Applications and Development of Microchip Lasers in Photoresist Repair
Lithography is the most critical process step in chip manufacturing, comprising three core elements: the lithography system, photoresist, and photoresist repair. The lithography system is the core equipment in the semiconductor industry, while photoresist is a layer of chemically sensitive material coated onto the surface of a silicon wafer that is highly sensitive to specific wavelengths. When light emitted by the lithography system strikes the photoresist, the photoresist’s solubility changes. Using a high-precision light source and lens system, the lithography system reduces the complex circuit patterns on the mask and projects them onto the silicon wafer coated with photoresist, serving as a protective mask for subsequent etching or ion implantation processes. If any localized defects are detected after lithography is complete but before the subsequent etching process begins, they can be repaired through deposition or precise removal. After reapplying the photoresist, the process can be repeated, thereby avoiding the scrapping of the entire wafer. This “fault tolerance and repair mechanism” in the lithography process is known as photoresist repair.
Laser repair of photoresist is a key technology for the repair of high-cost semiconductor masks or during the development phase of cutting-edge processes. It offers irreplaceable economic and technical value, can significantly improve manufacturing yield, reduce production costs, salvage high-value wafers, and protect expensive masks. It has become the mainstream choice in this application field, but it also faces extremely high physical and chemical process challenges and has its core process pain points:
1. Nanometer-level positioning accuracy and focus control
2. Thermal effects and edge thermal damage
3. Residual buildup and photochemical secondary contamination
Thanks to their high stability, high beam quality, and mature frequency-doubling/harmonic generation technology, ND:YAG microchip solid-state lasers are currently among the most cost-effective and technically mature repair light sources in the semiconductor industry, capable of effectively addressing the core challenges mentioned above.
1. Solves the issues of spot size and nanoscale positioning: The shorter the wavelength, the smaller the optically focused spot. Deep ultraviolet light at 266 nm or 213 nm, combined with a high numerical aperture (NA) objective lens, can reduce the focused spot size to less than 200 nm. When used with super-resolution technology, this enables the precise removal of photoresist residues at the micrometer and submicrometer levels.
2. Compared to infrared or visible light, DPSS microchip lasers produce UV light with a significantly smaller heat-affected zone, and pulse widths can be as short as the sub-nanosecond range.
3. The photolytic action of UV photons directly decomposes part of the photoresist into small molecular gases that are expelled, resulting in less particle spatter compared to infrared lasers.
The working principle of microchip lasers in photoresist repair can be simply summarized as follows: high-energy-density, short-pulse photons achieve submicron-level precision cold ablation of the photoresist through “photochemical bond breaking.” The specific workflow is as follows:
1. Generation of sub-nanosecond/picosecond ultrashort pulses: The microchip laser directly bonds the laser gain medium to the passive Q-switch, forming an “ultra-short resonator.” Due to the extremely short cavity length, the microchip laser can output pulses with extremely narrow widths in the sub-nanosecond or picosecond range while maintaining high peak power.
2. Frequency conversion (harmonic generation): The microchip laser emits near-infrared light at a fundamental frequency of 1064 nm, which undergoes third-harmonic (355 nm UV) or fourth-harmonic (266 nm deep UV) conversion via a nonlinear crystal.
3. Photochemical Bond Cleavage and Micro-Area Peeling: High-peak-power UV or deep-UV pulsed light is focused by a high-magnification objective lens, reducing the spot size to the order of hundreds of nanometers. High-energy 355 nm/266 nm photons act on the organic photoresist, breaking the carbon-carbon (C–C) and carbon-hydrogen (C–H) bonds in the polymer chains. The photoresist material instantly degrades and vaporizes into small gas molecules, which are then expelled, enabling “nanoscale etching” at the defect sites.
Compared to traditional benchtop nanosecond DPSS lasers, RealLight’s microchip lasers demonstrate key advantages in photoresist repair applications:
1. Supports sub-nanosecond pulse widths ranging from 300 ps to 1 ns; the pulse duration is shorter than the time it takes for heat to diffuse within the photoresist, significantly suppressing “thermal damage”;
2. The ultra-short planar resonator structure enables operation in the TEM00 mode, delivering exceptional beam quality;
3. Although the single-pulse energy is low, the extremely narrow pulse width allows for both extremely high peak power and high repetition rates;
4. High pulse-to-pulse energy stability (RMS < 3%), preventing damage to fragile silicon wafers or quartz substrates caused by energy fluctuations;
5. The laser head is miniaturized and structurally extremely stable, greatly simplifying optical path design and reducing the system’s overall maintenance costs and failure rate.
Thanks to these advantages, RealLight’s microchip laser has become a highly competitive laser light source for photoresist repair equipment.
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MCH Series 300ps SLM Microchip Laser
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