Advances in Immersion Related Defectivity on XT:1250i at IMEC

Advances in Patterning Materials for 193 nm Immersion Lithography

“…The water uptake of a resist per unit thickness is roughly constant and increases with exposure and increased resist hydrophilicity . In particular, the water uptake fraction of the fast diffusion process in Figure was observed to be roughly equivalent of the molar fraction of polar hydroxyl- and lactone-containing monomers in the resist polymer. , In addition to having a lower water diffusion coefficient than phenolic-based 248 nm resists, , typical 193 nm methacrylate resists were found to absorb less water (∼1.5−4 wt %) than hexafluoroisopropanol-functionalized norbornene addition polymers (5−8 wt %), poly(hydroxystyrene) (9−10 wt %), and novolac (2−5 wt %). , Polymeric topcoats (whether alkali soluble or organic-developable) have been shown to be permeable to water by reflectance , and quartz crystal microbalance ,,, measurements. Even though highly fluorinated organic-developable topcoats absorb very little water themselves (<0.1 wt %), , water still permeates through them (albeit less than through more hydrophilic alkali-soluble topcoats) and is taken up into the underlying resist .…”

“…Despite the inability of the topcoats to prevent water penetration into the resist film, they are an effective means by which to prevent PAG leaching into the immersion fluid. Typically, greater than 90% reduction in the amount of PAG leaching is observed with the use of a topcoat. ,,,,, Interestingly, topcoats are unable to reduce PAG leaching levels in direct proportion to their thickness. ,, In general, PAG leaching with a topcoat is predominantly from the topcoat surface with little PAG diffusion through the topcoat film itself. ,, Analysis of topcoat−resist film stacks reveals that PAG and other resist components can migrate into the topcoat film during casting. ,,,− For certain topcoat−resist pairs, this intermixing layer is substantial (see Figure ) . The intermixing of resist components with the topcoat is strongly dependent on the polarity of the topcoat casting solvent, with alcoholic solvents causing increased intermixing relative to less polar ethereal or hydrocarbon solvents. ,, In addition, the presence of a strong intermixing layer generally results in a region with slower dissolution rate during development, increased surface roughness after development, and T-top formation in the final resist profiles. , …”

“…In order to achieve defectivity levels similar to that of dry lithography, an enormous effort was directed toward identifying, classifying, and determining the root cause of various defects associated with immersion lithography. ,,,,,,,,,− As shown in Figure , typical defects can be classified into nonimmersion defects (particles, microbridging, and coating defects) and immersion-related defects (air bubbles, topcoat blister/resist swelling, drying stains, and watermarks). Since the mechanisms of defect formation in 193 nm immersion lithography and process-related defect reduction strategies have been recently reviewed by Wei and Brainard, , only a brief overview will be presented here.…”

Immersion Lithography: Photomask and Wafer-Level Materials

“…Despite these observations, there seem to be only subtle effects on sub-45-nm line and space interference imaging of some commercially available resists with both water and second-generation immersion fluids (vide infra). Both resist component extraction into the immersion fluid, and fluid permeation into the resist, may cause unwanted defects in the final resist image, and much work has been done to quantify and reduce the new defect types seen under immersion imaging (92)(93)(94). These defect types may be classified into five general categories: process-induced defects, watermark defects, defects arising from bubbles in the fluid, drying stain defects, and particle-borne defects.…”

Influence of Immersion Lithography on Wafer Edge Defectivity

“…To increase die yield, it is desirable to have EBR widths that are as small as possible. Immersion lithography [1][2][3][4] has changed the way we view defectivity issues at the wafer edge significantly. During the immersion exposure sequence, the wafer edge is in contact with the water from the immersion hood (IH), introducing additional concerns beyond direct contact of resist with the scanner.…”