Conventional Ion Implantation Research Articles

Characteristics of 6H-silicon carbide PIN diodes prototyping by laser doping

Silicon carbide PIN diodes have been fabricated using a direct-write laser-doping technique that reduces defect generation compared to the conventional ion-implantation technique. Nitrogen and aluminum were successfully incorporated into SiC as n-type and p-type dopants, respectively. Rutherford backscattering studies were conducted to compare the lattice defect generation by the laser-doping and ion-implantation techniques. No amorphization was observed in laser-doped samples, eliminating the need for high-temperature annealing. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the PIN diodes were also investigated. The silicon carbide diodes are intended for high-temperature and high-voltage power electronics applications.

Metal plasma immersion ion implantation and deposition (MPIII and D) using a metal plasma electron evaporation source (MPEES)

This paper describes a new type of metal plasma source for metal plasma immersion ion implantation and deposition (MPIII and D). The source is termed as Metal Plasma Electron Evaporation Source (MPEES). In certain aspect, its operation resembles electron beam evaporation, but the difference is that the electrons in MPEES are generated from the metal vapor plasma. They, in turn, also ionize the metal vapor to obtain the plasma. The system starts with an Ar plasma to evaporate and ionize metal vapor. Once the system is stabilized, Ar is turned off and the metal plasma sustains on its own. Then by combining this metal plasma source with conventional Plasma Immersion Ion Implantation and Deposition (PIII and D), we obtained Metal Plasma Immersion Ion Implantation and Deposition (MPIII and D). Using this system, we have implanted and coated Cr and Ti on test Si samples. Energy dispersive spectroscopy (EDS) and Auger electron spectroscopy (AES) have shown that Cr and Ti have been implanted into a large area of about 90 cm in diameter. The new technology can be applied to many areas such as in tribology to address wear, corrosion and fatigue issues, and in metallurgy for alloying materials that cannot be obtained using conventional methods. In this paper, we will describe the principle of the plasma source, source design considerations, and MPIII and D system set up and operation. Preliminary test data will also be presented.

Tribological improvements of ion implanted technological alloys: Plasma immersion vs. conventional ion implantation

This work reports a comparative investigation on tribological performance enhancement induced by nitrogen Plasma Immersion Ion Implantation (PI3) and conventional Nitrogen Ion Implantation (I2) on Ti and Al based alloys. The study has been carried out on the basis of the surface modification produced by both treatment techniques, in terms of the implanted nitrogen in-depth profiles, and its effect on surface hardening and wear resistance increase of the treated samples.Under the experimental conditions described, PI3 Ti-based alloys treated samples evidenced slightly better tribological performance than those subjected to I2 treatments. In the case of Al alloys, however, PI3 caused strong detrimental modification on the treated samples as revealed in the increase by a factor 100 of its surface roughness. Consequently, different criteria should be deemed in order to establish the adequacy of one or other technique, not only taking into account set up costs but also considering specific applications.

Vertical channel nMOSFET with an asymmetric graded lightly doped drain

A novel vertical channel nMOSFET with an asymmetric graded lightly doped drain (AGLDD) is first proposed and experimentally demonstrated. The vertical AGLDD structure is achieved by conventional ion implantation and impurity diffusion. The device fabrication is compatible with planar CMOS technology. The novel transistor shows very good immunity of short channel effects in DC characteristics.

High-intensity plasma ion nitriding of orthopedic materials: Part I. Tribological study

In this paper, we describe a newly developed technique—high-intensity plasma ion nitriding (HIPIN), which takes the advantages of low energy beam ion implantation at elevated temperatures that generates thick nitrided layers compared to conventional plasma nitriding and ion implantation, but overcomes the inherent line-of-sight shortcoming of beam implantation. In this technique, a low-pressure nitrogen plasma (<1 mTorr) is used. With an electron source (filament) to emit electrons and by drawing them to the anode (vacuum chamber), the plasma is generated and maintained due to electron-neutral gas collisions. With the application of a low voltage on the parts that are immersed in the plasma, ions are drawn and implanted to the surface of the parts. At elevated temperatures, nitrogen diffusion occurs, thus forming deep nitride layers. Using this technique, we have processed orthopedic materials made of Ti-6Al-4V and CoCrMo at various temperatures. It has been observed that for Ti-6Al-4V, nitriding at higher temperatures generate deep nitrided layers that are quite hard and wear resistant. For forged CoCrMo, nitriding at both low and high temperatures show much better performance than at medium temperatures. For comparison purposes, nitrogen plasma immersion ion implantation has also been performed. However, nitrided samples using the HIPIN technique out perform the one using implantation. A reduction of wear over 30 times has been observed. In contrast to the forged CoCrMo, nearly no improvement has been observed on cast CoCrMo possibly due to the microstructure effect.

Tailored conductivity in ion implanted polyetheretherketone

Ion implantation can be used to confer electrical conductivity upon conventional insulating polymers such as polyetheretherketone (PEEK). We have implanted PEEK films using three different types of ion implantation: conventional inert gas and metal ion implantation, and ion beam mixing. We have applied a number of analytical techniques to compare the chemical, structural and electrical properties of these films. The most effective means of increasing electrical conductivity appears to be via ion beam mixing of metals into the polymer, followed by metal ion implantation and finally, inert gas ion implantation. Our results suggest that in all cases, the conducting region corresponds to the implanted layer in the near surface to a depth of ∼750 Å (ion beam mixed) to ∼5000 Å (metal ion). This latter value is significantly higher than would be expected from a purely ballistic standpoint, and can only be attributed to thermal inter-diffusion. Our data also indicates that graphitic carbon is formed within the implant region by chain scission and subsequent cross-linking. All ion implanted samples retained their bulk mechanical properties, i.e. they remained flexible. The implant layers showed no signs of de-lamination. We believe this to be the first comparative study between different implantation techniques, and our results support the proposition that soft electronic circuitry and devices can be created by conductivity engineering with ion beams.

Doping concentration evaluation using plasma propagation models in plasma immersion ion implantation (PIII) system

Plasma immersion ion implantation (PIII) is a high dose-rate implantation process technique in the area of semiconductor device fabrication used to fabricate various device structures like shallow junction, silicon on insulators and in the processing of flat panel display materials, trench doping, etc. The basic mechanism of ions source and their acceleration in PIII technique is different from that of the conventional ion-implantation. In this, the target is immersed in a plasma source and the implantation is done by accelerating the ions with a negative pulse bias voltage, applied to the target. The dynamics of ion transport and the implantation is different from line-of-sight implantation. In this paper, the doping of individual ions (Ar, He and N), in a collisionless PIII system is studied analytically when a negative pulse of 10 kV is applied to the target. The net ion doping concentration in one pulse duration has also been computed during the propagation of plasma sheaths.

Ion penetration depth in the plant cell wall

This study investigates the depth of ion penetration in plant cell wall material. Based on the biological structure of the plant cell wall, a physical model is proposed which assumes that the wall is composed of randomly orientated layers of cylindrical microfibrils made from cellulose molecules of C 6H 12O 6. With this model, we have determined numerical factors for ion implantation in the plant cell wall to correct values calculated from conventional ion implantation programs. Using these correction factors, it is possible to apply common ion implantation programs to estimate the ion penetration depth in the cell for bioengineering purposes. These estimates are compared with measured data from experiments and good agreement is achieved.

Comparison of boron halide, decaborane and B implants in Si from Molecular Dynamics simulations

Ultra shallow junctions (depths <0.1 μm) are required for future generations of silicon devices. This requires either very low energy ion implantation (<1 keV for B for the shallowest of implants) or the use of heavier implanted species (either elemental or molecular). Many commercial implanters have problems operating at such low terminal voltages. For many years molecular ions, in particular BF 2 +, have been used to transport low velocity boron at higher energies, enabling the use of conventional implanters in the production of shallow junctions. However, with ever shrinking scales the energies required even for BF 2 are becoming too low. The investigation here is to look at the alternative heavier halides and decaborane as possible alternatives to allow continued use of conventional ion implanters. We use a molecular dynamics simulation to see if we can find any evidence of non-linear behaviour from the use of such molecular species for implantation, thereby making the modelling and simulation of such implants more complex than more conventional implantation. The simulation results presented suggest that there is no evidence of non-linear behaviour and all the standard parameters of implantation – ion ranges and displacements of silicon atoms – change in a well predicted manner.

Improved hot-carrier and short-channel performance in vertical nMOSFETs with graded channel doping

Graded doping profile in the channel of vertical sub-100-nm nMOSFETs was investigated in this study. Conventional single-step ion implantation was used to form the asymmetric graded doping profile in the channel. No large-angle-tilt implant is needed. The device processing is compatible with conventional CMOS technology. In a graded-channel-doping device, with the higher doping near the source, drain induced barrier lowering (DIBL) and the off-state leakage current are reduced significantly. The graded doped channel also has a lower longitudinal electric field near the drain. Therefore, hot-carrier related reliability is improved substantially with this type of device structure.

Semiconductor applications of plasma immersion ion implantation technology

Many semiconductor integrated circuit manufacturing processes require high dose of implantation at very low energies. Conventional beam line ion implantation system suffers from low beam current at low energies, therefore, cannot be used economically for high dose applications. Plasma immersion ion implantation (PIII) is emerging as a potential technique for such implantations. This method offers high dose rate irrespective of implantation energy. In the present study nitrogen ions were implanted using PIII in order to modify the properties of silicon and some refractory metal films. Oxidation behaviour of silicon was observed for different implantation doses. Diffusion barrier properties of refractory barrier metals were studied for copper metallization.

Lithographyless ion implantation technology for agile fab

A new type of ion implanter developed for an agile fab can eliminate the processes concerned. with photoresist lithography from the ion implantation process. This new ion implantation technology can reduce the raw process time, footprint, and the cost of ownership to less than one-half that of conventional ion implantation technology. The authors are making further developments on this ion implanter and evaluating technical issues related to ion implantation. This technique is suitable for manufacturing submicron node IC devices. Based on the results of evaluating the prototype machine, we will produce the next /spl beta/-machine.

Implementation of fully self-aligned bottom-gate MOS transistor

This letter reports the implementation of a bottom-gate MOSFET, which possesses the following fully self-aligned structural features: 1) self-aligned source-drain to bottom-gate; 2) self-aligned thick source-drain and thin channel; and 3) self-aligned and mask-free lightly doped drain (LDD). The complete self-alignment is realized by combining a conventional ion implantation and a subsequent chemical-mechanical polishing (CMP) step. The process is applied to poly-Si films crystallized from an a-Si film deposited by LPCVD using a metal-induced unilateral crystallization technique, and is grain-enhanced further in a high temperature annealing step. Deep submicron fully self-aligned bottom-gate pMOS transistors with channel length less than 0.5 /spl mu/m are fabricated. The measured performance parameters include threshold voltage of -0.43 V, subthreshold swing of 113 mV/dec, effective hole mobility of 147 cm/sup 2//V-s, off-current of 0.17 pA//spl mu/m, and on-off current ratio of 7.1/spl times/10/sup 8/.

Dependence of ion beam induced nitrogen diffusion in aluminum on oxygen impurities

The diffusion of nitrogen in aluminum is investigated for three different methods of nitrogen implantation. Low energy nitrogen implantation (LEI) at 1 keV and plasma immersion ion implantation (PIII) with −30 kV pulses were performed in the temperature range from 250 to 500 °C, together with conventional ion implantation at room temperature with 100 keV N+ ions and subsequent annealing in vacuum at 440 or 485 °C. For the LEI samples a rather high diffusion leading to AlN layers of a few microns in less than 1 h was found, whereas a low diffusion coefficient was obtained for the PIII samples, exhibiting a sharp step near 350 °C. In contrast no diffusion was measured in the implanted and annealed samples. Several different factors are proposed to influence the observed diffusion: A competing path between the formation of AlN by trapping of N and N diffusion is responsible for the dependence of the layer thickness on the supply of nitrogen. The oxygen contamination drastically reduces the diffusion constant by occupying the surface sites and blocking the diffusion path. Finally, the phase transformation from c-AlN to h-AlN may cause the sudden onset of diffusion around 350 °C.

Fabrication of Ge nanocrystals in SiO 2 films by ion implantation: control of size and position

We have fabricated Ge nanocrystals in SiO 2 films by ion implantation and thermal annealing. A uniform Ge depth-concentration profile in the SiO 2 layer is achieved by sequential Ge +-ion implantation at different kinetic energies (multi-energy ion implantation). After thermal annealing, the produced Ge nanocrystals have a narrow size distribution. In addition, low-energy ion implantation produced Ge nanocrystals in a very narrow region in the thin SiO 2 layer. The size fluctuation of nanocrystals produced by low-energy and multi-energy ion implantation is much smaller than that by conventional single-energy ion implantation and co-sputtering techniques. It is demonstrated that these improved ion implantation methods are useful for the control of the size and position of nanocrystals formed in dielectric materials.

Profile Changes and Self-sputtering during Low Energy Ion Implantation.

AbstractContinued device scaling requires the formation of ever-shallower junctions with low resistance. A desirable option to form these junctions is still the use of conventional ion implantation. However in order to meet the junction depth/sheet resistance goals, a strong reduction in implant energy and increase in implant dose is required. Earlier work for B and BF2-implants, has suggested that during low energy ion implantation self-sputtering may become an important factor influencing/limiting the retained dose. The basic mechanism for the selfsputtering with increasing dose is the increasing dopant concentration at the surface leading to an increased probability for re-emission by the sputtering process. Simple models describing ion retention in combination with sputtering are based on this concept and indeed predict a selfsputtering process limiting the final retained dose. Unfortunately the theoretical calculations only predict a significant sputtering at doses &gt;51016 at/cm2 whereas experimental results already show a limit in retained dose at 5 1015at/cm2.In order to confirm the experimental data, low energy B, BF2, As and Sb implants have been made. Dose retention was monitored using nuclear reaction analysis and RBS whereby details of the dopant profile (redistribution) were studied using high resolution SIMS. For As and Sb no self-sputtering up to a dose of 1 1016at/cm2 can be found. For B a small dose loss (&lt;10%) is seen significantly below the literature data. For BF2 a 20 % dose loss is observed. None of the SIMS profiles provide sufficient evidence for enhanced B-surface migration as required to explain the enhanced self-sputtering. On the other hand such a surface migration is reminiscent of the observations in SIMS whereby also an enhanced mobility of B during ion irradiation is required to explain the anomalous B-surface peak in many SIMS profiles. Based on the SIMS profiles a component sputter yield for B can be derived which is significantly higher than the matrix sputter yield suggesting a weak bonding of the segregated species leading to a reduced surface binding energy and thus enhanced sputtering yield.

PLASMA SOURCE ION IMPLANTATION INTO INSULATORS

Considerable development work has taken place in the novel technique of plasma source ion implantation (PSII) for the purpose improving the tribological properties of metal surfaces. Original studies involved using nitrogen plasmas to implant nitrogen ions into irregular shaped surfaces. More recently heavy ions have also been implanted. The advantages of the process over conventional ion implantation techniques are numerous, however one distinct disadvantage was the fact that the target had to be conductive, since it acted as the cathode of the system. We report here on a technique to overcome this problem, especially when implanting heavy ions into an insulator material of small dimensions (1-3 mm across) using the PSII system. Also reported are IBA techniques employed to characterize the implantation profile.

Calculation of demagnetization curves of nanocomposite Pr 2 Fe 14 B/α-Fe magnets using a one-dimensional model

The oxygen and silicon ions have been obtained respectively from pulsed energetic dense oxygen plasma and silane plasma generated by electrodeless discharge. The oxygen ions have been injected into superconducting Nb films, and the Si ions into superconducting YBCO films in order to investigate the variation of their superconductivity with the ions injected into them. Auger profile data show that the injection depths range from 20 to 40nm the films, depending on the injection condition and film material. The resistance-temperature relations (R-T curves) indicate that the superconductivity remains unchanged in the photoresist-masked part of the film, but is significantly changed in the exposed part. The evenness of the film surface remains unchanged after injection. This technique may serve as an alternative to the planar inhibiting fabrication technique in the fabrication of the multi-layer structure of superconducting films, and also possibly to the conventional plasma source ion implantation technique in material surface processing.

Superconducting film injected by ions from pulsed energetic dense plasma source

The oxygen and silicon ions have been obtained respectively from pulsed energetic dense oxygen plasma and silane plasma generated by electrodeless discharge. The oxygen ions have been injected into superconducting Nb films and the Si ions into superconducting YBCO films in order to investigate the variation of their superconductivity with the ions injected into them. Auger profile data show that the injection depths range from 20 to 40nm in the films, depending on the injection condition and film material. The resistance-temperature relations (R-T curves) indicate that the superconductivity remains unchanged in the photoresist-masked part of the film, but is significantly changed in the exposed part. The evenness of the film surface remains unchanged after injection. This technique may serve as an alternative to the planar inhibiting fabrication technique in the fabrication of the multi-layer structure of superconducting films and also possibly to the conventional plasma source ion implantation technique in material surface processing.

Damage in hydrogen plasma implanted silicon

The damage and defects created in silicon by hydrogen plasma immersion ion implantation (PIII) are not the same as those generated by conventional beamline ion implantation due to the difference in the ion energy distribution and lack of mass selection in PIII. Defect generation must be well controlled because damage in the implanted and surface zones can easily translate into defects in the silicon-on-insulator structures synthesized by the PIII/wafer bonding/ion-cut process. The defect formation and its change with annealing temperature were investigated experimentally employing channeling Rutherford backscattering spectrometry, secondary ion mass spectrometry, and atomic-force microscopy. We also calculated the damage energy density of the three dominant hydrogen species in the plasma (H+, H2+, and H3+) as well as displacement of silicon atoms in the silicon wafer. H2+ creates the most damage because its damage energy density is very close to the silicon threshold energy. The effects of atmospheric gaseous impurities unavoidably coimplanted from the overlying plasma are also modeled. Even though their concentration is usually small in the plasma, our results indicate that these gaseous impurities lead to significant silicon atom displacement and severe damage in the implanted materials.