Selective X-ray generation by heavy ions (Part 2) measurement of the concentration distribution of ion-implanted antimony in silicon by the use of selective heavy ion X-ray excitation

This investigation demonstrates how the total, concentration distribution of antimony, previously implanted into silicon at 100 keV, may be elucidated without recourse to the usual radioactive isotope techniques. It uses the fact that 100 keV Kr⁺ ions can preferentially excite characteristic X-rays from antimony, even in the presence of a huge excess of silicon. The resultant high sensitivity for the detection of antimony in silicon is accompanied by the fact that the X-rays arise predominantly from less than one hundred Angstroms below the surface of the specimen. Thus bombardment by 100 keV Kr⁺ íons is used ín conjunction with an anodic stripping technique (which removes 169±20 Å at a time) to obtain the antimony distribution profile in silicon. Consideration is also given to the possibility of obtaining the implanted antimony range distribution by using 100 keV Kr⁺ ions to detect the antimony and simultaneously remove silicon by sputtering.     

Rutherford backscattering study of crystal orientation dependent annealing effects in high-dose antimony implanted silicon

High dose implantations (10¹⁶ ions/cm²) of antimony in silicon result in concentrations far above the solid solubility of antimony in silicon. Rutherford backscattering was used to study the behaviour of damage and antimony concentration profiles for 〈100〉 and 〈111〉 substrates. The measurements were performed for various annealing treatments, implantation temperatures and implantation energies. A crystal orientation dependent outdiffusion of antimony towards the surface, a highly supersaturated phase of substitutional antimony at 600°C and a strong reverse annealing effect at higher temperatures were found.     

Complex refractive index and phosphorus concentration profiles in P+31 ion implanted silicon by ellipsometry and auger electron spectroscopy

Ellipsometrically measured complex retractive index profiles in high energy P⁺₃₁ ion implanted silicon have been compared with the phosphorus concentration profiles determined by in-depth profiling of the implanted surface using Auger electron spectroscopy in conjunction with in-situ ion sputtering. Structure was observed in the phosphorus profile which corresponds to structure in the complex refractive index profiles of unannealed specimens. This implies that the complex refractive index profile of the unannealed surface is sensitive to the concentration of the implanted species as well as the amount of structural disorder in the implanted layer. These results also indicate that the implanted phosphorus tends to build up in the more highly damaged regions, possibly through a radiation enhanced self-diffusion mechanism.     

Defects formation in the dual B+ and N+ ions implanted silicon

Silicon wafers were implanted with 40 keV B⁺ ions (to doses of 1.2×10¹⁴ or 1.2×10¹⁵ cm^–2) and 50 or 100 keV N⁺ ions (to doses from 1.2×10¹⁴ to 1.2×10¹⁵ cm^–2). After implantations, the samples were furnace annealed at temperatures from 100 to 450 °C. The depth profiles of the radiation damages before and after annealing were obtained from random and channeled RBS spectra using standard procedures. Two damaged regions with different annealing behaviour were found for the silicon implanted with boron ions. Present investigations show that surface disordered layer conserves at the annealing temperatures up to 450 °C. The influence of preliminary boron implantation on the concentration of radiation defects created in subsequent nitrogen implantation was studied. It was shown that the annealing behaviour of the dual implanted silicon layers depends on the nitrogen implantation dose.The authors would like to thank the members of the INP accelerator staff for the help during the experiments. The work of two authors (V.H. and J.K.) was partially supported by the Internal Grant Agency of Academy of Science of Czech Republic under grant No. 14805.     

Oxygen incorporation in polyethylene and polypropylene implanted with F+, As+ and I+ ions at high dose

Samples of PolyPropylene (PP) and PolyEthylene (PE) implanted with 150 keV F⁺, As⁺ and I⁺ ions with a dose of 1×10¹⁵ cm^–2 were studied using standard Rutherford Back Scattering (RBS) technique. No fluorine atoms above the present RBS detection limit were observed in the ion-implanted polymers. The measured depth profiles of As and I atoms are significantly broader than those predicted by the TRIM code for pristine polymers. The differences can be explained by stepwise polymer degradation due to ion bombardment. Massive oxidation of the ion-implanted polymers is observed. The oxidation rate and the resulting oxygen depth profile depend strongly on the polymer type and implanted ion mass. In the samples implanted with F⁺ ions, an uniformly oxidized layer is built up with a mean oxygen concentration of 15 at.%. In the samples implanted with As⁺ and I⁺ ions, a non-uniform oxygen depth distribution is observed with two concentration maxima on the sample surface and in a depth correlated with implanted ion range.     

Doping and radiation damage profiles of P+ ions implanted in silicon along the [110] axis

Several doses of 200 KeV phosphorus ions have been implanted under channeling conditions along the [110] direction in silicon.

Range distribution has been determined for the three implant doses 10¹³, 10¹⁴, 10¹⁵ P⁺/cm² both with the electrical measurements and the neutron activation techniques.

The radiation damage distribution has been determined both with 290 KeV proton back-scattering analysis and with transmission electron microscopy (TEM) observations.

Good agreement has been found between electrical and neutron activation profiles in the samples where 100% of the implanted dose had been electrically activated by means of annealing.

Carrier concentration profiles, from samples implanted with 10¹⁵ P⁺/cm², determined after two different annealing temperatures (500°C and 700°C) have bcen compared with the radiation damage distribution and a correlation between damage and phosphorus electrical activation process seems to be possible.

Maximum damage peak, as determined by back-scattering analysis, shifts from ～0.4 μ depth in the lower dose(5 × 10¹⁴ P⁺/cm²), to ～0.22 pm depth in the higher implanted dose (4 × 10¹⁵ P⁺/cm²). Damage distribution of phosphorus ions random implanted in the same experimental conditions shows 3 peak at ～0.2 μn depth.

In accordance with the back-scattering analysis, T.E.M. observations on 10¹⁵P⁺/cm² implanted samples show the presence of amorphous regions at depth between 0.25 and 0.5 μm from the surface. In the most damaged layer ～0.3μm in depth, a surface density of ～10¹²/cm² amorphous regions 25-50 A diameter was observed.     

Properties of ion implanted silicon,sulfur, and carbon in gallium arsenide

Work is described in which chromium-doped semi-insulating gallium arsenide has been successfully doped n-type with ion implanted silicon and sulfur, and p-type with ion implanted carbon. A dilute chemical etch has been employed in conjunction with differential Hall effect measurements to obtain accurate profiles of carrier concentration and mobility vs. depth in conductive implanted layers. This method has so far been applied to silicon-and sulfur-implanted layers in both Cr-doped semi-insulating GaAs and high purity vapor grown GaAs. In the case of sulfur implants, a strong diffusion enhancement has been observed during the annealing, presumably due to fast-diffusing, implantation-produced damage. Peak doping levels so far obtained are about 8 × 10¹⁷ electrons/cm³ for silicon implants and 2 × 10¹⁷ electrons/cm³ for sulfur implants. Mobility recovery has been observed to be complete except in regions near the surface which are heavily damaged by the implantation.     

CEMS study of silicon implanted iron

Thin layers of iron-rich Fe-Si alloys were formed by silicon implantation into iron at room temperature with different energies (100, 200, and 300 keV) and ion doses (2 × 10¹⁷ to 1×10¹⁸ cm^–2). The produced layers were investigated by⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS) to identify the phases formed by the ion implantation. Auger electron spectroscopy (AES) was used to measure the concentration depth profiles of the implanted silicon. Depending on the implantation parameters different disordered Fe-Si structures were detected. At low doses only magnetic phases were formed while at high doses a non-magnetic phase with a hitherto unknown structure appeared. Annealing of the samples resulted first in the formation of a D0₃-like short-range order and a slow decrease of the non-magnetic phase, and subsequently in the migration of Si out of the investigated depth range.     

Ellipsometric study of tellurium implanted silicon

Abstract

Ellipsometric parameters as a function of the dose (D = 2.10¹³ ? 2.10¹⁵ ions cm^?2) and annealing temperature have been measured on the silicon implanted with 30 keV Te ions. Obtained information on lattice disorder are to a great extent comparable with those of other methods, e.g. backscattering technique. Moreover optical constants of a damage surface layer may be estimated.     

Determination of the complex refractive index profiles in P+31 ion implanted silicon by ellipsometry

Ellipsometry was used to determine the complex refractive index profiles in silicon implanted with P⁺₃₁ ions with energies of 35, 52,5 and 70 keV. The profiles were determined both by anodization-stripping of the implanted layer and by numerical fitting of multiple-angle-of-incidence ellipsometer data taken on the as-implanted surface, assuming that the implantation would exhibit a Gaussian distribution. Good correlation was obtained between the two types of profiles, indicating that the non-destructive measurements on the as-implanted surface may be useful in process control. Good agreement with published results was also obtained on the increase in depth with energy of both the damage and the implanted species.     

The measurement of cone length and range in etched plastics

Abstract

Group V impurities implanted at 400 keV into silicon have been detected in substitutional lattice positions by EPR. Three samples of VFZ, p-type 1200–1500 ohm-cm silicon from the same ingot were implanted with As⁷⁵, Sb¹²¹, and Sb¹²³, respectively. The EPR spectrum of each implanted substitutional impurity was observed after annealing the lattice damage. Only the isotope implanted in each sample was seen. Since only those donors which are electrically active can be observed, this technique measures the electrically active fraction of the implanted species. Upon annealing to 970°C, most of the antimony was active whereas only about 1/5 of the arsenic was observed. Comparisons with backscattering results indicate that between 350 and 600°C, ～95 per cent of the implanted antimony is substitutional but ～0 per cent is electrically active. The increase in electrical activity at 600°C is due to the rise of the Fermi level to the donor level as the residual lattice damage anneals. The paramagnetic damage centers observed were those also seen in oxygen-implanted silicon, Si-P3 and Si-Pl, but the Si-P3 center was not as well resolved and grows upon annealing to 200°C.     

A SIMS study of ion beam induced migration of nitrogen in thermally oxidized silicon

The potential use of thin silicon nitroxide films as gate dielectrics in VLSI MOS devices has motivated much recent work. The present study shows that positive ion bombardment, as encountered in sputter depth profiling or ion implantation, can induce considerable movement of nitrogen in thin thermal oxide films on silicon. Low energy N⁺₂ implants are performed in-situ in a SIMS apparatus and are subsequently depth profiled. The effect of implant dose and oxide thickness are examined and comparisons are made to films prepared by rapid thermal nitridation and LPCVD. Profiles obtained under O⁺₂, O^-, and Cs⁺ bombardment are also compared. SIMS depth profiles of implanted 200 Å oxides using positive ion bombardment show a depletion of nitrogen near the surface, a shoulder in the nitrogen concentration near the Si-SiO₂ interface, and a peak in this concentration at the interface. Negative ion bombardment did not induce a shoulder-peak structure at the interface. The implications of these results are discussed.     

Depth profiles of metal ions implanted in dielectrics at low energies

The depth profiles of Cu⁺, Ag⁺, and Au⁺ ions implanted into amorphous dielectric SiO₂, Al₂O₃, and soda-lime silicate glass (SLSG) are simulated by the DYNA program. The algorithm follows projectile-ion-substrate-atom pair collisions giving rise to a dynamic variation in the phase composition in the surface layer of the irradiated material and takes into account surface sputtering. Ion implantation up to doses of ≤10¹⁶ ion/cm² at low ion energies of 30, 60, and 100 keV is considered. The measured dynamic variation of the depth profiles of implanted ions as a function of the dose is compared with the standard statistical distribution calculated by the TRIM algorithm.     

Sodium profiles in β″-alumina crystals: Modifications induced by argon bombardment

Abstract

Sodium depth profiles in implanted sodium β″-alumina single crystals have been measured by the nuclear resonance technique. A systematic investigation of the depth profile modifications as function of the implanted ion energy has been done using argon-ion (E = 50–600 keV) irradiation at fixed dose (Φ = 4 × 10¹⁶ions/cm²) and beam current (I = 1 μA/cm²). Argon doses were checked by Rutherford backscattering spectrometry. The changes in the sodium profiles are discussed in terms of transport equations which include three main processes: radiation enhanced transport, electric field assisted migration, and preferential surface sputtering of the alkali element. Special attention is devoted to the discussion of sputtering processes.     

A TDPAC study of the lattice location of implanted indium in silicon

Abstract

The annealing behaviour of indium implanted silicon (doses 10¹¹?10¹³ atoms/cm²) was studied by time differential perturbed angular correlation spectroscopy. Besides the substitutional site two types of defect configurations were observed. In the as-implanted condition the substitutional In fraction remains below 20% even at the lowest dose. This result is in accordance with the prediction of the track amorphization model.     

The application of correlated SIMS and RBS techniques to the measurement of ion implanted range profiles

A simple, inexpensive secondary ion mass spectrometer (SIMS) instrument is de. scribed and its application to the determination of the range profiles of 20–30 keV Cs⁺ ions implanted into silicon and aluminium targets is demonstrated. The results are compared with those obtained by the alternative method of Rutherford backscattering (RBS) analysis and it is shown that provided the SIMS sputtering yield, S, (which is required for the calculation of the depth scale of the SIMS data) is chosen as a fitting constant, the agreement between the two techniques is excellent. On this basis, therefore, it is proposed that, provided a trace implant of Cs⁺ is included to provide an in-built calibration of S, the SIMS apparatus offers a universal technique for the determination of the profiles of impurities present at concentrations of 1–100 ppm.     

Nitrogen implanted in iron: AES and Pes study

AES and PES studies of nitrogen in iron implanted with molecular nitrogen ions having an energy of 120 keV and doses on the order of 10¹⁷ N-atoms/cm² were performed. Measuring nitrogen concentration depth profiles, a remarkable accumulation of nitrogen near surface was found besides the ordinary concentration maximum at the depth of mean projected range R_p of nitrogen ions. In addition to strong nitride bonding state a weakly bonded nitrogen was also observed. It manifested itself by time-dependent changes in spectra and by a distinct value of N 1s binding energy. The reasons for the concept of weakly bonded nitrogen, probably of molecular form, are discussed.     

RBS analysis of ions implanted in light substrates exposed to hot plasmas laser-generated at PALS

Ge and Ta ion implantation of silicon and carbon substrates has been obtained at PALS Research Laboratory in Prague by using laser pulses of 400 ps duration, 438 nm wavelength, 10^14?16 W/cm² intensity. Substrates were exposed in vacuum at different distances from the target and at different angles with respect to the normal to the target surface. ‘On line’ measurements of ion energy were obtained with time-of-flight techniques by using an electrostatic deflector as ion energy analyzer. ‘Off line’ measurements of ion energy were obtained by Rutherford backscattering spectrometry (RBS) of 2.25 MeV He²⁺ beam at CEDAD Laboratory of Lecce University. The RBS spectra have given the depth profiles of the ion-implanted species and the implanted doses as a function of the laser intensity, angular position and target distance. A spectra deconvolution method based on the ion stopping power in the substrate matrix was applied in order to evidence the energy of the implanted ions. Measurements indicate that ions with energy ranging between 100 keV and 10 MeV and dose of the order of 10^14?16/cm² are implanted and that the process of ion implantation occurs mainly in substrates placed at little angles with respect to the normal to the target surface. Only a thin film deposition occurs for substrates placed at large angles with respect to the normal direction. Results indicate that the ion energies measured with the ‘on line’ and the ‘off line’ techniques are in good agreement.     

The investigation of ion implanted layers by scanning electron microscopy

SEM signals were used to image ion-implanted surfaces and to quantitatively analyze implanted layers. Silicon was used as substrate material for implantation, but some measurements on GaAs are also reported. Various ion species were implanted and the dependence of the signals upon fluence was studied. Electron backscattering and absorbed current were found to be influenced by the radiation damage rather than by the species of implanted ions. The degree of damage could be characterized by absorbed current measurements. The ion fluence necessary to produce amorphous layers was determined for N, P, and As in Si using this technique. This fluence was found to correspond to an energy deposition of 2.8×10²¹ keV/cm³. For the detection of very small amounts of implanted ions by characteristic X-rays, the electron energy must be fitted to the penetration depth of the ions under conditions maintaining reasonable excitation cross sections. The lowest value of the normalized detectability obtained in our measurements was 2.5×10¹³ Ions/cm² for 45 keV phosphorus.     

Laser annealing of Bi implanted <111> and <100> silicon

The influence of surface orientation in Bi implanted silicon, annealed by Q-switched ruby laser pulse irradiation was investigated. Depth distributions and lattice location of the Bi atoms were obtained using⁴He backscattering and channeling techniques and the electrical behavior studied by sheet resistance measurements. The dopant profiles show partial surface accumulation and in-depth broadening without influence of the substrate orientation. These profiles can be fitted by a numerical calculation based on the normal freezing model with an interfacial segregation coefficient much higher than the equilibrium one. The impurity atoms located in the in-depth profile are shown to be electrically active when their maximum concentration does not exceed 10²⁰ atoms/cm³.