DEFECT ACCUMULATION DURING ROOM-TEMPERATURE N+ IRRADIATION OF SILICON

The accumulation of disorder in Si crystals implanted with 40 keV N+ i ons at room temperature to fluences between 1X10(14) ions cm(-2) and 2 X10(15) ions cm(-2) and with ion fluxes between 5X10(11) ions cm(-2)s( -1) and 5X10(13) ions cm(-2)s(-1), was measured using low angle Ruther ford Backscattering Channelling techniques. It was found that fraction al disorder-fluence functions were sigmoidal and four disordering regi mes were identified. At very low disorder fractions the disorder is io n flux independent but at slightly higher disorder fractions the disor dering rate is a function of ion flux. For still higher disorder fract ions the flux density dependence of disordering rate is again absent a nd disorder finally saturates at complete layer amorphisation. A set o f models involving intra-cascade or bombardment induced defect - nativ e defect interaction processes, converting to intercascade process and finally enhanced direct impact amorphisation of defected crystal is d eveloped and shown to explain the observed results.