AVS 52nd International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuM

Paper PS-TuM8
Fluorocarbon Polymer Layers and Etching: the Role of Fluctuations, Cluster Ejection, and Redeposition

Tuesday, November 1, 2005, 10:40 am, Room 304

Session: Plasma Surface Interactions I
Presenter: J.J. Vegh, University of California, Berkeley
Authors: J.J. Vegh, University of California, Berkeley
D. Humbird, University of California, Berkeley
D.B. Graves, University of California, Berkeley
Correspondent: Click to Email
Fluorocarbon (FC) plasma etching is known to result in the formation of a FC-containing 'polymer' film during etch, but the nature of this film remains poorly understood. Understanding and control of this film are essential to meet goals for etch of novel materials (e.g. ultra low-k (ULK) dielectrics) and to minimize photoresist loss and surface roughening during FC plasma etch. Molecular dynamics (MD) simulations of Si etch with FC radicals, F atoms, and argon ions suggest that local film thickness fluctuations are common. These fluctuations result from ejection of clusters of FC (~C@sub 20@F@sub 20@) by Ar@super +@ impacts. Temporary, local thinning of the FC film by cluster removal allows subsequent Ar@super +@ impacts to penetrate into the underlying substrate and facilitate Si etch through the deposition of kinetic energy. Similarly, transport of F atoms to the underlying Si and of etch products to the vacuum are both facilitated by this mechanism. These phenomena have been observed in simulation previously, but the relationships between cluster removal and the formation and persistence at steady state of the fluctuating FC film are not yet clear. This fluctuation effect has not been reported experimentally, to our knowledge. We have collected statistics on the FC clusters formed during etching simulations. We report the relationship between cluster size and composition to various local and instantaneous properties in the near-surface region. These properties include the average FC film thickness and Si etch yield; fluctuations in FC film thickness and surface coverage; incident FC species type and energy; density of the FC film, and incident Ar@super +@ energy. We have simulated cluster re-deposition as well. We conclude that film fluctuation through cluster ejection and perhaps redeposition of clusters play an integral role in the maintenance of the FC overlayer.