PECVD process

A method of determining thickness of a layer during deposition of the layer on a subjacent layer of a substrate, comprising:

• reflecting a broad spectrum radiation from the substrate;
• analyzing the spectrum of the reflected light using a spectrograph;
• fitting a Fresnel model to the analyzed spectrum based on refractive index and extinction coefficient of the layer being deposited, and based on thickness of the subjacent layer;
• and
• determining optical properties of the subjacent layer and the layer thickness by repeated a process including minimizing the square of the difference between the analyzed spectrum and the model, wherein the process comprises:
• determining a deposition rate from a subset of the reflected spectrum;
• and
• determining the optical properties of the subjacent layer from the remainder of the reflected spectrum.

A method of determining thickness of a layer during deposition of the layer on a subjacent layer of a substrate, comprising:

• repeatedly reflecting a broad spectrum radiation from the substrate to define a reflectivity at multiple time points;
• analyzing the spectrum of the reflected light using a spectrograph;
• fitting a Fresnel model to the analyzed spectrum based on refractive index and extinction coefficient of the layer being deposited, and based on thickness of the subjacent layer;
• determining optical properties of the subjacent layer and the layer thickness by repeating a process including minimizing the square of the difference between the analyzed spectrum and the model, wherein the process comprises:
• determining a first deposition rate from the reflectivity using a subset of the time points and a subset of the spectrum of the reflected light;
• and
• determining optical properties of the subjacent layer using the subset of time points, the first deposition rate, and the remainder of the reflected spectrum;
• and
• determining a second deposition rate using the determined optical properties of the subjacent layer.