Sheet Resistance Measurements Research Articles

Preparation and Characterization of Silver Substrates Coated with Antimony-Doped SnO2 Thin Films for Surface Plasmon Resonance Studies

This paper reports on the preparation of silver/antimony-doped tin oxide (Ag/SnO(2):Sb) hybrid interfaces using magnetron sputtering and their characterization. The influence of the Sn target composition (doping with 2 or 5% Sb) on the electrochemical and electrical characteristics of the hybrid interface was investigated using X-ray photoelectron spectroscopy (XPS), sheet resistance measurements, cyclic voltammetry, scanning tunneling microscopy (STM) and surface plasmon resonance (SPR). The best interface in terms of electrical conductivity and SPR signal is a hybrid interface with a 8.5 +/- 0.3 nm thick SnO(2):Sb layer obtained from a Sn target with 2% Sb deposited on 38 nm thick silver film. Different strategies to link functional groups onto the Ag/SnO(2):Sb interface are also presented.

Accurate microfour-point probe sheet resistance measurements on small samples

We show that accurate sheet resistance measurements on small samples may be performed using microfour-point probes without applying correction factors. Using dual configuration measurements, the sheet resistance may be extracted with high accuracy when the microfour-point probes are in proximity of a mirror plane on small samples with dimensions of a few times the probe pitch. We calculate theoretically the size of the "sweet spot," where sufficiently accurate sheet resistances result and show that even for very small samples it is feasible to do correction free extraction of the sheet resistance with sufficient accuracy. As an example, the sheet resistance of a 40 microm (50 microm) square sample may be characterized with an accuracy of 0.3% (0.1%) using a 10 microm pitch microfour-point probe and assuming a probe alignment accuracy of +/-2.5 microm.

CO2 laser-induced crystallization of sol–gel-derived indium tin oxide films

Indium tin oxide (ITO) thin films prepared by the sol–gel method have been deposited by the dip-coating process on silica substrates. CO2 laser is used for annealing treatments. The electrical resistivity of sol–gel-derived ITO thin films decreased following crystallization after exposure to CO2 laser beam. The topological and electrical properties of the irradiated surfaces have been demonstrated to be strongly related to the coating solution and to the laser processing parameters. Optimal results have been obtained for 5 dip-coating layers film from 0.4 mol/l solution irradiated by 0.6 W/m2 laser power density. In this case, homogeneous and optically transparent traces were obtained with a measured sheet resistance of 1.46×102 Ω/□.

Enhancement of adhesion between carbon nanotubes and polymer substrates using microwave irradiation

This paper reports the enhancement of adhesive strength between single-walled carbon nanotubes (SWNTs) and polymer substrates using microwave irradiation of 0–5 min duration at 2.45 GHz and 800 W. Field emission scanning electron microscopy images, ultraviolet–visible data and four-point probe sheet resistance measurement data indicate that microwave irradiation is effective for enhancement of adhesion between SWNTs and polymer substrates. SWNTs could be locally welded onto a polymer substrate due to their active response to microwave irradiation.

Effect of Si target sputtering power on diffusion barrier properties of Ta–Si–N thin films

Ta–Si–N thin films and Cu/Ta–Si–N thin films were deposited on p type Si(111) substrates by magnetron reactive sputtering. Then the films were characterised by four point probe sheet resistance measurement, AFM, SEM and XRD respectively. According to the XRD results, the authors found that the crystallisation of Ta nitrides in Ta–Si–N/Si thin films is suppressed effectively when fabricated by a high Si target sputtering power. As the Si target power varies, the failure temperature of Cu/Ta–Si–N/Si is changed. The sample fabricated by the Si target power of 200 W fails after 800°C rapid thermal annealing and it has the highest failure temperature. The investigation of failure mechanism shows that Cu atoms diffuse through grain boundaries or amorphous structure of the Ta–Si–N barrier, and react with Si to form Cu–Si phase. And it causes the failure of the barrier.

Investigation on phosphorus doping using H3PO4 as doping source by simple dip method and its electrical characterisation

In this article, the authors present the work on emitter diffusion in crystalline silicon solar cell fabrication, and determine that phosphorus doping using phosphoric acid (H3PO4) with dipping is convenient and cost effective. H3PO4 was mixed with different solvents such as deionised water, ethanol, methanol and butanol. However, deionised water is hydrophobic to the silicon surface. The emitter layers were obtained by varying emulsion concentrations and diffusion temperatures. The sheet resistance of the prepared emitter layers was measured. The sheet resistance varied between 60 and 130 Ω/〉 using butanol as a solvent at 900°C for 5 min. Also, butanol as a solvent exhibited uniform sheet resistance over the wafer surface, compared to other solvents. The sheet resistance decreases as the annealing time and temperature was increased. Based on sheet resistance measurements it is evident that this method can be used for solar cell fabrication, and it is cost effective and easy to scale up.

Wafer-Scale, Sub-5 nm Junction Formation by Monolayer Doping and Conventional Spike Annealing

We report the formation of sub-5 nm ultrashallow junctions in 4 in. Si wafers enabled by the molecular monolayer doping of phosphorus and boron atoms and the use of conventional spike annealing. The junctions are characterized by secondary ion mass spectrometry and noncontact sheet resistance measurements. It is found that the majority ( approximately 70%) of the incorporated dopants are electrically active, therefore enabling a low sheet resistance for a given dopant areal dose. The wafer-scale uniformity is investigated and found to be limited by the temperature homogeneity of the spike anneal tool used in the experiments. Notably, minimal junction leakage currents (<1 microA/cm(2)) are observed that highlights the quality of the junctions formed by this process. The results clearly demonstrate the versatility and potency of the monolayer doping approach for enabling controlled, molecular-scale ultrashallow junction formation without introducing defects in the semiconductor.

Influence of a transient hexagonal phase on the microstructure and morphological stability of NiSi films

The morphological stability of NiSi is investigated when 40% of Si is mixed into an as deposited 10 nm Ni film. When annealing at 3 °C/s, scanning electron microscopy images and in situ sheet-resistance measurements show that NiSi agglomeration is delayed by more than 100 °C. In situ x-ray diffraction reveals that NiSi grows from an unusual transient hexagonal θ-nickel-silicide phase. The significant improvement of the NiSi film’s morphological stability can be related to its microstructure, with large grains and a strong texture. This peculiar microstructure is compared to the microstructure of the θ-nickel-silicide precursor by electron backscattering diffraction and pole figures.

Thermal degradation of Au/Ni 2Si/n-SiC ohmic contacts under different conditions

The thermal degradation of Au/Ni 2Si/n-SiC ohmic contact was investigated after long-time aging in air at 400 °C or rapid thermal annealing in Ar up to 700 °C. Current–voltage characteristics, sheet resistance measurements, Rutherford backscattering spectrometry, X-ray diffraction and scanning electron microscopy were used to characterize the contacts before and after heat treatments. Thermal stress at different conditions shows different influence on the properties degradation of Au/Ni 2Si/n-SiC ohmic contacts. It is shown that aging of the contacts in air at 400 °C resulted in complete degradation due to both oxygen penetration and inter-diffusion/reaction processes at the metal/SiC interface. In contrast, only a small change in contact morphology was detected on the contacts annealed in Ar at 700 °C.

Implantation, Diffusion, Activation, and Recrystallization of Gallium Implanted in Preamorphized and Crystalline Germanium

We investigated the as-implanted profiles, electrical activation, diffusion, and recrystallization of gallium implanted in germanium samples through the combination of secondary-ion mass spectrometry, transmission electron microscopy, and sheet resistance measurement. Because of their high activation level without preamorphization, low activation temperature , and absence of diffusion (up to ), Ga junctions in crystalline Ge are very promising candidates for implementation in germanium technology. In the amorphous Ge phase, an increased diffusivity of Ga was observed at temperatures above .

Improvement of the Diffusion Barrier Performance of Ru by Incorporating a WN[sub x] Thin Film for Direct-Plateable Cu Interconnects

A sputter-prepared Ru (7 nm)/WN x (8 nm) stacked layer was investigated as a diffusion barrier layer between Cu and Si for direct-plateable Cu interconnects, and its performance was compared with that of a Ru single layer with the same thickness (15 nm). X-ray diffractometry and sheet resistance measurements showed that the incorporation of WN x into the Ru single layer system significantly improved the barrier performance against Cu diffusion. The Ru/WN, bilayer barrier stack failed due to Cu diffusion attack after annealing at 750°C for 30 min, while the Ru single layer failed after annealing at 450°C by the formation of Cu silicide (η-Cu 3 Si). A high resolution transmission electron microscopy analysis clearly suggested that this was due to the excellent diffusion barrier performance of WN x film with a nanocrystalline structure embedded in an amorphous matrix.

Effect of Heating Rate on the Activation Energy for Crystallization of Amorphous Ge[sub 2]Sb[sub 2]Te[sub 5] Thin Film

The crystallization of the amorphous Ge 2 Sb 2 Te 5 film was investigated by in situ electrical sheet resistance measurement. The crystallization start temperature increases logarithmically with heating rate and is equated. The effective activation energy E A of the crystallization is 2.34 eV at slow heating rates below 40°C/min and decreases to 0.49 eV at higher heating rates because of the reduced activation energies for both nucleation and growth of the crystalline face-centered cubic phase by overheating at high heating rates.

High-Productivity Combinatorial PVD and ALD Workflows for Semiconductor Logic &amp; Memory Applications

AbstractWith materials innovation driving recent logic and memory scaling in the semiconductor industry, High-Productivity Combinatorial™ (HPC) technology can be a powerful tool for finding optimum materials solutions in a cost-effective and efficient manner. This paper will review unique HPC wet processing, physical vapor deposition (PVD), and atomic layer deposition (ALD) capabilities that were developed, enabling site-isolated testing of multiple conditions on a single 300mm wafer. These capabilities were utilized for exploration of new chalcogenide alloys for phase change memory, and for metal gate and high-K dielectric development for high-performance logic. Using an HPC PVD chamber, a workflow was developed in which up to 40 different precisely controlled GeSbTe alloy compositions can be deposited in discrete site-isolated areas on a single 300mm wafer and tested for electrical &amp; material properties, using a custom in-situ high-throughput sheet-resistance measurement setup, to get very accurate measurements of the amorphous – crystalline transition temperature. We will review how resistivity as a function of temperature, crystallization temperature, final and intermediate (if any) crystalline phases were mapped for a section of the GeSbTe phase diagram, using only a few wafers. Another area where HPC can be very valuable is for finding optimum materials for high-k dielectrics and metal gates for high-performance logic transistors. Assessing the effective work-function (EWF) for a given high-k dielectric metal-gate stack for PFET and NFET transistors is a critical step for selecting the right materials before further integration. One way to obtain EWF is by using a terraced oxide wafer with different SiO2 thickness bands underneath the high-k dielectric. We report a HPC workflow using our wet, ALD &amp; PVD capabilities, to quickly assess EWF for multiple different high-k dielectrics and metal gate stacks. This workflow starts with a HPC wet etch of thermal silicon oxide, creating different oxide thicknesses 1–10nm in select areas of the same substrate. This is followed by atomic layer deposition of a high-k dielectric film such as HfO2. Next, a metal e.g., TaN is deposited through a physical mask or patterned post-deposition to complete the formation of MOS capacitors. The final step is C-V measurements and C-V modeling to extract Vfb, high-k dielectric constant, EOT, and EWF from Vfb vs EOT plot. This workflow was used to extract EWF for a TaN metal gate with an ALD HfO2 high-k dielectric using a metal-organic precursor. We will discuss how EWF for this system was affected by annealing post-dielectric deposition &amp; post-metallization, different annealing temperatures &amp; ambients, Hf pre-cursors and interfacial cap layers e.g., La2O3 &amp; Al2O3. Finally, we will also discuss more advanced versions of this workflow where the ALD high-k dielectric and PVD metal gate is also varied on the same wafer using HPC versions of ALD &amp; PVD chambers.

Experimental and simulation studies of resistivity in nanoscale copper films

The effect of film thickness on the resistivity of thin, evaporated copper films (approximately 10–150 nm thick) was determined from sheet resistance, film thickness, and mean grain-size measurements by using four-point probe, profilometer, and electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) methods, respectively. The resistivity of these films increased with decreasing film thickness in a manner that agreed well with the dependence given by a versatile simulation program, published earlier, using the measured values for the mean grain size and fitting parameters for surface and grain boundary scattering. Measurements of the change in sheet resistance with temperature of these films and the known change in resistivity with temperature for pure, bulk copper were used to calculate the thickness of these films electrically by using Matthiessen’s rule (this is often referred to as an “electrical thickness”). These values agreed to within 3 nm of those obtained physically with the profilometer. Hence, Matthiessen’s rule can continue to be used to measure the thickness of a copper film and, by inference, the cross-sectional area of a copper line for dimensions well below the mean free path of electrons in copper at room temperature (39 nm).

Surface strain and its impact on the electrical resistivity of GaN channel in AlGaN/GaN high electron mobility transistor

Localized strain in AlGaN/GaN high electron mobility transistor (HEMT) device structures was studied by high resolution x-ray diffraction and rocking curve measurements, and the results were compared with the corresponding channel sheet resistance measurements. The map of in-plane tensile strain on the HEMT wafer showed a near one-to-one correspondence with the electrical resistivity. The in-plane strain variation in the range of (2.295–3.539)×10−4 resulted in a corresponding sheet resistance variation between 345 and 411 Ω/◻.

Supramolecular Functionalization of Single-Walled Carbon Nanotubes with Conjugated Polyelectrolytes and Their Patterning on Surfaces

The interaction between single-walled carbon nanotubes and two anionic conjugated polyelectrolytes, poly[2,5-bis(3-sulfonatopropoxy)-1,4-phenylene-alt-1,4-phenylene) sodium salt and poly[2,5-bis(3-sulfonatopropoxy)-1,4-ethynylphenylene-alt-1,4-ethynylphenylene] sodium salt, was investigated. It was found that the supramolecular polymer−nanotube assembly occurred efficiently and produced stable complexes that could be purified from excess free polymer in solution. These complexes were characterized using absorption spectroscopy, fluorescence spectroscopy, Raman spectroscopy, and electron microscopy. It was further found that patterning of these polymer−nanotube complexes could be accomplished by utilizing electrostatic attraction with a prepatterned, cationically charged surface. Patterned features were found to be electrically conducting with a measured sheet resistance value of 0.68 ± 0.01 MΩ for features having a thickness on the order of several nanometers.

Correlation of local structure and electrical activation in arsenic ultrashallow junctions in silicon

The understanding of the behavior of arsenic in highly doped near surface silicon layers is of crucial importance for the formation of N-type ultrashallow junctions in current and future very large scale integrated technology. This is of particular relevance when studying recently developed implantation and annealing methods. Past theoretical as well as experimental investigations have suggested that the increase in As concentration, and therefore the reciprocal proximity of several As atoms, leads to a drastic increase in electrically inactive defects giving only marginal reduction in sheet resistance. Monoclinic SiAs aggregates as well as various arsenic-vacancy clusters contribute to the deactivation of arsenic. This study aims to correlate between the results of electrical activation measurements and x-ray absorption fine structure measurements. Samples were doped with a nominal fluence of 1×1015–3×1015 atoms/cm2, implanted at 2 keV, and annealed by rapid thermal treatments, laser submelt treatments, and a combination of both. Hall effect and sheet resistance measurements have been performed to obtain the density of charge carriers. Secondary ion mass spectrometry has been employed to measure the depth profile and the total retained fluences. The percentage of substitutional arsenic has been obtained by least-squares fits of the measured x-ray absorption spectra with simulated spectra of relaxed structures of the defects obtained by density functional theory. A good agreement with the Hall effect measured electrically active dose fraction has been obtained and a quantification of the population of the different defects involved has been attempted.

Simultaneous real-time x-ray diffraction spectroscopy, Rutherford backscattering spectrometry, and sheet resistance measurements to study thin film growth kinetics by Kissinger plots

When the Kissinger method is used to investigate thin film growth kinetics, activation energies obtained are often significantly higher than those of Arrhenius plots based on isothermal studies. The reason for the higher activation energies is related to the sensitivity of the Kissinger analysis to nucleation effects. In fact, this often undesirable effect opens the possibility of studying nucleation barriers in a semiquantitative way. Furthermore, we show that these nucleation effects can be filtered out by a more careful application of the Kissinger method, and activation energies that are consistent with Arrhenius plots are then obtained.

The influence of Se doping upon the phase change characteristics of GeSb 2Te 4

Se substituted GeSb 2Te 4 films have been investigated for property contrast using electrical four-point-probe measurements, in-situ X-ray diffraction (XRD), a static tester probing the optical changes and atomic force microscopy (AFM). The temperature dependent sheet resistance measurements show two transitions at 125 and 262 °C. The first transition at 125 °C is accompanied by a large resistance change of three orders of magnitude. The resistance change for the second step is less pronounced. In-situ X-ray scattering experiments evidence that the first steep change in resistance is due to an amorphous → NaCl type structural transformation. The second change is caused by the transition from the cubic structure to the stable rhombohedral phase. Power–time effect (PTE) diagrams recorded to monitor the optical contrast of the films upon laser irradiation exhibit a fast recrystallization time of about 100 ns. The change of film roughness and topography between the amorphous and crystalline phase has been determined by AFM.

Properties of reactively sputtered W–B–N thin film as a diffusion barrier for Cu metallization on Si

Thin films of W–B–N (10 nm) have been evaluated as diffusion barriers for Cu interconnects. The amorphous W–B–N thin films were prepared at room temperature via reactive magnetron sputtering using a W2B target at various N2/(Ar + N2) flow ratios. Cu diffusion tests were performed after in-situ deposition of 200 nm Cu. Thermal annealing of the barrier stacks was carried out in vacuum at elevated temperatures for one hour. X-ray diffraction patterns, sheet resistance measurement, cross-section transmission electron microscopy images, and energy-dispersive spectrometer scans on the samples annealed at 500°C revealed no Cu diffusion through the barrier. The results indicate that amorphous W–B–N is a promising low resistivity diffusion barrier material for copper interconnects.