WO2021004181A1

WO2021004181A1 - Preparation method for gan-based vertical cavity surface emitting laser

Info

Publication number: WO2021004181A1
Application number: PCT/CN2020/092743
Authority: WO
Inventors: 应磊莹; 王灿; 张保平; 许荣彬; 徐欢
Original assignee: 厦门大学
Priority date: 2019-07-08
Filing date: 2020-05-28
Publication date: 2021-01-14
Also published as: CN110265864A; CN110265864B

Abstract

Provided is a preparation method for GaN-based vertical cavity surface emitting laser, forming a patterned metal substrate on a seed layer by using the photo-etching and patterned electroplating technologies; transferring a sample to a temporary substrate by using the glue bonding technology; removing a sapphire substrate by using the self-splitting laser stripping technology and separating devices simultaneously; removing a buffer layer, a u-GaN layer and part of an n-GaN layer; making an n metal electrode and a top dielectric film DBR; and removing the temporary substrate to obtain the discrete GaN-based vertical cavity surface emitting laser. The heat dissipation performance of devices is improved, and the problems of metal crimping and short circuit of devices caused by metal cutting are avoided. The process flow of device preparation is simplified, and the cost is reduced.

Description

Method for preparing GaN-based vertical cavity surface emitting laser

Technical field

The invention belongs to the technical field of vertical cavity surface emitting lasers, and specifically relates to a method for preparing a GaN-based vertical cavity surface emitting laser.

Background technique

GaN-based vertical cavity surface emitting laser (VCSEL) is a new type of semiconductor laser with great potential. Compared with traditional edge emitting lasers, vertical cavity surface emitting lasers have many obvious advantages, including low power consumption and low threshold current. Single longitudinal mode operation, circular symmetrical output beam, wafer-level testing, low production cost, efficient coupling with optical fiber, and easy to form dense two-dimensional array. These advantages make it have extremely broad application prospects and huge market value in the fields of information storage, laser display, laser printing, lighting, etc., and it has become a research hotspot in the field of optoelectronics in recent years.

GaN-based VCSELs generally use a dielectric film DBR as a reflector to achieve higher reflectivity, but the dielectric film has poor thermal conductivity and GaN-based VCSELs usually work at high current densities, which leads to serious heating inside the device. The increase in the internal temperature of the device will cause a series of materials and device performance degradation such as the decrease of the gain of the active region, the increase of the laser threshold, the decrease of the output power, the drift of the emission spectrum, and so on. In order to solve this problem, we usually use laser lift-off and substrate transfer technology to remove the original sapphire and other low thermal conductivity substrates and transfer them to a support substrate with higher thermal conductivity such as Si or metal. In 2017, Mei Yang and others of Xiamen University (Mei Y, Xu R B, Weng G E, et al. Tunable InGaN quantum dot microcavity light emitters with 129 nm tuning range from yellow-green to violet[J].Applied Physics Letters, 2017 ,111(12):121107.) Using copper electroplating technology, the device was transferred to a copper substrate with high thermal conductivity, and a GaN-based VCSEL with a copper substrate was fabricated, thereby improving the heat dissipation performance of the device.

At present, one of the main problems faced by this GaN-based VCSEL is the cutting problem of the metal substrate. After using laser lift-off and substrate transfer technology to transfer the device to the metal substrate, the device dicing must use a cutting machine or laser to cut the metal substrate. If you use a cutting machine to cut, you need to scribe multiple times, which is prone to curling of the metal substrate; if you use laser cutting, the metal melt may be sprayed to the sidewall of the device during cutting, causing leakage current. Therefore, these two cutting methods will adversely affect the performance of the device, and even cause the device to fail and reduce the process yield.

Summary of the invention

The purpose of the present invention is to provide a method for preparing a GaN-based vertical cavity surface emitting laser to solve the above-mentioned technical problems.

In order to achieve the above object, the technical solution adopted by the present invention is: a method for preparing a GaN-based vertical cavity surface emitting laser, including the following steps:

Step S1, grow a current spreading layer on a GaN-based epitaxial wafer with a sapphire substrate, and then use photolithography and etching to make a patterned current spreading layer unit, and then make a current confinement layer around the current spreading layer unit. A p metal electrode is made on the confinement layer, the p metal electrode is electrically connected to the current spreading layer unit, and the bottom dielectric film DBR is made above the current spreading layer unit;

Step S2, fabricating a metal layer on the sample on which the bottom dielectric film DBR is fabricated, as a seed layer for electroplating, and then using photolithography and electroplating techniques to form a patterned metal substrate on the seed layer;

Step S3, using glue bonding technology to fix the metal base on the temporary substrate to transfer the sample to the temporary substrate, and use the self-splitting laser lift-off technology to remove the sapphire substrate. During laser lift-off, the GaN-based area of the electroless metal base is The film will split and form fragments, so that the GaN-based film can successfully self-split and achieve device separation;

Step S4, removing the buffer layer, the u-GaN layer and a part of the n-GaN layer in the epitaxial wafer, and then fabricating the n metal electrode and the top dielectric film DBR;

Step S5, removing the temporary substrate to obtain a discrete GaN-based vertical cavity surface emitting laser.

Further, in step S1, the GaN-based epitaxial wafer is prepared by molecular beam epitaxy, metal organic chemical vapor phase epitaxy, hydride vapor phase epitaxy, or magnetron sputtering.

Further, in step S1, the current confinement layer adopts one of a silicon oxide insulating layer, a silicon nitride insulating layer, an aluminum oxide insulating layer, a tantalum oxide insulating layer, and an aluminum nitride insulating layer.

Further, in step S1, the current spreading layer is made of ITO material.

Further, in step S2, the metal layer is Ni layer/Au layer, Cr layer/Au layer, or Ti layer/Au layer.

Further, in step S2, the metal substrate is a copper substrate, a nickel substrate, a gold substrate, a zinc substrate or an aluminum substrate.

Further, in step S3, the glue used in the glue bonding is one of photosensitive glue, heat-sensitive glue and conductive glue.

Further, in step S3, the material of the temporary substrate is quartz material, glass material, semiconductor material or metal material.

Further, in step S4, polishing technology is used to remove the buffer layer, the u-GaN layer and a part of the n-GaN layer in the epitaxial wafer.

Further, in step S5, the tools used to remove the temporary substrate include acetone solution, a stereo microscope, and a scalpel.

The beneficial technical effects of the present invention:

The invention not only can effectively solve the heat dissipation problem of VCSEL devices, but also can successfully separate the devices without metal cutting, effectively avoiding the problems of metal crimping and device short circuit caused by metal cutting, while simplifying the process flow of device preparation and improving The process yield reduces the cost.

Description of the drawings

In order to more clearly describe the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings needed in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative work, other drawings can be obtained from these drawings.

Fig. 1 is a schematic diagram of a process flow of a specific embodiment of the present invention.

Detailed ways

To further illustrate the embodiments, the present invention is provided with drawings. These drawings are a part of the disclosure of the present invention, which are mainly used to illustrate the embodiments, and can cooperate with the relevant description in the specification to explain the operation principle of the embodiments. With reference to these contents, those of ordinary skill in the art should be able to understand other possible implementations and advantages of the present invention. The components in the figure are not drawn to scale, and similar component symbols are usually used to indicate similar components.

The present invention will now be further described with reference to the drawings and specific embodiments.

As shown in Figure 1, the present invention discloses a method for preparing a GaN-based vertical cavity surface emitting laser, which includes the following steps:

Step S1, grow a current spreading layer on a GaN-based epitaxial wafer with a sapphire substrate, and then use photolithography and etching to make a patterned current spreading layer unit, and then make a current confinement layer around the current spreading layer unit. A p metal electrode is made on the confinement layer, the p metal electrode is electrically connected to the current spreading layer unit, and a bottom dielectric film DBR is made above the current spreading layer unit.

In this embodiment, the GaN-based epitaxial wafer with a sapphire substrate includes a sapphire substrate, an N-type GaN layer, a quantum well layer, and a P-type GaN layer stacked in sequence. As shown in Figure 1(a), molecular beam epitaxy can be used , Metal-organic chemical vapor phase epitaxy, hydride vapor phase epitaxy method or magnetron sputtering method for preparation, the specific preparation process is already very mature existing technology, no more details.

The specific steps of step S1 are as follows:

S11: Use a standard cleaning method to clean the surface of the GaN-based epitaxial wafer on the sapphire substrate, that is, the upper surface of the P-type GaN layer. The cleaning method is as follows: acetone, alcohol, and deionized water are respectively ultrasonicated for 3 minutes for a total of three cleanings. But it is not limited to this.

In S12, an electron beam evaporation device is used to prepare a current spreading layer with a thickness of 30 nm on the epitaxial wafer. The current spreading layer is preferably made of ITO material, which is easy to realize, mature in technology and good in conductivity. Of course, in other embodiments, the current spreading layer can also be made of other materials, and the thickness of the current spreading layer can also be selected according to actual needs.

S13, using photolithography and wet etching processes to fabricate a patterned current spreading layer unit, that is, a plurality of spaced current spreading layer units are produced. In this specific embodiment, the current spreading layer unit is a disc-shaped structure with a diameter of 10 μm, but it is not limited to this. In other embodiments, the shape and size of the current spreading layer unit can be selected according to actual needs.

S14, using magnetron sputtering technology to make a 250nm thick SiO ₂ insulating layer around the current spreading layer unit as the current confinement layer. Of course, in other embodiments, the current confinement layer can also be a silicon nitride insulating layer or aluminum oxide. The thickness of the insulating layer, tantalum oxide insulating layer, aluminum nitride insulating layer, etc. can be set according to actual needs.

S15, using magnetron sputtering technology to fabricate a 250nm thick p metal electrode on the current confinement layer. The p metal electrode simultaneously covers the outer periphery of the upper surface of the current spreading layer unit to be electrically connected to the current spreading layer unit. In this specific embodiment The p-metal electrode adopts a Cr/Au electrode (Cr/Au means that a Cr layer and an Au layer are stacked). Of course, in other embodiments, the p-metal electrode can also be made of other metal materials or composite metal layers.

S16, fabricating a bottom dielectric film DBR (distributed Bragg reflector) above the current spreading layer unit through photolithography and electron beam evaporation processes to form the structure shown in FIG. In this embodiment, the bottom dielectric film DBR is formed by alternately stacking 12.5 pairs of TiO ₂ /SiO ₂ dielectric films, but it is not limited to this.

In step S2, a metal layer is fabricated on the sample on which the bottom dielectric film DBR is fabricated as a seed layer for electroplating, and then a patterned metal base is formed on the seed layer by photolithography and electroplating technology.

Specifically, on the above-mentioned sample of the patterned bottom dielectric film DBR (that is, as shown in FIG. 1(b)), an entire metal layer is grown by magnetron sputtering as a seed layer for electroplating. In this specific embodiment, The metal layer is a Cr/Au layer (that is, the Cr layer and the Au layer are stacked). Of course, in other embodiments, the metal layer can also be a Ni/Au layer, Ti/Au layer, etc., and the metal layer can also be deposited by evaporation preparation.

Next, a 20μm thick patterned photoresist is produced on the surface of the metal layer by photolithography, that is, there is no photoresist on the device mesa of the epitaxial wafer, and there is photoresist in the aisle between the mesas. The width of the aisle is 300um. But it is not limited to this.

Then 80μm thick copper is electroplated and deposited as the metal substrate. Because the photoresist has a certain thickness and is not conductive, the copper only grows on the mesa, reaching a patterned electroplated metal substrate (that is, forming a plurality of spaced metal substrates, and The purpose of one-to-one correspondence with the current spreading layer unit) is shown in Figure 1(c). Of course, in other embodiments, the metal substrate can also be a nickel substrate, a gold substrate, a zinc substrate, or an aluminum substrate, and the thickness is preferably Between 50-100μm.

Step S3, using glue bonding technology to fix the metal base on the temporary substrate to transfer the sample to the temporary substrate, and use the self-splitting laser lift-off technology to remove the sapphire substrate. During laser lift-off, the GaN-based area of the electroless metal base is The film will split and form fragments, so that the GaN-based film can successfully self-split and achieve device separation.

Specifically, the photosensitive adhesive spin-on bonding technology is first used to transfer the patterned electroplated sample to a temporary substrate. As shown in Figure 1(d), the material of the temporary substrate can be quartz material, glass material, semiconductor material Or metal materials. Of course, in other embodiments, the glue used in the glue bonding can also be other glues such as heat-sensitive glue and conductive glue.

Next, a KrF excimer laser with a wavelength of 248nm was used to remove the sapphire substrate through the sapphire irradiated sample. When the laser was lifted off, the GaN-based film in the area of the electroless metal substrate was split to form fragments, so that the GaN-based film was successfully self-split. To achieve device separation, as shown in Figure 1 (e).

Step S4, removing the buffer layer, the u-GaN layer and a part of the n-GaN layer in the epitaxial wafer, and then fabricating the n metal electrode and the top dielectric film DBR.

Specifically, firstly, a polishing technique is used to remove the high-defect buffer layer, u-GaN layer, and part of the n-GaN layer, and the cavity length is controlled to shorten it to 2 to 3 μm. Of course, in other embodiments, ICP etching can also be used to remove the high-defect buffer layer, u-GaN layer, and part of the n-GaN layer, or ICP etching and polishing techniques can be mixed to remove the high-defect buffer layer, u- GaN layer and part of n-GaN layer.

Next, the n metal electrode and the top dielectric film DBR are fabricated by photolithography, as shown in Figure 1(f). In this specific embodiment, the top dielectric film DBR is composed of 11.5 pairs of TiO ₂ /SiO ₂ dielectric films alternately stacked. But it is not limited to this.

Specifically, tools such as acetone solution, scalpel, stereo microscope, etc. are used to remove the temporary substrate to complete the production of the self-splitting GaN-based vertical cavity surface emitting laser to obtain a discrete GaN-based vertical cavity surface emitting laser, as shown in Figure 1(g) Shown.

Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, those skilled in the art should understand that the present invention can be modified in form and detail without departing from the spirit and scope of the present invention as defined by the appended claims. Various changes are within the protection scope of the present invention.

Claims

A method for preparing a GaN-based vertical cavity surface emitting laser is characterized in that it comprises the following steps:

Step S1, grow a current spreading layer on a GaN-based epitaxial wafer with a sapphire substrate, and then use photolithography and etching to make a patterned current spreading layer unit, and then make a current confinement layer around the current spreading layer unit. A p metal electrode is made on the confinement layer, the p metal electrode is electrically connected to the current spreading layer unit, and the bottom dielectric film DBR is made above the current spreading layer unit;

Step S2, fabricating a metal layer on the sample on which the bottom dielectric film DBR is fabricated, as a seed layer for electroplating, and then using photolithography and electroplating techniques to form a patterned metal substrate on the seed layer;

Step S3, using glue bonding technology to fix the metal base on the temporary substrate to transfer the sample to the temporary substrate, and use the self-splitting laser lift-off technology to remove the sapphire substrate, specifically: when laser lifts the sapphire substrate, electroless metal plating The GaN-based film in the substrate area will split and form fragments, so that the GaN-based film can successfully self-split and achieve device separation;

Step S4, removing the buffer layer, the u-GaN layer and a part of the n-GaN layer in the epitaxial wafer, and then fabricating the n metal electrode and the top dielectric film DBR;

Step S5, removing the temporary substrate to obtain a discrete GaN-based vertical cavity surface emitting laser.
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S1, the GaN-based epitaxial wafer adopts molecular beam epitaxy, metal organic chemical vapor phase epitaxy, hydride gas phase epitaxy, or Prepared by magnetron sputtering method.
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S1, the current confinement layer adopts a silicon oxide insulating layer, a silicon nitride insulating layer, an aluminum oxide insulating layer, and an oxide insulating layer. One of tantalum insulating layer and aluminum nitride insulating layer.
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S1, the current confinement layer is prepared by magnetron sputtering technology.
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S1, the current spreading layer is made of ITO material.
The method for manufacturing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S1, the current spreading layer is prepared by an electron beam evaporation method.
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S1, the p metal electrode simultaneously covers the outer periphery of the upper surface of the current spreading layer unit to be electrically connected to the current spreading layer unit .
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S2, the metal layer is a Ni layer/Au layer, a Cr layer/Au layer, or a Ti layer/Au layer.
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S2, the metal layer is grown by magnetron sputtering.
The method for manufacturing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S2, the metal substrate is a copper substrate, a nickel substrate, a gold substrate, a zinc substrate, or an aluminum substrate.
The method for manufacturing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S2, the thickness of the metal substrate is between 50 and 100 μm.
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S3, the glue used in the glue bonding is one of photosensitive glue, heat sensitive glue and conductive glue.
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S3, the material of the temporary substrate is quartz material, glass material, semiconductor material or metal material.
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S3, the laser is a KrF excimer laser with a wavelength of 248 nm.
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S4, polishing technology is used to remove the buffer layer, the u-GaN layer and a part of the n-GaN layer in the epitaxial wafer.
The method for preparing a GaN-based vertical cavity surface emitting laser according to claim 1, wherein in step S5, the tools used to remove the temporary substrate include acetone solution, a stereo microscope, and a scalpel.