Advanced resists for e-beam lithography: processing, exposure and characterization (Part II) Dra. Mariana Pojar de Melo Prof. Dr. Antonio Carlos Seabra Dep. Eng. de Sistemas Eletrônicos Escola Politécnica da USP mpojar@fei.edu.br, acseabra@lsi.usp.br M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 43 Processing Steps for Lithography Substrate cleaning Dehydration Adhesion Promoter Resist Spinning Pre-bake Plasma Flash Development Post-exposure Exposure Etching Hard Deposition (Lift-off) M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 44
Plasma Flash O plasma for 5s Very tricky! Before After Seabra, A.C. Uso de Resistes Amplificados Quimicamente e Sililação em Litografia pro Feixe de Elétrons, Tese de Doutorado, Escola Politecnica da USP (1997.). M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 45 Processing Steps for Lithography Substrate cleaning Dehydration Adhesion Promoter Resist Spinning Pre-bake Plasma Flash Development Post-exposure Exposure Etching Hard Deposition (Lift-off) M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 46
Hard (or post bake, HB or PB) Enhances profile stability during subsequent steps like plasma etching by careful thermal crosslinking M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 47 Processing Steps for Lithography Substrate cleaning Dehydration Adhesion Promoter Resist Spinning Pre-bake Plasma Flash Development Post-exposure Exposure Etching Hard Deposition (Lift-off) M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 48
Transferring patterns to the sample Etching (wet or dry) Metal and resist deposition resist metal Depositions Lift-off resist resist 1 Direct write resist resist 1 Exposure resist metal Development 1 resist resist1 Resist development metal Development resist resist 1 wet Etching metal Dry metal Deposition metal Lift-off M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 49 Reactive Etching ETCHING FLUX PRESSURE POWER/ RESISTS TONE GAS RATE OR (sccm) (mtorr) VOLTAGE SELECTIVITY PMMA positive CF 4 37.5 50W/ 00V 38nm/min C F 6 15 100W 30nm/min SF 6 15 100W 130nm/min ZEP-50 Positive CF 4 37.5 50W/ 00V 5.4nm/min C F 6 15 100W 0nm/min SF 6 15 100W 75nm/min HSQ Negative SiCl 4 /Ar 4/0 0 100W 11nm/min SF 6 /He 1.5/10 7.5 40W 9nm/min Calixarene Negative MC6AOAc CF 4 37.5 50W/ 00V 10nm/min Si CF 4 37.5 50W/ 00V 9nm/min SF 6 /He 1.5/10 7.5 40W 16nm/min SiO C F 6 15 100W 3nm/min M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 50
Lift-off using a Bilayer (ZEP50/PMGI) AFTER LIFT-OFF: For nanolithography, the production of highresolution objects requires a precise control of the undercut length. Cr line -90nm 90nm metal deposition ZEP-50 PMGI Cr line - 70nm Deyu et al., A ZEP 50-LOR bilayer Resist Lift-off Process by e- beam lithography for nanometer pattern Transfer, IIIE, 007. M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 51 Proximity Effect Electron Scattering in the Substrate and Resists M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 5
Proximity Effect Can be modeled by a double Gaussian : 1 1 I( r) e (1 ) r r e M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 53 May be a matrix of 50,000 x 50,000 points Proximity Effect Silicon and PMMA resist (thickness of 0,5 µm) = 0.75 (independent of beam energy) kev = 15 / 0 / 5 / 30 / 35 = 1.4 /. /.8 / 4.0 / 5.8 GaAs and PMMA resist (thickness of 0,5 µm) = 1.4 (independent of beam energy) kev = 15 / 0 / 5 / 30 / 35 = 0.7 / 1.0 / 1.3 / 1.8 /. M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 54
Proximity Effect Proximity Effect Parameters:,, M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 55 Nano Proximity Effect Software Photonic crystal 0nm, pitch 700nm Images from Raith GMBh uncorrected M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 56
Nano Proximity Effect Software Finger structure 50 nm lines 50 nm gaps Images from Raith uncorrected M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 57 Nano Proximity Effect Software Finger structure line scan results 50.1 nm 51.1 nm M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 58
Strategies to minimize the proximity effect Use thin resists Use thin s Adjust the acceleration voltage Divide the geometry into sub-structures with different doses M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 59 Proximity Effect Beam Accel. Beam Diam. Voltage spot Current Substrate Resist (nm) (kv) size (pa) α (μm) β (μm) η (μm) Si / SiO PMMA 5 10 nm 0. 0.5 1.45 1.6 0.7 Si / SiO ZEP 50A (30nm) 5 10 nm 0.505.99 1.054 spin valve / Si / SiO ZEP 50A (30nm) 5 10 nm 1.01.96 0.855 Si HSQ (40nm) 10 nm 50 8 Si HSQ (40nm) 10 nm 100 6 Si PMMA (10nm) 6,5 0. 1.9 0.45 Si PMMA (10nm) 50 0.5 1.9 0.45 Si PMMA (10nm) 1000 0.4 1.9 0.45 Si PMMA (10nm) 4000 0.5 0.35 Si PMMA (5nm) 6,5 0.5 0.5 Si PMMA (5nm) 50 0.3 0.55 Si PMMA (5nm) 1000 0.45 0.7 Si PMMA (5nm) 4000 0.5 0.5 Si PMMA (45nm) 6,5 0.35 0.75 Si PMMA (45nm) 50 0.3 0.85 Si ZEP 50A (30nm) 30 0.06 3.6 0.57 M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 60
Recommendations SOme words about resists Clearly identifiy the process to be used after exposure Evaporation/Sputtering/... Etching (Wet/Dry) PMMA has high resolution (~10nm) Barely stands dry etching, it almost evaporates! Good only for wet etching or liftoff M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 61 Recommendations Alignment Marks Must be visible under optical microscopes AND electron microscopes Crosses with about 80x80m dimension and arms of about 15m are great for our purposes Should be patterned in materials with different molecular weight compared to (gives good contrast in secondary electrons detection) or made like holes 15 80 In In next level aligned M. Pojar & A.C.Seabra Advanced resists for e-beam lithography 03/015 6