Apparatus and method for determining porosity

A method in accordance with claim 11 further comprising the steps of:

• selecting a gaseous substance being admissible to an exposed surface of the element formed on the substrate,
• setting the pressure in the chamber to a first predetermined value;
• admitting said gaseous substance in said chamber, the temperature of the gaseous substance being substantially identical to said predetermined constant temperature;
• after a predetermined period of time measuring the value of the pressure in the chamber and performing the 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 predetermined period of time the optical characteristics are determined by means of an ellipsometric measurement, and
• calculating the porosity using at least the measured optical characteristics.

An apparatus for determining the porosity of an element formed on a substrate, said apparatus comprising:

• a pressurizable chamber in which said substrate is positionable;
• a temperature control element for fixing the temperature in said chamber at a predetermined value;
• a pump for changing the pressure in said chamber;
• a supply for admitting a gaseous substance;
• an ellipsometer for determining the optical characteristics of said element when said element positioned in said chamber;
• and,
• at least a first controllable component and at least a second controllable component, said first component being positioned between said pump and said chamber and allowing a precise control of the pressure in the chamber, said second component being positioned between said supply and said chamber and allowing a precise control of the flow of said gaseous substance into said chamber.

A method for determining the porosity of an element formed on a substrate 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 predetermined constant temperature;
• setting the pressure in the chamber to a first predetermined value;
• admitting said gaseous substance in said chamber, the temperature of the gaseous substance being substantially identical to said predetermined constant temperature;
• after a predetermined period of time measuring the 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 predetermined 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.