Helium ion microscope

SHIM is a redirect to this article. For more, see under Shim .

A helium-ion microscope ( English scanning helium ion microscope , SHIM ) is an imaging method which, based on the fact that a helium - ion beam scans the object to be examined. The procedure is similar to that of a scanning electron microscope . The helium-ion microscope was developed by Bill Ward among others at the US company ALIS, which was taken over by Carl Zeiss Microscopy in 2006 . This is currently (2014) the only manufacturer of such a device.

Structure and beam generation

In the frozen apparatus , which is under high vacuum , a high voltage generates helium ions in the strong electrical field near a pointed tungsten needle: Helium atoms emit electrons (through the tunnel effect ) to the tungsten needle and are then accelerated away from the needle. The helium ion beam is prepared, i.e. H. bundled and directed, and directed to the material to be examined. The intensities of the beam passing through the sample and the beam reflected by the sample as well as the number of secondary electrons generated are measured.

Comparison with a scanning electron microscope

The technology of the SHIM has several advantages over the scanning electron microscope:

• The resolving power of microscopes has a theoretical limit, the Abbe resolution limit, which is mainly given by the wavelength of the light or by the De Broglie wavelength of the particle beam. Due to the larger particle mass, a helium ion beam has a shorter wavelength than a comparable electron beam and thus the corresponding resolution of a SHIM, which can only be achieved in the ideal theoretical case, is better than that of an electron microscope. In practice, however, this resolution limit hardly plays a role for both microscope types: even with relatively small acceleration voltages, the wavelength of an electron beam is below one nanometer and, for 10 kV electrons, at 12.3 pm, it is far from the resolution that can actually be achieved.
• When the ion beam penetrates the sample, the beam is widened less than an electron beam with the same energy. This reduces the information area with regard to the lateral extent and thus improves the resolution (accuracy). In scanning electron microscopes, the wide scattering of electrons creates what is known as an excitation bulb with a diameter of more than 100 nm to a few micrometers.
• In the highest-resolution operating mode, the helium ions come from an area in the vicinity of a single atom, i.e. H. from an almost point-shaped source.
• Compared to an electron beam, the yield of secondary electrons is relatively high. Since these are detected, their number determines the gray value of each individual picture element; The SHIM can therefore deliver higher-contrast images with the same primary beam intensity.
• As with the scanning electron microscope, the detectors in the SHIM provide information-rich images that reflect the topographical , material, crystallographic and electrical properties of the sample.
• Investigations show that with SHIM the proportion of detected electrons that come from the depth of the sample is significantly smaller, i.e. That is, secondary electrons generated in the depths reach the surface or the detector more difficult. The recordings are therefore more sensitive to the surface. Modern scanning electron microscopes with improved imaging performance with an acceleration voltage of less than 1 keV can, however, achieve similar improvements.
• The SHIM's depth of field is greater than that of a scanning electron microscope.
• The ion beam damages polymers less than an electron beam.

Comparison with other focused ion beam microscopes

Focused ion beam devices usually work with gallium ions to process surfaces in the micrometer range. Due to the low mass of the helium ions, the sputtering effect is much lower, but it is still present and can also be used. However, there are no systematic investigations into substrate damage.

The microscopes that have been on the market since 2007 have a magnification of up to one million times and a resolution of at least 0.75 nm. A resolution record of 0.24 nm was announced on November 21, 2008. The value is difficult to compare, however, since the width of the edge is measured here and not (as with the normal standard) the minimum distance between two objects.

literature

• Bill Ward, John A. Notte, Nicholas P. Economou: Helium-Ion Microscopy. A beam of individual helium ions creates images that challenge SEM and other microscopy technologies . In: Photonics Spectra . tape 41 , no. 8 , 2007, p. 68-70 ( online [PDF]).

Web links

• Function description (PDF file; 5400 kB)
• Manufacturer's website (Carl Zeiss Microscopy, German)
• Presentation: Nanometer-scale imaging and metrology (PDF; 3.3 MB) with numerous images, English

Individual evidence

1. ↑ Nanotechwire press release announcing new microscope, retrieved December 13, 2006 ( Memento of the original from November 7, 2007 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. 
2. ↑ Patent US7368727 : Atomic level ion source and method of manufacture and operation. Registered on 2004 , published on 2008 , inventor: Billy W. Ward. ‌
3. ^ BW Ward, John A. Notte, NP Economou: Helium ion microscope: A new tool for nanoscale microscopy and metrology . tape 24 . AVS, 2006, p. 2871-2874 , doi : 10.1116 / 1.2357967 .
4. ^ ^{A b c} David C. Joy: Scanning He + Ion Beam Microscopy and Metrology . 2013 International Conference on Frontiers of Characterization and Metrology for Nanoelectronics, 25.-28. March 2013 (presentation slides from the presentation at the National Institute of Standards and Technology (NIST), Gaithersburg, Maryland, USA, (PDF, 3.5 MB), presentation of helium-ion microscopy and comparison with electron microscopy).
5. ^ Carl Zeiss SMT Officially Launches ORION ™ Helium Ion Microscope at Microscopy & Microanalysis 2007
6. ^ Carl Zeiss ships first helium ion microscope
7. ↑ Carl Zeiss SMT AG - Nano Technology Systems Division: Orion PLUS Essential Specification  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (accessed on October 24, 2008; PDF; 1.5 MB)  
8. ↑ Fabtech.org: Microscopy resolution record claimed by Carl Zeiss , November 21, 2008 (accessed November 22, 2008)
9. ↑ Carl Zeiss SMT Press Release: Carl Zeiss Sets New World Record in Microscopy Resolution Using Scanning Helium Ions ( Memento of the original from May 1, 2009 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. . November 21, 2008 (accessed November 22, 2008)