Wafer Marking

The marking of silicon wafers facilitates traceability of the manufacturing process for fault analysis of semi-conductor devices. A laser system designed for wafer marking must meet the most stringent requirements. Thus, the marking must be machine-readable, miniaturized and have no negative influence on the further manufacturing steps and still permit clear identification at the end of the process chain. Even very minor deviations within the marking are not permissible. In addition to low-maintenance and fault-free operation, laser systems for these applications must in most cases be suitable for the most extreme clean-room environments (debris-free marking).

An ideal way for non-contact marking of silicon wafers is to use q-switched Nd:YAG lasers. Clear text, bar codes and dot matrix codes or a combination of all of them are engraved at the edge of the wafer.

Two methods are used which differ in terms of process, depth and location of the marking. With the deep marking method, which produces a durable marking even after a large number of etching and polishing steps, the dots have a depth of up to 90 micrometers and are created through material ablation. The debris-free marking, which is set for clean-room environments, can be as much as approximately 2.5 µm deep, which is achieved solely by melting of the silicon. The diameter of a dot is typically in the range of 70-110 µ, (deep marking) or 50-80 µm (debris-free marking).