Robertus A.M. Wolters

Systematic TLM Measurements of NiSi and PtSi Specific Contact Resistance to n- and p-Type Si in a Broad Doping Range

We present the data on specific silicide-to-silicon contact resistance (rhoc) obtained using optimized transmission-line model structures, processed for a broad range of various n- and p-type Si doping levels, with NiSi and PtSi as the silicides. These structures, despite being attractive candidates for embedding in the CMOS processes, have not been used for NiSi, which is the material of choice in modern technologies. In addition, no database for NiSi-silicon contact resistance exists, particularly for a broad range of doping levels. This letter provides such a database, using PtSi extensively studied earlier as a reference.

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.

Cross-Bridge Kelvin Resistor Structures for Reliable Measurement of Low Contact Resistances and Contact Interface Characterization

The parasitic factors that strongly influence the measurement accuracy of Cross-Bridge Kelvin Resistor (CBKR) structures for low specific contact resistances (¿c) have been extensively discussed during last few decades and the minimum of the ¿c value, which could be accurately extracted, was estimated. We fabricated a set of various metal-to-metal CBKR structures with different geometries, i.e., shapes and dimensions, to confirm this limit experimentally and to create a method for contact metal-to-metal interface characterization. As a result, a model was developed to account for the actual current flow and a method for reliable ¿c extraction was created. This method allowed to characterize metal-to-metal contact interface. It was found that in the case of ideal metal-to-metal contacts, the measured CBKR contact resistance was determined by the dimensions of the two-metal stack in the area of contact and sheet resistances of the metals used.

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.

Specific Contact Resistance of Phase Change Materials to Metal Electrodes

For phase change random access memory (PCRAM) cells, it is important to know the contact resistance of phase change materials (PCMs) to metal electrodes at the contacts. In this letter, we report the systematic determination of the specific contact resistance (ρ<i>c</i>) of doped Sb₂Te and Ge₂Sb₂Te₅ to TiW metal electrodes. These data are reported for both the amorphous and the crystalline states of these PCMs. The temperature and voltage dependences of ρ<i>c</i> are also studied. A detailed understanding of these contacts is essential for the scaling, design, device modeling, and optimization of PCRAM cells.

On the kinetics of platinum silicide formation

In this work, the kinetics of platinum silicide formation for thin Pt films (50 nm) on monocrystalline silicon is investigated via in situ resistance measurements under isothermal (197–275 °C) conditions. For Pt2Si diffusion limited growth was observed. For PtSi formation, however, no linear relation between silicide thickness and t was found. PtSi growth over time could be described using the Avrami relation rendering Avrami exponent n=1.4±0.1. Additionally, an effective activation energy EA=1.7±0.1 eV was derived using the Avrami k values. The findings are important for obtaining well defined silicide films and silicide-to-silicon contacts.

Specific contact resistance measurements of metal-semiconductor junctions

Our research comprises the manufacturing of test structures to characterize the metal-semiconductor junctions with a number of techniques and materials. An extensive subsequent physical and electrical testing of the junctions is carried out. We present our first results on specific silicide-to-diffusion contact resistance characterization using the known Scotts transmission line model (TLM) and our approach, considering particular geometry, with NiSi and PtSi as the silicides.

Growth Rate Determination through Automated TEM Image Analysis : Crystallization Studies of Doped SbTe Phase-Change Thin Films

A computer-controlled procedure is outlined here that first determines the position of the amorphous-crystalline interface in an image. Subsequently, from a time series of these images, the velocity of the crystal growth front is quantified. The procedure presented here can be useful for a wide range of applications, and we apply the new approach to determine growth rates in a so-called fast-growth-type phase-change material. The growth rate (without nucleation) of this material is of interest for comparison with identical material used in phase-change random access memory cells. Crystal growth rates in the amorphous phase-change layers have been measured at various temperatures using in situ heating in a transmission electron microscope. Doped SbTe films (20 nm thick) were deposited on silicon nitride membranes, and samples with and without silicon oxide capping layer were studied. The activation energy for growth was found to be 3.0 eV. The samples without capping layer exhibit a nucleation rate that is an order of magnitude higher than the samples with a silicon oxide capping layer. This difference can be attributed to the partial oxidation of the phase-change layer in air. However, the growth rates of the samples with and without capping are quite comparable.

A Tuneable Metal Gate Work Function Using Solid State Diffusion of Nitrogen

The work function of a metal gate electrode has been adjusted by the incorporation of nitrogen at the metaldielectric interface. The nitrogen was introduced using solid state diffusion from an over-stoichiometric TiN1+X layer. RBS measurements demonstrate that up to 35 at% nitrogen can be diffused into a 10nm Ta layer from the TiN layer and that the diffused concentration increases with anneal temperature. The effects of nitrogen incorporation upon the gate work function were studied for tantalum on Al2O3 and for molybdenum on SiO2 and on Al2O3. The work function of tantalum is slightly affected by the presence of the TiN exhibiting a change of -0.08±0.05eV, comparable to the work function change attributed to the thermal processing. Molybdenum is shown to be extremely sensitive with a work function change of -0.52±0.04eV for Mo/SiO2 and by -1.05±0.12eV for Mo/Al2O3. The absolute work functions for the Mo/SiO2 system are approaching the requirements of n- and p-MOSFET gate electrodes and there is evidence from the RBS measurements that there is a large process window for further optimisation.

The development of titanium silicide–boron-doped polysilicon resistive temperature sensors

Thin films of titanium silicide