Electrical characterization of silicide and process induced defects in silicon

Abstract

Metal deposition on Si has effects that may be detrimental to device operation such as diffusion, Fermi level pinning and silicide formation. Silicide formation is dependent on type of metal and temperature at which particular silicide is formed. Different defects have been observed during metallisation of Si to form electrical contact. The electrical characterisation of platinum silicides and palladium silicides were investigated using current-voltage and capacitance voltage measurements. Defects introduced were characterised by deep level transient spectroscopy (DLTS) and Laplace DLTS (L-DLTS) while silicidation process was monitored by Rutherford backscattering spectroscopy (RBS). The Rutherford utilities manipulation program (RUMP) and Genplot program were used to analyse the data from RBS. The electron beam deposition process was used to fabricate Pt Schottky contacts onto n-Si (111). Subsequently these contacts were annealed at temperatures varying from 50°C to 600°C for ten minutes at each temperature. The forward I-V characteristics show that the diodes were stable at lower voltages and suffer series resistance effects at voltages higher than 0.5 V. The reverse I-V curves shows increasing leakage current with increasing annealing temperature. At lower annealing temperatures, the reverse leakage current is constant at about 10-9 A. The ideality factor increased from 1.02 to 2.61 while the barrier height decreased from 0.80 to 0.70 eV as the annealing temperature increased. DLTS revealed that electron beam deposition introduced defects which were identified as the E-centre (VP centre), the A-centre (VO centre), the interstitial carbon (Ci) and the interstitial carbon-substitutional carbon (CiCs) pair. Isochronal annealing at 10 minutes intervals revealed that the E-centre vanishes between 125 and 175°C annealing while the concentration of the A-centre increased in this range. The A-centre annealed out above 350°C and after 400°C, all the electron beam induced defects were all removed. Palladium Schottky contacts were fabricated on epitaxially grown n-Si (111) by resistive deposition. Current-voltage (I-V), capacitance- voltage (C-V) measurement techniques were used to characterise the as deposited and annealed Pd/n-Si Schottky contacts. These contacts were annealed at temperatures ranging from 200°C to 700°C, in steps of 100°C for ten minutes each temperature. The ideality factor increased from 1.2 for as deposited to 1.6 after annealing at 700°C while the Schottky barrier height (SBH) decreased from 0.69 to 0.64 eV as the annealing temperature increased. In this study, silicides seem to form at 300°C where the ideality factor is at its lowest value and SBH begins to lower. The Rutherford backscattering Spectroscopy (RBS) technique was used to verify temperatures at which Pd2Si was formed. The results obtained suggest that the Pd2Si silicide phase begins to form at 200°C and at 300°C it is completely formed. The defects introduced in epitaxially grown p-type silicon (Si) during electron beam exposure were electrically characterised using deep level transient spectroscopy (DLTS) and high resolution Laplace-DLTS. In this process, Si samples were first exposed to the conditions of electron beam deposition (EBD) without metal deposition. This is called electron beam exposure (EBE). After 50 minutes of EBE, aluminium (Al) and nickel (Ni) Schottky contacts were fabricated using the resistive deposition method. For the Al contacts, the defect level H(0.33) was identified as the interstitial carbon (????) related defect. The defect level observed using the Ni contacts had an activation energy of H(0.55). This defect has an activation energy similar to that of the I-defect. DLTS depth profiling revealed that H(0.33) and H(0.55) could be detected up to a depth of 1.2??m and 0.8??m respectively. We found that exposing the samples to EBD conditions without metal deposition introduced a different group of defects which are not introduced by the EBD method.