Gate Structure Recess for Metal Fill Thickness in HKMG Devices
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Solution Overview
Problem
High-k metal gate (HKMG) devices in integrated circuits face challenges due to additional layers required for tuning work function values, which complicate device fabrication, especially for analog devices with thicker gate dielectric layers, leading to difficulties in maintaining the thickness of the upper-most metal layer and potential electrical shorts during contact etching.
Innovation Solution
The method involves forming recesses in the isolation structure beneath the gate contact, allowing for a thicker metal fill layer over the recess, reducing the risk of etch-through during contact hole formation and preventing electrical shorts, while maintaining the structural integrity of the gate structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If additional layers are added to the gate structure for work function tuning, then the work function values can be adjusted, but the thickness of the upper-most metal layer is reduced, increasing fabrication difficulty and risk of electrical shorts
Solution Approach 1:
The patent introduces a vertical dimension change by forming a recess in the isolation structure beneath the gate contact. This allows the metal fill layer to be deposited at different heights in different regions: thicker over the recess and thinner over the flat isolation structure, thereby maintaining adequate metal thickness while preserving work function tuning capability through multiple layers.
2Adaptability or versatility
If additional layers are added to the gate structure, then work function tuning is achieved, but the device fabrication complexity increases
Solution Approach 1:
The patent applies local quality by creating a non-uniform isolation structure with a recess only in the region where the gate contact is formed. This localized modification allows the metal fill layer to have different thicknesses in different areas, providing adequate thickness where needed while maintaining the multi-layer gate structure for work function tuning in other regions.
3Adaptability or versatility
If the metal layer thickness is reduced due to additional gate layers, then work function tuning is enabled, but the risk of electrical shorts during contact etching increases
Solution Approach 1:
The patent performs a preliminary action by forming the recess in the isolation structure before depositing the metal fill layer. This advance preparation ensures that when the metal layer is deposited, it automatically forms a thicker section over the recess area, providing a built-in protective measure against electrical shorts during subsequent contact etching processes.
Data Source
AI summary
A method includes providing a substrate having a first surface, forming an isolation structure disposed partly in the substrate and having an second surface higher than the first surface by a step height, removing a portion of the isolation structure to form a recess therein having a bottom surface spaced from the first surface by less than the step height, forming a gate structure, and forming a contact engaging the gate structure over the recess. A different aspect involves an apparatus that includes a substrate having a first surface, an isolation structure disposed partly in the substrate and having a second surface higher than the first surface by a step height, a recess extending downwardly from the second surface, the recess having a bottom surface spaced from the first surface by less than the step height, a gate structure, and a contact engaging the gate structure over the recess.