JP3740301B2 - Method for forming fluoride thin film, optical member having the thin film, and sputtering apparatus - Google Patents

Description

【００７２】
【発明の効果】
以上述べたように、本発明では、ＡｌＦ₃等の可視域および紫外域で低吸収かつ低屈折率のフッ化物薄膜をＤＣスパッタする際に、ターゲット表面でＦ−イオン等の負イオンが形成され、ターゲットシースで加速され基板に入射することが無いように、または、入射してもその数が少なくなるように、ターゲット表面が常に金属状態でスパッタされるようモニターを設置し、この条件を維持して成膜を行うことで、可視域および紫外域で低吸収かつ低屈折率のフッ化物薄膜を安定して形成できる。
【００７３】
また、ターゲット表面のＦを含むガス分圧を抑えることで、ターゲット表面のフッ化を抑え、ターゲット表面で負イオンが形成されるのを防ぎ、さらには、基板に入射する負イオンもしくはターゲットシースで加速され、プラズマ中で中性化した高エネルギー粒子をモニターし、この粒子数／スパッタレート比を所定値以下に抑えることで、可視域および紫外域で低吸収かつ低屈折率のフッ化物薄膜を安定して形成できる。
【００７４】
さらに、スパッタで可視から紫外域において、低吸収で低屈折率のフッ化物薄膜が形成できることから、スパッタの特徴である高屈折率の酸化物薄膜との交互層を形成することで、非常に優れた光学性能を有する光学部品を提供することが可能となった。
【図面の簡単な説明】
【図１】本発明の第１の実施例による直流マグネトロンスパッタリング装置の断面図である。
【図２】本発明の第２の実施例による直流マグネトロンスパッタリング装置の断面図である。
【図３】本発明の第３の実施例による直流マグネトロンスパッタリング装置の断面図である。
【図４】本発明の第４の実施例による多層膜の構成による反射率を示したグラフである。
【図５】本発明の第１の実施例によるターゲット電圧とＮＦ₃ガス流量との関係を示すグラフである。
【図６】本発明のスパッタ装置において、タ−ゲットと基板間に防着板を設けてスパッタさせる状態を示す側面図である。
【図７】本発明のスパッタ装置に用いられる防着板の一例を示す側面図である。
【図８】本発明の第１の実施例によるターゲット電圧とＮＦ₃ガス流量との関係を示す別のグラフである。
【符号の説明】
１ 真空容器
２ 冷却ボックス
３ バッキングプレート
４ ターゲット
５ アノード電極
６ 絶縁材
７ 被処理物
８ 被処理物支持機構
９ ゲートバルブ
１０ ロードロック室
１１ シヤッター
１２ 排気系
１３ スパッタガス導入ポート
１４ 反応成ガス導入ポート
１５ 直流電源
１６ 演算、制御装置
１７ 磁石
３１ 中性粒子アナライザー
３２ 水晶膜厚モニター
３３ フィードバック制御系
３４ 水晶振動子コントローラ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a fluoride thin film, an optical member having the thin film, and a sputtering apparatus.
[0002]
[Prior art]
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.
[0003]
Generally, an antireflection film, a mirror, etc. are made of magnesium fluoride (MgF₂) And other low refractive index materials and zirconium oxide (ZrO)₂), Tantalum oxide (Ta₂O_Five), Titanium oxide (TiO₂) And the like, or a multilayer film combining these materials, and the layer structure, film thickness, and the like are variously adjusted depending on the required optical performance.
[0004]
The vapor deposition method is simple as the equipment configuration, and can be deposited on a large area substrate at high speed and is excellent in productivity, but it is difficult to control the film thickness with high precision and develop an automatic production machine. When film formation is performed in a state where the substrate temperature is low, there are problems such as insufficient film strength, easy damage, and low adhesion between the film and the substrate.
[0005]
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 methods. The demand for coating by a sputtering method which is advantageous in terms of the above has increased.
[0006]
Sputtering is performed using zirconium oxide (ZrO₂), Tantalum oxide (Ta₂O_Five), Titanium oxide (TiO₂In the formation of an oxide dielectric thin film such as), a low absorption and high refractive index thin film can be easily formed. However, MgF is an important thin film material that has a low refractive index of 1.45 or less and greatly affects the optical performance of the multilayer optical thin film.₂, AlF_ThreeAnd other fluorides have a problem that a low absorption thin film cannot be easily formed.
[0007]
As a method for forming these fluoride thin films by a sputtering method, for example, a method as shown in JP-A-4-289165 is known. That is, MgF₂Alkaline earth metal fluoride films such as Ar and other inert gases and CF_FourSputtering using a mixed gas with a fluorine-based gas such as
[0008]
Moreover, as shown in JP-A-7-166344, an inert gas such as Ar and CF is used using a metal target._FourThere is known a method of DC sputtering using a mixed gas with fluorine gas such as.
[0009]
[Problems to be solved by the invention]
MgF used as the most common low refractive index material₂When a film is formed by sputtering, F is dissociated during sputtering, and the composition of the film deviates from the stoichiometric ratio and becomes a Mg-rich film, resulting in absorption of the film.
[0010]
In order to solve this, a method of using a fluorine-based gas as disclosed in JP-A-4-289165 and a sputtering method for supplementing F are disclosed.
[0011]
In JP-A-7-166344, by performing DC sputtering using a metal target, the substrate sheath voltage can be reduced and cation damage can be reduced.
[0012]
However, fluorine atoms tend to cause electron attachment and therefore tend to be negative ions. For this reason, if sputtering is performed with fluorine adsorbed on the target surface and the target surface is fluorinated, negative ions are formed on the target surface, and the negative ions are accelerated by the target sheath of several hundred volts, and the substrate Will be incident. For this reason, it was found that the fluoride thin film formed on the substrate was damaged and caused F defects. Negative ions accelerated by the target sheath usually have a high probability of being neutralized by collision with other gas molecules, and damage cannot be removed by a method such as applying a bias to the substrate.
[0013]
For this reason, in the above sputtering method, negative ions such as F atoms accelerated by the target sheath voltage, or cations accelerated by the substrate sheath and incident on the substrate are formed into the deposited MgF.₂The thin film was damaged and only a thin film with high absorption could be formed.
[0014]
An object of the present invention has been made in view of the circumstances as described above, and is an optical device for forming a film having a low refractive index of 1.45 or less and having no absorption in the ultraviolet and visible regions by a sputtering method. The object is to provide a method for producing a thin film.
[0015]
[Means for Solving the Problems]
The above object is achieved by the following means.
[0016]
  That is, the present invention relates to a self-bias voltage of a metal target being sputtered in a thin film forming method for forming a metal fluoride thin film by performing reactive sputtering with a gas containing at least an inert gas and fluorine using a metal target. In order to always perform sputtering in a metallic state, an inert gas is supplied from a target having a gas supply port, and sputtering is performed while controlling the gas partial pressure including fluorine in the vicinity of the target surface to be reduced. A method for forming a fluoride thin film characterized by the above is proposed. A component for reducing conductance is arranged between a metal target and a substrate on which the metal fluoride thin film is formed, and fluorine near the target surface is removed. Further reducing the gas partial pressure, and negative ions generated on the target surface The negative ion particles that are accelerated and incident on the substrate, and the high energy particle measuring means that the ions are neutralized in the plasma and incident on the substrate and the sputtering rate are measured, and the substrate incident high energy particle / sputter rate ratio is controlled. Film forming. On this occasion,The high-energy particle measuring means measures the number of high-energy particles neutralized in the plasma when negative ions generated on the target surface are accelerated by the target sheath and incident on the substrate. The sputtering power is controlled so that the number of high-energy particles incident on the substrate and the sputtering rate ratio do not exceed the predetermined values from the sputtering rate of the fluoride thin film formed on the substrate. Film formation can be performed while controlling the pressure.
[0018]
  The present invention also provides a thin film forming apparatus for forming a metal fluoride thin film by using a metal target and performing reactive sputtering with a gas containing at least an inert gas and fluorine.Because,The sputtering apparatus includes a metal target having a supply port for supplying at least an inert gas.Is to proposeArranging a component for reducing the conductance between the metal target and the substrate on which the metal fluoride thin film is formed, and the component for reducing the conductance being a deposition plate or a mesh with a variable deposition area, A target voltage measuring device for measuring the voltage of the target, and a feedback circuit for controlling a partial pressure of gas containing fluorine in order to maintain the target voltage;A sputtering apparatus is proposed in which a resistor of 10 to 1 k ohm is inserted in series between a DC power source and a target.
[0019]
According to the present invention, since DC sputtering is used, the electron temperature in the vicinity of the substrate is lower than that of high-frequency sputtering, the energy of cations incident on the substrate is suppressed, and film formation is performed without damaging the sputter-deposited fluoride thin film. Is possible. In addition, negative ions containing fluorine are not generated on the target surface, and therefore, the negative ions are accelerated by the target sheath voltage and do not enter the deposited thin film. It is possible to suppress the formation of a thin film and form a low-absorption fluoride thin film.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
The DC sputtering method according to the present invention will be described below with reference to the drawings.
[0021]
FIG. 1 is a sectional view of a DC magnetron sputtering apparatus according to the present invention. As shown in FIG. 1, the sputtering apparatus is provided with a vacuum container 1 for maintaining the inside in a substantially vacuum state. At the center of the bottom of the vacuum vessel 1, there is provided a cooling box 2 that houses a magnet inside and cools the target by circulating cooling water supplied from outside. A backing plate 3 as a cathode electrode is disposed on the upper surface of the cooling box 2, and an Al metal target 4 is fixed on the upper surface of the backing plate 3. Of course, the target material may be a target made of various metals, oxygen-added metals, fluorine-added metals, or the like as long as the electrical resistance is low. An anode electrode 5 disposed outside the target 4 with a predetermined gap is fixed to the vacuum vessel 1. An insulating material 6 is installed between the anode electrode 5 and the backing plate 3. Further, the workpiece 7 is provided on the upper surface of the vacuum vessel 1 so as to be movable between the workpiece support mechanism 8 and the load lock chamber 10 via a gate valve 9 by a moving mechanism (not shown). A shutter 11 is provided between the workpiece 7 and the target 4 so that no film adheres to the workpiece 7 until the discharge is stabilized. This shutter can be opened and closed at high speed by a moving mechanism (not shown). In addition, although it does not attach | subject a code | symbol in particular, in order to prevent the leak in the vacuum vessel 1, the sealing member is provided in the suitable place.
[0022]
Here, the vacuum vessel 1 is evacuated to a predetermined pressure by the exhaust system 12. When the exhaust is completed to a predetermined pressure, Ar gas and NF are supplied from the sputtering gas introduction port 13 and the reactive gas introduction port 14 by a gas supply system including a mass flow controller._ThreeIntroduce gas.
[0023]
Here, the flow rate, purity, and pressure of the gas to be introduced are controlled with high accuracy and are maintained at constant values.
[0024]
In addition to Ar shown here as inert gas, gases such as He, Ne, Kr, and Xe are used, and reactive gas is NF._ThreeCF other than gas_Four, F₂Reactive gas containing F such as oxygen, oxygen, H₂O, N₂A reactive gas containing oxygen such as O can be switched and introduced as necessary.
[0025]
In this state, when a predetermined DC voltage is applied from the DC power source 15 to the backing plate 3, it discharges to argon, NF_ThreeSince the gas is ionized and the magnetic field by the magnet 17 is formed above the target 4, electrons are trapped by the magnetic field, and magnetron plasma is generated on the target surface. A sheath is formed on the surface of the target by the discharge, and positive ions in the plasma are accelerated by the sheath and collide with the target 4. The sputtered particles are released from the target 4 and contain active F atoms in the plasma and on the substrate surface. By reacting with the gas, a fluoride thin film is deposited on the object 7 to be processed.
[0026]
In this example, a control device 16 is installed which can constantly monitor the target voltage from the DC power source and control the DC power source output and the reactive gas flow rate according to the voltage transformation. The target cooling water is adjusted to a desired temperature by a chiller (not shown), the flow rate is kept constant, and the target surface temperature is kept constant.
[0027]
【Example】
Hereinafter, the present invention will be specifically described by way of examples.
(Example 1)
An embodiment of a method of forming an aluminum fluoride thin film having low absorption and low refractive index on a glass substrate using the apparatus of FIG. 1 will be described in detail.
[0028]
A high-purity Al metal (99.9999%) target was used as the target, and a synthetic quartz substrate was used as the substrate.
[0029]
In performing the film formation, first, whether the target surface is in a metal state or a fluoride state was confirmed by a target voltage as follows.
[0030]
NF_ThreeWithout introducing gas, only 300 sccm of Ar gas was introduced, DC power was applied at 500 W, and the target voltage during sputtering was measured. Under the conditions of this example, it was 344V. The thin film to be formed is made of metal Al. The target voltage at this time varies depending on the applied power, the target size, the magnetron magnetic field strength, the gas pressure, etc., but usually shows 300 to 400V. That is, the target voltage in a state where the target surface is in an Al metal state and metal atoms are sputtered was confirmed.
[0031]
Next, in addition to Ar gas under the same film formation conditions, NF_ThreeGas is introduced and NF_ThreeIncreased flow rate. At this time, Ar and NF_ThreeThe gas flow rate was 300 sccm in total.
NF_ThreeAs the gas flow rate increases, the target voltage gradually decreases and NF_ThreeWhen the gas flow rate is 5 sccm or more, the target voltage changes rapidly.
NF_ThreeThe target voltage started to increase at the peak of the gas flow rate of 20 sccm.
[0032]
This is shown in FIG. This is because the target surface is fluorinated and covered with AlFx, the secondary electron emission effect is changed, and negative ions are formed on the target surface.
NF_ThreeWhen the gas flow rate is 5 sccm, the target surface is almost in a metal state, and when the substrate is placed close to the target, metal Al is deposited on the substrate.
In the range of 5 to 20 sccm, a fluorination reaction takes place on a part of the target surface, resulting in particles containing fluorine atoms such as AlFx.
NF_ThreeWhen the flow rate increases, the surface of the Al target is covered with the AlFx film, and almost becomes sputtered particles containing a fluorine element such as AlFx and enters the substrate. In such a situation, very high density negative ions are formed on the target surface, energy of several hundred eV is obtained by the target sheath formed on the target surface, and is incident on the substrate.
[0033]
When film formation is performed in such a situation, the film is damaged by the negative ion particles containing fluorine atoms, resulting in fluorine deficiency. In some cases, the film is sputtered, and the film cannot be formed.
[0034]
After confirming the change in the target voltage as described above, the substrate is attached to the workpiece support mechanism 8, and the vacuum vessel 1 is set to 2 × 10.^-FourExhaust to Pa. After that, the shutter is closed, Ar gas is 280 sccm, NF_ThreeGas was introduced at 20 sccm, and DC power was applied to the target 4 to discharge it. During the discharge, the DC voltage is constantly monitored, and based on this data, the controller 16 controls the DC power supply power, NF so that the target voltage does not fall below the set value._ThreeThe gas flow rate was controlled to maintain the condition where the metal was exposed on the target surface. Since the fluoride generation rate on the target surface depends on the sputtering rate of the target and the F atom density near the surface, if the voltage is decreased, the DC power is increased or NF is increased._ThreeReduce gas flow.
[0035]
When the discharge is stable, open the shutter and place AlF on the substrate._ThreeA film was formed. During film formation, the target voltage was constantly monitored, and the conditions under which the target surface could be sputtered in a metal state were maintained.
[0036]
After film formation, the shutter was closed and the discharge was stopped. Here, the substrate was carried out to the atmosphere via the load lock chamber.
[0037]
After that, AlF on the quartz substrate_Three The spectral characteristics of the film were measured with a spectrophotometer, and the thickness, absorption, etc. were calculated by optical interferometry or the like.
[0038]
When film formation was performed by controlling the target voltage within the range of -440V to -435V, AlF with low absorption and low refractive index was obtained._ThreeA thin film could be formed. AlF with a film thickness of 250 nm_ThreeThe absorption of the thin film was 0.2% or less at 500 nm and the refractive index was 1.37.
[0039]
In the present embodiment, the target voltage has the minimum value NF_ThreeAlthough the flow rate is used, it is of course possible to accurately control the voltage within the range of 5 to 20 sccm where the voltage changes rapidly.
However, in this case, the target voltage is likely to change greatly even with a slight change in the state of discharge (impedance).
[0040]
As a countermeasure, control is facilitated by inserting a DC resistance of several tens to several hundreds of ohms between the DC power source and the target.
Also, if the distance between the target and the substrate is too close, the metal Al film will be sputtered._ThreeIt is necessary to increase the distance between the target and the substrate according to the gas flow rate to promote the fluorination reaction.
[0041]
In addition, NF_ThreeEven if the target surface with a flow rate of 0 to 5 sccm is sputtered in a substantially metallic state, it is possible to form a film while preventing the generation of negative ions containing fluorine elements on the target surface. A chemical thin film can be formed.
However, when film formation is performed under these conditions, a metal thin film is easily formed on the substrate.
In such a case, in order to effectively fluorinate the sputtered metal, a deposition plate for adjusting the sputtering rate is installed between the target and the substrate to form a film.
An example of the shape of the adhesion preventing plate is shown in FIG.
In this figure, a wedge-shaped notch is provided, the deposition preventive plate is fixed, and the substrate is configured such that the relative position with respect to the deposition preventive plate can be always changed by a rotation and positive motion mechanism (not shown). Since sputtered particles reach the substrate from the target only from the cutout portion, metal sputtered atoms and the like that reach the substrate can be suppressed.
The shape of the notch portion does not need to be a wedge shape, and may be a shape according to the substrate shape. For example, the notch portion may be a curved shape or a mesh shape knitted with a metal wire. .
[0042]
The position of the deposition preventing plate and the substrate is always relatively changed during the film formation, and also serves as a film thickness correction on the substrate.
The metal sputtered from the target is partially blocked by the deposition plate and reaches the substrate, whereby metal atoms that reach the substrate are prepared, and fluorine radicals generated in a gas plasma containing fluorine near the substrate In addition, it can react efficiently with fluorine ions and the like, and a stoichiometric metal fluoride thin film can be formed.
Even if the deposition preventing plate as shown in FIG. 6 is used for film formation within a range of 5 to 20 sccm where the voltage changes rapidly, the same effect can be obtained.
[0043]
The deposition efficiency of the deposition plate shown in the present embodiment is desirably a configuration that can be varied depending on the film formation conditions, and as shown in FIG. 7, with a variable wing configuration that can arbitrarily change the deposition area, Wide application range.
[0044]
In this example, an Al metal target was used. However, if the same reactive sputtering is performed with an Mg metal target, the low absorption MgF.₂A thin film can be obtained.
Using metal Mg as a target, Ar as a sputtering gas, and NF as a reactive gas_ThreeIntroduce MgF₂Target voltage and NF for thin film sputtering_ThreeThe relationship of the gas flow rate is shown in FIG.
[0045]
In the case of the Mg target, NF is opposite to the Al target._ThreeAs the amount of introduction increases, the target voltage increases. A sudden voltage fluctuation is observed at a flow rate of 3 to 6 sccm.
From this result, it is considered that the target surface is sputtered in a metal state up to 3 sccm, and in the region of 3-6 sccm, the target surface is sputtered in a partially fluorinated state.
[0046]
In this case as well, in the situation where the target surface of 1 to 6 sccm is not completely fluorinated, the target voltage is kept constant and reactive sputtering is performed to form a metal fluoride thin film. Damage can be suppressed and a high-quality metal fluoride thin film can be formed.
In the situation of 1 to 3 sccm, the metal fluoride film can be stably formed by inserting an adhesion-preventing plate as shown in FIG. 6 between the target and the substrate.
[0047]
In this embodiment, the reactive gas is NF._ThreeHowever, any gas can be used as long as it contains a fluorine-containing gas that is difficult to be incorporated into the film and does not affect the optical properties even if incorporated. In particular, CF_Four, SF₆Gases such as, and the like are preferable because they are easy to use from the viewpoint of the usage environment and have little influence on the optical performance in the visible range.
[0048]
When forming a low-absorption thin film in the ultraviolet region, F diluted with an inert gas is used to minimize the contamination of impurities.₂Gas is suitable. However, AlF_ThreeFor thin films, NF_ThreeSince N is hardly taken into the film even with gas, there was almost no problem in practical use.
[0049]
Note that the present invention is not limited to the above-described embodiments, and can be variously modified.
(Example 2)
A DC sputtering method according to a second embodiment of the present invention will be described with reference to the drawings.
[0050]
FIG. 2 is a cross-sectional view of a DC magnetron sputtering target according to the second embodiment of the present invention.
[0051]
This target is made of Al metal and has a gas outlet 21 for supplying an inert gas. The inert gas is supplied from the inlet 22 next to the target via the target back surface. On the other hand, NF, which is a reactive gas_ThreeIs introduced into the sputtering chamber through the gas outlet 23 near the substrate, and the gas exhaust port 24 is disposed on the substrate side. Therefore, NF near the target_ThreeThe partial pressure is very low and it is difficult to form fluoride on the target surface.
[0052]
Therefore, in the configuration of this embodiment, the target surface is not easily fluorinated, and thus negative ions are not easily generated on the target surface, and film formation of aluminum fluoride without damage is possible.
[0053]
In this example, it is difficult to generate fluoride on the target surface, but it is completely NF._ThreeSince the gas cannot be removed from the target surface, the target surface potential is monitored and the DC output, NF_ThreeIt is necessary to control the gas flow rate, etc., but the gas pressure, NF_ThreeThe application range of sputtering conditions such as partial pressure and applied power can be expanded, and the negative ion concentration can be reduced.
[0054]
In the present embodiment, the sputter gas exhaust port 24 is disposed on the substrate side, and a component that reduces the conductance such as a mesh is disposed between the substrate and the target, so that the NF near the target surface is disposed._ThreeThe gas partial pressure can be lowered, which is effective.
(Example 3)
A DC sputtering method according to a third embodiment of the present invention will be described with reference to the drawings.
[0055]
FIG. 3 is a sectional view of a DC magnetron sputtering apparatus according to the third embodiment of the present invention.
[0056]
As shown in FIG. 3, the sputtering apparatus is provided with a vacuum container 1 that maintains the inside in a substantially vacuum state. At the center of the bottom of the vacuum vessel 1, there is provided a cooling box 2 that houses a magnet inside and cools the target by circulating cooling water supplied from outside. A backing plate 3 as a cathode electrode is disposed on the upper surface of the cooling box 2, and an Al metal target 4 is fixed on the upper surface of the backing plate 3. Of course, the target material may be a target made of various metals, oxygen-added metals, fluorine-added metals, or the like as long as the electrical resistance is low. An anode electrode 5 disposed outside the target 4 with a predetermined gap is fixed to the vacuum vessel. An insulating material 6 is installed between the anode electrode 5 and the backing plate 3.
[0057]
Further, on the upper surface of the vacuum vessel 1, there is a quartz vibration type membrane pressure monitor 31 and a neutral particle energy analyzer 32, which can measure the energy and amount of neutral particles incident on the substrate. Is configured to rotate. Neutral particle analyzer ionizes neutral particles that enter the measuring instrument by irradiating them with an electron beam. After ionizing the ionized particles with a 45-degree sector-type energy analyzer, the mass is measured with a quadrupole mass separator. An analyzer of a type that separates and counts ions with a secondary electron multiplier was used. Here, when the neutral particles incident on the analyzer are ionized, the energy of the neutral particles slightly changes, but the amount of change is considered to be less than 1 eV, which is a problem as the performance of the analyzer used in this example. It will not be.
[0058]
Even if it is not an energy analyzer as shown here, as long as it is a measuring instrument capable of measuring the energy of neutral particles, it can be used in any configuration.
[0059]
Number of neutral particles incident on the analyzer / AlF_ThreeDC power output, NF so that the sputter rate ratio does not exceed the specified value_ThreeA control system 33 that feeds back the gas flow rate is provided.
[0060]
In addition, although not indicated in particular, in order to prevent leakage in the vacuum vessel 1, seal members are provided at appropriate places.
[0061]
During sputtering of the Al target, Al metal is sputtered from the target, and fluorinated in the plasma and on the substrate surface._ThreeA thin film is formed on the substrate, but aluminum fluoride is formed by fluorination on the target surface. For this reason, negative ions such as F- are generated on the surface of the target during sputtering, are accelerated by the target sheath, change to neutral during the course, and enter the substrate. For this reason, the fluoride thin film formed on the substrate is damaged, fluorine is difficult to solve and absorption is increased.
[0062]
This absorption was found to depend on the energy and number of incident neutral particles. Absorption tends to increase as the energy and number increase, and absorption decreases as the sputtering rate of the fluoride thin film increases.
[0063]
Therefore, in order to form a low-absorption fluoride thin film, it is effective to monitor the deposition rate and the energy and density of neutral particles incident on the substrate and perform sputtering while maintaining an appropriate state. is there.
[0064]
In this embodiment, the film formation rate is measured using a crystal vibration type rate monitor. Also, the number of incident neutral particles is measured with a neutral particle energy analyzer, and the DC power output, NF, so that the neutral particle number / rate ratio does not exceed a predetermined value._ThreeThe film was formed while feeding back and controlling the gas flow rate.
[0065]
In this example, the number of F neutral particles of 50 eV was monitored. However, since the neutral particle monitor also changes depending on the measurement conditions, the voltage applied to the secondary electron multiplier, etc., neutral particles that have no problem in absorption in each device. The number / rate ratio is measured in advance and AlF_ThreeIt is only necessary to control this ratio at all times during production.
[0066]
In this embodiment, the number of neutral particles is monitored. However, depending on sputtering conditions, there are cases in which the particles enter the substrate in a negative ion state. In such a case, if a negative ion analyzer is used instead of the neutral particle monitor, negative ions incident on the analyzer are monitored, and the film is formed while adjusting the negative ion amount / sputter rate ratio to be a predetermined value or less. Good.
(Example 4)
Table 1 and FIG. 4 show the configuration and reflection characteristics of an antireflection film formed on an optical member used in an excimer laser or the like according to the fourth embodiment of the present invention.
[0067]
The antireflection film shown in this example was formed as follows.
[0068]
Set the quartz substrate in the vacuum chamber, and the inside of the vacuum chamber is 1 × 10^-6After exhausting to Torr, oxygen gas and NF_Three2 × 10 each of gas^-3Torr / 4 × 10^-FiveIntroduce until Torr pressure, DC power 500W, Al₂O_ThreeA thin film was formed to a predetermined thickness. Next, the gas to be introduced is Ar / NF._ThreeAnd each partial pressure is 1.5 × 10^-30.5 × 10^-3AlF while maintaining the condition that the target surface is in a metal state_ThreeA thin film is formed to a predetermined thickness. This is repeated and Al is formed on the quartz substrate.₂O_Three/ AlF_ThreeThe alternating layers are provided and configured.
[0069]
The antireflection film shown in this example has a high refractive index Al as a sputtering characteristic.₂O_ThreeAlF with low absorption and low refractive index_ThreeIn combination with the above, at an excimer laser wavelength, the absorption rate is 0.1% or less, the antireflection wavelength region is very wide, and good performance is exhibited.
[0070]
Although the antireflection film is shown in this embodiment, the present invention is not limited to the antireflection film. In particular, by forming a fluoride thin film with low absorption and low refractive index by sputtering, it can be combined with an oxide thin film with high refractive index and low absorption that can be formed by sputtering, and has an excellent optical performance. It became possible to provide.
[0071]
[Table 1]

[0072]
【The invention's effect】
As described above, in the present invention, AlF_ThreeWhen DC sputtering is performed on a fluoride thin film having a low absorption and a low refractive index in the visible region and the ultraviolet region, negative ions such as F- ions are formed on the target surface, and are accelerated by the target sheath and incident on the substrate. By installing a monitor so that the target surface is always sputtered in a metal state so that the number of the incident surface is reduced even if it is incident, the film is formed while maintaining this condition. A fluoride thin film having low absorption and low refractive index in the ultraviolet region can be formed stably.
[0073]
In addition, by suppressing the partial pressure of the gas containing F on the target surface, fluorination of the target surface is suppressed, and negative ions are prevented from being formed on the target surface. Accelerated high-energy particles neutralized in plasma are monitored, and the number / sputter rate ratio of this particle is kept below a predetermined value, resulting in a fluoride film with low absorption and low refractive index in the visible and ultraviolet regions. It can be formed stably.
[0074]
Furthermore, since it is possible to form a fluoride thin film with low absorption and low refractive index in the visible to ultraviolet region by sputtering, it is very excellent by forming alternating layers with oxide thin film with high refractive index, which is a feature of sputtering. It has become possible to provide optical components having excellent optical performance.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a DC magnetron sputtering apparatus according to a first embodiment of the present invention.
FIG. 2 is a sectional view of a DC magnetron sputtering apparatus according to a second embodiment of the present invention.
FIG. 3 is a sectional view of a DC magnetron sputtering apparatus according to a third embodiment of the present invention.
FIG. 4 is a graph showing reflectivity according to the configuration of a multilayer film according to a fourth embodiment of the present invention.
FIG. 5 shows target voltage and NF according to the first embodiment of the present invention._ThreeIt is a graph which shows the relationship with a gas flow rate.
FIG. 6 is a side view showing a state in which an adhesion prevention plate is provided between a target and a substrate and sputtering is performed in the sputtering apparatus of the present invention.
FIG. 7 is a side view showing an example of a deposition preventing plate used in the sputtering apparatus of the present invention.
FIG. 8 shows target voltage and NF according to the first embodiment of the present invention._ThreeIt is another graph which shows the relationship with a gas flow rate.
[Explanation of symbols]
1 Vacuum container
2 Cooling box
3 Backing plate
4 Target
5 Anode electrode
6 Insulation material
7 Workpiece
8 Workpiece support mechanism
9 Gate valve
10 Load lock room
11 Shutter
12 Exhaust system
13 Sputter gas introduction port
14 Reaction gas introduction port
15 DC power supply
16 Arithmetic and control devices
17 Magnet
31 Neutral particle analyzer
32 Crystal thickness monitor
33 Feedback control system
34 Quartz Crystal Controller

Claims (9)

  In a thin film formation method for forming a metal fluoride thin film by performing reactive sputtering with a gas containing at least an inert gas and fluorine using a metal target, the self-bias voltage of the metal target being sputtered is monitored and the metal target is constantly Sputtering is performed while supplying an inert gas from a target having a gas supply port so as to be sputtered in a state and controlling the gas partial pressure containing fluorine in the vicinity of the target surface to be reduced. Method for forming a chemical thin film.   The gas partial pressure containing fluorine in the vicinity of the target surface is further reduced by disposing a component for reducing conductance between the metal target and the substrate on which the metal fluoride thin film is formed. A method for forming a fluoride thin film as described.   The negative ions generated on the target surface are accelerated by the target sheath and incident on the substrate, and the high energy particle measuring unit and the sputtering rate in which the ions are neutralized in the plasma and incident on the substrate are measured by the measuring unit. The thin film forming method according to claim 1, wherein film formation is performed while controlling a substrate incident high energy particle / sputter rate ratio. The high energy particle measuring means measures the number of high energy particles neutralized in the plasma when negative ions generated on the target surface are accelerated by the target sheath and incident on the substrate, and the sputter rate measuring means The sputtering power is controlled so that the number of high-energy particles incident on the substrate and the sputtering rate ratio do not exceed predetermined values from the sputtering rate of the fluoride thin film formed on the substrate measured by 4. The method for forming a fluoride thin film according to claim 3, wherein the film formation is performed while controlling the gas partial pressure. A sputtering apparatus for forming a metal fluoride thin film by performing reactive sputtering with a gas containing at least an inert gas and fluorine using a metal target,
The sputtering apparatus has a metal target having a supply port for supplying at least an inert gas. The sputtering apparatus according to claim 5 , wherein a component for reducing conductance is disposed between the metal target and a substrate on which the metal fluoride thin film is formed. The sputtering apparatus according to claim 6 , wherein the component for reducing the conductance is a deposition plate or a mesh capable of varying a deposition area. A target voltage measuring device for measuring the voltage of the target;
8. The sputtering apparatus according to claim 5 , further comprising a feedback circuit that performs partial pressure control of a gas containing fluorine in order to maintain the target voltage. 9. The sputtering apparatus according to any one of claims 5 to 7 , wherein a resistor of 10 to 1 K ohm is inserted in series between the DC power source and the target.

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