Cryogenic Back Layer Separation for Semiconductor Substrates
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Solution Overview
Problem
Current methods for singulating semiconductor dies from wafers, such as scribing and plasma dicing, face challenges in efficiently removing or separating backside layers, which hinders subsequent processing and reduces manufacturing throughput.
Innovation Solution
A method and apparatus that expose the backside layer to a reduced temperature while constraining the substrate in one direction, using a cryogenic fluid to expand gaps between die and separate the backside layer, enabling batch separation of challenging materials like thick metal layers and die attach films, and supporting narrower scribe grids.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If plasma dicing is used to separate backside layers, then throughput is increased and scribe line width is reduced, but the etch process cannot effectively remove or separate backside layers from singulation lines
Solution Approach 1:
The patent changes the physical parameter of temperature to separate backside layers. By cooling the substrate to below its glass transition temperature, the backside layer becomes brittle and can be mechanically separated from the singulation lines, overcoming the limitation of plasma dicing which cannot effectively remove backside layers
Solution Approach 2:
The patent replaces the chemical etching process of plasma dicing with a physical thermal-mechanical process. Instead of using plasma to etch away material, the method uses temperature reduction to change the mechanical properties of the backside layer, making it brittle and separable through mechanical means
2Manufacturing precision
If scribing or dicing is used to separate die, then individual die can be obtained, but large scribe grid width is required consuming significant wafer area and time exceeds one hour per singulation line
Solution Approach 1:
The patent performs preliminary action by removing portions of the substrate to form gaps between adjoining die before the final separation step. This pre-cutting creates initial separation paths that guide the subsequent thermal separation process, reducing the time required for complete singulation
Solution Approach 2:
The patent segments the substrate removal process into multiple stages: first removing portions to form gaps, then using thermal expansion to complete the separation. This segmentation allows for more efficient processing compared to attempting to cut through the entire substrate in a single operation
3Ease of manufacture
If conventional methods are used to separate backside layers, then processing can proceed, but damage or contamination occurs to the separated die
Solution Approach 1:
The patent utilizes phase transition by cooling the substrate below its glass transition temperature to change the physical state and mechanical properties of the backside layer. This phase change makes the layer brittle and enables clean separation without the damage or contamination associated with conventional mechanical or chemical separation methods
Solution Approach 2:
The patent converts the potentially harmful effect of thermal stress into a beneficial separation mechanism. By carefully controlling the cooling process and utilizing the thermal expansion mismatch between different materials, the method achieves clean separation while minimizing damage to the die
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 allows for cost-effective batch separation of semiconductor wafers with backside layers, reducing damage and contamination, and enabling efficient processing of various substrate materials, including silicon carbide, while improving manufacturing throughput.
Implementation Method 1
the substrate expands in another direction to increase the width of the gaps thereby separating the back layer
Implementation Method 2
exposing the layer of material to a reduced temperature while being constrained in one direction
Data Source
AI summary
A method for processing a semiconductor substrate includes providing the semiconductor substrate having die formed as part of the semiconductor substrate and separated from each other by singulation lines. The semiconductor substrate has first and second opposing major surfaces and contacts disposed over the first major surface. A layer of material is disposed over the second major surface, and the singulation lines extend inward from the first major surface into the semiconductor substrate without extending through the layer of material so that the layer of material is under the singulation lines. The method includes separating the layer of material proximate to the singulation lines by exposing the layer of material to a reduced temperature below about minus 150 degrees Celsius. In some examples, a cryogenic fluid can be to provide the reduced temperature. The method provides a reliable and efficient way to bulk separate at least the layer of material.