Dec 17, 2013 |
Sharpening the focus in quantum photolithography
|
(Nanowerk News) A new protocol makes it possible to improve the accuracy of photolithography by addressing its physical limitations.
|
Photolithography uses light beams to design thin geometric patterns on the substrates of semiconductors used in microelectronic devices. This is achieved using a chemical reaction on a light-sensitive chemical, called photoresist. The trouble is that the phenomenon of light diffraction does not permit highly accurate patterns.
|
Often, the edges of stripes have low contrast, and the distances between the stripes and the stripes' width are limited by what is referred to as Rayleigh's diffraction limit. Now, a scientist from Russia has developed a quantum lithography protocol designed to improve the resolution of this technology. The findings of George Miroshnichenko, a physicist at Saint Petersburg National Research University of Information Technologies, Mechanics and Optics, have just been published in EPJ D ("Quantum lithography on bound-free transitions").
|
Until now, quantum lithograph protocols have been based on multi-photon absorption. This means that the frequency of the incoming light needed to be several times smaller than the frequency required for the absorption of a single photon, to trigger the absorption of multiple photons by the photoresist. As a result, this approach requires a higher wavelength, and produces lower resolution.
|
Instead, Miroshnichenko establishes the formula for the probability of a single - and no longer multiple - photon transition from a bound state of a quantum system to a state of continuous spectrum, using the so-called Markov approximation. This makes it possible to select the exposure time and the beam's intensity to obtain a narrow stripe in the photoresist on the substrate.
|
Thus, in negative photoresist, this protocol can be used to create a stripe with a width equal to half the wavelength and high-contrast edges. For positive photoresist, thin stripes can be formed on the substrate with a width that is substantially smaller than the wavelength, but the distance between these stripes is equal to half the wavelength.
|