Two-grid ion energy analyzer and methods of manufacturing and operating

An ion energy analyzer for use in diagnosing the ion energy distribution (IED) of plasma, comprising:

• a substrate;
• a first insulator disposed on said substrate;
• an ion current collector disposed on said first insulator;
• a second insulator disposed on said ion current collector, said second insulator having an aperture formed there through to expose a collection area on said ion current collector;
• a first conductive electrode disposed on said second insulator, said first conductive electrode having said aperture formed there through and aligned with said aperture in said second insulator;
• an electron rejection grid disposed on said first conductive electrode and extending over said aperture;
• a third insulator disposed on said first conductive electrode, said third insulator having said aperture formed there through and aligned with said aperture in said first conductive electrode;
• a second conductive electrode disposed on said third insulator, said second conductive electrode having said aperture formed there through and aligned with said aperture in said third insulator;
• an entrance grid disposed on said second conductive electrode and extending over said aperture, said entrance grid located at an outermost plane of the ion energy analyzer and exposed to the bulk plasma volume, wherein said entrance grid comprises a plurality of openings, and wherein a size of each of said plurality of openings is selected to be sub-Debye length or smaller for said plasma such that a plasma sheath at a boundary of said plasma at said outermost plane remains relatively unperturbed and said plasma sheath does not penetrate said entrance grid and extend into the ion energy analyzer;
• wherein said second conductive electrode is configured to develop a DC self-bias voltage in said plasma,
• wherein said first conductive electrode is configured to be coupled to a negative DC voltage referenced to said DC self-bias voltage on said second conductive electrode,
• wherein said ion current collector is configured to be coupled to a positive DC voltage referenced to said DC self-bias voltage on said second conductive electrode,
• wherein a selected ion current received at said ion current collector is configured to be measured by an ion current meter, and
• wherein said aperture permits said selected ion current to flow from said plasma to said ion current collector.

A method of measuring IED of plasma at one or more locations in a plasma processing system, comprising:

• placing one or more ion energy analyzers at said one or more locations on a substrate holder in a plasma processing system;
• and
• measuring an IED at each of said one or more locations by performing the following:
• exposing an entrance grid to said plasma at a DC self-bias potential, said entrance grid being exposed to the bulk plasma volume and located at an outermost plane of said one or more ion energy analyzers, wherein said entrance grid comprises a plurality of openings, and wherein a size of each of said plurality of openings is selected to be sub-Debye length or smaller for said plasma such that a plasma sheath at a boundary of said plasma at said outermost plane remains relatively unperturbed and said plasma sheath does not penetrate said entrance grid and extend into the ion energy analyzer;
• biasing an electron rejection grid proximate to said entrance grid by a negative DC voltage to reject electrons from said plasma;
• biasing an ion current collector proximate to said electron rejection grid by a positive DC voltage to discriminate between ions reaching said ion current collector;
• measuring an ion current at said ion current collector using a current meter;
• storing said ion current as a function of said positive DC voltage on said ion current collector;
• and
• varying said positive DC voltage on said ion current collector.