Direct impurity analysis of semiconductor photoresist samples with laser ablation ICP-MS

Abstract

A high-throughput method involving laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was developed for the determination of critical elements in semiconductor photoresist samples. An innovative procedure, including a sequence of spiking, mixing, spin-coating, and baking, was developed for the preparation of photoresist film standards to be used for calibration in the direct analytical process. The homogeneity of the photoresist sample was then evaluated using the radiotracer technique, and the effects of silicon substrate reflection, spin rate and baking temperature on the signal response of the analytes in the photoresist film were subsequently studied. The results indicated that sample pretreatment conditions (i.e., spin rate and baking temperature) strongly influenced the signal intensity. The signal variations with respect to photoresist thickness, due to the changes in spin rate, could be corrected by using an internal standard, while those due to the changes in baking temperature could not. Visual evidence of shock-wave motion, via a laser induced plasma, on the photoresist film was presented in the SEM images using a Nd-YAG laser in the Q-switched mode. For direct determination of impurities in photoresist samples, various calibration methods, including a matrix-matched external calibration curve, an internal standard with the major matrix element (i.e., carbon), and an internal standard with metal spiking (i.e., Co and Tl), were evaluated independently. The recoveries of spike metals (Al, Cu, Pt, Au, Th and U) ranged from 81 to 112%, with detection limits in the 20–285 ng mL−1 range for all elements except Al. The analytical throughput of the developed method was up to 12 samples per hour.