Reference Voltage Circuit Gate Structure Against Hydrogen Shift
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Solution Overview
Problem
In high temperature storage tests, P-type gate electrode MOS transistors in reference voltage circuits experience threshold voltage shifts due to hydrogen influence, leading to fluctuations in reference voltage and IC characteristics, which are critical for stability in semiconductor devices.
Innovation Solution
A semiconductor device with a reference voltage circuit configuration that includes an enhancement type MOS transistor with a P-type gate electrode covered by an impermeable film and a depletion type MOS transistor with a nitride film, where the nitride film is removed from the P-type gate electrode to prevent hydrogen diffusion, and a polyimide film or oxide film with corrosion resistance is used to prevent water ingress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a P-type gate electrode MOS transistor is used in a reference voltage circuit, then the reference voltage can be generated using conventional polycrystalline silicon gate electrodes, but the threshold voltage shifts in high temperature storage tests due to hydrogen influence
Solution Approach 1:
The gate electrode structure is segmented into multiple layers: a conventional P-type polycrystalline silicon gate electrode layer and a newly added N-type polycrystalline silicon layer formed on top. This segmentation allows the P-type gate to maintain its conventional manufacturing advantages while the N-type layer acts as a protective barrier against hydrogen diffusion, thus resolving the contradiction between ease of manufacture and threshold voltage stability.
Solution Approach 2:
The gate electrode is transformed from a single-material P-type polycrystalline silicon structure into a composite structure consisting of P-type polycrystalline silicon and N-type polycrystalline silicon layers. This composite structure combines the manufacturing simplicity of conventional P-type gates with the hydrogen-blocking properties of N-type silicon, thereby maintaining ease of manufacture while improving threshold voltage stability in high temperature storage conditions.
2Reliability
If the nitride film is removed from the P-type gate electrode, then hydrogen diffusion is prevented and threshold voltage stability is improved, but water ingress may occur
Solution Approach 1:
The N-type polycrystalline silicon layer serves as an intermediary barrier between the P-type gate electrode and the external environment. It replaces the nitride film's hydrogen-blocking function while being integrated into the gate structure, and works in conjunction with the interlayer insulating film to provide water ingress prevention, thus resolving the contradiction between threshold voltage stability and protection against harmful factors.
Solution Approach 2:
The interlayer insulating film acts as a flexible protective shell covering the gate electrode structure. This thin film provides water ingress prevention while allowing the underlying N-type silicon layer to maintain its hydrogen-blocking function, thereby resolving the contradiction between removing the nitride film for stability and preventing water ingress.
3Object-affected harmful factors
If an impermeable film is added to cover the P-type gate electrode, then water ingress is prevented, but the device structure becomes more complex
Solution Approach 1:
The interlayer insulating film is designed to serve multiple functions: it provides the impermeable barrier against water ingress, supports the N-type polycrystalline silicon layer, and maintains the electrical isolation between different circuit elements. This multi-functionality prevents water ingress without significantly increasing device complexity, as the film performs several protective and structural roles simultaneously.
Solution Approach 2:
The protective functions are merged into existing structural elements: the interlayer insulating film is combined with the gate electrode coverage function, and the N-type silicon layer is integrated with the gate structure. This merging approach provides water ingress prevention and hydrogen blocking without adding separate complex protective structures, thus resolving the contradiction between water ingress prevention and structure complexity.
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 configuration effectively suppresses threshold voltage shifts and IC characteristic fluctuations, maintaining reliability without process changes, and reduces hydrogen diffusion while preventing water ingress, thus stabilizing the reference voltage.
Implementation Method 1
One of the causes of the threshold voltage shift is the influence of hydrogen. Note that although the amount of shift of the threshold voltage is as small as several millivolts, there are applications where the intended performance is a high degree of stability of the reference voltage obtained from the threshold voltage.
Implementation Method 2
an impermeable film that is locally provided to cover the first gate electrode via an interlayer insulating film disposed on the first gate electrode
Implementation Method 3
a polyimide film or oxide film with corrosion resistance is used to prevent water ingress
Data Source
AI summary
Provided is a semiconductor device with a reference voltage circuit including an enhancement type transistor having P-type polycrystalline silicon as a first gate electrode, and a depletion type transistor having N-type polycrystalline silicon as a second gate electrode, in which the enhancement type transistor has an impermeable film that is locally provided to cover the first gate electrode via an interlayer insulating film disposed on the first gate electrode, and a nitride film that has an opening portion which is provided larger than the first gate electrode and smaller than the impermeable film, and is provided to cover a periphery of the impermeable film, and the depletion type transistor has a nitride film that is directly provided on an interlayer insulating film disposed on the second gate electrode and covers the depletion type transistor without a gap.