AVS 49th International Symposium
    Processing at the Nanoscale Thursday Sessions
       Session PN-ThA

Paper PN-ThA3
A Study of PMMA EBL Cross-sections Prepared by a Novel Process

Thursday, November 7, 2002, 2:40 pm, Room C-109

Session: Charged Particle Patterning and Emission
Presenter: W. Hu, University of Notre Dame
Authors: W. Hu, University of Notre Dame
T. Orlova, University of Notre Dame
G.H. Bernstein, University of Notre Dame
Correspondent: Click to Email
We have developed a novel technique of silicon cross-section preparation with high breaking precision with which we have studied cross-section profiles of sub-50 nm electron beam lithography (EBL) patterns in PMMA resist, including post-exposure aging effects. This technique enables us to break our samples along a desired axis with about 1 µm precision, and gives cross-sections allowing imaging with scanning electron microscope (SEM) at any angle. This is a complementary method to cleaving, wedge-polishing and focused ion beam, the last two of which create damage to the surface of the exposed edges. The precise breaking of the wafer or small sample was accomplished by high-aspect-ratio plasma etching of a 2~10 µm wide line in an inductively coupled plasma etcher using the Bosch process (Alcatel 601E) with small sample areas in the line unetched for EBL. After EBL, wafers were broken along the etched line using a simple mechanical. Cross-section studies can provide improved information on the nanometer scale about PMMA EBL profiles, development contrast, and the metal or molecule liftoff process. However, damage to PMMA by the SEM imaging, cross-section preparation and sample metal coating interfere with data analysis. We have developed an optimized process which enables us to obtain nearly original PMMA EBL profiles by coating samples with AuPd alloy using thermal evaporation first and followed by a plasma sputter coating. The fully-covered PMMA trenches are broken along the desired axis and imaged with our Hitachi S-4500 cold cathode field emission SEM. Using these techniques, we studied the aging effect of PMMA resist before development of EBL, which is seldom taken into consideration in fabrication processes. Our cross-section results of PMMA EBL trenches indicate a loss of contrast due to one week aging prior to development, and will result in unsuccessful liftoff. Other cross-sectional views of EBL in a variety of resists will be discussed.