Chemical Vapor Deposition of Germanium Nanocrystals on Hafnium Oxide for Non-Volatile Memory Applications
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Chemical Vapor Deposition of Germanium Nanocrystals on Hafnium Oxide for Non-Volatile Memory Applications Ying Qian Wang, Jing Hao Chen, Won Jong Yoo, and Yee-Chia Yeo. Silicon Nano Device Laboratory (SNDL), Department of Electrical & Computer Engineering, National University of Singapore, Singapore 117576.
ABSTRACT In this paper, we investigate the chemical vapor deposition (CVD) of Ge nanocrystals (NCs) directly on hafnium oxide HfO2 dielectric for non-volatile memory applications. Germane GeH4 was used as a precursor. Atomic force microscopy (AFM), X-ray diffraction (XRD), Xray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to characterize the Ge NCs. The dependence of the Ge NC size and density on the deposition temperature, deposition time, and flow rate was explored. A high Ge NC density of 1011 cm-2 was obtained at a deposition temperature of 600ºC, with a mean diameter of about 16 nm. MOS capacitors with CVD Ge NCs embedded in the HfO2 gate dielectric were fabricated. Hysteresis of capacitance-voltage (C-V) characteristics of capacitors with Ge NCs was observed, demonstrating memory effect. INTRODUCTION Flash memory devices employing nanocrystals (NCs) have received considerable attention as one of the promising candidates for future non-volatile, high density, and low power memory devices. Currently, commercial nonvolatile floating gate flash memory devices employ a continuous poly-Si floating gate and a thick SiO2 tunnel oxide to achieve ten-year retention time, resulting in high programming voltage, and slow programming speed. To meet future scaling requirements, the trade-off between data retention and program efficiency should be improved [1]. By using discrete NCs instead of continuous floating gate as charge storage nodes, local defect related leakage can be effectively reduced efficiently, and this can result in improvement of data retention [2]. By using a high-permittivity (high-k) dielectric in place of the conventional SiO2 based dielectric, NCs flash memory can achieve significantly improved programming efficiency and data retention [3-4]. To date, work on the integration of NCs with high-k dielectric materials has been limited. Ge NCs embedded in Hf-based dielectrics as the most attractive and promising high-k dielectrics were studied only recently [5]. In this study, we investigate the formation of Ge NCs by CVD on HfO2 dielectric. The influence of the CVD process parameters, such as CVD temperature, flow rate of the gas precursor, and deposition time, on the characteristics of the Ge NCs was studied. By optimizing the process conditions, we were able to achieve a Ge NC density of 1011cm-2 on HfO2. A capacitor with Ge NCs integrated with HfO2 dielectric was fabricated by a CMOS-compatible process. Memory effect due to the insertion of the Ge NCs was observed.
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GE NCS DEPOSITION ON HfO2 AND CHARACTERIZATION P-type Si (100) substrates were used in this experiment. Surface nitridation of the substrates was performed at 700ºC for 60 sec. in an
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