U.S. Philips Corporation

James P Beasley

Hewson Nicholas King

The electron beam 2 of the generator illuminates a first rectangular aperture 4 which is then imaged on a second rectangular aperture 10 by a magnetic lens 7 having reversible flux. The flux of the lens is chosen so that the focused image of the first aperture is rotated by 22.5+45n degrees where n=0,1,2 etc. One flux direction places the aperture image sides 8 parallel to the second aperture sides so that a rectangular shaped beam emerges. The other flux direction places the aperture image sides 8' at 45 degrees to the second aperture sides so that a triangular shaped beam emerges. A beam deflector 6 between the apertures allows rectangles or 45 degree isoceles triangles of a range of sizes to be produced. Thus triangles are produced without further generator components being needed.

Variable shaped spot electron beam pattern generator

When an electron beam is used to effect a process at two adjacent surface areas of a target, such as a semiconductor wafer coated with an electron sensitive resist, various alignment errors can occur, such as where the wafer becomes distorted. The provision of a reference marker, for example a square-etched depression, at the surface of the target between the areas of the target enables the detection of any such distortion. After carrying out the process at one of the areas, an electron beam with a rectangular-shaped spot is directed, in turn, toward the predetermined positions of two mutually transverse sides of the reference marker. In the absence of any alignment error, the beam spot overlies the side in question in order to overlap the marker and the area of the target in the immediate vicinity. Back-scattered electrons can then be detected to give a signal representative of any deviation between the actual position and the predetermined position of the marker so that the electron beam can be correctly aligned when effecting the process of the second of the two areas. For increased accuracy of alignment, a plurality of markers may be provided between the adjacent surface areas.

Method of using an electron beam

An apparatus, such as an electron beam column (1), with high-speed deflection capability comprises a gun (2) which directs a beam (3) of charged particles by several magnetic lenses (9,11,13a,13b) towards a target (4). Magnetic deflection coils (12a,12b) produce a variable magnetic field for controllably deflecting the beam. The beam is surrounded by an electrically conductive surface (16a,16b,22) which in the vicinity of the deflection coils is constituted by a tube (22) comprising a single wire of, for example, nichrome preferably coated by an oxide film formed naturally and comprising a close-wound helix. This tube construction has a longitudinal resistance which significantly impedes the flow of undesirable eddy currents therein. On the other hand the tube can readily conduct along a helical path so that charge accumulation on the tube walls is avoided.

Charged particle beam apparatus

When an electron beam is used to effect a process at two adjacent surface areas of a target, such as a semiconductor wafer coated with an electron sensitive resist, various alignment errors can occur including wafer distortion. The provision of a reference marker, for example a square-etched depression, at the surface of the target between the adjacent surface areas enables detection of any misalignment. Thus, after effecting the process at one of the areas, an electron beam having substantially the same size and shape as the reference marker is directed toward the predetermined position of the reference marker. Back-scattered electrons are then detected to give a signal representative of any deviation between the actual position and the predetermined position of the reference marker so that the electron beam can be correctly aligned before carrying out the process at the second of the two surface areas. For increased accuracy of alignment, an array of reference markers may be provided between the two adjacent areas.

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Tadworth, United Kingdom

James P Beasley