UV laser source has a number of advantages in the precision cutting market for metal and non-metal materials. The stability and reliability of laser tools, combined with precision processing and low mechanical stress, allow these lasers to enter the microelectronics manufacturing market. Due to the flexibility to work with a wide range of materials, UV lasers are easily adapted to process requirements and integrated into fast and accurate laser processing lines in the microelectronics industry. The article presents the capabilities of diode-pumped solid-state UV lasers emitting at a wavelength of 355 nm.
Traditionally, laser sources emitting near and far IR ranges (fiber and CO 2 lasers) are used in industry. IR radiation processing occurs as a result of intense local heating, which melts or evaporates the material. Such an impact has a thermal effect on nearby areas, which worsens the strength of the cut edges and imposes restrictions on the minimum allowable size of the elements. This is a major limitation in the processing of special materials such as sapphire, polymer films, printed circuit boards, semiconductor materials, etc.
The use of UV laser cutting systems has opened up new possibilities for processing special materials. In principle, ultraviolet is a universal tool for precision marking, cutting , and perforation of almost any material.
For many years, ultraviolet laser sources have been gaseous: pulsed excimer laser and cw He-Cd laser. Both types of sources have significant disadvantages for industrial applications: complex and cumbersome design, high power consumption, and limited resources. The excimer laser has a poor spot quality, which makes it necessary to use a photomask, which loses up to 95% of the output power.
Radiation with a wavelength of 355 nm is the third harmonic of the radiation of a diode-pumped solid-state laser. Generation is implemented according to the following scheme: the fundamental wavelength of 1064 nm excites the second harmonic (532 nm) on the first nonlinear crystal of potassium titanyl phosphate (KTiOPO4). Then the radiation of the fundamental and second harmonics is mixed on the second nonlinear crystal, as a result of which the third harmonic with a wavelength of 355 nm is emitted at the output
Laser radiation from UV laser source in the ultraviolet range (355 nm) has a high photon energy and a smaller spot diameter in the focusing region due to a shorter wavelength compared to fiber (1064 nm) and CO2 lasers (10.6 μm). The smallest possible diameter of the focusing spot corresponds to the wavelength of the laser radiation. Accordingly, for 355 nm it is 30 times smaller than for a CO2 laser wavelength of 10.06 μm, and amounts to several micrometers.
Reducing the wavelength of laser radiation reduces the reflectivity of materials and increases the amount of energy absorbed by the material. When UV radiation interacts with dielectric materials, such as polymers, intramolecular bonds are broken in a substance and the molecules of the substance are electronically excited. There is a photochemical mechanism of action, the so-called “cold” ablation. At a high power density of laser radiation, conditions are created under which the photon energy is sufficient both to break bonds between polymer chains, inside chains between individual molecules, and to break chemical bonds inside molecules (for example, C-C or C-H type in polymers) . Cold ablation is characterized by a small heat-affected zone – only a few microns.