Patent Application
20100214230
(a) Field of the Invention
The present invention is related to an ITO layer manufacturing process, known as a two-stage film process by crystallization, and more particularly, to an ITO layer provided with specific sheet resistance and/or thickness ITO layer structure best appropriately to be applied in a touch screen structure that delivers better environment durability property and better sheet resistance uniformity, lower sheet resistance variation, better scratch proof, and longer service life.
(b) Description of the Prior Art
Indium Tin Oxide (ITO) transparent conductive film is one of star products having research efforts and economic values and it is generally applied in car-laden LCD, touch panel, EMI RF shielding glass, liquid crystal wrist watch, liquid crystal panel on electric home appliance, solar cell, portable liquid crystal TV game unit, PDP, EL, LCD, and electrode for color filter.
The ITO is made by having indium oxide doped with small amount of tin oxide to have tin atoms to replace certain indium atoms existing in the structure of indium oxide. Therefore, in terms of the composition of its general structure, Indium oxide (In2O3) dominates. Indium oxide related to an oxide of semiconductor material not only presents a high band gap (Eg≧2.9 eV) for light to permeate but also contains high concentration of carriers and mobility. Of course, depending on the individual conductivity, the applied range of indium oxide varies. Conductive characteristic of the ITO layer essentially comes from two types of charge carriers, respectively tin doping and oxygen vacancy. That is, by having tin doping controlled at a constant amount, conductive characteristic varies depending on the charge carrier of oxygen vacancy. When the location of the lattice oxygen is not filled in oxygen vacancy in the ITO layer, two electrons otherwise bonded are then released to become free electrons; therefore, oxygen vacancy increases conductivity of ITO in taking a form of n-type donor. Concentration of oxygen vacancy will be affected by conditions of a sputtering process, e.g. vacuum and temperature; and the concentration of oxygen vacancy will also affect the charge and sheet resistance of the ITO layer as a whole.
Whereas demand of ITO transparent conductive film is increasing in the market, positively searching for a good and economic preparation process for ITO layer has been put on the top priority. As illustrated in
However, the crystalline ITO layer resulted from using high temperature sputtering in the prior art features high concentration of oxygen vacancy and good conductivity, but the film can best reach approximately 5-20 nm and is not thick enough when a specific sheet resistance (e.g. 500Ω/square) must be achieved; and its surface roughness, Ra, usually stays only in a range of 0.2˜0.5 nm and that is not rough enough. As a result, the ITO layer is not scratch resisting, friction resisting, and durable; meanwhile, rate of variation of its sheet resistance is comparatively greater for being subject to high temperature and high humidity environment. The consistence of the entire ITO layer is poor to create dispersion when applied in a touch screen to fail precise calculation of touch coordinates.
The single stage film process used by the prior art usually is applicable to formation of an ITO layer with lower sheet resistance, e.g., approximately a range of 20˜80052/square, and 200Ω/square inter alia. However, difficulties confront the manufacturing process of the prior art in the manufacturing an ITO layer with higher sheet resistance.
Furthermore, in the prior art, strength of the glass substrate is weakened since the glass substrate must be rapidly heated up at high temperature and completed with the sputtering process before cooling down rapidly while the sputtering temperature is too high for the plastic base material to handle. Therefore, application scope of the prior art is significantly compromised due to that it is not applicable to plastic base material
The primary purpose of the present invention is to provide an ITO layer manufacturing process that yields better environment durability property and better sheet resistance uniformity, scratch proof, and longer service life that is particularly applicable to the manufacturing of an ITO layer for touch screen.
To achieve the purpose, a substrate is prepared before going through ITO sputtering process in the sputtering chamber without heating (or at a temperature below the range of 200˜400° C. applied in the prior art) to form an ITO layer in amorphous state and finally the substrate is thermally treated for the ITO layer to turn into crystalline, known as a two-stage crystalline film process.
One efficacy of the present invention is that the substrate maintains its original strength since in the process the substrate is not experiencing the cycle of heating up and staying at high temperature for sputtering and then drastically cooled down.
Another efficacy of the present invention is that the ITO layer developed in the sputtering chamber is in its amorphous state under the process conditions without being heated up before the thermal treatment to turn into crystalline status; therefore, concentration of oxygen vacancy is lower than that made from the single stage crystalline film process of the prior art, thus is less vulnerable to heat and wet, i.e., better environment durability property; delivers better uniformity of the entire ITO layer, i.e., ITO layer uniformity having been improved, and lower variation rate of sheet resistance.
Another efficacy yet of the present invention is that the resultant ITO layer crystalline is complete and refine, containing comparatively larger grains, rougher surface of the ITO layer; and thus better friction resistant to better withstand scratch and provide longer service life.
The present invention essentially disclosing an ITO layer manufacturing process that delivers the ITO layer with better environment durability property and better sheet resistance uniformity, lower variation rate of sheet resistance, more scratch resistant and longer service life, is comprised of the following steps as also illustrated in
a. Preparing a substrate: the substrate may be related to a transparent glass or plastic substrate; if a glass substrate is selected, a Soda Lim Glass or a Quartz Glass is preferred; and if a plastic substrate is selected, a Polycarbonate (PC), polymethyl methacrylate (PMMA), or Polyethylene terephthalate (PET) is preferred, and PC inter alia. The cut glass substrate is cleaned first with detergent to rid of oil stains and dusts found on the surface and the glass substrate, and then the glass substrate is rinsed with deionized water (DI water) to eliminate residual detergent and impurities found on the surface of the glass substrate. The clean glass substrate is blown to dry using clean dry air (CDA) to rule out any residual water stain on the glass substrate while clearing off any dust attached to the surface of the glass substrate. The glass substrate is dried using a hot air knife and then properly stored for use.
b. An ITO layer process is provided on the surface of the substrate. A sputtering chamber is not heated or heated up to a temperature below the range 200° C.˜400° C. of the prior art to form the ITO layer on the surface of the substrate by means of a sputter to from a semi-finished product when the ITO layer is in its amorphous state. Wherein, the substrate may not be preheated before going through ITO layer sputtering process.
c. Thermal Treatment. The semi-finished product is then placed in or passes through a heating device (e.g., an oven) to be treated at a preset temperature depending on the nature of the individual substrate to form the ITO layer in different crystalline formation: (1) a crystalline ITO layer is formed on the glass substrate in thermal treatment for 30 minutes up to 3 hours at a temperature range of 150˜400° C., and 300˜400° C. is preferred; or (2) another crystalline state of ITO layer is formed on the plastic substrate in a thermal treatment provided at a temperature below 200° C., and 100˜160° C. is preferred for 10 minutes up to 2 hours. After the thermal treatment of (1) or (2), a finished product of crystalline ITO layer with a given conductivity is availed. As mentioned earlier, the two-stage crystalline film process yield a finished product with oxygen vacancy concentration lower than that from using the single stage film process. The finished product using the two-stage film process of the present invention has lower concentration of oxygen vacancy than that manufactured with single stage crystalline film process; therefore, the finished product using the manufacturing process of the present invention is less vulnerable to high heat and humidity while providing better environment durability property, thus the variation rate of sheet resistance is smaller resulting in good uniformity of the entire ITO layer.
Whereas in the single stage of crystalline film process of the prior art for preparation of the ITO layer, it takes to have the glass substrate heated up to a range of 200˜400° C. followed with sputtering at same high temperature before drastic cooling down to weaken the strength of the glass after the cycle of high temperature and drastic temperature drop. Furthermore, the single stage crystalline film process is not applicable to plastic substrate since the plastic substrate cannot take the high temperature process range process. In the present invention, a slow and stable thermal treatment is provided for ITO film process in the two-stage crystalline film process of the present invention, it is not necessary to heat up the substrate to a higher temperature range and drastic temperature drop after that; therefore, there is no problem of compromising the strength of the substrate.
Using of the two-stage crystalline film process for the preparation of the ITO layer, the sheet resistance range of the ITO layer may reach a range approximately of 200˜1500Ω/square, and 400˜600Ω/square inter alia. Furthermore, the film thickness of the ITO layer formed by using the manufacturing process of the present invention may reach a range approximately of 15˜50 nm, and 20˜35 nm inter alia.
A structure containing the ITO film produced to from the two-stage crystalline film process of the present invention involves having developed an ITO layer on a glass substrate; and the ITO layer is provided with an sheet resistance approximately of 200 up to 1500Ω/square and/or a film thickness of 15 up to 50 nm. The structure may be further applied in a structure of touch screen.
However, it is to be noted that the preferred embodiments disclosed in the specification and the accompanying drawings are not limiting the present invention; and that any construction, installation, or characteristics that is same or similar to that of the present invention should fall within the scope of the purposes and claims of the present invention.
