chapter  4
112 Pages

Chapter 4

Abstract ............................................................................... 118 4.1 Introduction ................................................................ 120 4.2 Ion Implantation ........................................................ 122

4.2.1 Fundamentals of Ion Implantation ................ 123 4.2.2 Tribological and Mechanical Property

Changes ............................................................ 131 4.2.3 Chemical Property Modification ..................... 136 4.2.4. Thermal Oxidation .......................................... 137 4.2.5 Implantation into Polymers and Ceramics ... 141 4.2.6 Ion Implantation as a Materials Science Tool143 4.2.7 Emerging Research Areas: MEMS and Nano-

Composite Structures ...................................... 144 4.2.8 Commercial Usage and Applications ............. 147

4.2.8.1 Precision Tooling ................................ 147 4.2.8.2 Medical Materials and Applications.. 147 4.2.8.3 Sensors ............................................... 151

4.2.9 Ion Implantation Equipment ......................... 153 4.3 Ion Beam-Assisted Deposition (IBAD) ..................... 154

4.3.1 Film Growth Without Ion Beams .................. 155 4.3.2 Ion Beam Effects on Film Growth ................. 157 4.3.3 Fundamentals of the IBAD Process .............. 158

4.3.3.1 Nucleation .......................................... 163 4.3.3.2 Adhesion ............................................. 164 4.3.3.3 Density ............................................... 165 4.3.3.4 Stress .................................................. 166 4.3.3.5 Grain Size .......................................... 167 4.3.3.6 Texture and Surface Roughness ....... 169

4.3.4 Application Areas of IBAD Coatings ............. 172 4.3.4.1 Optical Coatings by IBAD ................ 172 4.3.4.2 Wear Control Surfaces ...................... 178

4.4 Gas-Cluster Ion Beams ............................................ 192 4.4.1. Gas-Cluster Ion Beam (GCIB) Techniques ... 192 4.4.2 GCIB Smoothing, Etching, and Cleaning

Applications ..................................................... 201 4.4.3 Commercial Status of GCIB and Manufacturing

Use .................................................................... 213 4.4.4 Emerging Techniques and Applications ........ 217

4.4.4.1 Reactive-Gas GCIB Surface Treatment ........................................... 217

4.4.4.2 GCIB-Assisted Thin-Film Deposition............................................ 219

4.4.4.3 SIMS and High-Resolution Depth Profiling with GCIB .......................... 223

ABSTRACT

This chapter covers three distinct areas of ion beam research and their application to the study or modification of surfacemediated properties. These vacuum-based techniques include directed-beam ion implantation, ion beam-assisted deposition, and gas-cluster ion beams. Discussion of the general capabilities of these techniques and their application to surfaces are described at a non-specialist level to allow the assessment of their applicability for the study or modification of other surface properties. The ion implantation of directed beams of energetic

ions beneath the surface of materials is discussed first from the context of non-semiconductor substrates, i.e., metals, ceramics, and polymers. The extreme versatility of surface alloying virtually any substrate with any ion (element) at low temperatures makes it a powerful technique for surface studies and surface engineering. The technique, however, is subject to its intrinsic limitations of shallow alloying region and line-of-sight treatment requirements. Although best known for its predominant role in semiconductor fabrication since the 1970s, commercially driven uses of this unique near-surface modification technique in the non-semiconductor arena (as covered here) continue to evolve, and several examples are described herein. Ion beamassisted deposition (IBAD) involves the ion bombardment with energetic ions of a vacuum-deposited film during film growth. This hybrid coating process allows control of several important film properties (e.g., adhesion, density, stress, texture, and composition), and the non-equilibrium energetic bombardment can provide the possibility of low substrate temperature processing. Historically, this process has been most widely used for producing robust optical coatings, but other scale-up uses are emerging, including the production of template layers for hightemperature superconducting coatings. Gas-cluster ion beams (GCIB) have recently emerged in applications for surface modification, film deposition and secondary-ion analysis. Gas-cluster beam-generation apparatus and methods are briefly summarized along with a short history of the development of GCIB. More satisfactorily treated as a nanoscale phenomenon, the impact of these weakly bound condensed-gas ions can induce fine-scale smoothing of slightly rough surfaces, or low ionenergy reactive deposition of thin films. The ion-surface physics is quite distinct from that of conventional ion beams and the current understanding of this is described here. The early stage commercial relevance of GCIB to microelectronics and photonics manufacturing is sketched, and a few specific areas of technology application are presented. The potential for GCIB-assisted film deposition of metal oxides and metal nitrides is also reviewed, as is the use of cluster ions as a primary beam to stimulate secondary ions whose mass spectroscopy provides chemical analysis of the surface.