Leonhard Mader

Investigation of self-aligned phase-shifting reticles by simulation techniques

By means of simulation techniques using the SAMPLE and SPLAT programs the potential of self-aligned phase-shifting reticles for applications in microlithography is investigated and compared with conventional reticles and, to some extent, also with alternating and chromeless phase-shifter edge-line reticles. The analysis concentrates on partially coherent imaging ((sigma) equals0.5) of isolated spaces, line/space gratings and contact holes at k1 factors of 0.5 and 0.63, but wider and finer structures are also considered. The resist technique is found to have a considerable influence on the results. The work also includes a rough analysis of the necessary manufacturing tolerances of the phase reticles.

Reduction of linewidth variation for the gate conductor level by lithography based on a new antireflective layer

Abstract An antireflective bilayer consisting of a-Sin on top of a-Si has been developed in particular for the application over gate level topography with a TEOS/polySi substrate stack furnishing high substrate reflectivity, especially in case of i-line exposure. The increase in complexity of the optimized overall-process seems acceptable in view of the distinctly reduced CD variations obtained with 16M g- and i-line lots when compared to the standard technique using dyed resist.

High Contrast Single Layer Resists And Antireflection Layers - An Alternative To Multilayer Resist Techniques

Optical lithography is reflection limited within the limits of the image contrast provided by the exposure tool. The introduction of antireflection layers (ARLs) enables the use of high contrast resists which reproduce the optical image within the theoretically maximum possible range. If such resists are available, the need for multilayer resist techniques is appreciably reduced. This work reviews the known lithographic tools that counteract the reflection problem especially in the case of Al-layers, and extends the application of ARLs to silicide, poly-Si and dielectric layers on Si. The results are based on simulations performed with SAMPLE and experimental work on submicron devices.

Linewidth Control In Optical Projection Printing: Influence Of Resist Parameters

Photoresist linewidth profiles for optical projection printing with high performance stepper lenses were simulated using the SAMPLE program. Profile slopes and linewidth variations of resist structures on profiled surfaces (silicon and aluminum substrates) have been investigated in dependance on photoresist parameters such as optical absorption coefficient and thickness of the photoresist as well as exposure/development time. The study also discusses the influence of exposure wavelength (g-line vs. h-line vs. i-line) on line edge slope and standing wave effects.

Assessment of high-contrast G- and I-line resists using high-numerical-aperture exposure tools

Tests of several high contrast g- and i-line resists furnish data with respect to the resolution limit focus and exposure latitudes thermal stability and Dill parameters. A g. -line stepper of NA 0. 48 and an i-line stepper of NA 0. 40 were primarily used for exposure to a minor extent a g-line stepper of NA 0. 55. The contributions to the focus budget available under production conditions are discussed. SAMPLE simulations extending NA to 0. 60 in the gline and 0. 50 in the i-line case give latitude trends to be expected in the near future. 1.

High-NA illumination: a simulation study

Lithography simulation was used to calculate the influence of high-NA illumination on resolution, depth-of-focus, and exposure latitude evaluating the aerial image. Contour plots of exposure latitude versus NA & (sigma) at constant depth-of- focus values were calculated for dense lines, single contacts and isolated lines. All features were investigated using standard illumination and enhancement techniques (PSMs and/or annular illumination). For standard illumination the maximum exposure latitude is achieved for the highest NA possible if only small depth-of-focus is required e.g. thin resist layers over nearly plain or planarized substrates. In a production environment higher depth-of-focus values are necessary. In this case the optimum NA moves to lower values even for feature sizes near the resolution limit. However, in combination with PSMs (and/or annular illumination) the best conditions move to higher NA with decreasing feature sizes.

Evaluating the potential of alternating phase-shift masks using lithography simulation

This paper quantifies the expected gain in the process window of 150nm structures printed with DUV for alt PSM vs. COG masks and HT PSM. Most of the analysis was performed for dense lines and isolated lines using lithography simulation. Alt PSM show an increase of dose latitude by 9 percent and an improved DOF by 0.2 micrometers for dense liens. For isolated lines the real advantage is seen in the increase of DOF by 0.7 micrometers . Furthermore it will be demonstrated, that alternating PSM can improve the imagin performance of contacts significantly over competitive techniques. Chromeless PSM may push the ultimate resolution limit. However to vary the linewidth three adjacent quartz edges must be used, since two phase edges are instable in defocus. A phase shifting region needs to exceed a minimum width in order to enhance the contrast of the aerial image of the whole feature. Experimental data and simulations show that the required minimum phase-shifter width for an isolated line is in the region of 400nm. Simulation and experiment show, that 90 degrees edges are very sensitive to defocus and neighboring patterns. Using a 3D mask simulator, correction values for etch depth and parameters for a lateral underetch were determined in order to achieve intensity balancing for alt PSM for various feature sizes.

Imaging parameter optimization for advanced lithography based on STELLA

A methodology and software package STELLA (statistical evaluation of linewidth control for lithographic application) have been developed, which allow the optimization of imaging parameters for advanced optical lithography. The technique is based on calculating the CD variation distribution versus imaging parameters assuming specific process typical distributions of inter-die defocus and relative dose variation. As results a histogram of the CD distribution, the corresponding standard deviation, and the mean CD are obtained. With these numbers optimized processing conditions can be defined. The working scheme of our software package will be demonstrated. The technique will be compared to state-of-the-art imaging parameter optimization techniques. The applicability to real IC designs will be demonstrated. Our simulator allows consideration of the impact of basic resist performance parameters, like Gamma and dark resist thickness loss. Furthermore, it can deal with side lobe phenomena caused by phase-shifting masks, and considers resist feature slope criteria and resist feature loss criteria. Any NA, any scheme of illumination, and any type of mask can be applied. The simulator is well suited to compare various imaging techniques to each other. Simulation results will be compared with experimental data for advanced i-line using lithography circular and annular illumination, as well as binary and phase-shifting masks.

Search for the optimum numerical aperture

Abstract Results on the dependences of focus and exposure dose latitudes on the numerical aperture of lithographic g-line, i-line, and KrF exposure systems are given for 0.6, 0.8 and 1.0 um lines and spaces. This is done for two different resist systems by both SAMPLE 1.7 simulations and g-line experiments. The data are analysed by the use of k-factors and show some unique behavior that is strongly resist dependent.