Bonding Structure of Model Fluorocarbon Polymer Residue Determined by Functional Group Specific Chemical Derivatization

Abstract

The incorporation of porous low-k (k = 2.0) interlayer dielectrics (ILD) in BEOL (back-end-of-line) interconnects to reduce RC time delays continues to pose major integration challenges. Typically, low dielectric constants are achieved by replacing Si‐O bonds with Si‐C bonds to create nanoscale porosity in the silicon oxide dielectric matrix. 1 Porosity induced lowering of mechanical strength in carbondoped silicon oxide (CDO) makes them more susceptible to damage caused by common patterning processes such as fluorocarbon-based reactive ion etching (RIE). 1 Characterization of the post-RIE etch fluorocarbon polymer residues is essential because incomplete removal can cause problems with subsequent layers such as poor adhesion and coverage, fluoride contamination and poor electrical contact. 2 Electron and optical spectroscopy, electron microscopy, scanning probe microscopy and other probing tools have been used to identify and characterize model post-etch residues deposited on blanket Si substratesorcheckerboardpatternedwafersoflargedimensions. 3‐7 However, an improved understanding of chemical bonding structure of these fluoropolymer coatings is needed to facilitate more efficient process integration between trench etch and post-etch clean for small patterned features. In this study, the chemical bonding structure of model fluorocarbon polymer (MFP) residues deposited on a patterned CDO trench nanostructurewasdeterminedusingFouriertransforminfrared(FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The MFP residues (6‐28 nm) were deposited on 90 nm low-k dielectric lines using fabrication processes closely mimicking actual manufacturing conditions. Enabled by precise background cancellation, FTIR revealed detailed chemical bondingcompositionoftheMFPresidues.Functionalgroupspecificchemistry in conjunction with IR and XPS analyses showed that MFP residue consisted of amorphous fluorinated polymers with significant branching, C=C bonds and C=O functional groups. The chemical bonding composition of deposited fluorocarbon layers can be modified by altering the plasma chemistry which can potentially lead to a more clean-efficient plasma etching process.