Formation of Silicon-on-Insulator Films from Powders
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FORMATION OF SILICON-ON-INSULATOR FILMS FROM POWDERS KAMESH V. GADEPALLY*, ROGER M. HAWK**, and WILLIAM D. BROWN*** *Fairchild Research Center, National Semiconductor Corporation, Santa Clara, CA 950528090 ** University of Arkansas at Little Rock, Department of Electronics and Instrumentation, Little Rock, AR 72204 ***University of Arkansas, Department of Electrical Engineering, Fayetteville, AR 72701 ABSTRACT Silicon powders have been successfully deposited by a corona discharge assisted electrostatic process on insulating, semiconducting, and conducting substrates. Subsequently, the deposits were heat treated and films have been formed. We present data pertatining to silicon films on insulators. The insulating surfaces used were sapphire, Si0 2 on Si, and Si 3N4 on Si. The electrical, chemical, and physical characteristics of these films are presented along with the time and temperature effects on the film formation. The impact of the above method with emphasis to the microelectronics industry will be discussed. INTRODUCTION AND BACKGROUND Silicon on insulator films have gained prominence for their role in the fabrication of dielectrically isolated silicon islands, thin film transistors, solar cells, and for three dimensional utilization of the silicon real estate [1-4]. The method of choice for the deposition of the silicon films on insulators is using Chemical Vapor Deposition (CVD). The deposited silicon films which are polycrystalline in nature are further converted to epitaxial films by using the underlying substrate exposed through windows as seed material [2,5]. Melt recrystallization sources such as strip heaters [6,7], CW lasers [8,9], electron beams [10], and halogen lamps [11] are employed for these purposes. The conventional methods of silicon film deposition utilize expensive equipment and flammable, and toxic gases. Other methods of silicon deposition have utilized plasma spraying [12] and ionized cluster beams [13]. Polymer powders have been deposited using an electrostatic spray process described in references [14] and [15]. Recently, we demonstrated the feasibility of electrostatically depositing silicon powder on various conducting, semiconducting, and insulating substrates [16,17]. This paper will discuss the deposition of silicon powder on insulators and the subsequent formation of films. EXPERIMENTAL PROCEDURE Silicon powder was electrostatically deposited on various insulating substrates using a Ransburg Gema Model 706 corona charging cup gun. The substrates used were oriented single crystal sapphire obtained from Union Carbide and oxide and nitride coated samples contributed by the National Semiconductor Corporation. All deposition experiments were at atmospheric conditions while the heat treatment experiments were carried out in ultra purity argon. These procedures are described in greater detail in our earlier work [16,17]. Silicon on Sapphire The silicon powder count median aerodynamic diameter (CMAD) was 23 micrometers. The purity of the powder was 99.999% silicon. The substrates were c
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