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Currently semiconductor devices are manufactured using the photolithographic process wherein light is past through a mask which forms a pattern of shadows on the surface of a wafer. The pattern of shadows is reduced in size using a lens. The patterns are etched into the wafer surface and used to form
The process has a theoretical size limited by the wavelength of light. X-rays and electron beams have been proposed as alternatives to light since they have shorter wavelengths hence making smaller features, but they are harder to control. For example, neither can be focused with a lens.
To overcome this problem a diffraction grating could be used. The diffraction grating pattern would be the 2d Fourier Transform of the resultant image required.
Essentially this uses the interference of waves to create a focused image instead of a lens.
This would require a diffractive grating much larger than the image itself to reproduce the required detail (by capturing enough diffractive orders).
Manufacturing the diffraction grating would need to be smaller/sharper than a standard photolithographic mask, which could be made by electron beam lithography (EBL) or some nano-manufacturing technique.
Method and Apparatus for Alignment of Submicron Lithographic Features
[Freefall, Mar 14 2005]
||Would the process be more or less sensitive to surface variations than current photographic processes?
||As with a lens system there would be exactly one distance that the wafer would be 'in focus' so any surface variation would be 'out of focus'. I don't think it would be too much worse than a lens though.
||One of the main problems with this invention is a source of coherent x-rays or electron beams (ie x-ray or electron lasers).
||Electron beams can be focused using magnetic lenses, and
such is done regularly in
scanning/transmission electron microscopes. While
coherent electron sources are expensive, they are
available and are also used in TEM used for high-resolution
||Coherent sources are not strictly required for imaging,
only for hi-res and diffraction work.
||Some of the semiconductor manufacturing setups in the
electrical engineering department at this university have
an electron beam directed at the surface of the sample.
The beam diffracts off the surface - no grating required -
and the lines are visible on a phosphorent screen on the
||My understanding of interferometric lithography is limited to "light passing through a set of gratings will produce a pattern". However, I think this technology is being used, and has been used for several years to produce submicron circuitry.