Immersion specific defect mechanisms: findings and recommendations for their control

Abstract

Defectivity has been one of the largest unknowns in immersion lithography. It is critical to understand if there are any immersion specific defect modes, and if so, what their underlying mechanisms are. Through this understanding, any identified defect modes can be reduced or eliminated to help advance immersion lithography to high yield manufacturing. Since February 2005, an ASML XT:1250Di immersion scanner has been operational at IMEC. A joint program was established to understand immersion defectivity by bringing together expertise from IMEC, ASML, resist vendors, IC manufactures, TEL, and KLA-Tencor. This paper will cover the results from these efforts.The new immersion specific defect modes that will be discussed are air bubbles in the immersion fluid, water marks, wafer edge film peeling, and particle transport. As part of the effort to understand the parameters that drive these defects, IMEC has also developed novel techniques for characterizing resist leaching and water uptake. The findings of our investigations into each immersion specific defect mechanism and their influencing factors will be given in this paper, and an attempt will be made to provide recommendations for a process space to operate in to limit these defects.

Improving Equipment Defectivity Specifications Through Chip Yield Modeling: A Case Study for Immersion Lithography

“…Direct interfacing allows for a so-called soak treatment, wherein wafers are treated with DI water rinse to remove remaining water droplets and moisture just after exposure and before post-exposure bake. It is known that this treatment decreases the amount of pattern expansions up to 80% [17], [24], [25]. That does not come as a surprise since we explained in section IIIA that pattern expansions are caused by interaction of water droplets and the stack, and those water droplets are removed by this soak treatment.…”

“…Resist swelling is related to water loss by the immersion hood before exposure and can for example be minimized by an immersion hood that is improved on water confinement [12]. Another strategy is the utilization of hydrophobic resists [2], [17], [26], [27]. Those two latter efforts, as well as immersion hoods with bubble-free designs [28], [29], will further minimize bubble defects also.…”

“…be formed by contaminants mopped up by the immersion fluid when the immersion hood passed over the wafer edge. They could represent particles from the wafer edge (or peeling of the topcoat) [2], [12], [17], [18] or chuck (cross-contamination) [2], [17], [19]. Distributions II and III represent defects with sizes in the range of 1 -8 μm.…”

“…We first have to analyze the mechanisms that cause those defects before we can do so. Probably we have to minimize the interaction between the immersion fluid and the wafer edge (or wafer bevel) [2], [3], [12], [17]- [19], as discussed in Section IIIA. Further lowering of the impact can be achieved by reducing the amount of pattern expansions and bubble defects.…”

Influence of Immersion Lithography on Wafer Edge Defectivity

“…To increase die yield, it is desirable to have EBR widths that are as small as possible. Immersion lithography [1][2][3][4] has changed the way we view defectivity issues at the wafer edge significantly. During the immersion exposure sequence, the wafer edge is in contact with the water from the immersion hood (IH), introducing additional concerns beyond direct contact of resist with the scanner.…”