Backside Copper Layer Adhesion via Metal Seed and Diffusion Barrier
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional backside metal processes for semiconductor devices face challenges in achieving good adhesion and uniformity of metal seed layers, leading to metal peeling and copper diffusion into active areas, as well as oxidation issues, particularly when using copper as the backside metal.
Innovation Solution
A method involving the fabrication of backside via holes and trenches, followed by coating a thin metal seed layer and a copper layer, and applying an oxidation preventing layer to prevent peeling, diffusion, and oxidation, using materials like Pd, Au, Ni, and their alloys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If copper is used as backside metal layer, then manufacturing cost and resistivity are improved, but copper diffusion into GaAs substrate occurs causing device damage
Solution Approach 1:
A diffusion barrier layer comprising TiN and Ru is introduced between the copper backside metal layer and the GaAs substrate. This intermediary layer prevents copper atoms from diffusing into the substrate while maintaining electrical conductivity and adhesion, thus resolving the harmful effect of copper diffusion without sacrificing the cost and resistivity benefits of using copper.
2Quantity of substance
If copper is used as backside metal layer, then manufacturing cost and resistivity are improved, but oxidation of copper layer occurs
Solution Approach 1:
The backside metal structure is designed as a composite system with multiple layers: copper provides low cost and low resistivity, while the TiN and Ru diffusion barrier layers provide oxidation protection and prevent copper diffusion. This composite structure combines materials with complementary properties to simultaneously achieve cost reduction, resistivity improvement, and protection against oxidation and diffusion.
3Strength
If conventional sputtering method is used to coat metal seed layer, then adhesion to backside metal is achieved, but uniformity and defect-free coating are difficult to obtain
Solution Approach 1:
The conventional sputtering method (mechanical/physical deposition) is replaced with electroless plating (chemical deposition). The electroless plating process uses chemical reduction to deposit the metal seed layer uniformly across the backside surface and via holes, achieving both good uniformity and adequate adhesion without the defects associated with sputtering.
4Area of stationary object
If metal seed layer thickness is reduced to save space, then space is saved, but adhesion and uniformity deteriorate
Solution Approach 1:
The deposition method is changed from sputtering to electroless plating, which fundamentally alters the deposition parameters and mechanism. Electroless plating provides superior uniformity and adhesion even at reduced thicknesses, allowing space savings without sacrificing manufacturing precision. The chemical deposition process ensures consistent coating quality across varying thicknesses.
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 ensures good electrical contact, prevents metal peeling and copper diffusion, maintains uniformity, and protects against oxidation, resulting in cost reduction, improved yield, and reliable device performance.
Implementation Method 1
the backside metal processes for GaAs based integrated devices usually utilize a sputter to coat a metal seed layer on the rear surface and the backside via holes
Implementation Method 2
coating an oxidation preventing layer on the copper layer to protect the copper layer against oxidation
Data Source
AI summary
A method of processing copper backside metal layer for semiconductor chips is disclosed. The backside of a semiconductor wafer, with electronic devices already fabricated on the front side, is first coated with a thin metal seed layer by either electroless plating or sputtering. Then, the copper backside metal layer is coated on the metal seed layer. The metal seed layer not only increases the adhesion between the front side metal layer and the copper backside metal layer through backside via holes, but also prevents metal peeling from semiconductor's substrate after subsequent fabrication processes, which is helpful for increasing the reliability of device performances. Suitable materials for the metal seed layer includes Pd, Au, Ni, Ag, Co, Cr, Pt, or their alloys, such as NiP, NiB, AuSn, Pt—Rh and the likes. The use of Pd as seed layer is particularly useful for the copper backside metal layer, because the Pd layer also acts as a diffusion barrier to prevent Cu atoms entering the semiconductor wafer.