Paper EL+AS+EM+MS+TF-FrM2
Spectroscopic Ellipsometry of Pulsed Laser Deposited ZnO on Atomic Layer Deposited Al₂O₃ and HfO₂

Friday, October 22, 2010, 8:40 am, Room Cochiti

Zinc oxide thin films and coatings are an integral part of a number of devices because of their wide range of properties. Depending on the conductivity and transparency, these materials are of interest for electronic (diodes, FETs), optoelectronic (detectors, modulators, flat-panel displays, solar cells, etc.) and piezoelectric (BAW,SAW) devices. In this study, we examine FET ZnO active device layers in conjunction with atomic layer deposited (ALD) Al₂O₃ and HfO₂ for isolation and gate dielectrics. Stacks of pulsed laser deposited (PLD) ZnO on thermal and plasma ALD Al₂O₃ and HfO₂ are prepared on a variety of large area substrates.

The surface morphologies of PLD grown ZnO-based films and ALD dielectrics are critical to optimize the interface quality in multilayer structures. Therefore, the control and optimization of surface properties over large areas is essential for the successful application of PLD ZnO thin films in device configurations. We have previously reported high quality ZnO films being obtained over large areas using off-axis PLD [1, 2]. Film thickness and compositional uniformity control is a critical issue associated with the scale-up of PLD systems. Thus, spectroscopic ellipsometry (SE) has a significant role in the characterization of these films.

A commercial Phase-Modulated Ellipsometer (PME) is employed to study the interplay between structural, electrical and optical properties of single-layers and PLD ZnO/ALD dielectric stacks. Known for its precision and non-destructiveness, SE is an indirect measurement technique in the sense that the film properties of interest are obtained by a nonlinear regression analysis of measured data to an optical model. We examine the effect on the goodness of fit parameter from the use of various optical models. Furthermore, since we are employing a PME, the time to scan a wide spectral region is limited by the slew rate of the monochromater. This can be a significant burden when making uniformity determination over large-area substrates. Thus, we examine the effect on the goodness of fit parameter from minimizing data acquisition time. The optical properties of the individual thin films extracted by SE are compared to optical studies using normal incidence transmission. Film surface roughness is obtained from SE by employing the Bruggeman effective-medium approximation and subsequently compared to structural characterizations using atomic force microscopy and x-ray diffraction.

Reference:

1. K. D. Leedy, C. V. Varanasi, D. H. Tomich and B. Bayraktaroglu, 5^th International Workshop on ZnO and Related Material (2008).

2. D. Agresta, K. Leedy, R. Scott, T. Dang and B. Bayraktaroglu,, AVS-56 (2009).