Method for manufacturing metal electrode at top of ridge waveguide

Abstract

The invention relates to the technical field of semiconductor optoelectronic devices, in particular to a method for manufacturing a metal electrode at the top of a ridge waveguide, which comprises the following steps of: S1, manufacturing a metal electrode and a transition layer on the surface of a substrate; s2, growing a lower mask layer on the surface of the substrate; s3, coating photoresist on the lower mask layer to form an upper mask layer; s4, photoetching the upper mask layer to form a first waveguide pattern; s5, forming a second waveguide pattern on the lower mask layer; s6, etching the transition layer and the metal electrode exposed in the second waveguide pattern; s7, manufacturing a ridge waveguide on the substrate by using the lower mask layer as a mask; s8, removing the lower mask layer by using a BOE solution; s9, removing the transition layer; and completing a ridge waveguide top metal electrode manufacturing process. The method has the advantages that the metal electrode is manufactured on the substrate material, then etching and ridge waveguide manufacturing are sequentially conducted on the electrode according to the same waveguide pattern, it is effectively guaranteed that the relative positions of the metal electrode and the ridge waveguide are accurate, overlay errors are eliminated, and the product quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor optoelectronic devices, and particularly to a method for fabricating a metal electrode on the top of a ridge waveguide. Background Art

[0002] The ridge waveguide laser is a common semiconductor laser, and has become the mainstream of fiber-optic communication semiconductor lasers due to many advantages such as simple fabrication, good repeatability, and high yield. At present, the commonly used process for fabricating a metal electrode on the top of a ridge waveguide usually involves first fabricating the ridge waveguide and then realizing it by a lift-off process on the ridge waveguide. For example, the patent with the publication number CN107257082A discloses a method for fabricating an electrode contact window of a ridge waveguide laser, including: etching the waveguide layer deposited on the wafer to form a ridge waveguide structure and the structures on both sides of the ridge waveguide structure; depositing a dielectric layer on the surfaces of the ridge waveguide structure and the structures on both sides of the ridge waveguide structure; coating a photoresist on the surface of the dielectric layer; performing photolithography on the photoresist using a mask plate to remove the photoresist covering the ridge waveguide structure on the surface of the dielectric layer; performing heat treatment on the photoresist remaining on the surface of the dielectric layer to cause the remaining photoresist to deform; etching the dielectric layer using the photoresist as a mask to remove the dielectric covering the surface of the ridge waveguide structure to form an electrode contact window, and then growing a metal electrode on the surface of the electrode contact window, thus completing the fabrication of the metal electrode of the ridge waveguide laser.

[0003] The implementation scheme of the above fabrication method is to first fabricate the ridge waveguide, then etch the dielectric layer on the top of the ridge waveguide to form an electrode contact window, and then grow an electrode at the position of the electrode contact window. The disadvantages of the above process for fabricating a metal electrode on the top of a ridge waveguide are as follows: Since the ridge waveguide and the metal electrode are fabricated in two steps, that is, the etching of the ridge waveguide and the etching of the dielectric layer are carried out separately, there must be a photolithography overlay error, and it is easy to have a situation where the ridge waveguide and the metal electrode are misaligned. This results in the inability to fully achieve the design purpose, thereby affecting the chip performance. Summary of the Invention

[0004] The present invention provides a method for fabricating a metal electrode on the top of a ridge waveguide, which solves the problem of overlay error existing in the prior art when the ridge waveguide and the metal electrode are fabricated in two steps.

[0005] The technical solution of the present invention is realized as follows: A method for fabricating a metal electrode on the top of a ridge waveguide, comprising the following steps: S1, fabricating a metal electrode on the surface of a substrate, and fabricating a transition layer on the top of the metal electrode, the width of the metal electrode being greater than the width of the ridge edge of the ridge waveguide; ensuring that the metal electrode can completely cover the ridge edge position of the ridge waveguide to avoid the situation that the metal electrode is smaller than the ridge edge width after etching. S2. Grow a lower mask layer on the substrate surface; the transition layer is provided so that the lower mask layer can adhere better to the metal electrode, and the lower mask layer is used as a mask during the etching of the ridge waveguide. S3. Coat a photoresist on the lower mask layer to form an upper mask layer; the upper mask layer serves as a mask during the etching of the metal electrode, and at the same time, the upper mask layer is also the basis for generating the second waveguide pattern on the lower mask layer, ensuring that the positions of the two are corresponding when fabricating the metal electrode and the ridge waveguide, thereby eliminating the overlay error generated during the fabrication of the ridge waveguide and the metal electrode and improving the product quality. S4. Perform photolithography on the upper mask layer to form a first waveguide pattern; the first waveguide pattern is a rectangle arranged side by side, with adjacent two rectangles as a group, and the distance between the two rectangles in each group is equal to the ridge width of the ridge waveguide. S5. Use the upper mask layer as a mask to etch the lower mask layer and form a second waveguide pattern on the lower mask layer; ensure the accurate relative position of the upper mask layer for etching the metal electrode and the lower mask layer for etching the ridge waveguide, thereby ensuring the accurate relative position of the fabricated ridge waveguide and the metal electrode. S6. Use the upper mask layer and the lower mask layer as masks to etch the exposed transition layer and metal electrode in the second waveguide pattern; until the exposed transition layer and metal electrode in the second waveguide pattern are etched clean; avoid the influence of the exposed transition layer and metal electrode on the subsequent fabrication of the ridge waveguide. S7. Use the lower mask layer as a mask to fabricate a ridge waveguide on the substrate. S8. Remove the lower mask layer with BOE solution. S9. Remove the transition layer on the top of the metal electrode; the process of fabricating the metal electrode on the top of the ridge waveguide is completed.

[0006] In S1, first arrange the positions of the ridge waveguides on the substrate, and determine the positions of the metal electrodes according to the arrangement of the ridge waveguides. The positions of the metal electrodes correspond to the ridge positions of the ridge waveguides.

[0007] In S1, the metal electrode includes a bottom Ti layer, a Pt layer, and an Au layer arranged from bottom to top in sequence.

[0008] In S1, the transition layer is a top Ti layer. The top Ti layer has good adhesion, enabling the lower mask layer to adhere better to the metal electrode and ensuring the stability of the connection between the lower mask layer and the metal electrode.

[0009] The thickness of the top Ti layer is 50 - 100 nm.

[0010] When fabricating the metal electrode and the transition layer, the bottom Ti layer, Pt layer, Au layer, and top Ti layer are sequentially grown on the substrate using the lift-off process. The metal electrode and the transition layer are fabricated in one step using the lift-off process to ensure that the transition layer completely covers the metal electrode, thereby ensuring stable connection between the lower mask layer and the metal electrode.

[0011] In S2, the lower mask layer is a SiO2 layer; the thickness of the SiO2 layer is 250 - 500 nm.

[0012] In S3, the thickness of the upper mask layer is 1 - 3 μm.

[0013] In S7, the ridge waveguide is fabricated by sequentially performing etching and corrosion.

[0014] Both the first waveguide pattern and the second waveguide pattern correspond to the groove shape of the ridge waveguide. The groove width of the ridge waveguide is determined by the first waveguide pattern and the second waveguide pattern.

[0015] The beneficial effects of the present invention are as follows: 1. When fabricating the metal electrode on the top of the ridge waveguide, a method is adopted where the metal electrode is first fabricated on the substrate material, and then etching of the electrode and fabrication of the ridge waveguide are sequentially performed according to the same waveguide pattern, that is, the etching of the metal electrode and the fabrication of the ridge waveguide can be carried out synchronously, effectively ensuring the accurate relative position between the metal electrode and the ridge waveguide, eliminating the overlay error, and improving the product quality.

[0016] 2. A photoresist and a SiO2 layer are used as a double-layer mask. The waveguide pattern on the SiO2 layer is made according to the waveguide pattern on the photoresist to ensure the consistency of the waveguide pattern. The photoresist is used as a mask during the etching of the metal electrode, and the SiO2 layer is used as a mask during the fabrication of the ridge waveguide.

[0017] 3. A transition layer is provided on the top of the metal electrode. The transition layer ensures the adhesion between the lower mask layer and the top of the metal electrode, ensuring the stability of the connection between the lower mask layer and the metal electrode. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 Schematic diagram of method step S1 for fabricating a metal electrode on the top of a ridge waveguide according to the present invention; Figure 2 Schematic diagram of method step S2 for fabricating a metal electrode on the top of a ridge waveguide; Figure 3 Schematic diagram of method step S3 for fabricating a metal electrode on the top of a ridge waveguide; Figure 4 Schematic diagram of method step S4 for fabricating a metal electrode on the top of a ridge waveguide; Figure 5 Schematic diagram of method step S5 for fabricating a metal electrode on the top of a ridge waveguide; Figure 6 Schematic diagram of method step S6 for fabricating a metal electrode on the top of a ridge waveguide; Figure 7 Schematic diagram of method step S7 for fabricating a metal electrode on the top of a ridge waveguide; Figure 8 Schematic diagram of method step S8 for fabricating a metal electrode on the top of a ridge waveguide; Figure 9 Schematic diagram of method step S9 for fabricating a metal electrode on the top of a ridge waveguide.

[0020] In the figure: 1. Substrate, 11. Ridge waveguide groove, 2. Bottom Ti layer, 3. Pt layer, 4. Au layer, 5. Top Ti layer, 6. Lower mask layer, 61. Second waveguide pattern, 7. Upper mask layer, 71. First waveguide pattern. Detailed implementation manner

[0021] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] Embodiment 1, a method for fabricating a metal electrode on the top of a ridge waveguide, comprising the following steps: S1, fabricating a metal electrode on the surface of the substrate 1 and fabricating a transition layer on the top of the metal electrode, the width of the metal electrode being greater than the ridge width of the ridge waveguide; as Figure 1 shown, in this embodiment, the substrate 1 is a wafer, the metal electrode corresponds to the ridge position of the ridge waveguide to be fabricated on the wafer, and the width of the metal electrode being greater than the ridge width of the ridge waveguide can enable the metal electrode to still cover the ridge even in the case of left - right misalignment, increasing the tolerance during the fabrication of the metal electrode; S2, growing a lower mask layer 6 on the surface of the substrate 1; as Figure 2 shown, under the action of the transition layer, the lower mask layer 6 can adhere better to the metal electrode, ensuring the stability of the lower mask layer 6 at the position of the metal electrode; the lower mask layer 6 is used as a mask during the etching of the ridge waveguide; S3, coating photoresist on the lower mask layer 6 to form an upper mask layer 7; Figure 3 As shown, the upper mask layer 7 serves as a mask for the lower mask layer 6 and the metal electrode during etching, and the upper mask layer 7 serves as a basis for generating the second waveguide pattern 61 on the lower mask layer 6. That is, the same waveguide pattern is used when manufacturing the metal electrode and the ridge waveguide, ensuring that the positions of the metal electrode and the ridge waveguide remain corresponding during the manufacturing process, thereby eliminating the overlay error generated during the manufacturing of the ridge waveguide and the metal electrode, and improving the quality of the product. S4, photolithography is performed on the upper mask layer 7 to form a first waveguide pattern 71; Figure 4 As shown, the first waveguide pattern 71 is in the groove shape of a ridge waveguide. Specifically, the first waveguide pattern 71 is a plurality of rectangles arranged side by side, with two adjacent rectangles forming a group, and the distance between the two rectangles in each group is equal to the ridge width of the ridge waveguide; S5, using the upper mask layer 7 as a mask to etch the lower mask layer 6, forming a second waveguide pattern 61 on the lower mask layer 6; Figure 5 As shown, a second waveguide pattern 61 is formed on the lower mask layer 6 according to the first waveguide pattern 71 on the upper mask layer 7, ensuring that the positions of the first waveguide pattern 71 and the second waveguide pattern 61 correspond accurately, thereby ensuring that the relative positions of the ridge ridges and the metal electrodes of the produced ridge waveguide are accurate; S6, using the upper mask layer 7 and the lower mask layer 6 as masks to etch the transition layer and the metal electrode exposed in the second waveguide pattern 61; until the transition layer and the metal electrode exposed in the second waveguide pattern 61 are completely etched; Figure 6 As shown, the metal electrode is trimmed, and the remaining metal electrode is aligned with the ridge of the ridge waveguide, effectively ensuring the accuracy of the relative position between the metal electrode and the ridge of the ridge waveguide; S7, using the lower mask layer 6 as a mask to form a ridge waveguide on the substrate 1; Figure 7 As shown, the substrate 1 is etched to form ridge waveguide grooves 11 at both sides of the ridge ridge of the ridge waveguide, and the ridge waveguide grooves 11 and the ridge ridge together constitute the ridge waveguide; S8, removing the lower mask layer 6 with a BOE solution; Figure 8 As shown, S9, removing the transition layer on top of the metal electrode; Figure 9 As shown, the process of making the metal electrode on the top of the ridge waveguide is completed.

[0023] Furthermore, in S1, the positions of the ridge waveguides to be fabricated are first arranged on substrate 1. The positions of the metal electrodes are determined based on the positions of the ridge waveguides. The positions of the metal electrodes correspond to the positions of the ridge edges of the ridge waveguides. In this embodiment, three ridge waveguides are designed and arranged side by side on substrate 1.

[0024] Embodiment 2. Based on Embodiment 1, a method for fabricating a metal electrode on the top of a ridge waveguide. In S1, the metal electrode includes a bottom Ti layer 2, a Pt layer 3, and an Au layer 4 arranged in sequence from bottom to top. The bottom Ti layer 2, the Pt layer 3, and the Au layer 4 constitute the metal electrode.

[0025] Furthermore, in S1, the transition layer is a top Ti layer 5. The thickness of the top Ti layer 5 is 50 - 100 nm. In this embodiment, the thickness of the top Ti layer 5 is 80 nm. Since the adhesion of the uppermost Au layer 4 of the metal electrode is poor, the top Ti layer 5 is set as the transition layer. The top Ti layer 5 has good adhesion, enabling the lower mask layer 6 and the metal electrode to adhere better and ensuring the stability of the connection between the lower mask layer 6 and the metal electrode.

[0026] Furthermore, when fabricating the metal electrode and the transition layer, the metal lift-off process is used to sequentially grow the bottom Ti layer 2, the Pt layer 3, the Au layer 4, and the top Ti layer 5 on the substrate. Specifically, a photoresist with a rectangular pattern is formed on the substrate 1 using photolithography technology. Ti, Pt, Au, and Ti materials are sequentially deposited by electron beam evaporation or sputtering. Then, the photoresist is dissolved using a stripping solution, and the Ti, Pt, Au, and Ti materials on the surface of the photoresist are stripped together. The Ti, Pt, Au, and Ti materials on the substrate 1 are retained to form the metal electrode and the transition layer. The rectangular pattern on the photoresist is aligned with the ridge position of the ridge waveguide.

[0027] Embodiment 3. Based on Embodiment 2, a method for fabricating a metal electrode on the top of a ridge waveguide. In S2, the lower mask layer 6 is a SiO2 layer; the thickness of the SiO2 layer is 250 - 500 nm. In this embodiment, the thickness of the SiO2 layer is 300 nm, and the SiO2 layer serves as a mask when fabricating the ridge waveguide.

[0028] Furthermore, in S3, the thickness of the upper mask layer 7 is 1 - 3 μm. In this embodiment, the thickness of the upper mask layer 7 is 2 μm, and the upper mask layer 7 is a photoresist layer. Since the photoresist will be consumed during etching, the thickness of the photoresist is greater than the thickness of the photoresist consumed when etching the lower mask layer 6.

[0029] Furthermore, in S7, the ridge waveguide is fabricated by sequentially performing etching and corrosion. Both the first waveguide pattern 71 and the second waveguide pattern 61 correspond to the groove shape of the ridge waveguide. The groove width of the ridge waveguide is determined by the first waveguide pattern 71 and the second waveguide pattern 61.

[0030] Embodiment 4. A method for fabricating a metal electrode on the top of a ridge waveguide, comprising the following steps: S1. Use the metal stripping process to sequentially grow bottom Ti, Pt, Au, and top Ti materials on the surface of substrate 1. The bottom Ti, Pt, and Au materials form a metal electrode, and the top Ti is used as a transition layer. The shapes of the metal electrode and the transition layer are rectangular. The positions of the metal electrode and the transition layer are determined according to the position of the ridge waveguide to be fabricated on substrate 1. Specifically, the metal electrode corresponds to the ridge edge position of the ridge waveguide to be fabricated. The width of the metal electrode is greater than the width of the ridge edge of the ridge waveguide, which enables the metal electrode to still cover the ridge edge even when there is a left - right misalignment, increasing the tolerance during the fabrication of the metal electrode. S2. Grow an SiO2 layer on substrate 1. The SiO2 layer completely covers the upper surface of substrate 1 and the surface of the top Ti layer. Under the action of the top Ti layer, the SiO2 layer can adhere better to the metal electrode, ensuring the stability of the SiO2 layer on substrate 1 and the metal electrode. S3. Coat photoresist on the SiO2 layer. The thickness of the photoresist is greater than the thickness of the photoresist consumed during the etching of the SiO2 layer. S4. Lithograph the first waveguide pattern on the photoresist. The waveguide pattern is the groove shape of the ridge waveguide to be fabricated. S5. Use the photoresist as a mask to etch the SiO2 layer, so that a second waveguide pattern is formed on the SiO2 layer. The second waveguide pattern is the same as the first waveguide pattern, and part of the photoresist will be consumed during the etching of the SiO2 layer, that is, the thickness of the photoresist decreases. S6. Use the remaining photoresist and the SiO2 layer with the second waveguide pattern as a mask to etch the metal electrode and the transition layer, that is, etch the exposed bottom Ti, Pt, Au, and top Ti materials in the second waveguide pattern until the exposed bottom Ti, Pt, Au, and top Ti materials are etched clean. During the etching process, the substrate 1 exposed in the second waveguide pattern will also be partially etched. S7. Use the SiO2 layer as a mask to etch and corrode substrate 1, so that a ridge waveguide groove 11 is formed on substrate 1. S8. Remove the SiO2 layer with BOE solution. S9. Use the etching method to remove the top Ti material, and obtain a ridge waveguide with a metal electrode on the ridge. The process of fabricating the metal electrode on the top of the ridge waveguide is completed.

[0031] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for fabricating a metal electrode on the top of a ridge waveguide, characterized in that, It includes the following steps: S1. Fabricate a metal electrode on the surface of the substrate (1), and fabricate a transition layer on the top of the metal electrode. The width of the metal electrode is greater than the width of the ridge of the ridge waveguide. S2. Grow a lower mask layer (6) on the surface of the substrate (1). S3. Coating a photoresist on the lower mask layer (6) to form an upper mask layer (7). S4. Perform photolithography on the upper mask layer (7) to form a first waveguide pattern (71). S5. Use the upper mask layer (7) as a mask to etch the lower mask layer (6), and form a second waveguide pattern (61) on the lower mask layer (6). S6. Use the upper mask layer (7) and the lower mask layer (6) as masks to etch the exposed transition layer and metal electrode in the second waveguide pattern (61) until the exposed transition layer and metal electrode in the second waveguide pattern (61) are etched clean. S7. Use the lower mask layer (6) as a mask to fabricate a ridge waveguide on the substrate (1). S8. Use BOE solution to remove the lower mask layer (6). S9. Remove the transition layer on the top of the metal electrode. The process of fabricating the metal electrode on the top of the ridge waveguide is completed.

2. The method for fabricating a metal electrode on the top of a ridge waveguide according to claim 1, wherein In S1, first arrange the positions of the ridge waveguides on the substrate (1), and determine the positions of the metal electrodes according to the positions of the ridge waveguides. The positions of the metal electrodes correspond to the ridge positions of the ridge waveguides.

3. The method for fabricating a metal electrode on the top of a ridge waveguide according to claim 1 or 2, characterized in that, In S1, the metal electrode includes a bottom Ti layer (2), a Pt layer (3), and an Au layer (4) arranged in sequence from bottom to top.

4. The method for fabricating a metal electrode on the top of a ridge waveguide according to claim 3, wherein, In S1, the transition layer is a top Ti layer (5).

5. The method for fabricating a metal electrode on the top of a ridge waveguide according to claim 4, wherein The thickness of the top Ti layer (5) is 50 - 100 nm.

6. The method for fabricating a metal electrode on the top of a ridge waveguide according to claim 4 or 5, characterized in that, When fabricating the metal electrode and the transition layer, use the lift-off process to grow the bottom Ti layer (2), the Pt layer (3), the Au layer (4), and the top Ti layer (5) on the substrate in sequence.

7. The method for fabricating a metal electrode on the top of a ridge waveguide according to claim 1, characterized in that, In S2, the lower mask layer (6) is a SiO2 layer; the thickness of the SiO2 layer is 250 - 500 nm.

8. The method for fabricating a metal electrode on the top of a ridge waveguide according to claim 1 or 7, characterized in that, In S3, the thickness of the upper mask layer (7) is 1 - 3 μm.

9. The method for fabricating a metal electrode on the top of a ridge waveguide according to claim 1, wherein In S7, use a method of etching and corrosion in sequence to fabricate the ridge waveguide.

10. The method for fabricating a metal electrode on the top of a ridge waveguide according to claim 1, wherein, Both the first waveguide pattern (71) and the second waveguide pattern (61) correspond to the groove shape of the ridge waveguide.

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