EUV Debris Mitigation using Magnetic Nulls

TL;DR

This paper explores a novel magnetic null configuration to mitigate tin debris in EUV lithography, reducing mirror damage without trapping ions, thus potentially enhancing system lifetime and efficiency.

Contribution

It introduces a previously unconsidered magnetic null geometry for debris mitigation, optimizing coil placement and demonstrating its effectiveness in preventing ion trapping.

Findings

Magnetic null configuration reduces ion impact on mirrors.

Ion trajectories near the null are chaotic, preventing trapping.

Potential for improved EUV system lifetime and buffer gas efficiency.

Abstract

Next generation EUV sources for photolithography use light produced by laser-produced plasmas (LPP) from ablated tin droplets. A major challenge for extending the lifetime of these devices is mitigating damage caused by deposition of tin debris on the sensitive collection mirror. Especially difficult to stop are high energy (up to 10 keV) highly charged tin ions created in the plasma. Existing solutions include the use of stopping gas, electric fields, and magnetic fields. One common configuration consists of a magnetic field perpendicular to the EUV emission direction, but such a system can result in ion populations that are trapped rather than removed. We investigate a previously unconsidered mitigation geometry consisting of a magnetic null by performing full-orbit integration of the ion trajectories in an EUV system with realistic dimensions, and optimize the coil locations for the null configuration. The magnetic null prevents a fraction of ions from hitting the mirror comparable to that of the perpendicular field, but does not trap any ions due to the chaotic nature of ion trajectories that pass close to the null. This technology can potentially improve LPP-based EUV photolithography system efficiency and lifetime, and may allow for a different, more efficient formulation of buffer gas.