Photoinduced Selective Deposition of Aluminium Thin Film Using Dimethylaluminum Hydride
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PHOTOINDUCED SELECTIVE DEPOSITION OF ALUMINIUM THIN FILM USING DIMETHYLALIJMINUM HYDRIDE MITSIIGU HANABUSA*,HI.DEKI OUCHI%,KENJI ISHIDA*,MASAHIRO KAWASAKI** AND SATOSHI SHOGEN" *Toyohashi University of Technology, Tenpaku. Toyohashi 441, Japan *'Institute for Electronics Science, Hokkaido University, Sapporo 060, ,Japan ABSTRACT Aluminum thin film was deposited via a photochemical surface reaction of dimethylaluminum hydride (DMAH) using a deuterium lamp. The period required to initiate the film growth differed with substrate, and making use of this result the film could be grown preferentially on silicon nitride and silicon oxide layers rather than on wet-etched silicon. On the basis of an x-ray photoelectron spectroscopy the observed dependence of photodeposition on substrate surfaces can be attributed to how DMAH is chemisorbed initially. I. INTRODUCTION Highly conductive aluminum thin film can 1e produced at low temperatures via a photochemical surface reaction. We have succeeded in this by using dimethylaluminum hydride (DMAH)[1,2]. The photochemical surface reaction was selected over a gas phase reaction, because it is useful for selective area deposition and also because the surface reactions are not as well understood. Photodeposition of aluminum films are greatly influenced by the choice of' the material for substrate and its surface state[3,4]. For growth on a wet-etched silicon, deposition became unstable unless it was do3ed with DMAH at room temperature prior to substrate heating needed for deposition (typicallly above 160 t). Furthermore, it was found that the coating of silicon with silicon nitride or silicon oxide eliminated the need for such a pretreatment of the substrate surface to obtain reproducible photodeposition. In the present work we extended the previous works to study the substrate dependence in more detail, expecting to achieve selective deposition of aluminum film on insulators. Such an attempt may bear a practical significance, since normally aluminum films are deposited preferentially on silicon. In addition, we carried out an x-ray photoelectron spectroscopy (XPS) study to show that the difference observed on various surfaces could be traced to the way how DMAH was adsorbed. Some preliminary results taken with XPS were described in the previous article[4], while more detail of the experiment is described here. 2. EXPERIMENTAL The experimental apparatus used for photodeposition based on a deuterium lamp was described in the previous articlesri-3]. The XPS analysis was performed with a VG Scientific unit (VG ADS-400) equipped with an Al Ka x-ray source. The pass energy of the analyzer was 20 eV, and the instrument resolution was 1.2 eV (FWHM). The silicon oxide layer was grown 200 nm thick on silicon (100) wafers in an oxygen-moisture atmosphere at 1200 t. The silicon nitride layer was prepared by low pressure chemical vapor deposition. The uncovered silicon was etched in a BHF solution, as described previously[l]. We followed the procedure shown in Fig. 1 to deposit the aluminum film;
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