Oxygen Ion Defect Generation in Insulated‐Gate Field‐Effect Transistors and X‐Radiation Susceptibility of Ion‐Damaged Gate Insulators

Abstract

In the present paper, the residual electrical effects, before and after postmetal annealing, on insulated gate field‐effect transistor (IGFET) device characteristics due to implantation of oxygen at a dose of 1015 cm−2 into 36‐nm‐thick gate insulators following their growth have been studied. The primary defects detected via optically assisted injection of electrons into the gate insulators of the damaged IGFETs were neutral electron traps (NETs), present in concentrations as high as 1.4×1011 cm−2 . Secondary types of defects found appear to be fixed negative charge (FNC), approximately 0.7×1011 cm−2 in the worst case, and a smaller amount of fixed positive charge (FPC), less than 1010 cm−2 in the worst case. It is not surprising (unlike the case for silicon implantation under similar conditions) that a smaller number of defects is generated by oxygen implanted into gate insulators following its growth, since the device is subjected to a series of high‐temperature processing steps after the implantation. These high‐temperature processes appear to result in the redistribution and/or volatilization of most of the excess oxygen atoms; volatilization of silicon, on the other hand, is much less likely. Similar to what was observed with silicon‐implanted gate insulators, it was found that these defects could not be removed by employing conventional postmetal annealing (PMA) conditions in forming gas (10% H2 , 90% N2 ) at 400°C for 30 min. The defects created by ion implantation appear to be quite different from those created by x‐ray or electron irradiation, where large quantities of FPCs and NETs are generated, which can be annealed in PMA cycles. It is found that oxygen‐implanted gate insulators appear to be much more susceptible to x‐ray radiation than unimplanted devices. The residual defects in oxygen‐implanted devices, following x‐ray radiation and subsequent PMA annealing for up to 120 min, were found to be greater than that in unimplanted devices. The results with silicon ions earlier, and oxygen ions now, indicate that if the insulator is damaged by such species during processing, as might occur due to knock‐on from the gate electrode during source/drain formation, unannealable defects will form which would also tend to make the device structure more susceptible to radiation damage in a hostile environment, or to large hot electron drift, accompanying conventional use.

On the charge storage and decay mechanism in silicon dioxide electrets

“…It should be mentioned that Qot is still a collection of traps of different cause and nature. Results of detailed investigations, described in the literature, however are, rather confusing: it is on the one hand reported, that annealing in 0 2 removes electron traps, which suggests oxygen deficiency as the cause of the trap centers [12], whereas on the other hand it is reported, that NET is generated by oxygen ion implantation [13]. The number of NET/cm2 is in that case, however, too small to explain the electret behavior of Si02.…”