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Standard Operating Notes BNC Double Layer alignment on the UV aligner in the BNC by Lucy Hu Chrome Mask Required

Version 2015 May 21 I. Purpose This processing note outlines a microfabrication procedure written by Lucy Hu for the fabrication of multiple layers of photo resist, specifically the alignment of multiple resist layers.

II. Process procedure for the alignment of multiple resist layers on the OAI UV aligner Model 200 in the BNC.

Key to fabricating double layer designs is having appropriate fiducial (alignment marks). These should be on the outside edges of the mask sufficiently far from any important features. It is recommended to have macroscopic course alignment marks, and then finer small alignment marks clustered together.

1. Spin coat, soft bake, pattern, post exposure bake your initial layer according to protocol parameters. Now, depending on the thickness requirements of your layers, there are two potential courses of action: a. For ease of alignment, the contrast of the alignment makes can be greatly improved if the alignment marks are developed. i. If you have a sufficiently thin first layer, especially relative to the secondary layer, you can develop the entire wafer. (Sample dimensions 0.5 um first layer and 5 um second layer). If the height and feature of the first layer will affect the spin coating of the second layer, and option is to hold one edge of the wafer into SU-8 developer to only develop the alignment mark, though this is dependent on the design of the mask and is not the most ideal method. ii. After developing, rinse the wafer in IPA and then water. If only a section is developed, rinse liquid only in the direction from the features towards the edge. iii. Dehydrate wafer. b. If features cannot be developed or developing presents many potential problems, one can proceed to the next step.

2. Cut a small rectangle of scotch tape and fold itself over so you have a piece of scotch tape with no sticky sides that covers where your alignment marks are. 3. Cut a larger rectangle of scotch tape that is larger than the previously created piece, preferably with a long tail that will hang off of the wafer. 4. Stick the small piece of scotch tape to the larger piece as seen. Make sure there are sticky edges that will allow for a full seal around the smaller piece of scotch tape. 5. Place this collection of tape on top of the alignment mark, the longer tail ideally sticks off of the wafer as a easy handle to remove later. The folded over scotch tape will protect the alignment mark. Ensure the larger tape forms a full seal around the smaller scotch tape so no photoresist goes under the tape. 6. Spin coat on second layer. 7. Peel off scotch tape coverings carefully after spin coating. 8. If edge bead removal is to be done, do so now. 9. Soft bake the wafer 10. Set up the UV aligner. Load in sample. Turn on substrate vacuum. 11. Ideally, visually you will be able to manipulate the alignment marks to be approximately lined up without the microscope. 12. Ideally, your alignment marks can be seen by both microscope lenses at the same time, focus the eyepieces on the alignment marks on the mask. 13. Bringing the substrate closer to the mask will make marks easier to see, however if too close, you will not be able to move the substrate, so ensure that you are not in contact when attempting to move the x, y, and theta axis. 14. When properly aligned, bring into contact and proceed with the rest of the photolithography.

Procedure developed by Lucy Hu under support of the Bimolecular Nanotechnology Center.

Standard Operating Notes – Resolving 1μm thick lines at 5 microns pitch on the UV aligner 2