Method for forming a microfabricated structure
View Patent ↗A method for forming a feature in a device layer, including forming a first layer of a liftoff material and a second layer of photoresist over the liftoff material, exposing the photoresist and developing the photoresist and the liftoff layer. The photoresist develops at a slower rate than the liftoff layer. The development results in a first opening in the lift off layer and a second opening in the photoresist layer wherein the first opening is smaller than the second opening because of the different developing rates. The device layer is then dry etched or ion milled through the opening. Subsequent removal of the first layer and second layer leaves a clean surface of the patterned device layer, without the fences that can be formed using other methods.
1. A method for forming a microfabricated structure on a substrate, comprising:
applying a first layer of a lift off material over a device layer to a first thickness wherein the first thickness of the lift off material is at least twice the thickness of the device layer;
applying a second layer of photoresist over the first layer to a second thickness, wherein the photoresist develops at a different rate than the lift off material;
developing the first layer and the second layer to form a first opening in the first layer and a second opening in the second layer, wherein the second opening overhangs the first opening, forming an overhang;
patterning the device layer through the first opening and the second opening; and
removing the first layer and the second layer.
2. The method of claim 1 , wherein the device layer comprises a magnetic material.
3. The method of claim 1 , wherein the lift off material comprises a polymeric material, and is deposited to a thickness of between about 0.1 microns and about 2 microns.
4. The method of claim 1 , wherein the second layer comprises at least one of a positive and a negative photoresist, and is deposited to a thickness of between about 0.1 microns and about 2 microns.
5. The method of claim 1 , wherein the device layer comprises at least one of the following: a permeable magnetic material, a permanent magnetic material, and a conductive material.
6. The method of claim 1 , wherein the device layer comprises at least one of chromium (Cr), cobalt (Co), gold (Au), platinum (Pt), nickel (Ni), iron (Fe) and alloys thereof, and is deposited to a thickness of between about 0.01 microns and about 1 microns.
7. The method of claim 1 , wherein the device layer comprises a component of at least one of an AMR and a GMR structure, a magnetic field sensor, a compass or a gyroscope.
8. The method of claim 1 , wherein the first opening and the second opening are each about 0.5 microns wide to about 9 microns wide.
9. The method of claim 1 , wherein patterning the device layer comprises ion milling an opening in the device layer using argon ions through the first opening and the second opening.
10. The method of claim 1 , further comprising:
removing the first layer and the second layer with a solvent in an ultrasonic bath.
11. The method of claim 10 , wherein the overhang of the second opening over the first opening results when the lift off material develops at a faster rate by between about 25% and about 50% compared to the photoresist.
12. The method of claim 1 , wherein the overhang of the second opening over the first opening results from continuing to develop the lift off material after the photoresist material has been completely developed.
13. The method of claim 1 , further comprising exposing the photoresist to UV radiation.
14. The method of claim 1 , further comprising re-depositing material from the device layer onto nearby surfaces of the first opening and the second opening.
15. The method of claim 14 , wherein the re-deposited material has a discontinuity between the first opening and the second opening.
16. The method of claim 14 , further comprising removing the first layer, the second layer and the re-deposited material in a single same step.
17. The method of claim 16 , wherein the single step comprises removing the lift off material, the photoresist and the re-deposited material with a solvent that includes at least one of acetone, alcohol or methanol.
18. The method of claim 17 , wherein the single step further includes heating the solvent.
19. The method of claim 1 , wherein a lateral extent of the overhang is up to 50% larger than the thickness of the device layer.