1. SEM Magnification Calibration

2. 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

3. 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.

4. 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.

8. 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.

9. SEM Instrumentation

10. Independent of Accelerating Voltage

14. Calibration Based on Pitch

15. Pitch vs. Width

16. 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.

17. 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

20. Resiliency of the Standard High kV Low kV

21. SEM Magnification Calibration Samples Instrument Manufacturer –Hitachi –Biorad In-house standards –Company standards laboratory NIST Traceable Standards

22. SRM 484 –Traditional SEM magnification standard RM 8090 RM 8820 Reference material currently available ~$400-500 MRS-2/MRS-3 (Geller MicroAnalytical) VLSI Standards

23. 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

25. 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

29. SRM 484

31. Traceable SEM Standards MRS-5 NIST traceable standard commercially available. Accessory structures for distortion measurements and astigmatism correction are present.

35. 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!!

36. 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

37. 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