JP2001264512A - Method for post-treatment of thin film, post-treatment device, post-treated optical member and aligner provided with optical member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of drastic decrease of transmittance of a pure crystal of metal fluoride, which originally exhibits excellent transmitlance to an F2 eximer laser beam, caused by thin film forming with a general thin film forming method such as vacuum deposition or sputtering and to solve the problem of the decrease of transmittance in optical members such as a lens or a prism resulting therefrom. SOLUTION: The post-treatment method contains a housing step in which a fluoride thin film with a fluorine defect film formed on a substrate is placed in a fluorine atmosphere at a specifically controlled temperature and a time measuring step for measuring the time consumed to raise temperature from the specific temperature so as to replenish the fluorine defect with fluorine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a post-processing method, a post-processing apparatus, and a post-processing method for a fluoride optical thin film which can be used in the vacuum ultraviolet region and the ultraviolet region, and in particular, has improved light transmittance and durability in the vacuum ultraviolet region. An optical member having a thin film formed thereon,
The present invention relates to an exposure apparatus equipped with an optical member.

[0002]

2. Description of the Related Art Fluoride materials have excellent optical properties such that they are transparent over a wide light wavelength range from the infrared to the vacuum ultraviolet region. Especially at wavelengths below 180 nm, most oxide materials are opaque, whereas many fluoride materials are transparent. Therefore, fluoride is indispensable especially as an optical member material and an optical thin film for the vacuum ultraviolet region.
In recent years, high integration and high density of semiconductor integrated circuits have been advanced. In order to further reduce the line width of a circuit and to further refine a pattern, there is a demand for an ever-increasing photolithography resolution of a reduced projection exposure apparatus for manufacturing a semiconductor circuit.

In order to increase the resolution, the wavelength of the exposure light source has been g-line, i-line (365 nm), KrF excimer laser (wavelength: 24 nm).
8 nm) and has been shorter wavelength, in the future, ArF laser (wavelength 193 nm), it is inevitable that progresses is further shorter wavelength to F ₂ laser (157 nm). Optical members such as lenses and prisms, and optical thin films such as antireflection films and deflection films coated on the surfaces of these optical members, which are used in exposure apparatuses with shorter wavelengths, are naturally fluorides for the above reasons.

In a reduction projection exposure apparatus, dozens of optical members for various uses are arranged between a laser light source and a wafer on which a semiconductor circuit is exposed. Is coated with a fluoride thin film corresponding to. Since the optical member material itself and the fluoride thin film naturally absorb light, the amount of light finally reaching the wafer surface becomes considerably small. In order to improve the exposure performance and the productivity, this reduction in the amount of light must be made as small as possible. That is, the smaller the light absorption of each optical member and thin film, the better the performance of the exposure apparatus.

As a result of extensive research and development of optical member materials themselves, the content of defects and impurities that cause light absorption has been suppressed as much as possible, and scattering on the element surface has been reduced as much as possible by the development of polishing techniques. are doing. On the other hand, optical thin films have been formed by various PVD methods such as vacuum deposition by resistance heating or electron beam melting, vacuum deposition using ion assist, ion plating, sputtering, and ion beam sputtering. In short, it has been manufactured by a relatively simple method using a vacuum apparatus.

[0006]

However, in any of the above-described film forming techniques, a thin film is formed on a relatively low-temperature substrate (optical member) by a reaction under a thermodynamic non-equilibrium state. Therefore, the deposited thin film was deficient in fluorine as compared with the stoichiometric composition, was poor in crystallinity, and contained many structural defects and the like. As a result, the optical absorption edge wavelength shifts to a longer wavelength side as compared with the ideal crystal, and an absorption band caused by defects and impurities is also generated, so that light absorption in a vacuum ultraviolet region is increased. As a cause of fluorine deficiency, in the resistance heating type vacuum deposition method, when evaporating a fluoride deposition material on a resistance heating boat, fluorine dissociation due to heating, high temperature chemical reaction with the boat material, fluorine deficiency in the deposited film Occurred. The separated fluorine was exhausted.

[0007] In electron beam melting type vacuum deposition, the fluoride deposition material is evaporated by the energy of electron irradiation, and the energy causes a certain ratio of separation of fluorine atoms and metal atoms. occured. In ion-assisted vacuum deposition and ion plating, the surface of a thin film growing on a substrate is subjected to ion beam irradiation or plasma irradiation. Therefore, in addition to the above-described fluorine dissociation on the side of the deposition material, fluorine dissociation due to charged particle collision on the growth film surface also occurred. In sputtering or ion beam sputtering, when a fluoride target is sputtered by ion bombardment, only light fluorine atoms are selectively sputtered by a selective sputtering phenomenon, so that a fluorine deficiency occurs on the target surface. When a target having a fluorine deficiency was used as a raw material to form a film by sputtering, a stoichiometric composition film could not be obtained at all.

An optical thin film having such a fluorine deficiency and structural irregularity has been mounted on the vacuum ultraviolet exposure apparatus. The optical thin film is coated on each surface of the optical member, that is, the number of coated surfaces is twice the number of optical members. The amount of light that reached the wafer surface after passing through an optical thin film with fluorine deficiency and structural irregularity over several tens of coats was extremely low, about several percent of the original light source light amount. in short,
The optical thin film determined the exposure characteristics.

Further, the residual moisture and oxygen in the vacuum vessel react with the vapor-deposited raw material / target and the deposited film in which fluorine deficiency has occurred, thereby forming a fluoride film having oxygen-containing fluorine deficiency. It is even larger. As described above, a fluoride thin film having a fluorine deficiency, or
The fluoride thin film containing fluorine deficiency and oxygen contained laser defects that were not as high as expected because of structural defects and impurities, so that the frequency of replacement of optical member components had to be increased. In short, the optical thin film has determined the productivity of the exposure apparatus. In each of the above film formation processes, a fluorine-based gas is introduced into the film formation container during film formation in order to compensate for the fluorine deficiency of the deposited film, but the reaction control becomes complicated, and the stoichiometric composition film is not necessarily easily formed. Is not obtained.

An object of the present invention is to provide a fluoride optical thin film having a stoichiometric composition free of fluorine deficiency and solving the above problems, and a method for producing the same.

[0011]

According to a first aspect of the present invention, there is provided a storage step of storing a fluorine thin film having a fluorine deficiency formed on a substrate in a fluorine atmosphere controlled at a predetermined temperature. And a time measuring step of measuring a time from the predetermined temperature, to provide a post-treatment method for supplementing the fluorine deficiency with fluorine.

According to a second aspect of the present invention, there is provided a storage means for storing a fluoride thin film having a fluorine deficiency formed on a substrate in a fluorine atmosphere controlled at a predetermined temperature, and a timing means for measuring a time from the predetermined temperature. And a post-treatment apparatus for supplementing the fluorine deficiency with fluorine.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a method for post-treatment of a fluoride thin film having a fluorine deficiency according to the present invention will be described below.
The present invention is not limited to this example. Fluorine-based gases include pure fluorine gas, helium, neon, argon,
Krypton, fluorine gas diluted with at least one of the rare gases of xenon, fluorine gas generated by electrolysis of various metal fluorides represented by AgF, Xe
Sublimated and evaporated fluorine-rare gas compounds of F ₂ , XeF ₄ and XeF ₆ and fluorine gas generated by decomposition of these fluorine-rare gas compounds, NF ₃ , SF ₆ , SF ₄ , CF ₄ , C ₂ F ₆ ,
Activated fluorine of fluorine radicals and fluorine ions generated by gas plasma of at least one of C ₃ F ₈ fluorine-based compounds is desirable.

The fluoride optical thin film includes magnesium fluoride, calcium fluoride, lithium fluoride, lanthanum fluoride, aluminum fluoride, neodymium fluoride, gadolinium fluoride, yttrium fluoride, dysprosium fluoride, fluoride Barium, sodium fluoride, bismuth fluoride, strontium fluoride, lead fluoride, selenium fluoride,
It is a single layer or a multilayer film selected from cryolite and thiolite.

[0015]

(Embodiment 1) As an embodiment of the present invention, a post-processing method will be described with reference to FIG. FIG. 1 is a flowchart showing the post-processing method of the present invention. After cleaning the optical member coated with the fluoride thin film in advance, it is fixed to the optical member fixing jig 4 in the vacuum chamber 1 (step S001). Open the valve 10 and evacuate the inside of the vacuum chamber 1 by the exhaust system 8 to 10 ^-5 Pa
(Step S002).

The fluorine-based gas supplied from the fluorine-based gas generation source 7 is introduced into the vacuum chamber 1 via the flow rate control and pressure control device 9 (step S003). The flow control and pressure control device 9 is adjusted so that the indicated value of the pressure gauge 11 becomes a predetermined value (step S004). The introduction and evacuation of the fluorine-based gas may be continued while the valve 10 is kept open, so that the open-type reactor may be used. Alternatively, the valve 10 may be closed to stop the introduction of the fluorine-based gas, and the closed-type reactor may be used. Good. The external heater 3 is energized to heat the vacuum chamber 1 and raise the temperature inside the vacuum chamber 1 (step S
005).

The temperature inside the vacuum chamber 1 is measured by the thermocouple 2, and time counting from a predetermined temperature is started by the clock 32 (step S0).
06). Adjusting the current to the external heater 3
The inside temperature is made constant (step S007). When the predetermined time has elapsed, the power supply to the external heater 3 is stopped (step S008). When the temperature in the vacuum chamber 1 decreases to room temperature, a rare gas is introduced from the gas inlet 7 while the vacuum chamber 1 is evacuated by the exhaust system 8, and the inside of the vacuum chamber 1 is replaced with a rare gas atmosphere from a fluorine atmosphere. .

Next, the processing conditions of the post-processing will be described. The post-treatment is a diffusion reaction of fluorine atoms from the surface of the thin film to the inside. Therefore, the reaction ends when the fluorine atoms sufficiently reach from the surface of the thin film to the interface with the substrate and the entire film is completely fluorinated. The diffusion reaction rate depends on two points: the supply amount of the fluorine atom species in a form effective for diffusion to the surface and the temperature of the thin film as the diffusion medium. If the amount of supply to the thin film is sufficient, the temperature is limited, and if the temperature of the thin film is high, the supply is limited.

The pressure in the vacuum chamber may be under a reduced pressure of less than 1 × 10 ⁵ Pa. In order to achieve a sufficient supply of fluorine atoms to the surface of the thin film, the pressure is preferably 100 Pa or more. The higher the pressure, the higher the fluorine atom supply rate, and thus the higher the diffusion rate. It is desirable that the temperature of the optical member be between room temperature and 300 ° C. The diffusion rate increases as the temperature increases. However, if the temperature exceeds 300 ° C., the optical characteristics of the optical member itself change, which is not desirable.

Next, the configuration of the post-processing apparatus for the fluoride optical thin film will be described with reference to FIG. FIG. 2 is a configuration diagram showing a post-processing apparatus for a fluoride optical thin film of the present invention. In FIG. 2, a thermocouple 2 for measuring the temperature in the vacuum chamber 1 and an optical member fixing jig 4 for fixing an optical member 5 on which a fluoride optical thin film 6 is formed are installed inside the vacuum chamber 1. ing. The material of the vacuum chamber 1 and the optical member fixing jig 4 is nickel or a nickel alloy (including Monel) having high corrosion resistance to fluorine. The vacuum chamber 1 includes an external heater 3 for heating the inside of the vacuum chamber 1, an exhaust system 8 for exhausting the gas in the vacuum chamber 1 through a valve 10, a flow rate of fluorine gas from a fluorine-based gas generation source 7, and a vacuum. A flow rate control and pressure control device 9 for controlling the pressure in the vessel 1, a pressure gauge 11 for measuring the pressure in the vacuum chamber 1, and a clock 32 for measuring the time are connected. Connected.

A fluorine-based gas is introduced into the vacuum chamber 1 in advance, and the inner wall of the vacuum chamber 1 and the optical member fixing jig 4 are fluorinated to passivate the surface. In consideration of the danger of fluorine gas, the pressure in the vacuum chamber 1 is set to be lower than the atmospheric pressure.
In the above embodiment, the temperature inside the vacuum chamber was measured by a thermocouple, but the temperature may be measured on an optical member or an optical thin film.

(Embodiment 2) As a second embodiment of the present invention, a method of performing post-processing using sputtering will be described. After cleaning the optical member on which the fluoride thin film is formed, the optical member is fixed to the lower electrode 18 in the vacuum chamber 13 (Step S011). The valve 31 is opened, and the vacuum chamber 13 is
The inside is evacuated to 10 ^-5 Pa (step S012). The SF ₆ gas whose flow rate has been adjusted by the mass flow controller 26-2 is introduced into the vacuum chamber 13 in a shower shape (step S013). The mass flow controller 26-2 and the valve 31 are adjusted so that the indicated value of the pressure gauge 23 becomes a predetermined value (step S014). The heater 19 is energized to heat the optical member 21 (step S015). The high-frequency output oscillated by the high-frequency power supply 17 is applied to the upper electrode 15 via the matching box 16 to generate plasma 29 (step S016). When the indicated value of the thermocouple 20 indicates a predetermined value, time elapse is started by the clock 32 (step S017).

The current to the heater 19 is adjusted so that the indicated value of the thermocouple 20 becomes constant (step S).
018). When the predetermined time has elapsed, the power supply to the heater 19 is stopped, and the power supply to the high frequency power supply 17 is stopped (step S019).

The post-processing of the thin film is completed. Valve 24-1
Is opened, and argon gas 27 is introduced into the vacuum chamber 13 and replaced. By forming plasma and ionizing and separating SF ₆ , the inside of the vacuum chamber 13 is filled with active fluorine effective for the fluorination reaction, and the post-processing is started. The processing temperature, the processing pressure, and the selection factors are the same as those in the first embodiment, and a description thereof will be omitted. Next, the configuration of the post-processing apparatus for a fluoride optical thin film will be described with reference to FIG. FIG. 4 is a configuration diagram showing a post-processing apparatus for a fluoride optical thin film of the present invention.

In FIG. 4, an upper electrode 15 and a lower electrode 18 on which an optical member 21 on which a fluoride optical thin film 22 is formed are placed inside the vacuum chamber 13. A heater 19 and a thermocouple 20 for measuring the temperature of the heater 19 are provided inside the lower electrode 18. The upper electrode 15 is made of nickel or nickel alloy (including Monel) having high corrosion resistance to fluorine.

The vacuum chamber 13 includes a vacuum chamber 13.
An exhaust system 14 that the gas in the inner evacuated through the valve 31, pressure gauge 23 for measuring the pressure in the vacuum chamber 13, a clock 32 for measuring the time, valve 24-1 for introducing the argon gas 27, SF ₆ gas 28 Is connected. The valve 24-1 has a mass flow controller 26- for controlling the flow rate and pressure of the argon gas 27.
1. A mass flow controller 26-2 for controlling the flow rate and pressure of the SF ₆ gas 28 is connected to the valve 24-2.

A high frequency power supply 17 having a frequency of 13.56 MHz is connected to the upper electrode 15 via a high frequency matching box 16. A shielding plate 30 is inserted between the upper electrode 15 and the lower electrode 18, and the plasma 29 is formed only in a space between the upper electrode 15 and the shielding plate 30 by the shielding plate 30. This is a device for preventing the optical member 21 provided on the lower electrode 18 and the coated fluoride film 22 from being exposed to the plasma 29. If the optical member is placed in an active fluorine atmosphere, the fluorination reaction proceeds even with the shielding plate 30, and there is no need to directly expose the optical member to plasma.

In the above embodiment, the temperature inside the vacuum chamber was measured by a thermocouple, but an optical member or an optical thin film may be measured. Comparative Example 1 A lanthanum fluoride film having a thickness of 500 nm deposited on a fluorite substrate was prepared as a sample. When the chemical composition ratio of this lanthanum fluoride film was analyzed by electron probe microanalysis (hereinafter abbreviated as EPMA), it was found that La / F / O = 1.0 / 2.6 / 0.2. Admitted. Furthermore, when a state analysis of the lanthanum fluoride film surface was performed by X-ray photoelectron spectroscopy (hereinafter abbreviated as XPS), the bonding state of oxygen atoms present on the surface was determined to be La as well as the physically adsorbed water. -OH bond and La-
O linkage was observed. That is, the lanthanum fluoride film was partially hydroxylated and oxidized.

This sample was post-treated by the method shown in Example 1. The treatment pressure was 1.3 × 10 ⁴ Pa, the treatment temperature was 100 ° C., and the treatment time was 24 hours. When the chemical composition ratio of the lanthanum fluoride film after the treatment was analyzed by EPMA, it was found that La / F / O = 1.0 /
3.0 / 0.0. That is, the deficiency of fluorine was supplemented to form a stoichiometric composition, and oxygen became lower than the lower detection limit of the analysis method. Furthermore, from the results of XPS, the bonding state of oxygen atoms detected from the surface is only physically adsorbed water,
No chemically bonded components such as hydroxylation or oxidation were observed.

Next, the transmittance of the sample was measured before and after the post-processing, respectively. FIG. 5 is a diagram showing the presence or absence of post-processing and the change in transmittance. By the post-treatment method of the present invention, the transmittance in the vacuum ultraviolet region is clearly increased,
In other words, light absorption is greatly reduced. Furthermore, the crystal structure of the lanthanum fluoride thin film was confirmed to be trigonal by X-ray diffraction. The highest diffraction intensity was the 002 diffraction peak. The post-fluorination annealing showed that the lanthanum fluoride film grew with strong c-axis orientation. Furthermore, when the change of the 002 diffraction peak before and after the post-fluorination annealing treatment was measured by the X-ray diffraction rocking curve method, the full width at half maximum of the peak was small after the post-annealing. In addition, the data clearly show that the crystallinity has been improved.

Further, when the samples before and after the post-processing were evaluated using the laser durability evaluation method described in detail in Japanese Patent Application No. 9-34706, it was confirmed that the laser resistance was improved by the post-processing. Was. (Comparative Example 2) Using the same sample as in Comparative Example 1, post-treatment was performed by the method shown in Example 2. Processing pressure 100P
a, the processing temperature was 100 ° C., and the processing time was 5 hours. When the chemical composition ratio of the lanthanum fluoride film after the treatment was analyzed by EPMA, it was found that La / F / O = 1.0 / 3.0 / 0.0. It became the following. Furthermore, from the XPS results, the bonding state of oxygen atoms detected from the surface was only physically adsorbed water, and no chemical bonding components such as hydroxylation or oxidation were observed at all.

(Exposure Apparatus) Next, an apparatus to which the optical member formed by the method of the present invention is applied will be described.
The apparatus applied is a projection exposure apparatus, such as a stepper, for projecting an image of a reticle pattern onto a photoresist-coated wafer. FIG. 6 shows a basic structure of an exposure apparatus according to the present invention. FIG.
As shown in the figure, the exposure apparatus of the present invention has at least a surface 1
A wafer stage 1003 on which a substrate W coated with a photosensitive agent placed on the substrate 003a can be placed, and vacuum ultraviolet light of a prepared wavelength is irradiated as exposure light, and a mask pattern (reticle R) prepared on the substrate W Optical system 1001 for transferring an image, a light source 1100 for supplying exposure light to the illumination optical system 1001, and a first surface P1 on which a mask R for projecting an image of the pattern of the mask R on the substrate W is arranged. Projection optical system 1005 placed between (object plane) and a second surface (image plane) matched with the surface of substrate W
including. The illumination optical system 1001 includes a mask R and a wafer W
The mask R is disposed on a reticle stage 1002 that can move in parallel with the surface of the wafer stage 1003. Reticle exchange system 12
No. 00 exchanges and carries the reticle (mask R) set on the reticle stage 1002. Reticle exchange system 1
Reference numeral 200 denotes a stage driver for moving the reticle stage 1002 parallel to the surface 1003a of the wafer stage 1003. Projection optical system 1005
Has an alignment optical system applied to a scan type exposure apparatus.

The exposure apparatus of the present invention uses an optical member (for example, an optical lens made of fluorite) on which an antireflection film is formed by the method of the present invention. Specifically, the exposure apparatus of the present invention shown in FIG. 6 uses the optical lens 1009 of the illumination optical system 1001 or the projection optical system 100
An antireflection film is formed on the fifth optical lens 1010 by the method of the present invention.

[0034]

As described above, according to the present invention, a fluorine thin film having a fluorine deficiency or oxygen content is post-treated in a fluorine atmosphere reaction furnace to compensate for the fluorine deficiency and eliminate the oxygen content. Thus, a fluoride film having a high stoichiometric composition and high crystallinity can be obtained. Accordingly, absorption due to defects and impurities is also reduced, so that the transmittance in the vacuum ultraviolet region and the laser durability are improved.

Since the exposure apparatus to which the optical member of the present invention is applied employs an optical member having excellent transmittance, loss of illuminance of a light source can be reduced as compared with a conventional exposure apparatus.

[Brief description of the drawings]

FIG. 1 is a flowchart of a post-processing method according to the present invention.

FIG. 2 is a configuration diagram of a post-processing device according to the present invention.

FIG. 3 is a flowchart of a post-processing method according to another embodiment of the present invention.

FIG. 4 is a configuration diagram of a post-processing apparatus according to another embodiment of the present invention.

FIG. 5 is a diagram illustrating the presence / absence of post-processing and a change in transmittance.

FIG. 6 is a configuration diagram showing a basic configuration of an exposure apparatus using an optical member post-processed by the method of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum tank 5 ... Fluoride optical member 6 ... Fluoride optical thin film 7 ... Fluorine gas generation source 9 ... Flow control and pressure control device 13 ... Vacuum chamber 15 ... Upper electrode 19 ... Heater 21 ... Fluoride optical member 22 ... fluoride optical thin film 23 ... pressure gauge 27 ... argon gas 28 ... SF ₆ gas 29 ... plasma 1001 ... illumination optical system 1005 ... projection optical system 1009 ... illumination optical system of the optical lens 1010 ... projection optical system of the optical lens

Claims (7)

[Claims] 1. A storage step of storing a fluorine deficient fluoride thin film formed on a substrate in a fluorine atmosphere controlled at a predetermined temperature, and a timing step of measuring a time from the predetermined temperature, A post-treatment method for supplementing the fluorine deficiency with fluorine. 2. The fluoride optical thin film having a fluorine deficiency includes magnesium fluoride, calcium fluoride, lithium fluoride, lanthanum fluoride, aluminum fluoride, neodymium fluoride, gadolinium fluoride, yttrium fluoride, and fluoride. It is formed into a single-layer or multi-layer film using a substance selected from dysprosium, barium fluoride, sodium fluoride, bismuth fluoride, strontium fluoride, lead fluoride, selenium fluoride, cryolite, and thiolite. Post-processing method characterized by the following. 3. An optical thin film post-processed by the method according to claim 1. 4. An optical member comprising the optical thin film according to claim 3. 5. An apparatus for projecting and exposing a pattern image of a mask onto a substrate using a projection optical system, wherein the illumination optical system illuminates the mask with vacuum ultraviolet rays as exposure light, and the optical member according to claim 4. And a projection optical system for forming a pattern image of the mask on a substrate. 6. An apparatus for projecting and exposing a pattern image of a mask onto a substrate by using a projection optical system, the apparatus comprising the optical member according to claim 4, and illuminating the mask with vacuum ultraviolet rays as exposure light. And a projection optical system for forming a pattern image of the mask on a substrate. 7. Storing means for storing a fluorine thin film having a fluorine deficiency formed on a substrate in a fluorine atmosphere controlled at a predetermined temperature, and time measuring means for measuring time from the predetermined temperature, A post-treatment device for supplementing the fluorine deficiency with fluorine.