Thickness analysis of silicon membranes for stencil masks

Abstract

Sossna, E.; Kassing, R.; Rangelow, I. W.; Herzinger, C. M.; Tiwald, T. E.; Woollam, John A.; and Wagner, Th., "Thickness analysis of silicon membranes for stencil masks" (2000). Stencil masks are key to charged particle projection lithography, in particular for ion projection lithography. To fulfill pattern printing requirements in the sub-70 nm regime, excellent thickness uniformity and thermal emissivity control are critical parameters for high quality stencil mask fabrication. We propose and demonstrate a technique based on infrared variable angle spectroscopic ellipsometry ͑IR-VASE͒ to measure these parameters with adequate accuracy and precision. The refractive index of the Si membrane was evaluated using a Sellmeier dispersion model combined with a Drude model. Because of its spectral range from 2 to 33 m, the IR-VASE method is sensitive to the thickness of layers as well as to the concentration and profile of Si membrane doping.

Membrane-Based In Situ Mid-Infrared Spectroscopic Ellipsometry: A Study on the Membrane Affinity of Polylactide-co-glycolide Nanoparticulate Systems

“…These parameters are in the range of minutes for IRSE even after optimization. The mathematical uncertainty of the quantitative parameters (such as the thickness and the volume fractions) from the Levenberg–Marquardt fit is typically a few percent, similar to that published by Sossna et al . on stencil mask membranes.…”

“…The mathematical uncertainty of the quantitative parameters (such as the thickness and the volume fractions) from the Levenberg–Marquardt fit is typically a few percent, similar to that published by Sossna et al. 35 on stencil mask membranes. The noise is low enough to resolve absorptions related to chemical information.…”

Fabrication of open stencil masks with asymmetric void ratio for the ion projection lithography space charge experiment

“…This dependence is caused by the broadening of the depletion region with the reverse-biased voltage, which follows a square-root function. 5,6 Measurements of the dependence of the membrane thickness on the applied voltage are presented in Fig. 2͑c͒.…”

Mechanical, geometrical, and electrical characterization of silicon membranes for open stencil masks

“…1͒, the thin n-type Si region can be anodically passivated from the etch process, but the p-Si substrate ͑due to a potential drop at the pn junction͒ is insufficiently protected and is etched with TMAH. The thickness of the membrane and how much it varies depends here on the dopant ͑type and concentration͒ and on the applied bias voltage, 1 which influences the space-charge region, since it works through the pn wafer flow process. It follows that the thickness of the membrane as well as the stress depends only on the doping concentration N a for the p side and N d for the n side.…”

“…1 The spectral range employed, from 2 to 33 m, and varying angles of incidence ͑60°, 65°, and 70°͒, allow the IR-VASE method to be very sensitive to the thickness of layers as well as to the concentration and profile of Si membrane doping. The refractive index of the Si membrane was evaluated using a Drude model for the free-carrier effects 2 and is based on consideration of a superimposed Sellmeier model.…”