Normal-incidence in-situ process monitor sensor

A method for in-situ monitoring of an etch process in a plasma processing chamber, the method comprising:

• performing a first etch process on a substrate disposed in the plasma processing chamber based on a first etch process recipe;
• collecting, through a collection system and using a first light detector, a spectral intensity of a reflected light beam from an illuminated area on the substrate that is generated by directing an incident light beam from a continuous wave broadband light source, through an illumination system, at normal incidence to the substrate;
• determining, in a controller, a property of the substrate or structures formed thereupon based on the collected spectral intensity of the reflected light beam, the property being a physical property of the substrate or structures formed thereupon;
• determining whether the property of the substrate or structures formed thereupon is within a target range;
• and
• altering the first etch process in the plasma processing chamber based on the determined property of the substrate or structures formed thereupon,
• wherein the controller comprises a prediction algorithm, the prediction algorithm being indicative of a correlation between the property of the substrate or structures formed thereupon and the spectral intensity of the reflected light beam, and
• wherein the prediction algorithm is built by collecting physical properties of sample substrates or structures formed thereupon and spectral intensities of reflected light beams that are collected from the sample substrates and training the prediction algorithm based on the physical properties of sample substrates or structures formed thereupon and the spectral intensities of reflected light beams that are collected from the sample substrates.