1. Field of the Invention
This invention relates to the manufacturing process for ultra slim electrooptic display device units such as high intensity, high definition and sophisticated transmissive liquid crystal display device units (LCD; Liquid Crystal Display), semi-transmissive liquid crystal display device units, highly reflective liquid crystal display device units, top surface luminous organic EL (Electro Luminescence) display device units and under surface luminous organic EL display device units.
2. Description of Related Art
In the case of a transmissive, high temperature polycrystalline silicon (which we will call “Poly-Si” from here on) TFT (thin Film Transistor) LCD, a micro crystal Si thin film is formed by decreased pressure CVD (Chemical Vapor Deposition), etc. on quartz glass. After converting to amorphic Si, a large particle diameter poly Si thin film is formed by ion implantation using the solid phase deposition method, for example at a temperature of 620° C. for 12 hours and the LCD peripheral circuitry and the display element, etc. will be formed on the film.
In the case of transmitted or reflective low temperature Poly-SiTFT LCD or organic EL (Electro Luminescence) displays (which we will call “Organic EL” from here on), an amorphous Si thin film is formed on a low strain point glass such as borosilicate glass or aluminosilicate glass by plasma CVD, etc. Then a large particle diameter Poly-Si thin film will be formed via crystallization by excimer laser anneal (ELA) and the LCD peripheral circuitry and display element, or the organic EL peripheral circuitry and the display elements, etc. are formed on the film.
However, in the case of the high temperature Poly-SiTFT LCD, the low temperature Poly-SiTFT LCD or the organic EL, the LCD or organic EL peripheral circuitry is formed on the Poly-Si thin film where the high electron and positive hole mobility is not high in comparison with monocrystalline Si. Because of this, the device quality and especially high speed operational characteristics become a problem.
In recent years, a LCOS (Liquid Crystal On Silicon) also called reflective LCD has been adopted for projectors, etc. This is a result of utilizing the high electron and positive hole mobility of monocrystalline Si. The LCOS which utilizes general purpose MOSLSI technology, works with not only the peripheral circuitry and the display element on a monocrystalline Si substrate surface but also with functions such as video signal process circuitry and memory circuitry, etc. It has characteristics such as high intensity, high definition and advanced functionality.
However, with LCOS, it is easy to have problems with picture quality and with reliability resulting from TFT leak electric current due to strong incident light. As a result, there is an increase in manufacturing man-hours, and a yield and production decrease due to the light leakage issue. Although we can think of adopting a SOI (Silicon on Insulator) substrate (for instance, please see the patent document 1˜6) a monocrystalline Si substrate does not achieve optical transparency in this case. It is limited to a reflective LCD and an upper surface luminous organic EL.
This inventor has proposed a method of producing a transmissive LCD using a monocrystalline Si substrate in patent document 7. In this case, the transmissive LCD is formed by embedding the image display elements which have internal peripheral circuitry and a reflective film on a monocrystalline Si substrate surface in a transparent resin. By grinding and polishing the other side, a monocrystalline Si thin film matrix array is formed, to which a color filter substrate is attached with transparent resin.
(Patent Document 1) U.S. Pat. No. 2,608,351 Official Bulletin
(Patent Document 2) Open Patent Tokukaihei #11-195562 Official Bulletin
(Patent Document 3) U.S. Pat. No. 3,048,201 Official Bulletin
(Patent Document 4) Open Patent Tokukai #2000-196047 Official Bulletin
(Patent Document 5) Open Patent Tokukai #2001-77044 Official Bulletin
(Patent Document 6) Open Patent Tokukaihei #5-211128 Official Bulletin
(Patent Document 7) U.S. Pat. No. 3,218,861 Official Bulletin (Open Disclosure for the Patent)
However, in case where a transmissive LCD which is composed of the peripheral circuitry and the image element display on the surface of a monocrystalline Si substrate such as described in the patent document 7 is used in a unit such as a projector that reflects strong light, the monocrystalline Si substrate has high electron and positive hole mobility and very high sensitivity which causes a problem with TFT current leakage when exposed to strong incident light.
Even with a high intensity reflective LCD such as recent LCOS types, a problem with TFT current leakage of the display caused by strong incident radiation can be a problem. In the future, it is still possible to have a problem with TFT current leakage as a result of internally generated light as the intensity strengthens even with an under surface luminous organic EL.