Paper AS-TuP33
Topographical Study of TiN "Ion-CCD" Detector Surface: How damaging are sub-fA Ion Beams of 1‑keV Energy?
Tuesday, November 10, 2009, 6:00 pm, Room Hall 3
The development of ion-detector arrays with high spatial resolution enabled the miniaturization of double-focusing sector-field mass spectrometers (MS). A modified imager based on a charge-coupled device (CCD) provides the spatial resolution, ruggedness, and analytical sensitivity necessary to build a transportable mass spectrometer. The transportable (~ 40 lb) mass spectrometer, which was introduced by OI Analytical at the 2009 Pittsburg Conference1, is based on a double-focusing sector-field MS of Mattauch-Herzog geometry and an ion-CCD. The MS separates ions of different m/z spatially and focuses all ion beams onto a confocal plane of 2” width. The ion-CCD detects simultaneously all separated ion beams. The focal point of an ion beam is about 1500 x 300 mm2, covering roughly 10 pixels. The ion-CCD consists of 2126 active pixels with a pitch of 24 μm. Fig.1 is a contact mode Atomic-Force-Microscope image showing the width (21 μm) of the pixel and the insulation gap between two adjacent pixels (3 μm). The ion-CCD as described earlier2 has an upper layer of TiN, 100‑ nm thick. It is this layer that takes the full impact of the up to 1‑ keV ions at an incidence angle of 45o. In this work we will investigate the effect of the energetic ions on the ion-CCD and probe the extent of the surface damage, if any, as function of the ion flux and the overall ion-CCD exposure time. The ion-CCD is generally exposed to ion currents in the sub-fA regime and ion beam densities of up to about 109-1011 ions/cm2 per second. We will characterize an ion-CCD chip after operating for roughly one year and compare pixels with no ion impact history to those exposed to ion beams consisting of N2+, O2+, Ar+ and Xe+. In our system, the impact energy of the analyzed compounds falls right on the efficient sputtering regimes, especially for ions with masses close to N and Ti where momentum transfer is optimum3.
(1) “Compact GC/MS based on the Ion-Camera mass spectrometer”, Gottfried Kibelka, Omar Hadjar, Scott Kassan, Scott Shill, Chad Cameron. Pittsburgh Conference, Chicago. 2009.
(2) “CCD for Ion Detection” Omar Hadjar, Gottfried Kibelka, AVS International Symposium & Exhibition, Boston 2008.
(3) J. Vac. Sci. Technol. A, Volume 19, Issue 3, pp. 1004-1007 (May 2001).