Paper TF-TuM3
Employing Atmospheric Pressure Micro-Plasma Printer for ALD of TiO₂ Thin Films

Tuesday, October 31, 2017, 8:40 am, Room 20

A broad range of devices such as thin film transistors (TFTs), solar cells, sensors and microfluidic channels benefit from micron-scale patterns in their structure. These micron-scale patterns are often fabricated by means of costly methods such as (photo-)lithography. For this reason, there is a large interest in alternative simple and cost-effective approaches for micron-scale to sub-millimeter patterning that reduce the number of etch and lithography process steps.

A micro-plasma printer [1], which is based on a unique needle-to-plate micro-plasma dielectric barrier discharge (DBD), has recently been developed for spatially-resolved surface functionalization [2] and deposition of organic films [3] with sub-millimeter range resolution. In this contribution, the potential of the micro-plasma printer in delivering patterned, ultra-thin inorganic films at atmospheric pressure is addressed. Specifically, the setup is adopted to carry out thin film TiO₂ deposition in two configurations, namely plasma enhanced chemical vapor deposition (PE-CVD) and plasma-assisted atomic layer deposition (PA-ALD).

The properties of the TiO₂ layers as well as the patterning resolution have been investigated. The TiO₂ films deposited by PE-CVD mode have not shown satisfactory results in terms of purity and density of the layers (more than 5% C and refractive index of 1.8). However, the PA-ALD mode has been able to deliver patterns of amorphous TiO₂ films with low level of impurity and sub-nanometer thickness control. A growth rate of 0.15 nm/cycle has been obtained for 500 ms and 400 µs of TTIP and N₂/O₂ plasma exposures in each PA-ALD cycle, respectively. Rutherford backscattering spectroscopy (RBS) has revealed a growth rate of 2.4 Ti atoms per nm²_.cycle in saturation condition. Improvement of density and reduction of film impurities (H, C and N content) have been observed by prolonging the plasma exposure time. TiO₂ films with refractive index of 2 and less than 1% C have been deposited by 2 ms of plasma exposure. The width of the smallest features deposited by PE-CVD and PA-ALD modes have been determined by XPS line scan measurements to be 1.8 mm and 900 µm, respectively, for 7 nm thick layers.