Observation of ion bombardment damage in silicon

Abstract

Thin films of single crystals of both n-type and p-type silicon contain disordered zones ∼ 50 Å in diameter, discernible in the electron microscope after bombardment with ∼ 10¹³ Ne⁺ ions cm⁻². As the dose increases these zones become more numerous until eventually (≳ 10¹⁴ ions cm⁻²) they overlap, creating a continuous surface layer which electron diffraction shows to be amorphous silicon. The individual zones disappear on annealing between 400 and 500°C, and at ∼630°C the amorphous layer recrystallizes epitaxially upon the underlying silicon, leaving an array of dislocation loops and dipoles. The bombarded regions exhibit various hues until eventually when they become completely amorphous they appear ‘milky’ due to the Rayleigh scattering of light. This appearance has been used as a convenient method to study the ion dose needed to form amorphous silicon as a function of the temperature of the silicon during bombardment.