Gururaj A. Bhat

Nickel induced crystallization of amorphous silicon thin films

Nickel (Ni) induced crystallization of amorphous silicon (a-Si) has been studied by selective deposition of Ni on a-Si thin films. The a-Si under and near the Ni-covered regions was found to be crystallized after heat treatment at 500 °C from 1 to 90 h. Micro-Auger electron spectroscopy revealed that a large amount of Ni stayed in the region under the original Ni coverage, but no Ni was detected either in the crystallized region next to the Ni coverage or in the amorphous region beyond the front of the laterally crystallized Si. X-ray photoelectron spectroscopy revealed a nonuniform Ni distribution through the depth of the crystallized film under the original Ni coverage. In particular, a Ni concentration peak was found to exist at the interface of the crystallized Si and the buried oxide. It was found that a layer of 5-nm-thick Ni could effectively induce lateral crystallization of over 100 μm of a-Si, but the lateral crystallization rate was found to decrease upon extended heat treatment. Transmission e...

Characterization of the MIC/MILC interface and its effects on the performance of MILC thin-film transistors

Process and material characterization of the crystallization of amorphous silicon by metal-induced crystallization (MIC) and metal-induced lateral crystallization (MILC) using evaporated Ni has been performed. An activation energy of about 2 eV has been obtained for the MILC rate. The Ni content in the MILC area is about 0.02 atomic %, significantly higher than the solid solubility limit of Ni in crystalline Si at the crystallization temperature of 500/spl deg/C. A prominent Ni peak has been detected at the MILC front using scanning secondary ion mass spectrometry. The MIC/MILC interface has been determined to be highly defective, comprising a continuous grain boundary with high Ni concentration. The effects of the relative locations of this interface and the metallurgical junctions on TFT performance have been studied.

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

Compared to conventional solid phase crystallized (SPC) thin-film transistors (TFTs), metal induced laterally crystallized (MILC) TFTs exhibit significantly enhanced performance at reduced processing temperature. It is concluded that the major improvements in MILC-TFTs result from the growth of the crystal grains in a direction longitudinal to that of the current flow, whereas in SPC-TFTs, the grain boundaries are randomly oriented. It is also observed in this work that while the MILC-TFTs are less sensitive to short-channel effects (SCEs), 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.

Behavior of the drain leakage current in metal-induced laterally crystallized thin film transistors

Although conventional metal-induced laterally crystallized (MILC) thin film transistors (TFTs) are better than solid phase crystallized (SPC) TFTs in many device performance measures, they are less ideal in others, owing to the higher leakage current and early drain breakdown. It has been found that degradation can be reduced by eliminating the overlap of the metallurgical junctions of the source/drain regions, formed by metal-induced crystallization (MIC), and the grain boundaries at the MIC/MILC interface. Here, the drain leakage current (Ilk) behavior of MILC TFTs with and without overlap has been studied. It is observed that under certain gate bias conditions, the relative magnitude of Ilk for the two kinds of devices exhibits an interesting reversal as the drain bias is varied. ” 2000 Elsevier Science Ltd. All rights reserved.

The effects of MIC/MILC interface on the performance of MILC-TFTs

High mobility, low temperature polycrystalline silicon thin film transistors (poly-Si TFTs) potentially enable the integration of driver circuits and pixel transistors on the same glass panel for large area displays. Solid phase crystallized TFTs (SPC-TFTs) have been studied extensively at processing temperatures of about 600/spl deg/C. However, due to the presence of a large density of intra- and inter-granular traps, SPC-TFTs suffer from poor device performance, such as high threshold voltage, high leakage current and early kink effect. Metal-induced lateral crystallization (MILC) at 500/spl deg/C is an alternative technology for realization of TFTs. Due to the presence of large longitudinal grains and lower trap densities, these devices exhibit better performance than SPC-TFTs. With self-aligned deposition of the crystallization inducing metal, it is discovered that the behaviour of conventional MILC-TFTs is strongly influenced by the overlapping of the drain metallurgical junction and the MIC/MILC interface, which consists of a grain boundary and trapped metallic impurities. Detrimental effects of this overlap can be eliminated by separating the interface from the junction. In this work, the performance of SPC- and MILC-TFTs are compared, particularly with regard to scalability and the onset of the kink effect.

Plasma hydrogenation of metal-induced laterally crystallized thin film transistors

The device characteristics of conventional metal-induced laterally crystallized thin film transistors (MILC-TFTs) are adversely affected by the existence of the continuous grain boundaries in the depletion regions of the metallurgical source and drain junctions. It has been shown that by introducing an extra lithographic masking step, the detrimental effects can be eliminated by separating the grain boundaries from the junction depletion regions. In this work, it is demonstrated that the traps in these grain boundaries can also be efficiently passivated using simple plasma hydrogenation, resulting in simultaneous improvements in the threshold voltage, the subthreshold slope, the mobility, the drain breakdown voltage, and the leakage current.

Solid-Phase Reaction of Ni with Amorphous SiGe Thin Film on SiO2

A study on the reaction of Ni and amorphous Si0.68Ge0.32 film on SiO2 is reported. The reaction was performed at 520° C in a conventional furnace. The resulting film was characterized using X-ray photoelectron spectroscopy (XPS) and Raman scattering spectroscopy. Ni induced crystallization of SiGe was confirmed by the Raman spectra. XPS results indicate Ni piled up at or near the interface of the crystallized SiGe and the SiO2 substrate. The small amount of Ni inside the SiGe layer exists in more of a silicide- or germanide-like form. Ni enhanced oxidation of SiGe was found during the reaction and the oxidized layer was found to be a mixture of oxides of Si and Ge, with Ge piling up at the surface.

On the formation of solid state crystallized intrinsic polycrystalline germanium thin films

A two-step heat treatment process has been employed to crystallize low pressure deposited thin films of amorphous germanium. Large grain p -type polycrystalline germanium with a Hall effect hole mobility of greater than 300 cm 2 /Vs has been obtained. Films with near intrinsic conductivity, necessary for the construction of practical enhancement-mode insulated-gate thin film transistors, were obtained by introducing phosphorus as a compensating dopant. High Hall effect electron mobility of 245 cm 2 /Vs has been measured on the resulting n -type polycrystalline germanium thin films.

Reduction of threshold voltage in metal-induced-laterally-crystallized thin film transistors

In conventional metal-induced-laterally crystallized (MILC) thin film transistors (TFTs), the source and drain regions are crystallized by metal-induced crystallization (MIC) self-aligned to the edges of the gate electrodes. A distinct grain boundary exists at the border between the MILC and the MIC regions. It will be shown that the apparent threshold voltage (V/sub t/) of the MILC TFTs is affected by the presence of these MILC/MIC grain boundaries (MMGBs) at the edges of the transistor channels. Furthermore, V/sub t/ can be reduced either by eliminating the MMGBs from both the source and drain junctions or by hydrogen passivation of the traps in the MMGBs.

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

A reverse short-channel effect, manifested by an increase in the transistor threshold voltage as the channel length is reduced, is observed in conventional metal-induced laterally crystallized thin-film transistors. Such an effect has not been observed in regular solid phase crystallized thin-film transistors and can be eliminated by a brief hydrogen plasma treatment.