Semiconductors

Semiconductors in Microelectronics

Faculty
G. Xia


General Group Overview

To further advance the performance of microelectronic devices such as CMOS and HBTs, group IV elements and alloys such as germanium (Ge), SiGe and SiGe:C are integrated into silicon platforms to boost performance by stress, bandgap and defect engineering. The integration of these new materials, especially with the increasing Ge, C fractions and the resulting stresses, introduces new process phenomena and fabrication challenges such as dopant diffusion and segregation, Si-Ge interdiffusion, stress-diffusion interaction etc. We investigate these new phenomena experimentally, catch them in mathematical models and implement in TCAD simulation tools to assist industry in structure and fabrication design of these devices.

Ge-on-Si lasers

It has been a long-term dream for the semiconductor industry to integrate photonic devices (i.e., lasers, modulators, photodetectors, waveguides etc.) with electronic devices on a silicon platform to take advantage of the low-cost and mature silicon technology. Major applications of this integration include on-chip optical interconnects for ICs, which alleviates the bottlenecks currently encountered in metal interconnects, and lasers for telecommunications. The last missing element in optical interconnects is a laser on the Si platform. Ge-on-Si lasers have emerged to be a very promising candidate. We investigate options to optimize Ge laser performance towards an efficient Ge laser.

2D semiconductors

2D semiconductors are suitable for thin, quasi-transparent and flexible electronics and photonics. Black phosphorus was successfully isolated in 2013 and was shown to have unique properties such as direct and tunable bandgap from 0.3 to 2 eV, suitable for applications in thermal imaging, photovoltaics and telecomm. We investigate the fabrication and properties of single to few-layer black phosphorus and MoS2.

3D integration of ICs

Through-silicon-via (TSV) is a key element for 3-D integration in providing vertical interconnects for chip-stacking structures. Thermal-mechanical stress originating from the thermal expansion coefficient mismatch of Cu and Si can cause uniformity and reliability issues. We study the stress distribution around Cu-filled and carbon-nanotubes-filled TSVs, its influencing factors and the impact on carrier mobility and keep-out zone (KOZ) for logic devices near the TSVs, which is important for the design and reliability of 3D integrated circuits.

Raman spectroscopy

Micro-Raman spectroscopy is a powerful tool in studying chemical concentration, stress, crystallinity, chemical bonding, and temperature. We have the capability of doing in-situ Raman during thermal treatment. The material systems we are interested in include SiGe:C alloys, Ge nanowires, InGaAs/GaAs, carbon nanotubes, graphene, nanocrystalline Si, black phosphorus, FinFETs, Ti oxide and soils.

Projects

• Vertical doping profile control for PNP SiGe HBTs
• Stress engineering for Ge-on-Si lasers
• Fabrication of high tensile-strained stand-alone Ge for Ge-on-Si lasers
• Doping effects on Si-Ge interdiffusion
• Strain impact on black phosphorus

Experimental Facilities

• High resolution confocal micro-Raman LabRam HR by Horiba Scientific
• AMPEL nanofabrication facility

Computational facilities and specialized software packages

• TSUPREM-4, Medici, Sentaurus Process by Synopsys
• LASTIP, CSUPREM, APSYS by Crosslight Software
• INTERCONNECTS by Lumerical Solutions