JP2013081953A - Metal plate ablation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal plate ablation method which can prevent energy diffusion and laser beam reflection.SOLUTION: The metal plate ablation method ablates a metal plate by emitting laser beams thereto and comprises a protective film forming process which applies a liquid resin mixed with fine powder of oxide having absorbability with respect to laser beam wavelength to at least a metal plate area to be ablated so as to form a protective film containing the fine powder and a laser processing process which emits laser beams to the metal plate area with the protective film formed therein for ablation after the protective film forming process.

Description

  The present invention relates to a metal plate ablation method for performing ablation processing by irradiating a metal plate with a laser beam.

  A wafer such as a silicon wafer or a sapphire wafer formed on the surface by dividing a plurality of devices such as IC, LSI, LED, etc. by dividing lines is divided into individual devices by ablation processing by a laser processing apparatus, for example. Devices are widely used in various electric devices such as mobile phones and personal computers.

  In the ablation processing method using a laser processing apparatus, a laser processing groove is formed by ablation processing by irradiating the wafer with a pulsed laser beam having a wavelength that is absorptive to the wafer. Then, the wafer is cleaved by the braking device along the laser processing groove and divided into individual devices (see, for example, JP-A-10-305420).

  Also, an epitaxial layer (a light emitting layer made of an n-type semiconductor and a p-type semiconductor) laminated on the upper surface of the sapphire substrate is attached to the surface of a metal plate such as Cu or Mo with a brazing agent such as gold tin, A technique called lift-off is known in which a laser beam is irradiated to break a buffer layer interposed between a sapphire substrate and an epitaxial layer, and the epitaxial layer is transferred to a metal plate. A device having a metal plate on the back surface formed by dividing the metal plate is characterized by excellent heat resistance.

JP-A-10-305420 JP 2007-118011 A JP 2004-72052 A

  By the way, depending on the semiconductor wafer, an electrode for testing a characteristic of a device called TEG (Test Element Group) may be formed on a division line (street). When a metal film (metal plate) such as TEG is formed, the laser beam energy is diffused and reflected, and the laser beam energy is not sufficiently used for ablation, and the ablation process is blocked at the TEG part. There is a problem that.

  Further, when a metal plate having an epitaxial layer on the surface formed by the lift-off technique is irradiated with a laser beam and the metal plate is divided together with the epitaxial layer to form a light emitting device such as an LED, the energy of the laser beam in the metal plate is reduced. There is a problem that diffusion and reflection of the laser beam occur, energy loss is large, and laser processing is not performed sufficiently.

  The present invention has been made in view of these points, and an object of the present invention is to provide a metal plate ablation processing method capable of suppressing energy diffusion and laser beam reflection.

  According to the present invention, there is provided an ablation processing method for a metal plate in which a metal plate is irradiated with a laser beam to perform ablation processing, and at least a region of the metal plate to be ablated has an absorption property with respect to the wavelength of the laser beam. A protective film forming step of forming a protective film containing fine powder by applying a liquid resin mixed with fine powder of the product, and after performing the protective film forming step, in the region of the metal plate on which the protective film is formed And a laser processing step of performing ablation processing by irradiating a laser beam.

Preferably, the average particle diameter of the fine oxide powder is smaller than the spot diameter of the laser beam. Preferably, the wavelength of the laser beam is 355 nm or less, and the fine oxide powder is a metal oxide selected from the group consisting of Fe ₂ O ₃ , ZnO, TiO ₂ , CeO ₂ , CuO, Cu ₂ O and MgO. The liquid resin contains polyvinyl alcohol.

  According to the metal plate ablation processing method of the present invention, a protective film is applied by applying a liquid resin mixed with oxide fine powder having an absorptivity to the wavelength of the laser beam to at least the region of the metal plate to be ablated. As a result, the laser beam is absorbed by the fine oxide powder, reaches the band gap energy, and the bonding force of the atoms is broken, so that the metal plate is ablated in a chain, energy diffusion and laser beam Thus, the ablation processing of the metal plate substrate is efficiently and smoothly performed.

It is a perspective view of the laser processing apparatus suitable for implementing the ablation processing method of this invention. It is a block diagram of a laser beam irradiation unit. It is a perspective view of the metal plate which has an epitaxial layer on the surface supported by the annular frame via the adhesive tape. 1 is a perspective view of a semiconductor wafer in which a TEG is formed on a street supported by an annular frame via an adhesive tape. It is a perspective view which shows a liquid resin application | coating process. It is a graph which shows the spectral transmittance of various metal oxides. It is a perspective view which shows an ablation process process. It is a perspective view of the metal plate in which the epitaxial layer was formed in the surface supported by the cyclic | annular flame | frame via the adhesive tape of the state which ablation process was complete | finished.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of a laser processing apparatus suitable for carrying out the metal plate ablation processing method of the present invention.

  The laser processing apparatus 2 includes a first slide block 6 mounted on a stationary base 4 so as to be movable in the X-axis direction. The first slide block 6 is moved along the pair of guide rails 14 in the machining feed direction, that is, the X-axis direction, by the machining feed means 12 including the ball screw 8 and the pulse motor 10.

  A second slide block 16 is mounted on the first slide block 6 so as to be movable in the Y-axis direction. That is, the second slide block 16 is moved in the indexing direction, that is, the Y-axis direction along the pair of guide rails 24 by the indexing feeding means 22 constituted by the ball screw 18 and the pulse motor 20.

  A chuck table 28 is mounted on the second slide block 16 via a cylindrical support member 26, and the chuck table 28 can be moved in the X-axis direction and the Y-axis direction by the processing feed means 12 and the index feed means 22. . The chuck table 28 is provided with a clamp 30 that clamps the metal plate sucked and held by the chuck table 28.

  A column 32 is erected on the stationary base 4, and a casing 35 for accommodating the laser beam irradiation unit 34 is attached to the column 32. As shown in FIG. 2, the laser beam irradiation unit 34 includes a laser oscillator 62 that oscillates a YAG laser or a YVO4 laser, a repetition frequency setting unit 64, a pulse width adjustment unit 66, and a power adjustment unit 68. .

  The pulse laser beam adjusted to a predetermined power by the power adjusting means 68 of the laser beam irradiation unit 34 is reflected by the mirror 70 of the condenser 36 attached to the tip of the casing 35 and further collected by the condenser objective lens 72. The light is irradiated to the metal plate 11 held on the chuck table 28.

  At the tip of the casing 35, an image pickup unit 38 that detects the processing region to be laser processed in alignment with the condenser 36 in the X-axis direction is disposed. The image pickup unit 38 includes an image pickup element such as a normal CCD that picks up an image of a processing region of a metal plate with visible light.

  The imaging unit 38 further includes an infrared irradiator that irradiates the metal plate with infrared rays, an optical system that captures infrared rays emitted by the infrared irradiator, and an infrared CCD that outputs an electrical signal corresponding to the infrared rays captured by the optical system. An infrared imaging unit composed of an infrared imaging element such as an image sensor is included, and the captured image signal is transmitted to a controller (control means) 40.

  The controller 40 includes a central processing unit (CPU) 42 that performs arithmetic processing according to a control program, a read-only memory (ROM) 44 that stores a control program, and a random read / write that stores arithmetic results. An access memory (RAM) 46, a counter 48, an input interface 50, and an output interface 52 are provided.

  Reference numeral 56 denotes a processing feed amount detection means comprising a linear scale 54 disposed along the guide rail 14 and a read head (not shown) disposed on the first slide block 6. Is input to the input interface 50 of the controller 40.

  Reference numeral 60 denotes index feed amount detection means comprising a linear scale 58 disposed along the guide rail 24 and a read head (not shown) disposed on the second slide block 16. The detection signal is input to the input interface 50 of the controller 40.

  An image signal captured by the imaging unit 38 is also input to the input interface 50 of the controller 40. On the other hand, a control signal is output from the output interface 52 of the controller 40 to the pulse motor 10, the pulse motor 20, the laser beam irradiation unit 34, and the like.

  Referring to FIG. 3, there is shown a perspective view of a metal plate 11 having an epitaxial layer 13 on the surface which is the workpiece of the first embodiment of the present invention. In this metal plate 11 manufacturing method, an epitaxial layer 13 made of an n-type semiconductor and a p-type semiconductor is laminated on a sapphire substrate (not shown), and the epitaxial layer 13 side is gold tin or the like on the surface of the metal plate 11 made of Cu, Mo or the like. It is pasted with a lotion.

  Thereafter, the laser beam is irradiated from the sapphire substrate side to destroy the buffer layer interposed between the sapphire substrate and the epitaxial layer 13, the epitaxial layer 13 is lifted off from the sapphire substrate, and the epitaxial layer 13 is moved to the surface of the metal plate 11. Manufactured with alternative lift-off technology.

  In the epitaxial layer 13, the first street S1 and the second street S2 are formed to be orthogonal to each other, and a large number of LEDs and the like are formed in a region partitioned by the first street S1 and the second street S2. A light emitting device D is formed.

  The metal plate 11 is attached to a dicing tape T that is an adhesive tape, and the outer peripheral portion of the dicing tape T is attached to an annular frame F. As a result, the metal plate 11 is supported by the annular frame F via the dicing tape T, and is supported and fixed on the chuck table 28 by clamping the annular frame F by the clamp 30 shown in FIG.

  Referring to FIG. 4, there is shown a perspective view of a semiconductor wafer W that is a workpiece of the second embodiment of the present invention. Similar to the epitaxial layer 13 shown in FIG. 3, the first street S1 and the second street S2 are formed orthogonally on the surface of the semiconductor wafer W, and the first street S1 and the second street S2 are formed. A number of devices D are formed in the region partitioned by S2.

  As shown in the partially enlarged view of FIG. 4, a TEG (Test Element Group) 15 that is an electrode for testing the characteristics of the device D is formed on the second street S2. The TEG 15 is made of Au, Al, Cu or the like.

  A similar TEG 15 is also formed on the first street S1. Similar to the embodiment shown in FIG. 3, the wafer W is attached to a dicing tape T that is an adhesive tape, and the outer peripheral portion of the dicing tape T is attached to an annular frame F.

  The metal plate ablation method of the present invention will be described below with respect to the metal plate 11 which is the workpiece of the first embodiment shown in FIG. First, a liquid resin coating process is performed in which a liquid resin in which fine powder of an oxide having an absorptivity with respect to the wavelength of the laser beam is mixed is applied to a region of the metal plate 11 to be ablated.

For example, as shown in FIG. 5, the liquid resin supply source 76 includes PVA (polyvinyl alcohol) mixed with oxide fine powder (for example, TiO ₂ ) having an absorptivity with respect to the wavelength of the laser beam (for example, 355 nm). The liquid resin 80 is stored.

  By driving the pump 78, the liquid resin 80 stored in the liquid resin supply source 76 is supplied from the supply nozzle 74 to the surface of the metal plate 11, and the liquid resin 80 is applied to the surface of the metal plate 11. Then, the liquid resin 80 is cured to form a protective film 82 in which fine powder of oxide having an absorptivity with respect to the wavelength of the laser beam is mixed.

As a method for applying the liquid resin 80 onto the surface of the metal plate 11, for example, a spin coating method in which the metal plate 11 is applied while rotating can be employed. In this embodiment, TiO ₂ is used as a fine powder of oxide mixed in a liquid resin such as PVA (polyvinyl alcohol) or PEG (polyethylene glycol).

  In the embodiment shown in FIG. 5, the liquid resin 80 containing fine oxide powder is applied to the entire surface of the metal plate 11 to form the protective film 82. The protective film may be formed by applying only to the first street S1 and the second street S2. The average particle diameter of the fine oxide powder mixed in the liquid resin is preferably smaller than the spot diameter of the laser beam, for example, preferably smaller than 10 μm.

Referring to FIG. 6, the spectral transmittances of ZnO, TiO ₂ , CeO ₂ , and Fe ₂ O ₃ are shown. From this graph, it is understood that when the wavelength of the laser beam used for ablation processing is set to 355 nm or less, the laser beam is almost absorbed by the fine powder of these metal oxides.

In addition to the metal oxide shown in FIG. 6, CuO, Cu ₂ O, and MgO have the same tendency of spectral transmittance, and thus can be adopted as fine powder mixed in the liquid resin. Therefore, any one of TiO ₂ , Fe ₂ O ₃ , ZnO, CeO ₂ , CuO, Cu ₂ O, and MgO can be used as the fine oxide powder mixed in the liquid resin.

  Table 1 shows the extinction coefficient (extinction coefficient) k and melting point of these metal oxides. Incidentally, there is a relationship of α = 4πk / λ between the extinction coefficient k and the absorption coefficient α. Here, λ is the wavelength of light to be used.

  After performing the liquid resin coating process to form the protective film 82 on the surface of the metal plate 11, a laser processing process by ablation processing is performed. In this laser processing step, as shown in FIG. 7, a pulse laser beam 37 having a wavelength (for example, 355 nm) having an absorptivity with respect to the fine oxide powder in the metal plate 11 and the protective film 82 is collected by a condenser 36. While condensing and irradiating the surface of the metal plate 11, the chuck table 28 is moved at a predetermined processing feed speed in the direction of the arrow X1 in FIG. 7, and laser processing grooves 84 are ablated along the first street S1. Form.

  While indexing and feeding the chuck table 28 holding the metal plate 11 in the Y-axis direction, similar laser processing grooves 84 are formed by ablation processing along all the first streets.

  Next, after the chuck table 28 is rotated 90 degrees, similar laser processing grooves 84 are formed by ablation along all the second streets S2 extending in the direction orthogonal to the first streets S1. FIG. 8 is a perspective view showing a state in which the laser processing grooves 84 are formed along all the streets S1 and S2.

  The laser processing conditions of this embodiment are set as follows, for example.

Light source: YAG pulse laser Wavelength: 355 nm (third harmonic of YAG laser)
Average output: 0.5-10W
Repetition frequency: 10 to 200 kHz
Spot diameter: φ1-10μm
Feeding speed: 10 to 100 mm / sec

  The protective film forming step and the laser processing step by ablation described for the metal plate 11 shown in FIG. 3 are performed by the ablation processing method for the wafer W partially including the metal plate as the TEG 15 in the streets S1 and S2 shown in FIG. It can be similarly applied to.

  According to the ablation processing method of the first and second embodiments, the liquid resin 80 mixed with oxide fine powder having an absorptivity with respect to the wavelength of the laser beam is applied to the surface of the metal plate 11 or the wafer W for protection. Since the ablation process is performed after the film 82 is formed, the energy of the laser beam is absorbed by the fine oxide powder, reaches the band gap energy, and the bonding force of the atoms is broken, so that the metal plates 11 are chained. Alternatively, the wafer W is ablated.

  Therefore, the diffusion of energy and the reflection of the laser beam are suppressed, and the ablation process is efficiently and smoothly performed. The fine oxide powder mixed in the liquid resin serves as a processing accelerator.

  After forming the laser processing grooves 84 along all the streets S1 and S2, the dicing tape T is expanded in the radial direction by using a well-known braking device to apply an external force to the metal plate 11 or the wafer W. By this external force, the metal plate 11 or the wafer W is divided into individual light emitting devices or devices D along the laser processing grooves 84.

W Semiconductor wafer T Adhesive tape (dicing tape)
F Ring frame D Light-emitting device (device)
2 Laser processing apparatus 11 Metal plate 13 Epitaxial layer 15 TEG
28 Chuck table 34 Laser beam irradiation unit 36 Condenser 80 Liquid resin 82 containing fine powder Protective film 84 Laser processing groove

Claims (3)

A metal plate ablation method for performing ablation processing by irradiating a metal plate with a laser beam,
A protective film forming step of forming a protective film containing fine powder by applying a liquid resin mixed with fine powder of an oxide having an absorptivity with respect to the wavelength of the laser beam at least in the region of the metal plate to be ablated;
A laser processing step of performing ablation processing by irradiating the region of the metal plate on which the protective film is formed with a laser beam after performing the protective film forming step;
A metal plate ablation processing method characterized by comprising:   2. The metal plate ablation method according to claim 1, wherein an average particle diameter of the fine oxide powder is smaller than a spot diameter of the laser beam. The wavelength of the laser beam is 355 nm or less, and the fine oxide powder is a metal oxide selected from the group consisting of Fe ₂ O ₃ , ZnO, TiO ₂ , CeO ₂ , CuO, Cu ₂ O and MgO. The metal plate ablation processing method according to claim 1, wherein the liquid resin contains polyvinyl alcohol.

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