Semiconductor laser cavity surface coating method for non-airtight packaging

Abstract

The invention discloses a semiconductor laser cavity surface coating method for non-airtight packaging, and is suitable for the technical field of semiconductor lasers. The pressure stress of the obtained SiN film layer of the film system structure obtained by the method for coating the cavity surface of the semiconductor laser for non-airtight packaging is only 100Mpa and is 14 times lower than that of the existing SiN film layer, the hydrofluoric acid solution corrosion resistance rate is 12 times slower than that of SiN grown by PECVD (Plasma Enhanced Chemical Vapor Deposition), the stress defect is released, the compactness is further enhanced on the original basis, and the service life of the semiconductor laser is prolonged. The refractive index of the material in the near-infrared band is about 2.0, the requirement for theoretical parameters of laser optical thin film design is met, the isolation layer is very suitable for coping with the non-airtight environment and makes contact with a laser, the SiN film layer is compact, good in lattice matching with a bar, low in defect density, small in stress and firm in combination with the cleavage surface of the bar, and the performance of the isolation layer is greatly improved. External water and oxygen can be effectively prevented from permeating and contacting a cleavage surface, and the stability of the laser in a high-temperature and high-humidity environment is ensured.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor lasers, more particularly to a cavity surface coating method for non-hermetic packaging semiconductor lasers. BACKGROUND

[0002] As the core hardware device of network communication, the optical module requires hermetic packaging of the core optoelectronic chip, especially the semiconductor laser chip, to ensure the long-term stable operation of the entire optical module, which greatly increases the cost in the production process of the optical module. With the progress of optical communication technology, non-hermetic packaging technology is considered to be the future development trend, which can effectively reduce the difficulty and cost in the production of optical modules.

[0003] For optical modules, the cavity surface coating technology of semiconductor lasers is the key to determining whether the laser can work stably in a non-hermetic environment. The cavity surface of a semiconductor laser is formed by cleaving, and the dangling bonds on the cleaved surface are prone to form defect centers when exposed to water vapor or oxygen, causing rapid failure of the laser. Therefore, it is necessary to coat the laser cavity surface to effectively prevent the cavity surface from contacting water and oxygen from the outside. Generally, the cavity surface coating not only protects the cavity surface, but also controls the reflectivity of the cavity surface, which can significantly improve the output power of the laser.

[0004] In the process of manufacturing lasers, in order to prevent the cavity surface from being contaminated by water and oxygen, the process environment is strictly controlled during the cleaving and coating process, and the cleaving time is controlled within 1-4 hours. The cleaved cavity surface is quickly ion cleaned in a high vacuum environment, and thin film deposition is performed. Although this method can better improve the service life of the chip, it still cannot meet the requirements of non-hermetic packaging. In a high temperature and high humidity environment, it is difficult for general film systems to prevent water and oxygen in the environment from penetrating into the cavity surface, and even the film layer may fall off due to reaction with water and oxygen, causing rapid degradation of the optical performance of the chip.

[0005] Therefore, in order to ensure the stability of the laser in a high temperature and high humidity environment for a long time, a dense and stable cavity surface film layer must be designed to meet the application of the laser in harsh environments.

[0006] The comparative document (CN115896711A) discloses a laser cavity surface coating method applied to non-hermetic packaging conditions and a semiconductor laser, and specifically discloses the following technical features: (1) cleaving the semiconductor laser wafer into bars, and evaporating a passivation layer on the front and rear cavity surfaces of the bars, respectively; (2) evaporating an anti-reflection film on the front cavity surface of the bar and a high-reflection film on the rear cavity surface of the bar; (3) evaporating a Ta2O5 thin film on the front and rear cavity surfaces of the bar, respectively.

[0007] The prior art document (CN117004913A) discloses a semiconductor laser end face optical film coating method and a semiconductor laser, and specifically discloses the following technical features: a semiconductor laser end face optical film coating method, comprising: cleaning the light emitting cavity surface and the back cavity surface of the laser by using an electron cyclotron resonance sputtering machine microwave ion source; covering the light emitting cavity surface with a first aluminum oxide film and the back cavity surface with a third aluminum oxide film by using an electron cyclotron resonance sputtering machine through a radio frequency sputtering method; covering the remaining film layer of the antireflection film on the light emitting cavity surface by using an electron beam evaporation method; and covering the remaining film layer of the high-reflection film on the back cavity surface by using an electron beam evaporation method.

[0008] After the semiconductor laser cavity surface is coated by the above method, the stability of the chip can be improved, and a longer service life can be maintained in a normal environment, but it is difficult to meet the requirements of non-airtight packaging. In a high temperature and high humidity environment, the general film system is difficult to prevent water and oxygen in the environment from penetrating into the cavity surface, and even reacts with water and oxygen to cause the film layer to fall off. The stress of the Si3N4 film generated by the electron cyclotron resonance sputtering machine is generally a compressive stress of more than 1000 MPa, which is a common shortcoming of dense film layers. This not only cannot protect the cavity surface of the product, but even forms new film layer defects, resulting in failure of the laser. SUMMARY

[0009] The technical problem to be solved by the present application is to provide a semiconductor laser cavity surface coating method for non-airtight packaging which can reduce film layer stress and improve film layer density.

[0010] The technical solution adopted by the present application to solve the technical problem is: the semiconductor laser cavity surface coating method for non-airtight packaging, comprising the following steps:

[0011] A. dissociate the semiconductor laser wafer into bar strips and place them in a clamp for clamping the bar strips;

[0012] B. deposit a first film layer as a passivation film on the front surface and the rear surface of the bar strip cleavage surface by using an electron cyclotron resonance sputtering machine, wherein the first film layer is a silicon nitride film layer; and the film forming process of the silicon nitride film layer is as follows:

[0013] B1. place the clamp for clamping the bar strips into the electron cyclotron resonance sputtering machine, then close the baffle of the electron cyclotron resonance sputtering machine, and perform argon ion bombardment on the Si target material to be used for 1-5 min, with a microwave power of 250-400 W, a radio frequency power of 250-400 W, and an Ar flow rate of 40 sccm;

[0014] B2. open the baffle and perform N2 plasma milling on the front surface and the rear surface of the bar strip cleavage surface;

[0015] B3, then the bar bar cleavage surface light emitting front surface and back surface of the N2 plasma milling process, the process parameters are as follows: microwave power is 500 W, RF power is 500 W, kinetic gas is Ar, Ar flow is 40 sccm, sputtering time is 15 seconds;

[0016] B4, re-close the shutter, in the bar bar is not sputtered to 1min-5min of pre-sputtering process, the parameters of the pre-sputtering process are as follows: microwave power is 290 W, RF power is 275 W, kinetic gas is Ar, Ar flow is 40 sccm, process reaction gas source is N2, N2 flow is 4.5sccm, chamber ambient temperature is 150 degrees Celsius;

[0017] B5, open the shutter to the bar bar cleavage surface light emitting front surface and back surface for thermal deposition film, the thermal deposition film process parameters are as follows: microwave power is 290 W, RF power is 275 W, kinetic gas is Ar, Ar flow is 40 sccm, process reaction gas source is N2, N2 flow is 4.5sccm, chamber ambient temperature is 150 degrees Celsius;

[0018] B6, when the bar bar cleavage surface light emitting front surface and back surface of the SiN film growth is completed after the thermal annealing stress release treatment;

[0019] A, in the bar bar cleavage surface light emitting front surface and back surface of the first film layer surface respectively using electron beam evaporation technology to make the second film layer to get bar bar cleavage surface cavity film membrane system structure.

[0020] Further, in step B2, the parameters of the N2 plasma milling are as follows: microwave power is 150 W-200 W, RF power is 150 W-200 W, N2 flow is 20 sccm, while the N2 is imported, the flow of Ar is 3sccm, the N2 plasma milling position is P2, the distance from the cavity is 25 cm, the cleaning time is 3min-5min.

[0021] Further, in step B6, the thermal annealing stress release treatment process is as follows: first, the chamber ambient temperature is raised to 200 degrees Celsius for 30 min, then every 10 min, the temperature is raised by 20℃, until it is raised to 300℃, then maintain for 30 min, then close the heating function, and the chamber and the bar are naturally cooled.

[0022] Further, in step C, the second film layer is a dense anti-reflection film or a high reflection film composed of one or more of Si, SiO2, Ta2O5, TiO2, Al2O3.

[0023] The beneficial effects of the present application: the film system structure obtained by the method for coating the cavity surface of a non-hermetic packaged semiconductor laser according to the present application has a SiN film layer stress of only 100 MPa, which is 14 times lower than the stress of the existing SiN film layer, so that the overall compressed and regionally defective silicon nitride film layer structure is closer to the thermodynamic equilibrium state, the atomic arrangement is more regular, the network structure is more complete, the dissociation and transport process of the reaction gas is optimized, the stoichiometric ratio of the thin film is closer to the ideal Si3N4, and the Si-N bond network is more complete; the corrosion rate of the hydrogen fluoride solution is 12 times slower than that of the SiN grown by PECVD, while the stress defects are released, the density is further enhanced on the basis of the original, the refractive index of the material in the near-infrared band is about 2.0, which meets the design theoretical parameter requirements of the laser optical thin film, and it is a very suitable isolation layer for the laser contact in the non-hermetic environment, only 5-50 nm of the silicon nitride layer is needed as a water protection layer, the Si3N4 film layer is dense, well matched with the bar strip lattice, low in defect density and stress, and firmly combined with the bar strip cleavage surface, which can effectively prevent external water and oxygen from penetrating and contacting the cleavage surface, and ensure the stability of the laser in a high temperature and high humidity environment. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Figure 1 is a cross-sectional schematic diagram of the bar strip cleavage surface cavity surface film system structure according to the present application. DETAILED DESCRIPTION

[0025] The technical solutions of the present application will be described below in conjunction with the embodiments, obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0026] The method for coating the cavity surface of a non-hermetic packaged semiconductor laser according to the present application comprises the following steps:

[0027] A. dissociate the semiconductor laser wafer into a bar strip and place it in a clamp for clamping the bar strip;

[0028] B. use an electron cyclotron resonance sputtering machine to deposit a first film layer as a passivation film on the front surface and the rear surface of the bar strip cleavage surface, the first film layer is a silicon nitride film layer; the film forming process of the silicon nitride film layer is as follows:

[0029] B1, put the clamp clamping the bar into the electron cyclotron resonance sputtering machine, then close the shutter of the electron cyclotron resonance sputtering machine, and perform argon ion bombardment on the Si target to be used for 1-5 min, with a microwave power of 250-400 W, a radio frequency power of 250-400 W, and an Ar flow rate of 40 sccm. The purpose is to remove impurities such as dirt and oxide layer on the surface of the target;

[0030] B2, open the shutter and perform N2 plasma milling on the front and rear surfaces of the cleavage surface of the bar. The N2 plasma milling can be performed using existing conventional parameters, but the application provides a preferred scheme: the parameters of the N2 plasma milling are as follows: a microwave power of 150-200 W, a radio frequency power of 150-200 W, an N2 flow rate of 20 sccm, and an Ar flow rate of 3 sccm while the N2 is flowing in. The N2 plasma milling height is at position P2, which is 25 cm away from the cavity surface, and the cleaning time is 3-5 min. Since it is difficult for the electron cyclotron resonance sputtering machine to start resonance with pure N2 at this microwave power (150-200 W), by introducing a very low amount of Ar (3 sccm), on the one hand, the microwave source is stabilized to stabilize the ion beam current, and on the other hand, the minimum amount of argon required for stable microwave resonance is found to be 3 sccm, which minimizes the absolute number of heavy argon atoms and argon ions as much as possible, and as many light nitrogen atoms and nitrogen ions as possible are used to bombard the surface of the bar cleavage surface, that is, a more fine cleaning effect is achieved, and the laser cavity surface is prevented from being damaged by excessive ion bombardment. The application selects the maximum amount of N2 flow (20 sccm) for the electron cyclotron resonance sputtering machine, which maximizes the ionization degree of nitrogen ions. Under the condition of constant total microwave resonance power and as small as possible, each nitrogen ion is given a smaller ion kinetic energy, and the conventional N2 plasma milling height P5 of the bar cleavage surface (the best uniformity is probably the middle film forming position, which is 20 cm away from the cavity surface) is changed to P2, which is farther away from the microwave source, increasing the ion free path distance. This setting also reduces the bombardment intensity of nitrogen ions. Hydrogen ions are better here, but nitrogen is used to lay a layer of nitriding for the SiN to be formed, which has a linkage effect, so hydrogen ions are not used for cleaning. After N2 plasma milling, the P5 position most suitable for film formation is changed back to the film formation position during film formation. The main function of electron cyclotron resonance N2 plasma milling is that, compared with the commonly used magnetron radio frequency source and Hall source, the electron cyclotron resonance technology forms N ions with low energy and high density, which can effectively remove surface oxides and dirt impurities, obtain a cleaner and more active surface, and prevent high-energy particles from damaging the laser quantum well, causing the performance of the laser to decrease. At the same time, N particle cleaning performs nitriding treatment on the surface to form a nitride layer, which has a similar chemical composition to SiN, and can effectively improve the bonding force between the SiN layer and the bar cleavage surface;

[0031] B3, then the bar bar cleavage surface after N2 plasma milling light front surface and back surface of pure Si sputtering process, the process parameters are as follows: microwave power is 500 W, RF power is 500 W, kinetic gas is Ar, Ar flow is 40 sccm, sputtering time 15 seconds; this step is mainly to pave a layer of Si element, used to fill the bar cleavage surface defects, bond vacancy, combined with N element to form a more dense nitride layer, play a better isolation effect; the application of electron cyclotron resonance sputtering machine under specific parameters of N2 plasma cleaning, high density and low energy N2 plasma cleaning in time, power parameter control can effectively remove the natural oxide layer formed on the surface of the cavity and the possible organic contaminants, can activate the surface to make the surface atomic bond break, form a more active, cleaner surface, with SIN film has better chemical compatibility, in a more dense, less defect way nucleation and growth, reduce pinhole and interface state, thereby improving the quality and passivation ability of SiN film itself; using active nitrogen ions and atoms to clean the cavity surface, usually reacts with the exposed semiconductor material (generally GaAs, InGaAs or Si) surface, forming a very 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 surface dangling bond, reduce the surface state density;

[0032] B4, re-close the shutter, in the case of bar bar is not sputtered to 1min-5min of pre-sputtering process, the parameters of the pre-sputtering process are as follows: microwave power is 290 W, RF power is 275 W, kinetic gas is Ar, Ar flow is 40 sccm, process reaction gas source is N2, N2 flow is 4.5 sccm, chamber environment temperature is 150 degrees Celsius; pre-sputtering process is to change the whole chamber state to stable SIN deposition state;

[0033] B5, before the light emitting front surface and the back surface of the cleavage surface of the bar are deposited by thermal evaporation, the process parameters of the thermal evaporation deposition are as follows: the microwave power is 290 W, the radio frequency power is 275 W, the kinetic energy gas is Ar, the Ar flow rate is 40 sccm, the process reaction gas source is N2, the N2 flow rate is 4.5 sccm, and the chamber environment temperature is 150 degrees Celsius; because electron cyclotron resonance sputtering is a deposition method of normal temperature sputtering, the SiN obtained by electron cyclotron resonance at normal temperature is a large compressive stress film (the compressive stress of the SiN obtained by PECVD is generally 300 Mpa) with a stress exceeding 1400 Mpa, although the SiN grown by ECR has good compactness (the corrosion resistance of the SiN grown by PECVD is 9 times slower than that of the SiN grown by PECVD), but the film with too large compressive stress will cause the film to wrinkle or even bubble and fall off, which is not suitable for being used as a contact layer of a laser cavity surface, in order to obtain low-stress SiN, the chamber temperature is stably controlled at 150 degrees Celsius before film deposition, the constant temperature is maintained for 30 minutes, the chamber environment is kept stable, the microwave power is 290 W, the radio frequency power is 275 W, 40 sccm of argon is used as the kinetic energy gas / ion milling source during the film forming process, 4.5 sccm of N2 is used as the process reaction gas source, and the chamber environment is kept at 150 degrees Celsius to complete the film deposition of low-stress SiN;

[0034] B6, after the SiN film growth on the light emitting front surface and the back surface of the cleavage surface of the bar is completed, a thermal annealing stress release treatment is performed; at this time, the equipment is switched back to the manual operation mode, the temperature in the chamber is raised to 200 degrees Celsius and maintained for 30 minutes, then the temperature is raised by 20 degrees Celsius every 10 minutes until it is raised to 300 degrees Celsius and maintained for 30 minutes, then the heating function is turned off, and the chamber and the substrate are naturally cooled down; because it is in an extremely low pressure environment, the chamber itself cools down very slowly, the sequential temperature rising and falling process further releases the defects of the SiN film layer and releases the stress, and at the same time, it will not damage the film layer structure, and because it is a thermal annealing process for the whole substrate, all the bar products arranged on the fixture can complete this step, solving the problem that the annealing process of the bar itself is easy to damage and cannot be operated in batches, meeting the production efficiency requirement;

[0035] C, the second film layer is made of one or more of Si, SiO2, Ta2O5, TiO2 and Al2O3, which is a dense antireflection film or a high reflection film.

[0036] The film structure obtained by the above method has a SiN film layer stress of only 100 MPa, which is reduced by 14 times compared with the existing SiN film layer stress, and makes the originally compressed and regionally defective silicon nitride film layer structure closer to the thermodynamic equilibrium state, makes the atomic arrangement more regular and the network structure more complete, optimizes the dissociation and transport process of the reaction gas, makes the stoichiometric ratio of the thin film more close to the ideal Si3N4, and the Si-N bond network is more complete; the corrosion rate of the hydrogen fluoride solution is 12 times slower than the SiN grown by PECVD, the stress defects are released, at the same time, the density is further enhanced on the basis of the original, the refractive index of the material in the near-infrared wave band is about 2.0, which meets the design theoretical parameter requirements of the laser optical thin film, and is a very suitable isolation layer for the laser contact in the non-airtight environment, only 5-50 nm of the silicon nitride layer is needed as a water protection layer, the SiN film layer is dense, well matched with the bar strip lattice, low in defect density and small in stress, and firmly combined with the bar strip cleavage surface, which can effectively prevent the external water and oxygen from penetrating into the contact cleavage surface and ensure the stability of the laser in the high temperature and high humidity environment.

[0037] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above embodiments, and the above embodiments and descriptions in the specification are only preferred examples of the present application and are not intended to limit the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application 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 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. 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 flow rate 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.

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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