Patent Application
20090311869
The present invention relates to a shower plate for use in a plasma processing apparatus, more particularly, in a microwave plasma processing apparatus and a manufacturing method thereof, and a plasma processing apparatus, a plasma processing method and an electronic device manufacturing method using the shower plate.
A plasma process and a plasma processing apparatus are essential for the manufacture of a recent ultrafine semiconductor device called a deep sub-micron device or deep sub-quarter micron device having a gate length of about 0.1 μm or less, or the manufacture of a flat panel display of a high-resolution including a liquid crystal display.
Various plasma excitation methods are conventionally adopted for the plasma processing apparatus for use in the manufacture of the semiconductor device or the liquid crystal display. Especially, a high-frequency excitation plasma processing apparatus of a parallel plate type or an inductively coupled plasma processing apparatus is generally utilized. In the conventional plasma processing apparatus, however, since the plasma generation has been non-uniform and the electron density has been found to be high only in a limited region, it has been difficult to perform a uniform process over the entire surface of a target substrate with a high processing rate, i.e., with a high throughput. Especially, such problem becomes serious when processing a substrate having a large diameter. Besides, these conventional plasma processing apparatuses also have other essential problems such as the occurrence of damage on a semiconductor device formed on the target substrate due to the high electron temperature, the occurrence of a high level metal contamination due to the sputtering a processing chamber wall, and so forth. Accordingly, in the conventional plasma processing apparatus, it is getting more and more difficult to meet recent demands for further miniaturization of semiconductor devices or liquid crystal displays and enhancement of productivity.
Meanwhile, there has been conventionally proposed a microwave plasma processing apparatus which employs high-density plasma excited by a microwave electric field without using a DC magnetic field. For example, there has been proposed a plasma processing apparatus having a configuration in which microwave is emitted into a processing chamber from a planar antenna (radial line slot antenna) having a number of slots arranged to generate the microwave in a uniform manner, and plasma is excited by ionizing a gas in the processing chamber by an electric field of the microwave (see, for example, Patent Document 1). The microwave plasma excited by this method is capable of achieving high plasma density over a wide area directly under the antenna, and it is possible to perform a uniform plasma process in a short period of time. Further, in the microwave plasma generated by this method, the electron temperature is low because the plasma is generated by the microwave, and the damage or the metal contamination of the target substrate can be prevented. Moreover, since it is possible to easily excite the plasma uniformly even on a large-area substrate, the plasma processing apparatus can be effectively applied to a large-size liquid crystal display manufacturing process or a semiconductor device manufacturing process using a semiconductor substrate having a large diameter.
In such plasma processing apparatus, a shower plate having a plurality of gas discharge holes is typically used to uniformly supply a plasma excitation gas into the processing chamber. Due to the use of the shower plate, however, the plasma formed directly under the shower plate may flow backward through the gas discharge holes of the shower plate. If the plasma flows backward through the gas discharge holes, abnormal discharge or gas deposition takes place, resulting in deterioration of yield or transmission efficiency of the microwave for exciting the plasma.
As a means to prevent the backflow of the plasma toward the gas discharge holes, there have been proposed many improvements of the structure of the shower plate.
For example, Patent Document 2 discloses that it is effective to set the diameter of the gas discharge hole to be smaller than twice the sheath thickness of the plasma formed directly under the shower plate. However, reducing the diameter of the gas discharge hole is not sufficient as the means to prevent the backflow of the plasma. Especially, if plasma density is increased from about 1012 cm−3, which is conventional plasma density, to about 1013 cm−3 for the purpose of reducing damage while increasing processing rate, the backflow of the plasma becomes dominant, so that its prevention cannot be achieved only by controlling the diameter of the gas discharge hole. Moreover, it is actually difficult to form the gas discharge hole having such fine hole diameter in a shower plate main body by a hole processing, so that there occurs a problem of processability.
Further, Patent Document 3 proposes using a shower plate made of a porous ceramics sintered body having gas permeable property. This tries to prevent the backflow of the plasma by the wall of a number of pores constituting the porous ceramics sintered body. However, in case of a shower plate made of a general porous ceramics sintered body sintered under normal temperature and pressure, the pore diameters have a great variability in size, ranging from several μm to about 20 μm. Further, since the maximum crystal diameter is as large as about 20 μm and the structure is not uniform, the surface flatness is poor. In addition, if the shower plate's surface making contact with the plasma is made of the porous ceramics sintered body, an effective surface area increases, so that recombination of electrons and ions of the plasma increases, resulting in deterioration of power efficiency of plasma excitation. Moreover, also disclosed in Patent Document 3 is a structure in which, instead of forming the entire shower plate with the porous ceramics sintered body, a general porous ceramics sintered body sintered under normal temperature and pressure is installed at gas discharge openings formed in a shower plate made of alumina having high density, and the gas is discharged through the porous ceramics sintered body. In this structure, however, since the plasma still makes contact with the general porous ceramics sintered body having substantially the same property as that of the porous ceramics sintered body sintered under the normal temperature and pressure, the aforementioned problems caused by the poor surface flatness still remain.
Further, in Patent Document 4, the present applicant has already proposed a means to prevent backflow of plasma by the control of a diameter size of gas discharge hole, and not by the structure of the shower plate. That is, by setting the diameter of the gas discharge hole to be less than about 0.1 to 0.3 mm, with the precision of diameter size tolerance within ±0.002 mm, the backflow of plasma is prevented, while removing variability of gas discharge amount.
However, when this shower plate was actually used in a microwave plasma processing apparatus under the condition of plasma density increased up to 1013 cm−3, discolored portions of light brown, which are considered to be the result of plasma backflow, were found in a space 402 formed between a shower plate main body 400 and a cover plate 401, for charging plasma excitation gas therein, and vertical holes 403 communicating with this space.
Patent Document 1: Japanese Patent-Laid-open Publication No. H9-63793
Patent Document 4: International Publication No. 06/112392 pamphlet
In view of the foregoing, the present invention provides a shower plate capable of more securely preventing the occurrence of backflow of plasma and enabling efficient plasma excitation.
The present inventors conducted researches under the thought that the backflow of plasma is affected by a ratio of the length of a gas discharge hole to the hole diameter thereof (length/hole diameter, hereinafter referred to as an “aspect ratio”). The present inventors finally reached a conclusion that the backflow of the plasma can be suppressed dramatically if the aspect ratio is set to be equal to or greater than about 20, and completed the present invention.
That is, in accordance with the present invention, there is provided a shower plate disposed in a processing chamber of a plasma processing apparatus and provided with a plurality of gas discharge holes for discharging a plasma excitation gas to generate plasma in the processing chamber, wherein an aspect ratio of the gas discharge hole is equal to or greater than about 20 in order to prevent the backflow of the plasma.
It is difficult to form a minutely narrow and long gas discharge hole having such aspect ratio as defined in the present invention in a shower plate main body by a hole processing method using a drill or other machining tools, and a processability problem also arises. In the present invention, a ceramics member having one or a plurality of gas discharge holes is installed in a multiplicity of vertical holes of a shower plate. That is, the gas discharge holes are formed in the ceramics member which is separated from the shower plate, and this ceramics member is installed in the vertical hole opened in the shower plate. With this configuration, a yield loss of the shower plate due to processing errors of the gas discharge holes can be suppressed in comparison with the case of forming the gas discharge holes in the shower plate by a hole processing, and the minute and long gas discharge holes having the aspect ratio defined in the present invention can be easily formed. Furthermore, the ceramics member having the gas discharge holes can be formed by an injection molding, an extrusion molding, a special cast molding, or the like.
As for a specific size of the gas discharge hole, it is desirable that the diameter thereof is equal to or less than twice a sheath thickness of the plasma generated directly under the shower plate, and the length of the gas discharge hole is longer than a mean free path of electrons in the processing chamber.
Further, a plasma excitation gas can be supplied into a plasma processing apparatus by using a shower plate in accordance with the present invention; plasma can be generated by exciting the supplied plasma excitation gas by microwave; and oxidation, nitridation, oxynitridation, CVD, etching or plasma irradiation can be performed on a substrate by using the plasma.
Furthermore, a shower plate in accordance with the present invention, which includes a vertical hole provided with a ceramics member having one or more gas discharge holes, can be manufactured by inserting a green body, a debound body, a tentatively sintered body or a sintered body of a ceramics member having one or more gas discharge holes into a vertical hole of a green body, a debound body or a tentatively sintered body of a shower plate having the vertical hole formed by molding raw material powder, and then sintering them at the same time. Further, it can be manufactured by inserting, together with the ceramics member, a green body, a debound body, a tentatively sintered body or a sintered body of a porous gas flowing body into a vertical hole, and then sintering them at the same time.
In accordance with the present invention, the backflow of the plasma through the vertical hole portion of the shower plate can be prevented, and the abnormal discharge or the deposition of gas inside the shower plate can be suppressed. Therefore, the deterioration of yield or transmission efficiency of microwave for exciting plasma can be prevented.
Hereinafter, examples of the present invention will be described based on embodiments.
Disposed at an upper portion of the processing chamber 102 via a sealing O-ring 107 is a plate-shaped shower plate 106 which has a diameter of about 408 mm and a dielectric constant of about 9.8, and is made of dielectric alumina having a low microwave dielectric loss (equal to or less than about 9×10−4, desirably equal to or less than about 5×10−4). The shower plate 105 is installed at a position corresponding to the target substrate 103 on the holding table 104, and constitutes a part of an exterior wall of the processing chamber 102. The shower plate 105 is provided with a number of (e.g., 230) openings, i.e., vertical holes 105. Further, in the processing chamber 102, a cover plate 108 made of alumina is installed via a sealing O-ring 109 on the top surface side of the shower plate 106, i.e., on the opposite side from the holding table 104 with respect to the shower plate 106.
Further, as for each of the vertical holes 105 shown in
Further,
Now, a method for introducing the plasma excitation gas into the processing chamber will be explained with reference to
Provided on the top surface of the cover plate 108 covering the top surface of the shower plate 106 are a slot plate 116 of a radial line slot antenna opened by a number of slits for radiating microwave; a wavelength shortening plate 117 for propagating the microwave in a diametric direction, and a coaxial waveguide 118 for introducing the microwave into the antenna. Further, the wavelength shortening plate 117 is interposed between the slot plate 116 and a metal plate 119. The metal plate 119 is provided with a cooling flow path 120.
With this configuration, the plasma excitation gas supplied from the shower plate 106 is ionized by the microwave radiated from the slot plate 116, so that high-density plasma is generated in an area within several millimeters directly under the shower plate 106. The generated plasma reaches the target substrate 103 by the diffusion. Besides the plasma excitation gas, a gas for actively generating radicals, e.g., an oxygen gas or an ammonia gas may also be introduced from the shower plate 106.
In the illustrated plasma processing apparatus, a lower shower plate 121 made of a conductor such as aluminum, stainless steel or the like is disposed between the shower plate 106 and the target substrate 103 in the processing chamber 102. The lower shower plate 121 includes a plurality of gas flow paths 121a through which a processing gas supplied from a processing gas supply port 122 is provided to the target substrate 103 in the processing chamber 102, and the processing gas is discharged into a space between the lower shower plate 121 and the target substrate 103 through a multiplicity of nozzles 121b formed in gas flow paths 121a's surfaces facing the target substrate 103. Here, in case of a plasma-enhanced chemical vapor deposition (PECVD) process, a silane gas or a disilane gas is introduced as the processing gas when forming a silicon-based thin film, whereas a C5F8 gas is introduced when forming a low dielectric film. Furthermore, a CVD process using an organic metal film as the processing gas is also possible. Further, in case of a reactive ion etching (RIE) process, a C5F8 gas and an oxygen gas are introduced when etching a silicon oxide film, whereas a chlorine gas or a HBr gas is introduced when etching a metal film or silicon. When ion energy is needed for the etching, an RF power supply 123 is connected to an electrode inside the holding table 104 via a capacitor, and a self-bias voltage is generated on the target substrate 103 by applying an RF power thereto. The kind of the flowing processing gas is not limited to the above-mentioned examples, but the kind of the flowing gas and the pressure can be determined depending on the process.
The lower shower plate 121 is provided with an opening 121c between the neighboring gas flow paths 121a. The opening 121c has a size capable of allowing the plasma, which is excited by the microwave in the region above the lower shower plate 121, to pass therethrough effectively so as to be diffused into the space between the target substrate 103 and the lower shower plate 121.
Further, a heat flow introduced into the shower plate 106 as a result of the exposure to the high-density plasma is cooled by a coolant such as water flowing through the cooling flow path 120 via the slot plate 116, the wavelength shortening plate 117 and the metal plate 119.
Referring again to
Further, the thickness d of the sheath formed on the surface of an object in contact with the plasma is obtained from the following equation.
Here, V0 represents a potential difference (V) between the plasma and the object; Te indicates an electron temperature (eV); and λD is the Debye length calculated by the following equation.
Here, ∈0 indicates a vacuum permeability; k represents a Boltzmann constant, and ne stands for an electron density of the plasma.
As shown in Table 1, if the electron density of the plasma increases, the Debye length decreases. Thus, it can be said that the smaller the hole diameter of the gas discharge hole 113a is, the more desirable it is in the aspect of preventing the backflow of the plasma.
Further, by setting the length of the gas discharge hole 113a to be longer than a mean free path, which is a mean distance for electrons to travel before electrons are scattered, the backflow of the plasma can be greatly reduced. In Table 2, mean free paths of electrons are provided. The mean free path is in inverse proportion to the pressure, and it becomes 4 mm at 0.1 Torr. Though the mean free path actually becomes shorter than 4 mm because the pressure at the gas introducing side of the gas discharge hole 113a is high, in
Here, since the mean free path is literally a mean distance, it should be noted that there statistically exist electrons which proceed a longer distance without being scattered. Accordingly, as shown in
To suppress a backflow of plasma through the pores and an abnormal discharge in the second vertical hole 105b, the pore diameter of the porous ceramics sintered body 114 is desirably set to be equal to or less than twice the sheath thickness of the high-density plasma formed directly under the shower plate 106, and more desirably equal to or less than the sheath thickness. The average pore diameter of the porous ceramics sintered body 114 in
With the shower plate 106 having the above-described configuration, the backflow of the plasma toward the gas introducing side of the vertical holes 105 can be prevented, and the generation of abnormal discharge or gas deposition inside the shower plate 105 can be suppressed. Therefore, the deterioration of yield or transmission efficiency of the microwave for exciting the plasma can be prevented. Furthermore, an efficient plasma excitation is enabled without reducing the flatness of the surface in contact with the plasma. Besides, since the gas discharge holes 113a are formed in the ceramics member 113 separate from the shower plate 105 by the extrusion molding method or the like, long and minute gas discharge holes can be more easily formed in comparison with a case of forming the gas discharge holes in the shower plate by a hole processing.
Further, as a result of supplying the plasma excitation gas to the target substrate 103 uniformly and discharging the processing gas to the target substrate 103 from the lower shower plate 121 via the nozzles 121b, there is generated a uniform flow of the processing gas from the nozzles 121b of the lower shower plate 121 toward the target substrate 103, resulting in a reduction of processing gas components returning to the upper portion of the shower plate 106. As a consequence, decomposition of processing gas molecules as a result of excessive dissociation due to exposure to the high-density plasma can be suppressed, and deterioration of the microwave introducing efficiency due to deposition of the processing gas onto the shower plate 106 is unlikely to occur, though the processing gas is a deposition gas. Therefore, the time of the cleaning process can be shortened, while the process stability and reproducibility can be improved, resulting in enhancement of productivity and realization of high-quality substrate processing.
Besides, in the present embodiment, the numbers, the diameters and the lengths of the first vertical holes 105a and the second vertical holes 105b, and the number, the diameter and the length of the gas discharge holes 113a opened in the ceramics member 113 are not limited to the present embodiment.
In the present embodiment, disposed at an upper portion of a processing chamber 102 via a sealing O-ring 107 is a shower plate 200 which has a dielectric constant of about 9.8, and is made of dielectric alumina having a low microwave dielectric loss (equal to or less than about 9×10−4). The shower plate 200 is installed at a position corresponding to a target substrate 103 on a holding table 104, and constitutes a part of an exterior wall of the processing chamber 102. Further, at a wall surface 201 constituting the processing chamber 102, a ring-shaped space 203 surrounded by two sealing O-rings 202 and the lateral surface of the shower plate 200 is provided at a position corresponding to the lateral side of the shower plate 200. The ring-shaped space 203 communicates with the gas inlet port 110 for introducing a plasma excitation gas.
Meanwhile, a multiplicity of horizontal holes 204 each having a diameter of about 1 mm is provided in the lateral side of the shower plate 200 so as to be opened toward the center of the shower plate 200 in horizontal direction. At the same time, a number (e.g., about 230) of vertical holes 205 is opened to communicate with the processing chamber 102 as well as with the horizontal holes 204.
In the present embodiment, the plasma excitation gas from the gas inlet port 110 is introduced into the ring-shaped space 203 and finally introduced into the processing chamber 102 through the gas discharge holes 113a, which are provided at leading end portions of the vertical holes 205, via the horizontal holes 204 and the vertical holes 205.
In this embodiment, similar effects to those obtained in the first embodiment can also be achieved.
Further, in the present embodiment, the numbers, the diameters and the lengths of the first vertical holes 205a and the second vertical holes 205b, and the number, the diameter and the length of the gas discharge holes 113a opened in the ceramics member 113 are not limited to the present embodiment. Moreover, the porous ceramics sintered body installed at the gas introducing side of the gas discharge holes 113a is not an essential component.
In the embodiment of
The shower plates including the aforementioned ceramics members 113 and 113′ installed in the vertical holes in respective embodiments can be manufactured by the following methods.
About 100 parts by mass of Al2O3 powder having an average particle diameter of about 0.6 μm and a purity of about 99.99% was mixed and kneaded with about 5 parts by mass of extrusion molding binder and 15 parts by mass of moisture. Then, the mixture was extruded from a preset extrusion molding nozzle and dried, so that a ceramics member green body provided with lower holes of gas discharge holes (i.e., holes to become gas discharge holes after the sintering) was obtained.
A debound body obtained by heating the ceramics member green body at about 400 to 600° C., a tentatively sintered body obtained by heating the ceramics member green body at about 600 to 1200° C., a preliminarily sintered body obtained by sintering the ceramics member green body at about 1200 to 1400° C. (at which relative density reaches about 95%), and a sintered body sintered so as to obtain a relative density equal to or higher than about 95% were prepared. Further, measured were a heating shrinkage rate at each heating temperature (sintering temperature) and a size after the heating. Further, when performing the sintering at the same temperature as the sintering temperature of the shower plate, a sintering shrinkage rate was measured to be about 18.8% for the green body.
Meanwhile, as a shower plate material, a spray-dried and granular powder, which has an average particle diameter of about 70 μm and is obtained by mixing Al2O3 powder having an average particle diameter of about 0.6 μm and a purity of about 99.99% with 3 mass % of wax, was press-molded at various levels of pressure ranging from about 78 to 147 MPa, and then by molding and processing it to have preset sizes of outer diameter, thickness, horizontal holes and vertical holes, a shower plate green body was prepared. Further, the sintering shrinkage rate of this shower plate green body varied depending on the press-molding pressure. In addition, the sintering shrinkage rate was about 19% at 78 MPa, while it was about 16.2% at 147 MPa.
Here, the ceramics member green body (whose outer diameter corresponding to the second vertical hole 105b of
At this time, the size of the second vertical hole 105b after the sintering is calculated to have inner diameter×(100%−19%)=3.7×0.81=2.997 mm. Likewise, the outer diameter of the ceramics member corresponding to the second vertical hole 105b becomes 3.695×0.812=3.000 mm. The difference 0.003 mm between the inner diameter and the outer diameter corresponding to the second vertical hole 105b functions as a heat fixing force between them, so that a sintering binding force between them is generated, and firm installation and fixing can be achieved.
The same shower plate green body as prepared in the first manufacture example and a debound body, which is heated at 450° C. and hardly suffers a heating shrinkage, were prepared, and the debound body, the tentatively sintered body, the preliminarily sintered body and the sintered body for the ceramics member, which were prepared in the first manufacture example, were installed in each vertical hole, and their sintering was performed at the same time. In the present manufacture example, as in the first manufacture example, the debound body and the shower plate green body having the inner diameter of about 3.7 mm corresponding to the second vertical hole 105b shown in
Further, heat fixing stress, which corresponds to a size difference of about 0.103 mm (equal to or greater than about 100 μm), is generated by installing, in the vertical hole, a ceramics member allowing an outer diameter of its sintered body corresponding to the second vertical hole 105b to be about 3.1 mm, and sintering them at the same time. The majority of heat fixing stress is absorbed into the shower plate side by a dislocation of constituent crystalline particles, a diffusion sintering or a slight degree of plastic flow, while only a part of heat fixing stress is absorbed into the ceramics member. As a result, both the shower plate and the ceramics member can be firmly installed without suffering a damage or a crack due to a tensile stress or a compression stress.
The shower plate shown in
Further, by installing the sintered body of the ceramics member in a vertical hole of a preliminarily sintered body which is obtained by heating the shower plate green body to have a relative density ranging from about 95 to 97% and performing a HIP process at 1450° C. under a non-reactive gas atmosphere having a pressure of about −1500 kg/cm2, a simultaneously sintered firm installation can be accomplished.
Moreover, as for the sizes and shapes of the vertical holes of the shower plate and the ceramics member, it is desirable that they are formed in a straight shape, as shown in
As for the porous gas flowing body, a tentatively sintered powder is obtained by heating, at a temperature of about 80° C., a spray-dried and granular powder, which has an average particle diameter of about 70 μm and is obtained by mixing Al2O3 powder having an average particle diameter of about 0.6 μm and purity of about 99.99% with 3 mass % of wax. Then, 3 mass % of Al2O3 powder for the shower plate is added and mixed, and the mixture is press-molded, so that a green body is obtained. Then, by sintering the green body, there is obtained a material for the porous gas flowing body having a narrow passage whose pore diameter is about 2 μm in a gas flow path formed by communicating pores; a dielectric loss of about 2.5×10−4; an average crystal diameter of about 1.5 μM; a maximum crystal diameter of about 3 μM; a porosity of about 40%; an average pore diameter of about 3 μM; a maximum pore diameter of about 5 μM; and a flexural strength of about 300 MPa.
A tentatively sintered body or a sintered body, which is obtained by sintering the green body for the porous gas flowing body at a temperature equal to or higher than about 1200° C., is processed to have a preset outer diameter and thickness, and then it is cleansed by a ultrasonic cleaning. Then, by installing it in a vertical hole of a green body or a debound body for the shower plate in a similar way to those described in the first to third manufacture examples and then simultaneously sintering them, the shower plate as shown in
The shower plate of the present invention is applicable to various plasma processing apparatuses such as a high frequency excitation plasma processing apparatus of a parallel plate type, an inductively coupled plasma processing apparatus, and so forth, in addition to the microwave plasma processing apparatus.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-198762 | Jul 2006 | JP | national |
| 2007-182964 | Jul 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/064191 | 7/18/2007 | WO | 00 | 1/20/2009 |
