JP3849388B2 - Manufacturing method of liquid crystal device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention belongs to the technical field of cleaning a substrate on which a switching element is formed, and particularly to the technical field of cleaning a substrate used in a liquid crystal device.
[0002]
[Prior art]
An active matrix liquid crystal device is configured by sandwiching a liquid crystal layer between a counter substrate as two electrode substrates and a TFT array substrate, and by applying a voltage to the liquid crystal layer to change the optical characteristics of the liquid crystal molecules. Display.
[0003]
The TFT array substrate is configured, for example, by arranging scanning lines and data lines intersecting each other on a quartz glass substrate, and disposing a thin film transistor (hereinafter referred to as TFT) and a pixel electrode as switching elements at each intersection. . The switching element includes a semiconductor layer disposed on the substrate, a gate insulating film formed so as to cover the semiconductor layer, and a gate electrode disposed on the gate insulating film corresponding to the channel region of the semiconductor layer.
[0004]
The quartz glass substrate used for the above-mentioned TFT array substrate is manufactured, for example, as follows. First, after melting or synthesizing a glass raw material, a quartz glass ingot is formed. Thereafter, it is cut into a desired size, chamfered, polished, and then manufactured through a cleaning process.
[0005]
However, an abrasive or the like may remain on the quartz glass substrate manufactured as described above, or dust may adhere during transportation. When a TFT is formed on a substrate in which such impurities remain, the TFT switching characteristics are affected and appear as display defects when a liquid crystal device is formed.
[0006]
In order to prevent such display defects due to impurities adhering to the quartz glass substrate, the quartz glass substrate has been cleaned before forming an element such as a TFT. For cleaning, a method using sulfuric acid or a mixed solution of sulfuric acid and hydrogen peroxide solution as a cleaning solution, or a mixed solution of sulfuric acid or sulfuric acid and hydrogen peroxide solution is used as a cleaning solution for the first cleaning, and then ammonia and excess. A method of using a mixed solution with hydrogen oxide water as a cleaning solution for the second cleaning is general.
[0007]
[Problems to be solved by the invention]
However, even in the above-described cleaning method, the impurities attached to the quartz glass substrate cannot be removed sufficiently, and if the metal remains as impurities, the TFT characteristics are greatly affected, and the liquid crystal device is obtained. There was a problem that the display was poor.
[0008]
The present invention has been made to solve such problems, and provides a substrate cleaning method and an electrode substrate manufacturing method free from metal contamination, and a substrate and an electrode substrate manufactured by these methods. Objective.
[0009]
[Means for Solving the Problems]
In order to solve such a problem, the present invention employs the following configuration.
[0010]
According to the method for manufacturing a liquid crystal device of the present invention, a pair of substrates including a quartz substrate on which a plurality of switching elements are formed and a counter substrate disposed to face the quartz substrate are sandwiched between the pair of substrates. A method of manufacturing a liquid crystal device including a liquid crystal layer, wherein (a) the quartz substrate is washed with sulfuric acid or a mixed solution of sulfuric acid and hydrogen peroxide, and (b) the quartz substrate is fluorinated. Cleaning with hydrogen or a mixture of hydrogen fluoride and hydrogen peroxide, (c) cleaning the quartz substrate with ammonia or a mixture of ammonia and hydrogen peroxide, and (d) the quartz. The step of cleaning the substrate with hydrochloric acid or a mixed solution of hydrochloric acid and hydrogen peroxide and (e) the step of forming the switching element on the quartz substrate are performed in this order.
Further, the counter substrate is made of a low alkali glass substrate, (f) a step of washing the counter substrate with sulfuric acid or a mixed solution of sulfuric acid and hydrogen peroxide, and (g) the counter substrate with hydrogen fluoride. Or (h) cleaning the counter substrate with ammonia or a mixed solution of ammonia and hydrogen peroxide, and (i) cleaning the counter substrate. Are washed with hydrochloric acid or a mixed solution of hydrochloric acid and hydrogen peroxide, and (j) a step of forming a light shielding layer on the counter substrate is performed in this order.
Further, the semiconductor layer of the switching element is formed on the quartz substrate.
[0011]
According to such a configuration of the present invention, in step (a), organic substances adhering mainly to the glass substrate are decomposed and removed, and in step (b), the natural oxide film formed on the glass substrate surface is removed by etching. In step (c), particles and organic substances adhering to the glass substrate surface are removed. In step (d), Na, Mg, Al, K, Ca, Ti, Fe, Cr, Ni, Cu, Zn, and CeO are removed. ₂ , metal impurities such as Li, Mn, Zr, B, etc. are oxidized, dissolved as ions, and removed.
[0012]
The order of the washing steps is preferably (a) step, (b) step, (c) step, (d) step, or (a) step, (c) step, (b) step, (d) step. good. In step (a), the surface of the substrate is oxidized and a silicon oxide film is formed by using a liquid mixed with hydrogen peroxide as a cleaning liquid. This silicon oxide film has a role of reducing the etching amount of the substrate itself by these cleaning liquids at the time of cleaning containing hydrogen fluoride and ammonia used in the subsequent steps (b) and (c). Accordingly, there are few latent scratches on the substrate due to hydrogen fluoride and ammonia. Thereafter, in the step (d), by using a liquid mixed with hydrogen peroxide as a cleaning liquid,
The function of oxidizing the impurity metal, ionizing the impurity metal and dissolving it in the cleaning liquid is promoted.
[0013]
Here, as the glass substrate, a quartz glass substrate made of only silicon oxide, an aluminosilicate glass substrate, a soda-lime glass substrate, a borosilicate glass substrate, a low alkali glass substrate, a non-alkali glass substrate, or the like can be used.
[0014]
Further, the cleaning is performed in the order of the step (a), the step (b), the step (c), and the step (d). By setting it as such a process, the impurity adhering to a glass substrate can be removed efficiently and reliably. That is, in the step (a), organic substances adhering to the glass substrate are mainly decomposed and removed. In this case, a natural oxide film may be formed on the glass substrate by using sulfuric acid. In the step (b), the natural oxide film is removed by etching. Furthermore, particles generated by this etching that cannot be completely removed by rinsing with pure water or the like can be removed in step (c). Furthermore, the metal impurity adhering to the glass substrate is removed by the step (d).
[0015]
Moreover, quartz glass can be used for the glass substrate.
[0016]
The method for producing an electrode substrate according to the present invention includes a step of forming a switching element on the glass substrate cleaned by the cleaning method described above. According to such a configuration, since the switching element is formed on the glass substrate without adhesion of metal impurities, there is no abnormality in switching element characteristics, and a high-quality electrode substrate can be obtained.
[0017]
In addition, the glass substrate of the present invention is characterized by being cleaned by the glass substrate cleaning method described above. According to such a configuration, a glass substrate free from impurities can be obtained.
[0018]
In addition, the electrode substrate of the present invention is manufactured by the method for manufacturing an electrode substrate described above. According to such a configuration, since the switching element is formed on the glass substrate without adhesion of metal impurities, there is no abnormality in switching element characteristics, and a high-quality electrode substrate can be obtained.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
(Glass substrate cleaning method)
Hereinafter, an embodiment of the present invention will be described with reference to FIG.
[0020]
First, for example, a quartz glass substrate is prepared as a glass substrate.
[0021]
Thereafter, as shown in FIG. 1 (1), the quartz glass substrate is immersed in the first cleaning liquid accommodated in the first cleaning container. The first cleaning liquid is obtained by heating a mixed liquid in which sulfuric acid (H ₂ SO ₄ ) and hydrogen peroxide water (H ₂ O ₂ ) are mixed so that the volume ratio is 4: 1. The temperature of the mixed solution was 120 ° C., and the immersion time was 5 minutes. By this step, organic substances attached to the glass substrate can be removed. In addition, by using a cleaning liquid mixed with hydrogen peroxide, the substrate surface is oxidized and an oxide film is formed. Here, the mixing ratio and temperature of the first cleaning liquid are not particularly limited as long as the organic substance removing function is satisfied, and it is possible to use only sulfuric acid.
[0022]
Next, as shown in FIG. 1 (2), the sulfuric acid adhering to the quartz glass substrate is removed by immersing the quartz glass substrate in ultrapure water.
[0023]
Next, as shown in the process of FIG. 1 (3), the quartz glass substrate is immersed in the second cleaning liquid accommodated in the second cleaning container. The second cleaning liquid is a mixed liquid in which hydrogen fluoride (HF), hydrogen peroxide water (H ₂ O ₂ ), and ultrapure water (H ₂ O) are mixed at a volume ratio of 1: 1 to 195. The temperature of the mixed solution was 23.5 ° C., and the immersion time was 3 minutes. By this step, when an oxide film is formed on the glass substrate due to the use of sulfuric acid in the above step (1), the oxide film can be removed by etching and at the same time the metal contained in the oxide film can be removed by etching. Here, since the oxide film is formed, the amount of etching of the substrate itself with hydrogen fluoride can be kept low. Here, the mixing ratio and temperature of the second cleaning liquid are not particularly limited as long as the etching function is satisfied. Buffered hydrogen fluoride obtained by diluting hydrofluoric acid (aqueous solution of hydrogen fluoride) with ultrapure water. An acid aqueous solution (BHF) can also be used.
[0024]
Next, as shown in the step (4) of FIG. 1, the quartz glass substrate is immersed in ultrapure water to remove particles generated by the etching in the step (3).
[0025]
Next, as shown in FIG. 1 (5), the quartz glass substrate is immersed in the third cleaning liquid accommodated in the third cleaning container. The third cleaning liquid is a mixed liquid in which ammonia (NH ₄ OH), hydrogen peroxide water (H ₂ O ₂ ), and ultrapure water (H ₂ O) are mixed at a volume ratio of 1: 1 to 5. The temperature of the mixed solution was 45 ° C., and the immersion time was 7 minutes. By this step, it is possible to remove particles that could not be removed in the cleaning step with ultrapure water in the above-described step (4). Here, the mixing ratio and temperature of the third cleaning liquid are not particularly limited as long as the particle removal function is satisfied.
[0026]
Next, as shown in the step (6) of FIG. 1, the third cleaning liquid in the step (5) is removed by immersing the quartz glass substrate in ultrapure water.
[0027]
Next, as shown in the process of FIG. 1 (7), the quartz glass substrate is immersed in the fourth cleaning liquid accommodated in the fourth cleaning container. The fourth cleaning liquid is a mixed liquid in which hydrochloric acid (HCl), hydrogen peroxide water (H ₂ O ₂ ), and ultrapure water (H ₂ O) are mixed at a volume ratio of 1: 1 to 6. The temperature of the mixed solution was 70 ° C., and the immersion time was 5 minutes. Through this step, the metal impurities adhering to the glass substrate are oxidized, dissolved as ions in the cleaning liquid, and removed. Here, the mixing ratio and temperature of the fourth cleaning liquid are not particularly limited as long as the function of removing particles is satisfied.
[0028]
Next, as shown in the step (8) of FIG. 1, the fourth cleaning liquid in the step (7) is removed by immersing the quartz glass substrate in ultrapure water. Thereafter, as shown in FIG. 1 (9), the substrate is dried by pulling up the atmosphere of isopropyl alcohol while draining water.
[0029]
Through the above steps, the cleaning of the quartz glass substrate is completed.
[0030]
In the above-described embodiment, the cleaning liquid having hydrogen fluoride is used in the step (3) and the cleaning liquid having ammonia is used in the step (5). However, this order may be reversed.
[0031]
(Electrode substrate manufacturing method and liquid crystal device using the same)
A liquid crystal device in which a TFT array substrate as an electrode substrate manufactured using a glass substrate cleaned by the above-described cleaning method is incorporated as an example will be described below.
[0032]
First, the structure of the liquid crystal device will be described with reference to FIG. FIG. 2 is a longitudinal sectional view of the liquid crystal device.
[0033]
As shown in FIG. 2, the liquid crystal device 200 is configured such that a TFT array substrate 10 as an electrode substrate and a counter substrate 20 are disposed to face each other, and a liquid crystal layer 50 is sandwiched between the two substrates. On the TFT array substrate 10 and the counter substrate 20, alignment films 16 and 22 made of polyimide that determine the initial alignment state of the liquid crystal layer are formed on the side in contact with the liquid crystal layer 50, respectively.
[0034]
The TFT array substrate 10 includes a thin film transistor (hereinafter referred to as TFT) 30 as a plurality of switching elements and a plurality of pixel electrodes 9 connected to each TFT 30 on a quartz substrate 60 cleaned by the above-described cleaning method. Has been. The TFT 30 includes a semiconductor layer 1, a gate insulating film 2, and a gate electrode 3 a disposed on the gate insulating film 2. In the semiconductor layer 1, a source region 1b and a drain region 1c are arranged on both sides of the channel region 1a. A plurality of scanning lines 3 are arranged on the gate insulating film 2, and a part of the scanning lines 3 is arranged corresponding to the channel region and functions as the gate electrode 3a described above. A first interlayer insulating film 4 is disposed so as to cover the scanning line 3, and a data line 6 is disposed on the first interlayer insulating film so as to intersect the scanning line 3. A part of the data line 6 is electrically connected to the source region of the semiconductor layer by a contact hole 5 formed in the gate insulating film 2 and the first interlayer insulating film 4. Further, a second interlayer insulating film 7 is disposed on the data line 6, and the above-described pixel electrode 9 is disposed on the second interlayer insulating film. The pixel electrode 9 is electrically connected to the drain region 1 c through the contact hole 8.
[0035]
On the other hand, in the counter substrate 20, the light shielding layers 23 are arranged on the low alkali glass substrate 70 in a matrix corresponding to the scanning lines 3 and the data lines 6 formed on the TFT array substrate 10. Further, the counter electrode 21 and an alignment film 22 formed by aligning a polyimide film as an alignment film material are sequentially laminated on the substrate 70 so as to cover the light shielding layer 23. Here, the glass substrate cleaning method described above can also be used for the low alkali glass substrate used for the counter substrate 20.
[0036]
In the liquid crystal device configured as described above, a clean substrate without adhesion of impurities is used as the substrate 60, so that there is no influence on the TFT characteristics caused by the impurity metal or the like adhered to the substrate 60. A high-quality liquid crystal device free from display defects such as defects and line defects can be obtained.
[Brief description of the drawings]
FIG. 1 is a process diagram illustrating a glass substrate cleaning method in the present embodiment.
FIG. 2 is a longitudinal sectional view of a liquid crystal device.
[Explanation of symbols]
10 ... TFT array substrate 20 ... Counter substrate 30 ... TFT

Claims (3)

A method for manufacturing a liquid crystal device, comprising: a pair of substrates comprising a quartz substrate on which a plurality of switching elements are formed; a counter substrate disposed opposite to the quartz substrate; and a liquid crystal layer sandwiched between the pair of substrates. Because
(A) washing the quartz substrate with sulfuric acid or a mixed solution of sulfuric acid and hydrogen peroxide;
(B) cleaning the quartz substrate with hydrogen fluoride or a mixture of hydrogen fluoride and hydrogen peroxide;
(C) cleaning the quartz substrate with ammonia or a mixed solution of ammonia and hydrogen peroxide;
(D) cleaning the quartz substrate with hydrochloric acid or a mixed solution of hydrochloric acid and hydrogen peroxide;
(E) A method of manufacturing a liquid crystal device, wherein the step of forming the switching element on the quartz substrate is performed in this order. The counter substrate is made of a low alkali glass substrate,
(F) cleaning the counter substrate with sulfuric acid or a mixed solution of sulfuric acid and hydrogen peroxide;
(G) cleaning the counter substrate with hydrogen fluoride or a mixture of hydrogen fluoride and hydrogen peroxide;
(H) cleaning the counter substrate with ammonia or a mixed solution of ammonia and hydrogen peroxide;
(I) cleaning the counter substrate with hydrochloric acid or a mixed solution of hydrochloric acid and hydrogen peroxide;
(J) The method of manufacturing a liquid crystal device according to claim 1, wherein the step of forming a light shielding layer on the counter substrate is performed in this order.   The method for manufacturing a liquid crystal device according to claim 1, wherein a semiconductor layer of the switching element is formed on the quartz substrate.

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