Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Pyramidal Pits and Optical Wafer Inspection Systems M. Jordan, Jr., R.E. Díaz, and E.D. Hirleman 13 January 2000

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Presentation overview Design and pre-characterization of a pit standard Angle-resolved scatter from pyramidal pits A model of light scatter from pyramidal pits Comparison of scatter from pits and particles

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Design and pre-characterization of a pit standard Electron beam lithography was used to pattern the defect field. Critically-dimensioned pit sizes were generated. Individual pits were thoroughly characterized. Pit standard provided a continuous range of pit sizes.

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Angle-resolved scatter from pyramidal pits Used combinations of p- and s-polarization, incidence angles of 45° and 65°, and wavelength µm. Pits used in measurements range in size from 0.34 µm to 0.76 µm. A characteristic null moves forward with increasing pit size only with p-polarization. A characteristic peak increases with increasing pit size regardless of polarization and incidence angle.

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. A model of light scatter from pyramidal pits A simple model explains the scattering phenomenon. High refractive index of silicon and large electrical size of pits in the silicon foiled DDSUB. Developed a simple yet accurate model for s- polarization based on diffraction theory.

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Comparison of scatter from pits and particles Scatter was compared using pyramidal pits and equal diameter silicon dioxide spheres. Comparison was made using 65° incidence and wavelength µm for both s- and p-polarization. In s-polarization, the null and peak of the pit remain stationary with increasing size, but the null and peak of the particle move forward. In p-polarization, the null of the pit moves forward with increasing size, but the first peak of the particle remains within 5°.

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Floor plan of the defect field Target widths (µm) by row and column

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Pyramidal pit of size 0.34 µm

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Average pit widths and aspect ratios by column number column no. in width (µm) aspect ratiopit number average average s.d. average s.d.orientation —————————————————————————— vertical both both both horizontal both both ——————————————————————————

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. In-plane, differential scatter of pyramidal pits as measured s-polarization incidence angle 65° wavelength µm

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Peak/null values, positions for s- polarization,  i =65°, = µm sizepeak position, valuenull position, valuepeak-to-null (µm)(µm²/sr)(µm²/sr)difference —————————————————————————— 0.35*~0.034––– 0.41*0.056––– °0.110~0° µm²/sr °0.1302° µm²/sr °0.2682° µm²/sr °0.385~2° µm²/sr —————————————————————————— * unlocalized

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. In-plane, differential scatter of pyramidal pits as measured p-polarization incidence angle 65° wavelength µm

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Peak/null values, positions for p- polarization,  i =65°, = µm sizepeak position,valuenull position, valuepeak-to-null (µm)(µm²/sr)(µm²/sr)difference —————————————————————————— °0.047– 42° µm²/sr °0.060– 16° µm²/sr °0.096– 4° µm²/sr °0.0923° µm²/sr ° ° µm²/sr ° ° µm²/sr ——————————————————————————

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. In-plane, differential scatter of pyramidal pits as measured s-polarization incidence angle 45° wavelength µm

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Peak/null values, positions for s- polarization,  i =45°, = µm sizepeak position, valuenull position, valuepeak-to-null (µm)(µm²/sr)(µm²/sr)difference —————————————————————————— °0.075––– °0.135––– °0.145– 5° µm²/sr °0.316– 2° µm²/sr °0.391– 3° µm²/sr °0.663– 3° µm²/sr ——————————————————————————

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. In-plane, differential scatter of pyramidal pits as measured p-polarization incidence angle 45° wavelength µm

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Peak/null values, positions for p- polarization,  i =45°, = µm sizepeak position, valuenull position, valuepeak-to-null (µm)(µm²/sr)(µm²/sr)difference —————————————————————————— °0.066––– °0.100––– °0.131– 11° µm²/sr °0.1651° µm²/sr °0.2142° µm²/sr °0.2160° µm²/sr ——————————————————————————

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Qualitative comparison of trends by increase in size  i polari- peak null peak-to-null zation positionvalueposition value difference ———————————————————————— 65° sno trend  ~0° no trend  65° p  no trend  45° sno trend  ~0° no trend  45° pno trend  ————————————————————————

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Reflectance of air-Si interface for a wavelength of µm

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Model of light scatter from a pit – the physical equivalent

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Model of light scatter from a pit – the equation Assumes behavior approaching that of a perfect electric conductor Incorporates duality and physical equivalence Based on the Fraunhoffer diffraction approximation 22

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. In-plane, differential scatter for a pyramidal pit of size 0.35 µm s-polarization incidence angle 65° wavelength µm

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. In-plane, differential scatter of a pit and a particle, s-polarization s-polarization incidence angle 65° wavelength µm

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. In-plane, differential scatter of a pit and a particle, s-polarization s-polarization incidence angle 65° wavelength µm

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. In-plane, differential scatter of a pit and a particle, p-polarization p-polarization incidence angle 65° wavelength µm

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. In-plane, differential scatter of a pit and a particle, p-polarization p-polarization incidence angle 65° wavelength µm

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Conclusions A pit standard enabled the observation of light scatter as a function of size and shape. A characteristic null moves forward with increasing pit size using p-polarization. An analytical model predicts the light scatter of pyramidal pits using s-polarization and high incidence angle. Light scatter trends by size of pits and particles are switched as polarization is changed.

Consortium for Metrology of Semiconductor Nanodefects © 2000 ASU All rights reserved. Acknowledgements Howard HuffSEMATECH John C. StoverADE Optical Systems Corporation Stanley D. DukeDuke Scientific Corporation Robert JohnstonSumitomo Sitix Silicon, Inc.