Bilevel Polysiloxane Resist For Ion-Beam And Electron-Beam Lithography

A series of polysiloxane-based negative resists will be described which are applicable to both electron-beam and ion-beam lithography. Compositional changes have been made to nary the Fisitivitg to 20 keV electrons from 40 to 180 μC/cm 2 . A sensitivity of 9.4 tiC/cm (2.5 x 10 12 ions/cm 2 ) has been obtained with 150 keV silicon ions for the 40 iiC/cm E-beam resist. The resists have high glass transition temperaWes and re effective top layers of a bilevel resist system. A thin polysiloxane layer (400A to 1000A) makes an effective mask layer over 1 to 2 μm AZ type leveling layer. After the polysiloxane pattern was developed, the images were transferred to the AZ layer by reactive ion etching with oxygen. By properly adjusting the etching parameters, extremely high anisotropy and excellent selectivity (25:1 ratio between bottom and top layers) were achieved. Using this polysiloxane-topped bilevel system, good quality images have been prepared using both electron-beam lithography (EBL) and focused ion-beam lithography (FIBL). With a 600 -700w thick polysiloxane layer over 1 pm of AZ1370 we have produced a 6000 wide gap with parallel side walls in a 2 pm pitchimage by EBL. The same process has also demonstrated high quality images over 5000A steps. For FIBL a resist system consisting of 400w of polysiloxane over 1 pm AZ1370 was used with a focused 50 keV gallium ion beam2 Resist lines 0.12 pm wide and 1 μm high were produced with an exposure of 8 x 10 12 ions/cm 2 .