SELECTIVE CHEMICAL VAPOR DEPOSITION METHOD AND APPARATUS

Abstract: A method and apparatus for selectively depositing metal films on metal and semiconductive surfaces of a substrate wherein the depositing surface of the substrate is isolated from undesired impinging radiation, such as infrared radiation.

Description: ~ __ - SELECTIVE CHEMICAL VAPOR DEPOSITION METHOD AND APPARATUS BACKGROUND OF THE INVENTION The present invention relates generally to a chemical vapor deposition apparatus and process. More particularly, it relates to a chemical vapor deposition apparatus characterized by the selective formation of metal films on metal and semiconductor surfaces of a substrate, such as a patterned silicon wafer, and also a method for its use. There is a continuous trend in the development of solid state circuitry to reduce the dimensions of devices in integrated circuits and in this way increase the speed of operation and density of the circuitry. As the dimensions of devices on silicon wafers continues to shrink, there is a need' to increase the number of layers of conducting lines to interconnect the devices in the circuit. The conducting paths between these layers must be small, and consequently become very difficult to fill. An improved method for filling these openings with conductors is needed. A solution to this problem would be to grow a metal selectively on the conductor and semiconductor sur¬ faces by chemical vapor deposition. However, to deposit thick films of metals, one must use a reducing atmosphere. For example, to obtain tungsten films greater than 500 Angstroms thick, it is necessary to react tungsten hexafluoride with hydrogen. Selectivity is lost in such a reaction after about 1000 Angstroms of tungsten growth on the conductor surfaces, as disclosed by Saraswat et al, in Selective CVD of Tungsten for VLSI Technology, Stanford University, May 1984. - Z - The selectivity of metal deposition is known to be dependent on the deposition process conditions including temperature, pressure and reactant concentration in addition to the composition of the substrate surface. These reaction variables can be controlled within conventional chemical vapor deposition reactors. The apparatus and process of this invention provide enhanced selectivity of metal depo¬ sition by controlling additional variables, such as the level of infrared radiation which impinges upon the deposit- ing surfaces of the substrate. _ ' SUMMARY OF THE INVENTION The chemical vapor deposition' (CVD) apparatus of this invention" includes the improvement of a means for isolating the depositing surfaces of a substrate from infrared radiation. Such means may include, for example, filters or reflectors positioned to protect the substrate, such as a silicon wafer, from * * * radiation. The apparatus of this invention may be used to enhance the selective vapor deposition of metals on metal and semi- conductor surfaces of a substrate. Embodiments of this invention utilize a heating apparatus which heats a sub¬ strate and incorporates a means for isolating the depositing surfaces of said substrate from both impinging infrared radiation and nucleating species vaporized from the hot surface. The process of this invention is directed to a method of selectively depositing metal films on a substrate by heating a substrate to a temperature above about 200°C within a reaction chamber with radiant energy, without appreciable absorption of radiant energy by the reaction chamber walls. The heated substrate is then contacted with a gaseous reactant to form a metal film on the depositing surface. The metal is preferably selected from molybdenum and tungsten. The depositing surface of the substrate is isolated from a substantial portion of impinging infrared radiation within the reactor during contact with the gaseous reactant. For embodiments of this process, the depositing surfaces of the substrate are also isolated from a substan¬ tial portion of vaporized nucleating species formed during the deposition of tungsten. OBJECTS OF THE INVENTION An object of the present invention is to provide a method and apparatus which yill deposit' tungsten selectively at a thickness above 1000 Angstroms on a patterned substrate containing metal surfaces and/or semiconductor surfaces. A further object of the invention is to provide a method and apparatus capable of depositing tungsten selec¬ tively at rates in excess of 100 Angstroms per minute. Another object of the present invention is to provide a method and apparatus for heating substrates, such as silicon wafers, within conventional chemical vapor deposition reactors which permit the selective deposition of ■ metal films, such as tungsten. A further object of the present invention is to deposit tungsten selectively within a CVD reactor utilizing a resistance heater to heat the substrate. An additional object of the present invention is to provide a means for isolating the depositing surfaces of a substrate from infrared radiation and vaporized nucleating species which is adaptable to many reactor designs. Other objects will be apparent from the detailed description which follows. - V - BRIEF DESCRIPTION OF THE DRAWING Figure 1 is a schematic representation of a chemical vapor deposition apparatus of this invention which utilizes a filament lamp energy source. Figure 2 is a schematic representation of a chemical vapor deposition apparatus of this invention which utilizes a radio frequency energy source coupled with a susceptor. Figure 3 is a schematic representation of a chemical vapor deposition apparatus of this invention which utilizes a resis-tance heater as an energy source. Figure 4 is a schematic representation of a heating apparatus used in an embodiment' of this invention which comprises a resistance heater and a plate barrier. Figure 5 is a cross-sectional side view of the apparatus shown in Figure 4. Figure 6 is a schematic representation of a heating apparatus used in an embodiment of this invention which comprises a resistance heater and a quartz ring barrier. Figure 7 is a side view of the apparatus shown in Figure 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a chemical vapor deposition process and apparatus which enhances the selec¬ tive deposition of metal films on substrates, such as silicon wafers commonly employed in the electronics industry in the manufacture of integrated circuits, transistors, and the like. The term "selective deposition" utilized herein and in the claims refers to deposition on particular materials on a substrate to the exclusion of dissimilar materials of that substrate such as, for example, the deposition on metal and/or semiconductor surfaces to the exclusion of deposition on insulator surfaces of a sub- strate. The substrate may be glass, a silicon wafer or other suitable material. The most common are electronic devices having patterned metal and semiconductor surfaces thereon such as integrated circuits. The apparatus of this invention is for use with a wide variety of metal and semiconductor containing gases which deposit films on substrates, including metal carbon- yls, metal fluorides, silane and germane. The apparatus is adaptable to all chemical vapor deposition processes. The process of this invention is directed to the deposition of metal films selectively, such as tungsten and molybdenum. While in some cases, it is desirable to produce a selective film having a thickness in the tens of Ang¬ stroms, the process and apparatus of this invention can provide films having a thickness above one micron. Several embodiments of the apparatus comprising this invention are disclosed herein. Each of such embodi- •πtents employs the same basic concepts characteristic of the improved features of this apparatus, namely the use of a means for isolating the depositing surface of a substrate from radiation. A common element in all embodi¬ ments of the apparatus is the use of a cold-wall reaction chamber or reactor, which helps achieve the objectives of this invention. The process of this invention also incor¬ porates operating conditions which are characteristic of cold-wall reactors. The terms "cold-wall reaction chamber" and "cold wall reactor", as used herein, refer to a system wherein only the substrates and/or the surface on which the -_.- substrates are placed are heated to the reaction temperature within the reaction chamber. In a "hot-wall reactor", the entire reaction chamber is heated to the reaction tempera¬ ture, typically by a resistance heater wrapped around the chamber. In a cold-wall reaction chamber, the chamber walls remain unheated during the reaction. By maintaining the reaction chamber walls in an unheated state, such walls receive little or no film deposition during substrate coating. Therefore, the reactant gases are not depleted. By utilizing a cold-wall reactor, the radiation which impinges upon the substrate is controlled more easily. A common cold-wall system utilizes radio frequency (RF) induction heating to heat a conducting susceptor positioned within the. reaction chamber,'the walls of which are. formed of a non-conducting or insulating material to RF. The substrate is then heated by radiant energy emitted from the susceptor. For example, an external RF generator will transmit energy to a graphite susceptor within a quartz reaction chamber which, in turn, heats substrates positioned thereon, such as silicon wafers. The RF energy used typi¬ cally has a frequency in the order of 5 KHz to 500 KHz. In an embodiment of the apparatus, a radiant energy source is used to heat the substrate directly and/or a susceptor positioned within the reaction chamber. The walls of the reaction chamber are ' transparent to the radiant energy transmitted, which is predominantly short wave length radiation within the visible light or ultraviolet light range. The radiant energy source can be one or more in¬ candescent lamps positioned about the quartz reaction chamber. Such an embodiment is more particularly described by McNeilly et al, in U.S. Patent No. 4,496,609, the con¬ tents of which are incorporated herein by reference. Another embodiment is one in which a hot surface, such as that of a resistance heater or susceptor is used within the reaction chamber to heat substrates directly. Preferably, only the non-depositing surfaces of the sub- strates are heated directly by the hot surface. The depos¬ iting surfaces of the substrates are protected from radia¬ tion emitted by the resistance heater by such means as filters and reflectors positioned within the reactor. Since the source of undesirable radiation is limited in such a configuration, impingement of such radiation upon the depositing surfaces of the substrates can be controlled. It is preferable that this hot surface does not heat the depositing surfaces of the substrate directly in that it is inconsistent with isolating this surface from impinging infrared radiation.- It is.preferable to have the hot surface in close proximity to the non-depositing surfaces of said substrate. This enhances the efficiency of the heating process and provides greater control over the infrared radiation which strays from said hot surface. It may be desirable for the hot surface to contact the non-depositing surfaces. It should be noted that contact between the hot surface and the non-depositing surface is not essential to practice this invention and embodiments which utilize spacers or other means for separating these two elements are within the scope of this invention. It is preferable to maximize contact between the non-depositing surface and the hot surface so as to enhance the heating efficiency and uniformity. It should be real¬ ized, however, the hot ' surface can be either larger, smaller or equivalent in area to the non-depositing surface. Where a silicon wafer is utilized, it is preferable to have the hot surface conform to the shape of the silicon wafer. For a circular silicon wafer, a hot surface having a diameter - 5 - either equal to or slightly smaller than, i.e., up to about 1% smaller, is preferred. The hot surface preferably forms part of a heat source such as a resistance heater or a susceptor coupled with an external radio frequency generator or light source. The susceptor is a solid which is opaque to RF and/or visible radiation. Where opaque to RF radiation, a radio frequency generator heats the susceptor within the reaction chamber by radio frequency induction heating. The radio frequency energy used may have a frequency in the order of 5 KHz to 500 KHz. The non-depositing surfaces of the sub¬ strate are then .heated by the susceptor. Where an external light source is utilized with a susceptor opaque to visible light, the susceptor absorbs the visible light radiation and heats the substrate. The susceptors for radio frequency energy and visible light energy are preferably comprised of graphite. The resistance heaters which are suitable for use in this invention are those which are known to the .art. Resistance wires which heat a nickel or nickel alloy, for example, monel or stainless steel heat blocks are suitable. Customized resistance heaters may be preferred so as to improve the uniformity of heating. It will be recognized by those skilled in the art that the size and type of resis- tance heater and/or susceptor can be varied widely without departing from the scope of this invention. The apparatus and method of this invention are not limited by the configuration or dimensions of the reaction chamber. They encompass the several different types of reactor configurations which have evolved to meet selective requirements of chemical vapor deposition. Among those presently utilized are the horizontal, vertical, cylindri¬ cal, and tubular systems. In the horizontal system, silicon - ?- wafers are typically processed lying flat or on a moving belt in a continuous process furnace. The vertical reactor typically employs a vessel, such as a bell jar, in which the wafers are placed on a susceptor disc which rotates continu- ally for uniform coverage. The tubular and cylindrical reactors are similar to the horizontal system with the wafers being peripherally mounted in the cylindrical system and multi-tiered carr.iers being used in the tubular system. A conventional chemical vapor deposition appara- tus, upon which the apparatus of this invention is based, comprises: " (1) means for transporting the reactant gases to the substrate surface which permits absorption of the reactants on the. surface and (2) means for heating the surface of the substrate to permit reaction of the absorbed reactants. The chemical deposition procedures within the reaction chamber of this invention are very similar to those employed by known coating procedures, the primary distinc¬ tion being that undesired radiation does not impinge the depositing surface. The apparatus of this invention is suitable for depositing metal films and other vapor deposited materials by chemical reaction, typically a reduction reaction, and/or thermo- pyrolysis of the reacting gas. Alternative chemical vapor deposition processes are low pressure systems where reaction takes place at sub-atmospheric pressure. In addition, plasma-assisted chemical vapor deposition techniques, where lower deposition temperatures are utilized, can be performed in the apparatus of this invention. Alternative uses of the apparatus will be apparent to those skilled in the art from the detailed description herein. The means for isolating the depositing surface of a substrate from infrared radiation is more commonly a filter or reflector disposed between the source of radiation and the substrate. Filters will absorb infrared radiation while reflectors direct such radiation away from the depos¬ iting surface. The filter and/or reflector may be comprised of a material which both absorbs and reflects infrared radiation in varying degrees. Filters are preferred since they are often simple to utilize. In selecting an infrared filter, many materials are suitable including gases, solids, and liquids. However, the selection is- arrower where it is desirable to have the filter transparent to other forms of radiation, such as RF and visible light. Another factor which limits the selec- tion of materials is that the filter will emit infrared radiation after a significant quantity of radiation is 'absorbed. This necessitates replacement of the filter or- filter material. Where the materials are solid, this can be quite inconvenient, Filters comprised of liquid materials, such as water within a water jacket, are much easier to handle and can be replenished continuously so as not to emit infrared radia¬ tion. Although gas filters can be replenished, the higher density of liquids permits smaller volumes'Ho be utilized. Water filters are transparent to visible light radiation, and are preferred for cold wall reactor applications with external filters. The configuration and location of the filters and/or reflectors is dependent on the reactor system uti- lized. Where an external radiant energy source is utilized to heat the substrate surface or susceptor within the reactor, a filter disposed outside of the reaction chamber is typically utilized. Where the substrate is heated by a hot surface within the reaction chamber, solid reflectors or filters positioned within the reaction chamber are more conveniently utilized. Complex equipment is required to feed and retain a gas or liquid in the reaction chamber since free foreign liquids or gases within the reaction medium cannot be tolerated. Embodiments which utilize solid filters are less complex than those which utilize a liquid or gas filter. The preferred solid materials for infrared filters are inert within the chemical vapor deposition reactor, such as quartz and nickel. Quartz filters/re¬ flectors are most preferred in that the reaction chamber is often comprised of quartz and therefore the material is not foreign to the chemical vapor deposition reaction. The configuration of the filters and/or reflectors can vary widely. A suitable embodiment is to surround the periphery of the depositing surface with a filter/reflector material which extends a sufficient dis-- tance from the periphery to intercept infrared radiation that would otherwise impinge the depositing surface. The filter/reflector material may extend either above, below or along the plane of the depositing surface. filter/reflector materials which extend in the same direction as the heat transferred from the hot surface to the substrate need only extend a short distance to be effective. For example, where the hot surface is below the substrate, filters/reflectors which extend about 1/8" above the plane of the depositing surface, i.e., in the direction of heat radiated to the substrate, are suitable. Most preferably, the filter/reflector extends about 1" in this direction. filter/reflector materials which do not extend in the direction of heat radiation to the substrate must extend a longer distance than 1/8". For example, when the hot surface is below the substrate, filters/reflectors positioned below or along the plane of the depositing surface preferably extend across the width of the reaction chamber to ensure absorption or reflection of all infrared radiation which will impinge the depositing surface. It should be realized that the position of the hot surface with respect to the substrate _can be varied widely and the position of the hot surface affects the necessary length of the filter/reflector. For example, where the hot surface is above the substrate, the filter/re- flector need only extend 1/8" below the depositing surface of the substrate. Where the hot surface extends beyond the edge of the substrate, it is preferable for the filter/re¬ flector material to contact the periphery of the depositing surface. This ensures the infrared radiation emitted by the hot surface will not pass between the filter/re¬ flector material and the substrate. Where the hot surface does not extend beyond the edge of the substrate, the filter/reflector material need not contact the depositing surface. A space between the fil¬ ter/reflector material and the depositing surface of about 1 millimeter is often preferred. The vaporized nucleating species are preferably isolated from the depositing surface by the same element or apparatus which filters and/or reflects infrared radiation. Such an apparatus is referred to herein as a "barrier". A separate apparatus used to perform this function is referred to herein as an "absorb¬ er". The barrier or absorber must be an inert solid which has a temperature below the temperature of the depositing surface. The absorber or barrier must be cooler than the depositing surface so as to condense the vaporized nucleat- ing species thereon. This serves to intercept these nucle¬ ating species and prevent contact with the depositing sur¬ face. Preferably, the barrier or absorber has a temperature of about 100°C below that of the depositing surface and most preferably, this temperature has a value below 200°C. The number of inert materials which will function as an absorber is extensive. Materials which are suitable for use as solid, infrared filters and/or reflectors are also suitable absorber materials. Most solid metals are inert in the CVD reactor and are suitable, including nickel; however, quartz is preferred since it is already present within the reactor walls. The configuration of the absorber can vary widely. In that a barrier also functions as an infrared filter .and/or reflector, its configuration will principally be dictated by the need to isolate impinging infrared radia¬ tion. The edges of the absorbers and barriers must be in close proximity to the depositing surface, preferably within 1 millimeter. These absorbers and barriers are also in close proximity to the depositing surface. Those infrared filters and/or reflectors which surround the periphery of the depositing surface are well suited for intercepting vaporized nucleating species and are excellent barriers. As with infrared filters and/or reflectors, the absorber can extend above, below or along the plane of the depositing surface. However, the absorber need not extend as far from the periphery of the depositing surface as an infrared filter and/or absorber. For example, an absorber which extends along the plane of a depositing surface will _/4_- intercept a majority of the vaporized nucleating species within one inch from the periphery. Therefore, such an absorber need not extend across the width of the reaction chamber. The existence of the vaporized nucleating species is demonstrated by deposition on the barriers and absorbers utilized. It is believed hot surfaces within the reaction chamber vaporize materials which have formed on them during the CVD reaction. Some, or all, of these vaporized species provide sites for the CVD reaction. Referring to the embodiment shown in Figure 1, it should be understood that the chemical vapor deposition ' apparatus is shown in generally schematic fashion. The elements illustrated are typically within a surrounded enclosure in which the necessary gaseous reactant flow controls, electrical power sources, and other attendant mechanisms are housed and mounted. Such an enclosure is for safety purposes only and is not necessary for the remaining elements to provide the desired objects. The portions of the apparatus illustrated can be supported within such an enclosure in any suitable fashion. The reaction chamber of the chemical deposition apparatus wherein deposition takes place is generally designated 5. The reaction chamber illustrated comprises an elongated enclosed tubular structure formed from a material which is transparent to the radiant energy generated by source 7, described more particularly below. The reaction chamber preferably has its walls formed of quartz, which is transparent to radiant energy in the wavelength range of one micron or below and RF frequencies. A suitable dimension -Λ5 - for the tubular structure is one having a width of 6 inches with a length of about 20 inches, but the dimensions thereof may vary according to the production needs. In addition to the dimensions, the shape of the reactor may also vary within a wide range. The tubular structure illustrated is generally circular in cross-sectional area. As shown in Figure 1, .one end of the reaction chamber forms exhaust port 15 which is, in turn, connected to an exhaust system 20 so that spent reaction gases may be withdrawn from the reactor. Exhaust system 20 comprises a vacuum pump 1 and absorption trap 3 to collect by-products. At its opposite end, gaseous reactants to be "employed in a coating procedure are intro¬ duced into the reaction chamber through means, which in the embodiment illustrated, comprise a pair of conduits 9 and 10 which pass through a manifold 8 which seals off the reactor with backplate 11. These conduits terminate within the reaction chamber permitting gaseous reactants to emanate therefrom. It should be understood that a particular means chosen for introducing the gaseous reactants into the reaction chamber may be varied to meet particular manu¬ facturing and production requirements. A slideable door 18 permits access to the interior of the reaction chamber. Access to the hollow interior through the end of the reac¬ tion chamber is necessary so that substrates to be coated can be loaded and unloaded therefrom prior to and following deposition thereon. To control the flow of gaseous reac¬ tants over the substrates (and prevent impurities from entering the reactor during shut down), a nitrogen backfill inlet 4 may be used in exhaust port 15 to supply nitrogen to the system. The means for heating the substrate surface in the embodiment illustrated in Figure 1 is a radiant energy source designated 7. The radiant energy source comprises at least one incandescent lamp capable of producing and trans¬ mitting radiant energy in the visible range, preferably wavelengths of about one micron of less. In the embodiment illustrated, the radiant energy source comprises a number of such lamps, which surround the reaction chamber. The lamps can be supported by any suitable means and are typically mounted in sockets, the electrical connections to which are not illustrated. Conventional electrical connections can be utilized, however. The lamps preferably employed within the present apparatus are high intensity tungsten filament lamps having a transparent quartz envelope. Such lamps are' better known as conventional projector bulbs and are produced by General Electric Company under the name Multi-Mirror Projec¬ tion Lamp, model ENH. Although the laπφs employed in the ' embodiment of Figure 1 are mounted to radiate at an angle approximately perpendicular to the silicon wafer- and to the reaction chamber, any number of configurations may be suitable. Also illustrated in Figure 1 is a quartz water filter designated 6. This quartz water filter is positioned between the reaction chamber and the tungsten filament lamps. It comprises two layers of quartz which form a cavity for retaining water. Other configurations of water filters are possible and are considered within the scope of this invention. The quartz water filter illustrated is fed with water through conduit 50 which exits through conduit 51. A suitable dimension for the water filters is one which extends across the length of the radiant energy source having a width and length of about 10 inches and a thickness of about 1 inch. An optional element for this configuration is a susceptor, not shown in Figure 1. The susceptor can be used to support the substrates, such as silicon wafers in the -n- reactor. It is formed of the material opaque to the radiant energy emitted from the chief source, such as an RF source, or visible light source. It emits radiant energy to provide uniform heating of the wafers positioned thereon. Use of a susceptor is not particularly desirable in the apparatus illustrated in Figure 1 since the susceptor may generate undesirable infrared radiation within the reaction chamber. Reflectors or filters must be positioned within the reaction chamber to isolate the depositing surface from the infrared radiation generated. The apparatus illustrated in Figure 2 has a configuration more suitable for the use of a suscep¬ tor. The embodiment illustrated in Figure 2 is a cold-wall system which utilizes an RF frequency as a radiant energy source. Reaction chamber 5 is the same as that illustrated in Figure 1. It is generally an elongated, enclosed, tubular structure' formed of a material which is . transparent to RF radiation generated by the RF source 24, described more particularly below. The reaction chamber is preferably comprised of quartz, which is transparent to radiant energy in the RF range. The dimensions of the • chamber are similar to those of Figure 1 being of about 6 inches in diameter with an overall length of about 20 inches- but the dimensions thereof may vary according to the production needs. The shape of the reactor may also vary within : a wide range. As in the apparatus shown in Figure 1, the reaction chamber forms an exhaust port 15 which is connected to exhaust system 20. The exhaust system is comprised of a similar vacuum pump 1 and absorption trap 3. The gaseous reactants are introduced into the reaction chamber through conduits 9 and 10 which pass through mani¬ fold 8. which seals off the reaction chamber with backplate 11. The radiant energy. source 24, i.e. the RF source, generates and transmits a wave length in the range of about 0.1 to 100 meters. Any number of configurations are suit¬ able for the RF source 24 provided the radiation transmitted will impinge a susceptor 70 positioned within the reaction chamber. In the embodiment described within Figure 2, the RF generator is shown perpendicular to th.e silicon wafer and susceptor. Since the silicon wafer is typically transparent to RF radiation, the susceptor is a necessary element in this embodiment. The susceptor is positioned beneath the silicon wafer so as to contact only the non-depositing surface of the silicon wafer: For such a configuration, infrared radiati-on generated by the susceptor impinges only the non-depositing surface of the silicon wafer. The susceptor is preferably comprised of graphite, which readily absorbs and conducts radiant .heat energy from the RF fre¬ quencies at short wave lengths. Reflectors 80 are positioned within the reactor so as to deflect foreign infrared radiation generated within the reaction chamber. These reflectors are preferably comprised of gold. Since gold is not transparent to RF radiation, it is preferable to position the reflectors well above the depositing surface of the silicon waver. However, the configuration of the reflectors can vary widely. Figure 3 illustrates an alternative embodiment of this invention wherein the silicon wafer is heated within the reaction chamber by a resistance heater. " Reaction chamber 5 is as described in Figures 1 and 2. The partic¬ ular features of this reaction chamber are not repeated here for the sake of brevity. Common reference numerals of Figures 1, 2- and 3 label similar elements. Resistance heat source 100 is positioned within the reaction chamber and is similar to the susceptor utilized in Figure 2. It is powered by leads 110 and 111. The resistance heater -H- contacts only the non-depositing surfaces of the silicon wafer. This avoids direct impingement of the infrared radiation generated by the resistant heater onto the de¬ positing surface of said silicon wafer. Reflectors 105 are positioned within the reaction chamber so as to prevent stray infrared radiation from impinging on the depositing surface of the silicon wafer. These reflectors function in a similar manner to those described in Figure 2. It should be understood that reflectors are not required in such an apparatus and that a filter may provide the same function. For example, coating the inside surface of the reactor with an infrared absorbing layer and cooling the surface with a water jacket will serve to isolate the depositing surface of the silicon wafer from stray infrared radiation by absorbing such radiation. The resistance heater 100 can be of any type which is inert to the reactant gases that are passed through said reaction chamber. The resistance heater typically must provide a temperature in the range of about 100°C to 700°C. It is preferable to utilize a resistance heater which has a configuration that conforms to the profile of the silicon wafers or other substrates utilized. Referring to the heating apparatus shown in Figures 6 and 7, it should be understood that the apparatus shown will be supported within a cold wall chemical vapor deposition reaction chamber. Such support can be provided by any conventional means. The hot surface is provided by resistance heater 210, with leads 205 connected thereto and extending out of the reaction chamber to a current source. Silicon wafer 225 is supported thereon and is smaller in diameter than the resistance heater 210. The silicon wafer does not form part of this invention but is illustrated to show how the appara¬ tus performs. The means for isolating the depositing εurface of the silicon wafer from infrared radiation and the vaporized nucleating species produced by the resistance heater 210 is ring 230. Ring 230 rests on the resistance heater 210, centered about the silicon wafer. The ring contacts the outer periphery of the silicon wafer in the embodiment shown. The resistance heater is in direct contact with the non-depositing surface of the silicon wafer and transfers heat directly thereto. The embodiment illustrated in Figures 4 and 5 is a heating apparatus which utilizes a barrier that extends across the plane of the depositing surface. Resistance heater 211 is similar to that described in Figures 6 and 7. It supports silicon wafer 225 and is of an equal diameter to said wafer. Leads 205 provide current to the resistance heater from outside the reaction chamber. The barrier is a plate 240 having n aperture of an inner diameter 2 millime¬ ters longer than the diameter of the silicon wafer. This aperture is positioned over the resistance heater in the plane of the depositing surface (X, Y) . The width of the plate, W, is equivalent to the width of the cold wall reaction chamber. It should be realized that the shape of the plate and ring illustrated can vary widely with the reactor uti¬ lized. It should further be realized that a susceptor may be used in place of the resistance heater for these embodi¬ ments. The apparatus of this invention may be operated in either a "static mode", in which the chamber is closed off during deposition, or a "dynamic mode", in which a continu- ous flow of reactant deposition gas is passed through the chamber. The gas is preferably deposited in a dynamic mode to achieve thick films of the depositing material. - 2/ The process of this invention is directed to the selective deposition of metals on semiconductor and metal surfaces. It is based on conventional processes for the vapor deposition of metals coupled with the distinguishing feature of isolating the depositing surface of the substrate from infrared radiation during reaction of the gaseous reactant. The metal to be deposited is preferably tungsten or- molybdenum. To obtain thick films of these metals, the gaseous reactant. is reduced with a reducing atmosphere such as hydrogen. Suitable depositing gases for molybdenum and tungsten include WF &/ W(C0) g , MoF & , MoCl ς , Mo(CO) & and the like. The reduction reacti.on takes place at a 'temperature above about 200 e C. The preferred temperature falls within the range of about 250° to 650°C and the total pressure within the reactant is preferably within the range of 0.1 to 2 Torr. The preferred gaseous reactants are the combination of tungsten hexafluoride and hydrogen. Preferred mixtures of these constituents provide a hydrogen to tungsten hexa¬ fluoride ratio in the range of 1:1 to 3000:1. The through¬ put rate for such reaction mixtures preferably falls within the range of 0.1 to 5 liters per minute. Radiant energy which heats the substrate can be of any wavelength, including infrared radiation, provided that the infrared radiation does not impinge the depositing surface of the substrate. This can be accomplished with any of the embodiments for the apparatus provided by this invention. _ > , It to utilize an apparatus wherein the radiant energy source is external to the reac¬ tion chamber, such as a filament lamp or radio frequency ■ _3A- generator, with filament lamps being most preferred. Where these filament lamps are used, the radiation which heats the substrate is principally within the visible light range. Such radiation can impinge the surface of the substrate without affecting the selectivity of metal deposition on the metal and semiconductor surfaces. Where the radiant energy source is external to the reactor, particularly where filament lamps are used, it is preferable to filter the infrared radiation to protect the substrate surface. This can be achieved outside the reactor with a water filter as described more particularly above. Such a system is prefer¬ red since it is much easier to absorb the infrared radiation than to reflect such radiation. this can be accomplished with the filters, reflectors, barriers and absorbers described above. In that certain filters/reflec¬ tors need only extend 1/8" from the depositing surface, it is inferred that impinging infrared radiation having a low •*ngle of incidence from the plane of said depositing sur¬ face, i.e., from about 0° to 45°C, is most critical. However, it is preferable to isolate all of such infrared radiation. The substrates on which deposition takes place contain metal and semiconductor surfaces. They are most often silicon wafers with an integrated circuit pattern of insulators, metals and semiconductors. The insulator surfaces are typically Si0 2 and/or Si-N. and the semicon¬ ductor surfaces are silicon. The metals can include plati- num, molybdenum, titanium, tungsten, tantalum, aluminum and the like. Also included are the suicides of such metals described more particularly below. -A5- To perform this process efficiently, the silicon wafers are first loaded into a chemical vapor deposition apparatus. The reaction chamber of such an apparatus is typically at a reduced pressure, i.e. below one atmosphere. Next, the silicon wafer is heated to the desired deposition temperature with radiant energy. The gaseous reactant/hy- drogen mixture is then passed over the silicon wafer and metal deposition commences on the surfaces. The wafer is -isolated from a substantial portion of impinging infrared radiation while the wafer is contacted with the depositing gas. It will be understood that while the following examples primarily involve selective deposition of tungsten, the apparatus of the present invention is applicable to deposition of a wide variety of metallic compounds from a large number of deposition gases. The gases considered most useful for deposition in the context of the apparatus of the present invention are, without limitation: Mo(CO) β , W(C0) & , Cr(CO) 6 , Co(N0) 3 (C0) 3 , WFg, MoFg, MoClg, etc. In addition, although the examples are primarily directed to deposition on silicon surfaces, the apparatus of the present invention •is applicable to deposition on a wide variety of conductor and semiconductor surfaces. Suitable conductor surfaces are those provided by metals and alloys thereof including, for example, platinum, molybdenum, titanium, tungsten, tantalum, aluminum, and the like, including mixtures thereof. Other suitable conductors include transition metal silicides, such as tungsten silicide, molybdenum suicide, titanium sui¬ cide, titanium silicide, platinum silicide, and the like. The following examples are provided to illustrate the particular embodiments of this invention. These exam¬ ples are not provided with the intention of limiting the scope of this invention to the embodiments disclosed. -_2V- EXAMPLES 1-5 In each of Examples 1-5, a silicon wafer covered by an insulator surface of silicon dioxide (9000 Angstroms) with openings etched to expose the underlying silicon was used. Each of the wafers were placed in a reactor as shown in Figure 1. Tungsten filament Projection lamps (GE ENH) were utilized to heat the surface of the silicon wafer in each example. Four bulbs were positioned parallel to the reac¬ tion chamber on each side of the reactor . Two quartz water jackets were positioned on each side of the reaction chamber between the bulbs and the reactor. Water was passed through the water jackets at a rate of about one liter per minute for each example. Upon heating the silicon wafer to the temperature indicated in Table I below, a gas mixture of _. tungsten hexafluoride and hydrogen was passed over the wafer. The molar ratio of hydrogen to tungsten hexafluo¬ ride, the duration of the reaction, the pressure within the reaction chamber and the throughput rate for each example are indicated in Table I. Upon removal from the furnace, the wafers showed no deposition of tungsten on the insulator surfaces and provided a tungsten metal film on the semicon¬ ductive surface having an approximate thickness as indicated in Table I. The corresponding growth rate for each example is also provided in Table I. -*5- Table I Example Temp. Press. Mole Flow Time Thick¬ Growth (C°) (Torr) Ratio Rate (Min.) ness Rate (SCCM) (A) (A/min) 1 350 .60 30 310 20 10000 500 2 520 .60 30 310 3 10500 3500 3 330 .60 30 310 10 4500 450 4 365 .30 15 ' 160 20 6000 300 5 330 .80 45 460 20 7000 350 For comparative results, the reaction chamber used in Example 1 was loaded with a similar silicon wafer having insulator surfaces of silicon dioxide (9000 Angstroms) and semiconductor surfaces of silicon. The silicon wafer was heated in a manner similar to that of Example 1 in that 8 tungsten filament lamps were disposed about the reaction chamber. No quartz water jackets were used to filter the undesired radiation from the tungsten filament lamps. Upon heating the silicon wafer to a temperature of about 350°C, a gas mixture of tungsten hexafluoride and hydrogen was passed over the wafer for approximately twenty minutes. The molar ratio of tungsten hexafluoride to hydrogen fell within the range of about 1:30. Upon removal from the furnace, the wafer showed deposition of one micron of tungsten on the silicon surface. In addition, however, some deposition of tungsten also occurred on the silicon dioxide surface. EXAMPLE 6 Into a cylindrical, quartz reaction chamber having a width of 6" and a length of about 20" was placed a heating apparatus as shown in Figures 6 and 7. A onel plate having a diameter of 3" functioned as the resistance heater. Two insulated nickel leads provided current to the heating wire -_?6- through the access door of the reaction chamber. The monel blocks supported a circular silicon wafer having a diameter of 3". The barrier utilized was a quartz ring having a 3" outer diameter, a 1/8" thickness and 1/4" height. The barrier defined the periphery of the depositing surface. A slideable door in the reactor provided access- 'to the interi¬ or of the reaction chamber. The gaseous reactants, tungsten hexafluoride and hydrogen were introduced into the reaction chamber though a pair of conduits that passed through a manifold which sealed off the reactor. The reactor was exhausted at the opposite end of the reaction chamber with the use of a vacuum, pump and an absorption trap. A nitrogen backfill was also utilized to prevent impurities from entering the reactor during shutdown. The substrate utilized was a silicon wafer covered by an insulator surface of silicon dioxide (4000 Angstroms) which was etched for 30 seconds in 1% hydrofluoric acid. The pressure within the reactor was approximately 0.6 Torr and a flow of 300 seem of hydrogen was maintained during reaction. The heat block was heated from room temperature to 360°C over a 105 minute period, at which time tungsten hexafluoride was introduced to the system at 10 seem. After 10 minutes of the tungsten hexafluoride and hydrogen atmo¬ sphere, the wafer was' cooled and removed from the reactor. Tungsten was deposited on the outside edge of the wafer but no tungsten deposited on the oxide of the wafer inside the ring. As a comparative example, a similar wafer with the same conditions was heated to room temperature to 360°C over a 105 minute period without the use of the quartz ring. After heating, tungsten hexafluoride was introduced to the system at 10 seem per minute. After 5 minutes, the wafer was coated with a non-selective layer of tungsten over the entire oxide surface. EXAMPLE 7 _ 2 7- The same cold wall reactor and heating apparatus as used in Example 6 was utilized in this example. A 3" silicon wafer having a molybdenum layer with 16,000 Ang- stroms of silicon dioxide deposited thereon was utilized. Vias were etched in the silicon dioxide down to the molyb¬ denum surface. This wafer was placed on a secondary wafer having a 4000 Angstroms low pressure chemical vapor deposi¬ tion oxide (LPCVD) deposited thereon. This secondary wafer isolated the bare silicon back of the top wafer from the heated block. The same quartz ring as utilized in Example 2 was centered on top of the wafer. The running conditions were identical to that of Example 6 and the wafer was exposed to tungsten hexafluoride and hydrogen for 8 minutes. Deposition was selective with 8000 Angstroms of tungsten being deposited in the vias. EXAMPLE 8 A similar apparatus to that utilized in Example 6 was utilized in this example. A similar wafer as that utilized in Example 7 was placed on a secondary silicon wafer which served to isolate the wafer from the heated block. The same quartz ring as that utilized in Examples 6 and 7 was utilized in this example. Process conditions were identical to that of Example 7 except the exposure to tungsten hexafluoride and hydrogen was extended to 15 minutes. This resulted in a selective deposition of.tung¬ sten and a thickness of about 15,000 Angstroms within the 16,000 Angstroms deep vias. As a comparative example, a similar wafer was exposed to tungsten hexafluoride and hydrogen within the - _- <?- same apparatus under the same process conditions for a period of 15 minutes. Deposition of tungsten was found to be non-selective and continuous for about 1/2" around the perimeter of the wafer. EXAMPLE 9 The cold wall reactor of Example 6 was utilized in this example. The heating apparatus of this example was that as shown in Figures 6 and 7. The heated block having a diameter of 3" and a quartz ring barrier were also the same as that utilized in Example 6. The wafer to be treated was a 3" silicon wafer having a molybdenum layer over which was deposited silicon dioxide by plasma enhanced chemical vapor deposition (PECVD). The PECVD silicon dioxide had a thickness of approximately 22,000 Angstroms. Vias were etched into this silicon dioxide layer of about 22,000 Angstroms, which exposed the molybdenum layer. The pressure within the reactor was approximately 0.6 Torr with a flowing atmosphere of hydrogen at a rate of 300 seem during the reaction. The ring was centered around the outer periphery of the primary silicon wafer with the etched vias. The block was heated from room temperature to 425°C at the time the tungsten hexafluoride was introduced. The wafer was exposed to hydrogen and tungsten hexafluoride for 15 minutes, resulting in the selective deposition of 21,500 Angstroms of tungsten within the 22,000 Angstroms deep vias. EXAMPLE 10 A similar cold wall reaction chamber as that described in Example 6 was utilized in this example. The heating apparatus of this example was that illustrated in Figures 4 and 5. A heated block having a diameter of 3" was utilized to provide the hot surface. Insulated conducting leads provided the necessary current to the heating wire attached to the monel block via the manifold of the reactor. The barrier utilized in this example extended across the plane of the depositing surface and comprised a nickel plate having a 6" width, 6" length and a .02" thickness. The nickel plate had an aperture of 3" which was centrally disposed over the heated monel block. The nickel plate extended to within 1 milli-meter of the edge of said silicon wafer. The substrate utilized was a 3" silicon wafer having 4000 Angstroms of low pressure chemical vapor depo¬ sition silicon dioxide deposited thereon. The wafer was circular in configuration and had a diameter equal to the diameter of the heated block. The wafer was placed on the ■heating block and the reaction chamber evacuated to 0.6 Torr with a flowing atmosphere of hydrogen of about 300 seem. The block was heated from room temperature to about 400°C over a 100 minute period, at which time tungsten hexafluo- ride was introduced to the system at a rate of 10 seem. After 10 minutes of the tungsten hexafluoride/hydrogen atmosphere, the wafer was removed and tungsten deposition was found to be selective. No tungsten deposited on the oxide of the wafer. - _>- EXAMPLE 11 The same chemical vapor deposition reactor of Example 6 was utilized in this example and the reaction conditions and heating apparatus were as described in Example 10. A 3" silicon wafer having a molybdenum layer over which was deposited a 9000 Angstroms thick layer of PECVD silicon dioxide was utilized. The silicon dioxide was etched to expose the underlying molybdenum layer. Upon treating the silicon wafer to the conditions as described in Example 10 for about 15 minutes, a 15,000 Angstroms deposi¬ tion of tungsten was noted within the vias with no deposi¬ tion on the silicon dioxide surface. Although the above examples have shown various embodiments of the present invention, modifications of these embodiments will be obvious to those skilled in the art, including modified configurations of the heating apparatus and barriers. These obvious modifications are considered to be within the scope of this invention.

Claims: What is claimed is: 1. A chemical vapor deposition apparatus for depositing materials on a substrate which comprises a cold-wall reaction chamber, a means for heating the sub¬ strate to a temperature above 100°C and a means for trans- porting a gaseous reactant to the substrate surface, the improvement comprising: a means for isolating the depositing surface of a substrate containing metal surfaces, semiconductor surfaces, or both, from undesirable impinging radiation. 2. An apparatus as in claim 1 wherein the means for heating the substrate above 100°C is a radiant energy source. 3. An apparatus as in claim 2 wherein the radiant energy source is external to the reaction chamber. 4. An apparatus as in claim 1 adapted to deposit materials on a substrate consisting of a silicon wafer with an integrated circuit pattern having surfaces provided by materials selected from the group consisting of insulators, metals and semiconductors. 5. An apparatus as in claim 1 adapted to deposit a metal on a substrate. 6. An apparatus as in claim 5 adapted to deposit a metal selected from the group consisting of tungsten and molybdenum. 7. An apparatus as in claim 1 wherein the means for isolating undesirable impinging radiation from the depositing surface of said substrate is a reflector. 8. An apparatus as in claim 1 wherein the means for isolating undesirable impinging radiation from the depositing surface of the substrate is a filter. 9. An apparatus as in claim 8 wherein the filter is an infrared filter. 10. An. apparatus as in claim 9 wherein the filter is a water jacket. 11. An apparatus as in claim 10 wherein the means for-heating the substrate above 100°C is a radiant energy source and the water jacket is disposed-between the radiant energy source and the substrate. 12. An apparatus as in claim 11 wherein the radiant energy source is external to the reaction chamber. 13. An apparatus as in claim 12 wherein the radiant energy source is one or more filament lamps. 14. An apparatus as in claim 13" wherein said filter is disposed within the wall of the reaction chamber where deposition takes place. • 15. An apparatus as in claim 1 wherein the means for heating the substrate above 100°C comprises a susceptor within the reaction chamber which transmits radiant energy to the non-depositing surface of the silicon wafer and a means for heating the susceptor. 16. An apparatus as in claim 15 wherein the susceptor is opaque to radio frequencies and the means for heating the susceptor is a radio frequency generator. 17. An apparatus as in claim 1 wherein the means for heating the substrate above 100°C is a resistance heater positioned within the reaction chamber. 18. An- apparatus as in claim 15 wherein the means for isolating undesirable impinging radiation from the depositing surface of the substrate is a radiation reflector, disposed between the substrate and the wall of the reaction chamber. 19. An apparatus as in claim 15 wherein the means for isolating undesirable radiation from the depositing surface of the silicon wafer is an infrared absorbing surface coated on the inside surface of the reaction chamber which is cooled by a surrounding water jacket. 20. A method for effecting selective chemical vapor depositions on metal and semiconductor surfaces of a substrate comprising: (A) placing a substrate having a depositing surface comprised of metal surfaces, semiconductor surfaces or both within a reaction chamber, (B) heating the substrate above 200°C with radiant energy within the reaction chamber without apprecia¬ ble absorption of radiant energy by the reaction chamber walls, -3V- (C) contacting the heated substrate with a gaseous reactant to form a metal film on the depositing surface, said metal being selected from the group consisting of tungsten and molybdenum, and (D) isolating the depositing surface of the substrate from a substantial portion of impinging infrared radiation during Step C. 21. A method as in claim 20 wherein the substrate is heated to a temperature within the range of 250°C to 650°C and the total pressure is in the range of 0.1 to 2 Torr. 22.. A method as in claim 21 wherein the source of radiant energy is one or more filament lamps. 23. A method as in claim 22 wherein the infrared radiation is filtered so as to not impinge .the depositing surface of the substrate. 24. A method as in claim 22 wherein the radiant energy which heats the substrate is principally within the visible light range. 25. A method as " in claim 21 wherein the substrate is a silicon wafer with an integrated circuit pattern having surfaces provided by materials selected from the group consisting of insulators, metals and semiconductors. 26. A method as in claim 25 wherein the insulator surfaces are selected from the group consisting of SiO. and Si-N. and the metals are selected from the group consisting of platinum, molybdenum, titanium, tungsten, tantalum, aluminum and silicides thereof, and the semiconductor surface is silicon. 27. A method as in claim 21 wherein the gaseous reactants are tungsten hexafluoride and hydrogen. 28. A method as in claim 27 wherein the ratio of hydrogen to tungsten hexafluoride falls within the range of 3 to 50. 29. A method as in claim 28 wherein the throughput rate for the gaseous reactants is within the range of about 0.1 to 2 liters per minute. 3Q. An apparatus as in claim 1 comprising an ' apparatus for heating a substrate comprising: (A) a hot surface within the cold wall reaction chamber which heats said substrate above 200°C by heat transfer to the non-depositing surfaces of said substrate, (B) a means for isolating the depositing surface of said substrate from nucleating species vaporized by the -hot surface, said means being disposed within the cold wall reaction chamber. 31. An apparatus as in claim 30 wherein said hot surface is part of a heat source selected from the group consisting of (A) resistance heaters and (B } susceptors which absorb radiant energy from a radio frequency generator or a light source external to the reaction chamber. - _- 32. An apparatus as in claim 30 wherein the means for isolating the depositing surface of said substrate from • impinging infrared radiation and nucleating species vapor¬ ized by the hot surface is a barrier which surrounds the periphery of the depositing surface and extends a sufficient distance from the periphery to shield the depositing surface from infrared radiation and vaporized nucleating species generated by the hot surface, said barrier being comprised of an inert solid material which is cooler than the deposit- ing surface. 33. An_ apparatus as in claim 32 wherein said barrier extends along the same plane as the depositing surface. 34. An apparatus as in claim 33 wherein said barrier is a plate which approaches the periphery of the depositing surface to within 1 millimeter and extends the entire width of the reaction chamber. 35. An apparatus as in claim 34 wherein said plate is comprised of quartz or nickel. 36. An apparatus as in claim 32 wherein said barrier extends in the direction of heat transferred to the substrate from the hot surface. 37. An apparatus as in claim 36 wherein the barrier contacts the periphery of the depositing surface and extends at least 1/8" in the direction of heat transferred to the substrate from the hot surface. 38. An apparatus as in claim 37 wherein the hot surface is below the substrate and the barrier extends above the plane of the depositing surface. 39. An apparatus as in claim 38 wherein the depos¬ iting surface is circular and said barrier is a ring. 40. An apparatus as in claim 38 wherein said barrier is comprised of quartz or nickel. 41. A method for effecting selective chemical vapor deposition.of tungsten on metal and semiconductor surfaces of a substrate which comprises heating the deposit¬ ing surface ύf a substrate above 200°C within a reactor by heat transfer to the non-depositing surfaces of said sub¬ strate without appreciable absorption of heat by the reactor walls, and contacting the heated substrate with gaseous reactants that react to form a tungsten film on the depos¬ iting surface, the depositing surface of said substrate is isolated from both (A) undesirable impinging infrared radiation and (B) a substantial portion of vaporized nucleating species formed during the deposition of tungsten. 42. A method as in claim 41 wherein the depositing surface of said substrate is heated to a temperature within the range of about 350°C to 650°C. 43. A method as in claim 41 wherein the substrate is a silicon wafer with an integrated circuit pattern having surfaces provided by materials selected from the group consisting of insulators, metals and semiconductors. 44. A method as in claim 41 wherein the gaseous reactants are hydrogen and tungsten hexafluoride in a ratio of about 1:1 to 3000:1. 45. A method as in claim 41 wherein both the impinging infrared radiation and vaporized nucleation species generated during heating of the depositing surface are absorbed by a solid having a temperature below 200°C. 46. A method as in claim 45 wherein said solid is comprised of quartz or nickel.. 47. A method as in claim 41 wherein the isolated infrared radiation has an angle of incidence of 0° to 45°C from the plane of the depositing surface.

Inventors: CALACONE MICHAEL ANTHONY, STOLL ROBERT WINSTON, WILSON RONALD HARVEY, CALACONE, MICHAEL, ANTHONY, STOLL, ROBERT, WINSTON, WILSON, RONALD, HARVEY
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1986
Main classification: C23C16
IPC codes: C23C16, H01L21