ALD metal oxide deposition process using direct oxidation

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

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] 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.

[0004] 2. Description of the Related Art

[0005] 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.

[0006] 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.

[0007] 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.

[0008] 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.

[0009] 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

[0010] 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.

[0011] An exemplary embodiment of the invention deposits surprisingly uniform films of hafnium oxide from metalloamide 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 metalloamide 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 deposited hafnium oxide film deposition which can be used to form conventional semiconductor films such as a high k gate dielectric layers or a high k capacitor dielectric layers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] 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;

[0013] FIG. 2 is tetrakis(diethylamido)hafnium (TDEAH), a metalloamido compound used in the examples of the present invention;

[0014] 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;

[0015] 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;

[0016] FIG. 5 shows the effect of pulse time on uniformity of the hafnium oxide film of the present invention;

[0017] FIG. 6 shows that carbon is not detectable in the hafnium oxide film using the ALD method of the present invention; and

[0018] 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

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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 assist 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, e.g., substrate or chamber size and other hardware parameters, as well as on chamber conditions such as temperature and pressure and on the selection of precursor and reactive gas.

[0023] FIG. 3 is a cross-sectional view of the chamber assembly 200 of a processing system capable of depositing the metal films of the present invention. Heated chamber lid 205 is hinged to chamber body 210, and, together with O-ring 245, form a temperature and pressure controlled environment or processing region 202 for performing deposition processes and other operations. Chamber body 210 and lid 205 are preferably made of rigid material such as aluminum, various nickel alloys, or other materials having good thermal conductivity. O-ring 245 is formed from a chemical resistant elastomer, perfluoroelastomer, or rubber, such as Chemraz®, Kalrez®, or Viton®, respectively, or other suitable sealing material specifically designed for use in fluid seals.

[0024] When lid 205 is closed as shown in FIG. 3, a processing region 202 is formed that is bonded by a showerhead 240, a pumping plate 208, a substrate support 250, and chamber lid 205. Substrate support 250 (shown in the raised position for processing) is supported by heater shaft 256, which extends through the bottom of chamber body 210. Imbedded within substrate support 250 is a resistive heater that receives power via a resistive heating element electrical connector 257. A thermocouple in thermal contact with substrate support 250 senses the temperature of substrate support 250 and is part of a closed loop control circuit that allows precise temperature control of heated substrate support 250. A substrate 201 is supported by the upper surface of support 250 and is heated by the resistive heaters within substrate support 250 to processing temperatures of, for example, less than 350° C. for metal films formed using the methods and apparatus of the present invention. However, in one embodiment substrate support 250 is made of a ceramic material and is capable of attaining temperatures of up to 600° C. Substrate support 250 and substrate 201 are parallel to showerhead 240.

[0025] In an embodiment of the present invention, two sets of resistive heaters are imbedded within substrate support 250 in a manner that divides substrate support 250 into two heated areas. These heated areas are annular, allowing control of an outside area 297 and an inside area 294 of substrate support 250. Thermocouples are arranged within inside area 294 and outside area 297 to sense the temperatures of these areas and are part of two closed loop control circuits that allow for more precise overall temperature control of heated substrate support 250. In an embodiment of the invention, inner area 294 is heated to a percentage of outer area 297 with a single setpoint controlling the temperature. One of ordinary skill will appreciate that the present invention encompasses alternative embodiments in which multiple continuous or discontinuous embedded heaters are arranged within substrate support 250 to provide additional heat or greater temperature control.

[0026] Processing chamber assembly 200 is coupled to central transfer chamber (not shown) via an opening 214. A slit valve 215 seals processing region 202 from central transfer chamber. Substrate support 250 may also move vertically into alignment with opening 214 so that, when slit valve 215 is open, a substrate may be moved between the processing region 202 and central substrate transfer chamber.

[0027] Lift assembly 900 includes four lift pins 902 (two are shown), which move in evenly spaced holes 281 in substrate support 250 about heater shaft 256. Lift pins 902 interact with a lift tube 904 that attaches to an upper carrier by way of a bellows assembly (not shown). Lift tube 904 is made of aluminum with four ceramic buttons (not shown) for contacting ceramic lift pins 902. When in contact with lift tube 904, lift pins 902 slide vertically within holes 281 due to relative movement between substrate support 250 and lift tube 904. At some point when lowering lift tube 904 this relative movement causes lift pins 902 to retract below the surface of substrate support 250 and causes lift tube 904 to lose contact with lift pins 902. Substrate 250 then mechanically retains lift pins 902 by means known to one of ordinary skill in the art.

[0028] When slit 215 is closed and substrate support 250 is in the raised position for processing, processing region 202 is separated by substrate support 250 from enclosed volume 206. During processing, gap 207 allows material to pass into enclosed volume 206. This loss is undesirable since it reduces the efficiency of the deposition process and leads to this material condensing on chamber body 210 and chamber liner 298. To prevent this, enclosed volume 206 is kept at a pressure greater than processing region 202 by introducing an inert gas such as nitrogen into enclosed volume 206 via gas inlet (not shown). The inert gas flows through enclosed volume 206, and gap 207, to outlet port 260 and is collected by the heated exhaust system (not shown). Pressure transducers (not shown) monitor the pressures in enclosed volume 206 and processing region 202. Substrate support 250 is sometimes called a “lift” and this feature of having a greater pressure below the lift is sometimes called a “lift purge”. The pressure differential from enclosed volume 206 to processing region 202 reduces material flow from processing region 202 into enclosed volume 206, reduces maintenance, and improves deposition efficiency.

[0029] In another embodiment of the invention, heating channels 211 are provided within chamber body 210. A heated fluid, such as water, is passed through heating channels 211 to raise the temperature of chamber body 210. This results in less condensation on chamber body 210 with the advantages discussed above.

[0030] Pumping passage 203 and outlet port 260 are formed within chamber body 210 for removing by-products of processing operations conducted within processing region 202. Outlet port 260 provides fluid and gas communication between components of the heated exhaust system and processing region 202.

[0031] Turning now to the gas delivery features of chamber assembly 200, the process gas/precursor mixture from a vapor delivery system (not shown) and activated species from remote plasma generator system (not shown) are delivered via temperature controlled conduits 273 and 271, respectively, to a central conduit 231 and a bore-through 230 formed in lid 205. Form there, gases and activated species flow through blocker plate 237 and showerhead 240 into processing region 202.

[0032] Temperature controlled conduits 271 and 273 are formed integral to heated feed-through assembly 220 comprising central mixing block 262 and inlet and mixing block 272. Although the embodiment represented in chamber assembly 200 of FIG. 3 indicates a heated feed-through assembly 220 comprising two separate blocks 262 and 272, one of ordinary skill will appreciate that the blocks can be combined into a single block without departing from the spirit of the present invention. A plurality of cartridge heaters 264 are disposed internally to blocks 262 and 272 and proximally to the conduits 231, 273, 278, 265, and 276. Cartridge heaters 264 maintain a set-point in each conduit utilizing separate controllers and thermocouples for the heater of a particular conduit. For clarity, the separate thermocouples and controllers have been omitted.

[0033] Lid 205 is also provided with an annular cooling channel 244 that circulates cooling water within that portion of lid 205 in proximity to O-ring 245. Cooling channel 244 allows the majority of lid 205 to maintain the temperatures preferred for advantageous heating of showerhead 240 while protecting O-ring 245 from high temperatures that degrade the sealing qualities of O-ring 245. This protection is desired because, when degraded, O-ring 245 is more susceptible to attack by the reactive species generated and supplied to processing region 202 by the remote plasma generator (not shown). A flow meter (not shown) monitors the flow through cooling channel 244 and is interlocked to de-energize the water heater and other heater controllers should the flow be too low.

[0034] Another feature of processing chamber assembly 200 of the present invention also shown in FIG. 3 is an annular resistive heater 235 embedded within chamber lid 205. This feature of chamber assembly 200 provides elevated temperatures in lid 205 in proximity to both central bore-through 230 and the “gas box” (an area between the lower surface of the lid 205 and showerhead upper surface). Formed within the top surface of lid 205 is an annular groove shaped according to the size and shape of imbedded heater 235 in order to increase surface contact and heat transfer between resistive heater 235 and chamber lid 205. A backing plate 234 is secured in this groove by fasteners to help increase the surface area contact between embedded heater 235 and lid 205, thereby improving the efficiency of heat transfer between heater 235 and lid 205.

[0035] Without heater 235, cooling channel 244 could continuously remove heat from chamber lid 205. This would lower the temperature of portions of lid 205, particularly those in contact with precursor vapor, such as the area surrounding central bore-through 230 and the gas box. While cooler lid temperatures improve conditions for O-ring 245, cooler lid temperatures could result in undesired condensation of precursor vapor. Thus, resistive heater 235 is positioned to heat those portions of lid 205 in contract with the vaporized precursor flow, such as the gas box and the area surrounding central bore-through 230. As shown in FIG. 3, for example, heater 235 is located between cooling channel 244 and central bore-through 230 while also positioned to provide heating the lid surface adjacent to blocker plate 237.

[0036] Heated lid 205 provides support for showerhead 240 and blocker plate 237. As such, showerhead 240 is attached to lid 205 via a plurality of evenly spaced fasteners 242 and blocker plate 237 is attached to lid 205 by a plurality of evenly spaced fasteners 217. Fasteners 217 and 242 are formed from a rigid material such as aluminum, varieties of nickel alloys, and other materials having good thermal conductivity. Fasteners 242 and 217 have been advantageously placed to provide clamping force to increase contact between heated lid 205 and showerhead 240 in the case of fasteners 242 and heated lid 205 and blocker plate 237 in the case of fasteners 217. Increased contact area produces greater heat transfer between heated lid 205 and blocker plate 237 and showerhead 240.

EXAMPLES

[0037] 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.

[0038] 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.

[0039] 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.

[0040] The hafnium oxide films of the invention have utility in conventional devices such as replacing the hafnium oxide films described in the specification of Attorney Docket number 6412 entitled “System and Method for Forming a Gate Dielectric”, Craig R. Metzner, Sheryas S. Kher and Shixue Han inventors, filed September 2002. In addition to forming hafnium oxide films, the present invention can be used to formed mixed metal films containing hafnium oxide as described in the specification of Attorney Docket number 6412 entitled “System and Method for Forming a Gate Dielectric”, Craig R. Metzner, Sheryas S. Kher and Shixue Han inventors, filed September 2002.

[0041] 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.

Claims

1. A method of forming a film on a substrate, comprising: depositing a source reagent comprising the structure M(NR′R″)n, where n=1-4, on the substrate, where M is a metal, N is nitrogen, R is hydrogen or an alkyl group having from one to four carbon atoms, and R′ is an alkyl group having from one to four carbon atoms; and then reacting the source reagent with ozone or with oxygen radicals formed in a remote plasma source.

2. The method of claim 1 wherein the chamber is maintained at a pressure less than about 10 Torr.

3. The method of claim 2 wherein the substrate is maintained at a temperature of about 150 to about 225° C.

4. The method of claim 1 wherein a purge gas is delivered to the processing chamber between the -depositing a source reagent and the reacting of the source reagent.

5. The method of claim 1, wherein R′ and R″ are ethyl.

6. The method of claim 5, wherein the source reagent is TDEAH.

7. The method of claim 1, wherein the source reagent is reacted with a mixture of argon and oxygen radicals.

8. The method of claim 7, wherein the mixture of argon and oxygen radicals has an argon:oxygen ratio of 1:2.

9. The method of claim 1, wherein the source reagent is substantially free of solvents and excess ligands.

10. The method of claim 1, wherein the substrate temperature is 175° C.

11. A method of forming a hafnium oxide film on a substrate, comprising: a) introducing TDEAH into a processing chamber; b) purging the chamber with nitrogen; c) introducing ozone or an oxygen plasma into the processing chamber; d) purging the chamber with nitrogen; and then e) repeating a) through d).

12. The method of claim 11 wherein the oxygen plasma further comprises argon.

13. The method of claim 12 wherein the oxygen plasma has an Ar:O* ratio of 1:2.

14. The method of claim 11 wherein the chamber is maintained at a pressure of about 4 Torr.

15. The method of claim 14 wherein the substrate is maintained at a temperature of about 175° C.