Ultraprecision 3D probing system based on spherical capacitive plate

In order to make ultraprecision dimensional and profile measurement of small structures with large aspect ratio possible, a 3D probing system based on a spherical capacitive plate is proposed for use in making 3D non-contact probing at nanometer resolution. A spherical capacitive plate with identical sensing characteristic in any arbitrary spatial direction is used to convert the micro gap between the plate and the part being measured into a capacitive signal. Most of the electric lines of force of the spherical capacitive plate concentrate within a small region between the plate and the part being measured, so that the properties of 3D non-contact probing, isotropy characteristics, approximate point sensing and measurability of small structures with large aspect ratio are effectively combined in one probing system. Experimental results indicate that when a 3 mm probing head is used, the probing system has a resolution of better than 5 nm. With nonlinearity corrected, the residual nonlinear error is less than 10 nm in the full-range. The proposed system can therefore be used for submicron measurement of small structures with dimension larger than 3 mm and depth down to 100 mm.