JPH11228160A - Quartz glass substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a substrate having excellent performance for a thin film transistor(TFT) circuit in addition to a property which must be provided as a substrate for a high temp. polycrystalline Si TFT by specifying the difference between the virtual temp. before and after thermal oxidation and the content of impurity elements, eliminating the presence of striae and controlling strain to equal to or below a specific value. SOLUTION: In the quartz glass substrate for TFT obtained by patterning the polycrystalline silicon film on a pre-heated quartz glass substrate and thermally oxidizing, the content of the impurity elements such as Al, Fe, Ca, Ti, Zn, Cr, Mn, Mg, Ni, V, Cu, Co is respectively <=3 ppb, the content of Cl is <=0.5 ppm, the max. content of OH group is 10-150 ppm, the striae is not recognized, the strain is <=20 nm/cm and formula I to formula III are satisfied. In the formula, FT0 represents the virtual temp. of a quartz glass ingot, FTa1 represents the virtual temp. of the preheated quartz glass substrate and FTA2 represents the virtual temp. of the quartz glass substrate after the patterning of the polycrystalline silicon and the thermal oxidation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz glass substrate used for an active matrix type thin film transistor (hereinafter referred to as "TFT") of a liquid crystal display, and more particularly to a high-temperature polycrystalline silicon type. The present invention relates to a quartz glass substrate used for a TFT.

[0002]

2. Description of the Related Art TFT-type liquid crystal displays are composed of amorphous silicon (a-Si) type and polycrystalline silicon (p-Si).
Type (hereinafter referred to as p-Si-TFT). p ・ S
i-TFT has high temperature p-Si-
There are a TFT and a low-temperature p-Si-TFT, and strict quality is required for a substrate for a high-temperature p-Si-TFT, so a quartz glass substrate is used.

A quartz glass substrate is manufactured, for example, by the steps shown in Table 1. For example, quartz glass fine particles (soot) are synthesized by heating silicon tetrachloride (SiCl ₄ ) to about 100 ° C. and subjecting the vaporized SiCl ₄ gas to a hydrolysis reaction in an oxyhydrogen flame (step A). The soot is deposited to form a columnar soot body (step B). The obtained soot body is heated in an inert atmosphere to obtain a transparent preform (step C). The preform is pressed and molded in a hot press furnace or the like to form an ingot (Step D), and then annealed (Step E). The ingot is cut and polished to obtain a substrate (step F).

[0004]

[Table 1]

[0005] A p-Si-TFT is manufactured by using the above-described substrate by the steps 1 to 13 shown in Table 2 as an example. For example, p-Si-TFT has a polycrystalline S
After patterning the i-film and subjecting it to thermal oxidation, pattern the gate and address lines, implant phosphorus ions, inter-layer insulating film, anneal, pattern contact holes,
This is completed by depositing ITO and patterning pixel electrodes and signal lines. Note that the substrate preheating treatment (step 1) is performed using TF
Depending on the T manufacturer, this may or may not be performed.

[0006]

[Table 2]

Quality characteristics required for a substrate for a high-temperature p-Si-TFT (hereinafter simply referred to as a “substrate”) include the following three main items. In addition, it is also required that no bubbles or foreign substances exist, that the outer shape accuracy is good, and that the surface is polished well.

High heat resistance (low warpage and shrinkage after thermal oxidation treatment), high purity, and high optical homogeneity.

Heat resistance of substrate: High temperature p-Si-TFT
As shown in Table 2, the gate is heated to a temperature of 900 to 1150 ° C. between the polycrystalline Si formation patterning (step 3) and the gate address line patterning (steps 5 and 6), as shown in Table 2. A thermal oxidation process (step 4) for forming an insulating film is performed. If the substrate is warped or shrunk by this thermal oxidation treatment, the quality of the TFT product is degraded.

[0010] The warpage of the substrate occurs in a high-temperature treatment step such as a preheating treatment or a thermal oxidation treatment (900 to 1150 ° C) when manufacturing a TFT. When a large warp occurs on the substrate,
The warpage of the TFT circuit causes stress, resulting in a decrease in electrical characteristics such as a decrease in insulation. In addition, when injecting liquid crystal during the process of assembling the substrate on which the TFT circuit is formed into the TFT panel, the TFT substrate and the back surface may be used. It is said that the sealing with the glass substrate on the side becomes insufficient and causes troubles such as leakage of liquid crystal.

Heretofore, several proposals have been made regarding the method of improving the heat resistance by regarding the warpage of the substrate after the high-temperature heat treatment as heat resistance.

Generally, factors affecting the heat resistance of quartz glass are a fictive temperature and the content (purity) of an impurity element.

[0013] Regarding the effect of the fictive temperature on the heat resistance of quartz glass, the lower the fictive temperature is from 1000 to 1400 ° C, the better the heat resistance is.
tonington et al. (Physics and Chemistry of Glasses,
vol.5, NO.5 (1964), p.130-136).

The fictive temperature is a temperature at which the structure of the glass becomes equilibrium when the glass is extremely quickly changed to a certain temperature. In other words, the glass is supercooled or overheated and becomes equilibrium at a certain temperature. The temperature at which the glass has such a structure as is called the virtual temperature (AQTool J.Am.C
er. Soc., 29, 240 (1946)). It has characteristic values such as density, refractive index, viscosity, stress relaxation, and elastic modulus according to the temperature, and is interpreted as a general term for the state.

Impurity elements for improving heat resistance are, for example, aluminum (Al), nitrogen (N), etc. On the contrary, OH groups, chlorine (Cl), fluorine (F) and the like are known as elements for decreasing heat resistance. I have.

With respect to quartz glass to which Al has been added, for example, aluminum alkoxide is added to methyl silicate, and this is hydrolyzed in the presence of ammonia to produce aluminum-containing silica particles, which are then dehydrated, decarburized, and sintered. To a synthetic quartz glass ingot, and the powder obtained by crushing this is melt-molded to reduce aluminum to 0.1 to 100.
A high-viscosity synthetic quartz glass member containing 0 ppm and a method for producing the same have been proposed (see JP-A-8-40737).

Various reports have been made in the past on quartz glass doped with N (eg, THElmer).
(1988) Glastech. Ber. Vol. 61 Nr. 1 pp. 24-28).

On the other hand, impurities that lower the heat resistance are OH
Groups, Cl and F. However, since F is hardly present in synthetic quartz glass, it is not an object of the present invention. It is said that the OH group and Cl increase or decrease depending on the production conditions of the synthetic quartz glass, so that it is better to make them as small as possible or desirably not to contain them. For example, JP-A-8-40737
JP-A 8-48532 and JP-A-8-48532, the content of any of the OH group and Cl is 1 ppm or less, JP-A-9-40434,
Quartz glass having an OH group of 5 ppm or less and Cl of 1 ppm or less and a method for producing the same have been proposed.

Further, the OH group content of the quartz glass substrate is set to 50
By controlling the content to less than ppm, the generation of "warp" after heating to 1000 ° C or more is suppressed, and when chlorine (Cl) is contained, a problem occurs in the transistor characteristics, and the internal resistance of the TFT when the TFT is turned on and off is reduced. Therefore, a substrate containing no chlorine is used. Further, the presence of metal impurities, particularly alkali metal ions, causes non-uniform film formation or an adverse electrical effect on the TFT element. 6-67198 gazette).

In order to manufacture a high-temperature p-Si-TFT, as shown in Table 2, after performing polycrystalline Si formation patterning (step 3), heat treatment is performed at a temperature of 900 to 1150 ° C. to form a gate insulating film. Is subjected to a thermal oxidation treatment (step 4). When the substrate is shrunk by this thermal oxidation treatment, the distance between the gate and address lines to be subsequently applied changes, and the performance of the TFT circuit is reduced. Since the line width is 1 to 3 μm, the shrinkage amount after the thermal oxidation treatment needs to be 10 ppm or less.

A quartz glass substrate having small "warp" and "shrinkage" after high-temperature heat treatment and a method for obtaining the same are disclosed in Japanese Patent Application Laid-Open No. 8-87032. This is because a purified silicon compound such as silicon tetrachloride is hydrolyzed in an oxyhydrogen flame to form a porous silica material, and then subjected to a heat treatment under a hydrogen-containing atmosphere to remove OH groups.
Furthermore, by using quartz glass obtained by heating in a high-temperature atmosphere to form a transparent glass, the polycrystalline Si thin film transistor type L whose shrinkage is 10 ppm or less is used.
CD substrate and its manufacturing method.

In addition, if there is an optically inhomogeneous portion or strain called striae in the substrate glass, the localization of the optically inhomogeneous portion occurs when polarized light is transmitted through the substrate glass as in the TFT method. A problem arises in that the rotation of the objective polarization plane causes shading of the TFT image. Accordingly, the striae and strain in the substrate glass are required to have a level that does not affect the TFT image (for example, a grade A defined by the MIL standard for striae and a strain amount of 20 nm / cm or less). (See “Application Technology of High-Purity Silica” (1991), p.173, published by CMC Corporation).

[0023]

As described above, the heat resistance of a quartz glass substrate can be improved by adding elements such as Al and N, but cannot be used as a TFT substrate. Further, in order to reduce the OH group of the quartz glass to 5 ppm or less, it is necessary to remove water under vacuum or to perform a dehydration treatment using a halogen gas or the like at a manufacturing stage. As a result, a part of the tetrahedral coordination structure of Si and O (oxygen), which is the glass structure of the quartz glass substrate, collapses, and a part of O deviates from the tetrahedral coordination (-Si.Si-). Such a structural defect is generated. When a quartz glass substrate containing a large amount of (-Si.Si-) structural defects is irradiated with strong light such as a backlight light source as a TFT, blue or green fluorescence is likely to be generated. In addition, the virtual temperature can be 1000 ~
When the temperature is lowered in the range of 1400 ° C, the heat resistance improves, but TFT
A phenomenon occurs in which the performance of the circuit is reduced.

The invention disclosed in Japanese Patent Application Laid-Open No. 8-87032 discloses that the shrinkage after heat treatment at a temperature of 1150 ° C. for 30 minutes is reduced.
This is a substrate manufactured to be 10 ppm or less. However, even when such a substrate is put on an actual TFT production line, a phenomenon that the performance of the TFT circuit is reduced may occur.

An object of the present invention is to solve the above-mentioned problems and to excel in the performance of a TFT circuit in addition to the characteristics (heat resistance, purity and optical stability) that a quartz glass substrate for a high temperature p-Si TFT should have. To provide a quartz glass substrate.

[0026]

Means for Solving the Problems The present inventors have studied the causes of the performance degradation of the TFT circuit and obtained the following knowledge.

Even if the substrate has a shrinkage of 10 ppm or less after heat treatment at a temperature of 1150 ° C. for 30 minutes, the actual TF
The capacity (volume, heat source capacity,
Since the materials that make up the equipment are different, the amount of shrinkage after the heat treatment may be 10 ppm or more.

When a quartz glass substrate is subjected to heat treatment in equipment having different capacities, it may expand in addition to warpage and shrinkage.

When the expansion / contraction is defined as dimensional stability and an index obtained by dividing the dimensional change of the substrate by the original size is defined as the dimensional change, the absolute value of the difference between the dimensional change and the virtual temperature before and after the thermal oxidation treatment is defined. There is a correlation between Here, the absolute value of the virtual temperature difference is simply referred to as “virtual temperature difference”.

The present invention has been completed based on the above-mentioned knowledge and the definition of impurities and optical homogeneity of quartz glass, and the gist lies in the quartz glass substrates shown in the following (1) and (2).

(1) A quartz glass substrate for a thin film transistor manufactured by patterning a polycrystalline silicon film on a quartz glass substrate that has been subjected to a preheating treatment and performing a thermal oxidation treatment, wherein the impurity element (Al, Fe, Ca, Ti, Zn, Cr, Mn, Mg, N
i, V, Cu, Co, P, W, Pb, Ta, Zr, B, Na, K, Li) content is 3 ppb or less, Cl content is 0.5 ppm or less, and the maximum OH group content is A quartz glass substrate having 10 to 150 ppm, no striae, a maximum value of distortion of 20 nm / cm or less, and satisfying the following formulas:

| (FT ₀ ) − (FTa ₁ ) | ≦ 100 ° C. | (FTa ₁ ) − (FTa ₂ ) | ≦ 50 ° C. | (FT ₀ ) − (FTa ₂ ) | ≦ 150 ° C where (FT ₀ ) is the fictive temperature of the quartz glass ingot, and (FT ₀ )
a ₁ ) is the hypothetical temperature of the quartz glass substrate after the preheating treatment, (FT
a ₂ ) is the virtual temperature of the quartz glass substrate after the polycrystalline silicon film is patterned and then subjected to a thermal oxidation treatment.

(2) A quartz glass substrate for a thin film transistor manufactured by patterning a polycrystalline silicon film on a quartz glass substrate not subjected to a preheating treatment and performing a thermal oxidation treatment, wherein the impurity element (Al, Fe, Ca, Ti, Zn, Cr, Mn, Mg,
Ni, V, Cu, Co, P, W, Pb, Ta, Zr, B, Na, K, Li) content of 3 ppb or less, Cl content of 0.5 ppm or less, maximum content of OH group A quartz glass substrate having 5-150 ppm, no striae, a maximum value of distortion of 20 nm / cm or less, and satisfying the following expression.

| (FT ₀ ) − (FTb ₂ ) | ≦ 50 ° C. Here, (FTb ₂ ) is the surface of the quartz glass substrate after the polycrystalline silicon film is patterned and then subjected to a thermal oxidation treatment. It is a virtual temperature.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION The substrate of the present invention regulates the dimensional change rate of a substrate by defining the virtual temperature of a quartz glass ingot and the virtual temperature of the substrate before and after a thermal oxidation treatment performed in TFT production. It can be suppressed to 10 ppm or less. In addition, the impurity elements (Al, Fe, Ca, T
i, Zn, Cr, Mn, Mg, Ni, V, Cu, Co, P, W, Pb, T
a, Zr, B, Na, K, Li) content of 3 ppb or less, Cl content of 0.5 ppm or less, and maximum OH group content of 10 to 15
By setting the concentration to 0 ppm, it is possible to eliminate the occurrence of a leak current in a TFT circuit, a trouble in an electric system such as corrosion, a disconnection of the TFT circuit, and the like, and suppress the generation of fluorescence when irradiated with backlight or ultraviolet light. Further, a TFT image without unevenness in density can be obtained by suppressing striae on the substrate and setting the distortion to 20 nm / cm or less.

Regarding the virtual temperature of the substrate: As described above, when the virtual temperature (FT ₀ ) of quartz glass is between 1000 ° C. and 1400 ° C., the lower the temperature, the better the heat resistance. But,
Even if such a quartz glass substrate is used as a TFT substrate, dimensional stability may be impaired. The inventor measured the virtual temperature and the dimensional change before and after the heat treatment of the quartz glass substrate manufactured by changing the manufacturing conditions, and confirmed that there was a correlation between the two.

The measurement of the virtual temperature is performed by a method proposed by FL Galeneer, a laser Raman spectrometer (Nippon Bunko Co., Ltd.
R-1100) to compare the area intensity ratio of defect peaks at 492 cm ^-1 and 606 cm ^-1 (Non-Cr
ys. Solids, vol. 58, No. 6 (1986) pp. 363-365).

The dimensional stability of the substrate differs depending on the TFT manufacturing process (Table 2), and differs between the case where the preheating treatment (step 1) is performed and the case where the preheating treatment is not performed.

(A) In the case of performing the preheating treatment: the virtual temperature (FT ₀ ) of the quartz glass ingot, the virtual temperature (FTa ₁ ) of the substrate after the preheating treatment, and the substrate after the thermal oxidation treatment the fictive temperature (FTa _2), were measured using a laser Raman spectrometer described above. Also, after pre-heating treatment (FT
The dimensional change of the substrate after a ₁ ) and after the thermal oxidation treatment (FTa ₂ ) was measured by a microscope to 0.1 μm unit as a change in pattern line width.

FIG. 1 is a diagram showing the relationship between the difference in virtual temperature and the rate of dimensional change when preheating is performed. FIG.
Shows the results of the examples described below. From the figure, to reduce the dimensional change rate of the substrate to 10 ppm or less,
It turns out that it is necessary to satisfy the expression.

| (FT ₀ ) − (FTa ₁ ) | ≦ 100 ° C. | (FTa ₁ ) − (FTa ₂ ) | ≦ 50 ° C. | (FT ₀ ) − (FTa ₂ ) | ≦ 150 ° C. ··· (b) Without pre-heating treatment: fictive temperature of quartz glass ingot (FT ₀ ), fictive temperature of substrate after thermal oxidation treatment (FTb ₂ ), and (FT ₀ ) The dimensional change of the substrate at (FTb ₂ ) was measured in the same manner as in (a) above. The results are shown in FIG.

FIG. 2 is a diagram showing the relationship between the difference in virtual temperature and the dimensional change rate when no preheating treatment is performed. FIG.
Shows the results of the examples described below. From the figure, it can be seen that in order to reduce the dimensional change of the substrate to 10 ppm or less, it is necessary to satisfy the following expression.

| (FT ₀ ) − (FTb ₂ ) | ≦ 50 ° C. In the above formulas, the reason indicated by the absolute value of the virtual temperature difference will be described below.

In a temperature range where the virtual temperature is about 1500 ° C. or less, T
The substrate expands when the virtual temperature decreases with the progress of the FT manufacturing process, and contracts when the virtual temperature increases. On the other hand, the opposite tendency is observed in the temperature range of about 1500 ° C. or higher. In any case, since there is a correlation between the dimensional change rate of expansion or contraction and the virtual temperature difference, the absolute value of the virtual temperature difference is determined.

Regarding substrate purity: Impurities that degrade the TFT performance of the quartz glass substrate include metal impurity elements, OH groups, and Cl.

Impurity element (M element): The metal impurity elements of quartz glass are Al, Fe, Ca, Ti, Zn, Cr, Mn, Mg, Ni,
V, Cu, Co, P, W, Pb, Ta, Zr, B, Na, K, and Li. The content of each of these impurity elements is 3
Above ppb, TFT products using the substrate
A quality defect such as generation of a leak current in the T circuit or disconnection of the circuit occurs. In particular, when the alkali elements of Na, K and Li each exceed 3 ppb, the tendency becomes remarkable.
Therefore, it is desirable that these impurity elements be small, but the allowable contents are respectively 3 ppb or less.

OH group: The OH group decreases the viscosity of the quartz glass in proportion to the content. Therefore, if the OH group is excessively contained, the substrate may be warped due to thermal deformation in a high-temperature treatment such as a thermal oxidation process in a TFT manufacturing process. "In the TFT panel assembly process, which causes defects such as leakage of liquid crystal. If the maximum content exceeds 150 ppm, "warpage" due to thermal deformation becomes excessive and product defects occur. If the OH group is less than 10 ppm, structural defects of (-Si.Si-) (structural defects of homobond of Si) are inherent, and the substrate emits fluorescence when irradiated with strong light after the TFT product. Therefore, the maximum content of OH groups is set to 10 to 150 ppm.

When the transmittance of the substrate in the vacuum ultraviolet light region is measured using a vacuum ultraviolet spectrophotometer, the structural defect of (-Si.Si-) is found to be (-Si.Si-). , Wavelength 163nm
It has the characteristic that the transmittance in the wavelength region of about 170 nm or less is reduced due to its absorption peak.

Cl: When Cl is contained in the TFT substrate at a high concentration, the internal resistance ratio at the time of turning on / off the TFT circuit is reduced, and this adversely affects the TFT element. Therefore, it is desirable that the Cl content is small, and the allowable content is 0.5 ppm or less, which is the lower limit of measurement.

Striae and distortion of the substrate: If striae is observed on the substrate or if the amount of distortion is large, shading appears in the image when a TFT is used. If no striae is observed and the amount of distortion is 20 nm / cm or less, no shading is observed in the image when the TFT is used. Therefore, in the present invention, the striae is measured by the method specified in MIL-G-174, and the grade A
(Not recognized), the amount of distortion was 20 nm / cm or less.

[0051]

EXAMPLE A quartz glass ingot was prepared by using A to E shown in Table 1.
Up to the process.

Specimens 1 to 8, 10 and 11 were prepared by heating silicon tetrachloride (SiCl ₄ ) to about 100 ° C. and subjecting the vaporized SiCl ₄ gas to a hydrolysis reaction in an oxyhydrogen flame to produce fine quartz glass particles (soot). (Step A), the soot is deposited,
A cylindrical soot body S1 was produced (step B). Specimen 9 is
In step B of soot deposition, a columnar soot body S2 was produced in an atmosphere containing a small amount of impurities.

Step C for forming a preform from the soot body obtained, Step D for forming an ingot, Step E for annealing
Was performed under the conditions shown in Table 3.

[0054]

[Table 3]

From the obtained ingot, the fictive temperature, impurities, striae and strain were measured.

The measurement of the fictive temperature was performed using a laser Raman spectrometer (NR-110 manufactured by JASCO Corporation) proposed by FL Galeneer.
0).

The impurities were measured by a wet component analysis method using a flameless atomic absorption spectrometer and an IPC-Mass meter.

[0058] Striae was measured according to the United States Army standard (MIL-G-174).

The distortion was measured using a birefringence meter.

The ingots were cut and polished to obtain a disc-shaped substrate, and the pre-heating treatment and the non-pre-heating treatment were performed at the fictive temperature before and after the thermal oxidation treatment and the dimensions after the thermal oxidation treatment. The change and the thermal deformation (warpage) after the thermal oxidation treatment were measured.

The measurement of the dimensional change was carried out by a microscope to 0.1 μm unit as the change of the patterning line width before and after the thermal oxidation treatment.

The measurement of the thermal deformation (warpage) was performed by a flatness tester manufactured by Konica Corporation.

(Invention Example 1) The specimen 1 of the invention example was heated at a temperature of 1350 ° C. under a vacuum of about 20 pa using a clean soot body S1, and then heated to 1500 ° C. to obtain a 150 mm diameter. , Length 1
A 200 mm quartz glass transparent body (preform) was used. The obtained preform was placed in a high-purity carbon mold, and heated to 1700 ° C. in an Ar gas atmosphere using a uniaxially pressurized hot press furnace to a diameter of 210 mm and a length of 600 mm, and cooled for 6 hours. Then, a quartz glass molded body (ingot) was obtained. Next, using an annealing furnace, at 1150 ° C. in an N ₂ gas atmosphere
And kept for 10 hours, then slowly cooled over 40 hours.

From the obtained ingot, the fictive temperature, impurities, striae and strain were measured, and the results are shown in Tables 4 and 5.

[0065]

[Table 4]

[0066]

[Table 5]

As is apparent from Table 4, the fictive temperature (FT0) of the test piece 1 is 1050 ° C., and the impurity element (M element, that is, A
l, Fe, Ca, Ti, Zn, Cr, Mn, Mg, Ni, V, Cu, Co,
The contents of P, W, Pb, Ta, Zr, B, Na, K, and Li) were all 3 ppb or less, the Cl content was 0.5 ppm or less as the measurement limit, and the maximum OH group content was 100 ppm. Further, as is clear from Table 5, the striae of the test sample 1 was grade A (no striae was recognized) according to the MIL standard, and the maximum amount of strain was 10 nm / cm.

The ingot was cut and polished to a diameter of 200 mm,
A 1 mm thick quartz glass substrate (No. 1) was used. The hypothesis of the substrate before and after the thermal oxidation treatment (step 4, 1050 ° C. shown in Table 1) was obtained for the case where this substrate was subjected to the pre-heating treatment (step 1, 1050 ° C. shown in Table 1) and the case where the pre-heating treatment was not performed. temperature,
The dimensional change after the thermal oxidation treatment and the thermal deformation (warpage) after the thermal oxidation treatment were measured.

The dimensional change is the amount of change in the substrate before the thermal oxidation treatment, that is, the change in the patterning line width due to the combination of the patterning (mask 2) in step 6 and the patterning (mask 1) in step 3 shown in Table 2. The amount was determined by microscopic reading. Thermal deformation (warpage) was measured by a Konica flatness tester. The results are shown in Tables 4 and 5.

In the case of performing the preheating treatment: As is clear from Table 4, the substrate (No. 1) manufactured from the ingot of the test piece 1 of the invention example had an ingot fictive temperature (FT ₀ ) of 1050 ° C. The virtual temperature (FTa ₁ ) of the substrate after pre-heating treatment manufactured from the ingot is 1080 ° C, and the virtual temperature (F
Ta ₂ ) is 1100 ° C., and the difference between the virtual temperatures is | (FT ₀ ) − (FTa ₁ ) | = | 1050 ° C.−1080 ° C. = 30 ° C., | (FTa ₁ ) − (FTa ₂ ) | = | 1080 ° C-1100 ° C | = 20 ° C, | (FT ₀ ) − (FTa ₂ ) | = | 1050 ° C-1100 ° C | = 50 ° C.
Both are within the range defined by the present invention. Therefore, the dimensional change rate of the substrate after the thermal oxidation treatment is as small as 3 ppm, which is good.

When the preheating treatment is not performed: the virtual temperature (FT ₀ ) of the ingot is 1050 ° C., the virtual temperature (FTb ₂ ) of the substrate manufactured from the ingot after thermal oxidation is 1100 ° C. The difference is | (FT ₀ ) − (FTb ₂ ) | = | 1050 ° C.−1
100 ° C. | = 50 ° C., which is within the range defined by the present invention. Therefore, the dimensional change of the substrate after the thermal oxidation treatment is as good as 10 ppm.

The thermal deformation (warpage) is as small as 40 μm when the pre-heating treatment is performed and 30 μm when the pre-heating treatment is not performed, which is good. This is because the Cl content is 0.5 ppm or less, which is the measurement limit, the maximum OH group content is 100 ppm, and the impurity element (M element) content is all 3 ppb or less.

With respect to the TFT product manufactured using the substrate (No. 1), electrical characteristics, leakage of liquid crystal, and generation of fluorescence were examined. The results are also shown in Table 5.

As is clear from Table 5, in the TFT products using the substrate (No. 1), the difference of any virtual temperature is within the range defined by the present invention, the dimensional stability of the substrate is good, and the purity is low. Since it is high, the electrical characteristics are good. Further, impurities were also within the range defined by the present invention, and there was no leakage of liquid crystal due to small thermal deformation (warpage), and no generation of fluorescence was observed. Furthermore, since no striae was observed and the distortion was 10 nm / cm at the maximum, no shading of the TFT image was observed, and the TFT product was an excellent product satisfying all required quality.

(Invention Example 2) The test piece 2 of the invention example was heated to 1300 ° C. in a mixed gas flow of He: 70% by volume and N ₂ : 30% by volume using the soot body S1 described above, and then 1480 C. to obtain a preform having a diameter of 140 mm and a length of 1350 mm. Thereafter, it was pressed and molded in the same manner as in Example 1 to have a diameter of 160 mm,
It was a 0 mm ingot. Next, using an annealing furnace,
The mixture was heated to 1250 ° C. in an N ₂ gas atmosphere, maintained for 10 hours, and then gradually cooled for 40 hours.

From the obtained ingot, the fictive temperature, the impurity element, the striae and the amount of strain were measured in the same manner as in the case of the test piece 1. The results are shown in Tables 4 and 5.

As is clear from Tables 4 and 5, the fictive temperature (FT0) of the ingot of the specimen 2 was 1150 ° C., the maximum content of OH groups was 150 ppm, and the strain was 12 nm / cm at maximum. Specimen 1 for impurity element content, Cl content and stria
be equivalent to.

The ingot was cut and polished to a diameter of 150 mm,
A quartz glass substrate (No. 2) having a thickness of 1 mm was used. In the case where the substrate was subjected to the preheating treatment (step 1 shown in Table 2, 1100 ° C.) and the case where the preheating treatment was not performed, the thermal oxidation treatment temperature was set to 1100 ° C., and the same method as in Example 1 was examined.
The results are shown in Table 5.

In the case of performing the preheating treatment: As is clear from Table 4, the substrate obtained from the test piece 2 has a fictive temperature (FTa ₁ ) of the substrate after the preheating treatment of 1110 ° C. and the substrate after the thermal oxidation treatment. The virtual temperature (FTa ₂ ) of the substrate is 1100 ° C, and the difference between the virtual temperatures is
40 ° C., 10 ° C., and 50 ° C. are all within the range defined by the present invention. Therefore, the dimensional change of the substrate after the thermal oxidation treatment is as small as 2 ppm, which is excellent.

In the case where the preheating treatment is not performed: the virtual temperature (FT ₀ ) of the ingot is 1150 ° C., and the virtual temperature (FT
b ₂ ) is 1100 ° C., and the difference between the virtual temperatures is 50 ° C., which is within the range defined by the present invention. Therefore, the dimensional change of the substrate after the thermal oxidation treatment is as small as 10 ppm, which is favorable.

The thermal deformation (warpage) is as small as 50 μm when the preheating treatment is performed and 40 μm when the preheating treatment is not performed. This is because the CL content is below the measurement limit of 0.5 ppm, the maximum OH group content is 150 ppm, and the impurity element (M
Element) content is 3 ppb or less.

With respect to the TFT product manufactured using the substrate (No. 2), electrical characteristics, leakage of liquid crystal, and generation of fluorescence were examined. The results are also shown in Table 5.

As is clear from Table 5, the TFT product using the substrate (No. 2) has good dimensional stability of the substrate, good electrical characteristics due to high purity, and small thermal deformation (warpage). Therefore, there was no leakage of the liquid crystal, and no generation of fluorescence was observed.
In addition, since no striae was observed and the distortion was 12 nm / cm at the maximum, no shading of the TFT image was observed, and the TFT product had excellent performance and satisfied all the required qualities.

(Invention Example 3) The specimen 3 of the invention example has a soot body heating temperature of 1200 ° C. and a maximum OH group content of 10 ppm.
The test piece 2 was manufactured under the same conditions as those of the test piece 2 except for the above. The results are shown in Tables 4 and 5.

As is apparent from Table 4, the fictive temperature (FT0) of the ingot of the test piece 3 is 1150 ° C., and the impurity elements (M elements, ie, Al, Fe, Ca, Ti, Zn, Cr, Mn, Mg, Ni) , V, C
The contents of u, Co, P, W, Pb, Ta, Zr, B, Na, K, and Li) are all 3 ppb or less, the Cl content is 0.5 ppm or less of the measurement limit, and the maximum OH group content is 10 ppm. Was. Further, as shown in Table 5, the striae were grade A, and the amount of strain was 12 nm / cm at maximum.
Met.

The ingot was cut and polished to a diameter of 150 mm,
A quartz glass substrate (No. 3) having a thickness of 1 mm was used. The case where the substrate was subjected to the preheating treatment (step 1 shown in Table 2, 1100 ° C.) and the case where the preheating treatment was not carried out were investigated in the same manner as in Example 1 by setting the thermal oxidation treatment temperature to 1100 ° C. The results are shown in Table 5.

When preheating treatment is performed: As is clear from Table 4, the substrate obtained from the test piece 3 has a fictive temperature (FTa ₁ ) after the preheating treatment of 1110 ° C. and a fictive temperature after the thermal oxidation treatment.
(FTa ₂ ) is 1100 ° C, fictive temperature difference is 10 ° C, and
° C and 50 ° C, both within the range defined by the present invention. Therefore, the dimensional change rate of the substrate after the thermal oxidation treatment is 2 pp.
m and small, good.

In the case where the preheating treatment is not performed: the virtual temperature (FT ₀ ) of the ingot is 1150 ° C., and the virtual temperature (FT
b ₂ ) is 1100 ° C., and the difference between the virtual temperatures is 50 ° C., which is within the range defined by the present invention. Therefore, the dimensional change of the substrate after the thermal oxidation treatment is as small as 10 ppm, which is favorable.

The thermal deformation (warpage) is as good as 20 μm when the pre-heating treatment is performed and 15 μm when the pre-heating treatment is not performed. This is because the Cl content is below the measurement limit of 0.5 ppm, the maximum OH group content is 10 ppm, and the impurity element (M
Element) content is 3 ppb or less.

With respect to the TFT product manufactured using the substrate (No. 3), electrical characteristics, leakage of liquid crystal, and generation of fluorescence were examined. The results are also shown in Table 5.

As is clear from Table 5, the TFT product using the substrate (No. 3) has good electrical characteristics due to the high dimensional stability and purity of the substrate, and has a small thermal deformation (warpage) due to the liquid crystal. And no fluorescence was observed. Also,
No striae was observed and the strain was up to 12 nm / cm.
No shading of the FT image was observed, and the TFT product had excellent performance and satisfied all required quality.

(Invention Example 4) Soot body S1 as in Example 1
Was prepared and heated to 1250 ° C. under a vacuum of 1 to 3 Pa using a vacuum heating furnace, and then heated to 1550 ° C. to obtain a preform having a diameter of 160 mm and a length of 1000 mm. Thereafter, using a uniaxial pressing hot press furnace, pressure molding was performed in the same manner as in Example 1 to obtain an ingot having a diameter of 210 mm and a length of 560 mm.

From the obtained ingot, the fictive temperature, impurity element, striae, and strain were measured, and the results are shown in Tables 4 and 5.

As shown in Table 4, the fictive temperature (FT0) of the ingot of the test piece 4 was 1500 ° C., and the impurity elements (M elements, ie, Al, Fe, Ca, Ti, Zn, Cr, Mn, Mg, Ni, V, Cu, Co,
The contents of P, W, Pb, Ta, Zr, B, Na, K, and Li) were all 3 ppb or less, the Cl content was 0.5 ppm or less of the measurement limit, and the maximum OH group content was 50 ppm. In addition, as shown in Table 5, the stria was grade A, and the maximum amount of strain was 18 nm / cm.

The ingot was cut and polished to a diameter of 200 mm,
A quartz glass substrate (No. 4) having a thickness of 1 mm was used. After pre-heating (1150 ° C) this substrate, the thermal oxidation
Investigation was carried out in the same manner as in Example 1 at 50 ° C. The results are shown in Tables 4 and 5.

As is clear from Table 4, the substrate (No. 4)
The fictive temperature (FTa ₁ ) after the preheating treatment is 1420 ° C., and the fictive temperature (FTa ₂ ) after the thermal oxidation treatment is 1380 ° C.
80 ° C., 40 ° C., and 120 ° C. are all within the range defined by the present invention. Therefore, the dimensional change rate of the substrate after the thermal oxidation treatment is as small as 8 ppm, which is good. Further, since the Cl content is 0.5 ppm or less of the measurement limit, the maximum content of OH group is 50 ppm, and the impurity element (M element) content is all 3 ppb or less, the thermal deformation (warpage) is as shown in Table 5. Small and good. However, when the preheating treatment was not performed, the test was not performed because the dimensional change rate of the substrate was likely to exceed 10 ppm.

With respect to the TFT product manufactured using the substrate (No. 4), electrical characteristics, leakage of liquid crystal, and generation of fluorescence were examined. The results are also shown in Table 5.

As is clear from Table 5, the TFT product using the substrate (No. 4) has good electrical characteristics due to high dimensional stability and high purity of the substrate, and small thermal deformation (warpage). There was no leakage of liquid crystal and no generation of fluorescence was observed. In addition, since there was no striae and the distortion was as small as 18 nm / cm, no shading of the TFT image was observed, and the TFT product had excellent performance and satisfied all required quality.

Comparative Example 5 Specimen 5 of Comparative Example was manufactured under the same conditions as Specimen 2 except that the preform heating temperature was 1250 ° C. in order to make the maximum content of OH groups 5 ppm. The performance was examined in the same manner as the test body 2. Table 4 shows the results.
And Table 5 together.

As is evident from Tables 4 and 5, all were the same as Inventive Example 2 except that the maximum OH group content was 5 ppm. Therefore, TFT using substrate (No.5)
Since the product had a maximum OH group content of 5 ppm, generation of fluorescence was observed.

Comparative Example 6 A preform to an ingot were produced under the same conditions as in Example 1 using the soot body S1, but the annealing time of the annealing treatment was compared with that in Example 1.
50% longer (60 hours). The obtained ingot and substrate were examined in the same manner as in Example 1, and the results are shown in Tables 4 and 5.

As is evident from Table 4, the performance of the ingot of the test piece 6 was higher than the fictive temperature (FT0) in comparison with Example 1.
Are different from each other at 870 ° C., but the content of impurity elements, Cl and OH groups, striae and strain are all the same. However, as is clear from Table 5, the substrate (No. 6)
The difference between the virtual temperatures is 100 ° C. and 230 ° C., both of which are larger than the range defined by the present invention. Therefore, the dimensional change rate of the substrate is as large as 18 ppm. When the preheating treatment is not performed, the difference between the virtual temperatures is 230 ° C., which is larger than the range defined in the present invention. Therefore, the dimensional change rate of the substrate is as large as 40 ppm.

As is clear from Table 5, the TFT product using the substrate (No. 6) had a difference in virtual temperature, and both fell outside the range defined by the present invention. Was as large as 18 ppm and 40 ppm, and the electrical characteristics were poor.

(Comparative Example 7) A preform and an ingot were produced using the soot body S1 under the same conditions as in Example 2, but the annealing time for annealing was 50% less than that in Example 2.
Short (20 hours). The obtained ingot and substrate were examined in the same manner as in Example 2, and the results were shown in Table 4.
And Table 5 together.

As is clear from Table 4, the performance of the ingot of the test piece 5 was different from that of the second example in the fictive temperature (FT0).
Is different from 1300 ° C., but the content of impurity elements, Cl and OH groups, striae and strain are all the same. However, as is apparent from Table 4, the difference of the virtual temperature is 80 ° C.
Is 200 ° C., which is larger than the range defined by the present invention. Therefore, the dimensional change rate after thermal oxidation of the substrate is 15pp
m and big. If the pre-heating treatment is not performed,
The difference between the virtual temperatures is 200 ° C., which is larger than the range defined by the present invention. Therefore, the dimensional change rate of the substrate after thermal oxidation treatment is 34
It is as large as ppm.

As shown in Table 4, T using the substrate (No. 7)
The FT product has a difference in fictive temperature, and both are out of the range defined in the present invention. Therefore, the dimensional change rate after the thermal oxidation treatment is as large as 15 ppm and 34 ppm, and as is apparent from Table 5, the electrical characteristics are poor. It became.

(Comparative Example 8) A preform was produced using the soot body S1 under the same conditions as in Example 4. Next, in the same manner as in Example 4, only the cooling time after pressing and molding was performed.
The ingot was shortened by 20% (4.8 hours) to obtain an ingot (test body 8) having the same size as that of Example 4. The obtained ingot and substrate were examined in the same manner as in Example 4, and the results are shown in Tables 4 and 5.

As is clear from Table 4, the performance of the ingot of the test piece 8 was the same as that of Example 4 in that the content of the impurity element (M element), Cl and OH groups were equal, but the fictive temperature (FT0) Is 1530 ° C., the striae are grade B of the MIL standard, and the strain amount is different at a maximum of 30 nm / cm. Therefore, the substrate (N
In the TFT product using o.8), a cloudy polarized image was generated in the TFT image.

(Comparative Example 9) Using the soot body S2, the preform was converted into an ingot (test body 9) under the same conditions as in Example 1 and annealed. The obtained ingot and substrate were examined in the same manner as in Example 1, and the results are shown in Tables 4 and 5.

Since the soot body S2 contains impurities, the specimen 9
The performance of the ingot is based on impurity elements (Fe, Ca, Ni, Na,
K, Mn, Mg content is all 5ppb, other impurity elements (A
l, Ti, Zn, Cr, V, Cu, Co, P, W, Pb, Ta, Zr,
B, Li) content was all 4 ppb. However, the Cl content, the OH group content, the striae, and the strain amount are the same as in Example 1. Therefore, a TFT product using the test body 9 as a substrate
Since the content of the impurity element in the substrate exceeds the range defined in the present invention, defects due to impurity contamination of the substrate such as poor film formation accuracy and leakage current occurred.

(Comparative Example 10) A furnace pressure of about 10
After heating to a temperature of 1350 ° C under a vacuum of 0 Pa, the preform was heated to 1500 ° C to obtain a preform having a diameter of 150 mm and a length of 1200 mm.
Then, it was press-formed to form an ingot (test body 10) having a diameter of 210 mm and a length of 600 mm. Next, an annealing treatment was performed in the same manner as in Example 1. The obtained ingot and substrate were examined in the same manner as in Example 1, and the results are shown in Tables 4 and 5.

As shown in Table 4, the performance of the ingot of the test piece 10 was Cl
The content was 10 ppm and the content of OH groups was 140 ppm. However, other performances are the same as the test piece 1. Therefore, for TFT products using the substrate (No. 10), the Cl content of the substrate is 10p.
Due to the large number of pm, insulation failure occurred in the TFT circuit.

(Comparative Example 11) A gas obtained by heating and vaporizing a silicon compound containing no chlorine (tetramethoxysilane [Si (OCH ₃ ) ₄ ]) was subjected to a hydrolysis reaction in an oxyhydrogen flame with an increased heat input. The soot is synthesized and deposited at the same time, and is immediately vitrified (direct synthesis, [also known as CVD in the quartz glass industry]) with a diameter of 150 mm and a length of 1
A 200mm preform was manufactured. Then, using a uniaxial pressing hot press furnace, the diameter was 210 m as in Example 1.
An ingot (test body 11) having a length of m and a length of 600 mm was further heated and gradually cooled using an annealing furnace. The obtained ingot and substrate were examined in the same manner as in Example 1, and the results are shown in Tables 4 and 5.

As shown in Table 4, the performance of the ingot of the test piece 11 was such that the content of the impurity element (M element) was
And the maximum content of OH groups was 1200 ppm. However, other performances are the same as the test piece 1. Therefore,
In the TFT product using the substrate (No. 11), since the purity of the substrate was poor, electric defects due to an increase in leak current and warpage due to thermal deformation of the substrate increased, resulting in leakage of liquid crystal.

[0115]

The substrate according to the present invention is characterized in that the dimensional change of the substrate is suppressed by defining the difference between the virtual temperatures before and after the thermal oxidation treatment, and the content of the impurity element is adjusted.
Occurrence of leakage current, trouble in the electric system, disconnection, and the like are eliminated, and fluorescence generated when irradiating ultraviolet rays can be suppressed. Furthermore, there is no stria on the substrate, and the distortion is 20 nm / c.
By setting the value to m or less, a substrate from which a TFT image without uneven shading can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a difference in virtual temperature and a dimensional change rate when a preheating treatment is performed.

FIG. 2 is a diagram showing a relationship between a difference in virtual temperature and a dimensional change rate when a preheating treatment is not performed.

Claims (2)

[Claims] 1. A quartz glass substrate for a thin film transistor manufactured by patterning a polycrystalline silicon film on a quartz glass substrate that has been subjected to a pre-heating treatment and performing a thermal oxidation treatment, wherein the impurity element (Al, Fe , Ca, Ti, Zn, Cr, Mn, Mg, Ni, V,
The contents of Cu, Co, P, W, Pb, Ta, Zr, B, Na, K, and Li) are each 3 ppb or less, the content of Cl is 0.5 ppm or less, and the maximum content of OH groups is 10 to 150 ppm. No striae, maximum strain 20
A quartz glass substrate having a diameter of not more than nm / cm and satisfying the following expressions: | (FT ₀ ) − (FTa ₁ ) | ≦ 100 ° C… | (FTa ₁ ) − (FTa ₂ ) | ≦ 50 ° C… | (FT ₀ ) − (FTa ₂ ) | ≦ 150 ° C ... where (FT ₀ ) is the virtual temperature of the quartz glass ingot and (FT ₀ )
a ₁ ) is the hypothetical temperature of the quartz glass substrate after the preheating treatment, (FT
a ₂ ) is the virtual temperature of the quartz glass substrate after the polycrystalline silicon film is patterned and then subjected to a thermal oxidation treatment. 2. A quartz glass substrate for a thin film transistor manufactured by patterning a polycrystalline silicon film on a quartz glass substrate not subjected to a preheating treatment and performing a thermal oxidation treatment, wherein the impurity element (Al, Fe , Ca, Ti, Zn, Cr, Mn, Mg, Ni,
The contents of V, Cu, Co, P, W, Pb, Ta, Zr, B, Na, K, and Li) are each 3 ppb or less, the Cl content is 0.5 ppm or less, and the maximum OH group content is 10 to 10 ppm. A quartz glass substrate characterized by being 150 ppm, having no striae, having a maximum strain of 20 nm / cm or less, and satisfying the following expression. | (FT ₀ ) − (FTb ₂ ) | ≦ 50 ° C. Here, (FTb ₂ ) is the virtual temperature of the quartz glass substrate after the polycrystalline silicon film is patterned and then subjected to thermal oxidation treatment. is there.