1. Be careful what you wish for

2. SiO2 backside protection A coating of SiO2 is deposited on the backside of the wafer to insolate it from the doping process

3. PECVD P lasma E nhanced C hemical V apor D eposition PECVD is used extensively in the manufacture of microelectronic devices because it allows for lower temperature processes

4. Just like in sputtering, a plasma is formed in an electric field The plasma allows for the deposition or growth of films at lower temperature than would normally be required in just a CVD process

5. Trion ORION III PECVD tool The plasma can be viewed through a viewport on the side

6. Typical PECVD Process The wafer is loaded in into the vacuum chamber The chamber is pumped to vacuum conditions The wafer is heated to deposition temperatures (300 o C typical) Gas are introduced that will acts as precursors to the film growth

7. Typical PECVD Process (continued) Chamber pressure is regulated to provide an equilibrium pressure ( gas in, pumping out) RF power is applied to the chamber creating a plasma A film is grown based on the gases introduced

8. For our solar cell We will be using SiO2 as the protective layer

9. Trion ORION III PECVD Chamber lid open Heated substrate stage Can accommodate up to 8” wafers

10. Trion ORION III water chiller and dry (no oil) chemical vacuum pump

11. Trion ORION III process gas cabinet TEOS (tetraethylorthosilicon) SiO 2 precursor

12. The backside of the solar cell will have a color tint. The color will relate to the SiO2 thickness