Stress and Phase Engineered ZrO 2 /Ge for High-k Dielectric Applications
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Stress and Phase Engineered ZrO2/Ge for High-k Dielectric Applications Narayan K. V. L.V. Achari1,2, Amiya Banerjee2, Srinivasan Raghavan1,2 1 Materials Research Centre, Indian Institute of Science, Bangalore-12, India. 2 Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore-12, India. ABSTRACT ZrO2/Ge is potential high-k dielectric candidate to replace silicon based devices. Controlling stress in zirconia film and stabilizing high dielectric constant phase is crucial for high-k application. A precise control of stress and phase selectivity in high-k thin films is demonstrated. Thin films of ZrO2 were grown by reactive sputter deposition. Wide range of growth stress in thin films from -0.3 to -2.8 GPa can be tuned by growth rate control. Adatom incorporation into grain boundary was the dominant source of observed stress. Phase selectivity in zirconia was achieved by tuning growth parameters. INTRODUCTION Aggressive scaling of silicon based CMOS technology reached its material limits.[1] As the silica dielectric reached its quantum mechanic tunneling limit of thickness, a range of high-k dielectrics like ZrO2, HfO2, Al2O3, La2O3… were considered to reduce the gate leakage and to have the same control over channel.[2, 3] Even with high-k dielectrics, the channel performance in high speed devices was carrier injection limited.[4] This can overcome by replacing silicon channels with high mobility material like germanium, where electronic and hole mobility are 3900 and 1900 cm2V-1s-1 respectively.[5-9] ZrO2 and HfO2 were well known high-k dielectrics for silicon CMOS applications. ZrO2 is known to form stable interface with germanium compared to that of HfO2.[10] In this work, ZrO2/Ge is considered as a potential candidate to replace silicon based devices. Various groups have been reported ZrO2 using different techniques such as chemical vapor deposition,[11, 12] reactive sputtering,[13] oxidation of metallic zirconium films.[14] Present study concentrated on ZrO2 thin film growth by reactive direct current(R-DC) sputter deposition. Compared to other thin film deposition processes sputtering is simple to implement and easy to scale over large wafer sizes for inline processes. [15] ZrO2 is known to exhibit three different phases depend on temperature, crystallite size and stress.[16, 17] Depends on the phase and crystallographic direction, zirconia exhibits dielectric constants ranging from 15-42.[18, 19] Hence, precise control of phase and orientation of zirconia film is crucial for high-k dielectric application. Present work shows a precise way to control the phase of zirconia high-k thin films deposited by R-DC sputtering. EXPERIMENTAL DETAILS Table I. Thin film deposition conditions Power supply
Sputter Target
Current
Pressure
Ar:O2
Growth Rate
Temperature
DC
Zr Metal
10 - 100 mA
10 mTorr
24:1
0.1 - 4.4 nm/min
RT-700°C
Low resistivity n-Ge [100] was used as the substrate for ZrO2 film deposition. A series of pure-ZrO2 films on germanium were grown by off-axis R-DC sputtering in
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