Matrix substrate, liquid crystal display device using it,...

Details Matrix substrate, liquid crystal display device using it,... Matrix substrate, liquid crystal display device using it,...

2002-05-13

2004-10-26

Chowdhury, Tarifur R. (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S158000, C349S146000, C257S549000

Reexamination Certificate

active

06809790

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a matrix substrate, a liquid crystal device using the substrate, and a method for producing the matrix substrate.
2. Related Background Art
The world of today is a multimedia world, and equipment for communication by image information is becoming more and more important. Among others, the liquid crystal display devices are drawing attention because of their slimness and low power consumption. The liquid crystal display industry has grown to be a basic industry comparable to the semiconductor industry. Liquid crystal display devices are mainly used for 10-inch notebook-size personal computers at present. It is expected that liquid crystal display devices of larger screen sizes will be used not only for personal computers, but also for workstations and televisions for home use in the future. With an increase in screen size, however, manufacturing equipment becomes expensive, and, in addition, electrically exacting characteristics are demanded for driving of such large screens. The manufacturing cost will thus increase abruptly in proportion to the square to cube of the size with increasing screen size.
Recently, attention has been drawn to a projection method for preparing a compact liquid crystal display panel and optically enlarging a liquid crystal image to display an enlarged image. This is because the microstructure tendency of semiconductors permits decrease in size, improvement in the characteristics, and decrease in the cost, similar to the scaling rule to improve performance and cost. From these aspects, in the case of the liquid crystal display panel of the TFT type, TFTs have to be compact and have sufficient driving force, and transition is now occurring from TFTs using amorphous Si to those using polycrystal Si. Video signals of the resolution level conforming to the NTSC system, etc. used in ordinary televisions do not require so quick processing.
This allows not only the TFTs but also peripheral driving circuits such as shift registers or decoders to be made of polycrystal Si, whereby liquid crystal display devices can be constructed in a monolithic structure of a display region and a peripheral driving circuit region. Polycrystal Si is inferior to single crystal Si, however. For realizing high definition televisions having a higher resolution level than the NTSC system or display of the XGA (eXtended Graphics Array) or SXGA (Super eXtended Graphics Array) class in resolution standards for computers by polycrystal Si, a shift register needs to be composed of a plurality of segments. In this case, noise, called ghost, appears in the display region at portions corresponding to borders between the segments. A solution to this problem is desired in this field.
On the other hand, focus is also drawn to display devices using a single crystal Si substrate, which can realize extremely high driving force as compared to display devices of the monolithic structure of polycrystal Si. In this case, the transistors of the peripheral driving circuitry have sufficient driving force, and thus the divisional driving described above is not necessary. This solves the problem of the noise and the like.
Even with either of these polycrystal Si and single crystal Si, a reflection-type liquid crystal device can be provided in such a structure that a reflection-type liquid crystal element is formed by connecting the drain of each TFT to a reflective electrode and interposing the liquid crystal between the reflective electrodes and a transparent common electrode and that horizontal and vertical shift registers for scanning of the liquid crystal element are formed on the same semiconductor substrate. The applicant of the present application filed Japanese Laid-Open Patent Application No. 9-73103 to disclose the reflection-type liquid crystal device using a substrate of polycrystal Si or single crystal Si. The invention disclosed in the application solves the following problems: when light is incident to a pixel electrode, the incident light is scattered in all directions by unevenness of the surface, and reflection efficiency of light thus becomes very small; and this unevenness of surface becomes the cause of alignment failure in a rubbing step of the alignment layer in a liquid crystal packaging process, and this results in causing alignment failure of the liquid crystal, so as to degrade the display image due to lowering of contrast.
In the Japanese Laid-Open Patent Application No. 9-73103, the pixel electrode surface is polished by chemical mechanical polishing (hereinafter referred to as “CMP”). This smooths the pixel electrode surface like a mirror-finished surface and makes the whole pixel electrode surface be in a common plane. This prevents the irregular reflection and alignment failure caused by the unevenness and thus permits display of an image with high quality.
A method for producing an active matrix substrate, disclosed in the Japanese Laid-Open Patent Application No. 9-73103, will be described referring to
FIGS. 39A
to
39
E and
FIGS. 40F
to
40
H.
FIGS. 39A
to
39
E and
FIGS. 40F
to
40
H show a pixel section and, at the same time as a step of forming the pixel section, the peripheral driving circuits such as the shift registers for driving the switching transistors in the pixel section can also be made on the same substrate.
An n-type silicon semiconductor substrate
201
with an impurity concentration of not more than 10
15
cm
−3
is locally thermally oxidized to form LOCOS
202
, and, with the LOCOS
202
as a mask, ions of boron are implanted in a dose of about 10
12
cm
−2
to form PWL
203
, which represents p-type impurity regions with an impurity concentration of about 10
16
cm
−3
. This substrate
201
is again thermally oxidized to form gate oxide film
204
having an oxide film thickness of not more than 1000 Å (FIG.
39
A).
Gate electrodes
205
made of n-type polysilicon doped with phosphorus of about 10
20
cm
−3
are formed, and thereafter ions of phosphorus are implanted in a dose of about 10
12
cm
−2
over the entire surface of substrate
201
to form NLD
206
, which represents n-type impurity regions having an impurity concentration of about 10
16
cm
−3
. Subsequently, using a patterned photoresist as a mask, ions of phosphorus are implanted in the dose of about 10
15
cm
−2
to form source and drain regions
207
,
207
′ having an impurity concentration of about 10
19
cm
−3
(FIG.
39
B).
PSG
208
, which is an interlayer film, is formed over the entire surface of substrate
201
. This PSG
208
can be replaced by NSG (Nondoped Silicate Glass)/BPSG (Boro-Phospho-Silicate Glass) or TEOS (Tetraethoxy-Silane). The PSG
208
is patterned to form contact holes immediately above the source and drain regions
207
,
207
′, Al is evaporated by sputtering, and thereafter the Al layer is patterned to form Al electrodes
209
(FIG.
39
C). In order to improve ohmic contact characteristics of the Al electrodes
209
with the source and drain regions
207
,
207
′, a barrier metal such as Ti/TiN is desirably placed between the Al electrodes
209
and the source/drain regions
207
,
207
′.
Plasma SiN
210
is deposited in a thickness of about 3000 Å over the entire surface of substrate
201
, and then PSG
211
is deposited in a thickness of about 10000 Å thereon (FIG.
39
D).
Using the plasma SiN
210
as a dry etching stopper layer, the PSG
211
is patterned so as to leave only separating regions between pixels, and thereafter the plasma SiN
210
is patterned by dry etching to form through holes
212
immediately above the Al electrodes
209
in contact with the drain regions
207
′ (FIG.
39
E).
Then a pixel electrode layer
213
is deposited in a thickness of not less than 10000 Å on the substrate
201
by sputtering or EB (Electron Beam) evaporation (FIG.
40
F). This pixel electrode layer
213
is a metal film of Al, Ti, Ta, W, or the like, or a compound film

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