Growth and characterization of germanium expitaxial film on silicon (001) using reduced pressure chemical vapor deposition (RP-CVD)

• Main Author: Tan, Yew Heng.
• Other Authors: School of Electrical and Electronic Engineering
• Format: Theses and Dissertations
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/52548
• Institution: Nanyang Technological University

As the present Si Technology is reaching its physical and technological limits, the trend for the future would unlikely is based solely on Moore’s Law as the transistor geometrical scaling is coming to an end. As the Si substrate would still be the preferred by the semiconductor industries due to its technological importance, earlier operational costs invested and the challenges in wafer transportation, new device structures and materials have to be added onto the Si substrate in order for the CMOS technology to progress further onto the next level. Ge as a material has attracted much attention to augment Si. The properties of Ge have several advantages over Si, such as having smaller band gap which corresponds to ~1.55µm in wavelength, which make it a suitable for Ge photodetectors devices. Also, the higher hole and electron mobility of Ge over Si of 2.6 times 4.2 times respectively, making it an ideal candidates for MOSFET devices. But due to the 4.2% lattice mismatch between Ge and Si, epitaxial growth of Ge on Si remains a challenge since the growth mode is Stranski Krastanov resulting in poor quality Ge film of relatively high surface roughness and high threading dislocations that are not suitable for device applications. The first section of the thesis involves detailed studies on the developed three-step novel growth approach to grow Ge epitaxial films directly on Si substrate. The growth is basically sequences of low temperature growth, followed by low to high temperature growth via temperature ramp, high temperature growth and by thermal cycling in H2 environment with both end of annealing temperatures set at lower (TL) and upper (TH) limits and are higher than the growth temperature. The purpose of thermal cycling is to reduce both the surface roughness and threading dislocations resulted from the earlier Ge growth. The characteristic of the Ge films were analyzed using techniques such as the Ge thickness using scanning electron microscope (SEM). The quality of Ge films were determined based on low surface root mean square (RMS) roughness using atomic force microscope (AFM), and the low threading dislocation density of the film using iodine etch. The Ge/Si intermixing was studied using both transmission electron microscopy (TEM) and energy-dispersive x-ray spectroscopy (EDX). Both analyses indicated a thin intermixing zone along the Ge/Si interface. The study of Ge growth kinetics with the growth temperature ranging from 325 to 400 ºC and from 400 to 600 ºC indicates that the growths are in the surface and mass transport regimes respectively. The Ge/Si inter-diffusion was studied by using secondary ion mass spectrometry (SIMS) and the results obtained were compared with other findings. Ge/Si MOS capacitor was fabricated using the developed Ge/Si platforms and subsequent interfacial studies and electrical measurements obtained were used for material studies on Ge film. The effect of thermal cycling at different annealing temperatures on the Ge film quality was also studied. The Ge/Si platforms were also used for direct Ge-Ge wafer bondings where the Ge-Ge bond strength, contact angles of the Ge epitaxial film etc were investigated.