Method of designing photo mask pattern, photomask manufacturing method, and photomask

Abstract

To provide a method of designing a photomask pattern capable of improving a process margin.SOLUTION: According to one embodiment, a method of designing a photomask pattern includes: creating data of a photomask pattern formed from a mask film on a surface of a substrate using data of a target pattern of lithography; and calculating a distribution of a coverage of the target pattern or the photomask pattern. The method further includes creating, based on the distribution of the coverage, a distribution of light permeability which includes a distribution of first regions including patterned and non-patterned portions of the mask film, the distribution having a first value of light transmittance of the substrate and the mask film, and a distribution of second regions including patterned and non-patterned portions of the mask film, the distribution having a light transmittance of the substrate and the mask film of a second value different from the first value. The method further includes correcting and outputting the data of the photomask pattern on the basis of the distribution of the transmittance.SELECTED DRAWING: Figure 14

Description

[Technical field]

[0001] FIELD Embodiments of the present invention relate to a photomask pattern design method, a photomask manufacturing method, and a photomask. [Background technology]

[0002] In a process of exposing a resist film using a photomask, it is desirable to have a large process margin. With regard to the process margin, a problem arises in that the optimum value of the light transmittance through the photomask changes depending on the photomask pattern. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2022 / 0066313 [Patent Document 2] JP 2001-222097 A [Patent Document 3] JP 2003-303742 A Summary of the Invention [Problem to be solved by the invention]

[0004] The embodiments of the present invention provide a method for designing a photomask pattern, a method for manufacturing a photomask, and a photomask that can improve a process margin. [Means for solving the problem]

[0005] According to one embodiment, a method for designing a photomask pattern includes using data of a target pattern of lithography to create data of a photomask pattern formed by a mask film on a surface of a substrate, and calculating a distribution of a coverage of the target pattern or the photomask pattern. The method further includes creating a distribution of transmittance based on the distribution of coverage, the distribution including a first region including a patterned portion and a non-patterned portion of the mask film, in which the light transmittance of the substrate and the mask film is a first value, and a distribution of a second region including a patterned portion and a non-patterned portion of the mask film, in which the light transmittance of the substrate and the mask film is a second value different from the first value. The method further includes correcting the data of the photomask pattern based on the distribution of transmittance, and outputting the corrected data of the photomask pattern. [Brief description of the drawings]

[0006] [Figure 1] 1 is a cross-sectional view showing a structure of a photomask according to a first embodiment. [Diagram 2] 4 is a graph for explaining the photomask of the first embodiment. [Diagram 3] 6 is another graph for explaining the photomask of the first embodiment. [Figure 4] FIG. 2 is a plan view showing an example of a photomask pattern in the first embodiment. [Diagram 5] FIG. 4 is a plan view showing another example of the photomask pattern of the first embodiment. [Figure 6] 4 is a graph (1 / 4) for explaining the photomask of the first embodiment. [Figure 7] 1 is a graph (2 / 4) for explaining the photomask of the first embodiment. [Figure 8] 1 is a graph (3 / 4) for explaining the photomask of the first embodiment. [Figure 9] 11 is a graph (4 / 4) for explaining the photomask of the first embodiment. [Figure 10]FIG. 11 is a cross-sectional view showing the structure of a photomask according to a second embodiment. [Figure 11] FIG. 11 is a cross-sectional view showing the structure of a photomask according to a third embodiment. [Figure 12] 13 is a graph for explaining a photomask according to a third embodiment. [Figure 13] 13 is a flowchart showing a method of designing a photomask pattern in a comparative example of the fourth embodiment. [Figure 14] 13 is a flowchart showing a photomask pattern design method according to a fourth embodiment. [Figure 15] 13A to 13C are cross-sectional views showing a method for manufacturing a photomask according to a fifth embodiment. [Figure 16] 13A to 13C are cross-sectional views showing a method for manufacturing a photomask according to a sixth embodiment. [Figure 17] 13A to 13C are cross-sectional views showing a method for manufacturing a photomask according to a seventh embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In Fig. 1 to Fig. 17, the same components are denoted by the same reference numerals, and duplicated descriptions will be omitted.

[0008] (First embodiment) 1 is a cross-sectional view showing the structure of a photomask according to the first embodiment. The photomask according to the present embodiment is a half-tone mask, which is a type of phase shift mask.

[0009] The photomask of this embodiment includes a substrate 1 and a halftone film 2. The halftone film 2 includes a halftone film pattern 2a forming a photomask pattern. In the following description, the halftone film 2 is also referred to as an "HT film 2," and the halftone film pattern 2a is also referred to as an "HT film pattern 2a." The halftone film 2 is an example of a mask film.

[0010] The substrate 1 is, for example, a transparent substrate such as a glass substrate or a quartz substrate. FIG. 1 shows one surface S1 of the substrate 1 and the other surface S2 of the substrate 1. FIG. 1 further shows an X direction and a Y direction parallel to the surfaces S1 and S2 of the substrate 1 and perpendicular to each other, and a Z direction perpendicular to the surfaces S1 and S2 of the substrate 1. The X direction, the Y direction, and the Z direction intersect with each other. In this specification, the +Z direction is treated as the upward direction, and the -Z direction is treated as the downward direction. The -Z direction may or may not coincide with the direction of gravity. In FIG. 1, the surface S1 is the lower surface of the substrate 1, and the surface S2 is the upper surface of the substrate 1.

[0011] The HT film 2 is formed on the surface S1 of the substrate 1. The HT film 2 is, for example, a MoSi film (molybdenum silicon film). In this case, the HT film 2 may be formed of a SiN film (silicon nitride film), and as a result, may contain Mo atoms, Si atoms, and N atoms.

[0012] 1 shows a patterned portion P1 and a non-patterned portion P2 of the HT film 2. The patterned portion P1 and the non-patterned portion P2 are formed by processing the HT film 2 by etching to form an HT film pattern 2a. The patterned portion P1 is a portion where the HT film 2 remains after etching, and the non-patterned portion P2 is a portion where the HT film 2 has been removed during etching. In other words, the patterned portion P1 is a portion that corresponds to the HT film pattern 2a, and the non-patterned portion P2 is a portion that corresponds to a recess in the HT film 2.

[0013] As described above, the photomask of this embodiment is a halftone mask. Therefore, the phase of the light transmitted through the substrate 1 and the patterned portion P1 differs from the phase of the light transmitted through the substrate 1 and the non-patterned portion P2 by approximately 180 degrees. That is, the HT film 2 of this embodiment has the effect of approximately inverting the phase of the light.

[0014] As shown in FIG. 1, the substrate 1 and the HT film 2 of this embodiment include one region R1 including a patterned portion P1 and a non-patterned portion P2, and another region R2 including a patterned portion P1 and a non-patterned portion P2. The light transmittance of the substrate 1 and the HT film 2 in the region R1 is different from the light transmittance of the substrate 1 and the HT film 2 in the region R2. For example, the transmittance of the region R1 is a low value, and the transmittance of the region R2 is a high value. The former value is an example of a first value, and the latter value is an example of a second value. A region having a low transmittance such as the region R1 is called a dark region (dark mask). A region having a high transmittance such as the region R2 is called a bright region (bright mask). Further details of the regions R1 and R2 will be described later.

[0015] The above transmittance is an energy transmittance that represents the ratio of the energy of light after transmission to the energy of light before transmission. On the other hand, the amplitude transmittance represents the ratio of the amplitude of light after transmission to the amplitude of light before transmission. The energy transmittance is the square of the amplitude transmittance. In this specification, the energy transmittance is simply referred to as "transmittance".

[0016] In addition, the substrate 1 and the HT film 2 of this embodiment may have three or more regions having different transmittances. For example, the substrate 1 and the HT film 2 of this embodiment may have a region R1 having a low transmittance, a region R2 having a high transmittance, and another region having a transmittance between the transmittance of the region R1 and the transmittance of the region R2.

[0017] FIG. 2 is a graph for explaining the photomask of the first embodiment.

[0018] FIG. 2 shows the relationship between the duty ratio and the NILS value of a binary mask, a halftone mask, and a Levenson mask. The duty ratio corresponds to the area ratio between the patterned portion and the non-patterned portion in a plan view of each photomask. For example, when the area ratio between the patterned portion and the non-patterned portion is 3:1, the duty ratio is 0.75 (=3 / 4). The shapes of the patterned portion and the non-patterned portion of each photomask are the same as the shapes of the patterned portion P1 and the non-patterned portion P2 of the photomask shown in FIG. 1. The duty ratio of each photomask is also called the coverage of the photomask pattern of each photomask. For example, the duty ratio of the photomask shown in FIG. 1 is also called the coverage of the HT film pattern 2a. On the other hand, the NILS value is defined by the slope of the logarithmic value of the light intensity, and is an index of the process margin of each photomask. As the NILS value increases, the pattern dimension fluctuation on the wafer with respect to the fluctuation of the exposure dose decreases, so that a large NILS value corresponds to a large process margin.

[0019] According to Fig. 2, the process margin of a half-tone mask is larger than that of a binary mask. On the other hand, the process margin of a half-tone mask is smaller than that of a Levenson mask, but it is known that the Levenson mask has more design constraints than the half-tone mask. Therefore, in this embodiment, a half-tone mask is adopted as the photomask. This makes it possible to increase the process margin while reducing the design constraints.

[0020] The term "duty ratio" is generally used when the photomask pattern is a periodic pattern. Examples of periodic patterns are shown in FIG. 4 and FIG. 5, which will be described later. However, the description of FIG. 2 is also applicable to the case where the photomask pattern is a non-periodic pattern. This also applies to the description below, in which the term "duty ratio" appears. On the other hand, the term "coverage" is generally used when the photomask pattern is a periodic pattern or a non-periodic pattern. Therefore, the term "duty ratio" that appears in this specification can be replaced with the term "coverage."

[0021] FIG. 3 is another graph for explaining the photomask of the first embodiment.

[0022] 3 shows the relationship between the duty ratio and the NILS value of a halftone mask for two cases. One curve shows the relationship between the duty ratio and the NILS value when lithography is performed under condition 1, and the other curve shows the relationship between the duty ratio and the NILS value when lithography is performed under condition 2. For example, the exposure dose during lithography differs between condition 1 and condition 2.

[0023] 3, when the duty ratio of the half-tone mask is small, it is preferable to perform lithography under condition 1. On the other hand, when the duty ratio of the half-tone mask is large, it is preferable to perform lithography under condition 2.

[0024] This becomes a problem when the duty ratio of the halftone mask differs for each region of the halftone mask. For example, when the halftone mask has a region 1 with a low duty ratio and a region 2 with a high duty ratio, it is desirable to perform lithography in the region 1 under condition 1, and it is desirable to perform lithography in the region 2 under condition 2. In this case, when condition 1 is adopted, the process margin of lithography in the region 2 becomes smaller than that when condition 2 is adopted. On the other hand, when condition 2 is adopted, the process margin of lithography in the region 1 becomes smaller than that when condition 1 is adopted. Since the regions 1 and 2 are provided in the same halftone mask, it is not desirable to use them for exposure under different conditions, and it is desirable to use them for exposure under the same conditions. If the same conditions can be adopted for the regions 1 and 2, it is possible to simultaneously use the regions 1 and 2 for exposure under the same conditions while increasing the process margins of the regions 1 and 2.

[0025] As described above, the photomask shown in FIG. 1 also has two regions, region R1 and region R2. Therefore, if the duty ratio of region R1 is small and the duty ratio of region R2 is large, it is considered that the same problem as that of region 1 and region 2 may occur. However, in this embodiment, the transmittance of region R1 is low and the transmittance of region R2 is high. This makes it possible to suppress the above problem. The details will be described later.

[0026] FIG. 4 is a plan view showing an example of a photomask pattern in the first embodiment.

[0027] 4(a) and 4(b) show examples of regions R1 and R2 of this embodiment, respectively. Region R1 includes an HT film pattern 2a for forming an L / S (Line and Space) pattern. This HT film pattern 2a is used to form, for example, a word line of a two-dimensional NAND memory. The same is true for region R2. However, the width of the pattern portion P1 in region R2 is the same as the width of the pattern portion P1 in region R1, and the width of the non-pattern portion P2 in region R2 is narrower than the width of the non-pattern portion P2 in region R1. As a result, the duty ratio of region R2 is larger than the duty ratio of region R1.

[0028] FIG. 5 is a plan view showing another example of the photomask pattern of the first embodiment.

[0029] 5(a) and 5(b) also show examples of regions R1 and R2 of this embodiment, respectively. Region R1 includes an HT film pattern 2a for forming a hole pattern. This HT film pattern 2a is used to form memory holes of, for example, a 3D NAND memory. The same is true for region R2. However, the pitch between pattern portions P1 in region R2 is the same as the pitch between pattern portions P1 in region R1, and the diameter of pattern portion P1 in region R2 is larger than the diameter of pattern portion P1 in region R1. As a result, the duty ratio of region R2 is larger than the duty ratio of region R1.

[0030] The photomask pattern (HT film pattern 2a) of this embodiment may have the shape shown in FIG. 4(a) and FIG. 4(b), may have the shape shown in FIG. 5(a) and FIG. 5(b), or may have another shape.

[0031] 6 to 9 are graphs for explaining the photomask of the first embodiment.

[0032] [Figure 6] FIG. 6 shows the relationship between the duty ratio and the NILS value of the halftone mask in two cases. One curve shows the relationship between the duty ratio and the NILS value when the halftone mask is a dark mask, and the other curve shows the relationship between the duty ratio and the NILS value when the halftone mask is a light mask. As mentioned above, the transmittance of the dark mask is lower than that of the light mask. In FIG. 6, the transmittance of the dark mask is about 0.49 times that of the light mask, and the amplitude transmittance of the dark mask is about 0.7 times that of the light mask.

[0033] The relationship between the two curves shown in FIG. 6 is similar to the relationship between the two curves shown in FIG. 3. This means that changing condition 2 to condition 1 has the same effect as replacing a light mask with a dark mask. In FIG. 3, an example was described in which lithography using region 1 with a small duty ratio is desirably performed under condition 1, and lithography using region 2 with a large duty ratio is desirably performed under condition 2. According to FIG. 6, the effect of this example can also be obtained by using region 1 as a dark mask, region 2 as a light mask, and performing lithography using regions 1 and 2 under condition 2. This makes it possible to improve the process margin of lithography using region 1 and the process margin of lithography using region 2 under the same condition, condition 2. Therefore, it becomes possible to suitably use region 1 and region 2 provided on the same halftone mask for exposure under the same condition.

[0034] In order to obtain such an effect, the regions R1 and R2 shown in Fig. 1 are respectively a dark mask (dark region) and a light mask (light region). That is, the region R1 with a small duty ratio is a dark mask, and the region R2 with a small duty ratio is a light mask.

[0035] [Figure 7] Figure 7 shows the same two curves as in Figure 6 and the intersection point X of these curves. When comparing the NILS value of the dark mask and the NILS value of the light mask at the same duty ratio, the NILS value of the dark mask is higher than the NILS value of the light mask in the area where the duty ratio is lower than the intersection point X. On the other hand, the NILS value of the light mask is higher than the NILS value of the dark mask in the area where the duty ratio is higher than the intersection point X.

[0036] FIG. 7 further shows a method for setting the regions R1 and R2. In this embodiment, if the duty ratio in a certain region is lower than the duty ratio of the intersection X, the region is set as a dark mask. On the other hand, if the duty ratio in a certain region is higher than the duty ratio of the intersection X, the region is set as a light mask. As a result, a region having a duty ratio lower than that of the intersection X is included in the region R1, and a region having a duty ratio higher than that of the intersection X is included in the region R2. This makes it possible to improve the process margin of the lithography by the region R1 and the process margin of the lithography by the region R2 under the same conditions. Therefore, the region R1 and the region R2 provided on the same photomask of this embodiment can be suitably used for exposure under the same conditions. The duty ratio of the intersection X is an example of a threshold value of the coverage rate.

[0037] [Figure 8(a) to Figure 8(e)] Figures 8(a) to 8(e) show the latent image intensity distributions when using a dark mask and a light mask with duty ratios of 0.4 to 0.8, respectively. The dashed lines in Figures 8(a) to 8(e) represent slice levels. The transmittances of the dark mask and the light mask are the same as those in Figures 6 and 7.

[0038] It is desirable for the latent image intensity distribution to be steep. This is because if the latent image intensity distribution is steep, the boundary between the positive and negative parts of the resist film will be clear. According to Figs. 8(a) to 8(e), it is desirable to use a dark mask in the region where the duty ratio is 0.4 to 0.6, and it is desirable to use a light mask in the region where the duty ratio is 0.7 to 0.8. This result is consistent with the result shown in Fig. 6.

[0039] [Figure 9(a) and Figure 9(b)] FIG. 9(a) shows the relationship between the duty ratio and the NILS value for the dark mask and the light mask, similarly to FIG. 7. FIG. 9(b) shows the relationship between the duty ratio and the inverse of the MEF value for the dark mask and the light mask. The MEF value is the ratio at which the dimensional error on each photomask is magnified on the exposed wafer, and is an index of the mask specification of each photomask. As the MEF value increases, the dimensional variation on the wafer relative to the dimensional error on the photomask decreases, so that a large inverse of the MEF value means that the mask specification can be relaxed. The duty ratio at the intersection Y of the two curves shown in FIG. 9(b) is the same as the duty ratio at the intersection X of the two curves shown in FIG. 9(a). According to FIG. 9(b), it can be seen that the process margin (NILS value) is improved by this embodiment, and thus the mask specification (MEF value) is also improved.

[0040] As described above, the substrate 1 and the HT film 2 of the photomask of this embodiment include a region R1 (dark mask) having a low transmittance and a region R2 (light mask) having a high transmittance. For example, the HT film pattern 2a in the region R1 has a low duty ratio, and the HT film pattern 2a in the region R2 has a high duty ratio. According to this embodiment, by setting the transmittance of the region R1 and the transmittance of the region R2 to different values, it is possible to improve both the process margin of the lithography by the region R1 and the process margin of the lithography by the region R2. For example, the region R1 and the region R2, which are provided on the same photomask and have different duty ratios, can be suitably used for exposure under the same conditions.

[0041] Second embodiment FIG. 10 is a cross-sectional view showing the structure of a photomask according to the second embodiment.

[0042] The photomask of this embodiment includes, in addition to the components of the photomask of the first embodiment, a plurality of shading elements 1a provided in a substrate 1. In this embodiment, these shading elements 1a are provided only in region R1 of regions R1 and R2, and are provided in a plane parallel to the XY plane in region R1. In Fig. 10, each shading element 1a is diagrammatically indicated by the symbol "+".

[0043] The shading elements 1a have the effect of reducing the transmittance of light within the substrate 1. In this embodiment, the shading elements 1a are provided only within the region R1, so that the transmittance of the region R1 is lower than that of the region R2. For example, the transmittance of the substrate 1 within the region R2 is approximately 100%, the transmittance of the substrate 1 within the region R1 is approximately 49%, and the transmittance of the mask film 2 within the regions R1 and R2 is approximately 6%. As a result, the ratio of the transmittance of the region R1 to the transmittance of the region R2 is 49×6:100×6, and the transmittance of the region R1 is 0.49 times the transmittance of the region R2.

[0044] The shading elements 1a may also be provided in the region R2. For example, the shading elements 1a in the region R2 are provided in a plane parallel to the XY plane in the substrate 1, similar to the shading elements 1a in the region R1. In this case, the density of the shading elements 1a in the region R2 is set lower than the density of the shading elements 1a in the region R1. This makes it possible to make the transmittance of the region R1 lower than the transmittance of the region R2. In addition, when the shading elements 1a are not provided in the region R2 as in this embodiment, this corresponds to a case where the density of the shading elements 1a in the region R2 is zero.

[0045] The shading element 1a at a certain location in the substrate 1 is formed, for example, by irradiating that location in the substrate 1 with a laser. When the substrate 1 is irradiated with a laser, a phase transition occurs in the material of the substrate 1, and the shading element 1a is formed in the substrate 1. An example of such a laser is a femtosecond laser.

[0046] It is desirable that the distance between the surface S1 of the substrate 1 and the shading elements 1a in the substrate 1 is small, because if this distance is large, the latent image may become blurred. This distance is, for example, 166 μm to 500 μm.

[0047] As described above, the photomask of this embodiment includes shading elements 1a in the substrate 1. Therefore, according to this embodiment, the transmittance of region R1 and the transmittance of region R2 can be set to different values ​​by the shading elements 1a.

[0048] The transmittance of the substrate 1 may be adjusted by a component other than the shading elements 1a. For example, the transmittance of the substrate 1 may be adjusted by forming an uneven pattern on the surface of the substrate 1.

[0049] Third embodiment FIG. 11 is a cross-sectional view showing the structure of a photomask according to the third embodiment.

[0050] The photomask of this embodiment includes a phase shifter film 3 formed on the surface S1 of the substrate 1 in addition to the components of the photomask of the first embodiment. The phase shifter film 3 includes a phase shifter film pattern 3a that forms a photomask pattern together with the HT film 2. The phase shifter film pattern 3a is formed on the side of the HT film pattern 2a. In this embodiment, the phase of light transmitted through the substrate 1 and the phase shifter film 3 differs by approximately 180 degrees from the phase of light transmitted through the substrate 1 and the HT film 2. The phase shifter film 3, like the HT film 2, is an example of a mask film.

[0051] The substrate 1, HT film 2, and phase shifter film 3 of this embodiment include regions R1, R2, and R3. Each of the regions R1 to R3 includes a patterned portion P1 and a non-patterned portion P2. The regions R1 and R2 include the substrate 1 and the HT film 2, but do not include the phase shifter film 3. The regions R1 and R2 are a dark mask and a light mask, respectively, similar to the regions R1 and R2 of the first embodiment. The duty ratio of the region R1 is small, and the transmittance of the region R1 is low. The duty ratio of the region R2 is large, and the transmittance of the region R2 is high.

[0052] Region R3 includes a substrate 1, an HT film 2, and a phase shifter film 3. Thus, the patterned portion P1 in region R3 includes the HT film 2 and the phase shifter film 3. In region R3, the patterned portion P1 corresponds to the HT film pattern 2a and the phase shifter film pattern 3a, and the non-patterned portion P2 corresponds to the recessed portion in the HT film 2 and the phase shifter film 3. In this embodiment, the duty ratio of region R3 is larger than that of region R2, and the transmittance of region R3 is the same as that of region R2. The transmittance of region R3 is the light transmittance of the substrate 1, the HT film 2, and the phase shifter film 3 in region R3. Region R3 is an example of a third region.

[0053] Regions R1 and R2 include a substrate 1 and an HT film 2, and have a half-tone mask structure. On the other hand, region R3 has a structure in which a phase shifter film 3 is added to a half-tone mask, and has a structure similar to a Levenson mask or an attenuating phase shift mask. In the following description, a photomask having the structure of region R3 will be called a mixed mask.

[0054] The Levenson mask has favorable characteristics as described above with reference to Fig. 2. According to this embodiment, by incorporating elements of the Levenson mask into the halftone mask, more favorable lithography can be performed.

[0055] FIG. 12 is a graph for explaining the photomask of the third embodiment.

[0056] FIG. 12(a) shows the NILS values ​​of a halftone mask equivalent to a dark mask, a halftone mask equivalent to a light mask, and a Levenson mask. Here, the amplitude transmittance of the dark mask is 0.7 times that of the light mask. FIG. 12(a) further shows the NILS value of the photomask of the first embodiment including the dark mask and the light mask with a thick dotted line. The photomask of this embodiment has a dark mask structure in region R1 and a light mask structure in region R2. FIG. 12(b) shows the relationship between the mask duty ratio of the halftone mask equivalent to the dark mask and the halftone mask equivalent to the light mask. In FIG. 12(b), the horizontal axis shows the duty ratio of the resist pattern formed on the wafer, and the vertical axis shows the duty ratio of the mask pattern.

[0057] FIG. 12(c) shows the NILS value of the mixed mask in addition to the NILS value shown in FIG. 12(a). FIG. 12(c) further shows the NILS value of the photomask of this embodiment, which includes a dark mask, a light mask, and a mixed mask, with a thick dotted line. According to FIG. 12(c), the NILS value of the mixed mask is large in the area with a large duty ratio. Therefore, the photomask of this embodiment is manufactured so that it has a dark mask structure in the region R1 with a small duty ratio, a light mask structure in the region R2 with a medium duty ratio, and a mixed mask structure in the region R3 with a large duty ratio. This makes it possible to perform lithography more suitable than the first embodiment. FIG. 12(d) shows the relationship between the mask duty ratio of the mixed mask in addition to the mask duty ratio shown in FIG. 12(b). In FIG. 12(d), the horizontal axis shows the duty ratio of the resist pattern formed on the wafer, and the vertical axis shows the duty ratio of the mask pattern.

[0058] As described above, the photomask of this embodiment includes the region R1 corresponding to the dark mask, the region R2 corresponding to the light mask, and the region R3 corresponding to the mixed mask. Therefore, according to this embodiment, it is possible to perform more suitable lithography than when using a photomask including only the regions R1 and R2.

[0059] In this embodiment, the transmittance of region R3 is the same as the transmittance of region R2, but it may be the same as the transmittance of region R1, or may be different from the transmittance of regions R1 and R2.

[0060] (Fourth embodiment) In the fourth embodiment, a method of designing a photomask pattern for manufacturing a photomask will be described. For example, when manufacturing the photomask shown in Fig. 1, the layout of the photomask pattern (HT film pattern 2a) shown in Fig. 1 is designed. In this case, the HT film 2 is processed into the HT film pattern 2a according to the designed photomask pattern, thereby manufacturing the photomask shown in Fig. 1.

[0061] Below, a method for designing a photomask pattern (FIG. 13) of a comparative example of the fourth embodiment will be described as a premise for describing a method for designing a photomask pattern (FIG. 14) of the fourth embodiment.

[0062] 13 is a flowchart showing a method of designing a photomask pattern in a comparative example of the fourth embodiment. The method of this comparative example designs a photomask pattern for a half-tone mask equivalent to a light mask.

[0063] First, data of a target pattern for lithography is acquired (step S1). For example, when a semiconductor layer or a metal layer is processed by lithography and etching to form word lines of a two-dimensional NAND memory, data of the pattern of the word lines is acquired.

[0064] Next, photomask pattern data is created using the data of the lithography target pattern (step S2). For example, photomask pattern data for manufacturing a photomask for word lines is created. Examples of such photomask patterns are shown in Figures 4(a) and 4(b).

[0065] Next, the data of the photomask pattern is corrected by OPC (Optical Proximity Correction) or the like (step S3). For example, a SRAF (Sub-Resolution Assist Feature) pattern is added to the photomask pattern for the word lines.

[0066] Next, the corrected data of the photomask pattern is output (step S4). For example, the data of the photomask pattern including the L / S pattern for the word line and the SRAF pattern for OPC is output. When the method of this comparative example is executed by a computer such as a PC (Personal Computer), the data of the photomask pattern is output in a form in which the photomask pattern is displayed on a display, the data of the photomask pattern is stored in a storage, or the data of the photomask pattern is transmitted to another device.

[0067] Next, the photomask pattern is checked for lithography hot spots using the corrected data of the photomask pattern (step S5). The lithography hot spots are locations where lithography is likely not performed correctly. If no lithography hot spots are detected, the method of this comparative example is terminated.

[0068] On the other hand, if a lithography danger point is detected, the corrected data of the photomask pattern is re-corrected by OPC or the like (step S3). The re-correction is performed with the aim of eliminating the lithography danger point. Next, the re-corrected data of the photomask pattern is output (step S4). Next, the lithography danger point of the photomask pattern is checked using the re-corrected data of the photomask pattern (step S5). The subsequent processing is the same as the processing after the first correction.

[0069] 14 is a flowchart showing a method for designing a photomask pattern according to the fourth embodiment. The method according to the present embodiment designs a photomask pattern for the photomask of the first embodiment, i.e., a halftone mask including an area R1 corresponding to a dark mask and an area R2 corresponding to a light mask.

[0070] The method of this embodiment includes steps S11 to S14 in addition to steps S1 to S5 described in the comparative example. The method of this embodiment is executed by a computer such as a PC, for example, in the same manner as the comparative example.

[0071] In this embodiment, after step S1, not only step S2 but also step S11 is performed. Specifically, a tiling process is performed to calculate the distribution of the coverage of the target pattern (step S11). In the tiling process, the target pattern is divided into a plurality of square regions in a two-dimensional array by a grid (mesh). These square regions are called tiles. The tiling process of this embodiment is performed so that the dimensions of the grid are equal to or greater than the proximity correction distance (OPE distance: Optical Proximity Effect distance), which is a distance that affects OPC. In other words, the length of one side of the tile is set to be equal to or greater than the OPE distance. The shape of the tile may be other than a square (for example, a rectangle or a triangle).

[0072] Next, using these tiles, the distribution of the coverage of the target pattern is calculated (step S12). In this embodiment, the distribution of the coverage of the target pattern is calculated by calculating the coverage of the target pattern in each tile. The coverage of the target pattern in each tile is the ratio of the area of ​​the target pattern to the area of ​​each tile, and corresponds to the above-mentioned duty ratio. In this embodiment, the coverage of the target pattern in each tile becomes the coverage (duty ratio) of the photomask pattern in the area corresponding to each tile. Therefore, in steps S11 and S12, the photomask pattern may be divided into multiple tiles, and the coverage of the photomask pattern in each tile may be calculated.

[0073] Next, a condition for setting the transmittance of the photomask is created based on the distribution of the coverage of the target pattern (step S13). For example, a condition is created that, if the coverage of a certain tile is smaller than the coverage of the intersection X (FIG. 7) which is a threshold value, the transmittance of the area corresponding to the tile is set to a low value. This area is included in the above-mentioned area R1. Also, a condition is created that, if the coverage of a certain tile is larger than the coverage of the intersection X (FIG. 7) which is a threshold value, the transmittance of the area corresponding to the tile is set to a high value. This area is included in the above-mentioned area R2. In this embodiment, these conditions are created based on a table related to the coverage and transmittance. Any number of conditions may be created. In this embodiment, as shown in FIG. 7, a method is shown in which two types of transmittance are set based on data of two types of transmittance, with one intersection X as a boundary, but, for example, three types of transmittance may be set based on data of three types of transmittance, with two intersections as boundaries.

[0074] Next, based on these conditions, the transmittance distribution on the mask surface, i.e., the two-dimensional distribution of the transmittance of the photomask, is calculated (step S14). In this embodiment, the transmittance distribution of the photomask is calculated by calculating the transmittance of the photomask in areas corresponding to each tile. This creates a distribution of area R1 and a distribution of area R2. For example, an area with a low coverage is included in area R1 and is given a low transmittance. Also, an area with a high coverage is included in area R2 and is given a high transmittance. The process of step S14 may be performed taking into account the transmittance blur of the mask surface.

[0075] The process of giving a low transmittance to the region R1 and a high transmittance to the region R2 in steps S13 and S14 may be performed in any manner. For example, if the default value of the transmittance of the substrate 1 described above is 100%, the transmittance of the substrate 1 may be maintained at 100% in the region R2, and the transmittance of the substrate 1 may be reduced from 100% to 49% in the region R1. This makes it possible to manufacture a photomask such as that of the second embodiment. Such a reduction in transmittance can be achieved by using, for example, the shading element 1a described above. Meanwhile, in steps S13 and S14, only the transmittance of the region R2 may be changed, or both the transmittances of the regions R1 and R2 may be changed.

[0076] Next, the photomask pattern data is corrected by OPC or the like (step S3), and the corrected data of the photomask pattern is output (step S4). The correction in step S4 in this embodiment is performed taking into consideration the transmittance of each tile calculated in step S14. Therefore, the corrected data includes data on the transmittance distribution calculated in step S14. As a result, by manufacturing a photomask according to the corrected data, it is possible to manufacture a photomask having regions R1 and R2 with different transmittances.

[0077] Next, the photomask pattern is checked for lithography hot spots using the corrected data of the photomask pattern (step S5). If no lithography hot spots are detected, the method of this embodiment is terminated.

[0078] On the other hand, when a lithography danger point is detected, the processes of steps S13, S14, S3, and S4 are performed again. For example, the re-correction in step S3 is performed with the aim of eliminating the lithography danger point. Also, when the coverage of a certain region becomes high by OPC, the transmittance of the region may be changed from a low value to a high value in step S14. Conversely, when the coverage of a certain region becomes low by OPC, the transmittance of the region may be changed from a high value to a low value in step S14. This changes the shapes of the regions R1 and R2. Also, in step S13, one or both of the transmittance of the region R1 and the transmittance of the region R2 may be changed. For example, in the above example in which the transmittance of the substrate 1 in the region R1 is reduced from 100% to 49%, the value of 49% may be changed to another value (for example, 36%). In this way, when a lithography danger point is detected, the distribution and transmittance of the regions R1 and R2 may be corrected (changed) in step S14.

[0079] Next, the re-corrected data of the photomask pattern is output (step S4). Next, the re-corrected data of the photomask pattern is used to check the lithography hot spots of the photomask pattern (step S5). The subsequent processing is the same as the processing after the first correction.

[0080] As described above, in this embodiment, the distribution of the coverage of the target pattern or mask pattern is calculated, and data of a photomask pattern having a region R1 with a low transmittance and a region R2 with a high transmittance is created based on the coverage. For example, the region R1 has a low coverage, and the region R2 has a high coverage. According to this embodiment, by setting the transmittance of the region R1 and the transmittance of the region R2 to different values, it is possible to improve both the process margin of the lithography by the region R1 and the process margin of the lithography by the region R2.

[0081] The correction in step S4 of this embodiment may be performed using ILT (Inverse Lithography Technology) instead of OPC. The table referred to in step S13 of this embodiment may include a correspondence between coverage and transmittance. For example, this table may include a correspondence such that "when the coverage of a certain region is a value V1, the transmittance value of the region is V2." Meanwhile, in step S13 of this embodiment, the conditions may be set by simulation or numerical calculation. The photomask pattern of this embodiment may be a photomask pattern for manufacturing the photomask of the second or third embodiment.

[0082] Fifth embodiment Fig. 15 is a cross-sectional view showing a method for manufacturing a photomask according to the fifth embodiment. Fig. 15(a) and Fig. 15(b) show the process for manufacturing the photomask according to the first embodiment.

[0083] First, a substrate 1 is prepared (FIG. 15(a)). In FIG. 15(a), a surface S1 of the substrate 1 is the upper surface of the substrate 1, and a surface S2 of the substrate 1 is the lower surface of the substrate 1. Next, an HT film 2 is formed on the surface S1 of the substrate 1 (FIG. 15(a)).

[0084] Next, the HT film 2 is processed by lithography and RIE (Reactive Ion Etching) to form an HT film pattern 2a from the HT film 2 (FIG. 15(b)). As a result, a pattern portion P1 and a non-pattern portion P2 are formed in the HT film 2.

[0085] The substrate 1 and HT film 2 shown in Fig. 15(b) have regions R1 and R2. As described above, region R1 is formed to have a low duty ratio (coverage) and low transmittance. On the other hand, region R2 is formed to have a high duty ratio (coverage) and high transmittance. Such regions R1 and R2 can be formed by manufacturing a photomask using the data of the photomask pattern designed in the fourth embodiment.

[0086] The process of decreasing the transmittance of the region R1 and increasing the transmittance of the region R2 may be performed by any method. For example, such transmittance may be achieved by forming the above-mentioned shading element 1a in the substrate 1. The shading element 1a will be described in detail in the seventh embodiment described later.

[0087] According to this embodiment, by manufacturing the photomask of the first embodiment, it is possible to improve the process margin of lithography.

[0088] Sixth embodiment Fig. 16 is a cross-sectional view showing a method for manufacturing a photomask according to the sixth embodiment. Fig. 16(a) to Fig. 16(c) show the process for manufacturing the photomask according to the third embodiment.

[0089] The steps of Figures 16(a) and 16(b) are performed in the same manner as the steps of Figures 15(a) and 15(b), respectively. Figures 16(a) and 16(b) show a region R3 in addition to regions R1 and R2.

[0090] Next, the phase shifter film 3 including the phase shifter film pattern 3a is formed only in the region R3 among the regions R1 to R3 (FIG. 16(c)). The phase shifter film pattern 3a is formed, for example, by forming the phase shifter film 3 in the regions R1 to R3, and then processing the phase shifter film 3 so that the phase shifter film 3 is removed from the regions R1 and R2 and the phase shifter film 3 remains in the region R3. In this manner, the photomask of the third embodiment is manufactured.

[0091] According to this embodiment, by manufacturing the photomask of the third embodiment, it is possible to improve the process margin of lithography.

[0092] Seventh embodiment Fig. 17 is a cross-sectional view showing a method for manufacturing a photomask according to the seventh embodiment. Fig. 17(a) to Fig. 17(c) show the process for manufacturing a photomask according to the seventh embodiment.

[0093] First, a substrate 1 is prepared (FIG. 17(a)). Next, a laser L is irradiated onto the substrate 1 to form a plurality of shading elements 1a within the substrate 1 (FIG. 17(a)). In this embodiment, the shading elements 1a are formed only within region R1 of regions R1 and R2. The laser L is, for example, a femtosecond laser.

[0094] Next, an HT film 2 is formed on the surface S1 of the substrate 1 (FIG. 17(b)). Next, the HT film 2 is processed by lithography and RIE to form an HT film pattern 2a from the HT film 2 (FIG. 17(c)). As a result, a pattern portion P1 and a non-pattern portion P2 are formed in the HT film 2.

[0095] According to this embodiment, by manufacturing the photomask of the second embodiment, it is possible to improve the process margin of lithography.

[0096] Although several embodiments have been described above, these embodiments are presented only as examples and are not intended to limit the scope of the invention. The novel method and mask described in this specification can be embodied in various other forms. In addition, various omissions, substitutions, and modifications can be made to the forms of the method and mask described in this specification without departing from the spirit of the invention. The appended claims and their equivalents are intended to include such forms and modifications that fall within the scope and spirit of the invention. [Explanation of symbols]

[0097] 1: substrate, 1a: shading element, 2: Halftone film, 2a: Halftone film pattern, 3: Phase shifter film, 3a: Phase shifter film pattern

Claims

1. Using data of a lithography target pattern, data of a photomask pattern to be formed by a mask film on a surface of a substrate is generated; Calculating a distribution of a coverage of the target pattern or the photomask pattern; creating a distribution of transmittance based on the distribution of coverage, the distribution including a distribution of a first region including a patterned portion and a non-patterned portion of the mask film, in which the light transmittance of the substrate and the mask film is a first value, and a distribution of a second region including a patterned portion and a non-patterned portion of the mask film, in which the light transmittance of the substrate and the mask film is a second value different from the first value; correcting data of the photomask pattern based on the distribution of transmittance; outputting the corrected data of the photomask pattern; A method for designing a photomask pattern, comprising:

2. 2. The method for designing a photomask pattern according to claim 1, wherein the correction is performed by optical proximity correction.

3. 3. The method of designing a photomask pattern according to claim 2, wherein the distribution of the coverage is calculated on a grid having a dimension equal to or larger than a proximity correction distance that affects the optical proximity correction.

4. 2. The method of claim 1, wherein the correction is performed by an inverse lithography technique.

5. Detecting lithography hot spots of the photomask pattern using the corrected data of the photomask pattern; When the lithography danger point is detected, modifying at least one of the distribution of the first region, the distribution of the second region, the first value, and the second value included in the distribution of the transmittance; recorrecting the corrected data of the photomask pattern based on the modified distribution of transmittance; outputting the recorrected data of the photomask pattern; The method of claim 1 , further comprising:

6. 2. The method of designing a photomask pattern according to claim 1, wherein the first region includes a region where the coverage is smaller than a threshold value, and the second region includes a region where the coverage is larger than the threshold value.

7. 2. The method for designing a photomask pattern according to claim 1, wherein the transmittance distribution is created by changing the transmittance of the first region from a predetermined value to the first value and / or by changing the transmittance of the second region from the predetermined value to the second value.

8. the predetermined value is the second value, 8. The method of designing a photomask pattern according to claim 7, wherein the transmittance distribution is created by changing the transmittance of the first region from the second value to the first value and maintaining the transmittance of the second region at the second value.

9. The method of designing a photomask pattern according to claim 8 , wherein the first value is smaller than the second value.

10. A mask film is formed on the surface of the substrate; forming a photomask pattern using the mask film, and forming a first region and a second region in the substrate and the mask film; Including, the first region includes a patterned portion and a non-patterned portion of the mask film, and is formed such that a light transmittance of the substrate and the mask film in the first region is a first value; the second region includes a patterned portion and a non-patterned portion of the mask film, and is formed such that the light transmittance of the substrate and the mask film in the second region has a second value different from the first value. A method for manufacturing a photomask.

11. The method for manufacturing a photomask according to claim 10 , wherein the mask film is formed to include a half-tone film.

12. The method of claim 11 , wherein the mask film is further formed to include a phase shifter film.

13. forming a third region in the substrate and the mask film, the third region including a patterned portion and a non-patterned portion of the mask film; the pattern portion in the first region is formed to include the half-tone film, the pattern portion in the second region is formed to include the half-tone film, the pattern portion in the third region is formed to include the halftone film and the phase shifter film; The method for producing a photomask according to claim 12 .

14. The method of claim 10 further comprising forming shading elements in the substrate.

15. The method of claim 14 , wherein the shading elements are formed such that a density of the shading elements in the second region is different from a density of the shading elements in the first region.

16. The method of claim 14 , wherein the shading elements are formed by a laser.

17. A substrate; a mask film provided on a surface of the substrate and including a photomask pattern; The substrate and the mask film are a first region including a patterned portion and a non-patterned portion of the mask film, the first region having a light transmittance of the substrate and the mask film having a first value; a second region including a patterned portion and a non-patterned portion of the mask film, wherein the light transmittance of the substrate and the mask film in the second region is a second value different from the first value; Photomask.

18. The photomask of claim 17 , wherein the mask film comprises an attenuated film.

19. The photomask of claim 18 , wherein the mask membrane further comprises a phase shifter membrane.

20. The photomask of claim 17 , wherein the substrate includes shading elements disposed within the substrate.

Images