Low-Temperature-Grown Single-Crystal Si Epitaxially on Ge, Followed by Direct Deposition of High-κ Dielectrics–Attainment of Low Interfacial Traps and Highly Reliable Ge MOS

Abstract

Single-crystal silicon (Si) of six monolayer thickness was epitaxially grown on epi-germanium (Ge) in the (001) orientation at substrate temperatures lower than 300 °C, followed by direct deposition of hafnium oxide (HfO2) and aluminum oxide (Al2O3) under ultra-high vacuum. We monitored and studied the Si growth and its epitaxy with the epi-Ge substrate using in-situ reflection high-energy electron diffraction and high-resolution synchrotron radiation X-ray diffraction. Using the gate stacks, we obtained interfacial trap densities of (1–3) × 1011 eV–1 cm–2 without the use of high-pressure hydrogen annealing and a highly reliable Ge p-type metal-oxide semiconductor with a high acceleration factor of 11.

Scavenging Segregated Ge on Thin Single-Crystal Si Epitaxially Grown on Ge

“…The Ge segregation in the low temperature (<300 °C) MBE-grown epi- Si on Ge , was below the detection limit of X-ray photoelectron spectroscopy (XPS). We employed the SRPES technique with much higher surface sensitivity and resolution than XPS to study the six MLs thick- epi -Si on epi -Ge­(001).…”

“…The six MLs-thick single-crystal Si was grown epitaxially on an epi- Ge/Ge­(001) substrate using a group IV semiconductor MBE chamber in a multichamber growth/analysis system. , The substrate temperature was between 260 and 280 °C during the growth of epi -Si. The sample was transferred, via a UHV portable chamber, to the National Synchrotron Radiation Research Center (NSRRC) in Taiwan for photoemission measurements.…”

“…Si-capped SiGe is now employed in sub-5 nm pMOS technology. To minimize the Ge segregation (segGe) and the GeO x formation in the gate dielectrics, a Si layer on Ge using chemical vapor deposition (CVD) or molecular beam epitaxy (MBE) was employed. Compared with the approaches of oxidized Ge and high-κ deposition on Ge, where the formation of GeO x is inevitable, the diffusion of Ge (diff-Ge) into the thin Si layer and segGe on top of the Si surface lessened in the Si-layer approaches, although it still occurred; these were studied by synchrotron radiation photoelectron spectroscopy (SRPES) for the MBE epi -Si/Ge and by secondary-ion mass spectroscopy (SIMS) for the CVD Si/Ge. , A thick Si layer may reduce the segGe but degrades the electron mobility of the devices .…”

“…Therefore, it is a challenge to further reduce or completely remove the segGe and the GeO x formation in the gate dielectrics to attain reliable n-Ge MOS for the epi -Si/Ge or the Si-cap/Si approaches. , In this work, we have used sequential room-temperature oxidation followed by thermal annealing in ultra-high vacuum (UHV), called a scavenging process, in removing the diff-Ge in the thin epi- Si and reducing the segGe on the top epi -Si/Ge surface. A repeat of the scavenging process has further reduced the residual segGe and Si surface atoms, produced more Si 4+ oxidation states, and formed epi -Si/Ge free of GeO x .…”

High-Ge-Content Si1–xGex Gate Stacks with Low-Temperature Deposited Ultrathin Epitaxial Si: Growth, Structures, Low Interfacial Traps, and Reliability

“…First, epi -Ge buffer layers were grown on annealed Ge(001) substrates in a group IV MBE chamber (with a base pressure less than 10 –11 Torr) to ensure an atomically smooth Ge surface for the subsequent growth of HGC Si 1 –x Ge x epi -layers (0.5 < x ≤ 0.8) at 500 °C . Then, six ML-thick epitaxial Si was deposited on the Si 1 –x Ge x with the substrate temperature between 260 and 280 °C to minimize Ge segregation from Si 1 –x Ge x and diffusion to Si. , HfO 2 1–1.5 nm-thick was in situ deposited on the epi -Si in the oxide MBE chamber followed by the deposition of 5 nm-thick Al 2 O 3 in the ALD reactor. Before fabricating MOS capacitors (MOSCAPs), the samples were post-deposition annealed (PDA) in N 2 at 600 °C for 30 s. MOSCAPs were fabricated with Ni as the top metal electrode and Ti/Au as the back contact and were post-metallization annealed (PMA) in forming gas at 400 °C for 5 min.…”