PLASMA ETCHING OF THICK OXIDES WITHOUT PHOTORESIST RETICULATION
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2001-Nov-15
During very long (i.e. > 20 minute) plasma etched, such as those typically used to etch via through glass in metal interconnect structures, the wafers will reach temperatures high enough to cause reticulation or flow of the patterning photoresist. The wavers reach these temperatures (>130%) because of poor thermal conductivity between the wafer and the cooled pedestal against which'it rests during the etch. This problem is most prevalent in batch hexode systems where efficient backside cooling of wafers is mechanically very difficult. One way around this problem without com- promising the other characteristics of the etch (i.e. the etch rate and uniformity) is to add one or more "cool down" steps to the process. During these steps, the system is run at as high an operating pressure as the pumping package will allow (typically about 200 mTorr) with gas flowing, but without rf. The cool down step (or steps) is typically five minutes long. This high pressure, high flow step allows improved thermal conductivity between the wafer and the pedestal, which allows the wafer to cool. With the etch broken up by the appropriate number of cool down steps, the wafer is not allowed to reach a temperature high enough to cause resist flow.