Critical dimension sensitivity to post-exposure bake temperature variations in EUV photoresists

Abstract

Chemically amplified resists depend upon the post-exposure bake (PEB) process to drive the deprotection reactions (in positive resists) that lead to proper resist development. For this reason they often exhibit critical dimension (CD) sensitivity to PEB temperature variation. In this work the effects of variation in different aspects of the PEB step on post-develop CD are studied for two extreme ultraviolet (EUV) photoresists. The spatial and temporal temperature uniformity of the PEB plate is measured using a wireless sensor wafer. Programmed variations in the bake plate temperature set point are then used to measure the CD sensitivity to steady state temperature variation. In addition, the initial temperature ramp time is modified using a thin sheet of polyimide film between the wafer and the bake plate. This allows for measurement of the CD sensitivity to transient temperature variation. Finally, the bake time is adjusted to measure the CD sensitivity to this parameter.

Parameter analysis of hot plate in lithography process based on regression orthogonal experiment design

“…The length of asterisk arm r 2 is: (6) r : here, the value is 1.215 m 0 : the quantity of test repeated when every factor equal to the zero level respectively. here, the value is 1. p: the quantity of factors, here is 3. m c : the quantity of two level full factor test.…”

“…Since resist tension and the chemical substances in resist are so sensitive to the temperature, that a little change of the temperature will largely affect the line width that will be printed on the wafer [5]. As the line width of circuit is smaller and smaller, the temperature of hot plate surface is also need to become more and more uniform [5][6][7][8].…”

Temperature Cycling for Photoresist Processing

“…The variation in CD for this thermally activated process ranges generally between 1 to 10 nm/ • C in bake temperature (Parker, et al [1997]). Recent investigations also show the importance of proper temperature uniformity, both during steady state and transient conditions, in significantly enhancing the CD uniformity across a wafer (Cain, et al [2005], Goto, et al [2006]). In conventional resist processing, the bake step is performed by placing the substrate on a fixed temperature bake plate and then mechanically transferring it to a fixed temperature chill plate.…”