“
“Background Fabrication of nanoscale structures and devices such as nanoimprint lithography templates, dynamic random-access memory capacitors, zone plates (X-ray lenses), etc. requires a high-aspect-ratio (AR) and high-resolution patterning capability. Utilizing electron beam lithography (EBL) to fabricate such nanostructures further requires that the patterning be performed as rapidly as possible (high throughput) due to the serial writing nature of EBL. The requirement of high throughput often

imposes a trade-off between the Selleck FDA-approved Drug Library selection of processing conditions and performance. As an example, using a higher voltage in EBL enables the fabrication of higher AR nanostructures; however, the electron dose increases in proportion to the voltage, thus increasing the time of exposure. Careful selection of other processing parameters such as using a higher performance JQ1 developer solution can decrease the electron dose requirement (increase the process sensitivity) and, to a certain extent, compensate for such trade-offs. The well-known positive-tone resists polymethylmethacrylate (PMMA) and ZEP-520 (Zeon Corporation, Tokyo, Japan) can be patterned with sub-20-nm resolution for dense grating

patterns. However, the achievable ARs of PMMA on solid substrates are limited to 2:1 to 4:1 at 25 keV [1, 2], to approximately 5:1 at 50 keV [1, 3], and to 12:1 to 20:1 at 100 keV [1, 4, Palmatine 5]. Similarly, ZEP resist has ARs limited to 4:1 at 20 keV [6] and to 7:1 at 100 keV [7], albeit with over three times higher sensitivity than PMMA. Another positive-tone resist, polymethylglutarimide (PMGI), has been patterned with an AR of over 2:1 at 30 keV [8] and extremely high AR of 38:1 at 100 keV [9] using an optimized development process. However, the sensitivity of PMGI is four to nine times lower than that of PMMA, requiring up to 18,000 μC/cm2[9] to expose a single line. Similar trends are observed for negative-tone resists such as hydrogen silsesquioxane (HSQ). Reported ARs for HSQ are 4:1 at 10 keV [10], 7:1 at 50 keV [11], and 25:1 at 100

keV [12, 13]. HSQ’s main attraction is its extremely high resolution (<10 nm); however, its sensitivity is usually an order lower than that of PMMA. Other negative-tone resists such as AZ nLOF 2020 (Clariant Corporation, Muttenz, Switzerland) [14] and high molecular weight polystyrene (PS) [15] have sensitivities a fraction of that of PMMA; however, their AR performance is limited to 4:1 to 5:1 at 100 keV for AZ nLOF 2020 [14] and to less than 2:1 at 20 keV for PS [15, 16]. Recently, an EBL resist ‘SML’ [17] has been introduced by EM Resist Ltd. (Macclesfield, UK) in thicknesses ranging from 50 to 2,000 nm. SML is a positive-tone, organic resist that has been designed for high-AR patterning. The resist is anticipated to yield ARs of up to 10:1 at 30 keV and exceeding 50:1 at 100 keV [17].