Atomic Layer Deposition of Nanostructured Tunable Resistance Coatings: Growth, Characterization, and Electrical Properties

Abstract

We have developed ALD method to synthesize nanocomposite coatings comprised of conducting, metallic nanoparticles embedded in an amorphous dielectric matrix. These films are nominally composed of M:Al2O3 where M= W or Mo, and are prepared using alternating exposures to trimethyl aluminum (TMA) and H2O for the Al2O3 ALD and alternating MF6/Si2H6 exposures for the metal ALD. By varying the ratio of ALD cycles for the metal and the Al2O3 components in the film, we can tune precisely the resistance of these coatings over a very broad range (e.g. 1011-104 Ohm-cm). These films exhibit Ohmic behavior and resist breakdown even at high electric fields of 107V/m. Moreover, the self-limiting nature of ALD allows us to grow these films inside of high aspect ratio substrates and on complex, 3D surfaces. To investigate the ALD growth mechanism for the nanostructure composite films we employed in-situ quartz crystal microbalance (QCM), quadrupole mass spectrometry, and Fourier transform infrared (FTIR) absorption spectroscopy studies. For M:Al2O3 films, QCM showed that the metal ALD inhibits the Al2O3 ALD and vice versa. Despite this inhibition, the relationship between metal content and metal ALD cycle percentage was close to expectations. Depth profiling X-ray photoelectron spectroscopy showed that the M:Al2O3 films are uniform in composition and contained Al, O, and metallic Mo or W as expected, but also presence of moderate F and C. Attempts were also made to investigate the TMA as reducing precursor for MF6 and resulted in similar kind of resistive coatings but very significant F and C which shows influence on microstructure of the layers. Cross-sectional transmission electron microscopy (XTEM) revealed the film microstructure to be metallic nanoparticles (~1-2 nm) embedded in an amorphous matrix. The transport properties of these M:Al2O3 were studied as function of ratio of metal to Al2O3ALD cycles.We have utilized these nanocomposite coatings to functionalize capillary glass array plates to fabricate large-area MCPs suitable for application in large-area photodetectors. In addition, we have applied these films to serve as charge drain coatings in MEMS devices for a prototype maskless electron beam lithography tool, permitting high resolution electron beam patterns without charging artifacts. Here we will discuss the ALD growth, characterizations, and applications of ALD tunable resistive coatings.