Resist Requirements and Limitations for Nanoscale Electron-Beam Patterning

Abstract

Electron beam lithography still represents the most effective way to pattern materials at the nanoscale, especially in the case of structures, which are not indefinitely repeating a simple motif. The success of e-beam lithography depends on the availability of suitable resists. There is a substantial variety of resist materials, from PMMA to calixarenes, to choose from to achieve high resolution in electron-beam lithography. However, these materials suffer from the limitation of poor sensitivity and poor contrast.In both direct-write and projection e-beam systems the maximum beam current for a given resolution is limited by space-charge effects. In order to make the most efficient use of the available current, the resist must be as sensitive as possible. This leads, naturally, to the use of chemically amplified (CA) systems. Unfortunately, in the quest for ever smaller feature sizes and higher throughputs, even chemically amplified materials are limited: ultimately, sensitivity and resolution are not independent. Current resists already operate in the regime of < 1 electron/nm 2 . In this situation detailed models are the only way to understand material performance and limits.Resist requirements, including sensitivity, etch selectivity, environmental stability, outgassing, and line-edge roughness as they pertain to, high-voltage (100 kV) direct write and projection electron-beam exposure systems are described. Experimental results obtained on CA resists in the SCALPEL ® exposure system are presented and the fundamental sensitivity limits of CA and conventional materials in terms of shot-noise and resolution limits in terms of electron-beam solid interactions are discussed.

Fabrication of superconducting nanowire single-photon detectors by nonlinear femtosecond optical lithography

“…Alternative technologies for the fabrication of SNSPDs are based on local oxidation [8] and nanoimprinting [9]. Electronic lithography using electronic resists allows one to obtain high spatial resolution (of the order of several tens of nanometers), but this method has a number of limitations: a relatively small working area (~100 µm) with a high spatial resolution; a slow drawing speed; and the presence of the parasitic proximity effect that appears in resists due to secondary scattered electrons [10]. The development of nonlinear optical lithography below the diffraction limit [11,12] allows the fabrication of structures with a resolution of less than 100 nm in negative [13] and positive [14] resistive materials and, in particular, implementation of the maskless method for formation of the sensitive SNSPD element.…”

Spot Electron-Beam Lithography as a Novel Method of High Resolution Pattern Nanofabrication

“…One of the most advanced technology is maskless lithography based on the interaction of the polymer resist with an electron beam [3]. Electron beam lithography (EBL) produces polymer patterns with a resolution element of about 20 ÷ 40 nm (e.g., the width of a straight line or diameter of the disk) [4]. Under certain conditions (e.g., film development at low temperatures, the use of dose adjustment mechanism), one can achieve a resolution of 10 nm for single lines and 20-30 nm in diameter for the nanodots [5].…”