Gap-fill type HSQ/ZEP520A bilayer resist process-(I): HSQ-coated ZEP520A CD shrinkage for 32-nm trench patterns

Abstract

The CD shrinkage by thermal reflow technique was frequently used for the formation of contact hole (C/H) of fine size. However, such technique is seldom used for line (trench)/space type patterns with complicate layout, like 6T-SRAM pattern. One of the reasons is the shape distortion of the designed layout after thermal reflow which results in the difficulty in CD control. In this study ultra-thin hydrogen silsesquioxane (HSQ)-coated ZEP520A trenchs are used to investigate the CD shrinkage effect and integrity of the shape after thermal reflow. 6T-SRAM transistor gate with various width/length (W/L) ratios is used as the test pattern. HSQ diluted by methyl-isobutyl ketone (MIBK) with 1:3 and 1:14 volume ratios was coated on ZEP520A trenchs. Post-applied baking (PAB) conditions of non-HSQ coated ZEP520A are split to find the optimal CD uniformity. The effects of thickness of HSQ, dilution ratio, spin speed of HSQ on the CD and shape after thermal reflow at various temperatures for HSQ-coated ZEP520A trench patterns are also studied. Multiple thermal reflows at 160 o C-180 o C are applied to obtain the best shrinkage results. It is found that the non-HSQ coated ZEP520A trench with all W/L ratios shrunk at 160 o C. The smallest shrunk trench of 33.6 nm top-CD with 1/50 W/L ratio is obtained for HSQ (1:14)-coated ZEP520A for two thermal reflows at 160 o C/90 sec while 35.8 nm top-CD of the same W/L ratio is obtained after one 180 o C/90sec reflow. Both sizes could meet the CD requirement of 32nm node and beyond. Above all, the HSQ-coated ZEP520A keeps the shape of trench pattern after one or multiple thermal reflows.

Gap-fill type HSQ/ZEP520A bilayer resist process-(III): optimal process window for HSQ air-tip formation

“…Sub-20 nm radius of curvature on tip peak is also difficult to obtain. In previous study HSQ air-tip array structures with sub-20 nm radius of curvature were obtained by stripping ZEP520A after thermal reflow of ultra-thin HSQ (hydrogen silsesquioxane) gap-filled ZEP520A contact holes (C/H) [9,10]. In this paper, effects of HSQ spacer width and thermal reflow of ZEP520A for HSQ air-tip formation are investigated for obtaining optimal process window.…”