Analysis and classification of degradation phenomena in polycrystalline-silicon thin film transistors fabricated by a low-temperature process using emission light microscopy

The degradation phenomena in polycrystalline-silicon thin film transistors fabricated by a low-temperature process below 425degreesC (low-temperature-processed poly-Si TFTs) have been investigated. The types of degradation caused by self-heating and hot carriers have been classified, and these degradation phenomena have been investigated using emission light microscopy. Self-heating degradation is thought to originate in the breaking of Si-H bonds and regeneration of dangling bonds in the metal-oxide-semiconductor (MOS) interface and channel poly-Si layers. On the other hand, hot carrier degradation is considered to originate from the damage of the MOS interface and of the channel poly-Si layer near the drain of TFTs. When the gate stress voltage is equal to the threshold voltage, maximum degradation is induced because both the electric field near the drain in the channel and the electron density increase. Results of emission light spectra measurements confirmed the generation of high-energy carriers under this stress.