Formation method of semiconductor structure and photoelectric detector

Abstract

The invention discloses a semiconductor structure forming method and a photoelectric detector. The forming method comprises the following steps: providing a substrate; forming an oxide layer on the substrate; forming a cover layer on the oxide layer; the oxide layer and the cover layer are etched, openings are formed in the oxide layer and the cover layer, and the openings expose part of the surface of the substrate; forming an initial epitaxial layer in the opening, wherein the initial epitaxial layer protrudes out of the surface of the cover layer; and planarizing the initial epitaxial layer by taking the cover layer as a stop layer to form an epitaxial layer flush with the surface of the cover layer. A cover layer is formed on an oxide layer, the cover layer covers the oxide layer to reduce the exposed area of the surface of the oxide layer, so that a formed opening is easy to clean, good conditions are provided for epitaxial growth of an epitaxial layer, island-shaped defects of the epitaxial layer are reduced, and the epitaxial layer flush with the surface of the cover layer is formed after planarization treatment by taking the cover layer as a stop layer. The surface flatness of the epitaxial layer is improved, the thickness of the epitaxial layer is easier to regulate and control, and the performance stability of the semiconductor structure is improved.

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] Optical interconnects based on silicon photonics can achieve ultra-high bandwidth and low-power signal transmission. In addition, silicon photonics are compatible with complementary metal oxide semiconductor (CMOS) technology and rely on mature integrated circuit wafer manufacturing processes to achieve silicon photonic device integration. As the core device for photoelectric conversion in optical interconnects, germanium photodetectors are considered the best choice for preparing photodetectors required for on-chip optical interconnects. Germanium photodetectors have the following advantages: (1) they can achieve photoelectric conversion with a large responsivity; (2) they have a suitable germanium band gap, which can achieve efficient detection in the communication band (1300-1500nm); and (3) germanium has low thermal conductivity, which can achieve high saturation output power.

[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; forming a cap layer on the oxide layer; etching the oxide layer and the cap layer to form openings in the oxide layer and the cap layer, wherein the openings expose a portion of the surface of the substrate; forming an initial epitaxial layer in the opening, wherein the initial epitaxial layer protrudes from the surface of the cap layer; and planarizing the initial epitaxial layer using the cap layer as a stop layer to form an epitaxial layer flush with the surface of the cap layer.

[0006] Optionally, the material of the substrate includes silicon, and the material of the epitaxial layer includes germanium.

[0007] Optionally, the material of the capping layer includes silicon nitride.

[0008] Optionally, the thickness of the cover layer ranges from 10 nm to 200 nm.

[0009] Optionally, the method for forming the capping layer includes deposition.

[0010] Optionally, the step of forming the opening includes: forming a photoresist layer on the cover layer; forming a hard mask on the photoresist layer; using the hard mask as a mask, patterning the photoresist layer to form an opening mask layer; using the opening mask layer as a mask, etching the cover layer and the oxide layer to form openings in the oxide layer and the cover layer, wherein the openings expose a portion of the surface of the substrate.

[0011] Optionally, the etching process includes dry etching.

[0012] Optionally, the planarization method includes chemical mechanical polishing.

[0013] Optionally, before forming the initial epitaxial layer and after forming the opening, the method further includes: performing a cleaning process.

[0014] Optionally, the cleaning solution of the cleaning process includes hydrofluoric acid.

[0015] Optionally, in the step of forming the initial epitaxial layer in the opening, the initial epitaxial layer is formed in the opening by epitaxial growth.

[0016] Optionally, the opening is a photodetector window, and the opening is used to define the shape of the photodetector, that is, the layout of the photodetector.

[0017] 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.

[0018] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0019] In the method for forming a semiconductor structure of the technical solution of the present invention, a capping layer is formed on the oxide layer. The capping layer covers the oxide layer to reduce the exposed area of ​​the oxide layer surface, and can protect the oxide layer during the opening cleaning process to avoid excessive loss of the oxide layer, so that the formed opening is easy to clean, providing good conditions for the epitaxial growth of the epitaxial layer, and is conducive to reducing the island defects of the epitaxial layer. Moreover, in the planarization process, the capping layer is used as a stop layer to obtain the epitaxial layer that is flush with the surface of the capping layer, thereby improving the surface flatness of the epitaxial layer, making the thickness of the epitaxial layer easier to control, and improving the performance stability of the semiconductor structure.

[0020] In an optional solution of the present invention, before forming the initial epitaxial layer and after forming the opening, a cleaning process is further included. The cap layer covers the oxide layer to prevent large-area exposure of the oxide layer, thereby reducing the difficulty of the cleaning process and improving the reliability of the semiconductor device.

[0021] The photodetector structure of the technical solution of the present invention has a capping layer located on the oxide layer. The capping layer covers the oxide layer to reduce the exposed area of ​​the oxide layer surface, can protect the oxide layer during the opening cleaning process, avoid excessive loss of the oxide layer, make the opening easy to clean, provide good conditions for the epitaxial growth of the epitaxial layer, reduce the island defects of the epitaxial layer, and use the capping layer as a stop layer to obtain the epitaxial layer that is flush with the surface of the capping layer, thereby improving the surface flatness of the epitaxial layer, making the thickness of the epitaxial layer easier to control, and improving the performance stability of the photodetector structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figures 1 to 5 It is a schematic cross-sectional structure diagram of each step in the formation process of a semiconductor structure.

[0023] Figures 6 to 11 It is a schematic cross-sectional structural diagram of each step of the formation process of the semiconductor structure according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] 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.

[0025] Please refer to Figure 1 , providing a substrate 100; and forming an oxide layer 101 on the substrate 100.

[0026] Please refer to Figure 2 , a mask layer 102 is formed on the oxide layer 101 , wherein the mask layer 102 exposes a portion of the surface of the oxide layer 101 .

[0027] Please refer to Figure 3 The oxide layer 101 is etched using the mask layer 102 as a mask to form an opening 103 in the oxide layer 101 . The opening 103 exposes a portion of the surface of the substrate 100 .

[0028] Please refer to Figure 4 , an initial epitaxial layer 104 is formed in the opening 103 .

[0029] Please refer to Figure 5 , the initial epitaxial layer 104 is planarized to form an epitaxial layer 105 .

[0030] The epitaxial layer 105 is made of germanium. The substrate 100 is made of silicon.

[0031] Before forming the initial epitaxial layer 104 and after forming the opening 103 , the method further includes performing a cleaning process.

[0032] The oxide layer 101 is exposed over a large area and is prone to loss during the cleaning process, which leads to a sharp increase in the difficulty of the cleaning process. The surface cleanliness of the substrate 100 is low. When the initial germanium epitaxial layer 104 is epitaxially grown on the surface of the substrate 100, a large number of defects will be generated, affecting the crystal quality of the germanium epitaxial layer 105. In addition, the initial germanium epitaxial layer 104 is heteroepitaxially grown on the silicon substrate 100, and the formed initial epitaxial layer 104 protrudes from the surface of the oxide layer 101. When the initial epitaxial layer 104 is planarized to form the epitaxial layer 105, it is difficult to control the thickness of the epitaxial layer 105 and the flatness of the epitaxial layer surface, which reduces the performance stability of the semiconductor structure.

[0033] In order 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; forming a cap layer on the oxide layer; etching the oxide layer and the cap layer to form openings in the oxide layer and the cap layer, wherein the openings expose a portion of the surface of the substrate; forming an initial epitaxial layer in the opening, wherein the initial epitaxial layer protrudes from the surface of the cap layer; and planarizing the initial epitaxial layer using the cap layer as a stop layer to form an epitaxial layer flush with the surface of the cap layer.

[0034] In the method for forming a semiconductor structure of the technical solution of the present invention, a capping layer is formed on the oxide layer. The capping layer covers the oxide layer to reduce the exposed area of ​​the oxide layer surface, and can protect the oxide layer during the opening cleaning process to avoid excessive loss of the oxide layer, so that the formed opening is easy to clean, providing good conditions for the epitaxial growth of the epitaxial layer, and reducing the island defects of the epitaxial layer. Moreover, in the planarization process, the capping layer is used as a stop layer to obtain the epitaxial layer flush with the surface of the capping layer, thereby improving the surface flatness of the epitaxial layer and making the thickness of the epitaxial layer easier to control.

[0035] 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.

[0036] Please refer to Figure 6 , providing a substrate 200; forming an oxide layer 201 on the substrate 200.

[0037] The material of the substrate 200 includes silicon. In some specific embodiments, the substrate 200 is a silicon substrate 200. The material of the oxide layer 201 includes silicon oxide.

[0038] Please refer to Figure 7 , a capping layer 202 is formed on the oxide layer 201 .

[0039] The cap layer 202 covers the oxide layer 201, reducing the exposed area of ​​the oxide layer 201 surface so that the subsequently formed opening 204 (such as Figure 9 Easy to clean.

[0040] The cap layer 202 is formed by deposition. Specifically, in this embodiment, the cap layer 202 is made of silicon nitride.

[0041] The thickness of the cap layer 202 ranges from 10 nm to 200 nm. The thickness of the cap layer 202 is positively correlated with the thickness of the photodetector required in actual production process, that is, the thicker the required photodetector, the thicker the cap layer 202.

[0042] Please refer to Figures 8 and 9 , the oxide layer 201 and the cap layer 202 are etched to form openings 204 (such as Figure 9 As shown in FIG. 2 , the opening 204 exposes a portion of the surface of the substrate 200 .

[0043] The opening 204 is a photodetector window, and the opening 204 is used to define the shape of the photodetector, that is, the layout of the photodetector.

[0044] The steps of forming the opening 204 include: Figure 8 As shown, a photoresist layer (not shown) is formed on the cap layer 202; the photoresist layer is subjected to photolithography to form an opening mask layer 203. Figure 9 As shown, the cap layer 202 and the oxide layer 201 are etched using the opening mask layer 203 as a mask to form openings 204 in the oxide layer 201 and the cap layer 202 . The openings 204 expose a portion of the surface of the substrate 200 .

[0045] The opening mask layer 203 is used to define the position of the opening 204. The opening mask layer 203 is a photoresist layer, and is formed by coating, exposing, and developing.

[0046] The etching process includes dry etching. Specifically, in this embodiment, the dry etching is plasma dry etching.

[0047] After forming the opening 204, the method further includes performing a cleaning process. The cleaning solution for the cleaning process includes hydrofluoric acid. The purpose of the cleaning process is to obtain a substrate 200 with a clean surface and to improve the crystal quality of the initial epitaxial layer 205 subsequently epitaxially grown within the opening 204. The cap layer 202 covers the oxide layer 201, reducing the surface area of ​​the oxide layer 201 exposed. The oxide layer 201 can be protected by the cap layer 202, and the oxide layer 201 is less damaged. The cleaning process is relatively easy and has a good cleaning effect. The surface cleanliness of the substrate 200 after the cleaning process is relatively high.

[0048] Please refer to Figure 10 An initial epitaxial layer 205 is formed in the opening 204 , and the initial epitaxial layer 205 protrudes from the surface of the cap layer 202 .

[0049] The material of the initial epitaxial layer 205 includes germanium. In some specific embodiments, the initial epitaxial layer 205 is a germanium initial epitaxial layer. In the step of forming the initial epitaxial layer 205 in the opening 204, the initial epitaxial layer 205 is formed in the opening 204 by epitaxial growth. The growth of the germanium initial epitaxial layer 205 has high requirements for the substrate 200. The cap layer 202 is formed on the oxide layer 201. The cap layer 202 covers the oxide layer 201 to reduce the exposed area of ​​the oxide layer 201 surface, making the formed opening 204 easy to clean, providing good conditions for the epitaxial growth of the germanium initial epitaxial layer 205, reducing island defects in the epitaxial layer, and improving the crystal quality of the germanium initial epitaxial layer 205.

[0050] Please refer to Figure 11 , using the cap layer 202 as a stop layer, the initial epitaxial layer 205 is planarized to form an epitaxial layer 206 flush with the surface of the cap layer 202 .

[0051] During the planarization process, the cap layer 202 is used as a stop layer to obtain an epitaxial layer 206 flush with the surface of the cap layer 202, thereby improving the surface flatness of the epitaxial layer 206, making the thickness of the epitaxial layer 206 easier to control, and improving the performance stability of the semiconductor structure.

[0052] The planarization methods include mechanical polishing, chemical polishing, fluid polishing, and chemical-mechanical polishing. Specifically, in this embodiment, the planarization method is chemical mechanical polishing. Unlike traditional purely mechanical or purely chemical polishing methods, chemical mechanical polishing, through the combined action of chemical and mechanical forces, avoids the surface damage caused by mechanical polishing alone and the shortcomings of chemical polishing alone, such as slow polishing speed, poor surface flatness, and poor polishing consistency. Chemical mechanical polishing is widely used for high-planarization polishing of various materials at the nanoscale.

[0053] Correspondingly, an embodiment of the present invention also provides a photodetector, which includes a semiconductor structure formed by the above-mentioned semiconductor structure formation method, and the semiconductor structure includes: a substrate 200; an oxide layer 201 located on the substrate 200; a cap layer 202 located on the oxide layer 201; an epitaxial layer 206 located in the oxide layer 201 and in the cap layer 202, and the surface of the epitaxial layer 206 is flush with the surface of the cap layer 202.

[0054] In the photodetector structure of the technical solution of the present invention, there is a capping layer located on the oxide layer. The capping layer covers the oxide layer to reduce the exposed area of ​​the oxide layer surface, so that the opening is easy to clean, providing good conditions for the epitaxial growth of the epitaxial layer, and reducing the island defects of the epitaxial layer. In addition, the capping layer is used as a stop layer to obtain the epitaxial layer that is flush with the surface of the capping layer, thereby improving the surface flatness of the epitaxial layer, making the thickness of the epitaxial layer easier to control, and improving the performance stability of the photodetector structure.

[0055] The semiconductor structure includes a substrate 200 .

[0056] The substrate 200 is made of silicon. In some specific embodiments, the substrate 200 is a silicon substrate 200 .

[0057] The semiconductor structure includes an oxide layer 201 located on the substrate 200 .

[0058] The material of the oxide layer 201 includes silicon oxide.

[0059] The semiconductor structure includes a capping layer 202 located on the oxide layer 201 .

[0060] Specifically, in this embodiment, the material of the cap layer 202 includes silicon nitride.

[0061] The thickness of the cap layer 202 ranges from 10 nm to 200 nm. The thickness of the cap layer 202 is positively correlated with the thickness of the photodetector required in actual production process, that is, the thicker the required photodetector, the thicker the cap layer 202.

[0062] The semiconductor structure includes an epitaxial layer 206 located within the oxide layer 201 and the cap layer 202 , wherein a surface of the epitaxial layer 206 is flush with a surface of the cap layer 202 .

[0063] The epitaxial layer 206 is made of germanium. In some specific embodiments, the epitaxial layer 206 is a germanium initial epitaxial layer.

[0064] 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; forming a capping layer on the oxide layer; Etching the oxide layer and the cap layer to form openings in the oxide layer and the cap layer, wherein the openings expose a portion of the surface of the substrate; forming an initial epitaxial layer in the opening, wherein the initial epitaxial layer protrudes from a surface of the cap layer; The initial epitaxial layer is planarized using the cap layer as a stop layer to form an epitaxial layer flush with the surface of the cap layer.

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 1, wherein: The material of the capping layer includes silicon nitride.

4. The method for forming a semiconductor structure according to claim 1, wherein: The thickness of the cap layer ranges from 10 nm to 200 nm.

5. The method for forming a semiconductor structure according to claim 1, wherein: The method of forming the capping layer includes deposition.

6. The method for forming a semiconductor structure according to claim 1, wherein: The step of forming the opening includes: forming a photoresist layer on the cover layer; performing photolithography on the photoresist layer to form an opening mask layer; using the opening mask layer as a mask, etching the cover layer and the oxide layer to form an opening in the oxide layer and the cover layer, wherein the opening exposes a portion of the surface of the substrate.

7. The method for forming a semiconductor structure according to claim 1, wherein: The etching process includes dry etching.

8. The method for forming a semiconductor structure according to claim 1, wherein: The planarization method includes chemical mechanical polishing.

9. The method for forming a semiconductor structure according to claim 1, wherein: Before forming the initial epitaxial layer and after forming the opening, the method further includes: performing a cleaning process.

10. The method for forming a semiconductor structure according to claim 9, wherein: The cleaning solution of the cleaning process includes hydrofluoric acid.

11. The method for forming a semiconductor structure according to claim 1, wherein: In the step of forming the initial epitaxial layer in the opening, the initial epitaxial layer is formed in the opening in a manner of epitaxial growth.

12. The method for forming a semiconductor structure according to claim 1, wherein: The opening is a photodetector window, and the opening is used to define the shape of the photodetector, that is, the layout of the photodetector.

13. 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 12.

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