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17 Jun 2002
Eventually the electronics industry will need to use X-rays instead of ultraviolet light to print tinier and tinier details onto microelectronic circuits. Now Bell Labs has delayed that day by making a device with 80 nm details, two thirds the size of the smallest detail thought possible with optical techniques.
Optical methods currently fabricate commercial semiconductor devices with details as small as 180 nm across. The semiconductor industry believes that the limit is 120 nm with ultraviolet light before it will be forced to move to the shorter wavelengths of X rays.
The Bell Labs researchers worked with light with a 193 nm wavelength while semiconductor manufacturers are still working with 248 nm light. They developed a number of techniques to print the smallest details through a mask onto a substrate.
First, they shifted the phase of light as it passed through the mask. A Swiss group developed a similar method a few years ago that made beams of light pass through a mask and then form an interference pattern in the substrate.
Secondly, the Bell researchers developed new resists, the coating on the substrate which is printed with the circuit design, based on cyclo-olefin maleic anhydride chemistry. Many commercial resists are made of polymethyl methacrylate, better known as "superglue".
Thirdly, they added a layer between the resist and the substrate to absorb any excess light and preventing reflections from the silicon below. JB
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