Semiconductor device having two conductive layers and method of manufacturing the same

Abstract: A semiconductor device comprises a lower conductive layer (5) formed on a semiconductor substrate, a first insulation film layer formed at least on side faces of the lower conductive layer (5), a second insulation film layer (13) formed around the lower conductive layer (5) on which the first insulation film layer has been formed, a contact hole (15) formed on the second insulation film layer (13) in the vicinity of a side face of the lower conductive layer (5), and an upper conductive layer (17) formed in the contact hole (15) and over the second insulation film (13). The first insulation film layer is of a three-film structure comprising a first oxide film (7), a nitride film (9) and a second oxide film (11).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of semiconductor device which realized a very fine gap to be formed between a contact hole in which an upper conductive layer is formed and a lower conductive layer, and to a method of manufacturing semiconductor devices having such a structure. 2. Description of the Prior Art In some semiconductor devices, two conductive layers (wiring or electrode layers) which shall be insulated against each other are laminated one upon another with an insulation interlayer between them. A contact hole is formed on the insulation interlayer in the vicinity of the lower conductive layer, and a part of the upper conductive wiring or electrode layer is formed in the contact hole. Integration of this sort of semiconductor device may be improved by reducing a distance between the contact hole and the lower conductive layer. If the distance between the contact hole and the lower conductive layer is reduced, however, the insulation interlayer between the contact hole and the lower conductive layer will be thinned. As a result, an insulation property, i.e., voltage resistance of the insulation interlayer may be deteriorated due to defects, etc., in the insulation interlayer. This may cause the lower conductive layer and the upper conductive layer in the contact hole to short-circuit. To cope with this problem, a structure is proposed to form a contact hole firstly and then a nitride film (Si₃N₄) on an inner wall of the contact hole. After that, an upper conductive layer is formed on the nitride film in the contact hole. The nitride film of this structure can improve an insulation property between a lower conductive layer and the upper conductive layer formed in the contact hole. However, the nitride film formed on the inner wall of the contact hole narrows an actual opening area of the contact hole. Therefore, to obtain the same opening area as that of a contact hole with no nitride film, the opening area of the contact hole of this structure shall be widened. US-A-3996657 describes a double polycrystalline silicon gate memory in which contact holes to the source and drain are formed adjacent to the gate structure. An oxide film is provided between the control gate and the contact hole metal. EP-A-0 187 278 describes a MOS transistor including floating and control gates. Between the gates a composite insulation layer is provided including a silicon nitride layer. SUMMARY OF THE INVENTION To solve the problem, an object of the present invention is to provide a semiconductor device structure which enables a distance between a lower conductive layer and a contact hole to be reduced to improve integration of the semiconductor device, and a method of manufacturing semiconductor devices having such a structure. Another object of the present invention is to provide a semiconductor device structure which can remarkably reduce insulation failures to occur between upper and lower conductive layers as well as reducing a distance between the lower conductive layer and a contact hole, and a method of manufacturing semiconductor devices having such a structure. The objects of the invention are solved by a semiconductor device comprising a lower conductive layer, formed on a semiconductor substrate; a first insulation film layer formed aroung the lower conductive layer, said first insulation film layer having a contact hole at a portion adjacent to a side face of said lower conductive layer; and an upper conductive layer formed in said contact hole and over said first insulation film, characterised in that a second insulation film layer is formed at least on side faces of said lower conductive layer, said second insulation film layer being of a three-film structure comprising a first oxide film, a nitride film and a second oxide film and said first insulation layer is formed around said second insulation layer. The objects of the invention are also solved by a method of manufacturing a semiconductor device, comprising the steps of forming a lower conductive layer on a semiconductor substrate; forming a second insulation film layer formed of a three-film structure comprising a first oxide film, a nitride film and a second oxide film, at least on side faces of the lower conductive layer; forming a first insulation film layer around the lower conductive layer on which the second insulation film layer has been formed; opening and forming a contact hole in the first insulation film layer adjacent to the lower conductive layer; and forming an upper conductive layer in the contact hole and over the first insulation film layer. According to the semiconductor device and the manufacturing method of semiconductors of the present invention, the insulation film layer including the nitride film is formed at least on the side faces of the lower conductive layer (a wiring layer or an electrode layer), then the contact hole is opened in the vicinity of the lower wiring or electrode layer, thus reducing a distance between the contact hole and the lower wiring or electrode layer. These and other objects, features and advantages of the present invention will be more apparent from the following detaild description of preferred embodiments in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1a to 1d are views showing processes of a method of manufacturing a semiconductor device according to an embodiment of the present invention; and Fig. 2 is a view showing structure of a semiconductor device according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS Figures 1a to 1d show processes of the method of manufacturing a semiconductor device according to the embodiment of the present invention. This embodiment relates to an EPROM (a ultraviolet ray erasable PROM). Firstly, structure of the EPROM to be manufactured according to the method of the present invention will be explained with reference to Fig. 1d. In the figure, N⁺ diffusion layers 3 are formed just under the surface of a P-type silicon substrate 1. The diffusion layers 3 will be a source region and a drain region of a cell of the EPROM, respectively. On the silicon substrate 1, a gate electrode 5 of the cell is formed. The gate electrode 5 is a lower electrode layer (a lower conductive layer). The gate electrode 5 comprises two polysilicon layers. The two layers of the gate electrode 5 are covered with a first oxide film (an SiO₂ film) 7 to separate and insulate the electrode 5 from a peripheral region. On the SiO₂ film 7, a nitride film (an Si₃N₄ film) 9 is formed to cover the surface of the SiO₂ film. On the Si₃N₄ film 9, a second oxide film (an SiO₂ film) 11 is formed to cover the surface of the Si₃N₄ 9. Namely, the gate electrode 5 is covered with a three-film insulation layer comprising the SiO₂ film 7, Si₃N₄ film 9 and SiO₂ film 11. Around the three-film insulation layer, an insulation interlayer 13 is formed. The insulation interlayer 13 on one of the diffusion layers 3 is provided with a contact hole 15 which is opened adjacent to the gate electrode 5. In the contact hole 15, an aluminum (Al) wiring layer 17 is formed. The wiring layer 17 is an upper wiring layer (a conductive layer) for the one diffusion layer 3. The respective films of the three-film insulation layer, i.e., the first oxide film 7, nitride film 9 and second oxide film 11 are, for example, 10nm (100Å), 12nm (120Å) and 10nm (100Å) in thickness, respectively. The three-film insulation layer achieves a defective density of 0.01 cm⁻² or below, an electric field strength of 30 V or over irrespective of polarity, and a leak current of 10⁻¹⁰ A/mm⁻² or below with respect to an applied voltage of 20 V. Therefore, a thickness "d" of the insulation interlayer 14 between the three-film insulation layer and the contact hole will be about 0.1 µm. The aluminum wiring layer 17 is formed over the insulation interlayer 13, along the inner wall surface of the contact hole 15 and on the surface of the one diffusion layer 3. In this embodiment, the lower electrode layer is the two-layer gate electrode 5, and the upper wiring layer is the aluminum wiring layer 17. An example of process for manufacturing the semiconductor structure explained in the above will be described with reference to Figs. 1a to 1d. Firstly, the SiO₂ film 7 is formed on the silicon substrate 1. On the SiO₂ film 7, the first polysilicon layer is formed. On the first polysilicon layer, another SiO₂ layer 7 is formed and on which the second polysilicon layer is formed. By patterning these layers according to a photolithography technique, the two-layer gate electrode 5 is formed. Then, the N⁺ type diffusion layers 3 are formed with an ion implantation technique, as shown in Fig. 1a. After that, the SiO₂ film 7, Si₃N₄ film 9 and SiO₂ film 11 are thinly deposited over the gate electrode 5 in the thickness of, for example, about 10nm (100Å), 12nm (120Å) and 10 nm (100Å) respectively, as shown in Fig. 1b. Then, the insulation interlayer 13 is deposited on the SiO₂ film 11, and a resist material 19 is coated over the insulation interlayer 13. The resist material 19 is patterned according to the photolithography technique, and the contact hole 15 is opened on the diffusion layer 3 according to an RIE (Reactive Ion Etching) method as shown in Fig. 1c. After that, the resist material 19 is removed, and aluminum is deposited on the surface of one of the diffusion layers 3, in the contact hole 15 and over the insulation interlayer 13. The aluminum will form the upper wiring layer with respect to the gate electrode 5 which is the lower electrode layer. The deposited aluminum is patterned to form the aluminum wiring layer 17. Thus, the EPROM cell provided with the two-layer electrode 5 is completed as shown in Fig. 1d. As described in the above, the three-film insulation layer comprising the SiO₂ film 7, Si₃N₄ film 9 and SiO₂ film 11 is thinly formed, and then the contact hole 15 is opened and formed. Therefore, a distance between the gate electrode 5 and the contact hole 15 is short so that an opening area of the contact hole 15 may smaller than that of the conventional contact hole which has an insulation film. Accordingly, high integration is realized. The present invention is not limited to the above-mentioned embodiment but various modifications may be possible. For example, if the semiconductor element tends to retain charges in regions indicated with a reference mark "c" in Fig. 1d, the three-film insulation layer may firstly be formed as shown in Fig. 1b. Then, the three-film insulation layer formed on the gate electrode 5 and silicon substrate 1 is removed according to an etchback method to leave the three-film insulation layer only on side faces of the gate electrode 5 as shown in Fig. 2. With this structure, charges are hardly caught in the regions "c" while insulation properties of the upper aluminum wiring layer 17 and lower gate electrode 5 are maintained with no change. Although the embodiment has used polysilicon for the lower electrode layer and aluminum for the upper wiring layer, the materials are not limited to them. In summary, according to the present invention, thin insulation films including a nitride film are formed at least on side faces of a lower wiring or electrode layer, and then a contact hole is opened and formed adjacent to the lower wiring or electrode layer. As a result, insulation failures may rarely happen between the lower wiring or electrode layer and an upper wiring or electrode layer. In addition, a distance between the lower wiring or electrode layer and the contact hole is reduced to realize high integration.

Claims: A semiconductor device comprising: a lower conductive layer (5,5) formed on a semiconductor substrate (1); a first insulation film layer (13) formed around the lower conductive layer (5,5), said first insulation film layer (13) having a contact hole (15) at a portion adjacent to a side face of said lower conductive layer(5,5); and an upper conductive layer (17) formed in said contact hole (15) and over said first insulation film layer (13) characterized in that a second insulation film layer (7, 9, 11) is formed at least on side faces of said lower conductive layer (5, 5), said second insulation film layer (7, 9, 11) has a three-film structure comprising a first oxide film (7), a nitride film (9) and a second oxide film (11), and said first insulation film layer (13) is formed around said second insulation film layer (7, 9, 11). The semiconductor device as claimed in claim 1, wherein the thickness of said first insulation film layer (13) between said second insulation film layer (7, 9, 11) on said lower conductive layer (5, 5) and said contact hole (15) is 0,1 µm. The semiconductor device as claimed in claim 1, wherein the nitride film (9) is interposed between the first and second oxide films (7, 11), in said second insulation film layer (7, 9, 11). The semiconductor device as claimed in claim 3, wherein the thickness of the first oxide film (7) is 10 nm (100 Å) the thickness of the nitride film (9) 12 nm (120 Å) and the thickness of the second oxide film (11) 10 nm (100 Å). The semiconductor device as claimed in claim 1, wherein said first insulation film layer (13) is an insulation interlayer. A method of manufacturing a semiconductor device, comprising the steps of: forming a lower conductive layer (5,5) on a semiconductor substrate (1); forming a second insulation film layer (7,9,11) formed of a three-film structure comprising a first oxide film (7), a nitride film (9) and a second oxide film (11), at least on side faces of the lower conductive layer (5,5); forming a first insulation film layer (13) around the lower conductive layer (5,5) on which the second insulation film layer (7,9,11) has been formed; opening and forming a contact hole (15) in the first insulation film layer (13) adjacent to the lower conductive layer (5,5); and forming an upper conductive layer (17) in the contact hole (15) and over the first insulation film layer (13). The method as claimed in claim 6, wherein the thickness of the first insulation film layer (13) between the second insulation film layer (7,9,11) on the lower conductive layer and the contact hole (15) is 0,1 µm. The method as claimed in claims 6 and 7, wherein the nitride film (9) is interposed between the first and second oxide films (7,11), in the second insulation film layer (7,9,11). The method as claimed in claim 8, wherein the thickness of the first oxide film (7) is 10 nm (100 Å), the thickness of the nitride film (9) is 12 nm (120 Å), and the thickness of the second oxide film (11) is 10 nm (100 Å). The method as claimed in claim 6, wherein the first insulation film layer (13) is an insulation interlayer.

Inventors: MORI SEIICHI, SHINAGAWA TAKESHI TOSHIBAHIYOS, MORI, SEIICHI, SHINAGAWA, TAKESHI TOSHIBAHIYOSHIRYO
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1989
Main classification: H01L29
IPC codes: H01L23, H01L29, H01L21