Array-type microchip sampling to determine trace metal in photoresist used in semiconductor manufacturing process

Abstract

In this work, the picolitre sampling technique using a polydimethylsiloxane (PDMS) microchip was developed for laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS). Microchips with 5 × 5 and 6 × 7 arrays of islands, 100 μm in height, treated with oxygen plasma for polarity matching, were manufactured to allow photoresist (PR) sampling on the top of islands to analyze numerous samples. The PR sample of ∼94.7 pL was evenly dotted on the island and solidified by UV irradiation. Then the PR dot was ablated using a 213 nm laser in a single shot mode, and the generated particles were delivered into an inductively coupled plasma-mass spectrometer (ICP-MS) to determine ultra-trace metals. Using standard addition calibration, five measurements with ¹¹⁵In as an internal standard were repeated using this micro array chip sampling. Six laser shots for each island were enough to ablate a positive PR completely. Detection limits for ²⁷Al, ⁶³Cu, and ²⁰⁸Pb were determined to be 2.33 ng mL⁻¹, 15.4 ng mL⁻¹ and 5.72 ng mL⁻¹, respectively, which are about 10 times better than those reported using the spin coating sampling on a silicon wafer. For method validation of this microchip sampling, a microwave digestion method was employed to determine the amount of ⁶³Cu and ²⁰⁸Pb spiked to the PR sample using ICP-MS. In terms of the analytical results, the recovery rates of 101.0% and 114.1% for ⁶³Cu and ²⁰⁸Pb were obtained for the laser ablation (LA) with microchip sampling. The results of this research found that the microarray chip sampling technique has several significant advantages, such as picolitre sampling, a high throughput, a convenient sample preparation, and a reproducible sampling in size and shape on the confined surface of island. This technique also made it possible to analyze micro scale samples, such as biological samples, by spiking the samples to the PR for solidification followed by a single shot laser ablation.