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Using RCA Clean in a Wet Bench Process

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Using RCA Clean in a Wet Bench ProcessEditor’s Note: This article was originally published in May 2015 and has been updated with new information and re-posted in August 2023.

The semiconductor manufacturing industry relies heavily on complex and precise processes to create electronic components we rely on every day. One such process is wafer cleaning – an essential step that removes unwanted particles or residue from silicon wafer surfaces that could otherwise compromise product quality or reliability. RCA Clean has been established as an industry standard wafer cleaning process due to its effectiveness in removing both organic and inorganic contaminants from silicon wafer surfaces.

RCA clean is a wet chemical process developed at Radio Corporation of America that involves a series of sequential steps. The objective is to prepare wafer surfaces for further processing while maintaining their integrity, an aim that aligns directly with the needs of Process Engineers.

Process Engineers focus on cost efficiency, reliability and cleanliness, and equipment design for precise process control. Equipment must be easy to use and deliver repeatable processes while meeting specific demands of a facility’s wet processes requirements.

Understanding RCA Clean in a Wet Bench Process

At its core, RCA Clean is a three-step cleaning process aimed at effectively cleaning silicon wafers.  Each step addresses different types of contaminants, such as organic residues, thin layers of native oxide, and finally, ionic contamination.

In the first stage of RCA cleaning, commonly referred to as Standard Clean 1 (SC-1), the mixture consists of:

  • 1 part NH4OH (ammonium hydroxide)
  • 1 part H2O2 (hydrogen peroxide)
  • 5 parts deionized (DI) water.

The SC-1 solution efficiently removes organic residues while simultaneously creating a thin silicon dioxide coating to provide additional protection to the wafer surface. The second step is to rinse with deionized water to remove the SC-1 solution.

Next, a dip into hydrochloric acid and deionized water mixture removes the thin oxide layer formed during Step One. Following this, the Standard Clean 2 (SC-2) begins. This mixture consists of:

  • 1 part HCl (hydrochloric acid)
  • 1 part H2O2 (hydrogen peroxide)
  • 5 parts DI water

This step helps remove metallic ions and again forms a thin silicon dioxide layer. The process concludes with another rinse and final dip into deionized water heated to 80°C to remove any remaining residuals.

RCA Clean is essential when it comes to achieving cleanliness, consistency, and process control in semiconductor manufacturing. However, the effectiveness of RCA Clean depends on the reliability of the equipment being used. This means using equipment that effectively supports RCA clean and ensures accurate and repeatable results for process engineers.

How Wet Bench Stations Facilitate RCA Clean

Modutek’s wet bench stations have been carefully designed to enhance the RCA clean process and alleviate some of the challenges Process Engineers encounter. Their design places particular importance on chemical compatibility, cleanliness, control, and safety – essential characteristics for successful wafer cleaning.

The wet bench stations at Modutek builds use materials resistant to the chemicals used in the RCA clean process. This ensures that the equipment remains unaffected by the cleaning solutions, allowing for an uninterrupted process and a longer lifespan.

As for cleanliness, Modutek’s stations are designed to minimize particle contamination. Their design limits air movement and deposition of particulate matter. Additionally, all wet bench station components, including process tanks, are designed for easy cleaning, ensuring optimal cleanliness at all times.

Modutek’s stations feature advanced automation capabilities for process control. These automated systems offer high-precision control over process variables like temperature, cleaning time, and concentration of cleaning solutions. This ensures accurate and repeatable RCA clean results while saving time and minimizing human errors. Process Engineers can use this level of oversight to achieve their desired results consistently while saving time and avoiding human mistakes.

The wet bench stations Modutek provides incorporate numerous safety features that promote maximum protection during semiconductor manufacturing processes.  This includes chemical-resistant materials, fire suppression systems, safety interlocks, and emergency power-off capabilities.

One way that Modutek’s wet bench systems use to facilitate the RCA clean process is through their temperature control system. For instance, for optimal cleaning results in the RCA Clean process, the SC-1 and SC-2 solutions must be maintained at specific temperatures to work effectively. Modutek’s wet bench stations have been specifically designed to precisely control the temperature of solutions, ensuring an optimal cleaning process.

Incorporating Megasonic Cleaning with RCA Clean

To further enhance the results of an RCA clean process, the use of Megasonic cleaning can be instrumental. Megasonic cleaning utilizes high-frequency sound waves in a liquid medium to generate microscopic cavitation bubbles. When these microscopic bubbles collapse, they create strong local shockwaves that efficiently dislodge and remove contaminants from silicon wafer surfaces. Megasonic cleaning combined with the RCA process can significantly enhance the silicon wafer cleaning process, offering the precision necessary for creating high-quality semiconductor devices with microscopic geometries.

Modutek’s wet bench systems are designed to incorporate Megasonic cleaning seamlessly. Wet process equipment with Megasonic capabilities can operate at multiple frequencies, allowing Process Engineers to optimize the cleaning process for their specific requirements. This provides optimal particle removal, improved cleanliness, and higher yield without damaging wafers or creating defects. With the integration of Megasonic cleaning, Modutek’s wet bench systems provide a better-optimized solution for wafer cleaning.

Cost Efficiency and Ease of Use with Modutek’s Wet Bench Stations

While cleanliness and process control are essential to Process Engineers, cost efficiency and ease of use should be considered when selecting equipment for wet bench processes. Modutek’s wet bench stations are designed with the end user in mind. They provide high-quality, reliable results at an exceptional value proposition. Modutek recognizes the importance of cost control for semiconductor manufacturing facilities and offers solutions that enhance productivity while reducing the total cost of ownership.

The robust construction and quality of Modutek’s wet bench stations extend their lifespan, meaning fewer replacement costs over time and reduced frequency of replacements. Furthermore, their precise control enables businesses to reduce waste while improving yield for higher profits and increased profitability.

Modutek’s wet bench stations are also designed for maximum operator convenience. The intuitive user interface and clear control parameters enable Process Engineers and equipment technicians to master operations quickly, reducing the learning curve and training time. This easy operation also reduces human errors that could otherwise result in costly process defects.

In addition, Modutek stands behind its products by offering top-tier customer service and maintenance support. This helps facilities maintain productivity with minimal downtime for their equipment. Modutek is dedicated to ensuring minimal equipment downtime to maximize productivity for customers. Modutek also provides on-site service, technical support, and spare parts to address any potential issues promptly and effectively.

Conclusion

The need for meticulous and consistent wafer cleaning in semiconductor manufacturing is paramount, and the RCA clean method, combined with Megasonic cleaning, provides an effective solution for ensuring optimal cleanliness. However, the success of these processes relies heavily upon the equipment utilized.

Modutek’s wet bench systems are carefully designed with precision, ease of use, and cost efficiency in mind, making them an ideal choice for the RCA cleaning process. They address key requirements and challenges faced by Process Engineers, such as chemical compatibility and effective process controls, as well as providing safety and maintenance support.

For Process Engineers seeking reliable, effective, and easy-to-use solutions for their wet process requirements, Modutek provides leading-edge solutions. With a strong track record and expert service, Modutek is a trusted name in the semiconductor manufacturing industry. Contact Modutek to schedule a free consultation to discuss your wafer cleaning process requirements.

Why Pre-Diffusion Cleans Are Essential for Silicon Wafer Processing

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Why Pre-Diffusion Cleans Are Essential for Silicon Wafer ProcessingSilicon wafers must be completely clean before they go through the diffusion process. If contaminating particles are present on the wafer surfaces during the diffusion process, they will cause defects in the final semiconductor product. Pre-diffusion cleaning can be carried out with several methods. RCA clean and Piranha etch use chemicals to strip away wafer contamination. Megasonic cleaning uses high-frequency sound waves to dislodge surface contaminants and particles. No matter which cleaning method is chosen, cleaning must be done to reduce contaminating particle counts to a minimum. An experienced manufacturer of wet process stations can integrate the required cleaning methods into wet benches. They can then ensure that the silicon wafers are cleaned thoroughly.

RCA Clean is a Common Silicon Wafer Cleaning Method

RCA clean was originally developed at the RCA corporation and remains a popular all-round silicon wafer cleaning method. It consists of two parts: Standard Clean 1 and 2 (SC1 and SC2). SC1 removes organic material but leaves metallic contamination behind. SC2 cleans the remaining metallic particles and produces a completely clean wafer.

The SC1 cleaning bath contains a solution of ammonium hydroxide and hydrogen peroxide. The cleaning bath is heated to about 75 degrees centigrade, and the wafers are immersed for 10 to 15 minutes. All organic matter and many insoluble contaminants are removed, but some metallic ions stay attached to the wafer surface.

The metallic ions are removed during the SC2 cleaning step. The wafers are placed into a solution of hydrochloric acid and hydrogen peroxide. The solution is heated to about 75 degrees centigrade, and the wafers are immersed for about 10 minutes. Once the wafers are rinsed with deionized water and dried, they are ready for the diffusion processing steps.

Piranha Etch Quickly Cleans Heavy Contamination

When silicon wafers are heavily contaminated or need to be stripped of photoresist from previous process steps, a Piranha mixture is often used to begin the wafer cleaning process. The mix of sulfuric acid and hydrogen peroxide quickly removes large amounts of mainly organic contaminants. While it works more rapidly than RCA clean, it operates at an elevated temperature of 130 to 180 degrees centigrade and is hard to control precisely. Modutek’s proprietary “bleed and feed” process control improves process stability. The advanced controls allow for more precise temperature settings and better cleaning performance while maintaining the rapid removal of contaminants.

Megasonic Cleaning Provides Improved Removal of Contaminating Particles

Megasonic cleaning uses high-frequency sound waves in the cleaning bath to dislodge light contamination from wafer surfaces. The cleaning method features reduced use of toxic and expensive chemicals while reducing particle counts to a minimum. Even the smallest sub-micron particles can distort diffusion and cause defects in the final semiconductor product. These tiny particles are especially difficult to remove because they tightly adhere to wafer surfaces due to static charge and surface tension. Megasonic cleaning generates microscopic bubbles in the cleaning solution. When these bubbles collapse, the resulting scrubbing action removes the particles.

Modutek’s Wet Benches Support Pre-Diffusion Cleans for Specific Wafer Processing Requirements

Modutek wet process stations support all standard silicon wafer cleaning methods. Pre-diffusion cleans can be integrated into a wet bench to satisfy specific customer requirements. Since Modutek designs and builds equipment in-house, wet bench stations can be customized to meet specific customer needs. Based on its in-house expertise, Modutek can recommend solutions for wafer processing and propose equipment from its complete line of wet process stations. Once the equipment is built and delivered, Modutek can provide continuous customer support for the supplied stations. Contact Modutek for a free consultation to discuss your specific process requirements.

The Importance of Pre-Diffusion Cleans in Silicon Wafer Cleaning

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The Importance of Pre-Diffusion Cleans in Silicon Wafer CleaningWhen wafer cleaning immediately prior to diffusion is effective, semiconductor manufacturing output is of high quality and the defect rate is reduced. A major pre-occupation of pre-diffusion cleaning is the removal of microscopic particles from the surface of the silicon wafer. Particles can prevent even diffusion and may themselves be diffused into the silicon, causing defects.

Silicon wafer cleaning can be carried out in chemical baths or with megasonic cleaning systems. Several cleaning steps using different processes are sometimes required to get a specific level of cleanliness. The goal is to obtain wafers free from metallic or organic contamination and with as few surface particles as possible. As silicon microstructures are designed with smaller elements and with a higher component density, adequate wafer cleaning becomes more and more critical.

RCA Clean Uses Two Steps to Remove Organic and Metallic Contamination

RCA clean uses ammonium hydroxide, hydrogen peroxide and hydrochloric acid to remove surface contaminants from the silicon wafer. In the Standard Clean 1 (SC1) process, the wafers are placed in a mixture of ammonium hydroxide and hydrogen peroxide. The corrosive mixture removes organic matter but may leave metal ions behind.

In the Standard Clean 2 (SC2) process, the remaining metallic traces are removed by immersing the wafers in a mixture of hydrochloric acid and hydrogen peroxide. At the end of the RCA wafer cleaning process, organic and metallic contamination has been removed while as many remaining particles as possible are rinsed away as well.

Piranha Clean Removes Heavy Organic Contamination

When wafers are heavily contaminated with organic materials such as photo resist, the Piranha process cleans more quickly than RCA clean. The wafers are immersed in a mixture of sulfuric acid and hydrogen peroxide and the mixture may be heated to speed up the reaction. The piranha clean process hydroxilates the wafer surface, making it hydrophilic. This affinity for water is sometimes a useful feature for additional cleaning measures.

Megasonic Cleaning Removes Contaminants and Particles

Megasonic cleaning avoids the use of corrosive chemicals and is especially effective for dislodging microscopic particles from the wafer surface. The Megasonic process works by generating high-frequency sound waves in the cleaning bath. An ultrasonic generator produces the high-frequency electronic signal and a transducer converts the signal into sound waves that travel through the cleaning solution. The sound waves create tiny cavitation bubbles that produce a scrubbing action against the wafer surface. The action of the bubbles cleans the wafer.

Microscopic contaminating particles adhere to the wafer and are difficult to remove. With integrated circuits featuring increasingly smaller geometries, even the tiniest particles can cause defects. Megasonic silicon wafer cleaning operates in the frequency range near or above 1 MHz and the cavitation bubbles agitate the cleaning solution at the operating frequency. Such agitation breaks the bond holding the particle on the wafer surface and the floating particles can be rinsed away.

Modutek Wet Bench Equipment Supports Pre-Diffusion Cleaning Methods

RCA, Piranha and Megasonic cleans are commonly used in pre-diffusion clean, but each fabrication facility optimizes for its own sequence of semiconductor manufacturing processes. A production line may use one or several cleaning methods, and may have special requirements for production parameters such as size, temperature or timing.

Modutek designs and builds its own complete line of wet bench equipment and can advise customers on choosing the best processing stations for their applications. Ideal solutions often require extensive customization to optimize yield and reduce costs to a minimum. Modutek can provide custom solutions including pre-diffusion cleans, and can design new equipment for integration into the customer’s manufacturing line to meet specific wafer processing requirements.