Antonius A.I. Aarnink

Growth Kinetics and Oxidation Mechanism of ALD TiN Thin Films Monitored by In Situ Spectroscopic Ellipsometry

Spectroscopic ellipsometry (SE) was employed to investigate the growth of atomic layer deposited (ALD) TiN thin films from titanium chloride (TiCl4) and ammonia (NH3) and the followed oxidation in dry oxygen. Two regimes were found in the growth including a transient stage prior to a linear regime. The complementary ex situ characterization techniques showed a good agreement with the results obtained from SE measurements. A columnar structure of the as-deposited TiN film, which was composed of grains surrounded by amorphous material in between, was obtained. The X-ray photoelectron spectroscopy (XPS) analyses indicated low chlorine impurity content and slightly N-rich TiN films. The existence of an intermixed layer between the nitride and oxide during the oxidation was verified by the XPS depth profile analysis for a partially oxidized TiN film. A three-layer optical model was constructed for SE in situ monitoring the oxidation. A four-regime oxidation was found for 15-nm TiN films whereas only two regimes were seen in the case of 5-nm films. A new oxidation mechanism was proposed to explain the oxidation behavior of thin TiN films.

Atomic Layer Deposition of W1.5N Barrier Films for Cu Metallization Process and Characterization

An atomic layer deposition process to grow tungsten nitride films was established at 350 degrees C with a pulse sequence of WF6/NH3/C2H4/SiH4/NH3. The film composition was determined with Rutherford backscattering as W1.5N, being a mixture of WN and W2N phases. The growth rate was similar to 1 x 10(15) W atom/cm(2) per cycle (monolayer of W2N or WN). The films with a thickness of 16 nm showed root-mean-square roughness as low as 0.43-0.76 nm. The resistivity of the films was stable after 50 cycles at a value of 480 mu Omega cm. Results of four-point probe sheet resistance measurements at elevated temperature demonstrated that our films are nonreactive with Cu at least up to 500 degrees C. Results of I-V measurements of p(+)/n diodes before and after heat-treatment in (N-2 + 5% H-2) ambient at 400 degrees C for 30 min confirmed excellent diffusion barrier properties of the films. (c) 2005 The Electrochemical Society. All rights reserved.

Single-hole tunneling through a two-dimensional hole gas in intrinsic silicon

In this letter we report single-hole tunneling through a quantum dot in a two-dimensional hole gas, situated in a narrow-channel field-effect transistor in intrinsic silicon. Two layers of aluminum gate electrodes are defined on Si/SiO2 using electron-beam lithography. Fabrication and subsequent electrical characterization of different devices yield reproducible results, such as typical MOSFET turn-on and pinch-off characteristics. Additionally, linear transport measurements at 4 K result in regularly spaced Coulomb oscillations, corresponding to single-hole tunneling through individual Coulomb islands. These Coulomb peaks are visible over a broad range in gate voltage, indicating very stable device operation. Energy spectroscopy measurements show closed Coulomb diamonds with single-hole charging energies of 5–10 meV and lines of increased conductance as a result of resonant tunneling through additional available hole states.

Initial growth, refractive index, and crystallinity of thermal and plasma-enhanced atomic layer deposition AlN films

The authors have studied and compared the initial growth and properties of AlN films deposited on Si(111) by thermal and plasma-enhanced atomic layer deposition (ALD) using trimethylaluminum and either ammonia or a N2-H2 mixture as precursors. In-situ spectroscopic ellipsometry was employed to monitor the growth and measure the refractive index of the films during the deposition. The authors found that an incubation stage only occurred for thermal ALD. The linear growth for plasma-enhanced ALD (PEALD) started instantly from the beginning due to the higher nuclei density provided by the presence of plasma. The authors observed the evolution of the refractive index of AlN during the growth, which showed a rapid increase up to a thickness of about 30 nm followed by a saturation. Below this thickness, higher refractive index values were obtained for AlN films grown by PEALD, whereas above that the refractive index was slightly higher for thermal ALD films. X-ray diffraction characterization showed a wurtzite crystalline structure with a (1010) preferential orientation obtained for all the layers with a slightly better crystallinity for films grown by PEALD.

Comparison of tungsten films grown by CVD and hot-wire assisted atomic layer deposition in a cold-wall reactor

In this work, the authors developed hot-wire assisted atomic layer deposition (HWALD) to deposit tungsten (W) with a tungsten filament heated up to 1700–2000 C. Atomic hydrogen (at-H) was generated by dissociation of molecular hydrogen (H2), which reacted with WF6 at the substrate to deposit W. The growth behavior was monitored in real time by an in situ spectroscopic ellipsometer. In this work, the authors compare samples with tungsten grown by either HWALD or chemical vapor deposition (CVD) in terms of growth kinetics and properties. For CVD, the samples were made in a mixture of WF6 and molecular or atomic hydrogen. Resistivity of the WF6-H2 CVD layers was 20 lXcm, whereas for the WF6-at-H-CVD layers, it was 28 lXcm. Interestingly, the resistivity was as high as 100 lXcm for the HWALD films, although the tungsten films were 99% pure according to x-ray photoelectron spectroscopy. X-ray diffraction reveals that the HWALD W was crystallized as b-W, whereas both CVD films were in the a-W phase.

Green laser crystallization of α-Si films using preformed α-Si lines

In this work, amorphous silicon films with preformed a-Si lines were crystallized using a diode pumped solid state green laser irradiating at 532 nm. The possibility of controllable formation of grain boundaries was investigated. The crystallization processes in the rapidly melted silicon films were discussed. The influence of the crystallization parameters (i.e., energy density, scan velocity, etc.) and structure type (i.e., with and without preformed lines) on properties of the crystallized films was studied. The laser treatment with an energy density of 1.00 J/cm2 at a laser pulse overlapping of 90% provided the optimal crystallization process with predefined grain boundary location. X-ray diffraction (XRD), SEM and AFM microscopy have been used to characterize the crystallized silicon films.

On the verification of EEDFs in plasmas with silane using optical emission spectroscopy

We measured the electron density and electron energy distribution function (EEDF) of plasmas in our reactor which is intended for silicon oxide and nitride deposition. Langmuir-probe measurements showed that the EEDF of Ar plasma could largely be described by the Maxwell-Boltzmann (MB) distribution function, but it also contained a fraction (~0.5 %) of fast electrons in the energy range between 20 and 40 eV, strongly deviating from the MB distribution. We also measured relative mean electron temperatures (kTe) by optical emission spectroscopy (OES) which were calibrated by the absolute Langmuir-probe measurements. The kTe as measured by OES in Ar plasma decreased from 1.7 eV at 1.1 Pa to 1.4 eV at 12 Pa, while Langmuir-probe measurements showed a decrease from 1.7 eV to 0.8 eV. This difference is caused by the OES method, which is especially sensitive to the fraction of fast electrons in the plasma. OES can be used instead of Langmuir-probe measurements when depositing plasmas are used. Combining both methods, we demonstrated that EEDFs as measured by the Langmuir probe in Ar-N2, and Ar-N2O plasmas, resemble EEDFs in plasmas with small additions of silane, provided that (a) precursor fractions in plasma are small (SiH4 {less than or equal to} 0.8 % and N2O {less than or equal to} 15 %), and (b) total pressure does not exceed 3.6 Pa (27 mTorr). As such, the measured EEDF without silane can be used as input for chemical modeling and optimization of deposition processes in plasmas containing silane.

A miniaturized multiwire proportional chamber using CMOS wafer scale post-processing

This paper presents the technology of a new microsystem consisting of a CMOS chip with integrated high voltage electrodes, to be used as a detector for ionizing radiation. Its application ranges from particle detection in nuclear and high-energy physics to X-ray detection for materials research and medical purposes. In this paper, the process integration is detailed and system trade-off considerations are reported

Electrical properties of plasma-deposited silicon oxide clarified by chemical modeling

Our study is focused on Plasma Enhanced Chemical Vapor Deposition (PECVD) of silicon dioxide films at low temperatures (< 150 oC) using Inductively Coupled (IC) High-Density (HD) plasma source. We recently fabricated Thin Film Transistors (TFTs) with high-quality ICPECVD gate oxides, which exhibited a competitive performance. For better understanding of the influence of deposition parameters on both the deposition kinetics and oxide quality, we have modeled the Ar-SiH4-N2O plasma system with 173 chemical reactions. We simulated concentrations of 43 reactive species (such as e.g. SiHx radicals and SiHx + (x=0-3) ions, polysilanes, SiO, SiN, SiH3O, SiH2O, HSiO, etc., as well as atomic hydrogen, nitrogen and oxygen) in plasma. We further used our simulations to qualitatively explain (in terms of concentrations of the reactive species) the influence of SiH4/N2O gas-flow ratio and total gas pressure on film electrical properties and deposition rate.

From Single Atoms to Nanoparticles: Autocatalysis and Metal Aggregation in Atomic Layer Deposition of Pt on TiO2 Nanopowder

A fundamental understanding of the interplay between ligand-removal kinetics and metal aggregation during the formation of platinum nanoparticles (NPs) in atomic layer deposition of Pt on TiO2 nanopowder using trimethyl(methylcyclo-pentadienyl)platinum(IV) as the precursor and O2 as the coreactant is presented. The growth follows a pathway from single atoms to NPs as a function of the oxygen exposure (PO2 × time). The growth kinetics is modeled by accounting for the autocatalytic combustion of the precursor ligands via a variant of the Finke-Watzky two-step model. Even at relatively high oxygen exposures (<120 mbar s) little to no Pt is deposited after the first cycle and most of the Pt is atomically dispersed. Increasing the oxygen exposure above 120 mbar s results in a rapid increase in the Pt loading, which saturates at exposures >> 120 mbar s. The deposition of more Pt leads to the formation of NPs that can be as large as 6 nm. Crucially, high PO2 (≥5 mbar) hinders metal aggregation, thus leading to narrow particle size distributions. The results show that ALD of Pt NPs is reproducible across small and large surface areas if the precursor ligands are removed at high PO2 .