Lloyd F. Wright

Controlled Mass Flow of Low Volatility Liquid Source Materials

Chemical Vapor Deposition (CVD) of thin films for microelectronic devices has historically used source materials that are gases at room temperature [1]. The decision to use gases was largely a practical one based on the relative ease with which the flow of gaseous materials can be controlled. CVD of thin films plays a vital role in increased circuit density and performance of integrated circuits. Liquid sources offer alternative source composition, reaction kinetics and reaction mechanisms to optimize a given CVD process [2]. For example, CVD films of silicon dioxide (oxide) and oxide films modified to lower the glass transition temperature such a borophosphosilicate glass (BPSG) have traditionally used gaseous source materials such as silane, diborane and phosphine [3]. An all liquid system of tetraethylorthosilicate (TEOS), triethylborate (TEB) and triethylphosphine (TEPhine) has been found to offer superior conformality and overall safety [4]. However, from a practical standpoint, the all liquid system has historically suffered from reliable, reproducible mass flow control.