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  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
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  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
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  • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
  • C23C16/40—Oxides
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  • H10P14/6334—Deposition from the gas or vapour phase using decomposition or reaction of gaseous or vapour phase compounds, i.e. chemical vapour deposition
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  • H10P14/6338—Deposition from the gas or vapour phase using decomposition or reaction of gaseous or vapour phase compounds, i.e. chemical vapour deposition the reactions being activated by other means than plasma or thermal, e.g. photo-CVD
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  • H10P14/668—Formation of materials, e.g. in the shape of layers or pillars of insulating materials characterised by the type of materials the materials being characterised by the deposition precursor materials
  • H10P14/6681—Formation of materials, e.g. in the shape of layers or pillars of insulating materials characterised by the type of materials the materials being characterised by the deposition precursor materials the precursor containing a compound comprising Si
  • H10P14/6682—Formation of materials, e.g. in the shape of layers or pillars of insulating materials characterised by the type of materials the materials being characterised by the deposition precursor materials the precursor containing a compound comprising Si the compound being a silane, e.g. disilane, methylsilane or chlorosilane
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  • H10P14/668—Formation of materials, e.g. in the shape of layers or pillars of insulating materials characterised by the type of materials the materials being characterised by the deposition precursor materials
  • H10P14/6681—Formation of materials, e.g. in the shape of layers or pillars of insulating materials characterised by the type of materials the materials being characterised by the deposition precursor materials the precursor containing a compound comprising Si
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  • H10P14/6686—Formation of materials, e.g. in the shape of layers or pillars of insulating materials characterised by the type of materials the materials being characterised by the deposition precursor materials the precursor containing a compound comprising Si the compound comprising silicon and oxygen the compound being a molecule comprising at least one silicon-oxygen bond and the compound having hydrogen or an organic group attached to the silicon or oxygen, e.g. a siloxane
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  • H10P14/6921—Inorganic materials composed of oxides, glassy oxides or oxide-based glasses containing silicon
  • H10P14/6922—Inorganic materials composed of oxides, glassy oxides or oxide-based glasses containing silicon the material containing Si, O and at least one of H, N, C, F or other non-metal elements, e.g. SiOC, SiOC:H or SiONC
  • H10P14/6924—Inorganic materials composed of oxides, glassy oxides or oxide-based glasses containing silicon the material containing Si, O and at least one of H, N, C, F or other non-metal elements, e.g. SiOC, SiOC:H or SiONC the material being halogen doped silicon oxides, e.g. FSG
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  • H10P14/6326—Deposition processes
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  • H10P14/6334—Deposition from the gas or vapour phase using decomposition or reaction of gaseous or vapour phase compounds, i.e. chemical vapour deposition
  • H10P14/6336—Deposition from the gas or vapour phase using decomposition or reaction of gaseous or vapour phase compounds, i.e. chemical vapour deposition in the presence of a plasma [PECVD]
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  • H10P14/687—Organic materials, e.g. photoresists carbon-based polymeric organic materials, e.g. polyimides, poly cyclobutene or PVC the materials being fluorocarbon compounds, e.g. (CHxFy) n or polytetrafluoroethylene
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  • H10P14/6921—Inorganic materials composed of oxides, glassy oxides or oxide-based glasses containing silicon
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Definitions

• Lee et al. New Deposition Systems and Processes for Transport Polymerization and Chemical Vapor Deposition. Attorney Docket No.: QTII 8022 SRM/DBB. Lee et al., Low Dielectric Constant Materials with Improved Thermal and
• This invention relates to the precursors for manufacturing dielectric materials with low dielectric constants for use in the manufacture of semiconductor integrated circuits.
• the invention also relates to the polymers made from these precursors, the processes used to make polymers, and the integrated circuits made from these polymers.
• the first method described is the modification of Si0 2 by adding carbon and/or fluorine atoms.
• the fluorinated amorphous carbon products had dielectric constants as low as 2.2 but had very poor thermal stability. These materials shrank as much as 45% after annealing at 350° C for 30 minutes in nitrogen.
• Films made from Parylene AF-4TM have a dielectric constant of 2.28 and have increased thermal stability compared to the above-mentioned dielectric materials. Under nitrogen atmosphere, a polymer made of Parylene AF-4TM lost only 0.8 % of its weight over 3 hours at 450° C.
• the prior art contains no examples of dielectric material precursors for semiconductor manufacture which have desired properties of low dielectric constant, high thermal stability, and low cost.
• the present invention is directed to overcoming the disadvantages of the prior art.
• one object of the invention is to provide precursor materials which can be used to manufacture products including polymers with low dielectric constants for IC manufacture.
• Another object of the invention is to provide precursors which can be manufactured into products which have high thermal stability. Yet another object of the invention is to provide precursors which can be polymerized as thin layers on a substrate.
• An additional object of the invention is to provide precursor materials which are inexpensive.
• a further object is to provide materials which can be made into products with high efficiency.
• An additional object of the invention is to provide precursors which can be made into dielectric materials which can be easily and accurately shaped after manufacture.
• the invention includes novel precursors containing a fluorinated silane, a fluorinated siloxane or a fluorocarbon each containing a fluorinated aromatic moiety.
• the precursors are suitable for making polymers with low dielectric constants and high thermal stability.
• the polymers can be used for making integrated circuits.
• the invention includes methods for making polymers for integrated circuit manufacture using novel fluorinated silanes, fluorinated siloxanes, or fluorocarbons, each containing a fluorinated aromatic moiety.
• the invention includes integrated circuits comprising low dielectric constant polymers made using fluorinated silanes, fluorinated siloxanes, or fluorocarbons, each containing a fluorinated aromatic moiety.
• one aspect of the invention comprises precursors for using in manufacturing polymers with low dielectric constants which are useful in the manufacture of integrated circuits (ICs).
• Another aspect of the invention comprises precursors for use in manufacturing polymers with high thermal stability which are useful in the manufacture of ICs.
• Another aspect of the invention comprises methods for reacting the precursors and depositing them as thin films on substrates for IC manufacture.
• Yet another aspect of the invention comprises the deposited thin film made using the novel precursors and methods for their reaction and deposition.
• Another aspect of the invention is the integrated circuits comprised of thin films derived through the reaction and deposition of the novel precursors.
• Fig 1 Embodiment of an apparatus of this invention used for thermolytic transport polyme ⁇ zation of fluo ⁇ nated silanes, fluo ⁇ nated siloxanes, and fluorocarbons
• Fig 2 Embodiment of an apparatus of this mvention used for radio frequency plasma enhanced transport polyme ⁇ zation of fluo ⁇ nated silanes, fluo ⁇ nated siloxanes, and fluorocarbons
• Fig 3 Embodiment of an apparatus of this mvention used for high density plasma enhanced chemical vapor deposition of fluormated silanes, fluo ⁇ nated siloxanes, and fluorocarbons
• Fig 4 Embodiment of an apparatus of this mvention used for photon assisted transport polyme ⁇ zation of fluo ⁇ nated silanes, fluo ⁇ nated siloxanes, and fluorocarbons
• Fig 5 Embodiment of a universal deposition system of this mvention for deposition of fluo ⁇ nated silanes, fluo ⁇ nated siloxanes, and fluorocarbons
• Fig 6 Schematic cross-section view of a thin film of this mvention made of polymers de ⁇ ved from fluo ⁇ nated silanes, fluorinated siloxanes. and fluorocarbons
• This mvention discloses novel precursors for making three catego ⁇ es of fluo ⁇ ne-contammg low dielect ⁇ c mate ⁇ als These precursors mclude fluo ⁇ nated silanes, fluormated siloxanes, and fluorocarbons
• the d elect ⁇ c mate ⁇ als are useful m the manufacture of semiconductors for mtegrated circuits and other electronic devices
• Manufacture of smaller and faster mtegrated circuits requires lntermetal dielectnc (IMD) and mterlevel dielect ⁇ c (ILD) matenals which minimize the communication of elect ⁇ cal signals between adjacent conductive lmes, referred to as the interconnects
• Low dielectric materials are useful to mirrimize this "cross-talk" within and between layers of integrated circuits.
• the polymers prepared from the precursors of the present invention are rigid and contain a high degree of substitution of hydrogen atoms by fluorine atoms.
• the fluorine in the aromatic ring provides the low dielectric constant (K) and molecular rigidity.
• K dielectric constant
• This rigidity is reflected by high glass transition temperature (Tg), high elastic modulus (E) and high shear modulus (G).
• the elastic modulus is above about 2, and preferably is about 3.
• Bond Type sp 3 C-Si sp 2 C-Si sp 3 C-sp 3 C sp 2 C-H sp 2 C-F sp 3 C-H Bond Energy 72 92 92 111 126 86
• the presence of fluorine atoms in the aromatic moieties of the polymers of this invention decreases the dielectric constant, and the sp 2 C-F and hyperconjugated sp 3 C-F bonds confer greater thermal stability to a polymer containing them. In contrast, polymers which do not contain these types of bonds have lower thermal stability and higher dielectric constant.
• the precursors of this invention contain both single and conjugated double bonds. Additionally, hyperconjugation of sp 3 C-F with sp C bonds results in increased bond strength of the sp 3 C-F compared to other sp 3 C-F bonds (such as in polytetrafluoroethylene) which are not hyperconjugated.
• the dielectric constant K is too high to be useful in the newer, smaller integrated circuits.
• the invention comprises incorporating fluorine atoms bonded to the double bonded carbon atoms in the precursor molecules (sp 2 C-F) into dielectric materials.
• the precursors comprise compounds containing sp 2 C-F bonds and functional groups which can be cleaved or oxidized using a transport polymerization (TP) or chemical vapor deposition (CVD) process to yield reactive intermediates which spontaneously polymerize on the wafer substrate.
• TP transport polymerization
• CVD chemical vapor deposition
• Both linearly conjugated polymers and aromatic moieties can be used, but prefe ⁇ ed moieties are aromatic. Also preferred are multiple-ring aromatic moieties, and the most prefe ⁇ ed are single-ring aromatic moieties such as phenyl rings (e.g., -C 6 H 4 -, -C 6 H 5 ).
• a single fluorine atom incorporated into an aromatic moiety decreases the dielectric constant of that moiety, and further Increasing the number of fluorine atoms in the aromatic moiety further decreases K.
• the general formula for mono-functional aromatic precursors of the invention is: -C 6 H 5 _ n F wherein n is an integer selected from the group of 1, 2, 3, 4 or 5.
• the general formula for di-functional aromatic precursors is: -C 6 H 4 . n F n -, wherein n is an integer selected from the group of 1, 2, 3 or 4.
• the most prefe ⁇ ed embodiments are aromatic moieties which have maximal substitution of sp 2 C-H hydrogen atoms by sp 2 C-F fluorine atoms.
• the mono-fluorinated phenyl group -C 6 H 4 F works, but multi- fluorinated phenyl groups are preferred, and -C 6 F 5 is most preferred.
• the mono-fluorinated phenyl group -C 6 H 3 F- works, but multi-fluorinated phenyl groups are prefe ⁇ ed, and -C 6 F - is most preferred.
• the first category of precursors consists of precursors for making fluorocarbons, fluorinated silanes and fluorinated siloxane. These precursors are useful for modifying Si0 2 by incorporating Si-C bonds, Si-F bonds, and/or fluorinated aromatic bonds. Incorporation of these types of bonded moieties into Si0 2 can lower the dielectric constant, but with only small decreases of the Td, Tg, E, and G of the polymers from which they are made.
• Precursors of fluorinated silanes in this invention have the general structural formula: (C 6 H 5 . n F n ) m -SiH 4 ._ civil wherein n is 1, 2, 3, 4 or 5 and n is an integer of 1, 2, 3 or 4.
• the prefe ⁇ ed fluorinated silane of the present invention is C 6 F 5 -SiH 3 .
• Precursors of fluorinated siloxanes of this invention have the general structural formula: (C 6 H 5 . n F n ) ⁇ -Si(OCH 3 ) 4 . m , wherein n is 1, 2, 3, 4 or 5, and m is 1, 2, or 3.
• the prefe ⁇ ed fluorinated siloxane of the present invention is (C 6 F 5 )-Si(OCH 3 ) 3 .
• Precursors of fluorinated hydrocarbons have the general structural formula: CH 3 _-F n -C 6 H 4 . p F p -CH 3 _F m , wherein n and m are 1, 2 or 3, and p is 1, 2, 3, or 4.
• Preferred fluorinated hydrocarbon precursors are CF 3 -C 6 F 4 -CF 3 and CHF 2 -C 6 F 4 -CHF 2 .
• Table 2 shows the precursors, other reactants and TP and CVD processes used to manufacture fluorine-substituted aromatic Si0 derivatives of this invention. Although the fully fluorinated derivatives are described, mono-, di-, tri-, and tetra- fluorinated aromatic moieties, as appropriate, can also be used.
• Precursors for fluorinated polymers with one aromatic ring and one sp 2 C-sp 3 C-F type bond have the general formula: (C 6 H 5 . n F n )-CH 3 . m F m , where n is an integer of 1, 2, 3, 4, or 5, and m is an integer of 1, 2, or 3.
• a prefe ⁇ ed precursor of a fluorinated polymer is C 6 F 5 -CF 3 .
• Precursors for fluorinated polymers with one aromatic ring and two sp 2 C-sp 3 C- F type bonds have the general formula:
• the invention comprises new methods and precursors for depositing low dielectric materials. These new methods and precursors have advantages over conventional methods. During conventional manufacture of semiconductors using spin-on glass (SOG) methods, defects in the dielectric layers can form, especially in locations where there is a channel between metal lines. Such defects in the dielectric layers result in the formation of cracks or "voids" in the dielectric material. These voids and cracks result in trapping moisture, etching gas, or photoresist contaminants and ultimately lead to the degradation and loss of device reliability. Therefore, the present invention provides precursors which can be deposited using chemical vapor deposition (CVD) and transport polymerization (TP) to avoid the problem.
• CVD chemical vapor deposition
• TP transport polymerization
• a precursor is placed directly on the substrate which will have the thin film of low dielectric material applied.
• the wafer and precursor are exposed to an energy source such as heat, plasma, or electromagnetic radiation to "dissociate” or “crack” the precursor molecule directly on the wafer to form the reactive intermediate.
• the reactive intermediate molecules then polymerize with each other to form the thin film.
• the cracking step is performed an a chamber other than where the deposition step is performed.
• This "cold-chuck" method confers several advantages.
• the cracking efficiency can be optimized by selecting appropriate conditions of plasma density, photon energy, or temperature.
• the density of the intermediate molecules can be regulated to niinimize the formation of unwanted side products, such as re-formed precursors.
• the wafer is not exposed to the harsh conditions of precursor dissociation, fragile structures containing aluminum or other thermally sensitive materials are less likely to become damaged.
• Deposition of polymer layers of a few nanometers (nm) to >7000 nm can be achieved, along with eliminating or greatly reducing the number of voids. In principle, layers of polymer of molecular dimensions can be deposited.
• the invention provides the novel precursors for the deposition of void-free dielectric films.
• the type of functional group used deteirr ⁇ nes the optimal type of TP or CVD process should be used. These will be discussed below.
• the concentration of the fluorinated aromatic silane is in the range of from about 5% to 100%, and is preferably 20%.
• the fluorinated aromatic siloxane is used in the range of from about 5% to about 100%, and is preferably 20%.
• PECVD plasma enhanced chemical vapor deposition
• TP photon-assisted transport polymerization
• no oxidants are required, but in a thermal TP or thermal CVD process an oxidant such as H 2 0 2 or N0 2 is added to oxidize the Si atoms of SiH 4 or other silane.
• Other suitable oxidants are oxygen containing organic or in organic compounds, such as oxalic acid.
• H 2 0 2 its concentration should be in the range of about 10% to about 50%, and is preferably about 30%.
• Thermal TP is carried out in a chamber 100 shown in Figure 1.
• the precursors are contained within a precursor tank 104, flow through a pipe 108 into a mass flow controller 112 from which they are controllably released through another pipe 116 into the chamber 120 within which is a container 124 with a cracking device that may comprise a catalyst 128.
• the precursors are heated by a conventional resistive heater 132 to generate the reactive intermediate radicals. Rates of precursor flow range from 0.2 SCCM to 100 SCCM, preferably between 2 and 5 SCCM, and most preferably at 3 SCCM. Temperatures of reactions without catalysts should range from about 700° C to about 800° C, preferably are in the range of from about 700° C to about 750° C, and most preferably at about 750° C.
• temperatures can be as low as about 350° C.
• the pressure in the chamber 120 needed for the cracking reaction should be in the range of about 1 milliTorr to about 500 Ton, and is preferably about 10 milliTorr.
• the intermediates flow to a diffusion plate 136 where the bulk flow is diverted away from the wafer 140.
• the dif usion plate 136 can be positioned as desired within the chamber, to optimize the pattern of flow of intermediates to the wafer.
• the intermediates then diffuse to the wafer 140, which is held on a cold chuck 144 which is maintained at a temperature lower than the cracking device by a chiller 148. Temperatures are maintained by any conventional cooling method including liquid nitrogen or reverse Peltier methods.
• Temperatures of the chuck should be in the range of about -120° C to about 300° C are useful, prefe ⁇ ed temperatures are in the range of about -40° C to about 100° C. and the most preferred temperature is about -20° C.
• the chamber 120 is connected via a pipe 152, to a cold trap 156, and another pipe 160 connects the trap to a pump 156 to maintain low pressure in the chamber 120.
• the cold trap 156 protects the pump 160 from deposition of precursors and intermediates in the chamber 120.
• Thermal TP and CVD processes requiring catalysts to dissociate precursor molecules into reactive intermediates can use any conventional catalyst.
• An ideal catalyst useful for this invention should provide high reactivity, high selectivity, long process life cycle, high recycle capability, and less severe pressure and temperature requirements. It should be inexpensive, safe for human handling, and should be environmentally friendly.
• the catalyst should crack or cleave the Si-H and crack or oxidize the C-H bonds. Further, the catalyst should not add any metal or metal compound, or reactive ion such as F " into the dielectric film during deposition. Serious reliability problems occur when a metal contaminant resides within the dielectric materials. Other serious problems occur when a highly reactive ion such as F " is introduced into the film. The ion can break interatomic bonds within the hydrocarbon moieties of the dielectric material, resulting in lowered mechanical strength.
• Catalysts that are useful for this invention include dehydrogenation catalysts, reforming catalysts, and oxidative dehydration catalysts. a. Dehydrogenation Catalysts
• the temperatures and times needed to complete pyrolysis can be reduced by employmg a catalyst m the chamber
• An ideal catalyst useful for this mvention should provide high reactivity, high selectivity, long process life cycle, high recycle capability , and less severe pressure and temperature requirements It should be mexpensive, safe for human handling, and should be environmentally friendly
• the ideal catalyst should crack or cleave the Si-H and C-H bonds without crackmg or cleaving the C-F bonds Further, the catalyst should not add any metal or metal compound mto the dielect ⁇ c film during deposition Se ⁇ ous reliability problems occur when a metal contaminant resides within the dielect ⁇ c mate ⁇ als
• any commonly used dehydrogenation catalyst is suitable These catalysts are also called “protolytic crackmg catalysts”, or “oxidative dehydrogenation catalysts”, m petroleum processmg Additionally, most “dehydrocychzation catalysts” and some of the “aromatization catalysts” for hydrocarbon processmg are also useful for this mvention, because aromatization normally mvolves dehydrogenation
• Potassium fer ⁇ te (KFe0 2 ) on iron oxide is an example of a suitable catalyst which is commercially available
• the fer ⁇ te commonly comp ⁇ ses a promoter that may contain a salt of oxide of a Group (IIA) metal, such as Mg, Ca, or Sr, and a Group VB or VIB metal, such as V, Nb, Cr, Mo or W [See J I Krochiwitz ed , Encyclopedia of
• mdust ⁇ al catalysts mclude Cu and Zn oxides on alumina and Cu, Ag or Cu-Ag alloy m the form of gauge or as metal deposited on a low surface area support such as kaolin, clay and active carbon
• Other supports or earners can mclude asbestos, pumice, kiesselguhr, bauxite, CuO, Cr 2 0, MgC0 3 , Zr0 2 , and Zeolites
• These catalysts are active by virtue of an oxide layer on the metals, and are used for hydrogen generation from methanol
• Catalysts consist of copper chromite, bismuth molybdate, iron molybdate, or tm phosphate on similar supports are also useful [See J I Krochiwitz ed , Encyclopedia of Chemical Technology, 4th edition, Catalysis and Catalysts, Vol 5 320 (1991), mcorporated herem fully by reference, J J McKetta, Ed , Encyclopedia of Chemical Processing and Designs Dehydrogenation, Vol 14
• reformmg catalysts used m petroleum reforming processes can also be used A first group of these mclude transition metal oxides, such as V 2 0 5 , Mo0 3 , W0 3 and Cr 2 0 3 in bulk form or preferred on a non-acid support such as silica, neutral alumma or active carbon [See Me ⁇ audeau and
• catalysts include Shell 205TM, which consists of 62 5% Fe 2 0 3 , 2 2% Cr 2 0 3 , and 35 3% K 2 C0 3 , and Dow Type BTM catalyst, which consists of calcium and nickel phosphates promoted with a small amount of chromium oxide
• Another group of reformmg catalysts useful for dehydrogenation m clude noble metals on acid supports The most commonly used catalysts are Pt (0 3 to 0 7%) and Pt/Re on a chlo ⁇ ded (acidified) alumma (e g , ⁇ - or ⁇ -Al 2 0 3 )
• the bimetallic Pt/Re- alumina is preferred for its longer life time
• Pt, Ga or An modified H-ZSM- 5TM, or Pt on medium-pore zeolite support such as In-ZSM-5TM is also very effective
• MFI H-GalloSihcates
• M Si/Ga, Na/Ga, Al
• rare earth metal exchanged Y- zeohtes or ultra stable Y-zeohtes (8) Ti oxide paired with Zr oxide, (9) M plated onto aluminum, where M is Ni, and Ni, Cr, and Al alloys
• catalysts may lose reactivity due to changing their oxidative state or coke formation
• the life t me of the catalysts can be mcreased at high operatmg temperatures or high partial pressure of hydrogen If catalysts lose activity by coke accumulation, they can be regenerated by careful oxidation followed by reduction with hydrogen before bemg returned to service [See J J McKetta ed , Encyclopedia of Chemical Processing and Designs Catalysis and Catalysts Vol 6 420, Petroleum Processing, Catalyst Usage, Vol 35:89 Marcel Dekker, Inc. (1992), incorporated herein fully by reference.
• the intermediates After leaving the cracking device, the intermediates pass through a diffusion plate to disperse the intermediates evenly over the wafer surface.
• the intermediates deposit upon the wafer, which is held on a chuck, which, in turn, is connected to a chiller to maintain a temperature of the chuck and wafer below the temperature of the chamber and the intermediates.
• the temperature of the cold chuck is maintained in the range of about -30° C to about +20° C, preferably at -20° C.
• Low pressure in the system is maintained by a vacuum pump with sufficient capacity to maintain the desired pressure within the CVD system. Condensation of precursors and intermediates on the pump is minimized by a trap placed between the deposition chamber and the vacuum pump.
• the sp 2 C-F-modified Si0 2 thin films can be prepared from thermal oxidation of C 6 F 5 -SiH 3 .
• An admixture of 40 mole % of SiH 4 and 60 mole % of C 6 F 5 -SiH 3 in an aqueous solution with 30% by weight of H 2 0 2 are dispensed separately through two flash evaporators onto a cold wafer inside a CVD system.
• the molar ratio of H 2 0 2 /(SiH 4 +C 6 F 5 -SiH 3 ) is about 3.5.
• the mixtures of H 2 0 2 , SiH 4 , and C 6 F s -SiH 3 is chilled as a thin film on the wafer.
• the wafer is then heated from -20° C to 500° C in vacuum at a heating rate of 10° C/min.
• the resulting thin film has a dielectric constant of 2.7 and an initial decomposition temperature of 480° C when
• Plasma enhanced TP is carried out generally using methods in the art. Takai et al., J. Appl. Phys. 17:399-406 (1984), incorporated herein fully by reference.
• the electron density in the plasma is in the range of about 10 12 to about 10 13 electrons/cm 3 .
• Low density plasma TP and CVD can be carried out at about 100 milliTorr to about 100 Ton.
• High density plasma (HDP) is characterized by electron densities in the range of about 10 13 to about 10 14 electrons/cm 3 .
• High density plasma TP and CVD can be carried out at pressures of about 0.1 milliTon to about 100 milliTon.
• reactants such as SiH 4 , or more generally siloxane such as Si(OCH 3 ) 4 are used.
• SiH 4 silicon dioxide
• Si(OCH 3 ) 4 silicon dioxide
• the presence of oxygen at high temperatures will induce oxidation, resulting in the formation of silicon dioxide (Si0 2 ) films having varying K based on varying the relative compositions of Si0 2 and sp 2 C-F bonded molecules.
• sp 2 C-F-con1aining starting materials such as (C 6 H 5 -F-)-,- Si(0CH 3 ) 4 . m wherein n is an integer of 1, 2, 3, 4, or 5, and m is an integer of 1, 2, or 3, (C 6 H 5 . n F n ) m -SiH 4 _ m wherein n is an integer of 1, 2, 3, 4, or 5, and m is an integer of 1, 2,
• C 6 F 5 -CF 3 or admixtures of these starting materials are delivered into a plasma enhanced transport system 200 depicted in Figure 2.
• Precursors are stored in a precursor holder 204.
• a carrier gas typically helium, is passed through a bubbling device to volatilize the precursor.
• the vaporized precursors flow through a pipe 208 and to a mass flow controller 212.
• the mass flow controller provides a precursor feed rate ranging from about 0.2 to about 500 standard cubic centimeter per minute (SCCM).
• the precursors flow from the MFC 212 through a pipe 216 and into a quartz tube 220 under low pressures in the range of from about 0.1 milliTon to 10 Ton, and preferably in the range from about 1 milliTon to about 3 milliTon.
• a carbon source such as CH 4 or C 2 H 2 is provided via a second feeder (not shown) and a second
• MFC (not shown) with a feed rate ranging from 0 to 500 SCCM.
• the prefened flow- rates of precursor into the plasma tube should be in the range of from about 0.2 SCCM to about 10 SCCM, and is most preferably in the range of about 0.5 SCCM to about 1 SCCM. Pyrolization takes place within the quartz tube by action of a radiofrequency
• Effective plasma 230 can be maintained by radio frequencies in a range of between about 1 kHz and 2.5 GHz. A prefened range is between about 400 KHz and about 13.56 MHz. Ideally, the RF frequency is about 13.56 MHz.
• the RF power should be in the range of about 30 Watts to 300 Watts, preferably about 100 Watts to 250 Watts, and more preferably about 200 Watts.
• the plasma 230 then proceeds into the deposition chamber 234 which is heated by a heater 238 to prevent deposition of precursor intermediates on the chamber walls.
• the pressure within the chamber 230 is maintained at a pressure between about 0.1 milliTon and about 10 Ton.
• the flow of plasma is adjusted by a flow pattern adjuster 242, which can be moved within the chamber.
• Moving the flow pattern adjuster 242 in the vertical direction adjusts the flow rate and distribution pattern of the plasma as it enters the chamber.
• Moving the flow pattern adjuster in the horizontal direction adjusts the distribution of plasma to different parts of the wafer 250.
• a gas dispersion plate 246 evens the delivery of the intermediates to the wafer 250.
• the wafer 250 is cooled by the chuck 254, which is cooled by liquid nitrogen, reverse Peltier effect, or other conventional cooling device 258, and is maintained at a temperature in the range of about -30° C to about +20° C, and is preferably about -10° C.
• the deposition chamber 224 is connected via a pipe 262 to a cryogenic trap 266, which is connected via a pipe 270 to a pump 276, which maintains the pressure within the chamber at the desired level.
• a high density plasma deposition process can also be used to dissociate precursors.
• the electron density is in the range of from about 10 13 to 10 14 electrons /cm 3 . This process must be carried at lower pressures than conventional plasma processes.
• a inductively coupled high density plasma apparatus 300 is shown schematically in Figure 3.
• a precursor delivery system 304 volatilizes or vaporizes the precursor, which flows through a pipe 308 and an anode gas injector 312 into the deposition chamber 316.
• the anode gas injector 312 is attached to RF generators 320 which are matched by matching controllers 324.
• the output of the RF generators 320 passes through inductive coils 328 to produce an electrical field.
• the wafer 332 is held by a cathode electrostatic chuck 336, which is connected to the RF generator 320.
• IR sources 340 provide additional heating of precursors to decrease the needed plasma power and to inhibit condensation of materials on the walls of the chambers.
• the plasma source power needed for a wafer of 8 inch diameter is in the range of about 100 Watts to 4000 Watts, and preferably about 2000 Watts. For wafer of other sizes, the power should be adjusted accordingly.
• Power should range from about 1 Watt/cm 2 wafer surface area to about 15 Watts/cm 2 , preferably from about 2 Watts/cm 2 to about 10 Watts/cm 2 , and most preferably about 5 Watts/cm 2 .
• the chamber pressure is maintained in the range of 0.01 milliTon to 10 milliTon, and preferably below 5 milliTon.
• the wafer temperature is in the range from about 300° C to 450° C, and is preferably about 350° C.
• thin films made using plasma methods contain lower carbon content than films made using thermal methods.
• Films with decreased carbon content are made using greater plasma power.
• One theory to account for this is that increasing the plasma power increases the dissociation of the precursors by more completely cracking the precursors. Decreasing the carbon content of films decreases the trapping of electrons in the film, and leads to more reliable, long lasting devices.
• the deposition rate can be regulated by adjusting the flow rate of precursors into the plasma generator and thereby adjusting the flow rate of reactive intermediates over the wafer.
• the residence time within the plasma generator decreases, and this can result in less complete cracking.
• further increases in the efficiency of the plasma reactions can be achieved by heating the chamber. This can be done using a conventional resistive heater or using an infrared (IR) heater.
• IR inadiation is used, and the wavelength of the IR radiation is chosen to maximal absorption by the precursor.
• the above reaction is designed to accommodate wafers with diameters of about 200 mm.
• Thin films of this invention are deposited at a rate of about 1000 A/min. Films deposited using this system have dielectric constants of 2.3 to 3.5, and have Td in the range of about 350° C to 500° C, depending on the fluorine content. Increasing the fluorine content decreases the dielectric constant.
• the thin films have no initial weight loss; Td and Tg are temperatures ranging from 450° C to 500° C under nitrogen atmosphere.
• Example 2 Manufacture of a Thin Film Low Dielectric Layer Using Plasma Enhanced Transport Polymerization.
• a thin film of C 6 F 5 -Si(OCH 3 ) 3 is made using a parallel type of plasma reactor as depicted in Figure 3.
• the compound is delivered into the chamber employing a bubbling device using Ar as a carrier gas.
• the compound is introduced at a feed rate of 50 SCCM.
• the operating chamber pressure is 20 milliTon.
• Effective plasma is maintained by an RF frequency of 13.56 MHz at a power of 1.3 Watts/cm 2 applied to the upper electrode with a wafer placed on the lower electrode which is grounded.
• the wafer temperature is maintained at 400° C.
• the thin film made by this process has a dielectric constant of 2.65, and has no initial weight loss at 500° C under nitrogen atmosphere.
• photon assisted precursor cracking is also part of this invention. Because specific chemical bonds have specific energies, and because these energies can be supplied as photons, electromagnetic radiation is a prefened method of practicing this invention.
• a transport polymerization system 400 using electromagnetic radiation is shown in Figure 4.
• Precursors are stored in a precursor tank 404 and then flow through a pipe 408 to a mass flow controller 412, where the precursor flow rate is regulated. Volatile precursor then passes through pipe 416 into a transparent tube 420.
• tube 420 is made of quartz, preferably a single quartz crystal.
• IR infrared
• tube 420 may be made of glass.
• tube 420 is made of MgF 2 , LiF, or CaF 2 .
• An ultraviolet (UV) source 424 is used to photolytically dissociate the precursor.
• VUV vacuum ultraviolet
• IR infrared
• the intermediates pass into the deposition chamber 432, which is heated by a resistive heater 436 to prevent deposition of intermediates on the walls of chamber 432.
• the flow of intermediates is adjusted using flow pattern adjuster 440. Moving the flow pattern adjuster 440 in the vertical direction adjusts the flow rate of and the distribution pattern of intermediates in the deposition chamber 432. Moving the flow pattern adjuster 440 in the horizontal direction adjusts the distribution pattern of intermediates in the deposition chamber 432.
• a gas dispersion plate 444 evens the delivery of the intermediates to the wafer 448.
• the wafer 448 is held by a cold chuck 452, which is maintained at low temperatures by a conventional cooling device, using liquid nitrogen, reverse Peltier effect, or any other cooling apparatus known in the art.
• the chamber 432 is connected via a pipe 460 to a trap 464, which is connected via another pipe 468 to a pump 472. The pump maintains the pressure within the deposition chamber 432 at the desired level, and the trap 464 ntinimizes the deposition of intermediates on the pump 472.
• the photon sources can be provided by ultraviolet (UV) light generated by mercury vapor discharge or metal halide lamps.
• UV radiation for transport polymerization can include (1) a mercury lamp that provides from 50 to 220 mWatts/cm 2 of UV ranging from 200 to 450 nm or (2) a metal halide lamp that provides from 40 to 160 mWatts/cm 2 of UV ranging from 260 nm to 450 nm. These UV sources provide photon energies ranging from 2 to 5 eV, which are sufficient for generating many radical intermediates.
• VUV vacuum ultraviolet
• Incoherent excimer radiation can provide a large number of UV and VUV wavelengths for photolytic processing of various chemicals.
• the prefened source is incoherent excimer radiation derived from dielectric barrier discharge. UV and VUV photons that are in the ranges of 3 to 5 eV are especially useful. These energy levels are comparable with the bonding energies of most chemical bonds, thus are very effective for initiating photochemical reactions (see Table 4).
• Table 4 shows the bonding energies in electron volts (eV) conesponding to certain bonds of this invention. This data is from Streitwiesser et al., Introduction to Organic Chemistry, Appendix II, University of California Press, Berkeley, California (1992), incorporated herein fully by reference.
• VUV is the most desirable form of energy for photon assisted transport polymerization.
• VUV or incoherent excimer UV sources can be provided by dielectric barrier or silent discharge.
• VUV can be generated using KrBr, Ar 2 , ArCl, ArBr, Xe 2 and F 2 gases.
• Xe emits at 172 nm
• XeCl emits at 308 nm.
• Table 2 nearly all of the chemical bonds of interest in polymer manufacture can be broken using photolytic methods. Because excimer radiation is selective for the energy of the specific bonds, excimer radiation from another source or plasma may be used simultaneously if it is desired to break other bonds at the same time.
• Such a combination of excimer and plasma sources are useful to break bonds of precursors of cross-linked poly(para-xylylenes). Because the leaving groups of these precursors may be different, it is desirable to break those bonds selectively to generate tri- and tetra- functional reactive intermediates.
• the conventional stainless steel or ceramic pipe or reactor used in the pyrolyzer will have to be replaced with a quartz tube or reactor.
• the transparent tube shown in Figure 4 can be made of any UV transparent material such as quartz, preferably a single quartz crystal.
• the transparent tube When using VUV, the transparent tube must be made of a material transparent to VUV wavelengths. Crystals of MgF 2 , LiF, or CaF 2 are prefened. Table 5
• photon assisted dissociation occurs immediately above the wafer surface onto which the film is to be deposited. Because no transport of intermediates is needed, the efficiency of deposition is increased. Further, the photon energy or mixtures of photon energy (from mixed excimer gases) could be made to both dissociate the precursor as well as promote nucleation and adhesion of the polymer based films. D. General Methods for the Manufacture of Low Dielectric Thin Films
• a combined photon-plasma process is used for dissociation of precursors and deposition of thin films of low dielectric materials.
• Photon energy is used to generate a plasma in certain gases.
• the attributes of plasma generally high rates of dissociation, along with the cool photon energy source, provides a unique method for both precursor dissociation and even film deposition.
• infrared (IR) radiation can be used to heat reactor elements and precursors. Pre-heating precursors increases the efficiency of photon and plasma dissociation of the precursors.
• the photon plasma can be directed toward the surface on which films are being deposited.
• FIG. 5 depicts a schematic diagram of a TP and CVD reactor 500 embodying the elements for photon-plasma and IR dissociation and deposition.
• Precursors 504 are stored in a precursor container 508 which is connected via a pipe 512 to a mass flow controller 516.
• precursors are transported into a dissociation reactor 524 which houses the dissociation chamber 528.
• the wall of reactor 524 is made of crystalline materials such as LiF, MgF 2 , or CaF 2 , which permits light of vacuum ultraviolet wavelengths to pass.
• Vacuum ultraviolet and ultraviolet light is generated by a silent discharge plasma generators 532, which are place inside infrared heaters 536.
• the infrared heaters 536 are placed inside DC magnets 540 and AC magnets 544. The magnets regulate the flow of plasma during dissociation, and the reactive intermediates so generated are transported to a deposition reactor 550.
• the deposition reactor 550 contains a deposition chamber 560 contaiiiing a gas and reactant dispersion manifold 554, a gas and reactant dispersion plate 558.
• the walls of the deposition chamber are made of crystalline materials such as LiF, MgF 2 , or CaF 2 , which permits light of vacuum ultraviolet wavelengths to pass.
• the gas dispersion manifold 554 and the gas dispersion plate 558 are used to adjust the distribution and homogeneity of the intermediates.
• the intermediates are directed toward the wafer 562, which is held on a cold chuck 564.
• the gas dispersion manifold 554 and dispersion plate 558 are connected in parallel to a DC voltage bias anode 568, a DC voltage bias cathode 569, an AC voltage bias anode 570, and an AC voltage bias cathode 571.
• Silent discharge plasma generators 572 are placed outside the deposition chamber 560.
• Infrared heaters 574 are placed outside the silent plasma discharge generators 560 and DC magnets 578 and AC magnets 580 are placed outside the infrared heaters 574.
• the trap 588 protects the pump from deposition of intermediates.
• the deposition chamber can be used without the dissociation reactor.
• Precursors are placed directly on wafer 562, and the chuck 564 is not cooled.
• IR, UV, or VUV radiation is directed toward the wafer 562. The radiation dissociates the precursor, and deposition of intermediates and polymerization takes place on the wafer.
• Table 6 shows process conditions for combined photon-plasma assisted precursor dissociation using chamber 528
• Table 7 shows process conditions for combined photon-plasma precursor deposition in chamber 560.
• the plasma density is reported as electron density, but it is to be noted that ion density must be the same to maintain charge neutrality of the plasma. Any non-uniformity of charge distribution can result in plasma damage to the thin film of low dielectric material, as well as imparting charge to the integrated circuit components.
• Control of the plasma is by a magnetic field within the precursor chamber and in the deposition chamber.
• the plasma In the precursor reactor, the plasma is confined to any desired area, such as the center of the reactor. Additionally, by alternating the polarity of the magnetic field stirs the plasma, ensuring even energy distribution within the plasma, thereby increasing the efficiency of dissociation of precursor molecules into reactive intermediates.
• the magnetic field In the deposition chamber, the magnetic field is used to control the pattern of distribution of intermediates over the wafer. This would serve two purposes: (1) to direct the deposition of precursor to the desired portion of the surface, thus conserving the precursor, and (2) rniiiimize film deposition on other parts of the reactor chamber, thus minimizing the required cleaning, rriiiiimizing particle generation, and simplifying the reactor chamber design.
• a bias voltage in the form of direct cunent (DC) or alternating cunent (AC) can be applied and modulated. Pulsed voltages can be used to alter the flow pattern of ions to either accelerate, decelerate, or to regulate the density of the plasma ions in the stream reaching the wafer. Optimization of ion velocity and flow, thus can be obtained using various combinations of magnetic field and bias voltage.
• Table 8 shows the ranges of the various magnetic field and bias voltage variables which are regulated in this invention.
• Other reactors and reactor configurations may be used, as exemplified by the above cited co-pending applications incorporated herein fully by reference.
• FIG. 6 depicts a diagram of a multi-level integrated circuit chip 600 embodying the features of this invention.
• the substrate 604 has a source region
• a drain region 612 a drain region 612 a polysilicon gate 616.
• a first interlevel dielectric (ILD) layer 620 overlays the substrate 600 and polysilicate gate 616. The wafer is subsequently planarized using chemical mechanical polishing another method known in the art.
• a floating polysilicon gate 624 is overlain by a second ILD layer 628.
• the wafer is agam plana ⁇ zed, a first metal line 632 and a first lntermetal dielectric (IMD) layer 636 are deposited The wafer is agam polished On top of the IMD layer 636, a third metal lme 640 and a second ILD layer 644 is deposited The wafer is agam plana ⁇ zed
• the mvention mcludes novel precursors contorting a fluo ⁇ nated silane, fluo ⁇ nated siloxane and fluorocarbons, each containing a fluo ⁇ nated aromatic moiety
• the precursors are suitable for making polymers with low dielect ⁇ c constants and high thermal stability
• the mvention includes methods for making polymers for mtegrated circuit manufacture usmg novel fluo ⁇ nated siloxanes, fluorocarbons, and fluormated aromatic moieties
• the mvention mcludes mtegrated circuits made usmg fluormated siloxanes, fluorocarbons, or fluo ⁇ nated aromatic moieties, with low dielect ⁇ c constants
• the polymers made from the disclosed precursors have low dielect ⁇ c constant and high thermal stability Therefore, mtegrated circuits made from these precursors have improved elect ⁇ cal and mechanical properties

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