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E-beam lithography touts smaller chips

Posted: 08 Jul 2011     Print Version  Bookmark and Share

Keywords:E-beam  lithography  photolithography  chip manufacturing 

Photolithography has been in use since a long time, however, it is the very nature of light that limits the extent of chip miniaturisation that photolithography can produce. A team of researchers at MIT claim to have devised a method that uses e-beam lithography to produce smaller chips.

Electron-beam (e-beam) lithography has long been used to make prototype chips, but has proven to be much slower than photolithography. Increasing its speed generally comes at the expense of resolution. Previously, the smallest chip featured that high-speed e-beams could resolve were 25nm across, barely better than the experimental 32nm photolithography systems that several manufacturers have demonstrated. However, in a forthcoming issue of the Microelectronic Engineering journal, researchers at MIT's Research Laboratory of Electronics (RLE) has presented a way to get the resolution of high-speed e-beam lithography down to just 9nm. Combined with other emerging technologies, the process could point the way towards making e-beam lithography practical as a mass-production technique.

The most intuitive way for manufacturers to keep shrinking chip features, which is easier said than done, is to switch to shorter wavelengths of light—known in the industry as extreme UV. "Because the wavelength is so small, the optics [are] all different," said Vitor Manfrinato, an RLE graduate student and first author on the new paper. "So the systems are much more complicated ... [and] the light source is very inefficient."

Visible-light, UV and e-beam lithography all use the same general approach. The materials that compose a chip are deposited in layers. Every time a new layer is laid down, it is covered with a material called a resist. Much like a piece of photographic paper, the resist is exposed—to either light or a beam of electrons—in a carefully prescribed pattern. The unexposed resist and the material underneath are then etched away, while the exposed resist protects the material it covers. Repeating this process gradually builds up 3D structures on the chip's surface.

The main difference between e-beam lithography and photolithography is the exposure phase. In photolithography, light shines through a patterned stencil called a mask, striking the whole surface of the chip at once. With e-beam lithography, on the other hand, a beam of electrons scans across the surface of the resist, row by row, which is a more time-consuming operation.

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