Temperature and hydrogen diffusion length in hydrogenated amorphous silicon films on glass while scanning with a continuous wave laser at 532 nm wavelength

Abstract

Rapid thermal annealing by, e.g., laser scanning of hydrogenated amorphous silicon (a-Si:H) films is of interest for device improvement and for development of new device structures for solar cell and large area display application. For well controlled annealing of such multilayers, precise knowledge of temperature and/or hydrogen diffusion length in the heated material is required but unavailable so far. In this study, we explore the use of deuterium (D) and hydrogen (H) interdiffusion during laser scanning (employing a continuous wave laser at 532 nm wavelength) to characterize both quantities. The evaluation of temperature from hydrogen diffusion data requires knowledge of the high temperature (T > 500 °C) deuterium-hydrogen (D-H) interdiffusion Arrhenius parameters for which, however, no experimental data exist. Using data based on recent model considerations, we find for laser scanning of single films on glass substrates a broad scale agreement with experimental temperature data obtained by measuring the silicon melting point and with calculated data using a physical model as well as published work. Since D-H interdiffusion measures hydrogen diffusion length and temperature within the silicon films by a memory effect, the method is capable of determining both quantities precisely also in multilayer structures, as is demonstrated for films underneath metal contacts. Several applications are discussed. Employing literature data of laser-induced temperature rise, laser scanning is used to measure the H diffusion coefficient at T > 500 °C in a-Si:H. The model-based high temperature hydrogen diffusion parameters are confirmed with important implications for the understanding of hydrogen diffusion in the amorphous silicon material.

Impact of Laser Treatment on Hydrogenated Amorphous Silicon Properties

“…For the CW laser study, deuterosilane (SiD 4 ) was used for the upper 50 nm so that the interdiffusion between the two hydrogen isotopes 1 H (H, hydrogen proper) and 2 H (D, deuterium) could be studied. [11] DOI: 10.1002/adem.201901437 Herein, the application of laser radiation to locally modify the hydrogen distribution within hydrogenated amorphous silicon films on a short time scale is studied. The impact of laser power and irradiation time on the temperature of the silicon layer during the laser treatment and the hydrogen outdiffusion is analyzed.…”

“…Laser treatments were performed in ambient atmosphere using laser sources with a wavelength of 532 nm. The conditions used for the CW treatment were reported in Beyer et al [11] A circular laser spot with Gaussian intensity profile was used. For the treatment with laser pulses, an Edgewave HD30II-E Innoslab was used.…”

“…The influence of the laser treatment on hydrogen diffusion was studied by secondary ion mass spectrometry (SIMS) measurements, [11] and on hydrogen concentration by both SIMS and Raman spectroscopy in backscattering mode. [16] Here, a Raman excitation wavelength of λ ¼ 532 nm was used, which led to a Raman information depth of %50 nm [16] due to the Beer-Lambert law.…”

“…The temperature in the laser spot can be calculated from the treatment conditions. [11] For the scan speed of 2 mm s À1 (t* ¼ 0.35 s) a temperature of T % 780 C is determined, while for the scan speed of 10 mm s À1 (t* ¼ 0.07 s) a temperature of T %500 C is obtained. Note that the spike in hydrogen concentration at a (relative) sputter time of t ¼ 0.25 marks the interface between the hydrogenated and the deuterated material.…”

“…In this work, we first discuss some results obtained using a continuous wave (CW) laser which clarify the relation [11] between hydrogen diffusion in bulk material, hydrogen outdiffusion, and the optical photodarkening effect.…”