Reducing device yield fallout at wafer level test with electrohydrodynamic (EHD) cleaning

Unstable contact resistance (C_RES) during wafer test can significantly affect device yield, the need for reprobe, and equipment uptime. Abrasive cleaning during off-line probe card repair and maintenance is effective for reducing C_RES and removing surface contaminants from probe tips. This type of cleaning, however, shortens probe card life and can compromise probe card planarity and alignment. Off-line electrohydrodynamic (EHD) cleaning uses charged molecular microclusters to reduce C_RES without damaging probe card materials or misaligning the probe tips. An engineering evaluation was performed using two groups of probe cards that were regularly cleaned off-line with a tungsten carbide abrasive plate and the EHD cleaning tool respectively. For the evaluation, a very high volume device sensitive to C_RES stability and variation was identified and probe card performance was monitored for several weeks across multiple lots. Probe card performance after abrasive cleaning did not deviate significantly from the historical median. However, after EHD cleaning an increase of device yield was consistently observed. Based on the results, the EHD cleaning technique was found to be an effective addition to off-line abrasive cleaning that might have additional benefits to production