Wim Deweerd

Estimation of fixed charge densities in hafnium-silicate gate dielectrics

In this paper, an effective technique and methodology for the estimation of fixed charge components in high-k stacks was demonstrated by varying both the SiO2 and high-k dielectric thicknesses. The SiO2 thickness was scaled on a single wafer by uniformly changing the etch time of a thermally grown SiO2 layer across the wafer. This minimized wafer-to-wafer variations and enables acquisition of statistically significant datasets. Layers with different thickness of both the nitrided and non-nitrided hafnium-silicate layers were then grown on these wafers to estimate all the interfacial and bulk charge components. The reproducibility and validity of this technique were demonstrated, and this method was used to compare the fixed charge levels in Hf-silicates (HfSiO) and nitrided-Hf-silicate (HfSiON) layers

Characterization of field-effect transistors with La2Hf2O7 and HfO2 gate dielectric layers deposited by molecular-beam epitaxy

The electrical properties of La2Hf2O7 (LHO) and HfO2 (HO) high-k dielectric layers deposited by molecular-beam epitaxy are reported. Capacitors and transistors with LHO and HO gate dielectric layers and TaN metal gate electrodes deposited using physical vapor deposition were fabricated. The (SiO2) equivalent oxide thickness (EOT), the electrical oxide thickness in inversion toxinv, and the gate leakage current density (Jg) were determined on large area metal-oxide-semiconductor capacitors and metal-oxide-semiconductor field-effect transistors. HO layers with a physical thickness tph=30A showed an EOT (toxinv) of 15.1A (19.3A) with Jg=8.1×10−6A∕cm2 at Vg=Vfb−1V. LHO layers deposited on SiON showed a minimum EOT (toxinv) of 18.7A (25A) with Jg=4×10−8A∕cm2 at Vg=Vfb−1V. The (effective) electron mobility at high E field for LHO layers was observed for a 40-A-thick LHO layer deposited on Si with μeff=147cm2∕Vs at E=1MV∕cm. For a 30-A-thick HO layer at identical field, μeff=170cm2∕Vs was found. LHO layers depos...

Performance improvement of self-aligned HfO2/TaN and SiON/TaN nMOS transistors

Abstract Direct-etched HfO2/TaN nMOS transistors were fabricated. The performance of the transistors with aggressively scaled EOT is comparable or better than that of SiO2/poly transistors. The performance enhancement requires a combination of EOT scaling and an appropriate interface layer control. The performance of the direct-etched TaN gated HfO2 based transistors is also compared to the performance of similar TaN gated SiON based transistors. It is observed that for equal gm the leakage is lower for HfO2 based transistors, despite the lower EOT for the HfO2 based devices.

Flatband voltage shift of ruthenium gated stacks and its link with the formation of a thin ruthenium oxide layer at the ruthenium/dielectric interface

A systematic study about the flatband voltage (Vfb) shift of Ru gated metal-oxide-semiconductor stacks after thermal treatment in O2 has been performed. The dependence of the Vfb shift on the anneal time and temperature and the thickness of Ru was studied in detail, and a clear link between the Vfb shift and an oxygen diffusion process in Ru was observed. A high temperature thermal treatment of the devices prior to the O2 anneal has no significant impact on the Vfb shift. The Vfb shift is ascribed to the shift of metal gates’ work function, and is not intrinsic to HfO2 gated stacks as similar behavior was also observed on SiO2, from the combination of internal photoemission and conventional capacitance-voltage measurement. No similar Vfb shift was observed for TiN gated stacks and the Vfb shift seems to be more related to the properties of gate electrodes other than those of gate dielectrics. After thermal treatment in O182, from time-of-flight secondary ion mass spectrometry measurement, it was found tha...

Hyperfine interaction study of the decoration of the internal wall of nanosized voids by impurity probes

Abstract We observe the trapping of implanted radioactive 57 Co atoms at empty nano-cavities formed in {111} Si by the desorption of He from bubbles. The absorption of 14.4 keV γ-rays roughly monitors the displacement of the activity, while anodic stripping and counting the remaining 122 keV γ-ray intensity is employed to obtain an accurate depth profile and to isolate the wanted fraction of the sample. Mossbauer spectroscopy shows that only damage and/or CoSi 2 -nuclei related sites are present in samples implanted at 300 and 400°C. In a sample implanted with Co at RT at the same side as the cavity-generating He atoms, the Mossbauer spectra reveal two new quadrupole split components after 30 min annealing at 700°C. We present arguments for the tentative identification of these to a cavity edge site (79%, strong bonding) and to a cavity plane site (21%, weak bonding).

Nitrogen Incorporation in HfSiO(N)/TaN Gate Stacks: Impact on Performances and NBTI

Performance and negative-bias temperature instability (NBTI) on atomic-layer-deposited HfSiON metal-gated pMOSFETs are investigated. The impact of nitrogen incorporation either with plasma nitridation or NH3 anneal is studied and compared to the nonnitrided stacks. The capacitance equivalent thickness reduction that is observed in nitrided stacks is compensated by the slight decrease of the hole mobility for the same gate overdrive, resulting in no improvement of the performance. On the other hand, it is shown that nitridation strongly enhances NBTIs in these devices. Based on these results, the necessity of nitrogen incorporation in thin HfSiON/metal gate stacks should be reconsidered.

Study of the ion implantation of 119Sn in a-Si1−xCx:H

The Mossbauer spectroscopy and Rutherford backscattering spectroscopy studies presented here allow an investigation of the origins of the previously observed changes in optical absorption in sputter deposited a-Si1-xCx:H films caused by high dose Sn implantations. To this end, we investigate the microscopic surroundings and the bonding structures of the Sn atoms. At doses up to 1 x 10(17) cm(-2) a major fraction of Sn takes a quasi-substitutional site, sp(3) bonded to four Si neighbours, while a smaller fraction is present as Sn2+, presumably due to SnO formation. The latter fraction increases at the higher doses and the increase is paralleled by the formation of Sn4+ and a prominent metallic sn component. This beta-Sn fraction, presumably in the form of nanosized precipitates, becomes dominant at the higher doses, thus explaining the complete lack of optical transmission

Mechanism of O2-anneal induced Vfb shifts of Ru gated stacks

Abstract A systematic study of the flat-band voltage (Vfb) shift of Ru gated metal-oxide-semiconductor (MOS) capacitors subjected to thermal treatment in O2 has been performed. The dependence of the Vfb shift on the thickness of Ru, anneal temperature and time is studied. The Vfb shift is ascribed to the shift of metal gates’ work function (WF), and is not significantly dependent on the type of dielectric (HfO2 or SiO2). From time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurement, it was found that after thermal treatment in 18O2, 18O penetrated through Ru and was incorporated in the Ru/dielectric interface region. We believe that the formation of the thin interfacial RuOx layer is responsible for the Vfb shift.

Highly scalable ALD-deposited hafnium silicate gate stacks for low standby power applications

The electrical performance of hafnium silicate (HfSiOx) gate stacks grown by atomic layer deposition (ALD) has been evaluated in capacitors and transistors. First, scaling potential of HfSiOxlayers was studied as function of composition and thickness. It is shown that the equivalent oxide thickness scales down with decreasing layer thickness and increasing Hf-content. The gate leakage (at Vfb-1V), however, is mainly determined by the physical layer thickness. For the same equivalent oxide thickness (EOT) target, the lowest leakage is observed for the layers with the highest Hf-content. Leakage values as low as 1×10-3 A/cm 2 for an equivalent oxide thickness of 1.3 nm have been obtained, Second, the thermal stability against crystallization of the ALD HfSiO x has been studied and related to their electrical properties. The thermal stability of HfSiOx decreases with increasing Hf-content that necessitates the use of nitridation. The influence of various annealing conditions on the nitrogen incorporation is also studied, Finally, the effect of HfSiOx composition and postdeposition nitridation is discussed on transistor level. TaN metal gate transistor data indicate that nitridation reduces the gate leakage and that Hf-rich HfSiOx layers show the best scaling potential, i.e., highest performance for the lowest gate leakage.

Trapping of ion-implanted 57Co to cavities in c-Si: a qualitative study

Abstract We observe a pronounced dose dependence in the trapping of Co to the internal surface of nanosized cavities in c-Si. Mossbauer spectroscopy shows that cavity trapping is most explicit for low Co contamination levels ( 5 × 1014 at/cm2), silicide formation becomes predominant at first and then subsequently partially dissolves upon prolonged annealing at temperatures exceeding 750°C. In the intermediate region, a clear starting situation is only reached after several annealing steps. Again Co gets trapped at the cavities, reaching essentially an identical level as for the low dose case. For the low and intermediate dose case, the onset of cavity trapping is followed in detail, showing that a large initial fraction of weakly surface bound Co depopulates in favor of the formation of small CoSi2 precipitates in the vicinity of the voids. Subsequently, this CoSi2 phase then partially dissolves in favor of strongly surface bound Co.