Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
1997-10-07
2001-01-16
Nguyen, Nam (Department: 1753)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S586000
Reexamination Certificate
active
06174745
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of manufacturing, in four masking steps, an active matrix for a liquid crystal display screen whose control transistors are of the top-gate type. The liquid crystal display screen obtained by means of this method is particularly suitable for use in image projection systems.
Direct-vision or projection liquid crystal display screens are generally composed of rows (selection rows) and columns (data rows), with the pixel electrodes connected to these rows via transistors situated at their intersections. The gates of these transistors constitute the selection rows and are controlled by peripheral control circuits which scan the rows and turn on the transistors of each row in that the electrodes are biased by means of the data rows connected to the other peripheral control circuits, and the optical properties of the liquid crystal between these electrodes and the counter electrode (or the reference electrode) are modified so that images are formed on the screen.
OBJECTS AND SUMMARY OF THE INVENTION
The liquid crystal display screens used in projection systems are subject to considerable stresses because of the power of the required white light beam which may range as high as 300 mW/cm
2
. In the relevant case, in which the active matrix is constituted by top-gate thin-film transistors, it is necessary that, if these transistors are to withstand these stresses, the photoconducting silicon is protected from the beam by an opaque mask and has a storage capacity which is parallel with the capacity of the liquid crystal of the elementary pixel.
However, in such liquid crystal display screens which are suitable for projection systems, there are still serious drawbacks such as the strong resistance of the ITO columns or the risks of ITO fracture.
It is an object of the invention to provide a simple and reliable method, comprising only 4 masking steps, of manufacturing an active thin-film transistor (TFT) matrix in amorphous silicon a-Si in a direct step, taking the above-mentioned stresses into account and remedying the drawbacks of the existing solutions.
To this end, the invention relates to a method of manufacturing active matrix screens constituted by pixels controlled by transistors whose sources and drains constitute a column or a pixel electrode and the gate constitutes a selection row, and is wherein said method comprises the steps of:
depositing and etching a first opaque layer on a transparent insulating plate so as to mask the semiconductor layer from the transistor to be realized; this first layer preferably being conducting so as to realize a single storage capacity, and being etched so as to realize a grid to be biased by external circuits;
depositing an insulating transparent layer; on said grid
depositing and etching a transparent conducting layer on said insulating layer so as to realize pixel electrodes, sources and drains and external output tracks;
forming doped regions on the sources and drains to form ohmic contact, subsequently depositing an intrinsic semiconductor material and a gate insulating material, and etching of the resultant assembly in such a way that the external tracks of the active matrix are not covered;
depositing an opaque conducting layer on said resultant etched assembly and etching said layer; realizing the rows of the active matrix as well as the gates of the transistors, and
then etching the semiconductor etched layer and gate insulating layer by using the opaque conducting layer as a mask.
An opaque mask masking the semiconducting parts of the active matrix is preferably etched on the counter electrode.
This method is improved in that, in the first step of etching the combination of semiconductor layer and gate insulating layer, apertures are provided in this combined layer so as to establish contacts between the transparent conducting layer and the opaque conducting layer.
A supplementary step may be added, which consists of passivating the assembly by depositing an insulating layer through, for example, a metallic mask, thus passing only beyond the contacts required for controlling the active matrix.
The invention also relates to a flat screen obtained by means of this method.
The present invention will be better understood and additional advantages will be apparent from reading the following description illustrated by means of the following Figures:
REFERENCES:
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patent: 5466617 (1995-11-01), Shannon
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patent: 5796116 (1998-08-01), Nakata et al.
patent: 5821133 (1998-10-01), Kawai et al.
patent: 5830785 (1998-11-01), Sanson et al.
Szydlo Nicolas
Templier François
Vignolle Jean-Michel
Cantelmo Gregg
Fox John C.
Nguyen Nam
Spain Norman N.
U.S. Philips Corporation
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