Gas and liquid contact apparatus – With external supply or removal of heat – Processes
Reexamination Certificate
1998-02-27
2001-01-30
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
With external supply or removal of heat
Processes
C261S156000, C261S157000
Reexamination Certificate
active
06179277
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to liquid vaporizer systems and, more specifically, to liquid vaporizer systems for low vapor pressure liquids.
Semiconductor fabrication processes may include the use of chemical vapor deposition (CVD) to deposit a thin film of material on semiconductor wafers. CVD processes are often preferred because of their ability to provide highly uniform layers of film. CVD typically comprises introducing gases into a reaction chamber in the presence of a substrate, wherein the gases react and deposit a film on the substrate surface. Some of the CVD materials originate as liquids, and are evaporated and transported in the gaseous state to the desired reaction chamber for CVD.
Liquid reactant sources are often used with CVD processes. For example, titanium tetrachloride (TiCl
4
) is used as a reactant gas in CVD to deposit titanium-containing film layers onto a substrate surface. Tetrakisdimethyl-amidotitanium (TDMAT), a metal-organic material, also is used in CVD processes.
CVD using TiCl
4
and TDMAT typically involves the vaporization of liquid TiCl
4
or TDMAT and the transportation of the gaseous TiCl
4
or TDMAT to the reaction chamber using a carrier gas. Care must be exercised to fully vaporize the liquid compound. If the compound is not fully vaporized and is thus delivered to the reaction chamber as a gas/liquid mixture, liquid compounds in the reaction chamber can lead to poor uniformity of the deposited film and other undesired process results. This also can cause poor repeatability wafer to wafer because liquid droplets deposited on the walls of the process piping can later evaporate, causing fluctuations in vapor concentration in the reaction chamber. Once fully vaporized, care also must be exercised to maintain the compound in a gaseous state while it is being transported to the reaction chamber. Condensation of TiCl
4
or TDMAT can lead to undesirable deposition process variability and possibly the failure of line components.
The vaporization of TDMAT presents unique problems, in part due to the fact that TDMAT has a low vapor pressure. It is desirable, therefore, to provide an efficient mechanism for fully vaporizing TDMAT metal-organic compound, and for transporting the gaseous compound to the reaction chamber while avoiding the condensation of TDMAT liquid out of the gas.
SUMMARY OF THE INVENTION
The present invention provides for improved liquid vaporizer systems and methods for their use. Vaporizer systems of the present invention are likely to be particularly useful for the vaporization of TDMAT and other liquid sources having relatively low vapor pressures. The present invention uses a two-step vaporization process to assist in the full vaporization of such liquids.
In one embodiment, a liquid vaporizer system of the present invention includes a vaporizer unit having first and second inlets and an outlet. The vaporizer system further includes a vessel having an inlet and an outlet, whereby the vessel inlet is operably connected to the vaporizer unit outlet. The vessel contains a plurality of passages which operably connect the vessel inlet with the vessel outlet. In this manner, liquids and/or gases flowing into the vaporizer unit through either or both of its two inlets exit the vaporizer unit outlet and enter the vessel inlet. Liquids and/or gases pass through the plurality of passages and exit the vessel outlet.
In one aspect, the first vaporizer inlet is adapted to receive a liquid and the second vaporizer inlet is adapted to receive a carrier gas. The vaporizer unit preferably comprises a control valve for controlling the amount of liquid passing therethrough, and a vaporization valve for causing the liquid which has passed through the control valve to be at least partially vaporized and transported out the vaporizer outlet by the carrier gas. A vaporizer passageway is provided which connects the control valve with the vaporization valve to allow liquid to flow from the control valve into the vaporization valve.
The vaporizer unit further preferably comprises a temperature-controlled housing structure containing both the control valve and the vaporization valve. A temperature control mechanism is in communication with the housing structure for maintaining a thermostatic condition inside the housing structure. In this manner, a desired amount of heat can be transmitted to the liquids or gases passing through the control valve and vaporization valve, thereby assisting with the vaporization of the liquid. Exemplary vaporizer units of the present invention are disclosed in U.S. Pat. No. 5,440,887 and U.S. Pat. No. 5,272,880, the complete disclosures of which are hereby incorporated by reference. Both U.S. Pat. No. 5,440,887 and U.S. Pat. No. 5,272,880 are assigned to Applied Materials, Inc. of Santa Clara, Calif., the assignee of the present application.
The vessel passages preferably have a cumulative surface area that is at least two times greater than, and more preferably, at least ten times greater than an internal surface area of an identical size vessel without the passages. The vessel preferably comprises at least five passages, and more preferably, at least 10 passages connecting the vessel inlet and outlet.
In one aspect, the vessel is generally cylindrical in shape. The vessel further preferably comprises a thermally conductive material. In one aspect, the vessel comprises stainless steel and, in another aspect, the vessel comprises aluminum. In addition, other thermally conductive materials, such as other metals or metal alloys, may be used.
The liquid vaporizer system further preferably comprises a heat source in communication with the vessel. In one aspect, the vessel heat sources comprises a blanket heater wrapped at least part way around the vessel. In this manner, an outer surface of the vessel can be heated to a desired temperature by the vessel heat source. Use of a thermally conductive material for the vessel facilitates the transmission of heat throughout the vessel structure, and to liquid and/or gas passing through the vessel to assist with vaporization.
In another aspect, the vaporizer system further comprises a gas passageway operably attached to the vessel outlet and adapted to be attached to a reaction chamber. In this manner, gases exiting the vessel outlet may be transported to a desired reaction chamber for CVD or other processes. The gas passageway is preferably an insulated, heated passageway to help maintain gases exiting the vessel outlet in a gaseous state.
In another aspect, the liquid vaporizer system further includes a preheater operably connected to at least one of the vaporizer inlets. Such a preheater is preferably used for preheating a carrier gas before the carrier gas enters the vaporizer unit. In this manner, the heated carrier gas facilitates the vaporization of a desired liquid, such as liquid TDMAT.
The present invention further provides a method for vaporizing liquid/gas mixtures. The method includes the step of flowing a liquid and a carrier gas into the vaporizer unit wherein the liquid is at least partially vaporized to create a liquid/gas mixture. The liquid/gas mixture is passed through a heated vessel wherein the liquid/gas mixture is further vaporized into a product gas.
In one aspect of the method, the liquid/gas mixture is passed through a plurality of generally parallel passages contained within the vessel. The passages preferably have a cumulative surface area that is at least two times greater than an internal surface area of an identical size vessel without the passages. The liquid preferably has a vapor pressure that is less than about 82 Torr at 100 degrees Celsius. In one aspect, the liquid comprises TDMAT, however, other liquids may be used within the scope of the invention. In another aspect, the carrier gas comprises helium, however, other inert gases, such as argon, nitrogen, or a combination of inert gases, may be used. In still another aspect, the liquid/gas mixture comprises at least some liquid TDMAT. The product gas preferably co
Chen Fufa
Huston Joel M.
Applied Materials Inc.
Bushey C. Scott
Townsend and Townsend and Crew
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