N-type MOSFET Work Function Tuning via Conformal Doping
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Solution Overview
Problem
N-type MOSFETs with metal gate and high-k gate dielectric layers face challenges in achieving low threshold voltage due to the Fermi-Pinning Effect, making it difficult to integrate these layers thermally stably and maintain low gate resistance while avoiding boron penetration.
Innovation Solution
The method involves forming source/drain regions, an interfacial oxide layer, a high-k gate dielectric layer, and a metal gate layer, followed by conformal doping and annealing to adjust the effective work function by distributing dopants at specific interfaces, generating electrical dipoles to adjust the threshold voltage effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-k gate dielectric layer is used to reduce gate leakage current, then gate leakage is reduced, but integrating it with a metal gate layer presents challenges including thermal stability and interfacial states
Solution Approach 1:
An interfacial oxide layer is introduced between the semiconductor substrate and the high-k gate dielectric layer to serve as an intermediary that improves thermal stability and reduces interfacial states, enabling stable integration of the metal gate layer with the high-k gate dielectric layer
2Reliability
If a metal gate layer is combined with high-k gate dielectric layer to avoid depletion effect and decrease gate resistance, then device reliability is enhanced, but it is difficult to achieve adequately low threshold voltage due to the Fermi-Pinning Effect
Solution Approach 1:
The effective work function of the metal gate layer is adjusted by implanting dopants (such as phosphorus or arsenic) into the metal gate layer and performing annealing, which changes the electrical parameters of the gate stack to achieve the desired low threshold voltage while maintaining the benefits of the metal gate-high-k dielectric combination
Solution Approach 2:
Dopants are selectively implanted into specific regions of the metal gate layer to locally modify the work function characteristics, enabling precise control of the threshold voltage in the N-type MOSFET while maintaining other regions with different properties
3Ease of operation
If dopants are implanted into the metal gate layer to adjust effective work function, then threshold voltage can be controlled, but the process complexity increases
Solution Approach 1:
The dopant implantation step is combined with existing manufacturing processes, and the annealing process is integrated into the standard thermal processing sequence, reducing the overall process complexity despite adding dopant implantation
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 the stability and adjustability of the effective work function of N-type MOSFETs, improving thermal stability and device reliability by controlling the dopant distribution and interfacial reactions.
Implementation Method 1
implanting dopants to the first metal gate layer through conformal doping
Implementation Method 2
annealing a gate stack to change an effective work function of the gate stack
Implementation Method 3
dopants accumulated at the lower interface of the high-k gate dielectric layer can generate the electrical dipoles of proper polarity through the interfacial reaction
Data Source
AI summary
An N-type MOSFET and a method for manufacturing the same are disclosed. In one aspect, the method comprises forming source/drain regions in a semiconductor substrate. The method also includes forming an interfacial oxide layer on the semiconductor substrate. The method also includes forming a high-k gate dielectric layer on the interfacial oxide layer. The method also includes forming a first metal gate layer on the high-k gate dielectric layer. The method also includes implanting dopants into the first metal gate layer through conformal doping. The method also includes annealing a gate stack to change an effective work function of the gate stack which includes the first metal gate layer, the high-k gate dielectric, and the interfacial oxide layer.