SPI Supplies
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Brand Silicon Nitride Membrane Window Grids for TEM
Methods used for membrane thickness measurements
Measurement of membrane thickness:
We understand how important it is for some users of our membrane grid products to know the membrane thickness with some degree of accuracy and precision. Making these measurements does add to the cost, and does add value to our product, but we know that for some, the outcome of their experiments depends on the reliability of the value cited for membrane thickness. In order to give credibility to our numbers, we disclose our methods of membrane thickness measurement. It does require some mount of specialized equipment and instrumentation, and of the type not typically found in many laboratories. When you purchase the SPI Supplies brand of membrane window and grids, you can be sure of the best possible characterization of membrane thickness.
The methods:
All incoming wafers are batch checked with ellipsometry. We check the first, last and several intermediate wafers and if all are within our needed specification, then we assume the whole batch will also be within specification. If any are out of specification, then they are removed and we work along the batch length until we reach acceptable thickness. This is very unusual and does not happen very often. But it does happen. The thickness specification is nominal - i.e. +/- 10% - a 100 nm thick membrane should be between 91 and 100 nm thick but is typically between 95 and 105 nm. Having said that, membrane to membrane variation within a batch is normally within 2% and thickness variation across a single membrane within 1%.
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Tuesday September 30, 2008
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