Optimization of low-k UV Curing: Effect of Wavelength on Critical Properties of the Dielectrics

Abstract

The results of recent investigations show that after UV curing of CVD SiCOH low-k films deposited with organic material (porogen) some amount of the porogen remains in the cured films in the form of non-volatile graphitized phase, known as “porogen residue”. These residues could influence leakage current and reliability. The goal of the present work is investigation of the different parameters of UV curing that can influence amount of the porogen residue. In this work we focused generally on the study of the amount of porogen residues as function of the wavelength of curing light and the porosity of the material (amount of deposited porogen). To study the curing dependence on the wavelength, we compared optical properties (measured by spectroscopic ellipsometry) and IR adsorption (measured by FTIR) of samples cured by 172 nm monochromatic light (lamp A) with samples cured by broadband source with wavelength more than 200 nm (lamp B). To understand how the amount of porogen residue depends on the amount of deposited porogen (porosity), three films with different k-value were deposited: a film with k = 3 deposited without porogen and two porogen-based low-k with target k-value of 2.5 and 2.3. Furthermore, taking into account that He/H2 plasma effectively removes the porogen residues from porous films without any plasma damage of the matrix material, we exposed the films to that plasma. Then these films were cured by broadband lamp at different temperatures and amount of porogen residues was measured by ellipsometry. It was found that He/H2 plasma cannot fully remove the porogen and causes film shrinkage. The Subsequent UV curing does not produce significant changes.