Stochasticity is a major contributor to the resolution limit of fine mechanics and optical imaging, which is also an obstacle for achieving cutting edge EUV lithography performance. The root cause of stochasticity comes from the pattern edge random variation within the resist after exposure due to low contrast. High substrate adhesion is also very fatal as it further aggravates the variation at the substrate due to increased interaction, leading to stochastic failures. In this paper, Stochastic Area Thickness (SAT) and Dynamic Stochastic Area Thickness (DSAT) are used to evaluate the stochastic interactions. High optical foot exposure is proposed instead of conventional low substrate reflectivity to reduce SAT. Adhesion control by acid/quencher loading is proposed to minimize the stochastic interaction between resist and substrate.
Silicon hardmask (Si-HM) materials used in lithography processes play a critical role in transferring patterns to desired substrates. In addition, these materials allow for the tuning of optical properties such as reflectivity and optical distribution for better lithography. Si-HM materials also need to possess good compatibility with photoresists before and after optical exposure, during which the photoresist in the exposed area may change polarity. Therefore, Si-HM materials may benefit from adaptive or amphiphilic capabilities to keep both exposed and unexposed photoresist compatible with the substrate. In this work, we will demonstrate that Si-HM surfaces may be adaptive or amphiphilic through both experiments and computer simulation. Specifically, we will demonstrate that the functional groups (polar and nonpolar) at the Si-HM surface may be switchable, and the surface will be dictated by the environment to which the Si-HM is exposed. Knowing the adaptive capability of Si-HM materials will greatly facilitate the development of better underlayer materials for improved lithography.
Measuring properties of ultrathin optical films is based on optical interference. Ultrathin films are very challenging to test, because their thicknesses are far smaller than the measuring wavelength, so very little phase shift can be detected. In this work, test sensitivity and accuracy are improved by a rigorous algorithm in which all unknowns {n,k,t} in their full space are fit together without approximations and presumptions. As a result, a software for variable-angle spectroscopic ellipsometer (VASE) data fitting was developed. It gives very reliable ultrathin-film measurement down to 2.5 nanometers. The software not only improves the reliability, accuracy of {n,k,t} measurement, but it also extends VASE capabilities to characterize a film’s optical quality.
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