Non-invasive semiconductor laser cavity surface preparation method

Abstract

The application belongs to the technical field of semiconductor lasers, and particularly relates to a non-damage semiconductor laser cavity surface preparation method. The method comprises the following steps: positioning a crystal direction of a semiconductor wafer to obtain a most easily dissociated surface of the semiconductor wafer; etching a dissociation guide groove parallel to the most easily dissociated surface, and performing a circular arc transition treatment on the corners of a ridge-shaped protection area of the dissociation guide groove during the etching process; and using the dissociation guide groove to make the semiconductor wafer naturally dissociate through a scribing process and a breaking process to obtain a smooth semiconductor laser cavity surface. The application provides two technical solutions of circular arc transitions at turning points of the dissociation guide groove, can obtain a smooth, flat, non-damage and high-quality semiconductor laser cavity surface, can avoid a reaction between gallium nitride and other semiconductor materials and water vapor, oxygen and other gases in the air after the cavity surface film is plated, improves the service life of the gallium nitride and other semiconductor lasers, and can obtain a reliable and stable semiconductor laser.

Description

A non-destructive method for fabricating the cavity surface of a semiconductor laser Technical Field

[0001] This invention belongs to the field of semiconductor laser technology, specifically relating to a non-destructive method for fabricating the cavity surface of a semiconductor laser. Background Technology

[0002] Gallium nitride (GaN) is an inorganic material, a compound of nitrogen and gallium, and a direct bandgap semiconductor commonly used in light-emitting diodes (LEDs) since 1990. This compound has a wurtzite-like structure and is very hard. GaN has a wide bandgap of 3.4 electron volts, making it suitable for high-power, high-speed optoelectronic devices, such as semiconductor lasers. However, the widespread application of GaN semiconductor lasers relies on high output power and stable reliability; the quality of the laser cavity surface is a crucial factor limiting both reliability and output power.

[0003] Gallium nitride (GaN) semiconductor laser cavity surfaces utilize the property of the most easily dissociated surface in gallium nitride (GaN) material to achieve wafer dissociation, resulting in a smooth and flat high-quality GaN mirror. The key steps are: 1. Determining the crystal orientation of the wafer: Locating the direction of the most easily dissociated surface of the GaN wafer. 2. Fabricating the dissociation guide groove: During the front-end processing, photolithography and etching steps are used to etch a dissociation guide groove parallel to the most easily dissociated surface. 3. Wafer dissociation: Through a dicing process, a channel is diced in the dissociation guide groove at the edge of the wafer. Then, a dicing process is used to apply force to the wafer, causing the GaN wafer to naturally dissociate, ultimately yielding a smooth GaN mirror.

[0004] The dissociation guide groove is fabricated through an etching process. To avoid affecting the ridge shape of the gallium nitride laser during etching, a large area of ​​photoresist is used to protect the ridge. After etching, the area directly above the cavity surface of the gallium nitride laser exhibits a trapezoidal shape, as shown in Figures 1 and 2, with relatively sharp edges at the corners of the ridge protection area 3. Using existing dissociation techniques, cracks are prone to appearing on the cavity surface of the gallium nitride laser, as shown in Figure 3. Cracks on the cavity surface 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 coating is halved. During long-term aging, moisture, oxygen, and other gases in the air can seep into the cavity surface through the cracks, affecting the cavity surface and thus impacting the reliability of the gallium nitride laser. Summary of the Invention

[0005] To address the above-mentioned problems, this invention provides a non-destructive method for fabricating the cavity surface of a semiconductor laser.

[0006] The technical solution adopted in this invention is as follows:

[0007] A non-destructive method for fabricating the cavity surface of a semiconductor laser includes the following steps:

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

[0009] A dissociation guide groove parallel to the most easily dissociated surface is etched out. During the etching process, the corners of the ridge-shaped protection area of ​​the dissociation guide groove are rounded.

[0010] By using a dissociation guide groove, the semiconductor wafer is naturally dissociated through dicing and cleaving processes to obtain a smooth semiconductor laser cavity surface.

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

[0012] Photolithography is performed on the wafer to obtain trapezoidal photoresist;

[0013] Semiconductor wafers are etched using an inductively coupled plasma etching machine;

[0014] Using a gradient multi-step etching process, a dissociation guide trench is obtained by increasing the selectivity ratio of photoresist to gallium nitride, and its corners exhibit a rounded transition.

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

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

[0017] Furthermore, the gradient multi-step etching process includes the following etching parameters: the ratio of chlorine:boron chloride:hydrogen bromide gas gradually changes from (5-20):(10-60):(0-5) to (15-60):(0-20):0; the source power gradually increases 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 gradient time is 50-300 seconds; and the selectivity ratio of photoresist to gallium nitride gradually increases from 0.9-1.5 to 1.5-3.5, ultimately resulting in a dissociation guide trench with a depth of 1-4µm and an inclination angle of 55°-80°, with rounded corners.

[0018] Furthermore, the arc-shaped transition process is achieved through a photoresist self-correction process, which includes:

[0019] Photolithography is performed on the wafer to obtain trapezoidal photoresist;

[0020] The semiconductor wafer is etched using an inductively coupled plasma etching machine. The photoresist morphology is etched from a trapezoidal shape to a semi-circle, and the photoresist width and thickness are reduced. At the same time, the guide groove is etched into a trapezoidal shape, and then the etching continues. The corners are rounded due to the deformation of the photoresist.

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

[0022] Furthermore, the etching of the semiconductor wafer using an inductively coupled plasma etching machine includes the following etching parameters: source power of 50–1200W; bias power of 0–600W; and pressure of 1–50 mTorr.

[0023] Furthermore, in the photoresist self-correction process, after etching the dissociation guide groove to 1-4 μm, the photoresist morphology changes from a trapezoidal shape to a semi-circle, and the resist width and thickness decrease. At the same time, the dissociation guide groove is etched into a trapezoid with an inclination angle of 50°-70°, and then etching continues. The corners exhibit a rounded transition due to the deformation of the photoresist.

[0024] The present invention also provides a non-damaging semiconductor laser cavity surface prepared by the above method.

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

[0026] In existing technologies, the edges of the ridge-shaped protection area of ​​the dissociation guide groove fabricated by etching are relatively sharp, and the stress distribution at this location is complex, easily leading to random stress concentration and uneven stress. This can cause crack tips to form at the edges, and the crystal material can cause irreversible damage to the semiconductor mirror as the crack tip extends downwards, affecting the stability of the semiconductor laser and reducing its lifespan. However, the two rounded transition techniques at the turning points of the dissociation guide groove in this invention can round off the edges, reducing stress concentration at the edges of the dissociation guide groove and preventing crack tips from forming at the edges. After wafer dissociation, a smooth, flat, and high-quality semiconductor laser cavity surface is obtained without damage. After the cavity surface film is deposited, reactions between gallium nitride and other semiconductor materials and gases such as water vapor and oxygen in the air can be avoided, improving the lifespan of gallium nitride and other semiconductor lasers, thus resulting in a reliable and stable semiconductor laser. Attached Figure Description

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

[0028] Figure 2 is a cross-sectional view of section A in Figure 1, which is a schematic diagram of the trapezoidal shape that appears directly above the cavity surface of the gallium nitride laser after the etching process is completed in the prior art.

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

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

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

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

[0033] Figure 7 is a schematic diagram showing the rounded transition at the corners after the photoresist self-correction process in Scheme 2 of the present invention. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0035] The initiation point of dissociation cracks in gallium nitride lasers is at the corner of the ridge-shaped protective region in the dissociation guide groove. At the corner, the stress state is three-dimensional, with normal stress, shear stress, and normal stress existing simultaneously. The stress distribution is complex, and stress concentration and non-uniformity are prone to occur randomly, leading to the generation of crack tips and the destruction of the crystal material. To address this, this invention provides two technical solutions for resolving dissociation cracks.

[0036] Option 1: Achieve a circular arc transition at the turning point of the dissociation guide groove through a multi-step etching process.

[0037] 1. Perform a detachable guide groove photolithography process on the wafer. First, a thick photoresist is coated on the wafer surface, with a thickness between 6 and 9 μm or even thicker. The wafer is aligned and exposed according to its crystal orientation. The width of the ridge protection area of ​​the detachable guide groove in the photolithography pattern is greater than the width of the laser's ridge. Then, a photoresist development process is performed to obtain a trapezoidal photoresist with a tilt angle of 50° to 85°, as shown in Figure 4. The yellow area is the photoresist, and the small blue protrusions are the ridges (ridge waveguides) in the GaN laser, which are used to limit the light field distribution of the laser.

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

[0039] 2. Etch the gallium nitride wafer.

[0040] 1) Gallium nitride wafers are etched using an inductively coupled plasma etching (ICP-C) system. The etching parameters include:

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

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

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

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

[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 μm, preferably 2–3 μm, and more preferably 2.5 μm.

[0047] 2) Then, a gradient multi-step etching process is used, with etching parameters including:

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

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

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

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

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

[0053] The gradient multi-step etching mainly involves increasing the selectivity ratio of photoresist to gallium nitride, i.e., the ratio of the photoresist etching rate to the gallium nitride etching rate. The selectivity ratio gradually increases from 0.9 to 1.5 to 1.5 to 3.5, preferably from 1 to 3, ultimately resulting in a dissociation guide trench with a depth of 1 to 4 μm and a tilt angle of 55° to 80°, preferably a depth of 2 to 3 μm and a tilt angle of 60° to 70°, and even more preferably a depth of 2 μm and a tilt angle of 65°, with rounded corners, as shown in Figure 5.

[0054] 3. By using a dicing process, a groove is diced in the dissociation guide groove at the edge of the wafer. Then, a force is applied to the wafer using a dicing process, which causes the gallium nitride wafer to dissociate naturally. The ridge-shaped protection area of ​​the dissociation guide groove is arc-shaped, which reduces stress concentration problems and thus obtains a high-quality mirror surface without damage.

[0055] Option 2: Achieve a rounded transition at the turning point of the dissociation guide groove through a photoresist self-correction process.

[0056] 1. Photolithography is performed on the wafer, and a thick photoresist is coated, with a thickness greater than 6 μm, preferably 6–12 μm, and more preferably 8 μm. The wafer is then aligned and exposed according to its crystal orientation. The width of the ridge-shaped protection area of ​​the dissociation guide groove in the photolithography pattern is within 3–8 μm, preferably 4 μm. The photoresist is then developed to obtain a trapezoidal photoresist pattern with a thickness-to-width ratio of 1–4 (preferably 2) and a tilt angle of 55°–75° (preferably 65°), as shown in Figure 6.

[0057] 2. An inductively coupled plasma etching machine is used, employing etching gases such as chlorine, boron chloride, hydrogen bromide, argon, nitrogen, and oxygen (chlorine:boron chloride = (20-40):(0-20), preferably 30:10). The source power is 50-1200W, preferably 600W. The bias power is 0-600W, preferably 100W. The pressure is 1-50mTorr, preferably 10mTorr, to etch gallium nitride wafers.

[0058] During the etching process based on a photoresist to gallium nitride selectivity ratio of 1 to 3 (preferably 1.5), because the photoresist thickness-to-width ratio is 1 to 4 (preferably 2), after etching the dissociation guide trench to 1 to 4 μm (preferably 2 to 3 μm, more preferably 2.5 μm), the photoresist morphology changes from a trapezoidal shape to a semi-circular shape, with the width narrowing and the thickness decreasing. Simultaneously, the dissociation guide trench is etched into a trapezoid with an inclination angle of 50° to 70° (preferably 60°). Etching continues, and the corners exhibit a rounded transition state due to photoresist deformation, as shown in Figure 7. During the etching process, the photoresist narrows at both top sides, resulting in a rounded shape. Then, the inclination of the photoresist is changed, decreasing the inclination, and the shrinkage rate of the photoresist accelerates during subsequent etching, thus etching out the rounded shape.

[0059] 3. By using a dicing process, a groove is diced in the dissociation guide groove at the edge of the wafer. Then, a force is applied to the wafer using a dicing process, which causes the gallium nitride wafer to dissociate naturally. The ridge-shaped protection area of ​​the dissociation guide groove is arc-shaped, which reduces stress concentration problems and thus obtains a high-quality mirror surface without damage.

[0060] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and to implement it accordingly. Those skilled in the art will understand that various substitutions, 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 content disclosed in the embodiments of this specification; the scope of protection of the present invention is defined by the claims.

Claims

1. A method for fabricating the cavity surface of a semiconductor laser without damage, characterized in that, Includes the following steps: Locate the crystal orientation of the semiconductor wafer to obtain the easiest dissociation surface of the semiconductor wafer; A dissociation guide groove parallel to the most easily dissociated surface is etched out. During the etching process, the corners of the ridge-shaped protection area of ​​the dissociation guide groove are rounded. By using a dissociation guide groove, the semiconductor wafer is naturally dissociated through dicing and cleaving processes to obtain a smooth semiconductor laser cavity surface; The arc-shaped transition is achieved through a multi-step etching process for dissociating guide trenches. This process includes: performing photolithography on the wafer to obtain trapezoidal photoresist; etching the semiconductor wafer using an inductively coupled plasma etching machine; and using a gradient multi-step etching process to increase the selectivity ratio of photoresist to gallium nitride to obtain dissociating guide trenches, with rounded corners. Alternatively, the arc-shaped transition is achieved through a photoresist self-correction process. This process includes: performing photolithography on the wafer to obtain trapezoidal photoresist; etching the semiconductor wafer using an inductively coupled plasma etching machine, where the photoresist morphology changes from trapezoidal to semi-circular with a narrower width and reduced thickness, while simultaneously etching out a trapezoidal dissociating guide trench, followed by further etching, resulting in rounded corners due to photoresist deformation.

2. The method according to claim 1, characterized in that, In the multi-step etching and dissociation guide trench process, the tilt angle of the trapezoidal photoresist is 65° to 75°.

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

4. The method according to claim 1, characterized in that, In the multi-step etching process for the dissociation guide trench, the etching parameters of the gradient multi-step etching process include: the ratio of chlorine:boron chloride:hydrogen bromide gas gradually changes from (5-20):(10-60):(0-5) to (15-60):(0-20):0; the source power gradually increases 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 gradient 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, ultimately resulting in a dissociation guide trench with a depth of 1-4µm and an inclination angle of 55°-80°, with rounded corners.

5. The method according to claim 1, characterized in that, In the self-correcting photoresist process, the thickness-to-width ratio of the trapezoidal photoresist is 1-4, and the tilt angle is 55°-75°.

6. The method according to claim 1, characterized in that, In the photoresist self-correction process, an inductively coupled plasma etching machine is used to etch the semiconductor wafer. The etching parameters include: source power of 50-1200W; bias power of 0-600W; and pressure of 1-50mTorr.

7. The method according to claim 1, characterized in that, After etching the dissociation guide groove to 1-4 μm, the photoresist morphology changes from trapezoidal to semi-circular, with narrowing of the resist width and reduction of the resist thickness. At the same time, the dissociation guide groove is etched into a trapezoid with an inclination angle of 50°-70°. Then, etching continues, and the corners become rounded due to the deformation of the photoresist.

8. A non-destructive semiconductor laser cavity surface prepared by the method according to any one of claims 1 to 7.

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