content_image/889453.jpg content_image/889458.jpg
<img src='content_image/889453.jpg'>

All the inventive resist compositions (R-1 to R-48) com› prising the sulfonium compounds having formula (A) show satisfactory results with respect to resolution, dose margin, rectangular pattern profile, and LER. The comparative resist compositions (CR-1 to CR-4) are inferior in resolution and LER. This is because the acid generated upon EB writing diffuses to the unexposed region where negative working reaction takes place to some extent, leading to a decline of contrast. 

Since the inventive resist compositions comprising the sulfonium compounds having formula (A) have a higher acid-trapping ability than the resist compositions comprising the salts of Comparative Examples 2-1 and 2-2, they are less susceptible to the unwanted reaction than the comparative resist compositions. After image writing, the sulfonium compound having formula (A) converts to a phenolic com› pound, losing the acid diffusion controlling ability. As a result, the reaction contrast between the exposed (imaged) region and the unexposed (unimaged) region is increased. Comparative resist compositions (CR-3 and CR-4) show a low reaction contrast because the inhibitor Q-4 maintains its acid diffusion controlling ability even after image writing. Consequently, from the inventive resist compositions com› prising the sulfonium compounds, patterns with satisfactory resolution and reduced edge roughness are formed. 

## Examples 3-1 to 3-9 and Comparative Examples 3-1 to 3-4 

Each of the resist compositions (R-49 to R-57 and CR-5 to CR-8) was spin coated on a silicon wafer having an antireflective coating (DUV42 by Nissan Chemical Indus- 45 tries, Ltd.) of 61 nm thick, and baked on a hotplate at 100° C. for 60 seconds to form a resist film of 240 nm thick. The resist film was exposed to KrF laser radiation by means of KrF excimer laser seamier NSR-S206D (Nikon Corp., NA=0.80), then baked (PEB) for 60 seconds, and puddle developed in a 2.38 wt % TMAH aqueous solution for 60 seconds, thereby yielding a negative 1:1 line-and-space pattern. In the PEB step, an optimum temperature for a particular resist composition was employed. 

The patterned wafer was observed under TD-SEM. When a dark pattern of 150 nm line/300 nm pitch was observed under SEM, the exposure dose (mJ/cm 2 ) which finished to a size of 150 nm on SEM observation was defined as the optimum dose (Eop). Also a bright pattern of 150 nm line/150 nm pitch printed at the optimum dose was observed under SEM. A size difference (dark pattern size-bright pattern size, nm) was computed. A smaller difference indi› cates less chemical flare or better performance. For numeri› cally expressing the roughness of a pattern at the optimum dose, a variation ofline width (30 points measured, 30 value computed) was determined and reported as LWR (nm). The pattern profile was visually judged by top-down observation 

## 5) KrF Lithography Test 

and cross-sectional observation under SEM. As used herein, the "dark pattern" refers to a layout that a resist pattern is formed around a test pattern ( area surrounding the test pattern is also exposed), and inversely, "bright pattern" refers to a layout that no resist pattern is formed around a test pattern ( only the test pattern is exposed). The results are shown in Table 10. 

<img src='content_image/889458.jpg'>

It is evident from Table 10 that the inventive resist composition possesses improved lithography performance as demonstrated by little influence of chemical flare and a good pattern profile with reduced roughness. 

## Examples 4-1 to 4-8 and Comparative Examples 4-1 to 4-8 

A resist composition was prepared by dissolving a poly› mer (Polymer 25 to 29), acid generator and acid diffusion inhibitor in a solvent in accordance with the recipe shown in Table 11, and filtering through a Teflonfi filter having a pore size of 0.2 m. After a silicon wafer was baked at 200° C. for drying and vapor primed with HMDS at 100° C. for 90 seconds, the resist composition was spin coated on the silicon wafer and pre baked on a hotplate at 110° C. for 60 seconds to form a resist film of30 nm thick. Using a scanner NXE3300 (ASML, NA 0.33, dipole 90), the resist film was exposed to EUV. The resist film was baked (PEB) at 120° C. for 60 seconds and puddle developed in a 2.38 wt% TMAH aqueous solution for 60 seconds to form a negative line› and-space pattern. 

The resist pattern was evaluated. The patterned wafer was observed under TD-SEM. The exposure dose capable of resolving a 22-nm LIS pattern at 1: 1 is reported as sensi- tivity. The minimum size at that dose is reported as resolu› tion. For numerically expressing the roughness of a 22-nm LIS pattern at the optimum dose, a variation ofline width (30 

## 6) EUV Lithography Test 

