C. E. Christodoulides

Flux, fluence and implantation temperature dependence of disorder produced by 40 keV N+ ion irradiation of GaAs

Abstract Measurements of the lattice disorder and the depth distribution of disorder produced by 40 keV N+ ion irradiation of GaAs have been carried out before and after thermal annealing. The results show a significant dependence of lattice disorder on ion flux, ion fluence and implant temperature. A bimodal depth distribution of disorder was also observed under certain implantation conditions. The results suggest that point defect production processes in III-IV binary semiconductors (GaAs) are similar to those of Si, whilst the annealing behaviour of GaAs is rather complex and is strongly dependent on implant temperature.

The application of low angle Rutherford backscattering and channelling techniques to determine implantation induced disorder profile distributions in semiconductors

Abstract Low angle exit (9°) Rutherford backscattering geometry and chanelling of 2 MeV 4He+ are employed to investigate the disorder depth profiles created by 40 keV N+ implantation in (111) silicon and (100) GaAs targets. Parameters which can influence the disordering rate and its spatial distribution, such as ion fluence, flux, substrate type and substrate temperature are examined. Under certain implantation conditions, the damage profile distributions are asymmetric — exhibiting a bimodal form in silicon targets or confined much closer to the GaAs surface than the normally expected mean range of 40 keV N+ ions.

The recrystallization of ion-implantedsilicon layers: II. Implant species effect

Abstract Rutherford backscattering and channeling (RBS) has been employed to investigate the annealing characteristics of ion-bombarded silicon for a wide range of implant species. The general recrystallization behaviour is that high levels of remnant disorder are observed for high-dose (typically > 1015 ions cm-2) implants of all species investigated, and transmission electron microscopy indicates the presence of a polycrystalline reordered layer in such cases. The magnitude of the remnant disorder (misorientation of grains with respect to the underlying bulk substrate) is observed to increase with both implant dose and original amorphous-layer thickness and to exhibit a slight implant-mass dependence. Although the recrystallization behaviour is qualitatively similar for all species studied, certain species (mainly those soluble in silicon) are found to influence the regrowth process at low implant concentrations. It is suggested that stress/strain effects, attributed to high implanted concentratio...

The depth distribution of disorder produced by room temperature 40 keV N+ ion irradiation of silicon

Abstract The depth distribution of disorder produced by room temperature 40 keV N+ ion irradiation of silicon was monitored by high depth resolution RBS and channelling techniques. A bimodal depth distribution of disorder resulted under certain implantation conditions and a significant dependence of the damage on N+ flux and fluence was observed.

The determination of high-dose implantation profiles using low-angle Rutherford backscattering

Abstract The measurement of Pb+ and Cs+ high-dose distributions in silicon is investigated by low-angle Rutherford backscattering of 2 MeV He+ ions. Factors which can result in a distortion of the measured RBS profiles, such as surface contamination, lateral nonuniformity, surface topography and nonlinear depth scales, are discussed. A simple procedure is outlined for iteratively calculating a depth scale for high-dose composite targets. The Pb and Cs high-dose profiles in silicon are shown to indicate substantial outdiffusion and indiffusion of the implant during room temperature implantation.

Ion bombardment induced interface mixing in the AgSi system

Abstract High resolution Rutherford backscattering has been used to investigate the ion-beam-induced intermixing of silver films deposited onto silicon under increasing fluences of 40 keV Ar + ions. The onset of atomic mixing in the interface occurs when the Ag layer has been sputtered down to about 300 A (∼ R p + ΔR p for 40 keV Ar + → Ag ). The composition in the mixed layer varies in a uniform, almost linear way, and the layer spreads laterally with increasing fluences towards a constant value. There is no evidence for the formation of regions of specific composition, in contrast to other Simetal systems (e.g. SiPt, SiPd, SiAu). For higher doses, the amount of Ag remaining decays more or less exponentially. The width of the mixed layer and the exponential decay of residual Ag are shown to correspond reasonably with theoretical predictions of atomic mixing processes.

Fluence dependence of disorder depth profiles in Pb implanted Si

Abstract The total, depth integrated disorder, induced by Pb implantation into Si at room temperature, initially increases rapidly with implantation fluence and then reaches a quasi saturation level where the increase with fluence is slow. Measurements of the depth distributions of the disorder, using high resolution low angle exit Rutherford Backscattering/Channelling analysis, suggest that the quasi saturation results from overlapping of disordered zones generated deep in the tail of the disorder-depth profiles. The depth of the disordered solid-crystal boundary, XD increases with ion fuence φ, according to the relation XD = x- + f[φ).[sgrave]., where x- is the most probable projected depth and [sgrave] the projected standard deviation of disorder generation. It is shown that this relationship is consistent with an approximately Gaussian depth distribution of disorder production.

Ion range and damage depth parameters for 20–200 keV Pb+ ion implantation in Si

Abstract The depth distributions of both implanted atoms and radiation damage generated by 20–200 keV Pb + ion implantation of Si at room temperature have been measured by high resolution (low angle incidence or exit) Rutherford backscattering and channeling. The moments derived from these distributions are found to fit well to the Wilson, Haggmark and Biersack model calculations whilst the fit of the ion range data to Kalbitzer-Oetzmanns compilations is excellent. The variation of the damage depth distributions with increasing ion fluence were also determined and the increase in the depth of the amorphous layer—crystalline substrate interface was measured as a function of both fluence and energy. The variation of this interface depth with fluence and energy was found to agree well with a simple direct amorphous zone creation and overlap model.

Ion beam studies Part II: A calorimetric method for ion beam studies

Abstract A calorimeter for ion-beam studies is described. The device, which is simple to operate and which is based on a dynamic measurement of temperature rise, has a time constant of only 12 s. The calorimeter has an estimated accuracy of ⩾ 2% and has been operated from 2 to 60 mW. The design of the instrument allows the range to be readily extended. A description is also given of the use of an ion-implanted resistor to simulate the beam-heating effects for the calibration of the instrument.

Evidence for spike-effects in low energy ar ion bombardment of Si at room temperature

Abstract Measurements of the damage produced by 3-30 keV Ar+ room temperature irradiations of Si have been carried out. The results show a significant deviation between the measured disorder and that predicted by linear cascade binary collision theory. Comparison with a recently suggested semi-empirical model based upon a separation of the damage into a “spike” component and a “collisional” component provides strong evidence for the existence of spike phenomena at energies as low as 3 keV.