JP2001140067A - Method for depositing optical thin film and film deposition system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optical thin film of metallic fluoride of low absorption in a wide range from a visible radiation region to an ultraviolet region. SOLUTION: The space between a metallic target T and a substrate W in a reaction chamber 10 is separated into a plasma space S1 and a reaction space S2 by a cored partition board 15, then, the plasma space S1 is fed with sputtering gas, and the reaction space S2 is fed with gaseous fluorine as reaction gas, respectively. By exhausting the reaction space S2 by an exhausting means 12, the plasma space S1 is indirectly exhausted. For preventing the intrusion of the reaction gas into the reaction space S2, the side direction of the plasma space S1 is covered with a side face partition board 16, and moreover, for making a trace amount of reaction gas nevertheless intruding into the plasma space S1 inert, gaseous hydrogen is added to the sputtering gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for forming an optical thin film used for an anti-reflection film or an anti-reflection film (mirror) using an optical component such as a lens of a semiconductor exposure apparatus as a substrate. It is.

[0002]

_2. Description of the Related Art Conventionally, AlF ₃ , MgF ₂ , NdF ₃ ,
Optical thin films of metal fluorides typified by LaF _{6 and the} like are widely used as antireflection films and enhanced reflection films of optical components in the visible light region. An evaporation method using resistance heating or an electron beam using a powder or a sintered body thereof as an evaporation source, a sputtering method, and the like are known.

However, in the vapor deposition method, the controllability of the film quality and the film thickness is poor, and the lens glass material must be heated to about 300 ° C. However, it is difficult to uniformly heat a large-diameter lens substrate. It is difficult to apply an excimer laser stepper to a lens or the like, which requires a dense and uniform film to be formed with good controllability.

[0004] Therefore, a sputtering method which is lower in temperature, has better adhesion and denseness, has better controllability of film thickness, and is easier to automate than a vapor deposition method has been studied and put into practical use. Japanese Patent Application Laid-Open No. 7-198903 describes that Al
There is disclosed a technique of obtaining an optical thin film having a low refractive index and low absorption in a visible light region by reactive DC sputtering of a target obtained by adding a metal to a low refractive index fluoride material such as F ₃ .

The above technique has been developed by focusing on the fact that fluorine is dissociated when sputtering a target made of a fluoride material, thereby increasing absorption due to fluorine deficiency in a film being formed. By using a target obtained by adding metal aluminum, metal magnesium and the like to AlF ₃ and sputtering using a fluorine-based gas such as CF ₄ as a reaction gas, the dissociation of fluorine was suppressed and the dissociation was achieved. By incorporating fluoride into the metal component of the target to form fluoride, fluorine in the film to be formed is prevented from becoming smaller than the stoichiometric ratio, and as a result, absorption in the visible light region is reduced. An optical thin film of a low refractive index fluoride can be obtained.

[0006]

However, as an antireflection film or a reflection-enhancing film of a lens used in a semiconductor exposure apparatus such as an excimer laser stepper, a film having a thickness of 3 nm from the visible light region is required.
Up to the ultraviolet region of 00 nm or less, a higher-quality optical thin film that has low absorption in a wide range of wavelengths and a low or high refractive index is required, and furthermore, in environmental resistance, mechanical strength, and the like. Must also have sufficient reliability.

However, in the above-mentioned conventional reactive DC sputtering technique, it is difficult to completely prevent dissociation of fluorine from the target material at the time of sputtering because a target mainly containing a fluoride material is used. Was. In the visible light region, it was possible to form a fluoride optical thin film with little absorption even in the prior art, but especially as an optical thin film for an excimer laser stepper lens, a wide range from the visible light region to the ultraviolet region of 300 nm or less. An extremely low absorption and high reliability in a wavelength region is required, and there is an unsolved problem that such a requirement cannot be satisfied.

The present invention has been made in view of the above-mentioned unresolved problems of the prior art, and has an extremely low absorption in a wide wavelength region up to 300 nm or less in an ultraviolet region by using a reactive DC sputtering method. It is an object of the present invention to provide a method and an apparatus for forming a high-quality optical thin film of metal fluoride.

[0009]

In order to achieve the above object, a method for forming an optical thin film according to the present invention comprises supplying a sputtering gas to a target, and reacting sputter particles generated from the target with a reaction gas. A film-forming step of attaching to the substrate, wherein a space between the target and the substrate is separated into a first space portion on the target side and a second space portion on the substrate side by a perforated partitioning means. A pressure gradient is provided between the first and second spaces.

It is preferable that the perforated partitioning means has a side partition plate surrounding the periphery of the target and a perforated partition plate provided between the target and the substrate.

[0011] The target may be a metal target.

Preferably, a hydrogen gas is added to the sputtering gas.

It is preferable that the optical thin film is a metal fluoride optical thin film.

Further, in the film forming apparatus of the present invention, a target holder for holding a target, a substrate holder for holding a substrate, and a space between the target and the substrate are defined by a first space on the target side. Perforated partitioning means for separating into a second space on the substrate side, sputter gas supply means for supplying a sputter gas to the first space, and a reaction gas for supplying a reaction gas to the second space Supply means and exhaust means for exhausting the second space, wherein the first space is indirectly exhausted by the exhaust means via the second space. It is characterized by having.

It is preferable that the perforated partition means is configured to surround the first space portion by the perforated partition plate and the side partition plate.

[0016]

When an optical thin film is formed by sputtering using fluoride as a target material, fluorine is dissociated from the fluoride target, and absorption due to lack of fluorine increases. Therefore, a metal target such as Al or Mg is sputtered with a sputtering gas, and a highly reactive fluorine gas is supplied as a reaction gas near the substrate to react with sputtered particles and adhere to the substrate surface.

A perforated partitioning means is provided in a space between the substrate and the target, and is divided into a first space which is a plasma space on the target side and a second space which is a reaction space on the substrate side. By supplying a sputtering gas to the plasma space and a reaction gas to the reaction space, and exhausting the reaction space by an exhaust means, the plasma space is indirectly exhausted and a pressure gradient is provided between the plasma space and the plasma space. This prevents the reaction gas in the reaction space from entering the plasma space.

The fluorine gas entering the plasma space causes the target to be fluorinated, thereby lowering the sputtering rate, and effectively avoiding the generation of negative ions of fluorine in the plasma. It is possible to form an optical thin film of metal fluoride, which is small and extremely high in quality, at a high speed.

Further, by adding hydrogen to the sputtering gas, a very small amount of fluorine gas, which is surrounded by the perforated partitioning means and still enters the plasma space, is converted into chemically stable HF molecules. As a result, fluoridation of the target and generation of negative ions can be reliably avoided, and an optical thin film with lower absorption and higher reliability can be obtained.

[0020]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a film forming apparatus according to an embodiment, which comprises exhaust ports 11a and 11b provided at the bottom.
(SUS316L) reaction chamber 10 which is evacuated from the vacuum chamber by an exhaust means 12.
Inside, a target holder 13 having a cooling mechanism for cooling and holding a metal target T as a target,
A substrate holder 14 having a rotation and heating mechanism for holding the substrate W facing the metal target T; a perforated partition plate 15 disposed between the metal target T and the substrate W; And a plasma space S, which is a first space surrounded by the perforated partition plate 15, the side partition plate 16, and the metal target T that constitute the perforated partitioning means. _The sputter gas shower head 17 which is a sputter gas supply means for supplying a sputter gas to ₁ and the reaction space S ₂ which is a second space between the perforated partition plate 15 and the substrate W are highly reactive. A reactive gas shower head 18 serving as a reactive gas supply means for supplying a fluorine gas as a reactive gas; A shutter 19 is provided.

The target holder 13 has a DC for generating plasma in a plasma space S ₁ surrounded by the metal target T, the perforated partition plate 15, and the side partition plate 16.
Power supply 20 is connected.

That is, the space between the metal target T and the substrate W in the reaction chamber 10 is separated into the plasma space S ₁ and the reaction space S ₂ by the perforated partition plate 15, and the lower end is further perforated. Side partition plate 16 connected to plate 15
Plasma space S ₁ is completely surrounded by.

[0024] The substrate from a sputter plasma space S ₁ facing the metal target T from the supply port 17a of the gas supply source is in the connected sputter gas showerhead 17 supplying a sputter gas supply port 18a of the reaction gas showerhead 18 supplying a fluorine gas is a reaction gas into the reaction space S ₂ between W and perforated partition plate 15.

The plasma space S ₁ is provided with a perforated partition plate 1.
Is indirectly discharged from the fifth hole 15a through the reaction space S _2. The pressure in the reaction chamber 10 is controlled by the exhaust ports 11a and 11b.
Is set to a desired process pressure by the exhaust means 12 connected to the process.

While maintaining the pressure in the reaction chamber 10 at about 0.4 to 4 Pa, a DC voltage is applied between the metal target T and the substrate W, and the metal target T and the perforated partition plate 1 are applied.
5. The plasma space S ₁ surrounded by the side partition plate 16
To generate a plasma of a sputtering gas. The constituent atoms (sputtered particles) of the target sputtered by the plasma particles are applied to the opening 1 of the perforated partition plate 15.
It reaches the surface of the substrate W through 5a.

In the reaction space S ₂ between the perforated partition plate 15 and the substrate W, fluorine gas reacting with atoms constituting the metal target is present. An optical thin film of metal fluoride containing the constituent atoms and the reactive gas component can be formed on the substrate W.

If the perforated partition plate 15 and the side partition plate 16 are made of the same material as the metal target T, even if the plasma particles sputter both the partition plates 15 and 16, the optical thin film formed on the substrate W will not be formed. Has no effect. Further, the fluorine flowing into the plasma space S ₁ of the gas pressure gradient generated between the plasma space S ₁ and the reaction space S ₂ by the flow rate or the like of the vacuum pressure and a sputtering gas by the exhaust unit 12 is a reaction gas,
And it can be suppressed arbitrarily by the aperture ratio of the perforated partition plate 15.

Further, by covering the side surface of the plasma space S _{1 with} the side partition plate 16, the inflow of the fluorine gas can be more reliably prevented. It occurs preferentially on the surface. Further, by preventing the metal target T from being fluorinated, it is possible to suppress a decrease in the sputter rate due to the fluorination of the metal target T. As a result, an optical thin film satisfying the stoichiometric ratio can be formed at a high deposition rate.

The reaction space S _{2 is connected} to the plasma space S ₁
The side partition plate 16 may be omitted if a small amount of the reaction gas enters around the perforated partition plate 15 and enters therein.

As the sputtering gas, Ar, Kr, Xe
And the like. As the fluorine gas as a reaction gas, a gas diluted with Ar, Kr, Xe, or the like is preferably used.

The sputtering gas supplied to the plasma space S ₁ includes F-negative ions (fluorine negative ions) generated on the surface of the metal target T, which are chemically stable HF.
Hydrogen for molecularization is added. The reason for using a metal target as the target and adding hydrogen to the sputtering gas is as follows.

When a metal fluoride is used as a target material in the conventional sputtering method, the fluorine-deficient optical thin film is inevitably accompanied by the dissociation of fluorine. Further, even if the reactive sputtering method is used in combination, even if the fluoride material from which fluorine is released encounters an active fluorine-based reaction gas, its reactivity is poor, so that it is still difficult to satisfy the stoichiometric composition, and Absorption occurs.

Further, the metal fluoride target is sputtered, and the fluorine dissociated as a result or the fluorine supplied as a reaction gas easily forms F-negative ions in the plasma. Reverse accelerated by voltage (-200 to -500 eV),
As a result of intensive research, it collides with the growing film surface as high-energy particles, which damages the optical thin film, that is, appears as a color center and causes optical absorption.
It is clear.

This phenomenon appears more remarkably as the ionic crystallinity of the fluoride thin film becomes stronger. Particularly, in the case of the MgF ₂ film, optical absorption due to damage caused by negative ions is likely to occur.
Optical absorption due to the color center occurs near 260 nm of 00 nm or less. However, in this wavelength region, a large absorption is exhibited even by the lack of fluorine.
Difficult to distinguish from absorption due to damage.

Therefore, in the present embodiment, the metal target is sputtered as pure as possible without fluorinating the metal target. In addition, by adding hydrogen gas to the sputtering gas, negative ions generated on the target surface are chemically converted into stable molecules, so that negative ions that are inversely accelerated at the target potential are eliminated as much as possible. Avoids damage and reduces optical absorption.

Further, if hydrogen gas is added to the sputtering gas, M
The production of gO can be suppressed by a reduction reaction with active hydrogen such as a hydrogen radical. By preventing the generation of MgO having an extremely large absorption in the ultraviolet region by the hydrogenation as described above, there is also an effect that the absorption in the ultraviolet region can be reduced.

Further, the addition of hydrogen gas to the sputtering gas has the effect of preventing the metal target from being fluorinated by the fluorine gas reaching the vicinity of the target, so that sputtered particles from the metal target are converted into pure metal atoms on the substrate. It can be supplied to the vicinity. As a result, the active metal atoms that have reached the vicinity of the substrate rapidly undergo a fluorination reaction by the highly reactive fluorine gas supplied to the vicinity of the substrate, and the stoichiometric composition can be obtained without depletion of fluorine. Grows on the substrate surface. In this way, optical absorption due to fluorine deficiency can be significantly reduced.

As a result of the experiment, a remarkable effect appears when the amount of hydrogen gas added to the sputtering gas is 5% or more, and when it exceeds 20%, some of the fluorine gas contributing to the reaction near the substrate is converted into HF molecules. Therefore, it has been found that the promotion of the metal fluoride reaction is inhibited. Therefore, the hydrogen concentration in the sputtering gas is controlled in the range of 5 to 20%.

In addition, since the plasma space S ₁ and the metal target are surrounded by the perforated partition plate and the side partition plate as described above, the amount of the reactant gas entering the plasma space S ₁ is greatly reduced. You. Plasma space S ₁ fluorine gas is slightly flows into the F- and generate negative ions is HF molecules by hydrogen gas, as HF gas is exhausted through the openings 15a of the perforated partition plate 15. Therefore, F-negative ion damage on the surface of the growing thin film can be reliably avoided.

In this manner, a high-quality optical thin film of metal fluoride having extremely low optical absorption even in the ultraviolet region can be formed at a high speed.

Next, an embodiment will be described.

(First Embodiment) Metal magnesium was used as a metal target material, and 5% H was used as a sputtering gas and a reaction gas.
An optical thin film of metallic magnesium fluoride (MgF ₂ ) was formed using a ₂ / Ar gas and a 10% F ₂ / Ar gas, respectively. At this time, the perforated partitioning means was only the perforated partition plate facing the metal target, and the side partition plate covering the side surface of the target was removed, and the effect of adding hydrogen gas was examined. The results are shown in the graph of FIG.

From FIG. 2, it can be seen that, in the case where hydrogen is added to the sputter gas, an optical thin film having a low absorption and a low refractive index can be obtained even in the ultraviolet wavelength region from the visible light region to 300 nm or less.

On the other hand, when hydrogen is not added, Mg
It can be seen that the optical absorption of the F ₂ film is very large, and that the optical absorption can be effectively reduced by adding hydrogen to the sputtering gas. In particular, a large difference is observed in the absorption near 260 nm. This is probably because the MgF ₂ film has high ionic crystallinity and is particularly sensitive to F-negative ion damage.

(Second Embodiment) In the first embodiment, the effect of reducing the optical absorption of the hydrogen-added sputtering gas was confirmed. Even if there was no side partition plate (side shield) covering the side of the metal target, the KrF excimer laser could be used. Emission wavelength (248nm)
Was found to be sufficiently suppressed.

However, satisfactory absorption was not obtained at 193 nm, which is the emission wavelength of the ArF excimer laser. Therefore, an MgF ₂ film was formed in a similar manner with a configuration in which a structure of a side partition plate (side shield) covering the side surface of the metal target was added. FIG. 3 shows the optical characteristics, and the comparison was similarly made with or without hydrogen addition.

As can be seen from the graph of FIG. 3, the configuration using a hydrogen-added sputtering gas and using a side partition plate (side shield) covering the side surface of the target in addition to the perforated partition plate has a wavelength range of 193 nm. Also, a MgF ₂ film having low absorption was obtained. It is considered that the effect of preventing the diffusion of fluorine gas to the surface of the target and the generation of F-negative ions can be further ensured by the complete shield configuration in which a side partition plate covering the side surface of the target is added.

Further, even when no hydrogen is added, 1
Absorption occurs in the wavelength region of 93 nm, but 248
In the wavelength region of nm, the large absorption near 260 nm as seen in the first embodiment disappears, and it can be seen that the optical absorption characteristics are sufficiently small. This indicates that the side shield effect of the side partition plate covering the side of the target is extremely effective when no hydrogen is added.

(Third Embodiment) FIG. 4 shows the result of applying the same film forming experiment as in the second embodiment to an AlF ₃ film. Than the optical absorption characteristics of FIG. 4, for the AlF ₃ film, 193
It was confirmed that a thin film having low absorption up to the ultraviolet wavelength region of nm could be formed.

(Fourth Embodiment) As in the second and third embodiments, by using Nd and La for the metal target material, a high refractive index metal fluoride film of NdF ₃ and LaF ₆ is also studied. Done. Both the NdF ₃ film and the LaF ₆ film exhibited low absorption in the wavelength region of 193 nm and optical characteristics showing a high refractive index.

The optical characteristics of the optical thin films according to the first to fourth embodiments are summarized in Table 1 below.

[0053]

[Table 1]

[0054]

Since the present invention is configured as described above, the following effects can be obtained.

By a reactive DC sputtering method using a metal target, a hydrogen-added sputtering gas, and a reactive gas of a diluted fluorine gas, an ultraviolet region from a visible light region to 300 nm or less, in particular, KrF of 248 nm and 193 nm,
A low-refractive-index optical thin film of AlF ₃ or MgF _{2 having} extremely low absorption in the ArF excimer laser emission wavelength region,
A high refractive index optical thin film of NdF ₃ and LaF ₆ can be formed.
These realize sufficient optical performance as optical thin films for KrF and ArF excimer laser stepper lenses.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a film forming apparatus according to one embodiment.

FIG. 2 shows a fluoride (MgF) formed in the first embodiment.
₂ ) A graph showing the optical absorption characteristics of the film.

FIG. 3 shows a fluoride (MgF) formed in the second embodiment.
₂ ) A graph showing the optical absorption characteristics of the film.

FIG. 4 shows a fluoride (AlF) formed in a third embodiment.
₃ ) A graph showing the optical absorption characteristics of the film.

[Explanation of symbols]

T metal target W substrate S ₁ plasma space S ₂ reaction space 10 a reaction chamber 11a, 11b exhaust port 13 the target holder 14 substrate holder 15 perforated partition plate 16 side partition plates 17 and 18 sputtering gas showerhead 19 shutter 20 DC power supply

Claims (12)

[Claims] A film forming step of supplying a sputtering gas to a target, reacting sputter particles generated from the target with a reaction gas, and attaching the reaction gas to a substrate, wherein a space between the target and the substrate is perforated. The partitioning means separates the first space portion on the target side and the second space portion on the substrate side, and a pressure gradient is provided between the first and second space portions. Characteristic method of forming an optical thin film. 2. The optical thin film according to claim 1, wherein the perforated partitioning means has a side partition surrounding the periphery of the target, and a perforated partition disposed between the target and the substrate. Film formation method. 3. The method according to claim 1, wherein the target is a metal target. 4. The method for forming an optical thin film according to claim 1, wherein the sputtering gas contains at least one of Ar, Kr, and Xe. 5. The method for forming an optical thin film according to claim 1, wherein a hydrogen gas is added to the sputtering gas. 6. The method according to claim 5, wherein the amount of hydrogen gas added is in the range of 5 to 20%. 7. The method according to claim 1, wherein the optical thin film is a metal fluoride optical thin film. 8. The method for forming an optical thin film according to claim 1, wherein the reaction gas contains a fluorine gas. 9. An optical thin film comprising AlF ₃ , MgF ₂ , Nd
9. The method for forming an optical thin film according to claim 1, wherein the optical thin film is F ₃ or LaF ₆ . 10. A target holder for holding a target, a substrate holder for holding a substrate, and a space between the target and the substrate, a first space on the target side and a second space on the substrate side. A perforated partitioning means for separating into a part, a sputter gas supply means for supplying a sputter gas to the first space, a reaction gas supply means for supplying a reaction gas to the second space, Exhaust means for exhausting a space portion, wherein the first space portion is configured to be indirectly exhausted by the exhaust means via the second space portion. Membrane equipment. 11. The film forming apparatus according to claim 10, wherein the perforated partitioning means has a perforated partition plate provided between the target and the substrate. 12. The film forming apparatus according to claim 10, wherein the perforated partitioning means is configured to surround the first space by a perforated partition plate and a side partition plate.