Abstract:
Multi-step selective etching. Etching an unmasked region associated with each layer of a plurality of layers, the plurality of layers comprising a stack, wherein the unmasked region of each of the plurality of layers is etched while exposed to a temperature, a pressure, a vacuum, using a plurality of etchants, wherein at least one of the plurality of etchants comprises an inert gas and oxygen, wherein the etchant oxidizes the at least one layer that can be oxidized such that the etching stops, the plurality of etchants leaving substantially unaffected a masked region associated with each layer of the plurality of layers, wherein two or more of the plurality of layers comprises a memory stack, and preventing corrosion of at least one of the plurality of layers comprising a conductive metal oxide by supplying oxygen to the stack after etching the unmasked region without breaking the vacuum.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to semiconductors and memory technology. More specifically, etching for integrated circuit device fabrication is described. 
       BACKGROUND 
       [0002]    Memory (i.e., material used for data storage for electrical and electronic devices) is formed and fabricated using various types of material, such as metals, semiconductors, silicon dioxide, and others. Conventional fabrication process techniques for semiconductor-type memories typically use deposition of thin film materials on substrates (e.g., silicon wafers), which are then patterned etched away (“etched”) using various types of etchants that are generated to create plasma. In some conventional techniques, etchants are injected, provided, or otherwise supplied into a vacuum chamber and energized using radio frequency (RF) power at certain frequency ranges to generate and sustain plasma for etching unmasked regions of deposited materials. However, as a substrate is moved from one chamber to another, such as those found coupled to a cluster tool, conventional solutions typically break (i.e., lose) vacuum, which can lead to oxygen out-diffusion and corrosion of memory material such as complex metal oxides (CMO). Conventional deposition and fabrication techniques typically rely upon developing memories that are often constrained by size and features, thus requiring more features to be formed on a smaller die size. However, conventional processes typically require larger die sizes in order to achieve greater functionality. Further, conventional techniques for etching materials can also result in damage with other surrounding or adjacent materials or layers. 
         [0003]    In some conventional techniques, etchants that are typically used to etch away unmasked areas of memory material can cause problems such as oxygen out-diffusing. In some conventional physical etching techniques such as ion milling, unwanted redeposited particles can accumulate on the external surfaces (e.g., sides, walls) of memory, resulting in corrosion of materials such as CMO. Further, if a vacuum break occurs, ambient water and oxygen particles typically react with halogens resulting in the corrosion of CMO material. 
         [0004]    There are continuing efforts to improve upon fabrication techniques. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Various examples are disclosed in the following detailed description and the accompanying drawings. 
           [0006]      FIG. 1A  is a cross-sectional view of an exemplary cross-point memory etched using selective etching; 
           [0007]      FIG. 1B  is an alternative cross-sectional view of an exemplary cross-point memory etched using selective etching; 
           [0008]      FIG. 2A  is a cross-sectional view of a cross-point memory undergoing an exemplary etch in a selective etching process; 
           [0009]      FIG. 2B  is a further cross-sectional view of a cross-point memory undergoing an exemplary etch in a selective etching process; 
           [0010]      FIG. 3A  is a cross-sectional view of a cross-point memory undergoing another exemplary etch in a selective etching process; 
           [0011]      FIG. 3B  is a further cross-sectional view of a cross-point memory undergoing another exemplary etch in a selective etching process; 
           [0012]      FIG. 4A  is a cross-sectional view of a cross-point memory undergoing an exemplary etch of a memory stack in a selective etching process; 
           [0013]      FIG. 4B  is another cross-sectional view of a cross-point memory undergoing an exemplary etch of a memory stack in a selective etching process; 
           [0014]      FIG. 4C  is a cross-sectional view of a cross-point memory undergoing an exemplary etch of a memory stack in a selective etching process; 
           [0015]      FIG. 4D  is a cross-sectional view of a cross-point memory undergoing an exemplary etch of a memory stack preventing oxygen out-diffusion in a selective etching process; 
           [0016]      FIG. 5A  is a cross-sectional view of a cross-point memory undergoing a further exemplary etch in a selective etching process; 
           [0017]      FIG. 5B  is another cross-sectional view of a cross-point memory undergoing a further exemplary etch in a selective etching process; 
           [0018]      FIG. 6  is a cross-sectional view of a cross-point memory undergoing an exemplary anti-corrosion plasma treatment of a conductive metal oxide (CMO) layer in a selective etching process; 
           [0019]      FIG. 7A  is an exemplary process for selective etching; and 
           [0020]      FIG. 7B  is an exemplary process for optionally removing an etch mask from a hard mask. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Various examples may be implemented in numerous ways, including as a system, a process, an apparatus, or a series of program instructions on a computer readable medium such as a computer readable storage medium or a computer network where the program instructions are sent over optical, electronic, or other wired or wireless communication links. In general, operations of disclosed processes may be performed in an arbitrary order, unless otherwise provided in the claims. 
         [0022]    A detailed description of one or more examples is provided below along with accompanying figures. The detailed description is provided in connection with such examples, but is not limited to any particular example. The scope is limited only by the claims, and numerous alternatives, modifications, and equivalents are encompassed. Numerous specific details are set forth in the following description in order to provide a thorough understanding. These details are provided as examples and the described techniques may be practiced according to the claims without some or all of the accompanying details. For clarity, technical material that is known in the technical fields related to the embodiments has not been described in detail to avoid unnecessarily obscuring the description. 
         [0023]    Fabricating memory may be performed using the described techniques to prevent oxygen out-diffusing, CMO corrosion, and others when fabricating cross-point memory such as that described in U.S. patent application Ser. No. 11/095,026, filed Mar. 30, 2005 and entitled “Memory Using Mixed Valence Conductive Oxides,” hereby incorporated by reference in its entirety for all purposes, describes non-volatile third dimensional memory elements that can be arranged in a cross-point array. New memory structures are possible with the capability of this third dimensional memory array, which may be performed using selective etching, as described below. Using materials such as platinum (Pt), silicon dioxide (SiO 2 ) or oxide, titanium nitride (TiN), yttrium stabilized zirconium (YSZ), conductive metal oxide (CMO), tungsten (W), complex metal oxides (CMO) such as perovskites, and others, forming cross-point memory arrays such as those found in third dimensional memories may be performed using selective etching to identify and selectively form a memory stack (e.g., a set of vertically configured layers including CMO that are formed and etched to provide the memory material that allows for data to be stored based on how voltages are conducted through the material) using plasma etching. Further, selective etching may include treatment of a stack of thin-film layers using oxygen provided at high pressures without a preceding loss of vacuum. 
         [0024]      FIG. 1A  is a cross-sectional view of an exemplary cross-point memory etched using selective etching. Here, cross-point stack (“stack”)  100  is shown with photoresist (PR) layer  102  and includes silicon dioxide (i.e., SiO 2 ) layer  104 , titanium nitride (i.e., TiN) layer  106 , platinum (i.e., Pt) layer  108 , yttrium stabilized zirconium (i.e., YSZ) layer  110 , CMO layer  112 , platinum (i.e., Pt) layer  114 , titanium nitride (i.e., TiN) layer  116 , tungsten (i.e., W) sub-region  118 , oxide/dielectric sub-regions  120 - 122 , and substrate  124 . It should be noted that the composition, thickness, and quantity of thin film layers shown (i.e., layers  102 - 124 ) may be varied and are not limited to any specific width, thickness, or dimension. Further, platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114  form memory stack  126 . In some examples, memory stack  126  may be used to implement a third dimensional memory array, such as that described in U.S. patent application Ser. No. 11/095,026, which is herein incorporated by reference for all purposes. As used herein, photoresist layer  102 , silicon dioxide  104 , titanium nitride  106 , platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114 , titanium nitride layer  116 , and tungsten sub-region  118  may also be referred to as “layers” and may also be referenced by chemical compound formulae. 
         [0025]    Layers  102 - 122  may be formed on substrate  124 , using plasma etchants, as described herein, to etch away unwanted material to form a stack of thin-film materials, including memory stack  126 . In some examples, photoresist layer  102  may include photoresistive materials used to form a pattern for a desired geometry on stack  100 . SiO 2  may be used as a hard mask to form silicon dioxide layer  104 , which may be formed directly or indirectly below photoresist layer  102 . TiN (titanium nitride) can be used to form titanium nitride layers  106  and  116 , which may be located directly or indirectly below silicon dioxide layer  104  and platinum layer  114 , respectively. In some examples, platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , and platinum layer  114  may be implemented and collectively referred to as memory stack  126 . Here, YSZ may be used as an insulator configured to separate CMO from, for example, a top electrode such as platinum layer  108 . YSZ also works as an oxygen reservoir to store oxygen ions from perovskite materials such as PrCaMnO (i.e., “PCMO”), which is a complex metal oxide (“CMO”) material that allows oxygen ions to move freely in and out of the composition. Further, titanium nitride layer  116  may be used as a “glue” layer for stack  100 , as used between platinum layer  114  and tungsten sub-region  118 . In some examples, tungsten sub-region  118  may be implemented as a sub-region of layer  128 , which may also comprise other sub-regions (e.g., oxide/dielectric sub-regions  120 - 122 ), which are adjacent to tungsten sub-region  118 . As an example, oxide/dielectric sub-regions  120 - 122  may be implemented adjacent to tungsten sub-region  118 . In other examples, stack  100  and the above-described elements may be varied in materials, design, formation, process, and are not limited to the descriptions provided. 
         [0026]    Here, after photoresist layer  102  is formed and developed, a first etch may be performed to etch silicon dioxide layer  104 . Unmasked portions or regions (“regions”) of silicon dioxide layer  104  may be etched away while leaving masked regions. In some examples, titanium nitride layers  106  and  116  may be used as an etch stop layer. For example, titanium nitride layer  106  may be used as an etch stop layer for a first etch (i.e., etching away silicon dioxide layer  104 ). After completing the first etch, photoresist layer  102  may be removed using techniques such as those described herein. In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0027]      FIG. 1B  is an alternative cross-sectional view of an exemplary cross-point memory etched using selective etching. Here, stack  100  is shown with photoresist layer  102  and includes silicon dioxide layer  104 , titanium nitride layer  106 , platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114 , titanium nitride layer  116 , tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , and substrate  124 . Alternatively, strontium titanate SrTiO3 (i.e., “STO”) layer  111  may also be deposited or formed between yttrium stabilized zirconium (i.e., YSZ) layer  110  and CMO layer  112  to act as an ion barrier to prevent the escape of oxygen ions from CMO layer  112 . It should be noted that the composition, thickness, and quantity of thin film layers shown (i.e., layers  102 - 124 ) may be varied and are not limited to any specific width, thickness, or dimension. Further, platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114  form memory stack  126 . 
         [0028]    In some examples, a thin-film layer of a barrier to mobile oxygen ions may be optionally positioned between and in contact with CMO layer  112 , which may be implemented using PCMO, and the tunnel barrier layer (e.g., YSZ). The ion barrier layer is operative to improve data retention in a memory element using stack  100 . Suitable materials for an ion barrier layer (i.e., strontium titanate layer  111 ) may include, but is not limited to a perovskite material, such as strontium titanate, SrTiO3 (i.e., “STO”). In other examples, different materials may be used and are not limited to the example shown and described. In other words, strontium titanate layer  111  acts as an ion barrier and may be implemented using materials and compounds other than strontium titanate. In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0029]      FIG. 2A  is a cross-sectional view of a cross-point memory undergoing an exemplary etch in a selective etching process. Here, stack  100  is shown with photoresist mask  202  and includes silicon dioxide layer  104 , titanium nitride layer  106 , platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114 , titanium nitride layer  116 , tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , and substrate  124 . The composition, thickness, and quantity of thin film layers shown (i.e., layers  102 - 124 ) may be varied and are not limited to any specific width, thickness, or dimension. Further, platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114  form memory stack  126 . In some examples, the above-described layers  102 - 122  and substrate  124  may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0030]    In some examples, photoresist layer  102  ( FIGS. 1A-1B ) may be removed using material  210  using various techniques. For example, photoresist layer  102  may be removed using ashing or stripping processes. Ashing is a plasma process, whereas stripping can be a wet process in which a solvent is used to remove photoresistive material from a hard mask (i.e., silicon dioxide layer  104 ). In other examples, photoresist layer  102  may be removed differently, using different materials and processes apart from those shown and described. 
         [0031]    Here, when photoresist layer  102  is removed and photoresist mask  202  is left, etchant  210  may be applied to pattern  204 - 206  on silicon dioxide layer  104 , stopping at etch stop  208 . An underlying oxide hard mask (i.e., silicon dioxide layer  104 ) may be etched using etchant  210 , which may be gaseous compounds such as CF4 or CHF3/Ar that are used to plasma etch silicon dioxide layer  104 . Photoresist mask  202  protects underlying silicon dioxide from being etched up to boundaries identified by pattern  204 - 206 . After etching a hard mask (i.e., silicon dioxide layer  104 ), photoresist mask  202  may be stripped using a combination of dry and wet stripping processes. In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0032]      FIG. 2B  is a further cross-sectional view of a cross-point memory undergoing an exemplary etch in a selective etching process. Here, stack  100  is shown with photoresist mask  202  and includes titanium nitride layer  106 , platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114 , titanium nitride layer  116 , tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , and substrate  124 . Also included in stack  100  is silicon dioxide layer  212 , which has been etched to parameters specified by pattern  204 - 206  ( FIG. 2A ) and etch stop  208  ( FIG. 2A ) using etchant  210 . The composition, thickness, and quantity of thin film layers shown (i.e., layers  102 - 124 ) may be varied and are not limited to any specific width, thickness, or dimension. Further, platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114  form memory stack  126 . In some examples, the above-described layers  102 - 122  and substrate  124  may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. After etching silicon dioxide layer  104  and leaving behind silicon dioxide layer  212 , photoresist mask  202  may be stripped using a combination of dry and wet stripping processes. In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0033]      FIG. 3A  is a cross-sectional view of a cross-point memory undergoing another exemplary etch in a selective etching process. Here, stack  100  includes titanium nitride layer  106 , platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114 , titanium nitride layer  116 , tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , substrate  124 , and silicon dioxide layer  212 . Further, platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114  form memory stack  126 . After removing photoresist mask  202 , stack  100  may be further etched by applying an etchant to titanium nitride layer  106 . Boundaries for etching titanium nitride layer  106  are specified by pattern  304 - 306  and etch stop  302 . In some examples, etchant  308  may be used in a plasma etching process to remove unwanted material from titanium nitride layer  106 . 
         [0034]    In some examples, titanium nitride layer  106  may be etched using etchants such as those used in plasma etching (i.e., “etching”). Here, etchant  308  may be a plasma etchant used to selectively etch the unmasked region (i.e., as determined by pattern  304 - 306  and etch stop  302 ) of titanium nitride layer  106 . Platinum layer  108  acts as an etch stop for the second etch. In some examples, etchant  308  has a Cl 2 /Ar (chlorine/argon) chemistry and a high selectivity to silicon dioxide layer  212 . Other types of selective plasma etchants used for etchant  308  may be HBr/Ar (hydrogen bromide/argon), HBr, or Cl 2 . In some examples, Cl 2  may be supplied at a flow rate of about 10 sccm (standard cubic centimeters per minute) and Ar may be supplied at a flow rate of about 40 sccm. The plasma etching may be performed at a pressure of approximately 5 milliTorr, power of about 500 W in high frequency and about 50 W in low frequency, for a duration of approximately 30 seconds at an etch temperature of about 30 degrees Celsius. As an example, power used to excite provided gases (e.g., Cl 2 /Ar) may be 1100 W at a “high” frequency of 13.56 MHz and 250 W at a “low” frequency of 450 KHz. As another example, power may be provided in the range of 100 W to 1200 W at high frequency (i.e., 13.56 MHz) and 10 W to 500 W at low frequency (i.e., 450 KHz). In still other examples, different power levels and frequencies may be used and are not limited to the examples provide and described herein. It should be noted that the flow rates of Cl 2 /Ar, pressure, power, duration, and temperature may vary (e.g., temperature of the plasma (i.e., etchant  308 ) may be varied from 0 degrees to 500 degrees Celsius).  FIG. 3B  shows a cross-sectional view of the resulting structure after the second etch. In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0035]      FIG. 3B  is a further cross-sectional view of a cross-point memory undergoing another exemplary etch in a selective etching process. Here, stack  100  includes platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114 , titanium nitride layer  116 , tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , substrate  124 , silicon dioxide layer  212 , and titanium nitride layer  310 . Further, platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114  form memory stack  126 . In some examples, after titanium nitride layer  106  has been etched as described above, titanium nitride layer  310  remains. The upper level of platinum layer  108  provides etch stop  302  to etchant  308 . In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0036]      FIG. 4A  is a cross-sectional view of a cross-point memory undergoing an exemplary etch of a memory stack in a selective etching process. Here, stack  100  includes platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114 , titanium nitride layer  116 , tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , substrate  124 , silicon dioxide layer  212 , and titanium nitride layer  310 . Further, platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , and platinum layer  114  form memory stack  126 . Stack  100  may exhibit sloped (i.e., substantially vertical) walls or sides as indicated by the dotted lines of pattern  404 - 406  such that the base of the memory stack is wider than the top of the memory stack. In some examples, etchant  408 , which may be a plasma etchant, is used to etch the unmasked region of memory stack  126  (e.g., platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114 ), as outlined by pattern  404 - 406  and etch stop  402 . As an example, etchant  408  may have an argon and oxygen (Ar/O 2 ) chemistry with a high selectivity to oxide layers (e.g., oxide/dielectric sub-regions  120 - 122 ). During the etching process, argon may be supplied at a flow rate of about 50 sccm. Further, oxygen may be supplied at a flow rate of about 3 sccm. Etchant  408  is provided at an etch pressure of about 2 milliTorr, a power of approximately 1100 W at high frequency and a power of approximately 250 W in low frequency for a duration of about 360 seconds and an etch temperature of about 30 degrees Celsius. The flow rates of argon and oxygen, etch pressure, power, frequency, and etch temperature may be varied according to design and is not limited to the examples described above. In some examples, a layer of titanium oxide (TiOx) may form when O 2  oxidizes titanium nitride (i.e., titanium nitride layer  116 ), acting as an etch stop to etchant  408 , as shown in  FIGS. 4B-4D . In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0037]      FIG. 4B  is another cross-sectional view of a cross-point memory undergoing an exemplary etch of a memory stack in a selective etching process. Here, stack  100  includes titanium nitride layer  116 , tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , substrate  124 , silicon dioxide layer  212 , titanium nitride layer  310 , platinum layer  410 , yttrium stabilized zirconium layer  412 , CMO layer  414 , and platinum layer  416 . In some examples, platinum layer  410 , yttrium stabilized zirconium layer  412 , CMO layer  414 , and platinum layer  416  form a memory stack (i.e., memory stack  126 ). Further, platinum layer  410 , yttrium stabilized zirconium layer  412 , CMO layer  414 , and platinum layer  416  are etched from platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , and platinum layer  114  ( FIG. 4A ), as specified by pattern  404 - 406  and etch stop  402 . Also shown is remnant platinum in platinum layer  416 . In some examples, when titanium nitride layer  116  is exposed to etchant  408  (i.e., an argon/oxygen combination plasma), titanium oxide (TiOx), as shown in  FIG. 4C . In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0038]      FIG. 4C  is a cross-sectional view of a cross-point memory undergoing an exemplary etch of a memory stack in a selective etching process. Here, stack  100  includes titanium nitride layer  116 , tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , substrate  124 , silicon dioxide layer  212 , titanium nitride layer  310 , platinum layer  410 , yttrium stabilized zirconium layer  412 , CMO layer  414 , platinum layer  416 , and titanium oxide regions  418 - 420 . In some examples, platinum layer  410 , yttrium stabilized zirconium layer  412 , CMO layer  414 , and platinum layer  416  form memory stack  422 . Further, memory stack  422  is etched from platinum layer  108 , yttrium stabilized zirconium layer  110 , CMO layer  112 , platinum layer  114  ( FIG. 4A ), as specified by pattern  404 - 406  and etch stop  402 , which corresponds substantially to the top of titanium oxide regions  418 - 420 . As described above, titanium oxide regions  418 - 420  form when etchant  408  (i.e., argon/oxygen plasma etchant) is used to etch memory stack  422  (i.e., platinum layer  410 , yttrium stabilized zirconium layer  412 , CMO layer  414 , and platinum layer  416 ). In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects, and are not limited to those shown and described. 
         [0039]      FIG. 4D  is a cross-sectional view of a cross-point memory undergoing an exemplary etch of a memory stack preventing oxygen out-diffusion in a selective etching process. Here, stack  100  includes titanium nitride layer  116 , tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , substrate  124 , silicon dioxide layer  212 , titanium nitride layer  310 , platinum layer  410 , yttrium stabilized zirconium layer  412 , CMO layer  414 , platinum layer  416 , and titanium oxide regions  418 - 420 . Also shown is oxygen  430  introduced in etchant  408 , which acts to prevent or reduce oxygen out-diffusion. Using a plasma etchant containing O2 prevents or reduces out-diffusion of oxygen  432  from CMO layer  414 . In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0040]      FIG. 5A  is a cross-sectional view of a cross-point memory undergoing a further exemplary etch in a selective etching process. Here, stack  100  includes titanium nitride layer  116 , tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , substrate  124 , silicon dioxide layer  212 , titanium nitride layer  310 , platinum layer  410 , yttrium stabilized zirconium layer  412 , CMO layer  414 , platinum layer  416 , and titanium oxide regions  418 - 420 . Also shown is etch stop  502  (i.e., the lower layer of titanium nitride layer  116 ), pattern  504 - 506 , and etchant  508 . In some examples, a different plasma etchant other than those described above may be used to etch titanium oxide regions  418 - 420  and titanium nitride layer  116 . As an example, etchant  508  may be HBr and Ar, Cl 2  and Ar, HBr, or Cl 2 . The upper surface of tungsten layer sub-region  118  forms etch stop  502 . Further, HBr may be supplied at a flow rate of about 50 sccm and argon is supplied at a flow rate of about 20 sccm. Etchant  508  is used in a plasma etch performed at, in some examples, a pressure of about 5 milliTorr, about 500 W at high frequency and about 50 W in high frequency, for a duration of approximately 30 seconds, and at an etch temperature of about 170 degrees Celsius. The flow rate and temperature of the above-described plasma etch may be varied and is not limited to the examples provided. The selective etch described above leaves the walls or sides of stack  100  substantially free of redeposited contaminants. An exemplary resulting structure after the completion of the fourth etch is shown in  FIG. 5B . In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0041]      FIG. 5B  is another cross-sectional view of a cross-point memory undergoing a further exemplary etch in a selective etching process. Here, stack  100  includes tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , substrate  124 , silicon dioxide layer  212 , titanium nitride layer  310 , platinum layer  410 , yttrium stabilized zirconium layer  412 , CMO layer  414 , platinum layer  416 , and titanium nitride layer  510 . Also shown is etch stop  502  (i.e., the lower layer of titanium nitride layer  116 ) and etchant  508 . Stack  100  illustrates the remaining masked portions of layer  102 - 116  after the above-described etchants (e.g.,  210  ( FIGS. 2A-2B ),  308  ( FIGS. 3A-3B ),  408  ( FIGS. 4A-4D ),  508  ( FIGS. 5A-5B )) have been applied. Here, etchant  508  has been used to remove titanium oxide regions  418 - 420  and unmasked portions of titanium nitride layer  116 , leaving stack  100  and memory stack  422  as shown. In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0042]      FIG. 6  is a cross-sectional view of a cross-point memory undergoing an exemplary anti-corrosion plasma treatment of a conductive metal oxide (CMO) layer in a selective etching process. Here, stack  100  includes tungsten sub-region  118 , oxide/dielectric sub-regions  120 - 122 , substrate  124 , silicon dioxide layer  212 , titanium nitride layer  310 , platinum layer  410 , yttrium stabilized zirconium layer  412 , CMO layer  414 , platinum layer  416 , and titanium nitride layer  510 . As shown, oxygen (i.e., O 2 )  602  may be used to perform an anti-corrosion plasma treatment of CMO layer. In some examples, anti-corrosion plasma treatment may be performed in situ in a separate chamber of a cluster tool without breaking vacuum as stack  100  passes through different chambers. As commonly defined, a vacuum is any pressure that is less than atmospheric. Further, by providing oxygen at high pressures (e.g., 1 Torr) without breaking vacuum, corrosion of CMO layer  414  is prevented or reduced. Stack  100  does not come into contact with air, water (i.e., H 2 O), or other ambient elements that may contain water particles, thus providing that there is substantially no corrosion of CMO layer  414  due to the reaction of halogens in situ combining with water particles on surfaces  606 . As an example, the above-described plasma treatment may be performed by supplying oxygen at a flow rate of 1000 sccm, a pressure of approximately 1 Torr, a power of 800 W at high frequency (as described above), for a duration of 300 seconds at a temperature of 250 degrees Celsius. Further, nitrogen (N 2 ) may also be included to perform the anti-corrosion plasma treatment described above. In some examples, nitrogen may be provided at a flow rate of 100 sccm while using the other above-described parameters (e.g., oxygen flow rate of 1000 sccm, 1 Torr of chamber pressure, power of 800 W at high frequency, for 300 seconds at 250 degrees). Further, the above-described parameters, including the flow rates of oxygen and nitrogen and the plasma temperature may be varied and are not limited to the examples provided. In other examples, stack  100  and the above-described elements and processes may be varied in material, dimensions, configuration, implementation, and other aspects and are not limited to those shown and described. 
         [0043]      FIG. 7A  is an exemplary process for selective etching. Here, a mask layer is formed on a hard mask layer ( 701 ). In some examples, a mask layer may refer to a photoresist layer, such as that described above. Once formed, the mask layer is patterned ( 705 ). The mask layer is developed to form an etch mask ( 709 ). After forming the etch mask, the hard mask layer is selectively etched to form a hard mask ( 713 ). The selective etch used to form the hard mask ( 713 ) is terminated at a first predetermined layer ( 717 ). A further selective etch is performed on the first predetermined layer using a first etch plasma ( 721 ). The select etch of the first predetermined layer is terminated at a second predetermined layer ( 725 ). A further selective etch is performed on thin-film layers in a memory stack using a second plasma etch ( 729 ). The selective etch of the thin-film layers in a memory stack is terminated at a third predetermined layer ( 733 ). Yet another selective etch is performed on the third predetermined layer using a third plasma etch ( 737 ). The selective etch of the third predetermined layer is terminated at a fourth predetermined layer ( 741 ). Further, the previously etched layers are treated using a plasma including oxygen, which is introduced into a vacuum chamber at a high pressure (about 1 Torr) without breaking vacuum as the wafer (e.g., substrate  124  ( FIGS. 1A-6 )) passes from one chamber to another in, for example, a cluster tool ( 745 ). In some examples, nitrogen may also be introduced into a chamber during the plasma treatment of the previously etched layers, as described above. In other examples, the above-described process may be varied in design, order, or function, without limitation to the examples provided above. 
         [0044]      FIG. 7B  is an exemplary process for optionally removing an etch mask from a hard mask. Here, a determination may be made as to whether to remove an etch mask (e.g., photoresist layer  102  ( FIGS. 2B-3A )) ( 714 ). If a determination is made to remove the etch mask after the hard mask has been etched, then the etch mask is removed from the hard mask using techniques such as ashing or stripping (e.g., wet and dry stripping), as described above ( 715 ). If a determination is made to not remove the etch mask, then the process ends and resumes with terminating the selective etch at a first predetermined layer ( 717 ). In other examples, the above-described process may be varied in design, order, or function, without limitation to the examples provided above. 
         [0045]    The foregoing examples have been described in some detail for purposes of clarity of understanding, but are not limited to the details provided. There are many alternative ways and techniques for implementation. The disclosed examples are illustrative and not intended to be restrictive to the examples and details provided.