Healing pinhole shorts for applications using intermetal dielectric films

Abstract

Intermetal dielectric (IMD) films, as the insulation layers between two metal layers, are widely used in integrated circuit (IC) and Micro-electromechanical-systems (MEMS) field [1]. They are imperative to form metal-insulator-metal capacitors [2] in IC chips and multi-metal layer MEMS structures [3], and the film property determines power dissipation, cross-talk, interconnections, and breakdown performance for those applications [4]. The widely used IMD materials, such as silicon dioxide and silicon nitride, can be deposited on metal surface by using either physical vapor deposition (PVD) or chemical vapor deposition (CVD). The mechanisms of film deposition have been well studied, and the fabrication processes of those long established techniques are reasonably mature. However, to implement a completely defect-free IMD film is not always guaranteed. Pinhole is a common defect of an IMD film. It can cause failures of short-circuit or current leakage between the metal layers so that decrease the fabrication yield. Therefore, healing pinholes shorts is important for mass production of IMD-based applications, especially for the cases that IMD films have been deposited and pinhole defects appear. This topic has attracted a lot of research, and several groups and companies have introduced some approaches. Bell Laboratories developed a fabrication process to etch away the inter-metal sacrificial layer therefore to physically separate two metal layers [5]. However, this method requires the top metal features to be suspended by other structures so that applications are limited. Methods of using light-sensitive processes and materials to fill pinholes for repairing short defects have been reported [6][7], but the substrate has to be light-transmitting. An universal method for healing pinhole shorts is therefore more stringent.