JP2006112955A - Light scattering inspecting method, method of manufacturing optical element, and projection exposure equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystal material of good optical characteristic. <P>SOLUTION: In this light scattering inspecting method, the state in a fluoride crystal is detected by radiating light to a polished face of an inspected object 1 constituted by the fluoride crystal and detecting scattered light. The number of the polished faces of the inspected object 1 is one. The state in the fluoride crystal means whether an impurity is contained in the crystal, a defect occurs in the crystal, and an inclusion is contained in the crystal. This optical element is the inspected object 1, and includes the light scattering inspecting method. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light scattering inspection method, an optical element manufacturing method, and a projection exposure apparatus, and in particular, various optical elements, semiconductor elements, wavelength conversion elements and lenses used in a wide wavelength range from a vacuum ultraviolet region to a far infrared region, The present invention relates to a light scattering inspection method, an optical element manufacturing method, and a projection exposure apparatus that are suitable for window materials, prisms, and the like.

  Various semiconductors, oxides, and fluoride materials are used in a wide range as optical elements, semiconductor elements, and window materials by crystallizing each of them.

  In order to crystallize these, each material is made by raising the temperature from room temperature, melting it into a liquid state, and then slowly cooling it.

  The most important thing to obtain a high quality crystalline material is to control the solidification at a certain rate during the slow cooling of the material melted with the highest purity material possible.

  Thereby, a single crystal having high purity and uniform crystal orientation can be obtained.

  The obtained crystal is used in an exposure apparatus called a stepper in recent years.

  This is an optical lithography technique for exposing and transferring a fine pattern of an integrated circuit onto a wafer such as silicon.

  Since the processing line width is as fine as several tens of nanometers to several hundreds of nanometers, very strict specifications are required.

In the conventional inspection method, refractive index homogeneity, birefringence, transmittance, and durability are inspection items.
Japanese Patent Laid-Open No. 05-126737

  However, according to the above-described inspection method, abnormalities in the optical characteristics due to fluctuations in the micro part may occur when the performance test of the lithography apparatus is performed after actually processing into a lens shape instead of evaluating the micro part inside the crystal. There is sex.

  That is, there is a possibility of transmission loss that lowers the contrast of the image.

  This is mainly caused by light absorption and light scattering.

  In particular, light scattering has a higher scattering intensity when light having a short wavelength is used, and it is considered that the influence is significant in light in a vacuum ultraviolet region such as an excimer laser.

  In the present invention, attention was paid to the inner wall of the crucible containing the material, that is, the portion in contact with the material.

  The light scattering method has been known for some time.

  Since the light scattering method detects 90 ° scattering, the crystal surface needs to be mirror-polished in order to prevent the influence of the crystal surface when examining the light scattering of the crystal.

  In the conventional method, it is necessary to polish at least three planes, ie, two flat planes including the path of incident light to be scattered and the flat plane perpendicular to the direction of the scattered light. In this method, incident light is applied obliquely to a flat surface with a crystal, and scattered light appearing on the same surface in a direction of 90 ° to the incident light is detected.

  As a result, it is possible to measure if there is only one flat polished surface of the crystal to be measured, so the man-hour and time for crystal processing can be dramatically reduced compared to the conventional method, and in addition, it can be measured with minimal processing, It can be introduced as a crystal inspection method in the pre-process of lens processing.

  That is, since the material is generally processed into a disk shape before lens processing, the main measurement can be performed by polishing only one surface of the disk.

  An object of the present invention is to provide a crystal material having good optical properties.

  Still another object of the present invention is to provide a crystalline material that can be a highly reliable optical article.

  Yet another object of the present invention is to provide a crystalline material that can be produced relatively inexpensively.

  Still another object of the present invention is to provide a crystal material whose optical characteristics are not easily deteriorated even when repeatedly irradiated with high-power light at a short wavelength for a long period of time.

  As a means for solving the above-mentioned problem, the present invention irradiates the polished surface of an object to be inspected made of a fluoride crystal with light and detects scattered light to detect the inside of the crystal of the fluoride crystal. In the light scattering inspection method for detecting the above state, the polished surface of the inspection object is a single surface, and incident light is irradiated obliquely onto the single surface.

  Further, the present invention is characterized in that the state inside the crystal means whether or not impurities are contained in the crystal and whether or not a defect is generated in the crystal.

  According to the present invention, an optical element is the inspection object, and the light scattering inspection method according to claim 1 is included in a manufacturing process of the optical element.

  According to another aspect of the present invention, there is provided a projection exposure apparatus for projecting and exposing a mask pattern image onto a substrate using a projection optical system, wherein the optical element of the projection optical system is a fluoride crystal having a polished surface. Features.

  The present invention further includes an illumination optical system, and at least one of the illumination optical system and the projection optical system includes the fluoride crystal and quartz glass.

  According to the present invention, it is possible to provide an inspection method capable of providing a high-quality crystal with a high yield.

  In addition, a crystalline material that can be a highly reliable optical article can be provided.

  Furthermore, a crystal material that can be manufactured at a relatively low cost can be provided.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  The present inventor has measured many crystals by the light scattering method.

  As an example, fluorite was manufactured and is shown below.

  An example of a preferred manufacturing process of the present invention is shown in FIG. 1 as a flowchart.

  In order to mix a fluoride raw material and a scavenger, first, a fluoride raw material is prepared.

  For that purpose, calcium carbonate and hydrogen fluoride are prepared, and calcium carbonate and hydrogen fluoride are reacted to synthesize powdered calcium fluoride.

  Calcium fluoride is produced by the following reaction.

CaCO ₃ + 2HF → CaF ₂ + H ₂ O + CO ₂
In this synthesis, it is preferable to dry the CaF ₂ generated by the above reaction and then calcinate to remove moisture.

  The calcium fluoride raw material thus obtained is vacuum packed so as not to be exposed to the atmosphere as much as possible.

  Then, calcium fluoride and scavenger are mixed.

  At this time, calcium fluoride and a scavenger may be put in a container, and the container may be rotated and mixed.

  As the scavenger, zinc fluoride, bismuth fluoride, sodium fluoride, lithium fluoride, or the like that is more easily bonded to oxygen than the growing fluoride is desirable.

  A substance that reacts with the oxide mixed in the synthetic fluoride raw material to become an oxide that is easily vaporized is selected. Zinc fluoride is particularly desirable.

  For example, a zinc fluoride scavenger changes calcium oxide generated by the presence of moisture into calcium fluoride.

CaF ₂ + H ₂ O → CaO + 2HF (300 ° C.)
CaO + ZnF ₂ → CaF ₂ + ZnO ↑
The addition rate of the scavenger is 0.05 mol% or more and 5.00 mol% or less, more preferably 0.1 to 1.0 mol%.

  The calcium fluoride powder and scavenger mixture thus obtained is placed in a crucible of a refining furnace.

  Thereafter, the heater is energized to melt the mixture.

  Subsequently, the crucible is lowered by the Bridgeman Stock Burger method described above to grow crystal of molten calcium fluoride.

(Purification process)
This step does not require the temperature control as the single crystal growth step described later.

  Therefore, there may be a grain boundary of the obtained crystal.

  Thus, the upper part of the obtained crystal, that is, the last crystallized part with time is removed.

  Since this portion easily concentrates impurities, this removal step removes impurities that adversely affect the characteristics.

  Again, this crystal is put in a crucible and a series of steps of melting, crystallization, and removal of the upper part is repeated a plurality of times.

(Single crystal manufacturing process)
The fluoride purified in the purification step is melted by heating the crucible to about 1390 to 1450 ° C. and then gradually cooled.

  In this slow cooling, it is preferable that the crucible is lowered at a speed of 0.1 to 5.0 mm per hour to cool slowly.

(Annealing process)
The crystal-grown fluoride single crystal is heat-treated in an annealing furnace.

  In this step, the crucible is heated to 900-1300 ° C.

  The heating time is 20 hours or more, more preferably 20 to 30 hours.

  The fluoride single crystal obtained in this way can reduce oxygen to 25 ppm or less and undesirable amounts of impurities such as water, iron (Fe), nickel (Ni) and chromium (Cr) to 10 ppm or less, respectively.

(Molding process)
Before processing the annealed fluoride crystal into a lens shape, it is processed on a disk.

  In order to perform light scattering measurement, at least a flat surface is mirror-polished.

  Usually, at this time, transmittance, refractive index measurement and birefringence measurement are performed.

  The light scattering measurement of the fluoride single crystal obtained by the above process was performed.

[Embodiment]
Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2 is a schematic cross-sectional view of a crystal inspection method by light scattering according to the present invention.

  In FIG. 2, the formed crystal 1 is placed on a stage 2 and incident light 3 is entered obliquely.

  Usually, the incident light 3 uses a visible laser.

  Scattered light scattered in the 90 ° direction with respect to the incident light 3 is detected by the CCD 4.

  The stage 2 can move in a two-dimensional direction and can measure the entire surface of the crystal 1.

Example 1
Calcium carbonate and hydrofluoric acid were reacted to obtain powdered calcium fluoride.

This and ZnF ₂ was added 0.7% by weight relative to the calcium fluoride was mixed together.

  Next, this mixture was put in a crucible of a refining furnace, heated and melted to 1360 ° C. at a temperature measuring point under the crucible, and then cooled to obtain blocked calcium fluoride.

  Next, the block was placed in a crucible of a single crystal growth furnace. The surface of the crucible is unprocessed.

As a scavenger, ZnF ₂ in an amount of 0.1% by weight of calcium fluoride was added to the crucible.

The inside of the furnace was set to a high vacuum with a degree of vacuum of 799.9344 × 10 ⁻⁴ Pa or higher.

Then, the temperature was raised from room temperature to 1360 ° C., and the degree of vacuum was 266.6448 × 10 ⁻⁶ Pa and the temperature was 1360 ° C. and maintained for 11 hours.

  Next, the crucible was lowered at a speed of 1 mm / h. Then it was cooled to room temperature. The series of steps was repeated 10 times.

  The crystal thus obtained was subjected to transmittance, refractive index measurement and birefringence measurement.

  Among them, the material that passed the above inspection was processed into a lens shape and placed in a lithography apparatus.

  After installation, troubles related to image formation occurred due to transmission loss.

And the man-hour required in all processes is defined as follows.
Man-hour = total time × total cost A value obtained by dividing this value by the man-hour of this embodiment is shown as the total man-hour.

(Example 2)
Calcium carbonate and hydrofluoric acid were reacted to obtain powdered calcium fluoride.

This and ZnF ₂ was added 0.7% by weight relative to the calcium fluoride was mixed together.

  Next, this mixture was put in a crucible of a refining furnace, heated and melted to 1360 ° C. at a temperature measuring point under the crucible, and then cooled to obtain blocked calcium fluoride.

  Next, the block was placed in a crucible of a single crystal growth furnace. The inner surface of the single crystal growth crucible is machined to form a processed groove on the surface.

As a scavenger, ZnF ₂ in an amount of 0.1% by weight of calcium fluoride was added to the crucible.

The inside of the furnace was set to a high vacuum with a degree of vacuum of 799.9344 × 10 ⁻⁴ Pa or higher.

The temperature was raised from room temperature to 1360 ° C., and the degree of vacuum was 266.6448 × 10 ⁻⁶ Pa and the temperature was 1360 ° C. and maintained for 11 hours.

  Crystal growth was performed at a crucible lowering speed of 1 mm / h.

  Then it was cooled to room temperature. The series of steps was repeated 10 times.

  The crystal thus obtained was subjected to transmittance, refractive index measurement and birefringence measurement.

  Thereafter, light scattering measurement was performed.

  Among them, the material that passed the above inspection was processed into a lens shape and placed in a lithography apparatus.

  After installation, troubles related to image formation occurred due to transmission loss.

  And the whole man-hour defined in Example 1 is shown.

  The results are shown in Table 1.

[Table 1]
Trouble due to transmission loss (%) Total man-hour Example 1 70 1.0
Example 2 5 1.02
Thus, compared with Example 1, Example 2 has drastically reduced trouble due to transmission loss. The overall man-hours increased only slightly.

  Hereinafter, an exemplary exposure apparatus 700 of the present invention will be described with reference to FIG.

  Here, FIG. 3 is a schematic sectional view of an exemplary exposure apparatus 700 of the present invention.

  As shown in FIG. 3, the exposure apparatus 700 includes an illumination device 710, a mask 720, a projection optical system 730, a plate 740, and a stage 745.

  The exposure apparatus 700 is a scanning projection exposure apparatus that exposes a circuit pattern formed on the mask 720 to the plate 740 by a step-and-repeat method or a step-and-scan method.

  The illumination device 710 illuminates a mask 720 on which a transfer circuit pattern is formed, and includes a light source unit 712 and an illumination optical system 714.

  The light source unit 712 uses a laser as a light source, for example.

  As the laser, an ArF excimer laser having a wavelength of about 193 nm, a KrF excimer laser having a wavelength of about 248 nm, an F2 excimer laser having a wavelength of about 157 nm, and the like can be used. However, the type of laser is not limited to an excimer laser. It may be used, and the number of lasers is not limited.

  When a laser is used for the light source unit 712, it is preferable to use a light beam shaping optical system that shapes a parallel light beam from the laser light source into a desired beam shape and an incoherent optical system that makes a coherent laser beam incoherent. .

  The light source that can be used for the light source unit 712 is not limited to a laser, and one or a plurality of lamps such as a mercury lamp and a xenon lamp can be used.

  The illumination optical system 714 is an optical system that illuminates the mask 720, and includes a lens, a mirror, a light integrator, a diaphragm, and the like.

  For example, a condenser lens, a fly-eye lens, an aperture stop, a condenser lens, a slit, and an imaging optical system are arranged in this order.

  The illumination optical system 714 can be used regardless of on-axis light or off-axis light.

  The light 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 with an optical rod or a diffractive element.

  An optical element manufactured from the calcium fluoride crystal of the present invention can be used as an optical element such as a lens of the illumination optical system 714.

  A circuit pattern (or image) to be transferred is formed on the mask 720, and is supported and driven by a mask stage (not shown).

  The diffracted light emitted from the mask 720 passes through the projection optical system 730 and is projected onto the plate 740.

  The plate 740 is an object to be processed such as a wafer or a liquid crystal substrate, and is coated with a resist. The mask 720 and the plate 740 are in a conjugate relationship.

  In the case of a scanning projection exposure apparatus, the pattern of the mask 720 is transferred onto the plate 740 by scanning the mask 720 and the plate 740.

  In the case of a stepper (step-and-repeat exposure type exposure apparatus), exposure is performed with the mask 720 and the plate 740 being stationary.

  The projection optical system 730 includes an optical system composed of only a plurality of lens elements, an optical system having a plurality of lens elements and at least one concave mirror (catadioptric optical system), a plurality of lens elements and at least one kinoform, etc. An optical system having a diffractive optical element, an all-mirror 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.

  An optical element manufactured from the calcium fluoride crystal of the present invention can be used as an optical element such as a lens of the projection optical system 730.

  The plate 740 is coated with a photoresist.

  The photoresist coating process includes a pretreatment, an adhesion improver coating process, a photoresist coating process, and a prebaking process. Pretreatment includes washing, drying and the like.

  The adhesion improver coating process is a surface modification process for improving the adhesion between the photoresist and the base (that is, a hydrophobic process by application of a surfactant), and an organic film such as HMDS (Hexamethyl-disilazane) is applied. Coat or steam.

  Pre-baking is a baking (baking) step, but is softer than that after development, and removes the solvent.

  Stage 745 supports plate 740.

  Since any structure known in the art can be applied to the stage 745, a detailed description of the structure and operation is omitted here.

  For example, the stage 745 can move the plate 740 in the XY directions using a linear motor.

  For example, the mask 720 and the plate 740 are synchronously scanned, and the positions of the stage 745 and the mask stage (not shown) are monitored by, for example, a laser interferometer or the like, and both are driven at a constant speed ratio.

  The stage 745 is provided on a stage surface plate supported on a floor or the like via a damper, for example, and the mask stage and the projection optical system 730 are, for example, a base frame on which the lens barrel surface plate is placed on the floor or the like. It is provided on a lens barrel surface plate (not shown) supported by a damper or the like above.

  In the exposure, the light beam emitted from the light source unit 712 illuminates the mask 720 with, for example, Koehler illumination by the illumination optical system 714.

  Light that passes through the mask 720 and reflects the mask pattern is imaged on the plate 740 by the projection optical system 730.

  The illumination optical system 714 and the projection optical system 730 used by the exposure apparatus 700 include an optical element manufactured from the calcium fluoride crystal according to the present invention, and transmit ultraviolet light, far ultraviolet light, and vacuum ultraviolet light with high transmittance. Therefore, it is possible to provide a device (semiconductor, 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 above-described exposure apparatus 700 will be described.

  FIG. 4 is a flowchart for explaining a manufacturing process of a device (a semiconductor chip such as an IC or LSI, an LCD, a CCD, or the like).

  Here, the manufacture of a semiconductor chip will be described as an example.

  In step 1 (circuit design), the device circuit is designed.

  In step 2 (mask production), a mask on which the designed circuit pattern is formed is produced.

  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 mask 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, and includes processes such as an assembly process (dicing and bonding), a packaging process (chip encapsulation), and the like. .

  In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device formed in step 5 are performed.

  Through these steps, the semiconductor device is completed and shipped (step 7).

  FIG. 5 is a detailed flowchart of the wafer process in Step 4.

  In step 11 (oxidation), the wafer surface 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.

  In step 14 (ion implantation), ions are implanted into the wafer.

  In step 15 (resist process), a photosensitive agent is applied to the wafer.

  Step 16 (exposure) uses the exposure apparatus 1 to expose a circuit pattern on the mask 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 repeatedly performing these steps, multiple circuit patterns are formed on the wafer.

  According to the manufacturing method of the present embodiment, it is possible to manufacture a higher-quality device than before.

It is a flowchart which shows the example of a suitable manufacturing process of this invention. It is typical sectional drawing of the crystal inspection method by the light scattering concerning this invention. 1 is a schematic cross-sectional view of an exemplary exposure apparatus 700 of the present invention. It is a flowchart for demonstrating the manufacturing process of devices (semiconductor chips, such as IC and LSI, LCD, CCD, etc.). 5 is a flowchart showing in detail a wafer process in Step 4 of FIG. 4.

Explanation of symbols

1 Crystal 2 Stage 3 Incident Light 4 CCD
700 Exposure Device 710 Illumination Device 712 Light Source Unit 714 Illumination Optical System 720 Mask 730 Projection Optical System 740 Plate 745 Stage

Claims (5)

In the light scattering inspection method for detecting the state inside the crystal of the fluoride crystal by irradiating light on the polished surface of the inspection object composed of the fluoride crystal and detecting the scattered light,
A light scattering inspection method, wherein the polished surface of the inspection object is a single surface, and incident light is irradiated obliquely onto the single surface. 2. The light scattering inspection method according to claim 1, wherein the state inside the crystal means whether or not impurities are contained in the crystal and whether or not a defect is generated in the crystal. An optical element is the inspection object,
A method for manufacturing an optical element, comprising the light scattering inspection method according to claim 1 or 2 in the manufacturing process of the optical element. A projection exposure apparatus that projects and exposes a mask pattern image onto a substrate using a projection optical system,
A projection exposure apparatus, wherein the optical element of the projection optical system is a fluoride crystal having a polished surface. Further comprising an illumination optical system,
5. The projection exposure apparatus according to claim 4, wherein at least one of the illumination optical system and the projection optical system includes the fluoride crystal and quartz glass.

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