Plasma-assisted ALD of TiN/Al2O3 stacks for MOS trench capacitor applications

Abstract

The increasing demand for high performance and multifunctional electronic products requires more efficient system integration technologies. System in Package technology is a recent development in silicon based packaging technology. For integration of passives large interest exists in high-density MOS (Metal Oxide Semiconductor) trench capacitors for rf decoupling and filtering applications, with which high capacitance densities can be realized. To realize this, Atomic Layer Deposition (ALD) is used for deposition of oxides and metals in high aspect ratio structures. In this work the application of plasma-assisted ALD TiN/Al2O3 stacks deposited in situ at a single deposition temperature is studied for trench MOS capacitors. This investigation is pursued in three steps. First as-deposited planar TiN/Al2O3/p-Si stacks are characterized. Here, the objective is to gain a fundamental understanding of the processing and characterization of MOS trench capacitors. Based on this characterization possibilities for optimization of performance and processing are strived for in the next step. Finally, TiN/Al2O3 stacks are deposited in high aspect ratio trenches and its performance is characterized for MIM and MIMIM trench capacitors. The measurement and analysis techniques can be categorized into structural and electrical measurements. With structural measurements properties such as the atomic composition and the crystal structure are investigated. Electrical measurements include I-V and C-V measurements, which are extensively applied in this work. Prior to the processing of MOS capacitors, literature research of their theoretical background is performed allowing for a broad insight into the quality of MOS capacitors by means of the mentioned measurement and analysis techniques. Planar as-deposited TiN/Al2O3/p-Si stacks have successfully been deposited for different Al2O3 thicknesses and at different deposition temperatures from 300?C to 400?C. High quality of the asdeposited stacks is confirmed by high Al2O3 k values of ? 8, low leakage current (? 10?9 A/cm2), high intrinsic breakdown electric fields between 7 and 12 MV/cm and excellent Fowler-Nordheim tunneling behavior. No significant or unexpected trends are observed as a function of the deposition temperature or Al2O3 thickness. A series of TiN/Al2O3/p-Si stacks have successfully been deposited on planar substrates with different separation times between the end of the Al2O3 and beginning of the TiN deposition. Unprecedented separation times are achieved from 15 s to 60 s. TiN/Al2O3/n++-Si stacks are successfully deposited on trenched silicon with an aspect ratio of ? 17. High stepcoverage of Al2O3 (93 ± 7 %) and sufficient TiN (41 ± 6 %) stepcoverage is achieved. Despite the large area of the trenched capacitors, excellent scaling of the capacitance with the electrode area is confirmed. For the MIMIM stack with 10 nm Al2O3 for both oxides a total capacitance density of ? 180 nF/mm2 has been demonstrated. A broad understanding of the properties and the processing of TiN/Al2O3/Si MOS trench capacitors is obtained as a result of this work. The experience and knowledge gained this work can function as a first step towards in situ plasma-assisted ALD processing of other high-k oxides and/or electrodes in 3D silicon to achieve even higher capacitance densities.

Date of Award	31 Dec 2008
Original language	English
Supervisor	W.M.M. (Erwin) Kessels (Supervisor 1), F. Roozeboom (External coach), K.B. Jinesh (External coach) & Willem F.A. Besling (External coach)