Study on individual traps in metal-oxide-semiconductor field-effect transistors by means of thermally stimulated threshold voltage shift

A novel method, thermally stimulated threshold voltage shift (TSTVS), was introduced to investigate individual trap properties in the gate SiO2 oxide film of submicron p-type metal-oxide-semiconductor field-effect transistors (pMOSFETs). TSTVS measures temperature-dependent threshold voltage shift (a dagger V (th)(T)). First, electrical stresses are imposed on a pMOSFET to fill traps with carriers, resulting in a dagger V (th). Second, the sample temperature is raised at a constant rate. The captured carriers are thermally emitted and a dagger V (th) decreases. The trap properties can be revealed from a dagger V (th)(T). Although TSTVS is similar to the conventional thermally stimulated current (TSC) method, there are several advantages, e.g., higher sensitivity and discrimination ability of carrier polarity. TSTVS was applied to a pMOSFET subjected to electrical stress. The TSTVS signal exhibited several abrupt steps corresponding to individual carrier detrappings, meaning that TSTVS could detect even a single trap. In addition, the carrier polarity was determined by the sign of the steps (upsteps or downsteps). We also revealed the trap energy level through repetitive TSTVS measurements. The presence of two traps in the pMOSFET, i.e., hole and amphoteric traps, was confirmed from these features. We also compared the results with the conventional TSC and found that they could be interpreted by using the proposed atomic structures of traps.