Abstract:
An apparatus for controlling the flow of liquid material from a liquid material source to a process chamber is disclosed. The apparatus comprises an injector/vaporizer disposed proximate to the process chamber. The injector/vaporizer includes one or more piezoelectric grids located proximate to a vaporization chamber. The one or more piezoelectric grids function to control the flow of liquid material into the vaporization chamber. Each piezoelectric grid includes interlocking arrays of stripes attached to a frame.

Description:
BACKGROUND OF THE DISCLOSURE 
   1. Field of the Invention 
   The present invention relates to the field of manufacturing integrated circuits and, more particularly to an apparatus for controlling the flow of process material into a thin film deposition chamber. 
   2. Description of the Background Art 
   Chemical vapor deposition (CVD) processes are widely used to deposit material layers on semiconductor devices and integrated circuits. These CVD processes deposit material layers on semiconductor devices and integrated circuits by reacting gaseous precursors adjacent to the surfaces thereof. The reaction rate for CVD processes is controlled via temperature, pressure and precursor flow rates. 
   Some precursors are derived from low vapor pressure liquids. The low vapor pressure liquids are transported using a bubbler (or boiler). The bubbler includes an ampoule containing a source of the liquid precursor. A carrier gas provided to the ampoule saturates the liquid precursor and transports the vapor to a process chamber. The amount of vapor transported depends on the process chamber pressure, the carrier gas flow rate, as well as the vapor pressure in the ampoule containing the source of liquid precursor. As such, the flow rate of vaporized precursor is difficult to control, which decreases the quality of material layers produced therefrom. 
   Additionally, liquid precursor shut-off is problematic due to residual liquid precursor in the lines between the ampoule and the process chamber. This residual liquid precursor may be continuously leaked into the process chamber after shut-off resulting in chamber and/or substrate contamination. 
   Thus, there is a need to provide an apparatus for improved control of a liquid precursor to a process chamber. 
   SUMMARY OF THE INVENTION 
   An apparatus for controlling the flow of liquid material from a liquid material source to a process chamber is disclosed. The apparatus comprises an injector/vaporizer disposed proximate to the process chamber. The injector/vaporizer includes one or more piezoelectric grids located proximate to a vaporization chamber. The one or more piezoelectric grids function to control the flow of liquid material into the vaporization chamber. Each piezoelectric grid includes interlocking arrays of strips attached to a frame. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The teachings of the present invention can be readily understood by considering the following detailed description with the accompanying drawings, in which: 
       FIG. 1  is a schematic illustration of an apparatus that can be used for the practice of embodiments described herein; 
       FIG. 2  is a schematic illustration of an injector/vaporizer used for the practice of embodiments described herein; 
       FIG. 3  is a top view of the vaporizing chamber of the injector/vaporizer shown in  FIG. 2 ; 
       FIG. 4  is a cross-sectional view of a portion of the top view of the vaporizing chamber shown in  FIG. 3 ; 
       FIG. 5  is an expanded view of a portion of the liquid material outlet passage shown in  FIG. 4 ; 
       FIG. 6  illustrates a top view of a grid including interlocking arrays of strips attached to a frame; 
       FIG. 7A  illustrates two or more grids stacked perpendicular to one another; 
       FIG. 7B  is a top view of the grids depicted in  FIG. 7A  showing that the interlocking arrays of strips form a plurality of pores; 
       FIG. 8  is a flow diagram illustrating the operation of the injector/vaporizer; and 
       FIG. 9  depicts a timing diagram for operating the injector/vaporizer. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a schematic representation of a deposition system  10  that can be used to perform integrated circuit fabrication in accordance with embodiments described herein. The deposition system  10  typically includes a precursor delivery system  100 , a process chamber  110 , and a gas delivery system  120 , along with other hardware components such as power supplies (not shown) and vacuum pumps (not shown). Examples of such a deposition system include TxZ™ systems and DxZ™ systems, commercially available from Applied Materials, Inc., Santa Clara, Calif. 
   In the precursor delivery system  100 , a liquid precursor  112  is delivered to a gas delivery system  120  through conduction line  114 . A pressure regulator  116  is connected to the conduction line  114  between the precursor delivery system  110  and the gas delivery system  120 . The pressure regulator pressurizes the liquid precursor within a range of about 10 psi to about 100 psi. 
   In the gas delivery system  120 , a carrier gas, such as, for example, helium (He), is provided to an injector/vaporizer  122  via conduction line  124 . An optional liquid flow meter (LMF)  126  connected to conduction lines  121 ,  123  monitors the flow rate of liquid precursor to the injector/vaporizer  122 . 
   The gas delivery system  120  communicates with a showerhead (not shown) in the process chamber  110 . Process gases such as vaporized liquid precursor and/or carrier gas flow from the injector/vaporizer  122  to the process chamber  110  through heated conduction line  132 . 
   Referring to  FIG. 2 , the injector/vaporizer  122  comprises a body block  213  made of metallic materials superior in thermal conductivity, heat resistance and corrosion resistance such as, for example, stainless steel. The body block  213  includes at least one heater  214 . 
   A liquid material inlet passage  215  and a gas outlet passage  216  are formed within the body block  213  without crossing each other. A liquid material outlet opening  219  for the liquid material inlet passage  215  opens onto an upper surface  220  of the body block  213 , so as to introduce a liquid material (LM) into a vaporizing chamber  232 . 
   The gas outlet passage  216  opens onto the upper surface  220  of the body block  213 , such that a gas (G) generated in the vaporizing chamber  232  exits the body block  213  therethrough. A carrier gas inlet passage  217  also opens onto the upper surface  220  of the body block  213 . The carrier gas mixes with the vaporized liquid material in the vaporizing chamber and carries it out through the gas outlet passage  216 . 
   Referring to  FIG. 3 , the liquid material outlet opening  219  on the upper surface  220  of the body block  213  opens at a central portion  226  thereof. A groove  227  that is concentric with the liquid material outlet opening  219  is formed around the central portion  226 . The gas outlet passage  216  and the carrier gas inlet passage  217  are also encompassed by the groove  227 . 
   Typically, the inside diameter of the liquid material outlet opening  219  has dimensions of about 0.5 mm (millimeters) to about 1.5 mm. The inside diameter of the gas outlet passage  216  and the carrier gas inlet passage  217  have dimensions of about 2 mm to about 4 mm. The distance from the liquid material outlet opening  219  to the groove  227  formed concentrically therewith is about 3 mm to about 6 mm. The dimensions of the liquid material outlet opening  219 , the gas outlet passage  216 , the carrier gas inlet passage, as well as the distance between the liquid material outlet opening  219  and the groove  227  may be variable depending on the volume of liquid material (LM) introduced through the liquid material inlet passage  215 . 
   Referring again to  FIG. 2 , a diaphragm  234  and control valve plunger  236  is positioned on the upper surface  220  of the body block  213  over the groove  227 . The diaphragm  234  along with the control valve plunger  236  functions to shut-off the flow of the gas (G) generated in the vaporizing chamber  232  through the gas outlet passage  216 . The diaphragm  234  is pressed by the control valve plunger  236  against the central portion  226  to stop the flow of liquid material from the liquid material outlet opening  219  into the vaporization chamber  232 . 
     FIG. 4  shows a cross-section of the upper surface  220  of the body block  213  depicted in  FIG. 3 , taken along line  1 - 1 ′. At least one grid  405  is positioned at the top of the liquid material inlet passage  215  near the liquid material outlet opening  219 . The one or more grids  405  function to control the flow rate of the liquid material into the vaporizer chamber  232 . The one or more grids  405  may optionally be positioned perpendicular to each other as shown in FIG.  5 . 
     FIG. 6  illustrates a top view of a grid  405  including interlocking arrays of strips  502 ,  504  attached to a frame  500 . Each strip in the array of strips  502  is electrically connected to the others via contacts  508 . Each strip in the array of strips  504  is electrically connected to the others via contacts  506 . 
   The strips  502 ,  504  are made of a piezoelectric material that expands uniformly in each direction and has a maximum material expansion of n. Thus, the distance between each of the strips  502 ,  504  should be no more than 2n and the distance between the edges of each strips  502 ,  504 , and the frame  500  should be no more than n. 
   When the maximum expansion for the grid  405  is reached, the aperture opening thereof is zero. This is because each of the interlocking arrays expands such that adjacent strips  502 ,  504  touch one another as well as the edges of the frame. 
   Referring to  FIGS. 7A-7B , the two or more grids  405  may be stacked perpendicular to one another such that the interlocking arrays of stripes  502 ,  504  form a plurality of pores  702 . As the arrays of strips on each of the grids  405  expands to the maximum expansion of n, the diameter of each pore in the plurality of pores  702  is reduced to zero. The distance between each of the two or more grids  405  is variable. The distance between each of the grids is preferably less than about 1 cm. 
   The piezoelectric material should be formed of a material that is inert with respect to the liquid material to be vaporized. Additionally, the piezoelectric material should be inert with respect to pressure changes within the liquid material inlet passage  215 , as well as vaporization temperatures, magnetic noise and electrical noise. 
   A voltage is applied to each of the arrays of strips  502 ,  504  through contacts  506 ,  508 . The amount of expansion for each strip depends on the composition of the piezoelectric material as well as the magnitude of the applied voltage. As such, varying the voltage applied to the strips  502 ,  504  adjusts the size of the opening between adjacent strips, thereby affecting the flow rate of liquid material into the vaporizer chamber  232 . 
   The piezoelectric materials should have a Young&#39;s modulus of less than about 250 GPa. Examples of suitable piezoelectric materials include barium titanate (BaTiO 3 ) and lead zirconate titanate (PZT), among others. 
   Typically, there is a pressure-drop across the one or more grids  405  between the liquid material inlet passage  215  and the vaporizing chamber  232 . The liquid material (LM) is vaporized due to the pressure-drop along with the heating thereof in the vaporizing chamber  232 . As a result a desired flow rate of gas (G) can be provided to the process chamber  110  (FIG.  1 ). 
   Referring to  FIG. 3 , a flow of vaporized liquid material radiates from the liquid material outlet opening  219  across the center portion  226  toward the groove  227 . The carrier gas provided through carrier gas inlet passage  217  transports the vaporized liquid material out of the vaporizing chamber  232  through the gas outlet passage  216 . The carrier gas may be, for example, an inert gas (IG), such as nitrogen (N 2 ), argon (Ar), or helium (He). 
   Alternatively, the vaporizing chamber  232  may be formed within the body block  213 . Additionally, the heater  214  is not always positioned within the body block  213 , as shown in FIG.  2 . For example, a heater (not shown) may be wound around conduction lines  121 ,  123  to preliminarily heat the liquid material (LM) supplied to the injector/vaporizer  122 , thereby providing the thermal energy required for the vaporization to the liquid material (LM) in the vaporizing chamber  232 . For such an embodiment, vaporization of the liquid material (LM) within the injector/vaporizer  122  provides a larger flow rate of gas (G) to the process chamber  110  than for a heater  214  positioned within the body block  213 . 
   A close proximity for the injector/vaporizer  122  to the process chamber  110  is preferred, so the vapor created does not have to travel over a large distance before dispersion into the process chamber  110 . As such, less plating or clogging of transfer lines, such as conduction line  132 , is likely. Moreover, the close proximity of the injector/vaporizer  122  to the chamber  110  significantly reduces the likelihood of pressure gradients that affect the deposition process. 
   For example, if the deposition system  10  is operating at a pressure of about 1.5 torr, a 0.5 torr drop in pressure is significant enough to degrade the properties of the film being deposited. Additionally, the close proximity of the injector/vaporizer  122  provides for faster processing of wafers by reducing the time lag associated with removing gaseous material from a conduction line after injector/vaporizer  122  shut-off. Byproducts of the deposition process can be pumped out of just the chamber instead of the extra volume of the delivery system also. Less excess process material is carried to the chamber which results in less extraneous deposition on chamber components and cross-contamination of neighboring chambers during wafer transfer. 
   The flow of liquid material (LM) through the injector/vaporizer  122  may be pulsed by alternately opening and closing the one or more grids  405 .  FIG. 8  depicts a flow diagram of the method of the present invention. The method  800  begins at step  802  with the one or more grids  405  ( FIGS. 4-5 ) in the injector/vaporizer  122  at their maximum expansion, n, so the flow of liquid material (LM) into the vaporizing chamber  232  is shut-off. 
   In step  804 , the one or more grids  405  are opened for a first peirod of time T 1 . The one or more grids  405  are opened by contracting one or more of the interlocking arrays of strips  502 ,  504 . The strips  502 ,  504  may be contracted by varying the applied voltage provided through contacts  506 ,  508 . 
   At step  806 , the one or more grids  405  are expanded again to their maximum expansion, n, for a second time period T 2 , so the flow of liquid material (LM) into the vaporizing chamber  232  is shut-off. The opening and closing steps are repeatedly cycled at step  808  until a third period of time T 3  has elapsed. After the third period of time has elapsed, the method ends at step  808  with the one or more grids  405  closed. 
     FIG. 9  depicts a timing diagram of a drive signal  900  produced by a controller (not shown) that controls the operation of the injector/vaporizer  122 . The drive signal  900  represents a voltage or current delivered to the one or more piezoelectric grids  405 . When the drive signal  900  is at first level  902 , the arrays of strips  502 ,  504  are fully expanded to shut-off the flow of liquid material (LM). When the drive signal  900  is at a second level  904 , the arrays of strips  502 ,  504  are not fully expanded to provide a flow of liquid material (LM) therethrough. The controller maintains the drive signal  900  at the first level  902  for a peirod of time T 1 . T 1  is typically between approximately 2 milliseconds and 30 milliseconds. The controller then changes the signal  900  to level  904  for a peirod of time T 2 . T 2  is typically between approximately 1 second and 10 seconds. 
   The one or more piezoelectric grids  405  expand or contract over a duty cycle of duration T 1 +T 2 . The flow rate can be adjusted between about 0.5 sccm to about 500 sccm by varying the parameters. For example, if the one or more piezoelectric grids  405  operate with about a 2 second duty cycle during which the piezoelectric grids  405  are open for approximately 5 milliseconds, the flow rate for the liquid material can be increased by decreasing time period T 2 , for fixed T 1 . Alternatively, decreasing time period T 1 , for fixed T 2  decreases the flow rate. 
   For a fixed flow rate, the volume of liquid material flowing through the piezoelectric grids  405  can be controlled by repeating the duty cycle for a time period T 3 . T 3  is typically between about 10 seconds to about 600 seconds. Additionally, T 1  and T 2  may be shifted up or down in the duty cycle so that the piezoelectric grids  405  are opened at any time during the duty cycle. 
   The injector/vaporizer  122  may be controlled by a processor based system controller  150  (FIG.  1 ). The system controller  150  includes a programmable central processing unit (CPU) (not shown) that is operable with a memory, a mass storage device, an input control unit, and a display unit. The system controller  150  further includes power supplies (not shown), clocks (not shown), cache (not shown), input/output (I/O) circuits (not shown) and the like. The system controller  150  also includes hardware for monitoring wafer processing through sensors (not shown) in the deposition chamber  110 . Such sensors measure system parameters such as wafer temperature, chamber atmosphere pressure and the like. All of the above elements are coupled to a control system bus (not shown). 
   The memory contains instructions that the central processing unit (CPU) executes to facilitate the performance of the deposition system  110 . The instructions in the memory are in the form of program code. The program code may conform to any one of a number of different programming languages. For example, the program code can be written in C, C++, BASIC, Pascal, as well as a number of other languages. 
   The mass storage device stores data and instructions and retrieves data and program code instructions from a processor readable storage medium, such as a magnetic disk or magnetic tape. For example, the mass storage device can be a hard disk drive, floppy disk drive, tape drive, or optical disk drive. The mass storage device stores and retrieves the instructions in response to directions that it receives from the central processing unit. Data and program code instructions that are stored and retrieved by the mass storage device are employed by the central processing unit for operating the deposition system  110 . The data and program code instructions are first retrieved by the mass storage device from a medium and then transferred to the memory for use by the central processing unit. 
   The input control unit couples a data input device, such as a keyboard, mouse, or light pen, to the central processing unit to provide for the receipt of a chamber operator&#39;s inputs. The display unit provides information to a chamber operator in the form of graphical displays and alphanumeric characters under control of the central processing unit. 
   The control system bus provides for the transfer of data and control signals between all of the devices that are coupled to the control system bus. Although the control system bus is described as a single bus that directly connects the devices in the central processing unit, the control system bus can also be a collection of busses. For example, the display unit, input control unit and mass storage device can be coupled to an input-output peripheral bus, while the central processing unit and memory are coupled to a local processor bus. The local processor bus and input-output peripheral bus may be coupled together to form the control system bus. 
   The system controller  150  is coupled to various elements of the deposition system  110 , via the control system bus and the I/O circuits. These elements may include the injector/controller  122  and the liquid flow meter  126 . The system controller  150  provides signals to the chamber elements that cause these elements to perform operations for depositing a layer of material therein. 
   Although various embodiments which incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.