Flat-band Voltage Study Of Atomic-layer-Deposited Aluminum-oxide Subjected To Spike Thermal Annealing
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Flat-band Voltage Study Of Atomic-layer-Deposited Aluminum-oxide Subjected To Spike Thermal Annealing V. R. Mehta,1 A. T. Fiory,1 N. M. Ravindra,1 M. Y. Ho,2 G. D. Wilk,3 and T. W. Sorsch4 1
Department of Physics, New Jersey Institute of Technology, Newark, New Jersey Chartered Semiconductor Manufacturing, Singapore 3 ASM International, Phoenix, Arizona 4 Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey 2
ABSTRACT High-κ dielectrics based the oxide of Al were prepared by atomic layer deposition (ALD) on 200-mm p-type Si wafers. Films were deposited directly on clean Si or on 0.5-nm underlayers of rapid thermal oxide or oxynitrides grown in O2 and/or NO ambients. The purpose of the underlayer films is to provide a barrier for atomic diffusion from the crystal Si to the high-κ dielectric film. Deposited Al-oxide films varied in thickness from 2 to 6 nm. Post deposition anneals were used to stabilize the ALD oxides. Equivalent SiO2-oxide thickness varied from 1.0 to 3.5 nm. In situ P-doped amorphous-Si 160 nm films were deposited over the oxides to prepare heavily doped n-type gate electrodes in MOS structures. Samples were rapid thermal annealed in N2 ambient at 800 °C for 30 s, or spike annealed at 950, 1000, and 1050 °C (nominally zero time at peak temperature). Flat band voltages, VFB were determined from C-V measurements on dot patterns. The 800 °C anneals were used as a baseline, at which the poly-Si electrodes are crystallized and acquire electrical activation while subjecting the high-κ dielectrics to a low thermal budget. Positive shifts in VFB were observed, relative to a pure SiO2 control, ranging from 0.2 to 0.8 V. Spike annealing reduces the VFB shift for ALD films deposited over underlayer films. The VFB shift and the changes with annealing temperature show systematic dependence on the nitridation of the underlayer. INTRODUCTION The use of high-κ dielectric materials as gate oxides in MOS devices has been proposed since 70’s [1]. Alumina (Al2O3) has useful properties for a gate dielectric: a large band gap, an amorphous phase under conditions of interest and thermodynamically stability with SiO2 [2,3]. The Al-O bond is 60-70% ionic and it is not as good a glass former as SiO2, however, and Al2O3 is believed to have a large amount of fixed charge. This may result in significant threshold shift and mobility degradation in MOSFETs [4]. High-κ gate dielectrics such as Al2O3 and HfO2 and their silicates are some of the materials expected to replace SiO2 as the gate insulator. The present study is an attempt to understand the electrical characteristics of these promising materials grown by atomic layer deposition (ALD) technique. The flat band voltages, VFB, were determined from C-V measurements on circularly patterned MOS capacitors etched in blanket films. For phosphorous-doped polysilicon electrodes and Al-oxide based dielectrics, positive shifts in VFB were observed, relative to a pure SiO2 control, ranging from 0.2 to 0.8 V. It is believed that this is caused by fixed oxide charge
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