JP2013206936A - Reflective mask and method of manufacturing reflective mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective mask that removes reflection of light of EUV and DUV regions from a mask region corresponding to a boundary region of a chip to be multiple exposure on a semiconductor substrate, and a method of manufacturing the reflective mask.SOLUTION: There is provided a reflective mask for exposure that has a multi-layered reflective layer, a protective layer, and an absorptive layer laminated in this order on one surface of a substrate and also having a conductor layer formed on the other surface. The absorptive layer is partially etched away to form a circuit pattern portion, and the absorptive layer, protective layer, and multi-layered reflective layer are etched away to form a light shield frame portion on which the surface of the substrate is exposed at an outer periphery of the circuit pattern portion. A part of the substrate is removed to form a space at a bottom portion of the light shield frame portion, the space being sectioned in a V shape (an isosceles triangle shape having its vertex angle at a deepest portion on a substrate side) or in a wedge shape (a right-angled triangle shape having its oblique side on the substrate side).

Description

  The present invention relates to a reflective exposure mask and a method for manufacturing the same.

  In the manufacturing process of semiconductor devices, the demand for miniaturization of photolithography technology is increasing with the high integration of semiconductor devices. Already, lithography exposure has been replaced by exposure using light in the EUV (Extreme Ultra Violet) region with a wavelength of 13.5 nm, instead of conventional exposure using ArF excimer laser light with a wavelength of 193 nm.

  As for a mask for EUV exposure (EUV mask), since most substances have high light absorption with respect to light in the EUV region, a reflective mask is used unlike a conventional transmission mask (for example, , See Patent Document 1). For example, in Patent Document 1, a light reflecting layer composed of a multilayer film in which a molybdenum (Mo) layer and a silicon (Si) layer are alternately stacked on a glass substrate is formed, and tantalum (Ta) is a main component. A technique for forming a pattern with a light absorbing layer is disclosed.

Further, as described above, since an EUV light cannot use a refractive optical system that utilizes the transmission of light, the optical system of the exposure machine is also a reflection type. For this reason, deflection using a transmissive beam splitter is impossible. Therefore, the reflective mask has a drawback that the incident light to the mask and the reflected light cannot be designed on the same axis. For this reason, the EUV mask employs a method of guiding the reflected light of light incident on the mask to the semiconductor substrate with the optical axis inclined by about 6 °. In this method, since the optical axis is inclined, a problem called a projection effect is pointed out in which the wiring pattern of the mask on the semiconductor substrate has a line width different from that of the mask pattern depending on the incident direction of light with respect to the mask pattern. Yes.
Therefore, in order to suppress or reduce this projection effect, proposals have been made to reduce the thickness of the absorption layer forming the mask pattern.

  In this thinning method, the amount of attenuation of light necessary to absorb EUV light is insufficient, so that the reflected light to the semiconductor substrate increases and the resist film applied on the semiconductor substrate is exposed to light. Will occur. Further, in the semiconductor substrate, in order to expose the chips with multiple surfaces, multiple exposure occurs in the boundary region between adjacent chips. Furthermore, although the EUV light source has a peak of its emission spectrum at 13.5 nm, it is known to emit light in the near infrared region from vacuum ultraviolet rays other than the 13.5 nm band called out-of-band. Yes. This out-of-band is unnecessary in nature, and is unnecessary light that should be removed by a filter or the like because the resist applied to the semiconductor substrate is exposed.

However, the light absorption layer using tantalum (Ta) is not suitable for vacuum ultraviolet rays but deep ultraviolet rays (Deep).
Since the light in the Ultra Violet region is also reflected, as described above, the amount of light that cannot be ignored is integrated in the semiconductor wiring portion in the vicinity of the boundary region between adjacent chips, and there is a problem that affects the size of the wiring pattern. .

JP 2007-273651 A

  The present invention has been made to solve the above-mentioned problems, and the problem is that the reflection of light in the EUV and DUV regions is removed from the mask region corresponding to the boundary region of the chip that is multiple-exposed on the semiconductor substrate. It is an object to provide a reflective mask and a method for manufacturing the same.

As means for solving the above problems, the invention according to claim 1 of the present invention is a reflective mask,
A multilayer reflective layer, a protective layer, and an absorption layer are laminated in this order on one surface of the substrate, and a conductor layer is formed on the other surface,
A part of the absorption layer is etched away to form a circuit pattern portion;
On the outer periphery of the circuit pattern portion, a light-shielding frame portion is formed in which the absorption layer, the protective layer, and the multilayer reflective layer are etched away to expose the surface of the substrate,
At the bottom of the light shielding frame part, a structure is formed by removing a part of the substrate to form a space,
The cross-sectional shape of the space is V-shaped (an isosceles triangle in which the apex angle is disposed at the deepest part on the substrate side) or a wedge shape (a right-angled triangle in which the oblique side is disposed on the substrate side).
This is a reflective mask.

  In the invention according to claim 2, when the cross-sectional shape formed into a space by processing the substrate side in the stacking direction of the light shielding frame portion is an isosceles triangle having an apex angle disposed at the deepest portion on the substrate side, 2. The reflective mask according to claim 1, wherein an angle formed by the inclined surface of the prism structure that is isosceles with the surface of the surface is 22 ° or more.

  According to a third aspect of the present invention, when the cross-sectional shape that is processed into the space on the substrate side in the stacking direction of the light shielding frame portion is a right-angled triangle with the hypotenuse arranged on the substrate side, the surface of the substrate is a right-angled triangle. 2. The reflective mask according to claim 1, wherein an angle formed by the inclined surface of the prism structure corresponding to the oblique side is 48 ° or more.

The invention according to claim 4 is a method of manufacturing a reflective mask according to any one of claims 1 to 3, wherein at least
A circuit pattern portion forming step of forming a circuit pattern portion by patterning the absorption layer;
A light shielding frame forming step of forming a light shielding frame by etching and removing at least the absorption layer, the protective layer, and the multilayer reflective layer on at least a part of the periphery of the circuit pattern portion;
By processing the substrate exposed on the bottom surface of the light shielding frame by the light shielding frame forming step, the reflected light is absorbed by the absorption layer even if reflected light is generated at the bottom of the light shielding frame. And a prism structure forming step of forming a prism structure that does not reflect from the reflection mask.

  According to the present invention, a frame-shaped region is formed by selectively removing a part of the absorption layer, the protective layer, and the multilayer reflective layer in the mask region corresponding to the boundary region of the multiple-exposed chip on the semiconductor substrate. In addition, by forming the prism structure by processing the bottom part of the light shielding frame part, it is possible to prevent reflection of light in the EUV and DUV regions irradiated to the bottom part of the light shielding frame part.

It is a schematic sectional drawing explaining an example of the reflective mask blank of this invention, (a) shows the case where an absorption layer is a single layer, (b) shows the case where an absorption layer is a lamination | stacking of two or more layers, respectively. Yes. The schematic plan view and schematic sectional drawing explaining an example of the reflective mask of this invention. It is a schematic sectional drawing which shows the example of the prism structure of the bottom part of the light shielding frame part 17 of the reflective mask of this invention, (a) is V-shaped (isosceles triangle which arrange | positioned the apex angle on the board | substrate side) sectional shape (B) is an example of a prism structure having a wedge-shaped (right-angled triangle with the hypotenuse on the substrate side) cross-sectional shape. The conceptual diagram which shows the example of the simulation of the inclination angle of the prism structure of this invention. The flowchart explaining the process of the Example of this invention. The schematic sectional drawing explaining the process of a reflective mask corresponding to each step of the process of the Example of this invention. FIG. 7 is a schematic cross-sectional view illustrating a process of processing a reflective mask corresponding to each stage of the process of the embodiment of the present invention, and illustrates a process subsequent to the process illustrated in FIG. 6.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a first embodiment of the present invention will be described with reference to FIG.
1A and 1B are schematic cross-sectional views of a reflective mask blank 10, wherein FIG. 1A shows the case where the absorption layer is a single absorption layer 14a, and FIG. 1B shows the case where the absorption layer 14b has two layers. Other configurations are the same. More specifically, it is a reflective mask mask blank used for exposure using EUV light. The wavelength of EUV light is, for example, 13.5 nm. In the reflective mask blank, a multilayer reflective layer 12, a protective layer 13, and an absorbing layer 14 are formed in this order on one surface of a substrate 11. The substrate 11 is a quartz substrate, which is 6 inches square and has a thickness of 6.35 mm. The multilayer reflective layer 12 is composed of 40 pairs of molybdenum (Mo) and silicon (Si) alternately using an ion beam sputtering apparatus, with a total of 80 layers, and a thin film so that the uppermost layer is silicon (Si). Next, ruthenium (Ru) is laminated as a protective layer 13 with a magnetron sputtering apparatus, and then as an absorption layer, a compound containing tantalum (Ta) as a base material and silicon (Si) is used as a sputtering target, and nitrogen gas is supplied. Mixing in the atmosphere, laminating a thin film of a compound of these elements on the protective layer by a magnetron sputtering device, and further using a compound containing silicon (Si) as a base material with tantalum (Ta) as a base material, In some cases, a thin film is formed and laminated by magnetron sputtering using an atmosphere in which a mixture of nitrogen gas and oxygen gas is mixed. A back conductive film 15 is formed on the surface of the substrate 11 opposite to the multilayer reflective layer 12 by magnetron sputtering.

Next, second to fifth embodiments of the present invention will be described with reference to FIG. 2 is a reflective mask 100 using the reflective mask blank 10 shown in FIG. 1, wherein FIG. 2 (a) is a schematic plan view of the reflective mask 100, and FIG. 2 (b) is a schematic cross-sectional view. It is.
As shown in FIGS. 2A and 2B, the light shielding frame portion 17 is formed by etching and removing the absorption layer 14, the protective layer 13, and the multilayer reflective layer 12 on the outer periphery of the circuit pattern portion 18. This is the structure. Further, the light shielding frame 17 has a prism structure at the bottom. This prism structure is a structure provided on the substrate 11 and is formed by removing a part of the substrate 11. The shape may be any shape as long as EUV and DUV light incident from above the reflective mask is reflected from the back surface so as not to be reflected off the mask again from the light shielding frame portion 17, as shown in FIG. In addition, the cross-sectional shape is V-shaped (the cross-sectional shape of an isosceles triangle with the apex angle located at the deepest part on the substrate side), the wedge shape (the cross-sectional shape of a right-angled triangle with the hypotenuse on the substrate side), etc. Therefore, it is sufficient that the bottom of the light shielding frame 17 is an inclined surface.

  The shape of the prism structure will be described with reference to a conceptual diagram showing an example of the simulation of the inclination angle of the prism structure of the present invention shown in FIG. Here, a simulation is performed for the case where the bottom portion of the V-shaped light shielding frame portion 17 is manufactured.

  If the width of the light shielding frame 17 is 2x, the distance from the end of the multilayer reflective layer 12 to the V-shaped deepest position is x. The inclination angle of the V-shaped structure is a, the refractive index of the substrate 11 is n, and the thickness is t. It is assumed that light incident on the substrate 11 at an incident angle a is refracted at an angle b by the prism structure of the substrate 11.

したがって、屈折した光は、屈折した点からｘ方向に、式（２）で表されるｘ１の距離だけ離れたところで、基板１１の裏面で反射され、再び上方に向う。

この時の反射角は、９０−（ａ−ｂ）（度）となるため、裏面導電膜１５で反射した点から多層反射層１２の端部までの水平方向距離ｘ２は、式（３）となる。

したがって、ｘ１＋ｘ２≧ｘとなるようにプリズム構造体の傾斜角度ａを決めれば、裏面からの反射光が再びマスク外部に反射することはない。 When incident light 16 enters the prism structure at the bottom of the light shielding frame 17 from the vertical direction above the mask, the optical path of the incident light 16 is changed by the prism and proceeds in the direction of the refraction angle b. A distance D from the refracted point to the back surface conductive film 15 is expressed by Expression (1).

Therefore, the refracted light is reflected on the back surface of the substrate 11 at a distance of x1 expressed by the formula (2) in the x direction from the refracted point, and then goes upward again.

Since the reflection angle at this time is 90- (ab) (degrees), the horizontal distance x2 from the point reflected by the back surface conductive film 15 to the end of the multilayer reflective layer 12 is expressed by the following equation (3). Become.

Therefore, if the inclination angle a of the prism structure is determined so that x1 + x2 ≧ x, the reflected light from the back surface will not be reflected outside the mask again.

  For example, when a V-shaped prism structure is formed on 6-inch quartz glass used in an actual reflective mask, the refractive index is n = 1.48 and the thickness t = 6.35 mm. When the width 2x = 3 mm and the above formula is applied, the prism structure having an inclination larger than about 22 ° is used so that light incident on the bottom of the light shielding frame 17 is reflected outside the mask. Can be prevented.

  Further, when the wedge-shaped prism structure is formed on 6-inch quartz glass used in an actual mask, if it is considered in the same manner as the V-shaped prism structure, x = 3 mm may be used, which is larger than 48 °. By using the inclined prism structure, it is possible to prevent light incident on the bottom of the light shielding frame 17 from being reflected outside the mask.

  As a method for forming the prism structure, a known processing technique can be appropriately selected according to a desired structure. For example, a technique using a known lithography technique and a known etching technique, a known micromachining method, or the like can be used.

Next, a method for manufacturing a reflective mask according to the present invention is shown in FIGS. Here, FIG. 5 shows the steps of the process, and FIG. 6 shows a schematic cross-sectional view of the processing state in each process.
First, the reflective mask blank of FIG. 1 is prepared, and the circuit pattern portion 18 and the light shielding frame portion 17 are formed on the absorption layer 14. That is, a chemical amplification system or non-chemical amplification system resist 21 that reacts with an electron beam is applied to the surface of the absorption layer 14 with a film thickness of 200 nm (S1), and a predetermined circuit pattern portion 18 and a light shielding frame portion 17 are formed. Drawing is performed by the electron beam drawing apparatus (S2). Thereafter, development (S3) is performed with an alkaline solution or the like, and etching with gas plasma using fluorine-based gas or chlorine-based gas (S4) is performed using the pattern of the resist 21 formed thereby as a mask. The resist 21 pattern thus formed is removed by ashing with oxygen plasma, decomposition with an oxidizing chemical such as sulfuric acid or ozone water, or organic solvent (S5). After that, if necessary, cleaning treatment (S6) with ultrapure water, organic alkaline chemicals, surfactants, etc. in which acid / alkali chemicals, ozone gas or hydrogen gas are dissolved, and spin drying using centrifugal force ( Through the process of performing S7), the circuit pattern portion 18 and the light shielding frame portion 17 are formed.

  Next, a process of forming the protective layer 13 and the multilayer reflective layer 12 of the light shielding frame 17 will be described. First, a resist 21 that reacts to ultraviolet rays or electron beams is applied to the mask (S8). Thereafter, the light shielding frame 17 is drawn by exposure or electron beam (S9). As described above, development (S10), etching (S11), resist removal (S12), washing (S13), and drying (S14) are performed to complete the light shielding frame portion 17. In the etching step (S 11), first, the protective layer 13 is removed by etching using fluorine-based gas plasma, and the multilayer reflective layer 12 is a method in which fluorine-based gas plasma or chlorine gas-based plasma is alternately used in the same manner as the protective layer 13. Etching is removed to form the light shielding frame 17.

  Next, a process of forming a prism structure on the light shielding frame portion 17 of the substrate 11 will be described. Here, a case where a micromachining method is used will be described. The bottom of the light shielding frame 17 formed on the mask is ground by a machining center or an NC grinding machine (S15) to form a desired shape. Thereafter, in order to remove grinding scraps, cleaning treatment (S16) with ultrapure water, organic alkaline chemicals, surfactants, etc. in which acid / alkali chemicals, ozone gas, hydrogen gas, etc. were dissolved, and centrifugal force were used. Spin drying (S17) is performed.

Through the above steps, the reflective mask 100 is completed.
According to the present invention, the bottom portion of the light shielding frame portion 17 has the prism structure, and the optical path of light in the EUV and out-of-band regions can be bent. As a result, the exposure light is reflected from the light shielding frame portion 17. Since extra reflected light can be removed, it is possible to prevent multiple exposure in the boundary region between the chips on the wafer.

Examples of the method for manufacturing a reflective mask according to the present invention will be described below.
FIG. 1 shows reflective mask blanks 10a and 10b used in this example. In this reflective mask blank, 40 pairs of Mo and Si multilayer reflective layers 12 designed to have a reflectivity of about 64% with respect to EUV light having a wavelength of 13.5 nm are formed on the substrate 11. An Ru protective layer 13 having a thickness of 2.5 nm is formed thereon, and an absorption layer 14a or 14b made of tantalum silicide having a thickness of 70 nm is further formed thereon.

  A positive chemically amplified resist 21 (FEP171: manufactured by FUJIFILM Electronics Materials) is applied to the reflective mask blanks 10a and 10b with a film thickness of 300 nm, and an electron beam drawing machine (JBX3040: manufactured by JEOL Ltd.). ), And a resist pattern was formed on the resist portion by PEB (Post Exposure Bake) at 110 ° C. for 10 minutes and spray development (SFG3000: manufactured by Sigma Meltech).

Next, the absorption layer 14a and 14b are etched with CF ₄ plasma and Cl ₂ plasma using a dry etching apparatus (SLR, manufactured by Hakutosha), and the resist shown in FIG. 2 is removed, washed, and dried. A reflective mask 100 having a pattern portion 18 was produced. The circuit pattern portion 18 is a pattern in which a 1: 1 line & space pattern having a dimension of 200 nm is arranged at the center of the mask. The size of the pattern region was 10 cm × 10 cm.

  Subsequently, the process of forming the light-shielding frame part 17 of the reflective mask 100 which has said circuit pattern part 18 was performed. The i-line resist 22 is applied to the reflective mask 100 with a film thickness of 500 nm, and is drawn and developed there by an i-line drawing machine (ALTA3000: manufactured by Applied Materials), thereby removing the light shielding frame portion 17 later. A pattern was formed. At this time, the opening width of the resist pattern was 5 mm, and the resist pattern was arranged at a distance of 3 mm from the outer peripheral edge of the circuit pattern portion 18 of 10 cm × 10 cm in the center of the mask.

Then, using a dry etching apparatus (SLR, manufactured by Hakutosha), 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 : flow rate The absorption layer 14 and the multilayer reflective layer 12 at the opening of the resist are etched away by anisotropic dry etching after 20 sccm and a processing time of 6 minutes, and the resist is peeled off, washed and dried, and a portion corresponding to the light shielding frame 17 is Formed.

  Next, a step of forming a prism structure on the bottom of the light shielding frame 17 was performed. The bottom of the light shielding frame 17 of the reflective mask 100 was ground with an NC grinding machine to form a prism structure having a V-shaped cross section. At this time, the inclination angle of the prism structure was set to 25 °. Next, the reflective mask 100 was completed by washing and drying in order to remove the processing waste.

DESCRIPTION OF SYMBOLS 10 Reflective mask blank 11 Substrate 12 Multi-layer reflective layer 13 Protective layer 14a Absorbing layer (single layer)
14b Absorption layer (lamination)
15 Back surface conductive film 16 Incident light 17 Shading frame portion 18 Circuit pattern portion 21 Resist 22 i-line resist 100 Reflective mask

Claims (4)

A reflective exposure mask,
A multilayer reflective layer, a protective layer, and an absorption layer are laminated in this order on one surface of the substrate, and a conductor layer is formed on the other surface,
A part of the absorption layer is etched away to form a circuit pattern portion;
On the outer periphery of the circuit pattern portion, a light-shielding frame portion is formed in which the absorption layer, the protective layer, and the multilayer reflective layer are etched away to expose the surface of the substrate,
At the bottom of the light shielding frame part, a structure is formed by removing a part of the substrate to form a space,
The cross-sectional shape of the space is V-shaped (an isosceles triangle in which the apex angle is disposed at the deepest part on the substrate side) or a wedge shape (a right triangle in which the oblique side is disposed on the substrate side).
A reflective mask characterized by that.   When the cross-sectional shape that is processed into the space on the substrate side in the stacking direction of the light shielding frame portion is an isosceles triangle having an apex angle disposed at the deepest portion on the substrate side, the base angle of the isosceles triangle is 22 ° or more. The reflective mask according to claim 1, wherein   When the cross-sectional shape that is processed into the space on the substrate side in the stacking direction of the light shielding frame is a right triangle with the hypotenuse arranged on the substrate side, the slope of the prism structure corresponding to the hypotenuse of the right triangle forms the surface of the substrate. The reflective mask according to claim 1, wherein the angle is 48 ° or more. It is a manufacturing method of the reflective mask in any one of Claims 1-3, Comprising: At least,
A circuit pattern portion forming step of forming a circuit pattern portion by patterning the absorption layer;
A light shielding frame forming step of forming a light shielding frame by etching and removing at least the absorption layer, the protective layer, and the multilayer reflective layer on at least a part of the periphery of the circuit pattern portion;
By processing the substrate exposed on the bottom surface of the light shielding frame portion in the light shielding frame forming step, even if incident light is reflected on the bottom portion of the light shielding frame to generate reflected light, the reflected light is absorbed by the absorption layer. And a prism structure forming step of forming a prism structure that does not reflect from the reflective mask. A method of manufacturing a reflective mask, comprising:

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