Methods and apparatus for depositing and/or etching material on a substrate

A method for depositing material onto and etching material from a substrate in a surface processing tool having a processing chamber, a controller and one or more devices for adjusting process parameters within the chamber, the method comprising:

• instructing, using the controller, the one or more devices according to a series of control steps, each control step specifying a defined set of process parameters that the one or more devices are instructed to implement, wherein at least one of the control steps comprises:
• implementing, using the one or more devices, a defined set of constant process parameters for the duration of the step, wherein the process parameters comprise a chamber pressure and total gas flow rate through the chamber, wherein the duration of the step is less than the corresponding gas residence time (Tgr) of the processing chamber for the step such that there is insufficient time for the chamber to reach steady state conditions during the step, wherein:
• T
• gr
• =
• pV
• Q
• wherein:
• p is the chamber pressure in units of Pa;
• V is the volume of the processing chamber in units of m3;
• and
• Q is the total gas flow rate through the processing chamber in units of Pa·m3·s−1;
• and
• wherein a first sequential subset of one or more of the series of control steps constitutes a passivation process phase during which the processing parameters are selected for depositing a passivation layer on the substrate, and a second sequential subset of one or more of the series of control steps constitutes an etching process phase during which the processing parameters are selected for etching the substrate.