Development of a Focused Ion Beam System for High-throughput Maskless, Direct Lithography

Qing Ji
(Professor Tsu-Jae King)
(DARPA) DE-AC03-76SF00098

As the dimensions of semiconductor devices are scaled down in order to achieve higher levels of integration, optical lithography will no longer be sufficient for the needs of the semiconductor industry. There are some challenging issues with complicated mask technology and low throughput for some alternative lithography technologies such as X-ray, EUV, electron-beam lithography, etc. Focused ion beam (FIB) patterning of films is a well-established technique (e.g., for mask repair), but throughput has historically been a prohibitive issue in its application to lithographic processes in semiconductor manufacturing. The goal of this project is to develop a focused ion beam system for high-throughput resistless, direct patterning, and doping of films that can be made practical for high-volume production.

The compact FIB system being developed uses a multicusp plasma ion source and a novel electrostatic accelerator column. The multicusp plasma source can generate ion beams of various elements, such as O2+, BF2+, P+ etc., for surface modification and doping applications.

The beam brightness of a multicusp-plasma ion source has been substantially improved by optimizing the source configuration and extractor geometry. Measured beam brightness can be as high as 440 A/cm2Sr, which represents a 30 times improvement over previous work.

A multiple-beam system will be built by stacking multi-aperture electrode-insulator structure so that each beam is accelerated with the same electrode potentials. Parallel processing with multiple beams can greatly enhance the throughput of a FIB system.

We have investigated the process for direct patterning using focused O2+ ion beam. A thin surface oxide film on an Si wafer can be selectively formed using low energy focused O2+ ion beam. It can then serve as a hard mask for patterning of the Si film. We also investigated the formation of doped regions in bulk silicon wafers by scanning focused P+ beam implantation. To demonstrate the suitability of scanning FIB lithography for the manufacture of integrated circuits, the SOI MOSFET device fabrication using the process developed to pattern gate electrode and form source/drain region is in progress.

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