AVS 46th International Symposium
    Plasma Science and Technology Division Thursday Sessions
       Session PS1-ThA

Paper PS1-ThA8
Transfer Etching of Bilayer Resists in Oxygen-based Plasmas

Thursday, October 28, 1999, 4:20 pm, Room 612

Session: High Fidelity Pattern Transfer
Presenter: A.P. Mahorowala, IBM T.J. Watson Research Center
Authors: A.P. Mahorowala, IBM T.J. Watson Research Center
K. Babich, IBM T.J. Watson Research Center
Q. Lin, IBM T.J. Watson Research Center
D.R. Medeiros, IBM T.J. Watson Research Center
K. Petrillo, IBM T.J. Watson Research Center
J. Simons, IBM T.J. Watson Research Center
M. Angelopoulos, IBM T.J. Watson Research Center
G.W. Reynolds, University of Wisconsin, Madison
J.W. Taylor, University of Wisconsin, Madison
Correspondent: Click to Email
Thin film imaging offers the possibility of extending 248 nm lithography to sub-150 nm resolution. We have been working on a 248 nm bilayer resist scheme which utilizes a thin Si-containing resist on top of a thick, planarizing underlayer. The image is developed in the top layer and then transferred to the underlayer via an oxygen-based plasma etch. This paper will focus on two aspects of the critical transfer etch step - 1) etch resistance of the imaging resist and 2) control of profiles and resist roughening. The imaging resist thickness loss rate during the transfer etch is characterized by a rapid decrease in the first 10 seconds followed by a slow rate for the remaining etch. The relative importance of three phenomena occurring when Si-containing resists are exposed to oxygen-based plasmas - 1) oxidation of silicon, 2) deprotection of resist moieties, and 3) plasma etching of resist, will be discussed. FTIR studies on resist films indicate minimal film deprotection-related losses. XPS spectra show that the extent of surface oxidation increases initially and then becomes constant. Thus, this category of resists follows the model proposed by Watanabe and Ohnishi describing the etching of Si-containing resists as a combination of the oxidation of the silicon species and sputtering of the oxide-type layer formed. Post-transfer etch profiles using an oxygen plasma will be shown, and methods to reduce imaging layer resist faceting and thickness loss either by modifying the imaging layer silicon content or shifting to plasma chemistries causing sidewall passivation will be discussed. The effect of different etching chemistries and conditions on imaging layer roughening and striation formation on underlayer sidewalls will be explained with the aid of SEM micrographs and AFM images of etched feature sidewalls. The printing of 125 nm line/space patterns, and 150 nm trench features with 10:1 aspect ratios, in the underlayer will be demonstrated.