LIGBT Isolation via Heavily Doped p+ Layer
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Solution Overview
Problem
Conventional LIGBTs suffer from inadequate isolation due to low impurity concentration in deep p-well regions, leading to hole overflow, substrate noise, and current gain degradation, particularly when formed on silicon-on-insulator substrates where hole recombination at the BOX interface occurs.
Innovation Solution
The formation of a heavily doped p+ layer through backside implantation with a high impurity concentration, which improves isolation and minimizes hole recombination by creating a high impurity concentration region that effectively isolates the LIGBT, and the use of a dielectric layer to prevent hole recombination at the surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a deep p-well region is formed by implanting p-type impurities deeply into the substrate, then isolation is provided, but the impurity concentration is not high enough leading to hole overflow
Solution Approach 1:
The patent changes the doping concentration parameter by forming a p+ region with impurity concentration of 1×10^19 to 1×10^21 atoms/cm³, which is one to two orders of magnitude higher than conventional deep p-well regions. This high concentration parameter effectively blocks hole overflow while maintaining isolation functionality.
Solution Approach 2:
The patent performs preliminary doping action by forming the heavily doped p+ region before other LIGBT structure formations. This preliminary high-concentration doping creates an effective isolation barrier in advance, preventing subsequent hole overflow issues.
2Reliability
If formed on silicon-on-insulator substrate, then hole overflow is avoided, but hole recombination at BOX interface causes current gain degradation
Solution Approach 1:
The patent introduces a heavily doped p+ region as an intermediary between the n-type region and the BOX layer. This intermediary layer with high hole concentration acts as a hole reservoir, preventing holes from reaching the BOX interface where recombination would occur, thus preserving current gain while maintaining isolation.
Solution Approach 2:
The patent converts the potential harm of high impurity concentration (which could increase recombination) into a benefit by strategically placing the high-concentration p+ region away from the BOX interface. The high concentration creates a strong potential barrier that actually prevents holes from reaching recombination sites, turning what could be harmful into a protective mechanism.
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 enhances the isolation effect, reduces substrate noise, and improves the driving capability and leakage current performance of LIGBTs by maintaining high impurity concentration and minimizing hole recombination, thus addressing the limitations of conventional LIGBTs.
Implementation Method 1
a heavily doped p+ layer through backside implantation with a high impurity concentration, which improves isolation and minimizes hole recombination by creating a high impurity concentration region
Data Source
AI summary
A device includes a dielectric layer, and a heavily doped semiconductor layer over the dielectric layer. The heavily doped semiconductor layer is of a first conductivity type. A semiconductor region is over the heavily doped semiconductor layer, wherein the semiconductor region is of a second conductivity type opposite the first conductivity type. A Lateral Insulated Gate Bipolar Transistor (LIGBT) is disposed at a surface of the semiconductor region.