Ion-Dosage-Dependent Room-Temperature Hysteresis in MOS Structures with Thin Oxides

Two sets of metal-oxide-silicon (MOS) structures with oxide thicknesses of 115 and 350 A, respectively, were exposed to 16-keV Si ion beams after dry oxidation. Small-signal capacitance-voltage measurements at room temperature revealed a hysteresis effect in the ion exposed samples, whose magnitude and direction depended upon the ion dosage. No hysteresis could be detected in the control (unimplanted) samples. Mobile charge species in the oxide dominated the hysteresis effect for dosages below 10¹³/cm². Around this dosage, electron trapping/detrapping at the Si/Si0₂ interface began to take place. From the rate of the parallel voltage shifts of the C-V characteristics with respect to time, electron trapping and the mobile oxide charge transfer from the silicon/oxide to the aluminum/oxide interface were found to be faster than electron detrapping and the mobile oxide charge transfer from the oxide/A1 to the Si/Si0₂ interface. With increasing dosage, the magnitude of the hysteresis came down, and reversed its sign as the dosage approached 10¹³/cm². Experimental results suggest immobilization of the mobile oxide charge by lattice disorder induced by the energetic ions, and generation of oxide electron traps in the vicinity of the silicon/oxide interface after the lattice damage turns heavy.