Vertical Power MOSFET Termination with Half-Concentration Pillars
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Solution Overview
Problem
The tradeoff between breakdown voltage and on-resistance in vertical power MOSFETs limits the development of low power consumption devices, and existing solutions for the termination section, such as using a high-resistance layer without a superjunction structure, increase chip cost and on-resistance due to the need for longer termination distances and impurity concentration variations.
Innovation Solution
A semiconductor device with a superjunction structure in both the cell and termination sections, featuring a high-resistance layer outside the superjunction structure and a trench adjacent to it, where the impurity concentration in the outermost pillar layer is half that of the inner pillar layers, reducing the termination distance and maintaining high breakdown voltage without increasing chip size or on-resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-resistance layer without superjunction structure is used in the termination section, then the termination breakdown voltage is improved, but the termination distance must be lengthened resulting in decreased effective area ratio and increased chip cost
Solution Approach 1:
The invention changes the impurity concentration parameter in the outermost pillar layer of the termination section to approximately half that of inner pillar layers. This parameter modification allows the depletion layer to extend properly while maintaining high breakdown voltage with a shorter termination distance, thereby increasing the effective area ratio and reducing chip cost.
Solution Approach 2:
The invention applies different impurity concentration characteristics to different regions: the outermost pillar layer in the termination section has approximately half the impurity concentration of inner pillar layers. This local quality differentiation enables the depletion layer to extend from the high-resistance layer to the superjunction structure while maintaining high breakdown voltage with reduced termination distance.
2Length of stationary object
If the impurity concentration in the outermost pillar layer is reduced to half, then the termination distance is reduced, but the breakdown voltage may decrease due to impurity concentration variation
Solution Approach 1:
The invention carefully controls the impurity concentration parameter in the outermost pillar layer, setting it to approximately half that of inner pillar layers. This specific parameter change reduces the termination distance while the overall superjunction structure maintains the charge balance necessary for high breakdown voltage.
Solution Approach 2:
The invention maintains the continuous superjunction structure from the cell section through the termination section, ensuring that the depletion layer can extend continuously. This continuity allows the outermost pillar layer with reduced impurity concentration to function effectively without compromising the overall breakdown voltage through proper charge balance maintenance.
3Reliability
If the superjunction structure is discontinuous between cell section and termination section, then the termination breakdown voltage is improved, but the impurity concentration in the outermost pillar layer must be reduced resulting in decreased breakdown voltage
Solution Approach 1:
The invention maintains a continuous superjunction structure from the cell section through the termination section, eliminating the discontinuity problem. This continuity allows the depletion layer to extend properly while maintaining charge balance, reducing the need for complex impurity concentration adjustments at the boundary.
Solution Approach 2:
The invention modifies the impurity concentration parameter in the outermost pillar layer to approximately half that of inner pillar layers, enabling the continuous superjunction structure to function effectively in the termination section while maintaining high breakdown voltage and simplifying manufacturing precision requirements.
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 configuration allows for a significant reduction in termination distance while maintaining high breakdown voltage, reducing chip cost and increasing the number of chips per wafer without compromising on-resistance or breakdown voltage stability.
Implementation Method 1
a structure with p-type pillar layers and n-type pillar layers provided in the drift layer is known as a superjunction structure. In the superjunction structure, a non-doped layer is artificially produced by equalizing the amount of charge (amount of impurity) contained in the p-type pillar layer with that contained in the n-type pillar layer.
Implementation Method 2
the depletion layer does not extend from the high-resistance layer to the superjunction structure
Implementation Method 3
a control electrode provided on the fifth first-conductivity-type semiconductor region, the fourth second-conductivity-type semiconductor region, and the second first-conductivity-type semiconductor layer via an insulating film
Implementation Method 4
the amount of impurity in the outermost semiconductor layer of the first conductivity type or the second conductivity type adjacent to the sixth semiconductor layer in the periodic array structure being generally half the amount of impurity in the second first-conductivity-type semiconductor layer or the third second-conductivity-type semiconductor layer inside the outermost semiconductor layer
Data Source
AI summary
A semiconductor device includes a first first-conductivity-type semiconductor layer, a second first-conductivity-type semiconductor layer provided on a major surface of the first first-conductivity-type semiconductor layer; a third second-conductivity-type semiconductor layer being adjacent to the second first-conductivity-type semiconductor layer, provided on the major surface of the first first-conductivity-type semiconductor layer, and forming a periodic array structure in combination with the second first-conductivity-type semiconductor layer in a horizontal direction generally parallel to the major surface of the first first-conductivity-type semiconductor layer, and a sixth semiconductor layer located outside and adjacent to the periodic array structure of the second first-conductivity-type semiconductor layer and the third second-conductivity-type semiconductor layer, provided on the major surface of the first first-conductivity-type semiconductor layer, and having a lower impurity concentration than the periodic array structure. The amount of impurity in the outermost semiconductor layer of the first conductivity type or the second conductivity type adjacent to the sixth semiconductor layer in the periodic array structure is generally half the amount of impurity in the second first-conductivity-type semiconductor layer or the third second-conductivity-type semiconductor layer inside the outermost semiconductor layer.