METHOD OF MANUFACTURING A SEMICONDUCTOR DEVICE WITH A SEMICONDUCTOR BODY HAVING A SURFACE PROVIDED WITH A MULTILAYER WIRING STRUCTURE

Abstract: A method of manufacturing a semiconductor device with a semiconductor body (2) having a surface (1) which is provided with a multilayer wiring structure (3, 9) of conductor tracks made of a same conductive material. A first wiring layer (3) comprising conductor tracks (4, 16, 18, 19, 22, 23, 24, 29, 30) is formed on the surface. These tracks are covered with an insulating layer (5, 20, 21, 25, 26, 27, 31, 32) in which contact windows (8) are formed by means of a wet etching process capable of etching the material of the insulation layer selectively relative to the conductive material, which windows expose at least a portion of the conductor tracks of the first wiring layer locally. Then a layer (10) of the conductive material is deposited on the surface, and a second wiring layer (9) of conductor tracks (11) is formed therein. Before the contact windows are formed, an auxiliary layer (12, 15) of insulating material is provided on the insulation layer. Openings (13) are etched into the auxiliary layer at the areas of the contact windows. Then the contact windows are formed in that the semiconductor body is subjected to a wet etching process capable of selectively etching the insulating material of the insulation layer not only relative to the conductive material but also relative to the insulating material of the auxiliary layer. Thanks to the use of the auxiliary layer, the conductor tracks of the second wiring layer may be made comparatively narrow.

Description: Method of manufacturing a semiconductor device with a semiconductor body having a surface provided with a multilayer wiring structure. The invention relates to a method of manufacturing a semiconductor device with a semiconductor body having a surface provided with a multilayer wiring structure of conductor tracks of a same conductive material, whereby a first wiring layer of conductor tracks is formed on the surface and is subsequently covered with an insulation layer in which contact windows are formed by means of a wet etching process by which the material of the insulation layer can be etched selectively relative to the conductive material, which contact windows expose at least a portion of the conductor tracks of the first wiring layer locally, after which a layer of the conductive material is deposited on the surface, in which material a second wiring layer of conductor tracks is formed. The conductor tracks of the two wiring layers may be made, for example, from conductive polycrystalline silicon, aluminium, tungsten, or a metal silicide, and the insulation layer, for example, from silicon oxide. Such multilayer wiring structures are used inter alia in semiconductor memories and charge coupled devices. In practice, the first wiring layer may comprise conductor tracks of different thicknesses, and the insulation layer provided on the conductor tracks may also exhibit different thicknesses locally. Problems may accordingly arise during etching of the contact windows which expose conductor tracks of the first wiring layer locally. This is because the etching treatment must be continued until the conductor tracks have been exposed iri the contact windows also in those locations where the insulation layer is comparatively thick. The conductor tracks are subjected to the etching treatment for a comparatively long period in locations where the insulation layer is comparatively thin. These latter conductor tracks may then be etched away as well over part of their thickness. This may give rise to interruption of the conductor tracks in locations where the conductor tracks are also comparatively thin. Accordingly, the contact windows are provided in the insulating layer by means of a wet etching process whereby the material of the insulation layer can be etched selectively relative to the conductive material. An etching selectivity which is so high that the said problems are avoided can be achieved by means of a wet etching process. The English abstract of JP-A-57/31157 discloses a method of the kind mentioned in the opening paragraph whereby an insulating layer of silicon oxide is deposited on the first wiring layer. The contact windows are etched therein by means of a HF solution. The contact windows are thus formed- by a wet etching process, so that silicon oxide is etched highly selectively relative to the conductor track. The contact windows are etched into the insulation layer in that the semiconductor body is immersed in an etching bath after the insulation layer has been provided with a photoresist mask with openings at the areas of the contact windows. A disadvantage of the formation of contact windows in a wet etching process is that the etching process progresses isotropically. Etching then takes place substantially equally fast in horizontal direction and in vertical direction. The contact windows in the insulation layer accordingly become larger than the openings in the photoresist mask. Very small openings with a length and width of, for example, 0.5 μm can be realised in photoresist masks by modern photolithographical techniques. A contact window with a length and a width of approximately 0.9 μm is then created in a layer of insulating material of approximately 0.2 μm thickness. These contact windows are filled during the deposition of the layer of conductive material in which the second wiring layer is formed. Since the conductor tracks of the two wiring layers are formed from the same conductive material, the conductor tracks of the first wiring layer must not become exposed during etching of the conductor tracks of the second wiring layer. The conductor tracks of the second wiring layer must screen the contact windows in the insulating layer completely during this. A photoresist mask is also used for etching of these conductor tracks. If this photoresist mask can be aligned relative to the contact windows formed with a tolerance of ± 0.1 μ , then the conductor tracks of the second wiring layer must have a width of more than 1.1 μ at the areas of the contact windows. The invention has for its object inter alia to provide a method of the kind mentioned in the opening paragraph whereby the contact windows need not be completely screened by conductor tracks of the second wiring layer during the formation of the second wiring layer, so that these conductor tracks may have a comparatively small width. According to the invention, this method is for this purpose characterized in that an auxiliary layer of insulating material is provided on the insulation layer before the contact windows are formed, after which openings are first etched into the auxiliary layer at the areas of the contact windows, and then the contact windows are formed in the insulation layer in that the semiconductor body is subjected to a wet etching process whereby the insulating material of the insulation layer can be etched selectively not only relative to the conductive material but also relative to the insulating material of the auxiliary layer. As will become apparent below, openings can be etched in the auxiliary layer with a length and width which correspond substantially to those of the openings in the photoresist mask used for etching the contact windows. Windows are formed in the insulation layer larger than the openings in the auxiliary layer during etching of the contact windows in the insulation layer situated below the auxiliary layer. The insulation layer is removed in the contact windows below an edge of the auxiliary layer during this. The contact windows are also filled up below the edge of the auxiliary layer during the deposition of the layer of conductive material in which the second wiring layer is to be formed. Conductor tracks may now be formed in the creation of the second wiring layer of conductor tracks with a width which is practically equally large as that of the openings etched in the auxiliary layer. Etching of the conductive layer stops at the auxiliary layer, said edge of the auxiliary layer protecting the subjacent conductive material. Given a length and width of 0.5 μm of the openings in the auxiliary layer, conductor tracks with a width of no more than 0.7 μm can be formed on the auxiliary layer under the same conditions as prevailing above. Preferably, the auxiliary layer is deposited over the entire surface of the semiconductor body by means of a chemical vapour deposition process. A layer thus deposited exhibits a substantially homogeneous thickness over its entire surface area. The openings may be etched in such an auxiliary layer with a length and width which correspond substantially to those of the openings in the photoresist mask by means of an anisotropic plasma etching process such as, for example, a reactive ion etching process. Such an etching process does have an etching selectivity which is lower than that of wet etching processes, but since the deposited layer has a substantially homogeneous thickness all over the surface, the contact windows can be etched in this auxiliary layer without the subjacent layer being subjected locally to the etching plasma for any length of time. The etching treatment may be simply stopped after a time duration detrmined by means of tests, without the insulation layer situated below the auxiliary layer being appreciably attacked. If in addition the auxiliary layer is deposited to a thickness of less than 50 nm, the openings in the auxiliary layer may also be etched isotropically, for example in a wet etching process, whereby the openings in the auxiliary layer do become larger than the openings in the photoresist mask, but this enlargement remains limited. The enlargement can remain limited to the thickness of the auxiliary layer because the isotropic etching process progresses substantially equally fast in horizontal direction and in vertical direction. Given an opening in the photoresist layer of 0.5 μm length and width, as in the examples described above, and a thickness of the auxiliary layer of less than 50 nm, an opening will be created in the auxiliary layer with a length and width of more than 0.5 μm, but less than 0.6 μm. If a conductor track can be provided to an accuracy of ± 0.1 μm, this conductor track must have a width of more than 0.7 μm, but less than 0.8 μm, in order to protect the contact windows. Preferably, the conductor tracks of the first wiring layer are provided on an insulating sub-layer of a material relative to which the material of the insulation layer can be selectively etched, preferably of a same material as that of the auxiliary layer. The conductor tracks of the first wiring layer are then allowed to be narrower than the contact windows. The substrate is protected by the insulating sub-layer during etching of the contact windows, whereas without this sub-layer the substrate could also become etched. The contact window would have a length and width of approximately 0.9 μm with the use of the photolithographical process indicated above. Without the sub-layer, the conductor tracks situated below these contact windows would have to be at least 1.1 μm wide, but with the use of the sub-layer they are even allowed to be narrower than the 0.5 μm achievable by the lithographical process. Very narrow conductor tracks are formed when, for example, 0.5 μm wide tracks of polycrystalline silicon are provided with an insulating silicon oxide layer through thermal oxidation. The invention will be explained in more detail below by way of example with reference to a diagrammatic, cross-sectional drawing, in which: Figs. 1 to 4 show a few stages in the manufacture of a first semiconductor device where the method according to the invention is used, Fig. 4 is a cross-section taken on the line A-A in Fig. 3, Figs. 5 and 6 show a few stages in the manufacture of a second embodiment of a semiconductor device, Figs. 7 and 8 show a few stages in the manufacture " of a third embodiment of a semiconductor device, Fig. 9 shows a stage in the manufacture of a fourth semiconductor device, Figs. 10 and 11 show a few stages in the manufacture of a fifth semiconductor device, Figs. 12 and 13 show a few stages in the manufacture of a sixth semiconductor device, Fig. 14 is a cross-section taken on the line B-B in Fig. 13, and Figs. 15, 16 and 17 show a few stages in the manufacture of a seventh semiconductor device. Figs. 1 to 4 diagrammatically and in cross-section show a few stages in the manufacture of a first semiconductor device for which the method according to the invention is used. A first wiring layer 3 of approximately 200 nm thick conductor tracks 4 made of polycrystalline silicon is formed in usual manner on a surface 1 of a silicon semiconductor body 2, which tracks are subsequently covered with an approximately 200 nm thick insulation layer 5 of silicon oxide. Then a photoresist mask 6 with openings 7 is provided. The semiconductor body is subsequently immersed in an etching bath containing a usual buffered HF solution in which contact windows 8 are formed in the insulating layer 5 by means of a wet etching process capable of etching the material of the insulation layer selectively relative to the conductive material. Said windows 8 expose at least a portion of the conductor tracks 4 of the first wiring layer 3 locally. In the drawing, all conductor tracks 4 are exposed, but in practice conductors which are not drawn are also used in the first wiring layer 3, for example, interconnecting semiconductor zones provided in the semiconductor body 2. Such conductor tracks, however, are not important for the invention. After the formation of the contact windows 8, a layer 10 of the same conductive material from which the conductor tracks 4 were formed, so in this example polycrystalline silicon, is deposited, and a second wiring layer 9 of conductor tracks 11 is formed therein. According to the invention, an auxiliary layer 12 of insulating material is provided on the insulating layer 5 before the contact windows 8 are formed, after which first openings 13 are etched into the auxiliary layer 12 at the areas of the contact windows 8, using the photoresist mask 6, and then the contact windows 8 are formed in the insulation layer 5 in that the semiconductor body 2 is subjected to a wet etching process capable of etching the insulating material of the insulation layer 15 selectively not only relative to the conductive material but also relative to the insulating material of the auxiliary layer 12. A semiconductor device with a semiconductor body 2 has thus been obtained which has a surface 1 provided with a multilayer wiring structure of conductor tracks 4, 10 of a same conductive material. The conductor tracks 4 and 10 of the two wiring layers 3 and 9 in the examples given are made of conductive polycrystalline silicon, but they may alternatively be made from, for example, aluminium, tungsten, or a metal suicide; the insulation layer 5 in the examples is made of silicon oxide, but suitable alternative materials would be silicon nitride and silicon oxynitride. Openings 13 with a length and width corresponding substantially to those of the openings 7 in the photoresist mask 6 used for laying down the locations and sizes of the contact windows 8 can be etched into the auxiliary layer 12. During etching of the contact windows 8 in the insulation layer 5 situated below the auxiliary layer 12, windows 8 are formed in the insulation layer 5 larger than the openings 13 in the auxiliary layer 12. The insulation layer 5 is removed in the contact windows 8 below an edge 14 of the auxiliary layer 12 during this. The contact windows 8 are filled up also below the edge 14 of the auxiliary layer 12 during the deposition of the layer 10 of conductive material in which the second wiring layer 9 is to be formed. During the formation of the second wiring layer 9 of conductor tracks 11, it is now possible to form conductor tracks 11 with a width which is substantially equally large as that of the openings 13 etched in the auxiliary layer 12. Etching of the conductive layer 10 stops at the auxiliary layer 12, said edge 14 of the auxiliary layer 12 protecting the subjacent conductive material. Given a length and width of 0.5 μm of the openings 13 in the auxiliary layer 12, it is possible to form conductor tracks with a width of no more than 0.7 μm on the auxiliary layer when a photoresist mask (not shown) is used for etching these conductor tracks 11 which can be aligned with a tolerance of ± 0.1 μm relative to the contact windows 8 formed. Preferably, the auxiliary layer 12 is deposited on the semiconductor body 2 in a chemical vapour deposition process. In the present embodiment, for example, an approximately 200 nm thick layer of silicon nitride is deposited in a CVD process, the semiconductor body being heated to a temperature of approximately 900° C while a gas mixture of silane and ammonia is being conducted over the wafer. A layer 12 thus deposited exhibits a substantially homogeneous thickness over its entire surface area. The openings 13 may be etched into such an auxiliary layer 12 by means of an anisotropic plasma etching process, for example, a usual reactive ion etching process, such that they have a length and width which correspond substantially to those of the openings in the photoresist mask. Such an etching process does have an etching selectivity which is lower than that of wet etching processes, but since the deposited layer 12 has a substantially homogeneous thickness over its entire surface area, the contact windows 13 can be etched into this auxiliary layer 12 without the subjacent layer 5 being exposed locally to the etching plasma for a prolonged period. The etching treatment may be simply stopped after a time duration determined by means of tests without the insulation layer 5 situated below the auxiliary layer 12 being appreciably attacked. Figs. 5 and 6 diagrammatically and in cross-section show a few stages in the manufacture of a second semiconductor device for which the method according to the invention is used. In this embodiment, an auxiliary layer 15 of silicon nitride having a thickness of less than 50 nm is deposited in a manner similar to that of the auxiliary layer 12. The openings 13 in the auxiliary layer 15 may now be etched isotropically, for example in a usual wet etching process with hot phosphoric acid, which does make the openings 13 in the auxiliary layer 15 larger than the openings 7 in the photoresist mask 6, but this enlargement is limited. Since the isotropic etching process proceeds practically equally fast in horizontal direction and in vertical direction, the enlargement can remain limited to the thickness of the auxiliary layer. Given a length and width of 0.5 μm of the opening 7 in the photoresist layer 6, as in the examples described above, and a thickness of the auxiliary layer of less than 50 nm, an opening 13 will be created in the auxiliary layer 15 with a length and width of more than 0.5 μm, but less than 0.6 μm. When a conductor track 11 can be provided with an accuracy of ± 0.1 μm, this conductor track must have a width of more than 0.7 μm and less than 0.8 μm in order to protect the contact windows. Figs. 7 and 8 diagrammatically and in cross-section show a few stages in the manufacture of a third semiconductor device for which the method according to the invention is used. Conductor tracks 16 of the first wiring layer 3 in this embodiment are provided on an insulating sub-layer 17 of a material relative to which the material of the insulation layer 5 can be selectively etched, preferably of a same material as that used for the auxiliary layer 14, in the present example silicon nitride with a thickness of approximately 200 nm. The conductor tracks 16 of the first wiring layer 3 are then allowed to be narrower than the contact windows 8. During etching of the contact windows 8, the substrate 2 is protected by the insulating sub-layer 17. Without this sub-layer the substrate could also be attacked by the etchant. The contact windows 8 would have a length and width of approximately 0.9 μm with the use of the photolithographical process indicated above. The conductor tracks 16 situated below these contact windows 8 would have to be at least 1.1 μm wide without the sub-layer 17, but with the sub-layer 17 they are even allowed to be narrower than the 0.5 μm achievable with the lithographical process. Fig. 9 diagrammatically and in cross-section shows a stage in the manufacture of a fourth semiconductor device for which the method according to the invention is used. This embodiment is almost identical to the embodiment given in Figs. 7 and 8. The only difference is that the auxiliary layer 15 is a layer of silicon nitride here of less than 50 nm thickness. In this case, again, the conductor tracks 16 can have a width smaller than the dimensions of the contacct windows 8. In the examples given above, the conductor tracks 4 and 16 of the first wiring layer 3 were provided with an insulation layer 5 in that the latter was deposited on the conductor tracks 4 and 16. In the following examples, this layer is formed by thermal oxidation of the conductor tracks. Very narrow conductor tracks can be formed then also. For example, when 500 nm wide and 200 nm thick tracks of polycrystalline silicon are provided with an approximately 200 nm thick insulating silicon oxide layer through thermal oxidation, a conductor track with a width of approximately 300 nm and a thickness of approximately 100 nm will remain. Figs. 10 and 11 diagrammatically and in cross-section show a few stages in the manufacture of a fifth semiconductor device for which the method according to the invention is used. Conductor tracks 18 and 19 of polycrystalline silicon belonging to the first wiring layer 3 in this embodiment are provided with an insulating layer of thermal silicon oxide 20 and 21. The conductor track 18 in this embodiment has a thickness of approximately 200 nm and is provided with an insulating layer of approximately 200 nm thickness, while the conductor track 19 has a thickness of approximately 100 nm and is provided with an insulating layer of approximately 100 nm thickness. Such a situation, in which the first wiring layer 3 comprises conductor tracks 18 and 19 of different thicknesses and the insulation layers 20 and 21 provided on the conductor tracks 18 and 19 have different thicknesses, often occurs in practice. This situation is illustrated here with reference to an example where the insulating layer 20 and 21 is provided through oxidation of the conductor tracks 18 and 19, but a similar situation may occur in the cases described above where the insulating layer 5 was provided through deposition. Problems may accordingly arise during etching of the contact windows 8 which locally expose conductor tracks 18 and 19 of the first wiring layer 3. This is because the etching treatment must be continued until the conductor tracks 18 have been exposed in the contact windows 8 also in those locations where the insulation layer 19 is comparatively thick. In that case the conductor tracks 19 are exposed to the etching treatment for a comparatively long time in locations where the insulation layer 21 is comparatively thin. These conductor tracks 19 may then be etched away through part of their thickness in those locations. This may give rise to interruptions in the conductor tracks in locations where in addition the conductor tracks 19 are comparatively thin. The contact windows 18 are accordingly provided in the insulating layer 20 and 21 by means of a wet etching process capable of etching the material of the insulation layer 20 and 21 selectively relative to the conductive material. A wet etching process is capable of providing an etching selectivity which is so high that the said problems are avoided. After the openings 13 have been provided in the auxiliary layer 12, the contact windows 8 are etched into the insulating layer 20 and 21 and the conductor tracks 11 of the second layer 9 of conductor tracks are formed. Figs. 12, 13 and 14 diagrammatically and in cross-section show a few stages in the manufacture of a sixth semiconductor device for which the method according to the invention is used. Narrow conductor tracks 22, 23 and 24 of polycrystalline silicon with thicknesses of 100 nm, 75 nm, and 50 nm, respectively, and widths of 300 nm, 300 nm, and 100 nm, respectively, belonging to the first wiring layer 3 are provided on a sub-layer 17 of silicon nitride in this embodiment and are provided with insulating layers of thermal silicon oxide 25, 26 and 27 with thicknesses of 200 nm, 100 nm, and 50 nm, respectively. An auxiliary layer 17 of silicon nitride which is less than 50 nm thick is also used in this case. After the photoresist mask 6 provided with openings 7 has been applied, the openings 15 are etched into the auxiliary layer 14. The openings 15 are etched in a wet etching process in this example, but it is also possible to do this in a reactive ion etching process. Since the auxiliary layer 14 arid the sub-layer 17 are made of identical materials, here of silicon nitride, portions 28 of the sub-layer 17 are etched away next to the conductor track 24. It can be avoided that the sub-layer 17 is etched away over too great a portion of its thickness in that the etching treatment is stopped after a time duration determined beforehand by means of tests. The contact windows 8 are etched into the insulating layer 25, 26 and 27 after etching of the openings 15 into the auxiliary layer 14. The auxiliary layer still remains covered by a remainder of the insulating layer 25 next to the conductor track 22, and the sub-layer 17 is exposed next to the other conductor tracks 23 and 24. The second wiring layer 9 with the conductor tracks 11 is provided after etching of the contact windows 8. It is found that contact can be made with very narrow conductor tracks 22, 23 and 24 of the first wiring layer 3 in this manner. Fig. 14 shows a cross-section taken on the line B-B in Fig. 13. It is clearly visible from this Figure that it is also true for the very narrow conductor track 24 that the conductor track 11 can be narrower than the contact window 8. Finally, Figs. 15, 16 and 17 diagrammatically and in cross-section show a few stages in the manufacture of a seventh semiconductor device for which the method according to the invention is used. The first wiring layer 3 in this embodiment comprises overlapping conductor tracks 29 and 30 which are provided on a sub-layer of silicon nitride 17. Both tracks are provided with a thermally grown insulating layer of silicon oxide 31 and 32. In such a case the method according to the invention may also be advantageously applied. The contact windows 8 are etched after the provision of a silicon nitride auxiliary layer 14 of less than 50 nm thickness and of a photoresist mask 6 having openings 7. This is done here in a reactive ion etching process. Portions 23 of the sub-layer 17 exposed by this etching process are etched away over a small portion of their thickness. Portions 34 of the auxiliary layer 14 remain intact here. The conductive layer 10 in which the conductor tracks 11 of the second wiring layer 9 are formed, however, makes good contact with the overlapping conductor tracks 28 and 29, as is evident from Fig. 15. Fig. 17 shows a cross- section taken on the line C-C in Fig. 16. It is clearly visible from this Figure that the conductor track 11 may be narrower than the contact window 8 also in this complicated first wiring layer with overlapping conductor tracks 28 and 29.

Claims: Claims: 1. A method of manufacturing a semiconductor device with a semiconductor body having a surface provided with a multilayer wiring structure of conductor tracks of a same conductive material, whereby a first wiring layer of conductor tracks is formed on the surface and is subsequently covered with an insulation layer in which contact windows are formed by means of a wet etching process by which the material of the insulation layer can be etched selectively relative to the conductive material, which contact windows expose at least a portion of the conductor tracks of the first wiring layer locally, after which a layer of the conductive material is deposited on the surface, in which material a second wiring layer of conductor tracks is formed, characterized in that an auxiliary layer of insulating material is provided on the insulation layer before the contact windows are formed, after which openings are first etched into the auxiliary layer at the areas of the contact windows, and then the contact windows are formed in the insulation layer in that the semiconductor body is subjected to a wet etching process whereby the insulating material of the insulation layer can be etched selectively not only relative to the conductive material but also relative to the insulating material of the auxiliary layer. 2. A method as claimed in Claim 1, characterized in that the auxiliary layer is deposited over the entire surface of the semiconductor body by means of a chemical vapour deposition process. 3. A method as claimed in Claim 2, characterized in that the auxiliary layer is deposited on the entire surface of the semiconductor body to a thickness of less than 50 nm. 4. A method as claimed in any one of the preceding Claims, characterized in that the conductor tracks of the first wiring layer are provided on an insulating sub-layer of a material relative to which the material of the insulation layer can be selectively etched. 5. A method as claimed in Claim 4, characterized in that the conductor tracks of the first wiring layer are provided on an insulating sub-layer made from a same material as that of the auxiliary layer. 6. A method as claimed in Claim 5, characterized in that the sub-layer and the auxiliary layer are formed from silicon nitride. 7. A method as claimed in Claim 5, characterized in that the conductor tracks of the first wiring layer are formed from polycrystalline silicon, and in that the insulating layer on these conductors is formed through oxidation of the polycrystalline silicon.

Inventors: PEEK HERMANUS LEONARDUS, VERBUGT DANIEL WILHELMUS ELISA, PEEK, HERMANUS, LEONARDUS, VERBUGT, DANIEL, WILHELMUS, ELISABETH
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS ELECTRONICS N.V.
Application year: 1995
Main classification: H01L21
IPC codes: H01L21