(A) study on the plasma-enhanced atomic layer deposition of Ta-N, Ti-N and Ti-Si-N thin films

Abstract

As increasing demand for smaller, faster electronic devices in ultralarge scale integrated devices (ULSI), copper (Cu) with a lower resistivity and an enhanced electromigration resistance represents a promising material for providing better performance as an interconnect metal than aluminum (Al) alloys which are currently in use. However, Cu forms Cu-Si compounds and an easily drift through the oxide at a low temperature. Therefore, a diffusion barrier between Cu and its underlying layers is thought to be a prerequisite for Cu to be used in application for silicon integrated circuits. The plasma-enhanced atomic layer deposition (PEALD) of tantalum nitrides (TaN) thin films has been performed using terbutyl-imidotris(diethylamido)tantalum and hydrogen radicals at a temperature of 260℃. The films thickness per cycle is also self-limited at 0.8Å/cycle, which is thinner than that of the conventional atomic layer deposition (ALD), 1.1Å/cycle. The PEALD yielded superior Ta-N films with an electric resistivity of 400 μΩ-cm and no aging effect under exposure to air owing to the increased film density and crystallinity, and the presence of TaC bonding. X-ray diffraction analysis indicates that the as-deposited films are not amorphous but polycrystalline mixed with cubic TaN and TaC. The film crystallinity as well as the film density increases with the pulse time and the electrical power of the hydrogen plasma used. The films were Ta-rich in composition and contain around 15atom% of carbon impurity. In addition, it has been shown that films, which are formed by the PEALD, retain perfect step coverage on the submicrometer holes with an aspect ratio of 10:1. In Ti-N thin films deposited with TDMAT and $N_2$ plasma, nitrogen radical are used as a reducing agent instead of $NH_3$. Like Ta-N case, the Ti-N films formed by PEALD have a good resistivity with about 440 μΩ-cm and cubic TiN structure at 180℃. However, the carbon impurity in films decreases at 15 atom% as the po...