High-Voltage BCD Isolation Structure for 1200V Breakdown
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Solution Overview
Problem
In high-voltage BCD processes, particularly for 1200V devices, there is a need for an effective isolation structure that increases breakdown voltage and ensures the parasitic threshold voltage between aluminum wiring and the silicon surface is higher than 1200V, while minimizing the thickness of the field oxide layer to enhance product reliability and planarization.
Innovation Solution
A semiconductor substrate with a first type of doping and an epitaxial layer of a second type of doping, where the isolation region extends through the epitaxial layer into the substrate, and a field oxide layer is formed over the isolation region, with a stacked epitaxial structure and specific doping concentrations to achieve balanced doping states and reduced carrier concentration, thereby increasing breakdown voltage and preventing electric leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional isolation structure is used in high-voltage BCD process, then the manufacturing process is simpler, but the breakdown voltage cannot reach 1200V and the parasitic threshold voltage requirement cannot be met
Solution Approach 1:
The isolation structure is segmented into multiple functional layers: a first isolation layer extending from the silicon surface to a first depth, and a second isolation layer extending from the silicon surface to a second depth greater than the first depth. This segmentation allows each layer to perform specific isolation functions at different depths, achieving 1200V breakdown voltage requirement while maintaining manageable structural complexity.
Solution Approach 2:
Different regions of the isolation structure are assigned different doping types and concentrations. The first isolation layer has a first doping type with first doping concentration, while the second isolation layer has a second doping type with second doping concentration. This local quality variation optimizes the electrical characteristics at different depths, enabling the structure to meet both the high breakdown voltage and parasitic threshold voltage requirements.
2Reliability
If the field oxide layer thickness is increased to improve isolation, then the parasitic threshold voltage increases, but the planarization of oxide layer steps deteriorates and product reliability decreases
Solution Approach 1:
Instead of increasing field oxide layer thickness in the vertical dimension, the solution transitions to a different dimensional approach by creating isolation layers at different depths within the silicon substrate. The first isolation layer is positioned at a first depth and the second isolation layer at a second depth, providing isolation functionality without requiring excessive oxide thickness, thus maintaining planarization while achieving the required parasitic threshold voltage.
Solution Approach 2:
The isolation layers are formed with specific doping concentrations and depth positions before the field oxide layer is deposited. The first isolation layer is formed to a first depth and the second isolation layer to a second depth, preparing the substrate in advance so that a thinner field oxide layer can suffice to achieve the required parasitic threshold voltage, thereby improving planarization and product reliability.
3Reliability
If the doping concentration in the isolation region is increased to improve isolation effectiveness, then the breakdown voltage increases, but the carrier concentration increases causing electric leakage
Solution Approach 1:
The isolation structure employs different doping concentrations at different depths: the first isolation layer has a first doping concentration and the second isolation layer has a second doping concentration. This local quality variation allows the structure to achieve high breakdown voltage through optimized doping profiles while controlling carrier concentration to prevent electric leakage. The opposite doping types in different layers create balanced electric fields that enhance breakdown voltage without excessive carrier accumulation.
Solution Approach 2:
The isolation structure functions as a composite doped region with multiple layers having different doping types and concentrations. This composite structure combines the benefits of high doping concentration (for breakdown voltage) with controlled carrier distribution (to prevent leakage), as the alternating doping types create regions that simultaneously enhance breakdown characteristics and control carrier flow.
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
The solution effectively increases the breakdown voltage of high-voltage devices like LDMOS transistors, reduces the thickness of the field oxide layer, and enhances the reliability and planarization of the oxide layer steps, ensuring the isolation structure can withstand 1200V parasitic breakdown voltage while minimizing footprint area.
Implementation Method 1
a semiconductor substrate having a first type of doping; an epitaxial layer having a second type of doping over the semiconductor substrate, wherein the first type of doping is opposite to the second type of doping; an isolation region having the first type of doping
Implementation Method 2
a field oxide layer over the isolation region
Data Source
AI summary
The invention provides an isolation structure and a manufacturing method thereof for a high-voltage device in a high-voltage BCD process, the isolation structure comprising: a semiconductor substrate having a first type of doping; an epitaxial layer having a second type of doping over the semiconductor substrate, wherein the first type of doping is opposite to the second type of doping; an isolation region having the first type of doping, wherein the isolation region extends through the epitaxial layer into the semiconductor substrate, and wherein the isolation region has a doping concentration on the same order as a doping concentration of the epitaxial layer; a field oxide layer over the isolation region. This invention effectively isolates the epitaxial island where the BCD high-voltage device is located, thereby increasing the breakdown voltage of the high-voltage device in the BCD process. Further, with a minimum thickness of the field oxide layer, the parasitical threshold voltage between the aluminum wiring and the silicon surface of the high-voltage device can be higher than 1200V, thereby improving the planarization of oxide layer steps on the silicon surface in the whole high-voltage BCD process, and enhancing the reliability of the product.