JP7744157B2 - Photomask blanks and photomasks - Google Patents

Description

The present invention relates to a photomask used in the manufacture of semiconductor devices and a photomask blank used in the manufacture of such a photomask.

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 semiconductor devices.

Photomasks are obtained by creating a photomask blank with a light-shielding layer laminated on a support substrate made of quartz or a light-transmitting layer formed on the support substrate, forming a resist layer sensitive to electron beams on the photomask blank, drawing the 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.

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

In other words, to achieve high resolution and high patterning precision in the patterns formed on semiconductor device circuits, it goes without saying that high resolution and high patterning precision must also be ensured in the patterns on the photomask. Therefore, it is important to thin the resist layer when creating the photomask. On the other hand, ensuring the resist layer's resistance to etching during the light-shielding layer etching process limits how thin the resist layer can be. In other words, there is a trade-off between high resolution and high patterning precision and etching resistance. To reduce the load on the resist layer while thinning it and form a more accurate photomask pattern, it is necessary to make the light-shielding layer, which is the target of patterning, capable of being etched with high resolution and high patterning precision, even with a thinned resist layer.

In other words, in order to accurately form finer patterns with Cr-containing films used in light-shielding films for photomask blanks and photomasks, 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 the light-shielding film in response to the exposure light.

For this reason, conventionally, photomask blanks have been used that have a light-shielding layer formed by depositing a thick, high-etch rate layer that satisfies the desired light-shielding performance, followed by lamination of a low-reflection layer and a conductive layer.

For example, Patent Document 1 proposes a Cr-containing film, which is a light-shielding layer, containing Cr, O and/or N, and C, with the contents of Cr, O, N, and C specified.

However, using a thick, high-etch rate layer can dramatically increase the amount of side etching of the high-etch rate layer relative to the low-reflectivity layer or conductive layer, causing the sidewalls of the formed pattern to become constricted, which can lead to a decrease in the accuracy of the fine pattern or even its collapse. This tendency becomes particularly pronounced as the pattern line width becomes finer and its dimensions approach or become smaller than the film thickness of the light-shielding layer.

Patent No. 6540758

In view of the above-mentioned problems, the present invention aims to provide a photomask blank and photomask that, even when using a light-shielding layer that includes a high-etch rate layer, does not result in an extremely large side etch amount of the light-shielding layer relative to the low-reflection layer or conductive layer, resulting in the sidewalls of the formed pattern becoming constricted, thereby reducing the precision of the fine pattern and even causing it to collapse.

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 comprising a light-shielding layer formed on a support substrate made of quartz, the light-shielding layer being formed by alternately stacking multiple layers of two or more types of film compositions with different etching rates, and the multiple stacked light-shielding layers being capable of being etched with 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 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 of the light-shielding layers, which are alternately stacked in a plurality of layers each having two or more film compositions with different etch rates.
The invention described in claim 4 is the photomask blank according to any one of claims 1 to 3, characterized in that the film thickness of each of the high etch rate layers in each of the multiple laminated light-shielding layers is within 1/2 of the film thickness of the entire light-shielding layer.
The invention described in claim 5 is
5. The 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.

The photomask blank and photomask of the present invention have a light-shielding layer with a laminated structure made up of two or more film compositions with different etch rates, and by arbitrarily setting the film thickness of each, it is possible to adjust the amount of side etching, particularly of the high etch rate layer, thereby achieving the effect of improving the sidewall shape and preventing the collapse of fine patterns.

1 is an example of a cross-sectional view of a photomask blank according to an embodiment of the present invention. 1 is an example of a cross-sectional view of a photomask blank according to another embodiment of the present invention. 1 is an example of a photomask using a photomask blank according to an embodiment of the present invention. As a conventional example, this is an example of a photomask using a photomask blank in which the high etch rate layer is 1/2 or more of the entire light-shielding film.

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

In this embodiment, the objective is to prevent a decrease in precision 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 a light-shielding layer 12 is laminated on a support substrate 11 made of quartz.

The presence or absence of the transmissive layer 16 here is the difference between a half-tone mask and a binary mask. When manufacturing either a half-tone mask or a binary mask, the light-shielding layer 12 is provided. In this embodiment, the purpose is to prevent a decrease in precision or collapse of the fine pattern in this light-shielding layer 12 in both cases.

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

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, as shown in Figure 2, which utilize the phase shift effect of exposure light to transfer finer patterns onto a silicon wafer. Figure 2 shows one embodiment of the halftone mask blank, in which a light-shielding layer 12 is laminated on a transparent layer 16 formed on a support substrate 11 made of quartz. The transmittance of the transparent layer 16 here has any desired transmission performance depending on the optical design of the halftone mask blank and halftone mask.

As shown in Figure 4, which shows a conventional example, when the film thickness of the high etch rate layer 13 accounts for most of the light-shielding layer 12, the amount of side etching of the high etch rate layer 13 increases significantly, which can cause the sidewalls of the light-shielding layer 12 to become significantly constricted, resulting in problems such as reduced precision of the fine pattern and even collapse.

In order to solve the above-mentioned problems that have conventionally occurred, according to this embodiment, two or more film compositions with different etch rates are alternately stacked at 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 complex etching process.

The purpose of providing the low etch rate layer 14 in the light-shielding layer 12 is to prevent the high etch rate layer 13 from becoming too thick. 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 (FIGS. 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.

In fact, after 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 etch rates, rather than forming a light-shielding layer as a single layer, leading to the present invention.

CrONC films are known to have a high etching rate, and can be etched using the same etching gases or solutions 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 materials commonly used in photomask blanks and photomasks and have light-blocking properties at a specified exposure wavelength, can also be used, as long as they can be etched using the same etching gases or solutions.

In conventional light-shielding layers, the light-shielding layer 12 is composed only of a high etch rate layer 13, whereas the light-shielding layer 12 of this 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, such as high etch rate layer 13, low etch rate layer 14, high etch rate layer 13, low etch rate layer 14, in other words, multiple layers of two or more film compositions with different etch rates. Of course, other layers may be used as long as two or more film compositions are stacked alternately.

In addition, if the bare surface of the quartz support substrate 11 is designated the back surface, it is preferable to provide the outermost surface of the light-shielding layer 12 located on the opposite side with a low-reflection layer 15 having a low reflectance at the exposure wavelength, as shown in any of Figures 1 to 4, in order to suppress reflection from the photomask light-shielding layer surface during wafer exposure.

A conductive layer (not shown) may also be provided to prevent electrostatic damage to the pattern due to charging during handling during or after photomask production, and to prevent poor pattern drawing due to charge-up during electron beam drawing during production.

As shown in Figure 2, a photomask blank capable of producing 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 was prepared using quartz for the support substrate 11. A transparent layer 16 and a light-shielding layer 12 were sequentially laminated on the photomask blank. A 72 nm thick MOSi film was then formed as the transparent layer 16. Then, a 15 nm thick CrONC film was then formed as the high etch rate layer 13, a 3 nm thick CrN film was then formed as the low etch rate layer 14, a 15 nm thick CrONC film was then formed as the high etch rate layer 13, a 3 nm thick CrN film was then formed as the low etch rate layer 14, a 14 nm thick CrONC film was then formed as the high etch rate layer 13, and finally, a 5 nm thick CrON film was formed as the low-reflective layer 15 on top of the 15 nm thick CrONC film, thereby forming a total 55 nm thick light-shielding layer 12, thereby obtaining an example of a photomask blank of the present invention.

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

The resist may be removed after etching the transparent layer 16 using the resist pattern as a mask.

In the fabricated photomask having the structure shown in FIG. 3, the resolution of the pattern was confirmed by examining the cross section with a general scanning electron microscope. As a result, it was confirmed that the amount of side etching was improved in this example compared with the conventional example.

In detail, when the resist layer formation and writing-PEB-development-etching processes were carried out under the same conditions as above, in the case of a photomask using a photomask blank as shown in FIG. 4 of the conventional example, that is, a photomask having 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 film thickness of at least half the film 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 embodiment was used, an improvement was confirmed in the side etch amount 17 of this embodiment shown in FIG. 3, with the side etch amount being 8 nm.
The results are shown in Table 1.

As described above, the present invention makes it possible to provide photomasks and photomask blanks that, even when using a light-shielding layer 12 that includes a high-etch rate layer 13, do not suffer from the conventional problem of an extreme increase in the amount of side etching of the light-shielding layer 12, resulting in the sidewalls of the formed pattern becoming constricted, thereby reducing the precision of the fine pattern and even causing it to collapse.

11: Support substrate made of quartz 12: Light-shielding layer 13: High etch rate layer 14: Low etch rate layer 15: Low reflection layer 16: Transmission layer having any desired transmission performance 17: Amount of side etching in the high etch rate layer

Claims (7)

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; 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;
2. 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 photomask blank according to claim 1 or 2, wherein the light-shielding layer includes a CrONC film as a high etch rate layer. The photomask blank according to any one of claims 1 to 3, wherein the thickness of each high etch rate layer in each of the multiple laminated light-shielding layers is within half the thickness of the entire light-shielding layer. 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. A photomask blank according to any one of claims 1 to 4, wherein the light-shielding layer is a light-shielding layer formed by alternating two layers: a high-etch rate layer formed of a CrONC film and a low-etch rate layer formed of a CrN film. A photomask using the photomask blank according to any one of claims 1 to 6 .