EE143 F05 Lecture 12 1 Contact to source drain of MOSFET Al SiO2 SiO2 ideal n p Si Al SiO2 Alignment error Professor N Cheung U C Berkeley SiO2 n short ohmic contact p Si 1 EE143 F05 Lecture 12 Solution Design n region larger than contact hole Al SiO2 SiO2 n Professor N Cheung U C Berkeley 2 EE143 F05 Lecture 12 2 Poly Gate Overlap over FOX Ideal Fox poly gate Professor N Cheung U C Berkeley S D implant Electrical n short With alignment error 3 EE143 F05 Lecture 12 Solution Make poly gate longer to overlap the FOX Professor N Cheung U C Berkeley 4 EE143 F05 Lecture 12 Total Overlay Tolerance 2 total i 2 i i std deviation of overlay error for ith masking step total std deviation for total overlay error Layout design rule specification should be total Professor N Cheung U C Berkeley 5 EE143 F05 Lecture 12 Standing Waves Photoresist has a finite thickness hv Higher Intensity Faster Development rate Lower Intensity Slower Development rate Positive Photoresist substrate Positive Photoresist After development substrate Professor N Cheung U C Berkeley 6 EE143 F05 Lecture 12 Standing reflecting wave effect surface Air Photoresist Oxide Resist Resistprofile profileand andenergy energy deposition depositiondepend dependon on oxide oxidethickness thicknessunderneath underneath see seehandout handoutfor forderivation derivation E 4 E 3 E 2 E 1 x 0 x dr x d T 1 I23 x E x E3 x 2dt T 2 I23 max 0 1 E2 E3 2 2E2E3sin2 k d x 2 1 1 I23 max E2 E3 2 I 23 min E2 E3 2 2 2 I23 min x 2 n d x 0 2 2 n Intensity m axima occur at d x 2 3 2 5 2 d Intensity m inim a occur at Professor N Cheung U C Berkeley 7 EE143 F05 Lecture 12 x P R d SiO2 Si substrate Intensity minimum when x d m Intensity maximum when x d m 2n 4n m 0 1 2 m 1 3 5 n refractive index of resist Professor N Cheung U C Berkeley 8 EE143 F05 Lecture 12 Simulated Resist Cross section as function of development time Professor N Cheung U C Berkeley 9 EE143 F05 Lecture 12 Proximity Scattering Professor N Cheung U C Berkeley 10 EE143 F05 Lecture 12 Approaches for Reducing Substrate Effects Use absorption dyes in photoresist Use anti reflection coating ARC Use multi layer resist process 1 thin planar layer for high resolution imaging imaging layer 2 thin develop stop layer used for pattern transfer to 3 etch stop 3 thick layer of hardened resist planarization layer Professor N Cheung U C Berkeley 11 EE143 F05 Electron Beam Lithography 12 3 V Lecture 12 Angstroms for V in Volts Example 30 kV e beam 0 07 Angstroms NA 0 002 0 005 Resolution 1 nm But beam current needs to be 10 s of mA for a throughput of more than 10 wafers an hour Professor N Cheung U C Berkeley 12 EE143 F05 Lecture 12 Low Throughput for both raster and vector scanning Serial Process Variable Beam shape EBL Stencil Mask EBL Professor N Cheung U C Berkeley 13 e be a m lithogra phy EE143 F05 Lecture 12 re s olution fa ctors be a m qua lity 1 nm s e conda ry e le ctrons la te ra l ra nge fe w nm pe rforma nce re cords orga nic re s is t P MMA inorga nic re s is t b v AlF 3 Professor N Cheung U C Berkeley 7 nm 1 2 nm 14 EE143 F05 Lecture 12 The Proximity Effect Monte Carlo simulation of electron trajectories Professor N Cheung U C Berkeley 15 EE143 F05 X Ray Source Lecture 12 Synchrotron Radiation Professor N Cheung U C Berkeley 16 EE143 F05 Lecture 12 X Ray Proximity Printing 10 Angstroms lm g Professor N Cheung U C Berkeley 17 EE143 F05 Lecture 12 X Ray Projection Lithography Professor N Cheung U C Berkeley 18 EE143 F05 Lecture 12 Alpha Machine for EUV Lithography Stulen Sweeny Professor N Cheung U C Berkeley 19 EE143 F05 Lecture 12 Resist patterned by Extreme UV Lithography Professor N Cheung U C Berkeley 20 EE143 F05 Professor N Cheung U C Berkeley Lecture 12 21 EE143 F05 Lecture 12 Immersion Lithography A liquid with index of refraction n 1 is introduced between the imaging optics and the wafer Advantages 1 Resolution is improved proportionately to n For water the index of refraction at 193 nm is 1 44 improving the resolution significantly from 90 to 64 nm 2 Increased depth of focus at larger features even those that are printable with dry lithography Professor N Cheung U C Berkeley 22 EE143 F05 Lecture 12 B J Lin Sept 02 Drag a drop schemes also being considered by UTA Professor N Cheung U C Berkeley 23 EE143 F05 Professor N Cheung U C Berkeley Lecture 12 24 EE143 F05 Lecture 12 For Foryour yourreference referenceonly only Professor N Cheung U C Berkeley 25
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