Method of defining forbidden pitches for a lithography exposure tool
First Claim
1. A method of identifying forbidden pitches for a lithographic exposure tool, comprising:
- selecting a set of exposure conditions;
performing a simulation of an actual lithographic exposure process using a computer model, wherein the performing of the simulation comprises;
selecting a set of pattern pitches for a certain target critical dimension, andrunning the computer model using the selected set of exposure conditions for at least some of the pattern pitches from the set of pattern pitches to obtain a corresponding set of depth-of-focus (DOF) values for each pitch ran;
determining whether the DOF values are greater than a focus budget of the exposure tool for a set of frequently used pitches;
if the DOF values are not greater than the focus budget of the exposure tool for the set of frequently used pitches, selecting a new set of exposure conditions and re-performing the simulation using the new set of exposure conditions;
if the DOF values are greater than the focus budget of the exposure tool for the set of frequently used pitches, performing a verification test comprising;
providing a test mask having formed therein at least one of the pattern pitches used in a last performed simulation,exposing a wafer through the test mask using the exposure tool and using the set of exposure conditions of the last performed simulation, anddetermining an actual DOF value for at least one of the exposed pattern pitches;
for at least some of the exposed pattern pitches, comparing the corresponding actual DOF value with the focus budget of the exposure tool; and
if the actual DOF value is not greater than the focus budget of the exposure tool, designating that actual DOF value'"'"'s corresponding pattern pitch as a forbidden pitch.
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Abstract
A method of identifying and defining forbidden pitches or forbidden pitch ranges for a lithographic exposure tool under a given set of exposure conditions is provided. In the method, a computer simulation is performed, and its results are compared to frequently used pitches to see if such frequently used pitches may yield depth-of-focus (DOF) values greater than the focus budget for the exposure tool. If so, a verification test is performed by using a test mask and actually exposing a surface with the same pattern pitches simulated. From this, actual DOF values are obtained and compared to the focus budget of the exposure tool. Any pitches having a DOF value greater than the focus budget are designated as forbidden pitches. This forbidden pitch information may be integrated into a design rule to restrict the use of such forbidden pitches under the given exposure conditions where they are likely to arise.
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Citations
29 Claims
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1. A method of identifying forbidden pitches for a lithographic exposure tool, comprising:
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selecting a set of exposure conditions; performing a simulation of an actual lithographic exposure process using a computer model, wherein the performing of the simulation comprises; selecting a set of pattern pitches for a certain target critical dimension, and running the computer model using the selected set of exposure conditions for at least some of the pattern pitches from the set of pattern pitches to obtain a corresponding set of depth-of-focus (DOF) values for each pitch ran; determining whether the DOF values are greater than a focus budget of the exposure tool for a set of frequently used pitches; if the DOF values are not greater than the focus budget of the exposure tool for the set of frequently used pitches, selecting a new set of exposure conditions and re-performing the simulation using the new set of exposure conditions; if the DOF values are greater than the focus budget of the exposure tool for the set of frequently used pitches, performing a verification test comprising; providing a test mask having formed therein at least one of the pattern pitches used in a last performed simulation, exposing a wafer through the test mask using the exposure tool and using the set of exposure conditions of the last performed simulation, and determining an actual DOF value for at least one of the exposed pattern pitches; for at least some of the exposed pattern pitches, comparing the corresponding actual DOF value with the focus budget of the exposure tool; and if the actual DOF value is not greater than the focus budget of the exposure tool, designating that actual DOF value'"'"'s corresponding pattern pitch as a forbidden pitch. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method of adding information about forbidden pitches for a lithography exposure tool to a design rule relating to fabrication of semiconductor devices, comprising:
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selecting a set of exposure conditions; performing a simulation of an actual lithographic exposure process using a computer model, wherein the performing of the simulation comprises; selecting a set of pattern pitches for a certain target critical dimension, and running the computer model using the selected set of exposure conditions for at least some of the pattern pitches from the set of pattern pitches to obtain a corresponding set of depth-of-focus (DOF) values for each pitch ran; determining whether the DOF values are greater than a focus budget of the exposure tool for a set of frequently used pitches; if the DOF values are not greater than the focus budget of the exposure tool for the set of frequently used pitches, selecting a new set of exposure conditions and re-performing the simulation using the new set of exposure conditions; if the DOF values are greater than the focus budget of the exposure tool for the set of frequently used pitches, performing a verification test comprising; providing a test mask having formed therein at least one of the pattern pitches used in a last performed simulation, exposing a wafer through the test mask using the exposure tool and using the set of exposure conditions of the last performed simulation, and determining an actual DOF value for at least one of the exposed pattern pitches; for at least some of the exposed pattern pitches, comparing the corresponding actual DOF value with the focus budget of the exposure tool; if the actual DOF value is not greater than the focus budget of the exposure tool, designating that actual DOF value'"'"'s corresponding pattern pitch as a forbidden pitch; and adding information about the forbidden pitch(es) for the exposure tool to the design rule. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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27. A method of constraining a design rule relating to fabrication of semiconductor devices, comprising:
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selecting a set of exposure conditions; performing a simulation of an actual lithographic exposure process using a computer model, wherein the performing of the simulation comprises; selecting a set of pattern pitches for a certain target critical dimension, and running the computer model that simulates an exposure tool using the selected set of exposure conditions for at least some of the pattern pitches from the set of pattern pitches to obtain a corresponding set of depth-of-focus (DOF) values for each pitch ran; determining whether the DOF values are greater than a focus budget of the exposure tool for a set of frequently used pitches; if the DOF values are not greater than the focus budget of the exposure tool for the set of frequently used pitches, selecting a new set of exposure conditions and re-performing the simulation using the new set of exposure conditions; if the DOF values are greater than the focus budget of the exposure tool for the set of frequently used pitches, performing a verification test comprising; providing a test mask having formed therein at least one of the pattern pitches used in a last performed simulation, exposing a wafer through the test mask using the exposure tool and using the set of exposure conditions of the last performed simulation, and determining an actual DOF value for at least one of the exposed pattern pitches; defining one or more forbidden pitch ranges based on the actual DOF values from the verification test performed, wherein the defining of each forbidden pitch range comprises; for at least some of the exposed pattern pitches, comparing the corresponding actual DOF value with the focus budget of the exposure tool, if the actual DOF value is not greater than the focus budget of the exposure tool, designating that actual DOF value'"'"'s corresponding pattern pitch as a forbidden pitch, identifying groups of adjacent forbidden pitches, if any, and forming the forbidden pitch range based on the identified groups of adjacent forbidden pitches; and integrating information regarding the defined forbidden pitch range(s) into the design rule such that the defined forbidden pitch range(s) a restricted from use. - View Dependent Claims (28, 29)
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Specification