Patent Application
20050279457
The present invention relates to a plasma processing apparatus and method for performing, for example, an etching process on a substrate such as a semiconductor wafer by using plasma, and a plasma control member employed therein.
In a manufacturing process for a semiconductor device, a dry etching or a film forming process is performed on a substrate, for example, a semiconductor wafer (hereinafter, referred to as “wafer”) by using plasma in order to split up capacitors or devices or otherwise to form contact holes. One of the various apparatuses for performing such plasma processes is a single sheet parallel plate type plasma processing apparatus for generating plasma by applying a high frequency voltage between an upper and a lower electrode.
Since the processing gas reaching the vicinity of the surface of the wafer 100 is exhausted from the periphery of the wafer 100 downwardly and outwardly, the flow of the processing gas in the peripheral portion of the wafer 100 differs from that in the central portion thereof. As a result, at the peripheral portion of the wafer 100, the predetermined composition balance of the processing gas is disturbed, and the impedance or conductance components between the plasma and the lower electrode 12 in the region where the wafer 100 is placed deviate from those in the peripheral region located outer than that. Specifically, the dissociation level of the processing gas is higher in the peripheral portion of the wafer 100, which is closer to a gas exhaust space, than in the central portion of the wafer 100. Accordingly, the density of the plasma in the vicinity of the peripheral portion of the wafer 100 becomes higher, so that the etching rate of the peripheral portion of the wafer 100 becomes higher than that of the central portion, thus causing non-uniform etching over different parts of the wafer 100.
Meanwhile, to maximize utilizing the wafer 100 efficiently, devices need to be formed in part of the wafer 100 as close to its outer edge as possible. Thus, etching rates should be uniform throughout the central portion of the wafer 100 and its peripheral portion. For the purpose, the focus ring 13 made of, for example, a conductor, a semiconductor or a dielectric material is disposed to surround the wafer 100, to thereby control the density of plasma above the peripheral portion of the wafer 100. Specifically, the material for the focus ring 13 is selected depending on the kind of the processing gas or the material of the film to be etched, in order to install the focus ring 13 adequately for the process to be performed. For example, Patent Reference 1 discloses that in case of etching a refractory metal and its silicide (silicon compound) by using chlorine radicals generated by plasmarization, SiC is a preferable material for the focus ring 13 since it can mitigate the rise of chlorine radical concentration at the peripheral portion of the wafer 100 due to its strong tendency to adsorb chlorine radicals.
Further, for example, Patent Reference 2 discloses that, when using a quartz ring as the focus ring 13 serving as an insulator, the surface of the quartz ring is coated with, for instance, polyimide to prevent release of oxygen from the surface of the quart ring, which affects etching characteristics.
[Reference Patent 1] Japanese Patent Laid-open Publication No. 62-47130
[Reference Patent 2] Japanese Patent Laid-open Publication No. 11-317393
As desired patterns become progressively finer, however, a further improvement of in-surface uniformity of the wafer 100 is required when carrying out an in-surface treatment of the wafer 100. The method using the adsorption of chlorine radicals disclosed in Reference Patent 1, however, cannot satisfy the recent demands for even finer design specifications. That is to say, the method cannot suppress the increase in etching rate at the peripheral portion of the wafer 100 sufficiently. As a solution to the problem, the inventors of the present invention have considered using carbon to fabricate a focus ring. In case the focus ring 13 is formed of carbon and is exposed to plasma during a plasma processing, carbon radicals and the like are dissociated from the carbon and thereafter react with chlorine radicals to consume them. Therefore, the density of chlorine radicals around the peripheral portion of the wafer 100 can be reduced. However, since carbon becomes damaged by being exposed to plasma, the focus ring needs to be replaced periodically, for example, every 1000 hours, and the manufacturing cost thereof is increased due to the cost of carbon rings.
Moreover, as in Reference Patent 2, in case of coating the surface of the focus ring 13 with polyimide to thereby form a polyimide layer on the surface of the focus ring 13, the polyimide may be degraded as treatment of the wafer 100 is repeated. In such a case, the focus ring 13 needs to be separated from the apparatus to remove the degraded polyimide therefrom and coat it with a new polyimide layer again, which is labor intensive and troublesome.
It is, therefore, an object of the present invention to provide a plasma processing apparatus and method capable of readily replacing a plasma control member disposed to surround a substrate to control plasma.
In accordance with one aspect of the present invention, there is provided a plasma processing apparatus for converting a processing gas into a plasma by a high frequency power to perform a process on a substrate mounted on a susceptor by using the plasma in a processing vessel, the apparatus including a ring member disposed to surround the substrate on the susceptor; a plasma control sheet disposed on a surface of the ring member; and an adhesion layer, interposed between the ring member and the plasma control sheet, for allowing the plasma control sheet to be detachably attached to the ring member.
The adhesion layer may be an adhesive coated on a rear surface of the plasma control sheet. Further, the plasma control sheet may contain a material for dissociating a component which reacts with a primary active species for the plasma processing. Moreover, the plasma may include chlorine radicals and the plasma control sheet may be formed of an organic resin, and the plasma control sheet may be a polyimide sheet. In addition, tungsten or tungsten silicide surface layer on the substrate may be etched by the plasma.
In accordance with another aspect of the present invention, there is provided a plasma control member for use in a plasma processing apparatus for converting a processing gas into a plasma by a high frequency power to perform a process on a substrate mounted on a susceptor by using the plasma in a processing vessel, the member including: a ring member disposed to surround the substrate on the susceptor; a plasma control sheet disposed on a surface of the ring member; and an adhesion layer, interposed between the ring member and the plasma control sheet, for allowing the plasma control sheet to be detachably attached to the ring member.
The adhesion layer may be an adhesive coated on a rear surface of the plasma control sheet. Further, the plasma control sheet may be formed of an organic resin, and the plasma control sheet may be a polyimide sheet.
In accordance with still another aspect of the present invention, there is provided a plasma processing method using a plasma processing apparatus including a ring member disposed to surround a susceptor in a processing vessel, the ring member having a plasma control sheet attached on a surface thereof via an adhesion layer, the method including the steps of: loading a substrate on the susceptor; supplying a processing gas into the processing vessel, converting the processing gas into a plasma by a high frequency power and processing the substrate by using the plasma; and peeling the plasma control sheet off the ring member and replacing the plasma control sheet with a new one.
The plasma control sheet may contain a material for dissociating a component which reacts with a primary active species for the plasma processing. Further, the plasma includes chlorine radicals and the plasma control sheet may be formed of an organic resin, and the plasma control sheet may be a polyimide sheet. In addition, tungsten or tungsten silicide surface layer on the substrate may be etched by the plasma.
In accordance with the present invention, by configuring the plasma control sheet to be separable from the ring member by interposing the adhesion layer between the ring member and the plasma control sheet, the adhesion of the plasma control sheet to the ring member and the removal of the degraded plasma control sheet from the ring member can be performed easily. Therefore, the replacement of the plasma control sheet becomes easy, which relieves an operator from performing cumbersome maintenance and, also, improves the operating rate of the apparatus. Further, by using a material for dissociating components reactive with an active species which primarily contributes to the plasma processing, for example, by using an organic resin such as a polyimide sheet capable of dissociating carbon radicals, the dissociated components would consume the active species, for example, radicals existing near the peripheral portion of the substrate by reacting with them. Therefore, plasma density around the peripheral portion of the wafer can be prevented from becoming higher than the plasma density around the inner region. As a consequence, it is possible to perform a plasma processing of a substrate with a superior in-surface uniformity.
Installed inside the processing vessel 2 is an upper electrode 3 also serving as a gas shower head for introducing a processing gas, e.g., an etching gas into the vessel 2. The upper electrode 3 is provided in its lower surface with a plurality of gas diffusion holes 31 through which the processing gas supplied from a processing gas supply unit 32 via a supply line 33 is sprayed toward the entire surface of a wafer 100 disposed below. Further, an insulation member 34 formed of, for example, quartz is disposed to surround the upper electrode 3, so that the upper electrode 3 is electrically isolated.
Moreover, a susceptor 4 for mounting thereon a substrate is installed in the processing vessel 2 to face the upper electrode 3. The susceptor 4 is electrically isolated from the processing vessel 2 via an insulation member 40. Also, the susceptor 4 has a cylindrical support 41 formed of a conductive member such as aluminum, and the support 41 has on its top surface a mounting plate 42 for mounting the wafer 100 thereon. The mounting plate 42 is a dielectric plate formed of a dielectric material such as ceramic (e.g., aluminum nitride). Inside the mounting plate 42, a thin film shaped electrode (lower electrode) 43 is provided at a location closer to the upper surface of the mounting plate 42 while a mesh-shape heater 44 serving as a heating unit is installed at a location closer to the lower surface of the mounting plate 42. Further, reference numeral 45 is a gas exhaust ring provided with a number of perforations in its surface to allow the processing gas to be exhausted from the peripheral portion of the wafer 100 uniformly in a circumferential direction of the wafer 100. Also, though not shown, substrate supporting pins are installed in a way that they can be vertically movable to protrude above and lower below the surface of the susceptor 4 while supporting the rear surface of the wafer 100. The transfer of the wafer 100 between a wafer transfer arm and the susceptor 4 is carried out by the cooperation of the wafer transfer arm and the substrate supporting pins, the wafer transfer arm entering the processing vessel 2 from the outside of the apparatus.
One end of a power supply rod 50 is connected to the lower electrode 43 while its other end is coupled to a high frequency power supply 5 via a matching circuit 51. Further, the power supply rod 50 branches out in front of, e.g., the matching circuit 51, and the end of the branch line is connected to a DC power supply 52 via a switch 53. That is to say, the lower electrode 43 functions as an electrode for the application of a high frequency voltage and, also, an electrode for an the electrostatic chuck. Accordingly, the lower electrode 43 and the dielectric portion thereabove jointly form the electrostatic chuck for attracting and holding the wafer 100 electrostatically. Further, the heater is connected to a power supply unit 55 via a conductive bar 54.
A focus ring 6 for controlling plasma is disposed to surround the wafer 100 mounted on the mounting plate 42. The focus ring 6 has a ring member 61 formed of an insulation member such as quartz, alumina or yttrium oxide, the ring member 61 having a top surface width of about 55 mm. Further, a ring-shaped plasma control sheet 62 is detachably attached on the top surface of the ring member 61 via an adhesion layer 63, to be descried later in detail. The plasma control sheet 62 contains a material capable of dissociating, e.g., carbon of carbon radicals that react with plasma active species, e.g., chlorine radicals when it is exposed to plasma. An example of such a material is an organic resin such as polyimide. Further, the sheet 62 is configured to cover the entire top surface of the ring member 61 or to cover it partially with a width of about 10 to 20 mm, and has a thickness of, e.g., 0.5 to 1 mm. In
Here, the configuration of the plasma control sheet 62 and the adhesion layer 63 will be described in detail in accordance with the preferred embodiment of the present invention. The rear surface of the plasma control sheet 62 is coated with, for instance, an adhesive, so that the plasma control sheet 62 becomes adhesive and can be stuck to the surface of the ring member 61. Further, an operator can peel the control plasma sheet 62 off the ring member 61 by hand. Specifically, a polyimide sheet whose rear surface is coated with an adhesive can be used as the adhesive plasma control sheet. The inventors learned through experiments that “(No. 5414) Polyimide Tape” (product name) manufactured by Scotch Inc. can be used, for example. Further, the adhesion layer 63 may not be formed on the entire rear surface of the plasma control sheet 62. For example, adhesion layer 63 can be partially formed on the plasma control sheet 62 by coating an adhesive only on, for example, an outer or inner peripheral portion of the plasma control sheet 62.
During such a process in which a processing gas is converted into plasma by a high frequency voltage, the inside of the processing vessel 2 is maintained at a vacuum state to facilitate the generation of the plasma, and the temperature of the processing vessel 2 is set to be high, for example, about 300° C. Therefore, to prevent the plasma control sheet 62 from being separated from the ring member 61 under this condition, the strength of the adhesive forming the adhesion layer 63 needs to be strong enough not to be degraded at the high temperature. The Inventors confirmed through experiments that a silicon-based adhesive containing Si as its principal component meets such a requirement.
Moreover, the plasma control sheet 62 is preferably provided as close to the outer edge of the wafer 100 as possible. For example, it is installed within a range of 1 mm from the outer edge of the wafer 100. Further, the surface of the ring member 61 is disposed at the same level as the surface of the wafer 100 or higher than that by, for example, 0.5 to 0.7 mm. Accordingly, the plasma control sheet 62 is located higher than the surface of the wafer 100.
Hereinafter, a method for etching a substrate, e.g., a wafer 100 by using an etching apparatus with the above configuration and, e.g., a chlorine-based processing gas will be described.
Although there has been described the case of forming a gate electrode as an example of etching the barrier metal layer 7 formed of a W or a WSi layer, the present invention may also be applied to the case of, for example, etching a W or WSi layer of a barrier metal layer interposed between a wiring layer and an interlayer insulating film. Further, the object to be etched is not limited to a W or a WSi layer but may be a polysilicon or photoresist layer.
First, a gate valve 23 is opened, and a wafer 100 is loaded into the processing chamber 2 through the wafer transfer port 24 from a load lock chamber (not shown). Then, the wafer 100 is placed on the mounting plate 42 via the substrate elevating pins (not shown), wherein the mounting plate 42 is heated up to a preset temperature by the heater 44. Afterward, the switch 53 is turned on to apply a DC voltage, which is a chuck voltage, to the lower electrode 43, so that the mounting plate 42 attracts the wafer 100 electrostatically to hold it on the surface thereof. Meanwhile, the gate valve 23 is closed and the processing chamber 2 is hermetically sealed.
Subsequently, an etching gas containing, for example, chlorine (Cl2) and oxygen (O2) whose flow rates are set as, e.g., 150 sccm and 10 sccm, respectively is injected toward the surface of the wafer 100 via the gas diffusion holes 31 while vacuum evacuating the processing vessel 2 by means of the vacuum pump 22 such that the processing vessel 2 is maintained at a vacuum level of, for example, 5 to 10 mTorr. The etching gas injected toward the wafer 100 through the gas diffusion holes 31 flows along the surface of the wafer 100 radially outward and is exhausted from the periphery of the susceptor 4 uniformly by being dispersed due to the presence of the gas exhaust ring 45.
Afterward, if a high frequency voltage of, e.g., 100 MHz for plasma generation is applied to the lower electrode 43 at, e.g., 250 W from the high frequency power supply 5 via the matching circuit 51 and the power supply rod 50 in order, the high frequency voltage (high frequency power) is applied between the upper electrode 3 and the wafer 100 loaded on the mounting plate 42, so that the etching gas is converted into plasma and then, plasma active species serving as etchants, for example, chlorine radicals are generated. Further, a bias voltage of, e.g., 13.56 MHz is also applied to the lower electrode at, e.g., 200 W, thus allowing the plasma active species to be projected to the surface of the wafer 100 with high verticality, to thereby etch the portion of the barrier metal film 7 that is not covered with resist 71 (see
Then, after a certain period of time, the application of the high frequency voltage from the high frequency power supply 5 is stopped and the etching gas is no more injected. Further, a nonreactive gas such as nitrogen is introduced into the processing vessel 2 from a gas supply unit (not shown), and, at the same time, the vacuum evacuation by the vacuum pump 22 is stopped. Thereafter, the switch 53 is closed to cease the application of the chuck voltage, so that the electrostatic adsorption of the wafer 100 is stopped. Subsequently, the gate valve 23 is opened and the wafer 100 is unloaded from the etching apparatus, thereby completing the etching process. In addition, when processing a number of wafers 100 one after another, a new wafer 100 is loaded into the etching apparatus to undergo the same process as described above. After the operation time of the apparatus reaches, for example, 1000 hours while processing multiple wafers 100 repeatedly, a ceiling portion of the processing vessel 2 is opened and maintenance is performed. During the maintenance, the plasma control sheet 62 is peeled off from the ring member 61 and is replaced with a new one.
In accordance with the preferred embodiment of the present invention described above, by making the plasma control sheet 62 separable from the ring member 61 by interposing the adhesion layer 63 between the ring member 61 and the plasma control sheet 62, the attachment of the plasma control sheet 62 to the ring member 61 and the removal of the degraded plasma control sheet 62 from the ring member 61 can be performed easily. Therefore, the replacement of the plasma control sheet 62 becomes easy, which helps the operator in conducting the maintenance work and, also, improves the operating rate of the apparatus. In addition, by configuring the plasma control member as the sheet type, the manufacturing cost thereof can be reduced.
Moreover, in accordance with the preferred embodiment of the present invention, by forming the plasma control sheet with polyimide capable of dissociating components reactive with chlorine radicals serving as an etchant which becomes rate controlling factor for facilitating the etching of tungsten or tungsten silicide, carbon radicals dissociated from the polyimide consume the chorine radicals, thereby suppressing discrepancies in density of chlorine radicals between the peripheral portion and the inner portion of the wafer W. As a consequence, the wafer 100 can be etched at an etching rate with a superior in-surface uniformity.
As for the plasma processing apparatus exposed to the high-temperature plasma atmosphere, its components tend to be degraded readily and there may be deposits on the surface of some components. Thus, maintenance needs to be performed periodically, for example, every 1000 hours as mentioned above. Further, multiple plasma processing apparatuses frequently make up a processing system. Accordingly, easy replacement of consumable plasma control sheet 62 is very helpful for it reduces the burden of the operator's maintenance work. Here, since the thickness of the plasma control sheet 62 is slightly reduced sequentially as its component, e.g., carbon reactive with plasma are dissociated, the thickness of the plasma control sheet 62 should be set to be thick enough to endure until the next maintenance. The inventors found through simulations that the thickness of the plasma control sheet 62 necessary for operating the apparatus for 1000 hours is 1 mm.
Moreover, since the amount of dissociation of carbon radicals depends on the surface area of the plasma control sheet 62, if the surface area of the plasma control sheet 62 is set to be excessively large, plasma density at the peripheral portion of the wafer 100 may be reduced, resulting in deterioration of the in-surface uniformity of plasma density. Therefore, by setting the plasma control sheet 62 to have an appropriate surface area, for example, to have a width of 10 to 20 mm in this preferred embodiment, the plasma density at the peripheral portion of the wafer 100 can be controlled appropriately to thereby enable a precise control.
Further, the adhesion layer 63 is not limited to being an adhesive. For example, adhesion effects may be enhanced through reforming a surface of the ring member 61 by, e.g., a photochemical method, i.e., through substituting a hydrophobic C—H bond of the polyimide surface of the ring member 61 with a hydrophilic group by using a vacuum ultraviolet light (130 nm to 260 nm) and water. Likewise, a laser ablation method may also be employed, and the same effect as described above can be obtained.
In accordance with the present invention, in addition to the configuration in which the plasma control sheet 62 is provided on the entire surface of the ring member 61 along its circumferential direction, it is also possible to arrange plural band-shaped plasma control sheets 62 each having a radial width of, for example, 10 to 20 mm at predetermined intervals in the circumferential direction of the ring member 61, as shown in
Furthermore, the plasma control sheet 62 may not be disposed to cover the entire top surface of the ring member 61 but can be disposed only on the inner peripheral portion of the ring member 61, as shown in
In addition, the present invention is not limited to the configuration in which the plasma control sheet 62 is attached on the flat surface of the ring member 61. For example, as shown in
Further, the present invention is not limited to the configuration in which the plasma control sheet 62 is attached only on the top surface of the ring member 61. For example, as shown in
Also, the present invention can be applied to various plasma processes such as a CVD process and an ashing process besides the etching process exemplified in the preferred embodiment.
Hereinafter there will be described examples conducted for investigating the effect of the present invention.
In this example, a wafer 100 was etched by using an etching apparatus including a focus ring 6 prepared by attaching an adhesive plasma control sheet 62 formed of a polyimide sheet on the surface of a ring member 61. Specific processing conditions are as follows. In the example, the film thickness of the wafer 100 was measured along each of diametrical axes (X, Y, V and W axes) extending through the center of the wafer W to equally divide the wafer W before and after the etching process.
In this example, the same etching process as in Example 1 was conducted by using a focus ring 6 formed of a carbon ring.
In this example, the same etching process was conducted by using a focus ring 6 formed of a quartz ring without having a polyimide sheet. The results of calculating etching rates and the results of measuring the distribution of chlorine radicals are provided in
As can be seen from the results in FIGS. 7 to 10, in Comparative Example 1 using the focus ring formed of the quartz ring, the density of chlorine radicals at the peripheral portion of the wafer 100 is excessively high, and the etching rate is also much higher in the peripheral portion than in the central portion of the wafer 100. On the other hand, in both of Example 1 using the polyimide sheet and Comparative Example 1 using the carbon ring, the increase in the density of chlorine radicals and the increase in the etching rate at the peripheral portion of the wafer 100 are small. However, though the deviations of EE3 mm and EE30 mm are both ±10.6% in the comparative example 1, the deviations of EE3 mm and EE30 mm are ±10.2% and ±7.6% in Example 1, respectively, and the increases are also small in Example 1 than in Comparative Example 1. Further, EE3 mm refers to an average of measurement values in a region between the edge of the wafer 100 and a circular line inwardly apart by 3 mm therefrom while EE30 mm represents an average of measurement values in a region between the edge of the wafer 100 and a circular line inwardly apart by 30 mm therefrom.
From the above results, by attaching a polyimide sheet on the surface of the ring member 61 formed of a quartz ring, it is possible to suppress the increase in the density of chlorine radicals at the peripheral portion of the wafer 100, and, therefore, the increase of etching rate thereat can also be prevented. It is believed that the increase in the density of chlorine radicals at the peripheral portion of the wafer 100 can be prevented because carbon radicals dissociated from the polyimide sheet (carbon in Comparative Example 1) react with chlorine radicals.
2 processing vessel
22 vacuum pump
3 upper electrode
4 susceptor
42 mounting plate
43 lower electrode
6 focus ring
61 ring member
62 plasma control sheet
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-167093 | Jun 2004 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| 60589828 | Jul 2004 | US |
