A method for protecting a surface of a germanium substrate

Abstract

This invention discloses a method for protecting the surface of a germanium substrate. First, PMMA adhesive is dropped onto the surface of a cleaned and dried germanium substrate, and then spin-coated at a rotation speed of 400-1200 r / min for 5-20 s. Then, the rotation speed is increased to 1500-6000 r / min, and spin-coating is performed for 10-60 s to obtain a PMMA-germanium substrate. Finally, the PMMA-germanium substrate is dried at 60-150℃ for 30-240 s to form a germanium substrate with a PMMA layer on its surface. The protection method of the present invention can form a uniform PMMA protective layer on the surface of a germanium substrate, thereby isolating it from air or dust without modifying the germanium substrate, preventing disordered oxidation and dust particle contamination, and maintaining the initial state of the substrate surface after cleaning for 3-6 months. Furthermore, the PMMA protective layer can be completely decomposed and volatilized under epitaxial high temperature (400-800°C, hydrogen purging) and carried out of the cavity by the airflow without residue, without affecting the epitaxial furnace cavity environment and without affecting the epitaxial growth of the germanium substrate.

Description

Technical Field

[0001] This invention belongs to the field of substrate surface processing, and particularly relates to a method for protecting the surface of a germanium substrate. Background Technology

[0002] Germanium, a common substrate for epitaxy, is produced as wafers in upstream factories and then further epitaxially formed on the surface of downstream factories to create products. Qualified germanium substrates are generally produced from crystal ingots through processes such as cutting, grinding, polishing, cleaning, and packaging. Among these processes, the cleaning process uses physical or chemical methods to remove contaminants such as particles, metal ions, organic matter, and natural oxide layers from the substrate surface, thereby providing an ultra-clean and damage-free wafer surface for epitaxial growth.

[0003] However, after cleaning, the surface of the germanium substrate is in a highly active state and is very easy to react with oxygen and water vapor in the air (i.e., oxidation). It is also very easy to adsorb dust particles. This results in a short shelf life for the cleaned substrate, which needs to be put into the epitaxial process as soon as possible. Otherwise, during long-term storage, the substrate surface will be subject to disordered oxidation or contamination, which will lead to a large number of defects during epitaxy.

[0004] In actual production, germanium substrates are often physically passivated after cleaning. Common methods for physical passivation of germanium substrates include vacuum deposition, epitaxial growth, and external solid film coverage (Al2O3, Si layer, SiN). x Chemical passivation (such as BN, high-k dielectrics, etc.) physically isolates and prevents oxygen and water vapor from corroding the surface, thus avoiding direct covalent bonding with the dangling bonds on the Ge surface. However, physical passivation methods, such as vacuum deposition and epitaxy, involve high-temperature processes that introduce defects. In addition, the processing of dielectric thin films can exacerbate Fermi level pinning on the germanium surface. Therefore, in practical production applications, chemical passivation is preferred.

[0005] Chemical passivation is a process that forms a passivation layer of a certain thickness on the wafer surface to prevent disordered oxidation. Conventional chemical passivation involves reacting an acid or hydrogen peroxide with the surface of germanium to generate a germanium oxide coating. Before epitaxy, the treated germanium substrate is reduced by high-temperature hydrogen gas to remove the oxide layer, followed by epitaxial operations such as vapor deposition. However, chemical passivation struggles to guarantee sufficient oxidation depth, resulting in incomplete reduction of the germanium substrate surface during subsequent hydrogen purging. Areas with germanium oxide will still produce defects during epitaxy.

[0006] Therefore, there is a need for a method to protect the surface of germanium substrates that can extend the shelf life of the substrate, maintain the initial surface activity state after cleaning, and prevent dust particles from adhering to the surface, thus providing a perfect, clean, and repeatable substrate for epitaxial processes. Summary of the Invention

[0007] Purpose of the invention: The technical problem to be solved by the present invention is to provide a method for protecting the surface of germanium substrates, which can extend the shelf life of germanium substrates and restore the original surface activity of germanium substrates through simple cleaning without producing defects.

[0008] Technical solution: The present invention provides a method for protecting the surface of a germanium substrate, comprising the following steps:

[0009] (1) Apply PMMA adhesive to the surface of the cleaned and dried germanium substrate and spin coat it at a speed of 400-1200 r / min for 5-20 s;

[0010] (2) Increase the rotation speed to 1500-6000 r / min and spin coat for 10-60 s to obtain PMMA-germanium substrate;

[0011] (3) Dry the PMMA-germanium substrate at 60-150℃ for 30-240s to form a germanium substrate with a PMMA layer on the surface.

[0012] Furthermore, in step (1) of this surface protection method, the PMMA adhesive has a molecular weight of 15-1000K and a solid content of 0.5-3%. Preferably, the PMMA adhesive has a molecular weight of 50-600K and a solid content of 1-2%.

[0013] Furthermore, in step (1) of the surface protection method, the amount of PMMA adhesive used per unit area of ​​the germanium substrate is 0.01-0.64 mL.

[0014] Furthermore, in step (1) of this surface protection method, the spin coating speed is 600-800 r / min and the spin coating time is 8-12 s.

[0015] Furthermore, in step (1) of the surface protection method, the rotation speed is 2000-4000 r / min and the spin coating time is 20-30 s.

[0016] Furthermore, in step (3) of the surface protection method, the drying temperature is 80-100℃ and the drying time is 60-120s.

[0017] Furthermore, in step (4) of this surface protection method, the thickness of the PMMA layer is 10-200 nm.

[0018] Beneficial effects: Compared with the prior art, the significant advantage of the present invention is that the protection method can form a uniform PMMA protective layer on the surface of the germanium substrate, so as to isolate the germanium substrate from contact with air or dust without modifying the germanium substrate, prevent disordered oxidation and dust particle contamination, and maintain the initial state of the substrate surface after cleaning for 3-6 months; and the PMMA protective layer can be completely decomposed and volatilized under epitaxial high temperature (400-800℃, hydrogen purging) and carried out of the cavity by the airflow without residue, without affecting the epitaxial furnace cavity environment and without affecting the epitaxial growth of the germanium substrate. Detailed Implementation

[0019] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0020] It should be noted that in the following embodiments and comparative examples of the present invention, the epitaxial temperature range is 400-800℃, and hydrogen purging is used during epitaxy. Furthermore, in the following embodiments and comparative examples, epitaxy was performed after a 3-month storage period.

[0021] The yield of epitaxial substrates is tested by irradiating them with a strong light and then visually inspecting and counting the number of substrates with obvious defects such as particles, dark spots, and white spots. The yield is calculated as: (Number of substrates without obvious defects / Total number of substrates) * 100%.

[0022] Example 1

[0023] The method for protecting the surface of a germanium substrate in this embodiment 1 includes the following steps:

[0024] (1) Place the cleaned and dried 4-inch circular germanium substrate on the worktable of the fully automatic spin coater, turn on the vacuum device to hold the substrate, and automatically drop 1 ml of MOS grade 600K PMMA photoresist (1% solid content) into the center of the substrate.

[0025] (2) Turn on the motor to perform spin coating. The first stage rotation speed is 400 r / min and the rotation time is 5 s; the second stage rotation speed is 1500 r / min and the rotation time is 10 s.

[0026] (3) A 35 nm thick adhesive layer was formed on the substrate surface by spin coating. After spin coating, the substrate was dried at 80 °C for 70 s.

[0027] (4) After drying, the substrates are packaged, and nitrogen gas is filled into the packaging bags for protection. The yield of 100 germanium substrates produced according to the above process is 100% after epitaxy.

[0028] Example 2

[0029] This embodiment 2 describes a method for protecting the surface of a germanium substrate, which includes the following steps:

[0030] (1) Place the cleaned and dried 2-inch circular germanium substrate on the worktable of the fully automatic spin coater, turn on the vacuum device to hold the substrate, and automatically drop 1 ml of MOS grade 350K PMMA photoresist (solid content 1.5%) into the center of the substrate.

[0031] (2) Turn on the motor to perform spin coating. The first stage rotation speed is 600 r / min and the rotation time is 8 s; the second stage rotation speed is 4000 r / min and the rotation time is 15 s.

[0032] (3) A 25 nm thick adhesive layer was formed on the substrate surface by spin coating. After spin coating, the substrate was dried at 100 °C for 60 s.

[0033] (4) After drying, the substrates are packaged, and nitrogen gas is filled into the packaging bags for protection. The yield of 150 germanium substrates produced according to the above process is 99.3% after epitaxy.

[0034] Example 3

[0035] This embodiment 3 describes a method for protecting the surface of a germanium substrate, which includes the following steps:

[0036] (1) Place the cleaned and dried 4-inch circular germanium substrate on the worktable of the fully automatic spin coater, turn on the vacuum device to hold the substrate, and automatically drop 1.5ml of MOS grade 200K PMMA photoresist (1% solid content) into the center of the substrate.

[0037] (2) Turn on the motor to perform spin coating. The first stage rotation speed is 700 r / min and the rotation time is 7 s; the second stage rotation speed is 5000 r / min and the rotation time is 12 s.

[0038] (3) A 15 nm thick adhesive layer was formed on the substrate surface by spin coating. After spin coating, the substrate was dried at 90 °C for 60 s.

[0039] (4) After drying, the substrates are packaged, and nitrogen gas is filled into the packaging bags for protection. The yield of the 120 germanium substrates produced according to the above process is 100% after epitaxy.

[0040] Example 4

[0041] This embodiment 4 describes a method for protecting the surface of a germanium substrate, which includes the following steps:

[0042] (1) Place the cleaned and dried 4-inch circular germanium substrate on the worktable of the fully automatic spin coater, turn on the vacuum device to hold the substrate, and automatically drop 1.5ml of MOS grade 50K PMMA photoresist (1% solid content) into the center of the substrate.

[0043] (2) Start the motor for spin coating. The first stage rotation speed is 1200r / min and the rotation time is 7s; the second stage rotation speed is 6000r / min and the rotation time is 12s.

[0044] (3) A 15 nm thick adhesive layer was formed on the substrate surface by spin coating. After spin coating, the substrate was dried at 90 °C for 60 s.

[0045] (4) After drying, the substrates are packaged, and nitrogen gas is filled into the packaging bags for protection. The yield of the 120 germanium substrates produced according to the above process is 100% after epitaxy.

[0046] Comparative Example 1

[0047] The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that a rotation speed of 200 r / min is used for uniform rotation for 15 s. The specific steps are as follows:

[0048] (1) Under a closed nitrogen atmosphere, place the cleaned and dried 4-inch circular germanium substrate on the worktable of the fully automatic spin coater, turn on the vacuum device to hold the substrate, and automatically drop 1 ml of MOS grade 600K PMMA photoresist (1% solid content) into the center of the substrate.

[0049] (2) Turn on the motor to perform spin coating at a speed of 200 r / min for 15 seconds.

[0050] (3) After spin coating, the substrate is dried at 80°C for 70 seconds. The resulting adhesive layer on the substrate surface is uneven, and under fluorescent light, it appears as a ring-like structure. The resulting substrate cannot be used for epitaxy.

[0051] Comparative Example 2

[0052] The preparation method of Comparative Example 2 is basically the same as that of Example 1, except that a rotation speed of 1000 r / min is used for uniform rotation for 15 s. The specific steps are as follows:

[0053] (1) Under a closed nitrogen atmosphere, place the cleaned and dried 4-inch circular germanium substrate on the worktable of the fully automatic spin coater, turn on the vacuum device to hold the substrate, and automatically drop 1 ml of MOS grade 600K PMMA photoresist (1% solid content) into the center of the substrate.

[0054] (2) Turn on the motor to perform spin coating at a speed of 1000 r / min for 15 seconds.

[0055] (3) After spin coating, the substrate is dried at 80°C for 70 seconds. The resulting adhesive layer on the substrate surface is uneven and appears wavy under fluorescent light. The resulting substrate cannot be used for epitaxy.

[0056] Comparative Example 3

[0057] The preparation method of Comparative Example 3 is basically the same as that of Example 1, except that a rotation speed of 5000 r / min is used for uniform rotation for 15 s. The specific steps are as follows:

[0058] (1) Under a closed nitrogen atmosphere, place the cleaned and dried 4-inch circular germanium substrate on the worktable of the fully automatic spin coater, turn on the vacuum device to hold the substrate, and automatically drop 1 ml of MOS grade 600K PMMA photoresist (1% solid content) into the center of the substrate.

[0059] (2) Turn on the motor to perform spin coating at a speed of 5000 r / min for 15 seconds.

[0060] (3) After spin coating, the substrate is dried at 80°C for 70 seconds. The adhesive layer formed on the substrate surface is uneven and appears wavy under fluorescent light. The resulting substrate cannot be used for epitaxy.

[0061] Comparative Example 4

[0062] Comparative Example 4 is basically the same as Example 1, except that a PMMA photoresist with a molecular weight of 950K (3% solid content) is used for spin coating. The specific steps are as follows:

[0063] (1) Place the cleaned and dried 4-inch circular germanium substrate on the worktable of the fully automatic spin coater, turn on the vacuum device to hold the substrate, and automatically drop 1 ml of MOS grade 950K PMMA photoresist (3% solid content) into the center of the substrate.

[0064] (2) Turn on the motor to perform spin coating. The first stage rotation speed is 400 r / min and the rotation time is 5 s; the second stage rotation speed is 1500 r / min and the rotation time is 10 s.

[0065] (3) A 1000 nm thick adhesive layer was formed on the substrate surface by spin coating. After spin coating, the substrate was dried at 80 °C for 70 s.

[0066] (4) After drying, the substrates are packaged, and nitrogen gas is filled into the packaging bags for protection. The yield of 100 germanium substrates produced according to the above process after epitaxy is 67%.

[0067] Comparative Example 5

[0068] Comparative Example 5 is basically the same as Example 1, except that a PMMA photoresist with a molecular weight of 20K (3% solid content) is used for spin coating. The specific steps are as follows:

[0069] (1) Place the cleaned and dried 4-inch circular germanium substrate on the worktable of the fully automatic spin coater, turn on the vacuum device to hold the substrate, and automatically drop 1 ml of MOS grade 20K PMMA photoresist (3% solid content) into the center of the substrate.

[0070] (2) Turn on the motor to perform spin coating. The first stage rotation speed is 500 r / min and the rotation time is 5 s; the second stage rotation speed is 2000 r / min and the rotation time is 10 s.

[0071] (3) A 5 nm thick adhesive layer was formed on the substrate surface by spin coating. After spin coating, the substrate was dried at 80 °C for 70 s.

[0072] (4) After drying, the substrates are packaged, and nitrogen gas is filled into the packaging bags for protection. The yield of 100 germanium substrates produced according to the above process after epitaxy is 49%.

[0073] In addition to the above embodiments, it should be noted that the molecular weight of PMMA adhesive can be further selected from 50K, 120K, 200K, 350K, 495K, and 600K, within which the protective effect of the adhesive layer is better. The spin coating speed in step (1) can be 400-1200 r / min, and the spin coating speed in step (2) can be 1500-6000 r / min; the solid content of PMMA adhesive can be 1-2%. That is, the technical effects claimed by the present invention can be achieved by using the preparation process and the parameter range defined in this invention, and therefore no further examples will be given to support this claim.

Claims

1. A method for protecting the surface of a germanium substrate, characterized in that, Includes the following steps: (1) Apply PMMA adhesive to the surface of the cleaned and dried germanium substrate and spin coat it at a speed of 400-1200 r / min for 5-20 s; (2) Increase the rotation speed to 1500-6000 r / min and spin coat for 10-60 s to obtain PMMA-germanium substrate; (3) Dry the PMMA-germanium substrate at 60-150℃ for 30-240s to form a germanium substrate with a PMMA layer on the surface.

2. The method for protecting the surface of a germanium substrate according to claim 1, characterized in that, In step (1), the PMMA adhesive has a molecular weight of 15-1000K and a solid content of 0.5-3%.

3. The method for protecting the surface of a germanium substrate according to claim 2, characterized in that, The PMMA adhesive has a molecular weight of 50-600K and a solid content of 1-2%.

4. The method for protecting the surface of a germanium substrate according to claim 1, characterized in that, In step (1), the amount of PMMA adhesive used per unit area of ​​the germanium substrate is 0.01-0.64 mL.

5. The method for protecting the surface of a germanium substrate according to claim 1, characterized in that, In step (1), the spin coating speed is 600-800 r / min and the spin coating time is 8-12 s.

6. The method for protecting the surface of a germanium substrate according to claim 1, characterized in that, In step (1), the rotation speed is 2000-4000 r / min and the spin coating time is 20-30 s.

7. The method for protecting the surface of a germanium substrate according to claim 1, characterized in that, In step (3), the drying temperature is 80-100℃ and the drying time is 60-120s.

8. The method for protecting the surface of a germanium substrate according to claim 1, characterized in that, In step (4), the thickness of the PMMA layer is 10-200 nm.