Positive Resist Composition for ArF Lithography
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Solution Overview
Problem
Current micropatterning technologies using ArF excimer laser lithography face challenges with high line edge roughness (LER) due to poor affinity of base resins to developers, leading to issues like current leakage in transistor devices, and existing photoacid generators lack sufficient acid strength for high-resolution microelectronic device fabrication.
Innovation Solution
A positive resist composition comprising a polymer with specific recurring units and a sulfonium salt compound as an acid generator, which becomes soluble in alkaline developers upon acid action, effectively reducing LER and enhancing mask fidelity during photolithography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photoacid generators capable of generating perfluoroalkanesulfonic acid (5 or more carbon atoms) are used in ArF chemically amplified resist compositions, then acid strength is sufficient for high-resolution patterning, but stability and environmental problems arise due to C-F bonds and hydrophobic/lipophilic natures
Solution Approach 1:
The patent changes the carbon chain length parameter of the perfluoroalkanesulfonic acid from 5 or more carbon atoms to 3 or fewer carbon atoms. This parameter modification maintains the high acid strength needed for resolving acid-labile groups while eliminating the stability and environmental problems associated with longer carbon chains. Specifically, the patent uses perfluoropropanesulfonic acid (3 carbon atoms) which provides sufficient acid strength for high-resolution patterning without the excessive hydrophobicity and stability issues of perfluorooctanesulfonic acid (8 carbon atoms).
Solution Approach 2:
The patent employs a composite photoacid generator system combining perfluoroalkanesulfonic acid (3 or fewer carbon atoms) with specific counterions (quaternary ammonium salts or phosphonium salts). This composite approach creates a photoacid generator that delivers both the required acid strength for high-resolution patterning and improved stability by using shorter carbon chains that are less prone to degradation and environmental accumulation.
2Manufacturing precision
If the amount of photoacid generator is increased to reduce line edge roughness, then LER is reduced, but exposure dose dependency, mask fidelity and pattern rectangularity are substantially sacrificed
Solution Approach 1:
The patent changes the acid strength parameter by using perfluoroalkanesulfonic acid with 3 or fewer carbon atoms, which provides optimal acid strength for the resist system. This parameter optimization allows achieving low line edge roughness with minimal photoacid generator concentration (0.1-10 wt%, preferably 0.5-5 wt%), thereby maintaining mask fidelity and pattern rectangularity while still reducing LER effectively.
Solution Approach 2:
The patent uses a composite photoacid generator system with perfluoroalkanesulfonic acid combined with specific counterions (quaternary ammonium salts or phosphonium salts having specific structures). This composite formulation enhances the efficiency of the photoacid generator, allowing it to produce sufficient acid for low LER at lower concentrations, thus preserving mask fidelity and pattern quality.
3Illumination intensity
If carboxylic acid protective groups with bulky tertiary alkyl groups are used in resist materials, then transparency at 193 nm and dry etch resistance are achieved, but solubility in developer is reduced leading to poor line edge roughness
Solution Approach 1:
The patent modifies the protective group structure by using bulky groups with specific parameters: tertiary alkyl groups with 4-20 carbon atoms (preferably 4-15 carbon atoms) that provide both the required transparency at 193 nm and adequate solubility in developer. Examples include tert-butyl, tert-amyl, and adamantyl groups. The patent optimizes the balance between group bulk (for transparency and etch resistance) and carbon chain length (for solubility), achieving low LER while maintaining optical and chemical properties.
Data Source
AI summary
A positive resist composition comprises (A) a resin component which becomes soluble in an alkaline developer under the action of an acid and (B) an acid generator. The resin (A) is a polymer comprising specific recurring units, represented by formula (1). The acid generator (B) is a specific sulfonium salt compound. When processed by lithography, the composition is improved in resolution and forms a pattern with a satisfactory mask fidelity and a minimal LER.Herein R1 is H or methyl, R2 is an acid labile group, R3 is CO2R4 when X is CH2, R3 is H or CO2R4 when X is O, R4 is a monovalent C1-C20 hydrocarbon group, and m is 1 or 2.