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European Patent Specification. Contracting state: DE (Germany). Publication Number 0 022 356 B1, priority date 03.07.79 AU 9433/79. Scanning electron microscope and detection configuration therefor. Inventor: G.D Danilatos. Proprietor: Unisearch Limited.
This patent discloses an atmospheric scanning electron microscope (ASEM) or ESEM whereby detection takes place above a pressure limiting aperture, or integrally with the aperture. It uses two pressure limiting apertures with pumping between them. This allows for the examination of specimens at any pressure up to one atmosphere.
It is based on the earliest work the inventor did at the University of New South Wales in Sydney Australia, whilst patent rights were assigned to the university company Unisearch. This work demonstrated the possibility to operate the SEM with an open chamber to ambient pressure and the inventor could even observe his own finger briefly under the electron beam in TV imaging mode (but no images were recorded on film to avoid the health hazard associated with prolonged x-ray exposure).
This invention discloses a novel method and device for detection and imaging in an ESEM by way of detecting the photons produced by signal-gas interactions. It also discloses the use of specimen cathodoluminescence in ESEM.
With regard to the detection of photons, as preferred detection means (item 8 in Fig. 1) claimed are: a photomultiplier tube, or a photodiode, or a lithium drifted silicon detector, or a scintillation counter.
This was based on earlier work by the inventor
This invention provides for a method and a device for generating, amplifying and detecting secondary electrons from a surface of a sample in an ESEM. It comprises a biased electrode in the specimen chamber. The level of bias is adjustable. The strength of bias is chosen high enough so as to cause the SE to multiply in the gas (thus amplifying the SE signal).
The preferred range of bias is between 50 and 2000 volts. The preferred distance of the electrode from the specimen is between 1 and 200 mm. The preferred specimen chamber pressure is between 0.05 and 20 Torr. The preferred electron beam accelerating voltage is between 1 and 40 kV.
The basic idea of this patent was first disclosed by Danilatos in 1983
This patent discloses a system, which integrates the objective lens with two pressure limiting apertures and with the secondary electron detector of patent 3. Specifically, it describes the ElectroScan ESEM-20 model in its actual geometrical configuration.
The two pressure limiting apertures are attached on a removable carrier, which fits axially in the objective lens. The lower pressure limiting aperture protrudes below the lens pole-piece, whilst the upper pressure limiting aperture seals with an intermediate diaphragm inside the lens assembly. The intermediate diaphragm separates the lens in two chambers. The upper chamber is separated from the rest of the column with a second diaphragm sealing around the column liner. The chambers are independently pumped each with a separate pump. The bottom pressure liming aperture is electrically insulated from ground and serves as a biased electrode for the detection of SE signal in manner disclosed by patent 3. Thus, the detector is integrated with the pressure liming aperture and the pressure limiting apertures (i.e. differential pumping) are integrated with the objective lens of the ESEM.
The purpose of this patent is to protect the monopoly of this particular commercial product, at the given stage of development.
This is practically identical with patent 3. Its purpose appears to be a correction/amendment of claim 1 of patent 3. Namely, in line 31 of claim 1(d) of this new patent, the words "at a pressure of at least 0.05 Torr" have been deleted, and claim 1(g) states that the current amplifier is operatively connected within the device.
This is a continuation in part of patent 3. It uses the biased electrode concept of a GDD as in 3, but it extends the single detecting electrode to a system of concentric arc electrodes placed above the specimen, or above the pressure limiting aperture, in a three dimensional array. The purpose is to control and separate the SE and BSE signals. In addition, it discloses a control grid electrode placed between the specimen and the biased electrode of the GDD for the purpose of controlling the signal.
The arc electrodes may be placed at any particular plane above the specimen. A set of two arc electrodes are positioned in one direction, whilst an additional set of two such electrodes are disposed in a direction normal to the first set.
The electrodes are preferably made from thin metal wire with a thickness of between 50-100 microns.
Different types of signals can be detected and separated with the varied electrode configuration and bias applied.
This patent is similar to patent 4. It was filed by ElectroScan.
PCT/AU98/00953 (WO 99/27259) priority 24/11/1997; publication 3/6/1999. Differential Pumping via core of Annular Supersonic Jet; inventor Gerasimos D Danilatos
This patent application describes the use of an annular supersonic gas jet surrounding the pressure limiting aperture of an ESEM and supplying gas to the specimen chamber while it creates a substantial pumping action at its core. The pumping action is used to create a pressure differential between the specimen chamber and the electron optics of the microscope.
No prior art exists showing the possibility of creating at least one or two orders of magnitude pressure difference in a pressure regime such as that used in an ESEM. In fact, prior art rather excludes this possibility. No such technology has been used in electron microscopy before. Therefore, this patent has both novelty and an inventive step, as well as industrial applicability in ESEM type technologies.
PCT/AU98/00954 (WO 99/27559); priority 24/11/1997; publication 3/6/1999; title Radiofrequency Gaseous Detection Device (RF-GDD); inventor Gerasimos D Danilatos.
This patent discloses a novel gaseous detection device for an ESEM. The inventive step lies in the use of an alternating electromagnetic field to amplify the ionizing signals emanating from the specimen in an ESEM.
Whereas an alternating electromagnetic field to amplify ionizing signals is known prior art in other fields of science, it is not obvious from prior art that the same method and principle can be used in an ESEM. The ESEM has technical requirements quite distinct from all other art to the extent that it is initially unknown if an alternating electromagnetic field is compatible with competing requirements of an ESEM. In fact, a person skilled in the art of electron microscopy and of ESEM in general initially doubts about the feasibility and practicality of a RF-GDD. Therefore, this patent has novelty, inventive step and industrial applicability.
PCT/AU01/00943 (WO 02/15224); priority 11/08/2000; publication 21/02/2000. Environmental scanning electron microscope; inventor Gerasimos D Danilatos.
This patent discloses a novel and improved version of an ESEM, which provides the possibility to have wide field of view as is known in conventional SEM. This allows for inspection of specimens at very low magnification, before one zooms-in to study a particular feature at the highest magnifications allowed today with state of the art electron optics columns. This was not possible to do with hitherto ESEM technology because of the way it used a pair of pressure limiting apertures that created a "tunnel vision" limiting the field of view within the limits of the size of the final aperture. The latter method had the disadvantage that an increased size of aperture to widen the field of view had the concomitant lowering of the useful upper limit of pressure at the specimen while, at the same time, only high kV and high current electron beams were possible. Under those conditions, the ESEM created specimen damage that prevented the use of high magnifications at which the radiation dose is worse. The present invention allows the use of very small apertures without limiting the field of view. Concomitant with this is the possibility to use low kV and low current beams which are generally required for surface examination of specimens, as such is the primary purpose of any SEM. Furthermore, with small apertures, the specimen can be placed further away from the aperture, which frees the space to place other devices such as micro-injectors, etc.