Preparation method of silicon substrate for molecular beam epitaxy
Through the methods of organic solvent ultrasonic cleaning, strong acid corrosion and high-purity nitrogen drying, the problem of poor cleaning effect of silicon substrates in the prior art is solved, and the preparation of high-quality silicon substrates is achieved, which meets the high flatness of molecular beam epitaxial and Low defect density requirements.
Patent Information
- Application Number
- CN202411016555.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-28
- Publication Date
- 2024-12-13
AI Technical Summary
The prior art cannot effectively prepare high-quality silicon substrates, resulting in poor quality of thin film crystals during the molecular beam epitaxial process and cannot meet the needs of silicon-based optoelectronic integration and semiconductor quantum computing.
The methods of using organic solvent ultrasonic cleaning, strong acid corrosion, gas drying and in-situ heating and degassing are used. The specific steps include organic solvent cleaning, small molecule solvent cleaning, hydrofluoric acid corrosion and high-purity nitrogen blow-drying, controlling the temperature and time to ensure the lining High purity and cleanliness of the bottom.
The cleaning effect of silicon substrates is significantly improved, and high-quality substrates for molecular beam epitaxial are quickly obtained, ensuring high flatness and low defect density of the film, and meeting the experimental material requirements of silicon-based optoelectronic integration and semiconductor quantum computing.
Smart Images
Figure FT_1
Abstract
Description
Technical Field
[0001] The invention relates to the field of film preparation, and in particular to a method for preparing a substrate for molecular beam epitaxy of a high-quality single crystal film. Background Art
[0002] Molecular beam epitaxy is a physical vapor growth technology used to prepare single crystal materials. In a high vacuum chamber, high-purity source materials are heated to evaporate a directional atomic flow, which is deposited and migrated on the substrate, so that the grown material grows in the crystal direction induced by the substrate lattice potential field. In recent years, materials prepared by molecular beam epitaxy have played an important role in the fields of silicon-based optoelectronic integration and silicon-based semiconductor quantum computing.
[0003] In the process of molecular beam epitaxy, since a clean substrate surface is conducive to the crystal quality of the growing film, it is very important to clean the substrate as necessary. Common methods for cleaning molecular beam epitaxy substrates include solvent cleaning, acid cleaning, alkaline cleaning, flame cleaning and oxidation treatment. Solvent cleaning is to use organic solvents, such as acetone, ethanol, isopropanol or chloroform, to remove organic pollutants and grease on the substrate surface. Solvent cleaning usually puts the substrate into the solvent, takes it out after a certain period of ultrasound, and then blows it dry with nitrogen. Acid cleaning is to use concentrated hydrochloric acid or nitric acid solution to remove impurities such as iron oxide and iron hydroxide on the surface. Some substrates need to be alkaline washed, such as using ammonium hydroxide or sodium hydroxide solution to remove aluminum oxide on the surface. Some substrates also need to be baked in a hydrogen flame to remove possible residual organic pollutants and water. In addition, the substrate is oxidized in the atmosphere to form a clean surface layer of indium oxide, gallium oxide, etc., which is helpful for the bonding and quality of the growing film.
[0004] Molecular beam epitaxy of III-V group luminescent materials onto CMOS-compatible silicon substrates is an excellent solution for silicon-based optoelectronic integration. SiGe quantum well sandwich thin film structures with low defect density and high flatness are experimental materials for silicon-based semiconductor quantum computing. However, common cleaning methods cannot meet the requirements for the preparation of high-quality silicon substrates for molecular beam epitaxy. Summary of the invention
[0005] The invention provides a method for preparing a silicon substrate for molecular beam epitaxy, aiming to solve the problem that the cleaning effect is poor and a high-quality substrate for epitaxy cannot be obtained in the existing silicon substrate cleaning technology.
[0006] The specific method for preparing the silicon substrate for molecular beam epitaxy provided by the present invention is to add the silicon substrate to an organic solvent of a certain purity and perform heating and ultrasonic cleaning, clean the organic solvent with a small molecule solvent, etch the oxide layer on the surface of the silicon substrate with a strong acid, perform a deoxidation treatment, clean and dry with high-purity deionized water and nitrogen, and degas the substrate by in-situ heating. Importantly, etching with hydrofluoric acid at an appropriate concentration and degassing the substrate at an appropriate temperature significantly improve the cleaning effect, and quickly obtain a high-quality substrate for molecular beam epitaxy.
[0007] The present invention discloses a method for preparing a silicon substrate for molecular beam epitaxy, which is characterized in that the method includes strong acid etching, solvent cleaning, gas drying, cleaning sequence and time, and substrate in-situ degassing.
[0008] Furthermore, the temperature range of the ultrasonic thermal cleaning is 40 o C-70 o C.
[0009] Furthermore, the ultrasonic cleaning time ranges from 2 min to 5 min. Furthermore, the cleaning organic solvent includes one of chloroform and acetone.
[0010] Furthermore, the small molecule solvent includes one of anhydrous methanol and anhydrous ethanol.
[0011] Furthermore, the strong acid is hydrofluoric acid with a concentration of 5 wt%-10wt%.
[0012] Furthermore, the resistivity of the high-purity deionized water is ≥ 15MΩ•cm. Furthermore, the purity of the high-purity nitrogen is ≥ 99.99%.
[0013] Furthermore, the purity of the solvent is analytical grade or above.
[0014] Furthermore, when the substrate needs to be transferred after cleaning, the substrate should be isolated from the air and sealed in high-purity deionized water.
[0015] Furthermore, the temperature range of the substrate in-situ degassing is 600 o C-700 o C, heating rate ≤10 o C / min.
[0016] The method for preparing a silicon substrate for molecular beam epitaxy as described above comprises the following steps: Step 1: Place the substrate in a clean crystallization dish with the polished surface facing up, and add an organic solvent; Place the substrate in an ultrasonic machine, set the ultrasonic machine operating temperature and ultrasonic time, and start cleaning; Step 2: After cleaning, recover the organic solvent, add a small molecule solvent to clean the organic solvent remaining on the substrate; Set the ultrasonic machine operating temperature and ultrasonic time again, and start cleaning; Step 3: After cleaning, recover the small molecule solvent and rinse the substrate with high-purity deionized water; Step 4: Use clean plastic tweezers to place the substrate into a plastic beaker containing a certain concentration of hydrofluoric acid, and shake it evenly for a certain period of time to corrode the surface oxide layer. This step requires wearing special hydrofluoric acid operating clothes and be performed in a fume hood; Step 5: After the etching is completed, the hydrofluoric acid reagent is recovered and the silicon substrate is rinsed with high-purity deionized water; Step 6: Dry the surface of the silicon substrate with high-purity nitrogen gas; and immediately send it into the molecular beam epitaxy injection chamber; Step 7: In the molecular beam epitaxial growth chamber, heat the silicon substrate to degas, and observe it with an in-situ reflection high-energy electron diffraction gun. Diffraction fringes appear, indicating that the substrate meets the conditions for molecular beam epitaxial growth.
[0017] The beneficial effects of the method for preparing a silicon substrate for molecular beam epitaxy provided by the present invention are as follows: using an appropriately low concentration of hydrofluoric acid to corrode the oxide layer of the silicon substrate, and under the premise of having the corrosive ability, preventing the human body from inhaling volatile hydrofluoric acid and causing harm; using a method of sealing the transferred substrate with high-purity deionized water and blowing the substrate dry with high-purity nitrogen to prevent the silicon substrate from being secondary oxidized before being sent into the molecular epitaxy injection chamber. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 A high-quality diffraction fringe (RHEED) image of the silicon substrate surface is obtained through Example 1 of the present invention. DETAILED DESCRIPTION
[0019] Embodiment 1 A method for preparing a silicon substrate for molecular beam epitaxy, the specific steps are as follows: Step 1: Place the substrate in a clean crystallization dish with the polished surface facing up, add analytical grade organic solvent chloroform, place it in an ultrasonic machine, and set the operating temperature of the ultrasonic machine to 50 o C and ultrasonic time of 5 min, start cleaning; Step 2: After cleaning, recover the chloroform and add analytical pure anhydrous methanol to clean the residual chloroform on the substrate; set the ultrasonic machine working temperature to 50 o C and ultrasonic time of 5 min, start cleaning; Step 3: After cleaning, recover the anhydrous methanol and rinse the substrate with high-purity deionized water with a resistivity of 15 MΩ • cm; Step 4: Use clean plastic tweezers to place the substrate into a plastic beaker containing 5 wt% hydrofluoric acid and shake it evenly for 2 minutes to etch the surface oxide layer. This step requires wearing special hydrofluoric acid operating clothes and be performed in a fume hood; Step 5: After the etching is completed, the hydrofluoric acid reagent is recovered and the silicon substrate is rinsed with high-purity deionized water with a resistivity of 15 MΩ • cm; Step 6: Blow dry the surface of the silicon substrate with 99.99% high-purity nitrogen gas; immediately send it into the molecular beam epitaxy injection chamber; Step 7: In the molecular beam epitaxial growth chamber, heat the silicon substrate for degassing to 10 o C / min heating rate to 700 o C. Observed with an in-situ reflection high-energy electron diffraction gun, diffraction fringes appeared, and the substrate surface state that meets the requirements of molecular beam epitaxial growth was obtained.
[0020] Embodiment 2 A method for preparing a silicon substrate for molecular beam epitaxy, the specific steps are as follows: Step 1: Place the substrate in a clean crystallization dish with the polished surface facing up, add analytical grade organic solvent chloroform, place it in an ultrasonic machine, and set the operating temperature of the ultrasonic machine to 50 o C and ultrasonic time of 5 min, start cleaning; Step 2: After cleaning, recover the chloroform and add analytical pure anhydrous methanol to clean the residual chloroform on the substrate; set the ultrasonic machine working temperature to 50 o C and ultrasonic time of 5 min, start cleaning; Step 3: After cleaning, recover the anhydrous methanol and rinse the substrate with high-purity deionized water with a resistivity of 15 MΩ • cm; Step 4: Use clean plastic tweezers to place the substrate into a plastic beaker containing 5 wt% hydrofluoric acid and shake it evenly for 2 minutes to etch the surface oxide layer. This step requires wearing special hydrofluoric acid operating clothes and be performed in a fume hood; Step 5: After the etching is completed, the hydrofluoric acid reagent is recovered and the silicon substrate is rinsed with high-purity deionized water with a resistivity of 15 MΩ • cm; Step 6: Blow dry the surface of the silicon substrate with 99.99% high-purity nitrogen gas; immediately send it into the molecular beam epitaxy injection chamber; Step 7: In the molecular beam epitaxial growth chamber, heat the silicon substrate for degassing to 10 o C / min heating rate to 650 o C. Observed with an in-situ reflection high-energy electron diffraction gun, diffraction fringes appeared, and the substrate surface state that meets the requirements of molecular beam epitaxial growth was obtained.
[0021] Comparative Example 1 A method for preparing a silicon substrate for molecular beam epitaxy, the specific steps are as follows: Step 1: Place the substrate in a clean crystallization dish with the polished surface facing up, add analytical grade organic solvent chloroform, place it in an ultrasonic machine, and set the operating temperature of the ultrasonic machine to 50 o C and ultrasonic time of 5 min, start cleaning; Step 2: After cleaning, recover the chloroform and add analytical pure anhydrous methanol to clean the residual chloroform on the substrate; set the ultrasonic machine working temperature to 50 o C and ultrasonic time of 5 min, start cleaning; Step 3: After cleaning, recover the anhydrous methanol and rinse the substrate with high-purity deionized water with a resistivity of 15 MΩ • cm; Step 4: Use clean plastic tweezers to place the substrate into a plastic beaker containing 5 wt% hydrofluoric acid and shake it evenly for 2 minutes to etch the surface oxide layer. This step requires wearing special hydrofluoric acid operating clothes and be performed in a fume hood; Step 5: After the etching is completed, the hydrofluoric acid reagent is recovered and the silicon substrate is rinsed with high-purity deionized water with a resistivity of 15 MΩ • cm; Step 6: Blow dry the surface of the silicon substrate with 99.99% high-purity nitrogen gas; immediately send it into the molecular beam epitaxy injection chamber; Step 7: In the molecular beam epitaxial growth chamber, heat the silicon substrate for degassing to 10 o C / min heating rate to 580 o C. Observed using an in-situ reflection high-energy electron diffraction gun, the substrate diffraction fringes are not obvious.
[0022] The difference between Comparative Example 1 and Examples 1 and 2 is that the substrate degassing temperature of Comparative Example 1 is less than 600 o C. The removal effect of adsorbed substances on the substrate surface is not ideal, and it is difficult to obtain obvious diffraction stripes on the silicon substrate.
[0023] Although the present invention has been described in detail through the above embodiments, the above description is not intended to limit the present invention. It is obvious to those skilled in the art to modify the present invention. Therefore, within the principles of the present invention, any modifications made should be included in the scope of the claims of the present invention.
Claims
1. The method for preparing a silicon substrate for molecular beam epitaxy provided by the present invention is characterized in that: The preparation method includes strong acid etching, solvent cleaning, gas drying, cleaning sequence and time, and substrate in-situ degassing.
2. The method for preparing a silicon substrate for molecular beam epitaxy according to claim 1, characterized in that The temperature range of the ultrasonic thermal cleaning is 40 o C-70 o C.
3. The method for preparing a silicon substrate for molecular beam epitaxy according to claim 1, characterized in that The ultrasonic cleaning time ranges from 2 min to 5 min.
4. The method for preparing a silicon substrate for molecular beam epitaxy according to claim 1, characterized in that The cleaning organic solvent includes one of chloroform and acetone.
5. The method for preparing a silicon substrate for molecular beam epitaxy according to claim 1, characterized in that The small molecule solvent includes one of anhydrous methanol and anhydrous ethanol.
6. The method for preparing a silicon substrate for molecular beam epitaxy according to claim 1, characterized in that The strong acid is hydrofluoric acid, and the concentration is 5wt%-10wt%.
7. The method for preparing a silicon substrate for molecular beam epitaxy according to claim 1, characterized in that The resistivity of the high-purity deionized water is ≥15MΩ•cm.
8. The method for preparing a silicon substrate for molecular beam epitaxy according to claim 1, characterized in that The purity of the high-purity nitrogen is ≥ 99.99%.
9. The method for preparing a silicon substrate for molecular beam epitaxy according to claim 1, characterized in that The purity of the solvent is analytical grade or above.
10. When the substrate needs to be transferred after cleaning, the substrate should be isolated from the air and sealed in high-purity deionized water.
11. The temperature range of the substrate in-situ degassing is 600 o C-700 o C, heating rate ≤10 o C / min.
12. The method for preparing a silicon substrate for molecular beam epitaxy according to claim 1, characterized in that The following steps are involved: Step 1: Place the substrate in a clean crystallization dish with the polished surface facing up, add an organic solvent, place it in an ultrasonic machine, set the operating temperature and ultrasonic time of the ultrasonic machine, and start cleaning; Step 2: After cleaning, the organic solvent is recovered and a small molecule solvent is added to clean the residual organic solvent on the substrate; the ultrasonic machine operating temperature and ultrasonic time are set again to start cleaning; Step 3: After cleaning, recover the small molecule solvent and rinse the substrate with high-purity deionized water; Step 4: Use clean plastic tweezers to place the substrate into a plastic beaker containing a certain concentration of hydrofluoric acid, and shake it evenly for a certain period of time to corrode the surface oxide layer. This step requires wearing special hydrofluoric acid operating clothes and be performed in a fume hood; Step 5: After the etching is completed, the hydrofluoric acid reagent is recovered and the silicon substrate is rinsed with high-purity deionized water; Step 6: Dry the surface of the silicon substrate with high-purity nitrogen gas; immediately send it into the molecular beam epitaxy injection chamber; Step 7: In the molecular beam epitaxial growth chamber, heat the silicon substrate to degas, and observe it with an in-situ reflection high-energy electron diffraction gun. Diffraction fringes appear, indicating that the substrate meets the conditions for molecular beam epitaxial growth.