Laser Sources for Photolithography Equipment

What is Photolithography ?

Photolithography is the core microfabrication technology to transfer circuit patterns onto semiconductor wafers, PCB substrates and micro-optical components, and the laser light source is the heart that determines imaging resolution, exposure uniformity and mass production yield of lithography equipment. The basic principle of lithography is to use high-energy monochromatic ultraviolet laser to irradiate photoresist coated on the workpiece surface. The photons trigger photochemical reaction of the photoresist, and form micro patterns after subsequent developing and etching processes. With the continuous iteration of microfabrication requirements, different types of laser light sources are selected for different lithography equipment and manufacturing nodes.

The Mainstream laser Sources Applied in Lithography Systems

The resolution of lithography follows the optical principle: the shorter the laser wavelength, the finer the minimum feature size that can be printed. Therefore, the evolution of lithography equipment is essentially the continuous shortening of the working wavelength of light sources. The mainstream laser sources applied in lithography systems can be divided into two major categories: high-end semiconductor wafer optical lithography lasers, and UV/violet diode laser modules for maskless direct imaging lithography such as LDI.

1. Excimer lasers for semiconductor wafer DUV lithography

   • 248nm KrF excimer laser: It is widely adopted for mature chip manufacturing processes. It supports feature size down to 150nm, mainly applied in power devices, MEMS sensors and low-to-medium-end logic chip mass production. It features high pulse energy and stable single-pulse energy output.

   • 193nm ArF excimer laser: The mainstream light source of immersion DUV lithography. With immersion technology, it can realize sub-45nm chip manufacturing. It has extremely strict requirements on wavelength bandwidth, pulse energy stability and spectral purity, and is widely used for mass production of mid-range logic chips and memory products.

   • EUV lithography adopts 10.6μm pulsed CO₂ laser as driving source. The high-power laser pulse bombards tin droplets to generate plasma, which radiates 13.5nm extreme ultraviolet light for advanced chip lithography at 7nm and below nodes.

2. Diode UV / violet laser modules for maskless direct lithography (LDI / DLW) For PCB, FPC, IC carrier board and microfluidic chip digital lithography, fiber-coupled 375nm and 405nm violet laser diodes become the preferred light source. Compared with excimer lasers, these diode laser modules have compact volume, low power consumption, long service life and low maintenance cost. They cooperate with DMD spatial light modulator or galvanometer scanning system to realize mask-free digital pattern writing, which is exactly the laser product series our company customizes for lithography and LDI equipment manufacturers.

Lithography lasers have ultra-high requirements on optical performance: ultra-stable power output, excellent beam uniformity, low spectral drift, low noise and long-term low light decay. Any tiny fluctuation of laser energy will directly cause line width deviation, pattern distortion or partial exposure failure, resulting in mass scrapped workpieces. Our customized 375nm & 405nm laser modules for direct lithography integrate constant temperature closed-loop drive and power real-time feedback circuit. The power fluctuation can be controlled within ±2%, and the beam energy distribution is highly uniform, meeting the long-time continuous scanning exposure demand of digital lithography equipment.

The Core Functions of Laser Inside Lithography Equipment

The core functions of laser inside lithography equipment are as follows. First, provide monochromatic photon energy that precisely matches the absorption peak of photoresist, to trigger controllable photochemical crosslinking reaction only in the designated exposure area. Second, deliver high-uniformity collimated beam, to ensure consistent exposure dose across the whole exposure field and guarantee smooth, neat pattern edge. Third, support high-speed on-off modulation, which cooperates with digital control system to realize pixel-level pattern writing for maskless lithography. Fourth, maintain stable optical parameters during thousands of hours of continuous operation, to reduce equipment downtime and production cost.

At present, our lithography dedicated laser modules are widely used in PCB LDI direct imaging, micro-nano structure lithography, mask making, MEMS component processing and microfluidic chip manufacturing. We can customize laser power, fiber coupling design, spot homogenization optical path and constant-current driving scheme according to customers’ lithography machine optical architecture, and supply complete test data and aging reports.