multi-patterning
Multi-patterning is a lithography technique that splits a single densely packed layer's pattern across multiple separate exposure and etch steps, achieving finer feature spacing than a single lithography exposure could resolve on its own.
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{ "title": "Target pattern too dense for a single lithography exposure", "sub": "feature spacing falls below what one exposure can resolve", "tone": "neutral" }
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{ "type": "group", "title": "Pattern split across multiple separate exposures", "items": [
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**Multi-patterning exists because at some point, a chip design's required feature spacing becomes finer than a single lithography exposure of a given wavelength can reliably resolve, yet the industry still needed a way to produce that spacing before higher-resolution exposure tools like EUV became widely available.** Since splitting a dense target pattern into two or more separate, less dense sub-patterns lets each individual exposure work within its resolution limits, multi-patterning uses multiple separate exposure and etch steps, each handling only part of the final pattern, to combine into a final feature spacing finer than what any single exposure could achieve alone.
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| Aspect | Single-exposure lithography | Multi-patterning |
|---|---|---|
| Achievable feature spacing | Limited by exposure resolution | Finer, split across steps |
| Number of exposure and etch steps | One | Two or more per layer |
| Process complexity and cost | Lower | Higher |
| Common use | Less dense layers | Densest layers before EUV adoption |
**Multi-patterning comes in several specific variants, such as litho-etch-litho-etch and self-aligned double patterning, differing in exactly how the pattern is split and how precisely the sub-patterns must align relative to each other.** Because different multi-patterning approaches make different tradeoffs between alignment precision requirements, process step count, and cost, chipmakers have developed multiple distinct multi-patterning techniques, choosing among them based on the specific density target and available process capability for a given layer.
**Multi-patterning significantly increases both the number of process steps and the manufacturing cost for the layers where it's applied, since achieving the target pattern now requires multiple full exposure and etch cycles instead of just one.** Because each additional exposure and etch cycle adds its own equipment time, materials cost, and potential for defects, multi-patterning's finer resolution comes at a real cost in complexity and expense, a tradeoff that made extreme ultraviolet lithography, capable of achieving fine spacing in fewer exposures, an attractive alternative once it became commercially viable.
**Precise alignment between the multiple separate exposures in a multi-patterning sequence is critical, since any misalignment between them directly translates into spacing errors in the final combined pattern.** Because the whole point of multi-patterning is that the separate exposures combine seamlessly into the originally intended dense pattern, even small alignment errors between the sub-exposures can produce spacing variations or defects in the final pattern, making overlay accuracy between the multiple exposures an especially demanding requirement for successful multi-patterning.
Read multi-patterning through a fine-comb lens: rather than trying to cut impossibly fine teeth into a comb in a single pass, multi-patterning is like cutting two coarser interleaved sets of teeth and combining them, achieving a final comb finer than either single pass could cut alone.