Trench Slope Liner Oxides for Flat MOSFET Electric Fields
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Solution Overview
Problem
Existing processes for manufacturing trenches in MOSFETs are time-consuming and costly, requiring multiple masks, and struggle to achieve a substantially flat electric field distribution for optimal MOSFET performance and reliability.
Innovation Solution
A method for forming a slope liner oxide in trenches using a reduced number of masks, involving the deposition of multiple oxides with different etch-back ratios, followed by etching and chemical mechanical polishing to create a smooth morphology, which helps in distributing the electric field evenly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple masks are used to define and etch trench structures, then the trench structures can be formed with precise geometry, but the manufacturing process becomes time-consuming and costly
Solution Approach 1:
The patent combines multiple mask functions into a single mask structure that defines both the trench pattern and the slope liner regions simultaneously. This is achieved by using a multi-layer mask system where different layers are selectively removed to expose different underlying regions, eliminating the need for separate masks for each feature while maintaining precise geometric control.
Solution Approach 2:
The mask structure is segmented into multiple functional layers with different etch selectivities. Each layer serves a specific purpose: the first mask layer defines the trench opening, while the second mask layer defines the slope liner regions. This segmentation allows simultaneous definition of multiple features in a single masking step, reducing process time while maintaining precision.
2Manufacturing precision
If multiple masks are used to define and etch trench structures, then the trench structures can be formed with precise geometry, but the manufacturing cost increases
Solution Approach 1:
The patent merges multiple mask functions into a single integrated mask structure that simultaneously defines trench openings and slope liner regions. This reduces the number of masking steps and associated materials, directly lowering manufacturing cost while maintaining the precision needed for complex trench geometries through the use of selectively removable mask layers.
Solution Approach 2:
The multi-layer mask structure serves multiple functions: it defines trench patterns, defines slope liner regions, and provides selective etching protection. This universal mask design eliminates the need for separate specialized masks for each function, reducing overall process complexity and cost while maintaining manufacturing precision.
3Ease of manufacture
If a single oxide layer is deposited on trench sidewalls, then the process is simple, but the electric field distribution remains non-uniform
Solution Approach 1:
The patent applies different oxide layers with different properties to different regions of the trench sidewalls. The first oxide layer is deposited on the entire sidewall surface, while the second oxide layer is selectively deposited only on specific regions defined by the mask structure. This local differentiation allows precise control of electric field distribution in critical regions while maintaining process simplicity through sequential deposition steps.
Solution Approach 2:
The patent uses a composite oxide structure consisting of two different oxide layers with distinct electrical properties. The first oxide layer provides baseline insulation, while the second oxide layer with different dielectric properties is strategically placed to modify the electric field distribution. This composite approach achieves uniform electric field distribution while extending rather than fundamentally changing the deposition process.
4Reliability
If slope liner oxide is formed to distribute electric field evenly, then the MOSFET reliability improves, but the manufacturing process complexity increases
Solution Approach 1:
The patent implements slope liner oxide formation by selectively depositing a second oxide layer only on specific regions of the trench sidewalls defined by a mask structure. This localized approach targets critical high-field regions for electric field control, improving MOSFET reliability where needed most while avoiding unnecessary complexity in low-risk regions, thus balancing reliability improvement with process simplicity.
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 enhances the figure of merit (FOM) of MOSFETs by achieving a substantially flat electric field distribution, improving the performance and reliability of semiconductor devices like SGT-MOS, U-MOS, IGBT, and trench diodes, while reducing the complexity and cost of the manufacturing process.
Implementation Method 1
depositing a first oxide along an inner wall of the trench, the first oxide forming a first slob liner and having a first etch-back ratio. depositing a second oxide along the first oxide that has been deposited along the inner wall of the trench
Implementation Method 2
etching back the first oxide and the second oxide at the same time to form a slope morphology comprising the first oxide and the second oxide within the trench
Implementation Method 3
chemical mechanical polishing to create a smooth morphology
Data Source
Figure 1
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Figure 3~4
AI summary
A method of manufacturing a semiconductor device, comprising: forming a region of semiconductor material having a surface; forming a trench extending from the surface into the region of semiconductor material; depositing a first oxide along an inner wall of the trench, the first oxide forming a first slob liner and having a first etch-back ratio; depositing a second oxide along the first oxide that has been deposited along the inner wall of the trench, the second oxide forming a second slob liner and having a second etch-back ratio that is higher than the first etch-back ratio; and etching back the first oxide and the second oxide at the same time to form a slope morphology comprising the first oxide and the second oxide within the trench.