MeV Implantation Research Articles

Measured Lattice Damage and Optical Index Change in KNbo3

AbstractWe have used 2-MeV and 200-KeV He implantation into KNbO3 and LiNbO3 single crystals to generate a damaged layer of reduced optical index. MeV implantation enables the formation of optical waveguides of several µm thickness, which have been analyzed by dark and bright line spectroscopy in order to determine the refractive index profiles. In addition, 200-keV implants have been used to model the end-of-range-damage, which was measured by RBS/Channeling. KNbO3 and LiNbO3 show a distinctly different sensitivity of the radiation damage.

Characteristics of 56 Mev Oxygen Implantation into Si and III-V Semiconductors

AbstractHigh energy (56 MeV) oxygen implants into Si, GaAs and InP give rise to sharp, non-Gaussian depth profiles with the distributions skewed towards greater depths. This skewness is probably the result of channeling, and it is a common feature of MeV implants into semiconductors. The ratio of the peak concentration in the depth profile to the concentration at the surface is ≥103 for each material, and the full width at half maximum of each profile is ∼2 μm. The experimental projected ranges for the oxygen are ∼31 μm in GaAs, ∼36 μm in InP and ∼46 μm in Si. These are ∼10% larger than the values predicted by the PRAL code. The photoluminescence intensity from the top 1 μm from the surface of both GaAs and InP is reduced by more than an order of magnitude for 56 MeV oxygen implants at a dose of 1.3 × 1015 cm−2, due to point defect introduction in this region. Potential applications for these high energy implants in electronic and photonic device fabrication will be discussed.

Microstructure and hardness of titanium and iron surfaces after megaelectronvolt nitrogen implantation

Effects of MeV N + implantation in titanium and iron surfaces on the microstructure and hardening have been examined. In both metals, high nitrogen concentrations could easily be built up over a depth of about 1 μm, as observed with Rutherford backscattering spectrometry. Nitride formation was demonstrated by X-ray diffraction, both in titanium and iron. Hardness measurements indicated that the load-carrying abilities of unimplanted or even low energy nitrogen implanted specimens could be enhanced significantly by MeV implantation. In 1 MeV irradiated titanium, for example, an increase in surface hardness of 30% using a load as heavy as 100 g was observed, while no hardening effects could be detected using this load on 35–200 keV implanted specimens. MeV implantation of titanium induced some surface texturing, whereas iron surfaces remained smooth. At doses higher than 0.65 × 10 18 cm −2 blisters appeared at the iron surface and at even higher doses the apparent nitrogen peak concentration showed a saturation effect.

Carrier concentration profiles in multiply implanted silicon with 0.5–7.5 MeV phosphorus

MeV implantation is very important in fabricating semiconductor devices and VLSI. The carrier concentration profiles in high energy phosphorus implanted silicon have been investigated. Phosphorus with energies ranging from 0.5 to 7.5 MeV were implanted into Si with doses ranging from 2 × 10 12 to 1 × 10 13/cm 2. The results indicate that carrier concentration profiles consist of two half-Gaussians distribution with different stragglings σ f and σ b. According to these profiles the method of forming a uniform profile with multiple implantations was suggested. The various specific carrier concentration profiles can be got by multiple implantations with different energies, doses and masking technology with SiO 2. Rapid thermal annealing has been used to obtain good reliability and reproducibility of their profiles. The residual defects of the samples were measured by 1000 kV TEM. Specific transistors produced with phosphorus multiple implantations have satisfactory characteristics.

Electronic defects in silicon induced by MeV carbon and oxygen implantations

Electrical properties of silicon above buried defect layers formed by MeV carbon and oxygen implantation were investigated. Energies ranging from 2 to 4 MeV and doses from 5 × 10 14 to 10 16 cm −2 were used. By studying the reverse bias leakage currents of P +/N junction diodes after MeV implantation and subsequent annealing at 950 ° C for 1 h, it was found that the electrical defects are mostly localized near the peaks of the implant profiles. In cases of 4 MeV carbon and oxygen implantations at a dose of 10 15 cm −2, average leakage currents less than 5 nA/cm 2 at 10 V reverse bias were obtained. The average minority carrier lifetimes in the top 2 μm were about 100 μs.

Dynamic computer simulation of high energy ion implantation

For the simulation of high energy, high fluence implantations, dynamic codes are necessary which take into account the modification of the substance due to the presence of the implants and due to collisional effects. In the present paper, we give a brief description of such a binary collision simulation program and demonstrate its applicability to 200 keV and 1 MeV implantations of oxygen and nitrogen into silicon. The high fluence dynamic implantation profiles are considerably broadened with respect to the static profiles. It is found that the broadening is mainly related to the swelling and the altered slowing down in the implanted layer, whereas sputtering is only important for the surface erosion and thereby the net shift of the implantation profiles. The contribution of the collisional transport of target atoms can be neglected.

High energy implantation: Present and future facilities

Accelerators of the tandem type are in common use for high energy ion implantation. The necessary charge exchange at two stages limits the maximum ion current to < 1 mA. A single ended Van de Graaff can deliver ion currents up to 1 mA. The time-consuming opening of the pressurized tank for ion source exchange or service has been avoided in our l MV HVEE accelerator by a high-pressure load lock. This adapted version of the Van de Graaff accelerator is now in use for MeV implantation in semiconductors and metals. Future facilities requiring higher ion energy and more beam current are likely to use rf instead of dc acceleration. After the successful operation of a 115 kV so-called MEQALAC accelerator, a prototype multiple beam 1 MeV rf accelerator is under construction at our Institute. Dc type and different rf accelerators like RFQ, variable phase linac and MEQALAC are compared. MEQALAC is an acronym for a rf linac with electrostatic focusing and with multiple beams.

Present developments of research MeV Pelletron ion implantation systems

National Electrostatics Corp. has manufactured 79 ion beam systems. 17 of these Pelletron systems were designed with MeV ion implantation capability as a primary objective. Of these system, 8 were designed specifically for production ion implantation with a maximum beam energy of 4 MeV. For research applications, ion beam masses from carbon through gold have been accelerated with a maximum observed energy of 38 MeV from a 3 MV tandem S-series Pelletron. This paper will present performance charts which describe the observed ion beam capabilities of existing 3 MV tandem Pelletrons. In addition, the performance of the new high current, four charging chain, S-Series accelerator, currently in manufacture, will be given. A new 4 MV tandem S-Series Pelletron has been proposed, its expected capabilities will be stated. The NEC electrostatics raster scanner which is in use for MeV implantation provides uniform deposition at a maximum scan angle of ± 3.0 ° for 4 MeV doubly charged ions. The output wave form at ±10 kV scanning potential will be shown.

Materials modification by MeV ion implantation

A newly developed Van de Graaff-type mega-volt ion implantation facility is described. It is used for generation of up to several-hundred μA mass-analysed ion beams in the energy range from 10 keV to 2 MeV. A wide range of ion species can be extracted using different types of ion sources in combination with a source exchange system. Technical details of the facility are described and include a high-pressure source load-lock, integrated gas system, specially developed ion optics and injector system, mass-analysis at high voltage level and virtually no X-ray shielding necessary. Interesting new research topics in MeV implantation are briefly indicated. Mechanisms of damage formation and annealing, radiation enhanced diffusion, crystallization of amorphized layers and stopping and range theory are to be elucidated for MeV irradiation of semiconductors. In addition, MeV ion irradiation of metals, isolators and ceramic materials offers interesting possibilities to improve tribological properties, to synthesize new materials using ion implantation or ion mixing and to improve adhesion of thin films on solid substrates.

MeV Implantation of Gallium Arsenide

AbstractWe investigated n-type MeV implants into semi-insulating GaAs to fabricate fully implanted varactor diodes for monolithic millimeter-wave applications. Single and multiple implants of Si from 6 to 2.5 MeV and 6 MeV S implants in GaAs were studied before and after capless furnace annealing and rapid thermal annealing by chemical profiling using secondary ion mass spectrometry (SIMS) and electrochemical and traditional differential capacitance-voltage profiling. A buried active layer at a depth of 2.8 μ.m with a peak carrier concentration of 2.5 × 1018 cm-3 was achieved by using 6 MeV Si + 4 MeV Si + 6 MeV S implants and rapid thermal annealing them at a temperature 1050°C for 10 seconds. The chemical profiles are correlated to the electrical profiles to determine activation and annealing behavior of MeV Si and Simplants in semi-insulating GaAs.

Implanted boron profiles in silicon

10B and 11B implants into amorphous Si, with energies ranging from 50 keV to 2 MeV and 10 keV to 1 MeV respectively, were profiled by the nuclear reactions 10B(n, α) 7Li and 11B(p, γ) 12C. The projected range R p and straggling ΔR p agree within a few percent with recent calculations due to Ziegler, Biersack and Littmark (ZBL). These results show that the ZBL electronic stopping power is adequate to reproduce range parameters resulting from MeV implantations.

Defect Structure of MEV Si Implantation in GaAs

ABSTRACTThe defect and atomic profiles for MeV implantation of Si in GaAs were investigated using He++ channeling, TEM, and SIMS. Doses of 1–10 × 1015Si/cm2 at 1–3 MeV were used. MeV implantation at room temperature rendered only a small amount of lattice disorder in GaAs. Upon annealing at 400°C for 1 h or 800°C for 30 a, we observed a ‘defect-free’ surface region (- 1 μ for 3 MeV implant). Below this region, extensive secondary defects were formed in a band which was 0.7 μ wide and centered at 2 μ for 3 MeV implant. These defects were mostly dislocations lying in the [111] plane. SIMS depth profiles of Si implants showed the Si peak to be very close to the peak position of the defects. The experimental profiles of Si were compared to the TRIM calculation; generally good agreement existed among the peak positions.

Performance of the NEC production high energy implantation system

MeV ion implantation systems are now being used on a production basis, providing beam energies in the range from 200 keV to 4 MeV. Interest and demand for such systems has increased since the first system went on-line in May 1983. At present, eight systems have been sold with a maximum beam energy capability of 4 MeV for use in the production environment. Production machines are now available providing beam energies as high as 8 MeV. These systems are capable of providing a wide range of ion species without the use of toxic gases. Present beam current and beam species capabilities will be presented. In addition, we describe new techniques for measuring dose uniformity from MeV implants [W.A. Keenan, Prometrix Corp., 3255 Scott Blvd., Bldg. 2, Santa Clara, CA 95054-3077, USA] and present results of uniformity and particulate measurements. We describe MeV implanter developments, including a new wafer handler.

Device characteristics of mosfets in MeV implanted substrates

The operating characteristics of MOS transistors constructed in substrates subject to MeV ion implantation have been studied. A standard CMOS process was modified to include high-energy implantation in order to produce a buried layer for device isolation. The process included various high energy implant energies and CMOS well depths. It was seen that device behavior of MOSFETs in the substrate were virtually unaffected by the MeV implantation; channel surface mobility, transconductance and threshold voltage were unchanged. Some variations in body effect parameter and output resistance were noted. Further studies of the CMOS well behavior indicated an increase in well/substrate leakage currents as MeV implanted buried-layer depths decreased.

Bridging implant technique to characterize MeV implants

A bridging implant is used to connect an MeV implant to the surface for sheet resistance measurements. By performing the bridging implant first and mapping its sheet resistance, the contribution of the bridging implant can be subtracted from the combined profile to provide a map of the MeV implant alone. Initial results are very encouraging.

Critical aspects of high energy implants for CMOS technology: Channeling effects and masking problems

In this paper we describe some major problems related to the use of high energy ion implantation for fabrication of isolation wells for CMOS technology. MeV implants of phosphorus were performed on a Van de Graaff accelerator at different wafer orientations. Spreading-resistance data show very strong channeling effects. For phosphorus implantations over 1 MeV, ion beam masking was obtained through use of heavy metals, or large thicknesses (> 4 μm) of photoresist films. We present a large range of experimental profiles obtained after implantation through different deposited films. Masking material efficiencies were evaluated both for different energies (1 and 2 MeV) and for different film thicknesses of TiW, Ta and W.

Range distributions of MeV implants in silicon II: A comparison of SIMS and spreading resistance profiles of B, P and Ga

In an earlier paper [1] range moments were presented for B, P, As and Sn implants into silicon in the energy range 0.4–6 MeV. These moments were obtained using spreading resistance profilometry (SRP) after the samples had been annealed to activate the implants. The mean of the distributions agreed moderately well with theory but the straggle was significantly greater. In this paper we present SIMS data from the as-implanted and annealed samples from the earlier study as well as SRP and SIMS data on Ga implants in silicon. The larger straggle in the annealed samples seen with SRP is also seen in the SIMS data from the annealed samples but not in the as-implanted samples. In addition, distortion of some of the profiles is evident which is probably due to channeling. In the gallium profiles particularly there is broadening of the profile on the bulk side of the implant as if diffusion in undamaged material is easier than in damaged material. This effect is only visible in annealed samples.

Damage profiles of MeV implants of Ga and Si in silicon

To assist the production of layers 5–6 μm in thickness which are doped with gallium, MeV silicon implants have been used in conjunction with MeV gallium implants to determine whether the gallium will diffuse more readily in the damage created by the silicon atoms in gallium implanted substrates. This work requires that the damage and range profiles of the two species be known. There are significant differences in the theoretical moments for the distributions depending on the approach being used. Profiles of the damage and range are compared to theoretical estimates in particular with those obtained from the Monte Carlo code TRIM. The damage is observed to anneal in the same manner as damage at much lower energies.

The annealing of 1 MeV implantations of boron in silicon : S. Oosterhoff and J. Middelhoek. Solid-State Electron28 (5) 427 (1985)

The annealing of 1 MeV implantations of boron in silicon : S. Oosterhoff and J. Middelhoek. Solid-State Electron28 (5) 427 (1985)

Applications of MeV ion beams to material processing

The development of commercial ion implanters capable of implanting a wide range of elements with multi MeV energies has enabled ion implantation to be applied effectively to the modification of materials to a depth of several micrometers. For a silicon semiconductor technology the depth of penetration enables buried layers to be placed behind device structures to act as electrically isolating barriers. For high mass binary or ternary semiconductors, MeV ion implantation may be the only method of doping without resorting to chemically less pure film deposition techniques which tend to be unsuitable for large scale integration. In metals relatively thick (~1 μm) coatings can be penetrated to improve adhesion. Also, the corrosion properties of metals may be altered by changing the oxidation properties or by the creation of thick amorphous alloy coatings. With these effects come the added advantages that the smoothness and continuity of the surface is retained or may be enhanced. For polymers, MeV implantation enables thick electronic, wear or chemical modifications to be made to the material without loss of bulk integrity or properties.