Semiconductor Gate Electrode Barrier Layer for CVD Damage Prevention
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Solution Overview
Problem
The deposition of tungsten as an upper electrode in semiconductor devices using chemical vapor deposition (CVD) damages the underlying work function control metal and gate insulating film, leading to increased gate resistance and reduced transistor speed.
Innovation Solution
A method involving the sequential formation of a first gate electrode layer defining the work function, a second gate electrode layer with barrier properties to protect the underlayers, and a third gate electrode layer of lower resistance formed by CVD, which prevents damage from deposition gases and reduces gate resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin work function control metal is deposited over a substrate with the intermediary of a gate insulating film and then W is deposited as an upper electrode by CVD, then the gate resistance is decreased, but the deposition gas reacts with the underlying work function control metal and fluorine enters the gate insulating film, leading to damage to these underlayers and significantly deteriorating the yield of the semiconductor device
Solution Approach 1:
A barrier metal layer is introduced as an intermediary between the work function control metal and the CVD-deposited tungsten layer. This barrier layer prevents the deposition gas from reacting with the underlying work function control metal and stops fluorine from entering the gate insulating film, thereby protecting the underlayers during the tungsten deposition process while still achieving low gate resistance
Solution Approach 2:
The gate electrode is constructed as a composite structure consisting of multiple layers: a work function control metal layer, a barrier metal layer, and a tungsten layer deposited by CVD. Each layer serves a specific function - the work function control metal defines the threshold voltage, the barrier layer protects against chemical damage, and the tungsten layer provides low resistance, achieving a balance between electrical performance and device reliability
2Speed
If only work function control metal is used to form the gate electrode, then the threshold voltage is properly controlled, but the gate resistance increases, resulting in longer time for voltage to reach threshold and lower transistor speed
Solution Approach 1:
The gate electrode uses a composite structure combining work function control metal with low-resistance tungsten. The work function control metal layer maintains proper threshold voltage control, while the overlaid tungsten layer provides low gate resistance, enabling fast transistor switching speeds without sacrificing threshold voltage precision
Solution Approach 2:
Different regions of the gate electrode structure have different functional properties: the work function control metal layer provides electrical characteristics for threshold voltage control, while the tungsten layer provides low resistance for fast signal transmission. Each layer is optimized for its specific local function within the overall gate electrode system
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 method enhances transistor speed, reduces power consumption, and improves semiconductor device yield by preventing damage during CVD deposition and achieving lower gate resistance.
Implementation Method 1
a first gate electrode layer that defines the work function of the gate electrode is formed on the gate insulating film
Implementation Method 2
a second gate electrode layer that has a barrier property for the underlayers is formed on the first gate electrode layer
Implementation Method 3
a third gate electrode layer of which resistance is lower than that of the first gate electrode layer is formed on the second gate electrode layer by chemical vapor deposition (CVD)
Implementation Method 4
tungsten hexafluoride (WF6) employed as the deposition gas reacts with the underlying work function control metal
Data Source
AI summary
Disclosed herein is a method for manufacturing a semiconductor device, the method including the step of forming a gate electrode that contains a metal over a semiconductor substrate with intermediary of a gate insulating film, the step including the sub-steps of, forming a first gate electrode layer that defines a work function of the gate electrode on the gate insulating film, forming a second gate electrode layer that has a barrier property for underlayers on the first gate electrode layer, and forming a third gate electrode layer of which resistance is lower than a resistance of the first gate electrode layer on the second gate electrode layer by chemical vapor deposition.