Specific Process Knowledge/Lithography/LiftOff: Difference between revisions

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-'''Feedback to this page''': '''[mailto:labadviser@danchip.dtu.dk?Subject=Feed%20back%20from%20page%20http://labadviser.danchip.dtu.dk/index.php/Specific_Process_Knowledge/Lithography/LiftOff click here]'''
+{{cc-nanolab}}
-=Comparing Lift-off equipment=
+'''Feedback to this page''': '''[mailto:labadviser@nanolab.dtu.dk?Subject=Feed%20back%20from%20page%20http://labadviser.nanolab.dtu.dk/index.php?title=Specific_Process_Knowledge/Lithography/LiftOff click here]'''
-{| border="2" cellspacing="0" cellpadding="2"
+[[Category: Equipment|Lithography liftoff]]
+[[Category: Lithography|Liftoff]]
+__TOC__
+=Lift-off Comparison Table=
+{|border="1" cellspacing="1" cellpadding="10" style="text-align:left;"
 !colspan="2" border="none" style="background:silver; color:black;" align="center"|Equipment
-|style="background:WhiteSmoke; color:black" align="center"|<b>[[Specific Process Knowledge/Lithography/LiftOff#Lift-off Wet Bench|Lift-off Wet Bench]]</b>
+|style="background:WhiteSmoke; color:black" align="center"|<b>[[Specific Process Knowledge/Lithography/LiftOff#Lift-off_wet_bench_07|Lift-off (wet bench 07)]]</b>
-|style="background:WhiteSmoke; color:black" align="center"|<b>[[Specific Process Knowledge/Lithography/LiftOff#Lift-off (4", 6")|Lift-off (4", 6")]]</b>
+|style="background:WhiteSmoke; color:black" align="center"|<b>[http://labmanager.danchip.dtu.dk/function.php?module=Machine&view=view&mach=370 Fume hood 03: Solvents]</b> - '''requires login'''
 |-
 !style="background:silver; color:black;" align="center"|Purpose
 |style="background:LightGrey; color:black"|
 |style="background:WhiteSmoke; color:black"|
-* AZ 5214E lift-off
+Lift-off of e.g. metal using
+* UV resists
+* e-beam resists
 |style="background:WhiteSmoke; color:black"|
-* AZ 5214E lift-off
+General solvent work, including lift-off.
-* AZ nLOF lift-off
+'''DO NOT''' use other fume hoods for lift-off!
+* <s>Fume hood 04: Solvents</s>
+* <s>Fume hood 08: III-V solvents</s>
+* <s>Fume hood 09: UV development</s>
+* <s>Fume hood 10: e-beam development</s>
 |-
 !style="background:silver; color:black;" align="center"|Bath chemical
 |style="background:LightGrey; color:black"|
-|style="background:WhiteSmoke; color:black" align="center"|
+|style="background:WhiteSmoke; color:black"|
-Acetone
+Lift-off bath with NMP (Remover 1165)
-|style="background:WhiteSmoke; color:black" align="center"|
-NMP (Remover 1165)
+Rinse bath with diluted IPA
+|style="background:WhiteSmoke; color:black"|
+User defined
 |-
 !style="background:silver; color:black" align="center" valign="center" rowspan="2"|Process parameters
 |style="background:LightGrey; color:black"|Process temperature
-|style="background:WhiteSmoke; color:black" align="center"|
+|style="background:WhiteSmoke; color:black"|
-Room temperature
+*Heating of the bath is possible.
-|style="background:WhiteSmoke; color:black" align="center"|
+*The heating has been limited to 60°C
-Heating of the bath is possible.
+|style="background:WhiteSmoke; color:black"|
+Heating is possible using portable hotplate or portable ultrasonic bath
-The heating has been limited to 37°C
 |-
 |style="background:LightGrey; color:black"|Ultrasonic agitation
-|style="background:WhiteSmoke; color:black" align="center"|
+|style="background:WhiteSmoke; color:black"|
-Continuous
+*Continuous or pulsed
-|style="background:WhiteSmoke; color:black" align="center"|
+*The power may be varied
-Continuous or pulsed
+|style="background:WhiteSmoke; color:black"|
+Ultrasonic agitation is possible using portable ultrasonic bath
 |-
 !style="background:silver; color:black" align="center" valign="center" rowspan="3"|Substrates
 |style="background:LightGrey; color:black"|Substrate size
-|style="background:WhiteSmoke; color:black" align="center"|
+|style="background:WhiteSmoke; color:black"|
-* 100 mm wafers
-|style="background:WhiteSmoke; color:black" align="center"|
 * 100 mm wafers
 * 150 mm wafers
+|style="background:WhiteSmoke; color:black"|
+* In principle any, typically chips
 |-
 | style="background:LightGrey; color:black"|Allowed materials
-|style="background:WhiteSmoke; color:black" align="center"|
+|style="background:WhiteSmoke; color:black"|
-All cleanroom materials
+*Silicon or glass wafers
-|style="background:WhiteSmoke; color:black" align="center"|
+*Film or patterning of all except Type IV (Pb, Te)
-All cleanroom materials
+|style="background:WhiteSmoke; color:black"|
+Any cleanroom material
 |-
 |style="background:LightGrey; color:black"|Batch
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 - 25
 |style="background:WhiteSmoke; color:black" align="center"|
-- 8
 |-
 |}
+<br clear="all" />
-<br clear="all" />
+=Lift-off process=
+[[File:Lift-off process new.png|thumb|Illustration of the lift-off process.]]
-=Lift-off Wet Bench=
+The lift-off process is used to pattern a material that can be deposited as a film on a substrate. The material is patterned by depositing the film on top of a patterned masking material, which is then dissolved, thus leaving only parts of the substrate covered in the material. Although this may in theory be done using any combination of mask and material, the most common is using photoresist as a lift-off mask for metal.
-[[Image:Acetone_lift-off.jpg|300x300px|thumb|Acetone lift-off: positioned in cleanroom 3]]
-This bench is only for wafers with metal!
+The image to the left shows a schematic of the lift off process.
+#The substrate is coated with the masking material
+#The masking material is patterned. The mask must be a negative image of the desired material pattern
+#The material is deposited on top of both mask and substrate. The mask sidewall slope should be negative in order to prevent the material covering the sidewalls during deposition
+#The masking material is dissolved, thus lifting part of the deposited material
+#The remaining material forms the desired pattern on the substrate
-'''The user manual, and contact information can be found in [http://labmanager.danchip.dtu.dk/function.php?module=Machine&view=view&mach=255 LabManager]'''
-== Process information ==
+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)
-Here are the main rules for lift-off bench use:
+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.
-*Place the wafers in a dedicated wafer holder.
-*Put the holder in the acetone and start the ultrasound. The strip off time is depending of resist thickness.
-*Rinse your wafers for 4-5 min. in running water after stripping.
-Find more info about the lift-off process here: [[Specific Process Knowledge/Photolithography/AZ5214E standard resist - reverse 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.
-<br clear="all" />
-=Lift-off (4", 6")=
+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 starting points. Consider also if the edge of the substrate (exclusion zone) could be left covered with the deposited material.
-'''The user manual, and contact information can be found in [http://labmanager.danchip.dtu.dk/function.php?module=Machine&view=view&mach=71 LabManager]'''
-== Process information ==
+'''Please note:'''
+At the DTU Nanolab cleanroom facility, it is only allowed to do lift-off in:
+*<b>[[Specific Process Knowledge/Lithography/LiftOff#Lift-off_wet_bench_07|Lift-off (Wet bench 07)]]</b>
+*<b>[http://labmanager.danchip.dtu.dk/function.php?module=Machine&view=view&mach=370 Fume hood 03: Solvents]</b> - '''requires login'''
+Other fume hoods, such as Fume hood 04: Solvents, Fume hood 09: UV development, and Fume hood 10: e-beam development, should not be used for lift-off. For an overview of the fume hoods, click [[Specific_Process_Knowledge/Overview_of_Fume_Hoods|'''here''']].
+<br clear="all" />
-bla bla bla
+{{:Specific Process Knowledge/Lithography/LiftOff/liftoff_wetbench07}}