RUV technology

The Resonance Ultrasonic Vibrations technique was developed for in-line non-destructive crack detection in full-size silicon wafers and solar cells. The RUV methodology relies on deviation of the resonance frequency response curve measured on a wafer with peripheral or bulk millimeter-length crack and on identical non-cracked wafers.

The silicon wafer is a large contributor to the overall cost of the solar cell. In addition, the silicon raw material price has roughly doubled in the last two years due to a worldwide shortage of the polycrystalline silicon feedstock. To compensate for the feedstock shortage, solar Si wafers are sliced thinner with thicknesses down to 80-200 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 down time.

The RUV technology allows (1) rejection of mechanically unstable Si wafers after ingot cutting before they are introduced into further cell processing, (2) identification of wafers with mechanical defects (such as cracks) during production to avoid their in-line breakage, (3) detection of cracked cells before they will be laminated into modules to avoid panel efficiency reduction and product return from the field.

By using a RUV wafer, solar cell and module manufacturers will improve their production yield and reduce costs. They also can analyze machine efficiency regarding crack initiation as well as differences  in wafer and cell quality between venders.

Through a frequency sweep (20 -100 kHz) the RUV method enables crack detection with simple criteria for wafer or cell rejection. A crack introduced into Si wafer alters the RUV peak parameters: amplitude, bandwidth and peak position. This is illustrated in the figure (*) for two identical Cz-Si wafers. Specifically, the crack in the wafer shows the following features: (1) a frequency shift of the peak position; (2) an increase of the bandwidth, and (3) a reduction of the amplitude. Therefore the RUV approach is essentially based on fast measurement and analyses of a specific resonance peak and rejection of the wafer if peak characteristics deviate from the normal non-cracked wafers.

The sensitivity of the system, which refers to length of the cracks, is adjustable to the needs of the user. The rejecting method is based on a statistical approach. In several tests the accuracy of this method was between 91 - 95%. That means that the breakage caused by cracked wafers or cells is reduced by at least a factor of 10.

From the download page you can acquire official publications regarding the RUV technology, to give you more in depth information. RUV Systems can also provide you with examples and cases showing concrete results.