Date of Award
Master of Applied Science (MASc)
Electrical and Computer Engineering
Sequentially plasma activated bonding (SPAB) of silicon wafers has been investigated to facilitate chemical free, room temperature and spontaneous bonding required for integration of nanostructure on the wafer scale. The SPAB consists of surface activation using reactive ion etching (RIE) plasma followed by microwave (MW) radicals. The drop shape analysis and atomic force microscopy (AFM) results show that O2 RIE plasma is the most efficient in removing surface contaminations while keeping smooth surfaces. On the other hand, MW N2 radicals offer highly reactive, smooth and hydrophilic surfaces. These highly reactive, smooth and hydrophilic surfaces allow strong and spontaneous bonding of silicon/silicon at room temperature. Electrical characteristics show that the current transportation across the nano-bonded interface is dependent on plasma parameters. The infrared images show that plasma induced voids' nucleation at the bonded interface is dominated by O2 RIE power over O2 RIE activation time. The bonding strength achieved at room temperature in SPAB is about 30 times higher than that in hydrophilic bonding.
In order to explore the reliability of SPAB at high temperature, the bonded wafers are annealed from 200 to 900°C. The thermal induced voids' nucleation occurred preferentially at the plasma induced defect sites. The nucleation of void density is quantitatively determined and explained using high resolution transmission electron microscopy (HRTEM) observations. The electron energy loss spectroscopy results reveal the existence of silicon dioxide at the bonded interface. The reduction in bonding strength after annealing at high temperature is correlated to the increase in void density. The plasma induced defect sites such as nanopores and craters are identified using an AFM. The porous surface allows easy removal of interfacial water and spontaneous covalent bonding at room temperature. The HRTEM results confirm nanometer scale bonding which is needed for the integration of nanostructures. Based on the results, a bonding mechanism of SPAB is presented.
In order to expand the applicability of SPAB for diverse materials, a novel hybrid plasma bonding (HPB) process is developed to achieve void-free and strong silicon/glass and germanium/glass bonding at low temperature. The HPB combines sequential plasma activation with anodic bonding process. Void-free interface with high bonding strength is observed both for silicon/glass and germanium/glass at 200oe. The bonding strength of the silicon/glass and germanium/glass in the HPB at 2000e is 30 MPa and 9.1 MPa, respectively. The improved characteristic behavior of the interface in the HPB is attributed to higher hydrophilicity and smooth surfaces of silicon, glass and germanium after sequential plasma activation and high electrostatic force associated with anodic bonding. Based on the results, a bonding mechanism of HPB is discussed.
The chemical free strong bonding of silicon/silicon in SP AB at room temperature and void-free strong bonding of silicon/glass and germanium/glass in HPB at low temperature can be applied in spontaneous integration of nanostructures on the wafer scale.
Kibria, Golam, "Sequentially Plasma Activated Bonding for Wafer Scale Nano-Integration" (2010). Open Access Dissertations and Theses. Paper 4203.
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