Semiconductor Manufacturing Technologyweng/courses/IC...Semiconductor Manufacturing Technology...
Transcript of Semiconductor Manufacturing Technologyweng/courses/IC...Semiconductor Manufacturing Technology...
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Semiconductor Manufacturing Technology
Michael Quirk & Julian Serda© October 2001 by Prentice Hall
Chapter 14
Photolithography: Alignment and Exposure
Semiconductor Manufacturing Technology
Michael Quirk & Julian Serda© October 2001 by Prentice Hall
Chapter 14
Photolithography: Alignment and Exposure
© 2000 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Three Functions of the Wafer Stepper
1. Focus and align the quartz plate reticle(that has the patterns) to the wafer surface.
2. Reproduce a high-resolution reticle image on the wafer through exposure ofphotoresist.
3. Produce an adequate quantity of acceptable wafers per unit time to meet production requirements.
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Reticle Pattern Transfer to Resist
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, θ)
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
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Layout and Dimensions of Reticle Patterns
4) Poly gate etch1) STI etch 2) P-well implant 3) N-well implant
8) Metal etch5) N+ S/D implant 6) P+ S/D implant 7) Oxide contact etch
Top view
1
23
45
7
6
8 Cross section
Resulting layers
Figure 14.2
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Optical Lithography
Light Wavelength and Frequency
λ
λ = vf
Laser
v = velocity of light, 3 ´ 108 m/secf = frequency in Hertz (cycles per second)λ = wavelength, the physical length of one
cycle of a frequency, expressed in meters
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Wave Interference
A
B
A+B
Waves in phase Waves out of phase
Constructive Destructive
Figure 14.4
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Optical Filtration
Secondary reflections (interference)
Coating 1 (non-reflecting)
Coating 3
Glass
Coating 2
Reflected wavelengths
Transmitted wavelength
Broadband light
Figure 14.5
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Optical Lithography
Exposure Sources• Mercury Arc Lamp• Excimer Laser
– Spatial Coherence
• Exposure Control
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Emission Spectrum of Typical High Pressure Mercury Arc Lamp
120
100
80
60
40
20
0
200 300 400 500 600Wavelength (nm)
Rel
ativ
e In
tens
ity (%
) h-line405 nm
g-line436 nm
i-line365 nm
DUV248 nm
Emission spectrum of high-intensity mercury lamp
Mercury lamp spectrum used with permission from USHIO Specialty Lighting Products
Figure 14.7
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Mercury Arc Lamp Intensity Peaks
UV Light Wavelength (nm) Descriptor CD Resolution (µm)
436 g-line 0.5405 h-line 0.4365 i-line 0.35248 Deep UV
(DUV)0.25
Table 14.2
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Spectral Emission Intensity of 248 nm Excimer Laser vs. Mercury Lamp
100
80
60
40
20
0
Rel
ativ
e In
tens
ity (%
)
KrF laser
280210 240 260220
Wavelength (nm)
Hg lamp
Figure 14.8
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Excessive Resist Absorption of Incident Light
Photoresist (after develop)
Substrate
Sloping profile
Figure 14.9
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Optical Lithography
Optics• Reflection of Light• Refraction of Light• Lens• Diffraction• Numerical Aperture, NA• Antireflective Coating
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Law of Reflection
θi θrIncident light Reflected light
Law of Reflection: θi = θr
The angle of incidence of a light wavefront with a plane mirror is equal to the angle of reflection.
Figure 14.11
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Refraction of Light Based on Two Mediums
• Snell’s Law: sin θi = n sin θr
• Index of refraction, n = sin θi / sin θr
θθair (n ≅ 1.0)
glass (n = 1.5)
fast medium
slow medium
θθ
air (n ≅ 1.0)
glass (n = 1.5)
fast medium
slow medium
Figure 14.13
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Interference Pattern from Light Diffraction at Small Opening
• Light travels in straight lines.• Diffraction occurs when light hits edges of objects.• Diffraction bands, or interference patterns, occur when light waves
pass through narrow slits.
Diffraction bands
Figure 14.18
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Diffraction in a Reticle Pattern
Slit
Diffracted light rays
Plane light wave
Figure 14.19
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Lens Capturing Diffracted Light
UV
0
12
3
4
12
3
4
Lens
Quartz
Chrome Diffraction patterns
Mask
Figure 14.20
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Effect of Numerical Aperture on Imaging
Figure 14.21
Exposure light
Lens NA
Pinhole masks
Image results
Diffracted light
Good
Bad
Poor
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
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
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Photoresist Reflective Notching Due to Light Reflections
Polysilicon
Substrate
STISTI
UV exposure light
Mask
Exposed photoresist
Unexposed photoresist
Notched photoresist
Edgediffraction
Surfacereflection
Figure 14.22
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Incident and Reflected Light Wave Interference in Photoresist
Standing waves cause nonuniform exposure along the thickness of the photoresist film.
Incident wave
Reflected wave
PhotoresistFilm
Substrate
Figure 14.23
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Effect of Standing Waves in Photoresist
Photograph courtesy of the Willson Research Group, University of Texas at Austin
Photo 14.1
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Antireflective Coating to Prevent Standing Waves
The use of antireflective coatings, dyes, and filters can help prevent interference.
Incident wave Antireflective coating
PhotoresistFilm
Substrate
Figure 14.24
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Light Suppression with Bottom Antireflective Coating
BARCPolysilicon
Substrate
STISTI
UV exposure light
Mask
Exposed photoresist
Unexposed photoresist
Figure 14.25
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
BARC Phase-Shift Cancellation of Light
(A) Incident light
Photoresist
BARC (TiN)Aluminum
C and D cancel due to phase difference
(B) Top surface reflection
(C)(D)
Figure 14.26
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Top Antireflective Coating
Incident light
Photoresist
Resist-substrate reflections
Substrate
Incident light
Photoresist
Substrate reflection
Substrate
Top antireflective coating absorbs substrate reflections.
Figure 14.27
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Optical Lithography
Resolution• Calculating Resolution• Depth of Focus• Resolution Versus Depth of Focus
– Surface Planarity
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Resolution of Features
2.0
1.0
0.5
0.10.25
The dimensions of linewidths and spaces must be equal. As feature sizes decrease, it is more difficult to separate features from each other.
Figure 14.28
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Calculating Resolution for a given λ, NA and k
Lens, NA
Wafer
Mask
Illuminator, λ
R
k = 0.6
λ ΝΑ R365 nm 0.45 486 nm365 nm 0.60 365 nm193 nm 0.45 257 nm193 nm 0.60 193 nm
i-line
DUV
k λNAR =
Figure 14.29
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Depth of Focus (DOF)
+
-
Photoresist
Film
Depth of focusCenter of focusCenter of focus
Lens
Figure 14.30
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Resolution Versus Depth of Focus for Varying NA
λ 2(NA)2DOF =
Photoresist
Film
Depth of focusDepth of focusCenter of focus
++
--Lens, NA
Wafer
Mask
Illuminator, λ
DOF
λ ΝΑ R DOF365 nm 0.45 486 nm 901 nm365 nm 0.60 365 nm 507 nm193 nm 0.45 257 nm 476 nm193 nm 0.60 193 nm 268 nm
i-line
DUV
Figure 14.31
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Photolithograhy Equipment
• Contact Aligner• Proximity Aligner• Scanning Projection Aligner (scanner)• Step-and-Repeat Aligner (stepper)• Step-and-Scan System
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Contact/Proximity Aligner System
Illuminator
Alignment scope (split
vision)Mask
Wafer
Vacuum chuck
Mask stage (X, Y , Z , θ)
Wafer stage (X, Y, Z, θ)
Mercury arc lamp
Used with permission from Canon USA, Figure 14.32
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
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
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Scanning Projection Aligner
Redrawn and used with permission from Silicon Valley Group Lithography
Mask
Wafer
Mercury arc lamp
Illuminator assembly
Projection optics assembly
Scan direction
Exposure light(narrow slit of UV
gradually scans entire mask field onto wafer)
Figure 14.34
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Step-and-Repeat Aligner (Stepper)
Used with permission from Canon USA, FPA-3000 i5 (original drawing by FG2, Austin, TX)
Figure 14.35
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
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
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
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
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
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
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Step and Scan Exposure 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 system
Wafer stage
Reticle library (SMIF pod interface)
Used with permission from ASML, PAS 5500/900Figure 14.38
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Reticles
• Comparison of Reticle Versus Mask• Reticle Materials• Reticle Reduction and Size• Reticle Fabrication• Sources of Reticle Damage
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Comparison of Reticle Versus Mask
ParameterReticle
(Pattern for Step-and-RepeatExposure)
Mask(Pattern for 1:1 Mask-Wafer Transfer)
Critical Dimension
Easier to pattern submicrondimensions on wafer due to largerpattern size on reticle (e.g., 4:1,5:1).
Difficult to pattern submicron dimensions onmask and wafer without reduction optics.
Exposure Field Small exposure field that requiresstep-and-repeat process. Exposure field is entire wafer.
Mask TechnologyOptical reduction permits largerreticle dimensions – easier toprint.
Mask has same critical dimensions as wafer –more difficult to print.
Throughput Requires sophisticated automationto step-and-repeat across wafer.
Potentially higher (not always true if equipmentis not automated).
Die alignment & focus Adjusts for individual diealignment & focus.
Global wafer alignment, but no individual diealignment & focus.
Defect density
Improved yield but no reticledefect permitted. Reticle defectsare repeated for each fieldexposure.
Defects are not repeated multiple times on awafer.
Surface flatness
Stepper compensates during initialglobal pre-alignmentmeasurements or during die-by-die exposures.
No compensation, except for overall global focusand alignment.
Table 14.6
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Photolithography Reticle
Photograph courtesy of Advanced Micro Devices
Photo 14.2
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
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
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Principles of Electron Beam Lithography
Work chamber, load chamber,vibration isolation, ion pump, and vacuum system
Work Station
Transfer and drive
Stage position control
Height deflection
and dynamic
correction
Vacuum control module
TFE electron source control
Electron beam controlServo control
Operator console
9-track magnetic tape drive
Control computer
Super flash HTM
Printer/Plotter
Electronics Console
Data direct computer
Height detection assembly
Work table
Beam control and deflection
TFE electron beam column
Automatic loading chamberWork stage
Dynamic corrections
Utility Console
Cassette clamping control
Temperature control
Coolant flow
control
Air and nitrogen control
Water chiller
Backing pump
Roughing pump
Used with permission from Etec Systems, Inc., MEBES 4500 SystemsFigure 14.40
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Optical Enhancement Techniques
• Phase-Shift Mask (PSM)• Optical Proximity Correction (OPC)• Off-Axis Illumination • Bias
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Phase-Shifting Mask
b) 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
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Optical Proximity Effects
Rounded corners
Nonuniform CDs Shortened lines
Figure 14.43
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Off-Axis Illumination
A
B- A+
B+B+A-A-
BOff-axis illumination
(b)
Conventional illumination (on-axis)
- Order diffraction
+ Order diffraction
(a)
Pinhole mask
Projection optics
Wafer
Figure 14.44
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Serifs to Minimize Rounding of Contact Corners
(b) Corrected with feature biasing
(a) Uncorrected design (c) Feature assisting technique
Figure 14.45
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Alignment
• Overlay Accuracy• Alignment Marks
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Overlay Budget
-X +X
+Y
-Y∆X
−∆Y
Shift in registration
-X +X
+Y
-Y
Wafer patternReticle pattern
Perfect overlay accuracy
Figure 14.46
© 2001 by Prentice HallSemiconductor Manufacturing Technologyby Michael Quirk and Julian Serda
Alignment Marks
2nd Mask
1st Mask
2nd mask layer
1st mask layer
RA, Reticle alignment marks, L/RGA, Wafer global alignment marks, L/RFA, Wafer fine alignment marks, L/R
+ +++
RAL
RAR+ GA
+ FAL
+ FAR
+ GAR
+ GAL
Notch, coarse alignment
FAL
FAR
FAL/R +
+FAL/R +
For 2nd mask
+ From 1st mask
{
Figure 14.49