JP2007200937A - Optical element and exposure apparatus equipped therewith, and device manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element having a high transmissivity and a high refractive index in the vacuum ultraviolet region. <P>SOLUTION: This optical element has a wavelength of 190 nm or less at the light absorption end, and is used for exposure with vacuum ultraviolet light. The optical element consists of a fluoride containing scandium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention generally relates to an optical element, and more particularly to an optical element suitable for a lens, window material, prism and the like used in a wavelength range of 400 nm or less. The present invention provides, for example, a final lens (an optical element closest to the object to be processed) used in the projection optical system of an immersion exposure apparatus that exposes the object to be processed via a liquid between the projection optical system and the object to be processed ).

In recent years, demands for miniaturization of semiconductor elements mounted on electronic devices have been increasing due to the demand for smaller and thinner electronic devices, and various proposals have been made to increase the exposure resolution in order to satisfy such requirements. Yes. Shortening the wavelength of the exposure light source is an effective means for improving the resolution. In recent years, the exposure light source is going from an KrF excimer laser (wavelength of about 248 nm) to an ArF excimer laser (wavelength of about 193 nm), and practical use of F ₂ laser (wavelength of about 157 nm) and EUV light (wavelength of about 10 nm to 15 nm). Progress is also being made. However, with the shortening of the wavelength of the light source, most of the conventional glass materials cannot be used due to insufficient transmittance. Therefore, in an exposure apparatus using an excimer laser as an exposure light source, quartz glass (SiO ₂ ) and calcium fluoride (CaF ₂ ) are used as glass materials (see, for example, Patent Documents 1 and 2).

  Under such circumstances, immersion exposure has attracted attention as a technique for further improving the resolution while using a light source such as an ArF excimer laser. In immersion exposure, the effective wavelength of exposure light is reduced by filling the space between the final surface of the projection optical system (the final lens on the most wafer side) and the wafer with liquid (the medium on the wafer side of the projection optical system is liquid). The resolution is improved by shortening the wavelength and apparently increasing the numerical aperture (NA) of the projection optical system. The NA of the projection optical system is NA = n · sin θ, where n is the refractive index of the liquid. Therefore, the NA of the projection optical system can be increased to n by filling the space between the final surface of the projection optical system and the wafer with a liquid having a refractive index higher than the refractive index of air (n> 1). For example, when pure water (refractive index n = 1.44) is used as the liquid, the NA of the projection optical system is 1.44 times that in the case where the space between the final surface of the projection optical system and the wafer is air. . Therefore, substantially the same resolution as that in which the wavelength is shortened by 1.44 times that in the air can be obtained.

In immersion exposure, when the refractive index of the liquid is larger than the refractive index of the final lens of the projection optical system, the liquid crystal is constrained by the refractive index of the final lens of the projection optical system, and the NA of the projection optical system is increased above the refractive index. I can't. In recent years, the refractive index of a liquid tends to increase, and a liquid having a refractive index of 1.60 or more has been reported. Accordingly, a lens having a projection optical system is also required to have a larger refractive index, specifically, a refractive index greater than 1.60 (that is, the refractive index of the liquid).
JP-A 61-129828 JP-A-8-78324

However, the refractive index of SiO ₂ and CaF ₂ (refractive index with respect to the wavelength of 193 nm) used in the exposure apparatus using an excimer laser as the exposure light source is 1.50 and 1.56, and the NA of the projection optical system is increased. It is a small value to realize.

The refractive index n of the glass material is generally expressed by the following formula 1. Here, N is the density, m is the effective mass of electrons, ω _j0 is the resonance frequency, ω is the frequency of light, and f _j is the oscillator strength.

Referring to Equation 1, the closer the resonance frequency ω _j0 is to the light frequency ω, the higher the refractive index n of the glass material. On the other hand, there is a relationship that light absorption increases as the resonance frequency ω _j0 approaches the light source used.

In the case of CaF ₂ , the resonance frequency ω _j0 is higher than the frequency of the light source used, for example, ArF excimer laser. Therefore, the transmittance in the vacuum ultraviolet region is very excellent, but the refractive index is a small value.

Further, there is an aluminum oxide (Al ₂ O ₃ ) single crystal as a glass material that exhibits a low absorption rate and a high refractive index in the vacuum ultraviolet region. However, since the Al ₂ O ₃ single crystal has a trigonal corundum structure, it has a large optical anisotropy, that is, a large birefringence. Therefore, the Al ₂ O ₃ single crystal is unsuitable as a glass material for an exposure apparatus that requires high imaging performance.

  Accordingly, an object of the present invention is to provide an optical element having a high transmittance and a high refractive index in the vacuum ultraviolet region, an exposure apparatus having the optical element, and a device manufacturing method.

  In order to achieve the above object, an optical element according to one aspect of the present invention has an absorption edge of light of 190 nm or less, is an optical element used for vacuum ultraviolet light, and is composed of a fluoride containing scandium. It is characterized by that.

  An exposure apparatus according to another aspect of the present invention includes a projection optical system that projects a reticle pattern onto an object to be processed, and is provided between an optical element closest to the object to be processed and the object to be processed of the projection optical system. An exposure apparatus that exposes the object to be processed through a liquid supplied to at least a part thereof, wherein the optical element is the above-described optical element.

  An exposure apparatus according to still another aspect of the present invention uses vacuum ultraviolet light as exposure light, and irradiates the object to be processed through the optical system including the optical element described above to irradiate the object to be processed. It is characterized by exposing.

  According to still another aspect of the present invention, there is provided a device manufacturing method comprising: exposing a target object using the above-described exposure apparatus; and developing the exposed target object.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  According to the present invention, an optical element having a high transmittance and a high refractive index in the vacuum ultraviolet region can be provided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

The resonance frequency of the fluoride containing scandium (Sc) is lower than the resonance frequency of CaF ₂ and sufficiently higher than the frequency of the light source used (light in the vacuum ultraviolet region). Therefore, the fluoride containing Sc can realize an optical element having a high refractive index while keeping the light absorption rate low.

Further, a fluoride represented by Sc _(1-x) Lu _x F ₃ (0 ≦ x ≦ 0.45) (that is, a fluoride containing Sc) has a rhenium oxide type cubic crystal structure, and thus has a complex structure. An optical element that has extremely small refraction and can be applied to an exposure apparatus can be configured.

With reference to FIG. 1, the manufacturing method of the fluoride containing Sc is demonstrated. Such a manufacturing method uses the Bridgman method. In the present embodiment, the production of Sc _(1-x) Lu _x F ₃ crystal as a fluoride containing Sc will be described as an example.

First, the raw materials scandium fluoride (ScF ₃ ) and lutetium fluoride (LuF ₃ ) are mixed in a desired ratio (step 1002). Incidentally, when mixing the ScF ₃ and LuF ₃ is the mixing vessel is rotated to put ScF ₃ and LuF _3, it is preferable to ensure uniform mixing.

Next, a mixture of ScF ₃ and LuF ₃ is crystal-grown (step 1004). For crystal growth, for example, a crucible descending type Bridgman method growth furnace is used. Specifically, after a crucible containing a mixture of ScF ₃ and LuF ₃ is heated to 1550 ° C. and melted, the crucible is gradually lowered and cooled, and Sc _(1-x) Lu _x F ₃ crystals are formed. Grow.

Next, the crystal-grown Sc _(1-x) Lu _x F ₃ crystal is heat-treated (annealed) (step 1006). In the annealing, the Sc _(1-x) Lu _x F ₃ crystal grown using an annealing furnace is heat-treated to remove strain that causes crystal cracking. In the annealing, the crucible is uniformly heated to 900 ° C. or higher and 1300 ° C. or lower.

Thereafter, the Sc _(1-x) Lu _x F ₃ crystal is formed into a required optical element (step 1008). Incidentally, molding to _{Sc (1-x) Lu x} F 3 crystal optical element, heat treatment after the optical characteristics such as transmittance was measured, _{Sc (1-x) Lu x} F 3 having a desired optical performance Select crystals. Optical elements include lenses, diffractive elements, optical film bodies and their composites, such as lenses, multi-lenses, lens arrays, lenticular lenses, fly-eye lenses, aspherical lenses, diffraction gratings, binary optics elements and their Includes complex.

  The fluoride containing Sc thus obtained is excellent in optical characteristics such as transmittance and refractive index in the vacuum ultraviolet region. An optical element manufactured from such a fluoride is suitable as a final optical element (most optical element on the wafer side) that forms the final surface of the projection optical system of the immersion exposure apparatus.

  The inventor manufactured fluoride by the above-described manufacturing method and measured optical characteristics (absorption edge and refractive index).

First, a seed crystal of scandium fluoride (ScF ₃ ) for controlling the growth starting point and growth orientation was stored in a crucible of a crystal growth furnace. Subsequently, scandium fluoride (ScF ₃ ) as a raw material was stored in a crucible.

Next, after the crystal growth furnace was evacuated to about 10 ⁻⁴ Pa by an exhaust device, argon gas or fluorine gas was introduced into the crystal growth furnace and the pressure was restored to 1 atm. Then, the temperature of the crucible was raised from room temperature to 1550 ° C. to melt scandium fluoride (ScF ₃ ).

Next, after maintaining the melted scandium fluoride (ScF ₃ ) for 5 hours, the crucible was pulled down at a speed of 0.5 mm / h to 10 mm / h to grow scandium fluoride (ScF ₃ ) crystals.

Subsequently, the crystal grown scandium fluoride (ScF ₃ ) was heat-treated in an annealing furnace. Specifically, the crucible was heated to about 1000 ° C. in an atmosphere of fluorine gas or argon gas.

The scandium fluoride (ScF ₃ ) crystal thus obtained had an absorption edge of about 150 mm and a refractive index of 1.60 or more.

First, as raw materials, scandium fluoride (ScF ₃ ) and lutetium fluoride (LuF ₃ ) were mixed at a molar ratio of 0.55: 0.45, and the growth starting point and growth in the crucible of the crystal growth furnace A seed crystal for controlling the orientation was stored. Subsequently, Sc _0.55 Lu _0.45 F ₃ as a mixed raw material was stored in a crucible.

Next, after the crystal growth furnace was evacuated to about 10 ⁻⁴ Pa by an exhaust device, argon gas or fluorine gas was introduced into the crystal growth furnace and the pressure was restored to 1 atm. And the temperature of the crucible was raised from room temperature to 1550 ° C., and Sc _0.55 Lu _0.45 F ₃ as a raw material was melted.

Next, after maintaining Sc _0.55 Lu _0.45 F ₃ in a molten state for 5 hours, the crucible is pulled down at a speed of 0.5 mm / h or more and 10 mm / h or less, and Sc _0.55 Lu _0.45 F ₃ Crystals were grown.

Subsequently, the crystal-grown Sc _0.55 Lu _0.45 F ₃ was heat-treated in an annealing furnace. Specifically, the crucible was heated to about 1000 ° C. in an atmosphere of fluorine gas or argon gas.

The Sc _0.55 Lu _0.45 F ₃ crystal thus obtained had an absorption edge of 190 mm or less and a refractive index of 1.60 or more.

  The exposure apparatus 100 using the above-described fluoride containing scandium as a glass material will be described below with reference to FIG. Here, FIG. 2 is a schematic sectional view showing a configuration of an exposure apparatus 100 as one aspect of the present invention.

  The exposure apparatus 100 is a circuit formed on the reticle 120 via a liquid WT supplied to at least a part between the final lens 132 closest to the target object 140 and the target object 140 of the projection optical system 100. It is an immersion exposure apparatus that exposes a pattern onto a workpiece 140. Such an exposure apparatus is suitable for a lithography process of sub-micron or quarter micron or less, and in the present embodiment, a step-and-scan type exposure apparatus (also referred to as “scanner”) will be described as an example. Here, the “step and scan method” means that the wafer is continuously scanned (scanned) with respect to the reticle to expose the reticle pattern onto the wafer, and the wafer is stepped after completion of one shot of exposure. The exposure method moves to the next exposure area. The “step-and-repeat method” is an exposure method in which the wafer is moved stepwise to the exposure area of the next shot for every batch exposure of the wafer.

  As shown in FIG. 2, the exposure apparatus 100 includes an illumination device 110, a reticle stage 125 on which the reticle 120 is placed, a projection optical system 130, a wafer stage 145 on which the object 140 is placed, a liquid supply / discharge A mechanism 150 and a control unit (not shown) are included. A control unit (not shown) is connected to the illumination device 110, the reticle stage 125, the wafer stage 145, and the liquid supply / discharge mechanism 150 in a controllable manner.

  The illumination device 110 illuminates a reticle 120 on which a transfer circuit pattern is formed, and includes a light source unit 112 and an illumination optical system 114.

As the light source unit 112, for example, an ArF excimer laser having a wavelength of about 193 nm, a KrF excimer laser having a wavelength of about 248 nm, or the like can be used as the light source. However, the type of the light source is not limited to the excimer laser. A 157 nm F ₂ laser may be used, and the number of light sources is not limited. The light source that can be used for the light source unit 112 is not limited to the laser, and one or a plurality of lamps such as a mercury lamp and a xenon lamp can be used.

  The illumination optical system 114 is an optical system that illuminates the reticle 120, and includes a lens, a mirror, an optical integrator, a stop, and the like. For example, a condenser lens, an optical integrator, an aperture stop, a condenser lens, a slit, and an imaging optical system are arranged in this order. The illumination optical system 114 can be used regardless of on-axis light or off-axis light. The optical integrator includes an integrator configured by stacking a fly-eye lens and two sets of cylindrical lens array (or lenticular lens) plates, but may be replaced by an optical rod or a diffractive element.

  The reticle 120 is, for example, a reflective or transmissive reticle, on which a circuit pattern to be transferred is formed, and is supported and driven by a reticle stage 125. Diffracted light emitted from the reticle 120 is projected onto the object 140 via the projection optical system 130. The reticle 120 and the object to be processed 140 are arranged in an optically conjugate relationship. Since the exposure apparatus 100 is a scanner, the pattern of the reticle 120 is transferred onto the target object 140 by scanning the reticle 120 and the target object 140 at a speed ratio of the reduction magnification ratio. In the case of a step-and-repeat type exposure apparatus (also referred to as “stepper”), exposure is performed with the reticle 120 and the object 140 to be processed being stationary.

  The reticle stage 125 supports the reticle 120 via a reticle chuck (not shown) and is connected to a moving mechanism (not shown). A moving mechanism (not shown) is configured by a linear motor or the like, and can move the reticle 120 by driving the reticle stage 130 in the X-axis direction, the Y-axis direction, the Z-axis direction, and the rotation direction of each axis. The exposure apparatus 100 scans the reticle 120 and the workpiece 140 in a synchronized state by a control unit (not shown). Here, the scanning direction in the plane of the reticle 120 or the object to be processed 140 is defined as the Y axis, the direction perpendicular thereto is defined as the X axis, and the direction perpendicular to the surface of the reticle 120 or the object to be processed 140 is defined as the Z axis.

  The projection optical system 130 images the diffracted light that has passed through the pattern formed on the reticle 120 on the object 140. As the projection optical system 130, an optical system including only a plurality of lens elements, an optical system having a plurality of lens elements and at least one reflecting mirror (catadioptric optical system), or the like can be used. When correction of chromatic aberration is required, a plurality of lens elements made of glass materials having different dispersion values (Abbe values) can be used, or the diffractive optical element can be configured to generate dispersion in the opposite direction to the lens element. To do.

  The final lens 132 disposed on the final surface of the projection optical system 130 is composed of an optical element made of a fluoride containing scandium. Thereby, the final lens 132 has a refractive index larger than that of the liquid WT described later, specifically, a refractive index of 1.60 or more. Therefore, the projection optical system 130 achieves high NA and high resolution.

  The object to be processed 140 is a wafer in this embodiment, but widely includes a liquid crystal substrate and other objects to be processed. A photoresist is applied to the object 140 to be processed.

  The wafer stage 145 supports the object 140 by a wafer chuck (not shown). Similar to reticle stage 125, wafer stage 145 moves object 140 in the X-axis direction, Y-axis direction, Z-axis direction, and the rotational direction of each axis using a linear motor. The position of the reticle stage 125 and the position of the wafer stage 145 are monitored by, for example, a laser interferometer, and both are driven at a constant speed ratio. The wafer stage 145 is provided on a stage surface plate supported on a floor or the like via a damper, for example. The reticle stage 125 and the projection optical system 130 are provided on a lens barrel surface plate (not shown) supported via a damper on a base frame placed on a floor or the like, for example.

  The liquid supply / discharge mechanism 150 is connected between the projection optical system 130 and the target object 140 via the supply / discharge nozzle 152, specifically, the final surface of the projection optical system 130 on the target object 140 side and the target object 140. Liquid WT is supplied between the two. Further, the liquid supply / discharge mechanism 150 collects the supplied liquid WT. That is, the gap formed between the projection optical system 130 and the surface of the object 140 is filled with the liquid WT supplied from the liquid supply / discharge mechanism 150. The liquid WT is pure water in the present embodiment, but is not particularly limited to pure water. The liquid WT has a high transmission characteristic and a high refractive index characteristic with respect to the wavelength of the exposure light, and a liquid having a high chemical stability with respect to the photoresist applied to the projection optical system 130 and the object 140 to be processed. Can be used. As the liquid WT, for example, a fluorine-based inert liquid may be used.

  A control unit (not shown) has a CPU and a memory, and controls the operation of the exposure apparatus 100. The control unit is electrically connected to the illumination device 110, reticle stage 125, wafer stage 145, and liquid supply / discharge mechanism 150. The control unit also has a function of controlling the supply and recovery of the liquid WT or the switching of the stop and the supply / discharge amount of the liquid WT based on conditions such as the driving direction of the wafer stage 145 at the time of exposure. The CPU includes any processor of any name such as MPU and controls the operation of each unit. The memory is composed of a ROM and a RAM, and stores firmware that operates the exposure apparatus 100.

  In the exposure, the light beam emitted from the light source unit 112 illuminates the reticle 120 by the illumination optical system 114, for example, Koehler illumination. The light that passes through the reticle 120 and reflects the reticle pattern is imaged by the projection optical system 130 onto the object 140 via the liquid WT. The projection optical system 130 used by the exposure apparatus 100 uses an optical element made of a fluoride containing scandium as the final lens 132, and realizes excellent imaging performance. Therefore, the exposure apparatus 100 can provide a device (semiconductor element, LCD element, imaging element (CCD, etc.), thin film magnetic head, etc.) with high throughput and high economic efficiency.

  Next, an embodiment of a device manufacturing method using the exposure apparatus 100 will be described with reference to FIGS. FIG. 3 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, etc.). Here, the manufacture of a semiconductor chip will be described as an example. In step 1 (circuit design), a device circuit is designed. In step 2 (reticle fabrication), a reticle on which the designed circuit pattern is formed is fabricated. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the reticle and wafer. Step 5 (assembly) is called a post-process, and is a process for forming a semiconductor chip using the wafer created in step 4. The assembly process (dicing, bonding), packaging process (chip encapsulation), and the like are performed. Including. In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, the semiconductor device is completed and shipped (step 7).

  FIG. 4 is a detailed flowchart of the wafer process in Step 4. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition or the like. Step 14 (ion implantation) implants ions into the wafer. In step 15 (resist process), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus 100 to expose a reticle circuit pattern onto the wafer. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeating these steps, multiple circuit patterns are formed on the wafer. According to this device manufacturing method, it is possible to manufacture a higher quality device than before. Thus, the device manufacturing method using the exposure apparatus 100 and the resulting device also constitute one aspect of the present invention.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist. For example, as a method for producing a fluoride containing scandium, not only the Bridgeman method of cooling a raw material by pulling down a crucible but also a Czochralski method of pulling up a crystal from a melt may be used. In addition, an optical element made of a fluoride containing scandium can be used not only in an immersion exposure apparatus but also in a normal exposure apparatus (dry system).

It is a flowchart for demonstrating the manufacturing method of the fluoride containing a scandium. It is a schematic sectional drawing which shows the structure of the exposure apparatus as one side surface of this invention. It is a flowchart for demonstrating manufacture of devices (semiconductor chips, such as IC and LSI, LCD, CCD, etc.). 4 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Exposure apparatus 110 Illumination device 112 Light source part 114 Illumination optical system 120 Reticle 125 Reticle stage 130 Projection optical system 132 Final lens 140 To-be-processed object 145 Wafer stage 150 Liquid supply / discharge mechanism WT Liquid

Claims (6)

An optical element having an absorption edge of light of 190 nm or less and used for vacuum ultraviolet light,
An optical element comprising a fluoride containing scandium. The optical element is characterized in that the fluoride is Sc _(1-x) Lu _x F ₃ (0 ≦ x ≦ 0.45).   2. The optical element according to claim 1, wherein the optical element is one of a lens, a diffraction grating, an optical film body, and a composite thereof. A projection optical system for projecting a reticle pattern onto the object to be processed, the liquid being supplied to at least a part between the optical element closest to the object to be processed and the object to be processed in the projection optical system; An exposure apparatus that exposes a workpiece,
The exposure apparatus according to claim 1, wherein the optical element is an optical element according to claim 1.   Using vacuum ultraviolet light as exposure light, the object to be processed is exposed by irradiating the object to be processed through the optical system including the optical element according to any one of claims 1 to 3. An exposure apparatus characterized by that. Exposing the object to be processed using the exposure apparatus according to claim 4;
And developing the exposed object to be processed.