Interconnection structure of a semiconductor device and method of manufacturing the same

Abstract: A semiconductor device and a method of manufacturing the same wherein the first and second wirings (12, 14) with an interlayer insulating film (13) interposed therebetween are connected through a contact hole (15) formed in the interlayer insulating film (13). In the semiconductor device, the first and second wirings (12, 14) are connected via a low resistive, conductive metal layer (18) obtained by reducing a highly resistive oxide layer (16) with a highly oxidizing metal (17), the highly resistive oxide layer (16) being exposed within the contact hole (15) on the surface of the first wiring (12). In the method of manufactzuring a semiconductor device, a contact hole (15) is opened in the interlayer insulation (13) on the first wiring (12), a highly oxidizing metal (17) is deposited on the highly resistive oxide layer (16) on the surface of the hirst wiring (12) within the contact hole (15), and the highly resistive oxide layer (16) is reduced with the highly oxidizing metal (17) to change the highly resistive oyide layer to a low resistive, conductive metal layer (18). The second wiring (14) is connected to the first wiring (12) via the conductive metal layer. The reduction may be carried out before or after depositing the second wiring, or at the time when the highly oxidizing metal is deposited.

Description: BACKGROUND OF THE INVENTION (Field of the Invention) The present invention relates to a semiconductor device and a method of manufacturing the same and more particularly, to a semiconductor device having a multilayer wiring structure and a method of manufacturing the same. (Description of the Prior Art) A conventional multilayer interconnection structure of a semiconductor device will be described with reference to Fig. 3. A first aluminum wiring 2 is formed on a semiconductor substrate 1, and an interlayer insulating film 3 whose main components are silicon oxide film is formed over the aluminum wiring 2. A second aluminum wiring 4 formed on the interlayer insulating film 3 is electrically connected to the first aluminum wiring 2 via a contact hole 5 opened in the insulating interlayer film 3 so as to electrically connect the first aluminum wiring and the second aluminum wiring. The yield (conduction probability) of conduction decreases rapidly as the diameter of the contact hole 5 becomes very small as shown in Fig. 4. In Fig. 4, line (1) passing through white circles represents the case where the second aluminum wiring is deposited after sputter etching, and line (2) passing through black circles represents the case without sputter etching. As seen from line (2), there scarcely occurs conduction with the contact hole diameter of 1 micron (1 micron = 1000 nm), namely the conduction yield becomes 99.9 % or less. The reason for this is that after the contact hole 5 is formed, the surface of the first aluminum wiring 2 is in contact with air through the contact hole 5 until the second aluminum wiring 4 is formed thereon so that an alumina layer is formed on the surface of the first aluminum wiring 2 to prevent conduction between the first and second aluminum wirings 2 and 4. However, as the diameter of the contact hole 5 becomes large, it is likely for the alumina layer to have some defects such as pin holes or cracks through which conduction between the first and second aluminum wirings is allowed. In consideration of this, conventionally the alumina layer on the first aluminum wiring 2 has been removed by sputter etching with Ar ions. Thereafter, while shielding the alumina layer from air, i.e., maintaining in vacuum, the second aluminum wiring 4 is formed on the alumina layer under the same vacuum condition. With the above processes, the conduction yield was made in the order of 99.99 % even with the contact hole diameter of 1 micron as shown in Fig.4, at line (1). To further improve the yield of conduction, various sputter etching methods are now being developed. Although the conduction yield can be improved by such methods, it has been found that another problem may arise. Namely, where the first aluminum wiring 2 is connected to the gate electrode, a great amount of Ar ions through the sputter etching are implanted in the first aluminum wiring 2 via the contact hole 5 so that the gate oxide film is charged and destroyed. Such damage due to ion implantation becomes more serious as semiconductor devices become finer and the gate oxide film becomes thinner. As stated above, the conventional method of performing Ar ion sputter etching and removing the alumina layer on the aluminum wiring at the contact hole still poses the problem such as destroying the gate oxide film. From EP-A-0 042 926 there is known a semiconductor device in which a second metallic wiring is formed on a first metallic wiring formed on a semiconductor substrate via an interlayer insulating film, and the first metallic wiring conducts with the second metallic wiring through a contact hole formed in the interlayer insulating film. The first metallic wiring is a aluminum magnesium silicon layer and the second metallic wiring is a aluminum magnesium layer. During sintering the magnesium of either layer reacts with the native aluminum oxide layer between both metallic wirings to create an exothermic heat which removes the aluminum oxide film. From DE-A-3 414 781 there is known a similiar semiconductor device in which an intermediate layer of Ti or a Ti compound is provided between the insulating film and the second metallic wiring in order to prevent buckling between the second metallic wiring and the insulating film even during any thermal treatment without increasing the contact resistance between the first and second metallic wiring. The Article in Proc. of the 4th Int. IEEE VLSI Multilevel Interconnection Conf., June 1987, page 148-154, Santa Clara CA, USA: S. Murakami et al: "Plasma-nitrated Ti contacted sysetm for VLSI Interconnections" describes investigations on properties of TiN film for a Al/TiN/Ti/Si contact system interconnecting to n⁺- and p⁺⁻diffusion layers. A Ti layer is directly superposed on a Si layer or substrate to produe a TiSi₂ layer on the Si-layer during a heating process. A TiN layer superposed to the Ti layer apparently is not described to function as a barrier to reaction between the Ti layer and an upper Al layer. SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconductor device wherein the alumina layer on the first metallic wiring can be destroyed or removed without damaging the semiconductor device, in particular without increasing the contact resistance between the first and second wiring and further with preventing a negative influence on the second metallic wiring during removing the alumina layer on the first metallic wiring. The above object is solved according to claim 1 of the invention with a method of manufacturing a semiconductor device comprising the steps of: forming an interlayer insulating film on a first metallic wiring; opening a contact hole in the interlayer insulating film extending to the surface of the first wiring; depositing a highly oxidizing metallic layer on the interlayer insulating film and within the contact hole where a highly resistive oxide layer is formed on the first metallic wiring; depositing a barrier metallic layer on the highly oxidizing metallic layer, depositing a second wiring on the insulating film and within the contact hole for obtaining conduction between said first and second wirings; and reducing the highly resistive oxide layer with said highly oxidizing metallic layer to change the highly resistive oxide layer to a low resistive, conductive metal layer by means of heat treatment, said reduction step being performed at any time after said contact hole opening step. Therefore, the first and second metallic wirings can reliably conduct each other through the conductive metallic layer without giving any damage to the semiconductor device. Further features of the method of the present invention are apparent from dependent claims 2 to 9. The above object is also solved according to claim 10 of the invention with a semiconductor device comprising: a first metallic wiring formed on a semiconductor substrate, an interlayer insulating film having a contact hole through which said first metallic wiring conducts with a second metallic wiring, a highly oxidizing metal layer formed on the interlayer insulating film and in the contact hole, a second metallic wiring formed on the highly oxidizing metal layer, which is characterized in that a barrier metallic layer is formed between said highly oxidizing metal layer and said second metallic wiring, and at the junction between said first metallic wiring and said highly oxidizing metal layer a conductive alloy layer is formed, said conductive alloy layer being composed of the materials forming said first metallic wiring, said highly oxidizing metal layer and oxygen. The barrier metallic layer is excellent in adhesive strength with the second metallic wiring and reinforces the mechanical strength of the second metallic wiring. The first and second metallic wirings can reliably conduct each other without damage such as the semiconductor being damaged by ion etching. Further features of the semiconductor device of the present invention are apparent from dependent claims 11 and 12. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A to 1C show an example of the processes of manufacturing a semiconductor device leading to but not forming part of the present invention; Fig. 1D is a sectional view showing a different kind of a semiconductor device manufactured by the method of the first embodiment; Figs. 2A to 2C show the processes of manufacturing a semiconductor device according to the present invention; Fig. 2D is a sectional view showing a different kind of a semiconductor device according to the present invention. Fig. 3 is a sectional view showing a conventional semiconductor device; and Fig. 4 is a graph showing the probability of conduction between the first and second wirings. DESCRIPTION OF THE PREFERRED EMBODIMENTS The example depicted in Figs. 1A to 1C will be described below. As shown in Fig. 1A, a first aluminum wiring 12 is formed on a Si semiconductor substrate 11. An interlayer insulating film 13 whose main component is silicon oxide film is formed over the aluminum wiring 12. A contact hole 15 is formed in the insulating interlayer film 13. An alumina layer 16 in the order of 80 to 100 angstroms (10 Å = 1 nm) in thickness is present on the bottom of the contact hole 15. Next, as shown in Fig. 1B, a Ti film 17 is deposited on the alumina layer 16 and the interlayer insulating film 13 to a thickness of 500 angstroms by means of a sputter method. A second aluminum wiring 14 is deposited on the Ti film 17 to a thickness of 1 micron by the sputter method similar to the case of the first aluminum wiring 12, without exposing the Ti film 17 to the atmosphere. Next, a desired wiring pattern is formed by etching the second aluminum wiring 14 and the Ti film 17. Thereafter, the semiconductor device processed as above is subjected to heat treatment in a forming gas composed of N₂ and H₂ at 450 °C for 30 minutes. As a result, as shown in Fig. 1C, an alloy layer 18 is formed at the junction between the first and second wirings 12 and 14. The alloy layer 18 is made of titanium, aluminum and oxygen which are formed through reduction of the alumina layer 16 by the Ti film 17. The alloy layer 18 serves to considerably improve the conduction between the first and second aluminum wirings 12 and 14. The results of experiments applied to semiconductor devices with the contact hole 15 of 1 micron in diameter showed that the probability of conduction between the first and second wirings 12 and 14 was 99.999 % or more. Checking gate oxide films with 100 angstroms thickness showed that there was no destroyed gate oxide film. The processes according to the present invention are shown in Figs. 2A to 2C. The semiconductor device shown in Fig. 2A is similar to that shown in Fig. 1A. A Ti layer 17 and TiN layer 17A are sequentially deposited on the semiconductor device shown in Fig. 2A by means of a sputter method, without exposing both the layers to the atmosphere. Thereafter, a second aluminum wiring 14 is deposited by means of a sputter method. Next, a desired wiring pattern is formed by etching the second aluminum wiring 14, TiN layer 17A and Ti layer 17. The intermediate stage semiconductor device processed as above is subjected to heat treatment in a forming gas composed of N₂ and H₂ at 450 °C for 30 minutes. As a result, as shown in Fig. 2C, an alloy layer 18A is formed at the junction between the first and second aluminum wirings 12 and 14. The alloy layer 18 is made of titanium, aluminum and oxygen which were formed through reduction of the alumina layer 16 by the Ti film. The alloy layer 18A serves to considerably improve the conduction between the first and second aluminum wirings 12 and 14. The TiN film 17A is not deposited directly on the first aluminum wiring 12, but the Ti film 17 is interposed therebetween. Therefore, it is possible to avoid an increase of contact resistance due to the presence of N₂ at the interface between the first aluminum wiring 12 and the TiN film 17A. Further, since the Ti film 17 is positioned under TiN film 17A, the contact force increases between the TiN film 17A and the insulating interlayer film (SiO₂) 13. Furthermore, since the TiN film 17A is positioned under the second aluminum wiring 14, the resistance against electromigration or thermalmigration is improved. Formation of an alumina layer on the first aluminum wiring 12 may be prevented if an Mo layer is formed on the first aluminum wiring. However, this is not preferable since horizontal hillocks are formed. Also, such a two-layered structure is difficult to etch and likely to produce after-corrosion. The above embodiments are free from such disadvantages. In the first and second embodiments, the heat treatment is carried out after the second aluminum wiring was deposited. However, the heat treatment may be carried out before the second aluminum wiring 14 is deposited. Alternatively, the heat treatment may be omitted by raising the temperature of the substrate while the Ti film 17 is deposited, and enhancing the reaction of the Ti film 17 with the alumina layer 16. Instead of the Ti film 17 used in the first and second embodiments, highly oxidizing metal such as Hf, V, Mg, Li, Ni or the like and their alloys and the like, such as HfV, AlHf, NiSi₂, HfSi₂, VSi₂, HfB, VB, HfC, VC, HfN and VN. Also, instead of aluminum wiring material, Cu may be used and processed in the similar manner to that for aluminum. If the alumina layer 16 is thin and the Ti film 17 is excessive in quantity, the Ti film 17 reacts with Si in the substrate 11 to form alloy spikes which cause leakage in the PN junction. In view of this, a barrier layer 11A (refer to Fig. 1D and Fig. 2D) such as a TiN layer, W layer may be interposed between the first aluminum wiring 12 and the Si substrate 11 to avoid the reaction between aluminum and the Si substrate.

Claims: A method of manufacturing a semiconductor device comprising the steps of: forming an interlayer insulating film (13) on a first metallic wiring (12); opening a contact hole (15) in the interlayer insulating film (13) extending to the surface of the first wiring (12); depositing a highly oxidizing metal layer (17) on the interlayer insulating film (13) and within the contact hole (15) where a highly resistive oxide layer (16) is formed on the first metallic wiring (12); depositing a barrier metallic layer (17A) on the highly oxidizing metal layer (17), depositing a second wiring (14) on the insulating film (13) and within the contact hole (15) for obtaining conduction between said first and second wirings (12, 14); and reducing the highly resistive oxide layer (16) with said highly oxidizing metal layer (17) to change the highly resistive oxide layer (16) to a low resistive, conductive metal layer (18A) by means of heat treatment, said reduction step being performed at any time after said contact hole opening step. A method of manufacturing a semiconductor device according to claim 1, wherein said reduction step is performed after said second wiring deposition step. A method of manufacturing a semiconductor device according to claim 1, wherein said reduction step is performed before said second wiring deposition step. A method of manufacturing a semiconductor device according to claim 1, wherein said reduction step is performed at the time when said highly oxidizing metallic layer deposition step is performed. A method of manufacturing a semiconductor device according to anyone of claims 1 to 4, wherein the material of said first and second wirings (12, 14) is selected from the group consisting of Al and Cu. A method of manufacturing a semiconductor device according to anyone of claims 1 to 5, wherein said highly oxidizing metal (17) is selected from the group consisting of Ti, Hf, V, Mg, Li, Ni, HfV, AlHf, NiSi₂, HfSi₂, VSi₂, HfB, VB, HfC, VC, HfN and VN. A method of manufacturing a semiconductor device according to anyone of claims 1 to 6, wherein said barrier metallic layer (17A) is a TiN layer or W layer. A method of manufacturing a semiconductor device according to anyone of claims 1 to 7, wherein said reduction step is performed by heat treatment in a forming gas made of N₂ and H₂. A method of manufacturing a semiconductor device according to claim 1, wherein said highly oxidizing metal (17) is Ti which is deposited to the thickness of 50 nm (500 angstroms), and said first and second wirings (12, 14) are Al, the second wiring (14) Al being deposited to the thickness of 1 micron. A semiconductor device comprising: a first metallic wiring (12) formed on a semiconductor substrate (11), an interlayer insulating film (13) having a contact hole (15) through which said first metallic wiring conducts with a second metallic wiring (14), a highly oxidizing metal layer (17) formed on the interlayer insulating film (13) and in the contact hole (15), a second metallic wiring (14) formed on the highly oxidizing metal layer (17), characterized in that a barrier metallic layer (17A) is formed between said highly oxidizing metal layer (17) and said second metallic wiring (14), and at the junction between said first metallic wiring (12) and said highly oxidizing metal layer (17) a conductive alloy layer (18A) is formed, said conductive alloy layer being composed of the materials forming said first metallic wiring (12), said highly oxidizing metal layer (17) and oxygen. The semiconductor device according to claim 10, wherein the first metallic wiring (12) and the second metallic wiring (14) are aluminum wiring; the high oxidizing metal layer (17) is an element selected from the group consisting of Ti, Hf, V, Mg, Li and Ni or an alloy of these elements or an alloy including any one of these elements; and the barrier metallic layer (17A) is TiN. The semiconductor device according to claim 11, wherein the highly oxidizing metallic layer (17) has a thickness of 50 nm (500 angstroms) and the second metallic wiring (14) has a thickness of 1 micron.

Inventors: AOKI RIICHIROU, IDAKA TOSHIAKI TOSHIBA ISOGO D, OKUMURA KATSUYA, SHINKI TOSHINORI, AOKI, RIICHIROU, IDAKA, TOSHIAKI TOSHIBA ISOGO DAIROKU RYO, OKUMURA, KATSUYA, SHINKI, TOSHINORI
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1988
Main classification: H01L21
IPC codes: H01L21