JP5328209B2 - Substrate processing method - Google Patents

Description

  The present invention relates to a substrate processing method for generating a crack that is a starting point of substrate division.

  In the conventional brittle substrate cutting method, a groove or a crack is first generated on the surface of the substrate, and the substrate is divided by applying stress in the direction of dividing the substrate starting from this portion.

  As a method of forming grooves and cracks that are the starting point of cutting, in the case of a glass substrate such as a liquid crystal substrate or a semiconductor substrate, a method of scribing the substrate surface with a jig having a hard tip such as a diamond point is generally used. Is.

  As an alternative to mechanical scribing, a method for forming a crack in a surface by heating the substrate surface with a laser spot and rapidly cooling the substrate surface while scanning the substrate is proposed as in Patent Document 1 below. . Further, as in Patent Document 4 below, there is a method in which a thin groove is formed by directly ablating the surface using laser light having a wavelength absorbed by the substrate.

  Further, as in Patent Document 2 below, a method of generating a starting point for dividing a substrate by condensing a laser spot inside the substrate and causing a crack to proceed from the condensing point has been proposed.

Japanese Patent No. 3370310 (first page, FIG. 1) Japanese Patent No. 3626442 Japanese Patent No. 3408805 JP 2005-271563 A

  The method of performing mechanical scribing using a diamond point or the like is because the diamond point is in direct contact with the substrate and moved by applying pressure to make a mark on the substrate surface. When processing a hard brittle material substrate, there is a problem in that the diamond points are frequently exchanged. Further, in order to suppress wear as much as possible, there is a problem that the speed of marking a mark cannot be set too high, and the productivity does not increase. Furthermore, since foreign matter is generated from the contact point between the diamond scribe and the substrate, it is necessary to take measures against contamination of the substrate.

  On the other hand, as in Patent Document 1, a method of heating a substrate surface with a laser spot and immediately cooling it to generate a vertical crack can improve the above-mentioned drawbacks. However, in the case of surface heating by a laser spot, the heating region is expanded by conducting heat from the substrate surface to the inside. Therefore, in order to generate cracks on the substrate surface, it is indispensable to cool the substrate surface using a refrigerant jet or the like, and as a result, maintenance such as cooling equipment and its driving mechanism and refrigerant replenishment is required.

  Furthermore, since the thermal strain by only surface heating is used, the heating area becomes relatively large. Therefore, in a semiconductor wafer or the like having a function on the substrate surface, it is necessary to ensure a large width of the cut portion in order to avoid the influence of heating. For this reason, the utilization efficiency of the material is lowered, resulting in an increase in the price of the final product.

  Patent Document 2 proposes a method of collecting light inside a substrate, causing multiphoton absorption, growing a crack around the light collection point, and dividing the substrate using the crack as a starting point. Therefore, there is no need to worry about the size of the heating area as in Patent Document 1, and as a result, the heating area can be made relatively small, and cooling is not necessary. However, the generated cracks are likely to occur radially around the focal point. Therefore, when the substrate is divided, if separation starts with a crack extending in an undesired direction as a starting point, the dividing line becomes slanted or the dividing surface becomes uneven. As a result, the bending strength of the product varies, or the dimensional accuracy of the dividing surface is lowered, resulting in problems in subsequent manufacturing processes.

  The objective of this invention is providing the board | substrate processing method which can form a crack with high precision, preventing generation | occurrence | production of a foreign material.

In order to achieve the above object, the substrate processing method according to the present invention forms a crack in the substrate by irradiating the substrate made of a brittle material transparent to the wavelength of the processing light with pulsed processing light. A substrate processing method for performing
The processing light convergence position is set on the inner side of the substrate surface and in the range of the surface side from the thickness center of the substrate,
At the processing light convergence position, the processing light has a linear convergence distribution having a major axis substantially parallel to the substrate surface;
A linear crack is generated on the surface of the substrate by forming a decomposition / heating layer on the surface perpendicular to the surface of the substrate and including the convergence position by the irradiation of the processing light. To do.

  According to the present invention, when irradiating processing light, the convergence position of the processing light is set in a range on the inner side from the substrate surface and on the surface side from the thickness center of the substrate, and the long axis substantially parallel to the substrate surface at the convergence position. By condensing the processing light so as to have a linear convergence distribution having a linear crack distribution, a linear crack along the major axis of the linear convergence distribution can be formed on one or both of the substrate surface and the substrate interior. it can. Accordingly, when the substrate is divided, it is possible to divide the substrate by dividing lines extending in a desired direction starting from the linear crack, and the yield of substrate division is improved.

Embodiment 1 FIG.
FIG. 1a is a perspective view showing an example of a substrate processing method according to the present invention, and FIG. 1b is a partially enlarged view thereof. The substrate 1 is formed of a brittle material such as various semiconductor materials such as silicon or various dielectric materials such as glass. A brittle material has a property of breaking along a marking line without deformation when a tensile stress is applied after the marking line is formed on a part of the surface. In particular, various semiconductor materials are often crystal substrates, and in the case of crystal substrates, they often have cleavage properties. When cutting a semiconductor substrate, the cutting direction may be a direction other than the direction where the cleavage property is good due to the demand for the outer shape of the product.

  On the upper surface of the substrate 1 is generally a surface structure 2 made of electrical elements such as transistors, capacitors, wirings, electrodes, or optical elements such as waveguides and prisms, in a matrix or a strip shown in FIG. Many are arranged in a shape. A street 3 is provided between adjacent surface structures 2 to secure a separation space.

  In this street 3, the substrate 1 is generally exposed, and by performing the substrate division along the center line of the street 3, chip parts on which the individual surface structures 2 are mounted can be obtained. When the substrate is divided, the crack 4 serving as a starting point of separation is usually formed on the planned crack line 5 along the center of the street 3. Note that the present invention can be similarly applied to a case where a substrate on which the surface structure 2 does not exist is simply divided.

  In this embodiment, the processing light 7 is irradiated toward the substrate 1 to form linear cracks on the surface of the substrate 1. When a material transparent to the wavelength of the processing light 7 is selected as the substrate 1, the processing light 7 usually passes through the substrate 1 as it is and no light absorption occurs.

  However, when the electric field energy density of the processing light 7 exceeds a certain value, energy absorption that does not occur in a normal spectral absorptance curve occurs. This is a phenomenon generally called multi-photon-absorption. The amount of energy absorbed by multiphoton absorption is proportional to the nth power of the energy density of the input light 7 (n is the number of photons). For example, two-photon absorption is proportional to the square of the energy density, and four-photon absorption is It is proportional to the fourth power of energy density.

  In FIG. 1 a, the direction of the planned crack line 5 is the Y axis, the thickness direction of the substrate 1 is the Z axis, and the direction perpendicular to the Y axis and the Z axis is the X axis. Proceed along. The processing light 7 is supplied from, for example, a laser oscillator (not shown), and subsequently passes through a beam diameter shaping optical system or a condensing optical system, and then the substrate has an X direction convergence angle larger than the Y direction convergence angle. 1 enters street 3.

  At this time, as shown in FIG. 1 b, the convergence position 9 of the processing light 7 is set in the vicinity of the surface of the substrate 1, that is, inside the surface 10 of the substrate 1 and within the range of the surface side from the thickness center of the substrate 1. . Further, at the convergence position 9, the magnification of the condensing optical system is set so that the processing light 7 has a linear convergence distribution 11 having a long axis substantially parallel to the surface 10 of the substrate 1.

  For example, as shown in FIG. 1a, the processing light 7 has a long and narrow spot shape with a Y-direction spot diameter that is significantly larger than the X-direction spot diameter, and has a maximum peak intensity at a convergence position 9 that is a predetermined distance from the substrate surface. This is the smallest spot shown.

  In the linear convergence distribution 11, the major axis of the cross section perpendicular to the principal ray substantially coincides with the Y direction, and the light intensity distribution is not limited to the Gaussian distribution shape but may be an arbitrary distribution shape such as a rectangular shape. .

  The substrate 1 is mounted on a driving mechanism such as an XY stage, and a linear spot along the Y direction is formed along the planned crack line 5 by relatively moving the substrate 1 in the Y direction while irradiating the processing light 7. Can be scanned. Instead of moving the substrate, a condensing optical system for condensing the processing light 7 may be mounted on a drive mechanism such as an XY stage, and the processing light 7 itself may be scanned in the Y direction.

  Next, the crack generation process according to the present invention will be described. When a linear spot along the Y direction is formed at the convergence position 9 inside the substrate by irradiation with the processing light 7, multiphoton absorption as described above occurs due to the high energy density. Once multi-photon absorption starts, the material of the substrate 1 is decomposed and ionized, and the separated ions are further accelerated by the optical field that is still being irradiated and further absorb the energy of the light 7. . This energy collides and relaxes with materials other than the reaction part, so that the peripheral region is heated.

The region where the temperature has been increased due to heating spreads further to the surroundings as time elapses, but at the same time, the heated portion expands thermally, causing compressive stress and tension in the heated and unheated portions, respectively. Stress is generated. When the linear convergence distribution 11 is set at the convergence position 9 near the surface, a tensile stress is applied on the surface 10.

  When the tensile stress and the state of the surface 10 are equal to or greater than the fracture toughness value of the material surface 10, cracks are generated on the surface. In the present invention, since the heated part is inside the material, the surface is always kept at a low temperature. For this reason, an additional cooling means is not required unlike the case of surface heating, and a crack can be generated by a simple method. Moreover, no foreign matter is generated as in the case of using mechanical scribe.

  2A is a perspective explanatory view showing a tension distribution by linear spot irradiation according to the present invention, and FIG. 2B is an XZ sectional view of a portion having a linear convergence distribution. When the linear convergence distribution 11 is formed at the convergence position 9 inside the substrate so as to be parallel to the planned crack line 5, immediately after irradiation with the processing light 7, the substrate surface is caused by thermal expansion of the heated portion. It deforms so that it rises in a long and narrow mountain range with a ridge along the planned crack line 5.

  Due to such anisotropic deformation, the tension 22 perpendicular to the planned crack line 5 becomes larger than the tension 21 along the planned crack line 5, so that a linear crack is generated because the fracture related to the tension 22 precedes. . As a result, the crack line grows along the planned crack line 5, and cracks in other directions are unlikely to occur. When such a force is applied, a substrate having a cleavage property such as a semiconductor crystal substrate easily induces a crack in a desired direction regardless of the direction in which the cleavage property is good.

  Further, as shown in FIG. 2b, the actual linear convergence distribution is formed vertically above and below the convergence position along the shape of the processing light 7. For this reason, linear cracks along the linear convergence distribution are formed not only on the surface but also inside the substrate.

  FIG. 3 is an explanatory diagram showing a tension distribution by point spot irradiation as a comparative example. When the point-like convergence distribution 12 is formed at the convergence position 9 inside the substrate, the heating area is substantially spherical with the convergence position 9 as the center, and immediately after the processing light 7 is irradiated, the substrate surface is deformed so that it rises in a round mountain shape. To do.

  Due to such isotropic deformation, tensile stresses on the surface 10 are generated radially, and the tension 21 along the planned crack line 5 and the tension 22 perpendicular to the planned crack line 5 become approximately the same magnitude. As a result, cracks may occur in any direction. For example, a crack does not necessarily occur along the planned crack line 5 due to anisotropy or scratches on the surface properties, but linearity and continuity. No good cracks can be obtained. In addition, when the substrate is cleaved, represented by a semiconductor crystal substrate, and is cut in a direction different from the easy-cleavage surface, cracks tend to occur in the cleavage direction, and cracks in the required direction do not occur. It does not become a crack with good and continuous properties.

Instead of the linear convergence distribution 11 described above, for example, as disclosed in Patent Document 2 of the conventional example, the linear convergence is apparently performed by linearly scanning the point convergence distribution 12 using a stage or the like. A distribution method is also conceivable. However, the scanning speed is required to be high enough that surface deformation occurs at the same time, and a predetermined range must be scanned in nanoseconds or less as described later. If the major axis of the linear convergence point is 0.1 mm, the stage must be moved at a high speed of 10 ⁸ mm / sec, which is practically impossible.

  By irradiating the processing light 7 so that the linear spot is located inside the substrate in this way, a crack having excellent linearity and continuity can be formed on the substrate surface with high accuracy. Thereafter, the break blade is brought into contact with the back surface of the substrate 1 and a bending stress is applied to the entire substrate, whereby the substrate can be divided along the linear cracks generated on the substrate surface. As a result, a dividing line having excellent linearity is obtained along the planned crack line 5, and the dividing surface becomes flat, so that the yield of dividing the substrate can be improved.

  When the substrate is irradiated with the pulsed processing light 7, this causes a crack on the substrate surface or inside. When the next pulse is continuously irradiated to the crack, the processing light 7 is scattered by the crack, the effect of the processing light 7 is reduced, and the crack may not advance in the desired direction. Therefore, it is desirable that the pulse irradiation interval is outside the range of cracks generated by a single pulse.

  In the above description, an example in which the processing light 7 is incident from the surface of the substrate 1 and a linear spot is formed at the convergence position 9 inside the substrate is shown. However, when a transparent region exists on the back surface of the substrate 1 The processing light 7 can be incident from the back surface of the substrate 1 to form a linear spot at the convergence position 9 inside the substrate. The latter back surface irradiation is a particularly desirable method when a sufficient light transmission surface cannot be secured on the substrate surface on which the surface structure 2 is provided.

  As such processing light 7, it is preferable to use laser light. The optical electric field can be easily increased by the high coherence of the laser beam, and the convergent spot diameter becomes smaller due to the high monochromaticity, the optical electric field at the convergent spot becomes higher, and the occurrence of multiphoton absorption phenomenon occurs. Becomes easier.

  Further, it is preferable to use a pulse laser beam having a high peak intensity as the processing light 7. As a result, the peak light electric field intensity at the convergence spot can be increased, and the occurrence of the multiphoton absorption phenomenon is facilitated.

  Further, it is preferable to use a Q-switch pulse laser beam as the processing light 7. As a result, the peak light electric field intensity at the convergence spot can be further increased, and the occurrence of the multiphoton absorption phenomenon is facilitated.

  FIG. 4 is a graph showing an example of the spectral absorptance spectrum of the substrate. The vertical axis represents the spectral absorptance (%), and the horizontal axis represents the reciprocal of the wavelength, that is, photon energy. 4 shows an example of the spectral absorptance spectrum when the substrate material is not heated, and the solid line shows an example of the spectral absorptance spectrum when heated.

  Absorption by multiphoton absorption starts in a very short time (~ picoseconds). When the irradiation time of the processing light 7 is longer than this, the processing light 7 continues to irradiate the vicinity of the convergence position 9 inside the substrate for a time longer than the portion in which the portion is altered and heated. When the irradiation time elapses for nanoseconds or more, the heat transfer becomes remarkable from the heated portion due to multiphoton absorption and subsequent alteration, so the vicinity of the convergence position 9 is heated.

  In the linear convergence distribution 11 of the processed light 7, multiphoton absorption occurs only in a portion where the energy density is equal to or higher than a threshold value, and the other portions are transmitted. As shown in FIG. 4, the normal spectral absorptance tends to shift the light absorption start wavelength to the longer wavelength side as the substrate temperature increases.

  Therefore, the wavelength 31 of the processing light 7 has an energy density less than necessary between the surface of the substrate material and the processing point in the spectral absorptance spectrum (one-dot chain line) when the substrate material is not heated. It is set near the high energy side absorption band 30 so that the spectral absorptance is low to the extent that heating by photon absorption is not impossible, and the spectral absorptance is increased by heating in the later stage of processing, so that energy can be absorbed efficiently. It is preferable. From such a wavelength setting, even if the energy density of the processed light 7 is equal to or lower than the threshold for multiphoton absorption after the occurrence of multiphoton absorption, light energy absorption occurs due to an increase in spectral absorptance due to temperature rise, The vicinity of the convergence point can be heated more efficiently.

Next, specific examples will be described. A soda glass plate with a thickness of 1 mm is used as the substrate 1 and a 3rd harmonic wave of a Q-switched laser using Nd: YVO ₄ is used as the processing light 7 to generate a laser beam having a pulse width of 40 ns and a pulse energy of 200 μJ. I let you. A cylindrical lens was used as the condensing optical system, and a linear spot was condensed at the convergence position 9 inside the substrate. As a result, it was possible to generate a linear crack on the substrate surface and in the interior along the planned crack line 5 on the substrate surface.

As another example, a GaN substrate having a thickness of 0.1 mm, which is a semiconductor substrate, is used, and the second harmonic of a Q-switched laser using Nd: YVO ₄ which is transmitted light is used as the processing light 7. A laser beam having a pulse width of 40 ns and a pulse energy of 4.2 μJ was generated. A cylindrical lens was used as the condensing optical system, and a linear spot was condensed at the convergence position 9 inside the substrate. Since the crack range in a single pulse is 20 μm, the pulse interval was set to 20 μm. As a result, it was possible to generate a linear crack on the substrate surface and in the interior along the planned crack line 5 on the substrate surface.

It is a perspective view which shows an example of the board | substrate processing method which concerns on this invention. It is the elements on larger scale which show an example of the board | substrate processing method which concerns on this invention. It is a perspective explanatory view showing tension distribution by linear spot irradiation concerning the present invention. It is sectional explanatory drawing which shows tension distribution by the linear spot irradiation which concerns on this invention. As a comparative example, it is explanatory drawing which shows tension distribution by point-like spot irradiation. It is a graph which shows an example of the spectral absorptivity spectrum of a board | substrate.

Explanation of symbols

1 substrate, 2 surface structure, 3 street, 4 crack,
5 crack planned line, 7 machining light, 9 convergence position, 10 surface,
11 linear convergence distribution, 12 point convergence distribution, 21, 22 tension,
30 Near the high energy side absorption band, 31 wavelengths.

Claims (9)

A substrate processing method for forming a crack in the substrate by irradiating a pulsed processing light toward a substrate made of a brittle material transparent to the wavelength of the processing light,
The processing light convergence position is set on the inner side of the substrate surface and in the range of the surface side from the thickness center of the substrate,
At the processing light convergence position, the processing light has a linear convergence distribution having a major axis substantially parallel to the substrate surface;
A linear crack is generated on the surface of the substrate by forming a decomposition / heating layer on the surface perpendicular to the surface of the substrate and including the convergence position by the irradiation of the processing light. Substrate processing method. A substrate processing method for forming a crack in the substrate by irradiating a pulsed processing light toward a substrate made of a brittle material transparent to the wavelength of the processing light,
The processing light convergence position is set on the inner side of the substrate surface and in the range of the surface side from the thickness center of the substrate,
At the processing light convergence position, the processing light has a linear convergence distribution having a long axis substantially parallel to the substrate surface;
By forming the decomposition / heating layer in a plane perpendicular to the substrate surface and including the convergence position by irradiation with the processing light , along the surface including the planar decomposition / heating layer, A substrate processing method characterized by generating linear cracks distributed around a decomposition / heating layer .   The substrate processing method according to claim 1, wherein the substrate has a cleavage property, and a major axis direction of the linear convergence distribution is different from a surface having a cleavage property.   3. The substrate processing method according to claim 1, wherein when the processing light is irradiated with a continuous pulse, the next pulse is irradiated outside the range of the crack formed by the single pulse irradiation.   The substrate processing method according to claim 1, wherein a surface structure is provided on the substrate surface, and processing light is irradiated from the back surface of the substrate.   The substrate processing method according to claim 1, wherein the processing light is a laser beam.   The substrate processing method according to claim 6, wherein the processing light is Q-switched pulsed laser light.   The wavelength of the processing light has a transmittance that can be heated by multiphoton absorption at the convergence position of the processing light in the spectral absorption spectrum when the substrate material is not heated, and the spectral absorption increases when heated. The substrate processing method according to claim 1, wherein the substrate processing method is set to an absorption band.   3. The substrate according to claim 1, wherein after forming a linear crack on the surface and / or inside of the substrate, a bending stress is applied to the substrate to divide the substrate along the linear crack. Substrate processing method.

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