Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnet structure or material
Reexamination Certificate
2000-10-10
2002-04-23
Barrera, Ramon M. (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnet structure or material
Reexamination Certificate
active
06377149
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a magnetic field generator for magnetron plasma generation or, more particularly, relates to an improvement in a magnetic field generator of the dipole-ring magnet type in an instrument for magnetron plasma generation employed in the processes of magnetron plasma etching, magnetron plasma sputtering and so on.
It is a conventional practice in the electronic technology for the manufacture of various kinds of electronic devices that the processes of etching and sputtering are conducted by utilizing magnetron plasma which is generated in a magnetron plasma generating apparatus in the following manner.
Namely, electrodes are inserted into the gaseous phase under an appropriately reduced pressure in a chamber filled with a process gas, which is typically a halogen gas for etching and argon gas for sputtering, to cause electric discharge so that the molecules of the gas are ionized to produce secondary electrons which further collide with the gas molecules to further ionize the same. The electrons released by the discharge as well as the secondary electrons are acted on by the magnetic field and electric field generated in the magnetron plasma chamber to enter a drift movement.
The electrons thus under the drift movement further collide consecutively with the gas molecules resulting anew in releasing of secondary electrons which can again ionize gas molecules. Accordingly, magnetron plasma is advantageous in respect of the high efficiency for the ionization of gas molecules by virtue of the above mentioned repetition of the unit processes.
An example of the conventional etching apparatus by utilizing a magnetron discharge unit is described by making reference to
FIGS. 3A and 3B
, of which
FIG. 3A
is a schematic vertical axial cross sectional view of the apparatus and
FIG. 3B
is for schematic illustration of the movement of electrons therein by a perspective view.
In
FIG. 3A
, a pair of electrode plates
10
,
12
are installed up and down in parallel to define a zone therebetween in which plasma is generated as magnetron plasma. A workpiece
16
, which may be a semiconductor silicon wafer, is mounted on the lower electrode plate
12
so that the surface of the workpiece
16
is exposed to the magnetron plasma generated in the plasma-generating zone between the electrode plates
10
,
12
. A magnetic field generator for magnetron plasma
18
, referred to simply as the magnetic field generator hereinafter, is installed on the upper electrode plate
10
coaxially with the electrode plates
10
,
12
.
The magnetic field generator
18
consists of a combination of concentric two permanent magnets including an annular or ring magnet
22
and a cylindrical core magnet
24
, which is concentrically mounted within the center open space of the ring magnet
22
, and a yoke
26
which magnetically connects the ring and cylindrical magnets
22
,
24
. The direction of magnetization is reversed between the ring and cylindrical magnets
22
,
24
. In
FIG. 3A
, for example, the N to S direction of magnetization is down to up for the ring magnet
22
and up to down for the cylindrical magnet
24
so that the magnetic field in the plasma zone, i.e. the space between the electrode plates
10
,
12
, is as shown by he lines of magnetic force
28
A,
28
B. The magnetic field penetrating the upper electrode plate
10
reaches the surface of the workpiece
16
mounted on the lower electrode plate
12
as a leakage magnetic field.
With regard to the electric field, it is usual that a high-frequency voltage is applied between the electrode plates
10
,
12
so that the plasma zone between the electrode plates
10
,
12
is under a high-frequency electric field in the up-to-down direction. The downward arrow
20
indicates the direction of the high-frequency electric field at a moment when the upper electrode plate is positive and the lower electrode plate
12
is negative.
The lines of magnetic force
28
A,
28
B are depicted as the lines
30
in
FIG. 3B
which is given for schematic perspective illustration of the movement of electrons. Assuming that the direction of the electric field is up to down as indicated by the downward arrow
20
, an electron
32
on the surface of the workpiece
16
enters a drift movement under co-action of the magnetic and electric fields to run along the endless track
34
confined to the vicinity of the surface of the workpiece
16
to ionize innumerable gas molecules there. Accordingly, the apparatus illustrated in
FIGS. 3A and 3B
is suitable for obtaining high-density plasma with an efficiency higher by two to three times than in a plasma-generating apparatus of the high-voltage discharge type.
It should be noted here that contribution of the magnetic field to the drift movement of electrons is obtained only by the component of the magnetic field in the direction perpendicular to the direction of the electric field. In the case of
FIGS. 3A and 3B
, namely, contribution to the drift movement of electrons and to the ionization of gas molecules is given only by the component of the magnetic field in the direction parallel to the surface of the workpiece
16
or the lower electrode plate
12
, which is referred to as the horizontal component hereinafter.
The horizontal component of the magnetic field B, however, is not uniform over the whole surface but greatly varied as a function of the distance d from the axial center point O of the plasma zone as is graphically shown in FIG.
4
. Since the density of magnetron plasma depends on the horizontal component B of the magnetic field, the above mentioned situation leads to a serious problem relative to unevenness in the quality of the plasma-treated products such as localization of the effect of etching. In addition, the non-uniform density of the plasma induced there causes a potential difference by charging up within the surface of the workpiece
16
resulting in eventual damage to the workpiece surface.
In order to be free from the above described problems, it is desirable that the magnetic field is as uniform as possible and the magnetic field is constituted entirely of the horizontal component only. These requirements can be satisfied, for example, by a magnetic field generator illustrated in
FIG. 5A
by a top view and in
FIG. 5B
by a cross sectional view as cut and viewed along the line VB—VB in FIG.
5
A. The magnetic field generator of this type is known as a dipole-ring magnet
41
consisting of a plurality, e.g.,
16
in
FIG. 5A
, of magnetically anisotropic, columnar segment magnets
40
embedded in and supported by the non-magnetic cylindrical or tubular framework
42
in such a fashion that each of the columnar segment magnets
40
stands in parallel to the cylindrical axis. The cross sectional profile of each columnar segment
40
magnet is not particularly limitative including circular and rectangular cross sections but can be square as is shown in FIG.
5
A. It is essential that the direction of anisotropic magnetization of each segment magnet
40
is within a plane perpendicular to the cylindrical axis and the direction within the plane is varied between two adjacent magnets by an angle of 360°/16 as shown by the small arrow within the square profile of the top view of the magnets
40
in
FIG. 5A
arranged along a generally circular assembly contour of the 16 columnar magnets
40
completing 360° revolution by one rounding. When a good number of columnar segment magnets
40
each having a sufficiently large length are arranged in this fashion, a uniform magnetic field in the direction indicated by the broad open arrow
43
in
FIG. 5A
is generated in the space surrounded by the columnar segment magnets
40
in a ring arrangement. The uniformity of the thus generated magnetic field is best within the space
46
at a half height of the length RL of the columnar segment magnets
40
.
The magnetron plasma generating apparatus is installed with the thus obtained magnetic field with an upper electrode plate
10
and lower electrode pl
Barrera Ramon M.
Shin-Etsu Chemical Co. , Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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