Femtosecond laser cutting speed optimization for single crystal quartz wafers

Full text: Single crystal quartz is a widely used material in the microelectronics industry, with applications such as quartz crystal resonators being a key component in many integrated circuits. These resonators must have high structural and edge quality to ensure accurate resonance properties. Current mechanical dicing methods used to cut these components utilise diamond saw blades, which are expensive and wear down rapidly. This issue, coupled with the material wastage from the width of the saw blade and damage zone from the mechanical friction, represents a significant cost to the industry. If laser micromachining could be applied here, significant improvements could be made including reductions in cut widths and increased flexibility of cut shapes. Femtosecond laser micromachining is an excellent candidate for application in this area. The ultrashort pulse duration allows materials transparent to the laser wavelength, such as quartz, to be laser machined, and provides high cut quality with little or no heat affected zone. The major drawback to this method is the slow processing time - currently femtosecond laser cutting takes too long to be used in this setting. In this work we explore the available laser machining parameter space to determine optimal machining conditions for different types of laser micromachined features. We measure the effectiveness of the available laser power as a function of modifying the focal length, focal point position and laser wavelength. The effect of focal length was studied using uncoated BK7 lenses with focal lengths in the range of 50 to 300mm. We applied pulses from an amplified Ti:Sapphire laser (Coherent Legend Elite) with 110 fs duration at a 1kHz repetition rate. The maximum pulse energy available was approximately 3mJ. The beam was also directed through an optical parametric system (TOPAS, Light Conversions) to alter the wavelength of the output pulse to between 270 and 2600 nm. Quartz wafers were single crystal quartz, 100 mm diameter, 500 µm thick. (author)