Apparatus for Characterizing Gas-Phase Chemical Precursor Delivery for Thin Film Deposition Processes.

Thin film vapor deposition processes, e.g., chemical vapor deposition, are widely used in high-volume manufacturing of electronic and optoelectronic devices. Ensuring desired film properties and maximizing process yields require control of the chemical precursor flux to the deposition surface. However, achieving the desired control can be difficult due to numerous factors, including delivery system design, ampoule configuration, and precursor properties. This report describes an apparatus designed to investigate such factors. The apparatus simulates a single precursor delivery line, e.g., in a chemical vapor deposition tool, with flow control, pressure monitoring, and a precursor-containing ampoule. It also incorporates an optical flow cell downstream of the ampoule to permit optical measurements of precursor density in the gas stream. From such measurements, the precursor flow rate can be determined, and, for selected conditions, the precursor partial pressure in the headspace can be estimated. These capabilities permit this apparatus to be used for investigating a variety of factors that affect delivery processes. The methods of determining the pressure to (1) calculate the precursor flow rate and (2) estimate the headspace pressure are discussed, as are some of the errors associated with these methods. While this apparatus can be used under a variety of conditions and configurations relevant to deposition processes, the emphasis here is on low-volatility precursors that are delivered at total pressures less than about 13 kPa downstream of the ampoule. An important goal of this work is to provide data that could facilitate both deposition process optimization and ampoule design refinement.