Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Patent
1995-01-05
1996-02-27
Kunemund, Robert
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
117 94, 117 97, 117915, 437974, C30B 2304
Patent
active
054939860
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates generally to the fabrication of Active Matrix Flat Panel Display (AMFPD) devices, and more particularly, to a method of providing VLSI-quality crystalline semiconductor substrates for use in the production of AMFPDs, of which Active Matrix Liquid Crystal Displays (AMLCDs) are given as an example of application.
BACKGROUND OF THE INVENTION
It is widely acknowledged that the most important cause of reduction in yield in high volume production of large area AMFPDs is the high number of damaged active devices. The main causes for having damaged devices are the high defect density and also the grain boundaries that exist in the material which the substrates are made of. These causes place unavoidable limits on device dimension down-scaling, and therefore on circuit redundancy, as well as pixel size and density.
AMFPD devices are currently fabricated on amorphous silicon substrates. The use of amorphous silicon results from the fact that it is not possible to produce crystalline substrates by simply depositing silicon on an amorphous starting material such as glass. Although it is possible to obtain polycrystalline substrates, their fabrication requires more expensive starting materials to be used and/or more processing steps to be applied.
The standard LCD fabrication has been disclosed by W. C. O'Mara in "Active Matrix Liquid Crystal Displays Part I: Manufacturing Process", Solid State Technology December 1991, pp. 64-69, and statistics for the causes of failure of assembled panels are reported therein.
In the article "Present and Future Trend of Electron Device Technology in Flat Panel Display" by T. Uchida, IEEE IEDM Technical Digest 1991, pp. 1.2.1-1.2.6, there is disclosed a formula for the yield of LCD panels as a function of the defect density, circuit redundancy, pixel density, and total area of the panel.
The possibility of having a high quality crystalline semiconductor substrate, like the silicon wafers employed in VLSI technology, would drastically reduce the surface defect density, with a consequent reduction in the number of damaged devices and thereby a major improvement in the manufacturing yield.
SUMMARY OF THE INVENTION
The object of the present invention is a method of providing VLSI-quality crystalline substrates for use in mass production of AMFPDs.
Another object of the invention is to provide VLSI-quality crystalline substrates which are effective to improve the quality of transmission type AMFPDs.
These and other objects are attained in accordance with this invention by a method of providing a VLSI-quality crystalline substrate comprising a lithographic step to define the substrate areas which are not to be used for implementing active devices and the selected areas are etched to a certain depth and filled with a transparent material, such as silicon dioxide. After a planarization operation which uncovers the unetched silicon area and provides a flat surface, the wafers next undergo all the processing steps known per se for realizing the active matrix. Thereafter, the back sides of the wafers are thinned and polished with the previously deposited silicon dioxide acting as a polish stop. After being sawed to a sized rectangular format, the wafers are aligned on top of a glass substrate with their backsides facing the glass and with the spacing between their edges being smaller than what the distance a human eye can resolve. The wafers are permanently bonded to the glass substrate, and a conductive material is then deposited to make electrical interconnections between the wafer pieces. From then on, the usual AMLCD manufacturing procedures are performed.
The bonding operation can be performed using different techniques. For instance, the bonding operation can be performed at room temperature using a light-transparent glue, e.g. silicone, or at higher temperature using a wafer bonding technique known in the art of silicon-or-insulator technology. It is to be noted that when using a wafer bonding technique, the active devices may be
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