Shreyas Kher

Deposition and characterization of HfO2 high k dielectric films

As the scaling of complementary metal-oxide-semiconductor (CMOS) transistors proceeds, the thickness of the SiO 2 gate dielectrics shrinks rapidly and results in higher gate leakage currents. High k dielectric materials are acknowledged to be the possible solutions to this challenge, as their higher k values (e.g., 15-50) raise the physical thickness of the dielectrics that provide similar equivalent thickness of a thinner SiO 2 film. In order for the high k materials to be applicable in CMOS devices, there should exist deposition technologies that can deposit highly uniform films over Si wafers with diameters as large as 200 mm. This report discusses the deposition process and the correlation between the growth conditions, structural and dielectric properties of HfO 2 , which is one of the most promising high k dielectric materials. Judging from the thickness uniformity, surface roughness, k value, and interfacial density of state of the HfO 2 films, the metalorganic chemical vapor deposition technique was identified to be suitable for growing HfO 2 films targeted at applications as CMOS gate dielectrics.

Trends in gate stack engineering

MOSFET scaling requires an increase in the dielectric capacitance and hence a decrease in the dielectric electrical thickness. In this paper, we review the scaling trends for the gate dielectric and the gate electrode as the industry faces the challenges of introducing new materials into production.

Sub-300 Å (Bax,Sr1-x)TiO3 films by metal organic chemical vapor deposition: Nanostructure, step coverage, and dielectric properties

This is a preliminary report on the nanostructure and its evolution, step-coverage, and dielectric properties of sub-300 A (Bax,Sr1-x)TiO3 films. The (001)-oriented polycrystalline films were deposited at 50–70 A/min by metal-organic chemical vapor deposition (MOCVD) on (111) Pt-passivated Si substrates of 8-inch diameter. From the detailed nonstructural characterization of (Ba0.64,Sr0.36)TiO3 films, the orientation, cation stoichiometry, and an alternative but plausible mechanism of growth and the origin of roughness are forwarded. Additionally, the step-coverage in 2:1 to 5:1 aspect-ratio trenches, coupled with the frequency/voltage dependence of the dielectric properties of (Bax,Sr1-x)TiO3 films are reported. A 275 A (Ba0.64,Sr0.36)TiO3 film exhibited a dispersionless dielectric permittivity and loss tangent of 260 and 0.003, respectively, and the permittivity (er=340) of a 300 A (Ba0.5,Sr0.5)TiO3 film reduced by 53% at a dc-bias of 3 V.

Non-contact thickness and electrical characterization of high-k dielectrics

We have made non-contact thickness and electrical measurements on BST/Pt samples. We believe this is the first time that the BST thickness on top of a Pt electrode has been measured with high confidence. The thickness measurements were made using picosecond ultrasonics and could be correlated to TEM at certain points. In contrast to this destructive method, however, picosecond ultrasonics allowed fast measurements, determined film uniformity through 49-point contour maps, and simultaneously calculated the Pt thickness. The electrical measurements were made using a capacitance probe with COCOS-based (corona oxide characterization of semiconductors) technology. From the electrical measurements we were able to calculate the dielectric constant.