GaAs and Si Assisted Etching using a Scanning Tunneling Microscope
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GaAs AND Si ASSISTED ETCHING USING A SCANNING TUNNELING MICROSCOPE MASAKAZU BABA AND SHINJI MATSUI Fundamental Research Laboratories, NEC Corporation, 34, Miyukigaoka, Tsukuba, Ibaraki, Japan
ABSTRACT GaAs etching with Cl 2 gas is studied with a scanning tunneling microscope (STM). Both Cl 2 gas and tunnel electron assist etching occur under the tip during scanning and the etching profile is found to depend on the gas flow time. GaAs and Si patterns with nanometer dimensions are fabricated by STM assist etching with a very low voltage (-IV). Also atomic layer etching of GaAs is demonstrated by STM assist-etching using a Cl adlayer.
INTRODUCTION The scanning tunneling microscope (STM) has been used as a very powerful tool for analysis of semiconductor, metal, organic and other materials. It has recently been used for atomic level fabrication. STM has atomic resolution and positioning accuracy, making it useful in atomic-level fabrication. To date, many papers on atomic-scale fabrication have been reported. These fabrication mechanisms used mechanical method, electrical energy, chemical reactions, heat energy and control of atomic force.[1]-[5] Direct writing for deposition and etching are achieved by using electron beam induced selective etching and deposition (EBISED).[61 The STM electrical fields are produced in atomic size, and electron energy varies from field emission to tunneling level. In STM-EBISED, the electrons from the tip or sample cause source-gas molecules adsorbed on the substrate to dissociate. It has been reported that carbon and W deposition patterns with a 10-nm linewidth can be fabricated by STM-EBISED.[7] Moreover, etching of Si with STM has also been demonstrated.[8] In this paper, we describe in-situ observation of Cl2 gas etching of GaAs with STM and etching patterning of GaAs and Si using STM-EBISED. EXPERIMENTS The STM nanofabrication system is shown in Fig. 1. This system was constructed by modifying a conventional STM apparatus (USM-201, made by UNISOKU Corp.). The STM unit was assembled within a vacuum chamber into which gases could be introduced through a variable leak valve. This chamber is evacuated with a turbo molecular pump, and a base chamber pressure of 1.OxlO -7 Torr is established. Scanning areas from 50x50 nm2 to 3000x3000 nm2 can be selected. The vertical resolution is 0.3 nm. Pt mechanical tips were used. Imaging was typically performed using the regular constant current mode with a steady-state sample voltage of -1 V and a constant current of 1 nA. The temperature of the substrate was controlled from room temperature to 120TC. Cl2 and CIF 3 gases were used for etching of GaAs(100) and Si(1 11) Mat. Res. Soc. Symp. Proc. Vol. 236. @1992 Materials Research Society
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substrates, respectively. Of X107In the base pressure of lxl0" Torr, the surfaces of samples were covered by an oxide layer. The GaAs oxide layer was easily removed with C½.gas by heating the substrate above 65"C at the beginning of the etching process. On the other hand, the Si oxide layer was easily remov
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