Evaluation of HSQ resist Medusa 84 SiH regarding suitability for various process windows

Silsesquioxane as negative-tone resist for electron beam lithography (EBL) has not ceased its importance in the EBL community over the past 20 years, offering the advantages of high resolution, low line edge roughness and sufficient etch resistivity. Novel hydrogen silsesquioxane (HSQ) based resists continue to be developed, necessitating thorough evaluation of their corresponding process windows. Among the utilized developer chemistries, tetramethylammonium hydroxide (TMAH) is of note as highly concentrated (25 %) solutions can achieve superior contrast. Because 25 % TMAH solutions are highly toxic, finding alternative developers for HSQ-based resists is of interest in the light of minimizing occupational hazards. In this study, TMAH-, KOH- and choline hydroxide (chOH)-based development processes are investigated and compared, varying developer strength and development time, as well as the influence of soft bakes, in order to find and establish stable process windows for the Medusa 84 SiH resist (Allresist GmbH). Choline hydroxide offers advantages of non-toxicity even at high concentrations and metal ion free processing. Achieved contrast curves and critical dimensions (CD) as well as line profiles are compared to both investigated KOH- and TMAH-based developer solutions.