STI Insulator Convex Dome Shape for Fin Isolation
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Solution Overview
Problem
The concave shape of shallow trench isolation (STI) insulators between fins in integrated circuit devices reduces isolation between adjacent fins, leading to inconsistent device performance due to oxide footings formed during the fin reveal process.
Innovation Solution
A convex dome shape is formed at the top surface of the STI insulator between fins, achieved by controlling the flow rate and temperature of etchant gases like HF and NH3 during the fin reveal process, resulting in a thicker insulator at the fin interfaces and a thinner profile between fins, with divots where the insulator contacts the fins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the STI insulator thickness is reduced during fin reveal to expose fin tops, then fin exposure is achieved, but the insulator top surface becomes concave between fins reducing isolation
Solution Approach 1:
Instead of allowing the insulator to be etched uniformly or concavely, the process inverts the expected shape by using controlled differential etching to create a convex dome shape. The insulator is etched more at the fin interfaces (creating divots) and less at the center, producing the opposite of the conventional concave shape and achieving both fin exposure and improved isolation.
Solution Approach 2:
The etching process applies different removal rates to different locations on the insulator surface. By controlling gas flow and temperature, the process creates localized divots where the insulator contacts the fins while maintaining a thicker profile at the center, giving each region the specific thickness needed for its function.
2Ease of operation
If the STI insulator thickness is reduced during fin reveal, then fin tops are exposed, but oxide footings form on fin surfaces interfering with transistor parameters
Solution Approach 1:
The process inverts the typical oxide footing problem by etching divots that remove excess insulator material right at the fin interfaces. This prevents oxide material from climbing onto the fin surfaces during subsequent processing, eliminating the source of threshold voltage variations and other transistor parameter inconsistencies.
Solution Approach 2:
The etching process extracts or removes the problematic oxide material from the fin interfaces by creating divots. By removing the insulator material that would otherwise contact and climb the fin surfaces, the process eliminates the source of oxide footings before they can interfere with transistor operation.
3Productivity
If gas flow rate and temperature are increased during etching to form the dome shape, then etching speed increases, but process control complexity increases
Solution Approach 1:
The process achieves the convex dome shape by changing key etching parameters - specifically increasing gas flow rate and temperature. These parameter changes accelerate the etching reaction and enhance the differential etching effect, allowing the dome shape to form more quickly while maintaining process control through established parameter relationships.
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 electrical isolation between fins, improves transistor performance by minimizing oxide footings, and maintains consistent device operation.
Implementation Method 1
an etching process that uses a gas (e.g., HF)
Data Source
AI summary
Integrated circuit devices include trenches in a material layer that divide the material layer into fins. With such devices, an insulator partially fills the trenches and contacts the material layer. The top surface of the insulator (e.g., the surface opposite where the insulator contacts the material layer) has a convex dome shape between at least two of the fins. The dome shape has a first thickness from (from the bottom of the trench) where the insulator contacts the fins, and a second thickness that is greater than the first thickness where the insulator is between the fins. Further, there is a maximum thickness difference between the first and second thicknesses at the midpoint between the fins (e.g., the highest point of the dome shape is at the midpoint between the fins). Also, the top surface of the first insulator has concave divots where the first insulator contacts the fins.