JP2006301496A - Heating method of glass substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heating method of a glass substrate which prevents a part of the glass substrate from lifting from a hot plate due to thermal expansion in the contact heating even when the glass substrate is subjected to pre-baking according to three-stage heating using a hot plate. <P>SOLUTION: The heating method of the glass substrate comprises a process (1) of performing annealing by degrees and proximity heating for preventing breakage of a color filter substrate 60 due to thermal shock and a process (2) of subsequently performing re-proximity heating for correcting floating of the part of glass substrate due to heat expansion once in the way of the contact heating in the state that the color filter is sucked on the hot plate 21, and successively performing the contact heating. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a pre-bake process for forming a pattern on a glass substrate by a photolithography method, and in particular, a glass that eliminates a partial lack of heat caused by the rising of the glass substrate and forms a uniform pattern. The present invention relates to a method for heating a substrate.

FIG. 4 is a plan view schematically showing an example of a color filter used in the liquid crystal display device. FIG. 5 is a cross-sectional view taken along the line XX ′ of the color filter shown in FIG.
As shown in FIGS. 4 and 5, the color filter (4) used in the liquid crystal display device has a black matrix (41), a colored pixel (42), and a transparent conductive film (43) on a glass substrate (40). Are formed sequentially.
4 and 5 schematically show a color filter, and 12 colored pixels (42) are represented. In an actual color filter, for example, several hundreds are displayed on a 17-inch diagonal screen. A large number of colored pixels of about μm are arranged.

As a method of manufacturing a color filter having the above structure, which is used in many liquid crystal display devices, first, a black matrix is formed on a glass substrate, and then a colored pixel is aligned with this black matrix pattern. A method of forming a transparent conductive film and aligning a transparent conductive film is widely used.
The black matrix (41) is a matrix having light shielding properties, the colored pixels (42) have, for example, red, green, and blue filter functions, and the transparent conductive film (43) is transparent. Provided as a simple electrode.

The black matrix (41) is composed of a matrix portion (41A) between the colored pixels (42) and a frame portion (41B) surrounding the peripheral portion of the region (display portion) where the colored pixels (42) are formed. Yes.
The black matrix determines the position of the colored pixels of the color filter, makes the size uniform, and shields unwanted light when used in a display device, making the image of the display device uniform and uniform. In addition, it has a function of making an image with improved contrast.

Forming a black matrix on a glass substrate, chromium as the material of the black matrix on a glass substrate (40) (Cr), a metal such as chromium oxide (CrO _X), or a metal compound was formed into a thin film, An etching resist pattern is formed on the formed thin film using, for example, a positive type photoresist, and then etching of the exposed portion of the formed metal thin film and stripping of the etching resist pattern are performed. A method of forming a black matrix (41) made of a metal thin film such as CrO _x is employed.
Alternatively, the black matrix (41) is formed on the glass substrate (40) by photolithography using a black photosensitive resin for forming a black matrix.

The colored pixel (42) is formed by providing a coating film on the glass substrate on which the black matrix is formed using, for example, a negative type photoresist in which a pigment such as a pigment is dispersed. A method of forming colored pixels by exposure and development is used.
In addition, the transparent conductive film (43) is formed on a glass substrate on which a black matrix and colored pixels are formed by, for example, forming a transparent conductive film by sputtering using ITO (Indium Tin Oxide). ing.

The color filter (4) shown in FIG. 4 and FIG. 5 represents one color filter corresponding to one liquid crystal display device. When a large number of color filters are manufactured, one liquid crystal display is displayed. The color filter corresponding to the apparatus is manufactured in a state where it is applied to a large glass substrate.
FIG. 6 is a plan view showing an example of a color filter substrate (60) manufactured by attaching four color filters (4) having a diagonal size of 17 inches on a large glass substrate of about 650 mm × 850 mm. .

The color filter (4) shown in FIGS. 4 and 5 has a basic function as a color filter used in a liquid crystal display device. The liquid crystal display device incorporates such a color filter to realize full color display, and its application range is dramatically expanded, and many products using liquid crystal display devices such as liquid crystal color TVs and notebook PCs are created. It was done.
With the development and practical use of various liquid crystal display devices, the following various functions have been added to the color filters used in the liquid crystal display devices in addition to the above basic functions.

1) Highly reliable function When high reliability is required as a liquid crystal display device, in order to supplement the performance of colored pixels, such as heat resistance, moisture resistance, and chemical resistance, and eluate from the colored pixels As a barrier, a protective layer (overcoat layer) may be formed on the colored pixels.
Alternatively, a protective layer (overcoat layer) may be formed in order to improve the sealing strength between the color filter and the TFT side substrate.
Alternatively, when the display quality is improved by making the alignment of liquid crystal molecules more uniform, a protective layer (overcoat layer) may be formed on the colored pixels to obtain a highly flat color filter.

2) Combined transmission / reflection function A transflective liquid crystal display device that has both transmission and reflection functions in a single liquid crystal display device can be used both in bright outdoors and in dark indoor environments. . FIG. 9 is a cross-sectional view of an example of a color filter used in a transflective liquid crystal display device. As shown in FIG. 9, this color filter is obtained by forming a black matrix (41), colored pixels (42), and a transparent conductive film (43) on a glass substrate (40).
The colored pixel (42) includes a colored pixel (42Tr) for transmissive display and a colored pixel (42Re) for reflective display.

The spectral characteristics of the colored pixel (42Tr) for transmissive display and the colored pixel (42Re) for reflective display are respectively suitable for transmissive display and reflective display. Therefore, when the liquid crystal display device is displayed as a transmission type, it has excellent brightness and saturation, and when it is displayed as a reflection type, it has excellent brightness and saturation.
As the color filter, there are formed a total of six colored pixels, that is, three RGB colors of the colored pixels (42Tr) for transmissive display and three RGB colors of the colored pixels (42Re) for reflective display. That is, three colored pixels for transmissive display and three colored pixels for reflective display are formed.

3) Spectral Characteristic Adjustment Function FIG. 10 is a cross-sectional view of another example of a color filter used in a transflective liquid crystal display device. As shown in FIG. 10, this color filter is obtained by forming a black matrix (41), colored pixels (42), and a transparent conductive film (43) on a glass substrate (40).

  The colored pixel (42) includes a colored pixel (42Tr) for transmissive display and a colored pixel (42Re) for reflective display. The colored pixel (42Re) for reflection display is composed of a colored portion (45) and a transparent portion (46).

  The colored portion (45Tr) of the transmissive display colored pixel (42Tr) and the reflective display colored pixel (42Re) has spectral characteristics suitable for transmissive display. By providing the transparent portion (46) in the colored pixel (42Re) for reflective display, the color light of the colored portion (45) and the white light of the transparent portion (46) are mixed, and the spectral characteristics of the colored pixel (42Re) for reflective display. Is adjusted to an appropriate spectral characteristic for reflection display. The transparent portion (46) is formed of a transparent photoresist.

The above 1) high-reliability function, 2) transmission / reflection combined function, and 3) spectral characteristic adjustment function are all added to the color filter (4) shown in FIG. It is provided on the glass substrate before forming the film (43), and the transparent conductive film (43) is formed on the upper surface thereof.
On the other hand, examples of the function provided on the upper surface of the transparent conductive film (43) of the color filter (4) having basic functions include the following.

4) Spacer function In conventional liquid crystal display devices, transparent spherical particles (beads) of glass or synthetic resin called spacers are dispersed in order to form a gap between substrates. Since these spacers are transparent particles, if a spacer is included with the liquid crystal in the pixel, light will leak through the spacer during black display, and the substrate in which the liquid crystal material is enclosed Due to the presence of the spacers between them, the alignment of the liquid crystal molecules in the vicinity of the spacers is disturbed, and light leakage occurs at this part, and the contrast is lowered and the display quality is adversely affected.

As a technique for solving such a problem, a method of forming a photo spacer (projection) having a spacer function at a position of a black matrix between pixels by using a photosensitive resin and using a photolithography method has been developed and put into practical use.
FIG. 7 is a partial cross-sectional view of such a color filter for a liquid crystal display device. As shown in FIG. 7, in the color filter (7) for a liquid crystal display device, a black matrix (41), a colored pixel (42), and a transparent conductive film (43) are sequentially formed on a glass substrate (40). A photospacer (44) as a protrusion having a spacer function is formed on the transparent conductive film (43) above the black matrix (41). In the liquid crystal display device using the color filter (7) for such a liquid crystal display device, the photo spacer (44) is formed at a position avoiding the inside of the pixel, and thus the contrast is improved.

5) Orientation division function In the conventional liquid crystal display device, in order to uniformly align the liquid crystal molecules, polyimide is applied in advance onto the transparent conductive film provided on both substrates sandwiching the liquid crystal, and its surface A uniform rubbing process is performed.
However, in TN type liquid crystal used in many liquid crystal display devices, in principle, it is difficult to obtain a wide viewing angle. In a halftone display state, light leaks at an oblique viewing angle, and the contrast is lowered and displayed. Quality deteriorates. That is, there is a problem that the viewing angle with good contrast is narrow.

  As one technique for solving such a problem, the liquid crystal molecules in one pixel are controlled so that the alignment direction of the liquid crystal molecules is not a single direction but a plurality of directions, and uniform halftone display is performed in a plurality of directions. In other words, an alignment-divided vertical alignment type liquid crystal display (MVA, Multi-domain Vertical Alignment-LCD) having a wide viewing angle has been developed.

FIG. 8 is an explanatory view schematically showing a cross section of such an MVA-LCD. As shown in FIG. 8, the MVA-LCD (80) includes a TFT side substrate (9) provided with alignment control protrusions (2a) and (2b) via liquid crystal molecules (1), and an alignment control protrusion (3 ) Are arranged, and the alignment control protrusions (2a) and (2b) and the alignment control protrusion (3) are provided at different positions in one pixel.

As shown by the thick white arrow in FIG. 8, in the state at the time of voltage application, the liquid crystal molecules between the alignment control protrusions (2a) to the alignment control protrusions (3) in the pixel are inclined obliquely to the left in the figure. The liquid crystal molecules between the control protrusion (3) and the alignment control protrusion (2b) are inclined obliquely to the right. That is, instead of rubbing treatment, the alignment of liquid crystal molecules is controlled by providing protrusions.
In the example shown in FIG. 8, one pixel is divided into two, and the tilt direction of the liquid crystal molecules is two directions in one pixel, and the liquid crystal display device is excellent in viewing angle characteristics.

Among the above functions, one function or a plurality of functions are added to the color filter (4) shown in FIG. 4 based on the use and specification of the color filter.
These functions correspond to the layers associated with the basic color filter, respectively, and a protective layer (overcoat layer), colored pixels for reflective display, and spectral characteristic adjustment before forming the transparent conductive film (43). A transparent part of the film is formed and provided. Alternatively, after the transparent conductive film (43) is formed, a photospacer, an alignment control protrusion, and the like are formed and provided.
Therefore, for example, when manufacturing a color filter having a specification in which a spacer function and an orientation division function are added to the color filter (4) shown in FIG. 4, after producing the color filter (4) shown in FIG. Then, an alignment control protrusion is formed, and then a photo spacer is formed.

  When forming a layer associated with the basic color filter, all the layers except the protective layer (overcoat layer) not formed as a pattern are the black matrix (41), the colored pixel (42), and the like. Similarly, a pattern is formed by a photolithography method using a photoresist.

  When forming the black matrix, the colored pixels, and the associated layers as a pattern by photolithography, for example, first, a glass substrate is subjected to a cleaning treatment as necessary, and then a photoresist is applied by a coating apparatus. Then, a preliminary drying process by a reduced pressure drying apparatus, a pre-baking process by a pre-baking apparatus, a pattern exposure by an exposure apparatus, a developing process by a developing process unit, and a post-baking process by a heating unit are sequentially performed to form a predetermined pattern on the glass substrate.

  Immediately after application of the photoresist, the coating film of the photoresist is fluid because it is not dried. When the glass substrate is transported to the next process, the film thickness of the coating film is likely to change during transportation. May cause unevenness in thickness. The preliminary drying process is a preliminary drying process in which the solvent in the coating film is evaporated halfway under reduced pressure in order to prevent a change in the film thickness of the coating film accompanying the conveyance.

  The pre-baking process in the next step is a full-fledged drying process in which the solvent in the coating film is evaporated by heating. If the solvent in the coating film remains, the sensitivity of the photoresist is remarkably lowered and the adhesive force to the glass substrate is weakened. Therefore, it is not preferable that the solvent remains in the coating film.

  Fig.1 (a) is sectional drawing which shows the outline of an example of a prebaking apparatus. As shown to Fig.1 (a), the prebaking apparatus (10) is comprised by the heating chamber (20) and the cooling chamber (30). A vacuum table (22) having a hot plate (21) at the top is provided in the heating chamber (20), and a cool plate (31) is at the top in the cooling chamber (30). A provided vacuum table (32) is provided.

The glass substrate obtained by partially evaporating the solvent in the coating film by the preliminary drying process is placed on the hot plate (21) in the heating chamber (20) and subjected to a drying process by heating. Subsequently, the glass substrate is transferred to the cooling chamber (30), placed on the cool plate (31), cooled, and returned to room temperature.
FIG.1 (b) is sectional drawing which shows the outline of an example of the vacuum table (22) which equipped the hot plate (21) in the upper part. FIG. 1B shows a stage where the glass substrate (60) is transferred onto the lift pins (23) by a transfer robot (not shown).

  The glass substrate (60) is placed on the hot plate (21) with the bottom surface supported by two arms (not shown) by the transfer robot from the previous step, but if left as it is, it is hot. Since the arm cannot be retracted after being placed on the plate (21), the arm once protrudes from the upper surface of the hot plate (21) on the plurality of lift pins (23) provided at positions that do not interfere with the arm. The arm is retracted.

The lift pins (23) are vertically movable with respect to the hot plate (21). The lift pins (23) are lowered after the glass substrate (60) has been delivered and placed on the hot plate (21). The opening (24) provided in the hot plate (21) on which the lift pin (23) moves up and down is formed between the glass substrate (60) and the hot plate (21) after the lift pin (23) is lowered into the hollow portion (25). Also serves as an opening for sucking air between.
The hot plate (21) has a built-in heater. The vacuum table (22) has a hollow portion (25), is provided with a hot plate (21) in the upper portion, and an exhaust port (26) is provided in the lower portion. When the glass substrate (60) on the hot plate (21) is vacuum-adsorbed, it is exhausted from the exhaust port.

2A to 2C are cross-sectional views illustrating the operation of the pre-bake process using the heating chamber (20). FIG. 2 is an enlarged view of a portion of the hot plate (21), lift pins (23), and glass substrate (60) in FIG. 1 (b).
As shown in FIG. 2, the pre-baking operation to the glass substrate (60) is performed immediately on the glass substrate (60) conveyed from the previous step in order to avoid the destruction of the glass substrate due to a rapid change in temperature. Heating by adsorbing to the hot plate (21) is not performed, and the heating is performed in three stages: (a) leveling heating, (b) proxy heating, and (c) contact heating.

First, leveling heating is performed as shown in FIG. For example, in a state where a glass substrate (60) using non-alkali glass # 1737 (product number) having a thickness of about 0.7 to 1.0 mm is transferred onto the lift pins (23), a hot plate ( 21) The distance (D1) between the upper surface and the glass substrate (60) is, for example, about 45 to 50 mm, and heating is performed for about 5 seconds.
By separating the distance (D1) from the upper surface of the hot plate (21) to about 45 to 50 mm, a gentle first stage heating is performed from the hot plate (21) kept constant at a high temperature. The temperature of the hot plate (21) is about 80 to 150 ° C., and the distance (L) between the lift pins (23) is about 100 to 300 mm.

Next, as shown in FIG. 2B, in a state where the glass substrate (60) is transferred onto the lift pins (23), the lift pins (23) are lowered, and the upper surface of the hot plate (21) and the glass substrate ( The distance (D2) of 60) is reduced to, for example, about 2 mm, and proxy heating is performed for about 15 to 60 seconds.
By reducing the distance (D2) from the upper surface of the hot plate (21) to about 1 to 10 mm, the hot plate (21) kept at a high temperature is kept at a second temperature at a temperature substantially equal to that on the hot plate. Stage heating is done.

  Next, as shown in FIG. 2 (c), the lift pin (23) is further lowered, and the glass substrate (60) is placed on the hot plate (21) to effectively heat uniformly. A third stage of contact heating is performed, for example, for about 50 to 150 seconds while sucking air between the glass substrate (60) and the hot plate (21) and adsorbing the glass substrate (60) to the hot plate (21). This is an operation of heating in three stages.

  However, when the pre-baking process is performed by the three-stage heating operation as described above, a rapid change in temperature, that is, destruction of the glass substrate (60) due to thermal shock is surely avoided. Between the portions of the glass substrate corresponding to the openings (24), the glass plate floats from the hot plate (21) due to thermal expansion, and unevenness occurs in the pattern of the glass substrate (60) after exposure and development. is there.

FIG. 3 is a cross-sectional view for explaining the floating of the glass substrate (60) when heating is performed in the state shown in FIG. 2 (c). As shown in FIG. 3, a plurality of portions of the glass substrate corresponding to the plurality of openings (24) are adsorbed by the hot plate (21), but a portion between the openings (24) and the openings (24) is Floating from the hot plate (21) due to thermal expansion. The portion of the glass substrate (60) that has been lifted from the hot plate (21) has a shortage of heat in the pre-bake treatment, and the solvent in the coating film is insufficiently evaporated.
That is, the sensitivity of the photoresist in the floating portion is insufficient, the pattern dimensions after the exposure and development processes are different, and the pattern of the glass substrate (60) becomes non-uniform and uneven.
JP-A-11-112198 Japanese Patent Application No. 2000-268178

The present invention has been made to solve the above problems, and even if a pre-baking process is performed on a glass substrate using a hot plate by three stages of heating, proxy heating, and contact heating, the contact heating is performed. In the above, an object of the present invention is to provide a method for heating a glass substrate in which a portion of the glass substrate does not float from the hot plate due to thermal expansion.
As a result, the portion of the glass substrate corresponding to the space between the openings does not feel that the amount of heat in the pre-baking process is insufficient, and the glass substrate after the exposure and development processes can be obtained with a uniform pattern. .

In the present invention, a color filter is formed by forming a pattern on a glass substrate by a photolithography method in which a cleaning process, a photoresist application, a preliminary drying process, a pre-bake process, a pattern exposure, a development process, and a post-bake process are sequentially performed. In pre-bake processing using a hot plate when manufacturing,
1) Perform break-in heating and proxy heating to prevent the glass substrate from being destroyed by thermal shock.
2) In the middle of the subsequent contact heating while adsorbed on the hot plate, re-proxy heating is performed once to correct the floating of the glass substrate due to thermal expansion, and then the contact heating is continued. This is a method for heating a glass substrate.

  In the pre-baking process, the present invention performs break-in heating and proxy heating to prevent breakage of the glass substrate due to thermal shock, and then in the middle of contact heating while adsorbed on a hot plate, once due to thermal expansion The glass substrate is heated by re-proxy heating to correct the floating of the glass substrate, and the contact heating is continued. Therefore, the glass substrate is heated by using a hot plate, and heated by proxy. Even if the pre-baking process by the three-step heating of contact heating is performed, the glass substrate heating method does not cause the glass substrate portion to lift from the hot plate due to thermal expansion.

  Accordingly, the portion of the glass substrate corresponding to the space between the openings does not feel that the amount of heat in the pre-baking process is insufficient, and the glass substrate after the exposure and development processes can be obtained with a uniform pattern.

Hereinafter, embodiments of the present invention will be described in detail.
FIGS. 11A to 11F are cross-sectional views illustrating the operation of the pre-baking process in the glass substrate heating method of the present invention. FIG. 11 is an enlarged view of a portion of the hot plate (21), lift pins (23), and glass substrate (60).

As shown in FIGS. 11 (a) and 11 (b), first, leveling heating and then proxy heating are performed. These operations are the operations of the heat treatment shown in FIGS. 2 (a) and 2 (b). Is the same.
Next, as shown in FIG. 11 (c), the lift pins (23) are further lowered to place the glass substrate (60) on the hot plate (21), and the glass substrate (60) and the hot plate (21). The third stage contact heating is performed while the glass substrate (60) is adsorbed on the hot plate (21).

By the contact heating while adsorbed on the hot plate (21), a plurality of portions of the glass substrate corresponding to the plurality of openings (24) are adsorbed on the hot plate (21) as in the state shown in FIG. However, the portion between the opening (24) and the opening (24) is lifted from the hot plate (21) by thermal expansion (FIG. 11 (d)).
When a plurality of portions of the glass substrate are lifted, air suction between the glass substrate (60) and the hot plate (21) is interrupted, and the adsorption of the glass substrate (60) to the hot plate (21) is released. To do.

Next, as shown in FIG. 11E, the lift pins (23) are raised to perform re-proxy heating. The distance (D3) between the upper surface of the hot plate (21) and the glass substrate (60) when performing this re-proxy heating is substantially the same as the distance (D2) shown in FIG. The time is about 1 to 10 seconds of heating.
By raising the lift pins (23), the color filter substrate (60) is released from the hot plate (21), and the lifted portion is caused to expand in the horizontal direction of the glass substrate (60) as shown by the arrows. The glass substrate (60) is converted into a flat state on the lift pins (23).

  Next, as shown in FIG. 11 (f), the lift pins (23) are lowered again to place the glass substrate (60) on the hot plate (21), and the glass substrate (60) and the hot plate (21) are placed. ) Is resumed, and the third stage contact heating is continued while the glass substrate (60) is adsorbed to the hot plate (21).

In the third stage of contact heating performed continuously, since the temperature of the glass substrate (60) is already the same as the temperature of the hot plate (21), thermal expansion accompanying the increase in temperature no longer occurs. Thereafter, a plurality of portions of the glass substrate do not float between the opening (24) and the opening (24), and the glass substrate (60) remains in a flatly adsorbed state, and is uniformly applied to the glass substrate (60). The third stage of contact heating ends.

(A) is sectional drawing which shows the outline of an example of a prebaking apparatus. (B) is sectional drawing which shows the outline of an example of the vacuum table which equipped the hot plate in the upper part. (A)-(c) is sectional drawing explaining operation | movement of the prebaking process using a heating chamber. It is sectional drawing explaining the floating of the glass substrate at the time of heating in the state shown in FIG.2 (c). It is the top view which showed typically an example of the color filter used for a liquid crystal display device. FIG. 5 is a cross-sectional view taken along line X-X ′ of the color filter illustrated in FIG. 4. It is the top view which showed an example which manufactures a 17-inch diagonal color filter by attaching four faces to a large size glass substrate. It is a fragmentary sectional view of the color filter for liquid crystal display devices in which the photo spacer (projection part) was formed. It is explanatory drawing which showed typically the cross section of LCD provided with the alignment control protrusion. It is sectional drawing of an example of the color filter used for a transflective liquid crystal display device. It is sectional drawing of the other example of the color filter used for a transflective liquid crystal display device. (A)-(f) is sectional drawing explaining the operation | movement of the prebaking process by the heating method of the glass substrate of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal molecule 2a, 2b, 3 ... Orientation control protrusion 4, 7, 8 ... Color filter 9 ... TFT side substrate 10 ... Prebaking apparatus 20 ... Heating chamber 21 ... Hot plate 22 ... Heating chamber vacuum table 23 ... Lift pin 24 ... Opening 25 ... Hollow part 26 ... Exhaust port 30 ... Cooling chamber 31 ... Cool plate 32 ... Vacuum table 40 in cooling chamber ... Glass substrate 41 ... Black matrix 41A ... Black matrix 41B ... Black matrix frame 42 ... Colored pixel 42Tr ... Transparent display coloration Pixel 42Re ... Colored pixel 43 for reflection display ... Transparent conductive film 44 ... Photo spacer 45 ... Colored portion 46 ... Transparent portion 60 ... glass substrate 80 ... MVA-LCD
D1 ··· The distance between the hot plate and the glass substrate during leveling D2 · · · The distance between the hot plate and the glass substrate during proxy heating D3 · · · The distance L between the hot plate and the glass substrate during re-proxy heating・ Distance between lift pins

Claims (1)

When manufacturing a color filter by forming a pattern on a glass substrate by a photolithography method in which washing processing, photoresist application, pre-drying processing, pre-baking processing, pattern exposure, development processing, and post-baking processing are sequentially performed. In pre-baking using a hot plate,
1) Perform break-in heating and proxy heating to prevent the glass substrate from being destroyed by thermal shock.
2) In the middle of the subsequent heating of the contact adsorbed on the hot plate, re-proxy heating that corrects the floating of the glass substrate due to thermal expansion is performed once, and then the contact heating is continued. A method for heating a glass substrate.

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