Two-stage roughing and controlled deposition rates for fabricating laser ablation masks

The invention relates generally to methods and systems for fabricating laser ablation masks and more particularly to approaches to evacuating a vacuum chamber and depositing layers during the fabrication of such masks. A method of fabricating a high energy radiation mask, such as a laser ablation mask for manufacturing inkjet printheads, includes a multi-stage evacuation process and/or a step of reducing the deposition rate of silicon dioxide during formation of a dielectric stack. When the multi-stage evacuation procedure is combined with the slower deposition rate of silicon dioxide, the resulting mask has a surprisingly low defect density. In the first embodiment, the evacuation procedure is initiated using a low-rate first evacuation connection. The relatively slow purging of a vacuum chamber in which the dielectric stack is subsequently formed controls turbulence and environmental changes that can generate contamination and water along the surface of the substrate on which the dielectric stack is formed. When a pressure setpoint is reached, a second roughing connection is activated to increase the speed of the procedure. The second connection has a higher maximum rate than the first connection. In the preferred embodiment, there is an overlap in the activations of the first and second connections. When another setpoint is reached, a high vacuum connection is activated in order to bring the vacuum chamber to a high vacuum condition for deposition of the dielectric stack. The dielectric stack includes alternating layers of higher refractive index material and low refractive index material. The low refractive index material is silicon dioxide that is deposited at a rate in the optimal range of 1.0 /second to 3.0 /second. Practical considerations dictate a range of 1.6 /second to 2.4 /second.