Method and system for laser processing a semiconductor substrate

Abstract

A method for processing a semiconductor substrate is described. The method generally includes irradiating the semiconductor substrate with a mid-infrared pulsed laser beam having a center wavelength greater than a bandgap wavelength of the semiconductor substrate, the center wavelength of the mid-infrared pulsed laser beam being 2.4 µm or greater, the irradiating including performing a relative movement between a focal point of the mid-infrared pulsed laser beam and the semiconductor substrate, the movement causing the focal point of the mid-infrared pulsed laser beam to move along a path extending within the semiconductor substrate and forming a weakened region along the path, the semiconductor substrate being separable into a substrate portion upon application of a separation force to the semiconductor substrate.

Description

Technical Field

[0001] The improvements generally involve semiconductor substrate manufacturing, and in particular, the laser cutting of such semiconductor substrates. Background Technology

[0002] Various semiconductor substrate dicing techniques exist in this field. Examples of such techniques include, but are not limited to, conventional dicing and laser dicing. For example, dicing involves rotating a dicing blade to cut a semiconductor substrate into multiple desired substrate portions. It is known that dicing is often more suitable for thicker semiconductor substrates. However, dicing speeds are typically limited to 250 mm / s unless the cut quality is significantly affected. Furthermore, laser dicing involves irradiating a given substrate path with a narrow-focused laser beam that weakens a region within the semiconductor substrate. The semiconductor substrate can then be fractured or otherwise separated along the weakened region to form the desired substrate portions. Therefore, laser dicing is an attractive option when higher cutting speeds are sought. For thinner substrates, a single pass of the laser beam may be sufficient to create a sufficiently weakened path, while for thicker substrates, many subsequent passes may be required to form the weakened path. In multi-pass dicing, shallower passes are known to be less challenging than deeper passes because whenever the laser beam is focused on the bottom of the semiconductor substrate during a deeper pass, a larger area of ​​the substrate is exposed to the laser beam near the top surface of the semiconductor substrate. Such a large exposed area results in wider cuts, increasing material loss and reducing overall yield. Simultaneously, the laser beam is truncated by components within the substrate, leading to less energy being deposited in the focused area used for cutting. Therefore, laser cutting becomes impractical or too slow for semiconductor substrates thicker than 200µm. While existing semiconductor substrate cutting techniques are applicable to some extent, there is still room for improvement. Summary of the Invention

[0003] Existing laser cutting techniques typically involve the use of common laser sources operating in the near-infrared region of the electromagnetic spectrum, particularly in the 800 nm to 1.5 µm range. However, it has been found that in these regions of the electromagnetic spectrum, such as when the laser wavelength is below or close to the bandgap wavelength of the semiconductor substrate (which could favor direct single-photon absorption), self-limiting light-matter interaction mechanisms often impose an upper limit on the power of the laser beam. For example, in applications using Nd:YAG lasers operating at 1064 nm to cut silicon, saturation has been observed at average laser power as low as 1.5 W. In some cases, using laser power exceeding this limit can cause pre-focusing plasmonic shielding and / or self-limiting effects, preventing the laser beam from propagating through a given depth within the semiconductor substrate. Additionally or alternatively, using saturated laser power can cause undesirable crack propagation around weakened paths, thereby increasing their width. Because the laser power is limited for the desired path width, the speed at which passage is possible is also limited. Solutions to these challenges have been found by exploring unconventional pulsed laser sources operating in the deeper infrared regions of the electromagnetic spectrum (e.g., from wavelengths greater than the bandgap wavelength of semiconductor substrates, and more specifically 2.4 µm or larger). At these larger wavelengths, the effects of the detrimental self-limiting photomatter interaction mechanisms described have been significantly reduced (e.g., due to multiphoton absorption and the advantageous scaling of multiple photomatter mechanisms with higher wavelengths), enabling laser cutting of thicker semiconductor substrates at higher speeds, as modified lengths can be produced with finer profiles and the laser power saturation threshold can be significantly increased.

[0004] According to a first aspect of this disclosure, a method for processing a semiconductor substrate having a bandgap wavelength is provided. The method includes: irradiating the semiconductor substrate with a mid-infrared pulsed laser beam, the center wavelength of which is greater than the bandgap wavelength of the semiconductor substrate, the center wavelength of which is 2.4 µm or greater. The irradiation includes performing a relative movement between the focal point of the mid-infrared pulsed laser beam and the semiconductor substrate, the movement causing the focal point of the mid-infrared pulsed laser beam to move along a path extending within the semiconductor substrate and forming a weakened region along the path. The semiconductor substrate is capable of separating into substrate portions when a separation force is applied to the semiconductor substrate.

[0005] Furthermore, according to a first aspect of this disclosure, the center wavelength may be, for example, in the range of 2.4µm to 5µm.

[0006] Further according to the first aspect of this disclosure, the center wavelength may, for example, be in the range of 2.7µm to 3.0µm.

[0007] Further according to the first aspect of this disclosure, the semiconductor substrate may be, for example, a single-crystal silicon substrate.

[0008] Further according to a first aspect of this disclosure, the illumination may, for example, include a single pass of the focus along the path, which forms a weakened region.

[0009] Further according to the first aspect of this disclosure, the power of the mid-infrared pulsed laser beam can be, for example, about 0.75W or greater.

[0010] Further according to the first aspect of this disclosure, the semiconductor substrate may be, for example, a silicon substrate.

[0011] Further according to the first aspect of this disclosure, the thickness of the semiconductor substrate may, for example, be in the range of about 200 µm to 1000 µm.

[0012] Further according to the first aspect of this disclosure, relative movement can be carried out, for example, at an effective linear velocity in the range of 10 mm / s to 45 mm / s.

[0013] Further according to a first aspect of this disclosure, the irradiation may, for example, include a mid-infrared pulsed laser beam passing through the path more than once to form a weakened region.

[0014] Further according to a first aspect of this disclosure, the semiconductor substrate may, for example, have a first surface, a second surface opposite to the first surface, and a thickness extending between the first and second surfaces, and the irradiation may be performed, for example, through the first surface.

[0015] Further according to a first aspect of this disclosure, the irradiation may, for example, include one or more passes of the mid-infrared pulsed laser beam along the path to form a weakened region, wherein the deepest of the one or more passes may, for example, have a depth corresponding to about 75% (preferably about 60% of the thickness of the semiconductor substrate, most preferably about 50% of the thickness of the semiconductor substrate) of the semiconductor substrate thickness.

[0016] Further according to a first aspect of this disclosure, the weakened region may, for example, have a first dimension extending along a plane of the semiconductor substrate and a second dimension extending perpendicular to a plane of the semiconductor substrate, the second dimension being in the range of 200µm to 500µm.

[0017] Still further according to the first aspect of this disclosure, the first dimension may be, for example, less than 50µm (preferably less than 40µm, most preferably less than 30µm).

[0018] Further according to the first aspect of this disclosure, during relative movement, the focus of the mid-infrared pulsed laser beam may, for example, be located at a given depth from the surface of the semiconductor substrate, the given depth being in the range of 200 µm to 500 µm.

[0019] Still further according to the first aspect of this disclosure, the method may, for example, further include: applying a separation force to a semiconductor substrate, the semiconductor substrate separating into a substrate portion upon said application, the substrate portion having a separation interface having at least one of the following: a peak-to-peak roughness of about 30 µm or less and an RMS roughness of about 5 µm or less.

[0020] Further according to the first aspect of this disclosure, the mid-infrared pulsed laser beam may, for example, include laser pulses with pulse durations in the nanosecond range.

[0021] Further according to the first aspect of this disclosure, the mid-infrared pulsed laser beam may, for example, have laser pulses with pulse widths in the picosecond range.

[0022] Further according to the first aspect of this disclosure, the weakening region can be formed, for example, at an effective linear velocity of more than 40 mm / s, which is defined as the total distance traveled by the focal point of the mid-infrared pulsed laser beam relative to the semiconductor substrate divided by the total time period required for the mid-infrared pulsed laser beam to pass through the path one or more times individually, the total distance covering the mid-infrared pulsed laser beam passing through the path one or more times individually.

[0023] Further according to the first aspect of this disclosure, the pulse duration of the laser pulse can, for example, be in the range of about 20 fs to 1 µs.

[0024] Further according to the first aspect of this disclosure, relative movement can be performed, for example, at an effective linear velocity in the range of about 20 mm / s to 2 m / s.

[0025] Further according to the first aspect of this disclosure, the thickness of the semiconductor substrate may, for example, be greater than 100µm (preferably greater than 300µm, most preferably greater than 500µm).

[0026] Further according to the first aspect of this disclosure, the power of the mid-infrared pulsed laser beam can be, for example, about 2W or greater (more preferably more than 5W, and most preferably at least 10W).

[0027] Further according to the first aspect of this disclosure, the mid-infrared pulsed laser beam can be emitted, for example, by a fiber laser source.

[0028] It should be noted that, in this disclosure, the term "mid-infrared" is intended to cover the region of the electromagnetic spectrum with wavelengths ranging from about 2.4 µm to 20 µm. Therefore, "mid-infrared laser beam" is intended to refer to a laser beam with wavelengths ranging from about 2.4 µm to 20 µm. A "mid-infrared laser source" is a laser source capable of emitting a mid-infrared laser beam.

[0029] According to a second aspect of this disclosure, a system for processing a semiconductor substrate having a bandgap wavelength is provided. The system includes: a frame having a substrate support for receiving the semiconductor substrate; a mid-infrared laser source mounted to the frame and configured to emit a mid-infrared laser beam having a center wavelength greater than the bandgap wavelength of the semiconductor substrate, wherein the center wavelength of the mid-infrared pulsed laser beam is 2.4 µm or greater; and a scanning head optically coupled to the mid-infrared laser source, wherein the mid-infrared laser source and the scanning head irradiate the semiconductor substrate along a path extending within the semiconductor substrate through the focus of the mid-infrared laser beam and form a weakened region along the path, wherein the semiconductor substrate is capable of being separated into substrate portions when a separation force is applied to the semiconductor substrate.

[0030] Further according to a second aspect of this disclosure, the mid-infrared laser source may be, for example, a mid-infrared fiber laser source.

[0031] Further according to a second aspect of this disclosure, a mid-infrared fiber laser source may, for example, include an optical amplifier having: a segment of optical fiber including a low phonon energy glass having a laser-active doped region doped with a laser-active dopant; and a laser pump source adapted to pump the laser-active doped region of the segment of optical fiber.

[0032] Further according to a second aspect of this disclosure, the low phonon energy glass may be, for example, a fluoride glass.

[0033] All the technical implementation details and advantages described with respect to a particular aspect of the invention are obviously applicable to all other aspects of the invention with the necessary modifications.

[0034] After reading this disclosure, many further features and combinations thereof regarding the present improvement will become apparent to those skilled in the art. Attached Figure Description

[0035] In the attached diagram,

[0036] Figure 1 This is a perspective view of an example of a laser for processing a semiconductor substrate according to one or more embodiments, showing a mid-infrared pulsed laser beam moving along a path along the semiconductor substrate;

[0037] Figure 1A According to one or more embodiments Figure 1 An oblique view of the semiconductor substrate, showing the weakened region extending along the path;

[0038] Figure 1B This is a perspective view of a substrate portion according to one or more embodiments, the substrate portion being composed of Figure 1A This is produced by separating the semiconductor substrate along the weakened region;

[0039] Figure 1C According to one or more embodiments Figure 1 Enlarged view of the illustrations in the text;

[0040] Figure 2 A graph illustrating one or more embodiments. Figure 1 Different wavelength bands of mid-infrared pulsed laser beams;

[0041] Figure 3 This is a flowchart illustrating an example of a method for processing a semiconductor substrate according to one or more embodiments;

[0042] Figure 4A This is a top view of an example of a substrate portion according to one or more embodiments, which is subjected to a single pass of a mid-infrared pulsed laser beam (power 0.75W, travel speed 40mm / s) over a 675µm thick silicon substrate. Figure 3 It was separated by the method in the middle;

[0043] Figure 4B According to one or more embodiments Figure 4A Enlarged image;

[0044] Figure 4C According to one or more embodiments Figure 4A A side elevation view of the separation edge of the substrate portion in the image shows the weakened area;

[0045] Figure 4D According to one or more embodiments Figure 4C Enlarged image in the image;

[0046] Figure 5A According to one or more embodiments Figure 4A An oblique view of the separation edge of the substrate portion in the image shows a substantially vertical separation;

[0047] Figure 5B According to one or more embodiments Figure 4A A side elevation view of the separation edge of the substrate portion in the figure, showing a substantially vertical separation;

[0048] Figure 6AThis is a top plan view of an example of a semiconductor substrate according to one or more embodiments, the semiconductor substrate having a weakening region, the weakening region being performed on a 675µm thick silicon substrate by a single pass of a mid-infrared pulsed laser beam (wavelength 2.8µm, power 0.75W, travel speed 10mm / s). Figure 3 It was made using the method described in the article;

[0049] Figure 6B This is an enlarged view of a substrate portion according to one or more embodiments, the substrate portion being composed of... Figure 6A The semiconductor substrate is separated at the weakened region;

[0050] Figure 6C According to one or more embodiments Figure 6A A side elevation view of the separation edge of the substrate portion in the image shows the weakened area;

[0051] Figure 6D According to one or more embodiments Figure 6C Enlarged image;

[0052] Figure 7A According to one or more embodiments Figure 6A An oblique view of the separation edge of the substrate portion in the image shows a substantially vertical separation;

[0053] Figure 7B According to one or more embodiments Figure 6A A side elevation view of the separation edge of the substrate portion in the figure, showing a substantially vertical separation;

[0054] Figure 8A This is a top plan view of an example of a semiconductor substrate according to one or more embodiments, the semiconductor substrate having a weakening region, the weakening region being performed on a 675µm thick silicon substrate by means of a mid-infrared pulsed laser beam (wavelength 2.8µm, power 0.75W, travel speed 60mm / s) passing twice. Figure 3 It was made using the method described in the article;

[0055] Figure 8B This is a top plan view of a substrate portion according to one or more embodiments, the substrate portion being composed of Figure 8A It is produced by separating the semiconductor substrate in the process;

[0056] Figure 8C This is a top plan view of another substrate portion according to one or more embodiments, the substrate portion being composed of Figure 8A It is produced by separating the semiconductor substrate in the process;

[0057] Figure 8D According to one or more embodiments Figure 8C A side elevation view of the separation edge of the substrate portion in the image shows the weakened area;

[0058] Figure 8E According to one or more embodiments Figure 8D Enlarged image;

[0059] Figure 9A According to one or more embodiments Figure 8C An oblique view of the separation edge of the substrate portion in the image shows a substantially vertical separation;

[0060] Figure 9B According to one or more embodiments Figure 8C A side elevation view of the separation edge of the substrate portion in the figure, showing a substantially vertical separation;

[0061] Figure 10A This is a top plan view of an example of a substrate portion according to one or more embodiments, the substrate portion having a weakening region, the weakening region being performed on a 675µm thick silicon substrate by means of a mid-infrared pulsed laser beam (wavelength 2.8µm, power 0.75W, travel speed 80mm / s) passing twice. Figure 3 It was made using the method described in the article;

[0062] Figure 10B and Figure 10C According to one or more embodiments Figure 10A Side elevation view of different separation edges of the substrate portion;

[0063] Figure 11 The graphs, based on one or more embodiments, illustrate the use of... Figure 3 The method in the paper uses different parameter combinations to separate the root mean square (RMS) roughness of the separation edges of different substrate portions;

[0064] Figure 12 A graph illustrating one or more embodiments. Figure 11 Peak-to-peak roughness of the substrate portion;

[0065] Figure 13 A graph illustrating one or more embodiments. Figure 11 Three-dimensional surface measurement profile of one of the substrate portions;

[0066] Figure 14 A graph illustrating one or more embodiments. Figure 11 The surface roughness of the separation edge of one of the substrate portions;

[0067] Figure 15It is a side elevation view of the separation edge of a substrate portion according to one or more embodiments, the substrate portion being made of gallium arsenide (GaAs) and the substrate portion being cut out after a weakened region therein is formed using a mid-infrared pulsed laser beam;

[0068] Figure 16 This is a side elevation view of the separation edge of a substrate portion according to one or more embodiments, the substrate portion being made of indium phosphide (InP), and the substrate portion being cut after a weakened region therein has been formed using a mid-infrared pulsed laser beam; and

[0069] Figure 17 This is a schematic diagram of an example of a computing device with a controller according to one or more embodiments. Detailed Implementation

[0070] Figure 1 An example of a system 100 for processing a semiconductor substrate 10 having a bandgap wavelength is shown according to one embodiment. As shown, the system 100 has a frame 102, a substrate support 104, a mid-infrared pulsed laser source 106, and a scanning head 108 positioned relative to the frame. During processing, the substrate support 104 receives the semiconductor substrate 10. For example, the semiconductor substrate 10 may be received and held in place on the top surface 104a of the substrate support 104. The mid-infrared pulsed laser source 106 is configured to emit a mid-infrared pulsed laser beam 110, the center wavelength of which is greater than the bandgap wavelength of the semiconductor substrate. Furthermore, the center wavelength of the mid-infrared pulsed laser beam 110 is 2.4 µm or greater. For example, the wavelength of the mid-infrared pulsed laser beam 110 is typically in the range between 2.4 µm and 5 µm (preferably in the range between 2.5 µm and 4 µm, most preferably in the range between 2.7 µm and 3.0 µm). In some specific embodiments, the wavelength of the mid-infrared pulsed laser beam 110 is approximately 2.8 µm.

[0071] In this embodiment, the scanning head 108 is optically coupled to the mid-infrared pulsed laser source 106. As discussed in more detail below, the mid-infrared pulsed laser source 106 and the scanning head 108 are operable to irradiate the semiconductor substrate 10 with the focal point 112 of the mid-infrared pulsed laser beam 110 along a path P extending within the semiconductor substrate 10. By doing so, a weakened region 114 is formed along the path P within the semiconductor substrate 10. The formation of the weakened region 114 can occur due to multiphoton absorption, which is achieved by the central wavelength of the mid-infrared pulsed laser beam being greater than the bandgap wavelength of the semiconductor substrate 10. The weakened region 114 may be provided in the form of crack regions extending from the focused volume of the focal point toward the surface, and these crack regions may be connected together as the focal point of the mid-infrared pulsed laser beam scans along the path within the semiconductor substrate. In the illustrated embodiment, the weakened path 114 may be formed by two passes of the mid-infrared pulsed laser beam 112 along the path P at different depths. The mid-infrared pulsed laser source 106 and the scanning head 108 or any other substrate moving apparatus (not shown) may be controlled by the controller 109.

[0072] As shown in the rectangular inset, the first of the two passes is performed by irradiating the focal point 112 of the mid-infrared pulsed laser beam 110 along the path P of the semiconductor substrate at a depth z1 from the top surface 10a of the semiconductor substrate 10. The second pass is performed by irradiating the focal point 112 along the path P at a depth z2 (where z2 < z1) from the top surface 10a of the semiconductor substrate 10. However, in some other embodiments, only a single pass of the mid-infrared pulsed laser beam 110 may be sufficient to form the weakened region 114. Of course, more than two passes of the mid-infrared pulsed laser beam 110 may be required in some applications. Typically, the deepest pass is performed first to avoid impeding the transmission of the mid-infrared pulsed laser beam. As a result of these passes, Figure 1A a linear weakened region 114 extending between the opposite edges 10b and 10c of the semiconductor substrate 10 is shown. By means of such a weakened region 114, the semiconductor substrate 10 can be separated into two or more substrate portions 10' when a separation force F is applied to the semiconductor substrate 10, as Figure 1B shown. In some embodiments, the separation force is a shear force applied at the weakened region and oriented perpendicular to the plane of the semiconductor substrate. In some other embodiments, the separation force may be a tensile force, a torsional force, or the like. When the weakened region 114 is formed using the mid-infrared pulsed laser beam 110 disclosed herein, the separation edges 10d and 10e (i.e., the edges produced by separating the semiconductor substrate 10 into the substrate portions 10' at the weakened region 114) may have a suitable surface roughness, as discussed below.

[0073] Figure 1CAnother aspect of the disclosed method is highlighted, which allows the deepest pass of the mid-infrared pulsed laser beam's focus to be farther from the back surface 10b than a typical stealth cleaving laser beam operating in the 800 nm to 1.5 µm range. In fact, as shown, the deepest pass is located at a depth z1 from the top surface 10a. Accordingly, the distance between this first pass and the back surface 10b is derived by T-z1, where T represents the substrate thickness. With the focus spaced apart from the back surface 10b in this manner and a given numerical aperture (i.e., the cone shape of the beam), a first kerf width sw1 is obtained, defined by the width of the top surface 10a of the semiconductor substrate exposed to the mid-infrared pulsed laser beam 110 during this deepest pass. In contrast, the dashed line to the right of the semiconductor substrate illustrates a typical stealth cleaving laser beam operating in the 800 nm to 1.5 µm range. Because conventional laser sources are limited in the power they can deliver within a semiconductor wafer, conventional stealth dicing techniques may require the laser beam focus to pass through the semiconductor wafer many times, thus necessitating some of these passes close to the back surface 10b. As shown, the focal location of the deepest pass will be close to the back surface 10b, providing a second kerf width sw2 for a given numerical aperture, which will be greater than the first kerf width sw1. Therefore, it should be noted that the methods and systems disclosed herein can help reduce the kerf width associated with the formation of the weakening layer because the deepest pass can be relatively farther from the back surface compared to existing stealth dicing techniques. For purposes of understanding, the deepest pass formed using conventional stealth dicing techniques is typically located at approximately 40 µm from the back surface of the semiconductor wafer. With the methods and systems disclosed herein, it has been demonstrated that the deepest pass can be formed at depths ranging from 100 µm to 300 µm, and separation can still be readily achieved at the weakening region. Therefore, in some embodiments, the deepest passage of one or more passes of the mid-infrared pulsed laser beam has a depth corresponding to about 75% (preferably about 60% of the thickness T of the semiconductor substrate, and most preferably about 50% of the thickness T of the semiconductor substrate) of the semiconductor substrate.

[0074] The reduced number of passes of the mid-infrared pulsed laser beam and the increased saturation power jointly accelerate the formation of the weakened region 114. In some embodiments, the weakened region 114 can be formed at an effective linear velocity exceeding 40 mm / s (preferably 80 mm / s, most preferably 160 mm / s). The effective linear velocity is defined as the total distance traveled by the focal point of the mid-infrared pulsed laser beam relative to the semiconductor substrate divided by the total time required for the mid-infrared pulsed laser beam to make one or more individual passes along the path, the total distance encompassing one or more individual passes along the path. In general, in embodiments where N individual passes of the focal point are performed to form a weakened region of length L, the total distance traveled by the focal point is derived from N*L, where L represents the length of a single pass and the length of the weakened region. Therefore, the effective linear velocity, i.e., v, can be determined by dividing the total distance traveled by the focal point by the total time t required for all N individual passes. effective = N*L / t. It should be understood that the effective linear velocity is intended to encompass the potential movement of the semiconductor substrate and the potential movement of the focal point of the mid-infrared pulsed laser beam. For example, if the semiconductor substrate is moving at a first velocity value along a first direction and the mid-infrared pulsed laser beam is moving at a second velocity value along a second direction opposite to the first direction, then the effective linear velocity can be obtained by adding the first velocity value and the second velocity value.

[0075] By way of a few examples, the semiconductor substrate 10 may be a silicon (Si) substrate, a silicon carbide (SiC) substrate, a gallium nitride (GaN) substrate, a gallium arsenide (GaAs) substrate, an indium phosphide (InP) substrate, a silicon-on-insulator (SOI) substrate, or a silicon nitride (SiN) substrate. Preferably, the semiconductor substrate 10 is a single-crystal semiconductor substrate, a polycrystalline semiconductor substrate, an amorphous semiconductor substrate, or a combination thereof. Other suitable types of semiconductor substrates 10 will be apparent to those skilled in the art. It is intended that although the semiconductor substrate 10 has a rectangular shape in the illustrated example, the semiconductor substrate 10 may have other shapes, including but not limited to circular shapes (e.g., wafer shapes), oval shapes, etc.

[0076] It should be noted that all semiconductor materials possess their own bandgap energy and corresponding bandgap wavelength, which are linked by the Planck relation. The bandgap energy and bandgap wavelength define the wavelengths or photon energies at which the semiconductor material exhibits at least some degree of transparency. The intention is to select a mid-infrared pulsed laser beam such that its center wavelength is greater than the bandgap wavelength of the corresponding semiconductor substrate, and most preferably also greater than 2.4 µm. Equivalently, the mid-infrared pulsed laser beam can have photon energies lower than the bandgap energy of the semiconductor substrate. Due to this relationship between the center wavelength and / or bandgap energy of the mid-infrared pulsed laser beam and the bandgap wavelength of the semiconductor substrate, multi-photon absorption can occur.

[0077] For example, to name just a few, the direct bandgap of lead selenide (PbSe) is 0.27 eV or 4.57 µm; the direct bandgap of lead telluride (PbTe) is 0.32 eV or 3.86 µm; the direct bandgap of indium arsenide (InAs) is 0.36 eV or 3.43 µm; the direct bandgap of lead sulfide (PbS) is 0.37 eV or 3.34 µm; the indirect bandgap of germanium (Ge) is 0.67 eV or 1.84 µm; the direct bandgap of gallium antimonide (GaSb) is 0.726 eV or 1.70 µm; the indirect bandgap of silicon (Si) is 1.12 eV or 1.1 µm; the direct bandgap of indium phosphide (InP) is 1.35 eV or 915 nm; and the direct bandgap of gallium arsenide (GaAs) is 1.441 eV or 8 µm. The direct bandgap of cadmium telluride (CdTe) is 1.5 eV or 823 nm; the direct bandgap of cadmium selenide (CdSe) is 1.74 eV or 710 nm; the indirect bandgap of aluminum arsenide (AlAs) is 2.12 eV or 583 nm; the indirect bandgap of gallium phosphide (GaP) is 2.24 eV or 551 nm; the direct bandgap of cadmium sulfide (CdS) is 2.42 eV or 510 nm; the direct bandgap of gallium nitride (GaN) is 3.4 eV or 363 nm; the direct bandgap of cubic zinc sulfide (ZnS) is 3.54 eV or 349 nm; the direct bandgap of hexagonal zinc sulfide (ZnS) is 3.91 eV or 316 nm; and the direct bandgap of aluminum nitride (AlN) is 6.015 eV or 205 nm.

[0078] See now Figure 2 It should be noted that the semiconductor substrate of the photonic chip has a bandgap energy and a corresponding bandgap wavelength, defining the optical transmission window 33. The optical transmission window 33 can be in the range of about 1 µm to about 25 µm (preferably in the range of about 2.0 µm to about 20 µm, most preferably in the range of about 2.5 µm to about 10 µm). For example, in embodiments where the semiconductor substrate comprises silicon with a bandgap wavelength of about 1.1 µm, the optical transmission window 33 can be in the range of about 1.1 µm to about 15 µm. In these embodiments, the center wavelength of the mid-infrared pulsed laser beam can be selected to be greater than 2.4 µm. For example, the optical transmission window typically exhibits a transmittance in the range of about 1% / cm to about 10% / cm.

[0079] In view of the foregoing, it is intended that the center wavelength of the mid-infrared pulsed laser beam extends at least partially or entirely within the optical transmission window 33 of the semiconductor substrate. For example, depending on this embodiment, the center wavelength of the mid-infrared pulsed laser beam can be in the range of about 2.4 µm to about 20 µm (preferably in the range of about 2.5 µm to about 10 µm, and most preferably in the range of about 2.8 µm to about 3.4 µm). Therefore, optical energy can be delivered within a photonic chip, for example, including within and / or adjacent to the semiconductor substrate. In embodiments where the semiconductor includes silicon, it has been found that a mid-infrared pulsed laser beam having a narrow spectral bandwidth (or equivalent, center wavelength) in the range of, for example, between 2.8 µm and 3.2 µm can be readily used.

[0080] The mid-infrared pulsed laser source 106 can be any type of laser source that emits mid-infrared pulsed laser beams with a wavelength of 2.4 μm or greater. To name just a few examples, examples of such mid-infrared laser sources 106 may include, but are not limited to, fiber laser sources, wherein the laser active region includes low phonon energy glass or combinations thereof doped with rare earth ions, such as erbium-doped fluoride glass (Er:Fl) sources and / or other rare earth-doped glasses, including but not limited to dysprosium, holmium, praseodymium, thulium, periodically polarized lithium niobate (PPLN) sources, optical parametric oscillators (OPO) sources, optical parametric amplifiers (OPA) sources (e.g., in some embodiments, tunable OPA sources can cover the entire mid-infrared region of the electromagnetic spectrum), downconversion lasers (difference frequency generation (DFG), optical parametric generation lasers), erbium-doped yttrium aluminum garnet crystal (Er:YAG) sources, erbium-doped yttrium scandium gallium garnet crystal (Er: crystal or Er: glass, such as Er:YSGG) sources, quantum cascade laser (QCL) sources, and Cr:ZnSe / ZnS sources. In embodiments where the mid-infrared laser source is a pulsed laser source, the mid-infrared pulsed laser beam can have laser pulses with pulse widths in the nanosecond, picosecond, or femtosecond range. Depending on this embodiment, the pulse energy can be in the microjoule or nanojoule range. Depending on this embodiment, the mid-infrared pulsed laser beam can include continuous waves, stable laser pulse trains, or pulse groups.

[0081] See still Figure 2These mid-infrared laser sources 106 can each have their own emission wavelength bands. For example, some Cr: crystal (e.g., Cr:ZnSe / ZnS) sources have been found to emit mid-infrared pulsed laser beams 110 with a wavelength of approximately 2.4 µm. These Cr:ZnSe / ZnS sources can be pulsed sources that emit laser pulses with pulse widths in the femtosecond range and pulse energies in the microjoule or nanojoule range. Another Cr:ZnSe / ZnS source has been found to emit mid-infrared pulsed laser beams 110 with a wavelength of approximately 2.5 µm and a pulse width in the nanosecond range. An OPO source has been found to emit mid-infrared pulsed laser beams 110 with a wavelength of approximately 2.75 µm. An Er:YSGG source has been found to emit mid-infrared pulsed laser beams 110 with a wavelength of approximately 2.78 µm. These Er:YSGG sources can operate in pulsed mode, where the pulse width is in the microsecond range. An Er:FL source has been found to emit mid-infrared pulsed laser beams 110 with a wavelength of approximately 2.8 µm. One of these Er:FL pulse sources was found to have a pulse width in the femtosecond range, with pulse energies ranging from nanojoules to microjoules. Other Er:FL sources were found to emit mid-infrared pulsed laser beams 110 with wavelengths of approximately 2.8 µm and pulse widths in the nanosecond range. An exemplary PPLN source was found to emit a mid-infrared pulsed laser beam 110 with a wavelength of approximately 2.8 µm. Another diode-pumped OPO source was found to emit a mid-infrared pulsed laser beam 110 with a wavelength of approximately 2.8 µm and a pulse width in the nanosecond range. An OPA source was found to emit a mid-infrared pulsed laser beam 110 with a wavelength of approximately 2.8 µm, a pulse width in the femtosecond range, and pulse energies in the microjoule range. An Er:YAG source was found to emit a mid-infrared pulsed laser beam 110 with a wavelength of approximately 2.94 µm. These Er:YAG sources can emit mid-infrared pulsed laser beams with pulse widths in the nanosecond range. A fiber-pumped OPA source was discovered that emits a mid-infrared pulsed laser beam 110 with a wavelength of approximately 3.0 µm, a pulse width in the femtosecond range, and a pulse energy in the nanojoule range. Another OPA source was also discovered that emits a mid-infrared pulsed laser beam 110 with a wavelength of approximately 3.0 µm, a pulse width in the femtosecond range, and a pulse energy in the microjoule range. Generally, mid-infrared laser beams can have repetition rates from 1 Hz to 10 GHz. Some of these mid-infrared laser sources are free-space laser sources, while others are fiber laser sources. Other examples of mid-infrared laser sources can also be used with the systems and methods described herein.

[0082] Regarding low phonon energy glass mid-infrared fiber laser sources, the mid-infrared pulsed laser source 106 may include: an amplifier comprising a segment of optical fiber made of low phonon energy glass and having at least a laser-active doped region doped with one or more laser-active dopants (e.g., erbium); and one or more pump lasers adapted to generate one or more pump laser beams. The segment of optical fiber may have a first end and a second end, wherein a seed laser beam is emitted into the first end and a mid-infrared pulsed laser beam is output at the second end. In this disclosure, the term "low phonon energy glass" is intended to encompass the maximum phonon energy (i.e., below 800 cm⁻¹) of a glass with a phonon energy lower than that of silica-based glass. −1 Optical fibers made of low-phonon-energy glass typically have a transmission window in the mid-infrared range (i.e., 2.4 μm to longer wavelengths), unlike optical fibers made of high-phonon-energy glass (such as silica-based glass), which exhibit a transmission window only in a given portion of the near-infrared range (e.g., up to 2.4 μm). It is understood that using optical fibers made of low-phonon-energy glass allows photons at mid-infrared wavelengths to propagate along the length of the fiber, whereas high-phonon-energy glass fibers, on the contrary, prevent the propagation of these photons. In cases where the laser-active doped region is pumped in the near-infrared (e.g., erbium ions), the low-phonon-energy glass of that segment of the fiber has a transmission window extending into the near-infrared. However, in some other cases, the laser-active doped region is pumped in the mid-infrared, and therefore the transmission window extending into the near-infrared can be omitted. Examples of low-phonon-energy glasses include fluoride-based glasses, chalcogenide-based glasses, sulfide-based glasses, or telluride-based glasses. In some cases, even some oxide glasses (e.g., tellurite-based glasses) can be considered low phonon energy glasses. For example, in some embodiments, the low phonon energy glass is a zirconium fluoride glass whose composition includes ZrF4, such as ZBLAN (ZrF4 / HfF4, BaF2, LaF3, NaF, and AlF3). In other embodiments, the low phonon energy glass is an indium fluoride glass whose composition includes InF3. In alternative embodiments, the low phonon energy glass is an aluminum fluoride glass whose composition includes AlF3. In further embodiments, the low phonon energy glass is a chalcogenide glass whose composition includes As2S3, As2Se3, AsTe, AsSSe, AsSTe, GaLaS, GeAsS, or GeAsSe, etc. Any other suitable low phonon energy glass with a transmission window in the mid-infrared can be used. Examples of such mid-infrared laser sources are described in U.S. Patent No. 10,084,287 B2. These mid-infrared laser sources can be purchased from Femtum Inc. (Canada), with only one exemplary manufacturer listed.

[0083] See you again Figure 1A mid-infrared pulsed laser source 106 is mounted to a frame 102. In some embodiments, the mid-infrared pulsed laser source 106 may be mounted directly to the frame 102 or indirectly via a support bracket 120 or similar component. A scanning head 108 may also be mounted directly or indirectly to the frame 102. In this embodiment, the scanning head 108 is mounted to the frame 102 via a support bracket 120. More specifically, the scanning head 108 is configured to receive a mid-infrared pulsed laser beam 110 from the mid-infrared pulsed laser source 106 and redirect its focus 112 along a path P extending within the semiconductor substrate 10. Depending on this embodiment, the path P may be linear or arcuate, having smooth and continuous or discontinuous segments. In some other embodiments, the frame may have a first frame element, a second frame element, and a third frame element, wherein the mid-infrared laser source is mounted to the first frame element, the scanning head is mounted to the second frame element, and the support is mounted to the third frame element. The first, second, and third frame elements may be integrally formed with each other or may be mechanically independent of each other.

[0084] Figure 3 A flowchart of an exemplary method 300 for processing a semiconductor substrate 10 having a bandgap wavelength is shown. Method 300 can be achieved by combining... Figure 1 The system 100 described is used to execute.

[0085] In step 302, the semiconductor substrate is irradiated with a mid-infrared pulsed laser beam. The center wavelength of the mid-infrared pulsed laser beam is greater than the bandgap wavelength of the semiconductor substrate and is also 2.4 µm or greater. Irradiation step 302 may include a step of performing a relative movement between the focus of the mid-infrared pulsed laser beam and the semiconductor substrate. The relative movement moves the focus of the mid-infrared pulsed laser beam along a path extending within the semiconductor substrate, and by doing so, a weakened region is formed along the path (e.g., via multiphoton absorption).

[0086] It should be understood that the weakened region can have a first dimension extending in the plane of the semiconductor substrate and perpendicular to the path, and a second dimension extending across the semiconductor substrate (and thus perpendicular to the first dimension). The smaller this width, the better, because it can create a greater number of substrate portions for the corresponding semiconductor substrate. The second dimension is more analogous to the depth at which the semiconductor material is weakened within the semiconductor substrate. The larger the second dimension, the better, because it can reduce the number of passes required for a given semiconductor wafer. For example, in some embodiments, the second dimension d2 can be in the range of 200 µm to 500 µm, while the first dimension d1 can be less than 50 µm (preferably less than 40 µm, most preferably less than 30 µm). It is intended that these suitable ranges can be achieved using only mid-infrared pulsed laser beams (with the pulse width ranges disclosed herein), because when a mid-infrared pulsed laser beam propagates within the semiconductor substrate, it produces little or no adverse self-limiting light-matter interactions. In some cases, intensity clamping can also occur when using mid-infrared pulsed laser beams. However, the method described in this paper can use mid-infrared pulsed laser beams with lower peak-to-peak intensity to form a suitable weakening region in the semiconductor substrate, thereby avoiding triggering the undesirable self-limiting light-matter interactions discussed above.

[0087] In step 304, a separation force is applied to the semiconductor substrate at the weakened region. Step 304 separates the semiconductor substrate into substrate portions. The number of substrate portions is determined by the shape of the weakened region formed within the semiconductor substrate. In some embodiments, the substrate portions have a separation interface with a peak-to-peak roughness of about 30 µm or less. Additionally or alternatively, the substrate portions have a separation interface with an RMS roughness of about 5 µm or less.

[0088] In some embodiments, irradiation step 302 may include a single pass of the focal point of the mid-infrared pulsed laser beam along the path. However, in some other embodiments, irradiation step 302 may include two or more passes of the focal point of the mid-infrared pulsed laser beam along the path. Depending on the embodiment, these passes may be performed at similar depths from the top surface of the semiconductor substrate or at different depths.

[0089] In some embodiments, the wavelength of the mid-infrared pulsed laser beam is in the range of 2.4 µm to 5 µm, and preferably about 2.8 µm. In some embodiments, the mid-infrared pulsed laser beam is a pulsed laser beam. This pulsed laser beam has laser pulses with pulse widths in the nanosecond, picosecond, or femtosecond range. For example, the pulse width can be in the range of 20 fs to 1 µs. In some embodiments, the pulse energy of the laser pulse is in the microjoule or nanojoule range. More specifically, in some embodiments, the pulse energy of these laser pulses can be about 50 µJ or greater. The power of the mid-infrared pulsed laser beam can be about 2 W or greater (more preferably greater than 5 W, and most preferably at least 10 W).

[0090] In one exemplary embodiment, the power of the mid-infrared pulsed laser beam is about 0.75 W or greater, and its focal point travels at a linear velocity in the range of 10 mm / s to 45 mm / s. With a single pass of the focal point along the path, a silicon substrate with a thickness in the range of about 200 µm to 1000 µm is sufficiently weakened to allow separation when a separation force is applied at one or more suitable locations. Depending on the operating parameters, the thickness of the semiconductor substrate can be greater than 100 µm (preferably greater than 300 µm, most preferably greater than 500 µm). Based on the thickness of the semiconductor substrate, the number of passes, and the output power of the mid-infrared pulsed laser beam, the relative movement between the focal point and the semiconductor substrate can be carried out at a linear velocity of about 20 mm / s or greater (most preferably greater than 200 mm / s, most preferably greater than 300 mm / s). In some embodiments, the linear velocity can be up to 2 m / s. The depth of the pass can be in the range of about 200 µm to 600 µm. Although this embodiment involves the use of a mid-infrared pulsed laser beam with a power of 0.75W, a mid-infrared laser source with a higher power can be used, including but not limited to a mid-infrared laser source with a power of 5W or a mid-infrared laser source with a power of 20W.

[0091] Figures 4A to 4D This demonstrates a single pass through a 675µm thick silicon substrate using a mid-infrared pulsed laser beam (0.75W power, travel speed 40mm / s). Figure 3 The substrate portion separated by the method described in the article. Figure 4A and Figure 4B Top views of the substrate portion are shown at 4x and 20x magnification, respectively. These figures illustrate the separation quality, which can be identified by minute defects at the edges. As shown in the figures, Figure 4B The magnified view shows the defect extending 5.89 µm from the top surface of the substrate portion. Figure 4C and Figure 4DThe weakened regions resulting from a single pass of a mid-infrared pulsed laser beam are shown at magnifications of 4x and 20x, respectively. In this embodiment, the mid-infrared pulsed laser beam is focused at a depth of 560 µm from the top surface of the semiconductor substrate. As shown, the weakened region has dimensions extending along the thickness of the substrate portion. For example, the size of the weakened region can be approximately 350 µm. Figure 5A and Figure 5B The perpendicularity of the edges of the obtained separated substrate portion is shown.

[0092] Figures 6A to 6D This demonstrates a single pass through a 675µm thick silicon substrate using a mid-infrared pulsed laser beam (0.75W power, travel speed 10mm / s). Figure 3 The substrate portion separated by the method described in the article. Figure 6A A top view of the semiconductor substrate after the weakened region has been formed is shown at a magnification of 4x. The weakened region shown has a first dimension d1 extending along the plane of the semiconductor substrate. Figure 6B The image was shown at a magnification of 20x. Figure 6A The substrate portion produced by separating the semiconductor substrate. Figure 6C and Figure 6D The weakened regions resulting from a single pass of the mid-infrared pulsed laser beam are shown at magnifications of 4x and 20x, respectively, with emphasis on a second dimension extending in a direction parallel to the semiconductor substrate thickness and perpendicular to the top surface of the semiconductor substrate. In this embodiment, the mid-infrared pulsed laser beam is focused at a depth of 448 µm from the top surface of the semiconductor substrate. Figure 7A and Figure 7B It shows Figure 6A The perpendicularity of some edges of the separated substrate portion. In some embodiments, the first dimension d1 and the second dimension d2 extend perpendicularly to each other, wherein the second dimension d2 is in the range of 200µm to 500µm. The first dimension d1 may be less than 50µm (preferably less than 40µm, most preferably less than 30µm).

[0093] Figures 8A to 8E The experiment demonstrated two passes through a 675µm thick silicon substrate using a mid-infrared pulsed laser beam (wavelength 2.8µm, power 0.75W, travel speed 60mm / s). Figure 3 The substrate portion is separated by the method described above. In this embodiment, for the first pass, the mid-infrared pulsed laser beam is focused at a depth of 238µm from the top surface, and for the second pass, the mid-infrared pulsed laser beam is focused at a depth of 448µm from the top surface. Figure 8A A top view of a semiconductor substrate is shown, in which weakened regions have been formed by the two passes of a mid-infrared pulsed laser beam. Dislocations are observed. Figure 8B Showing with Figure 8A The first substrate portion of the dislocation. Figure 8C Another edge of this substrate portion is shown. Figure 8D and Figure 8E The weakened region resulting from the two passes of the mid-infrared pulsed laser beam after separation is shown.

[0094] Figures 10A to 10C The experiment demonstrated two passes through a 675µm thick silicon substrate using a mid-infrared pulsed laser beam (wavelength 2.8µm, power 0.75W, travel speed 80mm / s). Figure 3 The substrate portion is separated by the method described above. In this embodiment, for the second pass, the mid-infrared pulsed laser beam is focused at a depth of 238µm from the top surface, and for the first pass, the mid-infrared pulsed laser beam is focused at a depth of 395µm from the top surface. Figure 10A The edge of the substrate portion resulting from separation at the weakened region is shown. Figure 10B and Figure 10C The weakened region resulting from the two passes of the mid-infrared pulsed laser beam after separation is shown.

[0095] Figure 11 A graph is shown illustrating the RMS roughness of different substrate portions obtained using different parameter combinations. All these samples were obtained by performing a given number of passes on a 675µm thick silicon substrate using a mid-infrared pulsed laser beam (wavelength 2.8µm, power 0.75W, given travel speed). Figure 3 The parameters are obtained using the method described in the table below. Table 1 summarizes the other parameters:

[0096]

[0097] Table 1 – Processing parameters used to form weakened regions

[0098] Figure 12 This is a graph showing the peak-to-peak roughness of the samples presented in Table 1. Figure 13 It is a graph showing the three-dimensional surface measurement profile of substrate sample #6, while Figure 14 The graph shows the surface roughness of the separation edge of sample #2 on the substrate. In the latter part of the graph, the peak-to-peak roughness is measured to be approximately 10 µm, and the RMS roughness is measured to be approximately 2 µm.

[0099] As discussed above, it has been found that for each pass of a mid-infrared pulsed laser beam focused within a semiconductor substrate, the weakened region formed therein can have a length (or height) considered significant, especially compared to the weakened region length achievable using laser beams with wavelengths in the conventional 800 nm to 1.5 µm range. The reason why the mid-infrared pulsed laser beam disclosed herein can mark a weakened region along a greater length with each pass of the mid-infrared pulsed laser beam has not been confirmed. However, the following paragraphs provide different key physical aspects that, when considered individually or collectively, can explain why mid-infrared pulsed laser beams and conventional near-infrared laser beams behave so differently in the context of semiconductor dicing. While the following explanation pertains to a 2.8 µm wavelength and a silicon substrate, it is believed that a similar explanation can be applied to any wavelength of 2.4 µm or greater and / or substrates made of any semiconductor material.

[0100] It was found that for wavelengths below or close to the approximately 1.1 µm bandgap of silicon, the interaction between a nanosecond laser pulse and silicon will be limited to a single-photon ionization process. Therefore, substrate weakening will be limited by the penetration depth of the single photon (i.e., the depth to which the single photon will be absorbed by the silicon substrate). For wavelengths of approximately 1.2 µm or higher, the interaction between a nanosecond laser pulse and silicon will be a multiphoton ionization process because the silicon material is transparent to the laser beam. Therefore, there will be no theoretical limitation regarding the location where a mid-infrared pulsed laser beam can be focused within the thickness of the semiconductor substrate. As a result, cracks can be formed at any location within the semiconductor substrate, allowing for deeper and / or longer weakening regions where needed. However, it should be noted that practical limitations exist when considering laser beam propagation within the semiconductor substrate; for example, the top cut width should be greater than the input laser beam diameter, to name just one illustrative consideration.

[0101] Figure 15 An example is shown of a GaAs substrate 10' in which a weakened region was formed using the mid-infrared pulsed laser beam 1510 discussed above, based on an experiment. In this specific experiment, the mid-infrared pulsed laser beam 1510 was guided through the top surface 1510a of the GaAs substrate 10'. As shown, the path through which the focus of the mid-infrared pulsed laser beam 1510 was guided consisted of only one pass. This pass was parallel to the back surface 1510b of the GaAs substrate 10'. In this specific embodiment, the thickness of the GaAs substrate 10' is approximately 300 µm, and the depth of the first pass is approximately 250 µm from the top surface 1510a or approximately 50 µm from the back surface 1510b. Under these operating parameters, the weakened region is sufficient to allow the GaAs substrate 10' to be easily separated into GaAs substrate portions. In this experiment, the formation of the weakened region was carried out at an effective linear velocity of 200 mm / s and included four passes through the focus of the mid-infrared pulsed laser beam.

[0102] Furthermore, it was found that when nanosecond pulses with photon energies less than the band gap of silicon interact with silicon, the dominant ionization process is avalanche ionization. In this process, seed free electrons are provided via multiphoton ionization. Once these seed electrons are lifted from the valence band to the conduction band, they undergo inverse bremsstrahlung heating / free carrier absorption and impact ionization, ultimately leading to avalanche ionization. If the exponential increase in electron density due to avalanche ionization reaches a critical electron density, it can induce crack formation within the silicon substrate.

[0103] The following section details the theoretical explanation for why a 2.8µm mid-infrared pulsed laser beam can produce a longer crack via a 3-photon ionization process than a crack produced via a 2-photon ionization process in the conventional wavelength range (1.1µm to 2.2µm).

[0104] A key physical aspect is the higher dynamical energy. Once electrons freely enter the conduction band, they can gain energy from the oscillating laser field:

[0105]

[0106] Where Up represents the mass-driven kinetic energy, and ω represents the laser frequency. In the context of the above application, the mass-driven kinetic energy can be derived from the following formula:

[0107]

[0108] According to equation (2), it can be understood that the mass dynamic energy is proportional to the laser intensity I and the square of the laser wavelength λ. It should be noted that a laser wavelength of 2.8µm will induce a 3-photon ionization process, which may require a higher laser intensity to initiate multi-photon ionization. Therefore, due to the higher intensity and longer wavelength, electrons can obtain much higher mass dynamic energy.

[0109] Another key physical aspect involves a higher electron heating rate. In fact, because the kinetic energy gained by electrons can be converted into kinetic energy, this leads to a higher electron collision rate, and thus a higher electron heating rate.

[0110]

[0111] It should be noted that equation (3) is used for ionization in gases, as the ionization equation for silicon is not yet available. However, equation (3) provides a general understanding of how these parameters interact with each other in the context of semiconductor materials.

[0112] Another key physics aspect involves the lower laser intensity threshold for avalanche ionization. It has been found that inverse-square wavelength scaling can allow laser beams with longer wavelengths to drive avalanche ionization at lower laser intensities.

[0113]

[0114] Similarly, equation (4) is used for ionization in gases because the ionization equation for silicon is not yet available. It should be noted that equation (3) is used for ionization in gases because the ionization equation for silicon is not yet available. However, equation (3) provides a general understanding of how these parameters interact with each other in the context of semiconductor materials. Since a 2.8µm laser wavelength requires a higher laser intensity to initiate multiphoton ionization compared to a two-photon ionization process, this means that avalanche ionization is far more efficient when a 2.8µm laser beam interacts with silicon (which has higher laser intensity and a longer wavelength) than with other laser beams in the wavelength range of 1.1µm to 2.2µm.

[0115] Another key phenomenon occurring simultaneously is that the bandgap energy contracts as the internal temperature of the semiconductor increases; this is known as bandgap closure. Due to the localized temperature rise to extremely high levels during the pulse interaction within the semiconductor, the bandgap wavelength shifts to longer wavelengths. Therefore, the remainder of the pulse then "sees" the semiconductor as its optical, thermomechanical, and electronic properties continue to evolve. Compared to the higher mid-infrared wavelengths, bandgap closure at the lower near-infrared wavelengths leads to an enhanced pre-focusing self-limiting effect. As the bandgap characteristics evolve due to the spatiotemporal temperature evolution during the focusing volume of the laser pulse, the single-photon absorption coefficient, two-photon absorption coefficient, and three-photon absorption coefficient also evolve. Generally, mid-infrared wavelengths help to resolve or avoid the detrimental self-limiting effects of bandgap closure (such as induced single-photon or induced two-photon effects leading to plasma shielding).

[0116] Another key phenomenon relates to the square scaling of free carrier absorption (FCA), as defined by the equation below. Stronger free carrier absorption increases the probability of direct absorption, which raises the electron temperature. Due to the interaction between excitation and deexcitation mechanisms, higher free carrier absorption is thought to enhance collisional and avalanche ionization, thereby increasing the average energy of the entire free electron population. This, in turn, leads to stronger energy deposition into the lattice, thus contributing to crack formation.

[0117]

[0118] Another key physical aspect involves a lower critical electron density. In fact, inverse-square wavelength scaling allows for the initiation of crack formation at lower electron densities at longer wavelengths:

[0119]

[0120] Another key physical aspect involves a longer Rayleigh length. The focal size ω0 and the Rayleigh length Z R Limited by the following formula:

[0121] and

[0122]

[0123] Although two-photon ionization has a relatively longer interaction region compared to three-photon ionization, the interaction between nanosecond lasers and silicon is dominated by avalanche ionization. This means that once free electrons are generated by multiphoton ionization induced by a portion of the pulse's rising edge, avalanche ionization takes over for the remainder of the pulse. The longer Rayleigh length, combined with much more efficient avalanche ionization due to higher mass kinetic energy, higher electron heating rate, lower intensity required to drive avalanche ionization, and lower critical electron density required for crack formation, allows longer wavelength lasers to form longer cracks. Therefore, mid-infrared pulsed laser beams can be advantageously used to form weakened regions of greater length (i.e., greater height, larger second dimension) compared to the conventional 0.8µm to 2.4µm range.

[0124] The following paragraphs illustrate other exemplary results obtained using the methods and systems presented in this disclosure. As will be shown, satisfactory dicing was achieved by using a mid-infrared pulsed laser beam with a center wavelength greater than the bandgap wavelength of the semiconductor substrate. In most embodiments, the center wavelength of the mid-infrared pulsed laser beam is 2.4 µm or greater. The type of semiconductor substrate varied in different experiments. For example, p-type silicon substrates, unknown type silicon substrates, silicon-on-insulator (SOI) substrates, low-resistance semiconductor substrates, and semiconductor substrates other than silicon (such as indium phosphide semiconductor substrates) were tested. The parameters below are presented for indicative purposes only, as other parameters can be modified and successful dicing can still be achieved using a mid-infrared pulsed laser beam.

[0125] In the first set of experiments, a 680µm thick p-type silicon substrate was successfully fabricated to form a weakened region that allowed for separation into substrate portions. In this first set of experiments, the pulse energy of the mid-infrared laser beam was 74µJ, and its focal length was 25mm. In an embodiment where two mid-infrared laser beam passes were performed, the first pass was at a depth of 153.4µm from the surface, and the second pass was at a shallower depth of 76.7µm from the surface. Effective linear velocities of 40mm / s or 60mm / s were used in these cases. At both velocities, the results were satisfactory because the p-type silicon substrate could be easily separated into substrate portions after sufficient force was applied at the weakened region. In another experiment, a single mid-infrared laser beam pass was performed at a depth of 150µm from the surface and an effective linear velocity of 30mm / s. In this case, a sufficiently weakened region was also successfully formed.

[0126] In the second set of experiments, an unknown type of silicon substrate with a thickness of 730 µm was successfully fabricated to form weakened regions that allowed for separation into substrate portions. In this second set of experiments, the pulse energy of the mid-infrared laser beam was 76 µJ, and its focal length was 25 mm. In one experiment, the mid-infrared laser beam underwent two passes, with the first pass at a depth of 143 µm from the surface and the second pass at a shallower depth of 108 µm. An effective linear velocity of 40 mm / s was used in these cases. In another experiment, the mid-infrared laser beam underwent two passes at an effective linear velocity of 40 mm / s, with the first pass at a depth of 162 µm from the surface and the second pass at a shallower depth of 108 µm. In these cases, sufficiently weakened regions were successfully formed. It can even be observed that the weakened regions were visible on the surface of the substrate before separation. In some embodiments, the kerf width of these weakened regions was as low as 0.58 µm.

[0127] In the third set of experiments, an unknown type of silicon substrate with a thickness of 1060 µm was successfully fabricated to form a weakened region that allowed for separation into substrate portions. In this experiment, the pulse energy of the mid-infrared laser beam was 74 µJ, and its focal length was 25 mm. In this embodiment, the mid-infrared laser beam passed through four times at an effective linear velocity of 10 mm / s. The first pass was at a depth of 260 µm from the surface, the second at 208 µm, the third at 156 µm, and the fourth (final) pass at 104 µm. These parameters also enabled the formation of a successful weakened region.

[0128] In the fourth set of experiments, a silicon-on-insulator (SiIn) substrate with a silicon layer thickness of 400 µm and a silicon dioxide layer thickness of 7 µm was successfully fabricated to form a weakened region that allowed for separation into substrate portions. In these experiments, the pulse energy of the mid-infrared laser beam was 74 µJ, and its focal length was 25 mm. In one experiment, the mid-infrared laser beam passed through three times at an effective linear velocity of 40 mm / s (the first pass was at a depth of 240 µm from the surface, the second at 200 µm, and the third at 100 µm). In another experiment, the mid-infrared laser beam passed through twice at an effective linear velocity of 40 mm / s, with the first pass at a depth of 255 µm and the second at 216 µm. In both cases, a sufficiently weakened region was obtained, allowing for the dicing of the SiIn.

[0129] In the fifth group of experiments, an unknown type of silicon substrate with a thickness of 400 µm was successfully fabricated to form weakened regions that could be separated into substrate portions. In these experiments, the pulse energy of the mid-infrared laser beam was 74 µJ, and its focal length was 25 mm. In one experiment, the mid-infrared laser beam passed through twice at effective linear velocities of 40 mm / s and 60 mm / s, with the first pass at a depth of 90 µm from the surface and the second pass at a depth of 70 µm. In another experiment, a single pass of the mid-infrared laser beam was performed at an effective linear velocity of 40 mm / s and a depth of 78 µm from the surface. These parameters also allow for the formation of successful weakened regions.

[0130] In the sixth set of experiments, a low-resistivity (10-20 mOhm·cm) semiconductor substrate with a thickness of 500 µm was successfully fabricated to form a weakened region that allowed for separation into substrate portions. In these experiments, the pulse energy of the mid-infrared laser beam was 74 µJ, and its focal length was 25 mm. In one experiment, the mid-infrared laser beam underwent two passes at an effective linear velocity of 40 mm / s, with the first pass reaching a depth of 100 µm and the second pass reaching a depth of 80 µm from the surface. In another experiment, a single pass of the mid-infrared laser beam was performed at an effective linear velocity of 40 mm / s and a depth of 80 µm from the surface. In both cases, a sufficiently weakened region was successfully formed.

[0131] In the seventh set of experiments, a low-resistivity (5-10 mOhm·cm) semiconductor substrate with a thickness of 100 µm was successfully fabricated to form a weakened region that allowed for separation into substrate portions. In these experiments, the pulse energy of the mid-infrared laser beam was 13 µJ, and its focal length was 12.5 mm. In one experiment, a single pass of the mid-infrared laser beam was performed at effective linear velocities of 20 mm / s and 30 mm / s and a depth of 20 µm from the surface. A sufficiently weakened region was also successfully formed here.

[0132] In the eighth set of experiments, an indium phosphide (InP) semiconductor substrate with a thickness of 630 µm was successfully fabricated to form weakened regions that could be separated into substrate portions. For example, in one experiment, a mid-infrared laser beam was passed twice at an effective linear velocity of 1 mm / s. In this case, the two passes of the laser occurred from different surfaces of the InP semiconductor substrate. More specifically, the first pass occurred from the front side of the InP semiconductor substrate, and the second pass occurred from the back side. Each pass of the mid-infrared laser beam 1610 was performed at a distance of 140 µm from the corresponding surface, as... Figure 16 As shown. In this experiment, the InP semiconductor substrate can be sufficiently weakened along the weakening region to allow for proper separation.

[0133] While some specific parameters are presented in the experiments described above, these are merely exemplary. In practice, other parameters, other semiconductor substrates, or substrates with other thicknesses (e.g., narrower, larger) can also be used in conjunction with the methods and systems described herein.

[0134] See now Figure 17 , Figure 1 The controller 109 shown can be provided as a combination of hardware and software components. The hardware component can be implemented in the form of a computing device 1700, combined with... Figure 17 An example of this is described. The computing device 1700 may have a processor 1702, a memory 1704, and an I / O interface 1706. Instructions 1708 for performing the methods disclosed herein (e.g., controlling the scanning head, controlling the movement of the focal spot of a mid-infrared pulsed laser beam, generating the coordinates of the area to be irradiated) may be stored in the memory 1704 and accessible by the processor 1702.

[0135] For example, processor 1702 may be a general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, an integrated circuit, a field-programmable gate array (FPGA), a reconfigurable processor, a programmable read-only memory (PROM), a programmable logic controller (PLC), or any combination thereof.

[0136] The memory 1704 may include any suitable combination of computer-readable memory, whether internal or external, such as random access memory (RAM), read-only memory (ROM), optical disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or ferroelectric RAM (FRAM).

[0137] Each I / O interface 1706 enables the computing device 1700 to interconnect with one or more input devices (such as one or more mice, one or more keyboards, one or more sensors) or with one or more output devices (such as one or more monitors, one or more external storage systems, one or more accessible networks).

[0138] Each I / O interface 1706 enables the controller to communicate with other components, exchange data with other components, access and connect to network resources and server applications, and execute other computing applications by connecting to a network (or multiple networks) capable of carrying data, including the Internet, Ethernet, Common Old-Style Telephone Service (POTS) lines, Public Switched Telephone Network (PSTN), Integrated Services Digital Network (ISDN), Digital Subscriber Line (DSL), coaxial cable, fiber optic, satellite, mobile, wireless (e.g., Wi-Fi, WiMAX), SS7 signaling networks, fixed lines, local area networks, wide area networks, and any combination of these networks.

[0139] The computing device 1700 and any software application that can be run by the computing device 1700 are merely exemplary. Other suitable embodiments of the controller may also be provided, which will be apparent to those skilled in the art.

[0140] It is understood that the examples described and illustrated above are merely illustrative. For instance, the methods and systems described herein can be used to fabricate any photonic device, including but not limited to microelectromechanical systems (MEMS), silicon photonic devices, photonic integrated circuits, silicon-based bioMEMS and genome microarrays, water-sensitive cantilever and other fragile film devices, heterogeneous multi-project wafers (including non-traditional polygons such as hexagons and octagons), and small die applications (e.g., squares smaller than 1 mm × 1 mm). The methods and systems described herein can be used to cleave substrates of any type of semiconductor material (including but not limited to InP, SiC, Si, SiN, GaN, InGaAs, CdTe, Ge, SiGe, silicon-on-insulator, etc.). To name just a few examples, the methods and systems described herein can be used to cleave any type of crystal structure, including but not limited to… <100> Crystal structure, <110> Crystal structure, <111> Crystal structure, single crystal structure, polycrystalline structure. The focal point of the mid-infrared pulsed laser beam can be moved at a corresponding speed with each pass. It is intended that the relative movement between the focal point of the mid-infrared pulsed laser beam and the semiconductor can include movement of the semiconductor wafer, movement of the focal point of the mid-infrared pulsed laser beam, or a combination of both, depending on this embodiment. The semiconductor substrate can be received on a 3D motorized translation platform. The field of view of the scanning head may be very limited for the semiconductor substrate. Therefore, a translation stage is preferably used. A scanning head is not required. In fact, in some other embodiments, focusing lenses and / or microscope objectives can be used to focus the mid-infrared pulsed laser beam within the semiconductor substrate (which will be moved by one or more translation stages). This scope is indicated by the appended claims.

Claims

1. A method for processing a semiconductor substrate having a bandgap wavelength, the method comprising: The semiconductor substrate is irradiated with a mid-infrared pulsed laser beam, the center wavelength of which is greater than the bandgap wavelength of the semiconductor substrate, wherein the center wavelength of the mid-infrared pulsed laser beam is 2.4 µm or greater. The irradiation includes relative movement between the focal point of the mid-infrared pulsed laser beam and the semiconductor substrate. The movement causes the focal point of the mid-infrared pulsed laser beam to move along a path extending within the semiconductor substrate and form a weakened region along the path. The semiconductor substrate is capable of separating into substrate portions when a separation force is applied to the semiconductor substrate.

2. The method according to claim 1, wherein, The center wavelength is in the range of 2.4µm to 5µm.

3. The method according to claim 1, wherein, The center wavelength is in the range of 2.7µm to 3.0µm.

4. The method according to any one of claims 1 to 3, wherein, The semiconductor substrate is a single-crystal silicon substrate.

5. The method according to any one of claims 1 to 4, wherein, The illumination consists of a single pass of the focal point along the path, the single pass forming the weakened region.

6. The method according to claim 5, wherein, The relative movement is performed at least one of the following: the power of the mid-infrared pulsed laser beam is about 0.75 W or greater; the semiconductor substrate is a silicon substrate; the thickness of the semiconductor substrate is in the range of about 200 µm to 1000 µm; and the relative movement is performed at an effective linear velocity in the range of 10 mm / s to 45 mm / s.

7. The method according to any one of claims 1 to 6, wherein, The irradiation includes the mid-infrared pulsed laser beam passing through the path more than once to form the weakened region.

8. The method according to any one of claims 1 to 7, wherein, The weakened region has a first dimension extending along a plane of the semiconductor substrate and a second dimension extending perpendicular to the plane of the semiconductor substrate, the second dimension being in the range of 200µm to 500µm.

9. The method according to claim 8, wherein, The first dimension is less than 50µm, preferably less than 40µm, and most preferably less than 30µm.

10. The method according to any one of claims 1 to 9, wherein, During the relative movement, the focal point of the mid-infrared pulsed laser beam is located at a given depth from the surface of the semiconductor substrate, the given depth being in the range of 200µm to 500µm.

11. The method according to any one of claims 1 to 10, further comprising: A separation force is applied to the semiconductor substrate, which separates into a substrate portion upon application. The substrate portion has a separation interface having at least one of the following: a peak-to-peak roughness of about 30 µm or less and an RMS roughness of about 5 µm or less.

12. The method according to any one of claims 1 to 11, wherein, The mid-infrared pulsed laser beam has laser pulses with pulse widths in the nanosecond range.

13. The method according to any one of claims 1 to 12, wherein, The mid-infrared pulsed laser beam includes laser pulses with pulse durations in the picosecond range.

14. The method according to any one of claims 1 to 13, wherein, The weakened region is formed at an effective linear velocity exceeding 40 mm / s, whereby the effective linear velocity is defined as the total distance traveled by the focal point of the mid-infrared pulsed laser beam relative to the semiconductor substrate divided by the total time period required for the mid-infrared pulsed laser beam to pass through the path one or more times individually, the total distance covering one or more individual passes of the mid-infrared pulsed laser beam along the path.

15. The method according to any one of claims 1 to 14, wherein, The duration of the laser pulse is in the range of approximately 20 fs to 1 µs.

16. The method according to any one of claims 1 to 15, wherein, The relative movement is performed with an effective linear velocity in the range of approximately 20 mm / s to 2 m / s.

17. The method according to any one of claims 1 to 16, wherein, The thickness of the semiconductor substrate is greater than 100µm, preferably greater than 300µm, and most preferably greater than 500µm.

18. The method according to any one of claims 1 to 17, wherein, The power of the mid-infrared pulsed laser beam is approximately 2W or greater, more preferably higher than 5W, and most preferably at least 10W.

19. The method according to any one of claims 1 to 18, wherein, The mid-infrared pulsed laser beam is emitted by a fiber laser source.

20. A system for processing a semiconductor substrate having a bandgap wavelength, the system comprising: A frame having a substrate support that receives the semiconductor substrate; A mid-infrared laser source is mounted to the frame and configured to emit a mid-infrared laser beam, the center wavelength of which is greater than the bandgap wavelength of the semiconductor substrate, and the center wavelength of the mid-infrared pulsed laser beam is 2.4µm or greater. A scanning head is optically coupled to the mid-infrared laser source. The mid-infrared laser source and the scanning head irradiate the semiconductor substrate along a path extending within the semiconductor substrate through the focal point of the mid-infrared laser beam and form a weakened region along the path. The semiconductor substrate can be separated into substrate portions when a separation force is applied to the semiconductor substrate.

21. The system according to claim 20, wherein, The mid-infrared laser source is a mid-infrared fiber laser source.

22. The system according to claim 21, wherein, The mid-infrared fiber laser source includes an optical amplifier, which comprises: a section of optical fiber including low phonon energy glass, the section of optical fiber having a laser-active doped region doped with a laser-active dopant; and a laser pump source adapted to pump the laser-active doped region of the section of optical fiber.

23. The system according to claim 22, wherein, The low-phonon energy glass is a fluoride glass.

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