Plane-strain Bulge Test, introduced by Vlassak and Nix, is a powerful approach to test the mechanical properties of nano-scaled thin films. A free-standing sub-micron thick film is deposited on a rectangular window (2a×2b) which can be manufactured with the standard MEMS techniques on Si wafer. Applied with pressure on the backside, the film deforms under the plane-strain condition.

MEMS technique, which has been developed since last century, helps making high-quality, small-scaled specimen for bulge test. Micro-machining by anisotropically etching single crystal Si wafer with KOH solution has well known as an efficient way to make sharp and clean rectangular windows on small chips.

Another technique is called “photolithography”, which provides a way to make any pattern people like on a chip. Reactive ion etching (RIE) is another method to etch Si (SiN and SiO2, too), however, isotropically.

With the fabrication process shown above, I can make a thin, clean and low-prestressed film. Since film is deposited after KOH etching, it avoids being put into 80 °C solution for hours.