The demand for low cost lithography solutions in modern manufacturing has led to extended lifetime of optical lithography equipment. Use of steppers with “high mileage” has shown that heating of the projection lens with high energy input severely degrades the aerial image. This paper discusses the lens heating effects and discusses the common solutions to address this issue. This paper also demonstrates a practical solution used in high volume manufacturing environment.
     
      This paper will discuss how absorption increases with the summation of energy through a projection lens and its effect on lens aberrations. Classical techniques to reduce lens heating effects will be presented. Low NA, low Sigma resist process, targeted for lift-off  applications, is used to study its effect on lens heating.   Solution for high transmittance, high dose application will be presented with theory, data and images.