Patent Publication Number: US-7713868-B2

Title: Strained metal nitride films and method of forming

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is related to co-pending U.S. patent application Ser. No. 11/730,288. Publication No. US2008-0242116, entitled “METHOD OF FORMING STRAINED SILICON NITRIDE FILMS AND A DEVICE CONTAINING SUCH FILMS,” filed on even date herewith; co-pending U.S. patent application Ser. No. 11/730,342, Publication No. US2008-0241555, entitled “STRAINED METAL NITRIDE FILMS AND METHOD OF FORMING,” filed on even date herewith; co-pending U.S. patent application Ser. No. 11/730,334, Publication No. US2008-0241388, entitled “STRAINED METAL SILICON NITRIDE FILMS AND METHOD OF FORMING,” filed on even date herewith; co-pending U.S. patent application Ser. No. 11/730,434, Publication No. US2008-0242077, entitled “STRAINED METAL SILICON NITRIDE FILMS AND METHOD OF FORMING,” filed on even date herewith, and co-pending U.S. patent application Ser. No. 11/529,380 Publication No. US2008-0081470, entitled “A METHOD OF FORMING STRAINED SILICON NITRIDE FILMS AND A DEVICE CONTAINING SUCH FILMS,” filed on Sep. 29, 2006. The entire contents of these applications are herein incorporated by reference in their entirety. 
   FIELD OF THE INVENTION 
   The present invention relates to semiconductor processing, and more particularly to methods of forming strained metal nitride films and semiconductor devices containing these strained films. 
   BACKGROUND OF THE INVENTION 
   Nitride-based films are widely used in semiconductor devices and ultra-large-scale integrated (ULSI) circuits. For example, nitride films have been widely used in semiconductor devices as diffusion barriers for dopants and metals, as an etch-stop film during etching of fine features, as a final passivation film for encapsulation of fabricated devices, and as electrodes in capacitor and metal-oxide semiconductor field-effect transistor (MOSFET) structures, among many other uses. Nitride films can be deposited at low pressure or at atmospheric pressure using a variety of processing systems and process gases. 
   Recent innovations to improve complementary metal oxide semiconductor (CMOS) transistor performance have created an industry need for strained films that are compatible with current ULSI integration techniques. In particular, channel carrier mobility for negative metal oxide semiconductor (NMOS) transistors can be increased through introduction of tensile uniaxial or biaxial strain on a channel region of a MOS transistor. Typically, this has been accomplished by deposition of highly tensile strained silicon nitride films that are compatible with existing fabrication processes. With the advent of metal gate stacks, the strain imparted in the channel using stressed silicon nitride liner films over the MOSFET will be decreased due to the higher modulus of the metallic films. One proposed solution to this problem is to use stressed films within the gate stack, so that the stressed film is more proximate to the channel, thus increasing the imparted strain. 
   SUMMARY OF THE INVENTION 
   According to one embodiment, a method of depositing a strained metal nitride film on a substrate in a process chamber includes exposing the substrate to a gas comprising a metal precursor, and exposing the substrate to a gas comprising a nitrogen precursor activated by a plasma source at a first level of plasma power and configured to react with the metal precursor with a first reactivity characteristic. Also included is exposing the substrate to a gas comprising the nitrogen precursor activated by the plasma source at a second level of plasma power different from the first level and configured to react with the metal precursor with a second reactivity characteristic such that a property of the metal nitride film formed on the substrate changes to provide the strained metal nitride film. 
   According to another embodiment, the method includes a) exposing the substrate to a gas pulse comprising the metal precursor, b) exposing the substrate to a gas pulse comprising the nitrogen precursor activated by the plasma source at the first level of plasma power, and c) exposing the substrate to a gas pulse comprising the metal precursor. Also included is d) exposing the substrate to a gas pulse comprising the nitrogen precursor activated by the plasma source at the second level of plasma power, and e) repeating steps a)-d) a predetermined number of times. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the present invention and many attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
       FIG. 1  schematically shows a cross-sectional view of a device containing a strained metal nitride or metal silicon nitride film according to embodiments of the invention; 
       FIGS. 2A-2B  illustrate processing systems for forming strained metal nitride or metal silicon nitride films according to embodiments of the invention; 
       FIGS. 3A-3E  are process flow diagrams for forming strained metal nitride films according to embodiments of the present invention; 
       FIGS. 4A-4E  are process flow diagrams for forming strained metal nitride films according to embodiments of the present invention; 
       FIGS. 5A and 5B  show power graphs depicting different levels of plasma power coupled to a process chamber according to embodiments of the invention; 
       FIGS. 6A-6E  are process flow diagrams for forming strained metal silicon nitride films according to embodiments of the present invention; and 
       FIGS. 7A-7E  are process flow diagrams for forming strained metal silicon nitride films according to embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS 
   Embodiments of the invention describe processing methods to deposit strained metal nitride and metal silicon nitride films with good thickness and uniformity control. In the case of metal nitride films, the processing methods utilize a metal precursor and one or more nitrogen precursors having a difference in reactivity towards the metal precursor, thereby depositing metal nitride films having a density gradient across the film thickness that creates tensile or compressive strain within the deposited film. In the case of metal silicon nitride films, the processing methods utilize a metal precursor, a silicon precursor, and one or more nitrogen precursors having a difference in reactivity towards the metal precursor or the silicon precursor. 
   According to one embodiment of the invention, a difference in heat of formation (ΔH) of different nitrogen precursors may be utilized to achieve a difference in reactivity towards a metal precursor and/or a silicon precursor. NH 3  (ΔH=−45.9 kJ/mol) and N 2 H 4  (ΔH=95.35 kJ/mol) are examples of nitrogen precursors with a large difference in heat of formation. For example, using the same or similar processing conditions, a first metal nitride film portion deposited using N 2 H 4  will have a different deposition rate and different film density than a second metal nitride film portion deposited using NH 3  onto the first metal nitride film portion. Variations in density across the thickness of an amorphous or crystalline film such as TiN will result in TiN film strain due to variations in coefficient of thermal expansion created across the TiN film. In the case of metal silicon nitride films, this difference in density may be further affected by altering the silicon precursor or the processing conditions during processing. 
   Alternately, a difference in reactivity may be achieved by varying plasma activation of a nitrogen precursor during processing. For example, the reactivity may be controlled by the type of plasma activation and the level of plasma power used for the activation. According to embodiments of the invention, plasma activation may be accomplished using a direct plasma source within the process chamber or using a remote plasma source. 
   In one example, embodiments of the invention may be utilized for forming a strained metal nitride or metal silicon nitride film located between materials with very different coefficients of thermal expansion, thereby increasing adhesion between the materials and decreasing the possibility of delamination during thermal cycling. 
   Embodiments of the invention may utilize atomic layer deposition (ALD), plasma enhanced ALD (PEALD), chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), and pulsed CVD methods for depositing strained metal nitride and metal silicon nitride films. These deposition methods are well known methods for depositing a wide variety of materials. ALD is a CVD related film deposition method that uses sequential saturative surface reactions. In ALD, pulses of the gaseous precursors are alternately exposed to the substrate. In CVD, an uninterrupted flow of the gaseous precursors is exposed to the substrate, and in pulsed CVD, the flow of the gaseous precursors is periodically interrupted during the film deposition. In PEALD and PECVD, plasma excitation is utilized during at least a portion of the deposition process. The use of ALD, PEALD, CVD, PECVD, and pulsed CVD processing allows for varying the nitrogen precursor, ratio of nitrogen precursors, and/or processing conditions during the film deposition. In one example, the nitrogen precursor can be varied from N 2 H 4  to a combination of N 2 H 4  and NH 3 , to pure NH 3 , during CVD and pulsed CVD processing. In another example, the number of N 2 H 4  gas pulses versus NH 3  gas pulses can be varied during ALD or PEALD processing. In another example, a level of plasma power used to activate the N 2 H 4  or NH 3  gas can be varied during PEALD or PECVD processing. In yet another example, a dilution gas may be used in combination with plasma power to affect reactivity. 
   As used herein, metal nitride films refer to films containing a metal element (or multiple metal elements) and nitrogen (N) as the major elements, where the elemental composition of the metal nitride films can be varied over wide ranges of atomic concentrations for the metal or metals and N. Metal silicon nitride films refer to films containing a metal element (or multiple metal elements), silicon (Si) and nitrogen (N) as the major elements, where the elemental composition of the metal silicon nitride films can be varied over wide ranges of atomic concentrations for the metal or metals, Si and/or N. Furthermore, the metal nitride and metal silicon nitride films may contain impurities such as carbon (C), oxygen (O), halogen (e.g., chlorine (Cl)), and hydrogen (H), that may become incorporated into the films during the substrate processing or during substrate transfer. The terms “film” and “layer” are used interchangeably herein to refer to a material deposited or formed on a substrate. 
   Referring now to the drawings,  FIG. 1  schematically shows a cross-sectional view of a device containing a strained metal nitride or metal silicon nitride film according to an embodiment of the invention. The strained nitride film  118  is disposed in a MOS device  100 . The device  100 , as shown, includes a substrate  112  having doped regions  113  and  114  (e.g., source and drain), a gate stack  120 , a spacer  121 , and a liner  122 . The substrate  112  can for example be a Si, Ge, Si/Ge, or GaAs substrate wafer. The substrate  112  can be of any size, for example, a 200 mm substrate, a 300 mm substrate, or an even larger substrate. 
   The gate stack  120  includes a dielectric film  116  on the channel region  115 . The dielectric layer  116  can for example include a SiO 2  layer, a SiN layer, a SiON layer, or a combination thereof, or any other appropriate dielectric material. The dielectric film  116  can further include a high-dielectric constant (high-k) dielectric material. The high-k dielectric material can for example include metal oxides and their silicates, including Ta 2 O 5 , TiO 2 , ZrO 2 , Al 2 O 3 , Y 2 O 3 , HfO x N y , HfSiO x N y , HfSiO x , HfO 2 , ZrO 2 , ZrSiO x , ZrO x N y , ZrSiO x N y , TaSiO x , SrO x , SrSiO x , LaO x , LaSiO x , YO x , YSiO x , or BaO, or combinations of two or more thereof. 
   In one embodiment of the invention, a conductive film  117  (e.g., a gate electrode film) is formed on the dielectric film  116 , and a strained metal nitride film or metal silicon nitride film  118  is formed on the conductive film  117  to impart strain to the channel region  115 . A cap layer  119  can be positioned at the top of the gate stack  120  to protect the gate stack  120  and improve electrical contact to the gate stack  120 . The cap layer  119  can, for example, include one or more of a SiN layer, a W layer, a WSi x  layer, a CoSi x  layer, a NiSi x  layer or a polycrystalline or amorphous Si layer. 
   In one example, the conductive layer  117  can be tantalum nitride (TaN), and the strained metal nitride film  118  can contain titanium nitride (TiN). The gate stack  120  may include different and fewer or more films or layers than shown in  FIG. 1 . In one example, film  117  and film  118  may be composed of the same metal nitride or metal silicon nitride film with a vertical density gradient formed according to embodiments of the invention.  FIG. 1  further shows that spacer  121  is formed on either side of the gate stack  120  in order to protect the gate stack  120  from damage and ensure electrical performance of the gate. In addition, the spacer  121  can be used as a hard mask for the formation of the source and drain  113 ,  114  of the MOS device  100 . Alternately, in one embodiment, more than one spacer  121  may be used. 
   In one embodiment, the device  100  can be a NMOS device where the strained metal nitride or metal silicon nitride film  118  increases channel carrier mobility through introduction of a tensile stress on the channel region  115 . The strained nitride film  118  can also serve as a conductive film for improving electrical contact to the device  100 . 
   In another embodiment, the device  100  can be a PMOS device where the strained metal nitride film  118  increases channel carrier mobility through introduction of a compressive stress on the channel region  115 , thus enhancing transistor mobilities and hence overall transistor performance. The strained metal nitride film  118  can also serve as a conductive film for improving electrical contact to the device  100 . 
     FIG. 2A  illustrates a processing system  1  for forming strained metal nitride and/or metal silicon nitride films according to embodiments of the invention. The processing system  1  can be configured to perform an ALD process, a CVD process, or a pulsed CVD process. The processing system  1  includes a process chamber  10  having a substrate holder  20  configured to support a substrate  25 , upon which the strained film is formed. The process chamber  10  further contains an upper assembly  30  (e.g., a showerhead) configured for introducing process gases into the process chamber  10 , a metal precursor supply system  40 , a first nitrogen precursor supply system  42 , a second nitrogen precursor supply system  44 , a silicon precursor supply system  46 , a purge gas supply system  48 , and an auxiliary gas supply system  50 . Furthermore, the processing system  1  includes a substrate temperature control system  60  coupled to substrate holder  20  and configured to elevate and control the temperature of the substrate  25 . 
   In  FIG. 2A , singular processing elements ( 10 ,  20 ,  30 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 , and  60 ) are shown, but this is not required for the invention. The processing system  1  can include any number of processing elements having any number of controllers associated with them in addition to independent processing elements. The controller  70  can be used to configure any number of processing elements ( 10 ,  20 ,  30 ,  40 ,  42 ,  44 ,  46 ,  48 ,  50 , and  60 ), and the controller  70  can collect, provide, process, store, and display data from the processing elements. The controller  70  can comprise a number of applications for controlling one or more of the processing elements. For example, controller  70  can include a graphic user interface (GUI) component (not shown) that can provide easy to use interfaces that enable a user to monitor and/or control one or more processing elements. 
   Still referring to  FIG. 2A , the processing system  1  may be configured to process 200 mm substrates, 300 mm substrates, or larger-sized substrates. In fact, it is contemplated that the deposition system may be configured to process substrates, wafers, or LCDs regardless of their size, as would be appreciated by those skilled in the art. Therefore, while aspects of the invention will be described in connection with the processing of a semiconductor substrate, the invention is not limited solely thereto. Alternately, a batch processing system capable of processing multiple substrates simultaneously may be utilized for depositing the strained films described in the embodiments of the invention. 
   Still referring to  FIG. 2A , the purge gas supply system  48  is configured to introduce a purge gas to process chamber  10 . For example, the introduction of purge gas may occur between introduction of pulses of a metal precursor, a silicon precursor, a first nitrogen precursor, and a second nitrogen precursor gas to the process chamber  10 . The purge gas can comprise an inert gas, such as a noble gas (i.e., He, Ne, Ar, Kr, Xe), nitrogen (N 2 ), or hydrogen (H 2 ). 
   The substrate temperature control system  60  contains temperature control elements, such as a cooling system including a re-circulating coolant flow that receives heat from substrate holder  20  and transfers heat to a heat exchanger system (not shown), or when heating, transfers heat from the heat exchanger system to the substrate holder. Additionally, the temperature control elements can include heating/cooling elements, such as resistive heating elements, or thermo-electric heaters/coolers, which can be included in the substrate holder  20 , as well as the chamber wall of the process chamber  10  and any other component within the processing system  1 . The substrate temperature control system  60  can, for example, be configured to elevate and control the substrate temperature from room temperature to approximately 600° C., or higher. In another example, the substrate temperature can, for example, range from approximately 150° C. to 350° C. It is to be understood, however, that the temperature of the substrate is selected based on the desired temperature for causing deposition of a particular nitride film on the surface of a given substrate. 
   In order to improve the thermal transfer between substrate  25  and substrate holder  20 , substrate holder  20  can include a mechanical clamping system, or an electrical clamping system, such as an electrostatic clamping system, to affix substrate  25  to an upper surface of substrate holder  20 . Furthermore, substrate holder  20  can further include a substrate backside gas delivery system configured to introduce gas (e.g., helium (He)) to the back-side of substrate  25  in order to improve the gas-gap thermal conductance between substrate  25  and substrate holder  20 . Such a system can be utilized when temperature control of the substrate is required at elevated or reduced temperatures. For example, the substrate backside gas system can comprise a two-zone gas distribution system, wherein He gas-gap pressure can be independently varied between the center and the edge of substrate  25 . 
   Furthermore, the process chamber  10  is further coupled to a pressure control system  32 , including a vacuum pumping system  34  and a valve  36 , through a duct  38 , wherein the pressure control system  32  is configured to controllably evacuate the process chamber  10  to a pressure suitable for forming the nitride film on substrate  25 , and suitable for use of the precursor gases. The vacuum pumping system  34  can include a turbo-molecular vacuum pump (TMP) or a cryogenic pump capable of a pumping speed up to about 5000 liters per second (and greater) and valve  36  can include a gate valve for throttling the chamber pressure. Moreover, a device for monitoring chamber pressure (not shown) can be coupled to the process chamber  10 . The pressure control system  32  can, for example, be configured to control the process chamber pressure between about 0.1 Torr and about 100 Torr during deposition of the strained films. For example, the process chamber pressure can be between about 0.1 Torr and about 10 Torr, or between about 0.2 Torr and about 3 Torr. 
   The metal precursor supply system  40 , first nitrogen precursor supply system  42 , second nitrogen precursor gas supply system  44 , silicon precursor supply system  46 , a purge gas supply system  48 , and auxiliary gas supply system  50  can include one or more pressure control devices, one or more flow control devices, one or more filters, one or more valves, and/or one or more flow sensors. The flow control devices can include pneumatic driven valves, electro-mechanical (solenoidal) valves, and/or high-rate pulsed gas injection valves. According to embodiments of the invention, gases may be sequentially and alternately pulsed into the process chamber  10 . An exemplary pulsed gas injection system is described in greater detail in pending U.S. Patent Application Publication No. 2004/0123803. 
   In exemplary ALD and PEALD processes, the length of each gas pulse can, for example, be between about 0.1 sec and about 100 sec. Alternately, the length of each gas pulse can be between about 1 sec and about 10 sec. Exemplary gas pulse lengths for metal precursors can be between 0.3 and 3 sec, for example 1 sec. Exemplary gas pulse lengths for a nitrogen precursor and a silicon precursor can be between 0.1 and 3 sec, for example 0.3 sec. Exemplary purge gas pulses can be between 1 and 20 sec, for example 3 sec. 
   Still referring to  FIG. 2A , controller  70  can comprise a microprocessor, memory, and a digital I/O port capable of generating control voltages sufficient to communicate and activate inputs to the processing system  1  as well as monitor outputs from the processing system  1 . Moreover, the controller  70  may be coupled to and may exchange information with the process chamber  10 , substrate holder  20 , upper assembly  30 , metal precursor supply system  40 , first nitrogen precursor supply system  42 , second nitrogen precursor gas supply system  44 , silicon precursor supply system  46 , purge gas supply system  48 , auxiliary gas supply system  50 , substrate temperature control system  60 , and pressure control system  32 . For example, a program stored in the memory may be utilized to activate the inputs to the aforementioned components of the processing system  1  according to a process recipe in order to perform a deposition process. One example of the controller  70  is a DELL PRECISION WORKSTATION 610™, available from Dell Corporation, Austin, Tex. 
   However, the controller  70  may be implemented as a general purpose computer system that performs a portion or all of the microprocessor based processing steps of the invention in response to a processor executing one or more sequences of one or more instructions contained in a memory. Such instructions may be read into the controller memory from another computer readable medium, such as a hard disk or a removable media drive. One or more processors in a multi-processing arrangement may also be employed as the controller microprocessor to execute the sequences of instructions contained in main memory. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions. Thus, embodiments are not limited to any specific combination of hardware circuitry and software. The controller  70  can be coupled to one or more additional controllers/computers (not shown), and controller  70  can obtain setup and/or configuration information from an additional controller/computer. 
   The controller  70  includes at least one computer readable medium or memory, such as the controller memory, for holding instructions programmed according to the teachings of the invention and for containing data structures, tables, records, or other data that may be necessary to implement the present invention. Examples of computer readable media are compact discs, hard disks, floppy disks, tape, magneto-optical disks, PROMs (EPROM, EEPROM, flash EPROM), DRAM, SRAM, SDRAM, or any other magnetic medium, compact discs (e.g., CD-ROM), or any other optical medium, punch cards, paper tape, or other physical medium with patterns of holes, a carrier wave (described below), or any other medium from which a computer can read. 
   Stored on any one or on a combination of computer readable media, resides software for controlling the controller  70 , for driving a device or devices for implementing the invention, and/or for enabling the controller to interact with a human user. Such software may include, but is not limited to, device drivers, operating systems, development tools, and applications software. Such computer readable media further includes the computer program product of the present invention for performing all or a portion (if processing is distributed) of the processing performed in implementing embodiments of the invention. 
   The computer code devices may be any interpretable or executable code mechanism, including but not limited to scripts, interpretable programs, dynamic link libraries (DLLs), Java classes, and complete executable programs. Moreover, parts of the processing of the present invention may be distributed for better performance, reliability, and/or cost. 
   The term “computer readable medium” as used herein refers to any medium that participates in providing instructions to the processor of the controller  70  for execution. A computer readable medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical, magnetic disks, and magneto-optical disks, such as the hard disk or the removable media drive. Volatile media includes dynamic memory, such as the main memory. Moreover, various forms of computer readable media may be involved in carrying out one or more sequences of one or more instructions to processor of controller for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer can load the instructions for implementing all or a portion of the present invention remotely into a dynamic memory and send the instructions over a network to the controller  70 . 
   The controller  70  may be locally located relative to the processing system  1 , or it may be remotely located relative to the processing system  1 . For example, the controller  70  may exchange data with the processing system  1  using at least one of a direct connection, an intranet, the Internet and a wireless connection. The controller  70  may be coupled to an intranet at, for example, a customer site (i.e., a device maker, etc.), or it may be coupled to an intranet at, for example, a vendor site (i.e., an equipment manufacturer). Additionally, for example, the controller  70  may be coupled to the Internet. Furthermore, another computer (i.e., controller, server, etc.) may access, for example, the controller  70  to exchange data via at least one of a direct connection, an intranet, and the Internet. As also would be appreciated by those skilled in the art, the controller  70  may exchange data with the processing system  1  via a wireless connection. 
     FIG. 2B  illustrates a processing system  2  for forming strained metal nitride and/or metal silicon nitride films according to embodiments of the invention. The processing system  2  can be configured to perform an PEALD or a PECVD process. The processing system  2  is similar to the processing system  1  described in  FIG. 2A , but further includes a plasma generation system configured to generate a plasma during at least a portion of the gas exposures in the process chamber  10 . According to one embodiment of the invention, plasma excited nitrogen may be formed from a nitrogen-containing gas containing N 2 , NH 3 , or N 2 H 4 , or C 1 -C 10  alkylhydrazine compounds, or a combination thereof. 
   The plasma generation system includes a first power source  52  coupled to the process chamber  10 , and configured to couple power to gases introduced into the process chamber  10 . The first power source  52  may be a variable power source and may include a radio frequency (RF) generator and an impedance match network, and may further include an electrode through which RF power is coupled to the plasma in process chamber  10 . The electrode can be formed in the upper assembly  31 , and it can be configured to oppose the substrate holder  20 . The impedance match network can be configured to optimize the transfer of RF power from the RF generator to the plasma by matching the output impedance of the match network with the input impedance of the process chamber  10 , including the electrode, and plasma. For instance, the impedance match network serves to improve the transfer of RF power to plasma in process chamber  10  by reducing the reflected power. Match network topologies (e.g. L-type, π-type, T-type, etc.) and automatic control methods are well known to those skilled in the art. 
   Alternatively, the first power source  52  may include a RF generator and an impedance match network, and may further include an antenna, such as an inductive coil, through which RF power is coupled to a plasma in process chamber  10 . The antenna can, for example, include a helical or solenoidal coil, such as in an inductively coupled plasma source or helicon source, or it can, for example, include a flat coil as in a transformer coupled plasma source. 
   Still alternatively, the first power source  52  may include a microwave frequency generator, and may further include a microwave antenna and microwave window through which microwave power is coupled to a plasma in process chamber  10 . The coupling of microwave power can be accomplished using electron cyclotron resonance (ECR) technology, or it may be employed using surface wave plasma technology, such as a slotted plane antenna (SPA), as described in U.S. Pat. No. 5,024,716, the entire content of which is incorporated herein by reference. 
   According to one embodiment of the invention, the processing system  2  includes a substrate bias generation system configured to generate or assist in generating a plasma (through biasing of substrate holder  20 ) during at least a portion of the alternating introduction of the gases to the process chamber  10 . The substrate bias system can include a substrate power source  54  coupled to the process chamber  10 , and configured to couple power to the substrate  25 . The substrate power source  54  may include a RF generator and an impedance match network, and may further include an electrode through which RF power is coupled to substrate  25 . The electrode can be formed in substrate holder  20 . For instance, substrate holder  20  can be electrically biased at a RF voltage via the transmission of RF power from a RF generator (not shown) through an impedance match network (not shown) to substrate holder  20 . A typical frequency for the RF bias can range from about 0.1 MHz to about 100 MHz, and can be 13.56 MHz. RF bias systems for plasma processing are well known to those skilled in the art. Alternatively, RF power is applied to the substrate holder electrode at multiple frequencies. Although the plasma generation system and the substrate bias system are illustrated in  FIG. 2B  as separate entities, they may indeed comprise one or more power sources coupled to substrate holder  20 . 
   In addition, the processing system  2  includes a remote plasma system  56  for providing and remotely plasma exciting a gas (e.g., a nitrogen precursor) prior to flowing the plasma excited gas into the process chamber  10  where it is exposed to the substrate  25 . The remote plasma system  56  can, for example, contain a microwave frequency generator. 
   Examples of metal precursors, silicon precursors, and nitrogen precursors that may be utilized in embodiments of the invention to deposit strained metal nitride and metal silicon nitride films will now be described. As those skilled in the art will readily recognize, other metal precursors, silicon precursors, and nitrogen precursors not described below, but suitable for film deposition, may be utilized. 
   Embodiments of the invention may use metal precursors selected from the groups of volatile metal precursors suitable for depositing stable metal nitride or metal silicon nitride films. The metal precursor can, for example contain a metal element selected from alkaline earth elements, rare earth elements, Group III, Group IIIB, Group IVB, Group VB, and Group VIB of the Periodic Table, or a combination of two or more thereof. 
   Embodiments of the invention may utilize a wide variety of different alkaline earth precursors. For example, many alkaline earth precursors have the formula:
 
ML 1 L 2 D x  
 
where M is an alkaline earth metal element selected from the group of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). L 1  and L 2  are individual anionic ligands, and D is a neutral donor ligand where x can be 0, 1, 2, or 3. Each L 1 , L 2  ligand may be individually selected from the groups of alkoxides, halides, aryloxides, amides, cyclopentadienyls, alkyls, silyls, amidinates, □-diketonates, ketoiminates, silanoates, and carboxylates. D ligands may be selected from groups of ethers, furans, pyridines, pyroles, pyrolidines, amines, crown ethers, glymes, and nitriles.
 
   Examples of L group alkoxides include tert-butoxide, iso-propoxide, ethoxide, 1-methoxy-2,2-dimethyl-2-propionate (mmp), 1-dimethylamino-2,2′-dimethyl-propionate, amyloxide, and neo-pentoxide. Examples of halides include fluoride, chloride, iodide, and bromide. Examples of aryloxides include phenoxide and 2,4,6-trimethylphenoxide. Examples of amides include bis(trimethylsilyl)amide di-tert-butylamide, and 2,2,6,6-tetramethylpiperidide (TMPD). Examples of cyclepentadienyls include cyclopentadienyl, 1-methylcyclopentadienyl, 1,2,3,4-tetramethylcyclopentadienyl, 1-ethylcyclopentadienyl, pentamethylcyclopentadienyl, 1-iso-propylcyclopentadienyl, 1-n-propylcyclopentadienyl, and 1-n-butylcyclopentadienyl. Examples of alkyls include bis(trimethylsilyl)methyl, tris(trimethylsilyl)methyl, and trimethylsilylmethyl. An example of a silyl is trimethylsilyl. Examples of amidinates include N,N′-di-tert-butylacetamidinate, N,N′-di-iso-propylacetamidinate, N,N′-di-isopropyl-2-tert-butylamidinate, and N,N′-di-tert-butyl-2-tert-butylamidinate. Examples of □-diketonates include 2,2,6,6-tetramethyl-3,5-heptanedionate (THD), hexafluoro-2,4-pentanedionate (hfac), and 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate (FOD). An example of a ketoiminate is 2-iso-propylimino-4-pentanonate. Examples of silanoates include tri-tert-butylsiloxide and triethylsiloxide. An example of a carboxylate is 2-ethylhexanoate. 
   Examples of D ligands include tetrahydrofuran, diethylether, 1,2-dimethoxyethane, diglyme, triglyme, tetraglyme, 12-Crown-6, 10-Crown-4, pyridine, N-methylpyrolidine, triethylamine, trimethylamine, acetonitrile, and 2,2-dimethylpropionitrile. 
   Representative examples of alkaline earth precursors include: 
   Be precursors: Be(N(SiMe 3 ) 2 ) 2 , Be(TMPD) 2 , and BeEt 2 . 
   Mg precursors: Mg(N(SiMe 3 ) 2 ) 2 , Mg(TMPD) 2 , Mg(PrCp) 2 , Mg(EtCp) 2 , and MgCp 2 . 
   Ca precursors: Ca(N(SiMe 3 ) 2 ) 2 , Ca(iPr 4 Cp) 2 , and Ca(Me 5 Cp) 2 . 
   Sr precursors: Bis(tert-butylacetamidinato)strontium (TBAASr), Sr(N(SiMe 3 ) 2 ) 2 , Sr(THD) 2 , Sr(THD) 2 (tetraglyme), Sr(iPr 4 Cp) 2 , Sr(iPr 3 Cp) 2 , and Sr(Me 5 Cp) 2 . 
   Ba precursors: Bis(tert-butylacetamidinato)barium (TBAABa), Ba(N(SiMe 3 ) 2 ) 2 , Ba(THD) 2 , Ba(THD) 2 (tetraglyme), Ba(iPr 4 Cp) 2 , Ba(Me 5 Cp) 2 , and Ba(nPrMe 4 CP) 2 . 
   Representative examples of Group IVB precursors include: Hf(OtBu) 4  (hafnium tert-butoxide, HTB), Hf(NEt 2 ) 4  (tetrakis(diethylamido)hafnium, TDEAH), Hf(NEtMe) 4  (tetrakis(ethylmethylamido)hafnium, TEMAH), Hf(NMe 2 ) 4  (tetrakis(dimethylamido)hafnium, TDMAH), Zr(OtBu) 4  (zirconium tert-butoxide, ZTB), Zr(NEt 2 ) 4  (tetrakis(diethylamido)zirconium, TDEAZ), Zr(NMeEt) 4  (tetrakis(ethylmethylamido)zirconium, TEMAZ), Zr(NMe 2 ) 4  (tetrakis(dimethylamido)zirconium, TDMAZ), Hf(mmp) 4 , Zr(mmp) 4 , Ti(mmp) 4 , HfCl 4 , ZrCl 4 , TiCl 4 , Ti(NiPr 2 ) 4 , Ti(NiPr 2 ) 3 , tris(N,N′-dimethylacetamidinato)titanium, ZrCp 2 Me 2 , Zr(tBuCp) 2 Me 2 , Zr(NiPr 2 ) 4 , Ti(OiPr) 4 , Ti(OtBu) 4  (titanium tert-butoxide, TTB), Ti(NEt 2 ) 4  (tetrakis(diethylamido)titanium, TDEAT), Ti(NMeEt) 4  (tetrakis(ethylmethylamido)titanium, TEMAT), Ti(NMe 2 ) 4  (tetrakis(dimethylamido)titanium, TDMAT), and Ti(THD) 3  (tris(2,2,6,6-tetramethyl-3,5-heptanedionato)titanium). 
   Representative examples of Group VB precursors include: Ta(NMe 2 ) 5  (pentakis(dimethylamido)tantalum, PDMAT), Ta(NEtMe) 5  (pentakis(ethylmethylamido)tantalum, PEMAT), (tBuN)Ta(NMe 2 ) 3  (tert-butylimido tris(dimethylamido)tantalum, TBTDMT), (tBuN)Ta(NEt 2 ) 3  (tert-butylimido tris(diethylamido)tantalum, TBTDET), (tBuN)Ta(NEtMe) 3  (tert-butylimido tris(ethylmethylamido)tantalum, TBTEMT), (EtMe 2 CN)Ta(NMe 2 ) 3  (tert-amylimido tris(dimethylamido)tantalum, TAIMATA), (iPrN)Ta(NEt 2 ) 3  (iso-propylimino tris(diethylamido)tantalum, IPTDET), Ta 2 (OEt) 10  (tantalum penta-ethoxide, TAETO), (Me 2 NCH 2 CH 2 O)Ta(OEt) 4  (dimethylaminoethoxy tantalum tetra-ethoxide, TATDMAE), TaCl 5  (tantalum penta-chloride), Nb(NMe 2 ) 5  (pentakis(dimethylamido)niobium, PDMANb), Nb 2 (OEt) 10  (niobium penta-ethoxide, NbETO), (tBuN)Nb(NEt 2 ) 3  (tert-butylimino tris(diethylamido)niobium, TBTDEN), and NbCl 5  (niobium penta-chloride). 
   Representative examples of Group VIB precursors include: Cr(CO) 6  (chromium hexacarbonyl), Mo(CO) 6  (molybdenum hexacarbonyl), W(CO) 6  (tungsten hexacarbonyl), WF 6  (tungsten hexafluoride), and (tBuN) 2 W(NMe 2 ) 2  (bis(tert-butylimido)bis(dimethylamido)tungsten, BTBMW). 
   Embodiments of the inventions may utilize a wide variety of different rare earth precursors. For example, many rare earth precursors have the formula:
 
ML 1 L 2 L 3 D x  
 
where M is a rare earth metal element selected from the group of scandium (Sc), yttrium (Y), lutetium (Lu), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and ytterbium (Yb). L 1 , L 2 , L 3  are individual anionic ligands, and D is a neutral donor ligand where x can be 0, 1, 2, or 3. Each L 1 , L 2 , L 3  ligand may be individually selected from the groups of alkoxides, halides, aryloxides, amides, cyclopentadienyls, alkyls, silyls, amidinates, □-diketonates, ketoiminates, silanoates, and carboxylates. D ligands may be selected from groups of ethers, furans, pyridines, pyroles, pyrolidines, amines, crown ethers, glymes, and nitriles.
 
   Examples of L groups and D ligands are identical to those presented above for the alkaline earth precursor formula. 
   Representative examples of rare earth precursors include: 
   Y precursors: Y(N(SiMe 3 ) 2 ) 3 , Y(N(iPr) 2 ) 3 , Y(N(tBu)SiMe 3 ) 3 , Y(TMPD) 3 , Cp 3 Y, (MeCp) 3 Y, ((nPr)Cp) 3 Y, ((nBu)Cp) 3 Y, Y(OCMe 2 CH 2 NMe 2 ) 3 , Y(THD) 3 , Y[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Y(C 11 H 19 O 2 ) 3 CH 3 (OCH 2 CH 2 ) 3 OCH 3 , Y(CF 3 COCHCOCF 3 ) 3 , Y(OOCC 10 H 7 ) 3 , Y(OOC 10 H 19 ) 3 , and Y(O(iPr)) 3 . 
   La precursors: La(N(SiMe 3 ) 2 ) 3 , La(N(iPr) 2 ) 3 , La(N(tBu)SiMe 3 ) 3 , La(TMPD) 3 , ((iPr)Cp) 3 La, Cp 3 La, Cp 3 La(NCCH 3 ) 2 , La(Me 2 NC 2 H 4 Cp) 3 , La(THD) 3 , La[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , La(C 11 H 19 O 2 ) 3 .CH 3 (OCH 2 CH 2 ) 3 OCH 3 . La(C 11 H 19 O 2 ) 3 .CH 3 (OCH 2 CH 2 ) 4 OCH 3 , La(O(iPr)) 3 , La(OEt) 3 , La(acac) 3 , La(((tBu) 2 N) 2 CMe) 3 , La(((iPr) 2 N) 2 CMe) 3 , La(((tBu) 2 N) 2 C(tBu)) 3 , La(((iPr) 2 N) 2 C(tBu)) 3 , and La(FOD) 3 . 
   Ce precursors: Ce(N(SiMe 3 ) 2 ) 3 , Ce(N(iPr) 2 ) 3 , Ce(N(tBu)SiMe 3 ) 3 , Ce(TMPD) 3 , Ce(FOD) 3 , ((iPr)Cp) 3 Ce, Cp 3 Ce, Ce(Me 4 Cp) 3 , Ce(OCMe 2 CH 2 NMe 2 ) 3 , Ce(THD) 3 , Ce[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Ce(C 11 H 19 O 2 ) 3 .CH 3 (OCH 2 CH 2 ) 3 OCH 3 , Ce(C 11 H 19 O 2 ) 3 .CH 3 (OCH 2 CH 2 ) 4 OCH 3 , Ce(O(iPr)) 3 , and Ce(acac) 3 . 
   Pr precursors: Pr(N(SiMe 3 ) 2 ) 3 , ((iPr)Cp) 3 Pr, Cp 3 Pr, Pr(THD) 3 , Pr(FOD) 3 , (C 5 Me 4 H) 3 Pr, Pr[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Pr(C 11 H 19 O 2 ) 3 .CH 3 (OCH 2 CH 2 ) 3 OCH 3 , Pr(O(iPr)) 3 , Pr(acac) 3 , Pr(hfac) 3 , Pr(((tBu) 2 N) 2 CMe) 3 , Pr(((iPr) 2 N) 2 CMe) 3 , Pr(((tBu) 2 N) 2 C(tBu)) 3 , and Pr(((iPr) 2 N) 2 C(tBu)) 3 . 
   Nd precursors: Nd(N(SiMe 3 ) 2 ) 3 , Nd(N(iPr) 2 ) 3 , ((iPr)Cp) 3 Nd, Cp 3 Nd, (C 5 Me 4 H) 3 Nd, Nd(THD) 3 , Nd[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Nd(O(iPr)) 3 , Nd(acac) 3 , Nd(hfac) 3 , Nd(F 3 CC(O)CHC(O)CH 3 ) 3 , and Nd(FOD) 3 . 
   Sm precursors: Sm(N(SiMe 3 ) 2 ) 3 , ((iPr)Cp) 3 Sm, Cp 3 Sm, Sm(THD) 3 , Sm[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Sm(O(iPr)) 3 , Sm(acac) 3 , and (C 5 Me 5 ) 2 Sm. 
   Eu precursors: Eu(N(SiMe 3 ) 2 ) 3 , ((iPr)Cp) 3 Eu, Cp 3 Eu, (Me 4 Cp) 3 Eu, Eu(THD) 3 , Eu[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Eu(O(iPr)) 3 , Eu(acac) 3 , and (C 5 Me 5 ) 2 Eu. 
   Gd precursors: Gd(N(SiMe 3 ) 2 ) 3 , ((iPr)Cp) 3 Gd, Cp 3 Gd, Gd(THD) 3 , Gd[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Gd(O(iPr)) 3 , and Gd(acac) 3 . 
   Tb precursors: Tb(N(SiMe 3 ) 2 ) 3 , ((iPr)Cp) 3 Tb, Cp 3 Tb, Tb(THD) 3 , Tb[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Tb(O(iPr)) 3 , and Tb(acac) 3 . 
   Dy precursors: Dy(N(SiMe 3 ) 2 ) 3 , ((iPr)Cp) 3 Dy, Cp 3 Dy, Dy(THD) 3 , Dy[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Dy(O(iPr)) 3 , Dy(O 2 C(CH 2 ) 6 CH 3 ) 3 , and Dy(acac) 3 . 
   Ho precursors: Ho(N(SiMe 3 ) 2 ) 3 , ((iPr)Cp) 3 Ho, Cp 3 Ho, Ho(THD) 3 , Ho[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Ho(O(iPr)) 3 , and Ho(acac) 3 . 
   Er precursors: Er(N(SiMe 3 ) 2 ) 3 , ((iPr)Cp) 3 Er, ((nBu)Cp) 3 Er, Cp 3 Er, Er(THD) 3 , Er[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Er(O(iPr)) 3 , and Er(acac) 3 . 
   Tm precursors: Tm(N(SiMe 3 ) 2 ) 3 , ((iPr)Cp) 3 Tm, Cp 3 Tm, Tm(THD) 3 , Tm[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Tm(O(iPr)) 3 , and Tm(acac) 3 . 
   Yb precursors: Yb(N(SiMe 3 ) 2 ) 3 , Yb(N(iPr) 2 ) 3 , ((iPr)Cp) 3 Yb, Cp 3 Yb, Yb(THD) 3 , Yb[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Yb(O(iPr)) 3 , Yb(acac) 3 , (C 5 Me 5 ) 2 Yb, Yb(hfac) 3 , and Yb(FOD) 3 . 
   Lu precursors: Lu(N(SiMe 3 ) 2 ) 3 , ((iPr)Cp) 3 Lu, Cp 3 Lu, Lu(THD) 3 , Lu[OOCCH(C 2 H 5 )C 4 H 9 ] 3 , Lu(O(iPr)) 3 , and Lu(acac) 3 . 
   In the above precursors, as well as precursors set forth below, the following common abbreviations are used: Si: silicon; Me: methyl; Et: ethyl; iPr: isopropyl; nPr: n-propyl; Bu: butyl; nBu: n-butyl; sBu: sec-butyl; iBu: iso-butyl; tBu: tert-butyl; Cp: cyclopentadienyl; THD: 2,2,6,6-tetramethyl-3,5-heptanedionate; TMPD: 2,2,6,6-tetramethylpiperidide; acac: acetylacetonate; hfac: hexafluoroacetylacetonate; mmp: methoxy-2,2-dimethyl-2-propionate; and FOD: 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate. 
   Embodiments of the invention may utilize a wide variety of Group III precursors for incorporating aluminum into the nitride films. For example, many aluminum precursors have the formula:
 
AlL 1 L 2 L 3 D x  
 
where L 1 , L 2 , L 3  are individual anionic ligands, and D is a neutral donor ligand where x can be 0, 1, or 2. Each L 1 , L 2 , L 3  ligand may be individually selected from the groups of alkoxides, halides, aryloxides, amides, cyclopentadienyls, alkyls, silyls, amidinates, β-diketonates, ketoiminates, silanoates, and carboxylates. D ligands may be selected from groups of ethers, furans, pyridines, pyroles, pyrolidines, amines, crown ethers, glymes, and nitriles.
 
   Other examples of Group III precursors include: Al 2 Me 6 , Al 2 Et 6 , [Al(O(sBu)) 3 ] 4 , Al(CH 3 COCHCOCH 3 ) 3 , AlBr 3 , AlI 3 , Al(O(iPr)) 3 , [Al(NMe 2 ) 3 ] 2 , Al(iBu) 2 Cl, Al(iBu) 3 , Al(iBu) 2 H, AlEt 2 Cl, Et 3 Al 2 (O(sBu)) 3 , Al(THD) 3 , GaCl 3 , InCl 3 , GaH 3 , and InH 3 . 
   Examples of silicon precursors include, but are not limited to, silane (SiH 4 ), disilane (Si 2 H 6 ), monochlorosilane (SiClH 3 ), dichlorosilane (SiH 2 Cl 2 ), trichlorosilane (SiHCl 3 ), hexachlorodisilane (Si 2 Cl 6 ), diethylsilane, and alkylaminosilane compounds. Examples of alkylaminosilane compounds include, but are not limited to, di-isopropylaminosilane (H 3 Si(NiPr 2 )), bis(diethylamino)silane (H 2 Si(NEt 2 ) 2 , bis(diisopropylamino)silane (H 2 Si(NiPr 2 ) 2 , tris(isopropylamino)silane (HSi(NiPr 2 ) 3 ), bis(tert-butylamino)silane ((tBu(H)N) 2 SiH 2 ), tetrakis(dimethylamino)silane (Si(NMe 2 ) 4 ), tetrakis(ethylmethylamino)silane (Si(NEtMe) 4 ), tetrakis(diethylamino)silane (Si(NEt 2 ) 4 ), tris(dimethylamino)silane (HSi(NMe 2 ) 3 ), tris(ethylmethylamino)silane (HSi(NEtMe) 3 ), tris(diethylamino)silane (HSi(NEt 2 ) 3 ), and tris(dimethylhydrazino)silane (HSi(N(H)NMe 2 ) 3 ). 
   Examples of nitrogen precursors include N 2 , NH 3 , N 2 H 4 , and C 1 -C 10  alkylhydrazine compounds. Common C 1  and C 2  alkylhydrazine compounds include monomethyl-hydrazine (MeNHNH 2 ), 1,1-dimethyl-hydrazine (Me 2 NNH 2 ), and 1,2-dimethyl-hydrazine (MeNHNHMe). 
   The present inventors have realized that exposing a substrate to a metal precursor and one or more nitrogen precursors having different reactivity characteristics toward the metal precursor can be utilized to deposit a strained metal nitride film on the substrate. Thus, a strained metal nitride film can be formed as the metal nitride film is deposited, rather than by the conventional method of post processing of deposited films. Thus, embodiments of the present invention may reduce production time and equipment necessary for forming a strained metal nitride film. Further, the strain provided during deposition of the metal nitride film may be better controlled than that of post processing methods. For example, a predetermined strain gradient throughout the metal nitride film (rather than in only a surface region) can be provided by a particular process recipe for forming the strained metal nitride film. In particular, processing conditions such as the type of precursors used, the relative amounts of precursors used and/or exposure time to each precursor can be set to provide a predetermined strain in the metal nitride film. Further, embodiments of the invention may also provide better control of thickness and conformality of the metal nitride film than methods currently in practice. 
     FIGS. 3A-3E  and  FIGS. 4A-4E , are process flow diagrams for forming strained metal nitride according to embodiments of the invention.  FIGS. 6A-6E  and  FIGS. 7A-7E , are process flow diagrams for forming strained metal silicon nitride according to embodiments of the invention. The metal precursors, silicon precursors, and nitrogen precursors described above may be utilized to form these films. 
     FIG. 3A  is a process flow diagram for forming a strained metal nitride film on a substrate in a process chamber according to an embodiment of the invention. The process  300  of  FIG. 3A  may, for example, be performed to form a CMOS structure such as that shown in of  FIG. 1 . The process  300  may be performed in processing system  1  of  FIG. 2A , for example. In  FIG. 3A , the process  300  includes, in step  302 , exposing a substrate to a gas containing a metal precursor and optionally an inert gas such as Ar. 
   In step  304 , the substrate is exposed to a gas containing a first nitrogen precursor configured to react with the metal precursor with a first reactivity characteristic. For example, the first nitrogen precursor may react with the metal precursor within a processing space of the chamber, or with the metal precursor adsorbed on a surface of the substrate, or both. 
   In step  306 , the substrate is exposed to a gas containing a second nitrogen precursor configured to react with the metal precursor with a second reactivity characteristic different than the first reactivity characteristic. In the process  300 , the term reactivity characteristic refers to any characteristic of the reaction between a nitrogen precursor and a metal precursor that affects a property of a metal nitride film formed on the substrate. For example, as noted above, different reactivity characteristics may be expected based on different heat of formation (ΔH) for the first and second nitrogen precursors, and therefore different heat of formation for deposition of the metal nitride film. A property affected by a reactivity characteristic can be density of the metal nitride film. According to one embodiment, the first and second nitrogen precursors can be different precursor materials. For example, the first and second nitrogen precursors are selected from NH 3  and N 2 H 4 . However, the first and second precursors may be the same mixture of materials in different mixture ratios, as will be discussed below. In steps  304  and  306 , the gas containing the first and second nitrogen precursors may further contain an inert gas such as Ar. 
   The steps of the process  300  depicted in  FIG. 3A  can be continued for a predetermined time or repeated a predetermined number of times until a strained metal nitride film with a desired thickness has been deposited onto the substrate. Further, the sequence of steps  302 ,  304  and  306  of the process  300  can vary widely in accordance with embodiments of the invention. For example, the metal precursor, the first nitrogen precursor, and the second nitrogen precursor can be provided in a process chamber as discrete pulses having no temporal overlap (e.g., an ALD process). Alternatively, the metal precursor, the first nitrogen precursor, and the second nitrogen precursor can be provided simultaneously (e.g., a CVD process) while varying a ratio or the first and second nitrogen precursors. Some combination of these methods may also be used. For example, the metal precursor can be continuously provided to the process chamber while the first and second nitrogen precursors are pulsed, or both the metal precursor and first nitrogen precursors can be continuously provided, while the second nitrogen precursor is pulsed. As would be understood by one of ordinary skill in the art, various combinations are possible, and embodiments of the invention are not limited by the specific examples described in  FIGS. 3A-3E  herein. 
     FIG. 3B  is a process flow diagram for forming a strained metal nitride film according to an embodiment of the invention. The process  320  depicted in  FIG. 3B  is an ALD process that includes sequential gas exposures of a metal precursor and nitrogen precursors with partial or no temporal overlap between the different gas pulses. The process  320  includes, in step  322 , exposing a substrate to a gas pulse containing a metal precursor and optionally an inert gas such as Ar. 
   In step  324 , the substrate is exposed to a gas pulse containing a first nitrogen precursor or a gas pulse containing the first nitrogen precursor and a second nitrogen precursor in a first ratio. The first ratio may, for example, be defined as N 1 /N 2  or N 1 /(N 1 +N 2 ), where N 1  and N 2  refer to the amounts of the first and second nitrogen precursors, respectively. According to one embodiment, the first ratio may be varied from a ratio corresponding to substantially pure first nitrogen precursor, to another ratio corresponding to a combination of the first and second nitrogen precursors, to yet another ratio corresponding to substantially pure second nitrogen precursor. In one example, a ratio N 1 /(N 1 +N 2 ) may increase monotonically as 0, 0.05, 0.10, . . . , 0.90, 0.95, and 1.0, during deposition of the metal nitride film. The first and second nitrogen precursors can, for example, be selected from NH 3 , N 2 H 4 , and C 1 -C 10  alkylhydrazine compounds. According to one embodiment, the first and second nitrogen precursors are selected from NH 3  and N 2 H 4 . The gas pulse may further contain an inert gas such as Ar. 
   In step  326 , the substrate is exposed to a second gas pulse containing the metal precursor and optionally an inert gas such as Ar. In step  328 , the substrate is exposed to a gas pulse containing the second nitrogen precursor or a gas pulse containing the first nitrogen precursor and the second nitrogen precursor in a second ratio different from the first ratio. Thus, in the embodiment of  FIG. 3B , first and second nitrogen precursors, and first and second ratios of different nitrogen precursors are explicitly described. However, as noted above, the first and second precursors may be considered the same mixture of materials in different mixture ratios. The gas pulse can further contain an inert gas such as Ar. 
   The steps  322 - 328  may be repeated a predetermined number of times as shown by the process flow  334  until a strained metal nitride film with a desired thickness has been deposited onto the substrate. The process chamber may be purged with an inert gas, evacuated, or both purged and evacuated after each of steps  322 ,  324 ,  326 , and  328 . 
   According to one embodiment, steps  322  and  324  may be sequentially performed a first number of times as shown by the process flow  330 , prior to performing steps  326  and  328 . 
   According to another embodiment, steps  326  and  328  may be sequentially performed a second number of times as shown by the process flow  332 , prior to repeating steps  322  and  324  in the process flow  334 . In this regard, it is to be understood that the terms “a first number of times” and “a second number of times” are used to provide different terms for ease of understanding. However, the first and second number of times can be the same or a different number. 
   According to yet another embodiment, steps  322  and  324  may be sequentially performed a first number of times prior to performing steps  326  and  328  as shown by the process flow  330 , and steps  326  and  328  may be sequentially performed a second number of times as shown by the process flow  332 , prior to repeating steps  322  and  324  in the process flow  334 . 
   According to one embodiment, step  324  comprises exposing the substrate to a gas pulse containing a first nitrogen precursor and step  328  comprises exposing the substrate to a gas pulse containing a second nitrogen precursor. Furthermore, steps  322  and  324  may be sequentially performed a first number of times as shown by the process flow  330 , prior to performing steps  326  and  328 . Furthermore, steps  326  and  328  may be sequentially performed a second number of times as shown by the process flow  332 , prior to repeating steps  322  and  324  in the process flow  334 . 
   According to one embodiment, steps  322  and  324  may be sequentially performed a first number of times that decreases monotonically and steps  326  and  328  may be sequentially performed a second number of times that increases monotonically each time process flow  334  is performed. In one example, in step  322 , the substrate is exposed to a gas pulse containing a metal precursor, in step  324 , the substrate is exposed to a gas pulse containing a first nitrogen precursor, and steps  322  and  324  are repeating twice using the process flow  330 . Thereafter, in step  326 , the substrate is exposed to a gas pulse containing the metal precursor, and in step  328 , the substrate is exposed to a gas pulse containing a second nitrogen precursor. Next, in step  322 , the substrate is exposed to a gas pulse containing the precursor, in step  324 , the substrate is exposed to a gas pulse containing the first nitrogen precursor, and steps  322  and  324  are repeated once using the process flow  330 . Thereafter, in step  326 , the substrate is exposed to a gas pulse containing the metal precursor, in step  328 , the substrate is exposed to a gas pulse containing the second nitrogen precursor, and steps  326  and  328  are repeated once using the process flow  332 . Next, in step  322 , the substrate is exposed to a gas pulse containing the metal precursor, and in step  324 , the substrate is exposed to a gas pulse containing the first nitrogen precursor without repeat using process flow  330 . Thereafter, in step  326 , the substrate is exposed to a gas pulse containing the metal precursor, in step  328 , the substrate is exposed to a gas pulse containing the second nitrogen precursor, and steps  326  and  328  are repeated twice using process flow  332 . In this example, the first number of times decreases from 3 to 2 to 1 and the second number of times increases from 1 to 2 to 3 during deposition of the strained metal nitride film. In one example, the first and second nitrogen precursors can be selected from NH 3  and N 2 H 4 . 
   According to one embodiment of the invention, steps  322 ) and  324 ) of  FIG. 3B  may have at least partial temporal overlap. According to another embodiment of the invention, steps  326 ) and  328 ) may have at least partial temporal overlap. According to yet another embodiment of the invention, steps  326  and  328  may have no temporal overlap and steps  326  and  328  may have no temporal overlap. 
     FIG. 3C  is a process flow diagram for forming a strained metal nitride film according to another embodiment of the present invention. The process  340  includes, in step  342 , selecting a ratio of first and second nitrogen precursors. The ratio can range from a first nitrogen precursor only, to a mixture of the first and second nitrogen precursor, to the second nitrogen precursor only. In step  344 , the substrate is exposed to a gas pulse containing a metal precursor, and in step  346 , the substrate is exposed to a gas pulse containing the first and second nitrogen precursors in the selected ratio. In step  348 , the ratio is adjusted and step  344  is repeated as shown by the process flow  350 . According to one embodiment, the ratio of the first and second nitrogen precursors can monotonically increase or decrease during deposition of the metal nitride film. The process  340  may be performed as a pulsed CVD process that includes interrupted gas exposures of a metal precursor and different nitrogen precursors with at least partial temporal overlap of the gas pulses in steps  344  and  346 . Alternately, the process  340  may be performed as an ALD process with no overlap of the gas pulses in steps  344  and  346 . 
     FIG. 3D  is a process flow diagram for forming a strained metal nitride film according to another embodiment of the present invention. The process  360  includes, in step  362 , exposing a substrate to a gas pulse containing a metal precursor and a first nitrogen precursor or a gas pulse containing the metal precursor, the first nitrogen precursor, and a second nitrogen precursor, where the gas pulse contains the first and second nitrogen precursors in a first ratio. In step  364 , the substrate is exposed to a gas pulse containing the metal precursor and the second nitrogen precursor, or a gas pulse containing the metal precursor and the first and second nitrogen precursors in a second ratio. Steps  362  and  364  can be repeated to deposit the metal nitride film to a desired thickness as shown by process flow  366 . According to one embodiment, the first ratio can monotonically increase and the second ratio can monotonically decrease during deposition of the metal nitride film. 
     FIG. 3E  is a process flow diagram for forming a strained metal nitride film according to another embodiment of the present invention. The process  380  includes, in step  382 , exposing a substrate to a gas containing a metal precursor and first and second nitrogen precursors, where a ratio of the first and second nitrogen precursors is varied during the exposure. In one example the ratio of the first and second nitrogen precursors can monotonically increase or decrease during deposition of the metal nitride film. 
     FIG. 4A  is a process flow diagram for forming a strained metal nitride film on a substrate in a process chamber according to an embodiment of the present invention. The process  400  of  FIG. 4A  may be performed in a processing system  2  of  FIG. 2B , for example. As seen in  FIG. 4A , the process  400  includes, in step  402 , exposing a substrate to a gas containing a metal precursor and optionally an inert gas such as Ar. 
   In step  404 , the substrate is exposed to a gas containing a nitrogen precursor activated by a plasma source at a first level of plasma power to react with the metal precursor with a first reactivity characteristic. In one embodiment, the first level of plasma power is less than a plasma activation power (e.g., 0 W) and therefore a plasma is not activated. The plasma activation of the nitrogen precursor affects a property of a metal nitride film formed on the substrate, for example the deposition rate and the density of the metal nitride film. The plasma activated nitrogen precursor may react with the metal precursor within a processing space of the chamber, or with metal precursor adsorbed on a surface of the substrate, or both. 
   In step  406 , the substrate is exposed to a gas containing the nitrogen precursor activated by the plasma source at a second level of plasma power to react with the metal precursor with a second reactivity characteristic different than the first reactivity characteristic. 
   Plasma activation of a nitrogen precursor (or other precursors) can result in electronic excitation and/or ionization of the nitrogen precursor that affects reactivity towards a metal precursor. In addition, plasma activation can result in at least partial dissociation of the nitrogen precursor, thereby creating a modified nitrogen precursor with a different reactivity towards the metal precursor. Increasing the level of plasma power and plasma density, for example, will generally increase the amount of electronically excited, ionized, and at least partially dissociated nitrogen precursor. In addition, increased levels of plasma power and plasma density may be utilized to vary the concentration of additional charged species (e.g., Argon ions, electrons, or both) in the plasma environment. These additional charged species may interact with the metal nitride film and the substrate during deposition, thereby affecting a reactivity characteristic and a property (e.g., density, strain) of at least a portion of a thickness of the metal nitride film. 
   The steps of the process  400  depicted in  FIG. 4A  can be continued for a predetermined time or repeated a predetermined number of times until a strained metal nitride film with a desired thickness has been deposited onto the substrate. Further, the sequence of steps  402 ,  404  and  406  of the process  400  can vary widely in accordance with embodiments of the invention. For example, the metal precursor and the plasma activated nitrogen precursor can be provided in the process chamber as discrete gas pulses having no temporal overlap, where the level of plasma power is varied for the discrete gas pulses. Alternatively, the metal precursor and the nitrogen precursor may be flowed continuously while simply varying the level of plasma power. Some combination of these methods may also be used. For example, the metal precursor can be continuously provided to the chamber while the nitrogen precursor and the plasma are pulsed at different levels of plasma power, or both the metal and the nitrogen precursor can be continuously provided and the plasma is pulsed at different levels of plasma power. As would be understood by one of ordinary skill in the art, various combinations are possible, and embodiments of the invention are not limited by the specific examples described in  FIGS. 4A-4E  herein. 
     FIG. 4B  is a process flow diagram for forming a strained metal nitride film according to an embodiment of the invention. The process  420  is a PEALD process similar to the ALD process  320  of  FIG. 3B  and includes sequential gas exposures of a metal precursor and a plasma activated nitrogen precursor with partial or no temporal overlap between the different gas pulses. 
   The process  420  includes, in step  422 , exposing a substrate to a gas pulse containing a metal precursor and optionally an inert gas such as Ar. In step  424 , the substrate is exposed to a gas pulse containing a nitrogen precursor activated by a plasma source at a first level of plasma power. In step  426 , the substrate is exposed to a second gas pulse containing the metal precursor. In step  428 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at a second level of plasma power. 
     FIGS. 5A and 5B  show power graphs depicting different levels of plasma power coupled to a process chamber in accordance with embodiments of the invention. As shown by the exemplary power curve  510  in  FIG. 5A , the level of plasma power may be applied to the process chamber in a plurality discrete levels,  520 ,  530 , and  540 . In one example, the power level  520  may be at or below a lower limit for plasma formation and the power level  540  may correspond to a maximum desired level of plasma power. The maximum desired level of plasma power is preferably not higher than a level determined to disrupt or damage the substrate including any deposited films thereon. As seen in  FIG. 5B , the level of plasma power may be applied to the process chamber in a continuously changing fashion represented by the power curve  550 . 
   As would be understood by one of ordinary skill in the art, the power curves of  FIGS. 5A and 5B  are exemplary, and the varying level of plasma power may depend on the composition and characteristic of the film to be deposited by the process. For example, the plasma power of  FIG. 5A  can include more than three (3) discrete levels of plasma power, and the plasma power of  FIG. 5B  may change in a non-linear fashion. Moreover, a combination of stepped and ramped power can be used to vary the level of plasma power. Further, the power may be provided in discrete pulses where power is on or off. Still further, suitable high levels of plasma power that enable deposition of a film at improved deposition speeds and with reduced impurities in accordance with an embodiment of the invention can be determined by direct experimentation and/or design of experiments (DOE). Other adjustable process parameters such as substrate temperature, process pressure, type of process gas and relative gas flows can also be determined by direct experimentation and/or DOE. 
   Referring back to  FIG. 4A , steps  422 - 428  may be repeated a predetermined number of times as shown by the process flow  434  until a strained metal nitride film with a desired thickness has been deposited onto the substrate. The process chamber may be purged with an inert gas, evacuated, or both purged and evacuated after each of steps  422 ,  424 ,  426 , and  428 . 
   According to one embodiment, steps  422  and  424  may be sequentially performed a first number of times as shown by the process flow  430 , prior to performing steps  426  and  428 . 
   According to another embodiment, steps  426  and  428  may be sequentially performed a second number of times as shown by the process flow  432 , prior to repeating steps  422  and  424  in the process flow  434 . 
   According to yet another embodiment, steps  422  and  424  may be sequentially performed a first number of times prior to performing steps  426  and  428  as shown by the process flow  430 , and steps  426  and  428  may be sequentially performed a second number of times as shown by the process flow  432 , prior to repeating steps  422  and  424  in the process flow  434 . 
   According to one embodiment, the first number of times may decrease monotonically and the second number of times may increase monotonically each time process flow  434  is performed. In one example, in step  422 , the substrate is exposed to a gas pulse containing a metal precursor, in step  424 , the substrate is exposed to a gas pulse containing a nitrogen precursor activated by a plasma source at a first level of plasma power, and steps  422  and  424  are repeated twice using the process flow  430 . Thereafter, in step  426 , the substrate is exposed to a gas pulse containing the metal precursor, and in step  428 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at a second level of plasma power. Next, in step  422 , the substrate is exposed to a gas pulse containing the precursor, in step  424 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at the first level of plasma power, and steps  422  and  424  are repeated once using the process flow  430 . Thereafter, in step  426 , the substrate is exposed to a gas pulse containing the metal precursor, in step  428 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at a first level of plasma power, and steps  426  and  428  are repeated once using the process flow  432 . Next, in step  422 , the substrate is exposed to a gas pulse containing the metal precursor, and in step  424 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at the first level of plasma power. Thereafter, in step  426 , the substrate is exposed to a gas pulse containing the metal precursor, in step  428 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at the second level of plasma power, and steps  426  and  428  are repeated twice using process flow  432 . In this example, the first number of times decreases from 3 to 2 to 1 and the second number of times increases from 1 to 2 to 3 during deposition of the strained metal nitride film. In one example, the nitrogen precursor can be selected from NH 3  and N 2 H 4 . 
   Still referring to  FIG. 4B , according to one embodiment of the invention, the gas pulse in step  424  may further comprise a dilution gas in a first ratio with the nitrogen precursor, and step  428  may further comprise the dilution gas in a second ratio with the nitrogen precursor, where the second ratio is different from the first ratio. The addition of a dilution gas to a nitrogen precursor can affect the plasma density in the process chamber and thus the amount of activated nitrogen precursor available to interact with the metal precursor. The dilution gas may be selected from He, Ar, Ne, Kr, Xe, H 2 , or N 2 , or a combination of two or more thereof. The first ratio may, for example, be defined as D/N or D/(D+N), where D and N refer to the amounts of the dilution gas and the nitrogen precursor, respectively. According to one embodiment, the first ratio may be varied from ratio corresponding to substantially pure nitrogen precursor, to a another ratio corresponding to a combination of the dilution gas and the nitrogen precursor, to yet another ratio corresponding to substantially pure dilution gas. In one example, a ratio D/(D+N) may increase monotonically as 0, 0.05, 0.10, . . . , 0.90, 0.95, and 1.0, during deposition of the metal nitride film. 
     FIG. 4C  is a process flow diagram for forming a strained metal nitride film according to another embodiment of the present invention. The process  440  includes, in step  442 , selecting a level of plasma power. The level of plasma power can range from a first level at or below a lower limit for plasma formation to a second level of plasma power corresponding to a maximum desired level of plasma power. Thus, the first level of plasma power can be 0 W of plasma power. In step  444 , the substrate is exposed to a gas pulse containing a metal precursor, and in step  446 , the substrate is exposed to a gas pulse containing a nitrogen precursor activated by the plasma source at the selected level of plasma power. In step  448 , the level of plasma power is adjusted, and step  444  is repeated as shown by the process flow  450 . According to one embodiment, the level of plasma power can monotonically increase or decrease during deposition of the metal nitride film. The process  440  may be performed as a pulsed PECVD process that includes interrupted gas exposures of a metal precursor and a plasma activated nitrogen precursor with at least partial temporal overlap of the gas pulses in steps  444  and  446 . Alternately, the process  440  may be performed as a PEALD process with no overlap of the gas pulses in steps  444  and  446 . 
   Still referring to  FIG. 4C , according to one embodiment of the invention, the gas pulse in step  446  may further comprise a dilution gas in a first ratio with the nitrogen precursor, and step  448  may further comprise adjusting the amount of dilution gas from the first ratio to a second ratio different from the first ratio. 
     FIG. 4D  is a process flow diagram for forming a strained metal nitride film according to another embodiment of the invention. The process  460  includes, in step  462 , exposing a substrate to a gas pulse containing a metal precursor and a nitrogen precursor activated by a plasma source at a first level of plasma power. In step  464 , the substrate is exposed to a gas pulse containing the metal precursor and the nitrogen precursor activated by the plasma source at a second level of plasma power different from the first level of plasma power. According to one embodiment of the invention, the gas pulse in step  462  may further comprise a dilution gas in a first ratio with the nitrogen precursor and step  464  may further comprises the dilution gas in a second ratio with the nitrogen precursor, where the second ratio is different from the first ratio. 
     FIG. 4E  is a process flow diagram for forming a strained metal nitride film according to another embodiment of the present invention. The process  480  includes, in step  482 , exposing a substrate to a gas containing a metal precursor and a nitrogen precursor activated by a plasma source at a level of plasma power that is varied during the exposure. In one example the level of plasma power can monotonically increase or decrease during deposition of the metal nitride film. According to one embodiment of the invention, the gas pulse in step  482  may further comprise a dilution gas in a ratio with the nitrogen precursor where the ratio is varied during the exposure. In one example the ratio can monotonically increase or decrease during deposition of the metal nitride film. 
   The present inventors have realized that exposing a substrate to a metal precursor, a silicon precursor, and one or more nitrogen precursors having different reactivity characteristics toward the metal precursor or the silicon precursor can be utilized to deposit a strained metal silicon nitride film on the substrate. Thus, a strained metal silicon nitride film can be formed as the metal silicon nitride film is deposited, rather than by the conventional method of post processing of deposited films. Thus, embodiments of the present invention may reduce production time and equipment necessary for forming a strained metal silicon nitride film. Further, the strain provided during deposition of the metal silicon nitride film may be better controlled than that of post processing methods. For example, a predetermined strain gradient throughout the metal silicon nitride film (rather than in only a surface region) can be provided by a particular process recipe for forming the strained metal silicon nitride film. In particular, processing conditions such as the type of precursors used, the relative amounts of precursors used, exposure time to each precursor can be set to provide a predetermined strain in the metal silicon nitride film. Further, embodiments of the invention may also provide better control of thickness and conformality of the metal silicon nitride film than methods currently in practice. 
   The processes of  FIGS. 3A-3E  and  FIGS. 4A-4E  may further include activating a plasma during one or more of the exposing steps. Further, a power coupled to the plasma may be varied to provide a different reactivity characteristic, as will be discussed below. That is, the embodiments of  FIGS. 3A-3E  and  FIGS. 4A-4E  using different first and second nitrogen precursors (or different ratios of first and second nitrogen precursors) may be combined with the plasma power variation embodiments discussed below. 
     FIG. 6A  is a process flow diagram for forming a strained metal silicon nitride film on a substrate in a process chamber according to an embodiment of the invention. The process  600  of  FIG. 6A  may, for example, be performed to form a CMOS structure such as that shown in of  FIG. 1 . The process  600  may be performed in processing system  1  of  FIG. 2A , for example. As seen in  FIG. 6A , the process  600  includes, in step  602 , exposing a substrate to a gas containing a metal precursor and optionally an inert gas such as Ar. In step  604 , the substrate is exposed to a gas containing a silicon precursor and optionally an inert gas such as Ar. 
   In step  606 , the substrate is exposed to a gas containing a first nitrogen precursor configured to react with the metal precursor or the silicon precursor with a first reactivity characteristic. For example, the first nitrogen precursor may react with metal precursor or the silicon precursor within a processing space of the chamber, or with the metal precursor or the silicon precursor adsorbed on a surface of the substrate, or both. 
   In step  608 , the substrate is exposed to a gas containing a second nitrogen precursor configured to react with the metal precursor or the silicon precursor with a second reactivity characteristic different than the first reactivity characteristic. In the process of  608 , the term reactivity characteristic refers to any characteristic of the reaction between a nitrogen precursor and a metal precursor or a silicon precursor that affects a property of a metal silicon nitride film formed on the substrate. For example, as noted above, different reactivity characteristics may be expected based on different heat of formation (ΔH) for the first and second nitrogen precursors, and therefore different heat of formation for deposition of the metal silicon nitride film. A property affected by a reactivity characteristic can be density of the metal silicon nitride film. According to one embodiment, the first and second nitrogen precursors are selected from NH 3  and N 2 H 4 . In steps  606  and  608 , the gas containing the first and second nitrogen precursors may further contain an inert gas such as Ar. 
   The steps of the process  600  depicted in  FIG. 6A  can be continued for a predetermined time or repeated a predetermined number of times until a strained metal silicon nitride film with a desired thickness has been deposited onto the substrate. Further, the sequence of steps  602 ,  604 ,  606 , and  608  of the process  600  can vary widely in accordance with embodiments of the invention. For example, the metal precursor, the silicon precursor, the first nitrogen precursor, and the second nitrogen precursor can be provided in a process chamber as discrete pulses having no temporal overlap (e.g., an ALD process). Alternatively, the metal precursor, silicon precursor, the first nitrogen precursor, and the second nitrogen precursor can be provided simultaneously (e.g., a CVD process) while varying a ratio or the first and second nitrogen precursors. Some combination of these methods may also be used. For example, the metal precursor and the silicon precursor can be continuously provided to the process chamber while the first and second nitrogen precursors are pulsed, or the metal precursor, the silicon precursor, and the first nitrogen precursor can be continuously provided, while the second nitrogen precursor is pulsed. As would be understood by one of ordinary skill in the art, various combinations are possible, and embodiments of the invention are not limited by the specific examples described in  FIGS. 6A-6E  herein. 
     FIG. 6B  is a process flow diagram for forming a strained metal silicon nitride film according to an embodiment of the invention. The process  620  depicted in  FIG. 6B  is an ALD process that includes sequential gas exposures of a metal precursor, a silicon precursor, and nitrogen precursors with partial or no temporal overlap between the different gas pulses. The process  620  includes, in step  622 , exposing a substrate to a gas pulse containing a metal precursor and optionally an inert gas such as Ar. 
   In step  624 , the substrate is exposed to a gas pulse containing a first nitrogen precursor or a gas pulse containing the first nitrogen precursor and a second nitrogen precursor in a first ratio. The first ratio may, for example, be defined as N 1 /N 2  or N 1 /(N 1 +N 2 ), where N 1  and N 2  refer to the amounts of the first and second nitrogen precursors, respectively. According to one embodiment, the first ratio may be varied from a ratio corresponding to substantially pure first nitrogen precursor, to another ratio corresponding to a combination of the first and second nitrogen precursors, to yet another ratio corresponding to substantially pure second nitrogen precursor. In one example, a ratio N 1 /(N 1 +N 2 ) may increase monotonically as 0, 0.05, 0.10, . . . , 0.90, 0.95, and 1.0, during deposition of the metal silicon nitride film. The first and second nitrogen precursors can, for example, be selected from NH 3 , N 2 H 4 , and C 1 -C 10  alkylhydrazine compounds. According to one embodiment, the first and second nitrogen precursors are selected from NH 3  and N 2 H 4 . The gas pulse may further contain an inert gas such as Ar. 
   In step  626 , the substrate is exposed to a gas pulse containing a silicon precursor and optionally an inert gas such as Ar. In step  628 , the substrate is exposed to a gas pulse containing the second nitrogen precursor or a gas pulse containing the first nitrogen precursor and the second nitrogen precursor in a second ratio different from the first ratio. The gas pulse can further contain an inert gas such as Ar. 
   The steps  622 - 628  may be repeated a predetermined number of times as shown by the process flow  634  until a strained metal silicon nitride film with a desired thickness has been deposited onto the substrate. The process chamber may be purged with an inert gas, evacuated, or both purged and evacuated after each of steps  622 ,  624 ,  626 , and  628 . 
   According to one embodiment, steps  622  and  624  may be sequentially performed a first number of times as shown by the process flow  630 , prior to performing steps  626  and  628 . 
   According to another embodiment, steps  626  and  628  may be sequentially performed a second number of times as shown by the process flow  632 , prior to repeating steps  622  and  624  in the process flow  634 . 
   According to yet another embodiment, steps  622  and  624  may be sequentially performed a first number of times prior to performing steps  626  and  628  as shown by the process flow  630 , and steps  626  and  628  may be sequentially performed a second number of times as shown by the process flow  632 , prior to repeating steps  622  and  624  in the process flow  634 . 
   According to one embodiment, step  624  comprises exposing the substrate to a gas pulse containing a first nitrogen precursor and step  628  comprises exposing the substrate to a gas pulse containing a second nitrogen precursor. Furthermore, steps  622  and  624  may be sequentially performed a first number of times as shown by the process flow  630 , prior to performing steps  626  and  628 . Furthermore, steps  626  and  628  may be sequentially performed a second number of times as shown by the process flow  632 , prior to repeating steps  622  and  624  in the process flow  634 . 
   According to one embodiment, steps  622  and  624  may be sequentially performed a first number of times that decreases monotonically and steps  626  and  628  may be sequentially performed a second number of times that increases monotonically each time process flow  634  is performed. In one example, in step  622 , the substrate is exposed to a gas pulse containing a metal precursor, in step  624 , the substrate is exposed to a gas pulse containing a first nitrogen precursor, and steps  622  and  624  are repeated twice using the process flow  630 . Thereafter, in step  626 , the substrate is exposed to a gas pulse containing a silicon precursor, and in step  628 , the substrate is exposed to a gas pulse containing a second nitrogen precursor. Next, in step  622 , the substrate is exposed to a gas pulse containing the precursor, in step  624 , the substrate is exposed to a gas pulse containing the first nitrogen precursor, and steps  622  and  624  are repeated once using the process flow  630 . Thereafter, in step  626 , the substrate is exposed to a gas pulse containing the silicon precursor, in step  628 , the substrate is exposed to a gas pulse containing the second nitrogen precursor, and steps  626  and  628  are repeated once using the process flow  632 . Next, in step  622 , the substrate is exposed to a gas pulse containing the metal precursor, and in step  624 , the substrate is exposed to a gas pulse containing the first nitrogen precursor without repeat using process flow  630 . Thereafter, in step  626 , the substrate is exposed to a gas pulse containing the silicon precursor, in step  628 , the substrate is exposed to a gas pulse containing the second nitrogen precursor, and steps  626  and  628  are repeated twice using process flow  632 . In this example, the first number of times decreases from 3 to 2 to 1 and the second number of times increases from 1 to 2 to 3 during deposition of the strained metal silicon nitride film. In one example, the first and second nitrogen precursors can be selected from NH 3  and N 2 H 4 . 
   According to one embodiment of the invention, steps  622  and  624  of  FIG. 6B  may have at least partial temporal overlap. According to another embodiment of the invention, steps  626  and  628  may have at least partial temporal overlap. According to yet another embodiment of the invention, steps  622  and  624  may have no temporal overlap and steps  626  and  628  may have no temporal overlap. 
     FIG. 6C  is a process flow diagram for forming a strained metal silicon nitride film according to another embodiment of the present invention. The process  640  includes, in step  642 , selecting a ratio of first and second nitrogen precursors. The ratio can range from a first nitrogen precursor only, to a mixture of the first and second nitrogen precursors, to the second nitrogen precursor only. In step  644 , the substrate is exposed to a gas pulse containing a metal precursor, in step  646 , the substrate is exposed to a gas pulse containing a silicon precursor, and in step  648 , the substrate is exposed to a gas pulse containing the first and second nitrogen precursors in the selected ratio. In step  650 , the ratio is adjusted and step  644  is repeated as shown by the process flow  652 . According to one embodiment, the ratio of the first and second nitrogen precursors can monotonically increase or decrease during deposition of the metal silicon nitride film. The process  640  may be performed as a pulsed CVD process that includes interrupted gas exposures of a metal precursor, a silicon precursor, and different nitrogen precursors with at least partial temporal overlap of the gas pulses in steps  644 ,  646 , and  648 . Alternately, the process  640  may be performed as an ALD process with no overlap of the gas pulses in steps  644 ,  646 , and  648 . 
     FIG. 6D  is a process flow diagram for forming a strained metal silicon nitride film according to another embodiment of the present invention. The process  660  includes, in step  662 , exposing a substrate to a gas pulse containing a metal precursor and a first nitrogen precursor or a gas pulse containing the metal precursor, the first nitrogen precursor, and a second nitrogen precursor where the gas pulse contains the first and second nitrogen precursors in a first ratio. In step  664 , the substrate is exposed to a gas pulse containing a silicon precursor and the second nitrogen precursor, or a gas pulse containing the silicon precursor and the first and second nitrogen precursors in a second ratio. Steps  662  and  664  can be repeated to deposit the metal nitride film to a desired thickness as shown by process flow  366 . According to one embodiment, the first ratio can monotonically increase and the second ratio can monotonically decrease during deposition of the metal silicon nitride film. 
   According to one embodiment of the invention, the gas pulse in step  662  may further contain a silicon precursor and the gas pulse in step  664  may further contain a metal precursor. 
   According to one embodiment of the invention, in the process  660 , the first ratio, the second ratio, or both the first and second ratios, may be varied between a ratio corresponding to substantially pure first nitrogen precursor and a ratio corresponding to substantially pure second nitrogen precursor. In one example, the first or second ratios may be varied monotonically. 
     FIG. 6E  is a process flow diagram for forming a strained metal silicon nitride film according to another embodiment of the present invention. The process  680  includes, in step  682 , exposing a substrate to a gas containing a metal precursor, a silicon precursor and first and second nitrogen precursors, where a ratio of the first and second nitrogen precursors is varied during the exposure. In one example the ratio of the first and second nitrogen precursors can monotonically increase or decrease during deposition of the metal silicon nitride film. 
     FIG. 7A  is a process flow diagram for forming a strained metal silicon nitride film on a substrate in a process chamber according to an embodiment of the present invention. The process  700  of  FIG. 7A  may be performed in a processing system  2  of  FIG. 2B , for example. As seen in  FIG. 7A , the process  700  includes, in step  702 , exposing a substrate to a gas containing a metal precursor and optionally an inert gas such as Ar. In step  704 , the substrate is exposed to a gas containing a silicon precursor and optionally an inert gas such as Ar. 
   In step  706 , the substrate is exposed to a gas containing a nitrogen precursor activated by a plasma source at a first level of plasma power to react with the metal precursor or the silicon precursor with a first reactivity characteristic. In one embodiment, the first level of plasma power is less than a plasma activation power (e.g. 0 W) and therefore a plasma is not activated. The plasma activation of the nitrogen precursor affects a property of a metal silicon nitride film formed on the substrate, for example the deposition rate and the density of the metal silicon nitride film. The plasma activated nitrogen precursor may react with the metal precursor or the silicon precursor within a processing space of the chamber, or with the metal precursor or the silicon precursor adsorbed on a surface of the substrate, or both. 
   In step  708 , the substrate is exposed to a gas containing the nitrogen precursor activated by the plasma source at a second level of plasma power to react with the metal precursor or the silicon precursor with a second reactivity characteristic different than the first reactivity characteristic. 
   The steps of the process  700  depicted in  FIG. 7A  can be continued for a predetermined time or repeated a predetermined number of times until a strained metal silicon nitride film with a desired thickness has been deposited onto the substrate. Further, the sequence of steps  702 ,  704 ,  706  and  708  of the process  700  can vary widely in accordance with embodiments of the invention. For example, the metal precursor, the silicon precursor, and the nitrogen precursor can be provided in the process chamber as discrete gas pulses having no temporal overlap, where the level of plasma power is varied for the discrete gas pulses. Alternatively, the metal precursor, the silicon precursor and the nitrogen precursor may be flowed continuously while simply varying the level of plasma power. Some combination of these methods may also be used. For example, the metal precursor and the silicon precursor can be continuously provided to the chamber while the nitrogen precursor and the plasma are pulsed at different levels of plasma power, or the metal, the silicon precursor and the nitrogen precursor can be continuously provided and the plasma is pulsed at different levels of plasma power. As would be understood by one of ordinary skill in the art, various combinations are possible, and embodiments of the invention are not limited by the specific examples described in  FIGS. 7A-7E  herein. 
     FIG. 7B  is a process flow diagram for forming a strained metal silicon nitride film according to an embodiment of the invention. The process  720  is PEALD process similar to the ALD process  620  of  FIG. 6B  and includes sequential gas exposures of a metal precursor, a silicon precursor, and a plasma activated nitrogen precursor with partial or no temporal overlap between the different gas pulses. 
   The process  720  includes, in step  722 , exposing a substrate to a gas pulse containing a metal precursor and optionally an inert gas such as Ar. In step  724 , the substrate is exposed to a gas pulse containing a nitrogen precursor activated by a plasma source at a first level of plasma power. In step  726 , the substrate is exposed to a gas pulse containing a silicon precursor. In step  728 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at a second level of plasma power. As described above,  FIGS. 5A and 5B  show power graphs depicting different levels of plasma power coupled to a process chamber in accordance with embodiments of the invention. In one example the first and second levels of plasma power can monotonically increase or decrease during deposition of a metal silicon nitride film that contains multiple metal layers and silicon layers. In another example, the first and second levels of plasma power can have different starting levels and vary independently of each other or vary in a similar manner during deposition of the metal silicon nitride film. The first and second levels of plasma power may be selected and optimized for specific metal, silicon, and nitrogen precursors and desired film properties. 
   The steps  722 - 728  may be repeated a predetermined number of times as shown by the process flow  734  until a strained metal silicon nitride film with a desired thickness has been deposited onto the substrate. The process chamber may be purged with an inert gas, evacuated, or both purged and evacuated after each of steps  722 ,  724 ,  726 , and  728 . 
   According to one embodiment, steps  722  and  724  may be sequentially performed a first number of times as shown by the process flow  730 , prior to performing steps  726  and  728 . 
   According to another embodiment, steps  726  and  728  may be sequentially performed a second number of times as shown by the process flow  732 , prior to repeating steps  722  and  724  in the process flow  734 . 
   According to yet another embodiment, steps  722  and  724  may be sequentially performed a first number of times prior to performing steps  726  and  728  as shown by the process flow  730 , and steps  726  and  728  may be sequentially performed a second number of times as shown by the process flow  732 , prior to repeating steps  722  and  724  in the process flow  734 . 
   According to one embodiment, the first number of times may decrease monotonically and the second number of times may increase monotonically each time process flow  734  is performed. In one example, in step  722 , the substrate is exposed to a gas pulse containing a metal precursor, in step  724 , the substrate is exposed to a gas pulse containing a nitrogen precursor activated by a plasma source at a first level of plasma power, and steps  722  and  724  are repeated twice using the process flow  730 . Thereafter, in step  726 , the substrate is exposed to a gas pulse containing a silicon precursor, and in step  728 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at a second level of plasma power. Next, in step  722 , the substrate is exposed to a gas pulse containing the precursor, in step  724 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at the first level of plasma power, and steps  722  and  724  are repeated once using the process flow  730 . Thereafter, in step  726 , the substrate is exposed to a gas pulse containing the silicon precursor, in step  728 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at a first level of plasma power, and steps  726  and  728  are repeated once using the process flow  732 . Next, in step  722 , the substrate is exposed to a gas pulse containing the metal precursor, and in step  724 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at the first level of plasma power. Thereafter, in step  726 , the substrate is exposed to a gas pulse containing the silicon precursor, in step  728 , the substrate is exposed to a gas pulse containing the nitrogen precursor activated by the plasma source at the second level of plasma power, and steps  726  and  728  are repeated twice using process flow  732 . In this example, the first number of times decreases from 3 to 2 to 1 and the second number of times increases from 1 to 2 to 3 during deposition of the strained metal silicon nitride film. In one example, the nitrogen precursor can be selected from NH 3  and N 2 H 4 . 
   Still referring to  FIG. 7B , according to one embodiment of the invention, the gas pulse in step  724  may further comprise a dilution gas in a first ratio with the nitrogen precursor, and step  728  may further comprise the dilution gas in a second ratio with the nitrogen precursor, where the second ratio is different from the first ratio. The addition of a dilution gas to a nitrogen precursor can affect the plasma density in the process chamber and thus the amount of activated nitrogen precursor available to interact with the metal precursor. The dilution gas may be selected from He, Ar, Ne, Kr, Xe, H 2 , or N 2 , or a combination of two or more thereof. The first ratio may, for example, be defined as D/N or D/(D+N), where D and N refer to the amounts of the dilution gas and the nitrogen precursor, respectively. According to one embodiment, the first ratio may be varied from ratio corresponding to substantially pure nitrogen precursor, to another ratio corresponding to a combination of the dilution gas and the nitrogen precursor, to yet another ratio corresponding to substantially pure dilution gas. In one example, a ratio D/(D+N) may increase monotonically as 0, 0.05, 0.10, . . . , 0.90, 0.95, and 1.0, during deposition of the metal silicon nitride film. 
     FIG. 7C  is a process flow diagram for forming a strained metal silicon nitride film according to another embodiment of the present invention. The process  740  includes, in step  742 , selecting a level of plasma power. The level of plasma power can range from a first level at or below a lower limit for plasma formation to a second level of plasma power corresponding to a maximum desired level of plasma power. Thus, the first level of plasma power can be 0 W of plasma power. In step  744 , the substrate is exposed to a gas pulse containing a metal precursor, in step  746 , the substrate is exposed to a gas pulse containing a silicon precursor, and in step  748 , the substrate is exposed to a gas pulse containing a nitrogen precursor activated by the plasma source at the selected level of plasma power. In step  750 , the level of plasma power is adjusted, and step  744  is repeated as shown by the process flow  752 . According to one embodiment, the level of plasma power can monotonically increase or decrease during deposition of the metal silicon nitride film. The process  740  may be performed as a pulsed PECVD process that includes interrupted gas exposures of a metal precursor, a silicon precursor, and a plasma activated nitrogen precursor with at least partial temporal overlap of the gas pulses in steps  744 ,  746 , and  748 . Alternately, the process  740  may be performed as a PEALD process with no overlap of the gas pulses in steps  744 ,  746 , and  748 . 
   Still referring to  FIG. 7C , according to one embodiment of the invention, the gas pulse in step  748  may further comprise a dilution gas in a first ratio with the nitrogen precursor, and step  750  may further comprise adjusting the amount of dilution gas from the first ratio to a second ratio different from the first ratio. 
     FIG. 7D  is a process flow diagram for forming a strained metal silicon nitride film according to another embodiment of the invention. The process  760  includes, in step  762 , exposing a substrate to a gas pulse containing a metal precursor, a silicon precursor, and a nitrogen precursor activated by a plasma source at a first level of plasma power. In step  764 , the substrate is exposed to a gas pulse containing the metal precursor, the silicon precursor and the nitrogen precursor activated by the plasma source at a second level of plasma power different from the first level of plasma power. According to one embodiment of the invention, the gas pulse in step  762  may further comprise a dilution gas in a first ratio with the nitrogen precursor and step  764  may further comprise the dilution gas in a second ratio with the nitrogen precursor, where the second ratio is different from the first ratio. 
     FIG. 7E  is a process flow diagram for forming a strained metal silicon nitride film according to another embodiment of the present invention. The process  780  includes, in step  782 , exposing a substrate to a gas containing a metal precursor, a silicon precursor, and a nitrogen precursor activated by a plasma source at a level of plasma power that is varied during the exposure. In one example the level of plasma power can monotonically increase or decrease during deposition of the metal silicon nitride film. According to one embodiment of the invention, the gas pulse in step  782  may further comprises a dilution gas in a ratio with the nitrogen precursor where the ratio is varied during the exposure. In one example the ratio can monotonically increase or decrease during deposition of the metal silicon nitride film. 
   While the invention has been illustrated by the description of several embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended Claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative systems and method and illustrative examples shown and described. Thus, different aspects of the embodiments disclosed herein may be used in combination. For example, a metal nitride and a metal silicon nitride can alternately be formed in the same deposition process, plasma and non-plasma steps can be included in the deposition process etc. Accordingly, departures may be made from such details without departing from the scope of the general inventive concept.