Ch. Cardinaud

New polymer materials for nanoimprinting

We have investigated new aromatic polymers for nanoimprint and subsequent dry etching, namely thermoset and thermoplastic compounds. They were tested in a SiO2 patterning process under low pressure and high plasma density conditions and feature a selectivity about twice as high as poly(methylmethacrylate) (PMMA). The imprint behavior is comparable to PMMA and, in particular, the thermoplastic polymers show excellent imprint quality. This was demonstrated by replication of large arrays of lines down to 50 nm width. The thermoset polymers showed excellent dry etch stability and Teflon-like antisticking layers helped to imprint them without sticking.

Characterization of silicon dioxide films deposited at low pressure and temperature in a helicon diffusion reactor

Silicon dioxide films have been deposited at low pressure (a few millitorr) and low substrate temperature (<200 °C) by oxygen/silane helicon diffusion radio frequency plasmas. High deposition rates (20–80 nm/min) are achieved at 800 W rf source power. The effect of the oxygen/silane flow rate ratio (R) on the film properties has been investigated: characterization of the deposited films has been carried out by in situ ellipsometry, ex situ Fourier transform infrared spectroscopy, Rutherford backscattering, x‐ray photoelectron spectroscopy (XPS), and chemical etch rate measurements (P etch) and the results have been compared to thermally grown oxide. The deposition kinetics has a great effect on the internal film structure: for films presenting a good stoichiometry ([O]/[Si]≥1.95 for R≥3), a decrease in the deposition rate is accompanied by a decrease of the refractive index, P‐etch rate and XPS line width and by an increase of the Si–O stretching peak frequency toward the thermal oxide respective values. ...

Comparison of etching processes of silicon and germanium in SF6–O2 radio‐frequency plasma

Reactive ion etching of Si and Ge in SF6–O2 is investigated. Etch rate shows that Si etching is selective with respect to Ge in SF6–O2 (O2<50%); the reverse is observed in SF6–O2 (O2≳50%). In agreement with the compared evolution of the F and O concentration in the plasma and of the etch product formation rate obtained respectively, by optical emission spectroscopy and mass spectrometry, the x‐ray photon spectroscopy surface analysis reveals that the growth of a SiOxFy layer quenches the Si etching whereas the formation of GeOxFy does not inhibit Ge etching. Using a simple model, an experimental surface reactivity is defined and expressed in function of the experimental data. Results suggest a different behavior for sulfur and oxygen on both materials.

Etching processes of tungsten in SF6‐O2 radio‐frequency plasmas

The reactive ion etching of chemical vapor deposited tungsten in SF6/O2 radio‐frequency plasma has been studied by means of optical emission spectroscopy, mass spectrometry, and in situ x‐ray photoelectron spectroscopy. Two etch products are detected: WF6 and WOF4. A correlation is found between their concentration in the gas phase and the amount of atomic fluorine and oxygen, as measured by actinometry. In an atomic F‐rich plasma, WF6 dominates over WOF4, the latter appearing as soon as oxygen is introduced in the plasma. After etching, the tungsten surface contains three chemical elements: sulfur, oxygen and fluorine; their concentration depends on the reactor parameters (gas mixture, cathode material). Various species have been observed on this surface: S—W (with S 2p at 162 eV), Ox—S—Fy (with S 2p at 170 eV, O 1s at 533 eV, F 1s at 686.4 eV). Two types of tungsten fluorides have been identified: chemisorbed WFn (F 1s at 684.5 eV) and physisorbed WFn species (F 1s at 687.7 eV). The latter are thought to be the precursors of WF6 and O■W—F4 etch products. The role of sulfur, oxygen and fluorine during the etching process of tungsten is discussed.

Influence of the gas mixture on the reactive ion etching of InP in CH4-H2 plasmas

The influence of the CH4-H2 mixture composition on the etching process of InP is investigated by means of plasma diagnostics (optical emission spectroscopy and mass spectrometry) and quasi in situ x-ray photoelectron spectroscopy (XPS) surface analysis. Increasing the mixture composition in methane increases the InP etch rate. For example, it rises from 230 to 380 A/min when increasing the percentage in CH4 from 2.5% to 75%. In pure methane discharge, at a pressure of 50 mTorr, amorphous carbon is deposited on InP. Quasi in situ XPS reveals major changes in the surface chemistry. In particular P depletion decreases and the mean surface stoichiometry improves as the percentage of methane increases. The mass spectrometry PH3+ signal (m/e=34 amu) corresponding to PH3 molecules and the In* emission line (λ=451.1 nm), which are, respectively, characteristic signals of the individual removal rate of In and P, and the concentration of CH3 radicals in the plasma as measured by the threshold ionization technique d...

Selective and deep plasma etching of SiO2: Comparison between different fluorocarbon gases (CF4,C2F6,CHF3) mixed with CH4 or H2 and influence of the residence time

SiO2 is a well suited material for integrated optic applications and is also attractive for microelectromechanical system and micro-optical electromechanical system fabrication. Such optical components require deep oxide etching (several microns) and subsequent high selectivity with respect to the mask. In this article, we describe the influence of various process parameters (gas mixture, pressure, plasma power, and residence time) on the selective etching of SiO2 with respect to Si in inductively coupled plasma (ICP) fluorocarbon with the aim of finding the best compromise between high selectivity and high oxide etch rate. Oxide etch rate is improved by decreasing pressure or increasing source power within the acceptable process windows, respectively, 3–20 mTorr and 1000–2000 W, but the gain in selectivity is low (×1.5). Adding methane rather than more commonly usual hydrogen resulted in higher selectivity without significant decrease in the oxide etch rate. A relatively good correlation is found between the selectivity and the (C+H)/F ratio of the precursor molecule. However, we show that varying the hydrofluorocarbon mixture does not allow us to improve both oxide etch rate and selectivity. In this regard, the residence time is the most significant parameter: choosing the appropriate amount of methane mixed with C2F6, and decreasing tR leads to an improvement in both the selectivity (×7) and the oxide etch rate (×1.5). Finally, the influence of these parameters on pattern transfer is investigated.SiO2 is a well suited material for integrated optic applications and is also attractive for microelectromechanical system and micro-optical electromechanical system fabrication. Such optical components require deep oxide etching (several microns) and subsequent high selectivity with respect to the mask. In this article, we describe the influence of various process parameters (gas mixture, pressure, plasma power, and residence time) on the selective etching of SiO2 with respect to Si in inductively coupled plasma (ICP) fluorocarbon with the aim of finding the best compromise between high selectivity and high oxide etch rate. Oxide etch rate is improved by decreasing pressure or increasing source power within the acceptable process windows, respectively, 3–20 mTorr and 1000–2000 W, but the gain in selectivity is low (×1.5). Adding methane rather than more commonly usual hydrogen resulted in higher selectivity without significant decrease in the oxide etch rate. A relatively good correlation is found between...

Novel linear and crosslinking polymers for nanoimprinting with high etch resistance

Aromatic polymers based on methacrylates (linear polymers) and multifunctional allylesters (crosslinked polymers) have been prepared. They feature high dry etch resistance and good imprintability in a hot embossing process. The crosslinked polymers and their prepolymers were investigated in detail. Their characteristic molecular weight distribution and thermo-mechanical behaviour were studied with respect to the crosslinking process and compared with those of linear polymers. The thermal stability of imprinted patterns has been investigated for both, linear and crosslinked aromatic polymers. The latter ones show excellent stability up to test temperatures of 200 ^oC directly after the imprint process.

Etching mechanisms of Si and SiO2 in inductively coupled fluorocarbon plasmas: Correlation between plasma species and surface etching

Etching mechanisms of silicon and silicon oxide in a fluorocarbon environment are studied in an ICP reactor. Optimization of the process for deep etching of SiO2 with a Si mask has been discussed in a previous article. In this article, adequate plasma conditions are chosen both (a) to allow separation of parametric variables and (b) to get appreciable variation of the different plasma and surface experimental results versus parameters. Hence, pressure, source power, ion energy, and subsequently ion flux are kept constant. The influences of the gas composition and the residence time (varying gas flow rate) are studied. We show that silicon etching depends both on the atomic fluorine concentration in the plasma and of the fluorocarbon blocking layer at the surface. We pay particular attention to the formation of the fluorocarbon overlayer. We establish that the thickness of this layer is linked to the plasma species through the (C+H)∕F ratio, calculated from the radical densities in the gas, taking into acc...

Mechanistic studies of the initial stages of etching of Si and SiO2 in a CHF3 plasma

Abstract The objective of this paper is do to a comparative study of the mechanism of reactive ion etching of both Si and SiO 2 substrates using CHF 3 . XPS and ellipsometry in the visible are used to follow the surface modifications in relation to the plasma exposure time. For Si, a transient stage is observed before a steady-state etching regime is attained. This transient stage is separated into two distinct phases corresponding to the growth of a fluorocarbon overlayer and to the initiation of the Si etching, respectively. For SiO 2 no transient stage is noted so a stationary etching situation is obtained as soon as the plasma is created. These results suggest that the fluorocarbon overlayer is not a simple blocking overlayer, but is part and parcel of the Si etching mechanism: this overlayer provides fluorine atoms necessary for the etching. On the contrary, the plasma species react directly with an SiO 2 surface to form precursors of etch products. Consequently, no fluorocarbon overlayer is needed in the SiO 2 etching mechanism.

Etching behavior of Si-containing polymers as resist materials for bilayer lithography: The case of poly-dimethyl siloxane

This work is focused on the plasma development of siloxanes investigated as model Si-containing photoresist components that show a promise for bilayer lithography at 157 nm and other Next Generation Lithography technologies. In such lithography, the image is developed in the top photosensitive polymer and transferred to the (usually thick) organic underlayer by means of O2-based plasma etching. In this work particularly, the issue of line edge roughness (LER) induced by transfer etching and its reduction by means of plasma processing optimization is addressed. The experimental results reveal that low values of line-edge roughness are obtained in a high-density plasma reactor, if an F- but not O-containing etching first step is used in appropriate plasma conditions. The effect of different etching chemistries and processing conditions on imaging layer roughness formation is demonstrated with the aid of scanning electron microscopy images and image analysis for quantifying LER, and atomic force microscopy (...