Effect of ion doping on the dislocation-related photoluminescence in Si+-implanted silicon

The study is concerned with the effect of the additional implantation of Si samples with C⁺, O⁺, B⁺, P⁺, and Ge⁺ impurity ions followed by annealing at 800°C on the behavior of the dislocation photoluminescence line D1, induced in the samples by implantation with Si⁺ ions at a stabilized temperature followed by annealing in an oxidizing Cl-containing atmosphere. It is established that the intensity of the D1 line strongly depends on the type of incorporated atoms and the dose of additional implantation. An increase in the D1 line intensity is observed upon implantation with oxygen and boron; at the same time, in other cases, the D1 luminescence line is found to be quenched. The mechanisms of such behavior, specifically, the role of oxygen and its interaction with implanted impurities are discussed.     

Comparison of p–n junction formed by BF2 and B implantation in silicon microstrip detector with low and high thermal budget: impact of fluorine on electrical characteristics

The influence of crystal damage on the electrical properties and the doping profile of the implanted p⁺–n junction has been studied at different annealing temperatures using process simulator TMA-SUPREM4. This was done by carrying out two different implantations; one with implantation dose of 10¹⁵ BF₂⁺ ions/cm² at an energy of 80 keV and other with 10¹⁵ B⁺ ions/cm² at 17.93 keV. Substrate orientation 1 1 1 of phosphorus-doped n-type Si wafers of resistivity 4 kΩ cm and tilt 7° was used, and isochronally annealing was performed in N₂ ambient for 180 min in temperature range between 400°C and 1350°C. The diode properties were analysed in terms of junction depth, sheet resistance. It has been found that for low thermal budget annealing, boron diffusion depth is insensitive to the variation in annealing temperature for BF₂⁺-implanted devices, whereas, boron diffusion depth increases continuously for B⁺-implanted devices. In BF₂⁺-implanted devices, fluorine diffusion improves the breakdown voltage of the silicon microstrip detector for annealing temperature upto 900°C.For high thermal budget annealing, it has been shown that the electrical characteristics of BF₂⁺-implanted devices is similar to that obtained in B⁺-implanted devices.     

Doping and processing epitaxial GexSi1−x films on Si(100) by ion implantation for Si-based heterojunction devices applications

The question of whether one can effectively dope or process epitaxial Si(100)/GeSi heterostructures by ion implantation for the fabrication of Si-based heterojunction devices is experimentally investigated. Results that cover several differention species (B, C, Si, P, Ge, As, BF₂, and Sb), doses (10¹³ to 10¹⁶/cm²), implantation temperatures (room temperature to 150°C), as well as annealing techniques (steady-state and rapid thermal annealing) are included in this minireview, and the data are compared with those available in the literature whenever possible. Implantation-induced damage and strain and their annealing behavior for both strained and relaxed GeSi are measured and contrasted with those in Si and Ge. The damage and strain generated in pseudomorphic GeSi by room-temperature implantation are considerably higher than the values interpolated from those of Si and Ge. Implantation at slightly elevated substrate temperatures (e.g., 100°C) can very effectively suppress the implantation-induced damage and strain in GeSi. The fractions of electrically active dopants in both Si and GeSi are measured and compared for several doses and under various annealing conditions. Solid-phase epitaxial regrowth of GeSi amorphized by implantation has also been studied and compared with regrowth in Si and Ge. For the case of metastable epi-GeSi amorphized by implantation, the pseudomorphic strain in the regrown GeSi is always lost and the layer contains a high density of defects, which is very different from the clean regrowth of Si(100). Solid-phase epitaxy, however, facilitates the activation of dopants in both GeSi and Si, irrespective of the annealing techniques used. For metastable GeSi films that are not amorphized by implantation, rapid thermal annealing is shown to outperform steady-state annealing for the preservation of pseudomorphic strain and the activation of dopants. In general, defects generated by ion implantation can enhance the strain relaxation process of strained GeSi during post-implantation annealing. The processing window that is optimized for ion-implanted Si, therefore, has to be modified considerably for ion-implanted GeSi. However, with these modifications, the mature ion implantation technology can be used to effectively dope and process Si/GeSi heterostructures for device applications. Possible impacts of implantation-induced damage on the reliability of Si/GeSi heterojunction devices are briefly discussed.     

Optimization of RTA parameters to produce ultra-shallow, highly activated B+, BF 2 + , and As+ ion implanted junctions

The effects of time, temperature, ramp-up, and ramp-down rates with rapid thermal annealing employing a STEAG AST SHS3000 were investigated on 1.0 and 2.0 keV ¹¹B⁺, 2.2, 5.0, and 8.9 keV ⁴⁹BF ₂ ⁺ , and 2 KeV ⁷⁵As⁺, 1E15/cm² samples implanted in a Varian VIISion-80 PLUS ion implanter at 0^o tilt angles. These annealed samples were analyzed by four-point probe, secondary ion mass spectrometry (SIMS), and in select cases by spreading resistance profiling (SRP) and transmission electron microscopy (TEM). To ensure reproducibility and to minimize oxidation enhanced diffusion as an uncontrolled variable, the O₂ background concentration in N₂ was maintained at a controlled low level. Under these conditions, ramp-rates alone were found not to be significant. Spike anneals (1050°C, ～ 0 s) with fast ramp-rates (240°C/s) and fast cool down rates (86°C/s) provided the shallowest junctions, while still yielding good sheet resistance values. Post annealed samples were examined for extended defect levels (by TEM) and trapped interstitial concentrations. Fluorine concentration measurements were employed to qualitatively explain differences in the B diffusion from ¹¹B⁺ and ⁴⁹BF ₂ ⁺ ion implants at various energies. The 2.2 keV ⁴⁹BF ₂ ⁺ “fast” spike annealed sample at 1050°C exhibited limited, if any, enhanced diffusion, yielding a SIMS junction depth of 490Å, an electrical junction of 386Å (by SRP) and a sheet resistance of 406 ohm/sq.     

Activation analytical investigation of contamination and cross-contamination in ion implantation

In silicon layers, implanted at 100–150 keV with P⁺, As⁺ and Ar⁺ ions, considerable Fe, Cr, Ni, Co and Cu were detected by means of neutron activation analysis. With the elements of the Fe group, concentrations up to 5.10¹⁴cm⁻² were obtained, whereby the relationship of these elements to each other corresponds to the composition of the stainless steel apertures used. The contamination of the layers is dose dependent. In accordance with the sputter rates, As⁺ ion implanted layers are more contaminated than those implanted by P⁺ or Ar⁺ ions. Additionally, the implanting process introduces, besides the contamination with heavy metals, dopants from the previous implantation. This so-called cross-contamination amounted to approx. 0.3 % of the implanted ion dose. Essential parts of this work were presented at the symposium on “Solid State Device Technology” Munster, 1977     

The behaviour of boron molecular ion implants into silicon

Implants of boron molecular ions into silicon have been studied using a variety of experimental techniques, but with emphasis on sheet resistance annealing characteristics and transmission electron microscopy. Boron halide compound molecules have been implanted and equivalent dose sequential implants of atomic species used as control conditions. The implants studied were B⁺, BCl₂⁺, BCl⁺, Cl⁺ + B⁺, BF₂⁺, BF⁺ and B⁺ + F⁺ at 25 keV/B atom and B⁺, BBr₂⁺ and Br₂⁺ + B⁺ at 12 keV/B atom.The implantation of molecular ions enables conditions of varying damage to be studied with constant dose, dose rate and energy of the dopant species. In addition to damage effects the halogen atoms produce species effects in the implanted zone. The escape of the halogen atoms has been measured as a function of the annealing temperature.The significant differences which exist between the behaviour of silicon implanted with these various conditions are considered with reference to the damage structures observed by transmission electron microscopy. The boron-fluorine molecular implants are shown to offer some advantages as a means of implanting boron.     

The effect of ion-implantation damage on dopant diffusion in silicon during shallow-junction formation

Low-thermal-budget annealing of ion-implanted BF ₂ ⁺ , P, and As in Si was studied for shallow-junction formation. Implant doses were sufficient to amorphize the silicon surface region. Low-temperature furnace annealing and rapid-thermal annealing of ionimplanted boron, phosphorus and arsenic in silicon exhibit a transient enhanced diffusion regime resulting injunction depths considerably deeper than expected. The origin of this transient enhanced diffusion is the annealing of ion-implantation damage in the silicon substrate. We have found that point-defect generation during the annealing of either shallow end-of-range damage or small clusters of point defects dominates the transient enhanced diffusion process depending upon the annealing temperature and time. The net effect of damage annealing is to reduce the activation energy for dopant diffusion by an amount equal to the activation energy of the supersaturation of point defects in silicon. Models which can describe the transient enhancement characteristics in dopant diffusion during both furnace and rapid-thermal annealing of these implants are discussed.     

Electron microscopic study on residual defects of Al+ or B+ implanted 4H-SiC

The residual defects of Al⁺- or B⁺-implanted 4H-SiC were studied in combination with annealing temperature and implantation temperature using cross-sectional transmission electron microscopy technique. Noticeable defects structure is not observed before post-implantation annealing. But after annealing, a lot of black spots appear in the implanted layer. These black spots are composed of a dislocation loop, parallel to {0001} of 4H-SiC, and strained area at the upper and lower sides of the dislocation loop. This defect structure and its size do not depend on implantation temperature and implanted ion species. The size of defect area depends only on post-implantation annealing temperature. The size grows, when post-annealing temperature is raised.     

Diffusion of zinc into ion-implanted gallium arsenide

A study has been made of the diffusion of zinc, from a vapour source, into GaAs slices which had been previously implanted with various ion species. A radiotracer sectioning technique was used to measure the zinc diffusion profiles. It was found that the various implanted ion species (H⁺, He⁺, N⁺, Zn⁺, As⁺) had different effects on the zinc diffusion. The results could not be attributed solely to native defects produced by radiation damage. The heavier ion species increased the zinc concentration in the implanted region, but not beyond. The lighter species substantially increased the zinc diffusion rate and altered the resultant concentration profiles. Uphill diffusion was seen in slices which had been given a single high energy H⁺ implant. The results obtained are compared to those of Radiation-Enhanced-Diffusion experiments. It is suggested that the rate of incorporation of dopant species into the host semiconductor lattice is an important influence on the diffusion mechanism and the shape of the concentration profile.     

Role of a Si0.95Ge0.05 epilayer cap on boron diffusion in silicon under inert and dry oxidizing ambient annealing

Silicon (Si) and Si with a 60 nm Si_0.95Ge_0.05 epilayer cap (Si_0.95Ge_0.05/Si) were implanted with 60 keV, 1×10¹³ cm⁻² boron (B) followed by annealing in nitrogen (N₂) or dry oxygen (O₂) in two different anneal conditions. B⁺implantation energy and dose were set such that the B peak is placed inside Si in Si_0.95Ge_0.05/Si samples and concentration independent B diffusion is achieved upon annealing. For samples annealed above 1075 °C, Ge diffusing from the Si_0.95Ge_0.05 epilayer cap in Si_0.95Ge_0.05/Si samples reached the B layer inside Si and resulted in retarded B diffusion compared to the Si samples. For annealing done at lower temperatures, diffusion of Ge from Si_0.95Ge_0.05 epilayer cap does not reach the B layer inside Si. Thus B diffusion profiles in the Si and Si_0.95Ge_0.05/Si samples appear to be similar. B diffusion in dry oxidizing ambient annealing of Si_0.95Ge_0.05/Si samples further depends on the nature of Si_0.95Ge_0.05 oxidation which is set by the duration and the thermal budget of the oxidizing anneal.     

Al+ and B+ implantations into 6H-SiC epilayers and application to pn junction diodes

Aluminum (Al) and boron (B) ion implantations at room temperature into n-type 6H-SiC epilayers have been investigated. Rutherford backscattering spectroscopy (RBS) channeling measurements revealed larger lattice damage in Al⁺ implantation at a given total implantation dose. A nearly perfect electrical activation ratio (>90%) could be attained by high-temperature annealing at 1600°C for Al⁺ and 1700°C for B⁺ implantations. Mesa pn junction diodes formed by either Al⁺ or B⁺ implantation with a 1×10¹⁴ cm⁻² dose exhibited high blocking voltages of 950∼1070 V, which are 80∼90% of the ideal value predicted for the diode structure. The forward current can clearly be divided into two components of diffusion and recombination currents. B⁺-implanted diodes showed higher breakdown voltage on average but poor forward conduction. Comparison of the performance of Al⁺ and B⁺-implanted diodes is discussed.     

Annealing of AsGa-related defects in LT-GaAs: The role of gallium vacancies

We have studied the annealing properties of As_Ga-related defects in layers of GaAs grown at low substrate temperatures (300°C) by molecular beam epitaxy (low temperature[LTx]-GaAs). The concentration of neutral As_Ga-related native defects, estimated by infrared absorption measurements, ranges from 2×10¹⁹ to 1×10²⁰ cm⁻³. Slow positron annihilation results indicate an excess concentration of Ga vacancies in LT layers over bulk grown crystals. A sharp annealing stage at 450°C marks a rapid decrease in the As_Ga defect concentration. We propose that the defect removal mechanism is the diffusion of As_Ga to arsenic precipitates, which is enhanced by the presence of excess V_Ga. The supersaturated concentration of V_Ga must also decrease. Hence, the diffusivity of the As_Ga defects is time dependent. Analysis of isothermal annealing kinetics gives an enthalpy of migration of 2.0±0.3 eV for the photoquenchable As_Ga defects, 1.5±0.3 eV for the V_Ga, and 1.1±0.3 eV for the nonphotoquenchable defects. The difference in activation enthalpy represents difference energy between an As atom and Ga atom swapping sites with a V_Ga.     

Doping of 3C-SiC by implantation of nitrogen at high temperatures

Doping profiles and electrical properties are investigated on SiC samples doped with single energy implants from nitrogen. The profiles are analyzed using Pearson distributions for different implantation energies and temperatures. Implantations are performed for temperatures up to 1200°C. Diffusion during high temperature implantation is investigated and the diffusion coefficients measured range from 1.09 × 10⁻¹⁵ to 1.53 × 10⁻¹⁴cm²/s depending on temperature. The activation energy for implantation enhanced diffusion is estimated to be 0.91 eV. A comparison is made with diffusion during annealing. The activated dopants from high temperature implantation are investigated by the Hall probe method, showing that activation and mobility increase with temperature.     

Recent developments in rapid thermal processing

Rapid thermal annealing (RTA) with a short dwell time at maximum temperature is used with ion implantation to form shallow junctions and polycrystalline-Si gate electrodes in complementary, metal-oxide semiconductor (CMOS) Si processing. Wafers are heated by electric lamps or steady heat sources with rapid wafer transfer. Advanced methods use “spike anneals,” wherein high-temperature ramp rates are used for both heating and cooling while also minimizing the dwell time at peak temperature to nominally zero. The fast thermal cycles are required to reduce the undesirable effects of transient-enhanced diffusion (TED) and thermal deactivation of the dopants. Because junction profiles are sensitive to annealing temperature, the challenge in spike annealing is to maintain temperature uniformity across the wafer and repeatability from wafer to wafer. Multiple lamp systems use arrayed temperature sensors for individual control zones. Other methods rely on process chambers that are designed for uniform wafer heating. Generally, sophisticated techniques for accurate temperature measurement and control by emissivity-compensated infrared pyrometry are required because processed Si wafers exhibit appreciable variation in emissivity.     

Thermal activation of shallow boron-ion implants

Boron implanted into n-type Si at 10¹⁵ cm⁻² dose and energies from 500 eV to 1 keV was activated by annealing in nominally pure N₂ and in N₂ with small admixtures of O₂. Effective process times and temperatures were derived by thermal activation analysis of various heating cycles. The lowest thermal budgets used “spike anneals” with heating rates up to 150°C/sec, cooling rates up to 80°C/sec, and minimal dwell time at the maximum temperature. Dopant activation was determined by sheet electrical transport measurements. Surface oxidation was characterized by film thickness ellipsometry. P-n junction depths were inferred from analysis of sheet electrical transport measurements and secondary ion mass spectroscopy profiles. Boron activation increases with boron diffusion from the implanted region. Electrical activation has a thermal activation energy near 5 eV, while boron diffusion has an activation energy near 4 eV. Surface oxide can retard boron diffusion into the ambient for high-temperature anneals.     

Doping and impurity compensation by ion implantation in a-SiGe films

This paper discusses the electrical properties of a-SiGe films (N _Ge∼2.2 at. %) prepared by co-evaporation of Si and Ge from separate sources and doped by ion implantation of substitutional impurities (B⁺ and P⁺), as well as the results of controlled impurity compensation by ion-beam doping. It was found that B⁺ and P⁺ implantation into a-SiGe films in the dose range 1.3×10¹⁴–1.3×10¹⁷ cm⁻², followed by annealing at 350 °C, increased the conductivity of these films from 10⁻⁹ to 10⁻⁴ and to 10⁻⁵ S/cm for B⁺ and P⁺, respectively. The position of the Fermi level could be varied from (E _v+0.27) to (E _c−0.19) eV. These investigations indicate that compensation of pre-doped a-SiGe films by ion implantation is feasible and reproducible. It is also found that higher doping efficiency of a-SiGe films is obtained by using boron than by using phosphorus. Fiz. Tekh. Poluprovodn. 32, 1260–1262 (October 1998)     

Study of Arsenic ion implantation of patterned strained Si NWs

A systematic study of the impact of As⁺ ion implantation on strain relaxation and dopant activation of biaxially strained SSOI layers and uniaxially strained/unstrained NWs is presented. Three aspects are investigated: (i) the quality of the single crystalline layers and the NWs, (ii) strain relaxation of the implanted NWs and (iii) dopant activation of the layers and NWs. Optimization of the doping conditions resulted into very low contact resistivities of NiSi contacts on strained and unstrained 70 nm SOI layers and Si NWs. For NW contacts values as low as 1.2 × 10⁻⁸ Ω cm² for an As⁺ dose of 2 × 10¹⁵ cm⁻² were achieved, which is 20 times lower than for planar contacts made under the same implantation and annealing conditions.     

Diffusion Mechanism for Arsenic in Intrinsic and Extrinsic Conditions in HgCdTe

Due to its low diffusivity and high activation rate, arsenic has become the dopant of choice in p/n HgCdTe high operating temperature technology. Its diffusion mechanism, however, remains imprecise. In this work, arsenic diffusion was studied in molecular beam epitaxy HgCdTe structures consisting of alternatively As-doped and intrinsic layers grown on a CdZnTe substrate. The diffusion coefficient of As was extracted from secondary ion mass spectroscopy concentration profiles. Annealings were performed for different temperatures, mercury partial pressures (P _Hg), annealing times and cadmium atomic fractions. Fermi-level effect on diffusion was observed, indicating extrinsic conditions for diffusion at high As concentration. Based on the variation of As diffusivity with P _Hg and As concentration, we propose that As diffusion occurs on both II and VI sublattices. Our results are consistent with the fact that As_VI diffusion is assisted by the Te interstitial, introducing donor levels in the bandgap, while As_II diffusion is assisted by the cation vacancy.     

Experiments and simulation of the diffusion and activation of the n-type dopants P, As, and Sb implanted into germanium

The effects of implant dose and annealing conditions on the diffusion, activation, and out-diffusion of the typical n-type dopants in germanium (phosphorus, arsenic, antimony) were studied. First, short annealing times were used to limit the diffusion of dopants and to match the conditions needed for the realization of shallow junctions. Sb is not well suited to achieve high activation levels because honeycomb voids can already form at doses of 3 × 10¹⁴ cm⁻². Of the other two, P is a better candidate than As because it was possible to maximize the activation level to up to about 4.5 × 10¹⁹ cm⁻³ without noticeable diffusion. This absolute value has only a limited accuracy, though, since the mobility models available in literature lead to values which differ by more than one order of magnitude. Longer annealing times were then used to study the redistribution of the dopants. For P, a model based on migration predominantly via complexes with doubly negatively charged vacancies and dopant loss was implemented which allowed the simultaneous simulation of our experimental profiles with one set of parameters. The extracted diffusion coefficient with an activation energy of 2.2 eV is comparable to the results obtained in previous studies. No noticeable P clustering was observed in these experiments. The model was then adapted to simulate the redistribution of As and Sb. For Sb, clustering is apparent in the diffusion profiles and has to be taken into account in the simulations.     

Metallic impurity gettering to defects remaining in the RP/2 region of MeV-ion implanted and annealed silicon

Damage has been observed in MeV-ion-implanted Si away from the projected ion range, R_P, mainly around R_P/2, after annealing at temperatures between 700 and 1000°C. The most suitable way to detect this damage is to decorate it with metals and to measure the metal distribution. The formation and disappearance of the R_P/2 damage has been investigated by Cu gettering in Si⁺-ion implanted Si versus temperature and time of the annealing cycle. It is believed that an excess of vacancies around R_P/2 getter metal impurities. By means of positron annihilation spectroscopy no vacancy defects have been detected. In contrast, XTEM investigation reveals small (20–30 nm) interstitial loops in the R_P/2 region. The creation of these loops is triggered by interstitials injected during the ion milling procedure used for TEM specimen preparation. The ion bombardment of Si gives rise to self-interstitials that may modify the existing interstitial clusters to bigger agglomerates observable by XTEM.