JP2017183600A - Slice method and slice device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slice method capable of reducing cost of manufacture of a substrate, and a slice device.SOLUTION: A slice method includes: a modified layer forming step for converging a laser light through a convergence part into a processed material and forming a modified layer in the vicinity of a convergence point within the processed material; a discharge step for melting the modified layer within the processed material by heating the processed material, generating a gas, and discharging a molten modified layer substance to the outside of the processed material by a pressure of the generated gas; a scanning step for scanning the laser light converged into the processed material, thereby forming a boundary from the modified layer inside of the processed material; and a separation step for separating the processed material into at least two or more substrates with the modified layer defined as a boundary.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a slicing method and a slicing apparatus.

  When manufacturing a substrate such as a silicon (Si) wafer, a cylindrical ingot solidified while being pulled up from a silicon melt melted in a quartz crucible is cut into blocks of an appropriate length, a target shape, After grinding to a diameter, a block-shaped ingot is sliced with a wire saw to produce a substrate.

  However, when cutting with a wire saw (also referred to as a slice), a cutting allowance larger than the wire diameter is required due to the wire diameter and the warp of the wire, so the material loss is large and the thickness is 0.1 mm or less. There is a problem that it is very difficult to manufacture a substrate.

  In particular, in the case of hard and brittle materials such as GaN, SiC, and sapphire, processing is difficult compared to silicon (Si), so that the cutting margin is large and it is difficult to cut into a thin substrate.

  In addition, since the material cost is high, the material loss has a great influence on the substrate cost, and it is necessary to reduce the manufacturing cost of the substrate by increasing the number of substrates that can be manufactured from one ingot.

  As for GaN, development of a large number of pieces from a bulk material is in progress, and it can be expected to reduce the cost.

  As one of the methods, there is a method in which an internal modified layer is formed using a laser and separated into a wafer shape with the internal modified layer as a boundary.

  In the silicon wafer slicing step, a condensing point of the laser beam is aligned with the inside of the workpiece by a condenser lens, and a planar processing region is formed by relatively scanning the workpiece with the laser beam, A substrate manufacturing method and a manufacturing apparatus are disclosed in which a part of a workpiece is peeled off as a substrate using a processing region as a peeling surface using expansion / contraction due to heat generated inside the workpiece (for example, a patent). Reference 1).

FIG. 8 is a cross-sectional view of a substrate showing the substrate processing method described in Patent Document 1.
The laser light 190 penetrating into the substrate 100 is irradiated toward the substrate 100 via the laser condensing unit 160, and the thickness direction (optical axis direction) t and the width direction (light A condensing point Q in the direction orthogonal to the axis w is formed. In the vicinity of the condensing point Q, the substrate 100 is polycrystallized, and the substrate 100 is divided with this region as a boundary.

  At the condensing point of the laser light 190, the condensing point Q2 where the light rays of the component 190b on the outer peripheral side of the laser light 190 intersect is more than the condensing point Q1 where the light rays of the component on the inner peripheral side 190a of the laser light 190 intersect. It is configured to be on the laser condensing unit 160 side. The condensing point Q2 of the component 190b on the outer peripheral side of the laser light 190 is closer to the objective lens 170 and the plano-convex lens 180 side, that is, the surface of the substrate 100 than the condensing point Q1 on the inner peripheral side 190a of the laser light 190. is there.

  The laser condensing unit 160 includes an objective lens 170 and a plano-convex lens 180 as a condensing point shape adjusting unit. The laser condensing unit 160 mainly adjusts the distance between the surface 101 of the substrate 100 and the internal modification layer 14 by the distance L1 between the objective lens 170 and the substrate surface. Further, the laser condensing unit 160 increases the distance L2 between the plano-convex lens 180 and the surface 101 of the substrate 100 so that the position of the condensing point P2 at the condensing point P can be further increased with respect to the condensing point P1. 100 is moved to the surface 101 side. The laser condensing unit 160 is set to condense at a position close to the laser condensing unit 160 as the laser light 190 moves from the inner peripheral side to the outer peripheral side.

JP 2013-161976 A

  However, gas may be generated when the modified layer is formed inside the workpiece. For example, if the temperature at the processing point of the workpiece exceeds the boiling point of the workpiece, the workpiece itself sublimates and gasifies, or even if the boiling point does not reach the molecular bond of the workpiece As a result, part of the material may be gasified, or gas may be gasified due to sublimation of impurities inside the workpiece.

  In the conventional configuration, the generated gas can move in the range of the width w and the thickness t of the condensing point Q of the laser beam, but the gas moves in the region already processed by the laser beam. Since it is not possible, it stays within the range of the condensing point Q.

  When the gas generated at the condensing point Q is large, the pressure due to the gas remaining inside the workpiece is increased, so that the workpiece may be cracked or cracked. For example, in the case of GaN, since Ga and N are separated by laser irradiation and N2 gas is generated, N2 gas is not discharged to the outside of the condensing point Q, and the internal pressure (internal pressure) of the workpiece increases, cracks, Cause cracking.

  For this reason, it becomes difficult to slice a workpiece into a plurality of substrates, which causes a problem in reducing the manufacturing cost of the substrates.

  An object of the present invention is to solve the above-described conventional problems, and to provide a slicing method and a slicing apparatus that can reduce the manufacturing cost of a substrate.

In order to achieve the above object, the slicing method of the present invention comprises:
A modified layer forming step of condensing the laser beam inside the workpiece through the condenser and forming a modified layer in the vicinity of the focal point inside the workpiece;
By heating the workpiece, the modified layer is melted inside the workpiece, a gas is generated, and the molten modified layer material is converted into the workpiece by the pressure of the generated gas. A discharge process for discharging the processed material to the outside;
A scanning step of forming a boundary by the modified layer inside the workpiece by scanning the laser beam condensed inside the workpiece,
A separation step of separating the workpiece into at least two or more substrates with the modified layer as a boundary;
Is provided.

The slicing apparatus of the present invention comprises:
A substrate slicing device that forms a modified layer inside a workpiece and separates the workpiece into at least two or more substrates with the modified layer as a boundary,
A modified layer forming section for condensing a laser beam inside the workpiece through a focusing section and forming the modified layer in the vicinity of a focusing point inside the workpiece;
By heating the workpiece, the modified layer is melted inside the workpiece, a gas is generated, and the molten modified layer material is converted into the workpiece by the pressure of the generated gas. A discharge part for discharging to the outside of the work material;
Is provided.

  As described above, according to the slicing method and the slicing apparatus of the present invention, the manufacturing cost of the substrate can be reduced.

Schematic diagram of the slicing device according to the first embodiment of the present invention. Cross section of the processed part of the workpiece when not heated Cross section of the processing part of the workpiece when heated Edge photo of workpiece Schematic diagram of a slicing device according to the second embodiment of the present invention. Schematic diagram of a slicing device according to the third embodiment of the present invention. The schematic diagram of the heating method which concerns on the 1st-3rd embodiment of this invention. Schematic diagram of the slicing device described in Patent Document 1

  Hereinafter, various embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
The configuration of the slicing device according to the first embodiment of the present invention will be described with reference to FIG.
FIG. 1 is a schematic diagram of a slicing device according to the first embodiment of the present invention.

The slicing apparatus is an apparatus that irradiates a workpiece 1 with laser light, forms a modified layer 8 in the vicinity of the condensing point, and separates it into at least two substrates with the modified layer 8 as a boundary. .
The slicing apparatus includes a heat source 2, a drive stage 3, a laser oscillator 4, a mirror 6, an objective lens 7, a lens temperature sensor 9, a workpiece temperature sensor 10, a temperature controller 11, and a heat ray cut filter 12.

  The workpiece 1 is GaN (gallium nitride), which is said to be a hard and brittle material. In the present embodiment, a GaN wafer having a diameter of 2 inches and a thickness of 400 μm is used as the workpiece 1, but it is not particularly limited by the diameter or thickness, and a bulk material having a large thickness may be used.

  The workpiece 1 has at least a surface on which a laser beam is incident subjected to mirror finishing, and has a transmittance of at least 80% or more for visible light.

  The heat source 2 is a heat source that can contact the workpiece 1 and apply heat. Although not shown, the heat source 2 has a hole for adsorbing and has a function of fixing the workpiece 1 placed on the heat source 2 by setting the hole to a negative pressure with a vacuum pump or the like. May be. Let Ts be the temperature of the heat source 2. The heat source 2 corresponds to the “heating unit” of the present invention.

  The drive stage 3 is configured to be able to move a relative position in the x-axis direction of xyz in the laser beam with respect to the workpiece 1.

  The laser oscillator 4 has a wavelength that allows transmission of 80% or more with respect to the workpiece 1. For example, the laser oscillator 4 is a picosecond laser having a wavelength of 532 nm and can oscillate at a maximum repetition frequency of 1 MHz, with a maximum output of 50 W and a pulse width of 25 ps. The following laser light can be emitted.

  Although not shown, the laser oscillator 4 is configured to be capable of ON / OFF control of laser light by exchanging control signals with the drive stage 3.

  The laser beam 5 is a laser beam having a diameter of about 5 mm emitted from the laser oscillator 4 and is linearly polarized.

  The mirror 6 is a mirror that reflects 90% or more of the laser light emitted from the laser oscillator 4 and transmits it to the workpiece 1. In this embodiment, a multilayer dielectric mirror that reflects a wavelength of 532 nm is used.

  The objective lens 7 is made of a material that transmits laser light, can be corrected to an optimum amount of aberration according to the processing depth, and can be condensed by transmitting the laser light 5. The objective lens 7 corresponds to the “condenser” of the present invention. Further, the laser oscillator 4, the mirror 6, and the objective lens 7 correspond to a “modified layer forming part”.

  The condensing point A of the laser beam 5 a that has passed through the objective lens 7 is adjusted to a position of a distance L from the surface of the workpiece 1 inside the workpiece 1. In this embodiment, an aberration correction ring for a microscope that transmits a wavelength of 532 nm is used, and NA = 0.85, f = 2 mm, and a 100 × objective lens are used. Let TL be the heat resistant temperature of the lens.

  The modified layer 8 is formed of a modified component of GaN in the vicinity of the condensing point A. The laser beam 5a is condensed so that the thickness of the modified layer 8 is 10 μm or less. However, the modified layer 8 itself has an uneven shape due to the accuracy of the drive stage 3 and the surface accuracy of the workpiece 1. .

  The lens temperature sensor 9 is attached to the workpiece 1 side of the objective lens 7. The lens temperature sensor 9 corresponds to the “first temperature sensor” of the present invention.

  The workpiece temperature sensor 10 is attached to the surface side of the workpiece 1. The workpiece temperature sensor 10 corresponds to the “second temperature sensor” of the present invention.

  The temperature controller 11 is connected to the heat source 2, the lens temperature sensor 9, and the workpiece temperature sensor 10, and is based on the measured temperatures of the lens temperature sensor 9 and workpiece temperature sensor 10. Control the temperature. The temperature controller 11 corresponds to the “temperature controller” of the present invention.

  The heat ray cut filter 12 transmits the wavelength of the laser beam 5, but cuts (absorbs) the infrared wavelength, which is a heat ray.

  2 and 3 are sectional views in the vicinity of the condensing point A. FIG. 2 and FIG. 3, the same components as those in FIG.

  2 shows a case where the workpiece 1 is not heated by the heat source 2, and FIG. 3 shows a case where the workpiece 1 is heated by the heat source 2.

  Since the laser beam 5a has a wavelength that passes through the workpiece 1, the laser beam 5a is condensed near the condensing point A with a small attenuation. In the present embodiment, the distance L from the surface of the workpiece 1 at the condensing point A is set to 200 μm, which is 1/2 of the thickness 400 μm of the workpiece 1.

  Next, the operation of the slicing device according to the above embodiment will be described.

Since the aberration correction ring of the objective lens 7 is adjusted according to the depth of the workpiece 1, the laser beam 5a is most focused at the condensing point A. By using a picosecond laser, the modified layer 8 is formed at the focal point A by the following reaction by multiphoton absorption processing.
2GaN → 2Ga + N2

  From the EPMA (Electron Probe Micro Analyzer) analysis, it is known that the Ga component remains in the modified layer 8 but the N component is missing. Precipitates to form Ga portion 8a and N2 gas 8d is presumed to be generated. Ga is a metal having a melting point Tm of 29.8 ° C.

  The reforming part B (see FIGS. 2 and 3) formed for each pulse by the condensing point A of the laser beam 5a has a repetition frequency F of the laser oscillator 4 with respect to the moving direction of the drive stage 3, and They are formed at a constant interval C (= V / F) determined by the scanning speed V of the drive stage 3. For example, when the repetition frequency F = 100 kHz and the scanning speed V = 100 mm / s, the modified portion B is formed with an interval C (= 100 mm / 100 KHz) of 1 μm.

  Assuming that the width of the reforming portion B formed for each pulse is D (see FIG. 3), in this embodiment, the pulse interval CP in the scanning direction and the line interval CL perpendicular thereto are the width of the reforming portion B. The repetition frequency F and the scanning speed V are set so that D = 3 to 5 μm or less. Thereby, the planar modified layer 8 can be formed.

  In FIG. 2, the case where the heat source 2 does not heat will be described. In the laser irradiation part, the Ga part 8a and the N 2 gas 8d exist, but in the modified layer 8, the laser irradiation part 8b exists as solidified solid Ga. Therefore, the internal pressure (internal pressure) of the workpiece 1 is increased by generating the N2 gas 8d. The internal pressure is indicated by an arrow P1. In the case where the amount of N2 gas 8d generated is large or where the strength of the workpiece 1 is weak, there is no escape path for the internal pressure P1, and a crack 8e for relaxing the pressure is generated, as shown in FIG. When the crack extends in the thickness direction, the workpiece 1 is cracked as shown in FIG.

In FIG. 3, the case where the to-be-processed material 1 is heated more than melting | fusing point Tm of Ga with the heat source 2 is shown.
The temperature T1 of the objective lens 7 measured by the workpiece temperature sensor 10 and the temperature of the workpiece 1 measured by the lens temperature sensor 9 are T2.

T2> Tm
T1 <TL
Set to be. As described above, Tm is the melting point of Ga (29.8 ° C.), and TL is the heat resistant temperature of the objective lens 7.

  In the present embodiment, when the temperature Ts of the heat source 2 is 45 ° C., the temperature 1 of the workpiece 1 is T 2 = 40 ° C. (> Tm), and the temperature T 1 of the objective lens 7 is 35 ° C. (<TL). Even when 12 is not used, laser irradiation can be performed in a molten state of Ga. On the other hand, when the heat ray cut filter 12 is used, the temperature T2 of the workpiece, that is, the temperature of Ga can be further increased while maintaining the temperature T1 <40 ° C. of the objective lens 7.

  As in the case where heating is not performed in the laser irradiation portion, Ga portion 8a and N 2 gas 8d are generated, but in the modified layer 8, the existing laser irradiation portion 8f exists as molten Ga. The internal pressure (internal pressure) of the workpiece 1 due to the generated N2 gas 8d is indicated by an arrow P2 in FIG. Thereby, the internal pressure is relaxed by extruding molten Ga, and does not rise to a pressure at which cracks are generated. For this reason, the modified layer 8 is formed on the entire surface of the workpiece 1 without generating a rack. The molten Ga in the liquid state is hereinafter referred to as “liquid Ga”.

  At the end portion of the workpiece 1, a Ga portion 8g is produced in which the liquid Ga extruded by the internal pressure is solidified into a spherical shape.

  FIG. 4 is a photograph of the end of the workpiece 1 observed from above. FIG. 4 shows a portion 8g where molten Ga is extruded and solidified into a spherical shape.

  According to the slicing method and the slicing apparatus according to the above-described embodiment, a high-quality substrate can be obtained by preventing cracks caused by gas generated inside the workpiece 1. Reduction of defects that occur when separating into a plurality of substrates and a reduction in material loss due to a reduction in the amount of polishing, which is a subsequent process, can be expected, and it is possible to reduce the manufacturing cost of the substrate. In addition, by applying the present invention to a GaN wafer as the workpiece 1, it is possible to reduce the cost of LEDs, semiconductor lasers, and power devices, and by applying to a SiC wafer, it contributes to reducing the cost of power devices. it can.

(Second Embodiment)
FIG. 5 is a schematic diagram of a slicing device according to the second embodiment of the present invention. In FIG. 5, the same components as those in FIG.

  The vacuum chamber 20 is installed so as to cover the workpiece 1. The surface of the vacuum chamber 20 on the objective lens 7 side is constituted by a heat ray cut filter 12. The heat ray cut filter 12 transmits the laser beam 5 by 90% or more, but cuts (absorbs) the heat ray. The vacuum pump 21 is connected to the exhaust port of the vacuum chamber and can evacuate the inside of the vacuum chamber 20.

  According to the slicing device according to the second embodiment, the modified layer 8 is formed of Ga which is heated and melted by the heat source 2 at the time of laser irradiation, and the vacuum chamber 21 is evacuated inside the vacuum chamber 20 in this state. By evacuating the liquid Ga and N 2 gas inside the modified layer 8 can be forcibly discharged from the inside of the workpiece 1 to the outside. Thereby, the crack of a workpiece 1 and a crack can be prevented easily.

(Third embodiment)
FIG. 6 is a schematic diagram of a slicing device according to the third embodiment of the present invention. In FIG. 6, the same components as those in FIGS. 1 and 5 are denoted by the same reference numerals, and the description thereof is omitted.

  The negative electrode 31 a is an electrode formed as a thin film on or in contact with the upper surface of the workpiece 1.

  The negative electrode 31b is a transparent electrode formed as a thin film on the lower surface of the workpiece 1 or an electrode in contact therewith.

  The positive electrode 30 is an electrode installed so as to be in contact with the modified layer 8 exposed on the side surface of the workpiece 1.

  A power source (not shown) is connected to the negative electrode 31a, the negative electrode 31b, and the positive electrode 30, and can apply a voltage. The negative electrodes 31a and 31b, the positive electrode 30, and the power supply correspond to the “voltage application unit” of the present invention.

  In general, it is known that wettability is improved by applying a voltage to a liquid. According to such a configuration, the modified layer 8 is formed of the liquid Ga heated and melted by the heat source 2 during laser irradiation, and a voltage is applied between the negative electrode 31a, the negative electrode 31b, and the positive electrode 30 in this state. As a result, the wettability of the liquid Ga can be improved. Thereby, it becomes easy to discharge liquid Ga and N2 gas from the inside of the workpiece 1 to the outside by the pressure inside the modified layer 8.

  Although not shown, the vacuum chamber 20 is installed and evacuated by the vacuum pump 21 as in the second embodiment, so that the liquid Ga and N 2 gas melted from the inside of the workpiece 1 can be easily discharged to the outside. Become. Thereby, generation | occurrence | production of the crack of the workpiece 1 and a crack can be prevented.

  In the heat source 2 according to each of the first, second, and third embodiments, a contact-type heat source (for example, a hot plate) is used. However, the present invention is not limited to this, and for example, FIG. A non-contact heat source 40 as shown in FIG.

  Further, for example, even if a light source such as an IR heater or a halogen lamp that has a transmittance of 80% or more with respect to the workpiece 1 and the modified layer 8 exhibits an absorption of 50% or more is used. In addition, it is possible to process Ga deposited on the modified layer 8 while heating.

  In the present invention, the thickness and diameter of the workpiece 1 are not particularly limited. In the present invention, the material is not limited to GaN. Silicon substrate, sapphire substrate, substrate obtained by epitaxially growing a GaN layer on sapphire substrate, GaAs substrate InP substrate, AlGaN / GaN substrate, SiC substrate, SiC substrate Any material can be used as long as it is a substrate on which a GaN layer is epitaxially grown, a material such as diamond that can transmit the laser beam and can form the modified layer 8, and a material having a low melting point such as GaN is more preferable. It is.

  In the above embodiment, the wavelength 532 nm is used as the laser beam 5 oscillated from the oscillator 4. However, the present invention is not limited to this, and may be a wavelength that is transmissive to the workpiece 1, for example. Although there is no limitation, a shorter wavelength is more preferable because workability is good because dimensions in the thickness direction and horizontal direction of the focused spot inside the workpiece 1 are small.

  In the present invention, the pulse width is not limited as long as internal processing by multiphoton absorption is possible in the range of 1 fs to 1 ns. In addition, the repetition frequency may be selected within a range of 1 MHz or less in which the laser oscillator can oscillate from the relationship between productivity and workability due to the interaction between the material and the laser beam.

  Furthermore, in the present invention, the objective lens 7 is desirable because the larger the numerical aperture NA, the smaller the focused spot diameter. The aberration correction function is preferably a lens with an aberration correction function because the energy density at the condensing point can be increased. However, correction may be performed in advance using a phase modulation element or the like.

  In the present invention, multiple branches may be made by a mirror or the like, or multiple points may be processed simultaneously by a diffractive optical element or a phase modulation element. As a result, the same effects as those of the above embodiment can be obtained, and productivity such as shortening of processing time can be improved.

  The present invention can be applied to a slicing method and a slicing apparatus that are required to reduce the manufacturing cost of a substrate.

DESCRIPTION OF SYMBOLS 1 Work material 2 Heat source 4 Laser oscillator 5 Laser light 7 Objective lens 8 Modification layer 9 Lens temperature sensor 10 Work material temperature sensor 11 Temperature controller 12 Heat ray cut filter

Claims (11)

A modified layer forming step of condensing the laser beam inside the workpiece through the condenser and forming a modified layer in the vicinity of the focal point inside the workpiece;
By heating the workpiece, the modified layer is melted inside the workpiece, a gas is generated, and the molten modified layer material is converted into the workpiece by the pressure of the generated gas. A discharge process for discharging the processed material to the outside;
A scanning step of forming a boundary by the modified layer inside the workpiece by scanning the laser beam condensed inside the workpiece,
A separation step of separating the workpiece into at least two or more substrates with the modified layer as a boundary;
A slicing method comprising:   The slicing method according to claim 1, wherein the discharging step heats the workpiece to a temperature equal to or higher than a melting point of the modified layer, equal to or lower than a melting point of the workpiece and equal to or lower than a heat resistant temperature of the light collecting portion.   The said discharge | emission process has a process of making the circumference | surroundings of the said workpiece material into a negative pressure so that it may be easy to discharge | emit the fuse | melted modified layer substance to the exterior of the said workpiece material. Slicing method.   The discharging step applies a voltage to the modified layer so as to improve the wettability of the molten modified layer material and to facilitate discharging the molten modified layer material to the outside of the workpiece. The slicing method according to claim 1, further comprising a step of: A substrate slicing device that forms a modified layer inside a workpiece and separates the workpiece into at least two or more substrates with the modified layer as a boundary,
A modified layer forming section for condensing a laser beam inside the workpiece through a focusing section and forming the modified layer in the vicinity of a focusing point inside the workpiece;
By heating the workpiece, the modified layer is melted inside the workpiece, a gas is generated, and the molten modified layer material is converted into the workpiece by the pressure of the generated gas. A discharge part for discharging to the outside of the work material;
A slicing apparatus. A first temperature sensor for measuring the temperature of the light collecting unit;
A second temperature sensor for measuring the temperature of the workpiece;
Based on the measurement results of the first and second temperature sensors, the temperature for controlling the discharge unit so that the modified layer is not lower than the melting point, the workpiece is not higher than the melting point, and the light collecting portion is not higher than the heat resistant temperature. A control unit;
The slicing apparatus according to claim 5, further comprising:   The slicing apparatus according to claim 5 or 6, further comprising a filter that transmits the laser light between the laser light and the workpiece, but blocks heat.   The slicing apparatus according to any one of claims 5 to 7, wherein the discharge unit includes a contact-type heat source that heats the workpiece in contact with the workpiece.   The slicing apparatus according to any one of claims 5 to 7, wherein the discharge unit includes a non-contact heat source that heats the workpiece without contacting the workpiece.   The said discharge part has a vacuum chamber and a vacuum pump which make the circumference | surroundings of the said workpiece material negative pressure so that it may be easy to discharge | emit the said molten modified layer substance to the exterior of the said workpiece. The slicing device according to any one of 9.   The discharge unit applies a voltage to the modified layer so as to improve the wettability of the melted modified layer material and to easily discharge the melted modified layer material to the outside of the workpiece. The slicing device according to claim 5, further comprising a voltage applying unit that performs the operation.