TW201446378A - Laser processing using an astigmatic elongated beam spot and using ultrashort pulses and/or longer wavelengths - Google Patents

Abstract

An adjustable astigmatic elongated beam spot may be formed from a laser beam having ultrashort laser pulses and/or longer wavelengths to machine substrates made of a variety of different materials. The laser beam may be generated with pulses having a pulse duration of less than 1 ns and/or having a wavelength greater than 400 nm. The laser beam is modified to produce an astigmatic beam that is collimated in a first axis and converging in a second axis. The astigmatic beam is focused to form the astigmatic elongated beam spot on a substrate, which is focused on the substrate in the first axis and defocused in the second axis. The astigmatic elongated beam spot may be adjusted in length to provide an energy density sufficient for a single ultrashort pulse to cause cold ablation of at least a portion of the substrate material.

Description

Use astigmatic extended beam spots and use ultrashort pulse and/or longer wavelength thunder Shot processing method [Cross-application for related applications]

This application is a continuation-in-part of the co-pending U.S. Patent Application Serial No. 13,422,190 filed on March 16, 2012, which is filed on December 7, 2010. U.S. Patent Application Serial No. U.S. Patent Application Serial No. Serial No. No. No. No. No. No. No. No. No. No. No. No. No. No. No. No. No. No. No. No. No. No. No. No. No. Such U.S. Patent Application and U.S. Provisional Patent Application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to laser processing, and more particularly to laser processing (e.g., scribing) using an astigmatic elongated beam spot formed by a solid state laser. The raylines produce ultrashort pulses and/or longer wavelengths in the visible or infrared (IR) range.

A workpiece is typically processed or processed by laser, for example by cutting or scribing a substrate or semiconductor wafer. For example, in semiconductor manufacturing, lasers are often used to cut a semiconductor wafer process to separate individual devices (or grains) made from semiconductor wafers from each other. The individual dies on the wafer are separated by a street and the wafer can be diced along the via using a laser. The wafer can be completely cut using a laser, or the wafer can be completely cut and the remainder of the wafer separated by breaking the wafer at the point of perforation. For example, when a light emitting diode (LED) is fabricated, each die on the wafer corresponds to an LED.

As semiconductor devices are becoming smaller in size, the number of such devices that can be fabricated on a single wafer is increased. Increasing the device density per wafer increases throughput and similarly reduces the cost of manufacturing each device. To increase this density, it is desirable to manufacture such devices as closely as possible. The tighter the position of the device on the semiconductor wafer, the narrower the barrier between the devices. Therefore, the laser beam should be accurately positioned within the narrower channel and the wafer should be cut with minimal or no damage to the device.

According to one technique, a laser can be focused onto one surface of a substrate or wafer to ablate the material and achieve a partial cut. Laser cutting can be performed on a semiconductor wafer, for example, on the front side of the wafer on which the device is formed (referred to as front-side scribing (FSS)), or on the back side of the wafer (called For back-side scribing (BSS). The prior art systems and methods have used a astigmatically elongated beam spot or a straight line beam to perform a laser scribe, as described in more detail in U.S. Patent No. 7,709,768, incorporated herein by reference.

While these methods have many advantages over other techniques for forming a straight beam to scribe a workpiece, existing systems for scribing with an astigmatic elongated beam spot are limited to certain materials, wavelengths, and pulse durations. time. Lasers that produce ultrashort pulses and/or longer wavelengths in the visible range and in the infrared range are commercially available, but are expected to maintain high laser processing while minimizing melting and other thermal damage. Speed and accuracy have been a challenge in some laser scribing applications.

The main object of the present invention is to provide a method for forming an astigmatic elongated beam spot for processing a substrate, the method comprising: generating a laser beam having a plurality of pulse waves, The pulse waves have a pulse duration of less than 1 nanosecond (ns); the laser beam is modified to form an astigmatic beam that is collimated on a first axis and converges on a second axis And focusing the astigmatism beam to form an astigmatic elongated beam spot on a substrate, the focused astigmatism beam having a first focus on the first axis and a second focus on the second axis Separating the second focus from the first focus, causing the astigmatic elongated beam spot to be focused on the substrate on the first axis and defocused on the second axis, the astigmatic elongated beam spot Having a width along the first axis and a length along the second axis, the width being less than the length, such that the astigmatic elongated beam spot is narrower on the first axis and wider on the second axis .

A second object of the present invention is to provide a method of forming an astigmatic elongated beam spot for processing a substrate, the method comprising: generating a laser beam having a wavelength greater than 400 nm; a beam of rays to form an astigmatic beam that collimates on a first axis and converges on a second axis; and focuses the astigmatic beam to form an astigmatic elongated beam spot on a substrate The focused astigmatism beam has a first focus on the first axis and a second focus on the second axis, the second focus is separated from the first focus, causing the astigmatic extended beam spot to Focusing on the substrate and defocusing on the second axis, the astigmatic elongated beam spot has a width along the first axis and a length along the second axis, the width being less than the length The astigmatic elongated beam spot is narrower on the first axis and wider on the second axis.

10‧‧‧ Beam delivery system

12‧‧‧Solid laser

14‧‧‧beam expander

16‧‧‧Spherical plano-concave lens

18‧‧‧Spherical plano-convex lens

20a‧‧100% mirror

20b‧‧100% mirror

22‧‧‧ Beam Forming Aperture

24‧‧‧Transformation Lens System

26‧‧‧ cylindrical plano-concave lens

28‧‧‧ cylindrical plano-convex lens

30‧‧‧beam focusing lens

32‧‧‧Substrate

34‧‧‧x-y sports platform

36‧‧‧Rotating platform

38‧‧‧Double prism

50‧‧‧Original beam

52‧‧‧Expanded beam

54‧‧‧Edge trimmed beam

56‧‧‧Slightly compressed laser beam

58‧‧‧Astigmatic extended beam spot

60‧‧‧Short focus

62‧‧‧Long-distance focus

These and other features and advantages of the present invention will be more fully understood from the <RTIgt; a schematic diagram of a beam delivery system (BDS); Figure 2 is a schematic view of the BDS shown in Figure 1, which illustrates the sequential modification of the laser beam from the laser to the target; Figure 3 is a cross-sectional view of a beam, which is illustrated in each principal meridian (principal) The meridian forms two focal points respectively; the fourth figure is a cross-sectional view of a beam focusing lens in the BDS shown in Fig. 1, which illustrates the "y component" of the highly compressed beam passing through the beam focusing lens; A cross-sectional view of a beam focusing lens in the BDS shown in Fig. 1, which illustrates the "x component" of the highly compressed beam passing through the beam focusing lens; Fig. 6 is a cross-sectional view of the BDS shown in Fig. 1, which is illustrated in Two separate focal points are formed on one main meridian; FIG. 7 is a cross-sectional view of the BDS shown in FIG. 1 , which illustrates the formation of two separate focal points on the other main meridian; and FIGS. 8 and 9 are A cross-sectional view of the BDS shown in Figure 1 illustrates the flexibility of adjusting the processing parameters in the BDS.

In accordance with embodiments described herein, an adjustable astigmatic elongated beam spot can be formed from a laser beam having an ultrashort laser pulse and/or one of a longer wavelength to process a substrate made of a variety of different materials. A laser beam having a plurality of pulse waves having a pulse duration of less than 1 nanosecond and/or having a wavelength greater than 400 nanometers may be generated. The laser beam is modified to form an astigmatic beam that is collimated on a first axis and converges on a second axis. Focusing the astigmatic beam to form the astigmatic elongated beam spot on a substrate, the astigmatic elongated beam spot is focused on the substrate on the first axis and defocused on the second axis. The length of the astigmatic elongated beam spot can be adjusted to provide an energy density sufficient to cause a single ultrashort pulse to cause cold ablation of at least a portion of the substrate material. Therefore, the adjustable astigmatism extended beam spot allows The energy density is adjusted to avoid the loss of ablation using ultrashort pulse waves, as explained in more detail below.

As used herein, "laser machining" and "laser processing" refer to any action that uses a laser energy to change a workpiece, and "scratching" refers to scanning a mine by scanning a workpiece. The action of processing or processing a workpiece. Processing or processing may include, but is not limited to, ablation of the surface of the workpiece and/or crystal damage to the material within the workpiece. The scribe can include a series of ablated or crystal damage regions without the need for a continuous row of ablation or crystal damage. As used herein, "cold ablation" refers to the removal of heat by ablation or removal of material by absorption of laser energy while also by expelling the ablated material.

Laser induced photonic ablation occurs when an atom having a defined band gap material is excited to a higher quantum state by absorbing energy. In a cold ablation process, when the energy of a single photon reaches or exceeds the bandgap of the target material (quantum absorption energy), the laser energy can be absorbed, the exposed material is vaporized, and the heat and debris are in the electricity. The pulp was taken away. When the material band gap exceeds the energy of a single photon (eg, at longer wavelengths), multiple photon absorption may be required for cold ablation. The multiphoton absorption system is a nonlinear intensity dependent process, so the shorter the pulse wave provides the more efficient process. In particular, ultrashort laser pulses with high photon energy can have advantages in achieving multiphoton absorption.

However, when the energy density (joules per square centimeter) or average power (watts) used is too high above an optimum value, the benefit of using ultra-short laser pulses to achieve cold ablation may be eliminated. Since the efficiency of multiphoton absorption is less than 100%, part of the pulse energy can be converted into heat and retained in the material. Excessive heat accumulation can cause melting and/or other thermal damage. For example, excessive energy is locally applied to the material due to the use of energy density above one of the process and material dependent values. This amount of heat can accumulate during the material. In one example, for a pulse wave of 10 picoseconds (ps), the energy density should be maintained below 5 joules per square centimeter to avoid unwanted heat buildup. This heat may also accumulate when an ultrashort laser pulse is applied at a higher repetition rate (for example, 100 kHz or higher). A higher repetition rate can also cause the laser pulse to interact with the debris plume produced by the previous pulse (sometimes referred to as plasma shielding), which can reduce the efficiency of material removal. Although increasing the scanning speed can be a method of dissipating the heat of a high repetition rate laser, increasing the scanning speed may sacrifice accuracy.

According to embodiments described herein, the use of an astigmatic extended beam spot can increase the laser processing speed at lower repetition rates and lower part-movement speeds, thereby reducing energy distribution over a larger area. Locally heated and overcomes the problem of plasma shielding. By adjusting the length of the astigmatic elongated beam spot as explained in more detail below, it is possible to optimally utilize the energy density with available power to minimize heat buildup while simultaneously spreading the available energy over a large area. To achieve the desired production volume. Therefore, the use of ultrashort laser pulses facilitates multiphoton absorption required for cold ablation at longer wavelengths, and variable astigmatic extended beam spots achieve higher processing speeds without loss of ultrashort pulses. The benefits of cold ablation of the waves. Variable astigmatic extended beam spots allow the use of pulse energy over the entire range obtained from any laser (and especially ultrashort pulse), since the beam spot size can be optimized to align with optimal process fluence (fluence) matches.

Increasing the length of the variable astigmatism extended beam spot also results in an increase in linear processing speed. The linear machining speed can be determined by: speed (mm/sec) = pulse spacing (mm/pulse) × pulse frequency (pulse/second), where pulse spacing = beam length / at each position The total number of shots (shot). Therefore, for a given pulse spacing, increasing the beam length will increase the number of exposures at each location. In other words, a longer beam will increase the overlap (ie, to achieve a desired depth of the cut), which increases the cutting speed while maintaining optimal Concentration flux.

In addition to controlling the energy density used on the target by changing the beam length, the astigmatic extended beam spot can also produce a narrower cut than that obtained by focusing only the beam to a standard dot using conventional optical methods. incision. Since diffraction-limited focusing depends on the wavelength, astigmatically elongated beam spots are advantageous in achieving the ability to obtain narrower slits at longer wavelengths.

Referring to Figure 1, an embodiment of a beam delivery system (BDS) 10 capable of producing a variable astigmatic elongated beam spot is described in detail. The variable astigmatism extended beam spot can be used to cut or process a substrate made of various types of materials. In an exemplary application, the BDS 10 increases the productivity of LED die separation by forming a high resolution adjustable astigmatic elongated beam spot, which maximizes scribing speed and scribes on a wafer The consumption of the real-estate is minimized. The BDS 10 can also be used in other scribing or cutting applications.

In the illustrated embodiment, a solid state laser 12 (preferably a diode-excited solid state laser) produces an original laser beam. The original laser beam can be a pulsed laser beam having an ultrashort pulse (ie, a pulse duration of less than 1 nanosecond (ns)), the pulsed laser beam providing a peak that causes multiphoton absorption power. The ultrashort pulse duration may be in any possible range of laser pulse durations of less than 1 nanosecond, such as less than one of 10 picoseconds (ps), less than one picosecond, or less than one femtosecond ( A range of fs). The laser beam can also have any possible laser wavelength, including but not limited to: one wavelength in the ultraviolet range of about 100 nm to 380 nm (eg, a laser of 157 nm, a thunder of 266 nm) Shot, a 315 nm laser, or a 355 nm laser), one wavelength in the visible range of about 380 nm to 750 nm (for example, a green mine of 515 nm or 532 nm) Shot, at one of the near infrared ranges of about 0.75 microns to 1.3 microns (eg, a 1.01 micron laser, a 1.03 micron, or a 1.07 micron laser), in the infrared range of 1.3 microns to 5 microns One wavelength, and in the far infrared range of more than 5 microns One wavelength.

In some embodiments, an ultrafast laser can be capable of producing different wavelengths (eg, about 0.35 micrometers, 0.5 micrometers, 1 micrometer, 1.3 micrometers, 1.5 micrometers, 2 micrometers, or any increment therebetween) and An original laser beam having a different ultrashort pulse duration (eg, less than about 10 picoseconds, 1 picosecond, 1 femtosecond, or any increment in between). An example of an ultrafast laser includes one of the 5000 microsecond lasers available from the TruMicro series available from TRUMPF. The laser can also provide a pulse energy in the range of about 1 microjoule to 1000 microjoule at a repetition rate in the range of about 10 kilohertz to 1000 kilohertz. In other embodiments, the laser can be a fiber laser, such as the fiber laser type available from IPG Photonics.

The original laser beam is typically in a TEM ₀₀ mode with a Gaussian distribution and is amplified by a beam expanding telescope (BET) 14. An exemplary embodiment of BET 14 is comprised of a spherical plano-concave lens 16 and a spherical plano-convex lens 18. The magnification of BET 14 is determined by the focal length of each lens, and is generally represented by M = ( | f _sx | / | f _sv | ) , where M is the magnification and f _sx is the focal length of the spherical plano-convex lens 18 and f _sv is the focal length of the spherical plano-concave lens 16. To achieve a collimated beam expansion, the distance between the spherical plano-concave lens 16 and the spherical plano-convex lens 18 is determined by the general equation D _c = f _sx + f _sv , where D _c is a collimated distance. The combination of f _sx and f _sv can be used to satisfy the design value of the magnification M and the collimation distance D _c . The range of M can be about 2x to 20x, and is preferably 2.5x in the exemplary BDS 10. A combination of this preferred magnification of 2.5x, f _sx = 250 mm and f _sv = -100 mm and D _c = 150 mm is preferably used in this BDS 10.

In the illustrated embodiment, the enlarged beam is reflected by the 100% mirror 20a and then directed to a beam shaping iris 22. The beam shaping aperture 22 trims the low intensity edge of the beam symmetrically with a Gaussian distribution, thereby leaving a high intensity portion through the aperture 22. The beam is then directed to a variable anamorphic lens system (anamorphic lens) System) 24 center.

The exemplary variable anamorphic lens system 24 is comprised of a cylindrical plano-concave lens 26 and a cylindrical plano-concave lens 28. The components of the anamorphic lens system 24 preferably satisfy a condition | f _cx |=| f _cv |, where f _cx is the focal length of the cylindrical plano-convex lens 28 and f _cv is the focal length of the cylindrical plano-concave lens 26. In the anamorphic lens system 24, the incident beam is asymmetrically modified on one of the two principal meridians, one of which appears in the horizontal direction in Fig. 1. In the anamorphic lens system 24, when D < D _c (where D is a distance between a cylindrical plano-concave lens 26 and a cylindrical plano-convex lens 28 and D _c is a collimated distance), a parallel incident beam Divergence after passing through the anamorphic lens system 24. Conversely, when D > D _c , a parallel incident beam converges after passing through the anamorphic lens system 24 . In the embodiment of the anamorphic lens system 24 shown in Figure 1, the collimation distance is D _c = f _cx + f _cv = 0 , because | f _cx |=| f _cv | and f _cx has a positive value , f _cv has a negative value and D D _c . Thus, when D > 0, the collimated incident beam converges after passing through the anamorphic lens system 24.

The degree of convergence or combined focal length (f _as ) of the deformation system 24 is controlled by the distance D, and this is generally represented by the principle of two lenses: f _as = f _cx f _cv / ( f _cx + f _cv - D ). That is, the larger the distance D, the shorter the focal length f _as . As the distance D increases, the degree of convergence increases only on one principal meridian of the collimated incident beam. After passing through the anamorphic lens system 24, one of the principal meridians of the incident beam loses its collimation and converges; however, the other principal meridian is unaffected and maintains its beam collimation. Thus, by adjusting the distance between the two lenses of the deformation system 24, the size of the beam after passing through the variable deformation lens system 24 changes only on one principal meridian. Thus, the deformed BDS 10 intentionally introduces astigmatism to produce a separate focus on the two principal meridians (ie, vertical and horizontal). Although a series of anamorphic lenses having different focal lengths or convergence are preferably used to provide a variable astigmatic beam spot, a single anamorphic lens can be used in place of the variable anamorphic lens system to achieve a fixed convergence.

After passing through the anamorphic lens system 24, the beam is reflected by another 100% mirror 20b and then directed to the center of a beam focusing lens 30. The exemplary beam focusing lens 30 is an aberration corrected spherical multi-element lens having a focal length range of between about +20 mm and +100 mm. In one embodiment of the BDS 10, an edge contact doublet having a focal length of +50 mm is used. After passing through the beam focusing lens 30, one of the astigmatism focuses is sharply focused onto a substrate 32 (e.g., a semiconductor wafer). In a preferred embodiment, the substrate 32 is translated by a computer controlled x-y motion platform 34 for scribing. In semiconductor scribing applications where the semiconductor wafer comprises square or rectangular dies, the semiconductor wafer can be rotated 90 degrees by a rotating platform 36 to scribe in both the x and y directions.

The preferred combination of BET 14 and multi-beam focusing lens 30 produces a high resolution and adjustable astigmatic focused beam spot with minimal aberration and a minimum beam waist diameter. In general, the minimum beam waist diameter (w _o ) of a Gaussian beam can be represented by w _o = λf / πw _i , where λ is one of the wavelengths of an incident laser beam and f is one of the beam focusing lenses The focal length, π is the pi, and w _i is the diameter of one of the incident beams. In a given beam focusing lens 30, the minimum beam waist diameter (w _o ) or size of a focus point is inversely proportional to the incident beam diameter (w _i ). In an exemplary embodiment of the invention, the BET 14 deformably increases the incident beam diameter (w _i ) focused by the multi-beam focusing lens 30, thereby obtaining a minimized beam waist diameter and forming a high resolution focus. Beam point. This provides a sharply focused scribed beam spot that provides a scribed kerf width of about 5 microns or less on a semiconductor wafer. Thus, minimizing the scribe kerf width significantly reduces the slashing of space on a wafer, which enables more dies on a wafer and increases productivity.

The combination of the anamorphic lens system 24 and the high resolution beam focusing lens 30 produces two separate focal points on each of the principal meridians of the incident beam. Change the variable deformation The flexibility of beam convergence of mirror system 24 results in an immediate modification of a laser energy density on a target semiconductor wafer. Since the optimum laser energy density is determined by the light absorption characteristics of a particular target semiconductor wafer, the variable anamorphic lens system 24 can provide immediate modification to the optimal processing conditions determined by various types of semiconductor wafers.

While an exemplary embodiment of a variant BDS 10 is shown and described, other embodiments are also contemplated and are within the scope of the invention. In particular, the deformed BDS 10 can use different components to generate astigmatic focused beam spots, or the deformed BDS 10 can include additional components to provide further modification of the beam.

In an alternate embodiment, a double prism 38 or a set of double prisms can be inserted between the anamorphic lens system 24 and the BET 14. The double prism divides the enlarged and collimated beams from BET 14 equally, and then intersects the two divided beams to form a distribution that is inverted with a half Gaussian profile. When a set of double prisms is used, the distance between the two divided beams can be adjusted by varying the distance between the sets of prisms. In other words, the double prism 38 divides the Gaussian beam into two semicircles and inverts the two divided semicircles. One of the two circles is superimposed such that the edges of the Gaussian distribution of weak intensity are superimposed. This inversion of the Gaussian distribution and the redistribution of the intensity produces a uniform beam profile and eliminates some of the disadvantages of the Gaussian intensity distribution.

In another embodiment, the BDS 10 can include an array of anamorphic lens systems 24 that are used to form a small segment of the separated astigmatism "small beam" (similar to a dashed line). These astigmatic small beams enable the laser-induced plasma to escape effectively, which actively changes the scribing results. The distance between the lenses in the array of anamorphic lens systems controls the length of each beamlet segment. The distance between the small beam segments can be controlled by introducing a cylindrical plano-convex lens in front of the array of anamorphic lens systems.

In other embodiments, the BDS 10 can include a high speed galvanometer followed by a focusing element (eg, a flat field focus) (f-theta) lens). The galvanometer enables astigmatic extended beam spots to be scanned on a workpiece or substrate along one or more axes without moving the workpiece. The flat field focusing lens enables the scanning beam from the galvanometer to be focused onto a flat surface of the substrate or workpiece without moving the lens. Other scanning lenses can also be used.

Referring to Figure 2, a method of forming a variable astigmatic elongated beam spot is described in detail. The contour of the original beam 50 from the laser generally has a diameter of about 0.5 mm to 3 mm and is a Gaussian distribution. The original beam 50 is enlarged by the BET 14, and the enlarged beam 52 is about 2.5 times larger in diameter. The enlarged beam 52 passes through the beam shaping aperture 22 for edge trimming, and the enlarged and edge trimmed beam 54 is directed to the center of the anamorphic lens system 24. The anamorphic lens system 24 modifies the enlarged and edge trimmed beam 54 on only one principal meridian, thereby producing a slightly compressed beam shape 56. As the slightly compressed laser beam 56 travels toward the beam focusing lens 30, the degree of astigmatism increases in the beam shape because the variable anamorphic lens system 24 causes the beam to converge only on one main meridian. The highly compressed beam 57 then passes through the beam focusing lens 30 to form an astigmatic elongated beam spot 58. Since the highly compressed beam 57 has a concentrated beam characteristic on one principal meridian and a collimated beam characteristic on the other principal meridian, after passing through the beam focusing lens 30, a focus is separately formed on each principal meridian. Although such a method of forming astigmatic elongated beam spot 58 is set forth in the context of an exemplary BDS 10, this is not intended to limit the method.

The three-dimensional view in Fig. 3 illustrates in more detail the formation of two focal points on each of the main meridians as the highly compressed beam 57 passes through the beam focusing lens (not shown). Since the highly compressed beam 57 has a convergence characteristic on one main meridian (hereinafter referred to as 'y component'), the y component exhibits a short distance focal point 60. Conversely, since another meridian (hereinafter referred to as 'x component') has a collimated beam characteristic, the x component exhibits a long-distance focus 62. The combination of the x component and the y component produces an astigmatic beam spot 58.

Figure 4 shows the y component of the highly compressed beam 57, which is focused through the beam The lens 30 also forms a focus 60. After passing the focus 60, the beam diverges and forms the astigmatism side of the astigmatic elongated beam spot 58.

Figure 5 shows the x component of the highly compressed beam 57 which passes through the beam focusing lens 30 and forms the focus 62. The collimated x component of the highly compressed beam 57 is sharply focused at the focus 60, thereby forming an astigmatic lengthening type. The sharp focus side of the beam spot 58.

Figures 6 and 7 further illustrate the formation of two separate focal points 60, 62 on each major meridian. The schematic beam trajectories in Figures 6 and 7 include the two-dimensional layout of the BDS 10 shown in Figure 1, and for the sake of brevity, the 100% mirrors 20a, 20b and the beam shaping aperture 22 are not included. In Figure 6, the original beam from solid state laser 12 is enlarged by BET 14 and then collimated. The anamorphic lens system 24 modifies the collimated beam on this main meridian, thereby converge the beam. The concentrated beam is focused by the beam focusing lens 30. Because it converges after passing through the anamorphic lens system 24, the beam forms a focus 60 that is shorter than the nominal focal length of the beam focusing lens 30. The beam trajectory in Fig. 6 is similar to the view of the y component in Fig. 4.

In contrast, in Figure 7, the enlarged and collimated beam from BET 14 is unaffected by the anamorphic lens system 24 on this principal meridian. After passing through the anamorphic lens system 24, the beam can maintain alignment on this meridian. After passing through the beam focusing lens 30, the collimated beam is focused at a focus 62 that is formed at a nominal focal length of the beam focusing lens 30. The beam trajectory in Fig. 7 is similar to the view of the x component in Fig. 5. In Fig. 7, BET 14 increases the diameter of the incident beam focused by the multi-beam focusing lens 30, thereby minimizing a beam waist diameter and producing a high resolution elongated beam spot. Thus, target substrate 32 (eg, a semiconductor wafer) receives a wide and defocused astigmatic beam on one principal meridian and a narrow and sharply focused beam on the other principal meridian.

As shown in FIG. 3, the combination of the two separated focal points 60, 62 produces an astigmatic elongated beam spot having an astigmatism and a compression perimeter on one side of the astigmatic elongated beam spot, and The other side has a sharply focused and short perimeter.

When scribing a substrate, directing the astigmatic extended beam spot onto the substrate and applying a set of parameters to the astigmatic extended beam spot based on the material being scribbled (eg, wavelength, energy density, pulse repetition rate, beam size) ). According to one method, astigmatic elongated beam spots can be used to scribe semiconductor wafers, for example, in wafer separation or dicing applications. In such a method, the wafer can be moved or translated in at least one cutting direction under a focused laser beam to form one or more laser scribing cuts. To cut a die from a semiconductor wafer, a plurality of scribe cuts can be formed by moving the wafer in the x direction and then moving the wafer in the y direction after rotating the wafer by 90 degrees. When scribing in the x and y directions, the astigmatic beam spot is generally insensitive to polarization factors because the wafer is rotated to provide slits in the x and y directions. After the scribe cut is formed, the semiconductor wafer can be separated along the scribe by conventional techniques known to those skilled in the art to form dies.

An astigmatic extended beam spot provides an advantage in scribing applications by achieving faster scoring speeds. The scribe speed can be expressed by S = (l _b ‧ r _p )/n _d , where S is the scribe speed (mm/sec), l _b is the length of the focused scribe beam (mm), and r _p is the pulse The wave repetition rate (pulse wave/second) and n _d are the number of pulses required to achieve the best scribe depth. The pulse repetition rate r _p depends on the type of laser used. Solid-state lasers with a repetition rate of several pulses per second to more than 10 ⁵ pulses per second are commercially available. The number of pulses n _d is a material processing parameter determined by the material properties of the target wafer and a desired depth of the cut. If the pulse repetition rate r _p and the number of pulse waves n _{d are given} , the beam length l _b is a control factor that determines the cutting speed. The focused astigmatic elongated beam spot formed according to the above method increases the beam length l _b , thereby obtaining a higher scribing speed.

The anamorphic lens system 24 also provides greater flexibility to adjust processing parameters to achieve an optimal condition. For example, in laser material processing, the processing parameters should be preferably adjusted based on the material properties of a target to achieve optimal conditions. Excessive laser energy density can cause harmful thermal damage to the target, while insufficient laser energy density can result in improper ablation or other harmful results. In particular, it may be desirable to reduce the energy density of an ultrashort pulse having a higher irradiance to avoid the loss of the benefits of cold ablation. As discussed in more detail below, the variable anamorphic lens system 24 enables energy density to be adjusted as needed based on pulse duration and other parameters such as laser power, wavelength, and material absorption characteristics.

Figures 8 and 9 show the flexibility of adjusting the BDS processing parameters in the present invention. In Fig. 8, the lenses 26, 28 of the anamorphic lens system 24 are placed closely together to provide a low degree of convergence of the collimated incident beam. This low degree of convergence forms a focus 60 at a distance that is relatively farther from the beam focusing lens 30. Therefore, the length of the beam spot 58 is relatively short and the energy density is increased.

In contrast, in Fig. 9, the lenses 26, 28 of the anamorphic lens system 24 are spaced apart to provide a high degree of convergence of the collimated incident beam. This increased convergence introduces astigmatism and forms a focal point 60 at a relatively short distance from the beam focusing lens 30. Therefore, the length of the beam spot 58 is relatively long and the energy density is reduced.

In one scoring example, an astigmatic focused beam spot can be used to scribe a sapphire substrate for a blue LED. Optimal processing of a sapphire substrate for one of the blue LEDs typically requires an energy density of about 10 J/cm 2 . Since the blue LED wafer is typically designed to have a gap of about 50 microns between the individual grains to be separated, the optimum laser beam size is preferably less than about 20 microns for laser scribing. When a commercially available laser having a target position output power of 3 watts and a pulse repetition rate of 50 kHz is used, the conventional beam focusing at a 15 micron diameter causes the laser energy density to be 34 J/cm 2 . In systems using conventional beam spot focusing, the target position energy density must be adjusted by reducing the power output of the laser to achieve optimal processing to avoid excessive energy density. Therefore, the laser power output cannot be fully utilized to maximize the scoring speed or productivity.

In contrast, the preferred embodiment of the BDS 10 can adjust the size of the compressed beam spot to maintain an optimum laser energy density of 10 joules per square centimeter without reducing the power from the laser output. rate. The astigmatic elongated beam spot can be sized to be approximately 150 microns on the astigmatism axis and approximately 5 microns on the focus axis. Since the astigmatism axes are arranged along the scribed translational direction, such an increase in beam length causes the scribe speed to increase proportionally as described above. In this example, the astigmatic beam spot provides a processing speed that is 10 times faster than conventional beam focusing.

In another scribing example, the astigmatic focused beam spot can be used to couple with one or more gallium nitride (GaN) layers on the sapphire substrate (eg, about 4-7 microns above the sapphire substrate) rather than with sapphire Direct coupling to scribe a sapphire substrate. The lower bandgap of GaN provides a more efficient coupling to the incident laser beam, requiring only a laser energy density of approximately 5 J/cm2. Once the laser beam is coupled to the GaN, ablation of the sapphire substrate is easier than coupling directly to the sapphire. Thus, the astigmatic elongated beam spot can be sized to be approximately 300 microns on the astigmatism axis and approximately 5 microns on the focus axis. Therefore, the processing speed can be 20 times faster than conventional far field imaging or point focusing techniques.

The minimized spot size on the focus axis also significantly reduces the width of the scribe cut, which in turn reduces the consumption of a wafer space. In addition, by reducing the volume of the total removed material, a narrow scribe cut reduces the risk of incidental material damage and debris generated by ablation. In one example, a 266 nm DPSS laser with a target position power of about 1.8 watts and a repetition rate of 50 kHz can be utilized and a sapphire-based LED wafer can be scratched by focusing the beam spot from the BDS 10 . The astigmatic elongated beam spot can be sized to be approximately 180 microns on the astigmatism axis and approximately 5 microns on the focus axis to provide a kerf width of approximately 5 microns. Based on a 30 micron deep scribe, the BDS 10 can have a scribe speed greater than 50 mm/sec. The laser cut forms a pointed V-shaped groove which facilitates good control of cracking after scoring. The variable astigmatic extended beam spot from the adjustable BDS 10 utilizes the maximum power output from the laser to directly increase the processing speed. Thus, front cuts can be used to reduce the width of the vias and increase the yield of cracks, thereby increasing the available grain on each wafer.

An astigmatic extended beam spot can also be advantageously used to scribe other types of semiconductor wafers. Based on the absorption characteristics of the target material (eg, band gap energy and surface roughness), the astigmatic extended beam spot easily adjusts its laser energy density to an optimum value. In another example, a 266 nm DPSS laser with a target position power of about 1.8 watts and a repetition rate of 50 kHz can be utilized and a wafer can be scribed by focusing the beam spot from the BDS 10. The astigmatic elongated beam spot can be sized to be about 170 microns on the astigmatism axis and about 5 microns on the focus axis, thereby forming a 75 micron deep scribe at a speed of about 40 mm/sec.

In yet another example, a gallium phosphide (GaP) wafer can be etched using a 266 nm DPSS laser with a target position power of about 1.8 watts and a repetition rate of 50 kHz. The astigmatic elongated beam spot can be sized to be approximately 300 microns on the astigmatism axis and approximately 5 microns on the focus axis, thereby producing a 65 micron deep scribe at a rate of approximately 100 mm/sec. Similar results can be achieved in other compound semiconductor wafers (eg, GaA, indium phosphide (InP), germanium (Ge)).

It is also possible to scribe/process other semiconductor materials (such as cadmium or telluride) at high speed and high quality by using an astigmatic elongated beam spot and ultrashort pulse. For example, a 532 nm, 10 picosecond laser can be used to form a 600 micron long by 20 micron wide astigmatic extended beam spot, which in turn uses an average power of 3 watts at 200 kHz at high speed (eg, 2 meters). / sec) Perform multiple scribes to create a 500 micron deep scribe. In another example, the throughput can be substantially doubled by using a 1200 micron long, 6 watt, 200 kHz beam to adjust the beam size. If a higher pulse energy is available, the throughput can be further increased by correspondingly increasing the beam length while maintaining an optimum fluence.

Other substrates that can be scored include, but are not limited to, InP, alumina, glass, and polymers. The systems and methods described herein can also be used to scribe or process ceramic materials for optical conversion in LEDs, including but not limited to tantalum nitride, tantalum carbide, aluminum nitride or ceramic phosphors.

An astigmatic focused beam spot can also be advantageously used to scribe or machine a metal film (eg molybdenum). Due to the high thermal conductivity, laser cutting of metal films using conventional techniques has shown that the wake along the laser cut creates areas that are affected by overheating. By applying an astigmatic extended beam spot, a beam width of 5 microns on the focus axis can significantly reduce the width of the laser cut nick, which in turn reduces heat affected areas, incidental material damage, and debris generated by ablation. The astigmatic elongated beam spot is sized to be approximately 200 microns on the astigmatism axis and approximately 5 microns on the focus axis. This results in a 50 micron deep scribe at a speed of about 20 mm/sec and with a 266 nm DPSS laser with a target position power of about 2.5 watts and a repetition rate of 25 kHz. Other types of metals can also be cut, including but not limited to aluminum, titanium or copper. The metals may have different thicknesses, for example, films ranging from a few hundred microns thick to very thin (e.g., films used as metal layers for solar cell contacts).

While the examples show lines drawn in a substrate, astigmatic elongated beam spots can also be used to scribe other shapes or to perform other types of processing or cutting applications. Other operational parameters in addition to the operational parameters given in the above examples are also contemplated for scribing the LED wafer.

According to another scribing method, surface protection can be provided on the substrate by using a water-soluble protective coating. The preferred composition of the protective coating comprises at least one surfactant in a water soluble liquid glycerin and can be any of the general liquid detergents that meet the composition requirements. Surfactants in liquid glycerin form a thin protective layer due to their high wettability. After the film layer has dried, glycerin effectively withstands the heat of the laser-induced plasma and at the same time prevents debris generated by the laser from sticking to the surface. The film of the liquid detergent is easily removed by washing with high pressure water.

Thus, the preferred embodiment of the present invention has many advantages over conventional systems that utilize patterned laser projection and conventional systems that utilize far field imaging. Unlike simple far field imaging, the present invention has greater flexibility in modifying the laser beam to create astigmatic elongated beam spots by using a deformed BDS. Different from traditional patterning Laser projection, a deformed BDS delivers substantially the entire beam from a laser resonator to a target, thereby maintaining very high beam utilization. The formation of astigmatic extended beam spots also provides excellent characteristics of the laser beam in terms of optimum intensity and beam waist diameter. In particular, the preferred embodiment of the variable anamorphic lens system achieves an adjustable single plane compression of one of the laser beams, thereby obtaining a variable focus beam spot to quickly adjust the optimal laser intensity. By appropriately modifying the beam spot and by maximizing the use of an original beam, the formation of astigmatic extended beam spots has many advantages for separating various semiconductor wafers, including: high scribing speed, narrow scribe slit width Reduced laser debris and reduced collateral damage. In addition, the variable astigmatism elongated beam spot enables cold ablation at a desired processing speed with minimal melting or thermal damage using a longer wavelength laser with ultrashort pulse waves.

According to an embodiment, a method for forming an astigmatic elongated beam spot for processing a substrate is provided. The method includes: generating a laser beam having a plurality of pulse waves having a pulse duration of less than 1 nm; modifying the laser beam to form an astigmatism beam, the astigmatism beam Collimating on an axis and concentrating on a second axis; and focusing the astigmatic beam to form an astigmatic elongated beam spot on a substrate, the focused astigmatism beam having a first focus on the first axis And having a second focus on the second axis, the second focus being separated from the first focus, such that the astigmatic elongated beam spot is focused on the substrate on the first axis and on the second axis Defocusing on the line, the astigmatic elongated beam spot having a width along the first axis and having a length along the second axis, the width being less than the length, such that the astigmatic elongated beam spot is narrower on the first axis And wider on the second axis.

In accordance with another embodiment, the method includes: generating a laser beam having a wavelength greater than 400 nanometers; modifying the laser beam to form an astigmatic beam, the astigmatic beam on a first axis Collimating and concentrating on a second axis; focusing the astigmatic beam to form an astigmatic elongated beam spot on a substrate, the focused astigmatism beam having on the first axis a first focus and a second focus on the second axis, the second focus being separated from the first focus, causing the astigmatic elongated beam spot to be focused on the substrate on the first axis and Defocusing on the second axis, the astigmatic elongated beam spot having a width along the first axis and having a length along the second axis, the width being less than the length, such that the astigmatic elongated beam spot is at the first The axis is narrower and wider on the second axis.

Although the principles of the invention have been described herein, it is understood by those skilled in the art that Other embodiments are contemplated within the scope of the invention in addition to the example embodiments shown and described herein. The refinement and replacement of the present invention by those skilled in the art is still considered to be within the scope of the invention, and the scope of the invention is limited only by the scope of the following claims.

10‧‧‧ Beam delivery system

12‧‧‧Solid laser

14‧‧‧beam expander

16‧‧‧Spherical plano-concave lens

18‧‧‧Spherical plano-convex lens

20a‧‧100% mirror

20b‧‧100% mirror

22‧‧‧ Beam Forming Aperture

24‧‧‧Transformation Lens System

26‧‧‧ cylindrical plano-concave lens

28‧‧‧ cylindrical plano-convex lens

30‧‧‧beam focusing lens

32‧‧‧Substrate

34‧‧‧x-y sports platform

36‧‧‧Rotating platform

38‧‧‧Double prism

Claims (31)

A method of forming an astigmatic elongated beam spot for processing a substrate, the method comprising: generating a laser beam having a plurality of pulse waves having less than one nanometer Pulse duration; modifying the laser beam to form an astigmatic beam that is collimated on a first axis and converges on a second axis; and focusing the astigmatism beam to form a substrate An astigmatic elongated beam spot, the focused astigmatism beam having a first focus on the first axis and a second focus on the second axis, the second focus being separated from the first focus, causing The astigmatic elongated beam spot is focused on the substrate on the first axis and defocused on the second axis, the astigmatic elongated beam spot having a width along the first axis and along the second axis Having a length that is less than the length, such that the astigmatic elongated beam spot is narrower on the first axis and wider on the second axis. The method of claim 1, wherein the pulse duration is less than 10 picoseconds (ps). The method of claim 1, wherein the pulse duration is less than 1 picosecond. The method of claim 1, wherein the pulse duration is less than 1 femtosecond (fs). The method of claim 1 wherein the laser beam has a wavelength greater than 400 nanometers. The method of claim 1 wherein the laser beam has a wavelength in the infrared (IR) range. The method of claim 1 wherein the laser beam has a wavelength in the near infrared range. The method of claim 1, wherein the laser beam has a wave in the green visible range long. The method of claim 1 wherein the substrate comprises a ceramic material. The method of claim 1 wherein the substrate comprises a metallic material. The method of claim 1, wherein the substrate comprises ruthenium. The method of claim 1 wherein the substrate comprises glass. The method of claim 1, wherein the energy density of one of the astigmatic elongated beam spots is sufficient to cause cold ablation of at least a portion of the substrate by a single pulse of the laser. The method of claim 13, further comprising: moving the astigmatic elongated beam spot through the substrate in one of the second axes, causing each successive pulse to ablate at least a portion of the substrate Thereby scribing the substrate. The method of claim 14, wherein moving the astigmatic elongated beam spot through the substrate comprises moving the substrate in the direction of the second axis. The method of claim 1, further comprising: adjusting a convergence of the laser beam on the second axis to adjust the length of the astigmatic elongated beam spot and the astigmatic elongated beam spot on the substrate The energy density, without adjusting the width of the astigmatic elongated beam spot. The method of claim 16, wherein the energy density is adjusted such that a single pulse wave causes cold ablation of at least a portion of the substrate. The method of claim 1, wherein modifying the laser beam comprises passing the laser beam through an anamorphic lens system. The method of claim 18, wherein the anamorphic lens system comprises a cylindrical plano-concave lens and a cylindrical plano-convex lens (cylindrical) Plano-convex lens). The method of claim 19, further comprising: adjusting a length of the astigmatic elongated beam spot and the astigmatic elongated beam spot by adjusting a distance between the columnar plano-concave lens and the columnar plano-convex lens One of the energy densities on the substrate does not change the width of one of the astigmatic elongated beam spots. The method of claim 19, wherein the columnar plano-concave lens and the columnar plano-convex lens satisfy a condition |f _cx |=|f _cv |, wherein |f _cx | is a focal length of the columnar plano-convex lens and has A positive value, and wherein |f _cv | is a focal length of the cylindrical plano-concave lens and has a negative value. The method of claim 21, wherein the combined focal length (f _as ) of the anamorphic lens system varies in accordance with a distance (D) between the cylindrical plano-convex lens and the cylindrical plano-convex lens _as follows: f _as = f _cx *f _cv /(f _cx +f _cv -D). The method of claim 1, wherein the laser beam is generated by a diode pumped solid-state (DPSS) laser. The method of claim 1 wherein the laser beam is produced by a fiber laser. The method of claim 1, further comprising: expanding the laser beam and cropping the edge of the expanded laser beam before modifying the laser beam. A method of forming an astigmatic elongated beam spot for processing a substrate, the method comprising: generating a laser beam having a wavelength greater than 400 nm; modifying the laser beam to form an astigmatism a beam of light that collimates on a first axis and converges on a second axis; and focuses the astigmatic beam to form an astigmatic elongated beam spot on a substrate that has been focused The astigmatism beam has a first focus on the first axis and a second focus on the second axis, the second focus is separated from the first focus, and the astigmatic elongated beam spot is Focusing on the substrate on a first axis and defocusing on the second axis, the astigmatic elongated beam spot having a width along the first axis and having a length along the second axis, the width being less than the length, The astigmatic elongated beam spot is made narrower on the first axis and wider on the second axis. The method of claim 26, wherein the laser beam has a wavelength in the infrared (IR) range. The method of claim 26, wherein the laser beam has a wavelength in the green visible range. The method of claim 26, wherein the laser beam is generated with a plurality of pulse waves having a pulse duration of less than 10 picoseconds. The method of claim 26, wherein the focusing is performed with a fixed multi-element beam focusing lens. The method of claim 26, wherein a focus is performed following a focusing element using a high speed galvanometer.