Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2000-04-06
2002-02-05
Pham, Long (Department: 2823)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S057000, C438S073000, C438S096000
Reexamination Certificate
active
06344370
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for fabricating a detection element for detecting light or radiations in which a semiconductor film is used, and a method for fabricating a two-dimensional image detector using the detection element.
BACKGROUND OF THE INVENTION
Conventionally known as a radiation-sensitive two-dimensional image detector for detecting images by means of radiations has been an apparatus composed of semiconductor sensors (detection elements for detecting radiations) arranged in two dimension that generate charges (electron-hole) upon detection of X-rays. Each semiconductor sensor is provided with an electric switch, and the electric switches are consecutively turned on line by line so that charges in each semiconductor sensor are read out line by line. The Japanese Publication for Laid-Open Patent Application 342098/1994 (Tokukaihei 6-342098 [Publication Date: Dec. 13, 1994]), for example, describes concrete structure and principles of such a radiation-sensitive two-dimensional image detector.
The following description will explain the structure and principles of the foregoing conventional two-dimensional image detector.
FIG. 6
is a view schematically illustrating a structure of the foregoing conventional radiation-sensitive two-dimensional image detector.
FIG. 7
is a cross-sectional view schematically illustrating a structure of a part of the foregoing radiation-sensitive two-dimensional image detector corresponding to one pixel.
The conventional radiation-sensitive two-dimensional image detector is composed of an active matrix substrate, as well as a photoconductive layer (semiconductor layer)
56
, a dielectric layer
57
, and an upper electrode
58
that are formed over a substantial entirety of the active matrix substrate. The active matrix substrate includes electrode wires (gate electrodes
52
and data electrodes
53
) arranged in an XY lattice form, thin film transistors (hereinafter referred to as TFTs)
54
, charge storing capacitors (Cs)
55
, and the like provided on a glass substrate
51
.
To form the foregoing photoconductive layer
56
, a semiconductor material is used in which charges (electron-hole) are generated upon irradiation by radiations such as X-rays. In the foregoing document, as the semiconductor material, amorphus selenium (a-Se) is used that has a high dark resistance and excels in photoconductivity with respect to X-rays. The photoconductive layer
56
is formed to a thickness of 300 &mgr;m to 600 &mgr;m by the vapor deposition method.
Besides, as the foregoing active matrix substrate, an active matrix substrate formed in a liquid crystal display device fabricating process may be adopted. For example, an active matrix substrate used in an active-matrix-type liquid crystal display device (AMLCD) is arranged to include TFTs made of amorphus silicon (a-Si) or polysilicon (p-Si), electrodes arranged in an XY lattice form, and charge storing capacitors (Cs). Therefore, the AMLCD can be easily used, with slight changes in the design, as the active matrix substrate for use in the radiation-sensitive two-dimensional image detector.
Next, the operational principles of a radiation-sensitive two-dimensional image detector having the foregoing structure are explained below. Upon projection of radiations onto the photoconductive layer
56
composed of an a-Se film or the like, charges (electron-hole) are generated in the photoconductive layer
56
. As shown in
FIGS. 6 and 7
, since the photoconductive layer
56
and the charge storing capacitors (Cs)
55
are connected electrically in series, charges (electron-hole) generated in the photoconductive layer
56
move to the plus electrode side and the minus electrode side upon application of a voltage across the upper electrode
58
and charge storing capacitor electrodes (Cs electrodes)
59
. Consequently, charges are stored in the charge storing capacitors (Cs)
55
. Each charge storing capacitor (Cs)
55
is equipped with the charge storing capacitor electrode (Cs electrode)
59
and a pixel electrode
60
.
By the foregoing operation, the charges stored in the charge storing capacitors (Cs)
55
can be taken to outside through the data electrodes S
1
, S
2
, S
3
, . . . S
n
by turning on the TFTs
54
by using input signals to the gate electrodes G
1
, G
2
, G
3
, . . . , G
n
. Since electrode wires (gate electrodes
52
and data electrodes
53
), TFT
54
, and charge storing capacitors (Cs)
55
are all arranged in an XY matrix form, image information on the X lines can be two-dimensionally obtained by line-sequentially scanning signals inputted to the gate electrodes G
1
, G
2
, G
3
, . . . , G
n
.
Incidentally, in the case where the photosensitive layer
56
used in the foregoing radiation-sensitive two-dimensional image detector exhibits photoconductivity with respect to not only radiations such as X-rays but also visible light and infrared light, it functions also as a two-dimensional image detector for visible light and infrared light.
In the foregoing conventional two-dimensional image detector, the a-Se film used in the photoconductive layer is directly formed on the active matrix substrate by the vapor deposition method. In the case of such a structure, the following problems arise.
(1) In the case where another semiconductor material is used instead of a-Se to form the photoconductive layer, the semiconductor materials applicable are limited according to the thermal resistivity of the active matrix substrate. For example, a polycrystalline film of CdTe or CdZnTe that expectedly provides improvement of sensitivity with respect to X-rays requires a film forming temperature of not lower than 400° C. in the case where it is formed by the MOCVD (metal organic chemical vapor deposition) method, the close-spaced sublimation method, the paste burning method, or the like that is suitable for forming a film on a large-area surface.
On the other hand, a-Si formed in a film form at a temperature of approximately 300° C. is generally used in semiconductor layers of TFTs used as switching elements provided on an active matrix substrate. For this reason, a critical temperature of the TFTs regarding heat resistance (hereinafter referred to as heat resistance critical temperature) is approximately 300° C. Therefore, it is difficult to form a film of a polycrystalline material such as CdTe or CdZnTe directly on the active matrix substrate.
(2) Generally, the active matrix substrate is fabricated by repeated application of a micromachining process (photolithography) to semiconductors, and naturally the yield thereof decreases as the fabrication process is prolonged. In the case where a charge blocking layer, a photoconductive layer, and an upper electrode are further additionally formed on such an active matrix substrate, the following problem arises: a failure occurring during this addition-type process leads to a drastic fall of the yield in total.
Therefore, applicable to solve the foregoing two problems is a method in which an active matrix substrate and a counter substrate (detection element for detecting light or radiations) including a photoconductive layer are formed separately and independently, and are thereafter assembled so as to be connected with each other by using a conductive connection material. This ensures that the limitation relating to the film formation temperature of the semiconductor layer as the photoconductive layer is relaxed, and that the decrease in the yield can be avoided by combining a non-defective active matrix substrate and a non-defective counter substrate.
Incidentally, by using either anisotropic conductive material or a conductive material arranged in a pattern corresponding to pixels provided separately and independently from one another, a plurality of pixels provided on an active matrix substrate obtain conductivity with a connection surface only in the normal line direction. This enables prevention of electric crosstalk between adjacent pixels within the connection surface.
Appropriately adapted as the anisotropic
Izumi Yoshihiro
Sato Toshiyuki
Teranuma Osamu
Tokuda Satoshi
Yoshimuta Toshinori
Nixon & Vanderhye PC
Pham Long
Sharp Kabushiki Kaisha
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