Laser Fired Contacts

Particularly for thin wafers, it is advantageous to have a passivation layer (nitride or oxide) between the rear side of the wafer and the aluminium electrode. The passivation layer is insulating which leads to the problem of how to connect the metallisation to the silicon. A technology developed at the Fraunhofer ISE employs a 1um IR laser to irradiate the aluminium which is "fired" through the passivation layer and connects to the silicon - a laser fired contact. For a 125mm x 125mm wafer 15000 connections are required.

Low surface recombination makes passivated cells attractive. A solar cell can be produced with an oxide or nitride passivation layer. An elegant way to contact it is to deposit an aluminium layer over the passivation and fire contacts through the passivation layer by laser pulses incident on the    aluminium. The laser ablates the oxide or nitride and simultaneously     connects the aluminium to the underlying silicon by reflow.
Low recombination velocity at fully passivated solar cell surface
Efficiently combinines dielectric ablation with connection to metal
Can be effectively used with interdigitated back-contact schemes
IR ns-pulsed DPSS lasers are typically used for LFC formation
Throughput of  700 wafers/module/hour is possible 
15mm, 3s contact positioning available for interdigitated designs

The relatively small field and high processing rate required for inline manufacturing make (x,y) scanners the technology of choice. Scanners are a key technology of M-Solv where we have very great experience of processing and control hardware and software.