Michael A. Graf

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.

Optima HD: Single Wafer Mechanical Scan Ion Implanter

The trend toward single wafer high current ion implanters to support high tilt angles and to avoid damage during the implant process has led to the novel design of the Optima HD architecture. A high frequency (> 3 Hz) reciprocating pendulum coupled with a fixed spot beam has effectively extended the dose operating range without sacrificing wafer throughput. A high scan frequency enables more reliable dose uniformity by allowing a greater number of wafer passes through the ion beam in a given time period. A fixed spot beam preserves the important performance characteristics of rapid beam setup and precise angle control typical of conventional high current implanters. This paper will examine the design approach used to deliver high scan rates with a reciprocating pendulum mechanism. The challenges overcome include the minimization of vibration coupling, angle control, wafer handling and the preservation of the ion beam focal length to the wafer plane. Together with the novel wafer scan approach, the beamlin...

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.

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.