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Micro/Nano Lithography

Immersed in Lithography

SPIE Fellow and 2004 award winner Burn Lin has been pushing the lithography envelope for many years - his latest push is for immersion lithography.

From oemagazine May 2004
30 May 2004, SPIE Newsroom. DOI: 10.1117/2.5200405.0010

Burn Lin with his wife Sue, son John, and daughter Christiana.

Burn Lin began his love of optics thinking big. When he was 13, Lin and a friend converted a 6 x 9 camera into an enlarger by building a housing around the camera and replacing the back with a film holder. His fascination with making things bigger didn't last long, though. Now highly respected in the field of microlithography, Lin is the first winner of the Frits Zernike Award for Microlithography, given for fundamental achievements in the theory, practice, and extension of optical lithography.

A Step Ahead

One thing that distinguishes Lin is his ability to constantly push the limit of lithography. While at IBM (Armonk, NY) and currently at Taiwan Semiconductor Manufacturing Co. (Hsin-Chu, Taiwan), he has always seemed to be at least one step ahead of the current technology. In fact, his first paper in microlithography, which focused on deep-UV lithography, reported his first breakthrough.

"Wayne Moreau (at IBM) introduced me to his PMMA exposure technology that I adopted to build a deep-UV proximity printing system to make 0.5-µm magnetic bubble circuits," explains Lin. "That was in 1975, when the world was happy with making 5-µm integrated circuits using near-UV proximity printing."

This was just the beginning. He developed the first computer program to simulate partially coherent projected images from arbitrary 2-D patterns, which led to a bevy of breakthroughs, including the invention of the exposure-defocus diagrams, and he wrote the first article on diffraction with exposure-gap diagrams in x-ray lithography.

The firsts in Lin's career are too many to list here. Suffice it to say that with his work he is responsible for much of the nomenclature in microlithography. "In a very literal sense, Burn Lin has defined the field of lithography," says SPIE Fellow Timothy Brunner of IBM.

"In the '80s when I projected that the limit of optical lithography was 130 nm, many people disbelieved. Today, I am glad that people take me seriously when I project optical lithography for the 32-nm node," says Lin.

He has consistently proved and disproved concepts of lithography through the years, giving him strong credibility. This is a significant reason why immersion lithography has taken off and been taken seriously in recent years.

Lithography Immersed

Although the concept of immersion lithography has been around since the early 1980s, it wasn't well developed or considered viable for integrated circuit production until recently. In 2002, most companies were fixated on 157-nm lithography, and there was a sense that extreme UV (EUV) was the solution to the demand for shorter wavelengths and finer resolution.

"I was less trusting of the 157-nm technology and very concerned about EUV lithography," says Lin. At Microlithography 2002, he proposed immersion lithography as a possible alternative.

"In July 2002, in an invited paper at the SEMATECH-organized 157-nm workshop, I took the courage to tell the 200-plus attendees that 193-nm water-immersion has a better chance to succeed and a greater potential to reach for future technology nodes than 157-nm dry systems," says Lin. "The audience responded with enthusiasm, constructive concerns, and actions."

In SEMATECH workshops, immersion lithography was more actively explored. Lin took an integral role in examining the technical hurdles of immersion imaging. "Another role that I took was to motivate the exposure tool and the resist vendors to develop immersion systems and to convince potential users that immersion lithography is the best choice," Lin says. With so much money invested in dry 157-nm lithography, this was no easy task. "One argument I often used was 'the sooner you switch, the sooner the bleeding stops.'"

Now just this year, at both SEMATECH's Third Workshop on Immersion Lithography and at SPIE's Microlithography 2004, it was clear that 193-nm immersion lithography was placed firmly on the roadmap for 65-nm and 45-nm nodes (see oemagazine, April 2004, p. 14).

"With a good start in immersion lithography tooling and infrastructure, we have to concentrate on developing and optimizing the manufacturing process to fabricate integrated circuits in the 65-nm and 45-nm half-pitch nodes," Lin says. Always looking ahead, he adds, "I am also paying attention for a possible technology to succeed immersion lithography."

Affecting Society

As a Fellow of SPIE, Lin is very active with the Society. Along with his involvement in the Microlithography symposia, he is a short course instructor, and most notably a member of the Publications Committee and the editor-in-chief of SPIE's Journal of Microlithography, Microfabrication, and Microsystems (JM3). The journal debuted at Microlithography 2002 with eight articles; now only two years later, the January issue features 23 papers with 13 in the special section alone. (See www.spiedl.org.) The topic of this special section is, you guessed it, immersion lithography. Lin says one of the challenges of the journal now is convincing more authors from the industrial micro community to submit their work to JM3.

With 34 years in the lithography field, Lin hasn't just affected the science of lithography, he's also had a big effect on the people. "He has guided many younger engineers, and was always approachable for technical discussions," says Brunner. "He has inspired many more lithography workers via his presentations and papers."