Specific Process Knowledge/Lithography/LiftOff: Difference between revisions
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[[Category: Equipment |Lithography liftoff]] | '''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]''' | ||
[[Category: Equipment|Lithography liftoff]] | |||
[[Category: Lithography|Liftoff]] | [[Category: Lithography|Liftoff]] | ||
__TOC__ | |||
=Lift-off Comparison Table= | =Lift-off Comparison Table= | ||
{| border=" | {|border="1" cellspacing="1" cellpadding="10" style="text-align:left;" | ||
!colspan="2" border="none" style="background:silver; color:black;" align="center"|Equipment | !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_07|Lift-off]]</b> | |style="background:WhiteSmoke; color:black" align="center"|<b>[[Specific Process Knowledge/Lithography/LiftOff#Lift-off_wet_bench_07|Lift-off]]</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> | |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:silver; color:black;" align="center"|Purpose | ||
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|style="background:LightGrey; color:black"| | |style="background:LightGrey; color:black"| | ||
|style="background:WhiteSmoke; color:black"| | |style="background:WhiteSmoke; color:black"| | ||
NMP (Remover 1165) | Lift-off bath with NMP (Remover 1165) | ||
Rinse bath with diluted IPA | |||
|style="background:WhiteSmoke; color:black"| | |style="background:WhiteSmoke; color:black"| | ||
User defined | User defined | ||
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At the DTU Nanolab cleanroom facility, it is only allowed to do lift-off in: | 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>[[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> | *<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''']]. | 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" /> | <br clear="all" /> | ||
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[[Image:Lift_off.jpg|300x300px|thumb|Lift-off wet bench in D-3]] | [[Image:Lift_off.jpg|300x300px|thumb|Lift-off wet bench in D-3]] | ||
The user manual, and contact information can be found in [http://labmanager.danchip.dtu.dk/function.php?module=Machine&view=view&mach=384 LabManager] - '''requires login''' | |||
{| border=" | {|border="1" cellspacing="1" cellpadding="10" style="text-align:left;" | ||
!colspan="2" border="none" style="background:silver; color:black;" align="center"|Equipment | !colspan="2" border="none" style="background:silver; color:black;" align="center"|Equipment | ||
|style="background:WhiteSmoke; color:black" align="center"| | |style="background:WhiteSmoke; color:black"; align="center";|'''Lift-off''' | ||
|- | |- | ||
!style="background:silver; color:black; | !style="background:silver; color:black;"|Purpose | ||
|style="background:LightGrey; color:black"| | |style="background:LightGrey; color:black"| | ||
|style="background:WhiteSmoke; color:black"| | |style="background:WhiteSmoke; color:black"| | ||
*Lift-off | *Lift-off of UV or E-beam resist | ||
*Resist strip of wafers with metal | *Resist strip of wafers with metal | ||
|- | |- | ||
!style="background:silver; color:black; | !style="background:silver; color:black;"|Bath chemical | ||
|style="background:LightGrey; color:black"| | |style="background:LightGrey; color:black"| | ||
|style="background:WhiteSmoke; color:black | |style="background:WhiteSmoke; color:black"| | ||
NMP (Remover 1165) | *NMP (Remover 1165) | ||
*Rinse in diluted IPA | |||
|- | |- | ||
!style="background:silver; color:black | !style="background:silver; color:black" valign="center" rowspan="2"|Process parameters | ||
|style="background:LightGrey; color:black"|Process temperature | |style="background:LightGrey; color:black"|Process temperature | ||
|style="background:WhiteSmoke; color:black | |style="background:WhiteSmoke; color:black"| | ||
Heating of the bath is possible. | Heating of the bath is possible. | ||
The heating has been limited to | The heating has been limited to 65°C | ||
|- | |- | ||
|style="background:LightGrey; color:black"|Ultrasonic agitation | |style="background:LightGrey; color:black"|Ultrasonic agitation | ||
|style="background:WhiteSmoke; color:black | |style="background:WhiteSmoke; color:black"| | ||
Continuous or pulsed | Continuous or pulsed | ||
The power may be varied | The power may be varied | ||
|- | |- | ||
!style="background:silver; color:black | !style="background:silver; color:black" valign="center" rowspan="3"|Substrates | ||
|style="background:LightGrey; color:black"|Substrate size | |style="background:LightGrey; color:black"|Substrate size | ||
|style="background:WhiteSmoke; color:black"| | |style="background:WhiteSmoke; color:black"| | ||
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|- | |- | ||
| style="background:LightGrey; color:black"|Allowed materials | | style="background:LightGrey; color:black"|Allowed materials | ||
|style="background:WhiteSmoke; color:black | |style="background:WhiteSmoke; color:black"| | ||
Silicon or glass wafers | Silicon or glass wafers | ||
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|- | |- | ||
|style="background:LightGrey; color:black"|Batch | |style="background:LightGrey; color:black"|Batch | ||
|style="background:WhiteSmoke; color:black | |style="background:WhiteSmoke; color:black"| | ||
1 - 25 | 1 - 25 | ||
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<br clear="all" /> | <br clear="all" /> | ||
== Process information == | |||
Lift-off is used for lift-off using resists that are soluble in NMP (''N''-Methyl-Pyrrolidone), supplied in the cleanroom as "Remover 1165". Both AZ 5214E and AZ nLOF are soluble in NMP. | Lift-off is used for lift-off using resists that are soluble in NMP (''N''-Methyl-Pyrrolidone), supplied in the cleanroom as "Remover 1165". Both AZ 5214E and AZ nLOF are soluble in NMP. | ||
For information on processing of AZ nLOF, or image reversal of AZ 5214E, see here: [[Specific_Process_Knowledge/Lithography/ | For information on processing of AZ nLOF, or image reversal of AZ 5214E, see here: [[Specific_Process_Knowledge/Lithography/Resist/UVresist|Resist Overview]]. | ||
<br clear="all" /> | <br clear="all" /> | ||
==Poor metal (TiPt) adhesion/ Metal delaminating after lift-off== | |||
''This experiment was done by Gustav E. Skands(ges@sbtinstruments.com) in May 2024'' | |||
This entry details an observed issue with metal adhesion during a Ti/Pt deposition (10/160 nm) and lift-off process within DTU Nanolab. The employed photoresist was TI Spray from MicroChemicals, which is believed (but not confirmed) to share many properties with AZ5214E. The thickness of the resist was approximately 5 µm, and it was spray coated onto the substrate using the Spray Coater. | |||
'''Root cause:''' | |||
The core of the adhesion challenge was linked to the choice of photoresist developer. 2.08% TMAH facilitated excellent resist pattern development, but subsequent metal adhesion during the deposition process was consistently poor, observed across both Wordentec and both Temescal systems. This occurred despite the absence of any visible residues on the substrate surface. Attempts to enhance adhesion, including a descum procedure using 70 mL/min O2 and 70 mL/min N2, 150W, 5 minutes, prior to deposition, were unsuccessful. | |||
'''Solution:''' | |||
Changing the developer to AZ351B (2 minutes development time in beaker) in the process provided significant improvements. Although AZ351B exhibited reduced selectivity in dissolving the soluble vs. insoluble resist, thereby compromising the precision of the resist pattern, it considerably improved the adhesion properties of the deposited metal. | |||
A dual developer approach—using TMAH (3x 60s development in Developer: TMAH UV-lithography followed by a 30 second development step in AZ351B—was therefore implemented. This approach leveraged the high-resolution patterning capability of TMAH and the superior adhesion characteristics provided by AZ351B. | |||
The different adhesion properties observed with the two developers suggest underlying molecular interactions that may inhibit or promote metal-substrate bonding. It is hypothesized that TMAH may leave molecular residues that, although not detectable through optical inspection, could create a barrier to adhesion at the molecular level. Conversely, AZ351B appears to modify or clear these residues, thereby enhancing adhesion. | |||
A descum step of 70 mL/min O2 and 70 mL/min N2, 150W, 5 minutes, was still performed immediately before deposition. However, it is unknown if this has an effect. | |||
Process temperature considerations | |||
The process incorporated a deposition temperature of 50°C, which was maintained without further comparative analysis against room temperature deposition due to the successful outcomes achieved and considerations of operational cost efficiency. | |||
==Poor metal (TiAu) adhesion/ Metal delaminating after lift-off== | |||
''This experiment was done by Mathias Zambach (zambach@fysik.dtu.dk) in June 2024'' | |||
'''Problem:''' Mathias experienced the delamination of TiAu after the lift-off process, see the image. | |||
'''Solution:''' Adding a descum step (70 ml/min O2, 70 ml/min N2, 150W, 5 min (Plasma Asher 1)) right before metal depositions. | |||
[[File:Delamination of TiAu.jpg|thumb]] | |||
The process flow: | |||
1.) 2 um nLOF coating | |||
2.) Exposure | |||
3.) Development of nLOF | |||
'''4.) 5 min descum (70 ml/min O2, 70 ml/min N2, 150W, 5 min in Plasma Asher 1) was done right before TiAu deposition''' | |||
5.) 10 nm Ti depositing with 2 A/s by Temescal | |||
6.) 200 nm Au depositing with 2 A/s by Temescal | |||
7.) Lift-off (approx. 45 min) | |||
By adding step 4.) 5 min Descum, the problem with the delamination of metals was solved. | |||