Method and apparatus for using an alignment target with designed in offset

A method of determining the alignment of a first element with respect to a second element, said method comprising:

• providing an alignment target on said first element and said second element, the alignment target having at least one periodic pattern on said first element and at least one periodic pattern on said second element, said alignment target having at least two locations at least one of which having a designed in offset between said at least one periodic pattern on said first element and said at least one periodic pattern on said second element;
• illuminating said at least two locations on said alignment target with incident radiation that reacts with said alignment target, wherein said radiation is light that is diffracted diffracted from said at least two locations;
• detecting the radiation from said at least two locations after reacting with said alignment target;
• and
• calculating the difference between the light diffracted from one location and the light diffracted from a second location;
• modeling said two locations of said alignment target including modeling the light diffracted from said two locations;
• comparing said modeled light from said two locations with the measured light from said two locations;
• determining if said modeled light is an acceptable fit for said measured light for each location;
• remodeling either location until said modeled light is an acceptable fit for said measured light for each location;
• and
• averaging the modeled offset for the periodic patterns on said first element and said second element for each of said modeled location to determine the alignment of said first element with respect to said second element.

A method of determining the alignment of a first element with respect to a second element, said method comprising:

• providing an alignment target on said first element and said second element, the alignment target having a first overlay pattern, a second overlay pattern, and a third overlay pattern, each overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element, said first overlay pattern having a first designed in offset between the periodic pattern on said first and second elements, said first designed in offset having a first magnitude, said third overlay pattern having a third designed in offset between the periodic pattern of said first and second elements, said third designed in offset having a magnitude that is different than said first magnitude;
• illuminating said first overlay pattern, said second overlay pattern, and said third overlay pattern on said alignment target with incident radiation that reacts with said alignment target;
• detecting the radiation that is different from said first overlay pattern, said second overlay pattern, and said third overlay pattern;
• and
• calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said second overlay pattern to produce a first measured difference;
• calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said third overlay pattern to produce a second measured difference;
• and
• determining the approximate alignment error based on said first measured difference and said second measured difference, wherein determining the approximate alignment error is based on the ratio of said first measured difference and said second measured difference.

A method of determining the alignment of a first element with respect to a second element, said method comprising:

• illuminating at least three locations of an alignment target on said first element and said second element, wherein said at least three locations are a first overlay pattern and a second overlay pattern and a third overlay pattern, each overlay pattern including a periodic pattern on said first element and a periodic pattern on said second embodiment that have the same pitch, at least two of said at least three locations of said alignment target having a designed in offset between the periodic pattern on said first element and said periodic pattern on said second element;
• detecting light diffracted from said at least three locations;
• comparing the detected light diffracted from said at least three locations by calculating the difference between the light diffracted from a first location and the light diffracted from a second location to produce a first measured difference and calculating the difference between the light diffracted from said first location and the light from a third location to produce a second measured difference;
• and
• using said first measured difference with said second measured difference to determine the approximate alignment error between said first element and said second element.

A apparatus for determining the alignment of a first element with a second element by way of an alignment target having at least one periodic pattern on said first element and at least one periodic pattern on said second element, said alignment target including at least three locations at least two of which having a designed in offset between said at least one periodic pattern on said first element and said at least one periodic pattern on said second element such that when said first element and said second element are aligned there is an offset of different magnitudes between said at least one periodic pattern on said first element and said at least one periodic pattern on said second element at the two locations having a designed in offset, said apparatus comprising:

• a radiation source for producing radiation to be incident on said at least three locations of said alignment target;
• a detector for detecting radiation after it interacts with said at least three locations of said alignment target;
• and
• a computer and a computer-usable medium having computer-readable program code embodied therein for causing said computer to calculate the difference between the detected radiation from said at least three locations by:
• calculating the difference between the detected radiation from a first location and detected radiation from a second location to produce a first measured difference;
• calculating the difference between the detected radiation from said first location and the detected radiation from a third location to produce a second measured difference;
• and
• using said first measured difference and said second measured difference to determine if the first element and the second element are aligned.

An apparatus for determining the alignment of a first element with a second element by way of an alignment target having at least one periodic pattern on said first element and at least one periodic pattern on said second element, said alignment target including at least three locations at least two of which having a designed in offset between said at least one periodic pattern on said first element and said at least one periodic pattern on said second element such that when said first element and said second element are aligned there is an offset of different magnitudes between said at least one periodic pattern on said first element and said at least one periodic pattern on said second element at the two locations having a designed in offset, said apparatus comprising

• a radiation source for producing radiation to be incident on said at least three locations of said alignment target, wherein said radiation source produces light that is simultaneously incident on said at least three locations of said alignment target;
• an imaging spectrometer grating that receives diffracted light from said at three locations and focuses said diffraction light;
• a detector for detecting said focused diffracted light from said imaging spectrometer, wherein said light detector is a two dimensional array detector that receives said diffracted light with the spectra dispersed along one dimension of said detector and the spectra associated with different locations of said alignment target separated along the direction perpendicular to the direction of the spectral dispersion;
• and
• a computer and a computer-usable medium having computer-readable program code embodied therein for causing said computer to calculate the difference between the detected radiation from said at least three locations by:
• calculating the difference between the detected radiation from a first location and detected radiation from a second location to produce a first measured difference;
• calculating the difference between the detected radiation from said first location and the detected radiation from a third location to produce a second measured difference;
• and
• using said first measured difference and said second measured difference to determine if the first element and the second element are aligned.

A method of determining the alignment of a first element with respect to a second element, said method comprising:

• providing an alignment target on said first element and said second element, said alignment target having at least four locations, wherein said at least four locations are a first overlay pattern, a second overlay pattern, a third overlay pattern, and a fourth overlay pattern, each overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element that have the same pitch and a plurality of which have a designed in offset between the periodic pattern on said first element and said periodic pattern on said second element;
• illuminating said at least four locations on said alignment target with incident radiation that reacts with said alignment target;
• detecting the radiation from said at least four locations after reacting with said alignment target;
• and
• solving a polynomial equation using the detected radiation to determine the alignment of said first element with respect to said second element.