Improved Process Control with Modutek’s Silicon Nitride Wet Etching Bath

Improved Process Control with Modutek's Silicon Nitride Wet Etching BathWith over 30 years of experience in the design and manufacturing of silicon wet etching equipment, Modutek has recently introduced their series Nb silicon nitride etch baths, an upgrade to their previously available series Na. The new series features improved process control resulting in greater flexibility and better safety. The Nb series benefits include uniform nitride etching, smooth chemical boiling control, and remote DI water metering.

Silicon nitride etching takes place in a fluid that is 85% phosphoric acid and 15% DI water. The acidic solution boils at 160 degrees C, resulting in some water boiling off as steam. The Modutek Nb series etch bath includes a condenser that returns some of the steam back to the bath, but water has to be added to the bath to replace the steam that escapes.

Adding water to acid can be hazardous, but Modutek has developed a safe procedure to add the required water to the acid bath. When water is added to a viscous liquid such as phosphoric acid, the water stays on top of the acid. As more water is added, a sudden reaction can occur when the water mixes with the acid. Instead, the Modutek bath adds small amounts of water to the acid solution when the liquid is boiling. The boiling action ensures that the water to replace losses through steam is immediately mixed into the solution and avoids sudden large reactions.

To ensure that the acid solution is always boiling, the bath heater is on when the bath is operating. The bath solution remains at the boiling point, and the operation of the heater does not have to be controlled. Instead, the temperature controller monitors the temperature to determine when to add water to the bath.

The boiling point of the bath solution varies with the concentration of the acid. As the solution loses water through the escape of steam, the boiling point increases. The temperature controller detects the increase in temperature and adds a small amount of water to restore the concentration of the acid solution. In this way, the temperature controller uses the temperature of the boiling solution to maintain the bath concentration at its set point.

Because keeping the solution boiling is critical to the process and for safety, the Modutek silicon wet etching bath includes additional monitoring to detect boiling. A thermocouple located above the surface of the liquid activates an interlock if there is no hot steam over the solution. The interlock cuts power to the water valve and prevents water from being added when the bath solution is not boiling. The same interlock activates when the lid of the bath is off because the loss of steam and heat can cause the solution to stop boiling.

Additional safety interlocks are provided by thermocouples that detect bath overtemperature and tank overtemperature. The former activates an interlock to shut off the heaters when the bath temperature exceeds 170 degrees C, indicating there is a problem with the water supply, the set points, or the acid solution itself. The latter shuts off the heaters when the tank overheats, for example, if an empty tank is switched on.

Modutek’s silicon nitride etching baths which use etched foil resistance heaters, PVDF or Teflon condensers with safety covers, a heat-up rate of 2 to 3 degrees C per minute, and process temperature control of plus/minus 0.5 degrees C. The benefits of this design include accurate nitride etching control with good nitride etching uniformity, chemical boiling control without bumping, easy installation with remote metering, and a high level of safety.

To learn more about the Silicon Wet Etching products sold by Modutek, or to learn how our products can be redesigned to work with your Nitride Etch Baths or Quartz Baths and Sub Ambient Systems (BOE), contact us at 866-803-1533 or email to discuss your requirements and get a free quote.

How the IPA Vapor Dryer Improves Wafer Processing Time

How the IPA Vapor Dryer Improves Wafer Processing TimeImproving silicon wafer processing time and yields in a consistent and repeatable process is an on-going need among semiconductor manufacturers. Modutek’s customizable IPA Vapor Dryer design addresses the needs of facilities and process engineers who are constantly looking for ways to improve their manufacturing process. Modutek partners with your engineers to build an IPA Vapor Dryer that matches your specific requirements using SolidWorks Flow Simulation and Simulation Professional software. This system provides improved operations and drying time with one or two 150-450mm cassettes or glass substrates. For reliable performance, Modutek does not outsource the design and manufacturing of their wafer processing equipment. Equipment design, assembly, and DI water testing all occur on-site at our San Jose facility.

IPA Vapor Dryer Design

Combine rinsing and drying chambers using the Modutek IPA Vapor Dryer. This Marangoni drying system uses a single chamber to simplify the final stages in your cleaning process. Choose a freestanding cabinet or seamless integration into your current wet bench. Surface tension drying with stationary parts perfectly accommodates modern, flat substrates. In addition, potential wafer breakage and damage are essentially eliminated. This advanced system serves as your one-stop shop for IC, solar cell, fuel cell, MEMS and disk drives.

System Advantages

The IPA Vapor Dryer achieves high throughput with a variety of features and benefits. For maximum yield, our systems eliminate watermarks on substrates and hydrophilic/hydrophobic films with no feature damage. The system also provides 15-minute batch drying for most applications. In addition there is a secure system interface bottle change for quick, deck-level operations. Here, one-gallon IPA containers fill under level sensor protection. IPA consumption decreases through even vapor distribution at the top of the chamber.

Additional safety features include:

  • Overtemp protection on all heated devices
  • Teflon tubing for all wet plumbing
  • High/low flow cascade rinse
  • Touch screen interface

Optional features include:

  • Dump rinse
  • Resistivity monitor

Reliable Silicon Wafer Processing Equipment

Optimizing wafer production processes for over 30 years, Modutek supplies industry-trusted, custom wet processing equipment. Our experienced engineers and system integration specialists configure stations and software to minimize existing wet bench alterations and meet company-specific requirements. For extended customer satisfaction, all IPA Vapor Dryer stations come with a 2-year warranty. If malfunction occurs, we provide onsite service repair to minimize costs and potential production loss.

Call 866-803-1533 or email to get answers to any questions about your specific requirements. Our team is ready to provide you with the right wafer processing equipment and support you need.