The present invention relates to methods for removing surface deposits by using an activated gas mixture created by activating a gas mixture that includes a nitrogen source, a carbon or sulfur source, and a optionally, an oxygen source, as well as the gas mixtures and activated gases used in these methods.
One of the problems facing the operators of chemical vapor deposition reactors is the need to regularly clean the chamber to remove deposits from the chamber walls and platens. This cleaning process reduces the productive capacity of the chamber since the chamber is out of active service during a cleaning cycle. The cleaning process may include, for example, the evacuation of reactant gases and their replacement with an activated cleaning gas followed by a flushing step to remove the cleaning gas from the chamber using an inert carrier gas. The cleaning gases typically work by etching the contaminant build-ups from the interior surfaces, thus the etching rate of the cleaning gas is an important parameter in the utility and commercial use of the gases. Present cleaning gases are believed to be limited in their effectiveness due to low etch rates. In order to partially obviate this limitation, current gases need to be run at an inefficient flow rate, e.g. at a high flow rate, and thus greatly contribute to the overall operating cost of the CVD reactor. In turn this increases the production cost of CVD wafer products. Further attempts at increasing the pressure of the gases to increase the etch rates have instead resulted in lower etch rates. This is most likely due to the loss of gas phase species due to increased recombination at the increased pressures. For example, Kastenmeier, et al. in Journal of Vacuum Science & Technology A 16 (4), 2047 (1998) disclose etching silicon nitride in a CVD chamber using a mixture of NF3 and oxygen as a cleaning gas. K. J. Kim et al, in Journal of Vacuum Science & Technology B 22 (2), 483 (2004) disclose etching silicon nitride in a CVD chamber adding nitrogen or argon to mixtures of perfluorotetrahydrofuran and oxygen. U.S. Pat. No. 6,449,521 discloses a mixture of 54% oxygen, 40% perfluoroethane and 6% NF3 as a cleaning gas for cleaning silicon dioxide deposits from CVD chambers. Thus, there is a need in the art to reduce the operating costs of a CVD reactor with an effective cleaning gas capable of lowering the overall operating cost of the CVD chamber.
The present invention provides effective methods for removing surface deposits from the interior of a CVD reactor using novel cleaning gas mixtures and activated cleaning gas mixtures. The methods of the invention include, but are not limited to, the steps of providing a gas mixture, activating the gas mixture in a remote chamber or in a process chamber to form an activated gas mixture, where the gas mixture comprises a source of at least one atom selected from the group consisting of carbon and sulfur, NF3, and optionally, an oxygen source, wherein the molar ratio of oxygen:carbon source is at least 0.75:1; and contacting the activated gas mixture with surface deposits within the CVD reactor. The gas mixtures of the present invention include, but are not limited to, at least one inorganic fluorine source, a carbon source gas or a sulfur source, at least one nitrogen source, and optionally at least one oxygen source. The activated gas mixtures produced from the gas mixtures include but are not limited to mixtures of fluorine atoms, nitrogen atoms, at least one atom selected from the group consisting of carbon and sulfur, and optionally oxygen. In one embodiment of the invention, the activated gas mixture comprises (on a moles of atoms basis), from about 60% to about 75% fluorine atoms, from about 10% to about 30% nitrogen atoms, optionally from about 0.4% to about 15% oxygen atoms, and from about 0.3% to about 15% at least one atom selected from the group consisting of carbon and sulfur, optionally including a carrier gas.
Surface deposits as referred to herein comprise those materials commonly deposited by chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD) or similar processes. Such materials include nitrogen-containing deposits. Such deposits include, without limitation, silicon nitride, silicon oxynitride, silicon carbonitride (SiCN), silicon boronitride (SiBN), and metal nitrides, such as tungsten nitride, titanium nitride or tantalum nitride. In one embodiment of the invention, the surface deposit is silicon nitride.
In one embodiment of the invention, surface deposits are removed from the interior of a process chamber that is used in fabricating electronic devices. Such a process chamber could be a CVD chamber or a PECVD chamber. Other embodiments of the invention include, but are not limited to, removing surface deposits from metals, the cleaning of plasma etching chambers and removal of N-containing thin films from a wafer.
In one embodiment, the process of the present invention involves an activating step wherein a cleaning gas mixture is activated, either in the process chamber or in the remote chamber. For the purposes of this application, activation means that at least an effective amount of the gas molecules have been substantially decomposed into their atomic species, e.g. a CF4 gas would be activated to substantially decompose and form an activated gas (also known in the art as a plasma) comprising carbon and fluorine atoms. Activation may be accomplished by any energy input means allowing for the achievement of dissociation of a large fraction of the feed gas, such as: radio frequency (RF) energy, direct current (DC) energy, laser illumination, and microwave energy. One embodiment of the invention uses transformer coupled inductively coupled lower frequency RF power sources in which the plasma has a torroidal configuration and acts as the secondary of the transformer. The use of lower frequency RF power allows the use of magnetic cores that enhance the inductive coupling with respect to capacitive coupling; thereby allowing the more efficient transfer of energy to the plasma without excessive ion bombardment which limits the lifetime of the remote plasma source chamber interior. Typical RF power used has a frequency lower than 1000 kHz. In another embodiment of the invention the power source is a remote microwave, inductively, or capacitively coupled plasma source. In yet another embodiment of the invention, the gas is activated using glow discharge.
Activation of the cleaning gas mixture uses sufficient power for a sufficient time to form an activated gas mixture. In one embodiment of the invention the activated gas mixture has a neutral temperature of at least about 3,000 K. The neutral temperature of the resulting plasma depends on the power and the residence time of the gas mixture in the remote chamber. Under certain power input and conditions, neutral temperature will be higher with longer residence times. Under appropriate conditions (considering power, gas composition, gas pressure and gas residence time), neutral temperatures of at least about 6,000 K may be achieved.
The activated gas may be formed in a separate, remote chamber that is outside of the process chamber, but in close proximity to the process chamber. In this invention, remote chamber refers to the chamber other than the cleaning or process chamber, wherein the plasma may be generated, and the process chamber refers to the chamber wherein the surface deposits are located. The remote chamber is connected to the process chamber by any means allowing for transfer of the activated gas from the remote chamber to the process chamber. For example, the means for allowing transfer of the activated gas may comprise a short connecting tube and a showerhead of the CVD/PECVD process chamber. The means for allowing transfer of the activated gas may further comprise a direct conduit from the remote plasma source chamber to the process chamber. The remote chamber and means for connecting the remote chamber with the process chamber are constructed of materials known in this field to be capable of containing activated gas mixtures. For instance, aluminum and anodized aluminum are commonly used for the chamber components. Sometimes Al2O3 is coated on the interior surface to reduce the surface recombination. In other embodiments of the invention, the activated gas mixture may be formed directly in the process chamber.
The gas mixture (that is to be activated to form the activated gas mixture) comprises at least one inorganic fluorine source, at least one source of one or more atoms selected from the group consisting of carbon and sulfur, at least one nitrogen source, and optionally at least one oxygen source. Typical inorganic fluorine sources include NF3 and SF6. Where SF6 serves as the inorganic fluorine source, it can also serve as a source of sulfur. When a carbon source is used, a carbon source can be a fluorocarbon or a hydrocarbon, carbon dioxide or carbon monoxide. A fluorocarbon is herein referred to as a compound containing C and F, and optionally O and H. In one embodiment of the invention, a fluorocarbon is a perfluorocarbon or a mixture of one or more perfluorocarbons. A perfluorocarbon compound as referred to in this invention is a compound consisting of C, F and optionally oxygen. Such perfluorocarbon compounds include, but are not limited to tetrafluoromethane, hexafluoroethane, octafluoropropane, hexafluororcyclopropane, decafluorobutane, hexafluoropropene, octafluorocyclobutane and octafluorotetrahydrofuran. Without wishing to be bound by any particular theory, applicant believes that the fluorocarbon of the gas mixture serves as a source of carbon atoms in the activated gas mixture. Carbon source gasses also may include hydrofluorocarbons or hydrocarbons. In one embodiment of the invention, the hydrocarbon carbon source is methane. This was unexpected, as it is commonly held in the art that hydrogen atoms in the activated gas mixture are detrimental due to the expected recombination of F atoms with H atoms to form hydrogen fluoride (HF). This would decrease gas phase reactive F atoms concentrations as well as be deleterious to surfaces inside the apparatus. As illustrated in Example 11 (
In one embodiment of the invention, the percentage on a molar basis of inorganic fluorine source in the gas stream is from about 50% to about 98%. In another embodiment of the invention the percentage on a molar basis of inorganic fluorine source in the gas stream is from about 60% to about 98%. In yet another embodiment of the invention, the percentage on a molar basis of inorganic fluorine source in the gas stream is from about 70% to about 90%. In yet another embodiment of the invention, when NF3 is the source for nitrogen and fluorine and carbon dioxide is the carbon and oxygen source, the percentage on a molar basis of carbon dioxide in the gas stream is from about 2% to about 15%. The gas mixture may further comprise a carrier gas. Examples of suitable carrier gasses include noble gasses such as argon and helium.
In one embodiment, the activated gas mixture contains from about 66% to about 87% fluorine atoms. In one embodiment, the activated gas mixture contains from about 11% to about 24% nitrogen atoms. In one embodiment, the activated gas mixture contains from about 0.9% to about 11% oxygen atoms. In one embodiment, the activated gas mixture contains about 0.6% to about 11% carbon atoms, 0.6% to about 11% sulfur atoms, or mixtures thereof.
In one embodiment of the invention, the activated gas mixture includes from about 66% to about 74% fluorine atoms, from about 11% to about 24% nitrogen atoms, from about 0.9% to about 11% oxygen atoms, and from about 0.6% to about 11% carbon atoms.
In an embodiment of the invention, the temperature in the process chamber during removal of the surface deposits often may be from about 50° C. to about 200° C. Depending on the location within the apparatus, surface temperatures however may range as high as 400° C.
The total pressure in the remote chamber during the activating step may be between about 0.5 torr and about 15 torr using the Astron source. The total pressure in the process chamber may be between about 0.5 torr and about 15 torr. With other types of remote plasma sources or in situ plasma sources, the maximum pressure can be reduced.
It has been found that the combination of an inorganic fluorine source, a nitrogen source, and at least one source of an atom selected from the group consisting of carbon and sulfur, and optionally an oxygen source, results in significantly higher etching rates of nitride films such as silicon nitride. These increases also provide lower sensitivity of the etch rate to variations in source gas pressure, chamber pressure and temperature. Without wishing to be bound by any particular theory, applicant theorizes that a combination of activated gas phase species act to passivate the interior surfaces of the apparatus to significantly reduce the rate of surface recombination of gas phase species, thereby preventing the loss of species after activation. In addition to providing higher etch rates over a wider range of pressures than has been able to be utilized heretofore, it has been found that this also provides significantly enhanced cleaning of the downstream components of the apparatus due to the reduced rate of recombination of gas phase species.
Shown in
By throttling the flow from the chamber and to the pump using one or more throttle valves, 109 and 110, the process chamber can be controlled to control the partial pressure of the reactant during the cleaning process in the process chamber and/or in the exhaust line between the chamber and the pump. Using this invention, it has been demonstrated that the reduced loss rate of reactants by surface recombination allows the increase in cleaning gas pressure without excessive loss of the reactants. The higher partial pressure of the reactant gases can increase the cleaning rate and efficiency. The number, positions, and setting of the throttle valves 109 and 110 can be adjusted before or during the cleaning process to optimize the cleaning of the process chamber and pump exhaust (fore) line. Shown in this example is the use of two throttle valves; however one or more valves may be used. The settings of these valves to optimize the cleaning of the deposits are peculiar to the particular chamber and process conditions used during the PECVD process as well as a function of the temperature of the surfaces and other particulars of the system, but can readily be determined by one of ordinary skill in the art without undue experimentation.
As a result of the reduced dependence of etch rate on pressure and temperature, it is possible to operate the apparatus during the cleaning cycle at a lower temperature, thereby reducing the loss of gas phase species through recombination on interior surfaces and increasing etching rates, and cleaning of exhaust piping between the chamber and the pump.
The following Examples are meant to illustrate the invention and are not meant to be limiting.
The feed gases (e.g. O2, fluorocarbon, NF3 and carrier gas) were introduced into the remote plasma source from the left, and passed through the toroidal discharge where they were discharged by the 400 kHz radio-frequency power to form an activated gas mixture. The oxygen is manufactured by Airgas with 99.999% purity. The fluorocarbon in the examples is either Zyron® 8020 manufactured by DuPont with a minimum 99.9 vol. % of octafluorocyclobutane or Zyron® 116 N5 manufactured by DuPont with a minimum 99.9 vol. % of hexafluoroethane. The NF3 gas is manufactured by DuPont with 99.999% purity. Argon is manufactured by Airgas with a grade of 5.0. Typically, Ar gas is used to ignite the plasmas, after which time flows for the feed gases were initiated, after Ar flow was halted. The activated gas mixture then is passed through an aluminum water-cooled heat exchanger to reduce the thermal loading of the aluminum process chamber. The surface deposits covered wafer was placed on a temperature controlled mounting in the process chamber. The neutral temperature is measured by Optical Emission Spectroscopy (OES), in which rotovibrational transition bands of diatomic species like C2 and N2 are theoretically fitted to yield neutral temperature. See also B. Bai and H Sawin, Journal of Vacuum Science & Technology A 22 (5), 2014 (2004), which is herein incorporated by reference. The etching rate of surface deposits by the activated gas is measured by interferometry equipment in the process chamber. N2 gas is added at the entrance of the exhaustion pump both to dilute the products to a proper concentration for FTIR measurement and to reduce the hang-up of products in the pump. FTIR was used to measure the concentration of species in the pump exhaust.
This example illustrates the effect of the addition of fluorocarbon on the silicon nitride etch rate in NF3 systems with oxygen at different gas compositions and different wafer temperatures. In this experiment, the feed gas was composed of NF3, oxygen and C2F6. Process chamber pressure was 5 torr. Total gas flow rate was 1700 sccm, with flow rates for the individual gases set proportionally as required for each experiment. By way of illustration, in the experiment with 9% oxygen, 9% C2F6, and 82% NF3, the oxygen flow rate was 150 sccm, the C2F6 flow rate was 150 sccm, and the NF3 flow rate was 1400 sccm. The feeding gas was activated by the 400 kHz 5.9-8.7 kW RF power. The activated gas then entered the process chamber and etched the silicon nitride surface deposits on the mounting with the temperature controlled at 50° C. As shown in
This example illustrated the effect of the addition of fluorocarbon on the silicon nitride etch rate in NF3 systems with oxygen and the reduced effect of source pressure on etch rate. The results are illustrated in
This example illustrates the effect of the addition of C2F6 on the silicon nitride etch rate in mixtures of NF3 and oxygen with a chamber pressure of 3.0 torr. Total gas flow rate was 1700 sccm. The results are illustrated in
This example illustrates the effect of the addition of C2F6 on the silicon nitride etch rate in mixtures of NF3 and oxygen and variations in the molar ratio of C2F6 to oxygen with a chamber pressure of 5.0 torr. Total gas flow rate was 1700 sccm. The results are illustrated in
This example illustrates the effect of process chamber temperature on silicon nitride etch rate using a feed gas mixture of 9 mole percent C2F6, 9 mole percent oxygen, and 82 mole percent NF3 and a chamber pressure of 2 torr. Total gas flow rate was 1700 sccm. The results are illustrated in
This example illustrates the effect of process chamber temperature on silicon nitride etch rate using a feed gas mixture of 9 mole percent C2F6, 9 mole percent oxygen, and 82 mole percent NF3 and a chamber pressure of 3 torr. Total gas flow rate was 1700 sccm. The results are illustrated in
This example compares nitride etching using octafluorocyclobutane as the fluorocarbon. In this example, the feed gas mixtures were either 9 mole percent C2F6, 9 mole percent oxygen, and 82 mole percent NF3, or 4.5 mole percent C4F8, 9 mole percent oxygen, and 86.5 mole percent NF3. Total gas flow rate was 1700 sccm. The chamber pressure was 2 torr. The feeding gas was activated by the 400 kHz 6.5 Kw RF power to a neutral temperature of more than 3000 K. The results are illustrated in
This example compares nitride etching using octafluorocyclobutane as the fluorocarbon. In this example, the feed gas mixtures were either 9 mole percent C2F6, 9 mole percent oxygen, and 82 mole percent NF3, or 4.5 mole percent C4F8, 9 mole percent oxygen, and 86.5 mole percent NF3. The chamber pressure was 3 torr. Total gas flow rate was 1700 sccm. The feeding gas was activated by the 400 kHz 6.9 Kw RF power to a neutral temperature of more than 3000 K. The results are illustrated in
This example illustrates the effect of the addition of fluorocarbon on the silicon nitride etch rate in NF3 systems with oxygen at different gas compositions and different wafer temperatures. In this experiment, the feed gas was composed of NF3, with oxygen and C2F6. Process chamber pressure was 5 torr. Total gas flow rate was 4800 sccm, with flow rates for the individual gases set proportionally as required for each experiment. By way of illustration, in the experiment with 1.8% oxygen, 1.1% C2F6, and 97.1% NF3, the oxygen flow rate was 85 sccm, the C2F6 flow rate was 50 sccm, and the NF3 flow rate was 4665 sccm. The feeding gas was activated by the 400 kHz 5-8 kW RF power. The activated gas then entered the process chamber and etched the silicon nitride surface deposits on the mounting with the temperature controlled at 50° C. As shown in
This example illustrates the use of carbon dioxide as a carbon source and oxygen source etching silicon nitride with NF3. Process chamber pressure was 5 torr. Total gas flow rate was 1700 sccm, with flow rates for the individual gases set proportionally as required for each experiment. By way of illustration, in the experiment with 4.5% CO2, and 95.5% NF3, the CO2 flow rate was 75 sccm and the NF3 flow rate was 1625 sccm. The feeding gas was activated by the 400 kHz 5-8 kW RF power. The activated gas then entered the process chamber and etched the silicon nitride surface deposits on the mounting with the temperature controlled at 50° C. As shown in
This example compares CH4 and C2F6 as carbon sources in nitride etching experiments in NF3 systems with oxygen at different gas compositions. In this experiment, the feed gas was composed of NF3, with oxygen and carbon source. Process chamber pressure was 5 torr. Total gas flow rate was 1700 sccm, with flow rates for the individual gases set proportionally as required for each experiment. By way of illustration, in the experiment with 4.5% oxygen, 4.5% C2F6, and 91% NF3, the oxygen flow rate was 75 sccm, the C2F6 flow rate was 75 sccm, and the NF3 flow rate was 1550 sccm. The feeding gas was activated by the 400 kHz 5-8 kW RF power. The activated gas then entered the process chamber and etched the silicon nitride surface deposits on the mounting with the temperature controlled at 50° C. As shown in
This example compares a blend of NF3/C2F6/O2 (82/9/9) with NF3 alone and NF3 plus C2F6 with a wafer temperature of 200° C. Chamber pressures were varied from 0.7 torr to 10 torr. The pressure at the remote source was about 15 torr. Total gas flow rate was 4800 sccm, with flow rates for the individual gasses set proportionally as required for each experiment. For this experiment, the valve (104) as illustrated in
This example compares a blend of NF3/C2F6/O2 (82/9/9) with NF3 with a wafer temperature of 100° C. and chamber pressures from 0.7 torr to 5 torr. The pressure at the remote source was about 15 torr. Total gas flow rate was 4800 sccm, with flow rates for the individual gasses set proportionally as required for each experiment. For this experiment, the valve (104) as illustrated in
While specific embodiments of the invention have been shown and described, further modifications will occur to those skilled in the art. The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.
Number | Date | Country | |
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60704852 | Aug 2005 | US | |
60704840 | Aug 2005 | US | |
60736430 | Nov 2005 | US | |
60779470 | Mar 2006 | US |