Abstract:
Disclosed herein is a method of fabricating a capacitor. The method includes the steps of: forming a Ti 1−x Hf x N layer on a substrate, wherein x is in a range from 0 to 0.5; forming an electrode layer on the Ti 1−x Hf x N layer; and forming a HfO 2  layer on an interface between the electrode layer and the Ti 1−x Hf x N layer by performing a thermal treatment in an oxygen gas-containing atmosphere.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of fabricating a semiconductor device. More particularly, the invention relates to a method for fabricating a capacitor thereof. 
     2. Brief Description of Related Technology 
     As an integration of a semiconductor device becomes higher recently, studies are conducted to increase the charge storage area by forming a capacitor in a complicated structure such as a cylinder, fin, stack or hemispheric silicon (HSG) to secure sufficient capacitance. In addition, a dielectric layer of capacitor is formed of materials HfO 2 , Al 2 O 3 , Ta 2 O 5 , SrTiO 3 , (Ba,Sr)TiO 3 , BLT, etc., of which dielectric constants are higher than SiO 2  or Si 3 N 4 . In particular, a hafnium oxide (HfO 2 ) layer is a high dielectric layer currently studied for a gate insulation layer and a dielectric layer of a capacitor. 
     FIGS. 1A to  1 C are cross-sectional views illustrating a conventional method for fabricating a capacitor. 
     Referring to FIG. 1A, an inter-layer dielectric layer (ILD)  12  is formed on a surface of a semiconductor substrate  11  having transistors and bit lines, and a storage node contact mask (not shown) is formed on inter-layer dielectric layer (ILD)  12 . After that, a storage node contact hole is formed to expose a predetermined area of the surface of the semiconductor substrate  11  by etching the inter-layer dielectric layer  12  with the storage node contact mask. 
     Subsequently, a polysilicon layer is formed on the entire surface including the storage node contact hole, and then an etch-back process is carried out in order to form a polysilicon plug  13  in the contact hole to a predetermined depth. 
     After that, a titanium silicide (TiSi 2 )  14  and a titanium nitride (TiN) layer  15  are formed on the polysilicon plug  13 . The TiSi 2  layer  14  forms an ohmic contact with a following bottom electrode, and the TiN layer  15  serves as an anti-diffusion layer that prevents oxygen remaining inside the bottom electrode from diffusing into the polysilicon plug  13 , the storage node contact plug, or into the semiconductor substrate  11 . 
     Referring to FIG. 1B, a sacrificial oxide layer  16  that determines the height of the bottom electrode is formed on the inter-layer dielectric layer  12  and the TiN layer  15 , and then a storage node mask (not shown) using a photoresist is formed on the sacrificial oxide layer  16 . 
     Subsequently, the sacrificial oxide layer  16  is selectively etched with the storage node mask to form an opening in which a bottom electrode is aligned on the polysilicon plug  13  to be formed. 
     Thereafter, a bottom electrode  17  is formed of metal over the surface of the sacrificial oxide layer  16  including the opening. After that, the bottom electrode is made to remain in the opening only through the process of etch-back or chemical mechanical polishing method so that the bottom electrode in the concavity is isolated from the neighboring bottom electrodes. 
     Referring to FIG. 1C, on the entire surface including the bottom electrode  17 , a dielectric layer  18  and a top electrode  19  are formed successively. Here, the bottom electrode  17 , dielectric layer  18  and top electrode  19  are formed by the chemical vapor deposition (CVD) method, and the dielectric layer  18  is mostly made of a high dielectric layer, such as HfO 2 . 
     In the conventional method described above, a capacitor is formed connected to a plug by using a storage node contact mask. 
     However, in a dynamic RAM (DRAM) over 4 Gbits that a fine design rule should be applied to, the storage node contact plug and the bottom electrode should not be misaligned. Also, to secure a sufficient capacitance, the height of the bottom electrode should be increased. This is a difficult because the plug height for interconnection becomes higher as the height of the bottom electrode gets higher. In addition, because the isolation gap from the neighboring bottom electrode is reduced, the current technology forming a bottom electrode, dielectric layer and top electrode by the CVD method has reached its limitation, so an atomic layer deposition (ALD) method is under development recently. 
     However, the ALD method has a shortcoming that an extra thermal treatment, or plasma treatment should be performed in every step to improve the quality of the layers. This is because the ALD method conducts depositions at a low temperature to improve the step coverage. Due to such complicated processes and investment for new equipments, the production costs are high for the ALD method. 
     It would be desirable to provide a method for fabricating a capacitor that avoids a rise in the production cost and complexity in production processes caused by performing a deposition and a subsequent treatment thereof whenever a layer is formed. 
     It also would be desirable to provide a method for fabricating a capacitor that avoids a misalignment in masking or etching processes for connecting transistors and the capacitor. 
     SUMMARY OF THE INVENTION 
     Accordingly, disclosed herein is a method of fabricating a capacitor, comprising the steps of: (a) forming a Ti 1−x Hf x N layer on a substrate, wherein x is in a range from 0 to 0.5; (b) forming an electrode layer on the Ti 1−x Hf x N layer; and, (c) forming a HfO 2  layer on an interface between the electrode layer and the Ti 1−x Hf x N layer by performing a thermal treatment in an oxygen gas-containing atmosphere. Such a capacitor will include a bottom electrode formed from the Ti 1−x Hf x N layer, a dielectric layer formed from the HfO 2  layer, and a top electrode formed from the electrode layer. 
     Also disclosed herein is a method for fabricating a capacitor, comprising the steps of: (a) forming an inter-layer dielectric layer on a silicon semiconductor substrate; (b) forming a contact hole that exposes a surface of the semiconductor substrate by selectively etching the inter-layer dielectric layer; (c) forming a Ti 1−x Hf x N layer in the contact hole, wherein x is in a range from 0 to about 0.5; (d) forming an electrode layer on the Ti 1−x Hf x N layer; and forming a HfO 2  layer on an interface between the electrode layer and the Ti 1−x Hf x N layer by performing a thermal treatment in an oxygen atmosphere. Such a capacitor will include a bottom electrode formed from the Ti 1−x Hf x N layer, a dielectric layer formed from the HfO 2  layer, and a top electrode formed from the electrode layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     Additional features of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the appended claims and the accompanying drawings, in which: 
     FIGS. 1A to  1 C are cross-sectional views illustrating a conventional method for fabricating a capacitor; 
     FIGS. 2A to  2 C are cross-sectional views depicting a method for fabricating a capacitor in accordance with an embodiment of the present invention; and, 
     FIG. 3 is a graph showing a phase stability of TiO 2  and HfO 2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 2A, an inter-layer dielectric layer  22  is deposited on a semiconductor substrate  21  having transistors and bit lines to insulate the substrate  21  from a capacitor to be formed subsequently. Thereafter, a storage node contact mask (not shown) is formed on the inter-layer dielectric layer  22  by using a photoresist. The inter-layer dielectric layer  22  is formed with an oxide layer to a thickness of about 5000 Å to about 20000 Å. 
     Subsequently, a storage node contact hole is formed to expose a predetermined part of the semiconductor substrate  11  by etching the inter-layer dielectric layer  22  with the storage node contact mask. Here, the storage node contact hole can be formed in a shape of a circle, stick, rectangle or polygon. 
     Thereafter, a titanium layer is deposited on the entire surface including the storage node contact hole. After performing a rapid thermal process (RTP), an ohmic layer  23  of titanium silicide (TiSi 2 ) is formed on the exposed semiconductor substrate  21  in the storage node contact hole to improve the contact resistance between the substrate  21  and a bottom electrode to be formed. The titanium layer is deposited by a method of sputtering, a chemical vapor deposition (CVD), or an atomic layer deposition (ALD) to a thickness of about 100 Å to about 500 Å. The rapid thermal process for forming the titanium silicide (TiSi 2 )  23  is performed in a nitrogen or argon atmosphere at a temperature of about 700° C. to about 900° C. for about 10 seconds to about 180 seconds. After that, non-reacted titanium is removed by wet-etching with ammonium hydroxide or sulphuric acid. At this moment, the wet-etching is carried out for about one minute to about 40 minutes. Meanwhile, after the deposition of titanium layer, an extra layer of titanium nitride (TiN) can be formed to a thickness of about 100 Å to about 500 Å by sputtering, CVD, or ALD methods. 
     After removing any non-reacted titanium, a Ti 1−x Hf x N layer  24  layer is formed by a sputtering, CVD, or ALD method, to a thickness of about 100 Å to about 300 Å. In case of depositing Ti 1−x Hf x N layer  24  by the CVD or ALD methods, it can be deposited by gradually increasing the molar fraction of Hf relative to TiN to Ti 0.5 Hf 0.5 N. 
     Referring to FIG. 2B, a Ti 1−x Hf x N layer  24   a  is made to remain only in the storage node contact hole by removing the Ti 1−x Hf x N layer  24  from the inter-layer dielectric layer  22 . At this moment, a photo-resist layer or a spin-on-glass (SOG) layer is coated on the entire surface including on the Ti 1−x Hf x N layer  24 , and the photo-resist layer or the SOG layer is selectively removed in order to leave the photo-resist layer or the SOG layer in the storage node contact hole only. After that, the Ti 1−x Hf x N layer  24  is etched back or polished chemically and mechanically using the photo-resist or the SOG as an etch mask or an anti-polish layer until the surface of the inter-layer dielectric layer  22  is exposed. 
     Subsequently, an electrode layer  25  is formed on the entire surface including Ti 1−x Hf x N layer  24   a  which remains in the storage node contact hole. Here, the electrode layer  25  is formed of a noble metal such as platinum, iridium, and ruthenium, and the electrode layer may be formed of a conductive oxide, or a complex layer of a noble metal and a conductive oxide. The electrode layer  25  is deposited by a sputtering, CVD, or ALD method to a thickness of about 50 Å to about 2000 Å. 
     Here, the conductive oxides are IrO 2 , RuO 2 , SrRuO 3 , (Ba,Sr)RuO 3 , (Sr,Ca)RuO 3 , A 1−x Re x BzO 3  (0≦x≦0.5, 0≦y≦0.5, 0.9≦z≦1.1, A═Y, La; Re═Sr, Ca; B═Cr, Mn, Fe) or La 1−x Sr x Co 1−y Cr y O 3 (0≦x≦0.5, 0≦y≦0.5). 
     Referring to FIG. 2C, the substrate is thermally treated in an atmosphere containing a gaseous mixture of O 2 +N 2  or O 2 +Ar at a temperature of about 400° C. to about 800° C. for about 10 seconds to about 10 minutes. 
     In a thermal treatment performed an O 2 -containing gaseous atmosphere, the Ti 1−x Hf x N  24   a  is oxidized, thus forming a HfO 2  layer  26  to a thickness of about 50 Å to about 300 Å on the interface of the Ti 1−x Hf x N  24   a  and the electrode layer  25 . 
     The non-reacted Ti 1−x Hf x N  24   a  that has not participated in the formation of the HfO 2  layer  26  is used as a bottom electrode  24   b , and the thermally-treated electrode layer  25  is used as a top electrode  25   a , the HfO 2  layer  26  being used as a dielectric layer of the capacitor. 
     Just as mentioned above, the Ti 1−x Hf x N layer  24   a  forms the HfO 2  layer  26  and the bottom electrode  24 B. So, the Ti 1−x Hf x N layer  24   a  which is a storage node contact and anti-diffusion layer, is utilized as a bottom electrode  24   b  as well. Moreover, it simplifies a capacitor fabrication process by using the anti-diffusion Ti 1−x Hf x N layer  24   a  as a bottom electrode  24   b , and forming a top electrode  25   a  on top of the Ti 1−x Hf x N layer  24   a . That is, by forming only two layers (i.e., the Ti 1−x Hf x N layer  24  and the electrode layer  25 ) and performing a thermal treatment (unlike the conventional technology that forms the five layers of a titanium silicide/titanium nitride/bottom electrode/dielectric layer/top electrode in order), it is possible to simplify the fabrication procedure. 
     If the Ti 1−x Hf x N layer  24  is exposed in the O 2  atmosphere without an electrode layer thereon and oxidized, the surface reacts with O 2  so it becomes rough. Also, because the surface does not receive any compressive stress from outside, the Ti 1−x Hf x N layer  24  becomes swollen during the oxidation and forms fine cracks, thus inhibiting the obtainment of a quality HfO 2  as good as can be used for a dielectric layer. 
     Also, in the case of forming HfO 2  by the CVD method or the ALD method, a high-temperature thermal treatment is necessary to improve the quality of HfO 2  layer, because the oxidation reaction occurs at a low temperature. However, in an embodiment of the present invention, since the oxygen atom (O), which diffused through the electrode layer  25  on the Ti 1−x Hf x N layer  24   a  is made to react with the Ti 1−x Hf x N layer  24   a , the reaction time is very fast. Also, covered with the electrode  25 , the Ti 1−x Hf x N layer  24   a  receives compressive stress from it and the interface between the HfO 2  and the electrode layer  25  is smooth. Besides, with HfO 2  formed through a thermal treatment, the lattice mismatch is relieved as much as possible, and the amount of surface charges that adversely affects leakage current is minimized. 
     Extra nitrogen atoms (N) generated while the HfO 2  is formed resolve back into the Ti 1−x Hf x N layer  24   a , so no void is generated between the HfO 2  layer  26  and the electric layer  25 . 
     The capacitor formed in the above processes uses an electrode layer  25  as its top electrode  25 A; non-reacted Ti 1−x Hf x N layer  24  as its bottom electrode  24 A; and the reaction product HfO 2  layer  26  as its dielectric layer. A desired thickness of the dielectric layer can be obtained by controlling the temperature and time of a thermal treatment. 
     The oxide layer generated during the oxidation of Ti 1−x Hf x N is not a TiO 2  layer but a HfO 2  layer can be known by a thermodynamic observation. 
     FIG. 3 is a graph showing the phase stability of TiO 2  and HfO 2 . 
     With reference to FIG. 3, since the partial pressure of oxygen (PO 2 ) in the present of Hf/HfO 2  is lower than the partial pressure of oxygen (PO 2 ) in the present of Ti/TiO 2 , HfO 2  is more stable than TiO 2  thermodynamically. Accordingly, when Hf and Ti are mixed and thermally treated in an oxygen atmosphere, Hf which is less stable thermodynamically, is oxidized faster than Ti because the oxidation potential of Hf is bigger than that of Ti. 
     Likewise, in case Ti 1−x Hf x N is oxidized, HfO 2  is more stable thermodynamically than the TiO 2  formed on the surface. 
     A sacrificial oxide layer for a bottom electrode need not he formed, because the bottom electrode is directly formed in the storage node contact hole by the present invention, thus simplifying the processes by lowering the deposition height of the capacitor as well as ensuring the alignment of depositions. 
     Also, this invention can obtain high quality of HfO2 and low leakage current by a solid reaction method through one-time thermal treatment with no need for a chemical vapor deposition (CVD) device or atomic layer deposition (ALD) device to form the HfO 2 . 
     The present invention also simplifies the fabrication process as well by forming a HfO 2 , bottom electrode, top electrode through one-time thermal treatment after depositing a Ti 1−x Hf x N and a conductive layer successively. 
     While the present invention has been described with respect to certain preferred embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.