Characterization of porous low-k films using variable angle spectroscopic ellipsometry

Abstract

Variable angle spectroscopic ellipsometry ͑VASE™͒ is used as a tool to characterize properties such as optical constant, thickness, refractive index depth profile, and pore volume fraction of single and bilayer porous low-k films. The porous films were prepared using sacrificial pore generator ͑porogen͒ approach. Two sets of porous films with open-and closed-pore geometries were measured. Three models were used for data analysis: Cauchy, Bruggeman effective medium approximation ͑BEMA͒, and graded layer. Cauchy, a well-known model for transparent films, was used to obtain thickness and optical constant, whereas BEMA was utilized to calculate the pore volume fraction from the ellipsometric data. The Cauchy or BEMA models were then modified as graded layers, resulting in a better fit and a better understanding of the porous film. The depth profile of the porous film implied a more porous layer at the substrate-film interface. We found 3%-4% more porosity at the interface compared with the bulk for both films. This work shows that VASE™, a nondestructive measurement tool, can be used to characterize single-and multigraded layer porous films quickly and effectively.

Entropy driven spontaneous formation of highly porous films from polymer–nanoparticle composites

“…Such low refractive index films obtained by spin coating are unprecedented [28]. It is interesting to note that, even at sufficiently high porogen loadings (>80%), the refractive index of films reported using the sacrificial porogen approach is still comparatively high (∼1.13-1.18) [22,10]. In addition, due to the monolithic structure of these films, it is expected that the optical constants of these films (sacrificial porogen approach) remain constant as a function of calcination temperature provided complete porogen burn out occurs.…”

“…Optical characterization of these films was performed using variable angle spectroscopic ellipsometry (VASE™, J A Wollam, Inc.) to obtain their thickness and refractive index (measured at 630 nm wavelength) applying the Cauchy model [22]. Fourier transform infrared spectroscopy of the films was performed using a Thermo Nicolet FTIR system.…”

Spectroscopic Ellipsometry of Porous Low-κ Dielectric Thin Films

“…Using this as a basis, the entire spectral range was modeled using a generalized osciUator layer with two Tauc-Lorentz osciUators while ensuring Kramers-Kronig consistency. Because compositional and pore volume grading has been observed in some 1OW-K film stacks, the generalized osciUator layer was then optically graded [12]. One can see the effect of grading on the MSE, calculated here by Levenberg-Marquardt algorithm [12] as shown in Eq.…”

“…Because compositional and pore volume grading has been observed in some 1OW-K film stacks, the generalized osciUator layer was then optically graded [12]. One can see the effect of grading on the MSE, calculated here by Levenberg-Marquardt algorithm [12] as shown in Eq. (2).…”

“…Spectroscopic ellipsometry measurements from the infrared, visible & vacuum ultraviolet wavelengths can be used to measure the thickness, pore volume fraction, gradation in the refractive index, chemical composition and molecular bonds of porous 1OW-K SiCOH films [12][13][14][15][16][17]. Currently, spectroscopic ellipsometry systems in the visible and vacuum ultraviolet (VUV) wavelength range are present in all the semiconductor fabrication plants.…”