In-situ ion beam irradiation: X-ray scattering & diffraction experiments

Ion beam techniques are widely used in semiconductor industry e.g. for introducing dopant atoms into materials. Ion implantation is characterized by fast dynamic processes associated with the evolution of collision cascades resulting in formation of defects such as vacancies, interstitials, etc. As a consequence, normally a strained layer that expands in the direction normal to the substrate surface is formed. This is due to the point that the bulk material prevents any lateral macroscopic expansion and as a result the thin irradiated layer is subjected to an in-plane biaxial compressive stress. Ion irradiation is a very fast process and it is almost impossible to monitor it in-situ with the present x-ray sources. However, the accumulation of damage and the diffusion of defects in implanted species are much slower processes and can be studied in-situ.

An in-situ ion beam implantation experiment was set up at ROBL/MRH at ESRF. For this purpose an ion gas source with a maximal acceleration voltage of 5keV was mounted on a sputtering chamber. To realize sufficient volume damage the ion energy was further raised to 20keV by increasing the electrostatic potential of the irradiated sample using an additional power supply. Samples were irradiated at room temperature using He+.

Measuring reciprocal space maps the different behavior of the strain evolution from the accumulation of defects, over the formation of a strained layer to a complete (X-ray) amorphous layer of single crystal substrates of Si and Al2O3 was studied.