Etching is
either a chemical or physical process to selectively remove the Cr/CrO layer along the pattern formed on the surface. Wet etching (chemical etching) and dry etching (plasma or ion etching, thus, physical etching) are both commonly used methods in the manufacturing of photomask nowadays. Dry etching is preferred over the wet etching when patterns with finer geometries are required.
In general, there are three types of dry etchers, depending upon the mode of creating plasma:
(1) PE (Plasma Etching), (2) RIE (Reactive Ion Etching) , and (3) ICP (Inductively Coupled Plasma).
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| After Develop process, PR pattern is formed on top of the Cr layers of the photomask. The resultant PR layer protects the Cr layer underneath during the etching process, resulting in the removal of Cr layer which is exposed to the etching agent (either wet or dry). Wet etching is preferred for lower grade photomask which can tolerate relative higher etch bias. When finer geometries and tight CD control is desired, dry etching provides superior performance.
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| Cr
Etch of conventional reticle |
| Quartz
etch for Levenson phase shifters |
| MoSiON
etch for Embedded phase shifters |
| Precision
photoresist descum |
| X-ray
mask fabrication |
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Higher
plasma density |
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Higher
bias voltage |
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Anisotropic
profile |
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Good
CD uniformity |
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¢º Novolac based positive
(ex. OCG8951 or IP3500, £¾4000¡Ê,
Profile of 80¢ª±10¢ª) |
¢º Binary CrOx/Cr with a nominal
thickness
of 1000¡Ê, Exposed loading of ¡Â50% |
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| ¢º I-Line or DUV MoSiON with patterned
Cr or CrOx/Cr mask at a thickness of
1000¡Ê |
| ¢º Cr mask should be previously defined
by wet etching(Resist removal is optional) |
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| ¢º I-Line or DUV MoSiON with patterned
Cr or CrOx/Cr mask at a thickness of
1000¡Ê |
| ¢º Cr mask should be previously defined
by wet etching(Resist removal is optional) |
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