Analytical Instrument Documents

Introduction

As semiconductor device scaling advances, photoresists are required to provide high resolution, low line width roughness (LWR), and high pattern stability. To meet these requirements, PAG‑bound copolymers, in which a photo acid generator (PAG) is covalently bonded to the polymer main chain or side chain, have attracted increasing attention. Figure 1 shows the monomer structures of a model sample. The main backbone is a methacrylate polymer designed for ArF excimer laser lithography, which is currently the mainstream technology. In the photoacid generator monomer, photolysis of the triphenylsulfonium (C₁₈H₁₅S^⁺) produces a proton, which is captured by the difluoromethanesulfonate (CHF₂SO₃^⁻) counter anion to form a strong acid. In the deprotection monomer, an acid‑catalyzed reaction cleaves the ethylcyclopentyl protecting group (C₇H₁₄), exposing a hydroxyl group and thereby rendering the polymer soluble in alkaline developer solutions.

For the design and quality assurance of such high‑performance polymers, detailed evaluation of monomer composition, end groups, and molecular structures is essential. This MSTips introduces analytical examples using MALDI‑TOFMS and pyrolysis‑GC‑TOFMS. MALDI‑TOFMS enables direct observation of molecular ions even in the high‑molecular‑weight region. Although mass spectra of copolymers are often complex, Kendrick mass defect (KMD) analysis with msRepeatFinder allows visualization of repeating units and efficient acquisition of information on degree of polymerization and end‑group composition. Pyrolysis‑GC‑MS provides structural information on substructures originating from monomers and end groups. While many detected pyrolysis products are not registered in the NIST library, automated analysis be achieved using AI structure analysis with msFineAnalysis AI.