Microbumps and TSVs are the interconnects in 3D technology to electrically connect chips with different designs, technologies and functions to improve the functionality of the final product. This technology will enable Moore’s law to continue beside scaling transistor gate length. Cu is the conventional metal which is being used in semiconductor industry for interconnection within and between the silicon chips. With scaling size of interconnects, to have a better electromigration life and less material consumption, considering other metals such as cobalt, nickel, molybdenum, platinum, palladium, rhodium and ruthenium are necessary. Properties such as melting point, electromigration life, thermal expansion, corrosion resistance and better chemical resistance to the wet processing steps and lower electrical resistance are some features. More specifically in 3D technology features such as oxidation rate, solderability or wettability, IMC (intermetallic compound) phases, possibility for electroplating, grain size, grain orientation and resistance for submicron TSVs and bumps, TSV pumping after annealing, barrier/seed options, magnetic properties (for high Q passive inductor and shielding chip from stray magnetic fields) and capping options to have better bonding to Sn are very important to investigate. IMEC partners will be interested in this topic as well since it deals with future technology within 3-5 years from now.
The goal of this PhD thesis is to study those parameters for different metals and investigate the possibility of employing those metals in 3D technology as TSV material and microbump UBM (under bump metallization). In this study, different analyses techniques such as XPS, Auger, contact angle, TEM, AFM, EBSD and electrical measurement will be used to study the features of different metals for 3D applications and possible passivation options such as ELD layers and organic mono layers. Phase field and molecular dynamic simulations will be needed together with professors from KU Leuven to understand IMC evolutions for different metals more specifically when size of bumps are shrinking with pitch scaling.
Required background: material science, electrical engineering, chemistry
Type of work: 10% literature, 20% technology study, 40% experimental, 20% simulation, 10% publications
Supervisor: Ingrid De Wolf
Daily advisor: Jaber Derakhshandeh
The reference code for this PhD position is STS1712-13. Mention this reference code on your application form.