Electrical properties and diffusion behavior of hafnium in single crystal silicon

Electrical properties and diffusivity of Hf in single crystal Si have been studied. Several deep level defects were found for Hf in both the upper and lower half of the silicon band gap, and their parameters were measured. Energy levels, concentrations, and capture cross sections were determined for all Hf defects. The DLTS spectra depend on the cooling rate. Analysis of electrical properties yielded a dominant deep level defect at E_C -0.27 eV, which showed field enhanced emission due to Poole–Frenkel effect, confirming its donor nature. This agreed with results obtained using CV and TSCAP. In the lower half of the bandgap, a defect level at E_V +0.24 eV was found to have a capture barrier of 0.04 eV. Diffusivity of Hf was studied using two methods for Hf incorporation in Si – ion implantation and sputtering. Analysis of broadening of the Hf profile in implanted samples, which were annealed for 168 h, allowed us to estimate the diffusivity of Hf as 1.7×10^-15 cm²/s at 1250 °C: the spreading of implanted profiles at lower temperatures was too small. Analysis of Hf depth profiles in the sputtered and annealed samples reveals that Hf appears to have a fast and slow component to its diffusivity whose migration energy was determined to be 3.5±0.3 eV and 4.1±0.3 eV respectively. The fast and slow component are ascribed to interstitial and substitutional Hf with an energy level of E_C -0.27 eV and E_V +0.43 eV respectively. The mechanism for the fast component seems to indicate a direct interstitial diffusion mechanism whereas the diffusion of the substitutional Hf seems most consistent with the concerted exchange diffusion mechanism. In addition, estimates of solubility for both, interstitial and substitutional Hf, are included. PACS 61.72.Tt; 66.30.Jt; 71.55.Cn