Publisher Summary This chapter provides an overview of the new techniques for fabrication at a size scale below 100 nm. A number of nanometer-scale devices and scientific studies have become possible with these techniques, and research in this field has seen a number of recent successes. The chapter focuses on the limits and applications of the nanometer-scale fabrication techniques, not their practicality for current device production. The chapter presents the three-dimensional techniques that seem to permit fabrication of structures smaller than 10 nm. However, there are a variety of effects that limit their resolution. The most obvious is penumbra because of limited collimation of the ion beam or evaporant flux. This effect can be eliminated at the cost of reduced flux by simply using apertures or moving the source further from the sample. The chapter also describes the utilization of the third dimension and new three-dimensional lithographic approaches. Such approaches are of clear advantage for achieving high-aspect-ratio patterns, high resolution, and good line width control over a large field of view. When three-dimensional approaches are combined with other self-aligning or self-limiting processes, very powerful device micro-fabrication approaches can be developed.

Chapter 4 - Nanometer-Scale Fabrication Techniques

Summary

The helium ion microscope has recently emerged as a commercially available instrument. However, its roots go back more than 60 years to the development of the field ion microscope in Berlin, first reported in 1951. Over the intervening years, numerous researchers have pursued the development of a gas field ionization source with the goal of producing a suitable source for an ion microscope. This proved to be an elusive goal until early in this century when a number of discoveries led to a successful source, and shortly thereafter, an instrument fully able to exploit its advantages. Many individuals and many technical advances have come together to make this new class of microscope. The long history of this quest is reviewed along with the recent advances that led to the achievement of this milestone. A brief summary of the current status of the technology and its applications are given. SCANNING 33: 83–89, 2012. © 2011 Wiley Periodicals, Inc.

The history and development of the helium ion microscope.

Ion beam lithography

The ability to fabricate structures with lateral dimensions in the sub-100-nm range has opened a new field of research. This paper first reviews recent advances in nanolithography techniques, with a brief discussion of their relative merits and fundamental limits. Special emphasis is given to the scanning electron-beam method, which is the most widely used nanolithography method at the present time. The two main areas of nanostructure research are device technology and basic science. Highlights of a number of exploratory programs in these two areas are presented.

Nanostructure technology

High resolution masked ion beam lithography (MIBL) is demonstrated at large mask‐to‐sample gaps using two new types of membrane stencil masks. Single layer Si‐rich silicon nitride (SiN) membranes and Si3N4‐SiO2‐Si3N4 (N‐O‐N) sandwich structure membranes are deposited by processes which allow the stress in the films to be adjusted. Transmission holes are reactive‐ion etched entirely through the membranes. This type of stencil mask virtually eliminates mask‐induced scattering. Lines and spaces of 160 nm have been exposed in 0.5‐μm polymethylmethacrylate (PMMA) at gaps as large as 275 μm, using 100‐keV protons. Some of the stencil mask limitations are overcome by multiple exposures. The results suggest that MIBL can be an extremely high resolution proximity printing technique.

High resolution ion beam lithography at large gaps using stencil masks

We report an entirely new pattern‐replication technique for IC fabrication. It has demonstrated submicrometer (<0.5 μm) resolution and it has the capability of large throughput (wafer‐levels/h). It utilizes high‐energy protons as the exposing radiation through a mask placed in proximity to a wafer covered with resist. We call this new technique ’’ion‐beam lithography’’ (IBL). System parameters and measurements relevant to the use of IBL as a production technology are discussed and SEM micrographs of submicrometer patterns in PMMA are presented. The technique is similar to x‐ray lithography, in that a pattern is produced in a thin resist film after exposing it to radiation through a mask. High‐energy protons have the same advantage as x rays in eliminating wavelength diffraction problems which limit the resolution of photolithography. Also, a gap (∠15–25 μm) is permitted between the mask and wafer. Ions have an advantage over x rays in that penumbral distortion is avoided by using highly collimated ion beams which are available with present state of the art; ions are collimated using conventional ion‐optical techniques, whereas use of a distant ’’point’’ source is the only feasible scheme for collimation of x rays.

H. L. Stover

Papers

Ion-beam lithography for IC fabrication with submicrometer features