Wet bench semiconductor manufacturing relies on the SPM wafer cleaning process to quickly strip photoresist and other residue from silicon wafers. Because the hydrogen peroxide in the sulfuric acid peroxide mixture is unstable, hydrogen peroxide continuously degrades into water and the degradation is accelerated if the mixture is heated to increase the strip rate. To keep the SPM process concentration stable, hydrogen peroxide has to be added, spiking the concentration back to its original level. After several hours of repeated spiking, the mixture has to be replaced.
While other semiconductor equipment manufacturers provide less efficient solutions, Modutek has developed a “bleed and feed” method that keeps the SPM hydrogen peroxide concentration steady. The company has now collected operational results from customers using the new method and a comparison with the traditional SPM process shows substantial savings from reduced use of acid and better operational results.
How Modutek’s “Bleed and Feed” Method Works
The Modutek “bleed and feed” method uses a two-tank configuration with a clean tank and a dirty tank. Periodically an amount of mixture is drained from the dirty tank and replaced with mixture from the clean tank. The clean tank receives an amount of sulfuric acid to replace the drained amount and both tanks receive enough hydrogen peroxide to bring the concentration up to the set level.
The method is PLC-controlled with the initial drain amount, the replacement amount, the hydrogen peroxide amounts and the “bleed and feed” frequency all programmable. The SPM process concentration is maintained and the strip rate remains unchanged, but the SPM mixture has a much longer life. The cost savings result from the SPM mixture not having to be changed frequently.
The “Bleed and Feed” Method Reduces the Consumption of Chemicals
Operational data from customers shows that the Modutek “bleed and feed” method substantially reduces the use of the SPM process chemicals. Data was collected from a semiconductor manufacturing facility using a 2 6-inch carrier bath size and operating on an eight-hour shift.
The use of sulfuric acid was reduced by 77% while the volume of chemicals disposed at the end of the process went down 75%. Acid neutralizer and acid re-agent use declined as well. The reduced cost of chemicals and the savings from lower disposal volumes were substantial.
“Bleed and Feed” Can Increase Throughput
The spiking with hydrogen peroxide of the traditional SPM wafer cleaning process means that mixture replacement causes frequent down times for drain and re-pour. Use of the Modutek “bleed and feed” method reduced system drains from three times per day to once per week on average. The once-per-week change is supported by a quick-drain feature that lets the change-over to a new mixture take place quickly. Overall throughput was increased.
Operational Advantages of “Bleed and Feed”
In addition to cost savings from reduced chemical use and higher product volumes from increased throughput, customers saw operational advantages from using Modutek’s “bleed and feed” method. The reduction in chemical handling lowered the possibility of spills and increased operator and employee safety. At the same time, strip rates and other SPM process characteristics were at least maintained at previous levels or improved.
Customers Can Immediately Take Advantage of “Bleed and Feed”
The Modutek “bleed and feed” method is especially attractive to facility managers, process engineers and researchers concerned about the environmental impact of high volumes of toxic chemicals. Modutek can deliver the new method as part of its standard wet bench stations or prepare a custom design for a specific application. Since Modutek designs and builds its own equipment, the company has the expertise to propose custom solutions for any SPM process applications and allow all their customers to benefit from the new “bleed and feed” method. Contact Modutek for a free consultation or quote on equipment that is designed to meet your specific manufacturing requirements.
