Adrian Murrell

Elemental B distributions and clustering in low-energy B+ ion-implanted Si

A detailed study is presented of characteristic elemental B distributions in Si produced by low-energy B+ ion implantation and annealing. Implant concentration profiles have been determined with approximately nanometer spatial resolution using energy-filtered imaging in the transmission electron microscope, for a B+ ion dose close to those relevant to electronic device processing. It is demonstrated that, for as-implanted Si, the near-surface B distribution shows a smooth concentration peak which correlates well with theoretical simulation and shows no anomalous surface buildup of the type generally indicated by secondary ion mass spectrometry measurements. After annealing of the layers, the present direct observations reveal that the final B distribution is characterized by residual nanometer-scale elemental clusters which comprise disordered zones within the restructured Si lattice.

TCAD modeling and experimental investigation of indium for advanced CMOS technology

Indium is a key element in the formation of well, channel, and HALO profiles, especially for very deep sub-μm technologies with gate length below 150nm. Indium (115In+) has the advantage of being a large atom and having a small projected range. Hence ion implanted indium produces steeper profiles than boron, providing that the retrograde doping is maintained after the subsequent annealing steps. Therefore, knowledge of the diffusion behavior of indium is extremely important. In this work, Indium diffusion and dose loss are studied both experimentally and by TCAD simulation. N-type silicon wafers were capped with a 50Å thick SiO2 layer, followed by In+ implantation on an Applied Materials Quantum LEAP™ ion implanter at a range of energies from 50keV to 150keV, and at different doses from 1E13 ions/cm2 to 1E14 ions/cm2. The wafers were then annealed under different annealing conditions reflecting typical well and HALO anneal steps, and for calibration purposes. Calibration of the process simulation was done for indium implantation and diffusion, allowing us to describe Indium implantation and diffusion in general, and quantitatively for special effects such as double peak formation and dose loss. It is shown that the double peak, which appears for an Indium dose higher than 4E13/cm2 and energies higher than 50keV for selected anneal conditions, is strongly related to amorphization and defect distribution after implantation. The dose loss is diffusion limited and therefore controlled by the diffusion coefficients in the region close to the silicon surface.

Optimised Charging Performance On Quantum X Ion Implanters

A key parameter in the optimisation of CMOS device yield is the minimisation of charging‐induced damage and/or breakdown of the gate dielectric material during ion implantation. In typical ion beams used for transistor doping applications, beam potentials can charge up the wafer surface if not controlled, and hence this potential must be neutralised to avoid damage to devices. MOS capacitor TEG (Test Element Group) wafers are an industry standard metric for determining the charging performance of ion implanters. By optimising the performance of the High Density Plasma Flood System (HDPFS) of the Applied Materials Quantum X ion implanter, TEG device yields of >90% at antenna ratios of 1E5:1 for a gate dielectric thickness of 3.5 nm on 300 mm wafers have been demonstrated.

Effect of surface treatment during Ge/sup +//B/sup +/ two step ion implantation

For ultra-low energy implantation it is known that the wafer surface condition is very important. Thin oxide formation, for example, significantly affects the dose retention and activation of ultra-low energy processes, as the projected range is comparable to the thickness of the oxide film. In the case of 200 eV implants, Rp is less than 2 nm and typically the native oxide thickness is around 1 nm. This means that a large percentage of implanted boron cannot penetrate the native oxide and these boron atoms may become trapped and not activate. Thus the thickness of the surface film does have a significant affect on the effective dose. B/sup +//0.2 and 1 keV implants have been studied before and after rapid thermal annealing, and the effect of pre-amorphisation using Ge/sup +/ investigated. It is found that pre-amorphised wafers have lower activation (higher sheet resistance), especially for very low B/sup +/ implant energies. Analysis has correlated this shift with an increase in surface oxide thickness, as well as an increase in surface B concentration. Total B dose, measured by SIMS after annealing also decreases. It is therefore concluded that the increased resistance may be attributed to trapping and segregation of dopant into the surface oxide, associated with the increased oxide thickness, and evaporation from the surface. Use of a wet chemical treatment between Ge/sup +/ and B/sup +/ implants prevents the activation change, confirming the above mechanism and offering one processing strategy to achieve higher activation efficiency when using pre-amorphisation.

Applied Quantum X Implant System: Technology Enhancements to Enable Production‐Worthy Performance at the 45 nm Node

Mechanical scanning of the wafer in 2 dimensions is one approach that has been used to achieve single wafer processing for high current ion implantation. This approach simplifies the beamline design, compared to scanned beam or ribbon beam architectures, but has required a number of new technologies and methods in the scanner hardware and in dosimetry control. The Applied® Quantum X Implant system was designed to incorporate these new technologies, and has achieved the process performance and low energy productivity required for advanced junction formation at the 65 nm technology node. Since its introduction, extensive qualification and development work has been carried out, to extend its capability to the next technology generation. A number of further innovations and improvements to the beamline and platform have been developed, extending its throughput and process control capability to be production‐worthy at 45 nm.This paper will review the process control challenges associated with the 2d mechanical ...

Low energy ion implantation into SOI substrates

Low energy ion implantation into silicon-on-insulator substrates will play a crucial role in the drive towards manufacturing ultra-shallow junctions. There is however a relative paucity of published material in this key area. In this work, the implantation and diffusion characteristics of boron and arsenic into thin UNIBOND® SOI wafers have been investigated, as a function of energy, dose and thermal budget. Implants were carried out on an Applied Materials Quantum LEAP ion implanter, and subsequent RTP was undertaken on the Centura annealer. Implant energies were in the range 200eV-5keV for 11B+, and 1keV-10keV for 75As+. Electrical measurements were used to quantify the degree of dopant activation in implanted SOI wafers and these results were then compared to the values generated by identical low energy implants into bulk silicon. Dopant depth profiles were obtained using dynamic SIMS analysis of both as-implanted and annealed samples, with particular attention paid to identifying segregation of dopants at the buried interfaces.

Quantum IIatrade; : low energy beamline innovations for increased manufacturing productivity

An investigation into the processes that limit the performance of ion implanters at low energies (≤10keV) is described. Experimental results, obtained using an indirectly-heated cathode (IHC) ion source and tetrode extraction system are used to illustrate how the transmission of low energy ions can be optimised by matching the beam emittance produced by a specific beamline element to the acceptance of the subsequent beamline component. Emittance measurements on a 5keV BxFy (i.e. B, F, BF, BF2) beam immediately downstream of the extraction electrodes demonstrated that, for a standard source, the beam quality deteriorates dramatically when the it is tuned to maximise the cracking of molecular feed gases. Incorporation of a slotted cathode was shown to overcome this problem and resulted in enhanced beam transmission through the extraction lens. Quality measurements on a set of 1keV BxFy beams were also undertaken to investigate the effects of extraction lens voltages and electrode position on their current density profiles. A 100μm slit was used to section the beams and the transmitted beamlets were profiled to identify aberrations introduced by the extraction lens. By distorting the emittance diagram these aberrations lead to the requirement of a larger acceptance in the subsequent beamline and resulted in increased beam loss. Based on these finding a series of design modifications were made to Applied Materials QuantumLEAP™ implant system. Performance statistics from the resulting Quantum II™ ion implanter show a 30-50% improvement over its predecessor in beam transmission efficiency and, as a result, low energy ion currents.