Jae-Hoon Lee

Compatibility of dual metal gate electrodes with high-k dielectrics for CMOS

Dual metal electrodes such as Ru, Ru-Ta alloy, TaN and TaSiN were investigated on low EOT single layer HfO/sub 2/ and stacked HfO/sub 2//SiO/sub 2/ gate dielectrics. It was found that the work function values of metal gates on HfO/sub 2/ and on SiO/sub 2/ are similar. Thermal anneal studies of selected metals on the above dielectrics were also performed to evaluate the change in EOT and V/sub FB/ values.

Tunable work function dual metal gate technology for bulk and non-bulk CMOS

This paper describes a metal gate process, which provides tunable work function values and ease of integration for dual metal gate process flow. Vertical stacks of Ru and Ta layers were subjected to high temperature anneals to promote intermixing which resulted in /spl phi//sub m/ tuning. It was found that Ru/Ta stacks provided up to 0.4 eV reduction in /spl phi//sub m/ compared to Ru. To increase this change, stacks of Ru/sub 50/Ta/sub 50//Ru were also evaluated and nearly a 0.8 eV change in /spl phi//sub m/ was observed between Ru/sub 50/Ta/sub 50//Ru and Ru/sub 50/Ta/sub 50/ electrodes.

Analysis of the reverse leakage current in AlGaN/GaN Schottky barrier diodes treated with fluorine plasma

The carrier transport mechanism of CF4 plasma-treated AlGaN/GaN Schottky barrier diodes (SBDs) under reverse bias is investigated. The reverse leakage current is reduced by ∼2 orders of magnitude after the CF4 plasma treatment, but increases exponentially with increasing temperature, indicating that a thermally activated transport mechanism is involved. Based on the activation energy estimated from temperature-dependent current-voltage characteristics and the emission barrier height extracted from Frenkel-Poole emission model, it is suggested that the dominant carrier transport mechanism in the CF4 plasma treated SBDs is the Frenkel-Poole emission from fluorine-related deep-level states into the continuum states of dislocations.

Effect of the composition on the electrical properties of TaSi/sub x/N y metal gate electrodes

In this letter, the effect of silicon and nitrogen on the electrical properties of TaSi/sub x/N/sub y/ gate electrode were investigated. The TaSi/sub x/N/sub y/ films were deposited on SiO/sub 2/ using reactive cosputtering of Ta and Si target in Ar and N/sub 2/ ambient. The thermal stability of TaSi/sub x/N/sub y//SiO/sub 2//p-type Si stacks was evaluated by measuring the flatband voltage and equivalent oxide thickness at 400/spl deg/C and 900/spl deg/C in Ar. It was found that under high temperature anneals, Si-rich TaSi/sub x/N/sub y/ films increased and this was attributed to the formation of a reaction layer at the electrode-dielectric interface. Reducing the Si content alone did not prevent the formation of this reaction layer while removing Si completely by utilizing TaN resulted in work functions that were too high. The presence of both Si and N was deemed necessary and their content was critical in obtaining optimized TaSi/sub x/N/sub y/ gates that are suitable for NMOS devices.

Electrical Characteristics of HfO2 Dielectrics with Ru Metal Gate Electrodes

Hafnium dioxide, HfO 2 , thin films were prepared by radio frequency magnetron sputtering of thin hafnium layers, followed by an oxidation process. Ru was deposited on the HfO 2 as the gate electrode. An equivalent oxide thickness of 12.5 A was obtained in Ru/HfO 2 /n-Si metal oxide semiconductor (MOS) capacitor with a low leakage current density of 1.7 × 10 - 2 A/cm 2 at Vg - V F B = 1 V in accumulation. The work function of Ru gate extracted from capacitance-voltage analysis was 5.02 eV, suggesting Ru has the appropriate work function for p-MOSFETs. Using the conductance method, a high interface state density of 1.3 X 10 1 3 eV - 1 cm - 2 from the conduction band edge to the near midgap of Si was obtained in Ru/HfO 2 /n-Si MOS, compared to low interface density level of ∼ 10 1 1 eV - 1 cm - 2 in p + poly Si/SiO 2 /n-Si MOS. To evaluate the thermal stability, the samples were subjected to a rapid thermal anneal in an argon ambient up to 900°C. The electrical characteristics of Ru/HfO 2 /n-Si MOS capacitor are discussed in detail with post-metal annealing temperatures.

The effects of isoelectronic Al doping and process optimization for the fabrication of high-power AlGaN-GaN HEMTs

In order to improve the electrical characteristics of AlGaN-GaN heterostructures for applications in high electron mobility transistors (HEMTs), high-quality AlGaN-GaN was grown by way of metal-organic chemical vapor deposition on sapphire. We applied isoelectronic Al doping into the GaN-channel layers of modified AlGaN-Al-doped GaN channel-GaN heterostructures. We then compared the electrical performance of the fabricated heterostructures with those of conventional AlGaN-GaN heterostructures. The AlGaN-GaN HEMTs that were fabricated achieved power densities of up to 4.2 W/mm, some of the highest values ever reported for 0.25-/spl mu/m gate length AlGaN-GaN HEMTs. These devices exhibited a maximum drain current density of 1370 mA/mm, a high transconductance of 230 mS/mm, a short-circuit current gain cutoff frequency (f/sub T/) of 67 GHz, and a maximum frequency of oscillation (f/sub max/) of 102 GHz.

Embedded‐mirror semiconductor laser

Data are presented demonstrating the operation of a current‐injection laser diode with embedded reflectors instead of etched or cleaved facets. The laser structure, grown by molecular beam epitaxy, uses AlAs‐GaAs superlattices SL’s in place of conventional AlxGa1−xAs cladding layers. The sample is patterned, etched, and Zn diffused to selectively disorder the SL cladding layers producing a ∼200×∼100 μm rectangular laser cavity embedded in the surrounding AlxGa1−xAs. Following Si3N4 deposition and metallization, the diodes are cut (not cleaved) with intentionally damaged edges. These devices operate as lasers (77 K, pulsed operation) with a mode spacing corresponding to either the ∼100‐μm or the ∼200‐μm cavity length formed by the selective interdiffusion of the SL cladding layer. This embedded‐mirror laser structure may be useful in the development of optical integrated circuits by allowing semiconductor lasers to be monolithically integrated with other optical devices.

Evaluation of Fermi level pinning in low, midgap and high workfunction metal gate electrodes on ALD and MOCVD HfO/sub 2/ under high temperature exposure

The workfunction behavior and stability of several candidate metal gate electrodes on HfO/sub 2/ was carefully examined and correlated with processing parameters such as anneal temperatures and oxygen exposures. Transition metals and their nitrides, binary metal alloys and refractory metals were studied on MOCVD HfO/sub 2/ dielectrics of varying thicknesses. Binary low work function Mo-Ta alloys were also investigated on HfO/sub 2/.

Thermally stable AlGaN∕GaN heterostructure field-effect transistor with IrO2 gate electrode

A thermally stable AlGaN∕GaN heterostructure field-effect transistor (HFET) using an iridium oxide (IrO2) gate contact was demonstrated, compared with conventionally used Pt Schottky contact. The Schottky barrier height of the Pt contact significantly decreased from 0.71to0.52eV and the reverse leakage current at −20V increased by two orders of magnitude when the device was annealed at 450°C for 24h. This was due to the indiffusion of the Pt atoms into the AlGaN layer during the annealing. However, no electrical degradation of the contact was found in the IrO2 Schottky contact. This was due to the fact that the IrO2 suppressed the indiffusion of the contact metals into the AlGaN∕GaN heterostructure. As a result, the sheet-carrier concentration at which the two-dimensional electron gases are confined was not degraded at high temperature. It was found that the electrical properties of the HFET using the IrO2 gate contact are thermally stable and no distinct change of device performances was observed even af...

Physical and electrical analysis of RuxYy alloys for gate electrode applications

This letter describes RuxYy as a potential candidate for dual metal complementary metal–oxide–semiconductor applications. The characterization of RuY alloys indicate that the effective work function can be controlled from 3.9to5.0eV as the yttrium composition in the RuxYy is decreased in film for both PMOS and NMOS application. From x-ray photoelectron spectroscopy analysis, it was found that the Ru3d peaks do not change as the Y composition is changed, indicating the Ru–Y bonding is very weak or undetectable in RuxYy film. However, it was also found that Y reacts with the underlying SiO2 to form yttrium silicate. In addition, in situ x-ray diffraction results did not detect the presence of Ru–Y compound in the RuxYy films. Capacitance–voltage (C–V) characterization indicated that the oxide thickness decreased as the Y composition increased. We extracted the effective barrier height of RuxYy at the metal–oxide interface via Fowler–Nordheim current analysis. The barrier height decreases as the Y compositio...