Vertical cavity surface emitting laser preparation method and vertical cavity surface emitting laser

Abstract

The application discloses a preparation method of a vertical cavity surface emitting laser, wherein the vertical cavity surface emitting laser takes (100) crystal surface GaAs as a substrate material; the preparation method comprises the following steps: a wet oxidation step, which is used for taking the outer ring area of one or more high aluminum layers in a DBR as a target oxidation area, oxidizing the target oxidation area into aluminum oxide, and forming an unoxidized oxidation hole in the middle area of the one or more high aluminum layers; the preparation method further comprises an ion implantation step before the wet oxidation step, which is used for forming a defect area with ion implantation damage in part of the target oxidation area by means of ion implantation, and making the oxidation hole generated by the wet oxidation step into a non-circular oxidation hole based on the wet oxidation rate difference between the defect area and other areas in the target oxidation area. The application further discloses a vertical cavity surface emitting laser. The application can greatly reduce the production cost and chip cutting difficulty while ensuring the performance of the VCSEL laser.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a method for fabricating a vertical cavity surface-emitting laser. Background Technology

[0002] Low power consumption, low threshold current, fast modulation speed, high beam quality, compact chip structure, and low manufacturing cost make vertical-cavity surface-emitting lasers (VCSELs) ideal light sources for short-range optical communication. Furthermore, VCSEL lasers are widely used in attitude sensing, medical technology, 3D sensors, optical storage, and other technological fields. VCSEL lasers have thin active regions, short cavity lengths, and low single-layer gain; employing stacked multilayer quantum well (DBR) structures can significantly improve their effective photon lifetime. To improve the convergence of the current injected into the quantum well active layer, existing VCSEL lasers often use a wet oxidation process to remove one or more high-aluminum-content Al atoms from the DBR. x Ga 1-x As (x≥0.95) layer oxidized to AlO x The high-alumina DBR layer directly above the active layer is not oxidized, forming oxide holes and thus creating annular circular current channels. This structure is called an oxide-confined DBR structure. This constricted current channel can effectively reduce the threshold current of the VCSEL laser. Simultaneously, because the high-alumina DBR layer material at the oxide holes is not oxidized, the GaAs / Al ratio is maintained. x Ga 1-x With As remaining constant, the refractive index remains between 3 and 3.11, while the oxidized DBR high-alumina layer around the oxide pores is made of Al. x Ga 1-x As becomes AlO x The refractive index is reduced from 3.11 to 1.6. The resulting refractive index difference in the DBR material can significantly confine the light emitted from the active layer to the vertical direction, improving the photon lifetime of the laser and further reducing the threshold current of the VCSEL laser. A typical basic structure of an oxide-confined VCSEL is shown below. Figure 1 As shown, from bottom to top, the structure consists of GaAs substrate 1, buffer layer 2, N-type DBR 3, quantum well 4, oxide layer 5, P-type DBR 6, N-type electrode 7, and P-type electrode 8. A circular oxide hole is formed in the middle of oxide layer 5.

[0003] While traditional annular circular current and photonic channels can effectively reduce the threshold current of VCSEL lasers, the symmetry of the annular circular structure results in insufficient polarization state stability of the VCSEL laser beam. Instability in the polarization state of the VCSEL laser beam during data transmission increases data transmission noise, reducing bandwidth and quality. To address this issue, existing VCSEL lasers typically use non-(100) crystal plane GaAs substrates for DBR and quantum well material growth. This utilizes the anisotropy of gain in different directions of the (n11) crystal plane and the difference in wet oxidation rates between the [-110] and

[110] crystal directions to create non-circular oxide holes, thus improving the polarization state stability of the VCSEL laser beam. However, the difference in growth along different directions of the (n11) crystal plane results in a rough material growth surface, causing different quantum well materials to interpenetrate at the interface, affecting quantum well efficiency and reducing laser performance. Simultaneously, it reduces the carbon (C) doping concentration in the P-DBR, ultimately increasing the threshold current of the VCSEL laser and decreasing its reliability. In addition, non-(100) crystal GaAs substrates are relatively expensive and more difficult to cut into chips. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for fabricating a vertical cavity surface-emitting laser. It can realize non-circular oxide holes of arbitrary shape as needed without using non-(100) crystal GaAs substrate material. While ensuring the performance of VCSEL laser, it can significantly reduce production costs and chip cutting difficulty.

[0005] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems:

[0006] A method for fabricating a vertical-cavity surface-emitting laser (VCSEL) using (100) crystal GaAs as the substrate material; the fabrication method includes: a wet oxidation step, used to oxidize the outer region of one or more high-alumina layers in a DBR to aluminum oxide, and to form unoxidized oxide holes in the middle region of the one or more high-alumina layers; the fabrication method further includes: an ion implantation step before the wet oxidation step, used to form defect regions with ion implantation damage in a portion of the target oxidation region by ion implantation, and based on the difference in wet oxidation rate between the defect region and other regions in the target oxidation region, to make the oxide holes generated by the wet oxidation step non-circular oxide holes.

[0007] Preferably, the mask material used for ion implantation is photoresist.

[0008] Preferably, the mask used for ion implantation is disposed on the surface of a circular active region platform, and the mask has at least two ion implantation holes of the same shape.

[0009] More preferably, the ion implantation aperture is elliptical, with its minor axis located radially on the circular active region platform.

[0010] More preferably, the ratio of the minor axis to the major axis of the ion implantation hole is 0.2 to 0.9, and the ratio of the distance from the center point of the ion implantation hole to the center of the circular active region platform surface to the radius of the circular active region platform is 0.6 to 0.9.

[0011] More preferably, the ion implantation holes are uniformly distributed circumferentially on the surface of the circular active region platform.

[0012] More preferably, the ion implantation aperture is a rounded rectangle, rhombus, or triangle.

[0013] A vertical cavity surface-emitting laser has non-circular oxide holes, which are prepared using the preparation method described in any of the above technical solutions.

[0014] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0015] This invention employs ion implantation technology, commonly used in semiconductor manufacturing. Before the wet oxidation step, ion implantation is used to create defect regions with ion implantation damage in a portion of the target oxidation region. Based on the difference in wet oxidation rate between the defect region and other regions in the target oxidation region, the oxide holes generated by the wet oxidation step are non-circular. This eliminates the limitation of existing technologies that require the use of non-(100) crystal GaAs substrate materials to generate non-circular oxide holes. It allows the use of lower-cost (100) crystal GaAs substrate materials, which significantly reduces the production cost of VCSEL lasers and the difficulty of chip cutting while ensuring the performance of VCSEL lasers. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the longitudinal cross-sectional structure of a typical oxidation-limited VCSEL;

[0017] Figure 2 A schematic diagram of the longitudinal section structure of a VCSEL provided by the present invention;

[0018] Figures 3a to 3l for Figure 2 The diagram shows the preparation process of VCSEL.

[0019] Figure 4 Example of an ion implantation mask pattern;

[0020] Figure 5 for Figure 4 A detailed structural schematic diagram of the ion implantation mask pattern shown;

[0021] Figure 6 For use Figure 4 A schematic diagram of the oxide holes obtained by the ion implantation mask pattern shown.

[0022] The figure includes the following reference numerals:

[0023] 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 metal, 10. P-type via metal, 11. Water and oxygen barrier film, 12. P-type active region platform, 13. Light emission aperture, 14. Ion implantation region, 15. Circle on the active region platform, 16. Ion implantation hole. Detailed Implementation

[0024] To address the shortcomings of existing technologies that use non-(100) crystal GaAs substrates to achieve non-circular oxide holes, the present invention addresses this issue by first implanting ions into a portion of the target oxide region to create defect areas with ion implantation damage before the wet oxidation step. Based on the difference in wet oxidation rates between the defect areas and other areas in the target oxide region, the oxide holes generated by the wet oxidation step are non-circular. This eliminates the limitation of existing technologies that require the use of non-(100) crystal GaAs substrates to generate non-circular oxide holes, allowing the use of lower-priced (100) crystal GaAs substrates. This significantly reduces the production cost and chip cutting difficulty of VCSEL lasers while ensuring VCSEL laser performance.

[0025] The inventors discovered that when high-alumina layers are treated with ion implantation, ion implantation damage is formed within the high-alumina layer. These damaged areas contain defects, which accelerate the wet oxidation rate in the defective regions, typically by 20-50% compared to defect-free high-alumina layers. Based on this principle, the inventors proposed the following technical solution:

[0026] A method for fabricating a vertical-cavity surface-emitting laser (VCSEL) using (100) crystal GaAs as the substrate material; the fabrication method includes: a wet oxidation step, used to oxidize the outer region of one or more high-alumina layers in a DBR to aluminum oxide, and to form unoxidized oxide holes in the middle region of the one or more high-alumina layers; the fabrication method further includes: an ion implantation step before the wet oxidation step, used to form defect regions with ion implantation damage in a portion of the target oxidation region by ion implantation, and based on the difference in wet oxidation rate between the defect region and other regions in the target oxidation region, to make the oxide holes generated by the wet oxidation step non-circular oxide holes.

[0027] The ion implantation method of this invention can use commonly used implanted ions such as O and Ar, and the specific ion implantation process parameters can be flexibly set according to actual conditions. Since the purpose of ion implantation is to form a defect region with ion implantation damage in a certain area of ​​the target oxide region, and to utilize the difference in wet oxidation rate between the defect region and other areas of the target oxide region to generate non-circular oxide holes, the control requirements for ion implantation process parameters are relatively low. The thickness of the ion implantation region can be greater than or less than the thickness of the target oxide region, as long as the two intersect, the required defect region can be generated in the target oxide region.

[0028] The mask material used for ion implantation can be any existing mask material, preferably photoresist.

[0029] Preferably, the mask used for ion implantation is disposed on the surface of a circular active region platform, and the mask has at least two ion implantation holes of the same shape.

[0030] More preferably, the ion implantation aperture is elliptical, with its minor axis located radially on the circular active region platform.

[0031] More preferably, the ratio of the minor axis to the major axis of the ion implantation hole is 0.2 to 0.9, and the ratio of the distance from the center point of the ion implantation hole to the center of the circular active region platform surface to the radius of the circular active region platform is 0.6 to 0.9.

[0032] More preferably, the ion implantation holes are uniformly distributed circumferentially on the surface of the circular active region platform.

[0033] More preferably, the ion implantation aperture is a rounded rectangle, rhombus, or triangle.

[0034] To facilitate public understanding, the technical solution of the present invention will be described in detail below through a specific embodiment:

[0035] The basic structure of the VCSEL in this embodiment is as follows: Figure 2 As shown, it includes: GaAs substrate 1, buffer layer 2, N-type DBR 3, quantum well 4, oxide layer 5, P-type DBR 6, N-type electrode 7, P-type electrode 8, N-type via metal 9, P-type Ring metal 10, water and oxygen barrier film layer 11, P-type active region platform 12, and light-emitting aperture 13; wherein, the GaAs substrate material is (100) crystal plane GaAs; as Figure 2 As shown, there is an ion implantation region 14 near the oxide layer 5 that has undergone ion implantation treatment. 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. This part of the high-alumina layer material in the oxide layer 5 that has been implanted with ions will produce defects. During the wet oxidation process, the oxidation rate of the defective area is higher than that of the non-defective area. This difference in wet oxidation rate will cause the oxide holes generated by the wet oxidation step to be non-circular.

[0036] Figure 2 The specific fabrication process of the VCSEL shown is as follows:

[0037] Step 1: The epitaxial wafer grown on the (100) crystal plane GaAs substrate (e.g.) Figure 3a (As shown) A photoresist film with a thickness of 5-15 μm is coated on the surface; the photoresist is exposed and developed to obtain a ring-shaped photoresist pattern used to form the P-type active region platform, see... Figure 3b ;

[0038] Step 2: Using ICP dry etching, etch the epitaxial wafer obtained in Step 1. The etching gas is Cl2 / BCl3 or Cl2 / SiCl4. Etch down to the 1-10 pairs of P-DBRs below the quantum well layer, etching out the P-type active region platform structure, thus exposing the high-aluminum layer to be oxidized. Figure 3c As shown; after removing the photoresist, the P-type active region platform is obtained, see... Figure 3d ;

[0039] Step 3: Coat the surface of the epitaxial wafer obtained in Step 2 with ion implantation photoresist. The photoresist film thickness is 5-15 μm. Expose and develop the photoresist to obtain the ion implantation patterned photoresist. (See attached image) Figure 3e ;

[0040] Step 4, as follows Figure 3f As shown, the epitaxial wafer obtained in step 3 is subjected to an ion implantation process, and the P-DBR is subjected to O ion implantation with an implantation metering of 5E. 10 -5E 12 / cm 2 Ion implantation energy 350-700 KeV; after ion implantation, the photoresist is removed to obtain an epitaxial wafer with defect areas in the high-alumina layer to be oxidized, see... Figure 3g ;

[0041] Step 5, as follows Figure 3h As shown, the high-alumina Al layer from step 4 is oxidized using a wet oxidation process. x Ga 1-x Al oxidation in the As layer yields a P-type active region platform with an oxidation-restricted structure;

[0042] Step 6, as follows Figure 3i As shown, a water-oxygen barrier film is deposited on the surface of the epitaxial wafer obtained in step 5. The deposition process is PECVD or ALD. The film is made of SiNx, SiOx, SiON, AlOx, TiOx, etc., and can be a single layer or a stack of the above materials. The film thickness is 20-1000 nm. The water vapor barrier capacity (WVTR) of this water-oxygen barrier film is 5E. -2 ~1E -4 Oxygen barrier function (OTR) is 5E. 0 ~1E -1 ;

[0043] Step 7: Perform metal via etching on the epitaxial wafer completed in Step 6. The etching gas is CF4+Ar or BOE to obtain an epitaxial wafer with N-type and P-type metal vias. See [link to step 6]. Figure 3j ;

[0044] Step 8: Deposit metal onto the epitaxial wafer obtained in Step 7 to fill the vias. The metal may be Au, Pt, Ag, Al, etc., to obtain the following result: Figure 3k The structure shown;

[0045] Step 9: Deposit Pad metal on the epitaxial wafer obtained in Step 8. The metal can be Au, Pt, Ag, Al, etc., to obtain an epitaxial wafer with N-type and P-type electrodes. See [link to step 8]. Figure 3l ;

[0046] Step 10: Cleave the epitaxial wafer obtained in Step 9 to obtain... Figure 2 The VCSEL laser of the present invention is shown.

[0047] In the above preparation process, the ion implantation mask pattern can be flexibly designed as needed. A preferred solution is to set two or more ion implantation holes of the same shape on the mask. The ion implantation holes are preferably evenly distributed in the circumferential direction on the surface of the circular active region platform. The shape of the ion implantation holes is preferably elliptical, or a rounded rectangle, rhombus, or triangle. Figure 4 Several examples of elliptical ion implantation apertures are shown, namely three, four, and five elliptical apertures evenly distributed circumferentially on the surface of the circular active region platform; such as... Figure 5As shown, the major axis of the ellipse is AB, the minor axis is CD, the focus is O, the foci form a circle 15, the radius of circle 15 is EG, the distance from the focus O to the center of circle 15 (i.e. the center of the circular active area platform) is OE, and the radius of the circular active area platform is EF=R. Preferably, CD / AB=0.2-0.9, OE / EF=0.6-0.9. Figure 4 Oxide holes obtained from three ion implantation mask patterns, such as Figure 6 As shown, from left to right and Figure 4 A one-to-one correspondence shows that all of them are non-circular oxide pores.

[0048] As can be seen from the above embodiments, the present invention can create non-circular oxide holes of arbitrary shape in the epitaxial layer grown on the (100) crystal plane, which improves the problem of unstable beam polarization state of VCSEL laser and the stability of VCSEL laser. At the same time, the (100) crystal plane GaAs substrate is relatively inexpensive, which effectively reduces the manufacturing cost.

Claims

1. A method for fabricating a vertical-cavity surface-emitting laser, wherein the vertical-cavity surface-emitting laser uses (100) crystal plane GaAs as the substrate material; the fabrication method includes: A wet oxidation step is used to oxidize the outer region of one or more high-alumina layers in a DBR to aluminum oxide, and to form unoxidized oxide pores in the middle region of the one or more high-alumina layers. The method is characterized by further comprising an ion implantation step prior to the wet oxidation step, used to form defect regions with ion implantation damage in a portion of the target oxidation region through ion implantation, and based on the difference in wet oxidation rate between the defect regions and other regions in the target oxidation region, ensuring that the oxide pores generated by the wet oxidation step are non-circular.

2. The method for fabricating a vertical-cavity surface-emitting laser as described in claim 1, characterized in that, The mask material used for ion implantation is photoresist.

3. The method for fabricating a vertical-cavity surface-emitting laser as described in claim 1, characterized in that, The mask used for ion implantation is arranged on the surface of the circular active region platform, and the mask has at least two ion implantation holes of the same shape.

4. The method for fabricating a vertical-cavity surface-emitting laser as described in claim 3, characterized in that, The ion implantation aperture is elliptical, with its minor axis located radially on the circular active region platform.

5. The method for fabricating a vertical-cavity surface-emitting laser as described in claim 4, characterized in that, The ratio of the minor axis to the major axis of the ion implantation aperture is 0.2 to 0.9, and the ratio of the distance from the center point of the ion implantation aperture to the center of the circular active region platform surface to the radius of the circular active region platform is 0.6 to 0.

9.

6. The method for fabricating a vertical-cavity surface-emitting laser as described in claim 3, characterized in that, The ion implantation holes are uniformly distributed circumferentially on the surface of the circular active region platform.

7. The method for fabricating a vertical-cavity surface-emitting laser as described in claim 3, characterized in that, The ion implantation aperture is a rounded rectangle, rhombus, or triangle.

8. A vertical-cavity surface-emitting laser having a non-circular oxide aperture, characterized in that, It was prepared using the preparation method described in any one of claims 1 to 7.

Images