Methods for forming vertical cavity surface-emitting lasers
By forming a mask structure and a barrier layer on the initial protective layer, the problem of passivation layer damage during etching is solved, achieving better protection and improving the performance of the vertical cavity surface-emitting laser.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHANGZHOU CHEMSEMI CO LTD
- Filing Date
- 2022-12-30
- Publication Date
- 2026-06-30
AI Technical Summary
There is room for improvement in the formation process of existing vertical cavity surface-emitting lasers, especially in the etching process of the photoresist layer and the initial protective layer, where the passivation layer is easily damaged, affecting device performance.
By forming a mask structure on the initial protective layer, including a barrier layer and a photoresist layer, the barrier layer protects the initial protective layer during the etching process, and combined with selective etching, damage to the passivation layer is reduced.
It effectively protects the initial protective layer and passivation layer, reduces damage during the etching process, and improves the performance stability and reliability of the vertical cavity surface-emitting laser.
Smart Images
Figure CN116014562B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor technology, and in particular to a method for forming a vertical cavity surface-emitting laser. Background Technology
[0002] A vertical-cavity surface-emitting laser (VCSEL) is a semiconductor laser that emits laser light perpendicular to the substrate surface. Currently, most VCSELs are based on gallium arsenide semiconductors, and their emission wavelengths are mainly in the near-infrared band.
[0003] A vertical-cavity surface-emitting laser (VCSEL) typically consists of three parts: upper and lower Bragg mirrors (DBRs) and a central active region. The Bragg mirrors are generally made of two materials with different refractive indices, grown alternately, with a thickness equal to one-quarter of the wavelength of light. To reduce optical losses, N-type Bragg mirrors have near-100% reflectivity and can be used as total internal reflection mirrors in a resonant cavity, while P-type Bragg mirrors have relatively low reflectivity and can be used as exit mirrors. P-type Bragg mirrors typically contain one or more layers of high-aluminum AlGaAs as an oxide confinement layer.
[0004] However, the formation process of existing vertical cavity surface-emitting lasers still needs improvement. Summary of the Invention
[0005] The technical problem solved by the present invention is to provide a method for forming a vertical cavity surface-emitting laser (VCSEL) to improve the existing VCSEL formation process.
[0006] To address the aforementioned technical problems, the present invention provides a method for forming a vertical-cavity surface-emitting laser (VCSEL), comprising: providing a substrate, the substrate including a first region and a second region, the substrate including: a base; a first mirror structure located on the base; an active layer located on the first mirror structure; a second mirror structure located on the active layer, the conductivity type of the second mirror structure being opposite to that of the first mirror structure; a first groove penetrating the second mirror structure and the active layer, and embedded within the first mirror structure; forming an initial protective layer in the first groove, on the surface of the first region, and on the surface of the second region, the initial protective layer filling the first groove; forming a mask structure on the initial protective layer, the mask structure including a barrier layer and a photoresist layer located on the barrier layer, the mask structure exposing the surface of the initial protective layer in the first groove and a portion of the surface of the initial protective layer on the first region; etching the initial protective layer using the mask structure as a mask until the substrate surface is exposed, forming a protective layer on the surface of the first region and the surface of the second region, the protective layer exposing the first groove and a portion of the surface of the first region; and removing the mask structure after forming the protective layer.
[0007] Optionally, before forming an initial protective layer in the first groove, on the surface of the first region, and on the surface of the second region, the method further includes: forming a passivation layer on the sidewall surface and bottom surface of the first groove, on the surface of the first region, and on the surface of the second region, wherein the material of the passivation layer is different from the material of the protective layer; the protective layer exposes a portion of the passivation layer surface in the first groove and on the surface of the first region.
[0008] Optionally, the passivation layer may be made of silicon nitride.
[0009] Optionally, the material of the initial protective layer includes an organic material, which includes polyimide.
[0010] Optionally, the process for forming the initial protective layer includes spin coating or spray coating.
[0011] Optionally, the etching process of the initial protective layer has a higher etching rate for the initial protective layer than for the barrier layer; the etching process of the initial protective layer has a higher etching rate for the initial protective layer than for the passivation layer.
[0012] Optionally, the etching process for the initial protective layer includes a dry etching process, wherein the etching gas in the dry etching process includes oxygen.
[0013] Optionally, the barrier layer may be made of an inert metal material, such as titanium-tungsten, gold, or platinum.
[0014] Optionally, removing the mask structure includes: removing the photoresist layer; and after removing the photoresist layer, removing the barrier layer.
[0015] Optionally, the process for removing the photoresist layer includes an ashing process; the process for removing the barrier layer includes a wet etching process, wherein the etching solution for the wet etching process includes hydrogen peroxide.
[0016] Optionally, the thickness of the initial protective layer within the first groove is greater than 5 micrometers.
[0017] Optionally, the second reflector structure has at least two layers. While forming at least two layers of the second reflector structure on the surface of the active layer, it also includes: forming a light-transmitting material layer between two adjacent layers of the second reflector structure; forming a reflective material layer on the surface of the light-transmitting material layer; and exposing the sidewall surfaces of the light-transmitting material layer and the reflective material layer through the first groove.
[0018] Optionally, before forming a passivation layer on the sidewall surface and bottom surface of the first groove, the surface of the first area and the surface of the second area, the method further includes: modifying the light-transmitting material layer exposed by the first groove to form a light-blocking layer and a light-transmitting layer, wherein the light-transmitting layer is located between the light-blocking layers and the projection of the light-transmitting layer on the substrate surface is circular.
[0019] Optionally, the modification process includes a wet oxidation process or an ion implantation oxidation process.
[0020] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:
[0021] The technical solution of the present invention forms a mask structure on the initial protective layer, with a barrier layer between the initial protective layer and the photoresist layer. When the initial protective layer is etched using the mask structure as a mask, the barrier layer acts as a barrier, protecting the initial protective layer under the mask structure from being etched when the initial protective layer in the first groove is thicker and the photoresist layer is thinner and is subject to loss during the etching process. This prevents damage to the formed protective layer and better protects the surfaces of the first and second regions.
[0022] Furthermore, before forming the initial protective layer, a passivation layer is also formed on the sidewall and bottom surfaces of the first groove, the surface of the first region, and the surface of the second region. The etching rate of the initial protective layer is greater than that of the passivation layer, thus the etching process of the initial protective layer causes less damage to the passivation layer on the first region, and the passivation layer can better protect the surface of the first region and the surface of the first groove. Attached Figure Description
[0023] Figure 1 This is a schematic diagram of the formation process of a vertical cavity surface-emitting laser in one embodiment;
[0024] Figures 2 to 5 This is a schematic diagram of the formation process of a vertical cavity surface-emitting laser in an embodiment of the present invention. Detailed Implementation
[0025] As described in the background section, the formation process of vertical-cavity surface-emitting lasers still needs improvement. This will now be analyzed and explained in conjunction with specific embodiments.
[0026] Figure 1 This is a schematic diagram of the formation process of a vertical cavity surface-emitting laser in one embodiment.
[0027] Please refer to Figure 1The method for forming the vertical-cavity surface-emitting laser includes: providing a substrate, the substrate including a first region I and a second region II, the substrate including: a substrate 100; a first mirror structure located on the substrate 100, the first mirror structure including a plurality of first stacked structures, the first stacked structures including a first reflective layer 101 and a second reflective layer 102 located on the first reflective layer 101, the first reflective layer 101 and the second reflective layer 102 having different refractive indices; an active layer 103 located on the first mirror structure; a second mirror structure located on the active layer 103, the conductivity type of the second mirror structure being opposite to that of the first mirror structure, the second mirror structure having at least two layers, and while forming at least two layers of the second mirror structure on the surface of the active layer 103, also including forming a light-transmitting material layer 106 between adjacent two layers of the second mirror structure and a reflective material layer 10 on the surface of the light-transmitting material layer 106. 7. The second reflector structure includes several second stacked structures, the second stacked structures including a third reflective layer 104 and a fourth reflective layer 105 located on the third reflective layer 104, the third reflective layer 104 and the fourth reflective layer 105 having different refractive indices; a first groove is formed in the second region II of the substrate, the first groove being located within the second reflector structure, the active layer 103 and the first reflector structure; a passivation layer 108 is formed on the sidewall surface and bottom surface of the first groove, the surface of the first region I and the surface of the second region II; an initial protective layer 109 is formed in the first groove, on the surface of the passivation layer 108 in the first region I and the second region II, the initial protective layer 109 filling the first groove; a photoresist layer 110 is formed on the initial protective layer 109, the photoresist layer 110 exposing the surface of the initial protective layer 109 in the first groove and part of the surface of the initial protective layer 109 on the first region I.
[0028] In this embodiment, the method for forming the vertical cavity surface-emitting laser further includes: etching the initial protective layer 109 exposed on the first region I and the second region II using the photoresist layer 110 as a mask until the surface of the passivation layer 108 is exposed, thereby forming a protective layer on the substrate. The material of the initial protective layer 109 is usually polyimide (PI). During the etching of the initial protective layer 109, since the initial protective layer 109 in the first groove is thicker and the initial protective layer 109 on the first region I is thinner, a dry etching process containing oxygen is usually used when etching the thinner initial protective layer 109; however, when etching the thicker initial protective layer 109, a higher selectivity is required to ensure that the photoresist layer 110 can provide sufficient blocking. At this time, F ions (e.g., SF6, CF4) are added to the reactive gas. The added F ions are more likely to break the original molecular structure of polyimide. Therefore, by adjusting the ratio of ionized F ions and O ions, the selectivity of the photoresist layer 110 and polyimide can be improved.
[0029] However, since there is a passivation layer 108 between the initial protective layer 109 and the substrate, and the material of the passivation layer 108 is usually silicon nitride, it also plays a certain role in reflection. Therefore, the presence of SF6 in the existing dry etching process parameters can damage the silicon nitride, thereby affecting the performance of the vertical cavity surface-emitting laser.
[0030] To address the aforementioned problems, the present invention provides a method for forming a vertical cavity surface-emitting laser. By forming a mask structure on the initial protective layer, a barrier layer is provided between the initial protective layer and the photoresist layer. When the initial protective layer is etched using the mask structure as a mask, especially when the initial protective layer in the first groove is relatively thick and the photoresist layer is relatively thin and experiences wear during etching, the barrier layer acts as a barrier, protecting the initial protective layer under the mask structure from etching. This prevents damage to the formed protective layer and better protects the surfaces of the first and second regions.
[0031] To make the above-mentioned objectives, features and beneficial effects of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
[0032] Figures 2 to 5 This is a schematic diagram of the formation process of a vertical cavity surface-emitting laser in an embodiment of the present invention.
[0033] Please refer to Figure 2A substrate is provided, the substrate including a first region I and a second region II, the substrate including: a substrate 200; a first mirror structure located on the substrate 200; an active layer 203 located on the first mirror structure; and a second mirror structure located on the active layer 203, the conductivity type of the second mirror structure being opposite to that of the first mirror structure.
[0034] In this embodiment, the first reflector structure is an N-type Bragg reflector, and the second reflector structure is a P-type Bragg reflector. The material of the first reflector structure is doped with silicon ions, and the material of the second reflector structure is doped with carbon ions.
[0035] In this embodiment, the first reflector structure includes a plurality of first stacked structures, the first stacked structure including a first reflective layer 201 and a second reflective layer 202 located on the first reflective layer 201, the first reflective layer 201 and the second reflective layer 202 having different refractive indices.
[0036] The first reflective layer 201 and the second reflective layer 202 have different refractive indices, thus the first reflective mirror structure formed by multiple stackings of the first reflective layer 201 and the second reflective layer 202 can have high reflectivity. Specifically, the greater the difference in refractive indices between the first reflective layer 201 and the second reflective layer 202, the fewer stacking steps are required for the first stacked structure.
[0037] In this embodiment, the material of the first reflective layer 201 includes aluminum gallium arsenide (Al₂O₃). x Ga 1-x As), the material of the second reflective layer 202 includes gallium arsenide.
[0038] In this embodiment, the second reflector structure comprises at least two layers. While forming at least two layers of the second reflector structure on the surface of the active layer 203, it also includes a light-transmitting material layer 206 and a reflective material layer 207 located on the surface of the light-transmitting material layer 206 between two adjacent layers of the second reflector structure. The second reflector structure includes several second stacked structures. The second stacked structure includes a third reflective layer 204 and a fourth reflective layer 205 located on the third reflective layer 204. The refractive indices of the third reflective layer 204 and the fourth reflective layer 205 are different.
[0039] The third reflective layer 204 and the fourth reflective layer 205 have different refractive indices, thus the second reflective mirror structure formed by multiple stackings of the third reflective layer 204 and the fourth reflective layer 205 can have a high reflectivity. Specifically, the greater the difference in refractive indices between the third reflective layer 204 and the fourth reflective layer 205, the fewer stacking steps are required for the second stacked structure.
[0040] In this embodiment, the material of the third reflective layer 204 includes aluminum gallium arsenide (Al₂O₃). x Ga 1-x As), the material of the fourth reflective layer 205 includes gallium arsenide.
[0041] The substrate 200 is made of semiconductor materials. In this embodiment, the substrate 200 is made of gallium arsenide.
[0042] The active layer 203 includes a plurality of first barrier layers (not shown), second barrier layers (not shown), and well layers (not shown) stacked alternately along a direction perpendicular to the surface of the substrate 200.
[0043] The first barrier layer is made of P-type gallium arsenide, which is doped with carbon ions; the second barrier layer is made of N-type gallium arsenide, which is doped with silicon ions; and the well layer is made of gallium arsenide indium.
[0044] The first barrier layer, the second barrier layer, and the well layer between the first barrier layer and the second barrier layer constitute a strained quantum well.
[0045] In this embodiment, the material of the light-transmitting material layer 206 includes aluminum gallium arsenide; the material of the reflective material layer 207 is the same as that of the second reflective layer 202.
[0046] Please continue to refer to this. Figure 2 A first groove (not shown) is formed in the second region II of the substrate. The first groove penetrates the second reflector structure and the active layer 203 and is embedded in the first reflector structure.
[0047] The first groove exposes the sidewall surfaces of the light-transmitting material layer 206 and the reflective material layer 207.
[0048] In this embodiment, the method further includes: modifying the light-transmitting material layer 206 exposed by the first groove to form a light-blocking layer (not shown) and a light-transmitting layer (not shown), wherein the light-transmitting layer is located between the light-blocking layers and the projection of the light-transmitting layer on the surface of the substrate 200 is circular.
[0049] The modification process includes wet oxidation or ion implantation oxidation.
[0050] Please continue to refer to this. Figure 2 After modifying the light-transmitting material layer 206, the method further includes forming a passivation layer 208 on the sidewall surface and bottom surface of the first groove, the surface of the first region I, and the surface of the second region II.
[0051] The passivation layer 208 is used to protect the substrate surface and also serves as an insulator. At the same time, the passivation layer 208 located in the first groove also contributes to the luminescence performance of the vertical cavity surface-emitting laser.
[0052] In this embodiment, the passivation layer 208 is made of silicon nitride.
[0053] In other embodiments, the passivation layer may not be formed.
[0054] Please continue to refer to this. Figure 2 An initial protective layer 209 is formed in the first groove, on the surface of the first region I and the surface of the second region II, and the initial protective layer 209 fills the first groove.
[0055] The material of the passivation layer 208 is different from the material of the initial protective layer 209.
[0056] In this embodiment, the initial protective layer 209 is made of an organic material, including polyimide (PI). The polyimide material is waterproof, insulating, low-cost, and heat-resistant, thus effectively protecting the surface of the vertical-cavity surface-emitting laser.
[0057] In this embodiment, the process of forming the initial protective layer 209 includes spin coating or spray coating.
[0058] The thickness of the initial protective layer 209 in the first groove is greater than the thickness of the initial protective layer 209 on the surface of the first region I and the surface of the second region II.
[0059] In this embodiment, the thickness of the initial protective layer 209 in the first groove is greater than 5 micrometers; the thickness of the initial protective layer 209 on the surface of the first region I and the surface of the second region II is less than 1 micrometer.
[0060] Next, a mask structure is formed on the initial protective layer 209. The mask structure includes a barrier layer 213 and a photoresist layer 211 located on the barrier layer 213. The mask structure exposes the surface of the initial protective layer 209 within the first groove and a portion of the surface of the initial protective layer 209 on the first region I. Please refer to the process for forming the mask structure. Figure 2and Figure 3 .
[0061] Please continue to refer to this. Figure 2 An initial barrier layer 210 is formed on the initial protective layer 209; a photoresist layer 211 is formed on the initial barrier layer 210.
[0062] Please refer to Figure 3 The initial barrier layer 210 is etched using the photoresist layer 211 as a mask until the surface of the initial protective layer 209 is exposed, forming a barrier layer 213 and a photoresist layer 211 on the barrier layer 213. The mask structure exposes the surface of the initial protective layer 209 in the first groove and part of the surface of the initial protective layer 209 on the first region I.
[0063] The barrier layer 213 is made of an inert metal material, including titanium-tungsten, gold, or platinum. The inert metal material has a high etching selectivity with the initial protective layer 209 during subsequent etching processes, thus protecting the initial protective layer 209 at the bottom of the barrier layer 213.
[0064] Please refer to Figure 4 Using the mask structure as a mask, the initial protective layer 209 is etched until the surface of the passivation layer 208 is exposed, and a protective layer 214 is formed on the surface of the first region I and the surface of the second region II. The protective layer 214 exposes part of the surface of the passivation layer 208 on the surface of the first groove and the surface of the first region I.
[0065] In this embodiment, the etching rate of the initial protective layer 209 is greater than the etching rate of the barrier layer 213. Therefore, the etching process of the initial protective layer 209 causes less damage to the barrier layer 213 and the passivation layer 208.
[0066] In this embodiment, the etching rate of the initial protective layer 209 is greater than that of the passivation layer 208. Since the initial protective layer 209 on the first region I is thinner, the passivation layer 208 will be exposed before the initial protective layer 209 on the second region II. Therefore, the etching process of the initial protective layer 209 causes less damage to the passivation layer 208 on the first region I, and the passivation layer 208 can better protect the surface of the first region I and the surface of the first groove.
[0067] In this embodiment, the etching process for the initial protective layer 209 includes a dry etching process, wherein the etching gas in the dry etching process includes oxygen. This etching process has a high etching selectivity for the barrier layer 213, and the use of pure oxygen etching gas also minimizes damage to the passivation layer 208.
[0068] Because there is a barrier layer 213 between the initial protective layer 209 and the photoresist layer 211, when the initial protective layer 209 is etched using the mask structure as a mask, the barrier layer 213 acts as a barrier, protecting the initial protective layer 209 under the mask structure from being etched, so that the formed protective layer 214 is not damaged, thereby better protecting the surface of the first region I and the surface of the second region II.
[0069] Please refer to Figure 5 After forming the protective layer 214, the mask structure is removed.
[0070] Removing the mask structure includes: removing the photoresist layer 211; and after removing the photoresist layer 211, removing the barrier layer 213.
[0071] In this embodiment, the process of removing the photoresist layer 211 includes an ashing process; the process of removing the barrier layer 213 includes a wet etching process, wherein the etching solution of the wet etching process includes hydrogen peroxide.
[0072] The area exposed by the protective layer 214 in the first region I is used to form other structures according to the design.
[0073] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.
Claims
1. A method for forming a vertical-cavity surface-emitting laser, characterized in that, include: A substrate is provided, the substrate including a first region and a second region, the substrate including: a base; a first mirror structure located on the base; an active layer located on the first mirror structure; and a second mirror structure located on the active layer, the conductivity type of the second mirror structure being opposite to that of the first mirror structure; A first groove is formed in the second region of the substrate, the first groove penetrating the second reflector structure and the active layer, and is embedded in the first reflector structure; An initial protective layer is formed in the first groove, on the surface of the first region and on the surface of the second region. The initial protective layer fills the first groove. The thickness of the initial protective layer in the first groove is greater than the thickness of the initial protective layer on the surface of the first region I and the surface of the second region II. A mask structure is formed on the initial protective layer. The mask structure includes a barrier layer and a photoresist layer located on the barrier layer. The mask structure exposes the surface of the initial protective layer within the first groove and a portion of the surface of the initial protective layer on the first region. The initial protective layer is etched using the mask structure as a mask until the substrate surface is exposed, and a protective layer is formed on the surface of the first region and the surface of the second region, the protective layer exposing the first groove and part of the surface of the first region; After the protective layer is formed, the mask structure is removed.
2. The method for forming a vertical-cavity surface-emitting laser as described in claim 1, characterized in that, Before forming an initial protective layer within the first groove, on the surface of the first region, and on the surface of the second region, the method further includes: forming a passivation layer on the sidewall surface and bottom surface of the first groove, on the surface of the first region, and on the surface of the second region, wherein the material of the passivation layer is different from the material of the protective layer; the protective layer exposes a portion of the passivation layer surface within the first groove and on the surface of the first region.
3. The method for forming a vertical-cavity surface-emitting laser as described in claim 2, characterized in that, The passivation layer is made of silicon nitride.
4. The method for forming a vertical-cavity surface-emitting laser as described in claim 1, characterized in that, The material of the initial protective layer includes organic materials, including polyimide.
5. The method for forming a vertical-cavity surface-emitting laser as described in claim 4, characterized in that, The process for forming the initial protective layer includes spin coating or spray coating.
6. The method for forming a vertical-cavity surface-emitting laser as described in claim 2, characterized in that, The etching process of the initial protective layer has a higher etching rate for the initial protective layer than for the barrier layer; the etching process of the initial protective layer has a higher etching rate for the initial protective layer than for the passivation layer.
7. The method for forming a vertical-cavity surface-emitting laser as described in claim 6, characterized in that, The etching process for the initial protective layer includes a dry etching process, wherein the etching gas in the dry etching process includes oxygen.
8. The method for forming a vertical-cavity surface-emitting laser as described in claim 1, characterized in that, The barrier layer is made of an inert metal material, including titanium-tungsten, gold, or platinum.
9. The method for forming a vertical-cavity surface-emitting laser as described in claim 8, characterized in that, Removing the mask structure includes: removing the photoresist layer; and after removing the photoresist layer, removing the barrier layer.
10. The method for forming a vertical-cavity surface-emitting laser as described in claim 9, characterized in that, The process for removing the photoresist layer includes an ashing process; the process for removing the barrier layer includes a wet etching process, wherein the etching solution for the wet etching process includes hydrogen peroxide.
11. The method for forming a vertical-cavity surface-emitting laser as described in claim 1, characterized in that, The thickness of the initial protective layer within the first groove is greater than 5 micrometers.
12. The method for forming a vertical-cavity surface-emitting laser as described in claim 2, characterized in that, The second reflector structure comprises at least two layers. While forming at least two layers of the second reflector structure on the surface of the active layer, it also includes: forming a light-transmitting material layer between two adjacent layers of the second reflector structure; forming a reflective material layer on the surface of the light-transmitting material layer; and exposing the sidewall surfaces of the light-transmitting material layer and the reflective material layer through the first groove.
13. The method for forming a vertical-cavity surface-emitting laser as described in claim 12, characterized in that, Before forming a passivation layer on the sidewall surface and bottom surface of the first groove, the surface of the first area and the surface of the second area, the method further includes: modifying the light-transmitting material layer exposed by the first groove to form a light-blocking layer and a light-transmitting layer, wherein the light-transmitting layer is located between the light-blocking layers and the projection of the light-transmitting layer on the substrate surface is circular.
14. The method for forming a vertical-cavity surface-emitting laser as described in claim 13, characterized in that, The modification process includes wet oxidation or ion implantation oxidation.