The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems may be used to perform deposition and/or etching of film on a substrate such as a semiconductor wafer. Substrate processing systems typically include a processing chamber with a substrate support such as a pedestal, an electrostatic chuck, a plate, etc. A substrate such as a semiconductor wafer may be arranged on the substrate support. During chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes, a gas mixture including one or more precursors may be introduced into the processing chamber to deposit a film on the substrate. In some substrate processing systems, plasma may be used to activate chemical reactions. To obtain high quality film, it is important to deliver the precursor gas to the processing chamber at a desired temperature, a high uniformity, and with high purity. Gas mixtures are obtained by some combination of gases, vaporized liquids, and sublimed solids. Vaporized liquids, in particular, are almost always incompletely vaporized, and the resultant vapor contains liquid droplets of varying sizes. Unvaporized droplets cause wafer defects.
Heated filters may be used to heat and filter the precursor gas before delivery to the processing chamber. In addition, the heated filter can also prevent the unvaporized liquid droplets from entering the chamber due to pore size. Heated filters typically use one or more filter elements that are arranged inside a filter housing. An external heater jacket may be arranged around the filter housing to heat the filter element. When heating the filter element, heat travels through the filter housing to the center of the filter via convection or conduction. The mean heat conduction path for a typical heated filter is approximately 10″ through a 1/16″ porous wall, which also has a much lower thermal conductivity than its solid analogue. In addition, usually there is no direct conductive path from the filter element to the temperature monitoring and control system.
When using this heated filter arrangement, there is a large heating time lag due to the lack of direct contact between the heater and the temperature monitoring and control system. The time lag causes large temperature swings. Too much heat may cause thermal decomposition of precursors while too little heat may cause precursor condensation.
The filters are prone to clogging due to byproducts of decomposition clogging pores of the filter elements. The filters are also prone to clogging due to droplets diffusing through the filter element by capillary action and when the filter element cannot provide enough heat to vaporize the droplets. Other challenges include incomplete purging of atmospheric moisture due to poor and lagging thermal control, which increases clogging. Currently, the filter needs to be purged for 48 hours with inert gas prior to introducing precursor.
Additionally, it is difficult to maintain the required operating temperature as gases expand and cool down. When the gases cool down, heat is removed from the filter and the likelihood of precursor condensation increases. Furthermore, it is difficult to compensate for cold spots as droplets strike the filter element and remove heat.