How High Temperature Quartz Tanks Improve Silicon Wafer Processing

How High Temperature Quartz Tanks Improve Silicon Wafer ProcessingThe silicon wafer processing steps that include etching or cleaning the wafers with aggressive chemicals require tanks to hold the chemical process. Quartz tanks are impervious to the acids and bases used in wet process stations and the high temperature tanks can include heating and re-circulating. Modutek is a leader in the design and manufacture of high temperature quartz tanks and has over 30 years of experience in this field. As a result, Modutek quartz tanks are designed specifically for wet process etching and cleaning applications and reduce contamination to a minimum while ensuring precise heating for accurate process control.

Key Quartz Tank Characteristics for Silicon Wafer Processing

Silicon wafer processing involves etching the wafers to produce microscopic structures and cleaning the wafers in preparation for further process steps. Corrosive chemicals such as hydrochloric acid, sulfuric acid and hydrogen peroxide are used for the etching and cleaning process. Tanks made of quartz are not affected by these aggressive chemicals because quartz is a crystalline material made up of silicon and oxygen atoms held tightly in a crystal lattice. Semiconductor-grade quartz such as used in the Modutek quartz tanks is especially pure, reducing the possibility of contamination.

In addition to resisting corrosion by aggressive chemicals, quartz tanks are stable at high temperatures. Some etching processes work better at temperatures up to 180 degrees centigrade and the quartz crystal lattice remains intact at much higher temperatures. Modutek quartz tanks are designed to take advantage of the chemical and temperature stability of the quartz tanks to provide an ideal vessel for containing the silicon wafer etching and cleaning processes.

The Importance of Reduced Contamination

The use of high-purity flame-polished quartz in silicon wafer processing tanks ensures that there are few non-quartz substances in the crystal lattice and on the polished surface of the tanks. The possibility of contamination by the tanks is reduced to a minimum. Such contamination of the silicon wafers can affect the semiconductor products made from the wafers.

The functionality of semiconductor components relies of microscopic structures and current paths created on the silicon wafer. When a tiny particle or other contaminant interferes with the etching of these structures, the final semiconductor product may be defective or of inferior quality. The rejection rate for finished semiconductor products is heavily influenced by the presence of particles or other contaminants. Reducing the particle count by using high-quality quartz tanks reduces the number of defective components and increases output quality.

Why Precise Temperature Control Gives Improved Process Results

Depending on the chemicals used, a higher temperature may increase the etch rate and reduce processing times. While a high etch rate may be desirable, the amount of etching that takes place still has to be tightly controlled because the amount of etching determines the size and shape of the microscopic structures in the silicon. On the one hand, exactly the right amount of etching has to take place before the process finishes, and on the other hand, if the same process is run again, the amount of etching has to be the same.

The two main factors influencing the etch rate are chemical concentration and temperature. Modutek’s process controls ensure that the right chemical concentration is maintained and the quartz tank temperature controls keep the process at exactly the right temperature. Modutek’s quartz tank temperature controller can keep the temperature constant within plus/minus 1 degree centigrade for precise etching control and excellent repeatability from one batch to the next.

For improved silicon wafer processing, process tanks have to be free of contamination and have to accurately reproduce process conditions. With Modutek’s high temperature quartz tanks, reduced contamination during etching and cleaning of silicon wafers is ensured and the temperature controls of the tanks provide precise settings during the process and for subsequent batches.

How Quick Dump Rinsers Improve Silicon Wet Etching Results

Manufacturing lines in semiconductor fabrication facilities and research labs use corrosive chemicals to clean and etch silicon wafers. Depending on the semiconductor product, a silicon wafer may undergo multiple steps in baths containing chemicals such as hydrochloric acid or hydrogen peroxide. When the cleaning or etching process in a particular fabrication step is complete, the chemicals must be rinsed from the wafer before the silicon wafer can be processed further. Quick Dump Rinsers provide a quick and effective way of thoroughly rinsing the wafers without introducing new contaminants.

How Quick Dump Rinsers Work

Once wafers are placed into the rinser, powerful jets spray de-ionized water over the wafers to remove all traces of chemicals. As the rinse tank fills up, chemical residue and contaminating particles are flushed out and rise to the surface. A nitrogen gas bubbler system serves to agitate the de-ionized water further, removing additional contaminants from the surface of the wafers. An overflow weir allows the surface water to flush the chemicals and particles out of the tank. When the rinsing process is complete, the quick dump door at the bottom of the tank opens and the water drains out in a matter of seconds.

The key characteristics of a Quick Dump Rinser are rapid operation, complete removal of contaminants and avoiding the addition of new contamination. Rapid operation helps reduce the use of de-ionized water and saves process time. If traces of chemicals are not completely removed, etching of the wafer might continue and result in defective or low quality products. The same is true if particles are not eliminated or are added during the rinse. Since rinsing has to be carried out at the end of many process steps, Rinser performance is critical for product output quality.

Modutek’s DR Series Quick Dump Rinser Features

Modutek’s Quick Dumps Rinsers are designed to meet the needs of advanced semiconductor fabrication. Wet process semiconductor manufacturing facilities and research labs can use the Modutek rinsers as stand-alone units or integrated into a wet process manufacturing line. The rinsers work quickly and deliver completely clean wafers. They incorporate the following features:

  • Contoured vessel design
  • Nitrogen bubbler on all models
  • Natural polypropylene or PVDF (option) tanks, nozzles and fittings
  • Large machined dump door without gaskets or seals
  • 360 degree overflow weir

Modutek’s design minimizes de-ionized water consumption and reduces rinse times while ensuring effective rinsing. The tanks require a de-ionized water supply, a source of pressurized nitrogen and a 120 or 24 V AC power supply. Options include a reclaim system, Teflon nozzles, fittings and valves, and special process cover configurations. The rinsers are available in a variety of sizes.

How Modutek’s DR Series Rinsers Improve Silicon Etching Results

Semiconductor manufacturing makes use of ever smaller microstructures and circuit connections. During wet etching of the silicon wafers, even a tiny particle can block a circuit path or deform microstructure design. Modutek’s rinsers are designed and constructed to avoid particle contamination.

The contoured vessel and machined trap door avoid entrapment of particles in corners or in cracks around seals and gaskets. The nitrogen bubbler helps dislodge any particles remaining on the surfaces of the silicon wafers. The 360 degree overflow weir gets rid of contaminants in the surface water quickly and the polypropylene material avoids the addition of metallic particles from fittings.

Modutek’s DR Series Quick Dump Rinsers are state-of-the-art process rinsing modules that work quickly and rinse completely. Used together with wet bench stations from Modutek’s extensive line of silicon wet etching equipment they can deliver exceptional performance for semiconductor manufacturing facilities and research labs. Contact Modutek for a free consultation on selecting the best equipment that will meet your manufacturing requirements.

Improving Wafer Processing with Automated Equipment

Fully and semi-automated wafer processing equipment can help improve wafer output quality by providing consistent chemical processing dosages and timing, however these settings must be first be determined. One way to find optimal process settings is to operate in manual and then in semi-automated mode where settings can easily be adjusted. This is especially true of new process development where the exact parameters are not known. Wafer fabrication facilities can first try out initial settings in manual mode and tweak or “fine tune” them to obtain the desired output. Using semi-automated stations to run the parts of the process that are finalized while making additional adjustments gives optimal results. These can then be made permanent in a fully automatic station.

Steps for Improving the Fabrication Process

Although the overall process is known and the chemicals to be used are set, a new fabrication process may initially not work as desired. Perhaps the etching is not at the expected speed, or the results are not consistently reliable. While the effects of changing chemical concentrations and timing for bath exposure are known, the optimum variables for the specific process have to be found.

After an initial run, the problem areas can be identified and variables such as chemical dosages and timing can be adjusted. Skilled and experienced operators can carry out the fabrication steps and make changes easily on a manual station. In manual mode, the operator is completely in control and nothing happens unless the operator initiates the action. Such control can be important when determining initial settings for a new process.

Once the major parts of the new process work as expected, there may still be minor adjustments necessary to achieve targets such as faster processing, better quality output or reduced chemical use. For such adjustments, use of a semi-automated station saves time. Instead of carrying out all the steps manually, the semi-automated station can run the parts of the process that don’t need adjusting. These parts will run reliably without operator intervention, as programmed and without deviation from the correct set points. The operator can then focus on the final adjustments to optimize and then utilize fully automated wafer process equipment

Subsequent Tailor Made Full Automation

Once the parameters and variables for the desired yield and performance have been determined, a tailor-made software and automation package can be assembled. This package, in a fully automated station, reproduces the custom settings of the manual and semi-automated process steps and uses them to consistently produce the desired results. Carrying out the fine tuning of the process on manual and semi-automated stations first allows the fully automated station with the optimized settings to scale up to full production right away. The tailor-made solution for a specific new process can immediately produce the desired yields and process characteristics.

For semiconductor fabrication facilities that often bring online new processes, using manual and semi-automated stations to fine tune the process and develop a tailor-made solution can be an attractive alternative to optimization on a fully automated station. Full automation is still desirable for production runs because of the greater reliability, accuracy and reproducibility that such stations deliver. Once the optimized software and automation package is running production on a fully automated station, the station will produce consistently high-quality output, high yields, low defect rates and use chemicals efficiently.

Modutek can work closely with each customer to determine the best way of optimizing new processes. The company’s full line of wafer processing equipment including manual, semi-automated and fully automated wet bench stations lends itself to this kind of optimization to produce ideal outcomes. Wafer fabrication facilities that consistently optimize new processes can lower overall costs and improve facility performance. Contact Modutek for a free quote or consultation on selecting the right equipment to support your manufacturing process requirements.