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

Abstract

Plasma induced damage on a ∼68 nm low-k dielectric trench structure was evaluated and correlated to each plasma processing step using multiple internal reflection infrared spectroscopy (MIR-IR) complemented by XPS and SEM. The plasma stripping process causes significantly more Si-OH and C=O chemical bonding formation and breakage of Si-CH 3 bonds in porous low-k trench structure. Formation and removal of fluorocarbon post-etch residues can be monitored using the IR absorption band at 1530-1850 cm −1 . The Si-OH content provided by MIR-IR metrology can function as a sensitive and reliable quantitative metric for the rapid assessment of plasma induced dielectric damage.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-CH 3 bonds and form Si-OH (silanol) bonds on the top layer of organosilicate (SiOCH) glass low-k materials. 1 These surfaceanchored silanol groups readily adsorb water (ε ∼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 128 nm pitch was created through oxide hard mask plasma etching followed 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).

UV-Assisted Modification and Removal Mechanism of a Fluorocarbon Polymer Film on Low-k Dielectric Trench Structure

“…(see the Supporting Information, Figure S1) Using sensitive fourier transform infrared (FTIR) metrology, we have recently identified key bonding transformations during various IC manufacturing steps for porous low-k dielectrics fabrication. [9][10][11] For example, FTIR spectroscopy helped to establish the chemical bonding structure of model fluorocarbon polymer films deposited on trench structures patterned in porous low-k dielectric and evaluate plasma-induced dielectric damages on high aspect ratio trench patterns. [9][10] With functional group-specific chemical derivatization, the MFP coating on low-k trench structure was determined to consist of amorphous cross-linked fluorinated backbone decorated with fluorinated olefins and carbonyl functionalities.…”

“…9−11 For example, FTIR spectroscopy helped to establish the chemical bonding structure of model fluorocarbon polymer films deposited on trench structures patterned in porous low-k dielectric and evaluate plasmainduced dielectric damages on high aspect ratio trench patterns. 9,10 Proprietary experimental hardware built by Tokyo Electron consisting of a broadband light source (160−1100 nm) with specific filters to block UV emissions below 230 nm was used to irradiate samples in atmospheric conditions. Post-UV exposure, the samples were subsequently cleaned at 60 °C for 4 min in a proprietary cleaning solvent closely mimicking industrial cleaning standards.…”

“…Using sensitive Fourier transform infrared (FTIR) metrology, we have recently identified key bonding transformations during various IC manufacturing steps for porous low- k dielectrics fabrication. − For example, FTIR spectroscopy helped to establish the chemical bonding structure of model fluorocarbon polymer films deposited on trench structures patterned in porous low- k dielectric and evaluate plasma-induced dielectric damages on high aspect ratio trench patterns. , With functional group-specific chemical derivatization, the MFP coating on low- k trench structure was determined to consist of amorphous cross-linked fluorinated backbone decorated with fluorinated olefins and carbonyl functionalities . In this paper, we investigated UV-induced chemical modification and subsequent semiaqueous wet removal of ca.…”