Lithography focus control method

1 . A method of assessing a photolithography exposure, the method comprising:

performing the photolithography exposure of a photoresist coating on a semiconductor wafer using an optical projection system to form a latent image, the photolithography exposure further using a mask comprising a set of multiple pattern focus (MPF) marks wherein each MPF mark of the set of MFP marks comprises features having at least four different critical dimension (CD) sizes;

developing the latent image to form a developed photoresist pattern;

measuring dimension sizes of features of the developed photoresist pattern corresponding to the features of the MPF marks having at least four different CD sizes;

constructing a spatial focus map of the photolithography exposure based on the measured dimension sizes; and

determining at least one lens aberration of the optical projection system based on the spatial focus map of the photolithography exposure.

2 . The method of claim 1 , wherein the measuring of the dimension sizes of the features of the developed photoresist pattern corresponding to the features of the MPF marks having at least four different CD sizes includes:

acquiring at least one scanning electron microscope (SEM) image of the developed photoresist pattern; and

measuring the dimension sizes in the at least one SEM image.

3 . The method of claim 1 , wherein the measuring of the dimension sizes of the features of the developed photoresist pattern corresponding to the features of the MPF marks having at least four different CD sizes includes:

acquiring a microscope image of the developed photoresist pattern;

automatically contouring the features of the developed photoresist pattern corresponding to the features of the MPF marks having at least four different CD sizes in the microscope image to produce feature contours;

determining photoresist top loss and/or scumming based on the automatic contouring;

determining positive or negative direction of a focus deviation based on the determination of photoresist top loss and/or scumming; and

measuring the dimension sizes using the feature contours;

wherein the constructing a spatial focus map of the photolithography exposure is further based on the determined positive or negative direction of the focus deviation.

4 . The method of claim 3 , wherein the automatic contouring comprises using a convolutional neural network (CNN) to produce the feature contours from the microscope images.

5 . The method of claim 1 , wherein the constructing of the spatial focus map of the photolithography exposure includes, for each MFP mark:

determining ratios or differences between the measured dimension sizes of the features of the developed photoresist pattern corresponding to the features of the MPF marks having at least four different CD sizes; and

determining a focal distance of the photolithography exposure at a location of the spatial focus map corresponding to the MFP mark based on the determined ratios or differences.

6 . The method of claim 1 , wherein the mask further comprises an integrated circuit (IC) fabrication pattern and the set of MPF marks are distributed across the IC fabrication pattern and/or in a frame of the mask surrounding the IC fabrication pattern.

7 . The method of claim 6 , further comprising:

after the measuring of the dimension sizes of the features of the developed photoresist pattern corresponding to the features of the MPF marks having at least four different CD sizes, performing fabrication processing on the semiconductor wafer to produce an integrated circuit (IC) wafer in accordance with the IC fabrication pattern.

8 . The method of claim 1 , wherein:

the photolithography exposure includes multiple exposures performed of different photoresist coatings on different semiconductor wafers with different exposure energy settings to form corresponding latent images corresponding to the different exposure energy settings; and

constructing a focus-energy matrix (FEM) for each MPF mark of the set of MPF marks based on the multiple exposures.

9 . The method of claim 1 , wherein the features having at least four different critical dimension (CD) sizes comprise seven parallel lines having a same line length and arranged as a first set of two outermost lines having a width of a first CD, a second set of two lines adjacent the two outermost lines that have a width of a second CD, a third set of two lines adjacent the lines of the second set of lines that have a width of a third CD, and a central line having a width of a fourth CD, wherein the first CD is greater than the second CD, the second CD is greater than the third CD, and the third CD is greater than the fourth CD.

10 . The method of claim 1 , wherein one of:

the optical projection system is a deep ultraviolet (DUV) projection system used in DUV photolithography and the photolithography exposures are performed using DUV light; or

the optical projection system is an extreme ultraviolet (EUV) projection system used in EUV photolithography and the photolithography exposures are performed using EUV light.

11 . The method of claim 1 , wherein the determined at least one lens aberration comprises at least one of: a coma, an astigmatism, and a tilt.

12 . A method of assessing a photolithography exposure, the method comprising:

performing the photolithography exposure of a photoresist coating on a semiconductor wafer using an optical projection system to form a latent image, the photolithography exposure further using a mask comprising an integrated circuit (IC) fabrication pattern and a set of multiple pattern focus (MPF) marks distributed across the IC fabrication pattern and/or a frame of the mask surrounding the IC fabrication pattern wherein each MPF mark of the set of MFP marks comprises features having at least four different critical dimension (CD) sizes;

developing the latent image to form a developed photoresist pattern;

performing in-line photolithography exposure calibration including:

measuring dimension sizes of features of the developed photoresist pattern corresponding to the features of the MPF marks having at least four different CD sizes;

determining focal distances of the photolithography exposure at the respective MFP marks based on the measured dimension sizes;

identifying at least one lens aberration of the optical projection system based on the determined focal distances of the photolithography exposure; and

automatically adjusting manipulators of the optical projection system to correct the at least one lens aberration of the optical projection system identified based on the determined focal distances of the photolithography exposure; and

after the measuring, performing fabrication processing on the semiconductor wafer to produce an integrated circuit (IC) wafer in accordance with the IC fabrication pattern, the fabrication processing including performing at least one subsequent photolithography exposure/development cycle using the optical projection system with the corrected at least one lens aberration.

13 . The method of claim 12 , wherein the determining of the focal distances of the photolithography exposure at the respective MFP marks based on the measured dimension sizes includes:

for each MPF mark, determining ratios or differences between the measured dimension sizes of the features of the developed photoresist pattern corresponding to the features of the MPF marks having different CD sizes.

14 . A method of assessing a photolithography exposure, the method comprising:

performing a photolithography exposure of a photoresist coating on a semiconductor wafer to form a latent image, the photolithography exposure using an optical projection system and a mask comprising a set of focus marks wherein each focus mark of the set of focus marks comprises features having at least four different dimension sizes;

developing the latent image to form a developed photoresist pattern;

measuring dimension sizes of features of the developed photoresist pattern corresponding to the features of the focus marks by acquiring at least one scanning electron microscope (SEM) image of the developed photoresist pattern and measuring the dimension sizes of the features in the at least one SEM image;

identifying photoresist top loss and/or scumming based on automatic contouring of the features of the developed photoresist pattern corresponding to the features of the focus marks; and

constructing a spatial focus map of the photolithography exposure based on the measured dimension sizes, including determining positive or negative directions of focus deviations based on the identified photoresist top loss and/or scumming.

15 . The method of claim 14 , wherein the constructing of the spatial focus map of the photolithography exposure includes, for each focus mark:

determining ratios or differences between the measured dimension sizes of the features of the developed photoresist pattern corresponding to the features of the focus marks having at least four different dimension sizes; and

determining a focal distance of the photolithography exposure at a location of the spatial focus map corresponding to the focus mark based on the determined ratios or differences.

16 . The method of claim 14 , further comprising determining a coma of the optical projection system based on the spatial focus map of the photolithography exposure.

17 . The method of claim 14 , further comprising determining an astigmatism of the optical projection system based on the spatial focus map of the photolithography exposure.

18 . The method of claim 14 , further comprising determining a tilt of the optical projection system based on the spatial focus map of the photolithography exposure.

19 . The method of claim 14 , further comprising:

determining at least one lens aberration of the optical projection system based on the spatial focus map of the photolithography exposure; and

automatically adjusting manipulators of the optical projection system based on the determined at least one lens aberration.

20 . The method of claim 19 , wherein the determining of at least one lens aberration of the optical projection system includes:

determining at least one of a coma, an astigmatism, and/or a tilt of the optical projection system based on the spatial focus map of the photolithography exposure.