Patent Publication Number: US-2010116208-A1

Title: Ampoule and delivery system for solid precursors

Description:
FIELD 
     Embodiments of the present invention generally relate to semiconductor process equipment and more particularly to a gas delivery system for delivering a precursor to a process chamber. 
     BACKGROUND 
     During substrate processing, a gas delivery system may be utilized to deliver a precursor to a process chamber. In some embodiments, the precursor may be a molecule having a low vapor pressure, for example, hafnium tetrachloride (HfCl 4 ), that is stored, in solid form, in an ampoule coupled to the gas delivery system. To deliver such a precursor to the process chamber, the precursor is first sublimed into a gaseous form. Next, the gaseous precursor is delivered to the process chamber using a carrier gas that flows through the ampoule, mixes with the gaseous precursor, and continues to the process chamber. 
     The sublimation of the precursor may be enabled by supplying heat to the walls of the ampoule. For example, the exterior surface of the ampoule can be covered with external heaters, heating pads, or the like. Unfortunately, and partially due to the cylindrical shape of conventional ampoules, heat transfer to the precursor is inefficient. For example, the low surface to volume ratio of a cylindrical ampoule can result in sublimed precursor proximate the walls of the ampoule, while precursor disposed centrally within the ampoule remains in solid form. Moreover, particularly when using solid precursors with a high enthalpy of sublimation (e.g., 100,000 kJ/mole for HfCl 4 ), inefficient heating of the solid precursor combined with the loss of heat to neighboring particles of the precursor leads to slow reaction time to develop sufficient quantities of gaseous precursor. In addition, the ampoule may be configured such that the carrier gas flows through the ampoule. Thus, portions of the remaining solid precursor can be swept up by the carrier gas, and deposited in the gas delivery lines or in the process chamber. As a result, gas delivery lines can be clogged and particulate matter can be deposited in the process chamber. 
     Accordingly, there is a need in the art for an improved gas delivery system. 
     SUMMARY 
     Gas delivery systems for delivering gaseous precursors sublimated from solid form are disclosed herein. In some embodiments, the gas delivery system may include an ampoule to hold a solid precursor that can sublimate to a gaseous form within the ampoule; and a carrier gas line coupled to the ampoule at a junction disposed in the carrier gas line, wherein the carrier gas line has a first cross-sectional area proximate an inlet and an outlet of the junction and a smaller, second cross-sectional area within the junction, and wherein a carrier gas flowing through the junction creates a pressure within in the junction that is less than a pressure within the ampoule. 
     In some embodiments, a semiconductor processing system may include a process chamber having an internal processing volume; and a gas delivery system. The gas delivery system may include an ampoule to hold a solid precursor that can sublimate to a gaseous form within the ampoule; a carrier gas line coupled to the ampoule at a junction disposed in the carrier gas line, wherein the carrier gas line has a first cross-sectional area proximate an inlet and an outlet of the junction and a smaller, second cross-sectional area within the junction, and wherein a carrier gas flowing through the junction creates a pressure within in the junction that is less than a pressure within the ampoule; and a carrier gas source coupled to the carrier gas line. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic cross-sectional view of a process chamber in accordance with some embodiments of the present invention. 
         FIGS. 2A-B  respectively depict schematic front and side views of a gas delivery system in accordance with some embodiments of the present invention. 
         FIG. 3  is a schematic front view of a gas delivery assembly in accordance with some embodiments of the present invention. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The above drawings are not to scale and may be simplified for illustrative purposes. 
     DETAILED DESCRIPTION 
     A gas delivery system is disclosed herein, and may be utilized to deliver low vapor pressure precursors, such as hafnium tetrachloride (HfCl 4 ) to a process chamber. The gas delivery system includes an ampoule for holding a precursor in solid form and a carrier gas line coupled to the ampoule at a junction disposed in the carrier gas line. The gas delivery system advantageously improves heat transfer to the ampoule by providing an ampoule having a high surface to volume ratio, and/or additional heating mechanisms, such as a radiant energy source. Further, the design of the junction facilitates drawing the gaseous precursor out of the ampoule without the carrier gas entering the ampoule, thus advantageously reducing or eliminating any un-sublimed precursor from entering the carrier gas line. The gas delivery system of the present invention may be coupled to a process chamber configured for cyclical deposition. One such exemplary process chamber is described in  FIG. 1 . 
       FIG. 1  is a schematic cross-sectional view of an exemplary process chamber  102  including a gas delivery system  104  adapted for cyclic deposition, such as Atomic Layer Deposition or Rapid Chemical Vapor Deposition. The terms Atomic Layer Deposition (ALD) and Rapid Chemical Vapor Deposition as used herein refer to the sequential introduction of the reactant gas to deposit a thin layer over the substrate structure. The sequential introduction of the reactant gas may be repeated to deposit a plurality of thin layers to form a conformal layer to a desired thickness. The process chamber  102  may also be adapted for other deposition techniques. 
     The process chamber  102  includes a chamber body  106  having sidewalls  108  and a bottom  110 . A slit valve  112  in the process chamber  102  provides access for a robot (not shown) to deliver and retrieve a substrate  114 , such as a semiconductor wafer with a diameter of  200  mm or  300  mm or a glass substrate, from the process chamber  102 . The process chamber  102  may be various types of ALD chambers. The details of the exemplary process chamber  102  are described in commonly assigned United States Patent Application Publication No. 2005-0271813, filed on May 12, 2005, entitled “Apparatuses and Methods for Atomic Layer Deposition of Hafnium-Containing High-K Dielectric Materials,” and United States Patent Application Publication No. 20030079686, filed on Dec. 21, 2001, entitled “Gas Delivery Apparatus and Method For Atomic Layer Deposition”, which are both incorporated herein in their entirety by references. Two exemplary chambers suitable for use with the inventive gas delivery system may include GEMINI™ ALD or CVD chambers available from Applied Materials, Inc. 
     A substrate support  116  supports the substrate  114  on a substrate receiving surface  118  in the process chamber  102 . The substrate support (or pedestal)  116  is mounted to a lift motor  120  to raise and lower the substrate support  116  and the substrate  114  disposed thereon. A lift plate  122  connected to a lift motor  124  is mounted in the process chamber  102  and raises and lowers pins  126  movably disposed through the substrate support  116 . The pins  126  raise and lower the substrate  114  over the surface of the substrate support  116 . In some embodiments, the substrate support  116  may include a vacuum chuck, an electrostatic chuck, or a clamp ring for securing the substrate  114  to the substrate support  116  during processing. 
     The substrate support  116  may be heated to increase the temperature of the substrate  114  disposed thereon. For example, the substrate support  116  may be heated using an embedded heating element, such as a resistive heater, or may be heated using radiant heat, such as heating lamps disposed above the substrate support  116 . A purge ring  128  may be disposed on the substrate support  116  to define a purge channel  130  which provides a purge gas to a peripheral portion of the substrate  114  to prevent deposition thereon. 
     The gas delivery system  104  may be disposed in any suitable location, such as an upper portion of the chamber body  106 , to provide one or more gases, such as a reactant gas (e.g., a precursor) and/or a purge gas, to the process chamber  102 . A vacuum system  132  is in communication with a pumping channel  134  to evacuate any desired gases from the process chamber  102  and to help maintain a desired pressure or a desired pressure range inside a pumping zone  136  of the process chamber  102 . 
     The gas delivery system  104  includes an ampoule  148  coupled to a carrier gas line  152  having a junction  151  disposed therein. The ampoule  148  is configured for storing and vaporizing a solid precursor therein and is coupled to the carrier gas line  152  at the junction  151 . In some embodiments, the precursor can be a low vapor pressure precursor. In some embodiments, the precursor can be hafnium tetrachloride (HfCl 4 ) or the like. The precursor in the ampoule  148  may be sublimated from solid to gaseous form by, for example, heating the precursor. The ampoule may be fabricated from process-compatible materials suitable for holding the precursor and for transferring energy to the precursor. For example, the ampoule may by fabricated, at least in part, from highly heat conductive materials, such as stainless steel, aluminum, or the like, or from materials transparent to radiant energy provided to the precursor, such as quartz, or the like. 
     Upon sublimation, the gaseous precursor is ready to be transported to the process chamber via a carrier gas flowing through the carrier gas line  152 . In some embodiments, the carrier gas line  152  (or portions thereof may be heated to a temperature higher than ambient and above the sublimation temperature to prevent or limit condensation of any of the sublimed gases in the carrier gas line  152 . 
     The ampoule may have a geometry configured to improve the efficiency of the energy transfer to the precursor contained within the ampoule. In one non-limiting embodiment, the ampoule  148  may have a generally rectangular shape as depicted in  FIGS. 2A-B . As depicted in the front view of  FIG. 2A , the ampoule  148  may have a first rectangular cross-section  212  defined by a length  214  and height  216  of the ampoule  148 . The ampoule  148  further includes a second rectangular cross-section  218  defined by the height  216  and a width  220  of the ampoule  148  as depicted in side view in  FIG. 2B . Thus, in this one non-limiting embodiment, the ampoule  148  has a rectangular cross-section on each side of the ampoule  148 . In some embodiments, a ratio of the first rectangular cross-section to the second rectangular cross-section of the ampoule is between about 3 or higher. This exemplary configuration of the ampoule  148  facilitates providing a high surface area to volume ratio of the ampoule  148 . However, the ampoule  148  is not limited to a rectangular cross-section, and may include any suitable cross-section and/or shape. 
     The dimensions of the ampoule  148  (i.e. length  214 , height  216  and width  220 ) may be selected to provide a high surface area to volume ratio. In some embodiments, the surface to volume ratio is about 0.4 or more. For example, an ampoule with a volume of 1 liter (or 1000 cc) having a cylindrical shape (e.g., a regular cylinder with a circular cross-section) and a height of 10 cm, has a surface area (vertical wall) to volume ratio of approximately 0.36. In comparison, an ampoule of the same size (1000 cc) but having a rectangular cross-section (for example, 3 cm×20 cm and a height of 16 cm) has a surface area (vertical walls) to volume ratio of about 0.64. Larger values of this measure indicate better heat transfer ability from an external heat source to the precursor material inside the ampoule. A high surface area to volume ratio may facilitate improved sublimation of a precursor  222  disposed in the ampoule  148  when heat is supplied to the ampoule surface. In some embodiments, one or more heating elements (not shown) may be coupled to an exterior of the ampoule  148  to facilitate the heating thereof. The heating elements may comprise heating pads, or the like, and may cover some or the entire exterior surface of the ampoule  148 . In some embodiments, the precursor  222  may be mixed, stirred, or agitated to maximize the exposure of the precursor  222  to heat from the heating elements. The precursor  222  may be mixed by providing an agitator (e.g., agitator  164  depicted in  FIG. 1 ) such as a magnetic stirring agitator, a vibrator, or other suitable agitating mechanism. The agitator may be used for mixing, stirring, agitating, or the like. 
     In some embodiments, as depicted in  FIG. 3 , a radiant energy source may be alternatively or in combination coupled to the ampoule to provide sufficient energy to sublimate the precursor  222 .  FIG. 3  is a schematic front view of portions of a gas delivery assembly including an ampoule  300  coupled to the carrier gas line  152  at the opening  210  of the junction  151 . The ampoule  300  may be of any suitable shape as described above with respect to the ampoule  148 . As depicted in a non-limiting embodiment in  FIG. 3 , the ampoule  300  has a trapezoidal cross-section. In some embodiments, the shape of the ampoule  300  may be selected to maximize expose of the precursor  222  to a radiant energy source  302  coupled to the ampoule  300 . The radiant energy source  302  may be illustratively disposed above the ampoule  300 , and capable of transmitting radiant energy through a material that forms at least a portion the ampoule  300  (for example, a top portion as shown in  FIG. 3 ). For example, in some embodiments, the radiant energy source  302  is coupled to the ampoule  300  via a window  304 . The window  304  may comprise any suitable material for transmitting the radiant energy to the precursor  222 . In some embodiments, the window  304  comprises quartz. 
     The radiant energy source  302  may include any suitable source for providing energy to the precursor disposed in the ampoule, such as an ultraviolet radiation source, an infrared radiation source, a microwave radiation source, a halogen lamp, a laser, or the like. The radiant energy source may provide radiant energy at any suitable wavelength necessary to sublimate the precursor  222 . In some embodiments, the wavelength of radiant energy may include at least one of ultraviolet, infrared, microwave, and the like. 
     In some embodiments, heating elements (not shown) may be further coupled to an exterior surface of the ampoule  300  as described above. The heating elements may provide additional energy for subliming the precursor  222 . Further, the precursor  222  may be mixed, stirred, or agitated to maximize the exposure of the precursor  222  to the radiant energy of the radiant energy source  302 , and when heating elements are provided, maximize exposure of the precursor  222  to the walls of the ampoule  300 . 
     Returning to  FIG. 1 , a carrier gas source  150  is coupled to the carrier gas line  152  for providing the carrier gas. In some embodiments, the carrier gas may include at least one of nitrogen, helium, argon, or the like. As discussed below with respect to  FIGS. 2A-B , the junction  151  and the gas delivery line  152  are configured to draw the gaseous precursor from the ampoule  148  when the carrier gas flows through the gas delivery line  152  and the junction  151 , thereby forming a gaseous mixture which may be delivered to the process chamber  102 . 
       FIG. 2A  depicts a front view of a portion of the gas delivery system  104  including the ampoule  148 , carrier gas line  152  and the junction  151  in accordance with some embodiments of the present invention. The gas delivery line  152  has a first diameter, or cross-sectional area  206  on either side of the junction  151 . As depicted in the  FIG. 2A , the junction  151  is disposed inline within the carrier gas line  152  and includes a conduit  224  having a diameter, or cross-sectional area  208 , that is smaller than the cross sectional area  206  of the carrier gas line  152 . The conduit  224  includes a inlet  202  and an outlet  204  for facilitating the flow of a carrier gas therethrough. To facilitate smooth flow transition between the carrier gas line  152  and the junction  151 , a portion of the carrier gas line  152  proximate the inlet  202  may taper from the first cross-sectional area  206  down to the second cross-sectional area  208  of the junction  151 . Similarly, a portion of the carrier gas line  152  proximate the outlet  204  may taper upwards from the second cross-sectional area  208  to the first cross-sectional area  206 . Although as shown as having the same cross sectional area  206 , it is contemplated that the carrier gas line  152  may have different cross-sectional areas on either side of the junction  151 , provided that both are larger than the cross-sectional area of the junction  151 . 
     The junction  151  further comprises an opening  210  for coupling the junction  151  to the ampoule  148 . The opening  210  may include elements for coupling to ampoules made of dissimilar materials than the junction  151 . For example, in embodiments where the ampoule  148  is made of quartz, the opening  210  may comprise a metal-to-glass joint, for example, such as stainless steel on the junction side of the opening  210  and quartz on the ampoule side of the opening  210 . 
     Returning to  FIG. 1 , the gas delivery system  104  may further comprise a chamber lid  142 . The chamber lid  142  can include a gas inlet funnel  138  extending from a central portion of the chamber lid  142  and a bottom surface  140  extending from the gas inlet funnel  138  to a peripheral portion of the chamber lid  142 . The bottom surface  140  is sized and shaped to substantially cover the substrate  114  disposed on the substrate support  116 . The chamber lid  142  may have a choke  143  at a peripheral portion of the chamber lid  142  adjacent the periphery of the substrate  114 . The carrier gas line  152  is coupled to the gas inlet funnel  138  at a gas inlet  139 . 
     A portion of bottom surface  140  of a chamber lid  142  may be tapered from the gas inlet funnel  138  to a peripheral portion of the chamber lid  142  to help provide an improved velocity profile of a gas flow from the expanding channel  138  across the surface of the substrate  114  (e.g., from the center of the substrate to the edge of the substrate). The bottom surface  140  may include one or more tapered surfaces, such as a straight surface, a concave surface, a convex surface, or combinations thereof. In one embodiment, the bottom surface  140  is tapered in the shape of a funnel. 
     The gas inlet funnel  138  and gas delivery system  104  are depicted herein for ease of understanding. For example, the gas inlet funnel  138  may have multiple gas inlets (not shown) for receiving carrier gases, process gases, gaseous mixtures, or the like. Further, the gas delivery system  104  may further comprise multiple gas sources (not shown) coupled to inlets of the gas inlet funnel  138  through multiple gas lines (not shown). Gases from the multiple sources may be mixed prior to entering an inlet of the gas inlet funnel  138 , and/or flow rates of gases may be controlled by valves, mass flow controllers or the like. 
     A control unit  154 , such as a programmed personal computer, work station computer, or the like, may be coupled to the process chamber  680  to control processing conditions. For example, the control unit  154  may be configured to control supplying energy to an ampoule for subliming a precursor and the flow of a carrier gas during different stages of a substrate process sequence. Illustratively, the control unit  154  includes a Central Processing Unit (CPU)  156 , support circuitry  162 , and a memory  158  having associated control software  160 . 
     In operation, and referring to  FIGS. 1-3 , the precursor  222  is heated to form a vapor of the precursor  222  within the ampoule  148  (or ampoule  300 ). For example, the temperature of a precursor such as hafnium tetrachloride (HfCl 4 ) may be maintained above a critical temperature (about 135 degrees Celsius for HfCl 4 ) thereby sublimating a portion of the precursor  222  and forming a vapor pressure in the ampoule of, for example, about 0.1 Torr. A carrier gas is flowed from the carrier gas source  150  through the carrier gas line  152  having the first cross-sectional area  206 . The carrier gas enters the inlet  202  of the junction  151 , where the cross sectional area of the carrier gas line tapers down to the second cross sectional area  208  with the junction. As a result of the reduction in cross sectional area, the velocity of the carrier gas increases and the pressure decreases within the junction  151 . The reduced pressure within the junction  151  is less than the vapor pressure of the precursor within the ampoule  148  (or ampoule  300 ). Thus, the vapor of precursor  222  flows out of the ampoule  148  and into the junction  151  where the vapor mixes with the carrier gas flowing through the junction  151 . The gaseous mixture exits the junction  151  at the outlet  204 , and proceeds through the carrier gas line  152  to the gas inlet funnel  138  where the gaseous mixture enters the process chamber  102 . 
     Thus, an improved gas delivery system is disclosed herein. The gas delivery system may be utilized to delivery low vapor pressure precursors, such as hafnium tetrachloride (HfCl 4 ) to a process chamber. The gas delivery system advantageously improves heat transfer to the ampoule by providing an ampoule having a high surface to volume ratio, and/or by supplying additional heating mechanisms, such as a radiant energy source. Further, the gas delivery system facilitates delivering precursors to the process chamber without the carrier gas entering the ampoule, thus advantageously preventing or restricting any un-sublimed precursor from entering the carrier gas line. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof.