AVS 58th Annual International Symposium and Exhibition
    Plasma Science and Technology Division Tuesday Sessions
       Session PS-TuM

Paper PS-TuM6
Plasma Processing of Ti and TiN Metal Hardmasks for Dielectric Etch

Tuesday, November 1, 2011, 9:40 am, Room 201

Session: Advanced BEOL / Interconnect Etching I
Presenter: Florian Weilnboeck, University of Maryland, College Park
Authors: F. Weilnboeck, University of Maryland, College Park
E. Bartis, University of Maryland, College Park
S. Shachar, University of Maryland, College Park
G.S. Oehrlein, University of Maryland, College Park
D. Farber, Texas Instruments Incorporated
T. Lii, Texas Instruments Incorporated
C. Lenox, Texas Instruments Incorporated
Correspondent: Click to Email
Ti and TiN metal hardmasks are of interest for plasma-based pattern transfer into low-k materials due to their expected improvements of etch performance and process flow relative to resist masks. We have studied the performance of Ti and TiN in CF4/Ar and C4F8/Ar discharges along with organosilicate glass (OSG) - a reference low-k material. Plasma processes were characterized in real-time by in-situ ellipsometry and provided information on erosion stages, etch rates (ER) and selectivity (SEL), i.e. ER(OSG)/ER(hardmask). Post plasma characterization was performed by vacuum transfer x-ray photoelectron spectroscopy (XPS). Plasma parameters investigated were: 1) ion energy, 2) pressure, 3) Ar dilution, 4) O2 addition and 5) N2 addition to fluorocarbon/Ar mixtures. Furthermore, we have studied chamber wall contamination and surface reactions upon atmospheric exposure of processed Ti/TiN hardmasks. Ellipsometric multilayer modeling of real-time measurements showed three hardmask erosion stages: 1) initial removal of surface oxides, 2) steady state erosion with F-saturated hardmask surfaces (TiFx, x~3) covered with a FC film (0.8-1.6nm depending on plasma conditions) and 3) small amounts of Ti remaining on the underlayer after erosion of the hardmask layer. For all plasma conditions, Ti provides systematically lower ERs and higher SELs (~15) than TiN (~11). The higher ERs of Ti over TiN can be explained by the rapid removal of N by formation of NF3 and the smaller Ti-atom number density of TiN compared to Ti. Surprisingly, the more polymerizing C4F8 conditions lead to lower SELs than CF4. This observation is explained by FC layer-induced OSG ER reduction, whereas for the hardmasks materials ER are limited by product volatility and the FC surface layer effect is reduced, e.g. as compared to conventional organic masking layers. Chamber contamination studies have shown that only small amounts of Ti (<1%) are deposited together with FC on the chamber wall. Overall, metal hardmasks, especially Ti, showed excellent performance as a masking material in low-k etch and provide high SEL (~15) which can be further increased by systematically optimizing discussed plasma parameters.