Manufacturing method of terahertz semiconductor laser based on self-alignment etching

Abstract

The invention relates to a manufacturing method of a terahertz semiconductor laser based on self-alignment etching. The manufacturing method comprises the following steps: (1) plating a metal film on an epitaxial wafer; (2) sequentially spin-coating a bottom layer photoresist and a top layer photoresist on the epitaxial wafer; (3) forming a photoresist structure of which the bottom photoresist shrinks inwards; (4) manufacturing an upper electrode metal strip; (5) forming ridges and absorption edges; (6) manufacturing a lower electrode metal strip; (7) finishing the previous process; and (8) completing device packaging. According to the invention, the upper electrode metal strip is always centered and aligned with the ridge strip, the width of the absorption edge is adjusted by controlling photoetching development parameters, and the defect that the widths of the absorption edges on two sides of the ridge strip are inconsistent due to large photoetching alignment error in the prior art is overcome.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor devices, and in particular relates to a method for manufacturing a terahertz semiconductor laser based on self-aligned etching. Background Art

[0002] Terahertz semiconductor laser is a solid-state semiconductor device based on inter-subband transition, which can radiate laser with a frequency of 1 to 5 terahertz (THz). The size of the laser's resonant cavity, especially the ridge width, directly affects the laser output power. Generally, the larger the ridge width, the greater the laser output power. However, as the ridge width increases, the waveguide loss of the lateral high-order mode decreases, even lower than the waveguide loss of the fundamental mode, so the lateral high-order mode is more likely to be lased. The lateral high-order mode laser beam has poor quality, a large divergence angle, and multiple spots will appear in the far field. In order to suppress the generation of lateral high-order modes, absorption edges are made on both sides of the ridge of the terahertz semiconductor laser, that is, a certain width is left on both sides of the ridge without being covered by the upper electrode metal to increase the waveguide loss of the lateral high-order mode. The absorption edge width is reasonably designed to ensure that the waveguide loss of the fundamental mode will not be significantly increased when the lateral high-order mode waveguide loss is increased. The larger the ridge width, the wider the required absorption edge. Usually, the absorption edge width of a terahertz semiconductor laser is 0 to 10 μm.

[0003] The commonly used manufacturing process of terahertz semiconductor lasers is: first make the upper electrode metal strip, then perform dry etching to make the ridge strip, and then perform the lower electrode metal strip and subsequent processes. This process cannot ensure that the ridge strip and the upper electrode metal strip are aligned in the center. The absorption edges on both sides of the ridge strip often have inconsistent widths due to photolithography alignment errors. The size asymmetry affects the suppression effect of the absorption edge on the lateral high-order mode. Sometimes the photolithography alignment error is too large and even causes the upper electrode metal strip to be unable to be covered by the dry etching mask, so that it is damaged in the subsequent ridge strip dry etching. Summary of the invention

[0004] The purpose of the present invention is to provide a method for manufacturing a terahertz semiconductor laser based on self-aligned etching to solve the technical problems in the prior art that the ridge strip and the upper electrode metal strip cannot be aligned in the center, and the absorption edges on both sides of the ridge strip often have inconsistent widths due to lithography alignment errors.

[0005] The present invention provides a method for manufacturing a terahertz semiconductor laser based on self-aligned etching, comprising the following steps:

[0006] (1) coating a metal film on an epitaxial wafer; the structure of the epitaxial wafer is, from bottom to top, a substrate, a lower contact layer, an active region, and an upper contact layer;

[0007] (2) spin coating a bottom layer photoresist and a top layer photoresist on the epitaxial wafer in sequence;

[0008] (3) Photolithography and development using a mask to form a photoresist structure in which the bottom layer of photoresist is retracted;

[0009] (4) removing the metal film not covered by the bottom photoresist by wet etching to form an upper electrode metal strip;

[0010] (5) using dry etching to remove the upper contact layer and active area not blocked by the top photoresist to form ridge stripes and absorption edges;

[0011] (6) Removing the resist, followed by photolithography, metal plating, and stripping to produce the lower electrode metal strip;

[0012] (7) The front-end process is completed by back thinning, polishing, and back metal film plating;

[0013] (8) Device packaging is completed through scribing, cleavage, bonding, and wiring.

[0014] Preferably, the material of the metal film in step (1) includes one or more of titanium, gold, chromium, aluminum and copper; the total thickness of the metal film is 200 to 1000 nm; and the method of coating the metal film includes one of magnetron sputtering or electron beam evaporation.

[0015] Preferably, the bottom layer photoresist in step (2) is a non-photosensitive photoresist, which is insensitive to ultraviolet light and is soluble in a developer regardless of whether it is exposed or not, and has a thickness of 0.2 to 2 μm.

[0016] Preferably, the top layer of photoresist in step (2) is a photosensitive photoresist, including a positive photoresist or a negative photoresist, which can form a specific pattern after patterned exposure and development through a mask; the thickness of the top layer of photoresist is 3 to 10 μm.

[0017] Preferably, in the step (3), the shrinkage size of the bottom layer photoresist determines the width of the absorption edge, and the width of the absorption edge is 0 to 20 μm.

[0018] Preferably, in step (4), a corrosive liquid is used to corrode the metal film, and the wet corrosive liquid has substantially no corrosion to the photoresist. The corrosive liquid covers the surface of the epitaxial wafer and fills the indented gap between the bottom layer photoresist and the top layer photoresist, and the bottom layer photoresist acts as a mask for wet etching.

[0019] Preferably, the dry etching in step (5) is directional, with rapid etching in the vertical direction and substantially no etching in the horizontal direction, and the etching depth reaches the lower contact layer; the dry etching includes inductively coupled plasma (ICP) etching.

[0020] Preferably, in step (5), the top layer of photoresist acts as a mask for dry etching; the thickness of the top layer of photoresist needs to be large enough to ensure that there is still some top layer of photoresist left after the dry etching is completed.

[0021] Preferably, the de-resisting in step (6) includes removing the remaining top layer photoresist and bottom layer photoresist by using an organic solvent.

[0022] The present invention also provides a terahertz semiconductor laser prepared according to the above manufacturing method.

[0023] Beneficial Effects

[0024] The manufacturing method of the present invention realizes that the upper electrode metal strip is always aligned with the center of the ridge strip, and the absorption edge width is adjusted by controlling the photolithography development parameters, thereby overcoming the defect in the prior art that the photolithography alignment error roughly causes the absorption edge widths on both sides of the ridge strip to be inconsistent. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic flow chart of the manufacturing method of the terahertz semiconductor laser of the present invention.

[0026] Figure 2 This is a micrograph of a 50 μm wide ridge after dry etching and de-resisting in an embodiment of the present invention.

[0027] Figure 3 This is a micrograph of a ridge with a width of 75 μm after dry etching and de-resisting in an embodiment of the present invention.

[0028] Figure numerals: 1-substrate, 2-lower contact layer, 3-active area, 4-upper contact layer, 5-metal film, 6-bottom photoresist, 7-top photoresist, 8-mask, 9-upper electrode metal strip, 10-ridge strip, 11-lower electrode metal strip, 12-absorption edge, 13-back metal film. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0030] Example

[0031] This embodiment provides a method for manufacturing a terahertz semiconductor laser based on self-aligned etching. The manufacturing process is as follows: Figure 1 As shown, the following steps are included:

[0032] (1) On a terahertz semiconductor laser epitaxial wafer, a titanium (Ti) and gold (Au) metal film 5 is magnetron sputtered, wherein the Ti film thickness is 20 nm and the Au film thickness is 300 nm; the structure of the epitaxial wafer is, from bottom to top, a substrate 1, a lower contact layer 2, an active region 3, and an upper contact layer 4;

[0033] (2) Spin-coat the non-photosensitive LOR-10A bottom photoresist 6 and the photosensitive AZ4620 top photoresist 7 on the epitaxial wafer in sequence. Spin-coat the bottom photoresist 6 at a speed of 3000 rpm for 30 seconds, and place it on a hot plate at 150°C for 3 minutes; Spin-coat the top photoresist 7 at a speed of 3000 rpm for 30 seconds, and place it on a hot plate at 100°C for 3 minutes;

[0034] (3) using a mask plate 8 and a SUSS lithography machine to perform contact exposure on the epitaxial wafer for 36 seconds, and then developing with an AZ300MIF developer. After developing for about 110 seconds, the pattern appears, and then developing for another 30 seconds. Under a microscope, the pattern of the bottom photoresist 6 shrinks by about 2 μm;

[0035] (4) Wet etching is used to remove the metal film 5 not covered by the bottom photoresist 6 to form the upper electrode metal strip 9. 2 : KI gold etching solution was used to etch the Au layer for 60 seconds until the Au layer was completely etched. Then BOE diluted 1:10 was used to etch the Ti layer for 90 seconds until the Ti layer was completely etched;

[0036] (5) Inductively coupled plasma (ICP) etching is used to dry etch the epitaxial wafer. The AZ4620 top layer photoresist 7 serves as a mask for dry etching. The dry etching depth is about 10 μm to reach the lower contact layer 2. After the etching is completed, the photoresist is removed with a stripping solution. Figure 2 and Figure 3 The micrographs are respectively of ridge strips with widths of 50 μm and 75 μm after debonding. It can be seen that the upper electrode metal strip 9 and the ridge strip 10 are aligned in the center. The upper electrode metal strip 9 is slightly narrower than the ridge strip 10. The absorption edges 12 on both sides have the same width of about 2 μm, that is, the upper electrode metal strip 9 and the ridge strip 10 have achieved center self-alignment.

[0037] (6) Photolithography, metal plating, and stripping are performed on both sides of the ridge strip 10 and the surface of the lower contact layer 2 exposed by etching to produce GeAuNiAu (13 / 33 / 30 / 300 nm) lower electrode metal strips 11;

[0038] (7) The front-end process is completed by thinning, polishing, and coating the back side metal film 13 of the epitaxial wafer;

[0039] (8) Perform dicing, cleavage, bonding, and lead operations to complete device packaging.

[0040] The manufacturing method of the present invention utilizes the retracted bottom layer photoresist as a mask for wet etching of the upper electrode metal strip, and utilizes the slightly wider top layer photoresist as a mask for dry etching of the ridge strip, thereby realizing self-alignment of the upper electrode metal strip and the ridge strip etching. The upper electrode metal strip can always be aligned in the center of the ridge strip, and the absorption edge width can be adjusted by controlling the photolithography development parameters.

Claims

1. A method for manufacturing a terahertz semiconductor laser based on self-aligned etching, comprising the following steps: (1) coating a metal film (5) on an epitaxial wafer; the structure of the epitaxial wafer is, from bottom to top, a substrate (1), a lower contact layer (2), an active region (3), and an upper contact layer (4); (2) sequentially spin coating a bottom layer photoresist (6) and a top layer photoresist (7) on the epitaxial wafer; (3) using a mask plate (8) to perform photolithography and development to form a photoresist structure in which the bottom layer photoresist (6) is retracted; (4) removing the metal film (5) not covered by the bottom photoresist (6) by wet etching to form an upper electrode metal strip (9); (5) removing the upper contact layer (4) and the active region (3) not blocked by the top photoresist (7) by dry etching to form a ridge stripe (10) and an absorption edge (12); (6) removing the resist, followed by photolithography, metal plating, and stripping to produce a lower electrode metal strip (11); (7) completing the front-end process by back-side thinning, polishing, and back-side metal film plating (13); (8) Device packaging is completed through scribing, cleavage, bonding, and wiring.

2. The manufacturing method according to claim 1, characterized in that: The material of the metal film (5) in the step (1) includes one or more of titanium, gold, chromium, aluminum, and copper; the total thickness of the metal film (5) is 200 to 1000 nm; and the method of coating the metal film (5) includes one of magnetron sputtering or electron beam evaporation.

3. The manufacturing method according to claim 1, characterized in that: In the step (2), the bottom layer photoresist (6) is a non-photosensitive photoresist with a thickness of 0.2 to 2 μm.

4. The manufacturing method according to claim 1, characterized in that: The top layer photoresist (7) in the step (2) is a photosensitive photoresist, including a positive photoresist or a negative photoresist; the thickness of the top layer photoresist (7) is 3 to 10 μm.

5. The manufacturing method according to claim 1, characterized in that: In the step (3), the shrinkage size of the bottom layer photoresist (6) determines the width of the absorption edge (12), and the width of the absorption edge (12) is 0 to 20 μm.

6. The manufacturing method according to claim 1, characterized in that: In the step (4), the metal film is corroded by using an etching liquid, the etching liquid covers the surface of the epitaxial wafer and fills the double-layer photoresist shrinkage gap of the bottom photoresist (6) and the top photoresist (7), and the bottom photoresist (6) serves as a mask for wet etching.

7. The manufacturing method according to claim 1, characterized in that: The dry etching in the step (5) is directional, and the etching is rapid in the vertical direction, and the etching depth reaches the lower contact layer (2); the dry etching includes inductively coupled plasma etching.

8. The manufacturing method according to claim 1, characterized in that: In the step (5), the top layer of photoresist (7) acts as a mask for dry etching.

9. A terahertz semiconductor laser manufactured according to the manufacturing method according to any one of claims 1 to 8.

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