Vertical MOS Transistor Gate Insulation Oxygen Permeation Control
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Solution Overview
Problem
Vertical transistors face challenges in achieving time-dependent dielectric breakdown (TDDB) resistance and maintaining a stable threshold voltage due to variations in gate insulating film thickness, which are exacerbated by excessive oxygen permeation.
Innovation Solution
A semiconductor device design featuring a gate electrode buried in a concave portion of the semiconductor substrate with a low oxygen permeable insulating film over a first insulating film, which suppresses excessive oxygen permeation and densifies the gate insulating film, thereby improving TDDB resistance and stabilizing the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an insulating film is formed over the gate electrode and oxidative processing is applied, then TDDB resistance is improved, but oxygen permeation causes gate insulating film thickness variation
Solution Approach 1:
A low oxygen permeable insulating film is introduced as an intermediary layer between the gate electrode region and the external environment. This mediator layer selectively controls oxygen transport, allowing sufficient oxygen to reach the gate insulating film for TDDB improvement while blocking excessive oxygen permeation that would cause thickness variation. The low oxygen permeable insulating film thus acts as a controlled gateway for oxygen diffusion.
Solution Approach 2:
The oxygen permeability parameter of the insulating film is modified by introducing a low oxygen permeable insulating film with specifically controlled oxygen permeation characteristics. This parameter change enables the film to transmit adequate oxygen for gate insulating film densification while preventing excessive oxygen diffusion that would lead to thickness non-uniformity, thereby resolving the contradiction between TDDB resistance and thickness control.
2Reliability
If the gate electrode upper end is positioned lower than the substrate surface, then TDDB resistance improves, but oxygen permeation still causes threshold voltage fluctuation
Solution Approach 1:
The low oxygen permeable insulating film serves as a mediator that controls oxygen diffusion to the gate insulating film. It allows sufficient oxygen to penetrate for improving TDDB resistance while preventing excessive oxygen permeation that would cause gate insulating film thickness variation and subsequent threshold voltage fluctuation, thus maintaining electrical stability.
Solution Approach 2:
By changing the oxygen permeability parameter through the introduction of a low oxygen permeable insulating film, the system achieves optimal oxygen transport control. This parameter modification enables simultaneous improvement of TDDB resistance and stabilization of threshold voltage by regulating the amount of oxygen reaching the gate insulating film.
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 enhances TDDB resistance and reduces fluctuations in the threshold voltage of vertical transistors by controlling oxygen permeability and film thickness, leading to improved device performance.
Implementation Method 1
a low oxygen permeable insulating film formed over the first insulating film and having a lower oxygen permeability than that of the first insulating film
Implementation Method 2
oxygen reaches by way of an insulating film over the gate insulating film to a region of the gate insulating film not covered with the gate electrode and densifies the gate insulating film in this region
Data Source
AI summary
The upper end of a gate electrode is situated below the surface of a semiconductor substrate. An insulating layer is formed over the gate electrode and over the semiconductor substrate situated at the periphery thereof. The insulating layer has a first insulating film and a low oxygen permeable insulating film. The first insulating film is, for example, an NSG film and the low oxygen permeable insulating film is, for example, an SiN film. Further, a second insulating film is formed over the low oxygen permeable insulating film. The second insulating film is, for example, a BPSG film. The TDDB resistance of a vertical MOS transistor is improved by processing with an oxidative atmosphere after forming the insulating layer. Further since the insulating layer has the low oxygen permeable insulating film, fluctuation of the threshold voltage of the vertical MOS transistor can be suppressed.