JP2015123482A - Laser dicing device and laser dicing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser dicing device capable of realizing cutting with high energy efficiency.SOLUTION: A laser dicing device includes: a stage on which a processing target substrate can be mounted; a reference-clock generation circuit generating a clock signal; a laser oscillator emitting a pulsed laser beam; a laser oscillator controller synchronizing the pulsed laser beam with the clock signal; a pulse picker provided in an optical path between the laser oscillator and the stage, and switching over between radiation and non-radiation of the pulsed laser beam to the processing target substrate; and a pulse picker controller controlling passing or cutoff of the pulsed laser beam through or from the pulse picker per optical pulse synchronously with the clock signal. If it is assumed that an incident angle of an optical axis of the pulsed laser beam on the processing target substrate is α, and that a refractive index of the processing target substrate is n, a relation represented by arctan(n)-5≤α≤arctan(n)+5 is satisfied.

Description

  The present invention relates to a laser dicing apparatus and a laser dicing method using a pulse laser beam.

  A method of using a pulsed laser beam for dicing a semiconductor substrate is disclosed in Patent Document 1. In the method of Patent Document 1, a modified region is formed inside a workpiece due to optical damage caused by a pulsed laser beam. At the same time, a crack starting from this modified region is formed on the surface of the workpiece. And a processing target object is cut using this crack.

  In the conventional technique, the formation of cracks is controlled using parameters such as the energy of the pulse laser beam, the spot diameter, the relative moving speed of the pulse laser beam and the workpiece.

Japanese Patent No. 4813624

  However, in the conventional method, a part of the pulse laser beam is reflected on the surface of the object to be processed, and there is a possibility that cracking with high energy efficiency cannot be performed.

  The present invention has been made in view of the above-described circumstances. Laser dicing that adjusts the incident angle of a pulsed laser beam to suppress reflection of the pulsed laser beam on the surface of the workpiece and achieves energy-efficient cleaving. An object is to provide an apparatus and a laser dicing method.

A laser dicing apparatus according to one embodiment of the present invention includes a stage on which a substrate to be processed can be placed, a reference clock oscillation circuit that generates a clock signal, a laser oscillator that emits a pulse laser beam, and the pulse laser beam that is converted into the clock. A laser oscillator control unit that is synchronized with a signal, a pulse picker that is provided in an optical path between the laser oscillator and the stage, and switches between irradiation and non-irradiation of the pulsed laser beam on the substrate to be processed; and the clock signal A pulse picker control unit that controls passage and blocking of the pulse laser beam in the pulse picker in units of optical pulses in synchronization,
When the incident angle of the optical axis of the pulse laser beam to the substrate to be processed is α degrees and the refractive index of the substrate to be processed is n,
arctan (n) −5 ≦ α ≦ arctan (n) +5
It is characterized by satisfying the relationship.

  In the apparatus of the above aspect, it is preferable that a polarizing element that uses the pulsed laser beam incident on the workpiece substrate as a p-wave is provided between the laser oscillator and the workpiece substrate.

  In the apparatus of the above aspect, it is desirable that the polarizing element is a λ / 4 wavelength plate or a polarizer.

  In the apparatus according to the above aspect, it is preferable that an incident angle control unit that makes the incident angle variable is provided.

In the laser dicing method of one embodiment of the present invention, a substrate to be processed is placed on a stage, a clock signal is generated, a pulse laser beam synchronized with the clock signal is emitted, the substrate to be processed, the pulse laser beam, And moving the pulsed laser beam to the substrate to be processed is controlled to pass and block the pulsed laser beam using a pulse picker in synchronization with the clock signal. A laser dicing method that switches in units of light pulses to form a crack reaching the substrate surface on the substrate to be processed, wherein an incident angle of the optical axis of the pulsed laser beam with respect to the substrate to be processed is α degrees, and the substrate to be processed Is n and the refractive index of the incident side material is 1,
arctan (n) −5 ≦ α ≦ arctan (n) +5
It is characterized by satisfying the relationship.

  In the method of the above aspect, it is desirable that the pulse laser beam incident on the workpiece substrate is a p-wave.

  According to the present invention, there is provided a laser dicing apparatus and a laser dicing method that adjust the incident angle of the pulse laser beam to suppress the reflection of the pulse laser beam on the surface of the object to be processed and realize high energy efficient cleaving. It becomes possible.

It is a schematic block diagram which shows an example of the laser dicing apparatus of 1st Embodiment. It is the schematic which shows an example of the principal part of the laser dicing apparatus of 1st Embodiment. It is a figure explaining the effect | action of the laser dicing apparatus of 1st Embodiment. It is a figure explaining the effect | action of the laser dicing apparatus of 1st Embodiment. It is a figure explaining timing control of the laser dicing method of a 1st embodiment. It is a figure which shows the timing of the pulse picker operation | movement and modulated pulse laser beam of the laser dicing method of 1st Embodiment. It is explanatory drawing of the irradiation pattern of the laser dicing method of 1st Embodiment. It is a top view which shows the irradiation pattern irradiated on a sapphire substrate. It is AA sectional drawing of FIG. It is BB sectional drawing of FIG. It is explanatory drawing of an effect | action of 1st Embodiment. It is a figure explaining the relationship between the stage movement and dicing process of 1st Embodiment. It is a schematic block diagram which shows an example of the laser dicing apparatus of 2nd Embodiment. It is the schematic which shows an example of the principal part of the laser dicing apparatus of 3rd Embodiment.

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

  In this specification, the “processing point” is a point in the vicinity of the focused position (focal position) of the pulse laser beam in the substrate to be processed, and the degree of modification of the substrate to be processed is maximum in the depth direction. Means the point. The processing point depth means the depth of the processing point of the pulse laser beam from the substrate surface to be processed.

  Further, in this specification, the “picosecond laser” means a laser having a pulse width on the order of picoseconds, that is, 1 picosecond or more and less than 1 nanosecond. “Femtosecond laser” means a laser having a pulse width on the order of femtoseconds, that is, 1 femtosecond or more and less than 1 picosecond.

  Further, in the present specification, the “polarizing element” is an element that converts the polarization direction of light, and is a concept including, for example, a polarizer, a wavelength plate, and the like.

(First embodiment)
The laser dicing apparatus of this embodiment includes a stage on which a substrate to be processed can be placed, a reference clock oscillation circuit that generates a clock signal, a laser oscillator that emits a pulse laser beam, and a pulse laser beam that is synchronized with the clock signal. A laser oscillator control unit, a pulse picker provided in an optical path between the laser oscillator and the stage, which switches irradiation and non-irradiation of a laser beam to the substrate to be processed, and an optical pulse unit in synchronization with a clock signal A pulse picker control unit for controlling passage and blocking of the pulse laser beam in the pulse picker. When the incident angle of the optical axis of the pulse laser beam with respect to the substrate to be processed is α degrees and the refractive index of the substrate to be processed is n,
arctan (n) −5 ≦ α ≦ arctan (n) +5
Satisfy the relationship.

  FIG. 1 is a schematic configuration diagram showing an example of a laser dicing apparatus according to the present embodiment. As shown in FIG. 1, a laser dicing apparatus 10 according to the present embodiment includes, as main components, a laser oscillator 12, a pulse picker 14, a beam shaper 16, a condensing lens 18, an XYZ stage unit 20, and a laser oscillator control. Unit 22, pulse picker control unit 24, and machining control unit 26. The processing control unit 26 includes a reference clock oscillation circuit 28 that generates a desired clock signal S1 and a processing table unit 30.

  The laser oscillator 12 is configured to emit a pulsed laser beam PL1 having a period Tc synchronized with the clock signal S1 generated by the reference clock oscillation circuit 28. The intensity of the irradiation pulse light shows a Gaussian distribution. The clock signal S1 is a processing control clock signal used for controlling laser dicing processing.

Here, the wavelength of the laser emitted from the laser oscillator 12 is a wavelength that is transmissive to the substrate to be processed. As the laser, an Nd: YAG laser, an Nd: YVO ₄ laser, an Nd: YLF laser, or the like can be used. For example, when the substrate to be processed is a sapphire substrate, it is desirable to use an Nd: YVO ₄ laser having a wavelength of 532 nm.

  In addition, it is desirable to use a picosecond laser or a femtosecond laser having a large peak power from the viewpoint of improving the cleaving characteristics.

  The pulse picker 14 is provided in the optical path between the laser oscillator 12 and the condenser lens 18. Then, by switching between passing and blocking (on / off) of the pulse laser beam PL1 in synchronization with the clock signal S1, the irradiation and non-irradiation of the pulse laser beam PL1 on the substrate to be processed are switched in units of the number of light pulses. Has been. In this manner, the pulse laser beam PL1 is turned on / off for the processing of the substrate to be processed by the operation of the pulse picker 14, and becomes a modulated modulated pulse laser beam PL2.

  The pulse picker 14 is preferably composed of, for example, an acousto-optic element (AOM). Further, for example, an electro-optical element (EOM) may be used.

  The beam shaper 16 converts the incident pulse laser beam PL2 into a pulse laser beam PL3 shaped into a desired shape. For example, a beam expander that expands the beam diameter at a constant magnification. Further, for example, an optical element such as a homogenizer for making the light intensity distribution in the beam cross section uniform may be provided. Further, for example, an element that makes the beam cross section circular or an optical element that makes the beam circularly polarized light may be provided.

  The condensing lens 18 condenses the pulsed laser beam PL3 shaped by the beam shaper 16, and pulses the processed substrate W placed on the XYZ stage unit 20, for example, a sapphire substrate on which LEDs are formed on the lower surface. It is configured to irradiate laser beam PL4.

  The XYZ stage unit 20 is an XYZ stage (hereinafter simply referred to as a stage) on which a workpiece substrate W can be placed and can move freely in the XYZ directions, a drive mechanism unit thereof, and a laser interferometer that measures the position of the stage, for example. A position sensor or the like is provided. Here, the XYZ stage is configured such that its positioning accuracy and movement error are high in the submicron range. Then, by moving in the Z direction, the focal position of the pulse laser beam can be adjusted with respect to the substrate W to be processed, and the processing point depth can be controlled.

  The processing control unit 26 controls the processing by the laser dicing apparatus 10 as a whole. The reference clock oscillation circuit 28 generates a desired clock signal S1. The processing table unit 30 stores a processing table in which dicing processing data is described by the number of optical pulses of the pulse laser beam.

  FIG. 2 is a schematic diagram illustrating an example of a main part of the laser dicing apparatus according to the present embodiment. A laser head 50 for the pulse laser beam is provided so that the optical axis of the pulse laser beam is inclined with respect to the normal direction of the substrate W to be processed placed on the XYZ stage unit 20. That is, the incident angle α of the incident light incident on the workpiece substrate from the laser head 50 with respect to the workpiece substrate W is larger than 0 degree. For example, the condensing lens 18 in FIG. 1 may be incorporated in the laser head 50.

In this embodiment, when the incident angle of the optical axis of the pulse laser beam with respect to the substrate to be processed is α degrees and the refractive index of the substrate to be processed is n,
arctan (n) −5 ≦ α ≦ arctan (n) +5
Satisfy the relationship. In the present embodiment, it is assumed that the incident side material is a material that can be approximated by a refractive index of 1, such as air.

  3 and 4 are diagrams for explaining the operation of the laser dicing apparatus according to the present embodiment.

  As shown in FIG. 3, part of incident light that enters the work substrate having a higher refractive index than air from the air is reflected light that is reflected by the work substrate surface, and part of the light passes through the work substrate. Transmitted light (refracted light). When the ratio of reflected light increases, the ratio of energy used for cleaving among incident energy decreases, and there is a possibility that sufficient cracks cannot be formed on the substrate to be processed. Moreover, the energy efficiency at the time of cleaving falls.

  A surface including a ray of incident light and a normal line of the surface of the substrate to be processed is referred to as an incident surface. Of the incident light, the polarized light whose incident surface and the vibration direction of the light (electric field) are parallel is the p wave, and the perpendicular polarized light is the s wave.

If the refractive index of air or the like that is the incident side material is 1, the refractive index of the substrate to be processed is n, and the incident angle of incident light is α (degrees), α satisfies the following formula, that is, the incident angle is When the Brewster angle is reached, the reflectance of the p-wave component of the incident light becomes 0%.
α = arctan (n)

For this reason, by bringing the incident angle in the vicinity of α, the reflectance of the light whose polarization direction of the incident pulse laser beam is in the vicinity of the p-wave is suppressed, and high energy-efficient cleaving is realized. From the viewpoint of suppressing the reflectance of the p-wave component to about 10% or less,
arctan (n) −5 ≦ α ≦ arctan (n) +5
It is desirable that this relationship is satisfied.

  FIG. 4 shows a simulation result of the relationship between the incident angle α of the p-wave and the reflectance when the substrate to be processed is a gallium arsenide (GaAs) substrate. The refractive index of gallium arsenide is 3.2. As shown in the figure, when the incident angle α is 73 degrees (= arctan (3.2)), the reflectance is 0%, and within the range of 73 ± 5 degrees, the reflectance is suppressed to 10% or less. .

  For example, when the substrate to be processed is a sapphire substrate with a refractive index of 1.7, the reflectance is 0% when the incident angle α is 60 degrees (= arctan (1.7)). Therefore, in the case of a sapphire substrate, it is desirable that the incident angle α is 60 ± 5 degrees.

  With the above configuration, it becomes possible to provide a laser dicing apparatus that realizes excellent cleaving characteristics. Here, the excellent cleaving characteristics are (1) the cleaved portion is cleaved with good linearity, (2) the cleaved portion can be cleaved with a small cleaving force so as to improve the yield of the diced element, and (3) crack formation. The deterioration of an element provided on the substrate, for example, an LED element formed by an epitaxial layer on the substrate, is not caused by the influence of the laser irradiated at that time.

  Then, by forming continuous cracks on the surface of the substrate to be processed, dicing of a hard substrate such as a sapphire substrate is facilitated. Further, dicing with a narrow dicing width is realized.

  Further, the laser dicing apparatus according to the present embodiment makes the pulsed laser beam incident on the substrate to be processed while being inclined. Thereby, reflection of the pulse laser beam on the surface of the substrate to be processed is suppressed. Therefore, desired cracks can be formed, and cutting of the substrate to be processed with high energy efficiency can be realized.

  In order to realize the effect of the present embodiment, the optical axis of the laser head 52 with respect to the vertical direction can be used as long as the optical axis of the pulsed laser beam is inclined with respect to the substrate to be processed. Even if it is the structure which inclines, conversely, the structure which inclines the surface of the XYZ stage part 20 from a horizontal surface may be sufficient.

In the laser dicing method of this embodiment, a substrate to be processed is placed on a stage, a clock signal is generated, a pulse laser beam synchronized with the clock signal is emitted, and the substrate to be processed and the pulse laser beam are relatively moved. The pulse laser beam irradiation and non-irradiation on the substrate to be processed are switched in units of optical pulses by controlling the passage and blocking of the pulse laser beam using a pulse picker in synchronization with the clock signal. This is a laser dicing method for forming a crack reaching the substrate surface on a processed substrate. When the incident angle of the optical axis of the pulse laser beam to the substrate to be processed is α degrees, the refractive index of the substrate to be processed is n, and the refractive index of the incident side material is 1,
arctan (n) −5 ≦ α ≦ arctan (n) +5
Satisfy the relationship.

  Hereinafter, a laser dicing method using the laser dicing apparatus 10 will be described with reference to FIGS.

  First, the substrate W to be processed, for example, a sapphire substrate is placed on the XYZ stage unit 20. The sapphire substrate is, for example, a wafer having a GaN layer epitaxially grown on the lower surface and a plurality of LEDs patterned on the GaN layer. The wafer is aligned with respect to the XYZ stage based on a notch or orientation flat formed on the wafer.

FIG. 5 is a diagram for explaining timing control of the laser dicing method of the present embodiment. In the reference clock oscillation circuit 28 in the processing control unit 26, a clock signal S1 having a cycle Tc is generated. The laser oscillator control unit 22 controls the laser oscillator 12 to emit a pulsed laser beam PL1 having a cycle Tc synchronized with the clock signal S1. At this time, the rise of the rise and the pulse laser beam of the clock signal S1, is generated the delay time t _1.

  Laser light having a wavelength that is transparent to the substrate to be processed is used. Here, it is preferable to use a laser beam in which the photon energy hv of the irradiated laser beam is larger than the absorption band gap Eg of the substrate material to be processed. When the energy hν is much larger than the band gap Eg, laser light absorption occurs. This is called multiphoton absorption. When the pulse width of the laser beam is made extremely short and multiphoton absorption occurs inside the substrate to be processed, the energy of the multiphoton absorption is not converted into thermal energy, and the ionic valence. Permanent structural changes such as change, crystallization, amorphization, polarization orientation or microcrack formation are induced to form a color center.

  The irradiation energy (irradiation power) of this laser beam (pulse laser beam) is selected under the optimum conditions for forming continuous cracks on the surface of the substrate to be processed.

  If a wavelength having transparency is used for the substrate material to be processed, the laser light can be guided and condensed near the focal point inside the substrate. Therefore, it is possible to make a color center locally. This color center is hereinafter referred to as a modified region.

  The pulse picker control unit 24 refers to the machining pattern signal S2 output from the machining control unit 26, and generates a pulse picker driving signal S3 synchronized with the clock signal S1. The machining pattern signal S2 is stored in the machining table unit 30, and is generated with reference to a machining table that describes irradiation pattern information in units of light pulses by the number of light pulses. The pulse picker 14 performs an operation of switching between passing and blocking (ON / OFF) of the pulse laser beam PL1 in synchronization with the clock signal S1 based on the pulse picker driving signal S3.

By the operation of the pulse picker 14, a modulated pulse laser beam PL2 is generated. Note that delay times t ₂ and t ₃ occur at the rise of the clock signal S1 and the rise and fall of the pulse laser beam. Also, delay times t ₄ and t ₅ occur in the rise and fall of the pulse laser beam and the pulse picker operation.

When processing the substrate to be processed, the generation timing of the pulse picker drive signal S3 and the like and the relative movement timing of the substrate to be processed and the pulse laser beam are determined in consideration of the delay times t _{1 to} t ₅ .

  FIG. 6 is a diagram showing the pulse picker operation and the timing of the modulated pulse laser beam PL2 in the laser dicing method of the present embodiment. The pulse picker operation is switched in units of optical pulses in synchronization with the clock signal S1. Thus, by synchronizing the oscillation of the pulse laser beam and the operation of the pulse picker with the same clock signal S1, an irradiation pattern in units of light pulses can be realized.

  Specifically, irradiation and non-irradiation of a pulsed laser beam are performed based on a predetermined condition defined by the number of light pulses. That is, the pulse picker operation is executed based on the number of irradiation light pulses (P1) and the number of non-irradiation light pulses (P2), and the irradiation and non-irradiation of the substrate to be processed are switched. The P1 value and the P2 value that define the irradiation pattern of the pulse laser beam are defined, for example, as irradiation region register settings and non-irradiation region register settings in the processing table. The P1 value and the P2 value are set to predetermined conditions that optimize crack formation during dicing, depending on the material of the substrate to be processed, laser beam conditions, and the like.

  The modulated pulsed laser beam PL2 is a pulsed laser beam PL3 shaped into a desired shape by the beam shaper 16. Further, the shaped pulse laser beam PL3 is condensed by the condensing lens 18 to become a pulse laser beam PL4 having a desired beam diameter, and is irradiated onto a wafer which is a substrate to be processed.

  When dicing the wafer in the X-axis direction and the Y-axis direction, first, for example, the XYZ stage is moved at a constant speed in the X-axis direction, and the pulse laser beam PL4 is scanned. Then, after the desired dicing in the X-axis direction is completed, the XYZ stage is moved at a constant speed in the Y-axis direction to scan with the pulse laser beam PL4. Thereby, dicing in the Y-axis direction is performed.

  The irradiation non-irradiation interval of the pulse laser beam is controlled by the number of irradiation light pulses (P1), the number of non-irradiation light pulses (P2), and the stage speed.

  Regarding the Z-axis direction (height direction), adjustment is performed so that the condensing position (focal position) of the condensing lens is positioned at a predetermined depth in the wafer. This predetermined depth is set so that cracks are formed in a desired shape on the surface of the substrate to be processed during dicing.

At this time,
Deflection ratio of substrate to be processed: n
Processing position from the substrate surface to be processed: L
Z-axis travel distance: Lz
Then,
Lz = L / n
It becomes. That is, when the condensing position by the condensing lens is set to the position of the depth “L” from the surface of the substrate when the surface of the substrate to be processed is the Z-axis initial position, the Z axis may be moved “Lz”. .

  FIG. 7 is an explanatory diagram of an irradiation pattern of the laser dicing method of the present embodiment. As shown in the figure, the pulsed laser beam PL1 is generated in synchronization with the clock signal S1. The modulated pulse laser beam PL2 is generated by controlling the passage and blocking of the pulse laser beam in synchronization with the clock signal S1.

  Then, by moving the stage in the horizontal direction (X-axis direction or Y-axis direction), an irradiation light pulse of the modulated pulse laser beam PL2 is formed as an irradiation spot on the wafer. In this way, by generating the modulated pulse laser beam PL2, the irradiation spot is controlled and irradiated intermittently on the wafer in units of light pulses. In the case of FIG. 7, the number of irradiation light pulses (P1) = 2, the number of non-irradiation light pulses (P2) = 1, and the irradiation light pulses (Gaussian light) are set to repeat irradiation and non-irradiation at a spot diameter pitch. Has been.

here,
Beam spot diameter: D (μm)
Repetition frequency: F (KHz)
If processing is performed under the conditions, the stage moving speed V (m / sec) for repeating irradiation and non-irradiation of the irradiation light pulse at the spot diameter pitch is:
V = D × 10 ⁻⁶ × F × 10 ³
It becomes.

For example,
Beam spot diameter: D = 2 μm
Repetition frequency: F = 50KHz
If the processing conditions are
Stage moving speed: V = 100mm / sec
It becomes.

  If the power of the irradiation light is P (watts), the wafer is irradiated with a light pulse of irradiation pulse energy P / F per pulse.

  Cracks are continuously formed on the surface of the substrate to be processed by the parameters of the irradiation energy (irradiation light power) of the pulse laser beam, the processing point depth of the pulse laser beam, and the non-irradiation interval of the pulse laser beam. Determined to be.

  FIG. 8 is a top view showing an irradiation pattern irradiated on the sapphire substrate. When viewed from the irradiation surface, irradiation spots are formed at a pitch of the irradiation spot diameter with the number of irradiation light pulses (P1) = 2 and the number of non-irradiation light pulses (P2) = 1. 9 is a cross-sectional view taken along the line AA in FIG. FIG. 10 is a BB cross-sectional view of FIG. As shown in the figure, a modified region is formed inside the sapphire substrate. Then, cracks (or grooves) reaching the substrate surface along the scanning line of the light pulse are formed from the modified region. And this crack is continuously formed in the to-be-processed substrate surface. In the present embodiment, the crack is formed so as to be exposed only on the front surface side of the substrate and does not reach the back surface side of the substrate.

  FIG. 11 is an explanatory diagram of the operation of the present embodiment. For example, the pulse irradiable position in the case of irradiating the pulse laser at the maximum settable laser frequency of the pulse laser beam and at the maximum settable stage speed is indicated by a dotted circle in FIG. FIG. 11B shows an irradiation pattern when irradiation / non-irradiation = 1/2. A solid line circle is an irradiation position, and a dotted line circle is a non-irradiation position.

  Here, it is assumed that the shorter the interval between the irradiation spots (the length of the non-irradiation region), the better the cleaving property. In this case, as shown in FIG. 11 (c), it is possible to cope by setting irradiation / non-irradiation = 1/1 without changing the stage speed. If the pulse picker is not used as in the present embodiment, it is necessary to reduce the stage speed in order to bring out the same condition, resulting in a problem that the throughput of dicing processing is reduced.

  Here, it is assumed that the cleaving property is better when the irradiation spot is made continuous to make the length of the irradiation region longer. In this case, as shown in FIG. 11 (d), it is possible to cope with this by setting irradiation / non-irradiation = 2/1 without changing the stage speed. If the pulse picker is not used as in the present embodiment, it is necessary to lower the stage speed and change the stage speed in order to achieve the same conditions, and the dicing processing throughput is reduced. In addition, there arises a problem that control becomes extremely difficult.

  Alternatively, when a pulse picker is not used, it is conceivable to increase the irradiation energy with the irradiation pattern of FIG. 11 (b) to achieve a condition close to that of FIG. 11 (d). There is a concern that the power will increase and the crack width will increase and the linearity of the crack will deteriorate. Further, when processing a substrate to be processed in which an LED element is formed on a sapphire substrate, the amount of laser that reaches the LED region on the side opposite to the crack increases, and the LED element may be deteriorated. There is also.

  As described above, according to the present embodiment, for example, various cleaving conditions can be realized without changing the conditions of the pulse laser beam and the stage speed condition, and the productivity and device characteristics are deteriorated. It is possible to find the optimum cleaving condition without any problem.

  In this specification, “the length of the irradiation region” and “the length of the non-irradiation region” are the lengths shown in FIG.

  FIG. 12 is a diagram for explaining the relationship between stage movement and dicing. The XYZ stage is provided with a position sensor that detects the movement position in the X-axis and Y-axis directions. For example, after the stage starts moving in the X-axis or Y-axis direction, a position where the stage speed enters the speed stable region is set in advance as a synchronization position. When the synchronization position is detected by the position sensor, for example, the movement position detection signal S4 (FIG. 1) is sent to the pulse picker control unit 24 to allow the pulse picker operation, and the pulse picker driving signal S3 is used to activate the pulse picker. Make it work. For example, the synchronization position may be set as an end surface of the substrate to be processed, and the end surface may be detected by a position sensor.

in this way,
S _L : Distance from synchronization position to substrate W _L : Processing length W ₁ : Distance from substrate edge to irradiation start position W ₂ : Processing range W ₃ : Distance from irradiation end position to substrate edge is managed.

  In this manner, the position of the stage and the position of the workpiece substrate placed thereon are synchronized with the operation start position of the pulse picker. That is, the irradiation and non-irradiation of the pulse laser beam are synchronized with the position of the stage. Therefore, it is ensured that the stage moves at a constant speed (in a stable speed range) during irradiation and non-irradiation of the pulse laser beam. Therefore, the regularity of the irradiation spot position is ensured, and stable crack formation is realized.

  Here, when processing a thick substrate, it is possible to improve the cleaving characteristics by forming a crack by scanning the same scanning line of the substrate multiple times (multiple layers) with a pulse laser beam having different processing point depths. Conceivable. In such a case, the stage position and the operation start position of the pulse picker are synchronized, so that the relationship between the pulse irradiation positions can be controlled arbitrarily and accurately in scanning at different depths, and the dicing conditions can be optimized. It becomes possible.

  For example, it is desirable to synchronize the movement of the stage with the clock signal in order to further improve the accuracy of the irradiation spot position. This can be realized, for example, by synchronizing the stage movement signal S5 (FIG. 1) sent from the machining control unit 26 to the XYZ stage unit 20 with the clock signal S1.

Furthermore, in the present embodiment, when the incident angle of the optical axis of the pulse laser beam with respect to the workpiece W is α degrees, the refractive index of the workpiece W is n, and the refractive index of the incident side material is 1,
arctan (n) −5 ≦ α ≦ arctan (n) +5
Satisfy the relationship.

  With this configuration, the reflectance of light in the vicinity of the p-wave component in the incident light is suppressed. Therefore, it is possible to form a desired crack and realize high energy efficient cleaving.

  Like the laser dicing method of the present embodiment, the subsequent cracking of the substrate is facilitated by forming cracks that reach the surface of the substrate and are continuous on the surface of the substrate to be processed. For example, even a hard substrate such as a sapphire substrate can be easily cleaved by applying a force artificially with the crack reaching the substrate surface as the starting point for cleaving or cutting, and has excellent cleaving characteristics. It can be realized. Accordingly, dicing productivity is improved.

  In the method of continuously irradiating the substrate with the pulsed laser beam, even if the stage moving speed, the numerical aperture of the condenser lens, the irradiation light power, etc. are optimized, the cracks continuously formed on the substrate surface are desired. It was difficult to control the shape. As in the present embodiment, the generation of cracks reaching the substrate surface is controlled by switching the irradiation and non-irradiation of the pulse laser beam intermittently in units of light pulses and optimizing the irradiation pattern. A laser dicing method having characteristics is realized.

  That is, for example, it is possible to form a substantially linear and continuous narrow crack along the laser scanning line on the substrate surface. By forming such substantially linear continuous cracks, it is possible to minimize the influence of cracks on devices such as LEDs formed on the substrate during dicing. Further, for example, since a linear crack can be formed, the width of the region where the crack is formed on the substrate surface can be reduced. For this reason, it is possible to narrow the design dicing width. Therefore, it is possible to increase the number of chips of devices formed on the same substrate or wafer, which contributes to a reduction in device manufacturing costs.

  Further, by cutting the optical axis of the pulse laser beam with respect to the substrate to be processed, cutting with high energy efficiency is realized.

(Second Embodiment)
The laser dicing apparatus according to the present embodiment is the same as that of the first embodiment except that a polarization element that uses a pulse laser beam incident on the workpiece substrate as a p-wave is provided between the laser oscillator and the workpiece substrate. It is the same. Therefore, the description overlapping with that of the first embodiment is omitted.

  FIG. 13 is a schematic configuration diagram illustrating an example of the laser dicing apparatus according to the present embodiment. In addition to the configuration of the first embodiment, the laser dicing apparatus 70 according to the present embodiment converts the pulse laser beam PL5 incident on the workpiece substrate W between the laser oscillator 12 and the workpiece substrate W into linearly polarized light. The polarizing element 52 is used as the p-wave.

  The polarizing element 52 is a λ / 4 wavelength plate or a polarizer. For example, the polarization direction is changed by the polarizing element 52 so that the pulse laser beam, which has been circularly polarized, becomes p-wave linearly polarized light when it enters the substrate W to be processed.

  According to the present embodiment, the ratio of the reflected light to the entire incident light is further suppressed by setting the pulse laser beam incident on the substrate W to be processed as a p-wave. Accordingly, it is possible to realize a laser dicing apparatus and a laser dicing method with higher energy efficiency.

  In order to improve energy efficiency, it is desirable that all light incident on the substrate W to be processed is p-wave. However, if the ratio of the p-wave component to the entire incident light is increased as compared with the case where the polarizing element 52 is not provided, the effect of improving the energy efficiency can be obtained. For this reason, the incident light does not necessarily have to be all p-waves.

  Here, the polarizing element 52 is provided between the condenser lens 18 and the substrate W to be processed. However, as long as the incident pulse laser beam can be made to be p-polarized light, the polarizing element 52 may be provided at another position between the laser oscillator 12 and the substrate W to be processed. .

(Third embodiment)
The laser dicing apparatus according to the present embodiment is the same as that of the first embodiment except that the laser dicing apparatus includes an incident angle control unit that makes the incident angle with respect to the substrate to be processed variable. Therefore, the description overlapping with that of the first embodiment is omitted.

  FIG. 14 is a schematic diagram illustrating an example of a main part of the laser dicing apparatus according to the present embodiment. A laser head 50 for the pulse laser beam is provided so that the optical axis of the pulse laser beam is inclined with respect to the normal direction of the substrate W to be processed placed on the XYZ stage unit 20. Further, an incident angle control unit 54 that makes the incident angle with respect to the workpiece substrate W variable is provided.

  For example, the incident angle control unit 54 mechanically changes the inclination of the laser head 50 and changes the incident angle of incident light between α and α ′. Further, for example, a configuration in which the incident angle of incident light is optically changed may be used. Further, for example, a mechanism that makes the inclination of the XYZ stage unit 20 with respect to the horizontal plane variable may be used.

  According to the present embodiment, by making the incident angle of the incident light variable, it becomes possible to make the pulse laser beam incident at an optimum inclination angle corresponding to the refractive index of the substrate W to be processed. Therefore, it is possible to realize a laser dicing apparatus and a laser dicing method capable of dicing under optimum conditions from the viewpoint of energy efficiency in accordance with the substrate to be processed.

  The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. In the embodiment, the description of the laser dicing apparatus, the laser dicing method, etc. that is not directly necessary for the description of the present invention is omitted, but the elements related to the required laser dicing apparatus, the laser dicing method, etc. are omitted. It can be appropriately selected and used.

  In addition, all laser dicing apparatuses and laser dicing methods that include elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention. The scope of the present invention is defined by the appended claims and equivalents thereof.

  For example, in the embodiment, the sapphire substrate on which the LED is formed is described as an example of the substrate to be processed. The present invention is useful for a hard substrate such as a sapphire substrate that is hard to cleave and difficult to cleave, but the substrate to be processed is a semiconductor such as a silicon substrate, a group III-V substrate, a SiC (silicon carbide) substrate, etc. It may be a material substrate, a piezoelectric material substrate, a glass substrate, or the like.

  In the embodiment, the case where the substrate to be processed and the pulse laser beam are relatively moved by moving the stage has been described as an example. However, for example, a method of relatively moving the substrate to be processed and the pulsed laser beam by scanning the pulsed laser beam by using a laser beam scanner or the like may be used.

  Further, in the embodiment, the case where the number of irradiation light pulses (P1) = 2 and the number of non-irradiation light pulses (P2) = 1 is described as an example. However, the values of P1 and P2 are optimum conditions. It is possible to take any value. In the embodiment, the case where the irradiation light pulse repeats irradiation and non-irradiation at a pitch of the spot diameter has been described as an example. However, the pitch of irradiation and non-irradiation can be changed by changing the pulse frequency or the stage moving speed. It is also possible to find the optimum condition. For example, the pitch between irradiation and non-irradiation can be 1 / n or n times the spot diameter.

  For dicing patterns, for example, multiple irradiation area registers and non-irradiation area registers may be provided, or the irradiation area register and non-irradiation area register values may be changed to desired values at desired timing in real time. This makes it possible to handle various dicing patterns.

  Further, as an example of the laser dicing apparatus, an apparatus including a machining table unit that stores a machining table in which dicing data is described by the number of optical pulses of a pulse laser beam has been described. However, an apparatus having a configuration for controlling the passage and blocking of the pulse laser beam in the pulse picker in units of optical pulses may be used without necessarily providing such a processing table unit.

  In order to further improve the cleaving characteristics, after forming continuous cracks on the substrate surface, for example, it is also possible to add a melt processing or ablation processing to the surface by irradiating a laser, for example. is there.

DESCRIPTION OF SYMBOLS 10 Pulse laser processing apparatus 12 Laser oscillator 14 Pulse picker 16 Beam shaper 18 Condensing lens 20 XYZ stage part 22 Laser oscillator control part 24 Pulse picker control part 26 Processing control part 28 Reference clock oscillation circuit 30 Processing table part 50 Laser head 52 Polarizing element 54 Incident angle controller 70 Pulse laser processing apparatus

Claims (6)

A stage on which a substrate to be processed can be placed;
A reference clock oscillation circuit for generating a clock signal;
A laser oscillator that emits a pulsed laser beam;
A laser oscillator controller for synchronizing the pulsed laser beam with the clock signal;
A pulse picker that is provided in an optical path between the laser oscillator and the stage, and switches between irradiation and non-irradiation of the pulsed laser beam to the workpiece substrate;
In synchronization with the clock signal, a pulse picker controller that controls passage and blocking of the pulse laser beam in the pulse picker in units of optical pulses;
With
When the incident angle of the optical axis of the pulse laser beam to the substrate to be processed is α degrees and the refractive index of the substrate to be processed is n,
arctan (n) −5 ≦ α ≦ arctan (n) +5
A laser dicing apparatus characterized by satisfying the above relationship.   The laser dicing apparatus according to claim 1, further comprising a polarizing element that uses the pulsed laser beam incident on the substrate to be processed as a p-wave, between the laser oscillator and the substrate to be processed.   3. The laser dicing apparatus according to claim 1, wherein the polarizing element is a λ / 4 wavelength plate or a polarizer.   The laser dicing apparatus according to any one of claims 1 to 3, further comprising an incident angle control unit that makes the incident angle variable. Place the substrate to be processed on the stage,
Generate a clock signal,
A pulse laser beam synchronized with the clock signal is emitted,
Relatively moving the workpiece substrate and the pulsed laser beam;
The irradiation and non-irradiation of the pulsed laser beam on the substrate to be processed are switched in units of light pulses by controlling the passage and blocking of the pulsed laser beam using a pulse picker in synchronization with the clock signal,
A laser dicing method for forming a crack reaching the substrate surface in the workpiece substrate,
When the incident angle of the optical axis of the pulse laser beam to the substrate to be processed is α degrees and the refractive index of the substrate to be processed is n,
arctan (n) −5 ≦ α ≦ arctan (n) +5
A laser dicing method characterized by satisfying the above relationship.   6. The laser dicing method according to claim 5, wherein the pulse laser beam incident on the substrate to be processed is a p-wave.

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