Patent Publication Number: US-9887096-B2

Title: Differential silicon oxide etch

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of and claims benefit to U.S. application Ser. No. 13/841,009, filed Mar. 15, 2013, which claims the benefit of U.S. Prov. Pat. App. No. 61/701,964 filed Sep. 17, 2012, and titled “DIFFERENTIAL SILICON OXIDE ETCH,” both of which are hereby incorporated herein in their entirety by reference for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process which etches one material faster than another helping e.g. a pattern transfer process proceed. Such an etch process is said to be selective to the first material. As a result of the diversity of materials, circuits and processes, etch processes have been developed with a selectivity towards a variety of materials. 
     A wet HF etch preferentially removes silicon oxide over other dielectrics and semiconductors. However, wet processes are unable to penetrate some constrained trenches and sometimes deform the remaining material. Dry etches produced in local plasmas (plasmas within the substrate processing region) can penetrate more constrained trenches and exhibit less deformation of delicate remaining structures. However, local plasmas can damage the substrate through the production of electric arcs as they discharge. 
     A Siconi™ etch is a remote plasma assisted dry etch process which involves the simultaneous exposure of a substrate to H 2 , NF 3  and NH 3  plasma by-products. Remote plasma excitation of the hydrogen and fluorine species allows plasma-damage-free substrate processing. The Siconi™ etch is largely conformal and selective towards silicon oxide layers but does not readily etch silicon regardless of whether the silicon is amorphous, crystalline or polycrystalline. Silicon nitride is typically etched at a rate between silicon and silicon oxide. 
     Methods are needed to progressively expand this suite of selectivities in order to enable novel process flows. 
     BRIEF SUMMARY OF THE INVENTION 
     A method of etching exposed silicon oxide on patterned heterogeneous structures is described and includes a gas phase etch created from a remote plasma etch. The remote plasma excites a fluorine-containing precursor. Plasma effluents from the remote plasma are flowed into a substrate processing region where the plasma effluents combine with water vapor. Reactants thereby produced etch the patterned heterogeneous structures to remove two separate regions of differing silicon oxide at different etch rates. The methods may be used to remove low density silicon oxide while removing less high density silicon oxide. 
     Embodiments of the invention include methods of etching patterned substrates in a substrate processing region of a substrate processing chamber. The patterned substrates have exposed silicon oxide regions. The methods include flowing a fluorine-containing precursor into a remote plasma region fluidly coupled to the substrate processing region while forming a remote plasma in the remote plasma region to produce plasma effluents. The methods further include flowing water vapor into the substrate processing region without first passing the water vapor through the remote plasma region. The methods further include etching the exposed silicon oxide regions by flowing the plasma effluents into the substrate processing region. The exposed silicon oxide regions comprise a first silicon oxide region having a first density and a second silicon oxide region having a second density. The first density is less than the second density. The first silicon oxide region etches at a first etch rate and the second silicon oxide region etches at a second etch rate which is lower than the first etch rate. 
     Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the disclosed embodiments. The features and advantages of the disclosed embodiments may be realized and attained by means of the instrumentalities, combinations, and methods described in the specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A further understanding of the nature and advantages of the disclosed embodiments may be realized by reference to the remaining portions of the specification and the drawings. 
         FIG. 1  is a flow chart of a silicon oxide selective etch process according to disclosed embodiments. 
         FIG. 2A  shows a substrate processing chamber according to embodiments of the invention. 
         FIG. 2B  shows a showerhead of a substrate processing chamber according to embodiments of the invention. 
         FIG. 3  shows a substrate processing system according to embodiments of the invention. 
     
    
    
     In the appended figures, similar components and/or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If only the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A method of etching exposed silicon oxide on patterned heterogeneous structures is described and includes a gas phase etch created from a remote plasma etch. The remote plasma excites a fluorine-containing precursor. Plasma effluents from the remote plasma are flowed into a substrate processing region where the plasma effluents combine with water vapor. Reactants thereby produced etch the patterned heterogeneous structures to remove two separate regions of differing silicon oxide at different etch rates. The methods may be used to remove low density silicon oxide while removing less high density silicon oxide. 
     Selective remote gas phase etch processes have used a hydrogen source of ammonia (NH 3 ) and a fluorine source of nitrogen trifluoride (NF 3 ) which together flow through a remote plasma system (RPS) and into a reaction region. The flow rates of ammonia and nitrogen trifluoride are typically chosen such that the atomic flow rate of hydrogen is roughly twice that of fluorine in order to efficiently utilize the constituents of the two process gases. The presence of hydrogen and fluorine allows the formation of solid byproducts of (NH 4 ) 2 SiF 6  at relatively low substrate temperatures. The solid byproducts are removed by raising the temperature of the substrate above the sublimation temperature. Remote gas phase etch processes remove oxide films much more rapidly than, e.g. silicon. However, there is very little difference among etch rates between different preparations of silicon oxide. The inventors have discovered that the selectivity of low density silicon oxide over high density silicon nitride can be enhanced by exciting a fluorine-containing precursor in a remote plasma and combining the plasma effluents with water vapor which has not passed through a remote plasma system. 
     In order to better understand and appreciate the invention, reference is now made to  FIG. 1  which is a flow chart of a silicon oxide selective etch process according to disclosed embodiments. Prior to the first operation, the substrate is patterned and a high density silicon oxide is deposited onto the patterned substrate. A low density silicon oxide is then deposited over the high density silicon oxide and acts as a temporary sacrificial support structure, e.g., for a delicate vertical feature. Once the structural aspects of the low density silicon oxide are no longer needed, it can be removed with the etch process described herein, while retaining the high density silicon oxide. 
     The patterned substrate is then delivered into a processing region (operation  110 ). A flow of nitrogen trifluoride is initiated into a plasma region separate from the processing region (operation  120 ). Other sources of fluorine may be used to augment or replace the nitrogen trifluoride. In general, a fluorine-containing precursor is flowed into the plasma region and the fluorine-containing precursor comprises at least one precursor selected from the group consisting of atomic fluorine, diatomic fluorine, nitrogen trifluoride, carbon tetrafluoride, hydrogen fluoride and xenon difluoride. The separate plasma region may be referred to as a remote plasma region herein and may be within a distinct module from the processing chamber or a compartment within the processing chamber. The plasma effluents formed in the remote plasma region are then flowed into the substrate processing region (operation  125 ). Water vapor is simultaneously flowed into the substrate processing region (operation  130 ) to react with the plasma effluents. The water vapor is not passed through the remote plasma region and therefore is only excited by interaction with the plasma effluents. The water vapor is not passed through any remote plasma region before entering the substrate processing region in embodiments of the invention. 
     The patterned substrate is selectively etched (operation  135 ) such that the low density silicon oxide is removed at a significantly higher rate than the high density silicon oxide. This capability enables the use of one silicon oxide region as a sacrificial component (the low density silicon oxide) at the same time another silicon oxide region is exposed (the high density silicon oxide). The reactive chemical species are removed from the substrate processing region and then the substrate is removed from the processing region (operation  145 ). 
     Wet etches, such as buffered oxide etches, were also used to selectively remove low density silicon oxide relative to high density silicon oxide. The inventors have found that the selectivity was limited to about 6:1 or 7:1 (low density SiO etch rate:high density SiO etch rate). Using the gas phase dry etch processes described herein, the inventors have established that selectivities of 40:1 and even 50:1 (low density SiO etch rate:high density SiO etch rate) are possible. The low-density silicon oxide etch rate exceeds the high-density silicon oxide etch rate by a multiplicative factor of about 8 or more, about 10 or more, about 15 or more, or about 25 or more, in embodiments of the invention. 
     Examplary deposition techniques which result in low density silicon oxide include chemical vapor deposition using dichlorosilane as a deposition precursor, spin-on glass (SOG) or plasma-enhanced chemical vapor deposition. High density silicon oxide may be deposited as thermal oxide (exposing silicon to, e.g., O 2  at high temperature), disilane precursor furnace oxidation or high-density plasma chemical vapor deposition in embodiments of the invention. 
     Gas phase etches involving only fluorine (either remote or local) do not possess the selectivity needed to remove the low-density silicon oxide while leaving other portions of the patterned substrate (made of high-density silicon oxide) nearly undisturbed. The gas phase etches described herein have an added benefit, in that they do not produce solid residue. Elimination of solid residue avoids disturbing delicate features which may be supported by the sacrificial low-density silicon oxide. Elimination of solid residue also simplifies the process flows and decreases processing costs by removing the sublimation step. The fluorine-containing precursor is devoid of hydrogen in embodiments of the invention. The plasma effluents may also be devoid of hydrogen when no hydrogen precursors are included in the remote plasma region. This ensures no possible production of solid by-products on the patterned substrate. 
     Without wishing to bind the coverage of the claims to theoretical mechanisms which may or may not be entirely correct, some discussion of possible mechanisms may prove beneficial. Radical-fluorine precursors are produced by delivering a fluorine-containing precursor into the remote plasma region. Applicants suppose that a concentration of fluorine ions and atoms is produced and delivered into the substrate processing region. Water vapor (H 2 O) may react with the fluorine to produce less reactive species such as HF 2   −  which still readily remove low-density silicon oxide but do not readily remove high-density silicon oxide from the patterned substrate surface. The selectivity combined with the lack of solid residue byproducts, make these etch processes well suited for removing molds and other silicon oxide support structures from delicate non-silicon oxide materials while inducing little deformation in the remaining delicate structures. 
     The pressure in the substrate processing region may be above or about 0.1 Torr and less than or about 50 Torr, in disclosed embodiments, during the etching operation. The pressure within the substrate processing region may also be below or about 40 Torr and above or about 5 Torr or 10 Torr in disclosed embodiments. Any of the upper limits can be combined with any of these lower limits to form additional embodiments of the invention. The temperature of the patterned substrate may be about 0° C. or more and about 100° C. or less, in disclosed embodiments, during the etching operation. The temperature of the patterned substrate may be about 5° C. or more and about 40° C. or less during the etching operation in embodiments of the invention. 
     Additional water vapor and remotely-excited-fluorine etch process parameters are disclosed in the course of describing an exemplary processing chamber and system. 
     Exemplary Processing System 
     Processing chambers that may implement embodiments of the present invention may be included within processing platforms such as the CENTURA® and PRODUCER® systems, available from Applied Materials, Inc. of Santa Clara, Calif. Examples of substrate processing chambers that can be used with exemplary methods of the invention may include those shown and described in co-assigned U.S. Provisional Patent App. No. 60/803,499 to Lubomirsky et al, filed May 30, 2006, and titled “PROCESS CHAMBER FOR DIELECTRIC GAPFILL,” the entire contents of which is herein incorporated by reference for all purposes. Additional exemplary systems may include those shown and described in U.S. Pat. Nos. 6,387,207 and 6,830,624, which are also incorporated herein by reference for all purposes. 
       FIG. 2A  is a substrate processing chamber  1001  according to disclosed embodiments. A remote plasma system (RPS  1010 ) may process the fluorine-containing precursor which then travels through a gas inlet assembly  1011 . Two distinct gas supply channels are visible within the gas inlet assembly  1011 . A first channel  1012  carries a gas that passes through the remote plasma system RPS  1010 , while a second channel  1013  bypasses the RPS  1010 . Either channel may be used for the fluorine-containing precursor, in embodiments. On the other hand, the first channel  202  may be used for the process gas and the second channel  1013  may be used for a treatment gas. The lid  1021  (e.g. a conducting top portion) and a perforated partition (showerhead  1053 ) are shown with an insulating ring  1024  in between, which allows an AC potential to be applied to the lid  1021  relative to showerhead  1053 . The AC potential strikes a plasma in chamber plasma region  1020 . The process gas may travel through first channel  1012  into chamber plasma region  1020  and may be excited by a plasma in chamber plasma region  1020  alone or in combination with RPS  1010 . If the process gas (the fluorine-containing precursor) flows through second channel  1013 , then only the chamber plasma region  1020  is used for excitation. The combination of chamber plasma region  1020  and/or RPS  1010  may be referred to as a remote plasma system herein. The perforated partition (also referred to as a showerhead)  1053  separates chamber plasma region  1020  from a substrate processing region  1070  beneath showerhead  1053 . Showerhead  1053  allows a plasma present in chamber plasma region  1020  to avoid directly exciting gases in substrate processing region  1070 , while still allowing excited species to travel from chamber plasma region  1020  into substrate processing region  1070 . 
     Showerhead  1053  is positioned between chamber plasma region  1020  and substrate processing region  1070  and allows plasma effluents (excited derivatives of precursors or other gases) created within RPS  1010  and/or chamber plasma region  1020  to pass through a plurality of through-holes  1056  that traverse the thickness of the plate. The showerhead  1053  also has one or more hollow volumes  1051  which can be filled with a precursor in the form of a vapor or gas (such as a silicon-containing precursor) and pass through small holes  1055  into substrate processing region  1070  but not directly into chamber plasma region  1020 . Showerhead  1053  is thicker than the length of the smallest diameter  1050  of the through-holes  1056  in this disclosed embodiment. In order to maintain a significant concentration of excited species penetrating from chamber plasma region  1020  to substrate processing region  1070 , the length  1026  of the smallest diameter  1050  of the through-holes may be restricted by forming larger diameter portions of through-holes  1056  part way through the showerhead  1053 . The length of the smallest diameter  1050  of the through-holes  1056  may be the same order of magnitude as the smallest diameter of the through-holes  1056  or less in disclosed embodiments. 
     In the embodiment shown, showerhead  1053  may distribute (via through-holes  1056 ) process gases which contain oxygen, hydrogen and/or nitrogen and/or plasma effluents of such process gases upon excitation by a plasma in chamber plasma region  1020 . In embodiments, the process gas introduced into the RPS  1010  and/or chamber plasma region  1020  through first channel  1012  may contain fluorine (e.g. CF 4 , NF 3  or XeF 2 ). The process gas may also include a carrier gas such as helium, argon, nitrogen (N 2 ), etc. Plasma effluents may include ionized or neutral derivatives of the process gas and may also be referred to herein as a radical-fluorine precursor referring to the atomic constituent of the process gas introduced. 
     In embodiments, the number of through-holes  1056  may be between about 60 and about 2000. Through-holes  1056  may have a variety of shapes but are most easily made round. The smallest diameter  1050  of through-holes  1056  may be between about 0.5 mm and about 20 mm or between about 1 mm and about 6 mm in disclosed embodiments. There is also latitude in choosing the cross-sectional shape of through-holes, which may be made conical, cylindrical or a combination of the two shapes. The number of small holes  1055  used to introduce a gas into substrate processing region  1070  may be between about 100 and about 5000 or between about 500 and about 2000 in different embodiments. The diameter of the small holes  1055  may be between about 0.1 mm and about 2 mm. 
       FIG. 2B  is a bottom view of a showerhead  1053  for use with a processing chamber according to disclosed embodiments. Showerhead  1053  corresponds with the showerhead shown in  FIG. 2A . Through-holes  1056  are depicted with a larger inner-diameter (ID) on the bottom of showerhead  1053  and a smaller ID at the top. Small holes  1055  are distributed substantially evenly over the surface of the showerhead, even amongst the through-holes  1056  which helps to provide more even mixing than other embodiments described herein. A fluorine-containing precursor may be flowed through through-holes  1056  in dual-zone showerhead  1053  while water vapor passes through separate zones in the dual-zone showerhead entering the substrate processing region through small holes  1055 . The separate zones open into the substrate processing region but not into the remote plasma region. 
     An exemplary patterned substrate may be supported by a pedestal (not shown) within substrate processing region  1070  when fluorine-containing plasma effluents arriving through through-holes  1056  in showerhead  1053  combine with moisture arriving through the small holes  1055  originating from hollow volumes  1051 . Though substrate processing region  1070  may be equipped to support a plasma for other processes such as curing, no plasma is present during the etching of patterned substrate, in embodiments of the invention. 
     A plasma may be ignited either in chamber plasma region  1020  above showerhead  1053  or substrate processing region  1070  below showerhead  1053 . A plasma is present in chamber plasma region  1020  to produce the radical-fluorine precursors from an inflow of the fluorine-containing precursor. An AC voltage typically in the radio frequency (RF) range is applied between the conductive top portion  1021  of the processing chamber and showerhead  1053  to ignite a plasma in chamber plasma region  1020  during deposition. An RF power supply generates a high RF frequency of 13.56 MHz but may also generate other frequencies alone or in combination with the 13.56 MHz frequency. 
     The top plasma may be left at low or no power when the bottom plasma in the substrate processing region  1070  is turned on to clean the interior surfaces bordering substrate processing region  1070 . A plasma in substrate processing region  1070  is ignited by applying an AC voltage between showerhead  1053  and the pedestal or bottom of the chamber. A cleaning gas may be introduced into substrate processing region  1070  while the plasma is present. 
     The pedestal may have a heat exchange channel through which a heat exchange fluid flows to control the temperature of the substrate. This configuration allows the substrate temperature to be cooled or heated to maintain relatively low temperatures (from room temperature through about 120° C.). The heat exchange fluid may comprise ethylene glycol and water. The wafer support platter of the pedestal (preferably aluminum, ceramic, or a combination thereof) may also be resistively heated in order to achieve relatively high temperatures (from about 120° C. through about 1100° C.) using an embedded single-loop embedded heater element configured to make two full turns in the form of parallel concentric circles. An outer portion of the heater element may run adjacent to a perimeter of the support platter, while an inner portion runs on the path of a concentric circle having a smaller radius. The wiring to the heater element passes through the stem of the pedestal. 
     The substrate processing system is controlled by a system controller. In an exemplary embodiment, the system controller includes a hard disk drive, a floppy disk drive and a processor. The processor contains a single-board computer (SBC), analog and digital input/output boards, interface boards and stepper motor controller boards. Various parts of CVD system conform to the Versa Modular European (VME) standard which defines board, card cage, and connector dimensions and types. The VME standard also defines the bus structure as having a 16-bit data bus and a 24-bit address bus. 
     The system controller controls all of the activities of the etching chamber. The system controller executes system control software, which is a computer program stored in a computer-readable medium. Preferably, the medium is a hard disk drive, but the medium may also be other kinds of memory. The computer program includes sets of instructions that dictate the timing, mixture of gases, chamber pressure, chamber temperature, RF power levels, susceptor position, and other parameters of a particular process. Other computer programs stored on other memory devices including, for example, a floppy disk or other another appropriate drive, may also be used to instruct the system controller. 
     A process for differentially etching low-density silicon oxide and high-density silicon oxide on a substrate or a process for cleaning a chamber can be implemented using a computer program product that is executed by the system controller. The computer program code can be written in any conventional computer readable programming language: for example, assembly language, C, C++, Pascal, Fortran or others. Suitable program code is entered into a single file, or multiple files, using a conventional text editor, and stored or embodied in a computer usable medium, such as a memory system of the computer. If the entered code text is in a high level language, the code is compiled, and the resultant compiler code is then linked with an object code of precompiled Microsoft Windows® library routines. To execute the linked, compiled object code the system user invokes the object code, causing the computer system to load the code in memory. The CPU then reads and executes the code to perform the tasks identified in the program. 
     The interface between a user and the controller is via a flat-panel touch-sensitive monitor. In the preferred embodiment two monitors are used, one mounted in the clean room wall for the operators and the other behind the wall for the service technicians. The two monitors may simultaneously display the same information, in which case only one accepts input at a time. To select a particular screen or function, the operator touches a designated area of the touch-sensitive monitor. The touched area changes its highlighted color, or a new menu or screen is displayed, confirming communication between the operator and the touch-sensitive monitor. Other devices, such as a keyboard, mouse, or other pointing or communication device, may be used instead of or in addition to the touch-sensitive monitor to allow the user to communicate with the system controller. 
     The chamber plasma region or a region in an RPS may be referred to as a remote plasma region. In embodiments, the radical precursor (e.g. a radical-fluorine precursor) is created in the remote plasma region and travels into the substrate processing region to combine with the water vapor. In embodiments, the water vapor is excited only by the radical-fluorine precursor (aka the plasma effluents). Plasma power may essentially be applied only to the chamber plasma region, in embodiments, to ensure that the radical-fluorine precursor provides the dominant excitation to the water vapor. 
     In embodiments employing a chamber plasma region, the excited plasma effluents are generated in a section of the substrate processing region partitioned from a deposition region. The deposition region, also known herein as the substrate processing region, is where the plasma effluents mix and react with the water vapor to etch the patterned substrate (e.g., a semiconductor wafer). The excited plasma effluents may also be accompanied by inert gases (in the exemplary case, argon). The water vapor does not pass through a plasma before entering the substrate plasma region, in embodiments. The substrate processing region may be described herein as “plasma-free” during the etching operation of the patterned substrate. “Plasma-free” does not necessarily mean the region is devoid of plasma. Ionized species and free electrons created within the plasma region do travel through pores (apertures) in the partition (showerhead) but the water vapor is not substantially excited by the plasma power applied to the plasma region. The borders of the plasma in the chamber plasma region are hard to define and may encroach upon the substrate processing region through the apertures in the showerhead. In the case of an inductively-coupled plasma, a small amount of ionization may be effected within the substrate processing region directly. Furthermore, a low intensity plasma may be created in the substrate processing region without eliminating desirable features of the forming film. All causes for a plasma having much lower intensity ion density than the chamber plasma region (or a remote plasma region, for that matter) during the creation of the excited plasma effluents do not deviate from the scope of “plasma-free” as used herein. 
     Nitrogen trifluoride (or another fluorine-containing precursor) may be flowed into chamber plasma region  1020  at rates between about 25 sccm and about 200 sccm, between about 50 sccm and about 150 sccm or between about 75 sccm and about 125 sccm in different embodiments. Water vapor may be flowed into substrate processing region  1070  at rates between about 25 sccm and about 200 sccm, between about 50 sccm and about 150 sccm or between about 75 sccm and about 125 sccm in different embodiments. 
     Combined flow rates of water vapor and fluorine-containing precursor into the chamber may account for 0.05% to about 20% by volume of the overall gas mixture; the remainder being carrier gases. The fluorine-containing precursor is flowed into the remote plasma region but the plasma effluents has the same volumetric flow ratio, in embodiments. In the case of the fluorine-containing precursor, a purge or carrier gas may be first initiated into the remote plasma region before those of the fluorine-containing gas to stabilize the pressure within the remote plasma region. 
     Plasma power can be a variety of frequencies or a combination of multiple frequencies. In the exemplary processing system the plasma is provided by RF power delivered to lid  1021  relative to showerhead  1053 . The RF power may be between about 10 watts and about 2000 watts, between about 100 watts and about 2000 watts, between about 200 watts and about 1500 watts or between about 500 watts and about 1000 watts in different embodiments. The RF frequency applied in the exemplary processing system may be low RF frequencies less than about 200 kHz, high RF frequencies between about 10 MHz and about 15 MHz or microwave frequencies greater than or about 1 GHz in different embodiments. The plasma power may be capacitively-coupled (CCP) or inductively-coupled (ICP) into the remote plasma region. 
     Substrate processing region  1070  can be maintained at a variety of pressures during the flow of water vapor, any carrier gases and plasma effluents into substrate processing region  1070 . The pressure may be maintained between about 500 mTorr and about 30 Torr, between about 1 Torr and about 20 Torr or between about 5 Torr and about 15 Torr in different embodiments. 
     In one or more embodiments, the substrate processing chamber  1001  can be integrated into a variety of multi-processing platforms, including the Producer™ GT, Centura™ AP and Endura™ platforms available from Applied Materials, Inc. located in Santa Clara, Calif. Such a processing platform is capable of performing several processing operations without breaking vacuum. Processing chambers that may implement embodiments of the present invention may include dielectric etch chambers or a variety of chemical vapor deposition chambers, among other types of chambers. 
     Embodiments of the deposition systems may be incorporated into larger fabrication systems for producing integrated circuit chips.  FIG. 3  shows one such system  1101  of deposition, baking and curing chambers according to disclosed embodiments. In the figure, a pair of FOUPs (front opening unified pods)  1102  supply substrate substrates (e.g., 300 mm diameter wafers) that are received by robotic arms  1104  and placed into a low pressure holding area  1106  before being placed into one of the substrate processing chambers  1108   a - f . A second robotic arm  1110  may be used to transport the substrate wafers from the holding area  1106  to the substrate processing chambers  1108   a - f  and back. Each substrate processing chamber  1108   a - f , can be outfitted to perform a number of substrate processing operations including the dry etch processes described herein in addition to cyclical layer deposition (CLD), atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), etch, pre-clean, degas, orientation and other substrate processes. 
     The substrate processing chambers  1108   a - f  may include one or more system components for depositing, annealing, curing and/or etching a flowable dielectric film on the substrate wafer. In one configuration, two pairs of the processing chamber (e.g.,  1108   c - d  and  1108   e - f ) may be used to deposit dielectric material on the substrate, and the third pair of processing chambers (e.g.,  1108   a - b ) may be used to etch the deposited dielectric. In another configuration, all three pairs of chambers (e.g.,  1108   a - f ) may be configured to etch a dielectric film on the substrate. Any one or more of the processes described may be carried out on chamber(s) separated from the fabrication system shown in different embodiments. 
     System controller  1157  is used to control motors, valves, flow controllers, power supplies and other functions required to carry out process recipes described herein. A gas handling system  1155  may also be controlled by system controller  1157  to introduce gases to one or all of the substrate processing chambers  1108   a - f . System controller  1157  may rely on feedback from optical sensors to determine and adjust the position of movable mechanical assemblies in gas handling system  1155  and/or in substrate processing chambers  1108   a - f . Mechanical assemblies may include the robot, throttle valves and susceptors which are moved by motors under the control of system controller  1157 . 
     In an exemplary embodiment, system controller  1157  includes a hard disk drive (memory), USB ports, a floppy disk drive and a processor. System controller  1157  includes analog and digital input/output boards, interface boards and stepper motor controller boards. Various parts of multi-chamber processing system  1101  which contains processing chamber  400  are controlled by system controller  1157 . The system controller executes system control software in the form of a computer program stored on computer-readable medium such as a hard disk, a floppy disk or a flash memory thumb drive. Other types of memory can also be used. The computer program includes sets of instructions that dictate the timing, mixture of gases, chamber pressure, chamber temperature, RF power levels, susceptor position, and other parameters of a particular process. 
     A process for etching, depositing or otherwise processing a film on a substrate or a process for cleaning chamber can be implemented using a computer program product that is executed by the controller. The computer program code can be written in any conventional computer readable programming language: for example, 68000 assembly language, C, C++, Pascal, Fortran or others. Suitable program code is entered into a single file, or multiple files, using a conventional text editor, and stored or embodied in a computer usable medium, such as a memory system of the computer. If the entered code text is in a high level language, the code is compiled, and the resultant compiler code is then linked with an object code of precompiled Microsoft Windows® library routines. To execute the linked, compiled object code the system user invokes the object code, causing the computer system to load the code in memory. The CPU then reads and executes the code to perform the tasks identified in the program. 
     The interface between a user and the controller may be via a touch-sensitive monitor and may also include a mouse and keyboard. In one embodiment two monitors are used, one mounted in the clean room wall for the operators and the other behind the wall for the service technicians. The two monitors may simultaneously display the same information, in which case only one is configured to accept input at a time. To select a particular screen or function, the operator touches a designated area on the display screen with a finger or the mouse. The touched area changes its highlighted color, or a new menu or screen is displayed, confirming the operator&#39;s selection. 
     As used herein “substrate” may be a support substrate with or without layers formed thereon. The patterned substrate may be an insulator or a semiconductor of a variety of doping concentrations and profiles and may, for example, be a semiconductor substrate of the type used in the manufacture of integrated circuits. Exposed “silicon oxide” of the patterned substrate is predominantly SiO 2  but may include concentrations of other elemental constituents such as nitrogen, hydrogen, carbon and the like. In some embodiments, silicon oxide films etched using the methods disclosed herein consist essentially of silicon and oxygen. The term “precursor” is used to refer to any process gas which takes part in a reaction to either remove material from or deposit material onto a surface. “Plasma effluents” describe gas exiting from the chamber plasma region and entering the substrate processing region. Plasma effluents are in an “excited state” wherein at least some of the gas molecules are in vibrationally-excited, dissociated and/or ionized states. A “radical precursor” is used to describe plasma effluents (a gas in an excited state which is exiting a plasma) which participate in a reaction to either remove material from or deposit material on a surface. A “radical-fluorine precursor” is a radical precursor which contains fluorine but may contain other elemental constituents. The phrase “inert gas” refers to any gas which does not form chemical bonds when etching or being incorporated into a film. Exemplary inert gases include noble gases but may include other gases so long as no chemical bonds are formed when (typically) trace amounts are trapped in a film. 
     The terms “gap” and “trench” are used throughout with no implication that the etched geometry has a large horizontal aspect ratio. Viewed from above the surface, trenches may appear circular, oval, polygonal, rectangular, or a variety of other shapes. A trench may be in the shape of a moat around an island of material (e.g. a substantially cylindrical TiN pillar). The term “via” is used to refer to a low aspect ratio trench (as viewed from above) which may or may not be filled with metal to form a vertical electrical connection. As used herein, a conformal etch process refers to a generally uniform removal of material on a surface in the same shape as the surface, i.e., the surface of the etched layer and the pre-etch surface are generally parallel. A person having ordinary skill in the art will recognize that the etched interface likely cannot be 100% conformal and thus the term “generally” allows for acceptable tolerances. 
     Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosed embodiments. Additionally, a number of well known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention. 
     Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included. 
     As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the dielectric material” includes reference to one or more dielectric materials and equivalents thereof known to those skilled in the art, and so forth. 
     Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups.