Nondestructive evaluation of generation lifetime and surface generation velocity and the effect of etching, polishing and annealing on 5" Si wafer surface properties

In this work the nondestructive measurements of bulk generation lifetime, τgand surface generation velocity Sgare discussed and experimentally demonstrated. Te technique is based on transverse acoustoelectric voltage (TAV) transient measurements τgand Sgare evaluated to characterize the electrical properties of Si wafers prior to the device fabrication. The wafers have undergone different chemical etch removel, polish removal and forming gas annealing treatments. Measurements under the applied DC electric field are performed in order to distinguish between the surface and bulk effects. The results indicate: 1) Increase of the effective lifetime, τeffby about 100 times after etching and polishing due to the surface damage removal 2) A minimum of two orders of magnitude improvement is observed for the forming gas annealed half wafers as compared to the unannealed halves. In the above experiments both oxidized and unoxidized samples are investigated without the fabrication of any form of contact on the wafers. The spatial maps of τgand Sgare obtained for some wafers. The TAV amplitude and time constant dependence on the applied DC voltage reveals the surface condition (depletion or inversion) at zero bias and the approximate position of the recombination center within the Si bandgap.