New Laser Annealing Process Produces High Performance Integrated Circuits

Lithography represents one of the most important phases in the production of integrated circuits.  Photolithographic steps establish patterns on chips or light-sensitive material called a photoresist. After undergoing a series of chemical treatments, the exposure pattern can be engraved into the photoresist or through a deposition of new material underneath the photoresist.

Traditionally, semiconductor manufacturers use an extensive baking (hotplate) process at temperatures of 100-450°C. The low temperature is crucial to avoid degradation of the photoresist properties.

However, the hotplate process fabricates one wafer at a time – a time consuming process.  A single silicon wafer may require as many as 50 cycles, which prepares multiple levels of patterns on the resist.

Steady improvements in lithography have driven the expansion of the semiconductor industry. However, the baking method has been a mainstay for 50 years.

Cornell’s Laser Spike Solution

As the semiconductor industry moves toward creating smaller and smaller chips, two researchers at Cornell University’s Materials Science and Engineering department, Christopher Ober and Michael Thompson, have answered the call for innovative processes that that allows scalability of production.

The scientists have developed a laser annealing process that is applicable to thin photoresist films used in extreme ultraviolet (EUV) lithography and 193nm applications.

The process uses continuous wave lasers, which heats polymers (materials) at significantly higher temperatures, up to 800°C, for millisecond at a time. The breakthrough innovation limits chemical diffusion during the annealing process. Chemical diffusion compromises the quality and fidelity pattern transferred to the wafer, which affects device performance.

The scientists tested the cutting-edge laser process on diode and CO2 lasers. Using a EUV lithographic exposure tool, Ober and Thompson have fabricated IC features at 30nm or less, said Ober.

Benefits to Semiconductor Manufacturers

Professor Ober states that at one time many researchers in the semiconductor sector believed the industry had maximum optimization for photoresist heating, but the new technology “proves otherwise.”  Because patterns transfer faster and create a “better pattern fidelity process and line-edge roughness”, the innovation will lead to chips that perform better and cost less, according to Ober.

Semiconductor Research Corporation sponsored the Cornell research team.  Bob Havemann, the director of nano-manufacturing sciences for a research group states that several semiconductor companies are working on bringing advanced annealing processes to the marketplace.  The research consortium includes Intel, AMD, Texas Instrument, and IBM.

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