Patent Publication Number: US-7217669-B2

Title: Method of forming a metal oxide film

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional application of U.S. application Ser. No. 10/131,473 filed on Apr. 25, 2002, now U.S. Pat. No. 6,800,570 the entire contents of which are hereby incorporated by reference for which priority is claimed under 35 U.S.C. § 120; and this application claims priority of Application No. 01-55468 filed in the Republic of Korea on Sep. 10, 2001 under 35 U.S.C. § 119. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method of forming a metal oxide layer, and more particularly, to a method of forming a metal oxide layer, which can be used in a semiconductor device. 
     DESCRIPTION OF THE RELATED ART 
     A tantalum pentoxide (Ta 2 O 5 ) film has high dielectric constant and therefore, extensive practical use as a dielectric film in a capacitor for a new generation high-density DRAM of 1 giga bit or more. In order to put a tantalum pentoxide film into practical use, its leakage current characteristics should also be good. 
     Generally, a tantalum pentoxide film is formed by thermal chemical vapor deposition (CVD). During the thermal CVD, a metal organic precursor, such as Ta(OC 2 H 5 ) 5  as a metal source, and O 2  gas are used. However, impurities such as carbon and moisture may be included in the tantalum pentoxide film, which may provide a path for leakage current. Further, once the tantalum pentoxide film is formed, it is amorphous; as a result its film quality may be poor, and it may be difficult to combine with oxygen. Accordingly, electric current flowing through such a film is prone to leak, and oxygen deficiency may occur. 
     In a conventional method, a low-temperature oxidation annealing process is performed after a tantalum pentoxide film is formed in order to reduce a leakage current in the tantalum pentoxide film and improve the characteristics thereof as a dielectric film. Thereafter, the tantalum pentoxide film is heated at high temperature under an oxygen atmosphere to crystallize the tantalum pentoxide film and remove impurities in the tantalum pentoxide film. 
     According to the conventional method, a deposition process of forming a tantalum pentoxide (Ta 2 O 5 ) film and a low-temperature oxidation annealing process for supplementing oxygen deficiency are individually accomplished at different process temperatures. For this reason, two chambers are needed to perform these two processes. If these two processes are to be accomplished in the same chamber, it would take a long time to stabilize the temperature of the chamber. Therefore, time is wasted and throughput decreased. 
     These problems of the conventional method can occur during the formation of a metal oxide film to be used as a dielectric film in a semiconductor device, as well as in a process of forming a tantalum pentoxide (Ta 2 O 5 ) film. 
     SUMMARY OF THE INVENTION 
     At least one embodiment of the present invention provides a method of forming a tantalum pentoxide film, which reduces the time required for an annealing process performed to cure an oxygen deficiency occurring after the formation of the tantalum pentoxide film, thereby enhancing the film characteristics and throughput. 
     At least one embodiment of the present invention provides a method of forming a dielectric film, for a semiconductor device, using a metal oxide, which enhances the film characteristics and throughput. 
     At least one embodiment of the present invention provides a method of forming an amorphous tantalum pentoxide or dielectric film where annealing is performed in situ with the formation of the amorphous tantalum pentoxide or metal oxide film. 
     At least one embodiment of the present invention provides a method of forming an amorphous tantalum pentoxide or dielectric film where annealing is performed at the same or substantially the same temperature as the temperature used during the formation of the amorphous tantalum pentoxide or metal oxide film. 
     In at least one embodiment of the present invention the activated vapor may be one of O 3  gas, UV—O 3 , O 2  plasma, O 3  plasma, and N 2 O plasma. In at least one embodiment of the present invention, the Ta source may be one of Ta(OC 2 H 5 ) 5  and Ta(OC 2 H 5 ) 4 OCHCH 2 N(CH 3 ) 2 . 
     In at least one embodiment of the present invention, the concentration of the activated vapor during annealing is the same as or larger than the concentration of the activated vapor used during the deposition of the amorphous tantalum pentoxide film. In at least one embodiment of the present invention, O 2  gas as well as the activated vapor may be supplied to the substrate during the annealing. In at least one embodiment of the present invention, the annealing is performed at a temperature of 380–520° C. In at least one embodiment of the present invention, the formation of the amorphous tantalum pentoxide film and the annealing may be performed at the same or substantially the same temperature. 
     In at least one embodiment of the present invention, the annealing may be performed at a higher pressure than the pressure when the amorphous tantalum pentoxide film was formed. For example, the amorphous tantalum pentoxide film may be formed at a pressure of 0.1–10 Torr, and the annealing may be performed at a pressure of 0.1–50 Torr. 
     In at least one embodiment of the present invention, forming the amorphous tantalum pentoxide film and performing the annealing can be repeated several times until a tantalum pentoxide film is formed to a desired thickness. In at least one embodiment of the present invention, the amorphous tantalum pentoxide film can be crystallized after annealing. 
     At least one other embodiment of the present invention is directed to a method of forming a tantalum pentoxide film comprising: forming an amorphous pentoxide film on a substrate in a chamber in which an activated vapor atmosphere containing oxygen is maintained, using a Ta source and O 2  gas; and annealing the amorphous tantalum pentoxide film in-situ with the formation of the amorphous pentoxide film in an oxygen atmosphere at a lower temperature than the crystallization of tantalum pentoxide. 
     In yet another embodiment, the chamber can be purged while it is evacuated, between forming the amorphous tantalum pentoxide film and the annealing. 
     At least one other embodiment of the present invention is directed to a method of forming a dielectric film comprising: forming a metal oxide film on a substrate while the substrate is exposed to a first activated vapor containing oxygen, using a metal organic precursor; and annealing the metal oxide film in-situ with the formation of the metal oxide film while the substrate is exposed to a second activated vapor containing oxygen. 
     In at least one embodiment of the present invention, the metal oxide film may be one of a tantalum pentoxide film, an aluminum oxide film, a (Ba,Sr)TiO 3  (BST) film, and a PbZrTiO 3  (PZT) film. 
     In at least one embodiment of the present invention, during the formation of the metal oxide film, the metal organic precursor, the activated vapor, and O 2  gas may be supplied to the substrate. Further, in at least one embodiment of the present invention, during the annealing, the activated vapor and O 2  gas may be supplied to the substrate. 
     In at least one embodiment of the present invention, the formation of the metal oxide film and the annealing may be performed at the same or substantially the same temperature. Also, in at least one embodiment of the present invention, the formation of the metal oxide film and the annealing may be performed in the same chamber while maintaining the vacuum state of the chamber. 
     At least one other embodiment of the present invention is directed to a method of forming a dielectric film comprising: forming a metal oxide film on a substrate by supplying at least an metal organic precursor and an activated vapor; and annealing the metal oxide film at substantially the same temperature as the a temperature used to form the metal oxide film. 
     At least one other embodiment of the present invention is directed to a method of forming a dielectric film comprising: forming a metal oxide film on a substrate by supplying at least an metal organic precursor and an activated vapor, under a first pressure, a first vapor concentration, and a first vapor flow rate; and annealing the metal oxide film under a second pressure, a second vapor concentration, and a second vapor flow rate, wherein at least one of the second pressure, second vapor concentration, and second vapor flow rate is different from the first pressure, the first vapor concentration, and the first vapor flow rate used to form the metal oxide film. 
     According to one or more embodiments of the present invention, in order to form a dielectric film composed of a metal oxide, little or no additional time is required to stabilize the temperature of the chamber during the deposition of an amorphous dielectric film and a subsequent annealing, thereby raising throughput. Also, during the deposition of the amorphous dielectric film and the subsequent annealing, it is possible to improve deposition characteristics such as step coverage and deposition rate and electric characteristics such as leakage current characteristics by appropriately controlling the concentration of activated vapor containing oxygen and the flow rate and pressure of O 2  gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objectives and advantages of the present invention will become more apparent by describing in detail a preferred embodiment thereof with reference to the attached drawings in which: 
         FIGS. 1 through 3  are cross-sectional views for explaining a method of forming a dielectric film according to at least one embodiment of the present invention; 
         FIG. 4  is a graph showing variations in temperature according to processing time in a method of forming a tantalum pentoxide film according to at least one embodiment of the present invention; 
         FIG. 5  is a graph showing variations in pressure according to processing time in a method of forming a tantalum pentoxide film according to at least one embodiment of the present invention; 
         FIG. 6  is a graph showing variations in the concentration of O 3  according to processing time in a method of forming a tantalum pentoxide film according to at least one embodiment of the present invention; and 
         FIG. 7  is a graph showing variations in the thickness of a tantalum pentoxide film according to deposition time in a method of forming the tantalum pentoxide film according to at least one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 through 3  are cross-sectional views for explaining the sequence of a process of forming a dielectric film according to at least one embodiment of the present invention. 
     Referring to  FIG. 1 , a lower electrode  20  is formed on a semiconductor substrate  10 , and then an amorphous dielectric film  30  is formed thereon. The amorphous dielectric film  30  may be formed by chemical vapor deposition (CVD) using a metal organic precursor as a metal source and O 2  gas. The amorphous dielectric film  30  may be formed of a metal oxide film such as a tantalum pentoxide film, an aluminum oxide film, a (Ba,Sr)TiO 3  (BST) film, a PbZrTiO 3  (PZT) film. The CVD may be performed in a reaction chamber included in single-wafer type adopting a resistance heater, and activated vapor containing oxygen, as well as a metal organic precursor and O 2  gas, is supplied to the reaction chamber during the CVD. For the activated vapor containing oxygen, O 3 , UV—O 3 , O 2  plasma, O 3  plasma, and/or N 2 O plasma may be used. 
     Further, Ta(OC 2 H 5 ) 5  or Ta(OC 2 H 5 ) 4 OCHCH 2 N(CH 3 ) 2  can be used as a Ta source when the amorphous dielectric film  30  is formed of an amorphous tantalum oxide film. The amorphous tantalum oxide film is obtained by maintaining the temperature of the reaction chamber to be about 380–520° C. (preferably, about 440–480° C.), the pressure to be about 0.1–10 Torr (preferably, about 1–3 Torr) and supplying Ta(OC 2 H 5 ) 5  at a rate of about 30–40 mg/min, O 2  gas at a rate of about 50–1000 sccm (preferably, 50–200 sccm) and O 3  gas at a rate of 10–150 g/m 3  (preferably, 10–30 g/m 3 ). As a result, the amorphous tantalum oxide film is formed as the amorphous dielectric film  30  on the lower electrode  20 . 
     If the amorphous dielectric film  30  is formed of an aluminum oxide film, Al(CH 3 ) 3  can be used as an aluminum source. Further, if the amorphous dielectric film  30  is formed of the BST film, Ba(C 11 H 19 O 2 ) 2 , {Sr(C 11 H 19 O 2 ) 2 } 3 (C 11 H 20 O 2 ) and/or Ti(C 3 H 4 O) 4  can be supplied as metal sources. When the amorphous dielectric film  30  is formed of the PZT film, Pb(C 11 H 19 O 2 ), Zr(C 4 H 9 O) 4 , and/or Ti(C 3 H 7 O) 4  can be used as metal sources. 
     The above metal sources for the metal oxide films are, however, illustrative and are not meant to restrict the present invention. Except for the supply of the exemplified metal sources, the other conditions required in forming the respective metal oxide film may be the same as or different from those required in forming a tantalum oxide film. 
     After the amorphous dielectric film  30  is formed, the chamber may be purged for approximately 10–120 seconds, while maintained in a vacuum, to remove all or most of the metal sources that remain in the semiconductor substrate  10  having the amorphous dielectric film  30 . At this time, O 2  gas can be supplied to the chamber. 
     Referring to  FIG. 2 , annealing  32  may be performed on the amorphous dielectric film  30  at about 380–520° C., which is lower than the crystallization temperature of the dielectric film  30 , under activated vapor containing oxygen. The annealing  32  may be performed in the above purged chamber in-situ after the amorphous dielectric film  30  is formed, while vacuum is still maintained. To perform the annealing  32  under an oxygen atmosphere, activated vapor, such as O 3 , UV—O 3 , O 2  plasma, O 3  plasma and/or N 2 O plasma, is supplied to the chamber. During the annealing  32 , the concentration of the activated vapor should be the same as or larger than that of the activated vapor supplied to the amorphous dielectric film  30 , and the chamber should be maintained at a higher pressure than the pressure when forming the amorphous dielectric film  30 . 
     When the amorphous pentoxide film is formed as the amorphous dielectric film  30 , the semiconductor substrate  10  may be maintained at a temperature of about 380–520° C. (preferably, about 440–480° C.) and a pressure of about 0.1–50 Torr (preferably, about 25–35 Torr). Also, O 2  gas at a rate of about 50–20000 sccm (preferably, 1000–20000 sccm) and O 3  gas at a pressure of about 10–150 g/m 3  (preferably, 130–150 g/m 3 ) may be supplied to the semiconductor substrate  10 . More preferably, during the annealing  32 , the chamber is kept at the same or substantially the same temperature as when the amorphous dielectric film  30  is formed. 
     As described above, the formation of the amorphous dielectric film  30  and the annealing  32  are performed at the same or substantially the same temperature; instead, parameters, such as the pressure, the concentration of activated vapor containing oxygen and the flow rate and pressure of O 2  gas that may be properly controlled. For this reason, additional time is not required to stabilize the temperature of the chamber, thereby increasing the throughput. Further, deposition characteristics such as step coverage and deposition rate and electrical characteristics such as leakage current characteristics can be enhanced. 
     The amorphous dielectric film  30  may be formed to a desired thickness, e.g., 100 Å, by the method described with reference to  FIG. 1 , and then, the annealing  32  described with reference to  FIG. 2  may be performed on the amorphous dielectric film  30 . Additionally, referring to  FIGS. 1 and 2 , the formation of amorphous dielectric film  30  and the annealing  32  can be repeated more than once to form a dielectric film at a desired thickness. For instance, in order to obtain a dielectric film of 100 Å thickness, an amorphous dielectric film  30  having a thickness of 10 Å may be formed, and the annealing  32  is performed thereon. Then, other amorphous dielectric film having a thickness of 10 Å may be formed on the formed amorphous dielectric film  30  and the annealing  32  is performed thereon. This process is repeated a number of times until a dielectric film having the desired thickness of 100 Å is obtained. 
     Referring to  FIG. 3 , a thermal treatment  34  may be applied to the amorphous dielectric film  30 , on which the annealing  32  is performed, at a higher temperature than the crystallization temperature of a tantalum pentoxide film, thereby forming a crystallized dielectric film  30   a . If the amorphous dielectric film  30  is formed of an amorphous tantalum pentoxide film, the amorphous dielectric film  30  is heated at about 720–750° C. to form the crystallized dielectric film  30   a.    
       FIG. 4  is a graph illustrating variations in temperature according to processing time when a tantalum pentoxide film is formed according at least one embodiment of the present invention. Referring to  FIG. 4 , before forming a tantalum pentoxide film, the temperature in the chamber is raised to a first temperature. At this time, O 2  gas is preferably first supplied to the chamber to reduce the possibility of a rapid change in the pressure of the chamber. Once the temperature of the chamber has been raised to a desired temperature, e.g., about 460° C., a wafer is loaded in the chamber, and the deposition of a tantalum pentoxide film, the purging of the chamber, and annealing using O 3  are performed, while the temperature of the chamber is maintained constant or substantially constant. Thereafter, the temperature of the chamber is lowered and the wafer is removed from the chamber. At this time, O 2  gas may be supplied to the chamber so that the possibility of a rapid change in the pressure in the chamber can be reduced. 
       FIG. 5  is a graph showing variations in the pressure of a chamber according to processing time when a tantalum pentoxide film is formed according to at least one embodiment of the present invention. 
       FIG. 6  is a graph showing a variation in the concentration of O 3  used as activated vapor containing oxygen when a tantalum pentoxide film is formed according to at least one embodiment of the present invention. 
     It is noted that the principles illustrated by  FIGS. 4–6  with respect to tantalum pentoxide films may also be applied the other types of films mentioned herein, as would be evident to one ordinary skill in the art, when presented with the discussion above regarding tantalum pentoxide films. 
     In a method of forming a tantalum pentoxide film according to at least one embodiment of the present invention, it is possible to form a tantalum pentoxide film having a desired thickness by repeatedly depositing a tantalum pentoxide film, purging of a chamber, and annealing a desired number of times. 
       FIG. 7  is a graph showing variations in the thickness of a tantalum pentoxide film according to deposition time in a method of forming the tantalum pentoxide film according to at least one embodiment of the present invention. From  FIG. 7 , it is noted that the tantalum pentoxide film can be stably deposited by supplying all of a Ta source, O 2  gas, and activated O 3  gas to a chamber once. 
     According to at least one embodiment of the present invention, a dielectric film composed of a metal oxide may be obtained by supplying a metal source, O 2  gas, and activated vapor containing oxygen in a chamber all at once to form a metal oxide film, and then annealing the amorphous metal oxide film in the same chamber without a change in temperature, i.e., in situ, under activated vapor atmosphere containing oxygen to supplement oxygen deficiency in the amorphous metal oxide film. For this reason, no additional time is required to stabilize the temperature of the chamber during the deposition of an amorphous dielectric film and a subsequent annealing, thereby raising throughput. Also, during the deposition of the amorphous dielectric film and the subsequent annealing, it is possible to improve deposition characteristics such as step coverage and deposition rate and electric characteristics such as leakage current characteristics by appropriately controlling the concentration of activated vapor containing oxygen and the flow rate and pressure of O 2  gas. 
     While the present invention has been particularly shown and described with reference to the preferred embodiments thereof, the present invention is not restricted to the above embodiments. It is noted that many of the principles described above with respect to tantalum pentoxide films may also be applied the other types of films mentioned herein, as would be evident to one ordinary skill in the art, when presented with the discussion above regarding tantalum pentoxide films.