Fluoride-Free Tungsten Gate Stack for Semiconductor Reliability
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Solution Overview
Problem
The semiconductor industry faces challenges in forming reliable semiconductor devices at increasingly smaller sizes due to the complexity and difficulty of fabrication processes as feature sizes decrease, leading to issues with device performance and reliability.
Innovation Solution
A semiconductor device structure is formed using a process that includes forming fin structures, isolation features, and a metal gate stack with a tungsten bulk layer, where the seed and filling layers are substantially free of fluoride, preventing fluorine diffusion into the work function layer and maintaining stable threshold voltage and flat-band voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional fabrication processes are used to form semiconductor devices at smaller sizes, then geometric size decreases and functional density increases, but manufacturing complexity increases and device reliability deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the seed and filling layers by selecting materials that are substantially free of fluoride (such as tungsten, cobalt, copper, aluminum, or their nitride/oxide variants). This parameter change prevents fluorine diffusion into the work function layer, thereby maintaining stable threshold voltage and flat-band voltage even as device dimensions are scaled down, resolving the contradiction between smaller geometric size and device reliability
Solution Approach 2:
The patent employs composite material structures including the work function layer (such as titanium nitride or tantalum nitride) combined with fluoride-free seed and filling layers. This composite approach creates a multi-layer gate structure where each layer serves specific functions: the work function layer provides appropriate work function, while the fluoride-free filling layers prevent contamination, thereby maintaining device reliability at scaled dimensions
2Productivity
If feature sizes continue to decrease to increase functional density, then production efficiency increases, but fabrication process complexity and difficulty increase
Solution Approach 1:
The patent simplifies the fabrication process by changing the material selection parameter - choosing seed and filling layer materials that are substantially free of fluoride from the outset. This prevents the need for additional complex process steps to control or remove fluorine contamination, thereby maintaining production efficiency while reducing fabrication process complexity at smaller feature sizes
3Ease of manufacture
If fluoride-containing materials are used in seed and filling layers, then deposition processes are easier to perform, but fluorine diffusion into work function layer occurs causing threshold voltage and flat-band voltage instability
Solution Approach 1:
The patent changes the chemical composition parameter of the seed and filling layers by selecting materials that are substantially free of fluoride (such as tungsten, cobalt, copper, aluminum, or their nitride/oxide variants). This parameter change eliminates fluorine diffusion into the work function layer, thereby maintaining stable threshold voltage and flat-band voltage while still being compatible with standard deposition processes
Solution Approach 2:
The patent introduces an intermediary barrier concept by using the fluoride-free seed and filling layers as protective intermediaries between the deposition process and the work function layer. These intermediary layers prevent fluorine contamination while allowing the deposition process to proceed, thus maintaining both ease of manufacture and compositional stability
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 enhances device performance and reliability by reducing fluorine diffusion, ensuring consistent threshold voltage and flat-band voltage, and improving the semiconductor device structure's overall stability and efficiency.
Implementation Method 1
the seed and filling layers are substantially free of fluoride, preventing fluorine diffusion into the work function layer and maintaining stable threshold voltage and flat-band voltage
Data Source
AI summary
Structures and formation methods of a semiconductor device structure are provided. A method for forming a semiconductor device structure includes patterning a semiconductor substrate to form a fin structure. The method also includes forming a sacrificial material over the fin structure. The method further includes forming spacer elements adjoining sidewalls of the sacrificial material. Furthermore, the method includes removing the sacrificial material so that a trench is formed between the spacer elements. The method also includes forming a gate dielectric layer in the trench. The method further includes forming a work function layer in the trench to cover the gate dielectric layer. In addition, the method includes depositing a tungsten bulk layer with a precursor to fill the trench. The precursor includes a tungsten-containing material that is substantially free of fluoride.