Remote Plasma Descumming for Wafer Level Packaging Seed Layers
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Solution Overview
Problem
Conventional descumming processes in wafer level packaging often result in oxidation of the metal seed layer, leading to poor adhesion and wetting issues during electroplating, and can cause structural integrity problems in WLP structures due to incomplete removal of photoresist scum.
Innovation Solution
A method involving a remote plasma treatment using a reducing plasma, such as hydrogen-based plasma, to remove photoresist scum and oxidized portions of the metal seed layer, followed by an optional stripping plasma treatment to ensure complete removal of photoresist, thereby preventing oxidation and enhancing the structural integrity of WLP structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional oxygen-based plasma descumming is used to remove photoresist scum, then photoresist removal is effective, but the metal seed layer becomes oxidized leading to poor adhesion and wetting
Solution Approach 1:
The patent changes the chemical composition parameter of the plasma from oxygen-based to reducing gas-based (hydrogen, nitrogen, carbon monoxide, or hydrocarbon mixtures). This parameter change transforms the plasma from an oxidizing environment that causes seed layer oxidation to a reducing environment that removes photoresist scum while preventing oxidation and even reducing existing oxides on the seed layer surface.
Solution Approach 2:
The patent creates an inert or reducing atmosphere using gases such as hydrogen, nitrogen, carbon monoxide, or hydrocarbon mixtures. This inert/reducing atmosphere protects the metal seed layer from oxidation during the plasma treatment process while still enabling effective removal of photoresist scum through the plasma's chemical and physical action.
2Reliability
If reducing plasma is used to prevent seed layer oxidation, then adhesion and wetting improve, but photoresist scum removal may be less effective
Solution Approach 1:
The patent employs a multi-step periodic plasma treatment process. First, an oxygen-based plasma is used to effectively remove photoresist scum. Then, a reducing plasma treatment follows to remove any oxides formed on the seed layer during the first step. This periodic alternation between oxidizing and reducing plasma treatments ensures both complete scum removal and prevention of seed layer oxidation.
Solution Approach 2:
The patent ensures continuous useful action by performing plasma treatments in immediate sequence without exposing the substrate to ambient air. The process flows continuously from oxygen-based plasma (for scum removal) to reducing plasma (for oxide removal), maintaining a controlled atmosphere throughout to prevent re-oxidation and ensure both scum removal and adhesion quality.
3Reliability
If multiple plasma treatment steps are implemented, then both scum removal and oxidation prevention are achieved, but process complexity increases
Solution Approach 1:
The patent uses a universal plasma treatment system that can operate with different gas compositions to achieve multiple functions. The same plasma generation apparatus can produce oxygen-based plasma for scum removal, reducing plasma for oxide removal, or mixed plasma for combined effects. This multi-functionality reduces the need for separate dedicated equipment for each treatment step.
Solution Approach 2:
The patent merges multiple plasma treatment functions into a single integrated process sequence. Both the oxygen-based plasma treatment and reducing plasma treatment are performed in the same or adjacent processing chambers without breaking vacuum or exposing to air, combining what could be separate processes into one continuous operation that achieves both scum removal and oxidation prevention.
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 effectively removes photoresist scum and oxidized layers without oxidizing the seed layer, improving the adhesion and wetting properties for electroplating and resulting in WLP structures with enhanced structural integrity and reduced undercuts.
Implementation Method 1
Conventional descumming processes involve exposing the substrate to an oxygen-based plasma
Implementation Method 2
The oxygen-based plasma removes the photoresist scum from the bottom of the features
Implementation Method 3
exposing the substrate to a reducing plasma to remove photoresist scum and oxidation from an underlying seed layer
Implementation Method 4
electroplating metal on the metal seed layer in the photoresist features
Data Source
AI summary
Certain embodiments herein relate to methods and apparatus for processing a partially fabricated semiconductor substrate in a remote plasma environment. The methods may be performed in the context of wafer level packaging (WLP) processes. The methods may include exposing the substrate to a reducing plasma to remove photoresist scum and/or oxidation from an underlying seed layer. In some cases, photoresist scum is removed through a series of plasma treatments involving exposure to an oxygen-containing plasma followed by exposure to a reducing plasma. In some embodiments, an oxygen-containing plasma is further used to strip photoresist from a substrate surface after electroplating. This plasma strip may be followed by a plasma treatment involving exposure to a reducing plasma. The plasma treatments herein may involve exposure to a remote plasma within a plasma treatment module of a multi-tool electroplating apparatus.