Andrew Smith

Univeristy of New Mexico

Materials Science and Engineering

Phase Transistions in Ni-Si System with Ti diffusion Boundary Layer

Introduction

There has been an increase of interest in the nickel-silicon system due to the metal-like electrical conductivity of NiSi2. This, in conjunction with a silicon substrate, could lead to future work applied to modifying Metal Semiconductor Field Emission Transistors (MESFETs). If the NiSi2 forms directly on the substrate after annealing, then we could remove the unwanted top layers and the disilicide would take the place of the metal in the MESFET. A new approach has been suggested to better control the phases that appear during annealing. A 100A layer of titanium has been deposited on the silicon substrate and then the 500A thick nickel layer is deposited on the titanium by sputtering. The titanium interlayer will hopefully control the rate at which the nickel diffuses into the silicon and a new way of growing the disilicide phase may be found.

Project Objectives

To identify the phases that appear after different temperatures and times. To gain an understanding about the effects of the titanium interlayer.

Approach

Annealing at different temperatures (300oC, 500oC, 650oC, 800oC) and different times (10min, 30min, 90min, 5hr, 15hr) in a tube furnace under ambient nitrogen. Using x-ray diffraction to analyze the samples and, in comparison with a database, identify different phase formations.

Findings

While the boundary layer was intended to prevent the formation of higher nickel compounds (e.g., Ni2Si, Ni3Si, Ni3Si2), it appears that some of these phases form after 500oC. Results at 650oC suggest similar behavior. Neither temperatures show formation of the disilicide. X-ray diffraction of samples annealed at 800oC are not conclusive in showing the formation of the disilicide, although it is expected to be present.

Tube furnace used in annealing samples.
XRD Scan at 500oC for 90 minutes.
Final Research Presentation