Wafer Backside Plasma Etching and Fluid Cracking
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Solution Overview
Problem
Conventional plasma dicing methods face challenges in dividing wafers with device layers and test element groups, as they require high laser power, leading to reduced flexural strength of chip devices and potential damage to devices due to uneven mask thickness during plasma etching.
Innovation Solution
A method involving forming guide grooves in the device layer, applying a mask on the backside of the wafer, performing plasma etching through the mask, and using high-pressure fluid to crack the device layer, thereby avoiding laser irradiation and ensuring uniform processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a laser beam is used to remove the TEG and device layer from the front side of the wafer, then the wafer can be divided into chips, but the flexural strength of the device chips is reduced due to formation of affected regions in the substrate
Solution Approach 1:
The patent inverts the conventional approach by performing plasma etching from the back side of the wafer instead of the front side. This allows the laser to remove the TEG and device layer from the back side where devices are not present, thereby achieving chip division without reducing the flexural strength of the device chips on the front side.
Solution Approach 2:
The patent segments the wafer processing into distinct steps: forming guide grooves on the front side, creating a mask on the back side, performing plasma etching from the back side, and finally separating the chips. This segmentation allows the laser to act only on the back side without affecting the structural integrity of the device layer on the front side.
2Productivity
If plasma dicing is performed from the front side of the wafer, then the wafer can be divided into chips, but devices may be damaged due to uneven mask thickness and removal at thin mask areas
Solution Approach 1:
The patent performs plasma etching from the back side of the wafer where the mask is formed, rather than from the front side where devices are located. This inversion ensures that even if the mask thickness is uneven, the devices on the front side are never exposed to the plasma etching process, thereby preventing device damage while maintaining chip division efficiency.
3Manufacturing precision
If a mask is formed with non-uniform thickness on the front side to protect devices, then plasma etching can be performed, but the mask may be removed at thin areas exposing the front side and damaging devices
Solution Approach 1:
The patent forms the mask on the back side of the wafer and performs plasma etching from the back side, reversing the conventional approach. This eliminates the risk of mask removal at thin areas exposing devices, as the plasma etching never reaches the front side where devices are located, regardless of mask thickness uniformity.
Solution Approach 2:
The patent introduces guide grooves formed on the front side as an intermediary structure that guides the plasma etching process from the back side. These grooves ensure that the plasma etching follows the intended paths without exposing the device areas, providing an additional layer of protection beyond the mask itself.
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 effectively separates wafer devices without reducing flexural strength and prevents damage to devices by using a backside plasma etching and high-pressure fluid application, ensuring precise and robust chip formation.
Implementation Method 1
a plasma etching step of applying plasma etching from the back side of the wafer through the mask after performing the mask forming step, thereby forming the etched grooves in the substrate along the streets
Implementation Method 2
a pressing step of ejecting high-pressure fluid against the back side of the wafer with the wafer mounted at a front side thereof on a mounting surface after performing the plasma etching step, thereby pressing the wafer at the regions surrounded by the etched grooves
Data Source
AI summary
A wafer processing method includes the following steps: forming, on a back side of a wafer including a device layer, a mask to be used in forming grooves in a substrate along streets from the back side of the wafer; applying plasma etching from the back side of the wafer through the mask to form the grooves in the substrate along the streets; ejecting high-pressure fluid against the back side of the wafer with the wafer mounted at its front side on a mounting surface to press the wafer at regions surrounded by the etched grooves; and bonding a tape to the front side of the wafer before performance of at least the pressing step.