HPLC-CAD Analysis of a Photoacid Generator in Photoresist

1. Introduction

Photolithography is a key process in integrated circuit manufacturing and requires photoresist as a critical material. The photoacid generator (PAG) in photoresist is decisive for sensitivity and resolution.

Photoresist is composed mainly of organic solvent, polymer resin, photoacid generator and additives. Purity and impurity control of the photoacid generator directly affect photoresist quality and semiconductor yield.

A typical photoacid generator contains a triphenylsulfonium cation and a perfluorobutanesulfonate anion. Because the anion has almost no UV absorption and lacks a chromophore, CAD is suitable when optical detectors are limited.

2. Instruments and materials

Instruments: Agilent 1200 HPLC system with Instrumax CADetector a1 Charged Aerosol Detector.

Reagents: Watson’s distilled water, acetonitrile (HPLC grade), formic acid (analytical grade).

Sample: triphenylsulfonium perfluorobutanesulfonate.

3. Method and results

3.1 Chromatographic conditions

Column: InfinityLab Poroshell 120 EC-C18. Column temperature: 55 °C. Flow rate: 0.4 mL/min. Injection volume: 5 μL. Mobile phase A: 0.2% formic acid aqueous solution. Mobile phase B: acetonitrile. Gradient elution.

CAD conditions

Instrument: Instrumax CADetector a1. Drift tube temperature: 40 °C. Nebulizing gas flow: 3 L/min. Charging current: 1 μA. Charging gas flow: 1 L/min.

3.2 Sample preparation

Diluent: methanol and methanol/water (1:1). A 2000 µg/mL stock solution was prepared in methanol and serially diluted to 1, 2, 5, 10, 100 and 1000 µg/mL.

3.3 Experimental results

Method suitability: cation and anion retention times were appropriate; resolution, peak shape and peak response were good.

Sensitivity: at 1 µg/mL and 5 μL injection, the signal-to-noise ratio was 129.6 for triphenylsulfonium and 84.3 for perfluorobutanesulfonate, both by the ASTM method.

Repeatability: six consecutive injections gave a triphenylsulfonium peak-area RSD of 0.989 and a perfluorobutanesulfonate peak-area RSD of 0.433%.

Linearity: from 1–1000 µg/mL, correlation coefficients were R = 0.99998 for triphenylsulfonium and R = 0.99985 for perfluorobutanesulfonate.

4. Conclusion

HPLC-CAD provides high sensitivity, good ion separation and repeatability, and a wide linear range for photoacid generator analysis. It can be used for quality control and method evaluation of photoacid generators.