Patent ID: 12191143

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'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 toFIG.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 byFIG.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.2-9illustrate 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 S101. Referring toFIG.2, in some embodiments of block S101, a magnetic layer is formed over a substrate, and then a first cleaning process is performed to the magnetic layer. A substrate W1is shown inFIG.2. In some embodiments, the substrate W1may 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 W1may 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 W1may 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 W1.

As shown inFIG.2, a magnetic layer ML1is deposited over the substrate W1. In some embodiments, the magnetic layer ML1may be a magnetic foil or a magnetic film. In some embodiments, the magnetic layer ML1may 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 inFIG.8. In other words, the magnetic layer ML1may 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 ML1may 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 ML1may 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 inFIG.8. In other words, the magnetic layer ML1may 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 ML1may have a hysteresis coefficient greater than about 300 (A/m). In some embodiments, the magnetic layer ML1may be made of a low conductivity material. In other words, the magnetic layer ML1may 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 ML1may have a conductivity coefficient lower than about 1×107(S/m).

In some embodiments, the magnetic layer ML1may 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 ML1has 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 ML1. That is, any position in the magnetic layer ML1substantially 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 ML1. In some embodiments, an entirety of the magnetic layer ML1is made of the same magnetic material.

In some embodiments, the magnetic layer ML1may 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 ML1may 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 ML1may 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., Fe2O4) 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 ML1may 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., Fe5O12) 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 ML1may 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 ML1may 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 ML1may be made of a ferromagnetic material. By way of example but not limiting the present disclosure, the magnetic layer ML1may 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 ML1may 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 ML1may be made of CoFeB.

In some embodiments, the magnetic layer ML1can be deposited on the substrate W1using suitable processes, such as PVD, CVD, ALD, sputtering, electroplating, or the like. In some embodiments, the magnetic layer ML1has a thickness in a range from about 10 nm to about 100 nm. In some embodiments, because the magnetic layer ML1is exposed to the air, a metal oxide layer MOX may therefore be formed over the magnetic layer ML1due to oxidation. The metal oxide layer MOX is an oxide of the magnetic layer ML1. For example, if the magnetic layer ML1is made of cobalt (Co), the metal oxide layer MOX may be Cobalt oxide (CoO).

As shown inFIG.2, a first cleaning process C1is performed to clean the surface of the substrate W1. In greater detail, the first cleaning process C1is used to remove some contaminants on the metal oxide layer MOX. In some embodiments, the cleaning solvent of the first cleaning process C1is 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 toFIG.1, the method M then proceeds to block S102where a second cleaning process is performed to remove a metal oxide layer on the magnetic layer. With reference toFIG.3, in some embodiments of block S102, a second cleaning process C2is performed to remove the metal oxide layer MOX from the magnetic layer ML1. After the second cleaning process C2, a top surface of the magnetic layer ML1is exposed. In some embodiments, the cleaning solvent of the second cleaning process C2may be a mineral acid (e.g., inorganic acid), such as hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3), sulfuric acid (H2SO4), or the like. In some embodiments where a magnetic layer ML1is cleaned by a 5% nitride acid, the duration of the second cleaning process C2is 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 C2is too short, the metal oxide layer MOX may not be sufficiently removed. While if the duration of the second cleaning process C2is too long, the cleaning solvent of the second cleaning process C2may cause unwanted etch to the magnetic layer ML1.

With continued reference toFIG.1, the method M then proceeds to block S103where a third cleaning process is performed to remove a residue of the second cleaning process from the magnetic layer. With reference toFIG.4, in some embodiments of block S103, a third cleaning process C3is performed to remove a residue of the cleaning solvent of the second cleaning process C2. In some embodiments, the third cleaning process C3may use deionized water (DI water) to remove the cleaning solvent (e.g., mineral acid) of the second cleaning process C2.

Referring back toFIG.1, the method M then proceeds to block S104where the substrate is moved into a processing chamber of a deposition system. This is described in greater detail with reference toFIGS.10A and10B, which illustrate a schematic diagram of an exemplary deposition system10ain some embodiments of the present disclosure. As shown inFIGS.10A and10B, the deposition system10aincludes a processing chamber100, a gas delivery system200, an RF system300, a residue gas analysis system400, and a pumping system500. In some embodiments, the gas delivery system200is connected to the processing chamber100via a gas delivery line G1, and the residue gas analysis system400and the pumping system500are connected to the processing chamber100via a gas delivery line G2. The RF system300is coupled to the processing chamber100by a coil110wound around the exterior of the processing chamber100.

In some embodiments ofFIGS.10A and10B, the processing chamber100is an elongated tube extending laterally. By way of example but not limiting the present disclosure, the processing chamber100may be a quartz tube. In some embodiments, the gas delivery lines G1and G2are fluidly communicated with the processing chamber100, in which the gas delivery lines G1and G2are fluidly communicated with opposite sides of the processing chamber100. The coil110is wound around the processing chamber100from a top to a bottom of the processing chamber100. The processing chamber100can accommodate a wafer W2. For example, the wafer W2may 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 W2may 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 W2may 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 W2. A magnetic layer ML2can be deposited on the wafer W2. In some embodiments, the magnetic layer ML2can act as a catalytic layer for growing a graphene layer, which will be discussed below. In some embodiments, the magnetic layer ML2as shown inFIG.10Amay be substantially the same as or comparable to that of the magnetic layer ML1as shown inFIG.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 ML2can be deposited on the substrate W2using suitable processes, such as PVD, CVD, ALD, sputtering, electroplating, or the like.

In some embodiments, the inductive coil110is connected to the RF system300through a transmission line such as a wave guide or a co-axial cable. The coil110may be made of copper (Cu), or other suitable conductive materials. In some embodiments, the coil110has a multiple turn cylindrical configuration and may have an electrical length of about one-quarter wavelength (<λ/4) at the operating frequency. For example, the coil110is positioned outside the processing chamber100for coupling the RF magnetic fields MF into the processing chamber100. These induced RF magnetic fields MF ionize at least part of the process gases and thus form plasma in processing chamber100.

The gas delivery system200will now be described. In some embodiments, the gas delivery system200includes several sources202,204, and206. In the example shown inFIG.10A, three sources are illustrated, while more or less sources may be applied in some other embodiments. The gas delivery system200includes several mass flow controllers212,214,216, in which the mass flow controllers212,214,216are connected to the sources202,204, and206via valves V12, V14, V16, respectively. Moreover, the mass flow controllers212,214,216are connected to the gas delivery line G1via valves V22, V24, V26, respectively.

In some embodiments, the source202is a liquid source, and thus the source202may include a liquid tank. For example, the liquid of the source202may be liquid aromatic hydrocarbon, such as benzene (C6H6) or toluene (C7H8). 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 sources204and206are gas sources, and thus the sources204and206may include gas cylinders. The gases of the sources204and206may be, for example, H2, Ar, N2, Cl2, or other suitable gases.

The RF system300will now be described. The RF system300includes an RF source302, a matching box304, a controller306, an isolator308, and a remote control module310. In some embodiments, the RF energy is supplied to the processing chamber100by the inductive coil110which is powered by the RF source302and the matching box304.

The input of the matching box304is coupled to the RF source302, which provides RF power for plasma generation. The matching box304is used to match the impedance of the coil110to the impedance of the RF source302, in order to deliver the maximum power to the plasma in the processing chamber100. In some embodiments, the matching box304includes 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 controller306may control the operation of the RF source302. The controller306may include, for example, a computer including a central processing unit (CPU), a memory, and support circuits. The controller306operates 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 module310is electrically coupled between the controller306and the RF source302. In some embodiments, the remote control module310enables the controller306to operate the RF source302remotely.

The isolator308is electrically coupled to the RF source302, the remote control module310, and the controller306. Generally, the isolator308is used to isolate the RF source302from the remote control module310. The isolator308is used to protect high-power RF energy from the RF source302. If the RF source302is connected directly to a load (such as the coil110), and the load is not well matched with the RF source302, some power reaching the load will be reflected back to the remote control module310and then the controller306that could destroy the controller306. The isolator308between the controller306and the RF source302will absorb most of the reflected RF energy, which in turn will protect the controller306from being destroyed.

The residue gas analysis system400will now be described. The residue gas analysis system400includes a residue gas analyzer (RGA)402, a main pump404, and a backing vacuum pump406. The RGA402is connected to the gas delivery line G2via a valve V4. In some embodiments, the RGA402is a spectrometer that effectively measures the chemical composition of a gas present in a low-pressure environment. For example, the RGA402can 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 pump404is connected to the RGA402, and the backing vacuum pump406is connected to the main pump404. In some embodiments, the pumps404and406are connected in series so as to improve the pumping speed of the RGA402. The backing vacuum pump406is used to lower pressure from one pressure state (typically atmospheric pressure) to a lower pressure state, after which the main pump404is used to evacuate the process chamber down to high-vacuum levels needed for processing. In some embodiments, the main pump404may be a turbo pump, a cryo pump, an ion pump, a diffusion pump, or the like. The backing vacuum pump406may 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 system500will now be described. In some embodiments, the pumping system500includes a pressure gauge502, a foreline trap504, and a vacuum pump506. The foreline trap504in connected to the gas delivery line G2via a valve V5. The remainder of the gas mixture exhausted from the processing chamber100, including reaction products or byproducts, is evacuated from the processing chamber100by the vacuum pump506. In some embodiments, the foreline trap504may be a particle collector or a particle filter, which is positioned downstream from the exhaust gas source (e.g., processing chamber100). In some embodiments, the foreline trap504is positioned as close as possible to the processing-chamber100in order to maximize the amount of powder and other particulate matter that is collected within the processing chamber100and minimize the amount that is deposited within other areas of the gas delivery line G2. In some other embodiments, the foreline trap504may be a cooling trap, which recycles process gases by removing condensable material from the process gases when flowing through the foreline trap504.

With reference toFIG.5, in some embodiments of block S104, after the third cleaning process C3, the substrate W1is loaded into the processing chamber100of the deposition system. In some embodiments, the gas delivery system200of the deposition system10dinFIG.5only includes two sources202and204. For example, the source202is a liquid source, and thus the source202may include a liquid tank. The liquid of the source202may, for example, be liquid aromatic hydrocarbon, such as benzene (C6H6) or toluene (C7H8). 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 source204is a gas source, and thus the source204may include gas cylinder. In some embodiments, the gas of the source204may be H2. In some embodiments, a gas delivery line G12connects the source202to the gas delivery line G1(or the processing chamber100), and a gas delivery line G14connects the source204to the gas delivery line G1(or the processing chamber100).

Referring back toFIG.1, the method M then proceeds to block S105where a fourth cleaning process is performed to the magnetic layer in the processing chamber of the deposition system. With reference toFIG.6, in some embodiments of block S105, a fourth cleaning process C4is performed to clean the substrate W1. The fourth cleaning process C4is performed by, for example, turning on the valves14and24of the gas delivery system200, such that the gas inside the source204can flow through the mass flow controller214and then flows into the gas delivery lines G14and G1. For example, H2flows from the source204into the processing chamber100through the gas delivery lines G14and G1. In some embodiments, the mass flow controller214is controlled such that the flow rate of H2is in a range from about 1 sccm to about 5 sccm.

Meanwhile, the RF source302of the RF system300is turned on with an RF power in a range from about 150 W to about 200 W, such that the H2that flows into the processing chamber100becomes hydrogen plasma (H2plasma). The hydrogen plasma may etch and clean the magnetic layer ML1over the substrate W1. The plasma can remove unwanted metal oxide on the substrate W1. For example, H++CoO→Co+H2O, in which a reduction-oxidation process takes place, such that the CoO becomes Co. In some embodiments, the duration of the fourth cleaning process C4is 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 C4is too short, the magnetic layer ML1may not be sufficiently cleaned. While if the duration of the fourth cleaning process C4is too long, the hydrogen plasma of the fourth cleaning process C4may cause unwanted consumption to the magnetic layer ML1. On the other hand, the fourth cleaning process C4can also activate the surface of the magnetic layer ML1. The hydrogen plasma removes unwanted metal oxide on the magnetic layer ML1to make sure the surface of the magnetic layer ML1is 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 ofFIG.6, the valve V22of the gas delivery system200is turned off, such that only the gas (e.g., H2) in the source204is supplied into the processing chamber100during cleaning of the substrate W1. That is, during the fourth cleaning process C4, the processing chamber100is free of aromatic hydrocarbon. On the other hand, during the fourth cleaning process C4, the pumping system500is turned on, so as to pump out the gas (e.g., H2) in the processing chamber100. In greater detail, the gas (e.g., H2) in the processing chamber100is pumped out to the pumping system500through the gas delivery line G2. In some embodiments, during the fourth cleaning process C4ofFIG.8, the gas environment of the processing chamber100is substantially a pure hydrogen (H2) environment.

Referring back toFIG.1, the method M then proceeds to block S106where an aromatic hydrocarbon precursor is supplied into the processing chamber of the deposition system. After cleaning the magnetic layer ML1ofFIG.6, the valve24of the gas delivery system200is turned off, such that supply of the gas (e.g., H2) in the source204to the processing chamber100is stopped. Meanwhile, the RF system300is turned off. That is, the RF power of the RF system300in this step is a zero value or negligibly small. On the other hand, the pumping system500may pump out (remove) the remaining gas (e.g., hydrogen gas H2) in the processing chamber100, so as to create a vacuum environment in the processing chamber100.

With reference toFIG.7, in some embodiments of block S106, an aromatic hydrocarbon precursor can be provided into the processing chamber100and over the magnetic layer ML1. Subsequently, the valves12and22of the gas delivery system200are turned on. As mentioned above, the source202is a liquid source. The liquid source may be liquid aromatic hydrocarbon, such as benzene (C6H6) or toluene (C7H8). In some embodiments, the aromatic hydrocarbon (e.g., benzene or toluene) is used as a precursor for depositing a graphene layer discussed inFIG.8. Although the source202is a liquid aromatic hydrocarbon source, the liquid aromatic hydrocarbon may volatilize easily. Accordingly, as the valve12is turned on, the liquid aromatic hydrocarbon in the source202may 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 controller212and then flows into the gas delivery lines G12and G1. For example, the aromatic hydrocarbon gas flows from the source202into the processing chamber100through the gas delivery lines G12and G1. In some embodiments, the mass flow controller212is 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 chamber100without using a carrier gas, such as Ar or H2. That is, the gas environment of the processing chamber100is substantially a pure aromatic hydrocarbon gas environment in this step, which will facilitate the formation of the graphene layer inFIG.8.

In some embodiments, when a precursor for depositing a graphene layer is methane (CH4), acetylene (C2H2), or ethylene (C2H4), 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., C6H6or C7H8) than a molecule of methane (CH4), acetylene (C2H2), or ethylene (C2H4). 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 ofFIG.8, the valve V24of the gas delivery system200has been turned off, such that only the aromatic hydrocarbon in the source202is supplied into the processing chamber100. In some embodiments, the aromatic hydrocarbon gas is used as a precursor in the deposition process inFIG.8, and thus aromatic hydrocarbon gas can be interchangeably referred to as an aromatic hydrocarbon precursor in the following content.

With reference again toFIG.1, the method M then proceeds to block S107where 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 toFIG.8, in some embodiments of block S107, the RF source302of the RF system300is turned on, so as to generate plasma of aromatic hydrocarbon in the processing chamber100. The aromatic hydrocarbon precursor is decomposed (or ionized) into several active radical species, which constitute the plasma over the magnetic layer ML1. 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 ML1and may diffuse on the surface of the magnetic layer ML1. 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 ML1. “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 source302of the RF system300is turned on to decompose the aromatic hydrocarbon precursor into active radicals, and the active radicals are then cyclized into a graphene layer.

Referring back toFIG.8, as mentioned above, before the RF source302of the RF system300is turned on, the processing chamber100is already filled with the aromatic hydrocarbon precursor (seeFIG.7). Accordingly, once the RF source302of the RF system300is 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 system300is 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 ML1.

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 1×10−2torr to about 2×10−2torr. In some embodiments, the RF power of the RF source302of the RF system300is 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 ML1.

As shown inFIG.8, a high frequency induction heating process is also performed on the magnetic layer ML1, which allows for speeding up the deposition rate of the graphene layer GL. In greater detail, the magnetic layer ML1may be heated by the RF system300through the coil110wound around thereof to speed up the deposition rate of the graphene layer GL on the magnetic layer ML1. The RF source302may supply high-frequency alternating current to the coil110. The alternating current may be supplied to the coil110at 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 inFIG.10Bat the coil110. Therefore, the magnetic layer ML1is positioned within the time-varying magnetic field MF generated by the coil110.

Next, the magnetic layer ML1may be heated to a predetermined temperature within a few seconds or less by induced eddy current generated by putting a coil110with high-frequency electrical current in the vicinity of the magnetic layer ML1. In other words, by controlling the RF source302, 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 ML1without using a heater other than the RF system300, by way of example but not limiting the present disclosure. Stated another way, the deposition system10ais free of a heater other than the RF system300. Thus, heating the magnetic layer ML1by 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 ML1.

By way of example but not limiting the present disclosure, the magnetic layer ML1may be heated to about 800° C. for less than about 30 secs in the operation of the RF source302, 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 source302through the coil110, because the operation of the RF source302may 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 source302of the RF system300and turning off the RF source302of the RF system300. In some embodiments, the duration of deposition time of the graphene layer GL on the magnetic layer ML1may be less than about 30 secs during the operation of the RF source302. In some embodiments, the duration of deposition time of the graphene layer GL on the magnetic layer ML1may 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 source302. For example, in the operation of the RF source302to deposit the graphene layer GL, the magnetic layer ML1may 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 ML1is shorter than a time duration of performing the fourth cleaning process C4. 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 ML1has 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 ML1having 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 ML1having 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 chamber100of the deposition system10amay be determined by the RF source302. In greater detail, the RF source302of the RF system300may generate plasma of aromatic hydrocarbon through the coil110, which may raise the ambient temperature in the processing chamber100. By way of example but not limiting the present disclosure, the ambient temperature inside the processing chamber100may be raised to about 200° C. to about 300° C. during the operation of the RF source302. At the same time, the magnetic layer ML1on the substrate W1may 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 source302, the ambient temperature inside the processing chamber100is lower than the temperature of the magnetic layer ML1. In some embodiments where a semiconductor device, such as a transistor, is formed on the substrate W1, the processing chamber100having 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 chamber100is higher than about 400° C., some devices formed on the substrate W1may be destroyed.

FIG.11Aillustrates experimental results showing different operation time durations of an RF source effect on temperatures of a magnetic layer.FIG.11Billustrates a partial enlarged view ofFIG.11A. InFIGS.11A and11B, 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 inFIGS.11A and11B, the RF source was operated at predetermined time durations of about 0, 7, 12, 20, 30, 250, and 600 secs.

As shown inFIGS.11A and11B, 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 inFIGS.11A and11B, 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 ML1as 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 ML1as 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 ML1as 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<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 to12Cillustrate experimental results of a Raman spectrum of graphene formed over a magnetic layer with different operation time durations of the RF source. InFIGS.12A to12C, the samples including a graphene layer formed by a precursor (e.g., benzene (C6H6)) 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 inFIGS.12A to12C, 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 inFIG.12A, the RF source is operated at predetermined time durations about 3, 5, 10, 20, and 30 secs. In the example shown inFIG.12B, the RF source is operated at the predetermined time duration about 7 secs. In the example shown inFIG.12C, the RF source is operated at the predetermined time duration about 12 secs.FIG.13illustrates 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 ofFIGS.12A to12C.

As shown inFIGS.12A,12B,12C, and13, 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 ofFIG.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 coil110and the processing chamber100. For example, in some embodiments where the area of the magnetic layer ML1may be in a range from about 1*2 cm2to about 12*2 cm2, experimental results show that the graphene layer GL has a uniform region having an area about 8*2 cm2to about 10*2 cm2(e.g., about 9*2 cm2).

After an entirety of the magnetic layer ML1is covered by the graphene layer GL and/or after the graphene layer GL is grown to a desired thickness, the RF source302of the RF system300can 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 ML1may 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.34and35illustrate schematic transmission electron microscopy images showing different graphene growth experimental results formed in different deposition time durations. InFIG.34, when the deposition time of the graphene layer GL2formed on the magnetic layer ML2is about 12 seconds, the graphene layer GL2may have a thickness of about 5.74 nm in about 17 layers. InFIG.35, when the deposition time of the graphene layer GL3formed on the magnetic layer ML3is about 7 seconds, the graphene layer GL3may have a thickness of about 1.8 nm in about 4 layers. In the example shown inFIG.35, the magnetic layer may be heated to about 200° C. in about 7 seconds. In the example shown inFIG.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 ML1may be achieved to improve a production efficiency, quality, and sheet resistance of the graphene layer. Moreover, as illustrated inFIGS.34and35, the graphene layer GL3formed in a shorter time duration may have a higher thickness non-uniformity than the graphene layer GL2formed in a longer time duration, which means that the thickness uniformity of graphene may increases as deposition time increases.

FIG.14illustrates experimental results showing different operation time durations of the RF (radio frequency) source effect on electrical properties. InFIG.14, the samples including a graphene layer formed by a precursor (e.g., benzene (C6H6)) 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 inFIG.14, the RF source is operated at predetermined time durations about 3, 5, 10, 12, 15, 30, 60, and 120 secs. As shown inFIG.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 ofFIG.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 chamber100without using a carrier gas, such as Ar or H2. This will improve the quality of the deposited graphene layer GL, because the RF power provided by the RF system300may transform the carrier gas into plasma (e.g., Ar plasma or H2plasma), while the such plasma may etch the graphene layer GL during deposition.

Referring back toFIG.1, the method M then proceeds to block S108where the substrate is moved out from the processing chamber of the deposition system. With reference toFIG.9, in some embodiments of block S108, after the RF source302of the RF system300(seeFIG.8) is turned off, the substrate W1is moved out from the processing chamber100(seeFIG.9). In some embodiments, before moving out the substrate W1from the processing chamber100, the valve22of the gas delivery system200may be turned off, so as to stop providing aromatic hydrocarbon precursor into the processing chamber100.

Reference is made toFIGS.15to32.FIGS.15to32illustrate a method in various stages of forming a semiconductor device in accordance with some embodiments of the present disclosure.

Reference is made toFIG.15. An initial structure is received. The initial structure includes a substrate610. The substrate610includes an N-well region600N and a P-well region600P, in which the N-well region600N may be doped with N-type impurities, and the P-well region600P may be doped with P-type impurities. The substrate610may 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 substrate610. Alternatively, the silicon substrate610may 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 structures605are disposed in the substrate610. In some embodiments, the isolation structures605may include oxide, such as silicon dioxide. The isolation structures605, which act as a shallow trench isolation (STI) around the P-well region600P from the N-well region600N, may be formed by chemical vapor deposition (CVD) techniques using tetra-ethyl-ortho-silicate (TEOS) and oxygen as a precursor.

A gate structure600A is disposed over the P-well region600P of the substrate610, and a gate structure600B is disposed over the N-well region600N of the substrate610. In some embodiments, each of the gate structure600A and the gate structure600B includes a gate dielectric602and a gate electrode604. In some embodiments, the gate dielectric602may 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 electrode604may include polycrystalline-silicon (poly-Si) or poly-crystalline silicon-germanium (poly-SiGe). In some other embodiments, the gate structure600A and the gate structure600B 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 layers625are disposed over the gate structures600A and600B. In some embodiments, the capping layers625may be oxide. A plurality of gate spacers612are disposed on opposite sides of the gate structure600A and the gate structure600B. In some embodiments, the gate spacers612may include SiO2, Si3N4, SiOxNy, SiC, SiCN films, SiOC, SiOCN films, and/or combinations thereof.

Source/drain structures620N are disposed in the P-well region620P of the substrate610and on opposite sides of the gate structure600A, and source/drain structures620P are disposed in the N-well region620N of the substrate610and on opposite sides of the gate structure600B. In some embodiments, the source/drain structures620N may be doped with N-type impurities, and the source/drain structures620P may be doped with p-type impurities. In some embodiments, the source/drain structures620N,620P may be may be formed by performing an epitaxial growth process that provides an epitaxy material over the substrate610, and thus the source/drain structures620N,620P can be interchangeably referred to as epitaxy structures620N,620P in this context. In various embodiments, the source/drain structures620N,620P may include Ge, Si, GaAs, AlGaAs, SiGe, GaAsP, SiP, or other suitable materials.

A contact etch stop layer (CESL)630is disposed over the isolation structures605and over the capping layers625. An interlayer dielectric (ILD) layer640is disposed over the CESL630and surrounds the gate structures600A and600B. In some embodiments, the CESL630includes silicon nitride, silicon oxynitride or other suitable materials. The CESL630can be formed using, for example, plasma enhanced CVD, low pressure CVD, ALD or other suitable techniques. In some embodiments, the ILD layer640may 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 layer640may be formed using, for example, CVD, ALD, spin-on-glass (SOG) or other suitable techniques.

Source/drain contacts650are disposed in the ILD layer640and contact the source/drain structures620A and620P. In some embodiments, each source/drain contact650includes a liner652and a plug654. The liner652is between the plug654and the underlying source/drain structures600A or600B. In some embodiments, the liner652assists with the deposition of the plug654and helps to reduce diffusion of a material of the plug654through the gate spacers612. In some embodiments, the liner652includes titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), or another suitable material. The plug654includes 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)700is disposed over the ILD layer640and the source/drain contacts650. An inter-metal dielectric (IMD) layer705is disposed over the ESL700. The material and the formation method of the ESL700are similar to those of the CESL630. Moreover, the material and the formation method of the IMD layer705are similar to those of the ILD layer640.

Reference is made toFIG.16. The ESL700and the IMD layer705are patterned to form openings O1. Subsequently, a liner710and a magnetic layer715are formed in the openings O1. In some embodiments, the liner710includes titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), or another suitable material. In some embodiments, the magnetic layer715may be made of a higher permeability coefficient material than the liner710. The magnetic layer715may be made of a higher hysteresis coefficient material than the liner710. The magnetic layer715may be made of a lower conductivity material than the liner710. In some embodiments, the magnetic layer715may have a greater thickness than the liner710.

In some embodiments, the magnetic layer715may 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 layer715has 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 layer715. That is, any position in the magnetic layer715substantially 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 layer715. In some embodiments, an entirety of the magnetic layer715is made of the same magnetic material.

In some embodiments, the magnetic layer715may 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 layer715may 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 layer715may 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., Fe2O4) 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 layer715may 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., Fe5O12) 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 layer715may 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 layer715may 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 layer715may be made of a ferromagnetic material. By way of example but not limiting the present disclosure, the magnetic layer715may 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 layer715may 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 layer715may be made of CoFeB.

Reference is made toFIG.17. A graphene layer720is deposited over the magnetic layer715. In some embodiments, the graphene layer720can be formed by using the method and deposition systems described inFIGS.1-10B, and thus relevant details will not be repeated hereinafter. For example, the magnetic layer715is similar to the magnetic layer ML1ofFIGS.2-9, and the graphene layer720is similar to the graphene layer GL ofFIGS.2-9. In some embodiments, the thickness of the graphene layer720is in a range from about 1 nm to about 3 nm. With respect to the deposition process ofFIG.8, the deposition time of the graphene layer720may 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 layer720may have a smaller thickness than the magnetic layer715.

Reference is made toFIG.18. A filling metal730is deposited over the graphene layer720and fills the openings O1. In some embodiments, the filling metal730is made of a highly conductive material. In some embodiments, the filling metal730may include metal, such as tungsten (W), ruthenium (Ru), aluminum (Al), copper (Cu), or other suitable conductive materials. In some embodiments, the conductive material170may 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 layer715may be made of a higher permeability coefficient material than the filling metal730. The magnetic layer715may be made of a higher hysteresis coefficient material than the filling metal730. The magnetic layer715may be made of a lower conductivity material than the filling metal730.

Reference is made toFIG.19. A chemical mechanical polishing (CMP) process is performed to remove excessive materials of the filling metal730, the graphene layer720, the magnetic layer715, and the liner710until the IMD layer705is exposed. In some embodiments, the remaining filling metal730, the graphene layer720, the magnetic layer715, and the liner710can be referred to as a metal-1 (M1) layer in a back end of line (BEOL) process.

Reference is made toFIG.20. A plurality of graphene layers740are deposited on the remaining filling metal730, the graphene layer720, the magnetic layer715, and the liner710. In greater detail, the graphene layer720grows on the filling metal730because the filling metal730is heated by the surrounding magnetic layer715. The filling metal730may 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 layer715by the RF source of the deposition system of the present disclosure. Thus, heating the filling metal730through the surrounding magnetic layer715by 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 layers740tend to grow on a graphene surface and/or a metal surface rather than on a dielectric surface. As an example inFIG.20, the graphene layers740are selectively formed on the filling metal730, the graphene layer720, the magnetic layer715, and the liner710, while the graphene layers740are not formed on the IMD layer705. In some embodiments, the graphene layers740can be formed by using the method and deposition systems described inFIGS.1-10B, and thus relevant details will not be repeated hereinafter. For example, the graphene layers740are similar to the graphene layer GL ofFIGS.2-9. In some embodiments, the thickness of the graphene layers740is in a range from about 1 nm to about 3 nm. With respect to the deposition process ofFIG.8, the deposition time of the graphene layers740may 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 toFIG.21. An ESL800, an IMD layer802, an ESL804, and an IMD layer806are formed sequentially over the IMD layer705. The ESLs800and804are similar to the ESL700, the IMD layers802and806are similar to the IMD layer705, and thus relevant details will not be repeated for brevity. This is described in greater detail with reference toFIG.21, the ESL800has non-uniform thickness due to the underlying graphene layers740. That is, the ESL800on the graphene layers740may have a thinner thickness than that on the IMD layer705. In some embodiments, the ESL800has uniform thickness, but the IMD layer802has non-uniform thickness due to the ESL800being conformal over the graphene layers740.

Reference is made toFIG.22. The ESL800, the IMD layer802, the ESL804, and the IMD layer806are patterned to form via openings O2. In some embodiments, the via openings O2are aligned with and expose the graphene layers740. In some embodiments, via openings O2may be formed by, for example, forming a patterned photoresist layer over the IMD layer806, followed by an etching process to remove portions of the ESL800, the IMD layer802, the ESL804, and the IMD layer806, and then removing the photoresist layer.

Reference is made toFIG.23. The ESL804and the IMD layer806are patterned to form trenches TR2that are aligned above the via openings O2. In some embodiments, the trenches TR2may be formed by, for example, forming a patterned photoresist layer over the IMD layer806, followed by an etching process to remove portions of the ESL804, and the IMD layer806, and then removing the photoresist layer.

Reference is made toFIG.24. A liner810, a magnetic layer815, and a graphene layer820are formed sequentially over the IMD layer806and in the via openings O2and the trenches TR2. The liner810and the magnetic layer815are similar to the liner710and the magnetic layer715, respectively, and thus relevant details will not be repeated for brevity. In some embodiments, the graphene layer820can be formed by using the method and deposition systems described inFIGS.1-10B, and thus relevant details will not be repeated hereinafter. For example, the graphene layer820is similar to the graphene layer GL ofFIGS.2-9. In some embodiments, the thickness of the graphene layer820is in a range from about 3 nm to about 5 nm. With respect to the deposition process ofFIG.8, the deposition time of the graphene layer820may 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 layer820may have a smaller thickness than the magnetic layer815. In some embodiments, the graphene layer820is thicker than the graphene layer720, and the deposition time of the graphene layer820is longer than the deposition time of the graphene layer720. In some embodiments, the magnetic layer815may be made of a higher permeability coefficient material than the liner810. The magnetic layer815may be made of a higher hysteresis coefficient material than the liner810. The magnetic layer815may be made of a lower conductivity material than the liner810. In some embodiments, the magnetic layer815may have a greater thickness than the liner810.

Reference is made toFIG.25. A filling metal830is deposited over the graphene layer820and fills the via openings O2and the trenches TR2. The filling metal830is similar to the filling metal730, and thus relevant details will not be repeated hereinafter. In some embodiments, the magnetic layer815may be made of a higher permeability coefficient material than the filling metal830. The magnetic layer815may be made of a higher hysteresis coefficient material than the filling metal830. The magnetic layer815may be made of a lower conductivity material than the filling metal830.

Reference is made toFIG.26. A chemical mechanical polishing (CMP) process is performed to remove excessive materials of the filling metal830, the graphene layer820, the magnetic layer815, and the liner810until the IMD layer806is exposed. In some embodiments, the remaining filling metal830, the graphene layer820, the magnetic layer815, and the liner810can 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 (seeFIG.19), and so the graphene layers820of the metal-2 layer can be formed thicker than the graphene layer720of the metal-1 layer.

Reference is made toFIG.27. A plurality of graphene layers840are deposited on the remaining filling metal830, the graphene layer820, the magnetic layer815, and the liner810. In some embodiments, the graphene layers840tend to grow on a graphene surface and/or a metal surface rather than on a dielectric surface. For example, the graphene layers840are selectively formed on the filling metal830, the graphene layer820, the magnetic layer815, and the liner810, while the graphene layers840are not formed on the IMD layer806. In some embodiments, the graphene layers840can be formed by using the method and deposition systems described inFIGS.1-10B, and thus relevant details will not be repeated hereinafter. For example, the graphene layers840are similar to the graphene layer GL ofFIGS.2-9. In some embodiments, the thickness of the graphene layer840is in a range from about 3 nm to about 5 nm. With respect to the deposition process ofFIG.8, the deposition time of the graphene layers840may 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 toFIG.28. An ESL900, an IMD layer902, an ESL904, and an IMD layer906are formed sequentially over the IMD layer806. The ESLs900and904are similar to the ESL700, the IMD layers902and906are similar to the IMD layer705, and thus relevant details will not be repeated for brevity.

Reference is made toFIG.29. The ESL900, the IMD layer902, the ESL904, and the IMD layer906are patterned to form via openings O3and trenches TR3above the via openings O3. The formation of the via openings O3and the trenches TR3are similar respectively to the via openings O2and the trenches TR2described inFIGS.23and24, and thus relevant details will not be repeated for brevity.

Next, a liner910, a magnetic layer915, and a graphene layer920are formed sequentially over the IMD layer906and in the via openings O3and the trenches TR3. The liner910and the magnetic layer915are similar to the liner710and the magnetic layer715, respectively, and thus relevant details will not be repeated for brevity. In some embodiments, the graphene layer920can be formed by using the method and deposition systems described inFIGS.1-10B, and thus relevant details will not be repeated hereinafter. In some embodiments, the thickness of the graphene layer920is in a range from about 3 nm to about 10 nm. With respect to the deposition process ofFIG.8, the deposition time of the graphene layer920may 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 layer920may have a smaller thickness than the magnetic layer915. In some embodiments, the graphene layer920is thicker than the graphene layer820, and the deposition time of the graphene layer920is longer than the deposition time of the graphene layer820. In some embodiments, the magnetic layer915may be made of a higher permeability coefficient material than the liner910. The magnetic layer915may be made of a higher hysteresis coefficient material than the liner910. The magnetic layer915may be made of a lower conductivity material than the liner910. In some embodiments, the magnetic layer915may have a greater thickness than the liner910.

Reference is made toFIG.30. A filling metal930is deposited over the graphene layer920and fills the via openings O3and trenches TR3. The filling metal930is similar to the filling metal730, and thus relevant details will not be repeated hereinafter. In some embodiments, the magnetic layer915may be made of a higher permeability coefficient material than the filling metal930. The magnetic layer915may be made of a higher hysteresis coefficient material than the filling metal930. The magnetic layer915may be made of a lower conductivity material than the filling metal930.

Reference is made toFIG.31. A chemical mechanical polishing (CMP) process is performed to remove excessive materials of the filling metal930, the graphene layer920, the magnetic layer915, and the liner910until the IMD layer906is exposed. In some embodiments, the remaining filling metal930, the graphene layer920, the magnetic layer915, and the liner910can 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 (seeFIG.26), and so the graphene layers920of the metal-3 layer can be formed thicker than the graphene layer820of the metal-2 layer.

Reference is made toFIG.32. A plurality of graphene layers940are deposited on the remaining filling metal930, the graphene layer920, the magnetic layer915, and the liner910. In some embodiments, the graphene layers940tend to grow on a graphene surface and/or a metal surface rather than on a dielectric surface. For example, the graphene layers940are selectively formed on the filling metal930, the graphene layer920, the magnetic layer915, and the liner910, while the graphene layers940are not formed on the IMD layer906. In some embodiments, the graphene layers940can be formed by using the method and deposition systems described inFIGS.1-10B, and thus relevant details will not be repeated hereinafter. In some embodiments, the thickness of the graphene layers940is in a range from about 3 nm to about 10 nm. With respect to the deposition process ofFIG.8, the deposition time of the graphene layers940may 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 layers940are thicker than the graphene layers840, and the deposition time of the graphene layers940is longer than the deposition time of the graphene layers840.

Next, a plurality of conductive layers950are formed respectively over the graphene layers940. In some embodiments, conductive layers950may be aluminum, or other suitable conductive materials. In some embodiments, the conductive layers950can be formed by PVD, CVD, ALD, or other suitable process. In some embodiments, the conductive layers950can be formed by, for example, depositing a conductive material over the substrate610, followed by a photolithography process to pattern the conductive material to form the conductive layers950.

FIG.33illustrates another semiconductor device at a stage corresponding toFIG.28according to some alternative embodiments of the present disclosure. A difference betweenFIGS.32and33is that the liner710, the liner810, and the liner910are omitted. Therefore, the magnetic layer715is formed to directly contact the IMD layer705. The magnetic layer815is formed to directly contact the IMD layer802, the ESL804, and the IMD layer806and lands on the graphene layer740. The magnetic layer915is formed to directly contact the IMD layer902, the ESL904, and the IMD layer906and lands on the graphene layer840, such that the conductivity of interconnects of the semiconductor device may be improved. In some embodiments, the magnetic layer715,815, and/or915is configured to block diffusion of the material of the filling metal730,830, and/or930to the IMD layer705,802,806,902, and/or906.

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 H2plasma 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 H2plasma 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.