Sheron Shamuilia

Amorphous lanthanum lutetium oxide thin films as an alternative high-κ gate dielectric

Lanthanum lutetium oxide thin films were grown on (100) Si by pulsed laser deposition. Rutherford backscattering spectrometry, atomic force microscopy, x-ray diffraction, and x-ray reflectometry were employed to investigate the samples. The results indicate the growth of stoichiometric and smooth LaLuO3 films that remain amorphous up to 1000°C. Internal photoemission and photoconductivity measurements show a band gap width of 5.2±0.1eV and symmetrical conduction and valence band offsets of 2.1eV. Capacitance and leakage current measurements reveal C-V curves with a small hysteresis, a dielectric constant of ≈32, and low leakage current density levels.

Internal photoemission of electrons at interfaces of metals with low-κ insulators

Energy barriers for electrons at interfaces of several low-permittivity insulators with metals (Ta, TaNx, TiNx, Au, and Al) are characterized using internal photoemission spectroscopy. In sharp contrast to thermal SiO2, the barriers show little sensitivity to the Fermi energy of the metal, suggesting that the uppermost occupied electron revels at the interface are states localized in the near-interfacial insulator layer. Moreover, despite large differences in the defect spectrum of the studied low-κ materials as revealed by electron spin resonance, all the measured energy barriers are found to be close to 4.5eV. The latter indicates an extrinsic nature of the corresponding common electron state, which is tentatively ascribed to traces of moisture at the interface.

Electronic structure of the interface of aluminum nitride with Si(100)

The band alignment at the interfaces of Si(100) with amorphous (a-) and crystallized (c-) AlN layers was analyzed using internal photoemission and photoconductivity spectroscopy. The bandgap of thin a-AlN layers grown using atomic layer deposition is found to be 5.8±0.1 eV, widening to 6.5±0.2 eV after annealing induced crystallization into the wurtzite phase. Internal photoemission of electrons from the Si valence band to the AlN conduction band was found to exhibit the same energy threshold of 3.2±0.1 eV in amorphous and crystallized AlN. The energy band diagrams of a-AlN/Si(100) and c−AlN/Si(100) interfaces are established.The band alignment at the interfaces of Si(100) with amorphous (a-) and crystallized (c-) AlN layers was analyzed using internal photoemission and photoconductivity spectroscopy. The bandgap of thin a-AlN layers grown using atomic layer deposition is found to be 5.8±0.1 eV, widening to 6.5±0.2 eV after annealing induced crystallization into the wurtzite phase. Internal photoemission of electrons from the Si valence band to the AlN conduction band was found to exhibit the same energy threshold of 3.2±0.1 eV in amorphous and crystallized AlN. The energy band diagrams of a-AlN/Si(100) and c−AlN/Si(100) interfaces are established.

Flatband voltage shift of ruthenium gated stacks and its link with the formation of a thin ruthenium oxide layer at the ruthenium/dielectric interface

A systematic study about the flatband voltage (Vfb) shift of Ru gated metal-oxide-semiconductor stacks after thermal treatment in O2 has been performed. The dependence of the Vfb shift on the anneal time and temperature and the thickness of Ru was studied in detail, and a clear link between the Vfb shift and an oxygen diffusion process in Ru was observed. A high temperature thermal treatment of the devices prior to the O2 anneal has no significant impact on the Vfb shift. The Vfb shift is ascribed to the shift of metal gates’ work function, and is not intrinsic to HfO2 gated stacks as similar behavior was also observed on SiO2, from the combination of internal photoemission and conventional capacitance-voltage measurement. No similar Vfb shift was observed for TiN gated stacks and the Vfb shift seems to be more related to the properties of gate electrodes other than those of gate dielectrics. After thermal treatment in O182, from time-of-flight secondary ion mass spectrometry measurement, it was found tha...

Nitrogen Implantation - An Alternative Technique to Reduce Traps at SiC/SiO2-Interfaces

A near-surface Gaussian nitrogen (N) profile is implanted into the Si- or C-face of n-/ptype 4H-SiC epilayers prior to a standard oxidation process. The corresponding MOS capacitors are investigated by conductance and internal photoemission spectroscopy. The effect of N-implantation on the density of interface traps Dit is studied and a model is proposed, which consistently explains the observed results.

Photoconductivity of Hf-based binary metal oxide systems

To explore the possibility of bandgap engineering in binary systems of oxide insulators we studied photoconductivity of nanometer-thin Hf oxide layers containing different concentrations of cations of different sorts (Si, Al, Sr, or Ce) deposited on (100)Si. The lowest bandgap of the Hf:Al oxide is close to the value 6–6.2 eV of elemental amorphous Al2O3 and insensitive to the Al content for concentrations of Al exceeding 36%. This result suggests that the Al oxide subnetwork with the largest bandgap preserves this energy width while development of a narrower gap of HfO2 is prevented possibly by dilution of the second cation subnetwork. When Ce is admixed to HfO2 an intermediate bandgap value (between the CeO2 and HfO2 bandgap widths) of 5.3+0.1 eV is observed for all concentrations of Ce, suggesting that the electronic structure of both elemental oxide subnetworks which form the binary metal oxide system, is affected. In Hf:Si oxide samples photoconductivity thresholds of 5.6–5.9 eV corresponding to the ...

Internal photoemission of electrons from Ta-based conductors into SiO2 and HfO2 insulators

The origin of annealing-induced variations in the effective work function of Ta-based conductors (TaC, Ta2C, and TaNx) at interfaces with SiO2 and HfO2 dielectrics is investigated using the spectroscopy of internal photoemission (IPE) of electrons. Two physical mechanisms were considered that could affect the Ta-based metal/oxide barrier: (a) oxidation of the metal conductor after thermal treatment by oxygen supplied from the oxide layer, resulting in a variation in the density of electron states inside the metal emitter, and (b) annealing-induced variations in the barrier at the interface. Field-dependent and differential IPE experiments allowed us to identify the latter as the dominant mechanism causing the barrier instability after thermal treatment in nonoxidizing ambient. The incorporation of negatively charged centers in the near-interface oxide layers is the most likely explanation for the significant increase (∼0.6 eV) of the barrier height after annealing, leading us to the hypothesis that Ta may...

On the Electrical Activity of Misfit and Threading Dislocations in p-n Junctions Fabricated in Thin Strain-Relaxed Buffer Layers

The electrical activity of threading dislocations (TDs), occurring in a thin SiGe Strain Relaxed Buffer (SRB) layer has been investigated by a number of techniques and its impact on the reverse current of p-n junction diodes has been evaluated. It is shown that besides the density of TD, there are at least two other parameters playing an important role. The distance with respect to the metallurgical junction of the 5 nm C-rich layer, used for the strain relaxation and the dopant type in the well region also affect the leakage current. This complex behaviour is further reflected in the Emission Microscopy (EMMI) images, showing different breakdown sites for p+/n or n+/p junctions. Results will be presented whereby one of these parameters is varied, while the others are kept constant, in order to arrive at some idea of the relative importance of the different factors.

Second Generation High-k Gate Insulators

Very high (k>25) permittivity materials have been investigated as a second step high-k gate insulator. These are all formed by adding other materials to the basic HfO2. Hafnium titanate thin films were deposited by chemical vapor deposition (CVD). It was observed that both the interfacial layer (IL) EOT and the permittivity increase with Ti content and that films with higher Ti content are also more immune to crystallization. Permittivities as high as 50 were achieved. In the MOSFET devices with the hafnium titanate films, normal transistor characteristics were observed, including electron mobility degradation. In SrHfO3 films, deposited by physical vapor deposition (PVD), a permittivity as high as 35 was achieved. These films appear to be highly stable upon high temperature annealing, but show a thick, anomalous interfacial layer.