Abstract:
A process for manufacturing a PCM device comprises forming a dielectric, producing a via in the dielectric starting at an area on the surface of the dielectric by forming a via opening in the area and extending the opening into the dielectric toward and then terminating at an electrode comprising a first electrode in the dielectric. We form a spacer layer contiguous with the side walls of the via and fill the via with a PCM. We then remove the surface of the dielectric to leave a PCM cusp at the opening of the via, cap the PCM cusp with a low density capping film; densify the PCM and capping film to obtain a high density capping film that exerts compressive pressure on the high density PCM in a direction toward the first electrode to enhance electrical contact between the PCM and the first electrode.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention comprises phase change memory cells, a process for their manufacture, and products made by such process. 
       BACKGROUND OF THE INVENTION 
       [0002]    There are two major categories of computer memory: non-volatile memory and volatile memory. Non-volatile memory does not require constant input of energy in order to retain information whereas volatile memory does. In non-volatile memory devices, the memory state can be retained for days to decades without power consumption. Examples of non-volatile memory devices comprise Read Only Memory (ROM), Flash Electrical Erasable Read Only Memory, Ferroelectric Random Access Memory (FRAM), Magnetic Random Access Memory (MRAM), and Phase Change Memory. 
         [0003]    Examples of volatile memory devices comprise Dynamic Random Access Memory (DRAM) and Static Random Access Memory (SRAM); where DRAM requires the memory element to be constantly refreshed while SRAM requires a constant supply of energy to maintain the state of the memory element. 
         [0004]    Phase change materials (PCM) are poised to play a fundamental role in new solid state phase change memory and storage devices. In order to comply with the requirements imposed by the scaling road map, it is expected that the memory cells will be of the confined type, where the PCM is deposited via chemical vapor deposition (CVD) or atomic layer deposition (ALD) processes into a predefined cavity. 
         [0005]    Phase change memory involves manipulating specific materials (PCM&#39;s) into different phases to store information. Each phase exhibits different electrical properties which enables the PCM to store information. The amorphous and crystalline phases are typically two phases used for bit storage (1&#39;s and 0&#39;s) since they have detectable differences in electrical resistance. Specifically, the amorphous phase has a higher resistance than the crystalline phase. 
         [0006]    Chalcogens comprise non-metallic Group VIA elements (Periodic Table Group VIA [IUPAC Form]) commonly used to form phase change materials, i.e., compounds or alloys (also referred to herein as “a combination or combinations”) with another element, and sometimes referred to as “chalcogenide” PCM&#39;s. Selenium (Se) and tellurium (Te) are the two most common chalcogens used to produce these compounds or alloys (“combinations”). 
         [0007]    Exposing the PCM to laser or electrical pulses of different intensity and duration repeatedly switches the PCM between crystalline and amorphous phases. A short intense pulse melts the material, which is subsequently quenched into the amorphous phase; a less intense pulse heats the material above the crystallization temperature and reverses the process. 
         [0008]    An important step to obtain optimal performance of PCM cells is to densify the PCM after deposition via a rapid thermal annealing or laser annealing process. The latter steps may have unintended consequences due to action of capillary forces at the PCM/spacer interface of the cell during the densification process. This could produce a detachment of the PCM at the bottom contact of the PCM cell. 
       RELATED ART 
       [0009]    The following patents and published applications provide examples of the state of the art of PCM memory cells:
   Breitwisch, et al., United States Patent Application Publication 2010/0078621;   Horii, et al., United States Patent Application Publication 2010/0081263, and U.S. Pat. No. 7,767,491;   Kang, United States Patent Application Publication 2009/0206317;   Chen, United States Patent Application Publication 2009/0189140;   An et al., U.S. Pat. No. 7,777,212;   Chae, et al., U.S. Pat. No. 7,772,101;   Shin, et al. U.S. Pat. No. 7,777,214.   
 
       SUMMARY OF THE INVENTION 
       [0017]    The present invention comprises structures, articles of manufacture, processes and products produced by the processes that address the foregoing needs, and provides substantially optimal performance PCM cells. 
         [0018]    We form a PCM cell by depositing a PCM in a via opening in a dielectric layer lined with spacer material to form a PCM/spacer interface that extends into the dielectric layer for a distance and terminates at an electrode contact. We then remove part of the dielectric layer at the opening to leave a small part of the PCM to extend out of the opening and form a cusp, and then place a low density capping film on the dielectric layer to envelop the cusp. We densify the PCM after deposition via a rapid thermal annealing or processing (RTP) to substantially prevent a diffusion process from taking place in the selecting devices. The thermal processing also densifies the low density capping film causing it to compress the PCM in the via against the electrode contact. This densification substantially avoids or minimizes detachment of the PCM at the electrode contact of the PCM cell. 
         [0019]    The low density capping film could be for example Si-Nitride, Al-Nitride, Boron Nitride all deposited at low temperature in the range of about 150 to about 300 Degree C. 
         [0020]    Rapid thermal annealing or processing (RTP) refers to a semiconductor manufacturing process which heats silicon wafers to high temperatures (up to about 1,200° C. or greater) on a timescale of several seconds or even millisecond range. During cooling, however, wafer temperatures must be brought down slowly so they do not break due to thermal shock. Such rapid heating rates are often attained by high intensity lamps or lasers. The latter are more appropriate for ultra-fast heating. These processes are used for a wide variety of applications in semiconductor manufacturing including dopant activation, thermal oxidation, metal reflow and chemical vapor deposition. 
         [0021]    Stated otherwise, RTP comprises (a) a pre-anneal step which includes heating to a temperature and for a period sufficient to preheat the wafer so as to reduce thermal shock due to a main annealing step, (b) the main annealing step being at a temperature and for a period sufficient to provide the densification of the PCM and the capping film, and (c) a post-anneal step carried out at a temperature and for a period sufficient to relieve stresses which may result from the main-annealing step. 
         [0022]    In one embodiment RTP comprises, in succession, exposure of the device in a pre-anneal step at temperatures ranging from about 400.degrees to about 500.degrees C. for a period of from about 20 to about 40 seconds, the main annealing step at a peak temperature within a range of from about 650.degrees to about 850.degree C. for a period of from about 5 to about 2000 milliseconds, and the post-anneal step at temperatures ranging from about 400.degrees to about 500.degrees C. for a period of from about 25 to about 35 seconds, followed by cool down at a rate of from about 5 degrees to about 10 degrees C. per second, in either a nitrogen, oxygen, Ar, or He atmosphere 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The accompanying drawings are not necessarily drawn to scale but nonetheless set out the invention, and are included to illustrate various embodiments of the invention, and together with this specification also serve to explain the principles of the invention. These drawings comprise various Figures that ilustrate a compressive strucutre for enhancing contacts in phase change material memory cells. 
           [0024]      FIGS. 1 to 4  comprise side elevations in cross-section illustrating PCM devices in various stages of manufacture according to the invention and inherently show steps in a process for manufacturing these PCM devices. 
           [0025]      FIG. 5  comprises a side elevation in cross-section illustrating the additional steps used to convert these PCM devices into PCM cells. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    To achieve the foregoing and other advantages, and in accordance with the purpose of this invention as embodied and broadly described herein, the following detailed description comprises disclosed examples of the invention that can be embodied in various forms. 
         [0027]    The specific processes, compounds, compositions, and structural details set out herein not only comprise a basis for the claims and a basis for teaching one skilled in the art to employ the present invention in any novel and useful way, but also provide a description of how to make and use this invention. Not only do the written description, claims, abstract of the disclosure, and the drawings that follow set forth various features, objectives, and advantages of the invention and how they may be realized and obtained, but these features, objectives, and advantages will also become apparent by practicing the invention. 
         [0028]    We obtain optimal performance of PCM by densification of the PCM after deposition via a rapid thermal annealing or laser annealing process where the PCM is positioned in a via formed in a dielectric material lined with a spacer material. The latter steps may have unintended consequences due to action of capillary forces at the PCM/spacer interface during the densification process, which could produce a detachment of the PCM at the bottom contact in the via which comprises an electrode. 
         [0029]    In order to preserve a robust and reliable bottom electrical contact during the densification process, i.e., enhancing this electrical contact, a low density layer or capping film is coated on a cusp we form in the profile of the exposed PCM following a chemical mechanical polishing step, and capping the exposed PCM. During densification, the capping film also becomes densified and will exert a compressive force on the PCM in a direction toward the bottom contact or electrode which substantially eliminates or minimizes detachment of the PCM at the bottom contact Referring to  FIG. 1 , the structure  10  comprises a dielectric layer  14  having a tubular via opening  12  with a spacer layer  18  contiguous with, and substantially extending around the circumference of the outside wall of via  12 . In one embodiment, dielectric  14  comprises silicon oxide, silicon nitride, silicon oxy-nitride, aluminum oxide and/or titanium oxide. Spacer layer  18  may comprise one of SIC, SiN, SiCOH, TiO 2  and Ta 2 O s . or combinations thereof. The spacer layer  18  is introduced to improve the wetting of the phase change material (PCM) to be deposited, and to control the heat transfer during setting, and it is selected to fit the desired properties of the particular PCM/spacer interface. 
         [0030]    After forming spacer  18  we introduce PCM  16  into via  12  by either a chemical vapor deposition process (CVD) or atomic layer deposition process (ALD) known in the art and chemical deposition. This is followed by Chemical Mechanical Polishing (CMP). which has the role of removing the surface part of the spacer and planarizing the surface of the spacer. 
         [0031]    The phase change material  16  comprises a material having two stable states. For example, the phase change material may comprise chalcogenide elements such as tellurium (Te) and/or selenium (Se). In addition, the phase change material may further comprise compounds or alloys (“combinations”) of germanium (Ge), antimony (Sb), bismuth (Bi), palladium (Pd), tin (Sn), silver (Ag), arsenic (As), sulfur (S), silicon (Si), phosphorus (P), oxygen (O) and/or nitrogen (N). For example, the phase change material may comprise Ge—Sb—Te; As—Sb—Te; As—Ge—Sb—Te; Sn—Sb—Te; Ag—In—Sb—Te; In—Sb—Te; a compound layer of a Group VA element (IUPAC Form), antimony (Sb) and tellurium (Te); a compound layer of a chalcogen, antimony (Sb) and tellurium (Te); a compound layer of a Group VA element (IUPAC Form), antimony (Sb) and selenium (Se); and/or a compound layer of a chalcogen (with the exception of selenium (Se)), antimony (Sb) and selenium (Se). 
         [0032]    In one embodiment, “chalcogenide” PCM&#39;s, comprise for example, Ge 2 Sb 2 Te 5 , SbTe, and In 2  Se 3 . The so-called Ge—Sb—Te (GST) materials, however, are the PCM&#39;s of choice for optical memory devices. They are also the leading candidates for a new generation of non-volatile electronic memory. 
         [0033]    Via  12  and spacer  18  extend toward and terminate at electrode  20  which may comprise at least one of titanium (Ti), titanium nitride (TiN), tantalum nitride (TaN), molybdenum nitride (MoN), niobium nitride (NbN), titanium silicon nitride (TiSiN), titanium aluminum nitride (TiAlN), titanium boron nitride (TiBN), zirconium silicon nitride (ZrSiN), tungsten (W), tungsten nitride (WN), graphite, carbon nitride (CN), tungsten silicon nitride (WSiN), tungsten boron nitride (WBN), zirconium aluminum nitride (ZrAlN), molybdenum silicon nitride (MoSiN), molybdenum aluminum nitride (MoAlN), tantalum silicon nitride (TaSiN), tantalum aluminum nitride (TaAlN), titanium oxynitride (TiON), titanium aluminum oxynitride (TiAlON), tungsten oxynitride (WON) and tantalum oxynitride (TaON). Electrode  20  may be formed by a deposition process such as a physical vapor deposition (PVD) method, a CVD method or an ALD method and a patterning process known in the art. We form the electrode  20  prior to forming the via  12  by methods know in the art, such as patterning an electrode layer, depositing the electrode in the resulting patterned area, followed by building the electrode layer to a greater thickness before forming the via  12 . 
         [0034]      FIG. 2  illustrates a process for recessing dielectric  14  after deposition by means of CMP, the latter also removing the spacer  18  at the surface, exposing the silicon oxide. In order to obtain a cusp on the PCM, a timed wet process using HF is utilized. The latter does not attack the PCM but recesses the silicon oxide field, leaving a PCM cusp. 
         [0035]      FIG. 3  illustrates the next step in the process comprising applying a low density film  24  to coat cusp  22  and extend outwardly from cusp  22  to also coat the surface of dielectric  14 . We then obtain optimal performance of the PCM  16  by densification using rapid thermal processing via a capacitor discharge quartz lamp or laser pulse, densifying the film  24 , and the PCM to high density PCM  28  as illustrated in  FIGS. 4 and 5 . For this process to be effective, the recess is programmed such that, the volume of the PCM cusp  22  must be smaller than volume of the PCM inside the via. This reduces the volume forces arising from the cusp  22  which may counterbalance the pressure effect of the densification of film  24 , which aims at attaining a density within 5% of their sintered value: Si-Nitride (˜3.3 g/cc), Al-Nitride˜(3.2 g/cc), B Nitride (˜1.9 g/cc). 
         [0036]    Low density film  24  becomes operatively associated with cusp  22  in the coating process so that PCM  16  densification to high density PCM  28  via rapid thermal processing also converts low density film  24  to high density film  26  that in turn exerts compressive forces on PCM  16  in a direction toward electrode  20  as illustrated in  FIG. 4 . These compressive forces substantially eliminate or minimize detachment of PCM  16  from electrode  20  during rapid thermal annealing or laser annealing. The low density films, are not restricted to but preferably comprise dielectrics, and are usually formed by physical or chemical deposition usually at low temperatures. The latter prevents surface diffusion and thus condensation of the film. 
         [0037]    In  FIG. 5  we illustrate removal of high density film  26  by CMP to expose dielectric  14  and the top part of the PCM material.  FIG. 5  also illustrates the application of an electrode  30  operatively associated with high density PCM  28  at the opening of via  12 . The role of this electrode is to prevent inter-diffusion of PCM/TEC (top electrical contact) materials while being electrically conductive. We then construct a top electrical contact (TEC)  32  by means of a Back End Of Line (BOEL) processes well known to those skilled in the art. 
         [0038]    Throughout this specification, and abstract of the disclosure, the inventors have set out equivalents, of various materials as well as combinations of elements, materials, compounds, compositions, conditions, processes, structures and the like, and even though set out individually, also include combinations of these equivalents such as the two component, three component, or four component combinations, or more as well as combinations of such equivalent elements, materials, compositions conditions, processes, structures and the like in any ratios or in any manner. 
         [0039]    Additionally, the various numerical ranges describing the invention as set forth throughout the specification also includes any combination of the lower ends of the ranges with the higher ends of the ranges, and any single numerical value, or any single numerical value that will reduce the scope of the lower limits of the range or the scope of the higher limits of the range, and also includes ranges falling within any of these ranges. 
         [0040]    The terms “about,” “substantial,” or “substantially” as applied to any claim or any parameters herein, such as a numerical value, including values used to describe numerical ranges, means slight variations in the parameter. In another embodiment, the terms “about,” “substantial,” or “substantially,” when employed to define numerical parameter include, e.g., a variation up to five per-cent, ten per-cent, or 15 per-cent, or somewhat higher. 
         [0041]    All scientific journal articles and other articles, including internet sites, as well as issued and pending patents that this written description or applicants&#39; Invention Disclosure Statements mention, including the references cited in such scientific journal articles and other articles, including internet sites, and such patents, are incorporated herein by reference in their entirety and for the purpose cited in this written description and for all other disclosures contained in such scientific journal articles and other articles, including internet sites as well as patents and the references cited therein, as all or any one may bear on or apply in whole or in part, not only to the foregoing written description, but also the following claims, and abstract of the disclosure. 
         [0042]    Although the inventors have described their invention by reference to some embodiments, other embodiments defined by the doctrine of equivalents are intended to be included as falling within the broad scope and spirit of the foregoing written description, and the following claims, and abstract of the disclosure.