Charged Balanced Shielded Gate Trench MOSFET
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Solution Overview
Problem
Conventional manufacturing technologies for high voltage semiconductor power devices face challenges such as complex and costly processes, low throughput, and limited scalability, which hinder the production of devices with high breakdown voltage and low on-resistance, especially due to the need for multiple epitaxial and buried layers, and the sensitivity of trench gates during voltage breakdown.
Innovation Solution
A semiconductor power device structure and manufacturing method utilizing a single thin epitaxial layer grown in and over deep trenches, with self-aligned doped shielding regions to shield trench gates and adjust dopant concentration, allowing for simplified processing and scalability across various voltage ranges without requiring etch-backs or chemical mechanical polishing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional high voltage semiconductor power devices are manufactured using standard processes, then breakdown voltage can be achieved, but manufacturing complexity increases and throughput decreases
Solution Approach 1:
The device structure is segmented into alternating superjunction columns (first conductivity type) and drift region portions (second conductivity type) within a single epitaxial layer. This segmentation enables charge balance that supports high breakdown voltage while simplifying manufacturing by eliminating the need for multiple separate epitaxial and buried layers required in conventional approaches.
Solution Approach 2:
The single epitaxial layer serves multiple functions simultaneously: it forms the drift region, contains the superjunction columns for charge balance, and provides the matrix for trench gate formation. This multi-functionality reduces manufacturing complexity by consolidating what would traditionally require multiple separate layers and processing steps.
2Reliability
If multiple epitaxial layers and buried layers are used to achieve high breakdown voltage, then device performance improves, but manufacturing time and cost increase
Solution Approach 1:
Multiple functional layers (drift region, superjunction columns, and burial layer functionality) are merged into a single epitaxial layer. The alternating doped columns provide both the charge balance for high breakdown voltage and the structural foundation for trench gates, eliminating the need for separate epitaxial and buried layers that would require additional growth and processing time.
Solution Approach 2:
The superjunction columns are formed within the epitaxial layer during the epitaxial growth process itself, before trench gate formation. This preliminary action of creating charge-balanced regions during growth simplifies subsequent processing by eliminating the need for post-growth layer additions or complex ion implantation sequences.
3Ease of operation
If trench gates are exposed during voltage breakdown, then device operation is achieved, but gate reliability decreases due to high electric fields
Solution Approach 1:
The doped columns of the first conductivity type act as intermediary charge-balancing regions between the trench gates (second conductivity type) and the drift region. During voltage breakdown, these intermediary columns provide charge balance that reduces peak electric fields at the gate edges, protecting the gates from damage while maintaining device operation.
Solution Approach 2:
The superjunction structure preliminarily counteracts the harmful high electric fields that would otherwise concentrate at trench gate edges during breakdown. By pre-establishing alternating doped columns that create charge balance, the structure prevents the formation of excessive electric fields before breakdown occurs, thereby protecting gate reliability.
4Reliability
If drift layer thickness is increased to support higher breakdown voltage, then breakdown voltage improves, but on-resistance increases
Solution Approach 1:
The drift region is given non-uniform local quality through the alternating superjunction columns. The doped columns provide localized charge balance that enables the drift region to support high breakdown voltage without requiring uniform thickness increases. This local charge balancing allows thinner overall drift regions with lower on-resistance while maintaining high voltage capability.
Solution Approach 2:
The invention changes the doping parameter distribution within the drift region by introducing alternating doped columns. This parameter change in doping concentration and distribution creates charge balance that decouples the relationship between drift region thickness and breakdown voltage, enabling high breakdown voltage with thinner drift regions and thus lower on-resistance.
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 reduces processing steps, enhances reliability and stability, and allows for flexible adjustment of device performance parameters, achieving high breakdown voltage with reduced on-resistance and improved manufacturability, independent of epitaxial layer thickness.
Implementation Method 1
a single thin epitaxial layer with improved manufacturability for manufacturing flexibly scalable charge balanced vertical semiconductor power devices
Implementation Method 2
shielded gate trench with simple manufacturing processes flexibly adjustable for applications to different targeted breakdown voltages
Data Source
AI summary
This invention discloses a semiconductor power device disposed on a semiconductor substrate includes a plurality of deep trenches with an epitaxial layer filling said deep trenches and a simultaneously grown top epitaxial layer covering areas above top surface of said deep trenches over the semiconductor substrate. A plurality of trench MOSFET cells disposed in said top epitaxial layer with the top epitaxial layer functioning as the body region and the semiconductor substrate acting as the drain region whereby a super-junction effect is achieved through charge balance between the epitaxial layer in the deep trenches and regions in the semiconductor substrate laterally adjacent to the deep trenches. Each of the trench MOSFET cells further includes a trench gate and a gate-shielding dopant region disposed below and substantially aligned with each of the trench gates for each of the trench MOSFET cells for shielding the trench gate during a voltage breakdown.