IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Plasma Science Wednesday Sessions
       Session PS1-WeM

Paper PS1-WeM2
Low-k Etch Selectivity Enhancement Through Ion Energy Control

Wednesday, October 31, 2001, 8:40 am, Room 103

Session: Dielectric Etch II
Presenter: R. Silapunt, University of Wisconsin-Madison
Authors: R. Silapunt, University of Wisconsin-Madison
A.E. Wendt, University of Wisconsin-Madison
K.H.R. Kirmse, Texas Instruments, Inc.
F.G. Celii, Texas Instruments, Inc.
Correspondent: Click to Email
Organosilicate glass (OSG) is a low-k dielectric material under development for high speed interconnects in integrated circuit manufacturing, but selective etching of OSG over etch stop layers, Silicon Carbide (SiC) and Silicon Nitride (SiN), has proven challenging. Because the energy of ions bombarding the substrate has been shown to play an important role in etch selectivity, it has been proposed that improved ion energy control may provide a solution for improving OSG etch selectivity. However, the conventional sinusoidal substrate bias voltage waveform leads to a broad ion energy distribution (IED), allowing only crude control over average ion energy. Using a narrow IED may significantly enhance selectivity, especially when the ions have energy above the etching threshold energy of one material, but below the threshold energy of the other. We have applied a technique for producing a narrow IED to evaluate its potential for improving OSG/SiN and OSG/SiC etch selectivity. This method replaces the sinusoidal substrate bias voltage waveform with a specially tailored bias voltage waveform consisting of a short voltage spike in combination with longer periods of constant voltage. This produces a nearly constant voltage drop across the substrate sheath and thus a narrow IED. Etching experiments have been conducted in a helicon plasma etching reactor with a C@sub 4@F@sub 8@/Ar/N@sub 2@ gas mixture. A comparison of OSG/SiC and OSG/SiN selectivities between sinusoidal and tailored substrate bias voltage waveform has been made. Etch rates as a function of average ion energy for sinusoidal and tailored bias voltage waveforms show significant differences. With the tailored bias voltage waveform, infinite selectivity is achieved for a 40 V range of bias voltage, while a maximum selectivity of ~2:1 is achieved for the sinusoidal waveform.