NbN PMOS High-k Metal Gate Stack for Low-EOT Bandedge Vfb
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Solution Overview
Problem
Current PMOS high-κ metal gate stacks face challenges in maintaining switching speeds as device dimensions shrink, requiring improved bandedge Vfb performance without incurring an equivalent oxide thickness (EOT) penalty, which TiN-based materials struggle to achieve effectively.
Innovation Solution
The use of NbN as a PMOS work function material in a metal gate stack, deposited by atomic layer deposition, provides improved flatband voltage (Vfb) performance with minimal EOT penalty, offering an effective work function of greater than or equal to 4.75 eV and maintaining stability across varying temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TiN is used as PMOS work function material, then device switching speed is maintained, but bandedge Vfb performance is insufficient
Solution Approach 1:
The patent changes the material parameter from TiN to NbN, which has different work function characteristics. NbN provides superior bandedge Vfb performance while maintaining the necessary switching speed characteristics, resolving the contradiction by selecting a material with optimized electrical parameters for the specific application.
Solution Approach 2:
The gate stack employs a composite structure combining high-κ metal oxide (HKMO) dielectric layer with NbN work function material. This composite approach allows the dielectric to provide high capacitance while NbN provides the necessary work function and bandedge characteristics, achieving both speed and Vfb performance.
2Reliability
If new PMOS work function materials are used to improve bandedge Vfb performance, then Vfb performance increases, but EOT penalty occurs
Solution Approach 1:
The patent optimizes the NbN layer thickness parameter to a specific range (5-50 Å) to achieve the desired work function (≥4.75 eV) without excessive thickness. This precise parameter control allows achieving improved Vfb performance while minimizing EOT penalty, avoiding the trade-off that plagues other material solutions.
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
NbN-based PMOS work function materials demonstrate enhanced Vfb performance, increasing by up to +254.5 mV relative to TiN, with minimal EOT penalty and stable growth, ensuring improved switching speeds and device performance without increasing EOT.
Implementation Method 1
A positive metal-oxide-semiconductor (PMOS) work function material comprising NbN is deposited at a thickness in a range of greater than or equal to 5 Å to less than or equal to 50 Å by atomic layer deposition on the substrate
Data Source
AI summary
Metal gate stacks and integrated methods of forming metal gate stacks are disclosed. Some embodiments comprise NbN as a PMOS work function material at a thickness in a range of greater than or equal to 5 Å to less than or equal to 50 Å. The PMOS work function material comprising NbN has an effective work function of greater than or equal to 4.75 eV. Some embodiments comprise HfO2 as a high-κ metal oxide layer. Some embodiments provide improved PMOS bandedge performance evidenced by improved flatband voltage. Some embodiments exclude transition metal niobium nitride materials as work function materials.