content_image/909347.jpg content_image/909352.jpg
diffusion during the exposure step. When the composition is coated as a resist film and processed to form a pattern, the resist film exhibits a very high resolution during pattern formation, and forms a pattern with minimal LER and minimal line width variation relative to dose changes and pattern layout dependency. Owing to the recurring units of formula (B 1 ), the adhesion of the resist film to a processable substrate is improved, and the solubility of the resist film in alkaline developer is controlled. 

The pattern forming process using the negative resist composition can form a resist pattern with minimal LER while maintaining a high resolution. The invention is best suited for a micropatterning process, typically KrF, EUV or EB lithography. 

FIG. 1 is a diagram showing $^{1}$H-NMR spectrum of Compound Q-1 in Example 1-1. 

FIG. 2 is a diagram showing $^{1}$H-NMR spectrum of Compound Q-2 in Example 1-2. 

FIG. 3 is a diagram showing 19F-NMR spectrum of Compound Q-2 in Example 1-2. 

30 As used herein, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. "Optional" or "optionally" means that the sub› sequently described event or circumstances may or may not occur, and that description includes instances where the event or circumstance occurs and instances where it does not. The notation (Cn-Cm) means a group containing from 35 n to m carbon atoms per group. In chemical formulae, Me stands for methyl, Ac stands for acetyl, and the broken line designates a valence bond. 

The abbreviations and acronyms have the following meaning. 

EB: electron beam EUV: extreme ultraviolet Mw: weight average molecular weight Mn: number average molecular weight Mw/Mn: molecular weight distribution or dispersity GPC: gel permeation chromatography PEB: post-exposure bake PAG: photoacid generator LER: line edge roughness CDU: critical dimension uniformity 

It is understood that for some structures represented by chemical formulae, there can exist enantiomers and diaste- reamers because of the presence of asymmetric carbon atoms. In such a case, a single formula collectively repre› sents all such isomers. The isomers may be used alone or in admixture. 

## Negative Resist Composition 

The negative resist composition of the invention is defined as comprising (A) a sulfonium compound and (B) a base polymer. 

## (A) Sulfonium Compound 

Component (A) is a sulfonium compound having the formula (A). 

## BRIEF DESCRIPTION OF DRAWINGS 

## DESCRIPTION OF EMBODIMENTS 

In formula (A), R1, R 2 and R 3 are each independently a C$_{1 }$-C$_{20 }$straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom. Examples of the monovalent hydrocarbon group include alkyl groups such as methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, t-butyl, n-pentyl, t-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, cyclo› pentyl, cyclohexyl, 2-ethylhexyl, cyclopentylmethyl, cyclo› pentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclo› hexy lethy 1, cyclohexy lbuty 1, norborny 1, tricyclo [ 5 .2 .1. 0 2 • 6 ] decanyl, adamantyl, and adamantylmethyl, and aryl groups such as phenyl, naphthyl, and anthracenyl. In these hydro› carbon groups, one or more hydrogen may be replaced by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, or a moiety containing a heteroatom such as oxygen, sulfur or nitrogen may intervene between carbon atoms, so that the group may contain a hydroxy moiety, cyano moiety, carbonyl moiety, ether bond, thioether bond, ester bond, sulfonic acid ester bond, carbonate bond, carbamate bond, lactone ring, sultone ring, carboxylic anhy› dride or haloalkyl moiety. 

In formula (A), p and q are each independently an integer of O to 5, and r is an integer of O to 4. Each of p, q and r is preferably 0, 1 or 2 for ease of synthesis and availability of reactants. 

When p is 2 to 5, two adjoining groups R 1 may bond together to form a ring with the carbon atoms to which they are attached. When q is 2 to 5, two adjoining groups R $^{2 }$may bond together to form a ring with the carbon atoms to which they are attached. When r is 2 to 4, two adjoining groups R 3 may bond together to form a ring with the carbon atoms to which they are attached. 

Examples of the sulfonium compound having formula (A) are given below, but not limited thereto. 

<img src='content_image/909347.jpg'>

<img src='content_image/909352.jpg'>

