Abstract:
On a semiconductor film to function as a lead-out electrode of a semiconductor element, a metal silicide film and a metal nitride film are successively provided, whereby alloying and inferior contact resistances attributed to heat during wiring with aluminum can be effectively suppressed, so that the reliability of a semiconductor device can be enhanced.

Description:
This is a continuation of application Ser. No. 07/063,023, filed June 17, 1987 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor device, and more particularly to a technique which is effective when applied to the formation of an electrode in the case of employing a semiconductor film for leading out the electrode. 
     In, for example, a bipolar LSI of SICOS (Side Wall Base Contact) structure, the base of a bipolar transistor is led out by a boron-doped polycrystalline Si (silicon) film, on which an Al-alloy electrode is formed (refer to, for example, the official gazette of Japanese Patent Application Laid-open No. 1556/1981). 
     Besides, the emitter, base and collector of a bipolar transistor are led out by multilayer films each consisting of a polycrystalline silicon film and platinum silicide (PtSi), and aluminum electrodes (wiring layers) are formed on the polycrystalline silicon films (described in, for example, IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. SC-15, No. 4, AUGUST 1980, pp. 455-458). 
     Hereinbelow, for the sake of convenience, the expression &#34;electrode&#34; shall sometimes refer to, for example, a lead-out conductor layer which is connected near the contact hole of an aluminum wiring layer or to a base, emitter or collector or a source or drain diffused layer. 
     SUMMARY OF THE INVENTION 
     The inventors studied the electrode formation on the polycrystalline Si film and the electrode formation on the multilayer film consisting of the polycrystalline Si film and platinum silicide. The technique studied by the inventors, which was not known, will be outlined below: 
     According to the results of experiments conducted by the inventors, a polycrystalline Si film doped with boron is far more difficult with respect to controlling the growth of crystal grains as compared with using a polycrystalline Si film doped with arsenic or phosphorus, and that crystal grain growth of the former hardly takes place in the manufacturing process of an LSI. As a consequence, the boron-doped polycrystalline Si film remains in an unstable state in which the film itself stores large quantities of grain boundary energy. Therefore, in the case where an electrode made of an Al-alloy film is formed directly on the boron-doped polycrystalline Si film, a problem arises in that the electrode is alloyed with the polycrystalline Si film during the formation thereof, thereby resulting in the manufacture of a defective unit. 
     For such a reason, in a bipolar LSI wherein a base is led out by the boron-doped polycrystalline Si film, after the polycrystalline Si film has been formed, an electrode made of an Al-alloy film is formed thereon through a platinum silicide (PtSi) film. 
     The inventors, however, have found out that, even in the case where the electrode made of the Al-Si-alloy film is formed on the polycrystalline Si film through the platinum silicide film as stated above, the refractory characteristics of the electrode is not sufficient, so the alloying between the electrode and the polycrystalline Si film is prone to occur during the formation of the Al-alloy electrode. Further,.in a case where a transition metal or an alloy thereof, such as W, Mo or TiW, is used instead of the platinum silicide film, the refractory characteristics is still insufficient because the material itself has the property wherein it easily reacts with Si to form a silicide. 
     An object of the present invention is to provide a technique capable of enhancing the refractory characteristics of an electrode. 
     The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings. 
     A typical aspect of performance of the present invention is as summarized below: 
     A metal silicide film and a metal nitride film which is electrically conductive are successively disposed on a semiconductor film, and an electrode is disposed on the metal nitride film. 
     According to the above expedient, the alloying between the semiconductor film and the electrode is effectively prevented especially by the metal nitride film, so that the refractory characteristics of the electrode can be enhanced. Moreover, the contact resistance of the electrode can be stabilized by the metal silicide film. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view which shows a bipolar LSI of SICOS structure according to Embodiment I of the present invention; and 
     FIG. 2 is a sectional view which shows complementary metal-oxide semiconductor field effect transistors (CMOSFETs) according to Embodiment II of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, the construction of the present invention will be described on the basis of embodiments with reference to the drawings. 
     Embodiment I 
     As illustrated in FIG. 1, in a bipolar LSI of SICOS structure according to Embodiment I, a semiconductor substrate 1 such as a p -  -type Si substrate by way of example is provided with a buried layer 2 of n +  -type. A Si epitaxial layer 3 of, for example, n -  -type is disposed on the semiconductor substrate 1. The part of the Si epitaxial layer 3 overlying one end of the buried layer is etched into the shape of a mesa, on which a base region 4 of p-type is disposed. Further, an emitter region 5 of n +  -type is formed in the base region 4. An emitter electrode 6 made of, for example, an Al-Si-alloy film is disposed on the emitter region 5 through a metal silicide film 13 and a metal nitride film 14 which will be described later. A collector region of n-type is configured by the Si epitaxial layer 3 between the base region 4 and the buried layer 2. Numeral 7 denotes an electrode lead-out region of n +  -type which is connected with the buried layer 2, and a collector electrode 8 made of, for example, an Al-Si-alloy film is formed on the electrode lead-out region 7 through a metal silicide film 13 and a metal nitride film 14 to be described later. 
     Meanwhile, a field insulator film 9 such as an SiO 2  film, by way of example, is formed around the mesa-shaped part of the Si epitaxial layer 3, whereby the elements of the LSI are isolated. Under the field insulator film 9, a channel stopper region 10 of p +  -type is formed, thereby insert preventing a parasitic channel from appearing. In addition, a polycrystalline Si film 11 of p +  -type which is heavily doped with boron by way of example is formed on the field insulator film 9 so as to be connected with the base region 4, whereby the base is led out. On the surface of the polycrystalline Si film 11, an insulator film 12, for example, SiO 2  film which is formed by, for example, the thermal oxidation of this polycrystalline Si film 11 is provided continuously to the field insulator film 9. 
     A contact hole 12a is provided in the part of the insulator film 12 corresponding to one end of the polycrystalline Si film 11. Through this contact hole 12a, the polycrystalline Si film 11 is overlaid with a metal silicide film 13 such as a platinum silicide film or palladium silicide film having a thickness of about 200 Å, by way of example, and a metal nitride film 14 such as a titanium nitride (TiN) film having a thickness of about 1000 Å, by way of example, and a base electrode 15 made of an Al-Si-alloy film by way of example is formed on the metal nitride film 14. The metal nitride film 14 is a ceramic having an electric conductivity, which is very stable thermally, has excellent refractory characteristics and which also exhibits a low reactivity with Si. Therefore, the metal nitride film 14 can effectively prevent the occurrence of the alloying of the electrode 15 with the polycrystalline Si film 11 at the step of forming this electrode, and it can consequently enhance the refractory characteristics of the electrode. Accordingly, enhancement in the reliability of the electrode can be achieved. Furthermore, owing to the metal silicide film 13, the contact resistance of the electrode 15 with respect to the polycrystalline Si film 11 can be stabilized. In the case where the metal silicide (PtSi) film 13 and the metal nitride (TiN) film 14 are formed on the polycrystalline Si film 11 in the order mentioned, the contact resistance of the aluminum electrode (wiring layer) 15 remains constant for above 10 hours in spite of annealing at 475° C. 
     Next, a method of manufacturing the bipolar LSI according to the embodiment I will be described. 
     First, as illustrated in the drawing, a buried layer 2, a Si epitaxial layer 3, a field insulator film 9, a channel stopper 10 and a boron-doped polycrystalline Si film 11 are formed, whereupon the surface of the Si epitaxial layer 3 is thermally oxidized in the state in which it is covered with an oxidation impermeable film (not shown) such as an Si 3  N 4  film, by way of example, thereby to form an insulator film 12 on the surface of the polycrystalline Si film 11. Subsequently, an electrode lead-out region 7 is formed within the Si epitaxial layer 3 by, for example, the selective diffusion of phosphorus, whereupon a p-type impurity and an n-type impurity are successively ion-implanted, by way of example, thereby to successively form a base region 4 and an emitter region 5 within the Si epitaxial layer 3. Subsequently, the predetermined parts of the insulator film 12 are etched and removed to form contact holes 12a. Subsequently, a metal film such as a platinum film or palladium film by way of example is formed on the whole surface of the resulting structure by, for example, evaporation and is sintered by a predetermined annealing, whereupon the unreacted metal film is etched and removed with, for example, aqua regia (a mixed solution consisting of HCl and HNO 3 ), thereby to form metal silicide films 13 such as platinum silicide films or palladium silicide films on the parts of the polycrystalline Si film 11, the emitter region 5 and the electrode lead-out region 7 corresponding to the contact holes 12a. Subsequently a metal nitride film 14 such as a titanium nitride film by way of example is formed on the whole surface by, for example, sputtering, whereupon an Al-Si-alloy film, for example, is further formed on the whole surface of the metal nitride film 14. These films are successively patterned into predetermined shapes by, for example, dry etching, thereby to form electrodes 6, 8 and 15. Then, an intended bipolar LSI is completed as shown in the drawing. 
     Embodiment II 
     As illustrated in FIG. 2, in complementary metal-oxide semiconductor field effect transistors (hereinbelow, abbreviated to CMOSFETs) according to Embodiment II, a semiconductor substrate 1 such as a p -  -type Si substrate by way of example is provided with an n-type well region 6. A field insulator film 9 made of, for example, an SiO 2  film is disposed on the selected area of the surface of the semiconductor substrate 1. The active region of the n-type well region 16 is overlaid with a gate insulator film 17 which is made of an SiO 2  film, a gate electrode 18 which is made of a polycrystalline Si film formed by, e.g., CVD, a p-type diffused layer 19 which is formed by the ion implantation of boron (B), a side wall 21 which is made of an SiO 2  film formed by CVD, and p +  -type source and drain diffused layers 22 which are formed by the ion implantation of boron (B), whereby a p-type MOSFET of lightly doped drain (hereinbelow, abbreviated to &#34;LDD&#34;) structure is constructed. Meanwhile, likewise to the p-type MOSFET, the active region of the other region than the N-type well region 16 is overlaid with a gate insulator film 17 which is made of an SiO 2  film, a gate electrode 18 which is made of a polycrystalline Si film, an n -  -type diffused layer 20 which is formed by the ion implantation of phosphorus (P), a side wall 21 which is made of an SiO 2  film, and n +  -type source and drain diffused layers 23 which are formed by the ion implantation of arsenic (As), whereby an n-type MOSFET of LDD structure is constructed. Polycrystalline Si films of p +  -type 11A which are heavily doped with, e.g., boron (B) are disposed on the p-type source and drain diffused layers 22 of the p-type MOSFET, while polycrystalline Si films of n +  -type 11B which are heavily doped with, e.g., phosphorus (P) are disposed on the n +  -type source and drain diffused layers 23 of the n-type MOSFET, whereby the sources and drains of both MOSFETs are respectively led out. On each of the polycrystalline Si films 11A and 11B, a metal silicide film 13 which is a platinum silicide film about 200 Å thick by way of example and a metal nitride film 14 which is a titanium nitride (TiN) film about 1000 Å thick by way of example are provided for the same purpose as in Embodiment I. An inter-layer insulator film 24 made of an SiO 2  film is formed on the whole surface of the resulting p -  -type Si substrate 1, and it is selectively etched, whereby contact holes 12B are provided in predetermined parts. Wiring layers 15 made of Al-Si-alloy films by way of example are provided, and are respectively connected to the metal nitride films 14 through the contact holes 12B. The wiring layers 15 selectively connect the electrodes of elements. As in Embodiment I, the lead-out electrodes constructed of the polycrystalline Si films 11A, 11B, metal silicide films 13 and metal nitride films 14 have excellent refractory characteristics and stabilize the contact resistances of the wiring layers 15 made of the Al-Si-alloy films. A protective film 25 which is made of a multilayer film consisting of an SOG film and a PSG film by way of example is provided on the wiring layers 15, etc. 
     Next, a method of manufacturing the CMOSFETs according to Embodiment II will be described. 
     As illustrated in the drawing, an n-type well region 16, a field insulator film 9, gate insulator films 17, gate electrodes 18, p -  -type diffused layers 19, n -  -type diffused layers 20, side walls 21, p +  -type diffused layers 22 and n +  -type diffused layers 23 are successively formed by well-known processes for producing MOSFETs. Thereafter, a polycrystalline silicon film for forming p-type polycrystalline silicon films 11A and n-type polycrystalline silicon films 11B is formed on the whole surface of the resulting p -  -type Si substrate 1 by, e.g., CVD, and impurities such as boron (B) and phosphorus (P) are respectively diffused into the selected parts of the polycrystalline silicon film formed. After the selective diffusion of the impurities, a metal silicide film made of platinum silicide and a metal nitride film made of titanium nitride are successively stacked and formed on the whole surface of the polycrystalline silicon film by the same method as in Embodiment I. Further, the selected parts of the metal nitride film, metal silicide film and polycrystalline silicon film formed as described above are continuously etched by, for example, anisotropic dry etching, to thereby form source and drain lead-out electrodes made up of the polycrystalline silicon films 11A, 11B, metal silicide film 13 and metal nitride film 14. Thenceforth, inter-layer insulator films 24 made of SiO 2 , wiring layers 15 made of an Al-Si alloy, and a protective film 25 consisting of an SOG film and a PSG film are successively formed by well-known processes, whereby intended CMOSFETs are produced. 
     Although, in the above, the invention made by the inventors has been specifically described in conjunction with the embodiments illustrated, it is not to be construed as being limited to the disclosed embodiments, but that it may include various other embodiments including obvious variations of the embodiments disclosed without departing from the spirit and scope thereof. 
     By way of example, while the g embodiments have referred to the cases of applying the present invention to bipolar LSI and the CMOSFETs which employ the boron-doped polycrystalline Si film 11 for leading out the base, the present invention is also applicable to a case as explained below. As already stated, a polycrystalline Si film doped with phosphorus or arsenic is more liable to effect in the growth of crystal grains than that of a polycrystalline Si film doped with boron. However, when the phosphorus or arsenic-doped polycrystalline Si film has the quantity of doping set smaller than the limit of solid-solubility of the impurity in Si to the end of using the film as, for example, a resistance element, it is difficult to undergo a growth of crystal grains similar to the boron-doped polycrystalline Si film, and the sizes of the crystal grains sometimes have values which are smaller than the thickness of the polycrystalline Si film by way of example. Even in the case of forming an electrode on such a polycrystalline Si film doped with phosphorus or arsenic below the limit of solid-solubility, the present invention can be applied and can thus enhance the refractory characteristics of the electrode. 
     In addition, the present invention can be applied to bipolar LSIs not having the SICOS structure and also to various semiconductor devices other than bipolar LSIs.