Patent Publication Number: US-2023154752-A1

Title: Method For Highly Anisotropic Etching Of Titanium Oxide Spacer Using Selective Top-Deposition

Description:
BACKGROUND 
     The present disclosure relates to the processing of substrates. In particular, it provides a novel method for forming multiple patterning structures during the processing of substrates. 
     As geometries in substrate processing continue to shrink, the technical challenges to forming structures on substrates via photolithography techniques increase. As requirements for smaller geometry structures arose, a variety of photolithography techniques have been utilized for achieving suitable photolithography for such structures, including extreme ultraviolet (EUV) lithography, multiple patterning schemes (including self-aligned multiple patterning (SAMP) schemes such as, for example, self-aligned double patterning (SADP), self-aligned triple patterning (SATP), self-aligned quadruple patterning (SAQP), self-aligned octuple patterning (SAOP), etc.), or other small geometry patterning methods. Conventional SAMP processes may superimpose two or more multi-color pattern arrays to form the various designed structures on a substrate by selectively cutting overlapping portions of materials. 
     As known in the art, SAMP processes may utilize a mandrel (or core or backbone) structure having spacers formed on the sides of the mandrel to increase the structure density of the substrate surface. For example, in SADP, a mandrel may be formed on the substrate through known photolithography techniques. Mandrels may be formed of a wide variety of materials, including but not limited to, silicon, silicon nitride, hard mask materials, spin on carbon (SOC), photoresist, silicon oxide, etc. Sidewall spacers may then be formed adjacent to the mandrel. The spacers may be formed from any of a wide variety of materials (such as, for example, oxides, nitrides, titanium oxide, titanium nitride etc.) through use of a conformal deposition process (including but not limited to atomic layer deposition (ALD) techniques, chemical vapor deposition (CVD) techniques, etc.) and subsequent spacer etch. At some point, a mandrel pull step may be performed to remove the originally patterned mandrel, leaving the two sidewall spacers, thus forming two structures for each mandrel. 
     As line pitches go below 40 nm, the etching of the spacer has become increasingly difficult. For example, as pitches decrease, the ability to achieve bottom separation of the spacers formed along the mandrels has become more difficult. Efforts to achieve adequate bottom separation often result in significant spacer sidewall loss and damage to the mandrel during the spacer etch. In one example, titanium oxide spacers formed along amorphous silicon mandrels are etched in capacitively coupled (CCP) plasma etch tools. Narrow pitches (such as below 40 nm) obtaining desirable bottom separation of the spacer may result in significant sidewall loss and damage to the mandrel. 
     It would be desirable to provide an improved technique for forming spacers adjacent mandrels for narrow pitch structures. 
     SUMMARY 
     Improved process flows and methods are provided herein for forming spacers on a patterned substrate. In the disclosed process flows and methods, a self-aligned multiple patterning (SAMP) process is utilized for patterning structures, spacers formed adjacent mandrels, on a substrate. In one embodiment, a novel approach of etching titanium oxide (TiO 2 ) spacers is provided. Highly anisotropic etching of the spacer along with a selective top deposition is provided. In one embodiment, an inductively coupled plasma (ICP) etch tool is utilized. The etching process may be achieved as a one-step etching process. More particularly, a protective layer may be selectively formed on the top of the mandrel/spacer structure to protect the mandrel as well as minimize the difference of the etching rates of the spacer top and the spacer bottom. In one embodiment, the techniques may be utilized to etch TiO 2  spacers formed along amorphous silicon mandrels using an ICP etch tool utilizing a one-step etch process. 
     In a first embodiment, a method of forming spacers on a substrate for use in a self-aligned multiple patterning process (SAMP) is provided. The method comprises forming a plurality of structures on the substrate, the plurality of structures comprising at least mandrels, the mandrels being used as part of the SAMP process; forming a spacer layer over the mandrels; and providing an inductively coupled plasma apparatus. The method further comprises generating a one-step plasma in the inductively coupled plasma apparatus, the one-step plasma formed in a presence of a reactive etching gas and a passivating agent gas. The method also comprises utilizing the one-step plasma to etch the spacer layer with a reactive etching species with to form the spacers on sidewalls of the mandrels; and utilizing the one-step plasma to forming a protective layer on tops of the mandrels, the protective layer lessening the etch of the mandrels when the spacers are formed with the one-step plasma. 
     In a second embodiment, a method of forming titanium oxide spacers on a substrate is provided. The method comprises forming a plurality of structures on the substrate, the plurality of structures comprising at least mandrels, the mandrels being formed to have a pitch of 40 nm or less; forming a titanium oxide spacer layer over the mandrels; providing an inductively coupled plasma apparatus; and generating a plasma in the inductively coupled plasma apparatus, the plasma formed in a presence of a reactive etching gas and a passivating agent gas. The method further comprises utilizing the plasma to etch the titanium oxide spacer layer with a reactive etching species with to form the titanium oxide spacers on sidewalls of the mandrels; and utilizing the plasma to forming a protective layer on tops of the mandrels, the protective layer providing at least some protection to the mandrels while the titanium oxide spacer layer is being etched to form the spacers. 
     In various alternatives of the described embodiments, the spacer layer may comprise titanium oxide and the mandrels may comprise amorphous silicon. In some alternatives, the reactive etching gas comprises chlorine. In some alternatives, and the passivating agent gas comprises methane. In some alternatives, the one-step plasma is formed in a presence of carbon tetrafluoride (CF4) and/or nitrogen trifluoride. In some alternatives the mandrels have a pitch of 40 nm or less. In some alternatives, the mandrels are utilized as part of a self-aligned multiple patterning process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present inventions and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features. It is to be noted, however, that the accompanying drawings illustrate only exemplary embodiments of the disclosed concepts and are therefore not to be considered limiting of the scope, for the disclosed concepts may admit to other equally effective embodiments. 
         FIGS.  1 A- 1 D  illustrate forming mandrels and spacers for use in a self-aligned multiple patterning process. 
         FIGS.  2 A- 2 C  illustrate an exemplary embodiment of a one-step spacer etch according to the techniques described herein. 
         FIGS.  3 A- 3 B  illustrate exemplary methods of utilizing the techniques described herein. 
         FIG.  4    illustrates an exemplary inductively coupled plasma system which may be utilized to perform the etch techniques described herein. 
         FIG.  5    illustrates experimental results for an etch according to the techniques described herein for varying passivation agent flow rates. 
     
    
    
     DETAILED DESCRIPTION 
     Improved process flows and methods are provided herein for forming spacers on a patterned substrate. In the disclosed process flows and methods, a self-aligned multiple patterning (SAMP) process is utilized for patterning structures, spacers formed adjacent mandrels, on a substrate. In one embodiment, a novel approach of etching titanium oxide (TiO 2 ) spacers is provided. Highly anisotropic etching of the spacer along with a selective top deposition is provided. In one embodiment, an inductively coupled plasma (ICP) etch tool is utilized. The etching process may be achieved as a one-step etching process. More particularly, a protective layer may be selectively formed on the top of the mandrel/spacer structure to protect the mandrel as well as minimize the difference of the etching rates of the spacer top and the spacer bottom. In one embodiment, the techniques may be utilized to etch TiO 2  spacers formed along amorphous silicon mandrels using an ICP etch tool utilizing a one-step etch process. 
       FIGS.  1 A- 1 D  illustrates a general SAMP spacer/mandrel process flow to which the techniques described herein may be applied. It will be recognized that the embodiment and structures of  FIGS.  1 A- 1 D  are merely exemplary and the techniques described herein may be applied to other process flows. In the embodiment shown in  FIG.  1 A , the structures formed on the patterned substrate  100  include at least a plurality of mandrels  108 . The mandrels  108  may generally be formed over one or more underlying layers, such as a hard mask layer  106 , an etch stop layer  104 , and a substrate  102 . The underlying layers described, however, are merely exemplary; more, less or other underlying layers may be utilized. 
     Substrate  102  may be any substrate for which the use of patterned features is desirable. For example, in one embodiment, substrate  102  may be a semiconductor substrate having one or more semiconductor processing layers formed thereon. In one embodiment, the substrate  102  may be a substrate that has been subject to multiple semiconductor processing steps which yield a wide variety of structures and layers, all of which are known in the substrate processing art. 
     The hard mask layer  106  and etch stop layer  104  may be formed of any of a wide variety of materials as is known in the art. Likewise, the mandrels  108  may be formed from a wide variety of materials. In one embodiment, mandrels  108  may be formed of amorphous silicon. Mandrels  108  may be formed of a wide variety of other materials, though, including but not limited to silicon nitride, hard mask materials, spin on carbon (SOC) or other organic layers, photoresist, silicon oxide, etc. 
     The techniques for forming mandrels  108  in a multiple patterning process are well known in the art. As known, mandrels  108  may be patterned by any of a number of photolithography or other patterning techniques. In one embodiment, mandrels  108  may be formed through a process that utilizes photolithography techniques to pattern a resist layer over a mandrel layer. A variety of photolithography techniques may be utilized to pattern the mandrel layer to form mandrels  108 . Examples of photolithography techniques that may be used to form mandrels  108  include, but are not limited to, 193/193i lithography, EUV lithography, a combination of lithography and etch steps, etc. In some embodiments, one or more intervening layers may be used as part of the photolithography process between the mandrel layer and the resist layer, including one or more spin on glass (SOG) layers, spin on carbon (SOC) layers, antireflective coatings, etc., all as is known in the art. After patterning the mandrel layer, the mandrels  108  remain as shown in  FIG.  1 A . It will be recognized that the concepts disclosed herein are not limited, however, to any particular mandrel formation technique and are applicable to any techniques utilized to form the mandrels  108 . 
     After the formation of the mandrels  108 , a spacer layer  110  may be formed on the mandrels  108  as shown in  FIG.  1 B . In one embodiment, the spacer layer  110  may generally be formed through the use of an atomic layer deposition (ALD) process. However, any of a wide variety of spacer formation techniques may be utilized and the spacers described herein are not limited to those formed by ALD techniques. In one embodiment, the spacer may be formed of TiO 2 . Other spacer materials may also be utilized. 
     In  FIG.  1 C , the spacer layer  110  is etched to leave sidewall spacers  114  on either side of the trimmed mandrels  112 . The sidewall spacers  114  may be formed using any of a wide variety of etch techniques, including but not limited to, plasma etch chemistries. The plasma etch chemistries used to etch the spacer layer  110  and form sidewall spacers  114  may generally depend on the spacer layer  110  material formed or deposited onto the patterned substrate  100  during the spacer formation step (shown in  FIG.  1 B ). In some embodiments, the spacer layer  110  material may comprise silicon dioxide, silicon nitride, titanium oxide, or titanium nitride, for example. In such embodiments, plasma etch chemistries suitable for etching the spacer layer  110  and forming the sidewall spacers  114  may include, but are not limited to, Cl 2 , BCl 3 , NF 3 , CF x H y , SF 6 , C x F y , O 2 , N 2 , Ar, He, etc. Other plasma etch chemistries may be used to etch other spacer layer materials, as is known in the art. As described in the background above, using conventional spacer etch techniques the etching of the spacer has become increasingly difficult as pitches narrow. For example, as pitches decrease, the ability to achieve bottom separation of the spacers formed along the mandrels has become more difficult. Efforts to achieve adequate bottom separation often result in significant spacer sidewall loss and damage to the mandrel during the spacer etch. The disclosed achieve techniques described in more detail below provide for bottom separation without significant spacer sidewall loss and damage to the mandrel during the spacer etch. 
     In  FIG.  1 D , the trimmed mandrels  112  are removed via another etch process commonly referred to as a mandrel pull step. In the mandrel pull step shown in  FIG.  1 D , the trimmed mandrels  112  are removed, leaving two sidewall spacers  114  on the patterned substrate  100  for each mandrel. The trimmed mandrels  112  may be removed using any of a wide variety of etch techniques, including but not limited to, plasma etch wet etch, and ash techniques. The mandrel pull step (shown in  FIG.  1 D ) may be performed in the same or different chamber as the spacer etch step (shown in  FIG.  1 C ). In some embodiments, the etch process used to remove the trimmed mandrels  112  may preferably demonstrate selectivity between the material of the sidewall spacers  114  (e.g., silicon oxide, silicon nitride, titanium oxide, or titanium nitride) and the material used to form the mandrels  108 . 
     In some embodiments, one or more downstream processing steps may be performed after the mandrel pull step shown in  FIG.  1 D . For example, the pattern formed by the sidewall spacers  114  may be transferred to the hard mask layer  106  by subjecting the patterned substrate  100  to another etch process, which etches the hard mask layer  106  selectively to the sidewall spacers  114 . The sidewall spacers  114  may then be removed via another etch or strip step to leave patterned hard mask structures (not shown) on the substrate  102 . 
     The process flow shown in  FIGS.  1 A- 1 D  is one example of a SAMP process that the etch techniques described in more detail below may be applied to. Although described above in the context of a SADP process flow, the etch techniques described herein may be utilized in a variety of SAMP process flows including SADP, SAQP, SAOP, etc. process flows. 
     In the process flow shown in  FIGS.  1 A- 1 D , a mandrel material and a spacer material are formed on a variety of underlying layers and materials, such as but not limited to, a hard mask layer  106 , an etch stop layer  104 , and a substrate  102 . The hard mask layer  106 , etch stop layer  104  and substrate  102  may be formed of any of a wide variety of materials as is known in the art. It will be recognized by those skilled in the art that the particular materials used and described in the figures are merely exemplary, and a wide range of materials may be utilized depending upon the particular process flow for which the etch techniques disclosed herein are being utilized. 
       FIGS.  2 A- 2 C  illustrate a spacer etch technique for use in a SAMP process, for example, the process flow shown in  FIGS.  1 A- 1 D . It will be recognized that the spacer etch technique of  FIGS.  2 A- 2 C  may be utilized with other process flows. As shown in  FIG.  2 A , a substrate  200  is provided with mandrels  205  formed on an underlying layer  210 . A spacer layer  215  is then formed over the mandrels  205 . Next, the substrate  200  is subjected to a plasma  220 . The plasma  220  contains both a reactive etching species  221  and a passivating agent  222 . As shown in  FIG.  2 B , the plasma  220  has partially etched the spacer layer  215  to expose the tops of the mandrels  205 . When the tops of the mandrels  205  are exposed, the passivating agent  222  of the plasma  220  forms a protective layer  222 A on at least the tops of the mandrels as shown in  FIG.  2 B . The protective layer  222 A may also form on the tops of the spacer layer. As the substrate is continued to be exposed to the plasma  220 , the process continues to etch the bottom areas of the spacer layer  215 . The etching is continued until the bottom areas of the spacer layer  215  are cleared leaving spacers  230  formed on the sidewalls of the mandrels  205 . In this manner, a highly anisotropic etching of the spacer along with a selective top deposition is provided. The etching process may be achieved as a one-step etching process that contains both an etching species and a passivation agent. The protective layer may be selectively formed on the top of the mandrel/spacer structure to protect the mandrel as well as minimize the difference of the etching rates of the spacer top and the spacer bottom. Thus, the disadvantages of prior art techniques which provide undesirable etching of the mandrel and excessive etching of the tops of the spacers may be overcome. 
       FIGS.  3 A- 3 B  illustrate exemplary methods for use of the processing techniques described herein. It will be recognized that the embodiments of  FIGS.  3 A- 3 B  are merely exemplary and additional methods may utilize the techniques described herein. Further, additional processing steps may be added to the methods shown in the  FIGS.  3 A- 3 B  as the steps described are not intended to be exclusive. Moreover, the order of the steps is not limited to the order shown in the figures as different orders may occur and/or various steps may be performed in combination or at the same time. 
       FIG.  3 A  illustrates one embodiment of a method  300  of forming spacers on a substrate for use in a self-aligned multiple patterning process. The method comprises step  305  of forming a plurality of structures on the substrate, the plurality of structures comprising at least mandrels, the mandrels being used as part of the SAMP process. The method further comprises step  310  of forming a spacer layer over the mandrels and step  315  of providing an inductively coupled plasma apparatus. The method also comprises step  320  of generating a one-step plasma in the inductively coupled plasma apparatus, the plasma formed in the presence of a reactive etching gas and a passivating agent gas. The method further comprises step  325  of utilizing the one-step plasma to etch the spacer layer with a reactive etching species to form spacers on the sidewalls of the mandrels. The method also comprises step  330  of utilizing the one-step plasma to form a protective layer on tops of the mandrels, the protective layer lessening the etch of the mandrels when the spacers are formed with the one-step plasma. 
       FIG.  3 B  illustrates one embodiment of a method  350  of forming titanium oxide spacers on a substrate. The method comprises step  355  of forming a plurality of structures on the substrate, the plurality of structures comprising at least mandrels, the mandrels being formed to have a pitch of 40 nm or less. The method further comprises step  360  of forming a titanium oxide spacer layer over the mandrels and step  365  of providing an inductively coupled plasma apparatus. The method also comprises step  370  of generating a plasma in the inductively coupled plasma apparatus, the plasma formed in the presence of a reactive etching gas and a passivating agent gas. The method further comprises step  375  of utilizing the plasma to etch the titanium oxide spacer layer with a reactive etching species to form spacers on the sidewalls of the mandrels. The method further comprises step  380  of utilizing the plasma to form a protective layer on tops of the mandrels, the protective layer providing at least some protection to the mandrels while the titanium oxide spacer layer is being etched to form the spacers. 
     As mentioned above, one exemplary etch tool for use with the techniques described herein is an inductively coupled plasma apparatus. However, the techniques are not limited to an inductively coupled plasma and other etch apparatus may be utilized.  FIG.  4    is a schematic cross-sectional view of an exemplary inductively coupled plasma processing apparatus that may be utilized with the techniques disclosed herein. It will be recognized that the apparatus of  FIG.  4    is merely an exemplary inductively coupled plasma processing apparatus and a wide range of other inductively coupled plasma processing apparatus may be utilized. This apparatus can be used for multiple operations including ashing, etching, and deposition. Plasma processing can be executed within processing chamber  401 , which can be a vacuum chamber made of a metal such as aluminum or stainless steel. The processing chamber  401  is grounded such as by ground wire  402 . The processing chamber  401  defines a processing vessel providing a process space PS for plasma generation. An inner wall of the processing vessel can be coated with alumina, yttria, or other protectant. The processing vessel can be cylindrical, square, column-shaped, etc. 
     At a lower, central area within the processing chamber  401 , a susceptor  412  (which can be disc-shaped) can serve as a mounting table on which, for example, a substrate W to be processed (such as a semiconductor wafer) can be mounted. Substrate W can be moved into the processing chamber  401  through loading/unloading port  437  and gate valve  427 . The susceptor  412  can be made of a conductive material. Susceptor  412  is provided thereon with an electrostatic chuck  436  for holding the substrate W. The electrostatic chuck  436  is provided with an electrode  435 . Electrode  435  is electrically connected to DC power source  439  (direct current power source). The electrostatic chuck  436  attracts the substrate W thereto via an electrostatic force generated when DC voltage from the DC power source  439  is applied to the electrode  435  so that substrate W is securely mounted on the susceptor  412 . The susceptor  412  can include an insulating frame  413  and be supported by support  425 , which can include an elevation mechanism. The susceptor  412  can be vertically moved by the elevation mechanism during loading and/or unloading of the substrate W. A bellows  426  can be disposed between the insulating frame  413  and a bottom portion of the processing chamber  401  to surround support  425  as an airtight enclosure. Susceptor  412  can include a temperature sensor and a temperature control mechanism including a coolant flow path, a heating unit such as a ceramic heater or the like (all not shown) that can be used to control a temperature of the substrate W. A focus ring (not shown), can be provided on an upper surface of the susceptor  412  to surround the electrostatic chuck  436  and assist with directional ion bombardment. 
     A gas supply line  445 , which passes through the susceptor  412 , is configured to supply heat transfer gas to an upper surface of the electrostatic chuck  436 . A heat transfer gas (also known as backside gas) such as helium (He) can be supplied between the substrate W and the electrostatic chuck  436  via the gas supply line  445  to assist in heating substrate W. 
     A gas exhaust unit  430  including a vacuum pump and the like can be connected to a bottom portion of the processing chamber  401  through gas exhaust line  431 . The gas exhaust unit  430  can include a vacuum pump such as a turbo molecular pump configured to decompress the plasma processing space within the processing chamber  101  to a desired vacuum condition during a given plasma processing operation. 
     The plasma processing apparatus can be horizontally partitioned into an antenna chamber  403  and a processing chamber  401  by a window  455 . Window  455  can be a dielectric material, such as quartz, or a conductive material, such as metal. Embodiments in which the window  455  is metal, the window  455  can be electrically insulated from processing chamber  401  such as with insulators  406 . In this example, the window  455  forms a ceiling of the processing chamber  401 . In some embodiments, window  455  can be divided into multiple sections, with these sections optionally insulated from each other. 
     Provided between sidewall  404  of the antenna chamber  403  and sidewall  407  of the processing chamber  401  is a support shelf  405  projecting toward the inside of the processing apparatus. A support member  409  serves to support window  455  and also functions as a shower housing for supplying a processing gas. When the support member  409  serves as the shower housing, a gas channel  483 , extending in a direction parallel to a working surface of a substrate W to be processed, is formed inside the support member  409  and communicates with gas injection openings  482  for injecting process gas into the process space PS. A gas supply line  484  is configured to be in communication with the gas channel  483 . The gas supply line  484  defines a flow path through the ceiling of the processing chamber  401 , and is connected to a process gas supply system  480  including a processing gas supply source, a valve system and the corresponding components. Accordingly, during plasma processing, a given process gas can be injected into the process space PS. 
     In antenna chamber  403 , a high-frequency antenna  462  (radio frequency) is disposed above the window  455  so as to face the window  455 , and can be spaced apart from the window  455  by a spacer  467  made of an insulating material. High-frequency antenna  462  can be formed in a spiral shape or formed in other configurations. 
     During plasma processing, a high frequency power having a frequency of, e.g., 13.56 MHz, for generating an inductive electric field can be supplied from a high-frequency power source  460  to the high-frequency antenna  462  via power feed members  461 . A matching unit  466  (impedance matching unit) can be connected to high-frequency power source  460 . The high-frequency antenna  462  in this example can have corresponding power feed portion  464  and power feed portion  465  connected to the power feed members  461 , as well as additional power feed portions depending on a particular antenna configuration. Power feed portions can be arranged at similar diametrical distances and angular spacing. Antenna lines can extend outwardly from power feed portion  464  and power feed portion  465  (or inwardly depending on antenna configuration) to an end portion of antenna lines. End portions of antenna lines are connected to the capacitors  468 , and the antenna lines are grounded via the capacitors  468 . Capacitors  468  can include one or more variable capacitors. 
     With a given substrate mounted within processing chamber  401 , one or more plasma processing operations can be executed. By applying high frequency power to the high-frequency antenna  462 , an inductive electric field is generated in the processing chamber  401 , and processing gas supplied from the gas injection openings  182  is turned into a plasma by the inductive electric field. The plasma can then be used to process a given substrate such as by etching, ashing, deposition, etc. 
     High-frequency power source  429  (as second high-frequency power source) is connected to the susceptor  412  via a matching unit  428 . The high-frequency power source  429  supplies a high frequency bias power having a frequency of, e.g., 3.2 MHz (or other frequency), to the mounting table during plasma processing. Applying high frequency bias power causes ions, in plasma generated in the processing chamber, to be attracted to substrate W. 
     Components of the plasma processing apparatus can be connected to, and controlled by, a control unit  450 , which in turn can be connected to a corresponding storage unit  452  and user interface  451 . Various plasma processing operations can be executed via the user interface  451 , and various plasma processing recipes and operations can be stored in storage unit  452 . Accordingly, a given substrate can be processed within the plasma processing chamber with various microfabrication techniques. 
     The techniques for providing a one-step etching process of a TiO 2  spacer described herein may be accomplished with a variety of etch process conditions (power, pressure, temperature, gasses, flow rates, etc.). An exemplary process recipe is described herein for use with an inductively coupled plasma processing apparatus; however other process tools, process conditions and variables may be utilized. In one embodiment, an inductively coupled plasma etch may utilize a single step etch process having a source power (high frequency) in a range of 100-300 W, a bias power (low frequency) in a range of 100-250 W, a pressure in a range of 10-15 mTorr, and a temperature in a range of 40-70 degrees Celsius. Gasses utilized may include argon (Ar) in a range of 100-250 standard cubic centimeters per minute (sccm), chlorine (Cl 2 ) in a range of 70-90 sccm (the reactive etching species), carbon tetrafluoride (CF 4 ) or nitrogen trifluoride (NF 3 ) and methane (CH 4 ) in a range of 10-40 sccm (the passivation agent). The use of such an etch process provides a one-step etch that achieves a highly anisotropic profile, has bottom separation of the spacer structures, and selectively forms a protective layer on the mandrel top and the spacer top. As described above, the formation of the protective layer allows for etching of the spacer layer to leave sidewall spacers on the mandrels without sidewall loss and damage to the mandrel when etching the spacer material long enough to provide for bottom separation of adjacent spacer structures. These techniques are particularly useful when using mandrels that have line pitches of 40 nm or less. 
       FIG.  5    illustrates exemplary experimental data utilizing an inductively coupled plasma process as described above to etch a TiO 2  spacer formed on an amorphous silicon mandrel. In the example utilized, 36 nm pitch mandrels having a starting height of 35-45 nm are utilized along with spacer deposition height of 7-9 nm. More particularly,  FIG.  5    illustrates the impact of varying the flow rate of the passivation agent, in this case CH 4 . As shown in  FIG.  5   , flow rates of the passivation agent were changed from 15 sccm to 40 sccm. Plot  505  illustrates the mandrel height after etch at differing flow rates for the passivating agent. As shown by plot  505 , the mandrel height after etch may vary significantly depending upon the passivating agent flow rate. More particularly, the higher flow rates of a passivating agent provide increased protection to the mandrel during the etch leaving significantly more of the mandrel after the etch. As seen in the graph, the mandrel height post etch may range from almost 0 nm to almost 20 nm depending upon the passivating agent flow rate. While the passivating agent flow rate dramatically changes the etching of the mandrel, the passivating agent has less of impact on the etch rate of the TiO 2  at the top of the spacer and at the bottom of the spacer. More particularly, plot  510 A illustrates the change in etch depth of the spacer at the top of the spacer: ranging from about 18 nm to 22 nm. Furthermore, plot  510 B illustrates the change in etch depth of the spacer at the bottom of the spacer: ranging from about 10 nm to 14 nm. 
     The differing impact on the mandrel versus the spacer seen in  FIG.  5    may be the result of various mechanisms such as for example, but not limited to, a chemically driven reaction between the mandrel material and the passivating agent and/or enhanced polymerization on the mandrel as a result of the increased passivation agent flow rate. Other mechanisms may also occur and the techniques described herein are not limited to a particular mechanism. 
     Further modifications and alternative embodiments of the inventions will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the manner of carrying out the inventions. It is to be understood that the forms and method of the inventions herein shown and described are to be taken as presently preferred embodiments. Equivalent techniques may be substituted for those illustrated and described herein and certain features of the inventions may be utilized independently of the use of other features, all as would be apparent to one skilled in the art after having the benefit of this description of the inventions.