Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Patent
1996-09-30
1998-06-02
Regan, Maura K.
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
324765, G01R 1512
Patent
active
057605947
ABSTRACT:
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=G.times.BW, 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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Regan Maura K.
VLSI Technology Inc.
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