Lanthanum Oxide Hard Mask for Work Function Metal Patterning
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Solution Overview
Problem
Conventional methods for fabricating metal oxide semiconductor (MOS) devices face challenges such as high thermal budget and leakage current due to the diffusion of lanthanum oxide (LaO) into high dielectric constant layers, leading to incomplete etching and removal issues with polysilicon hard mask layers, affecting device reliability and performance.
Innovation Solution
The method involves using lanthanum oxide (LaO) as a hard mask layer to pattern work function metal layers, reducing thermal budget and preventing diffusion into high dielectric constant layers, allowing for complete removal of the work function metal layer and avoiding residual issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If polysilicon hard mask layer is used to pattern metal materials, then the work function metal layer can be patterned, but the thermal budget becomes too high and LaO diffuses into the high dielectric constant layer causing leakage current
Solution Approach 1:
The patent changes the material parameter of the hard mask layer from polysilicon to lanthanum oxide (LaO). This material substitution fundamentally alters the thermal and diffusion characteristics, allowing the patterning process to proceed without high-temperature steps that would cause LaO diffusion into the high dielectric constant layer, thereby preventing leakage current while maintaining patterning precision.
Solution Approach 2:
The patent employs a disposable LaO hard mask layer that is intentionally designed to be removed after serving its patterning function. This LaO layer is deposited, used for patterning the work function metal layer, and then completely removed via wet etching, avoiding the need for high-temperature processes and subsequent difficult removal of polysilicon residues.
2Ease of manufacture
If high temperature process is used to form polysilicon hard mask layer, then the hard mask layer can be formed, but LaO diffuses into the high dielectric constant layer causing leakage current
Solution Approach 1:
The patent changes the deposition temperature parameter by using low-temperature atomic layer deposition (ALD) to form the LaO hard mask layer. This eliminates the high-temperature process that would cause LaO diffusion into the high dielectric constant layer, thereby preventing leakage current while still achieving complete and precise patterning.
Solution Approach 2:
The patent introduces LaO as an intermediary hard mask material that mediates between the patterning requirement and the prevention of harmful diffusion. LaO serves as a effective hard mask for patterning the work function metal layer but does not diffuse into the high dielectric constant layer, thus acting as a harmful-free intermediary material.
3Manufacturing precision
If polysilicon material is used as hard mask layer, then the metal materials can be patterned, but the etching is incomplete and removal becomes troublesome
Solution Approach 1:
The patent changes the chemical composition parameter of the hard mask layer from polysilicon to LaO. This material substitution enables complete and easy removal through wet etching processes, eliminating the troublesome residual polysilicon material that plagued conventional approaches while maintaining precise patterning of the work function metal layer.
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 reduces thermal budget, prevents leakage current, ensures complete removal of the hard mask layer, and enhances the electrical properties of semiconductor devices by maintaining the integrity of the metal layers, thereby improving device reliability and performance.
Implementation Method 1
preventing diffusion into high dielectric constant layers
Implementation Method 2
reducing thermal budget
Data Source
AI summary
A method for fabricating a semiconductor device is provided. A high dielectric constant (high-k) layer and a work function metal layer are formed in sequence on a substrate. A hard mask layer is formed on the work function metal layer, where the material of the hard mask layer is lanthanum oxide. The work function metal layer is patterned by using the hard mask layer as a mask. The hard mask layer is then removed. Afterwards, a gate structure is formed on the substrate.