Method and apparatus for gas delivery

Methods and apparatus for gas delivery are disclosed herein. In some embodiments, a gas delivery system includes an ampoule for storing a precursor in solid or liquid form, a first conduit coupled to the ampoule and having a first end coupled to a first gas source to draw a vapor of the precursor from the ampoule into the first conduit, a second conduit coupled to the first conduit at a first junction located downstream of the ampoule and having a first end coupled to a second gas source and a second end coupled to a process chamber, and a heat source configured to heat the ampoule and at least a first portion of the first conduit from the ampoule to the second conduit and to heat only a second portion of the second conduit, wherein the second portion of the second conduit includes the first junction.

FIELD

Embodiments of the present invention generally relate to methods and apparatus for gas delivery, and more specifically to the delivery of a gas having a low vapor pressure.

BACKGROUND

The remote delivery of low vapor pressure precursors in solid or liquid form to a process chamber requires heating of an ampoule that holds the low vapor pressure precursor and a long gas line that carries the vaporized low vapor pressure precursor to a process chamber, for example, to expose a substrate to the precursor. However, the heating/isolating of the long gas line is apt to fail and is often difficult to maintain. Moreover, the inventors have observed that remote delivery of the precursor may also have a slow response believed to be due to the line volume and the limited flow rate of the precursor from the ampoule. The inventors have further observed that such heated delivery systems also require an upstream mass flow controller (MFC) to control the gas flow rate in order to avoid any condensation problems inside the MFC. However, positioning the MFC upstream of the ampoule makes the ampoule susceptible to downstream pressure fluctuation, which impacts the delivery accuracy of the precursor.

Thus, the inventors have provided herein improved methods and apparatus for gas delivery of low vapor pressure precursors.

SUMMARY

Methods and apparatus for gas delivery are disclosed herein. In some embodiments, a gas delivery system includes an ampoule for storing a precursor in solid or liquid form, a first conduit coupled to the ampoule and having a first end coupled to a first gas source to draw a vapor of the precursor from the ampoule into the first conduit, a second conduit coupled to the first conduit at a first junction located downstream of the ampoule and having a first end coupled to a second gas source and a second end coupled to a process chamber, and a heat source configured to heat the ampoule and at least a first portion of the first conduit from the ampoule to the second conduit and to heat only a second portion of the second conduit, wherein the second portion of the second conduit includes the first junction.

In some embodiments, a method of delivering a precursor to a process chamber includes vaporizing a precursor while flowing a first gas to form a concentrated precursor gas mixture in a first heated volume, mixing the concentrated precursor gas mixture with a second gas in a second heated volume to form a diluted precursor gas mixture, wherein the partial pressure of the precursor in the diluted precursor gas mixture is less than the vapor pressure of the precursor at about 25 degrees Celsius, and flowing the diluted precursor gas mixture to a process chamber via a non-heated third volume.

DETAILED DESCRIPTION

Methods and apparatus for gas delivery are disclosed herein. Methods and apparatus of the present invention advantageously provide vaporization of low vapor pressure precursors in solid or liquid form at high efficiency and delivery accuracy while reducing energy input costs and improving delivery rate. For example, embodiments of the inventive gas delivery system may require heating of only a portion of the conduits carrying the vaporized precursor. Further, some embodiments of the inventive gas delivery system advantageously allow for flow control devices, such as mass flow controllers or the like, to be disposed downstream of the vaporized precursor due to limited possibility of condensation of the precursor during delivery. Other and further embodiments and advantages of the inventive methods and apparatus are discussed below.

FIGS. 1A-Bdepict a gas delivery system100in accordance with at least some embodiments of the present invention. The gas delivery system100may include an ampoule102for storing a precursor in solid or liquid form. For example, the precursor may be any suitable low vapor pressure precursor used in processes, such as deposition processes or the like. Exemplarily precursors may include dichlorosilane (DCS), trichlorosilane (TCS), carbon tetrachloride (CCI4), or the like. A first conduit104may be coupled to the ampoule102. The first conduit102may include a first end106coupled to a first gas source108. The first gas source108is disposed upstream of the ampoule102as illustrated inFIG. 1A. The first conduit104may be used to draw a vapor of the precursor from the ampoule into the first conduit104.

For example, as illustrated inFIGS. 2A-B, various embodiments of the first conduit104are possible. For example, when using a liquid form of the precursor, the first conduit104may be coupled to the ampoule102such that the first conduit enters the volume of the ampoule102and has an end202disposed beneath the surface of the liquid precursor such that the first gas may bubble through the precursor to carry vapor and/or small droplets of the precursor within the gas stream. A second end204may be disposed above the liquid precursor to receive a concentrated precursor gas mixture of the first gas and precursor (end204) as illustrated inFIG. 2A. Alternatively, the first end202may be disposed above the surface of the liquid precursor.

Alternatively, in some embodiments, the first conduit104may be coupled to the ampoule102such that a sublimed precursor from a solid form of the precursor may be drawn through an opening in the ampoule102to enter the first conduit104, as illustrated inFIG. 2B. The sublimed precursor may mix with the first gas flowing through the first conduit104to form a concentrated precursor gas mixture from the first gas and the sublimed precursor.

Returning toFIG. 1A, the flow of the first gas may be controlled by a first flow controller110. The first flow controller may be coupled to the first conduit104between the first end106of the first conduit104and the ampoule102. The first flow controller110may be a mass flow controller or the like.

A second conduit112may be coupled to the first conduit104at a first junction114located downstream of the ampoule102. As used herein, the term “junction” may include the intersection of multiple flow paths or sections of conduit, such as by a T-shaped joint or section of conduit, a selective valve such as a valve which allows for the selection of either a first or second path, or the like. The second conduit112may have a first end116coupled to a second gas source118. The second conduit112may have a second end120coupled to a process chamber122. The second gas source118may provide a second gas to dilute the concentrated precursor gas mixture entering the second conduit112at the first junction114.

In some embodiments, heat may be required over portions of the gas delivery system100to vaporize the precursor and/or to maintain the precursor in a vaporized state. For example, a heating source124may be configured to heat the ampoule102and at least a first portion126of the first conduit104from the ampoule102to the first junction114at the second conduit112. The heating source124may be any suitable heating source, such as heating tape, forced air heated cabinet, heat exchanger, or the like. Further, and optionally, as illustrated inFIG. 1A, the heating source124may heat the entirety of the first conduit104up to the first flow controller110, or the entirety of the first conduit up to the first gas source108(not shown). In some embodiments, the first conduit104may be heated up to the first gas source108. In such embodiments, the flow controller should be configured for operation in a heated environment. In some embodiments, a contained heated environment160may be provided to facilitate efficient heating of the system. For example, in some embodiments, the contained heated environment may include an enclosure to contain or surround the heated components and portions of the conduit. Such embodiments may facilitate more uniform heating as well as efficiency. However, use of an enclosure may cause the system to take longer to stabilize. In some embodiments, the contained heated environment160may include a heat exchanger style heat bath having the portions of the system to be heated disposed therein. The high thermal mass and thermal arrest provided by the heat bath may help reduce the possibility of catastrophic overheating that could lead to decomposition of the precursor.

The heating source124may be configured to heat only a second portion128of the second conduit112, where the second portion128includes the first junction114. The second portion128may extend on both sides of the first junction114as illustrated inFIG. 1A, or may extend only downstream of the first junction114(not shown). The second portion128of the second conduit112may include the portion where the concentrated precursor gas mixture received from the first conduit104mixes with the second gas to form a diluted precursor gas mixture. As discussed above, heating of the concentrated precursor gas mixture may be required to prevent the precursor from condensing out of the concentrated precursor gas mixture. However, once the partial pressure of the precursor is below the vapor pressure of the precursor at room temperature, e.g., about 25 degrees Celsius, then the likelihood of condensation of the precursor may be limited. For example, by mixing the second gas with the concentrated precursor gas mixture, such a condition for the partial pressure of the precursor can be achieved in the newly formed diluted precursor gas mixture in the second portion128of the second conduit112. Accordingly, the partial pressure of the precursor in the diluted precursor gas mixture may be less than the vapor pressure of the precursor at room temperature. Thus, the remainder of the second conduit112, i.e., the portion of the second conduit112downstream of the second portion128, may require less heating or may require no heating because condensation of the precursor from the diluted precursor gas mixture may be less likely.

The second conduit112may include a second flow controller130coupled to the second conduit112. In some embodiments, for example as illustrated inFIG. 1A, the second flow controller130is disposed between the first end116of the second conduit112and the first junction114, or upstream of the first junction114. For example, in the embodiment illustrated inFIG. 1A, the second flow controller130provides the second gas at a desired flow rate to mix with the concentrated precursor gas mixture in the second portion128of the second conduit112.

Further, in some embodiments, such as shown inFIG. 1A, the second conduit112may include a pressure regulator132disposed in the second conduit112between the first junction114and the second end120of the second conduit112to regulate the pressure in the second conduit112between the pressure regulator132and the second flow controller130, e.g., upstream of the pressure regulator132. In some embodiments, the pressure in the second conduit112using the embodiments shown inFIG. 1Amay be about 200 Torr. For example, the pressure regulator132may be necessary to prevent pressure fluctuations in the second conduit112that could occur if the second conduit112were to be directly exposed to the pressure of the process chamber122. For example, the pressure in the process chamber122may change frequently due to various processes being performed that may introduce process gases in the process chamber122or require the pressure in the process chamber122to be changed. The presence of the pressure regulator132may stabilize the pressure in the second conduit112which, for example, may result in consistent and reproducible precursor loading in diluted precursor gas mixture that may be flowed to the process chamber122.

Alternatively, the second flow controller130and the pressure regulator132may be configured as illustrated inFIG. 1B. For example, as illustrated inFIG. 1B, the second flow controller130may be disposed between the first junction114and the second end of the second conduit120, or downstream of the first junction114. For example, in the embodiments illustrated inFIG. 1B, the second flow controller130may provide a desired flow rate of the diluted precursor gas mixture to the process chamber122. The downstream position of the second flow controller130as shown inFIG. 1Bmay be enabled by the methods and apparatus of the present invention. For example, flow controllers, such as mass flow controllers, are not typically used downstream of precursor gas mixtures because condensation of the precursor gas mixture may occur resulting in inaccuracy of the delivery of the gas mixture to the process chamber or damage to the flow controller. However, as discussed herein, the methods and apparatus of the present invention reduce or eliminate the possibility of condensation of the precursor in the diluted precursor gas mixture, thus enabling the downstream positioning of the flow controller without the attendant risk of condensation forming in the flow controller.

As illustrated inFIG. 1B, and also alternative toFIG. 1A, the pressure regulator may be disposed between the first end116of the second conduit112and the first junction114to regulate the pressure in the second conduit112between the regulator132and the second flow controller130. In some embodiments, the pressure in the second conduit112may be higher than in the embodiments ofFIG. 1A, for example, at least about 500 Torr. The pressure in the second conduit112may be higher in the embodiments ofFIG. 1Bto provide a sufficient upstream pressure to the second flow controller130for accurate operation. In some embodiments, sufficient upstream pressure in the second conduit112to operate the second flow controller may be at least about 500 Torr.

In some embodiments, the gas delivery system100may include a real-time monitoring device downstream of the second portion128of the second conduit112. The real-time monitoring device may be disposed in-line or along a sample line, for example, such as a third conduit134as discussed below. The real-time monitoring device may be enabled by the methods and apparatus of the present invention. For example, the low concentration of the precursor in the diluted precursor gas mixture and the absence of heating in the second conduit112outside of the second portion128may enable real-time monitoring devices in the gas delivery system100.

The third conduit134may be coupled to the second conduit between the first junction114and the pressure regulator132(as shown inFIG. 1A) or between the first junction114and the second flow controller130at a second junction136(as shown inFIG. 1B). The third conduit134may have a first end138coupled to the second junction136and a second end140coupled to a vent142. The vent142may be an exhaust line or the like, for example, coupled to an abatement system or the like.

The real-time monitoring device may be a concentration sensor144coupled to the third conduit134. The concentration sensor may be any suitable sensor for determining concentration, such as one of the Piezocon® line, available from Lorex Industries, Inc. of Poughkeepsie, N.Y. The concentration sensor144may determine the concentration of the precursor in the diluted precursor gas mixture flowing to the process chamber122via the second conduit112. A flow restrictor146may be disposed in the third conduit134between the concentration sensor144and the vent142to, for example, limit flow of the diluted precursor gas mixture to the third conduit134at the second junction136, such that a substantial portion of the diluted precursor gas mixture flows towards the process chamber122. Since the concentration after mixing is very low and the sampling line flow is limited, vapor wasted by sampling is limited. Also, since the concentration sensor144is off-line, any condensation problems that do occur will cause little or no problems. Also, any maintenance services performed on the concentration sensor144will have minimum impact on the main operation of the gas delivery system100.

The gas delivery system100may include a third junction148proximate the second end120of the second conduit112. The fourth conduit149has a first end coupled to the third junction148and a second end coupled to a vent150. In some embodiments, the vent142and the vent150may be the same exhaust line, or may be coupled to the same exhaust line. Similarly, the vent150may be coupled to an abatement system or the like. The third junction148may include a valve (not shown) for selecting between flow to the process chamber122and flow to the fourth conduit149(and vent150). For example, this type of selective flow may be used during processing in the process chamber122such that the precursor is continuously vaporized over the time period of processing in the process chamber122to limit variations, such as in concentration in the diluted precursor gas mixture or the like that may otherwise result from starting and stopping the flow of the first gas or the like.

A controller152may be coupled to the process chamber122and/or support systems, such as the gas delivery system100, directly (as shown inFIG. 1A) or, alternatively, via computers (or controllers) associated with the process chamber and/or the support systems. The controller152may be one of any form of general-purpose computer processor that can be used in an industrial setting for controlling various chambers and sub-processors. The memory, or computer-readable medium,154of the CPU156may be one or more of readily available memory such as random access memory (RAM), read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. The memory154may store routines to be performed by the process chamber122and/or various support systems, such as the gas delivery system100. Exemplary routines may include a method300for delivering the precursor to the process chamber122as described below. Support circuits158are coupled to the CPU156for supporting the processor in a conventional manner. These circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and the like.

FIG. 3depicts a flow chart for the method300of delivering a precursor to a process chamber, such as the process chamber122. The method300is described below with respect toFIGS. 1A-Band2A-B. The method300begins at302by vaporizing the precursor while flowing the first gas to form the concentrated precursor gas mixture in a first heating volume. The first heating volume may include the first conduit104and the ampoule102. The first gas, as discussed above, may be provided by the first gas source108. The first gas may include a carrier gas, such as an inert gas. In some embodiments, the first gas may be one or more of nitrogen (N2), hydrogen (H2), argon (Ar), helium (He), or the like. The flow of the first gas may be controlled by the first flow controller110. As discussed below, the flow of the first gas may be adjusted in response to sampling the concentration of the precursor in the diluted precursor gas mixture formed downstream of the concentrated precursor gas mixture formed in the first heating volume at302.

The precursor may be vaporized by alternative methods. For example, as discussed above, the precursor may be in liquid form. Accordingly, in some embodiments, such as illustrated inFIG. 2A, the first gas may be flowed into a portion (e.g., the ampoule102) of the first heated volume holding the precursor. The first gas may be bubbled into the liquid precursor to form the concentrated precursor gas mixture. Alternatively, as discussed above, the precursor may be in solid form. Accordingly, in some embodiments, such as illustrated inFIG. 2B, the solid precursor may be sublimed and enter the first conduit104where the sublimed precursor mixes with the flowing first gas to form the concentrated precursor gas mixture.

At304, the concentrated precursor gas mixture may be mixed with the second gas in a second heated volume (e.g., the second portion128) to form the diluted precursor gas mixture. As discussed above, the second gas may be provided by the second gas source118. The second gas may be the same as the first gas. In some embodiments, the second gas may be one or more of nitrogen (N2), hydrogen (H2), argon (Ar), helium (He), or the like. The second gas may be different from the first one. However, providing a different second gas introduces more complexity, making downstream concentration monitoring more difficult since it will be a mixture of three components rather than a mixture of two components.

The second gas may be flowed at a higher flow rate than the first gas. For example, the flow rate of the second gas may be about 5 or more times the flow rate of the first gas. The higher flow rate of the second gas may be enabled by the present invention. Typically, a single conduit is provided to an ampoule for delivering the precursor, thereby limiting the maximum flow rate of the carrier gas due to the risk of splashing or entraining particles in the gas stream. To the contrary, however, the gas delivery system100of the present invention provides a second gas along the second conduit112which does not flow through the ampoule102. Accordingly, events that may necessitate reducing a flow rate, such as splashing of the precursor in the ampoule102or the like, may be avoided in the gas delivery system100. Thus, the flow rate of the second gas in the second conduit112(and thus the total flow rate of the gas delivery system) may be higher than in conventional gas delivery systems. The higher flow rate of the second gas may advantageously improve response time in the gas delivery system by up to about 100 times over a conventional gas delivery system.

At306, the diluted precursor gas mixture may be flowed to the process chamber122via a non-heated third volume, e.g., the remaining portion of the second conduit112, downstream of the second portion128. As discussed above, the diluted precursor gas mixture formed in the second heated volume may have a partial pressure of the precursor that is less than the vapor pressure of the precursor at room temperature, e.g., about 25 degrees Celsius. Accordingly, the diluted precursor gas mixture may require no additional heating in the non-heated third volume because condensation of the precursor is less likely.

The pressure of the diluted precursor gas mixture may be regulated in the second heated volume and the non-heated third volume. For example, the pressure of the diluted precursor gas mixture may be regulated downstream of the second flow controller130used to controller the flow of the second gas from the second gas source118as illustrated inFIG. 1A. Alternatively, the pressure of the diluted precursor gas mixture may be regulated upstream of the second flow controller130, where the second flow controller may be used to control the flow of the diluted precursor gas mixture to the process chamber122and downstream of the second gas source118use to provide the second gas to the second volume as illustrated inFIG. 1B.

The diluted precursor gas mixture may be flowed to the process chamber122selectively. For example, the diluted precursor gas mixture may be selectively flowed to the process chamber122or to the vent150. For example, the flow to the process chamber122and the vent150may be alternated according to the process being performed in the process chamber122, such as a deposition process, a cyclical deposition process, or the like.

In some embodiments, the method300may include sampling a portion of the diluted precursor gas mixture from the third volume, for example, using the sample line (e.g., the third conduit134). Sampling of the portion of the diluted precursor gas mixture may occur at a first flow rate that is slower than a second flow rate of a second portion of the diluted precursor gas mixture that is flowing to the process chamber122. For example, the flow restrictor146may facilitate the disparity between the first and second flow rates to ensure that a substantial portion of the diluted precursor gas mixture flows to the process chamber122. A concentration of the precursor in the diluted precursor gas mixture may be determined, for example, using the concentration sensor144as discussed above.

If the determined concentration of the precursor in the diluted precursor gas mixture is not within a desired tolerance level, parameters of the gas delivery system that may control the concentration of the precursor may be adjusted. For example, at least one of heating temperature of the first or second heated volumes, flow rate of the first gas, flow rate of the second gas, or pressure in the second heated volume and third non-heated volume may be adjusted until the desired tolerance level is reached. In some embodiments, the first gas flow may be increased such that the amount of precursor in the final mixture will increase. Control of the flow rate of the first gas or the second gas may provide a faster response time than controlling the heating temperature. For example, the maximum flow possible will be limited by the type of precursor and the temperature. There are no special requirements for the flow rate of the second gas other than providing enough dilution. For gas delivery over long lines, a total flow rate as high as 5 slm might be desirable. However, the specific temperatures and flow rates will depend upon the specific configuration of the system and the precursors being used.

Thus, methods and apparatus for gas delivery have been disclosed herein. Methods and apparatus of the present invention advantageously provides vaporization of a low vapor pressure precursor in solid or liquid form at high efficiency and delivery accuracy while reducing energy input costs and improving delivery rate.