Abstract:
A structure which ensures against deterioration of an underlying silicide layer over which a refractory material layer is deposited by physical vapor deposition (PVD) or chemical vapor deposition (CVD) is realized by first providing a continuous polysilicon layer prior to the refractory material deposition. The continuous polysilicon layer, preferably no thicker than 50 Å, serves a sacrificial purpose and prevents damage to an underlying silicide layer by blocking interaction between any fluorine and the underlying silicide that is released when the refractory material is formed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This Application is a Division of application Ser. No. 09/826,036 filed on Apr. 4, 2001 now U.S. Pat. No. 6,762,121, the entire contents of which are incorporated herein by reference. 

   BACKGROUND 
   This invention relates to a method of forming a refractory metal contact over a silicon substrate in a solid state structure, and to related structures. More particularly, the invention relates to a method employing a sacrificial silicon layer that serves as a nucleation layer for subsequent deposition of a refractory material to form a contact. 
   Conductive metal contacts are frequently found in semi-conductor devices, and typically are formed by deposition of a refractory material, such as tungsten or the like, confined by a silicon oxide layer previously deposited over a conducting substrate containing, for example, a silicide. Steps in the conventional method of forming such contacts, and the nature of a problem that sometimes arises, are best understood with reference to  FIGS. 1 ,  2 ,  3  and  4 (A)-(B) hereof. 
     FIG. 1  is a cross-sectional view of a relevant portion of the underlying structure, wherein an underlying silicide layer  100  serves as a substrate  4  with an oxide layer  102  formed thereon. The location, shape and size of the desired conductor is determined by a through opening  104  formed in the oxide layer  102 , with exposed surface  106  of the silicide serving as a bottom  106  of the opening  104 . As best seen in  FIG. 2 , a thin metallic layer  200  is then deposited at the bottom of aperture  104  to serve as a contact liner. Then, per  FIG. 3 , a thin nucleation layer  300  of a refractory material such as tungsten is formed in the presence of silane gas to cover oxide layer  102 , the sides  108  of aperture  104 , per liner  200 . This is followed, per FIG.  4 (A), by the deposition of a layer  400  containing the desired refractory material in an amount sufficient to totally cover and fill up the inside of aperture  104  and to extend over the upper surface of oxide layer  102 . Note that the nucleation layer  300  becomes, in effect, absorbed within the refractory layer  400 . 
   Unfortunately, when a refractory material such as tungsten is deposited from decomposition of WF 6  through the use of either physical vapor deposition (PVD) or chemical vapor deposition (CVD), particularly during a chemical vapor deposition step, some of the fluorine released from decomposition of WF 6  combines with silicon in the silicide layer  100  and a propensity to form an undesirable region  402 , as is probably best seen in the enlarged view in FIG.  4 (B). 
   An example of a prior patent which appears to address a similar problem is U.S. Pat. No. 5,804,499, to Dehm et al., titled “Prevention of Abnormal WSi x  Oxidation by In-Situ Amorphous Silicon Deposition”, which suggests a process in which amorphous silicon is deposited in a thin layer on top of tungsten silicide to prevent abnormal WSi x  oxidation during subsequent process steps. The layer of amorphous silicon as mentioned in this patent is bounded by a spacer also made of amorphous silicon. The reference does not teach the provision of a continuous layer of silicon to address the problem at issue. 
   The present invention seeks to address this particular problem in a simple and efficient manner. 
   BRIEF SUMMARY 
   This invention provides a method by which a refractory material may be deposited in and over an opening in a non-conducting layer over a conducting layer, employing a known PVD or CVD step, without damage to the underlying conducting layer. 
   The present invention also provides a structure which includes a refractory material contact formed over an opening in a non-conductive layer deposited over a conductive metal silicide layer. 
   Accordingly, in a first aspect of this invention, there is provided a method of filling an opening in an oxide layer, over a liner layer formed on a silicide layer underlying both the oxide layer and the liner layer, which includes the step of forming a continuous first layer of silicon on the oxide layer, a wall of the opening and the liner layer and, thereafter, forming a second layer of a refractory material on the first layer so as to cover the same and to also substantially fill the opening. 
   In another aspect of this invention, there is provided a multi-layer structure which includes a silicide layer having a first surface; an oxide layer formed on the first surface and having a second surface with a through opening defined in the oxide layer from the second surface to the first surface; a liner layer formed on the first surface at a bottom of the opening, a continuous silicon layer formed to extend over the second surface, the opening surface and the liner layer; and a refractory material layer formed on the silicon layer so as to substantially fill the opening. 
   These and other aspects, objectives and advantages of the present invention will become clearer from an understanding of the following detailed description with reference to the appended figures. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIGS. 1 ,  2 ,  3  and  4 (A)-(B) all relate to the prior art. 
       FIG. 1  is a cross-sectional view showing a metal silicide layer over which is formed a non-conducting oxide layer with a through aperture defined therein. 
       FIG. 2  is a cross-sectional view showing the structure per  FIG. 1 , with a metallic liner layer formed at a bottom surface of the aperture. 
       FIG. 3  is a cross-sectional view at a stage following  FIG. 2 , showing the deposition of a nucleation layer  300  of tungsten over the oxide layer, the sides of the opening formed therein, and the liner at the bottom of the opening. 
     FIG.  4 (A) is a cross-sectional view at a later stage in the known process, wherein a deposit of a refractory material covers the oxide layer and fills the opening above the liner, and also indicates the presence of an undesirable region that may sometimes be formed during deposition of the refractory material due to interaction with the underlying silicide. 
     FIG.  4 (B) is an enlarged view of a relevant portion of FIG.  4 (A), to show more clearly the undesired contamination of the underlying silicide layer at the bottom of the opening that is otherwise filled with refractory material. 
       FIG. 5 , per the method according to the present invention, is a cross-sectional view of the structure per  FIG. 2  with the deposit of a continuous silicon layer over the oxide layer, the sides of the opening formed therein, and the underlying liner at the bottom of the opening. 
       FIG. 6  is a cross-sectional view after deposition of a refractory material over the continuous silicon layer shown in FIG.  5 . 
   

   DETAILED DESCRIPTION 
   As indicated above, the present invention is aimed at providing a method that ensures against contamination of an underlying suicide substrate by any constituent of a refractory conducting layer during its deposition into the desired structure. 
   Referring to the structure illustrated in cross-sectional view in  FIG. 2 , note that a silicide layer  100 , of the order of 300-800 Å in thickness and deposited on a silicon substrate  150 , typically serves as a substrate for an oxide layer  102  deposited thereon with a through opening  104  defined therein, with a liner layer  200  deposited at the bottom  106  of opening  104  in known manner. Liner layer  200  may comprise at least one of titanium, titanium nitride, tungsten, and an alloy of titanium and tungsten, and may incidentally be deposited on the oxide layer  102 . The preferred method according to this invention includes these steps of the prior art. 
   In the prior art, as best understood with reference to  FIG. 3 , a layer  300  of tungsten (W) deposited from WF 6  decomposition in the presence of silane was then formed as a nucleation layer. 
   According to the present invention, a continuous layer  500  of amorphous or polycrystalline silicon is deposited to a controlled thickness preferably by either physical vapor depositions (PVD) or by chemical vapor deposition (CVD), to extend over the oxide layer  102  and the upper surface of liner layer  200 . This is best understood with reference to FIG.  5 . 
   The continuous silicon layer  500  is intended to be a sacrificial layer, i.e., it is anticipated that it may chemically interact and combine with any fluorine (F) that becomes available when, for example, WF 6  is decomposed to generate a tungsten contact layer  400 . In other words, it is intended in the present invention that some of this silicon be consumed in preference to any silicon from the underlying silicide layer  100 . The deposited silicon layer  500  must be in the form of a continuous amorphous or polycrystalline silicon layer. The deposited polysilicon may be obtained by decomposition of a silane such as silane, disilane or trisilane. However, silanes containing ions such as dichlorosilane may advantageously be used and are preferred for this purpose. 
   The resulting structure is best understood with reference to  FIG. 6 , in which the silicide substrate  100  supports oxide layer  102  and liner  200 , and the continuous sacrificial amorphous or polycrystalline silicon layer  500  formed thereon serves as a base for the refractory layer  600  which extends over oxide layer  102  and substantially fills the opening  104 . Note that a small imperfectly filled region  502  may exist in the refractory material  600  within the volume of the substantially filled opening  104  without any deleterious effects on the resulting contact structure and its functionality. 
   The structure as illustrated in  FIG. 6  can then be subjected to conventional subsequent processing such as planarization of  600 ,  500  and  200 . 
   As previously indicated, the present invention is intended to provide a satisfactory refractory layer while avoiding the known problems associated with the related prior art. It is intended, further, that the “refractory material” may be a refractory metal, e.g., tungsten, titanium, tantalum or molybdenum employed directly as a “metal”; a refractory metal employed as a constituent of a “compound” thereof, e.g., titanium nitride, tantalum nitride, etc.; or even as a constituent of an “alloy” with another metal, e.g., titanium-tungsten. With any of these available options, the provision of a continuous silicon layer as discussed above ensures against the known problem. 
   It is intended that the desired refractory material layer  600  be formed in known manner by either a PVD or CVD process step. 
   It is preferred that the continuous sacrificial silicon layer  500  be provided as an amorphous or polysilicon film of a thickness not greater than about 50 Å. 
   The application of the continuous sacrificial silicon layer  500  by either the PVD or the CVD process is preferably accomplished at a temperature in the range 500°-650° C., with 600° C. being particularly preferred. It should be noted that when a PVD process is employed there may be little or no deposition of the silicon on sides  108 ,  108  of opening  104 . 
   It should also be noted that the traditional way of providing a silicon deposition is to flow the silane gas in one process chamber over the underlying structure and, subsequent to depositing the desired silicon layer, to move the wafer supporting the desired structure into another process chamber where a WF 6  environment, for example, could be provided for the subsequent step of depositing tungsten thereon. An obvious problem in doing this is that the timing and conditions required to form the proper layer of silicon to protect the wafer from the chemically active WF 6  gas has a narrow process window and is subject to control problems. 
   The present invention, by utilizing the silicon layer as it does, i.e., as both a sacrificial layer and a nucleation layer, advantageously eliminates the need to do this. In other words, the wafer may be maintained in a single chamber and first be exposed to the silane or dichlorosilane to obtain the desired silicon layer under controlled conditions of time, temperature and flow rate, and this may be followed by passage of WF 6  gas over the same wafer in the same chamber under appropriate process conditions of controlled temperature, pressure and flow rate. The process is readily adaptable to either physical vapor deposition or chemical vapor deposition conducted in known manner. Any adaptation to employ any refractory metal, compound or alloy, may be made in known manner. It is considered that under all circumstances such as these, the sacrificial use of the continuous polysilicon film as taught in this invention ensures against deterioration of the underlying silicide layer. 
   It is considered that persons of ordinary skill in the art will consider obvious modifications of the present invention, both of the method and of the structure, and all such modifications are considered to be comprehended within the present invention which is limited solely by the claims appended below.