Radio frequency monitor for semiconductor process control

In a plasma processing apparatus, having a reactor for processing a gas and wherein said reactor is coupled to a radio frequency (RF) source by a transmission line, a method of manufacturing a semiconductor device by accurately monitoring RF voltage and current being supplied by said RF source to said reactor on said transmission line, comprising the steps of:

• providing a first capacitor coupled between a first node and said transmission line;
• providing a second capacitor coupled between said first node and a common return;
• said first and second capacitors providing a capacitive voltage divider network wherein a first voltage output at said first node is a proportional representation of said RF voltage on said transmission line;
• providing a wire loop disposed next to said transmission line at a point on said transmission line where said first capacitor is coupled but having an air gap between said loop and said transmission line, such that electromagnetic field lines generated by current flow in said transmission line is inductively coupled to said loop, wherein voltage induced in said loop by said current flow provides a second voltage output which is a proportional representation of said RF current on said transmission line;
• providing an electromagnetic shielding, disposed around said first and second capacitors, inhibits electromagnetic interference from interacting with said first and second capacitors which interference can cause erroneous first voltage output at said first node;
• said first and second voltage outputs providing for accurate measurement of said RF voltage and current and said measurement is also used to accurately determine a phase difference between said RF voltage and RF current.