A method for manufacturing a vertical ridge structure of a semiconductor laser with controllable height

Abstract

The application provides a manufacturing method of a vertical ridge structure of a semiconductor laser, which can accurately control the height, and comprises the following steps: growing a semiconductor epitaxial film layer and an ESL; sequentially forming a first silicon dioxide mask and a first photoresist mask on the epitaxial wafer, and photoetching the first silicon dioxide mask and the first photoresist mask into periodic ridge window; ICP etching the silicon dioxide mask; continuously ICP etching the epitaxial layer to a certain depth to form a narrow ridge structure; removing the residual photoresist; etching a GaAs contact layer to form an inner shrink structure; growing and ICP etching a second silicon dioxide mask; wet etching the epitaxial film layer to an etching barrier layer; removing the mask to grow a SiO2 current barrier layer, and forming a second photoresist mask pattern; ICP etching the current barrier layer on the top of the GaAs to leak out a current injection window, and completing the ridge structure manufacturing. The ridge height can be accurately controlled by combining the dry etching and the wet etching, the sidewall is vertical, the current injection area on the ridge is reduced, and the current injection density is improved.

Description

TECHNICAL FIELD

[0001] The application relates to a manufacturing method of a vertical ridge structure of a semiconductor laser with controllable height, and belongs to the technical field of semiconductor lasers. BACKGROUND

[0002] The semiconductor laser has the advantages of small volume, light weight and power saving, and is widely applied in the fields of laser printing and printing, optical measurement, robot and automatic control, beauty, medical treatment and the like.

[0003] At present, the light-emitting area structure of the semiconductor laser is usually in the form of a ridge strip. For a laser requiring stable output of a single transverse mode light spot, a narrow and rectangular ridge structure is crucial. A commonly used method for manufacturing the ridge structure is wet etching or dry etching. For an epitaxial structure of a multi-layer film system, isotropy and selectivity of the wet etching can cause the ridge strip to be non-vertical or can easily form a "cap". The dry etching (such as ICP) can obtain a rectangular ridge strip with a vertical sidewall, but the etching depth cannot be accurately controlled due to the precision limitation of the etching equipment. The simple use of the wet etching or the dry etching restricts the stable output of the single mode light spot of the laser.

[0004] In order to improve the photoelectric conversion efficiency of the single mode semiconductor laser, in the case of a certain input current, reducing the current channel area and improving the injection current density is a common method. First, a photoresist mask pattern consistent with the ridge strip width is photoetched, the photoresist size is reduced in a certain way, a current blocking layer is regrown, and then the photoresist and the current blocking layer on the surface thereof are removed. In this way, the area of the ridge strip without the current blocking layer becomes an effective area, and the other areas of the ridge strip are protected by the blocking layer to prevent current leakage. However, this method is complex in process, high in cost and poor in repeatability.

[0005] Chinese patent document CN105226502A discloses a preparation method of a narrow ridge type GaInP quantum well structure semiconductor laser based on GaAs. After the photoresist is spin-coated on the epitaxial wafer, the mask for dry etching is grown by PECVD, a suitable photoetching plate is selected to prepare the required mask pattern by photoetching, the mask and the photoresist without protection are etched away by dry etching, the required mask pattern and the photoresist pattern consistent with the mask pattern are prepared, the photoresist pattern is under the mask pattern, the ridge structure with a vertical side and good appearance is prepared by dry etching, and finally the current blocking layer is grown, the photoresist is stripped to remove the current blocking layer on the ridge strip, and the ridge structure with a vertical side and good appearance is prepared. However, the structure of the photoresist under the SiO2 mask is easily loose, deformed or even carbonized and fallen off in the dry etching process due to the high temperature and plasma, which causes the failure of the whole etching process. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a method for manufacturing a vertical ridge structure of a semiconductor laser with controllable height, which adopts a dry etching and wet etching combined mode, the ridge height can be accurately controlled, the sidewall is vertical, the current injection area on the ridge is reduced, and the current injection density is improved.

[0007] Term explanation:

[0008] ESL: etch stop layer.

[0009] PVD: physical vapor deposition.

[0010] PECVD: plasma enhanced chemical vapor deposition.

[0011] Epitaxial film layer: the lower limiting layer, lower waveguide layer, active layer, upper waveguide layer, etch stop layer, upper limiting layer and GaAs contact layer grown on the substrate from bottom to top are collectively referred to as an epitaxial film layer.

[0012] The technical scheme of the present application is as follows:

[0013] A method for manufacturing a vertical ridge structure of a semiconductor laser with controllable height, the operation steps are as follows:

[0014] (1) growing a lower limiting layer, a lower waveguide layer, an active layer, an upper waveguide layer, an etch stop layer, an upper limiting layer and a GaAs contact layer on a substrate from bottom to top to manufacture an epitaxial wafer;

[0015] (2) depositing SiO2 on the epitaxial wafer by PVD or PECVD to serve as a dry etching mask;

[0016] (3) spin-coating photoresist on the epitaxial wafer with the mask, using a photoetching plate with a set size to photoetch a periodic photoresist mask pattern suitable for the size of the ridge, and performing hardening and baking;

[0017] (4) using ICP etching to etch the SiO2 with the photoresist as a mask to form a narrow strip structure;

[0018] (5) continuing to use ICP etching to form a ridge structure from the narrow strip structure;

[0019] (6) removing the photoresist by ICP etching plasma or chemical methods;

[0020] (7) using the characteristics of wet selective etching, using GaAs special etching liquid to etch the GaAs contact layer to form a ridge structure with the GaAs contact layer inwardly retracted;

[0021] (8) Using PVD magnetron sputtering to grow SiO2 mask again, so that the whole ridge surface, including the inner GaAs surface after shrinkage, is coated with a layer of SiO2 mask again;

[0022] (9) Using ICP dry etching to etch the secondary mask, and controlling the etching conditions to ensure that the SiO2 in the etching groove is etched clean while the ridge surface and the inner GaAs surface still have SiO2 remaining;

[0023] (10) Using the characteristics of selective corrosion, using hydrochloric acid solution to continue to etch the epitaxial film layer to the corrosion barrier layer;

[0024] (11) Using a silicon dioxide etching solution to remove the SiO2 mask, forming a ridge structure with vertical sidewalls and controllable depth;

[0025] (12) Using PECVD to grow a layer of SiO2 current blocking layer on the prepared sample;

[0026] (13) Spinning photoresist on the current blocking layer, then using photoetching, hardening and baking to control the thickness of the photoresist

[0027] (14) Using ICP dry etching to etch the SiO2 current blocking layer on the top of GaAs sufficiently, while retaining the SiO2 current blocking layer in other areas.

[0028] Preferably, the thickness of the mask in step (2) is

[0029] Preferably, the ridge size in step (3) is width ≤ 5 μm, and the thickness of the photoresist is

[0030] Preferably, in step (5), the etching depth is controlled to be

[0031] Preferably, in step (6), the ICP etching gas is oxygen, and the chemical method is to use chemical solution acetone to completely clean and remove the residual photoresist.

[0032] Preferably, in step (7), the components and mass ratio of the GaAs special etching solution are H3PO4: H2O = 2:3.

[0033] Preferably, in step (8), the thickness of the secondary mask is

[0034] Further preferably, in step (8), the thickness of the secondary mask is

[0035] Preferably, in step (10), the component and mass ratio of hydrochloric acid solution is HCl:H2O=1:5, and the corrosion time is 10-200 seconds.

[0036] Preferably, in step (11), the component and mass ratio of the silicon dioxide etching solution is HF:H2O=1:10.

[0037] Preferably, in step (12), the thickness of the SiO2 current blocking layer is 0.1-1.0 microns.

[0038] The present application has the following advantages:

[0039] 1. The present application adopts the combination of dry etching and wet etching, solves the problems of poor verticality of ridge structure caused by isotropic wet etching and inaccurate depth control of dry etching, and makes the ridge height controllable and the sidewall vertical.

[0040] 2. The present application reduces the current injection area by selectively etching the inner GaAs contact layer by wet etching, improves the current injection density, and suppresses the lateral expansion of current, thereby improving the single-mode laser output efficiency of the semiconductor laser.

[0041] 3. In steps (4) and (5) of the present application, the photoresist and SiO2 are used as masks to etch the ridge, and the organic ion groups of the photoresist are used to coat the sidewall of the ridge to avoid ion bombardment, thereby effectively improving the verticality and smoothness of the sidewall of the ridge.

[0042] 4. In steps (13) and (14) of the present application, the SiO2 current blocking layer at the top of GaAs is removed by dry etching, and the anisotropy of dry etching is used to effectively solve the problem that the SiO2 on the sidewall of GaAs is easily etched by wet etching. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 It is a schematic diagram of the structure of the ridge after etching according to the present application;

[0044] Figure 2 It is a schematic diagram of the structure of the ridge after etching and GaAs shrinkage according to the present application;

[0045] Figure 3 It is a schematic diagram of the structure of the ridge after secondary mask growth according to the present application;

[0046] Figure 4 It is a schematic diagram of the structure of the ridge after secondary mask etching according to the present application;

[0047] Figure 5 It is a schematic diagram of the structure of the ridge after dry etching and wet etching according to the present application;

[0048] Figure 6This is a schematic diagram of the ridge structure of GaAs after shrinkage according to the present invention;

[0049] Figure 7 This is a schematic diagram of the ridge structure after etching the SiO2 current blocking layer of the present invention.

[0050] Figure 8 This is a schematic diagram of the light spot generated in Embodiment 1 of the present invention;

[0051] Figure 9 This is a schematic diagram of the light spot generated in the comparative example of the present invention;

[0052] The components are: 1. Substrate; 2. Etching barrier layer; 3. Photoresist; 4. GaAs contact layer; 5. Primary mask; 6. Epitaxial film layer; 7. Secondary mask; 8. Current blocking layer. Detailed Implementation

[0053] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0054] Example 1:

[0055] This embodiment provides a method for fabricating a vertical ridge structure for a semiconductor laser with precisely controllable height. The operation steps are as follows:

[0056] (1) A lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an etch barrier layer 2, an upper confinement layer and a GaAs contact layer 4 are grown sequentially from bottom to top on substrate 1. The etch barrier layer is a material film layer that is difficult to be etched by hydrochloric acid solution based on the principle of selective corrosion.

[0057] (2) A primary mask 5 is formed by dry etching using PVD or PECVD to deposit SiO2 on the epitaxial wafer. The thickness of the primary mask 5 is [missing information].

[0058] (3) Photoresist 3 is spin-coated onto the epitaxial wafer with the mask grown. The thickness of the photoresist is... A periodic photoresist mask pattern adapted to the ridge size is obtained by photolithography using a photomask of a set size, and then hardened and baked.

[0059] (4) ICP etching is used to etch SiO2 with photoresist as a mask to form a narrow strip structure;

[0060] (5) Continue to use ICP etching to form the ridge structure from the narrow strip structure, and control the etching depth from the corrosion barrier layer. like Figure 1 As shown, photoresist and SiO2 are used as masks at the same time. Under the action of plasma, the organic ion clusters of photoresist cover the sidewalls of the ridges, effectively protecting the sidewalls of the ridges from excessive ion bombardment and ensuring the authenticity of the ridge pattern.

[0061] (6) Using ICP etching to remove the photoresist on the ridge surface, the ICP etching gas is oxygen, and then using chemical solution acetone to clean and completely remove the residual photoresist;

[0062] (7) Using the characteristics of wet selective etching, using GaAs special etching solution to etch the GaAs contact layer, forming a ridge structure with the GaAs contact layer inside, as shown in Figure 2 ;

[0063] (8) Using PVD magnetron sputtering to grow SiO2 mask again, so that the entire ridge surface including the inside GaAs surface is covered with a layer of SiO2 secondary mask 7, as shown in Figure 3 , the thickness of the secondary mask is

[0064] (9) Using ICP dry etching to etch the secondary mask, controlling the etching conditions, etching the SiO2 in the etching groove completely while ensuring that the ridge surface and the inside GaAs surface still have SiO2 remaining, as shown in Figure 4 ;

[0065] (10) Using the characteristics of selective etching, using hydrochloric acid solution to continue etching the epitaxial film layer 6 to the etching barrier layer, due to the isotropy of wet etching, there is a slight slope on both sides of the lower end of the ridge, as shown in Figure 5 ;

[0066] (11) Using a silicon dioxide etching solution to remove the SiO2 mask, forming a ridge structure with a vertical sidewall and controllable depth, as shown in Figure 6 ;

[0067] (12) Using PECVD to grow a layer of SiO2 current blocking layer 8 on the prepared sample, the thickness of the SiO2 current blocking layer is

[0068] (13) Spin coating photoresist on the current blocking layer, then use photoetching, hardening and baking to control the thickness of the photoresist

[0069] (14) Using ICP dry etching, etching the SiO2 current blocking layer on the top of GaAs completely, leaving the SiO2 current blocking layer in other areas, as shown in Figure 7 .

[0070] Example 2:

[0071] A method for manufacturing a semiconductor laser vertical ridge structure with controllable height, the operation steps are as described in Example 1, the difference is that in step (2) the thickness of the primary mask is In step (3) the thickness of the photoresist is Etching depth in step (5) from the etching stop layer Thickness of the second mask in step (8) Thickness of the SiO2 current stop layer in step (12) Thickness of the photoresist in step (13)

[0072] Example 3:

[0073] A method for manufacturing a vertical ridge structure of a semiconductor laser with controllable height, the operation steps are as described in Example 1, except that the ridge size in step (3) is 5 μm in width.

[0074] In step (7), the components and mass ratio of the GaAs special etching solution are H3PO4:H2O = 2:3.

[0075] Thickness of the second mask in step (8)

[0076] In step (10), the components and mass ratio of the hydrochloric acid solution are HCl:H2O = 1:5, and the etching time is 10-200 seconds.

[0077] In step (11), the components and mass ratio of the silicon dioxide etching solution are HF:H2O = 1:10.

[0078] Comparative Example:

[0079] The comparative example provides a method for manufacturing a vertical ridge structure of a semiconductor laser. A mask for dry etching is grown on an epitaxial wafer by PECVD, and then a suitable photoetching plate is selected to prepare the required mask pattern by photoetching. Finally, a ridge structure with a relatively vertical sidewall is manufactured by dry etching. The height of the ridge structure manufactured in the comparative example is controlled by etching time or depends on the experience of the operator for rough judgment, and cannot be accurately controlled, resulting in low and unstable product pass rate. It is easy to emit a multimode light spot, and the mode measurement is serious, as shown in FIG. 1; and the width of the ridge structure manufactured in the comparative example is consistent from top to bottom, which is easy to cause current expansion and reduce current injection density. Figure 9

[0080] The height of the ridge structure manufactured in Example 1 can be accurately controlled, and the sidewall is vertical, which can stably output a single-mode light spot, as shown in FIG. 2, and reduces the current injection area, improves the current injection density, and suppresses the lateral expansion of the current, thereby improving the single-mode laser output efficiency of the semiconductor laser. The production pass rate of Example 1 is significantly improved, and the experimental data comparison between Example 1 and the comparative example is shown in Table 1. Figure 8 Table 1: Comparison of experimental data between Example 1 and the comparative example

[0081]

[0082] ​​ Current injection density (KA / CM 2 ) Pass rate Example 1 0.74-0.76 ≥85％ Comparative Example 0.69-0.72 ≤50％

Claims

1. A method for fabricating a vertical ridge structure of a semiconductor laser with precisely controlled height, characterized in that, The operation steps are as follows: (1) growing a lower limiting layer, a lower waveguide layer, an active layer, an upper waveguide layer, an etching barrier layer, an upper limiting layer and a GaAs contact layer on a substrate from bottom to top to prepare an epitaxial wafer; (2) depositing SiO2 on the epitaxial wafer by PVD or PECVD to form a dry etching mask; (3) spin-coating photoresist on the epitaxial wafer with the mask, and using a photoetching plate with a set size to photoetch a periodic photoresist mask pattern suitable for the size of the ridge, and performing film hardening and baking, the ridge size is ≤5 μm, and the thickness of the photoresist is 10000-50000 Å; (4) using ICP etching to etch SiO2 with the photoresist as a mask to form a narrow strip structure; (5) continuing to use ICP etching to form a ridge structure from the narrow strip structure, and controlling the etching depth to be 500-2000 Å from the etching barrier layer; (6) removing the photoresist by ICP etching plasma or chemical method; (7) using the characteristics of wet selective etching, using GaAs special etching solution to etch the GaAs contact layer to form a ridge structure with the GaAs contact layer inwardly retracted; (8) using PVD magnetron sputtering to secondly grow a SiO2 mask to cover the surface of the whole ridge structure including the inwardly retracted GaAs surface, and the thickness of the second mask is 1000-3000 Å; (9) using ICP dry etching to etch the second mask, and controlling the etching conditions to etch the SiO2 in the etching groove completely while ensuring that the surface of the ridge and the inwardly retracted GaAs surface still have residual SiO2; (10) using the characteristics of selective etching, using hydrochloric acid solution to continue etching the epitaxial film layer to the etching barrier layer; (11) using a silicon dioxide etching solution to remove the SiO2 mask to form a ridge structure with vertical sidewalls and controllable depth; (12) using PECVD to grow a SiO2 current barrier layer on the prepared sample; (13) spin-coating photoresist on the current barrier layer, and then using photoetching, film hardening and baking to control the thickness of the photoresist to be 8000-20000 Å; (14) using ICP dry etching to etch the SiO2 current barrier layer on the top of GaAs completely while retaining the SiO2 current barrier layer in other areas.

2. The method of claim 1, wherein the height of the semiconductor laser vertical ridge structure is controlled by the thickness of the first and second sacrificial layers. The thickness of the mask in step (2) is 2000-6000 Å.

3. The method of claim 1, wherein the height of the semiconductor laser vertical ridge structure is controlled by the thickness of the first and second sacrificial layers. In step (6), the ICP etching gas is oxygen, and the chemical method is using chemical solution acetone to clean and remove residual photoresist completely.

4. The method of claim 1, wherein the height of the semiconductor laser vertical ridge structure is controlled by the thickness of the first and second cladding layers. In step (7), the components and mass ratio of the GaAs special etching solution are H3PO4:H2O=2:

3.

5. The method of claim 1, wherein the height of the semiconductor laser vertical ridge structure is controlled by the thickness of the first and second cladding layers. In step (8), the thickness of the second mask is 2000 Å.

6. The method of claim 1, wherein the height of the semiconductor laser vertical ridge structure is controlled by the thickness of the first and second cladding layers. In step (10), the components and mass ratio of the hydrochloric acid solution are HCl:H2O=1:5, and the etching time is 10-200 seconds.

7. The method of claim 1, wherein the height of the semiconductor laser vertical ridge structure is controlled by the thickness of the first and second cladding layers. In step (11), the components and mass ratio of the silicon dioxide etching solution are HF:H2O=1:

10.

8. The method of claim 1, wherein the height of the semiconductor laser vertical ridge structure is precisely controlled. In step (12), the thickness of the SiO2 current barrier layer is 500-2000 Å.

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