CN109510061B

CN109510061B - Gallium nitride laser bar cleavage method

Info

Publication number: CN109510061B
Application number: CN201811573795.XA
Authority: CN
Inventors: 邓泽佳; 谢武泽; 王文杰; 李俊泽; 杨浩军; 廖明乐; 李沫
Original assignee: Institute of Electronic Engineering of CAEP
Current assignee: Institute of Electronic Engineering of CAEP
Priority date: 2018-12-21
Filing date: 2018-12-21
Publication date: 2021-01-19
Anticipated expiration: 2038-12-21
Also published as: CN109510061A

Abstract

The invention discloses a method for cleaving a gallium nitride laser bar, which belongs to the technical field of semiconductor photoelectronic device processes, wherein a wide cleavage guide groove and a V-shaped narrow guide groove are formed by deep etching, so that the etching depth can penetrate through the whole epitaxial layer, back thinning, etching and electrode growth processes are carried out, and cleavage is carried out on the front surface of a sample by a laser cutting and Loomis cleavage machine roller method, so that a bar cavity surface is obtained.

Description

Gallium nitride laser bar cleavage method

Technical Field

The invention relates to a method for cleaving a gallium nitride-based semiconductor laser bar, belonging to the technical field of semiconductor photoelectronic device processes.

Background

The GaN-based laser refers to a device that generates laser light using GaN material as a basic working substance. The main working principle of the GaN material quantum dot-based quantum. Both the high-power gallium nitride laser and the DFB (distributed feedback) laser based on the F-P cavity adopt an active region light-emitting mode of edge emission, a resonant cavity is formed by using a natural cleavage plane of a semiconductor crystal as a reflecting plane, and self-excited oscillation is formed in the resonant cavity, so that light is emitted from the end face of the resonant cavity. Due to the excellent performance characteristics of the GaN-based laser, the GaN-based laser can be widely applied to the technical fields of quantum technology, underwater communication, optical information storage, laser display and the like.

As an important process technology in the preparation process of the GaN-based laser, the quality of the cavity surface quality obtained after the bar cleavage can directly influence the threshold current and the output power of the GaN-based laser, thereby further influencing the stability and the reliability of the laser. However, unlike InP, GaAs-based materials, etc., hexagonal GaN has a wurtzite structure, and the low-index crystal plane a-plane and m-plane are perpendicular to the c-plane, and the m-plane is the first cleavage plane of GaN, and therefore, the m-plane of GaN is generally used as the cavity surface of a laser. However, when a laser structure is grown on a GaN epitaxial layer, a large stress is generated in the laser epitaxial layer due to lattice mismatch, thermal mismatch, and the like, and the stress is easily released when mechanically cleaving bars, so that the laser epitaxial layer with a large internal stress is easily separated from the GaN substrate, and the threshold characteristics of the laser are easily affected in this case.

At present, a bar cleavage method of a gallium nitride laser mainly focuses on two mechanical dissociation methods of laser end face cutting, a splitting machine and a diamond-knife jump cutting and a roller, and the two methods are also mainly applied to the condition that the thickness of a P-face structure of the GaN laser is reduced to be below 120 mu m after the P-face structure is constructed. However, the dissociation method of the laser end face cutting and splitting machine often has a situation that the dissociation direction is not split according to the direction of the dissociation groove, the cleavage success rate is not high, and a bad stripe is easily formed on the cavity surface and extends to the active region, thereby affecting the photoelectric performance of the laser. In addition, the diamond skip cutting + roller method also often causes the dissociation surface to deviate from the expected guide groove due to the poor cutting precision of the diamond, and small-area and high-density steps are easy to occur on the bar cavity surface, and the diamond is easy to form harmful cracks in the high-strain epitaxial layer beside the guide groove due to the mechanical pressure of the diamond in the cutting process, thereby affecting the final performance of the laser.

Disclosure of Invention

The invention aims to provide a method for splitting bars of a GaN-based laser, which improves the success rate of splitting bars and the quality of a cavity surface of the GaN-based laser, thereby improving the stability and the reliability of the GaN-based laser.

A method for Barbar cleavage of a GaN-based laser is characterized by comprising the following steps:

step 1: preparing a GaN-based laser ridge structure and a P-surface electrode on a GaN epitaxial wafer by photoetching, etching, coating and other processes, wherein SiO is arranged on the surface of the sample except the ridge structure region₂And covering the insulating layer, cutting by a laser scribing process to obtain a GaN laser sample, and leaving a certain blank distance between the two ends of the bar and the edge of the sample for etching the large channel.

Step 2: and preparing a photoetching graph of a large cleavage guide groove with the length being more than or equal to 300 mu m and the width being more than or equal to 40 mu m and a photoetching graph of a small cleavage guide groove with the width being less than or equal to 3 mu m on the P surface of the sample obtained by scribing by using a photoetching technology, and interrupting the photoetching graph at a certain distance from each ridge structure and a photoetching graph of a single-tube isolation guide groove with the width being more than or equal to 20 mu m and perpendicular to the cleavage edge.

The areas for preparing the photoetching patterns of the large and small cleavage guide grooves and the photoetching patterns of the single-tube isolation guide groove are glue-free areas.

And step 3: SiO by using reactive ion etching technology and using photoresist as soft mask₂Etching the insulating layer to expose SiO in the space₂And after the etching is finished, cleaning and removing the residual photoresist by adopting an organic cleaning method.

And 4, step 4: adopts inductive coupling plasma etching technology to form SiO₂And the insulating layer is used for etching the GaN by using a hard mask, and the etching depth is greater than or equal to 3 mu m. Wherein a V-shaped groove needs to be formed on the small cleavage guide groove figure with the width of less than or equal to 3 mu m, the steep degree of the V-shaped groove is about 63-75 degrees, and the etching depth of the bottom of the V-shaped groove is also greater than or equal to 3 mu m, so that the etching depth exceeds the depth of the whole epitaxial layer, and most of stress is concentrated at the bottom of the V-shaped groove.

And 5: baking the front surface of the etched sample by spin-coating photoresist, thinning the back surface of the sample by a thinning machine, grinding and polishing the sample, cleaning the sample by acetone, isopropanol and deionized water, and then carrying out Cl treatment on the back surface₂Etching and back electrode growing.

Step 6: the central area of the large cleavage guide groove with the width more than or equal to 40 mu m is precisely aligned by a laser cutting machine for laser cutting, and then the roller of the loomis cleavage machine is used for rolling and sliding along the large and small cleavage guide grooves parallel to the cleavage edge, so that the bar cavity surface is obtained.

The invention has the following beneficial effects:

1) the method adopts the large cleavage guide grooves as the two ends of the opening in the dissociation direction and the jumping small cleavage guide grooves (V-shaped), and the deep-etched V-shaped small cleavage guide grooves can concentrate most of stress at the bottom of the V-shaped groove and have strong dissociation directivity, so that stronger directivity is provided for the cleavage of the bars, and the success rate of the dissociation of the bars is greatly improved finally.

2) According to the method, the etching depth of the cleavage guide groove is greater than or equal to 3 mu m, and the etching depth extends beyond the whole epitaxial layer structure, so that the formation process of the cleavage guide groove is almost carried out in a stress-free GaN crystal, and a smoother cavity surface is easily generated.

3) The method adopts laser to accurately cut the large cleavage guide grooves at two ends, overcomes some defects of the traditional diamond cutter jumping cutting dissociation, and avoids the problem that the dissociation success rate and the tube core quality are influenced by surface cracks generated in the use process of the diamond cutter.

Drawings

FIG. 1 is a structural diagram of a P-facet ridge structure of a GaN-based laser according to the present invention.

FIG. 2 is a schematic diagram of a lithographic pattern of the guide groove of the present invention.

Fig. 3 is a cross-sectional view of a V-shaped small cleavage guide groove of the present invention.

Description of reference numerals:

L1-GaN substrate; L2-GaN epitaxial layer; l3-ridge structure (containing GaN ridge region, P electrode); l4-lithographic pattern of large cleavage guide grooves; l5-lithography pattern of small cleavage guide grooves; l6-lithography pattern of single-tube isolated guide trenches; l7-cleavage edge direction; l8-small V-shaped cleavage guide groove formed by etching; l9-perpendicular to the cleavage edge direction.

Detailed Description

To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following embodiments of the present invention are described with reference to the accompanying drawings. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention. The method comprises the following specific steps:

step P1: on the GaN epitaxial wafer, etching of ridge structure is realized by adopting soft mask or hard mask mode and using methods such as photoetching and dry-wet etching, as shown in FIG. 1 (P electrode, SiO)₂Omission of insulating layer), and then using PECVD to deposit SiO with the thickness of more than 600 nanometers on the surface of the sample₂Insulating layer, gas flow rate of PECVD: SiH₄/N₂O/N₂Power 20W, gas pressure 2000mT, =4/710/180sccm, but the p-electrode of the ridge surface needs to be exposed by photolithography and RIE process. The method comprises the steps of cutting a sample into samples with the size of (5-9) mm by using a laser cutting machine, wherein the adopted scribing laser wavelength is 355nm, the power is less than 2W and is adjustable, the light spot focusing depth is 0-30 mu m, the scribing speed is 10-30 mm/sec, and blank distances which are more than or equal to 400 mu m from the edges of the samples need to be arranged at two ends of a Bar effective area in the samples obtained after laser scribing.

Step P2: baking the scribed sample on a hot plate at 180 ℃ for 10min, then placing the sample on a sucker of a spin coater, coating AZ5214 or 6130 photoresist on the surface of the sample, starting the spin coater, wherein the forward rotation speed of the spin coater is 600r/min for 5s, the backward rotation time is 4000 r/min for 30s, then placing the sample after spin coating on a hot plate at 95 ℃ or 100 ℃ for baking for 90s or 100s, making a pattern by using a photoetching machine, the exposure time is 4-7 s, and developing for 40-45s, thereby obtaining a sample with a photoresist pattern, as shown in FIG. 2, and thus forming a photoetching pattern L4 of a large cleavage guide groove, a photoetching pattern L5 of a small cleavage guide groove, and a photoetching pattern L6 of a single-tube isolation guide groove. Wherein: the length of the photoetching pattern L4 of the large cleavage guide groove is greater than or equal to 300 mu m, and the width is greater than or equal to 40 mu m; the width of the photoetching pattern L5 of the small cleavage guide groove is less than or equal to 3 mu m, and the photoetching pattern of the small cleavage guide groove is interrupted at a distance of +/-3 mu m-8 mu m from each ridge; the width of the photoetching pattern L6 of the single-pipe isolation guide groove is greater than or equal to 20 mu m.

Step P3: etching SiO by using photoresist as mask by RIE process₂The etching depth RIE has the following process parameters: vacuum 1850mTorr, RF power: 200W, substrate temperature 100-₂After etching, the photoresist is cleaned by acetone, isopropanol and deionized water.

Step P4: adopting ICP process with SiO₂Etching GaN for mask, etching parameters of ICP: ICP power 1500W, RF power 100W, Cl₂=20ml/min，BCl₃The etching depth exceeds the whole GaN epitaxial layer, the etching steepness of GaN is about 70-75 degrees at 20 ℃ under the pressure of 666.61mPa, so that the small cleavage guide groove figure forms a V-shaped guide groove L8, and the depth of the V-shaped guide groove L8 is greater than or equal to 3 mu m, as shown in FIG. 3.

Step P5: and (3) spin-coating photoresist (the types of the selected photoresist are AZ6130, AZ5214 and AZ 4620) on the surface of the sample, baking for 5min, and then taking down the sample. Placing the attenuate mill on 80 ℃'s hot plate, coating paraffin on the mill, treat that paraffin melts the back on 80 ℃'s hot plate, hug closely the front of sample (the one side of coating photoresist) on the mill through paraffin, through the attenuate machine attenuate to below 120 mu m after the cooling hot pressing, rethread grinding and polishing makes the sample back become bright, take off the sample and carry out its washing through acetone, isopropanol, deionized water paraffin and photoresist, rethread ICP technology sculpture sample's the back, the sculpture parameter: etching time is 5min, RF power is 50W, ICP power is 1000W, Cl₂=18sccm, Pressure =3 mTorr. And then growing a back electrode, wherein the deposited metal is Ti/Pt/Au.

Step P6: the laser scribing machine is used for accurately aligning and cutting along the large cleavage guide groove, in order to guarantee the effectiveness of the guide groove, the adopted scribing laser wavelength is 355nm, the power is less than 2W and can be adjusted, the focusing depth of a light spot is 0-30 mu m, and the scribing speed is 10-30 mm/sec. And rolling the bar along the large and small cleavage wire grooves by using a roller of a loomis cleavage machine, thereby cleaving the bar into bars and finally obtaining the bar cavity surface.

Claims

1. A method for cleaving a gan laser bar, comprising the steps of:

step 1, preparing and finishing a ridge type etching process, P electrode growth and an insulating layer SiO on a GaN epitaxial layer of a sample₂A P surface deposition process, namely cutting the whole sample into a rectangular sample with a size suitable for splitting the sliver;

step 2, forming a photoetching pattern of a large cleavage guide groove parallel to a cleavage edge, a photoetching pattern of a small cleavage guide groove and a photoetching pattern of a single-tube isolation guide groove perpendicular to the cleavage edge on the surface of a rectangular sample through photoetching, wherein the formed photoetching pattern of the small cleavage guide groove is interrupted at a position which is +/-3-8 mu m away from the ridge structure; the length of the photoetching pattern of the large cleavage guide groove is greater than or equal to 300 mu m, and the width of the photoetching pattern of the large cleavage guide groove is greater than or equal to 40 mu m; the width of the photoetching pattern of the small cleavage guide groove is less than or equal to 3 mu m; the width of the photoetching pattern of the single-pipe isolation guide groove is more than or equal to 20 mu m;

step 3, taking the photoresist as a mask to carry out SiO₂Thereby transferring the lithographic pattern to SiO₂Cleaning the photoresist completely on the hard mask in an organic cleaning mode;

step 4, using SiO₂Etching the GaN for the hard mask, wherein the etching depth is greater than the thickness of the whole GaN epitaxial layer, and etching the small cleavage guide groove into a V-shaped groove; the large cleavage guide groove and the small cleavage guide groove are both formed by a deep etching method, and the etching depth of the large cleavage guide groove and the small cleavage guide groove is greater than or equal to 3 mu m;

step 5, protecting the P surface of the sample, and then performing thinning and polishing, etching and electrode growth processes on the back surface;

step 6, cutting along the central area of the large cleavage guide groove by laser cutting, and rolling along the large cleavage guide groove and the small cleavage guide groove by a roller of a loomis cleavage machine to obtain a bar cavity surface; the large cleavage guide groove and the small cleavage guide groove which are positioned on the same edge side are connected, and the single-tube isolation guide groove is intersected with the small cleavage guide groove.

2. The method of claim 1, wherein the photoresist pattern of the large cleave guide trench, the photoresist pattern of the small cleave guide trench, and the photoresist pattern of the single pipe isolation guide trench are formed in a photoresist-free region.

3. The method according to claim 1, wherein in step 6, a laser cutter is used to cut the bar in the central area of the large cleavage guide groove.