Multi-layer wiring structure in a semiconductor device and method of manufacturing the same

Abstract: After an interlayer insulator film (4) is deposited on a wiring conductor (3) formed on a semiconductor device element and is then planarized, a first conducting film (5) and a first insulating film (9) are deposited in that order. Thereafter, a through hole (8) is formed, and a second conducting film (10) and a second insulating film (11) are deposited and then etched back so that these films remain on only a side wall surface of the through hole. The through hole is then filled with a metal plating (Fig. 1D), and the etching-back is performed again. Thereafter, an upper level wiring conductor (7) is plating-grown by supplying an electric current to the first conducting film (5), and the second conducting film (10) remaining on the side wall surface and the lower level wiring conductor (3). Thus, a planarized wiring conductor having only a slight step can be obtained in a process for forming a wiring for a semiconductor device by an electroplating method.

Description: Background of the Invention Field of the invention The present invention relates to a multi-layer wiring structure in a semiconductor device and a method for manufacturing the same. Description of related art In a typical conventional process of manufacturing a semiconductor device, a multi-layer wiring formation using a plating method has been performed for example as follows: A lower level wiring conductor is formed on a field insulator film formed on a semiconductor substrate, and then, an interlayer insulating film is formed. Thereafter, a through hole is formed for connecting between the lower level wiring conductor and a possible upper level wiring conductor. In the case of an electroplating method, a conducting film is formed as an electric current supplying layer. In addition, a photoresist is coated on the conducting film, and then, patterned into a desired shape by photolithography. By the electroplating process, an upper level wiring conductor is formed on a portion of the conducting film that is not covered by the photoresist. Thereafter the photoresist is removed, and an exposed portion of the conducting film is removed, so that a desired wiring conductor is obtained. In the above mentioned conventional multi-layer wiring forming process using electroplating, the shape of the upper level wiring conductor becomes concave or recessed to reflect the shape of the lower level wiring conductor and the shape of the through hole portion for connecting between the upper level wiring conductor and the lower level wiring conductor. Therefore, if the number of the conductor levels becomes large in the multilayer wiring structure, it becomes difficult to planarize, and in addition, it is also becomes difficult to form a wiring conductor in the uppermost level. Several methods for maintaining a planar surface at the top of a structure interconnecting two layers of a semiconductor structure are known, but these do not use electrodeposited connections between the layers. These known methods are as follows. A paper by Kakum et al published in the 1987 Symposium on VLSI Technology, Digest of Technical Papers, May 1987, Karuizawa, Japan, pages 77-78 describes a method for interconnecting an Al or Al/Si layer with a Si substrate. An insulating layer with a through hole is first formed over the Si substrate. Successive layers of polysilicon and Mo silicide are then deposited, extending across the upper surface of the insulating layer, down the side walls of the hole and across the exposed Si substrate at the base of the through hole. The surface of the Mo silicide is then oxidised to form an insulating SiO 2 layer, and the through hole is filled with a deposit of polysilicon. The upper surface of the structure is then etched back to remove the exposed portion of the SiO 2 layer from the upper surface of the insulating layer and to leave a substantially planar surface on which the Al or Al/Si conducting layer can be deposited. US Patent No. 4800176 describes a method and structure substantially identical to that described by Kakum. In addition, US-A-4800176 describes an alternative method in which no MoSi layer is deposited and in which the SiO 2 insulating layer is formed by oxidising the polysilicon layer before the through hole is filled with polysilicon. In each of these structures the function of the SiO 2 layer appears to be (as described in US-A-4800176 at column 3, line 65, to column 4, line 5) to provide a stopper for limiting the etching of the structure later on in the described process. When the polysilicon is deposited to fill the through hole, it deposits also on the upper surface of the structure beside the through hole and must then be etched back so that it is only present within the through hole. The SiO 2 layer limits this etching process. European Patent Application No. EP-A-0380327 describes a method for connecting a metal wiring strip to a Si substrate. Two insulating layers are deposited over the substrate, a lower layer of phosphosilicate glass and an upper layer of SiO 2 . A through hole is formed in both layers in two steps, by an isotropic etch step followed by an anisotropic etch step resulting in a parallel sided through hole in the phosphosilicate glass layer and an outwardly flared hole in the SiO 2 layer. The funnel-shaped through hole so formed is then filled with polysilicon to form an interconnection structure. The funnel-shaped through hole enhances the polysilicon deposition so as to produce a planar upper surface to the structure. Summary of the Invention The invention provides a multilayer wiring structure in a semiconductor device, and a method for making the same, as defined in the appendant claims to which reference should now be made. Advantageous or preferred features of the invention are defined in dependent subclaims. In a preferred embodiment the present invention may thus provide a multi-layer wiring structure for a semiconductor device in which the shape of the upper level wiring conductor is not limited by the lower level wiring conductor and the shape of the through hole, and therefore, in which the upper level wiring conductor is relatively planar. Advantageously, the method of the invention may allow formation of a multi-layer structure, which can form a relatively planar upper level wiring conductor without being limited in its shape by the lower level wiring conductor and the shape of the through hole. The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings. Brief Description of the Drawings Figures 1A to 1G are sectional views illustrating, in order, various steps of a first embodiment of the method in accordance with the invention; and Figure 2 is a sectional view illustrating a second embodiment of the invention. Description of the Preferred embodiments Now, preferred embodiments of the present invention will be described by way of illustration with reference to the accompanying drawings. As shown in Figure 1A, a semiconductor substrate 1, on which semiconductor circuits elements are formed, is isolated with a field insulator film 2, and a gold wiring conductor of a desired pattern is formed on the field insulator film 2 by an electroplating process, so as to form a lower level wiring conductor 3. An interlayer insulating film 4 is formed on the lower level wiring conductor 3, and then, is planarized. For example, this interlayer insulating film 4 can be formed by growing a silicon oxide film by a CVD process, and then, by spin-coating a polyimide layer, and by heating the coated polyimide layer. On the planarized interlayer insulating film 4, a first conducting film 5 is formed for example by sputtering titanium or an alloy of titanium so as to have a thickness of about 0.1 µm. Thereafter, a first insulating film 9 is formed by depositing a silicon oxynitride film by a CVD process so as to have a thickness of about 0.1 µm to 0.2 µm. As shown in Figure 1B, a through hole 8 of a desired size is formed at a position where it is desired to connect between the lower level wiring conductor 3 and a possible upper level wiring conductor, and then, a second conducting film 10 is formed to coat the overall surface by sputtering for example titanium or an alloy of titanium so as to have a thickness of about 0.1 µm. The through hole 8 can be formed by, for example, forming a photoresist on all places other then the position where the through hole is to be formed, removing the first insulating film 9 and the first conducting film 5 by reactive ion etching using for example a CF 4 gas, and then, removing the interlayer insulating film 4 by reactive ion etching using for example a CF 4 gas or an O 2 gas. After the through hole is fonned, the remaining photoresist is removed by an organic solvent. Thereafter, the second conducting film 10 is deposited as mentioned above. As shown in Figure 1C, on the deposited conducting film 10, a second insulating film 11 is formed by depositing a silicon oxynitride film by a CVD process so as to have a thickness of about 0.1 µm. As shown in Figure 1D, the reactive ion etching is performed using the CF 4 gas until the first insulating film 9 is exposed, so that the second conducting film 10 and the second insulating film 11 remain only on a side wall surface of the through hole. With the electroplating process, gold is plating-grown in the through hole 8 until the grown gold reaches the same height as a level of a surface of the first conducting film 5. At this process, an electric current for the electroplating is supplied to the first conducting film 5, the second conducting film and the lower level wiring conductor 3. As shown in Figure 1E, after the through hole 8 is filled with the gold plating, a portion of the second insulating film 11, a portion of the second conducting film 10 and the first insulating film 9 are removed by reactive ion etching using the CF 4 gas, so that a planarized surface is obtained. As shown in Figure 1F, a photoresist 6 is formed on places other than a place where an upper level wiring conductor is to be formed, and an upper level wiring conductor 7 is grown by gold plating, by supplying an electric current for electroplating to the first conducting film 5, the second conducting film 10, the lower level wiring conductor 3, and the gold within the through hole 8. As shown in Figure 1G, after the photoresist is removed, the first conducting film 5 is selectively removed by ion milling using an argon gas. Thus, the present invention is realized. Thus, the multi-layer wiring structure in the present embodiment has the structure as shown in Figure 1G. Specifically, it comprises the semiconductor substrate 1, the field insulator film 2 formed on the semiconductor substrate 1, the lower level wiring conductor 3 in the desired pattern formed on the field insulator film, and the interlayer insulating film 4 formed on the field insulator film 2 to completely cover the lower level wiring conductor 3. The interlayer insulating film 4 has a thickness sufficiently larger than that of the lower level wiring conductor 3. The interlayer insulating film also has the through hole 8 formed therethrough so as to reach an upper surface of the lower level wiring conductor 3. The conducting film 10 is coated on the side wall surface of the through hole 8, and the insulating film 11 is coated on the conducting film 10. In addition, the conducting film 5 is coated on the interlayer insulating film 4 so as to surround the conducting film 10. The electric conductor material is filled in the through hole 8 in such a manner that one planar surface is constituted of an upper surface of the conducting film 5, an upper end surface of the conducting film 10, an upper end surface of the insulating film 11, and an upper surface of the electric conductor material filled in the through hole 8. The upper level wiring conductor 7 is formed on the planar surface so that the upper level wiring conductor 7 is electrically connected to the lower level wiring conductor 3 through the electric conductor material filled in the through hole 8. In other words, the through hole 8 in the form of a recessed groove is perforated through the interlayer insulating film 4 for separating the upper level wiring conductor 7 and the lower level wiring conductor 3 from each other, so as to reach a desired position of the lower level wiring conductor 3, and the inside of the through hole 8 in the form of a recessed groove is filled with an electric conductor until the filled conductor reaches a height which is substantially at the same level as the surface of the interlayer insulating film 4, and in addition, the upper level wiring conductor 7 is formed on the interlayer insulating film 4 and on the conductor filled in the inside of the through hole 8. Figure 2 illustrates at second embodiment of the present invention. In this second embodiment, only the surface of the titanium constituting the second conducting film 10 is oxidized to form an insulating film, by performing a heat-treating at 300°C to 400°C in oxygen atmosphere, in place of depositing the second insulating film 11 in the first embodiment. In this embodiment, it is possible to omit the step of depositing the insulating film by the CVD process, and also, it is possible to thin the insulating layer. Therefore, it is possible to reduce the through hole 8 in size. As mentioned above, according to the present invention, the through hole filling and the upper level wiring conductor formation are separately performed by different plating processes, respectively. Therefore, the through hole filling conductor is plating-grown from the surface of the lower level wiring conductor within the through hole, and accordingly, the through hole is compactly filled with the plating metal, with no void at a comer of the through hole. In addition, since the upper level wiring conductor is plating-grown after the planarization, the shape of the upper level wiring conductor is not limited by the lower level wiring conductor and the shape of the through hole, and therefore, the upper level wiring conductor is relatively planar and may only have a step of the order of a few tens of nanometres high. The invention has thus been shown and described with reference to the specific embodiments. However, it should be noted that the present invention is in no way limited to the details of the illustrated structures but changes and modifications may be made within the scope of the appended claims.

Claims: A multi-layer wiring structure in a semiconductor device, comprising: a lower level wiring conductor (3) of a desired pattern formed on a semiconductor substrate (1,2); an interlayer insulating film (4) formed on said substrate and said lower level wiring conductor, said interlayer insulating film being planarized and having a thickness larger than that of said lower level wiring conductor so as to completely cover said lower level wiring conductor; a first conducting film (5) coated on an upper surface of said interlayer insulating film, a through hole (8), having a sidewall and a base, being formed through the interlayer insulating film and the first conducting film so as to reach an upper surface of said lower level wiring conductor; a second conducting film (10) coated on the side wall of said through hole, and contacting said lower level wiring conductor and said first conducting film; an insulating film (11) coated on said second conducting film; an electrodeposited electric conductor contacting said lower level wiring conductor at the base of said through hole and filling said through hole such that an upper surface of said first conducting film, an upper end surface of said second conducting film, an upper end surface of said insulating film, and an upper surface of said electric conductor filling said through hole lie in one planar surface; and, an electrodeposited upper level wiring conductor (7) formed on said planar surface so that said upper level wiring conductor is electrically connected to said lower level wiring conductor through said electric conductor filling said through hole. A multi-layer wiring structure as claimed in Claim 1 wherein said insulating film (11) is formed of a surface oxidized film of said second conducting film. A multi-layer wiring structure As claimed in Claim 2 wherein said second conducting film (10) is formed of titanium, and said insulating film (11) is formed of titanium oxide. A method of manufacturing a multi-layer wiring structure in a semiconductor device comprising the steps of: depositing an interlayer insulating film (4) to completely cover a lower level wiring conductor (3) of a desired pattern on a semiconductor substrate (1,2), whereby the thickness of the interlayer insulating film is larger than that of the lower level wiring conductor, and planarizing an upper surface of the deposited interlayer insulating film; forming a first conducting film (5) and a first insulating film (9) on the planarized interlayer insulating film in the named order; forming a through hole (8) by selectively removing said first insulating film, said first conducting film and said interlayer insulating film at a position where a connection is to be made to said lower level wiring conductor; forming a second conducting film (10) and a second insulating film (11), in the named order, to cover said first insulating film and an inner surface of said through hole; etching back said second insulating film and said second conducting film so that only those parts of said second insulating film and said second conducting film covering a side wall of said through hole remain, performing an electroplating process by supplying an electric current by means of said first conducting film to said second conducting film remaining on said side wall of said through hole and to said lower level wiring conductor, so that an electrically conducting material fills the inside of said through hole to substantially the same height as the level of the upper surface of said first conducting film; etching back said first insulating film and adjacent uppermost end portions of the parts of said second conducting film and said second insulating film remaining on said side wall of said through hole until the upper surface of said first conducting film is exposed, so that the upper surface of said first conducting film, upper end portions of said second conducting film and said second insulating film remaining on said side wall of said through hole, and an upper surface of said electrically conducting material filling said through hole form a planar surface; forming a photoresist (6) on said planar surface except at a place where an upper level wiring conductor (7) is to be formed; performing an electroplating process by supplying an electric current via said first conducting film to said second conducting film remaining on said side wall of said through hole, said lower level wiring conductor and said electrically conducting material filling said through hole, to form an upper level wiring conductor (7) on at least the upper surface of said electrically conducting material filling said through hole and a portion of said first conducting film not covered by said photoresist; and, removing said photoresist and said first conducting film except any portion thereof over which said upper level wiring conductor was formed. A method as claimed in Claim 4 wherein said formation of said second conducting film and said second insulating film is performed by sequentially depositing said second conducting film and said second insulating film. A method as claimed in Claim 4 wherein said formation of said second conducting film and said second insulating film is performed by depositing a metal layer as said second conducting film and then oxidizing a surface of said metal layer so as to form a surface oxidized film as said second insulating film. A method as claimed in Claim 4, 5 or 6 wherein said first conducting film and said second conducting film are formed of titanium. A method as claimed in any of Claims 4 to 7 wherein said formation of said interlayer insulating film is performed by growing a silicon oxide film by a CVD process, and then by spin-coating a polyimide layer, and by heating the coated polyimide layer. A method as claimed in Claim 4, 5, 7 or 8 wherein said first insulating film and said second insulating film are formed by depositing silicon oxynitride films by a CVD process.

Inventors: MORISHITA YASUYUKI, MORISHITA, YASUYUKI
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1992
Main classification: H01L23
IPC codes: H01L21, H01L23