Lithographic projection apparatus, a method for determining a position of a substrate alignment mark, a device manufacturing method and device manufactured thereby
View Patent ↗Alignment to buried marks is carried out by using electromagnetic radiation to induce waves in the layers covering the buried layer. The acoustic or thermal waves cause reflectivity changes and displacements in the surface whose position and/or time dependence reveals the true position of the buried alignment mark. The buried alignment mark may be revealed by mapping the thickness of covering layers in its vicinity, e.g. by measuring the time dependence of the decay of a standing wave induced in the covering layers or by measuring the delay time of echoes of a travelling wave created at interfaces between different ones of the covering layers. Alternatively, a travelling wave can be created over the whole area of the mark so that echoes off the top and bottom of the buried mark carry positive and negative images of the mark; these cause reflectivity differences and displacements when they reach the surface which can be aligned to.
1. A method for determining a position of a substrate alignment mark, comprising:
inducing a wave in a surface layer of a substrate at least partially covering the substrate alignment mark;
measuring surface effects of the surface of said substrate where said wave has been induced;
determining a thickness of the surface layer at least partially covering the substrate alignment mark using said measuring said surface effects; and
determining the position of said substrate alignment mark using the thickness of the surface layer.
2. A method according to claim 1 , wherein said inducing a wave and said measuring the surface effects are repeated at a plurality of positions in a region of said substrate alignment mark so as to generate a map of the thickness of the surface layer at least partially covering said substrate alignment mark and said map is used in said determining the position of said substrate alignment mark.
3. A method for determining a position of a substrate alignment mark according to claim 1 , wherein said inducing a wave in a surface layer of the substrate comprises directing an excitation beam of radiation upon the surface layer of the substrate to create a physical change in the surface layer covering at least partially said substrate alignment mark.
4. A method for determining a position of a substrate alignment mark according to claim 5 , wherein said measuring surface effects of the surface of said substrate includes directing a probe beam of radiation upon the surface layer of the substrate and measuring a diffraction of the probe beam of radiation induced by the physical change in the surface layer covering at least partially said substrate alignment mark or measuring a change in reflectivity in the surfac layer covering at least partially said substrate alignment mark.
5. A device manufacturing method comprising:
providing a substrate provided with an alignment mark that is at least partially covered by a layer of radiation sensitive material;
projecting a patterned beam of radiation onto a target portion of the layer of radiation-sensitive material; and
determining a position of the substrate alignment mark, comprising:
inducing a wave in a surface layer of the substrate at least partially covering the substrate alignment mark;
measuring surface effects of the surface of said substrate where said wave has been induced; and
determining a thickness of the surface layer at least partially covering the substrate alignment mark using said measuring said surface effects; and
determining the position of said substrate alignment mark using the thickness of the surface layer.
6. A device manufactured according to the method of claim 5 .
7. A method for according to claim 5 , wherein said inducing a wave in a surface layer of the substrate comprises directing an excitation beam of radiation upon the surface layer of the substrate to create a physical change in the surface layer at least partially covering at least said substrate alignment mark.
8. A method according to claim 7 , wherein said measuring surface effects of the surface layer of said substrate includes directing a probe beam of radiation upon the surface layer of the substrate and measuring a diffraction of the probe beam of radiation induced by the physical change in the surface layer at least partially covering said substrate alignment mark or measuring a change in reflectivity in the layer at least partially covering said substrate alignment mark.