photolithography – ii ( part 3 ) - ntnufolk.ntnu.no/jonathrg/fag/tfe4180/slides/ch14...
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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
•Operator-controlledmanual alignment Variable repeatability
•”Overlay accuracy” problems with increased disc size
1960s, CD > 5 m (now: 0.4 m),mask, 1:1
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Lens Capturing Diffracted Light
UV
0
12
3
4
12
3
4
Lens
Quartz
Chrome Diffraction patterns
Mask
Figure 14.20 Quirk and Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Proximity 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 contamination
Negetives:
• Mask- resist gap = 2.5 – 25 m Diffraction
• Operator- controlled manual alignmentvariable repeatability
• ”Overlay accuracy” problems with increased disc size
1970s, CD > 2 m, mask, 1:1
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Edge Diffraction and Surface Reflectivity on Proximity Aligner
UV
Mask
Diffraction of light on edges results in reflections from underside of mask causing undesirable resist exposure.
UV exposure light
Substrate
Resist
Diffracted and reflected
light
Gap
Mask
Substrate
Figure 14.33 Quirk & Serda
2.5 – 25 μm
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Scanning Projection Aligner
Redrawn and used with permission from Silicon Valley Group Lithography
Mask
Wafer
Mercury arc lamp
Illuminator assembly
Scan direction
Exposure light(narrow slit of UV
gradually scans entire mask field
onto wafer)
1980s, CD > 1 m, mask, 1:1
Figure 14.34 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Step-and-Repeat Aligner (Stepper)
Single field exposure, includes: focus, align, expose, step, and repeat process
UV light source
Reticle (may contain one or more die in the reticle field)
Shutter
Wafer stage controls position of wafer in X, Y, Z, q)
Projection lens (reduces the size of reticle field for presentation to the wafer surface)
Shutter is closed during focus and alignment and removed during wafer exposure
Alignment laser
Figure 14.1 Quirk & Serda
1990s, CD > 0.25 m, reticle, 5:1
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Stepper Exposure Field
UV light
Reticle field size20 mm × 15mm,4 die per field
5:1 reduction lens
Wafer
Image exposure on wafer 1/5 of reticle field4 mm × 3 mm,4 die per exposure
Serpentine stepping
pattern
Figure 14.36 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Optical System of Lenses
Mercury lamp
Lamp position knob
Lamp monitor
Ellipsoidal mirror
Shutter
Fly’s eye lens
Flat mirror
Masking unitMirror
MirrorCollimator lens
Condenser lensCondenser lens
Optical filter
Fiber optics
Reticle
Reticle stage (X, Y, )
Projection optics
Optical focus sensorInterferometer mirror
X-drive motor
Y-drive motor
-Z drive stage
Vacuum chuckWafer stage assembly
Light sensor
Used with permission from Canon U.S.A., FPA-2000 i1 exposure systemFigure 14.14
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Step-and-Repeat Aligner (Stepper)
Used with permission from Canon USA, FPA-3000 i5 (original drawing by FG2, Austin, TX)
Figure 14.35 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Wafer Exposure Field for Step-and-Scan
5:1 lens
UVUV
Step and ScanImage Field
Scan
StepperImage Field
(single exposure)
4:1 lens
ReticleReticle Scan
Scan
Wafer WaferStepping direction
Redrawn and used with permission from ASM LithographyFigure 14.37 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Step-and-Scan SystemIlluminator
optics
Beam line
Excimer laser (193 nm ArF )
Operator console
4:1 Reduction lensNA = 0.45 to 0.6
Wafer transport system
Reticle stage
Auto-alignment systemWafer stage
Reticle library (SMIF pod
interface)
Used with permission from ASML, PAS 5500/900
Figure 14.38 Quirk & Serda
2000s, CD < 0.25 m, reticle, 4:1
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Step-and-Scan Aligner
Photograph courtesy of Silicon Valley Group Lithography, Micrascan II
Photo 14.3 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Step-and-Scan Aligner
Modern Step-and-Scan System:
http://www.asml.com/asml/show.do?ctx=6720&rid=36951
Little History:
http://www.asml.com/asml/show.do?ctx=33254&year=2006-present
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Typical NA Values for Photolithography Tools
Type of Equipment NA Value
Scanning Projection Aligner with mirrors(1970s technology) 0.25
Step-and-Repeat 0.60 – 0.68
Step-and-Scan 0.60 – 0.68
Table 14.5 Quirk & Serda
Step-and-Scan Technology in 2011: NA = 0.85 – 1.35 (immersion lithography)
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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
Reticle Vs. MaskParameter
Reticle (Pattern for Step-and-Repeat
Exposure)
Mask (Pattern for 1:1 Mask-Wafer Transfer)
Critical Dimension
Easier to pattern submicron dimensions on wafer due to larger pattern size on reticle (e.g., 4:1, 5:1).
Difficult to pattern submicron dimensions on mask and wafer without reduction optics.
Exposure Field Small exposure field that requires step-and-repeat process. Exposure field is entire wafer.
Mask Technology Optical reduction permits larger reticle dimensions – easier to print.
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
Optical Enhancement Techniques
• Phase-Shift Mask (PSM)• Optical Proximity Correction (OPC)• Off-Axis Illumination • Bias
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Phase-Shift Maskb) APSMa) BIM c) Rim PSM
Chrome Absortive phase shifters
Rim phase shifters
Blockers
-1
+10
-1
+10
+10
Intensity on wafer
Electric field on
mask
Electric field on
wafer
Reprinted from the January 1992 edition of Solid State Technology, copyright 1992 by PennWell Publishing Company
Figure 14.42 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Optical Proximity Effects
Rounded corners
Nonuniform CDs Shortened lines
Figure 14.43 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Serifs to Minimize Rounding of Contact Corners
(b) Corrected with feature biasing
(a) Uncorrected design (c) Feature assisting technique
Figure 14.45 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Off-Axis IlluminationA
B- A+
B+B+A-A-
BOff-axis illumination
(b)
Conventional illumination (on-axis)
- Order diffractio
n
+ Order diffraction
(a)
Pinhole mask
Projection optics
Wafer
Figure 14.44 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Alignment
• Baseline Compensation• Overlay Accuracy• Alignment Marks• Types of Alignment
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Optical System of Lenses
Mercury lamp
Lamp position knob
Lamp monitor
Ellipsoidal mirror
Shutter
Fly’s eye lens
Flat mirror
Masking unitMirror
MirrorCollimator lens
Condenser lensCondenser lens
Optical filter
Fiber optics
Reticle
Reticle stage (X, Y, )
Projection optics
Optical focus sensorInterferometer mirror
X-drive motor
Y-drive motor
-Z drive stage
Vacuum chuckWafer stage assembly
Light sensor
Used with permission from Canon U.S.A., FPA-2000 i1 exposure systemFigure 14.14
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Alignment
• Baseline Compensation• Overlay Accuracy• Alignment Marks• Types of Alignment
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Overlay Budget
-X +X
+Y
-YX
Y
Shift in registration
-X +X
+Y
-Y
Wafer patternReticle pattern
Perfect overlay accuracy
Figure 14.46 Quirk & SerdaTypically 1/3 of CD
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Grid of Exposure Fields on Wafer
1 2 3 4
11 12 13 14 15 16
10 9 8 7 6 5
23 24 25 26 27 28
22 21 20 19 18 17
32 31 30 29
Start
Stop
Figure 14.47 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Alignment
• Baseline Compensation• Overlay Accuracy• Alignment Marks• Types of Alignment
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
On-Axis vs. Off-Axis Alignment System
Alignmentlaser (633 nm)
Optical fiber
Video
Off-axisalignment unit
Alignment BLC fiducial
Off-Axis Alignment System
Alignmentlaser (633 nm)
Microscope objectives for video
camera
Projection optics
Wafer stage
Alignment BLC fiducial
Reticle
On-Axis Alignment System
Used with permission from Canon USA, redrawn after FPA-2000i1
schematicsFigure 14.50 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Step-and-Repeat Alignment System
Used with permission from Canon USA, FPA-2000 i1
Figure 14.48 Quirk & Serda
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
Environmental Conditions
• Temperature• Humidity• Vibration• Atmospheric Pressure• Particle Contamination
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TFE4180 Semiconductor Manufacturing Technology, Photolithography - II
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