Segmented Polysilicon Field Plate for MOSFET Stress and Conductivity
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Solution Overview
Problem
The use of polysilicon field plate electrodes in trench structures for MOSFETs leads to excessive phosphorus doping, causing volume expansion and stress-induced dislocations, as well as inconsistent contact areas due to surface protrusion, which hinders the achievement of high breakdown voltage and low on-resistance.
Innovation Solution
The semiconductor device incorporates a field plate electrode with a Y-shape configuration and recesses in the upper portion, using thinner insulating layers to mitigate electric field concentration and reduce stress, while maintaining low on-resistance through phosphorus doping in polysilicon.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If polysilicon field plate electrode is doped with high concentration of phosphorus to reduce on-resistance, then electrical conductivity is improved, but volume expansion occurs causing stress and dislocations in adjacent layers
Solution Approach 1:
The field plate electrode is divided into multiple segments along its length, with each segment having independent phosphorus doping concentration. This allows the electrode to be segmented into high-conductivity regions (for low on-resistance) and low-expansion regions (for structural stability), resolving the contradiction between electrical performance and structural integrity
Solution Approach 2:
Different regions of the field plate electrode are assigned different phosphorus doping concentrations based on their functional requirements. The region requiring low on-resistance receives high phosphorus concentration, while regions adjacent to sensitive layers receive lower concentrations to minimize volume expansion and stress,实现ing local optimization of both electrical and mechanical properties
2Reliability
If polysilicon field plate electrode is doped with high concentration of phosphorus to reduce on-resistance, then electrical conductivity is improved, but top surface protrudes preventing consistent contact area
Solution Approach 1:
The field plate electrode is segmented with different doping concentrations, where only specific segments receive high phosphorus doping. This prevents uniform volume expansion across the entire electrode, maintaining a flat top surface profile that ensures consistent contact area with upper layers while still achieving low on-resistance in the conductive segments
Solution Approach 2:
High phosphorus concentration is applied locally only to regions where low on-resistance is critical, while other regions maintain lower doping levels to preserve flat surface topology. This local differentiation resolves the conflict between achieving low electrical resistance and maintaining manufacturing precision for consistent contact areas
3Reliability
If thicker insulating layer is used to reduce electric field concentration, then breakdown voltage is improved, but device size increases
Solution Approach 1:
The insulating layer thickness is made asymmetric, being thicker at the bottom of the trench where electric field concentration is highest, and progressively thinner towards the top. This asymmetric configuration optimizes breakdown voltage protection at critical regions while minimizing the overall volume occupied by the insulating layer, thus reducing device size
Solution Approach 2:
Instead of uniformly increasing insulating layer thickness in one dimension, the patent employs a gradient thickness profile that varies along the vertical dimension of the trench. This dimensional variation allows the insulating layer to provide maximum field concentration mitigation where needed while occupying minimal overall volume, resolving the contradiction between breakdown voltage and device size
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 design enhances breakdown voltage and ensures consistent contact areas between the field plate and source electrodes, reducing stress and dislocations, thereby improving the reliability and efficiency of the MOSFET.
Implementation Method 1
Phosphorus atoms are therefore introduced into the polysilicon layer by thermal treatment in an atmosphere of H3POCl
Implementation Method 2
Phosphorus atoms are therefore introduced into the polysilicon layer by thermal treatment in an atmosphere of H3POCl
Implementation Method 3
a field plate electrode disposed on the first insulating layer and the second insulating layer and having a recess extending from an upper surface of the field plate electrode towards the bottom surface of the opening
Data Source
AI summary
According to one embodiment, a semiconductor device includes a semiconductor layer having an opening formed therein, a first insulating layer disposed on a bottom surface of the opening and on a sidewall of the opening, a second insulating layer disposed on the sidewall of the opening above the first insulating layer, the second insulating layer being thinner than the first insulating layer, a field plate electrode disposed on the first insulating layer and the second insulating layer and having a recess extending from an upper surface of the field plate electrode towards the bottom surface of the opening, and a first layer disposed in the recess and including a material that is different from a material of the field plate electrode.