JP2012049243A - Reflective mask for euv exposure and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective mask having an auxiliary pattern for EUV exposure, which prevents the auxiliary pattern from chipping, peeling from a surface of a substrate or falling, and is relatively easily manufactured and can transfer a pattern with high accuracy, and to provide a method for manufacturing the same.SOLUTION: The reflective mask for EUV exposure comprises at least: the substrate; a reflective layer which is formed on the substrate and reflects EUV light; a buffer layer which is formed on the reflective layer and prevents etching damage in the reflective layer; and an absorber layer which is formed on the buffer layer and absorbs the EUV light. The mask pattern of the reflective mask for EUV exposure comprises a main pattern to be transferred on a wafer and the auxiliary pattern which is provided in a vicinity of the main pattern and has a size equal to or less than the resolution limit of a projection optical system. The auxiliary pattern comprises a buffer layer.

Description

  The present invention is for EUV exposure for transferring a mask pattern onto a wafer using extreme ultraviolet light (Extreme Ultra Violet: hereinafter referred to as EUV) used for manufacturing high-density integrated circuits such as LSI and VLSI. In particular, the present invention relates to a reflective mask in which an auxiliary pattern is disposed in the vicinity of a main pattern and a method for manufacturing the same.

  Along with the miniaturization of semiconductor devices, a photolithography technique for transferring a pattern onto a wafer using a photomask is currently being performed by an optical projection exposure apparatus using an ArF excimer laser. In these exposure methods using an optical projection exposure apparatus, the resolution limit will eventually be reached, so a new pattern forming method such as a direct drawing technique using an electron beam drawing apparatus, an imprint lithography technique, or an EUV exposure technique has been proposed. .

  Among these new lithography techniques, the EUV exposure technique is a technique that uses EUV light having a wavelength shorter than that of an excimer laser and a wavelength of about 13.5 nm, and reduces the mask pattern to about 1/4, and exposes it. It is regarded as the limit of shortening the wavelength of ultraviolet exposure, and is attracting attention as a lithography technique for semiconductor devices. In EUV exposure, since a refractive optical system cannot be used due to a short wavelength, a reflective optical system is used, and a reflective mask has been proposed as a mask.

  The reflective mask for EUV exposure includes at least a substrate, a reflective layer that reflects EUV light in a multilayer film structure provided on the substrate, and an absorber layer that absorbs EUV light provided on the reflective layer, The mask pattern is formed by the absorber layer. The EUV light incident on the reflective mask is reflected by the reflective layer, absorbed by the absorber layer, and a reduced transfer pattern is formed on the wafer by the reflected EUV light.

  In the EUV exposure technology, in order to further improve the pattern transfer resolution by EUV exposure, the principle of the phase shift mask used in conventional ultraviolet and excimer laser exposure is changed to EUV exposure using a reflective optical system. Development is also underway. As a reflection type phase shift mask, proposals have been made to locally change the phase of exposure light and improve the resolving power by using interference between light whose phase has been changed and light whose phase has not changed.

  In a photomask, as one form of a phase shift mask, near the resolution limit of the projection optical system and on the wafer near a pattern such as a circuit pattern (hereinafter referred to as a main pattern) transferred onto the wafer. Has proposed a photomask having an auxiliary pattern in which a pattern that is not transferred (hereinafter referred to as an auxiliary pattern) is arranged (see, for example, Patent Document 1).

  For example, by arranging one or more fine auxiliary patterns around an isolated pattern, a photomask in which auxiliary patterns are arranged forms a pattern configuration similar to a periodic pattern, and the effect of increasing the depth of focus can be obtained. Thus, the auxiliary pattern is very fine, and the auxiliary pattern itself is not transferred because it does not form an image on the semiconductor substrate, but is excellent in improving the resolution of the main pattern. The auxiliary pattern is also called an assist bar or a scattering bar. For example, when the main pattern is a rectangular line-type pattern, the auxiliary pattern is also a rectangular pattern, and the length is set according to the length of the main pattern and the design rule, and is generally longer than the main pattern. In many cases, it is formed several times to several tens of times the auxiliary pattern line width dimension, and is formed in parallel to the main pattern at a position about several times the auxiliary pattern line width dimension away from the main pattern.

  Conventionally, since EUV exposure is a pattern forming method with essentially high resolving power, an auxiliary pattern is considered unnecessary for the mask. However, in order to further improve the resolving power, the 22 nm node and beyond are supported. There is an increasing demand for using a pattern, and a reflective mask for EUV exposure having an auxiliary pattern has also been proposed (see, for example, Patent Document 2 and Patent Document 3).

  6 and 7 are cross-sectional schematic diagrams (FIGS. 6A and 7A) and plan views (FIGS. 6B and 6B) of the conventional reflective masks 60 and 70 for EUV exposure having auxiliary patterns. 7 (b)), FIG. 6 shows an example of a line-type mask pattern, and FIG. 7 shows an example of a hole-type mask pattern. As shown in FIGS. 6 and 7, multilayer reflective films 62 and 72 are formed on the substrates 61 and 71, and auxiliary patterns 66 and 76 are formed in the vicinity of the main patterns 65 and 75.

  As shown in FIG. 6, each of the line-type main pattern 65 and auxiliary pattern 66 includes a buffer layer pattern 63 and an absorber pattern 64 formed on the reflective layer 62. As shown in FIG. 7, each of the hole-based main pattern 75 and the auxiliary pattern 76 includes a buffer layer pattern 73 that opens an absorber layer on the reflective layer 72 and an absorber pattern 74.

JP-A-9-288346 Japanese Patent Laid-Open No. 11-305417 JP 2009-237339 A

  However, the reflective mask for EUV exposure having the conventional auxiliary pattern as shown in FIGS. 6 and 7 and described in Patent Document 2 and Patent Document 3 has a difficulty in manufacturing the mask. First, as described above, it is necessary that the auxiliary pattern does not form an image on the wafer as described above, and the auxiliary pattern must have a dimension smaller than that of the main pattern. As a result, the required auxiliary pattern line width dimension is further miniaturized with the miniaturization of the main pattern dimension, and the auxiliary pattern such as the scattering bar is generally about half the size of the actual pattern. There is a problem that is approaching the limit.

  In addition, the mask provided with the auxiliary pattern, particularly in the case of a mask having a line type auxiliary pattern as shown in FIG. 6, is a mask that becomes dirty in the mask manufacturing process such as cleaning or during use in the exposure apparatus. In the case of re-cleaning, a phenomenon occurs in which part of the auxiliary pattern is often chipped (chipped), the auxiliary pattern is peeled off from the substrate surface (peeling), or the auxiliary pattern is collapsed in the line width direction (falling down). As the auxiliary pattern is miniaturized, the above phenomenon has occurred more frequently. In the cleaning of the mask, ultrasonic waves are often used in combination with the ultrasonic wave in order to enhance the cleaning power when cleaning in pure water, and the auxiliary pattern chipping, peeling and falling phenomenon tend to become more remarkable. A portion where the auxiliary pattern is missing, peeled off or collapsed cannot be corrected by a conventional mask correction technique because the line width of the auxiliary pattern is very small, and the mask is treated as a defect.

  As described above, chipping, peeling, and falling of the auxiliary pattern in cleaning the mask provided with the auxiliary pattern reduce the mask manufacturing yield, contribute to an increase in mask manufacturing cost, and are used for pattern transfer to the wafer. In the mask cleaning at the time, there is a problem of shortening the mask life.

  Therefore, the present invention has been made in view of the above problems. That is, an object of the present invention is to prevent the auxiliary pattern from being chipped, peeled off from the substrate surface, or to tilt the auxiliary pattern in the reflective mask for EUV exposure having the auxiliary pattern, making the mask easy to manufacture and highly accurate pattern transfer. It is an object of the present invention to provide a reflective mask and a method for manufacturing the same.

  In order to solve the above problems, a reflective mask for EUV exposure according to the first aspect of the present invention includes a substrate, a reflective layer that reflects EUV light formed on the substrate, and the reflective layer. A reflection layer for EUV exposure having at least a buffer layer formed on the layer for preventing etching damage to the reflection layer and an absorber layer formed on the buffer layer for absorbing the EUV light, and provided with a mask pattern The mask pattern is composed of a main pattern transferred onto a wafer and an auxiliary pattern provided in the vicinity of the main pattern and having a size less than a resolution limit of the projection optical system. Is composed of a buffer layer.

  The reflective mask for EUV exposure according to claim 2 of the present invention is the reflective mask for EUV exposure according to claim 1, wherein the main pattern is formed on the reflective layer. The auxiliary pattern is composed of the buffer layer formed on the reflective layer.

  The reflective mask for EUV exposure according to claim 3 of the present invention is the reflective mask for EUV exposure according to claim 2, wherein the main pattern is a line pattern. It is.

  The reflective mask for EUV exposure according to the invention described in claim 4 of the present invention is the reflective mask for EUV exposure according to claim 1, wherein the main pattern comprises a reflective layer opened in the absorber layer. The auxiliary pattern is composed of the buffer layer opened in the absorber layer.

  The reflective mask for EUV exposure according to claim 5 of the present invention is the reflective mask for EUV exposure according to claim 4, wherein the main pattern is a hole pattern. It is.

  The reflective mask for EUV exposure according to the invention described in claim 6 of the present invention is the reflective mask for EUV exposure according to any one of claims 1 to 5, wherein the reflective mask is formed on the reflective layer. And a capping layer for protecting the reflective layer.

  According to a seventh aspect of the present invention, there is provided a method for manufacturing a reflective mask for EUV exposure, comprising: a substrate; a reflective layer that reflects EUV light formed on the substrate; and the reflective layer that is formed on the reflective layer. A reflective mask blank for EUV exposure comprising at least a buffer layer that prevents etching damage to the reflective layer and an absorber layer that is formed on the buffer layer and absorbs the EUV light is prepared, and the absorber layer A method of manufacturing a reflective mask for EUV exposure, comprising: forming a resist pattern on the substrate; and dry-etching the absorber layer using the resist pattern as a mask to form an absorber pattern, wherein the absorber layer comprises: After the step of dry etching to form an absorber pattern and exposing the buffer layer and stripping the resist pattern, the exposed buffer Forming a second resist pattern in a predetermined region of the substrate, dry-etching the buffer layer using the second resist pattern and the absorber pattern as a mask, and a main pattern transferred onto the wafer, and the vicinity of the main pattern And a step of forming an auxiliary pattern having a size equal to or smaller than the resolution limit of the projection optical system and a step of peeling off the second resist pattern.

  According to the reflective mask for EUV exposure of the present invention, when the auxiliary pattern is formed by the buffer layer and used as the auxiliary pattern of the line-type main pattern, the height (thickness) is low. The mask pattern can be easily prepared, and it is possible to suppress chipping of the auxiliary pattern, peeling from the substrate surface, or collapse during mask cleaning. Further, when the auxiliary pattern of the line-type main pattern is used, only the buffer layer is used, and the EUV light absorption is weaker than that of the absorber layer. Thus, the auxiliary pattern can be easily created. On the other hand, when the auxiliary pattern of the Hall-type main pattern is used, the buffer layer surface acts as a reflection surface, but the EUV light reflection is weaker than that of the multilayer reflective film, so that it is compared with the auxiliary pattern of the prior art. As a result, the pattern width of the auxiliary pattern opening can be increased, and the auxiliary pattern can be easily created.

  According to the manufacturing method of the reflective mask for EUV exposure of the present invention, the auxiliary pattern is formed by the buffer layer, so that the pattern width can be increased as compared with the auxiliary pattern of the prior art, and the auxiliary pattern can be generated. It becomes easy.

It is sectional drawing and top view which show 1st Embodiment of the reflective mask for EUV exposure of this invention. It is sectional drawing and top view which show 2nd Embodiment of the reflective mask for EUV exposure of this invention. It is a cross-sectional schematic diagram which shows the manufacturing process of the reflective mask for EUV exposure of this invention in case the main pattern is a line type | system | group. It is a cross-sectional schematic diagram which shows the manufacturing process of the reflective mask for EUV exposure of this invention in case a main pattern is a Hall system. It is sectional drawing of the reflective mask blank used for the reflective mask for EUV exposure of this invention, and its manufacturing method. It is sectional drawing and a top view of the reflective mask for EUV exposure which has the conventional auxiliary pattern, and shows the example of a line type mask pattern. It is sectional drawing and a top view of the reflection type mask for EUV exposure which has the conventional auxiliary pattern, and shows the example of a hole type mask pattern.

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

(Reflective mask)
The reflective mask for EUV exposure of the present invention includes a substrate, a multilayer reflective layer formed on the substrate and reflecting EUV light, and a buffer layer formed on the reflective layer to prevent etching damage to the reflective layer, A mask having at least an absorber layer that is formed on the buffer layer and absorbs EUV light, the mask pattern being provided in the vicinity of the main pattern transferred onto the wafer and the projection optics The mask is composed of an auxiliary pattern having a size less than the resolution limit of the system, and the auxiliary pattern is constituted by a buffer layer.

  In the present invention, the main pattern means a pattern transferred onto a wafer by exposure among mask patterns formed on a reflective mask for EUV exposure. For example, a circuit pattern, an alignment pattern, a TEG pattern, etc. Is mentioned. The auxiliary pattern is provided near the main pattern and contributes to the improvement of transfer characteristics such as the resolution of the main pattern in pattern transfer, but it is below the resolution limit of the projection optical system and itself is on the wafer. It means a pattern that is not transferred.

  Hereinafter, a mask in which an auxiliary pattern is provided on a line main pattern and a mask in which an auxiliary pattern is provided on a hole main pattern will be described as typical auxiliary patterns.

(First embodiment)
The reflective mask of this embodiment is a mask in which the main pattern is composed of an absorber layer and a buffer layer formed on the reflective layer, and the auxiliary pattern is composed of the buffer layer formed on the reflective layer. is there.

  FIG. 1 is a partial cross-sectional view (FIG. 1 (a)) and a plan view (FIG. 1 (b)) showing a first embodiment of a reflective mask for EUV exposure according to the present invention. Fig.1 (a) is sectional drawing in the AA of FIG.1 (b). In the example of the reflective mask 10 shown in FIG. 1, the main pattern 15 shows a case of a line system, and the main pattern 15 formed on one main surface side of the substrate 10 and the projection optical system in the vicinity of the main pattern 15. A pair of line-shaped auxiliary patterns 16 having a size equal to or smaller than the resolution limit is provided, and the longitudinal direction of the auxiliary pattern 16 is longer than the longitudinal direction of the main pattern 15.

  As shown in FIG. 1A, the main pattern 15 includes a buffer layer (buffer layer pattern) 13 and an absorber layer (absorber pattern) 14 patterned on the multilayer reflective layer 12. The auxiliary pattern 16 includes a buffer layer (buffer layer pattern) 13 patterned on the multilayer reflective layer 12.

  The auxiliary pattern 16 of the reflective mask 10 of the present invention is composed of only the buffer layer 13 patterned without using the absorber layer, thereby reducing the aspect ratio (pattern thickness / pattern width) of the auxiliary pattern. This makes it easy to create auxiliary patterns. Furthermore, it is possible to suppress chipping of auxiliary patterns, peeling from the substrate surface, or collapse during mask cleaning. Furthermore, since the auxiliary pattern 16 has a low height (thickness) and is composed of only a buffer layer, the absorption of EUV light is weaker than that in the case where an absorber layer is provided. The width can be increased, and an effect of facilitating creation of the auxiliary pattern can be obtained.

  In FIG. 1, a pair of auxiliary patterns 16 is illustrated as an example. However, the auxiliary pattern 16 is not limited to the above, and a plurality of auxiliary patterns may be provided on both sides of the main pattern. For example, only one may be provided on one side of the main pattern.

(Second Embodiment)
The reflective mask of the present embodiment is a mask in which the main pattern is composed of a reflective layer opened in the absorber layer, and the auxiliary pattern is composed of a buffer layer opened in the absorber layer.

  FIG. 2 is a partial cross-sectional view (FIG. 2 (a)) and a plan view (FIG. 2 (b)) showing a second embodiment of the reflective mask for EUV exposure of the present invention. FIG. 2A is a cross-sectional view taken along line BB in FIG. In the example shown in FIG. 2, the main pattern 25 shows a case of a hole system, and is composed of the reflective layer 22 that is patterned into the absorber layer 24 and exposed in a square shape. The auxiliary pattern 26 is provided at four locations in parallel as a line pattern in the vicinity of the main pattern 25, and is configured by a buffer layer 23 that is exposed and opened in the absorber layer 24.

  Since the auxiliary pattern 26 of the reflective mask 20 of the present invention is composed only of the buffer layer 23 opened in the absorber layer 24, further etching of the buffer layer 23 in the region to be the auxiliary pattern is unnecessary, and the auxiliary pattern 26 is provided. It is easy to create a pattern. That is, the EUV light reflectivity of the buffer layer 23 exposed at the opening of the auxiliary pattern 26 is weaker than that of the reflective layer 22, so that the auxiliary pattern width can be increased compared to the auxiliary pattern of the prior art. The auxiliary pattern can be easily created.

  In the reflective mask for EUV exposure of the first embodiment and the second embodiment described above, a capping layer (not shown) for protecting the reflective layer is provided on the reflective layers 12 and 22, and the capping layer is provided on the capping layer. The buffer layer may be provided.

(Reflective mask manufacturing method)
Next, a method for manufacturing a reflective mask for EUV exposure according to the present invention will be described in the case where an auxiliary pattern is provided in a line main pattern and in the case where an auxiliary pattern is provided in a hole main pattern.

(First embodiment)
FIG. 3 is a process cross-sectional schematic diagram showing the first embodiment in the manufacturing method of the reflective mask for EUV exposure of the present invention, and the reflection provided with the auxiliary pattern of the main pattern of the line system as shown in FIG. This is a mold mask manufacturing process.

  First, as shown in FIG. 3A, a substrate 31, a reflective layer 32 that reflects EUV light formed on one main surface (front surface) of the substrate 31, and a reflective layer formed on the reflective layer 32. A reflective mask blank for EUV exposure having at least a buffer layer 33a that prevents etching damage to 32 and an absorber layer 34a that is formed on the buffer layer 33a and absorbs EUV light is prepared, and the absorber layer 34a described above is prepared. An electron beam resist is applied on the surface, and an electron beam drawing apparatus is used to draw a pattern with an electron beam based on a predetermined design pattern, followed by development to form a first resist pattern 37a.

  Next, using the first resist pattern 37a as a mask, the absorber layer 34a is dry-etched, and then the first resist pattern 37a is peeled off to form the absorber pattern 34 as shown in FIG. While forming, the buffer layer 33a is exposed.

  Next, a second electron beam resist is applied to cover the absorber pattern 34 and the exposed buffer layer 33a, and an auxiliary pattern is drawn on a predetermined region of the exposed buffer layer 33a using an electron beam drawing apparatus. Development is performed to form a second resist pattern 37b as shown in FIG.

  Next, the buffer layer 33a is dry-etched using the second resist pattern 37b and the absorber pattern 34 as a mask, and then the second resist pattern 37b is peeled off. As shown in FIG. A layer pattern 33 is formed, and a main pattern 35 transferred onto the wafer and an auxiliary pattern 36 provided in the vicinity of the main pattern 35 and having a size equal to or smaller than the resolution limit of the projection optical system are formed. A reflective mask for exposure is obtained.

(Second Embodiment)
FIG. 4 is a process cross-sectional schematic diagram showing a second embodiment of the manufacturing method of a reflective mask for EUV exposure according to the present invention, and a reflection in which an auxiliary pattern is provided on the main pattern of the hole system as shown in FIG. This is a mold mask manufacturing process.

  First, as shown in FIG. 4A, a substrate 41, a reflective layer 42 that reflects EUV light formed on one main surface (front surface) of the substrate 41, and a reflective layer formed on the reflective layer 42. A reflective mask blank for EUV exposure having at least a buffer layer 43a that prevents etching damage to 42 and an absorber layer 44a that is formed on the buffer layer 43a and absorbs EUV light is prepared, and the absorber layer 44a described above is prepared. An electron beam resist is applied on the top, and an electron beam drawing apparatus is used to draw a pattern with an electron beam based on a predetermined design pattern, followed by development to form a first resist pattern 47a. At this time, in the first resist pattern 47a, both the main pattern and the auxiliary pattern which are openings of the absorber layer 44a are formed.

  Next, using the first resist pattern 47a as a mask, the absorber layer 44a is dry-etched, and then the first resist pattern 47a is peeled off to form the absorber pattern 44 as shown in FIG. While forming, the buffer layer 43a is exposed. In the dry etching described above, the absorber layer 44a of the main pattern portion and the auxiliary pattern portion is simultaneously etched to form an opening that exposes the buffer layer 43a.

  Next, a second electron beam resist is applied to cover the absorber pattern 44 and the exposed buffer layer 43a, and an auxiliary pattern is drawn on a predetermined region of the exposed buffer layer 43a using an electron beam drawing apparatus. Development is performed to form a second resist pattern 47b as shown in FIG.

  Next, the buffer layer 43a is dry-etched using the second resist pattern 47b and the absorber pattern 44 as a mask, and then the second resist pattern 47b is peeled off. As shown in FIG. A layer pattern 43 is formed, and a main pattern 45 transferred onto the wafer and an auxiliary pattern 46 provided in the vicinity of the main pattern 45 and having a size equal to or smaller than the resolution limit of the projection optical system are formed. A reflective mask for exposure is obtained.

  The reflective layers 12 and 22, the absorber patterns 14 and 24, and the buffer layer patterns 13 and 23 are the basic thin film layers constituting the reflective mask of the present invention, but are not shown in FIGS. The reflective mask of the present invention may have another thin film layer. For example, a capping layer that protects the reflective layer may be provided on the reflective layers 12 and 22. In this case, the capping layer is not patterned. Further, a low reflection layer having a low reflectivity with respect to the inspection light may be formed on the absorber patterns 14 and 24 in order to increase detection sensitivity when optically inspecting the mask. Further, a conductive layer may be formed on the other main surface (back surface) of the substrates 11 and 21 for an electrostatic chuck when the mask is installed in the exposure apparatus.

  As the resist for forming the first resist pattern 37a, 47a and the second resist pattern 37b, 47b, either negative type or positive type electron beam resist can be used. Different resists may be used.

  As described above, in the reflective mask manufacturing method of the present invention, the resist pattern forming process by electron beam drawing is performed in two steps. However, by forming the auxiliary pattern with the buffer layer, the auxiliary pattern of the prior art is formed. The pattern width can be increased as compared with the above, and the auxiliary pattern can be easily created. In the line pattern, it is possible to prevent the auxiliary pattern from falling or chipping or peeling from the substrate surface. In addition, the hole pattern does not require alignment accuracy as much as the line pattern, and the auxiliary pattern can be enlarged, thereby reducing the requirement for the minimum mask pattern size.

(Reflective mask blank)
The desirable form of each material which comprises the reflective mask for EUV exposure of said this invention and the reflective mask blank used for the manufacturing method is demonstrated below. FIG. 5 is a schematic cross-sectional view showing an example of a reflective mask blank used in the present invention, and the same reference numerals as those in FIG.

(substrate)
In FIG. 5, the substrate 11 constituting the reflective mask blank has a low thermal expansion coefficient in order to maintain high pattern position accuracy, and smoothness and flatness to obtain high reflectivity and transfer accuracy. A glass substrate such as a synthetic quartz glass, a SiO ₂ —TiO ₂ low thermal expansion glass, or a crystallized glass on which β quartz solid solution is deposited is preferable. Can be used.

(Reflective layer)
The multilayer reflective layer 12 is made of a material that reflects EUV light (usually having a wavelength of about 13.5 nm) used for EUV exposure with a high reflectance, and a multilayer film made of molybdenum (Mo) and silicon (Si) is often used. For example, a reflective layer made of a multilayer film in which 40 layers each of 2.74 nm thick Mo and 4.11 nm thick Si are stacked. In the case of a multilayer film composed of Mo and Si, an ion beam sputtering method is used to first form a Si film using a Si target, and then form a Mo film using a Mo target. A multilayer reflective layer is obtained by laminating ˜60 periods, preferably 40 periods.

(Capping layer)
Although not shown in FIG. 5, a capping layer for protecting the reflective layer 12 may be provided on the reflective layer 12. In order to increase the reflectivity of the multilayer reflective layer 12, it is preferable to use Mo having a large refractive index as the uppermost layer. However, Mo is easily oxidized in the atmosphere and the reflectivity is lowered, so that it is protected during oxidation prevention and mask cleaning. As a protective film for this, it is preferable to form a capping layer by depositing Si or ruthenium (Ru) by sputtering or the like. For example, Si as a capping layer is provided in a thickness of 11 nm on the uppermost layer of the reflective layer.

(Buffer layer)
As shown in FIG. 5, in the present invention, when the absorber layer 14a that absorbs EUV light is subjected to dry etching to form a pattern, the underlying capping layer (not shown) and the reflective layer 12 are damaged by dry etching. In order to prevent this, a buffer layer 13a is provided between the reflective layer 12 and the absorber layer 14a. As a material of the buffer layer 13a, a thin film such as SiO ₂ , Al ₂ O ₃ , Cr, or CrN is used. For example, the CrN film has high etching resistance when dry etching is performed with chlorine gas using a tantalum nitride (TaN) film as the absorber layer 14a. When forming a CrN film, it is preferable to form a film with a film thickness in the range of about 5 nm to 20 nm in a mixed gas atmosphere of argon (Ar) and nitrogen using a Cr target by a DC magnetron sputtering method.

(Absorber layer)
The material of the absorber layer 14a that forms a mask pattern and absorbs EUV light includes tantalum (Ta), tantalum nitride (TaN), tantalum boride (TaB), tantalum boride (TaBN), and tantalum / hafnium compounds. A material mainly composed of Ta, such as (TaHf), is used in a film thickness range of about 35 nm to 60 nm, more preferably in a range of 40 nm to 55 nm. However, the above thickness is an example when CrN is used with a thickness of 10 nm for the buffer layer 13a. When the material and thickness of the buffer layer are changed, the thickness of the absorber layer 14a is adjusted to match the buffer layer. There is a need to. For example, when the buffer layer has a CrN thickness of 20 nm, it is necessary to reduce the thickness of the absorber layer 14a by about 10 nm.

(Low reflective layer)
Although not shown in FIG. 5, when the mask pattern is optically inspected, a low reflection layer that has low reflection with respect to inspection light (199 nm or 257 nm) may be provided on the absorber layer 14a. Good. Examples of the material of the low reflection layer include tantalum compounds containing oxygen such as tantalum oxide (TaO), oxynitride (TaNO), boron oxide (TaBO), and boron oxynitride (TaBNO), and silicon oxide ( SiO _x ), silicon oxynitride (SiON), chromium nitride (CrN), and the like can be given. The film thickness is in the range of about 5 nm to 30 nm, and more preferably in the range of about 10 nm to 20 nm.

(Conductive layer)
In many cases, a conductive layer is provided on the surface (back surface) opposite to the pattern side of the reflective mask blank for EUV exposure for an electrostatic chuck when the mask is installed in an exposure apparatus. Also in the case of the present invention, a conductive layer can be provided on the back surface of the substrate. Examples of the material for the conductive layer include thin films such as conductive metals and metal nitrides. For example, chromium (Cr) or chromium nitride (CrN) is formed to a thickness of about 20 nm to 150 nm. .
Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1
A reflective mask blank for EUV exposure was produced by the following procedure.
On a main surface of a synthetic quartz substrate having a size of 6 inches square (thickness: 0.25 inches) that is optically polished, a 4.2 nm Si film is formed using an Si target by ion beam sputtering. Then, a Mo film is formed to 2.8 nm using a Mo target, and this is set as one period to form a reflective layer by laminating 40 periods, and finally a Si film is formed to 4.2 nm to form the final stage of the reflective layer. A reflective layer for reflecting EUV light composed of a multilayer film of Mo and Si was formed.
Next, a CrN film having a thickness of 20 nm was formed on the multilayer reflective layer using a Cr target in a mixed gas atmosphere of Ar and nitrogen by a DC magnetron sputtering method to form a buffer layer.

  Subsequently, a TaBN film having a thickness of 25 nm is formed on the Cr film buffer layer by a DC magnetron sputtering method using a target containing Ta and B in a mixed gas atmosphere of Ar and nitrogen. Then, an absorption layer that absorbs EUV light was formed, and a TaBO film having a thickness of 15 nm was formed on the absorption layer to form a low reflection layer in optical inspection, thereby obtaining a reflective mask blank for EUV exposure. The EUV reflectivity in the above film configuration was 2.5%, 13%, and 63% on the absorber surface, buffer layer surface, and reflective layer surface, respectively.

  Next, a negative electron beam resist having a thickness of 200 nm was applied using this EUV exposure mask blank, and a pattern was drawn by an electron beam drawing apparatus to form a gate pattern resist pattern as a main pattern. The main pattern was an isolated line pattern with a line width of 80 nm and a length of 500 nm on the mask.

  Next, using the resist pattern as a mask, the low reflection layer of the TaBO film is dry-etched with fluorine gas, then the etching gas is changed and the absorption layer of the TaBN film is dry-etched with chlorine gas to expose the buffer layer. In addition, a low reflection layer pattern and an absorber pattern were formed, and then the resist pattern was peeled off using oxygen plasma.

  Next, a second negative electron beam resist having a thickness of 100 nm is applied so as to cover the low reflection layer pattern, the absorber pattern, and the exposed buffer layer, and an auxiliary pattern is drawn on a predetermined region of the exposed buffer layer. And developed to form a second resist pattern for the auxiliary pattern. The auxiliary pattern is a pattern having a line width of 50 nm and a length of 600 nm on one side on one side, symmetrically to the main pattern, at a position 60 nm away from the main pattern on the mask, in parallel with the main pattern. .

  Next, using the second resist pattern and the absorber pattern as a mask, the buffer layer made of a Cr film is dry-etched with a mixed gas of chlorine and oxygen, and then the second resist pattern is peeled off to form a buffer layer pattern Thus, a reflective mask for EUV exposure according to the present invention was obtained in which a main pattern transferred onto the wafer and an auxiliary pattern provided in the vicinity of the main pattern and having a size equal to or smaller than the resolution limit of the projection optical system were formed. .

  In the reflective mask according to the present invention, the line width of the auxiliary pattern can be made larger than before, and thus the mask can be easily manufactured. Moreover, although the reflective mask having the above mask pattern was washed with pure water with ultrasonic waves, the auxiliary pattern was not chipped, peeled off, or tilted, and a reflective mask having a clean mask surface was obtained.

(Example 2)
Using a reflective mask blank having the same film configuration as in Example 1, with the buffer layer CrN thickness changed to 10 nm and the absorption layer TaBN thickness changed to 35 nm, a positive electron beam resist was applied on the blank, and electron beam drawing was performed. A pattern was drawn with an apparatus and developed to form a resist pattern. The resist pattern is a contact hole pattern as a main pattern and auxiliary patterns formed at four locations around the hole pattern. On the mask, the main pattern is a square with a side of 100 nm, and the auxiliary pattern is provided at four positions in parallel with each side of the main pattern at a position 60 nm away from the main pattern. The width was 70 nm and the length was 120 nm.

  Next, using the resist pattern as a mask, the low reflection layer of the TaBO film is dry-etched with fluorine gas, then the etching gas is changed and the absorption layer of the TaBN film is dry-etched with chlorine gas, and then the resist pattern is peeled off. The buffer layer was exposed, and a low reflection layer pattern and an absorber pattern were formed.

  Next, a second positive type electron beam resist is applied so as to cover the low reflection layer pattern, the absorber pattern, and the exposed auxiliary pattern buffer layer, and a predetermined region is drawn with an electron beam, developed, and second The resist pattern was formed.

  Next, using the second resist pattern and the absorber pattern as a mask, the buffer layer made of the CrN film is dry-etched with a mixed gas of chlorine and oxygen, and then the second resist pattern is peeled off and transferred onto the wafer. Main pattern and an auxiliary pattern provided in the vicinity of the main pattern and having a size equal to or smaller than the resolution limit of the projection optical system were formed to obtain a reflective mask for EUV exposure according to the present invention.

  In the reflective mask of the present invention, the line width of the auxiliary pattern can be made larger than that of the conventional pattern in the same manner as in Example 1. Therefore, the mask can be easily manufactured, and the mask is cleaned with pure water using ultrasonic waves. However, the auxiliary pattern was not chipped, peeled off or collapsed.

10, 20 Reflective mask 11, 21 Substrate 12, 22 Reflective layer 13, 23 Buffer layer pattern (patterned buffer layer)
13a Buffer layers 14, 24 Absorber pattern (patterned absorber layer)
14a Absorber layer 15, 25 Main pattern 16, 26 Auxiliary pattern 30, 40 Reflective mask 31, 41 Substrate 32, 42 Reflective layer 33a, 43a Buffer layer 33, 43 Buffer layer pattern 34a, 44a Absorber layer 34, 44 Absorption Body pattern 35, 45 Main pattern 36, 46 Auxiliary pattern 37a, 47a First resist pattern 37b, 47b Second resist pattern 50 Reflective mask blank 60, 70 Reflective mask 61, 71 Substrate 62, 72 Reflective layer 63, 73 Buffer layer pattern 64, 74 Absorber pattern 65, 75 Main pattern 66, 76 Auxiliary pattern

Claims (7)

A substrate, a reflective layer reflecting the EUV light formed on the substrate, a buffer layer formed on the reflective layer to prevent etching damage to the reflective layer, and the EUV light formed on the buffer layer A reflective mask for EUV exposure having at least an absorber layer for absorbing
The mask pattern is composed of a main pattern transferred onto a wafer and an auxiliary pattern provided in the vicinity of the main pattern and having a size less than the resolution limit of the projection optical system, and the auxiliary pattern is configured by a buffer layer. A reflective mask for EUV exposure characterized by the above.   The main pattern includes the absorber layer and the buffer layer formed on the reflective layer, and the auxiliary pattern includes the buffer layer formed on the reflective layer. The reflective mask for EUV exposure according to claim 1.   The reflective mask for EUV exposure according to claim 2, wherein the main pattern is a line pattern.   2. The EUV exposure according to claim 1, wherein the main pattern includes a reflective layer having an opening in the absorber layer, and the auxiliary pattern includes the buffer layer having an opening in the absorber layer. Reflective mask.   The reflective mask for EUV exposure according to claim 4, wherein the main pattern is a hole pattern.   The reflective mask for EUV exposure according to any one of claims 1 to 5, further comprising a capping layer for protecting the reflective layer on the reflective layer. A substrate, a reflective layer reflecting the EUV light formed on the substrate, a buffer layer formed on the reflective layer to prevent etching damage to the reflective layer, and the EUV light formed on the buffer layer And a reflective mask blank for EUV exposure comprising at least an absorber layer that absorbs, a resist pattern is formed on the absorber layer, and the absorber layer is dry-etched using the resist pattern as a mask. A method of manufacturing a reflective mask for EUV exposure, including a step of forming an absorber pattern,
After the step of dry etching the absorber layer to form an absorber pattern and exposing the buffer layer, and stripping the resist pattern,
Forming a second resist pattern in a predetermined region of the exposed buffer layer, dry-etching the buffer layer using the second resist pattern and the absorber pattern as a mask, and a main pattern transferred onto the wafer; Forming an auxiliary pattern provided in the vicinity of the main pattern and having a size less than or equal to the resolution limit of the projection optical system;
Peeling the second resist pattern;
The manufacturing method of the reflective mask for EUV exposure characterized by including these.

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