"For example, if the spacers 50, conductor 72 and conductor 20 are polysilicon, the insulator 60 and pad 23 are nitride, the substrate 22 is silicon and the collar insulator 21 is an oxide, the etchant is preferably a nitride reactive ion etch which does not significantly etch silicon, polysilicon, or oxide, such as a plasma containing CH3F" . . . .