Method for cleaning a wafer having high aspect ratio structures

Abstract

The application provides a wafer cleaning method with high aspect ratio structure, comprising the following steps: providing a closed first cleaning tank; lowering the wafer to be cleaned in a vertical state at a speed lower than 3mm / s until it is completely immersed in deionized water in the first cleaning tank, the wafer surface has a high aspect ratio structure, and IPA gas is sprayed to the wafer surface during the lowering process; turning the wafer to a horizontal state in the deionized water, and then pulling it up to make the wafer separate from the water surface of the deionized water; transferring the wafer to a second cleaning tank, immersing the wafer in an aqueous cleaning solution, turning the wafer to a vertical state for cleaning; and transferring the cleaned wafer to a drying tank for drying. The application can realize the cleaning of multiple wafers at a time, can significantly improve the cleaning efficiency, has the advantages of simple operation and low cost, and the like. In addition, the adverse effects caused by capillary force can be reduced, and the collapse of the aspect ratio structure can be avoided.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a cleaning method for wafers with a high aspect ratio structure. Background Technology

[0002] With the continuous development of the semiconductor industry, integrated circuits are gradually moving towards higher integration and ultra-fine linewidth. As a result, there are more and more high aspect ratio structures involved in the chip manufacturing process (in the semiconductor industry, structures with a depth / height to width ratio greater than 1 are generally defined as high aspect ratio).

[0003] High aspect ratio structures present significant challenges not only during etching and deposition but also in post-etching cleaning. On one hand, current mainstream cleaning methods remain water-based wet cleaning, which struggles to penetrate the bottom of the trenches to achieve proper cleaning for these micro / nano structures with small openings but great depths. On the other hand, once the cleaning liquid enters the deep trenches, it is difficult to remove due to surface tension, leaving contaminant residues that pose a potential threat to subsequent processes and can even lead to device failure. Furthermore, capillary forces present during the drying process of these high aspect ratio structures can also cause them to collapse, resulting in device failure.

[0004] There are generally three existing cleaning methods for improving high aspect ratio structures: single-wafer cleaning (see the scheme disclosed in patent application CN201510282159.1), megasonic cleaning (see the scheme disclosed in patent application DOI:10.13290), and dry cleaning (see the scheme disclosed in patent application CN201510543852.X). However, each of these methods has its own problems. For example, single-wafer cleaning involves spraying and immersing a low-surface-tension solution onto the surface of a single silicon wafer, followed by spraying deionized water for cleaning, and then drying. This method cannot utilize a cleaning tank and suffers from low cleaning efficiency and high cleaning solution consumption. Megasonic cleaning utilizes the enormous kinetic energy generated by megasonic waves to achieve a cleaning effect, but this method is prone to wafer damage and still struggles to address the problem of contaminant residue in deep trenches. Dry cleaning, on the other hand, suffers from low cleaning efficiency and residue problems. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a cleaning method for wafers with high aspect ratio structures, which solves the various deficiencies of existing cleaning methods for high aspect ratio structures, such as contaminants remaining in the high aspect ratio structure, and capillary forces during the drying process that may cause the high aspect ratio structure to collapse, thereby leading to device failure.

[0006] To achieve the above and other related objectives, the present invention provides a cleaning method for a wafer with a high aspect ratio structure, comprising the following steps:

[0007] A closed first cleaning tank is provided, the first cleaning tank contains deionized water, the surface of the deionized water is covered with an IPA membrane and the first cleaning tank is in an IPA atmosphere;

[0008] The wafer to be cleaned is lowered vertically at a speed of less than 3 mm / s until it is completely immersed in the deionized water of the first cleaning tank. The wafer surface has a high aspect ratio structure. During the descent, IPA gas is sprayed onto the wafer surface.

[0009] The wafer is flipped into a horizontal position in deionized water so that the high aspect ratio structure opening of the wafer faces upward, and then pulled upward to remove the wafer from the surface of the deionized water.

[0010] After transferring the wafer to the second cleaning tank and immersing it in the cleaning solution, the wafer is flipped to a vertical position for cleaning.

[0011] The cleaned wafers are then transferred to a drying tank for drying.

[0012] Optionally, the wafer descends at a speed of 1 to 1.5 mm / s during the descent of the first cleaning tank.

[0013] Optionally, the wafer is dried using the Marangoni drying method, and the drying tank and the first cleaning tank are of the same type.

[0014] Optionally, the cleaning solution includes one or more of DHF, SC1, SC2, SPM, and EKC.

[0015] Alternatively, IPA gas is loaded onto nitrogen and sprayed onto the wafer surface.

[0016] Optionally, during the wafer cleaning process, diffusion or ultrasonic oscillation is used to allow the cleaning solution to enter the high aspect ratio structure of the wafer.

[0017] Optionally, the wafer is immersed in deionized water in the first cleaning tank and then left to stand for 5 seconds to 1 minute.

[0018] Optionally, the high aspect ratio structure includes multiple deep trenches, the aspect ratio of which is greater than or equal to 5.

[0019] Optionally, during the cleaning process, the wafers are placed on a tray, and multiple wafers are placed on the tray at the same time.

[0020] Optionally, one or two batches of wafers may be placed on the tray at the same time.

[0021] As described above, the cleaning method for wafers with high aspect ratio structures of the present invention has the following beneficial effects: The cleaning method of the present invention effectively reduces capillary height by reversing the Marangoni drying method, allowing the cleaning solution to easily and fully penetrate the bottom of the high aspect ratio structure, thereby improving the cleaning effect of the high aspect ratio structure. The present invention facilitates the use of a tank cleaning system, thus enabling the cleaning of multiple wafers in a single operation, significantly improving cleaning efficiency. Furthermore, the cleaning process does not require the use of surfactants or other chemical reagents, and does not introduce new pollution (including contamination of the wafer itself and environmental pollution from waste liquid), offering advantages such as simple operation and low cost. In addition, it can reduce the adverse effects of capillary forces, preventing the collapse of the high aspect ratio structure. Attached Figure Description

[0022] Figure 1 The flowchart shown is a process for cleaning a wafer with a high aspect ratio structure provided by the present invention.

[0023] Figure 2-6 The diagram shows the operation of each step in the cleaning method for wafers with a high aspect ratio structure provided by the present invention.

[0024] Figure 7 This diagram illustrates the wetting state of a high aspect ratio structure during wafer cleaning using conventional methods.

[0025] Figure 8 The diagram shows the wetting state of a high aspect ratio structure when the cleaning method provided by this invention is used for wafer cleaning.

[0026] Component designation explanation

[0027] 1 First cleaning tank

[0028] 11 Deionized water

[0029] 2 wafers

[0030] 21. High aspect ratio structure

[0031] 3 Second cleaning tank

[0032] 4. Drying tank Detailed Implementation

[0033] The following specific examples illustrate the embodiments 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 be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. For ease of explanation, when detailing the embodiments of the present invention, the cross-sectional views showing the device structure are partially enlarged, not according to the general scale, and the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. Furthermore, in actual manufacturing, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0034] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0035] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0036] 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 illustrations only show 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. To keep the illustrations as concise as possible, not all structures are shown in the figures.

[0037] As device feature sizes shrink and chip integration increases, structures such as trenches are becoming increasingly dense and have larger aspect ratios during device manufacturing. Traditional cleaning techniques, such as single-wafer cleaning, megasonic cleaning, and dry cleaning, all have various problems when used to clean these high aspect ratio structures. The inventors of this application have proposed an improved solution through extensive research over a long period of work.

[0038] Specifically, such as Figure 1 As shown, the present invention provides a cleaning method for a wafer with a high aspect ratio structure, the cleaning method comprising the following steps:

[0039] S1: A closed first cleaning tank 1 is provided, which contains deionized water. The surface of the deionized water is covered with an IPA membrane, and the first cleaning tank 1 is in an IPA atmosphere. For example, a closed IPA tank containing an IPA (isopropanol) solution is connected to the first cleaning tank 1, which has been pre-filled with a certain amount of deionized water (DIW), through a gas pipeline. An inert gas (such as nitrogen, which acts as a carrier gas) is continuously introduced into the IPA tank, so that the IPA solution enters the gas pipeline under the action of gas pressure to form IPA gas. The IPA gas is loaded onto the inert gas and enters the first cleaning tank 1. The inert gas can be preheated to avoid the IPA gas from liquefying and settling in the gas pipeline during the process of being transported to the first cleaning tank. After the IPA gas is transported to the first cleaning tank 1, it uniformly covers the surface of the deionized water with an IPA membrane, and the first cleaning tank 1 is filled with an IPA atmosphere.

[0040] S2: The wafer 2 to be cleaned is lowered vertically at a speed of less than 3 mm / s until it is completely immersed in the deionized water of the first cleaning tank 1. The surface of the wafer 2 has a high aspect ratio structure 21. During the descent, IPA gas is sprayed onto the surface of the wafer 2. Specifically, several wafers 2 (which can be single or multiple wafers, preferably multiple wafers 2 being cleaned simultaneously, such as 25 wafers in a single batch or 50 wafers in two batches, which can greatly improve cleaning efficiency and improve inter-wafer uniformity) can be vertically fixed on a bracket. The bracket drives the wafers 2 to move vertically downwards, immersing the wafers 2 slowly and uniformly into the deionized water, while simultaneously spraying the carrier gas. The IPA carried by a gas (such as nitrogen) is on the surface of wafer 2. Due to the difference in surface tension between IPA and DIW (the surface tension of DIW is greater than that of IPA (IPA surface tension is 22 mN / m while that of DIW is 72 mN / m), under the same temperature conditions, the surface tension of IPA is about one-third that of DIW. Therefore, the capillary height is also about one-third that of DIW. Thus, this step can effectively reduce the capillary height, allowing DIW to slowly wet wafer 2, especially the high aspect ratio structure 21, thereby achieving the effect of completely filling the high aspect ratio structure 21. A schematic diagram of this step is shown below. Figure 2 and Figure 3 As shown;

[0041] S3: After wafer 2 is fully immersed in DIW, rotate wafer 2 90 degrees so that it is horizontal in the deionized water, with the opening of the high aspect ratio structure 21 facing upwards. Then, lift it upwards to remove wafer 2 from the deionized water surface. A schematic diagram of this step is shown below. Figure 4 As shown; during this process, IPA gas can be continuously introduced into the first cleaning tank 1 to maintain the IPA atmosphere in the first cleaning tank 1, and at the same time, it can prevent the wafer 2 from being oxidized and contaminated during the process of removing deionized water.

[0042] S4: Wafer 2 is then transferred to the second cleaning tank 3 and immersed in the cleaning solution (preferably an aqueous cleaning solution, i.e., miscible with water). Wafer 2 is then flipped to a vertical position for cleaning. After the preceding steps, the high aspect ratio structure 21 is completely filled with deionized water and is fully wetted. During the cleaning process, the cleaning solution effectively diffuses to the bottom of the high aspect ratio structure 21 to achieve the cleaning effect. Of course, to further improve the cleaning quality, in this step, an ultrasonic device or other similar device can be installed on the second cleaning tank 3 (at the bottom or outside of the tank) to transmit the cleaning solution to the high aspect ratio structure 21 of wafer 2 through diffusion or ultrasonic vibration. Simultaneously, the vibration promotes the decomposition and removal of impurities on the surface of wafer 2, thereby thoroughly cleaning wafer 2, including the interior of the high aspect ratio structure 21. A schematic diagram of this step is shown below. Figure 5 As shown;

[0043] S5: Finally, the cleaned wafer 2 is transferred to the drying tank 4 for drying. In this embodiment, as an example, this step uses the Marangoni drying method to dry the wafer 2, that is, the drying tank 4 is a Marangoni drying tank 4. In other words, the drying tank 4 and the first cleaning tank 1 are the same type of equipment. Considering that the cleanliness of the wafer 2 before and after cleaning is very different, in order to avoid cross-contamination, the drying step and the wetting step are preferably not performed in the same tank. The operation diagram of this step is shown below. Figure 6 As shown. Although the same type of equipment is used as in step S2, while step S2 involves slowly lowering the wafer 2 to be cleaned into deionized water for wetting and pre-cleaning, this step involves slowly lifting the cleaned wafer 2 upwards (or by slowly draining water) to remove the wafer 2 from the surface of the deionized water. Since the surface tension of IPA is much lower than that of water, a surface tension gradient will be formed on the surface of the sloping water flow during the upward lifting of the wafer 2, generating Marangoni convection. The water is "drawn back" to the water surface, thereby removing the moisture in the high aspect ratio structure 21 and achieving a drying effect.

[0044] The cleaning method of this invention effectively reduces capillary height by reversing the Marangoni drying process, allowing the cleaning solution to fully penetrate the bottom of the high aspect ratio structure 21, thereby improving the cleaning effect of the aspect ratio structure. This invention facilitates tank cleaning, enabling the cleaning of multiple wafers 2 in a single operation, significantly improving cleaning efficiency. Furthermore, the cleaning process does not require the use of surfactants or other chemical reagents, avoiding the introduction of new contamination (including contamination of the wafers 2 themselves and environmental pollution from waste liquid), and offers advantages such as simple operation and low cost.

[0045] To ensure a good cleaning effect while also considering cleaning efficiency, as an example, the descent speed of wafer 2 in the first cleaning tank 1 is 1–1.5 mm / s, so that the deionized water can fully contact wafer 2 and enter the aspect ratio structure. If the Marangoni drying method is used in the drying step, the upward pulling speed of wafer 2 can also be used.

[0046] As an example, the cleaning solution preferably includes, but is not limited to, one or more of the following: DHF (diluted hydrofluoric acid solution), SC1 (a mixed solution of ammonia, hydrogen peroxide, and water), SC2 (a mixed solution of hydrochloric acid, hydrogen peroxide, and water), SPM (e.g., a solution prepared by mixing 98% H2SO4 and 30% H2O2 in a 4:1 volume ratio), and EKC (a mixed solution with hydroxylamine, catechol, etc. as active ingredients). This means that a single cleaning solution can be used to clean wafer 2 in a single operation, or multiple cleaning solutions can be used sequentially to clean wafer 2. Of course, the cleaning solution is not limited to the above-mentioned types; any cleaning reagent used in the semiconductor field after etching can be applied to this invention. Since the aforementioned steps have sufficiently wetted and pre-cleaned the high aspect ratio structure of the wafer, subsequent cleaning steps using any conventional cleaning method will achieve the effect of improving cleaning quality.

[0047] To ensure that deionized water fully enters the high aspect ratio structure 21, as an example, the wafer 2 is immersed in the deionized water in the first cleaning tank 1 and then left to stand for 5 seconds to 1 minute, preferably 5 seconds to 10 seconds.

[0048] As an example, the high aspect ratio structure 21 includes multiple deep trenches with an aspect ratio greater than or equal to 5. Of course, the cleaning method of the present invention is also applicable to the cleaning of general wafers 2 (i.e., trenches with an aspect ratio less than 5), but the advantages of the present invention are more prominent when used for cleaning wafers 2 with a high aspect ratio structure 21.

[0049] The inventors verified the cleaning method of the present invention. Specifically, when a wafer 2 with a high aspect ratio is placed in a deionized water bath without any treatment using a conventional cleaning method, according to the capillary formula:

[0050]

[0051] Where h is the capillary height, σ is the surface tension, θ is the contact angle, Δρ is the density difference between the liquid and gas, and R is the capillary radius. Because deionized water has a relatively large surface tension, it also has a relatively large capillary height. This makes it difficult for deionized water 11 to completely fill the high aspect ratio structure 21 (such as a deep tank), thus forming a cleaning blind zone at the bottom of the deep tank (i.e., the cleaning solution cannot enter this area and therefore cannot perform cleaning). The schematic diagram is shown below. Figure 7As shown. Simultaneously, capillary forces present during the subsequent drying process may also cause these high aspect ratio structures 21 to collapse, leading to device failure. Using the cleaning method of this invention, the wafer 2 is first immersed in deionized water 11 containing an IPA atmosphere. The IPA is used to wet the wafer 2, especially the inner surface of the high aspect ratio structures 21. Utilizing the principle that the surface tension of IPA is much lower than that of deionized water, after wetting, the deionized water 11 can gradually penetrate into the aspect ratio structure until it is completely filled. This process is as follows: Figure 8 As shown. Therefore, in the subsequent cleaning process, the aqueous cleaning solution can penetrate to the bottom of the depth-to-width ratio structure to achieve a thorough cleaning effect, and can reduce the adverse effects of capillary force, thus preventing the collapse of the high depth-to-width ratio structure.

[0052] In summary, this invention provides a cleaning method for wafers with high aspect ratio structures, comprising the steps of: providing a closed first cleaning tank containing deionized water, the surface of which is covered with an IPA film and the first cleaning tank is in an IPA atmosphere; lowering the wafer to be cleaned vertically at a speed of less than 3 mm / s until it is completely immersed in the deionized water of the first cleaning tank, the wafer surface having a high aspect ratio structure, and spraying IPA gas onto the wafer surface during the descent; flipping the wafer in the deionized water to a horizontal position so that the opening of the high aspect ratio structure faces upward, and then lifting it upward to remove the wafer from the surface of the deionized water; transferring the wafer to a second cleaning tank and immersing it in an aqueous cleaning solution, then flipping the wafer to a vertical position for cleaning; and transferring the cleaned wafer to a drying tank for drying. The cleaning method of this invention effectively reduces capillary height by reversing the Marangoni drying method, allowing the cleaning solution to easily and fully penetrate the bottom of the high aspect ratio structure, thereby improving the cleaning effect of the high aspect ratio structure. This invention facilitates the use of a tank-type cleaning system, enabling the cleaning of multiple wafers in a single operation and significantly improving cleaning efficiency. Furthermore, the cleaning process eliminates the need for surfactants or other chemical reagents, preventing the introduction of new contamination (including wafer contamination and environmental pollution from waste liquid), and offers advantages such as simple operation and low cost. In addition, it reduces the adverse effects of capillary forces, preventing the collapse of aspect ratio structures. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0053] 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 cleaning method for wafers with a high aspect ratio structure, characterized in that, Including the following steps: A closed first cleaning tank is provided, the first cleaning tank contains deionized water, the surface of the deionized water is covered with an IPA membrane and the first cleaning tank is in an IPA atmosphere; The wafer to be cleaned is lowered vertically at a speed of less than 3 mm / s until it is completely immersed in the deionized water of the first cleaning tank. The wafer surface has a high aspect ratio structure. During the descent, IPA gas is sprayed onto the wafer surface. The wafer is flipped into a horizontal position in deionized water so that the high aspect ratio structure opening of the wafer faces upward, and then pulled upward to remove the wafer from the surface of the deionized water. After transferring the wafer to the second cleaning tank and immersing it in the cleaning solution, the wafer is flipped to a vertical position for cleaning. The cleaned wafer is then transferred to a drying tank for drying. The cleaning solution includes one or more of DHF, SC1, SC2, SPM, and EKC. During the cleaning process, the wafers are placed on a tray, and multiple wafers are placed on the tray at the same time.

2. The cleaning method according to claim 1, characterized in that, During the descent of the wafer in the first cleaning tank, the descent speed is 1 to 1.5 mm / s.

3. The cleaning method according to claim 1, characterized in that, The wafer is dried using the Marangoni drying method, and the drying tank and the first cleaning tank are of the same type.

4. The cleaning method according to claim 1, characterized in that, IPA gas is loaded onto nitrogen and sprayed onto the wafer surface.

5. The cleaning method according to claim 1, characterized in that, During the wafer cleaning process, diffusion or ultrasonic oscillation is used to allow the cleaning solution to penetrate the high aspect ratio structure of the wafer.

6. The cleaning method according to claim 1, characterized in that, After immersing the wafer in the deionized water of the first cleaning tank, let it stand for 5 seconds to 1 minute.

7. The cleaning method according to claim 1, characterized in that, The high aspect ratio structure includes multiple deep trenches, and the aspect ratio of the deep trenches is greater than or equal to 5.

8. The cleaning method according to claim 1, characterized in that, One to two batches of wafers are placed on the tray at the same time.

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