Postexposure Delay Effect on Linewidth Variation in Base Added Chemically Amplified Resist

Abstract

Chemically amplified resist based on acid catalysis for deep UV lithography is a promising technology for patterns of 0.18 m or less. To improve the process stability and resist performance, extensive efforts have been made to understand how each component in resist formation influences lithographic performance. 1-13 Previously, the main problems for deep ultraviolet (DUV) resists were airborne contamination and linewidth change with different delay times. For the positive DUV resist, the generation of "T-top" at the resist-air interface is attributed to neutralization of the photogenerated acid by airborne organic bases, such as ammonia, during postexposure delay (PED). Employing a carbon filtration system, overcoat films and pretreating the substrate, can minimize the effects of contamination. 1-5 Linewidth variation is mainly induced by the effect of acid diffusion during exposure and baking. Therefore, the diffusion behavior of photogenerated acid has been widely investigated for both high and low activation energy (Ea) resist systems. 7-20 Adding base additives has been reported to reduce linewidth slimming of low Ea system such as acetal-based resists owing to reducing acid diffusion. 7,21 To stabilize the latent acid image of high Ea resist systems such as tertbutoxycarbonyl (t-BOC) containing resins, an additional base component was added not only to quench photogenerated acid, but also to suppress the acid diffusion reaction within the resist film. 8 Theoretical studies have also indicated that limited diffusion is essential for achieving high resolution chemically amplified DUV resists. 26,27 While inherent resist characteristics such as acid diffusion behavior, the effect of base components, and phenomenon of linewidth variation have been widely studied, presently no relationship has been established for these three components. This work evaluated the influence of organic base additive on acid concentration and lithographic performance in t-BOC-protected type chemically amplified positive DUV resist. A resist system comprising of a chemically amplified positive resist and an organic base, such as N-methyl pyrrolidone (NMP), not only prevents a T-top formation, but also suppresses acid diffusion reaction within resist film. 1 Based on the mechanism of neutralization of organic base and photogenerated acid, a model is established herein to describe the behavior of linewidth variation. Furthermore, a very useful equation has also been derived based on the diminution of photogenerated acid in resist film. This equation can accurately predict linewidth variation based on the delay time for various pattern sizes.The concentration of photogenerated acid is defined by the aerial image of the resist by a power equal to the reaction order of the acid. Therefore, the effect of exposure energy was investigated to clarify the behavior of linewidth variation during postexposure delay. The simulation result, calculated from the lithographic modeling tool PROLITH/2, has been used to evaluate exposure energy dependence...

Method to improve the throughput and retain the CD performance for DUV process

“…'8 Thus, the diffusion behavior of photogenerated acid has been widely investigated for both high and low activation energy (Ea) resist systems.3" Our previous study examined how an organic base additive influences the acid concentration and lithographic performance in a t-BOC protected type chemically amplified positive DUV resist. 12 In this work, the influence of PED and PEB baking conditions have been investigated based on the measured linewidth, i.e., critical dimension (CD). Our previously established model has been employed to describe the linewidth for various resists and process conditions.…”

Expanding the Process Window and Reducing the Optical Proximity Effect by Post-Exposure Delay

“…27,28 Our previous work investigated how an organic base additive affects the acid concentration and lithographic performance in tertbutoxycarbonyl ͑t-BOC͒ protected type chemically amplified positive DUV resist. 1 The resists included a t-BOC protected polystyrene base resin ͑substitution ratio around 25%͒ and an onium salt as a photoacid generator. A resist system composed of a chemically amplified positive resist and an organic base, such as NMP, not only prevents formation of a ''T-top,'' but also suppresses the acid diffusion reaction within resist film.…”

“…Considerable effort has been made to stabilize the exposure condition and to more accurately measure the best focus and threshold energy ͑or ''energy to clear,'' i.e., the minimum required energy to remove photoresist͒ E th , to maintain a safe process margin for mass production. [1][2][3][4][5] However, expanding the process window of the most critical linewidth, such as gate length, is the best way to solve this problem.…”