Dr. Zhigang Xiao, Professor of Electrical Engineering at Alabama A&M University, in collaboration with the ALD group in the Kurt J. Lesker Company recently developed the plasma-enhanced atomic layer deposition process and grow high dielectric constant (K) oxide for the application of electronic materials. They grew nanoscale hafnium dioxide (HfO2) and zirconium dioxide (ZrO2) thin films using remote plasma-enhanced atomic layer deposition (PE-ALD) and fabricated complementary metal-oxide semiconductor (CMOS) integrated circuits using the HfO2 and ZrO2 thin films as the gate oxide. Miniaturization in modern semiconductor industry requires thin film deposition to have atomic level control and the deposited film to be conformal and pinhole-free. As MOSFETs are scaled down to nanometer sizes, the tunneling currents through the gate dielectrics (the gate leakage current) has become a major concern in today’s fabrication of integrated circuits (ICs). High-K dielectric metal oxide could be a solution to the problem of the gate leakage current. The plasma-enhanced atomic layer deposition of HfO2 and ZrO2 thin films meets the requirement and can produce conformal and ultra-thin films with precise thickness control at the atomic layer level. The experimental results measured from the HfO2 and ZrO2 thin films were compared. The findings were reported in the AVS 66rd International Exhibition & Symposium in Columbus, OH in October 2019 [Ref. 1] and published in the journal of Crystal [Ref. 2].
The HfO2 and ZrO2 thin films were grown at a low substrate temperature (270°C) with tetrakis (dimethylamino) hafnium (Hf[N(CH3)2]4) and Tetrakis (dimethylamino) zirconium (IV) (Zr[N(CH3)2]4) as the precursors, respectively. The X-ray photoelectron spectroscopy (XPS) measurements show that the ZrO2 film has the stoichiometric compositions with atomic concentrations of 34% Zr, 2% C, and 64% O, while the HfO2 film has the atomic concentrations of 29% Hf, 11% C, and 60% O. The high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) measurements show both films have polycrystalline structures with excellent interface with silicon [Ref. 2&4]. Figure 1 shows the HRTEM images of the cross-section of HfO2 and ZrO2 films.
MOSFETs, CMOS inverters, and CMOS ring oscillators were fabricated with the HfO2 and ZrO2 thin films as the gate oxide. The fabricated MOSFETs and CMOS inverters present excellent electrical current (I)–voltage (V) curves and transfer characteristics, while the fabricated ring oscillators demonstrated satisfactory oscillation waveforms, indicating that both HfO2 and ZrO2 thin films function very well as the gate oxide [Ref. 2].
The films were grown using a Kurt J. Lesker Company ALD-150LX atomic layer deposition (ALD) system equipped with a high vacuum load lock, 150mm wafer handling capability and integrated FS-1 in-situ ellipsometry for real-time film thickness monitoring. The ALD-150LX has substrate heating capability to 500°C, vapor draw and flow-through source delivery with independent input lines and remote inductive plasma capability utilizing ultra-high purity gases such as Ar, O2 for deposition of high-quality oxides. The ALD-150LX can be configured or upgraded to accommodate 15 precursors as well as 6 plasma gas lines.
 S. Banks, K. Bell, S. Chance III, B. Rodgers, and Z. Xiao, "Growth of Hafnium Oxide and Zirconium Oxide for the Fabrication of Electronic Devices Using Plasma-Enhanced Atomic Layer Deposition", presented in the AVS 66nd International Exhibition & Symposium in Columbus, OH in October 2019.
 Z. Xiao, K. Kisslinger, S. Chance, S. Banks, "Comparison of Hafnium Dioxide and Zirconium Dioxide Grown by Plasma-Enhanced Atomic Layer Deposition for the Application of Electronic Materials", Crystals, Vol.10, 136, 2020.
 G. B. Rayner, Jr., U.S. Patent No. 9,695,510, "Atomic Layer Deposition Apparatus and Process" (2017).
 Z. Xiao, L. Williams, K. Kisslinger, J. T. Sadowski, and F. Camino, "Fabrication of field-effect transistors with transfer-free nanostructured carbon as semiconducting channel material," Nanotechnology, 31, 485203 (2020). DOI: 10.1088/1361-6528/abb04a