Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Including integrally formed optical element
Reexamination Certificate
2002-11-20
2004-07-27
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Including integrally formed optical element
C438S154000, C438S157000, C438S158000, C438S163000
Reexamination Certificate
active
06767755
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of producing an electrooptical device and also to a method of producing a driving substrate for such an electrooptical device, the method being particularly suitable for production of, for example, a liquid crystal display device having an active region and a passive region, wherein the active region including a thin-film insulating-gate field-effect transistor of dual-gate type (hereinafter referred to as dual-gate MOSTFT)or of a bottom-gate type (hereinafter referred to as bottom-gate MOSTFT) using a single-crystal silicon layer grown by graphoepitaxy on an insulating substrate. The bottom-gate MOSTFT includes both an inverse-stagger NSI type and an inverse stagger ISI type MOSTFTs.
Various types of active-matrix liquid crystal displays are known: for example, a liquid crystal display having a display section using amorphous silicon for TFTs and an IC for an external driving circuit; a liquid crystal display integrating a driving circuit and a display section using solid-phase-deposited polycrystalline silicon for TFTs, as disclosed in Japanese Patent Application Laid-Open No. 6-242433); and a liquid crystal display device integrating a driving circuit and a display section using excimer laser annealing polycrystalline silicon TFTs, as disclosed in Japanese Patent Application Laid-Open No. 7-131030.
Although these known amorphous silicon TFTs have high productivity, they are not suitable for production of p-channel MOSTFTs (hereinafter referred to as pMOSTFTs) due to a low electron mobility of 0.5 to 1.0 cm
2
/v·sec. Since a peripheral driving section using pMOSTFTs and a display section cannot be formed on the same substrate, the driver IC must be an external component, which is mounted by, for example, a tape automated bonding (TAB) method, causing an impediment to reduction of the cost. This configuration inhibits production of high-resolution devices. Furthermore, the electron mobility as small as 0.5 to 1.0 cm
2
/v·sec can produce only a small ON current; hence, the size of the transistors in the display section is inevitably large, resulting in a small aperture ratio of pixels.
Conventional polycrystalline silicon TFTs have an electron mobility of 70 to 100 cm
2
/v·sec and can facilitate production of high-resolution devices, so that liquid crystal displays (LCDs) which use polycrystalline silicon and which are integrated with driving circuits are becoming conspicuous. The above electron mobility, however, is insufficient for driving a large LCD of 15 inches or more, and thus ICs for an external driving circuit are still required.
TFTs using polycrystalline silicon formed by a solid-phase deposition process require annealing at a temperature of 600° C. or more for ten or more hours and thermal oxidation at approximately 1,000° C. to form a gate SiO
2
layer, necessitating the-use of a semiconductor production apparatus. Thus, the wafer size is limited to 8 to 12 inches and the use of expensive heat-resistant quartz glass is inevitable, causing an impediment to reduction in the cost. Thus, the use of such TFTs is limited-to EVF and audiovisual (AV) projectors.
Polycrystalline silicon TFTs produced by excimer laser annealing have many problems, including unstable output of the excimer lasers, low productivity, increasing price of the apparatus with increasing size, low yield and low quality.
These problems are pronounced when large glass substrates having a side length of, for example, 1 meter are used.
SUMMARY OF THE INVENTION
It is an object of the present invention is to make it possible to produce an active matrix substrate incorporating a high-performance driver, as well as an electrooptical device which is typically a display thin-film semiconductor device using such an active matrix substrate, through a uniform deposition of a single-crystal silicon layer having high electron/hole mobility particularly in a peripheral-driving-circuit section.
It is also an object of the present invention to implement a structure in which a display section and a peripheral-driving-circuit portion are integrated, wherein the display section comprises an n-channel MOSTFT (referred to as “nMOSTFT”, hereinafter) or a pMOSTFTs employing an LDD (Lightly Doped Drain) structure having high switching characteristic and operable with reduced leak current, or a complementary insulating gate field effect transistor (referred to as cMOSTFT) having high driving performance, while the peripheral-driving-circuit is constituted by a cMOSTFT, nMOSTFT, pMOSTFT or a combination thereof.
It is also an object to implement a large-size display panel having high image quality, high definition, narrow peripheral frame and high efficiency, while allowing the use of a large-sized glass substrate having a comparatively low distortion point, and while achieving a high yield and reduction in the production cost due to elimination of necessity for the use of expensive production facilities, as well as easy control of the threshold value which permits reduction in the electrical resistance to offer high-speed of operation and greater size of the display.
To these ends, according to one aspect of the present invention, there is provided a method of producing an electrooptical device having a first substrate, i.e., a driving substrate, carrying a display section provided with pixel electrodes, e.g., pixel electrodes arranged in the form of a matrix, and a peripheral-driving-circuit section provided on a periphery of the display section, a second substrate, i.e., a counter substrate, and an optical material such as a liquid crystal disposed between the first substrate and the second substrate, as well as a method for producing the driving substrate for such an electrooptical device; the method comprising the steps of: a gate-forming step for forming a gate portion including a gate electrode and a gate insulating film on one face of the first substrate; a step-forming step for forming a step difference on the one face of the first substrate; a layer-forming step for forming a polycrystalline or amorphous silicon layer having a predetermined thickness on the first substrate having the gate portion and the step difference and then forming a low-melting-point metal layer on or under the polycrystalline or amorphous silicon layer, or of forming a low-melting-point metal layer containing silicon on the first substrate having the step difference; a heating step for dissolving silicon of the polycrystalline or amorphous layer or of the low-melting-point metal layer into the low-melting-point metal layer by heating; a deposition step for depositing on the first substrate a single-crystal semiconductor layer by allowing the silicon of the polycrystalline or amorphous silicon layer or of the low-melting-point metal layer to grow by graphoepitaxy by a cooling treatment using as a seed the step difference on the substrate; a treating step-for effecting a predetermined treatment on the single-crystal semiconductor layer, thereby forming a channel region, a source region and a drain region; and a step for forming a first thin-film transistor MOSTFT) of dual-gate type having the gate portions on the above and below the channel region and constituting at least part of the peripheral-driving-circuit section. In accordance with the present invention, the thin-film transistor may be either a field effect transistor (FET) or a bipolar transistor, and the FET may be either a MOSFET or a junction type.
The present invention offers the following remarkable advantages (A) to (G), by virtue of the use of a single-crystal silicon layer as a dual-gate MOSTFT of a peripheral driving circuit as a driving substrate such as an active matrix substrate or as a dual-gate MOSTFT of a peripheral driving circuit of an electrooptical device such as an LCD of the type having a display-driver integrated structure, wherein the single-crystal silicon layer is graphoepitaxially grown from a polycrystalline or amorphous silicon layer or from a low-melting-point metal layer using the step di
Sato Yuuichi
Yagi Hajime
Yamanaka Hideo
Yamoto Hisayoshi
Picardat Kevin M.
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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