Patent Publication Number: US-6218301-B1

Title: Deposition of tungsten films from W(CO)6

Description:
BACKGROUND OF THE DISCLOSURE 
     1. Field of the Invention 
     The invention relates to a method of tungsten film deposition and, more particularly, to a method of forming a tungsten film having good film morphology and low resistivity. 
     2. Description of the Background Art 
     In the manufacture of integrated circuits, tungsten (W) films are often used as contact metallization or plug metallization for aluminum (Al) interconnect schemes. Tungsten (W) films may also be used as a diffusion barrier for copper (Cu) metallization. 
     Tungsten layers are typically formed using chemical vapor deposition (CVD) techniques. For example, tungsten may be formed by thermally decomposing a tungsten-containing precursor. For example, W may be formed when tungsten hexafluoride (WF 6 ) decomposes. 
     However, when tungsten films formed from the decomposition of WF 6 , are deposited on oxides (e.g., silicon dioxide (SiO 2 )) poor film morphology may occur. The morphology of a film refers to its thickness, film continuity, surface roughness, and grain structure. For example, tungsten films formed on silicon dioxide (SiO 2 ) from the thermal decomposition of WF 6  typically may have a discontinuous film morphology. Such discontinuous film morphology is undesirable because it may affect the electrical characteristics of the tungsten film increasing the resistivity thereof. 
     Therefore, a need exists in the art for a method of forming tungsten films having good film morphology and low resistivity. 
     SUMMARY OF THE INVENTION 
     A method of forming tungsten films on oxide layers is provided. The tungsten films are formed on the oxide layers by treating the oxide using a silane based gas mixture followed by the thermal decomposition of a W(CO) 6  precursor. After the W(CO) 6  precursor is thermally decomposed, an additional layer of tungsten may be optionally formed thereon from the thermal decomposition of tungsten hexafluoride (WF 6 ). 
     The tungsten film formation is compatible with integrated circuit fabrication processes. In one integrated circuit fabrication process, the tungsten film is used as a barrier layer for copper metallization (Cu). For a copper metallization process, a preferred process sequence includes providing a substrate having a dielectric material (e.g., oxide) thereon. The dielectric material has vias therein. A tungsten film is formed on the dielectric material by treating the dielectric material using a silane based gas mixture followed by the thermal decomposition of a W(CO) 6  precursor. After the tungsten film is formed on the dielectric material, the integrated circuit structure is completed by filling the vias with a conductive material, such as, for example, copper (Cu). 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
     FIG. 1 depicts a schematic illustration of an apparatus that can be used for the practice of embodiments described herein; and 
     FIGS. 2 a - 2   c  depict schematic cross-sectional views of an integrated circuit structure at different stages of a fabrication sequence incorporating a tungsten (W) film. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a schematic representation of a wafer processing system  10  that can be used to perform tungsten (W) film formation in accordance with embodiments described herein. System  10  typically comprises a process chamber  100 , a gas panel  130 , a control unit  110 , along with other hardware components such as power supplies  106  and vacuum pumps  102 . One example of the process chamber  100  has been previously described in commonly assigned U.S. patent application Ser. No. 09/211,998, entitled “High Temperature Chemical Vapor Deposition Chamber”, filed Dec. 14, 1998, and is herein incorporated by reference. The salient features of this system  10  are briefly described below. 
     Chamber  100   
     The process chamber  100  generally houses a support pedestal  150 , which is used to support a substrate such as a semiconductor wafer  190 . This pedestal  150  can typically be moved in a vertical direction inside the chamber  100  using a displacement mechanism (not shown). 
     Depending on the specific process, the wafer  190  can be heated to some desired temperature prior to the tungsten (W) film deposition. For example, the wafer support pedestal  150  is heated by an embedded heater element  170 . The pedestal  150  may be resistively heated by applying an electric current from an AC power supply  106  to the heater element  170 . The wafer  190  is, in turn, heated by the pedestal  150 . 
     A temperature sensor  172 , such as a thermocouple, is also embedded in the wafer support pedestal  150  to monitor the temperature of the pedestal  150  in a conventional manner. The measured temperature is used in a feedback loop to control the power supplied to the heater element  170 , such that the wafer temperature can be maintained or controlled at a desired temperature which is suitable for the particular process application. The pedestal is optionally heated using radiant heat (not shown). 
     A vacuum pump  102 , is used to evacuate the process chamber  100  and to maintain the proper gas flows and pressure inside the chamber  100 . A showerhead  120 , through which process gases are introduced into the chamber  100 , is located above the wafer support pedestal  150 . The showerhead  120  is coupled to a gas panel  130 , which controls and supplies various gases used in different steps of the process sequence. 
     In the present embodiment, tungsten film deposition is accomplished via thermal decomposition of, for example, a W(CO) 6  precursor. W(CO) 6  may be introduced into the process chamber  100  under the control of gas panel  130 . The W(CO) 6  may be introduced into the process chamber as a gas with a regulated flow via heated line  125  and heated ampoule  135 . 
     Proper control and regulation of the gas flows through the gas panel  130  is performed by mass flow controllers (not shown) and the controller unit  110 . The showerhead  120  allows process gases from the gas panel  130  to be uniformly introduced and distributed in the process chamber  100 . 
     Illustratively, the control unit  110  comprises a central processing unit (CPU)  113 , support circuitry  114 , and memories containing associated control software  116 . The control unit  110  is responsible for automated control of the numerous steps required for wafer processing—such as wafer transport, gas flow control, temperature control, chamber evacuation, and other steps. Bi-directional communications between the control unit  110  and the various components of the wafer processing system  10  are handled through numerous signal cables collectively referred to as signal buses  118 , some of which are illustrated in FIG.  1 . 
     The central processing unit (CPU)  113  may be one of any form of general purpose computer processor that can be used in an industrial setting for controlling process chambers as well as sub-processors. The computer may use any suitable memory, such as random access memory, read only memory, floppy disk drive, hard drive, or any other form of digital storage, local or remote. Various support circuits may be coupled to the CPU for supporting the processor in a conventional manner. Process sequence routines as required may be stored in the memory or executed by a second CPU that is remotely located. 
     The process sequence routines are executed after the substrate  190  is positioned on the wafer support pedestal  150 . The process sequence routines, when executed, transform the general purpose computer into a specific process computer that controls the chamber operation so that the deposition process is performed. Alternatively, the chamber operation may be controlled using remotely located hardware, as an application specific integrated circuit or other type of hardware implementation, or a combination of software or hardware. 
     Tungsten (W) Film Deposition 
     The following embodiment is a method for tungsten (W) film deposition, which advantageously provides tungsten films with good film morphology and low film resistivity. 
     FIGS. 2 a - 2   c  illustrate an integrated circuit structure at different stages of a fabrication sequence, incorporating a tungsten diffusion barrier. In general, the substrate  200  refers to any workpiece upon which film processing is performed, and a substrate structure  250  is used to generally denote the substrate  200  as well as other material layers formed on the substrate  200 . 
     Depending on the specific stage of processing, the substrate  200  may be a silicon semiconductor wafer, or other material layer, which has been formed on the wafer. FIG. 2 a,  for example, shows a cross-sectional view of a substrate structure  250 , having a material layer  202  thereon. In this particular illustration, the material layer  202  may be an oxide (e.g., silicon dioxide, fluorosilicate glass (FSG), undoped silicate glass (USG)). The material layer  202  has been conventionally formed and patterned to provide a contact hole  202 H having sidewalls  202 S, and extending to the top surface  200 T of the substrate  200 . 
     Prior to tungsten (W) film deposition, the substrate structure  250  is treated with a gas mixture comprising a silicon compound. The silicon compound, for example, may be selected from the group of silane (SiH 4 ), disilane (Si 2 H 6 ), dichlorosilane (SiCl 2 H 2 ), and combinations thereof. Carrier gases such as argon (Ar), nitrogen (N 2 ), and hydrogen (H 2 ), among others may be mixed with the silicon compound. 
     In general, the following process parameters can be used to treat the substrate structure  250  with the silicon compound in a process chamber similar to that shown in FIG.  1 . The process parameters range from a wafer temperature of about 250° C. to about 550° C., a chamber pressure of about 0.5 torr to about 2 torr, a silicon compound gas flow rate of about 5 sccm to about 50 sccm, and a carrier gas flow rate of about 100 sccm to about 1000 sccm. 
     The substrate structure  250  is treated for about 5 seconds to about 30 seconds. The treatment of the substrate structure  250  with the silicon compound is believed to improve the nucleation of tungsten (W) thereon. Additionally, it is believed that residual silicon compound may remain in the process chamber after the substrate structure is treated, so that some silicon (Si) may be incorporated in the tungsten film. 
     After the substrate structure  250  is treated, a tungsten film  204  is formed thereon as shown in FIG. 3 b.  The tungsten (W) film  204  is formed by thermally decomposing a W(CO) 6  precursor. Carrier gases such as argon (Ar), and nitrogen (N 2 ), among others may be mixed with the W(CO) 6  precursor. 
     In general, the following deposition process parameters can be used to form the tungsten (W) film  204  in a deposition chamber similar to that shown in FIG.  1 . The process parameters range from a wafer temperature of about 250° C. to about 550° C., a chamber pressure of about 0.5 torr to about 2 torr, a W(CO) 6  precursor flow rate of about 2 sccm to about 20 sccm, and a carrier gas flow rate of about 100 sccm to about 1000 sccm. The above process parameters provide a deposition rate for the tungsten (W) film in a range of about 200 Å/min to about 400 Å/min when implemented on a 200 mm (millimeter) substrate in a deposition chamber available from Applied Materials, Inc., located in Santa Clara, Calif. 
     Other deposition chambers are within the scope of the invention, and the parameters listed above may vary according to the particular deposition chamber used to form the tungsten (W) film. For example, other deposition chambers may have a larger (e.g., configured to accommodate 300 mm substrates) or smaller volume, requiring gas flow rates that are larger or smaller than those recited for deposition chambers available from Applied Materials, Inc. 
     The thermal decomposition of the W(CO) 6  precursor advantageously forms tungsten (W) films with a smooth continuous film morphology. The thickness of the tungsten (W) film  204  is variable depending on the specific stage of processing. Typically, the tungsten (W) film  204  is deposited to a thickness of about 50 Å to about 200 Å. 
     Additional tungsten (W) layers may optionally be deposited over the film formed from the decomposition of the W(CO) 6  precursor, so as to form thick tungsten (W) layers having a desired thickness up to about 4000 Å. The subsequently deposited tungsten (W) films may optionally be formed from the thermal decomposition tungsten hexafluoride (WF 6 ). Carrier gases such as argon (Ar), and nitrogen (N 2 ), among others may be mixed with the tungsten hexafluoride (WF 6 ). 
     In general, the following deposition process parameters can be used to form the tungsten (W) films from the thermal decomposition of tungsten hexafluoride (WF 6 ) in a deposition chamber similar to that shown in FIG.  1 . The process parameters range from a wafer temperature of about 300° C. to about 500° C., a chamber pressure of about 300 torr to about 400 torr, a tungsten hexafluoride (WF 6 ) flow rate of about 200 sccm to about 400 sccm, and a carrier gas flow rate of about 100 sccm to about 1000 sccm. The above process parameters provide a deposition rate for the tungsten (W) film at a rate greater than about 5000 Å/min when implemented on a 200 mm (millimeter) substrate in a deposition chamber available from Applied Materials, Inc., located in Santa Clara, Calif. 
     Referring to FIG. 3 c,  after the tungsten (W) film  204  is deposited, the holes  202 H are filled with a conductive material  206  such as, for example, aluminum (Al), copper (Cu), and combinations thereof, among others. The conductive material  206  may be deposited using chemical vapor deposition (CVD), physical vapor deposition (PVD), electroplating, or combinations thereof. 
     Although several preferred embodiments which incorporate the teachings of the present invention have been shown and described in detail, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.