EUV Lithography: The next-generation Technology for the Semiconductor industry

Dr. Gordon Moore, cofounder of Intel Corp., described the progress of the development of semiconductor devices with a sentence that is now commonly used to define Moore’s Law: The number of transistors on a computer chip doubles every 1.5 to 2 years. Moore’s Law is not only a description of the evolution of semiconductors, but has also served as a roadmap for both chip manufacturers and the suppliers of chip production tools.

In semiconductor chip production, lithography is a critical manufacturing method used to ensure both sufficient quality and high-throughput. Optical lithography remains the traditional technique used in the semiconductor industry.

The lithography chip manufacturing process can be defined as follows:

• Light (any wavelength) from the source passes through optics to generate homogenous illumination of mask
• The mask image is projected on the photo-resist coated wafer using another set of optics with certain demagnification to produce fine structures
• The illuminated areas from the wafer are removed using a chemical process
• This is followed by etching or coating uncovered parts

This process is repeated over and over to produce current super complex chips.

Although the semiconductor industry is using the light source of wavelengths from 365 nm to 248 nm to 193 / 157 nm, and producing feature sizes < 100 nm, it has reached the technological limit of optical lithography. Recognizing this limitation, the industry has spent the past several years identifying a potential successor technology in order to produce features even < 100 nm. Next-generation lithography technologies (NGL’s) investigated by the semiconductor industry include EUV lithography, X-ray lithography, ion-beam projection lithography and electron-beam projection lithography.

Although EUV lithography has its share of challenges, it is often used because it (1) retains the look and feel of the current optical lithography process (uses 13.5 nm wavelength) as described above and (2) uses the same basic design tools.

Since the 13.5 nm (~ 92eV) wavelength is absorbed in the air and requires a high-vacuum for transmission, it places extreme challenges on all parts of production tools. First of all, the light source has to deliver a narrow band of high-EUV power (preferably with a high-spectral purity) in order to guarantee high-throughput. Secondly, all components that move the mask and the wafer with the precision in the nm range need to be operated in ultra-high vacuum (UHV). Third, projection optics also need to deliver the same dynamic positioning precision in the Angstrom-range and be contamination-free to a few nanometers level in order to deliver high efficiency.

To keep all these components in good working condition and delivering the highest performance possible, the best diagnostics and monitoring tools are required. One of the tools that has served the EUV research community well for diagnostics and monitoring the EUV light source are soft X-ray imaging systems from Princeton Instruments.

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