Abstract:
The present invention relates to a diffusion barrier layer for a semiconductor device and fabrication method thereof. The diffusion barrier layer according to the present invention is fabricated by forming a diffusion barrier layer containing a refractory metal material and an insulating material on an insulating layer and in a contact hole, wherein the insulating layer being partially etched to form the contact hole, is formed on a semiconductor substrate; and annealing the diffusion barrier layer. Therefore, an object of the present invention is to provide a diffusion barrier layer for a semiconductor device, which is of an amorphous or microcrystalline state and thermodynamically stable even at a high temperature since an insulating material is bonded to a refractory metal material in the diffusion barrier layer.

Description:
This application is a continuation-in-part of application No. 09/196,330 filed on Nov. 19, 1998, now abandoned the entire contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a semiconductor device, and more particularly to a diffusion barrier layer for a semiconductor device and a fabrication method thereof which is stable even at a high temperature by combining an insulating material and a refractory metal. 
     BACKGROUND OF THE INVENTION 
     A diffusion barrier layer in a semiconductor device delays diffusion or prevents a chemical reaction between an interconnection material and a substrate material or between interconnection materials. Therefore, a stable diffusion barrier layer is essential for the development of reliable semiconductor devices. Since it is almost impossible for the diffusion barrier layer to completely prevent the diffusion, the performance of the diffusion barrier layer depends upon how long the diffusion barrier layer can play its part under various annealing conditions. The diffusion barrier layer is required to have properties, such as being stable thermodynamically even when being in contact with the interconnection and the substrate material, having low contact resistance and excellent adhesivity, being tolerable to thermal and mechanical stress and having high electric conductivity. Further, it is desirable that a coefficient of thermal expansion of the diffusion barrier layer is similar to that of the substrate material. 
     Such diffusion barrier layer is mainly divided into a passive barrier, a sacrificial barrier and a stuffed barrier. More specifically, the passive barrier prevents the reaction with the interconnection and the substrate material by using a material which is thermodynamically stable and chemically inert. The sacrificial barrier layer reacts with the interconnection material or the substrate material, but the reaction is very slow. Thus, the sacrificial barrier layer serves as the diffusion barrier layer until it is exhausted due to the reaction with the interconnection material or the substrate material. Lastly, the stuffed barrier prevents the diffusion by filling other materials into grain boundaries that become the paths of the diffusion. Here, the diffusion barrier layer according to the present invention belongs to the stuffed barrier. As mentioned above, stuffing implies filling of other material into the grain boundaries. 
     Generally, the grain boundaries have been known as fast diffusion paths, since the diffusion along the grain boundaries occurs much more easily than through crystallites in a poly-crystalline thin film. Therefore, to prevent the diffusion along the grain boundaries, single crystal or material which has no grain boundary, or the stuffed film in which other materials are filled in the grain boundaries is used as conventional diffusion barrier layers. Among the conventional diffusion barrier layers, however, the amorphous diffusion barrier layer which is thermodynamically unstable is transformed into a crystalline structure and thus there exists grain boundaries. 
     As a fabrication method of the conventional stuffed barrier layer, there is a method for blocking the grain boundaries by precipitating into the grain boundaries a precipitation, or implanting a material into the grain boundaries by diffusing a impurity gas in the atmosphere. Most popular examples are nitrogen stuffing and oxygen stuffing. Particularly, the nitrogen stuffing is to precipitate nitrogen into grain boundaries by depositing a thin film which contains nitrogen in excess of its limit. The oxygen stuffing is to implant oxygen into the grain boundaries by performing the oxygen plasma treatment or annealing in oxygen atmosphere after thin film deposition. Using such implantation, nitrogen can be implanted. 
     However, in these methods, since nitrogen or oxygen is weakly bound with the matrix thin film, the stuffing effect becomes extinct when the annealing process is performed for a long time. Also, in implantation by using the plasma treatment, the thin film is damaged due to high ion energy, which results in bond break in the thin film and crystal defects such as dislocation, void and interstitial, etc. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a diffusion barrier layer and a fabrication method thereof that obviate the problems according to the related art. 
     An object of the present invention is to provide a diffusion barrier layer for a semiconductor device that is thermodynamically stable even at a high temperature and a fabrication method thereof. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, there is provided a diffusion barrier layer including an insulating material and a refractory metal, the insulating material being bonded to the refractory metal material and the diffusion barrier layer being in a microcrystalline or amorphous state. 
     Further, in order to achieve to the object of the present invention, there is provided a fabrication method of a diffusion barrier layer for a semiconductor device includes the steps of: forming a diffusion barrier layer containing a refractory metal material and an insulating material on an insulating layer and in a contact hole, wherein the insulating layer being partially etched to form the contact hole is formed on a semiconductor substrate; and annealing the diffusion barrier layer. 
     The foregoing and other objectives of the present invention will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIGS. 1A-1C are vertical cross-sectional diagrams sequentially illustrating a method of fabricating a diffusion barrier layer of a semiconductor device according to the present invention; 
     FIG. 2 is a graph illustrating sheet resistance of a Ta—CeO 2  diffusion barrier layer that has been subjected to annealing between 500° C. and 800° C. at various sputtering power according to an embodiment of the present invention; 
     FIG. 3 is a graph showing Ta 4 f XPS spectra of a Ta thin film; 
     FIG. 4 is a graph showing Ta 4 f XPS spectra of a Ta-CeO 2  diffusion barrier layer formed at 150 W of sputtering power without an annealing process according to the present invention; 
     FIG. 5 is a graph showing Ta 4 f XPS spectra of a Ta—CeO 2  diffusion barrier layer formed at 150 W of sputtering power and annealed at a temperature of 800° C. according to the present invention; 
     FIG. 6 is a graph illustrating XRD patterns of a Ta—CeO 2  diffusion barrier layer formed at 170 W of sputtering power and annealed at various temperatures according to the present invention; and 
     FIG. 7 is a graph illustrating XRD patterns of a Ta—CeO 2  diffusion barrier layer formed at 150 W of sputtering power and annealed at various temperatures according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIGS. 1A-1C are vertical cross-sectional diagrams sequentially illustrating a fabrication method of a diffusion barrier layer of a semiconductor device according to the present invention. 
     First, FIG. 1A shows a cross-sectional diagrams in which a contact hole  30  is formed by etching a predetermined portion of an insulating layer  20  applied on a semiconductor substrate  10 . As shown in FIG. 1B, a diffusion barrier layer  40  consisting of Ta—CeO 2  is formed on the insulating layer  20  and in the contact hole  30  by co-sputtering and then an annealing process is performed at a temperature of 750° C. for 30 minutes to the Ta—CeO 2  diffusion barrier layer  40  for achieving the thermal stabilization thereof. 
     Such co-sputtering deposition employs a first target containing Ta, a refractory metal, and a second target containing CeO 2 , an insulating material. While, the diffusion barrier layer  40  can be formed in other ways such as a sputtering deposition using a target or a pallet which contains the refractory metal material and the insulating material. The diffusion barrier layer  40  can be formed in another ways such as any kind of chemical vapor deposition, including a chemical vapor deposition which employs a compound containing the refractory metal material and the insulating material in CVD equipments. 
     Here, it is noted that at least one of  4 B,  5 B and  6 B groups is used as the refractory metal, the  4 B,  5 B and  6 B groups including Ti, Ta, Mo and W, and the insulating material consists of oxide or nitride. Further, the annealing process is performed for at least 10 minutes and preferably for 10 minutes to an hour, at a temperature of 450° C. to 750° C. Here, it is noted that the optimum conditions of the annealing process are determined by a material of an interconnection to be formed in a following process. 
     Accordingly, the fabrication of the diffusion barrier layer is completed and then followed by a next process including the forming of the interconnection. That is, as shown in FIG. 1C, an interconnection  50  is formed on the diffusion barrier layer  40 , the interconnection  50  consisting of at least one of Al, Al alloy, Cu and Cu alloy. 
     FIG. 2 illustrates relation between sheet resistance of the Ta—CeO 2  diffusion barrier layer and annealing temperature when the Ta—CeO 2  diffusion barrier layer is deposited at a thickness of 100 nm according to the embodiment of the present invention and annealed between 500° C. and 800° C. at various sputtering power(e.g., 130 W, 150 W and 170 W) in a vacuum. As shown therein, the sheet resistance of the Ta—CeO 2  diffusion barrier layer is considerably low in the measuring range, except for which the sputtering power is 170 W and the annealing temperature is about 800° C. The thin film formed at 170 W of the sputtering power and annealed at 800° C., shows the relatively high sheet resistance, because much CeO 2  exist in the diffusion barrier layer. However, although the sheet resistance in the above case is relatively high among sheet resistance values, it still belongs to a range of low sheet resistance values required for the diffusion barrier layer. Therefore, the diffusion barrier layer shows the excellent property, that is, low sheet resistance in the entire measuring range when the Ta—CeO 2  diffusion barrier layer is formed at 130 W, 150 W and 170 W of the sputtering power and annealed at the temperatures from 500° C. to 800° C. 
     The diffusion barrier layer according to the present invention maintains the low sheet resistance even at the high temperature of 800° C., because CeO 2  stuffed in the Ta—CeO 2  diffusion barrier layer is not just filled therein, but bonded to Ta. The above fact can be certified by analyzing Ta bonds by performing X-ray photoelectron spectroscopy (XPS). FIG. 3 shows Ta 4 f XPS spectra when only Ta is deposited by a sputtering method. As shown therein, there are shown three spectra at about 22 eV ( 1 ), 24 eV ( 2 ) and 34 eV ( 3 ), respectively. Therefore, there exist bonds having binding energy of about 22 eV, 24 eV and 34 eV, respectively, in the Ta thin film, and the three peaks ( 1 ,  2 ,  3 ) are the specific spectra of Ta 4 f. 
     FIG. 4 shows Ta 4 f XPS spectra for a Ta—CeO 2  diffusion barrier layer formed at 150 W of the sputtering power without annealing. As can be seen, two more peaks are shown at about 26 eV ( 4 ) and 28 eV ( 5 ), respectively, in addition to the three peaks ( 1 ,  2 ,  3 ) of 22 eV, 24 eV and 34 eV, respectively as shown in FIG.  3 . Such two more peaks ( 4 ,  5 ) result from Ta—O bond and Ta—O—Ce bond, because, when Ta—CeO 2  are deposited, some oxygen, decomposed from the CeO 2  target, is combined with Ta in a plasma condition. Here, it is noted that the peak ( 4 ) at about 26 eV more increases after the annealing process. 
     FIG. 5 illustrates Ta 4 f XPS spectra for a Ta—CeO 2  diffusion barrier layer formed at 150 W of the sputtering power and annealed at a temperature of 800° C. As shown therein, peaks ( 1 ,  2 ,  3 ) of the Ta thin film itself are shown at around 22 eV, 24 eV and 34 eV, respectively and the peak ( 4 ) at around 26 eV is considerably increased. Therefore, it can be realized that the annealing process increases the bond number of Ta and oxygen. Consequently, XPS shows that CeO 2  which is the insulating material is not simply filled in the Ta—CeO 2  diffusion barrier layer, but bonded to Ta which is the refractory metal. Further, as mentioned above, the diffusion barrier layer according to the present invention is in a microcrystalline or amorphous state, and which can be seen from X-ray diffraction (XRD) patterns. 
     FIG. 6 illustrates XRD patterns of a Ta—CeO 2  diffusion barrier layer formed at a thickness of 100 nm at 170 W of the sputtering power and annealed for about 30 minutes at various temperatures according to the present invention. As shown therein, in the XRD patterns when the diffusion barrier layer is formed without the annealing process, there appears a broad peak at about 37°, showing that the Ta—CeO 2  layer is an amorphous or microcrystalline state. The broad peak showing the amorphous or microcrystalline state has no change even if annealing temperature is increased up to 800° C. Accordingly, it can be seen that the Ta—CeO 2  diffusion barrier layer according to the present invention maintains its microcrystalline or amorphous state even at the high temperature, for example, at 800° C. 
     Further, any peak of Ta-silicide crystal generated by a reaction between Ta and the Si substrate, can not be seen, showing that the Ta—CeO 2  diffusion barrier layer according to the present invention has an excellent property that does not react on the semiconductor substrate. 
     FIG. 7 illustrates XRD patterns of a Ta—CeO 2  diffusion barrier layer deposited at a thickness of 100 nm at 150 W which is different from the sputtering power of FIG.  6  and annealed for about 30 minutes at various temperatures according to the present invention. As shown therein, the Ta—CeO 2  layer deposited in the sputtering power of 150 W is still of the amorphous or microcrystalline state up to an annealing temperature of 750° C. However, when the annealing temperature reaches 800° C., the broad peak at 37° is split as in dotted lines respectively indicating crystalline planes and thus the amorphous or microcrystalline structure is destroyed, showing that the Ta—CeO 2  diffusion barrier layer is crystallized. 
     As described above, the diffusion barrier layer for semiconductor device and the fabrication method thereof according to the present invention has several advantages. The diffusion barrier layer according to the present invention can be stable even at the high temperature of 800° C., since the insulating film is bonded to the refractory metal material in the diffusion barrier layer, while in the conventional nitrogen or oxygen stuffing, stuffed nitrogen or oxygen is diffused along the grain boundaries when annealing process is performed and thereby stuffing effect become extinct. 
     Further, the present invention does not induce the crystal defects in the thin film, due to the high ion energy needed to in conventional nitrogen or oxygen implantation by using the plasma treatment. In addition, since the refractory metal material and the insulating material constituent of the diffusion barrier layer according to the present invention are thermodynamically stable, reaction with the semiconductor substrate does not occur, thereby improving the reliability of the semiconductor device. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the diffusion barrier layer for the semiconductor device and the fabrication method thereof of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.