Patent ID: 8150653

Claim:
A method of normalizing sensor readings, the method comprising: (i) receiving a reading from a sensor configured to detect light reflected from a substrate; and (ii) normalizing the sensor reading, using a processor, based on a function of sensed mass on the substrate wherein the normalized function is defined as: V spec_read ⁡ ( x ) - DarkOffset V spec_Clean ⁢ _read ⁡ ( x ) + ( V spec_read ⁡ ( x ) V spec_Clean ⁢ _read ⁡ ( x ) ) β ⁢ δ ⁡ ( x ) - DarkOffset , where: x is a position of the substrate in a process direction; Vspec_read(x) is the sensor's reading; DarkOffset is the sensor's bias; Vspec_Clean_read(x) is a sensor reading taken of the substrate with no mass on the substrate; β is an exponent greater than 0; and δ(x) is a function of mass deviation on the substrate.