Method and test structure for estimating focus settings in a lithography process based on CD measurements
By encoding process-related non-uniformities, such as different height levels, which may be caused by CMP or other processes during the fabrication of complex device levels, such as metallization structures, respective focus parameter settings may be efficiently evaluated on the basis of well-established CD measurement techniques.
1. A method for estimating a parameter setting of a lithography process for forming microstructure features, the method comprising:
obtaining a first measurement data from a first test site representing a specific feature type formed by said lithography process based on a specified focus setting, said first test site being formed above a first area;
obtaining a second measurement data from a second test site representing said specific feature type, said second test site being formed by said lithography process based on said specified focus setting, said second test site being formed above a second area, said first and second areas differing in at least one characteristic affecting focus conditions during said lithography process, wherein said at least one characteristic represents an averaged material composition in said first and second areas below said first and second test sites, respectively; and
estimating said specified focus setting on the basis of said first and second measurement data.
2. The method of claim 1 , wherein said averaged material composition in said first and second areas is determined by a respective pattern density of device features formed in at least one material layer provided in said first and second areas below said first and second test sites, respectively.
3. The method of claim 1 , further comprising controlling, on the basis of said first and second measurement data, a focus adjustment process during a lithography process for forming features of said specific type above one or more product substrates.
4. The method of claim 1 , wherein said specific feature type represents metal regions of a metallization structure of a semiconductor device.
5. The method of claim 1 , further comprising obtaining at least one further measurement data from at least one further test site representing said specific feature type, said further test site being formed above at least one further area during said lithography process based on said specified focus setting, said at least one further test site differing from said first and second test sites in at least one characteristic affecting focus conditions during said lithography process.
6. The method of claim 1 , wherein estimating said specified focus setting comprises evaluating a critical dimension of said specific feature type on the basis of said first and second measurement data.
7. The method of claim 6 , further comprising establishing a new focus setting when critical dimensions of said first and second test sites are outside a specified value range.
8. A method, comprising:
evaluating at least one lateral dimension of a first test feature of a semiconductor device, said first test feature being formed on the basis of a specified design above a first area by using a lithography process, said first area comprising a first density of metal below said first test feature;
evaluating at least one lateral dimension of a second test feature of a semiconductor device, said second test feature being formed on the basis of said specified design above a second area by using said lithography process, said second area comprising a second density of metal below said second test feature that differs from said first density of metal below said first test feature; and
determining the validity of at least one parameter used for adjusting a focus during said lithography process on the basis of said at least one evaluated lateral dimension of said first and second test features.
9. The method of claim 8 , wherein said first and second areas are formed by using a chemical mechanical polishing process for planarizing a surface topography prior to forming said first and second features.
10. The method of claim 8 , further comprising evaluating at least one lateral dimension of at least one further test feature of a semiconductor device, said at least one further test feature being formed on the basis of said specified design above at least one further area by using said lithography process, said at least one further area comprising at least one further density of metal that differs from said first and second densities, wherein the validity of said at least one process parameter is determined on the basis of the evaluated at least one lateral dimension of said at least one further test feature.
11. The method of claim 8 , wherein said at least one lateral dimension represents a critical dimension of a device feature of a metallization layer of a semiconductor device.
12. The method of claim 8 , wherein determining the validity of said at least one process parameter comprises assessing said at least one process parameter as having a valid value when said evaluated first and second lateral dimensions are within a predefined range.
13. The method of claim 12 , further comprising forming features corresponding to said first and second test features on a plurality of product substrates when the validity of said at least one process parameter is positively determined.
14. A method for estimating a parameter setting of a lithography process for forming microstructure features, said method comprising:
obtaining a first measurement data from a first test site formed above a first device area having a first pattern density of device features formed in at least one material layer thereof below said first test site, said first test site representing a specific feature type formed by said lithography process based on a specified focus setting;
obtaining a second measurement data from a second test site formed above a second device area having a second pattern density of device features formed in at least one material layer thereof below said second test site, said second test site representing said specific feature type formed by said lithography process based on said specified focus setting, and said second pattern density being different from said first pattern density;
estimating said specified focus setting by evaluating a critical dimension of said specific feature type in each of said first and second test sites on the basis of said first and second measurement data; and
establishing a new focus setting when said critical dimension of said specific feature type in said first and second test sites are outside a specified value range.
15. The method of claim 14 , wherein said specific feature type represents metal regions of a metallization structure of a semiconductor device.
16. The method of claim 14 , further comprising obtaining a third measurement data from a third test site formed above a third device area having a third pattern density of device features formed in at least one material layer thereof, said third test site representing said specific feature type formed by said lithography process based on said specified focus setting, and said third pattern density being different from said first and second pattern densities.