Carbon-Controlled Ohmic Contact Layer for SiC Power Devices
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Solution Overview
Problem
The formation of Ohmic contacts on thinned silicon carbide (SiC) substrates for high-power semiconductor devices is challenging due to excessive carbon production and distribution, leading to poor metal adhesion and stability issues, particularly during furnace or rapid thermal processing (RTP) anneal.
Innovation Solution
A semiconductor power device with a backside Ohmic contact layer comprising Nickel Silicide (NiSix) is formed using a pulsed laser anneal, where a first silicide region with non-reacted carbon precipitates is sandwiched between second and third silicide regions, with the third region containing refractory metal carbides and minimal non-reacted carbon, ensuring excellent adhesion with solder metal layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If furnace or rapid thermal processing (RTP) anneal is used to form Ohmic contacts, then contact formation temperature is achieved, but poor metal adhesion and stability occur due to excessive carbon production
Solution Approach 1:
The patent extracts and removes excessive carbon from the contact structure through laser annealing, which selectively evaporates carbon while preserving the metal-silicide contact. This extraction process eliminates the harmful carbon that would otherwise cause poor adhesion and instability in furnace or RTP annealed contacts.
Solution Approach 2:
The patent replaces traditional thermal annealing (furnace or RTP) with laser annealing. The laser provides localized, controlled energy delivery that achieves contact formation without the excessive carbon production associated with conventional thermal processing methods.
2Reliability
If pulsed laser anneal is used to form Ohmic contacts, then low contact resistance and high adhesion are achieved, but process complexity increases
Solution Approach 1:
The patent employs pulsed laser annealing with specific pulse durations (nanosecond to picosecond range) to deliver energy in controlled intervals. This periodic action allows precise thermal management, achieving contact formation and carbon removal without requiring complex multi-step processing sequences.
3Reliability
If thinned SiC substrates are used to reduce electrical and thermal resistance, then device performance is improved, but compatibility with front-end SiC device processing is lost
Solution Approach 1:
The patent performs substrate thinning as a preliminary action before front-end device processing. By thinning the SiC substrate beforehand, the device achieves lower electrical and thermal resistance while remaining compatible with standard fabrication processes, as the thinning is done when the substrate is still mechanically robust.
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 enables the formation of reliable Ohmic contacts with low contact resistance and high adhesion, capable of withstanding thermal and mechanical stress, thereby enhancing the reliability and performance of SiC power devices.
Implementation Method 1
Annealing of the backside contact to achieve the desired Ohmic behavior and low contact resistance may be done in such scenarios using a source of pulsed energy, such as a pulsed laser with a pulse duration of a few nanoseconds to a few hundred nanoseconds
Implementation Method 2
Nickel silicide can be formed on silicon carbide through reaction of SiC with metallic nickel, in a manner that is similar to that for formation of nickel silicide on silicon. On silicon carbide, this reaction is accompanied by release of excessive carbon
Data Source
AI summary
A semiconductor power device may include a Silicon Carbide (SiC) layer having an active power device formed on a first surface thereof. An Ohmic contact layer may be formed on a second, opposing surface of the SiC layer, the Ohmic contact layer including Nickel Silicide (NiSix) with a first silicide region containing a first precipitate of non-reacted carbon disposed between the SiC layer and a second silicide region. The second silicide region may be disposed between the first silicide region and a third silicide region, and may include a mixture of a first precipitate of refractory metal carbide and a second precipitate of non-reacted carbon. The third silicide region may contain a second precipitate of refractory metal carbide. A solder metal layer may be formed on the Ohmic contact layer, with the third silicide region disposed between the second silicide region and the solder metal layer.