Modeling and Analysis of Scatterometry Signatures for Optical Critical Dimension Reference Material Applications

Abstract

We use an optical critical dimension (OCD) technique, matching modeled to measured scatterometry signatures, to obtain critical dimension linewidth of lines in grating targets fabricated on SIMOX (separation by implantation of oxygen) substrates using the single-crystal critical dimension reference materials (SCCDRM) process. We first compare experimentally obtained reflectance signatures for areas of the unpatterned substrate with signatures modeled using Fresnel theory, and show that the buried oxide (BOX) layer of the SIMOX is not well described optically by a single homogeneous layer of SiO 2 , but can be so described if a mixed Si-SiO 2 boundary layer is included between the Si wafer and the BOX layer. We then obtain linewidths from OCD measurements on a series of grating targets with a range of design linewidths and pitches, and show that the linewidth obtained from the OCD technique is linearly related to the linewidth obtained from scanning electron microscopy (SEM), with a slope near unity and zero offset. While these results are very promising, further work in improving the fit of the simulated signatures to the measured signatures for some of the targets, reducing the target line roughness, and analyzing the uncertainties for potential optical critical dimension reference materials, is anticipated.

Optical Measurement of Surface Topography

“…Under these conditions it is often possible to calculate the average linewidth and other geometrical parameters of the fabricated features. 12.14 Schematic diagram of a variable angle scatterometer useful for measuring the specular reflectance as a function of incident angle (Raymond 2001, reprinted with permission) One example of research results obtained with OCD scatterometry is from Patrick et al (2007) where scattering signatures were obtained for both s-and p-plane polarized light from linewidth targets fabricated on separation by implantation of oxygen (SIMOX) wafers. 12.14 (Raymond 2001) where the flux of the specular reflected beam is measured as a function of the angle of incidence.…”

“…12.14 (Raymond 2001) where the flux of the specular reflected beam is measured as a function of the angle of incidence. 12.15 Model of a patterned wafer surface used by Patrick et al (2007) for OCD experiments. Moreover, because different states of polarization produce different angle-resolved scattering signatures, separate scattering results are measured for s-and p-plane polarized light in the incident beam.…”

“…While example measurements using the θ, 2θ mode are discussed below, it is more common to measure either the specular reflectance (for example, Yang et al 2004), or the polarization change upon reflection (for example, Niu et al 2001), at a fixed angle as a function of optical wavelength to obtain the signature. Patrick et al (2007) for specular reflectance of a patterned silicon surface as a function of angle compared with results (curves) calculated from the model of Fig. Fig.…”