Semiconductor laser with spherical-crown-shaped substrate bottom surface and spherical-crown-shaped bottom surface processing method

Abstract

The invention discloses a semiconductor laser with a spherical-crown-shaped substrate bottom surface and a spherical-crown-shaped bottom surface processing method, and belongs to the technical field of semiconductor lasers. In a device packaging process in the prior art, residual bubbles and holes in a channel on the bottom surface of a substrate cannot be thoroughly eliminated. The semiconductor laser with the spherical-crown-shaped bottom surface of the substrate is provided with a radiating linear channel, and the bottom surface of the substrate is a spherical-crown-shaped bottom surface. Corroding the bottom of the substrate by adopting a wet etching method to obtain a spherical crown-shaped bottom surface, clamping the epitaxial wafer and a corrosive liquid with one side of the substrate facing downwards by a mechanical arm, controlling the mechanical arm to move the epitaxial wafer downwards at a constant speed in a certain speed range of 4.5-5.5 mm / s, immersing the bottom of the substrate into the corrosive liquid and staying for 25-35 seconds, the mechanical arm is controlled to move the epitaxial wafer upwards at a constant speed which is the same as the downward moving speed, and the bottom of the substrate is separated from the corrosive liquid and stays for 4.5-5.5 s; the process is repeated for 35-25 times, the corrosion depth of the bottom of the substrate of each tube core is gradually increased from the center of the bottom of the substrate of the tube core to the periphery, and the bottom surface of the substrate is in a spherical crown shape.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor laser technology. Background Technology

[0002] Semiconductor lasers are laser devices that use semiconductor materials (such as GaAs and InP) as their working medium. Based on the band structure of semiconductor materials, semiconductor lasers utilize electrical injection to induce electrons to transition from the valence band to the conduction band. When these electrons recombine with holes, photons are released, and stimulated emission amplification occurs under the feedback of the resonant cavity, ultimately outputting coherent laser light. The electro-optical conversion efficiency of semiconductor lasers is 30%–60%, with the remainder being converted into heat due to thermal effects. If this heat is not dissipated in time, it will accumulate inside the device, reducing its performance in three ways: First, increased device temperature leads to a narrowing of the semiconductor material's bandgap, causing a redshift in the emission wavelength and affecting wavelength stability; second, nonradiative recombination of charge carriers intensifies, reducing internal quantum efficiency; third, thermal stress causes cavity surface damage or solder layer failure, shortening device lifespan; and fourth, for high-power devices, the thermal lensing effect can degrade beam quality. Therefore, it is necessary to reduce the thermal effects of semiconductor lasers to stabilize the lasing wavelength, improve photoelectric conversion efficiency, suppress carrier leakage, extend device lifespan, and maintain the beam quality of high-power devices.

[0003] One existing method to improve heat dissipation in semiconductor lasers is to optimize the heat sink structure. One approach involves etching a set of channels 3 on the bottom surface 2 of the semiconductor laser die substrate 1. These channels 3 are either parallel straight lines, such as... Figure 1 As shown, it either presents as a radial curve, such as Figure 2 As shown, this is done to increase the heat dissipation area and reduce thermal resistance. However, the bottom surface 2 is a plane. After the lower electrode 4 is fabricated on the bottom surface 2, as shown... Figure 3 As shown, during the die packaging process, the solder layer 6 between the lower electrode 4 and the heat sink 5 is simultaneously filled into the channel 3. Air bubbles are very likely to remain inside the channel 3, forming voids. Due to the large depth-to-width ratio of the channel 3, the solder filling is incomplete, resulting in a high void rate, which will significantly increase the interface thermal resistance between the bottom surface 2, or more precisely, between the lower electrode 4 and the heat sink 5, thus reducing the heat dissipation effect. Summary of the Invention

[0004] In order to thoroughly eliminate residual air bubbles and voids inside the channel on the bottom surface of the semiconductor laser device during the packaging process, thereby reducing the interfacial thermal resistance between the substrate and the heat sink, improving heat dissipation, and thus enhancing the output characteristics of the device, this invention proposes a technical solution entitled "Semiconductor laser with a spherical bottom surface and a method for processing the spherical bottom surface".

[0005] The semiconductor laser of this invention, with a substrate bottom surface shaped like a spherical cap, is a front-mounted packaged device. The substrate bottom surface is etched with radially distributed channels. The key feature is that the radially distributed channels are radially linear channels 7, such as... Figure 4 As shown; the bottom surface of the substrate is a spherical cap-shaped bottom surface 8, and the depth of the linear channels 7 radiating outwards from the center of the spherical cap-shaped bottom surface 8 gradually decreases, with the maximum depth being a value within the range of 30~40μm; the distance from the top surface of the substrate to the apex of the spherical cap-shaped bottom surface 8 is the substrate thickness, with a substrate thickness ranging from 90~110μm; the height h of the spherical cap ranges from 5~25μm; and the radius of curvature R of the spherical cap is determined by the following formula: , In the formula, 'a' is the side length of the substrate, such as... Figure 5 As shown.

[0006] The present invention discloses a method for fabricating a spherical bottom surface of a semiconductor laser with a spherical bottom surface. This method involves thinning an epitaxial substrate containing several semiconductor laser die structures and etching radial channels on the bottom of the substrate. The method is characterized by using photolithography and ICP etching to etch radial linear channels 7 on each semiconductor laser die substrate on one side of the epitaxial substrate. The depth of the cleaving channels ranges from 30 to 40 μm. Simultaneously, cleaving grooves are etched between the individual dies. The depth of the cleaving grooves is the same as the depth of the radial linear channels 7, and the width of the cleaving grooves ranges from 20 to 40 μm. These cleaving grooves create an island-like structure on one side of each semiconductor laser die substrate on the epitaxial wafer. Finally, a wet etching method is used to etch the bottom of the substrate to obtain a spherical bottom surface. Crown-shaped bottom surface 8: The etchant used has isotropic etching characteristics on the substrate material. The epitaxial wafer is held by a robotic arm with one side of the substrate facing the downward etchant. The robotic arm is controlled to move the epitaxial wafer downward at a uniform speed within the range of 4.5~5.5 mm / s. The bottom of the substrate is immersed in the etchant and stays for 25~35 s. Then, the robotic arm is controlled to move the epitaxial wafer upward at the same speed as the downward movement. The bottom of the substrate is removed from the etchant and stays for 4.5~5.5 s. The above process is repeated 35~25 times. The etching depth of the substrate bottom of each die gradually increases from the center of the substrate bottom to the periphery. The bottom surface of the substrate presents a spherical crown-shaped bottom surface 8. The etching depth difference is the height h of the crown, and the value of the height h is a value within the range of 5~25 μm.

[0007] The reason why the method for processing the spherical bottom surface of the semiconductor laser with the substrate bottom surface being spherical is able to process the bottom shape of the substrate from a planar shape to a spherical shape is that during each immersion in the etching solution, the bottom of the island-shaped substrate of each die displaces the etching solution to the surrounding areas. Under the guidance of the radial linear channels 7, the displaced etching solution gradually accelerates its flow from the center to the surrounding areas, eroding the bottom of the substrate in a dynamic scouring manner. During the residence period, the bottom of the substrate is eroded in a static immersion manner, resulting in a difference in etching depth. After repeated etching in this manner, the spherical bottom surface 8 is finally obtained.

[0008] The technical effects of this invention are as follows: I. Compared with parallel straight channels and radial curved channels, radial straight channels 7: 1. Compared with parallel straight channels, radial straight channels 7 can form a stress concentration guidance path, reduce thermal stress effect, reduce random cracking or bifurcation, and at the same time adapt to the stress of heterogeneous structures, release stress locally, avoid crack penetration of the active area, and are less likely to break when cleaving epitaxial wafers, thus greatly improving the device yield. This is an important incidental technical effect brought about by this technical measure; 2. Compared with radial curved channels, the radial straight channels 7 have shorter and smoother channel paths, which is conducive to the smooth discharge of air bubbles generated in the thickness gradient welding layer 9 between the lower electrode 4 and the heat sink 5 during die packaging and welding. This effectively reduces the generation of voids and further improves the heat dissipation effect.

[0009] II. Comparison of the two: 8. Substrate spherical bottom surface and substrate planar bottom surface: 1. While reducing substrate thickness is beneficial for device heat dissipation, excessive thinning can lead to substrate embrittlement and cracking. By gradually thinning the bottom surface from the center outwards while keeping the substrate thickness constant—essentially making the bottom surface of the substrate spherical—the overall substrate thickness is effectively reduced, significantly improving device heat dissipation. 2. The space freed up by the de facto thinning is filled with solder, and the thermal conductivity of the solder is much stronger than that of the substrate material (such as InP, GaAs), further improving the heat dissipation of the device; and the thickness-gradient solder layer 9 gradually thickens from the center to the periphery, such as... Figure 6 As shown, the heat conduction effect gradually increases, guiding heat to spread more evenly and quickly to the surroundings, avoiding overheating in the central area and improving the heat dissipation effect; 3. It will not significantly cause substrate embrittlement, adapts to the stress of heterogeneous device structures, and releases stress locally. Even if cracks appear in the substrate, they will not penetrate the active region. 4. The bottom surface of the substrate is spherical. During the die packaging and soldering process, the solder can be more evenly distributed under the action of surface tension, avoiding solder accumulation, improving the uniformity of solder filling the channel, reducing the formation of voids, and then using the channel to diffuse and discharge voids and bubbles from the central area to the surrounding area, reducing the impact of voids and bubbles on device heat dissipation. 5. The contact area between the substrate spherical bottom surface 8 and the thickness-gradient welding layer 9 is increased. Due to the mechanical interlocking effect, that is, the two complementary concave and convex curved surfaces form a physical locking structure similar to gear meshing through contact and compression, which significantly improves the friction and connection stability between the two. The interface bonding force between the substrate bottom surface and the welding layer is increased, thereby reducing the risk of solder delamination and detachment, and ensuring that the heat generated by the die is conducted to the heat sink. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of a set of parallel straight channels etched on the bottom surface of a die substrate using existing technology, viewed from below.

[0011] Figure 2 This is a schematic diagram of a set of radially curved channels etched on the bottom surface of a die substrate using existing technology, viewed from below.

[0012] Figure 3 This is a magnified front view of a partial cross-section of the bottom channel of the die substrate in the prior art and the present invention.

[0013] Figure 4 This is a bottom view schematic diagram of the radial linear channel distribution on the bottom surface of the die substrate in this invention.

[0014] Figure 5 This is a front view schematic diagram illustrating the shape and parameter meaning of the spherical crown-shaped bottom surface of the die substrate in this invention.

[0015] Figure 6 This is a schematic front view of a partial structure of the die in this invention, and it also serves as an abstract drawing.

[0016] Figure 7 This is a bottom view schematic diagram of the radial linear channels and cleavage grooves etched on the epitaxial wafer of several quantum cascade semiconductor laser die structures fabricated according to the present invention.

[0017] Figure 8 This is a bottom view schematic diagram of the radial straight channels and cleavage grooves etched on the epitaxial wafer of several vertical cavity surface-emitting semiconductor laser die structures fabricated according to the present invention. Detailed Implementation

[0018] The invention will be further illustrated below by way of example.

[0019] Example 1: The semiconductor laser with a spherical cap-shaped substrate bottom surface of the present invention is a front-mounted packaged device, and its type is a quantum cascade semiconductor laser. Radial channels are etched on the bottom of the substrate, and the radially distributed channels are radial linear channels 7, such as... Figure 4 As shown. The bottom surface of the substrate is a spherical cap-shaped bottom surface 8. Straight grooves 7 radiate outwards from the center of the spherical cap-shaped bottom surface 8, with the depth gradually decreasing. The maximum depth is 30 μm. The distance from the top surface of the substrate to the apex of the spherical cap-shaped bottom surface 8 is the substrate thickness, which is 90 μm. The height h of the spherical cap is 5 μm, and the radius of curvature R of the spherical cap is given by the formula... Determine, where 'a' is the substrate side length, as shown in the formula. Figure 5 As shown.

[0020] The quantum cascaded semiconductor laser has a Ti-Au film as its upper electrode, an InGaAs layer as its ohmic contact layer, an InP layer as its upper waveguide layer, an InGaAs / InAlAs layer as its active cascaded gain region, a quantum well cascade structure, an emission wavelength of 9 μm, an InP layer as its lower waveguide layer, an InP layer as its substrate 1, a Ti-Au film as its lower electrode 4, and a gradually thickening bonding layer 9 that increases in thickness from the center outwards. Figure 6 As shown, the solder is an Au-In alloy.

[0021] The fabrication and packaging process of the quantum cascade semiconductor laser with a spherical bottom surface is described below. An epitaxial substrate with several quantum cascade semiconductor laser die structures is thinned to 90 μm using grinding and polishing processes. Radial linear channels with a depth of 30 μm are etched on one side of each semiconductor laser die substrate using photolithography and ICP etching. Simultaneously, cleavage grooves 10 between the individual dies are etched. Figure 7 As shown, the depth of the cleavage groove 10 is the same as the depth of the radial linear channel, and the width of the cleavage groove 10 is 20 μm. On an epitaxial wafer on which several quantum cascade semiconductor laser dies have been fabricated, these dies are arranged in a single row, as shown... Figure 7As shown, the cleavage grooves 10 are distributed in parallel straight lines, making each semiconductor laser die substrate on the epitaxial wafer appear as an island on one side. A wet etching method is used to etch the bottom of the substrate to obtain a spherical bottom surface 8. The etching solution is a mixed solution of HCl:H2O2:H2O with a volume ratio of 5:1:1. This etching solution has isotropic etching characteristics for InP substrate material, with an etching rate of 1 μm / min, and is kept at a constant temperature of 30°C in the water. The epitaxial wafer is held by a robotic arm with one side of the substrate facing downwards towards the etching solution. The robotic arm is controlled to move the epitaxial wafer downwards at a uniform speed of 5.5 mm / s, immersing the bottom of the substrate in the etching solution and holding it for 25 seconds. Then, the robotic arm is controlled to move the epitaxial wafer upwards at the same speed as downwards, removing the bottom of the substrate from the etching solution and holding it for 5.5 seconds. This process is repeated 25 times, with a new etching solution every 5 times to ensure that the volume ratio of the mixed solution remains constant, thereby maintaining the isotropic etching characteristics. The etching depth at the bottom of the substrate of each die gradually increases from the center to the periphery, forming a spherical crown-shaped bottom surface 8. The etching depth difference is the height h of the crown, which is 5 μm. After etching, the epitaxial wafer is rinsed clean with deionized water. The etching morphology is observed under a microscope, and the etching depth is measured using a profilometer to ensure it meets the requirements. CH4 / H2 plasma is introduced, and graphene with a thickness of 3 μm is grown in the radial linear channel 7 using plasma-enhanced CVD. A lower electrode 4 is fabricated to cover the spherical crown-shaped bottom surface 8, and Au-In solder is used to solder the lower electrode 4 to the Cu heat sink 5, completing the packaging of the quantum cascade semiconductor laser with a spherical crown-shaped bottom surface.

[0022] Example 2: The semiconductor laser with a spherical cap-shaped substrate bottom surface of the present invention is a front-mounted packaged device, specifically a vertical-cavity surface-emitting semiconductor laser. Radial channels are etched on the bottom of the substrate; these radially distributed channels are radially linear channels 7, such as... Figure 4 As shown. The bottom surface of the substrate is a spherical cap-shaped bottom surface 8. Straight grooves 7 radiate outwards from the center of the spherical cap-shaped bottom surface 8, with the depth gradually decreasing. The maximum depth is 40 μm. The distance from the top surface of the substrate to the apex of the spherical cap-shaped bottom surface 8 is the substrate thickness, which is 110 μm. The height h of the spherical cap is 25 μm, and the radius of curvature R of the spherical cap is given by the formula... Determine, where 'a' is the substrate side length, as shown in the formula. Figure 5 As shown.

[0023] The upper electrode of the vertical-cavity surface-emitting semiconductor laser is a Ti-Pt-Au film, the ohmic contact layer is a p-type GaAs layer, the upper DBR layer is 20 pairs of alternately stacked AlGaAs layers of different compositions, the oxide confinement layer is a high-Al AlGaAs layer, the active region is a multilayer quantum well structure GaAs / AlGaAs layer, the emission wavelength is 850nm, the lower DBR layer is 36 pairs of alternately stacked AlGaAs layers of different compositions, the substrate 1 is a GaAs layer, the lower electrode 4 is a Ti-Pt-Au film, and the thickness-gradient bonding layer 9 gradually increases in thickness from the center to the periphery. Figure 6 As shown, the solder is an Au-Sn alloy.

[0024] The packaging and fabrication process of the vertical-cavity surface-emitting semiconductor laser (VCSEL) with a spherical bottom surface is described below. An epitaxial substrate containing several VCSEL die structures is thinned to 110 μm using grinding and polishing processes. Radial linear channels with a depth of 40 μm are etched on each semiconductor laser die substrate on one side of the epitaxial substrate using photolithography and ICP etching. Simultaneously, cleavage grooves 10 between the individual dies are etched. Figure 8 As shown, the depth of the cleavage groove 10 is the same as the depth of the radial linear channel, and the width of the cleavage groove 10 is 40 μm. On an epitaxial wafer on which several vertical-cavity surface-emitting diode (VCSEL) dies have been fabricated, the CCSEL dies are arranged in rows and columns, as shown... Figure 8As shown, the cleavage grooves 10 are distributed in a cross-shaped straight line, making each semiconductor laser die substrate side on the epitaxial wafer appear as an island. A wet etching method is used to etch the bottom of the substrate to obtain a spherical bottom surface 8: the etching solution is a mixed solution of H2SO4:H2O2:H2O with a volume ratio of 2:1:7. This etching solution has isotropic etching characteristics for GaAs substrate material, with an etching rate of 1.5 μm / min, and the water is kept at a constant temperature of 40℃. The epitaxial wafer is held by a robotic arm with one side of the substrate facing downwards towards the etching solution. The robotic arm is controlled to move the epitaxial wafer downwards at a uniform speed of 4.5 mm / s, immersing the bottom of the substrate in the etching solution and holding it for 35 s. Then, the robotic arm is controlled to move the epitaxial wafer upwards at the same speed as downwards, removing the bottom of the substrate from the etching solution and holding it for 4.5 s. This process is repeated 35 times, with a new etching solution every 5 times to ensure that the volume ratio of the mixed solution remains constant, thereby maintaining the isotropic etching characteristics. The etching depth at the bottom of the substrate of each die gradually increases from the center to the periphery, forming a spherical crown-shaped bottom surface 8. The etching depth difference is the height h of the crown, which is 25 μm. After etching, the epitaxial wafer is rinsed clean with deionized water. The etching morphology is observed under a microscope, and the etching depth is measured using a profilometer to ensure it meets the requirements. CH4 / H2 plasma is introduced, and graphene with a thickness of 3 μm is grown in the radial linear channel 7 using plasma-enhanced CVD. A lower electrode 4 is fabricated to cover the spherical crown-shaped bottom surface 8, and the lower electrode 4 is soldered to a Cu heat sink 5 using Au-Sn solder, completing the packaging of the vertical cavity surface-emitting semiconductor laser with a spherical crown-shaped bottom surface.

Claims

1. A semiconductor laser with a spherical cap-shaped substrate bottom surface, which is a standard packaged device, wherein radially distributed channels are etched on the substrate bottom surface, characterized in that, The radially distributed channels are radial straight channels (7); the bottom surface of the substrate is a spherical cap-shaped bottom surface (8), and the depth of the radial straight channels (7) gradually decreases from the center of the spherical cap-shaped bottom surface (8) to the surrounding area, with the maximum value of the depth being a certain value in the range of 30~40μm; The distance from the top surface of the substrate to the apex of the spherical cap (8) is the substrate thickness, which ranges from 90 to 110 μm. The height h of the spherical cap ranges from 5 to 25 μm, and the radius of curvature R of the spherical cap is determined by the following formula: ， In the formula, a is the side length of the substrate.

2. A method for fabricating the spherical bottom surface of a semiconductor laser with a spherical bottom surface, comprising thinning an epitaxial substrate having fabricated several semiconductor laser die structures, and etching radial channels on the bottom of the substrate, characterized in that... A radial linear channel (7) is etched on each semiconductor laser die substrate on one side of the epitaxial wafer substrate using photolithography and ICP etching technology. The depth ranges from 30 to 40 μm. A cleaving groove is simultaneously etched between each die. The depth of the cleaving groove is the same as the depth of the radial linear channel (7). The width of the cleaving groove is a value within the range of 20 to 40 μm. The cleaving groove makes one side of each semiconductor laser die substrate on the epitaxial wafer appear as an island. A spherical bottom surface (8) is obtained by etching the bottom of the substrate using a wet etching method. The etching solution has isotropic etching characteristics for the substrate material. The epitaxial wafer is held by a robotic arm with one side of the substrate facing the etching solution. The robotic arm is controlled to move the epitaxial wafer downward at a speed within the range of 4.5 to 5.5 mm / s. The bottom of the substrate is immersed in the etching solution and stays for 25 to 35 seconds. Then, the robotic arm is controlled to move the epitaxial wafer upward at the same speed as the downward movement. The bottom of the substrate is removed from the etching solution and stays for 4.5 to 5.5 seconds. Repeat the above process 35 to 25 times. The bottom etching depth of the substrate of each die gradually increases from the center of the bottom of the die substrate to the periphery. The bottom surface of the substrate presents a spherical crown-shaped bottom surface (8). The etching depth difference is the height h of the spherical crown. The value of the height h is a certain value in the range of 5 to 25 μm.

3. The method for processing the spherical bottom surface of a semiconductor laser with a spherical bottom surface according to claim 2, characterized in that, The semiconductor laser is a quantum cascade semiconductor laser or a vertical cavity surface-emitting semiconductor laser. The cleavage grooves (10) are distributed in parallel straight lines or in a cross-shaped straight line distribution. The substrate (1) is an InP layer or a GaAs layer. The etching solution is a mixed solution of HCl:H2O2:H2O with a volume ratio of 5:1:1 or a mixed solution of H2SO4:H2O2:H2O with a volume ratio of 2:1:

7. The etching rate of the etching solution on the substrate (1) is 1 μm / min or 1.5 μm / min. The constant temperature of the etching water is 30℃ or 40℃.

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