Epitaxial Layer for STI Isolation and Threshold Control
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Solution Overview
Problem
Ion implantation in semiconductor devices can cause surface damage to the substrate and lead to issues like the 'moat phenomenon' in Shallow Trench Isolation (STI) techniques, requiring an annealing process and potentially damaging gap-fill dielectric films.
Innovation Solution
A method involving the formation of a pad oxide and nitride film on a semiconductor substrate, followed by selective etching to expose the substrate, forming trenches, and creating an epitaxial layer with dopants to control threshold voltage, which surrounds the gap-fill dielectric film, thereby reducing surface damage and protecting the oxide film corners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If ion implantation is performed to control threshold voltage, then threshold voltage control is achieved, but surface damage occurs on the semiconductor substrate
Solution Approach 1:
An epitaxial layer is formed on the semiconductor substrate before ion implantation. This preliminary layer serves as a protective barrier that prevents surface damage during the ion implantation process while still allowing the implanted ions to reach the substrate and control the threshold voltage effectively.
Solution Approach 2:
The epitaxial layer acts as an intermediary between the ion implantation process and the semiconductor substrate. It mediates the interaction by absorbing the harmful effects of ion collision while transmitting the necessary doping effect to the substrate, thus protecting the substrate from surface damage.
2Object-affected harmful factors
If annealing process is performed to overcome ion implantation damage, then surface damage is reduced, but process complexity increases
Solution Approach 1:
Instead of applying a corrective annealing process after ion implantation to fix surface damage, the invention uses an epitaxial layer formed beforehand that prevents surface damage from occurring in the first place. This proactive approach eliminates the need for subsequent annealing steps, reducing process complexity.
3Reliability
If STI technique is used for isolation, then isolation stability is improved, but moat phenomenon occurs at oxide film corners
Solution Approach 1:
The epitaxial layer is selectively formed only in the active areas where transistors will be created, not in the isolation regions. This local differentiation allows the STI structure to maintain its stability while the epitaxial layer protects the active areas from moat phenomenon during subsequent processing steps.
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 prevents surface damage during ion implantation, eliminates the need for an annealing step, enhances isolation effects, and reduces the occurrence of the 'moat phenomenon, while protecting the gap-fill dielectric film.
Implementation Method 1
forming an epitaxial layer (for controlling a threshold voltage) including a dopant in the exposed active area
Implementation Method 2
Ion implantation is a process wherein impurity atoms are ionized and accelerated in an electric field to be implanted into a wafer
Data Source
AI summary
A method of fabricating a semiconductor device includes forming a pad oxide film and a nitride film on a semiconductor substrate; exposing the semiconductor substrate by selectively etching the pad oxide film and the nitride film; forming a trench in the exposed semiconductor substrate; forming a gap-fill dielectric film in the trench; exposing an active area of the semiconductor substrate by removing the pad oxide film and the nitride film; forming an epitaxial layer including a dopant in the exposed active area; forming a gate electrode on the epitaxial layer; and forming source and drain regions in the active area beside the gate electrode. The semiconductor device can prevent surface damage of a semiconductor substrate, may occur when performing ion implantation for threshold voltage control, and does not require annealing after ion implantation. Additionally, the semiconductor device can enhance an isolation effect by protecting an oxide film in a corner portion of the STI, to prevent an occurrence of a moat phenomenon in the STI, and to prevent the damage of the gap-fill dielectric film.