National Research Development Corporation

Other

Xerox Corporation

Kenneth C Smith

Stephen J Erasmus

Jeffrey W Ryan

Christopher Pearce

David Andrew Thomas

Michael Ernest Garrett

William J Tee

David Thomas

A print media sheets trailing edge knockdown stacking assistance system, in a compiler or other stacking system with a substantial sheet gravity drop, activated for each ejected sheet to move substantially linearly and perpendicularly downwardly from above, but adjacent to, the sheet ejection position to engage a sheet end area and rapidly push it down towards the underlying stack of sheets and into engagement with any sheet compiling device, then automatically rapidly reciprocally lifting up out of the way above the sheet ejection position before another sheet is ejected, without any significant pause between its up and down movements.

High speed vertical reciprocating sheet trail edge stacking assistance system

An electron beam instrument having an objective lens coil 14 and stigmator coils 18 has its astigmatism corrected for by measurement of the contrast in the final image. The currents through the objective lens and the stigmator coils are adjusted in sequence iteratively to optimize the contrast. The optimum contrast may be either a maximum contrast or a minimum contrast depending on the nature of the instrument and its mode of operation. Measurement of contrast may be made by measuring the magnitudes of successive points of an image and calculating the variance. Alternatively two measurements of magnitude at each point of an image may be made and the covariance calculated.

Correction of astigmatism in electron beam instruments

In a scanning transmission electron microscope 1 the image of the diffraction pattern formed on a phosphor screen 6 as a result of electron beam impingement on a point on the specimen 4 is converted by a camera 7 into a video signal and digitized in an ADC convertor 9 and stored in a digital store 10. The stored signal is then modified by a weighting factor representing a notional pattern overlaying screen 6. The weighting factor may have one of two binary values, representing a notional opaque and transparent pattern, or may have a multiplicity of different values. The modified signals are then added together to provide a picture value for the point of impingement. By this means a complete picture is built up point-by-point. To speed up the picture taking operation diffraction images from different points may be displayed on different parts of screen 6 so that several images can be scanned together by camera 7.

Scanning transmission electron microscopes

The fabrication of a microcircuit by beam lithography requires an economic distribution of processing time between the high resolution portions of the exposure pattern and areas of much lower resolution. At least one ion beam provides the high resolution performance and at least one electron beam satisfies the lower resolution requirement. The beams are independently operable and are relatively inclined for substantial convergence at the substrate. The convergence is such that all beams can be scanned simultaneously in a single elemental area of substrate or in adjacent elemental areas which are presented for exposure in sequence. For registration the substrate is imaged by electron scanning and the positions of registration marks are related in the image to predetermined positions which represent the required position of the substrate. A positional correction signal is derived by observation of image brightness, size and orientation at the predetermined positions. The signal is processed by a computer which holds all positional control and scan control data and instructs the relevant controls.

Microcircuit fabrication

In electron beam lithography apparatus a substrate, on which an exposure pattern is to be produced, is exposed to a plurality of electron beams. In a double beam arrangement one beam is capable of the highest resolution required and has a necessarily low writing speed. The other beam is relatively coarse in beam width but carries a higher current and has a much higher writing speed. Single-pole magnetic lens focusing is used with close angular spacing between the beams. Scanning of the pattern is programmed for economy of time so that the beams produce complementary portions of the pattern, the fine beam defining for example the edges of a structure while the coarse beam scans the area bounded by the edges. Scanning may be simultaneous or sequential. Selection of the relative values of beam potential and the use of energy selective detectors enable the two scanned regions to be imaged.

Electron beam lithography

In an electron-beam probe instrument such as a scanning electron microscope in which the electron gun employs a field-emission cathode the condenser lens is of the `snorkel` design. The term `snorkel` is used to denote a single-pole magnetic lens in which the pole-piece has an axially extending nose portion. The lens is positioned so that the cathode region is immersed in the radial field at the nose of the lens. Preferably the lens is placed closely behind the cathode but outside the vacuum envelope.

Electron beam apparatus

Supplies for the objective lens scanning coils and stigmator coils of a scanning electron microscope are arranged for digital control by a small computer which receives a digitized input from an imaging electron collector. For a specimen of suitable structure the computer can be programmed for automatic focusing and astigmatism correction or the operator can intervene to apply a manual correction. Astigmatism is detected by comparing the directional derivatives of intensity for corresponding points in two frames with lens settings above and below focus. By taking the difference between the derivatives for each direction of measurement the effect of structural directional features is eliminated; by summing the differences for all directions a value (S) is obtained which represents the magnitude of astigmatism. The required orientation of the stigmator field can be calculated and the excitation current scanned through a range of values to determine the setting for which S is a minimum.

Astigmatism in electron beam probe instruments

Pure oxygen or a gas containing more oxygen than air is injected under pressure into sewage held in or flowing through a sewer. This injection can be used to prevent the concentration of dissolved oxygen in the sewer falling to a level at which there occurs bacterial reduction to hydrogen sulfide of sulfate present in the sewage. The injection can also be used to oxidize to sulfur any sulfide dissolved in the sewage. The pure oxygen or the gas containing more oxygen than air may be injected into sewage flowing through a sewage pipe forming part of a gravity sewer, into a pump used to transfer the sewage through the sewer, or into a part of the sewer where sewage is collected before being transferred through the sewer.

Process for treatment of sewage in a gravity sewer

Pure oxygen or a gas containing substantially more oxygen than air is injected under pressure into sewage held in or flowing through a rising or pumping sewer. This injection may be used to prevent the concentration of dissolved oxygen in the sewer falling to a level at which there occurs bacterial reduction to hydrogen sulphide of sulphate present in the sewage and/or to reduce the Biochemical Oxygen Demand of the sewage. The injection can also be used to oxidize to sulphur any sulphide dissolved in the sewage. The pure oxygen or the gas containing more oxygen than air may be injected into sewage flowing through a sewage pipe forming part of a rising or pumping sewer, into a pump used to transfer the sewage through the sewer, or into a part of the sewer (e.g. a sump) where sewage is collected before being transferred through the sewer.

Growing community of inventors

Cambridge, United Kingdom

Kenneth C Smith