Inhibition of carbon growth and removal of carbon deposits on extreme ultraviolet lithography mirrors by extreme ultraviolet irradiation in the presence of water, oxygen, or oxygen/ozone mixtures

摘要

Experiments involving the inhibition of carbon growth and removal of carbon deposits on extreme ultraviolet (EUV) lithography mirrors were carried out. First, a carbon film was deposited on a Ru-capped Mo/Si multilayer mirror by introducing n-decane gas at a pressure of 1.3 × 10~(-5) Pa into the vacuum chamber and irradiating this mirror with an EUV dose of 380 J/mm~2. Following, the mirror was further exposed to EUV irradiation while introducing water vapor, oxygen, or oxygen/ ozone mixtures at a gas pressure of 1.0 × 10~(-2) Pa into the chamber. The reflectivity of the mirror, which was decreased upon carbon-film growth, could be recovered by the introduction of oxygen or oxygen/ozone mixtures. In the inhibition experiment, EUV irradiation was carried out while introducing n-decane gas at a pressure of 1.3 × 10~(-5) Pa and, simultaneously, water vapor, oxygen, or oxygen/ozone mixtures with a pressure of about 1 × 10~(-2) Pa. No remarkable inhibition of carbon-film growth was observed for water vapor and oxygen gas. However, a definite inhibition was observed with the introduction of oxygen/ozone mixtures.