Designing with Light
Semiconductor manufacturers use optical lithography in a highly specialized printing process used to put detailed patterns onto silicon wafers. An image containing the desired pattern is projected onto the silicon wafer, which is coated with a very thin layer of photosensitive material called "resist." The bright parts of the image pattern cause chemical reactions that make the resist material become soluble. After development, the resist forms a stenciled pattern across the wafer surface that accurately matches the desired pattern of a circuit. Finally, this pattern is transferred onto the wafer surface
in via another chemical process.
To gain performance increases in chips, semiconductor researchers are constantly looking for ever-higher resolutions for printing circuit lines. Current industry efforts are aimed at achieving printing resolutions smaller than 250 nanometers (nm). (250 nm -- the current standard resolution -- is over 200 times narrower than the width of a human hair!) The motivation is two-fold: smaller features will allow silicon chips to contain more circuit elements, and also smaller devices are typically higher performance (i.e. - faster).
For years, IBM has been a leader in the drive to reduce the wavelengths used in optical lithography. Exposure wavelengths that started in the "blue" spectrum of 436nm are expected to go down to 193 nm during the next decade. IBM researchers at the Almaden Research Center in San Jose, Calif., pioneered the development of special high-resolution resists. Termed "chemically amplified resists," these enabled the industry to switch from 365 nm manufacturing to 248 nm manufacturing, which is currently used worldwide to manufacture circuits with 250 nm features.
Most recently, IBM Almaden researchers pioneered the adaptation of "chemical amplification" to use at 193 nm. This lithography is expected to be a factor in semiconductor manufacturing in the year 2000.