The successful implementation of extreme ultraviolet lithography (EUVL) requires the use of an electrostatic chuck to both support and flatten the mask during scanning exposure. The EUVL Mask Standard, SEMI P37, specifies the nonflatness of the mask frontside and backside, as well as the thickness variation, to be 30 to 100 nm peak-to-valley, dependent on the class of substrate. Thus, characterizing and predicting the capability of the electrostatic chuck to reduce mask nonflatness to meet these specifications are critical issues. In this research, the ability of such chucks to deal with the presence of particles trapped between the substrate and chuck is investigated. Analytical and finite element modeling are used to identify the forces needed to fully embed or deform a particle during electrostatic chucking. Simulation results (using an elastic analysis) show that the forces generated by both Coulomb and Johnsen-Rahbek chucks should be able to sufficiently deform, or flatten, particles that are nearly 1.0 µm in size.
The successful implementation of extreme ultraviolet lithography (EUVL) requires the use of an electrostatic chuck to
both support and flatten the mask during scanning exposure. The EUVL Mask Standard, SEMI P37, specifies the
nonflatness of the mask frontside and backside, as well as the thickness variation, to be 30 nm to 100 nm peak-to-valley,
dependent on the class of substrate. Thus, characterizing and predicting the capability of the electrostatic chuck to
reduce mask nonflatness to meet these specifications are critical issues. In this research, the ability of such chucks to
deal with the presence of particles trapped between the substrate and chuck is investigated. Analytical and finite
element modeling have been used to identify the forces needed to fully embed or deform a particle during electrostatic
chucking. Simulation results (using an elastic analysis) have shown that the forces generated by both Coulomb and
Johnsen-Rahbek chucks should be able to sufficiently deform, or flatten, particles which are nearly 1.0 μm in size.
The International Technology Roadmap for Semiconductors requires improvements in resolution for each lithographic node. In order to meet the resolution requirements for the sub-65-nm nodes, image placement (IP) errors induced by chucking the mask during e-beam patterning, metrology, and exposure must be characterized and minimized. This study focused on a 200-mm electron projection lithography (EPL) stencil mask designed for high throughput. Finite element models were developed to simulate the response of the mask throughout a typical fabrication process flow, including the electrostatic chucking during e-beam patterning and EPL exposure. The results of this predictive study were used to identify the primary sources of IP error as a function of the system parameters.
The timely development of a Next-Generation Lithography depends upon its progress in many technology-dependent areas. Common to all high-throughput systems is the requirement of strict mask distortion control. Thus, in support of the Nikon electron-beam projection lithography tool program, three-dimensional finite element (FE) models have been developed to simulate the transient thermal and structural response of a 200-mm prototype stencil mask during electron beam exposure. Due to the relative size of pattern features, equivalent modeling techniques were employed for computational expedience. Equivalent thermal properties (conductivity and emissivity) have been calculated for perforated membranes as a function of pattern void fraction. Resulting temperature distributions were used as input for the FE structural models to characterize and quantify the local displacement fields. The structural models also utilized equivalent material properties (elastic modulus, shear modulus and Poisson's ratio). Support conditions corresponded to electrostatic chucking with four symmetrically located pad regions. The FE simulations predicted that under typical exposure conditions, the localized thermal distortions within the individual subfields are all less than 1.0 nm, which is well below the allotted error budget.
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