A method for passivating the cavity surface of a semiconductor laser chip

Abstract

The present invention provides a cavity surface passivation method for a semiconductor laser chip. By selecting a front cavity surface passivation film and a back cavity surface passivation film made of different materials, and selecting different process chambers and process conditions to grow the front cavity surface passivation film and the back cavity surface passivation film, the method can meet the requirements that the front cavity surface passivation film has a wide band gap, a small absorption coefficient, high temperature resistance, good adhesion to a substrate, and small interface loss of light from the front cavity surface passivation film to the front cavity surface optical film, and the front cavity surface passivation film has a stable structure and is not decomposed by light when high-power light is emitted, and can also meet the requirements that the back cavity surface passivation film has high thermal conductivity, small stress, and good stress matching with the back cavity surface optical film.

Description

Technical Field

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

[0002] The semiconductor laser chip is first coated with a passivation film on its front and rear cavity surfaces, and then optical films are grown on the passivation films on the front and rear cavity surfaces. During the operation of the semiconductor laser chip, the laser is emitted through the passivation film on the front cavity surface and the optical film on the front cavity surface, and the laser passes through the passivation film on the rear cavity surface and is totally reflected by the optical film on the rear cavity surface and then returns to the resonant cavity. The materials of the optical films on the front and rear cavity surfaces are also different, so the requirements for the passivation films on the front and rear cavity surfaces of the semiconductor laser chip are different.

[0003] Therefore, in order for the semiconductor laser chip to work stably, the requirements for the passivation film on the front cavity surface and the passivation film on the back cavity surface are different. The existing technology uses the same material and the same growth process to coat the front cavity surface and the back cavity surface, which cannot meet the different requirements of the semiconductor laser chip for the front and back cavity surface passivation films for stable operation. Summary of the invention

[0004] The present invention provides a method for passivating the cavity surface of a semiconductor laser chip, and the specific scheme includes:

[0005] A method for passivating the cavity surface of a semiconductor laser chip comprises the following steps:

[0006] Step 1, transferring the semiconductor laser chip to the front cavity surface passivation cavity, and growing a front cavity surface passivation film on the front cavity surface of the semiconductor laser chip;

[0007] Step 2, high temperature annealing of the passivation film on the front cavity surface;

[0008] Step 3, transferring the semiconductor laser chip to the back cavity surface passivation cavity, and growing a back cavity surface passivation film on the back cavity surface of the semiconductor laser chip;

[0009] Step 4, performing low temperature annealing on the back cavity surface passivation film;

[0010] Step 5, transferring the semiconductor laser chip to a coating device, growing a silicon nitride optical film on the surface of the passivation film on the front cavity surface of the semiconductor laser chip, and growing a multilayer silicon oxide / silicon nitride film combination on the surface of the passivation film on the back cavity surface of the semiconductor laser chip;

[0011] Step 6: anneal the semiconductor laser chip again.

[0012] Preferably, the aforementioned semiconductor laser chip is a bar, and before step 1, the following steps are also included: first, the laser bar is transferred to the injection chamber, and the laser bar is subjected to low-temperature treatment; secondly, in a vacuum cleavage chamber, the laser bar is cleaved into bars, and the cleavage surface of the bar is prepared.

[0013] Preferably, the material of the front cavity surface passivation film is hafnium oxynitride.

[0014] Preferably, in step 1, the vacuum degree of the front cavity passivation cavity is less than 5.0×10 -10 Torr, a hafnium oxynitride front cavity surface passivation film is grown by ion source assisted electron beam deposition. The front cavity surface passivation cavity includes a nitrogen ion source and an oxygen ion source. First, the nitrogen ion source is ignited, and then the oxygen ion source is ignited. Finally, the electron beam current is gradually increased to evaporate the metal hafnium, forming a hafnium oxynitride passivation film on the front cavity surface of the semiconductor laser chip.

[0015] Preferably, in step 1, the electron beam evaporation rate is 0.1A / S-0.2A / S.

[0016] Preferably, the front surface passivation cavity comprises gas flow meters for nitrogen and oxygen respectively. In step 1, the refractive index of hafnium oxynitride is controlled to be around 2.0 by adjusting the flow rates of the nitrogen ion source and the oxygen ion source.

[0017] Preferably, the thickness of the front cavity surface passivation film is 10nm-15nm.

[0018] Preferably, in step 2, the annealing temperature is T1, and the total annealing time is t1, comprising:

[0019] Step 2.1, heating the front cavity surface passivation film to a temperature of 1 / 2T1, preheating the front cavity surface passivation film, and the preheating time is 1 / 2t1;

[0020] Step 2.2, continue heating the front cavity surface passivation film to a temperature of T1, and the heating time is 1 / 2t1.

[0021] Preferably, in step 3, the back cavity surface passivation film is aluminum oxide.

[0022] Preferably, in step 3, the vacuum degree in the back cavity passivation cavity is less than 5.0×10 -8 Torr, the back cavity passivation chamber includes an oxygen ion source, first the oxygen ion source is ignited, and then the electron beam current is increased to evaporate the metal aluminum.

[0023] Preferably, in step 3, the electron beam evaporation rate is 0.6A / S-0.8A / S.

[0024] Preferably, in step 3, the thickness of the back cavity surface passivation film is 2nm-5nm.

[0025] Preferably, in step 4, the annealing temperature is T2, and the total annealing time is t2. Compared with the annealing temperature T1 and the total annealing time t1 of the front cavity surface passivation film, T1>T2, t1 <t2。

[0026] Preferably, in step 4, the annealing temperature T1 is 350°C <T1<400℃。

[0027] The present invention provides a method for passivating the cavity surface of a semiconductor laser chip, which has the following technical effects:

[0028] 1. The present invention sets a front cavity surface passivation cavity and a back cavity surface passivation film for the front cavity surface and the back cavity surface passivation film respectively, uses different process conditions for growth, and improves the stability of the front cavity surface passivation film through a high temperature annealing process, and releases the stress of the back cavity surface passivation film through a low temperature annealing process to meet the different requirements for the front cavity surface passivation film and the back cavity surface passivation film during the normal operation of the semiconductor laser chip.

[0029] 2. The present invention uses hafnium oxynitride as the front cavity surface passivation film, which can fully meet the requirements of the front cavity surface passivation film having a wide band gap, a small absorption coefficient, high temperature resistance, and good adhesion to the substrate.

[0030] (1) Hafnium oxynitride has a large bandgap and can act as a potential barrier on the substrate surface of the semiconductor laser chip, preventing electrons from transferring to the cavity surface film layer when the semiconductor laser chip is working, causing damage to the film layer;

[0031] (2) Hafnium oxynitride is transparent in the infrared band and has a small absorption coefficient, resulting in less loss of the emitted laser;

[0032] (3) On the front cavity surface, the high-power density laser passes through the front cavity passivation film and is emitted, while hafnium oxynitride has the characteristics of thermal shock resistance and high temperature resistance;

[0033] (4) The hafnium oxynitride film has good adhesion to the substrate of the semiconductor laser chip. The presence of nitrogen atoms in the film can passivate the GaAs substrate, while the presence of oxygen atoms can enhance the adhesion between the film and the substrate, making the combination of the hafnium oxynitride film and the substrate more stable.

[0034] 3. In the process of preparing the front cavity surface passivation film using hafnium oxynitride,

[0035] (1) The present invention uses a nitrogen ion source and an oxygen ion source as dual ion sources, and adjusts the refractive index of the hafnium oxynitride passivation film by adjusting the ratio of nitrogen to oxygen, so that its refractive index is closer to the refractive index of the silicon nitride film subsequently plated thereon. When the emitted laser passes through the hafnium oxynitride passivation film and the silicon nitride film in sequence, the light will not be significantly offset, thereby reducing the loss of light at the interface between the two.

[0036] (2) The laser passes through the front cavity surface passivation film and emits. The front cavity surface passivation film needs to withstand the laser with a large power density to remain stable and will not be decomposed by light. Therefore, in the preparation process of the front cavity surface film, the present invention limits multiple process conditions such as the electron beam evaporation rate, the chamber vacuum, the thickness of the front cavity surface passivation film, and the high-temperature annealing step to improve the stability of the front cavity surface passivation film.

[0037] 4. The present invention uses aluminum oxide as the back cavity surface passivation film. The high thermal conductivity of aluminum oxide can meet the thermal conductivity requirements of the back cavity surface passivation film.

[0038] 5. In the process of using aluminum oxide to grow the back cavity surface passivation film,

[0039] (1) By controlling the evaporation rate of the electron beam and the thickness of the back cavity surface passivation film, the thermal conductivity of the back cavity surface passivation film is further improved;

[0040] (2) Since the film layer of the rear cavity surface optical film is thicker than that of the front cavity surface optical film, the stress of the rear cavity surface optical film increases with the thickness during the deposition process. Therefore, the rear cavity surface passivation film needs to have a smaller stress to better match the rear cavity surface optical film, reduce the overall stress of the rear cavity surface optical film and the rear cavity surface passivation film, and improve the adhesion between the rear cavity surface passivation film and the rear cavity surface optical film. The present invention reduces the stress of the rear cavity surface passivation film by controlling the annealing process conditions of the rear cavity surface passivation film, thereby improving the stress matching degree between the rear cavity passivation film and the rear cavity optical film. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0042] Figure 1 Schematic diagram of the coating on the front and back surfaces of a semiconductor laser chip.

[0043] Figure 2 This is a diagram of the cavity surface passivation equipment of the semiconductor laser chip of the present invention.

[0044] In the figure, 1. optical film on the front cavity surface, 2. passivation film on the front cavity surface, 3. passivation film on the back cavity surface, 4. optical film on the back cavity surface, 5. semiconductor laser chip, 6. sample inlet cavity, 7. passivation cavity on the front cavity surface, 8. passivation cavity on the back cavity surface, 9. sample outlet cavity, 10. valve, 11. vacuum cleavage cavity. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present invention will be described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0046] The embodiment of the present invention provides a method for passivating the cavity surface of a semiconductor laser chip, such as Figure 1 , Figure 2 As shown, Figure 1 Schematic diagram of the coating of the front cavity surface passivation film 2 and the back cavity surface passivation film 3 of the semiconductor laser chip 5 in this embodiment, Figure 2 The device diagram of the cavity surface passivation of the semiconductor laser chip 5 of this embodiment includes a sample inlet chamber 6, a vacuum cleavage chamber 11, a front cavity surface passivation chamber 7, a rear cavity surface passivation chamber 8, and a sample outlet chamber 9, a total of five process chambers, and each process chamber is connected by a valve 10. The cavity surface passivation method provided in this embodiment includes the following steps:

[0047] Step 1, transferring the semiconductor laser chip 5 to the front cavity surface passivation cavity 7, and growing a front cavity surface passivation film 2 on the front cavity surface of the semiconductor laser chip 5;

[0048] Step 2, high temperature annealing of the front cavity surface passivation film 2;

[0049] Step 3, transferring the semiconductor laser chip 5 to the back cavity surface passivation cavity 8, and growing a back cavity surface passivation film 3 on the back cavity surface of the semiconductor laser chip 5;

[0050] Step 4, performing low temperature annealing on the back cavity surface passivation film 3;

[0051] Step 5, transferring the semiconductor laser chip 5 to a coating device, growing a silicon nitride optical film 1 on the surface of the passivation film 2 on the front cavity surface of the semiconductor laser chip 5, and growing a multilayer silicon oxide / silicon nitride film combination as a back cavity surface optical film 4 on the surface of the passivation film 3 on the back cavity surface of the semiconductor laser chip 5;

[0052] Step 6: After the growth of the front cavity surface optical film 1 and the back cavity surface optical film 4 of the semiconductor laser chip 5 is completed, the semiconductor laser chip 5 is annealed again to improve the matching of the front cavity surface optical film 1 and the front cavity surface passivation film 2, and the back cavity surface optical film 4 and the back cavity surface passivation film 3.

[0053] Furthermore, the semiconductor laser chip 5 is a bar, and before step 1, the following steps are also included: first, the laser bar is transferred to the sample injection chamber 6, and the laser bar is subjected to low-temperature treatment; secondly, in the vacuum cleavage chamber 11, the laser bar is cleaved into bars, and the cleavage surface of the bar is prepared.

[0054] Furthermore, the front cavity surface passivation film 2 is hafnium oxynitride. Using hafnium oxynitride as the front cavity surface passivation film 2 can fully meet the requirements of the front cavity surface passivation film 2 having a wide band gap, a small absorption coefficient, high temperature resistance, and good adhesion to the substrate. The reasons are as follows:

[0055] (1) Hafnium oxynitride has a large bandgap and can act as a potential barrier on the substrate surface of the semiconductor laser chip 5, preventing electrons from being transferred to the cavity surface film layer when the semiconductor laser chip 5 is working, thereby causing damage to the film layer;

[0056] (2) Hafnium oxynitride is transparent in the infrared band and has a small absorption coefficient, resulting in less loss of the emitted laser;

[0057] (3) On the front cavity surface, the high-power-density laser passes through the front cavity passivation film 2 and is emitted, while hafnium oxynitride has the characteristics of thermal shock resistance and high temperature resistance;

[0058] (4) The hafnium oxynitride film has good adhesion to the substrate of the semiconductor laser chip 5. The presence of nitrogen atoms in the film can passivate the GaAs substrate, while the presence of oxygen atoms can enhance the adhesion between the film and the substrate, making the hafnium oxynitride film more stably bonded to the substrate.

[0059] Furthermore, in step 1, a hafnium oxynitride front cavity surface passivation film 2 is grown by ion source assisted electron beam deposition. The front cavity surface passivation cavity 7 includes a nitrogen ion source and an oxygen ion source. The nitrogen ion source is first ignited, and then the oxygen ion source is ignited. After the two are stable, the electron beam current is gradually increased to evaporate the metal hafnium, and a hafnium oxynitride passivation film is formed on the front cavity surface of the semiconductor laser chip 5.

[0060] Furthermore, in step 1, the evaporation rate of the electron beam is monitored to ensure that the evaporation rate of the electron beam is between 0.1A / S and 0.2A / S during the growth of hafnium oxynitride. By controlling the evaporation rate of the electron beam to be maintained at a relatively slow level, it is beneficial for the metal hafnium atoms to fully combine with nitrogen and oxygen atoms, so that the front cavity surface passivation film 2 can grow smoothly and slowly, forming a more stable hafnium oxynitride film, which can have better stability when high power density laser is emitted.

[0061] Furthermore, in step 1, the vacuum degree of the front cavity passivation cavity 7 is less than 5.0×10 -10 Since the front cavity surface is the light-emitting surface, the power density of the light emitted is relatively high, so the tolerance to defects of the passivation film 2 is relatively low. Therefore, the vacuum degree of the growth environment of the front cavity surface passivation cavity 7 is relatively high to avoid the generation of non-radiative recombination centers in the passivation film 2, which may cause the passivation film 2 to fail.

[0062] Further, in step 1, the front cavity passivation cavity 7 further includes gas flow meters for nitrogen and oxygen respectively. By regulating the flow rates of the nitrogen ion source and the oxygen ion source, the refractive index of hafnium oxynitride is adjusted to be near 2.0, which is close to the refractive index (n = 2.0) of the silicon nitride material of the front cavity optical film 1. Thus, when light passes through the passivation film 2 and the optical film 1 in sequence, the reflection degree at the interface between the two is lower and the transmittance is higher, reducing the interface loss.

[0063] Further, in step 1, the growth thickness of the front cavity passivation film 2 is 10 nm - 15 nm. Within this thickness range, the front cavity passivation film 2 is relatively stable and can avoid decomposition when high-power density laser passes through. Otherwise, if the front cavity passivation film 2 is thinner, film formation unevenness is likely to occur, and there are more defects and instability.

[0064] Further, in step 2, a graphite disk is arranged in the front cavity passivation cavity 7. The graphite disk is heated, and the bar is brought close to the graphite disk. The front cavity passivation film 2 is heated by the thermal radiation of the graphite disk, where the graphite disk is heated to a temperature of T1 and the total annealing time is t1. Preferably, the following method is used for high-temperature rapid annealing of the front cavity passivation film 2, including:

[0065] Step 2.1, heat the graphite disk to a temperature of 1 / 2T1 to preheat the front cavity passivation film 2 so that the front cavity passivation film is heated to a temperature of 1 / 2T1, and the preheating time is 1 / 2t1; Step 2.2, continue to heat the graphite disk to T1 and continue to heat the front cavity passivation film 2 so that the temperature of the front cavity passivation film is heated to T1, and the heating time is 1 / 2t1.

[0066] In step 2, through two-step heating, the temperature of the product cavity surface can be evenly increased, so that the front cavity passivation film 2 is heated evenly. Step 2 adopts the method of high-temperature rapid annealing, which can increase the atomic migration in the front cavity passivation film 2, reduce the number of defects, improve the crystallinity of the film layer, and release the stress of the front cavity passivation film 2 through annealing, so that the film layer is more stable and can withstand the passing of high-power density laser without decomposition. Preferably, in step 2, the high-temperature rapid annealing temperature T1 satisfies 350 °C < T1 < 400 °C. If the temperature is too low, the defects inside the passivation film 2 cannot be quickly eliminated, affecting the stability of the film layer.

[0067] Further, the rear cavity passivation film 3 is alumina.

[0068] In step 3, an oxygen ion source is included in the back cavity passivation cavity 8. First, the oxygen ion source is ignited. After stabilization, the electron beam current is gradually increased to evaporate metallic aluminum. Preferably, the electron beam evaporation rate in step 3 is 0.6 A / S - 0.8 A / S. Through rapid growth, the kinetic energy between the film material molecules can be greater. When the film material molecules reach the substrate surface of the semiconductor laser chip 5, they can move sufficiently, combine quickly, and form a denser film layer. The denser the film layer, the fewer pores there are between the film layer molecules, and the better the thermal conductivity of the back cavity passivation film 3.

[0069] Further, the vacuum degree in the back cavity passivation cavity 8 is less than 5.0×10 -8 Torr, which is lower than the vacuum degree requirement of the front cavity passivation cavity 7. This is because, compared with the front cavity surface, the optical power density of the back cavity surface is lower. Therefore, the failure ratio of the back cavity passivation film 3 is also relatively lower. Thus, the vacuum degree meeting less than 5.0×10 -8 Torr is sufficient, reducing the working difficulty of the equipment.

[0070] Further, the smaller the thickness of the back cavity passivation film 3, the better the heat dissipation performance. While the larger the thickness, the heat dissipation speed of the back cavity passivation film will be affected. Therefore, the thickness of the back cavity passivation film is preferably 2 nm - 5 nm.

[0071] Further, in step 4, the back cavity passivation film 3 is annealed at a low temperature for a long time. The annealing temperature is T2, and the total annealing time is t2. Compared with the annealing temperature T1 and the total annealing time t1 of the front cavity passivation film 2, T1 > T2, and t1 < t2. Using low-temperature and long-time annealing for the back cavity passivation film 3 will cause the aluminum on the surface of the passivation film to be fully oxidized, generating a thin film with small stress and stable structure. If the annealing temperature is too high, the substrate of the semiconductor laser chip 5 will be oxidized, seriously affecting the quality of the semiconductor laser chip 5.

[0072] In the embodiment of the present invention, by selecting front cavity passivation films and back cavity passivation films of different materials, and selecting different process chambers and process conditions to grow the front cavity passivation film and the back cavity passivation film, it can not only meet the requirements that the front cavity passivation film has a wide bandgap, a small absorption coefficient, high temperature resistance, good adhesion to the substrate, and small loss when light travels from the front cavity passivation film to the front cavity optical film interface, and the front cavity passivation film structure is stable and not decomposed by light when high-power light is emitted, but also meet the requirements that the back cavity passivation film has high thermal conductivity, small stress, and good stress matching with the back cavity optical film.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for passivating the cavity surface of a semiconductor laser chip, characterized in that: It includes the following steps: Step 1: Transfer the semiconductor laser chip to the front cavity surface passivation cavity, and grow a front cavity surface passivation film on the front cavity surface of the semiconductor laser chip; the material of the front cavity surface passivation film is hafnium oxynitride; Step 2: Perform high-temperature annealing on the front cavity surface passivation film; the annealing temperature is T1, 350 °C < T1 < 400 °C, and the total annealing time is t1, including: Step 2.1: Heat the front cavity surface passivation film to a temperature of (1 / 2)T1, and preheat the front cavity surface passivation film, and the preheating time is (1 / 2)t1; Step 2.2: Continue to heat and raise the temperature of the front cavity surface passivation film to a temperature of T1, and the heating time is (1 / 2)t1; Step 3: Transfer the semiconductor laser chip to the rear cavity surface passivation cavity, and grow a rear cavity surface passivation film on the rear cavity surface of the semiconductor laser chip; the rear cavity surface passivation film is alumina; Step 4: Perform low-temperature annealing on the rear cavity surface passivation film; the annealing temperature is T2, and the total annealing time is t2. Compared with the annealing temperature T1 and the total annealing time t1 of the front cavity surface passivation film, T1 > T2, t1 < t2; Step 5: Transfer the semiconductor laser chip to the coating equipment, grow a silicon nitride optical film on the surface of the front cavity surface passivation film of the semiconductor laser chip, and grow a multi-layer silicon oxide / silicon nitride film combination on the surface of the rear cavity surface passivation film of the semiconductor laser chip; Step 6: Anneal the semiconductor laser chip again.

2. A method for passivating the cavity surface of a semiconductor laser chip as claimed in claim 1, characterized in that: The aforementioned semiconductor laser chip is a bar. Before Step 1, it also includes the following steps: First, transfer the laser bar row to the sampling cavity, and perform low-temperature treatment on the laser bar row; second, in the vacuum cleavage cavity, cleave the laser bar row into bars to prepare the cleavage surface of the bars.

3. A method for passivating the cavity surface of a semiconductor laser chip as claimed in claim 1, characterized in that: In step 1, the vacuum degree of the front cavity passivation chamber is less than 5.0×10 -10 Torr, a hafnium oxynitride front cavity surface passivation film is grown by ion source assisted electron beam deposition. The front cavity surface passivation cavity includes a nitrogen ion source and an oxygen ion source. First, the nitrogen ion source is ignited, and then the oxygen ion source is ignited. Finally, the electron beam current is gradually increased to evaporate the metal hafnium, forming a hafnium oxynitride passivation film on the front cavity surface of the semiconductor laser chip.

4. A method for passivating the cavity surface of a semiconductor laser chip as claimed in claim 3, characterized in that: In Step 1, the electron beam evaporation rate is 0.1 Å / S - 0.2 Å / S.

5. A method for passivating the cavity surface of a semiconductor laser chip as claimed in claim 3, characterized in that: The front cavity surface passivation cavity includes gas flow meters for nitrogen and oxygen respectively. In Step 1, by adjusting the flow rates of the nitrogen ion source and the oxygen ion source, the refractive index of hafnium oxynitride is controlled to be near 2.

0.

6. A method for passivating the cavity surface of a semiconductor laser chip as claimed in claim 1, characterized in that: The thickness of the front cavity surface passivation film is 10 nm - 15 nm.

7. A method for passivating the cavity surface of a semiconductor laser chip as claimed in claim 1, characterized in that: In step 3, the vacuum degree in the back cavity passivation cavity is less than 5.0×10 -8 Torr, the back cavity passivation chamber includes an oxygen ion source, first the oxygen ion source is ignited, and then the electron beam current is increased to evaporate the metal aluminum.

8. A method for passivating the cavity surface of a semiconductor laser chip as claimed in claim 7, characterized in that: In Step 3, the electron beam evaporation rate is 0.6 Å / S - 0.8 Å / S.

9. A method for passivating the cavity surface of a semiconductor laser chip as claimed in claim 1, characterized in that: In Step 3, the thickness of the rear cavity surface passivation film is 2 nm - 5 nm.

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