System CPU
Lens distortion & aberration Illumination
Stage stepping Alignment accuracy
PSM Registration errors
Exposure Tool
Reticle
Illustration of contrast for SEs and BSEs
– OAI, PSM, OPC…
• As CD size smaller, the process window is narrow, it make process control more difficult
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CD Calibration of SEM
Top-down & xsection calibration
SEM proximity calibration
SEM Charging Effect
Before measurement
After 60 secs of imaging
Summary
• To shrink CD size→ Increase NA Equipment Decrease λ → RET is necessary • RET (Resolution Enhancement Technology)
Overlay Metrology Challenge
Overlay target after CMP
After target edge enhancement using coherence probe microscope
Express overlay errors by series expansion
CD Measurement
θ
Crossing section of featured: Threshold,
inflection points, maximum slope, linear approximation, minima or maxima.
(A) Interfield errors: ∆X=TX+EXX-RXY+higher order terms+eX, ∆Y=TY+EYY+RYX+higher order terms+eY, where T means the wafer translation factor, E the wafer scaling factor, R the wafer rotation factor. eX and eY represent the interfield residual errors. (B) Intrafield errors: δx=mxx-rxy+txxy+tyx2+ex, δy=myy+ryx+tyxy+txy2+ey, where m means the shot magnification factor, r the shot rotation factor, t the trapezoidal parameter. ex and ey represent the intrafield residual errors.
Translation
Rotation
Trapezoid
Magnification
Skew
The contributors of Overlay Error
Wafer process
Wafer processing Wafer deformation
Metrology
Image processing Target design