Daniel R. Tieger

Low energy ion beam transport

The need for ultra-shallow junction formation in advanced devices makes the development of high throughput ion implantation solutions at very low (sub-keV) energies increasingly more important. The fundamental challenges confronting the implant tool designer tasked with delivering these high throughput solutions are examined in this paper. A discussion of space charge and its implications for low energy beam transport is presented. The origins behind the shape of the classic beam current versus energy curve are detailed and the historical evolution of this curve is shown. Demonstration of the effects of space charge is made via consideration of beam current density and beam potential profiles under a variety of space charge conditions and highlights the importance of efficient space charge neutralization in the generation and transport of low energy beams. Issues resulting from space charge effects and related to the control of beam size, shape, and stability are outlined in the context of their importance to high productivity high current tool design. Improvements to ion source and beam extraction efficiency, and to overall beamline acceptance, have been the dominant historical paths leading to incremental improvements in low energy beam current performance. The adoption into production-worthy tools of deceleration mode and, more recently, molecular implantation for n-type dopants has further expanded the usable energy range of these leading edge tools. Most recently, significant developments to actively neutralize space charge have enabled even more substantial low energy beam current improvements. Performance details underlying this newest technology are presented.

ClusterBoron™ Implants on a High Current Implanter

Advanced p‐junction process tool throughput continues to be one of the principal drivers of the industry. First results from an octadecaborane (B18H22) ClusterIon® source integrated on an existing high current implant tool are presented. Beam current, throughput and process results are reported. The dose multiplication effect of the use of B18H22 means that an electrical current of 1mA produces a dopant flux equivalent to 18mA, while the energy equipartition means that a 20keV octadecaborane ion is process equivalent to a 1keV boron beam. Some modifications to a traditional high current beamline design were made in order to take advantage of the opportunities presented by this new ion source. A somewhat larger extraction slot was used and this, coupled with the fact that the ions have a large mass (210 amu) and therefore have high magnetic rigidity even at modest energies, drove the optics design toward a parallel‐to‐point configuration. Good mass resolution and control of beam size were demonstrated. Beam currents and throughput that are significantly higher than those available from traditional high current implanters were achieved, along with good process results.Advanced p‐junction process tool throughput continues to be one of the principal drivers of the industry. First results from an octadecaborane (B18H22) ClusterIon® source integrated on an existing high current implant tool are presented. Beam current, throughput and process results are reported. The dose multiplication effect of the use of B18H22 means that an electrical current of 1mA produces a dopant flux equivalent to 18mA, while the energy equipartition means that a 20keV octadecaborane ion is process equivalent to a 1keV boron beam. Some modifications to a traditional high current beamline design were made in order to take advantage of the opportunities presented by this new ion source. A somewhat larger extraction slot was used and this, coupled with the fact that the ions have a large mass (210 amu) and therefore have high magnetic rigidity even at modest energies, drove the optics design toward a parallel‐to‐point configuration. Good mass resolution and control of beam size were demonstrated. Bea...

Germanium operation on the GSDIII/LED and ultra high current ion implanters

Germanium is typically used in ultra-shallow junction formation as an amorphization implant to reduce channeling in subsequent low energy boron dopant implants. Several equipment and process considerations can be associated with germanium operation. For example, source life may be adversely affected due to the cycling of refractory metal fluorides from materials used in the arc chamber, and cross-contamination, especially implanted As, may occur on machines that run multiple species. Tool productivity also depends on beam current and beam setup time due to the relatively high doses and low energies required. A number of design and operational improvements have been implemented on the GSDIII/LED and Ultra to address these concerns. Hardware and tuning algorithms for germanium operation are described. Data showing improved source lifetime and low species cross-contamination are presented Strategies for achieving productivity, flexibility, and cycle time improvements, including mixed species operation and germanium-boron chaining, are discussed.

Dose Retention Effects in Atomic Boron and ClusterBoron™ (B18H22) Implant Processes

Dose control is often assumed to be a function of tool design and calibration. Fundamental interactions, including sputtering and backscattering of ions from the surface of the wafer, modulate the equipment effects. For high dose and low energy processes, such as those necessary for poly‐gate doping, these effects can be significant. The use of octadecaborane (B18H22) implantation enables production‐worthy throughput but can impact these surface interactions. In this work, we have investigated the dose retention in silicon after high dose, low energy B18H22 and B implants. A wide range of effective energies and doses was studied. This analysis provides insight into the physical mechanisms and can be used to guide process control development.

Beam Current Improvements on the Axcelis Optima HD Imax Implanter

The ability to use large molecular species such as octadecaborane (B18H22) has been investigated at semiconductor device manufacturers as a way to significantly increase wafer throughput relative to standard high current ion implanters. Over the past two years, improvements in the machine design to support the use of B18H22 have led to beam current increases of 50% from 30 pmA to 45 pmA of boron at an equivalent boron energy of 4 keV. This boron energy is required by p+ doping of dual poly gate (DPG) structures in DRAM. Beam current has also been significantly improved at the low equivalent boron energies anticipated to be required by 32 nm processes for PMOS source/drain extensions (SDE). For example, at 250 eV equivalent beam energy, a 100% increase in cluster boron beam current has been attained.This paper describes the techniques by which these beam current improvements were accomplished, primarily through the refinement of ion beam optics. Other techniques for increasing overall tool productivity are...

Optima HD Imax: Molecular Implant

Molecular implantation offers semiconductor device manufacturers multiple advantages over traditional high current ion implanters. The dose multiplication due to implanting more than one atom per molecule and the transport of beams at higher energies relative to the effective particle energies result in significant throughput enhancements without risk of energy contamination. The Optima HD Imax is introduced with molecular implant capability and the ability to reach up to 4.2 keV effective 11B from octadecaborane (B18H22). The ion source and beamline are optimized for molecular species ionization and transport. The beamline is coupled to the Optima HD mechanically scanned endstation. The use of spot beam technology with ionized molecules maximizes the throughput potential and produces uniform implants with fast setup time and with superior angle control. The implanter architecture is designed to run multiple molecular species; for example, in addition to B18H22 the system is capable of implanting carbon m...

Demonstration Of Cost‐Effective, Highly Productive Ultra‐Shallow Junctions Using Molecular Carbon And Boron As An Alternative To Ge/C/B Implantation

In this study we demonstrate a highly productive, cost‐effective route to formation of ultra‐shallow junctions (USJ) for p‐MOS extension implants. Using a modest dose of molecular carbon (C16H10) as a pre‐amorphizing implant, as well as a diffusion‐control “co‐implant”, we show that the requirement for Ge PAI can be eliminated. This allows a traditional three step process sequence Ge/C/ (B or BF2) to be replaced with a C16H10/B18H22 process, as indicated in Fig. 1, a) and b). The combination of eliminating the Ge implant (and associated source life degradation well known in Ge implantation), with effective beam current increases for the molecular carbon (30 mA @ 6 keV) and boron (6 mA @ 300 eV), provides a highly productive process alternative. The difference in materials cost is more than offset by the enhanced productivity and reduction of implant steps.

Model-based predictors for improved automated beam generation and tuning of high current ion implanters

Reliable and efficient beam generation and setup can provide significant cost-of-ownership advantages for modern high current ion implantation in the semiconductor industry. Automated tuning algorithms which make use of fundamental models to aid the decision-making process can be more effective at producing robust tuning solutions over the wide range of operating parameters typically called for in this industry. The ability to predict ion source, extraction, and beamline behavior over a range of energies from 0.2 to 160 keV, beam currents from 0.01 to 25 mA, using six or more ion species, over the full lifetime of the ion source, allows the full flexibility of the implant tool to be realized. Empirical and fundamental models which describe this behavior on a variety of Axcelis high current ion implant platforms are presented, and the ways in which these models may be used to improve overall implanter performance are demonstrated.