E. van der Drift

Characterizing size-dependent effective elastic modulus of silicon nanocantilevers using electrostatic pull-in instability

This letter presents the application of electrostatic pull-in instability to study the size-dependent effective Young’s Modulus ? ( ~170–70?GPa) of [110] silicon nanocantilevers (thickness ~1019–40?nm). The presented approach shows substantial advantages over the previous methods used for characterization of nanoelectromechanical systems behaviors. The ? is retrieved from the pull-in voltage of the structure via the electromechanical coupled equation, with a typical error of ? 12%, much less than previous work in the field. Measurement results show a strong size-dependence of ?. The approach is simple and reproducible for various dimensions and can be extended to the characterization of nanobeams and nanowires.

Hydrogen induced donor‐type Si/SiO2 interface states

Study of donor‐type Si/SiO2 interfaces states shows that these centers anneal at room temperature when neutral but are stable when charged positively. Moreover, the anneal process is accompanied by the release of H. We propose that the donor states are related to H attached to interfacial network sites, most likely O atoms, constituting electrically active complexes. When positively charged, H is strongly bonded; when neutral H is only weakly attached. In the latter case it can escape and dimerize so that the states disappear. Similar complexes tying down H in a positively charged state would constitute small cross‐section hole traps in the bulk of the oxide.

Fabrication of two-dimensional photonic crystal waveguides for 1.5 μm in silicon by deep anisotropic dry etching

Fabrication process for sharp waveguide bends in a two-dimensional photonic band gap structure in silicon is developed. The waveguide bend is defined by removing a row of pillars in a two-dimensional photonic crystal of 5 μm long, 205 nm diameter pillars placed on a square lattice with a pitch of 570 nm. To meet the severe nanotolerance requirements in such a device the SF6/O2 electron cyclotron resonance plasma process at reduced temperature is tailored to extreme profile control. The impact of main plasma parameters—i.e., temperature, oxygen/fluorine content, and ion energy—on the sidewall passivation process is unraveled in detail. Crystallographic orientation preference in the etch rate is observed.

Balancing the etching and passivation in time-multiplexed deep dry etching of silicon

For the Bosch deep silicon dry etch process with SF6–C4F8 a quantitative approach is developed. Essential plasma surface interactions and the transport properties of ions and radicals in high aspect ratio structures are unravelled. Balancing the interactions during etching and passivation pulses is essential for maximal profile control. In the anisotropic regime the etch rate is aspect ratio dependent largely due to depletion of fluorine radicals and with some involvement of passivation polymer redeposition. The anisotropic process tends to stop at a limiting aspect ratio because of improper removal of polymer passivation at the trench bottom. Both higher ion flux and ion energy are found to be crucial to push the Bosch process to higher achievable aspect ratios. Practical process implications are discussed. In situ ellipsometry shows that the polymer passivation step is a complex process with an ion induced component. More efficient removal of the passivation layer at the trench bottom by adjusting the p...

MEASUREMENT OF ION IMPACT ENERGY AND ION FLUX AT THE RF ELECTRODE OF A PARALLEL PLATE REACTIVE ION ETCHER

An experimental study on the ion impact energy distribution and the total ion flux at the driven electrode of a parallel plate reactive ion etcher is presented. Results are shown for 13.56 MHz discharges in Ar, Ar/H2, N2, O2, Cl2, and SF6/He over a pressure range of 0.3–40 Pa. The ion impact energy distribution consists of a collision‐free part and a collision‐induced part. It is observed that in Ar, N2, O2, and Cl2 the collision‐induced part contains single and double peaks at regular energy intervals. This peaked structure is attributed to charge exchange processes in the sheath. Both the collision‐free part and the collision‐induced part of the ion impact energy distribution are well described by a model based on a constant sheath width, a sinusoidal sheath voltage, and a power law for the electric field in the sheath. The only adjustable parameter in the model is the sheath thickness. The sheath thickness has also been determined independently from the total ion current density using the Child–Langmui...

Technology for high‐performance n‐channel SiGe modulation‐doped field‐effect transistors

A fabrication process for n‐channel SiGe modulation‐doped field‐effect transistors has been developed in which the strain in the heterostructure is completely preserved by taking into account an appropriate temperature range for the formation of ohmic contacts to source drain by implantation. It yields a low specific contact resistance of 7.1×10−5 Ω cm2 to be compared to 5.7×10−2 Ω cm2 for alloyed Au/Sb contacts. With the same thermal upper limit the application of different gate oxides has been studied. All oxides show negligible gate leakage enabling a superior gate voltage swing compared to devices with a Schottky gate. Application of thermal oxide grown at 650 °C yields a superior field‐effector transistor performance compared to devices with sputter and plasma‐enhanced chemical‐vapor deposition deposited oxides due to its lower and negative charge level. Gate recessing of 0.5 μm Schottky gates yields a transconductance increase up to 310 mS/mm.

Amorphous silicon waveguides for microphotonics

Amorphous silicon a-Si was made by ion irradiation of crystalline silicon with 1×1015 Xe ions cm−2 at 77 K in the 1–4 MeV energy range. Thermal relaxation of the amorphous network at 500 °C for 1 h leads to an amorphous layer with a refractive index of n=3.73, significantly higher than that of crystalline silicon (n=3.45 at λ=1.55 μm). a-Si can thus serve as a waveguide core in Si based optical waveguides. Channel waveguides were made by anisotropic etching of a 1.5 μm silicon-on-insulator structure that was partly amorphized. Transmission measurements of these waveguides as function of the amorphous silicon length show that the a-Si part of the waveguides exhibit a modal propagation loss of 70 cm−1 (0.03 dB μm−1) and a bulk propagation loss of 115 cm−1 (0.05 dB μm−1). Losses due to sidewall roughness are estimated, and are negligible compared to the modal loss.

Kinetics and crystal orientation dependence in high aspect ratio silicon dry etching

A quantitative study of dry etch behavior in deep silicon trenches in high density plasmas (electron cyclotron resonance, inductively coupled plasma) at low temperatures (160–210 K) is presented. The quantitative approach implies etch behavior being studied in relation to the relevant particle fluxes (atomic F and O and ions) as measured by in situ diagnostics. Two etch modes are observed. In one mode faceting shows up as due to crystallographic orientation preference, i.e., Si〈111〉 being etched slower than Si〈100〉. In the other mode the normal anisotropic ion-induced behavior is observed. Controlled switch from one mode to the other is studied under influence of process parameters like pressure, ion energy, and substrate temperature. The second part of this study deals with aspect ratio dependent etching (ARDE). Both vertical and horizontal trenches have been taken into account as to distinguish between radical and ion-induced effects. The flux of radical species into the deep trench is governed by Knuds...

InP-based two-dimensional photonic crystals filled with polymers

Polymer filling of the air holes of indium-phosphide-based two-dimensional photonic crystals is reported. After infiltration of the holes with a liquid monomer and solidification of the infill in situ by thermal polymerization, complete filling is proven using scanning electron microscopy. Optical transmission measurements of a filled photonic crystal structure exhibit a redshift of the air band, confirming the complete filling.

The etching of silicon carbide in inductively coupled SF6/O2 plasma

The etching mechanisms of silicon carbide in an inductively coupled plasma (ICP) reactor using a SF6/O2 gas mixture, have been investigated using optical emission spectroscopy (OES) and Langmuir probe measurements. The etching is shown to be ion induced with a high degree of anisotropy. An optimum etch rate is achieved with 20% oxygen content within the gas mixture. By studying the independent influence of the ICP power and the substrate bias voltage on the ion current density, as well as the fluorine and oxygen radical densities in the plasma, the etch mechanism is found to be dominated by the number of ions bombarding the SiC surface. The steady state sputter yield observed at P>0.7?Pa, despite the increase in F radical concentration indicates the dominant role of ion bombardment in this etch regime, while at P<0.7?Pa, the etch mechanism is limited by the number of F radicals in the plasma. The OES results have shown that the etch rate is dependent upon the concentration of reactive radicals present with the [F]/[0] ratio = 8 at the optimum. Whilst using the optimum gas composition, the parameters which dominate the physical side of the reaction, ICP power and bias voltage, produce an increase of the etch rate as the potential difference between the substrate and the plasma is increased.