Mask manufacturing method, mask substrate, and charged beam drawing method

A manufacturing method of a phase shift mask in an embodiment includes: forming a metal layer on a substrate, the metal layer having a first region and a second region, the first region being configured to emit secondary electrons by irradiation with electrons, the second region being configured to emit secondary electrons higher in density than the first region, by the irradiation with electrons; patterning the metal layer to form a main pattern in the first region and an alignment mark in the second region; forming a resist layer on the patterned metal layer; and aligning the substrate using a secondary electron image of the alignment mark.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2014-033232, filed on Feb. 24, 2014; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein generally relate to a mask manufacturing method, a mask substrate, and a charged beam drawing method.

BACKGROUND

To respond to miniaturization of a semiconductor device such as an LSI, optical lithography by a phase sift mask (PSM) is used. The PSM uses interference of light to enable exposure with resolution higher than that defined by wavelength of light.

Here, in a Levenson phase shift mask, for example, a pattern is created in a light shielding film formed on a light transmissive mask substrate as a first layer, and then a pattern for a shifter on the mask substrate as a second layer. Therefore, before drawing of the pattern of the second layer, alignment with the pattern of the first layer is performed. For the alignment, a secondary electron image of the pattern (alignment mark) of the first layer is used.

However, in recent years, the light shielding film significantly becomes thinner and therefore detection of the alignment mark becomes more difficult, so that it becomes more difficult to secure the accuracy of overlapping the patterns of the first layer and the second layer.

Note that a technology for obtaining a sufficient detection signal of the alignment mark is disclosed.

DETAILED DESCRIPTION

A mask manufacturing method in an embodiment includes: forming a metal layer on a substrate, the metal layer having a first region and a second region, the first region being configured to emit secondary electrons by irradiation with electrons, the second region being configured to emit secondary electrons higher in density than the first region, by the irradiation with electrons; patterning the metal layer to form a main pattern in the first region and an alignment mark in the second region; forming a resist layer on the patterned metal layer; and aligning the substrate using a secondary electron image of the alignment mark.

Hereinafter, an embodiment will be described in detail with reference to the drawings.

FIG. 1AandFIG. 1Bare schematic views of a mask drawing apparatus10.FIG. 1Ais a plan view of the mask drawing apparatus10.FIG. 1Bis a cross-sectional view of the mask drawing apparatus10. Hereinafter, a configuration of the mask drawing apparatus10will be described with reference toFIG. 1AandFIG. 1B. Note that inFIG. 1A, illustration of an electron beam optical column500is omitted.

As illustrated inFIG. 1AandFIG. 1B, the mask drawing apparatus10includes a load/unload interface (I/F)100, an input/output (I/O) chamber200, a robot chamber (R chamber)300, a writing chamber (W chamber)400, the electron beam optical column500, a control system unit600, and gate valves G1to G3.

The load/unload I/F100includes a mounting table110on which a container C (for example, SMIF Pod) housing a mask substrate W to be used in this embodiment is mounted, and a carrier robot120that carries the mask substrate W.

The mask substrate W is a substrate in which a light shielding film (for example, a later-described metal layer40) and a resist film (for example, a later-described resist layer50,55) are stacked. The light shielding film has a main pattern MP and alignment marks AM.

Here, when irradiation with electrons is performed under the same condition, the density of emitted secondary electrons is different between the vicinity of the alignment mark AM and the vicinity of the main pattern MP. More specifically, the density of secondary electrons emitted from the vicinity of the alignment mark AM is larger than the density of secondary electrons emitted from the vicinity of the main pattern MP. The main pattern MP and the alignment mark AM are different in characteristics (for example, film thickness, material) of the light shielding film and thus different in the density of the emitted secondary electrons. As a result of this, even when the light shielding film at the main pattern MP is thin, detection of the alignment mark AM is easy. Note that its details will be described later.

The I/O chamber200is a load lock chamber for carrying in/out the mask substrate W while keeping the inside of the R chamber300under vacuum (low pressure). The I/O chamber200is provided with the gate valve G1between the load/unload I/F100and the I/O chamber200and includes a vacuum pump210and a gas supply system220. The vacuum pump210is, for example, a dry pump, a turbo molecular pump, or the like, which evacuates the inside of the I/O chamber200. The gas supply system220supplies vent gas (for example, nitrogen gas or CDA) to the inside of the I/O chamber200when setting a pressure of the I/O chamber200to an atmospheric pressure.

When evacuating the inside of the I/O chamber200, the vacuum pump210connected to the I/O chamber200is used for evacuation. Further, when returning the inside of the I/O chamber200to the atmospheric pressure, the vent gas is supplied from the gas supply system220to set the inside of the I/O chamber200to the atmospheric pressure. Note that when evacuating the inside of the I/O chamber200and when setting the inside of the I/O chamber200to the atmospheric pressure, the gate valves G1, G2are closed (Close).

The R chamber300has a vacuum pump310, an alignment chamber320, a grounding body housing chamber330, and a carrier robot340. The R chamber300is connected to the I/O chamber200via the gate valve G2.

The vacuum pump310is, for example, a Cryo pump, a turbo molecular pump, or the like. The vacuum pump310is connected to the R chamber300and evacuates the inside of the R chamber300to keep it under high vacuum. The alignment chamber320is a chamber to position (align) the mask substrate W. The grounding body housing chamber330is a chamber that houses a grounding body H. Note that the alignment is not premised on the irradiation with an electron beam unlike later-described alignment in the W chamber400.

The grounding body H includes a plurality of (for example, three) grounding pins Ha and a frame body Hb in a picture frame shape. In the state that the grounding body H is set on the mask substrate W, drawing with an electron beam is performed on the mask substrate W. In this event, the grounding body H is connected to a not-illustrated ground. In short, the grounding body H prevents accumulation (charge) of electric charges in the mask substrate W due to the irradiation with the electron beam. The carrier robot340carries the mask substrate W between the I/O chamber200, the alignment chamber320, the grounding body housing chamber330, and the W chamber400.

The W chamber400includes a vacuum pump410, an X-Y stage420, drive mechanisms430A,430B, and a secondary electron detector440, and is connected to the R chamber300via the gate valve G3.

The vacuum pump410is, for example, a Cryo pump, a turbo molecular pump, or the like. The vacuum pump410is connected to the W chamber400and evacuates the inside of the W chamber400to keep it under high vacuum. The X-Y stage420is a platform for mounting the mask substrate W thereon. The drive mechanism430A drives the X-Y stage420in an X-direction. The drive mechanism430B drives the X-Y stage420in a Y-direction. The secondary electron detector440detects the secondary electrons emitted from the light shielding film (particularly from the alignment mark AM) of the mask substrate W, and outputs a secondary electron signal.

The electron beam optical column500includes an electron gun510, apertures520, deflector530, lenses540(illumination lens (CL), projection lens (PL), objective lens (OL)), an anti-reflection film ARF and so on, and irradiates the mask substrate W mounted on the X-Y stage420with an electron beam.

The control system unit600is, for example, a computer or the like, and controls the mask drawing apparatus10. The control system unit600controls the electron beam optical column500and the X-Y stage420in conjunction with each other to thereby draw a desired pattern on the mask substrate W with the electron beam.

The control system unit600further causes the electron beam optical column500to apply the electron beam, and detects the secondary electron signal from the secondary electron detector440while scanning the electron beam. As a result of this, it becomes possible to detect an image (secondary electron image) of the alignment mark AM of the mask substrate W and align the mask substrate W. In other words, it becomes possible to correct position/rotation of the mask substrate W and correct distortion of the main pattern MP.

First Embodiment

Hereinafter, a first embodiment will be described. Hereinafter, processing of creation, drawing and so on of the mask substrate W will be described taking a Levenson phase shift mask as an example. However, the Levenson phase shift mask is merely one example and other masks can be created.

A. Phase Shift Mask

Hereinafter, the phase shift mask according to this embodiment will be described.

FIG. 2is a top view and a partial cross-sectional view illustrating a phase shift mask20according to the first embodiment. (a) and (b) inFIG. 2correspond to the top view and the cross-sectional view respectively. The cross-sectional view illustrates an enlarged state of the phase shift mask20cut along a line A-A in the top view.

The phase shift mask20is a mask for exposing a resist or the like to be used for creating a semiconductor device such as an LSI or the like by photolithography. Here, a so-called Levenson phase shift mask is illustrated in which both of a light transmissive substrate30and the metal layer40being the light shielding film are patterned. Here, the phase shift mask20has the substrate30and the metal layer40.

For the constituent material of the substrate30, an optical material (for example, quartz glass) excellent in transmission characteristic (light transmitting property) of light (for example, ultraviolet) is used.

For the constituent material of the metal layer40, a metal material (for example, Cr, Ta, MoSi or Al) having a light shielding property and a secondary-emission characteristic is used. Note that, though not illustrated, the uppermost layer of the metal layer40is typically oxidized for antireflection. For example, a thin layer of chromium oxide is arranged on the metal layer of chromium (Cr).

A main surface of the substrate30is divided into a main pattern region A1and an alignment mark region A2.

In the main pattern region A1, the main pattern MP to be projected on a semiconductor wafer for creating a semiconductor device is arranged. Here, a plurality of openings41are formed in the metal layer40as a part of the main pattern MP. During exposure, light passes through the openings41and the substrate30. Namely, the openings41(41a,41b) are light transmitting parts through which light passes.

The substrate30is etched and is thus smaller in thickness at a part (opening41a) of the plurality of openings41. In the opening41a, as compared to the opening41bwhere the substrate30is not etched, a phase difference corresponding to the difference in thickness of the substrate30occurs. In short, the opening41aof the openings41is a phase shifter light transmitting part bringing about the phase difference.

Note that not the substrate30itself is etched but a light transmitting material layer arranged between the substrate30and the metal layer40may be etched. By patterning the layer of the light transmitting material layer, the phase shifter light transmitting part can be formed.

Appropriately arranging a light shielding part (portion having no opening), the light transmitting part, and the phase shifter light transmitting part within the main pattern region A1in the phase shift mask20enables highly accurate pattern exposure utilizing interference of light.

The alignment mark region A2is a region where the alignment marks AM for aligning the mask substrate W are arranged at the time of creating the phase shift mask20. The alignment mark AM here is composed of an opening42in the metal layer40having a cross shape. By irradiating the alignment mark region A2with the electron beam and detecting the secondary electron image in the vicinity of the alignment mark AM as described later, it becomes possible to check the position and so on of the mask substrate W in the mask drawing apparatus10and perform highly accurate drawing.

In this embodiment, the thickness of the metal layer40in the alignment mark region A2is larger than that in the main pattern region A1. As a result of this, it is possible to secure the quantity (density) of the secondary electrons when the alignment mark region A2is irradiated with electrons and to obtain a clear secondary electron image. Even when the thickness of the metal layer40in the main pattern region A1is small and the quantity (density) of the secondary electrons when the main pattern region A1is irradiated with electrons is low and therefore it is difficult to obtain a clear secondary electron image, it is easy to obtain a clear secondary electron image in the alignment mark region A2.

In this embodiment, the thickness of the substrate30is made different, in addition to the thickness of the metal layer40, between the main pattern region A1and the alignment mark region A2. The thickness of the metal layer40is set to, for example, 5 nm to 20 nm in the main pattern region A1and to 40 nm to 70 nm in the alignment mark region A2.

As a result, the heights of upper surfaces of the metal layers40are almost equal in the main pattern region A1and the alignment mark region A2. The reason why the heights of the main surfaces (upper surfaces) of the metal layers40are fixed is to secure stability of the position of the phase shift mask20when the phase shift mask20is placed on the exposure apparatus for photolithography. The main surfaces of the metal layers40are placed on a holding part of the exposure apparatus in this event, so that unless the heights of the main surfaces of the metal layers40are uniform, the phase shift mask20cannot be stably placed because of tilting, thus deteriorating the exposure accuracy.

Note that it is preferable to differ the compositions of the metal layers40between the main pattern region A1and the alignment mark region A2in terms of manufacturing steps of the phase shift mask20as described later.

B. Manufacture of Phase Shift Mask20

Hereinafter, a manufacturing method of the phase shift mask20will be described. According to the following procedures (1) to (4), the phase shift mask20can be manufactured.

(1) Preparation of Mask Substrate W1

A mask substrate W1in which the metal layers40and a resist layer50are formed on the substrate30is created. The mask substrate W1can be created by the following procedures a to d.

The substrate30is prepared (seeFIG. 3A), and a recessed portion34is formed in the alignment mark region A2(seeFIG. 3B). The recessed portion34is provided in the alignment mark region A2and is for uniforming the heights of the metal layers40in the main pattern region A1and the alignment mark region A2.

For the formation of the recessed portion34, etching or mechanical polishing can be utilized.

<In the Case of Etching>

For example, a resist layer having an opening corresponding to the recessed portion34is created in the substrate30, and the substrate30is etched using the resist layer as a mask. For this etching, for example, dry etching such as reactive ion etching (RIE) or the like can be used. Note that the resist layer is removed with a solvent or the like after the etching.

<In the Case of Mechanical Polishing>

The recessed portion34may be formed by mechanically polishing the alignment mark region A2of the substrate30. In this case, the mask of resist or the like is not always necessary.

b. Formation of the metal layer40in the main pattern region A1(seeFIG. 4A,FIG. 4B)

The metal layers40are formed in the main pattern region A1and the alignment mark region A2.

A mask MM1is placed in the alignment mark region A2and the metal layer40is formed by sputtering or the like. For the mask MM1, for example, a mechanical mask of a metal plate or the like can be used.

c. Formation of the metal layer40in the alignment mark region A2(seeFIG. 4C,FIG. 4D)

A mask MM2is placed in the main pattern region A1and the metal layer40is formed by the sputtering or the like. For the mask MM2, for example, a mechanical mask of a metal plate or the like can be used. Here, the metal layers40are formed to overlap each other near the boundary between the main pattern region A1and the alignment mark region A2to cause a projecting portion45.

The surfaces of the metal layers40are planarized using the chemical mechanical polishing or the like as necessary. Here, the aforementioned projecting portion45is removed by planarization.

e. Formation of the resist layer50(seeFIG. 5A)

Thereafter, the resist layer50is formed on the metal layers40, whereby the mask substrate W1is created (seeFIG. 5A).

Here, the metal layers40are formed in the main pattern region A1and the alignment mark region A2in this order, but this order may be inverted.

Further, the metal layers40are formed to overlap each other at the boundary between the main pattern region A1and the alignment mark region A2, but the metal layers40may be thin or no metal layers40may be provided at the boundary.

Here, it is preferable to change the materials of the main pattern region A1and the alignment mark region A2to make the etching rate of the metal layer40in the alignment mark region A2higher than that in the main pattern region A1. More specifically, the metal layer40in the main pattern region A1(first region) is etched at a first rate, while the metal layer40in the alignment mark region A2(second region) is etched at a second rate higher than the first rate.

This is for improving the accuracy of patterning of the metal layers40. It is assumed that the etching rates in the main pattern region A1and the alignment mark region A2are the same. In this case, whereas the etching in the main pattern region A1has been actually completed, the etching in the alignment mark region A2has not been completed, and the etching needs to be continued. In this case, the etching is excessively performed in the main pattern region A1, resulting in a decrease in accuracy of the patterning in the main pattern region A1.

Ideally, it is preferable that the etching is completed at the same time in the main pattern region A1and the alignment mark region A2. It is assumed here that the film thickness of the metal layer40in the main pattern region A1is D1and the film thickness of the metal layer40in the alignment mark region A2is D2. It is ideal that the etching rates in the main pattern region A1and the alignment mark region A2are proportional to the respective film thicknesses D1, D2. However, an error of a certain degree, for example, about 5 to 10% as compared with that in the ideal case is allowable.

The change of the materials of the main pattern region A1and the alignment mark region A2becomes possible by making film formation conditions (for example, sputtering conditions) differ from each other. For example, as the gas during the sputtering, an Ar/O2mixed gas is used for forming the main pattern region A1and a pure Ar gas is used for forming the alignment mark region A2. This forms the metal layer40in the state that chromium (Cr) and chromium oxide (CrO2) are mixed together in the main pattern region A1, and forms the metal layer40of chromium (Cr) in the alignment mark region A2. In short, the metal layer40in the main pattern region A1(first region) contains an oxide, and the metal layer40in the alignment mark region A2(second region) is substantially free of oxide. As described above, changing the film formation conditions makes it possible to change the materials of the metal layers40in the main pattern region A1and the alignment mark region A2from each other and thereby make the etching rates of the metal layers40differ from each other.

The metal layers40are patterned to form the main pattern MP and the alignment mark AM in the main pattern region A1and the alignment mark region A2respectively. The patterning of the metal layers40can be performed in the following procedures a to c.

a. The mask substrate W1(seeFIG. 5A) is carried into the W chamber400of the mask drawing apparatus10, and the mask substrate W1is irradiated with the electron beam.

b. Thereafter, the mask substrate W1is taken out of the mask drawing apparatus10and developed, whereby the resist layer50is patterned (seeFIG. 5B).

Different etching rates in the main pattern region A1and the alignment mark region A2as has been described enable creation of the main pattern MP with high accuracy.

c. The metal layers40are patterned by being subjected, for example, to dry etching using the patterned resist layer50as a mask (seeFIG. 5C), and the resist layer50is removed with a solvent or the like (seeFIG. 5D).

After the patterning of the metal layers40(first layer), patterning of the substrate30(second layer) is performed. Prior to the patterning, alignment of the substrate30needs to be performed to make the patterns of the first layer and the second layer correspond to each other. Exposures with electron beam of the first layer and the second layer are performed in the mask drawing apparatus10, but the substrate30is taken out of the mask drawing apparatus10before and after the exposures, so that the mask substrate W1is changed in position and so on and therefore needs to be adjusted.

Note that the exposures with electron beam of the first layer and the second layer may be performed in different mask drawing apparatuses10.

This alignment and drawing can be performed in the following procedures a to d.

a. Formation of a mask substrate W2

Prior to the alignment, a resist layer55and a conductive layer60are formed on the substrate30. As a result, the mask substrate W2is formed.

Note that the conductive layer60is to prevent deterioration of positional accuracy by charging the opening portion of the substrate30which has been exposed by etching when the mask substrate W2is irradiated with the electron beam, and is composed of, for example, a conductive material containing sulfonic acid as a main constituent.

b. Detection of the secondary electron image

The mask substrate W2is carried into the W chamber400of the mask drawing apparatus10and irradiated with the electron beam, and an image of secondary electrons emitted from the vicinity of the alignment mark AM is detected. By detecting the secondary electrons while scanning the electron beam on the substrate30, the image of secondary electrons in the vicinity of the alignment mark AM can be detected. Since the metal layer40does not exist at the alignment mark AM itself, the alignment mark is detected as a region from which no secondary electron is actually emitted. In this event, not the quantity of the secondary electrons itself but signal processing (for example, differential processing) performed thereon can make the boundary between the alignment mark AM itself (without the metal layer40) and its surroundings (with the metal layer40) clearer.

c. Alignment of the mask substrate W2

Detecting the alignment mark AM and its position makes it possible to correct distortion and position/rotation of the main pattern MP.

For example, when the internal stress of the metal layers40changes due to the etching, relative positional displacement in the pattern, namely, distortion of the pattern may occur. This distortion can be detected through a relative distance displacement between the alignment marks AM.

Further, the positional displacement and rotation of the mask substrate W2and accordingly the main pattern MP can be detected through average an position of the alignment mark AM.

In this event, the metal layer40in the alignment mark AM is large, so that the secondary electron signal becomes large to make it easy to detect the alignment mark AM.

Note that the alignment here does not always mean the positional change or rotation of the mask substrate W2. Changing the reference position of irradiation with the electron beam stored in the control system unit600without performing positional change or rotation of the mask substrate W2is allowed to be called alignment.

The position and distortion of the main pattern MP is detected by the alignment mark AM, and drawing is performed to the resist layer55by applying the electron beam so as to correspond to the detected distortion, positional displacement, or rotation. Since the drawing is performed in the state that the alignment has been performed using the surely detected alignment mark AM, a phase shift mask20with high accuracy of overlapping the first layer and the second layer can be manufactured.

The substrate30is patterned. The patterning can be performed in the following procedures a, b.

a. Patterning of the resist layer50

The mask substrate W2is taken out of the mask drawing apparatus10and developed, whereby the resist layer50is patterned (seeFIG. 6B)

b. Patterning of the substrate30(Development)

The substrate30is patterned by being subjected, for example, to dry etching using the patterned resist layer55as a mask (seeFIG. 6C), and the resist layer55is removed with a solvent or the like (seeFIG. 6D).

The phase shift mask20is created as described above.

COMPARATIVE EXAMPLE

A comparative example will be described. Also in the comparative example, a substrate30(mask substrate Wx1) on which a metal layer40xand a resist layer50are arranged is used, patterning of the metal layer40x, alignment, drawing, patterning of the substrate30are performed in sequence. Here, the material and the film thickness of the metal layer40xare the same in a main pattern region A1and an alignment mark region A2. A phase shift mask20xcan be manufactured by the following procedures (1) to (3).

These procedures (1) to (3) are the same as the procedures (2) to (4) in the first embodiment respectively and therefore detailed description thereof will be omitted.

In the comparative example, since the material and the film thickness of the metal layer40xare the same in the main pattern region A1and the alignment mark region A2, a problem may occur in alignment.

Its background is progressive reduction in thickness of the metal layer40xbeing the light shielding film. A taper is formed in a cross-section of the metal layer40xduring etching and affects the accuracy of the mask to be formed. Therefore, the metal layer40xbeing the light shielding film becomes thinner with miniaturization of the pattern.

FIG. 9AandFIG. 9Bare views illustrating states of the cross-sections at the time of alignment in mask substrates Wx2using a thick metal layer40x1and a thin metal layer40x2. The metal layers40x1,40x2have thicknesses of, for example, about 50 nm and 10 nm or less respectively.

The signal of secondary electrons is large in the thick metal layer40x1as illustrated inFIG. 9A, and the edge (contour) of the alignment mark AM can be easily detected.

On the other hand, the signal of secondary electrons is small in the thin metal layer40x2as illustrated inFIG. 9B, and the edge of the alignment mark AM cannot be easily detected. More specifically, even if scanning is performed in the vicinity of the alignment mark AM, electrons instantaneously pass through the metal layer40x2(light shielding film) and the quantity (density) of the secondary electrons generated is small, resulting in difficulty of securement of the signal strength.

When the detection accuracy of the alignment mark AM decreases as described above, the accuracy of overlapping the first layer and the second layer decreases.

In contrast, in the first embodiment, making the thicknesses of the metal layers40in the main pattern region A1and the alignment mark region A2different from each other enables both improvement in pattern accuracy in the main pattern MP and securement of the detection accuracy of the alignment mark AM.

Modification Example of First Embodiment

Hereinafter, a modification example of the first embodiment will be described. Here, the mask substrate W1is formed in the following procedures (1) to (3).

(1) Formation of the metal layer40in the main pattern region A1(seeFIG. 10AtoFIG. 10C)

The mask MM1is placed in the alignment mark region A2and the metal layer40is formed by sputtering or the like. For the mask MM1, for example, a mechanical mask of a metal plate or the like can be used. As a result, the metal layer40is formed only in the main pattern region A1of the substrate30.

(2) Etching of the substrate30(SeeFIG. 10D)

The substrate30is etched using the metal layer40as a mask. As a result, the substrate30in the alignment mark region A2is etched, whereby the recessed portion34is formed.

(3) Formation of the metal layer40in the alignment mark region A2(seeFIG. 11AtoFIG. 11C)

The mask MM2is placed in the main pattern region A1and the metal layer40is formed by the sputtering or the like. For the mask MM2, for example, a mechanical mask of a metal plate or the like can be used. Here, the metal layers40are formed to overlap each other near the boundary between the main pattern region A1and the alignment mark region A2to cause the projecting portion45.

The surfaces of the metal layers40are planarized using the chemical mechanical polishing or the like as necessary. Here, the aforementioned projecting portion45is removed by planarization.

Thereafter, the resist layer50is formed on the metal layers40, whereby the mask substrate W1is created (seeFIG. 5A).

In the above manner, the mask substrate W1can be created. Thereafter, the phase shift mask20can be created in the same procedures as those in the first embodiment.

Second Embodiment

Hereinafter, a second embodiment will be described.

A. Phase Shift Mask

Hereinafter, a phase shift mask according to this embodiment will be described.

FIG. 12is a top view and a cross-sectional view illustrating a phase shift mask20aaccording to the second embodiment. (a) and (b) inFIG. 12correspond to the top view and the cross-sectional view respectively. The cross-sectional view illustrates an enlarged state of the phase shift mask20acut along a line A-A in the top view.

In this embodiment, a secondary electron emitting rate η2in a metal layer40bin an alignment mark region A2is higher than a secondary electron emitting rate η1in a metal layer40ain a main pattern region A1. As a result of this, it is possible to secure the quantity (density) of secondary electrons when the alignment mark region A2is irradiated with electrons and to obtain a clear secondary electron image. In other words, even when the thickness of the metal layer40ain the main pattern region A1is small and the quantity (density) of the secondary electrons generated when the main pattern region A1is irradiated with electrons is low and therefore it is difficult to obtain a clear secondary electron image, it is easy to obtain a clear secondary electron image in the alignment mark region A2.

It is assumed that the thicknesses of the metal layers40a,40bare, for example, 5 nm to 20 nm (preferably, 5 nm to 10 nm).

As illustrated inFIG. 13, among metal elements, the one having a larger atomic number Z also has a higher secondary electron emitting rate η. For example, by constituting the metal layer40ain the main pattern region A1, for example, of Cr and constituting the metal layer40bin the alignment mark region A2, for example, of Ta, the secondary electron emitting rates η in the main pattern region A1and the alignment mark region A2can be made different from each other.

Note that examples of the combination of the metal layers40aand40binclude a combination of Cr and W and a combination of Cr and Pt in addition to a combination of Cr and Ta.

Such manufacturing steps of the substrate are illustrated inFIG. 14. Since the reflected electron emitting rate of the light shielding film in the alignment mark part is high, a reflected electron signal becomes large.

B. Manufacture of the Phase Shift Mask20a

Hereinafter, a manufacturing method of the phase shift mask20awill be described. Here, the phase shift mask20ais manufactured in the following procedures (1) to (4).

(1) Creation of a mask substrate Wa1

The mask substrate Wa1is created by the following procedures a to c.

a. Formation of the metal layer40ain the main pattern region A1(seeFIG. 14Ato FIG.14C)

A mask MM1is placed in the alignment mark region A2and the metal layer40ais formed by sputtering or the like. For the mask MM1, for example, a mechanical mask of a metal plate or the like can be used.

b. Formation of the metal layer40bin the alignment mark region A2(seeFIG. 14D,FIG. 14E)

A mask MM2is placed in the main pattern region A1and the metal layer40bis formed by the sputtering or the like. For the mask MM2, for example, a mechanical mask of a metal plate or the like can be used. Here, the metal layers40a,40bare formed to overlap each other near the boundary between the main pattern region A1and the alignment mark region A2to cause a projecting portion45b.

The surfaces of the metal layers40a,40bare planarized using the chemical mechanical polishing or the like as necessary. Here, the aforementioned projecting portion45bis removed by planarization.

Note that also when there is a film thickness difference between the metal layers40aand40b, it is preferable to uniform the film thicknesses using the chemical mechanical polishing or the like.

Thereafter, the resist layer50is formed on the metal layers40a,40b, whereby the mask substrate Wa1is created (seeFIG. 15A).

The mask substrate Wa1is created as described above.

Here, the metal layers40a,40bare formed in the main pattern region A1and the alignment mark region A2in this order, but this order may be inverted.

Further, the metal layers40are formed to overlap each other at the boundary between the main pattern region A1and the alignment mark region A2, but the metal layers40a,40bmay be thin or no metal layers40a,40bmay be provided at the boundary.

These procedures of (2) to (4) are the same as the procedures (2) to (4) in the first embodiment and therefore detailed description thereof will be omitted.

In the second embodiment, since the materials of the metal layers40in the main pattern region A1and the alignment mark region A2are different, it becomes easy to improve the pattern accuracy in the main pattern MP and secure the detection accuracy of the alignment mark AM.

Modification Example of Second Embodiment

In the second embodiment, the film thicknesses of the metal layers40a,40bin the main pattern region A1and the alignment mark region A2are the same. In contrast, the film thicknesses of the metal layers40a,40bin the main pattern region A1and the alignment mark region A2may be made different from each other.

Concretely, the constituent materials of the metal layers40a,40bin the main pattern region A1and the alignment mark region A2are made different from each other when creating the mask substrate Wa1in the procedures illustrated in the first embodiment or its modification example.

In this case, a metal layer40athat is thin and has a low secondary electron emitting rate η is arranged in the main pattern region A1, and a metal layer40bthat is thick and has a high secondary electron emitting rate η is arranged in the alignment mark region A2. For example, the thickness of the metal layer40ais set to 5 nm to 20 nm (preferably 5 nm to 10 nm), and the thickness of the metal layer40bis set to 30 nm to 60 nm (preferably 30 nm to 50 nm).

As a result, it becomes possible to more surely detect the alignment mark AM.