Radiation Absorption Control Layer for Ohmic Contact Alloying
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Solution Overview
Problem
Forming reliable ohmic contacts on wide band gap semiconductors like GaN and AlGaN is challenging due to difficulties in achieving consistent metal morphology and alloy temperature, with existing methods requiring high temperatures and suffering from pattern density dependency issues.
Innovation Solution
A method involving a stack of metal layers with a radiation absorption control layer, specifically a thin Titanium layer over Gold, to control radiant energy absorption and adjust alloy temperature, ensuring consistent heating and improved ohmic contact formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high alloy temperature is used to form reliable ohmic contact, then contact reliability is improved, but pattern density dependency issues occur and metal morphology consistency deteriorates
Solution Approach 1:
The patent applies local quality by introducing a radiation absorption control layer with specific optical properties that selectively absorbs radiation in certain wavelength ranges. This layer is positioned only where needed in the metal stack to control local heating characteristics during RTA, enabling precise temperature control at the contact region without affecting the entire wafer uniformly, thus resolving the contradiction between reliability and morphology consistency
Solution Approach 2:
The patent changes the optical parameters of the metal stack by adding a radiation absorption control layer with specific absorbance characteristics. This layer modifies how the stack interacts with radiation energy, allowing the same RTA process to achieve consistent alloy temperatures across different pattern densities. The parameter change enables reliable ohmic contacts while eliminating the pattern density dependency that previously caused morphology variations
2Reliability
If high alloy temperature is used to form reliable ohmic contact, then contact reliability is improved, but thermal variations across large contact areas increase
Solution Approach 1:
The radiation absorption control layer acts as an intermediary between the radiation source and the metal layers. It mediates the energy transfer by selectively absorbing radiation in specific wavelength ranges, converting optical energy to thermal energy in a controlled manner. This intermediary layer ensures uniform heat distribution across large contact areas, preventing thermal variations while maintaining the high temperatures needed for reliable ohmic contact formation
3Temperature
If radiation absorption is increased to improve heating efficiency, then alloy temperature is improved, but risk of overheating and loss of temperature control increases
Solution Approach 1:
The patent introduces dynamics by creating a multi-layer metal stack where the radiation absorption control layer has specific optical properties that enable dynamic control of heat absorption. The layer's selective absorbance characteristics allow it to absorb radiation efficiently at certain wavelengths while transmitting or reflecting others, providing a self-regulating mechanism that prevents overheating while maintaining adequate alloy temperature, thus improving both heating efficiency and temperature control precision
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 addresses the issues of ohmic contact morphology and pattern density dependency by effectively controlling alloy temperature, resulting in smoother, more reliable ohmic contacts with improved electrical conductivity and reduced thermal variations across large contact areas.
Implementation Method 1
controlling an amount of the radiant energy to be absorbed in the radiation absorption control layer during exposure of the stack to the radiation
Implementation Method 2
The heating lamps, such as, Tungsten Halogen heating lamps radiating energy primarily in the visible radiation band and extending in the Infrared bands
Data Source
AI summary
A stack of layers providing an ohmic contact with the semiconductor, a lower metal layer of the stack is disposed in direct contact with the semiconductor; and a radiation absorption control layer disposed over the lower layer for controlling an amount of the radiant energy to be absorbed in the radiation absorption control layer during exposure of the stack to the radiation during a process used to alloy the stack with the semiconductor to form the ohmic contact.