FinFET Threshold Voltage Control via Variable Fin Height
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Solution Overview
Problem
The existing FINFET manufacturing process faces challenges in controlling the threshold voltage (VT) due to complexity in managing the work function of metal gates and difficulty in fabricating uniform processes.
Innovation Solution
A semiconductor structure with fins of different heights and a uniform shallow trench isolation (STI) oxide layer is developed, allowing for modulation of VT by adjusting fin heights and ensuring a uniform, even surface for improved electrical properties and reduced defect rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If work function in metal gate is controlled to modulate threshold voltage, then threshold voltage control is achieved, but the fabrication process becomes very complicated and difficult to control
Solution Approach 1:
The patent changes the control parameter from work function modulation to fin height modulation. By varying the fin height (a geometric parameter) instead of modifying the metal gate work function (a material property), the threshold voltage is controlled through a simpler physical dimension change that is easier to fabricate and control in the manufacturing process
Solution Approach 2:
The patent segments the fins into different height levels (first fins and second fins with different heights) to achieve different threshold voltages. This segmentation allows independent control of fin heights in different regions, enabling threshold voltage modulation without complex metal gate work function control
2Ease of manufacture
If fins of different heights are created to modulate threshold voltage, then threshold voltage modulation is simplified, but the fabrication process requires multiple etching steps and hard mask removal
Solution Approach 1:
The patent performs preliminary actions by forming an initial oxide layer before creating the different fin heights. This preliminary oxide layer serves as a foundation that simplifies subsequent etching steps, as the etching process can selectively remove oxide to expose fins of different heights without requiring complex hard mask removal sequences
Solution Approach 2:
The patent uses the vertical dimension (oxide layer thickness) to control fin height differences. By etching through a uniform oxide layer, the fins naturally emerge at different heights based on the oxide removal depth, transforming a complex multi-step height control problem into a simpler single-dimensional etching control problem
Data Source
AI summary
A semiconductor structure comprises a substrate, a plurality of fins, an oxide layer and a gate structure. The fins protrude from the substrate and are separated from each other by the oxide layer. The surface of the oxide layer is uniform and even plane. The gate structure is disposed on the fins. The fin height is distance between the top of the fins and the oxide layer, and at least two of the fins have different fin heights.