Abstract:
A first level interconnection layer of substantially a given width is formed on an insulating film on a semiconductor substrate. At least two second level interconnection layers, which cross the first level interconnection layer on another insulating layer, are formed. In a step for forming the first level interconnection layer, projections are formed at each side of the first level interconnection layer between the crossings of the second level interconnection layers. The total width of the first level interconnection layer including the width of the projection is larger than the given width. After the second level interconnection layers are formed, the projections of the first level interconnection layer are removed along with any second level interconnection layer material remaining intermediate the second level interconnection layers, thereby to prevent short-circuiting between the second level interconnection layers.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a manufacturing method of semiconductor devices and more particularly to a manufacturing method of semiconductor devices of the type in which interconnection layer groups are arranged in the form of multilayers. 
     Integrated semiconductor devices become more fine, and the interconnection layer groups are multilayered. Because of this tendency, the upper and lower interconnection layers cross with an insulating layer interposed therebetween, resulting in the crowding of the connection layer group with step portions on the upper portion of the semiconductor device. In order to form such an interconnection layer group by patterning, it is preferable to use an anisotropic etching method, e.g. a reactive ion etching (RIE) process. When such an anisotropic etching method is used, however, the etching progresses only in the direction vertical to the surface of the semiconductor substrate, but does not progress in a lateral direction in parallel with the surface of the semiconductor substrate. Accordingly, when a first level interconnection layer is formed on an insulating layer on a semiconductor substrate and a second level interconnection layer is formed crossing the first level interconnection layer with another insulation layer intervening therebetween, conductive material from forming the second level interconnection layer is left at each side end of the first level interconnection layer between the two crossing portions, and the conductive material left short-circuits the two adjacent second level interconnection layers. This problem will be described with reference to FIGS. 1 and 2. In FIG. 1, numeral 11 designates an insulating oxide layer formed on a semiconductor substrate 10. After a polycrystalline silicon film is formed on the oxide layer 11, this film is subjected to the patterning to form a polycrystalline silicon interconnection layer 12 of a first layer group or first level. Then, the oxide film corresponding to the element region is etched away with a mask of the polycrystalline silicon interconnection layer 12. In the next step, to form a polycrystalline silicon interconnection layer 14 of a second layer group or second level, an insulating layer 13 must be provided between the first and second level interconnection layers 12 and 14. To this end, the first level interconnection layer 12 is oxidized to form an insulating layer 13 of several hundreds A in thickness. FIG. 2 shows a cross section taken along line 2--2 of FIG. 1. After the formation of the insulating film 13, the polycrystalline silicon layer 14 of the second level must be formed by patterning a polycrystalline silicon film provided over the entire surface. As shown in FIG. 2, overhang portions 15 are formed on both the sides of the insulating film 13 when the first level interconnection layer 12 is oxidized. The polycrystalline silicon material coated over the entire surface for forming the second level interconnection layer 14, as a matter of course, enters under the overhang portions 15. In the patterning for the second level interconnection layer 14, as the RIE process is performed, the polycrystalline silicon material 14a under the overhang portions 15 is left, as shown in FIG. 2, without being removed. The residual polycrystalline silicon material 14a short-circuits between the second level interconnection layers 14. In the step of the patterning for forming the second level interconnection layer 14, if the isotropic etching is adapted, the polycrystalline material 14a is not left but use of the isotropic etching is problematic in the RIE method which is essential to the fine patterning. 
     Accordingly, an object of the present invention is to provide a method of manufacturing semiconductor devices which multilays interconnection layers by the antisotropic etching process, increases the integration density of circuit components, and improves the yield of products. 
     SUMMARY OF THE INVENTION 
     A manufacturing method of semiconductor devices according to this invention comprises a step for forming at least one first level interconnection layer with a given width on a first insulating layer and a step for forming at least two second level interconnection layers which cross the first level interconnection layer through a second insulating layer. The method further comprises steps of forming a projection at least at a location of each side end of the first level interconnection layer between the crossing portions of the first and second level interconnection layers when the first level interconnection layer is formed. The provision of the projection makes the width of the first level interconnection layer including the width of the projection to exceed the given width and removing at least a part of the projection so as to prevent the short-circuiting between the second level interconnection layers, after the formation of the second level interconnection layers. 
     When the present invention is applied to the manufacture of a semiconductor integrated circuit, fine, multilayered interconnection layers can easily be formed without any danger of short-circuiting between the interconnection layers. Therefore, the present invention provides a semiconductor device with improved reliability and yield of production. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 and 2 are for illustrating problems arising from the multilayered interconnection arrangement of a semiconductor device. 
     FIG. 1 is a plan view of a part of the semiconductor device, and 
     FIG. 2 is a cross sectional view taken along line 2--2 of FIG. 1, omitting a second level interconnection layer; 
     FIG. 3 is a plan view for illustrating a part of the manufacturing process according to the present invention; 
     FIGS. 4A to 4J are cross sectional views, taken along line 4A--4A in FIG. 3, for illustrating a sequence of steps of a manufacturing method of semiconductor devices according to the present invention; 
     FIG. 5 is a plan view of a modification of the process step shown in FIG. 3; and 
     FIG. 6 is a plan view of another modification of the process step shown in FIG. 3. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of a manufacturing method of semiconductor devices according to the present invention will be described with reference to FIG. 3 and FIGS. 4A to 4J. In FIG. 3, an oxide layer 21 is provided on a semiconductor substrate 20. Disposed on the oxide film 21 are first level interconnection layers 22a, 22b and 22c. Further layered on those first level interconnection layers are second level interconnection layers 24a and 24b crossing the first level interconnection layers through an insulating layer. Each of the first level interconnection layers 22a to 22c, after the final process step, has a width W. In the present embodiment, the interconnection layers are made of polycrystalline silicon. In the first step of forming the first level interconnection layers 22a to 22c, the interconnection layer 22a has a projection 30 having a width W 1  at the left side and a projection 31 having a width W 2  at the right side. The interconnection layer 22b has a projection 32 having a width W 2  at the left side and a projection 33 having a width W 2  at the right side. The interconnection layer 22c has a projection 34 having a width W 2  at the right side and a projection having a width W 1  at the left side. The projections 31 and 32, and 33 and 34 are continuous, respectively. Part of each of the projections is etched away, after the formation of the second level interconnection layers 24a and 24b, to prevent short-circuiting between the second level interconnection layers 24a and 24b. It will be understood that, in FIG. 3, although not illustrated, semiconductor devices to be connected to the interconnection layers are actually formed. 
     The manufacturing method of semiconductor devices according to the present invention will be described referring to the cross sectional views in FIGS. 4A to 4J, which are taken along line 4A--4A in FIG. 3. A field oxide layer or a gate oxide layer 21 is formed on a semiconductor substrate 20 by a known manner. Then, the first level interconnection layers 22a to 22c having projections 30 to 35 and made of polycrystalline silicon are formed by a known manner (FIGS. 3 and 4A), as a result, the polycrystalline silicon layer 22 is contained in the 4A--4A cross section. In the next step, an oxide film 21 in those region in which semiconductor elements are formed is selectively etched away by using ammonium floride NH 4  F, for example, using as a mask the first level interconnection layers 22a to 22c. The result of this process step is illustrated in FIG. 4B. In order to form an insulating separation layer for separating the first level interconnection layers 22a to 22c from the second layer interconnection layers 24a and 24b, the first level interconnection layers 22a to 22c are thermally oxided to form a thermal oxide layer 36 of 0.1 μm in thickness (FIG. 4C). 
     Then, a polycrystalline silicon film 37 is layered over the entire surface including the region in which the second level interconnection layers 24a and 24b are to be formed. To reduce resistance of the polycrystalline silicon layer 37, phosphorus is doped thereinto by the thermal diffusion process. Then, the polycrystalline silicon film 37 is oxided to form an oxide film 38 of approximately 1000 A in thickness (FIG. 4D). That area of the oxide film 38 where the second level interconnection layers 24a and 24b are to be formed is covered with photoresist (not shown), and oxide film 38 in areas other than that for the second level interconnection layers 24a and 24b is removed by the photo etching process (FIG. 4E). 
     In the subsequent step, the polycrystalline silicon film other than that defined by the second interconnection layers 24a and 24b is etched away by the RIE method with a mask of the photoresist layer (FIG. 4F). By using the photoresist on the second level interconnection layers 24a and 24b as a mask, the insulating layer 36 is etched away by ammonium fluoride (NH 4  F), for example (FIG. 4G). Then, the photoresist left on the second level interconnection layers 24a and 24b is removed. It is to be noted that, as shown in FIG. 4G, the polycrystalline silicon 37a used when the second level interconnection layers 24a and 24b are formed is left under the overhang portions of the insulating separation layer 36 shown in FIG. 4F. The polycrystalline silicon 37a short-circuits between the second level interconnection layers 24a and 24b. 
     Photoresist films 39a to 39c are formed by the photo etching process on those regions where the first level interconnection layers 22a to 22c with width W are formed (FIG. 4H). The widths of the photoresist films 39a to 39c are selected to be equal to the width W of the first level interconnection layers 22a to 22c finally formed. In FIG. 4H, the left end of the photoresist film 39a is patterned so as to be positioned at a position shifted to the right by W 1  from the left end of the first level polycrystalline silicon interconnection layer 22a (FIG. 3) formed in the step of FIG. 4A. The right end of the photoresist film 39c is patterned so as to be positioned at a position shifted to the left by W 1  from the right end of the first level polycrystalline interconnection layer 22c formed in the step of FIG. 4A. The photoresist film 39b is patterned to have the width equal to the width of the first level interconnection layer 22b shown in FIG. 3. 
     Following the step of FIG. 4H, the essential part of the first level polycrystalline silicon interconnection layer is masked by the photoresist films 39a to 39c and the unnecessary part of the first level polycrystalline interconnection layers are removed by the RIE method by the aid of the photoresist masks 39a to 39c (FIG. 4I). The residual polycrystalline silicon 37a left in the process shown in FIG. 4H is completely removed in the process shown in FIG. 4I. The projections 31 and 32 interconnecting the first level interconnection layers 22a and 22b and the projections 33 and 34 interconnecting the first level interconnection layers 22b and 22c, are completely removed in the step of FIG. 4I. Therefore, the short-circuiting between the second level polycrystalline silicon interconnection layers 24a and 24b is completely prevented. 
     The photoresist films 39a to 39c are removed in a known manner (FIG. 4J). The first interconnection layers 22a&#39;, 22b&#39; and 22c&#39; in FIG. 4J have each width W shown in FIG. 3. The subsequent necessary process steps are performed according to the known technique. 
     In the prior manufacturing method, when the first level interconnection layers 22a to 22c are formed, those layers are formed to have the final width, for example, W. When the second level interconnection layers 24a and 24b are formed, the polycrystalline silicons 37a at the side ends of the first level interconnection layers 22a to 22c are removed by the isotropic etching process. But, the isotropic etching is insufficient for a high precision patterning. 
     The above embodiment is an example where the first and second level interconnection layers are provided, but it is evident that the present invention is applicable for a semiconductor device with interconnection layers of N (N≧3) levels. In this case, it is assumed that, of those layers N, the nth layer and the (n+1)th layer are formed by the manufacturing method according to the present invention. More specifically, projections corresponding to those of W1 and W2 shown in FIG. 3 are previously provided at the sides of the nth level interconnection layer between the crossing parts of the nth level interconnection layer and the (n+1)th level interconnection layer. After the formation of the (n+1)th level interconnection layer, at least part of the projections of the nth level interconnection layer is removed. Although the above-mentioned embodiment employs the RIE method for the etching of the interconnection layers, other anisotropic etching method, for example, the ion beam etching method may be employed. 
     As shown in FIG. 5, the projection 31 is formed at the right side of the first level interconnection layer 22a; the projection 32 at the left side of the first level interconnection layer 22b; the projection 33 at the right side of the first level interconnection layer 22b; the projection 34 at the left side of the first level interconnection layer 22c (as in the case of FIG. 3); a projection 41 at the left side of the first level interconnection layer 22a; a projection 42 at the right side of the first level interconnection layer 22a. With this configuration, the width of the first level interconnection layers 22a to 22c may be set, in the step of FIG. 4A, to the width left in the final step. 
     Alternatively, as shown in FIG. 6, projections 43 are alternately formed on both sides of the first level interconnection layers 22a to 22c and those layers are arranged such that the projections of the adjacent first level interconnection layers are shifted longitudinally. This arrangement increases the density of the interconnection layers.