Ken M. Ring

Substrate effects on the ferroelectric properties of fine-grained BaTiO3 films

The development of ferroelectric properties in barium titanate (BaTiO3) polycrystalline films has been investigated as a function of substrate type. The films were deposited by physical vapor deposition (PVD) onto different, Pt-coated substrates (magnesium oxide, thermally oxidized silicon, and sapphire) and annealed at temperatures from 725 to 1050 °C. Grain sizes from 50 to 200 nm were produced, with structural and dielectric properties that showed a marked transition from nonferroelectric to ferroelectric behavior across this range. Anneal temperatures below 950 °C result in films with grain sizes less than 150 nm, and ferroelectric properties that are strongly suppressed, regardless of the substrate. Observations for this temperature range include low dielectric constant (e), no polarization hysteresis, and no peaks in the temperature dependence of the dielectric constant. The onset of ferroelectric behavior occurs for anneal temperatures above 950 °C, coinciding with the appearance of strong substrat...

Lateral variation in the Schottky barrier height of Au/PtSi/(100)Si diodes

The lateral variation in the Schottky barrier height (SBH) formed at UHV prepared Au/PtSi/(100)Si (n=4.5×1014) diodes was measured on length scales ranging from a few to several hundred nanometers using ballistic electron emission microscopy (BEEM). The spatial profile and the statistical distribution of the SBHs thus obtained were compared to broad area current–voltage (I–V) and capacitance–voltage (C–V) characteristics of these metal–semiconductor contacts. This comparison showed that the macroscopic SBHs obtained from I–V and C–V measurements can be successfully interpreted using the parallel conduction model applied to the BEEM derived barrier height distribution. In addition, we found that the variations in the SBH were strongly correlated, with an autocovariance length of ∼20 nm at short wavelengths and with a strong peak in the spectral density at a spatial frequency of ∼(225 nm)−1.

Au/ZnSe contacts characterized by ballistic electron emission microscopy

Ballistic electron emission microscopy (BEEM) has been performed on Au/ZnSe (001) diodes prepared in ultra high vacuum. An average barrier height (BH) of 1.37 eV is found for Au/n‐ZnSe in close agreement with previously published values for diodes measured by conventional techniques. The BH distribution is relatively narrow, from 1.32 to 1.43 eV, consistent with cross‐sectional transmission electron microscopy which indicates that the interface is abrupt, and without reaction products. These results differ from those reported for BEEM measurements on chemically etched Au/ZnSe diodes. [R. Coratger et al., Phys. Rev. B. 51, 2357 (1995)].

Structural investigation of self-aligned silicidation on separation by implantation oxygen

Self-aligned silicidation is a well-known process to reduce the source, drain, and gate parasitic resistances of submicron metal-oxide-semiconductor devices. This process is particularly useful for devices built on very thin Si layer (∼1000 A or less) on insulators. Since the amount of Si available for silicidation is limited by the thickness of the Si layer, once the Si in the source and drain region is fully consumed during silicidation, excessive silicide formation could lead to void formation near the silicide/silicon interface beneath the oxide edge. In this article, we study the effects of different metals (Ti, Ni, Co, and Co/Ti bilayer) with varying thickness on the formation of voids. A change in the moving species during lateral silicide formation was found to be the likely cause for the voids, even if the metals are the moving species during silicidation in the thin film case.

Role of interface microstructure in rectifying metal/semiconductor contacts: Ballistic electron emission observations correlated to microstructure

Ballistic electron emission microscopy (BEEM) is a technique for the measurement of nanoscopic spatial variations in the barrier height of metal‐semiconductor contacts. We have used BEEM in conjunction with simultaneous scanning tunneling microscopy observations of topography, as well as cross‐sectional and plan‐view transmission electron microscopy, to investigate diode nonidealities and relate them to microstructure. Au/ZnSe and PtSi/Si diodes were examined using these techniques. When analyzed with the parallel conduction model, distributions of barrier heights observed by BEEM in area scans agree well with values measured by conventional techniques and reported in the literature. The wider Au/ZnSe barrier height distribution is thought to be correlated with a rougher interface structure than the PtSi/Si.

Structural and Electrical Characterization of Si-Implanted TiN as a Diffusion Barrier for Cu Metallization

The feasibility of Si-implanted TiN as a diffusion barrier between Cu and Si was investigated. Barrier effectiveness was evaluated via reverse leakage current of Cu/Ti x Si y N z /Si diodes as a function of post-deposition annealing temperature and time, and was found to depend heavily on the film composition and microstructure. TiN implanted with Si 28 , l0keV, 5xl0 16 ions/cm 2 formed an amorphous ternary Ti x Si y N z layer whose performance as a barrier to Cu diffusion exceeded that of unimplanted, polycrystalline TiN. Results from current-voltage, transmission electron microscopy (TEM), and Auger depth profiling measurements will be presented. The relationship between Si-implantation dose, Ti x Si y N z structure and reverse leakage current of Cu/Ti x Si y N z /Si diodes will be discussed, along with implications as to the suitability of these structures in Cu metallization.

Effect of Oxygen on the Degradation of Ti-Si-N Diffusion Barriers in Cu Metallization

Amorphous Ti-Si-N thin films are effective barriers to Cu diffusion in integrated circuits that use Cu interconnects. These films are believed to fail as diffusion barriers due to crystallization and subsequent diffusion of Cu along grain boundaries. We prepare thin films of Ti-Si-N by RF magnatron co-sputtering of Ti and Si in Ar/N 2 . Ti-Si-N films with Si concentrations of 6 to 22% have resistivities 40 Si 15 N 45 /Cu do not fail (increased reverse leakage current) until 600%C. When annealed, these films crystallize to yield TiN and Si 3 N 4 . In this work we have studied the effect of oxygen on the degradation of the barrier via TEM, diode I-V measurements, and RBS. Oxygen incorporated into the film deposition process improves the barrier effectiveness as measured by diode I-V reverse leakage current. We find no correlation between the amount of O 2 in the process gas feed stream and the film composition with O resonance analysis (RBS) or crystallinity (TEM).

Suppression of growth-induced perpendicular magnetic anisotropy in Co–Pt alloys by trace amounts of Si

(CoxPt1−x)1−ySiy alloys with Si content from 1 to 20 at. % have been grown over a range of growth conditions. Co-deposition of even trace amounts of Si with Co–Pt alloys causes the growth-induced magnetic anisotropy and chemical clustering found in these vapor-deposited alloy films to decrease or vanish. It also causes significant reduction in grain size. Addition of 5 at. % Si eliminates anisotropy completely. Addition of 1 at. % Si produces a film with magnetic properties identical to pure Co–Pt alloys grown at lower deposition temperatures. We suggest this suppression of anisotropy and related effects are due to a decrease in surface mobility during growth in the presence of even trace amounts of Si.

Compositional Effects on the Degradation of PVD-Tisin

PVD-Ti x Si y N z films formed by reactive RF-magnetron co-sputtering of Ti and Si in Ar/N 2 are evaluated as a diffusion barrier between Cu and Si. A complete range of compositions are obtained by Ti targets inlaid with Si. Film composition is controlled by the target ratio of titanium to silicon and N 2 partial pressure. Electrical results versus thermal history for films of∼6–18% Si as well as the composition and microstructure as determined by Rutherford back scattering (RBS), TEM and electron diffraction are reported. These films are an amorphous matrix with imbedded nanocrystals of titanium nitride as-deposited and undergo phase separation to yield titanium nitride and silicon nitride after a 1000°C anneal. As-deposited compositions which lie above the TiN-Si 3 N 4 phase line yield crystals of TiN. Compositions below the TiN-Si 3 N 4 phase line yield crystals of Ti 2 N. Bulk resistivity as-deposited ( 40 Si 15 N 4 5 and Cu show no significant increase in reverse leakage current at anneal temperatures below 700°C.

Lateral Variation in the Schottky Barrier Height and Observation of Critical Lengths at Au/PtSi/(100)Si and Au/(100)GaAs Diodes

Lateral variations in the Schottky barrier height (SBH) formed at Au/PtSi/(100)Si and Au/(100)GaAs diodes were measured on length scales ranging from a few to several hundred nanometers using ballistic electron emission microscopy (BEEM). All of the contacts investigated showed SBH spatial inhomogeneity. The most severe SBH variations observed were 0.09eV/0.7nm in Au/(100)GaAs contacts and 0.08eV/14nm for Au/PtSi/(100)Si contacts. Based on the lateral maps of the SBH at each interface, the difference between the locally averaged SBH and the globally averaged BEEM SBH was computed. This analysis showed that there is a critical diode length scale below which the SBH deviates significantly from the SBH averaged over a macroscopic length scale. This result implies that the uniformity of electrical characteristics of arrays of small devices (e.g.. PtSi/Si photodetectors and GaAs FET gates) can be expected to deteriorate significantly when device dimensions decrease below the critical length.