Abstract:
Systems and methods are provided for delivering solid precursors. In certain embodiments of the present application, a flow monitor is used to measure and regulate the flow of vaporized solid precursor material from a vaporization chamber to a deposition chamber. The flow monitor chokes the supply of vapor into the deposition chamber to regulate vapor flow. To avoid condensation of the solid precursor material in the delivery lines or flow monitor, a controller is placed in a feed back loop to monitor the flow rate and make adjustments to the amount of vapor available at the inlet of the flow monitor. Additional embodiments are disclosed and claimed.

Description:
The present application, U.S. Pat. application Ser. No. 11/026,721 is a continuation of U.S. Pat. application Ser. No. 10/788,146 now U.S. Pat. No. 6,839,505. 
     The present application also finds itself in the following family of related applications claiming priority to U.S. Pat. application Ser. No. 09/976,176, now U.S. Pat. No. 6,701,066; U.S. Pat. application Ser. No. 09/788,146, now U.S. Pat. No. 6,839,505; U.S. Pat. application Ser. No. 10/787,692; and U.S. Pat. application Ser. No. 11/026,721. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates in general to vapor delivery systems for deposition processes, and in particular to systems and methods for reliably delivering solid precursors to a deposition chamber. 
     Chemical vapor deposition (CVD) is a common process used in the manufacturing of films, coatings, and semiconductor devices. In a CVD process, a layer is formed on a substrate such as a semiconductor wafer by the reaction of vapor phase chemicals on or near the surface of the substrate. CVD processing is highly desirable in many applications due to it&#39;s relatively fast processing times and ability to form highly conformal layers on irregular shaped surfaces including deep contact openings. 
     CVD processes typically deliver one or more gaseous reactants to the surface of substrates positioned within a deposition chamber under temperature and pressure conditions favorable to the desired chemical reactions. As such, the types of layers that can be formed on a substrate using CVD techniques is limited by the types of reactants or precursors that can be delivered to the surface of the substrate. 
     Liquid precursors are commonly used in CVD processes due to the ease of their delivery to the deposition chamber. In typical liquid precursor systems, the liquid precursor is placed in a bubbler and heated sufficiently to transform the precursor to the vapor phase. A carrier gas typically either travels through the liquid precursor or passes over the bubbler at a controlled rate thus saturating the carrier gas with the precursor. The carrier gas then carries the liquid precursor to the surface of the substrate. Liquid precursors are commonly employed in CVD processes because the amount of liquid precursor can be precisely and consistently controlled. 
     The techniques developed for the delivery of liquid precursors cannot be used to reliably deliver solid precursors however. It is difficult to vaporize a solid precursor at a controlled rate such that reproducible flows are achieved. As a solid precursor sublimates, the shape and morphology of the remaining solid precursor changes. The changing volume of the solid precursor results in a continuously changing rate of vaporization. The changing rate of vaporization is notable particularly in thermally sensitive compounds. Additionally, an oversupply of vaporized solid precursor can result in condensation of the vapor back into a solid thus clogging vapor delivery lines and other monitoring equipment. Further, the use of a carrier gas is substantially ineffective as a means to implement rapid changes to the flow of the solid precursors. 
     Despite the difficulties in delivering solid precursors in CVD processes, there are many desirable precursor materials including for example, organometallic precursors, that are readily available in solid form. Further, many desirable precursor materials including organic and inorganic precursor materials may not be readily available in gas or liquid form. Also, solid precursors are particularly useful in the deposition of metal-based films, such as metal nitrides and metal silicides. 
     Therefore, there is a need in the art for a vapor delivery system for delivering solid precursors in a CVD process at a controllable rate. 
     SUMMARY OF THE INVENTION 
     This need is met by the present invention wherein systems and methods are provided for delivering solid precursors in deposition processes. A flow monitor is used to measure the flow of vaporized solid precursor material. The flow monitor is capable of measuring vapor flow that is maintained at a high temperature and low inlet and outlet pressure to avoid condensation of the precursor. The vapor flow measured by the flow monitor is fed back to a controller arranged to adjust the supply of vapor at the inlet of the flow monitor. 
     In accordance with one embodiment of the present invention, a solid precursor material is sublimated in a vaporization chamber by heating the solid precursor material with a fast response heater. As the vaporized solid precursor material is fed from the vaporization chamber into a deposition chamber, a flow monitor measures the vapor flow. The vapor flow measurements are input into a controller that communicates with the fast response heater to effect rapid changes to the temperature applied to the solid precursor material. As such, the temperature changes affect the rate at which the solid precursor sublimates, and thus the vapor flow is controlled. 
     In accordance with another embodiment of the present invention, a solid precursor material is sublimated in a vaporization chamber and fed into a deposition chamber. As the vaporized solid precursor material is fed into the deposition chamber, a flow monitor measures the vapor flow. The vapor flow measurements are input into a controller that communicates with a valve positioned upstream of the flow monitor to adjust the amount of excess vapor siphoned by the valve, and thus the vapor flow is controlled. 
     In accordance with another embodiment of the present invention, a solid precursor material is sublimated in a vaporization chamber by heating the solid precursor material with a fast response heater. As the vaporized solid precursor material is fed from the vaporization chamber into a deposition chamber, a flow monitor measures the vapor flow. The vapor flow measurements are input into a controller that communicates with the fast response heater to effect rapid changes to the temperature applied to the solid precursor material and/or the controller communicates with a valve positioned upstream of the flow monitor to adjust the amount of excess vapor siphoned by the valve, and thus the vapor flow is controlled. 
     Accordingly, it is an object of the present invention to provide systems and methods of delivering a solid precursor to a deposition process. 
     It is an object of the present invention to provide systems and methods to reliably measure the vapor flow of a solid precursor. 
     It is an object of the present invention to provide systems and methods to reliably and rapidly change the flow of vapor supplied to a deposition process. 
     Other objects of the present invention will be apparent in light of the description of the invention embodied herein. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The following detailed description of the preferred embodiments of the present invention can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals, and in which: 
         FIG. 1  is a schematic illustration of a vapor delivery system for a deposition process according to one embodiment of the present invention; 
         FIG. 2  is a flow chart illustrating a simplified controller scheme; 
         FIG. 3  is a schematic illustration of the vapor delivery system of  FIG. 1 , further illustrating multiple controller inputs and the use of a pressure regulator; 
         FIG. 4  is a flow chart illustrating a simplified controller scheme incorporating a check to determine whether vapor is within a pressure guard band; 
         FIG. 5  is a schematic illustration of the vapor delivery system of  FIG. 1 , further illustrating an external pressure sensor positioned along the delivery line upstream of a flow monitor; 
         FIG. 6  is a schematic illustration of a vapor delivery system for deposition processing according to another embodiment of the present invention; 
         FIG. 7  is a schematic illustration of the vapor delivery system of  FIG. 4 , further illustrating the use of a pressure regulator; and 
         FIG. 8  is a schematic illustration of a vapor delivery system for deposition processing according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, specific preferred embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the spirit and scope of the present invention. 
     Referring to  FIG. 1 , a vapor delivery system  100  for the controlled delivery of solid precursors is illustrated. A vaporization chamber  102  includes a housing  104  and a first surface  106  that is coupled to a heating device  108 . The heating device  108  regulates the temperature of the first surface  106  and includes a variable temperature control  110  to adjust the temperature that the heating device  108  supplies to the first surface  106 . The temperature control  110  is arranged to vary the temperature of the heating device  108  over a range of temperatures as more fully explained herein. 
     During deposition processing, a solid precursor material  112  is positioned on the first surface  106  of the vaporization chamber  102 , and the heating device  108  heats the first surface  106  to a temperature sufficient to transform the solid precursor material  112  to a vapor  114 . As such, at least a portion of the temperatures within the range of temperatures controllable by the temperature control  110  are sufficient to sublimate or otherwise transform the solid precursor material  112  to a vapor  114 . 
     The heating device  108  does not need to be in direct contact with the first surface  106 . Rather, it will be understood that any coupling can be used to transfer the energy generated by the heating device  108  to heat the first surface  106 . The exact relationship between the heating device  108  and the first surface  106  will depend upon such factors including the construction of the vaporization chamber  102 , the type of heating device  108  used, and the intended solid precursor material  112 . For example, the heating device  108  may comprise a fast response heater such as a thermoelectric heater that is based upon the thermoelectric (Peltier) effect. The temperature control  110  can be implemented as any device that adjusts the temperature output by the heating device  108 . For example, the temperature control  110  may comprise an analog switch, circuit, a PID temperature controller or other digital circuit. 
     As a solid precursor material  112  sublimates, the shape and morphology of the remaining solid precursor material  112  changes. The changing volume of the solid precursor results in a continuously changing rate of vaporization. As such, the heating device  108  is preferably capable of regulating the temperature of the first surface  106  over a wide range of temperatures, room temperature to 400 degrees Celsius for example. Further, the heating device  108  should be capable of rapid temperature change. For example, a change of 20-30 degrees within milliseconds is preferable. The present invention is in no way limited by the rate in which the heating device  108  can change temperatures, however, as explained more fully herein, results of controlling vapor flow may vary depending upon the ability of the heating device  108  to change temperature. 
     The vapor  114  travels out the vaporization chamber  102  and into a delivery line  116 . The delivery line  116  comprises any tubing or conduit suitable for routing the vapor  114 . A flow monitor  118  is positioned along the delivery line  116  in such a manner as to be able to measure the vapor flow therethrough. As illustrated, the flow monitor  118  is positioned inline with the delivery line  116  such that a first delivery line section  120  routes the vapor  114  from the vaporization chamber  102  to the flow monitor  118 , and a second delivery line section  122  routes the vapor  114  from the flow monitor  118  to a deposition chamber  124 . 
     The vapor  114  flows through the deposition chamber  124  and onto one or more substrates, wafers, or other surfaces  126 . Residual vapor is drawn from the deposition chamber  124  through the exhaust port  128  by the pump  130 . The deposition chamber  124  is also sometimes referred to as a process chamber, reactor chamber, or deposition reactor. It will be appreciated that the vapor delivery system  100  of the present invention can be configured to supply vaporized solid precursors to any deposition chamber  124  for material deposition performed using established CVD or any other deposition processes as are known in the art. 
     The flow monitor  118  comprises a device capable of accurately measuring the vapor flow therethrough. The flow monitor  118  must be capable of generating accurate flow measurements at both high temperatures and low inlet and outlet pressures with minimal and preferably no restriction to the vapor flow. The high temperatures and low pressures are required to maintain the solid precursor material  112  in the vapor phase. As illustrated, the flow monitor  118  comprises an inlet  132 , an outlet  134 , a flow sensor  136 , and associated electronics  140 . The flow monitor  118  may also optionally include therein, a flow restrictor  138 , a pressure sensor  142 , a temperature sensor  144 , or both. The electronics  140  provides the ability to output the measured flow, and optional temperature and pressure measurements. The electronics  140  may also perform calculations or processes required by the flow monitor  118 . 
     The flow monitor  118  may be implemented for example, as either an analog or digital mass flow controller. However, a digital mass flow controller based upon either pulsed gate flow or sonic nozzle technologies are preferred due to the accuracy and control afforded by such devices. It will be appreciated that the flow monitor  118  may require additional hardware depending upon its implementation. For example, a thermal mass flow controller gas stick may require additional components such as pressure transducers, filters, bypass valves, and in some cases, pressure regulators (not shown). Further, some mass flow controllers determine vapor flow based upon a measured pressure. As such, one pressure sensor and the appropriate electronics can output both the vapor flow and pressure. Accordingly, one physical sensor or device can embody one or more of the sensors schematically illustrated herein. 
     The flow monitor  118  is capable of controlling the flow rate into the deposition chamber  124 . By controlling the flow rate into the deposition chamber  124 , the deposition rate of the solid precursor material  112  onto the surface of the substrate  126  positioned within the deposition chamber  124  is controlled. The flow monitor  118  controls the flow rate of the vapor  114  into the deposition chamber  124  by choking the flow of vapor in the first delivery line section  120  to let the desired amount of flow through. This is accomplished for example, by closing the flow restrictor  138  within the flow monitor  118 . However, as the flow is choked off, the pressure upstream of the flow restrictor  138  increases. Should the pressure rise too much, condensation will occur as the vaporized solid precursor material  112  transforms back into the solid phase. If the solid precursor material  112  transforms from the vapor phase back to the solid phase, the flow monitor  118  and first delivery line section  120  can clog, jam, or otherwise suffer performance degradation. 
     To maintain the solid precursor material  112  in the vapor phase, a controller  146  is used to adjust the temperature of the heating device  108  to account for detected or expected changes in pressure. The controller  146  has a first input  148  coupled to the flow monitor  118 . The first input  148  receives as an input, the vapor flow measured by the flow monitor  118 . The controller  146  further includes a first output  150  coupled to the temperature control  110  of the heating device  108 . The first output  150  is arranged to adjust the temperature generated by the heating device  108  in such a manner to control the flow of vapor  114  through the vapor delivery system  100 . By reducing the flow of vapor  114 , the pressure in the first delivery line section  120  is also reduced. 
     It will be appreciated that the controller  146  can be implemented in a number of ways. For example, the controller  146  may be implemented as dedicated hardware, as a microprocessor based circuit, as a dedicated turnkey computer system, or a general-purpose computer running the appropriate software to implement the present invention. 
     Referring now to  FIG. 2 , a controller scheme  200  is illustrated. The measured vapor flow is read in block  202 . The measured vapor flow is then compared to a desired vapor flow in block  204 . In decision block  206 , the measured vapor flow is tested to determine whether the measured vapor flow is at too low a rate for the given deposition process. If the measured flow rate is too low, the flow rate is increased in block  208 , and a new measurement is taken by feeding back control to block  202 . If the measured flow is not too low, the measured flow is tested to determine whether it is too high in block  210 . If the measured flow is too high, the flow rate is reduced or choked in block  212  and a new measurement is taken by feeding back control to block  202 . Otherwise, the flow rate is acceptable, and control is fed back to block  202  to take a new measurement. It will be understood that this flow chart is only representative of the possible implementations of the invention more fully described herein. Further, the desired flow may actually be represented as a range of acceptable flows. 
     Referring back to  FIG. 1  with reference to  FIG. 2 , for a given solid precursor material  112 , the controller  146  (such as a general purpose computer) has preprogrammed therein, a desired flow rate or range of acceptable flow rates to achieve a desired deposition layer. When the deposition process begins, the controller  146  reads the measured flow and compares the measured flow to the desired flow rate. If the measured vapor flow is too low, the controller  146  adjusts the temperature of the first surface  106  of the vaporization chamber  102  by sending a control signal to the temperature control  110  of the heating device  108  to affect the necessary adjustment, for example, to increase the temperature of the first surface  106 . If the measured flow exceeds the desired flow, the output of the controller  146  signals the temperature control  110  to reduce the temperature applied to the first surface  106  of the vaporization chamber  102  thus lowering the quantity of solid precursor material  112  that vaporizes and thus reduces the vapor flow. It will be appreciated that the amount of a particular adjustment will depend upon the type of solid precursor, the response time of the heating device  108  used, the reaction time of the flow monitor  118  to determine the vapor flow rate, and other factors. Further, the desired flow rate may have different values during various portions of the deposition process. The system continues to monitor the vapor flow through the flow monitor  118  and make adjustments as necessary until the deposition process is complete. 
     The vapor delivery system  100  optionally includes pressure regulation to assist in maintaining the solid precursor material  112  in the vapor phase. There are a number of ways to accomplish pressure regulation. According to one embodiment of the present invention, an inert gas is fed into the delivery line  116  as illustrated in  FIG. 3 . The inert gas  152  is provided by a gas source  154  and is fed into the vaporization chamber  102  through a gas line  156 . A flow regulator  158  is provided to control the amount of inert gas  152  that enters the vaporization chamber  102 . The controller  146  optionally comprises a second output  160  that couples to the flow regulator to adjust the amount of inert gas  152  that is introduced during deposition processing. 
     It will be observed that any number of optional flow monitors  162  and valves  164  may be positioned inline with the gas line  156  before entering the inlet of the vaporization chamber  102 . Further, while schematically, the second output  160  of the controller  146  is illustrated as being coupled to the flow regulator  158 , it will be understood that other control schemes may be implemented. For example, if an optional flow monitor  162 , such as a digitally controlled mass flow controller is positioned inline with the gas line, the second output  160  of the controller  146  may couple to the mass flow controller to regulate the amount of inert gas  152  that enters the vaporization chamber  102  and delivery line  116 . 
     Additionally, depending upon the selection of solid precursor material  112 , an optional carrier gas  166  may be used to assist the vapor  114  in transmitting from the vaporization chamber  102  to the deposition chamber  124 . It will be appreciated that the carrier gas  166  is supplied by the carrier gas source  167  and may utilize a second gas line  168 , flow regulator  170 , flow monitor  172 , and other components as is known in the art. The carrier gas  166  may be fed into the vaporization chamber  102  using a second inlet (not shown), or alternatively, the carrier gas  166  may tie into the inert gas line  156  downstream from the inert gas flow regulator  158 . 
     If the flow monitor  118  includes the optional pressure sensor  142  and is capable of generating an output signal representing the measured pressure, this signal may be fed into the controller  146  as a second input  174 . Likewise, if the flow monitor  118  includes the optional temperature sensor  144  and is capable of generating an output signal representing the measured temperature, this signal may be fed into the controller  146  as a third input  176 . 
     The addition of measured pressure and temperature data allows for more sophisticated processing by the controller  146 . For example, the controller  146  contains predetermined data that provides the temperature and pressure conditions required to maintain a particular solid precursor in the vapor phase. This information may be stored for example, in the form of a formula or lookup table. Based upon given temperature conditions, a guard band, or range of acceptable pressures is determined. The guard band will vary depending upon the type of solid precursor being sublimated for deposition processing. The controller  146  can now monitor both the flow rate to ensure proper deposition processing, and make sure the pressure is maintained within the guard band to avoid condensation from forming in the flow monitor  118  and delivery line  116 . 
     Referring now to  FIG. 4 , a controller scheme  300  including pressure guard band testing is illustrated. The measured vapor flow is read in block  302 . The measured vapor flow is then compared to a desired vapor flow in block  304 . In decision block  306 , the measured vapor flow is tested to determine whether the measured vapor flow is at too low a rate for the given deposition process. If the measured flow rate is too low, the flow rate is increased in block  308 , and a new measurement is taken by feeding back control to block  302 . If the measured flow is not too low, the measured flow is tested to determine whether it is too high in block  310 . If the measured flow is not too high, then control is fed back to block  302  and a new flow measurement is taken. If the measured flow is too high, the flow rate is reduced or choked in block  312 . The measured pressure is checked against the pressure guard band in block  314  if the measured pressure is within the guard band, a new flow measurement is taken by feeding back control to block  302 . If the measured pressure is outside the guard band, the pressure is reduced in block  316 . It will be understood that this flow chart is only representative of the possible implementations of the invention more fully described herein. Further, the desired flow may actually be represented as a range of acceptable flows. 
     Referring back to  FIG. 3 , it will be appreciated that the temperature input can also come from the heating device  108 . For example, the heating device  108  may have a temperature output that couples to the third input  176  of the controller  146 . Under such an arrangement, the temperature sensor  144  in the flow monitor  118  is not required. It will be appreciated that numerous factors affect the decision to use a separate temperature sensor or whether the heating device  108  can generate sufficient temperature measurements including for example, the length of the first delivery line section  120  and the type of outputs available on the heating device  108 . 
     The optional temperature and pressure sensors  142 ,  144  need not physically reside within the flow monitor  118 . Referring to  FIG. 5 , the flow monitor  118  does not include a built in pressure sensor. Rather, a pressure sensor  178  is provided in line with the delivery line  116 . It is preferable to locate the pressure sensor  178  proximate to, and upstream from the flow monitor  118 , however, the pressure sensor  178  may also be positioned downstream of the flow monitor  118 . Further, the pressure sensor  178  may be positioned in any desired position along the delivery line  116 . It will be appreciated that a temperature sensor may also be positioned along the delivery line  116  (not shown) in a similar fashion as that described for the pressure sensor  178 . 
     Referring to  FIG. 6 , a vapor delivery system according to another embodiment of the present invention is illustrated. As pointed out above, the flow monitor  118  controls the flow rate of the vapor  114  into the deposition chamber  124  through the second delivery line section  122  by choking the flow of vapor in the first delivery line section  120  to let the desired amount of flow through. However, as the vapor flow is choked off, pressure upstream of the flow monitor  118  increases. Whereas an embodiment of the present invention discussed above with reference to  FIGS. 1–5  offsets the increased pressure during choked off periods by adjusting the temperature of the heating device  108 , the embodiment illustrated in  FIG. 6  offsets the increased pressure by bleeding off excess vapor  114 . 
     The delivery line  116  further includes a third delivery line section  180  that couples to the first delivery line section  120  upstream of the flow monitor  118 . A valve  182  is positioned inline with the third delivery line section  180 , and a pump  184  is provided to draw vapor  114  in the direction of the third delivery line section  180 . The valve  182  can be any implemented with any number of valve arrangements, including a mass flow controller. For example, the valve  182  may comprise a pulsed gate flow or sonic nozzle mass flow controller  146 . Digital valves and pulsed gate flow devices are preferred over analog counterparts due to the fast response time and control typically afforded by such devices. 
     The controller  186  includes a first output  188  coupled to the valve  182 , and the logic in the controller  186  is configured to adjust the valve  182  to selectively bleed off vapor  114  in the first delivery line section  120  by siphoning excess vapor  114  through the third delivery line section  180 . That is, the measured vapor flow is compared to a predetermined vapor flow. If the measured vapor flow exceeds the desired vapor flow, any excess vapor is bled of by opening the valve  182  to draw a portion of the vapor  114  into the third delivery line section  180  and away from the flow monitor  118 . The controller  186  inputs and variations thereof are similar to those described more fully herein with reference to  FIGS. 1–5 . 
     The heating device  108  is schematically illustrated as having a variable temperature control  110  because the temperature applied to the first surface  106  may require adjustment when switching from one solid precursor material  112  to the next. However, in this embodiment, it is not required that the heating device  108  be a fast response heater. 
       FIG. 7  illustrates the embodiment as illustrated in  FIG. 6  with the addition of optional pressure regulation to assist in maintaining the solid precursor material  112  in the vapor phase. Similar to the pressure system discussed with reference to  FIG. 3 , the inert gas  152  is provided by the gas source  154  and is fed into the vaporization chamber  102  through the gas line  156 . A flow regulator  158  is provided to control the amount of inert gas  152  that enters the vaporization chamber  102 . The controller  186  optionally comprises a second output  190  that couples to the flow regulator  158  to adjust the amount of inert gas  152  that is introduced during deposition processing. Further, depending upon the selection of solid precursor material  112 , an optional carrier gas  166  may be used to assist the vapor  114  in transmitting from the vaporization chamber  102  to the deposition chamber  124 . The carrier gas  166  is provided by a carrier gas source  167 , and is fed into the vaporization chamber  102  using a second gas line  168 , flow regulator  170 , and other components separate from the inert gas source  154 .  FIG. 7  also illustrates the use first, second and third controller inputs  148 ,  174 , and  176  from the flow sensor  136 , pressure sensor  142 , and temperature sensor  144  respectively. As previously described herein, the pressure and temperature sensors  142 ,  144  are optional. 
       FIG. 8  illustrates another embodiment of the present invention. The vapor delivery system is similar to that described with reference to  FIGS. 6–7 , and further includes a third output  192  that feeds back control from the controller  186  to the temperature control  110  of the heating device  108 . This structure allows a high degree of flexibility in the implementation of the controller  186 . For example, according to one embodiment of the present invention, the controller  186  is configured to adjust the temperature of the first surface  106  when coarse adjustments are required to the vapor flow. The controller  186  is configured to regulate the valve  182  when fine adjustments are required. It will be appreciated that depending upon such factors as the ability of the pump  184  to create a vacuum and the length of the third delivery line section  180 , the opening and closing the valve  182  can result in faster response times than regulating the heating device  108 . 
     According to another embodiment of the present invention, the controller  186  is arranged to regulate the valve  182  and adjust the temperature applied to the first surface  106  by adjusting the temperature control  110  generally at the same time. Alternatively, the controller  186  adjusts vapor flow by adjusting the third output  192  to change the temperature of the heating device  108 , and thus affecting vapor flow, and adjusting the first and second outputs  188 ,  190  to adjust for measured pressure. 
     While illustrated having a pressure sensor  178  and a flow sensor  118  that includes a built in temperature sensor  144 , it will be appreciated that the inputs to the controller  186  can include any of the configurations discussed above with reference to  FIGS. 1–7 . 
     Although the invention described above with reference to  FIGS. 1–8  are illustrated with a single vaporization chamber  102  and a single solid precursor material  112 , it will be appreciated that any number of vaporization chambers  102  may feed into a single deposition chamber  124  using the techniques, methods, and system described herein. 
     Further, any number of additional features of conventional vapor delivery systems may be used with the present invention as is known in the art. For example, optional delivery line heaters may be used to maintain the solid precursor in the vapor phase. The use of delivery line heaters may be advantageous under conditions where excessive line length is required to deliver the solid precursor. 
     Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.