Apparatus and method for composite image formation by scanning electron beam

Claim 2

Method for producing an electric signal representing an image of the junctures of a planar surface of a specimen and the two edges of a longitudinally extending projection on the planar surface, characterized by the steps of: positioning first and second electron detectors (30, 32) on opposite transverse sides, respectively, of the projection (20); transversely scanning a first electron beam (10) along a line across the planar surface (18), including the projection (20), and detecting, with only said first detector (30), electrons escaping from the scanned surface (18), including secondary electrons, to produce a first electric signal representing the electrons detected by only said first detector (30); transversely scanning a second electron beam (10) along the line across the planar surface ( 1 8), including the projection (20), and detecting, with only said second detector, electrons escaping from the scanned surface (18), including secondary electrons, to produce a second electric signal representing the electrons detected by only said second detector (32); and combining said first and second electric signals to produce a composite electric signal having pronounced symmetrical characteristics corresponding to the locations of the two junctures (24, 28) between the edges (22, 26) of the projection (20) and the surface (18) of the specimen (14).

Claim 3

Method in accordance with Claim 1, characterized by the steps of: during the scanning of said first electron beam (10), turning ON said first detector (30) and turning OFF said second detector (32); and during the scanning of said second electron beam (10), turning OFF said first detector (30), and turning ON said second detector (32).

Claim 4

Method in accordance with Claim 1, characterized in that said characteristics are signal amplitudes; and that said combining step comprises selecting the lower of the two amplitudes at corresponding points of the first and second signal as the amplitude of each corresponding point of the composite signal.

Claim 5

Method in accordance with Claim 1, characterized in that said characteristics are signal amplitudes; and that said combining step comprises selecting the higher of the two amplitudes at corresponding points of the first and second signals as the amplitude of each corresponding point of the composite signal.

Claim 6

Method in accordance with Claim 1, characterized by the step of feeding the composite signal to a visual image- producing device to produce a visual image of the junctures (24, 28).

Claim 7

Method in accordance with Claim 1, characterized in that the specimen is a semiconductor material, and that the energy of the electron beam (10) is chosen to be 2.5 keV or less.

Claim 8

Method in accordance with Claim 1, characterized by the step of processing the composite signal to provide a line-width signal corresponding to the distance between the junctures (24, 28).

Claim 9

Apparatus for producing an electric signal representing an image of the junctures of a planar surface of a specimen and the two edges of a longitudinally extending projection on the planar surface, characterized by first and second electron detector means (30, 32), positioned on transversely opposite sides of the projection (20), for producing respective electrical signals corresponding to detected electrons; control means for controlling said first and second electron detector means(30, 32) such that, during the transverse scanning of a first electron beam (10) along a line across the planar surface (18), including the projection (20), only said first detector means (30) detects electrons escaping from the scanned surface (18), including secondary electrons, to produce a first electric signal representing the electrons detected by only said first detector means (30), and such that, during the transverse scanning of a second electron beam (10) along the line across the planar surface (18), including the projection (20), only said second detector means (32) detects electrons escaping from the scanned surface (18), including secondary electrons, to produce a second electric signal representing the electrons detected by only said second detector means (32); and signal processing means (56) for combining the first and second electric signals to produce a composite electric signal having pronounced symmetrical characteristics corresponding to the locations of the two junctures (24, 28).

Claim 10

Apparatus for producing an electric signal representing an image of the junctures of a planar surface of a specimen and the two edges of a longitudinally extending projection on the planar surface, characterized by first and second electron detector means (30, 32), positioned on transversely opposite sides of the projection (20), for producing respective electrical signals corresponding to detected electrons; control means for controlling said first and second electron detector means(30, 32) such that, during the transverse scanning of a first electron beam (10) along a line across the planar surface (18), including the projection (20), only said first detector means (30) detects electrons escaping from the scanned surface (18), including secondary electrons, to produce a first electric signal representing the electrons detected by only said first detector means (30), and such that, during the transverse scanning of a second electron beam (10) along the line across the planar surface (18), including the projection (20), only said second detector means (32) detects electrons escaping from the scanned surface (18), including secondary electrons, to produce a second electric signal representing the electrons detected by only said second detector means (32); and signal processing means (56) for combining the first and second electric signals to produce a composite electric signal having pronounced symmetrical characteristics corresponding to the locations of the two junctures (24, 28).

Claim 11

Apparatus in accordance with Claim 8, characterized by switching means (46, 48, 54) for turning ON said first detector means (30) and turning OFF said second detector means (32) during the scanning of said first electron beam (10), and for turning OFF said first detector means (30) and turning ON said second detector means (32) during the scanning of said second electron beam (10).

Claim 12

1 0. Apparatus in accordance with Claim 8, characterized in that said characteristics are signal amplitudes and that said signal processing means (56) comprises means for selecting the lower of the two amplitudes at corresponding points of the first and second signals as the amplitude of each corresponding point of the composite signal.

Claim 13

Apparatus in accordance with Claim 8, characterized in that the specimen (14) consists of a semi-conductor material, and that said first and second electron beams (10) are generated by a scanning electron microscope, said first and second electron beam ( 1 0) having an energy of 2.5 keV or less.

Claim 14

Apparatus in accordance with Claim 8, characterized in that said first and second elactron detector means (30, 32) are Everhart-Thomley scintillator-photomultiplier electron detectors biased to collect secondary electrons.