The move to implement metal oxide based gate dielectrics in a metal-oxide-semiconductor field effect transistor is considered one of the most dramatic advances in materials science since the invention of silicon based transistors. Metal oxides are superior to SiO 2 in terms of their higher dielectric constants that enable the required continuous down-scaling of the electrical thickness of the dielectric layer while providing a physically thicker layer to suppress the quantum mechanical tunneling through the dielectric layer. Over the last decade, hafnium based materials have emerged as the designated dielectrics for future generation of nano-electronics with a gate length less than 45 nm, though there exists no consensus on the exact composition of these materials, as evolving device architectures dictate different considerations when optimizing a gate dielectric material. In addition, the implementation of a non-silicon based gate dielectric means a paradigm shift from diffusion based thermal processes to atomic layer deposition processes. In this report, we review how HfO 2 emerges from all likely candidates to become the new gold standard in the microelectronics industry, its different phases, reported electrical properties, and materials processing techniques. Then we use specific examples to discuss the evolution in designing hafnium based materials, from binary to complex oxides and to non-oxide forms as gate dielectric, metal gates and diffusion barriers. To address the impact of these hafnium based materials, their interfaces with silicon as well as a variety of semiconductors are discussed. Finally, the integration issues are highlighted, including carrier scattering, interface state passivation, phonon engineering, and nano-scale patterning, which are essential to realize future generations of devices using hafnium-based high- k materials.

Development of hafnium based high-k materials—A review

Si–Ge–Sn alloys: From growth to applications

This paper reviews progress and current critical issues with respect to the integration of germanium (Ge) surface-channel MOSFET devices as well as strained-Ge buried-channel MOSFET structures. The device design and scalability of strained-Ge buried-channel MOSFETs are discussed on the basis of our recent results. CMOS-compatible integration approaches of Ge channel devices are presented.

Germanium channel MOSFETs: opportunities and challenges

Due to its high intrinsic mobility, germanium (Ge) is a promising candidate as a channel material (offering a mobility gain of approximately??2 for electrons and??4 for holes when compared to conventional Si channels) However, many issues still need to be addressed before Ge can be implemented in high-performance field-effect-transistor (FET) devices One of the key issues is to provide a high-quality interfacial layer, which does not lead to substantial drive current degradation in both low equivalent oxide thickness and short channel regime In recent years, a wide range of materials and processes have been investigated to obtain proper interfacial properties, including different methods for Ge surface passivation, various high-k dielectrics and metal gate materials and deposition methods, and different post-deposition annealing treatments It is observed that each process step can significantly affect the overall metal?oxide?semiconductor (MOS)-FET device performance In this review, we describe and compare combinations of the most commonly used Ge surface passivation methods (eg epi-Si passivation, surface oxidation and/or nitridation, and S-passivation) with various high-k dielectrics In particular, plasma-based processes for surface passivation in combination with plasma-enhanced atomic layer deposition for high-k depositions are shown to result in high-quality MOS structures To further improve properties, the gate stack can be annealed after deposition The effects of annealing temperature and ambient on the electrical properties of the MOS structure are also discussed

https://iopscience.iop.org/article/10.1088/0268-1242/27/7/074012/pdf

Germanium surface passivation and atomic layer deposition of high-k dielectrics—a tutorial review on Ge-based MOS capacitors

The performance of strained silicon (Si) as the channel material for today's metal-oxide-semiconductor field-effect transistors may be reaching a plateau. New channel materials with high carrier mobility are being investigated as alternatives and have the potential to unlock an era of ultra-low-power and high-speed microelectronic devices. Chief among these new materials is germanium (Ge). This work reviews the two major remaining challenges that Ge based devices must overcome if they are to replace Si as the channel material, namely, heterogeneous integration of Ge on Si substrates, and developing a suitable gate stack. Next, Ge is compared to compound III-V materials in terms of p-channel device performance to review how it became the first choice for PMOS devices. Different Ge device architectures, including surface channel and quantum well configurations, are reviewed. Finally, state-of-the-art Ge device results and future prospects are also discussed.

/pdf/germanium-based-field-effect-transistors-challenges-and-515c01v580.pdf

Germanium Based Field-Effect Transistors: Challenges and Opportunities

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.

/pdf/effect-of-surface-nh3-anneal-on-the-physical-and-electrical-1tgjfb0alf.pdf

Chia Chin Yeo

Papers

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