Formation of stacked insulation layers in a semiconductor device

Abstract: A semiconductor device including a semiconductor substrate (1); a metal wiring layers (31) formed on the semi­ conductor substrate; a first insulation layer (411) formed on the metal wiring layer (31), the first insulation layer (411) being formed by a tensile stress insulation layer having a contracting characteristic relative to the substrate; and a second insulation layer (412) formed on the first insulation layer (411), the second insulation layer (412) being formed by a compressive stress insulation layer having an expanding characteristic relative to the substrate. The tensile stress insulation layer (411) is produced by thermal chemical vapor deposition or plasma assisted chemical vapor deposition which is performed in a discharge frequency range higher that 2 megahertz; and the compressive stress insulation layer (412) is produced by plasma assisted chemical vapor deposition which is performed in a discharge frequency range lower than 2 megahertz.

Description: The present invention relates to a semiconductor device and a method of manufacturing the same. More particularly, it relates to a semiconductor device having metal wiring layers and insulation layers formed on the metal wiring layers, and to a method of manufacturing the same. Generally, in producing a semiconductor device of the above type, the insulation layers formed on the metal wiring layers (e.g. aluminum wiring layers) are produced by chemical vapor deposition using insulation material such as phosphor silicated glass (PSG). In this method, however, during the formation of the above insulation layers, problems have arisen such as a disconnection of the metal wiring layers due to stress migration due to the effect of stress generated in the insulation layers, and cracks in the insulation layers. The present invention addresses the above-mentioned problems, and the present invention is concerned with not only the disconnection of the metal wiring layers due to stress migration but also a generation of cracks in the insulation layers. JP-A-57-45931 by the present applicant discloses a semiconductor device with a multilayer passivation film, and a method of manufacturing the same. The multilayer passivation film is formed over an aluminum wiring layer by a plasma CVD method, and by switching the frequency of the voltage applied to the substrate, the multilayer passivation film is formed with a lower tensile stress layer and an upper compressive stress layer. A paper in "Plasma Chemistry and Plasma Processing", Vol. 7, no. 1, March 1987, pages 109 to 124, by W. A. P. Claassen concerns ion bombardment-induced mechanical stress in plasma-enhanced deposited silicon nitride and silicon oxynitride films. The effects of different deposition conditions on the mechanical stress of the deposited films are disclosed. Japanese Journal of Applied Physics supplements, 17th Conference on Solid State Devices and Materials (1985), pages 329 to 332, discloses a planarization method using ECR (Electron Cyclotron Resonance) plasma deposition. Use of this method is disclosed for planarizing a single aluminum wiring layer. According to one aspect of the present invention, there is provided a semiconductor device comprising:- a semiconductor substrate; a plurality of metal wiring layers formed over said semiconductor substrate and including an uppermost wiring layer; a respective first insulation layer formed on each said metal wiring layer except for said uppermost wiring layer, each first insulation layer being formed by a tensile stress insulation layer having a contracting characteristic relative to said substrate; a respective second insulation layer formed on each said first insulation layer and a first second insulation layer formed on said uppermost wiring layer, each second insulation layer being formed by a compressive stress insulation layer having an expanding characteristic relative to said substrate; whereby each two adjacent metal wiring layers are separated by both a tensile stress insulation layer and a compressive stress insulation layer. According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising steps of:- (a) forming a metal wiring layer over a semiconductor substrate; (b) forming a first insulation layer on said metal wiring layer by thermal chemical vapor deposition or plasma assisted chemical vapor deposition which is performed at a discharge frequency higher than 2 MHz; (c) forming a second insulation layer on said first insulation layer by plasma assisted chemical vapor deposition which is performed at a discharge frequency lower than 2 MHz; (d) forming at least one further metal wiring layer, one of which is an uppermost wiring layer; (e) repeating steps (b) and (c) for any said further metal wiring layer apart from the uppermost wiring layer; and (f) repeating step (c) above for the uppermost wiring layer; whereby each two adjacent metal wiring layers are separated by both a said first insulation layer and a said second insulation layer. In the invention, preferably, the or each tensile stress insulation layer is formed by thermal CVD or plasma-assisted CVD performed at a discharge frequency higher than around 2 MHz, and the or each compressive stress insulation layer is formed by plasma-assisted CVD performed at a discharge frequency lower than 2 MHz. Reference is made, by way of example, to the accompanying drawings in which: Figure 1 is a drawing explaining a characteristic of a tensile stress insulation layer; Fig. 2 is a drawing explaining a characteristic of a compressive stress insulation layer; Fig. 3 is a drawing showing a tensile stress insulation layer formed on a metal wiring layer as a first insulation layer; Fig. 4 is a drawing showing a compressive stress insulation layer formed on the first insulation layer as the second insulation layer; Figs. 5(a) to 5(e) are drawings showing a process for manufacturing a semiconductor device according to a first embodiment of the present invention; Fig. 6 is a diagram showing how the value of the stress generated in the insulation layer produced by plasma CVD is changed in accordance with the change of discharge frequency used in a plasma CVD system; Figs. 7(a) to 7(d') are drawings showing a process for manufacturing semiconductor devices according to second and third embodiments of the present invention; Fig. 8 is a diagram showing experimental data regarding the generation of stress migration in various cases; and Fig. 9 is a diagram showing experimental data regarding the generation of cracks in the insulation layers in various cases. As above-mentioned, a tensile stress insulation layer has a contracting characteristic relative to the substrate, and thus, when the tensile stress insulation layer T is formed on the semiconductor substrate S as shown in Fig. 1, the tensile stress insulation layer T causes the substrate S to bend in a direction such that the insulation layer T contracts relative to the substrate S (i.e. a direction such that the insulation layer T compresses the metal wiring layer M formed on the substrate S). On the other hand, a compressive stress insulation layer has an expanding characteristic relative to the substrate, and thus, when the compressive stress insulation layer C is formed on the semiconductor substrate S as shown in Fig. 2, the compressive stress insulation layer C causes the substrate S to bend in a direction such that the insulation layer C expands relative to the substrate S (i.e., a direction such that the metal wiring layer M formed on the substrate S is expanded together with the insulation layer C when the metal wiring layer is heated by a current flowing therethrough). Thus, in embodiments of the first aspect of the invention, by forming the tensile stress insulation layer T on the metal wiring layer M as the first insulation layer, the insulation layer T applies stress to the metal wiring layer M, to compress the metal wiring layer as shown in Fig. 3, and as a result, a disconnection of the metal wiring layer due to stress migration is prevented. Also, by forming the compressive stress insulation layer C on the first insulation layer T as the second insulation layer, as shown in Fig. 4, the compressive stress insulation layer tends to expand together with the expansion of the metal wiring layer when the metal wiring layer is heated, and thus the stress applied by the metal wiring layer to the insulation layer at that time is reduced, and as a result, a generation of cracks in the insulation layer is prevented. Also, in embodiments of the second aspect of the invention, by forming the tensile stress insulation layers on the respective lower side metal wiring layers having a small wiring width (e.g., on the first and the second metal wiring layers), a disconnection of the metal wiring layers having a small wiring width due to stress migration is prevented. Also, by forming the compressive stress insulation layers on the respective upper side metal wiring layers having a large wiring width (e.g., on the third and the fourth metal wiring layers), generation of cracks in the insulation layers due to the expansion of the metal wiring layers having a large wiring width is prevented. In this connection, with regard to the metal wiring layers having a large wiring width, a disconnection thereof due to stress migration need not be considered. As described in detail below, the tensile stress insulation layer may be produced by thermal chemical vapor deposition (thermal CVD) or plasma assisted chemical vapor deposition (plasma CVD) performed in a discharge frequency range higher than 2 megahertz. On the other hand, the compressive stress insulation layer may be produced by plasma assisted chemical vapor deposition (plasma CVD) performed in the discharge frequency range lower than 2 megahertz. Also, when the above tensile stress insulation layer or compressive stress insulation layer is formed by a particular plasma assisted chemical vapor deposition such that the above plasma is produced by electron cyclotron resonance (ECR plasma CVD), the surface of the corresponding insulation layer can be made flat, and thus ensure a high reliability of the metal wiring layers formed on the flattened surfaces of the insulation layers. In this connection, United States Patent 4,446,194 discloses a method of forming a dielectric layer having a compressive stress (corresponding to compressive stress insulation layer) on the metal layer and forming a dielectric layer substantially free of compressive stress (corresponding to the tensile stress insulation layer) on the compressive stress insulation layer, to prevent a formation of voids in the metal layers. But, as shown in the experimental data described in detail below, a semiconductor device embodying the present invention (i.e., a semiconductor device comprising a tensile stress insulation layer formed on the metal layer and a compressive stress insulation layer formed on the tensile stress insulation layer) may effectively prevent both a disconnection of the metal layers due to stress migration and a generation of cracks in the insulation layers, compared with the device disclosed in the above U.S.P. Namely, in embodiments of the present invention, the above-mentioned particular advantages can be obtained, which cannot be expected from the above U.S.P. Figures 5(a) to 5(e) show a process for manufacturing a semiconductor device according to a first embodiment of the present invention. First, as shown in Fig. 5(a), a first metal wiring layer (e.g., aluminum wiring layer) 31 is formed on a semiconductor substrate 1 (e.g., a silicon substrate) via a silicon insulation film 2 (e.g., a silicon dioxide (SiO₂) film). Next, as shown in Fig. 5(b), a tensile stress insulation layer 411 is formed as a first insulation layer on the first metal wiring layer 31. The tensile stress insulation layer 411 functions to compress the metal wiring layer 31, due to the contracting characteristic thereof relative to the substrate, and thus prevents stress migration which will cause a disconnection of the metal wiring layer 31. Then, as shown in Fig. 5(c), a compressive stress insulation layer 412 is formed as a second insulation layer on the tensile stress insulation layer 411. In this connection, the compressive stress insulation layer 412 expands together with the metal wiring layer 31 when the metal wiring layer is heated by a current flowing therethrough, due to the expanding characteristic thereof relative to the substrate, and thus stress applied by the metal wiring layer to the insulation layer at that time is reduced, and as a result, generation of cracks in the insulation layer is prevented. In this connection, the tensile stress insulation layer 411 can be formed by thermal chemical vapor deposition (thermal CVD) or plasma assisted chemical vapor deposition (plasma CVD). When the thermal CVD method is used, an insulation material such as phosphor silicated glass (PSG) or silicon dioxide (SiO₂) is deposited on the metal wiring layer under the condition of a reduced atmospheric pressure or standard atmospheric pressure, and a processing temperature range higher than 200°C, preferably from 300°C to 450°C. When the plasma CVD method is used, an insulation material (reaction gas) such as the above PSG, SiO₂ , SiON, Si₃N₄ or BPSG (boron-phosphor silicated glass), is deposited on the metal wiring layer by supplying a high frequency power having the discharge frequency range higher than 2 megaherts (e.g., 13.56 megahertz) between flat electrodes arranged, for example, in parallel, one of which electrodes is connected to the substrate, under the processing temperature range of from 200°C to 450°C. The plasma CVD method is used for forming the compressive stress insulation layer 412, and the insulation material (the reaction gas) such as the above PSG, SiO₂ , SiON, Si₃N₄ , or BPSG is deposited on the first insulation layer by supplying a high frequency power having a discharge frequency range lower than 2 megahertz (e.g., 200 kilohertz) between the above electrodes, under a processing temperature range of from 200°C to 450°C. Note, the above plasma CVD is of a type other than a plasma CVD wherein the plasma is produced by electron cyclotron resonance (ECR plasma CVD) as described below. Figure 6 is a diagram showing how the value of the stress generated in the insulation layer produced by the plasma CVD is changed in accordance with a change in the discharge frequency of the high frequency power supplied from a high frequency generator connected between the above electrodes used in the plasma CVD system. In Fig. 6, the abscissa corresponds to the discharge frequency, and the ordinate corresponds to the value of the stress (using 10 n dyne/cm², where n = 8 for PSG, and n = 9 for Si₃N₄ , as a unit) generated in the insulation layer produced by the plasma CVD. This plasma CVD was performed by using the insulation material (reaction gas) of the above PSG and Si₃N₄. The value of the tensile stress generated in the insulation layer is represented as a positive value, and the value of the compressive stress generated in the insulation layer is represented as a negative value. The value of the stress becomes zero at the point where the discharge frequency is 2 megahertz, and the value of above tensile stress increases in accordance with the increase of the discharge frequency in the frequency range higher than 2 megahertz. On the other hand, the value of the above compressive stress increases in accordance with a decrease of the discharge frequency in the frequency range lower than 2 megahertz. Namely, the tensile stress insulation layer is formed when the plasma CVD is performed at the discharge frequency range higher than 2 megahertz, and the compressive stress insulation layer is formed at the discharge frequency range lower than 2 megahertz. These conditions remain unchanged even when the above ECR plasma CVD is adopted, instead of another type of plasma CVD, for forming the insulation layer. Then, as shown in Fig. 5(d), a second metal wiring layer 32 is formed on the second insulation layer 412. When the above-mentioned steps are repeated, a tensile stress insulation layer 421 and a compressive stress insulation layer 422 are successively formed on the second metal wiring layer 32, and a third metal wiring layer 33 is formed on the above insulation layer 422 corresponding to the second insulation layer. Then, in the above embodiment, the compressive stress insulation layer 432 is formed as a cover on the third metal wiring layer 33, as shown in Fig. 5(e), and subsequently, an anneal processing for the semiconductor device is carried out for about half an hour under a temperature of, for example, 450°C. Figures 7(a) to 7(d') show a process for manufacturing semiconductor devices according to second and third embodiments of the present invention; the step shown in Fig. 7(a) corresponds to that of the above Fig. 5(a). Next, in the second embodiment of the present invention, as shown in Fig. 7(b), a tensile stress insulation layer 411' is formed on the first metal layer 31 as the first insulation layer. This insulation layer 411' may be formed by the same means as used to form the tensile stress insulation layer 411 in the first embodiment. Then, as shown in Fig. 7(c), a compressive stress insulation layer 412' is formed as the second insulation layer on the first insulation layer 411'. The insulation layer 412' is formed so that the surface thereof is made flat. In this connection, the insulation layer 412' having the flattened surface is formed by the above-mentioned ECR plasma CVD method. In this case, this ECR plasma CVD is carried out under the condition that the microwave power for producing the ECR Plasma is, for example, 800 watts, and the discharge frequency and the output of the high frequency bias power applied between one electrode connected to the substrate and the other electrode (e.g., the earth electrode) are, for example, 400 kilohertz and 50 to 100 watts, respectively. Namely, as shown in Fig. 6, even when the above ECR plasma CVD is adopted, the compressive stress insulation layer may be produced in a discharge frequency range of the above bias power which is lower than 2 megahertz. Under this condition, the insulation layer 412' is produced by using an insulation material such as SiO₂ , PSG, SiON, Si₃N₄ or BPSG. Accordingly, the surface of the insulation layer 412' may be flattened, and then, as shown in Fig. 7(d), a second metal wiring layer 32 formed on the flattened surface of the insulation layer 412'. Further, the above steps for forming the first and second insulation layers and the metal wiring layer may be successively repeated a predetermined number of times. Also, in the third embodiment of the present invention, after the first step shown in Fig. 7(a), as shown in Fig. 7(b'), a tensile stress insulation layer 411'' is formed as the first insulation layer on the first metal wiring layer 31, in such a manner that the surface of the insulation layer 411'' is made flat. As above-mentioned, the insulation layer 411'' having a flattened surface, is formed by the above ECR plasma CVD method. In this case, this ECR plasma CVD is carried out under the condition that the above microwave power for producing the ECR plasma is, for example, 800 watts, and the discharge frequency and the output of a high frequency bias power applied between the above electrodes, one of which electrodes is connected to the substrate, are, for example, 13.56 megahertz and 50 to 100 watts, respectively. Namely, as shown in Fig. 6, even when the above ECR plasma CVD is adopted, the tensile stress insulation layer may be produced in the discharge frequency range of the above bias power, which is higher than 2 megahertz. Under this condition, the insulation layer 411'' is produced by using the insulation material such as PSG, SiO₂ , SiON, Si₃N₄ or BPSG. Then, as shown in Fig. 7(c'), a compressive stress insulation layer 412'' is formed as the second insulation layer on the flattened surface of the insulation layer 411''. The insulation layer 412'' may be formed by the same means used to form the compressive stress insulation layer 412 in the first embodiment. The surface of the insulation layer 412'', which is formed on the flattened surface of the insulation layer 411'' also may be flattened. Then, as shown in Fig. 7(d'), a second metal wiring layer 32 is formed on the flattened surface of the insulation layer 412''. Further, the above steps for forming the first and second insulation layers and the metal wiring layer can be successively repeated a predetermined number of times. Thus, according to the second and third embodiments of the present invention, since each of the metal wiring layers is formed on the flattened surface of the corresponding insulation layer, a high reliability of the metal wiring layers is ensured. Figure 8 shows experimental data regarding the generation of the above stress migration in various cases. The data was obtained under the condition that a current having a density of 3.0 x 10⁶ A/cm² (Amperes/cm²) is made to flow through the aluminum wiring layers having a wiring width of 1.5 µ (microns) and a wiring thickness of 0.7 µ (microns), at a temperature of 250°C. In Fig. 8, the abscissa corresponds to the test time, (in hours), and the ordinate corresponds to an accumulated ratio of the generation of the defect (i.e., the above stress migration), shown as a percentage. In Fig. 8, marks "*" along a line "C" correspond to test data in the case wherein each of the insulation interlayers is formed only by the tensile stress insulation layer produced by thermal CVD, and marks "o" along a line "d" correspond to test data in the case wherein each of the insulation interlayers is formed only by the compressive stress insulation layer produced by plasma CVD. Further, marks "□" along a line "b" correspond to test data in the case wherein each of the insulation interlayers comprises the compressive stress insulation layer as the first insulation layer and the tensile stress insulation layer formed on the compressive stress insulation layer as the second insulation layer, as shown in the above U.S.P. 4,446,194, and marks "▵" along a line "a" correspond to test data in the case wherein each of the insulation interlayers comprises the tensile stress insulation layer as the first insulation layer and the compressive stress insulation layer formed on the tensile stress insulation layer as the second insulation layer, as in the present invention. As shown in Fig. 8 it is apparent that a construction embodying the present invention can be remarkably effective for preventing stress migration, compared to other cases. Figure 9 shows experimental data regarding the generation of cracks in the insulation layers in various cases. In Fig. 9, test data I corresponds to the case wherein the insulation interlayers formed on the first, second, and third metal wiring layers are all formed only by the tensile stress insulation layers T, and only the cover formed on the fourth metal wiring layer is formed by the compressive stress insulation layer C. Also, test data III corresponds to the case wherein the insulation interlayers formed on the first and second metal wiring layers are formed only by the tensile stress insulation layers T, and the insulation interlayer formed on the third metal wiring layer comprises the compressive stress insulation layer C as a first insulation layer 3-1 of the corresponding insulation interlayer and the tensile stress insulation layer T formed on the first insulation layer 3-1 as a second insulation layer 3-2 of the corresponding insulation interlayer, as shown in the above U.S.P., and the cover formed on the fourth metal wiring layer is formed by the compressive stress insulation layer C. These test data I and III show that, according to the above constructions, it is impossible to prevent the generation of cracks in the insulation layers, as shown by marks "X". On the other hand test data II corresponds to a case (not according to the invention) wherein the insulation interlayers formed on the first and second metal wiring layers (i.e., metal wiring layers having a small wiring width) are formed by tensile stress insulation layers T, and the insulation interlayer formed on the third metal wiring layer and the cover formed on the fourth metal wiring layer (i.e., insulation interlayer and the cover formed on the metal wiring layers having a large wiring width) are formed by the compressive stress insulation layers C. Also, test data IV corresponds to the case wherein the insulation interlayer formed on the first metal wiring layer is formed by the tensile stress insulation layer T, and each of the insulation interlayers formed on the second and third metal wiring layers comprises the tensile stress insulation layer T as a first insulation layer 2-1 or 3-1 of the corresponding insulation interlayer and the compressive stress insulation layer C formed on the first insulation layer 2-1 or 3-1 as a second insulation layer 2-2 or 3-2 of the corresponding insulation interlayer, as shown in the first embodiment of the present invention, and the cover formed on the fourth metal wiring layer is formed by the compressive stress insulation layer C. Further, test data V corresponds to the case wherein each of the insulation interlayers formed on the first, second, and third metal wiring layers comprises the tensile stress insulation layer T as a first insulation layer 1-1, 2-1, or 3-1 of the corresponding insulation interlayer and the compressive stress insulation layer C formed on the first insulation layer 1-1, 2-1, or 3-1 as a second insulation layer 1-2, 2-2, or 3-2 of the corresponding insulation interlayer, as shown in the first embodiment of the present invention, and the cover formed on the fourth metal wiring layer is formed by the compressive stress insulation layer C. These test data IV and V show that, according to these embodiments of the present invention, the generation of cracks in the insulation layers can be effectively prevented, as shown by marks "o".

Claims: A semiconductor device comprising:- a semiconductor substrate (1); a plurality of metal wiring layers (31, 32, ...) formed over said semiconductor substrate and including an uppermost wiring layer (33); a respective first insulation layer (411, 421, ...) formed on each said metal wiring layer except for said uppermost wiring layer, each first insulation layer being formed by a tensile stress insulation layer having a contracting characteristic relative to said substrate; a respective second insulation layer (412, 422, ...) formed on each said first insulation layer and a first second insulation layer (432) formed on said uppermost wiring layer (33), each second insulation layer being formed by a compressive stress insulation layer having an expanding characteristic relative to said substrate; whereby each two adjacent metal wiring layers (31, 32; 32, 33) are separated by both a tensile stress insulation layer and a compressive stress insulation layer. A method of manufacturing a semiconductor device, comprising steps of:- (a) forming a metal wiring layer (31) over a semiconductor substrate (1); (b) forming a first insulation layer (411, 421) on said metal wiring layer by thermal chemical vapor deposition or plasma assisted chemical vapor deposition which is performed at a discharge frequency higher than 2 MHz; (c) forming a second insulation layer (412, 422, 432) on said first insulation layer by plasma assisted chemical vapor deposition which is performed at a discharge frequency lower than 2 MHz; (d) forming at least one further metal wiring layer (32, 33), one of which is an uppermost wiring layer (33); (e) repeating steps (b) and (c) for any said further metal wiring layer (32) apart from the uppermost wiring layer (33); and (f) repeating step (c) above for the uppermost wiring layer (33); whereby each two adjacent metal wiring layers (31, 32; 32, 33) are separated by both a said first insulation layer and a said second insulation layer. A method of manufacturing a semiconductor device according to claim 2, wherein at least one of said first and second insulation layers (411, 421; 412, 422, 432) is formed by plasma-assisted chemical vapor deposition in which said plasma is produced by electron cyclotron resonance.

Inventors: ITOH JUNICHI, KURITA KAZUYUKI, ITOH, JUNICHI, KURITA, KAZUYUKI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1988
Main classification: H01L21
IPC codes: H01L21, H01L23