Ion beam for target recovery
View Patent ↗A charged particle beam apparatus and method for locally removing material from a predetermined location on a workpiece, such as the removal of a metallization layer covering an alignment mark on a wafer. The invention is particularly suited for high-volume mass production of semiconductor chips or electromechanical devices. According to one embodiment of the invention, a layer of material covering an alignment mark on a wafer is removed by ion beam sputtering using a non-LMIS beam directed at an oblique angle to the sample surface.
1. A method for removing a material covering an alignment mark on a substrate, comprising:
mounting the substrate onto a stage in a focused ion beam system, said focused ion beam system having a non-liquid metal ion source;
directing an ion beam at the material covering an alignment mark, said ion beam having a beam current greater than 300 nanoamps and directed at an oblique angle relative to the surface of the substrate; and
removing said material by ion beam sputtering, said ion beam maintaining a substantially identical oblique angle relative to the surface of the substrate while material is removed by ion beam sputtering.
2. The method of claim 1 in which the focused ion beam system has a plasma ion source.
3. The method of claim 1 in which the ion beam is directed at an angle less than 80° relative to the substrate surface normal.
4. A method for removing a material covering an alignment mark on a substrate, comprising:
directing a focused ion beam of noble gas ions at the material covering an alignment mark;
said focused ion beam being directed at the substrate at an angle of between 40° and 80° relative to the substrate surface normal; and
removing said material by charged particle beam sputtering without using an etch assisting gas.
5. The method of claim 4 in which said focused ion beam is selected from the group consisting of an argon ion beam, a krypton ion beam, and a xenon ion beam.
6. The method of claim 4 in which the charged particle beam has a beam current of 300 nanoamps to 20,000 nanoamps.
7. The method of claim 4 in which the charged particle beam has a beam current of 1500 nanoamps to 5000 nanoamps.
8. The method of claim 4 in which the substrate is a silicon wafer.
9. The method of claim 4 in which the material covering an alignment mark is a metal film.
10. The method of claim 4 in which said focused ion beam is an argon ion beam.
11. An apparatus for removing a material covering an alignment mark on a substrate, comprising:
a device to load the substrate;
a device to align the substrate;
a device to position the substrate;
a noble gas ion beam system having a noble gas ion source suitable for emitting a noble gas ion beam, said source oriented at an oblique angle relative to the substrate surface normal, an optical system to focus the noble gas ion beam, and a computer controlled beam deflector to position the noble gas ion beam;
a device for controlling the charged particle beam dose applied to said material;
computer accessible memory in communication with said device to position the substrate and said device to control the charged particle beam dose applied to said material, the memory storing computer instructions for:
(i) directing a charged particle beam at material covering an alignment mark; and
(ii) removing said material by charged particle beam sputtering; and
a device to unload the substrate.
12. The apparatus of claim 11 in which the charged particle beam system is selected from the group consisting of an argon ion beam system, a krypton ion beam system, and a xenon ion beam system.
13. The apparatus of claim 11 in which the charged particle beam is directed at an angle of between 40° and 80° relative to the substrate surface normal.
14. The apparatus of claim 11 in which the charged particle beam has a beam current of 300 nanoamps to 20,000 nanoamps.
15. The apparatus of claim 11 in which the charged particle beam has a beam current of 1500 nanoamps to 5000 nanoamps.
16. The apparatus of claim 11 in which the device for aligning the substrate comprises an optical microscope.
17. A method for removing a material covering an alignment mark on a substrate, comprising:
mounting the substrate onto a stage in a focused ion beam system, said focused ion beam system having an ion column with an optical axis and a non-liquid metal ion source;
directing an ion beam at the material covering an alignment mark, said ion beam having a beam current greater than 300 nanoamps and said optical axis forming an oblique angle relative to the substrate surface normal; and
removing said material by ion beam sputtering without using an etch assisting gas.
18. The method of claim 17 in which the charged particle beam has a beam current of 300 nanoamps to 20,000 nanoamps.
19. The method of claim 17 in which the charged particle beam has a beam current of 1500 nanoamps to 5000 nanoamps.
20. The method of claim 17 in which the substrate is a silicon wafer.
21. The method of claim 17 in which the material covering an alignment mark is a metal film.
22. The method of claim 17 in which said focused ion beam is an argon ion beam.