Wave front phase imaging for silicon wafer metrology

Trujillo-Sevilla, Juan M.; Roqué-Velasco, Alex; Sicilia, Miguel Jesús; Casanova-González, Óscar; Rodríguez-Ramos, José Manuel; Gaudestad, J.; Velasco-Ocaña, Miriam

doi:10.1117/12.2632499

Cited by 5 publications

(11 citation statements)

References 5 publications

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“…These intensity images are acquired around the conjugated plane P′ in equidistant planes along the z-axis. Choosing focal lengths of lens L1 and lens L2 appropriately allows for adjusting the sample size to the image sensor size 7 .…”

Section: Wave Front Phase Imaging Systemmentioning

confidence: 99%

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New wafer shape measurement technique for 300mm blank vertically held silicon wafer

Trujillo-Sevilla¹,

Casanova-González²,

Roqué-Velasco³

et al. 2023

Photonic Instrumentation Engineering X

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Wave Front Phase Imaging (WFPI) is a new technique for measuring the free shape of a silicon wafer. To avoid the effects of gravity affecting the wafer shape, the silicon wafer is held vertically while measured using a custom made three-point wafer holder. The wave front phase is measuring using a non-coherent light source that is collimated and then reflected off the silicon wafer surface. The wave front phase is measured using a unique new method that only needs to record the intensity of the reflected light at two or more distances along the optical path. Since only intensity images are used to generate the phase, commercially available CMOS sensors with very high pixel count are used, which enables very high number of data points to be collected at the time required by the cameras shutter speed when using a dual camera setup with simultaneous image acquisition. In the current lab system, a single camera on a linear translation stage is used that acquires 16.3 million data points in 12 seconds, including the stage motion, on a full 300mm wafer providing lateral pixel resolution of 65μm. The flatness of the silicon wafers used to manufacture integrated circuits (IC) is controlled to tight tolerances to help ensure that the full wafer is sufficiently flat for lithographic processing. Advanced lithographic patterning processes require a detailed map of the free, non-gravitational wafer shape, to avoid overlay errors caused by depth-of-focus issues. We present WFPI as a new technique for measuring the free shape of a silicon wafer with high resolution and high data count acquired at very high-speed using a system where the wafer is held vertically without the effects of gravity.

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Section: Wave Front Phase Imaging Systemmentioning

confidence: 99%

“…The reflected beam will carry the wave front phase, which value is proportional to the surface height map. In our case, we are using a collimated red (λ = 590nm) light beam generated by an LED that reflects onto the surface, the reflection angle of each ray is exactly two times the angle of the surface normal 7 .…”

Section: Wave Front Phase Imaging Systemmentioning

confidence: 99%

New wafer shape measurement technique for 300mm blank vertically held silicon wafer

Trujillo-Sevilla¹,

Casanova-González²,

Roqué-Velasco³

et al. 2023

Photonic Instrumentation Engineering X

Self Cite

View full text Add to dashboard Cite

show abstract

“…, where I is intensity, z the propagation distance, λ is wavelength and 𝜙 is the phase 12 , is a computational approach to reconstruct the phase of a complex wave in an optical system, describing the relationship between the intensity and phase distribution 13 . When imaging the reflected light from a blank silicon wafer, one can assume the intensity distribution is constant and hence the term ∇ ⃗ ⃗ 𝐼 • ∇ ⃗ ⃗ ∅ = 0, which term is solved by Shack-Hartman 14 .…”

Section: Patterned Wafer Geometry Challengesmentioning

confidence: 99%

“…Due to the large intensity difference in the reflected light from a patterned silicon wafer, interferometry techniques generally use a phase difference map calculated based on the smoothed front and back phase differences to improve the quality of phase unwrapping 15 . The second term of the TIE, 𝐼 • ∇ 2 ∅, is the part that is attempted to be solved in the classic TIE inversion methods 12 . The novel approach of WFPI consists of solving this equation entirely, using a proprietary numerical method.…”

Section: Patterned Wafer Geometry Challengesmentioning

confidence: 99%

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New metrology technique for measuring the free shape of a patterned 300mm wafer held vertically

Trujillo-Sevilla

Casanova-González

Roqué-Velasco

et al. 2023

Metrology, Inspection, and Process Control XXXVII

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On product overlay (OPO) is one of the most critical parameters for the continued scaling according to Moore’s law. Without good overlay between the mask and the silicon wafer inside the lithography tool, yield will suffer1. As the OPO budget shrinks, non-lithography process induced stress causing in-plane distortions (IPD) becomes a more dominant contributor to the shrinking overlay budget2. To estimate the process induced in-plane wafer distortion after cucking the wafer onto the scanner board, a high-resolution measurement of the freeform wafer shape of the unclamped wafer with the gravity effect removed is needed. Measuring both intra and inter die wafer distortions, a feed-forward prediction algorithm, as has been published by ASML, minimizes the need for alignment marks on the die and wafer and can be performed at any lithography layer3. Up until now, the semiconductor industry has been using Coherent Gradient Sensing (CGS) interferometry or Fizeau interferometry to generate the wave front phase from the reflecting wafer surface to measure the free form wafer shape3,4,5. In this paper, we present a new method, Wave Front Phase Imaging (WFPI) for generating a very high-resolution wave front phase map of the light reflected off of the patterned silicon wafer surface. The wafer is held vertically to allow for the free wafer shape to be measured without having the wafer shape be impacted by gravity. We show data using a WFPI patterned wafer geometry tool that acquires 16.3 million data points on a 300mm patterned silicon wafer with 65μm spatial resolution using a total data acquisition time of 14 seconds.

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New wave front phase sensor used for 3D shape measurements of patterned silicon wafers

Ivanov Kurtev,

Trujillo-Sevilla,

Jiméneza

et al. 2023

38th European Mask and Lithography Conference (EMLC 2023)

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Wave front phase imaging for silicon wafer metrology

Cited by 5 publications

References 5 publications

New wafer shape measurement technique for 300mm blank vertically held silicon wafer

New wafer shape measurement technique for 300mm blank vertically held silicon wafer

New metrology technique for measuring the free shape of a patterned 300mm wafer held vertically

New wave front phase sensor used for 3D shape measurements of patterned silicon wafers

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