Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1996-06-28
2001-04-17
Chaney, Carol (Department: 1745)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298030, C204S298080, C204S298190, C204S298260
Reexamination Certificate
active
06217714
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a sputtering apparatus and more particularly, to a sputtering apparatus adapted to form thin films on angular substrates of a large area uniformly at high speeds.
A sputtering apparatus has been often used to manufacture semiconductor devices, optical discs, liquid crystal, or electronic components, etc., because of its capability to form a thin film of a target material stably on a substrate. As performance capabilities required for this kind of sputtering apparatus, speed and cost are important, that is, how quickly and stably the apparatus forms a uniform film all over the substrate at low costs.
Meanwhile, a stationary formation method has been increasingly employed in recent sputtering apparatuses, besides a substrate-moving method whereby a film is formed on a target while the substrate is moved to the target. The substrate is laid still and opposed to the target in the stationary method. The stationary method advantageously improves a film-forming speed, decreases dusts, and reduces an equipment cost.
During sputtering, atoms sputtered from on the target are radiated with a certain angle distribution. Therefore, it is necessary in the stationary method to optimize a shape of the target, structures, and sizes of magnets, etc. so as to fulfill the aforementioned performance capabilities in accordance with a shape and a size of the substrate to which a thin film is formed.
Since circular substrates represented by silicon wafers have been used for manufacturing semiconductor devices and optical discs, the sputtering apparatus of the stationary model has employed a disc-like target. A ring-shaped eroded part (referred to as an “erosion” below) is formed on the circular target to secure a uniform thickness of the thin film formed on the substrate, which ensures a thickness uniformity all over the surface of the circular substrate.
The above-referred erosion is generated when the plasma is locally distributed in consequence of the drift motion of electrons on the target surface. Therefore, a fixed magnet having a ring-shaped distribution of magnetic field is arranged below the target to realize the erosion in the form of a ring. Since the electrons are trapped while drifting within the ring in this case, the plasma is generated with a high density, so that many electrons are sputtered and a film is formed at high speeds.
In the meantime, when a film is to be formed on an angular substrate of a display device or the like, a fixed magnet to generate a linear erosion on an angular target is disposed below the target thereby to assure a film thickness distribution on the angular substrate.
However, the obtained linear erosion is not sufficient to confine the plasma through the drift of electrons, eventually making it hard to form the film at high speeds. As such, the magnet is generally constructed in such configuration that two linear erosion parts parallel to each other are connected at both ends thereof by semi-circular erosion parts. The electrons can thus be trapped in the same fashion as when the ring-shaped target is used, and a high-density plasma is generated thereby to form the film quickly.
In the case of forming a film on an angular substrate of a larger area in comparison with that of the above target, while the angular substrate with a large area is held by a substrate holder which is movable facing to the target, the substrate holder is moved thereby to form the film continuously. Thus, the film can be formed on the angular substrate of a larger area in comparison with that of the target. When the substrate holder is moved in parallel to the surface of the target, it is called as a tray system. On the other hand, when the substrate holder is rotated with a radius in a vertical direction of the target surface, this is called as a carousel system.
When the film formation is carried out by moving the substrate as above, the film is formed to the substrate holder as well, resulting in disadvantages of an increase of dusts as the film of the substrate holder is separated or an increase of mechanism elements in a vacuum which leads to an increase of the equipment cost, etc.
Under such being the circumstances, similar to the circular substrate, the angular substrate of a large area has been started to be treated in the stationary state.
A conventional method of forming a thin film on the angular substrate of a large area in the stationary state will be described with reference to the drawings.
FIG. 7
is a perspective sectional view showing the basic structure of a conventional apparatus forming a film to a large-area, angular substrate in the stationary method with the use of sputtering.
In
FIG. 7
, a reference numeral
12
is a magnet which is movable on a rear surface of a target
11
in parallel to the surface of the target
11
. Other reference numerals are respectively:
13
a large-area glass substrate;
14
a DC power source for impressing power to the target
11
;
15
a line of magnetic force generated on the target
11
by the magnet
12
; and 16 atoms of a target material sputtered from on the target
11
.
How the film-forming apparatus constituted as above operates to sputter in the stationary method will now be depicted.
Sputtering is a way of forming a thin film having a composition of a target
11
on a substrate
13
. Concretely, while an inert gas such as argon gas or the like is introduced in a vacuum chamber (not shown), the electric power is supplied from the power source
14
to an electrode part (cathode) including the target
11
. The introduced gas is turned into a plasma state, sputtering the material of the target
11
by means of gas ions, thereby forming a thin film on the substrate
13
.
In the apparatus of
FIG. 7
, in addition to the above-discussed principle of sputtering, the magnet (permanent magnet)
12
is disposed at a rear surface of the target
11
to generate lines of magnetic force as indicated by the dotted lines
15
on a front surface of the target
11
, and the electrons (not shown) as a cause to generate plasma are thus confined in an area surrounded by the lines
15
. As a result of this, the plasma is locally generated centering a part where components of each line
15
of magnetic force parallel to the target
11
are zero, and the target
11
is consequently sputtered by a lot of gas ions. Thus, since an amount of sputtered atoms
16
is increased, a film-forming speed is improved. As a result, an erosion as a local eroded part is formed on the sputtered target
11
.
FIG. 8
is a simulation result of a thickness distribution of the film formed on the substrate
13
when the magnet
12
is set still at the rear surface of the target
11
on a center point of the substrate
13
.
A position within a plane of the substrate
13
is indicated by its distance from the center point of the substrate
13
in X- and Y-axes directions in
FIG. 8. A
relative thickness of the film at the position is shown on a Z-axis.
As is understood from
FIG. 8
, the thickness distribution in the Y-axis direction can be uniformed by optimizing a distribution of magnetic field generated by the magnet
12
. However, the thickness in the X-axis direction is rapidly decreased as the position of the film is far from a central part (X=0) of the magnet
12
.
As a way to obtain a uniform thickness distribution all over the surface of the substrate
13
, the magnet
12
may be enlarged in size thereby to increase a uniform thickness area in the X-axis direction. However, a limit of a holding force of the magnet
12
weakens the line
15
of magnetic force generated on the surface of the target
11
if a distance between the N and S poles of the magnet
12
is increased. An effect of the magnet to confine the plasma tends to be null.
In the prior art, therefore, the magnet
12
is let to slide in the X-axis direction facing to the substrate
13
at the formation of the film, with the result that the film is obtained with a thickness distribution of an integration in time in the X-axis direc
Aokura Isamu
Kimura Teiichi
Nishihara Munekazu
Chaney Carol
Matsushita Electric - Industrial Co., Ltd.
Mercado Julian A.
Wenderoth , Lind & Ponack, L.L.P.
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