Modulated/composited CVD low-k films with improved mechanical and electrical properties for nanoelectronic devices

[0001] 1. Field of the Invention

[0002] Embodiments of the present invention relate to the fabrication of integrated circuits. More particularly, embodiments of the present invention relate to a process for depositing a dielectric film on a substrate.

[0003] 2. Description of the Related Art

[0004] Integrated circuit geometries have dramatically decreased in size since such devices were first introduced several decades ago. Since then, integrated circuits have generally followed the two year/half-size rule (often called Moore's Law), which means that the number of devices on a chip doubles every two years. Today's fabrication facilities are routinely producing devices having 0.13 m and even 0.1 m feature sizes, and tomorrow's facilities soon will be producing devices having even smaller feature sizes.

[0005] The continued reduction in device geometries has generated a demand for films having lower k values because the capacitive coupling between adjacent metal lines must be reduced to further reduce the size of devices on integrated circuits. In particular, insulators having low dielectric constants (k), less than about 4.0, are desirable. Examples of insulators having low dielectric constants include spin-on glass, such as un-doped silicon glass (USG) or fluorine-doped silicon glass (FSG), silicon dioxide, and polytetrafluoroethylene (PTFE), which are all commercially available.

[0006] Increasing the porosity of dielectric films is one approach that is being pursued to develop dielectric films having lower k values. However, it can be difficult to deposit a low k dielectric film that has both enough pores to reduce the k to a desired level and the mechanical strength to withstand further integrated circuit fabrication processing steps.

[0007] There is a need, therefore, for a method of depositing a low k dielectric film with good mechanical properties.

[0008] Embodiments of the present invention generally provide a method of depositing a low k dielectric film on a substrate that includes exposing two or more compounds, including at least one organosilicon compound, to pulsed RF power to deposit alternating low k dielectric sublayers on the substrate. The method provides a low k dielectric film comprising at least a carbon-doped silicon oxide sublayer that is about 1 nanometer to about 100 nanometers thick. Various low k dielectric sublayers are deposited under conditions such that each sublayer retains some of the chemical and/or mechanical properties of a compound from which it was deposited. The low k dielectric sublayers are deposited such that adjacent sublayers have different chemical and/or mechanical properties. Thus, a mechanical weakness in one sublayer may be compensated for by the different mechanical properties of the adjacent sublayers.

[0009] In one embodiment, a method of depositing a low k dielectric film on a substrate includes simultaneously exposing two or more compounds, including at least one organosilicon compound, to pulsed RF power to deposit alternating low k dielectric sublayers on the substrate. The pulsed RF power includes pulses delivered for a first period of time at a first frequency to deposit a sublayer primarily from one of the compounds and pulses delivered for a second period of time at a second frequency to deposit a sublayer primarily from another one of the compounds.

[0010] In another embodiment, computer storage media containing software that causes a computer to direct the low k dielectric film deposition methods described herein are provided.

[0011] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0012] FIG. 1 is a cross sectional view of one embodiment of a deposition chamber.

[0013] FIG. 2 is an illustrative flow chart of processes performed by a computer system in an embodiment.

[0014] FIG. 3 is a computer system according to an embodiment.

[0015] Embodiments of the present invention generally provide a low k dielectric film and a method of depositing a low k dielectric film. Generally, two or more compounds are introduced into a processing chamber and exposed to pulsed RF power to form alternating low k dielectric sublayers on a substrate in the processing chamber. The two or more low k dielectric sublayers form a multilayer low k dielectric film. Preferably, the sublayers are about 1 nanometer to about 100 nanometers thick. Most preferably, two alternating sublayers that are each about 10 nanometers thick are deposited.

[0016] The low k dielectric film may be deposited in any processing chamber in which pulsed RF power can be applied. For sublayers close to 1 nanometer in thickness, the low k dielectric film can be deposited in an atomic layer deposition chamber. An example of an atomic layer deposition chamber that may be used is described in commonly assigned U.S. patent application Ser. No. 09/776,329, entitled Formation of a Tantalum-Nitride Layer, filed on Feb. 2, 2001, which is incorporated herein by reference. Preferably, the low k dielectric film is deposited in a chemical vapor deposition chamber, such as a Producer or Producer SE chemical vapor deposition (CVD) chamber, available from Applied Materials, Inc., Santa Clara, Calif., using plasma enhanced chemical vapor deposition.

[0017] The Producer CVD chamber (200 mm or 300 mm) has two isolated processing regions that may be used to deposit carbon-doped silicon oxides and other materials. A chamber having two isolated processing regions is described in U.S. Pat. No. 5,855,681, which is incorporated by reference herein. FIG. 1 shows a cross sectional view of a Producer CVD chamber 100. The chamber 100 has processing regions 618 and 620. A heater pedestal 628 is movably disposed in each processing region 618, 620 by a stem 626 which extends through the bottom of the chamber body 612 where it is connected to a drive system 603. Each of the processing regions 618, 620 also preferably include a gas distribution assembly 608 disposed through the chamber lid 604 to deliver gases into the processing regions 618, 620. The gas distribution assembly 608 of each processing region also includes a gas inlet passage 640 which delivers gas into a shower head assembly 642. The showerhead assembly 642 is comprised of an annular base plate 648 having a blocker plate 644 disposed intermediate a face plate 646. An RF (radio frequency) feedthrough provides a bias potential to the showerhead assembly to facilitate generation of a plasma between the face plate 646 of the showerhead assembly and the heater pedestal 628.

[0018] The two or more compounds that are exposed to pulsed RF power include at least one organosilicon compound. The organosilicon compound may have a ring structure, linear structure, or fullerene structure. Examples of organosilicon compounds that may be used that have ring structures include octamethylcyclotetrasiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, 1,2,3,4-tetramethylcyclotetrasilane, hexaethylcyclotrisiloxane, hexamethylcyclotrisiloxane, hexaphenylcyclotrisiloxane, 1,3,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane, 1,3,5,7,9-pentamethylcyclopentasiloxane, 1,3,5,7,9-pentavinyl,-1,3,5,7,9-pentamethylcyclopentasilaxane, and octomethylscyclo-tetrasilazane. Examples of organosilicon compounds that may be used that have linear structures include trimethylsilane, tetramethylsilane, 1,1,3,3-tetramethyidisiloxane, tetravinylsilane, diphenylmethylsilane, tetraphenylsilane, tetra-n-propoxysilane, diethoxymethylsilane, 1,1,3,3,-tetramethyl-1,3-diethoxydisiloxane, and 1,1,3,3-tetramethyldisilazane. Examples of organosilicon compounds that may be used that have fullerene structures, e.g., spherical or cuboidal structures, include silsequioxane structures, such as hydro-T8-silsesquioxane, octamethyl-T8-silsequioxane, octavinyl-T8-silsesquioxane, and octakis(dimethylsiloxy)-T8-silsesquioxane. If an organosilicon compound having a ring structure or fullerene structure is used, the organosilicon compound can be dissolved in a solvent such as hexane before introducing the compound into the CVD chamber.

[0019] The two or more compounds may also include a hydrocarbon. The hydrocarbon may have a ring structure, linear structure, or fullerene structure. Examples of types of hydrocarbons that may be used that have ring structures include cyclic terpenes, cyclopentenes, cyclohexenes, cyclohexanes, cyclohexadienes, cycloheptadienes, and phenyl-containing compounds. For example, alpha terpinene (C₁₀H₁₆) (ATP), 1-methyl-4-(1-methylethenyl)-cyclohexene, 1 -methyl-4-isopropylcyclohexane, p-isopropyltoluene, vinylcyclohexane, norbornadiene, phenyl acetate, cyclopentene oxide, and combinations thereof may be used. Examples of hydrocarbons that may be used that have linear structures include ethylene, hexane, propylene, and 1,3-butadiene. Examples of hydrocarbons that may be used that have fullerene structures include C60, C70, C76, and C78. If a hydrocarbon having a ring structure or a fullerene structure is used, the hydrocarbon can be dissolved in a solvent such as hexane and tetrahydrofuran before introducing the compound into the CVD chamber.

[0020] Preferably, oxygen is present in at least one of the low k dielectric sublayers, which is a carbon-doped silicon oxide sublayer. One or more of the two or more compounds exposed to RF power may include oxygen to provide a source of oxygen for one or more of the sublayers. Alternatively or additionally, oxygen and/or an oxidizing gas, such as carbon dioxide, may also be exposed to the RF power.

[0021] Preferably, the low k dielectric film is a carbon-doped silicon oxide film that includes about 10% to about 60% silicon, about 20% to about 30% oxygen, and about 10% to about 60% carbon. Preferably, the low k dielectric film is a porous carbon-doped silicon oxide film that has a k<3.0. However, it is recognized that other types of low k dielectric films can be deposited using the methods described herein.

[0022] In a preferred embodiment, the two or more compounds, such as two or more organosilicon compounds, are simultaneously exposed to pulsed RF power in a deposition chamber. The pulsed RF power is delivered at different frequencies. For example, the RF power is delivered at a first frequency, such as about 350 kHz to about 100 MHz, for a first period of time, such as about 1 second to about 30 seconds and then delivered at a second frequency (different than the first frequency), such as about 350 kHz to about 100 MHz, for a second period of time, such as about 1 second to about 30 seconds. The RF power level may be about 50 watts to about 3000 watts. The duty cycle may be about 5% to about 60%. The organosilicon flow rates may be about 50 sccm to about 5000 sccm. Oxidizing gas flow rates may be from 0 sccm to about 3000 sccm, and hydrocarbon flow rates may from 0 sccm to about 5000 sccm. Preferably, the first and second frequencies are chosen such that a first sublayer is deposited on a substrate in the chamber primarily from one of the two or more compounds, e.g., compound A, and the second sublayer is deposited on the first sublayer primarily from another one of the two or more compounds, e.g., compound B. Typically, compounds A and B have sufficiently different chemical or physical properties such that A primarily contributes to the deposition of one sublayer during pulses at a first frequency, while B primarily contributes to the deposition of an adjacent sublayer during pulses at a second frequency. As used herein, deposition of a layer primarily or substantially from a compound A means that the source of at least 50% of the material of the layer is compound A. Thus, while the majority of the layer is deposited from compound A and has the characteristics of compound A, other precursor compounds, such as compound B, may contribute to the formation of the layer.

[0023] By using pulsed RF power rather than continuous RF power during the deposition of the sublayers, the compounds exposed to the RF power are not broken down completely. Thus, a sublayer formed primarily from one compound retains some of the chemical and physical characteristics of the compound from which it was primarily deposited. For example, a sublayer deposited from a compound having a ring structure is expected to include ring structures, while a sublayer deposited from a compound having a linear structure is expected to include linear structures.

[0024] It is believed that depositing adjacent sublayers having different types of structures contributes to the formation of a multilayer low k dielectric film that has adjacent sublayers with different mechanical properties, such as compressive stress, tensile stress, modulus, adhesion, and hardness. By using thin adjacent layers with different properties, a mechanical or structural weakness in one layer can be compensated for by the different characteristics of an adjacent layer.

[0025] While the deposition of two types of sublayers from compounds A and B has been described above, additional types of sublayers may be deposited by using additional compounds, C, D, E, etc. For example, a sublayer may be deposited from compound C by exposing C with A and B to pulsed RF power at a different frequency than the frequencies used to deposit sublayers from A and B. Alternatively, C may be added to the chamber after the flow of A and B into the chamber has been terminated and then deposited at a certain frequency using pulsed RF power. Some A and B may still be present in the chamber when C is introduced, or the chamber may be purged, such as with a carrier gas, before C is introduced.

[0026] In another embodiment, a low k dielectric film may be deposited by exposing two or more compounds sequentially to pulsed RF power. For example, compound A may be introduced into a chamber and exposed to pulsed RF power at one frequency to deposit a first low k dielectric sublayer, and then compound B may be introduced into the chamber and exposed to pulsed RF power at a second frequency to deposit a second low k dielectric sublayer. Alternatively, a first sublayer may be deposited from a first processing gas mixture comprising compound A and applying pulsed RF power at one frequency, and a second and third sublayer may be deposited from a second processing gas mixture comprising compounds B and C and applying pulsed RF power at two different frequencies. The two or more compounds may be continuously flowed into the chamber or delivered in pulses.

[0027] In another embodiment, a first group of one or more compounds, preferably two or more compounds, may be exposed to pulsed RF power at a first frequency in a first chamber to form a first low k dielectric sublayer, and a second group of one or more compounds, preferably two or more compounds, that includes at least one different member than the first group of compounds may be exposed to pulsed RF power at a second frequency in a second chamber to form a second low k dielectric sublayer.

[0028] In any of the embodiments described herein, after the desired number of sublayers is deposited, the low k dielectric film formed by the sublayers may be treated with an electron beam or a helium or hydrogen plasma treatment. Preferably, the low k dielectric film is transferred to another chamber without breaking vacuum for an electron beam treatment or a helium or hydrogen plasma treatment. An electron beam treatment and chamber for low k dielectric films is described in commonly assigned U.S. patent application Ser. No. 10/302,375, entitled Method For Forming Ultra Low K Films Using Electron Beam, filed on Nov. 22, 2002, which is incorporated herein by reference. In one embodiment, the electron beam treatment has a dose between about 50 and about 2000 micro coulombs per square centimeter (c/cm²) at about 1 to 20 kiloelectron volts (KeV). The electron beam treatment is typically operated at a temperature between about room-temperature and about 450 C. for about 1 minute to about 15 minutes, such as about 2 minutes. Preferably, the electron beam treatment is performed at about 400 C. for about 2 minutes. In one aspect, the electron beam treatment conditions include 4.5 kV, 1.5 mA and 500 c/cm² at 400 C. Although any electron beam device may be used, one exemplary device is the EBK chamber, available from Applied Materials, Inc.

[0029] The electron beam curing process improves mechanical strength of the deposited film network and also lowers the k-value. It is believed that the energized electron beam alters the chemical bonding in the molecular network of the deposited film and removes at least a portion of the molecular groups from the film. The removal of the molecular groups creates voids or pores within the film, lowering the k value. It is believed that the electron beam treatment also strengthens the film network by cross-linking SiOSi or SiCSi chains, as inferred from FTIR spectroscopy.

[0030] The low k dielectric films described herein may be used as intermetal dielectric layers, such as between conductive interconnects in an integrated circuit device. The low k dielectric films may be used as different layers in a dual damascene structure, such as a trench level dielectric layer or a via level dielectric layer, a cap layer, a hard mask, an etch stop, or a chemical mechanical polishing stop.

[0031] The low k dielectric films described herein may be deposited using a computer storage medium containing a software routine that, when executed, causes a general purpose computer to control a deposition chamber using a deposition method. The software routine may comprise instructions for depositing any of the low k dielectric films according to any of the embodiments described herein. An example of a deposition process performed according to one embodiment of a computer storage medium containing such a software routine is summarized in FIG. 2.

[0032] Two or more compounds in a deposition chamber are exposed to pulsed RF power. At least one of the compounds is an organosilicon compound. Pulses of RF power are delivered for a first period of time at a first frequency to form a first low k dielectric sublayer, as shown in step 200 of FIG. 2. Pulses of RF power are delivered for a second period of time at a second frequency to form a second low k dielectric sublayer, as shown in step 202 of FIG. 2. The low k dielectric sublayers form a low k dielectric film which is treated with an electron beam, as shown in step 204 of FIG. 2.

[0033] An example of a computer system that may be used to execute the software routines described herein is shown in FIG. 3. Illustratively, the computer system 340 includes a system bus 341 and at least one processor 343 coupled to the system bus 341. The processor 343 includes register file and execution units 345. The computer system 340 also includes an input device 344 coupled to the system bus 341 via an input interface 346, a storage device 354 coupled to the system bus 341 via a mass storage interface 352, a terminal 358 coupled to the system bus 341 via a terminal interface 356, and a plurality of networked devices 342 coupled to the system bus 341 via a network interface 350.

[0034] Terminal 358 is any display device such as a cathode ray tube (CRT) or a plasma screen. Terminal 358 and networked devices 342 may be desktop or PC-based computers, workstations, network terminals, or other networked computer systems. Input device 344 can be any device to give input to the computer system 340. For example, a keyboard, keypad, light pen, touch screen, button, mouse, track ball, or speech recognition unit could be used. Further, although shown separately from the input device, the terminal 358 and input device 344 could be combined. For example, a display screen with an integrated touch screen, a display with an integrated keyboard or a speech recognition unit combined with a text speech converter could be used.

[0035] Storage device 354 is DASD (Direct Access Storage Device), although it could be any other storage such as floppy disc drives or optical storage. Although storage 354 is shown as a single unit, it could be any combination of fixed and/or removable storage devices, such as fixed disc drives, floppy disc drives, tape drives, removable memory cards, or optical storage. Main memory 360 and storage device 354 could be part of one virtual address space spanning multiple primary and secondary storage devices.

[0036] The contents of main memory 360 can be loaded from and stored to the storage device 354 as processor 343 has a need for it. Main memory 360 is any memory device sufficiently large to hold the necessary programming and data structures of the invention. The main memory 360 could be one or a combination of memory devices, including random access memory (RAM), non-volatile or backup memory such as programmable or flash memory or read-only memory (ROM). The main memory 360 may be physically located in another part of the computer system 340. While main memory 360 is shown as a single entity, it should be understood that memory 360 may in fact comprise a plurality of modules, and that main memory 360 may exist at multiple levels, from high speed registers and caches to lower speed but larger DRAM chips.

[0037] In general, the routines executed to implement the embodiments of the invention may be implemented as part of an operating system or a specific application, component, program, object, module or sequence of instructions and may be generally referred to as a program. The inventive program typically comprises one or more instructions that are resident at various times in various memory and storage devices in a computer, and that, when read and executed by one or more processors in a computer, cause that computer to perform the steps necessary to execute steps or elements embodying the various aspects of the invention.

[0038] In addition, various programs and devices described herein may be identified based upon the application for which they are implemented in a specific embodiment of the invention. However, it should be appreciated that any particular program or device nomenclature that follows is used merely for convenience, and the invention is not limited to use solely in any specific application identified and/or implied by such nomenclature.

[0039] Moreover, while some embodiments have and hereinafter will be described in the context of fully functioning computers and computer systems, those skilled in the art will appreciate that the various embodiments of the invention are capable of being distributed as a program product in a variety of forms, and that embodiments of the invention apply equally regardless of the particular type of signal bearing media used to actually carry out the distribution. Examples of signal bearing media (also referred to herein as computer readable medium) include, but are not limited to, recordable type media such as volatile and nonvolatile memory devices, floppy and other removable disks, hard disk drives, optical disks (e.g., CD-ROMs, DVDs, etc.), controllers and transmission type media such as digital and analog communication links. Transmission type media include information conveyed to a computer by a communications medium, such as through a computer or telephone network, and includes wireless communications. The latter embodiment specifically includes information downloaded from the Internet and other networks. Such signal-bearing media, when carrying computer-readable instructions that direct the functions of the present invention, represent embodiments of the present invention.

[0040] An example of a low k dielectric film and a method of depositing a low k dielectric film are described below.

[0041] Octamethylcyclotetrasiloxane (OMCTS), diethoxymethylsilane (DEMS), alpha-terpinene (ATP), and carbon dioxide were simultaneously introduced into a Producer CVD chamber in which pulsed RF power was applied between the face plate and the pedestal at a power of about 800 watts at 13.56 MHz and 150 watts at 350 kHz. The OMCTS was introduced into the chamber at 2000 sccm, the DEMS was introduced into the chamber at 600 mgm, the carbon dioxide was introduced into the chamber at 1500 sccm, and the ATP was introduced into the chamber at 3000 mgm. The chamber temperature was about 200 C. to about 350 C. The RF power at 13.56 MHz was pulsed at about 50% duty cycle for 1 second, and a low k dielectric sublayer about 6 nm thick was deposited primarily from the OMCTS. The RF power at 350 kHz was then pulsed at about 50% duty cycle for 1 second, and a low k dielectric sublayer about 3 nm thick was deposited primarily from DEMS, although some material was deposited from the OMCTS and the ATP. The deposition of the sublayers was repeated until a low k dielectric film of 2000 nm was formed. The low k dielectric film had a k<2.5 and a hardness of about>0.5 GPa.

[0042] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.