Semiconductor Patterning With SADP Spacers for Sub-Lithographic Pitch
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Solution Overview
Problem
As semiconductor devices continue to shrink, the spacing between elements (pitch) approaches the limits of traditional optical masks and photolithography equipment, making it challenging to manufacture devices with increasingly smaller dimensions.
Innovation Solution
A self-aligned double patterning (SADP) process is employed, where mandrels are patterned, spacers are formed along their sidewalls, and the mandrels are partially removed, allowing the spacers to define a pattern at half the pitch of the mandrels. This process includes the use of carbon-rich layers to reduce etching damage during selective removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional photolithography equipment is used, then manufacturing process is simple, but minimum pitch achievable is large
Solution Approach 1:
The patterning process is divided into multiple sequential steps: first patterning mandrels, then forming spacers on mandrel sidewalls, selectively removing mandrels, and repeating the process. This segmentation allows achieving pitch values below the limit of single-step photolithography by breaking down the complex patterning task into manageable stages, with each stage operating within achievable process windows.
Solution Approach 2:
The patent transitions from two-dimensional planar patterning to three-dimensional structures by forming vertical mandrels and spacers. This dimensional change enables self-aligned patterning where the spacer thickness directly controls the final feature pitch, adding a vertical dimension (spacer thickness) that translates to horizontal pitch control, thereby achieving sub-lithographic pitch values.
2Quantity of substance
If pitch is reduced to increase device density, then device density increases, but photolithography process window decreases
Solution Approach 1:
The spacer structures are self-aligned to the mandrels, forming automatically on the mandrel sidewalls through conformal deposition. This self-alignment eliminates the need for additional alignment steps and processes, ensuring precise pitch control without requiring tighter process windows. The spacer width is determined solely by deposition thickness, not by lithographic patterning, thereby decoupling pitch control from photolithography process limitations.
3Ease of manufacture
If spacers are selectively removed to pattern different regions, then selective patterning is achieved, but etching damage to remaining spacers occurs
Solution Approach 1:
A sacrificial mandrel structure serves as an intermediary that is selectively removed while the spacer remains protected. The mandrel acts as a temporary support and pattern definition element that can be selectively etched away without damaging the spacer, enabling selective region patterning. The spacer's self-aligned position and structural integrity protect it from etching damage during mandrel removal, while allowing selective access in different device regions.
Data Source
AI summary
A method includes depositing a first mask over a target layer; forming a first mandrel and a second mandrel over the first mask; forming first spacers on the first mandrel and second spacers on the second mandrel; and selectively removing the second spacers while masking the first spacers. Masking the first spacers comprising covering the first spacers with a second mask and a capping layer over the second mask, and the capping layer comprises carbon. The method further includes patterning the first mask and transferring a pattern of the first mask to the target layer. Patterning the first mask comprises masking the first mask with the second mandrel, the first mandrel, and the first spacers.