Abstract
In this paper, we propose a cross-grating structure to enhance the critical dimension sensitivity of one dimensional nanometer scale metal gratings. Making use of the interaction between slight changes in refractive index and localized plasmons, we demonstrate sub-angstrom scale sensitivity in this structure. Compared to unaltered infinite metal gratings and truncated finite gratings, this cross-grating structure shows robust spectra dependent mostly on the dimension of the smaller line width and pitch. While typical scatterometry simulations show angstrom resolution at best, this structure has demonstrated picometer resolution. Due to the wide range of acceptable specifications, we expect experimental confirmation of such structures to soon follow.
Highlights
In the past decade, plasmons have been used extensively for a wide variety of applications
In order to test the sensitivity to changes in the line width of the copper lines, the simulated grating structure is based on copper metal lines with a barrier layer between the copper and the dielectric
To ensure that our structure is useful for whatever critical dimension (CD) or Px is produced, simulations were performed that vary both of these quantities over a large range of values
Summary
Plasmons (the quasi-particle that describes coupling of light with a collective oscillation of electrons) have been used extensively for a wide variety of applications. In order to test the sensitivity to changes in the line width (critical dimensions) of the copper lines, the simulated grating structure is based on copper metal lines with a barrier layer between the copper and the dielectric. We will use an implementation of rigorous coupled wave analysis (RCWA) which has already been used as an accurate simulation tool of non-destructive optical measurements of periodic grating structures [9],[10]. Metallic gratings can be altered to produce distinct plasmonic peaks that enhance sensitivity to critical dimension. RCWA simulations show a smooth and continuous variation over a range of physical and valid parameters. Comparing these to experimental data obtained from an ellipsometer, one can fit parameters such as CD, side wall angle, height, etc. Since copper is used extensively in the semiconductor fabrication process, that will be the metal of interest even though the noble metals could yield improved results
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