Difference between revisions of "Milestone-Proposal:First Practical Field Emission Electron Microscope, 1972-1984"

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The FE electron source was also applied to a transmission electron microscope (TEM) and a scanning transmission electron microscope (STEM). In physics, the application of an FE electron source with high interference characteristics to an FE-TEM developed for electron beam holography resulted in greatly improved coherency, i.e., from 300 to as many as 3000 lines of Fresnel fringes. The FE-TEM electron beam holography experimentally proved the Aharonov-Bohm effect in 1982, which confirmed the existence of gauge field and put an end to the vector-potential controversy.
 
The FE electron source was also applied to a transmission electron microscope (TEM) and a scanning transmission electron microscope (STEM). In physics, the application of an FE electron source with high interference characteristics to an FE-TEM developed for electron beam holography resulted in greatly improved coherency, i.e., from 300 to as many as 3000 lines of Fresnel fringes. The FE-TEM electron beam holography experimentally proved the Aharonov-Bohm effect in 1982, which confirmed the existence of gauge field and put an end to the vector-potential controversy.
 
In the semiconductor industry, the critical-dimension SEM (CD-SEM), i.e., an FE-SEM dedicated to semiconductor-device micro-pattern in-line measurement, was commercialized in 1984. The CD-SEM is suitable for measuring non-conductive semiconductor devices without charge-up. Application of the Schottky electron source, an FE electron source proposed by Dr. Swanson in the 1980's, enabled long-term, stable and reliable CD-SEM operation, which is required for semiconductor production lines. CD-SEMs have been contributing to “scaling” as an indispensable metrology tool for device fabrication.
 
In the semiconductor industry, the critical-dimension SEM (CD-SEM), i.e., an FE-SEM dedicated to semiconductor-device micro-pattern in-line measurement, was commercialized in 1984. The CD-SEM is suitable for measuring non-conductive semiconductor devices without charge-up. Application of the Schottky electron source, an FE electron source proposed by Dr. Swanson in the 1980's, enabled long-term, stable and reliable CD-SEM operation, which is required for semiconductor production lines. CD-SEMs have been contributing to “scaling” as an indispensable metrology tool for device fabrication.
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Development of FE electron source technology enabled ultra-high-resolution imaging with stability and reliability. FE electron microscopes, i.e., FE-SEMs, FE-TEMs, FE-STEMs, and CD-SEMs, are now widely used for advanced research and development in many fields of science, technology, and industry, including physics, biotechnology, medical science, materials, and semiconductors.|a5=The FE electrons are obtained by applying a high voltage (several thousand volts) to the tip of a metal needle (FE tip) with a radius of less than 100 nm. Application of a high electric field to the tip  extracts electrons from the top of the tip due to the tunnel effect, whereas heating of the tungsten filament in a conventional thermionic emission source extracts thermionic electrons.
 
Development of FE electron source technology enabled ultra-high-resolution imaging with stability and reliability. FE electron microscopes, i.e., FE-SEMs, FE-TEMs, FE-STEMs, and CD-SEMs, are now widely used for advanced research and development in many fields of science, technology, and industry, including physics, biotechnology, medical science, materials, and semiconductors.|a5=The FE electrons are obtained by applying a high voltage (several thousand volts) to the tip of a metal needle (FE tip) with a radius of less than 100 nm. Application of a high electric field to the tip  extracts electrons from the top of the tip due to the tunnel effect, whereas heating of the tungsten filament in a conventional thermionic emission source extracts thermionic electrons.
Because of the high electric field, the FE electron current density (10^4–10^6 A/cm2) is three orders of magnitude larger than that of thermionic electrons (1^–10 A/cm2). An FE electron source is ideally a point source, and the diameter of the virtual source ranges from 5 to 10 nm, which is 1/1000 the source size of thermionic emission (1–10 mm). The energy spread of FE electrons is 0.2–0.3 eV, which is much narrower than that of thermionic emission (2 eV). As a result, an FE electron source has 1000× the brightness, 1/1000 the source size, and 1/10 the energy spread of a conventional thermionic emission source. These features of the FE electron source result in much brighter and higher resolution images and high interference characteristics when applied to SEMs, TEMs, STEMs, and CD-SEMs.
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Because of the high electric field, the FE electron current density (10^4–10^6 A/cm2) is three orders of magnitude larger than that of thermionic electrons (1–10 A/cm2). An FE electron source is ideally a point source, and the diameter of the virtual source ranges from 5 to 10 nm, which is 1/1000 the source size of thermionic emission (1–10 mm). The energy spread of FE electrons is 0.2–0.3 eV, which is much narrower than that of thermionic emission (2 eV). As a result, an FE electron source has 1000× the brightness, 1/1000 the source size, and 1/10 the energy spread of a conventional thermionic emission source. These features of the FE electron source result in much brighter and higher resolution images and high interference characteristics when applied to SEMs, TEMs, STEMs, and CD-SEMs.
However, the instability of the FE emission current was an essential difficulty in the development of a practical FE electron microscope. After many years of fundamental research and development of FE electron source stability technology, Hitachi finally achieved a commercial FE-SEM featuring a stable and reliable FE electron source.|a6=For FE emission current stability, a steady-state ultra-high vacuum of 10−8 Pa was necessary since residual gas molecules cause the FE emission current to fluctuate. This is a much higher vacuum than that of a conventional thermionic emission electron source (order of magnitude of 10^−4 Pa). Moreover, maintaining an ultra high vacuum under electron beam emission conditions is quite a challenge because the electron beam stimulates outgassing from the anode, which degrades the vacuum.
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However, the instability of the FE emission current was an essential difficulty in the development of a practical FE electron microscope. After many years of fundamental research and development of FE electron source stability technology, Hitachi finally achieved a commercial FE-SEM featuring a stable and reliable FE electron source.|a6=For FE emission current stability, a steady-state ultra-high vacuum of 10^−8 Pa was necessary since residual gas molecules cause the FE emission current to fluctuate. This is a much higher vacuum than that of a conventional thermionic emission electron source (order of magnitude of 10^−4 Pa). Moreover, maintaining an ultra high vacuum under electron beam emission conditions is quite a challenge because the electron beam stimulates outgassing from the anode, which degrades the vacuum.
 
Hitachi succeeded in establishing an ultra-high vacuum technology for the FE electron source. Patented "innerbake” technology, i.e., heating and degassing of a heater built into the anode, was the breakthrough. A “flashing" technique, i.e., short-duration heating of the cathode to remove the gas molecules, produced a stable, clean state of the cathode surface. This low outgas material and surface treatment technology were integrated and used to reduce the effect of the residual gas molecules. As a result, the FE emission current was fundamentally stabilized, enabling development of a stable and reliable FE electron source, which realized the development of practical high-resolution electron microscopes.|a7=The plaque will be installed outside the main building at the sites where FE technology and electron microscopes were developed.  
 
Hitachi succeeded in establishing an ultra-high vacuum technology for the FE electron source. Patented "innerbake” technology, i.e., heating and degassing of a heater built into the anode, was the breakthrough. A “flashing" technique, i.e., short-duration heating of the cathode to remove the gas molecules, produced a stable, clean state of the cathode surface. This low outgas material and surface treatment technology were integrated and used to reduce the effect of the residual gas molecules. As a result, the FE emission current was fundamentally stabilized, enabling development of a stable and reliable FE electron source, which realized the development of practical high-resolution electron microscopes.|a7=The plaque will be installed outside the main building at the sites where FE technology and electron microscopes were developed.  
 
(1) Naka Division, Hitachi High Technologies Corporation (formerly Naka Works, Hitachi Ltd.) and (2) Central Research Laboratory, Hitachi Ltd.|a8=Yes|a9=The site is guarded by security officers at the entrance of the site. The entrance lobby of the building is open to visitors by registering at the security gate.|a10=The sites are owned by (1) Hitachi High Technologies Corporation and (2) Hitachi, Ltd.|a11=Yes|a12=Dr. Hideki Imai, Chair of the IEEE Tokyo Section, has agreed to sponsor the milestone nomination. Dr. Imai's e-mail address is imai@imailab.jp|a13name=Prof. Hideki Imai|a13section=Tokyo|a13position=Chair|a13email=tokyosec@ieee-jp.org|a14name=Prof. Ryuji Kohno|a14ou=Tokyo Section|a14position=Treasurer|a14email=treasurer@ieee-jp.org|a15Aname=Hidehito Obayashi|a15Aemail=obayashi-hidehito@nst.hitachi-hitec.com|a15Aname2=Toshio Masuda|a15Aemail2=masuda-toshio@naka.hitachi-hitec.com|a15Bname=Makoto Hanawa|a15Bemail=secretary@ieee-jp.org|a15Bname2=Toshio Masuda|a15Bemail2=masuda-toshio@naka.hitachi-hitec.com|a15Cname=Hidehito Obayashi, Ph.D.|a15Ctitle=President, Chief Executive Officer and Director|a15Corg=Hitachi High-Technologies Corporation|a15Caddress=24-14, Nishi-Shimbashi 1-chome, Minato-ku, Tokyo 105-8717, Japan|a15Cphone=81-3-3504-7111|a15Cemail=obayashi-hidehito@nst.hitachi-hitec.com}}
 
(1) Naka Division, Hitachi High Technologies Corporation (formerly Naka Works, Hitachi Ltd.) and (2) Central Research Laboratory, Hitachi Ltd.|a8=Yes|a9=The site is guarded by security officers at the entrance of the site. The entrance lobby of the building is open to visitors by registering at the security gate.|a10=The sites are owned by (1) Hitachi High Technologies Corporation and (2) Hitachi, Ltd.|a11=Yes|a12=Dr. Hideki Imai, Chair of the IEEE Tokyo Section, has agreed to sponsor the milestone nomination. Dr. Imai's e-mail address is imai@imailab.jp|a13name=Prof. Hideki Imai|a13section=Tokyo|a13position=Chair|a13email=tokyosec@ieee-jp.org|a14name=Prof. Ryuji Kohno|a14ou=Tokyo Section|a14position=Treasurer|a14email=treasurer@ieee-jp.org|a15Aname=Hidehito Obayashi|a15Aemail=obayashi-hidehito@nst.hitachi-hitec.com|a15Aname2=Toshio Masuda|a15Aemail2=masuda-toshio@naka.hitachi-hitec.com|a15Bname=Makoto Hanawa|a15Bemail=secretary@ieee-jp.org|a15Bname2=Toshio Masuda|a15Bemail2=masuda-toshio@naka.hitachi-hitec.com|a15Cname=Hidehito Obayashi, Ph.D.|a15Ctitle=President, Chief Executive Officer and Director|a15Corg=Hitachi High-Technologies Corporation|a15Caddress=24-14, Nishi-Shimbashi 1-chome, Minato-ku, Tokyo 105-8717, Japan|a15Cphone=81-3-3504-7111|a15Cemail=obayashi-hidehito@nst.hitachi-hitec.com}}

Revision as of 13:01, 27 February 2010