SiC Semiconductor Ohmic Contact via Two-Step Heat Treatment
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Solution Overview
Problem
The challenge in manufacturing silicon carbide semiconductor devices is the difficulty in achieving low contact resistance for ohmic contacts, particularly in micro-sized power devices, due to the small impurity diffusion coefficient of SiC, which limits the effectiveness of thermal diffusion methods and requires alternative carrier concentration control techniques like ion implantation.
Innovation Solution
A method involving a semiconductor substrate with a first conductivity type, a semiconductor deposition layer with lower impurity concentration, a high-concentration impurity region, and a thermal reaction layer formed through a two-step heat treatment process after Si ion implantation, using a metal electrode film such as Ni, to create a low resistance thermal reaction layer for the ohmic contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ion implantation method is used to control carrier concentration in SiC, then carrier concentration can be controlled effectively, but the process complexity increases compared to thermal diffusion methods
Solution Approach 1:
The patent segments the heat treatment process into two distinct stages: a first heat treatment to form a precursor layer with moderate temperature, and a second heat treatment to convert the precursor layer into the final thermal reaction layer with high temperature. This segmentation allows each stage to serve a specific function, achieving effective impurity diffusion and carrier concentration control while managing process complexity through structured approach
Solution Approach 2:
The first heat treatment serves as a preliminary action that creates a precursor layer containing impurities in a suitable form and distribution before the final high-temperature treatment. This preliminary preparation ensures that when the second heat treatment occurs, the impurity diffusion is highly effective, thereby achieving precise carrier concentration control through a preparatory step
2Volume of moving object
If element miniaturization is pursued in power devices, then device size is reduced, but contact resistance increases
Solution Approach 1:
The patent changes the thermal parameters by implementing a two-stage heat treatment process with different temperatures and durations. The first stage uses moderate temperature to form a precursor layer, and the second stage uses high temperature (900-1200°C) to convert it into a thermal reaction layer with optimized electrical properties. This parameter optimization enables low contact resistance even in miniaturized devices
Solution Approach 2:
The patent creates a composite structure at the contact interface by forming a thermal reaction layer that is a compound of the electrode film material and SiC substrate material. This composite thermal reaction layer combines the advantages of both materials, achieving low contact resistance that maintains reliability in miniaturized power devices
3Reliability
If high-temperature heat treatment is applied to form ohmic contact, then contact resistance is reduced, but the electrode film may react excessively with the SiC substrate
Solution Approach 1:
The patent segments the heat treatment into two phases: first, a moderate temperature treatment to form a precursor layer without excessive reaction, and second, a high temperature treatment to convert the precursor layer into the final thermal reaction layer. This segmentation prevents uncontrolled excessive reaction while achieving the desired low contact resistance
Solution Approach 2:
The first heat treatment performs a preliminary action of forming a precursor layer that is pre-prepared for the final conversion. This precursor layer has controlled composition and structure that enables the second high-temperature treatment to proceed with controlled reaction, preventing excessive electrode film consumption while achieving effective ohmic contact
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 a low contact resistance thermal reaction layer, facilitating element miniaturization without increasing contact resistance values, thereby enhancing the reliability and performance of silicon carbide semiconductor devices.
Implementation Method 1
ion implanting Si atoms in the opening
Implementation Method 2
performing a first heat treatment process of heat treating the semiconductor substrate in contact with the electrode film, so as to form a precursor layer of a thermal reaction layer between the electrode film in the opening and the semiconductor substrate
Data Source
AI summary
Heat treatment is performed twice with respect to a silicon carbide substrate. In the first heat treatment process, after Si ions are implanted in a front surface of the silicon carbide substrate, the silicon carbide substrate contacting an electrode film is heat treated, and a precursor layer of a thermal reaction layer is formed between the electrode film and the silicon carbide substrate that includes a high-concentration impurity region. Thereafter, the unreacted electrode film remaining on the precursor layer of the thermal reaction layer and on an oxide film is removed. In the subsequent second heat treatment process, the silicon carbide substrate from which the unreacted electrode film has been removed is heat treated and the precursor layer of the thermal reaction layer at a bottom area of the opening is converted into the thermal reaction layer.