Atomic Layer Deposition of SrO at Stanford Nanofabrication Facility
Michelle Rincon and Woo Shik Jung, Stanford Nanofabrication Facility
Our goal at the SNF is to enable users to develop any film they need using our Cambridge Nanotech Savannah (thermal ALD system) and Fiji (plasma-enhanced ALD) systems. One great example of this is our newly developed SrO deposition process.
The SrO film was developed using the Bis(1,2,4-tritertiarybutylcyclopentadienyl)strontium precursor. Since this precursor has a low vapor pressure (0.6mmHg at 150C), the boost system was used to improve the transfer of the precursor into the process chamber. The Ultratech/Cambridge boost system adds an ALD valve to inject carrier gas into the precursor cylinder to pressurize it prior to pulsing the ALD valve to the process chamber. The chemistry also requires high precursor temperatures and long purge times in order to stabilize the growth rate. The SrO film deposition rate (characterized by ellispometry) is 0.18A/cycle with less than 3% non-uniformity across a 4 inch wafer. The stoichiometry of a freshly deposited wafer is almost 1O:1Sr although it appears that the film does react with air and the stoichiometry becomes closer to 2 O:1 Sr after some time.
Characterization data for SNF films can be found here: https://snf.stanford.edu/SNF/equipment/chemical-vapor-deposition/ald/films-and-data