The two dimensional (2D) diffusion of self-interstitials (I) in crystalline Si, both at room temperature and at 800 C, has been studied by quantitative SCM measurements. The 2D I emission from a I source laterally confined down to sub-micron dimensions, obtained by lowœenergy implantation through a patterned oxide mask, has been observed. At room temperature, I diffusion was monitored by measuring the electrical deactivation of B corresponding to the diffusing interstitial tail and it was demonstrated that this deactivation is due to compensating levels introduced by defects in the Si bandgap. At 800 C I diffusion was monitored by measuring the transient enhanced diffusion of B spikes due to interstitial supersaturation produced during the annealing. In both cases, a dependence of the I depth-penetration on the original source size has been shown for mesoscopic window openings (from 0.5 to 3 µm).