Femtoliter to Picoliter Droplet Generation for Organic Polymer Deposition Using Single Reservoir Ejector Arrays

Abstract

Direct deposition of photoresist and other spin-on materials, such as low-k and high-k dielectrics, has the potential to reduce waste as well as production costs. A new design of acoustically actuated two-dimensional (2-D) micromachined droplet ejector arrays can eject various solvents and other fluids ranging from femtoliter to picoliter droplet volumes. These ejectors do not harm fluids that are heat or pressure sensitive. Moreover, they are chemically compatible with the materials used in integrated circuit manufacturing. Therefore, they can be used for benign deposition of photoresist and other spin-on materials, such as low-k and high-k dielectrics. A vibrating circular Si/sub x/N/sub y/ thin-film membrane with an orifice at the center forms the unit cell of a 2-D ejector array. Initially, one side of the membrane is loaded with the ejection fluid. Then, ultrasonic waves generated by a piezoelectric transducer force the membranes to displace at resonance. As a result of this actuation, droplets are ejected through the membrane orifice. We ejected water at 1.06 MHz, isopropanol at 1.14 MHz, ethyl alcohol at 1.06 MHz, and acetone at 1.04 MHz from a 20/spl times/20 single reservoir 2-D micromachined array with 160 /spl mu/m in diameter Si/sub x/N/sub y/ membranes and 10 /spl mu/m in diameter orifices. The performance of single reservoir flextensional membrane-based ejector arrays was compared to flextensional membrane-based ejector arrays with reservoirs. A 50% decrease in the required power per ejected droplet and a reduced design complexity were demonstrated over the 2-D micromachined arrays with individual reservoirs. In addition, we deposited Shipley SPR 3612 photoresist at 1.12 MHz in a dry lab environment. No spinning was done after deposition. We covered a 2/spl times/2-mm area on a wafer with a 5.5-/spl mu/m thick photoresist layer. The maximum thickness variation over the area was 0.4 /spl mu/m. Moreover, we present a directly written 1.6-/spl mu/m thick 900-/spl mu/m wide and 8-mm long homogeneous photoresist line. The photoresist thickness variation along the line was 0.2 and 0.4 /spl mu/m in vertical and horizontal directions, respectively.