Full field analysis of critical dimension uniformity due to focal variation for contact features in extreme ultraviolet lithography.

Extreme ultraviolet (EUV) lithography is the leading candidate for 22 nm node technology and beyond. This research studies the influence of focal contributor on critical dimension (CD) variation in the EUV lithography and calculates the CD sensitivity to focal contributor based on the resist CD. EUV lithography parameters used in the simulation include NA = 0.25, 6 degrees oblique incident on the mask and source wavelength at 13.6 nm. The reflection design of EUV mask consists of 40 alternating Si/Mo layers, a ruthenium capping layer, and an absorber layer. The Rayleigh-Sommerfeld diffraction theory is adapted to solve the aerial image of contact hole (CH) feature layouts on the EUV mask. Then the resist CDs for the CH feature are measured at the position of the 10% from the bottom of resist profile. The target CD is 35 nm on wafer. The simulation results reveal the 2 nm discrepancy of spatial position for the aerial image curves measured between on the X metrology and Y metrology planes. The CDs of CH features with the iso-pitch are more sensitive to focal variation than the CDs of the features with the dense pitch. The maximum CD uniformity is 3.1 nm for the focal range at 90 nm.