JP6167984B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a method for processing a semiconductor wafer, particularly a nitride semiconductor wafer.

  Conventionally, as a method of manufacturing a nitride semiconductor, for example, a GaN free-standing substrate, a method of peeling only a GaN layer from a different substrate such as sapphire or GaAs has been disclosed. Further, there is a technique in which a GaN single crystal ingot is manufactured by performing thick film growth using a GaN substrate obtained by such a method as a seed substrate, and a wafer having a desired thickness is obtained by slicing the GaN single crystal ingot. A GaN wafer peeled off from a different substrate or cut out from an ingot is finished to have a mirror finish on both sides by surface grinding, lapping, and chemical mechanical polishing (hereinafter abbreviated as CMP or polishing). In carrying out this processing, the wafer is first attached to a ceramic plate using an adhesive such as wax. Thereafter, the wafer is processed using a diamond grindstone, lapping liquid, or abrasive so as to obtain a desired thickness and polished surface. The GaN wafer thus obtained is used as a substrate for light emitting elements such as lasers and LEDs and for electronic devices.

  By the way, a GaN wafer is warped in thick film growth, slicing, and subsequent mirror processing. In order to process a wafer with such warpage flatly and to keep the thickness variation (Total Thickness Variation, hereinafter abbreviated as TTV) within a predetermined range with a good yield, the wafer is flattened on a plate. It is required to be pasted. A wafer bonding apparatus is used for attaching the wafer.

  One such wafer bonding apparatus is disclosed in Patent Document 1, for example. The wafer bonding apparatus disclosed in Patent Document 1 uses a pressure cylinder to attach a wafer to a plate. A convex elastic body is attached to the wafer pressing portion of this apparatus, and the air that enters and remains in the adhesive layer between the plate and the wafer is efficiently removed to the outer peripheral portion.

  Patent Document 2 discloses a method for controlling warpage by introducing a working strain layer into a nitride semiconductor substrate, and the following points. If the Ga surface side is concave, this surface is ground and a work-affected layer is introduced to extend the Ga surface and deform it into a convex shape. Only the Ga surface deformed into a convex shape is dry-etched to remove a part of the work-affected layer and shrink the convex surface, thereby bringing the substrate close to flat.

JP-A-5-82493 JP-A-2005-136167

  However, Patent Document 1 considers application to a wafer having excellent malleability and ductility compared to GaN such as Si and GaAs. A wafer having poor malleability and ductility, such as GaN, may be broken if it is pressed with a wafer bonding apparatus or the like for warping correction. In addition, since Patent Document 1 targets Si and GaAs, it is difficult to apply to a hard and easily cracked material such as GaN. Furthermore, when the wafer outer peripheral part is warped so as to be lifted with respect to the plate, it is conceivable that the correction of the warp becomes insufficient.

  In the method for correcting warpage as in Patent Document 2, the number of processes increases and the cost increases. Further, since warping cannot be sufficiently suppressed, it is difficult to manufacture a wafer having a good TTV. If the TTV of the wafer is large, it can be considered to adversely affect subsequent processes such as photolithography.

  The present invention has been made in view of the above problems. For example, a wafer having a good TTV can be obtained by grinding or polishing a warped wafer made of a hard and easily cracked material such as a nitride semiconductor such as GaN. Another object of the present invention is to provide a wafer processing method that can be processed at low cost.

In order to achieve the above object, the present invention is a wafer processing method in which a warped wafer is bonded and held on a plate using an adhesive, and the held wafer is ground or polished. While affixing to the plate using an adhesive, while correcting the warp of the wafer so as to apply a load only to the outer peripheral part of the wafer or only the center part according to the direction of the warp of the wafer, Provided is a wafer processing method characterized in that a back surface of a wafer is attached to the plate, and then the surface of the wafer is ground or polished.
With such a wafer processing method, the wafer can be processed with a high yield without breaking, and a warped wafer can be processed at a low cost into a wafer having a small TTV and falling within a desired range.

In addition, after processing the surface of the wafer, while correcting the warp of the wafer so as to apply a load only to the outer peripheral part of the wafer or only the center part according to the direction of the warp of the wafer, The front surface of the wafer can be attached to the plate using an adhesive, and then the back surface of the wafer can be ground or polished.
In this way, since the wafer can be affixed to the plate with a high flatness regardless of the direction of warping of the wafer, it can be reliably processed into a high flat wafer with good TTV.

When the wafer is affixed to the plate using the adhesive, if the outer periphery of the wafer is warped with respect to the plate, the ring-shaped pressing member is placed only on the outer periphery of the wafer. It is preferable to apply a load only to the outer peripheral portion of the wafer by pressing the wafer in contact.
In this way, since the wafer can be affixed to the plate with high flatness while correcting the warpage of the wafer that is warped so that the outer peripheral portion of the wafer is lifted, it can be reliably processed into a high flat wafer with good TTV.

Further, when the wafer is attached to the plate using the adhesive, when the wafer is warped so that the central portion of the wafer is lifted, a circular pressing member having a diameter smaller than the wafer diameter is used. It is preferable that a load is applied only to the central portion of the wafer by pressing the wafer while contacting only the central portion of the wafer.
In this way, the wafer can be affixed to the plate with high flatness while correcting the warpage of the wafer that is warped so that the center part of the wafer is lifted, so that it can be reliably processed into a high flat wafer with good TTV.

When the wafer is attached to the plate using the adhesive, the load applied to the wafer is t × 1/100 (g / cm ² ) or more when the wafer thickness is t (μm). It is preferable to do so.
With such a load, the warpage of the wafer can be corrected more reliably when the wafer is attached to the plate.

The wafer may be a nitride semiconductor.
Thus, even when processing a very fragile wafer such as a nitride semiconductor, according to the present invention, it can be processed into a highly flat wafer with good TTV without cracking.

  In the wafer processing method of the present invention, the wafer is attached to the plate while correcting the wafer warp so that only the outer peripheral part of the wafer or only the center part is loaded according to the direction of the warp of the wafer, Thereafter, since the wafer is ground or polished, it is possible to provide a wafer processing method that can be processed into a wafer having a good TTV at a low cost by grinding or polishing without breaking the wafer.

It is the schematic of an example of the wafer with the curvature of the object processed by the processing method of this invention. It is the figure which showed an example of the method of pressing a wafer when affixing a wafer on a plate in the processing method of this invention. It is the figure which showed a mode that the curvature of the wafer was corrected after pressing a wafer as shown to FIG. 2A. It is the figure which showed an example of the ring-shaped press member. It is the figure which showed another example of the method of pressing a wafer when a wafer is affixed on a plate in the processing method of this invention. It is the figure which showed a mode that the curvature of the wafer was corrected after pressing a wafer as shown to FIG. 3A. It is the schematic which shows an example of a general grinding | polishing apparatus. It is the schematic which shows an example of a general surface grinding apparatus. It is the schematic which shows an example of a common lap apparatus.

Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.
As described above, in order to obtain a wafer having a good TTV, it is necessary to correct the warpage of the wafer that occurs in the wafer manufacturing stage. However, in the conventional method, the correction of the warp is insufficient or the number of processes increases, resulting in high cost. For example, when trying to correct a warp of a hard and fragile wafer such as a GaN wafer, there is a problem that the wafer breaks.

  Therefore, the present inventors have intensively studied to solve such problems. As a result, the following has been conceived. While correcting the warpage of the wafer by applying a load only to the outer peripheral part of the wafer or only the center part depending on the direction of the warp of the wafer, if the wafer is attached to the plate, the wafer is prevented from cracking, Wafer warpage can be effectively corrected. By grinding or polishing the held wafer in this way, it can be processed into a highly flat wafer with good TTV. And the best form for implementing these was scrutinized and the present invention was completed.

  First, as shown in FIG. 1, a wafer 1 having a warp to be processed is prepared. The wafer 1 can be a wafer made of a nitride semiconductor such as GaN, for example. For example, a GaN wafer can be obtained by slicing an ingot with a wire saw or by peeling from a dissimilar substrate such as sapphire or GaAs. One surface of the prepared wafer 1 can be ground flat to form the reference surface 2. However, since the working strain layer 3 is formed on the reference surface 2, the reference surface 2 side ground to be flat is warped to have a convex shape.

  Next, as shown in FIG. 2A, the back surface of the wafer 1 can be attached to the plate 7 in order to process the surface of the wafer 1. When the reference surface 2 is formed as described above, the reference surface 2 can be attached to the plate 7. That is, in this case, the reference surface 2 corresponds to the back surface of the wafer 1. At this time, the back surface of the wafer 1 is attached to the plate 7 while correcting the warpage of the wafer 1 by applying a load only to the outer peripheral portion or only the central portion of the wafer 1 according to the warping direction of the wafer 1. Try to put it on. In this way, the wafer 1 can be attached to the plate 7 while correcting the warp without breaking the wafer 1.

  Below, the example in the case of affixing on the plate 7 by making the reference surface 2 which becomes convex into a back surface is demonstrated more concretely.

  The adhesive 6 is applied to the plate 7 as shown in FIG. 2A, and the wafer 1 is placed thereon. At this time, as shown in FIG. 2A, the outer peripheral portion of the wafer 1 is warped so as to be lifted with respect to the plate 7, so that only the outer peripheral portion of the wafer 1 is loaded in the direction toward the plate 7. Thereby, it can affix on the plate 7, correcting the curvature of the wafer 1 effectively. Furthermore, since the entire surface of the wafer is not pressed as in the prior art, only a necessary portion is loaded, so that even when a GaN wafer is attached to a plate, for example, cracking of the wafer can be prevented.

  Here, as a member that can apply a load only to the outer peripheral portion of the wafer 1, specifically, a ring-shaped pressing member 5 having a hollow center as shown in FIG. 2C can be used. Then, only the outer peripheral portion of the wafer 1 is pressed by the ring-shaped pressing member 5.

  Specifically, as shown in FIG. 2A, a ring-shaped pressing member 5 is placed on the wafer 1 and brought into contact with only the outer peripheral portion, and a load can be applied from above using a weight 4 or a pasting machine. . In this case, a load may be applied to the wafer 1 located on the lower surface of the plate 7 from below. Here, the direction in which the wafer 1 is pressed is not particularly limited. In this way, as shown in FIG. 2B, the wafer is attached to the plate in a state in which the warpage is corrected.

  By using such a ring-shaped pressing member 5, it is possible to easily correct the warp in which the outer peripheral portion of the wafer is lifted from the plate, and to attach the wafer with high flatness. However, the shape is not limited to this, and it is sufficient that only the outer peripheral portion of the wafer can be pressed.

  In the above, as shown in FIG. 2A, the outer periphery of the wafer is warped against the plate as shown in FIG. 2A, but when the center is warped as shown in FIG. 3A, as shown in FIG. 3A. The back surface of the wafer is attached to the plate while correcting the warpage of the wafer so that only the central portion of the wafer 1 is loaded.

  Here, as a member that can be pressed only on the central portion of the wafer 1, specifically, a circular pressing member 5 a as shown in FIG. 3A can be used. At this time, for example, the diameter of the circular pressing member 5a can be set to 20 to 30 mm. By using such a circular pressing member 5a, it is possible to easily correct the warp in which the central portion of the wafer is lifted with respect to the plate. The shape of the pressing member 5a is not limited to a circle, and only needs to be able to press only the central portion of the wafer, and may be, for example, a polygon.

  And only the center part of the wafer 1 is pressed with the circular pressing member 5a. Specifically, as shown in FIG. 3A, the wafer 1 can be put on the wafer 1 and brought into contact with only the central portion, and a load can be applied from above using the weight 4 or a pasting machine. In this manner, as shown in FIG. 3B, the wafer is attached to the plate in a state in which the warpage is corrected.

  Further, when the load applied only to the outer peripheral portion or only the central portion of the wafer when the wafer is attached is changed depending on the thickness of the wafer, the effect can be ensured. This is because if the wafer thickness is t (μm), a larger force is required to correct the warpage of the wafer when t is thicker.

At this time, the inventors preferably press with a force of t × 1/100 (g / cm ² ) or more. By setting the load to such a value, the wafer is more reliably attached to the plate with high flatness. It was found that it is possible to attach.

  Next, the surface of the wafer 1 is processed by grinding or polishing the surface of the wafer 1. Here, the wafer may be processed by both grinding and polishing. Either grinding or polishing may be performed, but at least grinding in the wafer processing method of the present invention includes surface grinding and lapping, and either or both may be performed. In the following, a case where processing is performed in the order of surface grinding, lapping, and polishing will be described as an example. However, the present invention is not limited to this and may be performed in any order or combination.

  As described above, after the wafer 1 is stuck flat on the plate 7, the surface of the wafer 1 is subjected to surface grinding. As shown in FIG. 5, the surface grinding can be performed using a surface grinding device 16 having a rotatable grinding machine 17 and a grindstone 18. The wafer 1 is affixed to the plate 7 using an adhesive 6 and is further held on a grinding machine 17 via the plate 7.

  Then, with the grindstone 18 and the grinding machine 17 rotated at high speed, the surface of the wafer 1 is ground by bringing the grindstone 18 into sliding contact with the surface of the wafer 1. At this time, as a method of fixing the plate 7 to the grinding machine 17, for example, a method of adsorbing and fixing with a vacuum device (not shown) can be used.

  Next, lapping is performed on the surface of the wafer 1. As shown in FIG. 6, the lap is performed using a lap device 19 having a rotatable lap machine 23 and a lap head 20. The wafer 1 is affixed to the plate 7 using an adhesive 6 and is further held by the lap head 20 via the plate 7. The lapping liquid 22 is supplied from the lapping liquid supply device 21 between the lapping machine 23 and the wafer 1, the wafer 1 is pressed against the lapping machine 23, and the lapping machine 23 and the lapping head 20 are rotated. The surface of the wafer 1 is mechanically wrapped by being brought into sliding contact with the surface. For example, a mixture of alumina or silicon carbide abrasive grains and glycerin can be used for the lapping liquid 22.

  Next, the surface of the wafer 1 is polished. As shown in FIG. 4, the polishing is performed using a polishing apparatus 12 having a rotatable polishing head 15 and a polishing surface plate 11. The wafer 1 is bonded to the plate 7 using an adhesive 6 and is further held by a polishing head 15 via the plate 7. A polishing cloth 10 is affixed to the polishing surface plate 11. Polishing is performed by applying a load to the rotating polishing cloth 10 on the surface of the wafer 1 while applying a load while supplying the polishing agent 14 onto the polishing cloth 10 attached to the polishing surface plate 11 from the polishing agent supply device 13. Is done.

  With such a wafer processing method of the present invention, a wafer having a small wafer TTV and a good yield can be obtained without breaking the wafer, so that a light-emitting element, electronic device, etc. can be obtained. Thus, it becomes possible to supply a high-yield TTV wafer with no problem in manufacturing.

  The wafer processing by grinding and polishing may be used in any order or in combination. Grinding and polishing may be performed continuously while the wafer 1 is attached to the plate 7 or may be detached and attached for each process.

  After the surface of the wafer 1 is processed, the back surface of the wafer 1 may be processed. In this case, in order to process the back surface of the wafer 1, the adhesive 6 between the wafer 1 and the plate 7 is removed, and after removing the wafer 1 from the plate 7, the surface of the wafer 1 is attached to the plate 7. At this time, the wafer is applied to the plate 7 while applying the load only to the opposite portion of the outer peripheral portion and the center portion of the wafer when the back surface of the wafer is attached to the plate 7. It is preferable to stick. For example, when the back surface is attached to the plate as shown in FIG. 2A, if only the outer peripheral portion of the front surface of the wafer is attached with a load, the back surface of the wafer is attached to the plate. It is preferable to apply the load only to the central part of the film.

  Next, the back surface of the wafer 1 attached to the plate 7 is ground or polished in the same manner as described above. In this way, if the front and back surfaces of the wafer are processed in the order of grinding, lapping, and polishing, a wafer having a very small TTV and mirror-finished on both sides can be obtained in a short time.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.
(Example)
A GaN wafer having a thickness of 1200 μm was attached to the plate, and one surface was thinned to 600 μm by surface grinding to form a reference surface. At this time, the warpage of the wafer was convex toward the reference surface. Then, as shown to FIG. 2A, the reference surface (back surface) was affixed on the plate. Since the wafer warped so that the outer peripheral part of the wafer was lifted was affixed to the plate, a ring-shaped pressing member was placed on the wafer, and a weight was placed thereon to press only the outer peripheral part of the wafer. The load at this time was 80 g / cm ² . After affixing the wafer to the plate, the surface was mirror-finished by surface grinding, lapping, and CMP. The wafer thickness after this processing was 520 μm. The same processing was performed on a total of five wafers. The shape of the processed wafer was 25 μm (average of 5 wafers) on the reference surface (back surface) side, which was better than the comparative example.

Next, the reference surface (back surface) was processed by attaching the mirror-finished surface to the plate. A circular pressing member having a diameter of 25 mm was used to concentrate the load only on the center portion. The load at this time was 100 g / cm ² . The back surface was also processed in the order of surface grinding, lapping, and CMP to give a mirror surface, and the wafer thickness was 500 μm. The same processing was performed on a total of five wafers. As shown in Table 1, the TTV of the five wafers after processing was as good as 3 to 9 μm.

(Comparative example)
Both sides of the wafer were processed in the same manner as in Example, except that the wafer was pressed onto the entire surface of the wafer. A sticking jig in which a resin was pasted on an Si ingot was prepared, and the jig was pressed by hand from above the wafer and pasted on a plate. When the wafer was applied to the plate by this method, the wafer was broken. Therefore, the back surface of the wafer was attached to the plate so that the wafer was pressed by hand with a force that did not break the wafer. Thereafter, the surface of the wafer was processed by surface grinding, lapping, and CMP to obtain a mirror surface. The same processing was performed on a total of five wafers. The shape of the processed wafer was 35 μm (an average of 5 wafers) on the reference surface (back surface) side, which was worse than the example.

  Next, the surface of the wafer processed previously was attached to a plate, and the back surface was processed. The wafer was affixed to the plate using a material in which a resin was affixed to an Si ingot in the same manner as described above, and was manually pressed from above the wafer with a force that did not break the wafer. Thereafter, the back surface of the wafer was processed by surface grinding, lapping, and CMP to obtain a mirror surface. The same processing was performed on a total of five wafers. As shown in Table 1, the TTV of the five wafers after processing was 9 to 25 μm, which was worse than the examples. This is presumably because the method of pushing the wafer to the plate against the entire surface of the wafer may cause insufficient correction of the warpage of the wafer.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

1 ... wafer, 2 ... reference plane, 3 ... work strain layer, 4 ... weight,
5 ... Ring-shaped pressing member, 5a ... Circular pressing member, 6 ... Adhesive, 7 ... Plate,
DESCRIPTION OF SYMBOLS 10 ... Polishing cloth, 11 ... Polishing surface plate, 12 ... Polishing apparatus, 13 ... Abrasive supply apparatus,
14 ... Abrasive, 15 ... Polishing head, 16 ... Surface grinding device, 17 ... Grinding machine,
18 ... Whetstone, 19 ... Lap device, 20 ... Lap head,
21 ... Lapping liquid supply device, 22 ... Lapping liquid, 23 ... Lapping machine.

Claims (4)

A wafer processing method in which a warped wafer is attached to a plate using an adhesive and held, and the held wafer is ground or polished,
When affixing the wafer to the plate using an adhesive, the wafer warp is corrected by applying a load only to the outer peripheral part of the wafer or only to the central part according to the direction of warpage of the wafer. While attaching the back side of the wafer to the plate,
When attaching the wafer to the plate using the adhesive,
When the outer peripheral portion of the wafer is warped so as to be lifted with respect to the plate, only the outer peripheral portion of the wafer is pressed by pressing the wafer by bringing a ring-shaped pressing member into contact with only the outer peripheral portion of the wafer. Load on the
When attaching the wafer to the plate using the adhesive,
When the wafer is warped so that the central portion of the wafer is raised, the circular pressing member having a diameter smaller than the wafer diameter is brought into contact only with the central portion of the wafer to press the wafer, Make sure that only the center of the wafer is loaded.
Then, the wafer processing method, wherein the surface of the wafer is ground or polished. After processing the surface of the wafer,
Using the adhesive to the surface of the wafer while correcting the warp of the wafer so that only the outer peripheral part of the wafer or only the center part is loaded according to the direction of warping of the wafer. pasting,
2. The wafer processing method according to claim 1, wherein the back surface of the wafer is then ground or polished. When attaching the wafer to the plate using the adhesive,
When the wafer thickness of the load applied to the wafer was t (μm), according to claim 1 or claim 2, characterized in that so as to be t × 1/100 (g / cm 2) or more Wafer processing method. The wafer processing method according to any one of claims 1 to 3 , wherein the wafer is made of a nitride semiconductor.

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