Wafer Backside Grinding to Prevent Edge Chipping
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Solution Overview
Problem
The existing wafer grinding methods often result in chipping of the outer peripheral edge during the grinding process, leading to reduced yield and increased costs due to the need for additional devices and steps to prevent chipping.
Innovation Solution
A two-stage grinding method where a coarse-grained first grindstone forms a recess on the wafer's back side, leaving the outer peripheral edge unground, and a finer-grained second grindstone finishes the entire back side, minimizing chipping by reducing grinding resistance and avoiding the use of separate devices for edge removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the back side of the wafer is ground to thin it to a predetermined thickness, then the wafer thickness is reduced to the required dimension, but the outer peripheral edge becomes knife edge-like and is liable to be chipped
Solution Approach 1:
The outer peripheral edge is ground in advance before the main grinding operation to prevent it from becoming knife edge-like during subsequent grinding. This preliminary action removes the harmful geometric feature before it can cause chipping, allowing the wafer to be ground to the required thickness without edge damage.
Solution Approach 2:
The grinding process is divided into two distinct stages: first grinding the outer peripheral edge, then grinding the main body of the wafer. This segmentation allows each region to be treated with appropriate grinding parameters, preventing the outer edge from becoming overly thin and susceptible to chipping while still achieving the required overall thickness.
2Object-affected harmful factors
If a separate device is used to remove the outer peripheral edge before grinding, then chipping is prevented, but productivity decreases and cost increases
Solution Approach 1:
The outer peripheral edge removal and main wafer grinding operations are merged into a single integrated grinding process. By using a single grinding device with appropriately sized grindstones, both the edge preparation and thickness reduction are accomplished in one setup, eliminating the need for separate devices and operations while maintaining chipping prevention.
Solution Approach 2:
The grinding device is designed to perform multiple functions: it can selectively grind the outer peripheral edge when a smaller grindstone is used, and then grind the entire wafer surface when a larger grindstone is used. This multi-functionality eliminates the need for separate specialized devices for edge preparation and maintains high productivity.
3Object-affected harmful factors
If a smaller grindstone is used to grind only the device formation region, then the outer peripheral edge is left unground and chipping-free, but an additional finishing step is required
Solution Approach 1:
The grinding process uses dynamically changeable grindstones of different sizes. The system can switch between a smaller grindstone for selective edge-region grinding and a larger grindstone for complete surface grinding. This dynamic adaptability allows the process to first prevent chipping by leaving the outer edge unground, then complete the finishing in one continuous operation without adding process steps.
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 prevents chipping of the outer peripheral edge during grinding, enhancing yield without increasing costs or productivity losses, as the entire process is integrated within the grinding steps, ensuring a flat and stable wafer surface.
Implementation Method 1
grinding a region, corresponding to the device formation region, of the back side by a rotating type first grindstone or grindstones
Data Source
AI summary
A wafer grinding method is disclosed, in which only a region, corresponding to a device formation region, of the back side of a wafer is ground in rough grinding conducted first, while the part surrounding the region thus ground is left unground as an annular projected part, to prevent the outer peripheral edge of the wafer from becoming knife edge-like in shape. In the subsequent finish grinding, the annular projected part is ground and, further, the whole area of the back side of the wafer is ground to be flat. Chippings of the outer peripheral edge may be generated only during the finish grinding, whereby the chippings are prevented from occurring or limited to minute ones.