Apparatus and method for vapor generation and film deposition

The process of creating a vapor from a liquid can be accomplished by heating the liquid to a sufficiently high temperature to cause the liquid to undergo a phase change and become a vapor. To generate vapor at a sufficiently high rate, it is necessary to supply an adequate amount of heating energy to the liquid in a relatively short time. This can be accomplished by increasing the operating temperature of the vapor generating apparatus or providing a larger heat transfer surface so that heat can be conducted more easily into the liquid.

In semiconductor applications, a wide variety of precursor chemicals are available in liquid form for vapor generation and for subsequent thin film deposition on a substrate by a vapor phase process. Processes such as chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVDP), metal-organic CVD (MOCVD), atmosphere pressure chemical vapor deposition (APCVD) and atomic layer deposition (ALD) are well known to those skilled in the art of semiconductor device fabrication. Some precursor chemicals such as metal-organic compounds can decompose at high temperatures to form undesirable by-products to cause process or equipment contamination. For such applications, the heating temperature must be kept low to avoid thermal decomposition and by-product formation. Increasing the heat transfer surface area will generally cause the overall physical size of the apparatus to increase, thus making the device less responsive to changing vapor demands in the process. The response speed of the apparatus will thus decrease. As a result, the traditional approach to increasing vaporization rate is not suitable for all applications.

The present disclosure is directed to a method of vapor generation that allows for a more compact vaporizer design, while reducing the maximum temperature to which the liquid and vapor are exposed to. The method includes flowing a mixture of gas and liquid droplets for vaporization through at least one heat exchanger having a plurality of surfaces for heat transfer to the gas, the increased surface area in the heat exchanger directing the gas and liquid mixture through a tortious flow path to further increase heat transfer and vaporization. The method may further include directing the mixture to a second heat exchanger to further vaporize any remaining liquid droplets in the gas. One or both heat exchangers may be configured with a tortious flow path comprising a plurality of tubular flow passageways.

Another aspect of the present disclosure relates to an apparatus for vaporization of the gas and liquid droplet mixture. The apparatus may be smaller and more compact in size, but able to maintain a high capacity for vaporization of liquid droplets in a gas. An increased heat transfer surface area in the apparatus allows for increased vaporization at a lower maximum temperature of the apparatus. The apparatus incorporates at least one heat exchanger having an increased surface area of heated flow paths for thermal transfer from a heating element to the gas comprising the liquid droplets. The apparatus is configured to vaporize the liquid droplets to form a vapor and comprises at least a first and preferably a second heat exchanger, the first heat exchanger in fluid communication with the second heat exchanger. The first heat exchanger is a primary heat exchanger comprising a housing having an inlet and an outlet allowing a gas carrying suspended liquid droplets to enter and flow through the first heat exchanger. This gas and liquid droplet mixture is flown through the first heat exchanger and the liquid droplets may be vaporized by a tortious flow path, in that the flow direction of the gas alternates in flow direction at least once in the first heat exchanger. The flow path may comprise a plurality of metal tubes within the first heat exchanger.

The primary heat exchanger may then be in fluid communication with a second heat exchanger, also referred to as a secondary heat exchanger. The secondary heat exchanger may have a construction substantially similar to the construction of the first heat exchanger and is configured to receive the gas and liquid mixture having at least some liquid droplets that were not vaporized after the gas and liquid mixture flows through the primary heat exchanger, and to further vaporize the gas and liquid mixture. One or both of the heat exchangers may comprise tubular flow passageways configured to provide a tortious flow path for vaporization.

Unless otherwise specified, the following terms as used herein have the meanings provided below:

The terms “preferred” and “preferably” refer to embodiments of the invention that may afford certain benefits, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the present disclosure.

The terms “about” and “substantially” are used herein with respect to measurable values and ranges due to expected variations known to those skilled in the art (e.g., limitations and variabilities in measurements).

FIG. 1A is a vertical sectional view of a vapor generating apparatus.

FIG. 1B is a horizontal sectional view along the line B-B of the vapor generating apparatus of the embodiment illustrated in FIG. 1A .

FIG. 2 is an enlarged view of the structure according to the embodiment illustrated in FIG. 1A .

FIG. 3A is a sectional view of an embodiment of the vapor generation apparatus.

FIG. 3B is a sectional view of an embodiment of the vapor generation apparatus along the line C-C in FIG. 3A .

FIG. 3C is a sectional view of an embodiment of the vapor generation apparatus along the line D-D in FIG. 3A .

FIG. 4 is a cross-sectional view of an embodiment of a vapor generating apparatus.

The present disclosure is directed to a vapor generating apparatus. A vertical sectional view of the vapor generating apparatus is illustrated in FIG. 1A , and FIG. 1B is a horizontal sectional view of the same apparatus along line B-B of FIG. 1A . Like reference characters will be used for like elements throughout the figures. FIG. 3B is a sectional view of an embodiment of the vapor generation apparatus along the line C-C n FIG. 3A .

Referring to FIGS. 1A-1B , the vapor generating apparatus is generally illustrated at 100 . The apparatus 100 includes a metal housing 110 , and an electric heater 120 surrounding the metal housing 110 and in good thermal contact with the metal housing 110 . Located above the vapor generating apparatus is an atomizer 140 . Liquid to be vaporized is introduced into the liquid inlet 120 of the atomizer 140 along with a carrier gas, which flows into a gas inlet 150 of the atomizer 140 , to form a droplet aerosol comprised of small liquid droplets suspended in the carrier gas. The droplet aerosol then flows out of the atomizer 140 through an outlet 160 and into a space 170 in the vapor generating apparatus 100 for heating and vaporization.

Under normal operating conditions, the atomizer 140 is located in a cleanroom. Both the precursor liquid and the carrier gas flowing into the atomizer 140 , as well as the droplet aerosol flowing out of the atomizer 140 , are both held at substantially the same temperature as the ambient air temperature (generally “room temperature”). The droplet aerosol then flows down a multitude of tubular gas flow passageways. One of the gas flow passage ways is illustrated by circular hole 180 in FIG. 1B . As the aerosol flows down the tubular gas flow passage ways, heat is transferred from heated metal surfaces by convection into the droplet aerosol, causing the suspended droplets in the aerosol to vaporize and form a vapor. The resulting gas/vapor mixture then flows out of the vaporization apparatus through the downstream flow passageways for additional heating and vaporization. The gas flow passageways shown as round holes 180 in FIG. 1B are considered as the first, primary heating stage for droplet vaporization. Any un-vaporized droplets can then be vaporized in a second heating stage described further below.

At high liquid flow rates, droplet vaporization in gas flow passage ways 180 may be incomplete. The droplet aerosol then enters into space 200 and into a metal structure 220 for further heating and vaporization. The metal structure 220 thus becomes a second vaporization stage for the un-vaporized liquid droplets in this two stage heating and vaporization process.

Illustrated at FIG. 2 is an enlarged vertical sectional view of the metal structure 220 . The metal structure may be generally cylindrical in shape. A base flange 270 is in good thermal contact with a vertical cylindrical wall 230 which is attached to an inner vertical cylindrical wall 250 and in good thermal contact with the cylindrical wall 250 . A cup shaped cylinder wall 240 is also attached to the vertical cylindrical wall 230 by contact (not shown in this vertical sectional view). All elements of the metal structure 220 , including the vertical walls 230 , 240 , and 250 and horizontal floor section 295 are in good thermal contact with each other allowing heat to flow easily by conduction from the outer wall 230 into inner walls 240 and 250 . The walls 230 , 240 and 250 may be cylindrical or tubular in nature and may be referred to as tubes or cylinders throughout this disclosure. As the gas flow enters metal structure 220 through an inlet opening 260 , as indicated by arrow 215 , the gas would first flow in a generally downward direction through an open space 252 in the tube 250 as indicated by arrow 225 then upwardly through the annular space between tubes 240 and 250 as indicated by arrow 235 . The gas then flows in a downward direction between tubes 230 and 240 as indicated by arrow 245 before exiting the metal structure 220 through outlet 250 as indicated by arrow 255 . The gas flow between vertical cylinders 230 , 240 , and 250 creates a tortuous flow path which greatly increases the surface area of contact between the heated metal tubes and the gas flowing along the walls of the tubes. As the gas flows through the metal structure 220 , heat is transferred from the metal surfaces to the gas which aids in the vaporization of any suspended droplets remaining in the gas.

The vaporization apparatus illustrated in FIG. 1A and FIG. 1B may be used in a semiconductor device lab for fabricating integrated circuit device chips. For such applications, a preferred material of construction is stainless steel. Stainless steel is generally used because of its resistance to corrosion and ability to provide a contaminant free surface as preferred for the application. Stainless steel is thermally conductive, however, compared to other metals, stainless steel is a relatively poor thermal conductor. Table 1 shows the thermal conductivity of stainless steel in comparison to other metals. The flow of heat from the electric heater 120 to the tortuous flow passage will be slower when less thermally conductive materials are used, resulting in an increased response time of the vaporization apparatus.

To improve or reduce the response time of the vaporization apparatus, a second electric heater 232 is provided. The second heater 232 may be located near the center of the vaporization apparatus 100 . The flow of heat from the second electric heater 232 to all parts of the vaporization apparatus 100 located near the center of the vaporization apparatus 100 will be improved, thus reducing overall response time of the apparatus.

Illustrated in FIG. 3A is a vertical sectional view of an additional embodiment 300 of the metal heat exchanger for heating and vaporizing the droplet aerosol. The heat exchanger is heated by an electric heater (not shown) similar to electric heater 120 illustrated in FIG. 1A . The droplet aerosol enters the heat exchanger through inlet hole 310 into empty space 320 in the direction of downward arrow 315 . The droplet aerosol flow then undergoes a change in flow direction and flows upward as depicted by group of arrows 325 . This droplet aerosol then flows into tubular flow passageways, one of which is identified at 330 in FIG. 3B , along the direction of arrows 345 . The droplet aerosol then flows through the multitude of tubular flow passageways for heating the gas and vaporizing the droplets contained therein.

At high gas and liquid flow rates, the gas flowing out of flow passageways 330 of the primary heat exchanger may still contain un-vaporized droplets suspended in the gas. This droplet aerosol then flows into space 340 and subsequently through secondary heat exchanger 350 . The aerosol then flows through gas flow passageways 360 in the secondary heat exchanger in order to vaporize the remaining un-vaporized droplets suspended in the gas. The gas and vapor mixture then flows out of the secondary heat exchanger through exit 370 .

As illustrated in FIG. 4 , the concepts of vapor generation described above with respect to FIGS. 1 and 3 have been combined. The embodiment illustrated in FIG. 4 further increases the vaporization capacity of the apparatus. To link the vapor generation apparatus and the heat exchanger, an orifice 400 is provided at or near a center well 402 . The orifice 400 for example is provided at the bottom of the center well 402 and aids in balancing the load of two sections of the heat exchanger. Thus, the orifice connects a heat exchanger to a multitude of tubular passageways for increasing the flow path and thus the vaporization capacity of the apparatus.

As illustrated in FIG. 4 , a vapor generating apparatus 460 is a housing comprising a vapor generation apparatus 420 (similarly described and illustrated in FIGS. 1A and 1B ) that is fluidly connected at the orifice 400 to heat exchanger 410 , such as a metal heat exchanger, for heating and vaporizing the droplet aerosol (similarly described and illustrated in FIGS. 3A, 3B , and 3 C). The droplet aerosol enters the heat exchanger 410 through an opening and into an empty space in the direction of downward arrow 430 . The droplet aerosol flow then undergoes a change in flow direction and flows upward as depicted by arrows 432 . This droplet aerosol then flows into tubular flow passageways, along the direction of arrows 434 . The droplet aerosol then flows through orifice 400 in the direction of downward arrow 440 and into the vapor generation apparatus including a multitude of tubular flow passageways for heating the gas and vaporizing the droplets contained therein. The droplet aerosol flow then undergoes a change in flow direction and flows upward as depicted by arrows 442 . This droplet aerosol then flows into tubular flow passageways, along the direction of arrows 444 and into the multitude of tubular flow passageways before exiting in the direction of arrow 450 via outlet 452 .

Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the disclosure.