Steven R. Walther

Plasma doping for the fabrication of ultra-shallow junctions

Pulsed plasma doping (P 2 LAD) is an alternate doping technique for the formation of ultra-shallow junctions in silicon wafers. In the P 2 LAD technique, a pulsed negative voltage applied to the silicon substrate creates a plasma containing the desired dopant species and also accelerates the positive dopant ions from the plasma toward the substrate, where they are implanted. BF 3 plasmas have been used to form p + -n junctions, while AsH 3 and PH 3 plasmas have been used for the formation of n + -p junctions. This paper will review the characteristics of ultra-shallow junctions formed by P 2 LAD. As-implanted and annealed profiles have been obtained by secondary ion mass spectrometry and compared with analogous profiles produced by B + , BF + 2 and As + ion implantation. Good sheet resistance uniformity, charging performance, structural quality, and photoresist integrity have been observed. In addition, junctions have been made which offer trade-offs between sheet resistance and junction depth that are better than those achieved with beamline implants. Finally, sub-0.2 μm pMOSFET devices have been fabricated with P 2 LAD and exhibit device characteristics that are similar to or better than beamline-implanted ones.

Using Multiple Implant Regions To Reduce Development Wafer Usage

The cost of new process development has risen significantly with larger wafer sizes and the increased number of fabrication steps needed to create advanced devices. The high value of each 300 mm development wafer has spurred efforts to find a way to explore more than a single process setting with each wafer. Traditional methods of defining multiple spatially distinct implant regions on a single wafer achieve poor utilization of device die. The need for efficient utilization of the die and wide process latitude for defining multiple implant regions per wafer has led to the development of an implant proximity mask (vMask™), which permits sharply defined borders between implant regions that may have different species, energy, angle, or dose. The capability of this system to achieve multiple spatially resolved implant conditions per wafer with high die utilization and using the same process parameters as production implants will be described. Specifically, results for measurement of the uniform process area, ...

Charge control in a ribbon beam high current ion implanter

Wafer charge control has evolved from systems that add gas to the beam or extract electrons from an external source to systems that respond directly to beam potential and current density via an externally coupled plasma. The capability of a plasma to add low energy electrons to an ion beam greatly exceeds the ability of any extracted electron system due to space charge effects. However, even plasma coupled charge neutralization systems still show that effective charge control is more difficult as the beam current density increases. Further improvements have often been obtained by controlling the beam current density by deliberately increasing beam size. This can result in a loss of throughput and can result in possible contamination problems. An alternative approach to further improve charge control is to use a large area ribbon beam, which offers a very low beam current density during high current implantation. This paper presents results for wafer charging on a ribbon beam implanter, the Varian VIISta 80, incorporating a Plasma Flood Gun for charge control. These results are based on sensitive antenna structures using thin oxides with antenna ratios up to 100,000:1 and EEPROM devices.

Electrostatic scanning of MeV ion beams

High energy implanters for 300 mm substrates are required to operate over a large range of energy and beam current. This must be accomplished without compromising throughput or the advantages of serial implant architecture, such as beam parallelism, high tilt angles, and low mechanical wafer stress. Modern ion implanters employing electrostatic scanning of the ion beam have typically limited the beam energies to the range of 250 keV. Applying this technology to scanning of 1.6 MeV beams for 300 mm applications requires significant adaptation in order to maintain high beam transmission for low energy beams as well. This is accomplished through the use of variable scan plate spacing and length. The details of scanner operation over a wide dynamic range of beam energy and space charge is presented.

Plasma doping as a tool for the fabrication of ultra-shallow junctions

In the plasma doping technique, a plasma is created near a substrate and a voltage applied to that substrate causes ions to be extracted across the plasma sheath and implanted. The method has been considered a potential alternative to conventional beamline ion implantation because of its high throughput and simpler, smaller architecture. Recent work has shown that the method can be applied to the production of ultra-shallow junctions. Junctions have been made which offer trade-offs between electrical activation and junction depth that are better than those achieved for beamline implants. Use of the technique in combination with SPE anneals offers the promise of further improvements.