Abstract
We present a novel technique to perform contactless and mask-free patterned plasma enhanced chemical vapour deposition and etching. When a powered electrode with narrow slits is placed very close to the substrate, plasma is selectively ignited within the slits due to the hollow cathode effect, and so deposition or etching occurs only within an area smaller than the size of the slit. This technique is demonstrated through the deposition of hydrogenated amorphous silicon using a gas mixture of hydrogen, argon and silane. Slits as small as 1 mm generate a plasma, and for this width, the lines deposited are about 750 μm wide, homogenous over their length (60 mm), and are deposited at a rate of 50 nm min−1. The phenomenon is studied using 2D Particle In Cell (PIC) modelling with a simplified argon chemistry. The electron localization observed in the PIC modelling provides an explanation of why the deposition is narrower than the slit.
Highlights
A well-known advantage of low-temperature plasma processing is its ability to provide uniform surface treatments over large areas
The most interesting outcome to be explained from the above results is that the line width of the deposited strips of amorphous silicon (a-Si):H is consistently smaller than the slit opening
The particular configuration of the slits suggests the presence of the hollow cathode discharge effect
Summary
A well-known advantage of low-temperature plasma processing is its ability to provide uniform surface treatments over large areas This uniformity finds advantageous applications in fields such as etching and deposition on wafers for the semiconductor industry (for wafers with diameters up to 450 mm) and for thin film deposition for flat panel displays and solar cells (substrates with areas up to almost 10 m2). The experiments presented were performed in a single chamber PECVD reactor with a grounded substrate holder, and a four-inch diameter radio-frequency (RF) powered electrode designed to implement the desired patterned deposition. Both substrate holder and electrode were at room temperature, and no active cooling was performed. A UVISEL 2 spectroscopic ellipsometer from Horiba was used to cross-check layer thickness and to characterize a-Si:H quality
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