Abstract:
Methods of forming metal compounds such as metal oxides or metal nitrides by sequentially introducing and then reacting metal organic compounds with ozone or with oxygen radicals or nitrogen radicals formed in a remote plasma chamber. The metal compounds have surprisingly and significantly improved uniformity when deposited by atomic layer deposition with cycle times of at least 10 seconds. The metal compounds also do not contain detectable carbon when the metal organic compound is vaporized at process conditions in the absence of solvents or excess ligands.

Description:
This application claims priority, from U.S. Provisional Application Ser. No. 60/388,929 filed Jun. 14, 2002, entitled, “ALD Metal Oxide Deposition Process Using Direct Oxidation”. The foregoing patent application, which is assigned to the assignee of the present application, is incorporated herein by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   Embodiments of the present invention relate to deposition methods for forming thin films of metal compounds, such as metal oxides or metal nitrides, on substrates for use in manufacturing semiconductor devices, flat-panel display devices, and other electronic devices. 
   2. Description of the Related Art 
   In the field of semiconductor processing, flat-panel display processing or other electronic device processing, chemical vapor deposition has played an important role in forming films on substrates. As the geometries of electronic devices continue to shrink and the density of devices continues to increase, the size and aspect ratio of the features are becoming more aggressive, e.g., feature sizes of 0.07 microns and aspect ratios of 10 or greater are contemplated. Accordingly, conformal deposition of materials to form these devices is necessary. 
   While conventional chemical vapor deposition has proven successful for device geometries and aspect ratios up to 0.15 microns, the more aggressive device geometries require new, innovative deposition techniques. Techniques that are receiving considerable attention include rapid cycle (pulsed) CVD and atomic layer deposition (ALD). In such schemes, reactants are introduced sequentially into a processing chamber where each reactant adsorbs onto the surface of the substrate where a surface reaction occurs. A purge step is typically carried out between the delivery of each reactant gas. The purge step may be a continuous purge with the reactant gases or a pulse purge between the delivery of the reactant gases. 
   Deposition of metal compounds from metal organic compounds typically results in trace amounts of carbon in the deposited film. The carbon is introduced into the film from the organic groups on the metal organic compound or a solvent such as toluene that may be added to assist in vaporizing the metal organic compound, or both. Although atomic layer deposition enhances molecular reaction at the surface of the substrate between the metal organic precursors and reactive gases, the process temperatures and reaction times used for ALD typically do not reduce the carbon content below detectable limits. The residual carbon typically is an impurity that may migrate to surrounding layers. 
   U.S. Pat. No. 6,200,893, entitled “Radical-assisted Sequential CVD” describes a method for CVD deposition on a substrate where radical species such as hydrogen and oxygen or hydrogen and nitrogen are introduced into a processing chamber in an alternating sequence with a precursor. Each compound, the radical species and the precursor, are adsorbed onto the substrate surface. The result of this process is two-fold; the components react with each other, as well as prepare the substrate surface with another layer of compound for the next step. By repeating the cycles, a film of desired thickness is produced. In a preferred embodiment the depositions from the molecular precursor are metals, and the radicals in the alternate steps are used to remove ligands left from the metal precursor reactions, as well as to oxidize or nitridize the metal surface in subsequent layers. However, the reference does not address removal of carbon from metal compounds produced from metal organic compounds. 
   Therefore, there is a need for a process for depositing metal compounds such as metal oxides and metal nitrides from metal organic compounds to provide thin films that do not have detectable carbon. 
   SUMMARY OF THE INVENTION 
   The present invention provides deposition processes in which metal organic compounds comprising the structure M(NR′R″) n , where n=1–4, are sequentially deposited on a substrate surface and reacted with ozone or a reactive oxygen or nitrogen species formed in a remote plasma chamber. Atomic layer deposition is the preferred deposition process and is obtained by controlling processing conditions such as temperature and pulse cycles. The metal organic compounds preferably exist in a gaseous state at process conditions and can be vaporized without addition of solvents. 
   An exemplary embodiment of the invention deposits surprisingly uniform films of hafnium oxide from compounds that include the structure Hf(NR′R) 4 , wherein either or both of R′ and R is an alkyl group having from one to four carbon atoms, and where R′ and R may be the same group or may be different groups. A preferred compound is tetrakis(diethylamido)hafnium (TDEAH). In a pulsed atomic layer deposition process, the TDEAH is adsorbed on a substrate surface at a temperature less than 220° C. and then reacted with ozone or oxygen radicals generated in a remote plasma chamber. A pulse time of about 12 seconds or less significantly and surprisingly provides uniform hafnium oxide film deposition which can be used to form conventional semiconductor films such as high k gate dielectric layers or high k capacitor dielectric layers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a generic structure for tetrakis(dialkylamido)hafnium compounds which are preferred metal organic precursors for the first and second embodiments of the present invention; 
       FIG. 2  is tetrakis(diethylamido)hafnium (TDEAH), a compound used in the examples of the present invention; 
       FIG. 3  is a cross sectional view of one processing chamber which can be used to advantage to deposit a metal compound according to embodiments of the invention; 
       FIG. 4  shows the surprising uniformity of hafnium oxide films deposited by the present invention using TDEAH and further shows the substrate temperatures that produce uniform hafnium oxide films; 
       FIG. 5  shows the effect of pulse time on uniformity of the hafnium oxide film of the present invention; 
       FIG. 6  shows that carbon is not detectable in the hafnium oxide film using the ALD method of the present invention; and 
       FIG. 7  (Comparison) shows that carbon is detectable in a hafnium oxide film produced from the precursor of  FIG. 2  using MOCVD. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention relate to an atomic layer deposition or a rapid chemical vapor deposition process for forming a thin layer of a metal compound on a substrate. A metal organic precursor comprising the structure M(NR′R) n , where n=1–4, and where at least one of R and R′ is an organic group, is introduced into a processing chamber, adsorbed on a substrate surface, then reacted with ozone or with another reactive oxygen species formed in a remote plasma chamber. 
   The deposited metal compounds do not contain detectable amounts of carbon. Removal of detectable carbon is aided by the absence of solvents and excess ligands in the metal organic precursors. The preferred metal organic precursors are hafnium compounds having the structure shown in  FIG. 1  wherein both R and R′ are an alkyl group having from one to four carbon atoms. Most preferably, R and R′ are the same alkyl group. The most preferred metal organic compounds include tetrakis(diethylamido)hafnium (TDEAH), which is shown in  FIG. 2  and is commercially available. 
   In order to form a conformal film on a substrate from TDEAH by atomic layer deposition, the substrate is heated to a temperature of between about 150° C. and about 220° C. The TDEAH is pulsed into the chamber through the gas delivery system using a carrier gas, such as nitrogen or argon, at a pressure from 0.1 Torr to 10 Torr. The pulse of TDEAH requires less than 12 seconds to deposit an adequate amount of TDEAH on the substrate surface under the conditions described; however one skilled in the art recognizes that the TDEAH pulse need only be long enough so that substantially a monolayer of TDEAH is deposited. Following the pulse of TDEAH, the carrier gas/TDEAH flow is discontinued, and a pulse of a purge gas, such as nitrogen, helium or argon, is introduced. The pulse of the purge gas may last for about 12 seconds or less, and need only be long enough to clear the excess TDEAH from the chamber. 
   Next, the purge gas pulse is terminated, and a reactive gas comprising ozone or other reactive oxygen species from a remote plasma chamber is pulsed into the chamber with a carrier gas. For reactive oxygen, the carrier gas is preferably argon or helium, either of which assists in maintaining a stable oxygen plasma. It takes a reactive gas/carrier pulse of less than about 12 seconds to react with the TDEAH to form hafnium oxide or hafnium nitride, but again, the pulse need only be long enough so that substantially a monolayer of reactive oxygen is deposited. After the reactive oxygen gas/carrier pulse, another pulse of purge gas is introduced into the chamber, and, as before, the time of the pulse of the purge gas need only be long enough to clear the unreacted reactive oxygen from the chamber. The pulse of the TDEAH/carrier, the pulse of the first purge gas, the pulse of the reactive oxygen gas/carrier, and the pulse of the second purge gas completes one sequential deposition cycle. The deposition cycles are repeated until a desired thickness of the hafnium oxide or hafnium nitride has been deposited. The time per cycle will vary depending on substrate or chamber size and other hardware parameters, on chamber conditions such as temperature and pressure and on the selection of precursor and reactive gas. 
     FIG. 3  is a schematic cross-sectional view of one embodiment of a processing chamber  200  which can be used to form films according to embodiments described herein. The chamber  200  includes a chamber body  202  and a movable substrate support  212  disposed in the chamber to support a substrate  210 . The substrate support  212  may include a vacuum chuck, an electrostatic chuck, or a clamp ring for securing the substrate  212  to the substrate support  212  during processing. The substrate support  212  may be heated using an embedded heating element, such as a resistive heater, or may be heated using radiant heat, such as heating lamps disposed above the substrate support  212 . A purge ring  222  may be disposed on the substrate support  212  to define a purge channel  224  which provides a purge gas to a peripheral portion of the substrate  210  to prevent deposition thereon. 
   The chamber  200  includes a vacuum system  278  in communication with a pumping channel  279  to evacuate any desired gases from the chamber  200  and to help maintain a desired pressure or a desired pressure range inside a pumping zone  266  of the chamber  200 . 
   A gas delivery apparatus  230  is disposed at an upper portion of the chamber body  202  to introduce the metal precursors, the reactive gases and the purge gases into the chamber  200 . The gas delivery apparatus  230  comprises a chamber lid  232  which includes an expanding channel  234  and a bottom surface  260 . The bottom surface  260  is sized and shaped to substantially cover a substrate  210  disposed on the substrate support  212 . The expanding channel  234  has gas inlets  236 A,  236 B to provide gas flows from two similar valves  242 A,  242 B via valve seat assemblies  244 A,  244 B and delivery lines  243 A,  243 B. The gas flows from the valves  242 A,  242 B may be provided together and/or separately. The valves  242 A,  242 B may be pneumatically actuated or may be electrically actuated. Programmable logic controller  248 A,  248 B may be coupled to the valves  242 A,  242 B to control actuation of the valves  242 A,  242 B. An electrically actuated valve typically requires the use of a driver coupled between the valve and the programmable logic controller. The valves  242 A,  242 B may be zero dead volume valves to enable rapid flushing of a reactant gas from the delivery lines of the valve  242 A,  242 B. 
   Valves  242 A and  242 B are coupled to one or the other of the separate precursors. Each is coupled to a purge gas source, preferably the same purge gas source. For example, valve  242 A is coupled to precursor gas source  238  and valve  242 B is coupled to reactant gas source  239 , and both valves  242 A,  242 B are coupled to purge gas source  240 . Each valve  242 A,  242 B may be adapted to provide a combined gas flow and/or separate gas flows of the precursor gas source  238  or reactant gas source  239  and the purge gas source  240 . The reactant gas source  239  includes remote plasma generation such as a microwave chamber to generate reactive gas species when desired. 
   In reference to valve  242 A, one example of a combined gas flow of the precursor gas source  238  and the purge gas source  240  provided by valve  242 A comprises a continuous flow of a purge gas from the purge gas source  240  and pulses of a reactant gas from the precursor gas source  238 . In reference to valve  242 A, one example of separate gas flows of the reactant gas source  238  and the purge gas  240  provided by valve  242 A comprises pulses of a purge gas from the purge gas source  240  and pulses of a reactant gas from the reactant gas source  238 . 
   The delivery lines of the valves  242 A,  242 B may be coupled to the gas inlets  236 A,  236 B through gas conduits  250 A,  250 B. Each gas conduit  250 A,  250 B and gas inlet  236 A,  236 B may be positioned in any relationship to the expanding channel. Each gas conduit  250 A,  250  B and gas inlet  236 A,  236 B are preferably positioned normal (in which +β, −β=to 90°) to the longitudinal axis of the expanding channel or positioned at an angle +β or an angle −β (in which 0°&lt;+β&lt;90°; 0°&lt;−β&lt;90°) from a centerline of the gas conduit  250 A,  250 B to the longitudinal axis of the expanding channel. Therefore, the gas conduit  250 A,  250 B may be positioned horizontally normal to the longitudinal axis of the expanding channel, may be angled downwardly at an angle +β, or may be angled upwardly at an angle −β to provide a gas flow toward the walls of the expanding channel  234  rather than directly downward towards the substrate  210  which helps reduce the likelihood of blowing off reactants absorbed on the surface of the substrate  210 . In addition, the diameter of the gas conduits  250 A,  250 B may be increasing from the delivery lines of the valves  242 A,  242 B to the gas inlets  236 A,  236 B to help reduce the velocity of the gas flow prior to its entry into the expanding channel  234 . For example, the gas conduits  250 A,  250 B may comprise an inner diameter which is gradually increasing or may comprise a plurality of connected conduits having increasing inner diameters. The expanding channel  234  comprises a channel which has an inner diameter which increases from an upper portion  237  to a lower portion  235  adjacent the bottom surface  260  of the chamber lid  232 . In one aspect, the diameter of the expanding channel  234  is gradually increasing from the upper portion  237  to the lower portion  235  of the expanding channel to allow less of an adiabatic expansion of a gas through the expanding channel  234  which helps to control the temperature of the gas. In one embodiment, the gas inlets  236 A,  236 B are located adjacent the upper portion  237  of the expanding channel  234 . 
   At least a portion of the bottom surface  260  of the chamber lid  232  from the expanding channel  234  may be downwardly slopping or funnel shaped to help provide an improved velocity profile of a gas flow from the expanding channel  234  across the surface of the substrate  210  (i.e., from the center of the substrate to the edge of the substrate). In one aspect, the bottom surface  260  is downwardly sloping to help reduce the variation in the velocity of the gases as it travels between the bottom surface  260  of the chamber lid  232  and the substrate  210  to help provide uniform exposure of the surface of the substrate  210  to a precursor or reactant gas. 
   The chamber lid  232  may have a choke  262  at a peripheral portion of the chamber lid  232  adjacent the perimeter of the substrate  210 . The choke  262  may comprise any circumferential downwardly extending protrusion. The choke  262  helps provide a more uniform pressure distribution within the volume or a reaction zone  264  defined between the chamber lid  232  and the substrate  210  by isolating the reaction zone  264  from the non-uniform pressure distribution of the pumping zone  266 . 
   In one aspect, since the reaction zone  264  is isolated from the pumping zone  266 , a minimal amount of gas adequately fills the reaction zone  264  to ensure sufficient exposure of the substrate  210  to the gas. In conventional chemical vapor deposition, a chamber is required to provide a combined flow of reactants simultaneously and uniformly to the entire surface of the substrate in order to ensure that the co-reaction of the reactants occur uniformly across the surface of the substrate. In atomic layer deposition based cyclical processing system, reactants are introduced sequentially into the chamber to provide adsorption of alternating thin layers of the reactants onto the surface of the substrate. Instead, a flow of a reactant needs to be provided repetitively in an amount that is sufficient to adsorb a thin layer of the reactant on the surface of the substrate. Since the reaction zone  264  may comprise a smaller volume when compared to the inner volume of a conventional CVD chamber, a smaller amount of gas is required to fill the reaction zone  264  for a particular process in an atomic layer deposition sequence. Because of the smaller volume of the reaction zone  264 , less gas, whether a deposition gas or a purge gas, is necessary to be flowed into the chamber  200 . Therefore, the throughput of the chamber  200  is greater and the waste may be minimized due to the smaller amount of gas used reducing the cost of operation. 
   The chamber lid  232 , as shown, includes a cap portion  272  and a chamber plate portion  270  in which the cap portion  272  and the chamber plate portion  270  form the expanding channel  234 . An additional plate may be optionally disposed between the chamber lid portion  270  and the cap portion  272 . In other embodiments, the expanding channel  234  may be made integrally from a single piece of material. 
   The chamber lid  232  may include cooling elements and/or heating elements depending on the particular gas being delivered therethrough. Controlling the temperature of the chamber lid  232  may be used to prevent gas decomposition, deposition, or condensation on the chamber lid  232 . For example, water channels may be formed in the chamber lid  232  to cool the chamber lid  232 . In another example, heating elements may be embedded or may surround components of the chamber lid  232  to heat the chamber lid  232 . In one embodiment, components of the chamber lid  232  may be individually heated or cooled. For example, referring to  FIG. 3 , the chamber lid  232  may comprise a chamber plate portion  270  and a cap portion  272  in which the chamber plate portion  270  and the cap portion  272  form the expanding channel  234 . The cap may be maintained at one temperature range and the chamber lid may be maintained at another temperature range. For example, the cap  272  may be heated by being wrapped in heater tape or by using another heating device to prevent condensation of reactant gases and the chamber plate portion  270  may be maintained at ambient temperature. In another example, the cap  272  may be heated and the chamber plate portion may be cooled with water channels formed therethrough to prevent thermal decomposition of reactant gases on the chamber plate portion  270 . 
   The chamber lid  232  may be made of stainless steel, aluminum, nickel-plated aluminum, nickel, or other suitable materials. In one embodiment, the cap portion  272  comprises stainless steal and the chamber plate portion  270  comprises aluminum. In one embodiment, the additional plate comprises stainless steal. 
   A control unit  280  may be coupled to the chamber  200  for controlling process conditions. For example, the control unit  280 , may be configured to control flow of various process gases and purge gases from gas sources  238 ,  239 ,  240  through the valves  242 A,  242 B during different stages of a substrate process sequence. The control unit  280  may be coupled to another controller that is located adjacent individual chamber components, such as the programmable logic controllers  248 A,  248 B of the valves  242 A,  242 B. Bi-directional communications between the control unit  280  and various other components of the chamber  200  are handled through numerous signal cables collectively referred to as signal buses  288 , some of which are illustrated in  FIG. 3 . In addition to control of process gases and purge gases from gas sources  238 ,  239 ,  240  and from the programmable logic controllers  248 A,  248 B of the valves  242 A,  242 B, the control unit  280  may be configured to be responsible for automated control of other activities used in wafer processing, such as wafer transport, temperature control, chamber evacuation, among other activities, some of which are described elsewhere herein. 
   In operation, a first gas flow may be injected into the expanding channel  234  of the chamber  200  by valve  242 A together or separately (i.e., pulses) with a second gas flow injected into the chamber  200  by valve  242 B. The first gas flow may comprise a continuous flow of a purge gas from purge gas source  240  and pulses of a precursor gas from precursor gas source  238  or may comprise pulses of a reactant gas from reactant gas source  239  and pulses of a purge gas from purge gas source  240 . The flows of gas travel through the expanding channel  234  as a vortex flow pattern which provides a sweeping action across the inner surface of the expanding channel  234 . The vortex flow pattern dissipates to a downwardly flow toward the surface of the substrate  210 . The velocity of the gas flow reduces as it travels through the expanding channel  234 . The gas flow then travels across the surface of the substrate  210  and across the bottom surface  260  of the chamber lid  232 . The bottom surface  260  of the chamber lid  232 , which is downwardly sloping, helps reduce the variation of the velocity of the gas flow across the surface of the substrate  210 . The gas flow then travels by the choke  262  and into the pumping zone  266  of the chamber  200 . Excess gas and by-products flow into the pumping channel  279  and are exhausted from the chamber  200  by a vacuum system  278 . In one aspect, the gas flows proceed through the expanding channel  234  and between the surface of the substrate  210  and the bottom surface  260  of the chamber lid  232  proceeds in a laminar manner which aids in an efficient exposure of a reactant gas to the surface of the substrate  210  and efficient purging of inner surfaces of the chamber lid  232 . 
   Examples 
   Hafnium oxide films were deposited at a chamber pressure of 4 Torr by pulsing TDEAH in a nitrogen carrier for 10 seconds. The chamber was then purged with a pulse of a nitrogen gas for 10 seconds. Next, reactive oxygen and an argon carrier (Ar/O* ratio=1:2) was pulsed to the chamber for 10 seconds. Once the reactive gas/carrier pulse was terminated, a second pulse of nitrogen gas was introduced into the chamber for ten seconds to complete the cycle. This process was repeated for 40 cycles with substrate temperatures ranging from 150° C. to 325° C. The resulting hafnium oxide films were tested for WIW Thickness Non-uniformity and the results are shown in  FIG. 4 . The results in  FIG. 4  show that atomic layer deposition (ALD) occurred at substrate temperatures between 150° C. and about 225° C. while pulsed CVD occurred above 225° C. The ALD films showed excellent uniformity. 
   Hafnium oxide films were then deposited at a chamber pressure of 4 Torr and a substrate temperature of 175° C. by pulsing TDEAH and a nitrogen carrier from 2 seconds to 14 seconds. After the TDEAH pulse, a nitrogen gas purge was pulsed into the chamber. For each cycle the nitrogen purge after the TDEAH/carrier pulse was the same length as the TDEAH/carrier pulse. Next, the nitrogen purge was terminated and a plasma of an argon carrier and oxygen (Ar/O* ratio=1:2) was pulsed to the chamber for 2 seconds to 14 seconds, matching the length of the TDEAH/carrier pulse. The cycle was then completed by a second nitrogen purge matching the length of the TDEAH/carrier pulse. The cycle was repeated 40 times and the resulting hafnium oxide films were measured for thickness, in addition to WIW Thickness Non-uniformity. The results are shown in  FIG. 5  and show that pulse times from 10 to 14 seconds provide significant improvement in uniformity. 
     FIG. 6  shows an Auger analysis of atomic concentrations of a hafnium oxide film deposited at a substrate temperature of 175° C. Although not calibrated, the analysis shows that the film contained about 60 atomic percent of oxygen and about 40 atomic percent of hafnium, and did not contain detectable amounts of carbon. The atomic concentration of a hafnium oxide film prepared from the same precursor using a MOCVD process is shown in  FIG. 7 . The results in  FIG. 7  show that the comparison film retained a measurable amount of carbon. 
   The hafnium oxide films of the invention have utility in conventional devices such as replacing the hafnium oxide films, forming hafnium oxide films, and forming mixed metal films containing hafnium oxide as described in the commonly assigned U.S. Pat. No. 6,858,547, filed Sep. 27, 2002. 
   While the invention has been described herein with reference to specific embodiments, features and aspects, it will be recognized that the invention is not thus limited, but rather extends in utility to other modifications, variations, applications, and embodiments, and accordingly all such other modifications, variations, applications, and embodiments are to be regarded as being within the spirit and scope of the invention.