Atomic Layer Deposition of High-κ Dielectrics on Sulphur-Passivated Germanium

Abstract

High mobility channels are currently being explored to replace the silicon channel in future CMOS technology nodes. However, until now the promising bulk properties are very difficult to translate into high transconductance due to a poor passivation of the interface between the gate dielectric and the channel. We have studied the S-passivation of the germanium surface combined with various high-permittivity dielectric gate stacks. (NH4)2S is used to achieve a S-terminated Ge surface. We found that the Ge/S/Al2O3 interface is superior to both the Ge/S/ZrO2 and Ge/S/HfO2 interfaces. Bi-layer stacks consisting of Ge/S/Al2O3/HfO2 or Ge/S/Al2O3/ZrO2 were built to achieve a gate stack with low EOT (Equivalent Oxide Thickness). In these bi-layer stacks, the Al2O3 thickness is reduced to a minimum without degradation of the interface properties. Rather thick Al2O3 interlayers (∼ 2 nm) are needed due to island growth on S-terminated Ge surface. A pMOSFET was built using a bi-layer gate stack (Ge/S/Al2O3/HfO2). The peak mobility of this device is > 200 cm2/Vs at an EOT of 1.5 nm.

Amorphous Gadolinium Aluminate as a Dielectric and Sulfur for Indium Phosphide Passivation

“…It can be inferred that the resonance peak A arises predominantly from S–In rather than S–P transitions as no P x –S y species were detected in the SRPES measurements (see above), and the starting surface is most likely In-rich. , Furthermore, the origin of resonance B (∼2475 eV) in the S K-edge NEXAFS cannot be clearly identified. As the intensity of this resonance is rather high and its width is narrow, this resonance may be assigned to sulfur species with a higher formal oxidation state (S 2+ ) rather than to a pure shape resonance (i.e., to multiple scattering). , Remarkably, this resonance has been also observed for other III–V/S/high-κ stacks regardless of the S deposition method and the high-κ dielectric but was not detected for a Ge/S/high-κ stack . In agreement with the SRPES measurements (Figure e), an oxidized S component (S–O) was present in the S K-NEXAFS spectra (peaks C and D).…”

“…62,64 Remarkably, this resonance has been also observed for other III−V/S/high-κ stacks regardless of the S deposition method and the high-κ dielectric 65 but was not detected for a Ge/S/ high-κ stack. 66 In agreement with the SRPES measurements (Figure 5e), an oxidized S component (S−O) was present in the S K-NEXAFS spectra (peaks C and D). From the position and shape of resonances C and D, it can be deduced that the dominant species is a sulfate SO 4 2− (S 6+ ).…”

“…67 Sulfates are consistently formed on semiconductor/S/high-κ stacks independent of the substrate (group IV, III−V), the high-κ material, or the S deposition method. 65,66 The amount of S in the InP/S/GAO stacks was quantified by using reference-free grazing incidence X-ray fluorescence analysis (GIXRF) 68 at the four crystal monochromator beamline of the Physikalisch-Technische Bundesanstalt at the BESSY II synchrotron. 69 The total amount of S was deduced to be (1.2 ± 0.3) × 10 15 at./cm 2 .…”

Challenges and opportunities in advanced Ge pMOSFETs

“…Sulfur passivation by dipping in a clean (NH 4 ) 2 S solution before HfO 2 or ZrO 2 atomic layer deposition did not show good interface properties [153]. Better results were obtained for the Ge/S/Al 2 O 3 /HfO 2 or -ZrO 2 gate stack, with a minimum Al 2 O 3 thickness of $2 nm required, because of the Al 2 O 3 island growth on an S-terminated Ge surface [153].…”

Passivation Challenges with Ge and III/V Devices

“…The same trend was still observed: low defect densities at the valence band edge and increasing defect densities towards the conduction band edge. However, the values are shifted up to 1 order of magnitude [7]. Therefore, another approach needs to be followed: bi-layers were made consisting of Ge/S/Al 2 O 3 /HfO 2 .…”