Highly hydrogen-sensitive thermal desorption spectroscopy system for quantitative analysis of low hydrogen concentration (∼1 × 10¹⁶ atoms/cm³) in thin-film samples

We developed a highly hydrogen-sensitive thermal desorption spectroscopy (HHS-TDS) system to detect and quantitatively analyze low hydrogen concentrations in thin films. The system was connected to an in situ sample-transfer chamber system, manipulators, and an rf magnetron sputtering thin-film deposition chamber under an ultra-high-vacuum (UHV) atmosphere of ∼10⁻⁸ Pa. The following key requirements were proposed in developing the HHS-TDS: (i) a low hydrogen residual partial pressure, (ii) a low hydrogen exhaust velocity, and (iii) minimization of hydrogen thermal desorption except from the bulk region of the thin films. To satisfy these requirements, appropriate materials and components were selected, and the system was constructed to extract the maximum performance from each component. Consequently, ∼2000 times higher sensitivity to hydrogen than that of a commercially available UHV-TDS system was achieved using H⁺-implanted Si samples. Quantitative analysis of an amorphous oxide semiconductor InGaZnO₄ thin film (1 cm × 1 cm × 1 μm thickness, hydrogen concentration of 4.5 × 10¹⁷ atoms/cm³) was demonstrated using the HHS-TDS system. This concentration level cannot be detected using UHV-TDS or secondary ion mass spectroscopy (SIMS) systems. The hydrogen detection limit of the HHS-TDS system was estimated to be ∼1 × 10¹⁶ atoms/cm³, which implies ∼2 orders of magnitude higher sensitivity than that of SIMS and resonance nuclear reaction systems (∼10¹⁸ atoms/cm³).