Hafnium Layer Surface Density Control in CMOSFET Threshold Voltage
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Solution Overview
Problem
The challenge in manufacturing MOSFETs and MISFETs is to maintain a predetermined threshold voltage while improving ON current, as lowering impurity concentration in the channel region leads to decreased threshold voltage, and existing methods lack an optimal surface density for hafnium layers in CMOSFETs and CMISFETs.
Innovation Solution
A semiconductor device is fabricated with a P-channel and N-channel insulated gate field effect transistors, where the surface density of the hafnium layer in the N-channel transistor is set lower than in the P-channel transistor, with hafnium layers inserted between the gate insulating films and electrodes to control threshold voltages without increasing impurity concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the impurity concentration of the channel region is lowered to improve ON current, then the ON current increases, but the threshold voltage decreases and a predetermined threshold voltage cannot be obtained
Solution Approach 1:
The invention changes the physical and chemical parameters of the gate insulating film by forming a composite structure with a first gate insulating film containing nitrogen and a second gate insulating film without nitrogen. This parameter change allows independent optimization of threshold voltage (through nitrogen content) and ON current (through overall insulating film properties), resolving the contradiction between improving ON current by lowering impurity concentration and maintaining predetermined threshold voltage
Solution Approach 2:
The invention uses a composite gate insulating film structure consisting of two different gate insulating films: a first gate insulating film containing nitrogen to increase threshold voltage, and a second gate insulating film without nitrogen to maintain good interface properties and high mobility. This composite structure enables simultaneous achievement of high ON current and controlled threshold voltage
2Reliability
If a hafnium layer is formed to increase threshold voltage, then the threshold voltage increases and predetermined threshold voltage can be maintained, but the optimal surface density for CMOSFET performance is not known
Solution Approach 1:
The invention extracts the nitrogen-containing component into a separate first gate insulating film layer, distinct from the second gate insulating film and the hafnium layer. This separation allows independent optimization of each layer's properties: the nitrogen concentration in the first film controls threshold voltage, while the hafnium layer surface density can be optimized for CMOSFET performance without interference, simplifying the overall optimization process
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 allows for improved ON currents and extended TDDB life time in MOSFETs and MISFETs by optimizing hafnium surface density, maintaining desired threshold voltages and enhancing semiconductor device performance.
Implementation Method 1
a technique is known that a threshold voltage is increased by forming a hafnium layer, for example, between a gate insulating film and a gate electrode
Implementation Method 2
depositing a hafnium layer on the second gate insulating film and the first hafnium layer to form a second hafnium layer on the second gate insulating film
Data Source
AI summary
A CMOSFET is composed of a P-channel MOSFET and an N-channel MOSFET formed on a silicon substrate. The P-channel MOSFET is formed a first gate insulating film, a first hafnium layer and a first gate electrode which are stacked on the silicon substrate. The N-channel MOSFET is formed a second gate insulating film, a second hafnium layer and a second gate electrode which are stacked on the silicon substrate. A surface density of the second hafnium layer is lower than a surface density of the first hafnium layer.