초록

Calibration of spot height offsets in a level sensor is performed on a resist-coated substrate to eliminate process dependencies of substrate position measurements obtained by the level sensor.

대표청구항 ▼

What is claimed is: 1. A device manufacturing method using a lithographic apparatus having a projection system and a level sensor system comprising a plurality of level sensor devices, the projection system configured to expose a substrate and each level sensor device configured to project a beam o

What is claimed is: 1. A device manufacturing method using a lithographic apparatus having a projection system and a level sensor system comprising a plurality of level sensor devices, the projection system configured to expose a substrate and each level sensor device configured to project a beam of light patterned by a respective grating of the level sensor device onto a surface of the substrate to be exposed, such that a surface height of the substrate is measured by the level sensor devices by detecting properties of a resulting image of the grating at respective points thereon, the method comprising: obtaining at least one calibration value for the level sensor system, the at least one calibration value compensating for a difference in measured surface heights among said plurality of level sensor devices, the at least one calibration value corresponding to a property of the substrate to be exposed; determining measured and calibrated surface heights of the substrate to be exposed using the plurality of level sensor devices based on the at least one calibration value; and, thereafter, exposing the substrate using the projection system based on the measured and calibrated surface heights. 2. The method according to claim 1, wherein the property relates to the thickness of a layer disposed in or on the surface. 3. The method according to claim 2, wherein the property is a nominal thickness value of the layer. 4. The method according to claim 2, wherein the property is a range of thickness values of the layer. 5. The method according to claim 2, wherein the layer is a layer selected from the group consisting of: resist, anti-reflective coatings, and product layers. 6. The method according to claim 1, wherein the property relates to the material properties of a layer disposed in or on the surface. 7. The method according to claim 6, wherein the layer is a layer selected from the group consisting of: resist, anti-reflective coatings, and product layers. 8. The method according to claim 1, wherein the property relates to the topology of a layer disposed in or on the surface. 9. The method according to claim 1, wherein obtaining the at least one calibration value comprises carrying out a calibration process when a resist layer having the property is disposed on the substrate. 10. The method according to claim 9, wherein the calibration process comprises measuring the position of a plurality of points on the surface of the substrate in a direction perpendicular to a nominal plane of the substrate using each of said level sensor devices. 11. The method according to claim 1, wherein obtaining the at least one calibration value comprises looking up a calibration value in a table of calibration values corresponding to different properties. 12. The method according to claim 1, wherein obtaining the at least one calibration value comprises calculating the at least one calibration value using a mathematical model of which the property is a parameter. 13. The method according to claim 1, wherein the level sensor devices are optical sensors. 14. The method according to claim 1, wherein the at least one calibration value is determined by air gauges. 15. A calibration method in a lithographic apparatus having a projection system and a level sensor system comprising a plurality of level sensor devices, the projection system configured to expose a substrate and each level sensor device configured to project a beam of light patterned by a respective grating of the level sensor device onto a surface of the substrate to measure a surface height of the substrate by detecting properties of a resulting image of the grating at respective points thereon, the method comprising: obtaining surface heights at a plurality of points on a surface of the substrate to be exposed, measuring the surface heights at the plurality of points on the surface of the substrate to be exposed using each of said level sensor devices, comparing corresponding obtained and measured surface heights and calculating corresponding calibration values, the calibration values corresponding to a property of the substrate; wherein the substrate has thereon a modified surface layer having a predetermined property. 16. The calibration method according to claim 15, wherein the modified surface layer comprises at least one of the group consisting of resist layers, anti-reflective coatings, and product layers. 17. The method according to claim 15, wherein the predetermined property is a thickness range. 18. The method according to claim 15, wherein the predetermined property is a nominal thickness value. 19. The method according to claim 15, wherein the property is a resist type. 20. The method according to claim 15, further comprising, repeating the method for a plurality of substrates, each having a predetermined property associated therewith and wherein the predetermined property associated with a first substrate of the plurality of substrates is different from the predetermined property associated with a second substrate of the plurality of substrates. 21. A lithographic apparatus having a level sensor system comprising a plurality of level sensor devices, each level sensor device configured to project a beam of light patterned by a respective grating of the level sensor device onto a surface of a substrate in order to measure a surface height of the substrate by detecting properties of a resulting image of the grating at respective points thereon, the level sensor system including a model to relate actual measurements of the level sensor devices to the predetermined surface heights, and a calibration unit configured to apply a calibration value of the model, the calibration value dependent on a property of a surface layer of a substrate being measured and wherein the calibration value is determined for a substrate that is about to be exposed using a projection system. 22. A computer program stored on a computer readable medium comprising program code to control a lithographic apparatus having a projection system and a level sensor system comprising a plurality of level sensor devices, the projection system configured to expose a substrate and each level sensor device configured to project a beam of light patterned by a respective grating of the level sensor device onto a surface of the substrate to be exposed, such that a surface height of the substrate is measured by the level sensor devices by detecting properties of a resulting image of the grating at respective points thereon, the computer program comprising: obtaining at least one calibration value for the level sensor system, the at least one calibration value compensating for a difference in measured surface heights by said plurality of level sensor devices and predetermined respective surface heights, corresponding to a property of the substrate to be exposed; measuring the surface heights of the substrate to be exposed using the level sensor devices based on the at least one calibration value; and, thereafter, exposing the substrate using the projection system based on the measured heights of its surface.