Patent Publication Number: US-2001000158-A1

Title: Silicide glue layer for W-CVD plug application

Description:
BACKGROUND OF THE INVENTION  
       1. (1) Field of the Invention  
       2. The invention relates to a method of metallization in the fabrication of integrated circuits, and more particularly, to a method of tungsten plug metallization in the manufacture of integrated circuits.  
       3. (2) Description of the Prior Art  
       4. Tungsten-plug metallization is widely used in the art for vertical interconnects of various metal layers in integrated circuit fabrication. A conventional tungsten chemical vapor deposition (W-CVD) process is illustrated in FIG. 1. A contact hole is opened in a dielectric layer  14  overlying a semiconductor substrate  10 . A glue layer  18  is deposited over the dielectric layer and within the contact opening. Typically, the glue layer, which is used as a nucleation layer for the CVD tungsten, comprises titanium nitride, 500 to 1500 Angstroms in thickness, with a thin titanium underlayer, 100 to 500 Angstroms, for adhesion. A tungsten layer  22  is then deposited by CVD and etched back, as shown in FIG. 2, to form the tungsten plug. However, this process if associated with high complexity and cost, high via resistance, and poor controllability of particulation. Moreover, the continuous scaling down of the contact hole size causes great difficulty in filling the contact hole.  
       5. U.S. Pat. No. 5,286,675 to Chen et al teaches a procedure for forming tungsten plugs including the conventional Ti/TiN as the glue layer and the use of reactive ion etching (RIE) to remove the tungsten layer to form the plug. U.S. Pat. No. 5,397,742 to Kim shows the use of a TiSi 2  glue layer overlying a Ti/TiN layer which is etched away after the tungsten plug is formed in order to remove tungsten residue.  
       SUMMARY OF THE INVENTION  
       6. A principal object of the present invention is to provide an effective and very manufacturable method of tungsten plug metallization.  
       7. Another object of the invention is to provide a method of tungsten plug metallization with reduced cost and complexity.  
       8. Yet another object is to provide a method of tungsten plug metallization with reduced glue layer thickness.  
       9. A still further object of the invention is to provide a method of tungsten plug metallization having improved contact resistance.  
       10. Yet another object is to provide a method of tungsten plug metallization using a silicide as a combined ohmic contact and glue layer.  
       11. Yet another object of the invention is to provide a method of tungsten plug metallization with reduced cost and complexity using a silicide as a combined ohmic contact and glue layer.  
       12. In accordance with the objects of this invention a new method of tungsten plug metallization using a silicide glue layer is achieved. Semiconductor device structures are provided in and on a semiconductor substrate. An insulating layer is provided covering the semiconductor device structures wherein a contact opening is made through the insulating layer to one of the semiconductor device structures. A silicide layer is deposited conformally over the surface of the insulating layer and within the contact opening as a combined ohmic contact and glue layer. In a first embodiment, a tungsten layer is deposited overlying the silicide layer. The tungsten layer not within the contact opening is removed to complete the formation of the tungsten plug metallization. In a second embodiment, the silicide layer not within the contact opening is selectively removed and a tungsten layer is selectively deposited overlying the silicide layer within the contact opening to complete formation of the tungsten plug metallization in the fabrication of an integrated circuit.  
       13. Also in accordance with the objects of this invention, an integrated circuit device having tungsten plug metallization using a silicide glue layer is described. Semiconductor device structures are formed in and on a semiconductor substrate. An insulating layer covers the semiconductor device structures. A patterned metal layer overlies the insulating layer. A tungsten plug extends through the insulating layer connecting the patterned metal layer with one of the semiconductor device structures. A silicide layer lies between the tungsten plug and the insulating layer and between the tungsten plug and the one of the semiconductor device structures wherein the silicide layer acts as an ohmic contact and glue layer.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     14. In the accompanying drawings forming a material part of this description, there is shown:  
     15. FIGS.  1  and  2  schematically illustrate in cross-sectional representation a conventional tungsten plug process of the prior art.  
     16. FIGS.  3  through  6  schematically illustrate in cross-sectional representation a first preferred embodiment of the present invention.  
     17. FIGS.  7  and  8  schematically illustrate in cross-sectional representation a second preferred embodiment of the present invention.  
     18.FIG. 9 schematically illustrates in cross-sectional representation a completed integrated circuit device of the present invention.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     19. The process of the present invention applies silicide as the nucleation or glue layer. Silicides have low contact resistance and provide a thinner barrier layer than titanium/titanium nitride. This is especially beneficial as contact hole sizes shrink. Silicide is already used in the fabrication of a contact structure. Usually, it is fabricated by rapid thermal processing after sputtering a thin titanium layer on the silicon substrate. In the process of the present invention, the inventors extend the application of this silicide layer by depositing a blanket layer of silicide. The silicide glue layer can be deposited using common manufacturing processes, thereby reducing the cost and complexity of tungsten plug metallization.  
     20. FIGS.  3  through  6  illustrate a first preferred embodiment of the present invention, a blanket CVD W plug process using a blanket silicide glue layer. A silicide film is blanket deposited as the nucleation or glue layer. Then a blanket W CVD process is used to form the tungsten plug.  
     21. Referring now more particularly to FIG. 3, there is illustrated a portion of a partially completed integrated circuit. There is shown a semiconductor substrate  10 , preferably composed of monocrystalline silicon. A junction  12  has been formed within the semiconductor substrate. This may be a buried contact junction or a source/drain region, or the like. Polysilicon gate electrodes (not shown) and interconnection lines  13  are formed as is conventional in the art.  
     22. An interlevel dielectric layer  14 , composed of silicon dioxide, borophosphosilicate glass (BPSG), borosilicate glass (BSG), or phosphosilicate glass (PSG), or the like, is deposited over the surface of the semiconductor device structures to a thickness of between about 200 to 500 Angstroms. Typically, the interlevel dielectric layer  14  comprises a first layer of undoped silicate glass (USG), a second layer of BPSG, and a third layer of USG. Contact holes  16  are opened through the insulating layer to the junction  12  within the semiconductor substrate and to the interconnection line  13  where contact is to be made. It will be understood by those skilled in the art that the process of the present invention can be used for higher level metallization as well and that the polysilicon interconnection line  13  could be a first level metal line where the tungsten plug to be formed will connect the metal line to a second level metal line.  
     23. Referring now to FIG. 4, a silicide layer  20  is blanket deposited conformally over the surface of the insulating layer  14  and within the contact holes  16 . For a low resistance glue layer, many silicide materials can be used, such as WSi x , TiSi 2 , CoSi 2 , NiSi x , PtSi 2 , PdSi 2 , and the like. The layer  20  may be deposited by chemical vapor deposition (CVD) or physical vapor deposition (PVD) to a thickness of between about 200 to 500 Angstroms.  
     24. Referring now to FIG. 5, tungsten  22  is blanket deposited over the surface of the substrate using WF 6  with SiH 4 , SiH 2 Cl 2 , or H 2  as precursors in a chemical vapor deposition chamber.  
     25. Referring now to FIG. 6, the tungsten is etched back using RIE or chemical mechanical polishing (CMP) to form tungsten plugs  22  within the contact holes. The silicide  20  not within the contact holes is also removed after tungsten etchback.  
     26. The contact silicidation process reduces contact resistance as well as the liner resistance compared with the conventional titanium nitride nucleation layer. Since a thinner glue layer is used, the problem of the glue layer&#39;s filling a small contact opening is avoided. An in-situ or clustered CVD W/silicide bi-layer may be formed in a single chamber or cluster tool. Because the silicide layer acts as both the adhesion layer and the nucleation layer, fewer steps are required in the process of the present invention than in the conventional process resulting in lower costs.  
     27. FIGS.  7  and  8  illustrate a second preferred embodiment of the present invention. In this embodiment, a silicide is deposited as a nucleation or glue layer and then selectively removed from the surface of the insulating layer. A selective CVD W process forms the tungsten plug  22 .  
     28. As above, the process of the present invention in the second preferred embodiment begins with the opening of the contact holes through the insulating layer as shown in FIG. 3. As in the first embodiment, the silicide layer  20  is deposited over the insulating layer and within the contact openings as shown in FIG. 4.  
     29. Referring now to FIG. 7, which follows FIG. 4 in this embodiment, selective chemical mechanical polishing (CMP) is used to remove the silicide layer  20  from the top surface of the insulating layer, leaving the silicide only on the sidewalls and on the bottoms of the contact openings.  
     30. Referring now to FIG. 8, selective W CVD is performed with precursors of WF 6  with SiH 4 , SiH 2 Cl 2 , or H 2 . For example, WF 6  is flowed at 100 sccm and H 2  is flowed at 1000 to 2000 sccm at a temperature of 430° C. and pressure of 200 mTorr. This process forms tungsten plugs  22 .  
     31. The selective CVD W plug process using a selective silicide glue layer solves the problem of filling contact openings of different depths because the tungsten grows from the sidewalls as well as from the bottom of the contact openings. In the traditional selective CVD W process, the W growth is from the bottom of the contact opening only. The tungsten growth from the sidewall provides better adhesion of the tungsten plug to the contact and reduces selectivity loss since deposition time is reduced.  
     32. The contact silicidation process reduces contact resistance as well as the liner resistance compared with the conventional titanium nitride nucleation layer. Because the silicide layer acts as both the adhesion layer and the nucleation layer, fewer steps are required in the process of the present invention than in the conventional process resulting in lower costs. The silicide barrier also allows for lower junction leakage.  
     33.FIG. 9 illustrates further processing after the tungsten plugs have been completed. FIG. 9 follows FIG. 8, but processing would be similar following FIG. 6. A second metallization  24 , such as an aluminum alloy, is deposited and patterned. A passivation layer  26  completes fabrication of the integrated circuit. Of course, other processes may be performed such as an intermetal dielectric deposition and further metallization, as is well known in the art. Higher level tungsten plug metallization may be performed using either of the two alternative embodiments of the present invention.  
     34. Referring now to FIG. 9, the integrated circuit device of the present invention having tungsten plug metallization using a silicide glue layer will be described. Semiconductor device structures are formed in and on a semiconductor substrate. These may include a buried contact junction or a source/drain region, or the like,  12 , polysilicon gate electrodes (not shown) and interconnection lines  13 . Alternatively, line  13  may be a first level of metallization. An insulating layer  14  covers the semiconductor device structures. A patterned metal layer overlies the insulating layer  24 . A tungsten plug  22  extends through the insulating layer  14  connecting the patterned metal layer  24  with the semiconductor device structures  12  and  13 . A silicide layer  20  lies between the tungsten plug  22  and the insulating layer  14  and between the tungsten plug  22  and the semiconductor device structures  12  and  13  wherein the silicide layer acts as an ohmic contact and glue layer.  
     35. The process of the present invention uses CVD deposited refractory metal silicide, which is widely used as an ohmic contact layer, as the glue layer for the tungsten plug. This process not only eliminates the complexity of the conventional process, but also reduces the thickness of the glue layer as compared to the conventional Ti/TiN glue layer.  
     36. While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.