Magnetic film forming apparatus which applies a parallel magnetic field across a substrate

A magnetic film forming apparatus includes a film forming source to emit film-forming particles, a substrate holder for holding a substrate on which a magnetic film is formed with the film-forming particles, and a magnetic field generating circuit for applying the magnetic field to the substrate. The magnetic field generating circuit includes two pairs of magnets. Each pair of magnets is composed of two bar-shaped magnets combined in a line apart from each other by a gap of distance d. The pair of magnets have respective pairs of magnetic poles, with the direction of each pair of the magnetic poles being perpendicular to the longitudinal direction of the pair of magnets and having the same orientation. The two pairs of magnets are arranged apart from each other by the distance L in the horizontal x-y plane, substantially symmetrically to the vertical central y-axis of the substrate. This way, the magnetic film forming apparatus can be decreased in size and uniform parallelism of the magnetic field can be applied to the substrate.

BACKGROUND OF THE INVENTION 
The present invention relates to a magnetic film forming apparatus, and in 
particular to a magnetic film forming apparatus capable of generating a 
uniform magnetic field to form a magnetic film with an excellent magnetic 
characteristic. 
As a method of forming a magnetic film in which the magnetic moment is 
arranged in one direction, an in-magnetic-field sputtering-method is known 
according this method, a magnetic film is formed while orienting the 
magnetization direction of film forming particles by applying a magnetic 
field to the film forming particles in one direction. 
In a conventional magnetic film forming apparatus for forming a magnetic 
film by using the in-magnetic-field sputtering method disclosed, for 
example, in Japanese Patent Application Laid-Open Hei-7 254603 and 
Japanese Patent Application Laid-Open Hei-8 30780. A substrate on which a 
magnetic film is formed is placed opposite to a target in a sputtering 
chamber. The substrate is held by a substrate holder, and further kept in 
parallel to the target at a predetermined distance by internal fittings. 
Moreover, two permanent magnets are provided on the substrate holder. In 
the upper part of the sputtering chamber, a guide bar of a heater is 
attached to the sputtering chamber via an o-ring. In the aperture part in 
the lower portion of the sputtering chamber, a target electrode is fixed 
to the sputtering chamber via an insulation member, and the target is 
attached to the target electrode. Also, an earth shield is provided around 
and apart from the target with a constant gap distance. 
The magnetic film forming apparatus generates plasma by applying voltage to 
the target from an RF (radio wave) power source via the target electrode, 
and ions in the generated plasma make sputtering-particles emit from the 
target. The sputtering-particles emit from the target arrive at the 
surface of the substrate, and form a magnetic film on the surface. Since 
the magnetic field near around the substrate is applied by the permanent 
magnets provided on the substrate holder, the magnetization direction of 
the sputtering-particles in the formed magnetic film is oriented in the 
same direction. 
In the space near the substrate in this magnetic film forming apparatus, 
two bar-shaped permanent magnets are arranged at the both sides of the 
substrate in parallel to the substrate. Moreover, the substrate is fixed 
in the center of the space between the two permanent magnets, and an 
orientation flat is provided on the substrate so it will not rotate. 
However, in the above-mentioned composition of this conventional magnetic 
film forming apparatus, in both the top portions of the substrate in the 
longitudinal direction, the generated magnetic field is not straight 
between the two permanent magnets, but instead expands somewhat toward the 
outside of the substrate. Therefore, to decrease the expansion of the 
magnetic field, a pair of auxiliary magnets are provided opposite to each 
other at places between pairs of end portions of the two permanent magnets 
arranged in parallel. Otherwise two auxiliary magnets are attached to the 
two ends of the respective permanent magnet. Thus, in a comparatively wide 
region between the two permanent magnets, a magnetic field perpendicular 
to those magnets can be realized. 
Such a composition or arrangement of the main permanent magnets and the 
auxiliary magnets is complicated, and has been difficult to optimize. 
Furthermore, to reduce the variance in the distribution of etching which 
is performed on the surface of the substrate in advance and in the 
property of a formed magnetic film, it is desirable to set a large 
distance L between the two permanent magnets, which in turn requires a 
larger length for the two magnets. Moreover, the optimal arrangement for 
the magnets of given sizes is uniquely determined. Accordingly, if the 
distance L between the two permanent magnets is changed to meet a 
requirement to change the strength or the distribution of the magnetic 
field, it becomes difficult to obtain the optimal arrangement of the 
magnets again by adjusting the positions of the auxiliary magnets. 
SUMMARY OF THE INVENTION 
The present invention has been achieved in consideration of the above 
described problems, and is aimed firstly at providing a magnetic film 
forming apparatus of a simple and small-sized composition, capable of 
applying a magnetic field of uniform distribution to the surface of a 
substrate, and secondly at providing a magnetic film forming apparatus 
capable of adjusting the strength or the distribution of the magnetic 
field applied to the substrate by changing the arrangement of the magnets 
while maintaining the uniform magnetic field distribution. 
The above-mentioned objects are attained by means having the following 
features. 
The fundamental feature of the present invention is a magnetic film forming 
apparatus including a film-forming source to emit film-forming particles, 
a substrate holder for holding a substrate on which a magnetic film is 
formed with the film-forming particles, and a magnetic field generating 
means for applying the magnetic field to the substrate; wherein the 
magnetic field generating means has a composition such that the ratio of 
an area of the substrate to an area in a horizontal x-y plane parallel to 
the surface of the substrate including the substrate inside the magnetic 
field generating means, is larger than about 0.14, and the skew angle of 
the magnetic field applied to the substrate is kept at less than 0.6 deg. 
by suppressing the vertical expansion of the magnetic field at places near 
both vertical peaks of the substrate. 
Another feature of the present invention is that, in the above magnetic 
film forming apparatus of the fundamental feature, the magnetic field 
generating means comprises two pairs of magnets, each pair of magnets 
being composed of two bar-shaped magnets combined in a line apart from 
each other by a gap of distance d, the pair of magnets having respective 
pairs of magnetic poles, with the direction of each pair of magnetic poles 
being perpendicular to the longitudinal direction of the pair of magnets 
and having the same orientation, and the two pairs of magnets being 
arranged apart from each other by the distance L in the horizontal x-y 
plane, almost symmetrically to the vertical central y-axis of the 
substrate. 
Still another feature of the present invention is that, in the above 
magnetic film forming apparatus, the pairs of magnets are all permanent 
magnets having almost the same shape. 
An additional feature of the present invention is that, in the above 
magnetic film forming apparatus, a pair of auxiliary magnets are arranged 
in the horizontal x-y plane between the two pairs of magnets, almost 
symmetrically to the central x-axis of the substrate. 
A further feature of the present invention is that, in the above magnetic 
film forming apparatus, a pair of auxiliary magnets are attached to the 
respective end portions of each pair of magnets. 
Yet another feature of the present invention is that, in the above magnetic 
film forming apparatus, the magnets are optimally arranged based on a 
three-dimensional magnetic field distribution calculated in advance. 
One more feature of the present invention is that, in the above magnetic 
film forming apparatus, the optimal value of the gap of distance d is 
given by a function of the distance L between the pairs of magnets in 
optimizing the arrangement of the magnets. 
Still another feature of the present invention is that, in the above 
magnetic film forming apparatus, the two pairs of magnets and each magnet 
of the pairs of magnets are attached so that the distance L between the 
pairs of magnets is variable, each magnet is rotatable, and the magnetic 
field applied to the substrate is adjusted to achieve a required magnetic 
field by changing the distance L and the rotational angle of each magnet. 
Still another feature of the present invention is that, in the above 
magnetic film forming apparatus, a magnetic field monitoring means for 
detecting the magnetic field applied to the substrate is provided in the 
sputtering chamber, and the arrangement of the magnets is optimally 
adjusted based on the detection results of the magnetic field monitoring 
means. 
Yet another feature of the present invention is that, in the above magnetic 
film forming apparatus of the fundamental feature, the magnetic field 
generating means comprises two solenoids with the same winding direction, 
the solenoids being arranged so that their axes are connected in one line 
in the parallel x-direction of the substrate placed between the two 
solenoids in a horizontal x-y plane including the central axes of the 
solenoids, and the two solenoid further being arranged almost 
symmetrically to the vertical central y-axis of the substrate, wherein 
current flows unidirectionally through the solenoids. 
An additional feature of the present invention is that, in the above 
magnetic film forming apparatus, the size of the solenoids and their 
arrangement are optimized based on a three-dimensional magnetic field 
distribution calculated in advance and applied to the substrate. 
Still another feature of the present invention is that, in the above 
magnetic film forming apparatus, a magnetic field monitoring means for 
detecting the magnetic field applied to the substrate is provided in the 
sputtering chamber, and the current flow in the solenoids is adjusted 
based on the detection results of the magnetic field monitoring means so 
that the magnetic field applied to the substrate matches a required 
magnetic field.

DETAILED DESCRIPTION OF THE EMBODIMENTS 
Hereafter, details of embodiments will be explained with reference to the 
drawings. 
FIG. 2 is a vertical cross section of a magnetic film forming apparatus of 
an embodiment according to the present invention. 
In this figure, numeral 12 indicates a magnet attachment plate to which the 
later-discussed magnets are attached, and numerals 20, 21, 22, and 23 
indicate the magnets. Here, the composition of the magnetic film forming 
apparatus shown in FIG. 2 is different from that of the above-mentioned 
conventional magnetic film forming apparatus only in that the four 
permanent magnets 20-23 are attached to the magnet attachment plate and 
the new arrangement of the magnets is established. Here, numerals 6, 9, 
10, and 11 indicate a heater, an o-ring, and an guide bar of the heater, 
respectively. Moreover, a magnetic monitoring element 30 to detect the 
magnetic field applied to the substrate 7 is provided in the vicinity of 
the substrate 7 as needed. 
FIG. 1 shows an example of the arrangement of the four bar-shaped magnets 
20-23 attached to a magnet attachment plate 12 and a substrate 7. 
As shown in FIG. 1, an N-pole magnetic field generating means is composed 
of a pair of magnets 20 and 21 whose N-pole is directed to the substrate 
7, and an S-pole magnetic field generating means is further composed of a 
pair of other magnets 22 and 23 whose S-pole is directed to the substrate 
7. The substrate 7 is placed almost at the central position between the 
N-pole and S-pole magnetic field generation means in the horizontal plane 
including the N-pole and S-pole magnetic field generation means. Moreover, 
an orientation flat part 14 is formed in the substrate in such a way as to 
not rotate. 
Furthermore, the magnetic field distribution applied to the substrate 7 is 
explained below with reference to FIG. 1. 
Generally, reading a bar-shaped permanent magnet whose longitudinal 
direction is perpendicular to its magnetized direction (the direction of 
the poles), the surface magnetic flux is strongest in the vicinity of its 
central position, and the magnetic flux is radiated from or centered on 
the central position. Therefore, if the four magnets 20-23 are arranged as 
shown in FIG. 1, the magnetic flux is radiated from or centered on the 
central position of each magnet. Accordingly, the respective vertical 
components (y-direction component) of the magnetic flux generated by the 
pair of magnets 20 and 21 (22 and 23) cancel each other out, and the 
magnetic field generated by the N-pole and S-pole magnetic field 
generation means is uniformly parallel to the x-direction. Thus, by using 
this arrangement of the four magnets, a magnetic field uniformly parallel 
to the x-direction can be applied to all places on the surface of the 
substrate 7 by the four magnets 20-23. 
Furthermore, the film-forming operations of the magnetic film forming 
apparatus of this embodiment are explained below with reference to FIG. 1 
and FIG. 2. 
Firstly, the magnets 20-23 and the substrate 7 are arranged and attached to 
the magnet attachment plate 12 and the substrate holder 6, respectively. 
Next, voltage is applied to the target 3 with the RF power source, and 
plasma is generated. Consequently, sputtering-particles are emitted from 
the target 3. The emitted sputtering-particles reach the surface of the 
substrate 7, and form a magnetic film on the substrate. Since the magnetic 
field uniformly parallel to the x-direction is applied to the whole area 
near the substrate 7 by the magnets 20-23 attached to the magnet 
attachment plate 12 as mentioned above, the sputtering-particles are 
magnetized in the same direction. Thus, a magnetic film with the 
unidirectional magnetization is formed. 
Next, the method of arranging the magnets in the magnetic film forming 
apparatus of this embodiment so that the magnetic field applied to the 
substrate 7 is uniformly focused in one direction parallel to the 
x-direction, is discussed with reference to FIG. 3 and FIG. 4. 
In FIG. 3, symbols d, L, and indicate the gap distance between the two 
magnets in each pair of magnets 20 and 21 (22 and 23 ): that is, the 
N-pole magnetic field generating means (20 and 21) and the S-pole magnetic 
field generating means(22 and 23), and the longitudinal length of these 
magnetic field generating means. 
FIG. 4 shows the relationship between the skew angle and the gap of 
distance d in each pair of magnets of a given sizes in the magnetic film 
forming apparatus. The skew angle is defined as the maximum angle 
difference among the angle differences in the horizontal direction between 
the magnetic field angle and the required magnetic field direction at 
every positions in the substrate 7 with respect to one set value of d. 
The strength and direction of the magnetic field (magnetic field 
distribution) applied to the substrate 7 is determined by the proper 
surface magnetic flux of each magnet and the relative positional 
relationships among the magnets 20-23. In this embodiment, the arrangement 
of the magnets 20-23 to obtain the magnetic field uniformly focused in one 
direction is determined as follows. 
To begin with, the distance L between the two pairs of magnets and the 
total length e of the two pairs are set. Next, parameter survey 
calculations of the magnetic field distribution are performed by using a 
three-dimensional magnetic field analysis program and varying the 
parameter d. In the parameter survey calculation, the size and remanence 
of each magnet and the arrangement of the magnets 20-23 are input to the 
three-dimensional magnetic field analysis program. 
From the example shown in FIG. 4, which is the result of a parameter 
survey, it is seen that the skew angle becomes smallest at a value of the 
gap of distance d. Therefore, it is possible to apply the optimal magnetic 
field to the substrate by optimizing the gap of distance d. Thus, in 
accordance with the above processing, it is possible to determine the size 
of each magnet and the arrangement of the magnets by which the uniformly 
parallel magnet field can be applied to the substrate 7. 
Furthermore, in this embodiment, since the optimal arrangement of the 
magnets depends on only the distance L between the pairs of magnets and 
the gap of distance d, the optimization of the magnet arrangement becomes 
comparatively easy. Also, since a pair of magnets is used as a magnetic 
field generation means for each pole it is not necessary to use a large 
magnet for each magnet of the pairs. 
In the following, the other embodiments according to the present invention 
will be explained with reference to FIGS. 5, 6, and 7. 
FIG. 5 shows the arrangement of magnets attached to the magnet attachment 
plate 12 and the substrate 7 in the magnetic film forming apparatus of 
another embodiment in which the positions of the magnets 20-23 and the 
rotational angle of each magnet are variable. In this embodiment, while 
the uniform parallelism of the magnetic field is kept, the strength of the 
magnetic field applied to the substrate 7 can be adjusted by changing the 
gap of distance d between the two magnets of each pair and the distance L 
between the two pairs. Furthermore, by the above adjustment, the 
distortion in the uniformly parallel magnetic field which is caused by the 
variance of the surface magnetic flux density in the four magnets can be 
also corrected. 
Thus, according to this embodiment, even if the distance L between the two 
pairs of magnets is varied, the strength of the magnetic field applied to 
the substrate 7 can be changed without losing the uniform parallelism of 
the magnetic field. The above adjustment is carried out based on the 
result of the pre-calculated magnetic field distribution or on the results 
of measurements performed by the magnetic field monitoring element 30. 
FIG. 6 shows the arrangement of magnets attached to the magnet attachment 
plate 12 and the substrate 7 in the magnetic film forming apparatus of 
still another embodiment in which a pair of auxiliary magnets 24 and 25 
are placed between the two pairs of magnets in the horizontal x-y plane 
symmetrically to the central x-axis of the substrate 7. In this 
embodiment, since the expansion in the vertical y-direction, of the 
magnetic field at places near both vertical tops of the substrate 7 can be 
more suppressed than in the embodiment shown in FIG. 1, it is possible to 
realize the more excellently uniform parallelism of the magnetic field 
applied to the substrate 7. 
Also, FIG. 7 shows the arrangement of magnets attached to the magnet 
attachment plate 12 and the substrate 7 in the magnetic film forming 
apparatus of still another embodiment in which each of a pair of auxiliary 
magnets 26 and 27 (28 and 29) is attached to each magnet of each pair 20 
and 21 (22 and 23) on the inside surface of the end portion at the side 
opposite to the gap, which is directed to the substrate 7. In this 
embodiment also, since the vertical expansion of the magnetic field at 
places near both vertical peaks of the substrate 7 can be suppressed more, 
it is possible to realize a more perfectly uniform parallelism in the 
magnetic field applied to the substrate 7 than that in the embodiment 
shown in FIG. 1. 
In the above embodiments, although magnets are used for the magnet field 
generation means, the excellently uniform parallelism of the magnetic 
field applied to the substrate 7 can also be realized by using solenoids. 
Furthermore, it has been confirmed by the inventors that the ratio of an 
area of the substrate 7 to an area in a horizontal x-y plane parallel to 
the surface of said substrate including the substrate inside said magnetic 
field generating means is larger than about 0.14, and the skew angle of 
the magnetic field applied to said substrate is kept at less than 0.6 deg. 
by the above embodiments. 
As explained above, in accordance with the present invention, since the 
uniformly parallel magnetic field can be applied to the whole of a 
substrate without increasing the size of the magnets even if the distance 
between the pairs of magnets is increased to correspond to a larger 
substrate, it is possible to obtain a magnetic film with a more 
outstanding magnetic characteristics than that formed by a conventional 
magnetic film forming apparatus. Furthermore, since it is possible to 
adjust the strength of the magnetic field applied to the substrate without 
losing the uniform parallelism of the magnetic field, by composing the 
magnet field generating system so that the positions of the magnets and 
the rotational angle of each magnet are adjustable, or by providing a pair 
of auxiliary magnets between the two pairs of magnets, the desired 
distribution of the magnetic field applied to the substrate can be 
realized.