Apparatus and method for determining porosity

A method for determining the porosity of an element formed on a substrate, the method comprising the steps of:

• selecting a gaseous substance being admissible to an exposed surface of the element formed on the substrate, said substrate being positioned in a pressurized chamber at a constant temperature;
• setting the pressure in the chamber to a first modified value;
• admitting said gaseous substance in said chamber, the temperature of said gaseous substance being substantially identical to said constant temperature;
• after a predetermined period of time measuring at least one value of the pressure in the chamber and performing an ellipsometric measurement to determine the optical characteristics of the element;
• changing the pressure in the chamber in a stepwise manner, whereby after each step and after a period of time the optical characteristics are determined by means of an ellipsometric measurement, to thereby determine an adsorption-desorption isotherm;
• and
• calculating the porosity using at least the measured optical characteristics and the adsorption-desorption isotherm.

A method for determining porosity of an element formed on a substrate using a gaseous substance, said substrate being positioned in a pressurizable chamber at a chamber temperature, said method comprising the steps of:

• modifying pressure in said chamber;
• introducing a gaseous substance in said chamber;
• performing at least one ellipsometric measurement to determine optical characteristics;
• and
• calculating said porosity of said element.