M. Nigam

Luminescent layers for ion-photon emission microscopy

Abstract Ion beam induced luminescence (IBIL) combined with ion beam induced charge collection (IBICC) is applied in a quantitative study of the IBIL generation yield and detection efficiency for several plastic phosphor materials. The main purpose of this study is to search for strongly luminescence materials that can be used to easily coat samples to be studied with ion-photon emission microscopy (IPEM). A special focus is given to plastic scintillation materials because thin films are easily prepared, and such films have already been used for single event triggering. The emission yield was found to be low for typical Bicron plastic phosphors (only ∼70 photons/ion/μm). The total collection, transmission and photon detection efficiency of the optical microscope used in this study was determined to be only ∼0.00003. For thin film plastic phosphors ∼20 μm thick, the detection efficiency was only 0.04 photons/ion. This means that using these plastics, IPEM would need to be performed with ∼20× more beam fluence to obtain data, such as IBICC, similar to a standard scanned nuclear microprobe. Improvements are discussed.

The high-energy heavy ion nuclear microprobe at the University of North Texas

Abstract The high-energy, heavy ion, microprobe recently installed at the University of North Texas (UNT) has a demagnification factor of ∼60. It has a probe-forming lens system with a new Russian quadruplet configuration. The microprobe is installed on a 3 MV NEC 9SDH-2 Pelletron tandem accelerator, which has ultra stable high energy for heavy ions ( ΔE / E ∼10 −4 ). Sputter and RF sources produce a variety of ions for microprobe applications. A resolution of ∼2 μm has been achieved for 2.0 MeV protons, 4.0 MeV C ions and 9.0 MeV α-particles with a current of about 50–100 pA. Materials characterization and failure analysis of microelectronics are discussed. Current limitations and future improvements to the system are outlined.

Ionoluminescence decay measured with single ions

A new ion beam analysis-based, single ion technique called the time to first photon has been developed to measure the decay of the luminescence signal of phosphors. Such measurements are currently needed to study luminescence decay mechanisms following high-density excitations and to identify strongly luminescent phosphor coatings with short lifetimes for ion photon emission microscopy (IPEM). The samples for this technique consist of thin phosphor layers placed or coated on the surface of PIN diodes. Single ions from an accelerator strike this sample and simultaneously create ion beam induced luminescence (IBIL) from the phosphor that is measured by a single-photon-detector, and an ion beam induced charge collection (IBICC) signal in the PIN diode. In this case, the IBICC signal provides the start pulse and the IBIL signal the stop pulse to a time to amplitude converter. It is straightforward to show that this approach also measures a signal proportional to activity versus time with an accuracy of 5% as long as the number of detected photons per ion is less than 0.1, which usually requires the use of absorbers for the IBIL detector or electronic discrimination for the IBIL signals. Details of the new analysis are given together with examples of luminescence decay measurements of several ceramic phosphors being considered to coat IPEM samples. IPEM is currently being developed at Sandia National Laboratory (SNL), the University of North Texas in Denton, and the Universities and INFN of Padova and Torino.

Diffusion-time-resolved ion-beam-induced charge collection from stripe-like test junctions induced by heavy-ion microbeams

Abstract To design more radiation-tolerant integrated circuits (ICs), it is necessary to design and test accurate models of ionizing-radiation-induced charge collection dynamics. A new technique, diffusion-time-resolved ion-beam-induced charge collection (DTRIBICC), is used to measure the average arrival time of the diffused charge, which is related to the average time of the arrival carrier density at the junction. Specially designed stripe-like test junctions are studied using a 12 MeV carbon microbeam with a spot size of ∼1 μm. The relative arrival time of ion-generated charge and the collected charge are measured using a multiple parameter data acquisition system. A 2-D device simulation code, MEDICI, is used to calculate the charge collection dynamics on the stripe-like test junctions. The simulations compare well with experimental microbeam measurements. The results show the importance of the diffused charge collection by junctions, which is especially significant for single-event upsets (SEUs) and multiple-event upsets (MEUs) in electronic devices. The charge sharing results also indicate that stripe-like junctions may be used as position-sensitive detectors with a resolution of ∼0.1 μm.

Impurity measurements in semiconductor materials using trace element accelerator mass spectrometry

Abstract Accelerator mass spectrometry (AMS) is commonly used to determine the abundance ratios of long-lived isotopes such as 10 B, 14 C, 36 Cl, 129 I, etc. to their stable counterparts at levels as low as 10−16. Secondary ion mass spectrometry (SIMS) is routinely used to determine impurity levels in materials by depth profiling techniques. Trace-element accelerator mass spectrometry (TEAMS) is a combination of AMS and SIMS, presently being used at the University of North Texas, for high-sensitivity (ppb) impurity analyses of stable isotopes in semiconductor materials. The molecular break-up characteristics of AMS are used with TEAMS to remove the molecular interferences present in SIMS. Measurements made with different substrate/impurity combinations demonstrate that TEAMS has higher sensitivity for many elements than other techniques such as SIMS and can assist with materials characterization issues. For example, measurements of implanted As in the presence of Ge in GexSi1−x/Si is difficult with SIMS because of molecular interferences from 74 GeH, 29 Si30Si16O, etc. With TEAMS, the molecular interferences are removed and higher sensitivities are obtained. Measured substrates include Si, SiGe, CoSi2, GaAs and GaN. Measured impurities include B, N, F, Mg, P, Cl, Cr, Fe, Ni, Co, Cu, Zn, Ge, As, Se, Mo, Sn and Sb. A number of measurements will be presented to illustrate the range and power of TEAMS.

The recent progress of the high-energy heavy ion nuclear microprobe at the University of North Texas

The paper reports the recent progress of a high-energy, heavy ion nuclear microprobe facility established at the University of North Texas. The microprobe system is installed on a 3MV NEC 9SDH-2 Pelletron tandem accelerator. A high demagnification factor (∼60) has been achieved with the system, using a probe-forming lens system (from MARC, Melbourne, Australia) with the new Russian quadruplet configuration. The spatial resolution of 2–3 μm has been achieved for 4.0 MeV carbon ions or 9.0 MeV alpha particles with a beam current of ∼50–100 pA. Better spatial resolution (approaching one μm) is achievable when an extremely low beam current (100–2000 ions/sec) is used in the applications of IBICC and IBIL. Applications of the analytical techniques with the nuclear microprobe are outlined and discussed.

Stopping powers of 2–10 MeV Si, P and S ions in Ni, Cu and Ge thin films using a novel ERD-based technique

The stopping powers of 2–10 MeV Si, P and S ions in Ni, Cu and Ge thin films has been measured using a novel technique based on elastic recoil detection (ERD). This technique eliminates the need to recalibrate the silicon surface barrier detector while changing the incident ion species. Results have been compared to SRIM 2000 and other theoretical predictions and experimental measurements.

The study of phosphor efficiency and homogeneity using a nuclear microprobe

Ion Beam Induced Luminescence (IBIL) and Ion Beam Induced Charge Collection (IBICC) have been used to study the efficiency and the homogeneity of the luminescence emission in phosphors. The IBIL imaging was made by using sharply focused ion beams or broad/partially-focused ion beams. Samples were examined to reveal possible distributed crystal-defects that may lead to the inhomogeneity of the luminescence emission. The purpose of the study is to search for suitable thin films that have high homogeneity of luminescence emission and large IBIL efficiency under heavy ion excitation. These films may be placed as a thin layer on the top of microelectronic devices to be analyzed with Ion Photon Emission Microscopy (IPEM). The emission yields were found to be low for organic materials, due to saturation of the light output dependence on the energy deposition of heavy ions. The emission yield of a typical Bicron plastic scintillator is about 70 photons/ion/micron. Inorganic materials may have higher IBIL yields u...