The NanoOCD/DUV 9010 measures thin-film and film-stack thickness on pads as well as that of oxides, nitride and trench profiles on arrays. Use of Mercury 3000 position encoders (right) provides sufficient bandwidth and precision to let the tool examine 300 wafers/hr.

New metrology equipment can resolve distances down to 19 nm on semiconductor wafers through use of positioning gear that incorporates special optical encoders.

The NanoOCD/DUV 9010 is said to be the first metrology tool to combine UV optical critical dimension spectroscopic ellipsometry and deep UV-spectroscopic reflectometry. It measures the thickness of thin films stacked up on 300-mm wafers created through various cutting-edge processing techniques such as copper CVD, dielectric CMP, CVD, and poly-Si or dielectric etch.

The manufacturer, Nanometrics Inc., Milpitas, Calif., custom designed a stage to handle the precision motion needed to get high resolution in X and Y directions on the wafer surface. Two linear motors do the work with position and velocity feedback coming from miniature Mercury 3000 programmable encoders from MicroE Systems Inc., Natick, Mass. A servomotor that rotates the wafer and a voice-coil actuator that focuses the instrument optics also employ the small encoders.

The 8.4-mm-tall optical encoder took up little space. Its programmability simplified the instrument design -- one model of encoder can handle the differing resolution requirements for each axis on the instrument. MicroE also modified the standard encoder design to minimize its footprint and boost the overall performance of the instrument.

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