Formation of thin laser ablated contacts using cylindrical lens
Laser contact opening (LCO) and Ni/Cu light induced plating is an established front side metallization process which provides the possibility of thinner contacts with high aspect ratios and inherently low contact resistances. In this study, we work towards the development of an optical system which combines the speed of state-of-the-art scanner systems and the high numerical apertures lenses used to create small structures. We successfully demonstrate the feasibility of cylindrical lens as the focusing lens for laser ablation. The lens generates elliptical openings with a major diameter of 2.6 mm and a minor diameter of 3.1 mm with a single pulse. Successful formation of contacts is achieved in this study with a contact opening of 3 mm and plated finger width of 15 mm. Lifetime measurements after LCO for an open area percentage of 2-3% using the conventional scanner systems and cylindrical lens shows that increase in J0e due to lasering with cylindrical lens is almost half as compared to LCO with state-of-the-art galvanometer scanner and f-theta lens setup at a similar opened area percentage and laser fluence. The optimum laser parameters and plating generate contacts with Rc values that are comparable to the ones achieved using standard LCO despite having smaller contacts. Thermal annealing after LCO is included as the standard protocol as it demonstrates the best performance for this setup. These results provide a proof-of-concept for the feasibility of using cylindrical lenses as the focusing lens. Our study lays the foundation for further experimentation on hybrid systems, where the high throughput of the scanner system is combined with the high numerical aperture (NA) of cylindrical lens.