Wavelength and polarization dependent absorbtion effects in millisecond annealing of metal gate structures

Finite difference time domain simulation of the electromagnetic coupling in millisecond radiation heating is used to explore how the energy couples, where it goes in the device structure, and wavelength dependencies. Millisecond annealing is advantageous for improving IC device characteristics; however, the application of short time scale annealing requires very careful control over the localized heating that can be pattern, device structure, and material dependent. The presence of metal gate structure introduces extra complexity. This paper considers the case of tungsten gates on poly-silicon pedestals with or without silicon nitride caps. Rigorous finite difference time domain techniques are used to compute the fields throughout the device structure as a function of polarization, angle of incidence, wavelength, CD, and pitch. One of the dominant effects is that a grating formed by a metal gate array acts like a polarizer. Thus the coupling changes with grating orientation. The coupling is the strongest when the incident plane is perpendicular to the gate and the electric field is p-polarized. In the case of laser light with a 10 μm wavelength incident near silicon’s Brewster angle, the absorptivity approaches 100% just as if the tungsten metal gates do not exist. Data from similar studies at shorter wavelengths is also presented as well as a comparison with experimental measurements.