Photolithography is the process used to make all modern computer chips. The circuit patterns on chips are built layer by layer, with electrical current flowing in a 3-D path through an extraordinarily complex maze of capacitors, resistors, and transistors. The smaller the wires become, the faster the chips can operate, and the more circuits can be squeezed into a small area. Engineers create a pattern, called a mask or reticle, that represents each layer of the circuit pattern. Then, in a process somewhat similar to darkroom photography, light is used to transfer the pattern, shrinking it down onto a light-sensitive film, called photoresist, that coats the current top layer of the chip. With successive developing, etching, and deposition steps, the complete chip circuitry comes to life.

Following the decades-old economic trend called Moore's Law, the chip-making industry seeks to increase the number of transistors on a chip at a geometrically increasing rate. This happens in discrete steps, as new and improved chip-printing technologies are brought into mass-production as they become ready. With each successive generation spanning the past 30 years, researchers develop ways to pack ever-smaller transistors onto faster-running chips. Soon, companies will switch from deep ultraviolet light (193-nm wavelength) to EUV light, an invisible color with a dramatically shorter, 13-nm wavelength. The physics of light focusing holds that light with a smaller wavelength can be focused to a smaller size and used to draw narrower circuit-pattern lines. So shrinking from 193-nm to 13-nm, gives the industry room to shrink, as it were.

The MET Optic.

Bringing a new lithography technology into mass-production requires a tremendous amount of basic research; every problem must be studied and solved, new materials and fabrication techniques can be developed, and the commercial infrastructure to produce tools, and raw materials, can become ready. Since 1993, our laboratory has been involved in basic research in many areas related to EUV lithography. The production, development, and testing of EUV-reflective multilayer-coated mirrors has been a major research effort, and measuring the precise optical properties of materials used in EUV lithography is a significant part of that research. The creation and use of high resolution EUV-focusing lenses, made from curved multilayer-coated mirrors, is a closely related activity. Reflectometry is used to qualify mirror surfaces for smoothness and EUV reflectivity. EUV interferometry is used to align and test the assembled lenses, to reach diffraction-limited performance. Bringing all of the techniques together, we have developed and now operate an EUV resist test center in which the highest quality EUV lithography performed to date is available for research by collaborating organizations.

The Berkeley Micro-Exposure Tool (MET) is a unique integrated system that performs micro-field EUV lithographic imaging in a program funded and organized by SEMATECH. Researchers come to test new photoresist formulations and reticle fabrication techniques. In 2005, the MET ran for 139 days, generating approximately 800 wafers, and 1100 focus-exposure matrices (FEMs).

Besides myself, a number of researchers have made essential contributions to this work. Patrick Naulleau is now the primary scientist on this project. Others currently or formerly involved include David Attwood, Jeffrey Bokor, Senajith Rekawa, Paul Denham, Erik Anderson, J. Alex Liddle, Michael Shumway, Jason Cain, Phil Batson, and Matt Bjork. Essential engineering and technical contributions have been made by Robert Gunion, C. Drew Kemp, Rene Delano, Brian Hoef, Gideon Jones, Rene Delano, Deirdre Olynick, Bruce Harteneck, Farhad Salmassi, Ron Tackaberry, Jeff Gamsby, and others. The daily operations and maintenance are overseen by Paul Denham and Brian Hoef. Expert guidance comes from our SEMATECH project leader, Kim Dean, and formerly Pat Gabella as well.

To learn more about this research, please browse the publication list where a number papers are available, view slides from recent public presentations, or contact me. Wikipedia.org has entries for Photolithography and Interferometry.