J. Pelletier

Anisotropic etching of polymers in SO2/O2 plasmas: Hypotheses on surface mechanisms

A study of the anisotropy of the etching of resists in SO2‐based plasmas is performed in a distributed electron‐cyclotron‐resonance plasma excited at 2.45 GHz with independent radio frequency biasing at 13.56 MHz. Emphasis is put on the comparison of the profiles and etch rates obtained in pure oxygen and SO2‐containing plasmas as a function of substrate temperature and ion bombardment energy. For a constant ion bombardment intensity, a significant decrease in the etch rate obtained using pure SO2 plasmas is observed as compared to pure O2 plasmas. The evolution of the etch rate with ion energy also shows quite different behavior. In contrast to pure oxygen plasmas, perfect anisotropic profiles can be obtained on cooled substrates with SO2‐containing gas mixtures. A likely explanation for these results is to assume that sulfur acts as a passivating layer at temperatures close to or below room temperature. The surface mechanisms involved in this sulfur passivation and the conditions required to obtain an e...

Resist degradation under plasma exposure: Synergistic effects of ion bombardment

Bulk resist degradation under O2 or Ar plasma exposure is experimentally demonstrated. The degradation mechanisms are analyzed in Ar plasma and a synergistic effect of ion bombardment is presented. Mechanical effects of ion bombardment lead to a surface degradation of the resist whereas thermal effects allow the extension of the degradation to the bulk. Self‐diffusion of chains is demonstrated which clearly emphasizes the role of the viscoelastic properties in polymer degradation.

Etching characteristics of thin films of tungsten, amorphous silicon carbide, and SAL‐603 resist submitted to a surface‐wave driven SF6 magnetoplasma near electron cyclotron resonance conditions

The etching of thin films of tungsten, amorphous silicon carbide (a‐SiC:H), and SAL‐603 resist has been investigated in a magnetoplasma sustained by microwaves under conditions close to the electron cyclotron resonance. This was done in a newly developed large diameter (280 mm i.d.) reactor operating in a uniform static magnetic field and supplied with the plasma from a surface‐wave‐sustained discharge. A pure SF6 discharge was used. The etch rate of W, a‐SiC:H, and SAL‐603 resist materials was systematically determined as functions of operating parameters such as the SF6 pressure in the 0.1–5 mTorr range, the absorbed microwave power, and the distance of the substrate to the surface‐wave launching gap. It is shown, in particular, that the etching selectivity of W with respect to a‐SiC:H and SAL‐603 resist is strongly influenced by the SF6 pressure. Optimal etching selectivities as high as 10 and 25 were obtained for W relative to a‐SiC:H and SAL‐603 resist, respectively, when the SF6 gas pressure is clos...

Development of Polymers in O2 Plasmas: Temperature Effects and Transition to Imperfect Anisotropy

A parametric study of the etching of a photoresist is performed in an O2 microwave multipolar plasma using a trilevel resist system. The etch rate and the anisotropy evolutions are reported as a function of ion energy, oxygen pressure and substrate temperature, which are important parameters likely to affect anisotropy. A transition from isotropic to imperfect anisotropic etching occurs when the ion energy is increased. However, residual lateral etching always subsists at room temperature, even at the lowest oxygen concentrations. Above room temperature, in contrast with ion-induced etching, the spontaneous lateral etch rate increases with temperature, suggesting a thermally activated reaction process. The phenomena are interpreted in terms of oxygen coverage on the polymer surface, with a threshold coverage being required for purely spontaneous chemical etching to occur, and on the assumption of a photon-induced desorption of volatile products proportional to the oxygen coverage.

Comparison of Dry Development Techniques using O2 and SO2/O2 Low-Pressure Plasmas

A parametric study of the pattern transfer step in a trilevel resist system using oxygen-based plasmas has been performed using a distributed electron cyclotron resonance reactor with independent rf biasing. In pure oxygen plasmas, critical dimension loss is always present. The mechanisms most likely to be responsible for these defects during the pattern transfer process are presented and discussed. A novel plasma etching process based on sidewall passivation by sulfur is proposed using SO2/O2 mixtures. Perfect anisotropy with negligiable critical dimension loss is obtained at room temperature.

Nitrogen profiles in materials implanted via plasma-based ion implantation

Abstract The lifetime of metallic components can be drastically increased by surface treatments ensuring a low friction coefficient, surface hardening and an anticorrosion coating. A promising method for such surface modifications is plasma-based ion implantation (PBII) of nitrogen. In order to improve and to obtain a better understanding of such a treatment, we have performed nitrogen implantation in different materials at various ion energy values using pure nitrogen and N 2 /H 2 gas mixture plasmas. Fe and Ti samples were simultaneously treated in a large-volume PBII reactor in which the plasma is excited at the distributed electron cyclotron resonance. Si substrates were also implanted in order to characterize the nitrogen implantation efficiency by Fourier-transform infrared (FTIR) analysis. Profiles of the relative concentration of elements in the samples were deduced from X-ray photoelectron spectroscopy (XPS) analysis as a function of depth. The absolute concentration of implanted nitrogen was also obtained by nuclear reaction with 15 N atoms implanted in metals via PBII from a 15 N 2 / 14 N 2 gas mixture. These results can be very useful for calibrating and improving PBII surface treatments of materials.

Plasma etching of polymers: A reinvestigation of temperature effects

Temperature effects in plasma etching of polymers have been reinvestigated. A stepwise increase in the etch rate is observed when the substrate temperature exceeds the glass transition temperature Tg of the polymer. This phenomenon is correlated with changes in the physical properties of the polymer such as heat capacity. Furthermore, whereas temperature is usually assumed to enhance the etching process, the ion‐induced etching component, below Tg, is shown to increase when the polymer temperature is decreased. This behavior can be explained by a simple model involving changes in the adsorption rate of reactive species with temperature.

Polymer behavior under plasma etching: Influence of physical properties on kinetics and durability

The influence of the physical properties of polymers on their plasma behavior has been investigated under O2 and Ar plasma treatments. The glass transition temperature (Tg) has been found to be an important parameter. A steplike increase in the etch kinetics in O2 plasmas has been correlated to the change in the heat capacity of the polymer occurring above Tg whatever the molecular weight of the polymer. Furthermore, above Tg, changes in the viscoelastic properties induce bulk polymer degradation if chain crosslinking cannot be achieved before or during plasma etching.

Anisotropy and kinetics of the etching of tungsten in SF6 multipolar microwave plasma

An experimental study of the etching of tungsten with SF6 has been performed in a microwave multipolar plasma using an electron cyclotron resonance excitation with an independent low dc biasing. The anisotropy and etch rate of tungsten have been measured as a function of atomic fluorine concentration in the plasma and compared with silicon characteristics. The etching mechanisms of tungsten are analyzed in light of published data on the fluorine‐tungsten interaction, and the results are explained in terms of the diffusion model for plasma etching developed for the Si‐F system. Atomic fluorine adsorption on tungsten appears to be monolayerlike, whereas it is of multilayer type on silicon, and associative desorption of WF6 occurs from WF3 and/or WF4 adspecies in nearest‐neighbor positions.

Plasma-based ion implantation of oxygen in stainless steel: influence of ion energy and dose

Abstract Implantation of oxygen in stainless steel (15% Cr) via plasma-based ion implantation in a distributed ECR plasma reactor has been studied as functions of ion energy and dose. Due to the formation at the surface of dielectric films with optical index and thickness depending on the implantation time and pulse voltage (up to 44 kV), various colorations can be obtained. The experimental results demonstrate the feasibility of uniform processing, the possibility of reaching perfect control of the coloring through the dose and energy of implanted ions, and that the resulting coloration varies monotonically when increasing the dose and penetration depth of implanted oxygen. Characterization of the films by scanning electron microscopy and X-ray microanalysis shows that oxygen implantation results in strong surface oxidation, but without any significant degradation of the surface aspect. The thickness and composition profiles of the oxide layers determined using X-ray photoelectron spectroscopy combined with ellipsometry indicate that the thickness, of course, increases with ion energy and dose, but that the composition of the oxide layer resulting from the implantation process is not uniform. A uniform iron oxide layer (with a stoichiometry closed to Fe 2 O 3 ), free from chromium, is formed in the near-surface region, while chromium segregates at the interface between the oxide layer and the bulk stainless steel to form chromium oxide Cr 2 O 3 .