FinFET Memory Gate Electrode Work Function Engineering
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Solution Overview
Problem
In FinFET-based semiconductor devices, electric field concentration at the corner portion of the fin can lead to deterioration of the charge retention film during data rewriting, resulting in poor data retention characteristics.
Innovation Solution
A two-layer structure for the memory gate electrode is implemented, where the lower layer is made of polysilicon with a relatively low threshold voltage and the upper layer is made of a metal gate electrode with a higher threshold voltage, with the boundary surface positioned below the upper surface of the fin, to alleviate electric field concentration and prevent ONO film deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a FinFET structure with a protruding semiconductor layer is used to reduce short channel effect, then current driving ability and channel controllability are improved, but electric field concentration occurs at the corner portion of the fin leading to deterioration of the charge retention film
Solution Approach 1:
The gate electrode is designed with different work function regions: a first gate electrode with lower work function and a second gate electrode with higher work function. This local differentiation allows the lower work function region to provide strong field effect for channel control while the higher work function region reduces electric field concentration at the fin corner, preventing ONO film deterioration.
Solution Approach 2:
The gate electrode is constructed as a composite structure with two different electrode materials having distinct work functions. This composite gate electrode combines the advantages of both materials: one providing enhanced channel control and the other mitigating harmful electric field concentration, thereby resolving the contradiction between improved reliability and reduced harmful effects.
2Productivity
If voltage is applied for data rewriting in a FinFET-based memory, then data can be rewritten, but the charge retention film deteriorates due to electric field concentration at the fin corner
Solution Approach 1:
The gate electrode structure implements local quality differentiation with two distinct work function regions. The lower work function region enables effective data rewriting by providing sufficient field effect, while the higher work function region locally reduces electric field concentration at the fin corner, protecting the ONO film from deterioration and maintaining data retention characteristics.
Solution Approach 2:
The invention converts the harmful electric field concentration into a beneficial distribution pattern. By strategically placing a higher work function material at the fin corner region, the electric field is redistributed to reduce peak concentration, transforming what was a harmful effect into a protective mechanism that preserves the charge retention film during rewriting operations.
3Device complexity
If a single-material gate electrode is used, then the structure is simple, but it cannot simultaneously achieve strong field effect for channel control and reduce electric field concentration at the fin corner
Solution Approach 1:
The gate electrode is constructed as a composite structure with two different electrode materials having distinct work functions. This composite design, while increasing structural complexity, enables the device to simultaneously achieve strong field effect for channel control and reduce electric field concentration at the fin corner, thereby improving overall device reliability and performance.
Solution Approach 2:
The gate electrode is segmented into two distinct regions with different materials and work functions. This segmentation allows each region to perform its specialized function: one region optimized for channel control and the other for reducing electric field concentration, achieving superior overall performance compared to a uniform single-material gate electrode.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration enhances data retention characteristics by reducing electric field concentration at the fin's corner portion, thereby improving the reliability and longevity of data storage in FinFET-based semiconductor devices.
Implementation Method 1
electric field concentration occurs at a round portion (corner portion) of the upper portion of the fin
Implementation Method 2
an upper portion and a lower portion of a memory gate electrode configuring a memory cell are made of electrode materials respectively different in work function
Data Source
AI summary
To provide a semiconductor device having improved reliability by relaxing the unevenness of the injection distribution of electrons and holes into a charge accumulation film attributable to the shape of the fin of a MONOS memory comprised of a fin transistor. Of a memory gate electrode configuring a memory cell formed above a fin, a portion contiguous to an ONO film that covers the upper surface of the fin and a portion contiguous to the ONO film that covers the side surface of the fin are made of electrode materials different in work function, respectively, and the boundary surface between them is located below the upper surface of the fin.