Method of manufacturing a contact in semiconductor devices

Abstract: A method of forming a contact in a semiconductor device involving cleaning the surface of a substrate exposed in a contact hole, formed for example through an SiO₂ film on the substrate, using the reducing effect of a nitrogen hydride or nitrogen hydride derivative gas, for example N₂H₄ gas. Thereafter, for example, a TiN barrier may be formed by a CVD method using a mixed gas of N₂H₄ and TiCl₄ (the surface not being exposed to air) and then a tungsten contact layer formed thereon by a CVD method using a mixed gas of N₂H₄ and WF₆. Alternatively, a TiN layer may be formed by a CVD method on a tungsten contact layer formed by a CVD method direct on the substrate.

Description: The present invention relates to semiconductor device manufacture, and is particularly concerned with surface treatment and formation of contacts. In recent years, as higher packing densities are provided for semiconductor devices, multilayer wirings are often employed and the sizes of contacts for wirings have been reduced, leading to increased contact resistances. Further, depths of p-n junctions formed in semiconductor devices have become less. Thereby, leakage current resulting from damage at a p-n junction in a contact area is increased. When contact resistance becomes large, to a level such that its effects cannot be neglected in terms of channel resistance and leakage current, for channel current, since these factors have a significant effect on device operations, reduction of contact resistance and leakage current become very desirable. Additionally, substrate flatness is an important factor in relation to reliability of wiring and stability of wiring with respect to thermal cycling. When forming contact layers using an aluminium system, or refractory metal, on a silicon substrate by a sputtering method or a CVD method, it is known that the cleanliness of the substrate surface is an important factor so far as contact resistance is concerned. For instance, when titanium (Ti) is formed on a Si substrate by a sputtering method, formation of silicide (TiSi x ) generated through reaction of Ti and Si, can become non-uniform due to contamination of the Si surface (by natural oxide, organic substances, etc.). Thereby, contact resistance may be increased. Moreover, in a case in which a tungsten (W) layer is grown by a CVD method, since nucleation does not occur smoothly on a natural oxide, the desired layer does not grow, or is grown with irregular corrosion. Therefore, surface cleanliness is important for attaining low contact resistance when forming contacts. As surface treatment of a lower base layer, a wet etching method or a dry etching method such as a plasma etching method and hydrogen reduction method have been employed. However, in such a wet or dry etching method, side products may easily be generated and, with the plasma etching method, surface damage may occur. Moreover, when reduction by hydrogen is employed, thermal damage may occur, a diffused layer may spread and aluminium wirings may be melted easily due to the high temperature (800°C) used, and thereby device characteristics may be adversely affected. As indicated above, a satisfactory surface processing method has not previously been provided. In order to realise low contact resistance, refractory metals (for example tungsten W or titanium Ti), silicides thereof (for example WSi x , TiSi x ) or nitrides thereof (for example WN, TiN) are used in place of aluminium (Al), the most widely used conventional wiring material. These refractory metal materials, when used for contacts, simultaneously perform the role of barrier metal for suppressing chemical reactions between substrate and (any overlying) aluminium wirings. Namely, even when a contact involves a shallow junction, spike generated by chemical reactions between substrate materials and wiring materials do not damage these shallow junctions. Therefore, such barrier metal can effectively prevent leakage current caused by damage to junction areas. With regard to contact metal layers, methods for sputtering Al related material such as aluminium (Al), AlSi and AlCu have been employed. However, in such cases, disadvantages have existed in that AlSi allows increase of contact resistance by segregation of Si, or in that defective wirings can occur due to the low migration resistance (electro migration or stress migration) of Al and Al alloys. This migration problem has been solved by employing a CVD method using tungsten W for the contact metal Layer or wirings. Namely, coverage of Al is improved by the use of a burying method and defective wirings do not occur, due to the high migration resistance of wirings based on tungsten W. However, this CVD method suffers a disadvantage in that Si or fluorine F, which is an element of a reactant gas forming element, is easily incorporated into the tungsten W layer when a low temperature reducing reaction using silane (SiH₄), etc., is employed, and thereby a contact resistance becomes larger and coverage rate is reduced. On the other hand, CVD of tungsten W using a reducing reaction using hydrogen (H₂) is characterised by the provision of a Large coverage rate but is also accompanied by a disadvantage in that corrosion of Si is significant and leakage current is manifest due to the high growth temperature employed and the generation of corrosive gas. A tungsten W layer obtained by a CVD method also suffers a disadvantage in that layer peeling may occur as a result of the poor adhesive property of this layer to an SiO₂ layer. Therefore, an adhesive layer which also functions as a contact barrier layer, for example of TiN, is first formed by a sputtering method and then a tungsten W layer is formed thereon by a CVD method. However, this adhesive layer exhibits poor coverage of stepped portions, due to employment of a sputtering method, and abnormal growth, zero growth or peeling of the tungsten layer may occur at contact regions. Patent Abstracts of Japan, Vol. 6-118 [C 111] & JP-A-57 047707 disclose the manufacture of a lump of silicon nitride containing Ti by blowing gaseous sources for depositing Si, N and Ti at a hot substrate after mixing at specified flow rates. NH₃, N₂H₄ or the like is used as a gaseous source for depositing nitrogen. Gaseous Si halide or hydride such as SiCl₄ or SiH₄ is used as a gaseous source for depositing Si and vapor or TiCl₄, TiBr₄ or the like is used as a compound source for depositing Ti. Patent Abstracts of Japan, Vol. 6-259 [E 149] & JP-A-57 157525 disclose that removal of C coated, and a clean surface, can be obtained after etching when the surface has been etched in a gas plasma of a compound containing C, by mixing NH₃ or N₂H₄, or exposing the surface in the plasma of NH₃ or N₂H₄ or the mixed gas of N₂ and H₂. According to the present invention there is provided a method of manufacturing a contact on a substrate surface, including forming a conducting material layer on an exposed surface region of the substrate structure, which exposed surface region may be that of a semiconductor or conductor material of the substrate structure, and cleaning an exposed surface region of the substrate, prior to forming the conducting material layer, using a gas comprising a nitrogen hydride or a nitrogen hydride derivative, then forming the conducting material layer containing a metal on the substrate using a gas mixture containing a gas comprising a nitrogen hydride or a nitrogen hydride derivative and a gas comprising a metal halide or an organic metal composition or a metal complex, without intermediate exposure of the substrate to atmospheric conditions. An embodiment of the present invention can provide for contact regions of low contact resistance to be obtained, through cleaning of substrate surface. An embodiment of the present invention can provide for contact regions to be obtained which suffer less leakage current. An embodiment of the present invention can provide for contact regions to be obtained with desirable substrate surface flatness. An embodiment of the present invention can provide for contact regions of high reliability to be obtained. Embodiments of the present invention can employ (a) and (b), in the course of manufacture of contacts:- (a) a substrate surface is exposed to a gas which is a nitrogen hydride or an organic nitrogen hydride and the surface is thereby cleaned. (b) a barrier metal layer is formed by a CVD method using a mixed gas as a raw material, the gas comprising a metal halide or an organic metal composition or a metal complex and a nitrogen hydride or a derivative of nitrogen hydride, and thereafter a metal layer is formed by a CVD method using such mixed gas. For surface processing and for growth of contact metal layering in accordance with an embodiment of the present invention, the reducing effect of, for example, hydrazine is utilised. Namely, a clean surface can be provided by utilising a nitrogen hydride or an organic nitrogen hydride such as hydrazine (N₂H₄) or methyl hydrazine (CH₃N₂H₃), maintaining the substrate temperature in the range of 200°C to 800°C, by a heating method using resistance heating or a method using a halogen lamp or an arc lamp, and by removing Si or metal impurity on the substrate surface, for example, Si oxide, metal oxide or organic substance through reduction thereof. Further, since a nitrogen hydride or a derivative thereof has strong reactivity, it reacts with metal halides, organic metals or metal complexes, depositing metal nitrides or pure metals on a substrate. Since side products include volatile nitrogen compounds or low order hydrocarbons, these are not incorporated into the deposited metal (or nitride) and thereby contact resistance is not increased. In such a CVD method, growth conditions may be set to the condition of surface reaction limited, growth layer thickness may be equalised, the growth layer may be deposited faithfully over the substrate surface including stepped portions, and a large coverage ratio may also be obtained. Moreover, in accordance with an embodiment of the present invention, a barrier metal layer may be grown by a CVD method on a cleaned substrate surface without exposing the surface to the air, with the contact metal layer successively grown by the CVD method by changing the reaction gas. Thereby, the respective CVDs are carried out and on the cleaned substrate surface, both resistivity and reflectivity of contact metal layer are improved in comparison with the layers provided by previously proposed methods and both contact hole coverage and p-n junction leakage current characteristics are also as much improved. Accordingly, the present invention can provide a more optimum method for cleaning the surface of a substrate and for providing lower contact resistance when forming wiring materials on the surface of a base substrate. Moreover, it is possible to sequentially form barrier metal layer and wiring materials within a series of processings including the surface treatment of a base substrate. Reference is made, by way of example, to the accompanying drawings, in which:- Fig. 1(a) is a schematic diagram illustrating in outline form a manufacturing apparatus used to form a contact region, in accordance with an embodiment of the present invention; Fig. 1(b) is a schematic diagram illustrating in outline form contact manufacturing apparatus combining a substrate surface treatment chamber and two contact metal layer growth chambers, for carrying out an embodiment of the present invention; Fig. 1(c) is a schematic diagram illustrating contact manufacturing apparatus combining two substrate surface treatment chambers, two contact metal layer growth chambers and two load lock chambers, for carrying out an embodiment of the present invention; Fig. 2(a) is a diagram in which produced free energy (- Δ G) is plotted against absolute temperature (K) for a variety of chemical reactions related to an embodiment of the present invention; Fig. 2(b) is a diagram in which time of deposition in WF₆ ambient is plotted against the value of sheet resistance of tungsten deposited on a substrate surface, after surface treatment using N₂H₂(CH₃)₂ has been effected, maintaining an Si substrate at 350°C, for assistance in explaining an embodiment of the present invention; Fig. 3(a) is a schematic sectional view indicating the condition of a substrate to be carried into a manufacturing apparatus as shown in Fig. 1(a), (b) or (c) for surface treatment, in accordance with an embodiment of the present invention; Fig. 3(b) is a schematic sectional view indicating the condition of the substrate after substrate surface contaminants have been reduced and eliminated by action of N₂H₄; Fig. 4(a) is a schematic sectional view of a substrate after surface-cleaning treatment; Fig. 4(b) is a schematic sectional view of a sample wherein a tungsten layer is formed by a CVD method within the contact hole seen in Fig 4(a), in accordance with an embodiment of the present invention; Fig. 4(c) is a schematic sectional view of a sample wherein a TiN layer is formed on the entire surface as seen in Fig. 4(b), in accordance with an embodiment of the present invention; Fig. 4(d) is a schematic sectional view of a sample wherein a tungsten layer is grown on the entire surface of the TiN layer of Fig. 4(c) and a tungsten wiring layer is formed by patterning the tungsten layer, in accordance with an embodiment of the present invention; Fig. 5(a) is a graph indicating a relationship between contact resistance (R) per 1 µ m x 1 µ m and surface-cleaning treatment time for a W/Si(n⁺) contact provided in accordance with an embodiment of the present invention; Fig. 5(b) is a graph indicating a relationship between diode leakage current and annealing time for a W/Si(n⁺) contact as per Fig. 5(a); Fig. 6(a) is a schematic sectional view of a sample after completion of substrate surface-cleaning treatment in accordance with an embodiment of the present invention; Fig. 6(b) is a schematic sectional view of the sample of Fig. 6(a) wherein a TiN₂ barrier metal layer is formed over a contact hole and interlayer insulation film, in accordance with an embodiment of the present invention; Fig. 6(c) is a schematic sectional view of the sample of Fig. 6(a) wherein a tungsten contact layer is formed on the TiN₂ barrier metal layer of Fig. 6(b), in accordance with an embodiment of the present invention; Fig. 6(d) is a schematic sectional view of a sample wherein the TiN₂ barrier metal layer and tungsten contact layer are buried in the contact hole, in accordance with an embodiment of the present invention; Fig. 7(a) is a graph in which resistivity of a tungsten contact layer is plotted against growth temperature (substrate temperature) for a CVD method employed in accordance with an embodiment of the present invention; Fig. 7(b) is a graph in which reflectivity of the tungsten contact layer is plotted against growth temperature (substrate temperature) for the CVD method; Fig. 7(c) is a diagram comparing coverage ratio of a contact hole provided by a tungsten contact layer manufacturing method embodying the present invention with that provided by a previous method; Fig. 8(a) is a schematic sectional view of a sample before surface-cleaning treatment is effected, prior to contact formation for multilayer wirings, in accordance with an embodiment of the present invention; Fig. 8(b) is a schematic sectional view of the sample with a tungsten contact layer is formed in a contact hole, after surface-cleaning treatment is carried out using apparatus as illustrated in Fig. 1(a), (b) or (c), in accordance with an embodiment of the present invention; Fig. 8(c) is a schematic sectional view of the sample with a TiN₂ barrier metal layer formed over the part shown in Fig. 8(b), in accordance with an embodiment of the present invention; Fig. 8(d) is a schematic sectional view of the sample wherein a tungsten layer is grown over the entire TiN layer shown in Fig. 8(c) and a tungsten wiring layer is formed by patterning the tungsten layer, in accordance with an embodiment of the present invention; Fig. 8(e) is a schematic sectional view of the sample wherein a contact hole is provided in an insulating interlayer formed covering the tungsten wiring of Fig. 8(d), in accordance with an embodiment of the present invention; and Fig. 8(f) is a schematic sectional view of the sample wherein the substrate surface exposed in the contact hole of Fig. 8(e) is cleaned, a tungsten layer is grown thereon and an aluminium layer for a second wiring layer is immediately formed over the entire part shown, in accordance with an embodiment of the present invention. Exemplary embodiments of the present invention will be explained with reference to Figs. 1 to 8. In those Figures, like elements are designated by the like reference signs throughout. First Embodiment : Fig. 1(a) is a schematic diagram for assistance in explaining a manufacturing apparatus used for manufacturing contacts in accordance with this embodiment and other embodiments of the present invention. In the apparatus shown in this Figure, a reactant gas for substrate surface treatment and a reactant gas for forming a contact metal layer are introduced respectively into a reaction chamber 21 through a gas shower 25 from gas supply ports 26 and 27 and exhausted via a gas exhaust port 34. A substrate 23 to be surface-treated is placed on a quartz window 22 provided in the lower side in the reaction chamber 21. At the lower side of (below) quartz window 22, a heater is provided (not illustrated) and thereby substrate temperature is controlled to a determined value. The N₂H₄ gas 28, for substrate surface treatment, is guided to the reaction chamber 21 through the gas supply port 26 and via a mass flow controller 29. Since N₂H₄ 28 decomposes, if it is in a liquid or high concentration condition, through contact with a metal surface, it is desirable that the N₂H₄ is prevented from having direct contact with metal by effecting teflon processing of the piping used for supplying the reactant gas. Reactant gas 31 such as TiCl₄, WF₆ and carrier gas such as Ar gas 33, H₂ 32, for forming a contact metal layer, are guided to the reaction chamber 21 through the gas supply port 27 and via the flow controllers 29. Gas pressure in the reaction chamber 21 is controlled to a predetermined value by adjusting speed of exhaustion from the exhaust port 34 by a vacuum pump and flow rate of gas introduced through the gas supply ports 26, 27. The apparatus illustrated in Fig. 1(a) provides for surface treatment of a substrate and growth of contact metal layer in the same reaction chamber by exchange of gas in the chamber. Fig. 1(b) is a diagram for assistance in explaining a manufacturing apparatus in which substrate surface treatment and growth of a plurality of contact metal layers are carried out in different reaction chambers, without the substrate being exposed to atmospheric conditions, in accordance with this and other embodiments of the present invention. In Fig. 1(b), a load lock chamber 35 is connected with a load/unload (L/UL) chamber 36, a surface processing chamber 37 and CVD chambers 38, 39 similar to that in Fig. 1 through gate valves 41, 42, 43, 44. A substrate to be processed is carried to any of the surface treatment chamber 37 and CVD chambers 38 or 39 from the L/UL chamber 36 and is then carried out again from the L/UL chamber 36 after completion of necessary processing. For example, an Si substrate surface is cleaned in the surface treatment chamber 37, a tungsten layer is grown in the CVD chamber 38 and then a TiN layer is grown in the CVD chamber 39. Or, alternatively, it is possible that the TiN layer is formed first and the tungsten layer is then formed subsequently. During this process, the chambers 37, 38, 39 can be kept in their normal operating conditions. Fig 1(c) illustrates an apparatus larger in size than that illustrated in Fig. 1(b), for use in accordance with this and other embodiments of the present invention. Using one system path, a substrate 54 introduced from an inlet load lock chamber 56 is processed in a surface treatment chamber 57a, passing through a valve 51 and a central chamber 60, then moved to a growth chamber 58a through the central chamber 60 after surface treatment and is then taken out from an outlet load lock chamber 50 through the central chamber 60 after layer growth. Moreover, using another system path, the substrate 54 introduced from the inlet load lock 56 is carried into a surface treatment chamber 57b through a valve 51 and the central chamber 60, then moved to a growth chamber 58b through the central chamber 60 after the surface treatment, and is then taken out from the outlet load lock chamber 50 through the central chamber 60 after layer growth. Exhaust apparatuses are not comprehensively shown; they are merely represented by the exhaust apparatus 59. A method of cleaning a substrate surface in accordance with this embodiment of the invention, as effected using manufacturing apparatus shown in Fig. 1(a), will now be explained. Of course, it is possible to carry out this cleaning method with the apparatuses shown in Fig. 1(b) and Fig. 1(c). Fig. 3(a) illustrates the condition of a substrate before it is carried into the manufacturing apparatus of Fig. 1(a). The substrate will hereafter be called a sample. In this sample, a contact hole 3 is opened in an SiO₂ film 2 formed to a thickness of 5000 Å on a p⁻ -Si substrate 1, and a shallow p-n junction is formed by forming an n⁺ layer 1A on the substrate 1 by ion implantation of As. Such a sample is carried into the manufacturing apparatus of Fig. 1(a) and is then placed on the quartz window 22 provided at the lower side of the reaction chamber 21. On the exposed substrate, there exist impurities 4 such as residual etching material, intentionally deposited contaminants or natural oxides, etc. Therefore, the surface is cleaned by keeping the substrate temperature at 300°C for 30 seconds. A typical condition established in the reaction chamber is as follows. As reactant gas N₂H₄ is used, at 10 SCCM flow, and as carrier gas any one of H₂, He or Ar is used, at 10 SCCM flow, respectively. The pressure in the reaction chamber 21 is set to 0.1 Torr and the substrate temperature may be set within the range from 200 to 900°C but an optimum temperature is 300°C. Chemical reactions between N₂H₄ and contaminants are as follows. If the contaminant is SiO₂:- N₂H₄ + SiO₂ --> N₂ + 2H₂O + Si or 2N₂H₄ + SiO₂ --> 2N₂ + 2H₂O + SiH₄ If the contaminant is an organic substance:- N₂H₄ + C n H m --> N₂ + CH + H₂ If the contaminant is Al₂O₃ (when the base substrate is formed by Al, refer to Fig. 8(f) concerning the fourth embodiment):- N₂H₄ + (2/3)Al₂O₃ --> N₂ + (4/3)Al + 2H₂O The above reactions will be explained with reference to Fig. 2(a). In Fig. 2(a), generated free energy (- ΔG) of a reaction formula is plotted against absolute temperature (K). [Refer to Ref. 1) JANA Thermochemical Tables:- (a) 2nd Ed. NSRDS-NBS-37 (1971), (b) 1974 Supplement, (c) 1975 Supplement]. In a reaction in accordance with formula (2), for example, - ΔG becomes positive at a temperature higher than 600K and therefore the reaction proceeds in the direction of the arrowed line in formula (2). In a reaction in accordance with formula (1), since - Δ G is negative at 1050K or less, when the reactions in accordance with formulas (1) and (2) are concerted reactions, the reaction of formula (2) occurs preferentially. Namely, the Si substrate surface is cleaned. The following reaction may be noted:- (2/3)N₂H₄ + Si --> (1/3)Si₃N₄ + (4/3)H₂ The reaction of formula (5) may be considered, but direct nitrogenation of Si does not occur even when NH₃ is used, if the temperature is lower than 1000°C. Moreover, since - ΔG becomes positive at 700K or higher in the reaction, Si₃N₄ + N₂H₄ --> N₂ + SiH₄ the reaction (5) does not actually occur at 700K or higher, and therefore nitride is not generated. Namely, the Si substrate surface is cleaned. In the case of the reaction of formula (4), since -ΔG is negative at all temperatures considered, this reaction seems to be difficult to promote. However, since an oxide at the surface does not have a thermally stable structure such as that of Al₂O₃ but is a natural oxide of weak coupling force such as Al x O y , the following reaction occurs easily:- N₂H₄ + Al x O y --> N₂ + Al + H₂O. It will therefore be understood that the Si substrate is cleaned, when the above reactions are considered. Next, the effect of a surface-cleaning process using N₂H₂(CH₃)₂, in accordance with an embodiment of the present invention, will be explained with reference to Fig. 2(b). Fig. 2(b) gives a plot of values of sheet resistance corresponding to film thickness of tungsten deposited at the substrate surface against contact time with WF₆ ambient, when the Si substrate is kept at 350°C, after surface treatment using N₂H₂(CH₃)₂. The substrate is exposed to the WF₆ ambient without contact to atmospheric ambient. In addition, for the purpose of comparison, values of sheet resistance for a substrate which has not undergone surface treatment using N₂H₂(CH₃)₂ are also depicted. The substrate which has undergone surface-cleaning treatment using N₂H₂(CH₃)₂ shows a constant sheet resistance, substantially unaffected by time of contact with WF₆ ambient. However, a tungsten layer practically does not grow on the substrate which has not undergone surface treatment using N₂H₂(CH₃)₂ when the time for contact with the WF₆ ambient is only 5 seconds, namely the sheet resistance value thereof is equal to the value for the Si substrate and it becomes about 4 Ω/□ as the contact becomes longer. In general, the reducing reaction of formula (7) occurs between WF₆ and Si:- WF₆ + (3/2)Si --> W + (3/2)SiF₄ Thereby, tungsten is deposited and the reaction is complete when the disposed (exposed) area of Si disappears. [For example, refer to Ref. 2) "Tungsten and Other Refractory Metals for VLSI Applications", Vols. I-IV, Pitsburgh, PA, U.S.A. (1986-1989)]. The provision of constant sheet resistance, unrelated to contact time with WF₆, indicates that efficient surface cleaning has been provided. Namely, the effect of surface-cleaning treatment by N₂H₂(CH₃)₂ is clearly demonstrated. If an oxide exists at the Si substrate surface, WF₆ invades into the Si substrate from the gap thereof and the film thickness of tungsten generated by the reaction of formula (7) becomes large. [Refer to Ref. 3) H. H. Busta and C. H. Tang; J. Electrochem. Soc., Vol. 133, page 1195 (1986); Ref. 4) T. Ohba, Y. Ohyama, S. Inoue and M. Maeda; Ref. 2) Vol. II, page 59 (1987)]. For the purpose of comparison, a surface-cleaning process using a reducing reaction employing H₂, followed by a deposition of tungsten using WF₆, was carried out. The results were assess by measurement of sheet resistance. The results ranged from 30 to 80 Ω/□ and these values are almost equal to those obtained using a surface-cleaning process employing N₂H₂(CH₃)₂ in accordance with an embodiment of the present invention. However, for the surface-cleaning treatment using a reducing reaction employing H₂, the substrate temperature is set to 700°C and it is high in comparison with the substrate temperature of 350°C in the case of the surface-cleaning treatment using N₂H₂(CH₃)₂. As described above, a substrate surface contaminant is reduced by N₂H₄ and can be eliminated from the surface. This condition, with contaminant eliminated, is shown in Fig. 3(b). Second Embodiment : In the apparatus of Fig. 1(a), a contact metal layer is formed on a sample as shown in Fig. 4(a) which has undergone surface-cleaning treatment of the substrate 1 as indicated in Fig. 3(b). The effects of the surface-cleaning treatment are apparent through a comparison of contact characteristics with those obtained using previously proposed methods. As shown in Fig. 4(b), the tungsten layer 5 is selectively grown by a CVD method using WF₆ to a thickness of 4000 Å within the contact hole 3. A typical condition for growth of tungsten is as follows:- The flow rates of N₂H₄ and WF₆, as the reaction gases, are respectively set to 10 SCCM, 15 SCCM, and the flow rate of H₂ as carrier gas is set to 50 SCCM. The pressure in the reaction chamber 21 is set to 0.1 Torr, while the substrate temperature is set to 300°C. Chemical reactions in relation to growth of tungsten are as follows:- (3/2)N₂H₄ + WF₆ --> (3/2)N₂ + HF + W (- ΔG = 109.35 kcal/mol at 600K) Next, as shown in Fig. 4(c), supply of WF₆ is changed to TiCl₄ and a TiN layer (or Ti layer) 6 is formed to a thickness of 500 Å as an adhesion layer on the entire surface of Fig. 4(b). Growth of the TiN layer is carried out under the following conditions:- As reactant gas, flow rates of TiCl₄ and N₂H₄ are set to 10 SCCM and the flow rate of H₂ as carrier gas is set to 100 SCCM. The pressure in the reaction chamber is set to 0.2 Torr. The substrate temperature is set in the range from 400°C to 800°C but desirably set in the range from 500°C to 700°C. At a substrate temperature of 600°C, the following chemical reaction occurs:- N₂H₄ + TiCl₄ --> TiN + (1/2)N₂ + 4HCl (- ΔG = 70.3 kcal/mol at 900K) For instance, when the substrate temperature is 500°C or less, N₂H₄ + TiCl₄ --> TiN + (1/2)N₂ + 4HCl (- ΔG = 70.3 kcal/mol at 500K) Next, as indicated by Fig. 4(d), supply of TiCl₄ is changed again to WF₆, and a tungsten layer is grown to a thickness of 3000 Å over the entire surface of TiN layer 6 under the same conditions as for the growth of the tungsten layer 5, and a tungsten wiring layer 7 is formed by patterning this tungsten layer. Evaluation of the quality of the contact thus provided will be explained hereunder. For a W/Si(n⁺) contact, formed by a tungsten layer on n-type Si, in accordance with an embodiment of the present invention, the relationship between contact resistance (R) per 1 µm x 1 µm and surface-cleaning treatment time is indicated in Fig. 5(a). In Fig. 5(a), for the purpose of comparison, contact resistance values obtained in a case of surface treatment carried out for 10 to 20 seconds using a diluted (1%) solution of hydrogen fluoride (HF) for the same type of contact W/Si(n⁺), and contact resistance values obtained in a case of surface-cleaning treatment carried out on a different kind of contact Al/Si(n⁺) are indicated. As can be seen in Fig. 5(a), contact resistance values relating to an embodiment of the invention become smaller as the surface-cleaning treatment is carried out for longer times and a minimum contact resistance value can be obtained using a method in accordance with an embodiment of the present invention wherein surface treatment time is 30 seconds or longer. Fig. 5(b) indicates relationships between a leakage current of a diode and annealing time, in relation to a W/Si(n⁺) contact provided in accordance with an embodiment of the invention as for Fig. 5(a), and in relation to the contact Al/Si(n⁺) of Fig. 5(a). The leakage currents of the W/Si(n⁺) contact immediately after formation of the tungsten layer on a surface treated by N₂H₄, after annealing at 450°C for 30 minutes and after annealing at 500°C for 30 minutes, are indicated by curve (1) in Fig. 5(b). Moreover, for the Al/Si(n⁺) contact, leakage currents obtained immediately after growth of Al, after annealing at 450°C for 30 minutes and after annealing at 500°C for 30 minutes, after carrying out surface cleaning using HF, are indicated by curve (2). As will be understood from Fig. 5, leakage current of the W/Si(n⁺) contact in accordance with this embodiment of the invention is smaller than that of the Al/Si(n⁺) contact and is also smaller than that obtained by annealing at 450°C or higher, by an order of magnitude or more. Third Embodiment Fig. 6(a) indicates a sample wherein an insulating interlayer film 2 is formed by depositing PSG (phosphosilicate glass) to a thickness of about 5000 Å on a silicon substrate 1, for example by the CVD method, and thereafter a contact hole with a width of 5000 Å is formed through selective etching of the insulating interlayer film 2, for example by RIE (reactive ion etching), and the cleaning process is carried out in respect of the surface of substrate 1 as shown in Fig. 3(b) within the apparatus of Fig. 1(a), in accordance with an embodiment of the present invention. The other method for forming the tungsten contact layer to the sample shown in Fig. 6(a) in the apparatus of Fig. 1(a). As shown in Fig. 6(b), a TiN barrier metal layer 4 is formed to a thickness of about 500 Å on the contact hole 3 and interlayer insulating film 2. The TiN barrier metal layer 4 is formed by a CVD method, not by a sputtering method as previously proposed. A typical condition for the CVD is as follows:- As reaction gas, TiCl₄ is introduced at 5 SCCM and N₂H₄ at 20 SCCM, while as carrier gas, H₂ is introduced at 50 SCCM, respectively into the reaction chamber together. Pressure is set to 0.1 to 1.0 Torr and substrate temperature is kept at 600°C. Next, as shown in Fig. 6(c), a tungsten contact layer 5 is formed to a thickness of about 5000Å on the TiN barrier metal layer 4. This is carried out in the same reaction chamber by exchanging reactant gas and carrier gas. A typical condition for this CVD is as follows:- As reaction gas, WF₆ is introduced at 10 SCCM and N₂H₄ at 10 SCCM, while as carrier gas, He is introduced at 100 SCCM, respectively to the reaction chamber together. Pressure is set to 0.1 to 10 Torr and substrate temperature is kept at 380°C. Finally, the sample is taken out from the apparatus of Fig. 1(a) and the wiring structure as shown in Fig. 6(d), burying the TiN barrier metal layer 4 and tungsten contact layer 5, can be obtained in the contact hole 3 by etching the tungsten contact layer 5 and TiN barrier metal layer 4 using, for example, a RIE (reactive ion etching) method. Since the contact layer is formed by a CVD method, unlike the previously proposed sputtering method, in order to form the wiring structure indicated in this embodiment, the TiN barrier metal layer 4 is more dense than the layer provided with the previously proposed method and coverage of the contact hole 3 is also good. This can also be said of the tungsten contact layer 5. Moreover, since reactive side products are not incorporated into the metal layer, the relevant layer has a low specific resistance. Figs. 7(a), 7(b) are graphs representing an evaluation of the tungsten layer 5 manufactured by the steps shown in Fig. 6. Fig. 7(a) is a graph plotting specific resistance of tungsten layer 5, while Fig. 7(b) is a graph plotting reflectivity of tungsten layer 5 to Al, respectively for the growth temperature (substrate temperature) of CVD. In Figs. 7(a), 7(b), the curves indicated by solid lines correspond to layers manufactured by the steps of Fig. 6, while the curves indicated by broken lines (1) correspond to tungsten contact layers manufactured by a previously proposed reducing reaction using SiH₄ and the graphs indicated by chain lines (2) correspond to tungsten layers manufactured by a previously proposed reducing reaction using H₂. The CVD growth condition for the reducing reaction using SiH₄ is that a mixed gas including WF₆ at 5 SCCM, SiH₄ at 5 SCCM and H₂ at 100 SCCM is used under a pressure of 0.1 Torr. The CVD growth condition for the reducing reaction using H₂ is that a mixed gas including WF₆ at 10 SCCM and H₂ at 1000 SCCM is used under a pressure of 5 Torr). As can be understood from Fig. 7(a) and 7(b), a tungsten layer having small resistivity and large reflectivity simultaneously cannot be obtained with the previously proposed methods. However, in the embodiment of the present invention, when the growth temperature is about 350 to 450°C, a tungsten layer is formed which has a smaller resistivity value and simultaneously larger reflectivity than provided by layers formed with the previously proposed methods. Fig. 7(c) provides a comparison of the coverage ratio of a contact hole formed with a tungsten layer formed by a manufacturing method in accordance with an embodiment of the invention with those provided by previously proposed methods (1) and (2). The previously proposed methods (1) and (2) are the same as those mentioned in relation to Figs. 7(a) and 7(b). The coverage ratio is expressed, as illustrated in the upper part of Fig. 7(c), by a percentage indication of the ratio of thickness on a side wall of a contact hole and thickness on the substrate. The coverage ratio provided by the method embodying the present invention is larger than that provided by the previous proposals. The coverage ratio can further be improved by reducing the flow rate of N₂H₄ with respect to that of WF₆, for example WF₆/N₂H₄ = 10/2. In the described method of this third embodiment of the present invention, a tungsten layer is formed on the TiN barrier layer. However, a Cu layer can alternatively be formed on the TiN barrier layer. In this case, the Cu layer may be formed by using a Cu halide, such as the WF₆ used for formation of the tungsten layer, as reaction gas. Alternatively, a metal complex gas such as Cu(HFA)₂ may be used. Fourth Embodiment : Next, an example of formation of a contact with multilayer wiring, manufactured using the apparatus of Figs. 1(a), 1(b) or 1(c), will be explained. In Fig. 8(a) to Fig. 8(d), processes for forming the contact with multilayer wirings are explained in schematic sectional views. Fig. 8(a) to Fig. 8(f) indicate the same series of processes as shown in Fig. 3(a) to Fig. 3(b), followed by the processes shown in Fig. 4(a) to Fig. 4(d). When the process shown in Fig. 8(d) is completed, the sample is once taken out of the manufacturing apparatus of Figs. 1(a), 1(b) or 1(c). Next, as shown in Fig. 8(e), an SiO₂ film 8 is formed to a thickness of 4000 Å, as an insulating interlayer covering the tungsten wiring 7, and a contact hole 9 is then opened therein. The sample is then set in the reaction chamber of the manufacturing apparatus of Fig. 1(a), 1(b) or 1(c) and surface treatment such as that conducted in Fig. 3(a) is conducted for 30 to 60 seconds. Thereby, impurity or oxide 10 adhered or remaining on the tungsten wiring 7 in the contact hole 9 can be eliminated. Finally, as shown in Fig. 8(f), the tungsten layer 11 is grown to a thickness of about 4000 Å in the contact hole 9 by a method similar to that in Fig. 3(b). Thereafter, the reaction gas WF₆ is immediately changed, for example, to AlCl₃ and an Al layer 12, as a second wiring layer, is grown on to the entire surface. For the formation of the Al layer, Al(CH₃)₃ or Al(i-C₄H₉)₃ may be used in place of AlCl₃. As explained above, the one contact with multilayer wirings can be formed. In above-described embodiments, WF₆, TiCl₄ are used as metal halide gas. However, a halogenide of molybdenum (Mo), vanadium (V), zirconium (Zr), gold (Au), copper (Cu) and platinum (Pt) may also be used. In addition, as organic metal or metal complex, tungsten carbonyl (W(Co)₆), copper hexafluoroacetylacetone (Cu(HFA)₂), gold hexafluoroacetylacetone (Au(HFA)) and other complexes including Ti or Zr can also be used. Moreover, as the nitrogen hydride, N₂H₄ is mainly used but N₂H₂, N₅H₅ can also be used. As derivatives of nitrogen hydride employable in embodiments of the present invention, N₂H(CH₃)₃, N₂H₂(CH₃)₂, N₂H₃(CH₃) and N₅H₄(CH₃) can also be used. An embodiment of the present invention provides a method of forming metal contact wiring layers in semiconductor devices by cleaning the surface of exposed substrate of a contact hole formed in an SiO₂ film on a semiconductor substrate, which cleaning employs the reducing effect of N₂H₄ gas, thereafter forming a TiN barrier layer by a CVD method using a mixed gas of N₂H₄ and TiCl₄ while the surface is not exposed to air, then forming a tungsten contact layer thereon by a CVD method using a mixed gas of N₂H₄ and WF₆, or forming the TiN layer by a CVD method on a tungsten contact layer formed by a CVD method directly on the substrate.

Claims: A method of manufacturing a contact on a substrate surface, including forming a conducting material layer on an exposed surface region of the substrate structure, which exposed surface region may be that of a semiconductor or conductor material of the substrate structure, and cleaning an exposed surface region of the substrate, prior to forming the conducting material layer, using a gas comprising a nitrogen hydride or a nitrogen hydride derivative, then forming the conducting material layer containing a metal on the substrate using a gas mixture containing a gas comprising a nitrogen hydride or a nitrogen hydride derivative and a gas comprising a metal halide or an organic metal composition or a metal complex, without intermediate exposure of the substrate to atmospheric conditions. A method as claimed in claim 1, wherein the cleaning is performed at a temperature such that nitrogenation of the exposed substrate region is substantially avoided. A method as claimed in claim 2, wherein the said temperature is between 200°C and 900°C, and preferably between 300°C and 600°C. A method as claimed in claim 1, 2 or 3, wherein the so-formed conducting material layer contains nitrogen. A method as claimed in claim 1, 2 or 3, wherein the forming of the conducting material layer is effected a temperature lower than 600°C, such that metal is deposited on the substrate. A method as claimed in claim 4, wherein the forming of the conducting material layer is effected at a temperature preferably between 300°C and 700°C, or higher than 400°C, such that metal containing nitrogen is deposited on the substrate. A method as claimed in any preceding claim, wherein a further conducting material layer containing a metal is formed using a gas mixture containing a gas comprising a nitrogen hydride or a nitrogen hydride derivative and a gas comprising a metal halide or an organic metal composition or a metal complex. A method as claimed in any preceding claim, wherein cleaning and the formation(s) of the conducting material layer(s) are performed in the same gas chamber. A method as claimed in any of claims 1 to 7, wherein cleaning and the formation(s) of the conducting material layer(s) are performed successively in different gas chambers, connected through a connecting chamber. A method as claimed in any preceding claim, wherein the or each said metal is selected from the group consisting of tungsten (W), titanium (Ti), molybdenum (Mo), vanadium (V), zirconium (Zr), gold (Au), copper (Cu), and platinum (Pt). A method as claimed in any preceding claim, wherein the or each said gas mixture contains a gas comprising a metal halide selected from the group consisting of tungsten hexafluoride (WF₆), titanium tetrachloride (TiCl₄) and halides of Mo, V, Zr, Au, Cu and Pt. A method as claimed in any of claims 1 to 10, wherein the or each said gas mixture contains a gas comprising a metal complex selected from the group consisting of tungsten carbonyl (W(Co)₆), copper hexafluoroacetylacetone (Cu(HFA)₂), gold hexafluoroacetylacetone (Au(HFA)) and complexes of Ti and Zr. A method as claimed in any preceding claim, wherein each molecule of the nitrogen hydride or the nitrogen hydride derivative employed contains more than two nitrogen atoms. A method as claimed in any one of claims 1 to 12, wherein hydrazine (N₂H₄) is used as the nitrogen hydride. A method as claimed in any one of claims 1 to 12, wherein dimethyl hydrazine (CH₃)₂N₂H₂ or monomethyl hydrazine (CH₃)N₂H₃ is used as the nitrogen hydride derivative. A method as claimed in any preceding claim, wherein the substrate has a base of silicon. A method as claimed in any preceding claim, wherein a region of the substrate is exposed through an insulating layer formed on the substrate. A method as claimed in claims 8 or 9, said method comprising the steps of:- (a) cleaning an exposed surface region of a silicon substrate at the bottom of a contact hole formed in a silicon dioxide film on said silicon substrate, said silicon substrate being heated at a temperature between 200 and 900°C, more preferably 300°C, using a mixed gas of hydrazine at a flow of 10 SCCM and hydrogen at a flow of 10 SCCM; (b) forming a tungsten (W) layer on said exposed surface region of the silicon substrate at the bottom of said contact hole at about 300°C by CVD (chemical vapour deposition), using a mixed gas of WF₆ at a flow of 15 SCCM, N₂H₄ at 10 SCCM and H₂ at 50 SCCM; (c) forming a TiN layer on said tungsten (W) layer at a temperature between 500 and 600°C, preferably at about 600°C, by CVD using a mixed gas of TiCl₄ at a flow of 10 SCCM, N₂H₄ at 10 SCCM and H₂ at 50 SCCM; (d) patterning a further tungsten (W) layer under atmospheric conditions, which further tungsten (W) layer is formed on said TiN layer under the same conditions as those of step (b); (e) cleaning an exposed surface region of the further tungsten (W) layer at the bottom of a contact hole formed in a silicon dioxide film formed on the further tungsten (W) layer, under the same conditions as those of step (a); and (f) forming a tungsten (W) layer on said exposed surface region at the bottom of said contact hole, under the same conditions of step (b).

Inventors: OHBA TAKAYUKI C O FUJITSU LIMI, OHBA, TAKAYUKI, C/O FUJITSU LIMITED PATENT DEPT.
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1990
Main classification: H01L21
IPC codes: H01L21