Isolation Trench Sidewall Doping via Selective Residue
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Solution Overview
Problem
Existing methods for producing isolation trenches with different sidewall dopings on silicon wafers are complex, costly, and inefficient, especially for deep trenches with high aspect ratios, as they require multiple masking layers and etching steps, making it difficult to achieve uniform doping across all trench sidewalls.
Innovation Solution
A method involving the use of trenches with different widths, where a narrow trench is completely filled and a wide trench is partially filled, allowing for isotropic etching to remove the material layer from the wide trench while leaving a residue in the narrow trench, enabling selective doping of sidewalls using a single photo mask and hard mask, thereby simplifying the process and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple masking layers and etching steps are used to produce isolation trenches with different sidewall dopings, then different doping types can be achieved, but the process complexity and production costs increase significantly
Solution Approach 1:
The patent divides the trench width into different segments (narrow trenches vs. wide trenches) to achieve different doping outcomes. Narrow trenches receive complete filling and subsequent doping, while wide trenches receive partial filling and different doping treatment, allowing different sidewall dopings without multiple masking layers
Solution Approach 2:
The patent applies different doping treatments to different local regions (trenches) based on their width characteristics. Narrow trenches are completely filled and doped uniformly, while wide trenches are partially filled and receive different doping, creating local quality differences without complex global process changes
2Reliability
If deep isolation trenches with high aspect ratios are produced using conventional methods, then isolation performance is achieved, but the number of filling and etching steps increases, extending production time and costs
Solution Approach 1:
The patent performs preliminary doping of trench sidewalls before the final trench filling step. By doping the sidewalls early when they are exposed, and then filling the trenches subsequently, the method eliminates the need for repeated filling and etching operations that would be required if doping were performed after filling deep trenches
3Manufacturing precision
If a material layer is deposited with thickness adapted to completely fill narrow trenches, then narrow trenches are properly filled, but wide trenches remain partially filled requiring additional processing
Solution Approach 1:
The patent accepts that different trench types (narrow vs. wide) will have different filling states as a deliberate local quality strategy. Narrow trenches are completely filled while wide trenches remain partially filled, and this difference is exploited to enable subsequent selective doping operations without requiring additional masking or etching steps
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 allows for the efficient production of isolation trenches with different sidewall dopings using a single photo mask, enabling the creation of n-conductive and p-conductive regions with varying doping concentrations, suitable for smart power technologies, without the need for additional structuring measures, thus reducing production complexity and costs.
Implementation Method 1
The material layer is removed from the second trench by isotropic etching and a residue of the material layer is kept in the first trench
Implementation Method 2
The sidewall doping can be effected for example by depositing a doped layer followed by a subsequent annealing step in which the doping atoms are diffused from the doped layer into the trench sidewalls
Data Source
AI summary
A description is given of a method for producing isolation trenches (32, 34) with different sidewall dopings on a silicon-based substrate wafer for use in the trench-isolated smart power technology. In this case, a first trench (32) having a first width and a second trench (34) having a second width which is greater than the first width are formed using a hard mask (30). The sidewalls of the first and second trenches are doped in accordance with a first doping type in order to produce sidewalls having a first doping. A material layer (50, 51, 60, 61) is deposited with a thickness determined so as to fill the first trench (32) completely up to and beyond the hard mask and to maintain the gap (34a) in the second trench (34). By means of isotropic etching the material layer is removed from the second trench, but residual material of the material layer is maintained in the first trench. A further doping of sidewalls of the first trench or of the second trench in the presence of the residual material is then performed.