Low Temperature Plasma for Compositional Depth Profiling of Thin Inorganic Multilayers
Shinichiro Muramoto, Joseph A. Bennett
RATIONALE: A helium low temperature plasma (LTP) containing 0.01% of SF6 was evaluated as a way to prepare bevel craters for the compositional depth profiling of thin inorganic multilayers. By using LTP and time-of-flight secondary ion mass spectrometry (TOFSIMS), inorganic depth profiling could be performed without the need for a separate sputter source. METHODS: A model inorganic thin multilayer system consisting of four 10 nm layers of silicon separated by three 50 nm layers of tungsten metal was used to evaluate the quality of two depth profiling approaches: SIMS sputter depth profiling and a TOFSIMS compositional bevel depth profiling of the plasma-etched crater. The depth profile quality was determined by measuring the FWHM and 1/e decay lengths of the buried Si layers. RESULTS: Using a substrate temperature of 100 ºC during plasma etching, the FWHM determined from the plasma crater edge averaged (6.4, 10.9, and 12.5) nm for the 2nd, 3rd, and 4th Si layers, respectively, while those obtained from the SIMS depth profile averaged (8.5, 9.9, and 10.9) nm, respectively. These values were very close to the actual layer thickness of 10 nm, and demonstrated the ability of plasma etching for effective depth profiling of Si/W multilayer systems. CONCLUSIONS: Plasma etching was found to be an effective method for preparing samples for compositional depth profiling of inorganic films. Its major benefit was the lack of ion bombardment artifacts such as mixing and roughening that could lead to a significant degradation of depth resolution.