Hydrogen depth profiling with nanometre resolution

The amount of hydrogen in semiconductors can highly influence electrical, physical and chemical properties on a microscopic as well as on a macroscopic scale. Many applications in the micro electronics industry, in solar cell research and in surface science require the precise knowledge of the actual hydrogen concentration and its concentration distribution near the surface. Nuclear Reactions Analysis (NRA) has been successfully established as a standard technique in chemical analysis within recent decades. In the particular case of hydrogen depth profiling the so-called ¹⁵N-method became one of the most successful, non-destructive and standard-free analysing technique. This method is based on the nuclear reaction ¹⁵N(¹H,αγ)¹²C, which is characterized by a pronounced resonance at 6.385 MeV. By variation of the initial ¹⁵N-ion energy the depth in the sample where the ¹⁵N resonance energy is reached can be easily adjusted according to the particular ion stopping in the material. Thus, a depth sensitive measurement of the absolute H-concentration becomes feasible. Using grazing incident angles the depth resolution near the surface can reach 1 nm. Detection limits under optimum conditions are as low as 0.05 at%. Fundamentals of the ¹⁵N-method and experimental set-up at the 6 MV accelerator at the FZD as well as particular examples of hydrogen depth profiling in ongoing state-of-the-art experiments are presented.