A method for preparing a high-quality, large-thickness silicon dioxide film layer

Abstract

The application relates to a preparation method of a high-quality large-thickness silicon dioxide film layer, and belongs to the technical field of silicon-based photonic device preparation. The application aims to solve the problem that the large thickness and the high-quality and high-performance film layer cannot be considered simultaneously in the prior art, and provides a preparation method of a high-quality large-thickness silicon dioxide film layer; the method combines a dry-wet oxidation process and high-temperature annealing, designs part of the dry oxygen and the annealing process while the dry-wet-dry process is reformed, and can improve the quality and the light binding property of the large-thickness silicon dioxide film layer while the growth rate is maintained.

Description

Technical Field

[0001] This invention relates to a method for preparing a high-quality, thick silicon dioxide film, belonging to the field of silicon-based photonic device fabrication technology. Background Technology

[0002] Optical microcavities are widely used in the structural design of silicon-based optoelectronic devices due to their low loss and high quality factor. Thick-film silicon dioxide is indispensable in the device fabrication process. Both the lower cladding of silicon nitride devices and silicon dioxide microcavities require high-quality, thick silicon dioxide films to support the superior performance of the microcavities.

[0003] There are many methods for preparing silica films, including solution gelation, magnetron sputtering, flame hydrolysis, and thermal oxidation. However, most of these film growth methods suffer from problems such as high impurity content, poor film uniformity, and loose film structure. Thermal oxidation, due to its simple raw materials and dense oxide layer structure, can be used as a cladding for optical waveguides with high confinement effect.

[0004] Currently, it is difficult to produce high-quality thin films with a thickness exceeding 2μm in China. Films with a thickness exceeding 2μm grow slowly and their density and uniformity do not meet the performance requirements of devices. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that existing technologies cannot simultaneously achieve both large thickness and high quality / performance of the film, and to provide a method for preparing a high-quality, large-thickness silica film. This method combines a dry-wet oxidation process with high-temperature annealing, and designs part of the dry oxidation and annealing processes while reforming the dry-wet-dry process. This can improve the quality and light confinement of the large-thickness silica film while maintaining the growth rate.

[0006] To achieve the above results, the technical solution implemented by the present invention is as follows:

[0007] A method for preparing a high-quality, thick silica film, characterized by comprising the following steps:

[0008] Step 1: Use the cleaned monocrystalline silicon wafer as the substrate;

[0009] Step 2: In a nitrogen atmosphere, raise the temperature to reaction temperature A, introduce oxygen, and begin dry oxygen growth of the first silicon dioxide layer; raise the temperature to reaction temperature B, and anneal with oxygen in a nitrogen atmosphere.

[0010] The thickness of the first silica layer grown in step two using dry oxygen is obtained by the following method, formula 1:

[0011]

[0012] x1 is the film thickness, t1 is the growth time, and τ1 is a constant obtained from the equipment.

[0013] Step 3: Lower the temperature to reaction temperature C, introduce water vapor to participate in the reaction, and grow the first silicon dioxide layer with wet oxygen; continue to raise the temperature to reaction temperature B, introduce nitrogen gas, and anneal in a nitrogen atmosphere;

[0014] The thickness of the first silica layer grown in step two using wet oxygen is obtained using the following formula 2:

[0015]

[0016] x2 is the film thickness, t2 is the growth time, and τ2 is a constant obtained from the equipment.

[0017] Step 4: Cool down to reaction temperature A, introduce oxygen, and add a chlorine-containing compound to grow the second silicon dioxide layer in dry oxygen.

[0018] Step 5: Change the temperature from reaction temperature A to reaction temperature C, introduce oxygen and water vapor, and grow the second silicon dioxide layer in moist oxygen; raise the temperature to reaction temperature B, and anneal with oxygen in a nitrogen atmosphere.

[0019] Step 6: Repeat steps 4, 5 and 4 to complete the preparation of the third silica layer grown by dry oxygen, the third silica layer grown by wet oxygen, and the fourth silica layer grown by dry oxygen.

[0020] Step 7: Annealing and cleaning; to obtain a high-quality, thick silica film.

[0021] According to claim 1, in the method described in step two, the ratio of oxygen to nitrogen introduced is not higher than one percent;

[0022] According to the method of claim 1, the amount of oxygen and chlorine-containing compound added in step four is in a certain proportion, that is, the proportion of chlorine-containing compound and oxygen added is not higher than five per thousand.

[0023] According to the method of claim 1, the annealing reaction temperature B is not lower than the dry oxygen oxidation reaction temperature A, and the dry oxygen oxidation reaction temperature A is not lower than the wet oxygen oxidation reaction temperature C.

[0024] Beneficial effects

[0025] 1. This invention provides a method for preparing a high-quality, thick silica film, which can ensure both the thickness and quality of the film during silica growth.

[0026] 2. The present invention reduces the disorder of the silicon-silicon oxide interface distribution and reduces stacking faults and stacking of the film by annealing after the first dry oxygen oxidation, thus providing a growth basis for the uniformity and high quality of the subsequent film growth.

[0027] 3. Annealing after the first dry oxygen growth can continue to ensure the quality of the dry oxygen film layer, and at the same time promote the quality of subsequent film layer regrowth.

[0028] 4. Adding a trace amount of oxygen during annealing can reduce the possibility of nitrogen coming into contact with silicon and being nitrided during annealing.

[0029] 5. Introducing a trace amount of dichloroethane (DCE) during the second and third dry oxygen processes can increase the reaction rate and compensate for the negative effects of uneven growth in this process through subsequent steps.

[0030] 6. Starting from the second dry oxygen process, the purpose of dry oxygen is to increase the density of the film layer, the purpose of wet oxygen is to increase the depth of oxygen elements entering the growth layer and increase the film thickness, and the purpose of annealing is to make the film layer molecules more orderly arranged and improve the film quality.

[0031] 6. This invention optimizes process parameters by combining dry and wet oxidation with annealing. Dry oxygen densifies the film, annealing improves the film structure quality, and wet oxygen increases the film thickness. The combination of these three processes yields a high-quality thick silica film. Compared to methods such as flame hydrolysis, this invention offers advantages such as simple operation and high process repeatability. Attached Figure Description

[0032] Figure 1 This is a flowchart of the preparation process of the present invention;

[0033] Figure 2 This is a schematic diagram of a structure grown by thermal oxidation layering;

[0034] Figure 3 The figure shows the thickness and refractive index of the experimental sample.

[0035] Among them, 1—substrate, 2—first silicon dioxide layer grown with dry oxygen, 3—first silicon dioxide layer grown with wet oxygen, 4—second silicon dioxide layer grown with dry oxygen, 5—second silicon dioxide layer grown with wet oxygen, 6—third silicon dioxide layer grown with dry oxygen, 7—third silicon dioxide layer grown with wet oxygen, and 8—fourth silicon dioxide layer grown with dry oxygen. Detailed Implementation

[0036] To more clearly illustrate the technical implementation method of the present invention, the following description is provided in conjunction with the appendix. Figure 1 , 2 The present invention will be further described with reference to Example 1.

[0037] Example 1:

[0038] like Figure 1 , 2As shown, this embodiment discloses a method for preparing a high-quality silica thick film, including:

[0039] Before film growth, the film growth process is designed, and the film thickness needs to exceed 2.5 μm. Since dry oxygen oxidation has a slow rate, it mainly serves to densify the film, improve film quality, and provide a high-quality growth substrate, while wet oxygen increases film thickness. Based on the growth coefficient ratio before the time variable in the formula, which is approximately 1:4, the thicknesses for dry and wet oxidation are equally allocated to 0.5 μm and 2 μm, respectively. Using Formula 1, the dry oxygen time t1 can be calculated as 5 h; using Formula 2, the wet oxygen time t2 can be calculated as 6 h. The same oxidation time ensures the longitudinal uniformity of the film. Since the uniformity of wet oxygen is slightly worse, the three wet oxygen oxidation times are equally divided into 2 h intervals. For dry oxygen oxidation, the initial oxidation time is much longer than the intermediate processes, and the intermediate oxidation time is greater than or equal to the final oxidation time. Therefore, the dry oxygen oxidation process is allocated to 2 h, 1 h, 1 h, and 1 h.

[0040] Step 1, prepare to use double-throw p-type <100> A single-crystal silicon wafer with a specific crystal orientation is used as the growth substrate 1. The surface of the silicon wafer is cleaned using a standard cleaning solution. After cleaning, the substrate is dried. The standard cleaning solutions used during the cleaning process at 75-85°C include: ammonia:hydrogen peroxide:water in a volume ratio of 1:1:5; hydrochloric acid:hydrogen peroxide:water in a volume ratio of 1:1:5. Each cleaning solution is used for an average of 10 minutes, followed by rinsing with deionized water for 15 minutes.

[0041] Step 2: Heat the equipment and introduce 6000 sccm of oxygen for the first dry oxygen oxidation. The temperature in the reaction chamber must reach 1150℃ during the dry oxygen reaction and be maintained for 2 hours. The resulting dry oxygen oxidation film layer is then formed. Continue to increase the reaction temperature and anneal in a nitrogen atmosphere for 2 hours. The temperature inside the chamber needs to reach 1200℃ during annealing, while a small amount of oxygen is introduced.

[0042] Step 3: Lower the reaction temperature, introduce water vapor to participate in the reaction, and carry out the first wet oxygen oxidation growth for 2 hours. When the wet oxygen reaction occurs, the temperature in the reaction chamber must reach 1100℃. The result is wet oxygen oxidation film layer 3. The equipment continues to heat up, and nitrogen and trace amounts of oxygen are introduced. The temperature in the chamber needs to reach 1200℃ during annealing. Anneal in a nitrogen atmosphere for 1 hour.

[0043] Step 4: Lower the reaction temperature, introduce 6000 sccm of oxygen and a trace amount of DCE, with the DCE being transported through nitrogen, to carry out a second dry oxygen oxidation, and grow for 1 hour. The temperature in the reaction chamber must reach 1150℃, and the resulting dry oxygen oxidation film layer 4 is obtained.

[0044] Step 5: Maintain the temperature in the reaction chamber at 1100℃, introduce water vapor to participate in the reaction, and carry out the second wet oxygen oxidation growth for 2 hours to obtain the wet oxygen oxidation film layer 5. Continue to heat the equipment, introduce nitrogen and trace amounts of oxygen, and anneal in a nitrogen atmosphere for 1 hour. The temperature inside the chamber needs to reach 1200℃ during annealing.

[0045] Step 6: Repeat steps 4, 5, and 4 to obtain dry oxygen oxidation film layer 6, wet oxygen oxidation film layer 7, and dry oxygen oxidation film layer 8, respectively.

[0046] Step 7: The equipment continues to heat up, nitrogen gas is introduced, and annealing is performed in a nitrogen atmosphere for 1 hour. The temperature inside the chamber needs to reach 1200℃ during annealing. The silicon oxide thick film is then prepared, and the surface is cleaned using organic solvents including acetone and ethanol.

[0047] After preparation, the film layer was characterized as follows: Figure 3 As shown, the film thickness and refractive index of the entire wafer sample were characterized, and the uniformity of the corresponding characteristic parameters was calculated. The film thickness of all samples reached over 2.5 μm, with a film thickness uniformity of 0.32%. The refractive index of all samples was above 1.45, with a refractive index uniformity of 0.07%. The film thickness reached the expected level of over 2.5 μm, and the uniformity was significantly improved compared to ordinary thermal oxidation.

[0048] Example 2:

[0049] Unlike Example 1, the wet oxidation process was carried out at the same temperature as the dry oxidation process, with all other conditions remaining the same. This reduced the heating and cooling time and increased the oxidation rate, but the film growth quality was slightly lower than in Example 1. The refractive index of 1.435 in Example 2 was slightly lower than that of 1.455 in Example 1. Since the density of silicon oxide is positively correlated with its refractive index, Example 1 exhibited better density.

[0050] Comparative Example 1:

[0051] Step 1: Select a substrate and grow a polycrystalline silicon thin film on the substrate using LPCVD process, with a thickness of 0.7um to 1.8um;

[0052] Step 2: Thermal oxidation treatment of polycrystalline silicon thin film. The thermal oxidation temperature is 1000℃~1300℃, and the temperature is gradually increased. The thermal oxidation time is 78~3 hours to form a silicon dioxide film with a thickness of 1.49~4.10um.

[0053] Step 3: Grow a new polycrystalline silicon film on the silicon dioxide film with a thickness of 0.7 μm to 1.8 μm;

[0054] Step 4: Perform thermal oxidation on the new polycrystalline silicon thin film at a temperature of 1000℃~1300℃ for 78~3 hours to form another layer of silicon dioxide film with a thickness of 1.49um~4.10um.

[0055] Step 5: Repeat steps 3 and 4 until a silicon dioxide thick film of the required thickness is obtained.

[0056] Unlike Example 1, this process uses a different raw material for thermal oxidation: a polycrystalline silicon thin film. This process has fewer limitations on thickness and can achieve the target thickness. However, the crystal orientation of polycrystalline silicon is irregular and different, which makes it impossible to control dislocations and stacking during film growth. This results in lower quality and poor uniformity when silicon oxide is used as a cladding layer, with uniformity only within 4%. Furthermore, the complete growth time from polycrystalline silicon to silicon oxide is long, and there will be residual silicon, leading to high stress.

[0057] The results further demonstrate that the technical effect brought about by this application is a significant improvement. Only under the technical solution described in this application can a silicon dioxide film layer that simultaneously satisfies the characteristics of large thickness, high quality, and high performance be obtained.

[0058] Comparative Example 2:

[0059] Step 1: A silicon dioxide layer is grown on the surface of the silicon wafer using the wet-dry oxidation method;

[0060] Step 2: Deposit another layer of silicon dioxide on the silicon dioxide layer using low-pressure chemical deposition.

[0061] Step 3: Use the dry oxygen method to add another layer of silica for densification.

[0062] The silicon dioxide layer deposited using low-pressure chemical deposition is deposited by thermally decomposing tetraethyl orthosilicate using low-pressure chemical deposition.

[0063] Unlike Example 1, this process uses a thermal decomposition method in step two. This method has a faster growth rate and no obvious thickness limitation. However, the limitation of the thermal decomposition method is that the quality of the generated film is low and the refractive index is small, around 1.41-1.43.

[0064] The results further demonstrate that the technical effect brought about by this application is a significant improvement. Only under the technical solution described in this application can a silicon dioxide film layer that simultaneously satisfies the characteristics of large thickness, high quality, and high performance be obtained.

[0065] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-quality, thick silica film, characterized in that: Includes the following steps: Step 1: Use the cleaned monocrystalline silicon wafer as the substrate; Step 2: In a nitrogen atmosphere, raise the temperature to reaction temperature A, introduce oxygen, and begin dry oxygen growth of the first silicon dioxide layer; raise the temperature to reaction temperature B, and anneal with oxygen in a nitrogen atmosphere. The thickness of the first silica layer grown by dry oxygen in step two is obtained by the following method: x1 is the film thickness, t1 is the growth time, and τ1 is a constant; Step 3: Lower the temperature to reaction temperature C, introduce water vapor to participate in the reaction, and grow the first silicon dioxide layer with wet oxygen; continue to raise the temperature to reaction temperature B, introduce nitrogen gas, and anneal in a nitrogen atmosphere; The thickness of the first silicon dioxide layer grown by wet oxygen in step three is obtained by the following method: x2 is the film thickness, t2 is the growth time, and τ2 is a constant; Step 4: Cool down to reaction temperature A, introduce oxygen, and add a chlorine-containing compound to grow the second silicon dioxide layer in dry oxygen. Step 5: Change the temperature from reaction temperature A to reaction temperature C, introduce oxygen and water vapor, and grow the second silicon dioxide layer in moist oxygen; raise the temperature to reaction temperature B, and anneal with oxygen in a nitrogen atmosphere. Step 6: Repeat steps 4, 5 and 4 to complete the preparation of the third silica layer grown by dry oxygen, the third silica layer grown by wet oxygen, and the fourth silica layer grown by dry oxygen. Step 7: Annealing and cleaning; to obtain a high-quality, thick silica film.

2. The method for preparing a high-quality, thick silica film as described in claim 1, characterized in that: In step two, the ratio of oxygen to nitrogen should not exceed one percent.

3. The method for preparing a high-quality, thick silica film as described in claim 1, characterized in that: The ratio of chlorine-containing compounds and oxygen added in step four shall not exceed five per thousand.

4. The method for preparing a high-quality, thick silica film as described in claim 1, characterized in that: The annealing reaction temperature B is not lower than the dry oxygen oxidation reaction temperature A, and the dry oxygen oxidation reaction temperature A is not lower than the wet oxygen oxidation reaction temperature C.

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