Controlled Mass Flow of Low Volatility Liquid Source Materials
- PDF / 742,288 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 15 Downloads / 196 Views
CONTROLLED MASS FLOW OF LOW VOLATILITY LIQUID SOURCE MATERIALS
ALAN D. NOLET, BRUCE C. RHINE, MARK A. LOGAN, LLOYD WRIGHT, and JOSEPH R. MONKOWSKI, Monkowski-Rhine, Inc., 9250 Trade Place, San Diego, California, 92126.
ABSTRACT Chemical Vapor Deposition (CVD) of thin films for used source microelectronic devices has historically The decimaterials that are gases at room temperature [1]. sion 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 cirLiquid sources offer alternative source composition, cuits. 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, An all liquid system of diborane and phosphine [3]. and tetraethylorthosilicate (TEOS), triethylborate (TEB) triethylphosphine (TEPhine) has been found to offer superior However, from a pracconformality and overall safety [4]. tical standpoint, the all liquid system has historically suffered from reliable, reproducible mass flow control.
NEED FOR LIQUID MASS FLOW CONTROL Traditionally microelectronic process steps such as CV), etching, diffusion, oxidation and ion implantation have used source materials that are gases at room temperature. The use of liquids (and also solids) has been limited to applications where mass flow control has not been critical. In the case of CVD, and LPCVD in particular, there is a need for alternative chemistries to provide desired film compositions and uniformities.
ALTERNATIVE METHODS Five different liquid mass flow control methods were evaluated. A summary description and brief outline of advantages and disadvantages of each method is presented in Table 1. The goal of the development program was to establish which of the five methods would be best for LPCVD applications. Sonic restriction [5] was eliminated because of its complexity and the lack of readily available parts. Traditional mass flow controllers were eliminated because of
Mat. Res. Soc. Symp. Proc. Vol. 131. @1989 Materials Research Society
320
the long flow stabilization time and the risk of condensation in the feed line. Direct vaporization was eliminated for the same reason. Carrier gas saturation was not considered because of the undesirable intrinsic requirement of adding a process gas diluent (i.e., the carrier gas) and the lack of process flexibility incurred. The combination of metering the material in the liquid phase with subsequent and immediate vaporization was explored further [6]. This method virtually eliminates the need for large diameter plumbing to prevent condensation; provides for an exceptionally large flow rate range; and can accommodate premixed liquids. By using premixed liquid precursors, only one liquid delivery system is requi
Data Loading...
