JP2019008254A - Substrate for photomask and manufacturing method therefor - Google Patents

Abstract

To prevent defects on a substrate end surface side from being generated without point contact of a mounding surface and a substrate end surface in a device when the substrate end part is held by a handling jig, transferred and mounted in a device.SOLUTION: There is provided a substrate 1 for photomask having at least a main surface and an end surface 2, in which the end surface has a cross section in a substrate thickness direction with a convex, an apex of the convex is positioned on an upper side of a substrate thickness direction in one end side of a substrate width direction, and on a lower side of the substrate thickness direction at another end side of the substrate width direction.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a photomask substrate and a method for manufacturing the same, and more particularly to a photomask substrate and a method for manufacturing the same that prevent damage to the substrate end surface during a handling operation by devising the shape of the substrate end surface.

Synthetic silica glass is used as a photomask substrate for IC and LCD photolithography because of its low thermal expansion and excellent light transmission.
Aiming at high integration of semiconductor integrated circuits, a shorter wavelength tends to be adopted year by year in the photolithography technology, and for example, an ArF excimer laser (wavelength 193 nm) is used as a light source (ArF-Dry).

In the photolithography using this light source, the resolution is increased by the ArF immersion technology (ArF-Wet) in which a liquid is immersed between the lens and the wafer (55 nm in trial calculation). As a technology to replace the node width of 50 nm of the F ₂ excimer laser (wavelength of 157 nm), which is used as the light source.
In this ArF-Wet, the photomask is required to have a property of low birefringence that suppresses disturbance of the polarization property of the light passing therethrough.

  As a method for producing a synthetic silica glass substrate for a photomask, an annealing process is generally performed in which a block of a synthetic silica glass is held for a certain period of time at a temperature above the annealing point and then gradually lowered to a temperature below the strain point. A method of performing slicing, chamfering, and polishing after applying and reducing thermal residual stress is known.

In the polishing process, the main surface of the substrate is flattened (mirror finished), and after cleaning, a reflective film is deposited on the surface.
On the other hand, in order to suppress the occurrence of defects such as pinholes caused by the irregularities generated by cutting and abrasive particles captured by fine fissures as disclosed in Patent Document 1 on the substrate end face, Mirror polishing is performed on the end face.

JP 2008-257132 A

  By polishing the substrate end surface as described above, it is possible to suppress the occurrence of defects due to dust generation from the substrate end surface. On the other hand, when the substrate end surface is mirror-finished, the end surface is smoothed, but is not necessarily flat. Depending on the degree of flatness at the substrate end face, the quality of the photomask substrate may be greatly affected.

In the case where the substrate end face has a convex portion with a mountain, for example, when the substrate is moved by a handling device (not shown) and placed on an automatic transfer device as shown in FIGS. 6 (a) and 6 (b) There has been a problem that defects such as cracks are likely to occur on the bottom end face of the substrate.
FIG. 6A is a plan view of an automatic transfer apparatus that can hold a plurality of substrates 60 in an upright state. FIG. 6B is a front view of the automatic transfer device of FIG.
The automatic transfer device 50 shown in the figure has a pair of support plates 52 and 53 erected on both left and right ends of a plate-like substrate transfer table 51. As shown in FIG. 6 (b), a plurality of sets of support grooves 52a, 53a extending in the vertical direction are formed in parallel on the inner side surfaces of the opposing support plates 52, 53 as shown in FIG. 6 (a). ing. The support grooves 52a and 53a are formed wider than the substrate thickness so that the left and right end portions of the substrate 60 can be loosely held.

  When the automatic transfer device 50 holds the substrate 60, the left and right ends of the substrate 60 are inserted into the support grooves 52a and 53a of the support plates 52 and 53 from above as shown in FIG. The substrate 60 is held when the bottom end surface of the substrate 60 lands on the substrate transfer table 51.

  Here, when the bottom end surface of the substrate 60 has a convex portion, the convex portion hits the substrate transport table 51 (becomes a point contact state), and the contact portion is likely to be defective. When such a defect occurs, the risk of dust generation, chipping and cracking from the defective portion increases. In particular, a photomask substrate made of a large and thin brittle material has a problem of seriously affecting its quality.

  The present invention has been made to solve the above-described problems, and in a glass substrate for a photomask, when the substrate edge is gripped and transferred by a handling jig and placed in the apparatus, It is an object of the present invention to provide a high-quality photomask substrate and a method of manufacturing the same that can prevent the occurrence of defects on the substrate end surface side without causing point contact between the mounting surface and the substrate end surface.

  The photomask substrate according to the present invention made to achieve the above object is a photomask substrate having at least a main surface and an end surface, and the end surface has a convex cross section in the substrate thickness direction. The convex vertex is located on the upper side in the substrate thickness direction on one end side in the substrate width direction and on the lower side in the substrate thickness direction on the other end side in the substrate width direction. The flatness of the end face is preferably 1 μm or more and 3 μm or less. The photomask substrate is preferably formed of silica glass.

  As described above, in the photomask substrate according to the present invention, the polishing process is performed on the substrate end surface after the cutting process, and the width from one end to the other end of the substrate end surface is not flat in the thickness direction but twisted. State. As a result, when the substrate end is gripped and transferred by the handling jig and placed in the apparatus, the placement surface does not make point contact with the substrate end surface, and stress concentration on the substrate end surface is suppressed. Damage can be prevented, and a high-quality photomask substrate can be obtained.

  In addition, in order to solve the above-described problems, a method for manufacturing a photomask substrate according to the present invention includes pressing an end surface of a silica glass substrate cut into a predetermined plate shape against a polishing pad rotating in one direction. In the step of polishing the end surface of the silica glass substrate, the polishing pad is in contact with the polishing pad in order from the upper side to the lower side in the substrate thickness direction, and the polishing pad is connected to the other end side. It is characterized in that control is performed so as to make contact in order from the lower side to the upper side in the substrate thickness direction. According to such a manufacturing method, the above-described photomask substrate according to the present invention can be obtained, and the effects can be obtained.

  According to the present invention, in a glass substrate for a photomask, when a substrate end is gripped and transferred by a handling jig and placed in the apparatus, the placement surface in the apparatus and the substrate end face make point contact. Therefore, it is possible to provide a high-quality photomask substrate capable of preventing the occurrence of defects on the substrate end face side and a manufacturing method thereof.

FIG. 1 is a perspective view schematically showing one end of a photomask substrate of the present invention. 2A is an enlarged view of the cross section of the central portion of the substrate end face of FIG. 1, and FIG. 2B is an enlarged view of the cross section of the left and right end sides of the substrate end face of FIG. (C) is the figure which expanded the cross section of the right-and-left other end side of the board | substrate end surface of FIG. FIG. 3 is a flow showing the flow of the method for manufacturing a photomask substrate of the present invention. FIG. 4 is a schematic diagram showing the configuration of a polishing apparatus used when manufacturing the photomask substrate of the present invention. FIG. 5 is a front view of a polishing pad used in the polishing apparatus of FIG. FIG. 6A is a plan view schematically showing the substrate transfer apparatus, and FIG. 6B is a front view thereof.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, an embodiment of a photomask substrate and a manufacturing method thereof according to the invention will be described with reference to the drawings.
FIG. 1 is a perspective view schematically showing one end of a photomask substrate of the present invention. 2A is an enlarged view of the cross section of the central portion of the substrate end face of FIG. 1, and FIG. 2B is an enlarged view of the cross section of the left and right end sides of the substrate end face of FIG. (C) is the figure which expanded the cross section of the right-and-left other end side of the board | substrate end surface of FIG.

  The photomask substrate 1 of the present invention is used, for example, as a photomask substrate for an IC or a photomask substrate for an LCD, and the size varies depending on the application. For example, in the case of an IC photomask substrate, it is formed of synthetic silica glass having a side length L of, for example, 152 mm and a thickness D of, for example, 6.3 mm. In the case of an LCD photomask substrate, the length L of one side is 850 mm (for example, the length L of the other orthogonal side is 1200 mm) and the thickness D is 10 mm, for example.

  In the substrate end face 2 shown in FIG. 1, the center in the width L direction is indicated by Lm, and the center in the thickness D direction is indicated by Dm. Further, left and right ends (left side in FIG. 1) in the width L direction are indicated by L1, and the other end (right side in FIG. 1) is indicated by L2. Further, as shown in FIG. 2 (a), at the center Lm in the width L direction on the one end surface 2 of the substrate, a convex shape having a gentle slope in the vertical direction about the thickness direction center Dm (position 2a). Is formed. The height difference of the inclination is, for example, 3 μm (flatness of 3 μm or less).

  Further, as shown in FIG. 2B, at the left and right ends L1 in the width L direction at one end of the substrate, the convex vertex is located at a position 2b above the center Dm in the substrate thickness D direction (most) The bulge is large). The height difference of the inclination is, for example, 3 μm (flatness of 3 μm or less).

  Further, as shown in FIG. 2C, in the left and right other ends L2 in the width L direction on the substrate one end surface 2, the convex vertex is located at a position 2c below the center Dm in the substrate D thickness direction. It is in a state (the largest bulge). The height difference of the inclination is, for example, 3 μm (flatness of 3 μm or less).

Thus, from one end L1 to the other end L2 in the substrate width L direction, the end face shape is gradually changed so that the position of the convex vertex in the thickness direction is the opposite position. In other words, the one end surface 2 of the substrate is not flat but formed to be twisted.
Although not shown, the other three substrate end faces 2 are similarly formed in a twisted state.

  Thus, when the substrate end surface 2 is formed in a twisted state along the width L direction, when the photomask substrate 1 is erected, the substrate end surface 2 is placed on the substrate placement surface of various apparatuses. Point contact at a specific location is avoided between the mounting surface and the lower end surface 2 of the substrate 1, and damage to the substrate end surface 2 due to local load can be prevented.

  Conventionally, as shown in FIG. 2A, the convex portion indicated by reference numeral 2a on the substrate end face 2 is formed on a substantially straight line in the width L direction. Therefore, the highest portion (convex portion) on this straight line is always in contact with the substrate mounting surface on the apparatus side every time the photomask substrate 1 is put into an automatic transfer device or the like. For this reason, there is a problem that the contact portion of the substrate 1 is damaged after being inserted and removed several times.

  On the other hand, in the present invention, the twisted state along the width L direction, in other words, the three convex portions (2a, 2b, 2c in FIG. 2) are straight lines substantially parallel to the long sides of the photomask substrate 1. They do not exist on the line, but are distributed within one plane of the substrate end surface 2. That is, it can be said that the three convex portions are located on one twisted curve.

  For this reason, every time the photomask substrate 1 is put into an automatic transfer apparatus or the like, the opportunity to come into contact with the substrate mounting surface on the apparatus side by the three different convex portions increases, and only a specific convex portion hits continuously. The risk of breakage of the specific convex portion is greatly reduced.

  Then, the manufacturing method of the photomask substrate which has the above end faces is demonstrated along the flow of FIG. First, synthetic silica glass as a substrate material is ground or lapped to obtain a predetermined plate shape (for example, 152 mm square, thickness 6.6 mm) (step S1 in FIG. 3).

  Next, the substrate side surface is polished. Here, the configuration of the apparatus for polishing the substrate end surface will be described. FIG. 4 is a side view schematically showing the configuration of the apparatus for polishing the substrate end surface, and FIG. 5 is a front view of the polishing pad showing the position of the polishing pad that presses against the substrate end surface. As shown in FIG. 5, the polishing pad 5 (for example, suede) is, for example, a circle having a diameter of 350 mm, and is disposed on a disk-shaped surface plate 6 that can be rotated by a rotating shaft 4 extending in the horizontal direction. The silica glass substrate 1 can be moved in the XY directions by the substrate transfer robot 3, that is, can move up and down and move forward and backward with respect to the polishing pad 5.

  In this configuration, for example, the substrate transport robot 3 moves the silica glass substrate 1 with respect to the polishing pad 5 that rotates at a constant speed (500 rpm) in the direction of the arrow in FIG. As a result, the substrate end surface 2 is pressed against a predetermined position of the polishing pad 5, and the substrate end surface 2 is polished (step S2 in FIG. 3). The position of the polishing pad 5 that presses against the substrate end surface 2 is controlled so that the center Lm in the width L direction of the substrate end surface 2 is positioned on the vertical axis VL passing through the center of the disc-shaped polishing pad 5 as shown in FIG. The For example, the substrate end surface 2 is pressed at the position of the pressing position T indicated by a broken line in FIG. 5 for 60 seconds, for example. As polishing abrasive grains, a slurry of cerium oxide (average particle diameter of 1 μm) can be used as in the polishing of the upper and lower surfaces of the substrate.

  By this polishing process, a substrate end face having a shape as shown in FIGS. 2A to 2C can be obtained. That is, at the position L1 of the substrate end surface, the polishing pad 5 rotating in one vertical direction comes in contact with the upper side sequentially from the lower side, and the amount of polishing at the lower part of the end surface 2 with a high speed at the time of contact increases.

On the other hand, at the position L2 on the opposite side, the polishing pad 5 rotating in one vertical direction comes in contact with the lower side in order from the upper side, and the polishing amount on the upper end face 2 where the speed at the time of contact is high increases. Further, since the polishing pad 5 is in contact with the polishing pad 5 in either the left or right direction (in the example of FIG. 5, from the right to the left toward the substrate end surface 2) in the vicinity of the center Lm of the end surface, the difference in polishing amount in the thickness direction. Will be small. The polishing amount of the substrate end face in this polishing step is desirably controlled so that the flatness of the entire end face becomes 1 μm or more and 3 μm or less depending on the pressing force and time.
A similar polishing process is performed on the other three end surfaces 2 of the substrate.

  Next, while supplying a slurry of cerium oxide (average particle size 1 μm) as polishing abrasive grains to a polishing pad (for example, suede) affixed to an upper and lower surface plate (not shown), it is pressed against the upper and lower surfaces of the substrate that rotate relatively The upper and lower surfaces of the substrate are polished to a flat and mirror surface (step S3 in FIG. 3).

  After the polishing process is completed, for example, the entire substrate is immersed in a storage tank of a KOH-containing detergent (silica glass soluble detergent) to perform scrub cleaning (step S4 in FIG. 3). Further, the entire substrate is immersed in a storage tank of dilute HF (0.1%) and rinsed to manufacture a photomask substrate (step S5 in FIG. 3).

  As described above, according to the embodiment of the present invention, the substrate end surface 2 is polished after the cutting process, and the width L direction from the one end L1 to the other end L2 of the substrate end surface 2 is flat in the thickness D direction. Rather than being in a twisted state. As a result, when the photomask substrate 1 is placed upright and placed on the substrate placement surface of various apparatuses, the bottom end surface 2 of the substrate 1 is in contact with the substrate placement surface on the apparatus side only at a specific point. Therefore, the stress concentration on the substrate end face 2 is suppressed to prevent breakage, and a high-quality photomask substrate can be manufactured.

  In the above embodiment, cerium oxide is shown as an example of the substrate polishing agent used in the method for manufacturing a photomask substrate, but the present invention is not limited to this, and colloidal silica, zirconium oxide, Aluminum oxide or a mixture thereof may be used. Further, although the suede pad is used as the polishing pad used in the polishing process, it is not limited to this, and either urethane foam or nonwoven fabric may be used.

The photomask substrate and manufacturing method according to the present invention will be further described based on examples.
<Example 1>
In Example 1, the end face of a plate-shaped material having a 152 mm square LSI photomask substrate and a thickness of 6.6 mm was processed. Specifically, the substrate end surface was cut and the substrate end surface was pressed while supplying a cerium oxide slurry to a flat polishing pad having a diameter of 350 mm to polish the substrate end surface.

With respect to one end surface, the polishing pad was rotated in one direction, and polishing was performed for 60 seconds without turning the substrate upside down (the position where the substrate end surface was applied to the polishing pad was in accordance with FIG. 5). As a result, the upper end in the substrate thickness direction was polished much at one end in the width direction on the substrate end surface, and the lower portion in the substrate thickness direction was polished much at the other end. The flatness was 1 μm or more and 3 μm or less.
The substrate was loaded into the automatic transfer device 200 times by handling the holding jig by the operator. As a result, generation of defects was recognized on the substrate end face only once (0.5%).

<Comparative Example 1>
In Comparative Example 1, the end face of a plate-shaped material having a 152 mm square LSI photomask substrate and a thickness of 6.6 mm was processed. Specifically, the substrate end surface was cut and the substrate end surface was pressed while supplying a cerium oxide slurry to a flat polishing pad having a diameter of 350 mm to polish the substrate end surface.

A total of four polishing processes were carried out for a total of 15 seconds with a combination of two rotation directions of the polishing pad and upside down of the substrate with respect to one end surface (the position where the substrate end surface is applied to the polishing pad is shown in FIG. 5). Follow). As a result, a flat surface with a flatness of 1 μm or more and 3 μm or less was obtained in the thickness direction on the substrate end face.
The substrate was loaded into the automatic transfer device 200 times by handling the holding jig by the operator. As a result, generation of defects was observed on the substrate end face three times (1.5%).

  As a result of the above examples, the effects of the present invention could be confirmed.

DESCRIPTION OF SYMBOLS 1 Photomask substrate 2 Substrate end surface 3 Substrate transfer robot 4 Rotating shaft 5 Polishing pad 6 Surface plate

Claims (4)

A photomask substrate having at least a main surface and an end surface,
The end face has a convex cross section in the substrate thickness direction,
The convex mask apex is located on the upper side in the substrate thickness direction on one end side in the substrate width direction, and is located on the lower side in the substrate thickness direction on the other end side in the substrate width direction.   2. The photomask substrate according to claim 1, wherein the flatness of the end face is not less than 1 μm and not more than 3 μm.   3. The photomask substrate according to claim 1, wherein the photomask substrate is made of silica glass. A method of manufacturing a photomask substrate,
Including pressing the end surface of the silica glass substrate cut into a predetermined plate shape against a polishing pad rotating in one direction for polishing,
In the step of polishing the end surface of the silica glass substrate, the polishing pad contacts in order from the upper side to the lower side in the substrate thickness direction on one end side in the substrate width direction, and the polishing pad on the lower side in the substrate thickness direction on the other end side. A method for manufacturing a photomask substrate, wherein the substrate is controlled so as to contact in order from the top to the bottom.

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