An Examination of Tantalum Pentoxide Thin Dielectric Films Using Grazing Incidence X-Ray Reflectivity and Powder Diffraction

Published

January 1, 2001

Author(s)

C H. Russell, S M. Owens, R Deslattes, A C. Diebold

Abstract

New materials with high dielectric constants (high-K materials) are needed for the further development of dynamic random access memory (DRAM) chips. The problem arises because the continued scaling of such chips toward smaller dimensions using traditional low-K dielectric materials is limited by the electron tunneling through these very thin layers. To make smaller and higher density chips while keeping storage capacitance at the required level, new materials with higherdielectric constants need to be found.Tantalum pentoxide, Ta₂O₅, is one member of this new class of materials with high dielectric constants. It has been shown that amorphous Ta₂O₅ thin films have dielectric constants in the 29.2 to 29.5 range, while crystalline Ta₂O₅ thin films have dielectric constants in the 45.6 to 51.7 range. One difficulty with Ta₂O₅ thin films is that they are difficult to grow reliably and precise measurements of film properties are needed for process qualification.Grazing incidence x-ray reflectivity (GIXR) is a non-destructive analytical technique that gives accurate measurements of layer thickness, layer interface widths, and densities for single and multilayer samples. Powder diffraction of patterns suchas shown in Figure 1 allow detection of crystallinity, identification of specific phases or verification of amorphous structure. The combination of these two methods allows detailed characterization of polycrystalline thin films.In this work, we use GIXR and x-ray powder diffraction to a small group of tantalum pentoxide films (thickness range 2 nm to 8 nm) fabricated under different process conditions. The densities vary over a considerable range from low values (6.31 g/cm³ and 5.08 g/cm3 respectively) to near the tabulated bulk value of {approximately equal to} 8.7 g/cm³. For the hexagonal form (d phase) expected from CVD process, the theoretical density is 8.316 g/cm³. The alternative orthorhombic form (b phase) of Ta₂O₅, produced when Ta is subjected to oxygen radical oxidation during growth, has a closely equal theoretical density. Crystal databases give structures for other oxides and an additional tetragonal form of Ta₂O₅.While this work has demonstrated useful structural characterization, useful conclusions await study of a well-designed sample matrix.

Citation

Electronic Publication

Volume

550

Issue

No. 1

Pub Weblink

/None

Pub Type

Websites

Keywords

DRAM, DRAM chips, dynamic random access memory, GIXR, Grazing incidence x-ray reflectivity, polycrystalline thin films, tantalum pentoxide

Citation

Russell, C. , Owens, S. , Deslattes, R. and Diebold, A. (2001), An Examination of Tantalum Pentoxide Thin Dielectric Films Using Grazing Incidence X-Ray Reflectivity and Powder Diffraction, Electronic Publication, [online], internal:/None (Accessed June 2, 2024)