JP4673039B2 - Mask blank substrate - Google Patents

Description

  The present invention relates to a mask blank substrate for forming an exposure mask used in photolithography.

  In a photolithography process which is one of semiconductor manufacturing processes, an exposure mask in which a light shielding film pattern is formed on a transparent substrate is used. This exposure mask is produced by electron beam lithography on the basis of a mask blanks substrate in which a light-shielding film such as chromium is formed on one main surface of a transparent substrate such as fused silica (for example, see Patent Document 1).

  The process for forming the pattern on the light shielding film of the mask blank substrate is as follows. First, a resist is applied to the surface of the light-shielding film, and an electron beam is irradiated to a place where a pattern is to be formed in a vacuum. After the electron beam irradiation, development is performed to obtain a resist pattern, and the light shielding film is etched using the resist pattern as a mask to obtain a light shielding film pattern.

  By the way, when forming a light shielding film on a transparent substrate in order to manufacture a mask blank substrate, a sputtering method is generally used. At that time, the four corners are clamped to support the transparent substrate, but the light-shielding film is not formed in the region supporting the transparent substrate because the holding mechanism for clamping becomes an obstacle. Therefore, at the four corners of the mask blank substrate, the light-shielding film is not formed, and the fused quartz that is a transparent substrate is exposed.

Fused quartz is an excellent insulator and has a volume resistivity of 10 ¹⁶ Ωm or more. Therefore, when patterning is performed using an electron beam, if electrons enter the fused silica portion, the portion is charged. The strength of the electric field at which dielectric breakdown occurs in vacuum varies depending on conditions, but according to the literature (for example, see Non-Patent Document 1), the order is about 50 MV / m, so the charge density is 20 nc / cm. ^When it is about ² , discharge may occur. When discharge occurs, the applied resist or glass is scattered on the light shielding film, and the scattered resist or glass causes a defect in the light shielding film pattern.

The part without the light shielding film has four corners, and the LSI pattern is formed in the part other than the periphery of the substrate. Therefore, it seems that the part without the light shielding film is not irradiated with the electron beam. Since the process mark and the like are formed in the peripheral portion of the substrate, the electron beam may be irradiated to the portion without the light shielding film.
Japanese Patent Laid-Open No. 11-54077 Discharge Handbook (Revised) The Institute of Electrical Engineers of Japan, Part 3, Chapter 4, P220

  Thus, conventionally, there are four portions where no light-shielding film is formed on the surface of the mask blank substrate, and when this portion is irradiated with an electron beam, resist charging or discharge breakdown occurs, and dust is generated. However, there is a problem of causing a defect in the light shielding film pattern.

  Further, the above problem is not limited to the case where a pattern is drawn by an electron beam, but the same can be said when a pattern is drawn by an ion beam.

  The present invention has been made in consideration of the above circumstances, and the object of the present invention is to prevent resist charging and discharge breakdown due to charged beam irradiation, and to improve and manufacture pattern accuracy in an exposure mask. An object of the present invention is to provide a mask blank substrate that can contribute to an improvement in yield and a method for manufacturing the same.

  In order to solve the above problems, the present invention adopts the following configuration.

That is , a mask blank substrate according to an aspect of the present invention is formed on a transparent substrate transparent to exposure light and on one main surface of the transparent substrate except for the four corners of the substrate. A light shielding film made of an opaque conductive material for forming a pattern by a process including charged beam lithography, a mark formed at at least one of four corners on one main surface of the transparent substrate, and the four corners And a transparent conductive film formed so as to cover the surface.

  Moreover, the manufacturing method of the mask blank board | substrate concerning another aspect of this invention is the state which clamped four corners on one main surface of the transparent substrate transparent with respect to exposure light, 4 on the one main surface of this board | substrate. A step of forming a light-shielding film made of a conductive material opaque to exposure light by sputtering or vapor deposition on a portion other than the corner and forming a pattern by a process including charged beam lithography; Using a shutter that shields a portion excluding the four corners on the main surface, with the two of the four corners clamped, the light shielding film or the light shielding film is formed by sputtering or vapor deposition on the two unclamped corners. In the state in which a conductive film made of a different material is formed, and the shutter is used and the clamping position is changed to two other corners, the two non-clamped corners are sputtered or deposited by sputtering. Characterized in that it comprises a and a step of forming a different conductive layer of material is a film or a light shielding film.

  Moreover, the manufacturing method of the mask blank board | substrate concerning another aspect of this invention is the state which clamped four corners on one main surface of the transparent substrate transparent with respect to exposure light, 4 on the one main surface of this board | substrate. A light shielding film for forming a pattern by a process including charged beam lithography is formed on a portion excluding the corner by a sputtering method or a vapor deposition method, and is made of a conductive material opaque to exposure light, and at least the four corners are formed. In a state where two of the four corners are clamped using a step of forming a mark made of the light-shielding film in one and a shutter that shields a portion excluding the four corners on one main surface of the transparent substrate. A step of forming a transparent conductive film by sputtering or vapor deposition at two unclamped corners, and two unclamped corners using the shutter and changing the clamping position to another two corners. A step of forming a sputtering or transparent conductive film by a vapor deposition method, to include the features.

  According to the present invention, since the entire surface including the four corners on one main surface of the transparent substrate is covered with the conductive film, the resist is not charged by the charged beam irradiation for forming the light shielding film pattern. , Discharge breakdown can be prevented in advance. Therefore, the generation of dust can be suppressed, the pattern accuracy of the light shielding film pattern can be improved, and the manufacturing yield can be improved.

  The details of the present invention will be described below with reference to the illustrated embodiments.

(First embodiment)
1A and 1B are diagrams for explaining a schematic configuration of a mask blank substrate according to a first embodiment of the present invention. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along line AA ′ in FIG. FIG.

  In the figure, reference numeral 11 denotes a transparent substrate made of fused quartz, and a light shielding film 12 made of chromium (Cr) is formed on the entire upper surface of the substrate 11. The light shielding film 12 is also formed on the side surface of the substrate 11.

  Here, a 152 mm reticle is considered as a typical configuration. The transparent substrate 11 is processed into a rectangular parallelepiped structure with a pattern forming surface of a square having a piece of 152 mm and a thickness of 6.25 mm. The light shielding film is formed on the pattern forming surface as follows.

  First, a 200-nm-thick metal chromium film (light-shielding film) is formed on one main surface of the transparent substrate by a sputtering apparatus having a normal holding mechanism. At this time, as shown in FIG. 2A, the four corners of the substrate 11 are clamped by the holding mechanisms 21a to 21d. For this reason, as shown in FIG. 2B, the chromium film 12 is not formed at the four corners 11 a to 11 d of the substrate 11. This state is the same as that of a conventional mask blank substrate. Further, the chromium film 12 is also formed on the side surface of the substrate 11 by utilizing the wraparound of sputtering.

  Next, as shown in FIG. 2 (c), of the four corners 11a to 11d, only one of the two pairs of corners at both ends of the diagonal line, here the 11b and 11d are held by the holding mechanism 21b, Clamp with 21d. Then, using the shutter 22 having the same shape as the chromium film forming region on the substrate 11, no film forming material is attached to the corners other than the four corners. In this state, a chromium film is formed by sputtering again. Then, as shown in FIG. 2D, a chromium film 12 is formed on 11a and 11c in the four corners.

  Next, as shown in FIG. 2 (e), only the remaining pair of corners 11a and 11c are clamped by the holding mechanisms 21a and 21c, and a chromium film is formed by sputtering using the shutter 22 as before. To do. Then, as shown in FIG. 2F, the chromium film 12 is also formed at the remaining two corners 11b and 11d. In this way, a conductor film can be formed on the entire pattern formation surface of the mask. Thereafter, if necessary, the shutter 22 is opened, and a chromium oxide film is formed on the surface of the chromium film 12.

  The same sputtering apparatus or different sputtering apparatuses may be used for the formation of the chromium film 12 at the four corners and the formation of the chromium film 12 at the four corners. Further, by forming the chromium film at the four corners, the chromium film 12 is also formed on the side surfaces corresponding to the four corners of the substrate 11.

  As described above, according to this embodiment, the chromium film 12 can be formed on the entire surface including the four corners of the substrate 11 on the pattern forming surface of the transparent substrate 11, and the entire substrate surface is covered with the conductor film. Become. Therefore, when a pattern is drawn by an electron beam using this mask blank substrate, the resist is not charged or discharged, and the pattern accuracy can be improved and the manufacturing yield can be improved.

  In the present embodiment, the chromium film 12 can be formed not only on the upper surface of the transparent substrate 11 but also on the side surfaces by utilizing the wraparound at the time of sputtering. Forming a conductive film on the side surface in this way is effective for preventing charging by electron beam irradiation.

(Second Embodiment)
3A and 3B are diagrams for explaining a schematic configuration of a mask blank substrate according to the second embodiment of the present invention, in which FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along line BB ′ in FIG. FIG. In addition, the same code | symbol is attached | subjected to FIG. 1 and an identical part, and the detailed description is abbreviate | omitted.

  In the present embodiment, mark patterns that can be visually confirmed are formed in part of four corners.

  A chromium film 12 is formed on one main surface of the transparent substrate 11 except for the four corners, and a mark 13 is formed at a part of the four corners. This mark 13 represents the characteristics of the mask, and can be formed by devising a clamp when forming the chromium film, as will be described later. Transparent conductive films 15 made of ITO are formed at the four corners.

  In the present embodiment, as in the previous embodiment, as shown in FIGS. 2A and 2B, sputtering is performed with the four corners of the transparent substrate 11 clamped by a sputtering apparatus having a normal holding mechanism. As a result, a metal chromium film 12 is formed on the substrate 11 to a thickness of 200 nm. As a result, regions where no light shielding film is formed remain at the four corners, and the transparent substrate 11 is exposed at the four corners. At this time, for example, a triangular mark 13 is attached to one of the four corners.

  The mark 13 represents the characteristics (type, exposure condition, etc.) of the mask. For example, as shown in FIG. 4, by providing a triangular notch 23 in a part of the holding mechanism 21, It is formed simultaneously with the formation of the light shielding film on the entire upper surface of the transparent substrate 11. By appropriately combining the number of the marks 13 to be formed or the formation position, marks can be formed according to the characteristics of the mask.

  Next, the substrate is set in a sputtering apparatus different from the above-described sputtering apparatus, and only one pair of corners, which is one of two corners at both ends of the diagonal line, among the four corners on the transparent substrate 11 is formed. Clamp with holding mechanism. Here, the same shutter as in the first embodiment is used so that no film material is attached to the corners other than the four corners. In this state, a conductive film that transmits visible light, for example, an ITO film 15 is formed by sputtering. This ITO film 15 is partially overlapped with the previously formed chromium film.

  Next, the transparent substrate 11 is supported by the remaining pair of corners, and the ITO film 15 is formed on the pair of corners that have been previously supported. In this manner, a conductor film can be formed over the entire pattern formation surface of the mask. In the above example, another sputtering apparatus is used for forming the chromium film and the ITO film, but the target may be changed using the same sputtering apparatus.

Here, it is considered that the four corners are isosceles triangles each having a side of 5 mm. The beam current of the electron beam lithography apparatus used for forming the mask pattern is at most 3 μA. If the potential difference when a current of 3 μA flows through a region having a width average of 2.5 mm and a length of 5 mm is about 10 kV at 5 mm, the allowable resistance value is about 3 GΩ. When the safety factor is 10 times, the allowable resistance value is 300 MΩ. Since the thickness of the film is usually about 0.1 μm, the volume resistivity of the film needs to be 6 × 10 ⁻² Ωm or less. Since the ITO film has a sufficiently lower resistivity, it can be sufficiently used as a conductive film covering the four corners.

  As described above, according to the present embodiment, the chromium film 12 can be formed on the pattern forming surface of the transparent substrate 11 except for the four corners of the substrate 11, and the ITO film 15 can be formed at the four corners. It will be in the state covered with the conductor film. Therefore, the same effect as in the first embodiment can be obtained.

(Modification)
The present invention is not limited to the above-described embodiments. In the embodiment, the pattern is drawn on the light-shielding film by electron beam drawing, but the present invention can also be applied to drawing by an ion beam. In addition, the transparent substrate is not necessarily limited to fused quartz, and may be any material that is transparent or sufficiently high in transmittance with respect to exposure light. Furthermore, the light-shielding film is not limited to chromium, but may be any material that shields exposure light and is conductive.

  Further, the method for forming the light shielding film or the conductive film is not necessarily limited to the sputtering method, and an evaporation method may be used. In addition, various modifications can be made without departing from the scope of the present invention.

The top view and sectional drawing which show schematic structure of the mask blanks board | substrate concerning 1st Embodiment. The top view which shows the manufacturing process of the mask blank of 1st Embodiment. The top view and sectional drawing which show schematic structure of the mask blanks board | substrate concerning 2nd Embodiment. The top view which shows the shape of the holding mechanism used for 2nd Embodiment.

Explanation of symbols

11 ... Fused quartz substrate (transparent substrate)
11a to 11d ... corner 12 ... chromium film (light-shielding film)
DESCRIPTION OF SYMBOLS 13 ... Mark 15 ... Transparent electrically conductive film 21 ... (21a-21d) ... Holding mechanism 22 ... Shutter 23 ... Notch

Claims (5)

A transparent substrate transparent to the exposure light;
A light-shielding film that is formed on one main surface of the transparent substrate except for the four corners of the substrate, is made of a conductive material that is opaque to exposure light, and forms a pattern by a process including charged beam lithography;
Marks formed in at least one of the four corners on one main surface of the transparent substrate;
A transparent conductive film formed to cover the four corners;
The mask blank board | substrate characterized by comprising. The mark is made of the same material as the light shielding film, the mask blanks substrate according to claim 1, characterized in that formed at the same time as the light-shielding film. With the four corners on one principal surface of the transparent substrate transparent to the exposure light clamped, the portion other than the four corners on the one principal surface of the substrate is opaque to the exposure light by sputtering or vapor deposition. A step of forming a light shielding film made of a conductive material and forming a pattern by a process including charged beam lithography,
The light-shielding film is formed by sputtering or vapor deposition at two unclamped corners in a state where two of the four corners are clamped using a shutter that shields a portion excluding the four corners on one main surface of the transparent substrate. Or forming a conductive film made of a material different from that of the light shielding film;
Using the shutter, the light-shielding film or a conductive film made of a material different from the light-shielding film is formed by sputtering or vapor deposition in two unclamped corners with the clamping position changed to two other corners. Process,
The manufacturing method of the mask blank board | substrate characterized by including. With the four corners on one principal surface of the transparent substrate transparent to the exposure light clamped, the portion other than the four corners on the one principal surface of the substrate is opaque to the exposure light by sputtering or vapor deposition. Forming a light shielding film made of a conductive material and forming a pattern by a process including charged beam lithography, and forming a mark made of the light shielding film in at least one of the four corners;
A transparent conductive film is formed by sputtering or vapor deposition at two unclamped corners in a state where two of the four corners are clamped using a shutter that shields a portion excluding the four corners on one main surface of the transparent substrate. Forming a film;
Using the shutter, with the clamping position changed to another two corners, forming a transparent conductive film by sputtering or vapor deposition at the two unclamped corners;
The manufacturing method of the mask blank board | substrate characterized by including. When clamping the four corners on one main surface of the transparent substrate, holding mechanisms partially contacting each corner were used, and at least one of these holding mechanisms was provided with a notch corresponding to the mark. The method for producing a mask blank substrate according to claim 4 .

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