Laser-Annealed Ohmic Contacts for High-Power Diodes
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Solution Overview
Problem
The formation of ohmic contacts on high-power electrical diodes, particularly on merged-PN Schottky (MPS) diodes, is challenging due to the need for high annealing temperatures that can damage underlying semiconductor structures and complicate the removal of metal layers, leading to unwanted reactions and reduced efficiency.
Innovation Solution
A method involving the deposition of a reflective first metal layer and an absorptive second metal layer, followed by a laser annealing process, where the second metal layer increases in temperature and forms ohmic contacts with the semiconductor contact points while minimizing heat transfer to the first metal layer, thus preventing unwanted reactions and limiting the expansion of ohmic contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high annealing temperatures are used to form ohmic contacts, then the electrical contact resistance is reduced, but the underlying semiconductor structures are damaged
Solution Approach 1:
The patent divides the metal contact structure into multiple layers (first metal layer, second metal layer, third metal layer) with distinct functions. The second metal layer is selectively positioned over the implanted region to absorb laser energy and generate localized heat, while the first and third metal layers reflect laser light and protect surrounding semiconductor structures from thermal damage. This segmentation enables localized high-temperature processing only where needed.
Solution Approach 2:
The patent applies different material properties to different regions of the contact structure. The second metal layer is specifically designed with high laser absorption characteristics and is positioned only over the implanted region, creating a localized heat source. This local quality differentiation ensures that high annealing temperatures are achieved only at the contact interface, while surrounding areas remain at lower temperatures to prevent damage.
2Reliability
If high annealing temperatures are used to form ohmic contacts, then the contact quality is improved, but the process complexity increases due to metal layer removal difficulties
Solution Approach 1:
The patent utilizes the different laser absorption parameters of various metal layers to achieve selective heating. The second metal layer is chosen specifically for its high laser absorption coefficient, while the first and third metal layers have high reflectivity. This parameter differentiation allows the annealing process to be initiated by laser irradiation without requiring complex heating equipment, and the metal layers can be removed more easily after contact formation because they were not subjected to prolonged high-temperature exposure.
3Reliability
If metal layers are deposited to form ohmic contacts, then the electrical connection is established, but unwanted reactions occur between metal layers and semiconductor material
Solution Approach 1:
The patent performs preliminary selective heating of the second metal layer before the metal layers come into contact with the semiconductor material in a way that would cause unwanted reactions. The laser annealing process is precisely controlled to heat only the second metal layer over the implanted region, forming the ohmic contact interface before any detrimental reactions can occur. The first and third metal layers act as protective barriers that prevent direct exposure of the semiconductor to excessive heat.
4Power
If ohmic contacts are formed with larger area, then the current capacity is increased, but the feature size of the semiconductor component increases
Solution Approach 1:
The patent segments the contact structure into multiple functional layers that can be independently optimized. The second metal layer is confined to the implanted region, allowing the ohmic contact area to be precisely controlled by the implantation geometry rather than being limited by the overall contact pad size. This enables high current capacity through optimized contact geometry without increasing the overall feature size of the semiconductor component.
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 reduces the complexity of ohmic contact formation, limits their expansion, and enables the creation of high-performing semiconductor components with smaller feature sizes by localizing the temperature increase and preventing damage to the semiconductor structure.
Implementation Method 1
a first metal layer is deposited on a top surface of a semiconductor drift layer comprising an electrical contact point, wherein the first metal layer reflects a laser light
Implementation Method 2
a second metal layer is deposited on portions of the first metal layer, wherein the second metal layer is aligned with the electrical contact point, and wherein the second metal layer absorbs the laser light
Implementation Method 3
The method further comprises exposing the first metal layer and the second metal layer to the laser light in a laser annealing process, wherein the second metal layer substantially increases in temperature due to the laser light
Implementation Method 4
The Method further comprises exposing the first metal layer and the second metal layer to the laser light in a laser annealing process, wherein the increase in temperature causes the ohmic contact to form between the electrical contact point and the first metal layer
Data Source
AI summary
A method for forming an ohmic contact on a semiconductor component, for example a high-power electrical diode, is provided. An example method includes depositing a first metal layer on a top surface of a semiconductor drift layer having an electrical contact point, the first metal layer highly reflective of a laser light. The method further includes depositing a second metal layer on portions of the first metal layer aligned with the electrical contact point, the second metal layer selected to absorb the laser light. The method further includes exposing the first and the second metal layers to the laser light in a laser annealing process, causing the second metal layer to substantially increase in temperature due to the laser light. The increase in temperature of the second metal layer causing the ohmic contact to form between the electrical contact point and the first metal layer.