Growth Rate Modifier for Uniform Gate Oxide Thickness
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Solution Overview
Problem
Current processes for forming transistors result in non-uniform gate oxide thicknesses, particularly at the edge of shallow trench isolation (STI), leading to performance and reliability issues due to the narrow-channel effect and time-dependent dielectric breakdown (TDDB) failures.
Innovation Solution
A method is introduced where a growth rate modifier (GRM) is applied in specific regions of the substrate to modify the intrinsic oxidation growth rates, ensuring a uniform thickness of the thermally oxidized layer by adjusting the growth rates of the device layer in different portions of the device region, such as the edge and center regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If standard thermal oxidation process is used to form gate oxide, then the oxidation process is simple and fast, but the gate oxide thickness becomes non-uniform at STI edge
Solution Approach 1:
The patent introduces a growth rate modifier (GRM) layer with different compositions in different regions of the substrate. The GRM layer has a first composition in the active center region and a second composition in the active edge region, creating local quality differences that compensate for the inherent non-uniform oxidation growth rates at different locations during thermal oxidation.
Solution Approach 2:
The patent modifies the intrinsic oxidation growth rate by changing the compositional parameter of the GRM layer. By adjusting the ratio of first material to second material in the GRM layer, the oxidation growth rate can be controlled to be faster in the center region and slower at the edge region, achieving uniform gate oxide thickness while maintaining standard thermal oxidation conditions.
2Productivity
If gate oxide thickness is reduced at STI edge to accommodate narrow channel effects, then device performance improves, but reliability decreases due to TDDB failures
Solution Approach 1:
The GRM layer provides local quality adjustment by having different compositions in different regions. This allows the gate oxide thickness to be uniformly maintained across the device, preventing the narrow-channel effect while also avoiding the thinning that leads to TDDB failures at the STI edge.
Solution Approach 2:
The GRM layer is formed beforehand to pre-compensate for the non-uniform oxidation growth. By having a modified composition in the GRM layer at the active edge region, the oxidation process is slowed down in advance at locations where excessive thinning would occur, preventing both performance degradation and reliability issues before they happen.
3Manufacturing precision
If GRM layer with different compositions is formed in different regions, then uniform gate oxide thickness is achieved, but process complexity increases
Solution Approach 1:
The GRM layer is segmented into different compositional regions: a first composition in the active center region and a second composition in the active edge region. This segmentation allows precise control of oxidation growth rates in different areas, achieving uniform gate oxide thickness while using a relatively simple single-layer structure rather than multiple complex layers.
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 approach achieves a more uniform gate oxide thickness, improving device performance and reliability by ensuring the oxide layer at the edge and center portions is within 5% of the target thickness, thereby mitigating the narrow-channel effect and TDDB failures.
Implementation Method 1
An oxygen containing layer is formed by thermal oxidation
Data Source
AI summary
A device includes a substrate with a device region on which a transistor is formed. The device region includes active edge regions and an active center region which have different oxidation growth rates. A growth rate modifier (GRM) comprising dopants which modifies oxidation growth rate is employed to produce a gate oxide layer which has a uniform thickness. The GRM may enhance or retard the oxidation growth, depending on the type of dopants used. Fluorine dopants enhance oxidation growth rate while nitrogen dopants retard oxidation growth rate.