We report the use of delta-doped charge-coupled devices ͑CCDs͒ for direct detection of electrons in the 50-1500 eV energy range. We show that modification of the CCD back surface by molecular beam epitaxy can greatly improve sensitivity to low-energy electrons by introducing an atomically abrupt dopant profile to eliminate the dead layer. Using delta-doped CCDs, we have extended the energy threshold for detection of electrons by over an order of magnitude. We have also measured high gain in response to low-energy electrons using delta-doped CCDs. The effect of multiple electron hole pair production on the observed signals is discussed. Electrons have been directly imaged with a delta-doped CCD in the 250-750 eV range. © 1998 American Institute of Physics. ͓S0003-6951͑98͒03549-9͔There is great interest in detecting and imaging electrons, especially low-energy electrons ͑tens of eV to thousands of eV͒ for scientific spectroscopy applications, such as low-energy electron diffraction spectroscopy and reflection electron energy-loss spectroscopy at reflection high-energy electron diffraction energies. 1,2 In addition, there are space science applications for low-mass, low-power plasma detectors and imagers. Imaging systems for low-energy particles generally use microchannel plate electron multipliers followed by position-sensitive solid-state detectors, or phosphors and position-sensitive photon detectors. These systems work well and can process up to 10 6 electrons/s; however, they have difficulties with gain stability, require high voltages, and the dynamic range and spatial resolution of these compound systems is considerably less than that of a solidstate imaging detector.Because of their high resolution, linearity, and large dynamic range, silicon charge-coupled devices ͑CCDs͒ could make major advances in particle detection. CCDs have been used to meet the needs of a wide range of scientific imaging applications which require accurate photometric imaging at low light levels with high dynamic range. They have been remarkably successful as imagers of x-ray, UV, visible, and near-IR photons. 3 As low-energy particle detectors and imagers, CCDs can make a great impact in many scientific fields. However, their use as particle detectors has been hampered by the inherent problems existing in the frontsideilluminated CCDs. Both the rapid radiation degradation caused by energetic electrons passing through the frontside gates and gate insulator structure, and the large dead layer to the low-energy electrons presented by the thick frontsidegate structure make frontside-illuminated CCDs unsuitable as electron detectors.While backside-illuminated, thinned CCDs offer the possibility of detecting low-energy electrons, they inherently possess a back surface dead layer associated with the backside potential well ͑caused by positive charge at the interface between Si and SiO 2 ). The problem is similar to the detection of UV photons because a significant fraction of the energy of incident electrons is deposited within a few hundr...

We use standard solubility relations and diffusion-limited rate equations to create a model for the gettering of Fe in silicon. The model employs experimentally determined values for diffusivity, ion pairing, binding potentials, and precipitate densities. The model provides a means to evaluate the relative effectiveness of solubility enhancement induced segregation gettering, internal gettering (IG), precipitation, and back-side gettering outdiffusion. The materials variables are p-type doping level, density of bulk IG sites, and back-side IG site density. From this work, an understanding of the interactions of the various gettering mechanisms is developed. We follow the contaminant concentration at various positions in the wafer as a function of time and temperature. Negative temperature ramps are modeled to simulate the inevitable cooling step following high-temperature processing. The results indicate that segregation from epitaxial layers to heavily doped substrates brings orders of magnitude improvement in Fe removal over IG alone and that segregation is effective in reducing contamination levels even when initial contamination levels are very low. The best gettering occurs when IG sites work together with segregation. A well-designed wafer has a high density of IG sites to accelerate equilibration during cooling and to enhance mass transport from the segregation interface. Higher p-doping levels in the substrate enhance the segregation coefficient, creating a steeper gradient of [Fe] from the front surface, and slower cooling allows for the greatest amount of equilibration to occur and therefore the most effective Fe gettering. A time-temperature-transformation diagram approach is introduced to provide a comprehensive description of the wafer and process design parameters for effective gettering.

In situ analysis of hydrocarbon desorption from hydrogen terminated Si(100) surfaces was performed in a silicon molecular beam epitaxy system, using reflection electron energy loss spectroscopy, in conjunction with conventional reflection high energy electron diffraction analysis. Measurements of C K edge core loss intensities demonstrate that this method is sufficiently sensitive to enable in situ analysis of hydrocarbon desorption at fractional monolayer coverages during low-temperature isothermal anneals. Hydrocarbon desorption was found to begin at 115 °C, and at 200 °C complete desorption occurred within 10 min. Hydrocarbon coverage was not measurably affected by operation of ionization gauge filaments during low temperature anneals, but was increased by transient outgassing of the sample holder, and its environs.

In this study, we investigate the gettering process of Fe in p-type Cz silicon after iron has been introduced at the solubility limit at 1000°C. Deep Level Transient Spectroscopy (DLTS) was used to measure [FeB], a fingerprint of [Fei], at the center of samples. The minority carrier diffusion length and lifetime were calculated from Electron Beam Induced Current (EBIC) measurements. The fact that [FeB] is proportional to the negative second power of the minority carrier diffusion length at the high [FeB] regime confirms that FeB donors are the dominant recombination centers limiting solar cell performance with high Fe contamination. By quenching after heat treatment, we can maintain and measure the kinetics and thermodynamics of gettering exclusively. The getter/silicon interface was studied by comparison of the gettering rates of molten Al at 620°C, 700°C, and 800°C, and iron silicide at 700°C. We model Fe gettering with respect to temperature, time, solubility and precipitate nuclei density. In the early stage of Fe gettering, the process is dominated by precipitate formation around oxygen precipitate nuclei. The precipitate density is estimated to be on the order of 5×108cm−3. In later stages, Fe outdiffusion contributes to the [Fei] reduction. The early stage precipitation limits [Fei] reduction after short time to the solubility at the gettering temperature.