A method for preparing a high-uniformity silicon dioxide thin film

Abstract

The application discloses a method for preparing high-uniformity silicon dioxide film based on plasma-enhanced chemical vapor deposition (PECVD), which comprises the following steps: cleaning a silicon wafer or a quartz wafer as a substrate in NMP cleaning solution, then performing ultrasonic cleaning with deionized water for 5 minutes and blowing dry with N2; cleaning the substrate by using a plasma cleaning machine; placing the substrate in a vacuum chamber, and preheating by inputting N2 and N2O; inputting SiH4, N2 and N2O into the vacuum chamber after preheating, starting glow discharge by using a radio frequency power higher than 100 W, and depositing a silicon dioxide film on the substrate. The method has the advantages of simple main steps, simple operation, no need for post-processing after completing the deposition of the silicon dioxide film, strong universality, dense deposited silicon dioxide film, good corrosion resistance, and the film uniformity can reach below 0.5%.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit manufacturing, and in particular to a method for preparing a highly uniform silicon dioxide thin film. Background Technology

[0002] Silica thin film is a dielectric film with excellent physical and chemical properties. It has good insulation and stability, high resistance to oxidation and corrosion, and excellent masking ability of impurity ions and water vapor. It is often used as a final protective layer and surface passivation layer in semiconductor devices and integrated circuits.

[0003] Plasma-enhanced chemical vapor deposition (PECVD) utilizes glow discharge to ionize a rarefied gas under a high-frequency electric field, generating plasma. These ions are accelerated in the electric field and gain energy, enabling the growth of silicon dioxide thin films at relatively low temperatures. PECVD silicon dioxide thin film deposition technology is widely used in semiconductor materials, light-emitting diode chips, and integrated circuit manufacturing processes. In the PECVD process, the actual chemical reaction process within the plasma is highly complex. The properties of the deposited film are closely related to the deposition conditions, and many parameters can affect the film quality. Furthermore, these factors interact with each other, and some are difficult to control. The reaction mechanism, reaction kinetics, and reaction process are not yet fully understood. Currently, poor uniformity and low corrosion resistance are prominent problems in the preparation of silicon dioxide thin films. Patents CN102828172A and CN105047544A each disclose a method for preparing silica thin films by PECVD. The resulting products have no obvious defects such as pinholes or pores, are composed of particles of uniform size, and have high shrinkage stress. However, both require subsequent annealing processes to make the particle clusters adsorbed on the film surface disappear, and their uniformity and corrosion resistance are not ideal.

[0004] Currently, the technical problem that needs to be solved is how to prepare highly uniform and corrosion-resistant silica films while adjusting and simplifying the deposition process and reducing costs. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of the existing technology and develop a method for preparing highly uniform silicon dioxide by improving the PECVD process flow and adjusting process conditions such as the reaction gas flow ratio, radio frequency power, and deposition chamber pressure.

[0006] A method for preparing a highly uniform silica thin film includes the following process steps:

[0007] (1) Place the substrate in N-methylpyrrolidone cleaning solution and clean it at 120°C for 20 minutes. Then, use deionized water to ultrasonically clean the substrate and blow it dry with N2.

[0008] (2) The substrate is placed in a plasma cleaner for cleaning;

[0009] (3) Evacuate the vacuum chamber to 1 Pa, control the temperature to 250-400℃, place the substrate in, preheat, introduce preheating gas, and stabilize for 10 minutes.

[0010] (4) Evacuate the vacuum chamber with the substrate placed to 1 Pa, control the temperature to 250-400℃, introduce the reaction gas, stabilize for 30 seconds and then start the ignition to deposit a silicon dioxide thin film on the substrate.

[0011] Preferably, the substrate is a silicon wafer or a quartz wafer.

[0012] In step (2), O2 and Ar are introduced into the plasma cleaner, with the flow rate of O2 being 200 sccm and the flow rate of Ar being 200 sccm, and the power of the plasma cleaner is adjusted to 200W.

[0013] In step (3), the preheating gas is N2 and N2O, wherein the flow rate of N2 is 200 sccm and the flow rate of N2O is 500 sccm.

[0014] Preferably, the pressure of the preheating gas is 150-400 Pa.

[0015] In step (4), the reacting gases are SiH4, N2 and N2O, wherein the flow rate volume ratio of SiH4:N2O:N2 is 1:8-82:17-91.

[0016] Preferably, the pressure of the reactant gas is 125-300 Pa.

[0017] Preferably, the radio frequency power of the ignition is 200-400W.

[0018] Preferably, the distance between the upper and lower electrode plates inside the process cavity is 12-20 mm.

[0019] Preferably, the radio frequency power source is 13.56MHz.

[0020] The method for preparing silica thin films provided by this invention, through a preheating process before deposition, ensures sufficient contact between the substrate and the reactive gas, thereby improving the uniformity of the resulting silica thin film. Improvements to different process parameters result in a denser film with better corrosion resistance. Furthermore, this invention is simple, using only one power source and eliminating the need for post-processing such as annealing, making it suitable for large-scale application. Detailed Implementation

[0021] As mentioned in the background section, the properties of the deposited film are closely related to the deposition conditions during the PECVD deposition process. Many parameters can affect the film quality, such as operating frequency, power, pressure, substrate temperature, reactant gas partial pressure, and electrode space. Therefore, the inventors of this application have studied these parameters and ultimately obtained a series of process parameters that can produce silicon dioxide films with superior overall performance.

[0022] In embodiments of the present invention, the substrate temperature range is 250-400°C. The applicant of this invention has discovered that substrate temperature has a relatively small impact on the deposition rate, but a significant impact on the properties of the thin film. This is because high temperatures enhance surface reactions and improve the composition of the thin film. When the temperature is too low, the film texture is porous, its corrosion resistance is poor, and its intrinsic stress is high. When the film thickness reaches a certain level, it is prone to cracking. Furthermore, as the temperature decreases, the thermal stress of the film changes drastically, and the film attached to the sidewalls of the reaction chamber and the surface of the upper electrode easily detaches and adheres to the substrate surface, causing particulate contamination. When the reaction temperature is within the above-mentioned range, the resulting thin film is denser and has better corrosion resistance.

[0023] In the embodiments of the present invention, the electrode spacing ranges from 12 to 20 mm. The applicant of the present invention has found that when the electrode spacing is small, the damage to the substrate is small, but it is not easy to form a film. As the electrode spacing increases, the edge effect of the electric field gradually intensifies, which will have a greater impact on the uniformity of the film layer. When the electrode spacing is within the above range, film can be formed quickly and effectively, and the uniformity of the sample can be ensured.

[0024] In embodiments of the present invention, the radio frequency power range is 200-400W. The applicant of the present invention has found that when the radio frequency power is low, the SiH4 concentration is high enough. Increasing the power will increase the concentration of free radicals in the reaction, accelerate the film formation process, increase the gas activation rate, increase the film density, and gradually reduce the uniformity. However, as the power gradually increases, the gas activation rate reaches saturation, and the increase in the film formation rate will become very small. At this time, the sample film layer is loose, the pinhole density increases, and the uniformity is high. When the radio frequency power is within the above range, the density and corrosion resistance of the obtained silicon dioxide film are the best.

[0025] In the embodiments of the present invention, the gas pressure range is 125-300 Pa. The applicant of the present invention has found that in the early stage of the reaction, the higher the gas concentration, the greater the density of active plasma obtained by the decomposition of the gas, and the faster the film formation rate. However, as the gas pressure continues to rise, more gas participates in the reaction, resulting in too many reaction products that cannot grow uniformly on the silicon wafer surface, which leads to a decrease in the uniformity of the film layer. When the gas pressure is within the above range, the obtained silicon dioxide film has more ideal uniformity.

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below.

[0027] The method of the present invention for preparing silicon dioxide thin films includes the following steps:

[0028] 1) Clean the substrate. The substrate is a silicon wafer. The standard cleaning process is used. The substrate is cleaned with NMP cleaning solution at 120°C for 20 minutes, then ultrasonically cleaned with deionized water for 5 minutes, and then dried with nitrogen gas.

[0029] 2) Place the cleaned substrate into a plasma cleaner for cleaning, while removing residual moisture from the sample. Control the gas flow rate in the plasma cleaner as follows: O2 flow rate is 200 sccm, Ar flow rate is 200 sccm, cleaner power is 200W, and cleaning time is 3 minutes.

[0030] 3) Evacuate the vacuum chamber to 1 Pa, maintain the temperature at 300°C, and introduce process gas containing N2 and N2O. The flow rate of N2 is 200 sccm, the flow rate of N2O is 500 sccm, and the pressure is maintained at 150 Pa for 10 minutes to allow the substrate to adapt to the 300°C temperature.

[0031] 4) Evacuate the vacuum chamber to 1 Pa, maintain the temperature at 250-400℃, and introduce process gas containing SiH4, N2, and N2O with a purity exceeding 99.99%. The flow rate volume ratio of SiH4:N2O:N2 is 1:8-82:3-91. Maintain the gas pressure at 125-300 Pa. After stabilizing for 30 seconds, ignite the sample using 200-400 W of RF power. The RF power source is 13.56 MHz. Control the electrode spacing to be 12-20 mm. Begin depositing a silicon dioxide thin film with a thickness of approximately 200 nm on the sample.

[0032] The temperature was maintained at 250-400℃, the SiH4:N2O:N2 flow rate volume ratio was 1:8-82:3-91, the gas pressure was maintained at 125-300Pa, 200-400W of radio frequency power was used for ignition, and the electrode spacing was controlled at 12-20mm. Examples 1-14 and Comparative Examples 1-3 were carried out respectively.

[0033] The uniformity of the prepared silica film samples was tested. Simultaneously, silica film samples prepared in Examples 1-5 and Comparative Examples 1-2 were placed in an NHF solution with a volume ratio of 49% HF aqueous solution: 40% NH4F aqueous solution: pure water = 1:6:49, and the corrosion rate was tested. The test results are shown in Table 1.

[0034] Table 1 Performance test data of silica thin film

[0035]

[0036] As shown in Table 1, the silica films of Examples 1-14 have low uniformity index and high etching rate, indicating that the silica film samples prepared according to this technical solution have both good uniformity and high corrosion resistance.

[0037] The test data from Comparative Examples 1-2 show that when the RF power is too high or the pressure is too low, the film uniformity is poor and cannot meet the usage standards.

[0038] The test data from Comparative Example 3 shows that when the distance between the upper and lower electrode plates in the process chamber is too small, it is almost impossible to form a film, and the uniformity is poor, making it unusable.

[0039] The present application has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present application. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and implementation methods of the present application without departing from the spirit and scope of the present application, and all such modifications and improvements fall within the scope of the present application. The scope of protection of the present application is determined by the appended claims.

Claims

1. A method for preparing a highly uniform silica thin film, characterized in that, The process includes the following steps: (1) Place the substrate in N-methylpyrrolidone cleaning solution and clean it at 120°C for 20 minutes. Then, use deionized water to ultrasonically clean the substrate and blow it dry with N2. (2) The substrate is placed in a plasma cleaner for cleaning; (3) Evacuate the vacuum chamber to 1 Pa, control the temperature to 350°C, place the substrate in, preheat it, introduce preheating gas, and stabilize for 10 minutes; (4) Evacuate the vacuum chamber with the substrate placed to 1 Pa, control the temperature to 350°C, introduce the reaction gas, stabilize for 30 seconds and then start the ignition to deposit a silicon dioxide thin film on the substrate. The step (2) of cleaning the substrate by placing it in a plasma cleaner includes: introducing O2 and Ar into the plasma cleaner, wherein the flow rate of O2 is 200 sccm, the flow rate of Ar is 200 sccm, and the power of the plasma cleaner is adjusted to 200W. The preheating gas in step (3) is N2 and N2O, wherein the flow rate of N2 is 200 sccm and the flow rate of N2O is 500 sccm; the pressure of the preheating gas is 150-400 Pa. The reactant gases in step (4) are SiH4, N2 and N2O, and the flow rates and volumes of the three reactant gases are 60 sccm, 200 sccm and 500 sccm, respectively; the gas pressure of the reactant gases is 150 Pa; and the radio frequency power of the ignition is 200 W. In step (4), the distance between the upper and lower electrode plates in the process cavity is 12-20 mm.

2. The preparation method according to claim 1, characterized in that, The substrate is a silicon wafer or a quartz wafer.

3. The preparation method according to claim 1, characterized in that, The cleaning time in step (2) is 3 minutes.

4. The preparation method according to claim 1, characterized in that, The radio frequency power source in step (4) is 13.56MHz.

Images