Method and apparatus for determining end-point in a chamber cleaning process

A method for determining end-point in a chamber cleaning process comprising the steps of:

• providing a chamber having a cavity for conducting a semiconductor fabrication process therein;
• mounting a crystal sensor on a surface of said chamber cavity at a position that the crystal sensor is exposed to gases or liquids used or generated by said fabrication process;
• conducting said semiconductor fabrication process in said chamber;
• flowing a cleaning fluid into and in-situ cleaning said surface of said chamber cavity;
• inputting an oscillating frequency into said crystal sensor and monitoring an output frequency of oscillation from said crystal sensor;
• and
• comparing said output frequency of oscillation to an output frequency from a crystal sensor having a clean surface and defining an end-point of said chamber cleaning process when said output frequency of oscillation is not more than 20% smaller than said output frequency from said crystal sensor that has a clean surface.