Optimization of materials for microelectronics industry by in-situ coupling of electrical and structural characterization techniques

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Perustieteiden korkeakoulu | Master's thesis
Advanced Materials for Innovation and Sustainability
Degree programme
Master’s Programme in Advanced Materials for Innovation and Sustainability
43 + 5
In microelectronics industry, one way to improve MOSFET performances is to reduce the gate “propagation” delay, i.e. the time between input and output signal in a transistor, by reducing the contact resistance between the Source/Gate/Drain and the metallic layer. These contacts are obtained by solid-state reaction of a metallic film with the Si substrate. The thermodynamics involved in these reactions are complex, especially for thin films. Thus, for a better understanding of these reactions driving forces, it is important to have a tool that enables the correlation of structural and electrical (here sheet resistance) properties during the formation of these contacts. The aim of this study is to build a setup that allows the optimization of materials for microelectronics industry by in-situ coupling of electrical (4 points probe method for sheet resistance measurement) and structural (XRD/XRR/Raman spectroscopy) characterization techniques and then to apply and validate the performances, capabilities, limitations of our setup with different materials… The setup consists on a heating stage that plays the role of a sample holder in a diffractometer/spectrometer while 4 tungsten based points’ probes are positioned on the sample surface and measures its sheet resistance. Both the Temperature Control Unit (TCU) and the SourceMeter are remotely controlled using a python script that reads and writes the TCU temperature and Ramp Rate (RR), and sources current and senses voltage using the SourceMeter. Various materials that are used in STMicroelectronics high technology chips were characterized using this setup e.g. Ni(Pt), Vanadium, ITO… with a high focus on silicides. This study aims to correlate the evolution of materials electrical and structural properties driven by physical mechanisms investigated in literature review. First, Ni(Pt) is studied. The in-situ coupling of XRD and sheet resistance measurement showed that the sheet resistance suddenly decreases at ~265°C. It corresponds to the Ni to NiSi phase transition temperature. A Raman spectroscopy analysis performed on a sample that was annealed at this temperature showed also the formation of the Ni2Si phase, and an XRR analysis showed that this phase possibly nucleates as an interlayer in the Ni/Si interface instead of clusters inside the Ni matrix. The Kissinger method, that estimates the activation energy of the Ni to NiSi phase transition using constant ramp rate annealing, was, for the first time, enabled in our laboratory. Measurements were performed in air atmosphere because a TiN capping layer was deposited to prevent thermal oxidation issues. The effect of alloying, i.e. metal incorporation in small quantities in the nickel layer, e.g. 10%at Pt, on sheet resistance evolution were investigated. It was shown, using an isothermal annealing, slightly above the phase transition temperature, that the amount of Pt in the Ni remaining layer increases. Second, Vanadium thin film was also investigated. This material is very sensitive to oxidation. We showed that even with a TiN capping layer, undesired oxidation issues were observed. To check that point, we tried on another sheet resistance measurement setup (not compatible with XRD or Raman spectroscopy) but working in vacuum/inert gas heating chamber. We can conclude from this study that a specific setup/furnace should be used for further studies, e.g. the effect of various inert gas annealing on microstructure.
Halme, Janne
Thesis advisor
Gergaud, Patrice
silicides, MOSFET, electrical characterization, structural characterization