Brent A. Morgan

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.

Hot-electron attenuation lengths in ultrathin magnetic films

Ballistic electron emission microscopy (BEEM) is used to measure hot-electron transport across magnetic metal multilayers. Room temperature measurements in air have been carried out on Au/M/Si(100), Au/M/Au/Si(100), and Au/M/PtSi/Si diodes, that were sputter deposited at 175 or 300 K, where M is Co, Fe, Ni, Cu, or Ni81Fe19. Plots of log BEEM current versus M thickness are linear giving hot-electron (1.5 eV) attenuation lengths (ALs), for Au/M/Si diodes (M=Co, Fe, Ni81Fe19, and Ni) of 0.3, 0.5, 0.8, and 1.3 nm, respectively (with typical standard uncertainties of ±10%). Magnetic metal sandwich diodes, (Au/M/Au/Si) show larger ALs, 0.8 and 2.1 nm, for M=Co and Ni81Fe19, respectively. PtSi interlayers improve the surface roughness but have little effect on the AL while low temperature depositions increase the AL. We presume that the increases in the AL are due to better microstructure, less silicide reaction, or to changes in elastic scattering at interfaces.

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)].

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.

Interfacial scattering of hot electrons in ultrathin Au/Co films

We have used room-temperature, ballistic electron emission microscopy (BEEM) to measure hot-electron transport through ultrathin Au/Co multilayer structures deposited onto Si. The samples consist of Au/Co/Si or (Au/Co)n/Au/Si diodes, sputter deposited at 175 or 300 K, where n is the number of repeat layers. The thin-film Co attenuation length, λCo, is extracted from the BEEM spectra as a function of Co thickness, in single Co layer samples. Similarly, the interface attenuation number, or the number of Co/Au interfaces required for a 1/e attenuation, is determined from the multi-interface samples. BEEM barrier heights of Au/Co/Si decrease with increasing Co thickness (for thicknesses <1 nm), as the film becomes continuous and develops a Schottky barrier for Co or CoSi2(<0.7 eV). For these diodes, λCo, increases from 0.3 to 0.5 nm, each with an estimated uncertainty of 0.1 nm, when the deposition temperature is decreased from 300 to 175K. This result is associated with decreased silicide formation at the lo...

Comparison of Au contacts to Si, GaAs, InxGa1 − xP, and ZnSe measured by ballistic electron emission microscopy

Abstract Ballistic electron emission microscopy (BEEM) measurements have been made on Au contacts to Si, GaAs, InxGa1 − xP, and ZnSe. For each semiconductor studied, a distribution of barrier heights (BHs) was observed. The distributions were compared with the current—voltage (I/V) and capacitance—voltage (C/V) characteristics of each metal/semiconductor contact. The BH distributions increase in width with increasing doping and/or complexity of the substrate. The effect of discrete, ionized dopants in the depletion region is considered as one source of BH distribution widening. Average BEEM measurements agree well with the BH computed from I/V and C/V measurements for all diodes if the effects of thermionic field emission and image force lowering are considered. These results demonstrate the unique application of BEEM for the nanoscale evaluation of semiconductor interface inhomogeneities critical to the control of macroscopic electronic properties.

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).

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.

Comparison of the spatial variation in the barrier height of Si and GaAs Schottky diodes as measured by ballistic electron emission microscopy

Nanometer-resolved spatial variations in the Schottky barrier height (SBH) formed at a chemically prepared Au/n-GaAs interface and a UHV prepared Au/PtSi/Si interface have been compared using ballistic electron emission microscopy (BEEM). The statistical distribution of the SBHs obtained were also compared to current-voltage (I/V) and capacitance-voltage (C/V) characteristics of each metal/semiconductor contact. BEEM detects a nanoscale variation in SBH but with a more uniform SBH distribution for the in-situ annealed PtSi/Si diodes versus the oxide passivated Au/GaAs diodes. The average SBH from BEEM agreed well with the SBH from I/V and C/V measurements for both diodes if the effects of thermionic field emission and image force lowering, respectively, were considered. These results demonstrate the unique application of BEEM for the nanoscale evaluation of semiconductor interface inhomogeneities critical to the control of macroscopic electronic properties.