JP6345530B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a wafer processing method, and more particularly to a wafer processing method in which processing is performed by irradiating a wafer with a laser beam.

  Conventionally, in manufacturing a wafer, an ingot made of sapphire or the like is cut into a plate shape with a wire saw or the like. Unevenness is formed on the front and back surfaces of the wafer formed by this cutting.

  On the other hand, in order to form an optical device, a wafer in which an optical device layer is laminated by epitaxial growth on an epitaxial substrate made of sapphire or the like may be used (see Patent Document 1). In this wafer, in order to separate the optical device layer from the epitaxy substrate, a laser beam is irradiated from the back side of the wafer with a condensing point aligned with a buffer layer located at the boundary between them. By this irradiation, the buffer layer inside the wafer is destroyed, and the epitaxy substrate is separated from the optical device layer.

JP 2013-206959 A

  However, unevenness is formed on the back surface of the wafer as described above, and when a laser beam is irradiated from the back surface side, the laser beam is irregularly reflected by the unevenness, making it difficult to focus the laser beam inside the wafer. For this reason, there is a problem that the buffer layer inside the wafer cannot be destroyed and the wafer cannot be separated.

  Here, when grinding is performed so that the back surface of the wafer with unevenness is smooth, the irradiated laser beam can be condensed inside the wafer, but in this case, it takes time to perform grinding and a work load. Increases the processing efficiency. This problem becomes particularly apparent because the harder the wafer, the more difficult it is to grind.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a wafer processing method capable of quickly and easily separating a wafer by irradiating a laser beam from the uneven surface side of the wafer. And

  The wafer processing method according to the present invention comprises at least two layers of a first wafer having one surface formed of an uneven surface and a second wafer laminated on the opposite surface of the uneven surface of the first wafer. A method of processing a wafer in which a laminated wafer is irradiated with a laser beam and separated into a first wafer and a second wafer, and a liquid having a refractive index equivalent to the refractive index of the first wafer is applied to an uneven surface. And a boundary portion between the first wafer and the second wafer by irradiating a laser beam having a wavelength transmissive to the first wafer from the uneven surface side where the liquid is applied after the coating process. A laser processing step in which a laser processing layer is formed between the first wafer and the second wafer by scanning a condensing point on which the laser beam is focused, and an external force is applied to the laminated wafer after the laser processing step. It characterized in that it comprises a separation step of separating into a first wafer and a second wafer, a.

  According to the wafer processing method described above, since the liquid is applied to the uneven surface of the wafer, a smooth liquid surface can be formed above the uneven surface. Therefore, irregular reflection of the laser beam due to unevenness can be prevented when the laser beam is irradiated from the uneven surface side after application of the liquid. As a result, the laser beam can be focused on the boundary between the first and second wafers without performing grinding to smooth the uneven surface, and a laser processing layer can be quickly and easily formed on this boundary. As a result, the processing efficiency can be increased.

In place of the coating step in the processing method of the wafer in the water tank for water storage the liquid in the first wafer and the same refractive index, conducted Chakueki step of Chakueki the irregular surface of the first wafer, the laser In the processing step, a laser beam may be irradiated from the uneven surface side that has been deposited in the landing step. According to this configuration, the liquid that has landed on the wafer flows down into the water storage tank after the laser processing step and can be easily reused, so that the amount of liquid consumption can be reduced compared to the case where the liquid is applied.

  According to the present invention, since the liquid is applied to the uneven surface of the wafer, the wafer can be quickly and easily separated by irradiating the laser beam from the uneven surface side of the wafer.

1 is a configuration diagram of a laminated wafer according to an embodiment. It is explanatory drawing of the joining process which concerns on embodiment. It is explanatory drawing of the application | coating process which concerns on embodiment. It is explanatory drawing of the laser processing process which concerns on embodiment. It is explanatory drawing of the isolation | separation process which concerns on embodiment. It is explanatory drawing of the liquid landing process which concerns on a modification.

  Hereinafter, a wafer processing method according to an embodiment will be described with reference to the accompanying drawings. First, the laminated wafer will be described with reference to FIG. FIG. 1A is a schematic perspective view of a laminated wafer, and FIG. 1B is an enlarged cross-sectional view of a main part of the laminated wafer.

  A laminated wafer 10 shown in FIGS. 1A and 1B is an optical device wafer for manufacturing an optical device. The laminated wafer 10 is a sapphire wafer (first wafer) 11 having a disk shape with a diameter of 50 mm and a thickness of 600 μm, and GaN (gallium nitride) that is laminated on the surface 11 a side of the sapphire wafer 11 to form an optical device. And a wafer (second wafer) 12. The sapphire wafer 11 is formed by cutting a sapphire ingot (not shown) into a plate shape, and before the GaN wafer 12 is formed, the surface 11a is flattened by grinding. The back surface 11b which becomes one surface of the sapphire wafer 11 is in a state where the above cutting is performed, and is formed by an uneven surface. Therefore, in the laminated wafer 10, the GaN wafer 12 is laminated on the side opposite to the uneven surface (back surface 11 b) of the sapphire wafer 11.

  The sapphire wafer 11 serves as an epitaxy substrate, and the GaN wafer 12 is formed from an n-type gallium nitride semiconductor layer 12A and a p-type gallium nitride semiconductor layer 12B (not shown in FIG. 1A) formed on the surface 11a of the sapphire wafer 11 by an epitaxial growth method. Become. When the GaN wafer 12 is stacked on the sapphire wafer 11, a buffer layer 13 having a thickness of, for example, 1 μm is formed between the surface 11a of the sapphire wafer 11 and the n-type gallium nitride semiconductor layer 12A (not shown in FIG. 1A). Is formed. In the present embodiment, the thickness of the GaN wafer 12 is, for example, 10 μm. In the GaN wafer 12, an optical device 16 (not shown in FIG. 1B) is formed in a plurality of regions partitioned by a plurality of division lines 15 formed in a lattice shape.

  Next, a wafer processing method according to the present embodiment will be described with reference to FIGS. 2 is an explanatory diagram of the bonding process, FIG. 3 is an explanatory diagram of the coating process, FIG. 4 is an explanatory diagram of the laser processing process, and FIG. 5 is an explanatory diagram of the separation process. Note that the steps shown in FIGS. 2 to 5 are merely examples, and the present invention is not limited to this configuration.

  First, as shown in FIGS. 2A to 2C, a joining process for joining the transfer substrate 20 to the GaN wafer 12 side of the laminated wafer 10 is performed. 2A is a schematic perspective view before joining the laminated wafer and the transfer substrate, FIG. 2B is a schematic perspective view after joining the laminated wafer and the transfer substrate, and FIG. 2C is an enlarged cross-sectional view of the main part of the joined laminated wafer and transfer substrate. FIG.

  In the bonding step, the transfer substrate 20 made of a copper substrate having a thickness of 1 mm is bonded to the surface 12 a of the GaN wafer 12 via the bonding metal layer 21. Note that molybdenum (Mo), silicon (Si), or the like can be used as the transfer substrate 20, and gold (Au), platinum (Pt), chromium (Cr) is used as a bonding metal for forming the bonding metal layer 21. Indium (In), palladium (Pd), or the like can be used. In this bonding step, the bonding metal is deposited on the surface 12a of the GaN wafer 12 or the surface 20a of the transfer substrate 20 to form a bonding metal layer 21 having a thickness of about 3 μm. Then, the bonding metal layer 21 and the surface 20a of the transfer substrate 20 or the surface 12a of the GaN wafer 12 face each other and are pressure-bonded. As a result, a bonded wafer 25 in which the laminated wafer 10 and the transfer substrate 20 are bonded via the bonding metal layer 21 is formed.

  After performing the bonding step, the coating step is performed on the back surface 11b of the sapphire wafer 11, as shown in FIG. In the coating process, the bonded wafer 25 is placed on the spinner table 30 of a coating apparatus (not shown) with the back surface 11b of the sapphire wafer 11 facing upward. And the liquid L is apply | coated from the nozzle 31 of a coating device (not shown) with respect to the back surface 11b of the sapphire wafer 11, rotating the bonding wafer 25 at high speed. Thereby, the smooth layer 18 made of the liquid L is formed on the back surface 11b of the sapphire wafer 11 by a so-called spin coating method. The smooth layer 18 is formed from the upper surface to such a thickness that the convex portions forming the uneven surface of the back surface 11b do not protrude, and the upper surface of the smooth layer 18 is flattened as a liquid surface.

In the liquid L, a liquid having a refractive index equivalent to that of the sapphire wafer 11 is used. Here, “equivalent” means that the reflectance R is 0.5 or less when light is vertically incident from the upper surface of the smooth layer 18. When this is expressed by a mathematical formula, the relationship of the following formula (1) is satisfied. In the formula (1), R is the reflectance (0.5), n ₁ is the refractive index of the sapphire wafer 11, and n ₂ is the refractive index of the liquid L.

  In the present embodiment, as the liquid L, in addition to PVP (refractive index 1.52), plant refined oil (refractive index 1.52), immersion oil (refractive index 1. 52), PVA (refractive index 1.52), pure water (refractive index 1.35) can be employed. Since the refractive index of the sapphire constituting the sapphire wafer 11 is 1.7 to 1.8, the relationship of the above formula (1) is satisfied.

After performing the coating process, a laser processing process is performed as shown in FIG. In this step, the transfer substrate 20 side of the bonded wafer 25 is placed on the upper surface (holding surface) of the chuck table 41 in a laser processing apparatus (not shown). Then, the bonded wafer 25 is sucked and held on the chuck table 41 by suction means (not shown) with the smooth layer 18 facing upward. After this suction and holding, the processing feed means (not shown) is operated to move the chuck table 41 to the laser beam irradiation area of the laser beam irradiation means 42. Thereafter, the laser beam irradiation means 42 irradiates the laser beam from the back surface 11b side (upper side in the figure) of the sapphire wafer 11 which is the smooth layer 18 side. In the laser beam irradiation means 42, the laser beam oscillation means 42 a oscillates a laser beam set to a wavelength having transparency to the sapphire wafer 11. Then, the condensing lens 42 b irradiates so that the condensing point where the laser beam is condensed is positioned on the buffer layer 13. As a result, the processing for breaking the buffer layer 13 located at the boundary between the sapphire wafer 11 and the GaN wafer 12 is performed by the laser beam irradiated from the laser beam irradiation means 42. The said laser processing process is implemented on the following laser processing conditions, for example.
Light source: YAG laser Wavelength: 257 nm
Repetition frequency: 50 kHz
Average output: 0.12W
Pulse width: 100ps
Peak power: 5μJ-3μJ
Spot diameter: 70 μm
Laser irradiation means moving speed: 50-100 mm / s

  In this way, the chuck table 41 is moved while irradiating the laser beam, and the region corresponding to the entire surface of the buffer layer 13 is scanned with the condensing point of the laser beam. Thereby, a laser processed layer 19 in which the buffer layer 13 is broken is formed between the sapphire wafer 11 and the GaN wafer 12. By this laser processing layer 19, the bonding function between the sapphire wafer 11 and the GaN wafer 12 by the buffer layer 13 is lost.

  After performing the laser processing step, a separation step is performed as shown in FIG. In this step, the processing feed means (not shown) described above is operated, and the chuck table 41 that sucks and holds the bonded wafer 25 is moved below a holding means 45 that constitutes a separation device (not shown). Then, the holding means 45 is lowered, the lower surface of the holding means 45 is brought into contact with the smooth layer 18 of the bonded wafer 25, the suction means (not shown) is activated, and the lower surface of the holding means 45 is moved to the bonded wafer 25. The smooth layer 18 side is adsorbed and held. In this attracted and held state, the holding means 45 is raised to apply an external force in a direction away from the top and bottom to the laser processed layer 19 in the laminated wafer 10. Thereby, the sapphire wafer 11 is separated from the GaN wafer 12, and the transfer of the GaN wafer 12 to the transfer substrate 20 is completed.

  Thus, in the processing method of the laminated wafer 10 according to the present embodiment, the smooth layer 18 is formed on the back surface 11b of the sapphire wafer 11 by applying the liquid L, and the refractive index of the liquid L is the refractive index of the sapphire wafer 11. It is equivalent to. Thereby, it is possible to prevent the laser beam irradiated in the laser processing step from being irregularly reflected by the uneven surface on the back surface 11 b of the sapphire wafer 11, and the condensing point can be easily and quickly positioned on the buffer layer 13. As a result, since the back surface 11b of the sapphire wafer 11 is smoothed, it is not necessary to perform processing such as grinding, and the processing efficiency can be improved. In particular, since the sapphire wafer 11 is hard and difficult to grind, the processing efficiency can be further improved.

  In addition, this invention is not limited to the said embodiment, It can change and implement variously. In the above-described embodiment, the size, shape, and the like illustrated in the accompanying drawings are not limited to this, and can be appropriately changed within a range in which the effect of the present invention is exhibited. In addition, various modifications can be made without departing from the scope of the object of the present invention.

  For example, in each of the above embodiments, a liquid landing process may be performed as shown in FIG. 6 instead of the coating process. FIG. 6 is an explanatory diagram of a liquid landing process in the wafer processing method according to the modification. In this step, the liquid L described above is stored in the water storage tank 50. As the material of the water storage tank 50, a material having a refractive index equivalent to the refractive index of the sapphire wafer 11 is used as in the liquid L. Then, the back surface 11b of the sapphire wafer 11 is directed downward, and the liquid L stored in the water storage tank 50 is immersed so that the back surface 11b of the sapphire wafer 11 is deposited. While maintaining this state, a laser beam is irradiated from the laser irradiation means 42 disposed on the lower outside of the water storage tank 50 toward the back surface 11 b of the sapphire wafer 11. At this time, the laser processing layer 19 can be formed similarly to the first embodiment by setting the condensing point of the laser beam as the buffer layer 13, and the condensing point is the sapphire wafer 11 or the transfer substrate 20, Similarly to the second embodiment, the modified layers R1 and R2 can be formed.

  By performing the above-mentioned liquid application process, the liquid L applied to the sapphire wafer 11 flows down into the water storage tank 50 only by raising the bonded wafer 25 after the laser processing process. Thereby, the liquid L can be reused easily and the consumption of the liquid L can be reduced compared with the case where the liquid L is applied.

  Moreover, in each said embodiment, the wafers 11 and 12 which comprise the laminated wafer 10 should just have at least 2 layer, The material and the number of layers may be changed suitably.

  As described above, according to the present invention, there is an effect that a laser beam can be irradiated from the concavo-convex surface side of a wafer to perform a process of separating the wafer quickly and easily, particularly in an optical device wafer. This is useful when the optical device layer is transferred to the transfer substrate.

10 Laminated wafer 11 Sapphire wafer (first wafer)
12 GaN wafer (second wafer)
15 Line to be divided 19 Laser processing layer 25 Bonded wafer L Liquid

Claims (2)

Irradiate a laser beam to a laminated wafer in which at least two layers of a first wafer having one surface formed of an uneven surface and a second wafer laminated on the opposite surface of the first wafer are laminated. And a wafer processing method for separating the first wafer and the second wafer,
An application step of applying a liquid having a refractive index equivalent to the refractive index of the first wafer to the uneven surface;
After the coating step, a laser beam having a wavelength having transparency to the first wafer is irradiated from the uneven surface side to which the liquid is applied, and the boundary between the first wafer and the second wafer A laser processing step of forming a laser processing layer between the first wafer and the second wafer by scanning a condensing point where a laser beam is focused on a portion;
After the laser processing step, a separation step in which an external force is applied to the laminated wafer to separate the first wafer and the second wafer;
A wafer processing method comprising: Instead of the coating process, the water storage tank for water storage the liquid of the first wafer and the same refractive index, conducted Chakueki step of Chakueki the concave convex surface of the first wafer,
2. The wafer processing method according to claim 1, wherein in the laser processing step, a laser beam is irradiated from the uneven surface side applied in the liquid application step.

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