High‐density remote plasma sputtering of high‐dielectric‐constant amorphous hafnium oxide films

Hafnium oxide (HfO x ) is a high dielectric constant ( k ) oxide which has been identified as being suitable for use as the gate dielectric in thin film transistors (TFTs). Amorphous materials are preferred for a gate dielectric, but it has been an ongoing challenge to produce amorphous HfO x while maintaining a high dielectric constant. A technique called high target utilization sputtering (HiTUS) is demonstrated to be capable of depositing high‐ k amorphous HfO x thin films at room temperature. The plasma is generated in a remote chamber, allowing higher rate deposition of films with minimal ion damage. Compared to a conventional sputtering system, the HiTUS technique allows finer control of the thin film microstructure. Using a conventional reactive rf magnetron sputtering technique, monoclinic nanocrystalline HfO x thin films have been deposited at a rate of ∼1.6 nm min −1 at room temperature, with a resistivity of 10 13  Ω cm, a breakdown strength of 3.5 MV cm −1 and a dielectric constant of ∼18.2. By comparison, using the HiTUS process, amorphous HfO x ( x  = 2.1) thin films which appear to have a cubic‐like short‐range order have been deposited at a high deposition rate of ∼25 nm min −1 with a high resistivity of 10 14  Ω cm, a breakdown strength of 3 MV cm −1 and a high dielectric constant of ∼30. Two key conditions must be satisfied in the HiTUS system for high‐ k HfO x to be produced. Firstly, the correct oxygen flow rate is required for a given sputtering rate from the metallic target. Secondly, there must be an absence of energetic oxygen ion bombardment to maintain an amorphous microstructure and a high flux of medium energy species emitted from the metallic sputtering target to induce a cubic‐like short range order. This HfO x is very attractive as a dielectric material for large‐area electronic applications on flexible substrates.