|
The ability to measure profiles of high-aspect structures is important for the development of new integrated circuit fabrication processes. Delays in the development learning cycle frequently occur due to turn-around time associated with the logistics of off-line laboratory sectioning and analysis. Sample preparation techniques associated with existing cross-sectional imaging methodologies also necessitate destruction of the whole sample. Focused ion beam (FIB) sectioning has recently been used in conjunction with SEM imaging for profile acquisition inside the fabrication facility. However, full acceptance of FIB inside the cleanroom processing area has been slowed by concerns over the threat of Gallium contamination arising from the ion beam. There also exists uncertainty in the fidelity of FIB-based profile acquisition, due to the various artifacts associated with the ion beam mill sectioning process. In this article, the application of and difficulties associated with electron beam induced processing (etch and deposition) for obtaining feature profile shape information on masks and wafers will be described. Purely chemical reactions with much higher material selectivity and less damage have been employed to obtain microstructure profile information using various scanned electron beam tools. The superiority of electron beam induced deposition (compared to FIB) for passivation and replication of the surface topography prior to etching has also been demonstrated. In addition to electron and ion beam based sectioning, a novel atomic force microscope based nano-machining process has been developed for three-dimensional tomographic imaging of high-aspect features on masks and wafers. Images and profiles of feature regions not accessible with FIB/SEM or CDAFM methodologies will be presented. The challenges encountered for practical implementation of this new, non-beam-based, approach to sectioning will also be discussed. Advantages of this approach are: immunity to maximum aspect ratio limitations, superior lateral spatial sampling in X and Y, and no reliance on high-aspect probes for imaging. Therefore, tip-shape issues associated with currently incumbent CDAFM methodologies can be avoided altogether.
|
