Full-Field feature profile models in process control

1. SPIE (2005) Vol 5755 - 16 Full-Field feature profile models in process control Terrence E. Zavecz – TEA Systems Inc. http://www.TEAsystems.com March 3, 2005 Contact tzavecz@TEAsystems.com (+01) 610 682 4146

2. Models for Reticle Performance • Introduction • Physical Process Window description and Perturbations • The Best Focus Feature Contour • Formalization • Removal of metrology and exposure systematic error • Examples • Duty Cycle • BARC • High k1 applications • Full-Field Process Window • Optimum Field Response • With tool defocus removed • Depth of Focus & Focus Contours • Application to Full-Wafer responses • Formalization • Addressing Film and Feature systematic • Exposure tool artifacts • Final Note • Exposure artifact influence on the Process Window • Conclusions Models for reticle performance

3. Two-variable process window Collapsed line BCD • The number of un-Collapsed lines visible in a group were rated from SEM photos ranging from 0 to “7” • Results are shown for an 80 nm feature width Models for reticle performance

4. Properties of the PW Surface C. Ausschnitt et al SPIE 5378 p38-47 C. Mack et al SPIE 5038-39 Models for reticle performance

5. CD-SEM with PW CD vs Dose Optimum Focus (for this case) • CD vs Dose is not linear • Surface “fit” quality can vary! deFocus CD vs Focus Models for reticle performance

6. Wafer flatness Device topography Effective Dose Why “Process Window” fit-quality varies? • Primary disturbances causing CD Uniformity (CDU) variations grouped upon their sources. Reticle Scanner Track & Process Substrate BARC coat Transmission Exposure Dose Flatness Resist Film coat Slit Uniformity CD’s PEB Temp & Time Focus SetUp Develop Chuck Flatness Up-Down Scan Effective Focus Scan Linearity CDU Models for reticle performance

7. Best Focus – Feature Contour • Derive CD @ Dose & Best Focus • Relationship functional for • Feature Widths • Side Wall Angle (SWA) • Resist & BARC thickness • Line Edge Roughness Best Focus (for Critical Dimension or CD) Set derivative = 0 & solve for “F” CD @ Best Focus Models for reticle performance

8. Dose Response of Best Focus (BF) & CD • Feature vs Dose • Will be near-linear if feature profiles are well resolved • Best Focus vs Dose • Slope should be ~0 if lens is near aberration free and films do not influence focus response Dose Best Focus Models for reticle performance

9. Example #1 – Duty cycle • 140 nm contacts • 3 sets of pitch • CD-SEM measured contact TCL=140nm p240 Best Focus p550 p420 Models for reticle performance

10. Example 2: BARC Performance • The ARC 3 data has • a lower CD vs dose, reducing it’s sensitivity to dose • A greater target dose to obtain CD size of 80 nm • A strong sensitivity of best focus to the dose No ARC at Best Dose ARC3 at Best Dose Models for reticle performance

11. Example #3; Pushing the envelope Response for 80 nm, 193 litho process • Dose values are arbitrary • At 80 nm, we are driving the imaging capabilities of the lens • Note response of BF to scan & lens aberrations • Response is caused by wavefront asymmetry and results in feature line edge asymmetry Site 30 Site 15 Models for reticle performance

12. Consider the Process Window • A CD-SEM based data sample of the process window Models for reticle performance

13. Focus -0.24 -0.16 -0.08 0.0 +0.08 +0.16 +0.24 Dose= 18 19 20 21 22 23 24 Process Window Scatterometry Process Window Side Wall Angle What can we learn? • Exposures • 193nm litho process for 100nm features • AT1100 scanner, 0.75NA with annular illumination • 90nm gratings at 1:1 with full field coverage • 240nm resist on 78nm Barc on Si • OCD metrology: NI, rotating polarized light (Nano9030) • diffractive optical metrology (scatterometry) - outputs spectral intensity changes of 0th order diffracted light intensity • Weir PW Software from TEA Systems Models for reticle performance

14. Optimal BCD Image BCD Vector Plot • BCD values as estimated for the reticle • Across-field Focus and metrology errors removed by process • Note that these values include both reticle offsets and exposure/lens aberrations BCD Contour Plot Y (scan) location (mm) X (slit) location (mm) 100 nm 1:1, 90nm TCD Models for reticle performance

15. Optimum Field Response thru Dose • BCD summarizes natural feature size response @ best Focus for each dose • DoF computed when in control Models for reticle performance

16. Metrology & Process Independent Characteristics Focus Uniformity Depth of Focus Uniformity Models for reticle performance

17. 5754-110 Poster Validation; wafer vs Reticle CD-SEM Reticle MEF+ = 4.3292 Optimized BCD from Wafer Nanometrics Reticle MEF+ = 4.305813 Models for reticle performance

18. BCD, TCD, SWA @ Best Focus/Dose Models for reticle performance

19. Dusa et al. SPIE Vol. 5378-11 BARC modeled wafer uniformity Models for reticle performance

20. T3 (PR) SWA BARC BCD TCD Derived variable distributions across the wafer Models for reticle performance

21. BCD & TCD Size vs PhotoResist Models for reticle performance

22. BARC Thickness & SWA Models for reticle performance

23. - Scan Direction Artifacts Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 1.5 - + - + - + - + + - + - + - + Reticle Scan Direction Models for reticle performance

24. Profile variation with Focus See Poster: 5754-87 Lens Before cleaning Lens After cleaning Scan direction - + - + - + - - + - + - + - Top CD + - + - + - + + - + - + - + Slope Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5 Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5 Bottom CD Process window Models for reticle performance

25. 5 18 19 6 9 10 11 12 Slope vs Dose across the slit Lens Before cleaning Lens After cleaning Up +Scan Down -Scan Models for reticle performance

26. Reticle scan-stage component removed. Provides view of lens perturbations Reticle Scan Removed Lens Before cleaning Lens After cleaning Top CD - + - + - + - - + - + - + - + - + - + - + + - + - + - + Slope Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5 Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5 Bottom CD Models for reticle performance

27. Lens aberrations removed. Provides view of scan uniformity Lens Slit Removed Lens Before cleaning Lens After cleaning Top CD - + - + - + - - + - + - + - + - + - + - + + - + - + - + Slope Scan speed nonlinearity start/end of scan Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5 Focus = -1.5 -1.0 -0.05 0.0 +0.05 +1.0 +1.5 Bottom CD - + - + - + - - + - + - + - + - + - + - + + - + - + - + Models for reticle performance

28. FR(x,y) @ Best Focus Lens Before cleaning Lens After cleaning CD response after field focus errors are removed. -Down + Up -Down + Up TopCD Slope BottomCD Models for reticle performance

29. A Note: Exposure artifacts & the model • Be aware of scan artifacts such as stage scan direction perturbations Models for reticle performance

30. Summary • Process Window surface models • The algorithm history extends through several formats • Extended to Dose Response of Features independent of metrology & Field focus • Best Focus vs Dose • Plot yields additional information on process response and extensibility • Full-Field Process Window • Provides the optimum feature response across the field • Traceable directly to reticle measurements • Can be extended to Depth of Focus and deFocus contours • Full Wafer Response • Implements Best Feature response of the Full-Field Process Window • Models were shown for addressing wafer-systematic perturbations • Scanner-specific field models shown in paper 5754-110 • Systematic feature response perturbations • Response to Film and and exposure tool artifacts • Final Note • Exposure tool induced perturbations can directly influence the accuracy of the process window calculation Models for reticle performance

31. End of Presentation – Thank You Please visit posters: “Feature profile control and the influence of scan artifacts” 5754-87 “Models for reticle performance and comparison of direct measurement ” 5754-110 Visit us at: http://www.TEAsystems.com BARC Uniformity

32. Models for reticle performance

33. Background and additional slides

34. Feature Response to process disturbance “m” • is the sensitivity coefficient Formalization of the Spatial Signatures • - IFp(x,y): IntraField periodic signature • reticle component and a systematic –within-wafer, periodic component • describing the scanner field (slit and scan signatures) • - Wp (x,y): feature response variability • This component is primarily a result of the “whole-wafer-at-a-time” process steps, characteristic to resist and track. • - DD (x,y): Die-to-Die variability • variations in discrete scanning disturbances such as effective dose, the incidental focus or scan direction. • - r: the residual component (1) (2) Most complex signature Ref. 2: Mircea Dusa et al, “Intra-wafer CDU characterization … ”, Proc. SPIE (2004), Vol. 5378-11 Models for reticle performance

35. Component Analysis of MEF • Definition • MEF = Mask Error Function • In terms if IntraField Periodic Signature IFp(x,y) = IFdReticle+IFSlit, scan aberrations + IFeffective Dose,Focus + IFResist + IFflare,scatter +Ifscatter MEF Objective: Identify the MEF Components of IFp Models for reticle performance

36. IntraField (IFp) Signature • IFslitPerturbations • Lens aberrations • Flare, scatter, proximity etc. • Photoresist artifacts • IFScanReticle Stage Distortions: • effective dose • scan speed • Effective Focus • Stage pitch, yaw tilt • travel height-offset • IFReticle • Effective feature width • Photomask Processing IFslit= Lens Aberrations Models for reticle performance

37. Lens-Slit Model, Row offsets Focus offsets • Modeled offset of each slit position • Repeatability of each reticle scan’s travel • Contributing about 1 nm of noise to BCD error budget • Lens-slit model is applied to every row of every field of the wafer. Results are summarized on the right. Models for reticle performance

38. Models for reticle performance

39. Right-side average Models for reticle performance

40. Average Field Models for reticle performance

41. BCD Raw Data Models for reticle performance

42. Modeled BCD-RET across wafer Models for reticle performance

43. Profile Response @ Best Focus (Before) Lens before cleaning UP +Scan Down -Scan Models for reticle performance

44. Profile Response @ Best Focus (After) Lens After cleaning UP +Scan Down -Scan Models for reticle performance

45. Slope Slope TopCD TopCD BottomCD Focus Uniformity Lens Before cleaning Lens After cleaning Calculated from Calculated from -Down + Up -Down + Up BottomCD Models for reticle performance

46. DoF Variation Lens Before cleaning Lens After cleaning After Clean • Both features plot to the same scale • Note however there is a problem with the lower left corner of the field with a shallow DoF • Partially hidden here by the scale TopCD -Down + Up -Down + Up BottomCD Models for reticle performance

47. Lens-Slit Uniformity • The piston BCD value of each columns yield a representation of the BCD perturbation caused by the lens. • This is the Average Field • Variation show is caused by the 8 focus-shifted fields • Slit contributes about 2 nm to error budget Models for reticle performance

48. Average Field BCD Scan Profile • Boxplot across Reticle Scan shown • Reticle & Wafer errors removed • The right-side (bottom) of the scan’s mid-points has been averaged and transposed to the left-side (top) graph. • Note the left-right pitch of the reticle-scan’s travel accounting for approximately 1 nm of variation Right-side average Models for reticle performance

49. Slit Wobble • Slit-wobble is contributing about 1.25 nm to error budget • Tilt contributes 3 nm to budget Models for reticle performance

50. IntraField Process Window • W(x,y) = Feature Response • located at (x,y) on reticle • Process window reduction • Site #8 • Soft data-sport • Easily corrected and handled • Site #6 response • Reticle Error • Lens and/or scan aberrations (MEF) Site #8 Site #6 Models for reticle performance