A new MOS radiation-induced charge: negative fixed interface charge

Abstract

Absfruct-The irradiation behavior [up to -1.3 Mrad(SiO,)]of MOS capacitors (SO nm thick dry grown SO,, AI, or poly-SI gate) with or without postoxidation anneal (POA) in Ar at 1OOO"C has been studied by conventional capacitance-voltage ( C Y ) analysis and thermally stimulated current techniques. The most important finding is that all of the samples processed for radiation hardness, i.e., without POA, exhibited a charge compensation effect. The radiation-induced positive oxide charge is partially compensated by a negative j k e d interface charge which lies either outside the energy range accessible by CY and similar techniques or extends spatially away from the interface into the oxide without acquiring the characteristics of a "bulk" oxide charge. The existence of this fixed charge may jeopardize long-term device reliability as an interface charge is more prone to change than an oxide charge.

Effect of bias on thermally stimulated current (TSC) in irradiated MOS devices

“…Taken together, these studies indicate that, while perhaps not perfect, C-V estimates of the net oxide-trap charge and interface-trap charge provide a reliable barometer of MOS radiation response. Thus, it is difficult to understand how errors in C-V estimates of oxidetrap charge could be entirely responsible for the large discrepancies between TSC and C-V estimates of AQot noted by Shanfield and co-workers [3,4]. However, we confirm later that it can be crucial to the comparison that TSC counts the total number of holes that transport across the oxide, while C-V measurements count only the net oxide charge.…”

“…7 is the strong dependence of QTsC on the magnitude and direction of the TSC bias. One crucial factor that determines this dependence is how the trapped-hole space charge compares to the applied bias [4]. The potential due to the space charge is = 16 V for the irradiation conditions of Fig.…”

The contribution of border traps to the threshold voltage shift in pMOS dosimetric transistors

“…Such sites are consistent with the observation that significant densities of trapped electrons are not present in irradiated Si02 in the absence of trapped holes, but can be present when holes are trapped in SiOz. Convincing evidence of significant electron trapping in the vicinity of the Si/SiOz interface in many (especially rad-hard) oxides was recently given by thermally simulated current measurements [ 141, [33], [34]. Also, each of these traps is consistent with the reversibility of trapped-positive charge neutralization in MOS devices [17]- [23].…”

Effect of 30 Mev Li 3+ ion and 8 MeV electron irradiation on n-channel MOSFETs

“…Thus, ionization damage produced in the gate oxide and the field oxide is the cause in the degradation in the above properties of MOS transistors [5][6][7][8][9]. One of the most critical parameters of MOSFET in radiation environment is the threshold voltage (V TH ) [10,11]. The shift in V TH (DV TH ) can result in the loss of ability to turn the MOSFET on or off, lack of current drive and a leakage current.…”