ENGINEERING & NANOTECHNOLOGY
Microscopy
Diamonds are a probe’s best friend
Long diamond tips could broaden the three-dimensional measuring capabilities of atomic force microscopes
Surface imperfections in devices such as gears or levers can have disastrous effects on reliability. Recent studies have demonstrated the usefulness of atomic force microscopes (AFMs) — instru- ments that use tiny silicon-based tips to trace out the topography of all kinds of substrates — in determining surface roughness non-destructively. Using AFMs effectively in industrial work- places, however, is not straightforward and requires a different approach to microscope design. As the AFM tip height and scanning mechanisms restrict measuring movements to fewer than ten micrometers vertically and several tens of micrometers laterally, most AFMs can only measure the surfaces of extremely small objects. Shihua Wang at the A*STAR Singapore’s National Metrology
Centre and co-workers have now developed an AFM that can measure groove structures that are 100 micrometers deep, thanks to a self-fabricated, razor-sharp tip made from diamond1
. By
attaching this tip to a large-range metrological AFM (LRM- AFM), the researchers have developed an AFM capable of scanning in millimeter-range with nanoscale resolution. Wang and his team were interested in using AFMs to measure nano- and micro-scale ‘steps’ made from rectangular grooves carved into solid silicon. These objects with depth over 10 micrometers, which are important metrological standards used to calibrate surface profiling instruments, are impossible to inspect using normal AFMs. In addition to scanner limitations, the normal design of an AFM probe — in which a short tip extends off a long horizontal cantilever — often causes collisions with groove sidewalls if the step is deeper than the tip’s height. To solve this problem, the researchers first used a novel cata-
lytic process to grow a thin diamond pillar, over 100 micrometers long, from a flat substrate. They then used a focused ion beam to sharpen the pillar’s end into a three-side pyramidal tip with a radius in the order of ten nanometers — a challenging procedure, according to Wang. Finally, they carefully glued the diamond tip onto a micro-cantilever into their recently developed LRM-AFM that has millimeter-scale scanning ranges. The researchers revealed that their diamond tip had a high mechanical quality, and could resolve surface structures with
82
greater than nanometer resolution. In addition, the tip’s extended length — over ten times greater than conventional tips — meant that the the diamond tips could easily scan step structures ranging from several nanometers to 100 micrometers in depth. This approach even enabled accurate measurements of the difficult-to- spot groove sidewalls. Once the researchers optimize the scanning parameters of this
new microscopy technique, they anticipate that this may lead to the exploration of new applications in the semiconductor and precision engineering industries, which may in turn help manu- facturers achieve even greater production consistencies.
1. Wang, S. H., Tan, S. L., Xu, G. & Koyama, K. Measurement of deep groove structures using a self-fabricated long tip in a large range metrological atomic force microscope. Measurement Science and Technology 22, 094013 (2011).
■
A*STAR RESEARCH OCTOBER 2011– MARCH 2012
©
iStockphoto.com/kWaiGon
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96