Photomask blanks and photomasks

Abstract

To provide a photomask and a photomask blank which do not cause reduction of accuracy of a fine pattern and consequently, collapse due to that a side etch amount of a light shielding layer is increased even when a light shielding layer including a high etch rate layer is used, and a lateral wall of a formed pattern has a constricted shape.SOLUTION: A photomask blank in which light shield layers are formed on a support substrate comprising quartz is such that: the multiple light shield layers are alternately laminated with two or more kinds of membrane compositions having different etch rates; and each layer of the plurality of laminated light shield layers can be etched by a same etching gas or solution.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a photomask used in the manufacture of semiconductor devices and a photomask blank used in the manufacture of the photomask. [Background technology]

[0002] Semiconductor devices are manufactured by applying resist to a silicon wafer and exposing it to light through a photomask, but the dimensional accuracy of the pattern formed as a light-shielding layer on the photomask has a significant impact on the quality and yield of the semiconductor devices.

[0003] The photomask can be obtained by preparing a photomask blank having a light-shielding layer laminated on a support substrate made of quartz or on a light-transmitting layer formed on the support substrate, forming a resist layer that is sensitive to electron beams on the photomask blank, drawing a desired pattern using an electron beam lithography device, and then performing a development process to create a resist pattern, etching the light-shielding layer other than the resist pattern, and peeling and washing the resist pattern.

[0004] As semiconductor device circuits become finer and denser, there is a demand for improved dimensional accuracy and reduced variation in the patterns formed, and in photomask blanks, there is a demand for a higher etch rate (faster etching speed) for the light-shielding layer.

[0005] In other words, to obtain high resolution and high patterning accuracy of the pattern formed on the semiconductor device circuit, it is necessary to ensure high resolution and high patterning accuracy of the pattern on the photomask. Therefore, it is important to thin the resist layer when creating the photomask. On the other hand, ensuring the etching resistance of the resist layer in the light-shielding layer etching process limits the thinning of the resist layer. In other words, there is a trade-off between high resolution and high patterning accuracy and etching resistance. In order to reduce the load on the resist layer while thinning it and form a photomask pattern with higher accuracy, it is necessary to make the light-shielding layer, which is the target of patterning, etchable with high resolution and high patterning accuracy even if the resist layer is thinned.

[0006] In other words, in order to accurately form finer patterns with a Cr-containing film used in a light-shielding film for a photomask blank or a photomask, it is necessary to increase the etching speed (etch rate) of the Cr-containing film while maintaining a thickness that ensures the optical density required for a light-shielding film against exposure light.

[0007] Therefore, conventionally, a photomask blank has been used which has a light-shielding layer in which a thick, high-etch rate layer that satisfies the desired light-shielding performance is formed, and then a low-reflection layer and a conductive layer are laminated thereon.

[0008] For example, Patent Document 1 proposes a Cr-containing film as a light-shielding layer that contains Cr, O and / or N, and C, and the contents of Cr, O, N, and C are specified.

[0009] However, the use of a thick high-etch rate layer significantly increases the amount of side etching of the high-etch rate layer relative to the low-reflection layer and conductive layer, resulting in a constricted shape of the sidewalls of the formed pattern, which may lead to a decrease in precision or collapse of the fine pattern. This tendency becomes particularly pronounced when the pattern line width becomes finer and its dimension approaches or is smaller than the film thickness of the light-shielding layer. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 6540758 Summary of the Invention [Problem to be solved by the invention]

[0011] In view of the above-mentioned problems, an object of the present invention is to provide a photomask blank and a photomask that, even when a light-shielding layer including a high-etch rate layer is used, do not cause the amount of side etching of the light-shielding layer to increase drastically relative to the low-reflection layer or conductive layer, resulting in the side walls of the formed pattern becoming constricted, thereby preventing a decrease in precision of the fine pattern and even its collapse. [Means for solving the problem]

[0012] Therefore, the present invention provides the following photomask blank and photomask. The invention described in claim 1 has been made to achieve the above object, A photomask blank having a light-shielding layer formed on a support substrate made of quartz, characterized in that the light-shielding layer is formed by alternately stacking multiple layers of two or more types of film compositions with different etching rates, and that each of the multiple stacked light-shielding layers can be etched using the same etching gas or solution. The invention described in claim 2 is 2. The photomask blank according to claim 1, wherein a transparent layer and a light-shielding layer having any desired light transmission performance are laminated on a support substrate made of quartz in the order of support substrate, transparent layer, light-shielding layer, and the transparent layer and the light-shielding layer are not etched with the same etching gas or solution, and the light-shielding layers are alternately laminated in multiple layers with two or more film compositions having different etching rates, and each of the multiple laminated light-shielding layers can be etched with the same etching gas or solution. The invention described in claim 3 is 3. The photomask blank according to claim 1, wherein the low etch rate layers are thinner than the high etch rate layers in each light-shielding layer, which is made up of two or more film compositions having different etch rates stacked alternately. The invention described in claim 4 is 4. The photomask blank according to claim 1, wherein the thickness of each of the high etch rate layers in each of the plurality of laminated light-shielding layers is within half the thickness of the entire light-shielding layer. The invention described in claim 5 is 5. A photomask blank according to claim 1, wherein the light-shielding layer is made of two or more of chromium, chromium oxide, molybdenum, silicon, molybdenum silicon, silicon nitride, zirconium nitride, and tantalum. The invention described in claim 6 is A photomask using the photomask blank according to any one of claims 1 to 5. [Effects of the Invention]

[0013] The photomask blank and photomask according to the present invention have a light-shielding layer with a laminated structure of two or more film compositions with different etch rates, and by arbitrarily setting the film thickness of each, it becomes possible to adjust the amount of side etching, and in particular, it becomes possible to adjust the amount of side etching of the high etch rate layer, thereby achieving the effect of improving the sidewall shape and preventing collapse of the fine pattern. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is an example of a cross-sectional view of a photomask blank according to an embodiment of the present invention. [Figure 2] 1 is an example of a cross-sectional view of a photomask blank according to another embodiment of the present invention. [Figure 3] 1 is an example of a photomask using a photomask blank according to an embodiment of the present invention. [Figure 4] As a conventional example, this is an example of a photomask that uses a photomask blank in which the high etch rate layer accounts for more than half of the entire light-shielding film. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an example of an embodiment of a photomask blank and a photomask according to the present invention will be described with reference to the drawings as necessary.

[0016] In this embodiment, the object is to prevent a decrease in accuracy or collapse of the fine pattern in the light-shielding layer 12 in a photomask blank in which a light-shielding layer 12 is laminated on a transparent layer 16 formed on a support substrate 11 made of quartz, and in a photomask blank in which the light-shielding layer 12 is laminated on a support substrate 11 made of quartz.

[0017] Here, the presence or absence of the transparent layer 16 is the difference between a half-tone mask and a binary mask, and the light-shielding layer 12 is provided when manufacturing either a half-tone mask or a binary mask. In this embodiment, the purpose is to prevent a decrease in the accuracy of or collapse of the fine pattern in this light-shielding layer 12 in either case.

[0018] The light-shielding layer 12 is formed by alternately laminating multiple layers of two or more film compositions with different etch rates at any thickness, and the two or more films with different etch rates can be etched using the same etching gas or solution, thereby reducing the amount of side etching in the high etch-rate layer 13, which is a problem. As a result, it is possible to improve the sidewall shape and prevent the collapse of the fine pattern.

[0019] Photomask blanks and photomasks include binary mask blanks in which only a light-shielding layer 12 is laminated on a support substrate 11 made of quartz, as shown in Figure 1, as well as halftone mask blanks that utilize the phase shift effect of exposure light to transfer finer patterns onto a silicon wafer, as shown in Figure 2. Figure 2 shows one embodiment of the halftone mask blank, in which a light-shielding layer 12 is laminated on a transmissive layer 16 formed on a support substrate 11 made of quartz. Here, the transmissivity of the transmissive layer 16 is set to any desired transmission performance depending on the optical design of the halftone mask blank and halftone mask.

[0020] As shown in FIG. 4, which is a conventional example, when the film thickness of the high etch rate layer 13 occupies most of the light-shielding layer 12, the amount of side etching of the high etch rate layer 13 increases significantly, and there is a risk that the side wall of the light-shielding layer 12 will be significantly constricted, resulting in a problem of reduced precision of the fine pattern and even collapse.

[0021] In order to solve the above-mentioned problems that have conventionally occurred, according to this embodiment, two or more types of film compositions with different etch rates are alternately laminated to any film thickness in the light-shielding layer 12, and the films with different etch rates can be etched using the same etching gas or solution, making it possible to adjust the amount of side etching of the high etch rate layer without using a complicated etching process.

[0022] The purpose of providing the low etch rate layer 14 within the light-shielding layer 12 is to prevent the high etch rate layer 13 from becoming too thick, and in order to achieve a high etch rate for the entire light-shielding layer 12, it is preferable that the low etch rate layer 14 be as thin as possible (Figures 1 and 2). In order to efficiently adjust the amount of side etching of the high etch rate layer 13, it is preferable that the thickness of each layer is within half the thickness of the entire light-shielding film.

[0023] In fact, as a result of extensive research, we discovered that, if the optical density is the same, the amount of side etching is smaller when a light-shielding layer is formed by alternately stacking multiple layers of two or more film compositions with different etching rates than when a light-shielding layer is formed by a single layer, leading to the present invention.

[0024] CrONC films are known to have a high etching rate and can be etched with the same etching gas or solution as CrN films. However, in the present invention, other combinations of two or more of chromium, chromium oxide, molybdenum, silicon, molybdenum silicon, silicon nitride, zirconium nitride, and tantalum, which are generally used in photomask blanks and photomasks and have light-shielding properties at a predetermined exposure wavelength, may also be used, as long as they can be etched with the same etching gas or solution.

[0025] In the conventional light-shielding layer 12, the light-shielding layer 12 is composed only of a high etch rate layer 13, whereas the light-shielding layer 12 of the present embodiment, which is composed of the same optical density, is characterized by having multiple layers of two or more film compositions with different etch rates stacked alternately, for example, high etch rate layer 13, low etch rate layer 14, high etch rate layer 13, low etch rate layer 14, in other words, having multiple layers of two or more film compositions stacked alternately.Of course, other layers may be used as long as two or more film compositions are stacked alternately.

[0026] In addition, when the surface of the support substrate 11 made of quartz on which nothing is laminated is defined as the back surface, it is preferable that the outermost surface of the light-shielding layer 12 located on the opposite side be provided with a low-reflection layer 15 having a low reflectance at the exposure wavelength as shown in any one of Figures 1 to 4 in order to suppress reflection from the surface of the photomask light-shielding layer during wafer exposure.

[0027] Furthermore, a conductive layer (not shown) may be provided to prevent electrostatic damage to the pattern due to charging during handling during and after the photomask production, and to prevent pattern drawing defects due to charge-up during electron beam drawing during production. [Example]

[0028] As shown in FIG. 2 , a photomask blank was prepared using quartz for the support substrate 11, with a transmissive layer 16 and a light-shielding layer 12 laminated in that order, enabling the production of a half-tone mask measuring 6 inches (152.4 mm) long x 6 inches (152.4 mm) wide x 0.09 inches (2.3 mm) thick. First, a 72 nm thick MOSi film was formed as the transmissive layer 16, followed by a 15 nm thick CrONC film as the high etch rate layer 13, a 3 nm thick CrN film as the low etch rate layer 14, a 15 nm thick CrONC film as the high etch rate layer 13, a 3 nm thick CrN film as the low etch rate layer 14, a 14 nm thick CrONC film as the high etch rate layer 13, and a 5 nm thick CrON film as the low reflective layer 15 thereon, thereby forming a 55 nm thick light-shielding layer 12 in total, thereby obtaining an example of a photomask blank of the present invention.

[0029] After that, after a predetermined cleaning process, a chemically amplified negative resist is formed to a thickness of 125 nm using ACTM manufactured by Tokyo Electron Ltd. (not shown). After drawing a desired pattern using an electron beam lithography device, post-exposure baking (PEB) and development were performed under specified conditions, and the light-shielding layer 12 was etched using the formed resist pattern as a mask.The resist was then peeled off under specified conditions, and the transparent layer 16 was then etched, thereby obtaining an example of the photomask shown in Figure 3.

[0030] The resist may be removed after etching the transmitting layer 16 using the resist pattern as a mask.

[0031] In the photomask with the structure shown in Figure 3, the pattern resolution was measured using a general scanning type When the cross section was examined using an electron microscope, it was confirmed that the amount of side etching was improved in this example compared to the conventional example.

[0032] In detail, when resist layer formation and writing-PEB-development-etching were performed under the same conditions as above, in the case of a photomask using a photomask blank of the conventional example shown in FIG. 4, that is, a film configuration in which 72 nm of MoSi, 50 nm of CrONC, and 5 nm of CrON were laminated on a support substrate made of quartz, with the high etch rate layer having a thickness of at least half the thickness of the entire light-shielding film, the side etch amount 17 was 13 nm, whereas when the photomask blank of FIG. 2 described in this example was used, an improvement was confirmed in this example shown in FIG. 3, with the side etch amount 17 being 8 nm. The results are shown in Table 1.

[0033] [Table 1]

[0034] As described above, according to the present invention, it is possible to provide a photomask and a photomask blank that, even when a light-shielding layer 12 including a high etch rate layer 13 is used in a photomask and a photomask blank, do not suffer from the conventional problem of an extreme increase in the amount of side etching of the light-shielding layer 12, causing the side walls of the formed pattern to have a constricted shape, thereby reducing the precision of the fine pattern and even causing collapse. [Explanation of symbols]

[0035] 11. Support substrate made of quartz 12...Light blocking layer 13. High etch rate layer 14. Low etch rate layer 15...Low reflection layer 16. Permeable layer with any permeability 17. Side etch amount in high etch rate layer

Claims

1. A photomask blank having a light-shielding layer formed on a support substrate made of quartz, characterized in that the light-shielding layer is formed by alternately laminating a plurality of layers each having two or more types of film compositions with different etching rates, and each of the laminated light-shielding layers can be etched using the same etching gas or solution; the light-shielding layer is made up of a plurality of layers alternately stacked with two or more types of film compositions having different etching rates, and the low etching rate layer is thinner than the high etching rate layer in each layer; a photomask blank, characterized in that among the light-shielding layers, the light-shielding layers other than the high etch rate layer are made of two or more of molybdenum, silicon, molybdenum silicon, silicon nitride, zirconium nitride, and tantalum;

2. A photomask blank in which a transparent layer and a light-shielding layer having any desired light-transmitting performance are laminated on a support substrate made of quartz in the order of support substrate, transparent layer, light-shielding layer, and the transparent layer and the light-shielding layer are not etched with the same etching gas or solution, characterized in that the light-shielding layers are laminated alternately in a plurality of layers each having two or more film compositions with different etching rates, and each of the laminated light-shielding layers can be etched with the same etching gas or solution; The photomask blank according to claim 1, characterized in that the low etch rate layers are thinner than the high etch rate layers in each light-shielding layer, which is made up of two or more film compositions having different etch rates stacked alternately.

3. 3. The photomask blank according to claim 1, wherein the light-shielding layer comprises a CrONC film as a high etch rate layer.

4. 4. The photomask blank according to claim 1, wherein the thickness of each of the high etch rate layers in each of the plurality of laminated light-shielding layers is within ½ of the thickness of the entire light-shielding layer.

5. 3. The photomask blank according to claim 2, wherein the transparent layer is formed of MoSi; the light-shielding layer includes a CrONC film as a high-etch-rate layer, A photomask blank, characterized in that, of the light-shielding layers, the layer closest to the transmissive layer is the high etch rate layer, and the high etch rate layer and the transmissive layer are in contact with each other.

6. 5. The photomask blank according to claim 1, wherein the light-shielding layer is a light-shielding layer formed by alternately stacking two layers: a high-etch rate layer formed of a CrONC film and a low-etch rate layer formed of a CrN film.

7. A photomask using the photomask blank according to any one of claims 1 to 6.

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