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SEM Magnification Calibration SEM Magnification Calibration

Magnification Errors • Proper calibration of the SEM scans (magnification) is primary to metrology. Magnification Errors • Proper calibration of the SEM scans (magnification) is primary to metrology. • SEM Magnification requires calibration – Standards needed • Instrument has inherent systematic problems – k. V compensation – Working distance compensation • Operator Errors – Working distance

Magnification Calibration • SEM magnification calibration is generally based on the measurement of the 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 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 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 SEM Instrumentation

Independent of Accelerating Voltage Independent of Accelerating Voltage

Calibration Based on Pitch Calibration Based on Pitch

Pitch vs. Width Pitch vs. Width

Magnification Calibration • Pitch measurements are considered to be self-compensating. • Width measurements are 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 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

High k. V Low k. V Resiliency of the Standard High k. V Low k. V Resiliency of the Standard

SEM Magnification Calibration Samples • Instrument Manufacturer – Hitachi – Biorad • In-house standards 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 NIST Traceable Standards • SRM 484 – Traditional SEM magnification standard • RM 8090 • RM 8820 • Reference material currently available • ~$400 -500 • MRS-2/MRS-3 (Geller Micro. Analytical) • VLSI Standards

Traceable SEM Standards SRM 484 • NIST certified standard • Electro-deposited gold and nickel Traceable SEM Standards SRM 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 ke. V SEM operation • SRM 484 • Developed before the emphasis on low ke. V 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

SRM 484 SRM 484

Traceable SEM Standards MRS-5 • NIST traceable standard commercially available. • Accessory structures for Traceable SEM Standards MRS-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 - Poly. Si Chip RM 8820 SEM Magnification Calibration Artifact • Metrology reference artifact - Poly. Si 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: – MTP will be presenting a paper on this standard Isolated and dense lines and spaces during this Conference!! – 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

New SEM Magnification Calibration Artifact SEM pitch calibration metrology patterns • NIST patterns dedicated New SEM Magnification Calibration Artifact SEM pitch calibration metrology patterns • NIST patterns dedicated to – – • Optical metrology section – – • Optical metrology SEM metrology Optical scatterometry X-ray scatterometry 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 – 4 x 70 nm to 4 x 1000 nm patterns • X-ray scatterometry – 4 x and 1 x 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

New SEM Magnification Calibration Artifact SEM pitch calibration metrology patterns Pitch patterns 1500 mm New SEM Magnification Calibration Artifact SEM pitch calibration metrology patterns 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