Formation method of semiconductor structure and photoelectric detector
By using selective etching to form Sigma-shaped openings in a silicon-based series of photodetectors and etching with TMAH solution, the problem of poor growth quality of the germanium epitaxial layer was solved, the layered growth of the epitaxial layer was promoted, and the quality of the semiconductor structure and the performance of the photodetector were improved.
Patent Information
- Application Number
- CN202410323926.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-03-20
- Publication Date
- 2025-09-23
AI Technical Summary
The growth quality of the germanium epitaxial layer in the silicon-based photodetectors in the prior art is poor, resulting in lattice matching problems and the appearance of large-area dislocations.
A Sigma-shaped second opening is formed on the substrate using selective etching technology, and different crystal planes are etched using wet etching solution TMAH. When forming an epitaxial layer, the epitaxial layer preferentially grows on the bottom surface of the second opening, inhibiting sidewall growth and promoting layered growth.
The lattice matching between the substrate material and the heteroepitaxial layer material is improved, large-area dislocations are reduced, and the quality of the semiconductor structure and the performance of the photodetector are improved.
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Figure CN120690685A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of semiconductor manufacturing, and in particular to a method for forming a semiconductor structure and a photodetector. Background Art
[0002] As a carrier of information, photons are playing an increasingly important role in science and technology. Photodetectors are crucial components for achieving this function and represent a technological fortress that all optoelectronic chips cannot bypass. The development of new technologies such as remote sensing, fiber-optic communications, and optical interconnects has led to a growing interest in photodetectors. To date, the introduction of III-V series main group materials, primarily IV, into silicon photonics platforms to create silicon-based photodetectors has effectively addressed the problem of pure silicon materials being unable to implement effective photodetectors in the communications band due to the limited bandgap structure of silicon. Consequently, photodetectors primarily based on germanium are the optimal choice.
[0003] However, the growth of germanium epitaxial layers in silicon-based photodetectors remains a challenge. Summary of the Invention
[0004] The problem solved by the present invention is how to improve the growth quality of the germanium epitaxial layer in a silicon-based series photodetector.
[0005] To solve the above problems, the present invention provides a method for forming a semiconductor structure, comprising: providing a substrate; forming an oxide layer on the substrate; performing a first etching on the oxide layer to form a first opening in the oxide layer, wherein the first opening exposes a portion of the surface of the substrate; performing a second etching on the portion of the surface of the substrate exposed by the first opening to form a second opening in the substrate, wherein the second etching is selective etching with different etching rates for different crystal planes of the substrate; and forming an epitaxial layer in the second opening.
[0006] Optionally, the material of the substrate includes silicon, and the material of the epitaxial layer includes germanium.
[0007] Optionally, the second opening is a Sigma-shaped opening.
[0008] Optionally, in the step of forming a first opening in the oxide layer, the surface of a portion of the substrate exposed by the first opening is a (110) crystal plane; in the step of forming a second opening in the substrate, the sidewall surface of the second opening is a (111) crystal plane; and the bottom surface of the second opening is a (100) crystal plane.
[0009] Optionally, the orientation of the (110) crystal plane of the substrate is perpendicular to the second opening direction, wherein the second opening direction is a direction perpendicular to the bottom surface of the second opening and facing away from the substrate.
[0010] Optionally, in the step of forming the epitaxial layer in the second opening, a growth rate of the epitaxial layer at the bottom of the second opening is greater than a growth rate of the epitaxial layer on the sidewall of the second opening.
[0011] Optionally, the second etching is wet etching.
[0012] Optionally, the etching solution of the second etching is an alkaline solution.
[0013] Optionally, the etching solution for the second etching includes: TMAH reagent.
[0014] Optionally, the first etching step includes: forming a mask layer on the surface of the oxide layer, the mask layer exposing part of the surface of the oxide layer; etching the oxide layer using the mask layer as a mask to form the first opening; and removing the mask layer after forming the first opening.
[0015] Optionally, the first etching is dry etching.
[0016] Correspondingly, the technical solution of the present invention further provides a photodetector, which includes a semiconductor structure formed by the method for forming a semiconductor structure as described in any of the above technical solutions.
[0017] Compared with the prior art, the technical solution of the present invention has the following advantages:
[0018] In the method for forming a semiconductor structure according to the technical solution of the present invention, the second etch is a selective etch with varying etching rates on different crystal planes of the substrate, and the epitaxial layer is formed within the second opening. Compared to the sidewall surfaces of the second opening, the epitaxial layer is more likely to grow on the bottom surface of the second opening, thereby allowing the epitaxial layer to grow in a direction perpendicular to the bottom surface of the second opening and suppressing the growth of the epitaxial layer on the sidewall surfaces of the second opening. This promotes the layered growth of the epitaxial layer and suppresses the three-dimensional island growth of the epitaxial layer. This improves the lattice matching between the substrate material and the heterogeneous epitaxial layer material, reduces the occurrence of large-area dislocations, and thus contributes to improving the quality of the semiconductor structure.
[0019] In an optional embodiment of the present invention, the second etching is a wet etching method. The first etching is a dry etching method. Compared to an etching method in which both the first and second openings are formed by the first etching, the etching method in which the first and second openings are formed by the first etching method and the second etching method are formed by the second etching method reduces damage to the substrate, resulting in a second opening with a regular morphology and a flat bottom, which is conducive to the growth of the epitaxial layer.
[0020] In an optional solution of the present invention, the sidewall surface of the second opening is a (111) crystal plane; the bottom surface of the second opening is a (100) crystal plane. The growth rate of the epitaxial layer at the bottom of the second opening is greater than the growth rate of the epitaxial layer at the sidewall of the second opening. The epitaxial layer grows in a direction perpendicular to the bottom surface of the second opening, suppressing the growth of the epitaxial layer on the sidewall of the second opening, thereby promoting the layered growth of the epitaxial layer and suppressing the three-dimensional island growth of the epitaxial layer, improving the lattice matching problem between the substrate material and the heterogeneous epitaxial layer material, reducing the occurrence of large-area dislocations, and thus helping to improve the quality of the semiconductor structure. BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Figures 1 to 3 It is a cross-sectional structural diagram of the formation process of a semiconductor structure.
[0022] Figures 4 to 8 It is a schematic cross-sectional structural diagram of the formation process of the semiconductor structure according to an embodiment of the present invention. DETAILED DESCRIPTION
[0023] As can be seen from the background art, there are problems with the growth quality of germanium epitaxial layers in the prior art. The reasons for the problems with the growth quality of epitaxial layers are now analyzed in conjunction with a method for forming a semiconductor structure.
[0024] Please refer to Figure 1 , providing a substrate 100; forming an initial oxide layer 101 on the substrate 100; forming a mask layer 102 on the initial oxide layer 101, wherein the mask layer 102 exposes a portion of the surface of the initial oxide layer 101.
[0025] Please refer to Figure 2 , with the mask layer 102 (such as Figure 1 ) is a mask, and the initial oxide layer 101 is first etched to form a first opening 103 and an oxide layer 104 , where the first opening 103 exposes a portion of the surface of the substrate 100 .
[0026] Please refer to Figure 3 , using the oxide layer 104 as a mask, the first opening 103 (such as Figure 2 A second etching is performed on the exposed portion of the surface of the substrate 100 (as shown) to form a second opening 105 in the substrate 100.
[0027] After forming the second opening 105, the method further includes: forming an epitaxial layer in the second opening 105. The epitaxial layer is made of germanium. The substrate is made of silicon.
[0028] Both the first etching and the second etching are dry etching, which will damage the substrate 100, resulting in excessive surface defects on the bottom and side walls of the second opening 105. In addition, the second etching is not selective etching with different etching rates for different crystal planes of the substrate 100. The morphology of the second opening 105 is similar to that of the first opening 103, and the second opening 105 exposing the (111) crystal plane cannot be obtained. The epitaxial layer subsequently formed in the second opening 105 is prone to grow on the side wall surface of the second opening 105. Therefore, large-area dislocations caused by three-dimensional island growth are prone to occur in the epitaxial layer formed in the second opening 105, that is, the growth quality of the epitaxial layer is poor.
[0029] To solve the technical problem, the present invention provides a method for forming a semiconductor structure, comprising: providing a substrate; forming an oxide layer on the substrate; performing a first etching on the oxide layer to form a first opening in the oxide layer, wherein the first opening exposes a portion of the surface of the substrate; performing a second etching on the portion of the surface of the substrate exposed by the first opening to form a second opening in the substrate, wherein the second etching is selective etching with different etching rates for different crystal planes of the substrate; and forming an epitaxial layer in the second opening.
[0030] In the method for forming a semiconductor structure according to the technical solution of the present invention, the second etch is a selective etch with varying etching rates on different crystal planes of the substrate, and the epitaxial layer is formed within the second opening. Compared to the sidewall surfaces of the second opening, the epitaxial layer is more likely to grow on the bottom surface of the second opening, thereby allowing the epitaxial layer to grow in a direction perpendicular to the bottom surface of the second opening and suppressing the growth of the epitaxial layer on the sidewall surfaces of the second opening. This promotes the layered growth of the epitaxial layer and suppresses the three-dimensional island growth of the epitaxial layer. This improves the lattice matching between the substrate material and the heterogeneous epitaxial layer material, reduces the occurrence of large-area dislocations, and thus contributes to improving the quality of the semiconductor structure.
[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.
[0032] Please refer to Figure 4 , providing a substrate 200; forming an oxide layer 201 on the substrate 200.
[0033] The substrate 200 is made of silicon. In some specific embodiments, the substrate 200 is a silicon substrate. The oxide layer 201 is made of silicon oxide.
[0034] Please refer to Figures 5 and 6, performing a first etching on the oxide layer 201 to form a first opening 203 in the oxide layer 201, wherein the first opening 203 exposes a portion of the surface of the substrate 200. The first etching step includes: Figure 5 As shown, a mask layer 202 is formed on the surface of the oxide layer 201, and the mask layer 202 exposes a portion of the surface of the oxide layer 201; Figure 6 As shown, the mask layer 202 (as Figure 5 ) is a mask, the oxide layer 201 is etched to form the first opening 203; after the first opening 203 is formed, the mask layer 202 is removed.
[0035] The mask layer 202 is used to define the position of the first opening 203. The mask layer 202 may be a photoresist layer, and may be formed by coating, exposing, and developing.
[0036] The first etching is dry etching.
[0037] In the step of forming the first opening 203 in the oxide layer 201 , the first opening 203 exposes a portion of the surface of the substrate 200 as a (110) crystal plane.
[0038] Please refer to Figure 7 , performing a second etching on the portion of the surface of the substrate 200 exposed by the first opening 203 to form a second opening 204 in the substrate 200, wherein the second etching is a selective etching with different etching rates on different crystal planes of the substrate 200.
[0039] The second etching is a wet etching method. The etching solution of the second etching is an alkaline solution. Specifically, in this embodiment, the etching solution of the second etching includes a TMAH reagent. The TMAH reagent is a tetramethylammonium hydroxide solution. The wet etching process has high process stability and is not easily affected by the concentration and pH of the etching reagent, resulting in a better morphology of the second opening 204.
[0040] The TMAH reagent has different etching rates for each crystal plane of the silicon material of the substrate 200. Specifically, in this embodiment, at 80°C, the ratio of the etching rate of the silicon (100) crystal plane to the silicon (110) crystal plane at a TMAH reagent concentration of 20% by mass is 0.54, and the ratio of the etching rate of the silicon (100) crystal plane to the silicon (111) crystal plane is 37. The TMAH reagent has a relatively large etching selectivity for the silicon (100) crystal plane and the silicon (111) crystal plane, resulting in a second opening 204 with a good morphology on the silicon (111) crystal plane, providing a structural foundation for the subsequent formation of the epitaxial layer 205.
[0041] The second etching is wet etching. Compared with dry etching, the substrate 200 at the bottom of the second opening 204 obtained by wet etching is less damaged, and there are fewer defects at the bottom of the second opening 204, which is beneficial to the subsequent growth of the epitaxial layer 205 and improves the growth quality of the epitaxial layer 205.
[0042] The second opening 204 is a Sigma-shaped opening. The angle between the sidewall of the second opening 204 and the normal to the surface of the substrate 200 is greater than the angle between the sidewall of the first opening 203 and the normal to the surface of the first opening 203. The width of the bottom of the second opening 204 is less than the width of the bottom of the first opening 203.
[0043] In the step of forming the second opening 204 in the substrate 200, the sidewall surface of the second opening 204 is a (111) crystal plane; and the bottom surface of the second opening 204 is a (100) crystal plane. An angle of 54.7° is formed between the sidewall surface of the second opening 204 and the bottom surface of the second opening 204. The atomic density of the (111) crystal plane is relatively high, and the energy barrier is relatively high. Therefore, the sidewall surface of the second opening 204 is a (111) crystal plane, which can inhibit the nucleation and growth of the germanium material of the epitaxial layer 205 on its surface; the atomic density of the (100) crystal plane is relatively low, and the energy barrier is relatively low. Therefore, the bottom surface of the second opening 204 is a (100) crystal plane, which can promote the nucleation and growth of the germanium material of the epitaxial layer 205 on its surface.
[0044] In this embodiment, the bottom surface of the second opening 204 is a (100) crystal plane, and the side wall surface is a (111) crystal plane, which can effectively promote the layered growth of the epitaxial layer 205 on the bottom surface and inhibit the growth of the epitaxial layer 205 on the side wall surface, reduce the gate area dislocation caused by three-dimensional island growth, improve the lattice matching problem between the substrate 200 material and the heteroepitaxial layer 205 material, and enhance the quality of the semiconductor structure.
[0045] The (110) crystal plane of the substrate 200 is oriented perpendicularly to the direction of the second opening 204, wherein the direction of the second opening 204 is perpendicular to the bottom surface of the second opening 204 and facing away from the substrate 200. The (110) crystal plane of the substrate 200 is oriented perpendicularly to the direction of the second opening 204, thereby improving the growth quality of the epitaxial layer 205.
[0046] The first opening 203 and the second opening 204 are germanium photodetector windows. The first opening 203 and the second opening 204 are used to define the shape of the photodetector, that is, the layout of the photodetector.
[0047] Please refer to Figure 8 , an epitaxial layer 205 is formed in the second opening 204 .
[0048] Compared with the side wall surface of the second opening 204, the epitaxial layer 205 is easier to grow on the bottom surface of the second opening 204, so that the epitaxial layer 205 grows in layers in a direction perpendicular to the bottom surface of the second opening 204, avoiding the three-dimensional island growth of the epitaxial layer 205 in the second opening 204, reducing the occurrence of large-area dislocations, and improving the lattice matching problem between the substrate 200 material and the heterogeneous epitaxial layer 205 material, which is beneficial to improving the quality of the semiconductor structure.
[0049] The epitaxial layer 205 is made of germanium. In some specific embodiments, the epitaxial layer 205 is a germanium epitaxial layer. The epitaxial layer 205 is made of a material different from that of the substrate 200 .
[0050] In the step of forming the epitaxial layer 205 in the second opening 204 , a growth rate of the epitaxial layer 205 at the bottom of the second opening 204 is greater than a growth rate of the epitaxial layer 205 at the sidewall of the second opening 204 .
[0051] Correspondingly, an embodiment of the present invention further provides a photodetector, which includes a semiconductor structure formed by the above-mentioned method for forming a semiconductor structure, and will not be described in detail here.
[0052] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.
Claims
1. A method for forming a semiconductor structure, characterized in that: include: providing a substrate; forming an oxide layer on the substrate; Performing a first etching on the oxide layer to form a first opening in the oxide layer, wherein the first opening exposes a portion of the surface of the substrate; Performing a second etching on the portion of the surface of the substrate exposed by the first opening to form a second opening in the substrate, wherein the second etching is a selective etching with different etching rates on different crystal planes of the substrate; An epitaxial layer is formed in the second opening.
2. The method for forming a semiconductor structure according to claim 1, wherein: The material of the substrate includes silicon, and the material of the epitaxial layer includes germanium.
3. The method for forming a semiconductor structure according to claim 2, wherein: The second opening is a Sigma-shaped opening.
4. The method for forming a semiconductor structure according to claim 2 or 3, wherein: In the step of forming a first opening in the oxide layer, the surface of a portion of the substrate exposed by the first opening is a (110) crystal plane; in the step of forming a second opening in the substrate, the sidewall surface of the second opening is a (111) crystal plane; and the bottom surface of the second opening is a (100) crystal plane.
5. The method for forming a semiconductor structure according to claim 4, wherein: The orientation of the (110) crystal plane of the substrate is perpendicular to the second opening direction, wherein the second opening direction is a direction perpendicular to the bottom surface of the second opening and facing away from the substrate.
6. The method for forming a semiconductor structure according to claim 4, wherein: In the step of forming the epitaxial layer in the second opening, a growth rate of the epitaxial layer at the bottom of the second opening is greater than a growth rate of the epitaxial layer on the sidewall of the second opening.
7. The method for forming a semiconductor structure according to claim 1, wherein: The second etching is wet etching.
8. The method for forming a semiconductor structure according to claim 7, wherein: The etching solution of the second etching is an alkaline solution.
9. The method for forming a semiconductor structure according to claim 7, wherein: The etching solution of the second etching includes: TMAH reagent.
10. The method for forming a semiconductor structure according to claim 1, wherein: The first etching step includes: forming a mask layer on the surface of the oxide layer, wherein the mask layer exposes a portion of the surface of the oxide layer; etching the oxide layer using the mask layer as a mask to form the first opening; After forming the first opening, the mask layer is removed.
11. The method for forming a semiconductor structure according to claim 10, wherein: The first etching is dry etching.
12. A photoelectric detector, characterized in that: include: A semiconductor structure formed by the method for forming a semiconductor structure according to any one of claims 1 to 11.