Stepped Gate Oxide Formation Using Sacrificial Etch Masks
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Solution Overview
Problem
Existing methods for forming stepped gate oxides in MOS devices are cost-inefficient and result in gate oxides that are not thick enough to withstand higher voltages, typically limited to around 1000 angstroms, affecting device performance.
Innovation Solution
A method involving the successive formation of pad oxide, nitride, and poly layers on a substrate, followed by etching to create a stepped trench, filling with dielectric material, and planarizing to form a stepped oxide with thicker and thinner portions, allowing for thicker gate oxides up to 3000 angstroms to withstand higher voltages, while reducing the number of masks needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional dual gate oxide process with multiple masks is used, then stepped gate oxide can be formed, but manufacturing cost increases and process complexity increases
Solution Approach 1:
The gate oxide formation process is segmented into multiple deposition steps (first gate oxide, second gate oxide) with different thicknesses, allowing selective etching to create the stepped structure. This segmentation enables precise control over the stepped profile without requiring multiple masks for patterning.
Solution Approach 2:
The method performs preliminary deposition of pad oxide and nitride layers before the main gate oxide formation. These preliminary layers serve as sacrificial masks and etch stop layers, enabling the stepped structure to be formed through selective etching rather than multiple mask alignments.
2Manufacturing precision
If conventional dual gate oxide process is used, then stepped gate oxide can be formed, but manufacturing cost increases
Solution Approach 1:
The process segments oxide deposition into separate steps, allowing each layer to be optimized independently and enabling simpler, fewer mask steps for the overall patterning process, thereby reducing manufacturing costs.
Solution Approach 2:
The nitride layer and pad oxide layers serve as intermediary sacrificial layers that facilitate the formation of the stepped structure through selective etching. These intermediary layers eliminate the need for multiple expensive mask alignments while achieving the desired stepped profile.
3Ease of manufacture
If gate oxide thickness is limited to 1000 angstroms, then conventional process can be used, but electrical strength decreases and device performance is affected
Solution Approach 1:
The gate oxide structure implements local quality variations with different thicknesses in different regions (thinner at edges, thicker at center). The method deposits a second gate oxide layer that is thicker than the first, creating a stepped profile where the central region has greater thickness (up to 3000 angstroms) to provide enhanced electrical strength and voltage withstand capability.
Solution Approach 2:
The gate oxide structure uses a composite of multiple oxide layers with different thicknesses. The first gate oxide layer and second gate oxide layer are deposited sequentially to create a composite structure that combines the advantages of both thin (good field effect) and thick (good electrical strength) regions.
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 method enables the formation of stepped oxides that can withstand higher voltages, improving device performance and reducing manufacturing costs by minimizing the number of masks required.
Implementation Method 1
etching the poly layer to have an opening for the stepped oxide region
Implementation Method 2
isotropically etching the second pad oxide layer to the nitride layer through the opening to form a stepped trench
Implementation Method 3
isotropically etching the nitride layer to the first pad oxide layer through the opening to expand the stepped trench
Implementation Method 4
filling the stepped trench with dielectric material to form a dielectric layer
Implementation Method 5
planarizing the dielectric layer
Data Source
AI summary
A method for forming a steeped oxide on a substrate is described: successively forming a first pad oxide layer, a nitride layer, a second pad oxide layer and a poly layer on the substrate; etching the poly layer to have an opening for the stepped oxide region; isotropically etching the second pad oxide layer to the nitride layer through the opening to form a stepped trench; isotropically etching the nitride layer to the first pad oxide layer through the opening to expand the stepped trench; filling the stepped trench with dielectric material to form a dielectric layer; planarizing the dielectric layer; removing the poly layer; removing the second pad oxide layer; removing the nitride layer; removing the portion of the first pad oxide layer uncovered by the dielectric layer such that the remaining first pad oxide layer together the remaining dielectric layer forms the stepped oxide.