Apparatus and method for measuring phase of extreme ultraviolet (EUV) mask and method of fabricating EUV mask including the method

An apparatus and a method for correctly measuring a phase of an extreme ultraviolet (EUV) mask and a method of fabricating an EUV mask including the method are described. The apparatus for measuring the phase of the EUV mask includes an EUV light source configured to generate and output EUV light, at least one mirror configured to reflect the EUV light as reflected EUV light incident on an EUV mask to be measured, a mask stage on which the EUV mask is arranged, a detector configured to receive the EUV light reflected from the EUV mask, to obtain a two-dimensional (2D) image, and to measure reflectivity and diffraction efficiency of the EUV mask, and a processor configured to determine a phase of the EUV mask by using the reflectivity and diffraction efficiency of the EUV mask.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2020-0034057, filed on Mar. 19, 2020, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety.

BACKGROUND

The inventive concept relates to an extreme ultraviolet (EUV) mask, and more particularly, to an apparatus and a method for measuring the phase of the EUV mask.

A lithography process is a technology having considerable influence on miniaturization of a semiconductor device. Research into a light source with a shorter wavelength is being performed in order to overcome the resolution limit in the lithography process. Recently, an EUV lithography process using EUV light is being developed. The EUV light is scattered in a medium such as a material or air and is absorbed well into most materials. Therefore, during an exposure process, instead of a transmissive mask, a reflective mask is used. On the other hand, when inspection or metrology equipment applied to the transmissive mask is applied to the reflective mask, the resolution or defect detecting sensitivity may not be satisfactory. In particular, when inspection or metrology equipment actually using EUV light is not used, it may be difficult to satisfy a required specification during fabrication of a mask.

SUMMARY

The inventive concept relates to an apparatus and a method for correctly measuring a phase of an extreme ultraviolet (EUV) mask and a method of fabricating an EUV mask including the method.

According to an aspect of the inventive concept, there is provided an apparatus for measuring the phase of the EUV mask, including an EUV light source configured to generate and output EUV light, at least one mirror configured to reflect the EUV light as reflected EUV light incident on an EUV mask to be measured, a mask stage on which the EUV mask is arranged, a detector configured to receive the EUV light reflected from the EUV mask, to obtain a two-dimensional (2D) image, and to measure reflectivity and diffraction efficiency of the EUV mask, and a processor configured to calculate or determine a phase of the EUV mask by using the reflectivity and diffraction efficiency of the EUV mask.

According to an aspect of the inventive concept, there is provided an apparatus for measuring the phase of the EUV mask, including an EUV light source configured to generate and output EUV coherent light, at least one mirror configured to reflect the EUV coherent light as reflected EUV coherent light into an EUV mask to be measured, a mask stage on which the EUV mask is arranged, a detector configured to receive the EUV coherent light reflected from the EUV mask, to obtain a two-dimensional (2D) image, and to measure reflectivity and diffraction efficiency of the EUV mask, and a processor configured to calculate or determine a phase of the EUV mask by using the reflectivity and diffraction efficiency of the EUV mask. The EUV mask includes a first mask pattern area for measuring reflectivity and a second mask pattern area for measuring diffraction efficiency.

According to an aspect of the inventive concept, there is provided a method of measuring the phase of an EUV mask, including measuring reflectivity of a multilayer of a first mask pattern area of an EUV mask to be measured using a phase measuring apparatus, measuring reflectivity of an absorber layer of the first mask pattern area using the phase measuring apparatus, measuring diffraction efficiency of patterns of an absorber layer of a second mask pattern area of the EUV mask using the phase measuring apparatus, and calculating or determining a phase of the EUV mask using the reflectivity of each of the multilayer and the absorber layer of the first mask pattern area and the diffraction efficiency of the patterns of the absorber layer of the second mask pattern area.

According to an aspect of the inventive concept, there is provided a method of fabricating an EUV mask, including fabricating a first EUV mask, measuring reflectivity of a multilayer of a first mask pattern area of a second EUV mask to be measured using a phase measuring apparatus, measuring reflectivity of an absorber layer of the first mask pattern area using the phase measuring apparatus, measuring diffraction efficiency of patterns of an absorber layer of a second mask pattern area of the second EUV mask using the phase measuring apparatus, calculating a phase of the first EUV mask using the reflectivity of each of the multilayer and the absorber layer and the diffraction efficiency of the patterns of the absorber layer, determining whether the calculated phase is in an allowable range, and completing fabrication of the first EUV mask when the phase is in the allowable range.

DETAILED DESCRIPTION

FIG.1is a block diagram schematically illustrating an apparatus1000for measuring a phase of an extreme ultraviolet (EUV) mask according to an embodiment of the inventive concept.

Referring toFIG.1, the apparatus1000for measuring the phase of the EUV mask (hereinafter, referred to as ‘a phase measuring apparatus’) according to the current embodiment may include an EUV light source100, a coherence unit or coherence system200, a mirror unit or mirror system300, a mask stage400, a detector500, and a processor600.

The EUV light source100may be an apparatus for generating and outputting EUV light and may generate and output, in particular, EUV light of 13.5 nm. For example, the EUV light source100may generate the EUV light through plasma discharge. Laser plasma, discharge plasma, or high temperature plasma may be used for the plasma discharge.

On the other hand, a femto-second laser apparatus may be used for the laser plasma. In more detail, the femto-second laser apparatus may include, for example, a femto-second titanium (Ti):sapphire laser apparatus. The femto-second Ti:sapphire laser apparatus may generate pulse laser light with a frequency of dozens of MHzs and may have a correlator connected thereto. The laser light from the femto-second laser apparatus may be irradiated into or onto a discharge chamber by using a focusing lens. In the discharge chamber, a plasma generating gas, for example, a neon gas may be stored. By irradiating the laser light onto the neon gas stored in the discharge chamber, plasma is generated and light with various wavelengths including the EUV light may be emitted from the plasma.

The coherence unit200may include a pin-hole plate210and a filter220. The pin-hole plate210may be arranged at a rear end of the EUV light source100and may reduce the EUV light by a pin-hole size. In addition, the pin-hole plate210may improve spatial coherence of light so that the EUV light of the EUV light source100may become coherence light or coherent light. On the other hand, in the phase measuring apparatus1000according to the current embodiment, the pin-hole plate210is arranged between the EUV light source100and the filter220. However, a position of the pin-hole plate210is not limited thereto. For example, according to an embodiment, the pin-hole plate210may be arranged at a rear end of the filter220.

The filter220may selectively transmit only the EUV light among light components emitted from the EUV light source100and may remove the other light components. For example, light emitted from the EUV light source100first, that is, light emitted from the plasma may include light with various wavelengths such as EUV light or vacuum ultraviolet (VUV) light. Therefore, the filter220may have only the EUV light irradiated onto an EUV mask2000by blocking the other light components excluding the EUV light among the light components emitted from the EUV light source100. The filter220may be considered as improving spectrum coherence of light.

The filter220may include, for example, a zirconium filter. On the other hand, EUV light output through the filter220may be EUV light having a center wavelength of 13.5 nm. For example, the filter220may include an X-ray mirror. The X-ray mirror may irradiate the EUV light with the center wavelength of 13.5 nm in the EUV light onto the EUV mask2000. That is, the X-ray mirror may select the EUV light with the center wavelength of 13.5 nm and may irradiate the selected EUV light onto the EUV mask2000using the mirror unit300.

On the other hand, according to an embodiment, the coherence unit200may further include a shutter arranged between the EUV light source100and the pin-hole plate210or between the EUV light source100and the filter220. The shutter may control an amount of the EUV light irradiated onto the EUV mask2000by controlling an amount of the EUV light output from the EUV light source100.

The mirror unit300may include a first mirror310and a second mirror320. The first mirror310may condense the EUV light, and the second mirror320may direct the EUV light incident on the EUV mask2000at a predetermined angle. In the phase measuring apparatus1000according to the current embodiment, the first mirror310may be or include a concave mirror and the second mirror320may be or include a flat mirror. For example, the first mirror310may be or include a concave mirror such as a spherical mirror or an elliptical mirror.

Positions and functions of the first mirror310and the second mirror320will be described in more detail. The first mirror310may be arranged on the other side of the coherence unit200from the EUV light source100around the EUV mask2000. In addition, the first mirror310that is the concave mirror may have a concave surface reflecting the EUV light and condensing the reflected EUV light onto the second mirror320. Therefore, the EUV light may be incident on the first mirror310and then, may be reflected toward an upper space in which the second mirror320is arranged. In addition, the EUV light may be condensed through the first mirror310and may be incident on the second mirror320. Specifically, for example, when the first mirror310is a spherical or elliptical mirror, the second mirror320may be arranged in a focus position of the spherical or elliptical mirror. Therefore, the EUV light incident on the first mirror310may be reflected from the first mirror310and may be condensed onto the second mirror320arranged in the focus position of the first mirror310.

The second mirror320may be arranged in the upper space of the EUV mask2000(e.g., above the EUV mask2000). For example, the second mirror320may be arranged in a position higher than the first mirror310. However, according to an embodiment, the second mirror320may be arranged in a position lower than the first mirror310. In addition, the second mirror320that is the flat mirror may have a plane reflecting the EUV light to the EUV mask2000. Therefore, the EUV light incident from the first mirror310may be reflected by the second mirror320and may proceed toward an upper surface of the EUV mask2000.

On the other hand, a slope angle of the second mirror320may be controlled so that an angle of incidence θ of the EUV light onto the upper surface of the EUV mask2000is 2° to 10° (e.g., relative to vertical). In the phase measuring apparatus1000according to the current embodiment, the slope angle of the second mirror320may be controlled so that the angle of incidence θ of the EUV light is about 6°. Furthermore, light incident on the EUV mask2000may be diffracted and reflected due to patterns of an absorber layer formed on the upper surface of the EUV mask2000. InFIG.1, among light components reflected from the EUV mask2000, a portion marked with a solid line may mean 0thorder diffracted light and a portion marked with a dashed line may mean first order diffracted light. In accordance with a shape of each of the patterns of the absorber layer formed on the upper surface of the EUV mask2000, above second order diffracted light may be obtained.

The phase measuring apparatus1000according to the current embodiment may effectively irradiate the EUV light onto the EUV mask2000even in a narrow space due to layout structures of the first mirror310that is the concave mirror and the second mirror320that is the flat mirror.

The EUV mask2000to be measured may be arranged on the mask stage400. The mask stage400may horizontally move on an X-Y plane and may vertically move on a Z axis according to an embodiment. According to two or three-dimensional movement of the mask stage400, the EUV mask2000may also two or three-dimensionally move. According to an embodiment, the mask stage400may include a position sensor controlling a position or a measuring position of the EUV mask2000.

The detector500detects the EUV light reflected and diffracted from the EUV mask2000. The detector500as an apparatus capable of performing spatial decomposition may include a kind of imaging apparatus capable of obtaining a far-field diffracted image as a two-dimensional (2D) image. The imaging apparatus may collect a field spectrum of reflected light, may convert the reflected light into an electrical signal, and may output the electrical signal. For example, in the phase measuring apparatus1000according to the current embodiment, the detector500may include a charge coupled device (CCD) camera using an X-ray. However, the detector500is not limited to a CCD camera. For example, the detector500may include a photo-diode array (PDA) detector and a CMOS image sensor (CIS) camera.

The detector500may measure the reflectivity of each of a multilayer (refer to2100ofFIG.2A) and a first absorber layer (refer to2200ofFIG.2A) of the EUV mask2000and diffraction efficiency of a pattern of a second absorber layer (refer to2200aofFIG.2B) of the EUV mask2000. The reflectivity of each of the multilayer and the first absorber layer and the diffraction efficiency of the pattern of the second absorber layer will be described in more detail with reference toFIGS.4A to4C.

The processor600may reconstruct imaging through a program based on imaging information received from the detector500. In addition, the processor600may calculate the phase of the EUV mask based on the imaging information. Here, the imaging information may include the reflectivity of each of the multilayer and the first absorber layer of the EUV mask2000and the diffraction efficiency of the pattern of the second absorber layer of the EUV mask2000. Therefore, the processor600may specifically calculate an absolute value of the phase of the EUV mask2000by using the reflectivity and the diffraction efficiency of the EUV mask2000to be measured. Phase calculation through the processor600will be described in more detail with reference toFIG.5. On the other hand, the processor600may include an interface such as a personal computer (PC) so that a large amount of data from the detector500may be processed in a short time.

The phase measuring apparatus1000according to the current embodiment may measure the reflectivity of each of the multilayer and the absorber layer in a first mask pattern area of the EUV mask by using the EUV light and the detector such as the CCD camera, may receive the diffracted light in a second mask pattern area of the EUV mask, and may measure the diffraction efficiency of the diffracted light by using the reflectivity of the multilayer or intensity of the reflected light. In addition, the phase measuring apparatus1000according to the current embodiment may accurately measure the phase of the EUV mask by specifically calculating the absolute value of the phase of the EUV mask through the formula of the diffraction efficiency or a phase measuring algorithm based on the reflectivity of each of the multilayer and the absorber layer and the diffraction efficiency of the diffracted light. Therefore, the phase measuring apparatus1000according to the current embodiment may significantly contribute to improvement of quality of the EUV mask by providing correct phase information on the EUV mask.

For reference, since a current EUV mask with an absorber layer area with reflectivity of around 2% is not a perfect binary mask, it is necessary to manage the reflectivity and phase of the EUV mask. Here, the binary mask may mean a mask with a multilayer area with reflectivity of almost 100% and with an absorber layer area with reflectivity of almost 0. In addition, in an EUV phase shift mask (PSM) expected to be developed, the phase of the EUV mask is one of the very important factors defining the quality of the EUV mask. Conventional measurement equipment may not specifically measure the absolute value of the phase of the EUV mask. The phase measuring apparatus1000according to the current embodiment may correctly measure the phase of the EUV mask through the above-described components and a phase measuring algorithm and accordingly, may significantly contribute to the improvement of the quality of the EUV mask.

FIGS.2A and2Bare cross-sectional views of the EUV mask2000to be measured by the apparatus for measuring the phase of the EUV mask ofFIG.1.

Referring toFIG.2A, the EUV mask2000may include a first mask pattern area2000A1. A first mask pattern area2000A1may include a multilayer2100and a first absorber layer2200. The multilayer2100may have a structure in which two kinds of different material layers are alternately stacked. For example, the multilayer2100may have a structure in which a silicon (Si) layer and a molybdenum (Mo) layer are alternately stacked. In more detail, for example, the multilayer2100may be formed by stacking about 40 to 60 bilayers each including the Si layer and the Mo layer. In addition, each of the Si layer and the Mo layer that form the multilayer2100may have a thickness of about 3 nm and 4 nm.

On the other hand, the multilayer2100may be formed on a mask substrate such as a Si substrate or a quartz substrate. The EUV mask in a more detailed structure including the mask substrate will be described with reference toFIG.3.

The first absorber layer2200may be arranged on the multilayer2100. In addition, as illustrated inFIG.2A, the first absorber layer2200with predetermined patterns may be arranged on the multilayer2100. For example, the first absorber layer2200may have line and space patterns apart from each other in a first direction (an x direction) and extending in a second direction (a y direction). The pattern of the first absorber layer2200is not limited to the line and space pattern. The pattern of the first absorber layer2200may have repeatability so that a phase may be more easily calculated. However, the pattern of the first absorber layer2200does not necessarily have repeatability.

The first absorber layer2200absorbing the EUV light may be formed of tantalum nitride (TaN), Ta, titanium nitride (TiN), or Ti. However, a material of the first absorber layer2200is not limited to the above-described materials. On the other hand, although not shown, between the first absorber layer2200and the multilayer2100, a capping layer may be present. The capping layer will be described in more detail with reference toFIG.3.

In the apparatus1000for measuring the phase of the EUV mask according to the current embodiment, the first mask pattern area2000A1of the EUV mask2000may include the pattern of the first absorber layer2200at an mm level. That is, in the first mask pattern area2000A1, when the first absorber layer2200in the line and space pattern is regularly repeated and a distance or space between the first absorber layers2200has a first width W1and a first pitch P1in the first direction (the x direction), each of the first width W1and the first pitch P1is about several mms and the first pitch P1is greater than the first width W1in accordance with the definition of a pitch.

Hereinafter, a portion between the first absorber layers2200, in which the multilayer2100is exposed, is referred to as a multilayer area MLA and a portion of the first absorber layer2200is referred to as an absorber layer area ALA. Due to a characteristic in which the multilayer area MLA is bright and the absorber layer area ALA is dark, the multilayer area MLA is referred to as a clear area and the absorber layer area ALA is referred to as a dark area.

The first mask pattern area2000A1may be used for measuring reflectivity of the multilayer area MLA and reflectivity of the absorber layer area ALA. In general, reflectivity may be defined as the intensity of reflected light to the intensity of incident light. When a size of the pattern of the absorber layer and a distance between the absorber layers are very small, it may be difficult to measure correctly the reflectivity of each of the multilayer area MLA and the absorber layer area ALA. That is, when the reflectivity of the multilayer area MLA is measured, light generated by reflection, diffraction, and scattering in the absorber layer area ALA may be included in reflected light of the multilayer area MLA so that the reflectivity of the multilayer area MLA may be incorrectly measured. In addition, when the reflectivity of the absorber layer area ALA is calculated, the reflected light of the multilayer area MLA may affect the measurement or reflection from a side surface of the absorber layer may affect the measurement, and thus, the reflectivity of the absorber layer area ALA may be incorrectly measured.

Therefore, the above-described problem may be solved by forming the pattern of the first absorber layer2200of the first mask pattern area2000A1relatively large to be at the mm level. Therefore, the apparatus1000for measuring the phase of the EUV mask according to the current embodiment may correctly measure the reflectivity of each of the multilayer area MLA and the absorber layer area ALA by using the first mask pattern area2000A1.

Referring toFIG.2B, the EUV mask2000may include a second mask pattern area2000A2and the second mask pattern area2000A2may include the multilayer2100and second absorber layers2200a. The second absorber layers2200amay be different from the first absorber layer2200of the first mask pattern area2000A1in size. In more detail, the multilayer2100may be the same as described for the multilayer2100of the first mask pattern area2000A1. On the other hand, a material or characteristic of the second absorber layers2200amay be the same as described for the first absorber layer2200of the first mask pattern area2000A1. However, a pattern of the second absorber layers2200amay be different from the pattern of the first absorber layer2200of the first mask pattern area2000A1in that the pattern of the second absorber layers2200ahas a size at a μm level. For example, the second absorber layers2200ain a line and space pattern may have a second width W2of about several μms and a second pitch P2of about several μms in the first direction (the x direction). In addition, in accordance with the definition of a pitch, the second pitch P2is greater than the second width W2.

The second mask pattern area2000A2may be used for measuring the diffraction efficiency of the pattern of the absorber layer. The diffraction efficiency may be defined as the intensity of diffracted light in the pattern of the absorber layer to the intensity of the reflected light of the multilayer area MLA. In addition, the diffraction efficiency may be defined for each of 0thorder diffracted light and higher order diffracted light components. That is, the diffraction efficiency of the 0thorder diffracted light may be defined as the intensity of the 0thorder diffracted light to the intensity of the reflected light of the multilayer area MLA and the diffraction efficiency of the first order diffracted light may be defined as the intensity of the first order diffracted light to the intensity of the reflected light of the multilayer area MLA.

The apparatus1000for measuring the phase of the EUV mask according to the current embodiment may actually measure the phase of the actual EUV mask and may correctly determine whether the phase of the actual EUV mask is defective by measuring the phase of the EUV mask2000by measuring the diffraction efficiency by using the second mask pattern area2000A2of the EUV mask2000including the pattern of the second absorber layer2200aat the μm level.

For reference, a size of the pattern of the actual EUV mask may be at the nm level. It may be very complicated to calculate the diffraction efficiency of light of the actual EUV mask having the pattern of the absorber layer at the nm level and the phase of the actual EUV mask in accordance with the diffraction efficiency. However, considering a conceptual aspect of the phase of the EUV mask, when a thickness of the absorber layer is almost 0, a difference between the phase of the EUV mask having the pattern of the absorber layer at the μm level and the phase of the EUV mask having the pattern of the absorber layer at the nm level may not be large. Therefore, the apparatus1000for measuring the phase of the EUV mask according to the current embodiment may calculate the phase of the EUV mask2000by making the thickness of the second absorber layer2200aalmost 0 after calculating the diffraction efficiency of the second mask pattern area2000A2having the pattern of the second absorber layer2200aat the μm level. The calculated phase of the EUV mask2000is similar to the phase of the actual EUV mask and may contribute to determining whether the phase of the actual EUV mask is defective.

FIG.3is a cross-sectional view illustrating a structure of the EUV mask2000ofFIG.2Ain more detail. Description previously given with reference toFIG.2Awill be omitted.

Referring toFIG.3, the EUV mask2000may include a mask substrate2010, a rear surface coating layer2020, the multilayer2100, a capping layer2030, and the first absorber layer2200. The mask substrate2010may be formed of a low thermal expansion material (LTEM). For example, the mask substrate2010may be or include a Si substrate or a quartz substrate.

The rear surface coating layer2020may be formed on a lower surface of the mask substrate2010and the multilayer2100may be formed on an upper surface of the mask substrate2010. The rear surface coating layer2020may be formed of a conductive material such as a metal. The multilayer2100may include a plurality of alternately stacked Si layers2120and Mo layers2110. The multilayer2100may be the same as described for the multilayer2100of the first mask pattern area2000A1ofFIG.2A.

The capping layer2030may be formed on the multilayer2100. The first absorber layer2200may be formed on the capping layer2030. That is, the capping layer2030may be between the first absorber layer2200and the multilayer2100. The capping layer2030may include one or more material layers and may protect the multilayer2100. For example, the capping layer2030may be formed of ruthenium (Ru). However, a material of the capping layer2030is not limited to Ru.

The first absorber layer2200may include an absorber body2210and an anti-reflective coating (ARC) layer2220. The absorber body2210may be a layer absorbing the EUV light and may be formed of TaN, Ta, TiN, or Ti as described above. However, a material of the absorber body2210is not limited to the above-described materials. The ARC layer2220preventing incident EUV light from being reflected may be omitted according to an embodiment.

As illustrated inFIG.3, the EUV light may be incident on the EUV mask2000with an angle of incidence of 6° and may be reflected with an angle of reflection of 6°. Here, the angle of incidence and the angle of reflection are defined with respect to a normal line NL perpendicular to the upper surface of the EUV mask2000and the normal line NL is marked with a dashed line inFIG.3. The normal line NL may be a vertical line. In addition, the EUV light incident on the EUV mask2000may be diffracted due to the pattern of the first absorber layer2200. InFIG.3, 0th order diffracted light 0th-Ld marked with a solid line and first order diffracted light 1st-Ld marked with a dashed line are illustrated. Diffracted light may include above second order diffracted light.

FIGS.4A to4Care conceptual diagrams illustrating a process of measuring a phase of an EUV mask by using the apparatus for measuring the phase of the EUV mask ofFIG.1. Description will be made with reference toFIGS.1to3and description previously given with reference toFIGS.1to3may be omitted in the interest of brevity.

Referring toFIG.4A, first, by using the phase measuring apparatus1000according to the current embodiment, reflectivity Rml of the multilayer area MLA of the first mask pattern area2000A1of the EUV mask2000is measured. InFIG.4A, for convenience sake, only the multilayer area MLA of the first mask pattern area2000A1is illustrated. Reflectivity R may be defined as the intensity of the reflected light to the intensity of the incident light as described above. Therefore, the reflectivity Rml of the multilayer area MLA may be calculated by measuring EUV light Lrm reflected from the multilayer area MLA through the detector500and dividing the intensity of the measured EUV light by intensity of the EUV light incident on the multilayer area MLA.

Referring toFIG.4B, by using the phase measuring apparatus1000according to the current embodiment, reflectivity Rabs of the absorber layer area ALA of the first mask pattern area2000A1of the EUV mask2000is measured. InFIG.4B, for convenience sake, the absorber layer area ALA of the first mask pattern area2000A1and only a part of the multilayer area MLA adjacent to the absorber layer area ALA of the first mask pattern area2000A1are illustrated. The reflectivity Rabs of the absorber layer area ALA may be obtained by the same method as a method of obtaining the reflectivity Rml of the multilayer area MLA. That is, the reflectivity Rabs of the absorber layer area ALA may be obtained by measuring EUV light Lra reflected from the absorber layer area ALA and dividing the intensity of the measured EUV light by the intensity of the EUV light incident on the absorber layer area ALA.

Referring toFIG.4C, after obtaining the reflectivity Rml of the multilayer area MLA of the first mask pattern area2000A1and the reflectivity Rabs of the absorber layer area ALA of the first mask pattern area2000A1, by using the phase measuring apparatus1000according to the current embodiment, the diffraction efficiency of the diffracted light from the pattern of the second absorber layer2200aof the second mask pattern area2000A2of the EUV mask2000is measured. In more detail, the diffracted light reflected from the pattern of the second absorber layer2200aof the second mask pattern area2000A2is measured through the detector500and the intensity of the measured diffracted light is calculated by component. For example, the intensity of the 0th order diffracted light 0th-Ld and the intensity of the first order diffracted light 1st-Ld are calculated. The diffraction efficiency may be defined as the intensity of the diffracted light of the pattern of the second absorber layer2200ato the intensity of the reflected light of the multilayer area MLA. In addition, the diffraction efficiency may be obtained by component. For example, diffraction efficiency I0 of the 0th order diffracted light 0th-Ld may be obtained by dividing the intensity of the 0th order diffracted light 0th-Ld by the intensity of the reflected light of the multilayer area MLA. In addition, diffraction efficiency I1 of the first order diffracted light 1st-Ld may be obtained by dividing the intensity of the 1st order diffracted light 1st-Ld by the intensity of the reflected light of the multilayer area MLA.

Then, by using the reflectivity Rml of the multilayer area MLA, the reflectivity Rabs of the absorber layer area ALA, and diffraction efficiency of each of the components of the diffracted light, an absolute value of the phase of the EUV mask2000may be specifically calculated. On the other hand, the calculated phase of the EUV mask2000is similar to the phase of the actual EUV mask as described above. A principle of obtaining the absolute value of the phase of the EUV mask will be described in more detail with reference toFIG.5.

FIG.5is a conceptual diagram illustrating a principle of measuring a phase of an EUV mask by using the apparatus for measuring the phase of the EUV mask ofFIG.1. Description previously given with reference toFIGS.1to4Cmay be omitted in the interest of brevity.

Referring toFIG.5, the EUV mask2000may include the multilayer2100and the second absorber layers2200a. On the other hand, as illustrated inFIG.5, the second absorber layer2200ahas repeated line and space patterns apart from each other in the first direction (the x direction) and extending in the second direction (the y direction). InFIG.5, A0,MLand A1,MLmay respectively mean 0th order diffracted light and first order diffracted light in the multilayer2100and A0,absand A1,absmay mean 0th order diffracted light and first order diffracted light in the second absorber layer2200a.

In accordance with a diffraction theory, when a thickness t of the second absorber layer2200ais almost 0, the diffraction efficiency I0 of the 0th order diffracted light and the diffraction efficiency I1 of the first order diffracted light in the patterns repeated lines and spaces may be represented by EQUATION 1 and EQUATION 2.
I0=[(w/p)2+Rr((p−w)/p)2+2w(p−w)/p2(Rr)1/2cos φ]  EQUATION (1)
I1=1/π2sin2(wπ/p)[1+Rr−2Rr1/2cos φ]  EQUATION (2)

wherein, w may mean a distance between the patterns of the second absorber layer2200ain the first direction (the x direction) or a width of the multilayer area MLA and p may mean a pitch of each of the patterns of the second absorber layer2200ain the first direction (the x direction). In addition, Rr may mean a ratio Rabs/Rml of the reflectivity Rabs of the absorber layer area ALA or the dark area to the reflectivity Rml of the multilayer area MLA or the clear area and φ may mean the phase of the EUV mask2000.

On the other hand, I0 and I1 may be calculated or determined by the phase measuring apparatus1000according to the current embodiment as described above. Therefore, by calculating or determining w and φ simultaneously satisfying I0 and I1 through EQUATION 1 and EQUATION 2, the phase of the EUV mask2000may be calculated or determined. In addition, when w is measured and obtained by a measuring instrument by another method or w is previously grasped or known, by calculating P by substituting w for EQUATION 1 and EQUATION 2, the phase of the EUV mask2000may be calculated.

On the other hand, when the distance between the patterns of the second absorber layer2200ais ½ of the pitch of each of the patterns of the second absorber layer2200a, that is, when w=p/2 is established, φ may be represented by EQUATION 3.
φ=cos−1{(4I0−π2I1)/4(Rr)1/2}  EQUATION (3)

The phase measuring apparatus1000according to the current embodiment may measure the reflectivity Rml of the multilayer area MLA and the reflectivity Rabs of the absorber layer area ALA by using the first mask pattern area2000A1of the EUV mask2000, may measure the diffraction efficiency values I0 and I1 of the diffracted light components by using the second mask pattern area2000A2of the EUV mask2000, and may specifically calculate the phase of the EUV mask2000by applying the diffraction efficiency values I0 and I1 to EQUATION 1 and EQUATION 2 in accordance with the diffraction theory.

For reference, when the second absorber layer2200ahas the patterns repeated in the form of lines and spaces, because above second order diffracted light is insignificant, it is not necessary to consider the above second order diffracted light. However, when the second absorber layer2200ahas repeated patterns different from the patterns repeated in the form of lines and spaces, in accordance with the diffraction theory, equations for the diffraction efficiency different from EQUATION 1 and EQUATION 2 may be induced and the above second order diffracted light may be considered. Furthermore, when the second absorber layer2200adoes not have the repeated patterns, the equation for the diffracted efficiency may become more complicated.

FIGS.6to8are block diagrams each schematically illustrating an apparatus for measuring a phase of an EUV mask according to embodiments of the inventive concept. Description previously given with reference toFIGS.1to5may be omitted in the interest of brevity.

Referring toFIG.6, a phase measuring apparatus1000aaccording to the current embodiment may be different from the phase measuring apparatus1000ofFIG.1in a configuration of a mirror unit or mirror system300a. Specifically, in the phase measuring apparatus1000aaccording to the current embodiment, the mirror unit300aincludes a first mirror310aand a second mirror320and the first mirror310amay not be a concave mirror and may be a flat mirror like the second mirror320. When the EUV light from the EUV light source100does not spread widely, condensing may not be required. Therefore, in the phase measuring apparatus1000aaccording to the current embodiment, the first mirror310aof the mirror unit300amay be formed of the flat mirror.

Referring toFIG.7, a phase measuring apparatus1000baccording to the current embodiment may be different from the phase measuring apparatus1000ofFIG.1in configurations of an EUV light source100aand a coherence unit or coherence system200a. Specifically, in the phase measuring apparatus1000baccording to the current embodiment, the coherence unit200amay include only a filter220and may not include a pin-hole plate. In addition, the EUV light source100amay not be a common EUV light source and may be a coherent EUV light source outputting coherent EUV light. For example, the EUV light source100amay be a high harmonic generation (HHG) EUV light source generating a higher order harmonic wave.

When the EUV light source100ais a coherent EUV light source, considering that the pin-hole plate is arranged in order to improve spatial coherence of light, the pin-hole plate may not be required. Therefore, in the phase measuring apparatus1000baccording to the current embodiment, the coherence unit200amay not include the pin-hole plate and may include only the filter220. Although the EUV light source100ais the coherent EUV light source, when it is necessary to reduce the size of the EUV light, a pin-hole plate in which a pin-hole with a corresponding size is formed may be arranged or provided.

Referring toFIG.8, a phase measuring apparatus1000caccording to the current embodiment may be different from the phase measuring apparatus1000ofFIG.1in a configuration of a mirror unit or mirror system300b. Specifically, in the phase measuring apparatus1000caccording to the current embodiment, the mirror unit300bmay include only the second mirror320and may not include the first mirror. Therefore, the EUV light from the coherence unit200may be incident on the second mirror320and may be reflected from the second mirror320and directly incident on the EUV mask2000to be measured.

The second mirror320as the flat mirror may have actually the same function as the second mirror320of the phase measuring apparatus1000ofFIG.1. That is, the second mirror320may have the EUV light incident on the EUV mask2000with an angle θ of incidence of about 6°. According to an embodiment, the second mirror320may condense the EUV light and may have the condensed EUV light incident on the EUV mask2000. In such a case, the second mirror320may have the form of the concave mirror.

In the phase measuring apparatus1000caccording to the current embodiment, in order to have the EUV light incident on the EUV mask2000with an angle θ of incidence of about 6°, the second mirror320may be arranged to be spaced apart from the EUV mask2000by a certain distance. However, in the phase measuring apparatus1000caccording to the current embodiment, only the second mirror320is arranged or provided, which may be advantageous in terms of optical loss.

FIG.9is a flowchart illustrating processes of a method of measuring a phase of an EUV mask according to an embodiment of the inventive concept. Description will be made with reference toFIGS.1to2Band description previously given with reference toFIGS.1to8may be omitted in the interest of brevity.

Referring toFIG.9, in the method of measuring the phase of the EUV mask according to the current embodiment (hereinafter, referred to as ‘a phase measuring method’), first, by using the phase measuring apparatus1000, the reflectivity of the multilayer2100or the multilayer area MLA of the first mask pattern area2000A1of the EUV mask2000is measured in operation S110. The reflectivity of the multilayer2100may be calculated by measuring the EUV light reflected from the multilayer2100through the detector500and dividing the intensity of the measured EUV light by the intensity of the EUV light incident on the multilayer2100based on the definition of the reflectivity.

Next, by using the phase measuring apparatus1000, the reflectivity of the first absorber layer2200or the absorber layer area ALA of the first mask pattern area2000A1of the EUV mask2000is measured in operation S120. The reflectivity of the first absorber layer2200may be calculated by measuring the EUV light reflected from the first absorber layer2200through the detector500and dividing the intensity of the measured EUV light by the intensity of the EUV light incident on the first absorber layer2200in the same way as calculating the reflectivity of the multilayer2100.

Then, by using the phase measuring apparatus1000, the diffraction efficiency of each of the patterns of the second absorber layer2200aof the second mask pattern area2000A2of the EUV mask2000is measured in operation S130. The diffraction efficiency may be calculated by dividing the intensity of the diffracted light from each of the patterns of the second absorber layer2200aby the intensity of the EUV light reflected from the multilayer2100. In addition, the diffraction efficiency may be calculated by each component of the diffracted light. For example, the diffraction efficiency I0 of the 0th order diffracted light may be calculated by dividing the intensity of the 0th order diffracted light by the intensity of the EUV light reflected from the multilayer2100. In addition, the diffraction efficiency I1 of the first order diffracted light may be calculated by dividing the intensity of the first order diffracted light by the intensity of the EUV light reflected from the multilayer2100.

InFIG.9, operations are performed in the order of operation S110of measuring the reflectivity of the multilayer, operation S120of measuring the reflectivity of the first absorber layer, and operation S130of measuring the diffraction efficiency of each of the patterns of the second absorber layer. However, the inventive concept is not limited thereto. For example, operations may be independently performed and the order in which operations are performed may be arbitrary.

After measuring the reflectivity of each of the multilayer2100and the first absorber layer2200of the EUV mask2000and measuring the diffraction efficiency of each of the patterns of the second absorber layer2200a, the phase of the EUV mask2000is calculated in operation S140. The phase of the EUV mask2000may be calculated by applying the measured reflectivity and diffraction efficiency to EQUATION 1 and EQUATION 2 in accordance with the diffraction theory. For example, when the patterns of the second absorber layer2200aof the EUV mask2000are repeated in the form of lines and spaces, a distance between the patterns of the second absorber layer2200ais w, and a pitch of each of the patterns of the second absorber layer2200ais p, the diffraction efficiency I0 of the 0th order diffracted light and the diffraction efficiency I1 of the first order diffracted light are represented by EQUATION 1 and EQUATION 2 and, by obtaining p simultaneously satisfying EQUATION 1 and EQUATION 2 or by obtaining φ by applying measured or previously grasped or known w to EQUATION 1 and EQUATION 2, the phase of the EUV mask2000may be calculated. Furthermore, the calculated phase of the EUV mask2000is similar to the phase of the actual EUV mask and may contribute to determining whether the phase of the actual EUV mask is defective as described above.

FIG.10is a flowchart illustrating processes of a method of fabricating an EUV mask according to an embodiment of the inventive concept. Description will be made with reference toFIGS.1to2Band description previously given with reference toFIG.9may be omitted in the interest of brevity.

Referring toFIG.10, in the method of fabricating the EUV mask according to the current embodiment, first, the EUV mask is fabricated in operation S210. The EUV mask may be fabricated by a method of fabricating a common EUV mask. For example, the EUV mask may be fabricated by performing a layout design of a pattern on a mask, by obtaining design data on a mask through an OPC method, by transmitting mask tape-out (MTO) design data, by preparing mask data, by exposing a mask substrate, and by performing a subsequent process.

Then, the phase of the EUV mask is measured in operation S220. The phase of the EUV mask may not be measured by measuring the phase of the previously fabricated actual EUV mask and may be measured by using the first mask pattern area2000A1and the second mask pattern area2000A2of the EUV mask2000as described for the phase measuring method ofFIG.9. The detailed method of measuring the phase of the EUV mask is the same as described with reference toFIG.9.

Next, it is determined whether the measured phase of the EUV mask is in an allowable range in operation S230. In general, the EUV mask must have a required phase. However, when a material or pattern of each of the first and second absorber layers2200and2200ais defective, the EUV mask may not have the required phase. On the other hand, defects in the pattern of each of the first and second absorber layers2200and2200amay be caused by a process error when the pattern of each of the first and second absorber layers2200and2200ais formed. Therefore, by measuring the phase of the EUV mask2000through the phase measuring method ofFIG.9, the phase of the actual EUV mask may be indirectly measured. As described above, the phase of the EUV mask2000may be similar to the phase of the actual EUV mask.

For reference, the EUV mask2000may be different from the actual EUV mask in scale and materials of the multilayer2100and the first and second absorber layers2200and2200amay be the same as materials of the multilayer and the absorber layers of the actual EUV mask and fabrication processes of the EUV mask2000may be the same as fabrication processes of the actual EUV mask. Therefore, during fabrication of the actual EUV mask, when a material or process condition of each of absorber layers is erroneous so that the phase of the actual EUV mask deviates from an allowable range, the same error may occur in the EUV mask2000and the measured phase may also deviate from the allowable range.

When the calculated phase is in the allowable range (Yes), fabrication of the EUV mask is completed in operation S240. When the calculated phase deviates from the allowable range (No), a cause is analyzed and/or process conditions are changed in operation S250. Here, the process conditions may include the materials of the multilayer2100and the first and second absorber layers2200and2200a. Then, the process returns to operation S210of fabricating the EUV mask, and a new EUV mask is fabricated based on the changed process conditions.

The method of fabricating the EUV mask according to the current embodiment may significantly contribute to improvement of quality of the EUV mask by correctly measuring the phase of the EUV mask through the phase measuring method described with reference toFIG.9and determining whether the phase of the EUV mask is defective.

While the inventive concept has been particularly shown and described with reference to embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the scope of the following claims.