*3.4.2. Direct etching*

The application of appropriate etching pastes can also be helpful in etching away the passi‐ vation layer directly [59-61]. The process is done by applying phosphoric acid-based etch pastes on the ARC layer followed by temperature curing (at 300~390 °C) to etch away the desired passivation layer. Thinner finger lines (85 μm wide) have been realized by screen printing a phosphoric acid paste and curing at 350 °C for 90 seconds on a textured surface [58]. Another form of the direct etching of the passivation layer was reported which uses a watersoluble acidic polymer with a fluoride-based solution for the etching of SiNx and SiOx layers [62]. The method uses the fluoride-based solution-it is safer to handle in comparison to HF- based etching solutions. Furthermore, lower expenses are involved and the method produces less waste.
