半导体前端制造wafer fab中必须要做静电防护的一个重要光刻工具-photomask（reticles），否则静电导致的photomask的CD（Critical Dimension，）不良（对65nm制程技术及以下有位敏感）必然会导致半导体器件的光刻良率损失甚至于全部报废。

转载自微信公众号“ESDiS Release”。原文链接：

https://mp.weixin.qq.com/s?__biz=MzkzMDU2MDkwNQ==&mid=2247483725&idx=1&sn=b99dfbc91d9e172b1c1125bd80771d63&chksm=c2792fabf50ea6bdea3c11752a06bc292c90345525f381578c6efc6d54d9376a91ff44158905#rd

Keywords of Glossary

Reticles, also called as photomask, it usually utilize quartz or glass as the substrate and coated with an opaque film (often chrome) of the designed pattern on it which is etched the design of the device being manufactured.

SMIF pod, it provides reticles users with a standard mechanical interface (SMIF) to the safe handling, storage and transportations within fabs.

EFM, it refers to electric field induced ion migrations (mainy for chrome ions coated on reticles).

ESD, Electro-Static Discharge, it refers to the abrupt transfer of static charges under the influences of electric fields.

The Electrostatics Susceptibility of Reticles

Regarding the features of large amounts of diverse chrome patterns with micro spaces (presently most reticles of IC products fall below 1um range) on the insulating glass or quartz, reticles would exhibit very high susceptibilities to electrostatics, involving EFM and ESD events.

Figure 1. the micro level isolated chromes patterns of SEMI reticles

Regarding EFM problems of reticles, usually it occurs when reticles approaches higher electrostatic sources or reticles substrate was electrostatically charged up higher during handlings in fabs. EFM would induce reticles inspection failures of CD (critical dimension) variations. EFM impacts of reticles could be accumulated over a long time electrostatics exposures. 

Figure 2. CD failures of reticles caused by EFM events

Regarding ESD problems of reticles, usually it occurs when reticles are exposed to very higher electrostatics than EFM events. ESD events of reticles (within reticles or between reticles and other items involved) often lead to chrome patterns with damages of mice bits or short bridges.

Figure 3. reticles with ESD damages of mice bites type

Figure 4. reticles with ESD damages of short bridges and / or melting

Electrostatics Risks evaluation Method

Wafer fabs could obtain the appropriate commercial E-reticles product to evaluate the electrostatics risks under control or out of control. This evaluation data could specifically help fabs to pin out the real electrostatics risks and take effective countermeasures for improvement. Fabs could also design and manufacture the E reticles by themselves.

Figure 5. E reticles used to evaluate reticles electrostatics risks

The Electrostatics Controls of Reticles in SEMI Wafer Fabs

The electrostatics controls of recticles in wafer fabs involves storage, handlings in production automation equipment (mainly for lithography) and transportations.

Storage: reticles shall be enclosed in the SMIF pods or boxes which could provide the complete electrostatics protections against EFM and ESD.

Figure 6. SMIF pods products with fully electrostatics protections

Figure 7. Common ESD protective SMIF pods incapable to offer EFM protections

Handlings within automation equipment: the enclosed electric field shielding approach cannot be feasible within automations, the environment of reticles moving must be controlled at low electrostatics level and AC fields especially near reticles needs also be controlled  at low levels.

Transportations: Due to many insulating materials used in fabs, reticles transportations shall be put into SMIF pods with fully electrostatics protections prior to transportations.