JP2005154833A - Fluorine-containing thin film deposition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce damage caused by negative ions or the like during deposition of a fluorine-containing thin film by a sputtering method. <P>SOLUTION: In a step of depositing a fluorine-containing thin film 21 by sputtering a target which faces a work W with sputtering gas introduced from a gas feed line 13 in a film deposition chamber 1, and allowing generated particles to react with fluorine-containing gas introduced from a gas feed line 14 so as to be deposited on a base body 20 of the work W, hydrogen is added to the sputtering gas for a short period of time after film deposition is started to suppress damages to the film caused by negative ions in plasma. Hydrogen is introduced only at the beginning of the film deposition because troubles such as abnormal discharge occur if hydrogen is continuously added for a long period of time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for forming a fluorine-containing thin film by sputtering for forming a high-quality fluorine-containing thin film used in an optical system using an excimer laser as a light source at a low temperature.

  Conventionally, when forming an optical thin film such as an antireflection film or a mirror, a vacuum deposition method in which a film forming material is heated by an electron beam in a vacuum and evaporated to adhere to a substrate has been mainly used.

  In general, antireflection films, mirrors, and the like are configured and required by a multilayer film combining a material with a low refractive index such as magnesium fluoride and a material with a high refractive index including zirconium oxide, tantalum oxide, and titanium oxide. Depending on the optical performance, the layer structure, film thickness, etc. are optimized.

  The vapor deposition method has a simple device configuration and can be deposited on a large-area substrate at high speed and has excellent productivity, but it is difficult to control the film thickness with high precision and to develop an automatic production machine. Further, when film formation is performed in a state where the substrate temperature is low, there is a problem that the film strength is insufficient, the film is easily damaged, and the adhesion between the film and the substrate is low.

  However, since more efficient production has been demanded in recent years, these optical thin films can also save labor and stabilize quality, film quality (adhesion, film strength) compared to vacuum deposition. The demand for coating by the sputtering method, which is advantageous in terms of the above, has increased.

When an oxide dielectric thin film such as ZrO ₂ , Ta ₂ O ₅ , or TiO ₂ is formed by sputtering, a thin film having a low absorption and a high refractive index can be easily obtained.

  A sputtering method that has been widely used for manufacturing a thin film has been attached to a target and a holder, which are materials for the thin film, in a vacuum vessel (film formation chamber) using a parallel plate magnetron sputtering apparatus. In this method, the substrate (substrate) is disposed so as to face the substrate, plasma is generated to sputter the target, and target particles knocked out by sputtering are deposited on the substrate. This is an excellent film forming method in that it is simple and capable of high speed film formation and large area film formation, and the target has a long life.

  Also, sputtering apparatuses other than the parallel plate type have been known in the past. For example, in Japanese Patent Application Laid-Open No. 06-17248, the substrate or the target is rotated 90 degrees from the parallel plate type sputtering apparatus in which the target and the substrate face each other. An off-axis type sputtering apparatus has been proposed.

  Further, Japanese Patent Laid-Open No. 05-182911 discloses that a surface to be sputtered is arranged so as to face a space, and a magnetic field in a direction perpendicular to the surface to be sputtered is generated so as to be lateral to the space between the targets. An opposed target sputtering apparatus has been proposed in which a thin film is formed on a substrate disposed on the substrate.

  In JP-A-08-167596, at least one plasma separation mesh plate is disposed between a plasma generation chamber for generating plasma and a plasma processing chamber for disposing a substrate on which a film is formed. There has been proposed a plasma processing apparatus or the like in which a plurality of openings are provided in the mesh plate, and the diameter of the openings is not more than twice the Debye length of plasma.

In recent years, devices using ArF excimer laser light source and F ₂ excimer laser light source have been developed as optical devices used for precision processing, and high-quality, high-durability fluorine-containing films are used as the optical components constituting the optical system. It has come to be desired.

  As a method for forming a fluorine-containing thin film such as aluminum fluoride or magnesium fluoride using a parallel plate type sputtering apparatus, the following has been proposed.

For example, as a method for forming a fluoride thin film by a sputtering method, a method disclosed in Japanese Patent Laid-Open No. 04-289165 is known. This is a method of sputtering an alkaline earth metal fluoride film such as MgF ₂ using a mixed gas of an inert gas such as Ar and a fluorine-based gas such as CF ₄ . Further, as disclosed in Japanese Patent Application Laid-Open No. 07-166344, there is also known a method of performing DC sputtering using a metal target with a mixed gas of an inert gas such as Ar and a fluorine-based gas such as CF _4. Yes. However, in these methods, it has been found that it is difficult to obtain desired characteristics because the deposited thin film or substrate is damaged by charged particles.

Furthermore, as disclosed in Japanese Patent Application Laid-Open No. 08-201601, by using a fluoride target, the oxygen-based gas to be input is made constant and the input power of the target is changed, that is, by changing the film formation rate. There is a method of changing the degree of oxidation, but when a highly oxidizable film is formed, the rate is considerably slowed, and there is a drawback in productivity. The case of forming the fluoride film has a high input power is too F ^- substrate shocked by charged particles, such as, it is difficult to obtain desired characteristics.
Japanese Patent Laid-Open No. 06-017248 JP 05-182911 A Japanese Patent Laid-Open No. 08-167596 Japanese Patent Laid-Open No. 04-289165 Japanese Patent Laid-Open No. 07-166344 Japanese Patent Laid-Open No. 08-201601

When a fluorine-based reaction gas such as NF ₃ or F ₂ gas is introduced to form a fluoride thin film on a lens or the like by sputtering, the negative ions of fluorine and fluorine compounds are accelerated by the cathode sheath voltage and generated. High energy particles are incident on the film, causing physical damage to the film or changing the composition ratio of the film. Depending on the target material and sputtering conditions, large damage may occur due to negative ions, such as etching the substrate instead of forming a film on the substrate.

  Furthermore, ions and electrons accelerated by the ion sheath may damage the film formed on the surface of the substrate, thereby increasing the temperature of the substrate and increasing the light absorption of the film. In particular, when used in an optical system such as an exposure machine that handles high-energy ultraviolet light, the light transmittance is remarkably lowered.

  In addition, if there are large fluctuations in the optical characteristics that occur when the cleaning process after film formation and the optical elements are incorporated into the exposure apparatus, it becomes difficult to predict the performance of the exposure apparatus from the characteristics after film formation. Even the performance of the machine may be reduced.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and stably and efficiently produces an extremely high-quality fluorine-containing thin film with high transmittance to ultraviolet light, particularly vacuum ultraviolet light. An object of the present invention is to provide a method for forming a fluorine-containing thin film that can be performed.

  In order to achieve the above object, a method for forming a fluorine-containing thin film according to the present invention is a method for forming a fluorine-containing thin film by a sputtering method, in which sputtering particles released from a target by a sputtering gas containing hydrogen contain fluorine. A first film-forming step of forming a lower layer portion of the fluorine-containing thin film by reacting with a gas and reacting the sputtered particles released from the target with a sputtering gas not containing hydrogen with the fluorine-containing gas. And a second film forming step for forming an upper layer portion of the fluorine-containing thin film.

  The film thickness of the lower layer formed by the first film forming process is preferably 10 to 25% of the total film thickness of the fluorine-containing thin film.

  The target may contain at least one of Mg, Al, La, and Nd.

  In the formation of a fluorine-containing thin film by sputtering, hydrogen gas is supplied for a time during which a lower layer portion having a thickness of 10 to 25% of the initial total film thickness of the film formation process is formed, and negative ions in the plasma And the like, and damage to the film due to negative ions is reduced.

  The damage suppression effect of hydrogen gas addition is almost the same as when hydrogen gas is introduced only in the initial stage even if the film formation is completed, and if hydrogen is added for a long time, troubles caused by unstable discharge such as abnormal discharge Was found to occur. Therefore, by introducing hydrogen only for a short time after the start of film formation of the fluorine-containing thin film, discharge is stably maintained and damage to the film due to negative ions or the like is suppressed.

  In this way, it is possible to stably manufacture a high-quality fluorine-containing thin film with little light absorption due to damage.

The sputtering apparatus shown in FIG. 1 opens the valve 2 of the film forming chamber 1 and exhausts it with the dry pump 3, then closes the valve 2 and opens the valve 4, and the turbo molecular pump 5 and the cryopump 6 that are activated in advance are Valves 7 and 8 are opened and evacuated to a high vacuum (5.0 × 10 ⁻⁷ Torr or less). The workpiece W in the load lock chamber 9 is held by a substrate holder 10 and is evacuated by opening a valve 11a with a dry pump 11 and further evacuating to a high vacuum with a turbo molecular pump 12 which is previously activated by closing the valve 11a. To do.

Thereafter, a rare gas (inert gas) such as Ar as a sputtering gas, a hydrogen gas (hydrogen-containing gas), and a fluorine gas as a reactive gas such as F ₂ so that a predetermined pressure is obtained from the gas supply lines 13 and 14. The contained gas is introduced into the film forming chamber 1, and a predetermined power is supplied from the power supply means 16 to the target installed in the target unit 15 through the high frequency superposition and abnormal discharge countermeasure power source 17 to cause discharge.

  After the plasma impedance is stabilized, the gate valve 9a of the load lock chamber 9 is opened, and the workpiece W is moved to a predetermined separation distance (target / substrate distance) with respect to the target using a substrate transfer robot, and fluorine is contained on the surface. Start film deposition. Of course, the gas used during the film formation and the occurrence of discharge uses a gas that must be treated. Therefore, the exhaust system is connected to an adsorption tower or a combustion tower, and a treatment for preventing exposure to the atmosphere is performed.

  After the film formation is started and a predetermined time has elapsed, the supply of hydrogen gas is stopped. Then, the film formation is continued without supplying hydrogen gas, and when the predetermined final film thickness is reached, the power supplied from the power supply means 16 to the target is cut to complete the film formation. Thereafter, the supply of the rare gas and the reactive gas supplied from the gas supply lines 13 and 14 is stopped, the substrate transfer robot is returned to the position before film formation, the gate valve 9a is closed, and the valve is closed and then nitrogen is loaded. After supplying to the lock chamber 9 and returning the load lock chamber 9 to atmospheric pressure, the workpiece W is taken out, and the absorption rate is measured and evaluated using a vacuum ultraviolet spectrophotometer.

  As described above, in the step of forming the fluorine-containing thin film, discharge is generated in the discharge space, and the target is sputtered by supplying the hydrogen gas and the inert gas from the gas supply line 13 only in the initial stage of the film formation. As shown in FIG. 5, a fluorine-containing thin film 21 is formed which is composed of a lower layer portion 21a containing hydrogen in the vicinity of the base 20 and an upper layer portion 21b not containing hydrogen. As for the thickness of the lower layer part 21a containing hydrogen, 10 to 25% of the whole film thickness is desirable.

The inert gas and hydrogen gas are supplied into the discharge space from the gas supply line 13 on the anode side, and the fluorine-containing gas is supplied from the gas supply line 14 outside the discharge space. The hydrogen-containing gas is at least one selected from H ₂ , HF, CH ₄ and C ₂ H ₆ , and the fluorine-containing gas is fluorine gas, nitrogen fluoride gas, carbon fluoride gas, sulfur fluoride gas, fluoride It is at least one selected from hydrogenated carbon gas, and the inert gas is selected from Ar, Xe, Kr, and Ne. The target is made of a metal containing at least one selected from Mg, Al, La, and Nd, and the substrate 20 is made of calcium fluoride or the like. The voltage applied to the target is monitored, and the gas supply amount is controlled so that the voltage applied to the target becomes substantially constant.

In the apparatus of FIG. 1, metallic magnesium is used as a target material, and 400 W of electric power is applied to the target from a DC power source to generate discharge, and H ₂ is supplied at 20 sccm, Ar is supplied at 200 sccm, and F ₂ is supplied at 20 sccm to cause discharge. It was. Thereafter, film formation was started after the discharge impedance was stabilized. At this time, the rate at the initial stage of film formation is confirmed in advance, and by using this rate, the supply of H ₂ added is stopped after film formation of 20 nm on the substrate by time control, and a predetermined film thickness of 80 nm is obtained. The film was formed up to.

For comparison, a magnesium fluoride thin film was prepared under the same conditions without initial hydrogenation. FIG. 2 is a graph showing the absorption relative value when the absorption with respect to light having a wavelength of 157 nm of the magnesium fluoride thin film formed without adding hydrogen in the initial stage is 1 as a solid line graph A and a broken line graph B _1. It is a comparison with the absorption relative value of the example. Thus, when hydrogen was added in the initial stage, a good result was obtained that the overall absorption was about ½ as compared with the case where hydrogen was not added.

As in Example 1, using the apparatus of FIG. 1, using metallic magnesium as a target material, applying a power of 400 W from a DC power source to the target for generating discharge, H ₂ at 20 sccm, Ar at 200 sccm, F ₂ was supplied at 20 sccm to cause discharge. Thereafter, film formation was started after the discharge impedance was stabilized. Hydrogen was added only when a film thickness of about 20 nm was formed at the initial stage of film formation, and then the film was formed to a film thickness of about 200 nm without hydrogen addition.

For comparison, hydrogen was added throughout the film formation until a film thickness of about 200 nm was formed. FIG. 3 shows the relative absorption value of the comparative example when the absorption with respect to light having a wavelength of 157 nm of the fluorine-containing thin film formed without adding hydrogen in the initial stage is 1 as a solid line graph C, and the broken line graph B _2. It compares with the absorption relative value of a present Example shown by. Thus, it was confirmed that even when hydrogen was added throughout, the results were almost the same as when hydrogen was added only in the initial stage.

  However, when hydrogen is added all the time, the Vdc at the time of film formation rises, abnormal discharge occurs frequently, the discharge during the film formation process is unstable and difficult to control, and the film quality is easily deteriorated. In order to form the containing thin film, it is desirable to add hydrogen only at the initial stage of film formation.

In the same manner as in Example 1, film formation was performed in the same manner using the apparatus shown in FIG. FIG. 4 shows the absorption relative value of the fluorine-containing thin film formed without adding hydrogen when the absorption with respect to light having a wavelength of 157 nm is 1, as a solid line graph D. The absorption relative of the fluorine-containing thin film of this example is shown in FIG. The value is indicated by a broken line graph B ₃ . As a result, it was confirmed that even when the LaF ₃ film was formed, there was less absorption when hydrogen was added only in the initial stage than when hydrogen was not added.

1 shows a film forming apparatus used in Examples 1 to 3 and a formed fluorine-containing thin film, where (a) is an explanatory view for explaining the film forming apparatus, and (b) shows a film configuration of the fluorine-containing thin film. It is. 3 is a graph showing the evaluation results of Example 1. 10 is a graph showing the evaluation results of Example 2. 10 is a graph showing the evaluation results of Example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Deposition chamber 3, 11 Dry pump 5, 12 Turbo molecular pump 6 Cryo pump 9 Load lock chamber 10 Base holder 13, 14 Gas supply line 15 Target unit

Claims (3)

A method for forming a fluorine-containing thin film by sputtering,
A first film forming step of forming a lower layer portion of the fluorine-containing thin film by causing sputtering particles released from a target by a sputtering gas containing hydrogen to react with a fluorine-containing gas and depositing the particles on a substrate;
And a second film forming step of forming an upper layer portion of the fluorine-containing thin film by reacting the sputtered particles released from the target with a sputtering gas not containing hydrogen to react with the fluorine-containing gas. Thin film deposition method.   2. The method for forming a fluorine-containing thin film according to claim 1, wherein the film thickness of the lower layer formed by the first film forming step is 10 to 25% of the total film thickness of the fluorine-containing thin film.   3. The method for forming a fluorine-containing thin film according to claim 1, wherein the target contains at least one of Mg, Al, La and Nd.

Images