US20070116913A1

US20070116913A1 - Glass substrate and a manufacturing method thereof

Info

Publication number: US20070116913A1
Application number: US11/598,803
Authority: US
Inventors: Yukiyasu Kimura; Yuhei Nitta
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 2005-11-17
Filing date: 2006-11-14
Publication date: 2007-05-24
Also published as: KR101345439B1; US8245538B2; CN1966436A; US20090305020A1; JP4752725B2; KR20070052681A; TW200720204A; JP2007161568A; CN1966436B; TWI406824B

Abstract

A method for manufacturing a glass substrate by fusion process comprising the following steps; flowing fused glass into a fusion pipe, and gradually cooling and solidifying the fused glass by flowing downward from the fusion pipe, wherein forming an asperity on a surface of the glass substrate by fastening and pressing the glass toward a direction of thickness of the glass with a pair of transfer rollers during the glass is flowing down from the fusion pipe.

Description

BACKGROUND

The present invention relates to a glass substrate, which is applied to the flat panel display (citing FPD hereinafter) such as the liquid crystal device panel and to a manufacturing method thereof. The present invention is particularly useful for a glass substrate using for a large size FPD for example televisions, computer displays and the like.
In a few years, FPD represented by a liquid crystal type and a plasma type, spreads rapidly. An emission type display was also released recently, and a development is further activated.
For manufacturing these types of FPD, it is necessary to precisely form minute patterns on a tabular glass plate. For example, the explanation will be provided below in accordance with a TFT type liquid crystal device. The TFT type liquid crystal device is made by forming and arranging plurality of thin film transistors on a glass substrate in precisely to match each TFT on each pixel. For arranging TFT precisely a photolithography technology is used.
Namely, a metal layer is formed on a first glass substrate, and then photoresist is coated on the metal layer. Next, after TFT patterns for plurality of panels are exposed and developed, etching is performed. As the result, the metal layer is remained in a shape of TFT patterns on the first glass substrate. In this specification, it is described that thing in this state as TFT substrate.
On a second glass substrate, a shading material layer is formed and further photoresist is coated on the shading material layer. Next, plurality of color filter (citing CF hereinafter) patterns, which will correspond to TFT patterns, are exposed and then etched. As the result, the shading material layer is remained in a shape of CF patterns on the second glass substrate. Next, by using photolithography technology, which is the same as that used for forming the TFT patterns, CF is formed in accordance with the patterns of the shading material layer. A red filter, a green filter, and a blue filter are formed by repeating CF forming process three times. In this specification, it is described that thing in this state as CF substrate.
After an alignment layer is coated on each of the TFT substrate and CF substrate, both substrates are adhered together through glass beads as spacers in a state that the alignment layer of each substrate becomes inner side, and further, out of pattern areas are adhered by sealant.
Next, after cutting out each panel, material of liquid crystal is injected to a space between the TFT substrate and the CF substrate through a hole previously provided for supplying the material of liquid crystal, and the hole is sealed. Finally, a polarizer is adhered on a screen, and then TFT type liquid crystal panel is completed.
Each pixel of TFT pattern should be aligned with each area of correspondent CF pattern. It is because; if both patterns misaligned in each other, a precise image cannot be processed. Therefore both of the TFT pattern and the CF pattern should be formed in high dimensional precision.
As an index for estimating whether the TFT pattern or the CF pattern is formed in predetermined dimensional precision, plurality of measurement patters are provided out of the TFT pattern or the CF pattern. After exposing the TFT pattern or the CF pattern and then developing, distances between these measurement patterns are measured and difference from design values are obtained, and then preciseness is estimated.
In the meantime, majority of glass substrates using for FPD are manufactured by a process what is called fusion process. The fusion process is the method for manufacturing a plate like glass in which; flowing fused glass into a container called fusion pipe, overflowing the fused glass from the fusion pipe, and solidifying the fused glass during flowing downward. The fusion process can manufacture glass substrates in a low cost because a polishing process is not needed.
A method for manufacturing a glass substrate by fusion process will be explained below. FIG. 8 shows a fusion pipe which is used for manufacturing a glass substrate by fusion process. As it is shown in To enlarge FPD and to increase efficiency of manufacturing FPD, a size of a glass substrate for FPD is expanding year by year. As far as a substrate for liquid crystal is concerned, a size of the substrate called as seventh generation, which is already practically used, is very large as 1870 mm×2200 mm, and still larger size substrate is proposed.
FIG. 8(a), a fusion pipe 4 has a structure that its upper part is a trough like portion 41 which is open to upper direction, and that both sides of the trough like portion 41 are bank like portions 42 whose levels are higher than the that of the trough like portion 41. A lower part of the fusion pipe 4 has a wedge like shape, and its bottom is a blade like portion 43. Heaters (not showing) are built in the fusion pipe 4 and surfaces of the fusion pipe 4 can hold a temperature at which maintaining a glass-fusing state. A cross sectional view of the fusion pipe 4 in A—A direction is shown in FIG. 8(b).
FIG. 9 shows a process for manufacturing a glass substrate by fusion process. A fused glass G is flown successively into the trough like portion 41 of the fusion pipe 4, which is maintained in high temperature. The fused glass G overflows from bank like portions 42 to both sides of the fusion pipe, further flowing down along side surfaces of the fusion pipe 4, and reaches to the blade like portion 43, which is bottom of the fusion pipe 4. At the blade like portion 43, flows of fused glass joins together and it turns a plate like glass GP, and the plate like glass GP is gradually cooled as it falls down. In this process, the plate like glass GP is gradually solidified, and further it is pulled down by a rotation of rollers 45. Afterwards, by cutting in desired dimension a glass substrate is completed.
Additionally, in accordance with manufacturing processes by fusion process are described in following documents.
(Patent document 1) Specification of the U.S. Pat. No. 3,338,696
(Patent document 2) Specification of the U.S. Pat. No. 3,682,609
To enlarge FPD and to increase efficiency of manufacturing FPD, a size of a glass substrate for FPD is expanding year by year. As far as a substrate for liquid crystal is concerned, a size of the substrate called as seventh generation, which is already practically used, is very large as 1870 mm×2200 mm, and still larger size substrate is proposed.
However, in case forming patterns on a large size glass substrate, there is a problem that the dimension of actually formed pattern occasionally has an error beyond allowable range in comparison with design value.
As far as this problem is concerned, as optical systems of an exposure apparatus, which is used for exposing patterns, is adjusted in high precision level, it is confirmed that patterns to be exposed have substantially no distortion. Namely, it does not due to a precision level of optical systems. Moreover, a stage of the exposure apparatus is finished as a very high precision flat surface, and it is confirmed that the surface of the vacuum contacted glass substrate on the stage is in the focus depth of the exposure optical system installed in the exposure apparatus. Therefore, it also does not due to a problem of flatness level of the stage. Accordingly, it can be considered that distances between measurement patterns exposed on the glass substrate are in allowable ranges at least in the state that the substrate is vacuum contacted on the stage of the exposure apparatus.
However, in spite of above confirmations, still there is a problem that the distances between measurement patterns which measured after exposing and developing are occasionally not in the allowable ranges.
Moreover, as another problem; there is a phenomenon that a static electricity is generated when the glass substrate being coated photoresist and being exposed the TFT patterns or CF patterns is unloaded from the stage; and by discharging the static electricity to a surface of photoresist, a defect of the TFT pattern or the CF pattern occurs.
The inventors of the present invention found out that there is an effect for these problems by decreasing contact area between a vacuum contact portion of the stage and the glass substrate. For decreasing the contact area between a vacuum contact portion of the stage and the glass substrate, the present inventors considered to form appropriate asperity on at least one of surfaces of the vacuum contact portion of the stage and the glass substrate. The present inventors formed minute asperity on the surface of the vacuum contact portion of the stage by a grinding process. Then it appears that in spite of an effect for preventing the static electricity is achieved in a short period after the grinding process, the effect decrease as time passes, and it also appears that the effect increases again by applying the grinding process again on the surface of the vacuum contact portion of the stage. This is the reason why the asperity on the surface of the vacuum contact portion shrinks during successively holding the glass substrates by attrition with the glass substrate, and as the result the effect for preventing the static electricity decreases.
Although it can be considered to form an asperity by applying a machining the glass substrate which is once manufactured, such process increase a cost for manufacturing the glass substrate. Therefore, for decreasing the cost, it is expected to establish a method for manufacturing the glass substrate in which an appropriate asperity is formed in process of making the substrate.
The present invention was made under these circumstances explained above, and objects of the present invention are to provide a glass substrate which enables to manufacture a FPD in keeping cost low and in efficient, and to provide an efficient manufacturing method of a glass substrate.

SUMMARY

To solve the above described subject matter, the present invention adopts a below described structures shown in embodiments which correspond to figures. However, each reference sign with parentheses, which indicates each element, is only an exemplification and it does not limit each element.
A first aspect of the present invention provides a glass substrate whose surface has an asperity of a height in the range from 10 nm to 20 nm and of a period in the range from 0.1 mm to 1 mm.
According to the glass substrate of the first aspect, it is possible to satisfy stabilization of contact and preventing generation of the static electricity simultaneously.
A second aspect of the present invention provides a glass substrate whose surface has an asperity of a height in the range from 15 nm to 20 nm and of a period in the range from 0.1 mm to 0.6 mm.
According to the glass substrate of the second aspect, it is possible to satisfy stabilization of contact and preventing generation of the static electricity simultaneously.
A third aspect of the present invention provides a method for manufacturing a glass substrate by fusion process, the method comprising the steps of; flowing fused glass (G) into a fusion pipe (1), and gradually cooling and solidifying the fused glass (G) by flowing downward from the fusion pipe (1), wherein forming an asperity on a surface of the glass substrate by depositing particles (GB) on a surface of the fused glass (G).
According to the method for manufacturing the glass substrate of the third aspect, it is possible to manufacture the glass substrate, which satisfies stabilization of contact and preventing generation of the static electricity simultaneously.
A fourth aspect of the present invention provides a method for manufacturing a glass substrate by fusion process, the method comprising the steps of; flowing fused glass (G) into a fusion pipe (1), and gradually cooling and solidifying the fused glass (G) by flowing downward from the fusion pipe (1), wherein forming an asperity on a surface of the glass substrate by colliding particles against the glass flowing down from the fusion pipe (1) from a side direction.
According to the method for manufacturing the glass substrate of the fourth aspect, it is possible to manufacture the glass substrate, which satisfies stabilization of contact and preventing generation of the static electricity simultaneously.
A fifth aspect of the present invention provides a method for manufacturing a glass substrate by fusion process having the following steps; flowing fused glass (G) into a fusion pipe (1), and gradually cooling and solidifying the fused glass (G) by flowing downward from the fusion pipe (1), wherein forming asperity on a surface of the glass substrate by fastening and pressing the glass (GP) toward a direction of thickness of the glass with a pair of transfer rollers (16A and 16B) during the glass is flowing down from the fusion pipe.
According to the method for manufacturing the glass substrate of the fifth aspect, it is possible to manufacture the glass structure, which satisfies stabilization of contact and preventing generation of the static electricity simultaneously.
A sixth aspect of the present invention provides a method for manufacturing a glass substrate by fusion process, the method comprising the steps of, flowing fused glass (G) into a fusion pipe (3), overflowing the fused glass (G) toward two directions of the fusion pipe (3) and flowing the fused glass (G) along two side surfaces (36 and 37) of the fusion pipe (3), joining the fused glass at a blade portion (33) which is a bottom end of the fusion pipe (3), and gradually cooling and solidifying the fused glass (G) by flowing downward from the blade portion (33), wherein forming an asperity on a surface of the glass substrate by periodically changing a temperature difference between the two side surfaces (36 and 37) of the fusion pipe (3).
According to the method for manufacturing the glass substrate of the sixth aspect, it is possible to manufacture the glass structure, which satisfies stabilization of contact and preventing generation of the static electricity simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual figure showing a glass substrate manufacturing by fusion process according to the first embodiment of the present invention.
FIG. 2 is a conceptual figure showing a glass substrate manufacturing by fusion process according to the first embodiment of the present invention.
FIG. 3 is a conceptual figure showing a glass substrate manufacturing by fusion process according to the second embodiment of the present invention.
FIG. 4 is a conceptual figure showing a glass substrate manufacturing by fusion process according to the third embodiment of the present invention.
FIG. 5 is a conceptual figure showing transfer rollers, which is used for a glass substrate manufacturing, by fusion process according to the third embodiment of the present invention.
FIG. 6 is a conceptual figure showing a glass substrate manufacturing by fusion process according to the fourth embodiment of the present invention.
FIG. 7 is a conceptual figure showing a fusion pipe, which is used for a glass substrate manufacturing, by fusion process according to the fourth embodiment of the present invention.
FIG. 8 is a conceptual figure showing a fusion pipe, which is used for a glass substrate manufacturing, by fusion process according to a prior art.
FIG. 9 is a conceptual figure showing a glass substrate manufacturing by fusion process according to a prior art.

DETAILED DESCRIPTION OF EMBODIMENTS

Now, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited by the embodiments.

Embodiment 1

FIG. 1 is a conceptual figure showing a manufacturing method according to the first embodiment. In FIG. 1, 1 shows a fusion pipe. Upper part of the fusion pipe 1 is made as a trough like portion 11, which is open to the air, and a bank like portions 12 are arranged on both sides of the trough like portion 11. Moreover, bottom part of the fusion pipe 1 is made as a blade like portion 13. Moreover, heaters (not shown) are installed inside the fusion pipe 1, and surfaces of the fusion pipe 1 can be kept in temperature for maintaining a glass fusing state by heating fusion pipe 1 with the heaters.
Fused non-alkaline glass G is flown into the trough like portion 11 of the fusion pipe 1. Wherein, non-alkaline glass means a glass, which does not content alkaline metal as Sodium (Na), Potassium (K), and so forth. Fused non-alkaline glass G fills the trough like portion 11.
Nozzle 14 is arranged above the fusion pipe 1, and glass particles GB comprise the same glass material as the fused glass G are discharged from the tip of the nozzle. The glass particles GB fall down on a surface of the fused glass G and adhere to the surface of the fused glass G. With maintaining this state, the fused glass G overflows the bank like portion 12 and flow down along side surface of the fusion pipe 1.
The fused glass G reached to the blade like portion 13, which is at a bottom of the fusion pipe 1, descents with solidifying as being plate like glass GP, and further the plate like glass GP is pulled down by revolution of rollers 15. Afterwards, the plate like glass GP is cut in desired size and a glass substrate is completed.
As the glass particles GB are adhered on the surface of the glass substrate manufactured in above described method, each glass particle is in the state that it protrudes from the surface of the glass substrate. Namely, an asperity according to the protrusion is formed on the surface of the glass substrate.
When forming TFT patterns or CF patterns on such glass substrate, a process control is conducted so as to vacuum contact a side on which asperity is formed. By this procedure, a condition for stabilization of contact and preventing generation of the static electricity are satisfied simultaneously, and defect prevention is stably accomplished. Moreover, as light is scattered in moderate by the asperity on the surface of the glass substrate, there is also an effect for anti reflection.
In the present embodiment, it is desirable that diameters of the glass particles are in the range from 15 nm to 40 nm. Moreover, it is only necessary to appropriately determine quantity of the glass particle discharged from the nozzle in accordance with quantity of flowing fused glass G and size of the glass particles.
In addition, FIG. 1 shows that the fused glass G flows down on both side surfaces of the fusion pipe 1 and joins at the blade like portion 13. However, it is also available that the fused glass G flows down on either side of the fusion pipe 1 and descents from the blade like portion 13.
Moreover, nozzle 14 does not have to be arranged above the fusion pipe 1. It can be arranged above a flow passage which leads the fused glass to the fusion pipe 1, and alternatively, it can be arranged side direction of the fusion pipe 1. The configuration in which the nozzle is arranged side direction of the fusion pipe 1 is shown in FIG. 2.
Moreover, in the present embodiment, the asperity is formed on the glass substrate by adhesion the glass particles on the fused glass G. However, it is available that the asperity can be formed by removing the glass particles, which once adhered on the fused glass G, from the glass substrate by method for example ultrasonic cleaning. In this case, glass particles comprise glass other than non-alkaline glass can be used, and further, particles comprise material other than glass can also be used. In these cases, it is convenient that melting point of such particles is higher than that of non-alkaline glass.

Embodiment 2

FIG. 3 is a conceptual figure showing a manufacturing method according to the Embodiment 2. In FIG. 3, the fusion pipe 1 has the same structure as that of one which is used in the Embodiment 1, and reference sign is used in common with the Embodiment 1.
In the present embodiment, a nozzle 14 is arranged obliquely downward of a fusion pipe 1. Glass particles having diameters of about 0.1 μm are discharged from the nozzle 14.
Fused non-alkaline glass G flown into the trough like portion 11 of the fusion pipe 1 fills the trough like portion 11, and after that, overflows and flows down along side surface of the fusion pipe 1.
The fused glass G reached to the blade like portion 13, which is at a bottom of the fusion pipe 1, descents with solidifying as being plate like glass GP, and further the plate like glass GP is pulled down by revolution of rollers 15.
During descending the plate like glass GP, the glass particles are discharged from the nozzle 14 and collided against the surface of the plate like glass GP before the plate like glass GP solidifies completely. Through this process, the asperity is formed on the surface of the plate like glass GP by being generated a plastic deformation. Afterwards, the plate like glass GP is cut in desired size and a glass substrate is completed.
When forming TFT patterns or CF patterns on such glass substrate, a process control is conducted so as to vacuum contact a side on which asperity is formed. By this procedure, a condition for stabilization of contact and preventing generation of the static electricity are satisfied simultaneously, and defect prevention is stably accomplished. Moreover, as light is scattered in moderate by the asperity on the surface of the glass substrate, there is also an effect for anti reflection.
In the present embodiment, diameters of the glass particles are not limited to about 0.1 μm, and it is only necessary to appropriately determine them in accordance with conditions of a placement of the nozzle, discharging speed of the glass particles, and so forth.
Moreover, glass particles are used in the present embodiment, however, material of particles is not limited to glass, and it is available to use ceramics or metal particles.
Moreover, a structure in the present embodiment is that the fused glass flown into the fusion pipe overflows and flows down along a side surface or (side surfaces) of the fusion pipe. However, it is only necessary that the fused glass flows down from a slit opened at the bottom of the fusion pipe without overflowing.

Enbodiment 3

FIG. 4 is a conceptual figure showing a manufacturing method according to the Embodiment 3. In FIG. 4, the fusion pipe 11 has the same structure as that of one which is used in the Embodiment 1, and reference sign is used in common with the Embodiment 1.
In the present embodiment, a pair of transfer rollers 16A and 16B is placed below the fusion pipe 11. An asperity is formed in advance on a surface of either one of the transfer rollers (16A or 16B). The pair of transfer rollers is placed to pinch and apply a pressure on both surfaces of a plate like glass GP in a direction of thickness of it in a phase in which solidification of the plate like glass GP is not completed.
Fused non-alkaline glass G flown into the trough like portion 11 of the fusion pipe 1 fills the trough like portion 11, and after that, overflows and flows down along side surface of the fusion pipe 1.
The fused glass G reached to the blade like portion 13 which is at a bottom of the fusion pipe 1 descents with solidifying as being plate like glass GP. The plate like glass GP is applied a pressure on both surfaces of it to a direction of thickness of the plate like glass by the pair of transfer rollers 16A and 16B firstly, and then is pulled down by revolution of rollers 15.
At that point, surfaces of the plate like glass are plastic deformed by a pressure applied by the pair of transfer rollers 16A and 16B, and an asperity is formed on the surface of the plate like portion. A configuration magnified A—A portion of FIG. 4 is shown in FIG. 5 Afterwards, the plate like glass GP is cut in desired size and a glass substrate is completed.
When forming TFT patterns or CF patterns on such glass substrate, a process control is conducted so as to vacuum contact a side on which asperity is formed. By this procedure, a condition for stabilization of contact and preventing generation of the static electricity are satisfied simultaneously, and defect prevention is stably accomplished. Moreover, as light is scattered in moderate by the asperity on the surface of the glass substrate, there is also an effect for anti reflection.
In the present embodiment, as the asperity formed on the surface of the transfer roller 16A or 16B is concerned, it is desired that a height is in the range from 10 nm to 40 nm and a period is in the range from 0.1 mm to 1.2 mm, however, it is only necessary to determine these values appropriately according to the pressure applying by the transfer rollers 16A and 16B and the degree of solidification of the glass. Moreover, the asperity can be formed on the surfaces of both of the transfer rollers 16A and 16B. In this case, as the asperity is formed on both sides of the glass, it makes not necessary to process control so as to vacuum contact a side on which asperity is formed.
In addition, a structure in the present embodiment is that the fused glass flown into the fusion pipe overflows and flows down along a side surface or (side surfaces) of the fusion pipe. However, it is available that the fused glass can be flown down from a slit opened at the bottom of the fusion pipe without overflowing.

Embodiment 4

FIG. 6 is a conceptual figure showing a manufacturing method according to the Embodiment 4. In FIG. 6, although a fusion pipe is similar to that used in the Embodiment 1, an applied temperature control is different from that used in the Embodiment 1. It will be provided an explanation according to this fusion pipe below by using FIG. 7.
Upper part of the fusion pipe 3 is made as a trough like portion 31, which is open to the air, and a bank like portions 32 are arranged on both sides of the trough like portion 31. Moreover, bottom part of the fusion pipe 3 is made as a blade like portion 33. Moreover, heaters 34 and 35 are installed inside the fusion pipe 3. These heaters maintain a temperature on the surfaces of the fusion pipe 3 in a glass fusing state, and in the same time, the heaters are controlled so as to generate periodic temperature difference between side surfaces 36 and 37 in accordance with time passage.
Fused non-alkaline glass G is flown into the trough like portion 31 of the fusion pipe 3. Fused non-alkaline glass G fills the trough like portion 31. The fused glass G filled the trough like portion 31 overrides the bank like portions 32 and overflows to both direction of the fusion pipe 3 and falls down along side surfaces 36 and 37.
The fused glass G reached to the blade like portion 33, which is at a bottom of the fusion pipe 3, descents with solidifying as being plate like glass GP.
At this point, as explained above, the heaters are controlled so as to generate periodic temperature difference between side surfaces 36 and 37 in accordance with time passage. In this embodiment, as the heater 35 is controlled to output virtually constant while the heater 34 is controlled to generate periodic output, the temperature of the side surface 37 is being constant while that of the side surface 36 is being up-and-down.
As the result, a flow rate of the fused glass flowing along the side surface 37 is being constant while a flow rate of the fused glass flowing along the side surface 36 is being up-and-down in accordance with time passage. Therefore, an asperity is formed on the surface of the plate like glass GP as which falling down after joining at the blade like portion 33.
The plate like glass descents with solidifying and is pulled down by revolution of rollers 15. Afterwards, the plate like glass GP is cut in desired size and a glass substrate is completed.
When forming TFT patterns or CF patterns on such glass substrate, a process control is conducted so as to vacuum contact a side on which asperity is formed. By this procedure, a condition for stabilization of contact and preventing generation of the static electricity are satisfied simultaneously, and defect prevention is stably accomplished. Moreover, as light is scattered in moderate by the asperity on the surface of the glass substrate, there is also an effect for anti reflection.
In the present embodiment, the heater 35 is controlled to output virtually constant while the heater 34 is controlled to generate periodic output. However, in the present invention, it is only necessary that periodic temperature difference be generated with time passage between side surfaces 36 and 37 of the fusion pipe. Therefore, it is applicable that the heater 34 is controlled to output virtually constant while the heater 35 is controlled to generate periodic output. Alternatively, it is also applicable that both of heaters 34 and 35 are controlled to generate periodic output. In the latter case, obtained glass substrate have asperities on both surfaces, and it makes unnecessary to apply a process control so as to vacuum contact a side on which asperity is formed.
In the present embodiment, it is possible to form asperities, which have various height and period, by controlling power supply to heaters 34 and 35. Industrial Applicability
The present invention can provide a large size glass substrate; which is used for FPD especially for display device like a TFT type liquid crystal device on which minute pattern is to be formed in good yield; and also provide a manufacturing method thereto.

Claims

1. A glass substrate comprising a surface having an asperity of a height in the range from 10 nm to 20 nm and of a period in the range from 0.1 mm to 1 mm.

2. The glass substrate of claim 1, wherein the height is in the range from 15 nm to 20 nm and the period is in the range from 0.1 mm to 0.6 mm.

3. The glass substrate of claim 1, wherein the asperity exists only on one side of said substrate.

4. The glass substrate of claim 1, wherein the glass substrate has a length and a width each 1000 mm or more, respectively, and a thickness of 1.2 mm or less.

5. The glass substrate of claim 1, which comprises non-alkaline glass.

6. A method for manufacturing a glass substrate by fusion process, the method comprising the steps of;

flowing fused glass into a fusion pipe, and

gradually cooling and solidifying the fused glass by flowing downward from the fusion pipe,

wherein an asperity is formed on a surface of the glass substrate by depositing particles on a surface of the fused glass.

7. The method for manufacturing a glass substrate of claim 6, wherein the particles comprise the same glass material as the fused glass.

8. The method for manufacturing a glass substrate of claim 6, wherein the glass particles are deposited on a surface of the fused glass at a flow passage of the fused glass leading to the fusion pipe.

9. The method for manufacturing a glass substrate of claim 6, wherein the glass particles are discharged from above the fusion pipe, and are deposited on a surface of the fused glass in the fusion pipe.

10. The method for manufacturing a glass substrate of claim 6, wherein the glass particles are discharged from one side or both sides of the fusion pipe and are deposited on a surface of the fused glass.

11. The method for manufacturing a glass substrate of claim 6, wherein a diameter of the glass particles is in the range from 15 nm to 40 nm.

12. The method for manufacturing a glass substrate of claim 6, wherein the asperity has a height in the range from 10 nm to 20 nm and a period in the range from 0.1 mm to 1 mm.

13. The method for manufacturing a glass substrate of claim 6, wherein the asperity has a height in the range from 15 nm to 20 nm and a period in the range from 0.1 mm to 0.6 mm.

14. The method for manufacturing a glass substrate of claim 6, wherein the glass substrate has a length and a width, each 1000 mm or more, respectively, and has a thickness of 1.2 mm or less.

15. The method for manufacturing a glass substrate of claim 6, wherein the glass substrate comprises non-alkaline glass.

16. A method for manufacturing a glass substrate by fusion process, the method comprising the steps of;

flowing fused glass into a fusion pipe, and

wherein an asperity is formed on a surface of the glass substrate by colliding particles against the glass flowing down from the fusion pipe from a side direction.

17. The method for manufacturing a glass substrate of claim 16, wherein the particles comprise at least one of glass, metal and ceramics.

18. The method for manufacturing a glass substrate of claim 16, wherein the asperity on a surface of said glass substrate is formed by colliding particles against only one side of the glass flowing down.

19. The method for manufacturing a glass substrate of claim 16, wherein the asperity has a height in the range from 10 nm to 20 nm and a period in the range from 0.1 mm to 1 mm.

20. The method for manufacturing a glass substrate of claim 16, wherein the asperity has a height in the range from 15 nm to 20 nm and a period in the range from 0.1 mm to 1 mm.

21. The method for manufacturing a glass substrate of claim 16, wherein the glass substrate has a length and a width, each 1000 mm or more, respectively, and a thickness of 1.2 mm or less.

22. The method for manufacturing a glass substrate of claim 16, wherein the glass substrate comprises non-alkaline glass.

23. A method for manufacturing a glass substrate by fusion process, the method comprising the steps of;

flowing fused glass into a fusion pipe, and

wherein an asperity is formed on a surface of the glass substrate by pinching and pressing the glass toward a direction of thickness of the glass with a pair of transfer rollers during the glass is flowing down from the fusion pipe.

24. The method for manufacturing a glass substrate of claim 23, wherein a surface of at least one of the pair of transfer rollers has an asperity of a height in the range from 10 nm to 40 nm and of a period in the range from 0.1 mm to 1.2 mm.

25. The method for manufacturing a glass substrate of claim 23, wherein the asperity has a height in the range from 10 nm to 20 nm and a period in the range from 0.1 mm to 1 mm.

26. The method for manufacturing a glass substrate of claim 23, wherein the asperity has a height in the range from 15 nm to 20 nm and a period in the range from 0.1 mm to 0.6 mm.

27. The method for manufacturing a glass substrate of claim 23, wherein the glass substrate has a length and a width, each 1000 mm or more, respectively, and a thickness of 1.2 mm or less.

28. The method for manufacturing a glass substrate of claim 23, wherein the glass substrate comprises non-alkaline glass.

29. A method for manufacturing a glass substrate by fusion process, the method comprising the steps of,

flowing fused glass into a fusion pipe,

overflowing the fused glass toward two directions of the fusion pipe and flowing the fused glass along two side surfaces of the fusion pipe,

joining the fused glass at a blade portion which is a bottom end of the fusion pipe, and

gradually cooling and solidifying the fused glass by flowing downward from the blade portion,

wherein an asperity is formed on a surface of the glass substrate by periodically changing a temperature difference between the two side surfaces of the fusion pipe.

30. The method for manufacturing a glass substrate of claim 29, wherein the asperity has a height in the range from 10 nm 20 nm and a period in the range from 0.1 to 1 mm.

31. The method for manufacturing a glass substrate of claim 29, wherein the asperity has a height in the range from 15 nm to 20 nm and a period in the range from 0.1 mm to 0.6 mm.

32. The method for manufacturing a glass substrate of claim 29, wherein the glass substrate has a length and a width, each 1000 mm or more, respectively, and a thickness of 1.2 mm or less.

33. The method for manufacturing a glass substrate of claim 29, wherein the glass substrate comprises non-alkaline glass.