Plasma-assisted Discharges and Charging in EUV-induced Plasma

TL;DR

This paper investigates how EUV-induced plasma in lithography systems can cause discharges and charging effects, impacting device fabrication, and proposes methods to control these phenomena to improve manufacturing reliability.

Contribution

It models and experimentally demonstrates EUV plasma-induced discharges below Paschen limits and introduces an unloading sequence to mitigate charging and defect issues.

Findings

EUV plasma can trigger discharges below classical Paschen limits.

EUV plasma causes charging of particles and surfaces, affecting device integrity.

A special unloading sequence can mitigate charging and defectivity.

Abstract

In the past years, EUV lithography scanner systems have entered High-Volume Manufacturing for state-of-the-art Integrated Circuits (IC), with critical dimensions down to 10 nm. This technology uses 13.5 nm EUV radiation, which is transmitted through a near-vacuum H2 background gas, imaging the pattern of a reticle onto a wafer. The energetic EUV photons excite the background gas into a low-density H2 plasma. The resulting plasma will locally change the near-vacuum into a conducting medium, and can charge floating surfaces and particles, also away from the direct EUV beam. This paper will discuss the interaction between EUV-induced plasma and electrostatics, by modeling and experiments. We show that the EUV-induced plasma can trigger discharges well below the classical Paschen limit. Furthermore, we demonstrate the charging effect of the EUV plasma on both particles and surfaces. Uncontrolled, this can lead to unacceptably high voltages on the reticle backside and the generation and transport of particles. We demonstrate a special unloading sequence to use the EUV-induced plasma to actively solve the charging and defectivity challenges.