Automated Characterization of Optical Image Quality SFR Workshop May 24, 2001 Andrew R. Neureuther, Garth Robins (SRC/DARPA), Kostas Adam Berkeley, CA 2001 GOAL: Complete initial simulations and experiments sufficient to design polarization masks and multi-parameter test structures 9/30/2001. 5/24/2001

Motivation Lithography at low k1, high NA and with phase-shifting masks is adversely affected by small residual aberrations in lenses. Test targets are needed: As ‘canaries’ that are more sensitive than product features To quantify individual aberrations to 0.01 waves rms The introduction of polarizing features allows an as yet an untapped degree of freedom for lithography. A combination of theoretical image analysis, simulation and experimentation can be used to gain insight and understanding to assure small feature reproducibility. Combining automatic (optical and/or SEM) wafer inspection with simulation interpretation gives leverage. 5/24/2001

Programmed-Probe Based Aberration Targets: Concept 0.5 l/NA The 0.4 l/NA by 0.4 l/NA programmed 180o phase defect provides an interferometric like reference electric field with magnitude 0.43 and phase of 180o compared to the clear area field. 0.4 l/NA 180o Sq. Defect 0.6 l/NA Line Sidelobe Coma Sidelobe -0.1 wave => 0.40 0.0 wave => 0.30 0.1 wave => 0.21 Detect Sidelobe by over exposing 2.5x and using automatic wafer inspection 5/24/2001

Programmed-Probe Based Aberration Targets: Layout Dark Field Patterns Grid is 0.1 l/NA Probe Astigmatism Spherical 1 at 90o Trefoil Coma 1 at 0o 1 at 180o 5/24/2001

Evolution of the Program-Probe Targets Improvement Sensitivity = Δ I / Δ l Target 0.1λ Coma(cos) -0.74 -0.93 1.74 0.1λ Coma(sin) -0.08 -0.07 -0.05 0.1λ Trefoil(cos) -0.47 -0.72 -0.20 0.1λ Trefoil(sin) -0.10 -0.22 5/24/2001

First Demonstration of Separation of Spherical and Defocus 90 180 5/24/2001

NEW Theoretical Foundation for PPBAT Approach Represent target diffraction as sum of Zernike’s in pupil Approx. exp[jOPD] as 1 + jOPD Result Orthogonality allows each aberration to be excited alone Target is the Fourier Transform of that particular Zernike Implications Diameter of target goes inversely with radial order Phase variation on target is similar to Airy function The center is a natural location for the probe because the weighted area of Zernike is zero and gives a null in the center. 5/24/2001

Tolerance Assessment of PPBAT Mask Dimensions Probe size – High 10% –Calibrate via isolated probe => 1% Feature Linewidth –Low – 0.8% Alignment Probe to feature – High 4% or with raster scan Low 1% Phase to feature – Moderate 1.5% Phase Process Phase – Low 0.25% Etch Bias – Moderate 1.5% – Fix: use flavors => 0.5% Profile shape – Low 1% (can be checked with TEMPEST) Ga stain – Low 0.1% Use to monitor mask quality? RSS Combined ~ 4.8% => 2.5% 5/24/2001

2002 and 2003 Goals Aberration Targets Electrical Test Measure with CD SEM Electrical Test Measure with Electroglass Haolin Zhang and Costas Spanos Conduct and quantitatively interpret polarization masks, and multi-parameter test structures, by 9/30/2002. Define apparatus, specify testing procedures, and interpret data for polarization masks, and multi-parameter test structures, by 9/30/2003. 5/24/2001