PR-Mask氧化硅湿蚀刻工艺中枝晶状缺陷的去除方法

Dendrites are ramifified crystals, exhibiting morphological features that display crystallographic directionality, such as straight primary stems, secondary side arm, and even tertiary branches. Dendritic crystals are commonly observed when a non-faceted material grows from a supercooled melt or supersaturated solution characterized by smooth, parabolic-like tips and side-branches behind the tips.1–5 Understanding the formation of dendritic structures has long been a challenging research topic in materials science. Through many theoretical analysis and experiments, it is now recognized that anisotropies in surface tension and/or in the atomic attachment kinetics play an important role to stabilize the tip region against tip splitting.6–9 Models of dendritic crystal growth include diffusion-limited aggregation (DLA) models,10 selective noise amplifification models,6 geometric models, which describe interfacial growth velocity in terms of the geometric properties of the phase boundary, typically curvature,11 cellular automata-type models,12 and phase fifield models,13 which take into account long range diffusional effect, and so on. In spite of many models, the mechanism that determines the generation and development of side-branches in dendritic growth remains as a subject of controversy.

Fig. 1a shows a typical oxide wet etch process with PR-mask, which oxide spacer in cell array is under etching by wet chemical with diluted HF (dHF), while oxide spacer in core/peri area is blocked by KrF PR pattern (b). After suffificient wet etchant with single wafer cleaner was applied for the removal of oxide spacer, 300 mm wafer was rinsed with deionized water (DIW) and dried by spinning at high rpm successively (c). The location of defects after spin-drying process was monitored with Surfscan SP2 (KLA-Tencor) and scanning electron microscope (SEM, Hitachi) was used for the close inspection of DLD.

Second approach for the removal of DLD is the introduction of ozonated deionized water (O3/DIW) in fifinal cleaning step. Because of its high effificiency on the removal of organic contaminant,26,27 ozonated water treatment is capable of effectively removing organic component from DLD in a short time at room temperature. Once the removal of organic frameworks is initiated, flfluorosilicate aggregates or nanocrystals itself can be easily removed by simple DIW cleaning process. Therefore, almost the same defect inspection map with Fig. 6d was observed after ozonated water treatment in fifinal wet etching process. H2SO4/H2O2 mixture is also commonly used to remove organic compounds such as PR and polymer generated during plasma etching. However, it can attack PR-mask patterns even in a few second, because H2SO4/H2O2 mixture is generally employed in high temperature (≥120◦C) and very concentrated form (2:1 ∼ 4:1 of H2SO4:H2SO4). Therefore, it is not suitable for the removal of DLD in PR-mask oxide wet etching process.

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This letter reports new kind of dendrite-like (DLD) defect observed after PR-mask silicon oxide wet etching in semiconductor manufacturing process. It is assumed that DLD is a kind of the mesocrystals composed with flfluorosilicate nanocrystals (inorganic cores) separated by some organic molecules (organic shells) and dendritic structure is produced by self-assembling or aggregation-mediated crystal growth composed with organic/inorganic hybrid structure during evaporation of solvent with spin-drying. It was revealed that formation of DLD was suppressed by the introduction of oxygen plasma treatment on PR surface before oxide wet etching. Finally, ozonated water (O3/DIW) treatment was very effective in removing DLD by the collapse of mesocrystal structure resulting from the elimination of organic frameworks.