Abstract:
A gate electrode, in which the slope of the profile of a gate electrode forming material layer, for example, a refractory metal silicide layer is prevented from being decreased due to thermal expansion by patterning a refractory metal silicide layer after performing a thermal process on a refractory metal silicide layer, thereby having a stable operation characteristic, and a method for manufacturing the same are provided.

Description:
RELATED APPLICATION 
     This application relies for priority upon Korean Patent Application No. 2000-66830, filed on Nov. 10, 2000, the contents of which are herein incorporated by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device and a method therefor, and more particularly, to a gate electrode structure with an improved profile, and a method for manufacturing the same. 
     2. Description of the Related Art 
     As the degree of integration in semiconductor memory devices increases, areas occupied by separate devices, for example, a transistor, are reduced. In the transistor, hot carriers are generated in a channel region due to a short channel effect according to the reduction in area. In order to solve problems associated with the hot carrier effects, a lightly doped drain and source (LDD) transistor, in which source and drain regions are formed after forming spacers on the sidewalls of the gate electrode of the transistor and the sidewalls of a capping layer, are provided. Here, the capping layer is an insulating film formed on the gate electrode to protect the gate electrode in subsequent processing steps. 
     In general, a polycide, a structure with a refractory metal silicide layer formed on top of the polysilicon gate, is used to form a gate electrode. Typically, a thermal process is used to decrease the resistance of the gate electrode after forming the capping layer and the gate electrode. However, the refractory metal silicide layer becomes much larger than the capping layer during thermal expansion due to a variation in the coefficients of thermal expansion between the two materials. Accordingly, the profile of the gate electrode structure is not vertical but sloped. 
     Recently, a self-aligned contact hole is formed between the gate electrodes and then filled with a conductive material. As the semiconductor device is highly integrated, the slope of the sidewall of the gate electrode decreases and a sidewall spacer becomes thinner. Accordingly, the possibility of shorts between a conductive layer formed in the self-aligned contact hole and the gate electrodes substantially increases. 
     In order to prevent such shorts between the gate electrodes and the conductive layer, there have been attempts to increase the thickness of the spacer. However, as the thickness of the spacer increases, the distance between the gate electrodes becomes smaller. Therefore, voids are generated when the space between the gate electrode structures is filled with an interlayer insulating layer. Subsequently, voids are filled with the conductive material and undesirably connected to the conductive layer formed in an adjacent self-aligned contact hole, resulting in device failure. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a gate electrode structure, in which the slope of the profile of the gate electrode structure increases. 
     Accordingly, to achieve the above object, after sequentially forming a gate electrode conductive layer, for example, a polycide formed of polysilicon and a refractory metal silicide layer, and an insulating layer to form a capping layer on a semiconductor substrate, a thermal process is performed on the semiconductor substrate. The capping layer and the gate electrode are then formed by patterning an insulating layer and a conductive layer. 
     In another embodiment, after forming the conductive layer for the gate electrode and the insulating layer for the capping layer, the capping layer is formed by patterning the insulating layer. The thermal process is performed on the semiconductor substrate including the conductive layer. Then, the gate electrode and the spacer are formed. 
     According to the above-mentioned method, it is possible to skip a thermal process between a process of patterning the gate electrode and a process of forming the spacer by performing a thermal process on the conductive layer before the patterning process for forming the gate electrode. Also, it is possible to prevent the slope of the profile of the gate electrode structure from being decreased by patterning the conductive layer for the gate electrode, which is already thermally expanded. Here, that the slope of the profile of the gate electrode structure becomes decreased may mean that the slope of the side surface of the gate electrode structure is less than 80° in a peripheral region and is less than 83° in a core region. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING(S) 
     The above object 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 illustrate a method of forming a gate electrode structure having an improved profile according to an embodiment of the present invention; 
     FIG. 4 illustrates a method of forming a gate electrode structure having an improved profile according to another embodiment of the present invention; 
     FIGS. 5A and 5B show profiles of a gate electrode structure manufactured according to a conventional technology; 
     FIGS. 6A and 6B show the profile of a gate electrode structure manufactured according to an embodiment of the present invention; 
     FIGS. 7A and 7B show the profile of a gate electrode structure manufactured according to another embodiment of the present invention; and 
     FIG. 8 shows the ranges of fluctuation of the critical dimensions (CD) of gate electrode structures formed according to a conventional technology and according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, an oxide film  12  for forming a gate insulating film, a polysilicon layer  14 , a tungsten silicide layer  16  that is one of refractory metal silicide layers, and a silicon nitride film  18  for forming a capping layer are formed on a semiconductor substrate  10 . It will be appreciated by a person skilled in the art that other silicide layers such as a cobalt silicide layer or a titanium silicide layer can be used instead of the tungsten silicide layer  16 . Metal oxide films such as a silicon oxide film, a silicon oxinitride film, an aluminum oxide film, or a tantalum oxide film can be used instead of the silicon nitride film  18  depending on process conditions. 
     After forming a silicon nitride film  18 , a thermal process can be performed on the semiconductor substrate  10 . The tungsten silicide layer  16  is expanded by the thermal process. A rapid thermal processing (RTP) or a furnace can be used for the thermal process. 
     In FIG. 2, a capping layer  18   a,  gate electrodes  16   a  and  14   a,  and a gate oxide film  12   a  are formed by sequentially patterning a silicon nitride film  18 , a tungsten silicide layer  16 , a polysilicon layer  14 , and a silicon oxide film  12 . During the above patterning process, the same mask can be used with respect to all the layers formed on the semiconductor substrate  10 . 
     In FIG. 3, spacers  20  are formed on the sidewalls of the gate electrodes  14   a  and  16   a  and the capping layer  18   a.  A stacked structure of a gate oxide film, a gate electrode, and a capping layer and spacers are referred herein to as a gate electrode structure. Although not shown, any damage to the sidewall surfaces of the gate electrodes  14   a  and  16   a  and the capping layer  18   a  can be cured by growing an oxide film in an oxygen atmosphere before forming the spacers  20 . 
     FIG. 4 shows another method of forming a gate electrode structure according to one embodiment of the present invention. After sequentially forming a silicon oxide film  52 , a polysilicon layer  54 , a refractory metal silicide layer  56 , and a silicon nitride film (not shown) on a semiconductor substrate  50 , a capping layer  58  is formed by patterning the silicon nitride film. The thermal process is performed after forming the capping layer  58 . A gate electrode (not shown) and a gate oxide film (not shown) are formed by sequentially patterning the refractory metal silicide layer  56 , the polysilicon layer  54 , and the silicon oxide film  52  using the capping layer  58  as a mask. As shown in FIG. 3, spacers (not shown) may be formed on the sidewalls of the gate electrode and the capping layer  58 . 
     The (sloped) profile of the sidewalls of the gate electrode manufactured according to the present invention and the profile of the gate electrode formed according to the conventional technologies are shown in FIGS. 5A,  5 B,  6 A,  6 B,  7 A, and  7 B. The gate electrodes and the capping layers shown in FIGS. 5A,  5 B,  6 A,  6 B,  7 A,  7 B, and  8  denote a gate electrode formed of a polysilicon layer of 800 Å and a tungsten silicide layer of 1000 Å, and a capping layer formed of a silicon nitride film of 1800 Å. They are thermally treated for approximately 15 seconds at approximately 1050° C. 
     FIGS. 5A,  6 A, and  7 A show the gate electrode and the capping layer formed in the peripheral region of the semiconductor integrated circuit. FIGS. 5B,  6 B, and  7 B show the gate electrode and the capping layer formed on the core region of the semiconductor integrated circuit. 
     In the peripheral region, an angle formed between the sidewall of the gate electrode and the semiconductor substrate is about 77° in the conventional technology. However, an angle formed between the sidewall of the gate electrode and the semiconductor substrate increases to 80° (in the first embodiment) and 84° (in the second embodiment) according to the present invention. In the core region, an angle formed between the sidewall of the gate electrode and the semiconductor substrate is about 82° in the conventional technology. However, an angle formed between the sidewall of the gate electrode and the semiconductor substrate is about 86° in accordance with the first and second embodiments of the present invention. 
     When the gate electrode is formed according to the present invention, as shown in FIG. 8, the range of fluctuation of the critical dimension (CD) of the gate electrode is 39 nm, which is less than 59 nm, which is the range of fluctuation of the CD of the gate electrode according to the conventional technologies. Therefore, it is possible to form the gate electrode having more stable operation characteristics with the present invention. In FIG. 8, the horizontal axis denotes a design CD of the gate electrode and the vertical axis denotes a delta CD, which shows the range of fluctuation. 
     Thus, it is possible to prevent the slope of the profile of the gate electrode from being decreased by patterning the already-heat-treated tungsten silicide layer  16 , i.e., which is thermal expanded, during the formation of the gate electrode. Therefore, the spacer formed on the sidewalls of the gate electrode structure can have a desired thickness. Accordingly, an insulating effect by the spacer is not reduced. Also, the range of fluctuation of the threshold value of the gate electrode is reduced. Accordingly, it is possible to form a gate electrode having stable operation characteristics. 
     Having illustrated and described the principles of our invention in a preferred embodiment thereof, it should be readily apparent to those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications coming within the spirit and scope of the accompanying claims.