Method of manufacturing a capacitor in a semiconductor device

The present invention relates to a method of manufacturing a capacitor in a semiconductor device. It is designed to solve the problem due to oxidization of the surface of the underlying tungsten electrode during thermal process performed after depositing Ta.sub.2 O.sub.5 to form a dielectric film in a Ta.sub.2 O.sub.5 capacitor of a MIM (Metal Insulator Metal) structure using tungsten (W) as an underlying electrode. Thus, the present invention includes forming a good thin WO.sub.3 film by processing the surface of the underlying tungsten electrode by low oxidization process before forming a Ta.sub.2 O.sub.5 dielectric film and then performing deposition and thermal process of Ta.sub.2 O.sub.5 to form a Ta.sub.2 O.sub.5 dielectric film. As a good WO.sub.3 film is formed on the surface of the underlying tungsten electrode before forming a Ta.sub.2 O.sub.5 dielectric film, the grain boundary of the tungsten film is filled with oxygen atoms, thus preventing diffusion of oxygen atoms from the Ta.sub.2 O.sub.5 dielectric film during a subsequent thermal process. Also, as a further oxidization of the surface of the underlying tungsten electrode by the WO.sub.3 film could be prevented, thereby improving the characteristic of the leak current of the Ta.sub.2 O.sub.5 capacitor.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates generally to a method of manufacturing a capacitor in
 a semiconductor device, and more particularly to, a method of
 manufacturing a capacitor in a semiconductor device which can prevent
 oxidization of the surface of an underlying electrode to improve the
 characteristic of the leak current of a Ta.sub.2 O.sub.5 capacitor, upon a
 thermal treatment process performed after Ta.sub.2 O.sub.5 is deposited in
 order to form a dielectric film, in a Ta.sub.2 O.sub.5 capacitor of a MIM
 (Metal Insulator Metal) structure using tungsten (W) as an underlying
 electrode.
 2. Description of the Prior Art
 Generally, when manufacturing a Ta.sub.2 O.sub.5 capacitor in a memory
 device, if metal materials such as Tungsten are used as underlying
 electrode materials, the work function of the metal materials with
 poly-silicon is large. Thus, the thickness of the effective oxide film Tox
 can be reduced and thus the leak current in the thickness of the same
 effective oxide film can also be reduced. Further, the value of .DELTA. C
 depending on the bias voltage is small. As a Ta.sub.2 O.sub.5 dielectric
 film lacks oxygen in the film formed by Ta.sub.2 O.sub.5 deposition
 process and also contains impurities such as carbon or hydrogen etc., in
 order to secure the dielectric characteristic of the Ta.sub.2 O.sub.5
 capacitor, oxygen must be flowed into it and a subsequent process for
 removing impurities must be performed after the Ta.sub.2 O.sub.5
 deposition is completed.
 This subsequent process is mainly thermally performed under oxygen
 atmosphere at a higher temperature, thus securing the dielectric
 characteristic of a Ta.sub.2 O.sub.5 dielectric film. However, if the
 temperature of the thermal process is too high or the time of the thermal
 treatment is too long, upon thermal treatment process, the surface of the
 underlying tungsten electrode is oxidized to form a WO.sub.3 film. The
 WO.sub.3 film has the dielectric constant of about 42, which is higher
 than that of Ta.sub.2 O.sub.5 dielectric film having about 25. However,
 when creating the WO.sub.3 film, there is a possibility that oxygen within
 the Ta.sub.2 O.sub.5 dielectric film can be diffused into the underlying
 tungsten electrode. Also, due to the difference of the thermal expansion
 coefficient with the Ta.sub.2 O.sub.5 dielectric film, there is a problem
 that the characteristic of the leak current of the Ta.sub.2 O.sub.5
 capacitor becomes degraded since a phenomenon of film lifting of the film
 is generated.
 SUMMARY OF THE INVENTION
 It is therefore an object of the present invention to provide a method of
 manufacturing a capacitor in a semiconductor device which can prevent
 oxidization of the surface of an underlying electrode to improve the
 characteristic of the leak current of a Ta.sub.2 O.sub.5 capacitor, upon a
 thermal treatment process performed after Ta.sub.2 O.sub.5 is deposited in
 order to form a dielectric film, in a Ta.sub.2 O.sub.5 capacitor of a MIM
 (Metal Insulator Metal) structure using tungsten (W) as an underlying
 electrode.
 In order to accomplish the object, a method of manufacturing a capacitor in
 a semiconductor device according to the present invention is characterized
 in that it comprises the steps of forming an underlying tungsten electrode
 on a substrate in which an underlying structure is formed; forming a
 WO.sub.3 film on the surface of the underlying tungsten electrode; forming
 a Ta.sub.2 O.sub.5 dielectric film on the WO.sub.3 film; and forming an
 upper electrode on the Ta.sub.2 O.sub.5 dielectric film.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 The present invention will be described in detail by way of a preferred
 embodiment with reference to accompanying drawings, in which like
 reference numerals are used to identify the same or similar parts.
 FIGS. 1A through 1D are sectional views for illustrating a method of
 manufacturing a capacitor in a semiconductor device according to the
 present invention.
 Referring now to FIG. 1A, a first doped poly-silicon layer 1 is formed on a
 substrate 10 in which an underlying structure is formed. Then, a barrier
 metal layer 2 is formed on the first doped poly-silicon layer 1.
 In the above, the barrier metal layer 2 is formed of a Ti film and a TiN
 film. The Ti film is formed by depositing Ti in 100 through 200 .ANG.
 thickness by means of sputtering method. The TiN film is formed in 100
 through 200 .ANG. thickness by means of metal organic chemical vapor
 deposition (MOCVD) method using Ti(N(CH.sub.3).sub.2).sub.4 (TDMAT) as raw
 materials and using He and Ar as carrier gases. At this time, the
 deposition conditions include 200-300 sccm in the flow rate of raw
 materials; 100 through 300 sccm in the flow rate of He and Ar,
 respectively, being carrier gases; 2-10 Torr in the pressure within the
 reactive furnace and 300-500.degree. C. in the temperature within the
 reactive furnace. Thereafter, a plasma process is performed for about 20
 through 50 seconds with the power of 500 through 1000W.
 Referring now to FIG. 1B, a tungsten film 3 is formed on the barrier metal
 layer 2 to complete an underlying electrode.
 In the above, the tungsten film 3 is formed by chemical vapor deposition
 (CVD) method under the conditions that WF.sub.6 is used as raw materials,
 H.sub.2 is used as a reactive gas, the pressure within the reactive
 furnace is maintained at 80-110 Torr, and the temperature within the
 reactive furnace is maintained at the temperature of 350-450.degree. C.
 Referring to FIG. 1C, after removing a native oxide film in which
 impurities created on the surface of the tungsten film 3 are contained by
 means of cleaning process, a WO.sub.3 film 100 is forcedly formed on the
 surface of the tungsten film 3. Then, a Ta.sub.2 O.sub.5 dielectric film 4
 is formed on the WO.sub.3 film 100.
 In the above, the cleaning process is performed using 50:1 HF for 30
 through 50 seconds. The WO.sub.3 film 100 is formed in thickness of 10-30
 .ANG. by oxidizing the tungsten film 3 by means of Rapid Thermal Anneal
 (RTA), plasma process or UV/O.sub.3 process etc. under a low temperature
 oxygen atmosphere. The WO.sub.3 film 100 formed thus is good in the
 quality of the film and also fills the grain boundary of the tungsten film
 3 with oxygen atoms. The rapid thermal process is performed under the
 atmospheres of O.sub.2 or N.sub.2 O at the temperature of 450-550.degree.
 C. for 5-20 seconds. The plasma process is performed under the atmospheres
 of O.sub.2 or N.sub.2 O at the temperature of 300-550.degree. C. for
 30-120 seconds by the power of 200-500W. The UV/O.sub.3 process is
 performed at the temperature of 300 14 550.degree. C. for 2-5 minutes at
 the strength of 15-30 mW/cm.sup.2.
 The Ta.sub.2 O.sub.5 dielectric film 4 is deposited with use Ta.sub.2
 O.sub.5 under the conditions that Ta(C.sub.2 H.sub.5 O).sub.5 is used as
 raw materials, N.sub.2 gas and O.sub.2 gas is used as a carrier gas and an
 oxidizer, respectively, the flow rate of the N.sub.2 gas is maintained at
 350-450 sccm, the flow rate of the O.sub.2 gas is maintained at 20-50
 sccm, the pressure within the reactive furnace is maintained at 0.1-0.6
 Torr, and the temperature within the reactive furnace is maintained at
 350-450.degree. C. Then, in order to prevent oxidization of the tungsten
 film 3 being an underlying electrode while obtaining a dielectric
 characteristic, the Ta.sub.2 O.sub.5 dielectric film 4 is experienced by a
 rapid thermal process by mixing inactive gases such as N.sub.2, Ar, He
 etc. in N.sub.2 O gas or O.sub.2 gas at the temperature of 550-700.degree.
 C. for 20-60 seconds, or by a plasma annealing process under oxygen
 atmosphere using O.sub.2 gas or N.sub.2 O gas by which a plasma power of
 10-100W is applied at the temperature of less 350.degree. C.
 Referring to FIG. 1D, a TiN film 5 and a second doped poly-silicon layer 6
 are sequentially formed on the Ta.sub.2 O.sub.5 dielectric film 4, thus
 completing an upper electrode of a capacitor. By means of a series of
 these processes, a Ta.sub.2 O.sub.5 capacitor of a MIM structure is
 manufactured.
 In the above, the TiN film 5 is formed in thickness of 200-500 .ANG. by
 means of chemical vapor deposition (CVD) method under the conditions that
 TiCl.sub.4 is used as raw materials, NH.sub.3 gas is used as a reactive
 gas, the temperature within the reactive furnace is maintained at
 300-500.degree. C. and the pressure within the reactive furnace is
 maintained at 0.1-2 Torr. The second poly-silicon layer 6 is formed in
 thickness of 800-1200 .ANG.. The TiN film 5 functions to reduce the work
 function with the second poly-silicon layer 6 and the Ta.sub.2 O.sub.5
 dielectric film 4.
 FIG. 2 is a graph of I-V characteristic for illustrating the leak current
 characteristic of a capacitor when comparing the method according to the
 present invention by which O.sub.2 -RTA is performed at the temperature of
 500.degree. C. under the atmosphere of oxygen with the conventional method
 in which no process is performed before a Ta.sub.2 O.sub.5 dielectric film
 is formed.
 In order to compare the leak current characteristic, the Ta.sub.2 O.sub.5
 dielectric films in the present invention and the conventional method are
 formed identically. As shown in FIG. 2, the thickness of the effective
 oxide film Tox is almost same in both cases of the conventional method and
 the present invention. However, it could be seen that the leak current in
 the present invention has been greatly improved. In other words, , the
 leak current at 1V in the conventional method shows 4.32E-5(A/cm.sup.2)
 while that in the present invention shows 2.58E-8(A/cm.sup.2). Also, it
 could be seen that the leak current in the present invention is greatly
 improved even in the negative voltage.
 As can be understood from the above description with the present invention,
 the present invention forms a good WO.sub.3 film on the surface of the
 underlying tungsten electrode before forming a Ta.sub.2 O.sub.5 dielectric
 film in a Ta.sub.2 O.sub.5 capacitor using tungsten as an underlying
 electrode. As the grain boundary of the tungsten film is filled with
 oxygen atoms, diffusion of oxygen atoms from the Ta.sub.2 O.sub.5
 dielectric film can be prevented during a subsequent thermal process.
 Thus, the intrinsic characteristic of the Ta.sub.2 O.sub.5 dielectric film
 can be intact. Also, a further oxidization of the surface of the
 underlying tungsten electrode by the WO.sub.3 film could be prevented,
 thereby improving the characteristic of the leak current of the Ta.sub.2
 O.sub.5 capacitor.
 The present invention has been described with reference to a particular
 embodiment in connection with a particular application. Those having
 ordinary skill in the art and access to the teachings of the present
 invention will recognize additional modifications and applications within
 the scope thereof.
 It is therefore intended by the appended claims to cover any and all such
 applications, modifications, and embodiments within the scope of the
 present invention.