OPC Scatterbars or Assist Features

Transcription

1 OPC Scatterbars or Assist Features Main Feature The isolated main pattern now acts somewhat more like a periodic line and space pattern which has a higher quality image especially with focus when off-axis illumination is used. The bars must be small enough that the image at their location does not print. Add nonprinting adjacent features A typical size is about 1/3 of the minimum feature size and they are placed about a minimum feature size from the feature edge. 40

2 Resolution Enhancement Techniques Resolution Enhancement Emphasizes High Frequencies Conventional Illumination Binary Mask 0 Frequency 0 Frequency Phase Mask Modified Illumination Lens Capture 0 0 Frequency Frequency 0 0 Frequency In-Lens Filter Frequency Bokor, Neureuther, Oldham, Circuits and Devices,

3 Two Ray Infinite DOF Ray # 1 θ 1 θ 2 k y Ray # 2 k x When θ 1 =θ 2 the contributions from Ray #1 and Ray #2 track each exactly with axial distance and an INFINITE depth of focus is produced. Period = Pitch k Transverse = = 2k 0 2π k Transverse sin( θ ) λ sin( θ ) = NA λ Pitch = 2sin( θ ) 2NA Doubled Resolution! With infinite DOF Tim Brunner 42

4 Top Hat General Shapes Illumination Schemes Annular DOF, Contacts k 1 = 0.67 k 2 = 1.3 k 1 = 0.55 k 2 = 1.7 σ IN = σ OUT = 0.85 Quadruple H,V lines, DOF k 1 = 0.45 k 2 = 2.0 Pupil -1 1 Pupil Dipole V lines, DOF k 1 = 0.35 k 2 = Pupil H lines and contacts formed 1 via a double exposure Pupil The k1 factor is inversely proportional to the lateral separation of the illumination k 1 = 1/(2 x separation) 43

5 Phase-Shifting Mask Types Alternating (Strong) Attenuating (Weak) Used for Contacts 6% to 10% gives slope improvement of 30%. Sidelobe issue. Phase Edge Requires second trim mask exposure. Chromeless (Only 0 order) 44

6 Attenuating Phase-Shifting Masks Intensity of 6% comes from an electric field of Going from positive electric fields to negative electric fields increases edge slope and creates darker intensity near edge. 45

7 EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006 Phase-Shifting Mask: Electric Fields Sheats and Smith 46

8 Resolution Enhancement: In-Lens Filter cos ( ) j2πβ r j2πβ r 2πβr = 0.5e + 0.5e Defocus away and toward the lens. The cos(2πβr 2 ) filter creates dual defocused images that are very effective in increasing the total focal range of contact patterns. Fukuda Fukuda, JVST B Hitachi Nov/Dec 91 47

9 Double Exposure Sharp Tip uv210 on bare silicon Apex-E on on bare silicon Apex-E on 80nm silicon nitride STORM simulation of uv210 DEST assuming quencher loss on the substrate and acid loss on the surface Lei Yuan SPIE 05 STORM simulation of APEX-E DEST assuming acid loss on the substrate 48

10 Immersion Lithography Concept Imaging in a liquid medium with refractive index n offers an a factor of n reduction in resolution n 193 nm = 1.44 to 1.46 n 193nm = 1.7? Implementation: Drop and Drag Dispense water from front side of lens, use the surface tension to make the drop follow the lens, and suck in the liquid on the back of the lens. Zeiss website 49

11 Immersion Lithography: Results and Promise Larger DOF at 90nm Promise Improve resolution of 193 to that of 157 using a lower NA (0.9 => 0.77) and an increase (1.5X) in DOF. NA = 1.25 for 45 nm generation NA = 1.55 for 32 nm generation ASML web site Issues Liquid (optics), liquid (resist), liquid (machine) 50

12 EUV Projection (X-Ray ) Lithography Absorbing Mask used off-axis 13.5 nm Sn 13.4 nm wavelength NA = λ/NA = 31 nm TFR = λ/na 2 = 149 nm λ/2 layer pairs 51

13 Nano-imprint Lithography Step&Flash Imprint Lithography 30 nm dense 20 nm isolated Recent Extensions: Works over Topography Can do multiple heights (G. Willson, UT Austin) Issues: Masks, Alignment, Inspection 52