Specific Process Knowledge/Lithography/LiftOff: Difference between revisions

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 *'''4'''. The masking material is dissolved, thus lifting part of the deposited material.
 *'''5'''. The remaining material forms the desired pattern on the substrate.
+A successful lift-off process is dependent on many factors, including:
+*Resist sidewall angle
+*Resist thickness relative to the deposited material
+*Layout of the design, especially the regions surrounding the device(s)
+If the resist sidewall angle is positive, the deposited material will coat the sidewall, thus preventing the solvent from reaching and dissolving the resist. Ultrasonic agitation may be able to pierce the material deposited on top of resist, allowing lift-off. A a positive sidewall angle will typically result in a very slow lift-off process, as well as line edge roughness of the deposited material. A negative, or at least vertical, resist sidewall is usually needed for a successful lift-off process.
+If the resist layer used for lift-off is too thin compared to the deposited layer, solvent access to the resist may be limited, due to partial or full coverage of the sidewalls. This would result in a slow lift-off, possibly with line edge roughness of the deposited material. As a rule of thumb, the resist should be 5-10 times thicker than the deposited material.
+Small, tightly packed structures result in a very fast lift-off process. It is usually the big, uncovered areas between or around the device(s) that limit the lift-off speed. The less of the deposited material is to remain on the substrate after lift-off, the longer the sample has to spend in the lift-off solvent while resist under the deposited material is being dissolved and transported out. During the design of the pattern used for lift-off, it should be considered to fill any voids between devices with lift-off assisting dummy structures (e.g. hatching or squares/circles), in order to punctuate the open spaces, and allow for multiple, parallel onsets of the lift-off.