Insertion effect of the 3-nm-thick Co(Pt) layer on AlN preferred orientation and residual stress in the c-axis textured
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Insertion effect of the 3-nm-thick Co(Pt) layer on AlN preferred orientation and residual stress in the c-axis textured AlN film Takashi Harumoto1,2, Shinji Muraishi1, Ji Shi1, Yoshio Nakamura1 and Takashi Ishiguro2 1 Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1-S8-6 O-okayama, Meguro-ku, Tokyo, 152-8552, Japan 2 Department of Materials Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan ABSTRACT The effect of the continuously inserted 3-nm-thick Co(Pt) layer on the preferred orientation of AlN film is investigated, and highly c-axis textured AlN film has been obtained. According to high resolution transmission electron microscope observations, the preferred orientation of sputter-deposited AlN film is improved from polycrystalline to (001) texture at the interface between AlN and Co(Pt)(111). The texture of AlN films are also examined using an xray diffractometer equipped with a two dimensional positive sensitive detector. The x-ray rocking curve full width at half maximum of 002AlN of (001) textured AlN with the Co(Pt) layer is 2.7°, and the residual stress of such specimen is 1.6 GPa in tensile stress. INTRODUCTION Aluminum nitride (AlN) films are adopted as piezoelectric films for bulk acoustic wave (BAW) resonators [1]. As AlN exhibits piezoelectric property along its c-axis, AlN films for BAW resonators should be c-axis orientated and the fabrication conditions for c-axis deposition have been investigated. It is generally known that the texture of bottom electrode influences the preferred orientation of following AlN and (111) plane of face centered cubic (fcc) and (110) of body centered cubic (bcc) enhance the c-axis texturing [1,2]. Thus, it is essential to fabricate strongly oriented bottom metal layer. According to the study of Kamohara et al., Mo deposited onto AlN/substrate exhibits strong (110) preferred orientation and such Mo layer improves the texture of AlN considerably [2]. However, the deposition of such multilayer structure yields the additional deposition process, as the deposition of AlN is conducted in Ar-N2 mixture gas while Mo is in Ar. Our previous study has shown that fcc-Co(Pt)/AlN multilayer could be obtained continuously without gas exchange [3,4]. In such multilayer, fcc-Co(Pt) layer is (111) textured and AlN layer exhibits c-axis preferred orientation. The Pt/AlN multilayer deposited in the same manner has been applied as a seed layer for fabricating (001) textured AlN films [5,6]. In this research, the preferred orientation of AlN film is dramatically enhanced using a continuously inserted 3-nm-thick fcc-Co(Pt) layer. EXPERIMENT AlN films and Co(Pt) layer have been deposited onto Si(100) substrate with the native oxide using the apparatus equipped with two pairs of facing targets. One pair of facing Al targets
is discharged with direct current (d.c.) power supply in Ar-N2 mixture gas. The gas composition is Ar-30%N2 and the sputtering pressure is 0.2 Pa. As Al reacts with nitrogen, AlN forms on the
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