Optical focus phase shift test pattern, monitoring system and process

A focus test mask for use in a projection imagery system, said focus test mask projecting on an object surface a fine test pattern which allows quantification of system defocus, said focus test mask comprising:

• a transparent substrate which allows light to pass therethrough;
• a first opaque line and a second opaque line disposed in association with said transparent substrate, said first opaque line and said second opaque line having a predefined spacial relationship;
• and
• a phase shift window associated with said substrate and shifting light passing therethrough by other than 180.degree. in relation to light passing through said transparent substrate to produce a phase difference between light passing therethrough and light passing through said substrate, said phase shift window being disposed between said first and second opaque lines, wherein when said pattern is optically projected by said system onto the surface of an object, the direction and magnitude of optical defocus is determinable by measuring the center-to-center spacing of the test pattern projected onto the object surface.

A focus test mask for use in a projection imagery system, said focus test mask projecting a fine test pattern on an object surface for quantification of system defocus, said focus test mask comprising:

• a transparent substrate;
• a first opaque line, a second opaque line and a third opaque line formed in association with said substrate, said opaque lines having a predefined spacial relationship, with said second opaque line disposed between said first opaque line and said third opaque line;
• a first window of phase shift material formed in association with said substrate to produce a phase difference of other than 180.degree. between light passing therethrough and light passing through said transparent substrate, said first phase shift window being disposed partially between said first opaque line and said second opaque line;
• and
• a second window of phase shift material formed in association with said substrate to produce a phase difference of other than 180.degree. between light passing therethrough and light passing through said substrate, said second phase shift window being disposed partially between said second opaque line and said third opaque line, said second phase shift window being offset relative to said second opaque line from said first phase shift window such that two alternating patterns of substrate and phase-shifted windows are formed transverse said opaque lines, wherein when projected onto an object's surface, measurements of the alternating test patterns can be combined for a magnified reading of the focus offset, the direction and magnitude of optical defocus being determinable by measuring the displacement of the center of the second line relative to the first and third lines.

A focus test mask for use in a projection imagery system, said focus test mask projecting on an object surface a fine test pattern which allows quantification of system defocus, said focus test mask comprising:

• a substantially non-phase-shifted, transparent substrate;
• a first opaque line forming a closed geometric shape and a second opaque line forming the same closed geometric shape, said first opaque line and said second opaque line being of different size and concentrically disposed in association with said substrate surface such that said geometric shapes have a predefined spacial relationship;
• and
• a phase shifter associated with said substrate and shifting light passing therethrough by other than 180.degree. to produce a phase difference between light passing therethrough and light passing through said non-phase-shifted substrate, said phase shifter being disposed between said first and second opaque lines such that an alternating pattern of non-phase-shifted material and phase-shifted material is defined transverse said spaced lines, wherein when said alternating test pattern is optically projected by said system onto the surface of an object, the direction and magnitude of optical defocus is determinable by measuring the center-to-center spacing of the lines projected onto the substrate surface.

An optical defocus monitoring system for use with a projection imagery system having an illumination source and a focus lens, said monitoring system comprising:

• a focus test mask for disposition between said illumination source and said focus lens for projecting a fine test pattern on an object surface which allows quantification of imagery system defocus, said focus mask including a substrate which allows light to pass therethrough,
• a phase shift pattern associated with said substrate and shifting light passing therethrough by other than 180.degree. in relation to light passing through said substrate to produce a phase difference between light passing therethrough and light passing through said substrate;
• and
• means for evaluating said fine test pattern once projected by said imagery system onto an object surface by measuring the dimensions of said projected test pattern.

In a projection imagery system having a focus lens, a method for monitoring the optical defocus of an object surface, said monitoring method comprising the steps of:

• (a) providing a focus test mask having a non-phase-shifted, transparent substrate, first and second opaque lines formed in association with said substrate in a predetermined spacial relationship and a window, of phase shift material disposed between said opaque lines such that an alternating test pattern of non-phase-shifted material and phase-shifted material is defined transverse said opaque lines, said phase shift window producing a phase difference of other than 180.degree. between light passing therethrough and light passing through said non-phase-shifted substrate;
• (b) illuminating said focus test mask to project said alternating test pattern onto an object surface through said imagery system's focus lens;
• and
• (c) measuring center-to-center spacing of two lines of said projected test pattern, said measured spacing being representative of optical defocus.