In semiconductor manufacturing, precision is king. From advanced logic chips to high-power devices, wafer integrity directly impacts yield, performance, and long-term reliability. One of the most subtle but critical challenges in laser-based microfabrication is controlling the Heat Affected Zone (HAZ)—the microscopic region surrounding a laser-processed area where thermal energy alters material properties. Minimizing HAZ is essential, particularly for silicon carbide (SiC), gallium nitride (GaN), and other wide-bandgap semiconductor wafers, where even tiny thermal distortions can induce cracking or warpage.

The Problem with Conventional Nanosecond Lasers

Traditional nanosecond (ns) pulsed lasers deliver energy over tens of nanoseconds. While this is fast on human timescales, it is relatively slow in the context of atomic lattice vibrations. When a nanosecond pulse hits a semiconductor wafer, heat has time to diffuse into the surrounding crystal lattice. The consequences include:

1. Thermal Expansion and Microcracks – Localized heating causes transient expansion, which, in brittle materials like SiC, can result in microscopic fractures.

2. Material Recast and Debris – Molten material can resolidify unevenly, leaving recast layers that interfere with subsequent processing or device performance.

3. Residual Stress and Warpage – Uneven heating introduces internal stresses, which are particularly problematic for large-diameter wafers.

In high-volume semiconductor fabs, these effects translate to lower yield and increased cost per chip.

Enter Picosecond Lasers: Ultra-Fast, Ultra-Precise

Picosecond (ps) lasers emit pulses on the order of 10^-12 seconds, approximately 1,000 times shorter than nanosecond lasers. This ultra-short pulse duration fundamentally changes how energy interacts with the wafer:

• Athermal Material Removal – The pulse duration is shorter than the time required for significant thermal diffusion. Instead of melting the material, the laser induces rapid electron excitation, breaking bonds almost instantaneously. This process, often called “cold ablation”, removes material with minimal heat conduction to surrounding areas.

• Minimal Heat Affected Zone – With heat unable to migrate far from the irradiated area, the HAZ is drastically reduced, often to sub-micrometer scales. This precision is crucial for delicate patterns in high-voltage SiC devices or high-frequency GaN transistors.

• Enhanced Microstructural Integrity – By avoiding prolonged melting, picosecond lasers preserve the crystal lattice, preventing microcracks, stress accumulation, and warpage.

Case Study: SiC Wafer Scribing

Consider wafer scribing, a process used to separate diced chips from the bulk wafer. Nanosecond lasers often create microcracks extending tens of microns beyond the scribe line, whereas picosecond lasers restrict the HAZ to less than a few microns. This difference is not merely cosmetic; it directly improves die yield, reduces edge chipping, and enhances device reliability, particularly in high-power applications.

Beyond HAZ: Picosecond Lasers Enable New Processing Possibilities

In addition to superior HAZ control, picosecond lasers offer ancillary benefits that drive innovation in semiconductor manufacturing:

• 3D Microstructuring – The precision enables complex geometries such as microvias, channels, or waveguides in GaN-on-Si or SiC substrates.

• Reduced Post-Processing – Less thermal damage reduces the need for chemical etching or mechanical polishing, saving time and reducing contamination risks.

• Compatibility with Transparent Substrates – Ultra-fast pulses can process sapphire or other optical substrates without cracking, opening pathways for optoelectronics and laser optics integration.

Conclusion

For next-generation semiconductor wafers, where thermal sensitivity, material brittleness, and microscopic precision are paramount, picosecond lasers represent a paradigm shift. By confining the heat affected zone to near-zero dimensions, these ultra-fast lasers protect wafer integrity, maximize yield, and enable processing possibilities that were previously impossible with nanosecond technology. In the race for smaller, faster, and more reliable devices, picosecond lasers are not just a tool—they are an enabler of the future of semiconductor manufacturing.