Effects of longitudinal grain boundaries on the performance of MILC-TFTs

Abstract

Compared to conventional solid phase crystallized (SPC) thin-film transistors (TFT's), metal induced laterally crystallized (MILC) TFT's exhibit significantly enhanced performance at reduced processing temperature. It is concluded that the major improvements in MILC-TFT's result from the growth of the crystal grains in a direction longitudinal to that of the current flow, whereas in SPC-TFT's, the grain boundaries are randomly oriented. It is also observed in this work that while the MILC-TFT's are less sensitive to short-channel effects (SCE's), their leakage current exhibits higher sensitivity to channel length reduction. These differences again can be traced to the different arrangements of the grain boundaries in the two types of devices.

Metal-induced laterally crystallized polycrystalline silicon: technology, material, and devices

“…This is depicted in Figure 10C. While "11 I"-MILC TFTs are better than their SPC counterparts in many device performance measures, they suffer from higher leakage current [12], higher effective V~h [13], reverse short channel effect (R-SCE) [14] and lower drain breakdown voltage (kink effect) [15]. The cause of the degradation has been traced to the superposition of the MMGB, with its high densities of defects, and the depletion region of the drain junction, with its high electric field.…”

“…A comparison of the relevant device parameters of the two kinds of devices is summarized in Table I. Clearly, the MILCTFTs have lower V,h, smaller sub-threshold slope (S), and higher pFE-However, the minimum current (Im,), which is a measure of the TFT leakage current, is higher for "11 1"-MILC [12]. …”

The effects of extended heat treatment on Ni induced lateral crystallization of amorphous silicon thin films

“…Recently, palladium (Pd) or nickel (Ni) [6], [7] was found to induce crystallization of -Si outside its coverage area. This phenomenon of metal induced "lateral" crystallization, or MILC for short, has been found to produce polycrystalline silicon thin films largely free of metal contamination, with better crystallinity than those produced by SPC, and resulting in better performing thin film transistors [8], [9].…”

Reverse short-channel effect in metal-induced laterally crystallized polysilicon thin-film transistors

“…Although solid phase crystallization (SPC) is a relatively inexpensive batch process, its processing temperature at around 600 C still exceeds the upper temperature limit of the inexpensive glass substrates popularly used for LCD's. An alternative low-temperature ( 500 C) crystallization process using metal-induced lateral crystallization (MILC) has been proposed [1], resulting in TFT's with excellent device properties because of the longitudinal grains in the active channels [2].…”

“…Because metal-induced crystallization (MIC), instead of MILC, occurs in the source and drain (S/D) regions of conventional MILC TFT's, continuous MIC/MILC interfacial grain boundaries (MMGB's) [3] are formed which are "selfaligned" [2] to the edges of the gate electrode. It has been shown previously that in TFT's also employing self-aligned S/D doping, these MMGB's overlap the S/D metallurgical junctions and fall within the corresponding depletion regions, thus resulting in higher leakage current [4] and lower drain breakdown voltage [5].…”