Method for manufacturing a semiconductor laser

Abstract

The application discloses a preparation method of a semiconductor laser, which comprises the following steps: providing a heat sink mother plate, cutting the heat sink mother plate to form a plurality of heat sink substrates, providing an epitaxial wafer, arraying the heat sink substrates on the epitaxial wafer, forming a plurality of interval gaps parallel to a resonant cavity direction and perpendicular to the resonant cavity direction, dividing the epitaxial wafer along the interval gaps, obtaining a plurality of laser chips, stacking the laser chips, and coating the stacked laser chips to form a plurality of semiconductor lasers. Through the above method, the semiconductor laser and the preparation method thereof provided by the application directly replace the support strip in the prior art with the heat sink substrate, save materials, and reduce the welding process of the support strip after coating and separation.

Description

[0001] This application is based on a divisional application filed on November 21, 2018, with application number CN201811393151.2 and title "Semiconductor Laser and Method for Fabrication Thereof". Technical Field

[0002] This application relates to the field of lasers, and in particular to a method for fabricating a semiconductor laser. Background Technology

[0003] Semiconductor-pumped all-solid-state lasers are a new type of laser that emerged in the late 1980s. Their overall efficiency is at least 10 times higher than lamp-pumped lasers. Due to the reduced heat load per unit output, higher power can be achieved, and the system lifespan and reliability are approximately 100 times that of flash lamp-pumped systems. Therefore, semiconductor laser pumping technology has injected new vitality into solid-state lasers, enabling all-solid-state lasers to possess the dual characteristics of both solid-state and semiconductor lasers. Its emergence and gradual maturation represent a revolution in solid-state lasers and also the future direction of their development. Furthermore, it has permeated various disciplines, such as laser information storage and processing, laser materials processing, laser medicine and biology, laser communication, laser printing, laser spectroscopy, laser chemistry, laser isotope separation, laser nuclear fusion, laser projection display, laser detection and metrology, and military laser technology, greatly promoting technological progress and unprecedented development in these fields.

[0004] Semiconductor linear array lasers used in side-pumped sources on the market often consist of four or more independent lasers. Currently, the packaging process for such lasers first involves splitting and spraying the entire laser chip. After splitting the laser chip into laser bar structures, a high-reflectivity film needs to be deposited along the rear cavity surface and an anti-reflection film needs to be deposited along the front cavity surface of the laser bar structure. Existing fabrication processes solve the shadowing effect of the coating process by stacking the laser bars with a support, and setting the area of ​​the support relative to the laser bars inward. Figure 1 As shown, a laser bar 400 is stacked with a support element 100. After the stacking is completed, an antireflection film and a high reflectance film are deposited on the front cavity surface and the rear cavity surface of the laser bar 400, respectively. After the coating is completed, the laser bar 400 needs to be separated from the support element 100 in order to carry out the next step of bonding the laser bar 400 to the heat sink substrate. Therefore, the existing laser bar coating process requires a separate process, which increases the production process and makes it impossible to significantly improve the production efficiency of the laser. Therefore, there is an urgent need for a new semiconductor laser manufacturing method. Summary of the Invention

[0005] This application provides a method for fabricating a semiconductor laser, which can solve the problems of complex and costly coating processes in the fabrication of semiconductor lasers in the prior art.

[0006] One technical solution adopted in this application is: a method for preparing a laser bar, the method comprising: S11: providing a heat sink mother plate and cutting the heat sink mother plate to form a plurality of heat sink substrates; S12: providing an epitaxial wafer, the epitaxial wafer including a plurality of resonant cavities arranged in parallel; S13: attaching the plurality of heat sink substrates in an array to the epitaxial wafer to form a plurality of gaps parallel to and perpendicular to the resonant cavity direction; S14: dividing the epitaxial wafer along the gaps to obtain a plurality of laser chips; S15: stacking the plurality of laser chips and depositing a film on the stacked plurality of laser chips to form a plurality of semiconductor lasers, such that the semiconductor lasers include at least one laser bar.

[0007] According to one embodiment of this application, step S14 includes: performing a first cleaving of the epitaxial wafer with a first depth and a first width along the spacer slit perpendicular to the resonant cavity to form the cleavage surface of the plurality of laser chips.

[0008] According to one embodiment of this application, step S15 includes: stacking a plurality of laser chips in sequence, such that the plurality of laser chips are perpendicular to the front cavity surface and the rear cavity surface of the resonant cavity and are respectively on the same plane.

[0009] According to one embodiment of this application, step S14 further includes: performing a second splitting of the epitaxial wafer with a second depth and a second width along the spacer parallel to the resonant cavity.

[0010] According to one embodiment of this application, step S15 includes: depositing a film on the cleavage surface of the stacked plurality of laser chips to form a resonant cavity, wherein an antireflection film is deposited on the front cavity surface of the resonant cavity and a reflective film is deposited on the rear cavity surface of the resonant cavity.

[0011] According to one embodiment of this application, step S12 or S13 includes: thinning and polishing the side of the epitaxial wafer facing away from the heat sink substrate.

[0012] According to one embodiment of this application, the heat sink substrate is one of a metal substrate, a ceramic substrate, or a sapphire substrate.

[0013] The beneficial effects of this application are as follows: Unlike the prior art, this application provides a method for fabricating a semiconductor laser. After the heat sink substrate array is fixed on the epitaxial wafer, it is split to form multiple laser chips, which are then stacked and coated. In this way, the heat sink substrate directly replaces the support strip of the prior art, saving materials and reducing the welding process between the support strip and the heat sink substrate after coating. It is formed directly in one step, simplifying the process and reducing costs. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0015] Figure 1 This is a front view schematic diagram of laser coating in the prior art;

[0016] Figure 2 This is a schematic flowchart of the first embodiment of the method for fabricating the semiconductor laser of this application;

[0017] Figure 3 This is a schematic flowchart of sub-step S14 of the method for fabricating the semiconductor laser of this application;

[0018] Figure 4 This is a side or front view schematic diagram of the heat sink substrate being fixed behind the epitaxial wafer in this application;

[0019] Figure 5 This is a side view schematic diagram of the S141 step segmentation of the epitaxial wafer in this application;

[0020] Figure 6 This is a top view schematic diagram of the S141 step segmentation of the epitaxial wafer in this application;

[0021] Figure 7 This is a top view schematic diagram of the further S142 segmentation of the epitaxial wafer in this application;

[0022] Figure 8 This is a front view of the stacked and coated laser chips of this application;

[0023] Figure 9 This is a top view schematic diagram of the semiconductor laser fabricated in this application;

[0024] Figure 10 This is a front view schematic diagram of the semiconductor laser fabricated in this application. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0026] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0027] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0028] Please refer to the following: Figure 2-7 This application provides a method for fabricating a semiconductor laser, including a process diagram and a structural diagram.

[0029] Please see Figure 2 , Figure 2 This is a schematic flowchart of the first embodiment of the method for fabricating the semiconductor laser of this application. The specific method includes the following steps:

[0030] S11, a heat sink mother plate is provided, and the heat sink mother plate is cut to form multiple heat sink substrates 300.

[0031] The heat sink substrate 300 provided in this application can be a metal substrate with good thermal and electrical conductivity, or a double-layer thermally conductive substrate with one layer being a metal plate and the other layer being a heat dissipation plate, or a ceramic substrate with good heat dissipation performance.

[0032] In a specific implementation, the length and width of the heat sink substrate 300 are greater than the length and width of the epitaxial wafer; the specific length and width of the heat sink substrate 300 are selected based on the material of the epitaxial wafer and the yield of subsequent processes, which will not be elaborated here.

[0033] The motherboard is cut to form multiple heat sink substrates 300. The cutting process can be photolithography, laser, split saw, water jet, etc. Preferably, the multiple heat sink substrates 300 are of the same size.

[0034] Among them, the linear thermal expansion coefficient of the heat sink substrate should be well matched with that of the epitaxial wafer material. If the heat generated during the operation of the semiconductor laser cannot be removed in time, the temperature of the entire semiconductor laser will rise. Due to the different expansion coefficients, the thermal deformation will be different, and stress will be generated between the epitaxial wafer material and the heat sink substrate material. This can easily lead to the SMILE effect, which can damage the semiconductor laser chip and degrade the optoelectronic properties of the semiconductor laser. If the stress is too great, it may even cause the laser chip to break, resulting in the sudden failure of the semiconductor laser. Therefore, high thermal conductivity materials such as copper, graphene, or ceramics are usually used as heat sink substrates.

[0035] S12, an epitaxial wafer 200 is provided, the epitaxial wafer 200 includes a plurality of resonant cavities 210 arranged in parallel.

[0036] The epitaxial wafer includes a substrate on which the epitaxial growth of the various layers of laser material is performed; a buffer layer disposed on the substrate to form a high-quality epitaxial surface, reduce stress between the substrate and other layers, and eliminate the propagation of substrate defects to other layers, thereby facilitating the growth of other layers of the device; an N-type lower confinement layer disposed on the buffer layer to limit the propagation of transverse modes of the optical field to the buffer layer and the substrate, reducing light loss, and also limiting carrier diffusion, reducing hole leakage current, thereby lowering the threshold current of the device and improving efficiency; a lower waveguide layer disposed on the lower confinement layer to strengthen the confinement of the optical field, reduce the far-field divergence angle of the beam, and improve the beam quality of the device, using lightly doped materials to reduce the absorption loss of light in this layer; and an active layer disposed on the lower waveguide layer, which acts as a laser... The active region of the optical device provides sufficient optical gain and determines the lasing wavelength and lifespan of the device. The upper waveguide layer, disposed on the active layer, aims to enhance the confinement of the optical field, reduce the far-field divergence angle of the beam, and improve the beam quality of the device. Lightly doped materials are used to reduce absorption losses in this layer. The P-type upper confinement layer, disposed on the upper waveguide layer, aims to limit the transverse mode expansion of the optical field towards the buffer layer and substrate, reducing light loss. It also limits carrier diffusion, reducing hole leakage current, thereby lowering the device's threshold current and improving efficiency. The transition layer, disposed on the P-type upper confinement layer, aims to reduce the stress between the upper confinement layer and the electrode contact layer, facilitating the transition from the upper confinement layer to the electrode contact layer. It is understood that in a modified embodiment, where the adhesion between the confinement layer and the electrode layer materials is well-matched, a transition layer is unnecessary.

[0037] In a specific embodiment, the epitaxial wafer 200 further includes a resonant cavity 210, which is formed by etching above the confinement layer. The etching depth does not exceed the confinement layer, that is, etching away part of the waveguide layer and confinement layer on both sides, leaving the waveguide layer and confinement layer in the middle that are not etched, i.e., the resonant cavity 210. The advantage of setting the resonant cavity 210 is that it forms a certain refractive index step on the side of the epitaxial wafer, which has a certain confinement effect on the side light. In addition, in some high-power lasers, this kind of resonant cavity is also used as a mode selection filter. The etching method, etching depth and width design of the resonant cavity 210 are conventional techniques in the art and will not be described in detail here.

[0038] The material of its epitaxial wafer 200 can be one or more of GaAs, AlGaAs, InAs, InGaAs, GaInP, GaInAsP, AlGaInP, GaN, GaInN, AlGaN, and AlGaInN.

[0039] S13, multiple heat sink substrates 300 array are attached to the epitaxial wafer.

[0040] like Figure 4 As shown, Figure 4 This is a side or front view of multiple heat sink substrates 300 arrayed and bonded to an epitaxial wafer 200. The bonding method can be welding or gluing, so that the multiple heat sink substrates 300 can be arrayed on the P-surface of the epitaxial wafer 200, forming multiple gaps parallel to and perpendicular to the resonant cavity direction. In the direction perpendicular to the resonant cavity 210, the edge lines of the same side of a row of heat sink substrates 300 are on the same straight line, and in the direction parallel to the resonant cavity 210, the edge lines of the same side of a row of heat sink substrates are also on the same straight line.

[0041] Furthermore, the array width and length of the multiple heat sink substrates 300 are slightly smaller than the width and length of the epitaxial wafer 200. The purpose of this design is to define the gaps by the edge lines of the multiple arrayed heat sink substrates, providing a reference line for the subsequent epitaxial wafer splitting process. Therefore, it is required that the edge lines of each heat sink substrate 300 be on the same line as much as possible in a certain direction to ensure the splitting yield in the later stage.

[0042] Furthermore, the side of the epitaxial wafer 200 facing away from the heat sink substrate 300 can be thinned and polished to make its N-side have a relatively high flatness and smoothness. At the same time, the N-side of the epitaxial wafer 200 can be vapor-deposited to form a negative electrode, specifically by patterning copper foil or using gold wire as the negative electrode.

[0043] It should be noted that the thinning and polishing process can also be performed in step S12, that is, before the epitaxial wafer 200 is split.

[0044] Preferably, whether it is a metal substrate or a double-layer thermally conductive substrate, the heat sink substrate 300 and the epitaxial wafer 200 provided in this application have a good coefficient of thermal expansion matching degree, so as to ensure that the heat generated by the semiconductor laser has the same or similar thermal deformation on the heat sink substrate 300 and the epitaxial wafer 200 in subsequent operations, reducing the stress caused by heat, so as to ensure that the entire laser will not be damaged and improve the life of the laser.

[0045] Furthermore, the epitaxial wafer 200 and the heat sink substrate 300 are bonded together by welding or bonding. Specifically, when the heat sink substrate 300 is a metal substrate, the epitaxial wafer is preferably bonded to the heat sink substrate by welding. In this case, the heat sink substrate not only has the function of heat dissipation but also acts as a conductive layer. When the heat sink substrate 300 is a non-conductive substrate such as ceramic or sapphire, the epitaxial wafer 200 is preferably bonded to the heat sink substrate by bonding. In this case, the heat sink substrate is only used for heat dissipation.

[0046] S14, the epitaxial wafer 200 is divided along the gap to obtain multiple laser chips.

[0047] like Figure 5-7 In a specific embodiment, the epitaxial wafer 200 needs to be divided according to specific requirements to obtain laser chips of the required model and size. The epitaxial wafer 200 is divided along the gap seams, including dividing the epitaxial wafer 200 along the gap seams perpendicular to and parallel to the resonant cavity 210, thereby obtaining multiple laser chips including a heat sink substrate 300.

[0048] Understandably, during the specific segmentation process, the laser can be segmented according to actual specifications to obtain the required laser chip model. This results in a laser chip containing the required number of laser bars, etc. Specifically, some laser chips contain one laser bar, while some semiconductor lasers contain multiple laser bars.

[0049] Please see Figure 3 , Figure 3 This is a sub-step of S14 in the method for fabricating the semiconductor laser of this application, which specifically includes:

[0050] S141, a first split of the epitaxial wafer 200 is performed along the spacer slit perpendicular to the resonant cavity 210 to obtain a plurality of laser chips.

[0051] Since the heat sink substrate 300 is fixed in an array on the epitaxial wafer 200, the spacers are arranged vertically and orthogonally, including multiple spacers perpendicular to the resonant cavity 210 and multiple spacers parallel to the resonant cavity 210.

[0052] A first split of the epitaxial wafer 200 at a first depth and a first width is performed along the gap perpendicular to the resonant cavity 210 to obtain... Figure 5 and Figure 6 The image shows multiple laser chips.

[0053] Furthermore, after the epitaxial wafer 200 is first cleaved, the laser chip with cleavage surface has been formed. It can then directly proceed to step S15 for coating operation, or it can be further cut according to the specific size requirements before performing the coating operation in S15. The specific cutting method is shown in S142.

[0054] S142, a second split with a second depth and a second width is performed on the epitaxial wafer 200 along the spacer parallel to the resonant cavity 210.

[0055] A second split, with a second depth and a second width, is performed on the epitaxial wafer 200 along the spacer parallel to the resonant cavity 210. This split can occur from the P-plane to the N-plane or from the N-plane to the P-plane, resulting in... Figure 7 The multiple laser chips shown.

[0056] Furthermore, it can be cleaved with the assistance of a diamond cutter, easily separating along the lattice of the epitaxial wafer 200 and producing a smooth cleavage surface. Dry etching or wet etching can also be used, along with other processing to produce a smooth co-cleavage surface. The second cleavage is similar to the first cleavage; its second depth is equal to the first depth and both are greater than or equal to the thickness of the epitaxial wafer 200 (specifically, the actual thickness of the epitaxial wafer 200). Its second width is equal to the first width and both are less than the width of the spacer. During cleaving, the cleavage center coincides with the center line of the gap.

[0057] The order of splitting the laser chip is not limited; it can be split first and then selectively split second. During the splitting process, the second split can be performed according to the required specifications to obtain the laser chip of the desired size.

[0058] Since both the second width and the first width are smaller than the width of the gap, the length of the epitaxial wafer 200 of the formed laser chip in the direction parallel to the resonant cavity 210 is greater than the length of the heat sink substrate 300. The advantage of this structure is that it reduces the shadow effect when the resonant cavity surface of the resonant cavity 210 is coated, which is beneficial to improving the coating uniformity of the front and rear cavity surfaces of the resonant cavity.

[0059] S15 involves stacking multiple laser chips and depositing a coating on the stacked laser chips to form multiple semiconductor lasers.

[0060] like Figure 8 After obtaining multiple laser chips including resonant cavities 210, the multiple laser chips are stacked. Since the size of the split laser chips may be different, the multiple laser chips are stacked sequentially according to the direction of the resonant cavity 210, so that the resonant cavity 210 of the multiple laser chips has the same direction, and the front cavity surface 220 and the rear cavity surface 230 of the multiple laser chips perpendicular to the resonant cavity 210 are on the same plane.

[0061] Specifically, the cleavage surface (split surface) of the resonant cavity 210 of the laser chip is coated with a film, including an anti-reflection film on the front cavity surface 220 (light-emitting surface) and a reflective film on the rear cavity surface 230 (rear end surface), to form a resonant cavity that generates stimulated emission photons.

[0062] The spraying of the front cavity surface 220 and the rear cavity surface 230 can be performed simultaneously or separately. After the coating is completed, multiple semiconductor lasers are formed. Since the electrode fabrication, coating, etc. have been completed, the semiconductor laser includes at least one laser bar, and the heat sink substrate 300 serves as the positive electrode of the laser chip to complete the electrical connection.

[0063] Understandably, during the specific splitting process, the splitting can be performed according to actual specifications to obtain the required type of semiconductor laser. This results in a semiconductor laser containing the required number of laser bars. Specifically, some semiconductor lasers contain one laser bar, while others contain multiple laser bars. Compared to the existing method of welding one laser bar at a time to form multi-bar semiconductor lasers, the fabrication of multi-bar semiconductor lasers can be completed by improving the epitaxial wafer splitting process, saving welding processes and further improving production efficiency.

[0064] Furthermore, the aforementioned splitting depth of the epitaxial wafer 200, namely the second depth and the first depth, is determined according to the specific operation. For example, if the epitaxial wafer 200 is thinned in advance, the depth is the current thickness of the epitaxial wafer 200, which is the thickness after thinning.

[0065] Please see Figure 9 and Figure 10 This application provides a schematic diagram of the structure of a semiconductor laser, which is a schematic diagram of the semiconductor laser fabricated by the above-described process, wherein... Figure 8 This is a top view schematic diagram of the semiconductor laser provided in this application. Figure 9For the frontal view schematic diagram, the semiconductor laser includes a heat sink substrate 300 and a laser bar 250 disposed on the heat sink substrate 300, wherein the laser bar 250 includes a resonant cavity 210.

[0066] like Figure 10 As shown, the length and width of the heat sink substrate 300 are smaller than the length of the laser bar 250. This makes the resonant cavity 210 slightly protrude from the heat sink substrate 300. The advantage of this design is that in the subsequent bar coating process, the coating shadow effect caused by the heat sink substrate can be reduced, which is conducive to improving the coating uniformity of the front and rear cavity surfaces of the resonant cavity, thereby improving the stability and service life of the laser.

[0067] In summary, this application provides a semiconductor laser and its fabrication method. After the heat sink substrate array is fixed on the epitaxial wafer, it is split to form multiple laser chips, which are then stacked and coated. The heat sink substrate directly replaces the support strip of the prior art, saving materials and reducing the welding process between the support strip and the heat sink substrate after coating. It is formed directly in one step, simplifying the process and reducing costs. Furthermore, this application prevents the generation of shadow effects by limiting the splitting width.

[0068] The above are merely embodiments of this application and do not limit the scope of this patent application. Any equivalent results or equivalent process changes made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of this application.

Claims

1. A method for fabricating a semiconductor laser, characterized in that, The method includes the following steps: S11: Provide a heat sink mother plate, and cut the heat sink mother plate to form multiple heat sink substrates; S12: Provide an epitaxial wafer, the epitaxial wafer including a plurality of resonant cavities arranged in parallel; S13: Attach multiple arrays of heat sink substrates to the epitaxial wafer to form multiple gaps parallel to and perpendicular to the resonant cavity direction, such that in the direction perpendicular to the resonant cavity, the edge lines of a row of heat sink substrates on the same side are on the same straight line, and in the direction parallel to the resonant cavity, the edge lines of a row of heat sink substrates on the same side are also on the same straight line. S14: Divide the epitaxial wafer along the gap to obtain multiple laser chips; S15: Stack the plurality of laser chips and coat the stacked plurality of laser chips to form a plurality of semiconductor lasers, such that the semiconductor lasers include at least one laser bar.

2. The preparation method according to claim 1, characterized in that, Step S14 includes: A first cleavage of a first depth and a first width is performed on the epitaxial wafer along the spacer slit perpendicular to the resonant cavity to form the cleavage surface of the plurality of laser chips.

3. The preparation method according to claim 2, characterized in that, Step S15 includes: Multiple laser chips are stacked sequentially such that the multiple laser chips are perpendicular to the front cavity surface and the rear cavity surface of the resonant cavity, respectively, on the same plane.

4. The preparation method according to claim 2, characterized in that, Step S14 further includes: The epitaxial wafer is split into a second depth and a second width along the spacer parallel to the resonant cavity.

5. The preparation method according to claim 3, characterized in that, Step S15 includes: A resonant cavity is formed by coating the cleavage surfaces of the stacked plurality of laser chips, wherein an antireflective coating is coated on the front cavity surface of the resonant cavity and a reflective coating is coated on the rear cavity surface of the resonant cavity.

6. The preparation method according to claim 4, characterized in that, The second depth is equal to the first depth, and both are greater than or equal to the thickness of the epitaxial wafer; the second width is equal to the first width, and both are less than the width of the gap.

7. The preparation method according to claim 1, characterized in that, Step S12 or S13 further includes: thinning and polishing the side of the epitaxial wafer facing away from the heat sink substrate.

8. The preparation method according to claim 1, characterized in that, The heat sink substrate is one of a metal substrate, a ceramic substrate, or a sapphire substrate.

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