SEM Magnification Calibration. Magnification Errors Proper calibration of the SEM scans...
Transcript of SEM Magnification Calibration. Magnification Errors Proper calibration of the SEM scans...
SEM Magnification Calibration
Magnification Errors• Proper calibration of the SEM scans
(magnification) is primary to metrology.• SEM Magnification requires calibration
– Standards needed
• Instrument has inherent systematic problems– kV compensation– Working distance compensation
• Operator Errors– Working distance
Magnification Calibration
• SEM magnification calibration is generally based on the measurement of the pitch (displacement) between two structures.– Pitch will be discussed later
• All traceable SEM magnification calibration is based on the measurement of a pitch.
SEM Magnification Calibration
• Procedures vary with instrument manufacturer.
• All require user supplied calibration sample.
• Most common sample for laboratory instruments is a copper grid.
• NIST SRM 484 is a sample with accurate pitch dimensions for SEM magnification calibration.
SEM Instrumentation
• Vast array of instruments in the field.
• Performance and capabilities vary substantially.– lab instruments– production line instruments
• Universally useful NIST sample preferred because of time and cost involved.
SEM Instrumentation
INSTRUMENT CLASS
RESOLUTION HIGHEST USEFUL MAGNIFICATION
RANGE In-lens FESEM
.4-.8 nm 1,000,000x+
Post-lens FESEM
.8- 1.2 nm 500,000x+
LaB6 Systems 4.0 - 5.0 nm 100,000x
Tungsten Systems
5.0+ nm 50-100,000x
Independent of Accelerating Voltage
Calibration Based on Pitch
Pitch vs. Width
Magnification Calibration
• Pitch measurements are considered to be self-compensating.
• Width measurements are NOT self compensating.
• There currently is NO accurate or traceable standard for the width of a line or a structure.
Pitch Measurements
• Electron beam modeling is not needed for pitch measurements or calculations based on pitch
• Pitch Measurements are self compensating
• But - the rules must be followed.– The edges measured must be the same
Resiliency of the Standard
High kV Low kV
SEM Magnification Calibration Samples
• Instrument Manufacturer– Hitachi– Biorad
• In-house standards– Company standards laboratory
• NIST Traceable Standards
NIST Traceable Standards
• SRM 484– Traditional SEM magnification standard
• RM 8090• RM 8820• Reference material currently available• ~$400-500
• MRS-2/MRS-3 (Geller MicroAnalytical)
• VLSI Standards
Traceable SEM StandardsSRM 484
• NIST certified standard• Electro-deposited gold and
nickel layers, cross sectioned and polished.
• Pitch is certified using a metrology SEM.
• Certified spacing*: 0.5, 1.0, 2.0, 5.0, 10.0, 30.0 and 50.0 micrometers.– *newer issues may vary from
these figures
SRM 484• Developed before the
emphasis on low keV SEM operation
• Much thicker than a semiconductor wafer.
• Does not easily fit in contemporary wafer inspection instruments.
• Suitable for many SEM applications
SRM 484
SRM 484
Traceable SEM StandardsMRS-5
• NIST traceable standard commercially available.
• Accessory structures for distortion measurements and astigmatism correction are present.
RM 8820 SEM Magnification Calibration Artifact• Metrology reference artifact - PolySi Chip
and Wafer
• Made with 193 nm phase shifting, 6 inch mask
• The design combines NIST and many leading IC manufacturing companies experts’ dimensional metrology patterns
• A very large variety of patterns:
– Isolated and dense lines and spaces
– Varying line width, space width, pitch
– Various contact holes
– Optical and SEM alignment and navigation patterns
– Scatterometry: optical and x-ray
– Line edge roughness
– Geometry distortion patterns
– Many other patterns
– Phase shifting and resolution enhancement patterns
• Grounded and electrically floating patterns
MTP will be presenting a paper on this standard during this Conference!!
• NIST patterns dedicated to– Optical metrology – SEM metrology– Optical scatterometry– X-ray scatterometry
• Optical metrology section– Based on the NIST SRM 2059 design– Linewidth model comparison features– Special, “noisy” scatterometry patterns– Binary and phase shifting patterns
• SEM linewidth metrology– Patterns sized for mask
measurements– Patterns sized for wafer measurements– Grounded and electrically floating
patterns– 70 nm to 1000 nm patterns– 4x 70 nm to 4 x 1000 nm patterns
• X-ray scatterometry– 4x and 1x dense structures
• Size 1500 mm by 1500 mm• Pitch patterns 1500 mm to 140
nm• Isolated and dense lines 1 mm to
70 nm• Vertical and horizontal structures• Beam focusing, navigation and
distortion measurement patterns• SEM, SPM, optical,
scatterometry and line scale interferometry
• Grounded structures – less charging
SEM pitch calibration metrology patterns
New SEM Magnification Calibration Artifact
New SEM Magnification Calibration Artifact
Pitch patterns
1500 mm to 140 nm
Isolated and dense lines 1 mm to 70 nm
Vertical and horizontal structures
Beam focusing, navigation and distortion measurement patterns
SEM pitch calibration metrology patterns