MOS Isolation Structure Nitrogen Oxygen Ion Implantation
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Solution Overview
Problem
Conventional shallow trench isolation structures for MOS transistors face challenges in size control and stress management, leading to poor electrical properties due to poor etching directivity and tensile or compressive stresses in PMOS and NMOS active regions.
Innovation Solution
A method involving the implantation of nitrogen ions into PMOS isolation regions and oxygen ions into NMOS isolation regions, with partial overlap to form a buffer isolation region, generating specific stresses that enhance hole and electron migration, while controlling the depth and size of the isolation structure through ion energy, dose, and annealing parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional shallow trench isolation structures are used, then electrical isolation between adjacent MOS transistors is achieved, but size control is poor due to poor etching directivity
Solution Approach 1:
The patent changes the fundamental parameter of isolation structure formation from etching-based (conventional STI) to ion implantation-based. By implanting nitrogen ions for PMOS isolation and oxygen ions for NMOS isolation, the method achieves precise size control through controlled ion implantation depth and distribution, eliminating the poor directivity issues of conventional etching processes.
2Reliability
If liner oxide layer is formed by oxidation process, then material permeation into semiconductor substrate is prevented, but tensile or compressive stress is generated in active regions
Solution Approach 1:
The patent applies local quality by selectively implanting different ions into different isolation regions: nitrogen ions are implanted into PMOS isolation regions to generate compressive stress beneficial for hole transfer, while oxygen ions are implanted into NMOS isolation regions to generate tensile stress beneficial for electron transfer. This localized differentiation eliminates the uniform stress problem of conventional liner oxide layers.
Solution Approach 2:
The patent converts the previously harmful stress effect into a beneficial one by deliberately controlling the type and distribution of implanted ions. Instead of trying to eliminate stress, the method generates specific stresses (compressive for PMOS, tensile for NMOS) that enhance carrier transfer, turning the stress problem into a performance enhancement opportunity.
3Stress or pressure
If ion implantation method is used, then stress control is improved, but process complexity increases
Solution Approach 1:
The patent segments the ion implantation process into distinct steps for different isolation regions. First, nitrogen ions are implanted into PMOS isolation regions, then oxygen ions are implanted into NMOS isolation regions. This segmentation allows independent optimization of stress characteristics for each transistor type while maintaining overall process manageability through clear process separation.
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 simplifies the process, improves electrical properties by managing stress effectively, and enhances the isolation performance and operational stability of MOS transistors.
Implementation Method 1
implanting nitrogen ions into the PMOS isolation region
Implementation Method 2
a tensile stress is generated in the PMOS isolation structure formed by implanting nitrogen ions into the PMOS isolation region due to the difference between silicon nitride (SiN) and silicon (Si) in physical properties, which causes a compressive stress in the PMOS active region, and further facilitates the migration of hole
Implementation Method 3
implanting oxygen ions into the NMOS isolation region
Implementation Method 4
a tensile stress is generated in the NMOS active region due to the difference between silicon oxide and Si in physical properties when a NMOS isolation structure is formed by implanting oxygen ions into the NMOS isolation region, which facilitates the migration of electron
Implementation Method 5
annealing the semiconductor substrate to form isolation structures of PMOS and NMOS, respectively
Data Source
AI summary
A method for forming isolation structure for MOS transistor is disclosed, which includes forming a first photoresist layer over a sacrificed oxide layer of a semiconductor substrate, patterning the first photoresist layer to define a PMOS active region and a PMOS isolation region; implanting nitrogen ions into the PMOS isolation region through the sacrificed oxide layer by using the first photoresist layer as a mask; removing the first photoresist layer; forming a second photoresist layer over the sacrificed oxide layer, patterning the second photoresist layer to define a NMOS active region and a NMOS isolation region; implanting oxygen ions into the NMOS isolation region through the sacrificed oxide layer by using the second photoresist layer as a mask; removing the second photoresist layer and the sacrificed oxide layer; and annealing the semiconductor substrate to form isolation structures of PMOS and NMOS, respectively.