Ion beams in silicon processing and characterization (original) (raw)
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Energetic Ion Beams in Semiconductor Processing: Summary of a Doe Panel Study
MRS Proceedings, 1995
The trend toward smaller dimensions in integrated circuit technology presents severe physical and engineering challenges for ion implantation. These challenges, together with the need for physically-based models at exceedingly small dimensions, are leading to a new level of understanding of fundamental defect science in silicon. Recently the DOE Council on Materials requested that our panel examine the current status and future research opportunities in the area of ion beams in semiconductor processing. Particularly interesting are the emerging approaches to defect and dopant distribution modeling, transient enhanced diffusion, high energy implantation and defect accumulation, and metal impurity gettering. These topics were explored both from the perspective of the emerging science issues and the technology challenges.
Applied Physics Letters, 1996
A new atomistic approach to Si device process simulation is presented. It is based on a Monte Carlo diffusion code coupled to a binary collision program. Besides diffusion, the simulation includes recombination of vacancies and interstitials, clustering and re-emission from the clusters, and trapping of interstitials. We discuss the simulation of a typical room-temperature implant at 40 keV, 5ϫ10 13 cm Ϫ2 Si into ͑001͒Si, followed by a high temperature ͑815°C͒ anneal. The damage evolves into an excess of interstitials in the form of extended defects and with a total number close to the implanted dose. This result explains the success of the ''ϩ1'' model, used to simulate transient diffusion of dopants after ion implantation. It is also in agreement with recent transmission electron microscopy observations of the number of interstitials stored in ͑311͒ defects.
Atomic scale models of ion implantation and dopant diffusion in silicon
Thin Solid Films, 2000
We review our recent work on an atomistic approach to the development of predictive process simulation tools. First-principles methods, molecular dynamics simulations, and experimental results are used to construct a database of defect and dopant energetics in Si. This is used as input for kinetic Monte Carlo simulations. C and B trapping of the Si self-interstitial is shown to help explain the enormous disparity in its measured diffusivity. Excellent agreement is found between experiments and simulations of transient enhanced diffusion following 20±80 keV B implants into Si, and with those of 50 keV Si implants into complex B-doped structures. Our simulations predict novel behavior of the time evolution of the electrically active B fraction during annealing.
Defect evolution in MeV ion-implanted silicon
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms - NUCL INSTRUM METH PHYS RES B, 1996
Lightly doped silicon samples of both n- and p-type have been implanted with low doses of H, B and Si ions using energies between 1 and 6 MeV. The resulting electrically active point defects were characterized by deep level transient spectroscopy (DLTS) and several of these defects involve oxygen and/or carbon, two major impurities in as-grown crystalline silicon. Both interstitial- and vacancy-type defects are observed; in particular, interstitial carbon is found to migrate at room temperature with a diffusion constant of ∼ 1 × 10−15 cm2 s−1 and is effectively trapped by interstitial oxygen atoms. The concentration of implantation-induced defects increases linearly with dose but the defect production decreases at high enough dose rates. This dose rate effect depends on the ion mass and is qualitatively predicted by computer simulations of the defect reaction kinetics.
Nucleation, growth and dissolution of extended defects in implanted Si: impact on dopant diffusion
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999
Transient Enhanced Diusion (TED) of boron in silicon is driven by the large supersaturations of self-interstitial silicon atoms left after implantation which also often lead to the nucleation and subsequent growth, upon annealing, of extended defects. In this paper we review selected experimental results and concepts concerning boron diusion and/or defect behavior which have recently emerged with the ion implantation community and brie¯y indicate how they are, or will be, currently used to improve``predictive simulations'' softwares aimed at predicting TED. In a ®rst part, we focuss our attention on TED and on the formation of defects in the case of``direct'' implantation of boron in silicon. In a second part, we review our current knowledge of the defects and of the diusion behavior of boron when annealing preamorphised Si. In a last part, we try to compare these two cases and to ®nd out what are the reasons for some similarities and many dierences in defect types and thermal evolution depending on whether boron is implanted in crystalline or amorphous silicon. While rising many more questions, we propose a``thermodynamical'' vision of the nucleation and growth of clusters and extended defects and stress the interactions between these defects and the free Si self-interstitial atoms which surround them and are the source for TED in all cases. A pragmatic approach to the simulation of TED for various experimental conditions is proposed.
Physical mechanisms of transient enhanced dopant diffusion in ion-implanted silicon
Journal of Applied Physics, 1997
Implanted B and P dopants in Si exhibit transient enhanced diffusion ͑TED͒ during annealing which arises from the excess interstitials generated by the implant. In order to study the mechanisms of TED, transmission electron microscopy measurements of implantation damage were combined with B diffusion experiments using doping marker structures grown by molecular-beam epitaxy ͑MBE͒. Damage from nonamorphizing Si implants at doses ranging from 5ϫ10 12 to 1ϫ10 14 /cm 2 evolves into a distribution of ͕311͖ interstitial agglomerates during the initial annealing stages at 670-815°C. The excess interstitial concentration contained in these defects roughly equals the implanted ion dose, an observation that is corroborated by atomistic Monte Carlo simulations of implantation and annealing processes. The injection of interstitials from the damage region involves the dissolution of ͕311͖ defects during Ostwald ripening with an activation energy of 3.8Ϯ0.2 eV. The excess interstitials drive substitutional B into electrically inactive, metastable clusters of presumably two or three B atoms at concentrations below the solid solubility, thus explaining the generally observed immobile B peak during TED of ion-implanted B. Injected interstitials undergo retarded diffusion in the MBE-grown Si with an effective migration energy of ϳ3.5 eV, which arises from trapping at substitutional C. The concept of trap-limited diffusion provides a stepping stone for understanding the enormous disparity among published values for the interstitial diffusivity in Si. The population of excess interstitials is strongly reduced by incorporating substitutional C in Si to levels of ϳ10 19 /cm 3 prior to ion implantation. This provides a promising method for suppressing TED, thus enabling shallow junction formation in future Si devices through dopant implantation. The present insights have been implemented into a process simulator, allowing for a significant improvement of the predictive modeling of TED.
A universal ion implantation model for all species into single-crystal silicon
IEEE Transactions on Electron Devices, 2002
A physically based model for ion implantation of any species into single crystal silicon has been developed, tested and implemented in the ion implant simulator, UT-MARLOWE. In this model, an interpolation scheme, based on mathematical properties of ion-target interatomic potential, was employed and implemented to calculate the scattering process. Using this scheme, the resulting energy, direction and momentum of the ion and target can be derived from the existing scattering tables of UT-MARLOWE without calculating the entire scattering process. The method has advantages in terms of both accuracy and computational efficiency, as well as significantly reduced cost of code development. The impurity profiles and damage profiles predicted by the model simulations have been compared with secondary ion mass spectroscopy (SIMS) and Rutherford backscattering spectrometry (RBS), and excellent agreement with experimental data has been achieved.
Thermal Evolution of Extrinsic Defects in Ion Implanted Silicon: Current Understanding and Modelling
MRS Proceedings, 2002
We present an extensive study of the thermal evolution of the extended defects found in ion implanted Si as a function of annealing conditions. We will first review their structure and energetics and show that the defect kinetics can be described by an Ostwald ripening process whereby the defects exchange Si atoms and evolve in size and type to minimise their formation energy. Finally, we will present a physically based model to predict the evolution of extrinsic defects during annealing through the calculation of defect densities, size distributions, number of clustered interstitials and free-interstitial supersaturation. We will show some successful applications of our model to a variety of experimental conditions and give an example of its predictive capabilities at ultra low implantation energies.
The energy dependence of excessive vacancies created by high energy Si + ion implantation in Si
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2006
We have used molecular beam epitaxy grown Sb markers within Si to detect vacancy fluxes created by high energy Si + ion implants at various energies. Our experiments show that for a constant ion fluence of 1 · 10 15 cm À2 , the number of free vacancies created by ion implantation, followed by annealing at 900°C, increases with implantation energy. This is in contrast to the instantaneous vacancy creation rate during ion bombardment at the surface, which decreases with increasing ion energy. The possible mechanisms are discussed based on the separation distance between excessive interstitials (at the projected range of ions) and vacancies (near the surface), and the interaction between free vacancies and vacancy clusters.
Defect evolution in ion implanted crystalline Si probed by in situ conductivity measurements
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1995
We have used in situ conductivity measurements to investigate the defect evolution and accumulation in ion implanted crystalline Si. Upon irradiation at room temperature with 400 keV Si ions the initial conductivity (4X10w2 an-l cm-') decreases by about 4 orders of magnitude to a value of 2X 10m6 fi2-l cm-l, characteristic of intrinsic silicon, at a fluence of 1X 1013/cm2 and then slowly increases at higher fluences. Deep level transient spectroscopy measurements, transmission electron microscopy analyses, and thermal annealings were performed on samples irradiated at various fluences. The data demonstrate that the strong conductivity decrease at low fluences is the result of a dopant compensation produced by deep levels introduced by divacancies and complex defects in the band gap. At higher iiuences the conduction is dominated by electron hopping in a buried continuous amorphous layer produced by irradiation. These results are reported and discussed.