Corona Discharge--Electrostatic Method for Deposition of Powdered Passivation Glass on Semiconductor Devices

Selective deposition of powdered passivating glass on either insulating or conducting regions of a device wafer can be accomplished by first depositing ions from a corona discharge on the insulating regions of the device wafer and then immersing the wafer in an insulating liquid containing a charged suspension of the powdered glass. The method is fast (about 15 s per wafer) and both sides can be coated simultaneously. Advantages compared to other methods are listed. The wafer charging process and the glass deposition process are discussed in terms of the relevant process parameters. Thus far, the main application has been deposition of glass in the grooves of mesa-type thyristors and rectifiers.