Pulsed DC Reactive Magnetron Sputtering of AlN Thin Films on High Frequency LTCC Substrates
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Pulsed DC Reactive Magnetron Sputtering of AlN Thin Films on High Frequency LTCC Substrates Jung W. Lee*, Jerome J. Cuomo*, Baxter F. Moody*, Yong S. Cho** and Roupen L. Keusseyan** *Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695, USA **DuPont Electronic Technologies, Research Triangle Park, NC 27709, USA
ABSTRACT This preliminary work reports the preparation of AlN thin films on an LTCC (low temperature co-fired ceramics) substrate by pulsed dc reactive magnetron sputtering and the limited characterization focusing on microstructure and crystal orientation. The main focus will be placed on the effects of changing pulsed frequency. The AlN thin film showed good adhesion with the substrate and columnar structures having small grains regardless of pulsed frequency. The crystal orientation of AlN thin films was dependent on pulsed frequency according to the result of XRD patterns. The preferred (002) orientation was obtained at a pulsed frequency of 100 kHz. The broad band of 300 to 650 nm observed in photoluminescence spectrum was believed due to defects associated with the presence of oxygen impurities. INTRODUCTION The LTCC technology has been recognized as a key solution concerning ceramic interconnect technologies particularly for automotive and telecommunication applications.1-3 Most of commercially available LTCC substrates possess very low thermal conductivities (~3 W/mK) since LTCC usually consists of low thermal conduction glass and ceramic materials. In particular, higher thermal conduction is required for certain LTCC –based modules or devices. This preliminary work is intended to find a potential solution to improving the thermal dissipation of the low thermal conduction LTCC substrates by depositing high thermal conduction AlN thin films on the LTCC substrate. Besides its high thermal conductivity (ktheo = 320 W/mK), aluminum nitride has many useful properties for electronic packaging applications including low thermal expansion coefficient (good thermal expansion match with Si and common LTCC substrates), high resistivity, low dielectric constant and dielectric loss at high frequencies, and high dielectric breakdown strength.4 Heat is carried by phonon (quantized lattice vibration) in nonmetallic solid like aluminum nitride. The phonons are scattered by various sources (defects, grain boundary, pores and other phonons etc) while the phonons travel. Lambropoulos et al.5,6 studied the thermal conductivities of thin films based on a large variety of materials such as oxides, fluorides, nitrides, amorphous metals and superconductors. The values are as much as two orders of magnitude lower than that of corresponding bulk solid. They attributed this difference to the unique microstructure of thin films, which prevents them from exhibiting bulk-like properties. When deposited with physical deposition methods like sputtering, these films may contain voids, pinholes and nodular defects, reducing the density and integrity of the film. Kuo et al.7 reported that the t
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