Patent Application
20120064259
This invention relates to a sputtering apparatus widely used in forming a film of metal or insulator and, in particular, relates to a magnetron sputtering apparatus using a rotary magnet, which is a processing apparatus for applying a predetermined surface treatment to a workpiece such as a liquid crystal display substrate or a semiconductor substrate.
Sputtering apparatuses are widely used in the manufacture of optical disks, in the manufacture of electronic devices such as liquid crystal display elements and semiconductor elements, and further, in the formation of metal thin films and insulator thin films in general. In the sputtering apparatus, a raw material for thin film formation is used as a target, an argon gas or the like is converted into plasma by DC high voltage or high-frequency power, and the target is activated by the plasma-converted gas so that the target is melted and scattered to be coated on a substrate to be processed.
As a sputtering film forming method, a predominant film forming method uses a magnetron sputtering apparatus in which, in order to raise the film forming rate, magnets are disposed on the back side of a target to generate the lines of magnetic force parallel to a target surface, thereby confining plasma to the target surface to obtain high-density plasma.
For the purpose of improving the target utilization efficiency to reduce the production cost and enabling the stable long-term operation, the present inventors have previously proposed a rotary magnet sputtering apparatus. This is a remarkable sputtering apparatus which is configured such that a plurality of plate-like magnets are continuously disposed on a columnar rotary shaft and, by rotating them, a magnetic field pattern on a target surface moves with time, thereby not only significantly improving the utilization efficiency of a target material, but also preventing charge-up damage and ion irradiation damage due to plasma (see Patent Document 1).
Patent Document 1: WO2007/043476
In general, in a magnetron sputtering method, in order to raise the film forming rate to improve the throughput, it is effective to increase the plasma excitation power. In this event, when the plasma excitation power is increased, the plasma heat flow increases so that it is not possible to prevent a target and a backing plate supporting the target from rising to a high temperature. As a consequence, there is a possibility that an indium layer bonding the target to the backing plate is melted to cause detachment of the target or that deformation or the like of the backing plate occurs.
Also in the sputtering apparatus shown in Patent Document 1, the necessity for cooling a target and so on is taken into account so that a coolant passage is provided at an end portion of a backing plate (outside its portion holding the target). However, a further improvement of the cooling mechanism is preferable in terms of efficient cooling.
It is an object of this invention to provide a sputtering apparatus that can efficiently cool a target and a backing plate to thereby deal with an increase in plasma excitation power.
Further, it is an object of this invention to provide a sputtering apparatus that can perform efficient cooling by selecting a position where a cooling medium flows.
According to a first aspect of this invention, there is provided a rotary magnet sputtering apparatus comprising a substrate placing stage for placing thereon a substrate to be processed, a backing plate on which a target is to be fixedly placed so as to face the substrate, and a magnet disposed on a side opposite to the substrate placing stage with respect to a portion where the target is placed, and adapted to confine plasma on a target surface by forming a magnetic field on the target surface using the magnet, the rotary magnet sputtering apparatus characterized in that the magnet comprises a rotary magnet group having a plurality of plate-like magnets on a columnar rotary shaft and a fixed outer peripheral plate-like magnet or a fixed outer peripheral ferromagnetic member which is arranged in parallel to the target surface around the rotary magnet group, the magnet is structured so that a magnetic field pattern on the target surface moves with time by rotating the rotary magnet group along with the columnar rotary shaft, and a passage for causing a cooling medium to flow therein is provided between the rotary magnet group and the backing plate.
According to another aspect of this invention, there is provided the rotary magnet sputtering apparatus according to the above described aspect, characterized in that the rotary magnet group forms one or a plurality of helical plate-like magnet groups by helically bonding the plate-like magnets to the columnar rotary shaft with either an N-pole or an S-pole directed toward the outer side in a diameter direction of the columnar rotary shaft.
According to another aspect of this invention, there is provided the rotary magnet sputtering apparatus according to any one of the above described aspects, characterized in that the even-numbered helical plate-like magnet groups are provided on the columnar rotary shaft such that helices adjacent to each other in an axial direction of the columnar rotary shaft form mutually different magnetic poles, i.e. an N-pole and an S-pole, on the outer side in a diameter direction of the columnar rotary shaft.
According to another aspect of this invention, there is provided the rotary magnet sputtering apparatus according to any one of the above described aspects, characterized in that the fixed outer peripheral plate-like magnet or the fixed outer peripheral ferromagnetic member is a magnet which is configured to surround the rotary magnet group as seen from the target side and which forms one of an N-pole and an S-pole on the target side.
According to another aspect of this invention, there is provided the rotary magnet sputtering apparatus according to any one of the above-described aspects, characterized in that the passage is formed so that the cooling medium flows helically in a space between the plurality of helical plate-like magnet groups.
According to another aspect of this invention, there is provided the rotary magnet sputtering apparatus according to any one of the above-described aspects, characterized in that the cooling medium is caused to flow by setting the Reynolds number thereof to 1000 to 5000.
According to another aspect of this invention, there is provided the rotary magnet sputtering apparatus according to any one of the above described aspects, characterized in that the passage includes a space surrounded by side walls of the helical plate-like magnet groups, the columnar rotary shaft, and a shielding plate disposed outside the helical plate-like magnet groups and the cooling medium flows helically along the helical plate-like magnet groups. According to another aspect of this invention, there is provided the rotary magnet sputtering apparatus according to any one of the above-described aspects, characterized in that at least part of the shielding plate is a ferromagnetic member.
According to another aspect of this invention, there is provided a sputtering method characterized by using the rotary magnet sputtering apparatus according to any one of the above described aspects and forming a film of a material of the target on the substrate while rotating the columnar rotary shaft.
According to another aspect of this invention, there is provided a method of manufacturing an electronic device, characterized by comprising a step of carrying out sputtering film formation on the substrate using the sputtering method according to the above-described aspect.
According to this invention, in a rotary magnet sputtering apparatus, it is possible to improve the cooling efficiency and thus to increase the allowable power application amount for plasma excitation, thereby realizing an improvement in film forming rate and throughput.
Hereinbelow, embodiments of this invention will be described with reference to the drawings.
Referring to
In
On the other hand, when the plasma excitation power is increased in order to raise the film forming rate to improve the throughput, the plasma heat flow increases.
The heat flow from plasma is greatest at the target portion 403 where plasma excitation is performed. Therefore, in this embodiment, in order to enhance the cooling efficiency, the cooling water passage 404 is provided as the cooling mechanism in the backing plate 401 adjacent to the target portion 403.
Since, as described above, the cooling water passage 404 is provided adjacent to the contact surface with the target portion 403, the cooling can be efficiently carried out.
In this case, the cooling water passage 404 is preferably as close to the target portion 403 as possible. Accordingly, the backing plate 401 should be relatively thick.
On the other hand, in order to improve the plasma excitation efficiency, it is necessary to increase the magnetic field strength on a surface of the target portion 403. The horizontal magnetic field strength (component, in a direction parallel to the target surface, of the magnetic field strength) in a plasma loop is preferably set to 500 gauss or more.
For this, the distance (T/S distance) 405 between the rotary magnet 402 and the surface of the target portion 403 shown in
Actually, when the cooling water passage 404 is provided in the backing plate 401 while setting the T/S distance to 20 mm, the thickness of the backing plate 401 is set to 12 mm and the backing plate 401 and the rotary magnet 402 are spaced apart from each other by 1 mm so as to prevent contact therebetween. In this case, it has been found that the thickness of the target portion 403 is preferably set to about 7 mm.
Herein, the target portion 403 and the backing plate 401 are bonded to each other by an indium layer. It has been confirmed that deformation of the backing plate 401 and so on can be prevented with the structure of
As described above, according to the first embodiment, since the cooling water passage 404 is provided in the backing plate 401, it is possible to prevent deformation of the backing plate 401 and detachment of the target layer 403, which are otherwise caused by the increase in plasma heat flow.
Next, a second embodiment of this invention will be described in detail with reference to the drawings.
Referring to
In
The power frequency of the RF power supply 9 is 13.56 MHz. Although this embodiment employs an RF-DC coupled discharge system which also enables superimposed application by the DC power supply, sputtering may be DC discharge sputtering only by the DC power supply or RF discharge sputtering only by the RF power supply.
A material of the columnar rotary shaft 2 may be an ordinary stainless steel or the like, but it is preferable that the columnar rotary shaft 2 be partly or entirely made of a ferromagnetic substance with a low magnetic resistance such as, for example, a Ni—Fe-based high magnetic permeability alloy or iron. In this embodiment, the columnar rotary shaft 2 is made of the iron. The columnar rotary shaft 2 can be rotated by a non-illustrated gear unit and motor.
Referring to
The columnar rotary shaft 2 is configured so as to be attached with the magnets on its outer periphery, can be easily made thick, and has a structure that is strong against bending deformation due to magnetic forces applied by the magnets. In order to stably generate a strong magnetic field, each of the plate-like magnets forming the helical plate-like magnet groups 3 is preferably a magnet with a high residual magnetic flux density, a high coercive force, and a high energy product, such as, for example, a Sm—Co-based sintered magnet with a residual magnetic flux density of about 1.1 T or a Nd—Fe—B-based sintered magnet with a residual magnetic flux density of about 1.3 T. In this embodiment, the Nd—Fe—B-based sintered magnet is used. The plate-like magnets of the helical plate-like magnet groups 3 are each magnetized in a direction perpendicular to its plate surface and are helically bonded to the columnar rotary shaft 2 to form a plurality of helices such that the helices adjacent to each other in an axial direction of the columnar rotary shaft form mutually different magnetic poles, i.e. N-poles and S-poles, on the outer side in a diameter direction of the columnar rotary shaft.
When the fixed outer peripheral plate-like magnet 4 is seen from the target 1, it is configured to surround a rotary magnet group composed of the helical plate-like magnet groups 3. Further, the fixed outer peripheral plate-like magnet 4 is magnetized so that the target 2 side thereof becomes an S-pole. An Nd—Fe—B-based sintered magnet is used also as the fixed outer peripheral plate-like magnet 4 for the same reason as for the plate-like magnets of the helical plate-like magnet groups 3.
Next, referring to
In the above-mentioned example, the surface of one of the helical plate-like magnet groups 3 has the N-pole while the surfaces of the other helical plate-like magnet groups 3 adjacent to such one of the helical plate-like magnet groups 3 and the surface of the fixed magnet 4 around the helical plate-like magnet groups 3 have the S-poles so that the S-poles are arranged to surround in a loop the N-pole of the surface of the first helix, but the N- and S-poles may be reversed. Even if a ferromagnetic member, i.e. not a magnet magnetized in advance, is used instead of each of the plate-like magnets of the other helical plate-like magnet groups 3 adjacent to such one of the helical plate-like magnet groups 3 and/or instead of the fixed magnet around the rotary magnets, a loop-shaped planar magnetic field surrounding in a loop the N-pole (or the S-pole) of the surface of the first helix is obtained and, as a result, loop-shaped plasma is obtained.
The placing stage 14 with the substrate 13 placed thereon has a moving mechanism adapted to pass under the target 1 and thus causes the substrate 13 to move thereto while plasma is excited on the target surface, thereby allowing film formation to be carried out (see
Referring back to
As described above, by surrounding the outside of the helical plate-like magnet groups 3 with the cooling mechanism formed by the first and second shielding plates 7 and 8, it is possible to form helical passages between side walls of the helical plate-like magnet groups 3 (i.e. spaces between the helical plate-like magnet groups 3) and the columnar rotary shaft 2.
In the illustrated embodiment, by causing the cooling water 6 to flow in the passages defined by the helical spaces, it is possible to cool the backing plate 5 and the target portion 1. In this case, the cooling water 6 flows helically along the helical spaces between the helical plate-like magnet groups 3.
As described above, with the configuration that the cooling water 6 is caused to flow in the passages defined by the helical spaces, as compared with the case where the cooling water passage is provided in the backing plate 5 as in the first embodiment, the cooling water passages can be provided over a wider area so that it is possible to further enhance the cooling efficiency. As a consequence, the film forming rate can be increased as compared with the first embodiment.
Further, using the cooling mechanism of this invention, it is not necessary to provide the cooling water passage in the backing plate 5 as in the first embodiment. Therefore, the backing plate 5 can be reduced in thickness as compared with the first embodiment and, further, the strength of the backing plate 5 can be increased as compared with the case where the cooling water passage is provided therein.
Further, since the backing plate 5 can be reduced in thickness, the target 1 can be increased in thickness as compared with the first embodiment so that it is possible to reduce the replacement frequency of a target as compared with the first embodiment and thus to improve the production efficiency. In this case, the thickness of the backing plate 5 can be reduced to about 5 mm and, as a result, the thickness of the target 1 can be increased to 14 mm.
However, if the plasma excitation power further increases to require further cooling, the above-mentioned cooling mechanism and the structure in which the cooling water passage is provided in the backing plate 5 may be used jointly.
In order to ensure heat conduction, the copper first shielding plate 7 and the backing plate 5 should be in tight contact with each other. The second shielding plate 8 is formed of iron being a ferromagnetic substance and thus also serves to form a magnetic circuit between the fixed outer peripheral magnet 4 and the rotary magnet portion so that it is possible to form a strong magnetic field on the target surface. Since the first shielding plate 7 is located at the position close to the target 1, if the first shielding plate 7 is formed of a ferromagnetic substance, it is not possible to form a strong magnetic field on the target 1 surface and, therefore, use is made of copper which is a material being not a ferromagnetic substance and is excellent in heat conduction.
In order to seal the cooling water 6, the shielding plate 7 is also attached through O-ring seals. The columnar rotary shaft 2 also uses the O-ring shaft seals 607, thereby preventing leakage of the cooling water 6 to the outside.
It is preferable to cause the cooling water 6 to flow substantially between the helical plate-like magnet groups 3 by providing the first and second shielding plates 7 and 8 as close to the helical plate-like magnet groups 3 as possible. With this configuration, since the cooling water 6 flows helically along the helical plate-like magnet groups 3, the cooling water 6 whose temperature is raised by cooling the target 1 in the vicinity of the backing plate 5 is rapidly transported to the side opposite to the backing plate 5 so that the heat is removed quite efficiently.
Further, in order to maximize the cooling efficiency in the cooling mechanism according to this invention, it is important to take into account the Reynolds number of the cooling water. The Reynolds number Re is defined by Re=V×d/v. Herein, V is the velocity of a fluid (herein, cooling water), d the pipe diameter, and v the coefficient of kinematic viscosity. The Reynolds number which is also used as an index for distinguishing between a turbulent flow and a laminar flow and which is obtained when the flow velocity increases so that a laminar flow transitions to a turbulent flow is called the critical Reynolds number. In the case of the flow in a circular pipe, the critical Reynolds number is 2,000 to 4,000. In general, the cooling efficiency is low when the flow velocity is small to form a laminar flow, while the cooling efficiency is improved when the flow velocity increases to reach a turbulent flow region. However, even if the flow velocity increases more than that, although the cooling efficiency is enhanced slightly, the pressure loss of the cooling water increases so that the energy for causing the cooling water to flow increases, which is thus not preferable. As a result, the cooling is enabled most efficiently when the cooling water flows at a flow velocity close to the critical Reynolds number. That is, it is preferable to set the Reynolds number to 1000 to 5000 and desirably 2000 to 4000. In this embodiment, in order to control the Reynolds number, the plate for adjusting the cross-sectional area of the cooling water passages is disposed at the helical magnet side walls as indicated by 16 in
While this invention has been described with reference to the embodiments, various settings such as the cooling water amount are not limited to the embodiments.
A magnetron sputtering apparatus according to this invention can be not only used for forming an insulating film or a conductive film on a semiconductor wafer or the like, but also applied for forming various films on a substrate such as a glass substrate of a flat display device, and can be used for sputtering film formation in the manufacture of storage devices or other electronic devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-118169 | May 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/054867 | 3/19/2010 | WO | 00 | 12/1/2011 |
