阅读说明：本技术 氧化孔生成方法及垂直腔面发射激光器 (Oxidized hole generating method and vertical cavity surface emitting laser ) 是由 郭海侠 李加伟 曼玉选 何强 赖明智 于 2021-09-14 设计创作，主要内容包括：本发明公开了一种氧化孔生成方法,用于在垂直腔面发射激光器制备过程中,对主动区平台进行氧化处理以在所述主动区平台内的氧化限制层中间形成氧化孔；所述氧化处理的具体方法如下：先使用氧等离子体对主动区平台的侧壁进行干法氧化,在所述氧化限制层外缘生成一圈疏松多孔结构；然后经由所述疏松多孔结构对主动区平台的侧壁进行湿法氧化,在氧化限制层中间形成所期望的氧化孔。本发明还公开了一种垂直腔面发射激光器。相比现有技术,本发明可在垂直腔面发射激光器制备过程中对氧化限制层的氧化进程进行更为精准的控制,同时有效减少氧化层及GaAs界面的分离或开裂现象。(The invention discloses an oxidized hole generation method, which is used for carrying out oxidation treatment on an active region platform in the preparation process of a vertical cavity surface emitting laser so as to form an oxidized hole in the middle of an oxidation limiting layer in the active region platform; the specific method of the oxidation treatment is as follows: firstly, carrying out dry oxidation on the side wall of the platform of the active region by using oxygen plasma, and generating a circle of loose porous structure at the outer edge of the oxidation limiting layer; the sidewalls of the active region mesa are then wet oxidized through the loose porous structure to form the desired oxidized pores in the middle of the oxidized confining layer. The invention also discloses a vertical cavity surface emitting laser. Compared with the prior art, the method can more accurately control the oxidation process of the oxidation limiting layer in the preparation process of the vertical cavity surface emitting laser, and simultaneously effectively reduce the separation or cracking phenomenon of the oxidation layer and the GaAs interface.)

1. An oxidation hole generation method is used for carrying out oxidation treatment on an active region platform in the preparation process of a vertical cavity surface emitting laser so as to form an oxidation hole in the middle of an oxidation limiting layer in the active region platform; the method is characterized in that the specific method of the oxidation treatment is as follows: firstly, carrying out dry oxidation on an oxidation limiting layer by using oxygen plasma through the side wall of an active region platform, and generating a circle of loose porous structure at the outer edge of the oxidation limiting layer; the oxidized confinement layer is then wet oxidized through the loose porous structure, forming the desired oxidized pores in the middle of the oxidized confinement layer.

2. The oxidized pore generation method according to claim 1, wherein the oxidation depth ratio of the dry oxidation to the wet oxidation is 1:3 to 1: 5.

3. The oxidized pore generation method according to claim 1, wherein the process conditions of the dry oxidation are specifically as follows: plasma mode: RIEmode, O₂Flow rate: 50-200sccm, plasma generation power: 200 and 400W, the process temperature is more than or equal to 25 ℃, and the process time is as follows: 10-40 min.

4. The method of generating an oxidized via of claim 1 wherein the oxygen plasma is generated using oxygen gas without an auxiliary gas.

5. A vertical cavity surface emitting laser is prepared by oxidizing an active region mesa to form an oxidized hole in the middle of an oxidation limiting layer in the active region mesa; wherein the oxidized pores are formed by the method according to any one of claims 1 to 4.

Technical Field

The invention relates to a Vertical-Cavity Surface-Emitting Laser (VCSEL) preparation process, in particular to an oxidized hole generation method, and belongs to the technical field of semiconductor lasers.

Background

Vertical Cavity Surface Emitting Lasers (VCSELs) have greater advantages in high-density integration and fiber coupling than edge emitting lasers, and therefore have great application prospects in the fields of optical communication and the like. However, because the device structure has the defects of thin active region, short cavity length, small single-layer gain and the like, in order to improve the effective photon limiting capability, the oxide DBR limiting type structure is basically adopted at present. The oxide-confined structure can reduce the lifetime of non-radiative recombination centers in the material and effectively limit the current injected into the active region.

The main process steps of the oxidation of the VCSEL with the limit type structure comprise: the epitaxial growth of the wafer, in the epitaxial growth process of the wafer, AlGaAs layers with high Al components are arranged on the lower Bragg reflector layer and/or the upper Bragg reflector layer close to the resonant cavity as oxidation limiting layers, and the VCSEL chip structure mainly comprises an N-type doped DBR reflector, a resonant cavity containing a quantum well/quantum dot active region and a P-type doped DBR reflector from bottom to top; etching an active region platform in a layer structure formed by epitaxial growth, wherein the oxidation limiting layer is required to be exposed on the side wall of the active region platform; the side wall of the active region platform is subjected to oxidation treatment, oxidation is carried out along the oxidation limiting layer in a transverse direction, the oxidized oxidation limiting layer forms an oxidation region which takes alumina as a main part, the alumina has good insulation property, can effectively block the passing of injection current and limit the lateral diffusion of the injection current, meanwhile, the alumina has a smaller refractive index, so that an optical field can be more concentrated in a circuit injection window region, the overlapping of the optical field and an active region is improved, a light limiting factor is increased, the threshold current of a device is reduced, and the region which is not oxidized in the middle forms an oxidation hole, namely, the light outlet hole and the current injection region of the VCSEL; and then carrying out surface passivation, a planarization process (filling the groove with polymers such as polyimide, benzocyclobutene and the like), manufacturing an electrode, leading out and the like.

In the above process engineering, the formation of oxidized pores is very critical, and the pore diameter and shape thereofAnd the surrounding structure of the peripheral oxide region, etc., all affect the performance, reliability, etc. of the final device. The existing oxidation process can be divided into a wet method and a dry method. Wherein, the wet oxidation process is a self-limiting oxidation reaction, aiming at AlAs/AlGaAs materials, the time for finishing the self-limiting reaction is generally far longer than the time required by the actual oxidation process, and the high-refractive-index AlO generated by the process_xThe structure acts to limit the optics to meet device requirements. The dry oxidation is used as an auxiliary oxidation process, the self-limiting reaction generally has short finishing time, and the target oxidation depth required by the device cannot be reached under the current process level. Therefore, wet oxidation processes for high aluminum content (e.g., Al) are commonly used in the prior art_0.98Ga_0.02As) to form compounds such As Al2O3, Ga2O3, As, etc., and the reaction process is complicated, so that factors affecting the oxidation process, such As: the requirements of process temperature, H2/O2 ratio, oxidation rate and the like are strict. If the wet oxidation process does not reach a steady state, or some intermediate products (such As2O3, As) are not completely released, a large oxide layer stress is generated, and this stress may cause severe separation or cracking at the interface between the oxide layer and GaAs.

Disclosure of Invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, and to provide an oxidized hole generating method, which can control the oxidation process of the oxidation limiting layer more precisely in the preparation process of the vertical cavity surface emitting laser, and simultaneously effectively reduce the separation or cracking phenomenon of the oxide layer and the GaAs interface.

The invention specifically adopts the following technical scheme to solve the technical problems:

an oxidation hole generation method is used for carrying out oxidation treatment on an active region platform in the preparation process of a vertical cavity surface emitting laser so as to form an oxidation hole in the middle of an oxidation limiting layer in the active region platform; the specific method of the oxidation treatment is as follows: firstly, carrying out dry oxidation on an oxidation limiting layer by using oxygen plasma through the side wall of an active region platform, and generating a circle of loose porous structure at the outer edge of the oxidation limiting layer; the oxidized confinement layer is then wet oxidized through the loose porous structure, forming the desired oxidized pores in the middle of the oxidized confinement layer.

Preferably, the oxidation depth ratio of the dry oxidation to the wet oxidation is 1: 3-1: 5.

Preferably, the process conditions of the dry oxidation are as follows: plasma mode: RIEmode, O₂Flow rate: 50-200sccm, plasma generation power: 200 and 400W, the process temperature is more than or equal to 25 ℃, and the process time is as follows: 10-40 min.

Preferably, the oxygen plasma is generated using oxygen gas without an auxiliary gas.

Based on the same inventive concept, the following technical scheme can be obtained:

a vertical cavity surface emitting laser is prepared by oxidizing an active region mesa to form an oxidized hole in the middle of an oxidation limiting layer in the active region mesa; the oxide pores are formed using the method of any of the above claims.

Compared with the prior art, the invention has the following beneficial effects:

the invention adopts an oxidation hole generation process combining dry oxidation and wet oxidation, and the dry oxidation is firstly used for oxidizing the AlGaAs material with the high aluminum component close to the outer layer into the insulating material Al₂O₃And As₂O₅And then the reaction gas of the subsequent wet oxidation process is controlled based on the generated porous structure, so that the oxidation rate does not depend on the oxidation temperature and the concentration of the reaction gas under a certain condition, and further accurate control of the oxidation process is possible.

The technical scheme of the invention can ensure that the actual oxidation rate is lower than that under the same wet process condition, increase the reaction time, and ensure that the intermediate product As₂O₃And As₂H₃The reaction is fully realized, As is fully released, the residual stress of the oxide layer is reduced, and the phenomenon of separation or cracking of the oxide layer and the GaAs interface caused by incomplete release of As is effectively solved.

Drawings

FIG. 1 is a schematic cross-sectional view of a VCSEL in an embodiment; which comprises the following steps: a GaAs substrate; 2. a metal electrode; an N-type DBR; 4. a quantum well; a P-type DBR; 6. an oxidation limiting layer; a Cap layer; a pasivation film layer;

FIG. 2 is a schematic diagram of the structure of the oxide confinement layer obtained in the example embodiment.

Detailed Description

Aiming at the defects that the oxidation process is difficult to accurately control and the separation or cracking phenomenon of an oxide layer and a GaAs interface is easy to occur when an oxidation hole is generated by adopting a wet oxidation process in the prior art, the solution idea of the invention is to adopt the oxidation hole generation process combining dry oxidation and wet oxidation and firstly oxidize a high-aluminum component AlGaAs material close to an outer layer into an insulating material Al by using the dry oxidation₂O₃And As₂O₅And then the reaction gas of the subsequent wet oxidation process is controlled based on the generated porous structure, so that the oxidation rate does not depend on the oxidation temperature and the concentration of the reaction gas under a certain condition, and further accurate control of the oxidation process is possible.

The method for generating the oxidized hole is used for carrying out oxidation treatment on the active region platform in the preparation process of the vertical cavity surface emitting laser so as to form the oxidized hole in the middle of the oxidation limiting layer in the active region platform; the specific method of the oxidation treatment is as follows: firstly, carrying out dry oxidation on an oxidation limiting layer by using oxygen plasma through the side wall of an active region platform, and generating a circle of loose porous structure at the outer edge of the oxidation limiting layer; the oxidized confinement layer is then wet oxidized through the loose porous structure, forming the desired oxidized pores in the middle of the oxidized confinement layer.

Preferably, the oxidation depth ratio of the dry oxidation to the wet oxidation is 1: 3-1: 5.

Preferably, the process conditions of the dry oxidation are as follows: plasma mode: RIEmode, O₂Flow rate: 50-200sccm, plasma generation power: 200 and 400W, the process temperature is more than or equal to 25 ℃, and the process time is as follows: 10-40 min.

The oxygen plasma may beThe plasma generator is prepared by adopting the existing plasma generating equipment, and oxygen plasma is formed by exciting oxygen; the conventional oxygen plasma generation process usually adds a part of Ar in oxygen as an auxiliary gas, in particular, to prevent Al from being formed by oxidation of metal aluminum₂O₃Then, it is bombarded by plasma Ar +, resulting in Al₂O₃Decomposition, affecting oxidation and uniformity, and also causing damage to the active region mesa sidewalls, is preferably generated using oxygen without a supporting gas.

For the public understanding, the technical scheme of the invention is explained in detail by a specific embodiment and the accompanying drawings:

the VCSEL structure to be fabricated in this embodiment is shown in fig. 1, and comprises, from bottom to top: the semiconductor device comprises a GaAs substrate 1, a metal electrode 2, an N-type DBR3, a quantum well 4, a P-type DBR layer 5, an oxidation limiting layer 6, a Cap layer 7 and a Passivation film layer 8; wherein an oxide confinement layer 6 is sandwiched between upper and lower P-type DBR layers 5. In the preparation process, an active region platform (i.e. the part covered by the pasivation film layer 8 in fig. 1) is formed in the layer structure grown by epitaxy by an etching process; then, a sidewall oxidation treatment is performed on the active region mesa to oxidize the high-alumina component material in the periphery of the oxidation limiting layer 6 into an oxidized region whose main component is alumina, and an oxidized hole of a desired shape and size is formed in the middle of the oxidation limiting layer 6. Wherein the oxidation treatment is specifically as follows:

step 1, performing dry oxidation on an oxidation limiting layer by using oxygen plasma through the side wall of an active region platform, and generating a circle of loose porous structure at the outer edge of the oxidation limiting layer:

to prevent the formation of Al in the oxidation of metallic aluminum₂O₃Then, it is bombarded by plasma Ar +, resulting in Al₂O₃Decomposition, affecting oxidation and uniformity, and causing damage to the sidewalls of the active region mesa, in this embodiment using oxygen without an assist gas to generate the oxygen plasma; the chemical reaction process of the dry oxidation is as follows:

AlGaAs(s)+o^-(g)→Al2O3(s)+As2O3(l)↑

AlGaAs(s)+o^-(g)→Al2O3(s)+As2O5(s)

GaAs(s)+o^-(g0→Ga2O3(s)+As2O3(l)↑

GaAs(s)+o^-(g)→Ga2O3(s)+As2O5(s)

in order to avoid that the loose porous structure becomes smaller or even disappears after the dry oxidation process, which leads to the failure of the subsequent wet oxidation process, the dry oxidation process conditions should be optimized, and the dry oxidation process adopted in the embodiment is specifically as follows:

dry oxidation temperature: not less than 25 ℃;

dry oxidation plasma generation power: 200-400W;

dry oxidation of O₂The gas flow is 50-200 sccm;

dry oxidation time: 5-20 min;

dry oxidation mode: RIE mode;

after the dry oxidation process, the AlGaAs material of the oxidation limiting layer is changed into Al after reaction₂O₃And As₂O₅And a circle of thin loose porous structure is formed on the platform of the active region along the inward direction of the side wall, and other products are discharged as gas in the reaction process.

Step 2, carrying out wet oxidation on the oxidation limiting layer through the loose porous structure, and forming expected oxidation holes in the middle of the oxidation limiting layer:

the wet oxidation process may adopt a process used in the conventional VCSEL process or various improved processes, and in this embodiment, an AET wet oxidation machine is used to perform the wet oxidation process, and the reaction formula is as follows:

AlGaAs(s)+H2O(g)→Al2O3(s)+As2O3(l)↑+H2(g)↑

GaAs(s)+H2O(g)→Ga2O3(s)+As2O3(s)+H2(g)↑

As2O3(s)+H2(g)→As(g)↑+H2O(g)↑

ideal wet oxidation process, the AlGaAs material of the oxidation limiting layer is changed into Al after reaction₂O₃Forming a loose porous structure and discharging other gas products. But the wet oxidation process is more complicated and the intermediate product isAn object, such as: as₂O₃，As₂H₃And the like are not easy to react completely in a short time, and easily cause As compounds or As not to be completely released, so that the oxide layer has larger residual stress, and further the oxide layer is cracked in the subsequent high-temperature process. The wet oxidation process adopted in the embodiment is specifically as follows:

wet oxidation temperature: 380-420 ℃;

wet oxidation chamber pressure: 50-400 mbar;

wet oxidation of H₂O flow rate: 10-30 g/L;

wet oxidation of H₂/N₂Flow rate: 0.6-1.1L/min;

wet oxidation time: 10-40 min;

the formula of the oxidation depth and the oxidation time of the wet oxidation is as follows:

g₀＝δw/δt|_t＝0＝K₁*N₀

wherein w (t) is a function of the depth of the oxide layer as a function of the oxidation time, K₁Is the proportionality constant, K₂Is the stopping constant of the self-limiting reaction, N₀Is the number of diffusion channels available for wet oxidation per unit area, t is the wet oxidation reaction time, g₀Is the oxidation rate.

The above formula shows that under the condition of fixed wet oxidation process parameters and oxide layer material, the oxidation rate is increased by N₀And (6) determining. Because the side wall of the oxidation limiting layer is formed by Al after the dry oxidation process₂O₃And As₂O₅A loose porous structure is formed, and the porous structure formed by the dry oxidation process is denser than that formed by the wet oxidation process, namely N in the wet oxidation process of the second stage₀Less than N formed by pure wet oxidation process₀. Based on the above formula, N₀The smaller, the smaller the depth of oxidation in the same time, the smaller the oxidation rate, i.e. the time required to reach the same depth of oxidationThe longer the time, the longer the reaction time under the same reaction conditions, the As₂O₃And As₂H₃And H₂O or H₂The more complete the reaction to form As and the more complete the release of As or As compound, the smaller the residual stress of the oxide layer. Therefore, the dense loose porous structure formed by the first-stage dry oxidation process effectively controls the wet oxidation rate of the second stage, so that the wet oxidation process is not only time-dependent or temperature-dependent any more, the reaction time is effectively prolonged under the target oxidation depth, the oxide layer stress is reduced, and the problem of oxide layer cracking caused by unreleased As is solved. In addition, due to the relative reduction of the oxidation speed, more precise control of the shape and the pore diameter of the oxidized pores can be realized, so that the finally generated oxidized pores are closer to the expectation. In fact, through experimental verification, the oxidation rate of the second stage wet oxidation process is lower than that of the oxidation pore generation by using the wet oxidation only under the same wet oxidation process.

The final structure of the oxide confining layer is shown in fig. 2, and it can be seen that there is a circle of denser porous structure generated by Dry oxidation (Dry oxidation) at the outer edge, a less dense porous structure generated by Wet oxidation (Wet oxidation) at the inner edge, and an oxidized pore (void) formed by unoxidized high aluminum component at the middle part of the oxide confining layer. As shown in FIG. 2, Ga is formed between the P-type DBR layer 5 and the oxide confinement layer 6 with the increase of the oxidation time during the oxidation process₂O₃This structure results in a rough layer (GaAs rough layer) of the AlGaAs/GaAs interface. The rough layer can reduce the adhesion between AlGaAs and GaAs interfaces, and if excessive film layer stress remains after the oxide layer is stopped in the oxidation process, the mechanical deformation caused by the release of the film layer stress in the subsequent high-temperature process can cause the film layer separation or cracking of the vertical cavity surface emitting laser multilayer stack structure from the rough layer (i.e. the layer with the weakest adhesion).