JP2011240363A - Method for splitting wafer-like substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate splitting method which has high-speed and easiness in cutting and prevents splash of fine particles.SOLUTION: The substrate splitting method has: a scanning step for scanning a substrate at a scanning speed V while irradiating the substrate with a laser beam of pulse period T to form a split base point line; and a pressurizing step for applying a line-like external force to the substrate from the rear surface of the substrate perpendicularly thereto along the split base point line to split the substrate while opening a modified region of the surface of the substrate. A pulse width τ of a laser beam is 10-30 pSec, and a pulse frequency F thereof is 100 KHz-50 MHz. A scanning pitch V/F specified by the pulse frequency F and the scanning speed V is set at V/F≤0.7 Φ, where Φ is a beam spot diameter of the laser beam.

Description

  The present invention relates to a method of dividing a substrate by irradiating a wafer-like substrate such as a semiconductor substrate with laser light to form a dividing base line, and then applying an external force, and particularly has high speed and easy cutting. In addition, the present invention relates to a dividing method capable of suppressing scattering of fine particles.

  A scribe break method is widely known as a processing method for dividing an optical semiconductor wafer such as an LED into chips. In recent years, the scribing method is being changed from mechanical scoring using a diamond point head to a V-groove cutting method in which laser light is irradiated (see Patent Documents 1 and 2).

  In the V-groove cutting method, a V-shaped cut groove is formed by applying a laser beam to the vicinity of the surface and melting the inside by thermal melting. However, in this V-groove cutting method, the melted substrate material overflows and re-adheres to the periphery of the cutting groove, or particles are scattered and re-adhered to the periphery of the irradiation position by ablation. It was a factor.

  Therefore, a splitting method (hereinafter referred to as a multiphoton absorption cutting method) in which the inside of the substrate is modified and embrittled by utilizing a multiphoton absorption phenomenon has been proposed (see Patent Document 3 and Patent Document 4). In this multiphoton absorption cutting method, even if a material has high transparency to laser light, the inside of the material is modified and embrittled by concentrating light energy and causing multiphoton absorption. Is.

Japanese Patent No. 3449201 (Nichia Corporation) Japanese Patent No. 4286488 (Canon Machinery) Japanese Patent No. 3624909 (Hamamatsu Photonics) Japanese Patent No. 3626442 (Hamamatsu Photonics)

  In the inventions of Patent Documents 3 to 4 described above, the modified region is formed inward by a predetermined distance from the substrate surface, which is excellent in that the problems in the V-groove cutting method are eliminated.

  However, none of the patent documents teach the optimum conditions for forming the cutting start line. That is, in the multiphoton absorption cutting method, the optimum irradiation condition of the laser beam corresponding to the properties of the substrate material is not yet known.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a dividing method capable of appropriately dividing a substrate by optimally irradiating a laser beam to form a dividing base line.

  It is known that even if a material has a high transmittance with respect to laser light, multiphoton absorption occurs when light energy is concentrated beyond a specific threshold corresponding to the material. And the substance that has been dissociated by multiphoton absorption is excited from the high energy region to the low energy region → ionization / radicalization → plasma ablation (melting / vaporization mixed state) inside the material → melting → high temperature solid → It is estimated that the state changes like the original solid.

  However, the above phenomenon differs in the speed of state change depending on the energy level and the duration. Therefore, the present inventor has completed the present invention by repeating various experiments with different conditions to detect the optimum irradiation conditions for the division.

  That is, the present invention scans a wafer-like substrate having a high spectral transmittance with respect to the laser beam used at a scanning speed V while irradiating the laser beam with a pulse period T, and forms a crystal breakdown layer inside the substrate. And a scanning step of forming a modified base line by forming a modified region that reaches the substrate surface continuously to the crystal breaking layer, and a line-shaped external force perpendicular to the substrate along the divided base line. A pressurizing step of opening and dividing the modified region of the substrate surface by adding from the back surface, the pulse width τ is 10 to 30 pSec, the pulse frequency F is 100 KHz to 50 MHz, The scanning pitch V / F specified by the frequency F and the scanning speed V is set to V / F ≦ 0.7Φ with respect to the beam spot diameter Φ of the laser light.

  In the present invention, laser light having a pulse width F and a pulse frequency F is used as shown in FIG. In the present invention, such a laser beam is scanned at a scanning speed V, so that a laser spot having a diameter Φ is formed every pulse period T (= 1 / F), and this laser spot is V * τ in the scanning direction. Will only continue. The laser light is condensed by a lens or a mirror and is reduced to the minimum diameter Φ at the focal position. The beam spot diameter of the present invention means the diameter of the laser light (beam waist diameter) at the focal position.

  FIG. 1B is a plan view of the focal position of the laser beam, and the laser spot having the beam spot diameter Φ is continuously formed in the form of scattered dots in the scanning direction by Φ + V * τ. Is shown. However, the pulse frequency F = 100 KHz to 50 MHz means the pulse period T = 0.02 to 10 μSec, and the relationship of τ << T is established with respect to the pulse width τ = 10 to 30 pSec. * Τ = Φ.

  According to the research of the present inventor, the overlapping distance on the scanning line of the laser spot is set to 30% or more of the beam spot diameter Φ under the pulse condition of the pulse period T = 0.02 to 10 μSec and the pulse width τ = 10 to 30 pSec. When set, it became clear that an appropriate division line can be formed with an appropriate energy (for example, about 1 to 10 μJ every pulse). In other words, if the overlap distance is less than 30%, the extension of the modified region becomes insufficient, and an appropriate division base line cannot be formed unless the irradiation energy is significantly increased.

  As shown in FIG. 1B, the overlapping distance of the laser spots is (Φ + V * τ) −P≈Φ−P in the scanning direction. Therefore, when the overlap distance is set to 30% or more of the beam spot diameter Φ, 0.3 * Φ ≦ Φ−P is established, and when this is arranged, the above relationship V / F ≦ 0. The relationship of 7Φ is established.

  The substrate to be processed in the present invention is typically a semiconductor substrate or a glass flat plate, and generally has a thickness of about 30 μm to 1 mm. In such a case, the beam spot diameter Φ is preferably set to about 1 μm to 10 μm on a plane perpendicular to the irradiation axis, and the focal depth in the irradiation direction is preferably set to 3 μm to 50 μm. The depth of focus means a Rayleigh length that specifies a range in which the minimum beam spot diameter Φ extends twice as much as the route.

  In the scanning process of the present invention, the substrate surface may be opened, but is not necessarily opened. In any case, in the present invention, by setting the irradiation energy optimally and setting the opening on the surface of the substrate to be narrow, it is possible to suppress the scattering contamination of vaporized and molten particles released from the opening.

In order to form a modified region from the crystal breakdown layer inside the substrate to the surface, it is necessary to irradiate a predetermined focal position with a laser beam having a predetermined energy at a predetermined wavelength, and an optimum value is specified for each material. . However, the pulse energy is preferably 1 to 10000 J / cm ² at the focal position, and is preferably set to about 1 to 10 μJ every one pulse.

  Further, the focal position should preferably be formed at a depth of 20 to 45% from the irradiation surface with respect to the thickness of the substrate. The plate thickness D of the substrate is not particularly limited, but typically is a plate thickness D of about 30 μm to 1 mm, and the position of D * 0.2 to D * 0.45 from the substrate surface is the optimum focal position. Become. Since the refractive index of the material of the substrate is generally larger than the refractive index of air, a position deeper than the focal position of the objective lens used for irradiation becomes the focal position.

  By the way, the substrate may be slightly warped or the plate thickness may be inaccurate. Therefore, in such a case, a measurement process for measuring the position of the substrate surface is provided prior to the scanning process, or the substrate surface is measured immediately before laser irradiation in the scanning process to irradiate an objective lens or the like. It is preferable to maintain the focal position at a predetermined position by scanning the laser beam while controlling the optical system.

The material of the substrate is not particularly limited, but a substrate material having a band gap energy of 3 to 9 eV is preferably used. In this case, it is preferable to use a laser beam having a wavelength of 500 to 1200 nm. In this case, no absorption occurs even if a low-energy light beam strikes a portion other than the focal point. Specific substrate materials include, for example, sapphire Al ₂ O ₃ 8.8 eV (absorption band 140 nm or less), silicon carbide SiC 3.3 eV (absorption band 376 nm or less), gallium nitride GaN 3.4 eV (absorption band 365 nm or less). Can be illustrated.

  Further, the present invention can be applied to a substrate such as a GaN-based LED composed of a combination of the above materials, and each material has high transparency. Concentrate energy on and do not damage other areas.

  In the pressurizing step of the present invention, a line-shaped external force is applied to expand the crack from the split base point and lead to the break. A substrate to be processed is generally a flat plate shape, and rectangular elements having a side of 10 mm or less are formed in a lattice shape. When the element size is as small as 500 μm to 100 μm, the gap between the elements is about 30 μm to 10 μm, and therefore, a highly accurate vertical fracture surface is required. However, in the present invention, a linear external force is applied perpendicular to the substrate, so that the above request can be met.

  Further, if the divided pieces are separated, it is not possible to collate with the individual side characteristic data measured in advance, and if the posture is random, the conveyance alignment becomes difficult. Therefore, preferably, an adhesive sheet is disposed on the opposite surface of the laser irradiation side, and the cutting edge of the pressing member is pressed through the adhesive sheet in the direction perpendicular to the substrate, the substrate is pushed up, and stress is applied so as to open the dividing base point. Is preferred (see FIG. 2).

  The reforming mechanism used in the scanning process and the demarcation mechanism used in the pressurizing process may be realized in the same apparatus, or may be implemented in a separate apparatus and sequentially processed. good. In addition, the number of scans in the scanning process may be a plurality of times as necessary.

  As described above, in the present invention, the internal modification and the generation of the dividing base point are performed by one scanning of the laser beam, so that the processing efficiency is excellent. In the present invention, since the material is not melted or lost of mass, the amount of energy is suppressed, and high-speed scanning with laser light is possible.

  Further, in the present invention, since the surface opening becomes a fractured surface without losing mass or a fragile modified closed surface, the debris scattering to the surface functional element portion is minimized or eliminated. In the scanning process of the present invention, since only the inside of the substrate is reformed, a compound based on an element derived from outside the crystal is not generated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. It is drawing explaining the pressurization process of an Example. 2 is a photograph illustrating Example 1. 6 is a photograph illustrating Example 2.

  Hereinafter, only two representative examples of the results of many experiments conducted by the present inventor will be described as examples. However, any embodiment does not particularly limit the present invention.

  The experimental conditions are as follows.

  A wafer-like workpiece attached to the pressure-sensitive adhesive sheet was mounted on an XY moving table with the sheet facing down, and was sucked and held on the moving table by vacuum suction for use in experiments. While irradiating the wafer surface with laser under the above conditions, the table was moved in a straight line, and the modified layer was made continuous to form a scribe line (divided base line).

  After that, it was divided into pieces using a divider with the following functions. That is, the singulation was performed by pushing a knife-like blade with a sharp tip from the surface opposite to the laser irradiation surface along the scribe line through the adhesive sheet.

  A protective sheet is applied to the laser irradiation surface, and the surface is protected by two support plates that are parallel to the scribe line and spaced apart symmetrically around the same line. The laser irradiation surface was divided by applying a force that opens from the opening base point created (see FIG. 2).

  This operation was performed with respect to the scribe line group orthogonal to the X direction and the Y direction at a constant pitch, and finally the adhesive sheet was stretched in all directions so that individual pieces could be taken out.

  FIG. 3A is a photograph showing a divided cross section of an individual side, and FIG. 3B is a plan photograph showing a state in which the sheet is stretched in all directions.

  The experimental conditions are as follows.

  Thereafter, the dividing operation was performed in the same procedure as in Example 1. FIG. 4A is a photograph showing a divided cross section of each side, and FIG. 4B is a plan photograph showing a state in which the sheet is stretched in all directions.

Claims (9)

A wafer-like substrate having a high spectral transmittance with respect to the laser beam to be used is scanned at a scanning speed V while irradiating a laser beam having a pulse period T to form a crystal breaking layer inside the substrate, and the crystal breaking layer A scanning step of forming a divided base line by forming a modified region that continuously reaches the substrate surface;
A pressing step of opening and dividing the modified region on the surface of the substrate by applying a linear external force from the back surface of the substrate perpendicular to the substrate along the dividing base line is configured.
The pulse width τ of the laser light is 10 to 30 pSec, the pulse frequency F is 100 KHz to 50 MHz, and the scanning pitch V / F specified by the pulse frequency F and the scanning speed V is relative to the beam spot diameter Φ of the laser light. The substrate dividing method is characterized in that V / F ≦ 0.7Φ is set.   The dividing method according to claim 1, wherein the focal position of the laser beam is set to a depth of 20 to 45% from the irradiation surface with respect to the thickness of the substrate.   3. The dividing method according to claim 1, wherein the beam spot diameter is set to 1 μm to 10 μm on a plane perpendicular to the irradiation axis, and the focal depth in the irradiation direction is set to 3 μm to 50 μm. Wavelength of the laser beam is 500-1200 nm, pulse energy, the method of division according to any one of claims 1 to 3 is 1~10000J / cm ^2.   5. The dividing method according to claim 1, wherein a substance having the same or high spectral transmittance as that of the substrate main body is laminated on the surface of the substrate.   The dividing method according to any one of claims 1 to 5, wherein the pressurizing step is performed in a state where an adhesive sheet is adhered to the back surface of the substrate.   The manufacturing method of the electronic device which uses the dividing method in any one of Claims 1-6. A wafer-like substrate having a high spectral transmittance with respect to the laser beam to be used is scanned at a scanning speed V while irradiating a laser beam having a pulse period T to form a crystal breaking layer inside the substrate, and the crystal breaking layer A scanning mechanism that continuously forms a modified region that reaches the substrate surface to form a split base line;
A pressure mechanism that opens and divides the modified region of the substrate surface by applying a line-shaped external force from the back surface of the substrate perpendicularly to the substrate along the dividing base line.
The pulse width τ of the laser light is 10 to 30 pSec, the pulse frequency F is 100 KHz to 50 MHz, and the scanning pitch V / F specified by the pulse frequency F and the scanning speed V is relative to the beam spot diameter Φ of the laser light. The substrate dividing system is set to V / F ≦ 0.7Φ.   The division system according to claim 7, wherein the scanning mechanism operates in advance with an inspection operation for specifying a position of the substrate surface by scanning the substrate surface in advance.