Patent Publication Number: US-2006006449-A1

Title: Semiconductor integrated circuit devices having a hybrid dielectric layer and methods of fabricating the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims the benefit of Korean Patent Application No. 2004-52414, filed Jul. 6, 2004, the contents of which are hereby incorporated herein by reference in their entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to semiconductor integrated circuit devices and methods of fabricating the same and, more particularly, to semiconductor integrated circuit devices having a hybrid dielectric layer and methods of fabricating the same;  
      2. Description of the Related Art  
      Semiconductor integrated circuit devices commonly include metal oxide semiconductor (MOS) transistors, resistors and capacitors. Capacitors are composed of upper and lower electrodes which overlap each other, and a dielectric layer interposed therebetween. The electrodes can be formed of a doped polysilicon layer. However, the polysilicon layer may be additionally oxidized during a subsequent heat treatment process, thereby degrading electrical characteristics of the capacitor. In addition, the capacitor may exhibit a non-uniform capacitance according to a magnitude of the voltage that is applied to the polysilicon electrodes. For example, when the upper and lower electrodes are formed of a polysilicon layer doped with N-type impurities and a negative voltage is applied to the upper electrode, holes are induced at a surface of the lower electrode. Accordingly, a depletion layer may be formed at the surface of the lower electrode. The width of the depletion layer is changed depending on the magnitude of the negative voltage, which is applied to the upper electrode. As a result, the capacitance of the capacitor may be changed depending on the magnitude of the voltage applied to the electrodes. Thus, capacitors employing polysilicon electrodes are not suitable for semiconductor integrated circuit devices that require the accurate capacitor characteristics, for example, semiconductor integrated circuit devices including analog circuits.  
      Furthermore, in order to increase the integration density of the semiconductor integrated circuit devices, it is desirable to form the dielectric layer of the capacitor using a material having a high dielectric constant. However, a high-k dielectric layer exhibits a large leakage current as compared to a low-k dielectric layer such as a silicon oxide layer.  
      Methods of fabricating a capacitor employing a high-k dielectric layer are disclosed in U.S. Pat. No. 6,071,771 to Schuegraf, entitled “Semiconductor processing method of forming a capacitor and capacitor constructions”. According to Schuegraf, a densified Ta 2 O 5  layer is employed as a high-k dielectric layer exhibiting a small leakage current, and a nitride layer is interposed between the Ta 2 O 5  layer and an electrode to suppress an oxidation reaction at an interface therebetween.  
      In addition, methods of improving the leakage current characteristics of a high-k dielectric layer are disclosed in U.S. Pat. No. 6,660,660 B2 to Haukka et al., entitled “Methods for making a dielectric stack in an integrated circuit”. According to Haukka et al, an aluminum oxide (Al 2 O 3 ) layer or a lanthanum oxide (LaO) layer is provided as an interface layer between the high-k dielectric layer and the electrodes. These interface layers operate as an oxidation barrier layer and a diffusion barrier layer.  
     SUMMARY OF THE INVENTION  
      One embodiment of the present invention provides semiconductor integrated circuit devices having a hybrid dielectric layer suitable for improving capacitance uniformity in response to applied voltage and for improving leakage current characteristics.  
      Another embodiment of the present invention provides methods of fabricating semiconductor integrated circuit devices having a hybrid dielectric layer suitable for improving capacitance uniformity in response to applied voltage and for improving leakage current characteristics.  
      In one aspect, the present invention is directed to semiconductor integrated circuit devices having a hybrid dielectric layer. The hybrid dielectric layer of the semiconductor integrated circuit devices includes a lower dielectric layer, an intermediate dielectric layer and an upper dielectric layer, which are sequentially stacked. The lower dielectric layer is a material layer containing hafnium (Hf) or zirconium (Zr), and the intermediate dielectric layer is a material layer having a voltage dependent capacitance variation lower than that of the lower dielectric layer. In addition, the upper dielectric layer contains hafnium (Hf) or zirconium (Zr).  
      In some embodiments, the lower dielectric layer may be one of a hafnium oxide (HfO) layer, a zirconium oxide (ZrO) layer and a hafnium-zirconium oxide (HfZrO) layer. In addition, the lower dielectric layer may be a combination layer of the HfO layer and the ZrO layer. For example, the lower dielectric layer may have a laminate structure in which the HfO layer and the ZrO layer are alternately and repeatedly stacked.  
      In other embodiments, the intermediate dielectric layer may be at least one layer selected from the group consisting of a tantalum oxide layer, a titanium oxide layer, a BST (Ba,Sr,TiO 3 ) layer, a STO (Sr, TiO 3 ) layer, a PZT (Pb,Zr,TiO 3 ) layer, a TaON layer, a Nb-doped TaO layer and a Ti-doped TaO layer.  
      In yet other embodiments, the upper dielectric layer may be one of a hafnium oxide (HfO) layer, a zirconium oxide (ZrO) layer and a hafnium-zirconium oxide (HfZrO) layer. In addition, the upper dielectric layer may be a combination layer of the HfO layer and the ZrO layer. For example, the upper dielectric layer may have a laminate structure in which the HfO layer and the ZrO layer are alternately and repeatedly stacked.  
      In another aspect, the present invention is directed to methods of fabricating a semiconductor integrated circuit device having a hybrid dielectric layer. These methods include forming a lower dielectric layer containing hafnium (Hf) or zirconium (Zr) on an integrated circuit substrate. An intermediate dielectric layer is formed on the lower dielectric layer. The intermediate dielectric layer is formed of a material layer having a voltage dependent capacitance variation lower than that of the lower dielectric layer. An upper dielectric layer containing Hf or Zr is formed on the intermediate dielectric layer.  
      In some embodiments, the lower dielectric layer may be formed of one of a hafnium oxide (HfO) layer, a zirconium oxide (ZrO) layer and a hafnium-zirconium oxide (HfZrO) layer. In addition, the lower dielectric layer may be formed of a combination layer of the HfO layer and the ZrO layer. For example, the lower dielectric layer may be formed of a laminate layer in which the HfO layer and the ZrO layer are alternately and repeatedly stacked. The lower dielectric layer may be formed using an atomic layer deposition (ALD) technique or a chemical vapor deposition (CVD) technique.  
      In other embodiments, the intermediate dielectric layer may be formed of at least one layer selected from the group consisting of a tantalum oxide layer, a titanium oxide layer, a BST (Ba,Sr,TiO 3 ) layer, a STO (Sr, TiO 3 ) layer, a PZT (Pb,Zr,TiO 3 ) layer, a TaON layer, a Nb-doped TaO layer and a Ti-doped TaO layer. The intermediate dielectric layer may be formed using an ALD technique or a CVD technique.  
      In yet other embodiments, the upper dielectric layer may be formed of one of a hafnium oxide (HfO) layer, a zirconium oxide (ZrO) layer and a hafnium-zirconium oxide (HfZrO) layer. In addition, the upper dielectric layer may be formed of a combination layer of the HfO layer and the ZrO layer. For example, the upper dielectric layer may be formed of a laminate layer in which the HfO layer and the ZrO layer are alternately and repeatedly stacked. The upper dielectric layer may be formed using an ALD technique or a CVD technique.  
      In another aspect, the present invention is directed to a capacitor comprising: a lower electrode on an integrated circuit substrate; a lower dielectric layer pattern on the lower electrode, the lower dielectric layer containing hafnium (Hf) or zirconium (Zr); an intermediate dielectric layer pattern on the lower dielectric layer pattern, a voltage dependent capacitance variation of the intermediate dielectric layer being lower than that of the lower dielectric layer pattern; an upper dielectric layer pattern on the intermediate dielectric layer pattern, the upper dielectric layer containing hafnium (Hf) or zirconium (Zr); and an upper electrode on the upper dielectric layer pattern.  
      In one embodiment, the lower electrode and the upper electrode are a metal layer.  
      In another aspect, the present invention is directed to a method of fabricating a capacitor, comprising: forming a lower electrode layer on an integrated circuit substrate; forming a lower dielectric layer on the lower electrode, the lower dielectric layer containing any one of hafnium (Hf) and zirconium (Zr); forming an intermediate dielectric layer on the lower dielectric layer, the intermediate dielectric layer being formed of a material layer having a voltage dependent capacitance variation lower than that of the lower dielectric layer; forming an upper dielectric layer on the intermediate dielectric layer, the upper dielectric layer containing any one of Hf and Zr; forming an upper electrode layer on the upper dielectric layer; and patterning the upper electrode layer, the upper dielectric layer, the intermediate dielectric layer, the lower dielectric layer and the lower electrode layer to form a lower electrode, a lower dielectric layer pattern, an intermediate dielectric layer pattern, an upper dielectric layer pattern and an upper electrode which are sequentially stacked.  
      In one embodiment, the lower electrode layer and the upper electrode layer are formed of a metal layer.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing and other objects, features and advantages of the invention will be apparent from the more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
       FIGS. 1 and 2  are cross-sectional views illustrating methods of forming a capacitor in accordance with an embodiment of the present invention.  
       FIGS. 3 and 4  are cross-sectional views illustrating methods of forming a capacitor in accordance with another embodiment of the present invention.  
       FIG. 5  is a graph comparing leakage current characteristics of capacitors fabricated in accordance with the conventional approach and in accordance with an embodiment of the present invention.  
       FIG. 6  is a graph illustrating voltage dependent capacitance characteristics of capacitors fabricated in accordance with the conventional approach and in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. In the drawings, the thickness of layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout the specification.  
       FIGS. 1 and 2  are cross-sectional views to illustrate methods of forming a capacitor in accordance with an embodiment of the present invention.  
      Referring to  FIG. 1 , an interlayer insulating layer  3  is formed on an integrated circuit substrate  1 . A lower electrode layer  5 , a lower dielectric layer  7 , an intermediate dielectric layer  9 , an upper dielectric layer  11  and an upper electrode layer  13  are sequentially formed on the interlayer insulating layer  3 . The lower dielectric layer  7 , the intermediate dielectric layer  9  and the upper dielectric layer  11  constitute a hybrid dielectric layer  12 . The lower electrode layer  5  and the upper electrode layer  13  can be formed of metal layers. For example, each of the lower electrode layer  5  and the upper electrode layer  13  can be formed of at least one layer selected from the group consisting of a titanium (Ti) layer, a tantalum (Ta) layer, a titanium nitride (TiN) layer, a tantalum nitride (TaN) layer, a tungsten (W) layer, a tungsten nitride (WN) layer, an aluminum (Al) layer, a copper (Cu) layer, a ruthenium (Ru) layer, a ruthenium oxide (RuO) layer, a platinum (Pt) layer, an iridium (Ir) layer and an iridium oxide (IrO) layer. In addition, the lower electrode layer  5  and the upper electrode layer  13  may be formed, for example, using a physical vapor deposition technique, an atomic layer deposition (ALD) technique or a metal organic CVD technique.  
      The lower dielectric layer  7  and the upper dielectric layer  11  are formed of a material layer exhibiting a relatively lower leakage current than the intermediate dielectric layer  9 . In other words, the lower dielectric layer  7  and the upper dielectric layer  11  are formed of a material layer having an energy band gap greater than that of the intermediate dielectric layer  9 . For example, the lower dielectric layer  7  and the upper dielectric layer  11  may be formed of a material layer containing hafnium (Hf) or zirconium (Zr). In detail, the lower dielectric layer  7  and the upper dielectric layer  11  may be formed of one of a hafnium oxide (HfO) layer, a zirconium oxide (ZrO) layer and a hafnium-zirconium oxide (HfZrO) layer. Alternatively, the lower dielectric layer  7  may be formed of a combination layer of the HfO layer and the ZrO layer. For example, the lower dielectric layer  7  may be formed by alternately and repeatedly depositing the HfO layer and the ZrO layer. That is, the lower dielectric layer may be formed of a laminate layer of the HfO layer and the ZrO layer. The upper dielectric layer may also be formed of the laminate layer of the HfO layer and the ZrO layer. The lower dielectric layer  7  and the upper dielectric layer  11  may be formed using an atomic layer deposition (ALD) technique or a CVD technique at a low temperature of 25° C. to 500° C.  
      The intermediate dielectric layer  9  is formed of a material layer having a voltage-dependent capacitance variation less than those of the lower dielectric layer  7  and the upper dielectric layer  11 . The voltage-dependent capacitance variation means a variation of a normalized capacitance of the dielectric layer when a voltage applied to the dielectric layer is increased or decreased. Accordingly, the intermediate dielectric layer  9  is preferably formed of a high-k dielectric layer having a capacitance that is constant regardless of the voltage. For example, the intermediate dielectric layer  9  may be formed of at least one layer selected from the group consisting of a tantalum oxide layer, a titanium oxide layer, a BST (Ba,Sr,TiO 3 ) layer, a STO (Sr, TiO 3 ) layer, a PZT (Pb,Zr,TiO 3 ) layer, a TaON layer, a Nb-doped TaO layer and a Ti-doped TaO layer.  
      The intermediate dielectric layer  9  can optionally be formed using an atomic layer deposition technique or a CVD technique at a low temperature of 25° C. to 500° C. In addition, the intermediate dielectric layer  9  can be thermally treated using a gas containing oxygen, prior to formation of the upper dielectric layer  11 . For example, the intermediate dielectric layer  9  may be thermally treated using an ozone gas, an oxygen plasma or an N 2 O plasma at a low temperature of 100° C. to 500° C. The heat treatment process enhances the leakage current characteristics of the intermediate dielectric layer  9 .  
      Referring to  FIG. 2 , the upper electrode layer  13 , the hybrid dielectric layer  12  and the lower electrode layer  5  are patterned to form a lower electrode  5   a , a lower dielectric layer pattern  7   a , an intermediate dielectric layer pattern  9   a , an upper dielectric layer pattern  11   a  and an upper electrode  13   a  which are sequentially stacked. The lower dielectric layer pattern  7   a , the intermediate dielectric layer pattern  9   a  and the upper dielectric layer pattern  11   a  constitute a hybrid dielectric layer pattern  12   a.    
      In the meantime, when the lower electrode layer  5  is formed of a metal layer such as a copper layer, it may be difficult to pattern the copper layer using conventional photolithography and etching processes. In this case, the lower electrode  5   a  may be formed using a damascene process as shown in  FIGS. 3 and 4 .  
      Referring to  FIGS. 3 and 4 , an interlayer insulating layer  23  is formed on an integrated circuit substrate  21 . A predetermined region of the interlayer insulating layer  23  is partially etched to form a trench region. A lower electrode layer filling the trench region, for example a copper layer, is formed on the substrate having the trench region. A diffusion barrier layer may be formed prior to formation of the copper layer. The diffusion barrier layer may be formed of a metal nitride layer such as a TiN layer or a TaN layer. The lower electrode layer and the diffusion barrier layer are then planarized using a chemical mechanical polishing (CMP) technique to expose an upper surface of the interlayer insulating layer  23 . As a result, a diffusion barrier layer pattern  25  covering an inner wall of the trench region, and a lower electrode  27  (i.e., a copper electrode) surrounded by the diffusion barrier layer pattern  25  are formed. The diffusion barrier layer pattern  25  prevents copper atoms in the copper electrode  27  from being diffused into the interlayer insulating layer  23 .  
      Subsequently, the hybrid dielectric layer pattern  12   a  and the upper electrode  13   a  are formed on the copper electrode  27  using the same methods as described with reference to  FIGS. 1 and 2 .  
     EXAMPLES  
      Hereinafter, the electrical characteristics of the hybrid dielectric layers fabricated according to the above-mentioned embodiments and the conventional art will be described.  
       FIG. 5  is a graph that compares leakage current characteristics of capacitors fabricated in accordance with embodiments of the present invention and in accordance with the conventional art. In  FIG. 5 , the abscissa indicates a voltage V A  which is applied to upper electrodes of the capacitors, and the ordinate indicates a leakage current density I L  which flows through the dielectric layers. The leakage current density I L  was measured at a temperature of 125° C.  
      Capacitors exhibiting the measurement results of  FIG. 5  were fabricated using the key process conditions described in the following Table 1.  
                           TABLE 1                           Conventional   Conventional   Present       Process parameters   art 1   art 2   invention                                        Lower electrode   TiN layer (PVD)                                 Dielectric   Lower dielectric layer   TaO layer   HfO layer   HfO layer       Layer       (600 Å,   (420 Å, ALD)   (50 Å, ALD)               MOCVD)           Intermediate           TaO layer           dielectric layer           (480 Å, MOCVD)           Upper dielectric layer           HfO layer                       (50 Å, ALD)                     Upper electrode   TiN layer (PVD)                  
 
      As can be seen from table 1, all dielectric layers formed, whether in accordance with the conventional approach or in accordance with the present invention, were formed to have an equivalent oxide thickness of about 84 Å.  
      Referring to the table 1 and  FIG. 5 , when a voltage V A  of −8V or +8V was applied to a conventional capacitor employing a single tantalum oxide layer as a dielectric layer, the conventional capacitor exhibited a leakage current density I L  Of about 1×10 −3  Ampere/cm 2  to 1×10 −1  Ampere/cm 2 . On the contrary, another conventional capacitor employing a single hafnium oxide layer as a dielectric layer exhibited a low leakage current density I L  of about 1×10 −7  Ampere/cm 2  at a voltage V A  of −8V or +8V. In addition, the capacitor employing a hybrid dielectric layer having a stacked structure of a hafnium oxide layer, a tantalum oxide layer and a hafnium oxide layer in accordance with the present invention also exhibited a low leakage current density I L  of about 1×10 −7  Ampere/cm 2  at a voltage V A  of −8V or +8V. As a result, the single hafnium oxide layer or the hybrid dielectric layer containing the single hafnium oxide layer exhibited a significantly low leakage current density I L  as compared to the single tantalum oxide layer.  
       FIG. 6  is a graph comparing capacitance vs. voltage (CV) plots of capacitors fabricated according to embodiments of the present invention and capacitors fabricated according to the conventional art. In other words,  FIG. 6  is a graph illustrating voltage-dependent capacitance variation characteristics. The capacitance was measured by applying a signal with a frequency of 100 kHz to the capacitors. In  FIG. 6 , the abscissa indicates a voltage V A  which is applied to upper electrodes of the capacitors, and the ordinate indicates a normalized capacitance (C N ) of the capacitors.  
      Capacitors exhibiting the measurement results of  FIG. 6  were fabricated using the same process conditions as described in the table 1.  
      Referring to  FIG. 6 , when the voltage VA applied to a single hafnium oxide layer was increased from 0V to +8V, the normalized capacitance C N  was increased by about 0.0075. On the contrary, when the voltage V A  applied to a single tantalum oxide layer was increased from 0V to +8V, the normalized capacitance C N  was increased by about 0.0015. In addition, when a voltage applied to a hybrid dielectric layer having a stacked structure of a hafnium oxide layer, a tantalum oxide layer and a hafnium oxide layer was increased from 0V to +8V, the normalized capacitance (C N ) was increased by about 0.0025. As a result, the tantalum oxide layer or the hybrid dielectric layer containing the tantalum oxide layer exhibited a relatively low voltage dependent capacitance variation as compared to the single hafnium oxide layer.  
      In conclusion, as can be seen from  FIGS. 5 and 6 , the hybrid dielectric layer having a stacked structure of a hafnium oxide layer, a tantalum oxide layer and a hafnium oxide layer exhibited not only a low leakage current but also a low voltage-dependent capacitance variation.  
      According to the present invention as mentioned above, a hybrid dielectric layer of an intermediate dielectric layer having a relatively low voltage-dependent capacitance variation, and upper and lower dielectric layers having a relatively low leakage current is provided. Accordingly, a high performance capacitor exhibiting a low leakage current and a uniform capacitance may be implemented irrespective of the voltage variation applied to the capacitor employing the hybrid dielectric layer.  
      While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made herein without departing from the spirit and scope of the invention as defined by the appended claims.