NANOPOROUS DIELECTRIC THIN FILMS

Abstract: A process for forming a nonoporous silica dielectric coating on a substrate. A substrate containing a deposited film is suspended within a sealable hotplate, while remaining free of contact with the hotplate. The hotplate is sealed and an inert gas is flowed across the substrate. The hotplate is heated to a temperature of from about 350 DEG C or higher, and the substrate is forced to contac the heated hotplate. The substrate is heated for a time that sufficiently removes outgassing remnants from the resultant nanoporous dielectric coating.

Description: NANOPOROUS DIELECTRIC THIN FILMS CROSS REFERENCE TO RELATED APPLICATION This application claims the benefit of U.S. provisional patent application serial number 60/098,515, filed August 31, 1998 which is incorporated herein by reference. BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention relates to dielectric films, more particularly nanoporous dielectric films, and to a process for their manufacture. The nanoporous dielectric films provide low dielectric constants. Such films are useful in the production of integrated circuits. DESCRIPTION OF THE PRIOR ART In the production of advanced integrated circuits that have minimum feature sizes of 0.25 micrometers and below, problems of interconnect RC delay, power consumption and crosstalk become significant. The use of low dielectric constant (K) materials for interlevel dielectric and intermetal dielectric applications partially mitigate these problems. However, each of the material candidates which are under consideration by the industry, having dielectric constants significantly lower than the currently employed dense silica, suffer from disadvantages. Most low dielectric constant materials developments use spin-on-glasses and fluorinated plasma chemical vapor deposition SiO with K of greater than 3. Some organic and inorganic polymers have dielectric constants in the range of about 2.2 to 3.5, however, these have the problems of low thermal stability, poor mechanical properties including low glass transition temperature, sample outgassing, and long term reliability questions. Another approach has been to employ nanoporous silica which can have dielectπc constants in the range of about 1 to 3. Porous silica is attractive because it employs similar precursors, e.g. tetraethoxysilane (TEOS) as is presently used for spm-on glass (SOG's) and CVD SιO , and due to the ability to carefully control pore size and pore distπbution. In addition to having low dielectπc constants, nanoporous silica offers other advantages for microelectronics including thermal stability up to 900°C; small pore size (« microelectronics features), use of mateπals, namely silica and its precursors, that are widely used in the semiconductor industry; the ability to tune dielectπc constant over a wide range; and deposition using similar tools as employed for conventional spm-on glass processing. EP patent application EP 0 775 669 A2, which is incorporated herein by reference, shows one method for producing a nanoporous silica film with uniform density throughout the film thickness. Higher porosity mateπals not only leads to a lower dielectπc constant than dense mateπals, but such also allow additional components and processing steps to be introduced. Mateπals issues include, the need for having all pores significantly smaller than circuit feature sizes; the strength decrease associated with porosity; and the role of surface chemistry on dielectπc constant, loss and environmental stability. Density, or its inverse, porosity, is the key nanoporous silica parameter controlling property of importance for dielectπcs Properties may be vaπed over a continuous spectrum from the extremes of an air gap at a porosity of 100% to dense silica with a porosity of 0% As density increases, dielectπc constant, hardness and mechanical strength increase but the pore size decreases. Nanoporous silica films are fabπcated by using a mixture of a solvent and a silica precursor which is deposited on a wafer by conventional methods such as sp -coating, dip-coating, etc. The precursor must polymeπze after deposition and be sufficiently strong such that it does not shπnk during drying. Film thickness and density/dielectπc constant can be controlled independently by using a mixture of two solvents with different volatility The more volatile solvent evaporates duπng and immediately after precursor deposition, while the less volatile solvent remains as the pore fluid The silica precursor, typically a partially hydrolyzed and condensed product of TEOS, is polymeπzed by chemical and/or thermal means until it forms a gel layer. Using this approach, a nanoporous silica film is obtained with uniform density throughout the film thickness. Normally in sol-gel processing to produce porous silica, a liquid catalyst such as an acid or base is added to the silica precursor/solvent mixture in order to initiate polymeπzation This catalyst addition is often accompanied by the addition of water which is a reactant in the silane hydrolysis and condensation reactions which result in polymeπzation In semiconductor processing, film cuπng is an essential step to allow the film to reach thermal equihbπum Often times the thermal budget for back end of the line integration processing (i.e. metallization) is different than that of the temperature needs to form low dielectπc constant (K) insulating layers, therefore it is essential that the low K film be exposed to the highest temperature it will see duπng integration processing to prevent remnant outgassing Outgassmg of the film will damage the device structuies and decrease processing yield. Wafer cuπng via a high temperature hotplate could have beneficial effects terms of improving the mechanical properties of the nanoporous silica thinfilm. A high temperature hotplate could increase the extent of crosslinkmg which would directly improve the mechanical integπty of the film In addition to mechanical properties, high temperature hotplates could improve the wafer throughput due to the short processing times. Conventional SOG's are typically cured via a hoπzontal tube furnace The time required to reach thermal equihbπum is on the order of 30 minutes with a ramp up and a ramp down time period which more than doubles the over-all processing time In conventional wafer curing or drying of low K nanoporous dielectric films, SOGs routinely requires 30 minutes of elevated temperature exposure time. Ramp up and ramp down time for thermal equilibrium more than doubles the exposure time. Thermal equilibrium is needed to expose the films to the highest temperature during integration to prevent remnant outgassing. Wafer curing may have adverse effects on film hardness and mechanical strength. The present invention solves these problems by conducting a series of processing steps which enable the production of nanoporous silica thin films with minimum process time and more consistent uniformity of film thickness. SUMMARY OF THE INVENTION The invention provides a process for producing a cured dielectric film on a substrate which comprises depositing a nanoporous silica dielectric precursor onto a substrate which precursor comprises at least one hydrolysed and condensed alkoxysilane composition, and then heating the substrate in a substantially oxygen free environment at a temperature of about SSO^C or greater, for a time period of at least about 5 seconds. The invention further provides a process for curing a dielectric film on a substrate which comprises the step of treating a suitable substrate comprising a dielectric film, in a substantially oxygen free environment by heating the substrate to a temperature of about SSO^C or greater, for a time period of at least about 5 seconds. The invention also provides a process for curing a nanoporous silica dielectric film on a substrate which comprises the step of treating a suitable substrate comprising a dried nanoporous silica film, in a substantially oxygen free environment by heating the substrate to a temperature of about 350^C or greater, for a time peπod of at least about 5 seconds The invention also provides a process for cuπng a nanoporous silica dielectπc film on a substrate which compπses the steps of (a) suspending a suitable substrate within a heating element, a substantially oxygen free environment, wherein the substrate remains free of contact with the heating element, the substrate compπs g a dπed nanoporous silica film, (b) cuπng the dπed nanoporous silica film sufficiently to remove outgassing remnants from the dπed nanoporous silica film; then, (c) removing the cured, dπed suitable substrate from the heating element. The invention further provides a process for cuπng a nanoporous silica dielectπc film on a substrate which compπses the steps of (a) suspending a suitable substrate within a sealable hotplate, wherein the substrate remains free of contact with the hotplate, wherein the substrate compπses a dπed nanoporous silica film; (b) sealing the hotplate, wherein the suspended substrate is contained therein; (c) passing an amount of inert gas across the substrate effective to displace non-inert gases adjacent to the substrate; (d) heating the hotplate to a temperature of from about SSO^C to about όOO^C, (e) contacting the substrate with the heated hotplate; and, (f) removing the substrate irom the hotplate Additionally, the invention provides a process for cuπng a nanoporous silica dielectπc film on a substrate which compπses the steps of (a) suspending a suitable substrate withm a sealable hotplate, wherein the substrate remains free of contact with the hotplate, wherein the substrate compπses a dπed nanoporous silica film; (b) sealing the hotplate, wherein the suspended substrate is contained therein; (c) drawing a vacuum within the hotplate effective to create a substantially oxygen free environment adjacent to the substrate, (d) heating the hotplate to a temperature of from about SSO^C to about όOO^C; (e) contacting the substrate with the heated hotplate; and, (f) removing the substrate from the hotplate. By means of this invention, the dielectric constant of the nanoporous silica dielectric coating on a substrate achieves a low dielectric constant (K) below 3, while maintaining improved hardness and mechanical strength. Remnant outgassing is minimized with rapid curing periods that significantly increase film production rates. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of the preferred embodiment having a substrate with a dried film thereon processed in a hotplate according to this invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is used in the production of advanced integrated circuits, preferably with integrated circuits having reduced minimum feature sizes, more preferably having minimum features sizes of from about 0.25 micrometers and below, and most preferably having minimum features sizes of from about 0.18 micrometers and below. A film on a substrate possesses dielectric properties through an improved curing process of the film. Preferably the dielectric film comprises a nanoporous dielectric coating, which more preferably is a spin-on film. This includes curing the film in a substantially oxygen free environment, such as by enveloping the wafer containing the film in an inert gas, and heating the enveloped wafer to an elevated temperature of from about 350 ^C or greater for a time period of greater than about 5 seconds. Fabrication of the Dried Nanoporous Silica Film In the practice of the present invention, a suitable substrate has been formed. The suitable substrate comprises a dried nanoporous silica film which has been deposited or placed on a substrate. Generally, the substrate is a silicon wafer substrate that is suitable to be processed into an integrated circuit or other microelectronic device. Suitable substrates for the present invention non-exclusively include semiconductor mateπals such as gallium arsenide (GaAs), silicon and compositions containing silicon such as crystalline silicon, polysihcon, amorphous silicon, epitaxial silicon, and silicon dioxide (SiO 2 ), germanium and mixtures thereof. Lines, when present, are typically formed by well known lithographic techniques and may be composed of a metal, an oxide, a nitπde or an oxynitπde. Suitable mateπals for the lines include silica, silicon nitπde, titanium nitπde, tantalum nitπde, aluminum, aluminum alloys, copper, copper alloys, tantalum, tungsten and silicon oxynitπde. These lines form the conductors or insulators of an integrated circuit. Such are typically closely separated from one another at distances of about 20 micrometers or less, preferably 1 micrometer or less, and more preferably from about 0.05 to about 1 micrometer. A liquid dielectπc layer, preferably a spm-on glass in a suitable solvent is applied to the substrate surface under ambient conditions. The dielectπc layer may compπse a silsesquioxane polymer, a siloxane polymer, a poly(arylene ether), a fluoπnated poly(arylene ether), polymeπc dielectπc mateπals or mixtures thereof. Polymeπc dielectπc mateπals useful for the invention include hydrogensiloxanes which have the formula [(HSiOi 5 ) x O y ] n hydrogensilsesquioxanes which have the formula (HSiOj 5 ) n , and hydroorganosiloxanes which have the formulae [(HSiOi 5 ) x O y (RSιOι 5 ) z ] n , [(HSiOi 5 ) x (RSiOi 5 ) y ]n and [(HSiOi 5 ) x O y (RSιO, 5 ) z ] n . In each of these polymer formulae, x= about 6 to about 20, y=l to about 3, z= about 6 to about 20, n=l to about 4,000, and each R is independently H, Cj to C 8 alkyl or C 6 to C 1 aryl. The weight average molecular weight may range from about 1,000 to about 220,000. In the preferred embodiment n ranges from about 100 to about 800 yielding a molecular weight of from about 5,000 to about 45,000. More preferably, n ranges from about 250 to about 650 yielding a molecular weight of from about 14,000 to about 36,000. Useful polymers within the context of this invention nonexclusively include hydrogensiloxane, hydrogensilsesquioxane, hydrogenmethylsiloxane, hydrogenethylsiloxane, hydrogenpropylsiloxane, hydrogenbutylsiloxane, hydrogentert-butylsiloxane, hydrogenphenylsiloxane, hydrogenmethylsilsesquioxane, hydrogenethylsilsesquioxane, hydrogenpropylsilsesquioxane, hydrogenbutylsilsesquioxane, hydrogentert- butylsilsesquioxane and hydrogenphenylsilsesquioxane and mixtures thereof. Useful organic polymers include polyimides, fluoπnated and nonfluoπnated polymers, in particular fluoπnated and nonfluoπnated poly(arylethers) available under the tradename FLARE M from AlhedSignal Inc., and copolymer mixtures thereof. The hydroorganosiloxanes, poly(arylene ethers), fluoπnated poly(arylene ethers) and mixtures thereof are preferred Preferred siloxane mateπals suitable for use in this invention are commercially available from AlhedSignal Inc. under the tradename Accuglass ® . The polymer component is preferably present in an amount of from about 10 % to about 50 % by weight of the composition. A more preferred range is from about 15 % to about 30 % and most preferably from about 17 % to about 25 % by weight of the composition. Typically, a nanoporous silica wet gel film is prepared using a mixture of at least one solvent and a silica precursor. The mixture is deposited on a silicon wafer substrate suitable for producing an integrated circuit, by conventional methods such as spin-coat g and dip-coatmg, and/or sol-gel techniques. A solvent composition having multiple solvents, preferably two solvents, with different volatilities may be used. Film thickness and density/dielectπc constant may be independently controlled by using a mixture of two solvents with distinct volatilities. The more volatile solvent evaporates duπng and immediately after precursor deposition. The silica precursor is applied to the substrate and polymeπzed by chemical and/or thermal means until it forms a gel. Typically, the silica component of the nanoporous silica film may compπse any silica mateπal known in the art, including alkoxysilanes such as tetraethoxysilane (TEOS) and tetramethoxysilane Preferably the solvent composition comprises at least one a relatively high volatility solvent and at least one a relatively low volatility solvent. The high volatility solvent evaporates duπng and immediately after deposition of the silica film. A relatively high volatility solvent is one which evaporates at a temperature below, preferably significantly below that of the relatively low volatility solvent. The relatively high volatility solvent preferably has a boiling point of about 120 °C or less, preferably about 100 °C or less. Suitable high volatility solvents nonexclusively include methanol, ethanol, n-propanol, isopropanol, n-butanol and mixtures thereof. Other relatively high volatility solvent compositions which are compatible with the other ingredients can be readily determined by those skilled in the art. Once applied on the substrate, the higher volatility solvent of the nanoporous silica wet gel film is then at least partially evaporated over a peπod of seconds or minutes. Slightly elevated temperatures may optionally be employed to accelerate this step. Typical temperatures may range from about 20 °C to about 80 °C, preferably range from about 20 °C to about 50 °C and more range from about 20 °C to about 35 °C. With the evaporation of the higher volatility solvent, the film is a viscous liquid of the silica precursors and the less volatile solvent, forming the dπed nanoporous silica film. The relatively low volatility solvent composition is one which evaporates at a temperature above, preferably significantly above that of the relatively high volatility solvent The relatively low volatility solvent composition preferably has a boiling point of about 175 °C or higher, more preferably about 200 °C or higher. Suitable low volatility solvent compositions nonexclusively include alcohols and polyols including glycols such as ethyl ene glycol, 1,4-butylene glycol, 1,5-pentanedιol, 1,2,4-butanetπol, 1,2,3-butanetπol, 2-methyl-propanetπol, 2-(hydroxymethyl)-l,3-propanedιol, 1,4-butanediol, 2-methyl-l,3- propanediol, tetraethylene glycol, tπethylene glycol monomethyl ether, glycerol and mixtures thereof Other relatively low volatility solvent compositions which are compatible with the other ingredients can be readily determined by those skilled in the art. With the removal of the low volatility solvent, the density/dielectric constant of the final film is fixed by the volume ratio of low volatility solvent to silica. The fabrication of the dried nanoporous silica film on the appropriate substrate, described above, provides a suitable substrate. A number of methods for the preparation of the suitable substrate comprising a nanoporous silica film on the substrate base are known to the art. Such substrates optionally have raised lines on the surface receiving the nanoporous film and preferably are suitable for the production of integrated circuits, e.g., with optional electronic elements and conduction pathways placed under, over and/or adjacent to the nanoporous film, in addition, a number of variations and improvements to these generally known methods for the preparation of nanoporous films are taught by co- owned U.S. patent application serial numbers, 09/046,473 and 09/046,474, both filed on March 25, 1998; U.S. patent application serial number 09/054,262, filed on April 3, 1998; U.S. patent application serial numbers 09/111,081; 09/111,082; 09/111,083 and 09/111,084 filed July 7, 1998; U.S. provisional patent application serial number 60/095,573 filed August 6, 1998; U.S. provisional patent application serial number 60/098,068 filed August 27, 1998; U.S. patent application serial numbers 09/140,855 and 09/141,287 filed August 27, 1998; U.S. provisional patent application serial number 60/098,515 filed August 31, 1998; U.S. patent application serial number 09/234,609 filed January 21, 1999; U.S. patent application serial number 09/235,186 filed January 22, 1999; U.S. patent application serial number 09/291,510 and 09/291,511 filed April 14, 1999; U.S. provisional patent application serial number 60/117,248 filed January 26,1999; and U.S. patent application serial number 09/360,131 filed July 23, 1999, the disclosures of which are incorporated herein by reference. Other dielectrics are taught in U.S. patent application serial numbers 09/055,244 and 09/055,516, both filed on April 6, 1998, and U.S. patent application serial number 08/955,802, filed on October 22, 1997, the disclosures of which are incorporated by herein by reference. The applied film component of the suitable substrate is further dπed and cured on the substrate in a manner consistent with the present invention, descπbed below Cunng of the Dπed Nanoporous Silica Film Cuπng the suitable substrate includes treating the film in an oxygen free environment by heating the enveloped treated substrate to an elevated temperature of from about 350 °® C or greater for a time peπod of greater than about 5 seconds. In a more preferred embodiment, the substrate is suspended within a heating element, such as a furnace, convection oven, hotplate or lamp which serves as a source of heat, while it remains free of contact with the heating element. An oxygen free environment is maintained by forcing an inert gas into the area around the substrate, which envelopes the suspended substrate in a non -reactive environment. The heating element is used to heat the substrate sufficiently to dry the film. After drying, the dπed substrate is then removed from the heating element. In the most preferred embodiment, the heating element compπses a sealable hotplate that seals the substrate m a controllable environment within the hotplate. An inert gas is used to displace non-mert gases adjacent to the substrate pπor to heating. The hotplate is heated to an appropπate temperature for drying the film, and the substrate is forced to be in contact with the heated hotplate, which dπes the film. A non-reactive, or substantially oxygen free, environment is maintained adjacent to the substrate to be treated. This non-reactive environment may be either an inert gas and/or vacuum that is placed along and against the sides of the substrate, that accordingly envelops or surrounds the film as well. This may be done by forcing a flow of an inert gas over the substrate to be treated in an amount and at a sufficient flow rate to displace oxygen adjacent to the substrate, which leaves the environment adjacent to the substrate substantially oxygen free. In another embodiment, a vacuum may be drawn around the substrate, which also creates a substantially oxygen free environment adjacent to the substrate Additionally, the sequential use of an inert gas in combination with drawing a vacuum may be used. As such, an inert gas may be passed adjacent to the substrate, followed by drawing a vacuum, in a manner to facilitate the creation of a substantially oxygen free environment. Thus, it will be appreciated that oxygen concentrations around the substrate to be treated are preferably maintained at a concentration that does not interfere and/or prevents oxidation of the film on the substrate. Preferably the oxygen concentration adjacent to the substrate to be treated e.g., by cuπng, is from about 20 ppm or less, more preferably from about 10 ppm or less, and most preferably from about 5 ppm or less. Exemplary inert gases include nitrogen, argon, and other like gases, including combinations thereof. The non-reactive environment adjacent to the substrate may be maintained at from about 1 atmosphere to about 1.5 atmosphere, when using inert gases. Using vacuum conditions, the environment is sufficiently evacuated to remove oxygen for the purpose of drying, preferably from about 0.001 atmosphere to about 0.5 atmosphere, more preferably from about 0.001 to about 0.3 atmosphere, and most preferably from about 0.001 atmosphere to about 0.2 atmosphere. The optimum amount of adjacent environmental ambient pressure for oxygen removal is determmable by those skilled in the art. Optionally the entire coating and cuπng process can be done while enveloped in an inert gas in a conventional cluster tool without breaking vacuum. The heating element may be any temperature controllable device known by those skilled in the art suitable to proper heating of the substrate. This includes, but is not limited to, combustion, electπcal, radiant, and/or other such devices. Preferably the heating element includes a furnace, convection oven or hotplate, more preferably a hotplate, and most preferably an electπcal hotplate. Preferably, the hotplate is heated to a temperature of from about 350^C or greater, more preferably from about 350°®C to about 600^C, still more preferably from about 400 "®C to about 500^0, and most preferably from about 425 ^ > C to about 450 =® C. The substrate is heated for a time that sufficiently removes outgassing remnants from the resultant nanoporous dielectπc coating Preferably, the substrate is heated for a time peπod of greater than about 5 seconds, and more preferably from about 1 minute or more. When the substrate is not placed in contact with a heating element, the heating preferably extends from about 1 minute to about 120 minutes, and more preferably from about 30 minutes to about 60 minutes. When the substrate is placed in contact with the hotplate, the heating preferably extends for a time peπod of from about 1 mmute to about 2 minutes, more preferably from about 1 mmute to about 1.5 minutes, and most preferably from about 1 minute to about 1.1 minutes. As seen m FIG. 1, in the preferred embodiment of the substrate 30 being placed in contact with the sealable hotplate 10, the hotplate 10 is pre-heated to a temperature of about 400 =® C. The substrate 30 is placed m a chamber 12 within the hotplate 10 on ceramic pms 14, and the hotplate 10 is closed with an airtight seal 16. Nitrogen 20 is flowed into the hotplate chamber 12 through an inlet 18 at approximately 60 liters per mmute for thirty seconds. The nitrogen 20 flowing into the chamber 12 displaces oxygen within the chamber 12 that is adjacent to the substrate 30, with the oxygen exiting from the sealed hotplate 10 through an outlet 22 having a pressure sensitive one-way valve. The substrate 30 is dropped from the pins directly onto the hotplate 10, where it remains for 1 mmute. The hotplate 10 is opened, and the substrate 30 is removed from the chamber 12 mside of the hotplate 10. Direct contact of the substrate 30 with the hotplate 10 causes a rapid drying of the wet gel film. The inert gas environment adjacent to the substrate 30 allows the drying to occur without contaminating the film. The resulting rapid process allows increased efficiency in the production of a nanoporous dielectπc coating formed on a substrate. The substrate produced by the inventive processes has a relatively high porosity, low dielectπc constant, silicon containing polymer composition formed thereon. The silicon containing polymer composition preferably has a dielectπc constant of from about 1 to about 3, more preferably from about 1.1 to about 2 5, and most preferably from about 1.3 to about 2.0. The pore size of the resulting nanoporous silica composition ranges from about 1 nm to about 100 nm, more preferably from about 2 nm to about 30 nm, and most preferably from about 3 nm to about 20 nm. The density of the silicon containing composition, including the pores, ranges from about 0.1 to about 1.9 g/cm , more preferably from about 0.25 to about 1.6 g/cm 3 , and most preferably from about 0.4 to about 1.2 g/cm 3 . Determination of the effectiveness of the produced nanoporous silica films is performed by elhpsometry, infrared spectra (IR) measurements, and dielectπc constant measurements. The following nonhmitmg examples serve to illustrate the invention. EXAMPLE 1 This example illustrates the use of a high temperature hotplate set at 400 °C yielding excellent nanoporous silica film qualities when fully characteπzed. The precursor is synthesized by adding 104.0 mL of tetraethoxysilane, manufactured by Pacific Pac of Holhster, CA, 47.0 mL of tπethylene glycol monomethyl ether, manufactured by Pacific Pac of Holhster, CA, 8.4 mL of deionized water, and 0.34 mL of IN mtπc acid, manufactured by J.T. Baker of Philhpsburg, NJ, together in a round bottom flask. The solution is mixed vigorously, then heated to -80 °C and refluxed for 1.5 hours to form a solution After the solution is allowed to cool, it is diluted 25% by weight with ethanol, manufactured by Ricca Chemical Company of Arlington, TX, to reduce the solution viscosity. The diluted precursor is filtered to 0.1 μm using a teflon filter. Approximately 8.0-10.0 ml of the precursor is deposited onto 8 " a. inch silicon wafers on a spin chuck, and spun at 2500 rpm for 30 seconds. The film is gelled and aged in a vacuum chamber by evacuating the chamber to -20 Hg, then 15M ammonium hydroxide, manufactured by Aldπch Chemical Company of Milwaukee, WI, is heated and equilibrated at 45 °C and dosed into the chamber to increase the pressure to -4.0 HHg foi 2-3 minutes. The chamber is then evacuated to -20.0 HHg and backfilled with nitrogen. The film is then solvent exchanged by which 20-30 mL of a 50/50 by volume mixture of acetone, manufactured by Pacific Pac of Holhster, CA, and hexamethyldisilazane, manufactured by Pacific Pac of Holhster, CA, are spun on the film at 250 rpmBs for 20 seconds without allowing the film to dry. The films are then spun dry at 1000 rpm for 5 seconds. The films are heated at elevated temperatures for 1 minute each at 175 °C and 320 °C in air. The film is then placed in a high temperature hotplate that had been pre-equilibrated to 400 °C. The process for the film placement includes opening the high temperature hotplate and placing the wafer on ceramic pins within the hotplate. The process further includes closing the hotplate such that it is air tight, and flowing nitrogen at 60 liters per minute for thirty seconds, thereby removing most of the oxygen in the hotplate to an oxygen content of less than 10 ppm. The process then includes dropping the wafer from the pins directly onto the hotplate which is equilibrated at 400°C, and processing the wafer within the hotplate for 1 minute and then removing the wafer from the hotplate. EXAMPLE 2 This example illustrates the use of a high temperature hotplate set at 450 °C yielding excellent nanoporous silica film qualities when fully characterized. Preparation of the precursor and wafer prior to placement into the hotplate is performed as described in Example 1. The film is then placed in a high temperature hotplate that had been pre- equilibrated to 450 °C. The process for the film placement includes opening the high temperature hotplate and placing the wafer on ceramic pins within the hotplate. The process further includes closing the hotplate such that it is air tight, and flowing nitrogen at 60 liters per minute for forty seconds, thereby removing most of the oxygen in the sealed hotplate. The process then includes dropping the wafer from the pins directly onto the hotplate which is equilibrated at 450°C, and processing the wafer within the hotplate for 1 minute and then removing the wafer from the hotplate. EXAMPLE 3 This example illustrates the use of a high temperature hotplate set at 350 °C yielding excellent nanoporous silica film qualities when fully characterized. Preparation of the precursor and wafer prior to placement into the hotplate is performed as described in Example 1. The film is then placed in a high temperature hotplate that had been pre- equilibrated to 350 °C. The process for the film placement includes opening the high temperature hotplate and placing the wafer on ceramic pins within the hotplate. The process further includes closing the hotplate such that it is air tight, and flowing nitrogen at 60 liters per minute for one minute, thereby removing most of the oxygen in the sealed hotplate. The process then includes dropping the wafer from the pins directly onto the hotplate which is equilibrated at 350°C, and processing the wafer within the hotplate for 1 minute and then removing the wafer from the hotplate. EXAMPLE 4 This example illustrates the use of a high temperature hotplate set at 600 °C yielding excellent nanoporous silica film qualities when fully characterized. Preparation of the precursor and wafer prior to placement into the hotplate is performed as described in Example 1. The film is then placed in a high temperature hotplate that had been pre- equilibrated to 600 °C. The process for the film placement includes opening the high temperature hotplate and placing the wafer on ceramic pins within the hotplate. The process further includes closing the hotplate such that it is air tight, and flowing nitrogen at 60 liters per minute for thirty seconds, thereby removing most of the oxygen in the sealed hotplate. The process then includes dropping the wafer from the pins directly onto the hotplate which is equilibrated at 600°C, and processing the wafer within the hotplate for 1 minute and then removing the wafer from the hotplate. EXAMPLE 5 This example illustrates the use of a high temperature hotplate set at 425 °C yielding excellent nanoporous silica film qualities when fully characterized. Preparation of the precursor and wafer prior to placement into the hotplate is performed as described in Example 1. The film is then placed in a high temperature hotplate that had been pre- equilibrated to 425 °C. The process for the film placement includes opening the high temperature hotplate and placing the wafer on ceramic pins within the hotplate. The process further includes closing the hotplate such that it is air tight, and flowing nitrogen at 60 liters per minute for thirty seconds, thereby removing most of the oxygen in the sealed hotplate. The process then includes dropping the wafer from the pins directly onto the hotplate which is equilibrated at 425°C, and processing the wafer within the hotplate for 1 minute and then removing the wafer from the hotplate. EXAMPLE 6 This example illustrates the use of a high temperature hotplate set at 500 °C yielding excellent nanoporous silica film qualities when fully characteπzed. Preparation of the precursor and wafer pπor to placement into the hotplate is performed as described in Example 1. The film is then placed in a high temperature hotplate that had been pre- equihbrated to 500 °C. The process for the film placement includes opening the high temperature hotplate and placing the wafer on ceramic pins withm the hotplate. The process further includes closing the hotplate such that it is air tight, and flowing nitrogen at 60 liters per minute for thirty-five seconds, thereby removing most of the oxygen in the sealed hotplate. The process then includes dropping the wafer from the pms directly onto the hotplate which is equilibrated at 500°C, and processing the wafer within the hotplate for 1 mmute and then removing the wafer from the hotplate. EXAMPLE 7 Examples 1-6 are conducted with flowing nitrogen at 65 liters per minute to remove the oxygen from inside of the sealed hotplate. EXAMPLE 8 Examples 1-6 are conducted with flowing nitrogen at 70 liters per mmute to remove the oxygen from inside of the sealed hotplate. EXAMPLE 9 Examples 1-8 are conducted with flowing argon used instead of flowing nitrogen to remove the oxygen from mside of the sealed hotplate. EXAMPLE 10 Examples 1-9 are conducted with processing the wafer within the hotplate for 30 seconds and then removing the wafer from the hotplate. EXAMPLE 11 Examples 1-9 are conducted with processing the wafer within the hotplate for 2 minutes and then removing the wafer from the hotplate. EXAMPLE 12 Examples 1-9 are conducted with processing the wafer within the hotplate for 1.5 minutes and then removing the wafer from the hotplate. EXAMPLE 13 Examples 1-9 are conducted with processing the wafer within the hotplate for 1.1 minutes and then removing the wafer from the hotplate. EXAMPLE 14 Examples 1-6 are conducted with the sealed hotplate evacuated to form a vacuum instead of flowing nitrogen to remove the oxygen from inside of the sealed hotplate EXAMPLE 15 This example illustrates the use of a high temperature furnace set at 400 °C yielding excellent nanoporous silica film qualities when fully characteπzed. Preparation of the precursor and wafer pπor to placement into the furnace is performed as descπbed in Example 1. The film is then placed in a high temperature furnace that had been pre- equihbrated to 400 °C. The process for the film placement includes opening the high temperature furnace and placing the wafer on ceramic p s within the furnace The process includes creating a nitrogen at one atmosphere, and processing the wafer within the furnace for 1 m ute and then removing the wafer from the furnace. EXAMPLE 16 Example 15 is conducted at a furnace temperature of 450 °C. EXAMPLE 17 Example 15 is conducted at a furnace temperature of 350 °C. EXAMPLE 18 Example 15 is conducted at a furnace temperature of 600 °C. EXAMPLE 19 Example 15 is conducted at a furnace temperature of 425 °C. EXAMPLE 20 Example 15 is conducted at a furnace temperature of 500 °C. EXAMPLE 21 Examples 15-20 are conducted with the wafer processed in the furnace for 120 minutes. EXAMPLE 22 Examples 15-20 are conducted with the wafer processed m the furnace for 30 minutes. EXAMPLE 23 Examples 15-20 are conducted with the wafer processed in the furnace for 60 minutes. EXAMPLE 24 Examples 15-23 are conducted in an inert atmosphere of argon. ANALYSIS OF EXAMPLES 1-24 After cooling, the wafers are measured by Ellipsometry for thickness and refractive index. Refractive index can be linearly correlated to the film porosity. A refractive index of 1.0 is 100% porosity and 1.46 is dense, 0% porosity silica. EXAMPLE 25 This example illustrates that the use of a high temperature hotplate set at 400 °C can yield excellent nanoporous silica film quality when fully characterized. The precursor was synthesized by adding 104.0 mL of tetraethoxysilane, 47.0 mL of triethylene glycol monomethyl ether, 8.4 mL of deionized water, and 0.34 mL of IN nitric acid together in a round bottom flask. The solution was allowed to mix vigorously then heated to -80 °C and refluxed for 1.5 hours to form a solution. After the solution was allowed to cool, it was diluted 25% by weight with ethanol to reduce the viscosity. The diluted precursor was filtered to 0.1 μm using a teflon filter. Approximately 8.0-10.0 ml of the precursor was deposited onto a 8" inch silicon wafers on a spin chuck, and spun at 2500 rpm for 30 seconds. The film was placed in a flow chamber and gelled and aged using the following conditions: Ammonia gas was bubbled through 15M ammonium hydroxide at a flow rate of 3 liters per minute. The ammonia/ammonium hydroxide was then flowed through the chamber for 3 minutes. Next the film was removed. The film was then solvent exchanged by which 20-30 mL of a 5% (by vol.) mixture of methyltriacetoxysilane in 3- pentanone were spun on the film at 250 rpm's for 20 seconds without allowing the film to dry. The films were then spun dry at 1000 rpm for 5 seconds. The films were baked at elevated temperatures for 1 min. each at 175 °C and 320 °C in air. The film was then placed in a high temperature hotplate that had been pre-equilibrated to 400 °C. The film was then processed in the following manner: The high temperature hotplate was opened and the wafer was placed on ceramic pins. The hotplate was closed such that that it was air tight. Nitrogen was flowed at 30 1/min. for thirty seconds to ensure that most of the oxygen in the hotplate had been removed. The wafer was dropped from the pins and heated for 5 minutes. The wafer was then lifted back on the pins and removed. The film was characterized by ellipsometry to determine the refractive index and thickness. In addition, the infrared spectra (IR) of the film was measured and compared to the post bake condition to ensure most of the water had been removed. TABLE 1 EXAMPLE 26 This example illustrates that the use of a high temperature hotplate set at 400 °C can yield excellent nanoporous silica film quality when fully characterized. The precursor was synthesized by adding 104.0 mL of tetraethoxysilane, 47.0 mL of triethylene glycol monomethyl ether, 8.4 mL of deionized water, and 0.34 mL of IN nitric acid together in a round bottom flask. The solution was allowed to mix vigorously then heated to -80 °C and refluxed for 1.5 hours to form a solution. After the solution was allowed to cool, it was diluted 25% by weight with ethanol to reduce the viscosity. The diluted precursor was filtered to 0.1 μm using a teflon filter. Approximately 8.0-10.0 ml of the precursor was deposited onto a 8" inch silicon wafers on a spin chuck, and spun at 2500 rpm for 30 seconds. The film was placed in a flow chamber and gelled and aged using the following conditions' Ammonia gas was bubbled through 15M ammonium hydroxide at a flow rate of 3 liters per m ute. The ammonia/ammonium hydroxide was then flowed through the chamber for 3 minutes. Next the film was removed. The film was then solvent exchanged by which 20-30 mL of a 5% (by vol.) mixture of methyltπacetoxysilane in 3- pentanone were spun on the film at 250 rpm's for 20 seconds without allowing the film to dry. The films were then spun dry at 1000 rpm for 5 seconds. The films were baked at elevated temperatures for 1 mm. each at 175 °C and 320 °C m air. The film was then placed in a high temperature hotplate that had been pre-equihbrated to 400 °C. The film was then processed m the following manner: The high temperature hotplate was opened and the wafer was placed on ceramic pins. The hotplate was closed such that that it was air tight. Nitrogen was flowed at 30 1/mm. for thirty seconds to ensure that most of the oxygen m the hotplate had been removed. The wafer was dropped from the pms and heated for 10 minutes. The wafer was then lifted back on the pms and removed. The film was characteπzed by ellipsometry to determine the refractive mdicex and thickness In addition, the infrared spectra (IR) of the film was measured and compared to the post bake condition to ensure most of the water had been removed. TABLE 2 EXAMPLE 27 This example illustrates that the use of a high temperature hotplate set at 450 °C can yield excellent nanoporous silica film quality when fully characteπzed The precursor was synthesized by adding 104.0 mL of tetraethoxysilane, 47.0 mL of tπethylene glycol monomethyl ether, 8.4 mL of deiomzed water, and 0.34 mL of IN nitπc acid together in a round bottom flask. The solution was allowed to mix vigorously then heated to -80 °C and refluxed for 1.5 hours to form a solution. After the solution was allowed to cool, it was diluted 25% by weight with ethanol to reduce the viscosity. The diluted precursor was filtered to 0.1 μm using a teflon filter. Approximately 8.0-10.0 ml of the precursor was deposited onto a 8" inch silicon wafers on a spin chuck, and spun at 2500 rpm for 30 seconds. The film was placed in a flow chamber and gelled and aged using the following conditions- Ammonia gas was bubbled through 15M ammonium hydroxide at a flow rate of 3 liters per mmute. The ammonia/ammonium hydroxide was then flowed through the chamber for 3 minutes. Next the film was removed. The film was then solvent exchanged by which 20-30 mL of a 5% (by vol.) mixture of methyltπacetoxysilane in 3- pentanone were spun on the film at 250 rpm's for 20 seconds without allowing the film to dry. The films were then spun dry at 1000 rpm for 5 seconds. The films were baked at elevated temperatures for 1 mm. each at 175 °C and 320 °C in air The film was then placed in a high temperature hotplate that had been pre-equihbrated to 450 °C The film was then processed in the following manner: The high temperature hotplate was opened and the wafer was placed on ceramic pms. The hotplate was closed such that that it was air tight. Nitrogen was flowed at 30 1/mιn. for thirty seconds to ensure that most of the oxygen in the hotplate had been removed. The wafer was dropped from the pins and heated for 5 minutes. The wafer was then lifted back on the pms and removed. The film was characteπzed by ellipsometry to determine the refractive indicex and thickness. In addition, the infrared spectra (IR) of the film was measured and compared to the post bake condition to ensure most of the water had been removed TABLE 3 EXAMPLE 28 This example illustrates that the use of a high temperature hotplate set at 450 °C can yield excellent nanoporous silica film quality when fully characteπzed. The precursor was synthesized by adding 104.0 mL of tetraethoxysilane, 47.0 mL of tπethylene glycol monomethyl ether, 8.4 mL of deionized water, and 0.34 mL of IN nitπc acid together in a round bottom flask The solution was allowed to mix vigorously then heated to -80 °C and refluxed for 1.5 hours to form a solution. After the solution was allowed to cool, it was diluted 25% by weight with ethanol to reduce the viscosity The diluted precursor was filtered to 0.1 μm using a teflon filter. Approximately 8.0-10.0 ml of the precursor was deposited onto a 8" inch silicon wafers on a spin chuck, and spun at 2500 rpm for 30 seconds. The film was placed in a flow chamber and gelled and aged using the following conditions: 1) Ammonia gas was bubbled through 15M ammonium hydroxide at a flow rate of 3 liters per mmute. The ammonia/ammonium hydroxide was then flowed through the chamber for 3 minutes. Next the film was removed The film was then solvent exchanged by which 20-30 mL of a 5% (by vol.) mixture of methyltπacetoxysilane in 3- pentanone were spun on the film at 250 rpm's for 20 seconds without allowing the film to dry. The films were then spun dry at 1000 rpm for 5 seconds. The films were baked at elevated temperatures for 1 mm. each at 175 °C and 320 °C in air The film was then placed in a high temperature hotplate that had been pre-equihbrated to 450 °C The film was then processed in the following manner The high temperature hotplate was opened and the wafer was placed on ceramic pms. The hotplate was closed such that that it was air tight. Nitrogen was flowed at 30 1/mm. for thirty seconds to ensure that most of the oxygen in the hotplate had been removed. The wafer was dropped from the pins and heated for 10 minutes. The wafer was then lifted back on the pins and removed. The film was characteπzed by ellipsometry to determine the refractive mdicex and thickness. In addition, the infrared spectra (IR) of the film was measured and compared to the post bake condition to ensure most of the water had been removed. TABLE 4 From the foregoing examples it can be seen that a nanoporous dielectπc silicon containing composition can be produced by the post deposition steps of exposing a deposited film to water vapor in a sealed chamber evacuated to a pressure below atmospheπc pressure followed by exposure to a base vapor.

Claims: What is claimed is- 1. A process for producing a cured dielectric film on a substrate which compπses depositing a nanoporous silica dielectπc precursor onto a substrate which precursor compπses at least one hydrolysed and condensed alkoxysilane composition, and then heating the substrate in a substantially oxygen free environment at a temperature of about 350° ® C or greater, for a time peπod of at least about 5 seconds. 2. The process of claim 1 wherein the alkoxysilane composition compπses a component selected from the group consisting of water, a base, an organic solvent and combinations therof 3. The process of claim 1 wherein the alkoxysilane composition compπses a component having the formula: R R wherein at least 2 of the R groups are independently Ci to C alkoxy groups and the balance, if any, are independently selected from the group consisting of hydrogen, alkyl, phenyl, halogen, and substituted phenyl 4. The process of claim 3 wherein each R is methoxy, ethoxy, propoxy or butoxy. 5. The process of claim 1 wherein the alkoxysilane composition compπses one or more components selected from the group consisting of tetraethoxysilane and tetramethoxysilane 6. The process of claim 1 wherein the alkoxysilane composition compπses at least one organic solvent component selected from the group consisting of methanol, ethanol, n- propanol, isopropanol, n-butanol, and alcohols and polyols including glycols such as ethylene glycol, 1,4-butylene glycol, 1,5-pentanedιol, 1,2,4-butanetπol, 1,2,3-butanetπol, 2-methyl-propanetπol, 2-(hydroxymethyl)-l,3-propanedιol, 1,4-butanediol, 2-methyl-l,3- propanediol, tetraethylene glycol, tπethylene glycol monomethyl ether, glycerol, and mixtures thereof. 7. The process of claim 1 wherein the alkoxysilane composition compπses a base selected from the group consisting of ammonia, an amme and combinations thereof. 8. The process of claim 1 wherein the substrate compπses at least one semiconductor mateπal. 9. The process of claim 1 wherein the substrate compπses at least semiconductor matenal selected from the group consisting of gallium arsenide, silicon, compositions containing silicon, germanium and combinations thereof. 10. The process of claim 1 wherein the substrate has a pattern of lines on its surface. 11. The process of claim 1 wherein the substrate has a pattern of lines on its surface wherein the lines compπse a metal, an oxide, a nitπde or an oxynitπde. 12. The process of claim 1 wherein the substrate has a pattern of lines on its surface wherein the lines compπse a mateπal selected from the group consisting of silica, silicon nitπde, titanium nitπde, tantalum nitπde, aluminum, aluminum alloys, copper, copper alloys, tantalum, tungsten and silicon oxynitπde 13. The process of claim 1 further compπsing the subsequent step of treating the nanoporous dielectπc coating with a surface modification agent under conditions sufficient to render the nanoporous dielectπc coating hydrophobic. 14. A process for cuπng a dielectπc film on a substrate which compπses the step of: treating a suitable substrate compπsing a dielectπc film, in a substantially oxygen free environment by heating the substrate to a temperature of about 350°^ or greater, for a time peπod of at least about 5 seconds. 15. The process of claim 14, further compπsing the step of providing a spm-on dielectπc film. 16. The process of claim 14, wherein the dielectπc film contains a silicon component. 17. The process of claim 14, wherein the dielectπc film provides a dielectπc constant of from about 3 or less. 18. A process for cuπng a nanoporous silica dielectπc film on a substrate which compπses the step of: treating a suitable substrate compπsing a dπed nanoporous silica film, m a substantially oxygen free environment by heating the substrate to a temperature of about 350^C or greater, for a time peπod of at least about 5 seconds. 19. A process for cuπng a nanoporous silica dielectπc film on a substrate which compπses the steps of: (a) suspending a suitable substrate withm a heating element, a substantially oxygen free environment, wherein the substrate remains free of contact with the heating element, the substrate compπsing a dπed nanoporous silica film; (b) curing the dried nanoporous silica film sufficiently to remove outgassing remnants from the dried nanoporous silica film; then, (c) removing the cured, dried suitable substrate from the heating element. 20. A process for curing a nanoporous silica dielectric film on a substrate which comprises the steps of: (a) suspending a suitable substrate within a sealable hotplate, wherein the substrate remains free of contact with the hotplate, wherein the substrate comprises a dried nanoporous silica film; (b) sealing the hotplate, wherein the suspended substrate is contained therein; (c) passing an amount of inert gas across the substrate effective to displace non-inert gases adjacent to the substrate; (d) heating the hotplate to a temperature of from about SSO^C to about όOO^C; (e) contacting the substrate with the heated hotplate; and, removing the substrate from the hotplate. 21. The process of claim 20 wherein steps (a) through (e) are conducted in an inert gas environment. 22. A process for curing a nanoporous silica dielectric film on a substrate which comprises the steps of: (a) suspending a suitable substrate within a sealable hotplate, wherein the substrate remains free of contact with the hotplate, wherein the substrate comprises a dried nanoporous silica film; (b) sealing the hotplate, wherein the suspended substrate is contained therein; (c) drawing a vacuum within the hotplate effective to create a substantially oxygen free environment adjacent to the substrate; (d) heating the hotplate to a temperature of from about 350 ° ^ to about όOO^C; (e) contacting the substrate with the heated hotplate; and, (f) removing the substrate from the hotplate.

Inventors: DRAGE JIM, RAMOS TERESA, ROBERTS RICK, SMITH DOUGLAS M, DRAGE, JIM, RAMOS, TERESA, ROBERTS, RICK, SMITH, DOUGLAS, M.
Applicants: ALLIED SIGNAL INC, ALLIEDSIGNAL INC.
Application year: 1999
Main classification: H01L21
IPC codes: C23C18, H01L21