A method for passivating the cavity surface of a GaN-based EEL laser chip

Abstract

The invention relates to the field of semiconductor technology, and proposes a method for passivating the cavity surface of a GaN-based EEL laser chip, comprising the following steps: S1, cavity surface dehumidification: heating the cavity surface of a bar strip to remove the moisture; S2, cavity surface cleaning: continuing to increase the temperature, and introducing gas to bombard the cavity surface; S3, cavity surface annealing: continuing to increase the temperature, and introducing gas to bombard the cavity surface, and then annealing to form a transition layer; the gas in steps S2 and S3 is one or more of O2, N2 and H2; S4, cavity surface passivation: transferring the bar strip into a passivation chamber, maintaining the annealing temperature, introducing one or more of O2, O3 or N2 to bombard the cavity surface, and forming an Al2O3, AlON or AlN single crystal film on the surface of the transition layer. The invention adopts high-temperature annealing to form a transition layer on the cavity surface. Compared with CaN, the mismatch rate between the transition layer and Al2O3, AlON and AlN is lower, it is easier to grow a single crystal film, and it will not cause light absorption of the cavity surface, thereby achieving the technical effect of increasing the cavity surface damage threshold and extending the service life of the laser.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, and in particular to a method for passivating a cavity surface of a GaN-based EEL laser chip. Background Art

[0002] Semiconductor lasers are widely used in measurement and sensing, laser radar, industrial processing, medical health, lithography and printing, laser printing and other fields due to their small size, light weight, and high electro-optical conversion efficiency. With the rapid development of high-power semiconductor lasers, more stringent requirements are also placed on the stability and reliability of laser chips.

[0003] In the manufacturing process of GaN-based laser chips, the natural cleavage surface of GaN is used as an optical resonant cavity. After high and low reflectivity dielectric films are coated on both sides of the cleavage surface, the photons in the device are amplified by the resonant cavity mode selection, and then form lasers in a direction parallel to the substrate surface and are emitted through the front cavity surface (such as Figure 1 ), therefore, the optical power density at the front cavity surface will be relatively high. Although the GaN surface is chemically inert, it will inevitably form dangling bonds after cleavage and exposure to the atmosphere. The Ga dangling bonds will react with O to form amorphous GaOX metastable oxides, and the N dangling bonds will combine with elements such as C and H. These substances will form non-radiative recombination centers on the surface. When the laser device is running, light absorption and non-radiative recombination will occur, and a large amount of heat will be generated, resulting in an increase in temperature at the cavity surface. The increase in temperature will cause the band gap at the interface to shrink, exacerbating the generation of light absorption and non-radiative recombination processes, and eventually forming COD, causing the laser device to fail.

[0004] In the existing GaN-based laser passivation technology, wide bandgap semiconductor materials such as Al2O3, AlON, and AlN are usually selected as passivation materials, and a single crystal film layer is deposited on the cavity surface to reduce the generation of dangling bonds and isolate oxygen and water vapor in the air, thereby increasing the device damage threshold. For example, CN100449888C, before coating the end face of the laser chip with optics, first uses the ECR sputtering method to coat a 3-50nm thick Al2O3 film as a passivation film, and the device's COD resistance level is significantly improved, but it is impossible to achieve customized development of a variety of passivation film materials; for example, CN102299479A, a general introduction to the passivation film AlON, Al2O3, SiAlON and other material systems and coating solutions is made, but because the lattice matching degree of each material with the GaN substrate is different, the coating difficulty is different, and the detailed description lacks pertinence and is not practical. Summary of the invention

[0005] In view of this, the present invention proposes a method for passivating the cavity surface of a GaN-based EEL laser chip, which is used to reduce the generation of catastrophic optical mirror damage (COD) and increase the service life of the laser.

[0006] The technical solution of the present invention is implemented as follows: The present invention provides a method for passivating the cavity surface of a GaN-based EEL laser chip, comprising the following steps:

[0007] S1, cavity surface degassing: cleave the CaN wafer to obtain laser chip bars, then transfer the bars into the OMBE equipment, heat the cavity surface at 180-200℃ to remove the water vapor adsorbed on the cavity surface;

[0008] S2, cavity surface cleaning: continue to raise the temperature to 200-250°C, and introduce one or more gases among O2, N2 and H2 to bombard the cavity surface to remove metastable, amorphous gallium oxides and C-containing pollutants on the cavity surface;

[0009] S3, cavity surface annealing: continue to raise the temperature to 350~400℃, and introduce one or more gases among O2, N2 and H2 to bombard the cavity surface, then anneal to repair the damaged surface of the film, form a transition layer on the cavity surface, and then use LEED to detect the surface recovery to ensure that the cavity surface after surface treatment maintains lattice integrity before plating the passivation film;

[0010] S4, cavity surface passivation: After annealing, the bar is transferred to the passivation chamber and the temperature is maintained at 350~400℃. The crucible filled with Al liquid is placed under the bar, and one or more gases of O2, O3 or N2 are introduced to bombard the cavity surface. The evaporated Al atoms react with the active O2 + / N2 + A chemical reaction occurs to form an Al2O3, AlON or AlN single crystal film on the surface of the transition layer.

[0011] The traditional cavity surface cleaning solution is to use Ar + Cleaning, by using the ion source physical bombardment to remove surface contaminants, but Ar + It is relatively heavy, causing great damage to the cavity surface, with a surface roughness of up to 3-5nm, and will introduce Ar + However, in this scheme, corresponding gases are introduced when depositing different films. + and N + The weight is light, and while removing the amorphous Ga2O and C-containing pollutants, the damage to the cavity surface is small. At the same time, the ultra-high vacuum annealing method is introduced to make the activated O + and N +It can react with the burrs on the cavity surface after bombardment to form a smooth surface, reduce the surface state of the cavity surface, and annealing can form a transition state structure of several atomic layers on the cavity surface. The transition state structure can effectively reduce the difficulty of growing a single crystal passivation film. High-quality / pollution-free wider bandgap semiconductor single crystal films can be further deposited on the surface of the transition film layer by OMBE, which can effectively prevent light absorption and non-radiative recombination, increase the cavity surface damage threshold, and improve the stability and service life of the laser.

[0012] On the basis of the above technical solution, preferably, in step S2, the gas flow rate is 2-5 sccm, the RF power is 500-700w, and the bombardment time is 5-10min.

[0013] On the basis of the above technical solution, preferably, in step S3, the gas flow rate is 20-50 sccm, the RF power is 50-100w, and the bombardment time is 30min.

[0014] On the basis of the above technical solution, preferably, in step S4, the gas flow rate is 10-20 sccm, the RF power is 200-500w, the bombardment time is 10-15min, and the film thickness is 5-30nm.

[0015] On the basis of the above technical solution, preferably, when growing the Al2O3 single crystal film, O2 is introduced into both steps S2 and S3, and O3 is introduced into step S4.

[0016] On the basis of the above technical solution, preferably, when growing the AlON single crystal film, N2 and O2 are introduced in steps S2, S3 and S4.

[0017] On the basis of the above technical solution, preferably, the flow ratio of N2:O2 is 1:2~2:1.

[0018] On the basis of the above technical solution, preferably, when growing the AlN single crystal film, N2 and H2 are introduced in both steps S2 and S3, and N2 is introduced in step S4.

[0019] On the basis of the above technical solution, preferably, the flow ratio of N2:H2 is 9:1~19:1.

[0020] On the basis of the above technical solution, preferably, after passivation is completed, an Al2O3 or SiO2 anti-reflection film is deposited on the front cavity surface, and a high-reflection film stacked with SiO2 and Ta2O5 is deposited on the rear cavity surface.

[0021] On the basis of the above technical solution, preferably, the anti-reflection film is Al2O3 or SiO2.

[0022] On the basis of the above technical solution, preferably, the high-reflective film is a high-reflective film stacked by SiO2 / Ta2O5, and SiO2 / Ta2O5 is one cycle, which requires 6-8 cycles of plating.

[0023] The method for passivating the cavity surface of a GaN-based EEL laser chip of the present invention has the following beneficial effects compared with the prior art:

[0024] (1) The present invention uses high-temperature annealing to reduce the surface state of the cavity surface and form a flat surface. At the same time, a transition layer (Ga2O3, GaON or complete GaN) of about 1nm is also formed on the cavity surface. Compared with CaN, the mismatch rate between the transition layer and Al2O3, AlON, and AlN is lower, and it is easier to grow a single crystal thin film, and it will not cause light absorption on the cavity surface, thereby achieving the technical effect of increasing the light output power, increasing the cavity surface damage threshold, and extending the service life of the laser.

[0025] (2) The present invention proposes to use O-MBE (Oxide Molecular Beam Epitaxy) technology to prepare a single crystal passivation film. OMBE is an oxide molecular beam epitaxy technology that relies on plasma O2 + Or the strong oxidation ability of O3 can realize the preparation of single-crystal oxide thin films at low temperatures. Compared with the possible pollution caused by sputtering ions in magnetron sputtering and ECR sputtering, OMBE can achieve purer single-crystal thin film growth because it is coated under ultra-high vacuum conditions, and the coating quality is better than that of sputtering. Secondly, according to the characteristics of each film material, the present invention proposes a matching cavity surface treatment method to reduce cavity surface defects as much as possible, reduce cavity surface light absorption, and improve output power. In addition, relying on the RHEED / LEED technology equipped with the MBE equipment, the quality of the passivation film can be effectively monitored. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 This is a structural diagram of a GaN-based laser chip in the prior art.

[0028] Figure 2 This is the passivation flow chart of Al2O3, AlON, and AlN single crystal films. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] The method for passivating the cavity surface of a GaN-based EEL laser chip of this embodiment comprises the following steps:

[0032] S1, dehumidification of cavity surface: cleave the GaN wafer to obtain laser chip bars, and collect the bars with a coating fixture. Then, transfer the fixture with collected bars into the sample chamber of the OMBE equipment, raise the fixture temperature to 180℃, and bake for 1.5 hours to remove the moisture adsorbed on the cavity surface.

[0033] S2, cavity surface cleaning: After baking, when the fixture temperature drops to 100°C, transfer the fixture to the pretreatment chamber. Raise the fixture temperature to 200°C (to prevent sputtering products from adsorbing on the substrate surface), introduce O2 at a flow rate of 2sccm, set the RF source energy to 500W, and set the time to 10min. + Plasma cleans the surface C and makes the surface in an amorphous state. x (Oxide) is etched away, and at the same time, the energetic O2 + Plasma penetrates several atomic layers into the GaN surface, partially opening the Ga-N bonds in the area, and O replaces N to form Ga-O bonds.

[0034] S3, cavity surface annealing: raise the temperature to 350℃, and add O2 + The plasma power was reduced to 50W to ensure that the gas could be ionized but not to damage the substrate surface. The O2 flow rate was set to 50sccm to ensure that the cavity surface was ionized with high concentration of O2. + plasma coverage, time set to 30 minutes, using O2 + The powerful oxidation ability of plasma causes all Ga-N bonds on the cavity surface to be replaced by Ga-O bonds, forming a stable Ga2O3 transition layer; at the same time, under high-temperature annealing, the cavity surface defects are also repaired, and LEED is used to detect the surface recovery.

[0035] S4, cavity surface passivation: After the above process is completed, the fixture is quickly transferred to the passivation chamber, the fixture temperature is raised to 350℃, the crucible temperature of the Al ingot is raised to 1050℃, and O2 is introduced with a flow rate of 10 sccm. +The plasma power was set to 500W to increase the ionization rate of O2. The baffles of the substrate and crucible were opened at the same time. The coating time was set to 15min and the coating rate was set to 0.5nm / min. A single-crystal Al2O3 film with a thickness of 7.5nm was formed on the cavity surface (RHEED was used to monitor the coating process). + Plasma can also be replaced by ozone, because ozone has a stronger oxidizing ability than O2 + Plasma is stronger and has no inherent energy, making it easier to form a good single crystal film at low temperatures. Therefore, ozone can be preferentially selected to complete the growth of the passivation film.

[0036] Before coating, the cavity surface is pre-treated and a layer of Ga2O3 of about 1nm is formed on the surface. The mismatch rate between Ga2O3 and Al2O3 is 7.4%, which is much smaller than the mismatch rate between Al2O3 and GaN of 16%, making it easier to grow single crystal thin films. In addition, the bandgap width of Ga2O3 is 4.9eV, that of GaN is 3.4eV, and that of Al2O3 is 8.75eV. The structure formed on the surface is GaN / Ga2O3 / Al2O3, and the corresponding bandgap width is GaN<Ga2O3<Al2O3. The bandgap width of the intermediate transition film layer Ga2O3 is larger than that of GaN. While ensuring the coating quality, it will not cause light absorption on the cavity surface, thereby effectively improving the light output power.

[0037] S5, optical film deposition on the cavity surface: After completing the passivation film on the double light-emitting surfaces of the cavity surface, the coating fixture is taken out of the OMBE equipment and transferred into the plasma-assisted deposition equipment. The fixture temperature is raised to 150°C, the ion source is turned on, the power is set to 500W, O2 is introduced with a flow rate of 5 sccm, and an Al2O3 anti-reflection film with an optical thickness of 1 / 4 of the emission wavelength is deposited on the front cavity surface; then the fixture is turned over and a high-reflection film of a stacked film system of SiO2 / Ta2O5 is deposited on the rear cavity surface. SiO2 / Ta2O5 is one cycle, and 8 cycles of plating are required to complete the preparation of the optical film.

[0038] Example 2

[0039] S1, dehumidification of cavity surface: cleave the GaN wafer to obtain laser chip bars, and collect the bars with a coating fixture. Then, transfer the fixture with collected bars into the sample chamber of the OMBE equipment, raise the fixture temperature to 200℃, and bake for 1 hour to remove the moisture adsorbed on the cavity surface.

[0040] S2, cavity surface cleaning: After baking, when the fixture temperature drops to 100°C, the fixture is transferred to the pretreatment chamber. First, the fixture temperature is raised to 230°C (to prevent sputtering products from being adsorbed on the substrate surface), and N2 and O2 are introduced. The flow rate is set to 3.5sccm, and the flow ratio of N2 and O2 is set to 1:1. The energy of the RF source is set to 600W, and the time is set to 7min. + and O2 + Plasma cleans the surface C and makes the surface in an amorphous state. x (Oxide) is etched away, and at the same time, the energetic N2 + and O2 + Plasma will penetrate several atomic layers into the GaN surface, and O2 + The Ga-N bonds in this area are partially opened, and O replaces N to form Ga-O bonds; the other part of the N2 + The plasma will maintain the existence of Ga-N bonds.

[0041] S3, cavity surface annealing: raise the temperature to 380℃, reduce the plasma power to 80W, ensure that the gas can be ionized but minimize damage to the substrate, set the N2 and O2 flow rates to 35sccm, and the N2 and O2 flow ratio to 1:1, to ensure that the cavity surface is ionized by O2 + and N2 + The plasma atmosphere is covered for 30 minutes. Under the action of plasma active gas and high temperature, several atomic layers on the surface of the cavity all generate stable Ga-ON bonds, thereby forming a stable GaON transition layer. At the same time, under high-temperature annealing, the cavity surface defects are also repaired, and LEED is used to detect the surface recovery.

[0042] S4, cavity surface passivation: After the above process is completed, the fixture is quickly transferred to the passivation chamber, the temperature is raised to 400℃, the temperature of the crucible containing the Al ingot is raised to 1100℃, high-purity O2 and N2 are introduced, the flow rate is set to 15 sccm, the plasma energy is set to 300W to increase the ionization rate of O2 and N2, and the baffles of the substrate and crucible are opened at the same time. The coating time is set to 10min, the coating rate is set to 2nm / min, and a 20nm thick single-crystalline AlON film is formed on the cavity surface (RHEED is used for monitoring during the coating process).

[0043] Because before coating, a layer of GaON of about 1nm has been formed on the cavity surface after pretreatment. The mismatch rate between GaON and AlON is much smaller than that between AlON and GaN, making it easier to grow a single-crystalline AlON film. At the same time, the structure formed on the cavity surface is GaN / GaON / AlON, and the corresponding band gap width is GaN<GaON<AlON. The band gap width of the intermediate transition film layer GaON is larger than that of GaN. While ensuring the coating quality, it will not cause light absorption on the cavity surface, thereby effectively improving the light output power.

[0044] S5, optical film deposition on the cavity surface: After completing the passivation film on the double light-emitting surfaces of the cavity surface, the coating fixture is taken out of the O-MBE equipment and transferred into the plasma-assisted deposition equipment. The fixture temperature is raised to 180°C, the ion source is turned on, the power is set to 100W, O2 is introduced with a flow rate of 10 sccm, and an Al2O3 anti-reflection film with an optical thickness of 1 / 4 of the emission wavelength is deposited on the front cavity surface; then the fixture is turned over and a high-reflection film of a stacked film system of SiO2 / Ta2O5 is deposited on the rear cavity surface. SiO2 / Ta2O5 is one cycle, and 6 cycles of plating are required to complete the preparation of the optical film.

[0045] Example 3

[0046] S1, dehumidification of cavity surface: cleave the GaN wafer to obtain laser chip bars, and collect the bars with a coating fixture. Then, transfer the fixture with collected bars into the sample chamber of the OMBE equipment, raise the fixture temperature to 190℃, and bake for 1 hour to remove the moisture adsorbed on the cavity surface.

[0047] S2, cavity surface cleaning: After baking, when the fixture temperature drops to 100°C, the fixture is transferred to the pretreatment chamber. First, the fixture temperature is raised to 250°C (to prevent sputtering products from being adsorbed on the substrate surface), and N2 and H2 are introduced. The flow rate is maintained at 5sccm, and the flow ratio of N2 and H2 is set to 9:1. The energy of the RF source is set to 700W, and the time is set to 5min. + Plasma cleans the surface C and makes the surface in an amorphous state. x (Oxide) is etched away, and at the same time, the energetic H2 + Plasma will make GaO x The Ga-O bond in the (oxide) dissociates, and the dissociated O generates H2O and evaporates, ensuring that all the oxides on the cavity surface are removed, while the dissociated Ga bond is in N2 + The plasma generates Ga-N bonds, ensuring that the GaN component does not segregate.

[0048] S3, cavity surface annealing: raise the temperature to 400℃, reduce the plasma power to 100W, ensure that the gas can be ionized but minimize damage to the substrate, set the N2 and H2 flow rates to 20sccm, and keep the N2 and H2 flow ratio at 9:1 to ensure that the cavity surface is ionized by N2 and H2. + The plasma atmosphere is covered for 30 minutes. Under the action of plasma active gas and high temperature, several atomic layers on the surface of the cavity are all present as stable Ga-N, and all O is removed, thereby forming a stable GaN transition layer. At the same time, under high-temperature annealing, the cavity surface defects are also repaired, and LEED is used to detect the surface recovery.

[0049] S4, cavity surface passivation: After the above process is completed, the fixture is quickly transferred to the passivation chamber, the temperature is raised to 400°C, the temperature of the crucible containing the Al ingot is raised to 1150°C, high-purity N2 is introduced, the flow rate is set to 20 sccm, the plasma energy is set to 500W to increase the ionization rate of N2, and the baffles of the substrate and crucible are opened at the same time. The coating time is set to 10min, the coating rate is set to 0.5nm / min, and a 5nm thick single-crystalline AlN film is formed on the cavity surface (RHEED is used for monitoring during the coating process).

[0050] Because before coating, the cavity surface is pre-treated to maintain the stable structure of GaN, the mismatch rate between GaN and AlN is small, and it is easier to grow single-crystalline AlN film; at the same time, the structure formed on the cavity surface is GaN / AlN, and the corresponding band gap width GaN<AlN. The wider bandgap can effectively reduce the light absorption of the cavity surface and increase the light output power.

[0051] S5, optical film deposition on the cavity surface: After completing the passivation film on the double light-emitting surfaces of the cavity surface, the coating fixture is taken out of the OMBE equipment and transferred into the plasma-assisted deposition equipment. The fixture temperature is raised to 165°C, the ion source is turned on, the power is set to 300W, O2 is introduced with a flow rate of 8 sccm, and Al2O3 anti-reflection film is deposited on the front cavity surface with an optical thickness of 1 / 4 of the emission wavelength; then the fixture is turned over and a high-reflection film of the stacked film system of SiO2 / Ta2O5 is deposited on the rear cavity surface. SiO2 / Ta2O5 is one cycle, and 7 cycles of plating are required to complete the preparation of the optical film.

[0052] Example 4

[0053] The difference between Example 4 and Example 2 is that in step S2, the flow ratio of N2 and O2 is set to 1:2; in step S3, the flow ratio of N2 and O2 is set to 1:2, and the rest of the contents are the same.

[0054] Example 5

[0055] The difference between Example 5 and Example 2 is that in step S2, the flow ratio of N2 and O2 is set to 2:1; in step S3, the flow ratio of N2 and O2 is set to 2:1, and the rest of the contents are the same.

[0056] Theoretically, the higher the O2 content, the higher the O content in the generated AlON film, because the band gap width of Al2O3 is much larger than that of AlN, and AlON is a ternary compound that combines the characteristics of both Al2O3 and AlN. Therefore, when the O content is higher (such as in Example 4), the band gap width is closer to Al2O3, so the protection effect is better; but when the N content is higher (such as in Example 5), the matching degree between the film and the substrate is higher, and the growth window of the passivation process is wider, which can reduce the difficulty of research and development.

[0057] Example 6

[0058] The difference between Example 6 and Example 3 is that in step S2, the flow ratio of N2 and H2 is maintained at 15:1; in step S3, the flow ratio of N2 and H2 is maintained at 15:1, and the rest of the contents are the same.

[0059] Example 7

[0060] The difference between Example 7 and Example 3 is that in step S2, the flow ratio of N2 and H2 is maintained at 19:1; in step S3, the flow ratio of N2 and H2 is maintained at 19:1, and the rest of the contents are the same.

[0061] Theoretically, the higher the H2 content, the less damage to the substrate during the cleaning process; conversely, the higher the N2 content, the greater the damage to the substrate. Therefore, the substrate cleaning process needs to determine the ratio of H2 and N2 according to the severity of the substrate contamination. If the contamination is large, the ratio of N2 can be increased (such as Examples 6 and 7). If the contamination is small, the ratio of H2 can be increased. Similarly, during the annealing process, the role of H2 is to remove the residual O element, and the H2 content can also be adjusted according to the remaining amount of O.

[0062] Comparative Example 1

[0063] The difference between Comparative Example 1 and Example 1 is that step S2 is missing, the temperature is directly raised to 350° C. for annealing after removing water vapor from the cavity surface, and the passivation film process is performed, and the rest of the contents are the same.

[0064] Comparison results: Since the cavity surface is not cleaned, the amorphous Ga2O and C-containing pollutants on the cavity surface cannot be removed, and non-radiative recombination centers will form on the surface. After the chip has been working for a period of time, COD phenomenon will occur on the cavity surface, and the device will fail.

[0065] Comparative Example 2

[0066] The difference between Comparative Example 2 and Example 1 is that in step S3, no annealing treatment is performed, and the substrate is directly introduced into the passivation chamber for passivation film process, and the rest of the contents are the same.

[0067] Comparison results: When the cavity surface is cleaned but not annealed, and the passivation film process is directly performed, the cavity surface is severely damaged and has many burrs, so a good quality passivation film cannot be generated, and the service life of the chip will be greatly shortened.

[0068] Comparative Example 3

[0069] The difference between Comparative Example 3 and Example 1 is that the temperature of cavity surface cleaning in step S2 exceeds the limited range, specifically: the temperature is increased from 200° C. to 350° C., and the rest of the contents are the same.

[0070] Comparison results: When the cavity surface cleaning temperature is 200℃, it is to increase the speed at which gases such as H2O and CO2 generated on the substrate surface are extracted and enhance the cleaning effect. However, too high a temperature will affect the effect of subsequent annealing process on substrate surface morphology correction.

[0071] Comparative Example 4

[0072] The difference between Comparative Example 4 and Example 3 is that in steps S2 and S3, the flow ratio of N2:H2 exceeds the limit range, specifically 8:1, and the rest of the contents are the same.

[0073] Comparison results: If the H content is too high, it will penetrate several atomic layers into the substrate surface. Since H is easily ionized, it will reduce the insulation performance of the passivation film.

[0074] Comparative Example 5

[0075] The difference between Comparative Example 5 and Example 2 is that in steps S2 and S3, the N2:O2 flow ratio exceeds the limit range, specifically 3:1, and the rest of the contents are the same.

[0076] Comparison results: Because N2 has poor activity and is difficult to decompose, if the N2 content is too high, it will make AlON difficult to generate.

[0077] Comparative Example 6

[0078] The difference between Comparative Example 6 and Example 3 is that in steps S2 and S3, the cleaning and annealing times are both beyond the specified range, the gas cleaning time in step S2 is 15 minutes, and the annealing time in step S3 is 40 minutes, and the rest of the contents are the same.

[0079] Comparison results: Too long a gas bombardment time will cause irreversible damage to the substrate surface, and too long an annealing time will be useless and will affect process efficiency.

[0080] Comparative Example 7

[0081] The difference between Comparative Example 7 and Example 3 is that the coating time in step S4 exceeds the limited range, specifically 30 minutes, and the rest of the contents are the same.

[0082] Comparison results: If the coating time is too long, the thickness of the passivation film will increase, and the stress between the passivation film and the substrate will increase, causing the passivation film to fall off, ultimately affecting the service life of the laser chip.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for passivating the cavity surface of a GaN-based EEL laser chip, characterized in that: The following steps are involved: S1, cavity surface degassing: cleave the CaN wafer to obtain laser chip bars, then transfer the bars into the OMBE equipment, heat the cavity surface at 180-200℃ to remove the water vapor adsorbed on the cavity surface; S2, cavity surface cleaning: continue to raise the temperature to 200-250°C, and introduce one or more gases among O2, N2 and H2 to bombard the cavity surface to remove metastable, amorphous gallium oxides and C-containing pollutants on the cavity surface; S3, cavity surface annealing: continue to raise the temperature to 350~400℃, and introduce one or more gases among O2, N2 and H2 to bombard the cavity surface, then anneal to repair the damaged surface of the film, form a transition layer on the cavity surface, and then use LEED to detect the surface recovery; S4, cavity surface passivation: After annealing, the bar is transferred to the passivation chamber, maintained at a temperature of 350-400°C, a crucible filled with Al liquid is placed under the bar, one or more gases of O2, O3 or N2 are introduced to bombard the cavity surface, and Al2O3, AlON or AlN single crystal film is formed on the surface of the transition layer; When growing Al2O3 single crystal film, O2 is introduced into both steps S2 and S3, and O3 is introduced into step S4; When growing AlON single crystal film, N2 and O2 are introduced in steps S2, S3 and S4; When growing an AlN single crystal film, N2 and H2 are introduced in steps S2 and S3, and N2 is introduced in step S4.

2. The method for passivating the cavity surface of a GaN-based EEL laser chip according to claim 1, characterized in that: In step S2, the gas flow rate is 2-5 sccm, the RF power is 500-700w, and the bombardment time is 5-10min.

3. The method for passivating the cavity surface of a GaN-based EEL laser chip according to claim 1, characterized in that: In step S3, the gas flow rate is 20-50 sccm, the RF power is 50-100 W, and the bombardment time is 30 min.

4. A method for passivating a GaN-based EEL laser chip cavity surface as claimed in claim 1, characterized in that: In step S4, the gas flow rate is 10-20 sccm, the RF power is 200-500w, the bombardment time is 10-15min, and the film thickness is 5-30nm.

5. The method for passivating the cavity surface of a GaN-based EEL laser chip according to claim 1, characterized in that: The flow ratio of N2:O2 is 1:2~2:

1.

6. A method for passivating a GaN-based EEL laser chip cavity surface as claimed in claim 1, characterized in that: The flow ratio of N2:H2 is 9:1~19:

1.

7. A method for passivating a GaN-based EEL laser chip cavity surface as claimed in claim 1, characterized in that: After the cavity surface passivation is completed, Al2O3 or SiO2 anti-reflection film is deposited on the front cavity surface, and SiO2 / Ta2O5 stacked high-reflection film is deposited on the back cavity surface.

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