Patent Document

This application is a continuation-in-part application of U.S. patent application Ser. No. 09/273,717, filed Mar. 22, 1999 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is for the fabrication of a dielectric-constant-enhanced film, and a method of forming a capacitor of high dielectric constant. 
     2. Description of the Prior Art 
     High density dynamic random access memory (DRAM) requires using material with high dielectric constant (ε) for adequate electrical charge storage in its size-limited capacitor unit. After the currently-in-use material, such as SiN (ε˜7), the next manufacturable high-dielectric-constant material would be tantalum oxide which gives a dielectric constant of about 25 for 100 Å thick film in metal-insulator-metal (MIM) capacitor structure. 
     The methods for forming a thin film of tantalum oxide include a sputtering method, a chemical vapor deposition method, and an anodic oxide method for tantalum film. From these methods, the chemical vapor deposition method is superior to other methods in its conformality and thus in its production worthiness. 
     When tantalum oxide film is integrated as a metal-insulator-semiconductor (MIS) capacitor in DRAM, it gives an effective dielectric constant less than 14 for 100 Å films on silicon bottom electrode. This only gives improvement less than 30%, reducing the equivalent silicon oxide thickness from 40 to 28 angstroms. 30% improvement from tantalum oxide is useful for the very next generation technology after SiN era, but not good enough to last for the next two generation technology. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a method is provided for forming a capacitor device using (Ta 2 O 5 ) 1−x (TiO 2 ) x  thin film, wherein 0.05≦x≦0.15. This (Ta 2 O 5 ) 1−x (TiO 2 ) x  film substantially increases dielectric constant, reduces leakage current and increases the integrity of integrated circuit. The dielectric constant is greatly improved by a factor of 2 to 3.5 when tantalum oxide is mixed with titanium oxide. The leakage current of this new material can be controlled to meet the requirement for DRAM cell by appropriate thermal treatment. This invention of dielectric-constant-enhanced thin film would prolong the usage of tantalum oxide based dielectric films in DRAM industry to 0.13 μm technology and beyond. 
     In one embodiment, one thin silicon nitride layer and one (Ta 2 O 5 ) 1−x (TiO 2 ) x  film with 0.05≦x≦0.15 are formed on the bottom electrode. After the (Ta 2 O 5 ) 1−x (TiO 2 ) x  film is deposited, the treatments that can reduce the impurities and oxygen vacancies to reduce leakage current comprise the following techniques: plasma treatment, remote plasma treatment, rapid thermal process, UV/O 3  treatment and furnace treatment. The deposition of a metal layer on top of the thermally treated (Ta 2 O 5 ) 1−x (TiO 2 ) x  film, by physical vapor deposition or chemical vapor deposition, completes the method of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic diagram showing the layer structure of the present invention for semiconductor memory device. 
     FIG. 2 is a schematic diagram employing an apparatus used in the manufacturing dielectric thin film method. 
     FIG. 3 shows the chemical materials of the two precursors and the solvent they are mixed with. 
     FIG. 4 shows the environment of fabricating the tantalum and titanium oxide film. 
     FIG. 5 shows that the ratio of Ti to Ta in the films can be controlled by the flow quantity of Ti(O-iso-Pr) 2 (DPM) 2 . 
     FIG. 6 shows the x-ray diffraction data for the (Ta 2 O 5 ) 1−x (TiO 2 ) x  film. 
     FIG. 7 shows a set of results using rapid thermal process. 
     FIG.  8  and FIG. 9 each show a set of results obtained from two-step thermal treatment using rapid thermal process technique. 
     FIG. 10 shows the effective dielectric constant for the capacitors produced using the method of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A specific embodiment of a high dielectric constant thin film according to the present invention will be described in detail with reference to accompanying drawings. An embodiment of the increased capacitance will be introduced first, and the fabrication and materials of dielectric thin film will be described next. The treatment that can reduce leakage current will be shown at last. 
     FIG. 1 is a schematic diagram showing the layer structure of the present invention for semiconductor memory device. The capacitor comprises a conductive layer  110  which is doped with an impurity polysilicon layer as the bottom electrode, a dielectric layer  112  that is silicon nitride, another dielectric layer  114  that is (Ta 2 O 5 ) 1−x (TiO 2 ) x  thin film with 0.05≦x≦0.15, and a conductive layer  116  with tungsten, tungsten nitride, or titanium nitride as the top electrode. 
     On the surface of the doped polysilicon bottom electrode  110 , a very thin layer  112  (˜20 Å) of silicon nitride (SiN) is grown by either chemical vapor deposition technique using silane (SiH 4 ) or rapid thermal process in ammonia (NH 3 ) gas. The layer  112  of silicon nitride (SiN) is for minimizing the growth of silicon oxide (SiO 2 ) at the interface between doped polysilicon bottom electrode  110  and the (Ta 2 O 5 ) 1−x (TiO 2 ) x  thin film  114 . 
     Subsequently, a thin layer of (Ta 2 O 5 ) 1−x (TiO 2 ) x  thin film  116  is deposited using chemical vapor deposition. FIG. 2 is a schematic diagram employing an apparatus used in the manufacturing dielectric thin film method. Two sets of liquid delivery system  10  are used to independently control the flow quantity of the two different precursors. These two different precursors are tantalum alkoxy (Ta(OEt)(O-iso-Pt) 4 ) and titanium ketones (Ti(O-iso-Pr) 2 (DPM) 2 ). The chemical formula of the tantalum alkoxy is Ta(C 2 H 5 O)(C 3 H 7 O) 4  and the chemical formula of the titanium ketones is Ti(C 3 H 7 O) 2 (C 11 H 19 O 2 ) 2 . After the two precursors vaporized separately in two vaporizers  20 , they are sent to the mixing box  40  right above the showerhead  50 . The substrate  100  (wafer) sitting on the heater  60  in the reaction chamber  1  will then receive the vapor-phase-mixed chemical vapor. The chemical vapor for the deposition of a film composed of tantalum oxide and titanium oxide precursors, wherein the ratio of TiO 2  to Ta 2 O 5  is in the range from 5 to 15 mole percent. Two sets of gas supply system  105  provide inert gas such as Ar that is used as carrier gas. Another gas supply system  107  provides oxygen that is used to assist the oxidation process during deposition. Two micropumps  70  are used in each liquid delivery system for accurate control of liquid flow. All mass flow controllers  30  are used to accurate control of liquid flow. 
     In FIG. 3, it shows the chemical materials and the solvent used for producing the two precursors. The chemical materials in the form of solid are dissolved in the solvent and become the form of liquid for easily controlling quantity. The vaporizing temperature and the decomposition temperature of precursors are also listed. 
     The above mentioned apparatus in FIG. 2 may be operated under the condition stated in FIG. 4 to produce tantalum oxide and titanium oxide films with the TiO 2 /Ta 2 O 5  ratio between 5 to 15 mole percent. According to the data shown in FIG. 4, the deposition of this embodiment is low pressure chemical vapor deposition. 
     The ratio of Ti to Ta in the (Ta 2 O 5 ) 1−x (TiO 2 ) x  film can be controlled by the flow quantity of Ti(O-iso-Pr) 2 (DPM) 2 , as is shown in FIG.  5 . The composition range of the present invention is the range studied: (TiO 2 )/(Ta 2 O 5 )=5 to 15 mole percent. 
     Although the as deposited (Ta 2 O 5 ) 1−x (TiO 2 ) x  film with 0.05≦x≦0.15 gives high dielectric constant, it also gives high leakage current. It is thus necessary to develop various treatments for this particular film in order to reduce the leakage current to a level that is acceptable for memory device such as DRAM. 
     The treatment recipes in the method of present invention is applied to the (Ta 2 O 5 ) 1−x (TiO 2 ) x  film before the deposition of conductive layer  116 , and it can be described in two categories: (a) for reducing film impurities due to the incomplete decomposition of the precursors, and (b) for decreasing the oxygen vacancies in the film. The techniques used for (a) and (b) include plasma treatment, remote plasma treatment, rapid thermal process, UV/O 3  treatment and furnace treatment. The treatments using these techniques at low and high temperatures (range from 300° C.-1000° C.) give the effects listed in (a) and (b). 
     The treatments for the category (a) and (b) can be carried out in one or two steps (in different temperatures) using one of the above techniques, and it can also be carried out in two or three steps using more than one of the above techniques. The electrical performance data shown here is from one-step and two-step recipes using rapid thermal process technique. 
     The one-step thermal treatment uses a single thermal cycle at high temperature fulfilled O 2  or N 2 O gas in order to reduce the leakage current by reducing the impurity level of carbon and the vacancies of oxygen atoms. During this treatment, the phase of film will transform from amorphous to crystalline if the temperature applied is above 750° C. FIG. 6 shows the x-ray diffraction data for the thin dielectric film of the present invention. The film deposited at about 400° C. changes from amorphous state to crystalline state at temperature of 750° C. FIG. 7 shows a set of results using rapid thermal process technique and will be recipe A. The recipe A of using RTP in O 2  gas for 120 seconds gives a leakage current below 1E-8A/cm 2  at 1.5 MV/cm. 
     The two-step thermal treatment uses a low temperature cycle to treat the film for the reduction of impurities and oxygen vacancies before any amorphous-to-crystalline phase transformation, and subsequently uses a high temperature cycle to further reduce the impurity level and oxygen vacancies during crystallization process. FIG.  8  and FIG. 9 each show a set of results obtained from two-step thermal treatment using rapid thermal process technique and will be recipe B and C respectively. For the data shown in FIG.  8  and FIG. 9, the (Ta 2 O 5 ) 1−x (TiO 2 ) x  films with x=0.078 are subjected to the first thermal treatment using rapid thermal process technique in O 2  for 5 minutes at 500° C. and 600° C., respectively. In both cases, the using of rapid thermal process technique in O 2  gas at 850° C. for 60 seconds as the second thermal step gives a leakage current below 1E-8A/cm 2  at 1.5 MV/cm. 
     The deposition of a metal layer  116  on top of the thermally treated (Ta 2 O 5 ) 1−x (TiO 2 ) x  film, by PVD or CVD, completes the method of the present invention. In this embodiment, the metal can be titanium nitride (TiN), tungsten nitride (WN), or tungsten (W). 
     FIG. 10 gives a table showing the effective dielectric constant for the capacitors produced using the method of the present invention. For the recipes A, B and C giving leakage currents below 1E-8A/cm 2  at 1.5 MV/cm (as is described above), the effective dielectric constants are still as high as 36.8, 41.5 and 38.8, respectively. These would give a SiO 2  equivalent thickness of about 10 Å for a capacitor produced in this method employing a 100 (Ta 2 O 5 ) 1−x (TiO 2 ) x  film with x=0.078. 
     Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended to be limited solely by the appended claims.

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