Abstract:
A phase change random access memory for actively removing residual heat and a method of manufacturing the same are presented. The phase change random access memory includes a semiconductor substrate, a phase change pattern, a heating electrode and a cooling electrode. The phase change pattern is on the semiconductor substrate. The heating electrode is electrically coupled to the phase change pattern for heating the phase change pattern. The cooling electrode is electrically coupled to the phase change pattern for removing residual heat from the phase change pattern.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
       [0001]    The present application claims priority under 35 U.S.C. 119(a) to Korean application number 10-2009-0041164, filed on May 12, 2009, in the Korean Patent Office, which is incorporated by reference in its entirety as if set forth in full. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to memory devices and methods of manufacturing the same. More particularly, the invention relates to phase change random access memory (PRAM) devices that are configured to efficiently remove residual heat. 
         [0004]    2. Related Art 
         [0005]    Memory devices can be classified into volatile memory devices or non-volatile memory devices. Volatile memory devices can include random access memory (RAM) devices in which input information is lost if power is shut off. Non-volatile memory devices can include read only memory (ROM) devices in which input information is preserved even if power is shut off. Presently dynamic RAM (DRAM) and a synchronous RAM (SRAM) are often used as RAM devices and flash memory devices are often times used as ROM devices. 
         [0006]    DRAMs are advantageous in that power consumption is relatively low and random access is possible. However, DRAMs are volatile and the capacitance of a capacitor in the DRAMs must be increased due to high charge storage capacity. SRAMs are often used as cache memories and are advantageous in that random access is possible and fast operation speeds are also possible. However, SRAM are volatile and their associated manufacturing cost is increased due to a large size of the SRAM. Further, although flash memories are non-volatile, flash memories have a stack structure of two gates, and therefore require higher operating voltages than supply voltage. That is, flash memories require a boosting circuit to generate necessary voltage needed to perform the record and erase operations. Further flash memories may not as easily adapted to be compressed into highly integrated formats and their operating speeds are relatively slow. 
         [0007]    In order to address some of these problems associated with memory devices, ferroelectric RAMs (FRAMs), magnetic RAMs (MRAMs) and phase change RAMs (PRAMs) have been developed. 
         [0008]    Among these, PRAMs contains phase change material that often times exhibit high resistances in an amorphous solid state and lower resistances in a crystalline ordered solid state. Accordingly, PRAMS can be used to record and read information based on the particular phase the phase change material by exploiting this change in resistance. PRAM promise faster operating speeds and higher integration degree as compared with the flash memory. 
         [0009]    Oftentimes PRAMs include a heating electrode for heating the phase change material to drive the phase change of the phase change material. The heating electrode often include a material having a relatively high resistivity to achieve a high heat efficiency under the condition of same electric current, and have a narrow sectional area. 
         [0010]    However, after the crystalline state of the phase change material has been initiated by the heating electrode, then residual heat in and around the phase change material remains which can cause thermal and mechanical stresses to the PRAM. 
         [0011]    In this regard, the latent heat, which remains after the phase change process, must be removed to improve the electrical reliability of the PRAM. 
       SUMMARY 
       [0012]    A phase change memory device capable of effectively removing heat remaining after a phase change process to improve the device reliability and a method of manufacturing the same are disclosed herein. 
         [0013]    According to one embodiment, a phase change random access memory includes a semiconductor substrate, a phase change pattern formed on the semiconductor substrate, a heating electrode structure electrically connected with the phase change pattern to heat the phase change pattern, and a cooling electrode structure electrically connected with the phase change pattern to remove heat remaining in the phase change pattern. 
         [0014]    According to another embodiment, a phase change random access memory includes a semiconductor substrate, an interlayer dielectric layer formed on the semiconductor substrate, a heating electrode structure formed in the interlayer dielectric layer, a cooling electrode structure formed in the interlayer dielectric layer while being spaced apart from the heating electrode structure by a predetermined distance, and a phase change pattern formed on the interlayer dielectric layer to be electrically connected with the heating electrode structure and the cooling electrode structure. 
         [0015]    According to further another embodiment, a method for manufacturing a phase change random access memory is provided. First, a semiconductor substrate is provided. An interlayer dielectric layer is formed on the semiconductor substrate. A heating electrode structure and a cooling electrode structure are formed in the interlayer dielectric layer. A phase change pattern is formed to be electrically coupled to the heating electrode structure and to the cooling electrode structure. 
         [0016]    These and other features, aspects, and embodiments are described below in the section entitled “Detailed Description.” 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The above and other aspects, features and other advantages of the subject matter of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0018]      FIG. 1  is a schematic sectional view of a PRAM for explaining a concept of the disclosure; 
           [0019]      FIG. 2  is a sectional view showing a structure of an example of a PRAM in accordance with one embodiment; 
           [0020]      FIGS. 3A to 3C  are sectional views illustrating a procedure for manufacturing the PRAM shown in  FIG. 2 ; 
           [0021]      FIG. 4  is a sectional view showing a structure of an example of a PRAM in accordance with another embodiment; 
           [0022]      FIGS. 5A and 5B  are sectional views illustrating a procedure for manufacturing the PRAM shown in  FIG. 4 ; 
           [0023]      FIG. 6  is a sectional view showing a structure of an example of a PRAM in accordance with further another embodiment; and 
           [0024]      FIGS. 7A and 7B  are sectional views illustrating a procedure for manufacturing the PRAM shown in  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  is a schematic sectional view of a PRAM for explaining a concept of the disclosure. It is understood herein that the drawings are not necessarily to scale and in some instances proportions may have been exaggerated in order to more clearly depict certain features of the invention. 
         [0026]    Referring now to  FIG. 1 , the PRAM  50  can include a heating electrode structure  20  that heats a phase change material  40  formed on a semiconductor substrate  10  and includes a cooling electrode structure  30  that removes residual heat. 
         [0027]    The heating electrode structure  20  can be in direct contact with the phase change material  40  so that it can efficiently apply heat to the phase change material  40  when electric current is applied to the heating electrode structure  20 . For example, the heating electrode structure  20  can include conductive material having high resistivity. 
         [0028]    The cooling electrode structure  30  can also be in direct contact with the phase change material  40  so that it can efficiently remove the residual heat in the phase change material  40  when electric current is applied to the cooling electrode structure  30 . A Peltier element can be used as the cooling electrode structure  30 . As generally known in the art, the Peltier element performs heating and cooling operations by switching the direction of electric current, and can include two metal materials different from each other or heterogeneous semiconductor materials. For example, when direct current is applied to the Peltier element, heat absorption, that is, cooling can occur at the junction between the two metal materials or between the heterogeneous semiconductor materials. According heat from a specific object can be is absorbed using the Peltier effect. The Peltier effect has been extensively employed in any number of different types of equipment such as in household dehumidifiers, functional cosmetics boxes, mechanical board cooling panels, and distribution panel test tube boxes. Representative thermoelectric material is generally used at the normal temperature and the intermediate temperature. The representative normal temperature Peltier element can include Bi—Te based material such as Bi 2 Te 3  and Bi 2 Se 3 . The intermediate temperature Peltier element can include PbS, PbTe, PdTe—Ge—Te and PbTe—SnTe-based material. 
         [0029]    Reference numeral  15  denotes an interlayer dielectric layer that is used to thermally insulate the heating electrode structure  20  away from the cooling electrode structure  30 . 
         [0030]    According to the present embodiment as described above, the cooling electrode structure  30  having a Peltier element is installed in the PRAM having the phase change material  40  so that residual heat can be more efficiently removed by the cooling electrode structure  30  when cooling is performed on the phase change material  40 . Accordingly, stress and resultant cracks caused by residual heat in the phase change material  40  can be protected against. 
         [0031]      FIG. 2  is a sectional view showing a structure of an example of a PRAM in accordance with one embodiment. 
         [0032]    Referring now to  FIG. 2 , the PRAM  100  of the present embodiment can include a semiconductor substrate  110 ; an interlayer dielectric layer  115  including a heating electrode structure  140   a  and a cooling electrode structure  140   b  formed on the semiconductor substrate  110 ; and a phase change pattern  150  electrically coupled to the heating electrode structure  140   a  and to the cooling electrode structure  140   b.    
         [0033]    The semiconductor substrate  110  can be a silicon substrate and can include a current source (not shown). The current source can include a junction area (not shown) or a switching device (not shown) in contact with the junction area. The heating electrode structure  140   a  and the cooling electrode structure  140   b  can be electrically connected with the current source of the semiconductor substrate  110 . 
         [0034]    The heating electrode structure  140   a  can include a first electrode  120   a  and a heating layer  130   a . The first electrode  120   a  can include various conductive layers capable of transmitting electric current therethrough. In consideration of adhesion properties of the interlayer dielectric layer  115  and the heating layer  130   a , Ti/TiN can be used for the first electrode  120   a . The heating layer  130   a  is formed on the first electrode  120   a  to heat the phase change pattern  150  by using electric current received from the first electrode  120   a . A polysilicon (Poly-Si) layer or a silicon germanium (SiGe) layer, either of which have relatively high resistivity, can be used as the heating layer  130   a . The heating layer  130   a  is preferably formed at the center of the bottom of the phase change pattern  150  to efficiently provide the requisite heat to drive the solid state phase changes of the phase change pattern  150 . It is preferable that the first electrode  120   a  can be formed with the same width as that of the heating layer  130   a.    
         [0035]    The cooling electrode structure  140   b  can include a second electrode  120   b  and a cooling layer  130   b . Similarly to the first electrode  120   a , the second electrode  120   b  can include various conductive layers capable of transmitting electric current therethrough. According to the present embodiment, the second electrode  120   b  preferably includes Ti/TiN which is the same material as that of the first electrode  120   a . The second electrode  120   b  can be disposed almost anywhere near or on the phase change pattern  150 . Preferably the second electrode  120   b  is at a bottom periphery of the phase change pattern  150  while being spaced apart from the first electrode  120   a  at a predetermined distance. The cooling layer  130   b  is formed on the second electrode  120   b  so that it can cool the phase change pattern  150  by using electric current received from the second electrode  120   b . The cooling layer  130   b  is preferably composed of a Peltier element layer, which can cause the Peltier effect. That is, the cooling layer  130   b  preferably has two conductive layers interfaced together (e.g. such as Bi/At) that cause endothermic reaction when receiving an electric current. The cooling electrode structure  140   b  is preferably spaced separately apart from the heating electrode structure  140   a  at a predetermined distance. Preferably the cooling electrode structure  140   b  efficiently removes residual heat that remains after the phase change operation has occurred without adversely influencing the heating operation of the phase change pattern  150  driven by the heating electrode structure  140   a.    
         [0036]    When viewed in a plan view, the heating electrode structure  140   a  can be in direct contact with a part of the phase change pattern  150 , and the cooling electrode structure  140   b  is shown formed along the lower periphery of the phase change pattern  150  and can have a ring shape. 
         [0037]    The phase change pattern  150  is formed on the interlayer dielectric layer  115  to be in contact with the heating electrode structure  140   a  and the cooling electrode structure  140   b  disposed along the outer surface of the phase change pattern  150 . Preferably, the phase change pattern  150  is disposed at one phase change memory cell in a one-to-one fashion. 
         [0038]    The phase change pattern  150  can be covered by a capping layer  155 . As generally known in the art, the capping layer  155  can protect against separation of the phase change pattern  150  due to volumetric displacement changes driven by solid phase changes of the phase change pattern  150 . The capping layer  155  can also protect against or block diffusion of material constituting the phase change pattern  150 . The capping layer  155  can preferably be composed of a silicon oxide layer or a silicon nitride layer. 
         [0039]    An upper interlayer dielectric layer  160  is also shown formed on the capping layer  155 . An upper electric contact  170  is also shown formed through the upper interlayer dielectric layer  160  and through the capping layer  155  so that the upper electric contact  170  efficiently electrically couples with the phase change pattern  150 . 
         [0040]    Accordingly it is preferable that the PRAM  100  has the above structure, in which the cooling electrode structure  140   b  including the cooling layer  130   b , that causes the Peltier effect, is disposed at a periphery around the heating electrode structure  140   a . The cooling electrode structure  140   b  is preferably in direct contact with the phase change pattern  150 , so that residual heat in the phase change pattern  150  can be efficiently extracted after the phase change operation of the phase change pattern  150 . 
         [0041]      FIGS. 3A to 3C  are sectional views illustrating a procedure for manufacturing the PRAM shown in  FIG. 2 . 
         [0042]    Referring now to  FIG. 3A , a first interlayer dielectric layer  115  is formed on the semiconductor substrate  110  in which the semiconductor substrate  110  includes a current source (not shown). First and second contact holes (not shown) are next formed through the first interlayer dielectric layer  115  so that the current source (not shown) can be exposed. The first and second contact holes are formed in each phase change memory cell. Preferably, the second contact hole surrounds a periphery of the first contact hole. A conductive layer, such as a Ti/TiN layer, is then deposited on the first interlayer dielectric layer  115  to fill in the first and second contact holes. Thereafter, the conductive layer is planarized to expose the surface of the first interlayer dielectric layer  115 , so that the first electrode  120   a  is formed in the first contact hole and the second electrode  120   b  is formed in the second contact hole. The first electrode  120   a  preferably has a width equal to or greater than the second electrode  120   b.    
         [0043]    Next, a second interlayer dielectric layer  115 ′ is formed on the first interlayer dielectric layer  115  including the first and second electrodes  120   a  and  120   b . The second interlayer dielectric layer  115 ′ can preferably be formed thinner than that of the first interlayer dielectric layer  115 . Then, the second interlayer dielectric layer  115 ′ is etched such that the first and second electrodes  120   a  and  120   b  are exposed, thereby forming a heating contact hole H 1  and a cooling contact hole H 2 . Preferably, the heating contact hole H 1  has a width the same as that of the first electrode  120   a , and the cooling contact hole H 2  has a width the same as that of the second electrode  120   b.    
         [0044]    As illustrated in  FIG. 3B , the heating layer  130   a  is selectively filled in the heating contact hole H 1  to form the heating electrode structure  140   a , and the cooling layer  130   b  including the Peltier element is selectively filled in the cooling contact hole H 2  to form the cooling electrode structure  140   b . The selective filling of the heating layer  130   a  and the cooling layer  130   b  can be variously performed by using photolithographic processes generally known in the art. 
         [0045]    As illustrated in  FIG. 3C , a phase change material layer is deposited on the second interlayer dielectric layer  115 ′, and is patterned such that the phase change material layer can be in contact with the heating electrode structure  140   a  and the cooling electrode structure  140   b , so that the phase change pattern  150  is formed in each memory cell. 
         [0046]    Next, the capping layer  155  is formed on the second interlayer dielectric layer  115 ′ to surround the phase change pattern  150 . As illustrated in  FIG. 2 , the capping layer  155  can surround only the phase change pattern  150 , or can be uniformly formed on the entire upper surface of the second interlayer dielectric layer  115 ′ including the phase change pattern  150 . Then, the upper interlayer dielectric layer  160  is formed on the capping layer  155 , and the upper interlayer dielectric layer  160  and the capping layer  155  are etched so that the phase change pattern  150  can be exposed to form an upper electrode contact hole (not shown). A conductive layer is filled in the upper electrode contact hole to form the upper electric contact  170 . 
         [0047]      FIG. 4  is a sectional view showing a structure of an example of a PRAM in accordance with another embodiment. 
         [0048]    Referring now to  FIG. 4 , the PRAM  200  of the present embodiment can include a cooling electrode structure  270  that surrounds upper and side surfaces of a phase change pattern  250 . 
         [0049]    In more detail, the PRAM  200  can include a semiconductor substrate  210  having a current source (not shown), and an interlayer dielectric layer  215 , similarly to the previous embodiment. 
         [0050]    A first electrode  220   a  constituting a heating electrode structure  240  and a second electrode  220   b  constituting a cooling electrode structure  270  are formed in the interlayer dielectric layer  215 . The first electrode  220   a  can be in connect with the center of the bottom of the phase change pattern  250  and the second electrode  220   b  can surround a periphery of the first electrode  220   a  while being spaced apart from the first electrode  220   a  at a predetermined distance. Similarly to the previous embodiment, the first and second electrodes  220   a  and  220   b  can be formed of a conductive layer such as a Ti/TiN layer. 
         [0051]    A heating layer  230 , which constitutes the heating electrode structure  240  together with the first electrode  220   a , is formed in the phase change pattern  250  on the first electrode  220   a.    
         [0052]    Further, a cooling layer  260 , which constitutes the cooling electrode structure  270  together with the second electrode  220   b , can serve as a capping layer to surround the outer surface of the phase change pattern  250 . The heating layer  230  and the cooling layer  260  can be formed with the material described in the previous embodiment. 
         [0053]    According to the PRAM  200  having the above structure, the cooling electrode structure  270 , that is, the cooling layer  260  is formed to completely surround the outer surface of the phase change pattern  250 , so that residual heat in the phase change pattern  250  can be more effectively removed. 
         [0054]    Reference numeral  280  represents an upper interlayer dielectric layer and reference numeral  290  represents an upper electrode contact. 
         [0055]      FIGS. 5A and 5B  are sectional views illustrating a procedure for manufacturing the PRAM shown in  FIG. 4 . 
         [0056]    Referring to  FIG. 5A , the interlayer dielectric layer  215  is formed on the semiconductor substrate  210  including the current source (not shown). Next, first and second contact holes (not shown) are formed in the interlayer dielectric layer  215  such that the current source can be exposed. Preferably, the first and second contact holes are formed in each phase change memory cell. Preferably, the second contact hole surrounds a periphery of the first contact hole. According to the present embodiment, the distance between the first and second contact holes can be larger than the distance between the first and second contact holes of the previous embodiment. 
         [0057]    Then, a conductive layer, such as a Ti/TiN layer, is deposited on the interlayer dielectric layer  215  to fill the first and second contact holes. Thereafter, the conductive layer is planarized to expose the surface of the interlayer dielectric layer  215 , so that the first electrode  220   a  is formed in the first contact hole and the second electrode  220   b  is formed in the second contact hole. Preferably the first electrode  220   a  has a width equal to or greater than that of the second electrode  220   b.    
         [0058]    Next, heating material having a predetermined thickness is deposited on the interlayer dielectric layer  215 , and is patterned such that the heating material is located on the first electrode  220   a , thereby forming the heating layer  230 . Preferably, the heating layer  230  can be formed with a width the same as that of the first electrode  220   a.    
         [0059]    Then, a phase change material layer is deposited on the interlayer dielectric layer  215  including the heating layer  230 , and is partially patterned to form the phase change pattern  250 . The phase change pattern  250  is formed in each memory cell in a one-to-one fashion and can include the heating layer  230 . 
         [0060]    Thereafter, the cooling layer  260  is formed on the interlayer dielectric layer  215  including the phase change pattern  250 . As described above, the cooling layer  260  can include the Peltier element. Preferably, in order to improve the cooling efficiency of the phase change pattern  250 , the sidewall of the cooling layer  260  coincides with the sidewall of the second electrode  220   b . To this end, the cooling layer  260  can be deposited with a width corresponding to the width of the second electrode  220   b . The cooling layer  260  can be spaced apart from an adjacent cooling layer  260  to individually surround each phase change pattern  250 . 
         [0061]    Then, the upper interlayer dielectric layer  280  and the upper electrode contact  290  are formed through the process generally known in the art. 
         [0062]      FIG. 6  depicts a sectional view showing a structure of an example of a PRAM in accordance with further another embodiment. 
         [0063]    Referring now to  FIG. 6 , the PRAM  300  of the present embodiment can include a phase change pattern  350  having a heating layer  330   a  and a cooling layer  330   b.    
         [0064]    In more detail, the PRAM  300  of the present embodiment can include a semiconductor substrate  310  having a current source (not shown), and an interlayer dielectric layer  315  including first and second electrodes  320   a  and  320   b , similarly to the previous embodiment. 
         [0065]    Further, the first and second electrodes  320   a  and  320   b  can be formed with a conductive layer such as a Ti/TiN layer. The first electrode  320   a  can be in contact with the center of the bottom of the phase change pattern  350  and the second electrode  320   b  can surround the first electrode  320   a  while being spaced apart from the first electrode  320   a  at a predetermined distance. 
         [0066]    The heating layer  330   a , which constitutes a heating electrode structure  340   a  together with the first electrode  320   a , is formed in the phase change pattern  350  on the first electrode  320   a . The cooling layer  330   b , which constitutes a cooling electrode structure  340   b  together with the second electrode  320   b , is formed in the phase change pattern  350  on the second electrode  320   b . The heating layer  330   a  and the cooling layer  330   b  can be formed with the material described in the previous embodiment. 
         [0067]    According to the PRAM  300  having the above structure, the heating layer  330   a , which constitutes a heating electrode structure  340   a , and the cooling layer  330   b , which constitutes a cooling electrode structure  340   b , are formed in the phase change pattern  350 , so that a solid state phase of the phase change pattern  350  can be efficiently converted and so that residual heat in the phase change pattern  350  can be efficiently removed. 
         [0068]    Reference numeral  370  represents an upper interlayer dielectric layer and reference numeral  380  represents an upper electrode contact. 
         [0069]      FIGS. 7A and 7B  are sectional views illustrating a procedure for manufacturing the PRAM shown in  FIG. 6 . 
         [0070]    Similarly to the previous embodiment, the interlayer dielectric layer  315  including the first and second electrodes  320   a  and  320   b  is formed on the semiconductor substrate  310 . 
         [0071]    As illustrated in  FIG. 7A , heating material having a predetermined thickness is deposited on the interlayer dielectric layer  315 , and is patterned such that the heating material is located on the first electrode  320   a  and forms the heating layer  330   a . Preferably, the heating layer  330   a  can be formed with the same width as that of the first electrode  320   a . Next, cooling material having a predetermined thickness is deposited on the interlayer dielectric layer  315 , and is partially patterned such that the cooling material can be in contact with the second electrode  320   b  form the cooling layer  330   b . The cooling layer  330   b  can be formed with the same width as that of the second electrode  320   b , and can be formed with the same thickness as that of the heating layer  330   a . Preferably, in order to maximize the cooling and heating transfer efficiencies, the sidewall of the heating layer  330   a  can coincide with the sidewall of the first electrode  320   a  and the sidewall of the cooling layer  330   b  can coincide with the sidewall of the second electrode  320   b . According to the present embodiment, the heating layer  330   a  is primarily formed. However, the present invention is not limited thereto. That is, the cooling layer  330   b  can be primarily formed. 
         [0072]    As illustrated in  FIG. 7B , a phase change material layer is deposited on the interlayer dielectric layer  315  including the heating layer  330   a  and the cooling layer  330   b . The phase change material layer is partially patterned to include the heating layer  330   a  and the cooling layer  330   b  to thereby form the phase change pattern  350  in each memory cell. Then, the capping layer  360 , the upper interlayer dielectric layer  370  and the upper electrode contact  380  are formed by using the generally known processes in the art. 
         [0073]    According to the present invention as described above, various cooling electrode structures including the Peltier element are formed in the phase change memory cells. Thus, heat remaining after change of the crystalline state of the phase change pattern can be easily cooled by the cooling electrode structures, so that thermal and mechanical stresses caused by the remaining heat can be reduced. 
         [0074]    However, the present invention is not limited to the above embodiments. 
         [0075]    According to some of the above embodiments, the cooling electrode structure can have a ring shape that surrounds the heating structure. However, the present invention is not limited thereto. That is, various cooling electrode structures can be employed if the cooling electrode structures can remove the latent heat by being in contact with the phase change pattern. 
         [0076]    Further, the cooling electrode structure includes a Bi/At laminate. However, the present invention is not limited thereto. That is, various layers, such as a Bi/Te laminate and a P type semiconductor layer/an N type semiconductor layer laminate, can be employed if they can provide the Peltier effect. 
         [0077]    While certain embodiments have been described above, it will be understood that the embodiments described are by way of example only. Accordingly, the systems and methods described herein should not be limited based on the described embodiments. Rather, the systems and methods described herein should only be limited in light of the claims that follow when taken in conjunction with the above description and accompanying drawings.