Patent Publication Number: US-2023154745-A1

Title: Cyclic Low Temperature Film Growth Processes

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. application Ser. No. 17/026,168, filed on Sep. 19, 2020, which application is hereby incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to low temperature film growth processes, and, in particular embodiments, to methods and apparatuses for film growth processes performed cyclically at low temperature. 
     BACKGROUND 
     Device formation within microelectronic workpieces may involve a series of manufacturing techniques including formation, patterning, and removal of a number of layers of material on a substrate. Film formation processes are essential during device formation and may be deposited and/or grown on a substrate surface. For example, film growth processes typically utilize a material in the substrate (e.g. an exposed surface) as a component of the film and/or as a seed region for crystal growth. 
     Nitride materials may be used in the manufacture of microelectronic devices as barrier layers, passivation layers, dielectric layers, mask layers, and as substrates. Some examples of useful nitrides for microelectronic devices are silicon nitride, silicon oxynitride, aluminum nitride, and gallium nitride. Nitridation processes such as thermal nitridation and plasma nitridation are typically used to form nitride films that include material from the substrate as a component. 
     Thermal and plasma assisted film growth processes such as nitridation may have several drawbacks. For example, thermal nitridation processes may exceed the thermal budget of many microelectronic workpieces (e.g. when devices have already been formed). Additionally, plasma assisted processes such as plasma nitridation may undesirably damage surfaces of the substrate. Therefore, film growth processes performed at low temperature that minimize substrate damage may be desirable. 
     SUMMARY 
     In accordance with an embodiment of the invention, a method of nitridation includes cyclically performing the following steps in situ within a processing chamber at a temperature less than about 400° C.: treating an unreactive surface of a substrate in the processing chamber to convert the unreactive surface to a reactive surface by exposing the unreactive surface to an energy flux, and nitridating the reactive surface using a nitrogen-based gas to convert the reactive surface to a nitride layer including a subsequent unreactive surface. 
     In accordance with another embodiment of the invention, a method of nitridation including cyclically performing the following steps in situ within a plasma processing chamber at a temperature less than about 400° C.: removing hydrogen from an unreactive region of a silicon substrate to convert the unreactive region to a reactive region by bombarding the silicon substrate with ions and photons from a plasma generated in the plasma processing chamber; and nitridating the reactive region using a hydronitrogen gas to convert the reactive region to a nitride region including a subsequent unreactive region. 
     In accordance with still another embodiment of the invention, a method of film growth including cyclically performing the following steps in situ within a processing chamber at a temperature less than about 400° C.: treating a hydrogenated surface of a substrate in the processing chamber to convert the hydrogenated surface to a reactive surface by removing hydrogen from the hydrogenated surface using an energy flux incident on the hydrogenated surface, the substrate including a first material, and exposing the reactive surface to a hydrogen-based gas including a second material to convert the reactive surface into a film including a subsequent hydrogenated surface and a compound including the first material and the second material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIGS.  1 A,  1 B,  1 C,  1 D,  1 E , IF,  1 G, and  1 H illustrate an example nitridation process performed cyclically in situ in a processing chamber at a temperature less than about 400° C. in accordance with an embodiment of the invention, where  FIG.  1 A  shows an initial state of a substrate including an unreactive surface,  FIG.  1 B  shows a first treatment step,  FIG.  1 C  shows a first nitridation step to form a nitride film,  FIG.  1 D  shows a subsequent unreactive surface formed on the nitride film,  FIG.  1 E  shows a second treatment step,  FIG.  1 F  shows a second nitridation step,  FIG.  1 G  shows another subsequent unreactive surface formed on the nitride film, and  FIG.  1 H  shows a third treatment step; 
         FIG.  2    illustrates another example nitridation process used to form silicon oxynitride at a temperature less than about 400° C. in accordance with an embodiment of the invention; 
         FIG.  3    illustrates an example carbonization process used to form silicon carbide at a temperature less than about 400° C. in accordance with an embodiment of the invention; 
         FIG.  4    illustrates an example film growth process performed at a temperature less than about 400° C. in accordance with an embodiment of the invention; 
         FIG.  5    illustrates an example film growth apparatus in accordance with an embodiment of the invention; 
         FIG.  6    illustrates an example plasma processing apparatus in accordance with an embodiment of the invention; 
         FIG.  7    illustrates an example method of nitridation in accordance with an embodiment of the invention; and 
         FIG.  8    illustrates an example method of film growth in accordance with an embodiment of the invention. 
     
    
    
     Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale. The edges of features drawn in the figures do not necessarily indicate the termination of the extent of the feature. 
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The making and using of various embodiments are discussed in detail below. It should be appreciated, however, that the various embodiments described herein are applicable in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use various embodiments, and should not be construed in a limited scope. 
     Nitridation (also called “nitriding”) is a method of forming nitride at exposed surfaces of a substrate. The nitride is formed by reacting nitrogen with the material of the substrate. Thermal nitridation (also referred to as “gas nitriding”) is usually conducted at high temperature (e.g. at least 600° C. and typically &gt;900° C.). Nitridation efficiency of thermal nitridation processes decreases the lower the temperature and ceases altogether below 400° C. in many cases. The nitrogen source is usually ammonia (NH 3 ) and is provided to the substrate by placing the substrate in an NH 3  ambient. 
     There are various drawbacks to thermal nitridation processes. The high required temperatures are typically very high relative to the thermal budget of microelectronic substrates resulting in unacceptably high substrate temperatures. For example, the elevated substrate temperatures may cause uncontrolled re-diffusion of dopants resulting in undesirable dopant redistribution. Other side effects to substrate materials are also possible such as device degradation and material modification. Consequently, thermal nitridation processes are frequently not compatible with device fabrication processes (e.g. for advanced nodes). 
     Plasma nitridation is also used as a method of forming nitride at exposed surfaces of a substrate. Although considered an alternative to thermal nitridation because of potentially lower temperatures, plasma nitridation is still typically carried out at around 400° C. Despite being lower than 600° C., plasma nitridation temperatures of 400° C. may be more accurately thought of as a moderate temperature relative to the thermal budgets of microelectronic substrates (e.g. not low temperature from a device perspective). Further, plasma nitridation has additional potential drawbacks of inducing damage to the substrate and non-conformal nitridation. 
     Other techniques may be used in addition to or in lieu of thermal nitridation and plasma nitridation. For example, sophisticated reactive chemicals may be used. However, this may raise cost and complexity. Techniques such as atomic layer deposition (ALD) may also be used. Yet, ALD is slow (e.g. 1-2 nm/min.), expensive, and sensitive requiring extremely pure materials, precise operating conditions, and involved pretreatment surface preparation. Further, ALD may also require high substrate temperature, such as in thermal ALD and in plasma enhanced ALD. 
     Conventional nitridation processes disadvantageously require high temperatures (e.g. above the thermal budget of a substrate) and different equipment (e.g. increasing complexity, decreasing throughput, and potentially increasing exposure to contaminants). Further, conventional mechanisms to lower nitridation processing temperature are expensive, complicated, and result in other undesirable effects such as substrate damage. These drawbacks of conventional nitridation processes also apply to various other conventional film growth processes. Therefore, film growth processes that may be performed at low temperature, minimize substrate damage, and may be performed without additional specialized equipment may be desirable. 
     The inventors have confirmed that no silicon (Si) nitridation occurs in an ammonia (NH 3 ) ambient below 400° C. However, the reaction barrier for nitridation at lower temperature (e.g. below 400° C.) may be due to the passivation of the Si surface by hydrogen (H) atoms dissociated from NH 3  chemisorbed on the Si surface. The inventors discovered that dangling bonds created by removal of H facilitate nitridation at lower temperatures. As a result, a completely different regime may be explored for achieving nitride formation at room temperature or any low temperature below 400° C. 
     Further, the reaction barrier of other film growth processes may also be overcome or reduced by removing terminating species from the surface. For example, this concept may be extended to not only Si nitridation, but also to any semiconductor and metallic surface nitridation. Additionally, potentially useful for other film growth processes such as nitride growth, area selective deposition (ASD), carbide formation, oxide formation, and others. 
     In various embodiments, a film growth process includes cyclically performing a treatment step and a surface exposure step in situ within a processing chamber at a temperature less than about 400° C. The treatment step includes generating an energy flux incident on an unreactive surface to convert the unreactive surface of a substrate in the processing chamber to a reactive surface. For example, the unreactive surface may be a hydrogenated (i.e. hydrogen terminated) surface and the energy flux may remove some or all of the hydrogen resulting in a reactive surface (e.g. with dangling bonds). 
     The surface exposure step includes exposing the reactive surface to a precursor gas (e.g. a hydrogen-based gas) that includes a reactive material. The reactive material of the precursor gas reacts with the surface and subsurfaces of the substrate that include a bulk material to form a film that includes a compound formed from the reactive material and the bulk material. The film formed from the reaction also includes a subsequent unreactive surface. That is, a surface of the film exposed to the precursor gas becomes less reactive over time resulting in another unreactive surface available for treatment in a subsequent treatment step of the next cycle (e.g., the process is self-limiting). 
     In various embodiments, the film growth process is a nitridation process. The temperature may be significantly lower than 400° C. (e.g. &lt;about 250° C. or room temperature). The energy flux may be provided using energetic particles, thermal flashing, or other suitable means. In some embodiments, the processing chamber is a plasma processing chamber and the energy flux is provided using a plasma generated in the plasma processing chamber. The substrate may be any suitable substrate, and includes Si in some embodiments. In one embodiment, the precursor gas is NH 3  gas. 
     The film growth processes described herein may advantageously enable film growth (e.g. thermal nitridation of Si or other surfaces) at low temperatures below about 400° C. such as less than about 250° C. or at about room temperature. Nitridation or nitride growth at room temperature/low temperature may be significantly beneficial for process integration and novel capital equipment development. For example, the film growth processes may add value to current equipment with expanded process window. 
     The embodiment film growth processes may be beneficial to both logic and memory devices and processes. The film growth processes (e.g. nitridation and/or nitride growth processes) may advantageously avoid the need of high temperature (e.g. in thermal processes) moderate temperature (e.g. in plasma processes), which may be beneficial to device properties and process integration. 
     Additionally, layer-by-layer self-limiting film growth processes may be advantageously achievable at room temperature/low temperature below about 400° C. A further advantage may be to enable area selected film growth (e.g. ASD) on different regions of Si surfaces. The mechanisms may be advantageously extended from Si surfaces to other suitable surfaces such as other semiconductor surfaces, metallic surfaces, and dielectric surfaces. 
     Embodiments provided below describe various methods and apparatuses for film growth processes, and in particular, film growth processes performed cyclically at low temperature. The following description describes the embodiments.  FIGS.  1 A- 1 H  are used to describe an example nitridation process. Another example nitridation process is described using  FIG.  2   .  FIGS.  3  and  4    are used to describe an example carbonization process and an example film growth process, respectively. Two example apparatuses are described using  FIGS.  5  and  6    while an example method of nitridation is described using  FIG.  7    and an example method of film growth is described using  FIG.  8   . 
       FIGS.  1 A,  1 B,  1 C,  1 D,  1 E,  1 F,  1 G, and  1 H  illustrate an example nitridation process performed cyclically in situ in a processing chamber at a temperature less than about 400° C. in accordance with an embodiment of the invention.  FIG.  1 A  shows an initial state of a substrate including an unreactive surface,  FIG.  1 B  shows a first treatment step,  FIG.  1 C  shows a first nitridation step to form a nitride film,  FIG.  1 D  shows a subsequent unreactive surface formed on the nitride film,  FIG.  1 E  shows a second treatment step,  FIG.  1 F  shows a second nitridation step,  FIG.  1 G  shows another subsequent unreactive surface formed on the nitride film, and  FIG.  1 H  shows a third treatment step. 
     Referring to  FIG.  1 A , a nitridation process  100  includes an initial state of a substrate no that includes a bulk region  118  and an unreactive surface in. The unreactive surface  111  may be a passivated surface that is passivated by terminated bonds. For example, the unreactive surface  111  may be a hydrogenated surface as shown. Alternatively, the unreactive surface  111  may be terminated with another species (i.e. a species different from the material of the substrate  110  that reacts with nitrogen to form a nitride). 
     In various embodiments the substrate no is a semiconductor substrate and is a silicon substrate in one embodiment. In other embodiments, the semiconductor substrate may be germanium (Ge) or be a compound semiconductor including, gallium (Ga), arsenic (As), nitrogen (N), etc. Alternatively, the substrate no may be a metallic substrate or a dielectric substrate. For instance, the substrate no may be aluminum, carbon (e.g. graphene), or silicon oxide (SiO 2 ). Additionally, the substrate no may include many different material layers and may be the top layer of a multilayer substrate. For example, the substrate no may be SiO 2  that is formed on top of another material. 
     The substrate no is disposed within a processing chamber  102 . The processing chamber  102  may be any suitable processing chamber  102 . However, the processing chamber  102  need only be a low temperature processing chamber (e.g. need not be capable of heating the substrate to greater than about 400° C.). In various embodiments, the processing chamber  102  is a multipurpose processing chamber and is a plasma processing chamber in one embodiment. 
     Referring now to  FIG.  1 B , the nitridation process  100  further includes a first treatment step performed in situ in the processing chamber  102  in which an energy flux  120  is provided to the unreactive surface in of the substrate no. The energy flux  120  converts the unreactive surface  111  to a reactive surface  112 . For example, in the case where the unreactive surface  111  is a hydrogenated surface (as shown) the energy flux  120  provides sufficient energy to the unreactive surface  111  to remove hydrogen leaving the reactive surface  112 . As shown, the reactive surface  112  may be reactive as a result of dangling bonds created at the surface (e.g. reactions with the reactive surface  112  may be energetically favorable). 
     In some cases, the energy flux  120  or the duration of the treatment may be such that only regions of the unreactive surface are made reactive. For example, unreactive regions (e.g. as qualitatively indicated by unreactive region  131 ) may be converted to reactive regions (e.g. reactive region  132 ) while other portions of the unreactive surface  111  remain unreactive (e.g. hydrogen terminated). That is, the treatment may not remove all of the hydrogen during each cycle. 
     The energy flux  120  may expose bulk material  140  of the substrate no at the reactive surface  112 . For example, the bulk region  118  of the substrate no may include the bulk material  140 . In this specific example, the bulk material  140  is Si, but other bulk materials are possible. For the purposes of this disclosure, the term bulk refers to a material that comprises a majority of the substrate no (which may be the top layer of a multilayer substrate). 
     In one embodiment, the energy flux  120  is generated by helium (He) plasma. Inert gas plasmas such as He plasma may function as an energy flux source that is a combination of energetic particle beams: ions, electrons, radicals, and photons. The He plasma may generate ions (He + ) and photons with sufficient energy to break bonds of a terminating species without otherwise damaging surfaces of the substrate no. For example, in the specific example of Si—H bonds (as shown), the energy flux  120  may provide at least about 4.06 eV to Si—H bonds at the unreactive surface in. That is, the average energy of the ions and photons may be at least about 4.06 eV. However, in some cases lower energy may also be sufficient to remove H from surfaces (e.g. providing necessary energy in the aggregate). For example, the average energy of the ions and photons may be lower than 4.06 eV (e.g. as low as 1.114 eV or lower). 
     In one embodiment, the energy flux  120  is generated by helium (He) plasma. Inert gas plasmas such as He plasma may function as an energy flux source that is a combination of energetic particle beams: ions, electrons, radicals, and photons. The He plasma may generate ions (He + ) and photons with sufficient energy to break bonds of a terminating species without otherwise damaging surfaces of the substrate no. For example, in the specific example of S—H bonds (as shown), the energy flux  120  may provide at least about 4.06 eV to S—H bonds at the unreactive surface in. That is, the average energy of the ions and photons may be at least about 4.06 eV. However, in some cases lower energy may also be sufficient to remove H from surfaces (e.g. providing necessary energy in the aggregate). For example, the average energy of the ions and photons may be lower than 4.06 eV (e.g. as low as 1.114 eV or lower). 
     The energetic particles generated by the He plasma may include, for example, energetic ions, radicals, electrons, and photons. For the specific example of He plasma, the emitted photons (e.g. UV photons) may have favorable energy (e.g. ˜24 eV). In particular, He may provide the dual advantage of being lightweight so that bombardment does minimal or no damage to the substrate surface (e.g. Si/SiN surfaces) and also high energy photons (˜24 eV), ions, and radicals which may advantageously efficiently remove terminating species (e.g. H) from the surface. 
     It should be noted that energy required to efficiently break surface bonds may vary depending on how the energy is absorbed by the unreactive surface in. For example, energy from incident particles may be spread out among several localized surface atoms which may increase the required particle energy. Additionally, the desorption cross section of terminating species may be energy dependent and maximizing the cross section may advantageously improve efficiency. Although not critical in most cases due to the self-limiting nature of the process, uniformity of the energy flux  120  to the substrate may be desirable. 
     In other embodiments the energy flux  120  may be partially or entirely generated using techniques such as thermal flashing (e.g. millisecond flashing) or focused particle beams (e.g. an ion beam source, electron beam source such as an e-gun, a photon source such as a UV lamp, a radical source such as a radical generator, etc.). For instance, thermal flashing and/or focused particle beams may advantageously direct energy to localized regions (e.g. unreactive regions  131 ) of the unreactive surface in allowing area selective film growth (e.g. ASD). The specific choice of energy source(s) may depend on a variety of factors including ease of implementation, energy budget, uniformity, efficiency, and device process compatibility. 
     Referring to  FIG.  1 C , the nitridation process  100  further includes a nitridation step which includes providing a precursor gas  122  in the processing chamber  102 . The precursor gas  122  includes a reactive material  141  (e.g. N) that reacts with the bulk material  140  (e.g. Si) from the substrate no. For example, the precursor gas  122  may be introduced into the processing chamber  102  after the treatment step or may be present throughout the nitridation process  100 . The precursor gas  122  is a hydrogen-based gas in various embodiments and is a hydronitrogen gas (N m H m , also referred to as a nitrogen hydride) in some embodiments. 
     For example, the precursor gas  122  may be an azane (N m H m+2 ) such as hydrazine (N 2 H 4 ) or a cycloazane (N m H m ) and may include nitrogen-based ions such as ammonium (NH 4 +). In one embodiment, the precursor gas  122  is ammonia (NH 3 ) as shown. The precursor gas  122  may be provided with other gases such as an inert gas (e.g. carrier gas). In one embodiment, the precursor gas  122  is NH 3  and provided with argon (Ar) in a 1:4 ratio (NH 3 :Ar). 
     However, other functional groups and elements other than N and H may also be included. Further, the precursor gas  122  may not include nitrogen. In some embodiments, the precursor gas  122  is a hydrocarbon gas, and in other embodiments, the precursor gas  122  is another hydrogen-based gas. The inclusion of hydrogen in the precursor gas may be influenced by the type of substrate. For example, hydrogen may be included in the precursor gas when the unreactive surface  111  is terminated with hydrogen each cycle, but may be another element or functional group in other cases. 
     NH 3  (as well as other hydronitrogen precursors, for example) may have an advantage during nitridation of being easily dissociated into NH x  (x=1, 2) and H (+H) without any substrate heating. Further, in the presence of a reactive surface  112  (e.g. with dangling bonds from surface Si atoms, for example) nitridation may advantageously be thermodynamically favorable at any substrate temperature (i.e. almost no reaction barrier to nitridation when dangling bonds are available). It should be noted that in  FIG.  1 C  and other similar figures, nitridated surface sites are illustrated as a N for clarity, but may also be other nitrogen-containing species such as NH x  (x=1, 2), for example. Analogous concepts also apply reactive species other than N. 
     The treatment step may be carried out in a vacuum (e.g. medium vacuum or high vacuum). Additionally, the treatment step may be performed in a non-hydrogen environment (e.g. without the presence of an ambient hydrogen-based gas such as NH 3 ) and then followed by the introduction of the precursor gas  122  simultaneously (or delayed after) turning off the treatment process (e.g. H removal process). For example, the source power for an energy source providing the energy flux  120  may be removed (i.e. turned off) and the precursor gas  122  may be introduced into the processing chamber  102  to begin the nitridation step. 
     Alternatively, the treatment step and the nitridation step may be performed concurrently. That is, the energy flux  120  (e.g. an inert plasma such as an He plasma) may be provided in the processing chamber  102  simultaneously with the precursor gas  122  (e.g. NH 3 ). In this scenario, H atoms may be continuously accumulated and removed at exposed surfaces of the substrate no allowing thermodynamically (i.e. energetically) favorable sites to be constantly generated even as H passivates regions of the surface. Such a scenario may be an example of a situation resulting in the formation of unreactive regions  131  and reactive regions  132  rather than entire surfaces or substantial portions of surfaces being unreactive or reactive at any given time. 
     Referring now to  FIG.  1 D , the nitridation step of the nitridation process  100  continues with the reactive material  141  of the precursor gas  122  continuing to form bonds with the bulk material  140  of the substrate  110  to form a nitride layer  142  comprising a nitride compound  144 . As shown the nitride compound  144  includes bonds (Si—N) between the reactive material  141  and the bulk material  140 . In one embodiment, the nitride compound  144  is Si 3 N 4 . 
     However, the precursor gas  122  also converts the reactive surface  112  into a subsequent unreactive surface in causing the nitridation step to be self-limited. That is, the nitridation reactions at the surface of the substrate  110  may slow down or stop as reaction sites (e.g. dangling bonds) are occupied by terminating species (e.g. H). For example, Si dangling bonds may facilitate nitridation, but the nitridation may not proceed if no dangling bonds are available, such as being passivated by H atoms as shown. 
     Consequently, the treatment and nitridation steps may be cyclically repeated to advantageously form a nitride layer in a layer-by-layer (or substantially layer-by-layer) process. Such layer-by-layer control may enable high uniformity and/or precise thickness control. 
     The in situ cyclic process may be advantageously performed at much higher rate compared to conventional layer-by-layer processes (such as ALD, with steps on the order of minutes). For example, both the treatment step and the nitridation step may take place on the order of seconds. In one embodiment, the treatment step is performed in less than about 5 s. In one embodiment, the nitridation step is performed in less than about 5 s. The timescale of the treatment and nitridation steps may depend on the energy flux, cycle efficiency, gas flowrate, pumping speed, and/or temperature (e.g. faster at higher temperature). The respective durations of the treatment step and the nitridation step may be similar or different depending on the specific details of a given implementation of the nitridation process. 
     Further, the in situ performance of the nitridation process may also beneficially enable nitride formation after other fabrication processes without removing the substrate from the processing chamber. For example, the processing chamber may be a multipurpose processing chamber used as a plasma processing chamber before and/or after being used as a nitridation processing chamber for the nitridation process. 
     Referring now to  FIGS.  1 E,  1 F,  1 G, and  1 H , the treatment step and the nitridation step is iterated in a cyclical manner to illustrate the continued formation of a nitride layer  142  of increased thickness at the substrate no. A second treatment step is performed ( FIG.  1 E ) to convert the subsequent unreactive surface in formed as a result of the self-limiting nature of the previous nitridation step into a reactive surface  112  which in turn is again converted during a second nitridation step ( FIG.  1 F ) into an unreactive surface in ( FIG.  1 G ) after the nitride layer  142  increases in thickness. The energy flux  120  is again applied in a third treatment step ( FIG.  1 H ) and so on. 
     Each of the above steps is performed at a temperature less than about 400° C. For example, the temperature may be less than about 250° C. and may be room temperature. Room temperature may defined as being generally low temperature (e.g. between about 20° C. and about 40° C. such as 25° C., 22° C., etc.) and may refer to the ambient temperature within the processing chamber. However, “room temperature” may also refer to situations in which no additional chamber or substrate heating is provided during the process (e.g. the energy flux may result in localized surface heating). Additionally, the above steps may also be performed at temperatures below room temperature (e.g. 0° C. and lower). 
     Importantly, the whole of the substrate does not rise above about 400° C. and is much lower in many cases. For example, additional chamber or substrate heating may be avoided unless desired for specific purposes (e.g. Si—NH), bonded films which may be useful in certain circumstances). For example, the chamber temperature may be maintained at about 250° C. to form ternary compounds including Si, N, and H (silicon nitrohydrides) in some embodiments. That is, temperature (below about 400° C. and may be below about 250° C.) may be useful to control hydrogen content of the nitride layer. 
     In the case of thermal flashing, the temperature of the substrate surface may be locally increased on the order of milliseconds to provide the requisite energy to the unreactive surface, but avoid damaging other regions of the substrate. 
       FIG.  2    illustrates another example nitridation process used to form silicon oxynitride at a temperature less than about 400° C. in accordance with an embodiment of the invention. The nitridation process of  FIG.  2    may be a specific implementation of other film growth processes (e.g. nitridation processes) described herein such as the nitridation process of  FIGS.  1 A- 1 H , or the film growth process of  FIG.  4   , as examples. Similarly labeled elements may be as previously described. 
     Referring to  FIG.  2   , a nitridation process  200  includes a substrate  210  that includes a bulk region  218  and a nitride layer  242 . It should be noted that here and in the following a convention has been adopted for brevity and clarity wherein elements adhering to the pattern [xio] may be related implementations of a plasma processing chamber in various embodiments. For example, the substrate  210  may be similar to the substrate no except as otherwise stated. An analogous convention has also been adopted for other elements as made clear by the use of similar terms in conjunction with the aforementioned three-digit numbering system. 
     The nitridation process  200  is illustrated only by the representative self-limited stage of the nitridation step, also for brevity and clarity, the remaining steps being analogous to those of  FIGS.  1 A- 1 H , but with differences, some of which are described in the following. In the nitridation process  200  the substrate  210  is an oxide (e.g. entirely or an oxide layer on a multilayer substrate). The bulk region  218  of the substrate  210  includes SiO 2  as shown resulting in a bulk material  240  that includes both Si and O. 
     A precursor gas  222  is provided during the nitridation step following or during a treatment step of delivering an energy flux to an unreactive surface  211  of the substrate  210 . The precursor gas  222  is a hydronitrogen gas including a reactive material  241  (N, as shown), but may also be other gases as previously described. In one embodiment, the precursor gas  222  is NH 3 . 
     The resulting nitride layer  242  includes an oxynitride compound  244  formed from the reaction of the reactive material  241  (N) with the bulk material  240  (Si and oxygen, O). In one specific example, the oxynitride compound  244  is silicon oxynitride (e.g. Si 2 N 2 O or with some degree of amorphousness with local variations between SiO 2  and Si 3 N 4 ), but the nitridation process  200  may be generalized to the formation of other oxynitrides. 
       FIG.  3    illustrates an example carbonization process used to form silicon carbide at a temperature less than about 400° C. in accordance with an embodiment of the invention. The carbonization process of  FIG.  3    may be a specific implementation of other film growth processes described herein such as the film growth process of  FIG.  4   , for example. Similarly labeled elements may be as previously described. 
     Referring to  FIG.  3   , a carbonization process  300  includes a substrate  310  that includes a bulk region  318  and a carbide layer  342 . As in  FIG.  2   , the carbonization process  300  is illustrated only by the representative self-limited stage of a carbonization step (which is analogous to a nitridation step), for brevity and clarity. The remaining steps are analogous to those of  FIGS.  1 A- 1 H , but with differences, some of which are described in the following. 
     In the carbonization process  300  the substrate  310  is a semiconductor and is Si in some embodiments (e.g. entirely or a Si layer on a multilayer substrate). The bulk region  318  of the substrate  310  includes a bulk material  340  of Si as shown. A precursor gas  322  is provided during a carbonization step following or during a treatment step of delivering an energy flux to an unreactive surface  311  of the substrate  310 . 
     In contrast to previously described precursors, the precursor gas  322  is a hydrocarbon gas including a reactive material  341  (carbon, C, as shown), but may also be other gases that include C. In various embodiments, the precursor gas  322  is an alkane. Alternatively or additionally, the precursor gas  322  includes other hydrocarbon gases such as alkenes, alkynes, and/or cyclic and substituted variations. In one embodiment, the precursor gas  322  includes methane (CH 4 ). In one embodiment, the precursor gas  322  includes ethylene (C 2 H 4 ). 
     The resulting carbide layer  342  includes a carbide compound  344  formed from the reaction of the reactive material  341  (C) with the bulk material  340  (Si). In one specific example, the carbide compound  344  is silicon carbide (SiC), but the carbonization process  300  may be generalized to the formation of other carbides. 
       FIG.  4    illustrates an example film growth process performed at a temperature less than about 400° C. in accordance with an embodiment of the invention. The film growth process of  FIG.  4    may be a general implementation of other film growth processes (e.g. nitridation processes, carbonization processes, etc.) described herein such as the nitridation process of  FIGS.  1 A- 1 H and  2    or the carbonization process of  FIG.  3   , as examples. Similarly labeled elements may be as previously described. 
     Referring to  FIG.  4   , a film growth process  400  includes a substrate  410  that includes a bulk region  418  and a film  442 . As in  FIG.  2   , the film growth process  400  is illustrated only by the representative self-limited stage of a film growth step (which is a generalization of a nitridation step), for brevity and clarity. The remaining steps are analogous to those of  FIGS.  1 A- 1 H , but with differences, some of which are described in the following. 
     The film  442  is formed during a film growth step where a precursor gas  422  is provided following or during a treatment step of delivering an energy flux to an unreactive surface  411  of the substrate  410 . The film  442  is the result of a reaction between a reactive material  441  of the precursor gas  422  and a bulk material  440  of the substrate  410 . 
     In this generalized scenario, the reactive material  441  is illustrated as some species Z (specific examples of which have been N and C) while the bulk material  440  is illustrated as some species X (specific provided examples including Si and Si, O). The film  442  then includes a compound  444  including X and Z (e.g. X—Z bonds). For example, X may be C (e.g. when the substrate  410  is graphene), aluminum (Al), and others that have not been specifically described. Similarly, Z may be O, a reactive functional group, and others. 
       FIG.  5    illustrates an example film growth apparatus in accordance with an embodiment of the invention. The film growth apparatus of  FIG.  5    may be a used to perform any of the film growth processes as described herein, such as the film growth processes of  FIGS.  1 A- 1 H and  2 - 4   . The film growth apparatus of  FIG.  5    may also be used to perform the film growth methods as subsequently described in  FIGS.  7  and  8   . Similarly labeled elements may be as previously described. 
     Referring to  FIG.  5   , a film growth apparatus  500  includes a substrate holder  504  supporting a substrate  510  within a processing chamber  502 . For example, the processing chamber  502  may be a multipurpose processing chamber. Various gases such as a precursor gas  522  (shown here as NH 3 ) may be provided into the processing chamber  502  through one or more gas inlets  506 . Pressure (e.g. medium vacuum, high vacuum, etc.) may be controlled in the processing chamber  502  using pumps  508  which evacuate the precursor gas  522  as well as other gases out of the processing chamber  502  through one or more gas outlets  507 . 
     An energy source  514  provides an energy flux  520  a surface  512  of the substrate  510 . As previously described, the energy flux  520  may be provided after or during the precursor gas  522 . The energy source  514  may be any suitable energy source or combination of energy sources such as a plasma source, ion beam source, electron beam source, photon source (e.g. UV light source), radical beam source, thermal flashing source, and others. 
     When temperature control (i.e. less than about 400° C.) is desired, an optional temperature controller  516  may be included to control the temperature of the substrate holder  504  and/or the substrate  510 . The optional temperature controller  516  may also include an energy source such as a thermal flashing source in some implementations. 
       FIG.  6    illustrates an example plasma processing apparatus in accordance with an embodiment of the invention. The plasma processing apparatus of  FIG.  6    may be a used to perform any of the film growth processes as described herein, such as the film growth processes of  FIGS.  1 A- 1 H and  2 - 4   . Additionally, the plasma processing apparatus of  FIG.  6    may be used to perform the film growth methods as subsequently described in  FIGS.  7  and  8   . Similarly labeled elements may be as previously described. 
     Referring to  FIG.  6   , a plasma processing apparatus  600  includes a substrate holder  604  supporting a substrate  610  within a plasma processing chamber  602 . The plasma processing apparatus of  FIG.  6    may be a specific implementation of the film growth apparatus of  FIG.  5    where the energy source is a plasma source  614  and the energy flux to a surface  612  of the substrate  610  is provided by plasma  620  generated in the plasma processing chamber  602 . For example, the plasma  620  may be an inert plasma (e.g. He plasma) generated using an inert gas  624  (e.g. He) supplied through one or more gas inlets  606 . 
     A precursor gas  622  may also be provided through the gas inlets  606  (e.g. the same gas inlets as the inert gas  624  or dedicated gas inlets). A pump  608  evacuates the precursor gas  622 , the inert gas  624 , and any other gases from the plasma processing chamber  602  through one or more gas outlets  607 . As before, an optional temperature controller  616  may be included if substrate temperature control is desired. 
       FIG.  7    illustrates an example method of nitridation in accordance with an embodiment of the invention. The method of  FIG.  7    may be combined with other methods and processes and may be performed using any of the film growth apparatuses described herein, such as the film growth apparatus of  FIG.  5    or the plasma processing apparatus of  FIG.  6   , as examples. Further, the method of  FIG.  7    may apply some or all of the steps of any of the embodiment processes as described herein such as the nitridation process of  FIGS.  1 A- 1 H  or the film growth process of  FIG.  4   , as examples. Although shown in a logical order, the arrangement and numbering of the steps of  FIG.  7    are not intended to be limited. The method steps of  FIG.  7    may be performed in any suitable order or concurrently with one another as may be apparent to a person of skill in the art. 
     Referring to  FIG.  7   , step  701  of a method of nitridation  700  includes treating an unreactive surface of a substrate to convert the unreactive surface to a reactive surface by exposing the unreactive surface to an energy flux. Step  702  of the method of nitridation  700  includes nitridating the reactive surface using a nitrogen-based gas to convert the reactive surface to a nitride layer comprising a subsequent unreactive surface. Steps  701  and  702  are performed in a processing chamber (i.e. in situ without removing the substrate from the processing chamber) and at a temperature less than about 400° C. 
     Step  703  is to cyclically perform steps  701  and  702 . Specifically, step  702  may be self-limited by the subsequent unreactive surface which may then be removed by a subsequently performed treatment step (step  701 ). The method of nitridation  700  may be continued until a desired uniformity and/or thickness of the nitride film is achieved. In some cases metrology (e.g. in situ) may be utilized to dynamically determine the state of the nitride layer so that the processing conditions may be adjusted or the cycle may be timely terminated. For example, in situ ellipsometry may be used. Additionally the ratio of species (e.g. N/H signal ratio) during the energy flux (e.g. plasma generation) may provide insight. 
       FIG.  8    illustrates an example method of film growth in accordance with an embodiment of the invention. The method of  FIG.  8    may be combined with other methods and processes and may be performed using any of the film growth apparatuses described herein, such as the film growth apparatus of  FIG.  5    or the plasma processing apparatus of  FIG.  6   , as examples. Additionally, the method of  FIG.  8    may apply some or all of the steps of any of the embodiment processes as described herein such as the nitridation process of  FIGS.  1 A- 1 H  or the film growth process of  FIG.  4   , as examples. Although shown in a logical order, the arrangement and numbering of the steps of  FIG.  8    are not intended to be limited. The method steps of  FIG.  8    may be performed in any suitable order or concurrently with one another as may be apparent to a person of skill in the art. 
     Referring to  FIG.  8   , step  801  of a method of film growth  800  includes treating a hydrogenated surface of a substrate to convert the hydrogenated surface to a reactive surface by removing hydrogen from the hydrogenated surface using an energy flux incident on the hydrogenated surface. The substrate includes a first material. The reactive surface is exposed to a hydrogen-based gas including a second material in step  802  to convert the reactive surface into a film. The film includes a subsequent hydrogenated surface and a compound comprising the first material and the second material. Steps  801  and  802  are performed in a processing chamber at a temperature less than about 400° C. Step  803  is to cyclically perform steps  801  and  802 . 
     Example embodiments of the invention are summarized here. Other embodiments can also be understood from the entirety of the specification as well as the claims filed herein. 
     Example 1. A method of nitridation including cyclically performing the following steps in situ within a processing chamber at a temperature less than about 400° C.: treating an unreactive surface of a substrate in the processing chamber to convert the unreactive surface to a reactive surface by exposing the unreactive surface to an energy flux; and nitridating the reactive surface using a nitrogen-based gas to convert the reactive surface to a nitride layer including a subsequent unreactive surface. 
     Example 2. The method of example 1, further including: where each treatment of an unreactive surface is performed for less than about 5 seconds; and where each nitridation of a reactive surface is performed for less than about 5 seconds. 
     Example 3. The method of one of examples 1 and 2, where the nitrogen-based gas includes ammonia (NH 3 ). 
     Example 4. The method of one of examples 1 to 3, where treating the unreactive surface includes providing the energy flux using a plasma generated in the processing chamber. 
     Example 5. The method of one of examples 1 to 4, where treating the unreactive surface comprises providing the energy flux using an ion beam source, an electron beam source, a photon source, a radical source, or a thermal flashing source. 
     Example 6. The method of one of examples 1 to 5, where treating the unreactive surface includes concurrently applying source power to generate the energy flux, and preventing dissemination of the nitrogen-based gas into the processing chamber; and nitridating the reactive surface includes concurrently removing the source power, and supplying the nitrogen-based gas to the processing chamber. 
     Example 7. A method of nitridation including cyclically performing the following steps in situ within a plasma processing chamber at a temperature less than about 400° C.: removing hydrogen from an unreactive region of a silicon substrate to convert the unreactive region to a reactive region by bombarding the silicon substrate with ions and photons from a plasma generated in the plasma processing chamber; and nitridating the reactive region using a hydronitrogen gas to convert the reactive region to a nitride region including a subsequent unreactive region. 
     Example 8. The method of example 7, where the ions and photons include an average energy greater than about 4.06 eV. 
     Example 9. The method of one of examples 7 and 8, where removing the hydrogen from the unreactive region and nitridating the reactive region are performed concurrently. 
     Example 10. The method of one of examples 7 to 9, where the hydronitrogen gas includes ammonia (NH 3 ). 
     Example 11. The method of one of examples 7 to 10, where the plasma generated in the plasma processing chamber is a helium plasma. 
     Example 12. The method of one of examples 7 to 11, where the temperature is less than about 30° C. 
     Example 13. A method of film growth including cyclically performing the following steps in situ within a processing chamber at a temperature less than about 400° C.: treating a hydrogenated surface of a substrate in the processing chamber to convert the hydrogenated surface to a reactive surface by removing hydrogen from the hydrogenated surface using an energy flux incident on the hydrogenated surface, the substrate including a first material, and exposing the reactive surface to a hydrogen-based gas including a second material to convert the reactive surface into a film including a subsequent hydrogenated surface and a compound including the first material and the second material. 
     Example 14. The method of example 13, further including: before cyclically repeating the steps, heating the substrate to the temperature, where the temperature is about 250° C., and where the temperature is maintained while cyclically repeating the steps. 
     Example 15. The method of one of examples 13 and 14, further including: before cyclically repeating the steps, treating the substrate within the processing chamber with a plasma process, where the substrate is not removed from the processing chamber between the plasma process and cyclically performing the steps. 
     Example 16. The method of example 15, where treating the hydrogenated surface of the substrate includes thermally flashing the hydrogenated surface to locally increase the temperature of the hydrogenated surface. 
     Example 17. The method of one of examples 13 to 16, where treating the hydrogenated surface includes treating the hydrogenated surface with a plasma generated in the processing chamber. 
     Example 18. The method of one of examples 13 to 17, where the first material is nitrogen, the second material is silicon, and the compound is silicon nitride. 
     Example 19. The method of one of examples 13 to 17, where the first material is nitrogen, the second material is silicon oxide, and the compound is silicon oxynitride. 
     Example 20. The method of one of examples 13 to 17, where the first material is carbon, the second material is silicon, and the compound is silicon carbide. 
     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.