UC San Diego

SiGe is a promising material for channel or contact applications because of its high hole and electron mobility and capacity for both compressive and tensile strain by integration with Ge-rich and Si-rich layers. The high hole mobility of SiGe can be used for p-channel FET as an alternative to Si. The larger lattice constant of SiGe compared to Si can provide tensile or compressive stress into the Si channel thereby enhancing the electron or hole mobility, respectively. Moreover, the multi-gate structure, which utilizes multiple crystalline planes such as (001) and (110) can be employed to overcome the challenges such as SCEs resulting from single-gate MOS devices.

In this work, cleaning, passivation, and functionalization of SiGe(001) and (110) surfaces were developed and studied using in-situ XPS, STM, and STS. XPS was utilized to understand the chemical compositions, oxidation states, and thickness of thin films on SiGe(001) and (110) surfaces. STM was used to study the topological structures and bonding configurations on the surfaces. STS was performed to probe the electronic structures such as pinning or unpinning effects by characterizing the density of states.

In order to avoid the oxygen and carbon contaminations after ex-situ native oxide removal, a combined wet and dry cleaning was performed. Wet in-situ HF clean method was successful to remove native oxides on SiGe(001) and contained no oxygen. Dry clean of atomic H via a thermal gas cracker method was found to be effective to remove the residual carbon contaminations. Sputter-cleaned SiGe(001) surface was terminated with only Ge dimers while SiGe (110) surface was terminated with both Si and Ge adtoms verified by STM. H2O2(g) was employed to passivate the SiGe surfaces and provide a high nucleation density for the metal ALD process confirmed by XPS. TMA was dosed onto the hydroxyl terminated SiGe surfaces to form a monolayer of Al2O3. TDMAT or TiCl4 was also exposed onto the hydroxyl terminated SiGe surfaces to form a monolayer of TiOx. Al atoms were bonded to one oxygen atom while Ti atoms were bonded to two oxygen atoms on the surfaces studied by STM and XPS. Furthermore, PDA resulted in the formation of selective Si-O-Al or Si-O-Ti on SiGe(001) and (110) surfaces.