A Study on unique Crystal Morphology observed in the Polycrystalline Copper CVD
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A Study on unique Crystal Morphology observed in the Polycrystalline Copper CVD Yuneng Chang, Yalian Chen, Kuanhon Chen [email protected] Lunghwa Institute of Technology, Dept. of Chemical Engineering, No. 300 Sec.1, Wan show Road, Guayshan, Taoyuan 333, Taiwan, R.O.C. ABSTRACT Nanostructure copper whisker growth was observed in an atmospheric pressure chemical vapor deposition (CVD) system, which used copper acetylacetonate vapor and 10-15 torr of water vapor as reactants, with 0.04-0.10 torr of chromium acetylacetonate vapor added as growth promoting catalyst. Water vapor initiated nucleation of these helical, spiral shape Cu(111) and (200) polycrystalline whiskers. While chromium acetylacetonate accelerated the growth rate. Copper whiskers had radii from 0.1 to 0.24 µm, lengths from 1 to 10 µm, and distribution density of 0.20-3.6 whiskers/µm2. Dependence of such whisker characteristics on temperature, partial pressures of H2O and chromium acetylacetonate was used to construct a kinetic model. From the Arrhenius equation, data analysis for whisker growth rate against deposition temperature showed that the activation energy for whisker growth along radial direction is 12.4 kcal/mol, and 19.6 kcal/mol for growth along axial direction. Based on such data and SEM observations, a base vapor-liquid-solid (VLS) model involving BCF theory was proposed to describe the governing mechanism for the axial growth. This model interpreted the competitive growth phenomena in both radial and axial directions, and controlling steps for radial and axial growth being assigned to mass transfer and surface reaction, respectively. Key words: Chemical vapor deposition, CVD, whisker, copper, acetylacetonates INTRODUCTION Due to potential applications and local economic market aspect, CVD of copper and related bimetallic oxide compounds using metal acetylacetonates have been a research project for several years in this group since 1990s[1]. In a study to investigate the CVD of copper chromite (CuCr2O4) spinel phase using copper acetylacetonate, Cu(C5H7O2)2 and chromium acetylacetonate, Cr(C5H7O2)3. As oxygen was replaced with water vapor as co-reactant to explore the chemical system, it was discovered that the deposits being primarily fibrous like polycrystalline copper deposits, but not copper chromite [2]. The analysis results indicated that such fibrous deposits being polycrystalline copper “whisker”. There are some differences between classical vapor grown whiskers and the materials found in the metal acetylacetonate/water vapor CVD system. As whiskers are usually single crystal, straight with sharp tips, whereas the fibrous copper deposits were polycrystalline, spiral or helical shape with round tips. Since the vapor grown whisker model is well established, we use this model to describe our observations. Whisker is a unique form of crystalline morphology with large aspect ratios to several hundreds. Whiskers can be produced by vapor growth techniques such as CVD or chemical vapor transport (CVT) technology. Industrial scale grown fil
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