Tapered Superjunction Structure With Ultrathin P-Type Layer
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Solution Overview
Problem
Superjunction metal-oxide-semiconductor transistors face challenges due to the majority of the superjunction volume being occupied by p-type regions that do not contribute to conductivity, reducing the n-type volume and current handling capacity, especially in high-voltage applications.
Innovation Solution
The implementation of a superjunction structure with an ultrathin p-type material layer and tapered sidewalls, allowing for uniform n-type doping and eliminating the need for graded doping profiles, thereby enhancing conductivity and manufacturing throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If p-type regions are made thick to provide sufficient charge balancing for high voltage applications, then voltage blocking capability is improved, but n-type volume is reduced and current handling capacity deteriorates
Solution Approach 1:
The patent changes the thickness parameter of the p-type layer from conventional thick designs to ultrathin (10-200 nm), and changes the doping concentration parameter to achieve sufficient charge balancing with much lower p-dopant concentrations (1E16/cm³ to 1E18/cm³) compared to conventional designs. This parameter transformation allows maintaining voltage blocking capability while dramatically increasing n-type volume for current handling.
2Reliability
If conventional vertical pillar superjunction structures are used with equal dopant amounts in n-type and p-type regions, then charge balancing is achieved, but majority of the volume is occupied by non-conductive p-type regions
Solution Approach 1:
The patent introduces asymmetric tapered sidewalls with inward taper angles of 80-89.5 degrees, creating a conical or frustoconical geometry where the p-type layer is concentrated at the periphery rather than uniformly distributed. This asymmetric structure allows the p-type charge to be effectively positioned for electric field termination while minimizing the volume occupied by non-conductive material.
Solution Approach 2:
The patent employs an ultrathin p-type material layer (10-200 nm) that functions as a thin film shell providing charge balancing. This thin film approach replaces the conventional thick p-type pillars, achieving the same charge termination function with minimal volume occupation, thereby maximizing the n-type conducting volume.
3Reliability
If graded doping profiles are used in conventional superjunction structures, then charge balancing is achieved, but manufacturing complexity increases
Solution Approach 1:
The patent uses uniform doping concentrations throughout the n-type and p-type regions rather than graded profiles. The n-type region maintains constant doping concentration from bottom to top, and the p-type layer also has uniform doping. This homogeneous doping approach simplifies the manufacturing process while the tapered geometry provides the necessary charge balancing function.
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 increases the n-type region width, reduces specific on-state resistance by a factor of two, and improves manufacturing efficiency by simplifying the trench fill process, making it suitable for high-voltage applications.
Implementation Method 1
thermally annealing the superjunction structure to diffuse the p-type dopant further into the sidewalls of the first n-type material layer to form the p-type material layer
Implementation Method 2
a p-type material layer that is formed into the sidewalls using a plasma doping (PLAD) process comprising generating plasma with a p-type dopant to dope the sidewalls of the first n-type material layer
Data Source
AI summary
Methods and structures relating to tapered superjunction structures with ultrathin p-type regions. In some embodiments, a method may comprise forming an opening in a first n-type material layer on a substrate where the opening has sidewalls with an inward taper of less than 90 degrees, forming a p-type material layer on or into the sidewalls of the first n-type material layer and into a bottom of the opening in the first n-type material layer, removing a portion of the p-type material layer at the bottom of the opening, and depositing a second n-type material layer to fill the opening. In some embodiments, the p-type material layers are formed by doping the sidewalls of the first n-type material layer with a plasma doping process or a solid-state diffusion doping process.