Multi-Technology Measurements of Amorphous Carbon Films
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J17.5.1
Multi-Technology Measurements of Amorphous Carbon Films Jingmin Leng, Jon Opsal, Heath Pois, Osman Sorkhabi, Xiaoping Liu, and Stephen J. Morris Therma-Wave Inc., 1250 Reliance Way, Fremont, CA94539, USA ABSTRACT We demonstrate that a multi-technology approach enables the accurate characterization of the thickness and optical properties of Amorphous Carbon (α-C) films used in semiconductor manufacturing. Because the material is found to be highly birefringent, with its measured refractive index and extinction coefficient depending strongly upon the polarization and angle-of-incidence of the optical probe beam that is used, conventional single angle-ofincidence Spectroscopic Ellipsometry (SE) has insufficient information-content to detect the ordinary and extraordinary refractive indices with sufficient accuracy. On the other hand, Beam Profile Reflectometry® (BPR®) is particularly strong in this case because it measures the actual reflectances for both polarization components (rather than just the difference between them) at multiple angles-of-incidence. Furthermore, the fact that BPR is a singlewavelength technique means that no assumptions must be made about the optical dispersion of the film and an absolute measurement can be made. It is then possible to combine this with other, spectral technologies to obtain ordinary and extraordinary n and k at all wavelengths. We show that, to first order, the birefringence can be modeled by assuming a single “anisotropy parameter”, the ratio between the ordinary and extraordinary refractive indices (or, more correctly, the complex dielectric functions). Using this approach in combination with a simple Bruggeman effective-medium dispersion model enables robust characterization of these films for production. INTRODUCTION Amorphous Carbon is an important material with many applications in the semiconductor, biotechnology and engineering fields, because of its physical hardness and chemical inertness. In the context of semiconductor manufacturing, it is increasingly prevalent in fabrication processes at the 90nm and 65nm technology nodes because it can be used as a hard mask, enabling the patterning of features significantly smaller than can be imprinted directly into Photoresist. Its chemical inertness (in particular, its lack of Nitrogen) make it compatible with 193nm Photoresist chemistries, and its optical absorption properties in the deep ultra-violet (DUV) part of the spectrum mean that it can also be used as an antireflective coating (ARC) layer. For the control of such manufacturing processes and the maintenance of acceptably high yields, it is therefore important to be able to characterize α-C films and in particular to find their thicknesses and optical properties. For the latter, the most important properties are the refractive index, n, and extinction coefficient, k, at 193nm because these determine their performance as ARC layers. Typical ranges of variation allowed for manufacturing processes are of the order of ∆t=0.25Å, ∆n,k =0.001-0.005, so the metrolog
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