JP2014216609A - Reflective mask blank, manufacturing method thereof and reflective mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective mask blank comprising a fiducial mark which has low defectiveness and high detection accuracy in a blank defect inspection machine or a mask drawing machine, a manufacturing method thereof and a reflective mask.SOLUTION: In the reflective mask blank, before depositing a multilayer reflection layer, a resist pattern is formed on a substrate and after at least the multilayer reflection layer is deposited, the resist pattern is removed (lifted off), thereby forming a fiducial mark. In the fiducial mark formed by this method, a sidewall of the mark is vertical and smooth, thereby providing the reflective mask blank comprising the fiducial mark which reduces the risk of defect generation and improves detection accuracy.

Description

  The present invention relates to a reflective mask blank and a method for manufacturing a reflective mask, and in particular, a reflection used in a semiconductor manufacturing apparatus using EUV lithography using extreme ultraviolet (hereinafter referred to as “EUV”) as a light source. The present invention relates to a method for manufacturing a mold mask blank and 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. Therefore, a photomask (hereinafter referred to as a mask) as an original plate must be a reflection type mask because a conventional transmission type mask cannot be used.

(Description of EUV mask and blank structure)
The reflective mask blank will be described with reference to FIG.
The reflective mask blank that is the basis of such a reflective mask includes a back conductive layer 17, a low thermal expansion substrate 16, a multilayer reflective layer 15, a protective layer 14, an absorption layer 13, an low reflective layer 12, The resist film 11 is configured. When processing from the reflective mask blank to the reflective mask, the absorption layer is partially removed by EB lithography and etching technique to form a circuit pattern composed of the absorption portion and the reflection portion. The light image reflected by the reflection type mask thus manufactured is transferred onto the semiconductor substrate via the reflection optical system.

(Explanation of film thickness and phase defect of multilayer reflective layer of EUV mask)
The multilayer reflective layer is constituted by alternately depositing Mo with a thickness of 3 nm and Si with a thickness of 4 nm, for example, and using the interference effect that EUV light transmitted through the material is repeatedly reflected, Reflectivity is increased.

  In particular, in EUV lithography having an extremely short wavelength, generation of particles is not allowed when a multilayer reflective layer is formed on a mask substrate. Since the wavelength of the exposure light is short, minute irregularities on the mask substrate affect the quality of the pattern transferred onto the wafer. This minute unevenness defect is called a phase defect, and even if the height is several nanometers, a dimensional error of a fine LSI pattern cannot be allowed.

  Such a minute unevenness defect is formed by a foreign matter that has been deposited on the unevenness or foreign matter on the substrate surface under the deposited multilayer reflective layer and dropped during the deposition of the multilayer reflective layer.

  Several correction methods have been proposed for such a micro uneven defect (phase defect), but the type of the defect is limited and practically difficult (see, for example, Patent Document 1). ). Therefore, in EUV masks, it is most important to prevent the occurrence of such phase defects. However, since the layer structure is more complicated than that of general transmission masks, the blank quality is far from being defect-free. ing.

JP 2010-034129 A

  In order to solve such problems, it has been proposed to grasp the position of the phase defect by inspection and form (draw) the pattern so as to avoid the phase defect before forming the pattern on the EUV mask. Yes. Specifically, by covering the phase defect with the absorption layer, the phase defect is not transferred, and a reflected light having a desired pattern without a defect can be obtained from the multilayer reflective layer without the absorption layer. it can. Therefore, a manufacturing method that enables the production of a high-quality reflective mask without making difficult corrections has been studied.

  In order to grasp the exact position of the phase defect and form a pattern while avoiding the phase defect accurately, it is necessary to form a mark (reference mark) called a fiducial mark on the EUV mask. Since the fiducial mark is used as a reference, it is important that a blank defect inspection machine (DUV light or EUV light) and a mask drawing machine (EB) can be detected with high accuracy and reproducibility.

  A conventional method for forming fiducial marks in a reflective mask will be described with reference to FIG. FIG. 2A shows a reflective type in which a second resist film 18 is applied on the multilayer reflective layer 15 formed on one surface of the substrate 16 and a back surface conductive layer 17 is provided on the other surface of the substrate 16. It is a schematic cross section of a mask blank. A resist pattern of a fiducial mark is formed by photolithography or electron beam lithography (FIG. 2B), then a multilayer reflective layer is dug by etching (FIG. 2C), and then the second resist film 18 is formed. By removing the film, a fiducial mark is formed (FIG. 2D). Furthermore, the reflective mask blank with a fiducial mark is completed by sequentially laminating the protective layer 14, the absorption layer 13, the low reflection layer 12, and the resist film 11 (FIG. 2 (e)).

  Since the fiducial mark thus formed is etched on the multilayer reflective layer 15, the etched surface (side wall and bottom surface) of the multilayer reflective layer becomes rough, and an increase in defects is inevitable (FIG. 3). (A) to (c)). That is, defects are increased by forming fiducial marks to avoid defects. In addition, in the etching of the multilayer reflective layer, it is difficult to etch vertically, and the pattern side wall is often tapered or bowed (rounded curved surface) (FIG. 3 (d)). When a mark is detected by a mask drawing machine, the edge of the mark becomes dull. Therefore, the mark detection accuracy and reproducibility are low, and a sufficient function as a fiducial mark cannot be achieved.

  Accordingly, the present invention seeks to solve the problems of the conventional forming method as described above, and provides a reflective mask blank having a low defect and high detection accuracy and a method of manufacturing the reflective mask. The purpose is to provide.

In order to achieve the above object, the invention of claim 1 of the present invention provides:
A method of manufacturing a reflective mask blank having a fiducial mark,
Forming a resist pattern corresponding to the fiducial mark on the substrate;
Forming a multilayer reflective layer on the substrate on which the resist pattern is formed;
And a step of removing (lifting off) the resist pattern.

The invention of claim 2
2. The method of manufacturing a reflective mask blank according to claim 1, further comprising a step of forming a protective layer and an absorption layer on the substrate from which the resist pattern has been removed.

The invention of claim 3
3. The reflective mask blank manufacturing method according to claim 1, wherein the resist pattern is formed by photolithography or electron beam lithography.

The invention of claim 4
In the step of forming a multilayer reflective layer by sequentially laminating reflective layers, the defect is inspected after the reflective layers are laminated, and the position of the defect is specified using a resist pattern corresponding to a fiducial mark. It is set as the manufacturing method of the reflective mask blank in any one of Claims 1-3.

The invention of claim 5
A reflective mask blank manufactured by the method for manufacturing a reflective mask blank according to claim 1.

The invention of claim 6
A reflective mask is produced using the reflective mask blank according to claim 5.

  According to the present invention, since the fiducial mark detection accuracy can be increased in the blank defect inspection machine, the phase defect position can be accurately grasped, and the fiducial mark detection accuracy is also high in the mask drawing machine. Therefore, phase defects detected by a blank defect inspection machine can be avoided with high accuracy. Furthermore, since a fiducial mark can be produced without performing an etching process, a reflective mask blank having a low defect can be obtained. Further, in the fiducial mark manufacturing method of the present invention, since a resist pattern that is later removed by lift-off can be used as a fiducial mark when forming a multilayer reflective layer, defect inspection for each layer during the formation of the multilayer reflective layer It is possible, and it is possible to manufacture a reflective mask blank of higher quality by performing a defect correction process immediately after detecting a defect. As described above, it is possible to provide a high-quality reflective mask blank and a reflective mask.

It is a schematic cross section of the conventional reflective mask blank. It is a schematic cross-sectional view of a reflective mask blank for sequentially explaining each process of forming fiducial marks in conventional reflective mask manufacturing. It is a schematic cross-sectional view of a badly formed fiducial mark formed by an etching process in the conventional reflective mask manufacturing. It is a schematic cross section of a reflective mask blank of the first example for sequentially explaining each process of forming fiducial marks using lift-off according to an embodiment of the present invention. It is a schematic cross section of the reflective mask blank of the 2nd example for demonstrating in order each process of fiducial mark formation using the lift-off which concerns on embodiment of this invention. It is a schematic cross section of the reflective mask blank of the 3rd example for explaining each process of fiducial mark formation using lift-off concerning the embodiment of the present invention in order. It is a schematic cross section of the reflective mask blank of the 4th example for explaining each process of fiducial mark formation using lift-off concerning the embodiment of the present invention in order. It is a top view of the reflective mask blank with a fiducial mark into which the foreign material which concerns on the Example of this invention was mixed intentionally.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  First, a reflective mask blank manufacturing method according to an embodiment of the present invention will be described in detail with reference to FIG.

  FIG. 4 is a schematic cross-sectional view of a reflective mask blank of a first example for sequentially explaining a forming method using lift-off in forming a fiducial mark according to an embodiment of the present invention. FIG. 4A is a schematic view of a reflective mask blank in which a third resist film 19 is applied to one surface on a low thermal expansion substrate 16 and a back surface conductive layer 17 is provided on the other surface of the low thermal expansion substrate 16. It is sectional drawing. Next, a fiducial mark by a resist pattern is formed by photolithography or electron beam lithography (FIG. 4B). Next, the multilayer reflective layer 15 is deposited (FIG. 4C), and the third resist film 19 is removed by lift-off (FIG. 4D). Thereafter, the protective layer 14, the absorption layer 13, the low reflection layer 12, and the resist film 11 are sequentially laminated to complete a reflective mask blank with a fiducial mark (FIG. 4E). The overall process in this case is as follows: FIG. 4A → FIG. 4B → FIG. 4C → FIG. 4D → FIG.

  Alternatively, as a second example, after forming a fiducial mark with a resist pattern in FIG. 4B, the multilayer reflective layer 15 and the protective layer 14 are sequentially laminated (FIG. 5F), and then the third resist film 19 may be removed by lift-off (FIG. 5G). Thereafter, the absorption layer 13, the low reflection layer 12, and the resist film 11 are sequentially laminated to complete a reflective mask blank with a fiducial mark (FIG. 5 (h)). The entire process in this case is as follows: FIG. 4A → FIG. 4B → FIG. 5F → FIG. 5G → FIG.

  Alternatively, as a third example, after forming the fiducial mark by the resist pattern in FIG. 4B, the multilayer reflective layer 15, the protective layer 14, and the absorption layer 13 are sequentially stacked (FIG. 6I), The third resist film 19 may be removed by lift-off (FIG. 6 (j)). Thereafter, the low reflective layer 12 and the resist film 11 are sequentially laminated to complete a reflective mask blank with a fiducial mark (FIG. 6 (k)). The overall process in this case is as shown in FIG. 4 (a) → FIG. 4 (b) → FIG. 6 (i) → FIG. 6 (j) → FIG.

  Alternatively, as a fourth example, after forming the fiducial mark by the resist pattern in FIG. 4B, the multilayer reflective layer 15, the protective layer 14, the absorbing layer 13, and the low reflective layer 12 are sequentially laminated (FIG. 7). (L)) The third resist film 19 may be removed by lift-off (FIG. 7 (m)). Thereafter, a resist film 11 is applied to complete a reflective mask blank with a fiducial mark (FIG. 7 (n)). The overall process in this case is as follows: FIG. 4A → FIG. 4B → FIG. 7L → FIG. 7M → FIG.

  Thus, in the fiducial mark forming method of the present invention, a resist pattern is formed prior to the formation of the multilayer reflective layer, and then the resist pattern is removed by lift-off after at least the multilayer reflective layer is formed. This is very important. By doing so, a fiducial mark whose side wall is smooth and vertical can be obtained. This is because the side walls of the resist pattern formed by lithography before forming the multilayer reflective layer are smooth and vertical if the optimal exposure conditions are used for the resist.

  The lithography in the fiducial mark forming method of the present invention may be either electron beam lithography or photolithography, but it is necessary to determine the conditions for forming a smooth and vertical resist pattern in advance by determining the lithography conditions. desirable. This is because in either case of electron beam lithography or photolithography, there is an optimum range for the dose (exposure amount). That is, if the dose amount is too large or too small, the line edge roughness is deteriorated (= surface roughness of the pattern side wall surface occurs), and the perpendicularity is also lowered.

  On the other hand, in the conventional fiducial mark forming method by dry etching, the side wall of the digging portion is unavoidable. In general, even when dry etching is performed on a single material, side wall roughness is generated to some extent. Particularly, in EUV mask blanks, side wall roughness is considerably large in dry etching of a multilayer reflective layer made of a plurality of different materials. Therefore, the conventional method has a high risk of occurrence of defects from the side walls. Also, the dry etching digging part tends to be tapered or bowed as a whole, so the detection accuracy and reproducibility when finally detecting the fiducial mark with a blank defect inspection machine or mask drawing machine is high. Low.

  In the fiducial mark forming method of the present invention, since the bottom surface of the fiducial mark portion is the substrate surface that is not damaged, the bottom surface of the digging portion does not become rough when the dry etching method is used. For this reason, in the method of the present invention, the risk of occurrence of defects from the bottom surface is low, and the advantage on the defect surface is great.

  As described above, in the present invention, since the fiducial mark can be formed without performing the etching process, the etched surface (side wall or bottom surface) of the multilayer reflective layer by the etching process is not roughened, and the low defect blank. Can be produced. Further, since the edge of the fiducial mark is sharp, the mark detection accuracy is high, and an accurate phase defect position can be grasped by a drawing machine, an inspection machine or the like.

Next, Embodiment 1 of the present invention will be described with reference to FIGS. 2 (e) and 4 (e).
FIG. 2E is a reflective mask blank with a fiducial mark produced by a conventional etching process, and FIG. 4E is a reflective mask blank with a fiducial mark of the present invention produced by lift-off. . The fiducial mark of this example is a cross mark having a line width of 1 μm and a length of 500 μm for both blanks, and four locations of the blank ((X, Y coordinates) = (72 mm, 72 mm), (72 mm, −72 mm), (-72 mm, 72 mm), (-72 mm, -72 mm)). With respect to these mask blanks, a blank defect inspection apparatus (M2350: Lasertec) was used to inspect a 140 × 140 mm area inside the arrangement of the fiducial marks at an inspection sensitivity setting of 90 nm. Further, as a reference, a similar inspection was performed on a reflective mask blank on which no fiducial mark was formed.

  First, the number of defects in the reflective mask blank without fiducial marks serving as a reference was 35. Moreover, the reflective mask blank with a fiducial mark of the present invention has 33 defects, and the defect quality is almost the same as that of the reflective mask blank without a fiducial mark. From this, it can be determined that there is no increase in defects due to the fiducial mark forming method of the present invention. On the other hand, the reflective mask blank with a fiducial mark of the conventional method has 891 defects, and in particular, many defects were detected near the fiducial mark, and the defect quality was poor.

  Next, both the fiducial mark FIG. 2 (e) formed by the conventional method and the fiducial mark FIG. 4 (e) formed by the method of the present invention are cut, and the cross-sectional shape of the mark is observed with a scanning electron microscope. As a result of measuring the side wall angle of the fiducial mark, the fiducial mark of the conventional method has a tapered shape as shown in FIG. 3 (d) and the side wall angle was 64 degrees. The fiducial mark was confirmed to be 90 degrees.

Next, Embodiment 2 of the present invention will be described with reference to FIG.
It was examined how accurately the blank mark defect can be drawn at the target location by the conventional and the present fiducial mark forming method. That is, in the case of an actual device pattern, this is the pattern shift accuracy. The blank defect in this evaluation does not include the defect caused by the fiducial mark formation, and the defect inspection of the substrate before the multilayer reflective layer film formation is performed in advance, and the phase defect caused by the substrate (that is, the substrate inspection) , And after detection of the multilayer reflective layer, 20 samples were arbitrarily extracted and used as objects of this evaluation. FIG. 8A shows an image of a blank defect map and a fiducial mark. A reflective mask blank with a fiducial mark according to the prior art and a reflective mask blank with a fiducial mark according to the present invention were prepared in the same manner as in Example 1.

  The drawing pattern was a square of 1000 nm (= 1 μm), drawn so as to overlap the coordinates detected by blank defect inspection (Teron610: KLA) after forming the multilayer reflective layer, and then an EUV mask pattern 22 was formed ( FIG. 8B). After that, by measuring the distance from the defect 20 to the edge of the square pattern with a length measuring SEM (E3620: ADVANTEST) (FIG. 8C), the center coordinates of the defect and the center of the drawing pattern 22 (rectangle) We investigated how much the coordinates were shifted. The results are shown in Table 1. In the conventional fiducial mark creation method, the amount of misalignment is an average of X = 225 nm and Y = 238 nm, whereas in the method of creating the fiducial mark 21 of the present invention, the amount of misalignment is an average and X = 66 nm and Y = 57 nm, and the amount of misalignment could be reduced to 1/3 or less (see Table 1). From this, it can be said that the pattern shift accuracy using the fiducial mark 21 of the present invention has improved three times or more.

As described above, according to the present embodiment, a reflective mask blank having a low defect and high detection accuracy and a method of manufacturing a reflective mask are manufactured by manufacturing a fiducial mark by lift-off. It is possible to provide.

DESCRIPTION OF SYMBOLS 10 ... Reflective type mask blank, 11 ... Resist film, 12 ... Low reflective layer, 13 ... Absorbing layer, 14 ... Protective layer, 15 ... Multilayer reflective layer, 16 ... Low thermal expansion substrate, 17 ... Back surface conductive layer, 18 ... 2nd Resist film, 19 ... third resist film, 20 ... phase defect, 21 ... fiducial mark, 22 ... pattern

Claims (6)

A method of manufacturing a reflective mask blank having a fiducial mark,
Forming a resist pattern corresponding to the fiducial mark on the substrate;
Forming a multilayer reflective layer on the substrate on which the resist pattern is formed;
And a step of removing (lifting off) the resist pattern.   2. The method of manufacturing a reflective mask blank according to claim 1, further comprising a step of forming a protective layer and an absorption layer on the substrate from which the resist pattern has been removed.   The method for manufacturing a reflective mask blank according to claim 1, wherein the resist pattern is formed by photolithography or electron beam lithography.   In the step of forming a multilayer reflective layer by sequentially laminating reflective layers, the defect is inspected after the reflective layers are laminated, and the position of the defect is specified using a resist pattern corresponding to a fiducial mark. The manufacturing method of the reflective mask blank in any one of Claims 1-3.   A reflective mask blank manufactured by the method for manufacturing a reflective mask blank according to claim 1.   A reflective mask produced by using the reflective mask blank according to claim 5.