Silicon Surface Modification Using C<SUB>4</SUB>F<SUB>8</SUB>+O<SUB>2</SUB> Plasma for Nano-Imprint Lithography

Abstract

The investigation of C4F8+O2 feed gas composition on both plasma parameters and plasma treated silicon surface characteristics was carried out. The combination of plasma diagnostics by Langmuir probes and plasma modeling indicated that an increase in O2 mixing ratio results in monotonically decreasing densities of CF(x) (x = 1-3) radicals as well as in non-monotonic behavior of F atom density. The surface characterization by X-ray photoelectron spectroscopy and contact angle measurements showed that the C4F8+O2 mixtures with less than 60% 02 result in modification of Si surfaces due to the deposition of the FC polymer films while the change of O2 mixing ratio in the range of 30%-60% provides an effective adjustment of the surface characteristics such as surface energy, contact angle, etc.

PLASMA PARAMETERS, DENSITIES OF ACTIVE SPECIES AND ETCHING KINETICS IN C4F8+Ar GAS MIXTURE

“…In order to obtain the densities of neutral species, we developed a simplified zero-dimensional kinetic model with using the data of Te and n+ as input parameters [12,13]. The set of chemical reactions was taken from previous works [14][15][16][17]. These works also provide the detailed discussion on both kinetic schemes and sources of chemical kinetics data.…”

“…Similarly to Refs. [13][14][15], the model used following assumptions: 1) the electron energy distribution function (EEDF) is close to Maxwellian one; 2) the electronegativity of the low-pressure C4F8 + Ar plasma is low enough to assume n-<< n+  ne; 3) the heterogeneous chemistry of atoms and radicals can be described in terms of the conventional first-order recombination kinetics; and 4) The temperature of the neutral groundstate species (Tgas) is independent on the feed gas composition. Since the experimental data on gas temperature were not available in this study, we took Tgas = 600 K as the typical value for the ICP etching reactors with similar geometry under the close range of experimental conditions [15][16][17].…”

PLASMA PARAMETERS AND COMPOSITION IN CF4/O2/Ar GAS MIXTURE

“…Similarly, to our previous works [10,11,14,15], the model was based on the Maxwellian electron energy distribution function (EEDF), and directly used the experimental data of Т е and n + as input parameters. Though the real EEDFs are not exactly Maxwellian, such a simplification for CF 4 -based and lowpressure (p < 50 mTorr) ICPs provides reasonable agreement between the diagnostic results and modeling [10-12, 16, 27].…”

“…The general model assumptions as well as the reaction scheme were the same with our previous works [14,15]. The rate coefficients for electron impact reactions were calculated as functions of Те using the fitting expressions in a form of k = AT e B exp(-C/T e ) [5,14].…”

“…The heterogeneous chemistry of atoms (F, C, O) and radicals (CF 3 , CF 2 , CF) was described in terms of the conventional first-order recombination kinetics. The corresponding ticking probabilities were obtained from Refs [5,14,15]. The electron density (n e ) was calculated using the simultaneous solution of the steady-state chemical kinetic equation for negative ions ν da n e ≈ k ii n + n -and the quasi-neutrality equation n + = n e +n -.…”