JP2004363571A - Mirror holding method, optical device and exposure device using it, and manufacturing method of device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the asymmetric deformation of a mirror due to the irradiation of EUV light. <P>SOLUTION: In an EUV exposure device 1 with a plurality of mirrors, the mirror 10 which absorbs a part of EUV light expands and changes its shape with heat. The axis of symmetry of a mirror holding mechanism 12 is made to coincide with that of a region where the light is irradiated and the center of the mechanism 12 is made to coincide with that of the region so that the deformation of the surface profile of the mirror 10 becomes symmetric. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a mirror holding method and an optical device having a mirror, and more particularly to an exposure apparatus used for manufacturing a semiconductor integrated circuit or the like as the optical device.

  A semiconductor exposure apparatus is an apparatus for transferring an original (reticle) having a circuit pattern onto a substrate (silicon wafer). Ultra-high pressure mercury lamps (i-line), KrF excimer lasers, and ArF excimer lasers are used as light sources, and a lens is used as a projection optical system for forming a reticle pattern on a wafer at these wavelengths. Have been.

  In order to produce a highly integrated circuit, a projection lens is required to have a high resolution. Therefore, the aberration of the lens for the semiconductor exposure apparatus is suppressed to be small.

However, as semiconductor integrated circuits have become finer in recent years, the wavelength of exposure light of an exposure apparatus has become shorter, and it is expected that EUV light (extreme ultraviolet light) will be used as exposure light in the future (Patent Document 1). .
JP 2003-172857 A

  When EUV light is used, there is no lens that transmits EUV light, so a mirror is used as the optical system. However, a mirror currently being developed as a mirror has a reflectance of about 70% at most for EUV light. Therefore, the remaining 30% is absorbed by the mirror and converted into heat, which causes a rise in the temperature of the mirror. Due to this temperature rise, the mirror thermally expands and is greatly deformed, so that aberrations are deteriorated. For this reason, by providing a mechanism for cooling the mirror and suppressing thermal distortion, deterioration of aberrations can be suppressed. However, although the temperature rise of the mirror is suppressed by cooling, the temperature rise cannot be reduced to zero in the entire mirror, so that deformation occurs. If the deformation of the mirror is a simple expansion or a simple contraction, the curvature mainly changes only.Therefore, it is possible to suppress the deterioration of the aberration by performing correction such as shifting the mirror position. In the mirror holding mechanism, the axis of symmetry of the light irradiation area on the mirror is greatly deviated from the axis of symmetry of the mirror holding mechanism, so that the mirror did not simply expand or contract.

  The present invention suppresses asymmetric surface deformation that greatly deteriorates the optical performance, suppresses the movement of the irradiation position of the mirror, reduces the amount of blur, and further releases the thermal stress in order to suppress the deterioration of the above-described aberration. The purpose of the present invention is to reduce the amount of deformation of the mirror to a low-order simple deformation.

  In order to achieve the above object, a mirror holding method according to claim 1, wherein in the optical system in which the center of the light irradiation area in the mirror is shifted from the center of gravity of the mirror, the axis of symmetry of the light irradiation area is symmetrical to the mirror holding mechanism. It is characterized by being substantially coincident with the axis. According to this, even in an optical system in which the center of the light irradiation area of the mirror is shifted from the center of gravity of the mirror, the symmetry axis of the light irradiation area and the symmetry axis of the mirror holding mechanism match (substantially match). Therefore, the stress distribution in the mirror generated by the heat of light becomes symmetric on both sides about the axis of symmetry. Therefore, the deformation of the mirror surface shape can be made symmetric.

  Here, the center of the light irradiation area in the mirror is, for example, as shown in FIGS. 3A, 4A, and 5A, where the light irradiation area is an arc, an ellipse, or an intermediate point between an arc and an ellipse. When the shape is circular, it is the center point of the major axis and minor axis (the circle is the major axis = minor axis and is included in the ellipse because it is a special case of the ellipse). Further, as shown in FIG. 2, the center of gravity of the mirror is a point that becomes the center of gravity of the optical surface when the optical surface of the mirror is projected on a surface whose normal is the optical axis.

  According to a second aspect of the present invention, in the mirror holding method according to the first aspect, the center of the light irradiation area further matches (substantially matches) the center of the mirror holding mechanism. According to this, since the light is irradiated to the center of the mirror holding mechanism, it is possible to prevent the center position of the light irradiation area on the mirror from being shifted due to the thermal expansion of the mirror.

  The center of the mirror holding mechanism is, as shown in FIG. 3C, a reference point at which the holding mechanism is arranged so as to divide the center angle substantially equally.

  According to a third aspect of the present invention, in the mirror holding method according to the first aspect, the center of gravity of the light irradiation area further matches (substantially matches) the center of the mirror holding mechanism. According to this, since the center of the mirror holding mechanism is irradiated with light, it is possible to prevent the position of the center of gravity of the light irradiation area on the mirror from being shifted due to the thermal expansion of the mirror.

  The center of gravity of the light irradiation area is a point that becomes the center of gravity of an area determined by projecting the light irradiation area on a plane whose normal is the optical axis.

  The invention according to claim 4 is the mirror holding method according to any one of claims 1 to 3, wherein the mirror is a mirror that reflects EUV light (extreme ultraviolet light). According to this, when the mirror is irradiated with the EUV light, even if the mirror absorbs the EUV light at a high rate, the mirror surface shape can be symmetrically deformed and the optical characteristics are greatly deteriorated. Can be suppressed.

  The invention according to claim 5 is an optical device having an optical system in which the center of the light irradiation area of the mirror is shifted from the center of gravity of the mirror, wherein the symmetry axis of the light irradiation area coincides with the symmetry axis of the mirror holding mechanism. It is characterized by having. According to this, even in an optical system in which the center of the light irradiation area of the mirror is shifted from the center of gravity of the mirror, the symmetry axis of the light irradiation area and the symmetry axis of the mirror holding mechanism match (substantially match). Therefore, the stress distribution in the mirror generated by the heat of light becomes symmetric on both sides about the axis of symmetry. Therefore, the deformation of the mirror surface shape can be made symmetric.

  According to a sixth aspect of the present invention, in the optical device according to the fifth aspect, the center of the light irradiation area further coincides with the center of the mirror holding mechanism. According to this, since the light is irradiated to the center of the mirror holding mechanism, it is possible to prevent the center position of the light irradiation area on the mirror from being shifted due to the thermal expansion of the mirror.

  According to a seventh aspect of the present invention, in the optical device according to the fifth aspect, the center of gravity of the light irradiation area further coincides with the center of the mirror holding mechanism. According to this, since the center of the mirror holding mechanism is irradiated with light, it is possible to prevent the position of the center of gravity of the light irradiation area on the mirror from being shifted due to the thermal expansion of the mirror.

  The invention according to claim 8 is the optical device according to claims 5 to 7, wherein the mirror is a mirror that reflects EUV light. According to this, when the mirror is irradiated with the EUV light, even if the mirror absorbs the EUV light at a high rate, the mirror surface shape can be symmetrically deformed and the optical characteristics are greatly deteriorated. Can be suppressed.

  According to a ninth aspect of the present invention, in the optical device according to the fifth to eighth aspects, the optical device is an exposure device. According to this, high-precision exposure can be performed by using this mirror holding method in the exposure apparatus.

  A tenth aspect of the present invention relates to a device manufacturing method including a step of exposing a substrate with a device pattern using the exposure apparatus according to the ninth aspect, and a step of developing the exposed substrate.

  ADVANTAGE OF THE INVENTION According to this invention, when the center of the light irradiation area | region in a mirror deviates from the center of a mirror holding point, asymmetric deformation | transformation of a mirror surface shape can be reduced or suppressed.

  Hereinafter, preferred embodiments applied to the present invention will be described.

  FIG. 1 is a schematic configuration diagram showing an example of an exposure apparatus incorporating a mirror holding method according to the first embodiment of the present invention. This exposure apparatus uniformly irradiates EUV light having a wavelength of about 13 nm to a reflective mask, and projects a pattern of the mask onto a wafer with reflected light from the mask.

  In FIG. 1, reference numeral 1 denotes a chamber for separating an exposure atmosphere from the atmosphere, which is evacuated by a pump (not shown). Exposure light L guided from an illumination optical system (not shown) is reflected by the reticle 2. The exposure light L reflected by the reticle 2 passes through the projection optical system 6 and irradiates the wafer 4, and the pattern on the reticle 2 is transferred to the wafer 4 positioned by the wafer stage 3.

  FIG. 2 is a diagram showing a mirror and a mirror holding mechanism in the projection optical system. The mirror holding member 12 is fixed to the wall of the lens barrel 5, and the mirror supporting member 11 is held by the mirror holding member 12. A position control mechanism 15 is provided between the mirror supporting member 11 and the mirror holding member 12, and controls the position and the posture of the mirror supporting member 11. By controlling the position and posture of the mirror support member 11, the position and posture of the mirror 10 are controlled. The mirror 10 is held by a mirror support member 11 via a ball 13. The mirror 10 has a V-groove 14, and the ball 13 is fitted into the V-groove 14. The mirror support member 11 has a conical hole, and the ball 13 is fitted in the hole. The position of the ball 13 is fixed to the mirror support member 11. The size of the mirror 10 falls within a range of about 60 mm in diameter to about 500 mm in diameter.

  In the case of an optical system constituted by a lens, the exposure light is applied substantially to the center. In a so-called mirror projection exposure apparatus as disclosed in Japanese Patent Application Laid-Open No. 09-213618, exposure light is applied to a substantially central object. However, in an optical system configured by a mirror and exposing only one side of the mirror to the exposure light, the mirror holding point is set to the symmetry axis 22 of the exposure light irradiation area 20 and the mirror 10 as shown in FIG. If the holding points are provided so that the symmetry axes 21 of the holding points do not coincide with each other, the symmetry of the mirror distortion deteriorates. In FIG. 3B, the irradiation amount is larger on the right side of the symmetry axis 21 of the mirror holding point than on the left side. Therefore, the right side has a larger thermal expansion than the left side, and the curvature of the mirror 10 differs between the left and right sides of the symmetry axis 21. The exposure light irradiation area of the EUV exposure apparatus may be in the form of an arc, an ellipse, an intermediate shape between an arc and an ellipse, or a circle. However, when those sizes are represented by a long axis and a short axis (a circle is a long axis) = Minor axis, which is a special case of an ellipse, so it is included in the ellipse), the major axis is about 100 mm to 300 mm, and the minor axis is about 20 mm to 300 mm.

  Therefore, when the irradiation area 20 of the exposure light has an arc shape as shown in FIG. 3A, the holding point is provided so that the symmetry axis 22 and the symmetry axis 21 of the holding point of the mirror 10 coincide. By doing so, the distortion of the mirror 10 becomes symmetrical, and the deformation of the surface shape that deteriorates the optical performance can be suppressed. Further, in the present embodiment, the symmetry axis 22 of the exposure light irradiation area 20 and the symmetry axis 21 of the holding point of the mirror 10 completely match, but if the angle formed by these symmetry axes is within 10 degrees. Even if the symmetric axis 22 of the exposure light irradiation area 20 and the symmetric axis 21 of the holding point of the mirror 10 are shifted, the effect of the present invention can be obtained.

  By maintaining the optimum position of the mirror 10 by the above-described method, it is possible to suppress the surface deformation of the asymmetric mirror that greatly deteriorates the optical performance.

  3A, the holding point of the mirror 10 is such that the symmetry axis 22 of the exposure light irradiation area 20 and the symmetry axis 21 of the holding point of the mirror 10 coincide with each other. It is held at three points that divide the corner into approximately three equal parts. For this reason, in FIG. 3A, the irradiation area is biased in the upper half of the mirror 10, the thermal expansion on the upper side of the mirror 10 is large, and the temperature of the mirror 10 becomes constant after the exposure light starts being irradiated. The position where the exposure light of the mirror 10 is irradiated gradually shifts. On the other hand, in FIG. 3C, the holding point of the mirror 10 is such that the symmetry axis 22 of the irradiation area 20 of the exposure light coincides with the symmetry axis 21 of the holding point of the mirror 10, and It is held at three points that divide the central angle of the irradiation area 20 into approximately three equal parts with respect to the irradiation area 20 of the exposure light. Here, the center of the exposure light irradiation region refers to the center point of the long axis and the short axis of the arc. Therefore, the amount by which the position of the mirror 10 where the exposure light is irradiated shifts can be reduced. According to this, the blur of the image is reduced, and the line width accuracy is improved. Further, in this embodiment, the center of the exposure light irradiation area 20 and the center of the mirror holding mechanism completely match, but up to 4% of the mirror diameter, the center of the exposure light irradiation area 20 and the mirror holding mechanism do not. The center may be off.

  FIG. 4 shows a second embodiment of the present invention. In FIG. 4, the irradiation area of the exposure light is elliptical. As shown in FIG. 4A, the holding mechanism is provided such that the symmetric axis 22 of the exposure light irradiation area 20 and the symmetric axis 21 of the mirror holding mechanism coincide. By doing so, the distortion of the mirror 10 becomes symmetrical, and the deformation of the surface shape that deteriorates the optical performance can be suppressed. In the present embodiment, the symmetry axis 22 of the exposure light irradiation area 20 and the symmetry axis 21 of the mirror holding mechanism are completely coincident. However, if the angle between these symmetry axes is within 10 degrees, the exposure The effect of the present invention can be obtained even if the symmetry axis 22 of the light irradiation area 20 and the symmetry axis 21 of the holding point of the mirror 10 are shifted.

  In FIG. 4B, the symmetry axis 22 of the exposure light irradiation area 20 coincides with the symmetry axis 21 of the mirror holding mechanism, and the center angle about the exposure light irradiation area 20 is substantially equally divided into three. Is held at three points. (The center of the exposure light irradiation area refers to a point that is the center of the major axis and the minor axis of the ellipse.) Therefore, the amount by which the mirror 10 is irradiated with the exposure light can be reduced in amount. . According to this, the blur of the image is reduced, and the line width accuracy is improved. Further, in this embodiment, the center of the exposure light irradiation area 20 completely coincides with the center of the mirror holding mechanism, but up to 4% of the mirror diameter, the center of the exposure light irradiation area 20 and the mirror holding mechanism have the same size. The center may be off.

  FIG. 5 shows a third embodiment of the present invention. In FIG. 5, the irradiation area of the exposure light has an intermediate shape between the arc and the ellipse. As shown in FIG. 5A, the holding point is provided so that the symmetry axis 22 of the irradiation area 20 of the exposure light coincides with the symmetry axis 21 of the mirror holding mechanism. By doing so, the distortion of the mirror 10 becomes symmetrical, and the deformation of the surface shape that deteriorates the optical performance can be suppressed. In the present embodiment, the symmetry axis 22 of the exposure light irradiation area 20 and the symmetry axis 21 of the mirror holding mechanism are completely coincident. However, if the angle between these symmetry axes is within 10 degrees, the exposure The effect of the present invention can be obtained even if the symmetry axis 22 of the light irradiation area 20 and the symmetry axis 21 of the holding point of the mirror 10 are shifted.

  In FIG. 5B, the axis of symmetry 22 of the exposure light irradiation area 20 and the axis of symmetry 21 of the mirror holding mechanism coincide, and the central angle of the exposure light irradiation area 20 as a center is almost equally divided into three. Is held at three points. (The center of the exposure light irradiation area refers to a point which is the center of the long axis and the short axis of the intermediate shape between the arc and the ellipse.) For this reason, the amount by which the position of the mirror 10 where the exposure light is irradiated is shifted. It can be made smaller. According to this, the blur of the image is reduced, and the line width accuracy is improved. Further, in this embodiment, the center of the exposure light irradiation area 20 and the center of the mirror holding mechanism completely match, but up to 4% of the mirror diameter, the center of the exposure light irradiation area 20 and the mirror holding mechanism do not. The center may be off.

  FIG. 6 shows a fourth embodiment of the present invention. In FIG. 6, the irradiation area of the exposure light has an arc shape. In FIG. 6A, the center of gravity of the exposure light irradiation area deviates from the exposure light irradiation area. Therefore, the symmetry axis 22 of the exposure light irradiation area 20 and the symmetry axis 21 of the holding mechanism of the mirror 10 coincide with each other, and the center of gravity of the exposure light irradiation area 20 is centered with respect to the exposure light irradiation area 20. The mirror 10 is held at three points that divide the central angle into approximately three equal parts. Therefore, the amount by which the position of the mirror 10 where the exposure light is irradiated shifts can be reduced. According to this, the blur of the image is reduced, and the line width accuracy is improved. Further, in this embodiment, the center of gravity of the exposure light irradiation area 20 and the center of the mirror holding mechanism are completely coincident, but up to 4% of the mirror diameter, the center of gravity of the exposure light irradiation area 20 and the mirror holding mechanism. The center may be off.

  Next, a mechanism for holding the mirror will be described. When the mirror 10 is thermally expanded by exposure heat, if the mirror 10 is constrained at three points x, y, and z in FIG. 2, thermal stress cannot be released, and the deformation of the surface shape increases. On the other hand, in the present embodiment, as shown in FIG. 2, the mirror 10 is held at three places by using a V-shaped groove 14 and a ball 13. Even if thermal expansion of the mirror 10 occurs due to a change in the temperature environment, the ball 13 rolls in the V-groove 14 in the radial direction, thereby allowing expansion in the radial direction. Therefore, the mirror 10 undergoes almost simple expansion and contraction, resulting in low-order simple deformation, and can suppress the deformation of the surface shape that greatly deteriorates the optical performance. The mirror holding mechanism is not limited to this, and any holding mechanism that does not cause asymmetric deformation can be applied.

  The aberration can be corrected by adjusting the distance between the mirrors if the deformation of the mirror is only a change in the curvature. Therefore, the present invention is to suppress the deformation other than the change in the curvature of the mirror by using the present invention. Thereby, it is possible to easily correct the aberration.

  In the embodiments described above, the term mirror holding method can be used interchangeably with mirror holding method, mirror holding (supporting) mechanism, or mirror holding (supporting) device.

  Next, an embodiment of a device manufacturing method using an exposure apparatus incorporating the above-described mirror holding (supporting) method will be described with reference to FIGS. FIG. 7 is a flowchart for explaining the manufacture of devices (semiconductor chips such as ICs and LSIs, LCDs, CCDs, etc.). In the present embodiment, a description will be given of the manufacture of a semiconductor chip as an example. In step 1 (circuit design), the circuit of the device is designed. Step 2 (mask fabrication) forms a mask on which the designed circuit pattern is formed. 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 the wafer. Step 5 (assembly) is called a post-process, and is a process of forming a semiconductor chip using the wafer created in step 4, and includes processes such as an assembly process (dicing and bonding) and a packaging process (chip encapsulation). Including. In step 6 (inspection), inspections such as an operation check test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, a semiconductor device is completed and shipped (step 7).

  FIG. 8 is a detailed flowchart of the wafer process in Step 4. Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms an insulating film on the surface of the wafer. Step 14 (ion implantation) implants ions into the wafer. In step 15 (resist processing), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus 500 to expose a circuit pattern on the mask onto the wafer. Step 17 (development) develops the exposed wafer. Step 18 (etching) removes portions other than the developed resist image. Step 19 (resist stripping) removes unnecessary resist after etching. By repeating these steps, multiple circuit patterns are formed on the wafer. According to the device manufacturing method of the present embodiment, it is possible to manufacture a higher-quality device than before. As described above, the device manufacturing method using the exposure apparatus and the resultant device also constitute one aspect of the present invention.

  The example in which the present cooling apparatus is applied to the exposure apparatus has been described. The cooling device of the present invention is not limited to EUV light, but can be applied to other excimer laser light. Further, the present invention can be applied to a mask, a wafer, and the like.

FIG. 1 is a schematic configuration diagram of an exposure apparatus according to the present invention. FIG. 2 is a schematic configuration diagram of a mirror and a mirror holding mechanism according to the present invention. FIG. 4 is a diagram showing an exposure light irradiation area and a mirror holding point in the mirror according to the first embodiment of the present invention. FIG. 10 is a diagram illustrating an exposure light irradiation area and a mirror holding point in a mirror according to a second embodiment of the present invention. FIG. 14 is a diagram relating to an irradiation area of exposure light and a mirror holding point in a mirror according to a third embodiment of the present invention. FIG. 14 is a diagram relating to an irradiation area of exposure light and a mirror holding point in a mirror according to a fourth embodiment of the present invention. Manufacturing flow of devices such as semiconductor chips Wafer process flow of FIG.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Main body chamber 2 Reticle stage 3 Wafer stage 4 Wafer 5 Lens barrel 6 Projection optical system 10 Mirror 11 Mirror support member 12 Mirror holding member 13 Sphere 14 V groove 15 Mirror position control mechanism 20 Exposure light irradiation area 21 Mirror axis of mirror holding point 22 Symmetry axis of exposure light irradiation area L Exposure light

Claims (10)

  A mirror holding method in an optical system in which the center of a light irradiation area of a mirror is shifted from the center of gravity of the mirror, wherein a symmetry axis of the light irradiation area coincides with a symmetry axis of a mirror holding mechanism.   2. The mirror holding method according to claim 1, wherein the center of the light irradiation area coincides with the center of the mirror holding mechanism.   2. The mirror holding method according to claim 1, wherein the center of gravity of the light irradiation area coincides with the center of the mirror holding mechanism.   The mirror holding method according to claim 1, wherein the mirror is a mirror that reflects EUV light.   An optical device having an optical system in which the center of a light irradiation area of a mirror is shifted from the center of gravity of the mirror, wherein the axis of symmetry of the light irradiation area coincides with the axis of symmetry of the mirror holding mechanism. .   6. The optical device according to claim 5, wherein the center of the light irradiation area coincides with the center of the mirror holding mechanism.   The optical device according to claim 5, wherein a center of gravity of the light irradiation region coincides with a center of the mirror holding mechanism.   The optical device according to claim 5, wherein the mirror is a mirror that reflects EUV light.   9. The exposure apparatus according to claim 5, wherein the optical apparatus is an exposure apparatus. A device manufacturing method, comprising: exposing a substrate with a device pattern using the exposure apparatus according to claim 9; and developing the exposed substrate.

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