Development Of A Testing Platform For Electrogenerated Chemical Polishing With Large Area Tool Based On The Principle Of Hydrostatic Support

Electrogenerated chemical polishing (EGCP) is a new ultra-precision surface processing technique, and has a great potential for use in ultra-precision machining of defect-free surfaces. In EGCP, the redox mediator in a polishing solution is changed into an etchant by electrochemical oxidation on an ultra-smooth electrode, and then the workpiece surface is polished through chemical etching by the etchant. The closer the workpiece to the electrode surface, the higher the etching rate, which is called "gap-sensitive etching". Therefore, an ultra-flat working electrode and uniform processing gap are key factors in EGCP. An ultra-flat working electrode is easy to obtain, but a uniform yet small enough processing gap is difficult to achieve. High precision control of the processing gap is necessary when EGCP is used to process large area workpieces.Based on the principle of the hydrostatic support, a novel micro-gap control method is proposed. A relationship between gap and inlet pressure is derived theoretically, and dominant factors are revealed. Through a rational choice of the hydrostatic parameters and precise adjustment of pumping pressure, a micro-gap control apparatus is developed which realizes 1 μm alignment accuracy and ±0.2 μm repetitive positioning accuracy with a large processing area (50 mm in diameter).In order to obtain large area work electrode applied to EGCP, two kinds of work electrodes, sputtered gold film electrode and carbon glass embedded electrode, are designed and manufactured. Also, the characters of the two kinds of electrodes are tested.The micro-gap control apparatus based on the hydrostatic support is successfully applied to the EGCP of Cu by an ultra-smooth electrode (with radius 25mm). It is found that the whole region covered by the working electrode is etched. The PV value of etched region is reduced to 120 nm from 290μm. The etching depth is about 0.35μm and the average roughness (Ra) of the Cu surface is reduced to 4 nm from 82 nm. When the work electrode rotates in EGCP, the planarization effect is not distinct compared with no rotation. However, the average roughness (Ra) is still improved from 216 nm to 6 nm.