Method for growing germanium epitaxial layer in deep silicon groove
By employing TMAH and wet chemical cleaning combined with thermal oxidation in deep silicon trenches, the growth process of germanium epitaxial layers was optimized, solving the problem of poor germanium epitaxial quality and achieving high-quality germanium epitaxial layers and improved optical chip performance.
Patent Information
- Application Number
- CN202511104294.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-07
- Publication Date
- 2025-11-18
AI Technical Summary
In existing technologies, poor germanium epitaxial quality leads to performance degradation of germanium devices and waveguide loss in optical chips, especially when the sidewalls and bottom are bonded in deep silicon trenches, voids and holes are prone to occur.
Before the traditional cleaning process, TMAH solution cleaning and wet chemical cleaning are added, followed by selective germanium epitaxy to form a germanium epitaxial layer. Then, the sidewall roughness is optimized by thermal oxidation to form an oxide layer to passivate and encapsulate the rough structure.
It improves the quality of germanium epitaxial layers, avoids small hole defects after CMP, stabilizes the performance of germanium devices, reduces waveguide losses in optical chips, and enhances the flatness and bonding effect of germanium epitaxial layers.
Smart Images
Figure CN120967497A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a method for growing germanium epitaxial layers in deep silicon trenches. Background Technology
[0002] Germanium, as an excellent semiconductor material, plays a crucial role in the design, development, and use of silicon-based optoelectronic chips. Germanium boasts high electron and hole mobilities, with the highest hole mobility among all semiconductor materials, making it highly suitable for optoelectronic chip applications. In practical processes, germanium is selectively epitaxially grown at appropriate locations on the silicon surface using a controlled low-pressure environment, appropriate gas flow rate, and suitable epitaxial temperature. This germanium is then combined with waveguides to form crucial germanium devices in optoelectronic chips, forming the core component of silicon-based optoelectronic chips and overcoming the inherent photoelectric conversion limitations of silicon, another semiconductor material. Silicon-based semiconductor process technology and procedures are already very mature, allowing for the development and improvement of high-performance silicon-based optoelectronic chips by combining selective germanium epitaxy with this foundation.
[0003] Selective deep silicon germanium epitaxy (SDSE) utilizes traditional silicon wafer fabrication processes to photolithographically and etch silicon windows into a silicon dioxide protective layer. These silicon windows are typically deeper than 3µm. The process of epitaxially growing germanium inside and outside these silicon windows is called deep silicon germanium epitaxy. SSE requires that germanium can only be epitaxially grown inside and outside the silicon windows, while no germanium should be epitaxial on the surface of the silicon dioxide protective layer. Furthermore, the epitaxial morphology of the germanium must essentially conform to a crystalline state, and there should be no defects such as voids on the surface after CMP (Chemical Mechanical Polishing) leveling.
[0004] Currently, when using conventional germanium epitaxy processes for deep silicon epitaxy, the silicon etching depth on the sidewalls of the silicon window is relatively large. During epitaxy, the bottom of the silicon window and the silicon surface of the sidewalls are epitaxial simultaneously. However, in conventional etching processes, the etching quality of the sidewalls is lower than that of the bottom, resulting in poor germanium epitaxial quality on the sidewalls. When the germanium epitaxial layers on the sidewalls and bottom combine, voids are generated, which appear after surface smoothing in the CMP process. Such void defects are unacceptable, causing performance degradation of germanium devices and loss in waveguides of optical chips. Therefore, there is an urgent need to design a method for growing germanium epitaxial layers in deep silicon trenches that can improve the performance of germanium devices. Summary of the Invention
[0005] One objective of this invention is to provide a method for growing germanium epitaxial layers in deep silicon trenches, thereby solving the technical problems in the prior art where poor germanium epitaxial quality leads to performance degradation of germanium devices and waveguide loss in optical chips.
[0006] A further objective of this invention is to improve the flatness of the silicon window sidewalls.
[0007] In particular, the present invention provides a method for growing a germanium epitaxial layer in a deep silicon trench, comprising the following steps: Provides a Si / SiO2 substrate; The Si / SiO2 substrate is photolithographically and etched to form a deep silicon trench of a predetermined depth; The Si / SiO2 substrate with the deep silicon trench was immersed in TMAH solution for the first cleaning. The Si / SiO2 substrate with the deep silicon trench is immersed in a wet chemical cleaning solution for a second cleaning. A selective germanium epitaxial process is performed in the deep silicon trench to form a germanium epitaxial layer.
[0008] Optionally, in the step of immersing the Si / SiO2 substrate with the deep silicon trench in a TMAH solution for the first cleaning, the mass percentage of TMAH in the TMAH solution ranges from 2% to 3%.
[0009] Optionally, in the step of immersing the Si / SiO2 substrate with the deep silicon trench in a TMAH solution for the first cleaning, the immersion time is 8 min to 15 min, and the temperature range of the TMAH solution is 70℃ to 80℃.
[0010] Optionally, the wet chemical cleaning solution includes SC2 solution and DHF solution; The volume ratio of HCl, H2O2 and H2O in the SC2 solution ranges from 1:1 to 2:5 to 20. The mass percentage of HF in the DHF solution ranges from 0.25% to 2%.
[0011] Optionally, the Si / SiO2 substrate having the deep silicon trench is immersed in a wet chemical cleaning solution for a second cleaning step, followed by the following steps: The Si / SiO2 substrate with the deep silicon trench is placed in a thermal oxidation device and subjected to a thermal oxidation process to form an oxide layer. The Si / SiO2 substrate with the deep silicon trench is subjected to BOE cleaning to remove the oxide layer.
[0012] Optionally, the thermal oxidation process is dry oxygen oxidation, with an oxygen flow rate ranging from 1 slm to 2 slm, an oxidation temperature ranging from 900℃ to 1200℃, and an oxidation time ranging from 10 min to 30 min.
[0013] Optionally, in the step of performing BOE cleaning on the Si / SiO2 substrate with the deep silicon trench to remove the oxide layer, the volume ratio of NH4F to HF in the BOE solution is in the range of 5-7:1.
[0014] Optionally, the Si / SiO2 substrate having the deep silicon trench is subjected to BOE cleaning to remove the oxide layer, followed by the following steps: The Si / SiO2 substrate with the deep silicon trench is subjected to DIW rinsing and drying.
[0015] Optionally, the preset depth ranges from 3µm to 10µm.
[0016] Optionally, the step of performing a selective germanium epitaxial process in the deep silicon trench to form a germanium epitaxial layer further includes the following steps: The germanium epitaxial layer was smoothed using a CMP process.
[0017] This invention first performs photolithography and etching on a Si / SiO2 substrate to form a deep silicon trench of a predetermined depth. Then, the Si / SiO2 substrate with the deep silicon trench is immersed in a TMAH solution for a first cleaning. Next, the Si / SiO2 substrate with the deep silicon trench is immersed in a wet chemical cleaning solution for a second cleaning. Finally, a selective germanium epitaxial process is performed in the deep silicon trench to form a germanium epitaxial layer. This technical solution optimizes the sidewall roughness of the deep silicon trench by adding a TMAH cleaning process before the traditional cleaning process, providing a good epitaxial foundation for subsequent germanium epitaxy. This improves the quality of the germanium epitaxial layer, avoids the formation of small holes after CMP surface polishing, stabilizes the performance of germanium devices, and reduces waveguide losses in optical chips.
[0018] Furthermore, in this invention, the Si / SiO2 substrate with deep silicon trenches is immersed in a wet chemical cleaning solution for a second cleaning step. Then, the Si / SiO2 substrate with deep silicon trenches is placed in a thermal oxidation device for a thermal oxidation process to form an oxide layer. By oxidizing and encapsulating the rough structure, morphological passivation and embedding are achieved, which can further improve the flatness of the sidewalls of the deep silicon trenches and thus further improve the quality of germanium epitaxy.
[0019] The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description
[0020] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings: Figure 1 This is a schematic flowchart of a method for growing a germanium epitaxial layer in a deep silicon trench according to an embodiment of the present invention; Figure 2 This is a schematic structural diagram of a Si / SiO2 substrate with deep silicon trenches according to an embodiment of the present invention; Figure 3 (a) is an electron microscope image of the sidewall of the deep silicon tank after wet chemical cleaning only; Figure 3 (b) is an electron microscope image of the sidewall of the deep silicon tank after TMAH cleaning and wet chemical cleaning; Figure 4 (a) is an image of a germanium epitaxial layer formed by selective germanium epitaxy in a deep silicon tank after only wet chemical cleaning; Figure 4 (b) is an image of a germanium epitaxial layer formed by selective germanium epitaxy in a deep silicon tank after TMAH cleaning and wet chemical cleaning. Figure 5 This is a schematic flowchart of a method for growing a germanium epitaxial layer in a deep silicon trench according to another embodiment of the present invention; Figure 6 (a) is Figure 4 (a) Image after CMP polishing; Figure 6 (b) is Figure 4 (b) Image after CMP process.
[0021] Figure label: 10-Si / SiO2 substrate, 11-Si layer, 12-SiO2 layer, 13-deep silicon trench. Detailed Implementation
[0022] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.
[0023] Figure 1 This is a schematic flowchart of a method for growing a germanium epitaxial layer in a deep silicon trench 13 according to an embodiment of the present invention. Figure 2 This is a schematic structural diagram of a Si / SiO2 substrate 10 with a deep silicon trench 13 according to an embodiment of the present invention. Figures 1 to 2 As shown, in a specific embodiment, the method for growing a germanium epitaxial layer in a deep silicon trench 13 includes the following steps: Step S100: Provide a Si / SiO2 substrate 10; Step S200: Photolithography and etching are performed on the Si / SiO2 substrate 10 to form a deep silicon trench 13 of a predetermined depth; In step S300, the Si / SiO2 substrate 10 with the deep silicon trench 13 is immersed in TMAH solution for the first cleaning. In step S400, the Si / SiO2 substrate 10 with the deep silicon trench 13 is immersed in a wet chemical cleaning solution for a second cleaning. In step S500, a selective germanium epitaxial process is performed in the deep silicon trench 13 to form a germanium epitaxial layer.
[0024] This embodiment optimizes the sidewall roughness of the deep silicon trench 13 by adding a TMAH cleaning process before the traditional cleaning process, providing a good epitaxial foundation for subsequent germanium epitaxy, improving the quality of the germanium epitaxial layer, avoiding small holes after the germanium epitaxial layer is smoothed by CMP, stabilizing the performance of germanium devices, and reducing the loss of the optical chip waveguide.
[0025] See Figure 2 The Si / SiO2 substrate 10 includes a Si layer and a SiO2 layer.
[0026] In step S200, the preset depth range is 3um-10um, for example, it can be 3um, 4um, 5um, 6um, 7um, 8um, 9um or 10um, etc.
[0027] In step S300, the mass percentage of TMAH in the TMAH solution ranges from 2% to 3%, for example, it can be 2%, 2.5% or 3%, etc.
[0028] In step S300, the soaking time is 8 min to 15 min, for example, it can be 8 min, 10 min, 12 min or 15 min, etc., and the temperature range of the TMAH solution is 70℃ to 80℃, for example, it can be 70℃, 75℃ or 80℃, etc.
[0029] In step S400, the wet chemical cleaning solution includes an SC2 solution and a DHF solution. The volume ratio of HCl, H2O2, and H2O in the SC2 solution ranges from 1:1 to 2:5 to 20, for example, it can be 1:1:5, 1:1:10, 1:1:20, 1:1.5:5, 1:1.5:10, 1:1.5:20, 1:2:5, 1:2:10, or 1:2:20, etc. The mass percentage of HF in the DHF solution ranges from 0.25% to 2%, for example, it can be 0.25%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2%, etc.
[0030] Figure 3 (a) is an electron microscope image of the sidewall of deep silicon tank 13 after wet chemical cleaning only. Figure 3(b) is an electron microscope image of the sidewall of deep silicon tank 13 after TMAH cleaning and wet chemical cleaning, as shown. Figure 3 (a) and Figure 3 As shown in (b), if cleaning is performed only by wet chemical cleaning solution, the sidewall of deep silicon tank 13 is relatively rough. After adding TMAH cleaning, the roughness of the sidewall of deep silicon tank 13 is significantly improved.
[0031] Figure 4 (a) is an image of a germanium epitaxial layer formed by selective germanium epitaxy in a deep silicon tank 13 after only wet chemical cleaning. Figure 4 (b) is an image of a germanium epitaxial layer formed by selective germanium epitaxy in a deep silicon tank 13 after TMAH cleaning and wet chemical cleaning. Figure 4 (a) and Figure 4 As shown in (b), the quality of the germanium epitaxial layer is significantly improved after TMAH cleaning.
[0032] Figure 5 This is a schematic flowchart of a method for growing a germanium epitaxial layer in a deep silicon trench 13 according to another embodiment of the present invention. Figure 5 As shown, in some embodiments, the following steps are included after step S400: In step S410, the Si / SiO2 substrate 10 with deep silicon trench 13 is placed in a thermal oxidation device and subjected to a thermal oxidation process to form an oxide layer. Step S420: The Si / SiO2 substrate 10 with deep silicon trench 13 is subjected to BOE cleaning to remove the oxide layer.
[0033] This embodiment generates a dense SiO2 layer on the silicon surface through thermal oxidation, which can achieve oxide encapsulation of rough structures, passivation and embedding of morphology, and expose the modified smooth silicon surface after removing the oxide layer, while avoiding over-etching or residue.
[0034] In step S410, the thermal oxidation process uses dry oxygen oxidation, with an oxygen flow rate ranging from 1 slm to 2 slm, an oxidation temperature ranging from 900℃ to 1200℃ (e.g., 900℃, 1000℃, 1100℃, or 1200℃), and an oxidation time ranging from 10 min to 30 min (e.g., 10 min, 20 min, or 30 min). Here, the oxide layer thickness ranges from 10 nm to 30 nm (e.g., 10 nm, 20 nm, or 30 nm).
[0035] In step S410, the thermal oxidation equipment can be a tubular oxidation furnace or an RTP system. After oxidation, the furnace is allowed to cool naturally to below 200°C before being removed from the furnace.
[0036] In step S420, the volume ratio of NH4F to HF in the BOE solution ranges from 5 to 7:1, for example, it can be 5:1, 6:1, or 7:1. BOE washing is performed at room temperature, i.e., 20℃-25℃.
[0037] In some embodiments, the following steps are included after step S420: Step S430 involves DIW rinsing and drying of the Si / SiO2 substrate 10 with deep silicon trench 13. Specifically, after BOE cleaning, the substrate is rinsed with a large amount of ultrapure water for more than 2 minutes to prevent chemical residues. The drying process keeps the silicon surface clean, free of water stains and particle deposits.
[0038] In some embodiments, the following step is further included after step S500: In step S600, the germanium epitaxial layer is ground flat using a CMP process.
[0039] Figure 6 (a) is Figure 4 (a) Image after CMP polishing. Figure 6 (b) is Figure 4 (b) Image after CMP (Chemical Mechanical Polishing) process. (e.g.) Figure 6 (a) and Figure 6 As shown in (b), after CMP grinding, the quality of the germanium epitaxial layer with added TMAH cleaning is significantly improved, and the defects of small holes disappear. In contrast, the germanium epitaxial layer without TMAH cleaning has small holes and is of poor quality.
[0040] This embodiment optimizes the cleaning process after silicon etching by adding TMAH cleaning before the traditional cleaning process. This optimizes the roughness of the sidewalls of the deep silicon trench 13, thus laying a good epitaxial foundation for subsequent germanium epitaxy. It enables high-quality germanium epitaxy to be performed simultaneously on the sidewalls and bottom of the deep silicon trench 13. It avoids voids when the sidewall and bottom germanium epitaxy are combined, thus forming a better germanium epitaxial morphology. It solves the problem of small holes in the germanium epitaxy after CMP surface smoothing in the deep silicon trench 13, stabilizes the performance of germanium devices, and reduces the loss of the optical chip waveguide.
[0041] Therefore, those skilled in the art should recognize that although numerous exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Thus, the scope of the present invention should be understood and construed as covering all such other variations or modifications.
Claims
1. A method for growing a germanium epitaxial layer in a deep silicon trench, characterized in that, Includes the following steps: Provides a Si / SiO2 substrate; The Si / SiO2 substrate is photolithographically and etched to form a deep silicon trench of a predetermined depth; The Si / SiO2 substrate with the deep silicon trench was immersed in TMAH solution for the first cleaning. The Si / SiO2 substrate with the deep silicon trench is immersed in a wet chemical cleaning solution for a second cleaning. A selective germanium epitaxial process is performed in the deep silicon trench to form a germanium epitaxial layer.
2. The method according to claim 1, characterized in that, In the step of immersing the Si / SiO2 substrate with the deep silicon trench in a TMAH solution for the first cleaning, the mass percentage of TMAH in the TMAH solution ranges from 2% to 3%.
3. The method according to claim 2, characterized in that, In the step of immersing the Si / SiO2 substrate with the deep silicon trench in the TMAH solution for the first cleaning, the immersion time is 8 min-15 min, and the temperature range of the TMAH solution is 70℃-80℃.
4. The method according to any one of claims 1-3, characterized in that, The wet chemical cleaning solution includes SC2 solution and DHF solution; The volume ratio of HCl, H2O2 and H2O in the SC2 solution ranges from 1:1 to 2:5 to 20. The mass percentage of HF in the DHF solution ranges from 0.25% to 2%.
5. The method according to any one of claims 1-3, characterized in that, The Si / SiO2 substrate having the deep silicon trench is immersed in a wet chemical cleaning solution for a second cleaning step, followed by the following steps: The Si / SiO2 substrate with the deep silicon trench is placed in a thermal oxidation device and subjected to a thermal oxidation process to form an oxide layer. The Si / SiO2 substrate with the deep silicon trench is subjected to BOE cleaning to remove the oxide layer.
6. The method according to claim 5, characterized in that, The thermal oxidation process is a dry oxygen oxidation process, with an oxygen flow rate ranging from 1 slm to 2 slm, an oxidation temperature ranging from 900℃ to 1200℃, and an oxidation time ranging from 10 min to 30 min.
7. The method according to claim 5, characterized in that, In the step of performing BOE cleaning on the Si / SiO2 substrate with the deep silicon trench to remove the oxide layer, the volume ratio of NH4F to HF in the BOE solution is in the range of 5-7:
1.
8. The method according to claim 7, characterized in that, The step of performing BOE cleaning on the Si / SiO2 substrate with the deep silicon trench to remove the oxide layer further includes the following steps: The Si / SiO2 substrate with the deep silicon trench is subjected to DIW rinsing and drying.
9. The method according to any one of claims 1-3, characterized in that, The preset depth ranges from 3um to 10um.
10. The method according to any one of claims 1-3, characterized in that, The step of performing a selective germanium epitaxial process in the deep silicon trench to form a germanium epitaxial layer is followed by the following steps: The germanium epitaxial layer was smoothed using a CMP process.