Patent Application
20140150975
The present invention relates to an inductively coupled plasma processing device which can be used for various surface processings of a base body and other purposes.
Plasma processing devices have been used for a film formation process in which a thin-film is formed on a base body, and for an etching process on the surface of a base body. Such plasma processing devices include: a capacitively-coupled plasma processing device in which plasma is produced by the electromagnetic field generated by applying a radio-frequency voltage between electrodes; and inductively-coupled plasma processing devices in which plasma is produced by the electromagnetic field generated by feeding a radio-frequency current to a radio-frequency antenna (coil). Capacitively-coupled plasma processing devices are advantageous in that they are inexpensive compared to inductively-coupled plasma processing devices, while inductively-coupled plasma processing devices are advantageous in that they can produce high-density plasma and therefore the film formation rate is large compared to capacitively-coupled plasma processing devices.
Inductively-coupled plasma processing devices generally use an external antenna system in which a radio-frequency antenna for forming an induction electromagnetic field is provided outside a vacuum chamber. In recent years, the area of substrate bodies to be processed and thin films formed thereon have grown in size. Consequently, the size of vacuum chambers increases, which leads to the use of thicker walls in the vacuum chambers due to the difference in pressure between the outside and the inside of the vacuum chambers. This disadvantageously lowers the intensity of the induction electromagnetic field formed in a vacuum chamber, and decreases the density of the produced plasma.
On the other hand, the inductively-coupled plasma processing device described in Patent Document 1 uses an internal antenna system in which a radio-frequency antenna is provided inside a vacuum chamber. With the internal antenna system, the density of plasma can be easily increased irrespective of the thickness of the walls of a vacuum chamber. Hence, this device is suitable both large-size substrate bodies and thin films to be processed.
However, placing a radio-frequency antenna inside a vacuum chamber makes it difficult to carry out maintenance on the device. Generally, in order to prevent heating by the radio-frequency current and the consequent increase in the impedance, the radio-frequency antenna is formed using a conductor tube, and coolant is circulated in the conductor tube. This requires elaborate connection configurations between the vacuum chamber and the radio-frequency antenna, and between the ends of the conductor tube and the coolant supply/discharge ports. This makes it difficult to attach and detach the radio-frequency antenna.
Another problem is that the radio-frequency antenna is directly exposed to plasma. In an inductively-coupled plasma processing device, a direct current self-bias voltage is generated between the radio-frequency antenna and the plasma. If the device uses an external antenna system, ions accelerated by the self-bias voltage are impeded by the walls of the vacuum chamber, whereas in an internal antenna system, the antenna conductor is sputtered.
In order to prevent this, in the invention described in Patent Document 2, the surface of the radio-frequency antenna conductor is covered by a pipe made of a dielectric (or insulating) material, such as ceramics that are less sputtered than the antenna conductor, quartz, or other materials. However, forming a dielectric pipe to match the shape of the antenna requires an advanced technology and a high manufacturing cost. In addition, even if the antenna conductor tube is cooled by circulating coolant, the dielectric pipe may not be adequately cooled and may reach a very high temperature (e.g. several hundred degrees Celsius). In this case, the dielectric pipe becomes vulnerable to rupture by the thermal stress, and the antenna conductor is not sufficiently cooled due to the heat transmitted from the dielectric pipe. This increases the impedance of the antenna conductor, and prevents a stable supply of plasma.
The problem to be solved by the present invention is to provide an internal antenna-type plasma processing device which is capable of producing stable plasma, easily maintained, and is low-cost.
To solve the aforementioned problem, the present invention provides a plasma processing device, including:
a) a vacuum chamber;
b) a radio-frequency antenna provided so as to protrude inwards from an inner wall of the vacuum chamber; and
c) a housing made of a dielectric material for isolating the radio-frequency antenna from an atmosphere inside the vacuum chamber, the dielectric housing having no contact with the radio-frequency antenna.
With the plasma processing device according to the present invention, the dielectric housing prevents the internal antenna system radio-frequency antenna from being sputtered. This housing need not be manufactured to match the shape of the radio-frequency antenna, as required in the case of the dielectric pipe. The housing may have an appropriate shape that is easy to manufacture, which can suppress the manufacturing cost. Another advantage is that the same shape can be used for antennas of any shape. Since the radio-frequency antenna and the housing are not in contact with each other, the heat generated by feeding a radio-frequency current to the antenna conductor will not be directly transmitted to the housing. This can suppress the temperature rise of the housing.
The plasma processing device according to the present invention may preferably include: an antenna insertion opening that connects the inside of the dielectric housing and the outside of the vacuum chamber, the antenna insertion opening being provided in the inner wall of the vacuum chamber; and a cover for closing the antenna insertion opening. This configuration allows an attachment and detachment of the radio-frequency antenna through the antenna insertion opening, facilitating the maintenance of the device. In this case, it is more preferable that the radio-frequency antenna be attached to the cover. This allows an easy setting and removal of the radio-frequency antenna just by attaching and detaching the cover to the opening.
It is preferable that the inside of the dielectric housing is filled with an inert gas, is in a vacuum, or is filled with a solid dielectric material. This prevents unrequired electric discharges from occurring inside the dielectric housing.
The radio-frequency antenna may be formed with a conductor tube through which a cooling medium can be supplied. This can suppress heating of the antenna conductor caused by radio-frequency current, and the consequent increase in the impedance.
In the case where the coolant is an inert gas, the plasma processing device according to the present invention may include: a gas passage hole or holes provided in a tube wall in a portion of the conductor tube contained in the dielectric housing; and a gas discharge port for allowing the inert gas flowing out through the gas passage hole or holes into the dielectric housing to be discharged to the outside of the dielectric housing and the vacuum chamber. This enables the inside of the dielectric housing to be filled with an inert gas, which can prevent unrequired electric discharges from occurring inside the dielectric housing. Simultaneously, the conductor tube is cooled both from outside and inside, which prevents increase in the impedance of the antenna conductor and enables a stable supply of plasma. In addition, since the dielectric housing can also be cooled, the dielectric housing is prevented from breaking due to thermal stresses.
The radio-frequency antenna may be formed by a linear conductor formed in a shape in which a U-shaped portion or a cornered U-shaped (or rectangular) portion is included. A U-shaped conductor or a cornered U-shaped portion includes two parallel straight sections. When an electric current is fed to the conductor, the directions of the electric current flowing through the two straight sections oppose (i.e. lie at 180 degree angle). Therefore, the directions of the magnetic field lines generated from the electric current flowing through the two straight sections become the same in the area between the two straight sections, which enables obtaining a large intensity of the magnetic field and the plasma density in this area.
The plasma processing device according to the present invention may include a plurality of the radio-frequency antennas and the dielectric housings. This allows a production of substantial plasma within the whole vacuum chamber with high uniformity of plasma density.
In the plasma processing device according to the present invention, the radio-frequency antenna is provided so as to protrude inwards from the inner wall of the vacuum chamber, and the radio-frequency antenna is surrounded by the dielectric housing which has no contact with the radio-frequency antenna. This prevents the radio-frequency antenna from being sputtered regardless of the shape of the antenna. Since this dielectric housing has a shape simpler than a dielectric pipe, it is easy to manufacture, which can lower the manufacturing cost. Maintenance of the radio-frequency antenna can be facilitated when the plasma processing device includes: the antenna insertion opening for connecting the dielectric housing and the outside of the vacuum chamber, the antenna insertion opening being provided in the inner wall of the vacuum chamber; and a cover for closing the antenna insertion opening. When the dielectric housing is filled with an inert gas and the inert gas is circulated, a production of unwanted electric discharges in the dielectric housing and a temperature rise of the antenna conductor are prevented. This enables a stable supply of plasma.
Embodiments of the plasma processing device according to the present invention are described with reference to
First, the plasma processing device 10 of the first embodiment will be described. As shown in
The antenna unit 20 will now be described. As shown in
A radio-frequency antenna 23 which is formed with a cornered U-shaped conductor is placed inside the dielectric housing 21. The portions of both ends of the cornered U-shaped conductor are fixed to the cover 22 via a feedthrough 24 for ensuring the air tightness and the electric insulation between the radio-frequency antenna 23 and the cover 22. One end of the cornered U-shaped conductor is connected to a radio-frequency power source and the other end is connected to a ground. The cornered U-shaped conductor is formed with a tube, to which second gas introduction ports 231 are provided at both ends for introducing an inert gas into the tube. Gas passage holes 232 for sending the inert gas in the tube into the dielectric housing 21 are provided on the outer side of the tube wall of the cornered U-shaped conductor, i.e. on the side facing the dielectric walls of the dielectric housing 21. The cover 22 has a second gas discharge port 25 for discharging the inert gas and the remaining gas (air) other than the inert gas in the dielectric housing 21 to the outside thereof. In this configuration, a gas passage is formed from the second gas introduction ports 231, the gas passage holes 232, and the dielectric housing 21 to the second gas discharge port 25.
In the present embodiment, the internal dimensions of the dielectric housing 21 are 5 cm in depth (the vertical direction of
As an example of the operation of the plasma processing device 10 of the first embodiment, the process of depositing a film-forming material on the base body S is hereinafter described. Initially, a base body S is loaded through the base-body transfer opening 15 into the vacuum chamber 11 and placed onto the base-body holder 12. After the base-body transfer opening 15 is closed, the air, steam and other contents in the vacuum chamber 11 are discharged through the first gas discharge port 13 using the vacuum pump. Meanwhile, an inert gas is introduced from the second gas introduction ports 231 into the dielectric housing 21 through the conductor tube and the gas passage holes 232. This replaces the air in the dielectric housing 21 with the inert gas and discharges the air and excess inert gas through the second gas discharge port 25 to the outside of the dielectric housing 21.
Subsequently, while the inert gas is being supplied, a plasma production gas and a material gas are introduced from the first gas introduction ports 14, and a radio-frequency power is supplied to the radio-frequency antenna 23. By means of this radio-frequency power supply, an induction electromagnetic field is produced around the radio-frequency antenna 23. This induction electromagnetic field is introduced through the walls of the dielectric housing 21 into the vacuum chamber 11 and ionizes the plasma production gas, whereby plasma is produced. The material gas, which has been introduced into the vacuum chamber 11 together with the plasma production gas, is decomposed by the resultant plasma, to be deposited on the base body S.
While the radio-frequency power is being supplied to the radio-frequency antenna 23, the inert gas is blown at the dielectric walls of the dielectric housing 21 through the conductor tube and the gas passage holes 232. Therefore, the inert gas serves as a coolant for suppressing the temperature rise of the radio-frequency antenna 23 and the dielectric walls caused by the radio-frequency power supply.
In comparison to an external type, the plasma processing device 10 of the present embodiment can create a stronger induction electromagnetic field within the vacuum chamber 11 as the radio-frequency antenna 23 is located in the dielectric housing 21 protruding into the vacuum chamber 11. Furthermore, since the radio-frequency antenna 23 is separated from the vacuum chamber 11 by the walls of the dielectric housing 21, the plasma is prevented from etching into the radio-frequency antenna 23 and shortening its life, and the material of the radio-frequency antenna 23 is prevented from being mixed, as an impurity, into the film being formed or the base body being processed.
In addition, the inert gas is introduced from the second gas introduction ports 231 through the conductor tube and the gas passage holes 232 into the dielectric housing 21, so that the dielectric housing 21 is filled with the inert gas. This can prevent unrequired electric discharge and can cool the radio-frequency antenna 23 with the inert gas which serves as a coolant. As just described, the plasma processing device 10 of the present embodiment can prevent an electric discharge, and cool the radio-frequency antenna 23 and the dielectric housing 21 by a single gas supply means, which allows a simplification of the apparatus.
A plasma production experiment was performed using the plasma processing device 10 of the present embodiment. In the experiment, a mixture gas of argon and hydrogen (plasma production gas) was introduced into the vacuum chamber 11 through the first gas introduction ports 14 to a pressure of 1 Pa. Simultaneously, a nitrogen gas (inert gas) was introduced from the second gas introduction ports 231 to the conductor tube and the dielectric housing 21 at a rate of 2.5 liters per minute. Then, a radio-frequency power of 13.56 MHz in frequency and 1 kW in output was supplied to the radio-frequency antenna 23. After a sufficient amount of time, a plasma with the plasma density of 1.2×1011 cm−3 was observed at a point located 10 cm below the bottom of the dielectric housing 21. The plasma density is almost inversely proportional to the distance from the bottom of the cornered U-shaped conductor. When the output of the radio-frequency power was varied within the range of 1 kW to 3 kW, the plasma density changed substantially in proportion to the output of the radio-frequency power (
In the plasma processing device 10 of the first embodiment, as shown in
In the plasma processing device 10 of the first embodiment, the dielectric housing 21 may be attached so as to cover the opening 1111 of the vacuum chamber 11 from below, and the cover 22 may be attached so as to cover the opening 1111 from above (
Instead of being filled with an inert gas, the inside of the dielectric housing 21 may become a vacuum by discharging gas from the second gas discharge port 25 using a vacuum pump (
Alternatively the inside of the dielectric housing 21 may be filled with a solid dielectric material 29 (
Next, an example is described in which the radio-frequency antenna 23A with a different shape is used (
In the present embodiment, the length of the two straight sections (a first straight section 3121 and a second straight section 3122) of the U-shaped section 312 is 10 cm, and the distance between the conductors of the first straight section 3121 and the second straight section 3122 is 3 cm. The “distance between the conductors” means the distance between the inner sides of the two parallel conductors. The short side length of the inside of the dielectric housing 21A is 6 cm, which is longer than that of the dielectric housing 21 of the first embodiment, so as to correspond to the shape of the radio-frequency antenna 23A. The depth and the long side length of the inside of the dielectric housing 21A are the same as those of the dielectric housing 21 of the first embodiment. The sizes of the opening 1111A and the cover 22A are larger in the short side direction than those in the first embodiment so as to correspond to the short side of the inside of the dielectric housing 21A.
In the radio-frequency antenna 23A having a shape of
An experiment was performed using the plasma processing device of the present embodiment under the same conditions as the first embodiment. That is, a mixture gas of argon and hydrogen was introduced into the vacuum chamber 11 to a pressure of 1 Pa. Simultaneously, a nitrogen gas was introduced from the second gas introduction ports 231 into the conductor tube and the dielectric housing 21 at a rate of 2.5 liters per minute. Then, a radio-frequency power of 13.56 MHz in frequency and 1 kW in output was supplied to the radio-frequency antenna 23A. After a sufficient amount of time, a plasma with the plasma density of 1.8×1011 cm−3 was observed at a point located 10 cm below the bottom of the dielectric housing 21. This value is greater than that (1.2×1011 cm−3) in the first embodiment.
In the present embodiment, the explanation for a U-shape is given. However, the U-shaped section 312 may be replaced by a cornered U-shaped unit, as in the first through the fourth embodiments, or may be replaced by an S-shaped section 312A as shown in
In the radio-frequency antenna 23B of the present embodiment, if the U-shaped section 312 is replaced by a commonly-used circular antenna conductor, the intensity H0 of the magnetic field generated in the center of the antenna conductor is expressed by the following formula:
H
0
=I/(2r),
where r denotes the radius, and I denotes the intensity of the applied electric current.
In the case where a U-shaped antenna conductor is used, the intensity H11 of the magnetic field in the center of the antenna conductor is expressed by the following formula:
H
11=2I/(πd),
where d denotes the distance between the two straight sections.
That is, when a U-shaped antenna conductor is used, the intensity of the magnetic field will be 4r/(πd) times as large as that of the circular antenna conductor. In this case, since the intensity of the magnetic field is inversely proportional to the value of d, as the distance between the two straight sections becomes narrower, the intensity of the inductive magnetic field increases. In the present embodiment, a U-shaped antenna conductor having the same length as that of the circular antenna conductor could produce a magnetic field of an approximately 1.7-fold strength. The value of the ratio d/L is not particularly limited, where d denotes the distance between the two parallel conductors in a U-shaped or cornered U-shaped section and L denotes the length of the two conductors in their longitudinal direction. However, it is preferable that the value of the ratio is between 0.05 and 0.5. The entire length of the antenna conductor may be preferably equal to or less than a quarter of the wavelength of the radio-frequency power supplied to the radio-frequency antenna.
Another example of the shape of the radio-frequency antenna is now described with reference to
Another example of the shape of the radio-frequency antenna is now described with reference to
In the present embodiment, a feedthrough is omitted in order to decrease the distance between the first foot 331A and the second foot 331B. Instead, an insulator cover 22 is used for electrical insulation from the radio-frequency antenna 23C, and a vacuum seal 34 is provided between the first foot 331A and the cover 22 and between the second foot 331B and the cover 22.
In the present embodiment, the total length of the linear section of the first U-shaped section 332A, the linear connector 334, and the linear section of the second U-shaped section 332B in the radio-frequency antenna 23C is 10 cm, the distance between the two linear sections of the U-shaped sections is 3 cm, and the outside diameter is 6.4 mm. The dimensions of the dielectric housing 21A are the same as those of the fifth embodiment (5 cm depth, 13 cm long side, and 6 cm short side).
In the present embodiment, the plane, including the first U-shaped section 332A and the second U-shaped section 332B, is provided so as to be parallel to the insertion direction of the radio-frequency antenna 21. Therefore, a strong oscillating magnetic field is formed on both sides of this plane, which can further increase the density of the plasma produced in the vacuum chamber 11. Since the direction of the magnetic field lines generated from the radio-frequency antenna 23C is almost parallel to the inner walls of the vacuum chamber 11, the electrons in the plasma bound by the magnetic field lines are prevented from being scattered toward the inner walls of the vacuum chamber 11. Hence, it is possible to generate stable electric discharge plasma in the vacuum chamber 11.
An experiment was performed using the plasma processing device of the present embodiment under the same conditions as those of the first and the fifth embodiments. That is, a mixture gas of argon and hydrogen was introduced into the vacuum chamber 11 to a pressure of 1 Pa. Simultaneously, a nitrogen gas was introduced from the second gas introduction ports 231 into the conductor tube and the dielectric housing 21 at a rate of 2.5 liters per minute. Then, a radio-frequency power of 13.56 MHz in frequency and 1 kW in output was supplied to the radio-frequency antenna 23A. After a sufficient amount of time, a plasma with the plasma density of 2.2×1011 cm−3 was observed at a point located 10 cm below the bottom of the dielectric housing 21. This value is higher than that (1.2×1011 cm−3) in the first embodiment and that (2.2×1011 cm−3) in the fifth embodiment. This is because high-density plasma was generated on both sides of the U-shaped portions of the radio-frequency antenna 23C, and the resultant plasma reached the space under the dielectric housing 21.
An example of the plasma processing device including a plurality of radio-frequency antennas is now described with reference to
The distances from the feeding points to the feeding terminals of the antennas 23B are approximately the same. The positions of the feeding points are adjusted so that the impedances of the two antennas 23B to the radio-frequency current are equal with respect to the feeding points. In the present embodiment, a mixture gas of argon and hydrogen of 0.5 Pa in gas pressure was introduced into the vacuum chamber, and a radio-frequency power of 13.56 MHz in frequency and 1 kW in output was supplied to the feeding point, so that electric discharge plasma was excited in the vacuum chamber.
With this configuration, approximately uniform electric discharge plasma was generated in the vacuum chamber 11 using both radio-frequency antennas 23B. The plasma density distribution at a certain distance from the top wall 111 varies depending on the pressure of the electric discharge gas, radio-frequency power, and other factors. However, the conditions for obtaining a uniform plasma density distribution are a design choice, and electric discharge plasma of any size can be generated.
The two radio-frequency antennas may be provided in one dielectric housing, or may be provided in different dielectric housings. Providing a plurality of radio-frequency antennas can increase the size of substrate bodies to be processed, and the size of thin films formed thereon, improving the mass productivity of the device.
In the aforementioned embodiment, a pair of radio-frequency antennas are used. However, the number of radio-frequency antennas is not limited to two, but may be three or more. Alternatively, a plurality of groups of multiple radio-frequency antennas may be aligned.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/065256 | 9/6/2010 | WO | 00 | 4/22/2013 |
