Evaluation of Plasma Damage to Low-k Dielectric Trench Structures by Multiple Internal Reflection Infrared Spectroscopy

Abstract

Plasma etch damage is the main cause of dielectric degradation of porous low-k materials during fabrication of advanced Cu/low-k interconnects. Highly energetic ions, reactive radicals and vacuum ultraviolet radiation generated during plasma etching have been shown to break Si-CH3 bonds and form Si-OH (silanol) bonds on the top layeroforganosilicate(SiOCH)glasslow-kmaterials. 1 Thesesurfaceanchored silanol groups readily adsorb water (e ∼80) degrading the effectiveness of the low-k materials. Although electrical characterization (e.g. reliability and leakage current measurements) of fully processed interconnects can reveal dielectric degradation, these methods are costly and cannot pinpoint any particular process causing the damage. 2 Other characterization techniques can also yield information about plasma induced damage to low-k materials. 3‐6 These methods, however, are most effective for blanket wafers. Thus, there is a pressing need for a convenient metrology to identify and quantify the damage on the side walls of dielectric trench structures from plasma processing such as photoresist stripping. In this study, we utilized multiple internal reflection infrared spectroscopy (MIR-IR) to monitor water adsorption, carbon stripping and post-etch residues during the formation of trench structures in low-k dielectric materials via plasma etch and strip processes. Fourier transform infrared spectroscopy (FTIR), a fast and non-contact metrology, can provide direct observation of water adsorption and the chemical bonding structure of blanket porous low-k dielectric materials. Recently, applications of FTIR to characterize patterned dielectric wafer were reported. 7‐9 MIR-IR spectroscopy can increase detection sensitivity up to 100-fold compared with conventional FTIR because the wafer itself serves as an IR waveguide allowing for multiple detections. 10,11 In this work, a test pattern of ∼68 nm trenches with 128nmpitchwascreatedthroughoxidehardmaskplasmaetchingfollowed by organic residue stripping. Damage to the dielectric in terms of silanol formation was quantified and correlated to each plasma processing step using MIR-IR complemented by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM).