JP2013081947A - Semiconductor substrate ablation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an semiconductor substrate ablation method which can prevent energy diffusion and laser beam reflection.SOLUTION: The semiconductor device ablation method ablates a semiconductor substrate 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 semiconductor substrate 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 semiconductor substrate area with the protective film formed therein for ablation after the protective film forming process is practiced.

Description

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

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

  A dicing method using a cutting device called a dicing saw is widely used for dividing the wafer. In the dicing method, the wafer is cut by cutting a wafer into a wafer while rotating a cutting blade having a thickness of about 30 μm by solidifying abrasive grains such as diamond with a metal or resin at a high speed of about 30000 rpm. Divide into devices.

  On the other hand, in recent years, a laser beam is formed by ablation processing by irradiating the wafer with a pulsed laser beam having a wavelength that is absorptive to the wafer, and the wafer is cut along a cutting device along the laser processing groove. A method of dividing into individual devices has been proposed (Japanese Patent Laid-Open No. 10-305420).

  The formation of laser-processed grooves by ablation processing can increase the processing speed compared to the dicing method using a dicing saw, and relatively easily process even a wafer made of a material having high hardness such as sapphire or SiC. be able to.

  Further, since the processing groove can be made narrow, for example, 10 μm or less, it has a feature that the amount of devices taken per wafer can be increased as compared with the case of processing by the dicing method. .

  However, when a semiconductor substrate such as a wafer is irradiated with a pulsed laser beam having an absorptive wavelength (for example, 355 nm), the energy of the absorbed laser beam reaches the band gap energy, destroying the bonding force of atoms and ablation. Although processing is performed, there is a problem that energy diffusion of the laser beam and reflection of the laser beam occur on the upper surface of the semiconductor substrate, and the energy of the laser beam is not sufficiently used for ablation processing, resulting in a large energy loss. In addition, the semiconductor substrate is melted by energy diffusion to generate debris, and the debris is scattered to contaminate the surface of the device.

  Therefore, in Japanese Patent Application Laid-Open No. 2004-188475, a water-soluble resin such as PVA (polyvinyl alcohol) or PEG (polyethylene glycol) is applied and protected on the processed surface of the wafer in order to solve such problems caused by debris. There has been proposed a laser processing apparatus in which a film is formed and a wafer is irradiated with a pulsed laser beam through the protective film.

JP-A-10-305420 JP 2004-188475 A

  By applying a protective film to the processing surface of the wafer, the problem of debris adhering to the device surface can be solved. However, there is a problem that the processing efficiency deteriorates due to diffusion of laser beam energy by the protective film.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a semiconductor substrate 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 semiconductor substrate in which a semiconductor substrate is irradiated with a laser beam to perform ablation processing, and at least a region of the semiconductor substrate 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 a fine powder of the product, and after performing the protective film forming step, in the region of the semiconductor substrate 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 semiconductor substrate ablation processing method of the present invention, at least a region of the semiconductor substrate to be ablated is coated with a liquid resin mixed with an oxide fine powder having an absorptivity with respect to the wavelength of the laser beam to form a protective film. As it forms, the laser beam is absorbed by the fine oxide powder, reaches the band gap energy, and the bond strength of the atoms is broken, so that it reaches the band gap energy of the semiconductor substrate in a chain, and ablation is performed. The diffusion of energy and the reflection of the laser beam are suppressed, and the ablation processing of the semiconductor 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 semiconductor wafer supported by the annular frame via the 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 semiconductor wafer supported by the cyclic | annular flame | frame via the adhesive tape of the state which ablation processing was complete | finished.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic configuration diagram of a laser processing apparatus suitable for carrying out the semiconductor substrate 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 for clamping the semiconductor wafer 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 semiconductor wafer W is irradiated with light and irradiated onto 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 device such as a normal CCD that picks up an image of a processing region of a semiconductor wafer with visible light.

  The imaging unit 38 further includes an infrared irradiator that irradiates the semiconductor wafer with infrared rays, an optical system that captures infrared rays irradiated 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.

  As shown in FIG. 3, on the surface of the semiconductor wafer W to be processed by the laser processing apparatus 2, the first street S1 and the second street S2 are formed orthogonally, and the first street S1. A number of devices D are formed in a region partitioned by the second street S2.

  The wafer W is attached to a dicing tape T that is an adhesive tape, and the outer periphery of the dicing tape T is attached to an annular frame F. Thus, the wafer W 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.

  In the semiconductor substrate ablation processing method of the present invention, first, a liquid resin in which fine powder of an oxide having an absorptivity with respect to the wavelength of the laser beam is applied to a region to be ablated on a semiconductor wafer (semiconductor substrate) W is applied. A liquid resin coating process is performed.

For example, as shown in FIG. 4, 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 wafer W, and the liquid resin 80 is applied to the surface of the wafer W. 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 wafer W, for example, a spin coating method in which the wafer W 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. 4, the liquid resin 80 containing fine oxide powder is applied to the entire surface of the wafer W to form the protective film 82. However, the liquid resin 80 is a region to be ablated, that is, a first film. The protective film may be formed only on the street S1 and the second street S2.

  In the present embodiment, the semiconductor wafer W is formed from a silicon wafer. Since the absorption edge wavelength of silicon is 1100 nm, ablation processing can be smoothly performed by using a laser beam having a wavelength of 355 nm or less. 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. 5, 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. 5, CuO, Cu ₂ O, and MgO also have the same tendency of spectral transmittance, and thus can be employed 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 wafer W, a laser processing process by ablation processing is performed. In this laser processing step, as shown in FIG. 6, a pulse laser beam 37 having a wavelength (for example, 355 nm) having an absorptivity with respect to the fine powder of oxide in the semiconductor wafer W and the protective film 82 is collected by a condenser 36. While condensing and irradiating the surface of the semiconductor wafer W, the chuck table 28 is moved in the direction of the arrow X1 in FIG. 6 at a predetermined processing feed speed, and laser processing grooves 84 are ablated along the first street S1. Form.

  While indexing and feeding the chuck table 28 holding the wafer W in the Y-axis direction, similar laser machining grooves 84 are formed by ablation 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. 7 shows a perspective view of the 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 semiconductor substrate to be processed of the present invention includes Si, SiGe, Ge, AlN, InAlN, InN, GaN, InGaN, SiC, and GaAs substrates. Further, Al ₂ O ₃ having a semiconductor laminated on the surface is included.

  According to the semiconductor substrate ablation processing method of the present embodiment, the protective film 82 is formed by applying the liquid resin 80 mixed with the fine powder of the oxide having the absorptivity with respect to the wavelength of the laser beam to the surface of the wafer W. After that, the ablation process is performed, so that 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 band gap energy of the wafer W is reached. Ablation processing is performed.

  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 radially expanded by using a well-known braking device, and an external force is applied to the wafer W. The wafer W is divided into individual devices D along the laser processing grooves 84.

W Semiconductor wafer T Adhesive tape (dicing tape)
F annular frame D device 2 laser processing device 28 chuck table 34 laser beam irradiation unit 36 condenser 80 fine powder-containing liquid resin 82 protective film 84 laser processing groove

Claims (3)

A semiconductor substrate ablation processing method for performing ablation processing by irradiating a semiconductor substrate 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 a region of the semiconductor substrate to be ablated;
A laser processing step of performing ablation processing by irradiating a region of the semiconductor substrate on which the protective film is formed with a laser beam after performing the protective film forming step;
A method of ablating a semiconductor substrate, comprising:   2. The semiconductor substrate 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 ablation processing method according to claim 1, wherein the liquid resin contains polyvinyl alcohol.

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