Roland Vanmeirhaeghe

Modeling the Conformality of Atomic Layer Deposition: The Effect of Sticking Probability

The key advantage of atomic layer deposition (ALD) is undoubtedly the excellent step coverage, which allows for conformal deposition of thin films in high-aspect-ratio structures. In this paper, a model is proposed to predict the deposited film thickness as a function of depth inside a hole. The main model parameters are the gas pressure, the deposition temperature, and the initial sticking probability of the precursor molecules. Earlier work by Gordon et al. assumed a sticking probability of 0/100% for molecules hitting a covered/uncovered section of the wall of the hole, thus resulting in a stepwise film-thickness profile. In this work, the sticking probability is related to the surface coverage θ by Langmuirs equation s(θ) = s 0 (1 - θ), whereby the initial sticking probability s 0 is now an adjustable model parameter. For s 0 ≅ 100%, the model predicts a steplike profile, in agreement with Gordon et al., while for smaller values of s 0 , a gradual decreasing coverage profile is predicted. Furthermore, experiments were performed to quantify the conformality for the trimethylaluminum (TMA)/H 2 O ALD process using macroscopic test structures. It is shown that the experimental data and the simulation results follow the same trends.

Conformality of Al2O3 and AlN Deposited by Plasma-Enhanced Atomic Layer Deposition

This paper focuses on the conformality of the plasma-enhanced atomic layer deposition (PE-ALD) of Al2O3 using trimethylaluminum [Al(CH3)(3); (TMA)] as a precursor and O-2 plasma as an oxidant source. The conformality was quantified by measuring the deposited film thickness as a function of depth into macroscopic test structures with aspect ratios of similar to 5, 10, and 22. A comparison with the thermal TMA/H2O process indicates that the conformality of the plasma based process is more limited due to the surface recombination of radicals during the plasma step. The conformality can slightly be improved by raising the gas pressure or the radio-frequency power. Prolonging the plasma exposure time results in further improvement of the conformality. Furthermore, there are indications that the H2O produced during the plasma step in the PE-ALD process for Al2O3 contributes to the observed conformality through a secondary thermal ALD reaction. The conformality of Al2O3 is also compared to the conformality of AlN deposited by PE-ALD from TMA and NH3 plasma. For the same exposure, O-2 plasma results in better conformality compared to NH3 plasma, suggesting a faster recombination of the radicals in the NH3 plasma.

Electrical characterization of Ar-ion-bombardment-induced damage in Au/Si and PtSi/Si Schottky barrier contacts

Au/Si and PtSi/Si Schottky contacts were prepared on n-Si(100) substrates which had been previously subjected to an Ar ion bombardment with well defined energies ranging from 100 eV to 1.5 keV. Samples were investigated by current-voltage (I-V) measurements, ballistic electron emission microscopy (BEEM) and deep-level transient spectroscopy (DLTS). Both I-V and BEEM results show that the effective Schottky barrier height (SBH) decreases with increasing Ar ion energy. The lowering of the barrier height is attributed to the bombardment-induced donor-like defects with relatively high densities near the silicon surface. DLTS spectra show the presence of defect levels both in the form of discrete energy levels and as a continuum of states. The oxygen-vacancy pair located at 0.16 eV below the conduction band is the dominant defect for the samples bombarded by 100 and 200 eV Ar ions and its peak signal intensity is similar for the two energies. For 300 eV or higher-energy ion-bombarded samples, other defects develop and become dominant. Their peak signal intensities increase monotonically with Ar ion energy. The variation of the DLTS spectra is in qualitative agreement with the tendency of effective SBH lowering for increasing energy of the bombarding Ar ions.

Formation and characterization of SPE grown ultra-thin cobalt disilicide film

Ultra-thin epitaxial CoSi 2 films formed by Co(3∼5nm)/Ti(1 nm)/Si(100) and Co(3∼5nm)/Si(lnm)/Ti(Inm)/Si are studied. The multilayers are deposited by ion-beam sputtering. Rapid thermal annealing (RTA) is used for silicidation. XRD, RBS, TEM, AFM, four-point probe, I-V and C-V measurements are carried out for characterization. The XRD spectra show the CoSi 2 film formed by Co/Ti/Si or Co/Si/Ti/Si solid phase epitaxy has, epitaxial characteristic. XTEM shows that the film is continuous. RBS/Channeling shows that the formed CoSi 2 has sharp interface with a minimum channeling yield of Co signal of 40%. AFM shows that the surface of ultra-thin CoSi 2 film is smooth with a roughness of nearly 0.7 nm. The Rs∼T relationship shows that the CoSi 2 films formed by Co/Si/Ti/Si reaction have the best thermal stability (stable up to 900°C). Those formed by Co/Ti/Si reaction are stable up to 850°C, while those formed by Co/Si reaction are only stable up to 750°C. By fitting the experimental I-V and C-V curves of the epitaxial CoSi 2 /Si Schottky diodes, barrier heights of around 0.6 eV and close to unity ideality factors are obtained.