Method for improving film thickness uniformity in low-pressure chemical vapor deposition process

Abstract

The invention provides a method for improving the thickness uniformity of a thin film in a low-pressure chemical vapor deposition process. According to the method, thin film deposition is carried out by adopting a wafer boat with a non-fully-matched accompanying wafer, and vacant slots at the top and / or the bottom of the wafer boat change local reaction gas concentration and temperature distribution, so that the deposition rate of an area adjacent to the edge of the wafer is increased, and the film thickness difference between the center and the edge is effectively compensated. Equipment does not need to be transformed, operation is easy and convenient, the film thickness uniformity can be remarkably improved, the effect on the uneven concentric circle shape is particularly remarkable, and the process stability, the product yield and the productivity can be improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for improving the uniformity of thin film thickness in low-pressure chemical vapor deposition processes. Background Technology

[0002] Low-pressure chemical vapor deposition (LPCVD) is a key thin film preparation technology in the manufacturing process of semiconductor integrated circuits. Thin films formed through this process can be used for a variety of purposes, such as as a masking film in field oxidation or local oxidation processes to block ions during ion implantation; as a dielectric layer for transistor gate capacitors or a filling material in shallow trench isolation processes; or directly as a gate electrode material for transistors.

[0003] LPCVD (Liquid Crystallization) is typically performed using horizontal or vertical furnace tubes and is a batch process where multiple wafers are simultaneously placed on a quartz or silicon carbide boat for processing. To ensure the stability of the process environment (such as gas flow, temperature, and pressure) within the furnace tube and the repeatability of process results, a number of dummy wafers are usually placed at the top and bottom of the boat. These dummy wafers help to make the distribution of reactive gases and temperature field within the boat more uniform, while also absorbing and radiating heat, buffering thermal effects, and preventing excessive local temperature differences between the product wafers at both ends of the boat due to positional effects. This ensures the uniformity of thin film deposition rate and quality.

[0004] However, achieving highly uniform film thickness across a batch of wafers and within a single wafer remains a challenge in actual production. To address the issue of uneven film thickness, existing technologies typically employ the following solutions:

[0005] Option 1 employs ringboat technology. This involves adding a ring of the same material to the outside of the traditional wafer boat's grooves, reducing the distance between the wafer edge and the boat's groove wall. This structure increases the flow rate of reactive gases in the wafer edge region, while the ring itself adsorbs some of the reactive gases, collectively reducing the reactant concentration in the wafer edge region and thus decreasing the thin film deposition rate at the wafer edge. This method aims to create a film thickness distribution with a thinner outer ring and a thicker inner ring to compensate for or optimize overall batch uniformity.

[0006] Option 2 employs teaching technology. Since there may be localized differences in the airflow distribution and temperature field within the LPCVD furnace tube, and the film thickness uniformity is highly sensitive to the precise position of the wafer within the boat and furnace tube, the temperature distribution on the wafer surface can be altered by fine-tuning the relative position of the boat within the furnace tube or adjusting the horizontal position of the base supporting the boat. This, in turn, compensates for and adjusts the film thickness distribution within the wafer surface.

[0007] However, the aforementioned existing technical solutions have limitations. For example, in some equipment that has adopted a boat-shaped configuration, the uneven film thickness of the wafer may present as a concentric circle distribution that is difficult to improve through physical position adjustments. In this case, the improvement effect of teaching techniques is limited. Furthermore, whether converting to a boat-shaped configuration or adding a calibration step for position adjustment, it may involve hardware modifications, increased process debugging time, or the introduction of new process variables, lacking flexibility and economy.

[0008] Therefore, the industry urgently needs a new method that requires no modification to the equipment hardware, is easy to operate, and can effectively improve the uniformity of film thickness in the LPCVD process furnace. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a new method that does not require modification of equipment hardware, is easy to operate, and can effectively improve the uniformity of film thickness in the furnace of low-pressure chemical vapor deposition (LPCVD) process, so as to overcome the limitations of the prior art.

[0010] To address the aforementioned technical problems, this invention provides a method for improving the uniformity of thin film thickness in low-pressure chemical vapor deposition processes, comprising:

[0011] A crystal boat is provided that carries multiple wafers and co-wafers, wherein the slots on the top and / or bottom of the crystal boat for configuring co-wafers are not fully filled;

[0012] A crystal boat is placed in the reaction chamber of a low-pressure chemical vapor deposition (LCV) apparatus, and a reactive gas is introduced to perform thin film deposition. In this process, the non-full packing state alters the reactive gas concentration and / or temperature distribution in local areas of the crystal boat, thereby improving the uniformity of the thickness of the deposited thin film on the wafer.

[0013] Preferably, the non-full-fit state is formed by reducing the number of supporting pieces from the full-fit state.

[0014] Preferably, reducing the number of wafers includes reducing the number of wafers at the bottom of the crystal boat.

[0015] Preferably, the number of accompanying pieces is reduced to 1 to 5.

[0016] Preferably, the number of supporting pieces is reduced to 3.

[0017] Preferably, the film is an oxide film or a nitride film.

[0018] Preferably, the film is a high-temperature oxide film.

[0019] Preferably, the non-full configuration increases the concentration of reactive gas in the wafer edge region adjacent to the vacant slots, thereby increasing the film deposition thickness in the wafer edge region.

[0020] Preferably, the crystal boat is an annular boat.

[0021] As described above, the method of the present invention for improving the uniformity of film thickness in low-pressure chemical vapor deposition processes has the following beneficial effects:

[0022] This invention creates vacant slots in the wafer carrier's supporting wafer area, forming a non-fully-fitted layout. This intentionally alters the gas flow path and heat exchange environment at both ends of the wafer carrier during the process, thereby increasing the thin film deposition rate at the wafer edge and effectively compensating for or improving the deposition rate difference between the wafer center and edge caused by equipment structure or process characteristics. This method significantly improves the problem of concentric circular film thickness uniformity, which is difficult to solve with existing technologies. More importantly, this method requires no hardware modification or complex process parameter adjustments to the LPCVD equipment; simply changing the placement of supporting wafers optimizes film thickness uniformity and improves process stability and repeatability. Practical verification shows that this method can significantly reduce film thickness variations and increase the concentration of product electrical parameters, thereby improving product yield and production efficiency. It has the advantages of simple operation, low cost, high flexibility, and significant economic benefits. Attached Figure Description

[0023] Figure 1 This is a schematic flowchart of a method for improving the uniformity of thin film thickness in a low-pressure chemical vapor deposition process, provided by an embodiment of the present invention.

[0024] Figure 2 This is a schematic diagram of the low-pressure chemical vapor deposition equipment to which the method of the present invention is applicable;

[0025] Figure 3 This is a schematic diagram illustrating the mechanism for reducing the influence of the auxiliary plate on local gas flow in an embodiment of the present invention;

[0026] Figure 4 This is a comparison diagram of the effects of different substrate configuration schemes on film uniformity in embodiments of the present invention;

[0027] Figure 5 This is a comparison table of wafer bottom film thickness measurement data before and after improvement in this embodiment of the invention;

[0028] Figure 6 for Figure 5 Contour map of film thickness data before improvement;

[0029] Figure 7 for Figure 5 Contour distribution map of the improved film thickness data;

[0030] Figure 8 This is a comparison chart of the stability trend of the bottom film uniformity before and after improvement in an embodiment of the present invention;

[0031] Figure 9 This is a comparison chart of the test results of the electrical parameters of the product before and after the improvement in an embodiment of the present invention. Detailed Implementation

[0032] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0033] Please see Figure 1 , Figure 1 This is a schematic flowchart of a method for improving the uniformity of thin film thickness in a low-pressure chemical vapor deposition process, provided by an embodiment of the present invention. The method includes:

[0034] Step 1: Provide a crystal boat that carries multiple wafers and co-wafers, wherein the slots on the top and / or bottom of the crystal boat for configuring co-wafers are not fully filled.

[0035] Step 2: Place the crystal boat in the reaction chamber of the low-pressure chemical vapor deposition equipment and introduce reactive gas for thin film deposition. In this process, the non-full packing state changes the reactive gas concentration and / or temperature distribution in local areas of the crystal boat to improve the uniformity of the thickness of the deposited thin film on the wafer.

[0036] Please see Figure 2 , Figure 2 A schematic diagram of a typical low-pressure chemical vapor deposition (LPCVD) apparatus suitable for implementing the methods of this invention is shown. The apparatus primarily comprises a vertical tube serving as the reaction chamber. During the process, a wafer-loaded boat is placed inside the reaction chamber. Reactive gases enter through a gas inlet, flow upwards at a high temperature, and pass over each wafer on the boat, participating in the thin film deposition reaction. The exhaust gases are then extracted by a vacuum pump through a top outlet to maintain the low-pressure environment required for the process. Co-wafers are typically placed at the top and bottom of the boat to stabilize the gas flow and temperature field throughout the reaction zone.

[0037] This invention utilizes a method that actively creates vacant slots in the wafer-supporting areas of the wafer boat, forming a non-fully-fitted layout. This layout intentionally alters the gas flow path and heat exchange environment at both ends of the wafer boat during the process. Specifically, the presence of vacant slots provides additional flow and diffusion space for the reactive gases, resulting in a relatively higher concentration of reactive gases at the wafer edge region adjacent to the vacant slots. Simultaneously, the reduced number of supporting wafers decreases the absorption of localized heat, potentially leading to a higher temperature in this region, both contributing to a higher film deposition rate at the wafer edge. This "compensatory" enhancement of the edge deposition rate effectively offsets or improves the difference in deposition rates between the wafer center and edge caused by equipment structure or process characteristics, particularly significantly improving the concentric circular film thickness unevenness problem that is difficult to address with existing technologies. More importantly, this method requires no hardware modifications or complex process parameter adjustments to the LPCVD equipment; film thickness uniformity can be optimized simply by changing the placement of supporting wafers. It offers advantages such as ease of operation, low cost, and high flexibility.

[0038] In some embodiments, the non-full-fill state increases the reactive gas concentration in the wafer edge region adjacent to the vacant slots, thereby increasing the thin film deposition thickness in the wafer edge region. See also Figure 3 , Figure 3 A detailed schematic diagram illustrates the mechanism by which reducing the number of co-wafers affects local gas flow and thin film deposition. In the baseline state shown on the left, multiple co-wafers are closely arranged. When the reactive gas flows through them, some of the gas is consumed due to the reaction on the co-wafer surface, and the gas flow path is also somewhat obstructed. In the embodiment of the invention shown on the right, by reducing one co-wafer, an empty slot is created. This empty slot provides a smoother flow channel for the reactive gas, allowing more gas to bypass the remaining co-wafers and be delivered directly upwards. As a result, the product wafer located above the area with reduced co-wafers, especially the edge portion of the wafer, can come into contact with a higher concentration of reactive gas, thereby increasing the thin film deposition thickness at the wafer edge and achieving the purpose of compensating for and improving in-plane uniformity.

[0039] In some embodiments, the crystal boat is a ring boat. While a ring boat is a design used to improve film thickness uniformity, it can also lead to concentric circle uniformity problems that are difficult to optimize using traditional teaching methods. The present invention, combined with ring boat technology, can specifically address the uniformity problems introduced or unresolved by the ring boat itself; the two work synergistically to achieve a superior level of film thickness uniformity control.

[0040] In some embodiments, the crystal boat is made of high-temperature resistant and high-purity materials such as quartz or silicon carbide to ensure stability and cleanliness in high-temperature process environments. The supported wafer can be various semiconductor substrates such as silicon (Si) wafers, silicon germanide (SiGe) wafers, and silicon-on-insulator (SOI) wafers.

[0041] In some embodiments, a non-full-fill state is achieved by reducing the number of co-wafers from a full-fill state. A "full-fill state" refers to a standard or baseline process flow where all slots on the wafer boat reserved for co-wafers are occupied. Reducing the number of co-wafers from this defined baseline state ensures the controllability and repeatability of process adjustments, facilitating the establishment of stable process specifications.

[0042] In some embodiments, reducing the number of substrates includes reducing the number of substrates at the bottom of the crystal boat. In many vertical or horizontal furnace tubes, the reactive gases typically enter from the bottom or one end of the furnace tube; therefore, adjusting the configuration of the bottom substrates has a more direct and significant impact on the initial gas flow distribution and the subsequent gas concentration gradient throughout the entire crystal boat region.

[0043] In some embodiments, the number of wafers reduced is 1 to 5. The choice of the reduction number can be adjusted based on the specific degree of film thickness unevenness, equipment characteristics, and process window to achieve the best compensation effect. Too little reduction may be ineffective, while too much reduction may lead to excessive changes in the process environment, introducing new unevenness. Please refer to [link to relevant documentation]. Figure 4 , Figure 4 This is a comparative graph illustrating the impact of different surrogate wafer (SD) configurations on film uniformity (UNIF). The graph compares the performance of various surrogate wafer reduction schemes across multiple consecutive boat batches. It can be seen that different configurations (such as UNIF (3 SDs) and UNIF (BL = 5 SDs) in the example) lead to different uniformity results and trends. Through such comparative experiments, the optimal non-full configuration can be selected for specific processes and equipment. For example, the scheme shown by the gray line in the graph has the lowest uniformity value and the most stable performance, thus providing experimental basis for selecting the specific number of surrogate wafers to be reduced.

[0044] In some embodiments, the number of auxiliary wafers is reduced by three. In a specific verification case, by removing three auxiliary wafers at the bottom of the wafer hull, the film thickness range within the batch was optimized from 26.3 Å to 9.2 Å, demonstrating a significant improvement in uniformity. Please refer to [link to relevant documentation]. Figure 5 , Figure 5This is a table showing the specific measurement data of the bottom thin film thickness (BTM THK) of the wafer before and after the improvement. The data clearly shows that before the improvement, there was a significant difference in thickness between the wafer center point (X=0, Y=0) and the edge points (e.g., X=±95 or Y=±95), with the thinnest point being only 202.9 Å, resulting in a thickness range of 26.3 Å. Please also refer to... Figure 6 , Figure 6 The thin film thickness contour plot, drawn based on the data before improvement, exhibits a typical concentric circle distribution characteristic, with the center thicker and the edges thinner. After reducing the number of bottom wafers by three using the method of this invention, as shown in the table, the thickness of the wafer edge region (e.g., X = ±95 or Y = ±95) significantly increases to the level of 221-222.3 angstroms, resulting in a substantial reduction in the overall thickness range to 9.2 angstroms. Please also refer to... Figure 7 , Figure 7 The improved thin film thickness contour plot shows a more compact transition between contour regions, indicating a more uniform thickness distribution across the entire wafer. Furthermore, the method of this invention also improves process stability. Please refer to [link / reference]. Figure 8 , Figure 8 The chart shows the long-term trend of bottom uniformity (BTM UNIF) before and after improvement. It can be seen that in the batches before improvement, the uniformity values ​​fluctuated significantly and remained at a high level; however, after implementing the method of this invention, the uniformity values ​​not only decreased significantly but also remained at a stable low level in subsequent batches, demonstrating the stability and repeatability of the method.

[0045] In some embodiments, the thin film is an oxide thin film or a nitride thin film. For example, the oxide thin film may be a silicon oxide thin film deposited at high temperature using dichlorosilane (DCS) and nitrous oxide (N2O) as reactant gases; the nitride thin film may be a silicon nitride thin film deposited using dichlorosilane and ammonia (NH3) as reactant gases. The method of the present invention is also applicable to other LPCVD processes, such as the deposition of polycrystalline silicon thin films.

[0046] In some embodiments, the thin film is a high-temperature oxide (HTO) thin film. As a commonly used dielectric layer in semiconductor manufacturing, the thickness uniformity of HTO thin films directly affects the electrical performance and reliability of devices. The method of this invention has been product-verified, increasing the number of workable batches for a specific product from 3 to 4 in the HTO process, resulting in a 33% increase in production capacity and significant economic benefits. This increase in capacity stems from higher process yield and more stable device performance. Please refer to... Figure 9 , Figure 9The results of slice electrical parameter testing (WAT) on actual products before and after applying the method of this invention are shown. The data in the figure (e.g., the qualified batches shown in the green boxes) indicate that the batches after applying the method of this invention (blue data points) have a more concentrated distribution and smaller dispersion of key electrical parameters (such as TOXN_AVERAGE, i.e., average oxide layer thickness) compared to the batches before improvement (red data points), thereby ensuring higher product yield and batch pass rate.

[0047] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0048] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for improving the uniformity of thin film thickness in a low-pressure chemical vapor deposition process, characterized in that, At least including: A crystal boat is provided that carries multiple wafers and co-wafers, wherein the slots on the top and / or bottom of the crystal boat for configuring the co-wafers are not fully filled. The crystal boat is placed in the reaction chamber of a low-pressure chemical vapor deposition apparatus, and a reactive gas is introduced to perform thin film deposition. The non-full-load state changes the reactive gas concentration and / or temperature distribution in a local area of ​​the crystal boat to improve the thickness uniformity of the thin film deposited on the wafer.

2. The method for improving the uniformity of film thickness in a low-pressure chemical vapor deposition process according to claim 1, characterized in that: The non-full-match state is formed by reducing the number of supporting pieces from the full-match state.

3. The method for improving the uniformity of film thickness in a low-pressure chemical vapor deposition process according to claim 2, characterized in that: The reduction in the number of wafers includes reducing the number of wafers at the bottom of the crystal boat.

4. The method for improving the uniformity of film thickness in a low-pressure chemical vapor deposition process according to claim 2 or 3, characterized in that: The number of accompanying pieces reduced is between 1 and 5.

5. The method for improving the uniformity of film thickness in a low-pressure chemical vapor deposition process according to claim 4, characterized in that: The number of accompanying pieces reduced is 3.

6. The method for improving the uniformity of film thickness in a low-pressure chemical vapor deposition process according to claim 1, characterized in that: The film is an oxide film or a nitride film.

7. The method for improving the uniformity of film thickness in a low-pressure chemical vapor deposition process according to claim 1, characterized in that: The film is a high-temperature oxide film.

8. The method for improving the uniformity of film thickness in a low-pressure chemical vapor deposition process according to claim 1, characterized in that: The non-full configuration increases the concentration of reactive gas in the wafer edge region adjacent to the vacant slots, thereby increasing the film deposition thickness in the wafer edge region.

9. The method for improving the uniformity of film thickness in a low-pressure chemical vapor deposition process according to claim 1, characterized in that: The crystal boat is a ring boat.

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