Thermal aberration control in projection lens

Abstract

In order to respond to the constant demand for more productivity in the manufacture of IC devices, higher throughput and higher resolution are fundamental requirements for each new generation of exposure tools. However, meeting both requirements lead to unwanted aberration we refer to as "thermal aberration". In our experience, the problem of the thermal aberrations does not correlated only to the duration of heavy use. It depends very strongly on both the optical settings and the mask patterns, also even on the specific interaction between the two. So, even if using the same illumination settings, there is a possibility to observe different distribution of thermal aberrations. In this paper, we define and investigate various patterns to be used as targets for thermal aberrations compensation. These patterns are identified as the "weak patterns" of the thermal aberration. We assess several cases of thermal aberrations, and show how the optimized compensation for each is determined and then applied on the actual exposure tools.

Simulated and experimental study of laser-beam-induced thermal aberrations in precision optical systems

“…The distributions of temperature in optical lenses are highly dependent on the illumination pattern that in general is nonuniform, inducing asymmetric thermal aberrations. The defocus effect, however, is not a big concern because it can be compensated by shift of optical elements [11]. The main concern to the mechanical designer is how to reduce these asymmetric thermal aberrations to an acceptable level without utilizing active deformable lens or other complicated compensation methods.…”

Simulation Research on the Thermal Effects in Dipolar Illuminated Lithography

“…To correct assembling errors like tilt and decentration, adjusting mechanisms are employed, which are also helpful for the compensation of low order rotational symmetrical aberrations, which indicate piston Z1, defocus Z4 and primary spherical Z9. The projection objective always performs well at the beginning, during the working hours, due to the fact that all materials have good absorption at such a short wavelength, the energy absorbed by the projection lens causes significant rise in temperature, which brings surface deformation and refractive index change, and this produces so called thermal aberration [4][5][6]. While as time goes on, the heat accumulates in the illuminated zone, thermal aberrations become dominant to make the optical performance bad.…”

Analysis and experiments of the thermal–optical performance for a kinematically mounted lens element

“…In order to satisfy the demand for large-scale integrated circuit development, higher laser power and off-axis illumination technology are used to increase the productivity and resolution of the projection lens [1]. Thus, thermal aberration induced by lens heating becomes more and more important.…”

“…Nikon used infrared aberration control (IAC) technology to compensate uniform astigmatism caused by dipole illumination [1]. ASML integrated a FlexWave module in a NA 1.35 immersion to minimize lens aberration under high productivity usage of a scanner [10].…”