DE19754784B4 - Process for producing a matrix from thin-film transistors with storage capacities - Google Patents

Abstract

Method for producing a matrix from thin-film transistors with storage capacitances (C), in particular for liquid crystal screens, characterized in that photostructurable materials (16, 17) are used in each case as the material for the passivation of the matrix and the pixel electrodes.

Description

State of the art

The invention is based on one Method for producing a matrix from thin-film transistors with storage capacities, in particular for liquid crystal screens according to the genus of the independent Claim.

From the DE 43 10 640 C1 and from the DE 43 39 721 A1 Methods for producing a matrix of thin-film transistors with storage capacities for liquid crystal screens are known, in which the manufacturing effort is limited to three or four by reducing the number of necessary photolithographic mask steps. In the known processes, a-Si: H is used as the semiconductor for the thin-film transistors. However, a reduction in the manufacturing outlay for the production of a thin-film transistor matrix by saving other process steps, such as etching, coating and cleaning, is not provided in these methods.

From the JP 61292183 A passivation from a photosensitive resin is known.

The inventive method with the characteristic Characteristics of the independent Has claim against the known methods have the advantage that fewer coating and etching steps and steps for photoresist removal are necessary.

This is achieved by using photostructurable materials as the material for the passivation of the matrix and the pixel electrodes. Compared to the known methods, in which SiN _{x is used} as passivation and ITO is usually used as pixel electrodes, one coating step, namely a PECVD method for SiN _x and one sputtering of ITO, can each have one etching step, namely dry etching of SiN _x and wet etching from ITO, and one step each to wash off the photoresist mask and the associated systems can be saved.

Through the measures listed in the dependent claims are advantageous further developments and improvements of the independent claim specified procedure possible.

So it’s particularly beneficial to use polymers as photostructurable materials. in this connection can for passivation is a photosensitive, transparent and highly insulating Polymer and for producing the pixel electrode an electrical conductive Polymer can be used.

By mechanical rubbing treatment of the conductive Polymers can also an orientation of the liquid crystal be made so that the application of an additional Orientation layer, for example a polymid, is completely eliminated can.

• – Aufbringen und Strukturieren einer ersten leitfähigen Schicht als Zeilen der Dünnschichttransistor-Matrix, als Gate-Kontakte der Transistoren und als Elektroden der Speicherkapazitäten,
• – Aufbringen eines Gate-Isolators;
• – Aufbringen einer undotierten Halbleiterschicht,
• – Aufbringen einer P- oder N-dotierten Halbleiterschicht als Drain- uns Source-Kontakte der Transistoren,
• – Aufbringen und Strukturieren einer weiteren elektrisch leitfähigen Schicht für die Spalten der Dünnschichttransistor-Matrix, für die Drain- und Source-Kontakte und die Gegenelektrode der Speicherkapazitäten,
• – Strukturieren der dotierten Halbleiterschicht und der undotierten Halbleiterschicht,
• Aufbringen, Belichten und Entwickeln eine photoempfindlichen, transparenten und isolierenden Materials,
• – Aufbringen und Belichten eines leitfähigen, photoempfindlichen, transparenten Materials.

In a preferred manufacturing process, the individual steps are as follows:

• Applying and structuring a first conductive layer as rows of the thin-film transistor matrix, as gate contacts of the transistors and as electrodes of the storage capacitors,
• - application of a gate insulator;
• - application of an undoped semiconductor layer,
• Applying a P- or N-doped semiconductor layer as drain and source contacts of the transistors,
• Applying and structuring a further electrically conductive layer for the columns of the thin-film transistor matrix, for the drain and source contacts and the counter electrode of the storage capacitors,
• Structuring the doped semiconductor layer and the undoped semiconductor layer,
• Applying, exposing and developing a photosensitive, transparent and insulating material,
• - Application and exposure of a conductive, photosensitive, transparent material.

Preferably, a-Si: H can be used as the semiconductor and SiN _x can be used as the gate insulator.

Because of the significant reduction the number of process steps significant cost savings and an increase in Achieve yield.

An embodiment of the invention is shown in the drawing and explained in more detail in the following description. 1 shows a cross section through a pixel of a liquid crystal screen in various stages of manufacture.

In in 1 a) shown manufacturing stage are on a glass substrate 10 a first metallization layer 11 , for example 200 nm MoTa, sputtered on and structured as a row line and as a storage capacitor line. Then a layer sequence was made from a gate insulator 12 , for example 350 nm SiN _x , an intrinsic semiconductor 13 , for example 150 nm ia-Si, and a highly doped semiconductor 14 , for example 50 nm n ⁺ -a-Si, and a cover metallization 15 , for example 200 nm Mo, applied.

1 b) shows the structure after etching the cover metal layer 15 and the doped semiconductor layer 14 as a column line, drain / source contacts D, S and as a cover electrode of the storage capacitor C.

In the process stage after 1 c) are the semiconductor layer 13 and the gate dielectric 12 shown in a single plasma etching step for separating the individual thin-film transistors of the pixels and for exposing the connection areas of the gate lines and storage capacitor lines.

In 1 d) was a photosensitive, transparent and highly insulating polymer on the structure 16 spun on, exposed, developed and annealed. For example, a so-called Photo-BCB can be used as the polymer. The task of the polymer is to passivate and planarize the structure. The top electrode of the storage capacitor C, which here also represents the drain contact of the thin-film transistor, and the connection regions of the column and row lines are stripped again by the polymer in the exposure and development step.

According to 1 e) then becomes a conductive, photosensitive, transparent polymer 17 spun as a pixel electrode. For this purpose, for example, a polymer called Bayer PEDT / PSS can be used. Exposing the areas between the pixel electrodes with UV light through a photomask causes the conductive polymer to be converted into an insulation layer. The insulating areas of the polymer are in 1 e) shown with dots. If a photosensitive conductive polymer is used, the areas between the pixel electrodes can also be removed by means of a developer step. The individual pixel electrodes are thus effectively electrically separated from one another. After an annealing step of the polymer PEDT / PSS at approx. 130 ° C, the unexposed areas of the pixel electrodes have a sheet-related sheet resistance of 200-1000 Ω and a transparency of greater than 70% in the visible area, based on a dry layer thickness of 900 nm the dry layer thickness, an increase in the transmission is possible. The layer 17 can then be rubbed mechanically so that it can bring about an orientation of the liquid crystal. This also means that there is no need to apply an additional orientation layer.

The structuring of the gate dielectric 12 can - as shown - together with the structuring of the undoped semiconductor 13 or with passivation 16 can be carried out as a mask in an additional plasma etching process.

Claims (7)

A process for producing a matrix of thin film transistors with storage capacities (C), particularly for liquid crystal displays, characterized in that as material for the passivation of the matrix and the pixel electrodes each photopatternable materials ( 16 . 17 ) be used. A method according to claim 1, characterized in that as photostructurable materials ( 16 . 17 ) Polymers are used. A method according to claim 2, characterized in that a photosensitive, transparent and highly insulating polymer ( 16 ) and an electrically conductive polymer to produce the pixel electrodes ( 17 ) be used. A method according to claim 3, characterized in that the conductive polymer ( 17 ) is subjected to a mechanical rubbing treatment. Method according to one of claims 1 to 4, characterized by the steps: - applying and structuring a first conductive layer ( 10 ) as rows of the thin-film transistor matrix, as gate contacts (G) of the transistors and as electrodes of the storage capacitors (C), - application of a gate insulator ( 12 ), - application of an undoped semiconductor layer ( 13 ), - application of a P- or N-doped semiconductor layer ( 14 ) as drain and source contacts (D, S) of the transistors, - application and structuring of another electrically conductive layer ( 15 ) for the columns of the thin-film transistor matrix, for the drain and source contacts (D, S) and the counter electrodes of the storage capacitors (C), - structuring of the doped semiconductor layer ( 14 ) and the undoped semiconductor layer ( 13 ), - application, exposure and development of a photosensitive, transparent and insulating material ( 16 ), - application and exposure of a conductive, photosensitive, transparent material ( 17 ). Method according to Claim 5, characterized in that a-Si: H is used as the semiconductor and SiN _{x is} used as the gate insulator. Method according to claim 5 or 6, characterized in that the gate insulator ( 12 ) with the photostructurable passivation ( 16 ) is structured as a mask in a separate step.