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Precursors for the Atomic Layer Deposition of Electropositive Metal Films (invited)

3:40 pm - 4:20 pm

Our laboratory is developing new chemical precursors for the growth of electropositive metal and element thin films by atomic layer deposition (ALD). We are also interested in processes that exhibit area selective growth. ALD has many current applications in copper metallization, diffusion barriers, liners, and transistor fabrication. Thermal ALD is often preferred because plasmas can afford low conformal coverage due to radical recombination on the walls of deep and narrow features.  There has been extensive progress in the thermal ALD of copper and noble metal films in recent years, because the positive electrochemical potentials allow relatively easy reduction of precursor ions to the metals. Thermal ALD approaches to most other metals and elements in the periodic table are not well developed, due to the negative electrochemical potentials of the ions and a current lack of ALD co-reagents that can convert the ions to the metals or elements. Herein, we will describe the thermal ALD growth of electropositive metals such as nickel, cobalt, aluminium, and others. The ALD of nickel and cobalt metal films has been achieved using precursors containing diazadienyl ligands (precursors 1 and 2). These precursors enable the deposition of cobalt and nickel metal films at temperatures below 200 °C and use alkylamines as benign co-reagents. Growth rates are high (0.60 Å/cycle for nickel, 0.98 Å/cycle for cobalt), high purity, low resistivity metal films are obtained, and the films have low rms roughnesses. The processes exhibit inherent selective growth on metal substrates such as platinum, ruthenium, and copper. By contrast, no growth is observed on insulating substrates. We will also overview a new thermal ALD process for the growth of aluminum metal films. This process entails treatment of surface-bound AlCl3 with a thermally stable, volatile aluminium hydride co-reagent. The growth rate for the aluminium metal ALD process is high, and high purity, low resistivity aluminium metal films are obtained. Prospects for the area selective growth of aluminum metal films will be presented. These examples demonstrate that ALD processes can be enabled for electropositive metals through careful design of precursors and chemistry.  

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Speaker

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Prof. Charles H. Winter

Professor, Wayne State University

Charles H. Winter, Ph.D. has been in the Chemistry Department at Wayne State University since 1988. Professor Winter’s research efforts are directed toward the development of new precursors and processes for the thermal ALD growth of electropositive metal thin films. These materials are difficult to grow by thermal ALD with currently available precursors. Recent metals that have been deposited by thermal ALD in the Winter laboratory include cobalt, nickel, titanium, and aluminum.

Winter obtained his B.S. degree from Hope College in 1982. He then went on to the University of Minnesota, and obtained doctoral degree in organic and organometallic chemistry in 1986 under the direction of the late Prof. Paul G. Gassman. After an NIH postdoctoral fellowship in organometallic chemistry with Prof. John A. Gladysz at the University of Utah, he joined the faculty at Wayne State University in 1988, where he is currently Professor of Chemistry.