H. C. Wen

Work function engineering using lanthanum oxide interfacial layers

A La2O3 capping scheme has been developed to obtain n-type band-edge metal gates on Hf-based gate dielectrics. The viability of the technique is demonstrated using multiple metal gates that normally show midgap work function when deposited directly on HfSiO. The technique involves depositing a thin interfacial of La2O3 on a Hf-based gate dielectric prior to metal gate deposition. This process preserves the excellent device characteristic of Hf-based dielectrics, but also allows the realization of band-edge metal gates. The effectiveness of the technique is demonstrated by fabricating fully functional transistor devices. A model is proposed to explain the effect of La2O3 capping on metal gate work function.

Metal gate work function engineering using AlNx interfacial layers

Metal gate work function enhancement using thin AlNx interfacial layers has been evaluated. It was found that band edge effective work functions (∼5.10eV) can be achieved on hafnium-based high dielectric constant (high-k) materials using the AlNx interfacial layer and TiSiN electrodes. It was also found that the effective work function enhancement by the AlNx interfacial layer increased when the concentration of SiO2 in the gate dielectric was increased. Thus, the enhancement was minimal for HfO2 and maximum for SiO2. A model is proposed to explain these results and a bonding analysis is presented to support the proposed model.

Effective work function modification of atomic-layer-deposited-TaN film by capping layer

We demonstrate that the metallic capping layer has a strong impact on the effective work function (EWF) of the metal gate. Specifically, the EWF of atomic-layer-deposited (ALD)-TaN could be increased from 4.5to4.8eV with chemical-vapor-deposited-TiN capping, which is sufficient amount of work function modification for silicon on insulator based devices. A strong interdiffusion of Ti atoms into the ALD-TaN film is observed and correlated well with the changes in the EWF change. Ti capping experiments confirm that the Ti interdiffusion can actually modify the EWF of Ti/ALD-TaN stack.

Comparison of effective work function extraction methods using capacitance and current measurement techniques

The effective work function (EWF) extracted on terraced oxide structures by capacitance-voltage-based techniques was compared with the work function calculated from the barrier height extracted by current-voltage measurements. The results show a reasonable correlation-within /spl plusmn/ 0.1 eV-in the EWF values for various metal gate electrodes, validating both techniques for EWF extraction.

Composition dependence of the work function of Ta1−xAlxNy metal gates

It is shown that the work function of Ta1−xAlxNy depends on the electrode and gate dielectric compositions. Specifically, the work function of Ta1−xAlxNy increased with SiO2 content in the gate dielectric, reaching as high as 5.0eV on SiO2; the work function was nearly 400mV smaller on HfO2. In addition, the work function decreased with increasing nitrogen content in the Ta1−xAlxNy metal gate. Increasing Al concentration increased the work function up to about 15% Al, but the work function decreased for higher Al concentrations. Chemical analysis shows that Al–O bonding at the interface correlates with the observed work function values.

The effect of metal thickness, overlayer and high-k surface treatment on the effective work function of metal electrode

We demonstrate that the effective work function (EWF) of atomic layer deposited (ALD) TiN electrodes is a function of the TiN film thickness and that the metal/dielectric interface and the bulk metal film influence this measured response. It is shown that anneal treatments and chemical processing of the underlying dielectric surface prior to electrode deposition may be exploited to modify the effective work function of metal electrodes. The effect of physical vapor deposited (PVD) and ALD metal overlayers on the effective work function of metal electrodes is also presented.

Thermal annealing effects on a representative high-k/metal film stack

A high-k/metal film stack in a conventional complementary metal oxide semiconductor (CMOS) flow is a key candidate in the semiconductor industry for replacing the existing poly-silicon gate and silicon dioxide (SiO2) gate dielectric to reduce poly depletion and gate leakage. During conventional CMOS integration, the high-k/metal film stack is exposed to a high thermal budget process. In this work, an atomic layer deposition (ALD)-based hafnium oxide (HfO2)/titanium nitride (TiN) film stack (representative of the high-k/metal film stack) was annealed at 1000 °C to determine any change in the physical and electrical properties, such as thickness, surface roughness, density, sheet resistance, refractive index, extinction coefficient, composition, C–V characteristics, work function and etch rate. Although there was no significant electrical impact, some significant physical changes have been observed, which impact the process of integrating high-k/metal film stacks, especially in dual metal gate CMOSs.

Gate First Metal-Aluminum-Nitride PMOS Electrodes for 32nm Low Standby Power Applications

The effective work function (EWF) of ternary metal-aluminum-nitride (M-Al-N, M=Ta, Ti, Mo, W) metal gate electrodes in high-k dielectric gate stacks has been investigated. With the addition of Al, the EWF can be tuned toward p-type (~5 eV) by 250 meV compared to the EWF of the binary metal nitride. Low threshold voltage (Vt) of ~ -0.35 V, an equivalent oxide thickness (EOT)~1.2 nm, and performance suitable for gate-first 32 nm low standby power applications are demonstrated.

Simplified manufacturable band edge metal gate solution for NMOS without a capping layer

We describe an NMOS band edge solution that uses a metal gate doped with Lanthanide elements to achieve work functions as low as 4.05eV. The capping interlayers used in previous works are no longer necessary, and metal gate implementation became much simpler. Using this electrode, low Vth value and high mobility suitable for high performance devices are achieved at a practical EOT of 8Aring

Evaluation and integration of metal gate electrodes for future generation dual metal CMOS

An overview of factors that contribute to the effective work function of metal gate electrodes are presented and reasons for disparity in reported values for effective work function of similar metals from different groups are discussed. Utilizing a standardized technique to accurately extract the effective work function of metal gates, the potential of amorphous metal gate materials and hafnium-based electrodes is presented. Also, the influence of metal gate materials and processing on the physical and electrical stability of the high-k metal gate stacks are discussed.