JP2009188047A - Method of remedying dark defect of euvl mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of remedying a dark defect of an EUVL (Extreme-Ultraviolet Lithography) mask which causes no overhang and gives less damage to a substrate. <P>SOLUTION: A part of a dark defect area 5 that is in contact with a normal pattern 3 is subjected to slope processing by physical spatter etching using a focused ion beam 6. A dark defect 3 surviving after the slope-processing is then removed by gas-assist etching using a xenon fluoride gas. Otherwise, the part of a dark defect area 5 that is in contact with the normal pattern 3 is subjected to trenching processing by physical spatter etching using the focused ion beam 6. A dark defect surviving after the trenching processing is then removed by gas assist etching. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for correcting black defects in EUVL masks.

  Currently, an optical projection exposure apparatus using an ArF excimer laser is used for pattern transfer onto a wafer. Up to a half pitch of 65 nm can be handled by a reduction projection exposure system using a conventional ArF excimer laser, but for a half pitch of 45 nm, the numerical aperture can be further increased (the numerical aperture can be increased to 1 or more). A reduction projection exposure apparatus using a laser is about to be used. For half-pitch 32nm, a reduced projection exposure system using an ArF excimer laser with a larger numerical aperture by changing the immersion solvent from water to a fluorinated solvent, or a reduced projection using a water immersion ArF excimer laser. There are many attempts to cope with this by combining an exposure apparatus and a double exposure technique. However, since the life extension of ArF excimer laser immersion reduction projection exposure apparatus is difficult in principle after half-pitch 22 nm, soft X-ray reduction exposure (Extreme Ultra Violet Lithography, EUVL) and nanoimprint lithography are promising. EUVL is a technology that reduces and exposes soft X-rays with a wavelength of about 13.5 nm with a reflective optical system. It is considered the limit of shortening the wavelength of ultraviolet exposure, and is vigorously developed as a lithography technology that can be used for more than two generations. Is underway.

In EUVL, a TaN or TaGeN absorber pattern that absorbs EUV light on a reflective layer that reflects EUV light composed of a Mo / Si multilayer film, and a Cr or SiO ₂ buffer layer between the Mo / Si multilayer film and the absorber pattern Is used. Even in EUVL masks, as with photomasks, if defects exist in the mask, the defects are transferred to the wafer and cause a defective device on all transferred wafers. If defects exist, transfer to the wafer. A defect correction process must be performed by a defect correction device before.

In order to reduce damage to the underlying buffer layer, black defect correction has been attempted by gas-assisted etching using xenon fluoride with an electron beam or a focused ion beam (for example, Non-Patent Document 1 or 2), but is in contact with the corrected portion. Since an overhang is observed in the normal pattern of the portion and the reflectivity is affected, processing without an overhang is required.
T. Abe, M. Nishiguchi, T. Amano, T. Motonaga, S. Sasaki, H. Mohri, and N. Hayashi, Proc. Of SPIE 5446 832-840 (2004) T. Liang, E. Frendberg, D. Bald, M. Penn, and A. Stiver, Proc. Of SPIE 5567 456-466 (2004)

  An object of the present invention is to provide a method for correcting a black defect in an EUVL mask that does not cause an overhang of the absorber and causes little damage to the base.

  Secondary electrons generated from the cross section during processing give energy to the assist etching gas (xenon fluoride) to promote chemical reaction, and overhang the normal pattern in contact with the black defect (isotropically as the etching deepens) Therefore, the portion in contact with the normal pattern is formed by physical sputter etching of a focused ion beam that can be processed without using an assist etching gas. First, slope processing by physical sputter etching of a focused ion beam is performed so that the portion in contact with the normal pattern has a vertical cross section in the portion in contact with the normal pattern. By performing slope processing, the material removed by physical sputter etching is prevented from being buried by reattachment. In order to prevent the focused ion beam from hitting the cross-section of the normal pattern that was subsequently produced by slope processing (so that secondary electrons are not generated from the cross-section), only the black defect portion remaining in the slope processing is selectively irradiated with the focused ion beam, and fluorinated. Xenon gas-assisted etching removes black defects left by slope processing.

  Alternatively, the portion of the normal pattern in contact with the normal pattern is etched by physical sputter etching of the focused ion beam to form a groove having a rectangular side surface by groove processing so that the focused ion beam does not hit the cross section of the normal pattern. Only black defects remaining in the processing are selectively irradiated with a focused ion beam and removed by gas-assisted etching (xenon fluoride). The width of the groove for grooving is set so that the material removed by physical sputter etching is not buried by reattachment.

  Like the Bosch method used in MEMS fabrication, a carbon-based protective film is formed on the normal cross section that appears in the slope processing or grooving, and the black defects remaining in the slope processing are removed by gas-assisted etching. Protects the machined cross section.

  The carbon-based protective film with a processed cross section that is no longer necessary after the removal of black defects is removed by irradiation with UV light in an RF plasma or ozone atmosphere in an oxygen atmosphere. Alternatively, the carbon-based protective film having a processed cross section that is no longer necessary is removed with an electron beam or a focused ion beam in a water vapor atmosphere.

  Since the processing of the black defect region in contact with the normal pattern is performed by physical sputter etching, secondary electrons generated from the cross-section during processing react with xenon fluoride like gas-assisted etching using xenon fluoride. It does not cause an overhang. Although it is difficult to avoid overhanging with an electron beam because etching proceeds by a chemical reaction, a focused ion beam can perform processing without overhanging due to its physical removal capability.

  The remaining black defects are removed by gas-assisted etching using xenon fluoride, which has a high selection ratio with the underlying layer, so that the underlying buffer layer and the Mo / Si multilayer film can be repaired with little damage.

  While a black defect is removed by gas-assisted etching with xenon fluoride, an overhang can be prevented by covering the normal pattern cross section with a carbon-based film that is not etched with xenon fluoride.

  RF plasma irradiation in an oxygen atmosphere and UV light irradiation in an ozone atmosphere can remove only the carbon-based protective film without damaging the absorber pattern. Even with electron beam or focused ion beam etching in a water vapor atmosphere, the absorber pattern can be removed without removing the carbon-based protective film.

  Embodiments of the present invention will be described below in detail with reference to the drawings.

  FIGS. 1A to 1C show a slope process of a portion in contact with a normal pattern of black defects by physical sputter etching of a focused ion beam that best represents the characteristics of the present invention, and the black defects remaining in the slope process are gasified. It is a schematic sectional drawing explaining the case where it removes by assist etching.

  An EUVL mask having a black defect is introduced into the focused ion beam apparatus, the XY stage is moved to a position where the black defect 5 is found by the defect inspection apparatus, the region including the defect is observed, and the black defect 5 is recognized. The EUVL mask has a normal pattern (absorber) 1 having a Mo / Si multilayer 3, a buffer layer 2, and a black defect 5 in this order on a glass substrate 4.

  The focused ion beam system has an evacuated working chamber and a preparation chamber. The working chamber has an XY stage for positioning, a focused ion beam column consisting of an ion source, an ion optical system, and a scanning system, a secondary Equipped with an electron detection system, an assist etching gas supply system 7 for black defect removal, and a deposition film material supply system for white defect correction. Has a system. A focused ion beam apparatus focuses ions extracted from an ion source (for example, a gallium liquid metal ion source) with a desired current using an electrostatic lens and a diaphragm of an ion optical system, and the focused ion beam is sampled in a scanning system. It is an apparatus that can observe a minute region by detecting secondary electrons generated from a sample while scanning the top and displaying the secondary electron intensity according to the irradiation position. The focused ion beam device can also be used to perform physical sputter etching and assist by selectively irradiating the defined area with a scanning system if the area to be processed (black defect or white defect in the case of mask correction) is defined from the observed image. It is a device that can perform removal processing (black defect correction) by gas-assisted etching in the presence of gas and deposition film formation (white defect correction) by ion beam induced chemical vapor deposition in the presence of deposition gas. .

  A portion of the recognized black defect 5 in contact with the normal pattern 1 is subjected to physical sputter etching using a focused ion beam that can be processed without using an assist etching gas. First, slope processing by physical sputter etching of the focused ion beam 6 from the focused ion beam column 11 is performed so that the portion in contact with the normal pattern 1 has a vertical cross section in the portion in contact with the normal pattern (FIG. 1 (a)). Here, the slope processing means slope processing, and the region 16 in which the defect region 5 in the sputter etching cross section of FIG. The slope processing here is such that one side (normal pattern side) is vertical and one side (black defect portion) is slanted so that the surface is wide and gradually narrows in the depth direction. By performing slope processing, the material removed by physical sputter etching is prevented from being buried by reattachment. In order to prevent the focused ion beam 6 from hitting the cross section of the normal pattern 1 that is subsequently produced by the slope processing (so that secondary electrons are not generated from the cross section), only the black defect portion remaining in the slope processing from the assist etching gas supply system 7 The focused ion beam 6 is selectively irradiated while supplying an assist etching gas (for example, xenon fluoride) to the beam irradiation point (FIG. 1 (b)), and the black defect portion 5 remaining in the slope processing is removed by gas assist etching. (Fig. 1 (c)).

  FIGS. 2A to 2C show other embodiments, in which a strip-shaped portion of a portion in contact with a normal pattern of black defects is processed by physical sputter etching of a focused ion beam, and the black remaining by the strip-shaped processing is shown. It is a schematic sectional drawing explaining the case where a defect is removed by gas assist etching.

  In the present embodiment, the portion of the recognized black defect 5 in contact with the normal pattern 1 is grooved into the portion of the black defect region 5 in contact with the normal pattern 1 by physical sputter etching of the focused ion beam 6 to provide a groove 17 ( Fig. 2 (a)). Subsequently, while supplying the assist etching gas (e.g., xenon fluoride) from the assist etching gas supply system 7 to the beam irradiation point only in the black defect portion 5 remaining in the groove processing so that the focused ion beam 6 does not hit the cross section of the normal pattern. A focused ion beam is selectively irradiated (FIG. 2 (b)) and removed by gas-assisted etching (FIG. 2 (c)). The width of the groove is set so that the material removed by physical sputter etching is not buried by reattachment.

  Since the portion of the black defect region that is in contact with the normal pattern is processed by physical sputter etching, secondary electrons generated from the cross-section being processed do not react with xenon fluoride to cause overhang. Further, the remaining black defects are removed by gas-assisted etching using xenon fluoride, so that the underlying buffer layer 2 and the Mo / Si multilayer film 3 can be corrected with little damage.

  Even if secondary electrons are not generated, the processed cross section can be cut slightly even by exposure to xenon fluoride. By introducing the following protective film formation and removal process, additional cutting of the processed cross section can be eliminated. Can do. Examples are shown in FIGS. 3A to 3C, FIGS. 4A and 4B, and FIGS. 5A and 5B.

A region where a protective film source gas such as CF ₄ , naphthalene, or phenanthrene is introduced from the carbon source gas supply system 8 into the normal pattern cross section that appears in the slope processing or strip processing from the protective film source gas supply system 8 to form a protective film Only the ion beam 6 is irradiated to form a carbon-based protective film 9 (FIG. 3 (a)). While removing the black defects 5 left by the slope processing and groove processing by gas assist etching, the normal pattern processing cross section is protected (FIG. 3 (b) and FIG. 3 (c)).

  As shown in FIGS. 4 (a) and 4 (b), oxygen is supplied from the oxygen supply system 10 to the carbon-based protective film 9 in the processed cross section that is no longer necessary after the black defect is removed, and is similar to the Evactron anticontamination system of XEI. Then, the carbon-based protective film 9 is removed with an apparatus for removing with RF plasma 11 in an oxygen atmosphere. Alternatively, ozone is supplied from the ozone supply system 10, and the unnecessary carbon-based protective film 9 is removed by irradiating the UV light 11 in an ozone atmosphere. Since carbon is a light element and does not absorb much EUV light with a wavelength of 13.5 nm, it can be used as an EUV mask without removing the carbon protective film 9, but it is desirable to remove it.

  Alternatively, as shown in FIGS. 5 (a) and 5 (b), water vapor is supplied to the carbon-based protective film 9 having a processed cross section that is no longer necessary after removing the black defects, and the focused ion beam 6 or the electron beam 13 is supplied. Is applied to only the carbon-based protective film 9 to remove the unnecessary carbon-based protective film 9.

  FIGS. 6A to 6D are schematic cross-sectional views illustrating a case where correction is performed using an apparatus that combines an electron beam and a focused ion beam.

  In the case of an apparatus that combines a focused ion beam and an electron beam, defect positioning and defect recognition are performed by the electron beam 13 from the electron beam column 15 (FIG. 6 (a)), and a normal pattern in the black defect region is touched. Slope processing or groove processing of the part is performed by physical sputter etching of the ion beam 6 (FIG. 6 (b)), and the black defect region remaining in the next process is removed by the electron beam 13 in the presence of xenon fluoride. By selectively irradiating only the defect region 5, it can be removed by gas-assisted etching (FIG. 6 (c) and FIG. 6 (d)). In this method, gallium implantation of the ion beam does not occur at the time of defect positioning and defect recognition, and gallium implantation of the ion beam does not occur at the time of removal of the remaining black defect region. It is possible to make corrections that suppress this.

(A)-(c) perform slope processing of a portion in contact with a normal pattern of black defects by physical sputter etching of a focused ion beam that best represents the characteristics of the present invention, and gas assisted etching of black defects remaining in the slope processing It is a schematic sectional drawing explaining the case where it removes by. (A) to (c), when strip-shaped processing of a portion in contact with the normal pattern of black defects is performed by physical sputter etching of a focused ion beam, and black defects remaining in the strip-shaped processing are removed by gas-assisted etching. It is a schematic sectional drawing explaining these. (A)-(c) is a schematic sectional drawing explaining the case where the process of protecting a process cross section is added while forming a carbon-type protective film in a process cross section, and removing a black defect by gas assist etching. is there. (A), (b) is a schematic sectional drawing explaining the case where the process of removing a carbon-type protective film is further added after black defect removal. (A), (b) is a schematic sectional drawing explaining the case where the process of removing a carbon-type protective film with an electron beam or a focused ion beam is added after black defect removal. (A)-(d) is a schematic sectional drawing explaining the case where it corrects with the apparatus which combined the electron beam and the focused ion beam.

Explanation of symbols

1 Normal pattern (absorber)
2 Buffer layer 3 Mo / Si multilayer 4 Glass substrate 5 Black defect 6 Focused ion beam 7 Assisted etching gas supply system 8 Carbon-based source gas supply system 9 Carbon-based protective film 10 Oxygen introduction system or ozone introduction system 11 RF plasma or UV Light 12 Water supply system 13 Electron beam 14 Focused ion beam column 15 Electron beam column 16 Slope processed region 17 Groove

Claims (6)

A first step of removing a portion in contact with the normal pattern in the black defect region by a slope process so that a portion in contact with the normal pattern becomes a vertical cross section by physical sputter etching of the focused ion beam,
A second step of removing black defects left by the slope processing by gas-assisted etching;
A method for correcting black defects in an EUVL mask, comprising: A first step of grooving a portion of the black defect region in contact with the normal pattern into a rectangular shape when viewed from the side surface by physical sputter etching of the focused ion beam;
A second step of removing black defects left by the trench processing by gas-assisted etching;
A method for correcting black defects in an EUVL mask, comprising:   3. The EUVL mask black defect correction method according to claim 1 or 2, further comprising a step of forming a carbon-based protective film on the normal pattern cross section appearing in the first processing after the first step.   4. The method for correcting a black defect in an EUVL mask according to claim 3, further comprising a step of removing a carbon-based protective film formed on the cross section of the normal pattern after the second step.   5. The EUVL mask black defect correcting method according to claim 4, wherein the carbon-based protective film is removed by RF plasma irradiation in an oxygen atmosphere or UV light irradiation in the presence of ozone.   5. The EUVL mask black defect correcting method according to claim 4, wherein the carbon-based protective film is removed by electron beam irradiation or focused ion beam in a water atmosphere.

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