Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1998-04-17
2002-01-29
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192150, C204S192200
Reexamination Certificate
active
06342131
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a multilayer thin film and a sputtering deposition method thereof. In particular, the present invention relates to a method of depositing a multilayer thin film by means of magnetron sputtering which controls the magnetic field.
At present, a multilayer film is formed by depositing it with an evaporation or a sputtering method using two or more different materials. When two or more materials are deposited, two or more sputtering cathodes are needed (as taught by, for example, Masaki Koike et al. “Nanofabrication of Multilayer Zone Plates by Helicon Plasma Sputtering” Jpn. J. Appl. Phys. Vol. 34 (1995), pp. 6754-6757). The reference discloses a technique of forming multilayer zone plates by depositing alternately Ag layers and Al layers with the sputtering technique which employs two helicon cathodes. In addition, a one cathode technique using composite targets is proposed (as taught by, for example, Brij. B. Lai et al. “Magnetic and recording properties of monolayer and multilayer thin-film media by using composite targets. J. Appl. Phys. 79(8), Apr. 15, 1995, pp. 5336-5338). The reference discloses a method of forming a magnetic film with Cr as an underlayer using concentric annular shaped composite targets of Cr and magnetic materials.
The use of two or more cathodes, however, makes a sputtering system complex and makes it difficult to control thicknesses of respective layers and impurity contents. That is, if two materials are deposited simultaneously, compositions within a substrate become uneven due to separation in the space. Meanwhile, if alternate deposition is conducted between two materials, interfacial films of quite low nanometer level are disadvantageously formed among the layers due to switching of deposition modes.
It is meanwhile well known that the sputtering system is a system for depositing layers of certain materials on a substrate. This includes a magnetron sputtering system utilizing a magnetic field for purposes of accelerating the sputtering rate of deposited materials. In the system, the application of a magnetic field crossing an electrical field causes electrons emitted from a cathode to make a trochoid movement and high density plasma is generated on a target, thus making it possible to increase sputtering rate with relatively low voltage.
FIG. 1
is a typical magnetron sputtering system. It has a cathode section
13
and an anode
15
within a vacuum chamber
11
. A to-be-processed substrate
17
is provided at the anode
15
. The cathode section
13
has a plurality of magnets
19
. A material
21
referred to as a target hereinafter is mounted on a susceptor
23
of the cathode section
13
. In recent years, a system wherein an anode
15
and a cathode section
13
are turned upside down has been frequently used. This is because it is preferable for carrying a to-be-processed substrate.
If the system is operated, a container
11
is evacuated from an exhaust outlet and inert gas, such as argon, is injected from an injection port at low pressure. DC or RF power is applied onto the cathode section
13
. The magnets
19
form a closed magnetic circuit of strong magnetic field on the surface of the target
21
. If such a magnetic field exists on the target
21
, then electrons make a trochoid movement and enclosed in the vicinity of the target
21
and the electrons and gas molecules collide with each other more frequently.
The inert gas within the container
11
collides with accelerated electrons and turns into ions. As a result, plasma occurs in the vicinity of the cathode section
13
. Positive gas ions from the plasma, which are accelerated in the cathode section direction, collide with the target
21
and expel some of target materials out of the target
21
. The expelled materials are deposited on the substrate
17
.
In this way, the magnetic field increases electron density on the target
21
, thereby increasing ionization ratio in this region. Although the magnetic field has been long used for improving the degree of sputtering deposition, it has been aimed only to increase the deposition rate of materials.
The magnetron sputtering system now on the market employs a fixed magnetic field or an alternating magnetic field. The fixed magnetic field is realized by installing permanent magnets to cover the entire back surface of a target as shown in the above description. It is also realized by using electromagnets through which fixed magnetizing current flows. The alternating magnetic field can be realized by moving periodically permanent magnet pieces to the back surface of the target or by using electromagnets with which a single or a plurality of coils are magnetized by periodically changing current.
As described above, sputtering rate can be increased by using the magnetic field. A method of controlling thicknesses of the layers of the multilayer film and impurity concentration with high accuracy has not been however known.
BRIEF SUMMARY OF THE INVENTION
It is therefore the first object of the present invention to provide a method of depositing a multilayer film, which method is capable of accurately controlling film thickness.
It is the second object of the present invention to provide a method of depositing a multilayer film, which method is capable of accurately controlling composition.
To attain the above objects, a thin film deposition method in the first aspect of the present invention comprises the steps of:
preparing a magnetron sputtering system having magnetic field generation means for changing a magnetic field;
mounting, as a target, a composite material including not less than two components on a cathode of the magnetron sputtering system;
providing a to-be-processed substrate on an anode of the magnetron sputtering system;
evacuating a chamber of the magnetron sputtering system and thereafter filling the chamber with inert gas; and
controlling a cycle of the alternating magnetic field to change a ratio of the not less than two components of the thin film in a film thickness direction of the thin film, by applying, onto the cathode, one of DC power and RF power and, at the same time, the alternating magnetic field from a lower portion of the target.
The magnetic field generation means has an electromagnet, and the step of controlling a cycle of the alternating magnetic field can include a step of changing a cycle of magnetizing current of the electromagnet.
The magnetic field generation means has a permanent magnet, and the step of controlling a cycle of the alternating magnetic field can include a step of controlling a cycle of moving the permanent magnet below the target.
It is preferable that the composite material serving as the target is a composite metal including not less than two metal elements.
The composite metal is preferably one selected from a group consisting of WSi, CoFe, CoCu, CoCr, FeCu, FeNi, MnNi, ternary combinations of three components, CoCrTa and FeNiCoMnCu, the ternary combinations of three components including three selected from a group consisting of Co, Fe, Cu, Cr, Ni and Mn.
A multilayer thin film deposition method in the second aspect of the present invention comprises the steps of:
preparing a magnetron sputtering system having magnetic field generation means for changing a magnetic field;
mounting, as a target, a composite material including not less than two components on a cathode of the magnetron sputtering system;
providing a to-be-processed substrate on an anode of the magnetron sputtering system;
evacuating a chamber of the magnetron sputtering system and thereafter filling the chamber with inert gas; and
applying, onto the cathode, one of DC power and RF power and, at the same time, an alternating magnetic field having a predetermined maximum value from a lower portion of the target to obtain a predetermined composition changing in a film thickness direction of the thin film.
The magnetic field generation means has an electromagnet, and the step of applying the alternating magnetic field can include a step of changing a maximum valu
Benedict John
Katata Tomio Y.
Parks Christopher
Sardesai Viraj Y.
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