Analysis of thermal properties of liquid for exposure in ArF immersion lithography

The liquid which is inserted between the final lens and the wafer is an imaging medium in ArF immersion lithography system. During the lithographic exposure, the change of temperature distribution in the liquid can result in the change of its refractive index and the decrease of the quality of its lithography. So, it is necessary to determine the distribution of the temperature. In this work, a finite element method was applied to establish a two-dimensional computational model so that the temperature distribution of the liquid at different inlet pressure can be analyzed when the flow direction of the liquid is consistent or opposite with the movement direction of the wafer. By the analyses above, the influence of the residual thermal energy in the wafer on the temperature distribution of the liquid was analyzed. The results show that the maximum increment of the temperature is about 0.15 K and the thermal penetration depth is 0.4 mm when the residual thermal energy in the wafer is not considered and they are respectively 0.02 K and 0.45 mm when the residual thermal energy in the wafer is considered.