Cleaning method for high aspect ratio structures and applications thereof

Abstract

The application discloses a cleaning method for a high-depth-width-ratio structure and application thereof, and the cleaning method comprises the following steps: providing a wafer with a high-depth-width-ratio structure; first spray treatment is performed on the high-depth-width-ratio structure by using a first oxidizing cleaning solution; a first spray period is set; the high-depth-width-ratio structure is periodically sprayed according to the first spray period; and reciprocating breathing flow is formed in the high-depth-width-ratio structure; second spray treatment is performed on the high-depth-width-ratio structure by using a particle removal cleaning solution; the wafer is heated; the temperature of the top of the wafer is lower than that of the bottom of the wafer; a surface tension gradient is formed by using the temperature difference between the top of the wafer and the bottom of the wafer; and the particle removal cleaning solution flows along the inner wall of the high-depth-width-ratio structure from the bottom of the wafer to the top of the wafer. The liquid periodic switching forms the liquid periodic breathing effect in the high-depth-width-ratio structure, and the temperature difference regulation and the like are combined, so that the fluid renewal rate and the particle removal efficiency are improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing technology, specifically relating to a cleaning method for high aspect ratio structures and its application. Background Technology

[0002] In advanced semiconductor manufacturing processes, polymers, organic matter, and metal particles often remain on the surface of etched wafers. If these residual particles are not effectively removed, they can cause defects (yield killer defects) during subsequent deposition or oxidation processes, leading to a decrease in yield. Existing single-wafer cleaning machines (such as SCREEN SU-3200) typically employ a sequential multi-liquid spray process for wafer cleaning. The spraying process can be performed in the following order: 1. Ozone aqueous solution (OZW) spraying treatment; 2. Diluted hydrofluoric acid solution (DHF) spraying treatment; 3. SC-1 cleaning solution (composed of ammonia, hydrogen peroxide, and water) spraying treatment; 4. Isopropanol (IPA) drying.

[0003] While the sequential multi-liquid spraying process described above can achieve multi-chemical cleaning of ordinary wafers, one or more of the following technical problems still exist in the cleaning of wafers with high aspect ratio (HAR) structures: Firstly, fluid renewal at the bottom of trenches with HAR structures is difficult and the renewal rate is low, see [link to relevant documentation]. Figure 1 ,like Figure 1 As shown in area A, the liquid at the bottom of the trench easily forms a dead zone under tension, preventing liquid exchange and resulting in poor cleaning. Secondly, directly spraying chemical solutions onto trenches with high aspect ratios easily generates bubbles (bubble areas formed when the trench is sealed by the liquid). These bubbles remain trapped within the trenches, affecting chemical reactions, wafer surface repair, and particle removal. Thirdly, the liquid in the above multi-liquid spraying process is static, lacking periodic disturbance and flow field resonance, making it difficult to achieve the expected particle removal efficiency. Figure 1 As shown, the bottom of the trench contains particles that cannot be removed. Summary of the Invention

[0004] In view of all or part of the deficiencies of the prior art described above, the purpose of this invention is to provide a cleaning method for a high aspect ratio structure and its application, which improves the fluid renewal rate and particle removal efficiency by forming a periodic breathing effect of the liquid in the high aspect ratio structure / deep trench through periodic liquid switching and combined with temperature difference control, etc.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a cleaning method for a high aspect ratio structure, which includes a wafer having a high aspect ratio structure and further comprises the following steps: Step 1: The high aspect ratio structure is subjected to a first spray treatment using a first oxidizing cleaning solution. A first spray cycle is set, and the high aspect ratio structure is periodically sprayed according to the first spray cycle to form a reciprocating breathing flow within the high aspect ratio structure. Step 2: The high aspect ratio structure is subjected to a second spray treatment using a particle removal cleaning solution. The wafer is heated so that the temperature of the top of the wafer is lower than that of the bottom of the wafer. The surface tension gradient is formed by the temperature difference between the top and bottom of the wafer, causing the particle removal cleaning solution to flow along the inner wall of the high aspect ratio structure from the bottom to the top of the wafer.

[0006] In this paper, "high aspect ratio" generally refers to a structure with an aspect ratio greater than 5:1, but it is not a limitation on the aspect ratio. In existing technologies, the larger the aspect ratio, the more difficult the cleaning becomes. This invention has significant advantages for cleaning high aspect ratio structures. The "top" of the wafer refers to the upper surface of the wafer, i.e., the surface where the opening of the high aspect ratio structure is located. The "bottom" of the wafer refers to the lower surface of the wafer, i.e., the surface opposite to the upper surface. Typically, the lower surface of the wafer is in contact with the heating device used for heating, and heat is conducted from the bottom to the top of the wafer. The "top" and "bottom" in this paper are not used to limit the wafer structure, but are used to facilitate the description of the temperature difference formation path between the top and bottom of the wafer.

[0007] In this article, reciprocating breathing flow refers to the periodic back-and-forth movement of liquid within a high aspect ratio structure / deep trench, caused by the periodic injection of liquid. Periodic spraying refers to a spray direction that is usually fixed, but the flow rate or pressure changes periodically over time; for example, there may be a period of no spraying between two spraying treatments. The formation process of reciprocating breathing flow includes: (1) Spraying stage: The nozzle injects high-speed liquid into the trench, pushing the existing liquid in the trench forward; (2) Retreat / re-inhalation stage: When the spraying stops or the pressure drops, due to the recovery of the pressure in the trench, some liquid will retreat along the original path or around the path, forming an exhalation effect. Periodic repetition: With the periodic opening and closing of the spray, the liquid continuously undergoes a reciprocating motion of pushing and pulling within the trench.

[0008] This invention utilizes the principle of fluid resonance renewal. A first oxidizing cleaning solution is used for periodic liquid spraying, creating a localized resonant flow (reciprocating breathing flow) within the high aspect ratio structure / deep trench, promoting periodic fluid replacement at the bottom of the trench. This periodic fluid replacement reduces bubble adhesion within the trench, allowing the chemical solution, such as the first oxidizing cleaning solution, to re-contact the bottom of the high aspect ratio structure / deep trench. The first oxidizing cleaning solution fills pits and defects within the high aspect ratio structure through oxidation and loosens residual particles on the surface. A heat-driven convection mechanism is also utilized; as the temperature increases, the surface tension of the liquid decreases. Heating the wafer while simultaneously applying a particle removal cleaning solution for a second spray treatment creates a temperature difference between the top and bottom surfaces of the wafer. This temperature difference forms a surface tension gradient, driving the liquid, such as the particle removal cleaning solution, to flow along the wall, achieving spontaneous liquid renewal and effectively removing residual particles within the high aspect ratio structure / deep trench.

[0009] Step two, the process of ensuring the top temperature of the wafer is lower than the bottom temperature of the wafer, includes: controlling the temperature of the wafer through a heating device, and reducing the top temperature of the wafer through the processing temperature of the second spray treatment. The maximum temperature difference is the difference between the bottom temperature of the wafer and the temperature of the chemical solution itself. Chemical solution spraying on the front of the wafer provides the top temperature, and the temperature difference is not fixed.

[0010] The process also includes step three, drying the high aspect ratio structure using dynamic alternating rinsing, which involves alternating spraying of isopropanol and water. By alternating spraying of isopropanol (IPA) and deionized water (DIW), a surface tension difference is created, which is then used to generate a capillary suction effect (surface tension suction mechanism) to achieve liquid self-drainage and drying.

[0011] Between steps one and two, a process is included where the high aspect ratio structure is sprayed with a diluted hydrofluoric acid solution to remove the oxide layer formed after the first oxidizing cleaning solution treatment in step one. The first oxidizing cleaning solution treatment forms a thin oxide layer on the wafer surface and the surface of the high aspect ratio structure, which is then removed using a diluted hydrofluoric acid solution (DHF).

[0012] In the diluted hydrofluoric acid solution, the volume ratio of hydrofluoric acid to water is 1:(100-200), and the solution temperature is 20-25℃. In step two, the particle removal cleaning solution is SC1 solution, in which the volume ratio of ammonia, hydrogen peroxide, and water is 1:2:(25-50).

[0013] In step two, the spraying time of the particle removal cleaning solution is 30-90 seconds. If the spraying time is too long or the spray flow rate is too high, it will increase the temperature difference, i.e., the difference between the temperature at the bottom and top of the wafer. The spraying time of the diluted hydrofluoric acid solution is 10-20 seconds.

[0014] In step one, the first oxidizing cleaning solution is an ozone aqueous solution, wherein the volume concentration of ozone dissolved in the water is 20ppm-30ppm, and the solution temperature is 20-25℃.

[0015] In step one, the total spraying time for the first spraying treatment is 15-45 seconds, with the first spraying cycle being 5-15 seconds and the interval between two sprays being 0.2-0.8 seconds. During spraying, the wafer rotates at high speed, and a reasonable spraying interval range is set to prevent the sprayed solution from drying on the wafer surface. A reasonable spraying time is set according to relevant processes to allow the wafer surface to reach a stable state.

[0016] The wafer is selected from one of silicon wafers, silicon carbide wafers, or gallium nitride wafers.

[0017] The present invention also provides an application of a high aspect ratio cleaning method in the pre-cleaning process of the oxide layer of a shallow trench isolation liner. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of fluid dead zones and particle retention during the cleaning process of high aspect ratio structures in existing technologies; Figure 2 This is a schematic flowchart of a cleaning method for high aspect ratio structures provided by the present invention; Figure 3 This is a schematic diagram of the first spray treatment performed by the first oxidizing cleaning solution in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the particle removal cleaning solution undergoing a second spray treatment and wafer heating in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the shallow trench isolation to be processed in Embodiment 2 of the present invention.

[0020] Figure reference numerals: 1-Wafer; 2-High aspect ratio structure; 3-Heating device; 4-Pad oxide layer; 5-Silicon nitride layer. Detailed Implementation

[0021] The technical solutions in specific embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that, in order to describe the technical solution more specifically, the steps described in the following embodiments do not strictly correspond one-to-one with the steps described in the invention content section.

[0023] Example 1

[0024] A cleaning method for high aspect ratio structures, see [link to relevant documentation]. Figure 2 A wafer 1 with a high aspect ratio structure 2 is provided, wherein the aspect ratio of the high aspect ratio structure is greater than 5:1. In this embodiment, the thickness of the wafer 1 is 775±25um. In this embodiment, the wafer 1 is selected from one of silicon wafers, silicon carbide wafers, or gallium nitride wafers, specifically silicon wafers. This embodiment uses a single-wafer cleaning machine to clean the wafer, and also includes the following steps: Step 1: The high aspect ratio structure 2 is subjected to a first spray treatment using a first oxidizing cleaning solution. In this embodiment, the first oxidizing cleaning solution is an ozone aqueous solution. In other embodiments, other chemical solutions with similar oxidizing properties that can fill pits can also be selected. The ozone aqueous solution (OZW) is a solution of ozone dissolved in deionized water (DIW). The volume concentration of ozone dissolved in the water is 20ppm-30ppm, and the solution temperature is 20-25℃. A first spray cycle is set, and the high aspect ratio structure 2 is periodically (intermittently) sprayed according to the first spray cycle, forming a reciprocating breathing flow within the high aspect ratio structure 2. The total spray duration of the first spray treatment is 30 seconds, of which the first spray cycle is 10 seconds, and the interval between two spray treatments is 0.5 seconds. Pre-oxidation is performed using an ozone aqueous solution to smooth out pit defects in the high aspect ratio structure 2 / deep trench and loosen residual particles on the surface of the high aspect ratio structure 2. See [link to relevant documentation]. Figure 3 The reciprocating breathing flow within the grooves can also be used to remove air bubbles and residue.

[0025] In this embodiment, the high aspect ratio structure 2 is further sprayed with a diluted hydrofluoric acid solution (DHF). The volume ratio of hydrofluoric acid to water in the diluted hydrofluoric acid solution is 1:100, and the solution temperature is 20-25°C. The spraying time of the diluted hydrofluoric acid solution is 15 seconds. The thin oxide layer is etched by the diluted hydrofluoric acid solution (DHF) to remove the thin oxide layer generated after the treatment with the first oxidizing cleaning solution in step one.

[0026] Step 2: The high aspect ratio structure 2 is subjected to a second spray treatment using a particle removal cleaning solution. In this embodiment, the particle removal cleaning solution is SC1 solution, in which the volume ratio of ammonia, hydrogen peroxide, and water is 1:2:50. The spraying time of the particle removal cleaning solution is 60 seconds. Simultaneously with or before the second spray treatment, the wafer 1 is heated by a heating device 3, such as a heating plate. The temperature of the heating plate can be adjusted according to the power. The top temperature of the wafer 1 is lower than the bottom temperature of the wafer 1. The temperature of the wafer 1 is controlled by the heating device 3, and the top temperature of the wafer 1 is reduced by the processing temperature of the second spray treatment. The processing temperature of the second spray treatment, i.e., the top temperature range of the wafer 1, is, for example, 20-65℃, and the bottom temperature range of the wafer 1 can be 25-70℃. The temperature difference is not fixed, as long as the temperature control of the heating device 3 is kept higher than the temperature control of the chemical solution treatment. The surface tension gradient is created by the temperature difference between the top and bottom of wafer 1, causing the particle removal cleaning fluid to flow along the inner wall of the high aspect ratio structure 2 from the bottom to the top of the wafer. This temperature difference from bottom to top creates a surface tension gradient, driving the liquid to flow along the wall and achieving spontaneous liquid renewal, further renewing the fluid at the bottom of the high aspect ratio structure 2. See also... Figure 4 , Figure 4 The high temperature mentioned only represents the relative high temperature at the bottom of the wafer. Figure 4 The low temperature mentioned only refers to the relatively low temperature at the top of the wafer and does not imply a specific temperature value.

[0027] Example 2

[0028] A cleaning method for a high aspect ratio structure is identical to steps one and two of Example 1. It further includes step three: drying the high aspect ratio structure 2 using dynamic alternating rinsing. This dynamic alternating rinsing involves alternating sprays of isopropanol and water, with the isopropanol and water alternating 2-8 times. By alternating sprays of isopropanol (IPA) and deionized water (DIW), a surface tension difference is created. This surface tension difference generates a capillary suction effect (surface tension suction mechanism), achieving liquid self-drainage and drying. The process is ultimately completed using Marangoni drying.

[0029] Example 3

[0030] The application of a high aspect ratio cleaning method provided in Example 1 or Example 2 in the pre-cleaning process of the oxide layer of a shallow trench isolation (STI) gasket. See also Figure 5Several high aspect ratio structures 2, i.e., deep trenches, are formed on the wafer 1 as shallow trench isolation. These shallow trench isolations are used to form electrical isolation structures between different transistors on the chip. A pad oxide layer 4 and a silicon nitride layer 5 are sequentially formed in a flat area of ​​the wafer 1 (not within the high aspect ratio structures 2 / not within the trenches). After etching the high aspect ratio structures 2 / deep trenches, a thin layer of silicon dioxide (SiO2) is grown or deposited inside the high aspect ratio structures 2 / deep trenches as a pad oxide layer. This pad oxide layer serves as a stress buffer layer for subsequent fillers and a substrate to improve interface quality. Before depositing the pad oxide layer, the surface of the wafer 1 is wet-cleaned or dry-cleaned to remove etching residues, native oxide layers, particles, and metal contaminants, ensuring that the subsequent pad oxide layer deposition is uniform, clean, and well-bonded. In the shallow trench isolation process, before depositing the liner oxide layer, the high aspect ratio structure 2 / deep trench and wafer 1 are cleaned using a cleaning method for high aspect ratio structures provided in Example 1 or Example 2 to ensure the quality and reliability of the isolation structure.

[0031] The innovative mechanism of this invention lies in employing multiple mechanisms, such as fluid resonance renewal to achieve periodic fluid replacement at the bottom, utilizing temperature differences to create a surface tension gradient that drives liquid flow along the wall, and alternating spraying of isopropanol and water to create a surface tension suction mechanism. These mechanisms work synergistically to enable dynamic breathing of the liquid within the high aspect ratio structure 2 / deep trench, improving both fluid renewal rate and particle removal efficiency. Specifically, this invention utilizes a single-piece cleaning machine to dynamically clean the trench with multiple liquids, creating a periodic breathing effect within the high aspect ratio structure 2 / deep trench through periodic liquid switching, combined with temperature difference control, thereby improving fluid renewal rate and particle removal efficiency. It is applicable to single-piece wet cleaning machines used in advanced node processes such as 28nm, 40nm, and 55nm.

[0032] The above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A cleaning method for high aspect ratio structures, characterized in that, Providing a wafer with a high aspect ratio structure, further comprising the following steps: Step 1: The high aspect ratio structure is subjected to a first spray treatment using a first oxidizing cleaning solution. A first spray cycle is set, and the high aspect ratio structure is periodically sprayed according to the first spray cycle to form a reciprocating breathing flow within the high aspect ratio structure. Step 2: The high aspect ratio structure is subjected to a second spray treatment using a particle removal cleaning solution. The wafer is heated so that the temperature of the top of the wafer is lower than that of the bottom of the wafer. The surface tension gradient is formed by the temperature difference between the top and bottom of the wafer, causing the particle removal cleaning solution to flow along the inner wall of the high aspect ratio structure from the bottom to the top of the wafer.

2. The cleaning method for a high aspect ratio structure according to claim 1, characterized in that, In step two, the process of making the top temperature of the wafer lower than the bottom temperature of the wafer includes: controlling the temperature of the wafer by a heating device, and reducing the top temperature of the wafer by the processing temperature of the second spray treatment.

3. The cleaning method for a high aspect ratio structure according to claim 1, characterized in that, It also includes step three, drying the high aspect ratio structure by using dynamic alternating rinsing, wherein the dynamic alternating rinsing includes alternating spraying of isopropanol and water.

4. The cleaning method for a high aspect ratio structure according to claim 1, characterized in that, Between step one and step two, the high aspect ratio structure is sprayed with a diluted hydrofluoric acid solution to remove the oxide layer generated after the first oxidizing cleaning solution treatment in step one.

5. The cleaning method for a high aspect ratio structure according to claim 4, characterized in that, In the diluted hydrofluoric acid solution, the volume ratio of hydrofluoric acid to water is 1:(100-200), and the solution temperature is 20-25℃; in step two, the particle removal cleaning solution is SC1 solution, and in the SC1 solution, the volume ratio of ammonia, hydrogen peroxide and water is 1:2:(25-50).

6. The cleaning method for a high aspect ratio structure according to claim 4, characterized in that, In step two, the spraying time of the particle removal cleaning solution is 30-90 seconds; the spraying time of the diluted hydrofluoric acid solution is 10-20 seconds.

7. The cleaning method for a high aspect ratio structure according to claim 1, characterized in that, In step one, the first oxidizing cleaning solution is an ozone aqueous solution, wherein the volume concentration of ozone dissolved in the water is 20ppm-30ppm, and the solution temperature is 20-25℃.

8. The cleaning method for a high aspect ratio structure according to claim 7, characterized in that, In step one, the total spraying time of the first spray treatment is 15-45 seconds, of which the first spraying cycle is 5-15 seconds and the interval between two sprays is 0.2-0.8 seconds.

9. The cleaning method for a high aspect ratio structure according to claim 1, characterized in that, The wafer is selected from one of silicon wafers, silicon carbide wafers, or gallium nitride wafers.

10. The application of a high aspect ratio cleaning method according to any one of claims 1-9 in the pre-cleaning process of the oxide layer of a shallow trench isolation liner.

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