Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material
Reexamination Certificate
2002-04-09
2004-09-21
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
C438S597000, C438S099000
Reexamination Certificate
active
06794278
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing an organic thin-film device by forming a conductive or insulating thin-film on a functional organic film, and more particularly to a method for producing an organic thin-film device by use of a facing-targets-type sputtering apparatus configured such that a pair of facing targets are disposed a predetermined distance away from each other and such that a magnetic field extending between the targets from one target to the other is generated in such a manner as to laterally surround a space provided between the facing targets (the space is hereinafter called a confinement space), to thereby confine plasma within the confinement space and form a film on a substrate disposed at a position beside the confinement space under vacuum.
2. Description of the Related Art
In recent years, organic electroluminescent devices (hereinafter simply referred to as “organic EL device(s)”), which are a type of organic thin-film device, have become of interest as light-emitting thin-film displays, and extensive studies have been conducted in order to put these thin-film displays into practical use. A typical organic electroluminescent device includes a positive electrode of a transparent electrode constituted by indium-tin oxide (ITO) or a similar substance formed on, for example, a glass or plastic transparent substrate; an organic layer formed from a hole-transporting organic compound such as triphenyldiamine (TPD), the layer being formed on the transparent electrode through a conventional thermal evaporation method; a light-emitting layer formed from a fluorescent substance such as 8-hydroxyquinoline aluminum (Alq
3
), the layer being formed on the organic layer; and a negative electrode of a metal of small work function such as Mg, the electrode being formed on the light-emitting layer. Such organic EL devices have become of interest, since they provide a considerably high luminance of 100 to 10,000 cd/m
2
when operated at a low driving voltage of about 10 V.
Many studies have been performed with an aim to improve properties of such organic EL devices. Particularly, various methods for forming a negative electrode on an organic layer such as a light-emitting layer have been proposed, the method being considered one of key technologies for improving device properties and productivity and for attaining reliable production.
For example, Japanese Laid-Open Patent Publication (kokai) No. H08-250284 discloses a method for forming a negative electrode, through sputtering, on a substrate disposed so as to face a target. The publication describes the following. A negative electrode formed through a typical method of thermal evaporation raises a problem in that an oxide of a metal serving as the raw material of the electrode is generated in the interface between the electrode and an organic layer or in the electrode, to thereby vary electron-injecting properties, resulting in failure to obtain desired device properties. In addition, because of poor adhesion between the electrode and the organic layer, emission intensity is lowered with passage of voltage application time, and the electrode is exfoliated and dissipated, resulting in difficulty in forming a reliable device. In contrast, in the case where a negative electrode thin film is formed through sputtering, adhesion between the electrode and an organic layer is improved as compared with the case where a negative electrode is formed through a thermal evaporation method. Furthermore, an oxide layer formed on the target can be removed under vacuum through pre-sputtering, and water or oxygen adsorbed on the surface of the organic layer can be removed through reverse-sputtering, attaining satisfactory formation of a clean electrode on an organic layer, leading to the production of a reliable organic EL device.
Japanese Laid-Open Patent Publication (kokai) No. H10-255987 discloses a method for producing an organic EL device including an electrode formed by means of a facing-targets-type sputtering method in which a film is formed on a substrate disposed at a position beside a space provided between a pair of facing targets. In the course of production of the organic EL device, a negative electrode is formed on an organic film of the organic EL device by use of a facing-targets-type sputtering apparatus. The apparatus includes a pair of parallel facing targets disposed a predetermined distance away from each other; magnetic-field generation means which generates a magnetic field in a direction substantially perpendicular to the targets; and a shield disposed so as to cover a portion of each target other than the facing surface. In the apparatus, a substrate is disposed at a position beside a space provided between the facing targets, power is applied between the target and the shield, and the thus-generated plasma is confined within the space, to thereby form a film on the substrate.
The publication describes the following. In the case of conventional sputtering method such as the aforementioned magnetron-type sputtering method, in which a substrate and a target are disposed so as to face each other, secondary electrons generated from the surface of the target and sputtered particles of high kinetic energy; specifically, large amounts of secondary electrons and ionized sputtered particles, impinge on an organic layer, to thereby physically break the organic layer. As a result, the electrostatic breakdown voltage of an organic EL device is lowered, and application of voltage between negative and positive electrodes may cause leakage of current. Alternatively, the device may fail to function, as a result of breakage associated with an increase in temperature. Furthermore, driving voltage increases and luminance decreases, to thereby deteriorate EL properties.
In contrast, in the aforementioned facing-targets-type sputtering apparatus, a plasma generation region and a film formation region are completely separated from each other, and a film is formed in a plasma-free-like state. Therefore, a substrate is substantially not exposed to plasma, and film formation is carried out such that an organic layer and a film deposited on the layer are not damaged by high-energy particles. As a result, problems arising from the aforementioned conventional sputtering method are solved, and the resultant organic EL device has a high luminance at an initial stage, and the time until the luminance becomes half increases. Furthermore, the device has very small amounts of dark spots at an initial stage, and generation and growth of dark spots after operation are reduced.
A conventional facing-targets-type sputtering apparatus will next be described. The sputtering apparatus is disclosed in Japanese Publication of Examined Patent Application (kokoku) Nos. S63-20303, S63-20304, and S62-14633, and has the following basic configuration as shown in
FIG. 1. A
pair of targets
110
a
and
110
b
are disposed a predetermined distance away from each other within a vacuum chamber
10
having a chamber wall
11
, thereby defining a confinement space
120
therebetween. Permanent magnets
130
a
and
130
b
serving as magnetic-field generation means are disposed behind the corresponding targets
110
a
and
110
b
in order to generate a magnetic field which extends in a direction perpendicular to the targets
110
a
and
110
b
and whose flux uniformly surrounds the confinement space
120
. A substrate holder
21
disposed at a position beside the confinement space
120
holds a substrate
20
such that the substrate
20
faces the confinement space
120
. Reference numerals
140
a
and
140
b
represent shields for protecting from sputtering portions of target units
100
a
and
100
b
other than the front surfaces of the targets
110
a
and
110
b.
After the vacuum chamber
10
is evacuated through an evacuation port
30
by means of an unillustrated evacuation system, a sputtering gas, such as argon, is introduced into the vacuum chamber
10
through a gas inlet
40
by means
Kadokura Sadao
Kido Junji
Yokoi Akira
Kido Junji
Mulpuri Savitri
Westerman Hattori Daniels & Adrian LLP
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