METHOD AND SYSTEM FOR PROCESSING MEASUREMENT SIGNALS TO OBTAIN A VALUE FOR A PHYSICAL PARAMETER

摘要

PCT No. PCT/US97/21308 Sec. 371 Date Nov. 21, 1997 Sec. 102(e) Date Nov. 21, 1997 PCT Filed Nov. 27, 1997 PCT Pub. No. WO98/22814 PCT Pub. Date May 28, 1998In a measurement system wherein time-varying physical signals containing frequency information related to a physical parameter of an object are measured to obtain corresponding time-varying measurement signals, a method and system are disclosed for processing the measurement signals to obtain a value for the physical parameter by first extracting the frequency information from the measurement signals. The frequency information includes at least one desired frequency and its amplitude and decay rate. Then, the frequency information is converted to a value for the physical parameter. The measurement signals are discrete time ultrasonic signals. Extraction is performed by transforming the ultrasonic signals to a Z-domain and converting at least one zero or pole in the Z-domain to the at least one frequency and its decay rate. The physical signals may be coherent light signals which are modulated based on the frequency information which is related to propagation of longitudinal ultrasonic waves in the object. When the object is a static film such as a cured layer formed on a substrate, the physical parameter may be thickness of the layer. When the object is a dynamic curable film such as a wet or dehydrated layer, its thickness changes over time from an initial value to an intermediate value and then to a final value. The initial value is obtained by processing the frequency information with a model of the propagation of the waves in the film. The intermediate value is predicted from the initial value and the final value is predicted from the intermediate value.