Asymmetric Trench Oxide Formation With Capillary Wet Etching
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Solution Overview
Problem
Current manufacturing processes for trench gate IGBTs and MOSFETs with non-constant oxide layers are unreliable, leading to significant variations in etch depth and reduced yield due to inaccuracies in photolithographic exposure and instability of photoresist during etching, resulting in high gate collector and emitter capacitance and energy losses.
Innovation Solution
A method involving the deposition of a hydrophilic layer, which facilitates capillary action during wet etching, allowing for precise control and uniformity in etching depths and widths, thereby enabling the formation of asymmetric or symmetric trench gate regions with consistent insulation layer thicknesses, reducing defects and improving process control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If photolithographic exposure dose is used to determine etch depth, then the etch depth can be controlled, but the etch depth varies significantly across wafer, wafer to wafer, and between batches due to inherent inaccuracy
Solution Approach 1:
A hydrophilic layer is introduced as an intermediary between the photoresist and the insulation layer. This layer facilitates capillary action during wet etching, allowing the etchant to penetrate and etch the insulation layer uniformly below the photoresist surface, thereby achieving consistent etch depth independent of photoresist stability
Solution Approach 2:
The patent utilizes capillary action (a hydraulic principle) by depositing a hydrophilic layer that attracts the wet etchant. The etchant flows through capillary channels formed by the hydrophilic layer, enabling controlled and uniform etching of the insulation layer beneath the photoresist mask, thus achieving precise and consistent etch depth
2Ease of manufacture
If photoresist is used to mask during etching, then the insulation layer can be selectively removed, but the photoresist becomes unstable and loses integrity within the trench during the etch process
Solution Approach 1:
The hydrophilic layer serves as a stable intermediary that remains intact during wet etching. It provides a consistent pathway for etchant flow while the photoresist maintains its masking function, thereby stabilizing the overall etching process and preventing photoresist degradation
Solution Approach 2:
The hydrophilic layer is deposited in advance before photoresist application. This preliminary action creates a stable foundation that guides etchant flow and protects the interface between photoresist and insulation layer, preventing photoresist instability during subsequent etching
3Productivity
If asymmetric trench oxide is implemented to reduce capacitance and improve switching speed, then the manufacturing process becomes more complex and unreliable
Solution Approach 1:
The patent applies local quality by creating asymmetric oxide thickness only where needed - thin oxide in conduction channel regions and thick oxide in non-conduction regions. The hydrophilic layer enables this selective asymmetric etching through capillary action, achieving the desired electrical performance without excessive process complexity
Solution Approach 2:
Capillary action through the hydrophilic layer provides automatic and uniform etching distribution, eliminating the need for complex process controls. The etchant naturally flows through capillary channels to achieve the desired asymmetric profile, simplifying the manufacturing process while maintaining reliability
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
The method enhances the uniformity and consistency of channel etch depth and width, leading to improved electrical performance and increased yield by reducing defects caused by photoresist instability, and is applicable to various semiconductor materials like Silicon, SiC, and GaN.
Implementation Method 1
The hydrophilic layer means that the etchant, in the later step of performing a wet etch, uses capillary action to etch the insulation layer on the sidewalls, below the surface of the photoresist material
Data Source
Figure 1(a)~1(b)
Figure 2(a)~2(c)
Figure 2(d)~2(f)
AI summary
We herein describe a method of manufacturing a semiconductor device having one or more trenches with an insulation layer. The one or more trenches with an insulation layer are manufactured using the steps of performing an etching process to form the one or more trenches, forming a first insulation layer on a lower surface and sidewalls of the one or more trenches, depositing a hydrophilic layer over the first insulation layer, depositing a photoresist material in the one or more trenches, wherein depositing a photoresist material comprises exposing the hydrophilic layer on an upper region of a first side of the one or more trenches, performing a wet etch process to etch the insulation layer on the sidewall of the first side of the one or more trenches to a predetermined distance below a surface of the photoresist material, removing the photoresist material, removing the hydrophilic layer, and after performing the wet etch process, removing the photoresist material, and removing the hydrophilic layer, and forming a second insulation layer on the sidewall of the first side of the one or more trenches.