Metal-gate-induced reduction of the interfacial layer in Hf oxide gate stacks

Abstract

The properties of high-metal oxide gate stacks are often determined in the final processing steps following dielectric deposition. We report here results from medium energy ion scattering and x-ray photoelectron spectroscopy studies of oxygen and silicon diffusion and interfacial layer reactions in multilayer gate stacks. Our results show that Ti metallization of HfO 2 / SiO 2 / Si stacks reduces the SiO 2 interlayer and ͑to a more limited extent͒ the HfO 2 layer. We find that Si atoms initially present in the interfacial SiO 2 layer incorporate into the bottom of the high-layer. Some evidence for Ti-Si interdiffusion through the high-film in the presence of a Ti gate in the crystalline HfO 2 films is also reported. This diffusion is likely to be related to defects in crystalline HfO 2 films, such as grain boundaries. High-resolution transmission electron microscopy and corresponding electron energy loss spectroscopy scans show aggressive Ti-Si intermixing and oxygen diffusion to the outermost Ti layer, given high enough annealing temperature. Thermodynamic calculations show that the driving forces exist for some of the observed diffusion processes.

XAFS atomistic insight of the oxygen gettering in Ti/HfO2 based OxRRAM

“…Also, the rather small discrepancy cannot be attributed to an intermixing or roughening at the Ti/HfO 2 interface, which would increase the O atoms in the interface Ti environment without oxygen diffusion, since both XRR and TEM results show that the Ti/HfO 2 interface is not affected. Some authors [48,49] attributed the presence of O atoms in the Ti layer after a mild annealing at 300 • C in forming gas of Ti/HfO 2 /Si stacks, to the diffusion of O from the very thin SiO 2 layer present on top of the silicon substrate. Although in the present study the HfO 2 layers are about three times thicker than those of the above-mentioned papers, the migration of O atoms from the SiO 2 layer cannot be excluded.…”

Diffusion and interface growth in hafnium oxide and silicate ultrathin films on Si(001)

“…Figure 1 shows an H + backscattered energy spectrum from an as-deposited Therefore, we performed controlled atomic-force microscopy measurements for selected asdeposited and annealed samples, which revealed rms values of ~ 2Å for as-deposited and less than 5 Å for the annealed films. 9 To investigate the mobility of oxygen, samples were reoxidized in 18 Figure 2a shows the part of the backscattered H + spectrum corresponding to the two oxygen isotopes in HfO 2 /SiO 2 /Si(001) films as reoxidation proceeds. A pronounced 18 O peak (spanning from the outer surface of HfO 2 to the SiO 2 interfacial layer, as illustrated by the matched 16 O and 18 O peak base energy range) is observed after 10min of 18 O 2 exposure (p 18O2 =0.01Torr, 763K).…”

“…The Hf oxide (silicate)/Si interface region is strongly affected by the surface preparation prior to dielectric growth, 7 by growth chemistry, thermal treatment and, often, also by the nature of the metal gate. [8][9][10] There is a large body of work that addresses issues pertaining to interface preparation and characterization. 7,8,[11][12][13] Although SiO 2 films are thermodynamically stable on Si, some higher-κ oxides are not.…”

Statistical characterization and reliability modeling of novel high-K gate dielectric stacks

“…Lastly, there is a driving force in the industry to try and eliminate the presence of the IL layer as it limits the ability to aggressively scale down the EOT of sub-16 nm technology node devices [65,66]. One of the techniques proposed to achieve a zero IL layer (ZIL) solution is to use the oxygen gettering MG to induce the reduction of SiO x → Si [67]. Though initial efforts from a process technology perspective have shown positive results, the reliability of a ZIL gate stack is still questionable considering that the grain boundary lines in the HK would directly short the gate to the substrate in the absence of the IL layer.…”

“…The reduction in EOT can be attributed to the use of the higher permittivity oxide as well as the MG electrode which has an "oxygen-gettering" ability ( Fig. 2.4) that causes the reduction reaction of SiO x → Si, thereby effectively removing the IL layer contribution to overall oxide thickness [67]. For any given EOT value, the fresh device leakage levels in HK stack are about 1-2 orders (Fig.…”