The liquid crystal displays (LCD) are widely applied in electrical products, such as digital watches, calculator, etc. for a long time. Moreover, with the advance of techniques for manufacture and design, the thin film transistors-liquid crystal display (TFT-LCD) is introduced into the portable computers, personal digital assistants, color televisions, and replaced gradually the kinescopes that are used for conventional displays. However, following the design rules of TFT-LCD tend to large scale, there are a lot of problems and challenges, such as low yields and low throughput, in manufacturing and developing TFT-LCD apparatus.
In general, the TFT-LCD comprises a bottom plate on which formed with thin film transistors and pixel electrodes, and a top plate on which constructed with color filters. The liquid crystal molecules are filled between the top plate and the bottom plate. In the operation, a signal voltage is applied to the TFT that is the switching element of each unit pixel. The TFT receives the signal voltage, it turns on so that data voltage carrying image information can be applied to the corresponding pixel electrode and the liquid crystal via the TFT. When the data voltage is applied to the TFT, the arrangement of the liquid crystal molecules is changed, thereby changing the optical properties and displaying the image.
There is a requirement to reduce the photolithography processes in manufacturing TFT devices for decreasing the process cycle time and cost at all times. Namely, it is better to reduce the number of the photomasks used in forming the TFT devices. According to the prior art of manufacturing inverted gate TFTs device for a TFT-LCD, six or more photomasks are needed. As shown in FIG. 1, a first metal layer is defined to serve as the gate structure 24, and an insulating layer 28 is formed on the substrate 22 to cover the gate structure 24. An a-silicon layer 30 is formed above the insulating layer 28 and the gate structure 24. An n+ a-silicon layer 32 is formed above the a-silicon layer 30. Then, an ITO layer 34 is deposited on the insulating layer 28 to form the pixel electrode 26 and connect to the S/D structures formed in latter steps. Then, the S/D structures 38 are formed on the n+ a-silicon layer 32 by patterning the second metal layer, the connection structure 40 are formed on insulating layer 28 and filled into the contact hole 36 simultaneously. Moreover, a passivation layer 42 is formed on the substrate 22 to cover the S/D structures 38 and the a-silicon layer 32.
It is noted that the TFT device as illustrated in FIG. 1 is manufactured by using six photomasks. Wherein the first photomask is used to define the gate structure 24, the second photomask is used to define the a-silicon layer 30 and n+ a-silicon layer 32, the third photomask is used to define the pattern of the ITO layer 34, the fourth photomask is used to define the contact hole 36 on the insulating layer 28, the fifth photomask is used to define the S/D structures 38 and the connection structure 40, the sixth photomask is used to pattern the passivation layer 42. However, much process cycle time and cost are required for using six photomasks to manufacture the TFT device.
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