WO2012129122A1

WO2012129122A1 - Method for controlling dangling bonds in fluorocarbon films

Info

Publication number: WO2012129122A1
Application number: PCT/US2012/029550
Authority: WO
Inventors: Yoshiyuki KOKUCHI
Original assignee: Tokyo Electron Ltd; Tokyo Electron America Inc
Current assignee: Tokyo Electron Ltd; Tokyo Electron America Inc
Priority date: 2011-03-18
Filing date: 2012-03-16
Publication date: 2012-09-27
Anticipated expiration: 2013-09-18
Also published as: TWI469199B; TW201241901A

Abstract

Embodiments of the invention describe a method for forming fluorocarbon films for semiconductor devices. The method includes providing a substrate on a substrate holder in a plasma processing chamber, introducing in the plasma processing chamber a first process gas containing a C_aF_b gas, forming a first plasma from the first process gas by applying a first RF bias and a first positive DC bias to the substrate holder, and depositing a first fluorocarbon film on the substrate by the first plasma. The method further includes introducing in the plasma processing chamber a second process gas containing a C_aF_b gas, forming a second plasma from the second process gas by applying microwave power to the microwave antenna, and applying second RF bias and a second positive DC bias to the substrate holder, and depositing a second fluorocarbon film on the first fluorocarbon film by the second plasma.

Description

TITLE OF THE INVENTION

METHOD FOR CONTROLLING DANGLING BONDS IN FLUOROCARBON

FILMS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority to United States provisional application serial no. 61/454,320, filed on March 18, 201 1, the entire contents of which are herein incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention generally relates to depositing dielectric films on a substrate and in particular to a method for controlling dangling bonds in fluorocarbon films.

BACKGROUND OF THE INVENTION

[0003] In a manufacturing process for electronic devices, such as semiconductor devices, liquid crystal display devices, and organic electro-luminescent (EL) elements, a film forming process is performed to form a conductive film or an insulating film on the surface of a substrate. A plasma film forming process for forming a film on a substrate using plasma is often employed in this film forming process, for example for depositing interlayer dielectrics (ILDs) for integrated circuits.

[0004] Fluorocarbon (CF) films are promising materials for use as low-dielectric constant (low-k) ILDs and in other applications. A problem that is commonly encountered when integrating a CF film with other materials is that the contact between the CF film and the other materials thermally deteriorates during subsequent processing. The further processing can include annealing of a copper wiring layer formed in recessed features of the ILDs. The cause of the thermal deterioration is thought to be a decomposition reaction in the CF film due to the presence of dangling bonds in the CF film. The dangling bonds include unsaturated carbon bonds that lack fluorine atoms. The thermal deterioration results in fluorine diffusion and can lead to reduced adhesion between the CF film and the other materials in the integrated circuit. Eventually, the reduced adhesion can lead to film corrosion and film peeling that may be observed as film blistering on the substrate.

[0005] However, it is difficult to prepare high quality CF films by plasma processing, in particular high quality CF films that have low concentration of dangling bonds and good thermal stability. Increasing the thermal stability of the CF films prevents or reduces the fluorine atom diffusion and improves adhesion between the CF films and the other materials in contact with the CF films. Attempts to reduce the amount of fluorine on the surface of CF film have included performing a thermal treatment of the CF film before depositing other material layers on the CF film, or depositing a titanium metal on the CF film due to the relatively good adhesion properties at the interface of these two materials. However, these attempts have not yielded manufacturable solutions and new methods are needed for depositing CF films having a low concentration of dangling bonds and good thermal stability.

SUMMARY OF THE INVENTION

[0006] Embodiments of the invention describe a method for depositing CF films having a low concentration of dangling bonds and good thermal stability.

According to one embodiment, the method includes providing a substrate on a substrate holder in a plasma processing chamber, the plasma processing chamber containing a microwave antenna, a microwave power source for powering the microwave antenna, a radio frequency (RF) bias source for RF biasing the substrate holder, and a direct current (DC) voltage source for DC biasing the substrate holder, introducing in the plasma processing chamber a first process gas containing a C_aF_b gas, where a and b are positive integers, forming a first plasma from the first process gas by applying a first RF bias and a first positive DC bias to the substrate holder, and depositing a first fluorocarbon film on the substrate by the first plasma. The method further includes introducing in the plasma processing chamber a second process gas containing a C_aF_b gas, where a and b are positive integers, forming a second plasma from the second process gas by applying microwave power to the microwave antenna, and applying second RF bias and a second positive DC bias to the substrate holder, and depositing a second fluorocarbon film on the first fluorocarbon film by the second plasma. [0007] According to another embodiment, the method includes providing a substrate on a substrate holder in a plasma processing chamber, the plasma processing chamber containing a microwave antenna, a microwave power source for powering the microwave antenna, a radio frequency (RF) bias source for RF biasing the substrate holder, and a direct current (DC) voltage source for DC biasing the substrate holder, introducing in the plasma processing chamber a process gas containing a C_aF_b gas, where a and b are positive integers, forming a plasma from the process gas by applying a RF bias and a positive DC bias to the substrate holder, applying

microwave power to the microwave antenna, and depositing a fluorocarbon film on the substrate by the plasma, where the applied microwave power is increased from a first microwave power level to a second microwave power level during the depositing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a flow diagram for forming a fluorocarbon film on a substrate according to an embodiment of the invention;

[0009] FIGS. 2A-2D schematically show formation of a fluorocarbon film on a substrate according to an embodiment of the invention;

[0010] FIG. 3 is a schematic diagram of a plasma processing system containing a radial line slot antenna (RLSA) plasma source for depositing a fluorocarbon film on a substrate according to one embodiment of the invention;

[0011] FIG. 4 is a schematic diagram of another plasma processing system containing a radial line slot antenna (RLSA) plasma source for depositing a fluorocarbon film on a substrate according to an embodiment of the invention;

[0012] FIG. 5 illustrates a plan view of a gas supplying unit of the plasma processing system in FIG. 4;

[0013] FIG. 6 illustrates a partial cross-sectional view of an antenna portion of the plasma processing system in FIG. 4; and

[0014] FIGs. 7-9 schematically show changes in microwave power level, substrate holder temperature, and DC bias during fluorocarbon film deposition according to some embodiments of the invention. DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

[0015] Methods for depositing CF films with low concentrations of dangling bonds and good thermal stability are described in various embodiments. One skilled in the relevant art will recognize that the various embodiments may be practiced without one or more of the specific details, or with other replacement and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of various embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the invention. Furthermore, it is understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

[0016] Reference throughout this specification to "one embodiment" means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention, but do not denote that they are present in every embodiment. Thus, the appearances of the phrase "in one embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the invention.

[0017] There is a general need in semiconductor manufacturing for new methods for depositing CF films having a low concentration of dangling bonds and good thermal stability in order to enable the use of these films in advanced semiconductor devices. The inventor has discovered that high quality CF films that have a low concentration of dangling bonds and good thermal stability may be deposited on a substrate by extracting negative fluorine ions (F ) from a deposition plasma during CF film deposition from a process gas containing a fluorocarbon gas by applying a large positive DC bias to a substrate holder configured for supporting the substrate. The negative fluorine ions extracted from the plasma react with unsaturated carbon dangling bonds in the CF film that lack fluorine atoms. The reaction of the negative fluorine ions from the plasma with the unsaturated carbon dangling bonds replaces unsaturated carbon dangling bonds in the CF film with C-F bonds which results in the deposited CF film having few dangling bonds and good thermal stability. [0018] According to embodiments of the invention, a thick CF film may be formed on a substrate by first depositing on the substrate a first high quality CF film with few dangling bonds, and thereafter depositing a second CF film on the first CF film. The inventor has discovered that the first CF film can provide a high quality deposition surface for deposition of the second CF film on the first CF film. Without the deposition of the first high quality CF film, the second CF film (and thus the thick CF film which is a combination of the first and second CF films) will have unacceptably large number of dangling bonds and poor thermal stability. The second CF film may be deposited at a higher film deposition rate than the first CF film using different processing conditions during the deposition of the first and second CF films. This allows for the high substrate throughput that is required in manufacturing of semiconductor devices. The first CF film may be deposited on the substrate using a first plasma that is formed by applying a first RF bias and a first positive DC bias to a substrate holder configured for supporting the substrate, where the first plasma may be formed without applying microwave power to a microwave antenna in the plasma processing system. The second CF film may be deposited at high deposition rate by applying microwave power to the microwave antenna, and applying a second RF bias and a second positive DC bias to a substrate holder.

[0019] FIG. 1 is a flow diagram for forming a fluorocarbon film on a substrate according to an embodiment of the invention and FIGS. 2A-2D schematically show formation of a fluorocarbon film on a substrate according to an embodiment of the invention. Referring both to FIGs. 1 and 2A-2D, the flow diagram 100 includes, in 102, providing a substrate 200 on a substrate holder in a plasma processing chamber. According to some embodiments, a first etch stop film 202 (e.g., S1O2, SiN, or SiON) may be present on the substrate 200. According to other embodiments, the first etch stop film 202 may be omitted. The plasma processing chamber may contain a microwave antenna, a microwave power source for powering the microwave antenna, a radio frequency (RF) power source for RF biasing the substrate holder, and a direct current (DC) voltage source for DC biasing the substrate holder. The microwave antenna can include a radial line slot antenna (RLSA) as schematically shown in FIGs. 3-5. The substrate 200 can, for example, be a semiconductor substrate, such as a silicon substrate, a silicon germanium substrate, a germanium substrate, a glass substrate, a LCD substrate, or a compound semiconductor substrate such as for example GaAs. The substrate can be of any size, for example, a 200 mm wafer, a 300 mm wafer, a 450 mm wafer, or an even larger wafer or substrate.

[0020] In 104, a first process gas containing a C_aF_b gas is introduced in the plasma processing chamber, wherein a and b are positive integers. According to some embodiments, the C_aF_b gas may be selected from C4F4, C₄F₆, C₆F₆, C5F₈, and other C_aF_b gases. Gas flow rates of the C_aF_b gas can be less than 500sccm, less than 200sccm, or less than lOOsccm, for example. In some examples, the first process gas can further contain argon (Ar), nitrogen (N₂), or both Ar and N₂. Gas flow rates of the Ar and 2 gas can be less than 500sccm, less than 200sccm, or less than lOOsccm. The gas pressure in the plasma processing chamber can be less than lOOmTorr, less than 50mTorr, less than 30mTorr, or less than 20mTorr, for example.

[0021] In 106, a first plasma is formed from the first process gas by applying a first RF bias and a first positive DC bias to the substrate holder. The first RF bias can be less than 100W, less than 50W, or less than 25 W, for example. According to one embodiment, the first plasma may be formed without applying microwave power to the microwave antenna. The first positive DC bias can be greater than 1.5kV, for example 3kV, 3.5kV, or greater. In some examples, the first positive DC bias can be between 2kV and 5kV, between 2kV and 3kV, between 3kV and 4kV, or between 4kV and 5kV.

[0022] In 108, a first fluorocarbon film 204 is deposited on the first etch stop film by the first plasma (FIG. 2B). According to some embodiments, deposition of the first fluorocarbon film 204 may include maintaining the substrate holder at a temperature greater than 330°C, greater than 340°C, greater than 350°C, or greater than 360°C, for example. In some examples, the substrate temperature can be between than 350°C and 380°C, or between than 380°C and 400°C. In one example, the substrate holder can be maintained at temperature of approximately 360°C.

[0023] In 1 10, a second process gas containing a C_aF_b gas is introduced in the plasma processing chamber, where a and b are integers. According to some embodiments, the C_aF_b gas may be selected from C₄F₄, C₄F₆, C₆F₆, C5F₈, and other C_aFb gases. Gas flow rates of the C_aFb gas can be less than 500sccm, less than 200sccm, or less than lOOsccm, for example. In some examples, the second process gas can further contain argon (Ar), nitrogen (N₂), or both Ar and N₂. Gas flow rates of the Ar and 2 gas can be less than 500sccm, less than 200sccm, or less than lOOsccm. The gas pressure in the plasma process chamber can be less than lOOmTorr, less than 50mTorr, less than 30mTorr, or less than 20mTorr, for example.

[0024] In 1 12, a second plasma is formed from the second process gas by applying plasma forming microwave power to the microwave antenna, and applying a second RF bias and a second positive DC bias to the substrate holder. The second RF bias can be the same or different than the first second RF bias, for example less than 100W, less than 50W, or less than 25W. The second positive DC bias can be lower than the first positive DC bias, for example less than 3kV, less than 2.5kV, less than 2kV, or less than 1.5kV. In some examples, the second positive DC bias can be between lkV and 2kV, or between 2kV and less than 3kV. In one example, the first positive DC bias may be about 3kV and the second positive DC bias may be about 1.5kV.

[0025] In 1 14, a second fluorocarbon film 206 is deposited on the first fluorocarbon film by the second plasma (FIG. 2C). According to some embodiments, deposition of the second fluorocarbon film 206 may include maintaining the substrate holder at a temperature greater than 300°C, greater than 310°C, greater than 320°C, or greater than 330°C, for example. In some examples, the substrate temperature can be between than 300°C and 320°C, or between than 320°C and 350°C. In one example, the substrate holder can be maintained at temperature of approximately 330°C.

According to one embodiment, a deposition rate of the first fluorocarbon film 204 may be lower than a deposition rate of the second fluorocarbon film 206.

[0026] Referring to FIG. 2D, a second etch stop film 208 (e.g., Si0₂, SiN, or SiON) may be deposited on the second fluorocarbon film 206. According other embodiments, the second etch stop film 208 may be omitted.

[0027] According to some embodiments, the first positive DC bias may be greater than the second positive DC bias. In some examples the first positive DC bias can be equal to or greater than 3kV. In one example the second positive DC bias can be approximately 1.5kV.

[0028] According to some embodiments, the first fluorocarbon film 204 may be deposited at a first substrate holder temperature and the second fluorocarbon film 206 may be deposited at a second substrate holder temperature that is lower than the first substrate holder temperature. [0029] According to some embodiments, a thickness of the first fluorocarbon film 204 may be less than a thickness of the second fluorocarbon film 206. In one example, a thickness of the first fluorocarbon film may be 20nm or less, for example between 5nm and lOnm, or between lOnm and 20nm. In one example, a thickness of the second fluorocarbon film is 30nm or greater, for example between 30nm and 200nm, between 30nm and lOOnm, or between lOOnm and 200nm.

[0030] FIG. 3 is a schematic diagram of a plasma processing system containing a RLSA plasma source for depositing a fluorocarbon film on a substrate according to one embodiment of the invention. The plasma produced in the plasma processing system 500 is characterized by low electron temperature and high plasma density. The plasma processing system 500 can, for example, be a TRIAS™ SPA processing system from Tokyo Electron Limited, Akasaka, Japan. The plasma processing system 500 contains a plasma processing chamber 550 having an opening portion 551 in the upper portion of the plasma processing chamber 550 that is larger than a substrate 558. A cylindrical dielectric top plate 554 made of quartz, aluminum nitride, or aluminum oxide is provided to cover the opening portion 551.

[0031] Gas lines 572 are located in the side wall of the upper portion of plasma processing chamber 550 below the top plate 554. In one example, the number of gas lines 572 can be 16 (only two of which are shown in FIG. 3). Alternatively, a different number of gas lines 572 can be used. The gas lines 572 can be

circumferentially arranged in the plasma processing chamber 550, but this is not required for the invention. A process gas can be evenly and uniformly supplied into the plasma region 559 in plasma processing chamber 550 from the gas lines 572. The process gas can contain a C_aF_b gas that may be selected from C4F4, C₄F₆, C₆F₆, and C5F₈, and other C_aF_b gases. Gas flow rates of the C_aF_b gas can be less than 500sccm, less than 200sccm, or less than lOOsccm. The process gas may further contain argon (Ar), nitrogen (N₂), or both Ar and N₂. Gas flow rates of the Ar and 2 gas can be less than 500sccm, less than 200sccm, or less than lOOsccm. The gas pressure in the plasma process chamber can be less than lOOmTorr, less than 50mTorr, less than 30mTorr, or less than 20mTorr, for example.

[0032] In the plasma processing system 500, microwave power is provided to the plasma processing chamber 550 through the top plate 554 via a slot antenna 560 having a plurality of slots 560A. The slot antenna 560 faces the substrate 558 to be processed and the slot antenna 560 can be made from a metal plate, for example copper. In order to supply the microwave power to the slot antenna 560, a waveguide 563 is disposed on the top plate 554, where the waveguide 563 is connected to a microwave power supply 561 for generating microwaves with a frequency of about 2.45GHz, for example. The waveguide 563 contains a flat circular waveguide 563A with a lower end connected to the slot antenna 560, a circular waveguide 563B connected to the upper surface side of the circular waveguide 563 A, and a coaxial waveguide converter 563C connected to the upper surface side of the circular waveguide 563B. Furthermore, a rectangular waveguide 563D is connected to the side surface of the coaxial waveguide converter 563C and the microwave power supply 561.

[0033] Inside the circular waveguide 563B, an axial portion 562 of an

electroconductive material is coaxially provided, so that one end of the axial portion 562 is connected to the central (or nearly central) portion of the upper surface of slot antenna 560, and the other end of the axial portion 562 is connected to the upper surface of the circular waveguide 563B, thereby forming a coaxial structure. As a result, the circular waveguide 563 B is constituted so as to function as a coaxial waveguide. The microwave power can, for example, be between about 0.5 W/cm² and about 4 W/cm². Alternatively, the microwave power can be between about 0.5 W/cm² and about 3 W/cm². The microwave irradiation may contain a microwave frequency of about 300 MHz to about 10 GHz, for example about 2.45 GHz, and the plasma may contain an electron temperature of less than or equal to 5 eV, including 1 , 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5 eV, or any combination thereof. In other examples, the electron temperature can be below 5eV, below 4.5eV, below 4eV, or even below 3.5eV. In some examples, the electron temperature can be between 3.0 and 3.5 eV, between 3.5eV and 4.0eV, or between 4.0 and 4.5 eV. The plasma may have a density of about 1 x 10^u/cm³ to about 1 x 10¹³/cm³, or higher.

[0034] In addition, in the plasma processing chamber 550, a substrate holder 552 is provided opposite the top plate 554 for supporting and heating a substrate 558 (e.g., a wafer). The substrate holder 552 contains a heater 557 to heat the substrate 525, where the heater 557 can be a resistive heater. Alternatively, the heater 557 may be a lamp heater or any other type of heater. Furthermore the plasma processing chamber 550 contains an exhaust line 553 connected to the bottom portion of the plasma processing chamber 550 and to a vacuum pump 555.

[0035] The plasma processing system 500 further contains a substrate bias system 556 configured to bias the substrate holder 552 and the substrate 558 for generating a plasma and/or controlling energy of ions that are drawn to a substrate 558. The substrate bias system 556 includes a substrate power source configured couple power to the substrate holder 552. The substrate power source contains a RF generator and an impedance match network. The substrate power source is configured to couple power to the substrate holder 552 by energizing an electrode in the substrate holder 552. A typical frequency for the RF bias can range from about 0.1 MHz to about 100 MHz, and can be 13.56 MHz. In some examples, the RF bias can be less than 1 MHz, for example less than 0.8 MHz, less than 0.6 MHz, less than 0.4 MHz, or even less than 0.2MHz. In one example, the RF bias can be about 0.4 MHz. Alternatively, RF power is applied to the electrode at multiple frequencies. The substrate bias system 556 is configured for supplying RF bias power can be between 0W and 100W, between 100W and 200W, between 200W and 300W, between 300W and 400W, or between 400W and 500W. In some examples, the RF bias power can be less than 100W, less than 50W, or less than 25W, for example. RF bias systems for plasma processing are well known to those skilled in the art. Further, the substrate bias system 556 includes a DC voltage generator capable of supplying DC bias between - 5kV and +5kV to the substrate holder 552.

[0036] The substrate bias system 556 is further configured to optionally provide pulsing of the RF bias power. The pulsing frequency can be greater than lHz, for example 2Hz, 4Hz, 6Hz, 8Hz, 10Hz, 20Hz, 30Hz, 50Hz, or greater. It is noted that one skilled in the art will appreciate that the power levels of the substrate bias system 556 are related to the size of the substrate being processed. For example, a 300 mm Si wafer requires greater power consumption than a 200 mm wafer during processing.

[0037] Still referring to FIG. 3, a controller 599 is configured for controlling the plasma processing system 500. The controller 599 can include a microprocessor, a memory, and a digital I/O port capable of generating control voltages sufficient to communicate and activate inputs of the plasma processing system 500 as well as monitor outputs from the plasma processing system 500. Moreover, the controller 599 is coupled to and exchanges information with plasma processing chamber 550, the vacuum pump 555, the heater 557, the substrate bias system 556, and the microwave power supply 561. A program stored in the memory is utilized to control the aforementioned components of plasma processing system 500 according to a stored process recipe. One example of controller 599 is a UNIX-based workstation. Alternatively, the controller 599 can be implemented as a general-purpose computer, digital signal processing system, etc.

[0038] Processing conditions for depositing fluorocarbon films in the plasma processing system 500 can include a substrate temperature between about 300°C and about 500°C, for example between about 300° C and about 400° C. The pressure in the plasma processing chamber 550 can, for example, be maintained at less than lOOmTorr, less than 50mTorr, less than 30mTorr, or less than 20mTorr, for example.

[0039] FIG. 4 is a schematic diagram of a plasma processing system containing a radial line slot antenna (RLSA) plasma source for depositing a fluorocarbon film on a substrate according to another embodiment of the invention. As shown in FIG. 4, the plasma processing system 10 includes a plasma processing chamber 20 (vacuum chamber), an antenna unit 50, and a substrate holder 21. Inside of the plasma processing chamber 20 is roughly sectionalized into a plasma generation region Rl, located below a plasma gas supply unit 30, and a plasma diffusion region R2 above the substrate holder 21. A plasma generated in the plasma generation region Rl can have an electron temperature of several electron volts (eV). When the plasma is diffused into the plasma diffusion region R2, where the film formation process is performed, the electron temperature of the plasma near the substrate holder 21 may drop to a value of lower than about 2eV. The substrate holder 21 is located centrally on a bottom portion of the plasma processing chamber 20 and serves as a substrate holder for supporting a substrate W. Inside the substrate holder 21, there is provided an insulating member 21a, a cooling jacket 21b, and a temperature control unit (not shown) for controlling the substrate temperature.

[0040] A top portion of the plasma processing chamber 20 is open-ended. The plasma gas supply unit 30 is placed opposite to the substrate holder 21 and is attached to the top portion of the plasma processing chamber 20 via sealing members such as O rings (not shown). The plasma gas supply unit 30, which may also function as a dielectric window, can be made of materials such as aluminum oxide or quartz and has a planar surface. A plurality of gas supply holes 31 are provided opposite the substrate holder 21 on a planar surface of the plasma gas supply unit 30. The plurality of gas supply holes 31 communicate with a plasma gas supply port 33 via a gas flow channel 32. A plasma gas supply source 34 provides a plasma gas, for example argon (Ar) gas, or other inert gases, into the plasma gas supply port 33. The plasma gas is then uniformly supplied into the plasma generation region Rl via the plurality of gas supply holes 31.

[0041] The plasma processing system 10 further includes a process gas supply unit 40, which is centered in the plasma processing chamber 20 between the plasma generation region Rl and the plasma diffusion region R2. The process gas supply unit 40 may be made of a conducting material, for example an aluminum alloy that includes magnesium (Mg), or stainless steel. Similar to the plasma gas supply unit 30, a plurality of gas supply holes 41 are provided on a planar surface of the process gas supply unit 40. The planar surface of the process gas supply unit 40 is positioned opposite to the substrate holder 21.

[0042] The plasma processing chamber 20 further includes exhaust lines 26 connected to the bottom portion of the plasma processing chamber 20, a vacuum line 27 connecting the exhaust lines 26 to a pressure controller valve 28 and to a vacuum pump 29. The pressure controller valve 28 may be used to achieve a desired gas pressure in the plasma processing chamber 20.

[0043] A plan view of the process gas supply unit 40 is shown in FIG. 5. As shown in this figure, grid-like gas flow channels 42 are formed within the process gas supply unit 40. The grid-like gas flow channels 42 communicate with an upper-end of the plurality of gas supply holes 41, which are formed in the vertical direction. The lower portion of the plurality of gas supply holes 41 are openings facing the substrate holder 21. The plurality of gas supply holes 41 communicate with a process gas supply port 43 via the grid-patterned gas flow channels 42.

[0044] Further, a plurality of openings 44 are formed in the process gas supply unit 40 such that the plurality of openings 44 pass through the process gas supply unit 40 in the vertical direction. The plurality of openings 44 introduce the plasma gas, e.g., argon (Ar) gas, helium (He) gas, or other inert gases, into the plasma diffusion region R2 above the substrate holder 21. As shown in FIG. 5, the plurality of openings 44 are formed between adjacent gas flow channels 42. The process gas may be supplied from three separate process gas supply sources 45-47 to the process gas supply port 43. The process gas supply sources 45-47 may supply a CsFs gas (or in general a C_aF_b gas), Ar, and N₂.

[0045] The process gas flows through the grid-like gas flow channels 42 and is uniformly supplied into the plasma diffusion region R2 via the plurality of gas supply holes 41. The plasma processing system 10 further includes four valves (V1-V4) and four mass flow rate controller (MFC1-MFC4) for controlling a supply of the process gas.

[0046] An external microwave generator 55 provides a microwave of a predetermined frequency, e.g., 2.45 GHz, to the antenna unit 50 via a coaxial waveguide 54. The coaxial waveguide 54 may include an inner conductor 54B and an outer conductor 54A. The microwave from the microwave generator 55 generates an electric field just below the plasma gas supply unit 30 in the plasma generation region Rl, which in turn causes excitation of the process gas within the plasma processing chamber 20.

[0047] FIG. 6 illustrates a partial cross-sectional view of the antenna unit 50. As shown in this figure, the antenna unit 50 may include a flat antenna main body 51, a radial line slot plate 52, and a dielectric plate 53 to shorten the wavelength of the microwave. The flat antenna main body 51 can have a circular shape with an open- ended bottom surface. The flat antenna main body 51 and the radial line slot plate 52 can be made of a conductive material.

[0048] A plurality of slots 56 are provided on the radial line slot plate 52 to generate a circularly polarized wave. The plurality of slots 56 are arranged in a substantially T-shaped form with a small gap between each slot. The plurality of slots 56 are arranged in a concentric circle pattern or a spiral pattern along a

circumferential direction. Since the slots 56a and 56b are perpendicular to each other, a circularly polarized wave containing two orthogonal polarized components is radiated, as a plane wave, from the radial line slot plate 52.

[0049] The dielectric plate 53 can be made of a low loss dielectric material, e.g., aluminum oxide (AI₂O₃) or silicon nitride (S1₃N₄), that is located between the radial line slot plate 52 and the flat antenna main body 51. The radial line slot plate 52 may be mounted on the plasma processing chamber 20 using sealing members (not shown), such that the radial line slot plate 52 is in close contact with a cover plate 23. The cover plate 23 is located on the upper surface of plasma gas supply unit 30 and is formed from a microwave transmissive dielectric material such as aluminum oxide (A1₂0₃).

[0050] An external high-frequency power supply source 22 is electrically connected to the substrate holder 21 via a matching network 25. The external high- frequency power supply source 22 generates an RF bias power of a predetermined frequency, e.g. 13.56 MHz, for controlling the energy of ions in the plasma that are drawn to the substrate W. The power supply source 22 is further configured to optionally provide pulsing of the RF bias power. The pulsing frequency can be greater than lHz, for example 2Hz, 4Hz, 6Hz, 8Hz, 10Hz, 20Hz, 30Hz, 50Hz, or greater. The power supply source 22 is configured for supplying RF bias power between 0W and 100W, between 100W and 200 W, between 200 W and 300W, between 300W and 400 W, or between 400W and 500 W. One skilled in the art will appreciate that the power levels of the power supply source 22 are related to the size of the substrate being processed. For example, a 300 mm Si wafer requires greater power consumption than a 200 mm wafer during processing. The plasma processing system 10 further includes DC voltage generator 35 capable of supplying DC voltage bias between -5kV and +5kV to the substrate holder 21.

[0051] During deposition of a CF film, the plasma gas, e.g., argon (Ar) gas, may be introduced into the plasma processing chamber 20 using the plasma gas supply unit 30. On the other hand, the process gas may be introduced into the plasma processing chamber 20 using the process gas supply unit 40. Although not shown in FIG. 4, one or more of C₅F₈ (or in general C_aF_b,), Ar, and 2 may also be introduced into the plasma processing chamber 20 using the plasma gas supply unit 30.

[0052] According to some embodiments, a CF film may be deposited in a continuous process where one or more of the microwave power level, substrate holder temperature, and positive DC bias is changed during the film deposition. This is schematically shown in FIGs. 7-9.

[0053] FIGS. 7A-7C schematically show changes in microwave power level during fluorocarbon film deposition. The film deposition starts at tO. FIG. 7A shows a microwave power level curve 700 where a first microwave power level PI is applied between times tO and t. At time t, the microwave power level is increased from P 1 to a second microwave power level P2, and the film deposition is continued at the second microwave power level P2. FIG. 7B shows in trace 710, monotonically increasing the microwave power level from a first microwave power level PI to a second microwave power level P2 during the film deposition. FIG. 7C shows in trace 720, monotonically increasing the microwave power level at time t from a first microwave power level P I to a second microwave power level P2. In some examples, PI can be zero and thus no microwave power applied during deposition of a first fluorocarbon film between times tO and t. In some examples, the power level P2 can be greater that lkW, for example about 1.35kW.

[0054] FIGS. 8A-8C schematically show changes in substrate holder temperature during fluorocarbon film deposition. The film deposition starts at tO. FIG. 8A shows a substrate holder temperature curve 800 where a first substrate holder temperature T 1 is used between times tO and t. At time t, the substrate holder temperature is lowered from Tl to a second substrate holder temperature T2 and the film deposition is continued at the second substrate holder temperature T2. FIG. 8B shows in trace 810, monotonically decreasing the substrate holder temperature from a first substrate holder temperature Tl at tO to a second substrate holder temperature T2 during the film deposition. FIG. 8C shows in trace 820, monotonically decreasing the substrate holder temperature at time t from first substrate holder temperature Tl to a second substrate holder temperature T2. In some examples, Tl can be approximately 360°C and T2 can be approximately 330°C. According to some embodiments, a first fluorocarbon film may be deposited between times tO and t, and a second

fluorocarbon film deposited on the first fluorocarbon film at a time greater than t.

[0055] FIGS. 9A-9C schematically show changes in positive DC bias applied to a substrate holder during fluorocarbon film deposition. The film deposition starts at tO. FIG. 9A a DC bias curve 900 where a first positive DC bias DC1 is used between times tO and t. At time t, the DC bias is lowered from DC1 to a second positive DC bias DC2 and the film deposition is continued at the second DC bias DC2. FIG. 9B shows in trace 910, monotonically decreasing the DC bias from a first positive DC bias DC 1 at tO to a second positive DC bias DC 2 during the film deposition. FIG. 9C shows in trace 920, monotonically decreasing the DC bias at time t from first positive DC bias DC 1 to a second positive DC bias DC 2. In one example, DC 1 can be approximately 3kV and DC 2 can be approximately 1.5kV. According to some embodiments, a first fluorocarbon film may be deposited between times tO and t, and a second fluorocarbon film deposited on the first fluorocarbon film at a time greater than t.

[0056] According to embodiments of the invention, any permutations of the different microwave power levels, substrate holder temperatures, and DC bias schematically shown in FIGs. 7-9 may be used during CF film deposition.

[0057] According to embodiments of the invention, a method is provided for forming a semiconductor device. The method includes providing a substrate on a substrate holder in a plasma processing chamber, the plasma processing chamber containing a microwave antenna, a microwave power source for powering the microwave antenna, a radio frequency (RF) bias source for RF biasing the substrate holder, and a direct current (DC) voltage source for DC biasing the substrate holder. The method further includes introducing in the plasma processing chamber a first process gas containing a C_aF_b gas. In one example, the first process gas may include CsFs, Ar, and N₂. Thereafter, a first plasma is formed from the first process gas in the plasma processing system by applying a first RF bias and a first positive DC bias to the substrate holder, and the exposure to the first plasma deposits a first fluorocarbon film on the substrate at a first substrate holder temperature. In one example, the first substrate holder temperature can be about 360°C, the first RF bias can be about 25W, and the first positive DC bias can be about 3kV. In one example, the first plasma may be formed without applying microwave power to the microwave antenna.

[0058] Thereafter, the method further includes introducing in the plasma processing chamber a second process gas containing a C_aF_b gas. In one example, the second process gas may include C5F₈, Ar, and N₂. A second plasma is formed from the second process gas by applying microwave power to the microwave antenna, and applying second RF bias and a second positive DC bias to the substrate holder, where the exposure to the second plasma deposits a second fluorocarbon film on the first fluorocarbon film at a second substrate holder temperature. In one example, the second substrate holder temperature can be about 330°C, the microwave power can be about 1.35 kW, the second RF bias can be about 25 W, and the second positive DC bias can be about 1.5kV. Further processing conditions can include a gas pressure of about 23mTorr, Ar gas flow of about lOOsccm, and ₂ gas flow of about 20sccm. [0059] CF films deposited under different processing conditions were evaluated by performing a post-deposition anneal and monitoring any blistering or peeling of the films. The test structures contained CF deposited under different processing conditions. The test structures included (in order of deposition on a Si wafer): a first SiN etch stop film/a first CF film/a second CF film/a second SiN etch stop film/a SiC capping layer. A test structure containing a first CF film deposited using a first substrate holder temperature of 360°C and a first positive DC bias of 3kV, and a second CF film formed directly on the first CF film using a using a second substrate holder temperature of 330°C, a second positive DC bias of 1.5kV, and a microwave power of 1.35kW showed no signs of blistering or pealing. This demonstrates that this test structure had a low concentration of dangling bonds in the first and second CF film and hence good thermal stability.

[0060] For comparison, test structures containing a first CF film deposited at substrate holder temperatures of 300°C or 330°C and first bias power of 1.5kV or negative 3kV did not pass the annealing test. Further, test structures containing a first CF film deposited at substrate holder temperatures of 300°C or 330°C and a first bias power of 3kV did not pass the annealing test. The second CF films were deposited using a second substrate holder temperature of 330°C and a second bias power of 3kV. Further analysis of the test structures using Electron Energy Loss Spectroscopy (EELS) showed improved C-C bonding and increased C-F bonding in the test structure that passed the annealing test. The EELS analysis also showed an improved interface between the first SiN etch stop film and the first CF film in the test structure that passed the annealing test.

[0061] A plurality of embodiments for forming fluorocarbon films for semiconductor devices using a microwave plasma source have been described. The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. This description and the claims following include terms that are used for descriptive purposes only and are not to be construed as limiting. For example, the term "on" as used herein (including in the claims) does not require that a film "on" a substrate is directly on and in immediate contact with the substrate; there may be a second film or other structure between the film and the substrate. [0062] Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above teaching. Persons skilled in the art will recognize various equivalent combinations and substitutions for various components shown in the Figures. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.

Claims

What is claimed is:

1. A method of forming a semiconductor device, comprising:

providing a substrate on a substrate holder in a plasma processing chamber, the plasma processing chamber containing a microwave antenna, a microwave power source for powering the microwave antenna, a radio frequency (RF) bias source for RF biasing the substrate holder, and a direct current (DC) voltage source for DC biasing the substrate holder;

introducing in the plasma processing chamber a first process gas containing a C_aFb gas, where a and b are positive integers;

forming a first plasma from the first process gas by applying a first RF bias and a first positive DC bias to the substrate holder;

depositing a first fluorocarbon film on the substrate by the first plasma;

introducing in the plasma processing chamber a second process gas containing a C_aF_b gas, where a and b are positive integers;

forming a second plasma from the second process gas by applying microwave power to the microwave antenna, and applying second RF bias and a second positive DC bias to the substrate holder; and

depositing a second fluorocarbon film on the first fluorocarbon film by the second plasma.

2. The method of claim 1, wherein the first plasma is formed without applying microwave power to the microwave antenna.

3. The method of claim 1, wherein the first positive DC bias is greater than the second positive DC bias.

4. The method of claim 3, wherein the first positive DC bias is equal to or greater than 3kV.

5. The method of claim 1, wherein the first fluorocarbon film is deposited at a first substrate holder temperature and the second fluorocarbon film is deposited at a second substrate holder that is lower than the first substrate holder temperature.

6. The method of claim 1 , wherein the microwave antenna includes a radial line slot antenna (RLSA).

7. The method of claim 1, wherein the C_aF_b gas is selected from C4F4, C4F₆, C₆F₆,

8. The method of claim 1, wherein the first and second process gases contain the same C_aF_b gas.

9. The method of claim 1, wherein the first and second process gases further contains argon (Ar), nitrogen (N₂), or both Ar and N₂.

10. The method of claim 1, wherein a thickness of the first fluorocarbon film is less than a thickness of the second fluorocarbon film.

11. The method of claim 1, wherein a thickness of the first fluorocarbon film is 20nm or less, and wherein a thickness of the second fluorocarbon film is 30nm or greater.

12. The method of claim 1, wherein the deposition rate of the first fluorocarbon film is lower than the deposition rate of the second fluorocarbon film.

13. A method of forming a semiconductor device, comprising:

introducing in the plasma processing chamber a process gas containing a C_aF_b gas, where a and b are positive integers;

forming a plasma from the process gas by applying a RF bias and a positive DC bias to the substrate holder; applying microwave power to the microwave antenna; and depositing a fluorocarbon film on the substrate by the plasma, wherein the applied microwave power is increased from a first microwave power level to a second microwave power level during the depositing.

14. The method of claim 13, wherein the plasma is formed without applying microwave power to the microwave antenna.

15. The method of claim 13, further comprising decreasing the positive DC bias from a first positive DC bias to a second positive DC bias during the depositing.

16. The method of claim 13, further comprising decreasing the substrate holder temperature from a first substrate holder temperature to a second substrate holder temperature during the depositing.

17. The method of claim 13, wherein the microwave antenna includes a radial line slot antenna (RLSA).

18. The method of claim 13, wherein the C_aF_b gas is selected from C₄F₄, C₄F₆, C₆F₆,

19. The method of claim 13, wherein the process gas further contains argon (Ar), nitrogen (N₂), or both Ar and N₂.

20. The method of claim 13, wherein the deposition rate of the fluorocarbon film increases during the depositing.