SiC Ohmic Contact Phase Segmentation
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Solution Overview
Problem
Existing methods for forming ohmic electrodes in silicon carbide semiconductor devices face challenges such as unexpected reactions at the MOS interface, damage to the MOS interface, and poor adhesion between the ohmic electrode and the silicon carbide semiconductor substrate, leading to high contact resistance and reliability issues.
Innovation Solution
A method involving the formation of a nickel silicide film on a silicon carbide semiconductor substrate using a nickel film with 20-40 at% silicon, followed by annealing at temperatures between 700°C and 850°C, which results in a NiSi phase on the substrate side and a Ni2Si phase on the extraction electrode side, minimizing carbon presence and optimizing the annealing process to reduce contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If annealing is performed at high temperature to form nickel silicide, then good ohmic contact is achieved, but unexpected reactions occur at the MOS interface and the MOS interface property is damaged
Solution Approach 1:
The contact electrode is divided into two distinct phase regions: a NiSi phase region adjacent to the silicon carbide semiconductor substrate and a Ni2Si phase region adjacent to the extraction electrode. This segmentation allows each phase to perform its optimal function - NiSi provides good ohmic contact with the substrate while Ni2Si serves as the extraction electrode interface, preventing carbon contamination at the MOS interface while maintaining low contact resistance.
Solution Approach 2:
Different phases of nickel silicide are distributed at different locations within the contact electrode. The NiSi phase is localized at the substrate interface where low contact resistance is critical, while the Ni2Si phase is localized at the extraction electrode interface where carbon exclusion is critical. This local quality differentiation resolves the contradiction between achieving good ohmic contact and preventing MOS interface damage.
2Object-affected harmful factors
If annealing temperature is suppressed to 850°C or less to protect MOS interface, then MOS interface property is preserved, but contact resistance increases due to poor adhesion
Solution Approach 1:
The invention changes the compositional parameters of the nickel silicide by controlling the nickel film thickness and annealing temperature to specifically form a two-phase structure. By adjusting these parameters, the NiSi phase forms at the substrate interface providing low contact resistance, while the Ni2Si phase forms at the extraction electrode interface, achieving both low contact resistance and MOS interface protection at annealing temperatures of 850°C or less.
3Manufacturing precision
If nickel film thickness and annealing temperature are controlled to form nickel silicide, then composition is uniquely determined, but carbon contamination may occur at the ohmic electrode surface
Solution Approach 1:
The contact electrode is segmented into phases with different carbon tolerance characteristics. The NiSi phase at the substrate interface can tolerate some carbon presence while maintaining ohmic contact, while the Ni2Si phase at the extraction electrode interface effectively excludes carbon. This segmentation prevents carbon contamination from degrading the overall electrode performance.
Solution Approach 2:
The invention converts the potential harm of carbon contamination into a benefit by using it as a carbon trap. The NiSi phase region acts as a carbon sink, absorbing carbon that would otherwise contaminate the Ni2Si phase and the MOS interface. This transforms the harmful carbon diffusion into a protective mechanism that safeguards the critical interfaces.
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 an ohmic contact electrode with low contact resistance and improved driving reliability, suitable for next-generation power semiconductor devices.
Implementation Method 1
heat treatment at 700 degrees C. or less is performed whereby a silicide is formed by a solid-phase reaction of the nickel silicon alloy
Implementation Method 2
suppress the amount of carbon that reaches the ohmic electrode surface to a concentration that is less than that of the nickel element
Implementation Method 3
a technique of using laser irradiation after nickel silicon alloy formation to locally perform heat treatment for short periods
Data Source
AI summary
A silicon carbide semiconductor device includes a silicon carbide semiconductor substrate; a nickel silicide film provided on a surface of the silicon carbide semiconductor substrate and functioning as an ohmic contact; and an extraction electrode contacting the ohmic contact on a side different from a silicon carbide semiconductor substrate side. The silicon carbide semiconductor substrate side of the ohmic contact is mainly formed from a NiSi phase and an extraction electrode side thereof is mainly formed from a Ni2Si phase. The ohmic contact includes carbon on the silicon carbide semiconductor substrate and includes no carbon on the extraction electrode side.