Known-Thickness Die Stacking for Uniform Semiconductor Stack Height
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Variations in die thickness during the backgrind process of semiconductor wafers can lead to electrical performance issues and premature degradation in non-volatile memory devices, affecting the reliability and capacity of storage devices.
Innovation Solution
A method involving metrology tools to create a known thickness die (KTD) map, which classifies and selects semiconductor dies based on their thickness for optimal performance and uniform die stack height, using stealth dicing before grinding to minimize thickness variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the backgrind process is used to thin the semiconductor wafer, then the wafer can be processed and dies can be separated, but slight variations in die thickness occur which affect electrical performance
Solution Approach 1:
The patent applies preliminary action by performing stealth dicing (laser grooving) before the backgrind process. This pre-dicing creates separation lines in the wafer before thinning, allowing the grinding wheel to follow these pre-defined paths and maintain more consistent die thickness. The laser grooves are formed at specific depths, and the subsequent backgrind process removes material down to these grooves, ensuring uniform thickness across all dies.
Solution Approach 2:
The patent replaces purely mechanical dicing with a combination of laser-based stealth dicing and mechanical backgrinding. The laser creates precise grooves without mechanical contact, and the backgrind process uses these laser-defined paths as guides, substituting some mechanical dicing operations with optical/laser-based precision marking that enables better thickness control during subsequent mechanical grinding.
2Quantity of substance
If multiple dies are stacked in a package to increase capacity, then storage capacity increases, but variations in die thickness compound to cause significant variations in overall die stack height
Solution Approach 1:
By performing stealth dicing before backgrind, the patent establishes precise thickness references early in the process. This preliminary action ensures that each die in the stack has controlled thickness, which is critical when multiple dies are stacked. The pre-formed laser grooves serve as thickness stop references that prevent over-grinding and ensure uniformity across all dies in the stack.
Solution Approach 2:
The patent changes the processing parameter sequence by reversing the traditional dicing-then-grinding order to grinding-after-pre-dicing. This parameter change in process sequencing allows the backgrind thickness to be controlled relative to the laser groove depth, improving die thickness uniformity. The laser groove depth becomes a controllable parameter that directly influences final die thickness precision.
3Productivity
If dies with varying thicknesses are used in the die stack, then production yield is maintained, but electrical performance degrades due to dies that are too thin
Solution Approach 1:
The patent applies local quality by creating laser grooves at specific locations and depths across the wafer surface before backgrinding. Each die receives localized treatment through the stealth dicing process, with laser grooves formed precisely where needed. This local precision enables the backgrind process to maintain uniform thickness across different regions of the wafer, ensuring all dies meet minimum thickness requirements for electrical performance while maximizing usable dies per wafer.
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 ensures high-capacity, reliable semiconductor devices by selecting dies with optimal thickness for improved electrical performance and maintaining a uniform die stack height, thereby enhancing the overall yield and reliability of storage devices.
Implementation Method 1
A pulsed laser beam is focused to a point beneath the wafer's surface to heat and melt the material at the focal point
Implementation Method 2
the semiconductor wafer is thinned, typically with a grinding wheel in a so-called backgrind process
Data Source
AI summary
A semiconductor device includes a die stack having dies selected into the stack based on their thicknesses. After the dies are formed on a wafer and thinned, a metrology tool is used to determine the thicknesses of the dies in the wafer. These thicknesses are stored in a known thickness die (KTD) map, along with other information such as their standard and average deviations and their classification into a binning class. In one example, dies which have been classified into bin 1 (having an optimal thickness) are selected to provide a high capacity highly reliable semiconductor device. In a further example, dies of different bins are mixed and matched to provide a uniform, highly controlled overall die stack height.