SiC Barrier Metal Stack for High-Temperature Threshold Stability
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Solution Overview
Problem
Conventional silicon carbide semiconductor devices experience threshold fluctuation and void formation due to hydrogen diffusion when used at high temperatures, leading to reliability issues.
Innovation Solution
A three-layered barrier metal structure comprising a first TiN film with larger crystal grains, a pure Ti film, and a second TiN film is introduced, with the Ti film sandwiched between the TiN films to prevent hydrogen diffusion and enhance the barrier effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional two-layer barrier metal structure (Ti film and TiN film) is used, then the device can be manufactured with simpler process, but hydrogen diffusion occurs at high temperatures causing threshold fluctuation and void formation
Solution Approach 1:
The barrier metal structure is segmented into three distinct layers: a first TiN film (5-20 nm thick), a pure Ti film (20-50 nm thick), and a second TiN film (5-20 nm thick). This segmentation allows each layer to perform its specific function - the TiN layers provide hydrogen barrier properties while the pure Ti layer prevents alloying between Al and Ti, thereby suppressing threshold fluctuation and void formation without excessive complexity
Solution Approach 2:
The invention uses a composite barrier metal structure combining TiN and Ti materials in a three-layer configuration. The TiN layers provide hydrogen occlusion capability while the pure Ti intermediate layer prevents direct contact between Al and TiN, avoiding alloy formation. This composite structure effectively addresses both hydrogen diffusion prevention and alloying suppression, improving device reliability under high-temperature operation
2Reliability
If Al and Ti are directly alloyed to form barrier metal, then the manufacturing process is simpler, but the hydrogen occlusion effect is lost and alloying causes reliability issues
Solution Approach 1:
The first TiN film acts as an intermediary layer between the Al ohmic electrode and the pure Ti film. This intermediate TiN layer prevents direct alloying between Al and Ti while maintaining the hydrogen occlusion capability of the TiN material. The structure Al/TiN/Ti/TiN provides both hydrogen barrier function and prevents harmful alloy formation, resolving the contradiction between simplicity and reliability
3Reliability
If hydrogen barrier measures are implemented, then threshold fluctuation is suppressed, but void formation occurs between NiSi and Ti at high temperatures
Solution Approach 1:
The invention optimizes the thickness parameters of each layer in the three-layer barrier metal structure. The first TiN film is set at 5-20 nm to provide hydrogen barrier while the pure Ti film is set at 20-50 nm to prevent alloying. The second TiN film is set at 5-20 nm to provide additional hydrogen occlusion. These parameter optimizations suppress threshold fluctuation and prevent void formation between NiSi and Ti by controlling diffusion paths and stress distribution
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
The solution effectively suppresses threshold fluctuation and void formation, improving the reliability of silicon carbide semiconductor devices by preventing hydrogen from reaching the gate interface, even under high-temperature conditions.
Implementation Method 1
Hydrogen contained in the source electrode pad (Al electrode) diffuses to the gate interface and thus, is known to cause threshold fluctuation. Therefore, between the gate interface and the Al electrode, formation of a barrier metal constituted by a metal film capable of occluding hydrogen has been proposed. For example, the problem of threshold fluctuation is solved by using a hydrogen occlusion effect of titanium (Ti).
Implementation Method 2
Next, a Ti film is deposited on the ohmic electrode by a sputtering method (step S13). Next, a TiN film is deposited on Ti film by a sputtering method (step S14), thereby forming the barrier metal constituted by the Ti film and the TiN film.
Data Source
AI summary
A silicon carbide semiconductor device includes a starting substrate of a first conductivity type, a first semiconductor layer of the first conductivity type, a second semiconductor layer of a second conductivity type, a first semiconductor region of the first conductivity type, a gate insulating film, a gate electrode, an interlayer insulating film, an ohmic electrode, a barrier metal provided at the surface of the ohmic electrode and the surface of the interlayer insulating film, a surface electrode provided at the surface of the barrier metal, and a back electrode. The barrier metal has a three-layered structure including a first TiN film, a Ti film, and a second TiN film; the first TiN film contains TiN having a crystal grain size that is larger than a crystal grain size of TiN of the second TiN film.