CN115207774A

CN115207774A - Vertical cavity surface emitting laser and preparation method thereof

Info

Publication number: CN115207774A
Application number: CN202210747428.7A
Authority: CN
Inventors: 李加伟; 严磊
Original assignee: Suzhou Changrui Photoelectric Co ltd
Current assignee: Suzhou Changrui Photoelectric Co ltd
Priority date: 2022-06-28
Filing date: 2022-06-28
Publication date: 2022-10-18

Abstract

The invention discloses a preparation method of a vertical cavity surface emitting laser, wherein the vertical cavity surface emitting laser takes (100) crystal face GaAs as a substrate material; the preparation method comprises the following steps: a wet oxidation step of oxidizing an outer circumference region of one or more high aluminum layers in the DBR, which is a target oxidation region, to aluminum oxide, and forming an oxidation hole that is not oxidized in an intermediate region of the one or more high aluminum layers; the preparation method also comprises the following steps: and an ion implantation step before the wet oxidation step, wherein the ion implantation step is used for forming a defect area with ion implantation damage in a partial area in the target oxidation area by means of ion implantation, and the oxidation hole generated by the wet oxidation step is a noncircular oxidation hole based on the difference of the wet oxidation rate between the defect area and other areas in the target oxidation area. The invention also discloses a vertical cavity surface emitting laser. The invention can greatly reduce the production cost and the chip cutting difficulty while ensuring the performance of the VCSEL laser.

Description

Vertical cavity surface emitting laser and preparation method thereof

Technical Field

The invention relates to the technical field of semiconductor manufacturing, in particular to a preparation method of a vertical cavity surface emitting laser.

Background

The Vertical Cavity Surface Emitting Laser (VCSEL) is an ideal light source for short-distance optical communication, and has the advantages of low power consumption, small threshold current, high modulation speed, high light beam quality, compact chip structure and low manufacturing cost. In addition, the VCSEL laser is also widely applied to the technical fields of attitude sensing, medical technology, 3D sensors, optical storage, and the like. VCSEL laser with thin active region and long cavityShort, the single-layer gain is small, and the effective photon life can be greatly prolonged by adopting a stacked multi-layer DBR structure. In order to improve the convergence of current injected into the active layer of the quantum well, the conventional VCSEL laser mostly adopts a wet oxidation process to mix one or more layers of Al with high aluminum content in the DBR _x Ga _1-x Oxidizing As (x is more than or equal to 0.95) layer into AlO _x The DBR high aluminum layer directly above the active layer is not oxidized to form an oxidized hole, thereby obtaining an annular circular current path, which is called an oxidized confinement type DBR structure, and the collected current path can effectively reduce the threshold current of the VCSEL laser. Meanwhile, because the DBR high-aluminum layer material at the oxide hole is not oxidized, gaAs/Al is kept _x Ga _1-x As is unchanged, the refractive index is kept within 3-3.11, and the oxidized DBR high aluminum layer around the oxidation hole is made of Al _x Ga _1-x As becomes AlO _x The refractive index is reduced from 3.11 to 1.6, so that the difference of the refractive indexes of the DBR materials can greatly limit the light emitted by the active layer to the vertical direction, the photon life of the laser is prolonged, and the threshold current of the VCSEL laser is further reduced. As shown in fig. 1, a basic structure of a typical oxide-confined VCSEL includes, in order from bottom to top, a GaAs substrate 1, a buffer layer 2, an N-type DBR3, a quantum well 4, an oxide layer 5, a P-type DBR6, an N-type electrode 7, and a P-type electrode 8, and a circular oxide hole is formed in the middle of the oxide layer 5.

Although the threshold current of the VCSEL laser can be effectively reduced by the conventional annular circular current and photon channel, the stability of the beam polarization state of the VCSEL laser is insufficient due to the symmetry of the annular circular structure. In the data transmission process, the unstable polarization state of the VCSEL laser beam can increase the noise of data transmission and reduce the bandwidth and quality of data transmission. In order to solve the problem of unstable polarization state of the laser beam, the existing VCSEL laser generally selects a non (100) crystal face GaAs substrate to grow a DBR material and a quantum well material, and utilizes the anisotropy of gain of the material in different directions of a (n 11) crystal face and the difference of wet oxidation rates in two crystal directions of [ -110] and [110] to cause an oxidation hole to be non-circular, so that the stability of the polarization state of the VCSEL laser beam is improved. However, the difference of the growth of the materials in different directions of the (n 11) crystal face can cause the growth face of the materials to be rough, so that different quantum well materials can permeate into each other at the interface, the efficiency of the quantum well is influenced, and the performance of the laser is reduced; and meanwhile, the doping concentration of carbon (C) in the P-DBR is also reduced, the threshold current of the VCSEL laser is finally increased, and the reliability of the laser is reduced. In addition, the non- (100) plane GaAs substrate sheet is relatively expensive, and the dicing of the chip is relatively more difficult.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a preparation method of a vertical cavity surface emitting laser, which can realize a noncircular oxidized hole with any shape as required without using a non (100) crystal face GaAs substrate material, and can greatly reduce the production cost and the chip cutting difficulty while ensuring the performance of the VCSEL laser.

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

a vertical cavity surface emitting laser preparation method, the said vertical cavity surface emitting laser regards (100) crystal plane GaAs as the substrate material; the preparation method comprises the following steps: a wet oxidation step of oxidizing an outer circumference region of one or more high aluminum layers in the DBR, which is a target oxidation region, to aluminum oxide, and forming an oxidation hole that is not oxidized in an intermediate region of the one or more high aluminum layers; the preparation method further comprises the following steps: and an ion implantation step before the wet oxidation step, wherein the ion implantation step is used for forming a defect area with ion implantation damage in a partial area in the target oxidation area by means of ion implantation, and the oxidation hole generated by the wet oxidation step is a noncircular oxidation hole based on the difference of the wet oxidation rate between the defect area and other areas in the target oxidation area.

Preferably, the mask material used for the ion implantation is photoresist.

Preferably, the mask used for the ion implantation is arranged on the surface of the circular active region platform, and at least two ion implantation holes with the same shape are arranged on the mask.

Further preferably, the ion injection hole is elliptical, and the minor axis of the ion injection hole is located in the radial direction of the circular active region platform.

Still more preferably, the ratio of the minor axis to the major axis of the ion-injecting hole is 0.2 to 0.9, and the ratio of the distance from the center point of the ion-injecting hole to the center of the surface of the circular active region plateau to the radius of the circular active region plateau is 0.6 to 0.9.

Further preferably, the ion injection holes are uniformly distributed in the circumferential direction of the circular active zone plateau surface.

Further preferably, the ion-injection hole is a rounded rectangle, rhombus or triangle.

A vertical cavity surface emitting laser having a non-circular oxidized via prepared using the method of any of the above embodiments.

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

according to the invention, an ion implantation technology commonly used in semiconductor manufacturing is adopted, a defect region with ion implantation damage is formed in a partial region in a target oxidation region in an ion implantation mode before a wet oxidation step, and based on the difference of wet oxidation rates between the defect region and other regions in the target oxidation region, an oxidation hole generated in the wet oxidation step is a non-circular oxidation hole, so that the limitation that a non- (100) crystal face GaAs substrate material is required to be used for generating the non-circular oxidation hole in the prior art is eliminated, the (100) crystal face GaAs substrate material with lower price can be used, the performance of the VCSEL laser is ensured, and the production cost and the chip cutting difficulty of the VCSEL laser are greatly reduced.

Drawings

FIG. 1 is a schematic diagram of a longitudinal cross-sectional structure of a typical oxide-confined VCSEL;

FIG. 2 is a schematic diagram of a vertical cross-sectional structure of a VCSEL provided in the present invention;

FIGS. 3a to 3l are schematic diagrams illustrating a process of fabricating the VCSEL device shown in FIG. 2;

FIG. 4 is an example of an ion implantation mask pattern;

FIG. 5 is a detailed structure diagram of the ion implantation mask pattern shown in FIG. 4;

fig. 6 is a schematic view of an oxidized via obtained using the ion implantation mask pattern shown in fig. 4.

The following reference numerals are included in the figures:

1. GaAs substrate, 2, buffer layer, 3, N-type DBR,4, quantum well, 5, oxide layer, 6, P-type DBR,7, N-type electrode, 8, P-type electrode, 9, N-type via hole metal, 10, P-type via hole metal, 11, water-oxygen barrier film layer, 12, P-type active region platform, 13, light-emitting hole, 14, ion implantation region, 15, circle on the active region platform, 16, ion implantation hole.

Detailed Description

Aiming at the defect that a noncircular oxidized hole is realized by adopting a noncircular (100) crystal face GaAs substrate material in the prior art, the invention solves the problem that a part of a region in a target oxidized region forms a defect region with ion implantation damage in an ion implantation mode before a wet oxidation step, and the oxidized hole generated in the wet oxidation step is the noncircular oxidized hole based on the difference of wet oxidation rates between the defect region and other regions in the target oxidized region, thereby eliminating the limitation that the noncircular oxidized hole generated in the prior art must use the noncircular (100) crystal face GaAs substrate material, using the lower-price (100) GaAs crystal face GaAs substrate material, ensuring the performance of the VCSEL laser and greatly reducing the production cost and the chip cutting difficulty of the VCSEL laser.

The inventor finds that: the ion implantation process is used to treat the high aluminum layer, ion implantation damage can be formed in the high aluminum layer, the damaged high aluminum layer region has defects, and the defects can accelerate the wet oxidation rate of the defective region and are generally 20-50% faster than the wet oxidation rate of the defect-free high aluminum layer region. Based on the principle, the inventor provides the following technical scheme:

The ion implantation of the technical scheme of the invention can adopt the commonly used ions such as O, ar and the like for implantation, and the specific ion implantation process parameters can be flexibly set according to the actual conditions. Since the purpose of ion implantation is to form a defect region having ion implantation damage in a partial region of a target oxidation region to generate a non-circular oxidation hole by using a difference in wet oxidation rate between the defect region and other regions of the target oxidation region, the requirement for controlling the ion implantation process parameters is low, and the thickness of the ion implantation region may be greater than or less than that of the target oxidation region, as long as the two intersect to generate a desired defect region in the target oxidation region.

The mask material used for the ion implantation may be any of various existing mask materials, preferably a photoresist.

Further preferably, the ion-injection hole is a rounded rectangle, a diamond or a triangle.

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

the basic structure of the VCSEL of the present embodiment is shown in fig. 2, and includes: the semiconductor device comprises a GaAs substrate 1, a buffer layer 2, an N-type DBR3, a quantum well 4, an oxide layer 5, a P-type DBR6, an N-type electrode 7, a P-type electrode 8, an N-type via metal 9, a P-type Ring metal 10, a water-oxygen barrier film layer 11, a P-type active region platform 12 and a light emitting hole 13; wherein, the GaAs substrate material adopts a (100) crystal face GaAs; as shown in fig. 2, an ion implantation region 14 processed by ion implantation exists near the oxide layer 5, in this embodiment, the thickness of the ion implantation region 14 is greater than the thickness of the oxide layer 5 and overlaps with the oxide layer 5, the portion of the high aluminum layer material implanted with ions in the oxide layer 5 generates defects, the oxidation rate of the defect region during the wet oxidation process is higher than that of the defect-free region, and the difference in the wet oxidation rates may cause the oxidized pores generated by the wet oxidation step to be non-circular.

The VCSEL process shown in fig. 2 is specifically as follows:

step 1, coating photoresist on the surface of an epitaxial wafer (shown in figure 3 a) grown on a (100) crystal face GaAs substrate wafer, wherein the thickness of the photoresist is 5-15um; exposing and developing the photoresist to obtain a circular photoresist pattern for forming a P-type active region platform, as shown in fig. 3b;

step 2, etching the epitaxial wafer obtained in the step 1 by adopting an ICP (inductively coupled plasma) dry etching process, wherein the etching gas is Cl2/BCl3 or Cl2/SiCl4, etching to the lower layer 1-10 pairs of P-DBRs (P-type distributed Bragg reflectors) of the quantum well layer, and etching a P-type active region platform structure to expose the high aluminum layer to be oxidized, as shown in a figure 3 c; removing the photoresist to obtain a P-type active region platform, as shown in fig. 3d;

step 3, coating ion implantation photoresist on the surface of the epitaxial wafer obtained in the step 2, wherein the thickness of the photoresist is 5-15um, and exposing and developing the photoresist to obtain ion implantation pattern photoresist, which is shown in figure 3e;

step 4, as shown in fig. 3f, performing ion implantation process on the epitaxial wafer obtained in the step 3, performing O ion implantation on the P-DBR, and performing implantation metering 5E ¹⁰ -5E ¹² /cm ² The implantation energy is 350-700Kev; removing the photoresist after ion implantation to obtain an epitaxial wafer with a defect region on the high aluminum layer to be oxidized, which is shown in figure 3g;

step 5, as shown in fig. 3h, oxidizing the high aluminum layer Al in the step 4 by adopting a wet oxidation process _x Ga _1-x Oxidizing Al in the As layer to obtain a P-type active region platform with an oxidation limiting structure;

step 6, as shown in fig. 3i, a water and oxygen barrier film layer is plated on the surface of the epitaxial wafer obtained in the step 5, the film coating process is PECVD or ALD, the film layer is SiNx, siOx, siON, alOx, tiOx, etc., the film layer can be a single layer or a lamination of the above film materials, the film thickness is 20-1000nm, and the water and oxygen barrier film layer has a water vapor barrier capacity WVTR of 5E ^-2 ~1E ^-4 Oxygen barrier OTR of 5E ⁰ ~1E ^-1 ；

And 7, etching the metal through hole of the epitaxial wafer completed in the step 6, wherein the etching gas is CF ₄ + Ar or BOE, resulting in an epitaxial wafer with N-type metal vias and P-type metal vias, see fig. 3j;

step 8, depositing metal on the epitaxial wafer obtained in the step 7 to fill the via holes, wherein the metal is Au, pt, ag, al and the like, and a structure shown in a figure 3k is obtained;

step 9, depositing Pad metal on the epitaxial wafer obtained in the step 8, wherein the metal is Au, pt, ag, al and the like, and obtaining the epitaxial wafer with the N-type electrode and the P-type electrode, as shown in fig. 3l;

and step 10, splitting the epitaxial wafer obtained in the step 9 to obtain the VCSEL laser disclosed by the invention and shown in FIG. 2.

In the preparation process, the pattern of the ion implantation mask can be flexibly designed according to the requirement, and the preferred scheme is to arrange two or more ion implantation holes with the same shape on the mask; the ion implantation holes are preferably uniformly distributed in the circumferential direction of the surface of the circular active region platform; the shape of the ion-injection hole is preferably an ellipse, or a rectangle, a rhombus or a triangle with rounded corners. Fig. 4 shows several examples in which the ion-injection hole is elliptical, three, four, and five elliptical shapes, respectively, uniformly distributed in the circumferential direction of the circular active region mesa surface; as shown in fig. 5, the ellipse has a major axis length AB, a minor axis length CD, an ellipse focus O, and an ellipse focus forming a circle 15, the circle 15 has a radius EG, the ellipse focus O is located a distance OE from the center of the circle 15 (i.e., the center of the circular active region mesa), the circular active region mesa has a radius EF = R, preferably, CD/AB =0.2-0.9, and OE/EF =0.6-0.9. The oxide holes obtained by the three types of ion implantation mask patterns in fig. 4 are shown in fig. 6, and are all noncircular oxide holes as can be seen from left to right in one-to-one correspondence with fig. 4.

According to the embodiments, the noncircular oxidation hole with any shape can be manufactured on the epitaxial layer grown on the (100) crystal face, the problem of unstable beam polarization state of the VCSEL laser and the stability of the VCSEL laser are improved, and meanwhile, the GaAs substrate sheet of the (100) crystal face is relatively cheap, so that the manufacturing cost is effectively reduced.

Claims

1. A vertical cavity surface emitting laser preparation method, the said vertical cavity surface emitting laser regards (100) crystal plane GaAs as the substrate material; the preparation method comprises the following steps: a wet oxidation step of oxidizing an outer circumference region of one or more high aluminum layers in the DBR, which is a target oxidation region, to aluminum oxide, and forming an oxidation hole that is not oxidized in an intermediate region of the one or more high aluminum layers; characterized in that the preparation method further comprises the following steps: and an ion implantation step before the wet oxidation step, wherein the ion implantation step is used for forming a defect area with ion implantation damage in a partial area in the target oxidation area by means of ion implantation, and the oxidation hole generated by the wet oxidation step is a noncircular oxidation hole based on the difference of the wet oxidation rate between the defect area and other areas in the target oxidation area.

2. A method for fabricating a vertical cavity surface emitting laser according to claim 1, wherein said ion implantation uses a mask material of photoresist.

3. A method for fabricating a vertical cavity surface emitting laser according to claim 1, wherein a mask used for said ion implantation is disposed on the surface of the circular active region mesa, and at least two ion-injection holes having the same shape are disposed on the mask.

4. A method according to claim 3, wherein the ion-injecting hole is elliptical and has a minor axis located radially from the mesa.

5. A method of fabricating a vertical cavity surface emitting laser according to claim 4, wherein the ratio of the minor axis to the major axis of the ion injection hole is 0.2 to 0.9, and the ratio of the distance from the center point of the ion injection hole to the center of the mesa surface of the circular active region to the radius of the mesa of the circular active region is 0.6 to 0.9.

6. A method of fabricating a vertical cavity surface emitting laser according to claim 3, wherein said ion injection holes are uniformly distributed in a circumferential direction of the circular active region mesa surface.

7. A method according to claim 3, wherein the ion-injecting hole is rectangular, rhombus, or triangular with rounded corners.

8. A vertical cavity surface emitting laser having a noncircular oxidized hole, characterized by being produced by the production method according to any one of claims 1 to 7.