Radiant energy – Inspection of solids or liquids by charged particles – Analyte supports
Patent
1992-11-09
1994-04-26
Anderson, Bruce C.
Radiant energy
Inspection of solids or liquids by charged particles
Analyte supports
250306, H01J 3726
Patent
active
053069188
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an installation for the study of the surface of samples placed in a vacuum or controlled atmosphere. It applies in particular to electronic tunneling effect microscopy and/or spectroscopy, namely in ultravacuum, to optic tunneling effect microscopy and/or spectroscopy or further to the etching of nanometric structures through optic and/or electronic microlithographical processes.
2. Discussion of Background Information
It is a well known fact that certain microscopy, spectroscopy or microlithography processes can only be conducted in a particularly clean, controlled atmosphere especially in order not to pollute the surface of the samples being studied, or the samples on which tiny structures are to be realized, such as optic or electronic integrated circuits. In this respect, the vacuum is a particularly useful controlled medium and some applications even require the samples and measuring or etching means to be placed in an ultravacuum, i.e., in a high vacuum. In this sense, a series of microscopy or spectroscopy techniques have been developed employing a lateral scanning of the surface of a sample by an electricity or light conducting tip, this tip being an integral part of a microprobe collecting, by tunneling effect, electrons or photons in numbers that largely depend on an exponential function of the distance separating the tip from the surface; it is common usage to call electronic tunneling microscopy, or STM (Scanning Tunneling Microscopy), the technique using electrons, and optic tunneling microscopy, or PSTM (Photon Scanning Tunneling Microscopy) the technique using photons. As a general rule, these two techniques and equivalent techniques, i.e., those in which a microprobe should be positioned close to the surface of a sample to be studied, either in the air or in a vacuum will be collectively referred to as SXM. Moreover, these initials will be used to refer to microscopes or means of study using these techniques. Finally, it should be noted that SXMs all operate in the same way as a roughometer, and that this expression will be generally used without distinguishing the physical principle applied during measurement.
In all cases, the distances to be maintained between the surface and the microprobe or tip are extremely small, i.e., 1-2 nanometers for the STM and approximately one micrometer for the PSTM. Such small values mean that risks of error in manipulation should be reduced to a minimum and therefore require the use of highly reliable mechanical, electronic or optical components. Without such highly reliable components destructive impacts car more or less, occur between the microprobe and the surface of the sample to be studied or etched, these impacts being caused by the loss of control of the spatial position of the tip. Another cause of damage results from too quick a scanning of the surface with regard to the response time of the components or mechanical and/or electronic circuits controlling the distance between the tip and the surface. Moreover scanning speed is an obvious function of the roughness of the surface. This means that a smooth surface can be scanned quicker than a rough surface, but it is never easy to know exactly before the study. In the case of an impact caused for some reason, the microprobe or the tip must be changed frequently, or at least controlled, which is not always possible directly in an enclosure where a vacuum has been made or where a controlled atmosphere is concerned. In addition, the aging of the tips, especially metal tips in the case of STM, or optic tips in the case of PSTM, is a normal phenomenon requiring their replacement. For example, an STM tip might have to be replaced due to a rearrangement of the terminal atoms of the tip or due to capturing a foreign atom or due to a thermal expansion effect. A final case, also very important, for which it is essential to change the microprobe or tips in order to study the surface of a sample is that where the measurements taken
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International Search Report and Annex.
International Preliminary Examination Report.
Goudonnet Jean-Pierre
LaCroute Yvon
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