Schottky Electrode Interdiffusion Control in Semiconductor Detectors
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Solution Overview
Problem
In semiconductor detectors, the use of metals with low work functions for Schottky electrodes leads to interdiffusion with Au bump electrodes, resulting in defective bonding and increased leakage, especially in fine-pitch detectors, which deteriorates spatial resolution and mechanical strength.
Innovation Solution
The semiconductor detector employs a structure where the Schottky electrode and the outermost surface electrode, or an intermediate metal layer, are stacked to control interdiffusion coefficients, preventing alloy formation and maintaining mechanical strength and low leak current by using materials like Ti, Cr, or Au with controlled diffusion properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal having a low work function such as In or Al is used as a Schottky electrode to suppress leak current, then the leak current is reduced, but interdiffusion occurs between the Schottky electrode and Au bump material during thermocompression bonding, resulting in defective bonding and reduced mechanical strength
Solution Approach 1:
A barrier metal layer is introduced as an intermediary between the Schottky electrode (In or Al) and the Au bump material. This barrier layer prevents interdiffusion between the Schottky electrode and bump material during thermocompression bonding, while allowing the Schottky electrode to maintain its low leak current function. The barrier metal acts as a mediator that resolves the conflict between leak current suppression and bonding strength.
Solution Approach 2:
The electrode structure is designed as a composite multi-layer structure comprising a Schottky electrode layer (In or Al), a barrier metal layer, and an outermost electrode layer (Au). This composite structure combines the advantages of different materials: the Schottky electrode provides low leak current, the barrier metal prevents interdiffusion, and the outermost electrode layer ensures good bonding strength and electrical contact.
2Reliability
If In is used as a pixel electrode material to achieve low work function, then the Schottky function is improved, but the diffusion coefficient of In in semiconductor is very large, causing leakage between pixels and deteriorated spatial resolution in fine-pitch detectors
Solution Approach 1:
The barrier metal layer serves as a diffusion barrier that mediates between the In pixel electrode and the semiconductor substrate. It prevents In atoms from diffusing into the semiconductor, thereby maintaining spatial resolution in fine-pitch detectors, while still allowing the In layer to provide the necessary Schottky function at the electrode-semiconductor interface.
Solution Approach 2:
The electrode structure is segmented into multiple functional layers: the In layer provides Schottky function, the barrier metal layer controls diffusion, and the Au outer layer provides electrical contact. This segmentation allows each layer to perform its specific function independently, resolving the conflict between Schottky function and spatial resolution.
3Strength
If thermocompression bonding is applied to achieve high strength bonding between bump electrode and pixel electrode, then bonding strength is improved, but interdiffusion between Au bump material and Schottky electrode occurs, resulting in alloy formation and defective bonding
Solution Approach 1:
The barrier metal layer acts as a mediator during thermocompression bonding, preventing direct contact and interdiffusion between the Au bump material and the Schottky electrode. This allows thermocompression bonding to proceed with high strength while maintaining the compositional stability of both the bump material and Schottky electrode.
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 configuration achieves higher mechanical strength and reliability with reduced leak current, preventing alloy formation and maintaining Schottky function integrity, even in fine-pitch detectors, thereby enhancing spatial resolution.
Implementation Method 1
one semiconductor chip or substrate having a photoelectric conversion semiconductor layer which detects light or radiation
Implementation Method 2
a material of an electrode being in contact with the photoelectric conversion semiconductor layer has a Schottky function with respect to the photoelectric conversion semiconductor layer
Implementation Method 3
an interdiffusion coefficient between a material of the outermost surface electrode formed on the electrode having the Schottky function and a material of the electrode having the Schottky function is smaller than an interdiffusion coefficient between the material of the outermost surface electrode and Al
Data Source
AI summary
In a radiation detector, a Schottky electrode is formed such that an interdiffusion coefficient between the material of an outermost surface electrode formed on the Schottky electrode and the material of the Schottky electrode is smaller than an interdiffusion coefficient between the material of the outermost surface electrode and Al (aluminum). Consequently, the material of the outermost surface electrode does not diffuse into the Schottky electrode, and Schottky functions can be maintained, and at the same time, the material of the Schottky electrode does not diffuse into the outermost surface electrode, and the outermost surface electrode can be prevented from alloying.