Martin Trentzsch

Tunneling Effective Mass of Electrons in Lightly N-Doped

In this paper, we study the dependence of the tunneling effective mass of electrons on gate dielectric nitrogen concentration and thickness in MOSFETs with lightly doped silicon oxynitride (SiOxNy) gates. The direct tunneling current is modeled by applying a Schrodinger-Poisson solver with one-side-open boundary condition. The dependences of the effective mass on nitrogen concentration and dielectric thickness are extracted by fitting the computation results for the gate leakage current to the experimental data that we measured for samples with different thicknesses and nitrogen concentrations. Nitrogen concentration and thickness of samples are determined using X-ray photoemission spectroscopy. The obtained results show a strong dependence of the effective mass on the sample thicknesses and nitrogen concentration. The electron effective mass is found to increase as the thickness decreases, and the higher nitrogen concentration causes a reduction in effective mass.

\hbox{SiO}_{x} \hbox{N}_{y}

Future scaling of complementary metal oxide semiconductor (CMOS) technology requires high-k (HK) dielectrics with metal gate (MG) electrodes to realize higher gate capacitances and low gate leakage currents [1]. During the last decade the semiconductor industry has spent tremendous effort to find the right material. Hafnium-based dielectrics and particularly HfO2 are considered to be the most promising candidates to replace SiON in high volume manufacturing due to their relatively high dielectric constants, large band gap and conduction band offset to Si and their thermodynamic stability with Si [2-4]. However, compared to SiO2, HfO2 dielectrics suffer from threshold voltage instabilities, mobility degradation, charge trapping as well as reliability degradation [5,6]. Recently HfZrO4 has been shown to be a superior gate dielectric to HfO2 [7-11]. Addition of ZrO2 to HfO2 forming HfZrO4 helps to partially stabilize tetragonal phase being associated with higher kand lower CET values [7]. Besides smaller and more uniform grains, more uniform film quality, tighter leakage distribution, less charge trapping, lower CV hysteresis, lower Dit, higher transconductance and drive currents, reduced SILC and longer product reliability lifetimes have been reported among other things for HfZrO4 compared with HfO2 [7-11]. Simultaneously disadvantages like smaller band gap (~0,4eV) and lower conduction band offsets resulting in increased leakage have been presented as well [7]. Up to now atomic layer deposition (ALD) [7-10] as well as physical vapor deposition (PVD) [11] have been explored to form the HfZrO4 layers. As metal-organic chemical vapor deposition (MOCVD) stands out due to excellent manufacturability and high throughputs, we investigate HfZrO4 dielectrics deposited with MOCVD as well as ALD as high-k gate dielectric for 32nm high performance logic SOI CMOS devices in this work. The physical properties of the HfZrO4 films have been analyzed in detail by atom probe tomography [12,13], Xray photoelectron spectroscopy, Rutherford backscattering spectrometry, time-of-flight secondary ion mass spectrometry, transmission electron microscopy, reflectometry, atomic force microscopy, variable angle spectroscopic ellipsometry as well as high temperature grazing incidence X-ray diffraction. In addition electrical parameters such as gate leakage current, capacitance equivalent thickness, threshold voltage, interface trap density (charge pumping) and performance as well as reliability data have been taken into account to directly compare both deposition methods. All parameters indicate a comparable behavior for MOCVD and ALD. Therefore MOCVD is demonstrated to be a promising alternative to ALD in high volume manufacturing in this work.

Gate Insulators

In this work we present a comprehensive comparison of ultra thin thermally nitrided (TN) to plasma nitrided (PN) gate dielectrics (GD). We will show that thermal nitridation is a promising technique to increase the nitrogen concentration up to 25%. Furthermore, we will demonstrate that ultra thin thermally nitrided GD have the potential to be an alternative solution compared to plasma nitrided GD. This work includes the analysis of physical and electrical parameters as well as reliability results from reliability characterization. Additionally, we investigated the impact of Deuterium on electrical parameters and reliability behavior.