Conduction mechanisms and reliability of thermal Ta2O5–Si structures and the effect of the gate electrode

Abstract

The effect of metal gate electrodes (Al, W, Au, TiN, and TiN∕W) on dielectric properties, leakage currents, conduction mechanisms, and reliability characteristics of metal-oxide-semiconductor capacitors with thermal Ta2O5 is investigated. The results are discussed in terms of the relative influence of the gate deposition techniques and the intrinsic properties of the electrode material and the former appears to be more pronounced. It is found that some parameters such as interface state density, breakdown fields, and charge trapping are defined mainly by the properties of Ta2O5 itself. The global dielectric constant of the stack dielectric, oxide charge, leakage current level at high applied fields, charge-to-breakdown, and stress-induced leakage currents are remarkably affected by the upper electrode. It is concluded that the nature and spatial distribution of the gate deposition-induced defects are sensitive to the technological process (evaporation or sputtering); this effect is so strong that it tends to outweigh the effect of the intrinsic properties (e.g., work function) of the gate material. The bulk-limited Poole–Frenkel emission is the dominant conduction mechanism in Ta2O5. A Au gate is preferable and shows the best parameters in terms of the leakage current and stress-induced leakage current, whereas Al-gate capacitors reveal the best dielectric constant and charge to breakdown.

Challenges of Ta2O5 as high-k dielectric for nanoscale DRAMs

“…11. I-V curves for capacitors with various gates [3,16]. dependent on the electrode material regardless that PF mechanism appears to be dominant in the most of the cases.…”

“…One of the key issues here is the control of the electrode work function throughout processing. For example, the effect of various electrodes (Al, W, Au, TiN, TiN/W) on the characteristic of capacitors with Ta 2 O 5 [3,16] shows that some parameters such as interface state densities, breakdown fields and charge trapping are defined by the properties of Ta 2 O 5 itself. The dielectric constant, oxide charge, leakage current at high fields, charge to breakdown and stress-induced leakage currents are remarkably affected by the electrode.…”

Stress-induced leakage currents of the RF sputtered Ta2O5 on N-implanted silicon

“…The precise description of the behavior of high-k dielectrics requires considering them as stacked high-k/interfacial layer structures. The thickness and the composition of thin interfacial lower-k layer depend strongly on the technological history of the system Ta 2 O 5 /Si (including all annealing steps), and consequently are a subject of a great debate and ongoing investigations [2,5,9,13,15,[17][18][19][20][21][22]. Our structural studies of both RF sputtered and thermally grown Ta 2 O 5 have shown that the interfacial layer is composed of ultrathin SiO 2 and a near interfacial region containing Taand Si-suboxides [12,13].…”

“…A number of methods compatible with silicon technology are successfully developed for obtaining thin films Ta 2 O 5 [2][3][4][5][6][7][8][9]. During the formation of Ta 2 O 5 on Si, however, an interfacial SiO 2 -containing layer is inevitably formed at the Si substrate [9][10][11][12][13][14][15][16].…”

Tunable strain effect and ferroelectric field effect on the electronic transport properties of La0.5Sr0.5CoO3 thin films

“…Ferroelectric (1Àx)Pb(Mg 1=3 Nb 2=3 )O 3 -xPbTiO 3 single crystals with composition near the morphotropic phase boundary (x $ 0.33) display large remnant ferroelectric polarization, low coercive field, excellent piezoelectric activity 16 and have perovskite structure with lattice constants a $ b $ c $ 4.02 Å . 17 Because of the good ferroelectric, piezoelectric, and structural properties of (1-x)Pb(Mg 1=3 films can be reversibly modulated via the converse piezoelectric effect of the piezoelectric substrates.…”