Effects of nitrogen incorporation by plasma immersion ion implantation on electrical characteristics of high-k gated MOS devices

Nitridation treatments are generally used to enhance the thermal stability and reliability of high-k dielectric. It is observed in this work that, the electrical characteristics of high-k gated MOS devices can be significantly improved by a nitridation treatment using plasma immersion ion implantation (PIII). Equivalent oxide thickness, (EOT) and interface trap density of MOS devices are reduced by a proper PIII treatment. At an identical EOT, the leakage current of devices with PIII nitridation can be reduced by about three orders of magnitude. The optimal process conditions for PIII treatment include nitrogen incorporation through metal gate, ion energy of 2.5 keV, and implantation time of 15 min.     

Thermal stability of tantalum nitride diffusion barriers for Cu metallization formed using plasma immersion ion implantation

Plasma immersion ion implantation (PIII) technique was employed to form Tantalum nitride diffusion barrier films for copper metallization on silicon. Tantalum coated silicon wafers were implanted with nitrogen at two different doses. A copper layer was deposited on the samples to produce Cu/Ta(N)/Si structure. Samples were heated at various temperatures in nitrogen ambient. Effect of nitrogen dose on the properties of the barrier metal was investigated by sheet resistance, X-ray diffraction and scanning electron microscopy measurements. High dose nitrogen implanted tantalum layer was found to inhibit the diffusion of copper up to 700 °C.     

Plasma immersion ion implantation for SOI synthesis: SIMOX and ion-cut

We have demonstrated feasibility to form silicon-on-insulator (SOI) substrates using plasma immersion ion implantation (PIII) for both separation by implantation of oxygen and ion-cut. This high throughput technique can substantially lower the high cost of SOI substrates due to the simpler implanter design as well as ease of maintenance. For separation by plasma implantation of oxygen wafers, secondary ion mass spectrometry analysis and cross-sectional transmission electron micrographs show continuous buried oxide formation under a single-crystal silicon overlayer with sharp Si/SiO₂ interfaces after oxygen plasma implantation and high-temperature (1300°C) annealing. Ion-cut SOI wafer fabrication technique is implemented for the first time using PIII. The hydrogen plasma can be optimized so that only one ion species is dominant in concentration and there are minimal effects by other residual ions on the ion-cut process. The physical mechanism of hydrogen induced silicon surface layer cleavage has been investigated. An ideal gas law model of the microcavity internal pressure combined with a two-dimensional finite element fracture mechanics model is used to approximate the fracture driving force which is sufficient to overcome the silicon fracture resistance.     

The influence of dose and protecting mask on electrically active defects induced by ion implantation in silicon

We present a study of electrically active defects induced by ion implantation, for two dopants: arsenic and phosphorous. Our analysis technique is Deep Level Transient Spectroscopy (D.L.T.S.). We have studied the generation of defects by direct implantation, and indirect implantation, that is through an SiO₂ layer. We follow the defect spectrum evolution for different doses (10⁸ to 10¹⁴ atoms/cm²) and for different annealing temperatures (from room temperature up to 800° C). The comparison of our results with other published ones allows us to improve the knowledge about the role of a protecting oxide layer, the influence of moderate thermal annealing, and the effect of oxygen on deep centers produced by ion bombardment.     

PMOS integrated circuit fabrication using BF3 plasma immersion ion implantation

The feasibility of plasma immersion ion implantation (PHI) for multi-implant integrated circuit fabrication is demonstrated. Patterned Si wafers were immersed in a BF₃ plasma forp-type doping steps. Boron implants of up to 3 × 10¹⁵ atoms/cm² were achieved by applying microsecond negative voltage (-2 to -30 kV) pulses to the wafers at a frequency of 100 Hz to 1 kHz. After implantation the wafers were annealed using rapid thermal annealing (RTA) at 1060° C for 20 sec to activate the dopants and to recrystallize the implant damaged Si. For the PMOS process sequence both the Si source-drain and polycrystalline Si (poly-Si) gate doping steps were performed using PIII. The functionality of several types of devices, including diodes, capacitors, and transistors, were electrically measured to evaluate the compatibility of PIII with MOS process integration.     

Deterioration of insulating films on silicon wafer due to surface charging during ion implantation

Charge-up phenomena during ion implantation were studied using the wafers (1) covered with the 1 μm thick photoresist and (2) fabricated with the MOS capacitor devices. The wafers were implanted with 35 keV As⁺ at the beam currents of 1 mA to 10 mA. The surface potential was measured by a capacitive probe set in the chamber. The ion distribution was also measured by a beam profile monitor placed behind the rotating disc. Surface charging on the photoresist wafers in some cases led to the puncture of the resist layer. Probe measurement showed that the charge-up phenomena were to a large extent governed by the behavior of the secondary electrons generated at ion implantation. The wafers with the MOS devices hardly failed by the charge build-up because of the bulk conduction through the thin oxide. However, the C-V measurement indicated that the deterioration of the oxide were influenced by the beam distribution.     

Charge retention improvement of charge-trapping type flash device by plasma immersion ion implantation

Electrical characteristics of charge trapping-type flash devices with HfAlO charge trapping layer nitrided by plasma immersion ion implantation (PIII) technique with different implantation energies and time are studied. Utilizing Fowler–Nordheim (FN) operation, the programming speed of flash memory with charge trapping layer nitrided at low implantation energy is faster than that of control sample. The erasing speed of PIII-treated sample is slightly slower than that of control one, which might be due to the formation of silicon nitride in the tunneling oxide. The retention characteristics of all PIII-treated samples are significantly improved. Different peak locations of implanted nitrogen concentrations are formed by different implantation energies, which cause various electrical characteristics of flash devices.     

An EPR study of defects induced in 6H-SiC by ion implantation

Crystalline (0001) plane wafers of n-type 6H-SiC have been implanted at room temperature with 200 keV Ge⁺ ions in the dose range 10¹² to 10¹⁵ cm⁻². Electron paramagnetic resonance (EPR) measurements have been made on these samples both before and after annealing them at temperatures in the range room temperature to 1500°C. The as-implanted samples have a single isotropic and asymmetric line EPR spectrum whose width, ΔB_pp, increases with ion dose before falling when a buried continuous amorphous layer is produced. This increase is interpreted in terms of the change in the relative intensity of a line with g = 2.0028 ± 0.0002, ΔB_pp = 0.4 mT associated primarily with carbon dangling bonds in a-SiC and a line with g in the range 2.0033 to 2.0039 of uncertain origin. The variation with anneal temperature of the populations of these defects is reported.     

Photovoltaic effect in a structure based on amorphous and nanoporous silicon formed by plasma immersion ion implantation

A p-i-n structure with photovoltaic properties was proposed and fabricated by plasma immersion ion implantation. Implantation of helium ions with an energy of 1 to 5 keV with subsequent annealing creates a region of nanoporous silicon at a depth of ～20 to 80 nm from the silicon substrate surface. A nanocrystalline structure of this layer results in high light absorption and a change in the band-gap energy, which leads to the formation of a heterojunction. The upper layer of the modified region was additionally doped with boron to create a p region. The resulting structure showed a photovoltaic effect (0.15 V, 6.4 mA/cm²) under illumination with light equivalent to sunlight in terms of the spectral range and intensity.     

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     

Effects of aluminum incorporation on hafnium oxide film using plasma immersion ion implantation

The effects of aluminum implantation on HfO₂ thin films using plasma immersion ion implantation (Al–PIII samples) are investigated. X-ray photoelectron spectroscopy measurements reveal that most of the implanted aluminum atoms accumulated near the surface region of the oxide film. The greatly reduced leakage current, smaller flatband shift and steep transition from the accumulation to the depletion region in the capacitance–voltage characteristics for Al–PIII samples indicate that both bulk oxide and interface traps are significantly reduced by aluminum incorporation. Even though the aluminum concentration at the Si/HfO₂ interface is very low the results indicate that trace amount of aluminum at the interface leads to significant improvements in both material and electrical characteristics of the thin HfO₂ films.     

Compensation phenomena by ion implantation doping of an electroactive polymer,poly(para-phenylene)

We have shown that poly(para-phenylene) (PPP) can be obtained either n-type or p-type by ion implantation at low energy (E ≦ 50 keV); PPP is primarily an insulator pellet obtained from compacted powder synthetised by the Kovacic method. To compare with the chemical doping effect, we have studied the conductivity and thermopower of PPP samples after two successive ion implantations with Cs⁺ and I⁺. The experimental results show that we clearly obtain reversible doping only in the case of an initially I⁺-doped sample: the thermopower sign is changed after a Cs⁺ implantation with a fluence equal to 3 × 10¹⁴ ions cm^?2. In the other case (Cs⁺ initial implantation) we observe the change in thermopower sign at higher fluence (2 × 10¹⁶ I⁺ ions cm^?2). This last effect can be attributed to a metal transition induced by the accumulation of defects in the material because of too high implantation parameters (graphitisation).     

Optical properties of multicomponent nanometer dimension metal colloids formed in silica by sequential ion implantation of in and Ag and In and Cu

A series of nanometer dimension colloids in silica have been fabricated by sequential implantation of Ag and In, and a series by sequential implantation of In and Cu. Energies of implantation were chosen using TRIM 89 to overlay the depth distributions of the sequentially implanted ions. The implanted layers were characterized using Rutherford backscattering spectroscopy, transmission electron microscopy, and optical spectroscopy. Nanometer dimension metal multicomponent colloids were formed. The depth distribution, particle size, and optical response of the composites were found to depend strongly on the ion species implanted and the relative ratio of the ion species. The optical responses are correlated with composition of the multicomponent nanoclusters.     

Improved electrical characteristics of high-k gated MOS devices by nitrogen incorporation with plasma immersion ion implantation (PIII)

High-k gate dielectric process is the key technology for nano-scale MOS device. A nitridation treatment on silicon surface is promising for characteristic improvement on high-k dielectric. It is found in this work that the electrical characteristics of high-k gated MOS devices can be improved by a nitridation treatment at silicon surface using plasma immersion ion implantation (PIII) at low ion energy and with a short implantation time. A shallow nitrogen profile at Si surface is known to be favorable for further enhancement of device properties.     

Growth and visible photoluminescence of highly oriented (1 0 0) zinc oxide film synthesized on silicon by plasma immersion ion implantation

High-quality (1 0 0) ZnO films with smooth surface topography have been synthesized on Si substrate by plasma immersion ion implantation. The materials exhibit compressive stress because of room temperature growth. After annealing at different temperatures, various visible photoluminescence bands are observed. The optical phenomenon as well as the transition mechanism which may involve defects such as [Zn_I], [V_Zn], and [O_i⁻] induced by the high substrate bias are discussed in this paper.     

Formation of Ge nanocrystals in a silicon dioxide layer using pulsed plasma-immersion ion implantation

Pulsed plasma-immersion ion implantation (PIII) or Pulsed PLAsma Doping (P²LAD) is known as a cost effective solution for ultra shallow junction formation due to its capability to implant doping species at ultra-low energies (0.05–5 keV), the advantages of P²LAD, high concentration and sharp distribution of the implanted species, also make this technique a good candidate to fabricate nanocrystals (NCs) within silicon dioxide (SiO₂) layer. In this work, we report Ge NC fabrication within a SiO₂ layer by using the pulsed PIII technique for the first time. GeH₄ (4 sccm) and He (100 sccm) gases were flown to the plasma chamber, and a voltage of 4.5 kV was applied. After pulsed PIII process, furnace annealing was performed at 900 °C in nitrogen atmosphere for Ge agglomeration. By using such a process, we fabricated non-volatile memory devices and obtained relevant program/erase, retention, and cycling characteristics.     

Effect of ion beam irradiation on metal silicon junctions

The effect of MeV and low energy nitrogen implantation on the electrical properties of metal semiconductor junctions is studied. It is found that MeV implantation has better contact performance is comparison to keV nitrogen implantation. The defects introduced due to MeV implantation have very little effect on contact formation.     

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.     

Raman investigation of lattice defects in the CoSi2 synthesis using focused ion beam implantation

CoSi₂ layers were produced by 70 keV Co focused ion implantation into Si(111). Within a comparative study the CoSi₂ layer quality and implantation damage were investigated as a function of pixel dwell-time and substrate temperature. Irradiation damage measurements were done by micro-Raman analysis. The results suggest that the dwell-time dependence of the CoSi₂ layer formation — continuous layers for short and disrupted ones for long dwell-times — is caused by an accordant transition from crystalline to amorphous silicon.     

Properties of buried SiC layers produced by carbon ion implantation in (100) bulk silicon and silicon-on-sapphire

Buried layers of SiC were formed in (100) single-crystal bulk silicon and silicon-on-sapphire by ion implantation of 125–180 keV, (0.56-1.00) × 10¹⁸ C/cm² at 30–40 μA/ cm² into samples held at 450-650° C. The as-implanted and 950° C annealed samples were characterized by differential infra-red absorbance and reflectance, Rutherford backscattering and channeling spectrometry, x-ray diffraction, four-point probe measurements, Dektak profilometry, I-V measurements, spreading resistance measurements and secondary ion mass spectrometry. Work done while affiliated with Rockwell International Corporation, Microelectronics Research & Development Center, 3370 Miraloma Avenue, Anaheim, CA 92803 and a Visiting Associate at the California Institute of Technology, Department of Applied Physics, Mail Code 116-81, Pasadena, CA 91125.