1 TFE4180 Semiconductor Manufacturing Technology, Photolithography - II Photolithography – II ( Part 3 ) Chapter 14 : Semiconductor Manufacturing Technology by M. Quirk & J. Serda Saroj Kumar Patra, Department of Electronics and Telecommunication, Norwegian University of Science and Technology ( NTNU )
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Photolithography – II ( Part 3 )Chapter 14 : Semiconductor Manufacturing Technology by M. Quirk & J. Serda
Saroj Kumar Patra,Department of Electronics and Telecommunication,
Norwegian University of Science and Technology ( NTNU )
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Objectives
1. Discuss each of the five equipment eras for alignment and exposure.
2. Describe reticles, explain how they are manufactured and discuss their use in microlithography.
3. Discuss the optical enhancement techniques for sub-wavelength lithography.
4. Explain how alignment is achieved in lithography.
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Ten steps of Photolithography
10) Develop inspect7) Post-exposure bake (PEB)
8) Develop 9) Hard bake
UV Light
Mask
6) Alignmentand Exposure
Resist
4) Spin coat 5) Soft bake1-3) Vapor prime
HMDS
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Photolithography Exposure Equipment
• Contact Aligner: 1960s, CD > 0.4 m (CD > 5 m), mask, 1:1 • Proximity Aligner: 1970s, CD > 2 m, mask, 1:1 • Scanning Projection Aligner (scanner): 1980s, CD > 1 m,
mask, 1:1 • Step-and-Repeat Aligner (stepper): 1990s, CD > 0.25 m,
reticle, 5:1 (4:1) • Step-and-Scan System: 2000s, CD < 0.25 m, reticle, 4:1 (5:1)
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Contact Aligner System
Illuminator
Alignment scope (split
vision)Mask
Wafer
Vacuum chuck
Mask stage (X, Y , Z ,
Wafer stage (X, Y, Z,
Mercury arc lamp
Figure 14.32 Quirk & Serda
Positives:
• Avoids diffraction problems
Negetives:
• Particle contamination Mask must be replaced after 5-25 exposures
Mask has same critical dimensions as wafer – more difficult to print.
Throughput Requires sophisticated automation to step-and-repeat across wafer.
Potentially higher (not always true if equipment is not automated).
Die alignment & focus Adjusts for individual die alignment & focus.
Global wafer alignment, but no individual die alignment & focus.
Defect density
Improved yield but no reticle defect permitted. Reticle defects are repeated for each field exposure.
Defects are not repeated multiple times on a wafer.
Surface flatness
Stepper compensates during initial global pre-alignment measurements or during die-by-die exposures.
No compensation, except for overall global focus and alignment.
Table 14.6 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Reticles
• Comparison of Reticle Versus Mask• Reticle Materials
- Cr pattern (opaque) on fused silica (high optical transmission and low thermal expansion)- chrome thickness < 1000 Å- Sometimes 200 Å of CrO ARC on the Cr
• Reticle Reduction and Size• Reticle Fabrication• Sources of Reticle Damage
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Reticles
• Comparison of Reticle Versus Mask• Reticle Materials• Reticle Reduction and Size• Reticle Fabrication• Sources of Reticle Damage
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Comparison of Reticle Reduction Versus Exposure Field
Field size on reticle
Projection lens
Exposure field on wafer
Lens Type 10:1 5:1 4:1 1:1
Reticle FieldSize (mm)
100 × 100 100 × 100 100 × 100 30 × 30
Exposure Fieldon Wafer (mm)
10 × 10 20 × 20 25 × 25 30 × 30
Die per Field ofExposure(assume 5mm ×5mm die size)
4 16 25 36
Figure 14.39 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Reticles
• Comparison of Reticle Versus Mask• Reticle Materials• Reticle Reduction and Size• Reticle Fabrication (e-beam lithography p. 396)• Sources of Reticle Damage
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Reticles
• Comparison of Reticle Versus Mask• Reticle Materials• Reticle Reduction and Size• Reticle Fabrication• Sources of Reticle Damage
- dropping the reticle- surface scratching- electrostatic discharge (ESD)- particles of dirt
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Reticles
The particle on the pellicle surface is outside of optical focal range.
Antireflective coatings Pellicle filmChrome patternDepth of focus
Mask material
Reticle
Pellicle film
Frame
Chrome pattern
Figure 14.41 Quirk & Serda
5 – 10 mm separation
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Photolithography Reticle
Photograph courtesy of Advanced Micro Devices
Photo 14.2 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II