TiN Gate Electrode Work Function Tuning for CMOS
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Solution Overview
Problem
Semiconductor devices with CMOS structure face challenges in achieving low threshold voltages and preventing metal etching failures due to limitations in work function adjustment of TiN and TiAlN electrodes, particularly in nMOSFET and pMOSFET regions, and the difficulty in using high work function metals like Ru, Mo, and Pt for PMOS due to etching issues.
Innovation Solution
The solution involves forming Ti-rich TiN and N-rich TiN layers for nMOSFET and pMOSFET regions, respectively, within the TiN or TiAlN electrodes, allowing for dual-work function gates with adjusted nitrogen (N), aluminum (Al), and titanium (Ti) content, enabling low threshold voltages and preventing etching failures by using TiN or TiAlN materials advantageous for metal etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high work function metals (Ru, Mo, Pt) are used for PMOS gate electrode, then the work function is sufficient for pMOSFET, but etching difficulty and low thermal stability occur
Solution Approach 1:
The patent adjusts the composition parameters of TiN (specifically the Ti:N ratio) to achieve different work functions. By controlling the nitrogen content and titanium content, the work function of TiN can be tuned to provide sufficient work function for PMOS while maintaining etchability and thermal stability, thus resolving the contradiction between work function requirement and manufacturing ease.
2Ease of manufacture
If TiN is used for gate electrode, then etching is easy, but the work function is insufficient for both nMOSFET and pMOSFET
Solution Approach 1:
The patent modifies the compositional parameters of TiN by adjusting the titanium to nitrogen ratio. By creating Ti-rich or N-rich TiN layers, the work function can be increased to meet the requirements for both nMOSFET and pMOSFET while preserving the etching advantages of TiN material.
Solution Approach 2:
The patent employs composite structures such as TiN/SiO2/Si or TiAlN/SiO2/Si where the TiN layer is combined with other materials. This composite approach allows the TiN to provide etching ease while the interface and composition are optimized to achieve sufficient work function for CMOS operation.
3Reliability
If dual-metal gate electrode is used for CMOS, then ideal work functions for nMOS and pMOS are achieved, but etching failure of metal electrode occurs
Solution Approach 1:
The patent makes TiN a universal material that can serve both nMOS and pMOS gate electrodes by compositional adjustment. Instead of using different metals for different transistor types, TiN with adjusted Ti:N ratios can provide the necessary work functions for both device types, eliminating etching failures associated with dual-metal approaches.
Solution Approach 2:
The patent applies parameter changes to TiN composition to create regions with different work functions within the same material system. By controlling the Ti:N ratio in different gate regions, ideal work functions for both nMOS and pMOS are achieved while using a single etchable material.
4Ease of manufacture
If silicon oxide layer is used as gate dielectric, then it is compatible with standard process, but gate leakage current increases with design rule reduction
Solution Approach 1:
The patent uses composite dielectric structures such as SiO2/HfO2/SiO2 or similar high-k material combinations. The high-k dielectric layer (e.g., HfO2) is sandwiched between silicon oxide layers to provide both process compatibility and reduced gate leakage current, as the high-k material allows thicker equivalent oxide thickness while maintaining electrical performance.
Data Source
AI summary
The present disclosure relates to a semiconductor device and a method of manufacturing the same. The semiconductor device may include a first metal gate electrode provided in a NMOS region of a substrate; and a second metal gate electrode provided in a PMOS region of the substrate, wherein the first and second metal gate electrodes may be formed of TiN material or TiAlN material. Here, the first metal gate electrode may have a higher titanium (Ti) content than the second metal gate electrode, and the second metal gate electrode may have a higher nitrogen (N) content than the first metal gate electrode.