Development of a high resolution nanolithography technique on non-planar surfaces using an evaporated electron beam resist
Kelkar, Prasad S
Electron beam lithography systems used for patterning of extremely small structures are a very important tool for nanofabrication technologies. The on going miniaturization of electronic and photonic device, leads to a constant shrinking and increasing pattern density. Fundamental physical effects such as shot noise, which in lithography corresponds to the statistical fluctuations in the number of electrons contained in a beam, have a major impact on the achievable feature sizes as well as their roughness. Many different parameters in the lithography process must be taken into account in determining these fundamental limits, including exposure dose of the resist, resist thickness, beam energy, etc. A shot noise model has been developed in order to calculate the minimum exposure doses required for patterning electron beam resists at technology nodes of 50 nm and below while maintaining reasonable quality of the patterns. The doses must increase rapidly with reducing linewidth, thus imposing constraints on a variety of next generation lithography systems, such as massively parallel electron beam (MPEB) systems. The model results are applied to the particular case of MPEB systems for the patterning of integrated circuits on semiconductor wafers. An overall set of results is obtained indicating the minimum number of electron beams and electron beam current that will be required to meet industry standards. High resolution electron beam lithography poses severe constraints on the resist used for patterning, namely the need to work with very thin layers in order to achieve the highest resolutions. A new and interesting conformal resist is studied in this work, the sterol based QSR-5(TM) resist. The results of optimizing the resist properties and the development process are presented along with results for optimizing the sensitivity and contrast of this resist. Preserving and developing versatility in the applications has been one of the most important criteria in optimizing the QSR-5(TM) resist. Demonstrations include patterning a zone plate on the tip of an optical fiber for potential application in integrated optics. A very unusual application of patterning both sides of a silicon and a silicon nitride membrane in a single step are described which might be useful for the fabrication of high speed field effect devices such as double gate transistors (DGT). The Monte-Carlo simulation results for the case of the achievable gate length with silicon and silicon nitride membranes are also discussed. The results of conformability and patterning on V-grooves are also presented. The processes of fabrication of the high resolution metamaterial structures are discussed along with the initial measurement results via ellipsometry.
- Génie – Thèses