Effect of carbon coating on electron field emission from polysilicon

Carbon films deposited at relatively low temperatures were studied as a coa ting for polysilicon substrates to provide enhancement of the electron fiel d emission. Undoped and phosphor doped polysilicon substrates were coated b y carbon films grown by a very high frequency chemical vapor deposition pro cess. Critical process parameters include substrate temperature of 225 degr ees C, pressure of 56 mTorr, loaded power of 2 W/cm(2), and discharge frequ ency of 56 MHz. The substrates were pretreated prior to film deposition, an d bias enhanced nucleation was performed in hydrogen/C6H14 plasma. A carbon layer was grown to a thickness of 700 nm. Field emission measurements were Performed in an ultrahigh vacuum chamber equipped with an electron gun, a carousel for five samples, and a Faraday cup. A multigrid quasispheric ener gy analyzer was used for Anger electron spectroscopy and electron energy lo ss spectroscopy characterization. Additionally, before and after field emis sion measurements, the secondary emission coefficient sigma was measured by a scanning electron beam, which provided a two-dimensional sigma map of th e sample surface. The field emission current was measured in a diode config uration using a spacer thickness of 45-55 mu m through a current collection window 2x5 mm(2). Emission current-voltage curves were measured from three different regions of every sample by shifting the current collection windo w over the sample. A surface conditioning effect was observed, resulting in stabilization and better reproducibility of the emission current-voltage c haracteristics. The most significant changes in emission characteristics we re observed in undoped polysilicon substrates with carbon coatings. Low dep osition temperatures make this coating process very attractive because of i ts compatibility with addressing circuitry based on either silicon or poly- , microcrystalline, or amorphous silicon. (C) 2000 American Vacuum Society. [S0734-211X(00)08502-4].