Secondary Yield Enhancement Research Articles

Abstract: Characterization of multilayer thin films using secondary ion mass spectrometry and improvement of the analytical techniques

Secondary ion mass spectrometry (SIMS) has been shown to be a highly sensitive analytical technique for characterizing thin films. 1 In depth analysis results because of the inherent nature of the sputtering process. With the more sophisticated SIMS instruments an imaging mode is provided which also gives a spatial distribution analysis. When this spatial information is combined with depth analysis a truly three−dimensional characterization results. It has been shown that this combined analysis can prevent confusing variations in spatial distribution with uniform depth gradients in depth profile analysis. The most important advantage the SIMS technique has over other analytical techniques with good depth profiling capability (e.g.: Auger electron spectroscopy, AES) is that a much higher sensitivity can be achieved with SIMS. In favorable cases where the ion yield is high and large areas (diam ≳ 50 μ) are available this sensitivity has been shown to be 104 to 105 times higher than any other analytical techniques applicable to depth profiling. The depth profiles described in this paper have been obtained with a specific SIMS instrument. This is the direct imaging mass analyzer developed by Cameca following the original concepts of Slodzian and Castaing. 2,3 This instrument has been shown to be well suited to the depth profile analysis of multilayer thin films. The principal advantages and disadvantages of the SIMS technique are the following: Advantages: (1) A very high gram detection sensitivity (10−15−10−19 g) can be achieved. (2) Rapid depth profiling is possible (up to 500 Å/sec). (3) All elements can be detected (inert gases excepted). (4) A very high detection sensitivity occurs for the very light elements. (5) Surface into bulk analysis can be performed in the same experiment. Disadvantages: (1) Many polyatomic cluster ions are generated by the sputtering process which produce serious mass interferences, particularly at higher masses. (2) Secondary ion yield enhancement effects from the presence of reactive elements seriously interfere with quantitation. (3) Sputtering artifacts can limit depth resolution. (4) The destructive nature of sputtering limits certain types of analysis. These points are illustrated in the study of a series of multilayer thin films which have undergone various heat treatments producing interdiffusion. The principle limitation of SIMS depth profiling (item 1 above) is mass interference. This problem is considerably minimized when high mass resolution (m/Δm≳3000) is available. Recently an electrostatic analyzer has been integrated into the Cameca IMS 300 design which converts the geometry into a Neir Johnson type configuration. 4 This design allows a mass resolution up to 5000 to be achieved which greatly increases the applicability of the instrument for depth profiling and other microanalytical applications.