JP2007056292A - Electric discharge retaining method for sputtering process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem in the conventional sputtering film deposition system that electric discharge isapt to extinguished by repeating film deposition. <P>SOLUTION: In a reactive sputtering film deposition system where the inside of the same chamber is provided with a plurality of targets, also, at least one of them is a transition element target, and further, at least one among the plurality of targets is a metal target requiring hydrogenation for producing a fluoride thin film of low absorption, when discharge is performed using the metal target requiring hydrogenation, the transition element target and electrode parts at the circumferences thereof have been covered with a material different from the transition element, thus the discharge stability in the transition element target is retained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is a method for stably maintaining plasma discharge when an optical thin film used in a semiconductor exposure apparatus or other optical elements is formed by sputtering.

  In recent years, in order to meet the demand for miniaturization of integrated circuits, the wavelength of exposure light sources for steppers has been shortened. Along with this, the antireflection film used for the stepper and the material of the reflection film have been changed from oxide-based to fluoride-based.

When fabricating an antireflection film, and a reflective film for a stepper using a fluoride, such as MgF _2, AlF ₃ as a low refractive index film, such as LaF _3, GdF ₃ is generally used as a high refractive index film . The desired reflection characteristics are realized by sequentially stacking these films while controlling them to a predetermined thickness. When thin films of different types are sequentially stacked in this way, a method for increasing production efficiency by installing a plurality of metal targets in the same chamber and sequentially using them to form a film is widely used. One example is Japanese Patent Application Laid-Open No. 2002-88470.

However, when a fluoride thin film, especially a transition element fluoride thin film typified by LaF ₃ is formed with the above sputtering apparatus, the discharge becomes unstable as the number of film formation increases, and finally the discharge Has reached a state where it cannot continue. In general, when forming an insulating thin film in a reactive sputtering apparatus, it is known that when a discharge is performed, a dielectric film adheres to electrodes such as an anode, and the discharge becomes unstable because there is no place for electrons. It has been. As a countermeasure, for example, as shown in Japanese Patent Laid-Open No. 8-232064, an electrode structure that prevents the dielectric film from adhering has been devised.
JP 2002-88470 A JP-A-8-232064

Therefore, even in the sputtering apparatus as described above, it is considered that the dielectric film adhesion to the anode can cause discharge instability, and has the Mg target and the La target in the same chamber, and MgF ₂ and LaF ₃ In an apparatus for forming a film, a study was conducted. As a result, when only LaF ₃ film formation is repeated, the discharge is maintained for a long time, and the discharge stabilization time is clearly longer than when LaF ₃ film formation and MgF ₂ film formation are performed alternately. I understood it. That is, in the above sputtering apparatus, it was found that the dielectric film adhesion to the anode does not regulate the continuation of discharge during the LaF ₃ film formation. As a result of further investigation, it was found that discharge during LaF ₃ film formation is unstable due to H ₂ gas added during film formation of MgF ₂ . The H ₂ gas at the time of MgF ₂ deposition, as shown in JP 2000-297366, is essential in order to produce a low absorption MgF _2.

The influence of H ₂ gas on the La target and its surroundings is presumed to be due to the phenomenon of hydrogen embrittlement that tends to occur in transition elements. In fact, the above phenomenon was obtained even when other transition element targets were used regardless of the La target.

As described above, an object of the present invention is to prevent the discharge of the transition element target from becoming unstable due to the H ₂ gas.

In order to solve the above problem, the means provided by the present invention is to coat a transition element target such as La and an electrode in the vicinity thereof with a typical element such as Mg before starting the film formation of MgF _2. It is.

Thus, it is possible to prevent the transition element target side during MgF ₂ deposition is exposed to _H2 gas. In addition, when the film is formed using the transition element target, it is possible to prevent the coating material from being mixed into the film as an impurity by performing the pre-sputtering sufficiently in advance to remove the coating metal.

  The present invention is a film forming method and a film forming apparatus as described above, and has the following characteristics.

  1. Multiple targets in the same chamber, at least one of which is a transition element target, and at least one of the multiple targets requires hydrogenation to produce a low absorption fluoride thin film In a reactive sputter deposition apparatus that is a metal target such as, when performing discharge with a metal target that requires hydrogenation, the transition element target and the surrounding electrode portion are different from the transition element. By covering with a material, the discharge stability of the transition element target is maintained.

  2. The transition element target is La or Gd.

  3. The metal target that requires hydrogenation in order to produce the low-absorption rapefluoride thin film is an Mg or Al target.

  4). The sputtering apparatus is intended to produce a fluoride multilayer film.

  5. The method for coating the transition element target is a sputtering method or a vapor deposition method.

  6). In the sputtering apparatus, the sputtering gas contains at least one of Ar, Xe, Ne, and Kr.

  7). In the sputtering apparatus, the external power supply means used is a DC power supply, and a high frequency rectangular inversion voltage of 1 kHz to 350 kHz can be applied.

  As described above, by using the present invention, the influence of H2 on the transition element targets such as La and Gd can be reduced, and the discharge duration time of the transition element target can be extended.

(Example 1)
An embodiment of a sputtering apparatus using the present invention is described in FIG. This sputtering apparatus has a preliminary chamber 12 in addition to the film forming chamber 23, and after the substrate 14 is fixed to the substrate holder 13 in the preliminary chamber 12, it is evacuated to 1.0E-4 Pa or less by the vacuum pump 16. Since the substrate is transported to the film forming chamber 23 by the substrate transporting means 11, mixing of air into the film forming chamber 23 can be minimized. Further, when the film is not formed, the substrate 14 is returned to the preliminary chamber 12 and the valve 35 is closed, whereby the substrate 14 can be isolated from the film forming chamber 23, and unnecessary film adhesion can be prevented.

  The gas required for film formation is supplied into the film formation chamber 23 while controlling the flow rate with mass flows 17, 18, and 19, and a negative potential is externally applied to the Mg target 27 or La target 28 by a DC power source 33 to cause plasma discharge. . A high frequency can be superimposed on the DC power source as required by the rectangular high frequency superimposing device 32.

  The target unit 31 is provided with an Mg target 27 and an La target 28, and a magnet 26 is arranged behind each target to enable magnetron sputtering. The target unit 31 can be rotated, and the Mg target 27 and the La target 28 can be directed toward the substrate as necessary. A vapor deposition unit 34 is provided in the vicinity of the target unit 31, and vacuum deposition can be performed on the target and the anode associated therewith.

The above device results of an experiment conducted in a conventional manner using, if performed repeatedly LaF ₃ deposited using only La target, it was possible to maintain the discharge four hours or more, LaF ₃ formed When the film was alternately formed for 20 minutes and the MgF ₂ film was formed for 10 minutes, it was difficult to maintain the discharge when the LaF ₃ film was formed for a total of 2.5 hours.

On the other hand, when the present invention is used, that is, after LaF ₃ is formed for 20 minutes, the target unit 31 is rotated to the state shown in FIG. When 30 surfaces were coated with Mg and MgF ₂ film formation was started for 10 minutes, LaF ₃ film formation could be continued for a total of 4 hours or more.

(Example 2)
FIG. 2 shows an embodiment in which a Gd target is used instead of the La target in FIG. 1, and the rest is the same as FIG. In this case, when only the GdF ₃ film formation was repeated by the conventional method, the discharge could be continued for 10 hours or more. However, when 20 minutes of GdF ₃ film formation and 10 minutes of MgF ₂ film formation were performed alternately, it was difficult to maintain the discharge when GdF ₃ film formation was performed for a total of 4 hours. On the other hand, when the present invention is used, that is, in the same manner as in Example 1, when the MgF ₂ film is formed, the surface of the Gd target 35 and the Gd target anode plate 36 is coated with Mg, and the GdF 3 film is formed. When 20 minutes and MgF ₂ film formation were repeated for 10 minutes, the total film formation time of GdF ₃ was 10 hours or more.

An example of an apparatus used in the present invention An example of an apparatus used in the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Substrate conveyance means 12 Preliminary chamber 13 Substrate holder 14 Substrate 15 Valve 16 Vacuum pump 17 Mass flow 18 Mass flow 19 Mass flow 20 Ar cylinder 21 H2 cylinder 22 F2 cylinder 23 Deposition chamber 24 Valve 25 Vacuum exhaust, processing device 26 Magnet 27 Mg target 28 La target 29 Mg target anode plate 30 La target anode plate 31 Target unit 32 Rectangular high frequency superposition device 33 DC power supply 34 Vapor deposition unit 35 Gd target 36 Gd target anode plate

Claims (14)

  Multiple targets in the same chamber, at least one of which is a transition element target, and at least one of the multiple targets requires hydrogenation to produce a low absorption fluoride thin film In a reactive sputter deposition apparatus that is a metal target such as, when performing discharge with a metal target that requires hydrogenation, the transition element target and the surrounding electrode portion are different from the transition element. A reactive sputtering apparatus characterized by maintaining discharge stability of the transition element target by coating with a material.   The reactive sputtering apparatus according to claim 1, wherein the transition element target is La or Gd.   2. The reactive sputtering apparatus according to claim 1, wherein the metal target that requires hydrogenation to produce the low-absorption rape fluoride film is an Mg, Al target.   The reactive sputtering apparatus according to claim 1, wherein the sputtering apparatus is intended to produce a fluoride multilayer film.   The reactive sputtering apparatus according to claim 1, wherein the method of coating the transition element target is a sputtering method or a vapor deposition method.   The reactive sputtering apparatus according to claim 1, wherein the sputtering gas includes at least one of Ar, Xe, Ne, and Kr.   2. The reactive sputtering apparatus according to claim 1, wherein the external power supply means used in the sputtering apparatus is a direct current power source and can apply a high frequency rectangular inversion voltage of 1 kHz to 350 kHz.   Multiple targets in the same chamber, at least one of which is a transition element target, and at least one of the multiple targets requires hydrogenation to produce a low absorption fluoride thin film In the reactive sputter deposition method, which is a metal target such as, when the discharge is performed with the metal target that requires hydrogenation, the transition element target and the surrounding electrode portion are different from the transition element. A reactive sputter deposition method characterized by maintaining discharge stability of the transition element target by coating with a material.   9. The reactive sputter deposition method according to claim 8, wherein the transition element target is La or Gd.   9. The reactive sputter deposition method according to claim 8, wherein the metal target that requires hydrogenation to produce the low-absorption naphthafluoride thin film is an Mg, Al target.   9. The reactive sputter film forming method according to claim 8, wherein the sputtering apparatus is intended to produce a fluoride multilayer film.   9. The reactive sputter deposition method according to claim 8, wherein the method of coating the transition element target is a sputtering method or a vapor deposition method.   9. The reactive sputter deposition method according to claim 8, wherein in the sputtering apparatus, the sputtering gas contains at least one of Ar, Xe, Ne, and Kr.   9. The reactive sputter deposition method according to claim 8, wherein the external power supply means used in the sputtering apparatus is a direct current power source and can apply a high frequency rectangular inversion voltage of 1 kHz to 350 kHz.

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