Invited Paper PS2-ThM1
New Approaches for Overcoming Current Issues of Plasma Sputtering Process during Organic Based Micro-Electronic Device Fabrication : Room Temperature & Plasma Damage Free
While direct deposition of metal oxide thin films including transparent conductive oxide (TCO) and amorphous oxide semiconductor (AOS) on the organic layers, plasma damages against the organic materials are serious issues. These damages are believed to be mainly originated from highly energetic particles during the plasma sputtering process such as negative oxygen ions & reflecting neutrals from the target surface, etc. During the DC magnetron sputtering (DMS) process, most of energetic particles contribute in self-supplying of activation & crystallization energy and forming higher quality TCO thin film without an additional heating or post-annealing. However, the excessively accelerated negative oxygen ions can lead to fatal physical bombardment damages and defects in the oxide thin film, which are hardly recovered without post thermal annealing. To simply salve the inherent limitation of the DMS process, we are developing novel approaches for selectively filtering the negative ions by magnetic field arrays, named as Magnetic Field Shielded Sputtering (MFSS) process. The MFSS process effectively eliminates or suppresses the defect generation induced by the negative oxygen ion bombardments. The electro-optical properties of ITO thin films by the MFSS were superior to those by the conventional DMS at room temperature. While the DMS processed a-IGZO TFTs need a high temperature post annealing up to 400℃ for healing the internal defects in the AOS thin film, the MFSS processed a-IGZO TFT scarcely requires the post thermal annealing and shows very comparable electrical performance to the DMS processed one with a high temperature post annealing. To completely overcome the plasma related damage issues, we are developing the Neutral Beam Assisted Sputtering (NBAS) process; electro-optical properties of the ITO thin film by the NBAS were achieved in lower resistivity (< 4.0×10−4 Ω∙cm) and higher transmittance (> 90 % at 550 nm) with nano-crystalline structure at room temperature process. Furthermore, for a TCO top anode on the inverted structure OLED cell, the NBAS TCO deposition process has induced almost no damages on the underlying organic layers. On the other hand, gas barrier coatings are essential to prevent the permeation of water and oxygen for a high efficiency flexible AMOLED device. Key factors for formation of the high quality inorganic gas barrier to satisfy the extremely lower water vapor transition rate (WVTR) requirement for OLED cells (<1×10-6 g/m2/day) are suppression of nano-sized defect sites and gas diffusion pathways among the grain boundaries. To achieve the nano-sized defect free inorganic gas barrier layer, new nano-structured Al2O3 single gas barrier layer is developing by using the NBAS technology; current WVTR of the NBAS processed Al2O3 gas barrier films was as low as 5×10-6 g/m2/day by just single layer.