Abstract:
In one aspect, the invention includes a method of forming a material comprising tungsten and nitrogen, comprising: a) providing a substrate; b) depositing a layer comprising tungsten and nitrogen over the substrate; and c) in a separate step from the depositing, exposing the layer comprising tungsten and nitrogen to a nitrogen-containing plasma. In another aspect, the invention includes a method of forming a capacitor, comprising: a) forming a first electrical node; b) forming a dielectric layer over the first electrical node; c) forming a second electrical node; and d) providing a layer comprising tungsten and nitrogen between the dielectric layer and one of the electrical nodes, the providing comprising; i) depositing a layer comprising tungsten and nitrogen; and ii) in a separate step from the depositing, exposing the layer comprising tungsten and nitrogen to a nitrogen-containing plasma.

Description:
TECHNICAL FIELD  
       [0001]     The invention pertains to methods of forming materials comprising tungsten and nitrogen, and in an exemplary application pertains to methods of forming capacitors.  
       BACKGROUND OF THE INVENTION  
       [0002]     Tungsten nitride has properties which render it particularly suitable so for utilization in integrated circuitry. For instance, tungsten nitride is found to exhibit better or equivalent electrical properties when compared to such commonly utilized compositions as, for example, TiN. Further, tungsten nitride retains its good electrical properties after being subjected to relatively high temperature processing, such as a polysilicon anneal or borophosphosilicate glass (BPSG) reflow.  
         [0003]     Tungsten nitride materials can be formed by, for example, chemical vapor deposition processes, such as, for example, plasma enhanced chemical vapor deposition (PECVD). The tungsten nitride materials formed by such methods can have good step coverage over an underlying substrate and be continuous, particularly if formed at lower working ends of temperature and plasma power ranges. However, utilization of such tungsten nitride materials has been limited due to difficulties in working with the materials. Specifically, tungsten nitride can peel, and/or bubble, and/or crack when exposed to high temperature processing (such as, for example, the greater than 800° C. processing associated with anneal steps). The peeling, cracking and bubbling lead to a non-continuous film. It would be desirable to develop methods of forming materials comprising tungsten nitride which overcome problems associated with tungsten nitride exposure to high temperature processing conditions.  
       SUMMARY OF THE INVENTION  
       [0004]     In one aspect, the invention includes a method of forming a material comprising tungsten and nitrogen. A layer comprising tungsten and nitrogen is deposited over a substrate. Subsequently, and in a separate step from the depositing, the layer comprising tungsten and nitrogen is exposed to a nitrogen-containing plasma.  
         [0005]     In another aspect, the invention includes a method of forming a capacitor. A first electrical node is formed and a dielectric layer is formed over the first electrical node. A second electrical node is formed and separated from the first electrical node by the dielectric layer. A layer comprising tungsten and nitrogen is provided between the dielectric layer and one of the electrical nodes. The providing the layer comprising tungsten and nitrogen includes: a) depositing a layer comprising tungsten and nitrogen; and b) in a separate step from the depositing, exposing the layer comprising tungsten and nitrogen to a nitrogen-containing plasma.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     Preferred embodiments of the invention are described below with reference to the following accompanying drawings.  
         [0007]      FIG. 1  is a fragmentary, diagrammatic, cross-sectional view of a semiconductor wafer fragment at a preliminary step of a method of the present invention.  
         [0008]      FIG. 2  is a view of the  FIG. 1  wafer fragment shown at a processing step subsequent to that of  FIG. 1 .  
         [0009]      FIG. 3  is a view of the  FIG. 1  wafer fragment shown at a processing step subsequent to that of  FIG. 2 .  
         [0010]      FIG. 4  is a view of the  FIG. 1  wafer fragment shown at a processing step subsequent to that of  FIG. 4 .  
         [0011]      FIG. 5  is a fragmentary, diagrammatic, cross-sectional view of a semiconductor wafer fragment at a preliminary step of a second embodiment method of the present invention.  
         [0012]      FIG. 6  is a view of the  FIG. 5  wafer fragment shown at a processing step subsequent to that of  FIG. 5 .  
         [0013]      FIG. 7  is a view of the  FIG. 5  wafer fragment shown at a processing step subsequent to that of  FIG. 6 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8).  
         [0015]     The invention encompasses methods of forming materials comprising tungsten and nitrogen. An exemplary method of the present invention is described with reference to a semiconductor wafer fragment  10  in  FIGS. 1 and 2 . Referring to  FIG. 1 , wafer fragment  10  comprises a substrate  12  and a layer  14  formed over substrate  12 . Substrate  12  includes a step  16 . Substrate  12  can comprise, for example, a conductive material, or an insulative material. Exemplary conductive materials include, for example, conductively doped polysilicon and metals, such as, for example, copper. Conductive materials of substrate  12  can be incorporated into, for example, interconnect lines. Exemplary insulative materials include, for example, silicon dioxide, tantalum pentoxide (Ta, 2 O 5 ) and barium strontium titanate (BST). The insulative material can have a dielectric constant or “K” value which is greater than or equal to about 10. For instance, Ta 2 O 5  comprises a “K” value of from about 10to about 25, and BST comprises a “K” value of from about 80to about 1,000 or greater.  
         [0016]     Layer  14  comprises tungsten and nitrogen, and can, for example, consist essentially of tungsten nitride. Such tungsten nitride can have the chemical formula WN x , wherein “x” is from 0.05 to 0.5. In one aspect, layer  14  is a tungsten nitride layer. Tungsten nitride layer  14  can be formed by, for example, chemical vapor deposition utilizing WF 6  and N 2  and H 2  as precursors, with either He or Ar as a carrier gas. The deposition can be plasma enhanced, with a plasma power of from a about 50 watts to about 700 watts. A temperature of a substrate upon which deposition occurs can be from about 170° C. to about 550° C., and a pressure within the deposition chamber can be from about 500 mTorr to about 8 Torr. The described conditions are for deposition of tungsten nitride over a single semiconductor material wafer.  
         [0017]     Tungsten nitride layer  14  is preferably formed to a thickness of from about 30 Å to about 2000 Å, and more preferably from about 50 Å to about 500 Å. An exemplary thickness of layer  14  is from about 150 Å to about 500 Å. The shown layer  14  has a number of defects. Specifically, voids (or cracks)  20  occur throughout layer  14 . An additional defect is a bubble  22  formed within layer  14  at an interface of layer  14  and substrate  12 . The above-described defects can occur either during deposition of layer  14 , or during high temperature processing subsequent to the deposition.  
         [0018]     Referring to  FIG. 2 , layer  14  is exposed to a nitrogen-containing plasma in accordance with a method of the present invention. Such exposure removes at least some of defects  20  and  22 . After the exposure, layer  14  forms a stable film over substrate  12 , with the term “stable” indicating that layer  14  is resistant to formation of cracks, voids or bubbles during subsequent processing.  
         [0019]     The plasma to which layer  14  is exposed preferably comprises a nitrogen-containing compound that does not contain oxygen. Suitable compounds are, for example, N 2  and NH 3 .  
         [0020]     Exemplary conditions for treating layer  14  in accordance with the present invention include subjecting layer  14  to a plasma within a reaction chamber at a temperature of from about 170° C. to about 550° C., and a pressure of from about 500 mTorr to about 8 Torr. N 2  gas is flowed into the chamber at a rate of from about 50 standard cubic centimeters per minute (sccm) to about 800 sccm, and a plasma is maintained within the chamber at a plasma power of from about 100 watts to about 800 watts. One or more of H 2  and Ar can be flowed into the chamber in addition to the N 2 . If H 2  is flowed, it is preferably flowed at a rate of from about 50 sccm to about 800 sccm, and if Ar is flowed, it is preferably flowed at a rate of from about 200 sccm to about 2,000 sccm. An exposure time of a substrate to the plasma of from about 10 seconds to about 80 seconds is found to be generally sufficient to cure defects in a tungsten nitride layer having a thickness of less than or equal to about 2000 Å, and to convert such layer to a stable film.  
         [0021]     The treatment discussed above with reference to  FIG. 2  is conducted in a discrete step separate from the step of forming layer  14  that is discussed with reference to  FIG. 1 . The separate step of  FIG. 2  can, however, be conducted in the same chamber as the layer-forming step of  FIG. 1  by ceasing the forming step while maintaining a plasma utilized for the forming step. For instance, in embodiments wherein WF 6  and either N 2  or NH 3  are utilized as precursors in the layer-forming step of  FIG. 1 , the layer-forming step can be stopped by ceasing a flow of WF 6  into the reaction chamber. If the nitrogen precursor flow and plasma are maintained within the chamber, the treatment described with reference to  FIG. 2  can proceed.  
         [0022]     Another aspect of the invention is described with reference to  FIGS. 3 and 4 . In this aspect, the layer  14  formed above by the processing of  FIGS. 1 and 2  is utilized as a substrate for formation of a second layer  30  comprising tungsten and nitrogen. Second layer  30  can be formed by identical processing as that described above with reference to  FIG. 1 . Layer  30  can then be treated by processing analogous to that described above with reference to  FIG. 2  to eliminate defects and form the construction illustrated in  FIG. 4 .  
         [0023]     Layers  14  and  30  of  FIG. 4  together comprise a mass  32  of tungsten and nitrogen. The tungsten and nitrogen of mass  32  can, for example, be in the form of tungsten nitride.  
         [0024]     It is noted that although the above-described embodiments illustrate a tungsten nitride material being treated with a plasma after formation of defects in the material, the invention also encompasses methods wherein a tungsten nitride material is treated with plasma before defects occur. For instance, in one aspect the invention encompasses treating a tungsten nitride material that is substantially free of defects with a plasma comprising a nitrogen-containing compound (preferably a nitrogen-containing compound that lacks oxygen). Such treatment can densify the tungsten nitride material to render it less susceptible to prior art problems associated with high temperature processing of tungsten nitride materials.  
         [0025]     Another embodiment of the invention is described with reference to a semiconductor wafer fragment  50  in  FIGS. 5-7 . Referring to  FIG. 5 , wafer fragment  50  comprises a substrate  52  and an insulative layer  54  formed over substrate  52 . Insulative layer  54  can comprise, for example, BPSG. Substrate  52  can comprise, for example, monocrystalline silicon lightly doped with a p-type background dopant. To aid in interpretation of the claims that follow, the term “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive material such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.  
         [0026]     An electrical node  56  is provided within substrate  52 . Node  56  can comprise, for example, a conductively doped diffusion region. Such diffusion region can be formed by implanting a conductivity-enhancing impurity into substrate  52 .  
         [0027]     An opening  58  extends through insulative material layer  54  and to node  56 . Opening  58  can be formed by conventional methods, such as, for example, an etch utilizing CF/CHF 3  and a plasma.  
         [0028]     An electrically conductive material  60  is formed within opening  58 , and a dielectric material  62  is formed over conductive material  60 . Conductive material  60  and dielectric material  62  can be formed by conventional methods, such as, for example, chemical vapor deposition and photolithographic processing. Conductive material  60  can comprise, for example, a metal-containing layer, such as, titanium nitride or titanium. Alternatively, conductive material  60  can comprise conductively doped polysilicon. In yet other alternative embodiments, conductive material  60  can comprise tungsten nitride formed in accordance with the methods of the present invention described above. Dielectric material  62  can comprise, for example, a dielectric material having a “K” value greater than or equal to 10.  
         [0029]     A layer  64  comprising tungsten and nitrogen is formed over dielectric material  62 . Layer  64  can be formed by, for example, the processing described above with reference to  FIG. 1 , and comprises a number of defects. Generally, it is found to be particularly difficult to form tungsten nitride over dielectric materials having “K” values of a greater than 10 utilizing prior art methods.  
         [0030]     Referring to  FIG. 6 , layer  64  is exposed to a nitrogen-containing plasma under conditions such as those described above with reference to  FIG. 2 . The exposure to the plasma removes the defects from layer  64  and converts layer  64  to a conformal and stable layer over dielectric material  62 . Layers  60 ,  62  and  64  now together comprise a capacitor construction  70 , with layers  60  and  64  comprising electrodes of such capacitor construction.  
         [0031]     Capacitor construction  70  can be incorporated as is into integrated circuitry. Alternatively, subsequent processing can be conducted to add a second conductive layer over layer  64  to increase a thickness of the top electrode of capacitor  70 .  FIG. 7  illustrates wafer fragment  50  after such subsequent processing, and specifically illustrates an additional conductive layer  72  formed over layer  64 . Layer  72  can comprise, for example, an additional tungsten nitride layer formed in accordance with the processing described above with reference to  FIGS. 3 and 4 . Alternatively, layer  72  can comprise a conductive material other than tungsten nitride, such as, for example, conductively doped polysilicon, or a metal-containing layer. In alternative methods of describing capacitor structure  70  of  FIG. 7 , layer  64  can be considered as part of an upper electrode of the capacitor structure, or as being between dielectric layer  62  and an upper electrode consisting of layer  72 .  
         [0032]     In the shown embodiment, capacitor construction  70  is a container-type capacitor. The invention encompasses other embodiments (not shown) wherein the capacitor has a shape other than a container-type structure.  
         [0033]     In the shown embodiment, tungsten nitride layer  64  is formed between dielectric layer  62  and an upper conductive electrode  72 . However, it is to be understood that the invention encompasses other embodiments (not shown) wherein layer  64  is formed between dielectric layer  62  and lower electrode  60 , either in addition to, or alternatively to forming layer  64  between dielectric layer  62  and upper electrode  72 .  
         [0034]     It is noted that an advantage of providing tungsten nitride layer  64  between dielectric layer  62  and a capacitor electrode is that tungsten nitride layer  64  can function as a barrier layer to alleviate or prevent diffusion of materials between dielectric layer  62  and conductive layer  72 .  
         [0035]     In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.