Method and apparatus for determining surface profiles

Claim 1

A method of obtaining a representation of the surface profile of a portion of a specimen such as a semiconductor wafer comprising the steps of projecting a sharply defined beam through an optical imaging system to focus it onto a small spot upon the specimen surface and detecting a measurable characteristic of the beam reflected from said spot, relatively moving the projected beam and the specimen so that the spot scans a line on a portion of said specimen, recording and storing a signal with respect to said measurable characteristic at a plurality of closely spaced positions along said line, successively changing the relative spacing between the imaging system and the specimen by a small incremental distance after each scan of said line such that the focus level of the system with respect to the specimen surface is successively changed by said incremental distances in a given direction perpendicular to said scan line, and separately determining the relative spacing level for each of said points along said line at which a signal most characteristic of a surface indication was obtained to provide a cross-sectional representation of the surface of the specimen along said line.

Claim 2

A method of obtaining a representation of the surface profile of a portion of a specimen such as a semiconductor wafer comprising the steps of projecting a sharply defined beam through an optical imaging system to focus it onto a small spot upon the specimen surface and detecting a measurable characteristic of the beam reflected from said spot, relatively moving the projected beam and the specimen so that the spot scans a line on a portion of said specimen, recording and storing a signal with respect to said measurable characteristic at a plurality of closely spaced positions along said line, successively changing the relative spacing between the imaging system and the specimen by a small incremental distance after each scan of said line such that the focus level of the system with respect to the specimen surface is successively changed by said incremental distances in a given direction perpendicular to said scan line, and separately determining the relative spacing level for each of said points along said line at which a signal most characteristic of a surface indication was obtained to provide a cross-sectional representation of the surface of the specimen along said line.

Claim 5

A method according to any one of claims 1 to 3, wherein said optical imaging system is fixed in position except for changes in its focal depth and the specimen is moved in a plane beneath the imaging system to obtain said line scan.

Claim 7

A method according to any one of the preceding claims, including the step of displaying a graph of the cross-sectional representation for permitting an observer to make decisions with regard to further scanning of the specimen.

Claim 8

A method according to any one of the preceding claims, including the additional steps of selecting from said cross-sectional representation those levels which provide the maximum surface pattern information, and scanning an area adjacent said scan line by relatively moving the beam and the specimen over a plurality of lines parallel to said scan line at each of the selected levels while recording and storing said signals to thereby obtain all of the relevant surface pattern information within said area.

Claim 12

A method according to any one of claims 1 to 6, including the additional step of measuring- across the distance between the generally vertical portions of said cross-sectional representation to obtain the linewidths of a superimposed pattern of the specimen surface.

Claim 13

A system for determining the cross-sectional profile of a specimen such as a semiconductor wafer comprising an optical imaging system for focusing a beam on a small spot on an underlying specimen and including a photodetector for receiving the reflected spot from the specimen for detecting a measurable characteristic thereof and providing an output signal, means for effecting relative movement between the imaging system and the specimen in a plane parallel to the surface of the specimen such that the spot scans along a line across a portion of the specimen, means for obtaining and storing said photodetector signal at a plurality bf closely spaced points in a single scan along said line, means for successively shifting the focus of said imaging system with respect to the specimen by an incremental distance after each scan along said line, means for determining the focus level for the imaging system at which the maximum output signal is obtained for each of said spaced points along said line, and means for providing said focus levels as determined by said last named means as a representation of the cross-sectional profile of said specimen along said line.

Claim 14

A system for determining the cross-sectional profile of a specimen such as a semiconductor wafer comprising an optical imaging system for focusing a beam on a small spot on an underlying specimen and including a photodetector for receiving the reflected spot from the specimen for detecting a measurable characteristic thereof and providing an output signal, means for effecting relative movement between the imaging system and the specimen in a plane parallel to the surface of the specimen such that the spot scans along a line across a portion of the specimen, means for obtaining and storing said photodetector signal at a plurality bf closely spaced points in a single scan along said line, means for successively shifting the focus of said imaging system with respect to the specimen by an incremental distance after each scan along said line, means for determining the focus level for the imaging system at which the maximum output signal is obtained for each of said spaced points along said line, and means for providing said focus levels as determined by said last named means as a representation of the cross-sectional profile of said specimen along said line.

Claim 17

A system according to any one of claimε 12 to 14, wherein said imaging system includes an objective lens and said means for shifting the focus of the imaging system includes means for altering the spacing between said objective lens and the specimen along the path of the beam.

Claim 19

A system according to any one of claims 12 to 16, wherein said means for providing the determined focus levels comprises a graphical output display wherein the determined focus levels are connected in a continuous line defining the cross-sectional profile of the specimen.

Claim 20

A system according to any one of claims 12 to 17, including means for determining separate surface levels along the scanned specimen surface by providing from said means for providing the determined focus levels a histogram of the various focus levels versus the number of points along said line at which said focus levels were found.

Claim 21

A system according to any one of claims 12 to 18, including means for selecting from said representation of the cross-sectional profile those levels which provide the maximum surface pattern information, means for thereafter causing the focus shifting means to shift the focus of the imaging system successively to each of the selected levels, and means for causing the means for effecting relative movement to scan over a plurality of lines parallel to said scan line while the focus level is at each of the selected levels.

Claim 23

A system according to any one of claims 12 to 18, including means for measuring across the distance between the generally vertical positions of said cross-sectional profile to- obtain the linewidth of a superimposed pattern on the specimen surface.

Claim 24

A system for determining the cross-sectional profile of a specimen wafer such as a semiconductor wafer comprising means for mounting said wafer for oscillatory scanning movement along a line in a plane generally parallel to the surface of the wafer; a confocal optical imaging system overlying said wafer, said imaging system including a light source, means for focusing the light source on a spot on the wafer, and photodetector means for receiving the light reflected from the spot and providing an output signal varying in accordance with the intensity of the reflected spot; means for incrementally moving at least a portion of said imaging system in a direction substantially perpendicular to said plane to successively change the focal depth of the imaging system by a small amount relative to the surface profile of the wafer; means for recording said output signals at times corresponding to a plurality of closely spaced positions along said line during each scanning movement of the wafer; means connected to said recording means for determining the focal depth at which the maximum output signal was received at each of said closely spaced positions; and means connected to said last named means for providing the surface profile of said wafer along said line as represented by the focal depth determined for each of said positions.

Claim 25

A system for determining the cross-sectional profile of a specimen wafer such as a semiconductor wafer comprising means for mounting said wafer for oscillatory scanning movement along a line in a plane generally parallel to the surface of the wafer; a confocal optical imaging system overlying said wafer, said imaging system including a light source, means for focusing the light source on a spot on the wafer, and photodetector means for receiving the light reflected from the spot and providing an output signal varying in accordance with the intensity of the reflected spot; means for incrementally moving at least a portion of said imaging system in a direction substantially perpendicular to said plane to successively change the focal depth of the imaging system by a small amount relative to the surface profile of the wafer; means for recording said output signals at times corresponding to a plurality of closely spaced positions along said line during each scanning movement of the wafer; means connected to said recording means for determining the focal depth at which the maximum output signal was received at each of said closely spaced positions; and means connected to said last named means for providing the surface profile of said wafer along said line as represented by the focal depth determined for each of said positions.