Photomask and method for manufacturing the same

According to one embodiment, a photomask includes a substrate, a film portion, a pattern, and a plurality of detection marks. The film portion is provided on a surface of the substrate. The film portion has a light transmittance lower than light transmittance of the substrate. The pattern is provided in a surface of the film portion. The pattern is configured to be transferred to a transfer target. The plurality of detection marks is provided in the film portion, with intensity of light transmitted through the detection marks being suppressed so as to suppress transfer the detection marks to the transfer target.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2011-045150, filed on Mar. 2, 2011; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a photomask and a method for manufacturing the same.

BACKGROUND

Recently, patterns formed in microstructures such as semiconductor devices have become increasingly finer. This requires very strict accuracy in the photomask used in the photolithography process for forming such fine patterns.

A technique has been proposed in this context. In this technique, a detection mark formed in the writing region of the photomask is transferred to the light exposure surface of the wafer. By detecting the transferred detection mask, the accuracy of the photomask itself and the accuracy of superposition are inspected.

However, because the detection mark is transferred to the light exposure surface of the wafer, the position for forming the detection mark is significantly restricted.

This results in poor inspection measurement accuracy and makes it difficult to manufacture a photomask with high accuracy.

DETAILED DESCRIPTION

In general, according to one embodiment, a photomask includes a substrate, a film portion, a pattern, and a plurality of detection marks. The film portion is provided on a surface of the substrate. The film portion has a light transmittance lower than light transmittance of the substrate. The pattern is provided in a surface of the film portion. The pattern is configured to be transferred onto a transfer target. The plurality of detection marks is provided in the film portion, with intensity of light transmitted through the detection marks being suppressed so as to suppress transfer of the detection marks onto the transfer target.

Various embodiments will be illustrated hereinafter with reference to the accompanying drawings.

In the drawings, similar components are labeled with like reference numerals, and the detailed description thereof is omitted appropriately. By way of example, in the following is described a case where the photomask according to the embodiments is a halftone phase shift mask.

First, a photomask according to a first embodiment is illustrated.

FIGS. 1A to 1Care schematic views for illustrating a photomask according to the first embodiment.

More specifically,FIG. 1Ais a schematic plan view of the photomask according to the first embodiment.FIG. 1Bis a schematic enlarged view of the cross section taken in the direction of arrows A-A inFIG. 1A.FIG. 1Cis a view taken in the direction of arrows B-B.FIG. 1Dis a schematic enlarged view of the cross section taken in the direction of arrows C-C. Here, inFIG. 1A, the pattern6described later is omitted to avoid complexity, and the arrangement of detection marks7is conceptually shown.

As shown inFIGS. 1A and 1B, the photomask1includes a substrate2, a film portion3, a light shielding film4, a writing region5, a pattern6, and a detection mark7.

The substrate2is shaped like e.g. a rectangular plate. The substrate2can be formed from a material having high translucency. The substrate2can be formed from e.g. synthetic quartz glass.

The film portion3is provided on one surface of the substrate2. The film portion3can be configured to have a light transmittance lower than the light transmittance of the substrate2. The film portion3can be configured as a so-called halftone film. The film portion3is formed from a material based on e.g. chromium fluoride (CrF), molybdenum silicide (MoSiON, MoSiO), tungsten silicide (WSiO), or zirconium silicide (ZrSiO). The transmittance for deep ultraviolet light of the film portion3can be set to several %.

The light shielding film4is provided on the peripheral region of the substrate2so as to cover the film portion3. The light shielding film4can be formed from e.g. chromium (Cr).

The photomask1includes a writing region5.

The writing region5is provided on the central region of the substrate2. The writing region5is a region where the pattern6and the detection mark7are formed.

The pattern6is provided in the film portion3. The pattern6can include a circuit pattern to be transferred to a transfer target (such as a wafer), and an auxiliary pattern located adjacent to the circuit pattern for increasing the resolution of the circuit pattern.

The pattern6is formed by selectively removing part of the film portion3. More specifically, the pattern6is composed of e.g. openings which can transmit light having light intensity enabling transfer to the transfer target.

The detection mark7is provided in the film portion3. The detection mark7is configured to be able to suppress the intensity of transmitted light so as to suppress transfer to the transfer target. The detail of the suppression of transfer to the transfer target will be described later.

The detection mark7is provided to inspect the accuracy of the photomask1itself. For instance, if the detection mark7is provided in the photomask1, the position of the detection mark7and the dimension between the detection marks7can be measured by using e.g. a photomask inspection apparatus and a dimension measurement apparatus known in the art. Thus, the accuracy of the photomask1can be subjected to inspection measurement easily and accurately.

If a plurality of detection marks7are provided, detection can be performed for the plurality of detection marks7. Hence, by the averaging effect, variations in the detection result can be suppressed.

In general, the misplacement of e.g. the circuit pattern in the photomask is detected by comparison between the detection data (sensor data) and the reference data (design data). In this case, it is difficult to detect the misplacement of e.g. a so-called isolated hole distanced from e.g. other circuit patterns. However, if a plurality of detection marks7are provided, the detection mark7provided near e.g. the isolated hole can be used as a reference. Hence, it is also possible to improve the detection accuracy for the misplacement of e.g. an isolated hole.

The film portion3provided on one surface of the substrate2undergoes residual stress. Thus, if the film portion3is provided with a plurality of detection marks7which are also openings, the residual stress can be relaxed. As a result, the deformation of the photomask1can be suppressed. Hence, the positional accuracy of the pattern6can be improved.

When the photomask1is mounted on an exposure apparatus, the photomask1is mechanically held by the holding means provided in the exposure apparatus. In this case, if a plurality of detection marks7are provided in the photomask1, it is possible to detect the amount of strain, for instance, generated when the photomask1is mechanically held. Then, for instance, if the amount of strain is too large, it is also possible to weaken the holding force on the photomask1to relax the strain generated in the photomask1.

The detection information on the photomask1detected by using the detection mark7(such as misplacement information in the writing region5) is fed back to the correction data of the writing position of a photomask to be manufactured the next time (such as a photomask of the same specifications and a photomask of similar specifications to be manufactured the next time). Thus, the accuracy of the photomask can be improved cumulatively.

Next, the shape, arrangement condition and the like of the detection mark7are illustrated.

The detection mark7can be shaped to have an edge.

Then, detection can be performed easily and accurately. Hence, the detection accuracy of the detection mark7can be improved.

The detection mark7can be configured to include a first edge provided in a first direction and a second edge provided in a second direction crossing the first direction. Then, the detection accuracy of the detection mark7in the first and second directions can be improved.

The shape of the detection mark7can be configured to include a portion made of vertical and horizontal straight lines. Furthermore, symmetric shape is preferable. For example, a line symmetric shape, a point symmetric shape, a rotation symmetric shape, and bilaterally and vertically symmetric shapes can be employed. For instance, the shape of the detection mark7can be configured to include a portion made of an arbitrary polygon, or a combined shape of a plurality of arbitrary polygons.

By way of example, in the following is described a case where the shape of the detection mark7is a cross shape.

For instance, the shape of the detection mark7can include edges in orthogonal directions like a cross shape. Then, the detection accuracy of the detection mark7in the two-dimensional directions can be improved.

FIGS. 2A and 2Bare schematic plan views for illustrating the arrangement of the detection marks.

InFIG. 2A, as an example, a hole-like pattern6penetrating through the film portion3is written, inFIG. 2B, as other example, a line-like pattern6a penetrating through the film portion3, respectively.

BetweenFIGS. 2A and 2B, the dimension and arrangement of the hole patterns6and6aare different. However, there is no difference in that the detection mark7is provided in the film portion3, i.e., in the portion where the hole pattern6of the line pattern6ais not provided.

The detection marks7can be provided in a matrix configuration as shown inFIGS. 1A,2A, and2B. For example,

FIG. 1Ashows the case where the arrangement pitch of the detection marks7is 10 mm.FIG. 2Ashows the case where the arrangement pitch of the detection marks7is 1 mm.FIG. 2Bshows the case where the arrangement pitch of the detection marks7is 100 μm.

However, the arrangement of the detection marks7is not limited to the matrix configuration. For instance, the detection marks7may be arranged in other regular configurations such as a staggered configuration, or in a configuration in which the detection marks7are provided at arbitrary positions such as an isolated pattern.

The dimension between the detection marks7may be constant (equal pitch dimension) or may be varied. Furthermore, it is also possible to mix a portion where the dimension between the detection marks7is constant and a portion where the dimension is varied. In this case, if the dimension between the detection marks7is made too large, the inspection accuracy may be degraded. On the other hand, if the dimension between the detection marks7is made too small, the number of detection marks7becomes too large, which may decrease the measurement efficiency. Thus, the dimension between the detection marks7and the number of detection marks7can be appropriately changed depending on the required inspection accuracy and inspection efficiency.

Furthermore, the arrangement of the detection marks7can be unevenly distributed. For instance, if the portion prone to degradation in dimensional accuracy is empirically known, the dimension between the detection marks7in that portion can be decreased, or the number of detection marks7therein can be increased. Furthermore, if the portion likely to have good dimensional accuracy is empirically known, the dimension between the detection marks7in that portion can be increased, or the number of detection marks7therein can be decreased.

Here, the detection mark7is formed by selectively removing part of the film portion3. Hence, although light is transmitted through the detection mark7, the detection mark7is not transferred to the transfer target. Because the detection mark7is not transferred to the transfer target, the restriction on the position for providing the detection mark7can be significantly relaxed. Thus, the detection mark7can be easily provided at a position suitable for inspection measurement of the photomask. Hence, the inspection accuracy of the photomask1can be significantly improved.

That is, the intensity of light transmitted through the detection mark7is suppressed so as to suppress the transfer to the transfer target. For instance, in the case where the shape of the detection mark7is a rectangular shape or a combined shape of a plurality of rectangular shapes such as a cross shape, the transfer of the detection mark7to the transfer target can be suppressed by making the width dimension (length of the short side) of the rectangular shape smaller than a prescribed value.

FIG. 3is a schematic view for illustrating the dimensional condition and the like for avoiding the transfer of the detection mark to the transfer target.

Here,FIG. 3illustrates the case where the shape of the detection mark7ais a cross shape.

In this case, for instance, in the case where the wavelength of the exposure light is approximately 193 nm, the transfer of the detection mark7ato the transfer target can be suppressed by setting the width dimension W of the rectangular shape constituting the cross shape to less than 160 nm.

Furthermore, the transfer of the detection mark7ato the transfer target can be suppressed more reliably by setting the width dimension W of the rectangular shape constituting the cross shape to 120 nm or less.

However, even in the case of suppressing the transfer of the detection mark7a,if the detection mark7ais provided too close to the pattern6, the transfer accuracy of the pattern6and the like may be affected.

Thus, the detection mark7ais provided at a position such that the pattern6(in the case illustrated inFIG. 3, the hole-like pattern6) is excluded from a prescribed range around the detection mark7a.

According to the knowledge obtained by the inventors, the influence of the detection mark7aon the transfer accuracy of the pattern6and the like can be suppressed by excluding the pattern6from the range of 2 μm from the detection mark7a.

That is, preferably, the detection mark7ais provided so that the dimension between the pattern6and the detection mark7ais 2 μm or more.

Furthermore, the transfer of the detection mark7ato the transfer target is further hindered by decreasing the resolution of the detection mark7a.

In this case, the transfer of the detection mark7ato the transfer target is further hindered by decreasing the optical image (aerial image) contrast in the transfer of the detection mark7a.

FIGS. 4A to 4Dare schematic views for illustrating a detection mark for decreasing the optical image (aerial image) contrast when being transferred.

More specifically,FIG. 4Ais a schematic view for illustrating a detection mark before optical image contrast adjustment.FIG. 4Bis a schematic view for illustrating an illumination shape for light exposure.FIG. 4Cis a schematic view for illustrating the optical image in the transfer target.FIG. 4Dis a schematic view for illustrating a detection mark after optical image contrast adjustment.

Here,FIG. 4Cis obtained by simulation of the transfer of the detection mark illustrated inFIG. 4A. The optical image is represented by monotone shading, with a darker portion shaded more intensely, and a lighter portion shaded less intensely.

The detection mark17having a cross shape as illustrated inFIG. 4Ais irradiated with exposure light from a dipole illumination as illustrated inFIG. 4B. Then, the optical image in the transfer target is as illustrated inFIG. 4C.

In this case, as shown inFIG. 4D, the film portion18a can be provided at the position corresponding to the light portion18inFIG. 4C, and the opening19a(corresponding to an example of the first control portion) can be provided at the position corresponding to the dark portion19. Then, the difference in brightness between the light portion18and the dark portion19can be reduced. Hence, the optical image contrast can be decreased. That is, the detection mark17can be configured to include an opening19aand a film portion18a for decreasing the optical image contrast in the transfer target by transmitting light.

Thus, the detection mark17can be configured so as to decrease the optical image contrast when being transferred. Then, even if there are differences between the apparatuses in the light exposure condition or variations in the apparatus condition, the transfer to the transfer target can be further hindered.

The example illustrated inFIG. 4Dincludes a film portion18aand an opening19a.However, it is only necessary that at least one of the film portion18aand the opening19abe provided so as to decrease the optical image contrast when being transferred.

Here, in the case of a circuit pattern, an auxiliary pattern is provided at a position capable of increasing the resolution. The case of the detection mark17is different in that at least one of the film portion18aand the opening19ais provided at a position capable of decreasing the resolution.

Furthermore, the shape of the detection mark can be configured so as to decrease the optical image contrast when being transferred.

FIGS. 5A to 5Dare schematic views for illustrating the shape of a detection mark for decreasing the optical image contrast when being transferred.

For instance, in the case where the shape of the detection mark7is a cross shape, the brightness tends to be brighter at the position corresponding to the neighborhood of the center of the detection mark7in the transfer target.

In this case, for instance, as illustrated inFIG. 5A, the detection mark27can be configured to radially include slim rectangular openings27awith a spacing of a prescribed dimension from the center. This can suppress excessively high brightness at the position corresponding to the neighborhood of the center of the detection mark27in the transfer target.

Alternatively, as illustrated inFIG. 5B, the detection mark37can be configured to include slim rectangular openings37alike a frame with a spacing of a prescribed dimension from the center. This can suppress excessively high brightness at the position corresponding to the four corners of the detection mark37in the transfer target.

That is, the detection mark can be configured to include, at a prescribed position, a suppression portion (corresponding to an example of the second control portion) for suppressing light transmission to decrease the optical image contrast in the transfer target.

Here, the aforementioned film portion18acorresponds to an example of the suppression portion.

As shown inFIG. 5C, a plurality of the detection mark27shown inFIG. 5Acan be arranged side by side along one direction. By using this arrangement, accuracy of the detection of position can be further improved as the number of the openings27aas targets is increased. In this case, odd number of the detection mark27shown inFIG. 5Acan be arranged in order to make one of the detection marks27located center as shown inFIG. 5C.

As shown inFIG. 5D, a plurality of the detection mark37shown inFIG. 5Dcan be arranged side by side along one direction. By using this arrangement, accuracy of the detection of position can also be further improved. In this case, even number of the detection marks37can be arranged in order to make one of the openings37located center as shown inFIG. 5D.

In the embodiments, the arrangements of the plurality of detection marks27and37are not limited to the one-dimensional arrangement as shown inFIGS. 5C and 5D, but two-dimensional arrangements are also included.

Next, a method for manufacturing a photomask according to a second embodiment is illustrated.

FIGS. 6A to 6Care schematic process sectional views for illustrating the method for manufacturing a photomask according to the second embodiment.

First, as shown inFIG. 6A, on one surface of a substrate2formed from e.g. quartz glass, a film portion3having a light transmittance lower than the light transmittance of the substrate2is formed.

The film portion3can be formed by film formation of a material based on e.g. chromium fluoride (CrF), molybdenum silicide (MoSiON, MoSiO), tungsten silicide (WSiO), or zirconium silicide (ZrSiO) by the sputtering method.

Next, a light shielding film4is formed so as to be stacked on the upper surface of the film portion3.

The light shielding film4can be formed by film formation of e.g. chromium (Cr) by using the sputtering method. Thus, a photomask blank is formed.

Next, as shown inFIG. 6B, a resist8is applied to the upper surface of the light shielding film4. The resist8can be applied by using a known application method such as the spin-coating method.

Then, by using e.g. the electron beam writing method, a pattern6(such as circuit pattern and auxiliary pattern) to be transferred to a transfer target and a detection mark are written to the resist8based on writing data created previously.

At this time, based on the writing data, the detection mark in which the intensity of transmitted light is suppressed so as to suppress the transfer to the transfer target is written.

The detection mark to be written can be configured to have a rectangular shape with the width dimension of the rectangular shape set to less than 160 nm.

Furthermore, the writing can be performed so that the dimension between the pattern6and the center of the detection mark is 2 μm or more.

The detection mark to be written can be made similar to those described above, and hence the detailed description thereof is omitted.

Next, the resist8with the pattern6and the detection mark written thereto is baked and subjected to spray development with an alkaline developer to form a resist mask.

Then, the resist mask is used as an etching mask to sequentially remove the light shielding film4and the film portion3by using the RIE (reactive ion etching) method.

Next, the resist mask is removed by using e.g. the dry ashing method or washing method.

Next, as shown inFIG. 6C, the light shielding film4in the writing region5is removed by using e.g. the wet etching method. Thus, a photomask1including the pattern6and the detection mark is manufactured.

The photomask1thus manufactured is used in the light exposure process in manufacturing microstructures such as semiconductor devices.

Furthermore, the accuracy of the manufactured photomask1is detected by using the detection mark. The detected information of the photomask1is fed back to the correction data of the writing position of the photomask to be manufactured the next time (such as a photomask of the same specifications and a photomask of similar specifications to be manufactured the next time).

Next, by way of example, in the following is described a case where the detected information of the photomask is fed back to the manufacturing of a photomask to be manufactured the next time.

FIG. 7is a flow chart for illustrating a process for manufacturing a photomask.

As shown inFIG. 7, first, writing data on a first photomask11is created. Here, the created writing data includes not only data on a pattern6(such as circuit pattern and auxiliary pattern) but also data on a detection mark.

Next, similarly to the foregoing, writing for manufacturing the first photomask11is performed (step S1).

At this time, the detection mark is also written in conjunction with the pattern6.

Next, the accuracy of the writing position of the first photomask11with the detection mark written thereto is detected by the detection mark (step S2).

The detection of the accuracy of the first photomask11can be performed by measuring the position of the detection mark and the dimension between the detection marks by using e.g. a photomask inspection apparatus and a dimension inspection apparatus known in the art.

The information on the detected accuracy of the first photomask11is fed back to the writing data of a second photomask11ato be manufactured the next time. For instance, the correction data of the writing position can be modified based on the detected accuracy of the first photomask11.

Then, in the light exposure process, the first photomask11is used to transfer the pattern6to a transfer target (step S3).

At this time, the transfer of the detection mark formed on the first photomask11to the transfer target is suppressed.

Then, writing for manufacturing the second photomask11ais performed based on the writing data to which the information on the accuracy of the first photomask11has been fed back (step S1a).

That is, in the manufacturing of the second photomask11a,the pattern6is written based on the modified writing data. At this time, the detection mark is also written in conjunction with the pattern6.

Next, the accuracy of the second photomask11ais detected by using the detection mark (step52a). The information on the detected accuracy of the second photomask11ais fed back to the writing data of a photomask to be manufactured the next time.

Thus, the accuracy of the photomask can be improved cumulatively.

Then, similarly to the foregoing, in the light exposure process, the second photomask11ais used to transfer the pattern6to a transfer target (step S3a).

The embodiments illustrated above can realize a photomask capable of improving the inspection measurement accuracy and a method for manufacturing the same.

For instance, the shape, dimension, material, arrangement, number and the like of the components included in e.g. the first photomask11are not limited to those illustrated, but can be suitably modified.

In the foregoing, by way of example, the case where the photomask is a halftone phase shift mask has been described. However, the embodiments are not limited thereto.

For instance, the embodiments are applicable to various photomasks such as a binary mask, Levenson-type phase shift mask, chromeless phase shift mask, and EUV (Extreme Ultra Violet) mask.