Patent Publication Number: US-2023135735-A1

Title: Techniques and apparatus for selective shaping of mask features using angled beams

Description:
RELATED APPLICATIONS 
     The present application claims priority to and is a divisional application of U.S. Non-Provisional patent application Ser. No. 17/328,253, filed on May 24, 2021, entitled “TECHNIQUES AND APPARATUS FOR SELECTIVE SHAPING OF MASK FEATURES USING ANGLED BEAMS,” which is a divisional application and claims priority to U.S. Non-Provisional patent application Ser. No. 16/730,586, filed on Dec. 30, 2019, entitled “TECHNIQUES AND APPARATUS FOR SELECTIVE SHAPING OF MASK FEATURES USING ANGLED BEAMS,” which is now Patented as U.S. Pat. No. 11,043,394 issued on Jun. 22, 2021 which claims priority to U.S. Provisional Patent Application Ser. No. 62/949,582, filed Dec. 18, 2019, entitled “ RIBBON BEAM PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION SYSTEM FOR ANISOTROPIC DEPOSITION OF THIN FILMS,” all of which applications are incorporated by reference herein in their entirety. 
    
    
     FIELD 
     The present embodiments relate to substrate processing techniques, and more particularly, to etch processing for patterning structures and devices. 
     BACKGROUND 
     As devices such as a semiconductor devices, optical devices, or devices electronic devices, continue to scale to smaller dimensions, the ability to pattern features becomes increasingly difficult. In addition to challenging the ability to lithographically define smaller lateral mask features to pattern an underlying substrate or layer to generate features having similar lateral dimension, the maximum thickness of mask features is continuing to shrink to satisfy lithographic requirements. 
     Moreover, changing the size of such mask features after lithographic patterning may be useful, such as by etching. For example, to generate a given array of cavities at a targeted large size and small separation between cavities, one possible strategy is to pattern the array of cavities lithographically to a relatively smaller size with a larger separation between cavities, and then etch the cavities to enlarge the cavities. In particular, selectively etching a cavity along a given direction may be useful. Notably, a drawback of etching a cavity formed in a given mask layer is the loss of mask layer thickness during the etching, leading to the inability to pattern an underlying feature after the mask etching. Additionally, the cavities may be imperfectly etched, leading to a non-ideal mask shape. 
     With respect to these and other considerations the present embodiments are provided. 
     BRIEF SUMMARY 
     In one embodiment, a method of patterning a substrate is provided. The method may include providing a set of features in a mask layer, the mask layer being disposed on a layer of the substrate, wherein a given feature comprises a first dimension along a first direction, a second dimension along a second direction, orthogonal to the first direction, and a first thickness. The method may also include directing an angled ion beam to a first side region of the set of features in a first exposure, wherein the first side region is etched a first amount along the first direction. The method may further include directing an angled deposition beam to a second side region of the set of features in a second exposure, wherein a protective layer is formed on the second side region, the second side region being oriented perpendicularly with respect to the first side region. The method may include directing the angled ion beam to the first side region in a third exposure, wherein the first side region is etched a second amount along the first direction. 
     In another embodiment, a method of patterning a substrate, may include providing a set of features in a mask layer, the mask layer being disposed on a surface of the substrate and comprising a first material, wherein a given feature comprises a first dimension along a first direction, a second dimension along a second direction, orthogonal to the first direction, and a first thickness. The method may include repeatedly performing an etch cycle to selectively etch the set of features, the etch cycle comprising: directing an angled ion beam to the set of features in a first exposure, when the substrate is oriented at a first twist angle, wherein the set of features is etch a first amount along the first direction. The method may also include rotating the substrate to a second twist angle after the directing the angled ion beam, and directing an angled deposition beam the set of features in a second exposure, wherein a protective layer is formed on a protected portion of the set of features. 
     In a further embodiment, an apparatus may include a plasma chamber to generate a processing plasma, and a substrate stage, to support a substrate, and disposed adjacent to the plasma chamber. The apparatus may also include an extraction assembly, disposed along a side of the plasma chamber, between the plasma and the substrate stage, to extract plasma species from the plasma, and a bias voltage source to apply a bias voltage between the plasma chamber and the substrate. The apparatus may include a controller to send a first control signal to the bias voltage source to apply a first bias voltage between the plasma chamber and the substrate while the substrate stage is arranged at a first twist angle. The controller may be arranged to send a second control signal to the bias voltage source to apply second bias voltage between the plasma chamber and the substrate, the second bias voltage being less in absolute magnitude than the first bias voltage, and to send concurrently with the second control signal, a third control signal to rotate the substrate stage to a second twist angle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS.  1 A- 5 C  generally depict the structure of a substrate at different stages of processing, according to embodiments of the present disclosure; 
         FIG.  1 A  depicts a top view of a substrate after patterning to form a mask layer; 
         FIG.  1 B  depicts a side cross-sectional view of the substrate of  FIG.  1 A ; 
         FIG.  1 C  depicts an end cross-sectional view of the substrate of  FIG.  1 A ; 
         FIG.  2 A  depicts a top view of the substrate of  FIG.  1 A , subsequent to the instance of  FIG.  1 A , after processing by an ion beam; 
         FIG.  2 B  depicts a side cross-sectional view of the substrate of  FIG.  2 A ; 
         FIG.  2 C  depicts an end cross-sectional view of the substrate of  FIG.  2 A ; 
         FIG.  3 A  depicts a top view of the substrate of  FIG.  1 A , subsequent to the instance of  FIG.  2 A , after processing by a deposition beam; 
         FIG.  3 B  depicts a side cross-sectional view of the substrate of  FIG.  3 A ; 
         FIG.  3 C  depicts an end cross-sectional view of the substrate of  FIG.  3 A ; 
         FIG.  3 D  depicts an enlarged view of a portion of the substrate of  FIG.  3 C ; 
         FIG.  3 E  depicts an example of directional deposition beam processing of a set of patterned features, consistent with embodiments of the disclosure; 
         FIG.  4 A  depicts a top view of the substrate of  FIG.  1 A , subsequent to the instance of  FIG.  3 A , after further processing by an ion beam; 
         FIG.  4 B  depicts a side cross-sectional view of the substrate of  FIG.  4 A ; 
         FIG.  4 C  depicts an end cross-sectional view of the substrate of  FIG.  4 A ; 
         FIG.  5 A  depicts a top view of the substrate of  FIG.  1 A , subsequent to the instance of  FIG.  4 A , after further processing; 
         FIG.  5 B  depicts a side cross-sectional view of the substrate of  FIG.  5 A ; 
         FIG.  5 C  depicts an end cross-sectional view of the substrate of  FIG.  5 A ; 
         FIG.  5 D  and  FIG.  5 E  shown an example of processing during a given etch cycle, according to further embodiments of the disclosure; 
         FIG.  6 A  depicts a top view of the substrate of  FIG.  1 A , illustrating a targeted mask pattern after directional etching; 
         FIG.  6 B  depicts a side cross-sectional view of the substrate of  FIG.  6 A  after directional etching using an ion beam, while not employing a deposition beam; 
         FIG.  6 C  depicts an end cross-sectional view of the substrate of  FIG.  6 B ; 
         FIG.  7 A  depicts a side view of a processing apparatus during ion beam processing of a substrate, in accordance with embodiments of the present disclosure; 
         FIG.  7 B  depicts a to view of a portion of the processing apparatus of  FIG.  7 A , during the instance depicted in  FIG.  7 A ; 
         FIG.  7 C  depicts a side view of a processing apparatus during deposition beam processing of a substrate, in accordance with embodiments of the present disclosure; 
         FIG.  7 D  depicts a to view of a portion of the processing apparatus of  FIG.  7 A , during the instance depicted in  FIG.  7 C ; 
         FIG.  7 E ,  FIG.  7 F , and  FIG.  7 G  depict aspects of another apparatus, according to embodiments of the present disclosure; 
         FIG.  8    depicts the geometry for changing the shape of a patterned feature by combined directional ion beam processing and directional deposition beam processing, according to an embodiment of the disclosure; 
         FIG.  9    depicts the geometry for generating a composite merged shape by merging multiple patterned features using a combined directional ion beam processing and directional deposition beam processing, according to another embodiment of the disclosure; 
         FIG.  10    depicts an exemplary process flow, according to one embodiment; 
     
    
    
     DETAILED DESCRIPTION 
     The present embodiments will now be described more fully hereinafter with reference to the accompanying drawings, where some embodiments are shown. The subject matter of the present disclosure may be embodied in many different forms and are not to be construed as limited to the embodiments set forth herein. These embodiments are provided so this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art. In the drawings, like numbers refer to like elements throughout. 
     This present embodiments provide novel techniques and apparatus to pattern substrates and in particular novel techniques to etch a cavity disposed in a substrate, along a designed direction. In various embodiments, a feature such as a via or trench may be formed having an initial shape and size, and may be subsequently elongated along the designed direction using a series of etch operations. The designed direction may correspond to a horizontal direction within a plane of the substrate. According to various embodiments, the elongation of the feature may take place along the designed direction (first direction) while the cavity is not enlarged or enlarged to a lesser extent along a perpendicular direction to the designed direction (second direction) within the plane of the substrate. In this manner, a cavity may be selectively elongated along just one direction, providing various concomitant advantages for patterning substrates, as disclosed herein. 
     According to the embodiments disclosed herein, a mask having a set of patterned features may be processed in an iterative fashion to selectively etch mask features and selectively deposit a protective layer of material or replenishment material to avoid unwanted etching of the mask features in certain portions of the mask features. In some embodiments, a directional ribbon beam is employed to iteratively process etch a patterned feature. The iterative processing may involve repeating a directional etch operation that is interspersed with a directional deposition operation. In one example, a processing operation may involve etching certain regions of a patterned feature of a mask, such as a sidewall or endwall of a cavity in a desired direction, followed by rotation of the mask, and directional deposition of protective or replenishing layer on other regions of the mask. After the directional deposition, the mask may be rotated back to an original position, and directional etching of the cavity or other patterned feature along the desired direction resumed. In this manner, the patterned feature of the mask may be etched to a desired length along a desired direction, while preventing unwanted etching of patterned features that may otherwise occur during prolonged directional etching along a specific direction. According to some embodiments, disclosed below, the iterative directional etching and direction deposition may be performed on a mask, using a common processing plasma chamber, where biasing between a substrate containing the mask and the plasma chamber is switched from negative bias to zero bias between the direction etching operation and direction deposition operation, respectively. 
     In different embodiments of the disclosure, directional deposition and directional etching may be performed using a common plasma chamber to extract directional beams, where the directional deposition employs the same chemistry as the directional etching, where directional deposition is accomplished by decreasing the bias between plasma chamber and substrate, as compared to the bias applied to generate the directional etching. As an example, plasma species including ions may be extracted from the plasma chamber to form an ion beam to perform directional etching using a relatively high bias, while plasma species including radicals, neutrals, and possibly ions may be extracted from the plasma chamber to form a deposition beam to perform directional deposition using a relatively low bias or zero bias. 
     Turning now to the figures,  FIGS.  1 A- 5 C  generally depict the structure of a substrate at different stages of processing, according to embodiments of the present disclosure. According to various embodiments, as shown in the  FIGS.  1 A- 5 C , a selective etching operation is performed using a combination of a deposition operation and an etch operation that are performed in a sequential and iterative manner.  FIG.  1 A  depicts a top view of a substrate after patterning to form a mask layer, while  FIG.  1 B  depicts a side cross-sectional view of the substrate of  FIG.  1 A , and  FIG.  1 C  depicts an end cross-sectional view of the substrate of  FIG.  1 A . In  FIG.  1 A , a substrate  100  is shown, including a mask layer  112  that defines a mask having an array of patterned features, in this example, a set of cavities, shown as cavities  106 . The mask layer  112  is disposed on other parts of a substrate, such as a layer  114 , subjacent the mask layer  112 , and a layer  116 , subjacent the layer  114 . 
     According to various embodiments of the disclosure, the mask layer  112  may be a photoresist material, a hard mask material, a carbon material, an oxide such as silicon oxide, a nitride such as silicon nitride, or other suitable mask material. The mask layer  112  may be used to mask the layer  114 , so that the pattern of cavities  106  may be transferred into the layer  114 , for example, by a known etching process, such as reactive ion etching (RIE). In various embodiments, the layer  114  may be a different material than the material of mask layer  112 . For example, the mask layer  112  may be formed of silicon nitride or carbon, while the layer  114  is formed of silicon or silicon oxide. Likewise the layer  116  may be a different material than the material of layer  114 . For example, the layer  114  may be formed of silicon oxide, while the layer  116  is formed of silicon. The embodiments are not limited in this context. 
     In the present embodiments, before transferring of the pattern of the mask layer  112  into the layer  114 , the mask layer  112  may be processed to selectively change the pattern of the mask layer  112 , for example to selectively change the dimensions of the cavities  106 , to change the spacing between cavities  106 , and so forth. For example, device patterning of the substrate  100  may call for the cavities  106  to be separated by a tip-to-tip spacing, shown as S 2 , in  FIG.  5 A . After lithographic patterning, the mask layer  112  may exhibit a tip-to-tip spacing shown as S 1 . In some instances, lithographic patterning may be limited to image spacings between adjacent cavities less than a given amount, such as S 1 , along the Y-direction of the Cartesian coordinate system shown. For example, the value of S 1  may be on the order of a few nanometers, or a few tens of nanometers, where lithographic patterning may not resolve spacings smaller than S 1  within the mask layer  112 . For this reason, the mask layer  112 , after patterning to generate the pattern of  FIG.  1 A , having the length of cavities of L 1  and separation of Si along the Y-direction, may be subjected to selective etching and deposition processes, to change the dimension of the cavities, the spacing between cavities, long at least one direction, and in some cases to change the shape of the cavities. Such combined etching and deposition processes may be referred to herein as selectively shaping a patterned feature, such as a cavity. 
     At a subsequent instance,  FIG.  2 A  depicts a top view of the substrate of  FIG.  1 A , after processing by an angled ion beam  120 .  FIG.  2 B  depicts a side cross-sectional view of the substrate of  FIG.  2 A , while  FIG.  2 C  depicts an end cross-sectional view of the substrate of  FIG.  2 A . At the instance of  FIG.  2 A , the angled ion beam  120  is directed to a first side region of the set of features of the mask layer  112 , meaning a side region of the cavities  106 . The first side region may represent a sidewall, an endwall, a portion of a sidewall in various non-limiting embodiments. In this example, the first side region of the cavities  106  is represented by endwalls  106 A. In various non-limiting embodiments, the cavities  106  may be trenches that are elongated along the Y-axis. As such, the angled ion beam may etch the endwalls  106 A a first amount along a first direction, parallel to the Y-axis. Notably, the angled ion beam  120  may be directed as an angled reactive ion beam to the substrate  100  at a non-zero angle of incidence (shown as θ e ) with respect to a perpendicular  132  to a main plane P of the substrate  100 , where the main plane may be represented by the X-Y plane. Thus, the angled ion beam  120  may directly impact the endwalls  106 A as shown. In different non-limiting embodiments of the disclosure, the value of may vary between 5 degrees and 85 degrees, and in particular embodiments between 15 degrees and 60 degrees. 
     The angled ion beam  120  may be provided using a known etch chemistry chosen according to the nature of the mask layer  112 , as well as the layer  114 . For example, if the mask layer  112  is an SiN layer, the etch chemistry may be chosen to selectively etch SiN with respect to other materials, such as the material of layer  114 , which layer may be silicon oxide. In some embodiments, the etch operation involves directing a pair of an angled reactive ion beams at a non-zero angle of incidence where the two angled reactive ion beams have a value represented by ±(θc) and form mirror image with respect to the X-Z plane, as shown. As such, a pair of endwalls  106 A, opposing one another, may be etched. As further shown also in  FIG.  1 B , for example, the cavities  106  of mask layer  112  may be selectively etched along the Y-direction so as to reduce the spacing between adjacent cavities along the Y-direction to a value of S 2 , less than S 1 . As such, the cavities  106  are also elongated along the Y-direction to a value of L 2 . 
     Notably, during the etch operation of  FIG.  2 A- 2 C , the height of the mask layer  112  along the Z-axis may be reduced from the value of h 1 . 
     Notably, the angle of incidence of the angled ion beam  120  and duration of the etching during the instance of  FIGS.  2 A- 2 C  may be limited to limit removal of the mask layer material of mask layer  112  from the top surface of the mask layer  112 , and to prevent widening of the cavities  106  along the X-direction. For example, as shown in  FIG.  2 C , the cavities  106  may retain the original dimension, shown as W 1 , along he X-direction. 
     Turning to  FIG.  3 A  there is shown a top view of the substrate of  FIG.  1 A , subsequent to the instance of  FIG.  2 A , after processing by a deposition beam, in accordance with the present embodiments.  FIG.  3 B  depicts a side cross-sectional view of the substrate of  FIG.  3 A , while  FIG.  3 C  depicts an end cross-sectional view of the substrate of  FIG.  3 A , and  FIG.  3 D  depicts an enlarged view of a portion of the substrate of  FIG.  3 C . 
     In  FIG.  3 A , an angled deposition beam  140  is directed to a second side region of the mask set of features of mask layer  112 , meaning the sidewalls  106 B of the cavities  106 , in a second exposure. As such, a protective layer  134  is formed on the second side region. In this example, the second side region encompasses an upper portion of the sidewalls  106 B. The protective layer  134  is also formed on the top surface of the mask layer  112 . The protective layer  134  may be formed by directing the angled deposition beam  140  at a second non-zero angle of incidence with respect to the perpendicular  132 , where the second non-zero angle of incidence of angled deposition beam  140  is represented by θ D  . Depending upon the aspect ratio of the cavities  106  along the X-Z plane shown in  FIG.  3 C , as well as the value of the second non-zero angle of incidence, the extent of coverage of the sidewalls  106 B may be greater or lesser. Notably, in the example of  FIGS.  3 A- 3 C , the orientation of the mask layer  112  is rotated 90 degrees about the perpendicular  132  with respect to the orientation of the mask layer  112  in  FIG.  2 A . Thus, the angled deposition beam  140  is directed at a non-zero angle with respect to the Y-Z plane in the instance of  FIGS.  3 A-C  while the angled ion beam  120  is provided at a non-zero angle of incidence with respect to the X-Z plane in the instance of  FIGS.  2 A- 2 C .  FIG.  3 E  depicts an example of directional deposition beam processing of a set of patterned features  131 , consistent with embodiments of the disclosure, where a protective layer  134 A is deposited just on right sidewalls and upper surfaces, by directing an angled beam from the upper right of the figure. 
     By providing the protective layer  134  over sidewalls  106 B and over the top surface of the mask layer  112 , the mask layer  112  may be selectively replenished to prevent etching in unwanted portions of the mask layer. In particular embodiments, the replenishing provided by the protective layer  134  may be tuned to balance out or replace the same amount of material that is removed from certain surfaces by unwanted etching during the etch operation of  FIGS.  2 A- 2 C . For example, the amount of material deposited in the select regions where protective layer  134  forms, may be tuned to equal the amount of etching taking place in these select regions during a given etch operation. Thus, the protective layer  134  may be deposited on top surfaces of the mask layer  112  to a layer thickness that matches the amount of material removed from the top surface of the mask layer  112  during the etching operation of  FIG.  2 A , with the net result that the thickness of mask layer  112  remains constant after each cycle of etching and layer deposition. Likewise, the amount of material of the protective layer  134  deposited on sidewalls  106 B may be tailored to match and replenish the amount of material of mask layer  112  that is removed from sidewalls  106 B during a previous etch operation. Of course, net material will be removed from targeted surfaces of the mask layer, such as the endwalls  106 A. Notably, the relative duration of the deposition operation of  FIG.  3 A  may be adjusted according to the duration of etch operation of  FIG.  2 A , depending upon relative deposition rates and etch rates. 
     Subsequently to the operation of  FIGS.  3 A- 3 E , an etching operation similar to the operation of  FIGS.  2 A- 2 C  may be repeated to further elongate the cavities  106  along the Y-axis.  FIG.  4 A  depicts a top view of the substrate of  FIG.  1 A , subsequent to the instance of  FIG.  3 A , after further processing by an angled ion beam.  FIG.  4 B  depicts a side cross-sectional view of the substrate of  FIG.  4 A , while  FIG.  4 C  depicts an end cross-sectional view of the substrate of  FIG.  4 A . In this example, the angled ion beam  120  is directed to the first side region, meaning a portion of the endwalls  106 A, in a third exposure, wherein the first side region is etched a second amount along the first direction, that is, along the Y-axis. The angled ion beam  120  may represent the same conditions as the conditions of angled ion beam  120  in  FIG.  2 A  according to one embodiment. Notably, in the example of  FIGS.  4 A- 4 C , the orientation of the mask layer  112  may be rotated −90 degrees about the perpendicular  132  with respect to the orientation of the mask layer  112  in  FIG.  3 A , and thus back to the original orientation of the angled ion beam  120  with respect to mask layer  112 , as shown in  FIG.  2 A . At this stage, the separation of the cavities  106  may be at a value S 3 , which value may be a targeted value for the separation of the cavities. As such, further directional etching along the Y-axis of cavities  106  may cease. 
     In some embodiments a portion of the protective layer  134  may remain after the operation of  FIG.  4 A , as suggested in  FIGS.  4 A- 4 C . In examples where the material of protective layer  134  is different from the material of mask layer  112 , the protective layer may be subsequently removed, for example by known selective etching techniques. In other embodiments, residual amounts of protective layer  134  may not be removed before subsequent etching of the layer  114  using mask layer  112 . For example, the mask layer  112  and protective layer  134  may be formed from the same hard mask material. During the etch process of  FIG.  4 A , an appropriate amount of protective layer  134  may be removed to render the dimensions of cavities  106  and the spacing between cavities  106  at desired values. 
       FIG.  5 A  depicts a top view of the substrate of  FIG.  1 A , subsequent to the instance of  FIG.  4 A , after further processing.  FIG.  5 B  depicts a side cross-sectional view of the substrate of  FIG.  5 A , while  FIG.  5 C  depicts an end cross-sectional view of the substrate of  FIG.  5 A . In this example, any residual portion of the protective layer  134  has been removed, rendering the mask layer  112  with the dimension of L 3  for the cavities  106  and S 3  for separation between cavities  106 . Additionally, the width of cavities  106  along the X-axis remains at W 1 , the same value as the original width of the cavities  106 . 
     Notably in the embodiments, of  FIGS.  1 A- 5 C , directional etching and deposition processes may be alternated with one another in a cyclic fashion, through multiple etch cycles, where a given etch cycle involves the following set of operations. The etch cycle may start with 1) directing an angled ion beam to the set of features in a first exposure, when the substrate is oriented at a first twist angle, wherein the set of features is etch a first amount along a first direction; 2) rotating the substrate to a second twist angle after the directing the angled ion beam; and directing an angled deposition beam the set of features in a second exposure, wherein a protective layer is formed on a protected portion of the set of features. In various embodiments, the second twist angle may be a 90 degree rotation about a perpendicular to a main plane of the substrate, with respect to the first twist angle. In this way, the angled deposition beam will tend to strike regions of a surface feature that are oriented perpendicularly with respect to those regions of the surface feature that are impacted by the directional ion beam. According to some embodiments, an etch cycle may be repeated 5 times, 10 times, 20 times or more, depending upon the extent of etching to be performed. For example, to selectively elongate a cavity by 10 nm along an X-direction, a given etch process using an angled ion beam within a given etch cycle may remove 0.5 nm of an endwall along the X-direction, while a given deposition process using an angled deposition beam may deposit a protective layer having a thickness on the order of 0.2 nm. To elongate the cavity by 10 nm may therefore require 20 etch cycles. As a given etch cycle proceeds, a portion of cavity sidewalls and top surface of a mask layer may be continually replenished before faceting or rounding may take place. 
     In one variant of the processes depicted at  FIGS.  1 A- 5 C , multiple cycles may be performed where a given cycle includes an angled directional etching operation and angled directional deposition, in a manner that after a given cycle the structure and shape of a mask are preserved, as discussed above. Turning to  FIG.  5 D  and  FIG.  5 E , there is shown an example of processing during a given etch cycle, where the structure of  FIG.  5 D  represents a mask layer  112  after directional etching as generally discussed with respect to  FIG.  2 A- 2 C , and the structure of  FIG.  5 E  depicts the mask layer  112  from an end cross-section after replenishment by a directional deposition as generally discussed with respect to  FIGS.  3 A- 3 E . The dashed line in  FIG.  5 D  outlines a depletion zone  112 A, showing the contours of the original state of mask features  112 B that define the cavities  106  before etching, as well as the present surface of mask features  112 B of the mask layer  112  after etching, revealing that a certain amount of material has been removed from a top surface  106 T of the mask layer  112 , as well as from sidewalls  106 B. As shown in  FIG.  5 E , the directional deposition has replenished the mask layer  112 , so the cavities  106  of mask layer  112  retains the original dimensions and shape in terms of h 1  and w 1 . This process may be repeated for any number of cycles so that the mask features are repeatedly replenished to original shape and size within the X-Z plane, while the mask features  112 B are progressively etched along the Y-axis to selectively elongate the cavities  106 . In this manner, the final operation of a series of etch cycles may be represented by  FIG.  5 E , where the deposition layer  134 B may be a different material or the same material as mask layer  112 . At this stage, the mask layer  112  may then be used without further processing to etch the underlying layer, layer  114 . 
     To highlight the advantages of the embodiments as shown in  FIG.  1 A- 5 C ,  FIGS.  6 A- 6 C  illustrate an example of directional etching used to elongate a cavity, while not using directional deposition. In particular,  FIG.  6 A  depicts a top view of the substrate of  FIG.  1 A , illustrating a targeted mask pattern after directional etching.  FIG.  6 B  depicts a side cross-sectional view of the substrate of  FIG.  6 A  after directional etching using an ion beam, while not employing a deposition beam, and  FIG.  6 C  depicts an end cross-sectional view of the substrate of  FIG.  6 B . In  FIG.  6 A , the mask layer  112  is shown generally as in  FIG.  1 A , with the addition of a targeted mask pattern  106 D, where the cavities  106  are elongated to the dimension L 3  by employing the angled ion beam  120 , without using angled deposition beam  140 , discussed above. In this example, as shown in  FIG.  6 B  and  FIG.  6 C , the mask layer  112  may be eroded to exhibit rounding or faceting along sides of the cavities  106 , including along the X-Z plane, shown in  FIG.  6 C . Because of this erosion, poor pattern transfer may take place when pattern transfer of the mask pattern of mask layer  112  takes place by etching the layer  114 . 
     In some embodiments, the aforementioned processes may be performed using a ribbon beam-type processing system, where an angled ion beam and/or an angled deposition beam is provided having a ribbon beam shape, where the ribbon cross-section is elongated along one direction with respect to an orthogonal direction. 
       FIG.  7 A  depicts a side view of a processing apparatus  200  during ion beam processing of a substrate, in accordance with embodiments of the present disclosure.  FIG.  7 B  depicts a top view of a portion of the processing apparatus of  FIG.  7 A , during the instance depicted in  FIG.  7 A .  FIG.  7 C  depicts a side view of a processing apparatus during deposition beam processing of a substrate, in accordance with embodiments of the present disclosure.  FIG.  7 D  depicts a to view of a portion of the processing apparatus of  FIG.  7 A , during the instance depicted in  FIG.  7 C . 
     As to the general features of the processing apparatus  200 , this apparatus represents a processing apparatus for selectively etching processing portions of a substrate, such as selectively elongating a cavity. The processing apparatus  200  may be a plasma-based processing system having a plasma chamber  202  for generating a plasma  204  therein by any convenient method as known in the art. A power supply  230 , may, for example, be an RF power supply to generate the plasma  204 . An extraction plate  206  may be provided as shown, having an extraction aperture  208 , where a selective etching may be performed to selectively remove sidewall layers. A substrate, such as a substrate  100  having the aforementioned structure as shown at  FIGS.  1 A- 1 C , is disposed in the process chamber  222 . A substrate plane of the substrate  100  is represented by the X-Y plane of the Cartesian coordinate system shown, while a perpendicular to the plane of the substrate  100  lies along the Z-axis (Z-direction). 
     As further shown in  FIG.  7 A , a controller  240  may be provided to send control signals to the bias supply  220  and to the substrate stage  214 . 
     In one example, the view of  FIG.  7 A  may represent a variant of the selective etching operation shown in  FIG.  1 B , for example. During a directional etching operation, a plasma, such as a reactive plasma is formed using a reactive chemistry in the plasma chamber  202 , and an angled ion beam  120  is extracted as a pair of ion beams, as shown. Notably, the processing apparatus  200  includes a beam blocker  232 , disposed adjacent the extraction aperture  208 . The beam blocker  232  is sized and positioned to define a first aperture  208 A and a second aperture  208 B, where the first aperture  208 A forms a first angled ion beam  120 A, and the second aperture  208 B forms a second angled ion beam  120 B. The two angled ion beams may define angles of incidence with respect to the perpendicular  132 , equal in magnitude, opposite in direction. In one embodiment, the first angled ion beam  120 A and the second angled ion beam  120 B may represent an angled reactive ion beam. The beam blocker offset along the Z-axis with respect to extraction plate  206  may help define the angle of the angled ion beams. 
     In particular, as shown in  FIG.  7 A , and with reference to the geometry of  FIGS.  2 A- 2 C , the angled ion beam  120 , forming a non-zero angle of incidence with respect to the Z-axis (normal to the substrate plane), may strike the regions of cavities  106  oriented along the X-Z plane, as noted. As such, the first angled ion beam  120 A and the second angled ion beam  120 B may selectively etch the endwalls  106 A, while not etching the sidewalls  106 B (oriented along the Y-Z plane), and thus selectively elongate of the cavities  106  to generate the elongated structure of cavities  106 , as shown in  FIG.  5 A  to  FIG.  5 C . 
     In the example of  FIG.  7 B , the angled ion beam  120  is provided as a pair of ribbon ion beams that are formed by an elongated extraction aperture, extending to a beam width along the X-direction, where the beam width is adequate to expose an entire width of the substrate  100 , even at the widest part along the X-direction. Exemplary beam widths may be in the range of 10 cm, 20 cm, 30 cm, or more while exemplary beam lengths along the Y-direction may be in the range of 3 mm, 5 mm, 10 mm, or 20 mm. The embodiments are not limited in this context. 
     The angled ion beams  120  may be extracted when a voltage difference is applied using a bias voltage source, shown as bias supply  220 , between the plasma chamber  202  and substrate  100  as in known systems. The bias supply  220  may be coupled to the process chamber  222 , for example, where the process chamber  222  and substrate  100  are held at the same potential. In various embodiments, the angled ion beam  120  may be extracted as a continuous beam or as a pulsed ion beam as in known systems. For example, the bias supply  220  may be configured to supply a voltage difference between plasma chamber  202  and process chamber  222 , as a pulsed DC voltage, where the voltage, pulse frequency, and duty cycle of the pulsed voltage may be independently adjusted from one another. When configured in the shape of a ribbon beam as in  FIG.  7 B , these angled ion beams may expose an entirety of the substrate  100  to reactive ion etching of the cavities  106  distributed in devices across the substrate  100 , by scanning the substrate platen  214  along the scan direction  216 , as shown. 
     In various embodiments, the value of the non-zero angle of incidence may vary from 5 degrees to 85 degrees, while in some embodiments the value may range between 15 degrees and 60 degrees. The embodiments are not limited in this context. The angled ion beam  120  may be composed of any convenient gas mixture, including inert gas, reactive gas, and may be provided in conjunction with other gaseous species in some embodiments. Gas may be provided from a gas source  224 , where the gas source  224  may be a gas manifold coupled to provide a plurality of different gases to the plasma chamber  202 . In particular embodiments, the angled ion beam  120  and other reactive species may be provided as a predetermined etch recipe to the substrate  100  so as to perform a directed reactive ion etching of targeted sidewalls of patterning layers on substrate  100 . As discussed above, the etch recipe may be selective with respect to the material of the layer  114 , so as to remove material of the mask layer  112 , while not etching the layer  114 , or etching the layer  114  to a lesser extent. 
       FIG.  7 C  and  FIG.  7 D  depict a subsequent instance of processing the substrate  100 , generally as discussed above with respect to  FIGS.  4 A- 4 C . In this instance, the processing apparatus  200  generates angled deposition beam  140 , as a first angled deposition beam  140 A and a second angled deposition beam  140 B, using the same extraction geometry as discussed above with respect to  FIGS.  7 A and  7 B . Notably, in this instance, the substrate stage  214  has been rotated through a twist angle of 90 degrees with respect to the configuration of  FIG.  7 A  and  FIG.  7 B . 
     In one implementation, the angled deposition beam  140  may be generated using the same conditions as generating the angled ion beam  120 , discussed above, save for a change in the bias applied between the plasma chamber  202  and the substrate  100 . For example, to generate the angled ion beam  120 , a −500 V bias may be applied between the substrate  100  and plasma chamber  202 , to extract a reactive ion beam having ions with energies in the range of 500 eV for singly charged positive ions. As such, during a reactive ion etching process, the net result of competing processes of etching the mask layer  112  and depositing a polymer film on the mask layer  112 , may be to etch the mask layer  112 , due to the energy of the ions of angled ion beam  120 . In the example of  FIG.  7 C , the angled deposition beam may  140  be generated by reducing the bias between plasma chamber  202  and substrate  100  to a value of −50 V, for example, or 0 V, wherein the energy of any ions present in the angled deposition beam  140  will be much less than in the etching process of  FIG.  7 A , favoring a net deposition due to radicals, and other polymer-forming species in the angled deposition beam  140 . 
     In some embodiments, using processing apparatus  200 , the substrate  100  may be scanned along the Y-direction for at least one scan with a high bias voltage applied, followed by rotating the substrate  100  through 90 degrees about the perpendicular  132  within the X-Y plane, accompanied by reducing the level of or extinguishing the bias voltage, and scanning the substrate  100  along the Y-direction for at least one additional scan. This sequence of operations may be repeated through multiple cycles to selectively etch surface features of a mask layer along a given direction, while avoiding unwanted mask loss, rounding, faceting, and other side effects generated during continuous etching without the use of the angled deposition of the present embodiments. 
     While the embodiments of  FIGS.  7 A- 7 D  depict a single plasma chamber, in other embodiments, two plasma chambers may be provided, wherein a first plasma chamber is used to direct an angled ion beam to the substrate, and a second plasma chamber is used to direct an angled deposition beam to the substrate. The substrate may be transported between positions adjacent the first plasma chamber and second plasma chamber to perform an etch cycle. An advantage of this latter configuration is that the second plasma chamber may be configured with an extraction assembly that directs the deposition beam to the substrate at a different angle of incidence than the angle of incidence used for the angled ion beam, producing increased process flexibility. Additionally, different plasma chemistry may be employed in the deposition beam plasma chamber as opposed to the ion beam plasma chamber, so that a substrate may be processed rapidly by subjecting the substrate to an etch chemistry different than the deposition chemistry, without incurring process delay that may occur to switch chemistry within a common plasma chamber. 
       FIG.  7 E ,  FIG.  7 F , and  FIG.  7 G  depict aspects of another apparatus, according to embodiments of the present disclosure. The apparatus  250  includes a cylindrical plasma chamber, shown as plasma chamber  252 , elongated along the X-axis, and including an elongated aperture, shown as extraction aperture  208 , where the extraction aperture  208  is bounded by a nozzle structure  254  that extends radially outwardly from the plasma chamber  252 . In various non-limiting embodiments, the plasma chamber  252  may be rotatable about the X-axis, the substrate stage  214  may be tiltable about the X-axis, may be scannable along the Y-axis, and rotatable about the Z-axis. As such, the aforementioned operations of directional angled etching and directional angled deposition may be performed by alternately applying a bias voltage between the plasma chamber  252  and substrate stage  214  during a first exposure and removing the bias voltage between substrate stage  214  and plasma chamber  252  during a second exposure, while also rotating the substrate stage  214   90  degrees about the Z-axis between the first exposure and the second exposure. An advantage provided by the apparatus  250  is that the nozzle structure  254  may tend to collimate a deposition beam having neutral radicals that otherwise may tend to diverge after exiting the plasma chamber  252 , thus preserving and improving directionality of a deposition beam used to selectively deposit a protection layer. 
       FIG.  8    depicts the geometry for changing the shape of a patterned feature by combined directional ion beam processing and directional deposition beam processing, according to an embodiment of the disclosure. In this example, directional etching and directional deposition processes may be combined as generally described with respect to  FIGS.  1 A to  5 C , except in this instance a substrate  300  is provided with a mask layer  301  having a series of cavities shaped as vias or circles. By performing the operations of  FIGS.  2 A to  5 C , the cavities  302  may be selectively elongated along the Y-direction to form trenches  304 , where directional etching is interspersed with directional deposition in a direction orthogonal to the directional etching when viewed in the X-Y plane, as shown. As such, rounding or faceting of the trenches  304  may be avoided. 
       FIG.  9    depicts the geometry for generating a composite merged shape by merging multiple patterned features using a combined directional ion beam processing and directional deposition beam processing, according to another embodiment of the disclosure. In this example, directional etching and directional deposition processes may be combined as generally described with respect to  FIGS.  1 A to  5 C , except in this instance a substrate  400  is provided with a mask layer  401  having a series of cavities shaped as trenches  402 , offset from one another in a staggered fashion as shown. By performing the operations of  FIGS.  2 A to  5 C , the trenches  402  may be selectively elongated along the X-direction to form a merged shape  404 , where directional etching is interspersed with directional deposition in a direction orthogonal to the directional etching when viewed in the X-Y plane, as shown. As such, rounding or faceting of mask surfaces during formation of the merged shape  404  may be avoided. 
       FIG.  10    depicts an exemplary process flow  500 , according to one embodiment of the disclosure. At block  502 , a set of features is provided in a mask layer. A given feature of the set of features may be characterized by a first dimension along a first direction. In one example a cavity formed in a mask layer may have a first length along a given direction. 
     At block  504 , an angled ion beam is directed to a first side region of the set of features during a first exposure. The first side region may constitute an endwall of a cavity according to various embodiments. As such, the first side region is etched a first amount along the first direction. 
     At block  506 , an angled deposition beam is directed to a second side region of the set of features in a second exposure, where the second side region being is oriented perpendicularly with respect to the first side region. For example, the second side region may constitute an upper portion of sidewalls of a cavity whose endwalls are etched in the operation of block  404 . As such, a protective layer is formed on the second side region. 
     At block  508  an angled ion beam is directed to the first side region in a third exposure, wherein the first side region is etched an additional amount along the first direction. 
     The flow then proceeds to decision block  510 , where a determination is made as to whether a final or target dimension is reached. If so, the flow proceeds to block  512 , where the mask layer is used to etch a subjacent layer, If not, the flow returns to block  506 . 
     Notably, in the aforementioned embodiments, examples of using a common plasma chamber and a common plasma chemistry have been detailed. However, in other embodiments, a different chamber may be used to provide a deposition beam to a substrate. For added flexibility, a reactive etching ion beam could be provided using a CFx etch chemistry, while a deposition beam is provided with a different chemistry to deposit, for example, a C, SiO 2 , SiN, or other material. While adding flexibility, this approach may entail switching of gases provided to a plasma chamber, between rotations, and would add to process time. 
     Moreover, while the aforementioned embodiments illustrate the iterative use of angled ion beam etching and angled ion beam deposition, with the used of substrate rotation between etching and deposition, the relative amount of etching or deposition within a given operation may depend upon the application, where, for a given mask layer, and subjacent layer, experimentation may be used to determine the balance between deposition and erosion for each iteration or cycle of deposition and etch. For instance there could be one substrate scan for deposition performed for every ten etching scans, or the reverse where one etching scan is performed for every 10 deposition scans, depending on the etch chemistry, ion bias, etc. 
     The present embodiments provide various advantages over conventional processing to define features in a substrate. One advantage lies in the ability to selectively elongate a cavity along just one direction, while preserving the dimension of the cavity along a second direction, perpendicular to the first direction. Another advantage is the ability to reduce cavities below the spacing achieved by known lithography processes. An example of this ability is the reduction of tip-to-tip separation between adjacent trenches such as contact trenches. Another advantage provided by the present embodiments is the ability to prevent undue thickness loss of a hardmask and reduce corner rounding in a cavity formed in the hardmask layer, while still selectively elongating the cavity along a targeted direction. A further advantage is the ability to reduce the number of masks used to generate a pattern of features, where the features may be separated by a distance less than the threshold separation achievable by a single mask. This reducing the number of masks has the further advantageous effect of reducing overlay error for printing the pattern of features. 
     The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are in the tended to fall within the scope of the present disclosure. Furthermore, the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, while those of ordinary skill in the art will recognize the usefulness is not limited thereto and the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Thus, the claims set forth below are to be construed in view of the full breadth and spirit of the present disclosure as described herein.