Energy distribution measurements in radio frequency plasma discharges using a cubical analyzer

A compact and inexpensive cubical energy analyzer has been developed to measure ion and electron energy distributions at the boundaries of a rf plasma. It consists of two grids parallel to the plasma boundary behind which lies a 1 cmX 1 cm X1 cm cube. The absorbed current and voltage on the grids and on each face of the cube can be monitored and biased independently. A Helmholtz coil on the outside of the cube allows a 0–15 G field to be produced perpendicular to the path through the gridded apertures. The advantages over standard gridded energy analyzers include direct measurements of ion-induced secondary electrons and separation of electrons, negative ions, and heavy and light mass positive ions to different collection surfaces. Measurements of the ion and electron energy distributions at the grounded electrode of a parallel plate 13.56 MHz plasma discharges clearly show a time-varying rf sheath and a non-Maxwellian electron energy distribution. Data is presented for Ar, CH₄, and H₂plasmas.