Method for preparing cavity surface of non-destructive semiconductor laser

Abstract

The invention belongs to the technical field of semiconductor lasers, and particularly relates to a nondestructive semiconductor laser cavity surface preparation method. The method comprises the following steps: positioning the crystal orientation of a semiconductor wafer to obtain an easily dissociated surface of the semiconductor wafer; etching a dissociation guide groove parallel to the surface which is most easy to dissociate, and performing arc transition treatment on edges and corners of a ridge-shaped protection area of the dissociation guide groove in the etching process; the semiconductor wafer is naturally dissociated by using the dissociation guide groove through a scribing process and a splitting process, and a smooth semiconductor laser cavity surface is obtained. The invention provides two technical schemes of circular arc transition at the turning position of the dissociation guide groove, so that a smooth, flat, damage-free and high-quality semiconductor laser cavity surface can be obtained, and after the cavity surface film is plated, semiconductor materials such as gallium nitride can be prevented from reacting with gases such as water vapor and oxygen in the air; the service life of the semiconductor laser such as gallium nitride is prolonged, and the reliable and stable semiconductor laser can be obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor lasers, and in particular relates to a method for preparing a cavity surface of a semiconductor laser without damage. Background Art

[0002] Gallium nitride is an inorganic material with the chemical formula GaN, which is a compound of nitrogen and gallium. It is a direct bandgap semiconductor and has been commonly used in light-emitting diodes since 1990. The structure of this compound is similar to wurtzite and has a very high hardness. Gallium nitride has a wide bandgap of 3.4 electron volts and can be used in high-power, high-speed optoelectronic components, such as semiconductor lasers. However, the premise for the widespread application of gallium nitride semiconductor lasers is high output power and stable reliability. However, the quality of the semiconductor laser cavity surface is an important factor limiting the reliability and output power of semiconductor lasers.

[0003] The cavity facet of the gallium nitride semiconductor laser utilizes the properties of the most easily dissociated surface in the gallium nitride material to achieve wafer dissociation and obtain a smooth and flat high-quality gallium nitride mirror surface. The key steps are: 1. Locate the crystal orientation of the wafer and find the direction of the most easily dissociated surface of the gallium nitride wafer. 2. Make a dissociation guide groove. In the front-end process, use photolithography and etching steps to etch a dissociation guide groove parallel to the most easily dissociated surface. 3. Wafer dissociation. Through the dicing process, a channel is cut in the dissociation guide groove at the edge of the wafer, and then a force is applied to the wafer using the splitting process, so that the gallium nitride wafer is naturally dissociated, and finally a smooth gallium nitride mirror surface is obtained.

[0004] The dissociation guide groove is made by etching process. In order to avoid the influence of etching process on the ridge shape of GaN laser, photoresist is used to protect a large area of ​​the ridge shape. After the etching process is completed, the GaN laser cavity surface is in a trapezoidal state, such as Figure 1 , Figure 2 As shown, the corners of the ridge protection region 3 are relatively sharp. According to the prior art, cracks are prone to appear on the cavity surface of the gallium nitride laser. Figure 3 Cracks on the cavity surface will affect the quality of subsequent coating processes. For example, if the cavity surface coating cannot completely cover the cracks, the protective effect of the cavity surface film on the cavity surface will be halved. During the long aging process, water vapor, oxygen and other gases in the air will penetrate into the cavity surface through the cracks, affecting the cavity surface and thus the reliability of the GaN laser. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for preparing a semiconductor laser cavity surface without damage.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A method for preparing a damage-free semiconductor laser cavity surface comprises the following steps:

[0008] Position the crystal orientation of the semiconductor wafer to obtain the easiest dissociation surface of the semiconductor wafer;

[0009] Etching a dissociation guide groove parallel to the most easily dissociated surface, and performing a rounding transition treatment on the corners of the ridge protection area of ​​the dissociation guide groove during the etching process;

[0010] By utilizing the dissociation guide grooves and through scribing and splitting processes, the semiconductor wafer is naturally dissociated to obtain a smooth semiconductor laser cavity surface.

[0011] Furthermore, the arc transition process is achieved by a multi-step etching and dissociation guide groove process, and the multi-step etching and dissociation guide groove process includes:

[0012] Performing a photolithography process on the wafer to obtain a trapezoidal photoresist;

[0013] Etching a semiconductor wafer using an inductively coupled plasma etcher;

[0014] A gradual multi-step etching process is used to obtain a dissociation guide groove by increasing the selectivity ratio of photoresist to gallium nitride, and the edges and corners thereof present an arc-like transition.

[0015] Furthermore, the inclination angle of the trapezoidal photoresist is 65° to 75°.

[0016] Furthermore, the semiconductor wafer is etched using an inductively coupled plasma etcher, and its etching parameters include: the ratio of chlorine gas: boron chloride: hydrogen bromide gas is (5-20): (10-60): (0-5); the source power is 400-700W; the bias power is 50-300W; the pressure is 3-20mTorr; the etching time is 5-10 minutes; and the required depth of etching the dissociation guide groove is 1-4um.

[0017] Furthermore, the etching parameters of the gradual multi-step etching process include: the ratio of chlorine gas: boron chloride: hydrogen bromide gas gradually changes from (5-20): (10-60): (0-5) to (15-60): (0-20): 0; the source power gradually changes from 400-700W to 500-1200W; the bias power gradually changes from 50-300W to 0-200W; the pressure gradually changes from 3-20mTorr to 5-50mTorr; the total gradual change time is 50-300 seconds; the selectivity ratio of photoresist to gallium nitride gradually increases from 0.9-1.5 to 1.5-3.5, and finally a dissociation guide groove with a depth of 1-4um and an inclination angle of 55°-80° is obtained, and the edges and corners present an arc-style transition.

[0018] Furthermore, the arc transition process is implemented by a photoresist self-correction process, and the photoresist self-correction process includes:

[0019] Performing a photolithography process on the wafer to obtain a trapezoidal photoresist;

[0020] The semiconductor wafer is etched using an inductively coupled plasma etcher. The photoresist morphology is etched from a trapezoid to a semicircle, and the resist width is narrowed and the resist thickness is reduced. At the same time, the guide groove is etched into a trapezoid, and then etching continues. The corners present an arc-shaped transition due to the deformation of the photoresist.

[0021] Furthermore, the trapezoidal photoresist has a thickness:width ratio of 1 to 4, and a tilt angle of 55° to 75°.

[0022] Furthermore, the inductively coupled plasma etcher is used to etch the semiconductor wafer, and its etching parameters include: source power of 50 to 1200 W; bias power of 0 to 600 W; and pressure of 1 to 50 mTorr.

[0023] Furthermore, after etching the dissociation guide groove to 1-4 um, the photoresist self-correction process etches the photoresist morphology from a trapezoid to a semicircle, and the resist width is narrowed and the resist thickness is reduced. At the same time, the dissociation guide groove is etched into a trapezoid with an inclination angle of 50° to 70°, and then etching continues. The edges and corners present an arc-style transition due to the deformation of the photoresist.

[0024] The invention also provides a damage-free semiconductor laser cavity surface prepared by the method.

[0025] The beneficial effects of the present invention are as follows:

[0026] In the prior art, the edges and corners of the ridge protection area of ​​the dissociation guide groove made by etching process are relatively sharp, and the stress distribution at this position is relatively complex, which is prone to random stress concentration and stress unevenness, resulting in the generation of crack tips at the edges and corners, and the crystal material causes irreversible damage to the semiconductor mirror surface as the crack tip extends downward, which will cause the stability of the semiconductor laser and reduce the service life of the semiconductor laser. However, through the two technical solutions of arc transition at the turning point of the dissociation guide groove in the present invention, the edges and corners can be processed into arc transition, the stress concentration problem at the edges and corners of the dissociation guide groove is reduced, and the generation of crack tips at the edges and corners of the dissociation guide groove is avoided. Then, through wafer dissociation, a smooth, flat, damage-free, high-quality semiconductor laser cavity surface is obtained. After the cavity surface mask is plated, it can prevent semiconductor materials such as gallium nitride from reacting with water vapor, oxygen and other gases in the air, thereby increasing the service life of semiconductor lasers such as gallium nitride, thereby obtaining a reliable and stable semiconductor laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the structure of a semiconductor laser, wherein: 1-dissociation guide groove; 2-ridge shape; 3-ridge protection area in the dissociation guide groove.

[0028] Figure 2 yes Figure 1 The cross-sectional view at section A in the middle is a schematic diagram of a trapezoidal state just above the cavity surface of the gallium nitride laser after the etching process is completed in the prior art.

[0029] Figure 3 It is a schematic diagram of cracks appearing on the cavity surface of a gallium nitride laser after dissociation according to the prior art.

[0030] Figure 4 It is a schematic diagram of the trapezoidal photoresist in Scheme 1 of the present invention.

[0031] Figure 5 It is a schematic diagram of the arc-shaped transition at the corners after gradual multi-step etching in Scheme 1 of the present invention.

[0032] Figure 6 It is a schematic diagram of the trapezoidal photoresist in Scheme 2 of the present invention.

[0033] Figure 7 It is a schematic diagram of the arc-shaped transition at the corners after the photoresist self-correction process in the second solution of the present invention. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below through specific embodiments and drawings.

[0035] The starting point of the dissociation crack of the GaN laser is at the corner of the ridge protection area in the dissociation guide groove. At the corner, the stress state is three-dimensional, and there are normal stress, shear stress, and normal stress at the same time. The stress distribution is relatively complex, and it is easy to have random stress concentration and stress unevenness, which leads to the generation of crack tips and the destruction of crystal materials. To this end, the present invention provides two technical solutions to solve the dissociation crack.

[0036] Solution 1: A multi-step etching process for the dissociation guide groove is used to achieve an arc transition at the turning point of the dissociation guide groove.

[0037] 1. Perform the dissociation guide groove photolithography process on the wafer. First, apply thick photoresist on the wafer surface, the thickness of which is between 6 and 9 um or even thicker, and perform exposure according to the wafer orientation. The width of the ridge protection area of ​​the dissociation guide groove in the photolithography is greater than the ridge width of the laser. Then perform the photoresist development process to obtain a trapezoidal photoresist with an inclination angle of 50° to 85°, such as Figure 4 As shown, the yellow area is photoresist and the small blue protrusion is the ridge (ridge waveguide) in the GaN laser, which is used to limit the light field distribution of the laser.

[0038] The inclination angle of the trapezoidal photoresist is preferably 65° to 75°, and more preferably 70°.

[0039] 2. Etch the GaN wafer.

[0040] 1) Use an inductively coupled plasma etcher to etch the gallium nitride wafer, and the etching parameters include:

[0041] The ratio (volume flow ratio) of chlorine gas:boron chloride:hydrogen bromide gas is (5-20):(10-60):(0-5), preferably 10:30:2.

[0042] The source power is 400-700W, preferably 600W.

[0043] The bias power is 50-300W, preferably 100W.

[0044] The pressure is 3 to 20 mTorr, preferably 10 mTor.

[0045] The etching time is 5 to 10 minutes, preferably 7 to 10 minutes, and more preferably 10 minutes.

[0046] The required depth for etching the dissociation guide groove is 1-4 um, preferably 2-3 um, and more preferably 2.5 um.

[0047] 2) Then a gradual multi-step etching process is used, and the etching parameters include:

[0048] The ratio of chlorine gas: boron chloride: hydrogen bromide gas changes gradually from (5-20): (10-60): (0-5) to (15-60): (0-20): 0, preferably from 10:30:2 to 30:10:0.

[0049] The source power gradually increases from 400-700W to 500-1200W, preferably from 600W to 800W.

[0050] The bias power gradually changes from 50-300W to 0-200W, preferably from 100W to 50W.

[0051] The pressure changes gradually from 3-20 mTorr to 5-50 mTorr, preferably from 10 mTorr to 20 mTorr.

[0052] The total ramp time is 50 to 300 seconds, preferably 100 seconds.

[0053] Gradient multi-step etching is mainly achieved by increasing the selectivity of photoresist to gallium nitride, that is, the ratio of the etching rate of photoresist to the etching rate of gallium nitride. The selectivity gradually increases from 0.9 to 1.5 to 1.5 to 3.5, preferably from 1 to 3, and finally obtains a dissociation guide groove with a depth of 1 to 4 um and an inclination angle of 55° to 80°, preferably a dissociation guide groove with a depth of 2 to 3 um and an inclination angle of 60° to 70°, and further preferably a dissociation guide groove with a depth of 2 um and an inclination angle of 65°, and the edges and corners present an arc-style transition, such as Figure 5 shown.

[0054] 3. Through the scribing process, a groove is cut in the dissociation guide groove at the edge of the wafer, and then a force is applied to the wafer using the splitting process, so that the gallium nitride wafer is naturally dissociated. The ridge protection area of ​​the dissociation guide groove is arc-shaped, which reduces the stress concentration problem, thereby obtaining a damage-free, high-quality mirror.

[0055] Solution 2: Use the photoresist self-correction process to achieve an arc transition at the turning point of the dissociation guide groove.

[0056] 1. Perform photolithography on the wafer, apply thick photoresist, the thickness of which is greater than 6um, preferably 6-12um, and more preferably 8um, perform exposure according to the wafer orientation, the width of the ridge protection area of ​​the dissociated guide groove in the photoresist plate is within 3-8um, preferably 4um, and then perform photoresist development to obtain a trapezoidal photoresist pattern with a ratio of thickness to width of 1-4 (preferably 2) and an inclination angle of 55°-75° (preferably 65°), such as Figure 6 shown.

[0057] 2. Use an inductively coupled plasma etcher, using etching gases such as chlorine, boron chloride, hydrogen bromide, argon, nitrogen, and oxygen (chlorine: boron chloride = (20-40): (0-20), preferably 30:10), with a source power of 50-1200 W, preferably 600 W. The bias power is 0-600 W, preferably 100 W. The pressure is 1-50 mTorr, preferably 10 mTorr, to etch the gallium nitride wafer.

[0058] In the etching process based on the photoresist and gallium nitride selection ratio of 1 to 3 (preferably 1.5), because the photoresist thickness: width ratio is 1 to 4 (preferably 2), after etching the dissociation guide groove to 1 to 4 um (preferably 2 to 3 um, and more preferably 2.5 um), the photoresist morphology is etched from a trapezoid to a semicircle, and the width of the photoresist is narrowed and the thickness of the photoresist is reduced. At the same time, the dissociation guide groove is etched into a trapezoid with an inclination angle of 50° to 70° (preferably 60°), and then the etching is continued. The corners present a transition state of an arc style due to the deformation of the photoresist, such as Figure 7As shown. During the etching process, the upper two sides of the photoresist are narrowed, causing the photoresist to be in an arc state, and then the inclination of the photoresist is changed, the inclination is reduced, and the shrinkage speed of the photoresist is accelerated during the subsequent etching time, thereby etching an arc state.

[0059] 3. Through the scribing process, a groove is cut in the dissociation guide groove at the edge of the wafer, and then a force is applied to the wafer using the splitting process, so that the gallium nitride wafer is naturally dissociated. The ridge protection area of ​​the dissociation guide groove is arc-shaped, which reduces the stress concentration problem, thereby obtaining a damage-free, high-quality mirror.

[0060] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and implement it accordingly. It can be understood by those skilled in the art that various replacements, changes and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the contents disclosed in the embodiments of this specification, and the scope of protection of the present invention shall be subject to the scope defined in the claims.

Claims

1. A method for preparing a damage-free semiconductor laser cavity surface, characterized in that: The following steps are involved: Position the crystal orientation of the semiconductor wafer to obtain the easiest dissociation surface of the semiconductor wafer; Etching a dissociation guide groove parallel to the most easily dissociated surface, and performing a rounding transition treatment on the corners of the ridge protection area of ​​the dissociation guide groove during the etching process; By utilizing the dissociation guide grooves, the semiconductor wafer is naturally dissociated through scribing and cracking processes to obtain a smooth semiconductor laser cavity surface.

2. The method according to claim 1, characterized in that The arc transition process is achieved by a multi-step etching and dissociation guide groove process, and the multi-step etching and dissociation guide groove process includes: Performing a photolithography process on the wafer to obtain a trapezoidal photoresist; Etching a semiconductor wafer using an inductively coupled plasma etcher; A gradual multi-step etching process is used to obtain a dissociation guide groove by increasing the selectivity ratio of photoresist to gallium nitride, and the edges and corners thereof present an arc-like transition.

3. The method according to claim 2, characterized in that The inclination angle of the trapezoidal photoresist is 65° to 75°.

4. The method according to claim 2, characterized in that: The inductively coupled plasma etcher is used to etch the semiconductor wafer, and the etching parameters include: the ratio of chlorine gas: boron chloride: hydrogen bromide gas is (5-20): (10-60): (0-5); Source power is 400-700W; bias power is 50-300W; pressure is 3-20mTorr; etching time is 5-10 minutes; The required depth for etching the dissociation guide groove is 1 to 4 um.

5. The method according to claim 2, characterized in that: The gradual multi-step etching process has etching parameters including: the ratio of chlorine gas: boron chloride: hydrogen bromide gas changes gradually from (5-20): (10-60): (0-5) to (15-60): (0-20): 0; the source power changes gradually from 400-700W to 500-1200W; the bias power changes gradually from 50-300W to 0-200W; the pressure changes gradually from 3-20mTorr to 5-50mTorr; the total gradual change time is 50-300 seconds; the selectivity ratio of photoresist to gallium nitride increases gradually from 0.9-1.5 to 1.5-3.5, and finally a dissociation guide groove with a depth of 1-4um and an inclination angle of 55°-80° is obtained, and the edges and corners present an arc-style transition.

6. The method according to claim 1, characterized in that The arc transition process is implemented by a photoresist self-correction process, and the photoresist self-correction process includes: Performing a photolithography process on the wafer to obtain a trapezoidal photoresist; The semiconductor wafer is etched using an inductively coupled plasma etcher. The photoresist morphology is etched from a trapezoid to a semicircle, and the resist width is narrowed and the resist thickness is reduced. At the same time, the guide groove is etched into a trapezoid, and then etching continues. The corners present an arc-shaped transition due to the deformation of the photoresist.

7. The method according to claim 6, characterized in that The trapezoidal photoresist has a thickness:width ratio of 1 to 4 and a tilt angle of 55° to 75°.

8. The method according to claim 6, characterized in that The semiconductor wafer is etched using an inductively coupled plasma etcher, and the etching parameters include: source power of 50 to 1200 W; bias power of 0 to 600 W; and pressure of 1 to 50 mTorr.

9. The method according to claim 6, characterized in that After the photoresist self-correction process etches the dissociation guide groove to 1-4um, the photoresist morphology is etched from a trapezoid to a semicircle, and the resist width is narrowed and the resist thickness is reduced. At the same time, the dissociation guide groove is etched into a trapezoid with an inclination angle of 50° to 70°, and then etching continues. The edges and corners present an arc-style transition due to the deformation of the photoresist.

10. A damage-free semiconductor laser cavity facet prepared according to the method of any one of claims 1 to 9.

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