JP2006049596A - Euv exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EUV exposure device which is equipped with a spatial image detecting arrangement suitable for EUV light. <P>SOLUTION: The spatial image detecting arrangement 7 is provided with at least a light receiving sensor 8 which detects reduced transfer image formed by a projection optical system 5. The light receiving sensor 8 has function to detect photoelectrons and to generate current or voltage. When EUV light is made to enter the light receiving sensor 8, photoelectrons are generated. Intensity of EUV light can be measured by measuring e.g. the amount of current of the photoelectrons. When scanning by the spatial image detecting arrangement 7 mounted on a wafer stage 6 is performed in a widthwise direction of a spacial image by driving the wafer stage 6, the variation of current acquired from the light receiving sensor 8 is detected, and the image of a reference pattern formed in a transfer original recording pattern 9 is detected, so that the property of the projection optical system 5 is evaluated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an EUV exposure apparatus using EUV light ((Extreme Ultraviolet), which means light having a wavelength of 100 nm or less in the present specification and claims).

  As the degree of integration of semiconductor integrated circuits increases, the circuit pattern becomes finer, and the exposure apparatus using visible light or ultraviolet light that has been used conventionally has become insufficient in resolution. As is well known, the resolution of the exposure apparatus is proportional to the numerical aperture (NA) of the transfer optical system and inversely proportional to the wavelength of light used for exposure. Therefore, as one attempt to increase the resolution, an attempt has been made to use an EUV (sometimes referred to as soft X-ray) light source having a short wavelength for exposure transfer instead of visible light or ultraviolet light.

  As EUV light generators used in such exposure transfer apparatuses, laser plasma EUV light sources (hereinafter sometimes referred to as “LPP (Laser Produced Plasma)”) and discharge plasma EUV are particularly promising. Light source.

  LPP focuses pulse laser light on a target material in a vacuum vessel, converts the target material into plasma, and uses EUV light radiated from the plasma. Although it is small, it is comparable to an undulator. It has about the brightness.

  Further, an EUV light source using discharge plasma such as Dense Plasma Focus (DPF) is small in size, has a large amount of EUV light, and is low in cost. These have recently attracted attention as light sources of EUV exposure apparatuses using EUV having a wavelength of 13.5 nm.

  An outline of such an EUV exposure apparatus is shown in FIG. In the figure, IR1 to IR4 are reflectors of the illumination optical system, and PR1 to PR4 are reflectors of the projection optical system. W is a wafer and M is a mask.

  The laser light emitted from the laser light source L is focused on the target S, and X-rays are generated from the target S by a plasma phenomenon. The X-rays are reflected by the reflecting mirrors C and D, and enter the illumination optical system as parallel X-rays. Then, the light is sequentially reflected by the reflecting mirrors IR1 to IR4 of the illumination optical system to illuminate the illumination area of the mask M. X-rays reflected by the pattern formed on the mask M are sequentially reflected by the reflecting mirrors PR1 to PR4 of the projection optical system, and form an image of the pattern on the wafer W surface.

  Actually, the mask M is mounted on the mask stage, and the wafer W is mounted on the wafer stage. The illumination optical system cannot illuminate the entire surface of the mask M at a time, and the projection optical system cannot project the entire surface of the mask M at a time. Therefore, the mask stage and the wafer stage are moved synchronously to perform exposure. The pattern of the mask M is exposed and transferred onto the wafer W by scanning the transfer area.

  In order to form a desired pattern on the wafer W, it is preferable to sufficiently reduce the aberration of the projection optical system. In particular, the wavefront aberration (rms value) of the projection optical system is 1/30 or less of the wavelength, and the pattern distortion Is maintained at 1/10 or less of the exposure line width, a fine pattern with high contrast can be formed. For example, when the exposure wavelength is 13.5 nm and the NA of the projection optical system is 0.25, when the wavefront aberration is 0.5 nm rms or less and the pattern distortion is 5 nm or less, a resist pattern having a size of about 45 nm is formed. Can do.

  In order to maintain such minute wavefront aberration and pattern distortion for a long period, it is preferable to measure the optical performance of the projection optical system sequentially. Further, if necessary, the exposure apparatus may be provided with a function for restoring the performance of the deteriorated projection optical system.

  As a method for evaluating the optical performance of the projection optical system, a reference pattern formed on the mask M is exposed and transferred to the wafer M, and the shape of the pattern formed on the wafer by resist exposure and etching is measured with an SEM or the like. The method of evaluating is mentioned. However, such a method has the disadvantages that it takes time for evaluation and that errors due to instability of the resist process are large.

  As another method for evaluating the optical performance of the projection optical system, a method of detecting a projected image of a reference pattern formed on the mask M at a position where the wafer W should be used in a conventional ultraviolet exposure apparatus. I came. An example of such an aerial image detection mechanism in a conventional ultraviolet exposure apparatus is shown in FIG.

  A standard pattern having a predetermined shape is formed on the mask 32 mounted on the mask stage 31, and an image of this standard pattern is illuminated by illumination light from the illumination optical system 33, and the wafer 35 is projected by the projection optical system 34. Is formed on the surface to be present. A wafer stage 36 on which the wafer 35 is mounted is provided with a transmission slit 37 having a slit-like opening, and light transmitted through the slit is detected by the aerial image detection mechanism 38.

  The aerial image detection mechanism includes lenses 39 and 40, a mirror 41, and an optical sensor 43, and an image of light transmitted through a slit-like transmission pattern (transparent glass or the like) is transmitted by the lenses 39 and 40 to the optical sensor 43. An image is formed on the surface of the photoelectric element, and the amount of light transmitted through the slit is measured.

  In this state, by scanning the wafer stage 36 in the direction of the arrow in the figure (the horizontal direction in the drawing), the light quantity distribution of the aerial image in the horizontal direction in the figure can be measured. By measuring this light quantity distribution, the shape of the image of the standard pattern formed on the mask 32 can be known, and the performance of the projection optical system 34 can be evaluated from the shape of the detected image.

  However, when the above-described conventional aerial image detection mechanism is applied to the EUV exposure apparatus, there is a problem that the intensity loss of the EUV light is large. For example, a glass plate of a transmissive pattern substrate does not transmit EUV light at all. Although it is conceivable to use a very thin membrane for the substrate instead of the glass plate or a stencil pattern with a slit-like hole, there is a problem that the pattern is easily distorted. Further, the conventional lens optical system cannot be adapted to EUV light. Even when a reflective optical system is employed instead of the lens optical system, it is difficult to ensure a sufficient amount of light as in a conventional aerial image sensor due to low reflectance.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an EUV exposure apparatus including an aerial image detection mechanism suitable for EUV light.

  A first means for solving the above problem is that an illumination optical system that irradiates a mask on which a desired circuit pattern is formed with ultrashort ultraviolet rays, a mask stage that holds the mask, and an image of the circuit pattern on a wafer. An EUV exposure apparatus comprising: a projection optical system that reduces and transfers to a wafer; a wafer stage that holds the wafer; and an aerial image detection mechanism that detects a light intensity distribution of an image formed by the projection optical system. The image detection mechanism includes a light receiving sensor for detecting a reduced transfer image generated by the projection optical system of the reference mark formed at the mask position, and the light receiving sensor has at least a photoelectric conversion efficiency different on the surface of the light receiving unit. An EUV exposure apparatus having a structure in which two types of members are formed to have a predetermined shape.

  In this means, the light intensity distribution of the image formed by the direct projection optical system is detected by the light receiving sensor. Such a light receiving sensor can be realized by forming at least two types of members having different photoelectric conversion efficiencies on the surface of the light receiving portion so as to have a predetermined shape. That is, for example, if a member having a high photoelectric conversion rate is formed in a slit shape in the central portion of the surface of the light receiving portion and a member having a low photoelectric conversion rate is formed in the other portions of the light receiving portion, the light receiving sensor is moved. Thus, the same function as the conventional aerial image detection mechanism can be obtained. Since the aerial image detection mechanism of this means does not use a lens or a mirror, it is possible to obtain a light amount that can be sufficiently detected by the light receiving sensor by using these optical members. The reference mark only needs to be formed at the mask position, and may be formed on the mask or directly on the mask stage. The predetermined shape may be arranged in any pattern such as a slit shape or a cross shape as long as the intensity distribution of the reference mark image can be measured. The formation position and the predetermined shape of the reference mark are similarly interpreted in the present specification and claims, including second means described later.

  A second means for solving the above problem is that an illumination optical system for irradiating a mask on which a desired circuit pattern is formed with ultrashort ultraviolet rays, a mask stage for holding the mask, and an image of the circuit pattern on the wafer. An EUV exposure apparatus comprising: a projection optical system that reduces and transfers to a wafer; a wafer stage that holds the wafer; and an aerial image detection mechanism that detects a light intensity distribution of an image formed by the projection optical system. The image detection mechanism includes a light receiving sensor that detects a reduced transfer image of the reference mark formed at the mask position generated by the projection optical system, and the light receiving sensor is formed on a part of the surface of the light receiving unit with EUV light. An EUV exposure apparatus having a structure in which a member that absorbs or reflects light is formed to have a predetermined shape.

  In this means, a member that absorbs or reflects EUV light is formed on a part of the surface of the light receiving portion so as to have a predetermined shape. Therefore, the amount of light incident on the photoelectric conversion surface of the light receiving sensor changes according to the shape of this member. For example, if the shape of this member is made to have a slit-like hole in the center, the first Functions and effects similar to the means can be achieved.

  The third means for solving the problem is the first means or the second means, wherein at least one of a titanium layer and a nickel layer is formed on the outermost surface of the light receiving sensor. (Claim 3).

  In this means, since at least one of the titanium layer and the nickel layer is formed on the outermost surface of the light receiving sensor, the accumulation of impurities on the surface of the light receiving sensor can be suppressed.

  A fourth means for solving the above problem is any one of the first to third means, comprising a cleaning mechanism for blowing a gas containing at least oxygen on the surface of the light receiving sensor. (Claim 4).

  In this means, impurities deposited on the surface of the light receiving sensor can be purged and oxidized to be removed.

  A fifth means for solving the above problem is any one of the first to fourth means, wherein the light receiving sensor is fixed to the wafer stage ( Claim 5).

  By fixing the light receiving sensor to the wafer stage, it is possible to scan the light receiving sensor by driving the wafer stage, and it is easy to position the light receiving sensor on the image plane of the standard pattern.

  ADVANTAGE OF THE INVENTION According to this invention, the EUV exposure apparatus which comprises the aerial image detection mechanism suitable for EUV light can be provided.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an outline of an EUV exposure apparatus which is an example of an embodiment of the present invention.

  The EUV exposure apparatus includes an illumination optical system 2 that irradiates EUV light onto a mask 1 on which a circuit pattern is formed, a mask stage 3 that holds the mask 1, and a projection optical system 5 that reduces and transfers an image of the circuit pattern onto a wafer 4. And a wafer stage 6 that holds the wafer 4 and a spatial image detection mechanism 7 that detects the light intensity distribution of the image formed by the projection optical system 5. The aerial image detection mechanism 7 includes at least a light receiving sensor 8 that detects a reduced transfer image generated by the projection optical system 5, and the light receiving sensor 8 has a function of detecting a photoelectron to generate a current or a voltage. ing. When EUV light is incident on the light receiving sensor 8, photoelectrons are generated. For example, the intensity of the EUV light can be measured by measuring the amount of current.

  The wavelength of EUV light used in this embodiment is 13.5 nm, the numerical aperture of the projection optical system 5 is 0.25, and the projection magnification is 1/4.

  The transfer master pattern required for generating a standard aerial image may be a pattern provided on the mask 1, but as shown in FIG. 1, a dedicated transfer master pattern 9 is provided on the mask stage 3, The reduced projection image may be detected by the aerial image detection mechanism 7.

  In this embodiment, the transfer master pattern 9 is formed by forming a tantalum film in a pattern on the surface of the multilayer film. If five lines with a line width of 180 nm are used as the pattern, five patterns on the line with a line width of 45 nm are formed on the image plane.

  An example of the light receiving sensor 8 used in the aerial image detection mechanism 7 in the present embodiment is shown in FIG. In FIG. 2A, at least two types of members A and B having different photoelectric conversion efficiencies are provided on the surface of the light receiving sensor, and the current generated by receiving these EUV light is detected. That is, the substance A having a low photoelectric conversion efficiency is formed on the substrate 8a, and the substance B having a high photoelectric conversion efficiency is further formed in a predetermined shape on the substance A. The pattern of the substance B has a line shape having a width that is ½ of the aerial image size and the same length as the aerial image size. That is, the pattern width of the substance B is about 22.5 nm in order to detect a pattern with a line width of 45 nm.

  When the aerial image detection mechanism 7 mounted on the wafer stage 6 in FIG. 1 is scanned in the width direction of the aerial image by driving the wafer stage 6, the change in current obtained from the light receiving sensor 8 is shown in FIG. Show. 3A shows the positional relationship between the light receiving sensor 8 and the intensity distribution of the aerial image, and FIG. 3B shows the output of the light receiving sensor. In FIG. 3B, the horizontal axis represents the position of the light receiving sensor 8, and the vertical axis represents the output (current) of the light receiving sensor 8. The pattern of the aerial image can be detected from the output pattern of the light receiving sensor 8 as shown in FIG. In FIG. 3, only one aerial image is shown. However, since the transfer original pattern is actually composed of five lines, five aerial images are formed. The measurement is performed on these five aerial images, and the average value is adopted.

  In the above description, detection of the aerial image pattern in the left-right direction of the paper surface of FIG. 3 has been described. However, the transfer original plate pattern is a line pattern oriented in a direction perpendicular to the pattern in the above description, and a light receiving sensor. The pattern of the substance B in FIG. 5 is also directed in a direction perpendicular to the pattern in the above description, and the wafer stage 6 is moved in a direction perpendicular to the movement direction in the above description, thereby making a space in a direction perpendicular to the direction described above. Image pattern detection can be performed.

The selection of the substances A and B varies depending on the wavelength of the EUV light. For example, when the wavelength is 13 to 14 nm, the substance A is preferably Mo, Ru, Rh, SiC, B ₄ C or the like. Further, the substance B is preferably Au, Ta, or the like. The substance B is preferably selected from materials that can easily form a pattern. Further, the substance A may be a material with high photoelectric conversion efficiency, and the substance B may be a low material.

  FIG. 2B shows an example of another embodiment of the light receiving sensor 8. In this example, the multilayer coating 8b is provided on the layer made of the substance A in FIG. 2A, and the patterned substance B is provided thereon. Most of the EUV light incident on the substance A is reflected by the multilayer coating 8b and does not reach the substance A. As a result, the photoelectrons generated by the substance A are reduced, and the photoelectrons generated by the substance B are not reduced. Therefore, the S / N of the current change can be improved, and the aerial image can be measured more precisely.

  The multilayer coating 8b preferably has a high EUV reflectance. For example, for EUV light having a wavelength of 13 to 14 nm, a multilayer film in which molybdenum and silicon are alternately stacked is preferable. Ruthenium or rhodium may be used instead of molybdenum. Since these multilayer films are conductive, photoelectrons generated in the substance B can be taken out and measured through the multilayer film coat 8b and the substance A.

  In FIG. 2C, a multilayer coating 8b is provided on the layer made of the substance A, and a slit-like opening is provided at the center thereof. Even if this is the case, it will not be necessary to explain that the same effect as in FIG. 2B can be obtained.

  These aerial image detection mechanisms 7 have a feature that they can be configured using a simple light receiving sensor 8. As a result, it can be mounted on the wafer stage 6. By mounting on the wafer stage 6, the position of the light receiving sensor 8 can be precisely controlled, and the detection accuracy of the aerial image is increased.

  EUV light is generally highly absorbed by substances. Therefore, there may be a problem that the amount of photoelectrons changes due to the accumulation of impurities on the surface of the light receiving sensor 8. In order to reduce this influence, the EUV exposure apparatus preferably has a function of cleaning the surface of the light receiving sensor 8.

  For this purpose, in the embodiment shown in FIG. 1, a cleaning mechanism 10 for blowing gas to the light receiving sensor 8 is provided in the vicinity of the light receiving sensor 8. The gas is assumed to contain at least oxygen. By providing such a mechanism, the accumulation of impurities on the surface of the light receiving sensor 8 can be reduced, and the adhered impurities can be oxidized and removed. In the embodiment shown in FIG. 1, a cleaning mechanism 11 is provided in the vicinity of the transfer master pattern 9 for spraying gas onto the transfer master pattern 9 to clean the surface of the transfer master pattern 9.

  FIG. 2D shows a structure in which a layer of a substance C that suppresses impurity deposition is provided on the outermost surface of the light receiving sensor 8 as shown in FIG. For example, by using titanium or nickel as the substance C, impurity deposition can be reduced.

It is a figure which shows the outline | summary of the EUV exposure apparatus which is an example of Embodiment of this invention. It is a figure which shows the example of the light reception sensor used with the aerial image detection mechanism in this Embodiment. It is a figure which shows the change of the electric current obtained from a light receiving sensor, when an aerial image detection mechanism scans in the width direction of an aerial image by driving a wafer stage. It is a figure which shows the outline | summary of an EUV exposure apparatus. It is a figure which shows the example of the aerial image detection mechanism in the conventional ultraviolet exposure apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Mask, 2 ... Illumination optical system, 3 ... Mask stage, 4 ... Wafer, 5 ... Projection optical system, 6 ... Wafer stage, 7 ... Aerial image detection mechanism, 8 ... Light receiving sensor, 8a ... Substrate, 8b ... Multilayer film Coat, 9 ... Transfer master pattern, 10 ... Cleaning mechanism, 11 ... Cleaning mechanism

Claims (5)

An illumination optical system for irradiating a mask on which a desired circuit pattern is formed with ultrashort ultraviolet rays, a mask stage for holding the mask, a projection optical system for reducing and transferring an image of the circuit pattern onto the wafer, and holding the wafer An EUV exposure apparatus comprising a wafer stage for detecting a light intensity distribution of an image formed by the projection optical system, wherein the aerial image detection mechanism is a reference formed at the mask position. A light receiving sensor for detecting a reduced transfer image of the mark generated by the projection optical system is provided, and the light receiving sensor has at least two kinds of members having different photoelectric conversion efficiencies on the surface of the light receiving portion so as to have a predetermined shape. An EUV exposure apparatus having the structure described above. An illumination optical system for irradiating a mask on which a desired circuit pattern is formed with ultrashort ultraviolet rays, a mask stage for holding the mask, a projection optical system for reducing and transferring an image of the circuit pattern onto the wafer, and holding the wafer An EUV exposure apparatus comprising a wafer stage for detecting a light intensity distribution of an image formed by the projection optical system, wherein the aerial image detection mechanism is a reference formed at the mask position. A light receiving sensor for detecting a reduced transfer image of the mark generated by the projection optical system is provided, and the light receiving sensor has a predetermined shape with a member that absorbs or reflects EUV light on a part of the surface of the light receiving unit. An EUV exposure apparatus having a structure formed as described above. The EUV exposure apparatus according to claim 1, wherein at least one of a titanium layer and a nickel layer is formed on the outermost surface of the light receiving sensor. The EUV exposure apparatus according to claim 1, further comprising a cleaning mechanism that blows a gas containing at least oxygen on a surface of the light receiving sensor. The EUV exposure apparatus according to any one of claims 1 to 4, wherein the light receiving sensor is fixed to the wafer stage.

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