Defects In Ion Implanted Silicon Research Articles

Annealing studies of cluster defects in ion-implanted silicon using high resolution DLTS

High resolution Laplace deep level transient spectroscopy (LDLTS) has been applied to investigate the annealing behaviour of small cluster defects in n-type Si. The Si was implanted with either Ge or Si, with energies 1500keV and 850keV respectively, and doses of 1×1010cm−2. The low dose ensured that there was a minimum of carrier removal due to deep defect states after implantation. Defect states in the as-implanted samples were attributed to VO pairs, divacancies and very small interstitial cluster defects, after detailed depth profiling. LDLTS of Ge+ and Si+ implanted silicon shows that there are three closely spaced deep levels associated with these clusters, with energies in the region of Ec-400meV. Samples were then isochronally annealed in very small temperature intervals up to 560K, in situ in our high temperature measurement cryostat, and the LDLTS re-examined as a function of annealing temperature. A new deeper energy level emerges as the cluster-related signal reduces, and it is suggested that this new trap is a major recombination centre, by comparison with current–voltage data.

Identification by photoluminescence and positron annihilation of vacancy and interstitial intrinsic defects in ion-implanted silicon

Defect centers generated in crystalline silicon by MeV Si implants have been investigated by a combination of photoluminescence, variable-energy positron annihilation measurements, depth profiling by etching, annealing studies, and the dependence on impurities. The broad 935meV photoluminescence band occurs at intrinsic interstitial complexes, the 835meV band at small vacancy clusters, and the 1062meV line at a low concentration of vacancy clusters which are possibly formed by aggregation of the 835meV centers.

Effect of stress on the evolution of mask-edge defects in ion-implanted silicon

In an effort to extend the scaling of advanced complementary metal-oxide semiconductor devices, strain has been incorporated to enhance carrier mobility. In this study, the effect of strain on the solid-phase epitaxial regrowth process of patterned wafers was explored. Implants of 1×1015∕cm2 Si+ with an energy of 40keV were introduced into these patterned regions forming a continuous amorphous layer. After implantation, the oxide and nitride masks were removed and the wafers stressed uniaxially between 0 and 250MPa. The wafers were subsequently annealed under stress to crystallize the amorphous layer, which was monitored using transmission electron microscopy. It was found that without stress, defects formed at the mask edge where the vertical and lateral epitaxial regrowth fronts meet. These defects were threading dislocations which form at the amorphous-crystalline interface and propagate to the surface. Tensile stress levels of as little as 50MPa were found to begin to suppress the formation of mask-edge defects by altering the shape of the corner of the regrowing amorphous layer at the mask edge. Tensile stress appears to retard the lateral recrystallization velocity, creating the obtuse corner geometry necessary to prevent the occurrence of a pinch point at the corner and thereby suppressing defect formation. The evidence suggests that the half-loop threading dislocation nucleates at the corner. The role of varying the stress on the formation of mask-edge defects will be discussed.

Photoluminescence study of self-interstitial clusters and extended defects in ion-implanted silicon

We report on the photoluminescence (PL) studies of self-interstitial (I) clustering in ion-implanted Si at various stages of post-implantation annealing. Low-temperature PL measurements on as-implanted and low-temperature annealed (up to 450°C) samples show sharp X and W bands at 1200 and 1218nm which are attributed to I4 and I3 clusters, respectively. Annealing at 600°C shows a drastic change in the PL spectra. In case of high-energy self-ion-implanted samples, 600°C annealing produces several peaks in the range 1250–1400nm. For longer duration annealing, two broad bands form at 1322 and 1392nm irrespective of the ion fluence. These PL signatures are attributed to I8 clusters and/or (100) I-chains, and they are believed to be the precursor of {311} rod-like defects. For annealing above 600°C and for fluence ⩾1×1013cm−2, a sharp PL band is observed at 1376nm and it is attributed to {311} rod-like defects. At higher fluences, an additional broad band appears in the PL spectrum at ∼1576nm which is related to residual ion-damage or extended defect formation. These results illustrate the potential of silicon I-clusters as a possible source of light emission from Si.

Oxygen-related vacancy-type defects in ion-implanted silicon

Czochralski silicon samples implanted to a dose of5 × 1015 cm−2 with 0.5 MeV Oand to a dose of 1016 cm−2 with 1 MeV Si, respectively, have been studied by positron annihilation spectroscopy. The evolution ofdivacancies to vacancy (V)–O complexes is out-competed by V–interstitial (I) recombination at 400and 500 °C in the Si- and O-implanted samples; the higher oxygen concentration makes the lattertemperature higher. The defective region shrinks as the annealing temperatureincreases as interstitials are injected from the end of the implantation range(Rp).VmOn (m>n) are formed in the shallow region most effectively at700 °C for both Si and Oimplantation. VxOy (x<y) areproduced near Rp by theannealing. At 800 °C, implantedSi ions diffuse and reduce m and implanted O ions diffuse and increasen inVmOn.All oxygen-related vacancy-type defects appear to begin to dissociate at950 °C,with the probable formation of oxygen clusters. At1100 °C,oxygen precipitates appear to form just beforeRp in O-implanted silicon.

Hydrogen-terminated defects in ion-implanted silicon probed by monoenergetic positron beams

Hydrogen-terminated vacancies in Si+-implanted Si were studied by means of positron annihilation. After the Si+-ion implantation, hydrogen atoms were introduced into the damaged region using a hydrogen plasma [hydrogen-atom treatment (HAT)]. Monoenergetic positron beams were used to measure Doppler broadening spectra of the annihilation radiation and the lifetime spectra of positrons. It was found that the line shape parameter, S, corresponding to the annihilation of positrons trapped by vacancy-type defects, decreased after HAT. This was attributed to the trapping of positrons by H-decorated vacancy-type defects. Isochronal annealing experiments revealed a strong correlation between positron annihilation parameters and Raman intensities of Si–H, suggesting that hydrogen atoms are released from vacancy-type defects after annealing at 600 °C.

Vacancy and interstitial depth profiles in ion-implanted silicon

An experimental method of studying shifts between concentration-versus-depth profiles of vacancy- and interstitial-type defects in ion-implanted silicon is demonstrated. The concept is based on deep level transient spectroscopy measurements utilizing the filling pulse variation technique. The vacancy profile, represented by the vacancy–oxygen center, and the interstitial profile, represented by the interstitial carbon–substitutional carbon pair, are obtained at the same sample temperature by varying the duration of the filling pulse. The effect of the capture in the Debye tail has been extensively studied and taken into account. Thus, the two profiles can be recorded with a high relative depth resolution. Using low doses, point defects have been introduced in lightly doped float zone n-type silicon by implantation with 6.8 MeV boron ions and 680 keV and 1.3 MeV protons at room temperature. The effect of the angle of ion incidence has also been investigated. For all implantation conditions the peak of the interstitial profile is displaced towards larger depths compared to that of the vacancy profile. The amplitude of this displacement increases as the width of the initial point defect distribution increases. This behavior is explained by a simple model where the preferential forward momentum of recoiling silicon atoms and the highly efficient direct recombination of primary point defects are taken into account.

High resolution deep level transient spectroscopy studies of the vacancy-oxygen and related defects in ion-implanted silicon

We have carried out high resolution Laplace deep level transient Spectroscopy (DLTS) and conventional DLTS on silicon implanted with very low doses of either silicon, germanium, erbium, or ytterbium, and compared the results to those from electron-irradiated silicon. DLTS spectra of all the samples initially look very similar, and a peak at 95 K appears in all spectra which may be due to the vacancy-oxygen (VO) defect. We have carried out detailed measurements of the capture cross section and activation energy of this defect using Laplace DLTS. We show that, when the mass of the implanted ion exceeds that of silicon, the defect has a much smaller electron capture cross section than that expected for the VO defect, and a smaller activation energy. Hydrogen has been introduced, either by wet chemical processing or plasma, to all samples to observe the hydrogen–VO interactions resulting in VOH. By using high resolution DLTS we are able to establish that, after hydrogenation, the VOH defect exists with an identical emission rate in the silicon-implanted silicon and the electron-irradiated silicon, but not in the silicon implanted with heavier ions. We conclude that the peak at 95 K in the DLTS spectra in the case of the heavier ions is due to a different defect, confirming earlier reports in the literature. This defect is negatively charged, unlike VO, which is acceptor-like. We are also able to observe VOH in samples where VO is not present, after these samples have been annealed. We attribute this to release of V and H atoms from other defects during annealing.

High resolution Laplace DLTS studies of defects in ion-implanted silicon

We have used high resolution Laplace deep level transient spectroscopy (LDLTS) to investigate defects in n-type silicon caused by implantation of Si, Ge or Er with doses of the order of 1×10 9 cm −2 . These are compared with defects created in proton irradiated n-type silicon. Unlike the simple proton irradiated case, LDLTS spectra of ion implanted silicon show that there are many emission rates associated with defects with energies in the region of E c−400 meV. We have carried out annealing studies and Laplace DLTS depth profiling and show that the complex spectra measured from a region less than half way through the implant simplify as the profile is moved through the implant and towards the tail. Annealing studies show that these defects survive an anneal that should remove the E-centre.

Separation of vacancy and interstitial depth profiles in proton- and boron-implanted silicon

A new experimental method of studying shifts between concentration-versus-depth profiles of vacancy-type and interstitial-type defects in ion-implanted silicon is demonstrated. The concept is based on deep level transient spectroscopy (DLTS) measurements utilizing the filling pulse variation technique. The vacancy profile, represented by the vacancy-oxygen center and the interstitial profile, represented by the substitutional carbon-interstitial carbon pair, are obtained at the same sample temperature by varying the duration of the filling pulse. Thus the two profiles can be recorded with a high relative depth resolution. Point defects have been introduced in low doped float zone n-type silicon by implantation with 6 MeV boron ions and 1.3 MeV protons at room temperature, using low doses. For each implantation condition the peak of the interstitial profile is shown to be displaced by ∼ 0.5 μm towards larger depths compared to that of the vacancy profile. This shift is primarily attributed to the preferential forward momentum of recoiling Si atoms, in accordance with theoretical predictions.

Separation of vacancy and interstitial depth profiles in ion-implanted silicon: Experimental observation

An experimental concept of studying shifts between concentration-versus-depth profiles of vacancy and interstitial-type defects in ion-implanted silicon is demonstrated. This concept is based on deep level transient spectroscopy measurements where the filling pulse width is varied. The vacancy profile, represented by the vacancy-oxygen center, and the interstitial profile, represented by the substitutional carbon–interstitial carbon pair, are obtained at the same sample temperature and can be recorded with a high relative depth resolution. For 6 MeV B11 ions, the peak of the interstitial profile is displaced by ∼0.5 μm towards larger depths compared to that of the vacancy profile, which is primarily attributed to the preferential forward momentum of recoiling Si atoms.

Coarsening of End-of-Range defects in ion-implanted silicon annealed in neutral and oxidizing ambients

The evolution of End-of-Range defects during post-implantation anneals has been investigated in order to elucidate the role of the surface on the self-interstitial supersaturation near the damage region. In this work we have investigated both high dose Si +-implanted and Ge +-implanted silicon samples thermally treated under N 2, N 2O and O 2 ambients. It has been found that independently of the implanted species and annealing ambient conditions the EOR damage evolves into two distinguishable categories of extended defects, namely perfect and faulted dislocation loops. The main feature observed is that a non-conservative coarsening of the two populations of defects occurs as function of time and temperature and strongly depends on the chemical state of the surface and on the defect distance from the surface.

Rapid Migration of Defects in Ion-Implanted Silicon

ABSTRACTThe temperature dependence of the so-called reverse dose rate effect for generation of vacancy-type defects in silicon has been investigated using samples implanted with 1.3 MeV protons at temperatures between 70 and 300 K. The effect is found to involve a thermally controlled process which exhibits an activation energy of ∼0.065 eV, possibly associated with rapid migration of Si self-interstitials (I). Further, using a concept of dual Si ion-implants long range migration of I:s at room temperature has been studied. Annihilation of vacancy-type defects at a depth of ∼3 μm is obtained by injection of I:s from a shallow implant with sufficiently high dose.

Self-Interstitial Supersaturation During Ostwald Ripening of End-of-Range Defects in Ion-Implanted Silicon

AbstractModified Ostwald ripening theory is used to calculate the time evolution of the size distribution function of extended end-of-range defects in ion implanted silicon. This allows to compare the time dependent self-interstitial supersaturation during postimplantation annealing in the presence of Frank-type stacking faults with that in the presence of {311} - defects. It is shown that the latter affect self-interstitial concentrations up to the point where they dissolve whereas the former are irrelevant from the point of view of transient enhanced diffusion.

Impurity ion implantation into silicon single crystals: efficiency and radiation damage

The ion implantation method is analysed from the point of view of its efficiency as a technique for doping silicon with donor and acceptor impurities, for synthesising silicon-based compounds and for producing gettering layers and optoelectronic structures. The introduction, agglomeration, and annealing of radiation-produced defects in ion-implanted silicon are considered. The role of interstitial defects in radiation-related defect formation is estimated. Mechanisms of athermal migration of silicon atoms in the silicon lattice are analysed.

Sheet resistance and noise properties of ion-implanted silicon structures

Experimental-study results are presented on the sheet resistance and low-frequency current-noise spectra in silicon layers that have been implanted by phosphorous and boron ions as functions of the conditions of implantation and post-implantation heat treatment. Results of evaluation of the Pearson implantation profiles are presented to explain the obtained dependences, and data in the literature on defects in ion-implanted silicon are cited. The noise spectra are analyzed using Hooge's empirical formula.

The applications of transmission electron microscopy to the characterization of metal thin films on silicon

The applications of transmission electron microscopy (TEM) to the characterization of metal thin films on silicon are reviewed. A historical perspective and an account of the contribution of TEM to the study of interfacial reactions of metal thin films on silicon are given. Recent developments in the growth of transition metal silicides on silicon including (1) the formation and growth of amorphous interlayers between metal thin films and silicon, (2) the effects of lateral confinements, doping impurities, and rapid thermal annealing on the formation of silicides, and (3) the elimination of end-of-range defects in ion-implanted silicon by silicide formation are described.

TEM study of the formation of structural defects in ion implanted silicon at depths ofh ≲Rp andh ≳ 2Rp

A large number of vacancies and silicon interstitials (ISi) are generated by the process of ion bombardment in the region of the mean projected range (Rp) of the implanted species. The fast moving ISi atoms rapidly diffuse deeper into the crystal, to an approximate depth of 2Rp. In this study the surface layers of P+, B+, and As+ irradiated silicon are removed by anodic sectioning to depths of h ⪆ Rp and h ⪆ 2Rp prior to specimen annealing in vacuum. The structural defects formed following the interaction of the ISi atoms in isolation may then be observed in ‘h ⪅ 2Rp samples’ prepared in plan view for TEM by thinning from the unimplanted side. Similarly, defects formed following the interaction of ISi atoms with the near surface point defect distribution may be observed in ‘h ⪅ Rp samples’. Dislocation loops are prevalent at a depth of h ⪅ Rp in samples of P+ and B+ irradiated silicon annealed at both 700 and 900°C. In contrast either rod-like defects or extended dislocation loops are found at depths of h ⪆ 2Rp depending on whether the samples are annealed at 700 or 900°C. As+ irradiated silicon annealed at 800°C following anodic sectioning, exhibits a more complicated defect structure at a depth of h ⪅ Rp and a large number of small ‘black-white contrast’ interstitial defects in the h ⪆ 2Rp region. The influence of ion mass, beam flux, and energy on the formation of the rod-like defects is considered, and computer simulation is used to help explain the nature of the structural defects formed in the h ⪅ Rp and h ⪆ 2Rp regions in ion implanted layers. Eine grose Anzahl von Leerstellen und Siliziuminterstitials (ISi) werden wahrend des Ionenbombardements im Bereich der mittleren projezierten Reichweite (Rp) der implantierten Species generiert. Die schnell wandernden ISi-Atome diffundieren schnell tiefer in den Kristall, zu einer Tiefe von annahernd 2Rp. Die Oberflachenschichten von mit P+, B+ und As+ bestrahltem Silizium werden durch anodische Abtragung bis zu Tiefen von h ⪅ Rp und h ⪆ 2Rp beseitigt, bevor die Proben im Vakuum getempert werden. Die Strukturdefekte, die nach der Wechselwirkung der ISi-Atome in Isolierung gebildet werden, lassen sich dann in „h ⪆ 2Rp”-Proben beobachten, die fur ebene Beobachtung im TEM durch Abdunnung von der nichtimplantierten Seite prapariert werden. In ahnlicher Weise lassen sich Defekte, die der Wechselwirkung von ISi-Atome mit Punktdefektverteilung in Oberflachennahe folgen, in den „h ⪅ Rp”-Proben beobachten. Versetzungsschleifen sind in einer Tiefe von h ⪅ Rp in Proben von mit P+ und B+ bestrahltem Silizium vorherrschend, das sowohl bei 700 als auch 900°C getempert wird. Im Gegensatz dazu werden entweder Stabchendefekte oder ausgedehnte Versetzungsschleifen in Tiefen von h ⪆ 2Rp gefunden, in Abhangigkeit davon, ob die Proben bei 700 oder 900°C getempert werden. Mit As+ bestrahltes Silizium, das nach anodischer Abtragung bei 800°C getempert wird, zeigt eine kompliziertere Defektstruktur bei einer Tiefe von h ⪅ Rp und eine grose Zahl von kleinen „Schwarz-Weis-Kontrast”-Defekten im h ⪆ 2Rp-Bereich. Der Einflus der Ionenmasse, Strahlenflus und Energie auf die Bildung von Stabchen wird untersucht, und eine Computersimulation wird benutzt, um die Art der Strukturdefekte zu erklaren, die in den „h ⪅ Rp”-und „h ⪆ 2Rp”-Bereichen in ionenimplantierten Schichten gebildet werden.

Study of Carrier Dynamics and Radiation Defects in Ion-Implanted Silicon by Transient Grating Techniques

Investigations of photoelectrical properties of ion-implanted Si are performed by the optical transient grating technique. A lowering of carrier and thermal diffusion as well as faster recombination are observed. The existence of electrically active radiation defects in a region essentially exceeding the projected mean range of ions is proved by measurements of both light diffraction and photoconductivity. [Russian Text Ignored].

A systematic analysis of defects in ion-implanted silicon

A classification scheme for the different forms of implant-related damage which arise upon annealing consisting of five categories is presented. Category I damage is “subthreshold” damage or that which results prior to the formation of an amorphous layer. If the dose is increased sufficiently to result in the formation of an amorphous layer then the defects which form beyond the amorphous/crystalline (a/c) interface are classified as category II (“end of range”) damage. Category III defects are associated with the solid phase epitaxial growth of the amorphous layer. The most common forms of this damage are microtwins, hairpin dislocations and segregation related defects. It is possible to produce a buried amorphous layer upon implantation, If this occurs, then the defects which form when the two a/c interfaces meet are termed category IV (“clamshell”, “zipper”) defects. Finally, category V defects arise from exceeding the solid solubility of the implanted species in the substrate at the annealing temperature. These defects are most often precipitates or dislocation loops.