Stress Hysteresis and Mechanical Characterization of Plasma-Enhanced Chemical Vapor Deposited Dielectrics
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Stress Hysteresis and Mechanical Characterization of Plasma-Enhanced Chemical Vapor Deposited Dielectrics Jeremy Thurn, Robert F. Cook, Mallika Kamarajugadda1, and Laura C. Stearns1 Department of Chemical Engineering and Materials Science, University of Minnesota Minneapolis, MN 55455, U.S.A. 1 Wafer Process Development, Seagate Technology Bloomington, MN 55435, U.S.A. ABSTRACT Two plasma-enhanced chemical vapor deposited (PECVD) dielectric films pertinent to microelectronic-based applications were examined for thermo-mechanical stability. Both films—silicon nitride and silicon oxy-nitride—showed significant permanent nonequilibrium changes in film stress on thermal cycling and annealing. The linear relationship between stress and temperature changed after the films were annealed at 300 °C, representing a structural change in the film resulting in a change in coefficient of thermal expansion and/or biaxial modulus. A double-substrate method was used to deduce both properties before and after the anneal of selected films and the results compared with the modulus deconvoluted from the load-displacement data from small-scale depth-sensing indentation experiments. INTRODUCTION Plasma-enhanced chemical vapor deposited (PECVD) silicon nitride (SiNx) and silicon oxynitride (SiOxNy) films serve as inter- and intra-layer dielectrics and capping layers in microelectronic interconnection structures. Such films must be mechanically stable during the thermal cycling and annealing events that commonly take place during interconnection processing. Two techniques, wafer curvature measurement and depth-sensing indentation (DSI), were used to characterize PECVD SiNx and SiOxNy films and examine their thermo-mechanical stability. EXPERIMENTAL DETAILS Table I shows the deposition conditions for the films examined here. The films were deposited onto semiconductor substrate wafers from 100 % SiH4 with either N2O (SiOxNy) or NH3 (SiNx) in N2 with dual-frequency power sources (1188.4 mW cm–2 high-frequency and 792.2 mW cm–2 low-frequency) at Unaxis (St. Petersburg, FL). The SiNx films were deposited at 1200 mTorr total chamber pressure and the SiOxNy films at 1000 mTorr. Film thicknesses ranging between 2-4 µm (measured by ellipsometry) were generated to ensure a measurable wafer curvature change with small changes in temperature. The substrate wafers were 600 µm, 150 mm diameter, (100) Si and 700 µm, 150 mm, (100) GaAs. Curvature measurements were performed with a commercial tool (FSM 900TC, Frontier Semiconductor Inc., San Jose, CA) in an evacuated chamber (10–5 torr) heated by eight Whalogen lamps at 5 °C min–1 and cooled at the same rate (except under 100 °C where cooling was exponential). The wafers were rotated in situ to measure the stress in different orientations L3.9.1
Table I. Deposition conditions for PECVD dielectrics.
Film SiNx – 1 SiNx – 2 SiNx – 3 SiOxNy – 1 SiOxNy – 2 SiOxNy – 3
SiH4 (sccm) 45 45 45 110 110 110
N2 (sccm) 900 900 900 2200 1100 2200
NH3 (sccm) 20 30 20 0 0 0
N2O (sccm) 0 0 0 1100 2200 1100
Temp (°C)
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