Polarized Laser Diode Wafer Impurity Monitor
Original Publication Date: 1980-Nov-01
Included in the Prior Art Database: 2005-Feb-14
A knowledge of the impurity content of bulk wafer substrate materials, such silicon is critical to semiconductor device processing. For example, the amount of oxygen dissolved in silicon, present in tens of parts per million, directly impacts device yield. One established method for quantizing such impurities involves measuring the infrared (IR) radiation absorbed by them using an IR spectrophotometer. One shortcoming of that method is caused by the phenomenon of multiple internal reflections of the IR beam within the sample wafer. This gives rise to baseline irregularities (fringes) which can complicate the measurement of the actual absorption. Also, the internal reflections result in some part of the detected radiation traversing the sample more than once, causing errors in the measured absorbance.