Wafer Laser Processing via Resin Sheet Barrier
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Solution Overview
Problem
Current laser processing methods for MEMS device wafers face challenges in applying a laser beam from the back side without damaging the devices on the front side, as they require suction on the front side, leading to potential damage and vibration issues due to negative pressure and adhesive layer sticking problems.
Innovation Solution
A method involving a frame unit with an adhesive tape and a resin sheet that covers the wafer, allowing laser beam application from the back side with the resin sheet preventing suction on the front side devices and ensuring secure fixation to prevent damage and vibration, using through-holes for gas evacuation and an ultraviolet light-curable adhesive for reduced adhesive force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a laser beam is applied from the back side of the wafer to avoid damage to MEMS devices, then the risk of damage to MEMS devices is reduced, but the wafer cannot be securely fixed to the chuck table due to adhesive layer sticking problems
Solution Approach 1:
A release sheet is introduced as an intermediary layer between the wafer's back surface and the chuck table. This release sheet prevents the adhesive layer from directly contacting and sticking to the chuck table, thereby maintaining secure fixation while allowing laser beam application from the back side without damaging MEMS devices on the front side.
Solution Approach 2:
The system segments the contact interface by separating the adhesive layer from the chuck table through the release sheet. This segmentation allows the adhesive to bond the wafer to the frame structure while the release sheet manages the interface with the chuck table, resolving the contradiction between fixation needs and laser accessibility.
2Object-affected harmful factors
If a protective sheet with gas permeability is used to protect MEMS devices during back-side laser processing, then MEMS devices are protected from direct suction, but leakage occurs during suction causing the wafer to vibrate or move
Solution Approach 1:
The release sheet serves as a mediator that replaces the gas-permeable protective sheet. It provides a non-permeable barrier that prevents suction from reaching the wafer and MEMS devices, eliminating both the protection benefit and the leakage/vibration problem associated with gas-permeable sheets.
Solution Approach 2:
The harmful suction force is extracted or blocked from reaching the wafer by positioning the release sheet between the chuck table's suction surface and the wafer. This extraction of the harmful factor (suction) eliminates the need for gas-permeable materials and their associated leakage problems.
3Reliability
If the adhesive layer of the dicing tape is bonded to the chuck table for secure fixation, then the wafer is firmly fixed, but the adhesive layer sticks to the chuck table causing transfer failure
Solution Approach 1:
The release sheet acts as a temporary intermediary that prevents adhesive contamination of the chuck table during processing. After laser processing is complete, the release sheet is removed, allowing the adhesive-bonded wafer to be cleanly transferred to the next processing stage without adhesive residue causing transfer failures.
Solution Approach 2:
The release sheet is discarded after serving its protective function during laser processing. Its removal restores the adhesive layer's bonding capability, enabling successful transfer of the processed wafer without the adhesive sticking to the chuck table.
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
Enables safe application of a laser beam from the back side of the wafer, preventing damage to MEMS devices and ensuring secure fixation during processing, reducing the risk of vibration and adhesive residue on the chuck table.
Implementation Method 1
bonding an adhesive tape to a ring-shaped frame centrally defining an opening, so that the opening is closed by the adhesive tape, and bonding the wafer at a back side of the wafer to the adhesive tape
Implementation Method 2
providing a resin sheet that has a diameter greater than that of the opening of the ring-shaped frame and will serve as a protective member for the wafer, covering the opening of the ring-shaped frame with the resin sheet from the front side of the wafer
Implementation Method 3
the adhesive tape, which faces the resin sheet, is suctioned under a negative pressure acting from the holding surface via the through-holes of the resin sheet while the front side of the wafer is prevented by the resin sheet from being suctioned on the holding surface
Implementation Method 4
applying a laser beam of a wavelength, which has transmissivity through the adhesive tape and the wafer, to the wafer from a side of the adhesive tape with a condensing point thereof positioned inside the wafer, whereby modified layers are formed along the streets inside the wafer
Implementation Method 5
an ultraviolet light-curable adhesive for reduced adhesive force
Data Source
AI summary
A processing method for a wafer includes the steps of forming a frame unit having a ring-shaped frame, providing a resin sheet, fixing the resin sheet, which covers the wafer at its front side, at its outer peripheral edge, on the ring-shaped frame, forming through-holes in the resin sheet, holding the frame unit on a side of the resin sheet under suction on a holding surface to fix the ring-shaped frame, applying a laser beam to the wafer to form modified layers inside the wafer, and separating the resin sheet. In the holding step, the adhesive tape is suctioned under a negative pressure acting from the holding surface via through-holes while the front side of the wafer is prevented by the resin sheet from being suctioned on the holding surface.