Chemical amplification based on acid-catalyzed depolymerization.

Abstract

The chemical amplification concept proposed in 1982 to support high resolution short wavelength lithographic technologies that demand highly sensitive advanced resist systems is based on acid-catalyzed crosslinking, deprotection, and depolymerization reactions. Each approach has shown a tremendous progress. In this paper is reviewed the depolymerization concept for the design of sensitive positive resist systems formulated with triarylsulfonium salt acid generators.Three modes of the initiation of acid-catalyzed depolymerization are discussed; (1) attack of acids onto backbone oxygens as exemplified by depolymerization of polyphthalaldehyde (PPA), (2) scission of pendant ester groups followed by depolymerization with poly(a-acetoxystyrene ) (PACOST) as an example, and (3) unzipping from the polymer ends as demonstrated by depolymerization of cationically obtained polyp-hydroxy-a-methylstyrene) (pPHOMS). The positive resist systems based on depolymerization of PPA derivatives include a thermally-developable OZ reactive ion etch (RIE) barrier resist for use in the bilayer scheme and the use of PPA as a polymeric dissolution inhibitor for novolac resins. The deesterification of PACOST results in formation of poly(phenylacetylene) (PPA) and simultaneous depolymerization to provide positive images upon development with xylenes, which is briefly discussed. Cationically prepared pPHOMS exhibits 80 % thickness loss at ca. 1 mJ/cm2 upon postbake at 130°C whereas anionic pPHOMS and cationic meta-PHOST are very stable toward acidolysis, indicating that the depolymerization propagates from the termination side of the chain.

Amplified responses in materials using linear polymers that depolymerize from end‐to‐end when exposed to specific stimuli

“…This overall grouping of polymers has been given various names (self‐immolative, unzipping, metastable), but to better differentiate this type of polymer from other types of depolymerizable polymers and from other self‐immolative reagents (e.g., prodrugs and degradable dendrimers), we now refer to them as CD r polymers, which stands for continuous depolymerization after a reaction‐based detection unit responds to a specific stimulus . This nomenclature also differentiates this new class of linear depolymerizable polymers from polymers that continuously depolymerize when the backbone cleaves in response to a non‐specific signal (e.g., hydrolysis) (these polymers are termed CD b polymers) . It further differentiates this class of polymers from those that degrade via fragmentation depolymerization reactions (FD polymers) in which reaction with one stimulus cleaves the polymer into two shorter polymers, but where additional reactions between the stimulus and the polymer are required to complete the degradation process (these polymers do not provide amplified responses) …”

Chain-Scission Polyethers for EUV Lithography

“…These properties, however, have been found to be inversely related, a relationship commonly referred to as the RLS trade-off [1]. To overcome the RLS trade-off, the lithographic community is investigating alternative resist platforms such as molecular glasses [2][3][4], polymer-bound photoacid generators (PAGs) [5][6][7], and chain-scission polymers [8][9][10][11][12][13][14][15][16][17][18][19][20][21].…”

“…Despite some compelling advantages, PMMA resists have a number of drawbacks that have prevented their widespread use, such as the need for organic solvent development, high outgassing, poor etch resistance and poor sensitivity. Other important work in this area has included polyacetals [16][17], self-developing polymers [18], and non-chemically amplified polycarbonates ( Figure 1) [19]. Despite continuing research in these areas, organic solvent development, high outgassing levels, and achieving high molecular weights during polymerization continue to be problematic in the current literature.…”

Photoinduced depolymerization in poly(olefin sulfone) films comprised of volatile monomers doped with a photobase generator

“…Photopolymers play an important role in current technologies and enable the processing of a wide variety of novel materials 1. However, few of the photopolymers investigated to date exhibit photoinduced conversion to monomers under mild conditions 2–8. Poly(olefin sulfone)s possess sulfonyl groups (SO 2 ) in the main chain and are easily synthesized by radical polymerization of olefin monomers in liquefied sulfur dioxide 9.…”