Deformations and stress in PMMA during hard x-ray exposure for deep lithography

摘要

The availability of high-energy, high-flux, collimated synchrotrons radiation has211u001eextended the application of deep X-ray lithography (DXRL) to thickness values of 211u001ethe PMMA resist of several millimeters. Some of the most severe limitations come 211u001efrom plastic deformation, stress, and cracks induced in PMMA during exposure and 211u001edevelopment. We have observed and characterized these phenomena quantitatively. 211u001eProfilometry measurements revealed that the PMMA is subjected either to local 211u001eshrinkage or to expansion, while compression and expansion evolve over time. Due 211u001eto material loss and crosslinking, the material undergoes a shrinkage, while the 211u001eradiation-induced decomposition generates gases expanding the polymer matrix. The 211u001eoverall dynamics of the material microrelief and stress during and after the 211u001eexposure depend on the balance between compaction and outgassing. These depend in 211u001eturn on the exposure conditions (spectrum; dose, dose rate, seaming, 211u001etemperature), post-exposure storage conditions, PMMA material properties and 211u001ethickness, and also on the size and geometry of the exposed patterns.