Etching Silicon Wafers Without Using Hydrofluoric Acid

Etching Silicon Wafers Without Hydrofluoric AcidHydrogen fluoride is an excellent etching chemical for silicon wafer fabrication, etching rapidly to remove silicon oxide, for example after an initial RCA clean. While highly effective, hydrofluoric acid is extremely dangerous. Its vapor can cause death and it is toxic enough that even a small area of skin exposed to the chemical can cause cardiac arrest. As a result, storage and handling is difficult and disposal problematic. Safety and environmental considerations have resulted in a search for alternatives. Depending on the silicon wet etching application, other chemicals may be suitable for replacing hydrofluoric acid and Modutek can help customers make the change by recommending equipment that supports alternative chemical processes.

Why Hydrofluoric Acid is Especially Dangerous

Hydrofluoric acid is extremely toxic and penetrates the skin to cause secondary effects that require medical attention. Its vapor can cause lungs to fill up with liquid and exposure to even small amounts can cause death. Neutralization and disposal is difficult and any mistakes run the risk of severe environmental contamination. Given the dangers, silicon fabrication facility owners, managers and process engineers are looking for alternative process chemicals.

While hydrofluoric acid is dangerous as a corrosive chemical, its added danger comes from its absorption into the body. It affects the nerves at sites where the skin has been exposed to the acid and victims may initially feel little pain as a result, often delaying treatment. At the same time, hydrofluoric acid can penetrate deep into the body and attack underlying tissue and bones, causing lasting damage. It also disrupts the calcium chemistry of the blood, eventually leading to cardiac arrest. Exposure of as little as 25 square inches of skin can result in deep burns that are slow to heal and in death if medical treatment is delayed.

Bare skin and the eyes are the most common areas of exposure. Treatment starts with extensive rinsing, for about 15 minutes, of the exposure site. Repeated application of calcium gluconate gel helps mitigate the effect on blood calcium. Anyone with more than four square inches of skin exposed should be admitted to hospital for monitoring of blood chemistry. Normal safety measures to avoid contact with hydrofluoric acid are to cover all skin and wear eye protection.

Hydrofluoric acid is hazardous waste and its discharge is tightly regulated. The acid must first be neutralized and then discharge limits on fluoride and metals must be observed. A complete neutralization process often starts with adding a basic solution to the acid and then precipitating out other materials until they fall within discharge limits. After discharge, the resulting sludge represents an additional waste problem. While other chemicals may be subject to similar discharge procedures, hydrofluoric acid represents an additional risk if neutralization is not carried out properly.

Possible Alternative Etching Solutions

Depending on the particular silicon wet etching application, other etchants may be substituted for hydrofluoric acid. Potassium hydroxide (KOH) is a safer chemical and can be used for etching in many applications.  Tetramethylammonium hydroxide (TMAH) and nitride etch are other possible alternatives that may be used.

Modutek can help facilitate a switch from hydrofluoric acid where possible. The company has over 35 years experience with silicon wafer fabrication equipment and has the in house expertise to advise customers about possible alternatives.

In addition to analyzing customer process needs and making recommendations, Modutek can supply the equipment required from their complete line of wet bench and chemical delivery stations. Modutek’s equipment, while able to handle hydrofluoric acid, is also designed to work with other chemical processes that don’t use it. Modutek can offer standard or customized components such as Teflon tanks or quartz baths to help customers wishing to use other chemicals where they can. Contact Modutek for a free consultation and quote on selecting the right equipment to support the silicon wet etching process for your application.

Improving Process Control with Fully Automated Wafer Fabrication Equipment

Improving Process Control with Fully Automated Wafer Fabrication EquipmentAn increasing number of silicon wafer fabrication applications, such as those with large size substrates or densely packed components, require tight process control. Accurate chemical dosage and precise process timing become critical for a high-quality output. Manual and semi-automatic controls depend on operator training and reliable operator execution of instructions, leaving open the possibility of human error and a variation in how process steps are carried out. Fully automated wet benches and chemical stations can improve process control accuracy and help with consistent execution. Software can help calculate process variables and ensure correct dosages. Full automation of the wafer fabrication process with the use of software for process control and robotics for wafer handling can result in better repeatability, reduced waste and improve production line performance.

Advantages of Modutek’s Fully Automated Wafer Fabrication Equipment

Modutek designs, develops and manufactures its wafer fabrication equipment in house to the highest quality standards. The SolidWorks Simulation Professional and SolidWorks Flow Simulation software are developed and supported in house by Modutek’s technical personnel. As a result, Modutek has the expertise to determine what is needed to meet the requirements of a specific customer’s application. It can supply standard wet bench chemical stations or customized equipment to exactly meet the needs of its customers, tailoring its equipment and software to fit any special process control requirements.

To satisfy customer requirements, Modutek can draw upon its complete line of wafer fabrication equipment. Its wet benches and chemical stations can handle both solvent and acid applications, and the equipment can process sizes up to 30 inches by 60 inches. Its software can run simulations, calculate chemical dosage and track chemical use. With its in-house expertise, Modutek can offer unparalleled customer support and comprehensive after sales service.

Benefits of Fully Automated Wafer Processing Equipment

Full automation means that the process is set up and can then run repeatedly in exactly the same way without requiring any operator input. Key factors for improved process control are accurate chemical dosage, precise timing of process steps, exact replication of the process sequence and full neutralization of chemical waste. Because operation of the automated program is transparent and recorded, technical personnel can optimize the individual steps to minimize chemical use and reduce waste. Process times can be adjusted to take into account special features of the application and results can be monitored for potential problems.

When the process automation is fully optimized, consumption of chemicals is reduced. Process output stays constant, the number of defective products is lower and the products are of consistently high quality. There are fewer spills and dosage errors while employee safety is higher. Compliance with environmental regulations in terms of chemical use and discharge is easier because chemical consumption is tracked at all times and the neutralization of discharges is ensured. The process environment is consistent and the optimized process can be repeated reliably.

As a result, wafer fabrication facilities that implement full automation experience lower costs due to reduced chemical use. Yield and throughput increase while output quality remains consistent and high. Production line performance and productivity improve and facility profitability can rise.

How Modutek Can Help

With over 35 years experience in wet bench process and wafer fabrication equipment, Modutek can evaluate a customer’s process needs and offer standard equipment or customized solutions as appropriate. Their engineers can work closely with each customer to identify what is required and ensure that the equipment works as expected. Modutek’s fully automated stations are an excellent choice for reliable and technologically advanced solutions to challenging wafer fabrication requirements. If you need highly reliable wafer fabrication equipment to support your semiconductor manufacturing process call Modutek for a free consultation at 866-803-1533 or email [email protected].