Wafer cleaning method

Abstract

According to the wafer cleaning method provided by the invention, a slot position of a baffle wafer is reserved in a wafer carrier, and the baffle wafer is placed at the top of wafers stacked in batches; the separation blade wafer is a smooth silicon wafer, the separation blade wafer is covered with a corrosion buffer coating, ultrasonic wave is used for assisting in cleaning when the wafers stacked in batches are put into a cleaning tank for cleaning, the corrosion buffer coating is slowly dissolved to react with active ingredients in cleaning liquid, the metal corrosion rate of the wafers stacked in batches is reduced, and the corrosion resistance of the wafers stacked in batches is improved. While the wafer cleaning effect is ensured, the damage of a metal layer deposited in the wafer is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor manufacturing, and in particular relates to a wafer cleaning method. Background Art

[0002] Wafer manufacturing involves multiple steps: deposition, photolithography, etching, and ion implantation. Each step can introduce contaminants, such as residual photoresist and oxides left behind during photolithography. If these contaminants are not cleaned promptly, they can affect subsequent processes and, in severe cases, cause device shorts, disconnections, or even instability.

[0003] Traditional wafer cleaning methods mostly rely on wet cleaning, but this is inefficient. To improve wafer cleaning efficiency, existing technologies use supercritical fluid cleaning or ultrasonic-assisted cleaning to remove various contaminants. However, the cleaning fluid itself is acidic and corrosive to wafers, especially those with deposited metal layers, which are particularly sensitive to such corrosion. In existing technologies, ultrasonic cleaning can exacerbate the corrosion of the metal layer, causing damage, impacting device performance, and even creating the risk of short circuits.

[0004] In order to ensure cleaning efficiency, it is necessary to develop a method for wafer cleaning that can effectively protect the metal layer in the wafer. Summary of the Invention

[0005] The present invention provides a wafer cleaning method, which reduces damage to a metal layer deposited in the wafer while ensuring a wafer cleaning effect.

[0006] Other purposes and advantages of the present invention can be further understood from the technical features disclosed in the present invention.

[0007] In order to achieve one or part or all of the above-mentioned purposes or other purposes, a technical solution of the present invention provides a wafer cleaning method, in which a slot for a baffle wafer is reserved in a wafer carrier, and the baffle wafer is placed on top of a batch of stacked wafers; ultrasonic assisted cleaning is used when the batch of stacked wafers is placed in a cleaning tank for cleaning.

[0008] The baffle wafer is covered with a corrosion buffer coating, which slowly dissolves and reacts with active components in the cleaning tank to reduce the metal corrosion rate of the batch stacked wafers.

[0009] The corrosion buffer coating includes the following raw materials in the following mass percentages: 80%-90% polyvinyl alcohol, 5%-10% polyethylene glycol, 3%-5% crosslinking agent and 1%-3% nano-silicon dioxide; the cleaning liquid in the cleaning tank includes tetramethylammonium hydroxide, citric acid, ethylenediaminetetraacetic acid, polyoxyethylene ether surfactant and deionized water.

[0010] The polyoxyethylene ether surfactant in the cleaning solution includes any one of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether; and the cross-linking agent in the corrosion buffer coating is borax.

[0011] The corrosion buffer coating is deposited on the baffle wafer by a spin coating method, including: dissolving the active component in the cleaning solution in deionized water at 55°C-65°C to obtain a spin coating mixed solution, maintaining a spin coating speed of 500 rpm for 10s-12s to spread the spin coating mixed solution on the wafer, and spinning at a speed of 2000rpm-2800rpm for 30s-35s. After the spin coating is completed, it is maintained at 80°C for 3min-3.5min to form a cross-linked film.

[0012] The thickness of the corrosion buffer coating is 10 μm-50 μm. When the baffle wafer participates in a single wafer cleaning, the corrosion buffer coating dissolves more than 95%. After a single cleaning, the baffle wafer is recovered and re-covered with the corrosion buffer coating.

[0013] After the baffle wafer participates in multiple wafer cleanings, if the thickness of the baffle wafer body decreases by more than 10%, the baffle wafer is replaced.

[0014] When the number of wafers in a single batch exceeds the number of remaining slots after the reserved baffle wafer slots in the wafer carrier, the batch of wafers is divided into batches, and multiple wafer carriers are used to perform the same cleaning operation on the batched wafers, and a baffle wafer is placed on the top of each batch of stacked wafers.

[0015] An infrared counter is installed on the wafer transmission path to count the number of batch wafers to be cleaned; an optical slot detector is installed on the top or side wall of the wafer carrier to count the slot occupancy in the wafer carrier, and a slot reserved for the baffle wafer is subtracted from the statistics; based on the number of batch wafers counted by the infrared counter and the number of remaining slots in the wafer carrier counted by the optical slot detector, a decision is made whether to clean the batch wafers in batches, and the batch wafers to be cleaned in batches are divided into equal proportions and placed in the same cleaning tank for cleaning, or placed in different cleaning tanks for cleaning using the same cleaning steps and cleaning parameters.

[0016] After deciding to divide into batches, the stacked wafers in the same batch are divided into master batches and sub-batches. Serial numbers are established for the wafers in both the master batch and sub-batch, where the serial number of the sub-batch is associated with the serial number of the master batch. The serial numbers of the master batch and sub-batch include batch information of the stacked wafers, information of the wafer carrier, and process parameter information. During wafer circulation, the wafers are managed according to the serial numbers.

[0017] Compared with the prior art, the beneficial effects of the present invention mainly include: the present invention reserves a slot for placing a baffle wafer in the wafer carrier, and the baffle wafer can block the cleaning liquid from directly scouring the batch of wafers during wafer cleaning, and can also reduce ultrasonic vibration and thus reduce the damage of ultrasonic waves to the wafers; at the same time, the corrosion buffer coating pre-deposited on the baffle wafer can neutralize the active substances in the cleaning liquid in the cleaning liquid, and the dissolution of the corrosion buffer coating gradually decreases with time. When combined with ultrasonic cleaning, the dissolved corrosion buffer coating is neutralized with the active substances in the cleaning liquid, and the neutralization of the active substances by the corrosion buffer coating gradually decreases with time. The corrosion effect of the cleaning liquid on the metal layer can be greatly reduced at the beginning of cleaning. By appropriately extending the cleaning time, the cleaning effect is guaranteed while also having a good protective effect on the metal layer.

[0018] In order to make the above and other objects, features and advantages of the present invention more clearly understood, preferred embodiments are given below with reference to the accompanying drawings for detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a comparison chart of wafer metal corrosion rates in Examples 1, 2, 3, and 4 of the present invention. DETAILED DESCRIPTION

[0021] The foregoing and other technical aspects, features, and functions of the present invention are clearly presented in the following detailed description of a preferred embodiment with reference to the accompanying drawings. Directional terms such as up, down, left, right, front, and back, used in the following embodiments, are intended solely to refer to the directions in the accompanying drawings. Therefore, the directional terms used are for illustrative purposes only and are not intended to limit the present invention.

[0022] Example 1

[0023] A first embodiment provides a wafer cleaning method. A slot is reserved in a wafer carrier for a barrier wafer, which is placed on top of a batch of stacked wafers. The barrier wafer is a smooth silicon wafer, and ultrasonic cleaning is used when the batch of stacked wafers is placed in a cleaning tank for cleaning. The barrier wafer blocks the cleaning fluid from directly rinsing the batch of wafers during cleaning, and also reduces ultrasonic vibrations, thereby minimizing damage to the wafers.

[0024] Among them, in order to further reduce the damage of the cleaning liquid to the wafer during ultrasonic cleaning, a corrosion buffer coating is covered on the baffle wafer. The corrosion buffer coating slowly dissolves and reacts with the active components in the cleaning liquid to reduce the metal corrosion rate of the batch stacked wafers.

[0025] The wafer cleaning method of the present application is described in detail below.

[0026] To mitigate damage to the metal layer deposited on the wafers caused by ultrasonic vibrations and acidic components in the cleaning solution, thereby preventing damage to devices, the present invention reserves a slot in the wafer carrier for a baffle wafer. This slot is located on top of the batch of wafers to be cleaned. The baffle wafer, also known as a dunmy wafer, is a smooth silicon wafer with no patterned structures and has not undergone any processing. Placing the baffle wafer on top of the batch of wafers prevents the cleaning solution from directly eroding the batch during ultrasonic cleaning. It also reduces ultrasonic vibrations and, consequently, damage to the wafers.

[0027] In order to further protect the wafer during the cleaning step, in Example 1, a corrosion buffer coating is covered on the surface of the baffle wafer. The corrosion buffer coating can dissolve during cleaning and react with the active substances in the cleaning liquid to neutralize part of the cleaning liquid, thereby reducing the concentration of active substances in the cleaning liquid at the beginning of cleaning. However, as time goes on, the dissolution rate of the corrosion buffer coating gradually decreases, and the active substances in the neutralized cleaning liquid also decrease. That is, at the beginning of cleaning, the corrosion of the metal layer by the active substances in the cleaning liquid can be effectively reduced. As the cleaning time increases, the content of active substances in the cleaning liquid gradually stabilizes, and the cleaning effect also gradually stabilizes. At this time, as the cleaning time is adjusted, combined with ultrasonic cleaning, not only can a better cleaning effect be achieved, but also damage to the metal layer can be reduced.

[0028] The cleaning solution includes tetramethylammonium hydroxide, citric acid, ethylenediaminetetraacetic acid, polyoxyethylene ether surfactant and deionized water. The concentration range of tetramethylammonium hydroxide is 0.1mol / L-0.5mol / L, the concentration range of citric acid is 0.05mol / L-0.2mol / L, the concentration range of ethylenediaminetetraacetic acid is 0.01mol / L-0.05mol / L, the concentration range of polyoxyethylene ether surfactant is 0.005mol / L-0.02mol / L, and the remaining solution is deionized water; the polyoxyethylene ether surfactant includes any one of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

[0029] The corrosion buffer coating comprises the following raw materials in percentage by mass: 80%-90% of polyvinyl alcohol, 5%-10% of polyethylene glycol, 3%-5% of a cross-linking agent and 1%-3% of nano silicon dioxide.

[0030] Example 1 Borax is selected as the cross-linking agent in the corrosion buffer coating.

[0031] The corrosion buffer coating is deposited on the baffle wafer by a spin coating method, including: dissolving the active component in the cleaning solution in deionized water at 55°C-65°C to obtain a spin coating mixed solution, the spin coater maintains a rotation speed of 500rpm and spins for 10s-12s to spread the spin coating mixed solution on the wafer, and spins at a rotation speed of 2000rpm-2800rpm for 30s-35s. After the spin coating is completed, it is maintained at 80°C for 3min-3.5min to form a cross-linked film.

[0032] During cleaning, the temperature of the cleaning liquid is maintained at 35℃-45℃.

[0033] As an optional embodiment, the corrosion buffer coating has a thickness of 10μm-50μm, and the corrosion buffer coating can be dissolved by more than 95% when the baffle wafer participates in a single wafer cleaning. After a single cleaning, the baffle wafer needs to be recovered and re-covered with the corrosion buffer coating. The step of re-covering the corrosion buffer coating includes pickling the baffle wafer with a 5% NHO3 solution, and performing plasma cleaning after the pickling is completed. The reaction gas for plasma cleaning is argon or oxygen. After the plasma cleaning is completed, the corrosion buffer coating is re-deposited on the baffle wafer using a spin coating method. The spin coating method for depositing the corrosion buffer coating is the same as the spin coating method for depositing the corrosion buffer coating described above, and will not be repeated here.

[0034] As an optional implementation, after the baffle wafer participates in multiple wafer cleanings, if the thickness of the baffle wafer body decays by more than 10%, the baffle wafer should be replaced. This is because the baffle wafer body will be worn out after multiple cleanings, and the thickness of the baffle wafer body will decay. If the thickness of the baffle wafer body is reduced by 10%, the baffle wafer cannot effectively reduce the corrosion of the cleaning liquid on the wafer during wafer cleaning, and is no longer suitable for wafer cleaning protection.

[0035] As an optional embodiment, when the number of wafers that need to be cleaned at a time exceeds the number of remaining slots in the wafer carrier after excluding the slots for the baffle wafers, the batch of wafers is divided into batches, and multiple wafer carriers are used to perform the same cleaning operation on the batched wafers, with a baffle wafer placed on top of each batch of stacked wafers. After the batch operation is performed, the cleaning steps and cleaning methods of the batch wafers in the same batch need to be consistent, that is, the cleaning liquid components, cleaning liquid temperature, cleaning time and ultrasonic cleaning machine power in the cleaning steps of the batch wafers in the same batch need to be kept the same.

[0036] As an optional implementation, in order to facilitate automated batch processing, the present invention uses an infrared counter installed on the wafer transmission path to count the number of wafers to be cleaned in a certain batch; an optical slot detector is installed on the top or side wall of the wafer carrier to count the slot occupancy in the wafer carrier, and a slot reserved for the placement of the baffle wafer is subtracted from the statistics; based on the number of batch wafers counted by the infrared counter and the number of remaining slots in the wafer carrier counted by the optical slot detector, it is decided whether to clean the batch wafers in batches, and the batch wafers to be cleaned in batches are processed in equal proportions and placed in the same cleaning pool for cleaning, or placed in different cleaning pools for cleaning using the same cleaning steps and cleaning parameters.

[0037] As an optional implementation method, after deciding to divide into batches, the batch stacked wafers of the same batch are divided into a master batch and a sub-batch, and serial numbers are established for the wafers of the master batch and the sub-batch, wherein the serial number of the sub-batch is associated with the serial number of the master batch (for example, if the serial number of the master batch is AAA-BB-CC, then the serial number of sub-batch 1 is AAA-BB-CC-1, and the serial number of sub-batch 2 is AAA-BB-CC-2). The serial numbers of the master batch and the sub-batch include the batch information of the stacked wafers, the information of the wafer carrier, and the process parameter information. During the wafer circulation, the wafers are managed according to the serial number. The management of wafers during circulation is to ensure that the same cleaning parameters are maintained in the cleaning steps for the wafers of the same batch, and to ensure that the cleaning steps for the wafers of the same batch are exactly the same. When the sub-batch wafers are cleaned in different cleaning pools, the cleaning process parameters of the master batch can be derived based on the sub-batch serial number, and the cleaning parameters of the sub-batch wafer cleaning pool can be set based on the cleaning process parameters of the master batch for easy management.

[0038] In Example 1, the concentrations of the cleaning solution components are as follows: 0.1 mol / L tetramethylammonium hydroxide, 0.05 mol / L citric acid, 0.01 mol / L ethylenediaminetetraacetic acid, 0.005 mol / L alkylphenol polyoxyethylene ether, and the remainder is deionized water. The polyoxyethylene ether surfactant includes fatty alcohol polyoxyethylene ether. The mass percentages of the corrosion buffer coating components in Example 1 are as follows: 85% polyvinyl alcohol, 10% polyethylene glycol, 3% borax, and 2% nanosilica. Based on the cleaning solution formula and the corrosion buffer layer on the baffle wafer, the baffle wafer and batch wafers are placed in a cleaning tank for assisted ultrasonic cleaning. The cleaning solution temperature is maintained at 35°C, and the metal corrosion rate is calculated. The metal corrosion rate is calculated by using a quartz crystal microbalance to measure the change in film thickness in real time. This method of measuring film thickness change using a quartz crystal microbalance is conventional and will not be described in detail in this example.

[0039] Example 2

[0040] The steps of the second embodiment are basically the same as those of the first embodiment, except that the mass percentages of the components of the corrosion buffer layer in the second embodiment are changed, as follows:

[0041] The polyoxyethylene ether surfactant includes fatty alcohol polyoxyethylene ether. The mass percentages of the components of the corrosion buffer coating in Example 1 are as follows: 90% polyvinyl alcohol, 5% polyethylene glycol, 3% borax and 2% nano-silicon dioxide.

[0042] Example 3

[0043] The difference between the third embodiment and the first embodiment is that no corrosion buffer layer is provided on the baffle wafer in the third embodiment.

[0044] Example 4

[0045] The difference between the fourth embodiment and the first, second and third embodiments is that the wafer carrier in the fourth embodiment does not reserve a slot for a baffle wafer, and the baffle wafer is not used during wafer cleaning.

[0046] The wafers cleaned in Examples 1 to 4 are all the same, that is, the type, number, width, and thickness of the deposited metal layers are all the same.

[0047] The metal corrosion rates of Examples 1 to 4 are as follows: Figure 1 As shown, after using the baffle wafer with the corrosion buffer coating of the present invention in Example 1 and Example 2, the corrosion rate of the metal layer in the wafer to be cleaned is significantly lower than that of the baffle wafer without the corrosion buffer layer in Example 3. It can be seen that the corrosion buffer coating in this application can effectively reduce the damage of the cleaning liquid to the metal layer deposited on the wafer. At the same time, Figure 1 The corrosion rate of the metal layer of the wafer in Example 4 which is not protected by a baffle wafer is significantly higher than the corrosion rate of the metal layer of the wafer in Example 3 which is protected by a baffle wafer. It can be seen that the setting of the baffle wafer can alleviate the damage to the metal layer of the wafer caused by direct erosion of the cleaning liquid and ultrasonic vibration to a certain extent.

[0048] The above describes in detail a wafer cleaning method provided by the present invention. This article uses specific examples to illustrate the structure and working principle of the present invention. The description of the above embodiments is only intended to help understand the method and core concept of the present invention. It should be noted that those skilled in the art may make various improvements and modifications to the present invention without departing from the principles of the present invention, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A wafer cleaning method, characterized in that: A slot for a baffle wafer is reserved in the wafer carrier, and the baffle wafer is placed on top of the batch stacked wafers; Ultrasonic cleaning is used when batches of stacked wafers are placed in a cleaning tank for cleaning.

2. A wafer cleaning method according to claim 1, characterized in that: The baffle wafer is covered with a corrosion buffer coating, which slowly dissolves and reacts with active components in the cleaning tank to reduce the metal corrosion rate of the batch stacked wafers.

3. A wafer cleaning method according to claim 2, characterized in that: The corrosion buffer coating comprises the following raw materials in percentage by mass: 80%-90% polyvinyl alcohol, 5%-10% polyethylene glycol, 3%-5% crosslinking agent and 1%-3% nano-silicon dioxide; The cleaning liquid in the cleaning tank comprises tetramethylammonium hydroxide, citric acid, ethylenediaminetetraacetic acid, polyoxyethylene ether surfactant and deionized water.

4. A wafer cleaning method according to claim 3, characterized in that: The polyoxyethylene ether surfactant in the cleaning solution includes any one of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether; The cross-linking agent in the corrosion buffer coating is borax.

5. A wafer cleaning method according to claim 3, characterized in that: The corrosion buffer coating is deposited on the baffle wafer by a spin coating method, including: dissolving the active component in the cleaning solution in deionized water at 55°C-65°C to obtain a spin coating mixed solution, maintaining a spin coating speed of 500 rpm for 10s-12s to spread the spin coating mixed solution on the wafer, and spinning at a speed of 2000rpm-2800rpm for 30s-35s. After the spin coating is completed, it is maintained at 80°C for 3min-3.5min to form a cross-linked film.

6. A wafer cleaning method according to claim 5, characterized in that: The thickness of the corrosion buffer coating is 10 μm-50 μm. When the baffle wafer participates in a single wafer cleaning, the corrosion buffer coating dissolves more than 95%. After a single cleaning, the baffle wafer is recovered and re-covered with the corrosion buffer coating.

7. A wafer cleaning method according to claim 5, characterized in that: After the baffle wafer participates in multiple wafer cleanings, if the thickness of the baffle wafer body decreases by more than 10%, the baffle wafer is replaced.

8. A wafer cleaning method according to claim 1, characterized in that: When the number of wafers in a single batch exceeds the number of remaining slots after the reserved baffle wafer slots in the wafer carrier, the batch of wafers is divided into batches, and multiple wafer carriers are used to perform the same cleaning operation on the batched wafers, and a baffle wafer is placed on the top of each batch of stacked wafers.

9. A wafer cleaning method according to claim 8, characterized in that: Use an infrared counter installed on the wafer transport path to count the number of wafers in a batch to be cleaned; Install an optical slot detector on the top or side wall of the wafer carrier to count the slot occupancy in the wafer carrier, subtracting one slot reserved for the blank wafer. Based on the number of batch wafers counted by the infrared counter and the number of remaining slots in the wafer carrier counted by the optical slot detector, it is decided whether to clean the batch wafers in batches. The batch wafers to be cleaned in batches are divided into equal proportions and placed in the same cleaning pool for cleaning, or placed in different cleaning pools for cleaning using the same cleaning steps and cleaning parameters.

10. A wafer cleaning method according to claim 9, characterized in that: After deciding to divide into batches, the stacked wafers in the same batch are divided into master batches and sub-batches. Serial numbers are established for the wafers in both the master batch and sub-batch, where the serial number of the sub-batch is associated with the serial number of the master batch. The serial numbers of the master batch and sub-batch include batch information of the stacked wafers, information of the wafer carrier, and process parameter information. During wafer circulation, the wafers are managed according to the serial numbers.

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