JP2014107332A - Reflective mask and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective mask which is used for EUV lithography using, as a light source, extreme ultraviolet radiation having a light-shielding frame by which an image field (circuit pattern region) and a mask outer peripheral part are made electrically conductive and which does not cause defects due to electrification (charging up).SOLUTION: The outside of an image field formed in an absorber layer of EUV light is provided with a light-shielding frame which is a region where the absorber layer, a protective layer, and a multilayer reflection layer are removed and reflectivity of the EUV light is low. At least one or more of places of the light-shielding frame are made electrically conductive between the inside of an image field and the outside of the light-shielding frame.

Description

  The present invention relates to a reflective mask and a method for manufacturing the same, and more particularly to a reflective mask used in a semiconductor manufacturing apparatus using EUV lithography using extreme ultraviolet (hereinafter referred to as “EUV”) as a light source. And a method of manufacturing a reflective mask.

(Description of EUV lithography)
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. Accordingly, the photomask used as the original plate must be a reflective mask because a conventional transmissive mask cannot be used. (Hereinafter, in this specification, a reflective mask used for EUV lithography may be referred to as an EUV mask or an EUV reflective mask.)

(Description of EUV mask and blank structure)
A reflective mask blank, which is the basis of such a reflective mask, is a multilayer reflective layer (Mo and Si with a period of about 7 nm, 40 periods on a low thermal expansion substrate and having a high reflectance with respect to the exposure light source wavelength). = A total of 80 layers are formed) and an absorption layer having an exposure light source wavelength are sequentially formed. 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 mask having a structure having a multilayer reflection layer and a buffer layer between the absorption layers. When processing from a reflective mask blank to a reflective mask, the absorption layer is partially removed by EB (electron beam) lithography and etching technology, and in the case of a structure having a buffer layer, this is also removed and absorbed. A circuit pattern composed of a portion and a reflection portion is formed. The light image reflected by the reflection type mask thus manufactured is transferred onto the semiconductor substrate via the reflection optical system.

(Explanation of the film thickness and reflectance of the absorption layer of the EUV mask)
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, a shadow of the pattern itself is generated. Therefore, since the reflection intensity in the shadowed portion is smaller than that in the non-shadowed portion, the contrast is lowered, and the transferred pattern is blurred in the edge portion 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 portion and deviation from the design dimension, it is effective to reduce the thickness of the absorption layer and reduce the height of the pattern, but when the thickness of the absorption layer becomes small 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, since the thickness of the absorbing layer is too thick or too thin, it is currently in the range of 50 to 90 nm, and the reflectivity of the absorbing layer for EUV light (extreme ultraviolet light) is 0. About 5 to 2%.

(Explanation of multiple exposure of adjacent chips)
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 the productivity of increasing the number of chips that can be taken per wafer as much as possible. 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 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 provide 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 mask.

  In order to solve such a problem, by reducing the reflectance of the multilayer reflective layer by forming a groove dug from the absorption layer of the reflective mask to the multilayer reflective layer, the light shielding property with respect to the wavelength of the exposure light source is reduced. A reflective mask provided with a high light-shielding frame has been proposed (see, for example, Patent Document 1).

  A schematic plan view of a reflective mask 100 without a light shielding frame is shown in FIG. 1A, and a schematic cross-sectional view is shown in FIG. On the other hand, FIG. 1B shows a schematic plan view of a reflective mask 101 having a light shielding frame 11 dug up to the multilayer reflective layer, and FIG. In FIG. 1B, a light shielding frame 11 is formed so as to surround the image field (main pattern region) 10.

JP 2009-212220 A

  However, in a light-shielding frame in which the absorption layer and the multilayer reflective layer are simply dug, the image field (circuit pattern portion) inside the light-shielding frame and the outside of the light-shielding frame are electrically floating and conductive. I have not taken it. When this mask is used in an EUV exposure machine, photoelectrons are emitted from metal materials (mainly Ta, Mo, Si, etc.) used for the EUV mask due to the photoelectric effect of EUV light (extreme ultraviolet light), and are electrically positive. Is charged (charged up). This causes a problem that foreign matter in the exposure machine is attached and transfer defects are induced. Further, even in a length measurement SEM or electron beam inspection machine using an electron beam in the mask manufacturing process, negative charging occurs when the electron beam is irradiated, and there is a problem that the electron beam inspection cannot be performed.

  In Patent Document 1, as a countermeasure against such charging at the time of exposure, several layers (including at least Mo having conductivity) are left as the lowermost layer of the multilayer reflective layer, or Ta or Cr is contained in the base of the multilayer reflective layer. A structure in which one conductive layer is provided in advance is proposed.

However, the method of leaving the lowermost layers of the multilayer reflective layer is not uniform in the mask plane when etching the multilayer reflective layer by dry etching or wet etching. It ’s difficult.
Even if it can be processed, it is originally intended to reduce the reflectance of EUV light to zero as much as possible. In the area of the light shielding frame, it is contrary to the significance of forming the light shielding frame to leave several multilayer reflective layers. It becomes. For example, the reflectance when Mo / Si remains for two cycles is about EUV light reflectance of about 1.8% in calculation, and is less than 0.3%, which is said to be the standard of the light shielding frame of the EUV mask. It will be far higher.

  In the countermeasure by the structure in which one conductive layer containing Ta or Cr is previously provided on the base of the multilayer reflective layer, an additional layer of a new material is formed on the conventional EUV mask blank, which requires an increase in the manufacturing process. At the same time, there is a possibility of inviting new opportunities for defects.

  The present invention has been made in view of the above problems, and without adding a special process, the image field (circuit pattern portion) can be electrically connected to the outer peripheral portion of the mask, and defects caused by charging (charge-up) can be eliminated. It is an object of the present invention to provide a reflective mask having a light-shielding frame that does not invite.

In EUV masks with a digging-type shading frame that removes the multilayer reflective layer, the image field (circuit pattern area) inside the shading frame can be electrically connected to the outside of the shading frame. Charging can be prevented during measurement by SEM, pattern inspection by an electron beam inspection machine, and EUV exposure by EUV lithography.
For this reason, it is possible to provide a high-quality mask and to reduce the adhesion of foreign matter to the EUV mask during EUV exposure in EUV lithography, so that a high-quality wafer transfer pattern can be obtained. .

The schematic plan view of EUV reflective mask (a) which does not have a light-shielding frame, and EUV reflective mask (b) which has a light-shielding frame. FIG. 3 is a schematic cross-sectional view of an EUV reflective mask (a) having no light shielding frame and an EUV reflective mask (b) having a light shielding frame. The schematic plan view (a) and schematic sectional drawing (b) of the EUV reflective mask which has the light-shielding frame by this invention. FIG. 4 is a schematic plan view (a) (b) (c) of an EUV reflective mask having a light shielding frame according to the present invention. The schematic sectional drawing which shows an example of the manufacturing process (until mask pattern formation) of the EUV reflective mask which has the light-shielding frame by this invention. The schematic sectional drawing which shows an example of the manufacturing process (light-shielding frame formation) of the EUV reflective mask which has a light-shielding frame by this invention. The schematic plan view (a) and schematic sectional drawing (b) of the reflective mask by this invention.

(Configuration and layout of the reflective mask of the present invention)
Hereinafter, embodiments according to the present invention will be described with reference to the drawings.

First, the structure of the reflective mask of the present invention will be described. FIG. 3A is a schematic plan view of the structure of the reflective mask of the present invention, and FIG. 3B is a schematic cross-sectional view taken along the broken line AA ′ in FIG. .
In FIG. 3A, a light shielding frame 11 in which a multilayer reflective layer is dug so as to surround the image field (circuit pattern region) 10 is formed. However, the light shielding frame 11 is completely continuous, and the image field (circuit The conductive region 13 is formed in a part of the light shielding frame (side of the rectangular light shielding frame) instead of the configuration in which the pattern region 10 is closed.

  In FIG. 3B, the portion corresponding to the conductive portion 13 is the multilayer reflective layer 2, the protective layer 3, and the absorption layer 4 all remaining on the substrate 1, and the image field (circuit pattern region) 10 is separated from the multilayer reflective layer. It is electrically connected.

The conducting location 13 formed in a part of the light shielding frame is not limited to the example illustrated in FIG.
For example, a corner portion of the rectangular light shielding frame (FIG. 4A), one location on the bottom of the rectangular light shielding frame (FIG. 4B), two locations on the rectangular light shielding frame (FIG. 4C), etc. The formation location and number are arbitrary.
When setting the conduction points, the resistance value of the surface of the EUV mask material, the measurement environment using a length measuring SEM using an electron beam, the pattern inspection using an electron beam inspection machine, and the use environment such as an EUV exposure apparatus in EUV lithography Can be set appropriately.

  3 and 4, the multilayer reflective layer 2 and the absorption layer 4 remain, and the portion has EUV reflectance of about 0.5 to 2%, but the conductive portion 13 is shielded from light. At the time of EUV exposure in EUV lithography on a Si wafer, which is a part of the frame 11, the influence of multiple exposure (occurrence of a region where the chip outer peripheral portion overlaps between adjacent chips) is limited (at most) The exposure of the own chip + one exposure of the adjacent chip) and multiple exposure do not cause a problem that the outer periphery of the chip is exposed.

  In addition, since pattern chips are usually arranged in multiple faces on a single mask, if a conductive portion is formed in contact with the scribe (cutting) line between the chips, the problem of photosensitivity on the outer periphery of the chip is Further reduced.

  In addition, the structure of the conduction portion is not limited to the structure in which the multilayer reflection layer 2 and the absorption layer 4 are locally left as described above, but the EUV reflectance is low enough to be extraordinarily visible and electrical conduction is ensured. You may employ | adopt the structure removed together with the absorption layer 4, so that a part (including Mo) of the multilayer reflective layer 2 may be left.

The resistance value of the surface of the EUV mask material varies depending on the specific conductivity and film thickness of the material (Ta, Ru, Mo, Si) used, and the film formation state (porous, surface oxidation degree, etc.) of the material.
Prior to the formation of the conductive portion in the EUV mask, it is desired to confirm these parameter values and contribute to the design of the conductive portion having a suitable structure.
For example, when the resistance value of the surface of the EUV mask material is high, in order to ensure electrical continuity, the width of the conductive portion is widened, and a plurality of conductive portions are provided.

In addition, not only the physical properties of EUV mask materials, but also influences the design of conducting points depending on the usage environment, such as measurement with an electron beam measurement SEM, pattern inspection with an electron beam inspection machine, EUV exposure in EUV lithography, etc. May reach.
In the measurement by the length measuring SEM using the electron beam and the pattern inspection by the electron beam inspection machine, the condition of a large irradiation electron dose is assumed. It is effective to take measures such as having multiple conduction points.

In EUV exposure in EUV lithography, the kinetic energy of electrons emitted by the photoelectric effect is expressed by the following formula (1).
Since the wavelength of the EUV light to be irradiated is constant (13.5 nm), the kinetic energy is constant. However, when the intensity (light quantity) of the EUV light increases, the amount of emitted electrons also increases. The problem of (charge-up) becomes large, and in the same way, countermeasures such as widening the width of the conduction point and multiple conduction points are effective.
P in the formula (1) is called a work function, and is the minimum work amount (energy) necessary for ejecting electrons from the material, and has a value specific to the material.

eV = hμ-P (1)
<Left side>
eV: Kinetic energy of emitted electrons e: Charge of electrons V: Potential difference when energy of electrons is converted into potential difference <right side>
hμ: energy of incident light h: Planck's constant μ: frequency of light = 1 / λ (λ: wavelength = 13.5 nm for EUV)
P: Work function of plank material

  The reflective masks 102, 103, 104, and 105 shown in FIGS. 3 (a), 4 (a), 4 (b), and 5 (c) are all formed on the surface of the substrate 1 with a multilayer reflective layer 2, a protective layer 3, and an absorbing layer. 4 are sequentially formed. The back surface conductive film 5 is formed on the back surface of the substrate 1. A buffer layer may be formed between the protective layer 3 and the absorption layer 4. The buffer layer is a layer provided so as not to damage the underlying protective layer 3 when the mask pattern of the absorption film 4 is corrected.

  The reflective masks 102, 103, 104, and 105 include a pattern region 10 in which the absorption layer 4 is processed, and an absorption layer 4, a protective layer 3, and a multilayer reflection layer 2 on the outer peripheral portion (if there is a buffer layer, the buffer layer also Including a light shielding frame 11 formed by removing all layers.

(Details of the configuration of the reflective mask of the present invention: multilayer reflective layer, protective layer, buffer layer)
The multilayer reflective layer 2 in FIG. 3A is designed to achieve a reflectance of about 60% with respect to EUV light, and is a laminated film in which 40-50 pairs of Mo and Si are alternately laminated. The uppermost protective layer 3 is made of Ru (ruthenium) having a thickness of 2 to 3 nm or Si having a thickness of about 10 nm. The layer adjacent to the Ru layer is a Si layer.
The reason why Mo or Si is used in the multilayer reflective layer 2 is that the absorption (extinction coefficient) with respect to EUV light is small and the difference in refractive index between Mo and Si between EUV light is large, so that the interface between Si and Mo. This is because the reflectance at can be increased.
When the protective layer 3 is Ru, it plays a role as a protective layer against an etching stopper in processing the absorption layer 4 and a chemical solution during mask cleaning. When the protective layer 3 is Si, there may be a buffer layer between the absorption layer 4 and the protective layer 3. The buffer layer is provided to protect the Si layer, which is the uppermost layer of the multilayer reflective layer 2 adjacent to the bottom of the buffer layer, during etching or pattern modification of the absorption layer 4, and a chromium (Cr) nitrogen compound ( CrN).

(Details of the configuration of the reflective mask of the present invention: absorption layer)
The absorption layer 4 in FIG. 3A is made of a nitrogen compound (TaN) of tantalum (Ta) having a high absorption rate with respect to EUV. As other materials, tantalum boron nitride (TaBN), tantalum silicon (TaSi), tantalum (Ta), and oxides thereof (TaBON, TaSiO, TaO) may be used.

  The absorption layer 4 in FIG. 3A may be an absorption layer having a two-layer structure in which an upper layer is provided with a low reflection layer having an antireflection function with respect to ultraviolet light having a wavelength of 190 to 260 nm. 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.

(Details of Configuration of Reflective Mask of the Present Invention: Back Conductive Film)
The back conductive film 5 in FIG. 3A is generally made of chromium nitride (CrN). However, it is sufficient that the conductivity is higher than the electrostatic chuck can be used. Any material can be used.
Although FIG. 3A shows the configuration having the back surface conductive film 5, a reflective mask blank and a reflective mask that do not have the back surface conductive film 5 may be used.

(Details of the configuration of the reflective mask of the present invention: digging a multilayer reflective layer)
A method for forming the light shielding frame 11 of the reflective mask of the present invention will be described.
For an EUV mask with a pattern formed in the image field (main pattern region) or an EUV mask blank with a pattern to be formed later, a resist pattern having an opening at the periphery of the image field is formed by photolithography or electron beam lithography. Form.
Although the opening is preferably a rectangular strip, in the present invention, as described above, the opening is not completely continuous, and a non-opening is provided so that a part of the light-shielding frame later constitutes a conduction point. .
Next, the absorption film 4 and the protective layer 3 in the opening portion of the resist pattern are removed by dry etching using fluorine-based or chlorine-based gas (or both).
Next, the multilayer reflective layer 2 is penetrated and removed by dry etching using a fluorine-based gas and / or chlorine-based gas, or wet etching using an alkaline solution or an acidic solution.

When penetrating / removing the multilayer reflective layer 2 by dry etching, the fluorine-based gas and / or the chlorine-based gas is used for both Mo and Si, which are the materials of the multilayer reflective layer 2. It is for having. Examples of the fluorine-based gas used at this time include CF ₄ , C ₂ F ₆ , C ₄ F ₈ , C ₅ F ₈ , CHF ₃ , SF ₆ , ClF ₃ , Cl ₂ , and HCl.

  An etching solution for penetrating / removing the multilayer reflective layer 2 by wet etching needs to be suitable for etching Mo and Si that are materials of the multilayer reflective layer 2. For example, TMAH (tetramethylammonium hydroxide), KOH (potassium hydroxide), EDP (ethylenediamine pyrocatechol) and the like are suitable as the alkaline solution. As the acidic solution, a mixed solution of nitric acid and phosphoric acid is suitable, but hydrofluoric acid, sulfuric acid, and acetic acid may be added thereto.

The pattern formation in the image field of the reflective mask may be performed before or after the formation of the light shielding frame 11 (conduction portion 13).
As described above, the light shielding frame formed by removing the absorption layer 4, the protective layer 3, and the multilayer reflective layer 2 so as to define the image field of the reflective mask is electrically connected to a part of the light shielding frame. A reflective mask that is formed so as to have a portion and prevents charging (charge-up) in the image field is obtained.

EXAMPLES Hereinafter, the manufacturing method of the reflective mask of this invention is demonstrated in detail by an Example.
A reflective mask blank 201 shown in FIG.
The reflective mask blank 201 includes a Mo and Si 40-pair multilayer reflective layer 2 designed to have a reflectance of about 64% with respect to EUV light having a wavelength of 13.5 nm on the substrate 1. An Ru protective layer 3 having a thickness of 2.5 nm is formed thereon, and an absorption layer 4 made of tantalum silicide (TaSi) having a thickness of 70 nm is further formed thereon.

  A positive chemically amplified resist 9 (FEP171: manufactured by FUJIFILM Electronics Materials) is applied to the reflective mask blank 201 with a film thickness of 300 nm (FIG. 5B), and an electron beam drawing machine (JBX9000: After drawing by JEOL Ltd., development was performed at 110 ° C .; 10 minutes by PEB (Post Exposure Bake) and a spray developing machine (SFG3000: Sigma Meltech) to form a resist pattern on the resist portion (FIG. 5 ( c)).

Next, the absorption layer 4 is removed by etching with CF ₄ plasma and Cl ₂ plasma using a dry etching apparatus (VLR700 series: Unaxis) (FIG. 5 (d)), and then the resist is removed and cleaned. A reflective mask 211 having the evaluation pattern shown in FIG.
As the evaluation pattern, a chip of a 1: 1 line & space pattern having a dimension of 200 nm was arranged in the center of the mask with six faces. The size of the pattern region was 10 cm × 10 cm. Here, the interval of the scribe lines between the chips was 5 mm.

Next, the light shielding frame 11 was formed around the image field (pattern region) 10 of the reflective mask 211 having the above-described evaluation pattern.
The i-line resist 29 is applied to the reflective mask 211 (FIG. 6A) with a film thickness of 500 nm (FIG. 6B), and drawing / development is performed there by a laser drawing machine (ALTA3000: manufactured by Applied Materials). By doing so, a resist pattern was formed by removing an area that will later become the light shielding frame 11 (FIG. 6C).
At this time, the opening width of the resist pattern was 3 mm, and the resist pattern was arranged at a distance of 3 μm outward from the pattern edge of the circuit pattern region of 10 cm × 10 cm in the center of the mask.

Next, using a dry etching apparatus (VLR700 series: Unaxis), CHF ₃ plasma (pressure in the dry etching apparatus 50 mTorr, ICP (inductively coupled plasma) power 500 W, RIE (reactive ion etching) power 2000 W, CHF ₃ : With a flow rate of 20 sccm and a processing time of 6 minutes, which are the same in the following notation), the absorption layer 4 and the multilayer reflective layer 2 in the opening of the resist are penetrated and removed by vertical dry etching (FIG. 6). (D) (e)) Finally, the resist was removed and washed with a sulfuric acid-based stripping solution and ammonia hydrogen peroxide solution to remove the remaining resist by dry etching and wet etching (FIG. 6F). ).

3A and 3B show a reflective mask 102 manufactured according to this example.
The width of the light-shielding frame 11 in the reflective mask 102 is 3 mm, the width of the scribe line is 5 mm, and the width of the conductive portion 13 is 1 mm.

In the manufacturing process (shading frame forming process) of the reflective mask 102 in the present embodiment, a reflective mask including the light shielding frame 11 that does not have the conductive portion 13 is formed by the same process except that the conductive portion 13 is not formed. It produced as a comparative sample and measured by length measurement SEM about both masks.
In the mask of the comparative sample that does not have the conduction point 13, the drift phenomenon of the SEM image due to the charge-up occurred in the image field, which hindered measurement inside the light shielding frame, but in the mask according to the present embodiment, No charge-up occurred and measurement was possible without problems.

  The present invention is useful for a reflective mask or the like.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Multilayer reflective layer 3 Protective layer 4 Absorbing layer 5 Back surface conductive film 9 Resist 10 Image field (pattern region)
11 Light shielding frame 12 Outside light shielding frame 13 Conductive point 29 Resist 100 Reflective mask (no light shielding frame)
101 Reflective mask (with shading frame)
102, 103, 104, 105 Reflective mask 201 according to the present invention Reflective mask blank 211 Reflective mask (before light shielding frame formation)

Claims (4)

A reflective mask blank in which at least a multilayer reflective layer for reflecting EUV light, a protective layer for protecting the multilayer reflective layer, and an absorbing layer for absorbing EUV light are formed in this order on a substrate. In a reflective mask produced by patterning the absorption layer using
Outside the circuit pattern region (image field) formed in the absorption layer, a light shielding frame that is a low EUV light reflectance region from which the absorption layer, the protective layer, and the multilayer reflective layer are removed is provided. ,
A reflective mask comprising at least one portion of the light shielding frame having a portion that electrically connects a circuit pattern region (image field) and the outside of the light shielding frame.   The electrically conductive part is formed by leaving a multilayer reflective layer, a protective layer, and an absorption layer locally on the substrate in a part of the rectangular light shielding frame, and electrically through the metal material constituting the multilayer reflective layer. The reflective mask according to claim 1, wherein the reflective mask is electrically connected.   The conductive part formed in a part of the light shielding frame is one of the corner part of the rectangular light shielding frame and one or more places on the side of the rectangular light shielding frame, and between each chip in the circuit pattern area (image field) The reflective mask according to claim 2, wherein the reflective mask is formed in contact with a scribe line. A method of manufacturing a reflective mask,
Forming a multilayer reflective layer on one surface of the substrate;
Forming an absorption layer on the multilayer reflective layer;
Forming a circuit pattern on the multilayer reflective layer;
After defining an opening pattern composed of a discontinuous frame-like region so as to surround the outside of the circuit pattern, dry etching or wet etching is performed until one surface of the substrate is exposed to the multilayer reflective layer and the absorbing layer. And a step of forming a light shielding frame that is removed by the step of manufacturing a reflective mask.