Hafnium Gate Insulator Crystallization Control
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Solution Overview
Problem
High dielectric constant materials like hafnium oxide in semiconductor devices are thermally unstable, leading to crystallization issues, increased gate leak current, and reliability degradation, especially in the manufacturing process of semiconductor devices with buried word lines, where thermal treatment affects the gate insulating film, causing uncontrollable threshold voltage and decreased on-state current.
Innovation Solution
A semiconductor device design with a memory cell region and a peripheral circuit region, where the first buried gate insulating film and on-substrate gate insulating film in the memory cell and peripheral circuit regions respectively contain hafnium with different Hf content percentages, preventing crystallization and maintaining high dielectric constant without increasing gate leak current or threshold voltage variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gate insulating film with high relative dielectric constant (e.g., hafnium oxide) is used to suppress gate leak current and decrease EOT, then the gate leak current is suppressed and EOT is decreased, but the high dielectric constant material crystallizes during low-temperature heat treatment, causing threshold voltage uncontrollability and reliability degradation
Solution Approach 1:
A silicon oxide film is formed as a foundation layer before forming the high dielectric constant film. This preliminary action creates a stable base that prevents crystallization of the subsequent hafnium-containing film during heat treatment, while still enabling the high-k film to provide its desired dielectric properties for gate leak suppression.
Solution Approach 2:
The gate insulating film is constructed as a composite structure combining silicon oxide film and hafnium-containing film. The silicon oxide component provides thermal stability and prevents crystallization, while the hafnium-containing component provides high dielectric constant. This composite approach allows both low gate leak current and crystallization resistance to be achieved simultaneously.
2Stability of the object's composition
If the thickness of a low relative dielectric constant gate insulating film (e.g., silicon oxide) is increased to maintain stability, then the gate insulating film stability is improved, but EOT increases and on-electric current decreases
Solution Approach 1:
The dielectric constant parameter is changed by introducing a high-k hafnium-containing film. This allows the physical thickness to be reduced while maintaining or improving the electrical insulation performance, thereby increasing on-electric current while still preventing gate leak through the high dielectric constant material.
Solution Approach 2:
The composite gate insulating film combines the stability of silicon oxide with the high dielectric constant of hafnium-containing materials. This enables a thinner overall structure to achieve both stability and high on-current performance, as the high-k layer provides superior insulation per unit thickness compared to pure silicon oxide.
3Productivity
If the thickness of a low relative dielectric constant gate insulating film is thinned to increase on-electric current, then on-electric current increases, but gate leak current increases
Solution Approach 1:
The dielectric constant parameter is increased by using hafnium-containing materials, which allows the film thickness to be reduced while maintaining effective insulation. This thinning increases on-electric current through reduced resistance, while the high-k material's superior insulation properties prevent gate leak current from increasing despite the reduced thickness.
Solution Approach 2:
The composite structure leverages the high dielectric constant of the hafnium-containing film to provide enhanced insulation efficiency. This enables a thinner gate insulating film to achieve both high on-current (due to reduced thickness) and low gate leak (due to high-k material properties).
4Productivity
If high dielectric constant materials are used to decrease EOT, then EOT is decreased and on-electric current increases, but the materials react with metal gate electrode and silicon substrate, increasing leak current and degrading reliability
Solution Approach 1:
A silicon oxide film is introduced as an intermediary layer between the hafnium-containing high-k film and the metal gate electrode or silicon substrate. This intermediary prevents direct contact and chemical reactions between the reactive high-k material and the electrode/substrate, thereby preventing leak current increase and reliability degradation while allowing the high-k film to maintain its function of decreasing EOT and increasing on-current.
5Stability of the object's composition
If a dummy gate electrode method is used to prevent high dielectric material degradation during heat treatment, then the high dielectric material stability is improved, but the manufacturing process complexity increases and cannot be applied to devices with buried word lines
Solution Approach 1:
Instead of using a dummy gate electrode that requires formation and subsequent removal, this invention forms a stable silicon oxide film in advance as a foundation layer. This preliminary action protects the high dielectric material during heat treatment without requiring complex dummy structures or additional removal steps, thereby reducing manufacturing process complexity while maintaining material stability.
Solution Approach 2:
The protective function is extracted from the complex dummy gate electrode structure and implemented through a simple silicon oxide film layer. This extraction eliminates the need for dummy gate formation and removal processes, significantly simplifying the manufacturing workflow while still providing the necessary thermal protection for the high dielectric material.
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 design enhances on-state current and processing speed by preventing crystallization of hafnium-containing compounds, reducing equivalent oxide thickness, and improving transistor reliability in both memory cell and peripheral circuit regions.
Implementation Method 1
hafnium oxide is crystallized by the heat-treatment of a comparatively low temperature in a process of manufacture
Implementation Method 2
the gate insulating film (interface layer) of a silicon oxide film is formed in the peripheral circuit region by thermal oxidation
Data Source
AI summary
A semiconductor device comprises: a memory cell region having a first transistor and a peripheral circuit region having a second transistor. The first transistor has a first source electrode and a first drain electrode, a first buried gate insulating film which is formed along an inner wall of a trench and whose relative dielectric constant is higher than a relative dielectric constant of silicon oxide, and a buried gate electrode. The second transistor has a second source electrode and a second drain electrode, a first on-substrate gate insulating film whose relative dielectric constant is higher than a relative dielectric constant of silicon oxide, and an on-substrate gate electrode. A first Hf content percentage, which is a content percentage of hafnium in the first buried gate insulating film, is different from a second Hf content percentage, which is a content percentage of hafnium in the first on-substrate gate insulating film.