Atomic Layer Deposition of Gadolinium Aluminate using Gd( i PrCp) 3 , TMA, and O 3 or H 2 O** By Christoph Adelmann, * Dieter Pierreux, Johan Swerts, Daan Dewulf, An Hardy, Hilde Tielens, Alexis Franquet, Bert Brijs, Alain Moussa, Thierry Conard, Marlies K. Van Bael, Jan W. Maes, Malgorzata Jurczak, Jorge A. Kittl, and Sven Van Elshocht For future generations of non-volatile memory applications, the replacement of the interpoly dielectric by a suitable high-k material is required. Rare-earth aluminates are potential candidates because they are predicted to combine a high dielectric permittivity with a large band gap. We demonstrate the atomic layer deposition (ALD) of Gd x Al 2-x O 3 layers using Gd( i PrCp) 3 , trimethyl-aluminum (TMA), and H 2 O or O 3 . Process windows for both H 2 O and O 3 as oxidants are explored. H 2 O is shown to lead to better Gd x Al 2-x O 3 film properties than O 3 , although the accessible composition range is limited because of the hygroscopic nature of Gd 2 O 3 . Keywords: ALD, Cyclopentadienyl, Gadolinium aluminate, Gadolinium oxide, High-k oxides 1. Introduction In the past, high-k material research has primarily focused on alternative dielectrics to replace SiON for complementary metal-oxide-semiconductor (CMOS) transistor applications. Recently, high-k dielectrics have also been evaluated for non-volatile memory (NVM) applications such as NAND flash devices. A conventional non-volatile flash device consists of a structure that can be summarized as Si/tunnel oxide/poly-Si floating gate/ interpoly dielectric/poly-Si control gate, where the tunnel and interpoly dielectrics (IPD) are typically a silicon oxide and oxide/nitride/oxide (O/N/O) stack, respectively. [1] Data are being stored in the floating gate as charge, which is transported through the tunnel dielectric by Fowler- Nordheim tunneling when a voltage is applied to the control gate. For future generations of NVM devices, several issues have been identified as obstacles to further scaling of device dimensions. For embedded memory applications, there is a drive to lower program and erase voltages, which could be achieved by thinning down the tunnel dielectric. However, for SiO 2 there is a lower limit of 8 nm. When scaled below, the device specifications for 10-year data retention can no longer be met because of dielectric breakdown, and especially stress-induced leakage currents during cycling. [2,3] As a result, the replacement of the standard tunnel dielectric (to lower the tunnel barrier) by high-k materials has been explored. Also, multi-stack combinations of (high-k) dielectric layers as tunnel dielectric have been considered. [4–6] For standalone NVM applications, high-k materials are considered to overcome issues related to the device architecture. At present, the control gate wraps around the floating gate to increase capacitance, and hence to improve capacitive coupling. When cell dimensions become smaller, the spacing between the control gates of adjacent devices becomes too small for a wrap-around control gate. Cell planarization is a possible solution, but implies the need for a higher dielectric permittivity for the IPD to compensate for the capacitance loss and to ensure a sufficient gate coupling ratio. As a replacement IPD for conventional O/N/O stacks, Al 2 O 3 has been identified as a promising candidate, demonstrating good retention. [7] Hf x Al 1-x O y layers have also been studied because their dielectric permittivity k is higher than that of Al 2 O 3 , in combination with rather large band gap values. [8–11] As an alternative to hafnium oxide- based dielectrics, rare-earth oxide-based materials have also been considered. For La x Al 2-x O 3 , k values reaching 25, and band gap values between 5.75 eV and 6.35 eV have been DOI: 10.1002/cvde.200906833 Full Paper [*] Dr. C. Adelmann, Dr. J. Swerts, H. Tielens, Dr. A. Franquet, Dr. B. Brijs, Dr. A. Moussa, Dr. T. Conard, Dr. M. Jurczak, Dr. J. A. Kittl, Dr. S. Van Elshocht IMEC vzw. Kapeldreef 75, B-3001 Leuven (Belgium) E-mail: adelmann@imec.be Dr. D. Pierreux, Dr. J. W. Maes ASM Belgium Kapeldreef 75, B-3001 Leuven (Belgium) D. Dewulf, Prof. A. Hardy, Prof. M. K. Van Bael Institute for Materials Research, Inorganic and Physical Chemistry, Hasselt University B-3590 Diepenbeek (Belgium) D. Dewulf, Prof. A. Hardy, Prof. M. K. Van Bael IMEC vzw., Division IMOMEC B-3590 Diepenbeek (Belgium) [**] An Hardy is a postdoctoral research fellow of the Research Founda- tion–Flanders (FWO-Vlaanderen). Daan Dewulf is funded by a Ph.D. grant of the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT–Vlaanderen). 170 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Chem. Vap. Deposition 2010, 16, 170–178