A method for manufacturing an oxidation-confined vertical cavity surface emitting laser

Abstract

The present invention discloses a method for manufacturing an oxidation-limited vertical cavity surface emitting laser. The manufacturing method of the present invention includes: a wet oxidation step for oxidizing the outer ring area of ​​one or more high-aluminum layers in the DBR into aluminum oxide to form unoxidized oxidation holes in the middle area of ​​the one or more high-aluminum layers; the manufacturing method also includes an ion implantation step before the wet oxidation step for implanting ions into part or all of the outer ring area of ​​the one or more high-aluminum layers to reduce the process temperature in the wet oxidation step. The present invention also discloses an oxidation-limited vertical cavity surface emitting laser obtained by the above-mentioned manufacturing method. Compared with the existing technology, the present invention can significantly reduce the process temperature of wet oxidation while meeting the required wet oxidation rate, thereby reducing the stress generated during the wet oxidation process and improving the reliability of the oxidation-limited vertical cavity surface emitting laser.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor manufacturing, and in particular relates to a method for manufacturing an oxidation-confined vertical cavity surface emitting laser. Background Art

[0002] Vertical-cavity surface-emitting lasers (VCSELs) are widely used in optical communications due to their fast modulation speed, high beam quality, low power consumption, simple structure, and low manufacturing cost. They are ideal light sources for short-distance optical communications. VCSELs have a thin active region, a short cavity length, and low single-layer gain.

[0003] Existing VCSELs usually use an oxidation-limited DBR (distributed Bragg reflection) structure, which is to use a wet oxidation process to reduce the DBR layer (usually Al x Ga 1-x As / GaAs or AlAs / GaAs) in one or more DBR layers with high aluminum content (Al x Ga 1-x As layer, x ≥ 0.95 or AlAs layer) is oxidized to form aluminum oxide, thus obtaining an oxidation-limited DBR structure. The unoxidized area in the middle forms an oxide hole, which serves as the photon and current channel of the laser. Aluminum oxide has extremely poor conductivity, and the current cannot pass through the aluminum oxide layer in the oxidation-limited DBR structure. Most of the injected current enters the active layer from the oxide hole under the restriction of the aluminum oxide layer, forming an effective restriction on the current injected into the active area. Al with high aluminum content x Ga 1-x As layer, x≥0.95 or AlAs layer, refractive index n is 2.9-3.0, GaAs layer refractive index n is 3.5-3.6, refractive index difference Δn before wet oxidation is 0.6-0.7, aluminum oxide formed by wet oxidation has a refractive index n of 1.5-1.6, and refractive index difference Δn increases to 2.0-2.1 after wet oxidation. Therefore, the oxidation-confined DBR structure can greatly improve the effective photon confinement capability. The basic structure of a typical oxidation-confined VCSEL is as follows: Figure 1 As shown, from bottom to top are 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, and dielectric layer 9.

[0004] The wet oxidation process of existing oxidation-limited VCSELs usually uses high temperature conditions of 410-480°C. Under the action of high temperature, water vapor will 0.98 Ga 0.02As, etc.) are oxidized to form compounds such as Al2O3, Ga2O3, and As. The reaction process is relatively complex. Taking the wet oxidation atmosphere as an H2 / N2 mixed gas and H2O vapor as an example, the chemical reaction process is as follows:

[0005] 2AlGaAs + 3H2O(g) = Al2O3 + 2AsH3 + 2Ga

[0006] 2AlGaAs + 4H2O(g) = 2AlO(OH) + 2AsH3 + 2Ga

[0007] 2AsH3 = 2As(g) + 3H2

[0008] 2AsH3 + 3H2O = As2O3(g) + 6H2 As2O3(l) + 3H2 = 2As(g) + 3H2O(g)

[0009] The wet oxidation rate increases exponentially with increasing temperature, so higher process temperatures can increase the wet oxidation rate. However, excessively high wet oxidation temperatures can generate significant oxide layer stress, which can lead to severe separation or cracking at the oxide layer and GaAs interface, compromising the reliability of the VCSEL laser and even causing it to malfunction. While lowering the wet oxidation process temperature can mitigate abnormalities such as interface separation, the reaction may be incomplete, preventing the formation of a well-defined oxidation-restricted structure. Furthermore, the slow reaction process can result in prolonged oxidation times, which can also severely impact VCSEL laser production capacity. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a method for manufacturing an oxidation-limited vertical cavity surface emitting laser. Under the premise of meeting the required wet oxidation rate, the process temperature of wet oxidation can be greatly reduced, thereby reducing the stress generated during the wet oxidation process and improving the reliability of the oxidation-limited vertical cavity surface emitting laser.

[0011] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0012] A method for manufacturing an oxidation-limited vertical cavity surface emitting laser comprises: a wet oxidation step for oxidizing the outer ring region of one or more high-aluminum layers in a DBR into aluminum oxide, so as to form unoxidized oxide holes in the middle region of the one or more high-aluminum layers; the manufacturing method further comprises an ion implantation step before the wet oxidation step for implanting ions into part or all of the outer ring region of the one or more high-aluminum layers, so as to reduce the process temperature in the wet oxidation step.

[0013] Preferably, the process temperature in the wet oxidation step is 360°C to 380°C.

[0014] Preferably, the inner diameter of the outer ring region of the one or more high-aluminum layers subjected to ion implantation is 1 μm to 6 μm larger than the diameter of the oxidation pores.

[0015] An oxidation-confined vertical cavity surface emitting laser is obtained using the manufacturing method described in any of the above technical solutions.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0017] Prior to wet oxidation, the present invention performs ion implantation on part or all of the area of ​​the high-aluminum layer to be oxidized, thereby causing ion implantation damage to this portion of the high-aluminum layer. This portion of the high-aluminum layer with ion implantation damage can achieve the same oxidation rate at a lower wet oxidation temperature. Consequently, the process temperature of the wet oxidation step can be lowered, significantly reducing the stress generated during the wet oxidation process while still meeting the required wet oxidation rate, thereby improving the reliability of the oxidation-confined vertical-cavity surface-emitting laser. Furthermore, because the present invention utilizes a mature ion implantation process, it is relatively low in cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of a typical oxide-confined vertical-cavity surface-emitting laser. The reference numerals are as follows: 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. dielectric layer.

[0019] Figure 2 It is a schematic diagram of the principle of the present invention. DETAILED DESCRIPTION

[0020] In response to the problem of excessively high wet oxidation process temperature in the prior art, the solution of the present invention is to perform ion implantation on part or all of the area of ​​the high-aluminum layer to be oxidized before wet oxidation, so that ion implantation damage is formed on this part of the high-aluminum layer. This part of the high-aluminum layer with ion implantation damage can achieve the same oxidation rate at a lower wet oxidation temperature. Therefore, the process temperature of the wet oxidation process can be reduced, thereby significantly reducing the stress generated during the wet oxidation process while meeting the required wet oxidation rate, thereby improving the reliability of the oxidation-limited vertical-cavity surface-emitting laser.

[0021] The present invention specifically adopts the following technical solutions to solve the above technical problems:

[0022] A method for manufacturing an oxidation-limited vertical cavity surface emitting laser comprises: a wet oxidation step for oxidizing the outer ring region of one or more high-aluminum layers in a DBR into aluminum oxide, so as to form unoxidized oxide holes in the middle region of the one or more high-aluminum layers; the manufacturing method further comprises an ion implantation step before the wet oxidation step for implanting ions into part or all of the outer ring region of the one or more high-aluminum layers, so as to reduce the process temperature in the wet oxidation step.

[0023] Compared with the existing oxidation temperature of 410-480°C, the wet oxidation process temperature of the present invention can be greatly reduced. Through a large number of experiments, it was found that when the process temperature in the wet oxidation step is 360°C to 380°C, its oxidation rate is equivalent to the oxidation rate of the traditional process, which can reach 0.2-0.8um / min, but the resulting stress is greatly reduced. Therefore, the present invention preferably adopts a wet oxidation process temperature of 360°C to 380°C.

[0024] Ideally, the ion implantation area should be exactly the part of the high-aluminum layer to be oxidized, but considering the control accuracy of the ion implantation area, in order to prevent adverse effects on the oxidation pores, the ion implantation area should be slightly larger than the oxidation pores to be set. Preferably, the inner diameter of the outer ring area of ​​the one or more high-aluminum layers for ion implantation is 1μm to 6μm larger than the diameter of the oxidation pores.

[0025] The implanted ions used in the present invention can be O, Ar, and other ions commonly used in existing ion implantation processes. Theoretical and experimental results show that these ion implantations can cause ion implantation damage to the high-aluminum layer, thereby achieving the purpose of reducing the wet oxidation process temperature. The specific ion implantation process parameters need to be flexibly adjusted according to the selected ion implantation target area depth, ion type, etc. Considering that ion implantation is an existing mature technology, it will not be detailed here.

[0026] To facilitate public understanding, the technical solution of the present invention is further described in detail below through a specific embodiment:

[0027] by Figure 1 Taking the oxidation-confined vertical cavity surface emitting laser of the structure shown as an example, the manufacturing method adopted by the present invention includes the following steps:

[0028] Step 1: Using ICP dry etching process, the etching gas is Cl2 / BCl3 or Cl2 / SiCl4, to etch the P Mesa step structure on the epitaxial wafer, so that the high aluminum layer to be oxidized in the active area platform structure is exposed. The etching is generally carried out to 1-10 pairs of P-DBRs under the quantum well layer;

[0029] Step 2: Figure 2As shown, a photolithography process is used to cover the central area of ​​the active area platform structure with photoresist (PR). The photoresist coverage area is slightly larger than the target oxidation hole. In this embodiment, the horizontal distance between the edge of the photoresist and the edge of the target oxidation hole is 1-3μm, and the photoresist film thickness is 5-10μm. Ion implantation is performed, and the implanted ions are O, Ar, etc. The implantation energy refers to the required implantation depth. The deeper the required implantation depth, the greater the implantation energy, which is generally 350-400Kev. The implantation metering refers to the thickness of the high aluminum layer. The thicker the high aluminum layer, the greater the required implantation metering, which is generally 1E 11 -5E 12 / cm 2 ;

[0030] Step 3: Figure 2 As shown, a wet oxidation process is used to oxidize the Al in the high-aluminum layer after ion implantation. The wet oxidation temperature is 360-380°C, the flow rate of H2 / N2 mixed gas is 0.3-2 L / min, the flow rate of H2O steam is 0.2-1 L / min, and the pressure is 20-900 mBar to obtain a P Mesa step structure with an oxidation-restricted structure.

[0031] Step 4: Photolithography is performed on the epitaxial wafer completed in the above steps, leaving only the P-Metal area without photoresist, and the rest of the epitaxial wafer is covered with photoresist; then P-Metal metal deposition is performed, the metal is Ge / Au / Ni / Au, and the total metal film thickness is 0.5-1.5um; the photoresist is removed to obtain an epitaxial wafer with P-Metal;

[0032] Step 5: Photolithography the epitaxial wafer obtained in the above step, wherein the N-Mesa area to be etched has no photoresist and the rest of the epitaxial wafer is covered with photoresist; the N-Mesa is etched using a dry etching process, with the etching gas being Cl2 / BCl3 or Cl2 / SiCl4, until the buffer layer is etched; then the photoresist is removed to obtain an epitaxial wafer with a specific N-Mesa structure;

[0033] Step 6: Photolithography the epitaxial wafer obtained in the above step, leaving the N-Metal area without photoresist and covering the rest of the epitaxial wafer with photoresist; performing N-Metal metal deposition, wherein the metal is Ti / Pt / Au, and the total metal film thickness is 0.5-1.5 μm; finally, removing the photoresist to obtain an epitaxial wafer with N-Metal;

[0034] Step 7: Splitting the epitaxial wafer obtained in the above steps to obtain the oxidation-confined vertical cavity surface emitting laser of the present invention.

[0035] Since the wet oxidation process temperature in the above manufacturing process is only 360-380°C, the internal stress generated by the wet oxidation process is greatly reduced compared with the traditional process. Therefore, the oxidation-limited vertical cavity surface emitting laser obtained by the manufacturing method of the present invention has higher reliability.

Claims

1. A method for manufacturing an oxide-confined vertical cavity surface emitting laser, comprising: A wet oxidation step is used to oxidize the outer ring area of ​​one or more high-aluminum layers in the DBR into aluminum oxide to form unoxidized oxide pores in the middle area of ​​the one or more high-aluminum layers; it is characterized in that the manufacturing method also includes an ion implantation step before the wet oxidation step, which is used to implant ions into part or all of the outer ring area of ​​the one or more high-aluminum layers to reduce the process temperature in the wet oxidation step.

2. The method for manufacturing an oxidation-confined vertical cavity surface emitting laser according to claim 1, wherein: The process temperature in the wet oxidation step is 360°C to 380°C.

3. The method for manufacturing an oxidation-confined vertical cavity surface emitting laser according to claim 1, wherein: The inner diameter of the outer ring region of the one or more high-aluminum layers subjected to ion implantation is 1 μm to 6 μm larger than the diameter of the oxidation pores.

4. An oxide-confined vertical cavity surface emitting laser, characterized in that: The method according to any one of claims 1 to 3 is used.

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