In the ongoing pursuit of increasing transistor density, extreme ultraviolet (EUV) lithography has emerged as the most crucial tool. Costing over US $100 million, these trailer-sized systems utilize near x-ray wavelength light to create nanoscale patterns on silicon wafers. The complete apparatus operates in a vacuum since the 13.5-nanometer light is absorbed by air. However, the system and process introduce contaminants that need to be constantly removed to maintain the integrity of the delicate optics. This is managed using approximately 600 liters per minute of hydrogen, a number that is likely to increase in the future.
Currently, the contaminated hydrogen is burned to form water, necessitating a constant supply of new hydrogen. However, as most of the hydrogen is produced through steam reforming of natural gas, it leads to carbon dioxide emissions. In order to reduce EUV's environmental impact and ownership cost, engineers at Edwards, an England-based vacuum systems firm, have developed a method of recycling up to 80% of the gasSimilar to the concept of reverse fuel cell technology, recovering hydrogen is highly efficient. According to Anthony Keen, a technology manager at Edwards, recycling the hydrogen is more effective than converting it into electricity. In an EUV machine, hydrogen is used as a barrier between the optics and the silicon wafer and in the EUV light source to prevent vaporized tin from contaminating the optics.
Edwards's hydrogen recovery system ionizes the gas and uses an electric field to guide the resulting ions through a proton-exchange membrane. The protons then recombine with electrons to form pure hydrogen, while any remaining water is removed through a final purification step. All contaminants are collected and disposed of.
As a part of Imec's Sustainable Semiconductor Technologies and Systems program, Edwards and Imec tested the recovery system on Imec's 300-millimeter silicon pilot line. The trial demonstrated that the system could recover 70%-80% of the hydrogen whilst reducing energy consumption. Edwards is now advocating this technology to major chip manufacturers such as Intel, Samsung, and TSMC as they endeavor to minimize the carbon footprint of integrated circuit production. By 2040, Imec estimates that semiconductor manufacturing could account for 3% of global emissions.
