J. Van Steenbergen

Deposition of HfO2 on germanium and the impact of surface pretreatments

The deposition behavior of HfO2 by metalorganic chemical vapor deposition on germanium has been investigated. HfO2 films can be deposited on Ge with equally good quality as compared to high-k growth on silicon. Surface preparation is very important: compared to an HF-last, NH3 pretreatments result in smoother films with strongly reduced diffusion of germanium in the HfO2 film, resulting in a much better electrical performance. We clearly show that much thinner interfacial layers can be obtained, approximately half the thickness of what is typically found for depositions on silicon, suggesting the possibility of more aggressive equivalent oxide thickness∕leakage scaling.

New interface state density extraction method applicable to peaked and high-density distributions for Ge MOSFET development

A method for extracting parameters of weakly Fermi-level pinned germanium (Ge) capacitors is introduced. This method makes progress toward a more generally valid reliable interface state parameter extraction. Such a general method is needed to evaluate and explain the behavior of Ge MOS capacitors, which show characteristics deviating considerably from silicon. The encountered weak pinning confirmed by the new extraction method explains the degraded Ge nMOSFET performance.

Effect of hafnium germanate formation on the interface of HfO2/germanium metal oxide semiconductor devices

We have studied the thermal stability of HfO2 thin layers on germanium and the substrate interface development. HfO2 was deposited on Ge substrates and annealed in O2 or N2 at 500°C (substrate temperature). After O2 anneal, we observed the formation of hafnium germanate, which is stable at 500°C in N2 as opposed to GeO2 that desorbs as GeO. We believe that this hafnium germanate is an oxygen barrier and as such is at the origin of the much thinner interface between HfO2 and germanium as compared to silicon. In addition, results suggest that the HfGeOx is related to the high interface state density frequently reported for germanium metal oxide semiconductor devices.

Experimental and theoretical evidence for vacancy-clustering-induced large voids in Czochralski-grown germanium crystals

Optical inspection of polished Czochralski-grown Ge wafers typically reveals the presence of surface pits similar to the Crystal Originated Particles (COP’s) observed in silicon but in a wider variety of sizes and shapes. Computer simulation of vacancyclustering during the Cz germaniumcrystal growth suggests that the surface pits originate from large voids formed by the diffusion-limited clustering of an excess of vacancies.

Ge deep sub-micron pFETs with etched TaN metal gate on a high-k dielectric, fabricated in a 200mm silicon prototyping line

We report for the first time on deep sub-micron Ge pFETs with physical gate lengths down to 0.151 /spl mu/m. The devices are made using a silicon-like process flow, with a directly etched gate stack consisting of TaN gate on an ALD or MOCVD HfO/sub 2/ dielectric. Promising drive currents are found. Various issues such as the severe short channel effects (SCE), the increased diode leakage compared to Si and the high amount of interface states (N/sub it/) are addressed. The need for an alternative Ge substrate pre-treatment and subsequent high-k gate dielectric deposition to push EOT values below 1 nm is illustrated.

Germanium Deep-Submicron p -FET and n -FET Devices, Fabricated on Germanium-On-Insulator Substrates

A key challenge in the engineering of Ge MOSFETs is to develop a proper Ge surface passivation technique prior to high-κ dielectric deposition to obtain low interface state density and high carrier mobility. A review on some possible treatments to passivate the Ge surface is discussed. Another important aspect is the activation of p- and n-type dopants to form the active areas in devices. Finally, Ge deep submicron n- and p-FET devices fabricated with this technique on germanium-on-insulator substrates, yield promising device characteristics, showing the feasibility of these substrates.

Germanium FETs and capacitors with rare earth CeO2/HfO2 gates

Long channel Ge FETs and capacitors with CeO2/HfO2/TiN gates were fabricated by photolithography and gate wet etch. Rare earth CeO2 in direct contact with Ge was used as a passivating layer producing lowest Dit values in the mid 1011 eV?1 cm?2 range. HfO2 cap reduces leakage and improves equivalent oxide thickness scaling of the whole gate stack. The p-FETs show exceptionally high ION/IOFF ratio ~ 106, mainly due to low OFF current, and peak channel mobility around 80 cm2/Vs. The n-FETs, although functional, show inferior performance producing ON currents an order of magnitude lower compared to p-FETs.

Physical characterization of HfO/sub 2/ deposited on Ge substrates by MOCVD

In this paper, we study the growth properties of HfO/sub 2/ on Ge by MOCVD, using TDEAH and O/sub 2/ precursors and compare the results to similar layers deposited on silicon substrates. Analysis techniques include ellipsometry, Rutherford Backscattering Spectra (RBS), transmission electron microscopy (TEM),X-ray diffraction (XRD), and time of flight secondary ion mass spectroscopy (TOFSIMS).