JP2013074058A - Reflective mask blank, method for manufacturing the same and reflective mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective mask blank which has a light-shielding frame with a high light blocking effect, and can form a transfer pattern with high accuracy, a method for manufacturing the same, and a reflective mask.SOLUTION: Particle adhesion to a circuit pattern area 85 is suppressed, and deterioration of mask defect quality is suppressed since a light-shielding frame 25 is formed at a pre-stage of forming the circuit pattern area 85, and a multilayer reflection layer 21 is not removed for forming the light-shielding frame 25. In addition, there is no fear that several layers of the multilayer reflection layer 21 remain, intensity of reflected light to be generated from the multilayer reflection layer 21 is suppressed, and the light-shielding frame 25 with a high light blocking effect is formed since the multilayer reflection layer 21 is not removed for forming the light-shielding frame 25. Thus, a transfer pattern is formed with high accuracy by using reflective masks 101, 201, 301, 401.

Description

  The present invention relates to a reflective mask blank, a manufacturing method thereof, and a reflective mask. In particular, the present invention relates to a reflective mask blank used in a semiconductor manufacturing apparatus using EUV lithography that uses extreme ultraviolet (EUV) as a light source, a manufacturing method thereof, and a reflective mask.

  In recent years, with the miniaturization of semiconductor devices, EUV lithography using EUV having a wavelength of around 13.5 nm as a light source has been proposed. Since EUV lithography has a short light source wavelength and very high light absorption, it needs to be performed in a vacuum. In the EUV wavelength region, the refractive index of most substances is slightly smaller than 1. For this reason, the EUV lithography cannot use a transmission type refractive optical system which has been used conventionally, and becomes a reflection optical system. Therefore, a photomask used as an original (hereinafter referred to as a mask) must be a reflective mask because a conventional transmission mask cannot be used.

  A reflective mask blank that is the basis of such a reflective mask has a multilayer reflective layer showing a high reflectivity with respect to the exposure light source wavelength and an absorption layer of the exposure light source wavelength sequentially formed on a low thermal expansion substrate. Further, a back surface conductive film for an electrostatic chuck in the exposure machine is formed on the back surface of the substrate. There is also an EUV reflective mask blank having a structure having a buffer layer between the multilayer reflective layer and the absorbing layer. When processing from a reflective mask blank to a reflective mask, the absorber layer is partially removed by EB lithography and etching technology, and in the case of a structure having a buffer layer, this is also removed, and from the absorber and reflector A circuit pattern is formed. The light image reflected by the reflection type mask thus produced is transferred onto the semiconductor substrate through a reflection optical system.

  In an exposure method using a reflective optical system, irradiation is performed at an incident angle (usually 6 °) tilted by a predetermined angle from the vertical direction with respect to the mask surface. Therefore, when the absorption layer is thick, the pattern itself is shaded. Therefore, since the reflection intensity in the shadowed portion is smaller than that in the non-shadowed portion, the contrast is lowered, and the edge portion of the transfer pattern is blurred and deviated from the design dimension. This is called shadowing and is one of the fundamental problems of the reflective mask.

  In order to prevent such blurring of the pattern edge and deviation from the design dimension, it is effective to reduce the film thickness of the absorption layer and reduce the height of the pattern, but if the film thickness of the absorption layer is reduced In addition, the light shielding property in the absorbing layer is lowered, the transfer contrast is lowered, and the accuracy of the transfer pattern is lowered. That is, if the absorption layer is too thin, the contrast necessary for maintaining the accuracy of the transfer pattern cannot be obtained. That is, if the thickness of the absorption layer is too thick or too thin, there is a problem, so it is currently between 50 and 90 nm, and the reflectance of the EUV light at the absorption layer is 0.5 to 2%. Degree.

  On the other hand, when a transfer circuit pattern is formed on a semiconductor substrate using a reflective mask, chips having a plurality of circuit patterns are formed on one semiconductor substrate. There may be a region where the outer periphery of the chip overlaps between adjacent chips. This is because the chips are arranged at a high density in order to improve productivity in order to increase the number of chips that can be taken per wafer. In this case, this region is exposed (multiple exposure) a plurality of times (up to four times). The chip outer peripheral portion of this transfer pattern is also the outer peripheral portion on the reflective mask, and is usually the absorption layer portion. However, as described above, since the reflectance of EUV light on the absorption layer is about 0.5 to 2%, there is a problem that the outer periphery of the chip is exposed by multiple exposure. For this reason, it has become necessary to form a region (hereinafter referred to as a light-shielding frame) having a higher light-shielding property of EUV light than a normal absorption layer on the outer periphery of the chip on the reflective mask.

The multiple exposure described above has a problem that not only EUV light but also the near-infrared region light from vacuum ultraviolet rays other than the 13.5 nm band called out-of-band (OoB: Out of Band) is sensitive to the outer periphery of the chip. is there. These OoB lights are reflected by the EUV absorption layer (the main material is a large amount of Ta) on the outermost surface of the reflective mask, and are emitted to the wafer. Therefore, light having various wavelengths other than 13.5 nm is irradiated on the resist on the wafer and exposed to light, which adversely affects the pattern size in the vicinity of the chip boundary region.
In order to solve such a problem, the groove of the reflective mask is dug from the absorption layer to the multilayer reflective layer to reduce the reflectance of the multilayer reflective layer, thereby reducing the exposure light source wavelength. A reflective mask provided with a light-shielding frame having a high light-shielding property against light is proposed. (Patent Document 1)

JP 2009-212220 A

However, in the reflective mask described in Patent Document 1, when the multilayer reflective layer is dug after forming the circuit pattern region, it is necessary to process a total of 80 layers of different materials Si and Mo. In order to realize the etching process, very complicated conditions are essential. Further, in this reflective mask, the multilayer reflective layer is removed to provide a light shielding frame, and therefore, if several multilayer reflective layers remain, there is a concern that the reflectance may be increased. Furthermore, since the multilayer reflective layer is removed, the generation of particles from the processed surface of the multilayer reflective layer is inevitable, leading to a reduction in mask quality on the defective surface.
Accordingly, the present invention has been made to solve the above-described problems, and an object thereof is to provide a reflective mask blank with high pattern transfer accuracy in which particle generation is suppressed, a manufacturing method thereof, and a reflective mask. .

  In order to achieve this object, the invention according to claim 1 is a reflective mask blank in which a substrate, a multilayer reflective layer formed on a surface of the substrate, and an absorption layer formed on the multilayer reflective layer are provided. A reflective mask blank comprising a light shielding frame and a circuit pattern forming region surrounded by the light shielding frame, wherein the absorbing layer of the light shielding frame is thicker than the absorbing layer of the circuit pattern forming region. To do.

The invention according to claim 2 is characterized in that the absorption layer of the light shielding frame is 150 nm or more thicker than the absorption layer of the circuit pattern region.
The invention according to claim 3 is characterized in that the light shielding frame has a reflectance of 0.25% or less with respect to EUV light.
According to a fourth aspect of the present invention, in the method of manufacturing the reflective mask blank, the light-absorbing layer is partially removed by electron beam lithography or photolithography and dry etching to form the light-shielding frame. Features.

According to a fifth aspect of the present invention, in the reflective mask, a circuit pattern region is formed in the circuit pattern forming region of the reflective mask blank or the reflective mask blank manufactured by the method of manufacturing the reflective mask blank. It is characterized by being manufactured.
The invention according to claim 6 is characterized in that the light shielding frame is spaced 200 nm or more outward from the circuit pattern region.

  In the present invention, since the light shielding frame is formed in the previous stage of forming the circuit pattern region, and the multilayer reflective layer is not removed to form the light shielding frame, it is possible to suppress the adhesion of particles to the circuit pattern region. That is, it is possible to suppress deterioration of mask defect quality. In addition, since the multilayer reflective layer is not removed to form the light shielding frame, there is no concern that several multilayer reflective layers remain, and the intensity of the reflected light generated from the multilayer reflective layer is suppressed, and the light shielding frame has high light shielding properties. Can be formed. For these reasons, there is an effect that a transfer pattern can be formed with high accuracy by using the reflective mask of the present invention.

It is a schematic sectional drawing of the structure of the reflective mask blank of this invention. It is the schematic of the reflective mask blank of this invention. It is a schematic sectional drawing of the structure of the reflective mask of this invention. It is the schematic of the reflective mask of this invention. It is a figure which shows the preparation processes of the light shielding frame of the reflective mask blank of this invention. It is a figure which shows the preparation processes of the reflective mask blank of an Example. It is a figure which shows the manufacturing process of the reflective mask blank of an Example, and a reflective mask.

Hereinafter, embodiments according to the present invention will be described with reference to the drawings.
First, the configuration of the reflective mask blank of the embodiment according to the present invention will be described. 1A to 1D show cross sections of reflective mask blanks 100, 200, 300, and 400 according to an embodiment of the present invention. That is, any of the reflective mask blanks 100, 200, 300, and 400 may be used as the configuration of the reflective mask according to the embodiment of the present invention. 2A is a view of the reflective mask blanks 100, 200, 300, 400 of the present invention of FIGS. 1A to 1D as viewed from the surface, and FIG. 2B is a reflective mask blank. FIG. 2C is a diagram of the reflective mask blanks 100 and 300 viewed from the back surface.

  In the reflective mask blank 100 shown in FIG. 1A, a multilayer reflective layer 21 and an absorption layer 51 are sequentially formed on the surface of a substrate 11. The reflective mask blank 200 shown in FIG. 1B has a structure in which a multilayer reflective layer 21 and an absorption layer 51 are sequentially formed on the surface of the substrate 11, and a back conductive film 71 is formed on the back surface of the substrate 11. It has become. That is, in the reflective mask 200 of FIG. 1B, the back conductive film 71 is formed on the back surface of the substrate 11 of the reflective mask 100 of FIG. In the reflective mask blank 300 of FIG. 1C, the multilayer reflective layer 21, the buffer layer 41, and the absorption layer 51 are sequentially formed on the surface of the substrate 11. The reflective mask blank 400 of FIG. 1D has a structure in which a back conductive film 71 is formed on the back surface of the substrate 11 of the reflective mask 300 of FIG.

  The peripheral portion of the absorption layer 51 on the multilayer reflective layer 21 in FIGS. 1A to 1D, that is, the portion that becomes the light shielding frame 25 is formed thicker than other regions. The absorption layer 51 of the light shielding frame 25 is preferably 150 nm or more thicker than the absorption layer 51 in the circuit pattern formation region 80 surrounded by the light shielding frame 25. When the thickness is 150 nm or more, the reflectance of the light shielding frame 25 with respect to EUV can be made 0.25% or less. By setting the reflectance to 0.25% or less, there is no problem that the light shielding frame 25 is transferred onto the wafer by multiple exposure. In the case of FIGS. 1C and 1D, the buffer layer 41 has a structure between the multilayer reflective layer 21 and the absorption layer 51. When the reflective mask blanks 100, 200, 300, 400 of the present invention of FIGS. 1A to 1D are viewed from the surface, a circuit pattern forming region 80 and a light shielding frame 25 are formed as shown in FIG. Has been. In addition, as shown in FIG. 2B, the reflective mask blank 200 and the reflective mask blank 400 are exposed to the back conductive film 71 as shown in FIG. 2B, and the reflective mask blank 100 and the reflective mask blank 300 are back. As seen from FIG. 2, the substrate 11 is exposed as shown in FIG.

  The reflective mask blanks 100, 200, 300, and 400 of FIGS. 1A to 1D are designed to achieve a reflectivity of about 60% with respect to EUV light near 13.5 nm. It is a laminated film in which 40-50 pairs of molybdenum (Mo) and silicon (Si) are alternately laminated, and the uppermost layer is made of ruthenium (Ru). The layer adjacent to the Ru layer is a Si layer. The reason why Mo and Si are used is that the absorption (extinction coefficient) for EUV light is small and the difference in refractive index between Mo and Si EUV light is large. This is because it can be high. The uppermost Ru of the multilayer reflective layer 21 plays a role as a stopper in processing of the absorption layer 51 and a protective layer against chemicals during mask cleaning.

The buffer layer 41 of the reflective mask blanks 300 and 400 in FIGS. 1C and 1D is the uppermost layer of the multilayer reflective layer 21 adjacent to the buffer layer 41 when the absorbing layer 51 is etched or modified. It is provided to protect the Si layer and is composed of a chromium (Cr) nitrogen compound (CrN).
The absorbing layer 51 of the reflective mask blanks 100, 200, 300, and 400 in FIGS. 1A to 1D is a tantalum (Ta) nitrogen compound (TaN) that has a high absorption rate for EUV near 13.5 nm. It consists of As other materials, tantalum boron nitride (TaBN), tantalum silicon (TaSi), tantalum (Ta), and oxides thereof (TaBON, TaSiO, TaO) may be used.

The absorption layer 51 of the reflective mask blanks 100, 200, 300, and 400 in FIGS. 1A to 1D is provided with a low reflection layer having an antireflection function for ultraviolet light having a wavelength of 190 to 260 nm as an upper layer. An absorption layer having a two-layer structure may be used. The low reflection layer is for increasing the contrast and improving the inspection property with respect to the inspection wavelength of the mask defect inspection machine.
The back conductive film 71 of the reflective mask blanks 200 and 400 in FIGS. 1B and 1D is generally made of CrN, but it only needs to be conductive, so any material made of a metal material can be used. good.

The configuration of the reflective mask of the present invention will be described.
A reflective mask 101 produced from the reflective mask blank 100 of FIG. 1A is shown in FIG. A reflective mask 201 produced from the reflective mask blank 200 of FIG. 1B is shown in FIG. A reflective mask 301 prepared from the reflective mask blank 300 of FIG. 1C is shown in FIG. A reflective mask 401 made from the reflective mask blank 400 of FIG. 1D is shown in FIG. The reflective masks 101, 201, 301, 401 are circuit pattern regions formed by digging the buffer layer 41 when there is an absorption layer 51 and a buffer layer 41 above the multilayer reflective layer 21 in the circuit pattern formation region 80. 85. The light shielding frame 25 is preferably separated from the circuit pattern region 85 by 200 nm or more outside. By being separated by 200 nm or more, the influence of shadowing of the light shielding frame 25 can be prevented.

  FIG. 4A is a view of the reflective masks 101, 201, 301, 401 of the present invention shown in FIGS. The reflective masks 101, 201, 301, 401 are composed of a light shielding frame 25 and a circuit pattern region 85. FIG. 4B is a view of the reflective masks 201 and 401 of the present invention shown in FIGS. 3B and 3D as viewed from the back side, and the back surface conductive film 71 is exposed. FIG. 4C is a view of the reflective masks 101 and 301 of the present invention of FIGS. 3A and 3C as viewed from the back side, and the substrate 11 is exposed.

Next, a method for forming the light shielding frame of the reflective mask blank of the present invention will be described.
A reflective mask blank in which an electron beam resist 61 is applied on the absorption layer 51 shown in FIGS. 5A and 5B is prepared, and after forming a resist pattern of the light shielding frame 25 by electron beam lithography, fluorocarbon plasma or chlorine plasma. If necessary, the reflective mask blank 100 shown in FIGS. 1A and 1B, in which the light shielding frame 25 is formed by etching the absorption layer 51 with both plasmas and cleaning the resist film, or Get 200.

  Alternatively, a reflective mask blank in which an electron beam resist 61 is applied on the absorption layer 51 shown in FIGS. 5C and 5B is prepared, and after forming a resist pattern of the light shielding frame 25 by electron beam lithography, fluorocarbon plasma or The reflective mask blank shown in FIGS. 1C and 1D, in which the light-shielding frame 25 is formed by etching the absorption layer 51 with chlorine plasma and, if necessary, both plasmas and cleaning the resist film. Get 300 or 400.

Next, a reflective mask and a method for manufacturing the reflective mask will be described.
A reflective mask blank 100 or 200 having the light shielding frame 25 shown in FIGS. 1A and 1B is prepared, and after forming a resist pattern in the circuit pattern region 85 by electron beam lithography, fluorocarbon plasma or chlorine plasma, If necessary, the absorption layer 51 in the circuit pattern formation region 80 is etched from both plasmas, and the resist pattern is cleaned by removing the resist, thereby having a circuit pattern region 85 in which the circuit pattern is formed in the absorption layer 51. FIG. ), A reflective mask 101 or 201 shown in FIG.

  Alternatively, a reflective mask blank 300 or 400 on which the light shielding frame 25 shown in FIGS. 1C and 1B is formed is prepared, and after forming a resist pattern in the circuit pattern region 85 by electron beam lithography, fluorocarbon plasma or chlorine The absorption layer 51 in the circuit pattern formation region 80 is etched from the plasma, and if necessary, both plasmas, and then the buffer layer 41 is etched by chlorine plasma, and the resist is peeled and washed to form the absorption layer 51 and the buffer layer 41. A reflective mask 301 or 401 shown in FIGS. 3C and 3B having a circuit pattern region 85 in which a circuit pattern is formed is obtained.

  In the present invention, the light shielding frame 25 is formed before the circuit pattern region 85 is formed, and the absorption layer 51 of the light shielding frame 25 is thicker than the absorption layer 51 of the circuit pattern formation region 80. Since the multilayer reflective layer 21 is not removed in order to form the light shielding frame 25, the adhesion of particles to the circuit pattern region 85 can be suppressed. That is, it is possible to suppress deterioration of mask defect quality. In addition, since the multilayer reflective layer 21 is not removed to form the light shielding frame 25, there is no concern that several multilayer reflective layers 21 remain, and the intensity of reflected light generated from the reflective layer is suppressed, and the light shielding property is high. The light shielding frame 25 can be formed. For these reasons, there is an effect that a transfer pattern can be formed with high accuracy by using the reflective mask of the present invention.

Examples of the method for manufacturing a reflective mask blank and a reflective mask according to the present invention will be described below.
FIG. 6A shows a low thermal expansion glass substrate 111 prepared in this example. Thereafter, a back surface conductive film 171 for electrostatic chucking was formed on the back surface as shown in FIG. A 40-pair reflective layer 121 of Mo and Si designed to have a reflectance of about 64% with respect to EUV light having a wavelength of 13.5 nm was laminated on the glass substrate 111 as shown in FIG. Subsequently, an absorption layer 151 made of TaN was formed by a sputtering apparatus (FIG. 6D). The film thickness of the absorption layer 151 at this time was 200 nm. Thus, the reflective mask blank 202 was completed.

Next, a reflective mask blank 203 in which an electron beam resist 161 is applied on the absorption layer 151 shown in FIG. 7A is prepared, and the reflective mask blank 203 is subjected to electron beam lithography, dry etching, and resist peeling cleaning. A reflective mask blank 204 on which the light shielding frame 125 was formed was produced (FIG. 7B). For electron beam lithography, a chemically amplified positive resist FEP171 (manufactured by Fuji Film Electronics Materials) is used to draw a dose of 15 μC / cm by a drawing machine JBX9000 (manufactured by JEOL), and then TMAH (tetramethylammonium hydroxide). A resist pattern was formed with 2.38% developer. Cl ₂ inductively coupled plasma was applied to the etching of the absorption layer 151. Subsequently, the reflective mask blank 204 was subjected to electron beam lithography, dry etching, and resist film cleaning to form a circuit pattern region 185, thereby producing a reflective mask 205 having a light-shielding frame of the present invention (FIG. 7C). )). For electron beam lithography, a chemically amplified positive resist FEP171 (manufactured by FUJIFILM Electronics Materials) is used to draw a dose of 18 μC / cm by a drawing machine JBX3040 (manufactured by JEOL Ltd.), and then a resist is developed with a TMAH 2.38% developer. A pattern was formed. Cl ₂ inductively coupled plasma was applied to the etching of the absorption layer 151.

The reflectance of EUV light (wavelength: 13.5 nm) on the absorption layer side of the reflective mask 205 in FIG. 7C was measured. The reflectance in the region other than the light shielding frame 125 is 1.24%, whereas the reflectance of the light shielding frame 125 is 0.00%. Further, in order to investigate the influence of OoB, the reflectance at a wavelength in the near-infrared region from vacuum ultraviolet rays was measured and found to be 0.00%.
Exposure using 13.5 nm EUV as a light source was performed using the reflective mask 205 of FIG. 7C, and four adjacent chips were transferred onto the semiconductor substrate. In the adjacent chip, although a part of the region corresponding to the light shielding frame on the manufactured reflective mask was overlapped, the resist exposure in the region on the semiconductor substrate was not confirmed.

DESCRIPTION OF SYMBOLS 11 ... Board | substrate 21 ... Multilayer reflection layer 25 ... Light-shielding frame 41 ... Buffer layer 51 ... Absorption layer 61 ... Electron beam resist 71 ... Back surface conductive film 80 ... Circuit pattern Formation area 85 ... Circuit pattern area 100, 200, 300, 400, 202, 203, 204 ... Reflective mask blank 101, 201, 301, 401, 205 ... Reflective mask 111 ... Glass substrate 121 ... multilayer reflective layer 125 ... light shielding frame 151 ... absorbing layer 161 ... electron beam resist 171 ... back conductive film 185 ... circuit pattern region

Claims (6)

  Circuit pattern formation surrounded by a light shielding frame and the light shielding frame in a reflective mask blank comprising a substrate, a multilayer reflective layer formed on the surface of the substrate, and an absorption layer formed on the multilayer reflective layer A reflective mask blank, wherein the absorption layer of the light shielding frame is thicker than the absorption layer of the circuit pattern formation region.   The reflective mask blank according to claim 1, wherein an absorption layer of the light shielding frame is 150 nm or more thicker than an absorption layer of the circuit pattern region.   The reflective mask blank according to claim 1, wherein the light shielding frame has a reflectance of 0.25% or less with respect to EUV light.   4. The method of manufacturing a reflective mask blank according to claim 1, wherein the light-absorbing layer is partially removed by electron beam lithography or photolithography and dry etching to form the light shielding frame. A method for manufacturing a reflective mask blank.   A circuit pattern region is formed in the circuit pattern formation region of the reflective mask blank according to any one of claims 1 to 3 or the reflective mask blank manufactured by the method of manufacturing a reflective mask blank according to claim 4. A reflective mask characterized in that it is manufactured in the manner described above.   The reflective mask according to claim 5, wherein the light shielding frame is spaced 200 nm or more outward from the circuit pattern region.

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