Since GaSb(001) is a candidate surface channel material for p-MOSFET and an interfacial passivation layer for buried channel quantum well and tunneling FETs (GaSb static dielectric constant of ~ 16), it is necessary to understand its interface with high-κ dielectric materials which would act as gate dielectrics in these devices[1]. An in-situ half-cycle atomic layer deposition/X-ray photoelectron spectroscopy (ALD/XPS) study is conducted in order to investigate the evolution of the HfO₂ dielectric interface with the GaSb(001) surface after sulfur passivation procedures and HCl etching designed to removed the native oxides. Monochromatic XPS is used to examine the surfaces following the various surface treatments and then without breaking vacuum, after each individual ALD pulse of tetrakis-dimethyl-amino-hafnium (TDMA-Hf) and deionized water (DIW) precursors (i.e. single TDMA-Hf pulse/XPS scan; single DIW/XPS scan; etc.) for two full cycles and finally after 1 nm of HfO₂ deposition to determine whether there is any “clean up” effect of the native oxides due to the ALD process. The various surface preparation techniques are compared to determine which is more effective at minimizing native oxides. The behavior of the sulfides and the effect of HCl surface cleaning procedure upon HfO₂ deposition are discussed as well as a comparison to previous results from half cycle Al₂O₃ deposition on GaSb [2]. This work is supported by the Semiconductor Research Corporation FCRP MSD Focus Center, the Nanoelectronics Research Initiative and the National Institute of Standards and Technology through the Midwest Institute for Nanoelectronics Discovery (MIND). and the NSF (ECCS-0925844).

[1] A. Nainani, T. Irisawa, Z. Yuan, Y.Sun, T. Krishnamohan, M. Reason, B.R. Bennett, J.B. Boos, M. Ancona, Y. Nishi, K.C. Saraswat, International Electron Devices Meeting, (IEDM) Tech. Dig. (2010).

[2] S. McDonnell, D. M. Zhernokletov, A. P. Kirk, J. Kim, and R. M. Wallace. Applied Surface Science Letters, submitted (2011).

High-k HfO₂-based gate oxides have recently been put into production in CMOS-based integrated circuits, and their future use in this capacity depends on how well they can continue to be downscaled. To this end, efforts to increase the dielectric constant (k) of HfO₂-based gate oxides are ongoing. Recent work has shown that by tailoring annealing procedures, k values for HfO₂ films of greater than 30 have been obtained.¹ These higher k values for HfO₂ occur for the metastable tetragonal and cubic crystalline phases, while the thermodynamically preferred monoclinic phase has a lower k value (~20). To evaluate the crystalline structure of ultra-thin (< 100 Å) HfO₂ films which have undergone various annealing treatments, we used several techniques, including grazing incidence in-plnae X-ray diffraction (GIIXRD), X-ray and UV photoemission spectroscopy (XPS and UPS, respectively) and spectroscopic ellipsometry (SE). GIIXRD measurements showed that ~60 Å HfO₂ films grown with a sequence of depositions and anneals (so-called DADA process²) were monoclinic, while those which were post deposition annealed (PDA) were in a mixture of monoclinic and either tetragonal or orthorhombic phases. Pole figure measurements of these films showed that the DADA film had a monoclinic (-111) fiber texture, while the PDA film was randomly oriented. For HfO₂ films with thicknesses of ~25 Å, GIIXRD measurements showed that DADA films were tetragonal or orthorhombic, while PDA films were also tetragonal or orthorhombic, but also possibly with a monoclinic component. XPS and UPS measurements of the valence bands of HfO₂ films were found to be useful in distinguishing between crystalline and non-crystalline films, but were not useful in distinguishing between crystalline phases.³ SE has been shown to be useful in indentifying crystallinity in HfO₂ through a feature that appears in the HfO₂ extinction coefficient curve at the absorption edge. We have observed this absorption edge feature for films that were crystalline and strongly monoclinic, but not for films that were only weakly crystalline or mostly non-monoclinic, in keeping with previous work.⁴

References:

[1] S. Migita, et al., 2008 Symposium on VLSI Technology, 152-153(2008).

[2] R.D. Clark, et al., ECS Trans., 35(4), 815-834 (2011).

[3] S. Toyoda, et al., J. Appl. Phys., 97, 104507 (2005).

[4] J. Schaeffer, et al., J. Electrochem. Soc., 150 (4), F67 (2003).

In this contribution, we investigate the influence of the SiO₂ thickness on the density and polarity of built-in charges in SiO₂/Al₂O₃ stacks deposited on Si(100). Such charges lead to the development of a space-charge region (SCR) in the Si at the dielectric interface, having consequences such as flat band voltage shifts in MOS devices and electric-field induced passivation in optoelectronic devices like solar cells. We have employed the nonlinear optical technique of second-harmonic generation (SHG) to probe the Si(100) SCR electric field through the effect of electric-field-induced SHG (EFISH). Using this non-intrusive and contactless technique we found previously that the built-in charge density at the SiO₂/Al₂O₃ interface is independent of the Al₂O₃ thickness down to ~2 nm.¹ Here we report on the influence of the interfacial SiO_x layer, present between the Si(100) substrate and the atomic layer deposited (ALD) Al₂O₃ film, addressing the origin, density, and polarity of the charges. For this reason, we have synthesized SiO₂/Al₂O₃ stacks with intentionally grown SiO₂ interlayers having a thickness in the range ~1.4-150 nm using various deposition methods (e.g. thermal oxidation, PECVD, ALD). Spectroscopic SHG measurements were carried out with a femtosecond pulsed Ti:sapphire laser tunable in the 1.33-1.75 eV photon energy range. From the obtained spectra we found that the charge density is highly influenced when increasing the SiO₂ thickness, dropping from 10¹³ to 10¹¹ cm^-2, with the polarity switching from negative to positive. These measurements were confirmed by C-V measurements and surface voltage measurements employing corona charging of the stacks. On the basis of the observations the mechanism and consequences of charge trapping in Si/SiO₂/Al₂O₃ stacks will be addressed.

¹ Terlinden et al., Appl. Phys. Lett. 96, 112101 (2010)

We report on the deposition and energy band diagram analysis of high-quality low-leakage Al₂O₃/GaN using atomic layer deposition. As GaN-based transistors are scaled to achieve higher frequency operation, atomic layer deposition techniques offer a promising way to achieve low leakage while scaling gate-to-channel distance. In addition, applications of GaN in power switching systems require ultra-low leakage that can be achieved using metal-insulator-semiconductor (MISHEMT) structures. In this work, we have made quantitative estimates of conduction band offsets and interface charge density.

MIS structures with varying oxide thickness were fabricated on an n+/n- GaN sample grown by RF plasma MBE on low dislocation density Lumilog GaN templates. Three Al₂O₃ layers of nominal 6 nm, 12 nm, and 18 nm were deposited by atomic layer deposition at 300˚C, using trimethylaluminum (TMA) and H₂O as precursors. The pre-deposition treatment of the surface consisted in a 10:1 HF-dip for 15s. All three samples were then annealed at 600˚C in forming gas for 1min. A new ALD deposition procedure was also developed to achieve low leakage in these structures.