Treatment method and cleaning method for metal oxyfluorides

Abstract

A treatment method according to the present invention includes bringing a metal oxyfluoride of the general formula: MO.sub.(6-x)/2F.sub.x (where 0<x<6; and M=W or Mo) into contact with a fluorine-containing gas at a reaction temperature higher than or equal to 0° C. and lower than 400° C., thereby converting the metal oxyfluoride to a metal hexafluoride of the general formula: MF.sub.6 (where M=W or Mo). This treatment method enables conversion of the metal oxyfluoride to the high vapor pressure compound without the use of a plasma generator and can be applied to cleaning of a metal fluoride production apparatus or cleaning of a film forming apparatus.

Claims

1. A treatment method for a metal oxyfluoride, comprising bringing a metal oxyfluoride of the general formula: MO.sub.(6-x)/2F.sub.x (where 0<x<6; and M=W or Mo) into contact with at least one kind of fluorine-containing gas selected from the group consisting of F.sub.2 gas, NF.sub.3 gas, ClF.sub.3 gas, and IF.sub.7 gas at a reaction temperature ranging from 10° C. to 200° C., thereby converting the metal oxyfluoride to a metal hexafluoride of the general formula: MF.sub.6 (where M=W or Mo).

2. The treatment method according to claim 1, wherein a contact pressure of the metal oxyfluoride and the fluorine-containing gas is 0.01 kPa to 300 kPa in terms of absolute pressure.

3. A cleaning method of a metal fluoride production apparatus, the metal fluoride production apparatus being configured for producing a metal hexafluoride of the general formula: MF.sub.6 (where M=W or Mo), the cleaning method comprising: converting a metal oxyfluoride of the general formula: MO.sub.(6-x)/2F.sub.x (where 0<x<6; and M=W or Mo) deposited on an inner surface of the metal fluoride production apparatus to a metal hexafluoride by the treatment method according to claim 1 and thereby removing the metal oxyfluoride.

4. A cleaning method of a film forming apparatus, the film forming apparatus being configured for forming a film from a metal hexafluoride of the general formula: MF.sub.6 (where M=W or Mo), the cleaning method comprising: converting a metal oxyfluoride of the general formula: MO.sub.(6-x)/2F.sub.x (where 0<x<6; and M=W or Mo) deposited on an inner surface of the film forming apparatus to a metal hexafluoride by the treatment method according to claim 1 and thereby removing the metal oxyfluoride.

5. The treatment method according to claim 1, wherein the fluorine-containing gas is F.sub.2 gas.

6. The treatment method according to claim 1, wherein the fluorine-containing gas is NF.sub.3 gas.

7. The treatment method according to claim 1, wherein the fluorine-containing gas is ClF.sub.3 gas.

8. The treatment method according to claim 1, wherein the fluorine-containing gas is IF.sub.7 gas.

9. The treatment method according to claim 1, wherein, in the general formula: MO.sub.(6-x)/2F.sub.x, x is 4.

10. The treatment method according to claim 1, wherein the fluorine-containing gas is diluted with an inert gas so that the fluorine-containing gas diluted with the inert gas comes into contact with the metal oxyfluoride.

11. The treatment method according to claim 1, wherein the metal oxyfluoride is brought into contact with the nitrogen-containing gas in a plasmaless manner.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a cleaning method of a metal fluoride production apparatus according to one embodiment of the present invention.

(2) FIG. 2 is a schematic view of a cleaning method of a film forming apparatus according to another embodiment of the present invention.

(3) FIG. 3 is a schematic view of an experimental apparatus used in Examples to evaluate a treatment method for a metal oxyfluoride.

DETAILED DESCRIPTION OF EMBODIMENTS

(4) Embodiments of a treatment method and cleaning methods for metal oxyfluorides according to the present invention will be described in detail below. It should be understood that the present invention is not limited to the following embodiments.

(5) The treatment method and cleaning methods according to the present invention are characterized by bringing a metal oxyfluoride of the general formula: MO.sub.(6-x)/2F.sub.x (where 0<x<6; and M=W or Mo) into contact with a fluorine-containing gas at a temperature higher than or equal to 0° C. and lower than 400° C., thereby converting the metal oxyfluoride to a metal hexafluoride of the general formula: MF.sub.6 (where M=W or Mo).

(6) By bringing the metal oxyfluoride into contact with the fluorine-containing gas, the metal oxyfluoride is converted to the metal hexafluoride through chemical reaction as shown in the above reaction schemes (9-1) to (9-4). The metal hexafluoride such as tungsten hexafluoride (melting point: 2.3° C., boiling point: 17.1° C.) or molybdenum oxyfluoride (melting point: 17.5° C., boiling point: 34.0° C.) formed by conversion from the metal oxyfluoride such as WOF.sub.4 (melting point: 106° C., boiling point: 187° C.) or MoF.sub.4 (melting point: 98° C., boiling point: 186° C.) is high in vapor pressure. Thus, dry cleaning and removal of the metal oxyfluoride deposited in the apparatus is accomplished by conversion of the metal oxyfluoride to the metal hexafluoride.

(7) It is preferable that the fluorine-containing gas is any selected from F.sub.2 gas, NF.sub.3 gas, ClF.sub.3 gas and IF.sub.7 gas. The F.sub.2 gas and the NF.sub.3 gas are preferred in that only a gas easy to separate, such as oxygen gas or nitrogen gas, is generated. The ClF.sub.3 gas and the IF.sub.7 gas are preferred in that the reaction of these gases with the metal oxyfluoride proceeds rapid so as to allow rapid conversion of the metal oxyfluoride to the metal hexafluoride for quick removal of the metal oxyfluoride.

(8) The temperature of the chemical contact reaction between the metal oxyfluoride and the fluorine-containing gas is preferably higher than or equal to 0° C. and lower than or equal to 400° C., more preferably higher than or equal to 10° C. and lower than or equal to 200° C., still more preferably higher than or equal to 50° C. and lower than or equal to 200° C. When the reaction temperature is lower than or equal to 0° C., the metal hexafluoride MF.sub.6 (M=W or Mo) formed in the reaction may be undesirably liquefied or solidified on the metal oxyfluoride so that the fluorine-containing gas and the metal oxyfluoride are not efficiently brought into contact with each other. When the reaction temperature is lower than or equal to 50° C., ClO.sub.2F gas may be generated as a by-product of the reaction with the use of ClF.sub.3 gas as the fluorine-containing gas; IOF.sub.5 gas may be generated as a by-product of the reaction with the use of IF.sub.7 gas as the fluorine-containing gas. The generation of such a by-product gas would not interfere with implementation of the present invention. When the reaction temperature is higher than or equal to 400° C., the apparatus may be undesirably corroded by the fluorine-containing gas. The present invention is particularly advantageous in that the metal oxyfluoride can be removed, even at a temperature lower than or equal to the boiling point, by fluorination of the metal oxyfluoride with the fluorine-containing gas.

(9) Further, the contact pressure of the metal oxyfluoride and the fluorine-containing gas in the reaction is preferably in the range of 0.01 kPa to 300 kPa, more preferably 0.01 kPa to 100 kPa, in terms of absolute pressure. When the contact pressure is lower than 0.01 kPa in terms of absolute pressure, the load on the equipment for maintaining the pressure may become undesirably high. When the contact pressure is higher than 300 kPa in terms of absolute pressure, there may undesirably occur leakage of the fluorine-containing gas from the apparatus.

(10) For the purpose of decreasing the partial pressures of the fluorine-containing gas, the metal oxyfluoride and the metal hexafluoride so as to prevent liquefaction or solidification of these gases and to allow the reaction of the fluorine-containing gas and the metal oxyfluoride to proceed gently, the fluorine-containing gas may be diluted with an inert gas. The inert gas can be of a kind that does not react with the fluorine-containing gas, the metal oxyfluoride and the metal hexafluoride. Preferred examples of the inert gas are nitrogen gas, argon gas, helium gas and the like. Among others, nitrogen gas is particularly preferred because of its low cost.

(11) Since the metal oxyfluoride is converted to an oxide by reaction with water in the gas, it is preferable that the content of water in the fluorine-containing gas and the inert gas is low. For example, the content of water in the gas is preferably lower than 10 volume ppm. It is feasible to supply the fluorine-containing gas by either a continuous system or a batch system. The supply system of the fluorine-containing gas can be selected as appropriate.

(12) The treatment method and cleaning methods according to the present invention enable dry removal of the metal oxyfluoride without the use of plasma. It is therefore possible in the present invention to remove the metal oxyfluoride at low cost. The metal oxyfluoride, even at a location where it is difficult to place a plasma generator, can be removed.

(13) Differently from the method of Patent Document 1 in which the metal oxyfluoride is removed with the use of a large amount of heated gas but without the aid of chemical reaction, the treatment method and cleaning methods for the metal oxyfluorides according to the present invention is characterized in that the metal oxyfluoride is converted to the metal hexafluoride by chemical reaction with the fluorine-containing gas and thereby removed as the metal hexafluoride. As the amount of the fluorine-containing gas used is small, the total amount of the gas fed through the apparatus is small. Consequently, the load on the apparatus to which the treatment method or cleaning method according to the present invention is applied is lowered.

(14) (Cleaning Method of Metal Fluoride Production Apparatus)

(15) A cleaning method of a metal fluoride production apparatus using the treatment method for the metal oxyfluoride according to the present invention will be explained below with reference to FIG. 1.

(16) As shown in FIG. 1, the metal fluoride production apparatus 11 has a reactor 13. For production of a metal fluoride, metal tungsten or metal molybdenum in powdery form, granular form or bulk form is charged in the reactor 13; and fluorine gas, nitrogen trifluoride gas or the like is supplied into the reactor 13. Then, the metal fluoride such as metal hexafluoride is obtained in gaseous form. During the reaction, a metal fluoride is generated as shown in the above reaction scheme (3-1) etc. and left as a deposit 17 on an inner surface of the reactor 13 or piping system. The following explanation will be given to the cleaning of the metal fluoride production apparatus 11 in which the deposit 17 is present on the inner surface of the reactor 13.

(17) A heater 15 is disposed around the reactor 13 such that the inside of the reactor can be heated by the heater. The fluorine-containing gas is supplied from a fluorine-containing gas supply unit 21 into the reactor 13, whereas the inert gas is supplied from an inert gas supply unit 31 into the reactor 13. The gas is discharged from the reactor through a gas discharge line 41 by a gas discharge device 45.

(18) The cleaning is performed by supplying the fluorine-containing gas and optionally the inert gas into the reactor 13 while heating the inner surface of the reactor 13 to a predetermined temperature by the heater 15 as needed or leaving the inner surface of the reactor 13 at room temperature. When the fluorine-containing gas is reacted with the deposit 17 of metal oxyfluoride, the metal oxyfluoride is converted to a metal hexafluoride and thus removed as a volatile gas.

(19) In this method, the deposit 17 inside the metal fluoride production apparatus 11 is removed by a dry process without the use of a plasma generator and with the reactor 13 being open to the atmosphere.

(20) (Cleaning Method of Film Forming Apparatus)

(21) A cleaning method of a film forming apparatus using the treatment method for the metal oxyfluoride according to the present invention will be next explained below with reference to FIG. 2.

(22) As shown in FIG. 2, the film forming apparatus 53 has a chamber 53. For used of the film forming apparatus, a treatment target object such as silicon wafer is place on a stage 57 inside the chamber 53; tungsten hexafluoride or molybdenum hexafluoride gas and optionally H.sub.2 gas are supplied into the chamber. Then, a film of tungsten, molybdenum or a compound thereof is formed on the treatment target object. During the reaction, a metal fluoride is generated under the influence of water or oxide and left as a deposit 59 on an inner surface of the chamber 55 or piping system and on a surface of the stage 57. The following explanation will be given to the cleaning of the film forming apparatus 51 in which the deposit 59 is present on the inner surface of the chamber 53 and on the surface of the stage 57.

(23) A heater 55 is disposed around the chamber 53 and in the stage 57 such that the inside of the heater can be heated by the heater. The fluorine-containing gas is supplied from a fluorine-containing gas supply unit 61 into the chamber 53, whereas the inert gas is supplied from an inert gas supply unit 71 into the chamber 53. The gas is discharged from the chamber through a gas discharge line 81 by a gas discharge device 85.

(24) The cleaning is performed by supplying the fluorine-containing gas and optionally the inert gas into the chamber 53 while heating the inner surface of the chamber 53 and the surface of the stage 57 to a predetermined temperature by the heater 15 as needed or leaving the inner surface of the chamber 53 and the surface of the stage 57 at room temperature. When the fluorine-containing gas is reacted with the deposit 59 of metal oxyfluoride, the metal oxyfluoride is converted to a metal hexafluoride and thus removed as a volatile gas. In the case where the deposit is present on an inner surface of the piping system such as gas discharge line 81 connected to the chamber 53, the deposit is cleaned away from the piping system by supplying the fluorine-containing gas and optionally the inert gas into the piping system while heating the piping system by a heater disposed therearound or leaving the piping system at room temperature.

(25) In this method, the deposit 59 inside the film forming apparatus 51 is removed by a dry process without the use of a plasma generator and with the chamber 53 being open to the atmosphere.

EXAMPLES

(26) The treatment method for the metal oxyfluoride according to the present invention will be described in more detail below by way of the following examples. FIG. 3 is a schematic view of an experimental apparatus used in Examples to evaluate the treatment method for the metal oxyfluoride. It should be understood that the treatment method for the metal oxyfluoride according to the present invention is not limited to the following examples.

Example 1

(27) In a container 103 of 100 cm.sup.3 volume, 33 g of tungsten oxyfluoride as a metal oxyfluoride 105 is charged. The inside of the container was replaced with nitrogen gas by supplying nitrogen gas from an inert gas supply unit 102 into the container and vacuuming the container with a gas discharge device 104. Fluorine gas was introduced from a fluorine-containing gas supply unit 101 into the container until the inside of the container reached an absolute pressure of 100 kPa as measured by a pressure gauge (not shown). The fluorine gas was thus brought into contact with the metal oxyfluoride 105. At this time, the molar ratio of the metal oxyfluoride to the fluorine gas was 30. Further, the temperature of the container 103 was set to 20° C. by a heater 106. In this state, the metal oxyfluoride was left still in the container for 2 hours. After that, a part of the gas in the container 103 was taken out as a sample. The concentration of tungsten hexafluoride in the sample gas was measured with an infrared spectrometer. Based on the measurement result, the conversion rate of the fluorine-containing gas was calculated. The conversion rate refers to the proportion of fluorine gas consumed for conversion of the metal oxyfluoride to the tungsten hexafluoride during the reaction time of 2 hours among the fluorine gas introduced into the container. As a result, the conversion rate of the fluorine gas was 1%. The longer the reaction rate, the higher the conversion rate.

Example 2

(28) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 1, except that nitrogen trifluoride gas was used as the fluorine-containing gas. As a result, the conversion rate of the nitrogen trifluoride gas was 1%.

Example 3

(29) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 1, except that chlorine trifluoride gas was used as the fluorine-containing gas. As a result, the conversion rate of the chlorine trifluoride gas was 53%.

Example 4

(30) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 1, except that idodine heptafluoride gas was used as the fluorine-containing gas. As a result, the conversion rate of the idodine heptafluoride gas was 43%.

Example 5

(31) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 1, except that molybdenum oxyfluoride was used as the metal oxyfluoride. As a result, the conversion rate of the fluorine gas was 1%.

Example 6

(32) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 2, except that molybdenum oxyfluoride was used as the metal oxyfluoride. As a result, the conversion rate of the nitrogen trifluoride gas was 1%.

Example 7

(33) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 3, except that molybdenum oxyfluoride was used as the metal oxyfluoride. As a result, the conversion rate of the chlorine trifluoride gas was 65%.

Example 8

(34) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 4, except that molybdenum oxyfluoride was used as the metal oxyfluoride. As a result, the conversion rate of the idodine heptafluoride gas was 57%.

Example 9

(35) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 1, except that the temperature of the container 103 was set to 150° C. by the heater 106. As a result, the conversion rate of the fluorine gas was 19%.

Example 10

(36) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 2, except that the temperature of the container 103 was set to 150° C. by the heater 106. As a result, the conversion rate of the nitrogen trifluoride gas was 14%.

Example 11

(37) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 3, except that the temperature of the container 103 was set to 150° C. by the heater 106. As a result, the conversion rate of the chlorine trifluoride gas was 86%.

Example 12

(38) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 4, except that the temperature of the container 103 was set to 150° C. by the heater 106. As a result, the conversion rate of the idodine heptafluoride gas was 78%.

Example 13

(39) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 9, except that molybdenum oxyfluoride was used as the metal oxyfluoride. As a result, the conversion rate of the fluorine gas was 25%.

Example 14

(40) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 10, except that molybdenum oxyfluoride was used as the metal oxyfluoride. As a result, the conversion rate of the nitrogen trifluoride gas was 16%.

Example 15

(41) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 11, except that molybdenum oxyfluoride was used as the metal oxyfluoride. As a result, the conversion rate of the chlorine trifluoride gas was 89%.

Example 16

(42) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 12, except that molybdenum oxyfluoride was used as the metal oxyfluoride. As a result of the reaction, the conversion rate of the idodine heptafluoride gas was 80%.

Comparative Example 1

(43) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 1, except that nitrogen gas was supplied from the inert gas supply unit in place of the fluorine-containing gas. As a result, the formation of tungsten hexafluoride was not seen. It was impossible to calculate the conversion rate.

Comparative Example 2

(44) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Example 5, except that nitrogen gas was supplied from the inert gas supply unit in place of the fluorine-containing gas. As a result, the formation of molybdenum hexafluoride was not seen. It was impossible to calculate the conversion rate.

Comparative Example 3

(45) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Comparative Example 1, except that the temperature of the container 103 was set to 150° C. by the heater 106. As a result, the formation of tungsten hexafluoride was not seen. It was impossible to calculate the conversion rate.

Comparative Example 4

(46) The contact reaction of the fluorine-containing gas and the metal oxyfluoride was carried out in the same manner as in Comparative Example 2, except that the temperature of the container 103 was set to 150° C. by the heater 106. As a result, the formation of molybdenum hexafluoride was not seen. It was impossible to calculate the conversion rate.

(47) The above examples and comparative examples are summarized in TABLE 2.

(48) TABLE-US-00002 TABLE 2 Metal oxyfluoride/ fluorine- Conversion Example/ Fluorine- containing gas rate (%) of Comparative containing Metal molar ratio Temp. fluorine- Example gas oxyfluoride (mol/mol) (° C.) containing gas Example 1 F.sub.2 WOF.sub.4 30 20  1% Example 2 NF.sub.3 WOF.sub.4 30 20  1% Example 3 ClF.sub.3 WOF.sub.4 30 20 53% Example 4 IF.sub.7 WOF.sub.4 30 20 43% Example 5 F.sub.2 MoOF.sub.4 30 20  1% Example 6 NF.sub.3 MoOF.sub.4 30 20  1% Example 7 ClF.sub.3 MoOF.sub.4 30 20 65% Example 8 IF.sub.7 MoOF.sub.4 30 20 57% Example 9 F.sub.2 WOF.sub.4 30 150 19% Example 10 NF.sub.3 WOF.sub.4 30 150 14% Example 11 ClF.sub.3 WOF.sub.4 30 150 86% Example 12 IF.sub.7 WOF.sub.4 30 150 78% Example 13 F.sub.2 MoOF.sub.4 30 150 25% Example 14 NF.sub.3 MoOF.sub.4 30 150 16% Example 15 ClF.sub.3 MoOF.sub.4 30 150 89% Example 16 IF.sub.7 MoOF.sub.4 30 150 80% Comparative N.sub.2 WOF.sub.4 30 20 — Example 1 Comparative N.sub.2 MoOF.sub.4 30 20 — Example 2 Comparative N.sub.2 WOF.sub.4 30 150 — Example 3 Comparative N.sub.2 MoOF.sub.4 30 150 — Example 4

(49) As shown above, each of F.sub.2 gas, NF.sub.3 gas, ClF.sub.3 gas and IF.sub.7 gas was reacted with the tungsten oxyfluoride and with the molybdenum oxyfluoride even at 20° C. On the other hand, N2 gas was not reacted with the tungsten oxyfluoride and with the molybdenum oxyfluoride even at 150° C. In other words, these metal oxyfluorides were each converted to the metal hexafluoride by reaction with the fluorine-containing gas such as F.sub.2 gas and thereby removed. In particular, the heated reaction temperature of 150° C. leads to a higher conversion rate and a higher reaction rate than the reaction temperature of 20° C. The use of ClF.sub.3 gas or IF.sub.7 gas led to a higher conversion rate and a higher reaction rate than the use of F.sub.2 gas or NF.sub.3 gas.

DESCRIPTION OF REFERENCE NUMERALS

(50) 11: Metal fluoride production apparatus 13: Reactor 15: Heater 17: Deposit 21: Fluorine-containing gas supply unit 23: Valve 31: Inert gas supply unit 33: Valve 41: Gas discharge line 43: Valve 45: Gas discharge device 51: Film forming apparatus 53: Chamber 55: Heater 57: Stage 59: Deposit 61: Fluorine-containing gas supply unit 63: Valve 71: Inert gas supply unit 73: Valve 81: Gas discharge line 83: Valve 85: Gas discharge device 100: Experimental apparatus 101: Fluorine-containing gas supply unit 102: Inert gas supply unit 103: Container 104: Gas discharge device 105: Metal oxyfluoride 106: Heater 111, 112, 113: Valve