Pulsed Laser Wafer Dicing to Prevent Crystal-Structure Cracks
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Solution Overview
Problem
Laser processing of wafers with compound semiconductors like silicon carbide often results in cracks along crystal structures due to inadequate processing conditions, such as laser beam power and feed speed, leading to potential device damage.
Innovation Solution
A laser processing apparatus with a pulsed laser beam generation unit that adjusts repetitive frequency, pulse duration, and power, along with feed speed and focused spot position, to accommodate the kind and crystal structure of the workpiece, using a chuck table and feed mechanisms for precise processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser beam is applied along projected dicing lines on compound semiconductor wafers, then dicing processing is achieved, but cracks extend along crystal structures causing device damage
Solution Approach 1:
The patent applies periodic pulsed laser action instead of continuous laser beam. The laser oscillation source emits laser pulses at high repetitive frequency (e.g., 100 MHz or higher), and the pulse width is controlled to be short (e.g., 100 ps to 10 ns). This periodic pulsed action allows the material to cool between pulses, preventing heat accumulation that causes cracks along crystal structures while maintaining efficient dicing processing.
Solution Approach 2:
The patent changes key laser parameters including repetitive frequency (set to 100 MHz or higher), pulse width (controlled to be short duration), and power levels. By adjusting these parameters, the laser processing achieves clean cuts without inducing thermal stress cracks that would compromise device integrity, thus resolving the contradiction between processing efficiency and device reliability.
2Manufacturing precision
If processing conditions such as laser beam power and feed speed are adjusted to account for heat retention, then processing quality improves, but processing time increases
Solution Approach 1:
The use of high-frequency pulsed laser (100 MHz or higher) with short pulse widths enables rapid heating and cooling cycles. This periodic action allows for high-quality processing with minimal heat retention because the short pulse duration prevents excessive heat accumulation, while the high repetition rate maintains efficient processing speed, thus improving quality without significantly increasing processing time.
Solution Approach 2:
The patent sets the laser oscillation source to emit pulses at high repetitive frequency before the actual dicing process begins. This preliminary setup ensures that the laser is ready to immediately process the wafer with optimal parameters, eliminating setup time and allowing high-quality processing to proceed at full speed from the start.
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 flexible adjustment of processing conditions to prevent cracks and achieve desired outcomes in processing wafers, effectively dividing them into individual device chips without damage.
Implementation Method 1
a laser oscillation source for emitting laser pulse signals at a high repetitive frequency
Implementation Method 2
a beam condenser for converging the pulsed laser beam emitted from the laser beam generation unit and applying the pulsed laser beam to the workpiece
Data Source
AI summary
A laser processing apparatus includes a laser beam generation unit having a laser oscillation source for emitting laser pulse signals at a high repetitive frequency, a pulsed laser beam setting section for setting the number of laser pulse signals so as to emit a single pulsed laser beam that includes the set number, a pulse period setting section for decimating laser pulse signals from the laser oscillation source to set a period between pulsed laser beams that are adjacent to each other, and a power amplifying section for amplifying the pulsed laser beams. The pulsed laser beams have a repetitive frequency set to a value calculated by dividing the high repetitive frequency by a sum of the number of laser pulse signals that make up the single pulsed laser beam and the number of laser pulse signals to be decimated at one location.