METHOD OF MANUFACTURING A SEMICONDUCTOR DEVICE INCLUDING FORMING A MULTI-LEVEL INTERCONNECTION LAYER

Abstract: A method of manufacturing a semiconductor device com­ prising the steps of preparing a semiconductor substrate (31) on which a first insulation film (30) is formed, forming a first conductive layer (35) on the first insulation film (30), forming a hillock (36) on the first conductive layer (35), forming a second insulation film (35, 38) on the structure, removing that portion of the second insulation film (37, 38), in self-align with the hillock (36), which is on the hillock (36), thereby forming a contact hole leading to the first conductive layer (35), and for­ ming on the structure a second conductive layer (41) exten­ ding into the contact hole and contacting the first conductive layer (35).

Description: This invention relates to a method of manufacturing semiconductor devices, and more particularly to the improvement of the method of forming the multi-layered conductive structure semiconductor devices. According to "Zeitschrift für Metallkunde", vol. 52, no. 9, September 1981, pages 615 to 622, electro- and thermal-transport effects on conductor lifetimes of integrated circuits are disclosed. The high electric current densities in the metallic conductor stripes of integrated circuits cause defects by mass transport. Paths of transport are the grain boundaries of the thin films. Divergencies of the mass flux can occur at temperature gradients and especially at structural inhomogenities. In the regions of mass accumulation hillocks and whiskers are growing. In the regions of mass depletion voids are forming whose growth can lead to stripe-cracking and a failure of the entire device. A reduction of the mass transport and thus an enhancement of conductor lifetime is achieved by alloy additions and multiple film structures. An SiO₂ layer is formed on conductor stripes in which a small hole is etched. Owing to mass accumulation, Al-metal is pushed under high pressure through said hole in the form of a whisker. In semiconductor memory devices, attempts have been made to reduce the pattern size. This is due to the requirement of improving on integration density to improve the operation speed of the integrated circuit. Partiuclarly, in a semiconductor device of the multi-layered conductive structure type, further reduction has been made of the width of each conductive layer and of the interval between adjacent conductive layers. With this tendency, the through-hole size is further reduced. It is for this reason that the RIE (reactive ion etching) process has been employed for forming through-holes. The RIE process is characterized by a small amount of side etching and also high etching controllability. For better understanding the background history, a conventional method of manufacturing a double conductive layer structure semiconductor device will be described by referring to Figs. 1A through 1D. The manufacturing method following includes the step of forming through-holes. Fig. 1A First conductive layer 12 made of Al-Si and with thickness of 1.0 µm is formed on semiconductor substrate 11 having silicon oxide film 10 formed on the surface by thermal oxidation. Then, SiN film 13 is formed on the structure by the plasma process. This film will be referred to as a P-SiN film. Fig. 1B To flatten the surface, the substrate is coated with silica solution. Then, it is thermally processed. As a result, silica insulating film 14 is formed with a thickness of 0.4 µm. Fig. 1C A photoresist film is formed on the structure. Then, it is patterned by the photolithography process, to form patterned photoresist film 15. Using this photoresist film 15, silica insulating film 14 and P-SiN film 13 are selectively etched by the RIE process, to form through-hole 16. Fig. 1D Subsequently, resist film 15 is removed by the O₂ plasma process. Al-Si is deposited on the structure by the ordinary spattering process. The deposition is continued up to 1.0 µm in thickness. Then, it is patterned to form second conductive layer 17. In this way, the semiconductor device of the double conductive layer structure type is formed. The above manufacturing method, however, has the disadvantages as given below. (1) It is preferable to taper the side walls of P-SiN film 13 and silica insulating film 14 at about 45° to 55° so that that portion 17' of the second conductive layer 17 which is on through-hole 16 is made thick. However, in the conventional method, the taper is selected steep, about 65° to 75°. Such a steep taper comes from some restrictions such as the selectivity of resist film 15 to P-SiN film 13, the etching rate of P-SiN film 13, and stability of the etching. For this reason, the portion 17' of second conductive layer 17 is thinner than that portion of the second conductive layer 17 which is on the major surface of P-SiN film 13. The thickness of the conductive layer portion 17' is at most 20 to 40 % of that of the thin portion of the conductive layer 17. At the thin portion, current density is high and therefore disconnection tends to occur. (2) Wehn the thickness of the interlayer insulating film made up of P-SiN film 13 and silica insulating film 14 is 1.0 µm or more, the variation in the etching dimension due to the recession of the photoresist film 15 is great. For example, in the case of the interlayer insulating film of 1.0 µm in thickness, the etching dimension is varied approvimately 0.5 µm at one side. This fact makes it difficult to reduce the size of the through-hole. If the opening width of the through-hole of the photoresist film 15, which serves as the mask is 2 µm, for example, the through-hole to be formed in the interlayer insulating film after the etching processing has an opening width of a maximum of 3 µm, as shown in Fig. 3. In Fig. 3, L1 designates the opening width of the through-hole of P-SiN film 13 which is defined by the combination of silica insulating film 14 and P-SiN film 13 after the etching processing. L2 represents the opening width of the through-hole at photoresist film 15. Accordingly, an object of this invention is to provide a method of manufacturing semiconductor devices which is free from thinning or disconnection of the conductive layer. According to the invention, this object is solved by a first solution in that there is provided a method of manufacturing a semiconductor device comprising the steps of: forming a first insulation film (30) on a semiconductor substrate (31); forming a first conductive layer (35) on said first insulation film; forming a hillock (36) of said first conductive layer at a predetermined place on said first conductive layer; forming a second insulation film (37, 38) on the structure; removing that portion of said second insulation film, which is above said hillock, and that portion which is on said hillock, thereby forming a contact hole (40) leading to said first conductive layer; and forming on the structure a second conductive layer (41) extending into said contact hole and contacting said first conductive layer. According to another solution of the object a method of manufacturing a semiconductor comprises the steps of: forming a first insulation film (30) on a semiconductor substrate (31); forming a first conductive layer (51) on said first insulation film; forming on said first conductive layer a second insulation film (53) having a hillock-supressing function; forming a third insulation film (54, 55) on said second insulation film; forming a hole (57) in said second and third insulation films; forming a hillock (58) of said first conductive layer by thermally heating said first conductive layer through said hole; and forming on the structure a second conductive layer (59) extending into said hole and contacting said first conductive layer. Further embodiments of the invention are characterized in claims 1 to 5 and 7 to 12. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Figs. 1A to 1D show cross sections of structures of a semiconductor device at various steps in a prior manufacturing method; Fig. 2 and 3 show cross sections of prior semiconductor devices of two conductive layer structure, respectively; Figs. 4A through 4F show cross sections of structures of a semiconductor device at various steps in a manufacturing method according to an embodiment of the present invention; Fig. 5 shows a cross section of a semiconductor device of three conductive layer structure manufactured by a method of the present invention; Fig. 6 shows a cross section of a semiconductor device of three conductive layer structure manufactured by a conventional method; and Figs. 7A through 7E show cross sections of structures of a semiconductor device at various steps in a manufacturing method according to another embodiment of the present invention. A method of manufacturing semiconductor devices, according to the first embodiment of this invention, will be described with reference to Fig. 4A through 4F. Fig. 4A Silicon substrate 31 is a semiconductor substrate on which silicon oxide film 30 as a first insulation film has been formed by thermal oxidation onto the surface of silicon oxide film 30. Polyimide is applied to the top silicon substrate 31, then heat-treated to make a 1.3 µm thick lift-off layer of polyimide film 32. After that, polyimide film 32 is patterned by normal photolithography and RIE processes. Then the photoresist film (not shown) which was used as a mask when the polyimide film was patterned is removed. Using the normal spattering process, a 1.0 µm thick Aℓ-Si film 33, and a 0.1 µm thick Ti-Si2 film 34 are sequentially formed. Fig. 4B Using the O₂ ashing method, polyimide film 32 is lifted off, to remove the films of Aℓ-Si and Ti-Si2. As a result, only the films 33 and 34 as directly formed on silicon oxide film 30 are left. The Aℓ-Si film 33 on the film 30 will be referred to as a first conductive layer, and renumbered as 35, for simplicity. Further, by using the normal photography and RIE processes, the predetermined regions are removed, to form through-holes. Fig. 4C The photoresist film (not shown), which was used as the mask in removing the predetermined regions of film 34, is removed. The device was heated at 500°C for 15 minutes, thereby to sinter first conductive layer 35, to form hillock 36 of about 1.0 µm in height on the surface of first conductive layer 35, which is exposed to the through-hole. Fig. 4D A 1.0 µm thick P-SiN film 37 was formed on the structure by the plasma method. The structure is coated with silica solution, and thermally treated, to form silica insulation film 38 of 0.4 µm in thickness. Then, photoresist is coated on silica insulation film 38 to form photoresist film 39 of 2.5 µm in thickness. Incidentally, the P-SiN film 37 and silica insulating film 38 indicate a second insulation film referred to in "What is claimed is.". Fig. 4E The photoresist film 39 is etched back by the O₂ RIE processing. In the O₂ RIE process, O₂ amount was 60 sccm, pressure 3Pa, and the power 550 W. By this etching, silica insulation film 38 and P-SiN film 37 above and on hillock 36 are removed. Further, silica insulating film 38 and P-SiN film 37 are successively etched away to form through-hole 40. The through-hole 40 corresponds to hillock 36 in a self-aligned manner and exposes hillock 36. In this case, photoresist film 39 was used as a mask. The RIE process was used for the etching. The etching conditions for silica insulating film 38 were: The gas flow rate, CF₄/H₂ = 30/10 sccm, pressure 2 Pa, and the power 400 W. The etching conditions for the P-SiN film 37 were: The gas flow rate, SF6 100 sccm, pressure 10 Pa, and the power 500 W. Fig. 4F After the removal of photoresist film 39, the ordinary spattering process was employed to form an Aℓ-Si film (not shown) of 1.0 µm in thickness on the structure. This film formed is patterned by the ordinary photolithography and the wet etching method. Through the patterning, a patterned Aℓ-Si film 4, was formed, serving as a second conductive layer. The method of manufacturing the semiconductor of the double conductive layer type according to the first embodiment of this invention is performed in the above-mentioned way. As described above, according to the manufacturing method of this invention, hillock 36 is formed at the location where through-hole 36 is formed, by using the mask layer capable of limiting the hillock formation. Then, the interlayer film made up of P-SiN film 37 and silica insulation film 38 is formed. To remove the interlayer insulation films 37 and 38 in a self-aligned manner, through-hole 40 is formed providing a good coverage with the second conductive layer 41 to subsequently be formed. The manufacturing method of this invention thus arranged has the following useful effects. (1) Since hillock 36 is present in through-hole 40, the side walls of interlayer insulation films 37 and 38, which defines the through-hole 40, is terraced. The coverage with second conductive layer 41 is remarkably improved. Thus, the contact area between first and second conductive layers 35 and 41 is 1.5 to 4 times that of a prior semiconductor device, when the through-holes have the same opening width. Therefore, the operating current is distributed in this contact area at a low current density, thereby protecting against the occurrence of disconnection. (2) In forming through-hole 40, no tapering is required at the side walls of interlayer insulation films 37 and 38. Further, the TiSi₂ film as the hillock limiting film of about 0.1 µm is thin. Therefore, the size conversion difference in etching of TiSi₂ film is small, approximately 0.05 µm (one side). Therefore, the size reduction of the through-hole can easily be made. (3) The depth of through-hole 40 is smaller than the thickness of the films 37 and 38. Therefore, even in such a case that two through-holes are aligned in manufacturing a semiconductor device of three conductive layer type, as shown in Fig. 5, there is small possibility that the third conductive layer will be thinned or disconnected at the side walls of the through-hole. In Fig. 5, reference numeral 61 designates a Ti-Si₂ film, 62 a P-SiN film, 63 a silica insulation film, and 64 a third conductive layer. Incidentally, in the above case, the disconnection tends to occur if it is manufactured according to the conventional method. (4) No hillock is formed in other places than the through-hole. Therefore, no short circuiting occurs between the conductive layers. When unnecessary hillock is formed, such short circuiting frequently occurs. While in the above-mentioned embodiment, the TiSi₂ film is used for the hillock formation restricting film, it may be a metal film or metal compound film having the hillock formation restricting effect. The sintering employed for hillock formation in the embodiment as mentioned above was for forming the great hillock. It may, of course, be replaced by any other appropriate process, if necessary. A second embodiment of a method of manufacturing semiconductor devices according to this invention will be described referring to Figs. 7A to 7E. Fig. 7A Silicon substrate 31 is provided as a semiconductor substrate having silicon oxide film 30 formed on the surface by the thermal oxidation process. After forming a 1.0 µm thick Aℓ-Si film on silicon oxide film 30 by the usual spattering process, the predetermined patterning is applied to the structure by the lithography and RIE processes, thereby to form Aℓ-Si film 51 as a first conductive layer. In Fig. 7A, reference numeral 52 designates a photoresist film as used as a mask in forming Aℓ-Si film 51. Fig. 7B In the next step, following removal of photoresist film 52, a 0.1 µm thick P-SiN film 53 is formed by the plasma CVD process at temperature capable of preventing the hillock formation (e.g. 300°C). The film 53 serves as a second insulation film. At temperature of 380°C, P-SiN film 54 of 0.9 µm in thickness was formed. The formation of this film was made for securing a satisfactory insulation voltage toleration, and providing a good coverage on the step of first conductive layer 51. To smooth the stepped portions of the first conductive layer 51, silica solution is applied over P-SiN film 54. Then, it is subjected to thermal treatment, thereby to obtain a 0.4 µm thick silica insulation film 55. Fig. 7C Photoresist film 56 with a predetermined pattern was formed on silica insulation film 55 by the normal photolithography process. Under the same conditions as in the previous embodiment, using the RIE method, silica insulation film 55, P-SiN films 54 and 53 were successively etched, with a mask of the photoresist film 56. Through this etching process, through-hole 57 connecting to the first conductive layer 51 is formed at a predetermined location on the conductive layer 51. Fig. 7D The photoresist film 56 is removed by the O₂ ashing process. Then, the device is thermally treated at 500°C for 15 minutes. Through this thermal treatment, hillock 58 of about 1.0 µm in thickness was formed on the first conducted layer 57 exposing to the through-hole 57. Fig. 7E Further, second conductive layer 59 made of Aℓ-Si and with a predetermined pattern, contact in to hillock 58 through through-hole 57, was formed on the silica insulation film 55. In this way, the semiconductor device of the double conductive layer type was manufactured by the manufacturing method according to the second embodiment. This embodiment can also attain the useful effects comparable with those of the first embodiment. In this embodiment, the P-SiN film 53 was formed to 0.1 µm in thickness at 300°C or less. Its thickness may be any value above 0.05 µm for restricting the hillock formation. The conditions of 500°C and 15-minutes thermal treatment were used for hillock formation. Alternatively, the hillock is placed at less than 500°C, and this is repeated. Aℓ-Si for both the first and second conductive layers may be replaced by Aℓ or Aℓ alloy. Further, this invention is applicable not only to the double layers connection of the first and second conductive layers, but also to the connection of three or more layers. As seen from the foregoing description, this invention can provide the manufacturing method of semiconductor devices which is high in reliability, allows the formation of minute through-holes, and is free from thinning of the conductive layers or their disconnection at the through-holes.

Claims: A method of manufacturing a semiconductor device comprising the steps of: forming a first insulation film (30) on a semiconductor substrate (31); forming a first conductive layer (35) on said first insulation film; forming a hillock (36) of said first conductive layer at a predetermined place on said first conductive layer; forming a second insulation film (37,38) on the structure; removing that portion of said second insulation film, which is above said hillock, and that portion which is on said hillock, thereby forming a contact hole (40) leading to said first conductive layer; and forming on the structure a second conductive layer (41) extending into said contact hole and contacting said first conductive layer. A method of manufacturing a semiconductor device according to claim 1, characterized in that said step of forming said hillock comprises the steps of forming a film (34) having a hillock-suppressing function on said first conductive layer, forming a hole in said hillock-suppressing film, and thermally treating said first conductive layer through said hole formed in said hillock-suppressing film. A method of manufacturing a semiconductor device according to claim 1, characterized in that said hillock-suppressing film is made of a metal. A method of manufacturing a semiconductor device according to claim 1, characterized in that said hillock-suppressing film is made of a metal compound. A method of manufacturing a semiconductor device according to claim 1, characterized in that said hillock-suppressing film is made of silicon compound. A method of manufacturing a semiconductor device comprising the steps of: forming a first insulation film (30) on a semiconductor substrate (31), forming a first conductive layer (51) on said first insulation film; forming on said first conductive layer a second insulation film (53) having a hillock-supressing function; forming a third insulation film (54, 55) on said second insulation film; forming a hole (57) in said second and third insulation films; forming a hillock (58) of said first conductive layer by thermally heating said first conductive layer through said hole; and forming on the structure a second conductive layer (59) extending into said hole and contacting said first conductive layer. A method of manufacturing a semiconductor device according to claim 1 or claim 6, characterized in that said first conductive layer is made of an aluminium. A method of manufacturing a semiconductor device according to claim 1 or claim 6, characterized in that said first conductive layer is made of an aluminium alloy. A method of manufacturing a semiconductor device according to claim 6, characterized in that said second insulation film is formed under a temperature lower than 300°C. A method of manufacturing a semiconductor device according to claim 6, characterized in that said second insulation film is made of a silicon oxidation film having a thickness larger than 0.05 um. A method of manufacturing a semiconductor device according to claim 6, characterized in that said second insulation film is made of a silicon nitride film having a thickness larger than 0.05 µm. A method of manufacturing a semiconductor device according to claim 6, characterized in that said second insulation film is made of a metal oxidation film having a thickness larger than 0.05 µm.

Inventors: ABE, MASAHIRO PATENT DIVISION K.K. TOSHIBA, AOYAMA, MASAHARU PATENT DIVISION K.K. TOSHIBA, MASE, YASUKAZU PATENT DIVISION K.K. TOSHIBA
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1986
Main classification: H01L21
IPC codes: H01L21, H01L23, H01L27