Wafer Laser Spot Orientation for Low-k Film Removal
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Solution Overview
Problem
The low-k film on semiconductor wafers tends to peel off during cutting, causing damage to the devices and lowering the quality of the resulting device chips.
Innovation Solution
A method using linearly polarized laser beams to remove the low-k film along the dicing lines, forming a recess with a slender spot orientation to prevent deep ditches, combined with a laser applying apparatus that shapes the laser beam into a slender spot and positions it on slanted surfaces to expose the semiconductor substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a laser beam with spot diameter commensurate with the width of the projected dicing line is repeatedly applied to remove the functional layer, then the functional layer is effectively removed and the semiconductor substrate is exposed, but deep ditches with downwardly pointed sharp lower ends are formed in the semiconductor substrate, lowering the flexural strength and quality of individual device chips
Solution Approach 1:
The patent applies local quality by making the laser spot shape asymmetric (slender ellipse rather than circle) and orienting it at a specific angle (45 degrees) relative to the processing direction. This creates a localized modification in the energy distribution pattern, concentrating the laser energy removal effect primarily on one side of the recess while reducing it on the other side, thereby preventing the formation of symmetric deep ditches and preserving the flexural strength of the device chips.
2Productivity
If the laser spot is oriented with its longer side in the processing direction, then the functional layer removal is efficient, but deep ditches are formed on both sides of the recess
Solution Approach 1:
The patent applies asymmetry by orienting the laser spot's longer side perpendicular to the processing direction (at 45 degrees to the dicing line) rather than parallel to it. This asymmetric orientation causes the laser energy to be distributed unevenly across the width of the recess, with the majority of energy concentrated on one side. This prevents the formation of symmetric deep ditches on both sides, thereby maintaining the flexural strength of the device chips while still achieving efficient functional layer removal.
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
Prevents deep ditches with sharp lower ends, maintaining the flexural strength and quality of the device chips by effectively removing the low-k film without damaging the semiconductor substrate.
Implementation Method 1
a functional layer removing step of removing the functional layer by applying linearly polarized laser beams to the projected dicing lines
Implementation Method 2
a beam spot shaper disposed between the laser oscillator and the beam condenser and configured to shape the spot into a slender spot and orient a polarization direction of the laser beam along a longer side of the slender spot
Implementation Method 3
The removing step is carried out a plurality of times to remove the functional layer on the projected dicing lines, thereby exposing the semiconductor substrate... by orienting the longer side of the slender spot transversely across the projected dicing lines and to orient a shorter side of the slender spot in a processing direction along the projected dicing lines
Data Source
AI summary
A laser applying apparatus includes a beam spot shaper for shaping a spot of a laser beam into a slender spot and orienting the polarization direction of a linearly polarized laser beam of the laser beam along a longer side of the slender spot, and a spot control unit for positioning a P-polarized laser beam on slanted surfaces of a recess that is formed in a wafer by orienting the longer side of the slender spot transversely across projected dicing lines and for orienting a shorter side of the slender spot in a processing direction along the projected dicing lines. A method of processing a wafer includes a functional layer removing step that is a step of removing a functional layer on a semiconductor substrate of the wafer by applying laser beams to the projected dicing lines with the use of the laser applying apparatus. The functional layer removing step is carried out a plurality of times to remove the functional layer on the projected dicing lines.