Patent Application
20120118505
The present invention relates to a plasma processing apparatus for performing plasma processing on an object to be processed such as a semiconductor wafer, a substrate for liquid crystals, or an organic electroluminescent (EL) device.
Recently, a semiconductor device widely used is required to have higher speed operation and lower power consumption. In order to meet the requirements, the semiconductor device needs to be highly integrated and miniaturized. As the semiconductor device is highly integrated and miniaturized, an apparatus for manufacturing the semiconductor device is required to process fine structures on a semiconductor substrate with small damage.
As a plasma processing apparatus for performing processing with small damage, a microwave plasma processing apparatus which may generate plasma having a low electron temperature and a high density has drawn attention. In a microwave plasma processing apparatus used to etch a semiconductor substrate or form a film, a radial line slot antenna (RLSA) which is a planar antenna for uniformly generating plasma by uniformly introducing a microwave into a processing container is generally used. According to the RLSA, since a microwave may be uniformly supplied into the processing container, a semiconductor substrate may be uniformly processed in a plane. In addition, plasma having a high density may be generated in a wide area under the antenna. Also, since plasma having a low electron temperature may be generated, damage to a semiconductor substrate may be reduced.
The RLSA is connected to a coaxial waveguide which propagates a microwave. A microwave supplied from the coaxial waveguide propagates in a radial direction in a dielectric plate having a disc shape in the antenna. A wavelength of the microwave is compressed in the dielectric plate and the microwave having the compressed wavelength is radiated into a processing container through slots of a slot plate closely contacting a bottom portion of the dielectric plate. Due to an electric field of the microwave in the processing container, a plasma exciting gas in the processing container is excited to be in a plasma state.
The planar antenna is heated mainly by plasma during a process. When the planar antenna is heated, since the planar antenna is deformed due to a difference in thermal expansion coefficients between elements of the planar antenna, propagation characteristics of the microwave may be changed. The microwave propagates in a radial direction in the dielectric plate, which may be formed of alumina or the like, to form a standing wave, and is supplied into the processing container through the slots of the slot plate, which may be formed of copper or the like. When positions of the slots formed in the slot plate having a high thermal expansion coefficient are changed, since the microwave in the dielectric plate is disturbed, a propagation state of the microwave supplied into the processing container is changed. In this case, a plasma state excited by the microwave in the processing container is also changed. In particular, if the processing apparatus is large, an extent to which positions of the slots are changed due to a difference in thermal expansion coefficients is increased.
In order to prevent a planar antenna heated by plasma from being deformed, a cooling device in which a cooling jacket is provided on a planar antenna and a coolant flows in a coolant flow path of the cooling jacket to cool the planar antenna is disclosed in Patent Document 1.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2007-335346
However, in a conventional cooling device, since a coolant flowing in a coolant flow path is gradually heated, a temperature of the coolant at an inlet of the coolant flow path and a temperature of the coolant at an outlet of the coolant flow path are different from each other, and thus an amount of heat transferred to the coolant from a wall surface of the coolant flow path is not uniform. The amount of transferred heat is proportional to a temperature difference between the wall surface of the coolant flow path and the coolant. Accordingly, when the temperature of the coolant at the inlet and the temperature of the coolant at the outlet are different from each other, the temperature difference at the inlet and the temperature difference at the outlet are different from each other and thus the amount of transferred heat at the inlet and the amount of transferred heat at the outlet are different from each other.
In order to uniformly cool a planar antenna, in the conventional cooling device, one coolant flow path is folded at a middle point so that a front half of the coolant flow path and a front half of the coolant flow path are disposed adjacent to each other. When the coolant flow path is disposed in this way, an amount of heat transferred through the front half of the coolant flow path and an amount of heat transferred through the back half of the coolant flow path may be similar to each other.
However, when the coolant flow path is folded, a specific portion of the planar antenna may be uniformly cooled, but it is difficult to uniformly cool an entire circumferential portion of the planar antenna. Also, when the coolant flow path is folded, an amount of space which the coolant flow path fills is increased, thereby making it difficult to provide the coolant flow path in a narrow side wall of a processing container.
A recent microwave plasma processing apparatus for processing a semiconductor substrate which has a large diameter of 300 mm instead of 200 mm is required to not change a propagation state of a microwave of a planar antenna, as compared to a conventional apparatus. In order to meet the requirement, a cooling device is required to more uniformly cool the planar antenna.
Accordingly, an objective of the present invention is to provide a plasma processing apparatus and a cooling device for a plasma processing apparatus which may uniformly cool a planar antenna or a dielectric window in a circumferential direction.
In order to solve the above and other problems, according to an aspect of the present invention, there is provided a plasma processing apparatus including: a processing container which is sealable and in which plasma processing is performed on an object; a holding stage which is disposed in the processing container and holds the object; a dielectric window which is disposed on a ceiling portion of the processing container and seals the processing container; and a microwave antenna which is disposed on the dielectric window and radiates a microwave into the processing container, wherein a coolant flow path for cooling the dielectric window is provided in a side wall of the processing container, a coolant flows in a liquid or gaseous state in the coolant flow path without phase transition, and at least a portion of the coolant flow path elongated in a circumferential direction of the side wall has a cross-sectional area decreased toward downstream from upstream.
According to another aspect of the present invention, there is provided a plasma processing apparatus including: a processing container which is sealable and in which plasma processing is performed on an object; a holding stage which is disposed in the processing container and holds the object; a dielectric window which is disposed on a ceiling portion of the processing container and seals the processing container; a microwave antenna which is disposed on the dielectric window and radiates a microwave into the processing container; and a cooling plate which is disposed on the microwave antenna and includes a coolant flow path for cooling the microwave antenna, wherein a coolant flows in a liquid or gaseous state in the cooling plate without phase transition, and at least a portion of the coolant flow path extending in a circumferential direction of the cooling plate has a cross-sectional area decreased toward downstream from upstream.
According to another aspect of the present invention, there is provided a plasma processing apparatus including: a processing container which is sealable and in which plasma processing is performed on an object; a holding stage which is disposed in the processing container and holds the object; a plasma exciting unit which excites plasma in the processing container; and a coolant flow path which cools a member heated by the plasma, wherein a coolant flows in a liquid or gaseous state in the coolant flow path without phase transition, and at least a portion of the coolant flow path has a cross-sectional area decreased toward downstream from upstream.
According to another aspect of the present invention, there is provided a cooling device for a plasma processing apparatus which is provided in the plasma processing apparatus for performing plasma processing on an object and cools a member heated by plasma, the cooling device including a coolant flow path in which a coolant flows in a liquid or gaseous state without phase transition, wherein at least a portion of the coolant flow path has a cross-sectional area decreased toward downstream from upstream.
An amount of heat transferred to a coolant from a wall surface of a coolant flow path is defined by Q=hA(Tw−T0), where h denotes a heat transfer rate, A denotes a heat transfer area, and (Tw−T0) denotes a temperature difference between the coolant and the wall surface
When a cross-sectional area of the coolant flow path is reduced, a flow velocity of the coolant is increased, and thus the heat transfer rate h is increased. When a cross-sectional area of a coolant flow path is decreased toward downstream from upstream as in the present invention, since a decrement in a temperature difference as a temperature of a coolant is increased may be compensated by an increment in the heat transfer rate h, an amount of heat transferred in the coolant flow path in a longitudinal direction may be maintained almost constant. Accordingly, a planar antenna or a dielectric window may be uniformly cooled in a circumferential direction.
100: processing container
105: dielectric window
115: holding stage
140: upper plate (side wall of processing container, cooling device)
145: coolant flow path
145
a: first coolant flow path
145
b: second coolant flow path
210: cooling plate (cooling device)
905: planar antenna (microwave antenna, plasma exciting unit)
910: upper cover
915: coolant flow path
U: processing space
W: wafer (substrate to be processed)
A plasma processing apparatus according to an embodiment of the present invention will now be explained with reference to the attached drawings.
A processing container 100 having a substantially cylindrical shape is formed of aluminum or stainless steel containing aluminum. A protection coating film such as an aluminum oxide (alumina) coating film or an Yttria (Y2O3) coating film is formed on an inner wall surface of the processing container 100.
A dielectric window 105 which seals the processing container 100 and through which a microwave is transmitted is provided on a ceiling portion of the processing container 100 with a sealing member 110 therebetween. The dielectric window 105 is formed of quartz or ceramic (such as alumina or aluminum nitride). The dielectric window 105 is fixed to the processing container 100 by using a fixing ring 200 disposed on an upper portion of a side wall of the processing container 100.
A gas introduction unit 510 through which a process gas is introduced into a processing space U is provided in the side wall of the processing container 100. In the present embodiment, the processing space U is divided into two areas by a lower shower 515, and a plasma exciting gas such as an argon gas or a krypton gas is introduced from the gas introduction unit 510 disposed over the lower shower 515 and a process gas is introduced from the lower shower 515. The gas introduction unit 510 and the lower shower 515 are connected to a gas supply source 505. Alternatively, the lower shower 515 may not be provided, and a plasma exciting gas, a process gas, and a cleaning gas may be optionally introduced from the gas introduction unit 510. If the lower shower 515 is not provided, an upper portion (hereinafter, referred to as an upper plate 140) of the side wall of the processing container 100 divided by the lower shower 515 is integrally formed with the side wall. Also, the gas introduction unit 510 having a shower head shape may be provided in the ceiling portion of the processing container 100.
A coolant flow path 145 for cooling the dielectric window 105 is provided in the upper plate 140, which serves as a cooling device. A fluorine-based liquid having high electrical insulating characteristic and high thermal conductivity flows as a coolant in the coolant flow path 145. While the coolant flows in the coolant flow path 145, the coolant flows in a liquid state in the coolant flow path 145 without phase transition. When the dielectric window 105 is cooled by using the upper plate 140, a temperature of the upper plate 140 may be equal to or lower than 90° C. (a target temperature ranges from 70 to 80° C.) and a temperature of the dielectric window 105 may be equal to or lower than 150° C. A structure of the coolant flow path 145 will be explained below.
An inlet/outlet (not shown) through which a substrate to be processed is transferred is provided in a lower portion of the side wall of the processing container 100 divided by the lower shower 515. The inlet/outlet is opened and closed by a gate valve.
An exhaust port 135 for depressurizing the processing container 100 through vacuum suction is formed at a bottom of the processing container 100. The exhaust port 135 is connected to an exhaust device (not shown).
A holding stage 115 on which a wafer W, which is the substrate to be processed, is held is provided in the processing container 100. A high frequency power supply 125b for applying a bias to adsorb the wafer W by using an electrostatic force is connected to the holding stage 115.
A planar antenna 905 which has a disc shape and serves as a microwave antenna for exciting plasma by supplying a microwave into the processing space U is disposed on the dielectric window 105. The planar antenna 905 includes a slot plate 905b having two types of slots perpendicular to each other, and a dielectric plate 905a provided between the slot plate 905b and a conductive surface 210a which reflects a microwave. The planar antenna 905 is also called a radial line slot antenna (RLSA). The planar antenna 905 is fixed to the processing container 100 by using an antenna fixing unit. A microwave generated by a microwave source 335 propagates in a transverse electric (TE) mode through a rectangular waveguide 305, passes through a coaxial converter 310, and propagates in a transverse electromagnetic (TEM) mode in a coaxial waveguide 340. The coaxial waveguide 340 is connected to a center of the planar antenna 905. The microwave introduced from the center of the planar antenna 905 propagates in a radial direction through the dielectric plate 905a, in which a wavelength of the microwave is compressed, and is emitted into the processing space U from the slots formed in the slot plate 905b. A conductor of the coaxial waveguide 340 is cooled by a coolant supplied from a coolant supply source 405.
A cooling plate 210 which serves as a cooling device for cooling the planar antenna 905 is provided on the conductive surface 210a. The cooling plate 210 may be integrally formed with the conductive surface 210a. A coolant flow path 915 for cooling the planar antenna 905 is formed over the conductive surface 210a. A fluorine-based liquid having high electrical insulating characteristic and high thermal conductivity flows as a coolant in the coolant flow path 915. While the coolant flows in the coolant flow path 915, the coolant flows in a liquid state in the coolant flow path 915 without phase transition. When the planar antenna 905 is cooled by using the cooling plate 210, a temperature of the cooling plate 210 may be in a range of 110 to 120° C. and a temperature of the planar antenna 905 may be in a range of 150 to 160° C. A configuration of the coolant flow path 915 of the cooling plate 210 will be explained below.
The coolant flow path 145 may be formed such that a plurality of the coolant flow paths 145 each having a doughnut shape turning one time are vertically arranged instead of a spiral shape. In this case, each coolant flow path 145 turning one time has an inlet and an outlet. Each coolant flow path 145 turning one time has a constant width and a height decreased toward the outlet from the inlet. A height of the coolant flow path 145 turning a first time located at an upper stage, a height of the coolant flow path 145 turning a second time located at a middle stage, and a height of the coolant flow path 145 turning a third time located at a lower stage are the same when azimuths are the same.
When the coolant flow path 145 is actually formed, the upper plate 140 is vertically divided into a plurality of portions according to a number of times the coolant flow path 145 turns. A groove constituting the coolant flow path 145 is formed in each of the plurality of portions of the upper plate 140. The groove of the coolant flow path 145 is formed by using a numerically controlled (NC) lathe using a tool such as an endmill. When the groove of the coolant flow path 145 is formed via cutting process by using the tool, since a cutting depth of the tool may be controlled through numerical control, it is easier to change a depth (a height) of the groove instead of changing a width of the groove. As shown in
Since a cross-sectional area of each of the coolant flow paths 145 and 915 is decreased toward downstream from upstream, an amount of heat transferred in each of the coolant flow paths 145 and 915 may be maintained constant. A causal relationship between ‘decreasing a cross-sectional area of a coolant flow path’ and ‘maintaining an amount of transferred heat constant’ is as follows.
An amount of heat Q transferred to a coolant from a wall surface of a coolant flow path is defined by the following equation.
Q=hA(Tw−T0) [Equation 1]
In Equation 1, “Q” denotes an amount of transferred heat (W), “h” denotes a heat transfer rate (W/m2K), “A” denotes a heat transfer area (m2), “Tw” denotes a temperature of a surface of a wall surface (K), and “T0” denotes a temperature of a coolant (K).
Since a temperature of a coolant is gradually increased toward downstream from upstream due to heat exchange, in order to maintain an amount of transferred heat constant and a temperature of a wall surface constant in a coolant flow path, a heat transfer rate needs to be increased toward the downstream from the upstream. The heat transfer rate h is defined by Equation 2.
h=Nuk/L [Equation 2]
In Equation 2, “Nu” denotes a Nusselt number, “k” denotes a thermal conductivity (W/m2K), and “L” denotes a length of a flow path.
Since the thermal conductivity k of a fluid and the length of the flow path L are constant, in order to increase h, the Nusselt number Nu needs to be increased.
The Nusselt number Nu is defined by Equation 3.
Nu=0.664Re1/2Pr1/3
Re=UL/v [Equation 3]
In Equation 3, “Pr” denotes a Prandtl number, “U” denotes a flow velocity (m/s), and “v” denotes a kinematic viscosity coefficient (m2/s).
Since the kinematic viscosity coefficient v is constant, the Nusselt number Nu may be increased by increasing the flow velocity U. When a cross-sectional area of a coolant flow path is decreased toward downstream from upstream, a flow velocity is increased. Accordingly, the Nusselt number Nu is increased in Equation 3, and the heat transfer rate h is increased in Equation 2. When a cross-sectional area of a coolant flow path is decreased toward downstream from upstream, the heat transfer area A of Equation 1 is reduced. However, an increment in the heat transfer rate h may be greater than a decrement in the heat transfer area A. As a result, the amount of transferred heat Q of Equation 1 may be maintained constant.
Table 1 shows main conditions of results of the calculation.
As shown in Table 1, when a cross-sectional area of a coolant flow path is constant as in the conventional example, a difference in a heat transfer line density between an inlet and an outlet of the coolant flow path is about 40%. However, when a height of a coolant flow path is decreased, a difference in a heat transfer line density may be reduced to 4.6% (in the first-degree expression), 0.7% (in the second-degree expression), and 0.1% (in the third-degree expression).
Next, how a difference in a heat transfer line density is affected by a change in a flow rate (that is, a dependence of a difference in a heat transfer line density on a flow rate) was calculated. Calculation conditions of the third-degree expression where a difference in a heat transfer line density is the lowest were used. That is, the calculation was made under conditions: a width of a coolant flow path is 8 mm, a height of a portion of the coolant flow path at an inlet is 9 mm (a height is reduced in a third-degree expression manner toward downstream), a value obtained by subtracting a temperature of a coolant from a temperature of an upper plate is 20° C., and an amount of transferred heat is 2 kW. Results of the calculation are shown in
While a temperature distribution is changed according to a flow rate of a coolant, since a difference in a heat transfer line density is about 2% in a range, the difference in the heat transfer line density hardly depends on the flow rate of the coolant.
Table 3 shows results obtained after calculating how a difference in a heat transfer line density is affected by a structure of a coolant flow path (a dependence of a difference of a heat transfer line density on a structure of a coolant flow path).
Even when a coolant flow path turns two times by being folded as in a conventional example, a difference in a heat transfer line density may be reduced from 36.2% to 7.4% and 24.4% as compared to a case where a coolant flow path turns one time. However, since space is needed to fold a coolant flow path, there is a limitation in reducing a difference in a heat transfer line density. As in an example of the present invention (a slope type), a difference in a heat transfer line density may be reduced to a value less than 2% by changing a height without folding a coolant flow path.
Also, the present invention is not limited to the embodiments and various modifications may be made without departing from the scope of the present invention. For example, a coolant flow path of the present invention may be formed in a lower shower, and the lower shower may be cooled by flowing a gas such as an argon gas in the coolant flow path.
A conductive film may be integrally formed by plating or the like on a top surface and a bottom surface of a dielectric plate, the conductive film formed on the top surface may be used as a conductive plate which reflects a microwave, and the conductive film formed on the bottom surface may be used as a slot plate through which a microwave is transmitted.
This application claims the benefit of Japanese Patent Application No. 2009-146838 filed on Jun. 19, 2009.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-146838 | Jun 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/058499 | 5/20/2010 | WO | 00 | 1/23/2012 |
