Abstract:
Methods of forming a variable-resistance memory device include patterning an interlayer dielectric layer to define an opening therein that exposes a bottom electrode of a variable-resistance memory cell, on a memory cell region of a substrate (e.g., semiconductor substrate). These methods further include depositing a layer of variable-resistance material (e.g., phase-changeable material) onto the exposed bottom electrode in the opening and onto a first portion of the interlayer dielectric layer extending opposite a peripheral circuit region of the substrate. The layer of variable-resistance material and the first portion of the interlayer dielectric layer are then selectively etched in sequence to define a recess in the interlayer dielectric layer. The layer of variable-resistance material and the interlayer dielectric layer are then planarized to define a variable-resistance pattern within the opening.

Description:
REFERENCE TO PRIORITY APPLICATION 
     This application claims priority to Korean Patent Application No. 10-2010-0037911, filed Apr. 23, 2010, the contents of which are hereby incorporated herein by reference. 
     FIELD 
     The present invention relates to semiconductor devices and, more particularly, to resistance variable memory devices and methods for manufacturing the same. 
     BACKGROUND 
     Semiconductor devices are classified into memory devices and logic devices. The memory devices store data. In general, semiconductor memory devices may be classified into volatile memory devices and nonvolatile memory devices. The volatile memory devices lose data stored therein upon interruption of power supply and include Dynamic Random Access Memories (DRAMs) and Static Random Access Memories (SRAMs). On the other hand, the nonvolatile memory devices do not lose stored data even when power supply is interrupted. Examples of the nonvolatile memory devices include programmable read-only memories (PROMs), Erasable PROMs (EPROMs), Electrically EPROMs (EEPROMs), and flash memory devices. 
     Recently, next-generation semiconductor memory devices such as Ferroelectric RAMs (FRAMs), Magnetic RAMs (MRAMs) and Phase-change RAMs (PRAMs) are being developed in line with the tendency to achieve high performance and low power consumption of semiconductor memory devices. Materials constituting such next-generation semiconductor memory devices tend to vary in their resistance values according to current or voltage, and maintain their own resistances even when current or voltage supplies are interrupted. 
     SUMMARY 
     Methods of forming variable-resistance memory devices according to embodiments of the invention include patterning an interlayer dielectric layer to define an opening therein that exposes a bottom electrode of a variable-resistance memory cell, on a memory cell region of a substrate (e.g., semiconductor substrate). These methods further include depositing a layer of variable-resistance material (e.g., phase-changeable material) onto the exposed bottom electrode in the opening and onto a first portion of the interlayer dielectric layer extending opposite a peripheral circuit region of the substrate. The layer of variable-resistance material and the first portion of the interlayer dielectric layer are then selectively etched in sequence to define a recess in the interlayer dielectric layer. The layer of variable-resistance material and the interlayer dielectric layer are then planarized to define a variable-resistance pattern within the opening. This planarization step may include planarizing a bottom of the recess in the interlayer dielectric layer. 
     According to additional embodiments of the invention, the selectively etching is preceded by depositing a top electrode layer directly on the layer of variable-resistance material. In these embodiments, the selectively etching may then include selectively etching the top electrode layer, the layer of variable-resistance material and the interlayer dielectric layer in sequence to define the recess in the interlayer dielectric layer. Moreover, the planarizing may include planarizing the top electrode layer, the layer of variable-resistance material and the interlayer dielectric layer in sequence to define a variable-resistance pattern and an auxiliary top electrode extending within the opening. 
     Methods of forming a variable-resistance memory device according to additional embodiments of the invention may include forming a first interlayer dielectric layer on a surface of a substrate. This first interlayer dielectric layer has an uneven surface profile, which contains at least a second surface region that is relatively higher than a first surface region when measured relative to the surface of the substrate. The first surface region of the first interlayer dielectric layer is then patterned to define at least a first opening therein, which is subsequently filled with a diode and a bottom electrode of a variable-resistance memory cell. This bottom electrode is electrically coupled to a first terminal of the diode. A second interlayer dielectric layer is deposited on the first and second surface regions of the first interlayer dielectric layer. This second interlayer dielectric layer is patterned to define a second opening therein that exposes the bottom electrode of a variable-resistance memory cell. 
     A layer of variable-resistance material is deposited onto the exposed bottom electrode in the second opening and onto a raised portion of the second interlayer dielectric layer extending opposite the second surface region of the first interlayer dielectric layer. The layer of variable-resistance material and the raised portion of the second interlayer dielectric layer are sequentially etched in sequence to define a recess in the second interlayer dielectric layer. The layer of variable-resistance material and the second interlayer dielectric layer are then planarized to define a variable-resistance pattern within the opening. This patterning of the first surface region may include patterning the first surface region of the first interlayer dielectric layer to define at least a first opening therein that exposes the surface of the substrate. The planarizing of the layer of variable-resistance material may also include planarizing a bottom of the recess in the interlayer dielectric layer. According to still further embodiments of the invention, the depositing a layer of variable-resistance material may include depositing a layer of phase-changeable material onto the exposed bottom electrode in the second opening and onto the raised portion of the second interlayer dielectric layer. In addition, the selectively etching the layer of variable-resistance material is preceded by depositing a top electrode layer directly on the layer of variable-resistance material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the inventive concept, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the inventive concept and, together with the description, serve to explain principles of the inventive concept. In the drawings: 
         FIGS. 1 through 8  are cross-sectional views illustrating a resistance variable memory device and a method for manufacturing the same according to a first embodiment of the inventive concept; 
         FIG. 9  is a cross-sectional view illustrating a structure of a comparative example regarding the first embodiment of the inventive concept; 
         FIGS. 10 through 14  are cross-sectional views illustrating a resistance variable memory device and a method for manufacturing the same according to a second embodiment of the inventive concept; and 
         FIG. 15  is a block diagram illustrating an application of a resistance variable memory device to a memory system according to embodiments of the inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Objects, features and advantages will be apparent from the following detailed description, given by way of example, in conjunction with the accompanying drawings. The inventive concept 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 inventive concept to those skilled in the art. Also, like reference numerals are used to depict like elements, features and structures throughout the drawings. 
     It will also be understood that when a layer (or film) such as a conductive layer, a semiconductor layer, and a dielectric 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 be understood that although the terms first, second and third are used herein to describe layers or processes, these elements should not be limited by these terms. These terms are only used to distinguish one layer or process from another one. 
     In the following description, the technical terms are used only for explaining a specific exemplary embodiment while not limiting the present invention. The meaning of “include,” “comprise,” “including,” or “comprising,” specifies a property, a region, a fixed number, a step, a process, an element and/or a component but does not exclude other properties, regions, fixed numbers, steps, processes, elements and/or components. 
     Additionally, the embodiment in the detailed description will be described with sectional views as ideal exemplary views of the present invention. In the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. Accordingly, shapes of the exemplary views may be modified according to manufacturing techniques and/or allowable errors. Therefore, the embodiments of the present invention are not limited to the specific shape illustrated in the exemplary views, but may include other shapes that may be created according to manufacturing processes. For example, an etched region illustrated as a rectangle may have rounded or curved features. Areas exemplified in the drawings have general properties, and are used to illustrate a specific shape of a semiconductor package region. Thus, this should not be construed as limited to the scope of the present invention. 
     Hereinafter, a semiconductor device and a manufacturing method thereof according to embodiments of the inventive concept will be described in detail with reference to the accompanying drawings. A phase-change memory device will be described as an example in the present embodiments, but embodiments are not limited thereto. For example, embodiments may be applied to all structures in which residues may be generated in a resistance variable memory device such as FRAM or MRAM upon node separation. 
       FIGS. 1 through 8  are cross-sectional views illustrating a resistance variable memory device and a method for manufacturing the same according to a first embodiment of the inventive concept. 
     Referring to  FIG. 1 , a substrate  100  including a cell region A, a peripheral region C, and a boundary region B between the cell region A and the peripheral region C may be provided. In the present disclosure, the cell region A, the peripheral region C, and the boundary region B may represent regions of the substrate  100 , or may commonly designate a portion of the substrate  100  and all structures formed over the portion of the substrate  100 . For example, the top surface of the cell region A may indicate the top surface of a structure formed in the cell region A. Device isolation patterns  101   a  and  101   b  may be formed to define an active region of the substrate. The substrate  100  may include a semiconductor-based structure having a silicon surface. Such a semiconductor-based structure may denote silicon, Silicon-on-Insulator (SOI), and a silicon epitaxial layer supported by a semiconductor structure. The device isolation patterns  101   a  and  101   b  may be a trench-type device isolation pattern. For example, the device isolation patterns  101   a  and  101   b  may be formed by forming a trench and forming an insulating material filling the trench. The device isolation pattern  101   a  of the cell region A may be formed thinner than the device isolation pattern  101   b  of the boundary region B. 
     A peripheral transistor  110  may be provided in the peripheral region C. The peripheral transistor  110  may include a gate insulation pattern  111 , a gate electrode  112 , and an upper insulation pattern  113  that are sequentially stacked over the substrate  100 . The peripheral transistor  110  may further include a spacer  114  provided on the side wall of the gate insulation pattern  111 , the gate electrode  112 , and the upper insulation pattern  113 . A source/drain region  115  may be formed using the spacer  114  and the upper insulation pattern  113  as an implantation mask. Impurities may be implanted into the active region of the cell region A to form a word line  102 . 
     Referring to  FIG. 2 , a first interlayer dielectric  124  may be formed to cover the peripheral transistor  110  and the substrate  100 . The first interlayer dielectric  124  may be an oxide layer. Since the peripheral transistor  110  is formed on the substrate  100 , the top surface of the first interlayer dielectric  124  may be higher in the peripheral region C by a 1  than in the cell region A. That is, a step height a 1  may occur in the boundary region B. The first interlay dielectric  124  of the cell region A may be patterned to form an opening  116 . The opening  116  may expose the word line  102 . 
     Referring to  FIG. 3 , a diode  120  may be formed at a lower portion of the opening  116 . The diode  120  may be formed by forming an epitaxial layer (not shown) on the exposed substrate  100  through Selective Epitaxial Growth (SEG) and doping the epitaxial layer with impurity elements. The impurity elements may be n-type or p-type impurities. After the epitaxial layer is formed to reach the top surface of the first interlayer dielectric  124 , the epitaxial layer may be etched back to form a diode having the same height. 
     Referring to  FIG. 4 , a bottom electrode layer  125  may be formed on the diode  120  to fill the opening  116 . The bottom electrode layer  125  may be formed of at least one of transition metals, conductive transition metal nitrides, and conductive ternary nitrides. The transition metal may include at least one of titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta) and tungsten (W). The conductive transition nitride may include at least one of titanium nitride (TiN), hafnium nitride (HfN), vanadium nitride (VN), niobium nitride (NbN), tantalum nitride (TaN), and tungsten nitride (WN). The conductive ternary nitride may include at least one of titanium aluminum nitride (TiAlN), titanium carbonitride (TiCN), tantalum carbonitride (TaCN), titanium silicon nitride (TiSiN), and tantalum silicon nitride (TaSiN). The bottom electrode layer  125  may have a greater thickness b 2  in the peripheral region C than a thickness b 1  in the cell region A. This is because the pattern of the cell region A is denser than the pattern of the peripheral region C. A pit  127  may be formed in an upper portion of the bottom electrode layer  125 . The pit  127  may be formed at the final stage of the process where the bottom electrode layer  125  is conformally formed in the opening  116 . A metal silicide layer  121  may be formed between a bottom electrode  126  and the diode  120 . The metal silicide layer  121  may include titanium silicide, cobalt silicide, nickel silicide, or tungsten silicide. The metal silicide layer  121  may provide an ohmic contact between the diode  120  and the bottom electrode  126 . 
     Referring to  FIG. 5 , the bottom electrode layer  125  may be planarized. The planarization process may include Chemical Mechanical Polishing (CMP). Upon planarization, a planarization rate of the cell region A may be greater than a planarization rate of the peripheral region C. This is because the planarization rate in an area where the pit  127  exists is greater. After the planarization process is completed, the step height a 1  may be increased to a step height a 2 . That is, the step height a 2  may be formed between the cell region A and the peripheral region C due to a difference between the thicknesses b 1  and b 2  and a difference between the planarization rates according to the pit  127 . A bottom electrode  126  within the opening  116  may be formed by the planarization process. The bottom electrode  126  may have a cylindrical, U-shaped, linear, or half-ring shaped cross-section. 
     Referring to  FIG. 6 , a second interlayer dielectric pattern  118  may be provided on the first interlayer dielectric  124 . The second interlayer dielectric pattern  118  may be formed by forming a second insulation layer (not shown) on the first interlayer dielectric  124  and then patterning the second insulation layer (not shown) to expose the bottom electrode  126 . The second interlayer dielectric pattern  118  may include a recess region  119  exposing the bottom electrode  126 . The second interlay insulation pattern  118  may be an oxide layer. An etch stop layer  117  may be provided between the first interlayer insulation layer  124  and the second interlayer dielectric pattern  118 . The etch stop layer  117  may prevent over-etching that may be generated when the recess region  119  is formed. The etch stop layer  117  may be a nitride layer or an oxynitride layer. A resistance-variable material layer  130  may be formed to fill the recess region  119  on the second interlayer dielectric pattern  118 . The resistance variable material layer  130  may have a greater thickness c 2  in the peripheral region C than a thickness c 1  in the cell region A. This is because the pattern of the cell region A is denser than the pattern of the peripheral region C. Accordingly, the top surface of the resistance variable material layer  130  of the cell region A and the top surface of the resistance variable material layer  130  of the peripheral region C may have a step height a 3  greater than the step height a 2 . A pit  133  may be formed in an upper portion of the resistance variable material layer  130 . The pit  133  may be formed at the final stage of the process where the resistance variable material layer  130  is conformally formed in the recess region  119 . In an embodiment, the resistance variable material layer  130  may be a phase-change material layer. The phase-change material layer may include material that is reversibly changeable in its state. The phase-change material layer may be formed using compounds generated by combination of at least one of Te and Se that are chalcogenide-based elements, and at least one of Ge, Sb, Bi, Pb, Sn, Ag, As, S, Si, P, O, and C. 
     Referring to  FIG. 7 , the resistance variable material layer  130  of the peripheral region C may be removed. The dotted area H shows that the resistance variable material layer  130  is removed from the peripheral region C. When the resistance variable material layer  130  is removed, a portion of the first interlayer dielectric pattern  118  may be together removed. The removal of the resistance variable material layer  130  of the peripheral region C may also be performed in a portion of the boundary region B. The removal of the resistance variable material layer  130  may be performed by a photolithography process. That is, a dry or wet etching process may be performed in a state where the cell region A is masked. The etching process may be performed until the height of the top surface of the peripheral region C becomes substantially equal to the height of the top surface of the cell region A. For example, after the etching process, a difference between the height of the top surface of the peripheral region C and the height of the top surface of the cell region A may be less than about 150 Å. The above etching process may leave a protruding structure like that in the dotted line H in the boundary region B. 
     Referring to  FIG. 8 , the resistance variable material layer  130  may be planarized. The planarization process may be a CMP process. As shown in  FIG. 7 , since the surface of the peripheral region C has a height similar to the height of the surface of the cell region A, the planarization may be efficiently performed. The protruding structure H in the boundary region B may be easily removed upon planarization. A resistance variable material pattern  131  in the recess region  119  may be formed by the planarization. A top electrode  141  may be formed on the resistance variable material pattern  131 . The top electrode  141  may be formed of the same material as the bottom electrode  126 . 
       FIG. 9  is a cross-sectional view illustrating a structure of a comparative example regarding the first embodiment of the inventive concept. That is,  FIG. 9  shows a structure in which the peripheral region C is not etched unlike that in  FIG. 7 . The resistance variable material layer  130  in the boundary region B and the cell region A adjacent to the boundary region B may not be removed by the step height between the cell region A and the peripheral region C. Accordingly, a bridge like a structure in the dotted line K may be generated between adjacent cells. Also, since the height of the resistance variable material pattern  131  is not uniform, a reset current Ireset may not be uniform. According to the first embodiment of the inventive concept, the resistance variable material layer  130  of the peripheral region C may be removed in advance before the planarization as shown in  FIG. 7  to prevent the above phenomenon. 
     Hereinafter, a resistance variable memory device and a method for manufacturing the same according to a second embodiment of the inventive concept will be described in detail. 
     Except the pattern of the resistance variable material pattern and the presence or absence of an auxiliary top electrode, the second embodiment is similar to the first embodiment. Accordingly, detailed description of identical technical features will be omitted herein. 
       FIGS. 10 through 14  are cross-sectional views illustrating a resistance variable memory device and a method for manufacturing the same according to a second embodiment of the inventive concept. 
     Referring to  FIG. 10 , a second interlayer dielectric pattern  118  may be formed on an etch stop layer  117 . The second interlayer dielectric pattern  118  may include a recess region  119  exposing a bottom electrode  126 . The second interlayer dielectric pattern  118  may be an oxide layer. 
     Referring to  FIG. 11 , a resistance variable material layer  135  may be formed on the recess region  119  and the second interlayer dielectric pattern  118 . The resistance variable material layer  135  may be formed to fill a portion of the recess region  119 . The resistance variable material layer  135  may have a greater thickness d 2  in a peripheral region C than a thickness d 1  in a cell region A. This is because the pattern of the cell region A is denser than the pattern of the peripheral region C. For example, the resistance variable material layer  135  may be a phase-change material layer. The phase-change material layer may include material that is reversibly changeable in its state. The phase-change material layer may be formed using compounds generated by combination of at least one of Te and Se that are chalcogenide-based elements, and at least one of Ge, Sb, Bi, Pb, Sn, Ag, As, S, Si, P, O, and C. 
     Referring to  FIG. 12 , an auxiliary top electrode layer  150  may be formed on the resistance variable material layer  135 . The auxiliary top electrode layer  150  may fill the recess region  119 . The auxiliary top electrode layer  150  may be formed of the same material as a top electrode described below. The auxiliary top electrode layer  150  may have a greater thickness e 2  in the cell region A than a thickness e 1  in the peripheral region C. This is because the pattern of the cell region A is denser than the pattern of the peripheral region C. Accordingly, the top surface of the auxiliary top electrode layer  150  of the cell region A and the top surface of the auxiliary top electrode layer  150  of the peripheral region C may have a step height a 4  than the step height a 2 . 
     Referring to  FIG. 13 , the auxiliary top electrode layer  150  and the resistance variable material layer  135  of the peripheral region C may be removed. When the auxiliary top electrode layer  150  and the resistance variable material layer  135  are removed, a portion of the second interlayer dielectric pattern  118  may be together removed. The removal process may also be performed in a portion of the boundary region B. The removal process may be performed by a photolithography process. That is, a dry or wet etching process may be performed in a state where the cell region A is masked. The etching process may be performed until the height of the top surface of the peripheral region C becomes lower by a certain thickness a 5  than the height of the top surface of the cell region A. The above etching process may leave a protruding structure in the boundary region B. 
     Referring to  FIG. 14 , a planarization process may be performed. The planarization process may be CMP. As shown in  FIG. 13 , since the top surface of the peripheral region C is formed lower than the top surface of the cell region A, the protruding structure remaining in the boundary region B may be easily removed. By the planarization, a resistance variable material pattern  136  may be formed in the recess region  119 , and an auxiliary top electrode  150  may be formed on the resistance variable material pattern  136  to fill the recess region  119 . A top electrode  141  may be formed on the resistance variable material pattern  130 . The top electrode  141  may be formed of the same material as the bottom electrode  126 . When the auxiliary top electrode  151  is provided, a distance h 3  between the bottom surface of the resistance variable material pattern  136  and the bottom surface of the auxiliary top electrode  151  may be uniform in every cell. Accordingly, even when the height h 1  of the resistance variable material pattern  136  at a distant location from the boundary region B is greater than the height h 2  of the resistance variable material pattern  136  at an adjacent location to the boundary region B due to over-etching, a uniform reset current can be obtained. 
       FIG. 15  is a block diagram illustrating an application of a resistance variable memory device to a memory system according to embodiments of the inventive concept. 
     Referring to  FIG. 15 , a memory system  1000  may include a semiconductor memory device  1300  including a resistance variable memory device  1100  and a memory controller  1200 , a central processing unit (CPU)  1500  electrically connected to a system bus  1450 , a user interface  1600 , and a power supply  1700 . 
     The resistance variable memory device  1100  may store data supplied through the user interface  1600  or processed by the CPU  1500 , through the memory controller  1200 . The resistance variable memory device  1100  may include a Solid State Disk (SSD) and in this case a writing speed of the memory system  1000  will be considerably improved. 
     Although not shown, it will be understood by those skilled in the art that the memory system  1000  according to the embodiments of the inventive concept may further include an application chipset, a camera image processor (CIS), a mobile dynamic random access memory (DRAM), and so forth. 
     Also, the memory system  1000  may be applied to a personal digital assistant (PDA), a portable computer, a web tablet, a wireless phone, a mobile phone, a digital music player, a memory card, or any other devices capable of wirelessly receiving and/or transmitting data. 
     Furthermore, the resistance variable memory device or memory system of the inventive concept may be mounted using various kinds of packages. The various kinds of the packages of the resistance variable memory device or the memory system according to embodiments of the inventive concept may include Package on Package (PoP), Ball Grid Arrays (BGAs), Chip Scale Packages (CSPs), Plastic Leaded Chip Carrier (PLCC), Plastic Dual In-Line Package (PDIP), Die in Waffle Pack, Die in Wafer Form, Chip On Board (COB), Ceramic Dual In-Line Package (CERDIP), Plastic Metric Quad Flat Pack (MQFP), Thin Quad Flat Pack (TQFP), Small Outline Integrated Circuit (SOIC), Shrink Small Outline Package (SSOP), Thin Small Outline Package (TSOP), System In Package (SIP), Multi Chip Package (MCP), Wafer-level Fabricated Package (WFP), and Wafer-level Processed Stack Package (WSP). 
     Upon node separation of a resistance variable material layer, a step height between a cell region and a peripheral region can prevent a portion of the resistance variable material layer from remaining in a boundary region. Also, a variation of a reset current due to a height difference of a resistance variable material pattern can be inhibited by providing an auxiliary top electrode. 
     The above-disclosed subject matter is to be considered illustrative and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true spirit and scope of the inventive concept. Thus, to the maximum extent allowed by law, the scope of the inventive concept is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.