SMT14~1

Figure 14.10
SMT14~1
Optical Lithography
Optics
• Reflection of Light • Refraction of Light • Lens • Diffraction • Numerical Aperture, NA • Antireflective Coating
Alignment laser
Shutter is closed during focus and alignment and removed during wafer exposure
Single field exposure, includes: focus, align, expose, step, and repeat process
Sloping profile
Substrate
Figure 14.9
SMT14~1
Excimer Laser Sources for Semiconductor Photolithography
Table 14.3
SMT14~1
Spatial Coherence
Black box illuminator
SMT14~1
Optical Filtration
Broadband light
Reflected wavelengths
Coating 1 (non-reflecting) Coating 2 Coating 3
Glass
Secondary reflections (interference)
Transmitted wavelength
Figure 14.5
SMT14~1
Ultraviolet Spectrum
EUV
Ultraviolet spectrum
(nm)
Visible spectrum
VUV DUV
Mid-UV
Violet Blue Green Yellow Orange Red
4 50 100 150 200 250 300 350 400 450 500 550 600 650 700
Law of Reflection: qi = qr
Figure 14.11
SMT14~1
Flat mirror
Application of Mirrors
Illuminator for a simple aligner
Ellipsoidal mirror
Mask
Flat mirror
Used with permission from Canon USA
Figure 14.12
SMT14~1
Refraction of Light Based on Two Mediums
• Snell’s Law: sin qi = n sin qr • Index of refraction, n = sin qi / sin qr
fast medium
air (n 1.0)
– Spatial Coherence
• Exposure Control
SMT14~1
Emission Spectrum of Typical High Pressure Mercury Arc Lamp
Relative Intensity (%)
Emission spectrum of high-intensity mercury lamp 120
Figure 14.1
SMT14~1
Layout and Dimensions of Reticle Patterns
1) STI etch
2) P-well implant
3) N-well implant
4) Poly gate etch
5) N+ S/D implant
6) P+ S/D implant 7) Oxide contact etch
4. Explain resolution, describe its critical parameters, and discuss how it is calculated.
5. Discuss each of the five equipment eras for alignment and exposure.
Resulting layers
5 4
2
1
6
3 7 8
Cross section
8) Metal etch
Top view
Figure 14.2
SMT14~1
Optical Lithography
Light
• Interference of Light Waves
– Optical Filters
Incoherent light source of a single wavelength
Slit
Two slits closely spaced
Interference patterns
Coherent cylindrical wave front
Two coherent cylindrical wave fronts
6. Describe reticles, explain how they are manufactured and discuss their use in microlithography.
7. Discuss the optical enhancement techniques for sub-wavelength lithography.
13
126 157 193 248
365 405 436
i hg
Excimer laser
Mercury lamp
Photolithography light sources
Figure 14.6
SMT14~1
Optical Lithography
Exposure Sources
• Mercury Arc Lamp • Excimer Laser
SMT14~1
Law of Reflection
The angle of incidence of a light wavefront with a plane mirror is equal to the angle of reflection.
Incident light
qi
qr
Reflected light
cycle of a frequency, expressed in meters
Laser
Figure 14.3
SMT14~1
Wave Interference
Constructive
Destructive
Waves in phase
A Waves out of phase
B
A+B
Figure 14.4
SMT14~1
Optical System of Lenses
Masking unit Condenser lens Fly’s eye lens
Flat mirror
Mirror Condenser lens Mirror
Collimator lens
Optical filter Shutter
KrF laser 100
80 60 40 20
Hg lamp 0
210 220 240 260 280 Wavelength (nm)
Figure 14.8
SMT14~1
Excessive Resist Absorption of Incident Light
Photoresist (after develop)
Figure 14.7
SMT14~1
Mercury Arc Lamp Intensity Peaks
Table 14.2
SMT14~1
Relative Intensity (%)
Spectral Emission Intensity of 248 nm Excimer Laser vs. Mercury Lamp
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 of photoresist.
Reticle (may contain one or more die in the reticle field)
Projection lens (reduces the size of reticle field for presentation to the wafer surface)
Wafer stage controls position of wafer in X, Y, Z, q)
2. Describe the properties of light and exposure sources important for optical lithography.
3. State and explain the critical aspects of optics for optical lithography.
3. Produce an adequate quantity of acceptable wafers per unit time to meet production requirements.