Crack Detection in Silicon Wafers and Ceramic Plates Using Resonance Ultrasonic Vibrations (RUV) Technology

The Resonance Ultrasonic Vibrations (RUV) technique was developed for off-line and in-line non-destructive crack and flaw detection in full-size silicon wafers for solar cells and thin ceramic plates for solid oxide fuel cells. The RUV methodology relies on a deviation of the resonance frequency response curve measured on a wafer/plate with peripheral or bulk millimeter-length crack and on identical non-flawed wafers/plates.

The silicon wafer is a large contributor to the overall cost of the solar cell. To reduce cost per Watt of solar energy, Si wafers are sliced thinner with thicknesses below 150 microns. Wafer areas have also been increased to reduce overall production costs. These technological trends make wafer handling in production more challenging and reduce the yield of solar cell lines due to increased wafer and cell breakage. In-line wafer breakage also reduces equipment throughput as a result of downtime.

The RUV technology allows: (1) rejection of mechanically unstable bare Si wafers or ceramic plates before they are introduced into further processing, (2) identification of wafers with mechanical flaws (such as cracks) during production to avoid their in-line breakage and yield reduction, (3) detection of cracked solar and fuel cells before they will be combined into modules to avoid efficiency reduction and product return from the field, and (4) identify solar cells with sub-millimeter size pin-holes. RUV system also serves as a process control tool to increase yield by eliminating production flaws caused by mechanical defects.

The sensitivity of the system, which refers to the length of the cracks, is adjustable to the needs of the user. The rejecting method is based on a statistical approach. In case studies the accuracy of this method was between 91 - 95%. That means that after RUV inspection the breakage caused by cracked wafers or cells is reduced by at least a factor of 10. RUV tools are designed to satisfy various customer’s needs and demands. Our application group will perform an on-site inspection of your products and provide practical recommendations.

In-line and off-line RUV systems are readily available and can be customized to address specific features. Please Contact Ultrasonic Technologies for more information or to discuss your particular needs.