JP2014041963A - Semiconductor light-emitting element manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light-emitting element manufacturing method which can make a semiconductor wafer thinner without causing chip and cracks on an outer periphery of the semiconductor wafer in a grinding process of the semiconductor wafer.SOLUTION: A semiconductor light-emitting element manufacturing method of the present embodiment comprises in the following order: a process of forming a semiconductor wafer by laminating a nitride semiconductor layer on a sapphire substrate; a process of applying an adhesive on the semiconductor wafer on a surface on the nitride semiconductor layer side and subsequently sticking the semiconductor wafer to a fixed plate via the adhesive; and a grinding process of thinning the semiconductor wafer by grinding the sapphire substrate of the semiconductor wafer stuck to the fixed plate. A film thickness of the adhesive applied on the outer periphery of the semiconductor wafer is thicker than a film thickness of the adhesive applied on a central part of the semiconductor wafer.

Description

  The present invention relates to a method for manufacturing a semiconductor light emitting device.

_{Recently, Al x In y Ga 1-} x-y gallium nitride compound semiconductor represented by N has attracted attention as a material for blue and green LED. By using a compound semiconductor of such a material, it has become possible to emit light of blue, green, etc. with high emission intensity, which has been difficult until now. As a result, it is widely used for monitor backlights and lighting applications.

  In recent years, tablet terminals and the like have been reduced in thickness and size, and the semiconductor light-emitting elements incorporated therein are also required to be as thin as 200 μm or less. In order to manufacture such a semiconductor light emitting device, it is necessary to make the semiconductor wafer itself thin.

Here, a typical method for manufacturing a nitride semiconductor light emitting device will be described below.
An n-type nitride semiconductor layer and a p-type nitride semiconductor layer are stacked on a sapphire substrate, and an electrode electrically connected to the n-type and p-type nitride semiconductor layers is formed.

  As an electrode that is electrically connected to the p-type nitride semiconductor layer, a translucent electrode is formed on the p-type semiconductor layer, and a pad electrode made of metal is formed thereon. As the translucent electrode, a conductive oxide such as ITO, IZO, or ZnO is used. For the upper pad electrode, a layer made of Ni, Rh or the like and a bonding layer made of Au, Al or the like having good adhesion to the translucent electrode is used. The translucent electrode spreads the current injected from the pad electrode to the p-type nitride semiconductor layer, and allows light from the nitride semiconductor light emitting element to be transmitted and extracted to the outside.

  On the other hand, since an n-type nitride semiconductor generally has a low electric resistance, a pad electrode is formed directly on the n-type nitride semiconductor. As this n electrode, an ohmic contact layer such as Al, Cr, or Ti, a barrier layer such as Pt or Mo, and a bonding layer such as Al or Au are used in order to achieve good ohmic contact with the n-type semiconductor layer.

Thereafter, an insulating protective film made of SiO _x , SiN _x or the like is formed so as to cover the side surface of the pad electrode and a part of the surface.

  Thereafter, the back surface of the semiconductor wafer is processed using a grinding machine or a polishing machine, and is thinned to 200 μm or less. As a method of processing the back surface (back surface grinding), the surface on which the semiconductor light emitting layer is formed is coated with an adhesive to protect the semiconductor light emitting layer, and the surface coated with the adhesive is adhered to a fixing plate, A method is known in which a semiconductor wafer back surface is ground using a grinder while the semiconductor wafer is fixed to a fixed plate.

  In addition, a wafer processing adhesive sheet formed by laminating an adhesive on a soft substrate is attached to the surface on which the semiconductor light emitting layer is formed to protect the surface, and the wafer processing adhesive sheet A method is known in which the back surface of a semiconductor wafer is ground using a grinder while the affixed surface side is affixed to a fixed base of a grinder (see Japanese Patent Application Laid-Open No. 2003-94295).

  Conventionally, however, there have been the following problems in the back surface grinding for thinning the semiconductor wafer as described above.

  When a nitride semiconductor layer (particularly a group III nitride semiconductor layer) is formed on a sapphire substrate, the wafer warps due to the difference in thermal expansion coefficient between the substrate and the semiconductor layer. As the nitride semiconductor layer becomes thicker, the warpage increases and the warpage at this time becomes convex on the nitride semiconductor layer side. Thereby, when the semiconductor wafer 1 coated with the adhesive 3 is bonded to the fixing plate 7, a gap is generated between the fixing plate 7 and the semiconductor wafer 1 at the outer peripheral portion of the semiconductor wafer 1 (FIG. 12). If the back surface of the semiconductor wafer is ground in this state, cracks and cracks will occur in the outer periphery of the semiconductor wafer. This phenomenon becomes more noticeable as the semiconductor wafer becomes thinner with a larger diameter. In the case of a semiconductor wafer having a diameter of 2 inches, the center portion is about 40 to 60 μm higher than the outer peripheral portion when the nitride semiconductor layer side is turned up. Thus, in the case of a semiconductor wafer having a diameter of 4 inches, the central portion is approximately 80 to 120 μm higher than the outer peripheral portion.

  Even when a wafer processing adhesive sheet is used, the wafer outer periphery is not adhered to the adhesive sheet due to the warpage of the semiconductor wafer, resulting in a gap between the adhesive sheet and the semiconductor wafer. Cracks and cracks will occur in the part.

JP 2003-94295 A

  The present invention has been made in view of the above problems, and manufacture of a semiconductor light-emitting element capable of reducing the thickness of a semiconductor wafer without causing cracks or cracks in the outer periphery of the semiconductor wafer in a semiconductor wafer grinding process. It aims to provide a method.

The present invention includes a step of laminating a nitride semiconductor layer on a sapphire substrate to form a semiconductor wafer;
After applying a pressure-sensitive adhesive to the surface of the semiconductor wafer on the nitride semiconductor layer side, attaching the semiconductor wafer to a fixed plate via the pressure-sensitive adhesive;
Grinding the sapphire substrate of the semiconductor wafer adhered to the fixing plate, thereby thinning the semiconductor wafer in this order,
The method of manufacturing a semiconductor light emitting element, wherein the film thickness of the adhesive applied to the outer peripheral portion of the semiconductor wafer is thicker than the film thickness of the adhesive applied to the central portion of the semiconductor wafer.

  The film thickness of the adhesive applied to the outer periphery of the semiconductor wafer is preferably 5 μm or more thicker than the film thickness of the adhesive applied to the central part of the semiconductor wafer.

  The film thickness of the adhesive applied to the central portion of the semiconductor wafer is preferably 15 μm or more, and more preferably 20 μm or more and 25 μm or less.

  It is preferable that after the grinding step, the step of removing the semiconductor wafer from the fixed plate and removing the adhesive is included.

  In the present invention, the thickness of the adhesive applied to the outer peripheral portion of the semiconductor wafer is made 5 μm or more thicker than the thickness of the adhesive applied to the central portion of the semiconductor wafer, thereby reducing the thickness of the semiconductor wafer. It is possible to prevent cracking and cracking of the semiconductor wafer in the grinding process.

(A) And (b) is a schematic diagram for demonstrating Embodiment 1. FIG. 4 is a graph showing correlation data between the rotational speed of the spin coater and the film thickness of the adhesive for the first embodiment. FIG. 6 is another schematic diagram for explaining the first embodiment. FIG. 6 is still another schematic diagram for explaining the first embodiment. FIG. 6 is still another schematic diagram for explaining the first embodiment. FIG. 6 is still another schematic diagram for explaining the first embodiment. FIG. 6 is still another schematic diagram for explaining the first embodiment. (A) And (b) is another schematic diagram for demonstrating Embodiment 1. FIG. FIG. 6 is still another schematic diagram for explaining the first embodiment. FIG. 6 is still another schematic diagram for explaining the first embodiment. FIG. 6 is still another schematic diagram for explaining the first embodiment. It is a schematic diagram for demonstrating a prior art.

The present invention includes a step of laminating a nitride semiconductor layer on a sapphire substrate to form a semiconductor wafer;
After applying a pressure-sensitive adhesive to the surface of the semiconductor wafer on the nitride semiconductor layer side, attaching the semiconductor wafer to a fixed plate via the pressure-sensitive adhesive;
A grinding method of thinning the semiconductor wafer by grinding the sapphire substrate of the semiconductor wafer adhered to the fixing plate in this order,
The film thickness of the adhesive applied to the outer peripheral part of the semiconductor wafer is made larger than the film thickness of the adhesive applied to the central part of the semiconductor wafer.

  The semiconductor wafer is usually a compound semiconductor wafer. The nitride semiconductor layer is not particularly limited, but is preferably a group III nitride semiconductor layer. The sapphire substrate is not particularly limited as long as it is used for forming a semiconductor wafer.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

<Embodiment 1>
First, the surface of the semiconductor wafer 1 on which the nitride semiconductor layer 12 (semiconductor light emitting layer) is formed is placed on the spin coater 4 with the upper side facing upward. The pressure-sensitive adhesive 2 is supplied from the upper side (nitride semiconductor layer 12 side) through the nozzle 3 to the central portion of the upper surface of the semiconductor wafer 1 in a state of being installed on the spin coater 4 (FIG. 1A). Next, by rotating the spin coater 4, the adhesive 2 spreads from the central portion to the outer peripheral portion of the semiconductor wafer 1 by centrifugal force, thereby sticking to the entire surface of the semiconductor wafer 1 on the nitride semiconductor layer 12 side. Agent 2 is applied (FIG. 1 (b)).

  As the adhesive 2, it is preferable to use a material that can be removed after grinding the back surface of the semiconductor wafer 1. As such an adhesive, for example, commercially available products such as Sky Liquid and Space Liquid manufactured by Nikka Seiko Co., Ltd. can be used. The thickness after application of the pressure-sensitive adhesive 2 (the state shown in FIG. 1B) can be adjusted by changing the number of revolutions of the spin coater 3, the supply amount of the pressure-sensitive adhesive 2, and the like. The rotation time can be arbitrarily set since it does not affect the thickness of the pressure-sensitive adhesive even if it is changed for a predetermined time or longer. This is because the adhesive is spread from the central part to the outer peripheral part by utilizing the centrifugal force generated by rotating the semiconductor wafer. The centrifugal force increases as the rotational speed increases. However, since the centrifugal force does not change with the rotational time, the rotational time may be set arbitrarily.

  In the present invention, the rotational speed of the spin coater is set so that the thickness of the adhesive applied to the outer peripheral portion of the semiconductor wafer is larger than the thickness of the adhesive applied to the central portion of the semiconductor wafer. The Thereby, even when the semiconductor wafer has a warp, it is possible to prevent cracking or cracking of the semiconductor wafer in the grinding process for thinning the semiconductor wafer. Here, the film thickness of the adhesive applied to the outer peripheral portion of the semiconductor wafer is preferably 5 μm or more thicker than the film thickness of the adhesive applied to the central portion of the semiconductor wafer. When the difference between the film thickness of the adhesive on the outer periphery of the semiconductor wafer and the film thickness of the adhesive on the center is less than 5 μm, in the case of a semiconductor wafer with a large warp exceeding 100 μm, At the time of sticking, a gap is generated between the outer peripheral portion of the semiconductor wafer and the fixed plate.

  FIG. 2 shows correlation data between the rotational speed of the spin coater and the film thickness of the adhesive (the film thickness at the central part and the film thickness difference between the central part and the outer peripheral part). This data is based on the use of Nissei Seiko's ASTROLIQUID as the adhesive, supplying 4 cc of adhesive to the center of a circular semiconductor wafer with a diameter of 100 mm, and then rotating the semiconductor wafer for 5 seconds. Is. As shown in FIG. 2, the lower the spin coater rotation speed, the thicker the adhesive film thickness at the center of the semiconductor wafer and the greater the difference in film thickness between the center and outer periphery of the semiconductor wafer. . This is because the centrifugal force becomes smaller as the rotation speed is lower, so that the adhesive is less likely to spread, and the adhesive accumulated in the outer peripheral portion cannot be shaken off, so that a film thickness difference is likely to occur between the central portion and the outer peripheral portion. It is.

  In the data shown in FIG. 2, the rotational speed is 800 rpm or less, and the film thickness difference between the central portion and the outer peripheral portion of the semiconductor wafer is 5 μm or more. For this reason, for example, by setting the rotation speed of the spin coater to 500 rpm and the rotation time to 5.0 seconds, the film thickness of the adhesive applied to the outer peripheral portion of the semiconductor wafer is applied to the central portion of the semiconductor wafer. The thickness of the adhesive may be 5 μm or more.

  Next, using a hot plate, for example, baking is performed at 100 to 120 ° C. for 2 to 3 minutes to evaporate the solvent in the adhesive and cure the adhesive 2. This baking may be performed using an oven. When the oven 5 is used, for example, baking is performed at 90 to 100 ° C. for 10 to 20 minutes (FIG. 3). Thereby, for example, the thickness of the cured adhesive is 18 μm at the center and 25 μm at the outer periphery.

  The film thickness of the adhesive applied to the central portion of the semiconductor wafer 1 is preferably 15 μm or more, and more preferably 20 μm or more and 25 μm or less. Since the surface on which the semiconductor light emitting layer is formed is uneven, if the thickness of the adhesive to be applied is too thin, the adhesive will not spread evenly at the time of pasting to the fixing plate, and the fixing plate and the semiconductor wafer It becomes easy to produce a gap in. If the applied pressure-sensitive adhesive becomes too thick, the solvent in the pressure-sensitive adhesive does not evaporate sufficiently during baking and remains in the pressure-sensitive adhesive. If the solvent remains in the adhesive, the adhesive strength decreases, so when the semiconductor wafer is attached to the fixed plate and then ground with a grinding machine, the semiconductor wafer may come off from the fixed plate, or part of the semiconductor wafer This is because cracks and cracks occur.

  Next, the fixing plate 6 is heated using the hot plate 7 (FIG. 4). The fixing plate 6 is preferably heated at a temperature 20 to 30 ° C. higher than the baking described above. For example, heating is performed at 140 ° C. for 5 minutes.

  Next, the semiconductor wafer 1 is placed on the heated fixing plate 7 so that the surface coated with the adhesive 2 is on the fixing plate 6 side, and waits for 3 to 5 minutes until the adhesive 2 is melted (FIG. 5). .

  Next, in order to fix the semiconductor wafer 1 to the fixing plate 6, the fixing plate 6 is pressed while being cooled. By cooling the fixing plate 6, the melted adhesive 2 is recured, so that the semiconductor wafer 1 and the fixing plate 6 are attached. Specifically, the fixed plate 6 is placed on a cooling plate 81 in which cooling water is circulated, and is pressed from the semiconductor wafer 1 side by a press head 82 of a press machine (FIG. 6). The cooling temperature of the fixing plate 6 at this time may be arbitrarily set as long as it is equal to or lower than the softening point of the adhesive 2. Moreover, the press pressure should just be a pressure by which the stationary plate 6 and the semiconductor wafer 1 are stuck.

For example, when an adhesive having a softening point of 80 to 90 ° C. is used, pressing can be performed for 10 minutes at a cooling temperature of the cooling stage of 25 ° C. and a pressing pressure of 1000 g / cm ² . Thereby, due to the warp of the semiconductor wafer 1, the outer peripheral portion of the semiconductor wafer 1 is lifted from the fixing plate 6, but the thickness of the adhesive 2 applied to the outer peripheral portion of the semiconductor wafer 1 is thicker than the central portion. The semiconductor wafer 1 can be adhered to the fixed plate 6 without generating a gap between the fixed plate 6 and the semiconductor wafer 1.

  Next, the fixing plate 6 to which the semiconductor wafer 1 is bonded is placed on the stage 91 of the grinding machine, and the semiconductor wafer 1 is thinned to a desired thickness by the grinding blade 92 of the grinding machine to obtain the thinned semiconductor wafer 10 ( FIG. 7). Such back surface grinding of the semiconductor wafer 1 may be performed using not only a grinding machine but also a polishing machine. Moreover, you may further grind | polish with a grinder after grinding with a grinder.

  Thereafter, in order to remove the thinned semiconductor wafer 10 from the fixed plate 6, the fixed plate 6 is heated using the hot plate 7 (FIG. 8A). What is necessary is just to set the heating temperature of the fixed plate 6 more than the softening point of the adhesive 2. When an adhesive having a softening point of 80 to 90 ° C. is used, heating may be performed at 120 ° C. for 5 minutes, for example. After fixing plate 6 is heated and adhesive 2 applied to thinned semiconductor wafer 10 is sufficiently softened, thinned semiconductor wafer 10 is removed from fixed plate 6 and adhesive 2 is removed (FIG. 8 ( b)).

  When the adhesive is removable with an organic solvent, the adhesive 2 can be removed by immersing the thinned semiconductor wafer 10 in acetone for 5 minutes (FIG. 9).

  Thereafter, individual semiconductor light emitting elements are cut out from the thinned semiconductor wafer 10 by a known technique. Specifically, the front surface side (the side opposite to the grinding surface) of the thinned semiconductor wafer 10 is attached to the wafer processing adhesive sheet 21 so that the back surface (grinding surface) of the thinned semiconductor wafer 10 is on the upper side. It fixes on the adhesive sheet 21 for wafer processing (FIG. 10). As the wafer processing pressure-sensitive adhesive sheet 21, for example, a sheet capable of weakening the pressure-sensitive adhesive force after processing such as a UV cured sheet is used.

  Next, the semiconductor light emitting devices 100 fabricated on the thinned semiconductor wafer 10 are separated into individual semiconductor light emitting devices 100 using a dicing method or a scribe method (FIG. 11). After the individual semiconductor light emitting elements 100 are separated, UV is irradiated from the back surface of the wafer processing pressure-sensitive adhesive sheet 21. Thereby, the adhesive force of the wafer processing adhesive sheet 21 is weakened. Thereafter, the semiconductor light emitting device 100 is inverted and transferred to an arbitrary sheet so that the surface of the semiconductor light emitting device 100 faces upward.

<Embodiment 2>
In the first embodiment, an organic solvent is used to remove the adhesive, but in this embodiment, the adhesive is removed by a dry cleaning method using an etching gas. Since the other points are the same as those of the first embodiment, description thereof is omitted.

Specifically, a semiconductor wafer is set in a vacuum device, the pressure in the device is set to about 0.1 to 2.0 Pa, and O ₂ gas is allowed to flow about 10 to 20 sccm. The adhesive can be removed by generating plasma with an RF power source with an output of about 100 to 300 W. Note that since the nitride semiconductor layer or the like formed on the surface of the semiconductor wafer is not etched by O ₂ gas, only the adhesive can be removed.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Semiconductor wafer, 10 Thinned semiconductor wafer, 100 Semiconductor light emitting element, 11 Sapphire substrate, 12 Nitride semiconductor layer, 2 Adhesive, 21 Adhesive sheet for wafer processing, 3 Nozzle, 4 Spin coater, 5 Oven, 6 Fixed plate 7 Hot plate, 81 Cooling plate, 82 Press head, 91 Stage, 92 Grinding blade.

Claims (5)

Forming a semiconductor wafer by stacking a nitride semiconductor layer on a sapphire substrate;
After applying a pressure-sensitive adhesive to the surface of the semiconductor wafer on the nitride semiconductor layer side, attaching the semiconductor wafer to a fixed plate via the pressure-sensitive adhesive;
Grinding the sapphire substrate of the semiconductor wafer adhered to the fixing plate, thereby thinning the semiconductor wafer in this order,
A method of manufacturing a semiconductor light emitting device, wherein a film thickness of an adhesive applied to an outer peripheral portion of the semiconductor wafer is thicker than a film thickness of an adhesive applied to a central portion of the semiconductor wafer.   The manufacturing method according to claim 1, wherein the film thickness of the adhesive applied to the outer peripheral portion of the semiconductor wafer is 5 μm or more thicker than the film thickness of the adhesive applied to the central portion of the semiconductor wafer.   The manufacturing method of Claim 1 whose film thickness of the adhesive apply | coated to the center part of the said semiconductor wafer is 15 micrometers or more.   The manufacturing method of Claim 1 whose film thickness of the adhesive apply | coated to the center part of the said semiconductor wafer is 20 micrometers or more and 25 micrometers or less.   The manufacturing method according to claim 1, further comprising a step of removing the semiconductor wafer from the fixed plate and removing the adhesive after the grinding step.

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