Interface Stability of Metal Barrier and low K Dielectrics
- PDF / 212,625 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 40 Downloads / 211 Views
0990-B09-05
Interface Stability of Metal Barrier and low K Dielectrics T.-M. Lu1, Y. Ou2, and P.-I. Wang2 1 Center for Integrated Electronics and Department of Physics, Rensselaer Polytechnic Institute, 110, 8th Street, Troy, NY, 12180 2 Department of Physics, Rensselaer Polytechnic Institute, 110, 8th Street, Troy, NY, 12180 ABSTRACT It is known that the interface between a refractory metal barrier and a dielectric material is stable against thermal treatment at a conventional IC interconnect processing temperature. However, the interface may not be stable against thermal and electrical stress called the bias temperature stress (BTS) at moderate conditions of 150 oC and 0.5 MV/cm. Massive refractory metal ions are seen to drift into low K dielectric materials that contain a mixture of organic and inorganic elements. It is argued that the oxidation of the metal at the interface creates unstable metal ions that are ready to drift into the dielectric film under an electric filed during the BTS test. Dielectric or dielectric capping materials that do not contain oxygen can prevent metal oxidation and are desirable to create a stable metal and dielectric interface. INTRODUCTION Refractory metals have been successfully used as the diffusion barrier for Cu in modern integrated circuits. A good metal barrier should prevent Cu penetration into the barrier and then into the dielectric. At the same time, the barrier material itself should not penetrate into the dielectrics. It is well known that the interface between refractory metal and a dielectric such as the Ta family and SiO2 is very stable against thermal and electrical stresses. An important reason for the choice of refractory metal as the diffusion barrier is because of its high melting temperature. However, recently it was found that the interface between refractory metal and many low K systems may not be stable against a bias temperature stress [1]. Even under a moderate bias temperature stress condition, refractory metal ions are found to penetrate deep into the dielectric systems. In the study by Mallikarjunan et al., a hybrid organosiloxane polymer (HOSP, with Κ=2.5) was used as the low K dielectric in conjunction with different gate metals, including copper, aluminum, tantalum and platinum. For electrical measurements, 200 nm HOSP was spun on 50 nm of a thermally oxidized n-Si(100) substrate. BTS (bias temperature stress) experiments were performed at 150oC and at a bias of 0.5 MV/cm. The flat-band voltage shift was observed for Cu, Ta, and Al, but not for Pt. The shift was interpreted as due to the penetration of metal ions into the dielectric film and was confirmed by a triangle voltage sweep experiment [2]. The charge density accumulated at the interface was calculated from the BTS flat-band voltage shift and is plotted for each metal as shown in Figure 1. It was a surprise to see that a refractory metal such as Ta could penetrate into the dielectric under these moderate stress conditions. Even more surprising is the observation of the massive Al penetration
Data Loading...
