Cryst. Res. Technol. 38, No. 3 – 5, 297 – 301 (2003) / DOI 10.1002/crat.200310034 2003 © 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 0232-1300/03/3-504-0297 $ 17.50+.50/0 Application of tungsten films for substrate masking in liquid phase epitaxial lateral overgrowth of GaAs D. Dobosz 1 , Z. R. Zytkiewicz* 1 , T.T. Piotrowski 2 , E. Kaminska 2 , E. Papis 2 , and A. Piotrowska 1 1 Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02-668 Warszawa, Poland 2 Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warszawa, Poland Received 17 October 2002, accepted 5 December 2002 Published online 15 April 2003 Key words epitaxial lateral overgrowth, selective epitaxy, lattice mismatched epitaxial structures, liquid phase epitaxy. PACS 81.05.Ea, 81.15.Lm, 68.35.Gy, 68.55.Jk Liquid phase epitaxial lateral overgrowth of GaAs layers on GaAs substrates masked by tungsten films was studied. We show that at our growth conditions perfect growth selectivity was obtained, so the layers started growing from the openings cut in the mask only. However, serious damage of the mask during epitaxial growth was observed. As this deteriorates crystallographic quality of the layers a procedure was elaborated to eliminate degradation of the tungsten film by the melt. In particular, reduction of growth temperature and deposition of Au/Zn wetting layers between tungsten film and the GaAs substrate were found important to avoid degradation of the mask and for successful lateral growth of the layers. Tungsten masked GaAs substrates were then used for lateral overgrowth of GaAs by liquid phase electroepitaxy. Preliminary results are presented showing that application of electrically conductive tungsten mask, which allows a direct DC current flow from the melt to the substrate, results in much wider and thinner electroepitaxial layers than those grown on the substrates coated by insulating film. 1 Introduction Epitaxial lateral overgrowth (ELO) is a method of epitaxial growth on partially masked substrates (see [1, 2] for reviews). First, the substrate is covered by a thin masking film and patterned by conventional photolithography and etching to form on its whole area a grating of mask-free seeding windows. Then, an epitaxial layer is deposited on such substrate. The epilayer nucleates on the seeds and the growth proceeds in a direction normal to the substrate. As soon as the crystallisation front exceeds the top layer of the mask, the growth starts in lateral direction over the masking film. ELO technique is used mainly to reduce defect density in lattice mismatched heteroepitaxial systems (see [3] for a review). However, homoepitaxial version the ELO technique also finds its practical application in production of silicon-on-insulator structures [4], MOS transistors [5], field effect transistors [6], solar cells [7], pressure sensors [8] and for three-dimensional device integration [9]. Usually, dielectric films (SiO 2 , Si 3 N 4 , etc.) are used for substrate masking. However, since it is well known that they may introduce additional strain into ELO layers [3, 10, 11] there is a great interest in use of other mask materials. Metal films may be very useful for substrate masking in ELO procedure. They are easy to process and may be further used as buried electrical contacts to devices deposited on ELO substrates [6]. However, the questions are whether metals stable enough to survive undamaged at the chemically aggressive conditions of epitaxial growth can be found and whether selective epitaxy without any nucleation on the mask is possible at all on metal-masked substrates. Tungsten masks were successfully used already to grow GaN ELO layers on sapphire by metalorganic vapour phase epitaxy [12]. Dramatic reduction of strain in the layers has been found when tungsten film instead of common dielectrics was used to mask the substrate. ____________________ * Corresponding author: e-mail: zytkie@ifpan.edu.pl