Passivation Stack Etch Stop Layout for Uniform Bond Pad Etching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High variation in passivation stack thickness during integrated circuit fabrication leads to process issues such as prolonged etch times and over-etching, resulting in inefficiencies and die lot scrapping due to poor endpoint detection.
Innovation Solution
A passivation stack is formed with an etch stop layer, comprising multiple glass layers deposited and polished to maintain consistent thickness, reducing thickness variations and optimizing etch stop layer selectivity for efficient processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the passivation stack thickness is increased to protect the IC, then protection capability is improved, but etch time to reach bond pads increases excessively
Solution Approach 1:
The passivation stack is segmented into multiple layers: a first glass layer in direct contact with the metallization layer, an etch stop layer, and a second glass layer on top. This segmentation allows the etch process to stop at the etch stop layer, preventing excessive etching through the entire stack while maintaining adequate protection thickness in the glass layers.
Solution Approach 2:
The etch stop layer acts as an intermediary layer between the first and second glass layers. It provides a controlled termination point for the etch process, mediating between the need for thick passivation and the need to reach bond pads efficiently, thereby reducing etch time while maintaining protection.
2Productivity
If the passivation stack thickness is decreased to reduce etch time, then etch efficiency is improved, but over-etching occurs damaging bond pads
Solution Approach 1:
The etch stop layer is positioned beforehand within the passivation stack to cushion and prevent over-etching. It serves as a pre-placed protective barrier that stops the etch process before it can reach and damage the bond pads, ensuring bond pad integrity while allowing efficient etching.
3Manufacturing precision
If multiple glass layers are deposited to maintain consistent thickness, then thickness uniformity is improved, but process complexity increases
Solution Approach 1:
The passivation stack is divided into a first glass layer and a second glass layer separated by an etch stop layer. This segmentation enables better control over thickness uniformity in each layer while maintaining overall consistency, with the etch stop layer serving as a reference plane for polishing the second glass layer.
Solution Approach 2:
Different regions of the passivation stack have different properties: the first glass layer provides direct protection, the etch stop layer provides etch termination, and the second glass layer provides additional protection with controlled thickness. This local differentiation optimizes each layer's function while maintaining overall thickness uniformity.
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 minimizes pad etch time, maintains consistent passivation stack thickness, reduces glass layer deposition, and enhances processing efficiency by using an etch stop layer within the passivation stack, thereby reducing the risk of over-etching and improving endpoint detection.
Implementation Method 1
depositing a first glass layer on a metallization layer and depositing an etch stop layer on the first glass layer
Implementation Method 2
depositing a first glass layer on a metallization layer and depositing an etch stop layer on the first glass layer
Implementation Method 3
polishing the second glass layer down to at least a surface of the etch stop layer
Data Source
AI summary
In one aspect, a method includes depositing a first glass layer on a metallization layer and depositing an etch stop layer on the first glass layer. The method further includes depositing a second glass layer on the etch stop layer and polishing the second glass layer down to at least a surface of the etch stop layer.