Structural And Compositional Evolution Of SiO/sub 2/ Aerogel Film By Oxygen Plasma Treatment

Abstract

The basic technological trend in ultra large-scaled integration is the realization of a higher device speed with closer packing density, which results in multilevel interconnection structure. Interconnection delay, generally termed resistance-capacitance (RC) time delay, which is mainly dominated by parasitic capacitance between metal interconnections, has received a great deal of attention over the basic gate delay in the deep submicron devices. Therefore, low K (i.e., low dielectric constant) materials, which substitute for conventional intermetal dielectric (IMD), have become imperative for the reduction of parasitic capacitance between multi-level layers. Sol-gel derived SiO, aerogel film can be one of the prospective candidates for IMD material, because a very low dielectric constant can be achieved from its inherent high porosity. But from the characteristics of sol-gel derived process, skeletal network of SiO, aerogel film contains a number of Si-OR (R=alkoxyl group) and Si-OH bonds and absorbed water as internal species. And degradation of the electrical properties such as dielectric constant and leakage current density was observed due to the above polarizable species. A possible application of 0, plasma treatment using inductively coupled plasma (ICP) to SO, aerogel film at room temperature was introduced for the control of internal surface chemical species in the film. SiO, aerogel films were synthesized on a p-Si substrate by the supercritical drying method. After the supercritical drying process, the films were subjected to an 0, plasma treatment at room temperature. The chemical composition and film porosity were determined by Rutherford backscattering spectroscopy (RBS). The surface morphology and thickness of films were observed using scanning electron microscopy (SEM). To investigate the change of chemical species and surface chemical bonding state, X-ray photoelectron spectroscopy (XPS) was used. Leakage current behavior was evaluated. The composition of films, e.g., ratios of O/Si and C/Si, was measured to be 1:2.5.1.0 for as-prepared SO, aerogel film and 1:2.1:0.03 for oxygen plasma treated film using RBS The carbon content in the films decreased drastically after the oxygen plasma treatment. It was caused by the reduction of internal surface organics in SiO, aerogel film The widescan XPS results of SiO, aerogel films before and after the oxygen plasma treatment are given in Fig. 1. Even though Si, 0, and C peaks can be found in both films, the intensity of C I s peak remarkably decreased in oxygen plasma treated film. This result is in agreement with RBS analysis. The variation of surface morphology and thickness in SiO, aerogel film by oxygen plasma treatment is given in Fig. 2. 600 W of ICP power brought about the growth of particle size only at uppermost surface layer. Also, the thickness of the film decreased remarkably, however the porosity of the film decreased by only 5 Yo. Leakage current characteristics of SiO, aerogel films before and after the oxygen plasma treatment at up to 1 MV/cm of applying electric field is shown in Fig. 3. I-V characteristics were evaluated in terms of the amount of residual surface coverages. Better leakage current density was achieved after the oxygen plasma treatment, i.e., the removal of surface organic species.