Manufacturing method of semiconductor laser

Abstract

The invention belongs to the technical field of semiconductor optoelectronic device processes, and relates to a manufacturing method of a semiconductor laser, which can realize beam shaping of a semiconductor laser element. The selective area micromachining technology is creatively adopted, the selective area optical limiting microstructure of the laser cavity surface is achieved through wafer pretreatment before cavity surface cleavage, cavity surface light emission is eliminated, and the light beam quality is improved. The method has the greatest advantages that the preparation of the selected area optical limitation microstructure is completed before cavity surface cleavage, the cavity surface pollution can be avoided, the problem of a far-field'square window 'is solved, the product performance and the production yield are improved, and a reliable technical guarantee is provided for commercial application.

Description

Technical Field

[0001] The invention relates to a semiconductor laser optical preparation method, belonging to the technical field of semiconductor optoelectronic device process. Background Art

[0002] Gallium nitride (GaN)-based semiconductor lasers are the best choice for blue and green light sources in the three primary colors of laser display. They have important application value and broad market prospects in the fields of laser lighting and display, optical information storage, quantum technology, underwater communication, metal welding and laser additive manufacturing. Existing GaN lasers mostly use the edge-emitting active area light-emitting mode, using the natural cleavage surface of the substrate crystal as a reflection surface to form an FP resonant cavity, and form self-excited oscillation in the cavity, so as to achieve laser emission from the end face of the resonant cavity. The multi-layer cavity mask is an important component structure of the laser cavity surface. It can not only effectively ensure that the cavity surface is not oxidized when the device is working to improve the environmental stability, but also reduce the working current of the device by changing the reflectivity of the output cavity surface to improve the device life. The cavity surface of an ideal edge-emitting semiconductor laser is a pair of parallel natural cleavage surfaces of crystals, with a flat and smooth surface. Due to the sudden change in the refractive index of the interface between the laser material and the working environment, the spontaneous radiation light can achieve effective light reflection on the cleavage surface, and after multiple reflections, self-excited oscillation is formed, and finally laser emission is formed. Cavity surface coating technology can effectively achieve the selection of laser threshold, light emission direction and frequency through reflectivity regulation. The cavity surface mask can also effectively passivate the interface dangling bonds and defects caused by the cavity surface cleavage process, reduce cavity surface losses, and improve the performance and life of the device. However, during the lasing process, due to the unsatisfactory waveguide limitation in the chip thickness direction, the laser light leaks to the substrate and becomes the source of cavity surface emission. In addition, there is a refractive index difference between the interface of the cavity surface mask and GaN and the working environment, especially the interface between the cavity surface mask and the environment (generally air, whose refractive index is 1), which is easy to form a strong waveguide limitation effect, resulting in the waveguide leakage light being confined to the cavity surface mask and air interface, and ultimately causing the entire cavity surface to emit light.

[0003] The ideal laser beam is shaped by the optical system to obtain the far-field pattern of the specified requirements, which is widely used in laser lighting, laser display, laser ranging and laser marking devices. However, along with the cavity surface emission, stray light appears in the optical control system (that is, the light-emitting cavity surface is imaged in the far field after collimation and focusing), which affects the effect of optical shaping and leads to a decrease in the quality of the beam application. For example, in the laser marking application, the laser undergoes an optical collimation and focusing process, and the focus converges on a cylindrical lens (or Powell prism) to form a high-brightness and recognizable linear far-field pattern, which is used for marking in the fields of machinery manufacturing, precision instrument production, metallurgical cutting and architectural decoration. The laser beam carrying cavity surface emission inevitably forms stray light in the optical shaping system and presents a "square window" image of the cavity surface shape in the far field, which seriously affects the beam quality and reduces the accuracy and reliability of the equipment. In order to solve the cavity surface emission, the waveguide limitation of the cavity surface mask needs to be destroyed under the condition that the epitaxy remains unchanged, the cavity surface emission phenomenon is eliminated, and the beam quality is improved. To address this problem, first of all, we can cut in from the cavity mask, use the "shadow" effect to select absorption materials to be deposited in the specified area, weaken the cavity surface luminescence effect, and improve the beam quality, see Japanese Patent: Tokukai 2020-129653 (P2020-129653A). In order to achieve the "shadow" effect, this patent solution requires secondary arrangement of the laser bars and secondary selective coating of the cavity surface. The preparation process and coating difficulty increase, and the cavity surface is prone to secondary pollution and damage during the process, reducing production efficiency and yield. In addition, the coating equipment is required to have good deposition directionality to limit the lateral diffusion of the secondary grown absorption film on the cavity surface and ensure the accuracy of the selective coating. Secondly, it is also possible to cut in from the laser cavity surface and perform selective micromachining of the material for the cavity surface luminescence restriction area. The preparation of the selective microstructure increases the optical restriction capability and destroys the waveguide restriction capability of the cavity mask, solves the cavity surface luminescence, and improves the laser beam quality. Summary of the invention

[0004] The purpose of the present invention is to innovatively propose a method for manufacturing a semiconductor laser in response to the above technical difficulties and in combination with the needs of industrial production, which can realize the beam shaping of semiconductor laser elements. This method innovatively adopts the selective micromachining technology. Before the cavity surface is cleaved, the selective optical confinement microstructure of the laser cavity surface is realized by pre-processing the wafer, eliminating the cavity surface emission, solving the far-field "square window" problem, and improving the beam quality. The biggest advantage of the present invention is that the preparation of the selective optical confinement microstructure is completed before the cavity surface is cleaved, avoiding cavity surface contamination and solving the far-field "square window" problem, improving product performance and production yield, and providing reliable technical guarantee for commercial applications.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for manufacturing a semiconductor laser, which uses a thermal oxidation cavity surface selection method to prepare a selected area optical confinement microstructure, comprising the following steps:

[0007] Step 1: Deposit a SiO2 layer on the laser epitaxial wafer, wherein the SiO2 serves as an anti-oxidation protective layer.

[0008] Step 2: Define the thermal oxidation area on the surface of the epitaxial wafer by photolithography, and transfer the photolithography-defined pattern to the SiO2 layer by etching process. The area not covered by SiO2 is the thermal oxidation area.

[0009] Step 3: The SiO2 pattern-defined epitaxial wafer is oxidized by a thermal oxidation process, and finally a patterned modified area is obtained in the thickness direction of the wafer through the surface thermal oxygen diffusion effect, thus completing the preparation of the selected optical confinement microstructure.

[0010] Step 4: Use etching method to remove SiO2 anti-oxidation protective layer, and prepare laser ridge structure and P-side electrode through photolithography, etching, coating and other processes. The surface of the sample is covered with SiO2 insulating layer except the ridge window structure area.

[0011] Step 5: Spin-coat the photolithography protective film on the P surface of the sample, fix the wafer to the ceramic tray through the waxing equipment, and perform mechanical thinning, rough grinding, fine grinding and polishing on the back side of the substrate wafer to finally obtain a thinned wafer sample with a thickness of less than 150μm.

[0012] Step 6: The thinned wafer is subjected to cavity surface cleavage, cavity surface coating, single tube cracking, testing and sorting to complete the complete preparation process of the semiconductor laser chip.

[0013] A method for manufacturing a semiconductor laser, using ion implantation into a cavity surface selection to prepare a selected optical confinement microstructure, comprising the following steps:

[0014] Step 1: Deposit a SiO2 layer on the laser epitaxial wafer, wherein the SiO2 serves as an ion implantation protection layer.

[0015] Step 2: Define the ion implantation area on the surface of the epitaxial wafer by photolithography, and transfer the photolithography-defined pattern to the SiO2 layer by etching. The area not covered by SiO2 is the ion implantation area.

[0016] Step 3: Use the ion implantation process to perform selective ion implantation on the SiO2 pattern-defined epitaxial wafer, and finally obtain a patterned modified area in the thickness direction of the wafer through surface ion implantation, thus completing the preparation of the selective optical confinement microstructure.

[0017] Step 4: Use etching method to remove SiO2 ion implantation protection layer, and prepare laser ridge structure and P-side electrode through photolithography, etching, coating and other processes. The surface of the sample is covered with SiO2 insulation layer except the ridge window structure area.

[0018] Step 5: Spin-coat the photolithography protective film on the P surface of the sample, fix the wafer to the ceramic tray through the waxing equipment, and perform mechanical thinning, rough grinding, fine grinding and polishing on the back side of the substrate wafer to finally obtain a thinned wafer sample with a thickness of less than 150μm.

[0019] Step 6: The thinned wafer is subjected to cavity surface cleavage, cavity surface coating, single tube cracking, testing and sorting to complete the complete preparation process of the semiconductor laser chip.

[0020] A method for manufacturing a semiconductor laser, using laser to modify the cavity surface selection to prepare a selected area optical confinement microstructure, comprising the following steps:

[0021] Step 1: Polish the substrate surface of the laser epitaxial wafer using a grinding and polishing technique to obtain an epitaxial substrate with a smooth and light-transmitting surface.

[0022] Step 2: On the transparent substrate side, a patterned modified area is obtained in the wafer thickness direction through laser irradiation modification technology, thereby completing the preparation of the selected area optical confinement microstructure.

[0023] Step 3: On the front side of the epitaxial wafer, the laser ridge structure and the P-side electrode are prepared through processes such as photolithography, etching, and coating. The surface of the sample is covered with a SiO2 insulating layer except for the ridge window structure area.

[0024] Step 4: Spin-coat the photolithography protective film on the P surface of the sample, fix the wafer to the ceramic tray through the waxing equipment, and perform mechanical thinning, rough grinding, fine grinding and polishing on the back side of the substrate wafer to finally obtain a thinned wafer sample with a thickness of less than 150μm.

[0025] Step 5: The thinned wafer is subjected to cavity surface cleavage, cavity surface coating, single tube cleavage, test and sorting to complete the complete preparation process of the semiconductor laser chip.

[0026] Beneficial effects of the present invention:

[0027] This method creatively realizes the preparation of the selected microstructure of the semiconductor laser cavity surface by accurately processing the wafer surface. The selected microstructure increases the optical limitation ability and destroys the waveguide limitation ability of the cavity surface film, solves the cavity surface luminescence problem, and improves the laser beam quality. First of all, the greatest beneficial effect of the present invention is that the preparation of the cavity surface selected microstructure is before the laser process. The micro-nano processing technology is cleverly used to prefabricate the surface of the laser epitaxial wafer to the specified area of ​​the laser cavity surface to achieve effective cavity surface luminescence limitation. It completely avoids the pollution and damage of the laser cavity surface, reduces the process difficulty, and greatly improves the performance and yield rate of the laser. Secondly, the preparation of the selected microstructure is to accurately prefabricate the wafer surface on the laser cavity surface. Its preparation process is simple, efficient and compatible with the semiconductor processing flow, does not increase the investment in production equipment, is suitable for industrial promotion, and is practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The process diagram of preparing laser devices by using method 1 and method 2;

[0029] Figure 2 This is a process diagram of preparing a laser device using method 3;

[0030] Figure 3 Schematic diagram of the cavity surface structure of the laser prepared by method 1 and method 2;

[0031] Figure 4 This is a schematic diagram of the cavity surface structure of the laser prepared by method 3;

[0032] Figure 5 This is a schematic diagram of the three-dimensional structure of the semiconductor laser prepared by the present invention. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below through specific embodiments and drawings.

[0034] Embodiment 1:

[0035] A method for manufacturing a semiconductor laser, using thermal oxidation cavity surface selection to prepare a selected area optical confinement microstructure, the process of the method is as follows Figure 1 As shown, the following steps are included:

[0036] Step 1: Deposit a silicon oxide (SiO2) layer on the laser epitaxial wafer, wherein the SiO2 serves as an anti-oxidation protective layer. The thickness of the SiO2 layer is 2-5 μm, and the thickness of the SiO2 layer in this embodiment is 3 μm.

[0037] Step 2: Define the thermal oxidation area on the surface of the epitaxial wafer by photolithography, and transfer the photolithography-defined pattern to the SiO2 layer by etching process. The area not covered by SiO2 is the thermal oxidation area, where the width b of the SiO2 mask is 30μm.

[0038] Step 3: Use thermal oxidation process to place the treated epitaxial wafer into an oxidation furnace at a temperature of 800-1200°C, the temperature in this embodiment is 1000°C, the oxidation time is 1-5h, the oxidation time in this embodiment is 3h, and the epitaxial wafer defined by the SiO2 pattern is oxidized to finally obtain a patterned modified area in the wafer thickness direction through the surface thermal oxygen diffusion effect, thereby completing the preparation of the selected optical confinement microstructure.

[0039] Step 4: Use etching method to remove SiO2 anti-oxidation protective layer, and prepare laser ridge structure and P-side electrode through photolithography, etching, coating and other processes. The surface of the sample is covered with SiO2 insulating layer except the ridge window structure area.

[0040] Step 5: Spin-coat the photolithography protective film on the P surface of the sample, fix the wafer to the ceramic tray through the waxing equipment, and perform mechanical thinning, rough grinding, fine grinding and polishing on the back side of the substrate wafer to finally obtain a thinned wafer sample with a thickness of less than 150μm.

[0041] Step 6: Perform cavity surface cleavage on the thinned wafer, cavity surface coating, single tube cleavage, test sorting and other steps to complete the complete preparation process of the semiconductor laser chip. The three-dimensional structure of the semiconductor laser prepared in this embodiment is as follows Figure 5 shown.

[0042] In this embodiment, the ridge width a of the laser chip is 10 μm, the width c of the diffusion region is 10 μm, and b=a+2c. Figure 3 As shown, the reserved diffusion areas on both sides of the ridge can effectively reduce the influence of the diffusion during the thermal oxidation process on the light output point of the cavity surface below the ridge of the laser chip.

[0043] Embodiment 2:

[0044] A method for manufacturing a semiconductor laser, using ion implantation to select a cavity surface to prepare a selected optical confinement microstructure, the process of the method is as follows Figure 1 As shown, the following steps are included:

[0045] Step 1: Deposit a silicon oxide (SiO2) layer on the laser epitaxial wafer, wherein the SiO2 serves as an ion implantation protection layer. The thickness of the SiO2 layer is 100-1000 nm, and the thickness of the SiO2 layer in this embodiment is 300 nm.

[0046] Step 2: Define the ion implantation area on the surface of the epitaxial wafer by photolithography, and transfer the photolithography-defined pattern to the SiO2 layer by etching. The SiO2 uncovered area is the ion implantation area, where the SiO2 mask width b is 30 μm.

[0047] Step 3: Use ion implantation to place the processed epitaxial wafer into the ion implantation equipment. Heat the epitaxial wafer to 100°C. Use argon ions with an implantation energy of 30KeV to perform selective ion implantation on the epitaxial wafer defined by the SiO2 pattern. Finally, a patterned modified area is obtained in the thickness direction of the wafer through surface ion implantation, thus completing the preparation of the selective optical confinement microstructure.

[0048] Step 4: Use etching method to remove SiO2 ion implantation protection layer, and prepare laser ridge structure and P-side electrode through photolithography, etching, coating and other processes. The surface of the sample is covered with SiO2 insulation layer except the ridge window structure area.

[0049] Step 5: Spin-coat the photolithography protective film on the P surface of the sample, fix the wafer to the ceramic tray through the waxing equipment, and perform mechanical thinning, rough grinding, fine grinding and polishing on the back side of the substrate wafer to finally obtain a thinned wafer sample with a thickness of less than 150μm.

[0050] Step 6: Perform cavity surface cleavage on the thinned wafer, cavity surface coating, single tube cracking, testing and sorting to complete the complete preparation process of the semiconductor laser chip.

[0051] In this embodiment, the ridge width a of the laser chip is 10 μm, the width c of the diffusion region is 10 μm, and b=a+2c. Figure 3 As shown, the reserved diffusion areas on both sides of the ridge can effectively reduce the influence of the diffusion during the ion implantation process on the light output point of the cavity surface below the ridge of the laser chip.

[0052] Embodiment 3:

[0053] A method for manufacturing a semiconductor laser, using laser to modify the cavity surface selection to prepare a selected area optical confinement microstructure, the process of the method is as follows Figure 2 As shown, the following steps are included:

[0054] Step 1: Polish the substrate surface of the laser epitaxial wafer using a grinding and polishing technique to obtain an epitaxial substrate with a smooth and light-transmitting surface.

[0055] Step 2: On the transparent substrate side, a patterned modified area is obtained in the thickness direction of the laser epitaxial wafer by laser irradiation modification technology, that is, the preparation of the selected optical confinement microstructure is completed. A 1064nm picosecond pulse laser is used for laser irradiation modification, with a single pulse energy of 1.4μJ, a frequency of 50kHz, a laser energy of 50mW, a fixed-point focused beam with a step length of 5μm, a width a of 8μm across the target ridge, and a width of 10μm for the expansion area c reserved on both sides of the ridge. The laser energy of the fixed-point focused beam decreases by 5mW in the direction of decreasing distance from the active area of ​​the laser epitaxial wafer until the fixed-point focused beam reaches the top surface of the laser epitaxial wafer, such as Figure 4 As shown in (a).

[0056] Step 3: The laser ridge structure and P-side electrode are prepared through processes such as photolithography, etching, and coating. The surface of the sample is covered with a SiO2 insulating layer except for the ridge window structure area.

[0057] Step 4: Spin-coat the photolithography protective film on the P surface of the sample, fix the wafer to the ceramic tray through the waxing equipment, and perform mechanical thinning, rough grinding, fine grinding and polishing on the back side of the substrate wafer to finally obtain a thinned wafer sample with a thickness of less than 150μm.

[0058] Step 5: Perform cavity surface cleavage on the thinned wafer, cavity surface coating, single tube cleavage, test and sorting to complete the complete preparation process of the semiconductor laser chip.

[0059] Embodiment 4:

[0060] In step 2, a 1064nm picosecond pulse laser is used, with a single pulse energy of 1.4μJ, a frequency of 50kHz, a laser energy of 50mW, and a fixed-point focusing beam with a step length of 5μm. The laser energy of the fixed-point focusing beam decreases by 5mW in a direction decreasing from the active area of ​​the laser epitaxial wafer until the fixed-point focusing beam stops at a distance d of 20μm from the top surface of the laser epitaxial wafer, as shown in FIG. Figure 4 The rest is the same as in Example 3.

[0061] Embodiment 5:

[0062] In step 2, a 1064nm picosecond pulse laser is used, with a single pulse energy of 1.4μJ, a frequency of 50kHz, a laser energy of 50mW, and a fixed-point focused beam with a step size of 5μm. The laser energy of the fixed-point focused beam decreases by 5mW in the direction of decreasing distance from the active area of ​​the laser epitaxial wafer until the fixed-point focused beams on both sides of the laser ridge stop at a distance d of 20μm from the top surface of the laser epitaxial wafer, and the closest fixed-point focused beam below the laser ridge stops at a distance e of 25μm from the top surface of the laser epitaxial wafer, as shown in FIG. Figure 4As shown in (c), the rest is the same as Example 4.

[0063] The method for manufacturing a semiconductor laser of the present invention, by designing the preparation of the cavity surface selection area microstructure before the laser process cleavage, ingeniously uses micro-nano processing technology to prefabricate the surface of the laser epitaxial wafer to the specified area of ​​the laser cavity surface, thereby achieving effective cavity surface light emission limitation, which completely avoids the contamination and damage of the laser cavity surface, reduces the process difficulty, and greatly improves the performance and yield rate of the laser.

[0064] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and implement it accordingly. It can be understood by those skilled in the art that various replacements, changes and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the contents disclosed in the embodiments of this specification, and the scope of protection of the present invention shall be subject to the scope defined in the claims.

Claims

1. A method for manufacturing a semiconductor laser, characterized in that: The following steps are involved: Depositing a SiO2 layer on the laser epitaxial wafer, wherein the SiO2 serves as an anti-oxidation protective layer; A thermal oxidation area is defined on the surface of the laser epitaxial wafer by photolithography, and the photolithography-defined pattern is transferred to the SiO2 layer by etching process, and the area not covered by SiO2 is the thermal oxidation area; The thermal oxidation process is used to oxidize the SiO2 pattern-defined epitaxial wafer, and the patterned modified area is obtained in the wafer thickness direction through the surface thermal oxygen diffusion effect, completing the preparation of the selected area optical confinement microstructure; The SiO2 anti-oxidation protective layer is removed by etching, and the laser ridge structure and P-surface electrode are prepared by photolithography, etching and coating processes. The surface is covered with a SiO2 insulating layer except for the ridge window structure area. Performing mechanical thinning, rough grinding, fine grinding and polishing steps on the back side of the substrate wafer to obtain a thinned wafer; The thinned wafer is subjected to cavity surface cleavage, cavity surface coating, single tube scratching, and test sorting steps to complete the preparation of the semiconductor laser chip.

2. The method according to claim 1, characterized in that The thickness of the SiO2 layer is 2-5 μm.

3. The method according to claim 1, characterized in that The temperature of the thermal oxidation process is 800-1200° C., and the oxidation time is 1-5 hours.

4. The method according to claim 1, characterized in that: Diffusion areas are reserved on both sides of the ridge of the laser chip to reduce the influence of diffusion during thermal oxidation on the light-emitting point on the cavity surface below the ridge.

5. A method for manufacturing a semiconductor laser, characterized in that: The following steps are involved: Depositing a SiO2 layer on the laser epitaxial wafer, wherein the SiO2 serves as an ion implantation protection layer; The ion implantation area is defined on the surface of the laser epitaxial wafer by photolithography, and the photolithography-defined pattern is transferred to the SiO2 layer by etching process, and the area not covered by SiO2 is the ion implantation area; The ion implantation process is used to selectively implant ions into the SiO2 pattern-defined epitaxial wafer, and a patterned modified area is obtained in the wafer thickness direction through surface ion implantation to complete the preparation of the selective optical confinement microstructure; The SiO2 ion implantation protection layer is removed by etching, and the laser ridge structure and P-surface electrode are prepared by photolithography, etching and coating processes. The surface is covered with a SiO2 insulating layer except for the ridge window structure area. Performing mechanical thinning, rough grinding, fine grinding and polishing steps on the back side of the substrate wafer to obtain a thinned wafer; The thinned wafer is subjected to cavity surface cleavage, cavity surface coating, single tube scratching, and test sorting steps to complete the preparation of the semiconductor laser chip.

6. The method according to claim 5, characterized in that The thickness of the SiO2 layer is 100-1000nm.

7. The method according to claim 5, characterized in that Diffusion areas are reserved on both sides of the ridge of the laser chip to reduce the impact of diffusion during ion implantation on the light-emitting point on the cavity surface below the ridge.

8. A method for manufacturing a semiconductor laser, characterized in that: The following steps are involved: The substrate surface of the laser epitaxial wafer is polished by grinding and polishing technology to obtain an epitaxial substrate with a smooth and light-transmitting surface; On the transparent substrate side, a patterned modified area is obtained in the wafer thickness direction by laser irradiation modification technology to complete the preparation of the selected area optical confinement microstructure; The laser ridge structure and P-side electrode are prepared by photolithography, etching and coating processes, and the surface is covered with a SiO2 insulating layer except for the ridge window structure area; Performing mechanical thinning, rough grinding, fine grinding and polishing steps on the back side of the substrate wafer to obtain a thinned wafer; The thinned wafer is subjected to cavity surface cleavage, cavity surface coating, single tube scratching, and test sorting steps to complete the preparation of the semiconductor laser chip.

9. The method according to claim 8, characterized in that The selected optical confinement microstructures obtained by the laser irradiation modification technology include the following three types: The laser energy of the fixed-point focused beam decreases in a direction of decreasing distance from the active area of ​​the laser epitaxial wafer until the fixed-point focused beam reaches the top surface of the laser epitaxial wafer; The laser energy of the fixed-point focused beam decreases in the direction of decreasing distance from the active area of ​​the laser epitaxial wafer until the fixed-point focused beam stops at a distance d of 20 μm from the top surface of the laser epitaxial wafer; The laser energy of the fixed-point focused beam decreases successively in the direction of decreasing distance from the active area of ​​the laser epitaxial wafer, until the fixed-point focused beam on both sides of the laser ridge stops at a distance d of 20μm from the top surface of the laser epitaxial wafer, and the nearest fixed-point focused beam below the laser ridge stops at a distance e of 25μm from the top surface of the laser epitaxial wafer.

10. A semiconductor laser manufactured according to the method according to any one of claims 1 to 9.

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