The electrical properties and diffusivity of Hf in single crystal Si were studied (figure 8). Several deep-level defects were found for Hf in both the upper and lower half of the Si band gap, and their parameters were measured. Energy levels, concentrations and capture cross-sections were determined for Hf defects. The deep-level transient spectra depended upon the cooling rate. Analysis of electrical properties yielded a dominant deep level defect at EC -0.27eV, which showed field enhanced emission due to the Poole–Frenkel effect, confirming its donor nature. This agreed with results obtained using CV and TSCAP. In the lower half of the band-gap, a defect level at EV+0.24eV was found to have a capture barrier of 0.04eV. 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 168h, allowed the estimation of the diffusivity of Hf as being 1.7 x 10-15cm2/s at 1250C: the spreading of implanted profiles at lower temperatures was too small. Analysis of Hf depth profiles in the sputtered and annealed samples revealed that Hf appears to have a fast and slow component to its diffusivity whose migration energy was determined to be 3.5 and 4.1eV, respectively. The fast and slow component were ascribed to interstitial and substitutional Hf with an energy level of EC-0.27eV and EV +0.43eV, 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, were included.

Electrical Properties and Diffusion Behavior of Hafnium in Single Crystal Silicon. R.Sachdeva, A.A.Istratov, P.N.K.Deenapanray, E.R.Weber: Applied Physics A, 2006, 84[4], 351-67

Figure 8

Diffusivity of Hf in Si

(Upper line: fast component, lower line: slow component)