Contact Pad Structure with Liner and Diffusion Barrier
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Solution Overview
Problem
Conventional contact pads in integrated circuit structures face issues with material diffusion and short circuits due to the lack of a suitable interface for bond wires, leading to poor adhesion and long-term stability, especially when using materials like copper and aluminum.
Innovation Solution
A contact pad structure is developed with a dielectric layer and a contact structure that includes a metal pad with a liner and a conductive coating, forming a diffusion barrier to prevent material migration and enhance adhesion for gold bond wires, using a dual-damascene copper plating process and electro-less plated layers like nickel-phosphorus and gold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional contact pad structure is used without a liner structure and diffusion barrier, then the manufacturing process is simpler, but material diffusion occurs causing short circuits and reduced reliability
Solution Approach 1:
The contact pad structure is segmented into multiple functional layers: a metal structure (copper), a liner structure (tantalum or tungsten) disposed between the metal and dielectric, and a contact structure (nickel-phosphorus, palladium, gold) completely covering the metal surface. This segmentation allows each layer to perform its specific function - the metal provides conductivity, the liner prevents diffusion into the dielectric, and the contact structure provides bonding surface and additional diffusion protection.
Solution Approach 2:
The liner structure acts as an intermediary layer between the metal structure and the dielectric layer structure. It prevents direct contact between the metal and dielectric, thereby blocking diffusion paths that would otherwise cause short circuits. The contact structure serves as an intermediary between the metal contact pad and peripheral structures (such as bonding wires), providing a stable bonding surface while protecting the underlying metal from oxidation and diffusion.
2Reliability
If the contact pad surface is completely covered with liner structure, then diffusion protection is improved, but adhesion for gold bonding deteriorates
Solution Approach 1:
The liner structure is selectively positioned only between the metal structure and the dielectric layer structure, leaving the top surface of the metal structure exposed. This local application provides diffusion protection where it is most needed (at the metal-dielectric interface) while preserving the metal surface for bonding. The contact structure is then applied to completely cover the exposed metal surface, providing both bonding functionality and additional diffusion protection.
3Reliability
If a dual-damascene copper plating process with hard-coating layer stack is used, then adhesion and diffusion barrier performance are improved, but manufacturing complexity increases
Solution Approach 1:
The liner structure is deposited onto the metal structure before the contact structure is applied. This preliminary action ensures that the diffusion barrier is in place before the bonding surface is prepared, preventing any potential diffusion during subsequent processing steps. The dual-damascene copper plating process is performed in advance to create the metal structure with precise geometry and electrical properties before adding the liner and contact layers.
Solution Approach 2:
The contact pad structure employs a composite material system consisting of copper (metal structure), tantalum or tungsten (liner structure), and a stack of nickel-phosphorus, palladium, and gold (contact structure). Each material is selected for its specific properties: copper for high conductivity, tantalum/tungsten for diffusion barrier performance, and the nickel-phosphorus/palladium/gold stack for adhesion, oxidation resistance, and bonding compatibility. This composite approach optimizes overall performance while managing manufacturing complexity through standardized deposition processes.
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 improves the reliability and manufacturability of contact pads by preventing material diffusion and ensuring long-term stability, even at elevated temperatures, while providing a suitable interface for gold bond wires, thus enhancing the electrical and mechanical robustness of the contact pads.
Implementation Method 1
the liner structure and the contact structure form a diffusion bather for a material of the metal structure of the at least one contact pad
Implementation Method 2
using a dual-damascene copper plating process with a hard-coating layer stack of nickel-phosphorus, palladium, and gold
Data Source
AI summary
According to various embodiments, a contact pad structure may be provided, the contact pad structure may include: a dielectric layer structure; at least one contact pad being in physical contact with the dielectric layer structure; the at least one contact pad including a metal structure and a liner structure, wherein the liner structure is disposed between the metal structure of the at least one contact pad and the dielectric layer structure, and wherein a surface of the at least one contact pad is at least partially free from the liner structure, and a contact structure including an electrically conductive material; the contact structure completely covering at least the surface being at least partially free from the liner structure of the at least one contact pad, wherein the liner structure and the contact structure form a diffusion barrier for a material of the metal structure of the at least one contact pad.