Patent Publication Number: US-2022238332-A1

Title: Semiconductor device and method for forming the same

Description:
PRIORITY CLAIM AND CROSS-REFERENCE 
     This application claims priority to U.S. Provisional Application Ser. No. 63/142,536, filed Jan. 28, 2021, which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs. Each generation has smaller and more complex circuits than the previous generation. 
     In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometric size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling-down process generally provides benefits by increasing production efficiency and lowering associated costs. 
     However, these advances have increased the complexity of processing and manufacturing ICs. Since feature sizes continue to decrease, fabrication processes continue to become more difficult to perform. Therefore, it is a challenge to form reliable semiconductor devices at smaller and smaller sizes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  is a flowchart of a method for forming a semiconductor device in accordance with some embodiments of the present disclosure. 
         FIGS. 2 to 9  illustrate a method in various stages of forming a graphene layer in accordance with some embodiments of the present disclosure. 
         FIG. 10A  is a schematic diagram of a deposition system in accordance with some embodiments of the present disclosure. 
         FIG. 10B  illustrates a mechanism related to functioning of the deposition system in accordance with some embodiments of the present disclosure. 
         FIG. 11A  illustrates experimental results showing different operation time durations of an RF (radio frequency) source effect on temperatures of a magnetic layer. 
         FIG. 11B  illustrates a partial enlarged view of  FIG. 11A . 
         FIGS. 12A to 12C  illustrate experimental results of a Raman spectrum of graphene formed over a magnetic layer with different operation time durations of the RF (radio frequency) source. 
         FIG. 13  illustrates experimental results showing different operation time durations of the RF (radio frequency) source effect on ratios of d band to g band (d/g ratio) of graphene formed over a magnetic layer. 
         FIG. 14  illustrates experimental results showing different operation time durations of the RF (radio frequency) source effect on electrical properties. 
         FIGS. 15 to 32  illustrate a method in various stages of forming a semiconductor device in accordance with some embodiments of the present disclosure. 
         FIG. 33  illustrates a semiconductor device in accordance with some embodiments of the present disclosure. 
         FIGS. 34 and 35  illustrate schematic transmission electron microscopy images showing different graphene growth experimental results formed in different deposition time durations. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     As used herein, “around,” “about,” “approximately,” or “substantially” may generally mean within 20 percent, or within 10 percent, or within 5 percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term “around,” “about,” “approximately,” or “substantially” can be inferred if not expressly stated. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     In order to improve the conductivity of a multi-layer interconnect (MLI) of integrated circuit (IC) structure, a graphene layer may be formed on a metal line/via in the MLI by using a chemical vapor deposition (CVD) method. However, forming the graphene layer on the metal line/via by using the CVD method may require a lengthy deposition time because heating rate in the CVD method is too slow to reach a target temperature for graphene growth in a short time. 
     Therefore, the present disclosure in various embodiments provides a method for forming a graphene layer on a magnetic layer by using a deposition system with an RF source. An advantage is that a shortened deposition time for forming the graphene layer may be achieved to improve the production efficiency, quality, and sheet resistance of the graphene layer. In greater detail, the magnetic layer can be heated to a target temperature for graphene growth within few seconds by the RF source of the deposition system of the present disclosure, which in turn shortens the duration of depositing the graphene layer on the magnetic layer. 
     Referring now to  FIG. 1 , illustrated is a flowchart of an exemplary method M for fabrication of a semiconductor device in accordance with some embodiments. The method M includes a relevant part of the entire manufacturing process. It is understood that additional operations may be provided before, during, and after the operations shown by  FIG. 1 , and some of the operations described below can be replaced or eliminated for additional embodiments of the method. The order of the operations/processes may be interchangeable. The method M includes fabrication of a semiconductor device. However, the fabrication of the semiconductor device is merely an example for describing the manufacturing process according to some embodiments of the present disclosure. 
       FIGS. 2-9  illustrate the method M in various stages of forming a graphene layer in accordance with some embodiments of the present disclosure. The method M begins at block S 101 . Referring to  FIG. 2 , in some embodiments of block S 101 , a magnetic layer is formed over a substrate, and then a first cleaning process is performed to the magnetic layer. A substrate W 1  is shown in  FIG. 2 . In some embodiments, the substrate W 1  may include a semiconductor substrate, such as a bulk semiconductor, a semiconductor-on-insulator (SOI) substrate, or the like. An SOI substrate includes a layer of a semiconductor material formed on an insulator layer. The insulator layer may be, for example, a buried oxide (BOX) layer, a silicon oxide layer, or the like. The insulator layer is provided on a substrate, a silicon or glass substrate. Other substrates, such as a multi-layered or gradient substrate may also be used. In some embodiments, the semiconductor material of the substrate W 1  may include silicon; germanium; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. In some embodiments, the substrate W 1  may be undoped or doped (e.g., p-type, n-type, or a combination thereof). Other materials, such as germanium, quartz, sapphire, and glass could alternatively be used for the substrate W 1 . 
     As shown in  FIG. 2 , a magnetic layer ML 1  is deposited over the substrate W 1 . In some embodiments, the magnetic layer ML 1  may be a magnetic foil or a magnetic film. In some embodiments, the magnetic layer ML 1  may be made of a high permeability coefficient material in order to enhance the induced Eddy current thereon during the deposition process of the graphene layer as shown in  FIG. 8 . In other words, the magnetic layer ML 1  may be made of a material that has a higher permeability coefficient than the surrounding layers. By way of example but not limiting the present disclosure, the magnetic layer ML 1  may have a permeability coefficient greater than about 5×10 −5  (H/m). The term “permeability” as used herein refers to the increase of magnetization that occurs when a magnetic material is subjected to an applied magnetic field. In some embodiments, the magnetic layer ML 1  may be made of a high hysteresis coefficient material in order to enhance the induced Eddy current thereon during the deposition process of the graphene layer GL as shown in  FIG. 8 . In other words, the magnetic layer ML 1  may be made of a material that has a higher hysteresis coefficient than the surrounding layers. By way of example but not limiting the present disclosure, the magnetic layer ML 1  may have a hysteresis coefficient greater than about 300 (A/m). In some embodiments, the magnetic layer ML 1  may be made of a low conductivity material. In other words, the magnetic layer ML 1  may be made of a material that has a lower conductivity coefficient than the surrounding layers. By way of example but not limiting the present disclosure, the magnetic layer ML 1  may have a conductivity coefficient lower than about 1×10 7  (S/m). 
     In some embodiments, the magnetic layer ML 1  may be made of a magnetic material, such as iron (Fe), cobalt (Co), nickel (Ni), proper alloys, suitable materials, or combinations thereof. By way of example but not limiting the present disclosure, the magnetic material may be made of CoPt, CoPd, FePt, or FePd. In some embodiments, the magnetic material in the magnetic layer ML 1  has an atomic percentage greater than or equal to about 10% (e.g., about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%). In some embodiments, the magnetic material is evenly dispersed in the magnetic layer ML 1 . That is, any position in the magnetic layer ML 1  substantially has the same atomic percentage of the magnetic material. In some embodiments, the magnetic material in an upper portion of the magnetic material has a higher atomic percentage than a lower portion of the magnetic layer ML 1 . In some embodiments, an entirety of the magnetic layer ML 1  is made of the same magnetic material. 
     In some embodiments, the magnetic layer ML 1  may include a plurality of magnetic materials. By way of example but not limiting the present disclosure, the plurality of magnetic materials may include iron (Fe), cobalt (Co), nickel (Ni), proper alloys, or other suitable materials, such as CoFeTa, NiFe, CoFe, NiCo. By way of example but not limiting the present disclosure, the magnetic layer ML 1  may include nickel with an atomic percentage in a range from about 70% to about 90% and iron with an atomic percentage in a range from about 10% to about 30%. By way of example but not limiting the present disclosure, the magnetic layer ML 1  may include nickel with an atomic percentage in a range from about 30% to about 50%, zinc with an atomic percentage in a range from about 10% to about 30% and copper with an atomic percentage in a range from about 10% to about 30% plus ferric oxide (e.g., Fe 2 O 4 ) with an atomic percentage in a range from about 0.5% to about 10%. By way of example but not limiting the present disclosure, the magnetic layer ML 1  may include yttrium with an atomic percentage in a range from about 70% to about 90% and bismuth with an atomic percentage in a range from about 10% to about 30% plus ferric oxide (e.g., Fe 5 O 12 ) with an atomic percentage in a range from about 0.5% to about 10%. By way of example but not limiting the present disclosure, the magnetic layer ML 1  may include cobalt with an atomic percentage in a range from about 85% to about 95%, zirconium with an atomic percentage in a range from about 2.5% to about 7.5% and tantalum with an atomic percentage in a range from about 2.5% to about 7.5%. 
     In some embodiments, the magnetic layer ML 1  may be made of nitride or silicide of a magnetic material, such as nitride or silicide of iron (Fe), cobalt (Co), nickel (Ni), proper alloys thereof, suitable materials, or combinations thereof. In some embodiments, the magnetic layer ML 1  may be made of a ferromagnetic material. By way of example but not limiting the present disclosure, the magnetic layer ML 1  may include an alloy of a rare earth metal and a transition metal (RE-TM alloy), such as terbium iron cobalt (TbFeCo), terbium cobalt (TbCo), RE-cobalt palladium (RE-CoPd), RE-cobalt platinum (RE-CoPt), suitable materials, or combinations thereof. In some embodiments, the magnetic layer ML 1  may be made of a magnetic material with a dopant, such as boron (B), therein. By way of example but not limiting the present disclosure, the magnetic layer ML 1  may be made of CoFeB. 
     In some embodiments, the magnetic layer ML 1  can be deposited on the substrate W 1  using suitable processes, such as PVD, CVD, ALD, sputtering, electroplating, or the like. In some embodiments, the magnetic layer ML 1  has a thickness in a range from about 10 nm to about 100 nm. In some embodiments, because the magnetic layer ML 1  is exposed to the air, a metal oxide layer MOX may therefore be formed over the magnetic layer ML 1  due to oxidation. The metal oxide layer MOX is an oxide of the magnetic layer ML 1 . For example, if the magnetic layer ML 1  is made of cobalt (Co), the metal oxide layer MOX may be Cobalt oxide (CoO). 
     As shown in  FIG. 2 , a first cleaning process C 1  is performed to clean the surface of the substrate W 1 . In greater detail, the first cleaning process C 1  is used to remove some contaminants on the metal oxide layer MOX. In some embodiments, the cleaning solvent of the first cleaning process C 1  is an organic solvent. The organic solvent may have a polar function, such as —OH, —COOH, —CO—, —O—, —COOR, —CN—, —SO—, as non-limiting examples. In various embodiments, the organic solvent may include PGME, PGEE, GBL, CHN, EL, Methanol, Ethanol, Propanol, n-Butanol, Acetone, DMF, Acetonitrile, IPA, THF, Acetic acid, or combinations thereof. 
     Referring back to  FIG. 1 , the method M then proceeds to block S 102  where a second cleaning process is performed to remove a metal oxide layer on the magnetic layer. With reference to  FIG. 3 , in some embodiments of block S 102 , a second cleaning process C 2  is performed to remove the metal oxide layer MOX from the magnetic layer ML 1 . After the second cleaning process C 2 , a top surface of the magnetic layer ML 1  is exposed. In some embodiments, the cleaning solvent of the second cleaning process C 2  may be a mineral acid (e.g., inorganic acid), such as hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO 3 ), sulfuric acid (H 2 SO 4 ), or the like. In some embodiments where a magnetic layer ML 1  is cleaned by a 5% nitride acid, the duration of the second cleaning process C 2  is in a range from about 2 seconds to about 4 seconds (e.g., about 3 seconds in some embodiments). If the duration of the second cleaning process C 2  is too short, the metal oxide layer MOX may not be sufficiently removed. While if the duration of the second cleaning process C 2  is too long, the cleaning solvent of the second cleaning process C 2  may cause unwanted etch to the magnetic layer ML 1 . 
     With continued reference to  FIG. 1 , the method M then proceeds to block S 103  where a third cleaning process is performed to remove a residue of the second cleaning process from the magnetic layer. With reference to  FIG. 4 , in some embodiments of block S 103 , a third cleaning process C 3  is performed to remove a residue of the cleaning solvent of the second cleaning process C 2 . In some embodiments, the third cleaning process C 3  may use deionized water (DI water) to remove the cleaning solvent (e.g., mineral acid) of the second cleaning process C 2 . 
     Referring back to  FIG. 1 , the method M then proceeds to block S 104  where the substrate is moved into a processing chamber of a deposition system. This is described in greater detail with reference to  FIGS. 10A and 10B , which illustrate a schematic diagram of an exemplary deposition system  10   a  in some embodiments of the present disclosure. As shown in  FIGS. 10A and 10B , the deposition system  10   a  includes a processing chamber  100 , a gas delivery system  200 , an RF system  300 , a residue gas analysis system  400 , and a pumping system  500 . In some embodiments, the gas delivery system  200  is connected to the processing chamber  100  via a gas delivery line G 1 , and the residue gas analysis system  400  and the pumping system  500  are connected to the processing chamber  100  via a gas delivery line G 2 . The RF system  300  is coupled to the processing chamber  100  by a coil  110  wound around the exterior of the processing chamber  100 . 
     In some embodiments of  FIGS. 10A and 10B , the processing chamber  100  is an elongated tube extending laterally. By way of example but not limiting the present disclosure, the processing chamber  100  may be a quartz tube. In some embodiments, the gas delivery lines G 1  and G 2  are fluidly communicated with the processing chamber  100 , in which the gas delivery lines G 1  and G 2  are fluidly communicated with opposite sides of the processing chamber  100 . The coil  110  is wound around the processing chamber  100  from a top to a bottom of the processing chamber  100 . The processing chamber  100  can accommodate a wafer W 2 . For example, the wafer W 2  may include a semiconductor substrate, such as a bulk semiconductor, a semiconductor-on-insulator (SOI) substrate, or the like. An SOI substrate includes a layer of a semiconductor material formed on an insulator layer. The insulator layer may be, for example, a buried oxide (BOX) layer, a silicon oxide layer, or the like. The insulator layer is provided on a substrate, a silicon or glass substrate. Other substrates, such as a multi-layered or gradient substrate may also be used. In some embodiments, the semiconductor material of the wafer W 2  may include silicon; germanium; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP; or combinations thereof. In some embodiments, the substrate W 2  may be undoped or doped (e.g., p-type, n-type, or a combination thereof). Other materials, such as germanium, quartz, sapphire, and glass could alternatively be used for the substrate W 2 . A magnetic layer ML 2  can be deposited on the wafer W 2 . In some embodiments, the magnetic layer ML 2  can act as a catalytic layer for growing a graphene layer, which will be discussed below. In some embodiments, the magnetic layer ML 2  as shown in  FIG. 10A  may be substantially the same as or comparable to that of the magnetic layer ML 1  as shown in  FIG. 2 . Reference may be made to the detailed description provided in the foregoing paragraphs, and a description thereof will not be repeated. The magnetic layer ML 2  can be deposited on the substrate W 2  using suitable processes, such as PVD, CVD, ALD, sputtering, electroplating, or the like. 
     In some embodiments, the inductive coil  110  is connected to the RF system  300  through a transmission line such as a wave guide or a co-axial cable. The coil  110  may be made of copper (Cu), or other suitable conductive materials. In some embodiments, the coil  110  has a multiple turn cylindrical configuration and may have an electrical length of about one-quarter wavelength (&lt;λ/4) at the operating frequency. For example, the coil  110  is positioned outside the processing chamber  100  for coupling the RF magnetic fields MF into the processing chamber  100 . These induced RF magnetic fields MF ionize at least part of the process gases and thus form plasma in processing chamber  100 . 
     The gas delivery system  200  will now be described. In some embodiments, the gas delivery system  200  includes several sources  202 ,  204 , and  206 . In the example shown in  FIG. 10A , three sources are illustrated, while more or less sources may be applied in some other embodiments. The gas delivery system  200  includes several mass flow controllers  212 ,  214 ,  216 , in which the mass flow controllers  212 ,  214 ,  216  are connected to the sources  202 ,  204 , and  206  via valves V 12 , V 14 , V 16 , respectively. Moreover, the mass flow controllers  212 ,  214 ,  216  are connected to the gas delivery line G 1  via valves V 22 , V 24 , V 26 , respectively. 
     In some embodiments, the source  202  is a liquid source, and thus the source  202  may include a liquid tank. For example, the liquid of the source  202  may be liquid aromatic hydrocarbon, such as benzene (C 6 H 6 ) or toluene (C 7 H 8 ). In some embodiments, the carbon elements of the liquid aromatic hydrocarbon (e.g., benzene or toluene) are used as a source for depositing a graphene layer discussed below. 
     On the other hand, the sources  204  and  206  are gas sources, and thus the sources  204  and  206  may include gas cylinders. The gases of the sources  204  and  206  may be, for example, H 2 , Ar, N 2 , Cl 2 , or other suitable gases. 
     The RF system  300  will now be described. The RF system  300  includes an RF source  302 , a matching box  304 , a controller  306 , an isolator  308 , and a remote control module  310 . In some embodiments, the RF energy is supplied to the processing chamber  100  by the inductive coil  110  which is powered by the RF source  302  and the matching box  304 . 
     The input of the matching box  304  is coupled to the RF source  302 , which provides RF power for plasma generation. The matching box  304  is used to match the impedance of the coil  110  to the impedance of the RF source  302 , in order to deliver the maximum power to the plasma in the processing chamber  100 . In some embodiments, the matching box  304  includes a matching network, a Phase and Magnitude Detector (PMD) and a controller that automatically tunes the matching network using the information supplied by the PMD. 
     The controller  306  may control the operation of the RF source  302 . The controller  306  may include, for example, a computer including a central processing unit (CPU), a memory, and support circuits. The controller  306  operates under the control of a computer program stored in the memory or through other computer programs, such as programs stored in a removable memory. The computer program dictates, for example, the timing, mixture of gases, RF power levels and other parameters of a particular process. 
     The remote control module  310  is electrically coupled between the controller  306  and the RF source  302 . In some embodiments, the remote control module  310  enables the controller  306  to operate the RF source  302  remotely. 
     The isolator  308  is electrically coupled to the RF source  302 , the remote control module  310 , and the controller  306 . Generally, the isolator  308  is used to isolate the RF source  302  from the remote control module  310 . The isolator  308  is used to protect high-power RF energy from the RF source  302 . If the RF source  302  is connected directly to a load (such as the coil  110 ), and the load is not well matched with the RF source  302 , some power reaching the load will be reflected back to the remote control module  310  and then the controller  306  that could destroy the controller  306 . The isolator  308  between the controller  306  and the RF source  302  will absorb most of the reflected RF energy, which in turn will protect the controller  306  from being destroyed. 
     The residue gas analysis system  400  will now be described. The residue gas analysis system  400  includes a residue gas analyzer (RGA)  402 , a main pump  404 , and a backing vacuum pump  406 . The RGA  402  is connected to the gas delivery line G 2  via a valve V 4 . In some embodiments, the RGA  402  is a spectrometer that effectively measures the chemical composition of a gas present in a low-pressure environment. For example, the RGA  402  can ionize separate components of the gas to create various ions, and then detects and determines the mass-to-charge ratios. This process works better in vacuum, where quality is easier to monitor and impurities and inconsistencies are easier to detect because of the low pressure. 
     The main pump  404  is connected to the RGA  402 , and the backing vacuum pump  406  is connected to the main pump  404 . In some embodiments, the pumps  404  and  406  are connected in series so as to improve the pumping speed of the RGA  402 . The backing vacuum pump  406  is used to lower pressure from one pressure state (typically atmospheric pressure) to a lower pressure state, after which the main pump  404  is used to evacuate the process chamber down to high-vacuum levels needed for processing. In some embodiments, the main pump  404  may be a turbo pump, a cryo pump, an ion pump, a diffusion pump, or the like. The backing vacuum pump  406  may be a rotary vane pump, a scroll pump, or the like. The gas exhausted from the backing vacuum pump may be discharged into a gas handling system (not shown) of a fab via a gas conduit. 
     The pumping system  500  will now be described. In some embodiments, the pumping system  500  includes a pressure gauge  502 , a foreline trap  504 , and a vacuum pump  506 . The foreline trap  504  in connected to the gas delivery line G 2  via a valve V 5 . The remainder of the gas mixture exhausted from the processing chamber  100 , including reaction products or byproducts, is evacuated from the processing chamber  100  by the vacuum pump  506 . In some embodiments, the foreline trap  504  may be a particle collector or a particle filter, which is positioned downstream from the exhaust gas source (e.g., processing chamber  100 ). In some embodiments, the foreline trap  504  is positioned as close as possible to the processing-chamber  100  in order to maximize the amount of powder and other particulate matter that is collected within the processing chamber  100  and minimize the amount that is deposited within other areas of the gas delivery line G 2 . In some other embodiments, the foreline trap  504  may be a cooling trap, which recycles process gases by removing condensable material from the process gases when flowing through the foreline trap  504 . 
     With reference to  FIG. 5 , in some embodiments of block S 104 , after the third cleaning process C 3 , the substrate W 1  is loaded into the processing chamber  100  of the deposition system. In some embodiments, the gas delivery system  200  of the deposition system  10   d  in  FIG. 5  only includes two sources  202  and  204 . For example, the source  202  is a liquid source, and thus the source  202  may include a liquid tank. The liquid of the source  202  may, for example, be liquid aromatic hydrocarbon, such as benzene (C 6 H 6 ) or toluene (C 7 H 8 ). In some embodiments, the carbon elements of the liquid aromatic hydrocarbon (e.g, Benzene or Toluene) are used as a source for depositing a graphene layer discussed below. On the other hand, the source  204  is a gas source, and thus the source  204  may include gas cylinder. In some embodiments, the gas of the source  204  may be H 2 . In some embodiments, a gas delivery line G 12  connects the source  202  to the gas delivery line G 1  (or the processing chamber  100 ), and a gas delivery line G 14  connects the source  204  to the gas delivery line G 1  (or the processing chamber  100 ). 
     Referring back to  FIG. 1 , the method M then proceeds to block S 105  where a fourth cleaning process is performed to the magnetic layer in the processing chamber of the deposition system. With reference to  FIG. 6 , in some embodiments of block S 105 , a fourth cleaning process C 4  is performed to clean the substrate W 1 . The fourth cleaning process C 4  is performed by, for example, turning on the valves  14  and  24  of the gas delivery system  200 , such that the gas inside the source  204  can flow through the mass flow controller  214  and then flows into the gas delivery lines G 14  and G 1 . For example, H 2  flows from the source  204  into the processing chamber  100  through the gas delivery lines G 14  and G 1 . In some embodiments, the mass flow controller  214  is controlled such that the flow rate of H 2  is in a range from about 1 sccm to about 5 sccm. 
     Meanwhile, the RF source  302  of the RF system  300  is turned on with an RF power in a range from about 150 W to about 200 W, such that the H 2  that flows into the processing chamber  100  becomes hydrogen plasma (H 2  plasma). The hydrogen plasma may etch and clean the magnetic layer ML 1  over the substrate W 1 . The plasma can remove unwanted metal oxide on the substrate W 1 . For example, H + +CoO→Co+H 2 O, in which a reduction-oxidation process takes place, such that the CoO becomes Co. In some embodiments, the duration of the fourth cleaning process C 4  is in a range from about 20 seconds to about 40 seconds (e.g., about 30 secs in some embodiments). If the duration of the fourth cleaning process C 4  is too short, the magnetic layer ML 1  may not be sufficiently cleaned. While if the duration of the fourth cleaning process C 4  is too long, the hydrogen plasma of the fourth cleaning process C 4  may cause unwanted consumption to the magnetic layer ML 1 . On the other hand, the fourth cleaning process C 4  can also activate the surface of the magnetic layer ML 1 . The hydrogen plasma removes unwanted metal oxide on the magnetic layer ML 1  to make sure the surface of the magnetic layer ML 1  is pure metal (e.g., Co), such that the metal can act as a catalyst in the following graphene deposition process. 
     It is noted that in the step of  FIG. 6 , the valve V 22  of the gas delivery system  200  is turned off, such that only the gas (e.g., H 2 ) in the source  204  is supplied into the processing chamber  100  during cleaning of the substrate W 1 . That is, during the fourth cleaning process C 4 , the processing chamber  100  is free of aromatic hydrocarbon. On the other hand, during the fourth cleaning process C 4 , the pumping system  500  is turned on, so as to pump out the gas (e.g., H 2 ) in the processing chamber  100 . In greater detail, the gas (e.g., H 2 ) in the processing chamber  100  is pumped out to the pumping system  500  through the gas delivery line G 2 . In some embodiments, during the fourth cleaning process C 4  of  FIG. 8 , the gas environment of the processing chamber  100  is substantially a pure hydrogen (H 2 ) environment. 
     Referring back to  FIG. 1 , the method M then proceeds to block S 106  where an aromatic hydrocarbon precursor is supplied into the processing chamber of the deposition system. After cleaning the magnetic layer ML 1  of  FIG. 6 , the valve  24  of the gas delivery system  200  is turned off, such that supply of the gas (e.g., H 2 ) in the source  204  to the processing chamber  100  is stopped. Meanwhile, the RF system  300  is turned off. That is, the RF power of the RF system  300  in this step is a zero value or negligibly small. On the other hand, the pumping system  500  may pump out (remove) the remaining gas (e.g., hydrogen gas H 2 ) in the processing chamber  100 , so as to create a vacuum environment in the processing chamber  100 . 
     With reference to  FIG. 7 , in some embodiments of block S 106 , an aromatic hydrocarbon precursor can be provided into the processing chamber  100  and over the magnetic layer ML 1 . Subsequently, the valves  12  and  22  of the gas delivery system  200  are turned on. As mentioned above, the source  202  is a liquid source. The liquid source may be liquid aromatic hydrocarbon, such as benzene (C 6 H 6 ) or toluene (C 7 H 8 ). In some embodiments, the aromatic hydrocarbon (e.g., benzene or toluene) is used as a precursor for depositing a graphene layer discussed in  FIG. 8 . Although the source  202  is a liquid aromatic hydrocarbon source, the liquid aromatic hydrocarbon may volatilize easily. Accordingly, as the valve  12  is turned on, the liquid aromatic hydrocarbon in the source  202  may volatilize and transform from a liquid phase to a gas phase, and the aromatic hydrocarbon gas (e.g., Benzene gas or Toluene gas) may flow through the mass flow controller  212  and then flows into the gas delivery lines G 12  and G 1 . For example, the aromatic hydrocarbon gas flows from the source  202  into the processing chamber  100  through the gas delivery lines G 12  and G 1 . In some embodiments, the mass flow controller  212  is controlled such that the flow rate of the aromatic hydrocarbon gas is in a range from about 0.5 sccm to about 1 sccm. If the flow rate is too low (e.g., much lower than about 0.5 sccm), the concentration of the aromatic hydrocarbon gas may be too low to provide sufficient carbon. If the flow rate is too high (e.g., much higher than about 1 sccm), the carbon concentration may be too high and may affect the quality of the graphene layer. In some embodiments, the aromatic hydrocarbon gas is supplied into the processing chamber  100  without using a carrier gas, such as Ar or H 2 . That is, the gas environment of the processing chamber  100  is substantially a pure aromatic hydrocarbon gas environment in this step, which will facilitate the formation of the graphene layer in  FIG. 8 . 
     In some embodiments, when a precursor for depositing a graphene layer is methane (CH 4 ), acetylene (C 2 H 2 ), or ethylene (C 2 H 4 ), it will take a longer time to form a graphene layer because each molecule provides less carbon atoms. However, because the precursor for depositing the graphene layer is an aromatic hydrocarbon precursor, a molecule of an aromatic hydrocarbon can provide more carbon atoms (e.g., C 6 H 6  or C 7 H 8 ) than a molecule of methane (CH 4 ), acetylene (C 2 H 2 ), or ethylene (C 2 H 4 ). Accordingly, a deposition rate of the graphene layer can be increased when using an aromatic hydrocarbon precursor in some embodiments of the present disclosure, which in turn allows for improving a production efficiency of the graphene layer. 
     It is noted that in the step of  FIG. 8 , the valve V 24  of the gas delivery system  200  has been turned off, such that only the aromatic hydrocarbon in the source  202  is supplied into the processing chamber  100 . In some embodiments, the aromatic hydrocarbon gas is used as a precursor in the deposition process in  FIG. 8 , and thus aromatic hydrocarbon gas can be interchangeably referred to as an aromatic hydrocarbon precursor in the following content. 
     With reference again to  FIG. 1 , the method M then proceeds to block S 107  where an RF power of an RF system equipped to the processing chamber is turned on, so as to deposit a graphene layer over the magnetic layer. With reference to  FIG. 8 , in some embodiments of block S 107 , the RF source  302  of the RF system  300  is turned on, so as to generate plasma of aromatic hydrocarbon in the processing chamber  100 . The aromatic hydrocarbon precursor is decomposed (or ionized) into several active radical species, which constitute the plasma over the magnetic layer ML 1 . For example, the active radical species of the plasma may include aromatic radicals. “Aromatic radical” used herein refers to a radical including at least one ring of resonance bonds, such as a benzene ring. 
     Next, the active radicals may be deposited on the surface of the magnetic layer ML 1  and may diffuse on the surface of the magnetic layer ML 1 . In some embodiments, some radicals will be gathered together and are close to each other. This mechanism is called “surface diffusion” of the radicals. A dehydrogenation reaction and a cyclization reaction may take place, and then covalent bonding of the active radicals and/or rings form a graphene layer GL over the magnetic layer ML 1 . “Dehydrogenation” used herein refers to a chemical reaction that involves the removal of hydrogen from an organic molecule. “Cyclization” used herein refers to the process in which the radicals are combined and transformed into ‘benzene’ rings. Generally, the RF source  302  of the RF system  300  is turned on to decompose the aromatic hydrocarbon precursor into active radicals, and the active radicals are then cyclized into a graphene layer. 
     Referring back to  FIG. 8 , as mentioned above, before the RF source  302  of the RF system  300  is turned on, the processing chamber  100  is already filled with the aromatic hydrocarbon precursor (see  FIG. 7 ). Accordingly, once the RF source  302  of the RF system  300  is turned on, the plasma of aromatic hydrocarbon can be generated immediately, and the deposition of the graphene layer GL takes place. That is, the RF system  300  is operative to trigger the graphene deposition discussed herein. For example, the aromatic hydrocarbon precursor is decomposed into several active radicals. Subsequently, a dehydrogenation reaction and a cyclization reaction take place, thereby forming the graphene layer GL on the magnetic layer ML 1 . 
     In some embodiments, a flow rate of the aromatic hydrocarbon precursor is in a range from about 0.5 sccm to about 1 sccm. In some embodiments, the processing pressure is in a range from about 1×10 −2  torr to about 2×10 −2  torr. In some embodiments, the RF power of the RF source  302  of the RF system  300  is in a range from about 250 W to about 400 W. If the RF power is too low (e.g., much lower than about 250 W), the aromatic hydrocarbon may not be sufficiently decomposed. If the RF power is too high (e.g., much higher than about 400 W), the plasma may be too strong to cause unwanted etching to the magnetic layer ML 1 . 
     As shown in  FIG. 8 , a high frequency induction heating process is also performed on the magnetic layer ML 1 , which allows for speeding up the deposition rate of the graphene layer GL. In greater detail, the magnetic layer ML 1  may be heated by the RF system  300  through the coil  110  wound around thereof to speed up the deposition rate of the graphene layer GL on the magnetic layer ML 1 . The RF source  302  may supply high-frequency alternating current to the coil  110 . The alternating current may be supplied to the coil  110  at a radio frequency, such as a frequency greater than 1000 Hz. By way of example but not limiting the present disclosure, the alternating current may be in a frequency greater than 300 kHz. The time variation in the high-frequency alternating current produces a time-varying magnetic field MF as shown in  FIG. 10B  at the coil  110 . Therefore, the magnetic layer ML 1  is positioned within the time-varying magnetic field MF generated by the coil  110 . 
     Next, the magnetic layer ML 1  may be heated to a predetermined temperature within a few seconds or less by induced eddy current generated by putting a coil  110  with high-frequency electrical current in the vicinity of the magnetic layer ML 1 . In other words, by controlling the RF source  302 , the desired heating temperature can be achieved within a few seconds or less. By using the method and deposition systems described above, the graphene layer GL may begin to form when the temperature is greater than about 200° C. to about 400° C., and thus the graphene layer GL can be grown on the magnetic layer ML 1  without using a heater other than the RF system  300 , by way of example but not limiting the present disclosure. Stated another way, the deposition system  10   a  is free of a heater other than the RF system  300 . Thus, heating the magnetic layer ML 1  by using this method may be active and controllable, so as to speed up the deposition rate of the graphene layer GL on the magnetic layer ML 1 . 
     By way of example but not limiting the present disclosure, the magnetic layer ML 1  may be heated to about 800° C. for less than about 30 secs in the operation of the RF source  302 , which in turn allows for speeding up the deposition rate of the graphene layer GL formed thereon, so as to lower the duration of deposition time of the graphene layer GL. That is, the duration of the deposition time of the graphene layer GL may be determined by the operation duration of the RF source  302  through the coil  110 , because the operation of the RF source  302  may actuate a dehydrogenation reaction and a cyclization reaction, and then covalent bond the active radicals and/or rings of the aromatic hydrocarbon to form a graphene layer GL. In some embodiments, the deposition time of the graphene layer GL is defined as the duration between turning on the RF source  302  of the RF system  300  and turning off the RF source  302  of the RF system  300 . In some embodiments, the duration of deposition time of the graphene layer GL on the magnetic layer ML 1  may be less than about 30 secs during the operation of the RF source  302 . In some embodiments, the duration of deposition time of the graphene layer GL on the magnetic layer ML 1  may be less than or equal to about 12 secs (e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 secs) during the operation of the RF source  302 . For example, in the operation of the RF source  302  to deposit the graphene layer GL, the magnetic layer ML 1  may be heated to about 200° C. for about 7 secs, may be heated to about 250° C. for about 12 sees, may be heated to about 350° C. for about 18 secs, or may be heated to about 650° C. for about 32 secs. In some embodiments, a duration of deposition time of the graphene layer GL on the magnetic layer ML 1  is shorter than a time duration of performing the fourth cleaning process C 4 . Therefore, a short deposition time of the graphene layer GL may be achieved to improve a production efficiency of the graphene layer. 
     In some embodiments, the magnetic layer ML 1  has a better surface effect than a non-magnetic material, and therefore has a faster heating rate, which in turn allows for speeding up the deposition rate of the graphene layer GL formed thereon to ultimately result in lowering the duration of deposition time of the graphene layer GL. In some embodiments, the magnetic layer ML 1  having a greater permeability coefficient has a better surface effect than a magnetic layer having a lower permeability coefficient, and therefore has a faster heating rate. This in turn allows for speeding up the deposition rate of the graphene layer GL formed thereon to ultimately result in lowering the duration of deposition time of the graphene layer GL. In some embodiments, the magnetic layer ML 1  having a greater hysteresis coefficient has a better surface effect than a magnetic layer having a lower hysteresis coefficient, and therefore has a faster heating rate. This in turn allows for speeding up the deposition rate of the graphene layer GL formed thereon to ultimately result in lowering the duration of deposition time of the graphene layer GL and improving a production efficiency of the graphene layer. 
     Furthermore, an ambient temperature inside the processing chamber  100  of the deposition system  10   a  may be determined by the RF source  302 . In greater detail, the RF source  302  of the RF system  300  may generate plasma of aromatic hydrocarbon through the coil  110 , which may raise the ambient temperature in the processing chamber  100 . By way of example but not limiting the present disclosure, the ambient temperature inside the processing chamber  100  may be raised to about 200° C. to about 300° C. during the operation of the RF source  302 . At the same time, the magnetic layer ML 1  on the substrate W 1  may be heated to about 800° C. for speeding up the deposition rate of the graphene layer GL formed thereon. That is, during the operation of the RF source  302 , the ambient temperature inside the processing chamber  100  is lower than the temperature of the magnetic layer ML 1 . In some embodiments where a semiconductor device, such as a transistor, is formed on the substrate W 1 , the processing chamber  100  having an ambient temperature from about 200° C. to about 300° C. would not destroy the semiconductor device, thereby improving the device yield. If the ambient temperature of the processing chamber  100  is higher than about 400° C., some devices formed on the substrate W 1  may be destroyed. 
       FIG. 11A  illustrates experimental results showing different operation time durations of an RF source effect on temperatures of a magnetic layer.  FIG. 11B  illustrates a partial enlarged view of  FIG. 11A . In  FIGS. 11A and 11B , samples including a magnetic layer, such as a Co foil, on a substrate were prepared and the temperatures of the magnetic layer were measured at the predetermined time durations of operation of the RF source. For example, the magnetic layer may be heated by an RF system through a coil wound around the samples. The RF source may supply high-frequency alternating current to the coil. The alternating current may be supplied to the coil at a radio frequency, such as a frequency greater than 1000 Hz. By way of example but not limiting the present disclosure, the alternating current may be in a frequency greater than 300 kHz. In the example shown in  FIGS. 11A and 11B , the RF source was operated at predetermined time durations of about 0, 7, 12, 20, 30, 250, and 600 secs. 
     As shown in  FIGS. 11A and 11B , before the RF source of a RF system is turned on (i.e., the predetermined time is about 0 sec), the temperature of the magnetic layer is about room temperature, such as about 25° C. in some embodiments. Once the RF source of the RF system is turned on, a high frequency induction heating process is performed on the magnetic layer, which allows for heating the magnetic layer within a few seconds. In the example shown in  FIGS. 11A and 11B , the magnetic layer may be heated to about 200° C. in about 7 seconds, heated to about 250° C. in about 12 seconds, and heated to about 800° C. in about 30 secs, which in turn allows for speeding up the deposition rate of a graphene layer formed thereon, so as to lower the duration of deposition time of the graphene layer. Therefore, by controlling the RF source, the desired heating temperature can be achieved within a few seconds. By using the method and deposition systems described above, the graphene layer may begin to form when the temperature is greater than about 200° C. to about 400° C., and thus the graphene layer can be grown on the magnetic layer without using a heater other than the RF system, by way of example but not limiting the present disclosure. 
     Raman spectroscopy is a characterization technique for a graphene layer GL. Carbon-based materials, such as graphene, may have three intense Raman features including a defect band (D band), a band related to in-plan vibration of sp2 carbon (G band), and a stacking order (2D band). For monolayer graphene, the g band has a Raman Shift located at about 1580 cm −1 , the d band has a Raman Shift located at about 1350 cm −1 , and the 2d band has a Raman Shift located at about 2700 cm −1 . The relative intensity (a.u.) of the g band frequency of Raman spectra may be used as a measure for a number of features that provide information regarding sample purity, geometry, and the metallic or semi-conducting nature of the material. Another prominent feature in the Raman spectra of carbon-based materials is the d band. The d band is sensitive to differences in the carbon network that is characteristic of many carbon-based materials, and the intensity of the d band may provide information on the electronic character of a particular material. Because a carbon lattice may contain aromatic carbons that are sp2 hybridized and may be substantially more conductive, it may be beneficial to select for the graphene layer GL having fewer numbers of non-aromatic sp3 hybridized carbon sites, or “defects” in the carbon lattice. For example, higher intensity in the d band in a Raman spectrum may indicate that a particular sample has a higher concentration of defects and may not be as conductive as a sample having a relatively lower d band intensity. 
     In some embodiments, a ratio of the d band to the g band (d/g ratio) may also be used as a measure of both the purity of a sample and, in relatively pure samples, can be used to characterize the defects present on the graphene layer GL, where a lower d/g ratio may indicate the a sample containing higher general concentrations of sp2 carbons, a more complete carbon lattice on the graphene layer GL, and higher general electrical and/or thermal conductivity. 
     In some embodiments, by using the method and deposition systems described above, the d/g ratio of the graphene layer GL formed on the magnetic layer ML 1  as measured by Raman spectroscopy may be less than about 1 when the deposition time thereof is longer than about 3 secs. In some embodiments, by using the method and deposition systems described above, the d/g ratio of the graphene layer GL formed on the magnetic layer ML 1  as measured by Raman spectroscopy may be less than about 0.3 when the deposition time thereof is longer than about 10 secs. In some embodiments, by using the method and deposition systems described above, the d/g ratio of the graphene layer GL formed on the magnetic layer ML 1  as measured by Raman spectroscopy may be less than about 0.1 when the deposition time thereof is longer than about 12 secs. Therefore, by using the method and deposition systems described above, a short deposition time (e.g., about 3-30 secs in some embodiments, such as about 3, 5, 10, 20, or 30 seconds) of the graphene layer GL may be achieved to reduce the d/g ratio, which in turn allows for lowering the defect density (e.g., d/g ratio&lt;about 0.5 in some embodiments, such as about 0.1, 0.2, 0.3, 0.4, or 0.5) and improving the quality and uniformity of the graphene layer GL. 
       FIGS. 12A to 12C  illustrate experimental results of a Raman spectrum of graphene formed over a magnetic layer with different operation time durations of the RF source. In  FIGS. 12A to 12C , the samples including a graphene layer formed by a precursor (e.g., benzene (C 6 H 6 )) on a magnetic layer (e.g., Co foil) were prepared and intensities of Raman shift of the graphene layer were measured after the predetermined time durations of operation of the RF source. The RF source may be supplied to the samples at a radio frequency, such as a frequency greater than 1000 Hz. By way of example but not limiting the present disclosure, the alternating current may be in a frequency greater than 300 kHz. For the samples shown in  FIGS. 12A to 12C , the g band has a Raman Shift located at about 1580 cm −1 , the d band has a Raman Shift located at about 1350 cm −1 , and the 2d band has a Raman Shift located at about 2700 cm −1 . In the example shown in  FIG. 12A , the RF source is operated at predetermined time durations about 3, 5, 10, 20, and 30 secs. In the example shown in  FIG. 12B , the RF source is operated at the predetermined time duration about 7 secs. In the example shown in  FIG. 12C , the RF source is operated at the predetermined time duration about 12 secs.  FIG. 13  illustrates experimental results showing different operation time durations of the RF source effect on ratios of the d band to the g band (d/g ratio) of graphene formed over the magnetic layer of  FIGS. 12A to 12C . 
     As shown in  FIGS. 12A, 12B, 12C, and 13 , the d/g ratio of the graphene layer formed on the magnetic layer as measured by Raman spectroscopy is about 1 when the time duration is about 3 secs, the d/g ratio of the graphene layer formed on the magnetic layer as measured by Raman spectroscopy is about 0.3 when the time duration is about 10 secs, and the d/g ratio of the graphene layer formed on the magnetic layer as measured by Raman spectroscopy is less than about 0.1 when the time duration is about 20 secs. Therefore, as shown in the experimental results of  FIG. 13 , by using the method and deposition systems described above, a short deposition time of the graphene layer may be achieved to reduce the d/g ratio, which in turn allows for lowering the defect density and improving the quality of the graphene layer. 
     In some embodiments, the graphene layer GL can be deposited over a large area which depends on the sizes of the RF coil  110  and the processing chamber  100 . For example, in some embodiments where the area of the magnetic layer ML 1  may be in a range from about 1*2 cm 2  to about 12*2 cm 2 , experimental results show that the graphene layer GL has a uniform region having an area about 8*2 cm 2  to about 10*2 cm 2  (e.g., about 9*2 cm 2 ). 
     After an entirety of the magnetic layer ML 1  is covered by the graphene layer GL and/or after the graphene layer GL is grown to a desired thickness, the RF source  302  of the RF system  300  can be turned off, so as to stop depositing the graphene layer GL. In some embodiments, the deposition time of the graphene layer GL formed on the magnetic layer ML 1  may be less than about 30 seconds, and the graphene layer GL may have a thickness in a range from about 0.7 nm to about 7 nm, layers in a range from about 2 to about 20, and a sheet resistance lower than about 100 Ω/sq, by way of example but not limiting the present disclosure.  FIGS. 34 and 35  illustrate schematic transmission electron microscopy images showing different graphene growth experimental results formed in different deposition time durations. In  FIG. 34 , when the deposition time of the graphene layer GL 2  formed on the magnetic layer ML 2  is about 12 seconds, the graphene layer GL 2  may have a thickness of about 5.74 nm in about 17 layers. In  FIG. 35 , when the deposition time of the graphene layer GL 3  formed on the magnetic layer ML 3  is about 7 seconds, the graphene layer GL 3  may have a thickness of about 1.8 nm in about 4 layers. In the example shown in  FIG. 35 , the magnetic layer may be heated to about 200° C. in about 7 seconds. In the example shown in  FIG. 34 , the magnetic layer may be heated to about 250° C. in about 12 seconds. Thus, by using the method and deposition systems described above, a short deposition time of the graphene layer GL formed on the magnetic layer ML 1  may be achieved to improve a production efficiency, quality, and sheet resistance of the graphene layer. Moreover, as illustrated in  FIGS. 34 and 35 , the graphene layer GL 3  formed in a shorter time duration may have a higher thickness non-uniformity than the graphene layer GL 2  formed in a longer time duration, which means that the thickness uniformity of graphene may increases as deposition time increases. 
       FIG. 14  illustrates experimental results showing different operation time durations of the RF (radio frequency) source effect on electrical properties. In  FIG. 14 , the samples including a graphene layer formed by a precursor (e.g., benzene (C 6 H 6 )) and a magnetic layer (e.g., Co foil) were prepared, and sheet resistance (Ω/sq) was measured after the predetermined time durations of operation of the RF source. The RF source may be supplied to the samples at a radio frequency, such as a frequency greater than 1000 Hz. By way of example but not limiting the present disclosure, the alternating current may be in a frequency greater than 300 kHz. In the example shown in  FIG. 14 , the RF source is operated at predetermined time durations about 3, 5, 10, 12, 15, 30, 60, and 120 secs. As shown in  FIG. 14 , the sheet resistance (Ω/sq) of the graphene layer formed on the magnetic layer may be less than about 500 (e.g., about 480) when the time duration is about 3 secs, the sheet resistance (Ω/sq) of the graphene layer formed on the magnetic layer may be less than about 200 (e.g., about 190) when the time duration is about 5 secs, and the sheet resistance (Ω/sq) of the graphene layer formed on the magnetic layer is about 100 when the time duration is about 12 secs. Therefore, as shown in the experimental results of  FIG. 14 , by using the method and deposition systems described above, a short deposition time of the graphene layer may be achieved to improve a sheet resistance of the graphene layer within a few seconds. 
     It is noted that in the present disclosure, the aromatic hydrocarbon precursor is supplied into the processing chamber  100  without using a carrier gas, such as Ar or H 2 . This will improve the quality of the deposited graphene layer GL, because the RF power provided by the RF system  300  may transform the carrier gas into plasma (e.g., Ar plasma or H 2  plasma), while the such plasma may etch the graphene layer GL during deposition. 
     Referring back to  FIG. 1 , the method M then proceeds to block S 108  where the substrate is moved out from the processing chamber of the deposition system. With reference to  FIG. 9 , in some embodiments of block S 108 , after the RF source  302  of the RF system  300  (see  FIG. 8 ) is turned off, the substrate W 1  is moved out from the processing chamber  100  (see  FIG. 9 ). In some embodiments, before moving out the substrate W 1  from the processing chamber  100 , the valve  22  of the gas delivery system  200  may be turned off, so as to stop providing aromatic hydrocarbon precursor into the processing chamber  100 . 
     Reference is made to  FIGS. 15 to 32 .  FIGS. 15 to 32  illustrate a method in various stages of forming a semiconductor device in accordance with some embodiments of the present disclosure. 
     Reference is made to  FIG. 15 . An initial structure is received. The initial structure includes a substrate  610 . The substrate  610  includes an N-well region  600 N and a P-well region  600 P, in which the N-well region  600 N may be doped with N-type impurities, and the P-well region  600 P may be doped with P-type impurities. The substrate  610  may be a semiconductor material and may include known structures including a graded layer or a buried oxide, for example. Other materials, such as germanium, quartz, sapphire, and glass could alternatively be used for the substrate  610 . Alternatively, the silicon substrate  610  may be an active layer of a semiconductor-on-insulator (SOI) substrate or a multi-layered structure such as a silicon-germanium layer formed on a bulk silicon layer. 
     Isolation structures  605  are disposed in the substrate  610 . In some embodiments, the isolation structures  605  may include oxide, such as silicon dioxide. The isolation structures  605 , which act as a shallow trench isolation (STI) around the P-well region  600 P from the N-well region  600 N, may be formed by chemical vapor deposition (CVD) techniques using tetra-ethyl-ortho-silicate (TEOS) and oxygen as a precursor. 
     A gate structure  600 A is disposed over the P-well region  600 P of the substrate  610 , and a gate structure  600 B is disposed over the N-well region  600 N of the substrate  610 . In some embodiments, each of the gate structure  600 A and the gate structure  600 B includes a gate dielectric  602  and a gate electrode  604 . In some embodiments, the gate dielectric  602  may be, for example, silicon oxide, silicon nitride, a combination thereof, or the like, and may be deposited or thermally grown according to acceptable techniques. In some embodiments, the gate electrode  604  may include polycrystalline-silicon (poly-Si) or poly-crystalline silicon-germanium (poly-SiGe). In some other embodiments, the gate structure  600 A and the gate structure  600 B may be metal gate structures, which include a high-k dielectric layer, a work function metal layer over the high-k dielectric layer, and a gate metal over the work function metal layer. 
     Capping layers  625  are disposed over the gate structures  600 A and  600 B. In some embodiments, the capping layers  625  may be oxide. A plurality of gate spacers  612  are disposed on opposite sides of the gate structure  600 A and the gate structure  600 B. In some embodiments, the gate spacers  612  may include SiO 2 , Si 3 N 4 , SiO x N y , SiC, SiCN films, SiOC, SiOCN films, and/or combinations thereof. 
     Source/drain structures  620 N are disposed in the P-well region  620 P of the substrate  610  and on opposite sides of the gate structure  600 A, and source/drain structures  620 P are disposed in the N-well region  620 N of the substrate  610  and on opposite sides of the gate structure  600 B. In some embodiments, the source/drain structures  620 N may be doped with N-type impurities, and the source/drain structures  620 P may be doped with p-type impurities. In some embodiments, the source/drain structures  620 N,  620 P may be may be formed by performing an epitaxial growth process that provides an epitaxy material over the substrate  610 , and thus the source/drain structures  620 N,  620 P can be interchangeably referred to as epitaxy structures  620 N,  620 P in this context. In various embodiments, the source/drain structures  620 N,  620 P may include Ge, Si, GaAs, AlGaAs, SiGe, GaAsP, SiP, or other suitable materials. 
     A contact etch stop layer (CESL)  630  is disposed over the isolation structures  605  and over the capping layers  625 . An interlayer dielectric (ILD) layer  640  is disposed over the CESL  630  and surrounds the gate structures  600 A and  600 B. In some embodiments, the CESL  630  includes silicon nitride, silicon oxynitride or other suitable materials. The CESL  630  can be formed using, for example, plasma enhanced CVD, low pressure CVD, ALD or other suitable techniques. In some embodiments, the ILD layer  640  may include silicon oxide, silicon nitride, silicon oxynitride, tetraethoxysilane (TEOS), phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), low-k dielectric material, and/or other suitable dielectric materials. Examples of low-k dielectric materials include, but are not limited to, fluorinated silica glass (FSG), carbon doped silicon oxide, amorphous fluorinated carbon, parylene, bis-benzocyclobutenes (BCB), or polyimide. The ILD layer  640  may be formed using, for example, CVD, ALD, spin-on-glass (SOG) or other suitable techniques. 
     Source/drain contacts  650  are disposed in the ILD layer  640  and contact the source/drain structures  620 A and  620 P. In some embodiments, each source/drain contact  650  includes a liner  652  and a plug  654 . The liner  652  is between the plug  654  and the underlying source/drain structures  600 A or  600 B. In some embodiments, the liner  652  assists with the deposition of the plug  654  and helps to reduce diffusion of a material of the plug  654  through the gate spacers  612 . In some embodiments, the liner  652  includes titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), or another suitable material. The plug  654  includes a conductive material, such tungsten (W), copper (Cu), aluminum (Al), ruthenium (Ru), cobalt (Co), molybdenum (Mo), nickel (Ni), or other suitable conductive materials. 
     An etch stop layer (ESL)  700  is disposed over the ILD layer  640  and the source/drain contacts  650 . An inter-metal dielectric (IMD) layer  705  is disposed over the ESL  700 . The material and the formation method of the ESL  700  are similar to those of the CESL  630 . Moreover, the material and the formation method of the IMD layer  705  are similar to those of the ILD layer  640 . 
     Reference is made to  FIG. 16 . The ESL  700  and the IMD layer  705  are patterned to form openings O 1 . Subsequently, a liner  710  and a magnetic layer  715  are formed in the openings O 1 . In some embodiments, the liner  710  includes titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), or another suitable material. In some embodiments, the magnetic layer  715  may be made of a higher permeability coefficient material than the liner  710 . The magnetic layer  715  may be made of a higher hysteresis coefficient material than the liner  710 . The magnetic layer  715  may be made of a lower conductivity material than the liner  710 . In some embodiments, the magnetic layer  715  may have a greater thickness than the liner  710 . 
     In some embodiments, the magnetic layer  715  may be made of a magnetic material, such as iron (Fe), cobalt (Co), nickel (Ni), proper alloys, suitable materials, or combinations thereof. By way of example but not limiting the present disclosure, the magnetic material may be made of CoPt, CoPd, FePt, or FePd. In some embodiments, the magnetic material in the magnetic layer  715  has an atomic percentage greater than or equal to about 10% (e.g., about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%). In some embodiments, the magnetic material is evenly dispersed in the magnetic layer  715 . That is, any position in the magnetic layer  715  substantially has the same atomic percentage of the magnetic material. In some embodiments, the magnetic material in an upper portion of the magnetic material has a greater atomic percentage than a lower portion of the magnetic layer  715 . In some embodiments, an entirety of the magnetic layer  715  is made of the same magnetic material. 
     In some embodiments, the magnetic layer  715  may include a plurality of magnetic materials. By way of example but not limiting the present disclosure, the plurality of magnetic materials may include iron (Fe), cobalt (Co), nickel (Ni), proper alloys, or other suitable materials, such as CoFeTa, NiFe, CoFe, NiCo. By way of example but not limiting the present disclosure, the magnetic layer  715  may include nickel with an atomic percentage in a range from about 70% to about 90% and iron with an atomic percentage in a range from about 10% to about 30%. By way of example but not limiting the present disclosure, the magnetic layer  715  may include nickel with an atomic percentage in a range from about 30% to about 50%, zinc with an atomic percentage in a range from about 10% to about 30% and copper with an atomic percentage in a range from about 10% to about 30% plus ferric oxide (e.g., Fe 2 O 4 ) with an atomic percentage in a range from about 0.5% to about 10%. By way of example but not limiting the present disclosure, the magnetic layer  715  may include yttrium with an atomic percentage in a range from about 70% to about 90% and bismuth with an atomic percentage in a range from about 10% to about 30% plus ferric oxide (e.g., Fe 5 O 12 ) with an atomic percentage in a range from about 0.5% to about 10%. By way of example but not limiting the present disclosure, the magnetic layer  715  may include cobalt with an atomic percentage in a range from about 85% to about 95%, zirconium with an atomic percentage in a range from about 2.5% to about 7.5% and tantalum with an atomic percentage in a range from about 2.5% to about 7.5%. 
     In some embodiments, the magnetic layer  715  may be made of nitride or silicide of a magnetic material, such as nitride or silicide of iron (Fe), cobalt (Co), nickel (Ni), proper alloys thereof, suitable materials, or combinations thereof. In some embodiments, the magnetic layer  715  may be made of a ferromagnetic material. By way of example but not limiting the present disclosure, the magnetic layer  715  may include an alloy of a rare earth metal and a transition metal (RE-TM alloy), such as terbium iron cobalt (TbFeCo), terbium cobalt (TbCo), RE-cobalt palladium (RE-CoPd), RE-cobalt platinum (RE-CoPt), suitable materials, or combinations thereof. In some embodiments, the magnetic layer  715  may be made of a magnetic material with a dopant, such as boron (B), therein. By way of example but not limiting the present disclosure, the magnetic layer  715  may be made of CoFeB. 
     Reference is made to  FIG. 17 . A graphene layer  720  is deposited over the magnetic layer  715 . In some embodiments, the graphene layer  720  can be formed by using the method and deposition systems described in  FIGS. 1-10B , and thus relevant details will not be repeated hereinafter. For example, the magnetic layer  715  is similar to the magnetic layer ML 1  of  FIGS. 2-9 , and the graphene layer  720  is similar to the graphene layer GL of  FIGS. 2-9 . In some embodiments, the thickness of the graphene layer  720  is in a range from about 1 nm to about 3 nm. With respect to the deposition process of  FIG. 8 , the deposition time of the graphene layer  720  may be in a range from about 3 seconds to about 15 seconds (e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 seconds). In some embodiments, the graphene layer  720  may have a smaller thickness than the magnetic layer  715 . 
     Reference is made to  FIG. 18 . A filling metal  730  is deposited over the graphene layer  720  and fills the openings O 1 . In some embodiments, the filling metal  730  is made of a highly conductive material. In some embodiments, the filling metal  730  may include metal, such as tungsten (W), ruthenium (Ru), aluminum (Al), copper (Cu), or other suitable conductive materials. In some embodiments, the conductive material  170  may be deposited by CVD, physical vapor deposition (PVD), sputter deposition, ALD, electroplating, or other techniques suitable for depositing conductive materials. In some embodiments, the magnetic layer  715  may be made of a higher permeability coefficient material than the filling metal  730 . The magnetic layer  715  may be made of a higher hysteresis coefficient material than the filling metal  730 . The magnetic layer  715  may be made of a lower conductivity material than the filling metal  730 . 
     Reference is made to  FIG. 19 . A chemical mechanical polishing (CMP) process is performed to remove excessive materials of the filling metal  730 , the graphene layer  720 , the magnetic layer  715 , and the liner  710  until the IMD layer  705  is exposed. In some embodiments, the remaining filling metal  730 , the graphene layer  720 , the magnetic layer  715 , and the liner  710  can be referred to as a metal-1 (M1) layer in a back end of line (BEOL) process. 
     Reference is made to  FIG. 20 . A plurality of graphene layers  740  are deposited on the remaining filling metal  730 , the graphene layer  720 , the magnetic layer  715 , and the liner  710 . In greater detail, the graphene layer  720  grows on the filling metal  730  because the filling metal  730  is heated by the surrounding magnetic layer  715 . The filling metal  730  may be heated to a predetermined temperature (e.g., greater than about 200° C. to about 400° C. in some embodiments) within a few seconds (e.g., about 3-30 seconds in some embodiments) through the surrounding magnetic layer  715  by the RF source of the deposition system of the present disclosure. Thus, heating the filling metal  730  through the surrounding magnetic layer  715  by using a high frequency induction heating process of the present disclosure may lower the duration of deposition time of the graphene layer, which in turn allows for improving the production efficiency, quality, and sheet resistance of the graphene layer. In some embodiments, the graphene layers  740  tend to grow on a graphene surface and/or a metal surface rather than on a dielectric surface. As an example in  FIG. 20 , the graphene layers  740  are selectively formed on the filling metal  730 , the graphene layer  720 , the magnetic layer  715 , and the liner  710 , while the graphene layers  740  are not formed on the IMD layer  705 . In some embodiments, the graphene layers  740  can be formed by using the method and deposition systems described in  FIGS. 1-10B , and thus relevant details will not be repeated hereinafter. For example, the graphene layers  740  are similar to the graphene layer GL of  FIGS. 2-9 . In some embodiments, the thickness of the graphene layers  740  is in a range from about 1 nm to about 3 nm. With respect to the deposition process of  FIG. 8 , the deposition time of the graphene layers  740  may be in a range from about 3 seconds to about 15 seconds (e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 seconds). 
     Reference is made to  FIG. 21 . An ESL  800 , an IMD layer  802 , an ESL  804 , and an IMD layer  806  are formed sequentially over the IMD layer  705 . The ESLs  800  and  804  are similar to the ESL  700 , the IMD layers  802  and  806  are similar to the IMD layer  705 , and thus relevant details will not be repeated for brevity. This is described in greater detail with reference to  FIG. 21 , the ESL  800  has non-uniform thickness due to the underlying graphene layers  740 . That is, the ESL  800  on the graphene layers  740  may have a thinner thickness than that on the IMD layer  705 . In some embodiments, the ESL  800  has uniform thickness, but the IMD layer  802  has non-uniform thickness due to the ESL  800  being conformal over the graphene layers  740 . 
     Reference is made to  FIG. 22 . The ESL  800 , the IMD layer  802 , the ESL  804 , and the IMD layer  806  are patterned to form via openings O 2 . In some embodiments, the via openings O 2  are aligned with and expose the graphene layers  740 . In some embodiments, via openings O 2  may be formed by, for example, forming a patterned photoresist layer over the IMD layer  806 , followed by an etching process to remove portions of the ESL  800 , the IMD layer  802 , the ESL  804 , and the IMD layer  806 , and then removing the photoresist layer. 
     Reference is made to  FIG. 23 . The ESL  804  and the IMD layer  806  are patterned to form trenches TR 2  that are aligned above the via openings O 2 . In some embodiments, the trenches TR 2  may be formed by, for example, forming a patterned photoresist layer over the IMD layer  806 , followed by an etching process to remove portions of the ESL  804 , and the IMD layer  806 , and then removing the photoresist layer. 
     Reference is made to  FIG. 24 . A liner  810 , a magnetic layer  815 , and a graphene layer  820  are formed sequentially over the IMD layer  806  and in the via openings O 2  and the trenches TR 2 . The liner  810  and the magnetic layer  815  are similar to the liner  710  and the magnetic layer  715 , respectively, and thus relevant details will not be repeated for brevity. In some embodiments, the graphene layer  820  can be formed by using the method and deposition systems described in  FIGS. 1-10B , and thus relevant details will not be repeated hereinafter. For example, the graphene layer  820  is similar to the graphene layer GL of  FIGS. 2-9 . In some embodiments, the thickness of the graphene layer  820  is in a range from about 3 nm to about 5 nm. With respect to the deposition process of  FIG. 8 , the deposition time of the graphene layer  820  may be in a range from about 3 seconds to about 15 seconds (e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 seconds). In some embodiments, the graphene layer  820  may have a smaller thickness than the magnetic layer  815 . In some embodiments, the graphene layer  820  is thicker than the graphene layer  720 , and the deposition time of the graphene layer  820  is longer than the deposition time of the graphene layer  720 . In some embodiments, the magnetic layer  815  may be made of a higher permeability coefficient material than the liner  810 . The magnetic layer  815  may be made of a higher hysteresis coefficient material than the liner  810 . The magnetic layer  815  may be made of a lower conductivity material than the liner  810 . In some embodiments, the magnetic layer  815  may have a greater thickness than the liner  810 . 
     Reference is made to  FIG. 25 . A filling metal  830  is deposited over the graphene layer  820  and fills the via openings O 2  and the trenches TR 2 . The filling metal  830  is similar to the filling metal  730 , and thus relevant details will not be repeated hereinafter. In some embodiments, the magnetic layer  815  may be made of a higher permeability coefficient material than the filling metal  830 . The magnetic layer  815  may be made of a higher hysteresis coefficient material than the filling metal  830 . The magnetic layer  815  may be made of a lower conductivity material than the filling metal  830 . 
     Reference is made to  FIG. 26 . A chemical mechanical polishing (CMP) process is performed to remove excessive materials of the filling metal  830 , the graphene layer  820 , the magnetic layer  815 , and the liner  810  until the IMD layer  806  is exposed. In some embodiments, the remaining filling metal  830 , the graphene layer  820 , the magnetic layer  815 , and the liner  810  can be referred to as a metal-2 (M2) layer in a back end of line (BEOL) process. In some embodiments, the line width of the metal-2 layer is greater than the line width of the metal-1 layer (see  FIG. 19 ), and so the graphene layers  820  of the metal-2 layer can be formed thicker than the graphene layer  720  of the metal-1 layer. 
     Reference is made to  FIG. 27 . A plurality of graphene layers  840  are deposited on the remaining filling metal  830 , the graphene layer  820 , the magnetic layer  815 , and the liner  810 . In some embodiments, the graphene layers  840  tend to grow on a graphene surface and/or a metal surface rather than on a dielectric surface. For example, the graphene layers  840  are selectively formed on the filling metal  830 , the graphene layer  820 , the magnetic layer  815 , and the liner  810 , while the graphene layers  840  are not formed on the IMD layer  806 . In some embodiments, the graphene layers  840  can be formed by using the method and deposition systems described in  FIGS. 1-10B , and thus relevant details will not be repeated hereinafter. For example, the graphene layers  840  are similar to the graphene layer GL of  FIGS. 2-9 . In some embodiments, the thickness of the graphene layer  840  is in a range from about 3 nm to about 5 nm. With respect to the deposition process of  FIG. 8 , the deposition time of the graphene layers  840  may be in a range from about 3 seconds to about 15 seconds (e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 seconds). 
     Reference is made to  FIG. 28 . An ESL  900 , an IMD layer  902 , an ESL  904 , and an IMD layer  906  are formed sequentially over the IMD layer  806 . The ESLs  900  and  904  are similar to the ESL  700 , the IMD layers  902  and  906  are similar to the IMD layer  705 , and thus relevant details will not be repeated for brevity. 
     Reference is made to  FIG. 29 . The ESL  900 , the IMD layer  902 , the ESL  904 , and the IMD layer  906  are patterned to form via openings O 3  and trenches TR 3  above the via openings O 3 . The formation of the via openings O 3  and the trenches TR 3  are similar respectively to the via openings O 2  and the trenches TR 2  described in  FIGS. 23 and 24 , and thus relevant details will not be repeated for brevity. 
     Next, a liner  910 , a magnetic layer  915 , and a graphene layer  920  are formed sequentially over the IMD layer  906  and in the via openings O 3  and the trenches TR 3 . The liner  910  and the magnetic layer  915  are similar to the liner  710  and the magnetic layer  715 , respectively, and thus relevant details will not be repeated for brevity. In some embodiments, the graphene layer  920  can be formed by using the method and deposition systems described in  FIGS. 1-10B , and thus relevant details will not be repeated hereinafter. In some embodiments, the thickness of the graphene layer  920  is in a range from about 3 nm to about 10 nm. With respect to the deposition process of  FIG. 8 , the deposition time of the graphene layer  920  may be in a range from about 3 seconds to about 20 seconds (e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 seconds). In some embodiments, the graphene layer  920  may have a smaller thickness than the magnetic layer  915 . In some embodiments, the graphene layer  920  is thicker than the graphene layer  820 , and the deposition time of the graphene layer  920  is longer than the deposition time of the graphene layer  820 . In some embodiments, the magnetic layer  915  may be made of a higher permeability coefficient material than the liner  910 . The magnetic layer  915  may be made of a higher hysteresis coefficient material than the liner  910 . The magnetic layer  915  may be made of a lower conductivity material than the liner  910 . In some embodiments, the magnetic layer  915  may have a greater thickness than the liner  910 . 
     Reference is made to  FIG. 30 . A filling metal  930  is deposited over the graphene layer  920  and fills the via openings O 3  and trenches TR 3 . The filling metal  930  is similar to the filling metal  730 , and thus relevant details will not be repeated hereinafter. In some embodiments, the magnetic layer  915  may be made of a higher permeability coefficient material than the filling metal  930 . The magnetic layer  915  may be made of a higher hysteresis coefficient material than the filling metal  930 . The magnetic layer  915  may be made of a lower conductivity material than the filling metal  930 . 
     Reference is made to  FIG. 31 . A chemical mechanical polishing (CMP) process is performed to remove excessive materials of the filling metal  930 , the graphene layer  920 , the magnetic layer  915 , and the liner  910  until the IMD layer  906  is exposed. In some embodiments, the remaining filling metal  930 , the graphene layer  920 , the magnetic layer  915 , and the liner  910  can be referred to as a metal-3 (M3) layer in a back end of line (BEOL) process. In some embodiments, the line width of the metal-3 layer is greater than the line width of the metal-2 layer (see  FIG. 26 ), and so the graphene layers  920  of the metal-3 layer can be formed thicker than the graphene layer  820  of the metal-2 layer. 
     Reference is made to  FIG. 32 . A plurality of graphene layers  940  are deposited on the remaining filling metal  930 , the graphene layer  920 , the magnetic layer  915 , and the liner  910 . In some embodiments, the graphene layers  940  tend to grow on a graphene surface and/or a metal surface rather than on a dielectric surface. For example, the graphene layers  940  are selectively formed on the filling metal  930 , the graphene layer  920 , the magnetic layer  915 , and the liner  910 , while the graphene layers  940  are not formed on the IMD layer  906 . In some embodiments, the graphene layers  940  can be formed by using the method and deposition systems described in  FIGS. 1-10B , and thus relevant details will not be repeated hereinafter. In some embodiments, the thickness of the graphene layers  940  is in a range from about 3 nm to about 10 nm. With respect to the deposition process of  FIG. 8 , the deposition time of the graphene layers  940  may be in a range from about 3 seconds to about 20 seconds (e.g., about 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 seconds). In some embodiments, the graphene layers  940  are thicker than the graphene layers  840 , and the deposition time of the graphene layers  940  is longer than the deposition time of the graphene layers  840 . 
     Next, a plurality of conductive layers  950  are formed respectively over the graphene layers  940 . In some embodiments, conductive layers  950  may be aluminum, or other suitable conductive materials. In some embodiments, the conductive layers  950  can be formed by PVD, CVD, ALD, or other suitable process. In some embodiments, the conductive layers  950  can be formed by, for example, depositing a conductive material over the substrate  610 , followed by a photolithography process to pattern the conductive material to form the conductive layers  950 . 
       FIG. 33  illustrates another semiconductor device at a stage corresponding to  FIG. 28  according to some alternative embodiments of the present disclosure. A difference between  FIGS. 32 and 33  is that the liner  710 , the liner  810 , and the liner  910  are omitted. Therefore, the magnetic layer  715  is formed to directly contact the IMD layer  705 . The magnetic layer  815  is formed to directly contact the IMD layer  802 , the ESL  804 , and the IMD layer  806  and lands on the graphene layer  740 . The magnetic layer  915  is formed to directly contact the IMD layer  902 , the ESL  904 , and the IMD layer  906  and lands on the graphene layer  840 , such that the conductivity of interconnects of the semiconductor device may be improved. In some embodiments, the magnetic layer  715 ,  815 , and/or  915  is configured to block diffusion of the material of the filling metal  730 ,  830 , and/or  930  to the IMD layer  705 ,  802 ,  806 ,  902 , and/or  906 . 
     Based on the above discussion, it can be seen that the present disclosure offers advantages. It is understood, however, that other embodiments may offer additional advantages, and not all advantages are necessarily disclosed herein, and that no particular advantage is required for all embodiments. The graphene layer of the present disclosure is deposited on a magnetic layer by using a deposition system with an RF source. An advantage is that a short deposition time (e.g., about 3-30 seconds in some embodiments) of the graphene layer GL formed on the magnetic layer may be achieved to improve the production efficiency, quality, and sheet resistance of the graphene layer. In greater detail, the graphene layer may begin to be formed when the temperature is high enough (e.g., greater than about 200° C. to about 400° C. in some embodiments). The magnetic layer whereon the graphene layer will be formed may be heated to a predetermined temperature (e.g., greater than about 200° C. to about 400° C. in some embodiments) within a few seconds (e.g., about 3-30 seconds in some embodiments) by the RF source of the deposition system of the present disclosure. Thus, heating the magnetic layer by using a high frequency induction heating process of the present disclosure may lower the duration of deposition time of the graphene layer, which in turn allows for improving the production efficiency, quality, and sheet resistance of the graphene layer. 
     In some embodiments, a plasma enhanced chemical vapor deposition (PECVD) method includes loading a wafer having a magnetic layer thereon into a processing chamber equipped with a radio frequency (RF) system, introducing an aromatic hydrocarbon precursor into the processing chamber, and turning on an RF source of the RF system to decompose the aromatic hydrocarbon precursor into active radicals at a frequency greater than about 1000 Hz to form a graphene layer over the magnetic layer. In some embodiments, the frequency of the RF source is greater than about 300 kHz. In some embodiments, the magnetic layer is made of cobalt. In some embodiments, the magnetic layer is made of nickel. In some embodiments, the magnetic layer is made of iron. In some embodiments, the magnetic layer has a permeability coefficient greater than about 5×10 −5  (H/m). In some embodiments, the magnetic layer has a hysteresis coefficient greater than about 300 (A/m). In some embodiments, turning on the RF source of the RF system is performed at a time duration of less than about 60 seconds. In some embodiments, the method further includes performing an H 2  plasma treatment on the wafer to clean the magnetic layer after loading the wafer and prior to introducing the aromatic hydrocarbon precursor, wherein the turning on the RF source of the RF system is performed at a time duration shorter than a time duration of performing the H 2  plasma treatment. In some embodiments, turning on the RF source of the RF system is performed such that an ambient temperature inside the processing chamber is less than about 300° C. In some embodiments, turning on the RF source of the RF system is performed to heat the magnetic layer to a temperature greater than about 300° C. In some embodiments, turning on the RF source of the RF system is performed such that an ambient temperature inside the processing chamber is less than a temperature of the magnetic layer. 
     In some embodiments, a method includes forming a transistor on a substrate; forming a source/drain contact landing on a source/drain structure of the transistor; forming a dielectric layer over the source/drain contact; etching the dielectric layer to form an opening exposing the source/drain contact; depositing a magnetic layer in the opening of the dielectric layer; depositing a first graphene layer over the magnetic layer; depositing a filling metal to overfill a remainder of the opening of the dielectric layer, wherein the magnetic layer has a greater permeability coefficient than the filling metal; and performing a chemical mechanical polishing (CMP) process on the filling metal until the dielectric layer is exposed. In some embodiments, depositing the first graphene layer is performed by using an aromatic hydrocarbon precursor with a radio frequency (RF) power turned on. In some embodiments, depositing the first graphene layer is performed simultaneously with heating a temperature of the magnetic layer to greater than about 200° C. without using a heater. In some embodiments, the magnetic layer has a greater hysteresis coefficient than the filling metal. In some embodiments, the method further includes forming a liner in the opening of the dielectric layer prior to depositing the magnetic layer, wherein the magnetic layer has a greater permeability coefficient than the liner. In some embodiments, the method further includes forming a second graphene layer over the filling metal, the first graphene layer, and the magnetic layer, and not over the dielectric layer using an aromatic hydrocarbon precursor with an RF power turned on. In some embodiments, the magnetic layer has a permeability coefficient greater than about 5×10 −5  (H/m). In some embodiments, the magnetic layer has a hysteresis coefficient greater than about 300 (A/m). 
     In some embodiments, a structure includes a semiconductor substrate, a gate structure, a source/drain structure, a contact, a dielectric layer, and a metal line. The gate structure is on the semiconductor substrate. The source/drain structure is adjacent to the gate structure. The contact lands on the source/drain structure. The dielectric layer spans the contact and the gate structure. The metal line extends through the dielectric layer to the contact. The metal line comprises a liner over the contact, a magnetic layer over the liner, a graphene layer over the magnetic layer, and a filling metal over the graphene layer. The magnetic layer has a greater permeability coefficient than the filling metal. In some embodiments, the magnetic layer has a greater hysteresis coefficient than the filling metal. In some embodiments, the magnetic layer has a greater permeability coefficient than the liner. In some embodiments, the magnetic layer has a greater thickness than the graphene layer. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.