PORTLAND, Ore. -- A new super-resist has been formulated in collaboration with Intel Corp. at the U.S. Department of Energy’s Lawrence Berkeley National Lab (Berkeley Lab) and may help meet the demands of advanced nodes of 10 nanometer and below using extreme-ultra-violet (EUV) light.
The problem was that EUV light sources are designed to flash as fast as a femto second, to prevent damage to the chip, but only very sensitive resists could work with such short exposure times. The kind of resists needed -- cross-linked ones for their high-resolution and mechanical stability -- unfortunately require longer exposure times. Thus the task of Intel and Berkeley labs was to create a super-resist that could create smooth high-resolution lines, but with high sensitivity for the quick EUV flashes.
"Resists today either emphasizes cross linking for mechanical stability, but they have low sensitivity so are only used with e-beam lithography. When doing photolithography today they use amplified resists which have higher sensitivity to light," Paul Ashby, staff scientist at Berkeley Lab’s Molecular Foundry, a DOE Office of Science user facility, told EE Times. "So our idea was to dilute cross-linking and add that to an amplified resist so we can have the advantages of both high sensitivity and mechanical stability."
The new type of resist is specifically targeted at EUV, which needs both sensitivity and mechanical stability, but the researchers are also hopeful that the new resist will improve edge-line roughness, which is increasingly important at the 10-nanometer node and below.
Paul Ashby and Deirdre Olynick of Berkeley Lab at the Advanced Light Source (ALS) Extreme Ultra-Violet (EUV) Beamline. (Credit: Roy Kaltschmidt, Berkeley Lab; Source: Berkeley Lab)
"Those three properties -- the high-resolution, the line edge roughness and the sensitivity -- are the three most important properties in the lithography field today, so we wanted to improve all three at the same time," Ashby told EETimes. "Usually there is a trade off between sensitivity and either resolution or line-edge roughness. But here we were trying to maintain a high sensitivity resist that is still pushing out the resolution."
Having proven the concept in the lab, with Berkeley Labs EUV Advanced Light Source, the resist manufacturers will still need to do a lot of work to make the formulation commercially viable. Luckily they have a few years to perfect a commercial version, since most estimates predict the EUV will not be ready for mass production before 2017.
Super-resist uses smaller concentrations of crosslinker (left) and thus is able to pattern smaller features without requiring longer, expensive exposure times as with high concentrations of crosslinker (right). (Credit: Prashant Kulshreshtha, Berkeley Lab; Source: Berkeley Lab)
For the future, Berkeley Labs plans to extend its study of EUV by amassing data, and coming up with theories, about the chemical byproducts that result when high-intensity EUV light hits these new resists. They have already fine-tuned the formulation to produce smoother lines even as they are shrunk to smaller widths.
"What we want to understand is the mechanisms that lead to high-resolutions with low line roughness, and design even better resists around our findings," Ashby told EE Times.
The work was performed in collaboration with Deirdre Olynick, a staff scientist, and postdoctoral researcher Prashant Kulshreshtha. Funding was provided by Intel, JSR Micro, and the DOE Office of Science (Basic Energy Sciences).
— R. Colin Johnson, Advanced Technology Editor, EE Times