Monthly Archives: January 2020

Improvements to the SPM Process Provides Significant Results

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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.

How the IPA Vapor Dryer Provides Superior Wafer Processing

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After etching and rinsing, an IPA (isopropyl alcohol) vapor dryer can produce dry silicon wafers without watermarks and limited particle adders. In IPA drying, also known as Marangoni drying, the Marangoni effect relies on the low surface tension of IPA compared to water. When IPA vapor is introduced into the drying chamber, a surface tension gradient is established between the IPA and water on the surfaces of the silicon wafers. The surface tension gradient causes the water to flow off the wafers, leaving them clean and dry. The slow drain water feature also helps reduce particles contaminating the wafer surfaces. As a result, IPA vapor drying can be used to produce especially clean, wafers after a final etch and before the next semiconductor manufacturing step.

IPA Vapor Drying is Safe for Thin Silicon Wafers

IPA vapor dryers are especially suitable for drying thin, delicate silicon wafers. In other drying methods, the wafers are placed in a drying chamber and rotated or spun to remove the rinsing water, but handling and moving these wafers can result in damage. With the IPA vapor dryers, the Marangoni effect dries the wafers without moving them. Delicate wafers are not subjected to any stress and damage is minimized while drying performance is excellent.

IPA Vapor Dryers Improve Wafer Processing After HF Last Etching

As the final process in a silicon wafer fabrication step, the silicon oxide layer on the wafer has to be removed with hydrofluoric acid (HF) etching. The wafer is then rinsed with de-ionized water and dried before passing on to the next step in manufacturing the final semiconductor component. Providing a clean wafer with a low particle count is critical at this point because subsequent process steps are affected by the presence of contamination or particles. For high-density semiconductor components, a particle or film on the silicon wafer can prevent the correct etching of a structure or the deposit of a conductor. Because IPA vapor dryers remove water from the wafer surface and reduce particle counts with their Marangoni effect, IPA vapor dryers improve wafer processing results and ensure higher quality output.

Modutek Single Chamber Processing Delivers Further Improvements

At the end of a wet process wafer fabrication step, the wafers are etched with hydrofluoric acid in an etching chamber and then transferred to a dryer. The transfer exposes the wafers to particle contamination that can lead to elevated wafer surface particle counts, even after Marangoni drying. Modutek has eliminated this source of contamination by developing a method that allows etching and drying in a single chamber.

With the Modutek etching and drying station, hydrofluoric acid is injected into the chamber at a controlled ratio to etch the oxide layer down to the bare silicon. The wafers are then rinsed with de-ionized water to a set pH level. When the pH level is reached rinsing is complete and drying can begin.

IPA vapor is generated from a standard one-gallon bottle and introduced at the top of the drying chamber. The drying cycle takes about 10 to 15 minutes and the dry wafers are ready for their next fabrication step. The wafers are not moved during the whole etching, rinsing and drying process, reducing wafer breakage, especially for thin, delicate wafers. Since the wafers stay in the chamber from etching to drying, particle contamination is significantly reduced.

Modutek’s extensive experience in the semiconductor manufacturing industry allows it to support customers in integrating the new single chamber IPA vapor dryer in any new or existing wet processing equipment. Modutek designs and builds their own semiconductor manufacturing equipment and can therefore offer customized versions to meet the requirements of any application. The company’s staff work with a customer’s engineering team to make sure the equipment meets the customer’s process requirements. Contact Modutek for a free quote or consultation to discuss your manufacturing equipment requirements.