| 摘要 |
A method for monitoring contamination in a semiconductor wafer uses a capacitance-frequency measurement on MOS structures to calculate an impurity concentration. The silicon substrate along with an oxide layer is first biased into the inversion region using a variable frequency waveform generator superimposed upon a DC voltage bias. Next, the capacitance of the wafer is measured as a function of the varying frequency in order to develop a capacitance versus frequency curve. From this frequency response, a bandwidth (BW) is measured at a particular normalized capacitance point. The impurity concentration N is then derived using the formula N=GxBW, where G is the correlation constant. With an a priori knowledge of impurity concentration, N, the constant G may be derived by measuring a bandwidth of the capacitance versus frequency curve. Once the constant G is determined, future evaluation of impurity concentration can be made by a capacitance measurement. The method can be used on finished product wafers or as a routine monitoring tool on pre-processed wafers.
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