How to Improve Your Silicon Wet Etching Process

Semiconductor research labs and fabrication facilities employ high-precision silicon wet etching processes that are capable of delivering quality product in a consistent way. This is no mean feat: the microscopic structures etched on semiconductor wafers require processes that meet microscopic tolerances while reducing the minutest of impurities. Fabs are always on the lookout for improvements to make in these processes; the aim is to minimize the number of errors made during each of several processes. Results depend on constant efforts in the area of identifying the best etching processes, and utilizing the best equipment.

The Wafer Etching Process

The process of etching micro-circuitry on silicon wafers requires a complex multi-layered fabrication approach. It usually requires multiple cleaning, masking, and etching processes that involve the precise deposition of metal traces and components. At different stages along the way, these processes require the use of chemical baths of various kinds, each aimed at achieving different, specific results. At the end of one of these precisely designed processes, silicon wafers with traces, electrical connections and electronic components, all etched on a microscopic scale, emerge ready for market.

There are various requirements for an error-free process — precise control over the speed at which etching is done, and the ability to achieve extreme levels of cleanliness in the work areas in which etching is done, are two primary requirements. There are many others, as well.

Silicon nitride: Silicon nitride is applied to mask parts of wafers during the phosphoric acid etching process. Achieving greater precision in this process delivers superior results. In general, fabs do much better with the fabrication process when they possess over on-the-fly control over acid concentration and temperature.

Piranha etching: At semiconductor fabs, piranha etching is done using a mixture of piranha solution — a blend of hydrogen peroxide and sulfuric acid. Chemical baths need to be carefully controlled to supply the right chemical mix at the right time.

Potassium hydroxide: The etching process requires the use of potassium hydroxide solution in the creation of microscopic structures on semiconductor wafers. Achieving precise and error-free etches requires an ability to closely control the concentration of the solution, the temperature, the orientation of the silicon crystal and silicon purity. These variables can change during the etch process, and error-free results requires the ability to respond by speeding up or slowing down etch rate.

Buffered oxide etch: This is a process that employs hydrofluoric acid in addition to a buffering agent in order to etch fine masking films of silicon dioxide or silicon nitride. When correctly controlled, the process delivers a consistent and repeatable result that works with photoresist.

When it comes to improved silicon etching performance, the key to high-quality results is to utilize processing equipment from a vendor with proven experience and support. Modutek answers this requirement with 35 years in the field. Not only is Modutek able to supply the equipment, they are able to advise clients on the customizations needed to meet their requirements.

Choosing Equipment with the Right Features for Each Stage of the Wafer Etching Process

Modutek’s silicon wet etching equipment comes with some of the most advanced features on the market today:

Flow control and filtration control: Modutek’s precision acid filters are effective down to the 0.2 µm range and are able to work continuously to enable reuse of acid. This provides considerable savings in acid consumption.

Precision control of temperature: An ability to precisely control the temperature of an etching bath can result in lower error rates and reliable output. In any process, Modutek’s equipment comes with the ability to control temperatures to within 1 degree of required settings.

Precision tech design: Potassium hydroxide requires the use of Teflon tanks; piranha solution requires quartz. Modutek designs these tanks in a wide variety of configurations and sizes.

Modutek is dedicated to helping clients find ways to improve the efficiency of their silicon wet etching processes, improve productivity and output quality. To this end, Modutek’s offers extensive consultation and equipment customization needed to meet each customer’s requirements.

Determining Which Wafer Processing Station Will Meet Your Requirements

Wet bench stations come in a variety of configurations designed for different applications. It can be difficult to make a selection from the many possibilities and make sure the equipment you choose will best meet your requirements. One way to cut down on the uncertainty and to structure the selection process is to emphasize three areas where your needs have to be satisfied.

A Wafer Processing Station has to comply with the standards and regulations in effect for your operation; it has to be able to carry out the processes that you are considering; and it has to be automated in accordance with what you need. When you consider these three areas and find equipment that fulfills your requirements in each one, you will be closer to making a final selection.

Compliance with Standards

Wet bench standards aim to ensure safe operation and resistance to combustion. Modutek wet bench stations comply with the following standards:

  • NFPA 70 – National Fire Protection
  • NFPA 79 – Safety of Industrial Machinery
  • NEC – National Electrical Code
  • UL508a -Standard for Industrial Control Panels

If the equipment is to be installed outside the US, Modutek can also comply with the national standards of Europe (CE Mark), Canada (CSA) and Australia/New Zealand (AS/NZS3000). In addition to complying with these standards, Modutek can supply third party certification for compliance.

Applications

Depending on the process required, Modutek can supply the right systems and advise on the advantages of specific products from their complete line of wet bench equipment. Standard Modutek wet bench stations can support both acid and solvent processes while the stainless-steel line is designed for solvent processes such as those using acetone or IPA. Optional equipment for specific processes is also available.

Automation

Modutek offers manual, semi-automated and fully automated wet bench stations. Which best meets your requirements depends on how you plan to conduct wet process operations. A manual bench may be appropriate for low volume custom or prototype device processes. For higher volume with standard processes, a degree of automation improves your throughput and reduces human error. Modutek’s stations are all built with the same high-quality materials, but the company can supply the degree of automation that matches your needs.

Manual wet bench stations feature competitive pricing with a low total cost of ownership. Modutek can supply the benches at any size and length and to meet any wet process needs. Custom designs are possible and future expansion of the process line is easy.

Semi-automated wet bench stations include robots for uniformity of process execution without the cost of full automation. The servomotors of the robots operate with three degrees of freedom and give you precise control of etching and cleaning. The Modutek-designed software, SolidWorks Simulation Professional and SolidWorks Flow Simulation, calculates process flow. The semi-automated wet bench stations have all the features and characteristics of the manual stations but include a touch screen with a graphic user interface to control the robotics and run the process.

Fully automated wet bench stations track chemical use and ensure precise dosages and accurate process control for improved yields and excellent repeatability. The elimination of human error and fully automated control is especially important for processes with tightly packed semiconductor structures and dense circuitry. Full automation guarantees a consistent process environment that reduces defects and improves output quality.

Modutek designs, assembles and tests all robotic equipment in house and is therefore ideally situated to advise customers on solutions to meet their needs and customize equipment to fit any customer application. The company can help clearly define process requirements for their customers and then propose solutions that allow customers to determine which wafer processing station is ideal for their facility.