Determination of center of focus by diffraction signature analysis
AssigneeAccent Optical Technologies, Inc.
InventorsMichael E. Littau, Christopher J. Raymond
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Abstract
Methods for determination of parameters in lithographic devices and applications by diffraction signature difference analysis, including determination of center of focus in lithography devices and applications. Latent image analysis may be employed with exposed but undeveloped lithographic substrates. Control methods are provided for process control of center of focus in lithography devices utilizing diffraction signature difference analysis.
Claims50
A method of determining the center of focus in a lithography device utilizing latent image analysis, comprising the steps of
- providing a substrate comprising a plurality of latent image diffraction gratings made utilizing the lithography device, the plurality of diffraction gratings comprising different known focus settings;
- determining a diffraction signature for at least three of the plurality of latent image diffraction gratings by means of a radiation source-based tool;
- measuring the differences between the diffraction signatures between adjacent focus setting latent image diffraction gratings;
- and
- determining the center of focus as the focus setting wherein there is a minimal difference between the diffraction signatures of adjacent focus setting latent image diffraction gratings.
A method of determining the center of focus in a lithography device utilizing exposed wafers prior to development of the exposed wafers, comprising the steps of
- providing a wafer comprising a plurality of latent image diffraction gratings made utilizing the lithography device, the plurality of diffraction gratings comprising different known focus settings, wherein the wafer has not been subjected to a development process;
- determining a diffraction signature for at least three of the plurality of latent image diffraction gratings by means of a radiation source-based tool;
- measuring the differences between the diffraction signatures between adjacent focus setting latent image diffraction gratings;
- and
- determining the center of focus as the focus setting wherein there is a minimal difference between the diffraction signatures of adjacent focus setting latent image diffraction gratings.
A method of process control for center of focus in a lithography device, comprising the steps of
- providing a substrate comprising a plurality of latent image diffraction gratings made utilizing the lithography device, the plurality of latent image diffraction gratings comprising different known focus settings;
- determining a diffraction signature for at least three of the plurality of latent image diffraction gratings by means of a radiation source-based tool;
- measuring the differences between the diffraction signatures between adjacent focus setting latent image diffraction gratings;
- determining the center of focus as the focus setting wherein there is a minimal difference between the diffraction signatures of adjacent focus setting latent image diffraction gratings;
- and
- adjusting the focus setting of the lithography device to the determined center of focus.
A method of process control for center of focus in a lithography device, comprising the steps of
- providing a substrate comprising a plurality of diffraction gratings made utilizing the lithography device, the plurality of diffraction gratings comprising different known focus settings;
- determining a diffraction signature for at least three of the plurality of diffraction gratings by means of a radiation source-based tool;
- measuring the differences between the diffraction signatures between adjacent focus setting diffraction gratings;
- determining the center of focus as the focus setting wherein there is a minimal difference between the diffraction signatures of adjacent focus setting diffraction gratings;
- and
- adjusting the focus setting of the lithography device to the determined center of focus.
Dependencies are inferred from the claim text.