Flexible Cantilever Electrode for HEMT Wafer Characterization
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Solution Overview
Problem
Characterization of electrical properties of semiconductor layers on insulating substrates, such as AlGaN/GaN HEMT heterostructures, is challenging due to floating electrostatic potential and static interferences, which deteriorate measurement accuracy, especially when using noncontact Kelvin-probe measurements on insulating substrates like sapphire or semi-insulating SiC.
Innovation Solution
A noninvasive, temporary electrical contact is made to the topside layers using a flexible metal cantilever electrode positioned near the wafer edge, connecting the semiconductor layers to ground potential, thereby stabilizing the surface potential and eliminating floating effects, and employing corona charge bias with a noncontact Kelvin-probe for accurate capacitance-voltage measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If noncontact Kelvin-probe measurement is used on insulating substrates, then measurement speed and nondestructive characterization are improved, but measurement precision deteriorates due to floating electrostatic potential and static interferences
Solution Approach 1:
A conductive adhesive layer is introduced as an intermediary between the insulating substrate and the semiconductor device. This layer provides a reference potential path to ground while maintaining the noncontact measurement advantage, effectively mediating between the insulating substrate and the measurement system to eliminate floating potential effects
Solution Approach 2:
The conductive adhesive layer is connected to ground potential, creating an equipotential reference plane that stabilizes the electrostatic environment. This allows the Kelvin-probe to measure surface potential accurately by comparing against a known reference potential rather than a floating potential
2Reliability
If topside return contact is provided using large mercury contact, then electrical contact to floating layers is achieved, but hazardous contamination and operational safety are worsened
Solution Approach 1:
The conductive adhesive layer is a disposable, non-hazardous alternative to mercury. It provides the necessary electrical contact function during measurement and can be removed or replaced without environmental contamination, effectively replacing the hazardous mercury contact with a safe, short-lived conductive material
Solution Approach 2:
The invention changes the material parameter from mercury (high conductivity but hazardous) to conductive adhesive (sufficient conductivity for the application, non-hazardous). This parameter change maintains the electrical contact function while eliminating the harmful effects of mercury contamination
3Reliability
If diamond scribe is used to create perforation through dielectric layer, then electrical contact to wafer is achieved, but device complexity and manufacturing difficulty are increased
Solution Approach 1:
The invention extracts the electrical contact function from the substrate preparation process. Instead of modifying the substrate (scribing or perforating) to enable contact, the conductive adhesive layer is applied to the existing substrate surface, separating the contact function from the substrate structure and simplifying manufacturing
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 method provides highly accurate and reliable electrical property characterization of semiconductor layers without fabricating test devices, reducing time and expense, and effectively eliminates the impact of substrate capacitance, allowing precise measurement of HEMT properties.
Implementation Method 1
The metrology uses corona-charge biasing realized with corona charge deposition on the wafer surface
Implementation Method 2
the surface voltage, V, changes and it is measured with the noncontact Kelvin-probe
Data Source
AI summary
Methods of characterizing electrical properties of a semiconductor layer structure on a wafer with topside semiconductor layers on an insulating or semi-insulating substrate, the semiconductor layer structure including a high electron mobility transistor (HEMT) heterostructure with a two-dimensional electron gas (2DEG) at a heterointerface between the semiconductor layers of the heterostructure. The methods include: (a) physically contacting the topside of the wafer within a narrow border zone at an edge of the wafer with a flexible metal cantilever electrode of a contacting device, wherein the flexible metal cantilever electrode contacts one or more of the semiconductor layers exposed at the narrow border zone so that the flexible metal cantilever electrode is in electrical contact with the 2DEG; and (b) applying corona charge bias and measuring a surface voltage of the semiconductor layers using a non-contact probe while maintaining the electrical contact with the 2DEG. The physical contacting to the topside of the wafer is noncontaminating and noninvasive to the semiconductor layers.