CONTACT STRUCTURE FOR AN INTEGRATED SEMICONDUCTOR DEVICE

Abstract: An integrated device having: a first conductive region (6A); a second conductive region (11A); an insulating layer (9) arranged between the first and the second conductive region; at least one through opening (36) extending in said insulating layer (9) between the first and the second conductive region; and a contact structure (10A) formed in the through opening and electrically connecting the first conductive region (6A) and the second conductive region (11B). The contact structure (10A) is formed by a conductive material layer (30) that coats the side surface and the bottom of the through opening (36) and surrounds an empty region (35) which is closed at the top by the second conductive region (11A). The conductive material layer (30) preferably comprises a titanium layer (31) and a titanium-nitride layer (32) arranged on top of one another.

Description: CONTACT STRUCTURE FOR AN INTEGRATED SEMICONDUCTOR DEVICE TECHNICAL FIELD The present invention relates to a contact structure for integrated semiconductor devices and to a fabrication process thereof. More specifically, the invention relates to a contact structure for a ferro-electric memory device integrated in a semiconductor substrate and of the type comprising an appropriate control circuitry and an array of ferroelectric memory cells. The invention regards, in particular, but not exclusively, a ferro-electric memory device of the "stacked" type, and the ensuing description is made with reference to this application with the sole purpose of simplifying the presentation of the invention. In fact, the stacked configuration is particularly suited to the integration requirements of the new CMOS technologies. BACKGROUND ART In a stacked photo-electric memory device, each memory cell includes a MOS transistor integrated in a substrate of semiconductor material and connected to a ferroelectric capacitor arranged on top of the MOS transistor. The MOS transistor comprises a first and a second conduction terminal (source and drain regions) , formed in the substrate, and a control electrode, formed on top of the substrate inside an insulating layer that covers the substrate. The ferro-electric capacitor comprises a bottom electrode made on the insulating layer, above and in electrical contact with the first conduction terminals. The bottom electrode is coated with .a ferro-electric material layer and is capacitively coupled to a top electrode . As is well known, ferro-electric memories are starting to play an ever important role in the panorama of integrated circuits, thanks to their low consumption, as well as to the high read and erasing speeds as compared to conventional nonvolatile memories. Consequently, it is of great interest to be able .to build ferro-electric memory devices in combination with MOS devices integrated in a same semiconductor substrate. The known processes for the implementation of ferroelectric memory devices envisage, after forming the conduction terminals of the MOS transistor in the substrate, forming the insulating layer which covers the entire surface of the chip. The control electrode is formed inside the insulating layer, and then, on top of the insulating layer, the ferro-electric capacitor is formed. The article "Advanced 0.5 μm FRAM Device Technology with Full Compatibility of Half-Micron CMOS Logic Devices" by Yamazaki et al . (Proceedings of IEDM '97, Washington, DC, December 1997) describes a first known solution for implementing ferro-electric devices and the corresponding contacts . In particular, the aforesaid article describes the manufacture of contacts intended to electrically connect ferro-electric devices and MOS devices through contact regions . The contact regions are formed by opening openings in the insulating layer and filling them with a conductive material, such as tungsten (W) . This technique, referred to as the W-plug technique, enables forming contacts with high aspect ratio, namely, a high contact depth-to-width ratio, but it is not easy to use when the W-plugs are to undergo, in subsequent process steps, heat treatments in an oxidizing environment. This is the case of ferro-electric materials. The treatment of these materials envisages, in fact, after depositing the ferro-electric material, annealing and crystallization treatments at temperatures of between 500°C and 850°C in the presence of oxygen. These treatments constitute, however, a problem. In fact, tungsten, reacting with oxygen (0 2 ) , is converted into tungsten pentoxide (W 2 Os) , i.e., a non-conductive material, according to a strongly exothermic process. This phenomenon, known as a "volcano" phenomenon, may even cause explosion of the contact as a result of the formation of 2 O5, and moreover involves the risk of polluting the oxidation oven. Similar considerations apply in the case where the contact regions are filled with polysilicon (polySi-plugs) , which oxidizes and becomes insulating if it is subjected to the treatments necessary for the crystallization of ferro-electric materials. More specifically, the polysilicon, reacting with oxygen, is converted into silicon dioxide (Si0 2 ) , namely into a non-conductive material, according to a process that involves an increase in volume, and hence high stress induced on the structure. To solve this problem, the contacts filled with tungsten or polysilicon are "sealed" with barrier layers made of materials that are not standard in processes for manufacturing integrated circuits . The introduction of the process steps for forming the 01 00192 - 4 - barrier layers is at the expense of a considerable complication in the fabrication process. The device described in the cited document has an interconnection with the MOS device obtained through a titanium-nitride (TiN) layer used as a local interconnection. European patent application EP 0996160 filed in the name of the present applicant on 12 October 1998 discloses forming a contact structure for a semiconductor device using (Fig. 1) a Ti/TiN barrier layer, deposited before the plugs, in order to ensure conduction between the terminals of the MOS transistor (N + -type or P + -type junctions) and a capacitor overlying the insulating layer. The remaining space is filled with silicon dioxide ("oxide plugs") . This solution makes it possible to avoid the problem of "volcanoes" described previously. The above solution involves, however, an increase in the contact resistance with respect to the structure filled with tungsten. Although this drawback does not constitute a problem for biasing the capacitor, and hence for the memory device, it may impair the performance of the control circuits. European patent application No. 00830762.1, filed in the name of the present applicant, solves the problem referred to above by differentiating the use of the oxide plugs and the tungsten plugs, according to two possible solutions: a) using the oxide plugs for the contact between the source region of the MOS transistor and the bottom electrode of the ferro-electric capacitor (in the memory array) , and the tungsten plugs for the contact with the drain region of the MOS transistor and for all the contacts of the CMOS components of the circuitry; b) using the oxide plugs for both the contacts of the terminals of the MOS transistor (both between the source region and the bottom electrode of the capacitor - in the memory array - and between the drain region and the metal region of the bit line) , and the tungsten plugs for all the contacts of the CMOS components of the circuitry. Even though these solutions are advantageous, the fabrication process is rendered burdensome by the steps of filling the contact and of subsequent planarization or etching of the residual oxide. DISCLOSURE OF THE INVENTION The aim of the present invention is therefore to provide a process able to avoid the drawbacks described previously, and hence to provide a contact structure for a semiconductor device, in particular of the ferro-electric type, having structural and functional characteristics such as to overcome the limitations and drawbacks that still afflict the known devices, in particular as regards the contact structures. According to the present invention there are provided an integrated device and a fabrication process thereof, as respectively defined in Claim 1 and Claim 9. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, a preferred embodiment is now described, purely by way of non-limiting example and with reference to the attached drawings, wherein: - Figure 1 shows a cross-section of a portion of a known ferro-electric memory array; - Figure 2 shows a cross-section of a ferro-electric memory array comprising the contact structure according to the invention; - Figure 3 shows an enlarged detail of Figure 2: and - Figure 4 shows a variant of the contact structure according to the invention. BEST MODE FOR CARRYING OUT THE INVENTION Figure 2 shows a portion of a memory array 1 of ferroelectric type, integrated in a substrate 5 of semiconductor material and comprising some memory cells 2. Each memory cell 2 comprises, in particular, a MOS transistor 3, as well as a ferro-electric capacitor 4 connected thereto in series. The memory cells 2 of the memory array 1 are, in a known way, organized in word lines WL and bit lines BL, each cell 2 being identified uniquely by the intersection of a bit line with a word line. Each MOS transistor 3 is formed in the substrate 5 and comprises respective source regions 6A and drain regions 6B, N + -type or P + -type doped. In addition, a control-gate electrode 7, formed by a double polysilicon and suicide layer, overlies a channel region of the substrate 5, the channel region being comprised between the source region 6A and the drain region 6B, and is insulated from the surface of the substrate 5 by a thin oxide layer 8. In this configuration, pairs of transistors 3 that are adjacent and belong to the same bit line BL have a common drain terminal 6B. A first insulating layer 9, for example an oxide doped with boron and phosphorus (BPSG) , coats the substrate 5. Openings 36 are formed in the first insulating layer 9, above the source region 6A and drain region 6B and accommodate respective contacts 10A, 10B. The contacts 10A, 10B are of a conductive material layer 30 comprising a titanium layer 31 and a titanium-nitride layer 32, arranged on top of one another (see Figure 3) . The contacts 10A, 10B each comprise a coating portion 20A, 20B which coats the side walls and the bottom of the opening 36 of the first insulating layer 9, and a horizontal portion 21A, 21B, which extends on top of the first insulating layer 9. The region or volume 35 inside each coating portion 20A, 20B of the contacts 10A, 10B is empty. First and second conductive regions 11A, 11B, for example of platinum, cover the horizontal portions 21A and 21B of the contacts 10A, 10B and seal the contacts 10A, 10B at the top. The first conductive regions 11A form a bottom plate of the ferro-electric capacitors 4 and extend, at least partially, over the control electrode 7 of the transistor 3. Each capacitor 4 moreover comprises a ferro-electric material region 12 and a top plate 13. The ferro-electric material regions 12 form strips that extend, in a direction perpendicular to the plane of the drawing (as described in Italian patent application TO99A000356 filed on 30 April 1999), on top of and between pairs of adjacent first conductive regions 11A that belong to two memory cells 2 that do not have the drain region 11B in common. The top electrodes 13 are formed by strips of metal, for example platinum, which extend, perpendicularly to the plane of the drawing, on top of the ferro-electric material regions 12. In particular, the top electrodes 13 192 - 8 - have a smaller width than the first conductive regions 11A forming the bottom electrodes of the ferro-electric capacitors 4, as may be seen in the cross-section of Figure 2. On top of the ferro-electric capacitors 4 there extend in succession a second insulating layer 14, a first metal line 18 (Metal 1) , which forms a bit line and extends in the horizontal direction of the drawing, a third insulating layer 15, and second metal lines 19 (Metal 2) , that form word lines and extend in a direction perpendicular to the plane of the drawing, inside the third insulating layer 15. Contact regions 22 extend through the second insulating layer 14, between the first metal line 18 and the second conductive regions 11B, to electrically connect the first metal line 18 to the drain regions 6B through the second conductive regions 11B and the second contacts 10B. The structure of Figure 2 is obtained in the way described hereinbelow. Initially, thick oxide (field oxide) regions 16 are formed in the substrate 5 and define conduction areas or active areas of the ferro-electric memory device 1. Inside and on top of the active areas, the MOS transistor 3 is formed; namely, the thin oxide layer 8, the control-gate electrode 7, and the source regions 6A and drain regions 6B. In a per se known manner, not described in detail, the junctions (P + or N + ) of the source regions 6A and drain regions 6B can be possibly separated by oxide spacers to be subsequently contacted through the contact structure according to the invention. Next, the first insulating layer 9 is deposited on the substrate 5. In the first insulating layer 9, using a contact mask and a subsequent oxide etch, the openings 36 are made above the source regions 6A and drain regions 6B, so as to enable access to the substrate 5 through the first insulating layer 9. Then the contact structure 10A, 10B, which forms the subject of the present invention, is formed by depositing the conductive material layer 30. In a possible implementation, as a non-limiting example, on top of the first insulating layer 9 are deposited the Ti layer 31, by plasma vapor deposition (PVD) or using another deposition technique, and the TiN layer 32, by chemical vapor deposition (CVD) or using another deposition technique. For example, the Ti layer 31 has a thickness of between 10 and 100 nm, preferably 35 nm, and the TiN layer 32 has a thickness of between 50 and 200 nm, preferably 100 nm. It is possible to form a titanium layer alone or a titanium nitride layer alone, even though it is preferable to have both layers. Thereby, the conductive material layer 30 coats in an almost conform way the side walls and the bottom of the openings 36, forming the contacts 10A, 10B. At this point, the region 35 comprised between the walls of the contacts 10A, 10B is left empty. Next, a conductive layer, for example of platinum, is deposited in a non-conform way, and the conductive layer is shaped, together with the conductive material layer, so as to form simultaneously the horizontal portions 21A and 21B of the contacts 10A, 10B and the first and second conductive regions 11A, 11B. From experimental tests it has been noted that the 192 - 10 - conductive layer that is to form the first and second conductive regions 11A, 11B seals the contacts 10A, 10B at the top, maintaining a sufficient planarization. It is, anyhow, preferable that the width of the empty region 35 be similar to (or slightly greater than) the width of the conductive material layer 30. Conduction between the N + , P + junctions forming the source regions 6A and the drain regions 6B of the MOS transistor 3 and the conductive layer that is to form the first and second conductive regions 11A, 11B is thus ensured by the Ti/TiN conductive material layer 30, which, from the substrate 5, following the profile of the openings 36, reaches as far as the top surface of the first insulating layer 9. Finally, the ferro-electric capacitor 4 is formed according to the process steps known in the current technology and described in Italian patent application TO99A000356 filed on 30 April 1999, referred to previously. The contact structure 10A, 10B described above solves the above discussed problems of the known structures. In addition, the elimination of process steps, such as tungsten deposition, which take place in presence of hydrogen, is advantageous from the standpoint of the quality of the ferro-electric material, in so far as the latter is degraded by hydrogen. Finally, it is clear that modifications and variations may be made to the device and the fabrication process described and illustrated herein, without thereby departing from the scope of the present invention, as defined in the attached claims. In particular, it is emphasized that the described contact structure can be used in any electronic device wherein it is necessary to electrically connect a first conductive region, wherever 01 00192 - 1 1 - this is formed (either embedded in the substrate or surrounded by insulating layers on top of the substrate) with a second conductive region (for example, a metal region) arranged at a different level. In particular, the invention can be applied also to regions connecting successive metal layers, as shown by way of example in Figure 4, for a contact structure 40 formed between a first metal line 41 and a second metal line 42.

Claims: CLAIMS 1. An integrated device comprising: at least one first conductive region (6A; 6B; 40); at least one second conductive region (11A; 11B; 41); an insulating layer (9; 43) extending between said first and second conductive regions; at least one through opening (36) extending in said insulating layer (9; 43) between said first and second conductive regions; and a contact structure (10A; 10B; 40) formed in said through opening, said contact structure (10A; 10B; 40) comprising a conductive material layer (30) electrically connecting said first and second conductive regions, characterized in that said contact structure (10A; 10B; 40) comprises an empty region (35) . 2. The integrated device according to Claim 1, characterized in that said through opening (36) has a lateral delimiting surface and a bottom surface that faces said first conductive region ( 6A; 6B; 41), in that said conductive material layer (30) coats said side surface and said bottom surface of said through opening, and in that said empty region (35) is surrounded by said conductive material layer (30) . 3. The integrated device according to Claim 1 or 2, characterized in that said conductive material layer (30) comprises a titanium layer (31) . 4. The integrated device according to any of Claims 1 to 3, characterized in that said conductive material layer (30) comprises a titanium-nitride layer (32) . 5. The integrated device according to any of Claims 2 to 4, characterized in that said empty region (35) is closed at the top by said second conductive region (11A; 11B; 42) . 6. The integrated device according to Claim 5, characterized in that said second conductive region (11A, 11B) contains platinum. 7. The integrated device according to any of Claims 2 to 6, characterized in that said conductive material layer (30) comprises a coating portion (20A, 20B) which coats said side surface and said bottom surface of said through opening (36) , and a horizontal portion (21A, 21B) which extends on top of said insulating layer (9) and beneath said second conductive region (11A, 11B) . 8. The integrated device according to any of Claims 1 to 7, characterized in that said integrated device is a ferro-electric memory (1) comprising a substrate (5); a transistor (3) having a first conduction region (6A, 6B) formed in said substrate; and a ferro-electric capacitor (4) having a first plate (11A) and a second plate (13) separated by a ferro-electric material region (12) ; said first conductive region (6A) forming said first conduction region of said transistor (3), and said second conductive region (11A) forming said first plate of said ferroelectric capacitor. 9. A process for manufacturing an integrated device (1), comprising the steps of: forming at least one first conductive region ( 6A, 6B; 41); forming an insulating layer (9; 43) which coats said first conductive region; forming at least one through opening (36) in said insulating layer (9; 43) above said first conductive region; forming a contact structure (10A, 10B; 40) in said through T IT01/00192 - 14 _ opening, said contact structure (10A, 10B; 40) comprising a conductive material layer (30) delimiting a region (35) ; and forming a second conductive region (11A, 11B; 42) above said through opening of said insulating layer; characterized in that said region (35) delimited by said contact structure (10A; 10B; 40) is left empty. 10. The process for manufacturing an integrated device according to Claim 9, characterized in that said conductive material layer (30) is obtained by depositing a titanium layer (31) . 11. The process for manufacturing an integrated device according to Claim 10, characterized in that said titanium layer (31) is deposited by PVD. 12. The process for manufacturing an integrated device according to Claim 10 or 11, characterized in that said titanium layer (31) has a thickness of between 10 and 100 nm, preferably of 35 nm. 13. The process for manufacturing an integrated device according to any of Claims 9 to 12, characterized in that said conductive material layer (30) is obtained by depositing a titanium-nitride layer (32) . 14. The process for manufacturing a"n integrated device according to Claim 13, characterized in that said titanium-nitride layer (32) is deposited by CVD. 15. The process for manufacturing an integrated device according to Claim 13 or 14, characterized in that said titanium-nitride layer (32) has a thickness of between 50 and 200 nm, preferably of 100 nm. 16. The process for manufacturing an integrated device according to any of Claims 9 to 15, characterized in that said step of forming said second conductive region (11A; 11B; 42) comprises depositing conductive material in a non-conform way over said region (35) . 17. The process for manufacturing an integrated device according to Claim 16, characterized in that said second conductive region (11A, 11B) contains platinum. 18. The process for manufacturing an integrated device according to any of Claims 9 to 17, characterized in that said integrated device is a ferro-electric memory (1) comprising at least one transistor (3) and at least one ferro-electric capacitor (4); said step of forming a first conductive region comprises forming a first conduction region (6A) of said transistor (3) in a substrate (5) of semiconductor material; said step of forming an insulating layer (9) comprises depositing insulating material on top of said substrate (5) ; and said step of forming a second conductive region comprises forming a first plate (11A) of said ferro-electric capacitor (4) ; and further characterized by the steps of forming a ferro-electric material region (12) on top of said first plate, and forming a second plate (13) of said ferro-electric capacitor on top of said ferro-electric material region.

Inventors: ARTONI CESARE, CORVASCE CHIARA, ZAMBRANO RAFFAELE, ARTONI, CESARE, CORVASCE, CHIARA, ZAMBRANO, RAFFAELE
Applicants: ARTONI CESARE, CORVASCE CHIARA, ST MICROELECTRONICS SRL, ZAMBRANO RAFFAELE, ARTONI, CESARE, CORVASCE, CHIARA, STMICROELECTRONICS S.R.L., ZAMBRANO, RAFFAELE
Application year: 2001
Main classification: H01L21
IPC codes: H01L21, H01L23, H01L27