Passivation of Ion-Beam-Induced Defects at and around the Si-SiO 2 Interface by Ion Beam Hydrogenation
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PASSIVATION OF ION-BEAM-INDUCED DEFECTS AT AND AROUND THE SiSiO2 INTERFACE BY ION BEAM HYDROGENATION S. KAR*, K. SRIKANTH**, AND S. ASHOK**
*Department
of
Electrical
Kanpur- 208016, India **Center for Electronic
Engineering,
Materials
Indian
& Processing,
Institute The
of
Technology,
Pennsylvania
State
University, University Park, PA 16802 ABSTRACT Electronic defects were introduced at and around the Si-SiO2 interface by exposing thermally-oxidized silicon samples to a 16 keV Si ion beam in an ion implanter. The oxide thickness was 350 A. Following Si selfimplantation, hydrogenation was carried out at room temperature by a 400 eV hydrogen ion beam from a Kaufman source. Experimental results obtained from the admittance-voltage-frequency measurements of the metal-oxide-silicon structures indicated significant passivation of the ion-beam-induced defects.
INTRODUCTION Metal-oxide-silicon (MOS) devices pervade circuits with ultra large scale integration. With increasing miniaturization, the fabrication processes are characterized by an ever-increasing exposure of devices to energetic ions and other particles and attendant x-rays. As a result, extensive damage is caused to the devices during processing. This processinduced damage manifests itself as electron/hole traps, which severely alter device characteristics and performance. The Si-SiO2 interface and the gate oxide in MOS devices are among the elements, that are most sensitive to ion beam and radiation damage, and thermal annealing has been a standard procedure for passivation or removal of ion-beam-induced traps. However, as the scale of circuit integration goes up, the processing temperature needs to be brought down to avoid or reduce several undesirable effects of high temperature. Hence, the need arises for a low temperature passivation technique, that can bring atomic hydrogen into the device to neutralize the electron/hole traps. The present investigation was undertaken to examine how effective ion beam hydrogenation is for room-temperature passivation of ionbeam-induced defects in MOS structures.
EXPERIMENTAL DETAILS To fabricate the samples, p-type silicon wafers were oxidized in dry 02 at 950 °C to reach an oxide thickness of 350 A. Subsequently, the oxidized silicon wafers were exposed to 16 keV Si ions in a Varian 350D ion implanter at 300 K, such that the peak of the total target displacements was located in the oxide bulk, cf. Table I. Si ions were choen to deemyhasize the chemical effects. The ion dosage was varied from 102/cm2 to l10 /cm2. Following Si ion implantation, ion beam hydrogenation was carried out at 300 K, using a Kaufmann source. A low ion energy of 400 eV was chosen to reduce the hydrogen- ion- induced damage, cf. Table I. For all the hydrogenated 3 2 samples, the ion current density was 1.2x10 A/cm , and the hydrogenation time1 was I min, which means that the incident hydrogen ion dosage was about 2xl0 /cm . Following hydrogenation, Al front (1.0 mm dia dots) and Au back contacts were evaporated in an oil-free, ion-pump
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