JP2007531288A - Remote chamber method for removing surface deposits - Google Patents

Abstract

  The present invention relates to an improved remote plasma cleaning method for removing surface deposits from surfaces such as the interior of a deposition chamber used in the manufacture of electronic devices. The improvement involves using an activated gas at a high neutral temperature of at least about 3,000K. Improvements also involve optimizing the oxygen to fluorocarbon ratio for better etch rate and emission control.

Description

  The present invention relates to a method for removing surface deposits by using an activated gas produced by remotely activating a gas mixture comprising oxygen and a fluorocarbon. More specifically, the present invention is for removing surface deposits from the interior of a chemical vapor deposition chamber using an activation gas generated by remotely activating a gas mixture comprising oxygen and perfluorocarbon. Regarding the method.

  A remote plasma source for the generation of atomic fluorine is used for chamber cleaning in the semiconductor processing industry, especially for chemical vapor deposition (CVD) and plasma enhanced chemical vapor deposition (PECVD). Widely used in the cleaning of chambers used. The use of a remote plasma source avoids some of the erosion of the internal chamber material that occurs in an in-situ chamber clean where cleaning is performed by creating a plasma discharge in the PECVD chamber. Although capacitively coupled and inductively coupled RF and microwave remote sources have been developed for these types of applications, the semiconductor processing industry has found that the plasma has a toroidal configuration and secondary transformers. The transformer coupled inductive coupling source acting as a thing is moving rapidly. The use of lower frequency RF power allows the use of a magnetic core, which improves inductive coupling relative to capacitive coupling, thereby reducing excessive ion bombardment limiting the lifetime inside the remote plasma source chamber. Without it, it allows a more efficient transfer of energy to the plasma.

The semiconductor industry is shifting away from the mixture of fluorocarbon and oxygen for chamber cleaning, which was primarily the primary gas used for in-situ chamber cleaning for several reasons. First, global warming gas emissions from such processes were typically much higher than those of the nitrogen trifluoride (NF ₃ ) process. NF ₃ dissociates more easily in the discharge and is not significantly formed by recombination of product species. Thus, a low level of global warming emissions can be achieved more easily. In contrast, fluorocarbons are more difficult to decompose in electrical discharges and recombine to form species such as tetrafluoromethane (CF ₄ ) that are more difficult to decompose than other fluorocarbons. .

  Second, it has generally been found that fluorocarbon discharges produce “polymer” deposits that require more frequent wet cleans to remove accumulated “polymer” deposits after repeated dry cleans. The tendency of fluorocarbon cleans to deposit “polymer” occurs to a greater extent in remote cleans where ion bombardment does not occur during cleaning. These observations have restrained the semiconductor industry from developing industrial processes based on fluorocarbon feed gas. In fact, PECVD equipment manufacturers have tested remote cleans based on fluorocarbon discharges, but to date have been unsuccessful due to polymer deposition in the process chamber.

B. Bai and H. Sawin, Journal of Vacuum Science & Technology A 22 (5), 2014 (2004)

  However, fluorocarbon gases are desirable because of their low cost and low toxicity where the two drawbacks as described above can be solved.

  The present invention is a method for removing surface deposits comprising: (a) a gas mixture comprising oxygen and fluorocarbon, wherein the molar ratio of oxygen to fluorocarbon is at least 1: 4, wherein the gas mixture comprises at least Activating in a remote chamber to form an activated gas mixture using sufficient power for a sufficient amount of time to reach a neutral temperature of about 3,000 K, and thereafter (b) said activity Contacting the gasified gas mixture with the surface deposit, thereby removing at least some of the surface deposit.

  The surface deposits removed in the present invention include materials that are normally deposited by chemical vapor deposition or plasma enhanced chemical vapor deposition or similar processes. Such materials include silicon, doped silicon, silicon nitride, tungsten, silicon dioxide, silicon oxynitride, silicon carbide, and various silicon oxygen compounds referred to as low-K materials such as black diamond (Black Diamond). PECVD OSG or SiCOH and FSG (Fluorosilicate), including (Applied Materials), Coral (Novellus Systems), and Aurora (ASM International) Glass).

  One embodiment of the present invention is to remove surface deposits from the interior of a process chamber used in manufacturing electronic devices. Such a process chamber can be a chemical vapor deposition (CVD) chamber or a plasma enhanced chemical vapor deposition (PECVD) chamber.

  The process of the present invention involves an activation step that uses sufficient power to form an activated gas mixture having a neutral temperature of at least about 3000K. Activation can be accomplished by any means that considers achieving dissociation of most feed gases, such as RF energy, DC energy, laser illumination, and microwave energy. The neutral temperature of the resulting plasma depends on the power and residence time of the gas mixture in the remote chamber. Under certain power inputs and conditions, the longer the residence time, the higher the neutral temperature. Here, the preferred neutral temperature is greater than about 3,000K. Under appropriate conditions (considering power, gas composition, gas pressure, and gas residence time), a neutral temperature of at least about 6000 K can be achieved, for example, with octafluorocyclobutane.

The activation gas is formed outside the process chamber but in a remote chamber in close proximity to the process chamber. The remote chamber is coupled to the process chamber by any means that allows for transfer of the activated gas from the remote chamber to the process chamber. The remote chamber and the means for coupling the remote chamber with the process chamber are constructed from materials known in the art that can contain an activated gas mixture. For example, aluminum and stainless steel are typically used for chamber components. Sometimes Al ₂ O ₃ is coated on the inner surface to reduce surface recombination.

  The gas mixture that is activated to form an activated gas includes oxygen and a fluorocarbon. The fluorocarbon of the present invention is herein referred to as a compound containing C and F. A preferred fluorocarbon in the present invention is a perfluorocarbon compound. The perfluorocarbon compound in the present invention is referred to herein as a compound comprising C, F, and optionally oxygen. Such perfluorocarbon compounds include, but are not limited to, tetrafluoromethane, hexafluoroethane, octafluoropropane, hexafluorocyclopropane decafluorobutane, octafluorocyclobutane, carbonyl fluoride, and octafluorotetrahydrofuran. . A preferred perfluorocarbon is octafluorocyclobutane.

  The gas mixture that is activated to form the activated gas can further include a carrier gas such as nitrogen, argon, and helium.

  The total pressure in the remote chamber during the activation process can be about 0.5 torr to about 20 torr.

The gas mixture includes oxygen and fluorocarbon in a molar ratio of at least about 1: 4. Under the high neutral temperature conditions used in the present invention, oxygen exceeding 10 mole percent of the stoichiometric requirement (ie, the amount of oxygen required to convert all the carbon in the fluorocarbon to CO ₂ ) is surprisingly good It resulted Do deposition chamber cleaning rates, eliminate fluorocarbon emissions than COF _2, to prevent the fluorocarbon polymer deposited on the deposition surface.

  The gas mixture is activated using sufficient power for a sufficient time such that the gas mixture reaches a neutral temperature of at least about 3,000 K to form an activated gas mixture. For example, a power range of about 3,000 to 15,000 watts in a 0.25 liter remote chamber corresponds to a power density of about 12,000 to 60,000 watts / liter. These values scale for different sized remote chambers. The residence time of the gas mixture in the remote chamber under such power input must be sufficient for the gas mixture to achieve a neutral temperature of at least about 3,000K. Under appropriate conditions (considering power, gas composition, gas pressure, and gas residence time), a neutral temperature of at least about 6000 K can be achieved, for example, with octafluorocyclobutane. A preferred embodiment of the present invention is a method for removing surface deposits from the interior of a process chamber used in manufacturing electronic devices, comprising: (a) at least about 2: 1 to about 20: 1. A gas mixture comprising oxygen and perfluorocyclobutane in a molar ratio can be remoted using a power of at least about 3,000 watts for a sufficient time such that the gas mixture reaches a neutral temperature of at least about 3,000 K. Activating in the chamber to form an activated gas mixture, and then (b) contacting the activated gas mixture with the interior of the deposition chamber, thereby removing at least some of the surface deposits. A process comprising the steps of:

  It has also been found that under similar conditions of the invention, the disadvantages of perfluorocarbon compounds can be overcome, namely global warming gas emissions and polymer deposition. In the experiments of the present invention, no significant polymer deposition was found on the inner surface of the chamber. See also FIGS. 6a, 6b, and 6c. As shown in FIGS. 3a, 3b, 3c, and 3d, the greenhouse gas emissions were also very low.

  Alternatively, the system can be used to change the surface located in the remote chamber by contact with fluorine atoms and other components coming from this source.

  The following examples are intended to illustrate the invention and are not intended to be limiting.

FIG. 1 shows a schematic diagram of a remote plasma source and apparatus used to measure etch rate, plasma neutral temperature, and exhaust emissions. The remote plasma source is a commercially available toroidal type MKS Astron® ex reactive gas generator unit manufactured by MKS Instruments, Andover, MA, USA, Andover, Massachusetts. A feed gas (eg, oxygen, fluorocarbon, argon) was introduced into the remote plasma source from the left and passed through a toroidal discharge where they were discharged with 400 KHz radio frequency power to form an activated gas mixture. Oxygen is produced by Airgas with a purity of 99.999%. The fluorocarbon is Zyron (R) 8020 manufactured by the present applicant with a minimum of 99.9 vol% octafluorocyclobutane. Argon is produced by air gas with a grade of 5.0. The activated gas then passed through an aluminum water cooled heat exchanger to reduce the heat loading of the aluminum process chamber. The wafer coated with the surface deposit was placed on a temperature control mount in the process chamber. Neutral temperatures are measured by Optical Emission Spectroscopy (OES), because the rotational transition bands of diatomic species such as C ₂ and N ₂ produce neutral temperatures. Theoretically adapted to. See also (Non-Patent Document 1), which is incorporated herein by reference. The etch rate of the surface deposit with the activated gas is measured by an interferometric instrument in the process chamber. N ₂ gas is added at the inlet of the pump to dilute the product to an appropriate concentration for FTIR measurement and reduce product hang-up in the pump. The concentration of species in the pump exhaust was measured using FTIR.

Example 1
The feed gas includes O ₂ , perfluorocarbon, and Ar, and the perfluorocarbon is Zylon® 8020 (C ₄ F ₈ ), C ₃ F ₈ , C ₂ F ₆ , or CF ₄ . The perfluorocarbon flow rate in this example was adjusted so that the molar flow rate of elemental fluorine into the remote chamber was the same for all mixtures. In this example, the flow rates of C ₄ F ₈ , C ₃ F ₈ , C ₂ F ₆ , and CF ₄ are 250, 250, 333, and 500 sccm, respectively, which are all at 2000 sccm of elemental fluorine. equal. The percentage flow rate of O ₂ relative to the sum of O ₂ and perfluorocarbon was varied to detect the etch rate dependence on O ₂ percentage. Please refer to FIG. The total feed gas flow rate was fixed at 4000 sccm by adjusting the argon flow. Nitrogen was added between the process chamber and the pump at a flow rate of 20,000 sccm. The chamber pressure is 2 torr. The feed gas was activated by 400 KHz RF power to a neutral temperature above 5000K. Next, the activation gas entered the process chamber with the temperature controlled at 100 ° C. to etch the SiO ₂ surface deposit on the mount. The result is shown in FIG.

As a reference, the etch rate of NF ₃ + Ar plasma is shown in FIG. 2 because it is the standard gas used for remote chamber cleaning. Conditions all, NF ₃ flow rate for the NF ₃ is, except a 667sccm equal to 2000sccm elemental fluorine was the same as for perfluorocarbon was described above. As shown in FIG. 2, the percentage of O ₂ (O ₂ / (C _x F _y + O ₂ )) is critical to the perfluorocarbon etch rate. The optimal O ₂ percentage allows the perfluorocarbon etch rate to be close to the NF ₃ etch rate.

The O ₂ percentages corresponding to the maximum etch rates of CF ₄ , C ₂ F ₆ , C ₃ F ₈ , and C ₄ F ₈ were 55%, 77%, 80%, and 87%, respectively. The optimal O ₂ percentage differs from that for in-situ chamber cleaning with perfluorocarbon gas or with a remote microwave source. It is also more than expected stoichiometric amount of oxygen required to change all the carbon in the fluorocarbon CO _2.

(Example 2)
The common experimental conditions of FIGS. 3a, 3b, 3c, and 3d are described in the following paragraphs.

The chamber pressure was 2 torr. The feed gas was activated by 400 KHz RF power to a neutral temperature above 3000 K for the NF ₃ gas mixture and above 5000 K for the perfluorocarbon gas mixture. Next, the activation gas entered the process chamber with the temperature controlled at 100 ° C. to etch the SiO ₂ surface deposit on the mount. The concentration of released species in the pump exhaust was measured using FTIR.

For FIG. 3a, the feed gas included NF ₃ and argon, and the flow rates were 333 sccm and 3667 sccm, respectively.

For FIG. 3b, the feed gas included 125 sccm C ₃ F ₈ , 500 sccm O ₂ , and 3375 sccm argon.

With respect to FIG. 3c, the feed gas included 125 sccm C ₄ F ₈ , 1125 sccm O ₂ , and 2750 sccm argon.

With respect to FIG. 3d, the feed gas included 250 sccm of CF ₄ , 306 sccm of O ₂ and 3444 sccm of argon.

Figures 3a, 3b, 3c, and 3d show the concentration of released species in the pump exhaust as measured by FTIR. FIG. 3a shows that NF ₃ was almost completely decomposed by Astron® ex plasma. Similarly, C ₃ F ₈ , CF ₄ , and C ₄ F ₈ were almost completely destroyed in their respective optimal oxygen mixtures, and no measurable perfluorocarbon was observed in the pump exhaust. However, a large amount of COF ₂ was present in the pump effluent.

The results from C ₂ F ₆ are similar and are not shown here. Clearly, under the conditions of the present invention, there is no perfluorocarbon emission other than COF _{2 in the} perfluorocarbon containing mixed effluent. This is quite different from the results of in-situ chamber cleaning with perfluorocarbon gas with significant perfluorocarbon emissions.

(Example 3)
4a and 4b show the effect of perfluorocarbon flow rate and O ₂ percentage (O ₂ / (C _x F _y + O ₂ )) on the concentration of the emitted gas. For both figures, from left to right, each group of bars indicates the release concentration of C ₄ F ₈ , C ₂ F ₆ , C ₃ F ₈ , CF ₄ , and COF ₂ . For the experiment of FIG. 4a, the C ₄ F ₈ flow rate was 93.75 sccm, 125 sccm, 187.5 sccm, or 250 sccm, as shown in axis X of the figure. Corresponding flow rate of _{O 2,} respectively, 656,875,1313, and 1750Sccm. The total feed gas flow rate was fixed at 4000 sccm by adjusting the argon flow. The chamber pressure was 2 torr. The feed gas was activated by 400 KHz RF power to a neutral temperature above 5000K. Next, the activation gas entered the process chamber with the temperature controlled at 100 ° C. to etch the SiO ₂ surface deposit on the mount. The concentration of released species in the pump exhaust was measured using FTIR.

For the experiment of FIG. 4b, the C ₄ F ₈ flow rate was 250 sccm. The O ₂ flow rates were 250, 375, 750, 1000, 1417, 2250, and 2875 sccm, shown as O ₂ percentage on the axis X in the figure. The total feed gas flow rate was fixed at 4000 sccm by adjusting the argon flow. The chamber pressure was 2 torr. The feed gas was activated by 400 KHz RF power to a neutral temperature above 5000K. Next, the activation gas entered the process chamber with the temperature controlled at 100 ° C. to etch the SiO ₂ surface deposit on the mount. The concentration of released species in the pump exhaust was measured using FTIR.

In FIG. 4a, perfluorocarbon release was measured when the C ₄ F ₈ flow rate was varied while maintaining the O ₂ percentage at the optimum condition. No measurable perfluorocarbon release was detected.

FIG. 4b shows that when the O ₂ percentage is close to or higher than the optimum value, no perfluorocarbon release was detected that could be measured under the conditions of the present invention. However, perfluorocarbon emission began to appear when the O ₂ percentage was much lower than the optimum value. These results suggest that the amount of O ₂ added to the perfluorocarbon plasma is important for complete dissociation of the perfluorocarbon gas and reduction of perfluorocarbon emissions.

Example 4
In this experiment, the surface composition of the sapphire sample was measured before and after exposure to the activated gas in the process chamber. Figures 5a and 5b are X-ray Photoelectron Spectroscopy (XPS) of the sapphire surface. 6a, 6b, and 6c are atomic force microscope (AFM) measurements of the sapphire surface.

For the experiment of FIG. 5a and 6b, the feed gas is contained and _{O 2} of 2233Sccm, and _C 2 _{F 6} of 667, and Ar of 1100Sccm. The chamber pressure is 2 torr. The feed gas was activated by 400 KHz RF power to a neutral temperature above 5000K. The activation gas then entered the process chamber with the sapphire sample on the mount and the temperature controlled at 25 ° C.

For the experiments of FIGS. 5b and 6c, the feed gas included 667 sccm C ₂ F ₆ and 1100 sccm Ar. Other conditions were the same as those described above for the experiments of FIGS. 5a and 6b.

FIG. 5a was a measurement of the sapphire surface after 10 minutes exposure to the activation gas. Oxygen, aluminum, and fluorine indicia were present on the surface, but no carbon was observed. Similar results were observed for C ₄ F ₈ and CF ₄ discharges. This suggests that with an optimized O ₂ percentage, perfluorocarbon gas can be used for chamber cleaning without any perfluorocarbon deposition. AFM measurements confirmed this conclusion. FIG. 6a was a measurement of the sapphire surface before exposure, and FIG. 6b was a measurement of the sapphire surface after exposure for 10 minutes. FIGS. 6a and 6b show no measurable changes and no significant perfluorocarbon polymer deposition on the sapphire surface.

FIG. 5b was a measurement of the sapphire surface after 10 minutes exposure to an oxygen-free activated gas. In the absence of O ₂ in the feed gas, only carbon and fluorine indicia were observed in FIG. 5b, indicating deposition of a perfluorocarbon polymer film sufficiently coated with sapphire that the substrate could not be seen. This result was confirmed by the AFM measurement of FIG. 6c, where the smooth surface suggested the deposition of a perfluorocarbon polymer film on the surface.

1 is a schematic diagram of an apparatus useful for performing the process. FIG. FIG. 6 is a plot of silicon dioxide etch rate at 100 ° C. as a function of O ₂ percentage in a perfluorocarbon and O ₂ mixture. FIG. 4 is a plot of Fourier Transformed Infrared Spectroscopy (FTIR) measurement of the concentration of gas emitted from a pump with NF ₃ + Ar discharge. FIG. 2 is a plot of Fourier Transformed Infrared Spectroscopy (FTIR) measurements of the concentration of gas emitted from a pump with a C ₃ F ₈ + O ₂ + Ar discharge. FIG. 4 is a plot of Fourier Transformed Infrared Spectroscopy (FTIR) measurements of the concentration of gas released from a pump with a C ₄ F ₈ + O ₂ + Ar discharge. FIG. 5 is a plot of Fourier Transformed Infrared Spectroscopy (FTIR) measurement of the concentration of gas released from a pump of CF ₄ + O ₂ + Ar discharge. ₄ is a bar graph of FTIR measurement of the concentration of gas released from a pump with a C ₄ F ₈ discharge at different C ₄ F ₈ flow rates. ₄ is a bar graph of FTIR measurements of the concentration of gas released from a pump with a C ₄ F ₈ discharge at different O ₂ percentages. X-ray photoelectron spectroscopy (XPS) measurements on a flat sapphire wafer surface exposed to C ₂ F ₆ activated gas with O ₂ addition. X-ray photoelectron spectroscopy (XPS) measurement on a flat sapphire wafer surface exposed to C ₂ F ₆ activated gas without O ₂ addition. An atomic force microscope (AFM) micrograph of the surface of a sapphire wafer before exposure to a C ₂ F ₆ activated gas. An atomic force microscope (AFM) photomicrograph of the surface of a sapphire wafer after exposure to a C ₂ F ₆ activation gas with O ₂ addition. An atomic force microscope (AFM) photomicrograph of the surface of a sapphire wafer after exposure to a C ₂ F ₆ activated gas without O ₂ addition.

Claims (11)

A method for removing surface deposits, comprising:
(A) a gas mixture comprising oxygen and fluorocarbon, wherein the molar ratio of oxygen to fluorocarbon is at least 1: 4, for a time sufficient for said gas mixture to reach a neutral temperature of at least about 3,000 K; Using sufficient power to activate in a remote chamber to form an activated gas mixture;
(B) contacting the activated gas mixture with the surface deposit, thereby removing at least some of the surface deposit.   The method of claim 1, wherein the surface deposit is removed from within a deposition chamber used in manufacturing an electronic device.   The method of claim 1, wherein the power is generated by an RF source, a DC source, or a microwave source.   The method of claim 1, wherein the fluorocarbon is a perfluorocarbon compound.   The method according to claim 4, wherein the perfluorocarbon is selected from the group consisting of tetrafluoromethane, hexafluoroethane, octafluoropropane, octafluorocyclobutane, carbonyl fluoride, and perfluorotetrahydrofuran.   The method of claim 1, wherein the gas mixture further comprises a carrier gas.   The method of claim 6, wherein the carrier gas is at least one gas selected from the group of gases consisting of nitrogen, argon, and helium.   The method of claim 1, wherein the pressure in the remote chamber is between 0.5 and 20 torr.   The surface deposit is selected from the group consisting of silicon, doped silicon, silicon nitride, tungsten, silicon dioxide, silicon oxynitride, silicon carbide, and various silicon oxygen compounds referred to as low K materials. The method according to claim 1.   The method of claim 1, wherein the molar ratio of oxygen to fluorocarbon is at least about 2: 1 to about 20: 1. A method for removing surface deposits from within a deposition chamber used in manufacturing an electronic device comprising:
(A) a gas mixture comprising oxygen and perfluorocyclobutane in a molar ratio of at least about 2: 1 to about 20: 1 for a time sufficient for the gas mixture to reach a neutral temperature of at least about 3,000 K; Using a power of at least about 3,000 watts to activate in a remote chamber to form an activated gas mixture;
(B) contacting the activated gas mixture with the interior of the deposition chamber, thereby removing at least some of the surface deposits.

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