Showing papers by "F. Levent Degertekin published in 1998"
TL;DR: In this article, a two-dimensional array of Flextensional transducers with a thin piezoelectric ring and a fully supported, circular membrane is presented for generating sound in air or water.
Abstract: This letter presents micromachined two-dimensional array flextensional transducers that can be used to generate sound in air or water. Individual array elements consist of a thin piezoelectric ring and a thin, fully supported, circular membrane. We report on an optimum design for an individual array element based on finite element modeling. We manufacture the transducer in two-dimensional arrays using planar silicon micromachining and demonstrate ultrasound transmission in air at 2.85 MHz. Such an array could be combined with on-board driving and an addressing circuitry for different applications.
80 citations
TL;DR: In this paper, the phase of a high frequency ultrasound signal was monitored as it was reflected from the silicon/photoresist interface during photoresist prebake, and the glass transition temperature (Tg) for a freshly spun 2.2 μm Shipley 1813 resist was measured to be 50
Abstract: We have developed a method to measure the glass transition temperature of photoresist in situ. The purpose of photoresist prebake is to evaporate excess solvent from the photoresist and to allow the polymer chains to relax into an ordered matrix. The phase of a high frequency ultrasound signal was monitored as it was reflected from the silicon/photoresist interface during the photoresist prebake. There was an initial decrease in phase followed by a rapid increase once a given temperature was reached. It is believed that this repeatable temperature is the glass transition temperature of the resist/solvent mixture and that the rapid increase in phase following it is a result of solvent evaporation. The glass transition temperature (Tg) for a freshly spun 2.2 μm Shipley 1813 resist was measured to be 50 °C. The Tg measured increased from 50 to 66 °C as the time delay between coating and prebaking was increased from 0 to 20 min. It is believed that this change in Tg is a result of solvent evaporation.
12 citations
TL;DR: In this article, the phase of a high frequency ultrasound signal is measured as it is reflected from the silicon/photoresist interface during resist development, and the total phase change during development of 19° was consistent with theoretical calculations at 280 MHz.
Abstract: We have developed an in situ method to measure the change in thickness of photoresist during development. The phase of a high frequency ultrasound signal is monitored as it is reflected from the silicon/photoresist interface during resist development. The method was tested using a 1.5 μm film of Shipley 1811 resist. The total phase change during development of 19° was consistent with theoretical calculations at 280 MHz, and this change was used to obtain the resist thickness during development. The method was used to find the development rate of this positive-tone resist as a function of exposure dose in the 20–68 mJ/cm2 range. As expected, there was an increase in development rate as the exposure time increased; this continued up to about 40 s of exposure, beyond which the rates were essentially unchanged. Measurements on a wafer with microelectronic devices ranging in topography from 0.10 to 1.0 μm show that the method is applicable to wafers with typical circuit topography.
5 citations