Dummy Structural Features for IC Device Matching
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Solution Overview
Problem
As process geometries shrink, integrated circuit fabrication faces challenges in forming masks for lithographic layers, leading to increased manufacturing variance and performance degradation due to mismatched devices, particularly in circuits like operational amplifiers and sense amplifiers, where device matching is critical.
Innovation Solution
The use of dummy structural features positioned relative to matched devices forces them to be formed within the same pattern layer, reducing mismatch by allocating structural features based on the location of these dummy features during the lithographic process, effectively addressing the issue of device mismatch in integrated circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If double patterning is used to form lithographic layers, then mask formation becomes easier, but device matching precision deteriorates due to features being formed in different pattern layers
Solution Approach 1:
Dummy structural features are introduced as intermediary elements that mediate between the double patterning process and the matched devices. These dummy features act as anchors that force the allocation of structural features for matched devices into the same pattern layer, thereby maintaining device matching precision while preserving the ease of manufacture provided by double patterning
Solution Approach 2:
The dummy structural features are pre-positioned in the design before the lithographic process. This preliminary action ensures that during pattern layer allocation, the structural features of matched devices are automatically assigned to the same pattern layer based on their proximity to the pre-placed dummy features, preventing mismatch before it occurs
2Productivity
If process geometries are reduced to increase circuit density, then productivity improves, but manufacturing variance increases leading to device mismatch
Solution Approach 1:
The dummy structural features serve as intermediary reference points that are less sensitive to the increased manufacturing variance associated with smaller geometries. By anchoring the allocation of matched device features to these dummy features, the system achieves better device matching precision even as process geometries shrink and variance increases
Data Source
AI summary
An integrated circuit is formed using an lithographic process including a stage of forming a lithographic layer from a plurality of separately printed pattern layers. Within the integrated circuit there is formed a circuit including at least two devices that are matched devices such that the performance of the circuit is degraded if the match devices deviate from having matched performance characteristics. Dummy contacts 32 (structural features) are provided within the circuit design so as to force allocation of functional contacts (structural features) of the matched devices into the same pattern layer thereby reducing inter-device variation in contact position and/or size.