A method for coating the facet of a non-hermetically packaged semiconductor laser

Abstract

The application discloses a cavity surface coating method for a non-airtight packaged semiconductor laser, and is suitable for the technical field of semiconductor lasers. The film system structure obtained by the cavity surface coating method for the non-airtight packaged semiconductor laser has a SiN film layer stress of only 100 Mpa, which is 14 times lower than that of the existing SiN film layer, and a corrosion resistance to hydrofluoric acid solution which is 12 times slower than that of the SiN grown by PECVD. The stress defects are released, and the compactness is further enhanced on the basis of the original compactness. The refractive index of the material in the near-infrared waveband is about 2.0, which meets the requirement of the theoretical parameter of the optical thin film design of the laser, and the SiN film layer is compact, well matched with the bar strip lattice, low in defect density, small in stress, firmly combined with the bar strip cleavage surface, and can effectively prevent the external water and oxygen from penetrating the contact cleavage surface, so that the stability of the laser in the high-temperature and high-humidity environment is ensured.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, and more specifically, to a method for coating the cavity surface of a non-hermetic semiconductor laser. Background Technology

[0002] Optical modules are the core hardware foundation of network communication devices. The core optoelectronic chips, especially semiconductor laser chips, require hermetic packaging to ensure the long-term stable operation of the entire optical module, which significantly increases the cost of optical module production. With the advancement of optical communication technology, non-hermetic packaging technology is considered the future trend, effectively reducing the difficulty and cost of optical module production.

[0003] For optical modules, the surface coating technology of semiconductor lasers is crucial in determining whether the laser can operate stably in non-hermetically sealed environments. The surface of a semiconductor laser is formed by cleavage planes. When these cleaved surfaces encounter moisture or oxygen, dangling bonds easily form defect centers, causing rapid laser failure. Therefore, surface coating is necessary to effectively prevent contact between the surface and external water or oxygen. Typically, the surface coating not only provides protection but also controls surface reflectivity, significantly improving the laser's output power.

[0004] In laser manufacturing, to prevent water and oxygen contamination of the cavity surface, the cleavage coating process is strictly controlled, limiting the cleavage time to 1-4 hours. This involves rapid ion cleaning of the cleaved cavity surface under high vacuum, followed by thin film deposition. While this method can significantly improve chip lifespan, it still falls short of the requirements for non-hermetic packaging. In high-temperature and high-humidity environments, conventional film systems are insufficient to prevent water and oxygen from penetrating the cavity surface, and may even react with water and oxygen, causing the film to peel off and rapidly degrading the chip's optical performance.

[0005] Therefore, in order to ensure the stability of the laser during long-term operation in high temperature and high humidity environments, a dense and stable cavity film layer must be designed to meet the application requirements of the laser in harsh environments.

[0006] The prior art document (CN115896711A) discloses a method for laser cavity surface coating under non-hermetic packaging conditions and a semiconductor laser, and specifically discloses the following technical features: including the following steps: (1) cleaving the semiconductor laser wafer into bars, and depositing passivation layers on the front cavity surface and the back cavity surface of the bars respectively; (2) depositing an antireflection film on the front cavity surface of the bars and depositing a high reflectivity film on the back cavity surface of the bars; (3) depositing Ta2O5 thin films on the front cavity surface and the back cavity surface of the bars respectively.

[0007] Prior art document (CN117004913A) discloses a method for coating an optical thin film on the end face of a semiconductor laser and a semiconductor laser, and specifically discloses the following technical features: A method for coating an optical thin film on the end face of a semiconductor laser includes: cleaning the output cavity surface and the back cavity surface of the laser using an electron cyclotron resonant sputtering machine with a microwave ion source; coating the output cavity surface with a first aluminum oxide film and the back cavity surface with a third aluminum oxide film using an electron cyclotron resonant sputtering machine via radio frequency sputtering; coating the remaining film layer of the antireflection film on the output cavity surface using an electron beam evaporation method; and coating the remaining film layer of the high reflectivity film on the back cavity surface using an electron beam evaporation method.

[0008] While coating the cavity surface of semiconductor lasers using the methods described above can improve chip stability and extend lifespan under normal conditions, it is difficult to meet the requirements of non-hermetic packaging. In high-temperature and high-humidity environments, typical film systems are unable to prevent water and oxygen from penetrating the cavity surface, and may even react with water and oxygen, leading to film detachment. The Si3N4 thin films generated using electron cyclotron resonant sputtering typically exhibit compressive stress exceeding 1000 MPa, a common drawback of dense films. This not only fails to protect the cavity surface but may also create new film defects, causing laser failure. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a method for cavity surface coating of non-hermetic semiconductor lasers that can reduce film stress and improve film density.

[0010] The technical solution adopted by this invention to solve its technical problem is as follows: the method for coating the cavity surface of a non-hermetic-sealed semiconductor laser includes the following steps:

[0011] A. Disassemble the semiconductor laser wafer into bars and place them in a fixture that holds the bars;

[0012] B. A first film layer, which is a silicon nitride film, is deposited on the front and back surfaces of the bar cleavage plane using an electron cyclotron resonance sputtering machine. The deposition process of the silicon nitride film layer is as follows:

[0013] B1. Place the clamp holding the bar into the electron cyclotron resonant sputtering machine, then close the baffle of the electron cyclotron resonant sputtering machine, and bombard the Si target material to be used with argon ions for 1 min-5 min. The microwave power is 250W-400W, the radio frequency power is 250W-400W, and the Ar flow rate is 40sccm.

[0014] B2. Open the baffle and perform N2 plasma milling on the front and back surfaces of the bar strip cleavage surface before and after light output;

[0015] B3. Next, the front and back surfaces of the bar stripe cleavage surface after N2 plasma milling are subjected to pure Si sputtering. The process parameters are as follows: microwave power is 500W, radio frequency power is 500W, kinetic energy gas is Ar, Ar flow rate is 40sccm, and sputtering time is 15 seconds.

[0016] B4. Close the baffle again and perform a pre-sputtering process for 1-5 minutes without sputtering the bar strip. The parameters of the pre-sputtering process are as follows: microwave power is 290W, radio frequency power is 275W, kinetic energy gas is Ar with a flow rate of 40 sccm, process reaction gas source is N2 with a flow rate of 4.5 sccm, and the chamber ambient temperature is 150 degrees Celsius.

[0017] B5. Open the baffle and perform thermal deposition on the front and back surfaces of the bar strip cleavage surface. The thermal deposition process parameters are as follows: microwave power is 290W, radio frequency power is 275W, kinetic energy gas is Ar with a flow rate of 40 sccm, process reaction gas source is N2 with a flow rate of 4.5 sccm, and the chamber ambient temperature is 150 degrees Celsius.

[0018] B6. After the SiN thin film growth is completed on the front and back surfaces of the bar cleavage plane, thermal annealing is performed to release stress.

[0019] A. A second film layer is fabricated on the first film layer surface of the bar cleavage surface before and after light emission using electron beam evaporation technology to obtain the bar cleavage surface cavity thin film system structure.

[0020] Furthermore, in step B2, the parameters of the N2 plasma milling are as follows: microwave power 150W-200W, radio frequency power 150W-200W, N2 flow rate 20sccm, and Ar with a flow rate of 3sccm is introduced simultaneously with N2. The N2 plasma milling position is P2, 25cm away from the cavity surface, and the cleaning time is 3min-5min.

[0021] Furthermore, in step B6, the process of releasing stress through thermal annealing is as follows: First, the ambient temperature of the chamber is raised to 200 degrees Celsius and maintained for 30 minutes. Then, the temperature is increased by 20 degrees Celsius every 10 minutes until it reaches 300 degrees Celsius and is maintained for 30 minutes. Then, the heating function is turned off, allowing the chamber and the bar to cool down naturally.

[0022] Furthermore, in step C, the second film layer is a dense antireflection film or a high-reflection film composed of one or more of the following materials: Si, SiO2, Ta2O5, TiO2, and Al2O3.

[0023] The beneficial effects of this invention are as follows: The film structure obtained using the cavity surface coating method for non-hermetic semiconductor lasers described in this invention has a SiN film layer compressive stress of only 100 MPa, which is 14 times lower than the stress of existing SiN films. This makes the originally compressed silicon nitride film layer structure with regional defects closer to the thermodynamic equilibrium state, resulting in a more regular atomic arrangement and a more complete network structure. It optimizes the dissociation and transport processes of the reactant gases, making the stoichiometry of the film closer to the ideal Si3N4, and the Si-N bond network more complete. Furthermore, the corrosion rate of the film is lower than that obtained by PECVD. The growth of SiN is 12 times slower, and while stress defects are released, the density is further enhanced. The refractive index of the material is about 2.0 in the near-infrared band, which meets the theoretical parameter requirements for laser optical thin film design. It is a very suitable isolation layer for lasers in non-hermetically sealed environments. Only a 5-50nm silicon nitride layer is needed as a water-proof protective layer. The Si3N4 film is dense, has good matching with the bar strip lattice, low defect density, low stress, and strong bonding with the bar strip cleavage surface. It can effectively prevent external water and oxygen from penetrating into the contact cleavage surface and ensure the stability of the laser in high temperature and high humidity environments. Attached Figure Description

[0024] Figure 1 This is a cross-sectional schematic diagram of the bar-striped cavity thin film system structure described in this invention. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The present invention provides a method for coating the cavity surface of a non-hermetic-sealed semiconductor laser, comprising the following steps:

[0027] A. Disassemble the semiconductor laser wafer into bars and place them in a fixture that holds the bars;

[0028] B. A first film layer, which is a silicon nitride film, is deposited on the front and back surfaces of the bar cleavage plane using an electron cyclotron resonance sputtering machine. The deposition process of the silicon nitride film layer is as follows:

[0029] B1. Place the clamp holding the bar into the electron cyclotron resonant sputtering machine, then close the baffle of the electron cyclotron resonant sputtering machine. Perform argon ion bombardment on the Si target material to be used for 1-5 minutes, with microwave power of 250W-400W, RF power of 250W-400W, and Ar flow rate of 40 sccm. The purpose is to remove dirt, oxide layers, and other impurities from the target surface.

[0030] B2. Open the baffle and perform N2 plasma milling on the front and rear surfaces of the bar stripe cleavage surface. The N2 plasma milling can be performed using existing conventional parameters, but this invention provides a preferred solution: the parameters for the N2 plasma milling are as follows: microwave power 150W-200W, RF power 150W-200W, N2 flow rate 20 sccm, and Ar flow rate 3 sccm simultaneously with the N2 flow. The N2 plasma milling height is position P2, 25cm from the cavity surface, and the cleaning time is 3-5 minutes. Because the electron cyclotron resonant sputtering machine relies on pure N2... Achieving resonance at this microwave power (150W-200W) is difficult. By introducing an extremely low order of magnitude of Ar (3 sccm), the microwave source is stabilized, which in turn stabilizes the ion beam. Furthermore, the minimum order of magnitude of argon required for stable microwave resonance (3 sccm) is found. This minimizes the absolute number of high-mass argon atoms and ions, while maximizing the use of lower-mass nitrogen atoms and ions to bombard the bar cleavage surface. This achieves a finer cleaning effect while preventing excessive ion bombardment damage to the laser cavity surface. This invention utilizes an N2 flow rate on the order of magnitude of the maximum flow rate of an electron cyclotron resonance sputtering machine. (20 sccm) This approach maximizes nitrogen ion ionization. While keeping the total microwave resonant power constant and as low as possible, it imparts lower ionic kinetic energy to each nitrogen ion. Simultaneously, the conventional N2 plasma milling height P5 (approximately the central film formation position with the best uniformity, 20 cm from the cavity surface) on the bar cleavage surface was changed to P2, further from the microwave source, increasing the ion free path distance. This setting also aims to reduce the bombardment intensity of nitrogen ions. Hydrogen ions would be more effective here, but nitrogen is used to create a nitriding layer for the SiN film to be formed, creating a synergistic effect; therefore, hydrogen ions were not used for cleaning. After N2 plasma milling, the film can be deposited at the optimal P5 position during film formation. The main benefits of electron cyclotron resonance N2 plasma milling are: compared to commonly used magnetron radio frequency sources and Hall sources, electron cyclotron resonance technology produces N ions with lower energy and higher density, effectively removing surface oxides and contaminants to obtain a cleaner, more active surface. This prevents high-energy particles from damaging the laser quantum well and causing a decline in laser performance. Simultaneously, N particle cleaning nitrides the surface, pre-forming a nitride layer with a chemical composition similar to SiN, effectively improving the bonding force between the SiN layer and the bar cleavage plane.

[0031] B3. Next, the front and back surfaces of the bar cleavage surface after N2 plasma milling are treated with pure Si sputtering. The process parameters are as follows: microwave power 500W, RF power 500W, kinetic gas Ar, Ar flow rate 40 sccm, sputtering time 15 seconds. This step is mainly to lay a layer of Si to fill the surface defects and bond vacancies of the bar cleavage surface, and combine with N to form a denser nitride layer, resulting in better isolation. This invention uses an electron cyclotron resonant sputtering machine for N2 plasma cleaning under specific parameters. High-density, low-energy N2 plasma cleaning, when time and power parameters are properly controlled, can effectively remove cavities. The natural oxide layer formed on the surface and any organic contaminants that may be present can activate the surface, causing the surface atomic bonds to break and forming a more active and cleaner surface. This results in better chemical compatibility with the SiN film, allowing for nucleation and growth in a denser and less defective manner, reducing pinholes and interface states, thereby improving the quality and passivation capability of the SiN film itself. Using active nitrogen ions and atoms to clean the cavity surface typically reacts with the exposed semiconductor material (usually GaAs, InGaAs, or Si) surface to form an extremely thin nitride layer (such as GaN / SiNx). This in-situ generated nitride layer itself is a high-quality passivation layer, which can effectively fill the dangling bonds on the surface and reduce the surface state density.

[0032] B4. Close the baffle again and perform a pre-sputtering process for 1-5 minutes without sputtering the bar strip. The parameters of the pre-sputtering process are as follows: microwave power is 290W, RF power is 275W, kinetic gas is Ar with a flow rate of 40 sccm, process reaction gas source is N2 with a flow rate of 4.5 sccm, and the chamber ambient temperature is 150 degrees Celsius. The pre-sputtering process is to change the entire chamber state to a stable SIN deposition state.

[0033] B5. Open the baffle and perform thermal deposition on the front and back surfaces of the bar cleavage plane. The thermal deposition process parameters are as follows: microwave power is 290W, RF power is 275W, kinetic energy gas is Ar with a flow rate of 40 sccm, process reaction gas source is N2 with a flow rate of 4.5 sccm, and chamber ambient temperature is 150 degrees Celsius. Because electron cyclotron resonant sputtering is a room-temperature sputtering deposition method, SiN obtained by electron cyclotron resonant sputtering at room temperature is a high compressive stress film with a stress exceeding 1400 MPa (the compressive stress of SiN obtained by PECVD is usually 300 MPa). Although the SiN grown by ECR... It has excellent density (its resistance to hydrofluoric acid solution corrosion rate is 9 times slower than that of SiN grown by PECVD), but excessive compressive stress can cause the film to wrinkle or even bubble and fall off, making it unsuitable as a contact layer for the laser cavity surface. In order to obtain low-stress SiN, we first stabilized the cavity temperature at 150℃ before the coating process and held it at that temperature for 30 minutes to maintain a stable cavity environment. We used 290W microwave power, 275W RF power, 40sccm argon gas as the power gas / ion milling bombardment source during the film formation process, and 4.5sccm N2 as the process reaction gas source. The cavity environment was maintained at 150 degrees Celsius to complete the coating of low-stress SiN.

[0034] B6. After the SiN thin film growth is completed on the front and back surfaces of the bar strip cleavage surface, thermal annealing is performed to release stress. At this time, the equipment is switched back to manual operation mode. The temperature in the chamber is raised to 200 degrees Celsius and maintained for 30 minutes. Then, the temperature is increased by 20 degrees Celsius every 10 minutes until it reaches 300 degrees Celsius and is maintained for 30 minutes. Then, the heating function is turned off, allowing the chamber and the substrate to cool down naturally. Due to the extremely low pressure environment, the chamber itself cools down very slowly. This gradual heating and cooling process further releases the defects in the SiN film layer and releases stress without damaging the film structure. Since the thermal annealing process is performed on the entire substrate, all bar strip products can be arranged on the fixture to complete this step. This solves the problem that the annealing process of the bar strip itself is easily damaged and cannot be batch operated, meeting the production efficiency requirements.

[0035] C. A second film layer is fabricated on the surface of the first film layer on the front and back surfaces of the bar cleavage plane using electron beam evaporation technology to obtain a bar cleavage plane cavity thin film system structure. The second film layer is a dense antireflection film or a high reflection film composed of one or more of the following materials: Si, SiO2, Ta2O5, TiO2, and Al2O3.

[0036] The film structure obtained using the above method exhibits a SiN film compressive stress of only 100 MPa, which is 14 times lower than the stress of existing SiN films. This brings the previously compressed silicon nitride film structure, which contained regional defects, closer to a thermodynamic equilibrium state. The resulting atomic arrangement is more regular, the network structure is more complete, and the dissociation and transport processes of the reactant gases are optimized. This makes the stoichiometry of the film closer to the ideal Si3N4, and the Si-N bond network is more complete. Furthermore, the corrosion rate of the film in hydrofluoric acid solution is 12 times slower than that of SiN grown by PECVD, and the stress deficiency is reduced. While the trap is released, the density is further enhanced on the original basis. The refractive index of the material is about 2.0 in the near-infrared band, which meets the theoretical parameter requirements for laser optical thin film design. It is a very suitable isolation layer for lasers in non-airtight environments. Only a 5-50nm silicon nitride layer is needed as a water-proof protection layer. The SiN film is dense, has good matching with the bar strip lattice, low defect density, low stress, and strong bonding with the bar strip cleavage surface. It can effectively prevent external water and oxygen from penetrating into the contact cleavage surface and ensure the stability of the laser in high temperature and high humidity environments.

[0037] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for coating the cavity surface of a non-hermetic-sealed semiconductor laser, characterized in that: Includes the following steps: A. Disassemble the semiconductor laser wafer into bars and place them in a fixture that holds the bars; B. A first film layer, which is a silicon nitride film, is deposited on the front and back surfaces of the bar cleavage plane using an electron cyclotron resonance sputtering machine. The deposition process of the silicon nitride film layer is as follows: B1. Place the clamp holding the bar into the electron cyclotron resonant sputtering machine, then close the baffle of the electron cyclotron resonant sputtering machine, and bombard the Si target material to be used with argon ion for 1 min-5 min. The microwave power is 250W-400W, the radio frequency power is 250W-400W, and the Ar flow rate is 40sccm. B2. Open the baffle and perform N2 plasma milling on the front and back surfaces of the bar strip cleavage surface before and after light output; B3. Next, the front and back surfaces of the bar stripe cleavage surface after N2 plasma milling are subjected to pure Si sputtering. The process parameters are as follows: microwave power is 500W, radio frequency power is 500W, kinetic energy gas is Ar, Ar flow rate is 40sccm, and sputtering time is 15 seconds. B4. Close the baffle again and perform a pre-sputtering process for 1-5 minutes without sputtering the bar strip. The parameters of the pre-sputtering process are as follows: microwave power is 290W, radio frequency power is 275W, kinetic energy gas is Ar with a flow rate of 40 sccm, process reaction gas source is N2 with a flow rate of 4.5 sccm, and the chamber ambient temperature is 150 degrees Celsius. B5. Open the baffle and perform thermal deposition on the front and back surfaces of the bar strip cleavage surface. The thermal deposition process parameters are as follows: microwave power is 290W, radio frequency power is 275W, kinetic energy gas is Ar with a flow rate of 40 sccm, process reaction gas source is N2 with a flow rate of 4.5 sccm, and the chamber ambient temperature is 150 degrees Celsius. B6. After the SiN thin film growth is completed on the front and back surfaces of the bar cleavage plane, thermal annealing is performed to release stress. C. A second film layer is fabricated on the first film layer surface of the bar cleavage surface before and after light emission using electron beam evaporation technology to obtain the bar cleavage surface cavity thin film system structure.

2. The method for cavity surface coating of a non-hermetic-sealed semiconductor laser according to claim 1, characterized in that: In step B2, the parameters of the N2 plasma milling are as follows: microwave power 150W-200W, radio frequency power 150W-200W, N2 flow rate 20sccm, and Ar with a flow rate of 3sccm is introduced at the same time as N2. The N2 plasma milling position is P2, 25cm away from the cavity surface, and the cleaning time is 3min-5min.

3. The method for cavity surface coating of a non-hermetically sealed semiconductor laser according to claim 1, characterized in that: In step B6, the process of releasing stress through thermal annealing is as follows: First, the ambient temperature of the chamber is raised to 200 degrees Celsius and maintained for 30 minutes. Then, the temperature is increased by 20 degrees Celsius every 10 minutes until it reaches 300 degrees Celsius and is maintained for 30 minutes. Then, the heating function is turned off to allow the chamber and the bar to cool down naturally.

4. The method for cavity surface coating of a non-hermetically sealed semiconductor laser according to claim 1, characterized in that: In step C, the second film layer is a dense antireflection film or a high reflectance film composed of one or more of the following materials: Si, SiO2, Ta2O5, TiO2, and Al2O3.

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