M. F. Li

Energy gap and band alignment for (HfO2)x(Al2O3)1−x on (100) Si

High-resolution x-ray photoelectron spectroscopy (XPS) was applied to characterize the electronic structures for a series of high-k materials (HfO2)x(Al2O3)1−x grown on (100) Si substrate with different HfO2 mole fraction x. Al 2p, Hf 4f, O 1s core levels spectra, valence band spectra, and O 1s energy loss all show continuous changes with x in (HfO2)x(Al2O3)1−x. These data are used to estimate the energy gap (Eg) for (HfO2)x(Al2O3)1−x, the valence band offset (ΔEν) and the conduction band offset (ΔEc) between (HfO2)x(Al2O3)1−x and the (100) Si substrate. Our XPS results demonstrate that the values of Eg, ΔEν, and ΔEc for (HfO2)x(Al2O3)1−x change linearly with x.

N-type Schottky barrier source/drain MOSFET using ytterbium silicide

Ytterbium silicide, for the first time, was used to form the Schottky barrier source/drain (S/D) of N-channel MOSFETs. The device fabrication was performed at low temperature, which is highly preferred in the establishment of Schottky barrier S/D transistor (SSDT) technology, including the HfO/sub 2/ gate dielectric, and HaN/TaN metal gate. The YbSi/sub 2 - x/ silicided N-SSDT has demonstrated a very promising characteristic with a recorded high I/sub on//l/sub off/ ratio of /spl sim/10/sup 7/ and a steep subthreshold slope of 75 mV/dec, which is attributed to the lower electron barrier height and better film morphology of the YbSi/sub 2 - x//Si contact compared with other self-aligned rare earth metal-(Erbium, Terbium, Dysprosium) silicided Schottky junctions.

ELECTRONIC BAND STRUCTURES AND EFFECTIVE-MASS PARAMETERS OF WURTZITE GAN AND INN

The electronic band structures of wurtzite GaN and InN are calculated by the empirical pseudopotential method (EPM) with the form factors adjusted to reproduce band features which agree with recent experimental data and accurate first-principles calculations. The electron and hole effective masses at the Γ point are obtained using a parabolic line fit. Further, using the effective-mass Hamiltonian and the cubic approximation for wurtzite semiconductors, band edge dispersion at the Γ point obtained using the k.p method is fitted to that calculated using the EPM by adjusting the effective-mass parameters. Thus, we derived important band structure parameters such as the Luttinger-like parameters for GaN and InN which will be useful for material design in wide-gap nitride-based semiconductor lasers employing InGaN. The results also showed that the cubic approximation is fairly successful in the analysis of valence band structures for wurtzite nitrides.

Characterization and Physical Origin of Fast Vth Transient in NBTI of pMOSFETs with SiON Dielectric

Highly reliable characterization of fast transient in NBTI is achieved by performing initial and stressed I-V measurements in ultra-short time (100 ns). We further provide evidences that reaction-diffusion (R-D) model can not explain the fast transient in NBTI, while hole trapping (HT) model explains all experimental observations. We also establish that previous on-the-fly methods are sound except for the slow initial measurement. This caused the apparent disagreements among results from different groups using on-the-fly methods, which is resolved in this work by the fast on-the-fly technique

Effect of surface NH3 anneal on the physical and electrical properties of HfO2 films on Ge substrate

Metal-oxide-semiconductor capacitors were fabricated on germanium substrates by using metalorganic-chemical-vapor-deposited HfO2 as the dielectric and TaN as the metal gate electrode. It is demonstrated that a surface annealing step in NH3 ambient before the HfO2 deposition could result in significant improvement in both gate leakage current and the equivalent oxide thickness (EOT). It was possible to achieve a capacitor with an EOT of 10.5 A and a leakage current of 5.02×10−5 A/cm2 at 1 V gate bias. X-ray photoelectron spectroscopy analysis indicates the formation of GeON during surface NH3 anneal. The presence of Ge was also detected within the HfO2 films. This may be due to Ge diffusion at the high temperature (∼400 °C) used in the chemical-vapor deposition process.

Fermi pinning-induced thermal instability of metal-gate work functions

The dependence of the metal-gate work function on the annealing temperature is experimentally studied. We observe increased Fermi-level pinning of the metal-gate work function with increased annealing temperature. This effect is more significant for SiO/sub 2/ than for HfO/sub 2/ gate dielectric. A metal-dielectric interface model that takes the role of extrinsic states into account is proposed to explain the work function thermal instability. This letter provides new understanding on work function control for metal-gate transistors and on metal-dielectric interfaces.

A high-density MIM capacitor (13 fF/μm/sup 2/) using ALD HfO 2 dielectrics

Metal-insulator-metal (MIM) capacitors with different HfO/sub 2/ thickness have been investigated. The results show that both the capacitance density and voltage coefficients of capacitance (VCCs) increase with decreasing HfO/sub 2/ thickness. In addition, it is found that the VCCs decrease logarithmically with increasing thickness. Furthermore, the MIM capacitor with 10-nm HfO/sub 2/ shows a record high capacitance density of 13 fF//spl mu/m/sup 2/ and a VCC of 607 ppm/V, which can meet the requirement of the International Technology Roadmap for Semiconductors. It can also provide a low leakage current of 5.95 /spl times/ 10/sup -8/A/cm/sup 2/ at room temperature at 1 V, low tangent values below 0.05, and a small frequency dependence. These results indicate that the devices are suitable for use in silicon integrated circuit applications.

A high performance MIM capacitor using HfO 2 dielectrics

Metal-insulator-metal (MIM) capacitors with a 56 nm thick HfO/sub 2/ high-/spl kappa/ dielectric film have been fabricated and demonstrated for the first of time with a low thermal budget (/spl sim/200/spl deg/C). Voltage linearity, temperature coefficients of capacitance, and electrical properties are all characterized. The results show that the HfO/sub 2/ MIM capacitor can provide a higher capacitance density than Si/sub 3/N/sub 4/ MIM capacitor while still maintaining comparable voltage and temperature coefficients of capacitance. In addition, a low leakage current of 2/spl times/10/sup -9/ A/cm/sup 2/ at 3 V is achieved. All of these make the HfO/sub 2/ MIM capacitor to be very suitable for use in silicon RF and mixed signal IC applications.

Alternative surface passivation on germanium for metal-oxide-semiconductor applications with high-k gate dielectric

An alternative surface passivation process for high-k Ge metal-oxide-semiconductor (MOS) device has been studied. The surface SiH4 annealing was implemented prior to HfO2 deposition. X-ray photoelectron spectroscopy analysis results show that the SiH4 surface passivation can greatly prevent the formation of unstable germanium oxide at the surface and suppress the Ge out-diffusion after the HfO2 deposition. The electrical measurement shows that an equivalent oxide thickness of 13.5A and a leakage current of 1.16×10−5A∕cm2 at 1V gate bias was achieved for TaN∕HfO2∕Ge MOS capacitors with the SiH4 surface treatment.

Electronic properties of zinc‐blende GaN, AlN, and their alloys Ga1−xAlxN

The electronic properties of wide‐energy gap zinc‐blende structure GaN, AlN, and their alloys Ga1−xAlxN are investigated using the empirical pseudopotential method. Electron and hole effective mass parameters, hydrostatic and shear deformation potential constants of the valence band at Γ and those of the conduction band at Γ and X are obtained for GaN and AlN, respectively. The energies of Γ, X, L conduction valleys of Ga1−xAlxN alloy versus Al fraction x are also calculated. The information will be useful for the design of lattice mismatched heterostructure optoelectronic devices based on these materials in the blue light range application.