Method and apparatus for reducing substrate edge effect during inspection
An apparatus and method are introduced in this invention to reduce the edge effect of a substrate that causes image variation or distortion due to applied substrate bias. An edge plate with an edge effect eliminator are provided such that substrate is inspected by a charged particle beam can capture images without distortion at substrate edge.
1. A method for reducing edge effect of a substrate, comprising steps of:
capturing a central image and a peripheral image of a patterned surface of the substrate by using a charged particle beam; and
applying a voltage between the substrate and an edge plate enclosing the substrate, wherein the voltage is determined according to a difference between the central image and the peripheral image.
2. The method of claim 1 , wherein the edge plate is conductive with a top surface thereof substantial in the same height as the surface of the substrate.
3. The method of claim 1 , wherein a polarity of the voltage can be positive or negative correlated to a level of differences between the central image and the peripheral image.
4. The method of claim 3 , wherein a value of the voltage is proportional to the level of differences between the central image and the peripheral image.
5. The method of claim 4 , wherein the peripheral image differs from the central image in a level of distortion measured by a scaling factor.
6. The method of claim 4 , wherein the peripheral image differs from the central image in a level of shifting measured by an offset distance.
7. The method of claim 4 , wherein the peripheral image differs from the central image in a level of focus measured by a focus current/voltage change.
8. The method of claim 1 , further comprising a step of flooding the surface of the substrate before the capturing step.
9. A system for reducing edge effect of a substrate during inspection, comprising:
an inspection tool with a charged particle beam as a probe;
a substrate holding device with an edge plate enclosing the substrate, said substrate holding device for holding a substrate; and
means for applying a voltage between the substrate and the edge plate, wherein the voltage is determined by a difference between a central image and a peripheral image of a patterned surface of the substrate at targeting locations, wherein the central image and the peripheral image are captured by the same inspection tool for inspection.
10. The system of claim 9 , wherein the edge plate is conductive with a top surface thereof substantial in the same height as the surface of the substrate.
11. The system of claim 9 , wherein the peripheral image has distorted patterns compared to the central image.
12. The system of claim 9 , wherein the peripheral image has shifted patterns compared to the central image.
13. The system of claim 9 , wherein the peripheral image has defocused patterns compared to the central image.
14. The system of claim 9 , wherein the voltage is determined by a level of distortion measured by a scaling factor between the central and the peripheral images.
15. The system of claim 9 , wherein the voltage is determined by a level of shifting measured by a distance between the central and the peripheral images.
16. The system of claim 9 , wherein the voltage is determined by a level of defocus measured by a focus current/voltage change between the central and the peripheral images.
17. The system of claim 9 , wherein a polarity of the voltage can be positive or negative determined by a level of difference between the central and the peripheral images.
18. The system of claim 9 , wherein the inspection tool is a charged particle beam inspection tool.
19. A method for reducing edge effect of a substrate during inspection, comprising steps of:
pre-scan or irradiate a surface of the substrate with a charged particle beam to achieve a certain level of a surface charging;
capturing a central image of the surface of the substrate by using the charged particle beam;
capturing a peripheral image of the surface of the substrate by using the charged particle beam;
determining a voltage between an edge plate and the substrate according to a difference between the central image and the peripheral image; and
applying the voltage to the edge plate enclosing the substrate.
20. The method of claim 19 , wherein the surface charging can be positive or negative.
21. The method of claim 19 , wherein the edge plate is conductive with a top surface thereof substantial in the same height as the surface of the substrate.
22. The method of claim 19 , wherein a polarity of the voltage is positive or negative correlated to measures of a difference between the central and the peripheral images.
23. The method of claim 22 , wherein a value of the voltage is proportional to the measures of the difference between the central and the peripheral images.
24. The method of claim 22 , wherein the difference between the central and the peripheral images is of distortion measured by a scaling factor.
25. The method of claim 22 , wherein the difference between the central and the peripheral images is a position shift measured by a distance.
26. The method of claim 22 , wherein the difference between the central and the peripheral images is a focus change measured by a focus current/voltage.