ALD for semiconductors can produce films that are high in H, C, O and metals. XPS and SIMS depth profile analysis for composition & purity.
Composition Depth Profiles
Photoelectron emission intensity has very little dependence on surface chemistry. Intensity is dependent mostly on surface concentrations. Thus XPS is known to provide very good quantitative composition measurements. Depth profiles are done by alternating sputter etching of the surface with analysis cycles.
The result is concentration vs. depth profiles with good quantification regardless of the material. However in some materials preferential sputtering of one element over another can alter the original composition.
XPS for Composition in ALD Films
XPS for Carbon and Oxygen in ALD Films
XPS (X-ray Photoelectron Spectroscopy)
SIMS (Secondary Ion Mass Spectrometry)
Trace Element Depth Profiles
SIMS has ppm to ppt detection limits for every element in the periodic table including H. A primary ion beam sputter etches the sample surface, both generating ions from the sample material that can be mass analyzed to determine the element.
Sputter etching forms a crater enabling sampling with depth. SIMS quantification depends on standards. The standard must have the elements of interest in the same matrix material. Quantification is generally valid from 1 at% to trace level.
SIMS for Carbon and Oxygen in ALD Films
SIMS for Composition in ALD Films
H, C, O, and Fe Profiles by SIMS
Background from H, C, N and O comes from the residual gas in the instrument vacuum system. Gas arrives at the sample surface and the likely-hood of sticking to the surface depends on the gas, the sample material and the condition of the surface. A freshly sputtered surface increases the likely-hood of the gas sticking.
In XPS depth profiling, the surface is sputter etched, sputtering stops, and the analysis cycle begins. During the analysis cycle, gas from the vacuum has a chance to accumulate on the surface.
In dynamic SIMS (except for TOF), the surface is continuously sputtered and thus background is a balance between residual gas arrival rate and sample sputter rate. The sample sputter rate is much higher than the residual gas arrival rate and thus dynamic SIMS background is several orders of magnitude lower than XPS.
The Choice of XPS for Depth Profile Analysis
The Choice of SIMS for Depth Profile Analysis
 C. Ozgit-Akgun, E. Goldenberg, A. Kemal Okyay and N. Biyikli, J. Mater. Chem. C 2 (2014) 2123.
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