Contact structure using barrier metal and method of manufacturing the same

Abstract: A titanium film (4) is formed in a contact hole (9) defined in a silicon substrate (1). The titanium film (4) is transformed into a titanium silicide film (5) and a titanium nitride film (6) by high-temperature lamp anneal. Further, a titanium nitride layer (7) is stacked on the titanium nitride film (6) based on producing conditions under which crystal orientation is constructed with (200) as principal. The crystal orientation of the stacked titanium nitride film (7) is constructed with (200) as principal. According to the present invention, the crystal orientation of a plurality of titanium nitrides formed in a stack is constructed so that a granular crystal typified by (200) is taken as principal. It is therefore possible to improve a problem of a leakage current flowing into a contact. Further, barrier characteristics of the plurality of titanium--nitrides are not deteriorated even in the case of a subsequent high-temperature thermal treatment. The leakage current can be restrained from being generated in the contact and a failure in contact resistance can be restrained from occurring. It is therefore possible to realize a semiconductor device capable of providing high reliability and a method of manufacturing the semiconductor device.

Description: The present invention relates to a semiconductor device comprising a diffusion region formed in a silicon substrate, a metal interconnect layer, and an ohmic contact structure comprising a titanium silicide layer on the diffusion region, a first titanium nitride layer on the titanium silicide layer and a second titanium nitride layer on the first titanium nitride layer, the second titanium nitride layer being granular. Aluminium or an aluminium alloy is prinicipally used in a contact as a material for forming a metal interconnect ohmic-connected to an impurity diffusion region formed on a silicon substrate. In this case, a single-layer interconnect composed of aluminium or aluminium alloy reacts with silicon in a contact diffusion region during thermal treatment to produce alloy spikes or silicon nodules that cause an increase in the contact resistance. Means such as a method of interposing a barrier metal film between a metal interconnect and an impurity diffusion region etc. are used as countermeasures against this problem. Titanium nitride is principally used as such a barrier metal film. However, the conventional titanium nitride barrier is of a single-layer film and has a (111) crystal orientation. US-A-5049975 discloses a device with a multi-layer structure, in which one of the layers has a (111) crystal orientation. A problem arises with this crystal orientation in that it has a poor resistance to rapid or high-temperature thermal treatment as described in JP-A-05-13368, for example. A device according to the present invention is characterised in that the first titanium nitride layer is granular and both titanium nitride layers consist substantially of (200) oriented crystals. Preferably, the thickness of the silicide layer is in the range 16nm to 48nm. Preferably, the metal interconnect layer comprises a refractory metal. Preferably, the thickness of the first titanium nitride layer is 2nm. Preferably, the thickness of the second titanium nitride layer is in the range 30nm to 100nm. According to the present invention, there is also provided a method of forming such a semiconductor device, the method comprising the steps of:- forming the inpurity diffusion region in the substrate; forming a titanium layer on the diffusion region; thermally treating the titanium layer to form said first titanium nitride layer; and forming said second titanium nitride layer on said first titanium nitride layer by reactive sputtering. Preferably, the titanium layer is formed to a thickness in the range 10nm to 30nm. Preferably, the thermal treatment of the titanium layer comprises a rapid annealing process. Preferably, the thermal treatment of the titanium layer comprises lamp annealling in a nitrogen or ammonia atmosphere at a temperature in the range 800°C to 900°C. Preferably, the method includes thermally treating the device after forming said second titanium nitride layer. More preferably, said thermal treatment of the device comprises heating the device to a temperature in the range 850°C to 950°C. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a cross-sectional view showing a first contact according to the present invention; Fig. 2 is a cross-sectional view illustrating granular titanium nitride crystals; Fig. 3 s a cross-sectional view illustrating columnar titanium nitride crystals; Fig. 4 is a cross-sectional view showing a second contact according to the present invention; Fig. 5 is a graph illustrating the effect of glass flow temperature on sheet resistance for contacts having the general structure of that of Fig. 4; and Fig. 6 is a plot of X-ray diffraction showing the effect of lamp annealing temperature on the crystal structure of titanium nitride in contacts having the general structure of that of Fig. 4. Fig. 1 is a cross-sectional view of a contact showing the first embodiment of the present invention. In Fig. 1, a first interlayer insulating film 2 composed of a CVD oxide (SiO 2 ), a phospho-silicate glass (PSG), etc. is deposited on a silicon substrate 1. Thereafter, the first interlayer insulating film 2 is patterned to form a first contact hole 9. Next, impurity diffusion is effected on the silicon substrate 1 with the first contact hole 9 defined therein to form an impurity diffusion layer 3. Further, a titanium film 4 having a thickness of 10nm to 30nm is deposited on the impurity diffusion layer 3 by sputtering. Next, rapid thermal anneal such as lamp anneal is effected on the titanium film 4 in an N2 ambient at temperature ranging from 800°C to 900°C to thereby transform the titanium film 4 into a titanium silicide 5 having a thickness range of about 16nm to 48nm and a first titanium nitride 6 having a thickness of about 2nm. Further, a second titanium nitride 7 having a thickness range of 30nm to 100nm is deposited on the titanium nitride 6 by reactive sputtering. Reactive sputtering conditions include 100% N2 gas, a gas pressure of 4mm Torr and a power of 6KW. At this time, crystal orientation of the titanium nitride formed by reactive sputtering tends to take (200) as principal, which has been reported by the literature "Solid State Devices and Materials", Tokyo, 1988, pp. 569-572. Crystals of (200) as principal are of granular crystals. Further, patterning is performed on the resultant product and the second titanium nitride 7, the first titanium nitride 6 and the titanium film 4 are successively etched. Thereafter, an aluminum alloy 8 having a thickness range of about 300nm to 700nm is deposited on the second titanium nitride 7 by sputtering. According to the present contact structure, since a plurality of titanium nitrides are stacked on one another and the titanium nitrides are oriented in the form of the granular crystals, a stable contact can be obtained which can provide a low resistance and less silicon diffusion. This will be described later in detail in the paragraph of a second embodiment of the present invention. It is however considered that a lower titanium nitride becomes a film obtained by providing crystalline orientation for it with (200) as principal by lamp annealing using a temperature of 800°C or over and an upper titanium nitride also becomes a film obtained by providing more crystalline orientation for it with (200) as principal according to the lower titanium nitride. The silicon diffusion is considered to have been reduced because grain boundaries considered to be closely connected with a silicon diffusion path are not broadened orientationally but at random intervals by forming the titanium nitrides in the form of the granular crystals typified by (200) as typically shown in Fig. 2 as compared with a structure shown in Fig. 3 illustrative of a conventional columnar crystal represented by (111), and silicon diffusion paths for causing a diffusion current to flow between the upper and lower titanium nitrides are hard to connect owing to a stack structure and suppress silicon diffusion into silicon substrate, thereby enabling prevention of the silicon diffusion A second embodiment of the present invention will now be described. Fig. 4 is a cross-sectional view of a contact showing the second embodiment of the present invention. In Fig. 4, a first interlayer insulating film 12 composed of a CVD oxide , a phosopho-silicate glass, etc. is deposited on a silicon substrate 11. Thereafter, the first interlayer insulating film 12 is patterned to form a first contact hole 19. Next, impurity diffusion is effected on the silicon substrate 11 with the first contact hole 9 defined therein to form an impurity diffusion layer 13. Further, a titanium film 14 having a thickness range of 10nm to 30nm is deposited on the impurity diffusion layer 13 by sputtering. Next, lamp anneal is effected on the titanium film 14 in an N2 ambient at temperature of 800°C to 900°C to thereby transform the titanium film 14 into a titanium silicide 15 having a thickness range of about 16nm to 48nm and a first titanium nitride 16 having a thickness of about 2nm. Further, a second titanium nitride 17 having a thickness range of 30nm to 100nm is deposited on the titanium nitride 16 by reactive sputtering. Furthermore, a tungsten 18 having a thickness range of 200nm to 400nm is deposited on the second titanium nitride 17 by CVD and patterning is effected on the tungsten 18 to successively etch the tungsten 18, the second titanium nitride 17, the first titanium nitride 16 and the titanium film 14. Next, a second interlayer insulating film 20 such as a silicon oxide film, a phosopho-silicate glass or the like, is deposited on the first interlayer insulating film 12. A glass flow is made to the second interlayer insulating film 20 at temperature of 850°C to 950°C, followed by patterning, thereby defining a second contact hole 21 in the second interlayer insulating film 20. Further, an aluminum alloy 22 having a thickness range of about 300nm to 700nm is deposited on the second interlayer insulating film 20 by sputtering. Fig. 5 illustrates the dependence of a glass flow temperature on a sheet resistance of a tungsten interconnect in the contact shown in Fig. 4 for describing the second embodiment of the present invention. It is apparent from the drawing that even in the case of a high-temperature thermal treatment carried out at temperature of about 850°C to 950°C, which could not be achieved by a conventional device or method, a substantial increase in the contact sheet resistance does not take place and barrier characteristics of the titanium nitrides are maintained. This phenomenon has been referred to cursorily in the first embodiment but is considered to depend on the crystalline of each titanium nitride. Conventional titanium nitrides, which have been widely used at large, are of columnar crystals typically shown in Fig. 3 as mentioned above. Since the titanium nitrides are of the columnar crystals, stresses are concentrated on the titanium nitrides due to the completeness of crystalline at the time of the high-temperature thermal treatment and hence cracks are easy to occur. Further, owing to columnar grain boundaries, atoms are brought to intergranular diffusion so as to become easy to pass through the titanium nitrides. It is therefore considered in the conventional example that silicon atoms supplied from a silicon substrate pass through titanium nitrides and react with tungsten so as to become a tungsten silicide, thereby causing an increase in the resistance of a contact. Fig. 6 illustrates the intensity of X-ray diffraction of a glass-flowed sample employed in the second embodiment of the present invention, which is obtained by stacking first and second titanium nitrides on a titanium silicide. As is apparent from the drawing, it can be understood that the orientation of crystalline of the stacked titanium nitride is dependent upon a lamp annealing temperature of titanium for forming the first titanium nitride. In the case of lamp anneal carried out at a temperature of 700°C, the titanium nitride is crystal-oriented with (111) as principal, whereas the titanium nitride becomes a film obtained by firmly crystal-orienting the titanium nitride with (200) as principal in the case of lamp anneal carried out at a temperature of 800°C or more, It is inferable in the present embodiment that the first titanium nitride is crystal-oriented with (200) as principal by effecting lamp anneal on the titanium film at a high temperature of 800°C or higher, and the second titanium nitride is formed in a stack based on producing conditions under which it is considered that the first titanium nitride is easy to be crystal-oriented to the conventional (200) as a stacked crystal, thereby obtaining the crystal orientation of the titanium nitride to (200). According to the structure of the titanium nitrides crystal-oriented in granular form as in the case of (200), since the stresses are diffused upon thermal treatment even if the completeness of crystalline takes place, the cracks are hard to occur. It is believed that even if the diffusion of the grain boundaries takes place, the probability of causing the silicon atoms supplied from the silicon substrate to pass through the titanium nitrides is extremely low due to the grain boundaries defined in granular form. It is considered that owing to the above reasons, the leakage current flowing through the contact is less generated, the silicide does not react with the tungsten and the resistance of the contact is not increased. While the present invention has been described with reference to the illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art on reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.

Claims: A semiconductor device comprising a diffusion region (3; 13) formed in a silicon substrate (1; 11), a metal interconnect layer (8; 22), and an ohmic contact structure comprising a titanium silicide layer (5; 15) on the diffusion region (3; 13), a first titanium nitride layer (6; 16) on the titanium silicide layer (5; 15) and a second titanium nitride layer (7; 17) on the first titanium nitride layer (6; 16), the second titanium nitride layer (7; 17) being granular, characterised in that the first titanium nitride layer (6; 16) is granular and both titanium nitride layers (6, 7; 16, 17) consist substantially of (200) oriented crystals. A device according to claim 1, wherein the thickness of the silicide layer (5; 15) is in the range 16nm to 48nm. A device according to claim 1, wherein the metal interconnect layer (8; 22) comprises a refractory metal. A device according to claim 1, wherein the thickness of the first titanium nitride (6; 16) layer is 2nm. A device according to claim 1, wherein the thickness of the second titanium nitride layer (7; 17) is in the range 30nm to 100nm. A method of forming a semiconductor device according to any preceding claim, the method comprising the steps of:- forming the inpurity diffusion region (3; 13) in the substrate (1; 11); forming a titanium layer (4; 14) on the diffusion region (3; 13); thermally treating the titanium layer (4; 14) to form said first titanium nitride layer (6; 16); and forming said second titanium nitride layer (7; 17) on said first titanium nitride layer by reactive sputtering. A method according to claim 6, wherein the titanium layer (4; 14) is formed to a thickness in the range 10nm to 30nm. A method according to claim 6, wherein the thermal treatment of the titanium layer (4; 14) comprises a rapid annealing process. A method according to claim 6, wherein the thermal treatment of the titanium layer (4; 14) comprises lamp annealling in a nitrogen or ammonia atmosphere at a temperature in the range 800°C to 900°C. A method according to claim 6, including thermally treating the device after forming said second titanium nitride layer (17). A method according claim 10, wherein said thermal treatment of the device comprises heating the device to a temperature in the range 850°C to 950°C.

Inventors: KAWAZU YOSHIYUKI, MATSUMOTO RYOICHI, KAWAZU, YOSHIYUKI, MATSUMOTO, RYOICHI, KAWAZU, YOSHIYUKI, C/O OKI ELECTRIC IND.CO.LTD., MATSUMOTO, RYOICHI, C/O OKI ELECTRIC IND.CO.LTD.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY CO., LTD.
Application year: 1995
Main classification: H01L23
IPC codes: H01L21, H01L23