Method for improving compactness of super back-sealing LTO film

Abstract

The invention discloses a method for improving the compactness of a super back-sealing LTO film, and particularly relates to the technical field of semiconductor manufacturing processes, and the method comprises the following steps: S1, preparing an LTO film; s2, improving the compactness of the LTO film; s3, preparing a polycrystalline silicon thin film; s4, HF acid cleaning and measurement; and S5, obtaining a finished product. According to the method for improving the compactness of the super back-sealed LTO film, APCVD film forming parameters do not need to be modified or independent annealing equipment does not need to be additionally arranged, only the heat preservation time of the LPCVD non-film-forming step is adjusted, the method is seamlessly compatible with an existing AP + LP technology, the technology compatibility is high, performance improvement is achieved within a reasonable time range by setting the optimal heat preservation time to be 30 min, and the method is suitable for large-scale production. By adjusting the optimal heat preservation time of the LPCVD non-film-forming step, the single-batch processing period is prevented from being greatly prolonged, the productivity influence is small, and the compactness of the LTO film is improved to the maximum extent while the single-batch processing period is prevented from being greatly prolonged by adjusting the optimal heat preservation time of the LPCVD non-film-forming step.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing process technology, and in particular to a method for improving the density of a super back-sealed LTO film. Background Art

[0002] In the field of semiconductor device manufacturing, with the rapid development of integrated circuit technology, the integration of devices continues to increase, and the requirements for the precision and performance of the manufacturing process are becoming increasingly stringent. As a key link in semiconductor manufacturing, the super back-sealing process plays a vital role in ensuring the performance and reliability of the device. Oxide, low-temperature oxide, the main component of which is silicon dioxide) film has been widely used in the super back-sealing process due to its high hardness, good insulation, chemical stability and good adhesion to the silicon substrate. In the super back-sealing process, APCVD technology is usually used to deposit a layer of LTO film on the back of the silicon wafer. The main function of this LTO film is to suppress the self-doping phenomenon. Self-doping means that in the semiconductor manufacturing process, due to high temperature or other factors, impurity atoms on the surface or inside of the silicon wafer will diffuse to other areas, thereby affecting the electrical performance of the device. The presence of LTO film can effectively block the diffusion of these impurity atoms and ensure the stability of the electrical characteristics of the device. Subsequently, LPCVD technology is used to deposit polysilicon film on the front of the silicon wafer. The polysilicon film can play the role of getting impurities. It can absorb some impurity atoms inside or on the surface of the silicon wafer, further purify the silicon wafer environment, and improve the yield and performance of the device. However, The density of LTO film is one of the key factors affecting the back-sealing effect. LTO film with good density can more effectively block the diffusion of impurity atoms and provide better insulation performance, thereby improving the quality of the super back-sealing process. However, in actual production, the existing methods to improve the density of LTO film have many limitations. For example, increasing the APCVD temperature is a common attempt method. In the APCVD process, temperature is an important parameter affecting the growth and performance of the film. Properly increasing the temperature can increase the energy of the reaction atoms and promote the growth and densification of the film. However, too high a temperature will have an adverse effect on the stability of the existing process. On the one hand, high temperature may cause the thermal stress inside the silicon wafer to increase, causing the silicon wafer to warp or deform, thereby affecting the accuracy of subsequent processes and the performance of the device; on the other hand, high temperature may also change the properties of other materials on the surface or inside the silicon wafer, destroy the already formed structure or interface, and cause the electrical performance of the device to deteriorate. Summary of the Invention

[0003] The main purpose of the present invention is to provide a method for improving the density of a super back-sealed LTO film, which can effectively solve the limitations of existing methods for improving the density of LTO films.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] A method for improving the density of a super back-sealed LTO film comprises the following steps:

[0006] S1. Producing an LTO film: depositing an LTO film of target thickness on the back of a silicon wafer using an APCVD process;

[0007] S2. Improving the density of the LTO film: placing the silicon wafer with the LTO thin film deposited in the LPCVD equipment, and extending the holding time for heat treatment in the non-film forming step before vacuuming, the holding time being 15 minutes to 1 hour, which effectively improves the density of the LTO film;

[0008] S3, preparing a polycrystalline silicon thin film: after the heat preservation is completed, performing an LPCVD process to deposit a polycrystalline silicon thin film on the surface of the silicon wafer;

[0009] S4. HF acid cleaning and measurement: The film thickness at different positions is measured by the nine-point method. The LTO film is then etched with a certain concentration of HF for 5 minutes. The film thickness of the etched LTO film is measured again at different positions using the nine-point method.

[0010] S5. Finished product: Finally, a silicon wafer with a super back-sealed LTO film with good density is obtained.

[0011] Preferably, the processing temperature of the LPCVD process is 650°C to 670°C.

[0012] Preferably, the optimal value of the holding time is 30 min, at which time the corrosion removal rate of the LTO film is / min down to / min.

[0013] Preferably, the holding time in the step S2 of improving the density of the LTO film can be further optimized as a segmented holding process: a low temperature section of 600°C to 630°C, holding for 10 to 15 minutes; a high temperature section of 650°C to 670°C, holding for 15 to 30 minutes.

[0014] Preferably, inert gas is introduced during the insulation stage with a flow rate of 50-100 sccm, the equipment maintains a slight positive pressure of less than 10 Pa, and the gas flow direction is tangential to the surface of the silicon wafer.

[0015] Preferably, the LTO film can be modified by introducing a trace amount of dopant phosphorus through an APCVD process to form a PSG film, and the LTO film can be modified by introducing a trace amount of dopant boron through an APCVD process to form a BSG film.

[0016] Preferably, the LTO film can form a composite structure with the SiN layer, wherein the LTO film thickness is The SiN film thickness is

[0017] Preferably, the HF is not diluted, reacted or exposed for a long time to cause concentration changes, and maintains the original concentration at the time of shipment and preparation.

[0018] Preferably, the compactness is the corrosion removal rate, and the corrosion removal rate is calculated as follows:

[0019]

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention does not require modification of APCVD film-forming parameters or addition of independent annealing equipment. It only adjusts the holding time of the LPCVD non-film-forming steps. It is seamlessly compatible with the existing AP+LP process and has strong process compatibility.

[0022] 2. The present invention sets the optimal holding time to 30 minutes, achieving performance improvement within a reasonable time range, avoiding a significant extension of the single batch processing cycle, and having little impact on production capacity.

[0023] 3. The present invention adjusts the optimal holding time of the LPCVD non-film forming step to avoid significantly extending the single batch processing cycle while maximally improving the density of the LTO film. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the overall flow chart of the present invention. DETAILED DESCRIPTION

[0025] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0026] like Figure 1 As shown, a method for improving the density of a super back-sealed LTO film includes the following steps:

[0027] S1. Prepare LTO film by depositing the target thickness of LTO film on the back of silicon wafer using APCVD process. The specific process is as follows:

[0028] Gas mixing and control: First, the reaction gases are mixed, and the mixing ratio of precursors such as silane (SiH4) and oxygen (O2) is precisely controlled using a mass flow meter to ensure the uniformity and accuracy of the gas mixing. For example, the flow rate of silane can be controlled at 50-100 sccm, and the flow rate of oxygen can be controlled at 200-500 sccm to ensure the full progress of the reaction.

[0029] Reaction chamber design and parameter control: The reaction chamber usually adopts a parallel plate design. The distance between the substrate and the gas nozzle is set to 5-15mm to maintain laminar gas distribution and ensure uniform film deposition. The temperature gradient in the deposition area is controlled at ±5℃ / cm. The silicon wafer deposition temperature is usually maintained in the range of 300-450℃ to ensure the quality and performance of the film. For example, the deposition temperature can be set to 350℃. At this temperature, silane and oxygen can fully react to form a dense LTO film.

[0030] Thin film deposition principle: The gas diffusion rate is controlled by boundary layer theory, causing the gaseous precursor to undergo thermal decomposition or chemical reaction on the substrate surface to form a dense solid film. For example, silane and nitrous oxide react to form a silicon dioxide film. The reaction equation is SiH4(g)+2N2O(g)→SiO2(s)+2N2(g)+2H2O(g).

[0031] Tail gas treatment: A three-stage scrubber is configured to treat unreacted gases, ensuring that emission indicators meet environmental protection requirements and obtaining silicon wafers deposited with LTO thin films.

[0032] S2. To improve the density of the LTO film, place the silicon wafer with the LTO film deposited in the LPCVD equipment and extend the holding time for heat treatment in the non-film forming step before vacuuming. The holding time is 15 minutes to 1 hour, which effectively improves the density of the LTO film. The following are two specific examples of holding processes:

[0033] Conventional holding process: Raise the temperature of the LPCVD equipment to 650°C~670°C, for example, set it to 660°C, then place the silicon wafer into the equipment and maintain this temperature for 15 minutes to 1 hour before vacuuming. By extending the holding time, the atoms in the LTO film can obtain enough energy to rearrange, thereby improving the density of the film.

[0034] Segmented insulation process: first raise the equipment temperature to the low temperature range of 600℃~630℃, for example, set it to 620℃, and keep it warm for 10~15 minutes to make the LTO film undergo preliminary structural adjustment. Then raise the temperature to the high temperature range of 650℃~670℃, for example, set it to 660℃, and keep it warm for 15~30 minutes to further promote the diffusion and rearrangement of atoms and improve the density of the film. In the insulation stage, introduce inert gas, such as nitrogen, with a flow rate of 50~100sccm. The equipment maintains a slightly positive pressure of <10Pa. The gas flow direction is tangential to the silicon wafer surface to protect the film surface and avoid contamination or oxidation.

[0035] S3. Prepare a polycrystalline silicon thin film. After heat preservation, perform LPCVD process to deposit the polycrystalline silicon thin film on the surface of the silicon wafer. The processing temperature of the LPCVD process is 650℃~670℃, for example, it is set to 660℃. At this temperature, precursors such as silane decompose in a low-pressure environment and deposit on the surface of the silicon wafer to form a polycrystalline silicon thin film, which plays the role of gettingtering.

[0036] S4, HF acid cleaning and measurement, the film thickness at different positions is measured by the nine-point method. The specific operation is to measure the film thickness at nine positions such as the center and four corners of the silicon wafer, and take the average value as the average film thickness before corrosion. Then the LTO film is corroded by a certain concentration of HF for 5 minutes. The HF is not diluted, reacted or exposed for a long time to cause the concentration to change. The original concentration at the time of leaving the factory or preparing is maintained, such as the HF concentration of 49%. After corrosion, the LTO film is measured again by the nine-point method at different positions of the film thickness, and the average value is taken as the average film thickness after corrosion. According to the calculation formula of the corrosion removal rate:

[0037] The corrosion removal rate of the LTO film is calculated to evaluate its compactness. The lower the corrosion removal rate, the better the compactness of the LTO film.

[0038] S5, finished product, finally obtaining a silicon wafer with a super back-sealed LTO film with good density.

[0039] In addition, the optimal holding time in the step of S2 to improve the density of the LTO film is 30 min, at which time the corrosion removal rate of the LTO film is reduced from / min down to / min, LTO film can be modified by introducing trace dopants (phosphorus or boron) through APCVD process to form PSG or BSG film. LTO film can form a composite structure with SiN layer, where the LTO film thickness is The SiN film thickness is

[0040] It should be noted that the existing LPCVD process steps are as follows:

[0041] Substrate preparation: The substrate (usually silicon wafers, glass and other materials) needs to undergo a rigorous cleaning process to remove surface contaminants and oxides to ensure the quality of the deposited film. Then, according to specific needs, the substrate surface is subjected to specific treatments such as polishing and etching to improve the adhesion and uniformity of the film.

[0042] Reaction chamber preparation: Pump the reaction chamber to a low pressure state, usually 0.1-1 Torr or lower, to reduce collisions between gas molecules and improve the uniformity and quality of the deposited film. Heat the substrate to the required reaction temperature, which varies depending on the deposition material.

[0043] Gas introduction and reaction: First, gas pretreatment is performed. The properties of the reaction gas are adjusted through gas mixing, heating, etc. to ensure that it can be evenly distributed in the reaction chamber and an effective chemical reaction occurs. Then, gas introduction is performed to introduce chemical precursor gases (such as silane, ammonia, dichlorosilane, etc.) into the reaction chamber. These gases react chemically with the surface of the substrate under low pressure and high temperature conditions to generate a solid thin film and deposit it on the substrate. Then, reaction control is performed by precisely controlling parameters such as the flow rate of the reaction gas, the temperature and pressure of the reaction chamber to ensure that the thickness, composition and performance of the deposited film meet the design requirements.

[0044] Deposition and thin film formation: Thin film deposition. During the reaction process, gas molecules undergo chemical reactions on the substrate surface and gradually deposit to form a thin film. The LPCVD process has high uniformity, high purity and good step coverage, and can produce high-quality thin films. Monitoring and adjustment. During the deposition process, the thickness and composition of the film are monitored in real time, and adjustments are made as needed to ensure the stability and controllability of the deposition process.

[0045] Post-processing and film retrieval: waste gas emission and treatment, the by-products and excess gases produced by the reaction are discharged from the reaction chamber and treated to avoid pollution to the environment and equipment, cooling and film retrieval. After the deposition is completed, the reaction chamber is cooled to a safe temperature, and then the substrate with the thin film deposited is taken out for subsequent processing or testing.

[0046] In an embodiment, the present invention provides a method for improving the density of a super back-sealed LTO film, which is applied to silicon wafers in advanced memory devices to reduce crosstalk between memory cells, improve data storage density and display life, and support the development of big data and high-definition display technologies. The details are as follows:

[0047] First, the LTO film is prepared in S1 in the same steps as before, and the APCVD technology is used to deposit the LTO film on the back of the silicon wafer. The LTO film is processed under normal conditions. The S2 step of improving the density of the LTO film is directly executed according to the original process, but the holding time before vacuuming is 15 minutes. Then the polysilicon film is deposited, and then the S4 HF acid cleaning and measurement steps are performed. The nine-point method is used to measure the film thickness before and after etching, and the etching removal rate is calculated as follows: / min;

[0048] Secondly, when other steps remain unchanged and only S2 is changed to improve the density of LTO film, the holding time is extended to 30min and the corrosion removal rate is reduced to / min, the density is significantly improved;

[0049] Finally, while other steps remain unchanged, S2 is changed again to increase the holding time in the LTO film density step to 1 h, and the corrosion removal rate is / min, although it is better than the original process, the improvement is less than 30min, and the processing cycle is extended, which increases the impact on production capacity.

[0050] It can be seen from this that by adjusting the holding time of the LPCVD non-film-forming step, the density of the super back-sealed LTO film can be efficiently improved without significantly affecting the stability and production capacity of the existing process, among which 30 minutes is the optimal process parameter.

[0051] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for improving the density of a super back-sealed LTO film, characterized in that: The following steps are involved: S1. Producing an LTO film: depositing an LTO film of target thickness on the back of a silicon wafer using an APCVD process; S2. Improving the density of the LTO film: placing the silicon wafer with the LTO thin film deposited in the LPCVD equipment, and extending the holding time for heat treatment in the non-film forming step before vacuuming, the holding time being 15 minutes to 1 hour, which effectively improves the density of the LTO film; S3, preparing a polycrystalline silicon thin film: after the heat preservation is completed, performing an LPCVD process to deposit a polycrystalline silicon thin film on the surface of the silicon wafer; S4. HF acid cleaning and measurement: The film thickness at different positions is measured by the nine-point method. The LTO film is then etched with a certain concentration of HF for 5 minutes. The film thickness of the etched LTO film is measured again at different positions using the nine-point method. S5. Finished product: Finally, a silicon wafer with a super back-sealed LTO film with good density is obtained.

2. The method for improving the density of a super back-sealed LTO film according to claim 1, characterized in that: The processing temperature of the LPCVD process is 650°C to 670°C.

3. The method for improving the density of a super back-sealed LTO film according to claim 1, characterized in that: The optimal holding time is 30 min, at which time the corrosion removal rate of the LTO film is down to 4. A method for effectively improving the density of a super back-sealing LTO film according to claim 1, characterized in that: The holding time in the step S2 of improving the density of the LTO film can be further optimized as a segmented holding process: a low temperature section of 600°C to 630°C, holding for 10 to 15 minutes; a high temperature section of 650°C to 670°C, holding for 15 to 30 minutes.

5. The method for improving the density of a super back-sealed LTO film according to claim 1, characterized in that: In the insulation stage, inert gas is introduced with a flow rate of 50-100 sccm. The equipment maintains a slight positive pressure of less than 10 Pa, and the gas flow direction is tangential to the silicon wafer surface.

6. The method for improving the density of a super back-sealed LTO film according to claim 1, characterized in that: The LTO film can be modified by introducing a trace dopant of phosphorus through an APCVD process to form a PSG film, and the LTO film can be modified by introducing a trace dopant of boron through an APCVD process to form a BSG film.

7. The method for improving the density of a super back-sealed LTO film according to claim 1, characterized in that: The LTO film can form a composite structure with the SiN layer, and the LTO film thickness is The SiN film thickness is 8. The method for improving the density of a super back-sealed LTO film according to claim 1, characterized in that: The HF is not diluted, reacted or exposed for a long time to cause concentration changes, and maintains the original concentration at the time of shipment and preparation.

9. The method for improving the density of a super back-sealed LTO film according to claim 1, characterized in that: The compactness is the corrosion removal rate, and the corrosion removal rate is calculated as follows:

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