Wafer Grinding Rib Formation to Prevent Chipping
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Solution Overview
Problem
The formation of flaws such as chipping in the rib during machining of semiconductor wafers leads to reduced strength and increased breakage, while the provision of a transition region with a taper reduces the usable device area and productivity.
Innovation Solution
A method involving multiple grinding steps to form a fractured layer in the peripheral portion of the wafer before creating a recess, using a first grindstone to form a rib and a second grindstone with smaller abrasive grains to reduce wafer thickness, inhibiting chipping and breakage without reducing the effective area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a transition region with a taper is formed in the wafer, then wafer breakage during heat treatment is prevented, but the effective device area is reduced and productivity decreases
Solution Approach 1:
The patent applies preliminary action by forming a fractured layer in the peripheral portion of the wafer before creating the recess. This pre-formed fractured layer serves as a stress-absorbing structure that prevents chipping during subsequent machining operations, eliminating the need for a taper transition region and preserving the effective device area.
Solution Approach 2:
The patent segments the wafer structure into three distinct regions: a peripheral portion with a fractured layer, a central portion with a recess, and a rib portion. This segmentation allows each region to serve its specific function - the fractured layer absorbs stress to prevent breakage, while the central recess achieves the required thickness, eliminating the need for a taper that would reduce effective area.
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 prevents wafer breakage during machining by inhibiting chipping of the rib and maintains productivity by avoiding the need for a taper, thus enhancing wafer strength and handling capabilities.
Implementation Method 1
a first grinding step of grinding a peripheral portion of a back surface of the wafer with a first grindstone to form a fractured layer in the peripheral portion
Implementation Method 2
a second grinding step of grinding a central portion of the back surface of the wafer with the first grindstone to form a recess
Implementation Method 3
a third grinding step of grinding a bottom surface of the recess with a second grindstone of an abrasive grain size smaller than that of the first grindstone to reduce a thickness of the wafer
Data Source
AI summary
As a first grinding step, a peripheral portion of a back surface of a wafer (1) is ground with a first grindstone (17) to form a fractured layer (19) in the peripheral portion. Subsequently, as a second grinding step, a central portion of the back surface of the wafer (1) is ground with the first grindstone (17) to form a recess (21) while the peripheral portion in which the fractured layer (19) is formed is left as a rib (20). Subsequently, as a third grinding step, a bottom surface of the recess (21) is ground with a second grindstone (22) of an abrasive grain size smaller than that of the first grindstone (17) to reduce a thickness of the wafer (1).