LTO film thickness uniformity optimization method through APCVD method

Abstract

The invention discloses an LTO film thickness uniformity optimization method through an APCVD method, and particularly relates to the technical field of semiconductor manufacturing, and the method comprises the following steps: S1, prefabricating a silicon wafer; s2, selecting a tungsten filament ring; s3, installing a tungsten filament ring; s4, depositing an LTO thin film; s5, measuring the thickness of the LTO thin film of the silicon wafer; and S6, confirming the service life of the tungsten filament ring. According to the LTO film thickness uniformity optimization method through the APCVD method, the silicon wafer is chamfered, stress concentration and dislocation are reduced, wafer edge breakage and inward movement of thermal stress defects are effectively prevented, a more stable substrate is provided for follow-up film deposition, a tungsten filament ring of a specific specification is selected and correctly installed, and the uniformity of the thickness of the LTO film is improved. The diffusion and transmission conditions of gas in the APCVD process can be improved, the problems of stacking faults, crystal points, self-doping and the like after epitaxy caused by non-uniform films are reduced, and the consistency and reliability of device performance are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing, and particularly relates to a method for optimizing the thickness uniformity of an LTO film by APCVD method. Background Art

[0002] APCVD is atmospheric pressure chemical vapor deposition. As the name implies, compared with other common vapor deposition methods, the main feature of APCVD is that it is carried out under atmospheric pressure conditions without the need to use high-vacuum equipment. APCVD will deposit a layer of material, usually a few micrometers thick, on a wafer or other types of substrates. In microelectronic devices, APCVD can be used to deposit insulating layers such as silicon dioxide (SiO2). Silicon dioxide is commonly used as an insulating layer to isolate electronic components and wires with different electrical isolation degrees. It can prevent current leakage and mutual interference, ensuring the reliability and stability of the circuit.

[0003] In the APCVD process, silane SiH4 (highly diluted with nitrogen N2) and oxygen O2 are used as process gases. These gases thermally decompose at about 400 °C and react with each other to form the required thin film. The reaction formula is: SiH4 + O2 → SiO2 + 2H2 (T = 430 °C, p = 10·5°Pa); The advantages of APCVD are high deposition rate. Generally, the deposition rate is from dozens to hundreds of nanometers per minute. Secondly, the machine structure is simple. APCVD is a CVD reaction under atmospheric pressure. CVD reaction refers to chemical vapor deposition reaction. CVD is a technology in which a solid thin film is formed by chemical reactions of gaseous precursors on the surface of a substrate. First, gaseous precursors are introduced. Gaseous compounds containing target elements (such as silane, titanium tetrachloride, etc.) are introduced into the reaction chamber. Then, under the action of heating, plasma or other energies, the gaseous precursors decompose or undergo chemical reactions to generate solid products. The solid products are deposited on the surface of the substrate to form the required thin film (such as silicon dioxide, silicon nitride, metal thin film, etc.). APCVD is a specific form of CVD, and its characteristic is that the reaction is carried out under atmospheric pressure (atmospheric pressure) conditions without a complex vacuum system, and the equipment cost is relatively low. The concentration of reactants is relatively high under atmospheric pressure, and the deposition rate is relatively fast. Therefore, there is no need for a vacuum chamber, and a silicon carbide tray heated by quartz is used to heat the wafer; The disadvantage of APCVD is that the film uniformity is poor. When depositing under atmospheric pressure, due to the limitations of gas diffusion and transmission, there may be certain non-uniformities in the thickness and quality of the deposited thin film on the substrate surface, which may lead to epitaxial stacking faults, crystal points, self-doping, and even cause variability and inconsistency in device performance. Summary of the Invention

[0004] The main purpose of the present invention is to provide a method for optimizing the thickness uniformity of an LTO film by APCVD method, which can effectively solve the problem of poor film uniformity in the APCVD process.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] An optimization method for the thickness uniformity of LTO film by APCVD method, comprising the following steps:

[0007] S1. Preparing silicon wafers: Chamfer the silicon wafers to reduce stress concentration and dislocations, prevent the wafers from being impacted and causing edge cracking, prevent defects generated by thermal stress from occurring at the edges and prevent them from moving inward;

[0008] S2. Selecting tungsten wire rings: Select tungsten wire rings according to the diameter of the silicon wafers. The diameter of the tungsten wire is 0.1 ± 0.05 mm. The diameter of the tungsten wire ring corresponding to a 4-inch silicon wafer is 99.0 ± 0.15 mm, the diameter of the tungsten wire ring corresponding to a 5-inch silicon wafer is 124.1 ± 0.15 mm, and the diameter of the tungsten wire ring corresponding to a 6-inch silicon wafer is 148.9 ± 0.15 mm;

[0009] S3. Installing tungsten wire rings: Place the tungsten wire rings of corresponding sizes at the center of the tray, making the centers of the tungsten wire rings and the tray overlap, ensuring that the tungsten wire rings contact the chamfered surfaces of the silicon wafers to prevent the tungsten wire from contacting the inner surfaces of the silicon wafers;

[0010] S4. Depositing LTO film: Transfer the silicon wafers. Pick up and place the silicon wafers by a manipulator, place the silicon wafers on the tray containing tungsten wire, start the APCVD process to grow the LTO film, and after the APCVD process is completed, recover the silicon wafers;

[0011] S5. Measuring the thickness of the LTO film on the silicon wafers: Measure the thickness of the LTO film on the silicon wafers by using an ellipsometer or spectroscopic reflectometry to ensure that the film performance meets the process requirements;

[0012] S6. Confirming the service life of the tungsten wire rings: The tungsten wire rings cannot be processed more than 30 times in total. After 30 times, they need to be cleaned with pure water.

[0013] Preferably, the tungsten wire rings are made of tungsten wire, and the diameter of the tungsten wire is 0.1 ± 0.05 mm.

[0014] Preferably, the tray is a silicon carbide tray, and the silicon wafers are heated by the heated silicon carbide tray.

[0015] Preferably, silane and oxygen are used as reaction gases in the APCVD process, and deposition is carried out at 400 - 430 °C and atmospheric pressure.

[0016] Preferably, the deposition rate in the APCVD process is 50 nm / min - 600 nm / min.

[0017] Preferably, the flow ratio between silane and oxygen is 1:2 - 1:5.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. By chamfering the silicon wafer, the present invention reduces stress concentration and dislocation, effectively preventing the rupture of the wafer edge and the inward movement of thermal stress defects, and providing a more stable substrate for subsequent thin film deposition.

[0020] 2. By selecting a tungsten wire loop with a specific specification and installing it correctly, the present invention can improve the gas diffusion and transmission in the APCVD process, thereby significantly improving the thickness uniformity of the LTO thin film, reducing problems such as epitaxial layer faults, crystal points, and self-doping caused by non-uniform thin films, and improving the consistency and reliability of device performance.

[0021] 3. By clarifying the service life and cleaning requirements of the tungsten wire loop, the present invention ensures the stability and repeatability of the process, which is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the overall flowchart of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] To make the technical means, creative features, achieved objectives and functions of the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

[0024] As Figure 1 shown, an optimization method for the thickness uniformity of the LTO film by the APCVD method includes the following steps:

[0025] S1. Preparing the silicon wafer: Chamfer the silicon wafer to reduce stress concentration and dislocation, prevent the wafer from being impacted and causing edge rupture, and at the same time prevent the defects generated by thermal stress from occurring at the edge and preventing them from moving inward.

[0026] S2. Selecting the tungsten wire loop: Select the tungsten wire loop according to the diameter of the silicon wafer, where the diameter of the tungsten wire is 0.1 ± 0.05 mm. Specifically, for a 4-inch silicon wafer, the corresponding tungsten wire loop diameter is 99.0 ± 0.15 mm, for a 5-inch silicon wafer, the corresponding tungsten wire loop diameter is 124.1 ± 0.15 mm, and for a 6-inch silicon wafer, the corresponding tungsten wire loop diameter is 148.9 ± 0.15 mm.

[0027] S3. Installing the tungsten wire loop: Place the tungsten wire loop with the corresponding size at the center of the tray, so that the center of the tungsten wire loop coincides with the center of the tray, and ensure that the tungsten wire loop contacts the chamfered surface of the silicon wafer to prevent the tungsten wire from contacting the inner surface of the silicon wafer.

[0028] S4. Depositing the LTO thin film: Transfer the silicon wafer by means of a manipulator, place the silicon wafer on the tray containing the tungsten wire, start the APCVD process to grow the LTO thin film, and recover the silicon wafer after the process ends.

[0029] S5. Silicon wafer LTO film thickness measurement: Use ellipsometer or spectral reflectometry to measure the thickness of silicon wafer LTO film to ensure that the film performance meets the process requirements.

[0030] S6. Confirm the service life of the tungsten wire ring: the cumulative processing of the tungsten wire ring cannot exceed 30 times, and it needs to be cleaned with pure water after 30 times.

[0031] The tungsten wire ring is made of tungsten wire with a diameter of 0.1±0.05mm. The tungsten wire has a high melting point (3410℃), high density, high strength, high resistivity, low vapor pressure, slow evaporation rate, high temperature resistance, wear resistance, impact resistance, acid and alkali resistance, and excellent electrical conductivity and thermal conductivity. These characteristics make the tungsten wire perform well in high temperature environments and can work stably for a long time. The diameter of the tungsten wire cannot be too thin, otherwise it cannot contact the silicon wafer and cannot transfer heat; the tungsten wire cannot be too thick, otherwise the tungsten wire will lift the silicon wafer. The tray is a silicon carbide tray, and the silicon wafer is heated by the heated silicon carbide tray. Silane and oxygen are used as reaction gases in the APCVD (atmospheric pressure chemical vapor deposition) process, and deposition is carried out at 400-430℃ and normal pressure. The deposition rate in the APCVD process is 50 nanometers / minute-600 nanometers / minute, and the flow ratio between silane and oxygen is 1:2-1:5.

[0032] The cumulative processing of tungsten wire ring cannot exceed 30 times, because during the APCVD process, reactant SIO2 particles will also adhere to the tungsten wire ring. That is to say, as the service life of the tungsten wire ring increases, the diameter of the tungsten wire ring will also increase, thereby affecting the contact effect with the silicon wafer and affecting the LTO film thickness. Pure water cleaning is required after 30 times. Although the tungsten wire is acid and alkali resistant, using pure water cleaning will not cause the life or shape of the tungsten wire to change.

[0033] Ellipsometer or spectral reflectometry is used to measure the thickness of LTO thin films on silicon wafers. Specifically, the ellipsometer measures the change in polarization state (amplitude ratio and phase difference) after polarized light is reflected on the film surface to infer the thickness and optical constants of the film. It uses the change in polarization state after the interaction of elliptically polarized light with the film to establish an optical model and fit the experimental data to obtain information such as the thickness and refractive index of the film. The ellipsometer can measure films of nanometer thickness with extremely high accuracy and is suitable for occasions with strict requirements on film thickness. There is no contact with the sample during the measurement process, avoiding errors or damage that may be introduced by contact. The ellipsometer can not only measure the thickness of the film, but also simultaneously obtain the refractive index, extinction coefficient and other optical constants of the film.

[0034] Spectral reflectometry measures the reflection spectra of a thin film at different wavelengths and uses the relationship between the reflection spectrum and the thickness and refractive index of the thin film to estimate the thickness of the thin film. It is based on the interference phenomenon generated by the reflection of light on the upper and lower surfaces of the thin film. By analyzing the interference fringes of the reflection spectrum, the thickness information of the thin film can be obtained. The measurement process of spectral reflectometry is relatively simple and easy to operate, and is suitable for measuring the thickness of thin films of various materials, including metals, semiconductors, insulators, etc. It can also achieve real-time monitoring of the thin film growth process.

[0035] By measuring the comparison of film thickness uniformity before and after improvement, before improvement: the film is thin at the periphery and thick in the center, the film thickness range is 952 Å, and the uniformity is 9.6%; after improvement: the trend of the film being thin at the periphery and thick in the center decreases, the film thickness range is 463 Å, and the uniformity is 4.2%.

[0036] It should be noted that the existing APCVD process includes the following steps:

[0037] Reaction gas mixing: The mixing ratio of precursors such as silane (SiH4) and oxygen (O2) is precisely controlled by mass flow meters, and the mixing accuracy needs to be controlled within ±1.5%. If doping is required, doping gases such as phosphine (PH3) or diborane (B2H6) can be introduced. For example, when preparing PSG, phosphine needs to be added to SiH4 and O2 so that the deposited oxide contains 4% to 8% phosphorus.

[0038] Reaction chamber design and temperature control: The reaction chamber adopts a parallel plate structure and is heated by a graphite base. The distance between the substrate and the gas nozzle is set to 5 - 15 mm to ensure a laminar gas distribution. The temperature gradient in the deposition area is controlled within ±5°C / cm, and the deposition temperature of silicon-based materials is usually maintained in the range of 300 - 450°C.

[0039] Thin film deposition: The gas diffusion rate is regulated through the boundary layer theory to cause the reaction gas to chemically react on the substrate surface and deposit into a film. The reaction equation is such as SiH4(g)+2N2O(g)→SiO2(s)+2N2(g)+2H2O(g). The deposition rate can be controlled by adjusting the gas ratio and the silicon wafer temperature; when a thicker deposition layer needs to be formed, it can be achieved by increasing the number of nozzles.

[0040] Tail gas treatment: A three-stage scrubber is configured to treat unreacted gases, and the emission indicators need to meet relevant environmental protection standards.

[0041] Subsequent processing: According to specific application requirements, subsequent process steps such as high-temperature drive, etching, coating, screen printing, sintering, etc. may be required. For example, in the preparation of the emitter of crystalline silicon solar cells, after depositing PSG or BSG, high-temperature drive is required to push P

[0041] , , + , + or B + to the silicon wafer to form the cell emitter.

[0042] Example 1. Application of an APCVD method for optimizing the thickness uniformity of LTO films on 4-inch silicon wafers is as follows:

[0043] First, in step S1 of prefabricating the silicon wafer, a 4-inch silicon wafer is taken and its edges are chamfered to reduce stress concentration and dislocations. In step S2 of selecting the tungsten wire loop, a tungsten wire with a diameter of 0.1 mm is used to make a tungsten wire loop with a diameter of 99.0 ± 0.15 mm, which meets the requirements of a 4-inch silicon wafer. In step S3 of installing the tungsten wire loop, the made tungsten wire loop is placed at the center of the silicon carbide tray, and its position is adjusted so that the center of the tungsten wire loop coincides with the center of the tray, ensuring that the tungsten wire loop contacts the chamfered surface of the silicon wafer. In step S4 of depositing the LTO film, the prefabricated silicon wafer is placed on the tray with the tungsten wire loop by a manipulator, the APCVD process is started, and in the process parameter settings, the reaction gases are silane (diluted with nitrogen) and oxygen, the flow ratio of silane to oxygen is 1:3, the deposition temperature is 420 °C, deposition is carried out under normal pressure, the deposition rate is controlled at 300 nanometers per minute, the deposition time is determined according to the required film thickness, and after the process is completed, the silicon wafer is recovered by the manipulator. In step S5 of measuring the thickness of the LTO film on the silicon wafer, an ellipsometer is used to measure the thickness of the LTO film on the silicon wafer, and the result shows that the film thickness uniformity is good and meets the process requirements. In step S6 of confirming the service life of the tungsten wire loop, the tungsten wire loop is counted for the cumulative processing times after this processing. When the cumulative processing times reach 30 times, it is cleaned with pure water.

[0044] Example 2. On the basis of Example 1, this example uses an APCVD method for optimizing the thickness uniformity of LTO films on 5-inch silicon wafers, and the specific operations are as follows:

[0045] First, in step S1 of prefabricating the silicon wafer, a 5-inch silicon wafer is taken and its edges are chamfered to reduce stress concentration and dislocations. In step S2 of selecting the tungsten wire loop, a tungsten wire with a diameter of 0.12 mm is used to make a tungsten wire loop with a diameter of 124.1 ± 0.15 mm, which meets the requirements of a 5-inch silicon wafer. Step S3 of installing the tungsten wire loop remains unchanged. In step S4 of depositing the LTO film, the silicon wafer is transferred and placed on the tray by a manipulator, the APCVD process is started, and in the process parameter settings, the reaction gases are silane (diluted with nitrogen) and oxygen, the flow ratio of silane to oxygen is 1:2, the deposition temperature is 400 °C, deposition is carried out under normal pressure, the deposition rate is 50 nanometers per minute, and the silicon wafer is recovered after deposition. Steps S5 of measuring the thickness of the LTO film on the silicon wafer and S6 of confirming the service life of the tungsten wire loop remain unchanged.

[0046] Example 3. On the basis of Example 1, this example uses an APCVD method for optimizing the thickness uniformity of LTO films on 6-inch silicon wafers, and the specific operations are as follows:

[0047] First, in step S1 of prefabricating a silicon wafer, a 6-inch silicon wafer is taken and chamfered to reduce stress concentration and dislocations. In step S2 of selecting a tungsten wire loop, a tungsten wire with a diameter of 0.08 mm is used to make a tungsten wire loop with a diameter of 148.9 ± 0.15 mm, which meets the requirements of a 6-inch silicon wafer. Step S3 of installing the tungsten wire loop remains unchanged. In step S4 of depositing an LTO film, the silicon wafer is placed on a tray by a manipulator, the APCVD process is started, and in the process parameter settings, the reaction gases are silane (diluted with nitrogen) and oxygen, the flow ratio of silane to oxygen is 1:5, the deposition temperature is 430 °C, deposition is carried out under normal pressure, the deposition rate is 600 nanometers per minute, and the silicon wafer is recovered after deposition. Step S5 of measuring the film thickness of the LTO film on the silicon wafer and step S6 of confirming the service life of the tungsten wire loop remain unchanged.

[0048] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for optimizing the thickness uniformity of LTO films by APCVD method, characterized in that: Including the following steps: S1. Preparing the silicon wafer: Chamfer the silicon wafer to reduce stress concentration and dislocations, prevent the wafer from being impacted and causing edge cracking, prevent defects generated by thermal stress from occurring at the edge and prevent them from moving inward; S2. Selecting the tungsten wire loop: Select the tungsten wire loop according to the diameter of the silicon wafer. The diameter of the tungsten wire is 0.1 ± 0.05 mm. The diameter of the tungsten wire loop corresponding to a 4-inch silicon wafer is 99.0 ± 0.15 mm, the diameter of the tungsten wire loop corresponding to a 5-inch silicon wafer is 124.1 ± 0.15 mm, and the diameter of the tungsten wire loop corresponding to a 6-inch silicon wafer is 148.9 ± 0.15 mm; S3. Installing the tungsten wire loop: Place the tungsten wire loop of the corresponding size at the center of the tray, making the center of the tungsten wire loop overlap with the center of the tray, ensuring that the tungsten wire loop contacts the chamfered surface of the silicon wafer to prevent the tungsten wire from contacting the surface of the silicon wafer internally; S4. Depositing the LTO film: Transfer the silicon wafer. Pick up and place the silicon wafer by the manipulator, place the silicon wafer on the tray containing the tungsten wire, start the APCVD process to grow the LTO film. After the APCVD process ends, recover the silicon wafer; S5. Measuring the film thickness of the LTO film on the silicon wafer: Use an ellipsometer or spectroscopic reflectometry to measure the film thickness of the LTO film on the silicon wafer to ensure that the film performance meets the process requirements; S6. Confirming the service life of the tungsten wire loop: The tungsten wire loop cannot be processed more than 30 times cumulatively. After 30 times, it needs to be cleaned with pure water.

2. The APCVD method for optimizing the LTO film thickness uniformity according to claim 1, characterized in that: The tungsten wire loop is made of tungsten wire, and the diameter of the tungsten wire is 0.1 ± 0.05 mm.

3. An APCVD method for optimizing the thickness uniformity of LTO films according to claim 1, characterized in that: The tray is a silicon carbide tray, and the silicon wafer is heated by the heated silicon carbide tray.

4. A method for optimizing the thickness uniformity of an APCVD LTO film according to claim 1, characterized in that: In the APCVD process, silane and oxygen are used as reaction gases and deposited at 400 - 430 °C under atmospheric pressure.

5. The method for optimizing LTO film thickness uniformity by APCVD method according to claim 1, characterized in that: The deposition rate in the APCVD process is 50 nm / min - 600 nm / min.

6. The APCVD method for optimizing the thickness uniformity of the LTO film according to claim 4, characterized in that: The flow ratio between the silane and oxygen is 1:2 - 1:5.

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