Breakdown in ALD-processed oxide based thin film structures
- PDF / 6,592,341 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 60 Downloads / 203 Views
Breakdown in ALD-processed oxide based thin film structures Holger Spahr, Tim Bülow, Christine Nowak, Felix Hirschberg, Johannes Reinker, Sami Hamwi, Hans-Hermann Johannes and Wolfgang Kowalsky Technische Universität Braunschweig, Institut für Hochfrequenztechnik, Schleinitzstraße 22, 38106 Braunschweig, Germany ABSTRACT We report on the continuous increase of the breakdown electric field, also known as disruptive strength, of an ultra thin layer based on Al2O3 prepared by atomic layer deposition (ALD) by reducing its thickness from 90 nm down to 3 nm. By calculating the disruptive strength for lower thicknesses, we demonstrate that our observations are in agreement with recent reports. Additionally, the disruptive strength increases to lower thicknesses as the pinhole density rises. The pinholes, referred to as morphological defects, are detected by Cu electroplating and result in a lower permittivity of the dielectric. As a conclusion, the dielectric breakdown is predominantly attributed to intrinsic, meaning stoichiometric defects. Thus, morphological defects, consisting of pinholes generated by agglomerative growth of the dielectric, surprisingly do not have a negative influence on the dielectric breakdown of ALDprocessed ultra thin dielectric layers. INTRODUCTION Oxide based thin films with thicknesses below 100 nm are of great interest in current MOSFET and related technologies. Atomic layer deposition (ALD) provides the possibility of generating distinct layer compositions and thicknesses. Since ALD is based on alternate pulsing of metal organic precursors into an evacuated and heated reactor, no volume reactions will occur. All surfaces inside the reactor are coated, including the substrate [1]. ALD processed films show an agglomerative growth at the first pulsing cycles, which leads to a discontinuously closed surface [2]. Hence, the surface contains morphological defects or pinholes. These pinholes can be detected by using Cu electroplating [3]. When an increasing voltage ramp stress (VRS) is applied to the ALD processed oxide, electrical breakdown will occur at the breakdown voltage. The related breakdown electric field is called disruptive strength. The hard breakdown, meaning the irreversible damage of the device, is caused by Joule’s heat at increasing current densities through the oxide [5,6,7,8]. Regarding the breakdown effects, the influence of the morphological defects on the disruptive strength is of special interest. EXPERIMENT Glass substrates, precoated with lithographically structured ITO have been use to deposit Al2O3 onto the electrode, as shown in figure 1. ALD to deposit Al2O3 was performed at 80°C by pulsing water and TMA (Tri-methyl-aluminum) in N2 flow as purging gas in an alternating order into the reactor (Cambridge, Savannah). Oxide thicknesses between 3 and 85 nm were generated for the electrical breakdown measurements by varying the number of cycles.
Figure 1: 3D-sketch of the substrate used for the breakdown experiments. Al2O3 is deposited onto ITO bottom electrodes, followed by
Data Loading...
