Acoustic resonant imaging technique for characterization ofphotoresist properties depending on hard bake temperature
Photoresists are essential materials in semiconductor fabrication, specifically in lithography, where their physical and chemical properties influence pattern generation. However, their light-reactive make property measurements challenging. We investigated the effects of hard bake conditions o...
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| Main Authors: | , |
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| Format: | Article |
| Language: | deu |
| Published: |
NDT.net
2025-03-01
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| Series: | e-Journal of Nondestructive Testing |
| Online Access: | https://www.ndt.net/search/docs.php3?id=30813 |
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| Summary: | Photoresists are essential materials in semiconductor
fabrication, specifically in lithography, where their
physical and chemical properties influence pattern
generation. However, their light-reactive make property
measurements challenging. We investigated the effects of
hard bake conditions on photoresists using an acoustic
resonant imaging technique. This technique is based on
acoustic resonance, where sound passing through a thin
layer reaches extreme values in its transmission and
reflection coefficients at a resonant frequency. With
plotting these acoustic properties in two-dimensional, in
the case of photoresists, this method allows for the
identification of regions with distinct properties,
facilitating optimal alignment for mask positioning and
direction. This study contributes to the advancement of
non-destructive characterization methods for photoresists.
This study examines the impact of hard bake temperature on
photoresist film properties. By transmitting ultrasonic
waves into a silicon substrate with a photoresist film and
analyzing the reflected echo waveforms to determine the
resonant frequency and the maximum amplitude ratio. Then
plotting these properties with acquired echo position,
properties distribution of photoresist films are obtained.
The density of photoresist film showed a trend of
increasing with higher bake temperatures, likely due to the
evaporation of remaining solvents in the film.
Interestingly, around 160°C, the density exhibited a
temporary decrease before resuming an upward trend. This
anomaly is hypothesized to result from a reduction in the
diazonaphthoquinone (DNQ, sensitizer in positive
photoresist) concentration, leading to a decrease in
density at specific temperatures. As the temperature rises
further, thermal crosslinking begins, causing the density
to increase again. Other studies suggest that higher bake
temperatures initially reduce dark erosion—an effect where
unexposed photoresist regions are eroded during
development—until reaching a temperature threshold where
erosion increases slightly before decreasing again. This
observed trend suggests a potential inverse relationship
between density and dark erosion, as higher-density films
may exhibit greater resistance to developer-induced
erosion. This study provides new insights into the effect
of bake temperatures on photoresist density, which may help
optimize fabrication parameters for improved material
performance.
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| ISSN: | 1435-4934 |