Yoichiro Yoneda

60.4: Single Layer Al‐Ni Interconnections for TFT‐LCDs using Direct Contacts with ITO and a‐Si

It was demonstrated for the first time that the use of Al-Ni alloy films and a-Si surface nitridation for the direct contacts of interconnection lines with both ITO and a-Si were feasible for the TFT technology. The mechanism how the direct contact, described in the present paper, works was studied using various analysis technique.

Current Path Analysis of the Direct Contact Between ITO and Al–Ni Alloy Films

Al-Ni alloys for single-layer interconnections to be used for amorphous silicon thin-film transistors (a-Si TFTs) in liquid-crystal displays have been developed. The developed interconnections make possible a direct electrical contact with an indium-tin oxide (ITO) film without barrier metals, such as Mo and Cr, which are conventionally used for the electrical contacts. In the present paper, we investigated the major current path at the contact between ITO film and the Al-Ni alloy layer using nanoprobes. It was found that the Al 3 Ni precipitations between the ITO film and the Al-Ni alloy layer played an important role of electrically conducting contacts. This led us to a conclusion that it is important to increase local current paths via Al 3 Ni precipitations to achieve a low resistivity at the contact between the ITO film and the Al-Ni alloy layer, which was found to be strongly influenced by the photoresist stripping process successively used for the formation of SiN contact holes in the production of α-Si TFTs.

P‐149: Anode Electrode of Al‐Ni Alloy Film Directly in Contact with ITO for Top‐Emitting OLEDs

A bottom anode with high reflectivity is one of the most important materials for top-emitting OLEDs. As an anode electrode, stacked ITO/Al-Ni alloy-based films, as opposed to conventional stacked ITO/Ag films, were investigated for the first time. It was found that the direct contact technique of the Al-Ni alloy-based film with the ITO film using a film annealing process was applicable for OLEDs, as in the case of LCD interconnections that have already been developed by the authors. It was thus concluded that the Al-Ni alloy-based films were suitable materials for the anode electrode of OLEDs. They are a better choice than Ag film, due to their low material cost and ease of production of large-area sputtering targets for large-Size OLED-TVs.

24.2: Single Layer Al‐Ni‐La‐Si Interconnections for Source and Drain of LTPS‐TFT LCDs Using Direct Contacts with both ITO and poly‐Si

It was demonstrated for the first time that the use of Al-Ni-La-Si alloy films for the direct contacts of interconnection lines with both ITO and poly-Si was feasible for the LTPS-TFTs. Measured contact resistivity was in the order of 10−4 Ω.cm2 for ITO and Al-0.6 at.% Ni-0.1 at.% La-0.5 at.% Si. The Al alloy films patterned on poly-Si were found to be stable below 350 °C. It was also found that Al alloy has good dry etching characteristics such as a high etching rate and good selectivity to photo-resist, suitable for high-resolution LTPS-TFT LCDs.

Electrical Conduction across the Direct Contact between Indium–Tin Oxide and Al–Ni Alloy Layers

The electrical conduction across direct contacts between indium–tin oxide (ITO) and the newly developed Al–Ni alloys, used for amorphous silicon thin-film transistors (a-Si TFTs) in liquid crystal displays (LCDs), has been studied. The ITO/Al–Ni alloy interfaces were examined by both electrical measurements using nanoprobes and cross-sectional transmission electron microscopy (XTEM). It was found that the major conduction path across the ITO/Al–Ni alloy interface was via Al3Ni precipitates, and that the resistivity of the ITO/Al–Ni alloy contact strongly depended on the conditions of the Al–Ni alloy surface. It was thus concluded that the generation of non-oxidized Al3Ni precipitates after photoresist stripping is important for high-quality direct contacts. The present results on the Al–Ni alloy compositions and ITO/Al–Ni alloy interfaces have already been considered in the actual production of a-Si TFTs for LCDs.

56.4: Formation of Single‐Layer Al‐Alloy Interconnection for Source and Drain of a‐Si TFT Using One‐Wet‐One‐Dry Etching with Four‐Mask Process

Single layer Al-alloy interconnection for source and drain of amorphous Si (a-Si) thin film transistor (TFT) is demonstrated by direct-contact technology with no barrier metals at the interfaces with both ITO and a-Si. Thermally stable contacts were formed on a-Si with a buried nitridation layer while maintaining the contact resistivity as low as 0.1Ωcm2. Excessive interdiffusion between the Al-alloy electrode and a-Si that can degrade TFT characteristics was suppressed by the nitridation layer. The Al-alloy direct contact technology, combined with one-wet-one-dry etching with four-mask process, drastically simplifies the the TFT fabrication process and contributes to cost reduction of a-Si TFT LCD.