Method for Etching of Metal

A method of smoothing a surface, the method comprising:

• providing a substrate, a metal layer being over the substrate, the metal layer having a rough or oxidized surface;
• and
• performing one or more cycles of a smoothing process, wherein each cycle comprises:
• exposing the rough or oxidized surface to a plasma-excited H2 gas, wherein the plasma-excited H2 gas chemically reduces the oxidized surface of the metal layer and forms a layer of reaction products on the metal layer;
• and
• exposing the rough or oxidized surface to a plasma-excited Ar gas, wherein the plasma-excited Ar gas removes the layer of reaction products overlying the metal layer, wherein kinetic energy of the plasma-excited Ar gas is at or below a sputtering threshold for removing metal from the metal layer.

A plasma processing system comprising:

• a chamber, the chamber comprising a substrate holder configured to hold a substrate;
• a gas injection system coupled to the chamber;
• a vacuum pumping system coupled to the chamber;
• and
• a computer coupled to the gas injection system and the vacuum pumping system, wherein the computer is configured to execute a program, the program comprising instructions to:
• expose a metal layer on the substrate to an oxidizing gas;
• expose the metal layer to a plasma-excited H2 gas;
• and
• expose the metal layer to a plasma-excited noble gas.