Probabilistic process window: a new approach to focus-exposure analysis

Abstract

Background: Focus-exposure process window measurement and analysis is an essential function in lithography, but the current geometric approach suffers from several significant deficiencies.Aim: By clearly identifying the problems with the geometric process window approach, a process window measurement and analysis method will be proposed to address these problems. Approach:The probabilistic process window (PPW) proposed here takes metrology uncertainty into account and rigorously calculates the expected fraction of in-spec features based on settings for the best dose/focus and presumed random errors in dose and focus. Using the fraction of in-spec features thus calculated, a much more rigorous determination of the trade-off between exposure latitude and depth of focus (DOF) can be performed. Results:The PPW approach is demonstrated on focus-exposure data generated from a standard extreme ultraviolet lithography process at three different pitches, showing the value of this method. Conclusions:The PPW approach offers clear advantages in accuracy for both DOF determination and the best dose/focus determination. Consequently, its use is preferred both for process development applications and high-volume manufacturing.

EUV single patterning validation of curvilinear routing

“…Nominal dose of 77mj/cm 2 is used to expose FEM wafer. We used a probabilistic process window [7] to estimate the best process condition. Local measurement is done on four different gauges with distinguished feature configurations (Figure 18).…”

Evaluating the probabilistic process window for use in high volume manufacturing

“…Recently, the Probabilistic Process Window (PPW) was introduced to rigorously include stochastics effects into process window determination. 1 From the same SEM images used to measure CD, measurements of unbiased linewidth or line-edge roughness (LWR/LER) for lines and spaces or unbiased local CD uniformity (LCDU) or local pattern placement error (LPPE) for contact holes or pillars can be incorporated into the process window in a rigorous way. If these stochastic metrics are well correlated with stochastic defectivity, then defectivity measurements through focus and/or dose can be avoided.…”

“…The Probabilistic Process Window (PPW) takes a fundamentally different approach towards determining the process window as well as measuring its size. 1 The three PPW steps are:…”