An interconnection structure of a semiconductor device and a method of manufacturing thereof

Abstract: An aluminum interconnection film (49) has a three layered structure of an aluminum alloy film (33), a tungsten film (58), and a titanium nitride film (35). An aluminum interconnection film (61) and an aluminum interconnection film (49) are electrically connected through a through hole (55) formed in a silicon oxide film (51). Because light reflectivity of the titanium nitride film (35) is low, the exposed area of the resist can be kept within a predetermined area even if photolithography is carried out above a step (30) where light is irregularly reflected. Therefore, it is possible to form a through hole (55) of a desired dimension even if the through hole (55) is formed above the step (30). Even if the titanium nitride film (35) is etched and removed in forming the through hole (55), the aluminum alloy film (33) is not exposed since the etching speed of the silicon oxide film (51) is considerably slower than that of the tungsten film (58). The problem of denatured layer formation and residue formation caused by exposure of aluminum alloy film (33) does not occur.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an interconnection structure of semiconductor devices, and more particularly to the interconnection structure of a semiconductor device having each of multilayer interconnection layers connected through a connection hole, and a method of manufacturing thereof. Description of the Background Art Aluminum films and aluminum alloy films of low resistivity are widely used as the interconnection of semiconductor devices. Recently, interconnections of multilayer structure having refractory metals metallic compounds such as tungsten (W), titanium nitride (TiN), molybdenum silicide (MoSi) formed on aluminum films and aluminum alloy films are used for the purpose of improving tolerance for stress migration and electromigration. Stress migration is a phenomenon where the interconnection is discontinued due to film stress of interlayer insulting films and the like formed on the interconnection. Electromigration is a phenomenon where metal atoms migrate under high current density to generate local voids, resulting in increase in resistance and disconnection in the interconnection. Among the above-mentioned refractory metals, titanium nitride is widely used because of its low light reflectivity. The reason why lower light reflectivity is preferable will be explained with reference to Figs. 22-25. Referring to Fig. 22, a field oxide film 3 and a silicon oxide film 5 are formed on a silicon substrate 1. An aluminum interconnection film 7 is formed on silicon oxide film 5. A refractory metal film 9 having relatively high light reflectivity is formed on aluminum interconnection film 7. A silicon oxide film 11 is formed on refractory metal film 9. A resist 13 is formed on silicon oxide film 11. It is necessary to form a through hole in silicon oxide film 11 in order to electrically connect aluminum interconnection film 7 and another aluminum interconnection film that will be formed later on silicon oxide film 11. Resist 13 is exposed using a mask 15 for the purpose of forming this through hole. Reference number 17 denotes a light transmission blocking portion for blocking the transmission of light. Reference number 19 denotes a light transmission portion that transmits light. Because a through hole is to be formed over a step 6 in aluminum interconnection film 7, the portion of resist 13 above step 6 of aluminum interconnection film 7 is exposed. A portion of light reaches refractory metal film 9 since resist 13 and silicon oxide film 11 have the nature of transmitting light. Light reaches the area in refractory metal 9 comprising a step to be reflected irregularly. This light of irregular reflection exposes resist 13 beneath light transmission blocking portion 17. Fig. 23 shows the state after exposure, where 21 is the exposed portion of resist 13. Because refractory metal film 9 has high light reflectivity, not only the portion of resist 13 beneath light transmission portion 19, but also some portion of resist 13 beneath light transmission blocking portion 17 is exposed. Referring to Fig. 24, the exposed portion of resist 13 is removed. The remaining resist 13 is used as a mask to etch silicon oxide film 11 for forming a through hole 23. Referring to Fig. 25, resist 13 is removed and an aluminum interconnection film 25 is formed on silicon oxide film 11. Aluminum interconnection film 25 is applied the predetermined patterning. This completes the electrical connection between aluminum interconnection film 25 and aluminum interconnection film 7. Because the exposed portion of the resist has been enlarged due to irregular reflection of light, the dimension of through hole 23 is not the designed dimension W1, but dimension W2. Dimension W3 of aluminum interconnection film 25 is made larger than W1 taking into consideration the offset of the mask. However, aluminum interconnection film 7 is also etched at the time of patterning aluminum interconnection film 25 since the dimension of the through hole has become W2. This explains why titanium nitride of low light reflectivity is widely used as refractory metal film 9. Because the light reflectivity of titanium nitride is low, the portion of resist 13 beneath light transmission blocking portion 17 will not be exposed, as in Fig. 23. A technique of forming titanium nitride on an aluminum interconnection is disclosed in Japanese Patent Laying-Open No. 63-289935 (1988). It has been described above that high light reflectivity of refractory metal film 9 is responsible for the dimension of through hole 13 to become larger than the design value. The same thing can be said in patterning the area in aluminum interconnection film 7 comprising the step on which refractory metal film 9 is formed. The dimension of aluminum interconnection film 7 at the step differs from the design value. A possible method of electrically connecting a lower layer aluminum interconnection film and an upper layer aluminum interconnection film using titanium nitride as the refractory method will be explained hereinafter with reference to Figs. 17-21. Referring to Fig. 17, impurity regions 43 and 45 having a distance therebetween are formed in the proximity of the main surface of a silicon substrate 27. A gate electrode 47 is formed on the main surface of silicon substrate 27 between impurity regions 43 and 45. Gate electrode 47 has a multilayer structure formed of a polysilicon film 39 and a tungsten silicide film 37. Reference number 41 denotes a sidewall insulating film. Gate electrode 47, impurity regions 43, 45 and silicon substrate 27 implement a MOS (Metal Oxide Semiconductor) field effect transistor. At the main surface of silicon substrate 27, a field oxide film 29 is formed surrounding this MOS field effect transistor. A silicon oxide film 31 is formed over field oxide film 29 and gate electrode 47. An aluminum interconnection film 49 formed of an aluminum alloy film 33 and a titanium nitride film 35 is provided on silicon oxide film 31. Referring to Fig. 18, a silicon oxide film 51, and a resist 53 are formed in sequence all over the main surface of silicon substrate 27. In forming silicon oxide film 51, a phenomenon called side hillock occurs when silicon is included in aluminum alloy film 33. This hillock phenomenon is seen in Fig. 18 where hillocks 63 are generated in the sidewalls of aluminum alloy film 33. Side hillocks 63 are generated due to heat occurring in the formation of silicon oxide film 51. The generation of side hillock 63 causes electrical connection between interconnections which should actually be separated, resulting in decrease in yield and reliability. Resist 53 is exposed to remove a desired portion of resist 53. Then, using resist 53 as a mask, silicon oxide film 51 is subjected to reactive ion etching using CHF 3 gas or CF 4 type gas to form a through hole 55, as shown in Fig. 19. Since the difference of the etching speeds of the titanium nitride film and the silicon oxide film is small, titanium nitride film 35 is removed by this etching to expose the surface of aluminum alloy film 33. If aluminum alloy film 33 is exposed, the surface layer of aluminum alloy film 33 will be etched. The etched Aℓ and the etching gas are reacted to form a residue 59 at the sidewall of through hole 55. Residue 59 is a compound of Aℓ, F and C. Referring to Fig. 20, resist 53 is removed by ashing, but residue 59 remains due to its low volatility. It is therefore necessary to remove residue 59 by carrying out wet process of rinsing and with an organic type releasing solution and the like. A denatured layer 57 is generated during this process if aluminum alloy film 33 is exposed due to the high reaction of aluminum alloy. There are some cases where residue 59 is not completely removed so that residue 59 and denatured layer 57 exist at the same time. Referring to Fig. 21, an aluminum interconnection film 61 is formed on silicon oxide film 51 to be patterned. If there is residue 59 left in the sidewall of through hole 55, aluminum may not be introduced adequately into through hole 55, leading to a possibility that the electrical connection between aluminum interconnection films 49 and 61 is defective. This will degrade the yield and reliability of the semiconductor device. There is also a problem that the electrical connection between aluminum interconnection films 61 and 49 may be defective if the amount of denatured layer 57 formed is appreciable since denatured layer 57 is an insulator. This will also degrade the yield and reliability of the semiconductor device. An approach to increase the film thickness of titanium nitride 35 may be considered for preventing exposure of aluminum alloy film 33 by etching. However, this approach is contrary to obtain the lowest light reflectivity, since the reflectivity is at its minimum only at a certain thickness. The thickness of titanium nitride film 35 cannot be increased also from the standpoint of planarity. JP-A-62-132359 has considered the use of a TiW or W capping layer as a means of suppressing hillock formation at the surface of aluminium film. In order to suppress the diffusion of Si from the substrate and Ti, W from the cap layer via Al grain boundaries, and thus prevent the formation of a silicide high resistance film, a barrier layer formed of any one of TiN, TaN and ZrN is produced before capping. JP-A-2-264433 discloses the use of a high refractory metal or metallic compound film as an anti-reflective coating on aluminium alloy as means of improving pattern definition during optical lithography. An example is given of a titanium nitride, alumina, aluminium alloy structure. SUMMARY OF THE INVENTION In view of the foregoing, an object of the present invention is to provide an interconnection structure of a semiconductor device allowing the formation of a through hole of a desired dimension with reliable contact therein. An additional object of the present invention is to provide a method of manufacturing an interconnection structure of a semiconductor device allowing formation of a through hole of a desired dimension with reliable contact in the through hole. Preferred embodiments of the present invention can provide an interconnection structure of a semiconductor device allowing formation of a through hole of a desired dimension with reliable contact therein, in a semiconductor device having a step in a lower interconnection and a through hole over the step. Preferred embodiments of the present invention also can provide an interconnection structure of a semiconductor device that can prevent exposure of a layer of a main portion of a lower interconnection even when there is great difference in depths between a first through hole and a second through hole. In embodiments of the present invention it is possible to provide an interconnection structure of a semiconductor device that can have the intensity of light reflecting at a lower interconnection kept constant. In embodiments of the present invention it is possible to provide an interconnection structure of a semiconductor device that can have the generation of a side hillock prevented. A method of manufacturing a semiconductor device, and a semiconductor device, in accordance with the present invention, are defined in the appended claims. An interconnection structure of a semiconductor device embodying the present invention includes a first interconnection layer,an insulating layer formed on the first interconnection layer having a through hole reaching the surface of the first interconnection layer, and a second interconnection layer formed on the insulating layer electrically connected to the first interconnection layer through the through hole. The first interconnection layer includes a first conductive layer containing metal, a second conductive layer formed on the first conductive layer, and a third conductive layer formed on the second conductive layer. Under the etching conditions of the insulating layer, the etching speed of the second conductive layer is slower than that of the third conductive layer. The light reflectivity of the third conductive layer is lower than that of the second conductive layer. A method of manufacturing an interconnection structure of a semiconductor device embodying the present invention includes the steps of forming a first conductive layer containing metal, a second conductive layer, and a third conductive layer in sequence on the main surface of a substrate. An insulating layer is formed on a first interconnection layer including first, second and third conductive layers. Under the etching conditions of the insulating layer, the etching speed of the second conductive layer is made slower than that of the third conductive layer. The light reflectivity of the third conductive layer is made lower than that of the second conductive layer. Then, a resist is formed on the insulating layer. The resist is patterned to a predetermined configuration by photolithography. Using the resist as a mask, the insulating layer is selectively etched to form a through hole. A second interconnection layer is formed on the insulating layer to connect the first and second interconnection layers through the through hole. Because the etching speed of the second conductive layer is slower than that of the third conductive layer under the etching conditions of the insulating layer, the exposure of the first conductive layer can be prevented due to the presence of the second conductive layer even if the third conductive layer is etched and removed, in etching a portion of the insulating layer to form a through hole. Because the third conductive layer may be etched and removed, it is possible to select a material having low light reflectivity for the third conductive layer. It is also possible to establish the thickness of the third conductive layer to have the lowest light reflectivity. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view of a semiconductor device showing a first embodiment of an interconnection structure of a semiconductor device according to the present invention. Fig. 2 is a sectional view of the semiconductor device of Fig. 1 showing the first step of the manufacturing steps thereof. Fig. 3 is a sectional view of the semiconductor device of Fig. 1 showing the second step of the manufacturing steps thereof. Fig. 4 is a sectional view of the semiconductor device of Fig. 1 showing the third step of the manufacturing steps thereof. Fig. 5 is a sectional view of the semiconductor device of Fig. 1 showing the fourth step of the manufacturing steps thereof. Fig. 6 is a sectional view of the semiconductor device of Fig. 1 showing the fifth step of the manufacturing steps thereof. Fig. 7 is a sectional view of the semiconductor device of Fig. 1 showing the sixth step of the manufacturing steps thereof. Fig. 8 is a first model diagram for explaining that the film to be formed beneath titanium nitride film 35 preferably has an etching speed that is at most 1/10 of that of the plasma oxide film under the etching conditions of the plasma oxide film. Fig. 9 is a second model diagram of a semiconductor device for explaining that the film to be formed beneath titanium nitride film 35 preferably has an etching speed that is at most 1/10 of the etching speed of the plasma oxide film under the etching conditions of the plasma oxide film. Fig. 10 is a graph showing the relation between film thickness and reflectivity of various materials. Fig. 11 is a sectional view of an interconnection structure of a second embodiment of an interconnection structure of a semiconductor device according to the present invention. Fig. 12 is a sectional view of an interconnection structure showing a third embodiment of an interconnection structure of a semiconductor device according to the present invention. Fig. 13 is a sectional view of an interconnection structure showing a fourth embodiment of an interconnection structure of a semiconductor device according to the present invention. Fig. 14 is a sectional view of an interconnection structure showing a fifth embodiment of an interconnection structure of a semiconductor device according to the present invention. Fig. 15 is a graph showing the relationship between the thermal processing temperature and resistance of a sample having W formed above Aℓ. Fig. 16 is a graph showing the relationship between the sputter etching time and the counting numbers of Aℓ and W of a sample having W formed above Aℓ. Fig 17 is a sectional view of a conventional semiconductor device showing the first step of the manufacturing steps thereof. Fig. 18 is a sectional view of a conventional interconnection structure of a semiconductor device showing the second step of the manufacturing steps thereof. Fig. 19 is a sectional view of a conventional interconnection structure of a semiconductor device showing the third step of the manufacturing steps thereof. Fig. 20 is a sectional view of a conventional interconnection structure of a semiconductor device showing the fourth step of the manufacturing steps thereof. Fig. 21 is a sectional view of a conventional interconnection structure of a semiconductor device showing the fifth step of the manufacturing steps thereof. Fig. 22 is a first sectional view of an interconnection structure for explaining problems resulting from reflectance of light by exposure. Fig. 23 is a second sectional view of an interconnection structure for explaining problems resulting from reflectance of light by exposure. Fig. 24 is a third sectional view of an interconnection structure for explaining problems resulting from reflection of light by exposure. Fig. 25 is a fourth sectional view of an interconnection structure for explaining problems resulting from reflectance of light by exposure. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 is a sectional view showing a first embodiment of an interconnection structure of a semiconductor device according to the present invention. Impurity regions 43 and 45 having a distance therebetween are formed in the proximity of the main surface of a silicon substrate 27. The substrate may be formed of Ge, GaAs, InP, SiC, etc. A gate electrode 47 is formed on the main surface of silicon substrate 27 between impurity regions 43 and 45. Gate electrode 47 has a multilayer structure formed of a polysilicon film 39 of 0.2µm thickness and a tungsten silicide film 37 of 0.2µm thickness. Impurity regions 43 and 45, gate electrode 47 and silicon substrate 27 implement a MOS field effect transistor. Reference number 41 denotes a sidewall insulating film. A field oxide film 29 of 0.5µm thickness is formed at the main surface of silicon substrate 27 surrounding the MOS field effect transistor. A silicon oxide film 31 of 1.0µm thickness is formed over field oxide film 29 and the MOS field effect transistor. A barrier metal 56 of 0.1µm thickness is formed on silicon oxide film 31. An aluminum interconnection film 49 is formed on barrier metal 56. Aluminum interconnection film 49 has a multilayer structure of an aluminum alloy film 33, a tungsten film 58 and a titanium nitride film 35. Aluminum alloy film 33 has a thickness of 0.4µm containing copper. The aluminum alloy film may be replaced by aluminum film or copper film. The thicknesses of tungsten film 58 and titanium nitride film 35 are 0.1µm and 0.03µm, respectively. A silicon oxide film 51 of 1.0µm thickness is formed on aluminum interconnection film 49. An aluminum interconnection film 61 of 1.0µm thickness containing copper is formed on silicon oxide film 51. Aluminum interconnection film 49 and aluminum interconnection film 61 are electrically connected by a through hole 55. Through hole 55 is located above a step 30. Titanium nitride film 35 is not seen within through hole 55 since it has been etched and removed in forming through hole 55. The manufacturing steps of the first embodiment of the interconnection structure of the semiconductor device according to the present invention will be explained hereinafter with reference to Figs. 2-7. Referring to Fig. 2, aluminum alloy film 33 is formed by sputtering on barrier metal 56. Referring to Fig. 3, tungsten film 58 and titanium nitride film 35 are formed by sputtering in sequence on aluminum alloy film 33. Referring to Fig. 4, the layers of aluminum interconnection film 49 and barrier metal 56 are separated above silicon oxide film 31 using reactive ion etching. Referring to Fig. 5, silicon oxide film 51 is formed using plasma CVD (Chemical Vapor Deposition) method. A side hillock is not generated since silicon is not included in aluminum alloy film 33 of the first embodiment. The silicon oxide film may be formed using atmospheric pressure CVD. Alternatively, a coating insulating film (spin on glass, for example) may be formed instead of the silicon oxide film. Referring to Fig. 5, resist 53 is formed on silicon oxide film 51. A portion of resist 53 above the area where a through hole is to be formed is exposed. Because titanium nitride film 35 is used as the top layer of aluminum interconnection film 49 in the first embodiment, the reflectance of light can be prevented during exposure process to keep the dimension error of the exposed resist 53 within the allowable range. Fig. 10 is a graph showing the relation between film thickness and light reflectivity of various materials. Light is directed into aluminum and adjusted so that the intensity of the reflected light is equal to that of the incident light. Under the condition that this light reflectivity of aluminum is 100%, light is directed to a specimen and the intensity of the reflected light measured. This measured value (%) indicates the ratio of reflectivity with respect to aluminum. Fig. 10 shows that the reflectivity of titanium nitride is around the value of 30%. Tungsten silicide, tungsten, and titanium tungsten respectively indicate values of around 50%. It has been found out that the dimension error of through holes and interconnection patterns are within the allowable value range if the light reflectivity of the top film layer of aluminum interconnection film 49 is less than or equal to 35%. Therefore, titanium nitride film is used for the top layer film of aluminum interconnection film 49. Although light reflectivity of silicon indicates a value of 30% in the vicinity of 100Å, silicon is not suitable for the present invention. If silicon is used instead of titanium nitride, silicon will combine with the underlying tungsten during the heating process to form tungsten silicide. Tungsten silicide has high light reflectivity, as shown in Fig. 10. The film thickness of titanium nitride is chosen to be 300-500Å since the reflectivity of titanium nitride shows a value of less than 30% when the film thickness thereof is 300-500Å. Referring to Fig. 6, silicon oxide film 51 is subjected to reactive ion etching with CHF 3 /O 2 or CF 4 /O 2 type gas using resist 53 as a mask to form through hole 55. The following Table 1 shows the etching selectivity ratio of various materials to plasma oxide film. (At Through hole Process: Etching Gas CHF 3 /O 2 ) Material Etching Speed Plasma Oxide Film 1 W 1/15 WSi 1/7 MoSi 1/7 TiN 1/2 AℓCu 1/15 Table 1 shows the etching speed of each material with 1 as the etching speed of the plasma oxide film. It can be appreciated from Table 1 that titanium nitride will be etched and removed in the formation of a through hole since the etching speed of titanium nitride is 1/2. On the contrary, the etching speed of tungsten is 1/15 and will not be removed. Therefore, exposure of aluminum alloy film 33 can be prevented. As a result, generation of a denatured layer and a residue can be prevented. Because the object of the present invention can be achieved with a film having an etching speed that is lower than that of titanium nitride, tungsten, tungsten silicide, and molybdenum silicide may be used in the present invention. Since their etching speeds are slower than that of titanium nitride, denatured layers and residues are not formed by etching. The etching speed is varied depending on the type of the insulating film to be etched and the type of etching gas. Therefore, it is necessary to change the material of the film formed on the aluminum alloy film according to the types of the insulating film and etching gas. The fact that a more preferable etching speed of at most 1/10 will be explained with reference to Figs. 8 and 9 showing sectional views of a semiconductor device. Fig. 8 shows one during the etching process, and Fig. 9 shows one after the etching procedure. Reference number 65 denotes a field oxide film. An interconnection layer 67 is formed on field oxide film 65. A first interlayer insulating film 69 is formed all over the surface of a silicon substrate. Aluminum interconnection films 49a, 49b, and 49c are formed with distances therebetween on first interlayer insulating film 69. Reference number 71 denotes a second interlayer insulating film. A through hole 55a is formed above aluminum interconnection film 49a. A through hole 55b is formed above aluminum interconnection film 49b. Because of the effect of interconnection layer 67 and field oxide film 65, the difference in depths is often more than 1µm between depth D of through hole 55b and depth C of through hole 55a. It is not preferable to grow tungsten film 58 to 1000Å or more. It has been experienced that a void is more likely to be formed in second interlayer insulating film 71 at the time of second interlayer insulating film 71 formation if the aspect ratio (A/B) in spacing between the interconnections is increased. Since the thickness of aluminum alloy film 33 cannot be reduced from the standpoint of conductivity, the thickness of tungsten film 58 is preferably 1000Å and below. The value of D-C becomes ten times that of the thickness of tungsten film 58, so that a material having an etching speed of not more than 1/10 is preferable. The amount of exposure of the resist is determined according to the intensity of the incident light and the intensity of the reflected light. The intensity of the reflected light is regarded as the sum of the intensity of light reflecting from aluminum alloy film 33, from tungsten film 58, and from titanium nitride film 35. A stable light reflectivity is required in order to keep the intensity of the reflected light constant. It is appreciated from Fig. 10 that tungsten has a stable light reflectivity with a film thickness of more than 500Å. Therefore, the preferable film thickness of the tungsten film is 500Å and above. Because the value of D-C is at least 1µm, as described above, second interlayer insulating film 71 is etched more than 1µm to form a through hole 55b after the formation of the through hole 55a. It is necessary to have a tungsten film 58 of 1µm/15 thickness, i.e. at least approximately 660Å in order to prevent exposure of aluminum alloy film 33 of aluminum interconnection layer film 49a at the time of formation of through hole 55b. Titanium nitride film 35 is not regarded. Therefore, it is necessary to have a tungsten film 58 of at least 500Å thickness considering titanium nitride film 35. This also applies to a tungsten silicide film used as a substitute for a tungsten film. Referring to Fig. 7, resist 53 on silicon oxide film 51 is removed. Aluminum interconnection film 61 is formed on silicon oxide film 51 by the sputtering method. Aluminum interconnection film 61 has contact with tungsten film 58 through hole 53. Then, aluminum interconnection film 61 is subjected to a predetermined patterning. This completes the manufacturing steps of the first embodiment of the interconnection structure of the semiconductor device of the present invention. Although through hole 55 is formed over step 30 in the present embodiment, the bottom of through hole 55 may be planar. Fig. 11 is a sectional view showing a second embodiment of an interconnection structure of a semiconductor device according to the present invention. Aluminum interconnection film 49 and aluminum interconnection film 73 located thereabove are electrically connected through a through hole. Aluminum interconnection film 73 has a multilayer structure of aluminum alloy film 75 and titanium nitride film 77. Because aluminum interconnection film 73 is the top layer, etching is not carried out above aluminum interconnection film 73. Therefore, it is not necessary to form a tungsten film on aluminum interconnection film 73. Titanium nitride film 77 is required because exposure is carried out in patterning aluminum interconnection film 73. Titanium nitride film 77 is preferably removed after the patterning of aluminum interconnection film 73. This is because wire bonding of aluminum is higher in reliability than titanium nitride. Fig. 12 is a sectional view showing a third embodiment of an interconnection structure of a semiconductor device according to the present invention. Aluminum interconnection film 79 has a multilayer structure of titanium film 85, titanium nitride film 87, aluminum alloy film 83 and titanium nitride film 81. Such a structure can improve adherence between aluminum interconnection film 49 and aluminum interconnection film 79 since tungsten film 58 and titanium film 85, titanium film 85 and titanium nitride film 87, titanium nitride film 87 and aluminum alloy film 83 have superior intimacy. Fig. 13 is a sectional view showing a fourth embodiment of an interconnection structure of a semiconductor device according to the present invention. Aluminum interconnection films 73 and 49 are electrically connected by tungsten 89 formed in through hole 55. The dimension of through hole 55 is minimized according to miniaturization of semiconductor devices. If the dimension of through hole 55 becomes smaller than a predetermined value, aluminum cannot be formed within through hole 55 by sputtering. In this case, metal selective CVD method is used. By employing this method to form tungsten 89 in through hole 55, adherence is not degraded because tungsten 89 and tungsten film 58 are of the same type. It is also possible to reduce resistance in the contact since foreign metal compounds are not generated. Fig. 14 is a sectional view of an interconnection structure of a semiconductor device according to a fifth embodiment of the present invention. The difference from the second embodiment of Fig. 11 is that an Aℓ 2 o 3 film 91 is formed between aluminum alloy film 33 and tungsten film 58. Aℓ 2 O 3 film 91 is formed by exposing aluminum alloy film 33 to the atmosphere. Aluminum alloy easily reacts with tungsten, to form a layer of high resistance. Aℓ 2 O 3 film 91 is formed between aluminum alloy film 33 and tungsten film 58 in the fifth embodiment, so that a layer of high resistance will not be generated. The reaction of aluminum alloy with tungsten being suppressed by the presence of Aℓ 2 O 3 between aluminum alloy and tungsten will be described hereinafter according to experimental results. Sample 1 has a tungsten film formed after aluminum alloy is formed. Aℓ 2 O 3 does not exist between the interface of aluminum alloy and tungsten in sample 1. Four of sample 1 were prepared. Sample 2 has aluminum alloy formed, followed by exposure to the atmosphere, and formation of a tungsten film. Aℓ 2 O 3 exists at the interface of aluminum alloy and tungsten. Three of sample 2 were prepared. One sample 1 was not treated to thermal process, and the resistance measured. Another sample 1 was treated to thermal process for ten hours at 400°C, and had the resistance measured. Still another sample 1 was treated to thermal process for ten hours at 425°C, and had the resistance measured. Yet another sample 1 was treated to thermal process for ten hours at 450°C, and had the resistance measured. Sample 2 was subjected to the same conditions. However, the resistance was not measured after being thermal treated for ten hours at 425°C. The thermal process was all carried out under N 2 atmosphere. The results are shown in Fig. 15. The resistance in sample 1 increases, but not in sample 2. It is therefore understood that a layer of high resistance is not formed in sample 2. Three of sample 1 were newly prepared. One sample 1 was thermal treated for thirty minutes at 450°C. Another sample 1 was thermal treated for three hours at 450°C. A further sample 1 was thermal treated for ten hours at 450°C. One sample 2 was newly prepared. This sample 2 was thermal treated for ten hours at 450°C. The samples of 1 and 2 were etched by sputtering, whereby the numbers of Aℓ and W per second were measured. Because the upper layer is W and the lower layer is Aℓ, the subject to be etched proceeds from W to Aℓ in the elapse of time. The results are shown in Fig. 16. It can be seen from Fig. 16 that the counted numbers of W is greater in sample 1 than in sample 2 at the etching time of 10-20 minutes. It is therefore understood that W is diffused within Aℓ in sample 1. In other words, W and Aℓ react with each other. Even if the third conductive layer is etched and removed in forming a through hole, the exposure of the first conductive layer containing metal can be prevented since there is the second conductive layer, in the interconnection structure of the semiconductor device according to the present invention. This eliminates the problem that denatured layers and residues are formed due to exposure of the first conductive layer. Because the third conductive layer may be etched and removed, it is possible to select a material of low light reflectivity for the third conductive layer. It is also possible to grow the third conductive layer to a thickness in which the light reflectivity is minimum. The problem that the exposed area through the mask is enlarged to expand the dimension of the through hole to be larger than the design value due to high light reflectivity can be avoided. Separate layers for suppressing the light reflectance and the exposure of the conductivity layer gives easy material selection. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: A method of manufacturing a semiconductor device, which method comprises the steps of: forming on a surface of a semiconductor substrate (27, 29, 31, 56) a first-level metallisation layer (49) comprised of a first conductive layer (33) of a material selected from aluminium, aluminium alloys of copper, or copper and a covering low-reflectivity layer (35) of titanium nitride of thickness between 0.03 and 0.05 µm inclusive; forming a plasma-deposited silicon oxide insulating layer (51) on the surface of said first-level metallisation layer (49); forming a photolithographically defined patterned layer of resist (53) on said insulating layer; reactive ion etching said insulating layer (51) and low-reflectivity layer (35) using said patterned layer of resist (53) as a mask using a fluorocarbon gaseous etchant of either CF 4 /O 2 or CHF 3 /O 2 to form a through hole (55); and, after removal of said resist (53), forming a second-level metallisation layer (61) connected to said first-level metallisation layer (61) via said through hole (55); wherein said first-level metallisation layer (49) is formed having an intermediate layer (58) of a material selected from tungsten, tungsten silicide or molybdenum silicide, which is more resistant to said etchant than said low-reflectivity layer (35), and which intermediate layer is formed after said first conductive layer (33) and before said low-reflectivity layer (35) so that it lies therebetween; and etching by said etchant is discontinued after penetration of said low-reflectivity layer (35) and exposure of said intermediate layer (58) but before said first conductive layer (33) is reached. A method according to claim 1, wherein said through hole (55) is located above a step (30) in said substrate (27, 29, 31, 56). A method according to either preceding claim, wherein the etching speed of said intermediate layer (58) is at most 1/10 of that of said insulating layer (51). A method according to any preceding claim, wherein said intermediate layer (58) has a thickness of 0.1 µm or less. A method according to any preceding claim, wherein said second-level metallisation layer (73) is formed such that it comprises a main conductive layer (75) which contacts said intermediate layer, and a first titanium nitride containing layer (77) formed on said main conductive layer. A method according to claim 5, wherein said second-level metallisation layer (79) is formed such that it further comprises a second titanium nitride containing layer (87) formed beneath said main conductive layer (83), and a titanium containing layer (85) formed beneath said second titanium nitride containing layer (87), said titanium containing layer being in contact with said intermediate layer (58) through said through hole. A method according to any preceding claim, wherein tungsten (89) is formed in said through hole (55) to electrically connect said first-level metallisation layer (49) and said second-level metallisation layer (73). A method according to claim 7, wherein said tungsten is formed in said through hole by a selective CVD method, after formation of said hole. A method according to any preceding claim, wherein an Al 2 O 3 film (91) is formed between said first conductive layer and said intermediate layer (58). A method according to any preceding claim, wherein said first-level metallisation layer (49) is formed on a barrier metal (56). A semiconductor device comprising: a semiconductor substrate (27, 29, 31, 56); a first-level metallisation layer (49) comprising a first conductive layer (33) of aluminium, aluminium alloy of copper, or copper and a covering low-reflectivity layer (35) of titanium nitride of thickness between 0.03 and 0.05 µm inclusive; an insulator layer (51) formed on the surface of said first-level metallisation layer (49); and a second-level metallisation layer (61) connected to said first-level metallisation layer (49) via a through-hole (55) in said insulator layer (51); wherein the device further includes: an intermediate layer (58) of tungsten, tungsten silicide, or molybdenum silicide material in between said first conductive layer (33) and said low-reflectivity layer (35), the through-hole (55) extending through said low-reflectivity layer (35) to expose said intermediate layer (58) at its base. A device according to claim 11, wherein said first-level metallisation layer (49) comprises a step (30) with said through hole (55) located above said step (30). A device according to either of claims 11 or 12, wherein said intermediate layer (58) has a thickness of 0.1 µm or less. A device according to any of claims 11 to 13, wherein said second-level metallisation layer (73) comprises a main conductive layer (75) which contacts said intermediate layer, and a first titanium nitride containing layer (77) formed on said main conductive layer. A device according to claim 14, wherein said second-level metallisation layer (79) further comprises a second titanium nitride containing layer (87) formed beneath said main conductive layer (83), and a titanium containing layer (85) formed beneath said second titanium nitride containing layer (87), said titanium containing layer being in contact with said intermediate layer (58) through said through hole. A device according to any of claims 11 to 15, wherein said first-level metallisation layer (49) and said second-level metallisation layer (73) are electrically connected by tungsten (89) formed in said through hole (55). A device according to any one of claims 11 to 16, comprising an Al 2 O 3 film (91) positioned between said first conductive layer and said intermediate layer (58). A device according to any of claims 11 to 17, wherein said first-level metallisation layer (49) is on a barrier metal (56).

Inventors: ISHII ATSUSHI, MAEKAWA KAZUYOSHI, OHSAKI AKIHIKO, TAKATA YOSHIHUMI, ISHII, ATSUSHI, MAEKAWA, KAZUYOSHI, OHSAKI, AKIHIKO, TAKATA, YOSHIHUMI, Ishii, Atsushi, c/o Mitsubishi Denki k. k. ISI, Maekawa, Kazuyoshi, c/o Mitsubishi Denki k. k. ISI, Ohsaki, Akihiko, c/o Mitsubishi Denki k. k. ISI, Takata, Yoshihumi, c/o Mitsubishi Denki k. k. ISI
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1992
Main classification: H01L23
IPC codes: H01L23, H01L21