Patent Publication Number: US-11031247-B2

Title: Method and apparatus for depositing a monolayer on a three dimensional structure

Description:
This application is a divisional of, and claims the benefit of priority to, U.S. patent application Ser. No. 14/324,907, filed Jul. 7, 2014, entitled “Method and Apparatus for Depositing a Monolayer on a Three Dimensional Structure,” which application is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present embodiments relate to substrate processing, and more particularly, to processing apparatus and methods for depositing layers by atomic beam or molecular beam deposition. 
     BACKGROUND 
     Many devices including electronic transistors may have three dimensional shapes that are difficult to process using conventional techniques. The topology of such devices may be up-side down, re-entrant, over-hanging, or vertical with respect to a substrate plane of a substrate in which such devices are formed. In order to process such devices such as to grow layers on such topology, improved techniques may be useful that overcome limitations of conventional processing. For example, doping of substrates is often performed by ion implantation in which substrate surfaces that may be effectively exposed to dopant ions are limited by line-of-site trajectories of the ions. Accordingly, vertical surfaces, re-entrant surfaces, or over-hanging surfaces may be inaccessible to such dopant ions. It is with respect to these and other considerations that the present improvements have been needed. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended as an aid in determining the scope of the claimed subject matter. 
     In one embodiment a processing apparatus may include a plasma chamber configured to generate a plasma; a process chamber adjacent the plasma chamber and configured to house a substrate that defines a substrate plane; an extraction system adjacent the plasma chamber and configured to direct an ion beam from the plasma to the substrate, the ion beam comprising ions that form a non-zero angle with respect to a perpendicular to the substrate plane; and a molecular chamber adjacent the process chamber, isolated from the plasma chamber and configured to deliver a molecular beam to the substrate, wherein the ion beam and molecular beam are alternately delivered to the substrate to form a monolayer comprising species from the ion beam and molecular beam. 
     In a further embodiment a method may include providing a substrate in a first position, the substrate having a surface that defines a substrate plane and a substrate feature that extends from the substrate plane, the substrate feature having at least one surface that extends at a non-zero angle with respect to the substrate plane; directing an ion beam through an extraction system adjacent the substrate while in the first position, the ion beam comprising angled ions that are incident on the substrate at a non-zero angle with respect to a perpendicular to the substrate plane, the ion beam effective to form a first sub-monolayer comprising a first species on the substrate feature including the at least one surface; and directing a molecular beam to the substrate when the substrate is in a second position when the first sub-monolayer is disposed on the substrate feature, the molecular beam being effective to form a second sub-monolayer of a second species that is configured to react with the first sub-monolayer of the first species to form a monolayer of a product material on the substrate feature including the at least one surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  depicts a side view of a processing apparatus in one mode of operation for delivering ion beams to a substrate according to embodiments of the disclosure; 
         FIG. 1B  depicts the processing apparatus of  FIG. 1A  in another operation mode for delivering a molecular beam to a substrate; 
         FIG. 1C  depicts a close-up of the operation of  FIG. 1A ; 
         FIG. 1D  depicts a close-up of the operation of  FIG. 1B ; 
         FIG. 2A  depicts a top plan view of a processing system according to additional embodiments of the present disclosure; 
         FIG. 2B  depicts a top plan view of an exemplary substrate stage that may be implemented in the processing system of  FIG. 2A ; 
         FIG. 3  depicts an exploded isometric view of a processing apparatus according to embodiments of the disclosure; 
         FIG. 4A  to  FIG. 4F  depict an embodiment of the disclosure that details exemplary operations involved in a method for forming a multi-layer stack on three dimensional features using monolayer-by-monolayer growth; 
         FIG. 5A  to  FIG. 5D  depict details of a method for performing monolayer doping on a three dimensional structure according to embodiments of the disclosure; and 
         FIG. 6  provides a summary of representative conformal layers, ion beam constituents, and molecular beam constituents consistent with different embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present embodiments are related to apparatus and techniques for processing a substrate including forming thin layers on surface features of a substrate. The surface features of the substrate may extend from a substrate plane, and may form such structures as three dimensional lines, fins, pads, pillars, walls, trenches, holes, domes, bridges, cantilevers, other suspended structures, and the like. The embodiments are not limited in this context. Moreover, these features may be collectively or individually referred to herein as a “three dimensional” feature or features. A thin layer that is formed on a substrate feature may be a layer provided for doping, insulation, for encapsulation, or for other purposes. 
     In various embodiments, novel apparatus and systems are presented that facilitate growth and etching of thin layers on three dimensional features of a substrate. The apparatus of the present embodiments may apply multiple processes to carry out doping of a three dimensional feature. Included among these processes are a modified atomic layer deposition or by modified molecular layer deposition process, which techniques may share characteristics common to conventional atomic layer deposition (ALD) or conventional molecular layer deposition (MLD) except where otherwise noted. The present embodiments provide novel improvements over conventional ALD and MLD that facilitate formation on three dimensional surface features in which surface topography may be severe, such as that described above. 
     In some embodiments, processes that involve formation of a doping layer using ALD or MLD, may include a series of operations that form multiple layers on substrates that may include three dimensional features. In addition, the formation of each layer may involve multiple operations such as those characteristic of an ALD or MLD process. In one implementation for doping a substrate using a deposited layer formed by ALD or MLD, a surface of the substrate feature may first be cleaned to remove native oxide, which may involve providing a plasma using such species as hydrogen, oxygen, and/or ammonia radicals and molecular hydrides such nitrogen triflouride, arsine, and phosphine. 
     Secondly, a conformal plasma enhanced atomic layer deposition of dopant oxides may be performed to form a dopant oxide layer on a surface feature. This ALD process may involve deposition of species that include arsenic, boron, phosphorus, arsenic oxide, phosphorus oxide, boron oxides and/or doped silicon oxides such as silicon arsenic oxide, silicon phosphorus oxide, and silicon boron oxides. In particular, these oxides may be deposited using molecular precursors such as arsine, phosphine, and diborane together with plasma-generated atomic beams that contain a reactive gas such as hydrogen, oxygen, nitrogen, and/or ammonia. 
     In a subsequent operation, a sealing or encapsulating layer such as silicon nitride may be deposited using a combination of a molecular beam containing silane, for example, and another beam containing nitrogen, hydrogen, and/or ammonia. Once the native oxide is removed from a substrate feature to be doped and the dual layer of dopant oxide and sealing nitride is deposited dopants from the dopant oxide layer may be driven into the substrate feature using a known technique such as rapid thermal annealing. 
     In various embodiments of the disclosure, a layer or plurality of layers may be deposited on a substrate or etched from a substrate using a combination of angled ions and molecular beams, where the molecular beams may comprise undissociated molecules in some implementations. The directing of angled ions may be used in conjunction with other operations to create novel ALD or MLD processes that grow a layer or plurality of layers on a three dimensional substrate feature without the use of a mask. As used herein, unless otherwise noted or qualified by the context, the term “layer” may refer to a sub-monolayer, a monolayer of a material, or may refer to a thin coating or film that has the thickness of many monolayers. Thus, in some instances, a grown “layer” may be composed of a single monolayer that is formed over target portions of a substrate or may be composed of multiple monolayers. Moreover, consistent with various embodiments of the disclosure, a layer that has the thickness of many monolayers may be formed in a monolayer-by-monolayer-by-monolayer fashion as in conventional ALD or MLD processes. However, the present embodiments also cover growth of layers having the thickness of multiple monolayers in which a layer is not grown in a monolayer-by-monolayer fashion. 
     In various embodiments, novel multichamber apparatus and systems are disclosed that facilitate rapid processing of substrates using a combination of angled ions and molecular beams. These apparatus may in particular minimize cross-contamination between different sources of ions or molecules used to process a substrate. 
     Formation of a layer comprising a product material by an ALD or MLD process may involve deposition of one monolayer at a time of the product material. Each monolayer of the product material may include two or more different elements that together form a compound material, an alloy, or other multielement material such as silicon oxide, silicon nitride, doped oxides, or other material. The formation of a given monolayer may be accomplished by deposition of a sub-monolayer of a first species or component followed by providing a second sub-monolayer of a second species that reacts with the first sub-monolayer to form a monolayer of the compound. Thus, as used herein the term “sub-monolayer” may denote a layer of a first element that may react with a layer of a second element to form a monolayer of the compound. For example, during deposition of a binary compound such as silicon oxide the layer to be formed is deposited by the repetition of two different half-cycles. After each half-cycle, a fixed amount of reactive species supplied by a first precursor remains on the substrate surface. Ideally, though not necessarily, a single monolayer of a first species may be produced after a first half cycle. In the present context, this single monolayer of a first species of a compound to be formed is referred to as a “sub-monolayer” because the full monolayer of the compound requires the addition of second species to react with the first species. Thus, atoms of the sub-monolayer of first species may be reacted with atoms or molecules of the second species supplied in the next half cycle. In each half-cycle, subsequent to supplying a given species, a purge can be performed to remove any unreacted species of the depositing material. The total amount of material reacted in a cycle may thus be equivalent to a sub-monolayer of each of the first species or second species. 
     The present embodiments provide novel apparatus that are effective to fabricate layers, films or coatings in a monolayer-by-monolayer fashion, including on three dimensional structures, in a manner that may provide more uniform layer thickness over different surfaces of a three dimensional structure as compared to that achieved by conventional ALD processes. 
       FIG. 1A  depicts a processing apparatus  100  arranged according to various embodiments of the disclosure. The processing apparatus  100  may be employed in particular to grow or etch a layer employed to etch and deposit multiple different materials on a three dimensional structure. As detailed below, this capability may be particularly suitable to perform a novel doping process for doping of a three dimensional structure that may entail deposition of multiple materials as well as etching of at least one layer. In turn, the deposition of each material may entail multiple operations that are performed using a combination of ion beams containing angled ions as well as molecular beams. 
     As shown in  FIG. 1A  the processing apparatus  100  may include a plasma chamber  102  that may be used to generate angled ions to be provided to a substrate  124 , which is held or supported by the substrate stage  111  as shown. As further shown in  FIG. 1A , the processing apparatus  100  includes a process chamber  106  that is adjacent the plasma chamber  102  and in communication with the plasma chamber  102 . In operation, the plasma chamber  102  may deliver angled ions to the substrate  124  in the form of an ion beam  122  when the substrate  124  is disposed adjacent the plasma chamber  102 . The use of angled ions is discussed in more detail below. However, in brief, the term “angled ions” as used herein refers to an assemblage of ions such as ions in an ion beam, at least some of which are characterized by trajectories that have a non-zero angle of incidence with respect to a perpendicular to a plane P of substrate  124 , as illustrated in  FIG. 1C . For example, with reference to the Cartesian coordinate system shown, angled ions may have trajectories that form a non-zero angle with respect to the Z-axis. 
     The processing apparatus  100  also includes a plasma source  114 , which may include a power supply and applicator or electrode to generate a plasma according to known techniques. For example, the plasma source  114 , in various embodiments, may be an in situ source or remote source, an inductively coupled plasma source, capacitively coupled plasma source, helicon source, microwave source, arc source, or any other type of plasma source. The embodiments are not limited in this context. When gas is supplied by gas source  116  to the plasma chamber  102  the plasma source  114  may ignite a plasma that provides angled ions to the substrate  124  as discussed below. In some embodiments, such as apparatus that uses an inductively coupled source, the angled ions may be formed from molecular species such as oxygen or nitrogen, and may be highly fractionated such that the angled ions are predominantly atomic ions. However, the embodiments are not limited in this context. The processing apparatus also may include a bypass  119  so that gas from the gas source  116  is fed directly to the process chamber  106 . This may be used when the substrate  124  is heated by a heater  125  to a higher temperature such as 400-700° C. Under such circumstances gas such as nitrogen, ammonia, or oxygen may react with a substrate without being ionized. 
     In various embodiments, the gas pressure in a process chamber such as the process chamber  106  may be maintained below 50 mTorr in order to minimize or eliminate gas phase collisions of ions in the ion beam  122  before the ions strike the substrate  124 . This allows the angle of ions that are extracted from the plasma chamber to be controlled and maintained so that angle(s) of incidence of ions in an ion beam directed to the substrate  124  may be tailored for a desired result. As discussed in more detail, in various embodiments the substrate  124  may be scanned parallel to Y-axis with respect to the plasma chamber  102  either in a single direction, or back and forth, in order to provide uniform deposition of a layer or etching of a layer over an entire substrate, such as substrate  124 . 
     As further shown in  FIG. 1A , the processing apparatus  100  includes a molecular chamber  104 . The molecular chamber  104  may transport, for example, molecular gas that is received from a molecular source  118 . The molecular chamber  104  may provide the molecular gas to the substrate  124  in the form of a molecular beam  128  for reaction with species such as angled ions provided by the plasma chamber  102 . As further illustrated in  FIG. 1B , the substrate stage  111  may be movable in a manner that transports the substrate  124  from a first position adjacent the plasma chamber  102  ( FIG. 1A ) to a second position adjacent the molecular chamber  104 . 
     In some embodiments, and as illustrated in  FIG. 1A , a baffle or wall  112  may be provided in the process chamber  106 , which may divide the process chamber  106  into a sub-chamber  108  adjacent the plasma chamber  102  and sub-chamber  110  adjacent the molecular chamber  104 . The substrate stage  111  may be configured to engage the wall  112  such that the substrate stage  111  and wall  112  isolate sub-chamber  110  from the sub-chamber  108 . In some implementations a small gap may remain between the wall  112  and the substrate stage  111 . However, the wall  112  may be hollow such that the wall  112  may be differentially pumped by a pump (not shown) to evacuate gas  115  as illustrated. This gas may be either species from the plasma chamber  102  that are present in sub-chamber  108  when the substrate  124  is exposed to the ion beam  122 , or species that are present in the sub-chamber  110  when the substrate is exposed to the molecular beam  128 . The wall  112  may accordingly prevent unwanted deposition by blocking flow of molecular species such as SiH 4 , AsH 3 , and the like, from sub-chamber  110  into sub-chamber  108 . The wall  112  may also prevent plasma formed by the plasma chamber  102  from extending into the sub-chamber  110 , 
     In one implementation the substrate stage  111  may be movable back and forth between the positions shown in  FIGS. 1A and 1B  such that the substrate  124  may be exposed multiple times to the ion beam  122  and molecular beam  128 . This provides an efficient manner to deposit a monolayer or plurality of monolayers of a desired material on a three dimensional substrate. 
       FIG. 1C  depicts a close-up of certain components shown during the operation in  FIG. 1A  in which an ion beam  122  is directed to the substrate  124 , while  FIG. 1D  depicts a close-up of the operation of  FIG. 1B  in which the molecular beam  128  is provided to the substrate  124 . As shown in  FIG. 1B , the processing apparatus  100  includes an extraction plate  120  containing an extraction aperture  126  that provides a path for ions in the plasma chamber  102  to traverse to the sub-chamber  108 . In the instance shown in  FIG. 1C , a plasma  130  is present in the plasma chamber  102 . When a voltage supply  148  (shown in  FIG. 1A ) provides an extraction voltage between the plasma chamber  102  and substrate stage  111 , the ion beam  122  may be extracted from the plasma  130  and accelerated to the substrate  124 . In some instances an extraction voltage between 0 and 500 V may be applied to impart energy to ions of the ion beam  122  sufficient to generate surface reactions including attachment of ion species on a substrate surface, but below an energy in which significant sub-surface ion implantation takes place. 
     As shown in  FIG. 1C , the substrate  124  may be provided with three dimensional features such as substrate features  132 . Notably, the various components may not be drawn to scale, particularly in the illustration of  FIG. 1C . For example, features such as the extraction aperture  126  may have dimensions on the order of millimeters or centimeters, while the substrate features  132  may have dimensions on the order of micrometers or nanometers in some cases. As further shown in  FIG. 1C , the extraction aperture  126  may cause the plasma sheath boundary  140  to assume a curved shape adjacent the extraction aperture, which may result in ions of the ion beam  122  exiting the plasma  130  with trajectories that are spread over a range of angles of incidence. The ion beam  122  may in particular include angled ions that are effective to treat the different surfaces of the substrate features  132 , including sidewalls of the substrate features  132 , which may extend at an angle relative the substrate plane P. Such sidewalls may not be effectively treated by ions that are directed along the perpendicular to the substrate plane P. 
     It is to be noted that although the ion beam  122  is shown in  FIG. 1C  as having three trajectories the ion beam may be characterized by an ion angular distribution. The term “ion angular distribution” refers to the mean angle of incidence of ions in an ion beam with respect to a reference direction such as a perpendicular to a substrate, as well as to the width of distribution or range of angles of incidence centered on the mean angle, termed “angular spread” for short. In some examples, the ion angular distribution may be a single mode in which the peak in number of ions as a function of incidence angle is centered on a perpendicular to the plane P. In other examples, the ion angular distribution may involve a mean angle that forms a non-zero angle with respect to a perpendicular to the plane P of the substrate  124 . In particular examples, the ion angular distribution of ion beam  122  may be a bimodal distribution of angles of incidence. For example, the ion beam  122  may have trajectories where the greatest number of trajectories are centered at two angular modes. In various embodiments, by controlling apparatus settings such as plasma power, plasma chamber pressure, and so forth, the separation between peaks of a bimodal distribution may be varied. For example, the peak angles may set at angles between +/−15 degrees with respect to perpendicular to +/−45 degrees with respect to perpendicular in various embodiments, and in one particular embodiment at +/−30 degrees with respect to perpendicular to the plane P. In some implementations a beam blocker (not shown) may be positioned inside a plasma chamber adjacent an extraction aperture, which may have the effect of creating a pair of angled ion beams that may constitute a bimodal distribution of ions. 
     Referring also to  FIGS. 1A and 1B  it is further to be noted that the extraction aperture  126  may be elongated in the X-direction to cover an entire substrate, such as substrate  124 , in that direction. Accordingly, the ion beam  122  may be directed over the entire substrate to provide uniform ion flux to the substrate by scanning the substrate stage  111 , for example, in a continuous manner along the Y-direction while the substrate  124  is adjacent the extraction aperture  126 . Moreover, once the substrate  124  is located in the sub-chamber  110  and adjacent the molecular chamber  104 , the molecular beam  128  may in some implementations be sufficiently large that the entire substrate  124  may remain stationary and still be exposed to uniform molecular flux. 
     In some examples, the ion beam  122  may be composed of reactive ions such as atomic oxygen or atomic nitrogen ions. In other examples, the ion beam  122  may be composed molecular oxygen ions or molecular nitrogen ions, or may be composed of mixtures of atomic oxygen ions and molecular oxygen ions, or mixtures or molecular nitrogen ions and atomic nitrogen ions. The embodiments are not limited in this context. 
     As shown in  FIG. 1C  the ion beam  122  may be effective to generate a sub-monolayer  134  that covers the three dimensional surfaces of the substrate  124  including the substrate features  132 . In various implementations the exact ion angular distribution of the ion beam  122  may be adjusted by adjusting any combination of the aforementioned parameters such as plasma power, gas pressure, extraction voltage, aperture size, or other parameters. This may be useful to tailor the treatment of surfaces such as sidewalls  144 , trench bottoms  142 , or other parts of a three dimensional feature in order to ensure proper exposure of those surface to ions of the ion beam  122 . This may result in deposition of a uniform sub-monolayer, shown as the sub-monolayer  134 . 
     Turning now to  FIG. 1D  there are shown details of a gas plate  129  that is disposed between the molecular chamber  104  and sub-chamber  110 . The gas plate  129  may include multiple apertures  136  that allow gas to stream out of the molecular chamber  104  and form the molecular beam  128 . The molecular beam  128  may include molecular species that are effective to react with the sub-monolayer  134  to form a product monolayer, shown as the monolayer  138  as shown. Together, the sequence of operations shown in  FIGS. 1B and 1D  may constitute a process cycle that is used to form a layer of a material, such as a conformal monolayer of a nitride or a dopant oxide on a three dimensional feature. In implementations for doping of a substrate, for example, this sequence of operations may be repeated a desired number of times to deposit multiple monolayers according to the target level of doping and depth of dopants. However, in some embodiments a single monolayer of dopant oxide may be sufficient to generate a target doping profile in a substrate. 
       FIG. 2A  depicts a processing system  200  arranged according to further embodiments of the disclosure. The processing system  200  may be employed for high throughput processing of substrates having three dimensional features including ALD or MLD type processes. The processing system  200  includes a load station  210 , which may be used to load substrates  224  for processing in various stations or apparatus within the processing system  200 , which may take place under vacuum conditions. After loading in the load station  210 , the substrates  224  may be transferred by a robot  222  in a transfer chamber  220  to a preclean station  230 . The preclean station  230  may include at least one plasma chamber, shown as plasma chamber  232 , which may be configured similarly to the plasma chamber  102 . In particular, the plasma chamber  232  may direct angled ions such as nitrogen ions to clean surfaces of a substrate  224  including three dimensional features. In the case in which the substrate is a semiconductor material, this may be effective in removing oxide from the surface. In addition, substrates  224  may be heated to drive off other impurities. 
     The processing system  200  further includes a rotary chamber assembly  240  which may process the substrates  224  through multiple operations. The rotary chamber assembly  240  may perform a combined molecular and atomic beam deposition (MABD) processes that entails exposure to both angled ions from an ion beam and a molecular beam. The angled ions and molecular beam may be provided to a substrate in a manner similarly to that depicted in  FIGS. 1A to 1D  except as otherwise noted. As illustrated in  FIG. 2 , the rotary chamber assembly  240  may include a plurality of plasma chambers, shown as plasma chambers  242  that may be disposed around an axis A that lies parallel to the Z-axis as shown. The plasma chambers  242  may be configured to generate the same type of ions as one another or different ions according to alternative implementations. 
     From the perspective of  FIG. 2A , ions that form in the plasma chambers  242  may be extracted through extraction apertures  244  and directed toward substrates that lie below the extraction apertures  244  (into the page). The extraction apertures  244  may be elongated and may additionally be aligned such that their long axes lie along the radii R that extend from the center of the rotary chamber assembly  240 . As noted previously, the gas pressure in a chamber or region that houses substrates may be maintained below 50 mTorr to avoid gas phase collisions of ions that are directed through the extraction apertures  244  to a substrate, which allows the ion angular distribution generated by the extraction aperture  244  to be maintained when the ions impact a substrate. 
       FIG. 2B  depicts a top plan view of an exemplary substrate stage, shown as substrate stage  260 , that may be implemented in the processing system  200  of  FIG. 2A . The substrate stage  260  may include a plurality of recesses  262  configured to hold a plurality of substrates  224 . As also shown in  FIG. 2B , the substrate stage  260  may be configured to rotate around the axis A such that a substrate  224  may be rotatably scanned under an extraction aperture  244 . In this manner, an entire substrate may be sequentially exposed to angled ions from a narrow ion beam that is received from a plasma chamber  242 , even though the extraction aperture  244  (see  FIG. 2A ) and ion beam may be much narrower than a diameter of the substrate  224  in the direction perpendicular to R. 
     As further shown in  FIG. 2A , the rotary chamber assembly  240  may include a plurality of injectors or gas apertures  246  that may also extend radially from a center of the rotary chamber assembly. These gas apertures  246  may provide narrow molecular beams to a substrate  224  as the substrate is scanned under a given gas aperture  246 . In various embodiments, the molecular beams may include such materials as beam composed of silane (SiH 4 ), arsine (AsH 3 ), phosphine (PH 3 ), or diborane (B 2 H 6 ), which are configured to cover a surface of the substrates  224  and react with species provided by the plasma chamber(s)  242 . 
       FIG. 2A  additionally illustrates an embodiment in which the gas apertures  246  and extraction apertures  244  are wedge shaped such that a gas aperture  246  or extraction aperture  244  is wider at larger radial distances from a center of the rotary chamber assembly  240 . This allows the rotary chamber assembly  240  to deliver a more uniform flux of molecules or angled ions across different portions of a substrate  224  regardless of their radial position when the substrate  224  is rotated under a given extraction aperture  244  or gas aperture  246 . 
     As further depicted in  FIG. 2A , the processing system  200  includes an annealing station  250  which may perform annealing of substrates  224  after the substrates  224  are coated with one or more desired layers. 
       FIG. 3  depicts a variant of a rotary chamber assembly  302  according to various additional embodiments of the disclosure. The rotary chamber assembly  302  includes a source assembly  304  that contains a plurality of different sources. For simplicity, the sources are shown as simple three dimensional wedge shapes. The sources of source assembly  304  may represent at least one plasma chamber and molecular chamber. In some embodiments, a plasma chamber may be disposed adjacent a molecular chamber. For example, source  306  may be a plasma chamber and source  308  may be a molecular chamber, and so forth. 
     As further shown in  FIG. 3 , the rotary chamber assembly  302  includes a top plate  310 , which may support the source assembly  304 , and may include a plurality of apertures  312  that provide communication from a given source to a substrate below. Apertures in the top plate  310  that are coupled to a plasma chamber may be configured to generate angled ions as described above. 
     As also shown in  FIG. 3 , the top plate  310  is configured to engage a bottom plate  330 . When assembled the top plate  310  and bottom plate  330  may define a process chamber. A rotary substrate stage  320  is provided that is configured to rotate around the Z-axis with respect to the top plate  310  and source assembly  304 . The rotary substrate stage  320  may include a plurality of individual substrate holders, shown as the substrate holders  322 , which may be used to hold substrates  326 . In this manner, when the rotary substrate stage rotates, the substrates  326  may be scanned under plasma chamber(s) and molecular chamber(s) to generate a monolayer-by-monolayer deposition, in one example. The substrate holders  322  may be clamping chucks or electrostatic chucks, and may additionally be equipped with heating capability in some embodiments. For example, the substrate holders  322  may be heated to at least 300° C. in some instances. These substrate holders  322  may be slightly recessed below other portions of the rotary substrate stage  320 . 
     The rotary substrate stage  320  may also be equipped with pumping slots  324 , which may be disposed adjacent to substrate holders  322  as shown. The pumping slots  324  may provide a pumping path for pumping apparatus (not shown) to evacuate gas species received at an individual substrate holder  322  to provide isolation between substrates receiving plasma (ion) treatment and those receiving molecular gas exposure. This may be aided by the recessed position of the substrate holders  322 . In particular, the entrance of pumping slots  324  may be raised with respect to a plane of the substrate holders  322 , which may form a differentially pumped wall that is adjacent a given substrate holder  322 . 
     As noted above, the apparatus of the present embodiments may generate novel deposition techniques that provide improved processing of substrates having three dimensional structures to be processed. Although atomic layer deposition processes have been employed previously, the present embodiments provide advantages over conventional apparatus, which may not be ideally suited for treating substrates having surfaces features that include vertical or reentrant sidewalls, deep trenches, or other severe topology. By maintaining low pressure adjacent a substrate that is below, for example, 50 mTorr, angled ions may be extracted and delivered in a collisionless ion beam to a substrate over a desired angular ion distribution. For applications that entail ALD/MLD to deposit films for doping three dimensional features, various embodiments employ at least one operation that is configured to tailor the angle(s) of incidence of ions provided to a substrate to be coated. This allows a three dimensional substrate feature to be more uniformly coated with a sub-monolayer of a given species using angled ions to provide the given species to the substrate feature. 
       FIG. 4A  to  FIG. 4F  depict an embodiment of the disclosure that details exemplary operations involved in a method for forming a multi-layer stack on three dimensional features using monolayer-by-monolayer growth. 
     In  FIG. 4A  there is shown a substrate  402  that includes a plurality of substrate features  404  that extend above a plane P of the substrate  402 . In one example, the substrate features  404  may be fins of a finFET device to be fabricated. The substrate features  404  may have a surface layer  406 , which may be a native oxide or chemical oxide composed predominantly of silicon oxide, which is to be removed before substrate doping is performed. 
     In a subsequent set of operations shown in  FIG. 4B , the substrate  402  is treated to remove the surface layer  406 . In particular, the substrate  402  may be scanned back and forth to receive alternate exposure from an ion beam  416  that may be extracted from the plasma chamber  102 , and a molecular beam  418  that may be provided by the molecular chamber  104 . In particular implementations, the ion beam  416  may contain atomic nitrogen and hydrogen ions that are created when from ammonia gas (NH 3 ) is provided to the plasma chamber  102 . The molecular beam  418  may comprise a beam of nitrogen triflouride (NF 3 ) which is activated to remove the native oxide layer, surface layer  406 , by the presence of a sub-monolayer (not shown) of atomic hydrogen received in the ion beam  416 . 
     Turning now to  FIG. 4C  there is shown a further instance in which the substrate  402  is treated to form a dopant layer or dopant oxide layer, shown as layer  420 . In particular, the substrate  402  may be scanned back and forth to receive alternate exposure from an ion beam  422  that may be extracted from the plasma chamber  102 , and a molecular beam  424  that may be provided by the molecular chamber  104 . In a first operation, a hydrogen, ammonia, or nitrogen/hydrogen plasma may be generated in the plasma chamber  102 , which is used to form the ion beam  422 . In particular, the ion beam  422  supplies atomic hydrogen angled ions to the substrate  402 . The substrate  402  is moved back and forth to alternately expose it to the ion beam  422  and molecular beam  424 , which may be composed of silane (SiH 4 ), arsine (AsH 3 ), phosphine (PH 3 ), diborane B 2 H 6 , or other molecular gases, depending upon the type of dopant oxide layer to be formed. The molecular gase(s) may be effective to react with the atomic hydrogen to form a monolayer of a given material such as a semiconductor dopant. 
     In one particular example, the alternate exposures to the ion beam  416  and molecular beam  418  deposit a layer of arsenic material that is formed in a monolayer-by-monolayer fashion, and is highly conformal on the substrate features  404 . This may be represented by the layer  420  shown in  FIG. 4C . Depending upon whether oxygen is supplied in addition to or instead of hydrogen in the plasma chamber  102  to form the ion beam  416 , the layer  420  may be a dopant oxide layer. As noted above, the operations outlined in  FIG. 4C  may be accelerated and modified by the use of a pulsed DC or continuous substrate bias. 
     Moreover, by adjusting the gas flows, movement rate of substrate  402 , beam angle, gas pressure, substrate temperature, and other parameters, a wide range of composition may be imparted into a doped oxide film represented by the layer  420 . The composition of the layer  420  may range, for example, from pure arsenic oxide, to silicon oxide doped with arsenic, to pure silicon oxide. In addition multi-layers and gradients of doped nitrides oxides may be deposited in a similar fashion. Because angled ions may be tailored according to the geometry of the substrate features  404 , such dopant layers can be deposited with a high degree of uniformity and control on different surfaces of the substrate features  404 . 
     Turning now to  FIG. 4D , there is shown a further instance in which the substrate  402  is treated to form a silicon nitride layer that may act as a sealing layer on top of the layer  420 . This is shown as the sealing layer  426 . This layer may help drive dopants from the layer  420  into the substrate  402 . A nitrogen, ammonia, or nitrogen/hydrogen plasma may be created in the plasma chamber  102  to form an ion beam  422  that contains nitrogen ions including atomic nitrogen, which impinges on the substrate  402 . Silane or a similar gas may be introduced without plasma power in the molecular chamber  104 , to generate a molecular beam  430 . The substrate  402  may then be moved back and forth under the atomic nitrogen beam, that is, ion beam  428 , and the molecular beam  430  to form the sealing layer  426 . In particular, the substrate  402  may be scanned back and forth to receive alternate exposure from the ion beam  428  that may be extracted from the plasma chamber  102 , and a molecular beam  430  that may be provided by the molecular chamber  104 . As with the formation of a dopant oxide layer in  FIG. 4C , the uniformity of the deposition of the sealing layer  426  may be enhanced by adjusting the angle(s) of incidence of the ion beam  428  so as to enhance the deposition rate on the sidewalls  429  (see  FIG. 4B ). 
     In a subsequent operation, the substrate  402  may be exposed to a heat source  440  that provides heat  442  to the substrate. The heat source  440  may be a lamp system or other system that is effective to anneal the substrate to a desired temperature. The heat source  440  acts to drive in dopants from the layer  420  into the substrate features  404 . Subsequently the layer  420  and the sealing layer  426  may be removed, for example, by known wet chemical processing using HF, buffered oxide etch (BOE), hot phosphoric acid, or other chemistries. This results in a doped three dimensional structure composed of the substrate features  404  in which a three dimensional dopant layer  444  is formed, which may be of uniform thickness on different surfaces of the substrate features  404  as shown. 
       FIG. 5A  to  FIG. 5D  depict details of a method for performing monolayer doping on a three dimensional structure according to embodiments of the disclosure. In  FIG. 5A  there is shown an example of a substrate  500  that includes a layer stack that can be conformally deposited over severe and/or reentrant topology that may be presented by substrate features to be coated. In one example, a base layer  510  may represent a silicon substrate upon which a three dimensional transistor or other structure is to be formed. A layer stack may be formed on the silicon substrate, base layer  510 , where the layer stack is composed of a lightly doped p− silicon boron oxide layer  508 , an undoped silicon oxide layer  506 , a heavily doped n +  silicon arsenic oxide layer  504 , and a silicon nitride capping layer  502 . Instead of the oxide layers, in other embodiments it is also possible to deposit layers of pure boron, phosphorus, and arsenic. 
     Turning now to  FIG. 5B , there is shown the structure of a layer stack  520  formed after a Rapid Thermal Anneal (RTA) process is performed on the substrate  500  of  FIG. 5A . An n +  layer  522  is formed with arsenic doping at the top region of the original base layer, base layer  510 , and a graded lightly boron doped region, p −  layer  524 , is created underneath the n +  layer  522 . Separation of arsenic from a boron layer may be aided by the slower solid state diffusion rate of arsenic within the base layer  510 . In a subsequent operation shown in  FIG. 5C , the oxide and nitride layers are removed, such that a n + /p junction is retained in the substrate at the interface of the n +  layer  522  and p −  layer  524 . This junction can be uniformly created over difficult topology as shown in  FIG. 5D , including the sidewalls  532  and trench bottom  534  of the substrate structure  530 . This is not possible using other conventional techniques such as conventional ion implantation. 
       FIG. 6  provides a summary of representative conformal layers  602 , ion beam constituents  604 , and molecular beam constituents  606  that may be used to deposit the conformal layers consistent with different embodiments of the disclosure. 
     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 intended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Accordingly, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.