Patent Publication Number: US-6911362-B2

Title: Methods for forming electronic devices including capacitor structures

Description:
RELATED APPLICATION 
   This application claims priority from Korean Patent Application No. 2002-53116 filed Sep. 4, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
   FIELD OF THE INVENTION 
   The present invention generally relates to methods of fabricating electronic devices and, more particularly, to methods of fabricating electronic devices including capacitor structures. 
   BACKGROUND OF THE INVENTION 
   A ferroelectric memory device has a non-volatile property to retain previous data even when a power supply is interrupted. Similar to a dynamic random access memory (DRAM) or a static random access memory (SRAM), the ferroelectric memory device operates at a relatively low power supply voltage. For these reasons, the ferroelectric memory device may be a promising candidate for use in applications such as smart cards. 
   A conventional method of fabricating a ferroelectric memory device is now described below with reference to FIG.  1  through FIG.  3 . Referring to  FIG. 1 , device isolation layers  13  are formed at predetermined regions of a semiconductor device to define an active region therebetween. A plurality of insulated gate electrodes  15  (providing wordlines) are formed across the active region and the device isolation layer  13 . Impurities are implanted into portions of the active region between gate electrodes  15  to form source/drain regions  17   s  and  17   d . A first lower interlayer dielectric  19  is formed on a surface of the structure including source/drain regions  17   s  and  17   d , device isolation layers  13 , and gate electrodes  15 . The first lower interlayer dielectric  19  is patterned to form storage node contact holes exposing the source regions  17   s . Contact plugs  21  are formed in the storage node contact holes. 
   Referring to  FIG. 2 , ferroelectric capacitors  32  are formed on predetermined regions of the structure including the contact plugs  21 . Each of the ferroelectric capacitors  32  includes a lower electrode  27 , a ferroelectric pattern  29 , and an upper electrode  31  which are sequentially stacked. The lower electrodes  27  cover their respective contact plugs  21 . An inter-metal dielectric  33  is formed on a surface of the structure including the ferroelectric capacitors  32 . Typically, the inter-metal dielectric  33  is made of silicon oxide. 
   Referring to  FIG. 3 , the inter-metal dielectric  33  is planarized down to a top surface of the upper electrode  31  to provide an inter-metal dielectric pattern  33 ′. To planarize the inter-metal dielectric  33 , an etch-back process or a chemical mechanical polishing (CMP) process is carried out. 
   After planarization, a deposition thickness and an etch thickness may vary across different positions on a wafer. That is, the inter-metal dielectric  33  may be less etched at dotted circle  38  so that the upper electrode  31  is not exposed at dotted circle  38 , as shown in the FIG.  3 . In this case, the upper electrode  31  of ferroelectric capacitor  32  may be electrically isolated, thereby preventing proper operation. To address this situation, the inter-metal dielectric  33  may be overetched in the planarization process. However, the foregoing deviation in deposition and etch thickness may result in the inter-metal dielectric pattern  33 ′ being overetched to expose the ferroelectric pattern  29  at dotted circuit  39 . The exposure of the ferroelectric pattern  29  may give rise to deterioration of operation characteristics of the ferroelectric capacitor  32 . 
   Reducing deviations in thicknesses of an inter-metal dielectric may be difficult due to limitations of processing tolerances of existing processing technologies. A realizable approach may be to form an upper electrode whose thickness is greater than a maximum thickness deviation across a wafer. This approach may reduce problems associated with the thickness deviations, but may cause the ferroelectric capacitor  32  to be thicker. The thicker the ferroelectric capacitor  32  is, the more difficult vertically patterning a sidewall of the ferroelectric capacitor  32  may become. 
   SUMMARY 
   According to embodiments of the present invention, methods for forming an electronic device can include forming a capacitor structure on a portion of a substrate with the capacitor structure including a first electrode on the substrate, a capacitor dielectric on the first electrode, a second electrode on the dielectric, and a hard mask on the second electrode. More particularly, the capacitor dielectric can be between the first and second electrodes, the first electrode and the capacitor dielectric can be between the second electrode and the substrate, and the first and second electrodes and the capacitor dielectric can be between the hard mask and the substrate. An interlayer dielectric layer can be formed on the hard mask and on portions of the substrate surrounding the capacitor structure, and portions of the interlayer dielectric layer can be removed to expose the hard mask while maintaining portions of the interlayer dielectric layer on portions of the substrate surrounding the capacitor structure. The hard mask can then be removed thereby exposing portions of the second electrode while maintaining the portions of the interlayer dielectric layer on portions of the substrate surrounding the capacitor. 
   After removing the hard mask layer, a plate line can be formed on the exposed portions of the second electrode, and the capacitor dielectric may include a ferroelectric material such as Pb(Zr,Ti)O 3  (PZT), Sr x Bi 2+y Ta 2 O 9  (SBT), and/or Bi 4−x La x Ti 3 O 12  (BLT). Removing portions of the interlayer dielectric layer may include planarizing the interlayer dielectric layer down to a level of the hard mask using a technique such as chemical mechanical polishing and/or an etching back. 
   In addition, the interlayer dielectric layer, the hard mask, and the second electrode may comprise different materials. Accordingly, the hard mask may be removed by etching the hard mask using an etchant that selectively etches the hard mask with respect to the interlayer dielectric layer and the second electrode. More particularly, the etchant may include phosphoric acid, and the hard mask may include a layer of at least one material selected from the group consisting of silicon nitride and/or titanium nitride. 
   Forming the capacitor structure may include forming a first electrode layer on the substrate, forming a dielectric layer on the lower electrode layer, forming a second electrode layer on the dielectric layer, and forming a hard mask layer on the second electrode layer. The hard mask layer can be patterned to provide the hard mask on the second electrode layer. Portions of the second electrode layer, the dielectric layer, and the first electrode layer can then be etched using the hard mask as an etching mask to provide the first electrode, the capacitor dielectric, and the second electrode. In addition, each of the first and second electrodes may include at least one material selected from the group consisting of ruthenium (Ru), platinum (Pt), iridium (Ir), rhodium (Rh), osmium (Os), and/or oxides thereof. 
   The hard mask may have a thickness in the range of approximately 50 nanometers to 200 nanometers. Moreover, a thickness of the hard mask may be greater than a variation in thickness of the portions of the interlayer dielectric layer maintained on portions of the substrate surrounding the capacitor structure after removing portions of the interlayer dielectric layer. The interlayer dielectric layer, for example, may be a layer of silicon oxide. 
   Methods according to embodiments of the present invention may additionally include forming a hydrogen barrier layer on the capacitor structure including the hard mask, the first and second electrodes, and the capacitor dielectric prior to forming the interlayer dielectric layer. More particularly, the hydrogen barrier layer may be a layer of a material selected from the group consisting of titanium oxide (TiO 2 ), aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), and cerium oxide (CeO 2 ). In addition, a memory cell access transistor may be formed prior to forming the capacitor structure wherein the first electrode of the capacitor structure is electrically connected to a source/drain region of the memory cell access transistor. In addition, an insulating layer can be formed on the memory cell access transistor prior to forming the capacitor structure wherein the insulating layer includes a via therein exposing a portion of the source/drain region of the memory cell access transistor, and wherein the first electrode is electrically connected to the source/drain region through the via. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1  through  FIG. 3  are cross-sectional views illustrating a conventional method of fabricating a ferroelectric memory device. 
       FIG. 4  is a top plan view of a ferroelectric memory device. 
       FIGS. 5-10  are cross-sectional views illustrating steps of fabricating ferroelectric memory devices according to embodiments of the present invention. 
   

   DETAILED DESCRIPTION 
   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. The 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, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. It will also be understood that when an element is referred to as being “coupled” or “connected” to another element, it can be directly coupled or connected to the other element, or intervening elements may also be present. Like numbers refer to like elements throughout. 
   This disclosure also uses relative terms, such as “under”, “beneath”, “upper”, and/or “top” to describe some of the elements in the embodiments. These relative terms are used for the sake of convenience and clarity when referring to the drawings, but are not to be construed to mean that the elements so described can only be positioned relative to one another as shown. For example, when a first element is described as being under a second element in the viewer&#39;s frame of reference, it will be understood that the first element may also be located over the second element, if the embodiment were viewed from a different frame of reference, such as if the entire structure were inverted. 
   Ferroelectric memory devices are now described below with reference to FIG.  4 . Referring to  FIG. 4 , a device isolation layer is disposed at a predetermined region of a semiconductor device to define a plurality of active regions  53   a . A plurality of insulated gate electrodes  57  are disposed across the active regions  53   a  and the device isolation layer. The gate electrodes  57  may provide respective wordlines and are parallel in a row direction (y-axis). Each of the active regions  53   a  intersects a pair of gate electrodes  57 . Accordingly, each of the active regions  53   a  is divided into three parts. A common drain region is provided at an active region  53   a  between the pair of the gate electrodes  57 , and source regions are provided at active regions  53   a  adjacent to opposite sides of the common drain region. Thus, cell transistors may be disposed at intersections of the gate electrodes  57  and the active regions  53   a . The cell transistors can be 2-dimensionally disposed in a column direction (x-axis) and a row direction (y-axis). 
   A plurality of bitlines  71  are provided across the wordlines  57  to be electrically connected to common drain regions. Bitline contact holes  71   a  are provided at intersections of the common drain regions and the bitlines  71 . The bitline contact holes  71   a  provide electrical connection between the common drain regions and respective bitlines. The bitline contact holes  7  a can be filled with respective bitline pads. 
   Storage node contact holes  75   a  are provided over respective source regions and can be filled with respective contact plugs. Ferroelectric capacitors  82  are coupled to respective contact plugs. Each of the ferroelectric capacitors  82  includes a lower electrode, a ferroelectric pattern, and an upper electrode which are sequentially stacked. Each lower electrode is electrically connected to source region through a contact plug. 
   The upper electrodes of the ferroelectric capacitors  82  are connected to at least one plate line. A plate line can be connected to ferroelectric capacitors  82  on at least two adjacent rows. A main wordline  91  (coupled to the gate electrodes  57 ) can be sandwiched between the plate lines. 
   Methods of fabricating ferroelectric memory devices according to embodiments of the present invention are now described below with reference to  FIGS. 5-10  which are cross-sectional views taken along a line I-I′ of FIG.  4 . Referring to  FIG. 5 , device isolation layers  53  can be formed at predetermined: regions of a semiconductor substrate  51  to define a plurality of active regions  53   a . A gate insulation layer, a gate conductive layer, and a capping insulation layer can be sequentially formed on an entire surface of a semiconductor substrate where the active regions are formed. The capping insulation layer, the gate conductive layer, and the gate insulation layer can then be successively patterned to form a plurality of gate patterns  60  crossing over the active regions and the device isolation layers  53 . Each of the gate patterns  60  includes a gate insulation layer pattern  55 , a gate electrode  57 , and a capping insulation layer pattern  59  which are sequentially stacked. A pair of gate electrodes  57  may cross each active region, and each gate electrode  57  may provide a wordline. 
   Using the gate patterns  60  and the device isolation layer  53  as ion implanting masks, impurities (dopants) can be implanted into the active regions to provide three impurity regions at each active region. A central impurity region may provide a common drain region  61   d , and the other impurity regions may provide respective source regions  61   s . A pair of cell transistors can be formed at each active region. The cell transistors can be 2-dimensionally disposed on the semiconductor substrate  51  in row and column directions. Insulating spacers  63  can be formed on sidewalls of the gate patterns  60 . 
   Referring to  FIG. 6 , a first lower interlayer dielectric  65  can be formed on an entire surface of a structure including gate patterns  60  and spacers  63 . The first lower interlayer dielectric  65  can be patterned to form pad contact holes exposing the source/drain regions  61   s  and  61   d . Storage node pads  67   s  and bitline pads  67   d  can be formed in the pad contact holes. The storage node pads  67   s  are coupled to the source regions  61   s , and the bitline pads  67   d  are coupled to the common drain region  61   d . A second lower interlayer dielectric  69  can be formed on a surface of the structure including first lower interlayer dielectric  65  and pads  67   s  and  67   d . The second lower interlayer dielectric  69  is patterned to form bitline contact holes  71   a  (see  FIG. 4 ) exposing the bitline pads  67   d . A plurality of bitlines  71  can be formed covering the bitline contact holes. Bitlines  71  cross over wordlines  57 . 
   Referring to  FIG. 7 , a third lower interlayer dielectric  73  can be formed on an entire surface of a semiconductor substrate including the bitlines  71 . The first, second, and third interlayer dielectrics  65 ,  69  and  73  may provide a lower interlayer dielectric  74 . The second and third interlayer dielectrics  69  and  73  can be patterned to provide storage node contact holes  75   a  (see  FIG. 4 ) exposing the storage node pads  67   s . To increase an upper diameter of the storage node contacts, the storage node contact holes may be formed using a dry etch or a wet etch. Accordingly an upper sidewall of the storage node contact hole may have a sloped profile, as shown in FIG.  7 . The sloped profile may reduce an electrical resistance between a later-formed lower electrode and the source region  61   s . Contact plugs  75  can be formed in respective storage node contact holes. 
   Referring to  FIG. 8 , a lower electrode layer, a ferroelectric layer, an upper electrode layer, and a hard mask layer can be sequentially formed on the contact plugs  75  and the lower interlayer dielectric  74 . The hard mask layer can be patterned to form hard mask patterns  83  covering predetermined regions of the upper electrode layer. The predetermined regions covered with the hard mask patterns  83  can be patterned into ferroelectric capacitors over contact plugs  75 . Using the hard mask pattern  83  as an etching mask, the upper electrode layer, the ferroelectric layer, and the lower electrode layer can be successively patterned to form a plurality of ferroelectric capacitors  82  which are 2-dimensionally disposed in row and column directions. Each of the ferroelectric capacitors  82  can include a lower electrode  77 , a ferroelectric pattern  79 , and an upper electrode  81  which are sequentially stacked. The lower electrodes  77  contact respective contact plugs. As a result, lower electrodes  77  of ferroelectric capacitors  82  can be electrically connected to respective source regions  61   s.    
   The upper electrodes  81  and the lower electrodes  77  can include a layer of at least one selected from the group consisting of ruthenium (Ru), platinum (Pt), iridium (Ir), rhodium (Rh), osmium (Os), and/or oxides thereof. The upper electrodes  81  and the lower electrodes  77  may alternately include a layer of at least-one selected from the group consisting of SrRuO 3 , LaNiO 3 , LSCO, and/or YBCO. The ferroelectric pattern  79  may include a material having a ferroelectric property such as PZT, SBT, and BLT. The ferroelectric pattern  79  may include a layer of at least one material selected from the group of consisting of Pb(Zr,Ti)O 3 , SrTiO 3 , BaTiO 3 , (Ba,Sr)TiO 3 , SrBi 2 Ta 2 O 9 , (Pb,La)(Zr,Ti)O 3 , Bi 4 Ti 3 O 12 , and/or (Bi,La) 4 Ti 3 O 12 . 
   The hard mask pattern  83  may be a layer of a material having an etch selectivity with respect to silicon oxide as well as with respect to the upper and lower electrodes. The hard mask pattern can be made of silicon nitride or a combination of silicon nitride and titanium nitride which are sequentially stacked. 
   An inter-metal dielectric  85  can be formed on an entire surface of the structure including the ferroelectric capacitors  82 . The inter-metal dielectric  85  can be made of silicon oxide. Prior to formation of the inter-metal dielectric  85 , a hydrogen barrier layer  84  may be formed on at least a sidewall of the ferroelectric capacitor  82 . The hydrogen barrier layer  84  can include a layer of at least one selected from the group consisting of titanium oxide (TiO 2 ), aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), and cerium oxide (CeO 2 ). The hydrogen barrier layer  84  may reduce hydrogen atoms reaching the ferroelectric pattern  79 . The hydrogen barrier layer  84  can increase reliability of the ferroelectric memory device. 
   Referring to  FIG. 9 , the inter-metal dielectric  85  and the hydrogen barrier layer  84  can be planarized to form an inter-metal dielectric pattern  85   a  exposing a top surface of the hard mask pattern  83  and a hydrogen barrier pattern  84   a . The inter-metal dielectric pattern  85   a  may surround the ferroelectric capacitors  82 , and the hydrogen barrier pattern  84   a  may cover a bottom side and a sidewall of the inter-metal dielectric pattern  85   a . The planarization of the inter-metal dielectric  85  and the hydrogen barrier layer  84  can be done using an etch-back process or a chemical mechanical polishing (CMP) process. 
   The final thickness of the inter-metal dielectric pattern  85   a  may vary across different positions on a wafer. Formation of the hard mask pattern  83  can reduce deviations in etch thicknesses. A thickness of the hard mask pattern  83  can be greater than a maximum expected thickness deviation across different positions on the wafer. Portions of the hard mask pattern  83  remaining after the planarization process may have a thickness ranging from 50 nanometers to 200 nanometers. The planarization process may thus be carried out using an overetch such that hard mask patterns  83  are exposed across an entire surface of the wafer. As a result, the ferroelectric patterns  79  may remain unexposed during the planarization process while maintaining original thicknesses of the upper electrodes  81 . 
   The hard mask layer can be recessed in an etching process for forming the ferroelectric capacitor  82 , causing remaining portions of hard mask pattern  83  to be thinner than the initially-formed hard mask layer. During formation of the hard mask layer, there may be a need to consider a thickness of recess thereof. The thickness of the hard mask pattern can be greater than a maximum expected etch thickness deviation plus a recess thickness due to overetch. 
   The exposed hard mask patterns  83  can be selectively removed to expose the upper electrodes  81 . The exposure of the upper electrodes  81  can be done using an etch recipe having an etch selectivity with respect to the inter-metal dielectric patterns  85   a , the hydrogen barrier patterns  84   a , and the upper electrodes  81 . The removal of the hard mask pattern  83  can be done using a wet etch with an etchant containing a phosphoric acid. 
   Referring to  FIG. 10 , a lower plate film can be formed on a surface of the structure including the exposed upper electrodes  81 . The lower plate film can be patterned to provide a plurality of local plate lines  87  (PL shown in  FIG. 4 ) which are parallel with the wordlines  57 . The local plate lines  87  can be parallel in a row direction (y-axis). Each of the local plate lines  87  can be in direct contact with the upper electrodes  81  disposed along two adjacent rows. The local plate lines  87  may cover a portion of a top surface of the inter-metal dielectric pattern  85   a . The lower plate film may include a layer of at least one selected from the group consisting of ruthenium (Ru), platinum (Pt), iridium (Ir), rhodium (Rh), osmium (Os), palladium (Pd), and/or an oxide(s) thereof. 
   An upper interlayer dielectric can be formed on a surface of the structure including the local plate lines  87 . The upper interlayer dielectric may include a first upper interlayer dielectric  89  and a second interlayer dielectric  93  which are sequentially stacked. Before the second upper interlayer dielectric  93  is formed, a plurality of main wordlines  91  may be formed on the first upper interlayer dielectric  89 . One main wordline  91  may control four wordlines  57  through a decoder. 
   The upper interlayer dielectric can be patterned to form a slit-type via hole  95  exposing portions of the local plate line  87 . The slit-type via hole  95  can be disposed between the main wordlines  91  to be parallel with the main wordlines  91 . An upper plate film such as a metal film can be formed on an entire surface of the resultant structure where the slit-type via hole  95  is formed. The upper plate film can be patterned to form a main plate line  97  covering the slit-type via hole  95 . The local plate line  87  and the main plate line  97  may constitute a plate line. However, only one and/or the other of the local and main plate lines  87  and  97  may constitute the plate line. 
   As discussed above, a hard mask pattern having a sufficient thickness can be used as an etching mask for forming a ferroelectric capacitor. Accordingly, although an upper electrode of a ferroelectric capacitor is not thickly formed, a ferroelectric pattern can remain unexposed during planarization of an inter-metal dielectric. As a result, a thickness of the ferroelectric capacitor can be reduced and a ferroelectric memory device having improved characteristics can be fabricated. 
   A hard mask according to embodiments of the present invention can thus be used to pattern electrode and dielectric layers of a capacitor and to also protect the capacitor electrodes and dielectric when planarizing an interlayer insulating layer thereon. By providing the hard mask layer with a thickness greater than a variation in thickness of the interlayer insulating layer after planarization, the hard masks of all of the capacitor structures on a wafer can be exposed without exposing sidewalls of dielectric layers of the capacitor structures. The hard masks can then be selectively removed to expose the upper electrodes without exposing the dielectric sidewalls of the capacitor structures. 
   According to embodiments of the present invention methods of fabricating a ferroelectric capacitor may provide reduced thicknesses of upper electrodes. In accordance with embodiments of the present invention, a method of fabricating a ferroelectric memory device may include using a selectively removable hard mask pattern as an etch mask for forming a ferroelectric capacitor. This method may include forming a lower interlayer dielectric on a semiconductor substrate, sequentially stacking a ferroelectric capacitor and a hard mask pattern on the lower interlayer dielectric, forming an inter-metal dielectric to cover an entire surface of a resultant structure where the hard mask pattern is formed, and planarizing the inter-metal dielectric to expose the hard mask pattern. The exposed hard mask pattern can be selectively removed to expose a top surface of the ferroelectric capacitor, and then a plate line can be formed to be in contact with a top surface of the ferroelectric capacitor. 
   The selectively removable hard mask pattern may make it possible to reduce a problem associated with an etch thickness deviation occurring during exposure of the top surface of the ferroelectric capacitor. The hard mask pattern can be made of a material having an etch selectivity with respect to the inter-metal dielectric. For example, the hard mask pattern can be made of silicon nitride or silicon nitride and titanium nitride which are sequentially stacked. Materials of the hard mask pattern and the inter-metal dielectric can be selected such that a first etch chemistry can be used to selectively etch the inter-metal dielectric without significantly etching the hard mask pattern, and such that a second etch chemistry can be used to selectively etch the hard mask pattern without significantly etching the inter-metal dielectric or the upper electrode. 
   The formation of the ferroelectric capacitor and the hard mask pattern can include sequentially stacking a lower electrode layer, a ferroelectric layer, an upper electrode layer, and a hard mask layer on the lower interlayer dielectric, and patterning the hard mask layer to form a hard mask pattern. Using the hard mask pattern as a mask, the upper electrode layer, the ferroelectric layer, and the lower electrode layer can be sequentially patterned to form a lower electrode, a ferroelectric pattern, and an upper electrode which are sequentially stacked. Preferably, the lower electrode layer and the upper electrode layer can be made of at least one selected from the group consisting of ruthenium (Ru), platinum (Pt), iridium (Ir), rhodium (Rh), osmium (Os),. and/or oxides thereof. The lower and upper electrode layers may be made of one selected from the group consisting of SrRuO 3 , LaNiO 3 , LSCO, and/or YBCO. The ferroelectric layer can be made of at least one selected from the group consisting of PZT, SBT, and/or BLT. 
   The planarization of the inter-metal dielectric can be done by a chemical mechanical polishing (CMP) process or an etch-back process. The selective removal of the hard mask pattern can be done using an etch recipe having an etch selectivity with respect to the inter-metal dielectric and the ferroelectric capacitor. The selective removal thereof can be done using an etchant containing phosphoric acid. 
   To reduce problems associated with etch thickness deviation, a thickness of the hard mask pattern can be greater than a thickness deviation occurring in the planarization of the inter-metal dielectric. Thus, the hard mask pattern can have a thickness in the range of approximately 50 nanometers to 200 nanometers. 
   Prior to formation of the inter-metal dielectric, a hydrogen barrier layer can also be formed to cover at least a sidewall of the ferroelectric capacitor. The oxygen barrier layer can be made of at least one selected from the group consisting of titanium oxide (TiO 2 ), aluminum oxide (Al 2 O 3 ), zirconium oxide (ZrO 2 ), and/or cerium oxide (CeO 2 ). The inter-metal dielectric can be made of silicon oxide. 
   While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.