Pitch Multiplication Spacer Steps for Sub-50nm IC Features
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Solution Overview
Problem
The continuous reduction in feature sizes of integrated circuits is hindered by the limitations of photolithographic techniques, particularly the minimum pitch beyond which features cannot be reliably formed, limiting further size reduction and spacing between features.
Innovation Solution
The process involves forming mandrels and spacers through pitch multiplication, allowing for the decoupling of feature distance from feature width, enabling the formation of exceptionally closely spaced mask features by consolidating spacers on multiple levels and trimming them to precise dimensions, thereby overcoming the resolution limits of photolithographic techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If photolithographic techniques are used to form features, then manufacturing process is simplified, but manufacturing precision deteriorates due to minimum pitch limitations
Solution Approach 1:
The pitch multiplication process segments the feature formation into multiple discrete steps: forming mandrels at a first pitch, depositing spacer material around mandrels, selectively removing mandrels and some spacers, and repeating the process. This segmentation allows each step to be optimized independently, achieving precision beyond single-step photolithography limits while maintaining processability
Solution Approach 2:
The invention transitions from two-dimensional planar patterning to three-dimensional spacer formation. By depositing conformal spacer layers around mandrels and using vertical sidewalls as templates, the process exploits the third dimension (vertical height) to define horizontal feature spacing, thereby achieving pitch multiplication and overcoming photolithographic resolution limits
2Productivity
If feature size is reduced to increase integration density, then productivity improves, but manufacturing precision deteriorates due to approaching minimum pitch limits
Solution Approach 1:
The process changes the controlling parameter for feature spacing from photolithographic resolution (wavelength-dependent) to deposited layer thickness (process-controlled). By adjusting spacer material thickness through deposition parameters, precise control over final feature pitch is achieved, enabling sub-50nm spacing with better manufacturing precision
Solution Approach 2:
Mandrels are formed in advance at a relaxed pitch that is within photolithographic capabilities, then serve as templates for subsequent spacer formation. This preliminary action allows the less precise photolithography step to define a pattern that is later refined by more precise deposition and etching processes, achieving final precision beyond the initial patterning step
Data Source
AI summary
Multiple pitch-multiplied spacers are used to form mask patterns having features with exceptionally small critical dimensions. One of each pair of spacers formed around a plurality of mandrels is removed and alternating layers, formed of two mutually selectively etchable materials, are deposited around the remaining spacers. Layers formed of one of the materials are then etched, leaving behind vertically-extending layers formed of the other of the materials, which form a mask pattern. Alternatively, instead of depositing alternating layers, amorphous carbon is deposited around the remaining spacers followed by a plurality of cycles of forming pairs of spacers on the amorphous carbon, removing one of the pairs of spacers and depositing an amorphous carbon layer. The cycles can be repeated to form the desired pattern. Because the critical dimensions of some features in the pattern can be set by controlling the width of the spaces between spacers, exceptionally small mask features can be formed.