Browsing by Author "Johnston, PN"

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    Analysis of compound semiconductor materials using heavy ion recoil spectrometry
    (Australian and New Zealand Institutes of Physics, 1994-11-09) Walker, SR; Johnston, PN; Bubb, IF; Studd, W; Cohen, DD; Dytlewski, N; Hult, M; Whitlow, HJ; Zahring, C; Östling, M; Andersson, M; Martin, JW
    Heavy Ion Recoil Spectrometry has been used to examine various semiconductor material systems which cannot easily be studied using convensional ion beam techniques such as RBS. The technique enables the determination of seperate energy spectra for individual elements. This enables it to be used in many situations where RBS is inappropriate due to the superimposition of signals in the backscattering spectrum. We have employed Recoil Spectrometry to study; light element impurity concentrations, stoiciometry and metalisation contact systems for various compound semiconductor materials.- The experiments were performed at the ANTARES (TN Tandem) accelerator facillity at Lucas Heights using 61-91 MeV 12?I ions jn e incident " ' i ions cause nuclei of the sample to recoil following Rutherford scattering. The recoiling target nuclei are then analysed by a Time Of Flight and Energy (TOF-E) detector telescope composed of two timing pickoff detectors and a surface barrier (energy) detector. From the time of flight and energy, the ion mass can be determined and individual depth distributions for each element can be obtained.
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    Characterization of ion tracks in PMMA for single ion lithography
    (Elsevier, 2007-07) Alves, A; Johnston, PN; Reichart, P; Jamieson, DN; Siegele, R
    The ultimate resolution in ion beam lithography (IBL) can be achieved by etching tracks modified by the passage of a single ion impact which has a diameter in the order of 10 nm. For precise counting of single ions, a Si photodiode is used as a substrate onto which a PMMA film is spun. We have macroscopically investigated the sensitivity of PMMA using 3 MeV H end found that a deposited energy density of greater than 1 eV/nm(3) is required to remove the PMMA film for 60 s developing in a water:IPA 1:4 solution. From this sensitivity measurement we have determined that 8 MeV F, 71 MeV Cu and 88 MeV I ions should produce enough damage in a single ion strike to create a hole etched along the latent damage track. We have used AFM imaging to quantitatively characterise the hole diameter as a function of the incident ion and the developing time. It was found that for up to 8 min development in a water:IPA solution holes were created for the F, Cu and I ions. SEM imaging has also been used to verify the holes seen by AFM imaging. © 2007, Elsevier Ltd.
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    Characterization of single ion tracks in PMMA created by light and heavy ion microprobes
    (Australian Institute of Physics, 2006-12-05) Alves, A; Reichart, P; Siegele, R; Johnston, PN; Jamieson, DN
    The ultimate resolution in ion beam lithography can be achieved by etching the material modified by a single ion impact which has a diameter in the order of only 10 nm. The sensitivity of the resist needs to be as high as possible but also keeping the bulk etch rate at a minimum. Our study is focused on poly methyl methacrylate (PMMA) with a small bulk etch rate compared to other track detectors (e.g. CR-39). We investigated the sensitivity using 3 MeV H, 8 MeV F, 71 MeV Cu and 88 MeV I generated by ion microprobes. Precise ion counting into a spin coated PMMA film on top of an active substrate enables us to control the exact dose and fluence delivered to the PMMA from a homogenous dose down to separated single ion tracks. With homogenous irradiation, the sensitivity limit was found to be 1-2 eV/nm^3, hence the damage radius and LET determines the etchability of a single ion track. Analysis of the track radii was performed using non-contact AFM. A high aspect ratio Si nanowhisker tip was used to image the openings to the etched tracks. It was found that for up to 8 min development in a water:IPA solution holes were created for the F, Cu and I ions. The undamaged bulk PMMA is also etched at a significantly lower rate than the ion tracks and contributed to a roughening of the PMMA surface. At 16 min developing time the PMMA film was completely removed. This was attributed to a mechanical failure in the film and not gradual film etching. Hole diameter and depth has been quantitatively analysed in an effort to determine the relationship between the LET of the incident ion, the development time and the resulting hole diameter.