B. Pelissier

Improved release strategy for UV nanoimprint lithography

The adhesion between the fused silica mold and the resist remains a key issue in ultraviolet nanoimprint lithography (UV-NIL), especially in step and repeat processes. In this paper, we present results on antisticking layers (ASLs) of tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (F13-TCS) deposited in vapor phase and of a commercial product, Optool DSX™, from Daikin Chemical, deposited in liquid phase. The antisticking properties and structural morphologies of the formed self-assembled monolayer are investigated using contact angle, Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy (XPS) measurements. Obtained surface energies are as low as 10mN∕m for both types of ASL. The stability of these formed layers during the UV-NIL process remains the main important issue. It was tested on an EVG® step and repeat UV-NIL equipment using acrylate-based resists. After only 50 prints, we observed a high increase in the surface energy of the mold, which indicates a drastic degradati...

Double-anchoring fluorinated molecules for antiadhesion mold treatment in UV nanoimprint lithography

In this work, the authors evaluate a new type of perfluoropolyether molecule (FLUOROLINK® S10) to be used as an antisticking mold treatment in UV nanoimprint lithography. Unlike currently used ones, this molecule has two anchoring ends groups allowing two covalent grafting sites of the molecule to the mold surface. Obtained results on this molecule are compared to Optool DSX’s ones. Using contact angle measurement, x-ray photoelectron spectroscopy, and electron spin resonance, the authors carried out chemical analysis of the evolution of antisticking treatments as a function of the number of imprints. It is found that both molecules have a roughly equivalent behavior. FLUOROLINK® S10 has shown less chemical resistance, attributed to its larger number of C–O bonds in the molecule, but an improved mechanical resistance, attributed to the double grafting mechanism.

Passivated TiN nanocrystals/SiN trapping layer for enhanced erasing in nonvolatile memory

We present chemical vapor deposition of titanium nitride nanocrystals (ncs) on silicon nitride (SiN). Ncs are passivated in situ by a silicon shell and encapsulated in SiN. High density (3×1012 cm−2), crystalline and isolated ncs are observed by transmission electron microscopy and characterized by x-ray photoelectron spectroscopy. TiN ncs/SiN are integrated as charge trapping layer in a nonvolatile memory. Devices show large memory window (10 V) and fast erasing compared to devices using pure SiN trapping layer, explained by enhanced electrical field in SiN. Acceptable reliability in terms of cycling and data retention is also demonstrated.

Etch mechanisms of silicon gate structures patterned in SF6/CH2F2/Ar inductively coupled plasmas

Patterning complex metal gate stack becomes increasingly challenging since the gate dimension for all isolated as well as dense gate structures present on 300 mm wafer needs to be controlled within the nanometer range. In this article, the authors show that SF6/CH2F2/Ar plasma chemistries to etch the polysilicon gate present very interesting critical dimension (CD) control capabilities for advanced gate etch strategies compared to commonly used HBr/O2/Cl2 plasma chemistries, thanks to the different mechanisms involved in the passivation layer formation on the gate sidewalls. Indeed, contrary to HBr/Cl2/O2 plasma chemistries, the passivation layers in SF6/Ar/CH2F2 plasmas are not formed from deposition of etch by-products coming from the gas phase but the passivating species are chemically sputtered from the bottom of the etched structures and coat the silicon sidewalls by line of sight deposition. Such mechanisms result in thin and uniform CFX passivation layers on the gate sidewalls very similar in dense...

Control of carbon content in amorphous GeTe films deposited by plasma enhanced chemical vapor deposition (PE-MOCVD) for phase-change random access memory applications

Amorphous and smooth GeTe thin films are deposited on 200 mm silicon substrates by plasma enhanced—metal organic chemical vapor deposition (PE–MOCVD) using the commercial organometallic precursors TDMAGe and DIPTe as Ge and Te precursors, respectively. X-ray photoelectron spectroscopy (XPS) measurements show a stoichiometric composition of the deposited GeTe films but with high carbon contamination. Using information collected by Optical Emission Spectroscopy (OES) and XPS, the origin of carbon contamination is determined and the dissociation mechanisms of Ge and Te precursors in H2 + Ar plasma are proposed. As a result, carbon level is properly controlled by varying operating parameters such as plasma radio frequency power, pressure and H2 rate. Finally, GeTe films with carbon level as low as 5 at. % are obtained.

Quantitative depth profiling of ultrathin high-k stacks with full spectrum time of flight–secondary ion mass spectrometry

Elemental concentration depth profiles of high-k material stacks for 32 nm node devices and below were acquired by high resolution backscattering spectrometry (HRBS), parallel angle resolved-x-ray photoelectron spectroscopy (pAR-XPS), and time of flight–secondary ion mass spectrometry (ToF-SIMS). ToF-SIMS data were analyzed using an original calibration method which the authors shall refer to as the full spectrum protocol. Three different samples were studied in this work, one ultrathin insulating layer (IL) alone and two nitridized high-k/IL samples with different nitridation conditions for the IL. Although HRBS and AR-XPS already proved their ability in this domain, SIMS or ToF-SIMS characterization of high-k material stacks is still hampered by various matrix effects. Comparison of the elemental profiles obtained by all three techniques allows the accuracy of the full spectrum ToF-SIMS protocol to be assessed, both in terms of chemical composition quantification and depth resolution. This study reveals...

Use of optical spacers to enhance infrared Mueller ellipsometry sensitivity: application to the characterization of organic thin films.

Mueller ellipsometry in the mid-infrared (IR) spectral range can be used to obtain information about chemical composition through the vibrational spectra of samples. In the case of very thin films (<100  nm), the ellipsometric spectral features due to vibrational absorption are in general quite weak, and sometimes they are hidden by the noise in the measured data. In this work, we present one method based on the use of optical spacers as a tool to enhance the sensitivity of IR Mueller ellipsometry. An optical spacer is a thin film made of a known material which is between the substrate and the layer of interest. We show that, when the thickness of the two layers fulfills a given condition, the spectral features due to vibrational absorptions are enhanced. We explain the enhancement effect in terms of the Airy formula. The theoretical discussion is illustrated with two examples. We analyzed polystyrene thin films deposited on silicon wafers. Some of the wafers were covered by a thin film of thermal silicon dioxide (SiO2), which was used as a spacer. The results show the suitability of the proposed technique to overcome the lack of sensitivity in ellipsometric measurements when it comes to working with either very thin films or materials with low absorption.

First Experimental Functionalization Results of SiC Nanopillars for Biosensing Applications

DNA biosensors based on silicon carbide nanowire bioFET (SiC NW bioFET) benefit from both biocompatibility and semiconducting properties of SiC. One of the device realization key points is the functionalization of the SiC NW. This process is composed of two main steps: silanization and DNA grafting. It has been successfully carried out on both SiC single crystals and SiC nanopillars. Evidences of DNA detection are given by X-Ray photoelectron Spectroscopy (XPS) and fluorescence microscopy.

Structural defects in SiC ingots investigated by synchrotron diffraction imaging

4H silicon carbide as-grown ingots were investigated by diffraction imaging using synchrotron radiation. The white beam section topographs obtained for various sample geometries allowed us to reveal structural imperfections before slicing the bulky ingots to the thin wafers used as electronic device substrates. The systematic investigation indicated that the observed inclusions of different polytypes in 4H-SiC ingots are correlated with the 8° off-axis orientation of the seed. These inclusions, formed at the beginning of the crystal growth, provoke planar defects that propagate along the main vertical axis of the cylindrical crystal. New findings permitted us to understand the inclusion formation with the aim to increase the useful volume.

PECVD RF versus dual frequency: an investigation of plasma influence on metal?organic precursors' decomposition and material characteristics

Plasma enhanced metal organic chemical vapor deposition (PEMOVCD) of titanium nitride with dual frequency plasma sources were studied by means of plasma and material characterization. Adding a low frequency to a radio frequency plasma in order to enhance the deposition reaction mechanism is demonstrated. An in depth investigation of plasma by optical emission spectroscopy shows that due to secondary electrons heating the plasma, it enters a gamma-mode and that LF permits better dissociation of the H2 reactant gas. Moreover, it appears that the TiN metal organic precursor is not completely dissociated (no Ti* emission) but new species are observed that indicate a different fragmentation of the precursor. When LF plasma is used these modifications can be correlated to a change in the deposition reaction mechanism which affects the properties of the deposited material. Strong modifications of the TiN properties and deposition rate are observed when adding 17–60 W LF to a 200 W RF plasma. For example, with 35 W LF added to a 200 W RF, the deposition rate is increased by a factor two and the film appears to be less resistive (by 50%) and has a higher density. Such effects are not observed when only increasing the RF power (from 200 to 300 W with no LF power).