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In 193nm immersion lithography, immersion top coat was the first proposed technique for preventing the leaching of
photoresist (resist) components, such as photoacid generator (PAG) and quencher base, into the immersion fluid (DI
water). In this approach, the top coat is coated onto a resist film in a separate step including coating the top coat film and
baking the film. This approach certainly adds extra cost to the device manufacturing and incurs reduced throughput as
compared to the dry lithography process.
The embedded barrier layer (EBL) technology1-5 developed at Dow Electronic Materials has been demonstrated to be a
revolutionary approach, in which a suitable EBL material is formulated into an existing resist, and in a spin coating
process the EBL material comes to the resist surface to forms a leaching barrier in situ. This approach has now been
widely accepted and implemented in the integrated circuit manufacturing industry for replacing the conventional
immersion top coat process.
In addition to being an excellent leaching barrier, EBL materials, in general, result in a resist surface with a high receding
angle for water. This property makes the EBL approach more desirable in topcoat free immersion lithography, since it
allow for the latest scanners to perform at their maximum scan speed without generating watermark defects.
For immersion lithography, the most important issue for mass production is defectivity control. This is true for both top
coat and topcoat free approaches. In the top coat approach, the formulation optimization for both top coat and resists
was extensively involved for this technique finally to reach an acceptable defectivity level for mass production of
semiconductor devices.
As a later developed technology, the EBL approach has gone through a series of research and development stages
particularly in material innovation to reach the same low defectivity level as that of an immersion top coat process. After
achieving the target of low defectivity in lithography, the challenges left to the EBL approach were to solve high
defectivity in bulk exposed and bulk unexposed regions, which became prominent in both bright field and dark field
lithographic applications. To solve the high defectivity issues, a thorough understanding of the blob defect formation
mechanism was imperative. In this paper, the defect formation mechanism in both bulk exposed and unexposed regions
is proposed, and this proposed mechanism is applicable not only to the EBL approach but also to the immersion top coat
approach in general.
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