Al Diffusion in Polycrystalline Cu
- PDF / 294,937 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 93 Downloads / 221 Views
1079-N04-06
Al Diffusion in Polycrystalline Cu Florian Gstrein, Harold Kennel, Andre Budrevich, Barbara Miner, John Plombon, and Ebrahim Andideh Intel Corporation, Hillsboro, OR, 97214 ABSTRACT The diffusion of aluminum (Al) from a source sandwiched between polycrystalline copper (Cu) thin films was investigated as a function of time and temperature through secondary ion mass spectroscopy (SIMS) and continuum simulations. Extracted diffusion coefficients for the bulk were in line with literature values. In order to simulate the experimentally derived diffusion profiles at temperatures where bulk diffusion is not the dominant diffusion mechanism (room temperature to 350 °C), it was necessary to explicitly include the re-distribution of Al as a result of Cu grain growth during anneal. Aluminum has the tendency to segregate to the Cu/liner and Cu/etch stop (ES) interface. The tendency of Al to segregate to the liner is ten times stronger for ruthenium (Ru) than for tantalum (Ta). In 100 nm wide dual damascene structures lined with Ru, this segregation behavior was responsible for the Al depletion in bulk Cu and for the Al depletion at the Cu/ES interface. INTRODUCTION To meet the increasing feature-density requirements of future technology nodes, the dimensions of copper (Cu) dual damascene interconnects must be continuously scaled. Since the current density increases with shrinking feature size, Cu lines become more and more prone to electromigration-induced failure. The electromigration resistance of Cu can be improved through doping with elements such as Ag, Sn, and Al [1-3]. Relatively little is known about the fundamental diffusion properties of these dopants in polycrystalline Cu thin films and about the dopant distribution in Cu dual damascene structures. In the present study, we report on the diffusion mechanism of aluminum (Al) in Cu thin films. To understand the experimentally derived Al diffusion profile in terms of grain boundary diffusion, bulk lattice diffusion and grain size evolution during anneal, secondary ion mass spectroscopy (SIMS) depth profiles of Aldoped Cu thin films were complemented with continuum simulations. Aluminum segregation to the Cu/ES interface and to two technologically relevant liner materials, tantalum/tantalum nitride (Ta(N)) and tantalum nitride/ruthenium (TaN/Ru), were first investigated for simple planar stacks. The results are then compared with the spatial distribution of Al in Cu-filled trenches. EXPERIMENT All samples were fabricated in state-of-the-art 300 mm barrier/seed deposition tools with integrated degas and pre-clean capability, an electroplating tool and a CVD etch stop deposition tool. Figure 1 (a) shows the blanket wafer film stack used in this study. The bottom interface consisted of a PVD Ta(N) based barrier or a TaN/Ru bi-layer, respectively.
A 200 Å thick PVD Cu-Al layer was sandwiched between two 1000 Å thick PVD Cu layers. The total Al dose in the stack was on the order of 7x1015 atoms/cm2. Symmetrical diffusion stacks were capped either with a Ta or Ru
Data Loading...
