Patent ID: 8638437

Claim:
A method of aligning a sample comprising the steps of: a) providing a system comprising: a source (LS) of a beam of electromagnetic radiation; a sample (S), on a stage (STG) support that allows rotation about axes in a plane parallel to said sample surface, and translation adjustment of the position of said stage (STG) along a locus substantially normal to said plane of said sample surface; an imaging means (L 1 ) (L 2 ); a multi-element detector (MED) or single element position sensitive detector (SEPSD), said imaging means being disposed and applied to create an image of the source (LS) on said multi-element detector (MED) or single element position sensitive detector (SEPSD); and means for introducing (CL) astigmatism into said beam of electromagnetism, positioned between said source (LS) and multi-element detector (MED) or single element position sensitive detector (SEPSD); such that in use said source of a beam of electromagnetic radiation provides a beam of electromagnetic radiation which has astigmatism introduced thereto by said means for introducing (CL) astigmatism, and is acted on by said imaging means (L 1 ) (L 2 ) to create an image of the source (LS) on said multi-element detector (MED) or single element position sensitive detector (SEPSD); b) defining a criteria for what constitutes sample alignment; said method further comprising the step of: c) while: monitoring the location of, and geometric attributes of an image pattern of a beam of electromagnetic radiation resulting from reflection of a beam directed onto said sample (S), into said multi-element detector (MED) or single element position sensitive detector (SEPSD), wherein said monitored pattern is formed, adjusting said stage (STG) orientation by changing at least one selection from the group consisting of: rotation of said stage (STG) about at least one said rotational axis in the plane parallel to said sample surface; and translation of said stage (STG) along said locus which is substantially normal to said plane of said sample (S) surface; until the location of, and geometric attributes of said monitored beam image pattern formed by said multi-element detector (MED) or single element position sensitive detector (SEPSD) meet said step b predetermined criteria for what constitutes sample alignment.