Coating processes – Coating by vapor – gas – or smoke
Reexamination Certificate
1998-12-21
2002-04-30
Chen, Bret (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
C427S598000
Reexamination Certificate
active
06379747
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for forming a thin film on an object on which the thin film is to be formed, through having a thin film forming substance emitted from a thin film forming substance supply source arrive at and deposit on the object.
2. Description of the Related Art
A physical vapor deposition (PVD) which is a method of forming a thin film by a physical means such as sputtering or vacuum evaporation is known as one of methods of forming a thin film in a manufacturing process of a semiconductor and so on. Sputtering is a method in which a gas for discharge is introduced to a vacuum, a glow discharge is effected between a pair of electrodes so as to generate plasma, a target as a thin film forming substance supply source placed on the cathode is ejected by ions impinging thereon in the plasma and a film is deposited on a substrate (wafer) placed on the anode. Related-art methods of controlling a film thickness in PVD will now be described, taking a thin film forming apparatus using sputtering as an example.
There are mainly three methods as follows among the related-art methods of controlling a film thickness in the thin film forming apparatus using sputtering. The first method is to relatively rotate the substrate and the target as disclosed in Japanese Patent Application Laid-open Hei 6-349662 (1994). In the method the target is fixed and a substrate holder retaining the substrate is rotated, for example.
The second method is to provide a shutter between the substrate and the target, open the shutter only once for the substrate and control a film thickness by the opening duration. The third method is to fix the substrate and the target and control a film thickness by controlling the film forming time.
Reference is now made to
FIG. 6
for describing an example of a thin film forming apparatus used for controlling a film thickness by the above-mentioned second method. The thin film forming apparatus
110
comprises: a chamber
111
; a substrate holder
112
placed near the lower end in the chamber
111
and functioning as an anode as well; a target support plate
113
placed near the upper end in the chamber
111
; and a shutter
114
placed between the substrate holder
112
and the target support plate
113
. The substrate holder
112
may hold a plurality of substrates
115
. Two target holders
116
A and
116
B each functioning as a cathode as well are fixed to the target support plate
113
. The target holders
116
A and
116
B may each hold targets
117
A and
117
B, respectively. The shutter
114
has a circular opening
114
a
. The diameter of the opening
114
a
is greater than that of the substrate
115
. The shutter
114
is rotatable and allows the opening
114
a
to selectively face either the target
117
A or the target
117
B.
A drive axis of a motor
118
provided outside the chamber
111
is coupled to the substrate holder
112
so that the substrate holder
112
is rotated by the motor
118
. A cooling water duct
119
is provided near the substrate holder
112
. The substrate holder
112
is cooled by letting cooling water flow through the duct
119
.
Cooling water ducts
121
A and
121
B are provided near the target holders
116
A and
116
B. The target holders
116
A and
116
B are cooled by letting cooling water flow through the ducts
121
A and
121
B. Ends of power supply cables
122
A and
122
B are each connected to the target holders
116
A and
116
B, respectively. The other ends of the cables
122
A and
122
B are each connected to fixed contacts of a switch
123
, respectively. A moving contact of the switch
123
is connected to a power source
124
.
An end of an exhaust pipe
125
is coupled to the chamber
111
so as to communicate with inside the chamber
111
. A vacuum pump
126
is coupled to the other end of the exhaust pipe
125
. A valve
127
is provided at some midpoint in the exhaust pipe
125
. An end of a pipe
128
for a gas for discharge is coupled to the chamber
111
so as to communicate with inside the chamber
111
.
Thin film forming steps using the thin film forming apparatus
110
shown in
FIG. 6
will now be described. The inside of the chamber
111
is made vacuum by opening the valve
127
and operating the vacuum pump
126
. A gas for discharge such as Ar is then introduced to the chamber
111
through the pipe
128
. Next, power is supplied from the power source
124
selectively to either the target holder
116
A or
116
B through the switch
123
so as to generate a glow discharge and plasma in the chamber
111
. In this example power is supplied to the target holder
116
A so that the substance forming the target
117
A is deposited on the substrate
115
. At this point the opening
114
a
of the shutter
114
is located in a position not facing either the target
117
A or
117
B. The substrate holder
112
is rotated by the motor
118
. Next, the opening
114
a
of the shutter
114
is placed in a position facing the target
117
A. The substance forming the target
117
A is ejected by ions in the plasma and goes through the opening
114
a
towards the substrate holder
112
. Since the substrate holder
112
is rotating, the substance forming the target
117
A deposits on each substrate
115
when the substrate
115
faces the opening
114
a
and a thin film is thereby formed on the substrate
115
. The substrate holder
112
having completed one rotation or several rotations and given time having elapsed, the opening
114
a
is rotated and placed in a position not facing the target
117
A. Thin film formation on every substrate
115
is thus completed.
Developments in giant magnetoresistive (GMR) heads utilizing the GMR effect as thin film magnetic heads have been extensively made. Thin film forming methods such as sputtering described above are used for fabricating a GMR film of such a GMR head. The GMR film is made up of a plurality of layers each of which has a thickness of about some nanometers. Precise control of film thickness is therefore required for fabricating the GMR film.
A magnetic field is applied for fabricating a magnetic layer of the GMR film through a method such as sputtering. As shown in
FIG. 7
, magnets
132
and
133
may be placed at sides of a substrate
131
on a substrate holder to apply a magnetic field. The magnets
132
and
133
are placed such that surfaces of the magnets facing each other are magnetic poles different from each other.
However, if a magnetic field is applied for fabricating a layer while rotating the substrate as in the related-art first or second method of film thickness control, the magnets
132
and
133
are rotated as well with the substrate
131
on the substrate holder and the magnetic field is thereby changed in the chamber. As a result, the discharge is made unstable and accuracy of film thickness control is reduced.
In the related-art second method of film thickness control, the shutter is opened only once for the substrate and a thin film having a desired thickness is formed in a single step of film fabrication. It is therefore difficult to precisely form thin films having several types of thickness. In particular, precise control of forming thin films having a thickness of hundreds of picometers to tens of nanometers (some angstroms to hundreds of angstroms).
In the related-art technique, the opening of the shutter is a circle whose diameter is greater than that of the substrate when the foregoing second method of film thickness control is used. As a result, the thickness distribution on the substrate is made nonuniform. This problem will now be described, referring to FIG.
8
.
FIG. 8
illustrates a way in which an opening
135
of a shutter moves in the direction indicated with an arrow with respect to the substrate
131
. Although the substrate
131
is fixed and the opening
135
moves in
FIG. 8
, the reverse is acceptable, too, as long as relative movements of the substrate
131
and the opening
135
with respect to each other are achieved. As shown in
F
Chen Bret
Oliff & Berridg,e PLC
TDK Corporation
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