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(19) United States
(12) Patent Application Publication (io) Pub. No.: US 2005/0260420 Al
Collins et al. (43) Pub. Date: Nov. 24,2005
(54) LOW DIELECTRIC MATERIALS AND METHODS FOR MAKING SAME
(76) Inventors: Martha Jean Collins, Allentown, PA (US); Lisa Deis, Pittsburgh, PA (US); John Francis Kirner, Orefield, PA (US); James Edward Mac Dougall, New Tripoli, PA (US); Brian Keith Peterson, Fogelsville, PA (US); Scott Jeffrey Weigel, Allentown, PA (US)
AIR PRODUCTS AND CHEMICALS, INC.
7201 HAMILTON BOULEVARD
ALLENTOWN, PA 181951501
(21) Appl. No.: 10/404,195
(22) Filed: Apr. 1, 2003
Publication Classification (51) Int. CI.7 B32B 9/04; B05D 3/02
(52) U.S. CI 428/446; 428/447; 427/387
Low dielectric materials and films comprising same have been identified for improved performance when in integrated circuits as well as a method and a mixture for making same. In one embodiment of the invention, there is provided a mixture for forming a porous, low-k dielectric material comprising: at least one silica source having an at least one silicon atom and an organic group comprising carbon and hydrogen atoms attached thereto wherein at least one hydrogen atom within the organic group is removable upon exposure to an ionizing radiation source; and at least one porogen wherein the ratio of the weight of at least one porogen to the weight of the at least one porogen and Si02 provided by the at least one silica source is 0.4 or greater. The mechanical and other properties of the porous, silicabased material are improved via exposure to the ionizing radiation source.
LOW DIELECTRIC MATERIALS AND METHODS FOR MAKING SAME
BACKGROUND OF THE INVENTION
 The present invention relates generally to materials suitable for use in electronic devices. More specifically, the invention relates to a material and film comprising same having an improved elastic modulus and a low dielectric constant and to a mixture and a method for making same.
 There is a continuing desire in the microelectronics industry to increase the circuit density in multilevel integrated circuit devices such as memory and logic chips in order to improve the operating speed and reduce power consumption. In order to continue to reduce the size of devices on integrated circuits, it has become necessary to use insulators having a low dielectric constant to reduce the resistance-capacitance ("RC") time delay of the interconnect metallization and to prevent capacitive crosstalk between the different levels of metallization. Such low dielectric materials are desirable for premetal dielectric layers and interlevel dielectric layers.
 Typical dielectric materials for devices with 180 nm line width are materials with a dielectric constant between about 3.8 and 4.2. As the line width decreases, the dielectric constant should also be decreased. For example, devices with 130 nm line width require materials with a dielectric constant between about 2.5 and 3.0. Extremely low dielectric constant ("ELK") materials generally have a dielectric constant between about 2.0 and 2.5. Devices with 90 nm line width require materials with dielectric constants less than 2.4. According to the 2001 International Technology roadmap for Semiconductors (ITRS) interconnect roadmap, the projected dielectric constant requirements for interlevel metal insulators will be less than 2.1 for the 65 nm node, less than 1.9 for the 45 nm node, less than 1.7 for the 32 nm node, and less than 1.6 for the 22 nm node.
 The dielectric constant (k) of a material generally cannot be reduced without a subsequent reduction in the mechanical properties, i.e., modulus, hardness, etc. Mechanical strength is needed for subsequent processing steps such as etching, CMP ("Chemical Mechanical Planarization"), and depositing additional layers such as diffusion barriers for copper, copper metal ("Cu"), and cap layers on the product. In some of these processes, temperature cycling of multiple layers may induce stresses due to the thermal coefficient of expansion mismatch between the different materials thereby causing cracking or delamination. Surface planarity is also required and may be maintained through controlling processing parameters such as those during the film formation process and also through CMR Mechanical integrity, or stiffness, compressive, and shear strengths, may be particularly important to survive CMP. It has been found that the ability to survive CMP may be correlated with the elastic, or Young's, modulus of the material, along with other factors including polishing parameters such as the down force and platen speed. See, for example, Wang et al., "Advanced processing: CMP of CU/low-K and Cu/ultralow-K layers", Solid State Technol., September, 2001; Lin et al., "Low-k Dielectrics Characterization for Damascene Integration", International Interconnect Technology Conference, Burlingame, Calif., June, 2001. These mechanical properties are also important in the packaging of the final product.
 A number of processes have been used for preparing low dielectric constant films. Chemical vapor depostion (CVD) and spin-on dielectric (SOD) processes are typically used to prepare thin films of insulating layers. Other hybrid processes are also known such as CVD of liquid polymer precursors and transport polymerization CVD. A wide variety of low K materials deposited by these techniques have been generally classified in categories such as purely inorganic materials, ceramic materials, silica-based materials, purely organic materials, or inorganic-organic hybrids. Likewise, a variety of processes have been used for curing these materials to decompose and/or remove volatile components and substantially crosslink the films such as heating, treating the materials with plasmas, electron beams, or UV radiation.
 Since the dielectric constant of air is nominally 1.0, one approach to reducing the dielectric constant of a material may be to introduce porosity. Porosity has been introduced in low dielectric materials through a variety of different means. A dielectric film when made porous may exhibit lower dielectric constants compared to a dense film, however, the elastic modulus of the film generally decreases with increasing porosity. Consequently, it may be impractical to use these low dielectric compositions due to the trade-off in dielectric constant with elastic modulus.
 One concern in the production of low K dielectric films is the processing or cycle time. The cure or anneal step, in which the coated substrate is typically heated to decompose and/or remove volatile components and substantially cross-link the film, is a significant source of production bottlenecks. The majority of low and ultralow dielectric constant films currently made have a cure step which ranges from greater than 30 minutes to 2 hours. Consequently, reduction of the cure step time would reduce the overall process time and achieve higher manufacturing throughput.
 Another concern in the production of low K dielectric films is the overall thermal budget. Various components of IC devices such as Cu metal lines can only be subjected to processing temperatures for short time periods before their performance deteriorates due to undesirable diffusion processes. Most processes for preparing silica-based low K films require curing steps at temperatures of 450° C. or higher and times of 30 minutes or longer. Significant advantages could result if the curing step could be carried out at significantly lower temperatures and or shorter times.
 One method to process silica-based low K films without effecting the thermal budget of the device is by exposure to electron beam ("e-beam") radiation. The electron beam radiation step may be in addition to, or in lieu, of a thermal cure step. It is believed that the e-beam exposure may improve the mechanical properties of the film by removing most or all of the organic species from the film. For example, U.S. Pat. No. 6,042,994 describes a process wherein a nanoporous dielectric coated substrate is treated with a large area electron beam exposure system. The '994 patent contends based upon FTIR data that the e-beam cure has removed most of the organic species from the film. WO 97/00535 teaches a process for curing a dielectric material such as a spin-on-glass (SOG) having about 10-25% organic groups by exposure to e-beam irradiation. Using FTIR analysis, the WO 97/00535 application reports that there are no longer CH groups attached to the backbone of SOG starting compounds after curing with e-beam radiation.
Further, U.S. Pat. No. 6,132,814 teaches curing a SOG layer by irradiating the layer with a large-area electron beam at a dose sufficient to cure the layer, wherein the irradiating step results in the expulsion of carbon organic groups from the layer.
 The article, Kloster, G., et. al., "Porosity Effects on Low-k Dielectric Film Strength and Interfacial Adhesion" and related slides presented at the International Interconnect Technology Conference on Jun. 5, 2002 (referred to herein collectively as Kloster) describe treating porous, low-K organosiloxane films with e-beam radiation to improve the mechanical properties of the film by inducing microscopic Si—CH2—Si crosslinking. Kloster reports, however, that while the mechanical properties of the film are improved, the dielectric constant may increase. Further, Kloster reports a 25-50% depletion of carbon within the film. U.S. Patent Application 2001/0018129, teaches the formation of Si—C—Si bonds by irradiating a silica-based film with electron beams to provide a film with a dielectric constant of 3 or lower. However, unlike the '994 patent, the application teachs that the resultant film has a carbon content ranging from 5 to 17 mole %.
 Accordingly, there is a need in the art to provide improved dielectric materials having low dielectric constant and sufficient mechanical strength. There is also a need in the art to provide dielectric materials and films that have relatively low metal content yet still maintain the beneficial properties, i.e., lower K and higher modulus, that high levels of metals may impart. Further, there is a need in the art to provide processes for making low dielectric films at relatively low temperatures and relatively short cycle times.
 All references cited herein are incorporated herein by reference in their entirety.
BRIEF SUMMARY OF THE INVENTION
 The present invention satisifies some, if not all of the needs, of the art by providing a material and a film having a low dielectric constant and improved mechanical properties and a mixture and method for making same. Specifically, in one aspect of the present invention, there is provided a mixture for forming a porous, silica-based material having a dielectric constant of about 2.2 or less, comprising: at least one silica source having an at least one silicon atom and an organic group comprising carbon and hydrogen atoms attached thereto wherein the at least one hydrogen atom within the organic group is removable upon exposure to an ionizing radiation source; and at least one porogen wherein the ratio of the weight of at least one porogen to the weight of at least one porogen and the weight of Si02 provided by the at least one silica source is 0.4 or greater.
 In a further aspect of the present invention, there is provided a process for forming a dielectric film having a dielectric constant of 2.2 or less comprising: providing a mixture comprising an at least one silica source having an at least one silicon atom and an organic group comprising carbon and hydrogen atoms bonded thereto and at least one porogen; dispensing the mixture onto a substrate to form a coated substrate; curing the coated substrate with one or more energy sources for a time and at least one temperature sufficient to remove at least a portion of the porogen and form a porous film; and exposing the porous film to an
ionizing radiation source sufficient to remove at least a portion of the hydrogen atoms attached to the carbon atoms within the porous film and provide the dielectric film.
 In yet another aspect of the present invention, there is provided a process for forming a dielectric material comprising exposing a porous material comprising at least one silica source having at least one silicon atom and an organic group comprising carbon and hydrogen atoms attached thereto to an ionizing radiation source sufficient to remove at least a portion of the hydrogen atoms within the porous film and provide the dielectric material wherein the dielectric material has one or more bond types selected from the group consisting of silicon-carbon bonds, carbon-carbon bonds, silicon-oxygen bonds, and silicon-hydrogen bonds.
 In still a further aspect of the present invention, there is provided a mixture for forming a porous, silicabased material having a dielectric constant ranging from 2.2 to 3.7 and a normalized wall elastic modulus (E0'), derived in part from the dielectric constant of the material, of about 32 GPa or greater, comprising: at least one silica source having an at least one silicon atom and an organic group comprising carbon and hydrogen atoms attached thereto wherein at least one hydrogen atom within the organic group is removable upon exposure to an ionizing radiation source; and at least one porogen wherein the ratio of the weight of at least one porogen to the weight of the at least one porogen and the weight of Si02 provided by the at least one silica source is 0.4 or greater.
 These and other aspects of the invention will become apparent from the following detailed description.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF
 FIG. 1 illustrates the relationship between dielectric constant and elastic modulus for various films of the present invention before and after exposure to electron beam irradiation compared to normalized elastic wall modulus (E0').
DETAILED DESCRIPTION OF THE
 The present invention is directed to low dielectric materials and films and methods for making and using same. The process of the present invention provides a method for preparing a porous, low dielectric film that may exhibit, inter alia, improved mechanical properties, thermal stability, and chemical resistance to oxygen or aqueous oxidizing environments relative to other porous dielectric materials of the art. Unlike prior art methods, the method of the present invention improves the mechanical and other properties of the material with significant retention of the carbon within the film. The terms "dielectric film" and "dielectric material" are used interchangeably throughout this specification.
 In one embodiment of the present invention, a mixture, containing a silica source having at least one silicon atom and an organic group comprising carbon and hydrogen atoms attached to the silicon atom and a porogen, is cured thermally or by other means to substantially remove the porogen contained therein and form a porous material. Afterwards, the porous material is exposed to one or more ionizing radiation sources. The term "porous film" or