AVS 65th International Symposium & Exhibition
    2D Materials Focus Topic Thursday Sessions
       Session 2D-ThP

Paper 2D-ThP1
Activated Reduction Plasma Assisted Sulfurization in Layered WS2 Synthesis

Thursday, October 25, 2018, 6:00 pm, Room Hall B

Session: 2D Materials Poster Session
Presenter: Chien-Pao Lin, ITRC,NARL, Taiwan, Republic of China
Authors: C.-P. Lin, ITRC,NARL, Taiwan, Republic of China
C.-N. Hsiao, ITRC,NARL, Taiwan, Republic of China
P.-S. Chen, No Matching Affiliation, Taiwan, Republic of China
C.-A. Jong, No Matching Affiliation, Taiwan, Republic of China
Correspondent: Click to Email
CVD process is known as a promising method in large domain size and continuous 2D film synthesis. Sulfurization of Group VIB contained precursor (metal or metal oxide) for sulphide formation were widely studied. Sulfur is also reported as reduction agent of metal oxide at initial stage. In some cases, H2 flew along with sulfur vapor during reduction time in MOCVD [1] and ALD [2] process. H2 could be beneficial in the impurity removal and to enlarge the domain size effectively.

Plasma source in vacuum technology is useful especially in lowering the process temperature and for increasing the precursor decomposition efficiency in CVD or ALD process. R. Morrish et al., revealed that a and longer than 30 min at 500oC for sulfurization process using 10% H2S plasma could reduce the activation energy between WO3 and H2S [3]. The presence of energetic radicals such as atomic S and H during sulfurization, the temperature and the exposure time are important.

In this study, we demonstrated the sulfurization process by two steps: (1) The energetic hydrogen (H*) generated by ICP plasma in WO3 reduction at early stage, (2) Reaction between the activated hydrogen (H*) and sublimated sulfur vapor for WS2 formation. The hydrogen concentration, plasma exposure time, the reaction temperature and duration time are evaluated for the sulfurization of WO3.

WO3 film was deposited on Si substrate covered by 90 nm thermal dry oxide. Samples were sulfurized in a 4 inch inductively coupled plasma (ICP) reactor with copper coil connected to a 13.56 MHz RF power supply. The reaction temperature varied from 700 to 900oC. Raman and PL spectrum were adopted for the film quality inspection. The surface roughness of formed WS2 layers were examined by AFM. The best condition performed when the reaction temperature was 850oC with 5% H2 plasma pre-treatment for 20min. Higher H% is harmful for film formation, which was similar to the report by K. N. Kang et al. that sulfurization can etch the damage of the film [4]. Raman and photoluminescence (PL) spectroscopy were taken with 532 nm excitation. The uniform Raman signals and PL spectrum within 4 cm2 are shown and the center of the PL peak was at 629 nm (1.97 eV).

Reference:

[1] K. Kang et al, Nature, 520, 656 (2015).

[2] Y. Kim et al, Sci rep., 6, 18754 (2016)

[3] R. Morrish et al., Chem. Mater. 26, 3986−3992 (2014)

[4] K. N. Kang et al., Scientific Reports, 5, 13205 (2015)