SiC Barrier Metal Stack to Prevent Threshold Drift and Cracks
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Solution Overview
Problem
Conventional silicon carbide semiconductor devices face issues with threshold voltage fluctuations and cracks in the barrier metal due to internal stress, especially when the barrier metal is thickened to prevent diffusion, leading to unprotected local portions and propagation of cracks into the interlayer insulating film.
Innovation Solution
A two-layer structure for the barrier metal is introduced, where the first barrier metal, closer to the interlayer insulating film, is thinner and made of the same metallic material as the second barrier metal, providing stronger interatomic bonding and preventing crack propagation, even when the second barrier metal cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the barrier metal is made thicker to prevent diffusion and stabilize threshold voltage, then the barrier metal can better prevent metallic material diffusion, but the barrier metal becomes more prone to cracks due to internal stress
Solution Approach 1:
The barrier metal is divided into multiple layers (first barrier metal layer and second barrier metal layer) with different thicknesses and materials. The first layer is thinner and made of a first metallic material, while the second layer is thicker and made of a second metallic material. This segmentation allows each layer to contribute differently: the thinner first layer has lower internal stress and fewer cracks, while the thicker second layer provides sufficient diffusion barrier function.
Solution Approach 2:
Different regions of the barrier metal structure have different thicknesses and materials optimized for their specific functions. The first barrier metal layer closer to the gate insulating film is thinner to minimize stress and crack propagation risk in the critical region near the gate, while the second barrier metal layer is thicker to provide robust diffusion protection in regions where crack risk is lower.
2Reliability
If the barrier metal is made thicker to prevent diffusion, then diffusion protection is improved, but cracks can propagate into the interlayer insulating film causing unprotected local portions
Solution Approach 1:
The barrier metal is segmented into multiple layers where the first layer acts as a crack arrestor. When cracks occur in the thicker second layer, they are stopped at the interface with the first layer and do not propagate into the interlayer insulating film, thus maintaining diffusion protection without compromising structural integrity.
Solution Approach 2:
The first barrier metal layer is positioned between the gate insulating film and the second barrier metal layer to serve as a protective cushion. This layer prevents cracks from the second layer from reaching the gate insulating film, thereby cushioning the system against the harmful effects of crack propagation before they can cause damage.
3Adaptability or versatility
If different metallic materials are used for the first and second barrier metals, then material optimization is possible, but thermal stress increases due to coefficient of thermal expansion differences
Solution Approach 1:
The invention optimizes the thickness parameters of each barrier metal layer to compensate for thermal stress caused by using different metallic materials. By carefully controlling the thickness of the first and second layers, the overall thermal stress in the structure is reduced while maintaining the benefits of using different materials for different functions.
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 structure effectively prevents threshold voltage fluctuations and cracks, enhancing the reliability and productivity of the silicon carbide semiconductor devices by minimizing crack propagation and hydrogen ion entry into the gate insulating film.
Implementation Method 1
Since the first and second barrier metals are made of the same metallic material, interatomic bonding between the first and second barrier metals is stronger than that when the first and second barrier metals are made of different metallic materials. Thus, even when the first barrier metal is thinner, the strong bonding with the second barrier metal prevents hydrogen ions causing fluctuations in threshold voltage from entering a gate insulating film.
Implementation Method 2
The probability of having cracks in the thinner first barrier metal of the lower layer is less than that of the second barrier metal of the upper layer. Even when the second barrier metal of the upper layer has cracks, the first barrier metal of the lower layer prevent the cracks, and prevents propagation of the cracks into the interlayer insulating film.
Data Source
AI summary
The object of a silicon carbide semiconductor device according to the present disclosure is to prevent fluctuations in threshold voltage and prevent cracks in a barrier metal. A silicon carbide semiconductor device includes: a silicon carbide substrate; a semiconductor layer formed on the silicon carbide substrate; a gate electrode facing the semiconductor layer through a gate insulating film; an interlayer insulating film covering the gate electrode; a barrier metal formed on the interlayer insulating film; and a top electrode covering the barrier metal, wherein the barrier metal has a two-layer structure of a barrier metal and a barrier metal, and the barrier metal closer to the interlayer insulating film is made of a same metallic material as the barrier metal, the barrier metal being thinner than the barrier metal.