Wafer Laser Processing Phosphorus Contamination Control
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Solution Overview
Problem
Laser processing of wafers with phosphorus compounds results in the liberation and diffusion of phosphorus elements, which react with nitrogen, oxygen, or water to form foreign matter on metal electrodes, degrading device characteristics, and existing methods struggle to effectively remove this foreign matter simultaneously with the protective film during processing.
Innovation Solution
A wafer processing method involving the formation of a water-soluble protective film, followed by laser processing, cleaning to remove the film, and a subsequent foreign matter removal step after a predetermined time to allow phosphorus reaction products to evaporate and react with water, using water or etching to effectively remove the foreign matter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a protective film is formed on the wafer before laser processing, then debris generated during laser processing is prevented from depositing on the front side of devices, but phosphorus-containing foreign matter is produced on metal electrodes after the protective film is removed
Solution Approach 1:
The patent applies preliminary action by performing laser processing while the protective film is still on the wafer, before the phosphorus diffusion and foreign matter formation occur. This allows debris to be trapped under the protective film during the critical laser processing phase, preventing front-side contamination. The protective film is then removed after processing, and a subsequent cleaning step eliminates the phosphorus-containing foreign matter that formed on the metal electrodes during the interval between protective film removal and the next cleaning operation.
Solution Approach 2:
The protective film serves as an intermediary layer that mediates between the laser processing and the wafer surface. During laser processing, it acts as a barrier preventing debris from reaching the device front side. After processing, it allows controlled removal and enables a time-delayed cleaning approach that targets phosphorus-containing foreign matter on metal electrodes without affecting the already-protected device surfaces.
2Productivity
If the protective film is removed immediately after laser processing, then the film can be cleaned off, but phosphorus-containing foreign matter has insufficient time to form and cannot be removed together with the protective film
Solution Approach 1:
The patent implements periodic action by introducing a deliberate time interval between protective film removal and the next cleaning operation. Instead of immediate cleaning, the wafer is allowed to stand for a predetermined period (e.g., 1 hour to 1 day) that enables phosphorus-containing foreign matter to form on metal electrodes. This periodic timing is critical - long enough for foreign matter formation but controlled to prevent excessive contamination. The subsequent cleaning step then removes this foreign matter along with any remaining protective film residues.
3Object-generated harmful factors
If laser processing conditions or protective film composition are changed to suppress foreign matter production, then foreign matter formation may be reduced, but processing efficiency and productivity are compromised
Solution Approach 1:
The patent applies parameter changes by optimizing laser processing parameters (such as laser power, pulse duration, scanning speed) and protective film composition to minimize phosphorus diffusion and foreign matter formation during laser processing. By carefully controlling these parameters, the process achieves effective debris protection while limiting the generation of phosphorus-containing foreign matter, thus maintaining high processing speed without sacrificing cleanliness.
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 suppresses the production of foreign matter on metal electrodes, maintaining device characteristics by ensuring timely removal of phosphorus-containing reaction products, thereby improving the quality of devices.
Implementation Method 1
a laser beam applying step of applying a laser beam to the wafer along the streets
Implementation Method 2
the element (e.g., phosphorus) constituting the wafer is liberated and diffused by the laser processing
Implementation Method 3
a period of time until a phosphorus containing reaction product produced at a laser processed portion by performing the laser beam applying step is evaporated to react with water in the air
Implementation Method 4
forming a water-soluble protective film on the front side of the wafer held on the chuck table, a cleaning step of cleaning the wafer to thereby remove the protective film
Data Source
AI summary
A wafer processing method includes a wafer holding step of holding a wafer having devices formed on the front side, a protective film forming step of forming a water-soluble protective film on the front side of the wafer, a laser beam applying step of applying a laser beam to the wafer along streets, a cleaning step of cleaning the wafer to then remove the protective film, and a foreign matter removing step of removing foreign matter from the wafer when a predetermined period of time has elapsed after cleaning. This period of time is set as a period of time until a phosphorus containing reaction product produced at a laser processed portion is evaporated to react with water in the air, thereby producing the foreign matter containing phosphorus on bumps formed on each device.