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Polymer PFAS-free polymer membranes for semiconductor manufacturing

Source: Press release | Translated by AI 3 min Reading Time

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In semiconductor manufacturing, PFAS-containing membranes are used in numerous process steps. However, these chemicals are considered harmful to health and the environment and are to be banned. Researchers at the Fraunhofer IAP have developed a sustainable alternative with a PFAS-free membrane.

The PFAS-free polymer membrane is chemically stable, highly permeable and has a pore diameter of about seven nanometers.(Image: Fraunhofer IAP)
The PFAS-free polymer membrane is chemically stable, highly permeable and has a pore diameter of about seven nanometers.
(Image: Fraunhofer IAP)

The European Chemicals Agency (ECHA) therefore published a proposal in February 2023 for a ban on the production, use and placing on the market, including import, of PFAS, short for per- and polyfluoroalkyl substances, in the European Economic Area. The reason: PFAS chemicals are toxic, they permanently pollute water and soil and accumulate in humans and animals through food and consumer-related products. The semiconductor industry views the looming PFAS ban critically, as these chemicals are used, among other things, in etching and cleaning processes, but also, for example, as membranes and housings in filters. According to many manufacturers, the long-lasting per- and polyfluorinated chemicals are so far irreplaceable, and the production of most semiconductor products would then no longer be possible.

Membrane with a pore diameter of about seven nanometers

"During the chip manufacturing process, countless process steps such as sawing, cleaning, and planarizing occur to apply the structures onto the wafers. All these operations produce particulate contaminants that must be removed at each process, otherwise they would damage the production of nanometer-sized structures," explains Dr. Murat Tutus, engineer at the Fraunhofer Institute for Applied Polymer Research IAP and head of the "Membranes and functional films" department. Murat Tutus' team has now succeeded in developing a PFAS-free membrane from conventional, specifically stabilized polymers for a semiconductor industry supplier that can replace PFAS membranes. The membrane made of the polymer polyacrylonitrile (PAN) is characterized by its high chemical and mechanical stability. It also has an extremely small pore diameter of about seven nanometers. This is necessary to separate particulate contaminants from production and filter and recycle the operating fluids such as acids and solvents necessary for the process. The membrane can be customized to the customer's needs, so the new process can easily be integrated into existing facilities for the production of the next generation of chips.

For comparison, filters in the size range of 220 nanometers are used for sterile filtration in medical technology. "We were able to chemically modify the polymer with another component patented by us and stabilize it for harsh process conditions," says the researcher.

In addition, the researchers were faced with the task of achieving a distribution of pore size that should deviate only slightly from the seven nanometers. Furthermore, the membrane was supposed to be highly permeable. "The degree of permeability defines the number of pores on the surface. The smaller the pores, the less permeable it will be. Therefore, in the second step, we had to increase the number of pores while keeping the pore size constant in order to increase the permeability," Tutus explains.

Membrane can be customized to customer specifications.

As the membrane can be customized according to the pore size and permeability, it can be easily adapted to various applications in other industries. The advantage of adapting a membrane: existing facilities can continue to be used, employees do not have to be further trained. Dr. Tutus and his team see great potential for their developments especially in the pharmaceutical and chemical industry, where aggressive solvents are also used. During the manufacture of the membrane itself, sustainable, REACH-compliant (Registration, Evaluation, Authorisation and Restriction of Chemicals) solvents are used, the entire production process is designed to be sustainable at low temperatures. The membrane is produced using the NIPS process, short for non-solvent induced phase separation, where the researchers can also adjust the morphology, i.e. the pressure stability, of the membrane.

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