Horizontal Stealth Lasing for Uniform Wafer Thinning
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Solution Overview
Problem
Conventional backgrinding processes for thinning semiconductor wafers result in non-uniform thicknesses, cracks, reduced yield, additional screening costs, and debris generation, which are exacerbated by the fragile thicknesses of modern wafers.
Innovation Solution
A horizontal stealth lasing process is employed to thin semiconductor wafers by creating localized pinpoint holes at varying radii using a laser beam, followed by a vertical dicing process to form individual dies, eliminating the need for backgrinding and ensuring a smooth, uniform surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional backgrinding process is used to thin semiconductor wafers, then wafer thickness is reduced, but non-uniform thickness and cracks are generated
Solution Approach 1:
The patent replaces the mechanical backgrinding system with a laser-based ablation system. The laser beam precisely removes material from the wafer back surface through photothermal ablation, eliminating mechanical contact that causes non-uniform thickness and cracking. This substitution of mechanical processing with optical processing resolves the contradiction between thickness reduction and thickness uniformity.
Solution Approach 2:
The patent changes the processing parameters from mechanical force and abrasion to laser energy density and pulse duration. By controlling laser power, pulse width, and scanning speed, the process achieves uniform material removal without mechanical stress, thereby maintaining thickness uniformity while reducing wafer thickness to the desired level.
2Volume of moving object
If conventional backgrinding process is used to thin semiconductor wafers, then wafer thickness is reduced, but cracks and reduced yield occur
Solution Approach 1:
The laser ablation process eliminates mechanical contact with the wafer, preventing the generation of cracks that occur during backgrinding. The optical energy selectively removes material without applying mechanical stress, thereby maintaining wafer integrity and reducing defects that would lead to yield loss.
Solution Approach 2:
The laser beam acts as an intermediary between the processing system and the wafer, transferring energy without physical contact. This intermediary approach allows precise material removal while avoiding direct mechanical interaction that causes cracking and compromises wafer reliability.
3Volume of moving object
If conventional backgrinding process is used to thin semiconductor wafers, then wafer thickness is reduced, but additional screening steps are required
Solution Approach 1:
The laser-based process eliminates the need for subsequent mechanical screening and inspection steps required after backgrinding. The precision and uniformity of laser ablation produce a clean, crack-free surface that requires minimal additional processing, thereby reducing overall process complexity.
Solution Approach 2:
The laser ablation process performs the thinning operation with such precision that it pre-empts the need for subsequent screening and repair operations. By achieving the desired thickness uniformity and integrity in the primary processing step, the process eliminates or minimizes follow-up operations.
4Volume of moving object
If conventional backgrinding process is used to thin semiconductor wafers, then wafer thickness is reduced, but debris and foreign materials are generated
Solution Approach 1:
Replacing mechanical grinding with laser ablation eliminates the generation of debris and foreign materials. The laser vaporizes and ejects material directly from the wafer surface without producing particulate waste, thereby preventing contamination and the need for additional cleaning operations.
Solution Approach 2:
The laser processing induces phase transitions in the wafer material, transforming solid material directly into vapor or plasma state through photothermal heating. This phase change process eliminates mechanical particle generation, as material is removed through vaporization rather than mechanical fragmentation.
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
The process significantly reduces fabrication time, improves yield and die quality by preventing cracks and debris, and eliminates the need for additional screening steps, resulting in a more efficient and reliable semiconductor manufacturing process.
Implementation Method 1
focusing a horizontally-oriented laser through an outer edge of the wafer into a depth of the wafer
Data Source
AI summary
A method includes the step of thinning a semiconductor wafer by a horizontal stealth lasing process, and semiconductor wafers, dies and devices formed thereby. After formation of an integrated circuit layer on a semiconductor wafer, the wafer may be thinned by supporting an active surface of the wafer on a rotating chuck, and focusing a horizontally-oriented laser in multiple cycles at different radii within the rotating wafer. Upon completion of the multiple cycles, a portion of the wafer substrate may be removed, leaving the wafer thinned to its final thickness. Thereafter, a vertical stealth lasing process may be performed to cut individual semicondcutor dies from the thinned wafer.