 and the grinding wheel 11 are moved in a direction (arrow S direction) perpendicular to the axis of the rotating shaft 10 to perform grinding. Then, as shown in FIG. 3, the outer peripheral inclined surface Wb is formed over the entire outer periphery of the wafer W. The outer peripheral inclined surface Wb is an inclined surface that is inclined so that the outer diameter of the wafer W increases from the back surface W2 toward the front surface W1. At this time, as shown in FIG. 4, if the angle formed by the surface W1 and the outer peripheral inclined surface Wb is θ, grinding is performed so that θ is, for example, 30 to 85 degrees (inclined surface forming step).

  Next, as shown in FIG. 5, the support member 2 is prepared, and the adhesive 20 is applied on the surface of the support member 2. The support member 2 has a function of supporting the thinned wafer W, and is made of a film made of a material that can transmit ultraviolet rays, for example, polyethylene terephthalate (PET). In addition to this, when the wafer is a sapphire substrate, a rigid body such as glass or ceramics can be used as the support member 2. On the other hand, the adhesive 20 is made of a pressure-sensitive adhesive resin that is cured when irradiated with ultraviolet rays and swells when it contains moisture, resulting in a decrease in holding power. Can be used. It is possible to use a conventionally used hot melt wax as the adhesive 20, but there is a problem that it is difficult to peel off the wafer W later. It is desirable to use a lowering adhesive resin.

  As shown in FIG. 6, the surface W <b> 1 side of the wafer W is pressed onto the adhesive 20, and the entire outer peripheral inclined surface Wb and the entire surface W <b> 1 are bonded to the adhesive 20. On the other hand, the back surface W2 is exposed upward so that the adhesive 20 is not adhered to the back surface W2. Since the outer peripheral inclined surface Wb is a surface inclined such that the outer diameter of the wafer W increases from the back surface W2 toward the front surface W1, the adhesive 20 is deposited also above the outer peripheral inclined surface Wb. Therefore, the wafer W is held in such a manner that the adhesive 20 above the outer peripheral inclined surface Wb presses the outer peripheral inclined portion Wb downward. Then, the support member 2 is transmitted through the ultraviolet irradiator 3 disposed below the support member 2 to irradiate the adhesive 20 with the ultraviolet rays 3a. If it does so, since the adhesive 20 which received irradiation of the ultraviolet-ray 3a will harden | cure, the wafer W will be in the state fixed and supported by the support member 2 via the adhesive 20 (sticking process).

  In this state, the back surface W2 of the wafer W is ground while the wafer W is supported by the support member 2. For such grinding, for example, a grinding device 4 shown in FIG. 7 can be used. The grinding apparatus 4 includes a holding table 40 that can hold and rotate a wafer W supported by a support member 2 in a holding unit 40a, and a circular base 42 attached to a lower end of a rotary shaft 41 having a vertical axis. And a grinding means 44 constituted by a plurality of grinding wheels 43 fixed to the lower surface of the circular base 42. In this grinding apparatus 4, the grinding wheel 43 and the back surface W <b> 2 of the wafer W are arranged so that the outermost circumference of the rotation path of the grinding wheel 43 rotating in the B direction passes through the center of the wafer W while rotating the holding table 40 in the A direction. Are brought into contact with each other to uniformly grind the back surface W2. Then, as shown in FIG. 8, when the wafer W is thinned to a predetermined thickness, the grinding means 44 is raised to finish the grinding. Thus, the outer peripheral inclined surface Wb formed over the entire outer periphery of the wafer W is stuck to the support member 2 by the cured adhesive 20 and pressed from the outer peripheral side and the upper side of the outer peripheral inclined surface Wb by the adhesive 20. In this case, the outer periphery of the wafer is not peeled off from the adhesive 20 even if the wafer W is thinned so as to be warped if there is no outer peripheral inclined surface Wb. It is possible to prevent cracking and chipping of the wafer (grinding process).

  Next, as shown in FIG. 9, the front and back of the wafer W and the support member 2 are reversed, and the back surface W2 of the wafer W is adhered to the tape T. The tape T is obtained by applying an adhesive layer to one surface of a sheet base material made of polyvinyl chloride, for example, and the back surface W2 of the wafer W is adhered to the adhesive layer. A metal frame F formed in a ring shape is attached to the peripheral edge portion of the adhesive layer of the tape T, and the wafer W is supported integrally with the frame F via the tape T.

  Next, as shown in FIG. 10, the support member 2 is peeled from the surface W1 of the wafer W from this state, and the support member 2 is completely removed and the adhesive 20 is exposed as shown in FIG. . When the support member 2 is peeled off when a rigid body is used as the support member 2, it is desirable to facilitate the peeling by inserting a sharp peeling jig between the adhesive 20 and the support member 2.

  As shown in FIG. 12, for example, hot water 50 having a temperature of 90 degrees is stored in the water tank 5. A support base 51 is disposed at the center of the bottom of the water tank 5, the tape T is placed on the support base 51, and the wafer W above it is supported from below by the support base 51. In this way, the back surface W2 is adhered to the tape T and integrated with the frame F, and the wafer W in which the front surface W1 and the outer peripheral inclined surface Wb are covered with the adhesive 20 is immersed in the hot water 50. As a result, the adhesive 20 swells and the adhesive force decreases, and the wafer W can be peeled off. Then, as shown in FIG. 13, the adhesive 20 is peeled from the wafer W and the tape T and taken out of the hot water 50 while the wafer W is immersed in the hot water 50. Since the adhesive force of the adhesive 20 is reduced by being immersed in the hot water 50, the wafer W and the tape T can be easily peeled off (peeling step).

  Finally, when the tape T adhered to the back surface W2 of the wafer W is peeled and removed together with the frame F, a wafer W ′ having an outer peripheral inclined surface Wb is formed as shown in FIG. The wafer W ′ formed in this manner is ground with the outer peripheral inclined surface Wb formed and firmly held by the adhesive 20, and therefore has no cracks or chips.

  Note that the entire outer peripheral surface of the wafer W ′ shown in FIG. 14 is an outer peripheral inclined surface Wb, but an outer peripheral inclined surface Wc is formed on a part of the outer peripheral surface as in the wafer W ″ shown in FIG. You may make it do. In this case, the inclined surface forming step is performed so that the outer peripheral surface has a predetermined thickness T that forms the vertical surface Wd from the front surface W1 toward the back surface W2, and the outer diameter is reduced from the vertical surface Wd toward the back surface W2. An outer peripheral inclined surface Wc is formed.

The end face (outer peripheral edge) of the sapphire wafer having a diameter of 4 inches and a thickness of 600 mm before the circuit was formed was formed into three types of shapes shown in FIG. Then, three types of sapphire wafers are attached to a support member with an adhesive, and after grinding to a predetermined thickness, the adhesive is peeled off visually and with an optical microscope for each sapphire wafer. The presence or absence of cracks and the presence or absence of cracks were observed. This observation was conducted on five wafers for each wafer. The three types of outer peripheral shape are as follows.
(1) The outer peripheral end face is chamfered into a semicircular cross section as before.
(2) An outer peripheral inclined surface with an inclination angle θ = 45 ° is formed on the outer peripheral end surface (the present invention).
(3) The chamfering of the outer peripheral end surface is removed to form a vertical surface.

Other conditions are common to the three types of wafers and are as follows.
(4) Adhesive “Resilock” provided by Disco Co., Ltd. is used as an adhesive made of a pressure-sensitive adhesive resin that is UV curable and swells when it contains moisture, and its holding power decreases.
(5) Support member Quartz glass having a diameter of 8 inches and a thickness of 3 mm is used.
(6) Method of sticking sapphire wafer The adhesive was dropped onto the support member and pressurized with a precision press machine, and the three types of sapphire were each attached to a support substrate and molded and cured.
(7) Grinding method Grinding was performed using a vitrified grindstone so that the finished thickness was 40 μm.

  When each sapphire wafer was ground under the above conditions, the results shown in FIG. 16 were obtained. As can be seen from FIG. 16, in the case of “(1) chamfering the outer peripheral end surface in a semicircular cross section” and “(3) forming the vertical surface by removing the chamfer of the outer peripheral end surface” Except for No.4, peeling of the adhesive and cracking of the sapphire wafer were confirmed. Specifically, it was confirmed that the adhesive applied to the outer peripheral portion of the sapphire wafer was peeled off, and that the wafer was cracked and cracked from the peeled portion. On the other hand, in the case of “(2) Forming an outer peripheral inclined surface having an inclination angle θ = 45 ° on the outer peripheral end surface”, peeling of the adhesive and cracking / cracking of the sapphire wafer were not confirmed. Therefore, the usefulness of the present invention was demonstrated.

W, W ′: Wafer W1: Front surface W2: Back surface Wa: End surface Wb: Peripheral inclined surface T: Tape F: Frame W ″: Wafer Wc: Peripheral inclined surface Wd: Vertical surface 1: Peripheral grinding device 10: Rotating shaft 11 : Grinding wheel 2: Support member 20: Adhesive 3: UV irradiator 3a: UV light 4: Grinding device 40: Holding table 40 a: Holding part 41: Rotating shaft 42: Circular base 43: Grinding wheel 44: Grinding means 5: Water tank 50: Warm water 51: Support stand

Claims (2)

A wafer processing method for grinding a back surface of a disk-shaped wafer having a circuit forming surface on its surface and thinning it to a predetermined thickness,
An inclined surface forming step for forming an outer peripheral inclined surface having an outer periphery inclined such that the outer diameter of the wafer increases from the back surface to the surface over the entire outer periphery of the wafer;
An attaching step of applying an adhesive to the entire outer peripheral inclined surface of the wafer and the surface of the wafer and attaching the surface side of the wafer to a support member;
A grinding step of grinding the back surface until the wafer is formed to a predetermined thickness;
A peeling step of peeling the adhesive and the support member from the wafer after the grinding step;
Composed of,
Wafer processing method.   The wafer processing method according to claim 1, wherein the wafer is one of sapphire, SiC, and GaN.

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